Application Note AN006

Chipcon Application Note AN006 

AN006 

Testing of RF Modules based on Chipcon RFICs 

Keywords 

by P. M. Evjen 

• RF Testing 

• RF Instrumentation 

• Critical RF parameters 

• Troubleshooting RF circuits 

• Testing and verifying transceiver 

designs 

Introduction 

It is easy to do a successful design using 

Chipcon RFICs! The most difficult design 

tasks involving RF is already done 

because all RF functions needed to make 

a complete transceiver is integrated into 

the chip! 

However, it is important to take care of the 

special issues that a RF circuit design 

requires, and also know how to test and 

verify the design. 

This application note gives some advice 

on how to test, troubleshoot and verify 

correct operation of an application or 

design that make use of one of Chipcon’s 

transceiver ICs. 

Using the SmartRF Studio also in the test 

is explained. A list of the most important 

RF parameters that must be verified is 

given. And advice on practical 

troubleshooting is given. 

Chipcon is a supplier of RFICs for all kinds 

of short range communication devices. 

Chipcon has a world-wide distribution 

network. 

Chipcon AS AN006 Testing of RF Modules (Rev. 1.0) 2001-05-02 Page 1 of 7


Using the PC as controller 

To ease the testing of the RF module the SmartRF Studio software could be used. The 

SmartRF Studio operates through the PC parallel port. By connecting the parallel port control 

lines to the device under test, the module could be controlled very easily and changes in the 

configuration could be done very fast. 

The PC parallell port operates at 5V, so a voltage translator is needed between the PC and 

the RF module. The table below gives the pin numbering for the 25 pin PC parallel port 

connector. 

PC parallel port pin number 

Signal 

4 PDATA 

3 CLOCK 

5 STROBE 

13 LOCK (this pin is optional) 

2 5V (to supply translator) 

18-26 GND 

An alternative to building a 5-to-3 Volt translator is to use the one on the Evaluation Board. 

The control signals can be found at the board as given in the table below: 

CC400/CC900 Evaluation 

Signal 

Board connection 

U3#8 PDATA 

U3#4 CLOCK 

U3#12 STROBE 

TESTPIN TP2 

LOCK (this pin is optional) 

C26 

5V (to supply translator) 

GND 

Note: The Ampere meter short circuit (at the voltage supply connector) must be removed in 

order to disconnect the power supply for the on-board transceiver and thus avoid interference 

from that device. 

Please refer to the Evaluation Board schematics and layout for further details. The schematic 

and layout is found in the Development Kit User Manual. 

Using the Demonstration Board as a prototype 

The Demonstration Board is well suited for building the first prototype of your system. This 

module includes the complete RF part (using internal IF filter), antenna and a controller. 

To modify the board in order to use it as a RF module: 

• Remove the AT90LS2343 micro-controller 

• Strap between pin 1 and pin 2 at the micro-controller footprint 

• The control signals are now available at the edge connector as shown in the table below. 

Edge connector pin number 

Signal 

1 GND 

2 GND 

3 CLOCK 

4 Not used (LED) 

5 DIO 

6 STROBE 

7 PDATA 



8 VCC (3.0V) 

Start counting from the end where the polarity slot is. The two separate pins are the GND pins. 

The Demonstration Board is also provided with a RF antenna connector footprint. When using 

the antenna connector the PCB antenna must be disconnected. This can be done by 

removing L7 and L8. 

Please note that the crystal used on this low cost module is 50ppm tolerance, 50ppm over 

temperature –10 to 60 degrees. When using system parameters requiring better crystal 

accuracy, the crystal must be replaced. 

Instrumentation 

It is not possible to do RF development or RF module design without proper RF 

instrumentation. 

The minimum RF instrumentation that is required is: 

• Spectrum Analyser covering up to 3 times the RF frequency used (3 rd harmonic) 

• RF signal generator with FSK modulation capability 

• Network analyser would also be necessary if RF filter optimisation, input/output 

matching and antenna tuning must be done. 

Module testing 

Below is given a list of important RF parameters to verify once a new design is done. 

However, the list should not be considered as complete, but advisory. Also additional testing 

must be done to comply for type approval. 



Step-by-Step Testing Procedure 

DEVICE NUMBER: 

# Test Value Unit Condition 

1 Voltage Supply 

Supply voltage V Measure across device supply pins 

2 Current consumption 

RX mode 

mA 

TX mode mA at PA output power programmed: ____dBm 

and class: _____ 

PD mode uA Xtal oscillator is (on/off): _____ 

3 Crystal oscillator 

Crystal frequency 

MHz 

Oscillator voltage Vpp Measure at peak-to-peak voltage at XOSC_Q1 

pin 

4 VCO tuning range 

VCO frequency at 0.0V 

5 VCO tuning 

sensitivity 

MHz 

0.5V MHz 

1.0V MHz 

1.5V MHz 

2.0V MHz 

2.5V MHz 

3.0V MHz 

Insert DC voltage across C123 (loop filter 

capacitor). Set device to TX mode. Measure at 

antenna output. 

SPAN=200MHz, RBW=Auto, VBW=Auto 

K_1/0 MHz/V Calculate f(1V)-f(0V)/1V 




6 VCO gain margin 

Gain step margin - Increase the value of “VCO gain” from binary 

000 towards binary 111 and observe when the 

oscillator stops. Use tuning voltage = 0.5V 

7 Phase noise 

Phase noise at 10 kHz 

offset 

dBc/Hz 

SPAN=100kHz, RBW=1kHz, VBW=10Hz 

Phase noise at 100 kHz 

dBc/Hz SPAN=200kHz, RBW=1kHz, VBW=10Hz 

offset 

8 Modulation 

Peak to peak deviation kHz SPAN=500kHz, RBW=3kHz, VBW=1kHz 

Measure distance between the to tops in the 

spectrum 

9 TX output power at PA output power programmed: ____dBm 

and class: _____ 

Output power dBm SPAN=1MHz, RBW=10kHz, VBW=1kHz 

10 Harmonics 

2. harmonic 

3. harmonic 

SPAN=1MHz, RBW=10kHz, VBW=1kHz 

11 Receiver sensitivity 

Sensitivity dBm Use signal generator set up with correct 

modulation frequency and deviation. 

