Implementation of Component Characteristic Curve Tracer ... - LEDA

Implementation of the Component Characteristic CurveTracer Using PC-based Acquisition CardMarko Dimitrijević and Vančo LitovskiAbstract – The component characteristic curve tracer consistsof hardware and software parts. Hardware part is a PC-basedacquisition card mounted in standard personal computer. Softwarepart is developed in National Instruments LABVIEW package.The tracer can be used for educational purposes, as well as inscience purposes, for testing semiconductor or any other nonlinearelectronic component.Keywords - The component characteristic curve tracer, PCbasedacquisition card.I. INTRODUCTIONComputer based acquisition instruments followeddevelopment in personal computer industry. There areseveral types of acquisition equipment from variousvendors. Most new implementations of legacy instrumentslike oscilloscopes, AVΩ-meters and spectrum analysershave interface for connection with computer and softwarefor data acquisition and manipulation. New types of standaloneinstruments and measurement equipment areembedded systems with adapted operating systems andacquisition software.Measurement equipment based on computer hardwareis realised as PCI card for desktop or rack-mountedcomputers or PCMCIA acquisition card for portable orPDA computers. The acquisition card needs device driverfor operating system that runs on host machine andapplication software which provides data acquisition andmanipulation.counters. PCI-6014 is PCI based acquisition card. Externalsignals or devices under testing can be connected withacquisition card using CB-68LP block panel (figure 1) andSH68-68-EP cable.Software part is developed in LABVIEW package.LABVIEW provides intuitive developing interface withpossibility of developing GUI applications. NationalInstruments provides other development platforms such asMeasurement Studio for Microsoft Visual Studio, andANSI compatible LABWINDOWS. The operating systemdriver is common for all developing packages. It providesbasic application interfaces, and elementary functions forconfiguring acquisition card.II. HARDWAREThe analog outputs are used as DC voltage generatorsfor power supply and stimulus voltage. Maximal DC outputvoltage is limited to ±10V. This voltage is adequate forpower supply, polarisation and measurement of staticcharacteristics of the semiconductor components (figure 2).Fig. 1. CB-68LP connection blockThe component characteristic curve tracer isimplemented using National Instruments NIDAQ PCI-6014acquisition card [1]. This card has 16 analog inputs with200kS/s sampling rate, two analog outputs with 10kS/ssampling rate, 8 digital I/O channels and two 24-bitFig. 2. Circuits for BJT and MOSFET characteristic measurement

Fig. 3. User interface – measurement of BJT input characteristicFig. 4. User interface – measurement of MOSFET output characteristic

The analog inputs can be connected using NRSE –non-referenced single-ended, RSE – referenced singleendedand differential measurement method. Differentialmethod is used in implementation of the characteristiccurve tracer, in order to decrease noise and increase theCMRR. This noise influences to measurement precision ofsmall current and voltage values, such as saturation currentof the germanium diode. Both of the connection points of adifferential system are tied to instrumentation amplifier.There are no terminals connected to a fixed reference. Withdifferential method, the number of analog inputs is limitedto 8. In order to increase CMRR, a resistor can beconnected between inverted input of instrumentationamplifier and ground. The resistance must have value ofhundred equivalent Thevenin's resistance betweenconnection points (inverted and non-inverted terminal ofinstrumentation amplifier). It is also possible to connect thesecond resistor between non-inverted terminal and ground.This configuration provides greater CMRR, but there is asystematic error in measurement caused by serialconnection of resistors.III. SOFTWARESoftware part of the characteristic curve tracer isrealized in National Instruments LABVIEW developingpackage, which provides simple realization of virtualinstruments. Virtual instruments consist of interface toacquisition card and application with graphic user interface.Interface to acquisition card is realized as device driver.PCI 6013/6014 cards are supported by TraditionalNI-DAQ and NI-DAQmx drivers. All the measurementsare performed using virtual channels. A virtual channel iscollection of property settings that can include name, aphysical channel, input terminal connections, the type ofmeasurement or generation, and scaling information. Aphysical channel is a terminal or pin at which an analogsignal can be measured or generated. Virtual channels canbe configured globally at the operating system level, orusing application interface in the program. Every physicalchannel on a device has a unique name.When using NI-DAQmx drivers, a number of similarvirtual channels can be aggregated into a task. A task is acollection of one or more virtual channels with the sametiming, triggering, and other properties. A task represents ameasurement or generation process. As well as virtualchannels, tasks can be configured globally at the systemlevel, as well as using application interface.The user interface (figure 3 and figure 4) of thecomponent characteristic curve tracer consists of visualcontrols and indicators. It provides basic functions formeasurement. Visual controls – knobs and switches –provide control of analog signal generation. The indicators– gauges and graphs – show measured values. Allmeasured values are placed in a table, and after themeasurement process in appropriate file. User interfacealso provides controls for data manipulation and savingmeasured values.For better performance, the main application has beenseparated in two threads. The first thread has functions forfile manipulation and saving measured values (figure 6).All measured values will be saved in HTML file format.Fig. 5. Differential measurement methodThe measurement of voltages can be performeddirectly. Maximum input voltage is limited to ±10V. Themeasurement of currents can be performed only indirectly,by transforming current into voltage using parallel resistor.In this implementation we used 100Ω, 1% tolerance metalfilmresistor, due to better precision of measurement.Consequently, the value of 1mA is equivalent to 0.1V. Thevalue calculation is performed as software function.Fig. 6. Data manipulation and saving threadMain thread (figure 7) performs the measurementprocess. It is a connection between user interface and lowlevel device driver which controls acquisition card.Processes of signal generation and acquisition arecontrolled by DAQ Assistant. Main thread also includes

Fig. 7. Main threadfunctions for signal manipulations, range calculations,calculations of measured current, building data table andcharacteristic graphs.IV. CONCLUSIONThe component characteristic curve tracer haseducational purpose. It is a part of computer system forlaboratory exercises in Electronics [2 and 3]. The main goalof this system is to simplify manipulation of instruments,faster measurement and notation of the results, providingstudents to concentrate on measurement essence.This system can also be used in science purposes forcharacteristics measurement of low-power semiconductorelectronic components.REFERENCES[1] National Instruments PCI 6014 Product Data Sheet,http://ni.com.[2] Dimitrijević M., Litovski V., Jovanović S., „Računarskisistem za izvođenje laboratorijskih vežbi iz Elektronike“,V simpozijum Industrijska Elektronika Indel 2004, BanjaLuka, 11-12 novembar 2004, pp.156-160.[3] Litovski V., Petković P., Milenković S., MilovanovićD., Glozić D., Mrčarica Ž., Maksimović D., Ranđelović Z.,„Praktikum laboratorijskih vežbi iz Elektronike I“, šestoizdanje, Elektronski fakultet Niš, 1998.