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  1. #1
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    Controlling partial or the whole current in CMFB

    Dear friends,

    many designers use the CMFB amplifier to control the whole current of the intended branch, some others control half of it and provide the second part from normal biasing scheme. Some control 25 % of the current and provide the remaining by the biasing scheme.

    What I understood is that if we control the whole current we will get the higher loop gain, if this create a stability issue then reducing the loop gain by controlling part of the current is possible beside it is assumed to give faster settling response.

    But what I want to ask you is two things

    1. is it good idea to controll 25 % of the current ?
    2. if we are controlling 50 % of the current does it mean that our CMFB can correct properly for a mismatch in the circuit up to 50 %, smilarly if we talk about 10 %

    Thank you
    Best Regards

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  2. #2
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    Re: Controlling partial or the whole current in CMFB

    I don't think 25% is a good idea. 50% is ok. 100% may not be a good idea too. Suppose you control 100% through the CMFB. What will happen if the CMFB doesn't start properly or for one reason or another the circuit just get stuck in a state with no current and sits there forever? If you split it 50-50 then at least you are sure there is some initial current not controlled by the CMFB.


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