View DIO signal at oscilloscope. Adjust level 

until BER = 10-3 

12 LO leakage 



LO leakage dBm SPAN=1MHz, RBW=10kHz, VBW=1kHz 

Notes to the tests 

1. Supply voltage 

The supply voltage should be in the range 2.7 – 3.3 V. Operation is not guaranteed outside 

this range. If measured voltage is less than expected it could be a current limiter in the power 

supply causing the problem. 

2. Current consumption 

The typical current consumption for the different modes are calculated by SmartRF Studio, 

and can be seen in the Status bar of the Normal view. 

3. Crystal oscillator 

The crystal oscillator operation can be verified very simply on an oscilloscope. However, the 

actual frequency must be measured when testing the transmitter frequency because the 

oscilloscope probe would load the crystal and de-tune it during the test. The peak-to-peak 

voltage should be 400 – 600 Vpp. 

4. VCO tuning range 

The tuning range of the VCO is measured in “open loop” by forcing the tuning voltage by an 

external DC source. It is important to have a correct tuning range in order to cover the desired 

frequency for all expected component tolerances. The tuning range can be changed by 

altering the values of the VCO components (see data sheet for details). 

5. VCO tuning sensitivity 

From the VCO tuning range measurements the VCO tuning sensitivity is calculated. The 

tuning sensitivity must be verified because it is one of the parameters in the calculation of the 

PLL loop filter. 

6. VCO gain margin 

The VCO gain margin is the excess gain we have in the VCO before it stops oscillating. 

Normally the VCO should not stop until the value is increased to 100 binary. 

Low gain margin is an indication of low Q in the VCO tank. This could be due to insufficient Q 

in the VCO inductor or the varactor. The series capacitor to the VCO_IN pin also affects the 

gain. If this capacitor was too small, the gain would also be too low. 

7. Phase noise 

The phase noise will depend on the loop filter bandwidth, but should typically be: 

Part At 10 kHz offset At 100 kHz offset 

CC400 -70 dBc/Hz -90 dBc/Hz 

CC900 -60 dBc/Hz -80 dBc/Hz 

When measuring the noise using a spectrum analyser the measurement must be corrected 

for the resolution bandwidth. Using 1kHz resolution bandwidth, the measurement must be 

corrected with -30 dBHz (10 log 1000 Hz). That means, if you are measuring the noise 10 kHz 

away from the carrier to be –40 dBc using 1 kHz resolution bandwidth, the phase noise is (-40 

– 30) = -70 dBc/Hz at 10 kHz offset. 

8. Modulation 

Looking at the modulation spectrum can help to discover any problems with the loop 

bandwidth. The peak-to-peak deviation should be close to the specified frequency separation. 

If there is excess deviation that could be due to low phase/gain margin in the PLL leading to 

“peaking” in the closed loop response. If this is the case, the loop filter and VCO tuning 

sensitivity should be investigated. 



9. TX output power 

The output power should be close to the specified output power, but taking the harmonic filter 

loss into account. The insertion loss of a low pass LC filter is typically 1.5 – 2 dB. If the output 

power is too low, the LC filter should be checked. The filter is very sensitive to layout 

paracitics. 

10. Harmonics 

The transmitter harmonics should be attenuated sufficiently by the low-pass filter. Some 

spectrum analysers provide automatic measurement of harmonics presenting the result as a 

list for convenience. 

11. Sensitivity 

The sensitivity is measured using a signal generator with FSK modulation at the specified 

frequency and deviation. Please note that for most generators one enters the FM deviation, 

that is half of the frequency separation specified in the SmartRF Studio. The DIO signal is 

monitored with an oscilloscope together with the modulating signal from the generator if 

available. Trig the oscilloscope on the modulating signal. A bit error rate (BER) of 10-3 can 

then be determined visually. The expected sensitivity for different data rates, frequency 

separations and IF filters are given in AN005. Any loss in the front-end filter must be taken into 

account. 

Less than expected sensitivity can be due to mismatch at the LNA input, excess loss in the 

front end filter, or noisy local oscillator. 

12. LO leakage 

The LO leakage is measured at the antenna output when the transceiver is in receive mode. 

See also AN002. 

13. Still problems? 

Contact your local distributor (or Chipcon directly) if you still need help on your RF circuit 

design. Fill in the test table above as carefully as possible and send to us for further advice. 

We are here to help you!! 

Documentation, reference designs and application notes 

Please download all information from our web-site: www.chipcon.com 



This application note is written by the staff of Chipcon to the courtesy of our customers. 

Chipcon is a world-wide supplier of RFICs. For further information on the products from 

Chipcon please contact us or visit our web site. An updated list of distributors is also available 

at our web site. 

Contact Information 

Address: 

Chipcon AS 

Gaustadalléen 21 

N-0349 Oslo, 

NORWAY 

Telephone : (+47) 22 95 85 44 

Fax : (+47) 22 95 85 46 

E-mail : wireless@chipcon.com 

Web site : http://www.chipcon.com 

Disclaimer 

Chipcon AS believes the furnished information is correct and accurate at the time of this printing. However, Chipcon 

AS reserves the right to make changes to this application note without notice. Chipcon AS does not assume any 

responsibility for the use of the described information. Please refer to Chipcon’s web site for the latest update.

Application Note AN006

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