PXImate - Pickering Interfaces

PXImateThis book provides an overview of the PXI standard together with usefulinformation about the technology behind the switching and instrumentationmodules a typical chassis can contain. It is a guide for those new to PXI systemsand a useful source of reference material for the more experienced.The PXImate covers a wide variety of topics in a concise and easily read format.In addition to providing an overview of the PXI standard it describes many of theswitching and instrument functions that often occupy PXI chassis.At the time of writing the PXI standard is at Revision 2.2 and the first release ofthe PXI Express standard pending.This is a living document that Pickering Interfaces will continue to develop insupport of the PXI standard and its future evolution. We welcome any feedbackfrom users on subjects they would like to be included in future issues.David Owendavid.owen@pickeringtest.comCreated by the team at Pickering InterfacesFurther copies or new editions of the PXImate can be obtained fromwww.pickeringtest.com/pximate© Copyright (2005) Pickering Interfaces. All Rights Reserved.No part of this publication may be reproduced, transmitted, transcribed, translated or storedin any form, or by any means without the written permission of Pickering Interfaces.Technical details contained within this publication are subject to change without notice.www.pickeringtest.comThe following are terms are registered trademarks of the respective companies and/or organizations:LabVIEW, LabWindows/CVI: National Instruments CorporationPXI: PXI Systems AlliancePICMG-PCI: Industrial Computer Manufacturers Group, Inc.Page

1 - introdUCtion to PXi BasiCsPXI Chassis8 Slot PXI Chassis, Type 40-90814 Slot PXI Chassis, Type 40-914• 4U PXI chassis, front access, universal voltage supply• 350/400W Modular power supply (dual 175/200W hot swappable)• PXI BRIC Can Be Mounted in Rightmost Slot18 Slot PXI Chassis, Type 40-918• 4U 18 slot PXI chassis, front access, universal voltage supply• 800 W modular power supply (quad 200 W hot swappable)• 18 Slot PXI Backplane Utilizing Dual PXI-PXI BridgePage 1.2

1 - INTRODUCTION TO PXI BASICSBACKGROUND AND HISTORYPopulated 18 Slot PXI ChassisPXI is a modular instrument system designed to take advantage of the very fast data interfacesassociated with PCI and CompactPCI bus systems, and offers a cost effective solution thatsatisfies the requirements of test and measurement in industry today.The PXI standard defines the mechanical, electrical and software interfaces provided by PXIcompliant products, ensuring that integration costs and software costs are minimised, andallowing trouble free multi-vendor solutions to be implemented.In use a PXI system appears as an extension to the PCI slots in the user’s controller, regardless ofwhether the controller is embedded in the PXI chassis or is a separate computer.Most PXI instrument modules are simple register based products which use software drivers toconfigure them as useful instruments, taking advantage of the increasing power of computers toimprove hardware access and simplify embedded software in the modules. The open architectureallows hardware to be reconfigured to provide new facilities and features that are difficult toemulate in comparable bench instruments.The PXI modules providing the instrument functions are plugged into a chassis which mayinclude its own controller running industry standard operating systems, or a PCI to PXI bridgethat provides a high speed link to a desktop PC.CompactPCI and PXI products are interchangeable, i.e. they can be used in either CompactPCIor PXI chassis, but installation in the alternate chassis type limits the functionality of certainfeatures.Page 1.3

1 - INTRODUCTION TO PXI BASICSControllerExpansionSlotsSystemControllerSlotPeripheralModulesEmptySlotP2P11 2 3 4 5 6 7 8ChassisStar Trigger Controlleror Peripheral SlotEjectorHandlesBackplaneExample of a 33 MHz 3U PXI System (Single Bus Segment)Page 1.4

1 - INTRODUCTION TO PXI BASICSPXI ChassisThe PXI chassis provides the mechanical means of mounting the PXI modules and providing theforced air cooling to the modules. It also provides DC power poer the PCI CI bus us and the PXI I specific specicfunctions. The chassis are typically tpicall designed to house either or PXI modules modules the modules being twice the height of the modules. In general the size is more popular andthey can be fitted into 6U chassis using a simple adaptor. The PXI standard supports the design ofchassis which allow both and modules to be used.The chassis allows CompactPCI modules to be added but CompactPCI specific features are notsupported.The PXI specification supports the use of 32 bit and 64 bit backplane connections and 33 MHzand 66 MHz bus speeds ensuring theoretical bus speeds of 132 Mbytes/sec to 528 Mbytes/secrespectivel a speed far in excess of that available over GPIB or VXI interfaces.The standard allows up to 8 slots on each 33 MHz PCI segment or 5 slots per 66 MHz PCIsegment. This does not limit the number of slots available in the chassis since larger chassisinclude PCI to PCI bridges to interconnect segments. Each PCI bridge occupies one electrical sloton each of the segments it connects to.For 33 MHz PCI systems one PCI bridge conveniently provides a total of 14 slots (a Slot 1 and 13peripheral slots) since two electrical slots are occupied by the PCI bridge (one on each segment).Chassis based on 66 MHz are much less common since the number of available slots per PCIsegment are lower - a 14 slot chassis would need three PCI bridges. This leads to increased chassiscost. In addition the presence of a module not supporting 66 MHz operation will automaticallylimit the backplane to 33 MHz. There are very few PXI modules designed for 66 MHz (or 64 bit)operation.The presence of PCI Bridges should generally be transparent to the user of a PXI chassis.However if two modules require the exchange of trigger signals over the Trigger Bus additionalcomplications will arise because the Trigger Bus does not directly cross the PCI Bridge. The StarTrigger however is wired to cross the first PCI bridge. The PCI bridges introduce a one clockdelay in transferring information from one segment to another.If instruments require the use of two separate modules connected by the trigger bus the instrument’soperation can be complicated or disrupted if its modules are inserted either side of a PCI bridge. Itis therefore best to avoid dividing these modules with a bridge.The location of a PCI Bridge is marked on the chassis and backplane by a vertical black lineshown between the slot numbers.PCI Segment Divider GlyphPage 1.

1 - INTRODUCTION TO PXI BASICSThe PXI specification does not set out a rigorous standard for what can be included in a PXIchassis though all must comply with the mandatory parts of the specification. For that reasonPXI chassis vary in their capability and the user needs to choose the chassis that is right for theapplication. Things to consider are:• Number of modules required. Too much capacity makes the chassis larger and moreexpensive, too little forces the use of more than one chassis.• The module sizes (3U and 6U) required in the system. If 6U modules are required as well as3U a mixed size chassis may be needed.• Diagnostics support to check that power supplies and fans continue to operate correctly.• Power supply capacity. Too little power could prevent the inclusion of high power consumptionmodules. Some test systems may require more power on specific voltage supplies, forexample some analogue or RF functions may require higher currents on the ±12 V suppliesthan systems that only test logic circuits. Chassis designed in accordance with Version 2.1of the specification may provide more power than chassis designed against earlier versionsof the standard.• Fan air capacity affects cooling rate within PXI modules, and influences the maximumpower dissipation in each module. A fan speed controller can reduce acoustic noise at normaltemperatures and help reduce temperature changes in the test system, but in practice theimprovements are not major. If a chassis is required to work in an office environment and themodules do not generate a large thermal load a chassis with lower cooling capacity and loweracoustic noise may have some advantages..• A built-in display can help monitor test progress, but takes up space in the chassis. A built-inmonitor may help the design and development phase, but be less relevant once the test systemis deployed in an automatic test environment.• Inclusion of additional drives, such as CDs or DVDs, for directly loading programs or storingdata.Page 1.

1 - INTRODUCTION TO PXI BASICS3U and 6U ChassisThe standard permits a chassis to be designed to have both and modules inserted. Wherethe modules are located these slots can either be dedicated to modules or they can bedesigned to allow the mounting of two modules. Slots which allow the mounting of two modules or one module are provided with additional connectors P4 and P5. These connectorsprovide the same signals as the P1 and P2 connectors on 3U modules. In this instance thestandard requires the P4 and P5 connectors are run from a different PCI segment to the P1 andP2 connectors and the bridging function must not be provided by the Slot 1 controller. The 3Umodules can be mounted in the locations either using adapter systems or by mechanicaladjustments to the chassis. Some chassis may use J J4 and J5 connectors in ways not describedin the PXI standard. sers must be cautious when using these chassis since damage or unusualoperation may result if it is not used in the intended way (the chassis may be protected by useof polarizing keys to prevent these problems). This is particularly the case for the J4 and J5connectors that the PXI standard defines for use in 3U stacked systems.ControllerExpansionSlotsSlots Supporting3U stacking3U StackingNot Supported1415 16 17 18P5P53U 3UModule ModuleP4P46UModule6U 6U 6U 6U 6U 6UModule Module Module Module Module ModuleP2P2P2P23U 3UModule ModuleP1P1P1P11 2 3 4 5 6 7 8 9 10 11 12 13SystemSlotStar Trigger Controlleror Peripheral SlotExample of a 6U Chassis that Supports Stacking 3U ModulesPage 1.

1 - introdUCtion to PXi BasiCsPXi BaCkPlaneThe PXI backplane provides power to the PXI modules and provides the PCI interface. Theackplane has to include any CI ridges that are required to maintain the integrity of the CIinterface. In addition the backplane delivers other PXI features such as triggering local bus andStar Trigger described elsewhere in this book.Chasss PowerThe I standard species the minimum poer that can e delivered to each module and speciesthis for the chassis with and without support for . V operation. Most chassis support . Voperation and the folloing minimum specication applies for chassis conforming to Version 2.1of the I specication.SystemSlotPeripheralslotSystemSlotPeripheralslotPower Supply +5 V +5 V +3.3 V +3.3 V +12 V -12 VRecommended current 6 A 2 A 6 A 2 A 0.5 A 0.25 AChassis Power Supply Minimum RequirementsThe chassis power suppl must be capable of suppling the stated current on each suppl withall the available slots populated and full loaded. The table sets the minimum average currentthe chassis should provide it does not limit the current a single module can draw. There areadditional requirements covering this aspect. The chassis poer supply and ackplane must eale to deliver 1 Amp to any peripheral slot on the +12 V and -12 V supplies and any peripheralslot must be allowed to draw Amps on the +5 V suppl. It should be noted that chassis built toversions of the standard earlier than 2.1 do not necessarily conform to the aove requirements.If a chassis is tted ith many modules that have a high current consumption it is possile toexceed the power suppl rating but this is rarel the case in in most test sstems since manmodules have current consumption well below the average ratings.Each pin on each backplane connector passes a maximum of 1 Amp. Each connector uses multiplepins to pass the required current. In accordance with the above table the +5V and +.V supplieseach require 6 pins to e connected. Many chassis are capale of providing more current at eachvoltage. This information should be provided in the chassis manual.system reference ClockThe PXI backplane alwas provides a sstem reference clock operating at 10 MHz and havingan accuracy of 100 ppm (parts per million) or etter. The clock is specied to have a 50% ±5%dut ccle and each module is independentl driven to avoid module interaction. The referenceis distributed such that each slot receives the signal at the same time to within 1 ns.For some applications the sstem reference clock is not accurate or stable enough particularlfor RF applications. The Star Trigger slot has a specic pin assigned to allo it to provide thealternative Reference Clock. The I specication recommends that the ackplane provides afacility to sitch the clock to the alternative frequency source provided y the Star Trigger slot(slot 2).AllAllPage 1.8

Local Bus1 - INTRODUCTION TO PXI BASICSThe Local Bus is a daisy chain of 13 lines that interconnects adjacent PXI slots. Each Local Busline on the right of the slot is connected to the neighbouring Local Bus slot on its left. The busis used to allow adjacent modules to exchange analogue signals (up to ±42 V) or digital signalsdirectl. Software checks the compatibility of adjacent slots before the modules can make use ofthe facilit. If modules that make use of the Local Bus are not placed in the appropriate positionsthen the Local Bus functionality may be lost since there is no requirement for modules to providea bridge and different modules will use the Local Bus in different ways (or not at all).Star TriggersSystem Controller Slot 1Star Trigger Peripheral Slot 2LocalBusPeripheral Slot 3LocalBusPeripheral Slot 4LocalBusLocalBusPeripheral Slot N+1LocalBusPeripheral Slot NExternalBackplaneInterfacePCI Arbitration and Clock SignalsThe slot located next to the system controller (Slot 2 Star Trigger location) is a special case. TheLocal Bus lines on the left side (facing the controller) are dedicated to the Star Trigger functionand do not connect to the System Controller.The bandwidth and other characteristics of the local bus are not fixed in the standard limitinghow designers can use these connections.Trigger BusPXI Local Bus RoutingThe 8 PXI bus triggers provide a method of synchronising the operation of PXI modules. Thebus is configurable so that any module can control the operation of other modules in the systemand respond to events in other modules. The standard does not mandate the buffers or the supporttools required so most (or even no) chassis provide buffers.The Trigger Bus is not permitted to cross a PCI bridge without the addition of a buffering systemin chassis to electrically isolate the segments. The Trigger Bus length is also limited to a distanceof 252 mm. The standard does not mandate the buffers (and the support tools needed) may not beincluded. For this reason it is recommended that modules using the Trigger Bus to trigger eventsare placed on the same Trigger Bus segment. The PCI Segment Divider Glyph on the front of thechassis clearly identifies the location of any CI PCI Bridge.Page 1.

1 - INTRODUCTION TO PXI BASICSStar TriggerThe Star Trigger is a high performance trigger designed to provide a high speed trigger linebetween the first peripheral slot (Slot 2) and the other peripheral slots. The Star Trigger makesuse of the lines on the left hand side which would normally be part of the Local Bus. The StarTrigger slot is not an essential part of a chassis but in practice most chassis provide it. A StarTrigger slot can be used as an ordinary peripheral slot if a Star Trigger is not required.Star Trigger Slot GlyphThe position of the Star Trigger is marked on the backplane and the module by the Star TriggerSlot Glyph shown.When a Star Controller is installed in the chassis it can ensure that events in other peripheralsare simultaneously triggered with very low levels of differential time delay between modulesthrough the use of the Star Trigger. The trigger system is bi-directional so the Star Trigger modulecan allow an event in one peripheral module to trigger events in other modules.The Star Controller provides thirteen output lines each going to a different designated PeripheralModule. In a 14 slot chassis there are 12 Peripheral Slots (14 slots less Slot 1 and Slot 2) andtypically one PCI Bridge (for a 33 MHz PCI bus). The thirteen Star Triggers are connected to the12 Peripheral Slots. For a larger chassis the higher slot numbers (beyond physical slot 15) do notsupport the Star Trigger they should be occupied by modules not requiring this facility.For systems requiring more than one chassis fitting a Star Card into each chassis and connectingthem together either through cables or synchronising them through the use of GPS timingensures that PXI instrumentation systems can perform more complex measurements in distributedsystems.PXI Star TriggersBridge ControlsBus Segment 2System Controller Slot 1Star Trigger Peripheral Slot 2Peripheral Slot 3Peripheral Slot 7Peripheral Slot 8PCI - PCIBridgePeripheral Slot 9Peripheral Slot 10Peripheral Slot 16PXI Trigger Bus (Segment 1) PXI Trigger Bus (Segment 2)PXI Architecture for Two Bus SegmentsPage 1.10

1 - INTRODUCTION TO PXI BASICSPXI ModulesThe PXI standard defines the mechanical outline and connectors for both 3U and 6U modules.Ejector Handle6U PXIJ3PXIReserved3U PXIJ264-Bit PCI &PXI FeaturesJ264-Bit PCI &PXI FeaturesJ132-Bit PCIJ132-Bit PCIPXI Peripheral Module Form Factors and ConnectorsThe 3U modules have one ejector handle fitted at the bottom of the module. A screw fixing isprovided at the top and the bottom the bottom fixing being partly hidden by the ejector handle.Modules occupying more than one slot can have more than two screw fixings. Two connectorscan be fitted (J1 J2) but the module may have no functions requiring the use of the J2 connector(64 bit PCI and PXI features) and for that reason it may be omitted from the module to savecost.The 6 U modules have two ejector handles fitted and can have three connectors (J1 J2 J3). Thefunction of the J3 connector is not defined and is currently not used though some companieshave used the J3 (and J4 J5) connector for proprietary interconnections. Fixing screws are usedat the top and bottom of the module partly hidden by the ejector handles. Modules occupyingmore than one slot can have more than two fixing screws.It is good practice that modules are operated with all fixings tightly secured this is particularlyimportant on modules which require a good earth connection. The front panel ground mustbe isolated from the PXI power supply ground to avoid ground loop currents. The moduleperformance should be specified with the screws tightened.Page 1.11

1 - introdUCtion to PXi BasiCsIn addition to offering I modules ith specic instrument functionality manufacturers alsooffer prototping PXI modules which provide a PXI interface some control lines and otheruseful features. These modules allow users to create their own special purpose modules withoutthe need to invest in creating the PXI framework needed to make it operate in the PXI chassis.Once the hardware is created drivers can be written that turn this module into their own PXIbuilding block.Typical Prototyping Module produced by Pickering InterfacesPage 1.12

1 - INTRODUCTION TO PXI BASICSPXI Slot 1, System SlotThe left hand slot of the chassis is reserved for the system controller. The slot has one set ofconnectors to the backplane and occupies one notional slot. However in reality a controller mayrequire more than one slot and for this reason the standard allows the chassis to expand the Slot 1position to the left hand side (away from the rest of the peripheral modules). A typical chassismay have three Controller Expansion Slots allowing up to the equivalent of four module widthsto be occupied by the controller but using just one set of backplane connectors. The ControllerExpansion Slots do not have backplane connectors.The PXI chassis can use either an embedded controller in the Slot 1 position or an interfacemodule allowing connection to an external controller (such as a PC). The interface module istypically based on a proprietary serial interface sent over a copper or optical cable connectedbetween the controller and the module in the PXI chassis. The interface behaves as a PCI to PCIbridge and is therefore transparent to the system software. A PCI interface card is required in thecontroller to provide the serial output and a PXI interface module in the chassis decodes the dataand transfers it to the PCI bus. For example National Instrument’s MXI-3 uses a proprietary1.5 Gb/s serial link as the interconnection system Adlink use 4 open standard Star Fabric serialinterfaces that provide an aggregate 2.5 Gb/s serial link to perform the same function.The same interface modules can be used to expand the number of chassis in the system. Anadditional PXI interface module is installed in the any of the available slots of the first chassisand connected via the serial interface to an identical PXI interface module in the Slot 1 positionof the second chassis.PXI Slot 2, Star TriggerThe PXI Slot 2 position is occupied by the Star Card already described. If a Star card is insertedinto any other slot is will not be able to perform the Star Card functions. If a module other thana Star card is inserted in Slot 2 then the card will perform within in its normal operating criteriabut the PXI system will not have the features provided by a Star Card.The software tools ensure that when the chassis is powered on the status of Slot 2 is recognisedand the system configured automatically with minimal user set up required.Controlling GPIB instrumentsIf a test system includes GPIB instruments there are two ways of integrating the instruments intoa PXI based test system. The first method is to use a GPIB connector on the system controller.If this is an external controller a GPIB adaptor card needs to be added. If it is an embeddedcontroller it may have an integrated GPIB controller output.The second method is to add a GPIB module to the chassis that provides an interface fromthe chassis to the external GPIB instruments. These modules are available from a number ofsuppliers.Note that neither method permits the control of a PXI chassis by the GPIB equipment.Page 1.13

1 - INTRODUCTION TO PXI BASICSInstalling Modules in a ChassisThere are a number of precautions that should be taken when installing a module in a chassis.The chassis should not have power applied to it when modules are inserted – the PXI standarddoes not support the hot swapping of the peripheral modules.The PXI modules will often have exposed electrical contacts as part of the PCB. Devices on thePCB may be static sensitive. It is important to use Static Handling Precautions when installinga module to ensure that it is not damaged by accidental static discharges. The chassis can beconnected to ground via its power cord (but the power not switched on) to ensure the chassismetalwork is grounded.When the module is inserted into the top and bottom card guides the it should be carefully pushedback so the PXI connectors on the back engage – treating the cards roughly could damage themodule or the chassis.Switching-on a systemPower has to be applied to a PXI system in an orderly way to allow the controller to identify thePXI modules that appear as an extension of its PCI system.The chassis must be connected to the controller (if it is external) before power is applied.If more than one chassis is connected to the system the last chassis in the chain should be turnedon first.When the chassis connected to the controller is switched on then the power can be switched onto the controller (assuming it is an external controller).If the controller interface is disconnected from the chassis during operation it will usually resultin the system having to be restarted.When turning a system off the system controller should be closed down first so the status of theextended PCI bus does not cause the system controller to freeze or crash.Page 1.14

1 - INTRODUCTION TO PXI BASICSPXI ExpressFurther additions to the PXI standard are being introduced that will add new types of moduleand chassis to the current version of the standard. The changes incorporate PCI Express controlinto the PXI backplane that can increase the data rates for speed critical systems. The scheduledrelease date for this new version of the hardware standard is September 2005 just as this versionof PXImate is released for publication. The changes are based on the cPCI Express standard. Arevision of the software standard will also be released.The PXI Express standard adds a number of complications to the Version 2.2 of the PXI standard.There are significant changes in the design but the appearance will be very similar. In PXIExpress some slots will exchange data with the system slot using a serial interface based on thePCI Express standard rather than the parallel (33 MHz) PCI interface. It can provide a significantincrease in data bandwidth to those slots. Although the data rate is higher there can be latencyintroduced into the data exchange because of the need for serial to parallel conversion.The standard encourages the support of legacy PXI modules since these modules are likely todominate the PXI market for many years. The trigger system is supplemented by trigger signalsthat use differential signalling.The following is a short description of the differences between the PXI standard and the PXIExpress standard and concentrates on the more common arrangement.PXI Express Peripheral SlotModulePXI Express System Timing SlotPXI Express System SlotPXI Express Hybrid SlotBackplaneInterfaceConnectors- 1 SlotBackplaneChassisH51 2 63 4 7H8System Expansion SlotsPeripheral SlotsTypical system components of a PXI Express Chassis showing modules and slottypesPage 1.15

1 - INTRODUCTION TO PXI BASICSPXI_CLK10PXI_STARPXI_TRIG(0:7)PXI_CLK10_INPXIe_CLK100PXIe_SYNC100PXIe_SYNC_CTRLPXI_CLK10CircuitXP4XP3XP2LocalBus[6]1-2XP4XP3P1PXIe_DSTAR(A:C)0LocalBus[6]2-3XP4XP3P1LocalBus[6]3-4PXIe_DSTAR(A:C)1XP4XP3TP2PXIe_DSTAR(A:C)2LocalBus[6]4-5LocalBus[0:12]5-6LocalBus[0:12]6-7P2 P2 P2 P2LocalBus[0:12]7-8P1 P1 P1 P1PXIe_SYNC100PXIe_CLK100XJ1TP2(optional)PXIe_SYNC_CTRL12H3H45 6 7 8PXI EXPRESSSYSTEM SLOTHYBRID SLOTSPXI EXPRESSTIMING SLOTLEGACY SLOTSP1 Connector carrying 32 Bit PCI Bus (PXI)P2 Connector carrying upper 32 Bit PCI Bus (PXI), Trigger, Local BusXP2, XP3 Connector carrying PXI Express InterfaceXP4 Connector equivalent to partially populated P2XJ1 PXI Express System Slot connectorTP2 PXI Express Timing Slot connector (TP1 is optional)Backplane connection example for a PXI Express chassis with all the slot typessupported by the PXI Express standard and showing the interconnections available.Chassis BasicsA PXI Express chassis is potentially a lot more complicated than a PXI chassis. It uses a newSystem Controller slot an optional Timing Slot and a variety of peripheral module slot types. Itcan be or or a mixture of both. Different types of slots are marked on the chassis with aglyph mark which is generally different to designate different types of slots.The peripheral slots can be controlled through a 33 MHz PCI backplane or a PCI Express serialinterface. The Express connection is defined to use the 2.5 Gb/s PCI Express standard but PCIExpress is in the future expected to migrate to a 5 Gb/s interface. If the 5 Gb/s version is adoptedby PCI express some further revision of the PXI Express standard may be required.The backplane supports the PXI Trigger Bus and the Star Trigger but Local Bus support islimited to Legacy Slots and Hybrid Slots support just one of the Local Bus connections.Where a slot has a PCI Express connection it uses a new Trigger Bus system based of differentialtrigger signalling.Slots can also have both a PCI Express and a PCI interface but the module will only use oneinterface.A PXI Express chassis can provide 100 MHz clock references in addition to the 10 MHz referencespecified for the PXI standard.Page 1.16

1 - INTRODUCTION TO PXI BASICSSince a chassis can have a mix of different types of slot there is likely to be considerably morevariety of chassis variations than with the existing PXI standard.A PXI Express chassis carries a PXI Express logo to distinguish it from a PXI chassis.PXI Express System Slot and ModuleThe System Slot uses different backplane connections to the PXI standard and a PXI controllercannot be used in a PXI Express system slot. Any PCI slots present in the chassis are controlledthrough a transparent PCI Express to PCI bridge typically anticipated to be on the backplane orimplemented as a separate device. The system slot is identified by a glyph mark in the shape of atriangle but unlike PXI the triangle is filled in to show it’s a PXI Express System Slot.Legacy Slot and ModuleIn a legacy slot a PXI Express chassis supports modules that conform to all aspects of the PXIstandard including the Star Trigger PXI Trigger and Local Bus. The module can be fitted with afull set of PXI connectors (J1 and J2 for 3U) since the chassis supports both connectors. The slotis marked with a glyph mark identical to the PXI standard.PXI Express Hybrid Peripheral Slot and ModuleIn a hybrid slot a chassis supports the 32 bit PCI bus on J1 and has a PXI Express connector. TheJ2 connector is occupied by a shortened version that provides support for the PXI Trigger Busand Local Bus 6 (the remaining Local Bus connections are not supported). These slots can beoccupied by PXI modules that are fitted with just the J1 connector or PXI modules that are fittedwith J1 and a shortened version of the J2 connector. It will not support a PXI module that hasboth the J1 and the full J2 connector.Hybrid slots also support PXI Express modules. If a PXI Express module is fitted power issupplied through the PXI Express connector and the control is via a PCI Express interface.Hybrid slots are designated on the chassis by a filled circle glyph with a superscript “H” to thetop right.XJ4J1A PXI module with a full J1 connector but with a shortened version of the J2connector that allows it to be fitted into a PXI Chassis or a PXI Express chassisHybrid Peripheral SlotPage 1.17

1 - INTRODUCTION TO PXI BASICSPXI Express Peripheral Slot and ModuleIn a PXI Express Peripheral Slot the chassis just supports the shortened J2 connector and thePCI Express interface. The J1 connector is not supported. Consequently these slots can only beoccupied by PXI Express modules.PXI Express slots are identified by a filled circle glyph.XJ4XJ3A 3U PXI Express Peripheral Module carries the shortened version of the J2 (XJ4)connector and an Express connector (XJ3)PXI Express System Timing SlotThe PXI Express System Timing Slot replaces the Star Trigger Slot in a PXI chassis. It uses anentirely different connector arrangement and is not compatible with Star Trigger Controllersfrom PXI. The slot is optional on a chassis and unlike the Star Trigger can have any physicalposition in the chassis (in practice it is likely to be located in the centre of the available slots tominimize connection distances). Where fitted it supports the Star Trigger connection to otherslots (as in the PXI standard), PXI Trigger Bus and has additional capability for providing the 3differential triggers to PXI Express slots or hybrid slots. This slot can accept other PXI ExpressModules but not PXI modules.The System Timing Slot is marked by a glyph that is a square with a filled circle inside.System Power SuppliesPXI modules draw power from four supplies (+12 V +5 V +3.3 V and -12 V) however PXIExpress modules are supplied from just +12 V and +3.3 V supplies. This requires that modulesrequiring negative voltages to include a DC to DC converter to generate any negative voltage.As with the PXI standard the PXI Express standard sets minimum capabilities for the chassis tosupply to the modules. A Low Power chassis is also defined that has much lower power supplycapability and is aimed at applications that may require battery supported testing. As with the PXIstandard Low Power versions of PXI Express chassis are required to be marked.Page 1.18

1 - INTRODUCTION TO PXI BASICSMODULESSystem ModulePXI-1 & Hybrid SlotPXIe Peripheral ModuleTiming ModuleCompatible PXI-1Peripheral ModuleSLOTSH12345System SlotPXI-1Peripheral SlotHybrid SlotPXIe Peripheral SlotTiming SlotPXI Express FutureIt is unlikely that the PXI Express will be common in test systems for a few years from the timethis version of PXImate was written (July 2005). In most applications PXI Express has a limitedadvantage over PXI and for some time there will not be the breadth of products that is availablein PXI.The main opportunity for PXI Express will be in applications where there is a need to exchangelarge data files in a short period of time. However to achieve the increased speed PXI Expresswill also require the use of very fast embedded controllers or wide bandwidth bridges from anexternal controller to a chassis.The serial interface of PXI Express could (potentially) lead to lower cost and physically smallerbackplane connection hardware but for many applications requiring dual polarity power suppliesthis will be offset by other cost and space factors.The PXI industry is unlikely to migrate very quickly to PXI Express; it is likely to be a slowmigration for a few critical applications that eventually may lead to a more widespread adoption.sers will be able to continue to use PXI in its current form for very many years.Page 1.19

1 - INTRODUCTION TO PXI BASICSPage 1.20

2 - PXI SOFTWARE BASICSSECTION 2PXI SOFTWARE BASICSIntroduction .....................................................................................................2.3Operating Systems Supported ........................................................................2.3Unix, Linux and Mac OS .................................................................................2.3Register Versus Message Based ....................................................................2.4Program Development Environment ...............................................................2.5Graphical Environments ..................................................................................2.5Text Based Environments ...............................................................................2.6What is an Instrument Driver?.........................................................................2.8VISA and IVI Relationship ...............................................................................2.9What is VISA? .................................................................................................2.9What is IVI? .....................................................................................................2.10IVI Driver Architecture .....................................................................................2.11Page 2.1

2 - PXI SOFTWARE BASICS41-921, 51-921PCI to PXI Control Interface• Provides Seamless Interface Between a PC Controller PCI and PXI Chassis• Supports Two PXI Chassis From A Single PCI Card• 2.5 Gb/s StarFabric Serial Interface Ensures Fast Operation• Supports 32/64 Bit & 33/66 MHz PCI Interfacing• Uses RJ45 Connectors, Shielded Cat 5E Cables• Operating System Independent• Low Power Consumption, Supporting 5V and 3.3V PCI• Single Slot 3U PXIPage 2.2

2 - PXI SOFTWARE BASICSIntroductionThe PXI standard is reliant on a standardized software and hardware environment. The modulesin the PXI chassis have no front panel controls to control their functions and rely entirely onbeing able to control them via the PXI back plane.The PXI chassis is designed to appear as an extension to the PCI bus in the controller and manyof the processes that a user goes through in installing a new PXI system are similar to those youexpect in installing a PCI card.Operating Systems supportedThe PXI standard requires that manufacturers of PXI products must support a number of WIN32based operating systems.The operating systems required to be supported are:• Windows 95 (later versions of the standard do not require support)• Windows 98 and its various derivatives• Windows NT• Windows 2000• Windows XPSome manufacturers may support other operating systems, such as Linux, where there isdemand.Users of Linux need to check that all the modules they require are supported since it is not amandatory part of the standard.As operating systems evolve (particularly the newer systems) it can lead to compatibilityproblems occurring, software that worked on early versions of an operating system may haveproblems on later versions. It is always worth checking for the latest drivers for the PXI productin case any issues have arisen, particularly on the modules that use the more advanced featuresof the PCI bus.Unix, Linux and Mac OSOther operating systems like Unix, Linux or Mac OS (Operating System) can be used when thereis available software and hardware.For an operating system to successfully run a PXI platform there are two basic requirements:• The operating system must be able to connect to the PXI bus.• The drivers, development environment and other software must support the OS.Connecting to the PXI bus can be via an embedded controller or a PCI-to-PXI bridge interfacesystem. Embedded controllers for PXI are only available in IBM-PC compatible form, so theused OS must work on this platform. This excludes Mac OS and some Unix platforms.Page 2.

