question about spectre PSS/Pnoise on Sampling & Hold Cir

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spectre pss pnoise

I have run a PSS/Pnoise analysis for my sampling & hold circuit. The
structure of circuit is switched capacitor, flip around with a
gain-boosted amplifier. When printing noise summary, I found the top 8
noise contributers (they generated 70% of total noise) are not from
main amplifier, but from gain boost amplifier (AUX amplifier). It's
pretty much way out of my imagination, the noisy amplifier is on the
signal loop though. My PSS/Pnoise setting up are like following:

PSS: 80M beat frequency, number harmonics: 20; time of stable: 300n,
maxacfreq: 1.6G
Pnoise: start: 1, stop: 40M (Nyquist); Max Sideband: 20; Timedomain:
time point 7.1n (hold end point)


To interpret the Pnoise results, I did a noise analysis with a linear
test bench for amplifier (main amplifier with AUX one) only, there most
noise contributers are input and current soure transistors at main
amplifier. It's very interesting that AUX amplifier has shown almost
nothing with total noise this time. Does anyone has any idea with it?
Thanks a lot.

 

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switched capacitor noise pss pnoise

The following is the detail about previous question.

My circuit is a quite typical folded cascode amplifier
with pmos input. There are two AUX amplifiers working as gain booster
on cascode NMOS and PMOS, respectively.

There are several questions I want to figure out:


1. If I can count on PSS/PNoise analysis for the noise estimation?
Considering my circuit is working as switched capacitor way, looks like
I don't have so many choices to get noise info. Also, this circuit is a
Sampling & hold frount end stage for pipeline A/D, the next stage is
working as switched capacitor circuit too.
2. Is it correct that I choose "timedomain" within PNoise analysis? and
time point (for timedomain analysis) is same as S/H's holding end point
? should I change it to other kind of noise format within PNoise
analysis, like modulation, jitter or source?
3. In this case, what's the physical meaning of PNoise's output? Is it
really represent noise within this system?