Test time efficient group delay filter characterization technique using a discrete chirped excitation signal

2016 International Test Conference

November 16th

Peter Sarson

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Outline

What problem are we trying to resolve How to measure phase based metrics What does a discrete chirp buy us How to generate a chirp Implementation Measurements Correlation and stability Conclusion

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What problem are we addressing

Produce a Group Delay production style test• That gives full characterization data• That is faster than the standard approach• That can be reused easily like an IP Block

Save coding time for future projects Remove last minute requests for

characterization tests

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What is group delay

group delay is a measure of the slope of the phase response at any given frequency

• Tg = -d /d

Therefore – need to sweep filter frequency range to get characterization data

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Standard Method

Start and Stop of AWG for each and individual Frequency of interest

Full Digitizer capture for each frequency Long Test Time for a few or many frequencies

What does a discrete chirp buy us

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Chirp in the Frequency Domain

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How to generate a discrete chirp

By using the coherence formula we can build a discrete chirp using Ff

• Fs/Ft = N/M  - Coherence Condition• Ff = Fs/N  - Fourier Freq - Resolution• r = 2/N - Phase Resolution

If we build a wavelet by making sinewaves a multiples of Ff we will produce a discrete chirp

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Phase Calibration

As the starting phase of the AWG is unknown• We need to somehow remove the starting

phase By making a loopback circuit• We can capture the source waveform• and device response• In one capture

Hence subtracting the two removes the starting phase of the AWG

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Phase Calibration Circuit

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Production Implementation

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Filter and Reference extracted

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Points to note

To get from an FFT to real phase• We need to phase unwrap the signal• If the phase resolution is to small this will

not be possible

The phase response is described as• (t) =0 + 2( f0t + kt2/2)

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Phase Response

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Time delay through filter

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Group Delay Curve

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Correlation

Frequency(kHz)

Group Delay (us)

Simulation Chirp (ATE) Lab

50 5.4 5.7 5.6

100 4 5.6 5,5

120 3.2 5.5 5.4

Stability

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Reproducibility

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Test Time Saving

AWG setup time is 2ms• UTP of waveform is negligible in time• So 5 frequencies for Group Delay is 10ms

Using a chirp• You only setup once• Therefore more frequencies that are of

interest the more the chirp is cost effective

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Conclusion

Using a chirp for group delay measurements gives reliable, accurate and reproducible results that is not only test time efficient but also gives full characterization data that is priceless to a semiconductor integrated circuit designer.

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