2 - PXI SOFTWARE BASICSIf a PCI to PXI bridge interface system is used, then other operating systems like Linux, Mac OSand Sun Solaris can be used. National Instruments MXI-3 is just one example of a PCI to PXIBridge using a PXI module and a PC mounted card to provide the required functionality.Software support for operating systems like Mac OS, Linux and Solaris depends on themodule manufacturer. If a software driver is not available, an alternative is to use register levelprogramming. For some products, such as switching, this is likely to be relatively simple todo but for complex instruments it requires a detailed knowledge of the modules register levelprograming and knowledge about how it works.National Instrumentʼs PCI to PCI Bridge InterfaceREgISTER vERSuS mESSAgE BASEdMost PXI modules are register based modules rather than message based and this marks ainificant difference between traditiona benc intrent and PXI.In message based instruments remote control is achieved by sending the instrument a commandthat it recognises. The information is sent in a message format which is interpreted by embeddedsoftware in the instrument. It could, for instance, be CF100 MHz to set a carrier frequency (CF)to 100 MHz. Embedded software then determines the setting of the registers and sets them to therequired values.In most PXI modules the required signal is generated by simply setting the registers directly- usually there is no embedded software that will interpret the simple message to set a carrierfrequency of 100 MHz. Normally this would require the user to have a detailed knowledge ofhow the hardware works so he could set the latches. This is far too complicated to be a usefulmethod of control. Instead a software interface is created between the registers and a user, andinstead of being run on a controller embedded in the instrument it is run on the Slot 1 controller oran external controller connected to Slot 1. This interface is the software driver and the soft frontpanels that are normally supplied with every module.Having the software running on an open PC hardware target means that it can be written usingmore commercially accessible tools and can allow the software to adapt the hardware to newapplications by users and integrators with a good working knowledge of the target module.Page 2.4

2 - PXI SOFTWARE BASICSSome complex PXI modules have internal controllers or DSPs which provide higher levelfunctions which are similar to message based instruments. These aspects are mostly hidden fromthe user by the software driver to simplify programming, but a register level programmer mayhave access to these lower message based commands.Although the data transfer between the controller and the module registers is faster than in benchinstruments because of the speed of the PXI backplane, it should be remembered in any speedcomparisons that the bench instrument is performing functions that now have to be performedby the PXI controller. Message based instruments require shorter command strings than complexregister based instruments, register based instruments are much quicker to load data to but relyon a central controller for processing program instructions. Speed comparisons should take intoaccount these fundamental differences in architecture.Program Development EnvironmentThere are a number of different development environments that can be used on the PXI platform.Some of them are general for PC software development, some are more targeted to PXI testapplications. This section some of the most commonly used in test and measurement.PXI Software Specification v2.1 RECOMMENDS S support pport for the te following foowin environentenvironments:• LabVIEW, National Instruments, 4.0 or higher• LabWindows/CVI, National Instruments, 4.0 or higher• ATEasy Geotest-Marvin, Test Systems, Inc., 4.0 or higher• Visual Basic, Microsoft, 5.0 or higher• Visual C/C++, Microsoft, 5.0 or higherSince the standard only recommends support for the above environments it should not be assumedthat all are supported.Software programming environments are for convenience usually described as being either textbased or graphical based according to the user interface presented to the programmer.Graphical environmentsNational Instruments LabVIEW & Agilent VEE ProBoth LabVIEW and VEE Pro are easy to use, graphical programming environments that providean intuitive approach to building instrument control programs. Both are targeted towards test andmeasurement.They both provide useful tools for data acquisition and analysis, are easy to use and provide aquick design solution. They are ideal for low volume manufacturing test.For larger test systems, especially for high volume testing that is speed critical, other testenvironments may be more suitable. They can provide smaller proram files and efficient codinthat will run faster on the same type of controller.Page 2.

2 - PXI SOFTWARE BASICSLabView Demonstration VI (Virtual Instrument) for Pickering Interfaces SwitchesLabView Diagram for Pipx40 Example ProgramText based environmentsMicrosoft Visual C++ & Borland C++BuilderMicrosoft Visual C++ and Borland C++ are two of the most popular integrated developmentenvironments for C++.A C++ environment is often used when there’s a need to obtain total control over your test systemand when test speed is important.Visual C++ and Borland C++ offer very similar features and capabilities.Page 2.

2 - PXI SOFTWARE BASICSMicrosoft Visual BasicVisual C++, showing switch driver example codeVisual Basic provides an easy way of rapidly building Windows applications with drag and dropbuilding blocks for the Windows basic components. This makes it very easy to quickly build asoftware user interface. Visual Basic uses the BASIC programming language.Visual Basic, PIL PXI Demonstration ProgramPage 2.

2 - PXI SOFTWARE BASICSThere are many different drivers supporting different platforms, data busses and developmenttools. Since PXI is based upon PC technology, and the most commonly used operating system isWindows, the IVI and VISA standards have adopted Windows as it primary environment. Thissection provides a general overview of the IVI and VISA driver standards.vISA And IvI RELATIOnShIPTest Code andApplication ProgramIVI (if available)VISA or alternativeHardwareSimplified diagram showing the relationship of hardware, drivers and ApplicationProgram Interface (API)WhAT IS vISA?The VISA standard - Virtual Instrument Software Architecture – was originally created and ismaintained by the VXI plug & play system alliance (www.vxipnp.org). VISA has now been fullypdated by te PXISA to add PXI pport. Te objective of te tandard i to define a way ofcreatin intrent driver wit a deree of interoperabiity between different anfactrer’modules.The PXI standard encourages the use of the VISA standard.Key aspects of VISA are:• Allows you to install different drivers from different manufacturers on the same PXIyte witot ettin conflict.• The driver uses a standardized VISA I/O layer for all I/O functions to ensureinteroperability.• It define a way of writin driver.• A driver tat foow te VISA pecification e defined data type and in oe caedefined fnction nae.• It reduces the process of learning new instruments and the time to develop yourtest system.Page 2.9

2 - PXI SOFTWARE BASICSBy using drivers compliant with this standard, test engineers can in principle build hardwareindependent test systems. Instruments can be changed to newer models or to another manufacturersproduct without changing the test program.Current ClassesOscilloscopeDigital multimeter (DMM)Function generator & ArbDC power supplySwitchPower meterSpectrum analyzerRF signal generatorIvI Instrument ClassesFuture classes and classes in developmentAC power supplyChemical analyzerDigital test instrumentIVI instrument classes completed or planned (June 2003)It should be noted that IVI drivers provide interchangeability only where the IVI Foundationa copeted te tak of definin an intrent ca and no intrent pecific featreare included. A standardized driver cannot always take into account differences in hardwareperformance (accuracy, speed, features) between alternative models or manufacturers. Where theIVI driver includes information about hardware parameters (e.g. contact parameters for a switch)there is no guarantee that the programmer has made use of the feature, or that the information isaccurate, in order to simplify the programming task and meet timescale objectives. In practice iti eentia tat conideration i iven to te coneqence of canin fro one anfactrer’module to another, since the modules may not behave in exactly the same way.IVI cae iit te operation of intrent to te fnction defined in te tandard, oeinstruments might have additional functionality that can only be accessed using the customizedIVI functions. Consequently the use of IVI drivers may limit what can be achieved in a systemby using a more dedicated interface.IVI drivers have a built-in instrument simulation capability. With the simulation feature you canstart developing you test application without having the instrument in your system. It allowssoftware development to start before instruments are delivered, or while the instruments arebeing used in other test applications.It od ao be reebered tat IVI driver ipoe a inificant oftware overead wit aconsequent slowing of system speed. This performance penalty will reduce as more powerfulcontrollers become prevalent, but high level programming will always be slower to execute thanusing low level calls.IvI dRIvER ARChITECTuREIVI drivers can be created in a number of ways with or without following the above IVI classes.Wat’ coon wit a IVI driver i a nber of inherent capabilities that go beyond those oftraditional instrument drivers. These capabilities include advanced features such as instrumentsimulation, state caching, automatic range checking, and multi-thread safety. As long as a driversupports these inherent capabilities it can be classed as an IVI driver.Page 2.

2 - PXI SOFTWARE BASICSIVI Custom Specific DriversIVI custom specifi c drivers support only these inherent capabilities and instrument specifi ccapabilities that are not standardized upon by the IVI foundation and that are unique to aparticular instrument.IvI Class-compliant driversIn addition to these inherent capabilities, IVI drivers can comply with an instrument classpecification to pport te IVI fondation’ oa of intrent intercaneabiity. Tee driverinclude:• Base class capabilities common to most instruments in a class (e.g., edge-triggeredacquisition on an oscilloscope)• Class extension capabilities that represent more specialized features of an instrumentclass (e.g., TV trigger on an oscilloscope)IVI Class-compliant Specific DriversIVI class-compliant specifi c drivers contain inherent capabilities, base class capabilities, as wellas class extension capabilities that the instrument supports.IVI Custom SpecificdriversInherent CapabilitiesFor example thefollowing functions:initialize, reset, closeInstrument SpecificCapabilitiesFunctions that aredefi ned by themanufacturerIvI Class-CompliantdriversInherent CapabilitiesFor example the followingfunctions: initialize, reset,closeBase Class capabilitiesFor example the functionsconnect/disconnect in theswitch classClass ExtensionCapabilitiesFor example scannerfunctions of a switchInstrument SpecificCapabilitiesFunctions that are defi nedby the manufacturerIvI Class-CompliantSpecific DriversInherent CapabilitiesFor example the followingfunctions: initialize, reset, closeBase Class CapabilitiesFor example the functionsconnect/disconnect in the switchclassClass extension CapabilitiesFor example scanner functionsof a switchOverview of IVI Driver using a Switch as an examplePage 2.2

Application Program2 - PXI SOFTWARE BASICSTo achieve interchangeability, users program to an IVI class interface available through an IVIca-copiant pecific driver or a eparate IVI class driver. This is shown in the middle of theimage below. Programming through the “IVI-C Class Driver” makes the “IVI-C Class CompliantSpecific river” intercaneabe. In practice yo cannot intercane to any oter a copiantinstrument and driver without trouble, and of course, the instrument you change too, must haveat least the same features and the same performance as the old one for those performance areascritical to the application.IVI(C or COM)Custom SpecificDriverIVI-CClass DriverIVI-CClass CompliantSpecific DriverIVI-COMClass CompliantSpecific Driver&Class InterfaceI/O Library (Normally VISA I/O)Instrumentation HardwareRelationship between Classes of IVI DriversTo support all popular programming languages and development environments, IVI driversprovide either a C or a COM language API. Driver developers may provide both interfaces aswe a interface optiized for pecific deveopent environent.All IVI drivers communicate to the instrumentation hardware through an I/O Library. The VISAlibrary is used for the GPIB and VXI buses, while other buses can either utilize VISA or anotheribrary. In PXI ti ean tat te VISA I/ Library doen’t ave to be ed for IVI drivercompatibility, but it normally is.Other driversManufacturers may offer their own drivers that are designed to run on selected computingplatforms. The driver can be modeled on the VISA standard. The main advantage of a non-VISAdriver is that it permits the system to operate without a VISA implementation supporting the PXIbus, an important consideration for users of Visual Basic or Visual C/C++.Non-VISA drivers will continue to support users whose controllers are not PXI compliant (e.g. aPC driving a PXI system via a PCI to PXI bridge), contain no hardware or software componentsthat confer a VISA license, and who have not obtained VISA through a standalone license.Page 2.

2 - PXI SOFTWARE BASICSdriverversionsPlatforms depends on EnvironmentsIVI driversWindowsVISA I/O, IVI Enginein the systemcontrollerC/C++, LabVIEW,LabWindows.VISA driversWindows, Mac OS?,Solaris?, Linux?VISA I/O in thesystem controllerC/C++, LabVIEW,LabWindows.Registry based(Non IVI/VISA)Depends on driverpackage, could be anyOS.Normally onlyrequires the driverpackageAny program supportedby the instrumentmanufacturerMessage based(Non IVI/VISA)Depends on driverpackage, could be anyOS.Normally onlyrequires the driverpackageAny program supportedby the instrumentmanufacturerdriverversionsIVI driversVISA driversRegistry based(Non IVI/VISA)Messagebased(Non IVI/VISA)Programming EaseVery easy to program, short learning process.All different type of cards is programmed in thesame way independent of manufacturer.Quite easy. Some functions are the samebetween instruments and all data types ispredefi ned.Depends how well the interface is defi ned bythe manufacturer. Learning one instrumentdoesn’t help you to learn another one.Depends how well the interface is defi ned bythe manufacturer. Learning one instrumentdoesn’t help you to learn another one.Speed Over PXI BusVaries from slow to fastdepending if the driver cantake advantage of the stateNormalVery fastNot used over PXIPage 2.4

3 - LXISECTION 3LXILXI is a new instrumentation platform supported by nearly the whole Test and Measurementindustry, based on industry standard Ethernet technology designed to provide modularity,flexibility and performance for all Functional Test Systems.LXI ......................................................................................................................3.3LXI – an emerging standard ...............................................................................3.3What is LXI? .......................................................................................................3.3Comparing LXI and PXI ......................................................................................3.5LXI Overview ......................................................................................................3.6LXI Functional Class Models ..............................................................................3.7LXI Physical Overview ........................................................................................3.7Reset Mechanism ...............................................................................................3.8LXI LAN and Web Overview ...............................................................................3.8LXI Trigger Interface Overview ...........................................................................3.9LXI Programmatic Overview ...............................................................................3.11Page 3.1

3 - LXILXI Switching Chassis (60-102)• Fully LXI Compliant Interface• Accepts any of the large range of Pickering Interfaces 3U PXI switch module• Supports 7 Slots• Ethernet control interface with an integrated web based interface• Module control via IVI or kernel drivers• Allows Pickering Interfaces 3U modules to be used freely in PXI or LXI controlledenvironmentsPage 3.2

3 - LXILXIAs this version of the PXImate was being created two new standards are emerging or beingcreated, the LXI standard and the PXI Express standard. Of these the LXI standard is likely tomake the most impact on the test and measurement industry in the next few years. PXI Expresswill become a migration path for the current PXI standard that is likely to initially focus on a fewkey applications.As these are both emerging standards details are likely to be subject to change. PickeringInterfaces is involved in the creation of both these standards and are top level members of boththe controlling organisations.LXI – an emerging standardFor many years GPIB has been the de facto control method for bench instruments designedto mounted rack systems, PXI is now a more recent but mature standard for both switchingand instrumentation applications for modular architectures. Some instruments have adoptedUSB and LAN interfaces to compliment and occasionally replace GPIB. A new standard is nowemerging that will start the challenge to the dominance of GPIB in bench and rack systems andwill compliment the PXI standard.Although LXI is at an earlier stage of evolution products can be expected to become availableas the test and measurement companies adapt existing products and design new products to theLXI format. It is important that users understand the relative strengths and weaknesses of LXIcompared to the more mature technologies. This section provides an early insight to the path thatLXI is taking.What is LXI?LXI is an acronym for LAN eXtensions for Instrumentation, a standard being developed by theLXI Consortium. Pickering Interfaces is a Strategic member of the LXI Consortium.LXI devices are envisaged to eventually lead to designs that may have virtually no user frontpanel controls. User connections are typically on the front panel while power, trigger connectionsand the LAN interface on the rear panel.LXI Devices differ from legacy LAN devices in that they have an interface that has a commonfeel and way of being used – current LAN devices tend to be very proprietary in nature and canbe expected to behave in proprietary ways when connected to the LAN. Many of these olderLAN based instruments can be expected to be upgraded to LXI compliance. The first version ofthe standard has been defined by rules and recommendations in a way that permits these productsto become compliant.Each LXI device is self contained, it has its own power supply (usually AC, but can be DC orPower over Ethernet) and enclosure. Many new LXI Devices may be implemented in half rackwidth units as the need for front panel interfaces and displays allows the design of new formfactors to be implemented.Page 3.

3 - LXIThe LXI Consortium expects early systems to have a mixture of interfaces to test equipment, asituation which will have implications on the potentially diverse programming environment.LANMXIINTERFACERS232PCIBRIDGEGPIBADAPTORROUTER ORSWITCHLXIDEVICELXIDEVICELXI VXI RS232 PXIGPIB GPIBDEVICELXI devices being used with other legacy control interfacesAt a later stage the expectation is that adaptors will be used to produce hybrid systems thatprovide a greater degree of LXI compatibility and a more uniform programmatic environment.These are recognised in the standard as Hybrid Systems.ROUTER ORSWITCHLXIDEVICELXIDEVICELXIDEVICELXIDEVICELXIDEVICEROUTER ORSWITCHLXI/GPIBADAPTORLXI/PXIADAPTORLXI/VXIADAPTORGPIB PXI VXI LAN INSTRUMENTA hybrid LXI system where adaptors are used to make legacy devices LXI compatible.Page 3.4

3 - LXIComParIng LXI and PXIThere are important differences between LXI devices and PXI products, a summary of some ofthe differences being contained in the table below:PXILXIPower Central AC/DC to each moduleProgramming Register based (mainly) Message based (mainly)Controller PC based AgnosticOperating System Windows AgnosticCooling Chassis based Module basedMechanical size 3U or 6UDefined depthSmall PCB areaNot constrained (expect halfand full rack width, variousheights and depths)Multi-vendor At sub chassis level At chassis level onlyBus interfacePCI based, shared parallelbusSerial, star and hubconnectedTrigger Backplane connection External wired triggerIEEE1588 based eventtimingThere are some natural consequences of these differences.PXI modules do not have the burden of having an AC power supply in each module, do notrequire a microcontroller or PC to provide a message based LAN and web interface and do notrequire their own case or cooling. Compared to just a simple PXI module, LXI requires moreroom and has a higher cost. If several devices are needed to emulate the functions provided ina PXI chassis these LXI overhead costs and size issues will rapidly exceed the cost of the PXIchassis.However, LXI devices have more mechanical freedom, do not use a high speed parallel bus(replaced by a serial bus and message interface), have appropriate cooling designed for theapplication, have their own power supply conditioning (with the freedom of choice of voltagesand currents) and their own EMC shield. Consequently it is reasonable to expect higher parametricperformance, more complex functionality and more freedom to include larger building blocks.LXI and PXI clearly take differing approaches; as a consequence they will be better at solvingdifferent problems. PXI only challenges the parametric performance and complex functionalityof bench instruments in a few cases (such as DMMs), but LXI clearly will have the controlledenvironment and freedom of design to emulate the characteristics of a sophisticated and highperformance bench instrument.PXI will generally offer the capability of more diverse and denser (but simple) solutions and theability to mix many different functions in a single chassis that will probably not be achieved inLXI.Page 3.5

3 - LXIConsequently both approaches are likely to succeed in applications where they have the moresuitable approach. There will be some overlap in some systems, but these are not likely to be themajority of applications.As in most industries this definitely is a case of one standard does not solve all problemsIn some systems a PXI chassis can be added to a system with an LXI interface built-in, allowingPXI modules to be used through the same resources as other LXI devices. Pickering Interfacesare offering a range of chassis with this capability, providing support for all of its switchingmodules (and some of the instrument) range. The test system engineer does not need to decidebetween LXI and PXI as the control interface, the only choice being between PXI modules in aPXI chassis that is LXI enabled and a PXI system controlled as an extension to the PCI bus ofthe controller - a decision largely influenced by system level issues.LXI overviewThe LXI standard defines devices using open-standard LAN (Ethernet) for system interdevicecommunication. The standard will evolve to take advantage of current and futureLAN capabilities. It provides capabilities that go well beyond the capability of legacy test andmeasurement connectivity solutions. It will provide users with solutions that are denser, smaller,faster and cheaper than legacy solutions.The LXI Standard has three key functional attributes:• A standardized LAN interface that provides a framework for web based interfacing andprogrammatic control. The LAN interface can include wireless connectivity as well asphysically connected interfaces. The interface supports peer to peer operation as well asmaster slave operation.• A trigger facility based on IEEE1588 that enables modules to have a sense of time that allowsmodules to time stamp actions and initiate triggered events over the LAN interface.• A physical wired trigger system based on a LVDS electrical interface that allows modules tobe connected together by a wired interfaceThe LXI Consortium expects LXI devices to be used in a wide variety of systems, often includingdevices that are not by themselves LXI compliant. These devices are likely to include GPIB, PXI,VXI and LAN instruments with conversion devices where required.Trigger events over the LAN can be sent by UDP to minimize the latency that can be experiencedwith TCP/IP protocols. The wired trigger and IEEE1588 triggers are designed to address concernsabout the latency that is sometimes seen in LAN based systems. The defined wired trigger facilityprovides a triggered mode of operation that emulates trigger signals based on direct point to pointconnection between legacy instruments. The IEEE1588 facility allows triggers to be scheduledor events to be time stamped against a system clock.LXI Devices include web pages that can be opened with a web browser to view and changevarious parameters the LXI Device has been set to.Page 3.

3 - LXILXI Functional Class ModelsThe LXI Standard defines three functional classes of instrument to meet the requirements ofdifferent applications.• Functional Class C. These devices provide a standardized LAN and web browser interfacethat is compliant with the LXI Standard. These devices do not need to support eitherthe physical trigger or the IEEE1588 timing aspects. This class is particularly suited toapplications where legacy products have been adapted to the standard, but it is also wellsuited to applications where there is no necessity to offer triggered or timed functionality.This class may also include physically small products, such as sensors, that use battery poweror Power over Ethernet (PoE) where simple device architecture, low cost and small size arekey attributes.• Functional Class B. These devices provide a standardized LAN interface and support theIEEE1588 timing aspects. The IEEE1588 interface allows devices to execute triggeredfunctions equivalent to those available over GPIB and with similar or better timingaccuracy.• Functional Class A. These devices provide a standardized LAN interface, IEEE 1588operation and physically wired trigger interface. The wired trigger provides a standardizedability to support trigger events between devices whose timing accuracy is purely limited bythe physical limitations of cables and the physical instrument design. The trigger functionalityis broadly equivalent to the backplane triggers of modular instruments in card cages, thoughcable lengths may typically be higher than backplane trigger lengths.The standard does permit the wired trigger facility to be present on Class C devices.The Functional classes do not imply any particular physical size for a LXI Device.LXI Physical OverviewLXI modules are designed to provide a dense and compact solution for test systems. Many LXIdevices will provide only minimal manual user interfaces to reduce device complexity and space.Many modules are expected to be 1U to 4U high and half rack width, but modules occupying a fullrack width are expected to be implemented for legacy applications and more complex functions.Some modules, such as sensors, may be much smaller and have mechanical dimensions that arenot intended for rack mounting.Where devices are intended for rack mounting and are designed to occupy a half rack width,the standard includes recommendations and rules that encourage a “good neighbor” approach tominimize interaction between modules.The physical standard includes a definition of a recommended half rack width mechanicalstandard resulting in a LXI device described as an LXI Unit. The LXI Unit allows modules to bemounted side by side, irrespective of which vendor is selected, and permits the easy installationof devices with differing heights alongside each other. A mechanical structure is defined thatsupports and locates the LXI Units and blocks airflow between adjacent modules. Dimensionalinformation is supplied to ensure conformance to the LXI Unit standard for both the LXI Unitsand the mechanical structure that supports them. Where forced air cooling is required thenPage 3.

3 - LXILXI Units should provide air intakes on the side and an air exhaust to the rear. Devices shouldtolerate one side air intake being blocked by a neighbor to ensure that they do not have thermalcompatibility problems.Manufacturers can choose to use alternative half rack width approaches based on proprietarymechanical standards and interconnections systems, an approach most likely to be used forlegacy case designs.User connections to LXI Devices are recommended to be on the front while LAN, trigger andpower supply connections are on the rear. Indicator lights on the front panel show the presenceof power and have a LAN status indicator to ensure users can quickly spot simple functional orconnectivity problems. A recommended indicator shows the operating condition of the IEEE1588clock sytem.The module power can be provided by a standard AC power supply with automatic voltageselection or by a DC power source. Alternatively an isolated DC input connection can be provided(or a Power Over Ethernet source for lower power modules) for applications where AC supplyoperation is not desirable. A 48 V isolated supply is recommended for these applications to alignwith the standards for Power Over Ethernet, but other voltages are permitted.LXI devices are expected to conform to the relevant standards applicable for intended marketsfor safety and environmental standards.Reset MechanismLXI Devices must include a hardware reset mechanism for the LAN (LAN ConfigurationInitialize).The LAN reset provides a mechanism for recovering from mis-configured LAN settings thatcould render the device incapable of communicating over the LAN. Initiating the LAN resetrestores the manufacturer’s default settings and passwords – settings that must be disclosed inthe supporting documentation – and forces a Device reset.LXI LAN and Web OverviewThe LAN interface for LXI devices is intended to use 100baseT or better connections based onthe IEEE 802.3 standards. Modules have to be designed for fast boot times under all conditions(including circumstances where the network is disconnected). Network speed and duplex settingsare automatically detected to avoid users having to experiment with crossover cables or speedsettings.The LAN interface is defined to minimize the amount of user intervention required for configuringthe TCP/IP parameters and the standard ensures that instruments can be quickly ported from onesystem to another without risk of system hang-ups and a minimal amount of user intervention.Access to the instrument functions is via a web browser that provides essential information (suchas instrument type, serial number, Functional Class) and about key settings on the modules’Welcome page. The web interface is required to provide an additional IP Configuration pageand a Synchronization page (if the device is Functional Class A or B). The Synchronization pageincludes information about the IEEE1588 parameters and the settings of the wired trigger. If thePage 3.

