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2 Stage Opamp with SC CMFB

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Puppet123

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Hello,

I have designed a two stage opamp for use in switched capacitor applications.

I want to use Switched Cap CMFB for it - I only need the CMFB for the one stage of the opamp - is this correct - the bias voltage of the current mirror.

See attached picture - vbias in picture is vcontrol is the SC CFMB circuit and vbias of the opamp is vbias of the SC CMFB.

Is this correct ?

The "second" stage does not need a CMFB circuit - is this correct ?

Thank you.
 

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  • FD2Stage.png
    FD2Stage.png
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  • SCCMFB.png
    SCCMFB.png
    11.8 KB · Views: 114

The CMFB used to give a separate DC CM gain at the output. Here you are sensing second stage output (which is indeed the "main" output) and regulating "any" internal bias node on a negative feedback. That's why the CMFB is applied for the whole circuit, don't need to think about the stages individually.
 

Hello,

Thank you for your response.

So I am indeed, correct in my assumptions, that I can use this SC CFMB in this circuit for the 2 stage opamp ?

Thank you.
 

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