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  1. #1
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    2 Stage Opamp with SC CMFB

    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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  2. #2
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    Re: 2 Stage Opamp with SC CMFB

    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.
    Your life is all about ΔΣ, the narrow you estimate it, the precise it is ...



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  3. #3
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    Re: 2 Stage Opamp with SC CMFB

    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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