3 - LXILXI device allows the user to change any of the instrument settings these have to be passwordprotected. Examples of sample web pages are available to show how the web pages might bepresented by an LXI Device.LXI devices can be assigned aliases to make it easier for users to identify, particularly forcircumstances where more than one of the same type of module may be in the system.The LXI standard allows modules to have automatic lookup for the latest firmware or softwarethrough a homepage created by the module manufacturer.The LAN connection can be made with physical cables or through a wireless access systemto cater for applications where a physical connection is difficult to arrange or technically notdesirable. Provision has been made for the use of optical connection systems in the future.LXI Trigger Interface OverviewLXI provides three trigger mechanisms, one based on triggering over the LAN, the second basedon IEEE 1588 Precision Time Protocol running over the LAN interface, and the third based on awired trigger interface (LXI Trigger Bus).The LXI trigger facilities use the principal of a uniform approach – within the performancelimitations of each trigger mechanism trigger functions can be performed by any of the methodsand can be connected together. A trigger event on the wired trigger can, for example, initiate aLAN or IEEE1588 trigger event.The LAN trigger provides a way of programmatically triggering events through driver commandseither from the controller to the LXI device or by message exchange between LXI devices. Itis available on all Functional Classes of LXI devices that require trigger operation. This triggermode is the simplest to implement but has the lowest performance because of the potentiallatency in the LAN communication.IEEE 1588 Precision Time Protocol is available on Functional Class A and B devices andprovides a way of synchronizing clocks across many LXI devices, giving the system a coherentunderstanding of time that can be used to set up triggered events based on the system time.IEEE 1588 can either be implemented entirely in software or can be supported by dedicatedhardware that provides more accurate timing synchronization. Timing accuracy and uncertaintyis dependent on the module and the IEEE 1588 implementation, but can be expected to be in therange of 10’s of microseconds to 10’s of nanoseconds.Triggers or events (measurements) can be initiated at specified times, or can be generatedimmediately on receipt of the instruction, though in this case there will be a higher degree of timeerror because of latency in the control system.The LXI Trigger Bus available on Functional Class A devices connects LXI devices by a physicaldaisy chain or star configuration to proved a more deterministic trigger interface that can be eventdriven (by a module for example) or timed by IEEE 1588 (generating a trigger into the wiredtrigger system). The interface is based on an 8 channel multipoint LVDS (M LVDS) signalingsystem that allows LXI modules to be configured as sources and/or receivers of trigger signals.The interface can also be configured to a wired OR configuration.Page 3.

3 - LXIThe LXI Trigger Bus has an input and an output connector to allow easy daisy chaining of LXIdevices. The last device in a daisy chain must have its output connector terminated in a specifiedload to ensure that transmission lines are correctly terminated.The LXI Trigger Bus provides a more deterministic inter-module trigger than IEEE 1588 andmore closely emulates the trigger facilities provided on instruments, such as oscilloscopes, thatare connected directly by physical connectors. Trigger Adaptors can be used to translate triggersfrom the LXI Trigger Bus to other trigger levels, or to convey a trigger command from anothertrigger system to a LXI Wired Trigger event.The LXI Trigger Bus can be supported by a Star Hub that supports a number of LXI device daisychains from a single buffered hub. LXI devices can be connected to the Star Hub as a simple starnetwork, or they can be set up as hybrid system of star and daisy chain connections. In additionto extending the capacity of the trigger system the Star Hub can be used to translate a triggerfrom one channel to another which permits, for example, a device to send a trigger to otherdevices (including itself) with equal delay times if they are connected to the Star Hub with equallength cables. Since the Star Hub is at one end of each wired trigger chain it provides an internaltermination for each connection.The LXI Trigger Bus also permits the exchange of clock signals across one or more of the 8channels available.Trigger Bus with Integrated TerminationStar HubTRIGGER CABLESTriggerAdaptorGPIB, PXI, VXIor otherTrigger SystemsTERMINATORTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusCLASS ALXI INSTRUMENTSTrigger BusTrigger BusTrigger BusTERMINATORTERMINATORTERMINATORTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTrigger BusTERMINATORTriggerAdaptorGPIB, PXI, VXIor otherTrigger SystemsTERMINATORExample Wired LXI Trigger Bus supporting LXI devices in a hybrid star and daisy chainconfiguration with a Star Hub and including Trigger Adaptors to connect to other systemsPage 3.10

3 - LXILXI Programmatic OverviewThe LXI standard requires that LXI devices have an IVI driver and recommends that the relevantIVI class model is used where applicable. LXI devices are permitted to be supplied with otherdrivers to allow support of other operating environments. The IVI drivers are required to supportVISA resource names. LXI Devices must use VXI-11 to provide a discovery mechanism; otheradditional discovery mechanisms are permitted.The programmatic standard defines the way that trigger functions (LAN, IEEE1588 or LXI BusTrigger) are managed and operated for Class A and B LXI devices. It includes a comprehensiveexample state machine and architecture for the trigger functions, though LXI devices may onlyimplement the parts that are relevant to the functions it can usefully support.There is a requirement that all representations of time derived from the IEEE1588 are representedin a uniform way to ensure consistent interpretation of the information.The programmatic section of the standard contains a considerable amount of detail onprogramming rules, much of which may reside in separate documents to help improve the clarityof the standard.Page 3.11

3 - LXIPage 3.12

4 - PXI SWITCHINGSECTION 4PXI SWITCHINGSwitching systems are a key part of most test systems. Signals need to be routed to variousparts of the device under test and signals from the device need to be routed to measuringequipment so that test results can be obtained.Switch Types .....................................................................................................4.3Describes the switch types (Form A, B, etc.) that Switch manufacturers refer too.Switch Configurations .....................................................................................4.5Describes the switch architectures (cascade, multiplexer) commonly used.Maintenance of Switching Systems................................................................4.8Provides an overview of maintenance requirements to be taken into account whendesigning a switching productTesting with a Crosspoint Matrix ....................................................................4.9How to minimise the size of your crosspoint or matrix system.Testing with Resistor Switching Cards ..........................................................4.10Resistor chains are used to simulate the behaviour of sensors in many applications.This section explains these useful products and their specifications.Switch Technology ..........................................................................................4.13Explains the different types of switches used for switching and their problems.Optical Switching .............................................................................................4.15Optical switches cn be constructed to distribute a signal on a fibre to different connectors.This section explains how they work.Switch Specification Terminology ..................................................................4.18Switch specifications can use many terms that lead to user confusion. This sectionexplains all those strange terms.Platforms for Switching Products ...................................................................4.21Switches need to be controlled, and there are various platforms for providing thiscontrol. This section explains some of these available options.Page 4.1

4 - Pxi SWiTCHiNGPickering have more than 500 PXI Switching Modules, including many very sophisticatedmodules with very high density and very specific functionality. As an example, two of our FaultInsertion BRIC Modules are shown, these are used in the Aerospace and Automotive Industriesfor design verification of very complex ECUs (Electronic Control Units).124 x 8, 1Amp FIBO BRIC Module (40-592)30 x 8, 10Amp FIBO Power BRIC Module (40-595)Page 4.2

4 - pxi SWITCHINGSwitching SystemsThe complexity of switching systems varies greatly depending upon the type of test beingperformed. Functional or component testing on printed circuit boards can involve accessingmany test points, requiring the use of large arrays of relays, while other applications may onlyrequire the routing of a few input and input signals. The signals can vary from high current orhigh voltage applications in automotive, or motor control systems, to low voltage access pointsfor 4 wire measurements on low power PCBs.Switch TypesSPST (Single Pole Single Throw) (1 Form A or Form B)CommonNo connectionForm A switches are open circuit with no power appliedto the coil.Form B switches are closed when no power is applied tothe coil.SPDT (Single Pole Double Throw) (1 Form C)CommonNormally openForm C switches have two possible outputs from input.Normally closedDPST (Double Pole Single Throw) (2 Form A or Form B)No connectionCommonCommonNo connectionTwo switches operated by the same control, each switcheither being open circuit (no connection) or connected toan output.Page 4.

4 - pxi SWITCHINGDPDT (Double Pole Double Throw) (2 Form C)Normally openCommonCommonNormally closedNormally openTwo switches operated by the same control, each switchhaving an output connection for the normally open andnormally closed contact.Normally closedAbsorption Switches50 ohmsInputOutputOutputA switch where the contacts that are not being usedare terminated in 50 ohms. This avoids the presence oftransmission lines that are not correctly terminated andthe resonant structures they can generate. It requires thepresence of other (embedded) switches that connect theload to the unused contacts, but may not be shown onthe equivalent circuit.50 ohmsPage 4.

4 - pxi SWITCHINGSwitch ConfigurationsCascadeCascade switches can be used to connect a single device to one of many others. Connection toone device ensures that all other connections are isolated. The disadvantage with this method isthat the path length and the isolation varies with switch position resulting in variable insertionloss and screening depending on which path is in use.InputOutput 1Output 2Output 3Output 4MultiplexerCascade SwitchConfusion over the definition of the above term can arise because low frequency and microwaveswitch manufacturers have different definitions.Output 1Output 2InputOutput 3Output 4Output 5Output 6Single Channel MultiplexerA single channel multiplexer allows one instrument to be connected to any of a selection of otherinstruments. Some definitions allow more than connection, so one instrument could be connectedto more than one output. In terms of RF systems, this is not a satisfactory arrangement, since itincorrectly terminates transmission lines. Relay switches are bi-directional, allowing input andoutput to be swapped.Page 4.

4 - pxi SWITCHINGTreeTree networks expand a switch systems dimensions by connecting a series of switches inseries. The simplest networks are based on SPDT switches which can be used to create largermultiplexers.A tree switching network can also expand the capacity of the multiplexer at the expense of moreswitches and greater insertion loss. In tree networks each of the paths has the same number ofswitches, and to a first approximation, insertion loss will be the same for each input to outputroute.Output 1Output 2Output 3InputOutput 4Output 5Output 6Output 7Output 8Output 9MatrixTree Switching Network using SP3T switches to create a1 to 9 Channel MultiplexerA matrix switch allows several devices to be connected to a number of others. For RF applicationsonly one device should be connected to any one output, unless the switch includes powerdividers.1 to 3MUX1 to 3MUX1 to 3MUX1 to 3MUX1 to 3MUX1 to 3MUXA 3 x 3 Matrix Switch constructed from 3-way MultiplexersPage 4.

4 - pxi SWITCHINGSome types of matrix switch are configured as a blocking switch in order to reduce complexity.The example below shows a matrix where only one device at the input can be connected to onedevice at the output. All other inputs and outputs are disabled. Some manufacturers also refer toa blocking matrix as being sparse matrix.4 to 1MUX4 to 1MUXMatrix switches with no blocking limitations become very complicated, the number of switchestending to increase geometrically with the number of connections allowed. For applicationswhere the blocked paths are not required, or an alternate method can be adopted to circumventthem, the simpler matrix may offer better performance and lower cost because of the lower switchnumbers. The blocking matrix will, however, impose restrictions on future test applications.Crosspoint MatrixA Blocking 4 x 4 Matrix allowing only one connected pathCrosspoint switches are arranged in rows and columns. A switch located wherever a crosspointoccurs allows the row and column to be connected, hence the name. There is no limit to thenumber of connections a particular row or column has, but if more than one connection is madethe load on the signal source increases.=Crosspoint SwitchIn addition, unterminated transmission lines, which appear as parasitic loads, are attached to thecrosspoint switches. These can create resonant structures, and limit the bandwidth of the switch.The available bandwidth is also dependent on the switch position.The unwanted loading effects can be eased by adding extra relays, under software control, toautomatically isolate sections of unused transmission line. This can be important for very largecrosspoint switches.Crosspoint switches are also often described as (or are part of) matrix switches, especially inapplications where rows and columns are intended to have only one connection point.Page 4.

4 - pxi SWITCHINGMaintenance of Switching SystemsSwitching systems are often placed in vulnerable positions in a test system. They are often requiredto be operated many times during a test and hot switching of the loads may be unavoidable. Inaddition faults in the device under test may cause unexpected switching conditions to occur(voltage or current) that limit the relay life. During test system creation software errors or wiringproblems may result in fault conditions that exceed the switch ratings. Combined with a finitemechanical life it is apparent that switching has to designed with the expectation that relays mayfail, and that in turn means the product has to be maintainable.If a failure does occur the application often requires the failure to be fixed quickly, down time inthe system costs money. So it is essential that the system is designed to allow repair to be carriedout at, or close, to the point of use.• There are a number of considerations that need to be checked:• Does the manual identify the relay types used.• Does the supplier provide a fast way of obtaining replacements.• Does the product have spare relays installed that can be used to replace defective ones(remember to replace them though!)• Does the manual provide a cross check from the functional position of a relay to its physicalposition in the product.• For complex products where fault diagnosis may be complicated is their a tool to help locatethe defective relay.• Having identified the defective relay can it be extracted and replaced without the use ofcomplex tools or having to send it back to the supplier.Pickering Interfaces takes all these aspects into account when designing modules. The manualdoes provide all the information that is needed and offers to supply replacement relays from itsown stocks if the relay is hard to obtain or on long delivery. Where feasible modules do havespare relays supplied.For its large matrices a test tool, 90-100, is available that has supporting software designed tolocate faulty relays quickly with minimal user intervention. When the application requires a largematrix finding a fault any other way (or eliminating the matrix as a cause of a system failure) canbe time consuming to accomplish any other way.The relay packaging used is particularly important. Systems based on the use of leaded relays orrelays adapted for surface mount using folded leads are relatively easy to remove without specialtooling. Packages based on styles similar to ball grid arrays (BGA) however can cause seriousservice problems, particularly when they are densely packed. The inaccessibility of the solderjoints requires specialist tools to remove the devices, and the tools tend to stress the adjacentcomponents while the operation is being carried out – risking additional failures occurring.Pickering Interfaces does not recommend the use of BGA style packages for this reason, and donot use them on any of their switching modules.Page 4.

4 - pxi SWITCHINGTesting with a Crosspoint MatrixX1X12Y1=Y8Crosspoint MatrixA crosspoint matrix allows a set of connections on one axis (Y) to be connected to another set ofconnections on another axis (X) through the use of a crosspoint switch. It can be an extremelyuseful type of switching network since in principle any point on the Y axis can be connected toany point on the X axis.If a test system is using a matrix to connect test equipment on the Y axis to the device undertest on the X axis the resulting system can require a very large number of relays. The size of thematrix limits the bandwidth of the test system because of the high loading factors and increasesthe cost of the switch system. If, for example, the test equipment requires 32 access points and thedevice under test uses 400 access points the crosspoint matrix requires 12800 relays.In practice many of the relays may never be used, and there is a more practical way of configuringthe matrix.Instrument 1Instrument 2Instrument 3Instrument 7Instrument 8Device UnderTest No. 1Device UnderTest No. 2Device UnderTest No. X51 2 3 4 106 7 8 9 11 12 30 29 3531 32 33 34 4036 37 38 39 43 41 42 44 45 46426427428429430431432More Efficient Testing Using X-axis Connections OnlyTaking the above example if the test equipment and the device under test are arranged on justone axis (X) of the crosspoint matrix the X axis requires 432 access points. The Y axis is nowused to simply connect two points on the X axis together by closing the relays at both crosspointpositions.The number of Y axis connections required is now controlled by the number of simultaneousconnections that are required to connect the test equipment to the device under test. In manycases just 8 Y axis connections will enable the user to perform all his tests. The crosspoint matrixcomplexity is dramatically reduced since it requires a 432 by 8 matrix requiring 3456 relays.Page 4.

4 - pxi SWITCHINGSince the size of the matrix is reduced the cost is reduced and the bandwidth is likely to be higher.It will offer a more compact and flexible test solution with greater chances of module re-use infuture applications.The disadvantage is that each connection requires two relays in series rather than just one formore conventional methods. The additional relay marginally increases the resistance between thepaths, but the increase is relatively small compared to other factors.The Pickering Interfaces BRIC range of matrix switches are designed for this type ofapplication.Testing with resistor switching cardsSensors are used by many control systems to provide a measurement of the conditions presentin the systems they are managing. When evaluating the performance of these control systems,whether during design or in manufacturing, it is much more practical and controllable to use asimulation of the sensor rather than to try to control a real life sensor.Many sensors can be simulated using variable resistors, but rather than use mechanicallyadjustable parts it is easier and more predictable to use switched resistor systems.Other devices to be tested may require controls that simulate the effect of mechanically adjustablecontrols, and again they are best simulated in an ATE system by the use of switched resistorsystems.Simple Resistor ChainsA simple programmable resistor provides a series of binary weighted fixed resistors that canbe shorted out by a set of relays. The binary weighting allows the user to create any value ofresistor within the allowed range with a resolution equal to the value of the smallest resistor. Theresistor system will also include an optional “offset” resistor that determines the lowest value ofresistance that can be set. Manufacturers usually provide many resistor chains in a single moduleand can customise the resistor values and configuration to the user requirements.RESISTOR CHAIN 1R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16ROFFSETRESISTOR CHAIN 2R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16ROFFSETA Simple Resistor ChainPage 4.10

4 - pxi SWITCHINGOther ConfigurationsMany other configurations of programmable resistor are possible. A useful arrangement is simplyto combine resistor chains to form a potentiometer. Two resistor chains are connected in seriesand programmed such that as resistance is added to one chain it is taken away from the other,forming the digital equivalent of a potentiometer with a wiper contact.Some applications may simply require the selection of a few fixed resistor values and this canbe economically realised by simply using uncommitted relays, though such an arrangementhas obvious disadvantages if large numbers of values are required to be simulated or re-useof the module is a system requirement. PXI manufacturers can supply modules where arraysof uncommitted relays or relay chains are available with space to add the user’s own fixedresistors.Resistor Chain Specifications.Although resistor modules are in principle simple devices the specifications can be more complexthan first realised. A resistor module should have the following information:Residual resistance. This is the resistance of the chain when all the resistors are switched outof circuit. The residual resistance is caused by the sum of the connector, PCB track and relaycontact resistances.Maximum common mode voltage. This is the voltage to which the both ends of the resistor canbe raised above ground. The front panel connector or the relay design usually limits it.Expected Life. Normally quoted for low power and high power operation.Power dissipation. The maximum power the resistors in the chain can each dissipate. There maybe other limitations on carry current (for low set values) or voltage (for high set values.Roffset, not to be confused with the residual resistance. This is the value of offset resistor that isadded to the chain.Accuracy. Built up from the accuracy of the resistor fitted and the residual resistance effects.Differential Thermal Offset, caused by the thermoelectric voltage of the relays used. Each relayin the chain will create a voltage when the contact is closed, and these will add arithmetically.Since the sense of the voltage varies between samples the worse case offset is less than the productof a single relays thermoelectric voltage and the number relay contacts closed. The voltage can bemeasured as a residual value across the resistor chain with no external current applied.Resolution. The number of resistors in each chain that can switch, usually expressed as thenumber of bits. In typical modules adding chains in series with modified resistor values canincrease the resolution.Number of channels. Number of resistor chains in the module.Page 4.11

4 - Pxi SWiTCHiNG4 & 8 Slot, 3U & 6U BRIC Modules from Pickering Interfaces4-Slot 3U BRIC ModulePartially Loaded8-Slot 3U BRIC Module• BRIC4 & BRIC8, 3U & 6U, providing the highest density switching available on ANY switching platform• BRIC4 ultra high density switching module with up to 2208 high reliability Ruthenium reed relays• BRIC8 ultra high density switching module with up to 4416 high reliability Ruthenium reed relays• BRIC4 & BRIC8 design allows selection of the number of daughter cards for individual applications• BRIC4 & BRIC8 provided with extensive range of 1 Pole, Screened and 2 Pole switching configurations• BRIC4 & BRIC8 are available in a variety of matrix dimensions• BRIC4 & BRIC8 have fast operating time of

4 - pxi SWITCHINGSwitch technologyElectro-Mechanical RelaysElectromechanical Relays comprise an actuator or armature moved by a magnetic field, theactuator in turn moving the position of a contact to make or break a connection. The magneticcoil is physically separated from the contacts being moved to operate the circuit. These are themost common form of relays available and can be used for a large range of switching functions,including high power applications.Most relays of this type are not hermetically sealed and this can make them unsuitable forapplications where they are required to switch low level signals over long periods. Contaminationfrom the packaging process and plastic out gassing can result in partially insulating filmsappearing in the contact areas, leading to increased contact resistance even if the contacts aredesigned with a wiping action. At higher currents and voltages these problems do not occur asthe switching action cleans the contact and breaks down the films.Some switches may include a specification for low level contact switching contact resistance thatis worse than when switching high level signals. For switching low level DC signals hermeticallysealed switches, such as reed relays, should be used.The most reliable configuration for a reed relay is a SPST arrangement (Form A). SPDT (FormC) switches can be made but the difficulty in making them and the mechanical tolerance resultsin a product that has generally a lower life than SPST parts. If lifetime is important it can bebetter to use two SPST and drive the coils to synthesise a SPDT switch.Reed RelayReed Relay contact blades are made from a magnetic material encapsulated in a sealed glassenvelope which is in turn inserted into the centre of a magnetic coil. Applying current to the coilgenerates a magnetic field which deflects the contact blades, making or breaking the contact.The mechanical life of a reed relay is very long typically more than 10 9 for reed relays usedby Pickering Interfaces, in low current and medium current applications, through the use of ahermetic seal and precise metal contact materials in the contact areas. The magnetic field actsdirectly on the contact and there are few moving parts. The hermetic seal also makes reed relaysa good choice in hazardous environments since sparking does not create a safety problem.The coaxial form of these switches makes them a good choice for some RF applications.Reed relays are supplied graded according to their cost and performance.Lower qualitycommercial switches use Rhodium contacts that are less suited to switching low level signalsbecause of the build up of polymer films in the contact area of the reed.Instrument grade reed relays, used on all Pickering Interfaces reed relay modules unlessotherwise stated, use sputtered Ruthenium contacts that are suited for both low level and highlevel switching. The contact areas do not exhibit the same film problems that Ruthenium Reedrelays have (or the more severe problems of electro-magnetic relays).When purchasing reed relays or switching modules it is important to understand the type ofrelay that is fitted to the product. If the application is expected to include low level switchingwhere repeatable contact resistance is required then instrument grade Ruthenium reeds shouldbe specified.Page 4.13

4 - pxi SWITCHINGMercury Wetted RelayA reed relay with a film or ball of liquid mercury retained by surface tension in the contact areato provide the electrical contact. These switches, which typically need a specific mechanicalorientation to operate correctly, can have a long mechanical and electrical life, but the presence ofmercury has environmental and health issues. Their use is strongly discouraged where alternativesare available and in many countries they are banned by environmental legislation.Edgeline RelaysUsed in high frequency and microwave switches where a good 50 ohm impedance is requiredto very high frequencies. The 50 ohm transmission line is formed between the edge of a movingcontact ribbon and the RF ground plane or metal wall. By tightly controlling the gap betweenthe edge of the ribbon and the wall, a good 50 ohm impedance can be maintained regardless ofthe position of the ribbon. The gap involved is typically very small and requires precision in thedesign and manufacture of the part.PIN DiodeA PIN diode is a special type of diode made with a P type, Intrinsic type and N type semiconductormaterial. The structure results in diodes with a relatively long carrier lifetime. If PIN diodes areforward biased and used at frequencies well above the carrier lifetime they behave as resistors,the resistance being dependent on the forward current. This allows them to be used as switchesfor some RF and microwave applications, but at lower frequencies they become non-linear andbehave as conventional diodes.FETField Effect Transistors are used for d.c., RF and microwave applications. For RF and microwaveapplications, they can be used as a switch or an adjustable resistor whose state is determined bythe gate voltage. The on-resistance is much higher than mechanical relays and they can handle alimited amount of current or voltage before they cause distortion.Page 4.14

4 - Pxi SWiTCHiNG10 Slot, 3U Microwave BRIC Modules from Pickering InterfacesMicrowave BRIC 40-789Configurable 36 MUX with two outputs• Configurable 36 way MUX with 2 independent outputs• Use as 36:1, 30:1 plus 6:1 MUX, 24:1 plus 12:1 MUX or dual 18 way• Matched path loss on each microwave channel• Low VSWR on all channels• Ideal for evaluation spread and environmental performance of RF and Microwave devices• Suitable for use to 10 GHz or 20 GHzMicrowave BRIC 40-787 4x4 RFMatrix version• Up to 4x4 Microwave Matrix in a compact 3U PXI format• Optional Loop Through to allow matrix expansion• Optional termination to automatically terminate unused coaxial connections• Simple modular construction allows for easy customisation• Available in 10 GHz and 20 GHz versionsPage 4.

4 - pxi SWITCHINGMEMSMicro Electro Mechanical Systems are fabricated on semiconductor materials using specialprocesses based on those used for semiconductor manufacture. Three dimensional structures,such as cantilever beams, are formed that can be used as switches. The structure can be deformedby an electrostatic or magnetic field to make or break an electrical contact, which makes amechanical switch.At the present time there is limited product availability and a number of technical barriers to theintroduction of MEMS for commercial switching.MEMS are physically small structures which make them suitable for some switching applications,particularly where modest current or voltage capability are required. The switch contact materialshave to be compatible with semiconductor processing techniques (typically gold, aluminiumor polysilicon) and they require the use of hermetic or (preferably) vacuum sealed packages. Areported failure mechanism is when contacts stick or weld together - for example where goldcontacts are used. Increasing the MEMS switch current or voltage shortens the switch life in asimilar way to other mechanical solutions.Page 4.16

4 - pxi SWITCHINGOptical SwitchingOptical Switching is a general term applied to the switching of the electromagnetic waves carriedin glass fiber. Optical fiber behaves in a broadly similar way to microwave waveguide. Instead ofhaving a hollow metal waveguide which can be used to confine and propagate an electromagneticfield at microwave frequencies, an optical fiber confines and propagates an electromagnetic fieldat frequencies in the visible or infrared part of the spectrum.Optical transmission systems are used extensively in the transmission of broad bandwidth dataover the telecommunications network. One optical fiber can carry more information than manycoaxial cables carrying RF or microwave signals.The signals on the fiber still need to be switched, and clearly conventional switching technologycannot achieve this. Instead switching is accomplished by using mechanically adjustable mirrorsthat reflect the optical beam and steer the beam to other output fibers.The first generation of optical switches used mirrors mounted on moving armatures similar tothose used in electro-mechanical switches. A coil is used to generate a magnetic field whichalters the position of an armature. A mirror fixed to the armature deflects the optical beam, andas the coil is energised the mirror moves with the armature and deflects the beam to an alternateposition. The beam to the mirror is emitted from an optical fiber and the two alternate landingpoints for the reflected beam have fibers which guide the beam to the switch outputs.The problem with these switches is that they need very careful adjustment to make them workeffectively. Any change in the armature operation over time can increase the switch opticalinsertion loss. If the switch was mechanically vibrated the mechanical noise would couple tothe armature and the mirror, causing it to vibrate, again effecting the insertion loss of the opticalsignal.Many of this type of switch are still in use, but new designs are more rugged and based onMEMS technology.MEMS OPTICAL SwitchesMEMS switches also use moving mirrors to switch an optical signal. However, they use mirrorsthat are manufactured as part of a mechanical device chemically machined from silicon. Thesilicon is ‘machined’ by semiconductor process techniques to produce three-dimensionalmechanical structures which can be deflected by the use of electrostatic fields. The parts of thestructure that behave as mirrors can be deflected or moved to form a switch.PORT 1PORT 3PORT 1PORT 3PORT 2PORT 4PORT 2PORT 4Typical example of MEMS optical switch. Mirror moved to right to intercept light beamsPage 4.17

4 - Pxi SWiTCHiNGOptical PXI Modules from Pickering InterfacesFully Configured Fiber Optic PXI SystemDual 2 ChannelFiber Optic Multiplexer(40-855-022)8 ChannelFiber Optic Multiplexer(40-852-018)2 x 2Fiber Optic Matrix(40-860-012)• Over 80 PXI Fiber Optic Switch Cards• MEMS Technology Allows Fast & Reliable Operation• 2, 4 or 8 Channel Multiplexers• Choice of 5 Connector Types• Single or Multi-Mode VersionsPage 4.

