VLSI design and Technology

[Aalis]

can somebody plzz tell me what actually affects the gain of folded cascode operational amplifier..... n how to increase the gain of folded cascode aoperational amplifier...???????

 

[nitishn5]

The gain of any opamp topology is given by the Gm x Ro.

One of the features of the folded cascode is that its Gm and Ro are independent of each other to a certain extent.
The Gm is controlled by the current in the input pair.
The Ro is controlled by the current in the folded load side.

If you want to increase the gain, you can increase the current in the input pair which would give you increased Gm. This would also give you more bandwidth.

Or you can reduce the current in the folded leg which would increase the Ro. This would reduce the bandwidth since your pole moves in.

Also you have to be careful with the Current in input pair : Current in folded load.
The further this ratio goes from 1:1, the more your circuit becomes sensitive to mismatches.