designing of folded cascode

[royayeboodan]

I want to design a folded cascode amplifier with gain>70dB.
I can design it with gain=62db.please help me for increasing gain.[/b]

 

[naalald]

Hi,
If your opamp is working at low voltage and you can't stack more transistros, you can add more stages. But Multi-stage opamp has the drawback of complicated compensation.
So considering a specific number of stages, you can increase the gain by increasing the L of the output transistors. This is for a constant tail current and consequently a constant bandwidth.
You can also increase the gain by reducing the tail current but you will lose bandwidth instead.

 

[gaom9]

naalald is right, you can increase the L but keeping the value of W/L. So the output resistance will be enlarged, but the current is the same. It is the easiest way to increase the gain but not greatly.

 

[drming]

There is a free OPAMP design with > 76dB gain for you to download:

**broken link removed**

 

[IBO]

what transistor model are u using ?


Try using gain boosting,they are very handy.

 

[linkfox]

what transistor model are u using ?


Try using gain boosting,they are very handy.

that's an efficient way, but the GBW of the booster stages needs to be selected to increase the gain without sacrificing the speed

 

[suria3]

I believe you can easily design a folded cascode opamp with a gain of more than 70dB. Create a two stage opamp, which are folded cascode as a first stage and followed by another common source stage which will total up your gain up to 80dB. So, you no need to worry on the compensation as it is still considered as 2 stage opamp and you can apply miller compensation for stability purpose if it is in feedback application.

 

[wael_wael]

from my a little experience i can say that, there is 2 ways. first u add CS stage or u add AMP as gain boosting, dont use p mos as input because will reduce the gain and the phase margin
regards