4 - pxi SWITCHINGIn the normal state two optical beams from the left hand side are propagated by guide channels tothe outputs on the right hand side. In this case Port1 connects to Port 4 and Port 2 connects to Port3. On the left hand side there is double sided mirror which can be moved by a MEMS actuator.If the MEMS device is energised the mirror moves to the right until it enters the area where thetwo light beams intersect. The optical beams are now reflected from the mirror surfaces on bothsides and the beams are now diverted. Port 1 now connects to Port 3 and Port 2 now connects toPort 4. If only input beam is used the device behaves in the same was a SPDT switch.There are other configurations for MEMS switches used, but they are all based on the mechanicalmovement of mirrors to redirect the optical beam.MEMS based switches offer a number of advantages over other mechanical devices:• Very long service life• Relative immunity to vibration• Not subject to performance changes with time due to changing alignment• Need for precision alignment is transferred to a manufacturing process that isdesigned to provide a high degree of precision• Much faster operating time• It is possible to integrate many types of switch function into one MEMS deviceto provide more complex switching functionsOptical ConnectorsAs with wired connections there are a variety of optical connectors which can use variousmethods to connect two optical fibres together. The purpose of the connector is to bring the endsof the fibre into intimate contact, ensuring that the light conducting cores are accurately alignedand little of the light can escape the fibre. Typical connectors achieve less than 0.5 dB loss.Just like their coaxial counterparts optical connectors can use a variety of locking methods(bayonet styles, screw fixings) and are designed for different sizes of fibre.The connectors require careful handling when they being mated and protected when they are notin use. The fibre ends have to be highly polished in order to ensure good light connectivity. Theintroduction of dust or dirt can cause scratches that result in light scattering or a failure to comeinto intimate contact.The most common cause of connector failure in use is careless handling of the connectors.The optical connectors should always be protected when they are not being used and workshould be carried out in reasonably clean conditions. If a connector becomes dirty it is essentialit is carefully cleaned before attempting to mate it to another connector.More information on optical connectors is provided elsewhere in this book.Page 4.19

4 - pxi SWITCHINGSwitch Specification TerminologyCrosstalkMeasurement of the amount of signal that leaks from one switch system to another, usuallymeasured in dB relative the signal applied. The crosstalk is usually frequency dependent and isspecified at one or more frequencies. Inductive or capacitive coupling, the presence of groundcurrents or a combination of factors can cause the crosstalk.Measurement does not include any coupling of cables attached to the front of the PXI module.Insertion LossInsertion loss is measured at the front panel of the PXI module. It is defined as the loss of signallevel between the input and output connections of the switch and measured in dB for a definedsource and load impedance, usually 50 or 75 ohms.IsolationIsolation is frequency dependent and is defined as the reduction in signal level between two portson a switch when the switch is open. The isolation should be measured as the additional lossabove the insertion loss of the switch measured in dB for a defined source and load impedance,usually 50 or 75 ohms. Isolation is typically degraded if the load impedance is increased.Latching and Non-Latching (Failsafe)Some switches can be mechanically latched into one position, once a change of state is inducedby a current pulse. If the current is then removed the switch will stay in the same condition untilthe coil is pulsed again.Some latching switches include an indicator to show the current, to ensure that there is noambiguity.Non-Latching or Failsafe switches return to a specified state when power is removed. Theseswitches require continuous power to operate in a test system.Make-Before-Break, Break-Before-MakeThe time interval for a mechanical relay to switch is design dependent. The contacts may brieflyopen during transition, or they may maintain the first circuit until contact with the second pathis established.Make before Break ensures a contact path is always maintained and provides a smoothertransition, but temporarily connects the two output paths together.Break before Make ensures the first circuit is disconnected before making contacts with thesecond path, ensuring accidental paths are not connected.For some switch assemblies involving multiple switches this feature can be implemented bysuitable software control of the switch drive waveforms.Hot SwitchingSpecified current or voltages that can be switched while the contacts are live. This can causearcing as the switch contacts break, shortening the contact lifetime.Page 4.20

Cold Switching4 - pxi SWITCHINGA relay specification of the current and voltage that can be switched if the signal is first turnedoff before the relay changes state and the signal then reinstated once the relay has changed. Thisavoids the risk of contact arcing, increasing the contact lifetime. Typically, the cold switchingspecification is higher than the hot switching specification, but some switches rely on the signalbeing there to wet the relay contact.Contact WettingRelay contacts may accumulate oxides or dirt on the contacts, causing them to not switch correctly.In order to overcome this the relay is designed to remove or break through these contaminantswhen it is switched; this is referred to as contact wetting. It can be achieved using a wiping actionbetween the contacts, or by ensuring that there is a high contact pressure, or by hot switching.Many electro-mechanical switches have a minimum contact operating voltage and current neededto ensure that a contact is properly made. If the conditions do not meet the required minimumsthe contact may fail to wet, and give a high (and erratic) residual resistance. Instrument gradereed relays do not suffer from this problem.Switching SpeedTime taken for a switch to change state. There can be a number of phases separated out todescribe the speed:Command to Change StateInstruction to SwitchProcessing TimeDelay to Switch Change StateSwitch ResistanceContact Setting Time including Bounce if anySwitch BounceAs a switch changes position the contacts may briefly bounce from the mechanical movementinvolved. This causes the circuit to change state while the contact position settles down. It mayalso contribute to long-term variations in the contact resistance of the switch.• Processing time taken between a user initiating a change and the time when the coil (orother part) receives a changeDelay while the switch starts to change stateTime for the switch to change its conducting stateTime for the contacts to settle down•••Time behaviour of a Switch and the definition of Switching SpeedPage 4.21

4 - pxi SWITCHINGMechanical LifeThe mechanical life is the number of times that a switch can be operated with no (or little) load onthe contacts before there is a failure in the switching mechanism. The mechanical life is normallylonger than the contact life.Contact LifeThe contact life is the number of times the switch contacts can be operated with a load signal(current or voltage) present, before the switch starts to fail its specification. Failure can be dueto the contact resistance increasing, or the operating time being exceeded. The contacts may alsoweld together, particularly if a soft contact material (e.g. gold) is used.Voltage RatingVoltage that the switch contacts can sustain in the Off state. Normally specified for hot switching.It can be higher for cold switching.Current RatingMaximum current that the switch contacts can sustain in the On state. Normally specified for hotswitching. It can be higher for cold switching.Carry CurrentThe maximum current that a relay contact can carry assuming the contact is switched with thecurrent off. It can be limited by a number of factors, including temperature rise of the reed bladesin a reed relay. Where the current is limited by temperature rise it may be higher for pulsedcurrents (including AC) than for DC.Switch Current.The maximum current the switch can make and break. This will often be lower than the carrycurrent because the presence of a current (or voltage) can cause erosion of the contact material.Common Mode (Isolation) VoltageMaximum voltage that can be sustained between the switch connections and ground (or any otherspecified point). This can be greater than the voltage rating since it is stressing the insulationbetween the switch contacts and ground rather than contact materials.Thermoelectric VoltageVoltage developed across a relay contact due to the difference in temperature of the two contactseffectively forming a thermocouple. The temperature difference can be caused by any heat source,including heat from the relay drive coil. It is usually time dependent and can be influenced by theorientation of the switch. The voltage is present even when no current flows through the contactsand is often highly time dependent because of the way the contacts are heated. Data sheets forswitches used in applications where thermoelectric voltages are important usually quote thedifferential thermoelectric voltage where two connections (using a two pole switch) are madeto the source and the differential voltage is measured. The resulting voltage is much lower thanthe individual parts since there is a high degree of cancellation between voltages in a single reedrelay package.Page 4.22

4 - Pxi SWiTCHiNGPlATFormS For SWiTCHiNG SySTemSSwitching systems are offered in a variety of different, of which PXI is one important example.One platform may be more suitable than another for a particular application, for example a verysmall system may be more cost effectively implemented in PCI rather than PXI.Pickering Interfaces offer a variety of switching platforms to ensure users have a wide choice ofoptions. The principle platforms are as follows:• PXI (Compact PCI compliant)• System 10 and System 20 (IEEE-488, RS 232 or ETHERNET control)• VXI• PCI• Specialised switching card formatsEach format has its own advantages and limitations that can influence a decision on the mostsuitable platform for a given application.The following section describes the general characteristics of these platforms, what you need tooperate them and the issues that can effect platform choicePxi AND cPCiWhat you need for a PXI System• A chassis with the required number of slots• A PXI controller or an interface to an external controller• The switching and other modules required for your application• Supporting software for the chassis and modulesAn 8 Slot PXI ChassisPickering Interfaces Part Number 40-908A typical PXI Switching Modulefrom Pickering InterfacesPage 4.2

4 - Pxi SWiTCHiNGStrong FeaturesProvides platform for switchingsystems and instruments in onechassisSince it is an open standardproducts are available from othermanufacturersRobust module design withadditional functions availableThe number of available modules iscontinuously increasing because ofa commitment to continued productdevelopment.Chassis accepts low cost cPCIcards, and PXI switching modulescan be used in a cPCI chassisProduces very compact solutions forswitching applicationsThe chassis can have an embeddedcontroller (Slot 1) or an interface toan external controllerAspects that may adverselyeffect your applicationCost may be marginally higher thansystems only designed for switching,but are significantly lower cost thanother modular solutions like VXI3U modules have limited front panelspacePXI chassis available with UPSsupport for critical applicationsSimple, transparent chassisexpansion via PCI bridgetechnologiesPage 4.24

4 - Pxi SWiTCHiNGSySTem 0 AND SySTem 20System 10 Chassis (10-930-001)System 20 Chassis (20-935-001)What you need for a GPIB/RS232 SystemThere are four key parts required:• The chassis with the capability of accepting the specified System 10 or System 20 modules• A power supply module which is different for front plug in or rear plug in modules• A controller module which provides a GPIB, RS232 or Ethernet connection to allow thesystem to be remotely controlled• The selected switching modules to perform the required switching functionsStrong FeaturesProvides a low cost solution forswitching systemsInterfacing to a controller is simple andstraight forwardRobust module designVariety of standard module andcustom modules availableAspects that may adversely effectyour applicationNot able to support products other thanswitchingNo third party products are available for thesystemPage 4.2

4 - Pxi SWiTCHiNGVxi SySTemSWhat you need for a VXI System• A VXI chassis• A controller or an interface to an external controller• The switching and other modules for your applicationStrong FeaturesProvides for switching systems andinstruments in one chassisSince it is an open standard products areavailable from other manufacturersRobust module design with additionalfunctions available, especiallysophisticated self testThe chassis can have an embeddedcontroller or an interface to an externalcontrollerAspects that may adversely effectyour applicationRelatively high cost platform for switchingapplicationsMature technology generally consideredto be past its peak demandNumber of vendors has declined in recentyears and there are few new moduledesigns being introducedPage 4.2

4 - Pxi SWiTCHiNGPCi SySTemSWhat you need for a PCI system• A PC with available PCI slots• The selected PCI switching and other modulesLow costStrong FeaturesSince it is an open standardproducts are available fromother manufacturersSame software drivers as PXIequivalent modulePopular in very low cost labourareasAspects that may adversely effect yourapplicationSmall size and limited front panel area make it onlysuitable for relatively simple applicationsRequires the removal of the PC covers to fit the cardsThe card connectors are not designed to befrequently inserted and removed from the host PCLimited amount of power and cooling available to thecard (normally not a problem for switching cards)Limited number of instrument modules available,particularly ones with high performance, because ofthe relatively uncontrolled operating conditionsLimited number of cards can be fitted to the hostcontrollerPage 4.2

4 - Pxi SWiTCHiNGSPeCiAliSeD SWiTCHiNG PlATFormSSwitching systems can be supplied using more specialised platforms.A typical example of this is the SIM based solution in the 1000 Series of switching cards. Thecards are supplied without a mechanical enclosure and use an edge connector. The cards can bemounted in a standard 72 SIM card to plug into the users own host system. The cards can be RS-232 or I 2 C controlled. Multiple cards can be used by connecting them through an I 2 C interface.Switching systems based on this type of technology are only used in applications where space andcost may be a premium. No other type of card, such as an instrument, is typically available.The functionality is very limited because the card area available is relatively small compared tochassis based systems.CuSTom SoluTioNSPickering Interfaces is able to offer custom switching solutions for any of the platforms listedabove.Further information can be obtained from our web site or by contacting your local sales office.Page 4.2

5 - DIGITAL STIMULUS AND RESPONSESECTION 5DIGITAL STIMULUS AND RESPONSETest systems often require the inclusion of signal lines that either send or receive digital data.Some systems may include serial interfaces that need to be connected and disconnectedto the device under test using a switching system. This section explains some of the basicprinciples of providing digital inputs and outputs, and some of the issues involved. This is acomplex subject and consequently only an overview can be given in this section.Overview.............................................................................................................5.2Dynamic Digital I/O Modules..............................................................................5.3Isolated Digital Signals.......................................................................................5.5USB Interfacing..................................................................................................5.6RS232/RS422/RS485 Interfaces........................................................................5.7LVDS ..................................................................................................................5.9Page 5.1

5 - digital stimulus and responseOVERVIEWWhen testing digital systems there is often a requirement to provide digital information to emulatean external source of data and to measure an output response from the device under test.To meet this demand digital input and output devices are available in PXI format from a varietyof companies that allow input signals to be generated by a stimulus source and the response of thedevice under test to be captured. These modules are described in a variety of ways, but typicallythey are referred to as Digital I/O modules.There are wide differences in the capability, and cost, of digital I/O modules. The simplestmodules simply offer the ability to set the output on output channels to a known state and readfrom input channels.More complex modules allow outputs to be set as a function of time by loading new valuesclocked from a memory. For inputs the logical state can be read, either to the backplane be or toa memory device.Devices can have either fixed input and output values or programmable (thresholds and voltageswings).Basic digital I/O modules do not allow an output to be changed rapidly from an input to an outputon a clock by clock basis, and are therefore not suited to emulating bi-directional bus structures.Modules capable of being re-configured on a clock by clock basis are referred to as DynamicDigital I/O, and are more expensive than their static counterparts.Page 5.

5 - digital stimulus and responseDynamic Digital I/O ModulesIn principle these modules have a relatively simple architecture. Digital outputs from the modulecan be connected to the device under test and digital inputs to the module can be used to measurethe logical output of the device under test.The module used must be chosen to be compatible with the logic family under test and itsoperating voltage. Modules can be offered with a variety of different logic families and voltagesas options, or the input and output levels can be programmable so a module can be used with anytarget device over the modules specified operating voltage range. If the input and output voltagesare programmable the threshold voltage that determines if a signal is at a logical high or low mayalso be programmable. The programmable voltages are normally applied to all the digital I/Oconnections on a module, but the output voltages can be different to the input voltages.I/O modules use a clock to sequence through a pattern of digital input and output conditions.The output signals from the module simulate an external data source while the inputs to themodule record the device under test response. The clock can be provided from the module orfrom and external source, including from the device under test where synchronous operation isa requirement. Test applications can require that the output and input conditions are measuredat different times or that the module reacts after a timing delay, so digital I/O modules providefacilities to allow the clock timing to be adjusted between the input and output and from thetrigger events.LOGIC HIGHVOLTAGEMEMORYDIGITALPATTERNLOADLOGIC LOWVOLTAGELOGIC HIGHTHRESHOLDCOMPARATORLOGICGENERATORANDTIMINGDIGITAL I/ODIRECTIONALSWITCHMEMORYDIGITALPATTERNRECEIVECOMPARATORLOGIC LOWTHRESHOLDSimplified Block Diagram of a Dynamic Digital I/O ModuleThe digital information to be clocked out can be loaded into the module directly over the PXIinterface on a cycle by cycle basis, usually referred to as Static Operation. However, despite PXIhaving a very fast bus interface, this is only suitable for relatively low speed operation since datatraffic on the bus to service other modules in the test system can cause delays or interruption tothe data flow.Page 5.

5 - digital stimulus and responseThe alternative approach is to store a pattern of digital information for each of the digital outputsand then to sequentially clock this information out of the module, often referred to as DynamicOperation. This has the advantage that the timing of the signal is not dependent on the PXI bustraffic, so the timing accuracy of the signal is entirely under the control of the module.Modules are usually available with different memory depths behind each of the digital outputs,allowing the user to select a memory depth that meets the application without having to pay morethan is required for the module. The memory can also be used store more than one waveform in“segments” that can be loaded and then selected for replay. The segments can be played as once,continuously or played in sequences where the waveform is defined by a number of segments thatare played in defined sequence.The digital input to the module works in a similar way. The logical state of the input is recordedon each clock cycle. The recorded output can be sent directly to the PXI bus in lower speedapplications (Static Operation) or it can be directed to a memory buffer (Dynamic Operation) thatrecords the digital pattern for retrieval and analysis at a later time.To provide maximum flexibility a given pin on the front panel of the PXI module can be definedas being either an input or an output and changed on a clock by clock basis. To avoid havingto reload generation waveforms in memory, the memory for generation is separate from thememory for acquisition. If a module is stated to have 1 Mb/channel of memory it should have 1Mbit of generation memory and 1 Mbit of acquisition memory for every digital I/O connection(channel).The faster the module can be clocked the quicker a test pattern can be generated and thefaster the test system can gather results. At high speeds interfacing digital signals can becomeproblematic because of the need to correctly terminate any transmission line that is used to makea connection. Digital I/O connections often use a 50 ohm output impedance, but ribbon cableinterconnects (used on high-density connectors) may have a transmission line impedance closerto 100 ohms. The input impedance to a logic device is typically a few kohms in parallel withsome capacitance, requiring the user to add termination resistors if the transmission line is to becorrectly terminated.Not terminating the transmission may lead to ringing or overshoot on the waveforms if the digitalsource has fast pulse edges, giving rise to false changes of logical state. However, the voltagelevels of the signals will be well defined since the load and source impedance does not changethe voltage swing on the logic signals.Correctly Terminated SignalIncorrectly Terminated SignalPage 5.

5 - digital stimulus and responseAcquisition channels are normally provided with a selectable termination impedance (typicallybetween a high impedance and 50 ohms) but this may not correctly terminate the transmissionline used in many systems. Optimising the termination of transmission lines can be a timeconsuming exercise and require the user to adjust voltage swings to account for the changedvoltages, especially if the signal is terminated by more than one device. The loading could alsoresult in excessive current being drawn by the driving source, again problematic if more than oneload is involved.In many cases it is easier to use an un-terminated connection and avoid the use very high-speeddigital I/O devices if ringing or overshoot is likely to cause test problems. The data sheet forthe digital I/O device will state the rise and fall times of the output channels, but the impact onsystem performance is largely dependent on the interconnection system (both its impedance andlength).The performance of digital I/O systems can be affected by crosstalk between the channels thatcause fast edges to couple and corrupt the waveform. This is usually caused by crosstalk in theinterconnection system rather than the module.Generating DigitalReversing DigitalZ S = 50 ohmCoaxial or RibbonTransmission LineDUT SourceImpedanceCoaxial or RibbonTransmission LineV SZ T = 50 to 150 ohmGnd orAdjacent wiresof Ribbon CableZ LDUTLoadDUTV SZ T = 50 to 150 ohmGnd orAdjacent wiresof Ribbon CableZ LDigitalI/OLoad(there could be more than one loadon a single Digital Output)Effect of transmission line and mismatchA digital I/O module can support a limited number of inputs and outputs because of the need toback each channel with memory and drive electronics (consumes PCB space) and the limits onfront panel connector density. To expand the number of inputs and outputs available modulesare configured as “masters” and “slaves”. The master module controls the slave modules sothat digital information changes essentially at the same time across a number of modules. Amaster will be able to support a specified number of slave modules, each carrying a numberinput/output pins. The precise way in which the module does this is likely to be specific toa particular manufacturers module but typically relies on the exchange of timing signals andsoftware configuration tools. Using this approach a scalable digital I/O system can be created thatallows the testing of larger systems while providing an economic approach for smaller systems.Page 5.

5 - digital stimulus and responseIsolated Digital SignalsWhen dealing with signals provided by sources a significant distant away from the test systemthe intervening cabling can pick up a significant amount of noise and in some cases the sourceof digital signals may be at a different voltage potential to the PXI module. Making a directconnection could also cause ground loop currents to flow that might make it hard to determinethe logical state of the source.In these circumstances there maybe a need to use isolated digital inputs and outputs.PowerSupplyIsolationBarrierPowerSupplyDigitalInputDigitalReceiverOpticalInterfaceOutputDriverDigitalOutputIsolation of Digital I/O using an Optical InterfaceThere are alternative methods of providing digital isolation without the use optical devices. Auseful technique is based on the use of transformer coupled isolators where digital inputs to oneside generate narrow transformer coupled pulses that are decoded to provide an isolated logicaloutput. The transformer can be fabricated using modern semiconductor processes, allowingthe design of highly integrated couplers. Isolation devices based on transformer coupling canprovide very fast operation, but car must be taken to ensure that the input signals do not have fastcommon mode transients that cause false state changes, or that magnetic interference does notdirectly couple to the transformer.The most common form of isolation device is to use logic gates that are separated by an opticalinterface. Optical isolators allow the input and output devices to have a high differential barriervoltage, more than 100 V, and are very robust. In many cases an optically coupled interfacerestricts the maximum speed the devices can operate at since low cost optical devices arerelatively slow compared to modern logic systems.Page 5.

5 - digital stimulus and responseUSB InterfacingUSB is an increasingly used serial interface standard that can be found on professional andconsumer products. USB products can be connected to one USB controller through a hub thatexpands the number of devices in a tree network. However, this is not always a convenientarrangement in test systems since each device has to assume a unique identity. It can be moreconvenient to switch a single connection around the various test ports that need to be accessed.This is particularly true where a PXI system is used to test many examples of a product to deriveenvironmental or manufacturing spread information (bulk testing).The USB interface signals are carried by a cable with characteristics defined by the USB standard.The data signal is carried by twisted pair wires inside a coaxial shield, the twisted pair having adifferential line impedance of 90 ohms and a common mode impedance (to the coaxial shield)of 30 ohms.on-Twisted Power PairRed: VSUSBlack: Power GroundPolyvinyl Chloride (PVC) JacketOuter Shield > _ 65% InterwovenTinned Copper BraidInner Shield AluminumMetalized Polymer28 AWG TinnedCopper Drain WireTwisted Signal PairWhite: D-Green: D+Typical construction of a USB cableThe cable loss is also defined by the standard as a maximum of approximately 2 dB at100 MHz.For the purpose of multiplexing a USB connection the switching system must preserve thedifferential line impedance and ensure it has a wide frequency bandwidth. For this reason itis best to use a PXI module specifically designed for switching USB connections, such as thePickering Interfaces 40-735.The USB cables and connectors are relatively large compared to those used on PXI systemsand the USB signal is carried on a non-standard connector. It should also be noted that USBconnections can be made only over a limited distance (typically 5 meters), exceeding this distancemay cause errors in transmission.Page 5.

5 - digital stimulus and responseRS232/RS422/RS485 InterfacesA number of serial interface standards have evolved that are commonly used on items that areto be tested. Although in some applications they are being displaced by higher speed serialinterfaces, such as USB and Firewire, they will never be entirely displaced because they aremore suited than the newer interfaces.RS232RS232 is by far the most common that has historically been found on virtually every PC.It is a full duplex, single ended, point to point communication protocol. A negative voltage withrespect to ground represents a logic ‘1’ (or Mark) a positive voltage with respect to groundrepresents a ‘0’ (or Space). The voltages used to represent the two states are typically +/- 10 voltsbut can be as low as +/-3 volts on laptops and other low power devices.The full RS232 protocol and interface requires a transmit line, a receive line and 5 handshakinglines. The handshaking lines are, in most cases, not required unless the hardware/software isslow at processing the received data and the transmission needs to be halted to prevent bufferoverflows. It is usually possible to achieve a simplified connection using only the transmit,receive and ground lines. Sometimes, if the hardware/software is looking for handshaking signalsit is possible to connect the handshaking lines together locally so the equipment will still operatewith just the 3 wires.RS232 can be carried on a variety of connectors but are typically based on 25 way or 9 way.The protocol defines two types of equipment, DTE (Data Terminal Equipment, such as acomputer) and DCE (Data Communication Equipment, such as a modem). The two types havedifferent pin connections and so different cable configurations are required to connect variouscombinations of equipment that can often lead to confusion.DTE1 - DCD2 - RD3 - TD4 - DTR5 - GND6 - DSR7 - RTS8 - CTSDCE1 - DCD2 - RD3 - TD4 - DTR5 - GND6 - DSR7 - RTS8 - CTS1 - DCD6 - DSR4 - DTR2 - RD3 - TD5 - GND7 - RTS8 - CTSDTEDCE1 - DCD6 - DSR4 - DTR2 - RD3 - TD5 - GND7 - RTS8 - CTS1 - DCD6 - DSR4 - DTR3 - TD2 - RD7 - RTS8 - CTS5 - GNDDTE DTE DTE DTE4 - DTR1 - DCD6 - DSR2 - RD3 - TD8 - CTS7 - RTS5 - GND1 - DCD6 - DSR4 - DTR2 - RD3 - TD5 - GND7 - RTS8 - CTS1 - DCD6 - DSR4 - DTR3 - TD2 - RD5 - GND7 - RTS8 - CTSTypical wiring conventions for RS232. The conventions on the left use fullhandshaking, those on the right are handled locally.Page 5.

5 - digital stimulus and responseRS422RS422 is capable of greater distances/speeds than RS232, typically it is capable of several Mbpsover 1000 feet due to it using a differential signalling system. It uses two differential cable pairs,one pair for transmit and one for receive, but unlike RS232 has no handshaking lines. The signalon each wire is either 0 or 5 volts, but the other wire of the pair will always be the opposite andso the data is represented by the difference between the two wires.Although the original purpose was to extend the maximum distance and speed of a point to pointsystem it can be used in a master/slave multi-drop system. This type of system has one masterdevice talking to many slave devices, but each slave can only talk to the master device.There is no standard connector type used for RS422.TxRxRxTxPoint-To-PointTxRxRxTxMaster With Multiple SlavesRxTxTypical example of an RS422 multi-drop systemIn practice a terminating resistor of 100 ohms is be placed at the furthest end of each pair to helpminimise reflections and a ground signal is required. Although the signal levels on the cable pairsare never referenced to ground it is still required to prevent nodes floating to high potentials withreference to each other.RS485RS485 has many similarities to RS422.It uses a differential signalling system capable of high speed and distances using the same voltagesbut was designed primarily for use in multi-drop systems. It differs from RS422 in that it has only1 differential pair used for both transmitting and receiving data. The down side of this is that itis only capable of half-duplex operation. It goes one step further than RS422 in that it providesthe ability to have a true multi-drop system with up to 32 nodes (transmitter and receiver pairs)on the one cable pair bus. Although the RS485 specification only allows 32 nodes it is possibleto buy transceiver ICs that put only a half, quarter or even an eighth of a node loading on the busallowing up to 256 devices on a single bus.Page 5.

