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How to consider the cmfb loop stability ?

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ablue

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stability of cmfb loop

Hi all:
if i use discrete time cmfb in my design, how to consider the cmfb loop stability ? will that be unstable? what is the difference between discretetime cmfb and continuous time cmfb in loop stability
 

Re: stability of cmfb loop

In P.R.gray's 4th edition analog circuit design book, there are some discussion on this issue. You can consult it.
 

Re: stability of cmfb loop

to make stability when you make GBWcm>GBWdm
 

Re: stability of cmfb loop

Is it really necessary to make GBWcm > GBWdm?
 

stability of cmfb loop

I did not bother much about SC CMFB loop stability when designed fully-diff OTA. Just followed the caps sizing considerations from Johns&Martin (swicthed caps should be 1/4~1/10 of non-switched), played a bit with PSS to see the CM level dynamics during the clock and it worked fine for me..

I think loop stability is a problem for continuous-time CMFB, not discrete.
 

Re: stability of cmfb loop

You can see this paper
”Determination of stability using return ratios in balanced fully differential feedback circuits” IEEE transactions of circuits and systems II, vol 42, NO.12 DEC. 1995.
 

Re: stability of cmfb loop

when stability

always check the loopgian T=a*f
you can use bode
 

Re: stability of cmfb loop

I think GBWcm<GBWdm is better
kkoko said:
to make stability when you make GBWcm>GBWdm
Click to expand...
 

Re: stability of cmfb loop

layes2 said:
when stability

always check the loopgian T=a*f
can u explain in detail?3x
you can use bode
Click to expand...
 

Re: stability of cmfb loop

borodenkov said:
I did not bother much about SC CMFB loop stability when designed fully-diff OTA. Just followed the caps sizing considerations from Johns&Martin (swicthed caps should be 1/4~1/10 of non-switched), played a bit with PSS to see the CM level dynamics during the clock and it worked fine for me..

I think loop stability is a problem for continuous-time CMFB, not discrete.
Click to expand...

What do you mean swicthed caps and non-switched caps?
 

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