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  1. #1
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    Such design of Diff_In Signle_Out OpAmp has CMRR?

    Hi, Gurus,
    I designed a Diff_In and Single-ended out audio amplifier,
    in ADS simulation, it can works, have the same amplitude and the phase is 180 deg diff on the output.
    But I wonder such design have CMRR?
    Pls comment.
    many thanks.
    Tony Liu

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    Re: Such design of Diff_In Signle_Out OpAmp has CMRR?

    Drawing error. R5 has to be connected to ground not output. As sketched, the circuit misses negative feedback.

    The corrected circuit has CMRR but high sensitivity to resistor mismatching. Also asymmetrical input impedance. Source impedance mismatching affects CMRR.

    Nevertheless it's often used as cheap differential input stage for audo.


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    Re: Such design of Diff_In Signle_Out OpAmp has CMRR?

    Hi, FvM,
    Thanks.
    But if modified as your comment, the simulation result shows that two ways' amplitude is much different, as following.
    My initial design can have the same amplitude on the two ways.
    So how to achieve the same amplitude on two ways as your comments?
    Best,
    Tony Liu



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    Re: Such design of Diff_In Signle_Out OpAmp has CMRR?

    That's not the suggested circuit but it should amplify at least.
    OPAMP component however misses a bipolar power supply to work with zero DC bias.


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