5 - digital stimulus and responseA 120 ohm terminating resistor is placed at each end of the cable pair to help minimise reflections.A ground signal is also required between nodes. As with RS422 the data signals are neverreferenced to ground but it is required to prevent nodes floating to high potentials which cancause transceiver damage.A typical multi-node system is shown below:120 Ohm 120 OhmNODE NODE NODE NODESwitching RS232 Based ConnectionsUnlike USB the RS232 standard has no special requirements for transmission line impedance andthe serial interface can be switched with simple multiplexers or matrix switching systems.Page 5.10

5 - digital stimulus and responseLVDSLVDS (Low Voltage Differential Signalling) is a fast serial interface standard defined by twostandards organisation – ANSI/TIA/EIA 644 (electrical only) and IEEE1596 primarily intendedfor point to point communications but is also capable of being configured in many other ways.It was initially defined as an interface for LCD panels but has been adapted to many otherapplications. A more detailed description of LVDS can be found on the National Semiconductorweb site (www.national.com).DRIVERCurrentSource3.5 mA_+-350 mV+RECEIVER_+_LVDS DriverThe standard uses differential signalling to ensure that signals can be sent over significantdistances and maintain a relatively low radiated field. It uses a driver that switches a 3.5 mAcurrent source between the two differential wires with termination impedance of approximately100 ohms. The differential input voltage across the receiver is nominally 350 mV.The use of 100 ohm transmission lines allows LVDS signals to be carried by ribbon cables forshort cable runs but longer cable runs require the use of more specialised cables.Most applications for LVDS are unidirectional, but it is possible to have a bi-directionalarrangement.+DRIVERRECEIVER_LVDS Point-To-Point ConfigurationPage 5.11

5 - digital stimulus and responseThe LVDS standard is not a rigorously defined standard in the sense that there are not mandatedconnectors or clock rates. Each end of an LVDS interface needs to be designed and be configuredto work with the intended load.+DRIVERRECEIVER_RECEIVER_MinimizeStubLengthsMinimizeStubLengthsDRIVER+LVDS Bi-Directional Half-Duplex ConfigurationDRIVERMinimizeStubLengthsMinimizeStubLengths+RECEIVER__RECEIVER+_RECEIVER+LVDS Multi-Drop ConfigurationThe LVDS serial interface is often arranged to provide a parallel interface simply by providingmany of the serial interfaces and decoding each channel, again many configurations are possible.For slower communication rates parallel data is carried by including parallel to serial conversionat the driver end and serial to parallel at the receiver end.For LVDS interfaces it is essential that line lengths are kept the same for the two differentialdata lines. Where high speed communications or fast drivers are being used (there are devicestheoretically capable of up to 2.5 Gb/s available at present) it is advisable to make sure thatconnectors are designed for equal path lengths on adjacent connections to avoid skew errors.The LVDS standard defines the acceptable rise times of the differential signals carried on the datalines. For low speed communication (less than 200 Mb/s) the rise and fall time has to be less than30% of the clock rate. For faster systems the rise and fall time has to be between 0.26 ns and 1.5ns. Depending on the speed of the system that can make the system sensitive to termination ortransmission line mismatches, or to limitations in the bandwidth of the interconnection system. Aninterconnection or switching system suited for one application may not be suitable for others.Page 5.12

6 - POWER SUPPLIES AND LOADSSECTION 6POWER SUPPLIES AND LOADSDevices under test need power supplies to enable them to operate and often require loadsto simulate what they need to drive. This section describes the general types of powersupplies available to the system designer and some of the methods used to simulate theloads where required.Power Supplies in PXI Test .............................................................................6.3A general overview of the power supplies used in test and the reasons why theyare used. It includes a description of the basic features that may be required andthe different types of power supply. The use of voltage sense lines that allow powersupplies to regulate the load voltage rather than just their terminal output voltage isdescribed.Load Simulation ................................................................................................6.9Describes how loads can be simulated or emulated. Covers the use of sample loads,fixed loads and electronic loads.Page 6.1

6 - Power suPPlies and loadsDual Programmable +10V Power Supply 41-735The Pickering Interfaces 41-735 Dual Programmable +10V Power Supplyprovides two programmable positive output voltages. The module provides highquality regulated voltages from a linear regulator to ensure low levels of outputnoise.Programmable DC Power Supply Modules 41-740/742The Pickering Interfaces 41-740/742 Programmable Power Supplies are designedspecifically for test applications that demand precision output voltage/current andtightly coupled measurement capabilities.Page 6.2

6 - power supplies and loadsPower Supplies in PXI TestMost test applications require the use of a power supply to provide voltage or current to a deviceunder test.Using a separate power supply rather than relying on the device’s embedded supply (assuming itis fitted) allows a degree of independent test and the opportunity to measure the current drawn bythe device or its tolerance to power supply variations. A general purpose power supply may alsoprovide better protection in the event that the device under test has a significant manufacturingfault.The independent power supply can be either a bench power supply or it can be provided by a PXImodule in the chassis that uses power from the backplane or from an external source.Bench Power SuppliesPower supplies are available from a large number of manufacturers and can be used to providepower to the system under test. They are offered in a variety of physical formats and, dependingon price, can have a variety of useful features. Typically they are GPIB controlled, though thelowest cost products may have no remote control possibilities.PXI Power SuppliesPower supplies can also be included in the PXI chassis.For modest power supply requirements a range of power supply modules are available that takepower from the PXI chassis power supply and deliver it to the device under test using a DC to DCconverter. The module can deliver regulated output voltages to the load. Assuming the moduleis confined to one PXI slot and the power is taken from the +5 V supply, the PXI backplanecan provide up to 6 Amps (30 Watts), for a chassis conforming to Version 2.1 of the standard.Allowing for losses in the DC to DC converter this limits the output power that can be deliveredto the load to approximately 20 Watts. This is adequate to test a wide variety of devices.-12V+12VCHASSISPOWERSUPPLY+5V+3.3VPXI BACKPLANE GROUNDPXI I/OPOWER SUPPLYCONTROLAND MONITORINGDC - DCCONVERTERV+ ISOLATEDOUTPUTCOMMONV+GNDCHASSIS GROUNDA PXI module can be used to convert one or more of the PXI backplane voltages to a variety of regulatedoutput voltages. Each PXI module is separately driven by the PXI chassis power supply from a starconnection and a common ground. In this drawing the other modules are not shown. The output from theconverter can be referenced to the chassis ground or can be floating.Page 6.

6 - Power Supplies and loadsAn alternative to using the PXI backplane as a power source is to have a module that allows aninput from an external fixed voltage power supply. The DC to DC converter is used to translatethis voltage (e.g. 24 Volt) to a variety of other voltages. It allows a relatively simple powersupply to provide the power to the device under test without using the available backplane powersources. The amount of power that can be delivered to the device under test is limited either by theexternal source, or by thermal considerations in the PXI module. The PXI standards recommendsthat a 3U single width module dissipates less than 25 Watts, which for a reasonably efficientswitched mode power supply allows the delivery of approximately 75 Watts to an external load.EXTERNALPOWERSUPPLYDC INPUTV1+-DC - DCCONVERTERCONNECTORCONTROLAND MONITORINGPXI I/OV2+-An external DC supply can be used to provide power to a PXI module which translatesit to a variety of regulated output voltages.Isolated and Non-Isolated SuppliesREGULATORREGULATORInputOutputInputOutputNON-ISOLATEDCommon connection betweenthe input and outputISOLATEDNo DC connection betweenthe input and output. The outputis permitted to be at a different DClevel to the input.Page 6.

6 - power supplies and loadsIn isolated power supplies the DC output from the power supply has no DC connection to theinput. In practice this means the power is transferred as an AC signal through a transformer.The output from the power supply has two terminals (usually labelled common and a positiveoutput). The user can commit either of the outputs to the test system ground to produce either apositive or negative output voltage. The output can also be stacked on top of a DC pedestal toprovide a higher output voltage (including another isolated power supply) and even to connectthe power supply output to a voltage pedestal at the device under test. The lack of a groundconnection to the PXI ground in some circumstances can avoid the creation of unwanted groundloop currents.A non-isolated power supply is always referenced to the ground of the PXI chassis. It shouldbe connected to the front panel ground of the chassis and not the PXI ground on the backplaneconnector in order to avoid ground loop problems in the system.Voltage Sense LinesV+ADJCOMPARATORDIFFERENCEAMPLIFIERVS+VS-LOADVrefV-PXIFRONTPANELVoltage sense lines are used to sense the voltage at the load rather than the frontpanel. The sense lines force the power supply to increase its output voltage to providethe required voltage at the load rather than the front panel.When a power supply is connected to a load the wires that make that connection will have avoltage drop across them because of the wire resistance and the reactance. The voltage at thedevice under test can therefore be lower that is intended. If the load current is variable the deviceunder test also has a varying voltage applied to it, conditions that may not exist in real operatingconditions.Page 6.

6 - Power Supplies and loadsThe use of sense wires can alleviate this problem. Instead of the output voltage being sensed atthe power output terminals they are sensed through an additional set of sense wires that carryvery little current. As the load current is varied the power supply increases or decreases thevoltage at the output terminals to compensate, and in the process potentially damaging the deviceunder test. Providing the rate of change of load current is not excessive, the power supply canmaintain the set voltage at the device under test.Some care is needed if the sense wires are being used and are inadvertently not connected.The regulator may drive the output voltage to its maximum in an attempt to get the correctsensed output voltage. Relying on the sense wiring to control the load voltage may mask cablingproblems in the test system that might be noticed if the sense wires are not in use.Battery SimulatorsThere is an increasing requirement to test devices that are battery operated in normal use. Thebattery used is part of the device design and testing the device with a system power supply maynot simulate the operating conditions well enough to be useful.Battery simulators use voltage sense lines to detect the voltage at the device under test. Whenthe load current of the device changes rapidly, for example when a mobile RF device transmits,the power supply has to react very quickly to compensate for the change in voltage drop acrossthe wiring system.In some cases the power supply may be required to simulate the output resistance of the battery,intentionally making the power supply voltage drop when the current load changes. It may needto simulate the conditions when a battery has been nearly fully discharged, or when the batteryis fully charged.Battery Simulators are designed with voltage sense lines to:• regulate the voltage• close the load output voltage• provide a fast transient response to compensate for changes in load current• be programmed to have an apparent output resistance covering the ranges expected oftypical batteriesPower Supply RoutingIn many applications the PXI test system may be required to route power to different parts of thedevice under test or to different devices if the test system is being to test a number of identicaldevices.Typically the switching systems will use a simple two pole multiplexer to route the signal.However, the switching system will introduce additional series resistances in the power supplydistribution system best compensated for by using a power supply with sense lines. In thesecircumstances the switching system will require a 4 pole multiplexer to provide the powerdistribution if both the positive and negative supply need to be switched.Pickering Interfaces offer switching modules that include both the power and sense switchingmultiplexers in one module.Page 6.

6 - Power suPPlies and loadsPower and Sense Multiplexer Module 40-658The Pickering Interfaces Power and Sense Multiplexer is specificallydesigned for switching both power and sense in one module. Themodule contains a Dual 18-way Power MUX and a Dual 18-way SenseMUX in a single 3U PXI slot.Isolated Power Supply Module 41-720The Pickering Interfaces Isolated Power Supply Module provides up to 4fixed voltage isolated outputs. The module is available with output voltageoptions from 3.3 to 15 VoltsPage 6.7

6 - Power Supplies and loadsThe device under test will usually have power supply system that includes decoupling capacitors.If a system power supply with a large output current capability is used and applied to the devicethe inrush current to the load can be high and may damage the relays in the power supply routingsystem. It is always best practice to cold switch the power supply routing - turn the power sourceoff while the relays are operated. Relays can carry current surges in the closed position muchmore effectively than when using hot switching. If the system power supply has built-in currentlimiting this can help protect the routing system.Switch Mode Power SuppliesSwitch mode power supplies generate an AC signal that is rectified and smoothed to generatea DC signal. The switched AC signal results in ripple being present on the DC output that mayhave an impact on the performance of a device under test. It could add jitter to timing signalsor generate spurious signals from analogue circuits. Switched mode power supplies can radiatesignals from the magnetic components they use and need to be well screened from other modules.Some designs of switch mode power supply are isolated, while others may not be.For switched mode designs isolated power supplies are preferable since it is easier to controlwhere the ripple current from the supply flows in the test system.The power supply for a PXI chassis is a switched mode design. Designers of PXI modules arerequired to be careful of how they use this power supply in order to avoid injection of AC groundcurrents into the PXI chassis.Linear RegulatorsLinear regulators simply regulate one DC voltage to a lower DC voltage. They can produceoutputs substantially free of spurious signals or ripple and are better suited to applications whereparametric measurements of spurious signals is required. Compared to switch mode designshowever, they are relatively inefficient and dissipate more thermal power. For high powerapplications linear regulators may not be practical because they require large heatsinks.Current MeterSome tests may require the current drawn by the device under test be measured. An excessivecurrent might indicate a fault, or it may be the device is battery operated and battery life is animportant parameter that must be checked for. A power supply may have a current (and voltage)meter built into it, but it is unlikely that such a meter will challenge the accuracy of a DMM.Some of Pickering Interfaces power supplies provide a convenient monitoring point to use anexternal DMM without the need for additional switching systems.UPS OperationSome applications require that test solutions remains active even if the normal AC power is lost.Uninterruptable power supplies UPS) allow the power source to be switched to a battery so thatuninterrupted testing can continue. In some applications, such as field use, there could be a needto have battery operation as a capability because there is not an accessible AC power sourceavailable.Page 6.

6 - power supplies and loadsLoad SimulationMany devices are required to be tested that have to control or switch other devices that consume asignificant amount of power. The power consumption of the connected device is such that it maybe unwise to assume that the device under test that drives it has the capability to drive it correctly.Examples can include electronic switches that drive microwave relay coils, switching systemsthat control lighting and battery chargers. The test system will need to include a set of loads thatallow the device to be tested under realistic operating conditions.Sample LoadA simple, and often the most cost effective way, of simulating a load may be to provide a sampleof the device that is being controlled and connect it to the device under test. In some cases this isa cost effective solution to the problem. A relay coil, for example, can be simulated by the coil.The life of the simulated load is very long and its behaviour accurately reflects the conditions thatthe device under test is likely to meet.Fixed LoadsIn other cases a load can be simulated by a collection of components (capacitors, resistors,inductors) that can be mounted in a test fixture that is dedicated to the task.Neither a fixed load or sample load approach is an ideal solution when the test system is requiredto be general purpose and capable of testing a wide variety of devices. The number of specialto type fixtures increases as the variety of products increases, leading to the need for ever morecomplex switching systems.In other cases samples of the device under test load may have limited life times that make themunsuitable as example loads. Batteries and light bulbs, for example, have limited lifetimes andtherefore are not always suitable for inclusion in the test system. They may also limit the speed atwhich tests can be done to avoid unrepresentative heating effects.There is also little opportunity to vary the load conditions to provide worse case tests, a useful testfeature for testing critical components or performing long term stress analysis.In some cases an Electronic Load may be a better approach.Electronic LoadIn an electronic load a programmable load simulates the loading effect of a device. Typically aFET or similar device is arranged as a constant current sink, the amount of current being takenbeing programmable.When arranged as a constant current sink the Electronic Load consumes the same amount ofcurrent no matter what voltage is applied across its load terminals. If, for example, a load is setto 0.5 Amps and 12 V is applied across it the load will consume 6 Watts of power. If the loadvoltage is increased the power consumption increases linearly with load voltage since the currentdoes not increase.Page 6.

6 - Power Supplies and loadsA load that behaves as a constant current sink may not be ideal for all circumstances andElectronics Loads can have other modes of operation. In constant resistance mode the currentneeds to increase linearly as the applied voltage is increased. This can be achieved by simplyapplying a conditioned version of the output voltage to the control circuit that sets the outputcurrent. As the voltage increases, so does the set current just as it would with a resistive load.In constant voltage mode and electronic load includes a feedback mechanism that adjusts the loadcurrent to try to keep the voltage constant.In addition to providing a controllable load Electronic Loads may also allow the load conditionsto be changed with time. This is particularly useful with loads that have a time varying behavioursuch as lighting systems. It also allows the electronic load to simulate the time varying behaviourof reactive loads with capacitors or inductors.Electronic Loads are usually supplied in configurations that are fully isolated to ensure they canbe connected in different ways to the device under test.Care has to be taken that the isolation voltage and maximum load voltage are not exceeded.PXI LoadsLoads can be provided in PXI form provided their power dissipation is not excessive. The PXIstandard recommends that the average thermal power consumed in a single 3U slot does notexceed 25 Watts (by implication scaling up as the number of slots is increased and doubling for6U modules). Manufacturers of PXI modules provide breadboard modules that can be adaptedfor this purpose.For higher load powers the loads have to supplied outside the PXI chassis, but switching the loadcan be performed by PXI based switching systems.Electronic Loads are available as PXI modules or bench instruments. The bench instrumentsoffer higher power capability, but the PXI based solutions provide a more integrated testenvironment.Page 6.10

7 - PXI INSTRUMENTSSECTION 7PXI INSTRUMENTSMeasuring Instruments are a key part of any test system. PXI systems commonly includea selection of measuring instruments, the most common of which are DMMs, ARBs, DirectDigital Synthesizers and digital oscilloscopes. This section explains some of the keyparameters and compromises.DMM Measurements of Resistance ................................................................7.3Explains how a DMM is used for making resistance measurements using 2 wire, 4wire and 6 wire measurement techniques.DDS and ARB Basics .......................................................................................7.7Explains how a DDS generates variable output frequencies and how an ArbitraryWaveform generator works. The two architectures are compared and their differencesare highlighted.Digital Storage Oscilloscope (DSO) Basics ...................................................7.11Explains how a DSO works.Selecting a Digitizer .........................................................................................7.15A guide to the key specification parameters for digitizers and the care needed whenselecting a device for a user’s applications.Page 7.1

7 - PXI INSTRUMENTS6 1/2 Digit DMM (40-200)7 1/2 Digit DMM (40-210)Page 7.2

7 - PXI INSTRUMENTSDMM MEASUREMENTs of resistanceDMM’s can be used to measure resistors in a variety of ways. There are three basic technicquescommonly used, two wire, four wire and 6 wire.Two wire ohms measurement are commonly used when the resistance of the test leads is muchless than the resistance being measured. The results are generally good enough for most functionaltest measurements. To eliminate errors associated with test lead resistance in two wire ohmsmeasurements a “Relative” operation is available or alternatively the test system can provide thefunction.Four wire measurements substantially eliminate the test lead resistance from the system, and arevery useful when measuring lower value resistors. The four wire system is particularly usefulwhen the lead resistor varies because, for example, the DMM is switched through a multiplexeror matrix that does not have the same lead resistance for each path. The 4 wire method should beavoided for measuring high resistor values.Six wire measurements can allow resistors to be measured in situ where they may be shunted byother components. It requires the switching system that connects the DMM to the device undertest to provide 6 connections, so can add complexity to the switching system.TWO WIRE MEASUREMENTSMost resistance measurements can be made using the simple 2-wire Ohms method.To perform a measurement with a DMM such as the Pickering Interfaces 41-200, simply connectV+ to one end of the resistor and V - to the other end and set the DMM to measure resistance.The DMM supplies a constant current source to the resistor and the meter measures the voltageacross it, the voltage being proportional to the resistance.41-200 DMMV+R leadI s V I sR xV-R leadEquivalent Circuit 2-Wire Ohms MeasurementAs shown by the equivalent circuit diagram in Figure 1 the lead resistance can introduce asignificant error since the measured voltage is across both the load and resistance of the leads.The error is most significant on low resistance measurements and usually needs to be consideredonly for resistances below 30 kohms.Page 7.

7 - PXI INSTRUMENTSThe impact of the lead resistance on the measurement can be corrected by using the Relativefunction on the DMM. To make the correction you should null out any lead resistance errors byfirst by connecting the V, + and V, - test leads together and then performing a Relative function.The reading will be changed from that of the test leads to 0 ohms. Any resistor now placedbetween the ends of the test leads will now be measured relative to that the new test referenceplane at the end of the two leads.If the user is making measurements above 300 k ohms shielded or twisted leads may have to beused to avoid unstable readings due to signal pick up on the leads. The problem of noise pick-upbecomes worse as the resistance to be measured is increased.FOUR WIRE MEASUREMENTS41-200 DMMV+R leadI+R leadI s V I sR xI-R leadV-R leadEquivalent Circuit 4-Wire Ohms MeasurementFour Wire resistance measurements are ideal for making measurements of lower value resistancesince the DMM is able to remove the effects of the leads without resorting to the use of theRelative Function. The correction is entirely automatic.In Four Wire measurements the V+ and V- terminals still supply the current to the resistor via thetest leads. The voltage drop across V+ and V- is determined by the sum of the lead resistance andthe resistor being tested.The sense lines are connected to the terminals of the resistors and measure the voltage acrossthe resistor, it does not include the voltage across the test leads and the input impedance issufficiently high that is does not divert any current. The reading is therefore dependent on just theresistor and is virtually independent of the test lead resistance.Four wire measurements produce very accurate, repeatable and stable measurement ofresistance and are particularly suited to the measurement of low values. The 41-200-044 fourwire measurements permit measurements on resistors as low as 10 milliohms. It is less suitedto the measurement of high value resistance since the input impedance and leakage current tothe voltmeter may effect the reading. In general four wire measurements are not recommendedabove 330 Kohms despite the fact that the 41-200 series has very high input impedance and lowinput current.Page 7.

7 - PXI INSTRUMENTSSIX WIRE MEASUREMENTS41-200 DMMV+I+I s V510 ohm30 KohmGuardI-V-220 ohmGUARD SOURCEGUARD SENSEEquivalent Circuit 6-Wire Ohms MeasurementDMMs such as Pickering Interfaces’ 41-200-044 also provide a guarded 6-wire resistancemeasurement mode.Six wire measurements are used where the resistor to be measured is shunted by other resistors, acommon problem in ATE systems where the resistor is to be measured in situ on a PCB.The technique isolates the resistor under test by maintaining a guard voltage at a user-definednode, the guard voltage being driven by a voltage buffer from the V+ terminal. The guard voltageensures the constant current source from the DMM does not have current diverted into thealternate path. The following is an example of how it works:Assume a 30 kohm resistor is in parallel with two series resistors (510 ohms and 220 ohms (as inFigure 3). In a normal resistance measurement, the 510 ohms and 220 ohms would shunt most ofthe DMM Ohms source current, causing a very inaccurate reading. By sensing the voltage at thetop of the 30 kohm resistor, and then applying this same voltage to the junction of the 510 ohmsand 220 ohms, there is no current flow through the shunt path. The guard has forced the junctionto be the same as the voltage at V+ and current required through the 220 ohm resistor is suppliedby the Guard Source. The DMM accurately measures the 30 kohm resistor since the current I sflows through the 30 kohm resistor.The current capability of the Guard Force terminal is limited, in the case of the PickeringInterfaces 41-200 to a maximum of 20 mA, so there are limitations on the amount of driving thatcan be achieved.The resistor connected between the low of the 4-wire terminals and the guard point is the burdenresistor, or Rb. Due to the limited guard source current, this resistor cannot be lower than R bminwhere:R bmin = I o * R x / I gwhere I o is the ohms source current for the selected rangeR x is the resistance being measured.I g is the guard current capability in ampsPage 7.

7 - PXI INSTRUMENTSFor example, selecting the 330 ohm range and measuring a 300 ohm resistor imposes a limit onR b of at least 15 ohm or greater.Since the top burden resistor, R a , does not have this limit imposed on it, choosing the measurementpolarity can help since R a can become R b and vice versa. It is best to set the measurementpolarity such that Ra is the higher of the two burden resistors.The 6 wire method is specified for measurement of resistors to 330 kohms, for resistors abovethis range the 6 wire configuration can be maintained but the DMM should be set to two wiremeasurement mode (with its lower source current).Page 7.

7 - PXI INSTRUMENTSDDS and ARB BasicsDirect Digital Synthesizer (DDS)A direct digital synthesizer enables the generation of repetitive waveforms, such as a sine or atriangle wave, with a variable output frequency, using digital circuits to look-up the instantaneousvoltage of the waveform, and a Digital to Analogue converter to produce an analoguerepresentation of it.ClockSourceFrequencyInstructionAdderLatchAddressInMemorycontainingwaveformmapDataOutD to AConverterLowPassFilterDDS OutDataAccumulatorAddressA Direct Digital Synthesizer (DDS)A DDS works by applying a frequency instruction to an accumulator to calculate the phaseof the waveform. An accumulator is simply a digital adder and a latch clocked from a clocksource. When there is a clock event the output of the accumulator is increased by the value of thefrequency instruction.If the accumulator (adder) overflows the overflow information is discarded, so that the outputdrops back to a low value again, as shown in the following example.Suppose the accumulator can deal with numbers up to 100, and a frequency instruction of 10 isentered. Each cycle of the clock will cause the accumulator to increase by 10, and after 10 cyclesthe output (representing phase) will return to zero. The accumulator is cycling at one tenth of theclock frequency. If the frequency instruction is reduced to 5 the output of accumulator (its phase)will advance more slowly.Once the phase of the signal is calculated it needs to be converted into an output voltage. Thisis achieved by utilising a memory device where the voltage for one cycle of the required outputwaveform (typically a sine wave) is stored for different phases of the signal. The phase isrepresented by the memory address, the voltage is represented by a digital number stored at thataddress. The accumulator output is a calculation of the phase of the required output signal, sousing it as the memory address converts the signal to a digital voltage value.The output from the memory is then passed on to a D to A converter which changes the signal toan analogue representation.Page 7.

7 - PXI INSTRUMENTSARB Modules from Pickering Interfaces•••••••••41-620 Function GeneratorDC to 10MHzUp to Three Channels in One 3U Slot48-bit Frequency ResolutionSimple Generation of Repetitive Arbitrary WaveformsDC Offset CapabilityFlexible Sweep CapabilityAmplitude Modulation CapabilityUses 10MHz PXI Clock or External Clock ReferenceComprehensive Triggered Support41-610 Arbitrary Wavefrom Generator•••••Dual channel in a singel PXI slotDifferential outputsUp to 100 Ms/s sample rateExtensive triggering capabilityFile creation and import facilities41-650 High Voltage Programmable Amplifier•••••Up to 5 Amplifier ChannelsProgrammable GainPowered by the PXI ChassisShort Circuit and Thermal ProtectionUp to 60 Volts pk-pk OutputPage 7.8

7 - PXI INSTRUMENTSThe output from the D to A is filtered by a low pass filter to remove unwanted harmonically relatedsignals. In theory the DDS can produce a signal with a frequency up to half the clock frequency,but this requires the use of a ‘brick wall’ output filter to remove the unwanted alias signals. Inpractice a real filter might limit the maximum frequency to one third the clock frequency. Moreinformation on alias signals is provided later in this section.The DDS can change its output frequency quickly by simply changing the frequency instructionto the accumulator, ensuring that the frequency settling time is very fast.With a perfect D to A converter noise will be added to the output signal because of thequantisisation of the signal. The noise level is given by the formula:Noise = - (6.02N + 1.74) dBwhere noise is expressed relative to a full scale signal and N is the number of bits in theconverter.As an example the noise from a perfect 12 bit converter is –73.98 dB. The noise is spread overthe frequency range of the converter, so the faster the converter (spreading the noise over a widerbandwidth) and the greater the number of bits (lowering the noise level) the lower the spectralnoise density is.In practice this is a level of performance unachievable by real converters; they all have defects,and these are more likely to be apparent when generating high frequency signals than lowfrequency signals and at higher clock rates.The same defects also mean that the output is not free of spurious signals. The non-linearitycauses other signals to be present, some related to the clock and the output frequency (in a similarway to intermodulation products but behaving in a rather different way).A DDS is inherently capable of generating waveforms with shapes other than a sine wave byplacing a different data file of address versus voltage in the memory. It can easily generatetriangle waves, square waves or trapezoidal signals.Page 7.

