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what is the role of this two switch?

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wjxcom

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Hi, all: this circuit is a full differential OPA whose CMFB is controlled by switchs and capacitance. but there has a question: what is the role of the switch M19 and M22? I think the role of the switch of M20 and M21 is clear. But why there have M19 and M22? I do not know how to analyse the circuit.

Help me. please!!
 

VSMVDD

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they are used as an active bias adjust in the gain stage
to limit any overdrive signal
 

wjxcom

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Hi VSMVDD: can you explain this problem detailed? or can you introduce some data about this problem to me?
Regards!!!
 

flushrat

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dummy device to absobe charge injection
 

wjxcom

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Hi, flushrat: your answer remind me that the book writed by Razavi has mentioned this kind of circuit.
thacs flushrat, and thacs VSMVDD.
 

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