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    switch capacitor integrator

    hi :

    I have a question about switched capacitor integrator.

    The integrator was constructed from a folded cascode op-amp ,

    which have common mode feedback.

    If i give a "dc" input signal , what will i see at op-amp output?

    the output voltage will accumulate form the common mode voltage?

    or keep at common voltage?

    Because i try to use this way to find the op-amp gain, is it correct?

    (From the transfer function (z=1, DC), can get the finite gain of op-amp)

    thanks

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    Re: switch capacitor integrator

    the output of integrator will step up if you apply a positive dc input. if you use fully-differential structure, the common-mode voltage of two outputs of opamp will be maintained on what you set by common-mode feedback.

    this is a method to find the finite gain of opamp. in general, i simulate the gain of opamp in frequency domain by applying ac small signal to the input of opamp.



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    Re: switch capacitor integrator

    Thanks for your reply :

    Do you mean if i use fully-differential structure,

    the output of integrator will not step up if i apply a positive voltage?

    But will set by common mode voltage, so i need to simulate it in frequency domain.

    thanks



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  4. #4
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    Re: switch capacitor integrator

    Quote Originally Posted by crazyfox
    Thanks for your reply :

    Do you mean if i use fully-differential structure,

    the output of integrator will not step up if i apply a positive voltage?

    But will set by common mode voltage, so i need to simulate it in frequency domain.

    thanks
    i mean the integrator will step up when applied a positive voltage for single-end and fully-differential both. when using fully-differential structure the common-mode voltage(not differential voltage) of integrator will be the setting in cmfb circuit.

    as for the opamp gain, using ac small signal method to simulate the open-loop response of opamp.


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  5. #5
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    Re: switch capacitor integrator

    Quote Originally Posted by crazyfox
    hi :

    I have a question about switched capacitor integrator.

    The integrator was constructed from a folded cascode op-amp ,

    which have common mode feedback.

    If i give a "dc" input signal , what will i see at op-amp output?

    the output voltage will accumulate form the common mode voltage?

    or keep at common voltage?

    Because i try to use this way to find the op-amp gain, is it correct?

    (From the transfer function (z=1, DC), can get the finite gain of op-amp)

    thanks
    Because of INT, the output will become saturate.



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