7 - PXI INSTRUMENTSARBAn ARB, sometimes referred to as an AWG (Arbitrary Waveform Generator), but not to beconfused with an Additive White Noise Generator, can also be used to generate a repeatingsignal, but has a different architecture to a DDS which results in a different behaviour.The ARB generates a file comprising a digital representation of how the required output signalvaries with time. This file is loaded into a memory device, with the values of the required outputvoltage being stored at memory addresses representative of different times.A clock source drives an address sequencer that simply increases the output address by 1 for eachclock cycle. As with the DDS the output is then converted to an analogue signal and filtered toremove unwanted signals.More sophisticated ARBs may use other techniques, such as interpolation, to reduce the storedfile size while maximising the sampling rate at the D to A converter.Clock SourceAddressSequencerMemoryLoadMemoryBlockD to AConverterLowPassFilterARB OutputSimple representation of an ARBAn ARB can generate repetitive signals in a similar way to a DDS by ensuring that when thehighest wanted address is reached, the address sequencer returns to the lowest address and thenrepeats the cycle. Provided the waveform stored has been designed without any discontinuitiesbetween the start and the finish the signal will keep repeating without any errors.There are, however, important differences in the behaviour of the ARB compared to a DDS.The most significant is that in a DDS changing a frequency instruction can change the outputfrequency. This is not possible with an ARB – to change frequency the clock frequency has to bechanged or the waveform in the memory has to be changed.ARBs are usually designed to have very large memory blocks in order to generate signals withvery long periods between repetition, or signals with a very complex behaviour. The memoryalso has to be large if signals that are only indirectly related to the clock frequency are required.As an example, suppose a clock of 100 MHz is used and the required output frequency is10.000001 MHz. An ARB has to store 10,000,000 cycles of sine waves (one second) in orderthat the end of the file can be stitched to the beginning of the file and produce a repetitive signalwith no discontinuities.Page 7.10

7 - PXI INSTRUMENTSDDS sources typically have smaller memories and are used to generate signals that are repetitiveand may have fractional frequency relationship to the clock source. In the example above a DDSstill only needs one cycle of the signal to be stored, since it computes the phase values and looksupwhat the output voltage should be.Essentially an ARB plays a stored file that is loaded in memory, a DDS computes a repetitivesignal from one stored cycle of the waveform.Understanding Alias Signals and Frequency ResponseBoth the DDS and the ARB use low pass filters at their outputs to reject unwanted high frequencysignals. The need for this filter is a basic requirement for generating analogue signals from digitalsignals.When a D to A converter is used to generate an analogue version of a signal it does so for a periodof time until the next sample of the signal is generated. Theory shows that the perfect D to Aconverter has a frequency response described by the classic sinx/x curve.LevelSampling rate/2Sampling rateFrequencySin x/x Response of Sampled Data SystemAt low frequencies the output response is flat but as the wanted output frequency increasescompared to the sample rate of the converter the actual output declines in accordance with thesinx/x curve. At the sampling rate of the converter (and all of its harmonics) the output reachesa null value.Because of the nature of the signals, if a DDS (or ARB) is generating a 10 MHz signal froma 100 MHz clocked system then, in addition to the 10 MHz signal, a set of other signals aregenerated. These appear 10 MHz either side of the 100 MHz clock and all of its harmonics. Thelevel of this signal is determined by the sinx/x curve.As the frequency to be generated increases these other signals become more problematic. Inthe above example if the output frequency was increased to 45 MHz then an alias signal wouldappear at 55 MHz (100 MHz less 45 MHz), and from the sinx/x curve amplitude would beincreased significantly (at 50 MHz the signals are equal amplitude and at the same frequency).Page 7.11

7 - PXI INSTRUMENTSIt is for this reason that a low pass filter has to be added to reduce the amplitude of the alias signal,and since the filter cannot have an abrupt ‘brick wall’ frequency response the useful maximumoutput frequency from the DDS has to be less than 50 MHz. A maximum output frequency of30 MHz (for example) means that the alias is at 70 MHz and the frequency band from 30 MHzto 70 MHz can be used by a filter to attenuate the unwanted signal.All DDS and ARB sources need the low pass filter to remove the alias components. In somedesigns the filter can be switched to reduce the maximum frequency which can be generated andreduce broadband noise.The signal output will decline as the frequency is increased in accordance with the sinx/x curve.If an accurate output level is required the frequency response due to the sinx/x response and theanti-alias low pass filter must be corrected either by the DDS software or by the user.Page 7.12

Digital Storage Oscilloscope (DSO) Basics7 - PXI INSTRUMENTSAC/DC CoupledSwitched Gain AmplifierAnalogueInputD to AConverterN bitsMemoryScopeOutputClockGeneratorTriggerSystemPXI TriggersFrequencyStandardAnalogueTriggerSystemA Very Basic DSO Block DiagramA DSO captures an analogue input waveform and converts the time varying signal into a digitalrepresentation. The digital representation can then be displayed in much the same way as aconventional oscilloscope but, instead of using a CRT to display the waveform, a soft front paneldisplays the signal on the monitor attached to the PXI system controller.Many of the available functions on an analogue oscilloscope can be emulated on a DSO, butthere are also many additional functions which can be added through the use of an embeddedDSP (in the PXI module) or the driver software. The record of how the signal varies with timeis captured as digital data, rather than as fleeting visual information on a screen, and providesopportunities for data analysis and easy expansion on the display.The concept of a DSO is relatively simple, though real implementations are likely to be muchmore complex than that shown.The input signal is first buffered and either attenuated or amplified by a variable gain inputamplifier. The signal can be either AC or DC coupled and is then captured by an A to D converter,the resulting digital data is stored in a memory device. The contents of the memory can beread out for processing by a DSP or by the PXI controller. In reality almost all DSOs have anembedded DSP to provide the scope output to the PXI backplane.The input buffer prevents backfire from the A to D converter and other digital signals frombeing conducted out of the front panel and into the device under test. It also allows the inputsignal amplitude to be scaled so that it drives the A to D converter over its full operating levelrange, ensuring maximum use of the dynamic range of the converter. The input buffer can havea bandwidth that is different to that of the sampling rate of the A to D converter and is quotedseparately on the data sheet. If the analogue bandwidth is very large it may be possible to usethe A to D converter to deliberately down convert the input frequency of the signal, effectivelyproviding a function similar to high frequency analogue sampling oscilloscopes.Page 7.13

7 - PXI INSTRUMENTSThe A to D converter is driven by a variable clock generator that determines the sampling rate ofthe scope. The faster the sampling rate the higher the maximum frequency input can be withoutcausing aliasing signals. Alias signals occur when a fast changing input signal has a frequencycontent which exceeds half the A to D sampling rate, the alias signal appears at a much lowerfrequency signal. Consequently, the sampling rate needs to be at least twice the highest frequencysignal of the input that needs to be captured to avoid the complication of aliasing. Manyapplications require much higher ratios of sample rate to analogue signal bandwidth than a factorof two, and it is common for the sampling rate (or resolution) to be the limiting parameter.Some products, such as analog sampling oscilloscopes with very broadband front ends,deliberately under sample the input signal so that high frequency signals are aliased down to alower frequency. Provided the input signal is repetitive a picture of the input waveform can bedisplayed, but if other signals are present, or the signal is not repetitive, a confusing display ofsignals are generated.The A to D resolution limits the ability of the DSO to see to small defects and events in the inputsignal. More resolution results in lower quantisisation noise, but high resolution is likely to limitthe maximum sampling rate that can be sustained. Higher sampling rate and resolution bothincrease the cost of DSO solutions.The clock signal is often derived from a fixed frequency source and then divided by integer factors(typically factors of two) to provide a variable sampling rate. Using this technique simplifies thedesign and can provide lower phase jitter than a fully adjustable clock signal provides.The output from the A to D converter is then stored in memory. The contents of the memory canbe read out by an embedded DSP or to the PXI backplane for further processing.The trigger circuits allow the DSO to ignore A to D samples until an event forces the DSO to storethem in memory. Trigger events can be initiated from analogue features of the input signal (suchas a rising positive edge at a given voltage) or from the PXI trigger systems.The amount of memory in the DSO can significantly effect the suitability of a DSO for anapplication. For a given sample rate the more memory the DSO has the longer the sampling timethat can be recorded by the DSO. DSO products often have ways of segmenting the availablememory so that more than waveform can be stored at the same time. This is less important on PXIsolutions since the waveforms can also be stored in the PXI controller.Software, running on an embedded DSP or in the PXI controller, can be used to manipulate theinformation displayed. It can, for instance, be used to low pass filter the input signal and reducethe displayed noise. The software can be used to continually capture, buffer and discard samplesuntil a trigger event occurs, at which point the buffered and future data can be retained and soallow analysis of events both before and after the trigger occurred.Page 7.14

7 - PXI INSTRUMENTSSelecting a DigitizerDigitizers are designed to capture analog signals and convert them into a time varying digitalrepresentation. Their function is similar to that of an oscilloscope, but they usually do not includeall the functions and features normally associated with an oscilloscope. Some applications fordigitizers require closer attention to parametric performance (e.g. clock dither, harmonics) thanis required of an oscilloscope because additional information (e.g. noise, spurious or harmonics)is extracted from the digital information when it is processed by the test system.8-bit, 1-2 GS/s dual-channel digitizer with 1 GHz analogue bandwidth8-bit, 0.5-1 GS/s dual-channel digitizer with 500 MHz analogue bandwidth(Courtesy of Acqiris SA, Switzerland an Executive Member of the PXI Systems Alliance,www.acqiris.com)Selection from Quoted SpecificationsTrying to select the best digitizer solution for any application can be a complex task. It involvesan in-depth evaluation of what must be measured, how it can be measured, and the requireddegree of accuracy.A number of digitizer “banner” specifications are often presented primarily indicating bandwidth,resolution and sampling rate. Although they are presented as an indication of instrument“quality”, for a number of applications these banner specifications have little or no impact onfinal measurement fidelity.Page 7.15

7 - PXI INSTRUMENTSUnfortunately there is no simple answer to the question “Which digitizer should I use?” as eachapplication and device needs to be reviewed on a case to case basis. No system is ideal. Everydigitizer adds noise to the analog signal being sampled, creates signal distortion (harmonics), andhas some amount of clock jitter. All these elements, and more, contribute to system performance,and should be reviewed in the device specifications.Device ComparisonGreat care should be taken in the comparison of devices because different manufacturers may usedifferent test procedures, and the procedures affect the measured performance. For example, onemanufacturer may quote a harmonic distortion value including the first six harmonics, while asecond manufacture includes only the first five harmonics, which could result in a lower distortionvalue. It is unclear in this instance which device presents the lowest distortion properties for anygiven input signal.As a rule device specifications should be compared like to like. However this is not alwayspossible. Attention has to be paid not only to the specifications, but also to the definition of thosespecifications and how it might affect the users application.Measurement Accuracy and Bit ResolutionResolution is understood to define the fineness of detail that can be distinguished. Usually quotedas a number of bits, it indicates the number of discrete levels used in the encoding of the inputsignal. As resolution of 8, 10, 12 and 14 bits should represent the ability to distinguish 1 part in256, 1024, 4096 and 16384 respectively.2 4 8 16 32 64 128 256Resolution quoted as bits indicates the number of discrete measurement levels used to represent the signal,the more bits used the finer the signal that can be resolved.Page 7.16

7 - PXI INSTRUMENTSResolution is often taken as an indication of measurement accuracy, but in reality the two issuesare not necessarily related. Overall accuracy can be one of the most difficult specifications todetermine from the specifications presented on a data sheet since it is built up from a number offactors.The resolution value quoted as bits does not include any indication of the levels of noise ordistortion that reduces the device’s ability to distinguish accurately between the discrete levels.A better evaluation of the performance of a system with respect to the measurement accuracy isprovided by the Effective Bits (Effective Number of Bits, ENOB).Effective Number of Bits (ENoB)The term ENOB measures the effective resolution of a digitizer when all error sources areincluded. Evaluation of system performance is made without considering the individual errorsources.Theoretically a 16-bit digitizer will be able to measure 1 part in 65,536. Operating under realworldconditions a good 16-bit digitizer is at best about 13.5 bits accurate. A poorly designed 14-bit digitizer may perform less accurately than a well designed 12-bit digitizer. This is especiallytrue when reviewing effective number of bits as a function of input signal frequency since thereal world performance will be frequency dependent.Real-life comparison of Effective Number of Bits, between commercial 14-bit and 12-bit digitizers,100 MS/s sampling rate, 2 MHz to 100 MHz input frequency, input signal amplitude 97.5% of 1V FullScaleThe ENOB value is calculated from, the Signal to Noise and Distortion (SINAD) ratio:ENOB.=.. SINAD-1.75. . ..... 6.02.Where the SINAD ratio is expressed in dB and is the ratio of the total signal power compared tothe distortion and noise power that the digitizer adds.Page 7.7

7 - PXI INSTRUMENTSCare should be taken in comparing ENOB specifications since it varies with the test conditions.The value quoted must indicate the signal input level used, the sampling rate, and the bandwidthover which it is measured –t he value can be highly amplitude and frequency dependant and thedependency can be non-linear.In the example shown (above) if quoted only at 10 MHz, the 14-bit digitizer shows more effectivebits. However, at higher frequencies the 14 bit digitizer performance degrades significantly andthe lower resolution 12-bit digitizer is clearly significantly better at 50 MHz and is the betterchoice for higher frequency applications.Example of a high-resolution high-speed PXI compatible digitizer12-bit, 400 MS/s dual-channel digitizer with 100 – 300 MHz analogue bandwidth(Courtesy of Acqiris SA, Switzerland an Executive Member of the PXI Systems Alliance,www.acqiris.com)Page 7.18

7 - PXI INSTRUMENTSSNR and SINAD DefinitionSignal to Noise Ratio (SNR) is the ratio, expressed in dB, of the r.m.s. value of the input signal,measured at the output, to the r.m.s. value of the sum of all other spectral components.Signal to Noise and Distortion ratio (SINAD) is the ratio, expressed in dB, of the r.m.s value ofthe total input signal, measured at the output and including all the noise and distortion terms, tothe rms value of all of the other spectral components, including harmonics. As this includes boththe noise and the distortion it can be used directly to calculate the Effective Number of Bits.Care should be taken in comparing SINAD specifications. The value, as with ENOB, shouldbe quoted with the signal input level used, the sampling rate, and the bandwidth over which thespecification is measured as the value can be both highly amplitude and frequency dependant.Sampling Rate, Clock Accuracy, Sampling Jitter and Time-to-Digital ConversionAnalogous to bit resolution sampling rate, quoted in samples per second (S/s), is often regardedas a measure of temporal (time) accuracy. As with resolution, the value given for the SamplingRate of a digitizer does not indicate the levels of temporal noise added to the signal.Sampling and all device timing functions of a digitizer are driven by some clock circuitry, eitherinternal or external, that is assumed to be stable. Commonly based around a crystal oscillator,timing circuits are susceptible to frequency drift, phase noise (jitter) and spurious signals.Clock accuracy, quoted as parts per million (p.p.m.), indicates clock frequency drift. As, in theprocess of digitizing a signal it is assumed that the samples are equally spaced in time, any clockinaccuracy will introduce a false frequency shift in the measurement of an input signal.Sampling jitter indicates the random inaccuracies in the sampling of a signal. Normally quotedin picoseconds (ps), jitter introduces random noise into the signal by dispersion of the real signalin time.Trigger Time Interpolation, allows the precise placement of an external trigger between sample points tosome given resolution, normally quoted in picosecondsPage 7.19

7 - PXI INSTRUMENTSSome digitizers include Time-to-Digital Conversion (TDC) or Trigger Time Interpolation (TTI)circuitry in the device architecture. This function allows the precise placement of an externaltrigger with respect to the internal clock of the digitizer, even when that trigger falls betweensample points. TDC performance is quoted in picoseconds (ps), and is particularly important whenmeasuring repetitive signals since, if no interpolation is used, phase errors may be introduced inthe measurement.On lower cost digitizers the user may need to add an additional external clock reference device toachieve comparable timing performance to a digitizer with a better clock source.It should also be noted that in some cases, particularly measurement of repetitive signals, theSampling Rate value can be ignored completely if large acquisition memories are present in thesystem.Bandwidth (BW) and the Bode PlotThe analogue bandwidth of a device defines the difference between the lowest-frequency signalcomponent and the highest-frequency signal component that can be measured before the inputsignal is attenuated to -3 dB of its original value. Often quoted as a single value in Hz, indicatingthe upper frequency limit, a more useful indication of the frequency response of a digitizer isprovided by a Bode plot (or diagram) indicating the gain as a function of frequency.From the Bode plot it is possible to see the levels of attenuation over all frequencies. Ideally thecurve should be flat, following an asymptotic limit, and then roll off steeply to the bandwidthlimit. This is very difficult to obtain and often the Bode plot of a device can show variousinconsistencies in the gain as a function of input frequency, even for devices with similar quotedbandwidth values.Bode diagram showing signal gain as a function of frequencyIt should also be noted that where measuring the relative amplitude of signals of fixed frequency,the bandwidth of the digitizer and the Bode plot will be of little relevance, as input signals of thesame frequency will all experience the same level of attenuation provided the digitizer responseis linear. Bandwidth and the Bode plot have the greatest influence when measurement is requiredof signals over a significant frequency range.Page 7.20

Total Harmonic Distortion (THD)7 - PXI INSTRUMENTSTotal Harmonic Distortion is the ratio, expressed in dB, of the total of the first few harmoniclevels to the level of the input signal at the output.Usually calculated from an FFT of a test signal as:where f is the fundamental (input) frequency and f1 through fn are the first n harmonicfrequencies.Harmonic distortion values should always be quoted with the number of harmonics included inthe calculation, the input frequencies over which the measurement is valid, the sampling rateof the measurement quoted, the full scale voltage range and the input voltage in that full scale.Unlike most analog systems, high order harmonics can be more problematic on digitizers, in turnmaking an impact on quoted distortion values.Spurious Free Dynamic Range (SFDR)Spurious Free Dynamic Range (SFDR) is the difference, expressed in dB, between the r.m.s.values of the input signal, measured at the output, and the peak spurious signal. A spurious signalis any signal present in the output that is not present at the input.Spurious Free Dynamic RangeSpurious Free Dynamic Range values should always be quoted with the input frequencies overwhich the measurement is valid the sampling rate of the measurement quoted, the full scalevoltage range and the input voltage in that full scale.Page 7.21

7 - PXI INSTRUMENTSThe Impact of the Key SpecificationsThe small number of specifications described here demonstrates that it is not an insignificant taskto make a product selection from a manufacturer’s specifications alone.ENOB (and SINAD) provide some indication of amplitude measurement linearity and noise.Clock accuracy and sampling jitter provide an indication of the frequency measurement accuracyand the temporal noise introduced in the measurement.There are many other specifications that can be used for digitizers which have differentimplications for different applications, a few of which are indicated below.Linearity addresses the fact that the discrete measurement levels described by the bit resolutionare not necessarily equally spaced, leading to amplitude measurement error which is leveldependent. Linearity can also be quoted by using intermodulation specifications where two equalamplitude signals are applied to a digitizer at the same time and the resulting spurious responsesmeasured.Voltage Standing Wave Ratio (VSWR) describes the reflection of the input signal at the inputterminals, influencing the signal amplitude before it is measured and introducing signal echoes into the system. VSWR is frequency dependant, introducing more complication.Basic noise ratios have been described, but other noise specification definitions exist, such as theSparkle Code Rate, indicates the probability of a sampled point exceeding a specified deviationthreshold. This noise specification could have an effect on any peak detection routine basedaround the digitization of a signal.In most cases, to obtain the best measurement system for a specific application, it is advisableto consult not only the published data sheets of the digitizer, but also the manufacturer for anyadditional useful information relevant to the user’s application.Page 7.22

8 - RF SYSTEMSSECTION 8RF SYSTEMSPXI is well suited to supporting RF test applications and there are an increasing number ofRF switching and instrument modules available. This section covers some of the importanttechnical issues and components that can form a key part of a PXI test system that supportsRF testing.For information on RF switching the user should refer to the switching section of this book.RF Level Measurements ..................................................................................8.3Ever wondered why two instruments might give different answers on RF levelmeasurements? This section may be able to explain some of your variances. This isan increasingly important issue as more communication systems use signals whoseamplitude varies rapidly with time.RF Conversion and VSWR ...............................................................................8.6This section includes useful tables that turn return loss to VSWR and the consequentlevel errors and convert RF levels between different units of measure.Frequency Conversion.....................................................................................8.11Until D to A and A to D converters are able to generate or measure high quality RFsignals directly frequency upconverters and downconverters will continue to be used tofrequency translate signals. This section explains the principles involved.Intermodulation - Non-Linear Behaviour of Devices .....................................8.18Whenever more than one signal is passed through a non-linear device it will causeunwanted effects. This section explains the principles of intermodulation and theterminology used.Directional Couplers ........................................................................................8.21Directional couplers are useful to separate the forward and reverse signal in RFtransmission lines. This section explains their general principles and the terminologyused.RF Splitters and Combiners ............................................................................8.24Combining or splitting signals in a test system is a common requirement. This sectionexplains the basic options available.RF Mixers ..........................................................................................................8.25RF mixers are used to up-convert or down convert signals too or from RF frequencies.There are many different types of mixer, this section explains their principles andprovides a useful table of their intermodulation performance.Page 8.1

8 - RF SYSTEMS3GHz Programmable Step Attenuator (41-180)• 63 dB range, 1 dB Step• 1 or 2 Channel Versions Available• Choice of RF Connector TypesPage 8.2

8 - RF SYSTEMSRF Level measurementsMeasuring RF levels causes considerable confusion because of the different types of detectorswhich are commonly used. Often these detectors are calibrated in terms of the root mean square(or thermal) power of the signal and for signals whose amplitude does not vary, all of the detectionmethods will measure the same. If the signal has a time varying amplitude the detectors willrespond differently. Often there is a simple conversion factor that needs to be applied, but onother occasions it may not be as simple.A conversion table for power to voltage is provided in this book in the section on Useful Data.Power Law DetectorsThese detectors include thermal devices and diodes operated in the region where the output signalis the square of the applied voltage. The indicated output is a measure of the r.m.s. or thermalpower of the signal. It is usually expressed on a logarithmic scale relative to one milliwatt in50 ohms using the symbol dBm.One watt is +30 dBm, one milliwatt is 0 dBm and one microwatt is –30 dBm.Peak DetectorsOften implemented by a diode and capacitor the diode will typically detect the peak voltage ofthe signal. When the signal level drops the capacitor will retain the value of the peak voltage untilthe charge decays or is topped-up by the next voltage peak. The response of peak detector canbe very dependent on both the attack time (the speed with which it responds to rapid increase inapplied level) and the decay time (how long it remembers the last detected peak signal).Average Voltage DetectorIn these detectors the input voltage is rectified and then averaged by low pass filtering the signalto leave a value representative of the average voltage. The response of an average detector todifferent types of signal is usually mathematically predictable and for this reason it is often moreuseful in test systems.Detector followed by a Logarithmic AmplifierUsually used with a peak or average detector, the signal is amplified by a logarithmic amplifier toincrease the dynamic range of the following stages. This technique is commonly used in spectrumanalysers with analogue detector systems. The display allows both large and small signals to beseen at the same time, so it is ideal for displaying both wanted signals and unwanted signals inthe common format. The logarithmic conversion will effect the measured value if the processingincludes averaging after the conversion.A-D SamplingAs analogue to digital converters become faster there are increasing numbers of detectors thatsimply sample the signal and then compute the signal power. This technique is used on modernspectrum analysers with digital IF systems. With a sufficiently powerful computing system thedetector can be arranged to measure power or voltage and simulate most types of detector.Page 8.

8 - RF SYSTEMSExample of Impact of Detector on Measured Level.Consider a CW signal that has increasing amounts of amplitude modulation applied to it, asshown below:CW Signal with AM appliedEach type of detector will respond differently.A power law detector will measure an increasing amount of power as the AM depth is increased.The peaks of the AM signal contribute more power than is ‘lost’ in the troughs because the poweris dependent on the square of the voltage. The graph shows how the thermal power changes withAM depth.Modulation Depth (%)100.090.080.070.060.050.040.030.020.010.00.01 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5Measured power/carrier powerPlot of increasing Thermal Power as AM Depth is increasedBy convention a signal generator generating an AM signal displays an average power, not thethermal power in the signal. So if a power meter is connected to a signal generator generating1 mW (0 dBm), and AM is then set to 100%, the signal generator will continue to indicate 1 mW(0 dBm), but the power meter will indicate a higher level (1.5 mW). The power meter is correctlydisplaying the power, but engineering convention is to define the power of an AM signal as itsaverage power.Page 8.

8 - RF SYSTEMSA peak detector can read almost anything. If the hold time of the peak detection is much longerthan the repetition rate of the AM then the meter will read twice the average voltage of the signal(four times the power) when 100% AM is set compared to 0%. If the detector peak hold timeis very short the detected voltage will follow the AM envelope and read the average voltage. Atintermediate rates the detector will give intermediate answers.An average detector will continue to measure the same output voltage, the peaks of the signal willbalance the troughs of the signal. The measured value will agree with what is set on the signalgenerator.Other waveforms will behave differently, and the waveform may have a very specific definitionof level that is different to that used by the detector.Page 8.

8 - RF SYSTEMSconvERSIon oF RETuRn LoSS To vSWR anD LEvEL ERRoRThis table provides a conversion factor for return loss (dB) to VSWR and the voltage error thatcan appear when a perfect source and transmission line provides a signal to that load.Return Loss(dB)vSWRvoltageReflectionCoefficientMaximum PositiveError (dB)Maximumnegative Error (dB)1 17.39 0.891 5.53 -19.22 8.72 0.794 5.07 -13.73 5.85 0.708 4.65 -10.74 4.42 0.631 4.24 -8.75 3.57 0.562 3.88 -7.26 3.01 0.501 3.53 -6.047 2.61 0.447 3.21 -5.148 2.32 0.398 2.91 -4.419 2.1 0.355 2.63 -3.8110 1.92 0.316 2.38 -2.5111 1.78 0.282 2.16 -2.212 1.67 0.251 1.95 -1.9313 1.58 0.224 1.75 -1.714 1.5 0.2 1.58 -1.4915 1.43 0.178 1.42 -1.3216 1.38 0.158 1.28 -1.1717 1.33 0.141 1.15 -1.0318 1.29 0.126 1.03 -0.9219 1.25 0.112 0.92 -0.8120 1.22 0.1 0.83 -0.7221 1.195 0.089 0.74 -0.6422 1.173 0.079 0.66 -0.5723 1.152 0.0708 0,59 -0.524 1.135 0.0631 0.53 -0.4525 1.119 0.0562 0.48 -0.426 1.106 0.0501 0.42 -0.3527 1.094 0.0447 0.38 -0.3128 1.083 0.0398 0.34 -0.2829 1.074 0.0354 0.3 -0.2530 1.065 0.0316 0.27 -0.22Page 8.6

8 - RF SYSTEMSuncERTaInTY oF PoWER DuE To SouRcE anD LoaD RETuRn LoSSWhen a loss-less cable connects an RF source and a load the VSWR of each device will createa standing a wave in the cable. This in turn will introduce uncertainty in the accuracy of the RFsignal power delivered to the load.The table below shows the maximum error in the signal power. The table assumes the cable is aperfect match for the nominal source and load impedance. The error can be positive or negativedepending on the length of the coaxial line, frequency and the complex source impedance of thesource and load.SourcevSWRLoad vSWR . .2 . . . .6 .7 .8 .9 21 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.001.05 0.00 0.01-0.010.02-0.020.03-0.030.04-0.040.04-0.040.05-0.050.05-0.060.06-0.060.07-0.070.07-0.071.1 0.00 0.02-0.020.04-0.040.05-0.050.07-0.070.08-0.080.09-0.100.11-0.110.12-0.120.13-0.130.14-0.141.15 0.00 0.03-0.030.05-0.060.08-0.080.10-0.100.12-0.120.14-0.140.16-0.160.17-0.170.19-0.190.20-0.201.2 0.00 0.04-0.040.07-0.070.10-0.100.13-0.130.16-0.160.18-0.180.20-0.210.22-0.230.24-0.250.26-0.271.25 0.00 0.05-0.050.09-0.090.12-0.130.16-0.160.19-0.200.22-0.230.25-0.250.27-0.280.29-0.300.32-0.331.3 0.00 0.05-0.050.10-0.100.15-0.150.19-0.190.22-0.230.26-0.270.29-0.300.32-0.330.34-0.360.37-0.391.35 0.00 0.06-0.060.12-0.120.17-0.170.21-0.220.25-0.260.29-0.300.33-0.340.36-0.380.39-0.410.42-0.441.4 0.00 0.07-0.070.13-0.130.19-0.190.24-0.240.28-0.290.33-0.340.37-0.380.40-0.420.44-0.460.47-0.501.45 0.00 0.08-0.080.14-0.150.21-0.210.26-0.270.31-0.330.36-0.380.40-0.420.44-0.470.48-0.510.52-0.551.5 0.00 0.08-0.080.16-0.160.22-0.230.28-0.290.34-0.350.39-0.410.44-0.460.48-0.510.52-0.560.56-0.601.55 0.00 0.09-0.090.17-0.170.24-0.250.31-0.320.37-0.380.42-0.440.47-0.500.52-0.550.56-0.600.60-0.651.6 0.00 0.09-0.0100.18-0.180.26-0.270.33-0.340.39-0.410.45-0.480.50-0.540.55-0.590.60-0.650.64-0.701.65 0.00 0.10-0.100.19-0.200.27-0.280.35-0.360.42-0.440.48-0.510.54-0.570.59-0.630.64-0.690.68-0.741.7 0.00 0.11-0.110.20-0.210.29-0.300.37-0.380.44-0.460.50-0.540.57-0.600.62-0.670.67-0.730.72-0.791.75 0.00 0.11-0.110.21-0.220.30-0.310.39-0.400.46-0.490.53-0.560.59-0.640.65-0.700.71-0.770.76-0.831.8 0.00 0.12-0.120.22-0.230.32-0.330.40-0.420.48-0.510.55-0.590.62-0.670.68-0.740.74-0.810.79-0.871.85 0.00 0.12-0.120.23-0.240.33-0.340.42-0.440.50-0.530.58-0.620.65-0.700.71-0.770.77-0.840.82-0.911.9 0.00 0.13-0.130.24-0.250.34-0.360.44-0.460.52-0.560.60-0.650.67-0.730.74-0.810.80-0.880.86-0.951.95 0.00 0.13-0.130.25-0.260.36-0.370.45-0.480.54-0.580.62-0.670.70-0.760.76-0.840.83-0.910.89-0.992 0.00 0.14-0.140.26-0.270.37-0.390.47-0.500.56-0.600.64-0.700.72-0.790.79-0.870.86-0.950.92-1.02Page 8.7

