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Zigbee Compliance Test

Refer zigbee tutorial covering following sub topics:
About zigbee   Zigbee network   Stack   PHY   frame   MAC   Bands   Conformance  AODV protocol  Products 

This article covers zigbee device compliance and manufacturing tests and test set up typically followed by the test and certification or pre-certification companies.

In order to perform compliance tests on transmitter and receiver part, RF Signal generator/analyzer along with baseband zigbee application is needed. This RFSG and RFSA generates and analyze zigbee compliant RF signal. Automation application is also needed to put zigbee DUT in various modes so that all the transmitter and receiver specifications are tested. Figure depicts typical set up.

To perform tests on DUT's transmitter part it is interfaced with RFSA and to perform tests on DUT's receiver part it is interfaced with RFSG. RS232 is needed to control DUT through firmware so that various parameters as per tests can be set.Following are typical transmitter and receiver tests performed during zigbee pre-compliance test.

zigbee compliance test

Zigbee Transmitter Tests

The zigbee transmitter tests include Instantaneous Transmit power, Power Spectral Density, Error Vector Magnitude or EVM, PLL Frequency convergence, Phase Noise, Spurious Emission, IQ Measurements i.e. constellation diagram, LO Leakage or carrier suppression and Tx/Rx turn around time. We will see major tests in detail below.

Transmission Power:
The aim of this test is to verify the transmitter output power of the zigbee DUT conforms to the limit set by the standard.
➤Set the DUT to the unmodulated continuous transmit mode with appropriate output power level. This is done either using smartRF studio or using RS232 control.
➤Measure the output power on the spectrum analyzer.
➤Verify whether measured power is as set using program on the DUT.
➤Repeat the above steps for different frequencies and tabulate the result.

Power Spectral Density (PSD) Mask:
The aim of the test is to verify PSD of zigbee DUT conforms to the limit set by the standard mask. For example, standard specifies:
For frequency |f-fc| > 3.5MHz , relative limit is -20dB and absolute limit is -30dBm

➤Set the DUT to continuous transmit mode
➤Verify the output power spectrum is well within the developed standard mask on the spectrum analyzer.

Error Vector Magnitude:
This test helps us verify transmission modulation accuracy. For more refer EVM basics.

➤Set the DUT to continuous Tx mode with random modulated data. ➤Measure the EVM of transmitted zigbee signal using appropriate application software. Rohde and Schwarz FSQ also provides the EVM measurements of zigbee compliant signal.

Transmission Center Frequency Offset:
The aim of this test is to verify that center frequency offset is within the limits.

➤Set the zigbee DUT to continuous Tx mode.
➤Set the RF center frequency to desired RF channel and make sure it is unmodulated signal.
➤Note down the actual frequency displayed on the spectrum analyzer. The difference between this frequency and RF center frequency is the frequency offset.
➤Compare the difference obtained above with the ppm limit specified in the standard limit or conformance document.

Spurious Emissions:
The aim of the test is to verify conducted spurious emissions are under limit. Refer spurious vs harmonics for basic information on the spurious. Also refer RF measurements tutorial for performing spurious test.

➤Set the zigbee DUT to continuous Tx mode with random modulated data. Also set the RF center frequency to the desired channel frequency.

➤Measure the spurious in the entire span of the spectrum analyzer.

Zigbee Receiver Tests

Typical zigbee receiver tests include maximum Input Power, receiver sensitivity, adjacent channel rejection, alternate channel rejection and RSSI. Let us understand few of these tests below.

Receiver sensitivity:
The aim of the test is to verify that receiver sensitivity is conforming to the standard limit.

➤Put the Tx-Rx in the loopback mode with variable resistor in between.
➤Start the receiver first and set the payload and pattern type appropriately.
➤Start the transmitter and measure the RSSI on receiver side.
➤Calculate PER as per equation or read out this value in the zigbee DUT's registers if available.
➤Increase the attenuation until PER reaches to the value of 1% .
This will define the receiver sensitivity threshold.

Maximum Input Power:
The aim of the test is to verify that DUT performs satisfactory with the maximum input power level defined in the standard. Do this test and measured PER should be less than 1% value.

Adjacent Channel Rejection:
➤Set the DUT to the desired RF channel frequency.
➤Note down the power at this RF channel as well as adjacent channel.
➤Calculate the difference between them.
➤Compare the result with the rejection limit specified. Pass criteria is 0 dB for adjacent channel rejection.

zigbee adjacent alternate channel rejection

Alternate Channel Rejection:
➤Set the DUT to the desired RF channel frequency.
➤Note down the power at this RF channel as well as alternate channel frequency.
➤Calculate the difference between them.
➤Compare the result with the rejection limit specified for Alternate Channel Rejection. Pass criteria is 30dB for alternate channel rejection.

Energy Detection/RSSI:
Refer RSSI basics to understand this specification. This can be measured using spectrum analyzer. It can also be read out from the register's of the DUT.

Zigbee Manufacturing tests

In the manufacturing tests few of the tests mentioned above are performed. The idea of manufacuring tests is to check the functionality of the operation of the zigbee device(DUT).
In manufacturing tests more than one DUT's are being tested simultaneously. Special provision and zig need to be designed to perform parallel tests on the multiple zigbee devices. All the results are collected in the text or excel files in the application running in the computer. The tests per device need to be performed in few seconds and results will be checked at the later moment of the time.

Zigbee Related Links

•  what is zigbee
•  Zigbee network architecture basics
•  Zigbee Protocol Stack
•  Zigbee Physical layers
•  Zigbee physical layer frame
•  Zigbee MAC layer frames
•  Zigbee frequency bands
•  Zigbee Gadgets
•  Zigbee Products

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