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switch capacitor integrator

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crazyfox

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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
 

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.
 

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
 

crazyfox said:
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
Click to expand...

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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    crazyfox

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crazyfox said:
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
Click to expand...

Because of INT, the output will become saturate.
 

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