8 - RF SYSTEMSconvERSIon oF RF LEvEL unITSThe following tables provide a handy way of converting different RF level units.e.m.f. voltagep.d. voltage50 ohm sourceSignalSource50 ohmloadConversion of RF Level Units (+30 dBm to 0 dBm)dBm dBuv emf dBuv pd Linear p.d(volts)Linear emf(volts)Power(Watts)30 143.01 136.99 7.071 14.142 1.0000027 140.01 133.99 5.006 10.012 0.5011924 137.01 130.99 3.544 7.088 0.2511920 133.01 126.99 2.236 4.472 0.1000018 131.01 124.99 1.776 3.552 0.0631016 129.01 122.99 1.411 2.822 0.0398114 127.01 120.99 1.121 2.241 0.0251212 125.01 118.99 0.890 1.780 0.0158510 123.01 116.99 0.707 1.414 0.010008 121.01 114.99 0.562 1.123 0.006316 119.01 112.99 0.446 0.892 0.003984 117.01 110.99 0.354 0.709 0.002512 115.01 108.99 0.282 0.563 0.001580 113.01 106.99 0.224 0.447 0.00100Page 8.8

8 - RF SYSTEMSConversion of RF Level Units (0 dBm to –60 dBm) ContinueddBm dBuv emf dBuv pd Linear p.d(millivolts)Linear emf(millivolts)Power(milliwatts)0.00 113.01 106.99 223.607 447.214 1.00-2.00 111.01 104.99 177.617 355.234 6.31 x 10 -1-4.00 109.01 102.99 141.086 282.173 3.98 x 10 -1-6.00 107.01 100.99 112.069 224.138 2.51 x 10 -1-8.00 105.01 98.99 89.019 178.039 1.58 x 10 -1-10.00 103.01 96.99 70.711 141.421 1.00 x 10 -1-12.00 101.01 94.99 56.167 112.335 6.31 x 10 -2-14.00 99.01 92.99 44.615 89.231 3.98 x 10 -2-16.00 97.01 90.99 35.439 70.879 2.51 x 10 -2-18.00 95.01 88.99 28.150 56.301 1.58 x 10 -2-20.00 93.01 86.99 22.361 44.721 1.00 x 10 -2-22.00 91.01 84.99 17.762 35.523 6.31 x 10 -3-24.00 89.01 82.99 14.109 28.217 3.98 x 10 -3-26.00 87.01 80.99 11.207 22.414 2.51 x 10 -3-28.00 85.01 78.99 8.902 17.804 1.58 x 10 -3-30.00 83.01 76.99 7.071 14.142 1.00 x 10 -3-32.00 81.01 74.99 5.617 11.233 6.31 x 10 -4-34.00 79.01 72.99 4.462 8.923 3.98 x 10 -4-36.00 77.01 70.99 3.544 7.088 2.51 x 10 -4-38.00 75.01 68.99 2.815 5.630 1.58 x 10 -4-40.00 73.01 66.99 2.236 4.472 1.00 x 10 -4-42.00 71.01 64.99 1.776 3.552 6.31 x 10 -5-44.00 69.01 62.99 1.411 2.822 3.98 x 10 -5-46.00 67.01 60.99 1.121 2.241 2.51 x 10 -5-48.00 65.01 58.99 0.890 1.780 1.58 x 10 -5-50.00 63.01 56.99 0.707 1.414 1.00 x 10 -5-52.00 61.01 54.99 0.562 1.123 6.31 x 10 -6-54.00 59.01 52.99 0.446 0.892 3.98 x 10 -6-56.00 57.01 50.99 0.354 0.709 2.51 x 10 -6-58.00 55.01 48.99 0.282 0.563 1.58 x 10 -6-60.00 53.01 46.99 0.224 0.447 1.00 x 10 -6Page 8.9

8 - RF SYSTEMSConversion of RF Level Units (-60 dBm to –120 dBm) continueddBm dBuv emf dBuv pd Linear p.d(microvolts)Linear emf(microvolts)Power(milliwatts)-60.00 53.01 46.99 223.607 447.214 1.00 x 10 -6-62.00 51.01 44.99 177.617 355.234 6.31 x 10 -7-64.00 49.01 42.99 141.086 282.173 3.98 x 10 -7-66.00 47.01 40.99 112.069 224.138 2.51 x 10 -7-68.00 45.01 38.99 89.019 178.039 1.58 x 10 -7-70.00 43.01 36.99 70.711 141.421 1.00 x 10 -7-72.00 41.01 34.99 56.167 112.335 6.31 x 10 -8-74.00 39.01 32.99 44.615 89.231 3.98 x 10 -8-76.00 37.01 30.99 35.439 70.879 2.51 x 10 -8-78.00 35.01 28.99 28.150 56.301 1.58 x 10 -8-80.00 33.01 26.99 22.361 44.721 1.00 x 10 -8-82.00 31.01 24.99 17.762 35.523 6.31 x 10 -9-84.00 29.01 22.99 14.109 28.217 3.98 x 10 -9-86.00 27.01 20.99 11.207 22.414 2.51 x 10 -9-88.00 25.01 18.99 8.902 17.804 1.58 x 10 -9-90.00 23.01 16.99 7.071 14.142 1.00 x 10 -9-92.00 21.01 14.99 5.617 11.233 6.31 x 10 -10-94.00 19.01 12.99 4.462 8.923 3.98 x 10 -10-96.00 17.01 10.99 3.544 7.088 2.51 x 10 -10-98.00 15.01 8.99 2.815 5.630 1.58 x 10 -10-100.00 13.01 6.99 2.236 4.472 1.00 x 10 -10-102.00 11.01 4.99 1.776 3.552 6.31 x 10 -11-104.00 9.01 2.99 1.411 2.822 3.98 x 10 -11-106.00 7.01 0.99 1.121 2.241 2.51 x 10 -11-108.00 5.01 -1.01 0.890 1.780 1.58 x 10 -11-110.00 3.01 -3.01 0.707 1.414 1.00 x 10 -11-112.00 1.01 -5.01 0.562 1.123 6.31 x 10 -12-114.00 -0.99 -7.01 0.446 0.892 3.98 x 10 -12-116.00 -2.99 -9.01 0.354 0.709 2.51 x 10 -12-118.00 -4.99 -11.01 0.282 0.563 1.58 x 10 -12-120.00 -6.99 -13.01 0.224 0.447 1.00 x 10 -12Page 8.0

8 - RF SYSTEMSFrequency ConversionFrequency conversion products are an essential part of RF test systems. Measurement systemsneed to convert an RF signal to a frequency sufficiently low that it can be captured and analysedby a suitable data acquisition system. Current data acquisition products do not have enoughbandwidth to achieve this directly at RF.Frequency generation systems may also need a signal to be converted to the RF frequencies thatthe system actually uses. In some cases this may be by direct modulation of an RF carrier but inother cases may involve frequency conversion of a low frequency (modulated) signal to a higherfrequency.Simple DownconverterRF InputRMixerILow PassFilterIF OutputLLocal OscillatorSimple DownconverterIn a simple downconverter the signal to be converted is applied to the RF port of a mixer. Aseparate (fixed) oscillator is applied to the LO port. The output from the mixer is filtered toremove the sum component and leave just the difference frequency on the output.If the RF input is 950 MHz and the LO frequency is 900 MHz the IF output will be 50 MHz.The advantage of using this scheme is that the conversion is very simple, but the disadvantageis that the output signal has unwanted signals at other frequencies. Taking the above example,if the input signal also has a component at 850 MHz (the image frequency) that signal will alsoappear at the output as a 50 MHz output, so the output signal has some additional components.Non-linear behaviour in the mixer also generates other intermodulation products that may beimportant to some applications. The higher the signal level applied to the RF port of the mixer thegreater the level of intermodulation products produced, so closely managing the RF level appliedto the RF port can reduce the unwanted signals.A table of typical intermodulation products for a double balanced mixer and a section describingintermodulation is provided in this publication.The origin of these signals can also be checked by offsetting the LO frequency and observinghow the output signal changes. In the above example increasing the LO frequency reduces the IFfrequency, but increases the frequency of the image signal. With the aid of software the artefactscan be identified and eliminated.Page 8.11

8 - RF SYSTEMSThe LO frequency is generally not a swept source, so frequency coverage is limited, but thequality of the LO is better than that usually included in a spectrum analyser, and that allows higherdynamic range and lower noise signals to be measured. For applications where measurementsover a limited bandwidth are required and multiple signals are not expected this type of downconversion can offer better performance.Aeroflex Downconverter and DigitizerPXI CHASSISPCI INTERFACE3030 DOWNCONVERTER & DIGITIZERMXI-33010LOCALOSCILLATORFREQUENCYDIVIDER46 MHzFILTERATTENUATORA/DCONVERTER15 to 3GHz LORF INPUTLVDSOUTPUTCOMPUTERSPECTRUMORMODULATIONDISPLAYAeroflex Downconverter System based a Downconverter Module driven by an OctvaeBandwidth Local Oscillator ModuleAn example of a simple downcoverter is the Aeroflex 3030 PXI RF Digitizer used in conjunctionwith their 3010 RF Synthesizer. The 3010 provides a fixed output level CW RF source coveringthe frequency range 1.5 GHz to 3 GHz and is used as the RF source for the 3030 RF Digitizer. The3030 frequency divides the signal as required and uses the resulting RF as the Local Oscillator fora RF mixer that converts an input signal of up to 3 GHz to a lower frequency (IF) of 46 MHz. TheIF signal is then digitized by a high speed A to D converter and the resulting data stored and thentransferred to the system controller via the PXI Bus where the signals are analyzed by the modulePage 8.12

8 - RF SYSTEMSdriver. The module driver provides the primary functions normally expected of spectrum analyzer.Alternatively the captured data can be exported directly from the front panel of the module via aLVDS interface to a dedicated instrument for real time analysis of the information. This approachto frequency conversion allows users to analyse RF signals over a bandwidth of approximately20 MHz with greater precision and lower noise than that available from a spectrum analyzerbecause of its simpler architecture and better quality of LO source. The 3010 LO source avoidsthe use of YIG oscillators by using a proprietary synthesis technology, and therefore avoids theproblems that magnetic fields can cause to YIG oscillators in the PXI environment. If the inputsignal has multiple frequencies present then these may produce other responses from the digitizeroutput since, unlike a spectrum analyzer, the architecture is not frequency selective.Spectrum AnalyserUp conversionDown conversionRF InputInputAttenuatorInputFilterInputMixerBandpassFilterSecondMixerBandpassFilterThirdMixerLocal OscillatorSecondLocalOscillatorThirdLocalOscillatorSpectrum Analyser DownconverterIn a spectrum analyzer the input signal is again applied to a mixer via a programmable attenuator,but the frequency of the signal is first converted to a higher frequency using a high frequencylocal oscillator. The output from the first mixer is above the highest input frequency the spectrumanalyser can measure. The mixer input filter prevents input signals going directly through themixer into the later stages.The mixer output is filtered by a bandpass filter before it is applied to a second mixer forconversion to a lower frequency. Subsequent conversion stages filter the signal and further lowerits frequency. Filters (digital or analogue) are used to select the frequency being measured.The LO frequencies are adjusted or swept to avoid variable frequency filters and provide thetraditional swept signal analysis of a spectrum analyser.This method of first increasing and then decreasing the frequency is used to avoid mirror imagesignals producing spurious outputs. The spectrum analyser can uniquely identify the origin of thesignal and it can also be designed to have broad frequency cover (down to almost DC).The filters and the LO frequency are carefully chosen to avoid spurious signal generation in theconversion system, but if the spectrum analyser is used in ways it was not intended for (e.g. withhigh frequency out of band signals present or at high mixer input levels) it can create spuriousresponses.Page 8.13

8 - RF SYSTEMSThe noise performance and dynamic range are limited by the complexity of the conversion systemand the need for a high frequency swept signal source to do the first up conversion and a highfrequency LO for the first down conversion. Consequently noise performance and dynamic rangeare likely to be less than the simpler frequency conversion system.In order to maintain good linear performance the signal applied to the input mixer is typicallyaround –40 dBm, so an attenuator is usually included to optimise the input drive level to themixer. Having a switched attenuator with fine resolution will provide the best performance.NI PXI-5660 Spectrum AnalyzerAn example of a spectrum analyser available in PXI format is the NI 5600. The spectrum analyseris formed from two separate modules; a PXI-5600 RF Downconverter and a PXI-5620 FrequencyDomain Digitizer.PXI CHASSISPCI INTERFACEMXI-35600RFDOWNCONVERTER5620DIGITIZER15 +/- 10 MHzCOMPUTERRF INPUTTO 2.7 GHzSPECTRUMANALYZERDISPLAYNI 5660 Spectrum Analyzer in PXI with external PC providing the displayThe RF Downcoverter accepts input signals up to 2.7 GHz. The converter uses a YIG LO basedupconversion stage and then a series of down conversion stages to produce an IF with a nominalfrequency of 15 MHz with a bandwidth of ±10 MHz.Page 8.14

8 - RF SYSTEMSThe IF signal from the RF Downconverter is then digitised by a PXI-5620, turning the analoguesignal into a digital data stream with 14 bit resolution at a 64 Ms/s rate. The digital data canbe used to generate an FFT of the signal that provides a variety of common spectrum analyserfunctions. The use of an FFT over a broad bandwidth ensures the spectrum analyser has a fastanalysis capability on narrow spans as well as wider spans. The spectrum analyser filters arecreated in the digital domain rather than being hardware filters.The two modules use the PXI backplane facilities to ensure they work together while the YIGLO is being swept on wider band measurements. For this reason it is recommended that the twomodules are placed side by side in a chassis with no PXI bridge between them.The Spectrum Analyser’s functionality is provided by a software package included with themodules. The software provides the facilities normally associated with bench operated spectrumanalysers.Simple UpconverterRF InputMixerLow PassFilterIF OutputLocal OscillatorSimple UpconverterSimple up conversion can take a signal at relatively low frequencies and increase its frequencyby applying it to a mixer driven by a high frequency LO.If the input frequency is 50 MHz and the LO is at 950 MHz the mixer will produce a signal at1 GHz. However, it will also generate a signal at 900 MHz (the difference product) which hasan equal amplitude. For many applications (e.g. receiver sensitivity measurements) this does notaffect a measurement, but for other applications the signal will need to be filtered to remove theunwanted component. Eliminating the unwanted signal can be problematic since its frequencycan be close to the wanted frequency.Page 8.15

8 - RF SYSTEMSLevelImage signalWanted signalBaseband breakthroughLObreakthroughIntermodulationproductsFrequencySSB Frequency ConversionOutput Spectrum of a Simple UpconverterA more complicated up conversion system uses SSB (Single Side Band) mixers.SSB mixers use two mixers whose outputs are added. Each mixer is driven by a LO and anRF input whose signals are in phase quadrature. When the two signals are added the sum anddifference signals from each mixer are 180 degrees out of phase and one set of signals will addand the other will subtract.The result is that one of the signals is reinforced and the other is, to a first approximation, cancelledout. The degree to which one of the signals is cancelled is dependent on the accuracy of the phaseshifters and the balance of the mixers. Typically 30 dB of cancellation can be obtained using welldesigned SSB mixers.Page 8.16

8 - RF SYSTEMSRF InputSplitter90 o PhaseShifterIFMixerRFHigh PassFilterRF OutputIFMixerRFSplitter90 o PhaseShifterLocal Oscillator I/PLevelSSB ImagesuppressionWanted SignalImage SignalIntermodulationProductsBaseband BreakthroughLOBreakthroughFrequencyNot all intermodulation products are shown.High order products reduce rapidly with decreasing signal level to the MixerSSB MixerPage 8.17

8 - RF SYSTEMSIntermodulation - Non-Linear Behaviour of DevicesDevice CompressionAs the input level to a device is increased it will start to exhibit non-linear behaviour. As theability of the device to produce an ever increasing output level is compromised the overall gaindecreases, or its insertion loss increases (for switches and attenuators).If the input and output levels are plotted, eventually the RF output is 1 dB less than what wasexpected of it if it had been perfectly linear. This is defined as the 1 dB compression point. Thecompression point can be (and usually is) frequency dependent.Device Output1 dBcompressionpoint1 dBLinearResponseActualResponseDevice InputDefinition of 1 dB Compression PointActive switches often have a lower compression at low frequencies than at high frequencies,making it essential that the user is aware of the limitations of power handling versus frequency.Some applications may need to consider the non-linear behaviour of the switch at lower RFlevels, especially when measuring intermodulation. For this reason some devices may be specifiedto have 0.1 dB or 0.2 dB compression points, which will be significantly lower than the 1 dBcompression point.IntermodulationWhen two or more signals are passed through a device with non-linear amplitude behavioura variety of unwanted signals can be produced. These signals (intermodulation products) areproduced in many devices, including mixers and amplifiers. Mechanical switches do not producesignificant levels of intermodulation but those based on solid-state switches (PIN diodes, FETs)can produce these unwanted products. The performance of these devices can also be frequencydependent.Even devices that are considered linear can introduce intermodulation products because of nonlinearcontact behaviour or the presence of ferrite materials, but for most applications the powerlevels needed to observe this effect (> 1 Watt) are not relevant for PXI applications.Page 8.18

8 - RF SYSTEMSIntermodulation DistortionWhen two signals at frequencies of F 1 and F 2 pass through a non-linear device they produceharmonic signals which interact with each other (essentially a multiplying effect) and producesignals at other frequencies.The frequencies produced are of the form:mF 1 ± nF 2where m and n are integers with a value of ≥ 0.Intermodulation products are classified as having an ‘order’ which is the sum of m and n. So thirdorder products are produced from values of m and n being 2 and 1, or 3 and 0 (the numbers areassigned to any of m or n). Fourth order products include all products where m and n are 3 and 1,2 and 2, or 0 and 4. Second order products include values of 2 and 0 and 1 and 1.Second Order ProductsF1 F2Third Order ProductsF1 F22F1 - F22F2 - F13F12F1 + F22F2 + F13F2F2 - F12F1F2 + F1F2FrequencyFrequencyFourth Order ProductsF1 F22F2 - F13F1 - F23F2 - F1Higher frequencies not shown4F1FrequencyStylised Spectral Plots showing the frequency of Common Intermodulation ProductsPage 8.19

8 - RF SYSTEMSSecond and Third Order Intercept PointWhen two signals are producing intermodulation products the level of the unwanted signalswill depend on the level of the two signals. As the signal level increases the level of theintermodulation products will increase.For third order products (the ones most often of interest) many devices have a reasonablypredictable behaviour as the level is increased. If the input level (and therefore the output level)increases by 1 dB, the third order products increase in level by 3 dB (so the ratio of the outputlevel to the intermodulation product gets worse by 2 dB).This simple model gives rise to the concept of Intercept Points.If the input and output levels are plotted along with the level of the intermodulation productsthen, for reasonable levels, they can be plotted as straight lines. If these lines are extrapolated thepoint at which the line crosses the extrapolated line of output versus input level is known as theIntercept Point. If this is done for third order products (the most common) it is called the ThirdOrder Intercept Point (TOI or IP3). The same can be done for other products. For second orderproducts the IMD signals increase by 2 dB for every 1 dB increase of input level. For fourthorder products they increase by 4 dB for every 1 dB of input.Device Output1 dBcompressionpointSecond Order InterceptThird OrderInterceptActual FundamentalResponseActual SecondOrder ResponseActual ThirdOrder ResponseDevice InputDefinition of Second and Third Order Intercept PointsIt should be noted that these intercept points are invariably at a higher level than the 1 dBcompression point, and they must not be used to assume that a device will be able to handle thesepower levels safely.The concept of second and third order intercepts points works well for many devices but tendsnot to work well for devices that have bias current management to improve efficiency.Page 8.20

8 - RF SYSTEMSDIREcTIonaL couPLERSDirectional couplers are useful components which can be used as part of a PXI system formeasuring power (voltage) and reflection parameters (VSWR).InputPortOutputPortCoupledPortTerminationThree Port Directional Coupler for detecting reflected signals from the load at theoutput portIn a 3 port directional coupler signals at the input port pass through to an output port, ideallywithout producing any signal at the coupled port. A proportion of the forward signal is coupled toa terminated port. Signals coming from the output port to the input port have a proportion of theirsignal routed to the coupled port where they can be measured. The device is therefore directionaland can be used to measure the reflected power from the output port.A 4 port directional coupler (or bi-directional coupler) can be constructed in two ways;• by providing access to the terminated port of the ‘three port’ version• or by constructing two independent three port couplers (dual directional coupler).The latter has the advantage that the coupling factors involved can be different in the twodirections.Directional Couplers have a number of important specification parameters:Insertion Loss. The transmission loss from the input to the output port. Since some of the poweris routed into the terminated port (or the fourth port) there is a theoretical minimum insertionloss as below:Coupling Factor dB 6 10 15 20 30Insertion Loss 1.2 dB 0.46 dB 0.14 dB 0.04 dB 0.004 dBMinimum Insertion Loss for different Coupling FactorsIn reality the insertion loss will be higher and will be frequency dependent. The theoretical lossis sometimes referred to as the Coupling Loss.Page 8.2

8 - RF SYSTEMSCoupling Factor or Coefficient. The loss between the input port and the coupled port of thedirectional coupler. The loss will be frequency dependent.Directivity. For a three port coupler the difference in power at the coupled port to the signalapplied to the input port. The definition is the same for a 4 port coupler but it also applies to thesignal from the output port to the 4 port. The directivity is expressed in dB and can be differentfor each direction, depending on the coupler type. Directivity is measured with the couplerterminated in a ‘perfect’ load.Power Rating. The maximum power that can be sent through the coupler. This can be quite highsince the insertion loss can be low for a low coupling factor product. For 3 port couplers thepower limitation may be the internal termination.If a signal is connected to a device under test with a measurable VSWR the reflected signal fromthe load goes back through the coupler and can be measured to give an indication of the VSWRafter applying correction factors for the insertion loss and coupling factor. To be useful thedirectivity must be significantly larger than the coupling factor, since the directivity limitationsresult in some of the signal leaking to the coupled port, even in the presence of a perfect load.If a 4 port coupler is used it is important that the coupled ports are correctly terminated to avoidport interaction. For four port applications the hardest part is often ensuring the input source is agood match and does not degrade the measurement.Directional couplers are always bandwidth limited and use transformer or microstrip techniquesto achieve their performance.Since they are passive devices input and output functions can be exchanged.Page 8.22

8 - RF SYSTEMSRF Multiplexer Modules from Pickering Interfaces3.5 GHz RF Multiplexer Module(40-770)20 GHz TripleRF Multiplexer Module(40-786)4 GHz RF Multiplexer Module(40-783)20 GHz RF Relay Module(40-780)20 GHz DualRF Multiplexer Module(40-785)• Wide Range of Microwave Switch Cards• 20GHz, 26.5GHz, 40GHz, 50GHz and 65GHz Versions• Complements Large RF Switch Card Range• Custom Microwave Networks Built To SpecificationPage 8.2

8 - RF SYSTEMSRF SPLITTERS anD coMBInERSTransformer Based or hybrid SplitterTransformer based splitters or combiners provide lower insertion loss than resistive splitterssince (ideally) no power is dissipated in the splitter.In reality there will be some additional losses in the device. The transformer arrangement willalso limit the frequency range of the device and may have a worse VSWR.It does however provide a degree of isolation between the two output ports that can reduce theeffects of VSWR and improve intermodulation effects when used as a combiner.number ofoutput PortsTheoretical MinimumLoss (dB)number ofoutput PortsTheoretical Minimum Loss(dB)2 3.0 5 7.03 4.8 6 7.84 6.0 8 9.0When used to combine two RF sources a transformer base combiner provides more isolationbetween the input sources than a resistive solution and can improve the intermodulationperformance.Resistive SplittersThese are more simple to make and are much more broadband in terms of frequency thantransformer based solutions.Two designs are commonly used:The symmetric splitter is harder to manufacture but presents 50 ohms at all the ports when theyare correctly terminated.A signal splitter does not provide a 50 ohm source impedance when looking at the output, butdoes correctly match the input signal.The insertion loss of each type of splitter is exactly the same since the input voltage is halved(6.01 dB) when all ports have 50 ohm terminations.Symmetric SplitterSignal Splitter16.66 ohms 50 ohms16.66 ohms16.66 ohms 50 ohmsPage 8.2

8 - RF SYSTEMSRF MixersTransformer and Diode Based MixersTransformerTransformerLO PortR PortI PortClasses of MixerRF mixers come in a variety of forms and classes. The most commonly used variety is the doublebalanced mixer using a ring of diodes. The ring of diodes can be altered to improve the linearityof the mixer, and reduce the intermodulation products, at the expense of more complexity andhigher LO drive levels.Mixer class circuit used in each arm Typical Lo Drive Levelclass class 2, Type class 2, Type 2+7 dbm to + dbm+ dbm to +2 dbm+ dbm to +2 dbmclass , Type +20 dbm to +0 dbmclass , Type 2+20 dbm to +0 dbmclass , Type +20 dbm to +0 dbmPage 8.25

8 - RF SYSTEMSTypical Intermodulation Products from a Double Balanced Mixer (Diode Type)Performance of RF mixers is level and manufacturer dependent. This chart shows the typicalperformance of a double balanced mixer, for more accurate data consult the manufacturer.The IMD products produced by a mixer are shown relative to the RF output (I port) for two powerinputs (0 dBm and –10 dBm) and for three classes of mixer (Class 1, 2, 3).Note that signals involving the third harmonic of the LO port are generally larger than those forthe even harmonics, since the mixer uses a balanced structure.harmonic of the Local oscillator and class0 1 2 3 4 5RFharmonicclass 2 2 2 2 2 2 RFLevel0 -10 dBm 26 27 18 35 31 10 39 36 23 50 47 14 41 36 190 dBm 36 39 29 45 42 20 52 46 32 63 58 24 45 37 291 -10 dBm 24 23 24 0 0 0 35 39 34 13 11 11 40 46 42 24 14 180 dBm 25 25 24 0 0 0 39 39 35 13 11 11 45 50 42 22 16 192 -10 dBm 73 86 73 73 75 83 74 84 75 70 75 79 71 86 80 64 74 800 dBm 69 68 64 72 67 71 79 76 62 67 67 70 75 80 63 66 66 703 -10 dBm 67 87 >90 64 77 >90 69 87 >90 50 78 >90 77 >90 >90 47 75 >900 dBm 51 63 81 49 58 73 53 65 85 51 60 69 55 65 85 48 55 684 -10 dBm 86 >90 >90 >90 >90 >90 86 >90 >90 88 >90 >90 88 >90 >90 85 >90 >900 dBm 80 96 83 79 80 >90 82 96 >90 77 80 >90 82 >90 >90 76 82 >905 -10 dBm >90 >90 >90 80 >90 >90 >90 >90 >90 71 >90 >90 >90 >90 >90 68 >90 >900 dBm 72 >90 >90 70 73 >90 >90 87 >90 52 72 >90 77 88 >90 46 66 >906 -10 dBm >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >900 dBm >90 >90 >90 86 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 >90 84 >90 >90Intermodulation Levels for a Typical Double Balanced Mixeractive MixersModern semiconductor processes have lead to the design of high frequency mixers based onintegrated circuits.Mixers which incorporate active components exhibit no gain and can use lower LO drive levels– the LO signal is translated internally to provide the required drive levels. Their characteristicsare similar to double balanced mixers, but closer matching of the component can provide betterbalance and repeatability than transformer based designs.Page 8.26

8 - RF SYSTEMSRF and Microwave Modules from Pickering InterfacesRF Switching Module(40-710)RF Multiplexer Module(40-746)Microwave Multiplexer Module(40-786)RF Matrix Module(40-725)• Large range of RF and microwave switch systems for all your switching applications• Signal bandwidths from 500 MHz to 65 GHz depending on switch type• Customised switching systems availablePage 8.27

8 - RF SYSTEMS20GHz Microwave Matrix BRIC Module (40-787)• Available in Various Sizes to 4 x 4• Option for Loop Thru or Auto Input Termination.• 10Ghz or 20GHz VersionsPage 8.28

9 - CONNECTORSSECTION 9CABLING AND CONNECTORSAny test system needs to connect the test equipment to the test target through a connectionsystem. In large systems the connector and cabling complexity can be such that it is byfar the the most expensive part of of the system. This section provides some guidance onthe cabling issues, the principles of mass interconnect systems and describes some of theconnectors used in PXI systems.Cabling PXI Systems ........................................................................................9.3A rough guide on some of the precautions to be taken in cabling test systems.Mass Interconnect Systems ............................................................................9.5Mass connection systems can speed up the process of connecting a test system to itstest target. It can also provide a generic interface to simplify test fixture management.This section provides a brief introduction to mass interconnect systems.PXI System Connectors ...................................................................................9.7A brief guide to some of the connectors used in PXI test systems, including RFconnectors.Optical Connectors and Fibre .........................................................................9.11Optical connectors and fibre come in a variety of different formats. This section providesa brief overview of the connectors and fibres used.Page 9.1

9 - CONNECTORSPickering Interfaces’ comprehensive range of cableforms and connectorsPage 9.2

9 - ConnectorsCabling PXI SystemsCabling is often overlooked when developing a Test System, but the cables are an integral partof the success or failure of any test system. Routing signals to and from the DUT demands carewhen signal purity, or the lack of it, is important to get accurate test results. PXI provides a verycompact format for testing products, and that requires the use of high density solutions to someaspects of the cabling, and precautions need to be taken to ensure its suitability.Some useful issues to consider when planning the test cabling are given below.Cable PlanningDecide if the systems is to be mounted in a rack, if it is consider the advantages of rear or frontfacing modules. Make sure decisions on doors or other cable protection mechanisms are madeearly.Bundling of similar cables in a card-by-card or by signal level is helpful during maintenance ortroubleshooting.If the cabling is to be installed in a harsh environment choose a cable cover material that willstand up to the environment.If the cabling will is to be subjected to bending around tight or sharp corners choose an exteriorcover that will withstand tight radius bends and chafing.Carefully consider is the length of the cable and the gauge wire used. Making the cable longermay help servicing and maintenance but will increase loss and potential for external coupling.Consider the use of a commercially available “Mass Interconnect” for larger systems. If they areused make sure that the chassis is recessed into the rack to allow space for the interconnect tofit.Power DistributionIf system requirements specify control of power to the D.U.T., it is wise to select a cable thatutilizes an entirely different connector (or cabling) order to minimize the risk of damage bymisplacement of similar style connectors.High Voltage cards and cabling should be separated from the rest of the system as far as thelocation in the chassis will allow.Cable LabelingLabeling cables with information such as card part number, card location (chassis slot number),bus address and channel or crosspoint number, allows quick accurate cable re-attachment to thecards when troubleshooting.Cable SelectionCables should be properly dressed with proper shielding if required. Attention should be paid tochoosing the correct wire diameter, most low level signals can use 28-30 AWG.Power cables need a larger diameter/gauge and a different style of connector.Page 9.

