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How to compensate unstable Switched CMFB

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prince_123

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Dear All

I have a standard two stage standard OTA, first stage is folded cascode, output of first stage is given to gate of NMOS transistor with PMOS current source on top.

I am using Switched CMFB to adjust the voltage at the gate of first stage PMOS current sources.

I would like to know what are the various ways to compensate an "UNSTABLE" Switched CMFB loop.

Thanks in advance
 

swiched CMFB is basically discrete type,
so the unstable problem probably come from your OP not the switched CMFB
 

Btrend thanks for your reply

My OTA is stable with a phase margin of 86 degrees.
My CMFB is unstable because its has a phase margin of -20 degrees, I am getting some ripples before the output common mode voltage settles to its desired value.
One way can be to decrease the gain of the CMFB , but it may not be a good solution. Is there some compensation that I can do to stabilize it?

If you can also point out to some links that discuss the stability of switched CMFB , it will be of great help
 

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