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    Closed loop gain of this fully-differential amplifier

    I am trying to figure out how Razavi in his book got the following expression for Closed loop gain of a fully diff. amplifier. The circuit schematic and the equation are below.

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    I have come across this explanation of the calculation of the feedback factor of an inverting amplifier. This is the first time I am seeing the factor "k" being mentioned in the closed loop voltage gain.

    https://electronics.stackexchange.co...ting-amplifier

    is there any book which talks about this?

    - - - Updated - - -

    NVM, after looking at this link https://electronics.stackexchange.co...pamp-amplifier

    I figured out how he got the expression.

    Am I right about the taylor series approximation though? It is taken when x <<< 1?

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    Re: Closed loop gain of this fully-differential amplifier

    I don't know how he got to the second line. He may have used the Taylor series or perhaps long division.
    However, note that the result is approximately - R2/R1 Vin if the open loop gain is very high.

    I have attached an analysis of a diff in, singled out amp that I did years ago. I used this method to analyse your amp.

    Hope this helps



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    Re: Closed loop gain of this fully-differential amplifier

    Quote Originally Posted by tenso View Post

    Am I right about the taylor series approximation though? It is taken when x <<< 1?
    Yes.. If A0 is large (and is typically the case) then the 'x' term will be such that x<<1..



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  4. #4
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    Re: Closed loop gain of this fully-differential amplifier

    Of course, we do not need any Taylor series approximation or something like this.
    We need only the classical feedback formula (for finite gain) introduced by H. Black - supplemented by a forward damping factor.
    Last edited by LvW; 30th September 2019 at 08:56.



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