opamp in sigma delta modulator

[glacieryy]

hi all,

how do i get the specific requirements of opamps (gain,bandwidth,...)in sigma delta modulator?

thanks a lot!

 

[nagula suresh]

the selection of the opamp depends upon the gain error allowed and sampling frequencies u are using.
for a sampling frequency of fs,your opamp gbw shud be greater than 5fs.
and for a small gain error u need very high gain.
in that cases,a fully differential gain boosted opamp will solves u r problem.

 

[Vamsi Mocherla]

If you are using a cascaded multistage sigma delta modulator, the requirements of the opamp also vary because the first integrator will have higher gain than the succeding stages. The first stage sigma delta integrator will have bigger capacitor loads to drive.

Also, importantly, the first stage should have a GBW which is not very much because the noise generated by the first stage should not be very high.

 

[glacieryy]

Thanks very much!

but,is there any theory to calculate these parameter?
maybe,in other words,how do i get the exact parameter for the opamp?

thanks again!

Added after 12 minutes:


Vamsi Mocherla,
do you mean in order to minimise the noise in first stage,the capacitor size in first stage should be largest?
thanks!

 

[pfd001]

Sure. The capacitor size in the first stage should be the largest.

 

[rfic]

Could you find some example at Stanford University web site.

Professor B.Wooly

https://cis.stanford.edu/icl/wooley-grp/

 

[glacieryy]

rfic:
Thanks for your advice!

But I am still puzzled by this problem!
Thanks for everybody's help!
bowing!