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Simulators >> RF Simulators >> PAC analysis for switched capacitor amplifier
https://designers-guide.org/forum/YaBB.pl?num=1167338905

Message started by hpham on Dec 28^th, 2006, 12:48pm

Title: PAC analysis for switched capacitor amplifier
Post by hpham on Dec 28^th, 2006, 12:48pm

Hi,
For my switched capacitor amplifier design (input at 12.5Khz, clock at 200Khz, gain = 0dB) I noticed that if my output is non-reset(not return to zero type), then PAC simulation show 0dB with notches at 200Khz, 400Khz and so on.. as expected. But if my output is reset(return to zero type), the PAC simulation shows -6dB gain and notches at 400Khz,800Khz ...?? Please explain. Transient simulation in both cases show 0dB gain. Nothing special about my amplifer, just a conventional switched capacitor amplifier with narrow band CDS technique applied.
regards,
ha

Title: Re: PAC analysis for switched capacitor amplifier
Post by Ken Kundert on Dec 28^th, 2006, 1:51pm

PAC in essence is performing a transient followed by a Fourier analysis. The Fourier coefficients computed by the Fourier analysis for the return to zero case will be 6db lower than the non-return to zero case because the signal is zero half the time. In otherwords, when you look at the transient results you are comparing just the peaks, whereas PAC is evaluating the whole signal. If you were to perform a Fourier analysis on the transient results, you would see the same behavior.

-Ken

Title: Re: PAC analysis for switched capacitor amplifier
Post by hpham on Jan 4^th, 2007, 9:54am

thank you, Ken. You are right.
regards,
ha