How to simulate the PSS+PAC, PSS+PSTB for Switched capacitor

Hi everybody!

Hope you enjoy the good health!

Now i am designing the Switched capacitor for Pipeline ADC. I want to check the loop stability for that circuit such as PSS + PSTB. I try to follow several document which i search on the internet. however, there are have some problem in my simulation. When i check the loop gain, the result is too different from what i calculate.

Here is the document which i referred: www.lumerink.com/.../HW2_Kehan.pdf

Currently, i am using Ideal Opamp and Ideal switch

Gain : Gm*Rout = 120 dB.

when i check the Open Loop gain by using the PSS+ PAC simulation like below simulation cell. the result is the same. 

 - Simulation cells

- Result : 

- and then i do the PSTB simulation.as you can see. in my circuit, there are have two loop individually (SAMPLING LOOP and AMP LOOP) and the AMP is differential amp. so, i use diffstbprobe to check the stability.

However, when i check the loop gain, the result is too low compare to Open loop gain which i checked by using PAC simulation. The loop gain is about 52 dB. you can see below. 

actually, i am confusing about the method how to check stability of AMP. i have a question. 

It is possible to use diffstbprobe to check the loop gain of switched capacitor? because as we know,  the gain is ratio between OUTPUT and INPUT signal. But the diffstbprobe have only checked OUTPUT signal. 

and There are have anyone know about that please help me!

Thanks & Best Regard