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How to use PSS+PSTB or PSS+PAC to simulation the loop gain of the amplifier in the MDAC in each clock phases

ringamplifier

Hello, everyone!

I am currently designing  a amplifier for the multiplying dac (MDAC) for the pipeline ADC. The circuit diagram is show in Fig. 1. This circuit operates  in two clock phases: phi1 and phi2. In phi1, the amplifier is auto-zeroing and its offset will be sampled in capacitor Cc. Vin is sampled in C1 and C2. In phi2, the amplifier will do the amplification. Clearly, the feedback factor of the amplifier in phi1 and phi2 is different. So I want to simulation the loop gain in phi1 and phi2 separately and also want to see the effect of different feedback factors.

Since this circuit is a discrete time circuit, it seems that I should use PSS analysis to find its operation point and do the small signal analysis to analysis the loop gain. 

I also found a slide in the internet to teach how to use the PSS+PSTB simulation to analysis the loop gain of switched capacitor CMFB. The link is   

lumerink.com/.../Loop%20Stability%20Analysis.pdf

However, I have a question about the method using in this slide. For better description, pls see Fig. 2 (actually page 28 of the slide). The SC CMFB also operates in two clock phases. The feedback capacitor of the CMFB circuit is different is each phase. So the question is how can the PSS analysis distinguish two clock phases and PSTB simulation results is corresponding to which clock phase?

So I want to make a clear statement of my question:

How to use PSS+PSTB or PSS+PAC to simulation the loop gain in each clock phase

Fig. 1

Fig. 2

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  • Andrew Beckett

    Hi Shen,

    OK - I'd not looked at the small diagram with the two phases indicated. You have two feedback loops - each switched by a different phase. You need to insert the iprobe (or diffstbprobe if it's differential - your Fig 1 only shows a single-ended amplifier) in the loop you're interested (you can have both components there and just pick the one you want when simulating). If the probe is at the output of the amplifier it would include the effects of both loops; if it was in just the loop for phase 1 or phase 2, it would include just that feedback path.

    You definitely don't want to use acnames/actimes with tran analysis for this (I said that was unlikely to be what you want).

    Regards,

    Andrew.

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  • Andrew Beckett

    Hi Shen,

    OK - I'd not looked at the small diagram with the two phases indicated. You have two feedback loops - each switched by a different phase. You need to insert the iprobe (or diffstbprobe if it's differential - your Fig 1 only shows a single-ended amplifier) in the loop you're interested (you can have both components there and just pick the one you want when simulating). If the probe is at the output of the amplifier it would include the effects of both loops; if it was in just the loop for phase 1 or phase 2, it would include just that feedback path.

    You definitely don't want to use acnames/actimes with tran analysis for this (I said that was unlikely to be what you want).

    Regards,

    Andrew.

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