9 - connectorsTwisted pair cables will reduce radiated signals and can lower spurious signal pickup, but theyneed to be managed to ensure the cables are not too tightly stressed (causing intermittent breaks)and remember the two wires may more tightly couple together.Low level signal cables should be kept as short as possible and shielded in order to minimizesignal attenuation and crosstalk. Route low level signal cables away from the AC power cables/sources and any noise generating equipment, i.e. computers, switching power supplies, etc.Cable Strain ReliefCables should be properly dressed with back shells that contain cable strain relief hardware.Proper strain relief allows the cable to survive abuse without damage to the internal conductors.Tracking down broken conductors caused by the lack of strain relief is a very time consumingendeavour.Page 9.

9 - ConnectorsMass Interconnect SystemsWiring the test equipment or switching systems directly to the unit under test can be complicatedon large test systems, the profusion of wires and connectors can take time and in some applicationsconstant connection and disconnection can cause reliability problems.One solution to this problem is to use a mass interconnect system that acts as an interface betweenthe test system and the device under test.A Typical Mass Interconnect SystemIn a mass interconnect system a separable adaptor is provided, one side of which connects to thedevice under test and the other side connects to the test system. The mass interconnect systemcan be separated into the two halves, usually with a single mechanical actuator.Connection between the Device Under Test and the Test SystemUsing a mass interconnect adaptor the user can define a set of test fixtures and a set of testequipment that have common interfaces. One test system can be connected to a number ofdifferent test targets, or a test target can be connected to a number of different test systems via acommon interface during manufacture. This can be very useful when test system is required totest a variety of broadly similar items requiring the same test equipment, or where an item has togo through several stages of test that uuse different test equipment.Page 9.

9 - ConneCtorsThe ITA (Interchangeable Test Adaptor) half of the mass interconnect system is connected to thedevice under test, typically through a bed of nails fixture or by simply connecting to the input andoutput connectors of the target device.The Receiver carries the signals from (or to) the switching system and the test equipment. Theconnectors are housed in a frame that locates the connectors and provides the mechanism forpulling the two halves of the system together. For large systems the force required to pull the twohalves together can be very high and the matting mechanism may be complicated to ensure thateven pressure is applied across the interface and that the two halves correctly align.The use of a mass interconnect systems can reduce system set up time, reduce the risk or errorsin connecting equipment and reduce wear and tear on the test system connectors. It adds cost indefining and purchasing the two halves of the system.Mass interconnect systems are available from a number of suppliers, including Virginia PanelCorporation and MAC Panel.Example of a BRIC Based Functional Test SystemThe PXI based tester illustrated is for functional test of complex commercial aerospace subsystems. Itcontains a bank of PXI instrumentation together with a 352 x 4 BRIC Matrix (40-560-122-352x4) and isconnected to the device under test using a Virginia Panel Gemini receiver connected via an elegant ribboncable assembly developed by the system integrator.(Courtesy of Amfax Ltd, England who are an NI Select Integrator, www.amfax.co.uk).Page 9.6

9 - ConnectorsPXI System ConnectorsLow Frequency ConnectorsIn order to do anything useful PXI modules need to have connectors on their front panel toallow a connection to be made to the device under test. The small size of the front panel of PXImodules limits the size of connector that can be usefully used. Many modules require the useof high density connectors, particularly in high density switching systems. Pickering Interfacesusually use D type or SCSI type connectors for switching applications. There are a number ofkey reasons:• High contact density• Easy mass interconnection to standard ribbon cables• Screw thread retainers ensure the connector and lead assembly cannot beaccidentally disconnected during testing• Availability of a variety of connectors with different mounting arrangementsD Type connectors tend to be used for lower density applications and offer high current carryingcapability and breakdown voltage.SCSI type connectors tend to be used in higher density applications with lower carry currents andbreakdown requirements.When selecting mating connectors it is important to ensure that the specification of the connectordoes not effect the module performance. There can be differences in current carrying capacitydue to differences in the method of construction of connectors that seem to be very similar.RF ConnectorsThere are a number of different connector types available for connecting RF modules to the restof the system. The small size of the PXI module limits the type of connector that can be usefullyused and some connectors, such as the Type N connector, commonly found in bench test systemsare not found in PXI systems.Some PXI modules are offered with user defined connectors on the front panel. The characteristicsthat usually influence the decision on which connector to use are the method of securing theconnectors and the RF performance.There are three common methods of mating RF connectors:• Screw locking, the most secure method and likely to result in the best connectorperformance. Connector access in dense systems may require the use of specialspanners. Wherever possible a torque spanner should be used to tighten theconnector.• Snap on, a quick and convenient method of making an RF connection but usuallyresulting in inferior VSWR and leakage performance.• Latching connector, currently not commonly used at present in PXI, but provides aperformance similar to snap on connectors but with the security mechanism thatprevents accidental disconnection.Page 9.

9 - connectorsThe RF performance is largely determined by the characteristics of the mechanical interfaceand its variability. Some connector types may be offered with different performances accordingto the design and manufacturability of the connector interface. As an example it is common forSMA connectors to be available in different grades according the maximum frequency of use.An 18 GHz SMA has better control of its interface dimensions than a general purpose SMA andconsequently better RF performance.RF power handling and voltage breakdown is rarely a performance issue in PXI systems.If the leakage of RF signals between cables or connectors is likely to be a test issue, connectorsthat use a screw locking system are likely to offer lower leakage levels because of the improvedand more consistent grounding impedance. Screw lock connectors are also more likely to becompatible with semi-rigid cables.In many systems the availability of a connector to use a particular type of cable may be animportant consideration in connector choice.Some connector systems are available in both 75 ohm and 50 ohm versions. Great care should betaken not to mix these connectors since mating a 75 ohm and 50 ohm connector can damage theinterface, 50 ohm female connectors are particularly vulnerable.SMA ConnectorAn effective RF and Microwave connector ideal for use to 18 GHz and beyond. It uses a screwlock mechanism and interfaces easily to low loss cables. It is the largest connector commonlyused in PXI systems. SMA connectors are available from a great number of suppliers to fit awide variety of standard and proprietary cables. Even at 18 GHz a SMA connector can achievetypically 1.05 VSWR when connected to a 0.141 cable. SMA connectors generally perform bestwith cables around 0.141 inch diameter because it is close to the connector diameter.SMC ConnectorThis is a smaller connector than the SMA that uses a screw lock mechanism. It provides a secureand repeatable RF performance but is significantly inferior to a SMA. They are often quoted tohave a frequency range of up to 10 GHz but at this frequency the VSWR is likely to be worsethan 1.5 for a single connector. For many applications it is only suitable to 3 GHz.In general these connectors are used with thinner coaxial cables which also have higher loss than0.141 diameter cables.SMB ConnectorThis is a similar size to SMC connectors but uses a snap on connection rather than a screw lock.The lack of screw thread to lock the two parts together results in a lower performance than SMCconnectors, a typical connector having a VSWR of 1.25 at 4 GHz. For many applications theyare only suitable for use to about 1.5 GHz.They should only be used with thin flexible cables to avoid loading the connector springs.There are also versions of this connector style that have a locking mechanism.Page 9.

9 - ConnectorsAPC 3.5The APC3.5 connector is a precision connector that can be mated with a SMA connector. Thecentre pin of the connector is supported on a bead rather than a solid dielectric. APC3.5 connectorsoffer better performance at a higher cost than SMA connectors. They can be used for frequenciesup to 34 GHz.APC 3.5 connectors are commonly used on bench instruments front panels and some types ofmicrowave switch modules.They can be less robust than a SMA connector. Microwave engineers will often use a “connectorsaver” for APC 3.5 to reduce the wear and tear on the connector.SMA 2.9Similar in design to SMA connectors but uses a smaller diameter to allow the connector to operate46 GHz without moding. It is the connector of choice for microwave application where a SMAconnector frequency cover is not adequate.There are smaller diameter versions of this type of connector available for higher frequencyapplication in coaxial cable.SMA 2.9 can be found on microwave switches designed for operation to 40 GHz or higher.MCX ConnectorThe MCX connector uses an electrical interface similar to the SMB and uses a snap-on connection.The connectors are smaller than SMB and are claimed to be more robust. The maximum frequencyis 6 GHz with a typical VSWR of 1.13 for a single connector. As with SMB connectors they arebest used with flexible cables, though versions designed for use with thin or conformable semirigidcables are available.BT Type 43 (SMZ)This is a miniature RF connector specified for use in Telecomms networks, particularly in theUK. The connector uses a simple latching mechanism that prevents accidental disconnection ofthe connector. It is specified for use to 3 GHz.SSMBThis is a miniature version of the SMB connector, again using a snap on connection method. It isspecified to 4 GHz but VSWR at this frequency for a single connector can be typically 1.3. Sinceit is a small connector it is usually used with thin flexible coaxial cables.DIN 1.0/2.3RF connectors designed for use in Telecomms systems, used particularly in Europe. Theconnectors are specified to 10 GHz (depending on type) and are available in snap on, slide on andscrew lock forms. They can be used as part of a DIN 41612 multi-way connector.Page 9.

9 - connectorsBNC ConnectorThis is a common connector used on many engineers’ benches to connect low frequency RFconnections. The bayonet locking arrangement provides a fast method of connecting to a device.It is often abused and used to higher frequencies than the connector is capable of reliablysupporting. Some manufacturers claim good performance to 4 GHz but for most applications it isrecommended to only 500 MHz. Users need to be wary of 75 ohm connectors being mixed with50 ohm connectors.TNCTNC connectors use a similar interface to BNC connectors but use a screw locking mechanismthat improves the overall RF performance and repeatability. It does not match the performanceof SMA connector but good quality versions can carry signals to 18 GHz. The connector handleslarger diameter connectors than SMA. TNC connectors are not commonly used in PXI systemsbecause they are physically large.Type N ConnectorsThese connectors are very common on bench instruments since they provide a robust connectorwith very good VSWR to their maximum frequency of 18 GHz. They are not generally used inPXI systems because of their large physical size.Page 9.10

9 - ConnectorsOptical ConnectorsJust as with RF connectors there are a range of optical connectors available for connectingfibres together. The objective of the connector is to bring the ends of the active part of the fibreinto intimate contact to avoid the loss of light (insertion loss). Since fibres can have a verynarrow diameter it is important that the fibre ends are presented in very accurate alignment – anymisalignment will introduce an optical loss.Optical connectors should always be handled with care to ensure abrasive materials are notintroduced. They can cause scratches on the fibre ends that will increase the connector insertionloss. Most are supplied with dust caps to protect the connector when it is not in use.The assembly of optical connectors requires specialist skills and training and can be labourintensive.Connectors may be offered with different polishing options for the fibre. PC is a PolishedConnector one of the standard end face finishes. APC is an Angled Polished Connector that hasan 8 degree angle on the end of the connector to improve back reflection performance. Someconnectors may be offered as ‘duplex’ versions where the connector supports two fibres in thesome mechanical assembly. One fibre is typically used for transmission while the other is forreception.FC Style ConnectorFC is a good connector with metal screw on housing - very good alignment and the screw fixingensures a secure connection. Available for single mode fibre.SC ConnectorA Typical FC ConnectorSC is a (slightly) less expensive connector with a positive mating push on plastic housing. It hasgood alignment and is very easily connected/disconnected. Available for single-mode or multimodefibre.A Typical SC ConnectorPage 9.11

9 - connectorsLC and MU ConnectorLC and MU connectors are Small Form Format connectors, the connectors and the ferrules aretypically half the size of FC or SC connectors (MU is commonly called mini SC). These Lucentconnectors are fairly new to the industry.Available for single-mode fibre.LCMCTypical LC and MU ConnectorsST ConnectorST is a very common multi-mode connector with a metal push and twist type connection. It iscost effective and easily terminated.Available for multi-mode fibre.Common Types of fibreA Typical ST ConnectorJust as with RF cables, optical fibre comes in a variety of forms with different core types, corediameters and different cladding to protect the delicate core. The core is the part that carries mostof the optical signal.Multimode fibre commonly has a 50 or 62.5 micron core, with 125 micron cladding (referredto as 50/125 or 62.5/125). Multimode fibre has a larger core diameter than single mode fibre. Inmultimode fibres the signal is allowed to travel down the fibre by a variety of routes – straightdown the fibre (the quickest) or through a series of reflections from the core boundary. Thevariety of routes leads to dispersion of the signal in the fibre as some parts of the signal arrivebefore other parts. This dispersion limits either the data rate or the transmission distance that canbe supported.Single Mode fibre has a 9 micron core, 125 micron cladding (9/125). The small core diameterlimits the transmission to a single mode – straight down the fibre. The reduced dispersion allowshigher data rates and longer distances to be supported. The small diameter of the core makesconnecting fibres more difficult since small misalignments can increase the connectors opticalloss.Page 9.12

10 - USEFUL INFORMATIONSECTION 10USEFUL INFORMATIONThis section provides useful information sources for PXI products and standards.PXISA .................................................................................................................10.3The PXISA is responsible for the maintenance of the PXI standard and its promotion.This section explains its aims and membership, including a list of current members.PICMG and PCISIG ...........................................................................................10.10The PICMG is responsible for the cPCI standard, on which the PXI standard is based.The PCISIG supports the PCI standard.LXI Consortium .................................................................................................10.10The LXI Consortium is responsible for the creation and promotion of the LXI standardUseful Websites ................................................................................................10.11Some useful web sites to get more information about PXI.PXI Terminology ...............................................................................................10.12A glossary of terms that you might come across in PXIPage 10.1

10 - USEFUL INFORMATIONPage 10.

10 - USEFUL INFORMATIONPXISAThe PXI Systems Alliance is a not for profit organisation run by companies involved in PXIproducts.The organisation is responsible for the production of the technical specifications for PXI and thepromotion of the PXI concept in the market.Membership of the PXISA is open to any company that is willing to promote the PXI standard.Membership CategoriesPXISAThere are three levels of Membership in the PXI Systems Alliance.Membership of the PXISA allows participation in the PXISA technical and marketing programsand the use of the PXI logo.Only PXISA members are permitted to use the PXI logo on their products and marketingmaterial.Sponsor MemberSponsor Members, such as Pickering Interfaces, view PXI as a vital part of their ongoing businessand want to be involved in all decisions.To be a Sponsor Member the company must be an Executive Member for at least 1 Year prior toapplying for Sponsor Membership.Sponsor members have a seat on the Board of Directors and voting rights.Executive MemberExecutive Members view the PXI architecture as important to their business. They have a voicein technical specification and approval and Marketing direction of the PXISA.Executive members have voting rights.Associate MemberApplicant wants to be a member of the Alliance supporting PXI and be informed of progress.Associate members do not have voting rights and this membership level is for informationpurposes only.Membership application forms are available on the PXISA web site.Page 10.

10 - USEFUL INFORMATIONPXISA Membership ListThe PXISA members and contact details are as follows as of August 2005.Sponsor MembersCompany Contact Products/Services Web PageADLINKPC Lee/ PXI & PC-based www.adlinktech.comJames Gau/ Data Acquisition,Bruce McGrath Instrument andComputer platformsfor Measurement andAutomationASCOR Jeff Lum Switching and DigitalModuleswww.ascor-inc.comGeotest - MarvinTest SystemsNationalInstrumentsPickeringInterfacesLoofieGuttermanGreg Caesar/Robert Jacksonbob StasonisPXI & PC-basedFunctional TestSolutionsHardware andSoftware forComputer-BasedMeasurementand AutomationapplicationsPXI Switch andInstrument Cards/Systemswww.geotestinc.comwww.ni.comwww.pickeringtest.comTeradyne Bob Fogarty Solutions forwww.teradyne.comAdvanced Diagnosticsand ElectronicManufacturingExecutive MembersCompany Contact Products/Services Web PageAcqiris Richard Soden High-speeddata conversioninstruments. Digitizersand WaveformAnalyzers with GS/sperformanceAdvantest Kenji Inaba Electronic Measuringinstruments,automatic testequipment, andelectron beamlithography systemsAeroflex Bill Burrows Integrator andManufacturer of PXIProductswww.acqiris.comwww.advantest.co.jpwww.aeroflex.comPage 10.4

10 - USEFUL INFORMATIONExecutive Members (continued)Company Contact Products/Services Web PageAlfautomazione Mauro Arigossi Automotive and www.alfautomazione.itGeneral PurposeFunctional TestSystemsCHROMA ATEInc.www.chromaate.com/pxiCharles ChuangVic ChengJackson WenPrecision Testand MeasurementInstrumentsElma Electronic Suzana Berlin Provides PXI Systemsenclosures &mainframesGoepel ElectronicMAC PanelMarekMicroGmbHPX InstrumentTechnology (PXIT)Virginia PanelCorpStefenMeissner/Thomas WenzelAnthonySedberryPeter MarekDylan McCarthyDylan WillifordIntelligent PXIsolutions for extendedJTAG/BoundaryScan and customizedAutomotive TestSolutionsInstrumentmainframes, chassis,fixturingPXI Hardeare andSoftware ConsultationDevelops andmanufactures Test& Measurementsystems, primarilyfor use in high-speeddata communicationsPXI MassInterConnectSolutionswww.elma.comwww.goepel.comwww.macpanel.comwww.marekmicro.dewww.pxit.comwww.vpc.comZTEC Vicki Veretto PXI System Products www.ztec-inc.comAssociate MembersCompany Contact Products/Services Web PageAcculogic Greg LeBlonc High Performance www.acculogic.complug&play controllersAdvancedIntegrationJohn Albert PXI ATE Systems forMilitary (ruggedized)and Manufacturingapplicationswww.advint.comPage 10.5

10 - USEFUL INFORMATIONAssociate Members (continued)Company Contact Products/Services Web PageAmplicon John Hayward Specialists in Data http://www.amplicon.co.ukAcquisition, DataCommunication &Industrial ComputingApplicos bv KarsA/D to D/A and D/A to www.applicos.comSchaapman A/D Products for thetest industryB&B Technologies Timothy Brooks Systems Integration www.bbtechno.comutilizing PXIBloomy Controls Rob Michell System Integration www.bloomy.comBi2SAlexanderBibikoffSystem Integration www.bi2s.comChroma SystemsSolutionsConduantCorporationFred SabatineTom SkrobaczPrecision PowerSuppliesPXI, PCI andCPCI direct todisk recording andplayback boardsCorelis Inc. Jim Rodgers PXI and PCI basedhardware andsoftware solutionsfor IEEE-1149.1(JTAG) boundaryscanTest, In-SystemProgramming, andEmulation4DSP Inc. Pierrick Volltez High quality systemssolutions in PXIand cPCI systems,including unique HWmodulesData Device Corp George Los High ReliabilityData NetworkingTechnology,Commercial-Off-The-Shelf (COTS)Products andSubsystemsDigalog Rick Wagner Test Equipment,Systems, & ProvidesTest Solutionswww.chromausa.comwww.conduant.comwww.corelis.comwww.4dsp.comwww.ddc-web.comwww.digalogsys.comPage 10.6

10 - USEFUL INFORMATIONAssociate Members (continued)Company Contact Products/Services Web PageDiagnoSYSLimitedRoland Andrews Systems Integrator forsytems from in-circuitfunctional testers,roving probers tooptical inspectionsystemswww.diagnosys.comExacqTechnologies Inc.DaveUnderwoodTom BuckleyPXI and PCI-basedLow-Cost, IntelligentData Acquisitionboards with onboardDSP, onboardmemory, andextensive softwareHuntron, Inc Bill Curry Automatic Probingstation for PXI-basedtest systemsInvisarJTAGTechnologiesKaparelCorporationKinetic Systems/Gage AppliedTechnologiesKonradTechnologiesGmbHMapsukaIndustriesMeilhausElectronic GmbHMEN MikroElektronikJamesLestienneRay DelleckerPC-based Test,MeasurementSolutionsPXI Boundary ScanTest Solutionswww.exacq.comwww.huntron.comwww.invisar.comwww.jtag.comTom Sutherland PXI Products www.kaparel.comNicole FaubertRolandBlaschkeData AcquisitionModules for PXI/CompactPCIPXI SystemsIntegratorY. C. Kao Designer andmanufacturer ofcustom PXI/cPCIchassis andcomponentsDietmarSperlingHans JürgenBaumgartnerErnest GodseyData Aquisition,Industrial I/OProducts FieldbusCommunicationBoard-level and turnkeyindustrial realtimeand embeddedcomputer systemswww.kscorp.comwww.gage-applied.comwww.konrad-technologie.dewww.mapsuka.com.twwww.meilhaus.com/pxiwww.menmicro.comwww.men.dePage 10.7

10 - USEFUL INFORMATIONAssociate Members (continued)Company Contact Products/Services Web PageNextronics Tony Su Manufacturer for www.nextron.com.twconnectors andbackplanes.OpenSystemsPublishingPatrick Hopper Publisher of PXITechnology Reviewopensystems-publishing.comPXIdirect GmbH Gerd von Garrel Sales company www.pxidirect.comoffering cPCI andPXI products to theGerman marketRacal Instruments Steve Lowry Innovative ElectronicTest Solutionswww.racalinst.comRohde & SchwarzGmbH & Co KGSignametricsCorporationSMARegelsystemeGmbHLotharTschimpkeTee ShefferRalf AndraeTest andMeasurementEquipmentManufacturerManufacturer of PXI/CompactPCI and PCITest & MeasurementInstrumentsDesigner &Manufacturer of 3UCompactPCIwww.rsd.dewww.signametrics.comwww.sma.deSpectrum GmbH Oliver Rovini PXI, CompactPCI andPCI high-speed dataacquisition, signalgeneration and digitalI/OStrategic Test AB Bob Giblett UltraFast WaveformDigitizers, SignalSources andDigital I/O for PXI,CompactPCI and PCIwith large on-boardmemory and widesoftware supportSundance Nory Nakhaee Supplier of AdvancedMulti DSP and FPGAhardware/softwareplus high speed ADCand DACwww.spectrum-gmbh.comwww.strategic-test.comwww.sundance.comPage 10.8

10 - USEFUL INFORMATIONAssociate Members (continued)Company Contact Products/Services Web PageTracewell Mike Long Computer and www.tracewellsystems.comSystemsElectronic PackagingTriple ECorporationUnited ElectronicsIndustriesViewpointSystemsX-rayInstrumentationAssociatesAllen HillmanShaun MillerPXI Eurocardelectronic packagingsolutionsThe HighPerformanceAlternative inPC-based DataAcquisitionwww.tripleease.comwww.ueidaq.comDavid Smith PC-based DataAcquisition andAnalysis Systemswww.viewpointusa.comPeter Grudberg X-ray Products www.xia.comPage 10.9

10 - USEFUL INFORMATIONPICMGPICMG (PCI Industrial Computer Manufacturers Group) is a consortium of over 600 companieswho collaboratively develop open specifications for high performance telecommunications andindustrial computing applications, including the CompactPCI (cPCI) standard.CompactPCI products can be used in PXI chassis and PXI products can be used in cPCI chassiswith some limitations in each case.As with PXISA, the PICMG is a not-for-profit organisation.PICMG MissionFounded in 1994, PICMG’s original mission was to extend the PCI standard, as approved bythe PCI Special Interest Group (PCISIG) for computer systems such as PCI/ISA, PCI/EISA andthe PCI/3U or 6U Eurocard form factor known as CompactPCI. PICMG continues to developimportant extensions and improvements to CompactPCI.PICMG PurposePICMG’s purpose is to offer equipment vendors common specifications, thereby increasingavailability and reducing costs and time to market. The PCI specifications provide a clear upgradepath for OEMs wishing to migrate to new designs.PCISIGThe purpose of the PCI-SIG is to deliver a stable, straightforward and compatible standard forPCI devices.The organisation is important to PXI since the control interface is built on the PCI standard anduses common electrical devices to PCI cards, including the PCI bridges incorporated into the PXIbackplane.LXI ConsortiumThe LXI Consortium is responsible for the creation and promotion of the LXI standard. It has asimilar structure to the PXISA since it has different membership levels and working groups tocreate and maintain the specification.Page 10.10

10 - USEFUL INFORMATIONUSEFUL WEbSITESIEC Specifi cationsIEEE Specifi cationsLXI ConsortiumPCI Specifi cationsPickering InterfacesPICMG Specifi cationsPXI Specifi cationsVISA Specifi cationsVME Specifi cationsVXI Specifi cationshttp://www.iec.orghttp://www.ieee.orghttp://www.lxistandard.orghttp://www.pcisig.comhttp://www.pickeringtest.comhttp://www.picmg.orghttp://www.pxisa.orghttp://www.vxipnp.orghttp://www.vita.comhttp://www.vxi.orgPage 10.11

10 - USEFUL INFORMATION3U, 6U Refers to the height of the module, the 6U modules beingapproximately twice the height of the 3U module.APIApplication Programming Interface.CompactPCI A ruggedised version of PCI card conforming to PICMG 2.0specifi cation, providing superior mechanical performance andeasier insertion or removal of cards.GPIBISAGeneral Purpose Interface Bus, a standard used forinterconnecting bench instruments using an 8 bit wide datasystem. Standard is defi ned by IEEE 488.Industry Standard Architecture, an older standard used by thecomputer industry to add additional cards to PC’s.J1, J2, J3 Connectors on PXI modules that mate to P1, P2 and P3. On 3Umodules fi tted to slots J1 and J2 may mate to P1 and P2.Local BusPCIPCISIGPICMGPXIStar TriggerTrigger BusVISAVMEVPPVSOVXIP1P2P3P4P5System Slot orSlot 1PXI TERMINOLOgYBus that can be used to connect adjacent PXI modules in achassis without the use of PXI features. The Bus can be used foranalogue or digital signals and is module defi ned.Peripheral Component Interconnect, bus system commonly usedin computers to provide additional functionality.PCI Special Interest GroupPCI Industrial Computer Manufacturers GroupPCI eXtensions for InstrumentationFast trigger system driven from Slot 2 that provides low latencysynchronised trigger to the peripheral modules.A bus defi ned in PXI standard that can be used to trigger events.The triggers can be conditioned by software.Virtual Instrument Software ArchitectureVersa Module Europe, an interface specifi cation governed by theVSO.VXI Plug and Play Specifi cationVITA Standards OrganisationVME Extension for InstrumentationBackplane connector on a chassis carrying the 32 bit PCI bus.Backplane connector on the chassis carrying the 64 bit PCI busand PXI specifi c features.Reserved connector whose use is undefi ned by the PXI standardand can be fi tted to 6U chassis.Connector used on 6U chassis that allows 3U cards to be fi tted in6U Slots. It provides the same functions as P1.Connector used on 6U chassis that allows 3U cards to be fi tted in6U slots. It provides the same functions as P2.Slots on the left hand side of the chassis reserved for use by thesystem controller.Page 10.1