A presenation on a technique that was developed to correlate Adjecent channnel rejection of a VHF reiciever to a new method that involves a much simpler technique that can be deployed on production ATE testers

1. Confidential © ams AG 2015
ACR BER Correlation to ATE for an
COFDM VHF RX
20th International Mixed Signal Test
Workshop
Peter Sarson CEng MIET CMgr MCMI
Full Service Foundry
24th – 26th June 2015

2. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Introduction
What will I discuss
• In this presentation I will discuss how to correlate Adjacent Channel Rejection
using a Signal to Noise Method using a COFDM DQPSK signal that is used in
the application
I will show
• How this saved test time
• How this increased yield
• How it increased confidence in the shipped product to the customer

4. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Device Issues
Design Issue – Device performance marginal (ACR)
Required 3 tests to measure 1 parameter
• Long test time
• Yield performance was terrible due to marginality of device
• Sensitivity of RF tests also influenced yield due to guardbands
• Fast time to market

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Original Test Data
Test Time and Yield Data
• 6.5sec per devices
• 20 – 30% Bin1 Yield
Obviously economically not viable

7. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Causes for Bad ACR
ACR is based on several mechanisms all of which interact
• Image – IQ amplitude & phase imbalance of the modulator
• Intermodulation Distortion
• Phase Noise of the modulator
COFDM signals contain "multi carriers" i.e. many components at different
frequencies, all of which interact. It is not possible to accurately test the effect
of the interaction of these sub carriers using single or dual tones.

9. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Adjacent Channel Rejection Test
Bench
An ACR test is carried out by the following
• Receiver tuned to a low wanted signal level
• Signal present in the Adjacent Channel (upper or lower) is increased
- Performance limit is when the power in the adjacent channel causes the
BER specification to fail.

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Adjacent Channel Rejection Test
Bench

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Problem for Production
Production Test has 4 generators, 2 modulation sources
• Would need to use the two tone setup with modulation
- System doesn’t allow to modulate 2 sources at once or in two tone setup
• If you could you would only get single site (not cost effective)
• Test time would be huge due to modulated search
- Simply not viable
- Another solution is simply needed

13. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Modulated Waveform (COFDM)
OFDM is complicated to generate and not all modulation schemes are available
from ATE vendors
Unrealistic to source full bench data due to
• Hardware memory constraints
• Test Time constraints
• Select 2 symbols with the greatest Peak to Average Ratio
- 2 symbols of data for the modulating signal were selected which equated
to approximately 320K of AWG Memory.
- Exercise the device to worst case

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2 symbols DQPSK

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Substitute Test Implementation
Wanted Signal – Measure the Power Density inband
• Device set to receiving frequency
• Generator set to specified power level for bench ACR test, modulated and
adjusted for PAR
• Measure the power density in the specified bandwidth i.e. dBm/Hz at the centre
frequency of the device.
• A power density of approx -156dBm/Hz was measured in a 1.3MHz bandwidth
for a device with ACR of 35dB.

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ACR Measurement – Captured Wanted Signal

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Substitute Test Implementation
Adjacent Channel Signal – Measure the Power Density inband
• Device set to receiving frequency
• RF generator frequency shifted to the adjacent channel
• RF power set to the expected ACR plus the wanted input power
• Measure the power density in the specified bandwidth i.e. dBm/Hz at the centre
frequency of the device.
• A power density of approx -169dBm/Hz was measured in a 1.3MHz bandwidth
for a device with ACR of 35dB.

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Influence from Adjacent Channel

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Substitute Test Implementation
Signal to Noise Ratio – Compare wanted to adjacent power density
• The ACR measurement is the difference between the wanted and adjacent
measurement
• It can be observed that the std of the measurement is extremely stable for a
noise measurement, std = 0.3dB

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Ratio – Signal to Noise
Repeatability

22. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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ACR Correlation – Bench to ATE
Lower ACR Bench Vs Lower ACR Tester
y = 0.9527x + 23.503
R2
= 0.9883
29.5
30
30.5
31
31.5
32
32.5
33
33.5
34
34.5
35
35.5
36
6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5
SNR Ratio (dB)
ACRBench(dB)
correlation lower
Linear (correlation lower)

24. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Benefits – ROI
• Test Time reduction 50%
• Yield increased by 30%
• 100% increase in confidence of quality of the shipped product
• Cost of product reduced by around 15%

26. Confidential © ams AG 2015
Agenda
Introduction
Device Issues
What is ACR
How is ACR tested on the bench
Substitute for ACR Measurement
Correlation
Benefits
Conclusion

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Conclusion
It can be seen from the correlation graph that by comparing the actual
measured difference between the inband and outband that there is a good
correlation to the ACR measured on the bench. This is due to the fact by using
the same excitation signal and measuring output in the same bandwidth that is
being used in the application that all influences from Phase Noise and Image
are taken into account that would be seen on the bench.

28. Confidential © ams AG 2015
Thank you
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