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How to increase the loop gain in a two-stage opamp (cmos)?

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saspas

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Hi. Is anybody of you have idea how to increase the loop gain in a two-stage opamp (cmos). My circuit is the simpliest two stage opamp. Now i have 55db and i want to reach 75db at least.

Thanks!
 

Re: Increase GAIN!!!

If you want to increase the loop gain in your design, you have to improve the open loop gain of your 2 stage opamp itself. This is because the loop gain is determined by the (beta*Aol). For the ideal design which is for voltage buffer, the beta value is 1. But when it comes to any loop design, the beta factor will be less then 1. So, the best thing to improve your loop gain is by improving the open loop gain itself. You may use the folded cascode or gain boosting cascode architecture to improve your gain until 75dB. Hope this helps you.
 

Re: Increase GAIN!!!

saspas said:
Hi. Is anybody of you have idea how to increase the loop gain in a two-stage opamp (cmos). My circuit is the simpliest two stage opamp. Now i have 55db and i want to reach 75db at least.

Thanks!

one way is simply increase the gm of the first stage input transistors pair, by enlarge the W/L ratio, not by adding the bias current. and the second stage input transistor also.
the other way is decreasing the bias current of first stage, on the condition that the unit frequency is high enough for you application.
if these two method does not reach you purpose, you can enlarge the L of the load transistors both of the first and second stage.
 

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