IDT2014 Chirp Presentation
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This document discusses using a chirp signal to characterize filters. It begins by introducing the problem of filter characterization and describing what a chirp signal is. It then explains how to generate a discrete chirp signal and use it to take filter measurements. The document shows the chirp signal provides repeatable results that correlate well with a tester. It also discusses how the chirp signal provides flexibility since it can be scaled to different frequency ranges. Using a chirp signal saves test time compared to discrete tones. Finally, it proposes future work using on-chip chirp generation for built-in self-test applications.
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IDT2014 Chirp Presentation
- 1. Confidential © ams AG 2014 Filter Characterization using a Chirp 9th IEEE International Design and Test Symposium Peter Sarson CEng MIET CMgr MCMI Full Service Foundry 16th – 18th December 2014
- 2. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 3. Confidential © ams AG 2014 Page 3 Problem Statement What is the problem we want to address • Initial Silicon always needs some kind of characterization on ATE • Time pressure causes issues and discussion of bench or ATE • If a generic approach can be generated then this becomes plug and play with some minor changes, only test time is a discussion • Based on the above we will discuss how to characterize filter characteristics easily with great reuse possibilities using a chirp
- 4. Confidential © ams AG 2014 Page 4 Test Setup
- 5. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 6. Confidential © ams AG 2014 Page 6 What a chirp consists of is quite simple, in a continuous system the instantaneous frequency of the signal linearly increases. f(t) = f0 + kt What is a chirp Picture from wikipedia
- 7. Confidential © ams AG 2014 Page 7 Why Chirp and not Multitone? • Unfortunately for devices that have a very low input power sensitivity, a multitone can cause some issues. • Max Tone Power = Max Input Power / NUM_FREQS • i.e. tones in the noise floor • intermodulation distortion product effects between individual tones • i.e. IM3, IM5, IM7 etc
- 8. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 9. Confidential © ams AG 2014 Page 9 Chirp Signal Requirements • What is the required accuracy of the measurement for the corner frequencies of the bandpass filter? • What are the corner frequencies and bandwidth of the filter being measured? • How do we make this waveform reusable? • How do we do all this and not violate the max operating conditions of the AWG (Arbitrary Waveform Generator)?
- 10. Confidential © ams AG 2014 Page 10 Chirp Signal Constraints • Ensure that Max Sampling frequency is not exceeded − i.e. Sampling Frequency/Tone Frequency = NUM POINTS/BIN NUMBER − Also Frequency Resolution = Sampling Frequency / NUM POINTS • Ensure that Max memory depth is not exceeded − i.e. 16MB for LTX AWGHSB (High Speed AWG) • Use a nomalised frequency so that the waveform is scalable i.e. a frequency resolution of 1
- 11. Confidential © ams AG 2014 Page 11 Bandpass filter Centre - 40kHz Low Pass - 7kHz High Pass - 80kHz Therefore create Chirp with: Freq Resolution = 1kHz Max Freq = 100kHz Hence NUM TONES = 100 Hence the waveform is scalable Chirp Creation example
- 12. Confidential © ams AG 2014 Page 12 Generic Chirp Example Code
- 13. Confidential © ams AG 2014 Page 13 Chirp Frequency Domain
- 14. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 15. Confidential © ams AG 2014 Page 15 Using same setup for the Digitiser as the AWG we can make an initial time domain measurement of the filter. By performing an mag fft on the time domain data we can analyze the frequency domain. From the mag fft the magnitude characteristic should be observable How do we extract the data we need from this? Filter Characteristic Measurement
- 16. Confidential © ams AG 2014 Page 16 • Normalise array i.e. convert to log dbc • Add 3dB or required attenuation point • Clip array at ± small number • Find max value and point in array, this lower atten point • Reverse array • Find max point in array and subtract from NUM POINTS, this is upper atten point • Multiply the atten points by frequency resolution and this is the actual atten frequencies Frequency Domain Capture
- 17. Confidential © ams AG 2014 Page 17 DSP code
- 18. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 19. Confidential © ams AG 2014 Page 19 Correlation Test Bench ATE 40kHz Lower Frequency -3dB point 7.72 kHz 7.480 KHz 40kHz Upper Frequency -3dB point 83.98 kHz 84.32 KHz
- 20. Confidential © ams AG 2014 Page 20 Repeatability
- 21. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 22. Confidential © ams AG 2014 Page 22 Waveform Flexibility • Waveform has a 1kHz Frequency Resolution • Waveform has 100 tones • Hence waveform can be scaled easily hence saving more waveforms being generated if system allows • Waveform can be scaled in frequency with a change to Sampling Frequency • By multiplying sampling frequency by 10, the waveform now has a max frequency of 1MHz with a Frequency Resolution of 10kHz
- 23. Confidential © ams AG 2014 Page 23 Waveform Flexibility – 550kHz filter Capture
- 24. Confidential © ams AG 2014 Page 24 Waveform Flexibility - Correlation Test Bench ATE 550kHz Lower Frequency -3dB point 196.60kHz 198.3 kHz 550kHz Upper Frequency -3dB point 822.00kHz 819.3 kHz
- 25. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 26. Confidential © ams AG 2014 Page 26 Test Time • Original test program code using discrete frequencies and start/stop of AWG and DIG was 250ms, this was 5 frequencies not 100! • Using chirp with no start stop is purely dependant on the UTP time of the source which is 100ms for this example. • Difference is 150ms • If UTP is faster i.e. faster Sampling Frequency the gain is more, why? − Start and stop and hardware stable time is fixed − Chirp test time is fixed by the UTP time, so 1 start/stop and 1 source/capture
- 27. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 28. Confidential © ams AG 2014 Page 28 Extension to Phase Information • Waveform is not stopped between frequency segments − Due to this we have full phase information • By doing an FFT instead of Mag FFT all phase information is available − i.e. Cosθand Sinθ
- 29. Confidential © ams AG 2014 Page 29 Unexpected Phase Response
- 30. Confidential © ams AG 2014 Page 30 Expected Phase Response
- 31. Confidential © ams AG 2014 Page 31 Phase Response • Not expected phase response • Due to frequency changing over time and hence causing a t^2 effect • Once phase is differentiated the phase response looks correct • However Phase Response result isn’t stable and doesn’t correlate • Due to this group delay is a non starter • Issue is due to the instantaneous phase of the AWG not being known • Require a loopback onboard so as to do calibration during testing
- 32. Confidential © ams AG 2014 Page 32 New Board – Loopback facility
- 33. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 34. Confidential © ams AG 2014 Page 34 BIST – Future work • Add an on chip VCO with frequency range of the filter • Ramp voltage on VCO input with cheap analogue resource • Effect is an on-chip chirp generator
- 35. Confidential © ams AG 2014 Agenda Problem Statement What is a chirp How to make a discrete chirp Filter measurements Correlation and Repeatability Waveform Flexibility Test Time Saving Phase and group delay Extension to BIST Conclusion
- 36. Confidential © ams AG 2014 Page 36 Conclusion • By using a Chirp test time can be improved. • Aid Design in initial ramp up and characterization. • Possibility of Software IP and code reusability. • With correct hardware design this can also be applied to Phase Response and Group Delay
- 37. Confidential © ams AG 2014 Thank you Please visit our website www.ams.com