OPA in sigma delta modulator

[kuohsi]

Hi ,all
Is the "overload level factor" important in sigma delta?
I ready a peper(Mohammad Yavari,Omid Shoaei, A very low-voltage,low-power and high-resolution sigma-delta modulator for digital audio in 0.25-um CMOS) that present the gain should be low in passband!!!it can improve "overload level factor"!!

But the high gain of OPA is better than low gain,isn't it??
thanks!!

 

[elbadry]

I think there is a misunderstanding here

The Open Loop gain of the Opamp should be large

However, the Closed Loop gain should be small. This is the gain of the Opamp with the feedback netwok connected.

 

[kuohsi]

I think there is a misunderstanding here

The Open Loop gain of the Opamp should be large

However, the Closed Loop gain should be small. This is the gain of the Opamp with the feedback netwok connected.

Thanks for your answer!! Thank you very much!!

 

[beckchm]

high gain is to increase resolution

 

[hubert008]

how did you know the relation between gain of opa and resolution?

 

[gingerjiang]

how did you know the relation between gain of opa and resolution?

finite opa gain makes the transfer function of integrator non-ideal, increasing the noise floor. you can develop the modulator's transfer function including the opa's finite gain to determinate the resolution, or set the gain by resolution.