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Gain Boosting Cascode amplifier design - New Member

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ashishvora

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Hello Friends

I am a new member in the group. I am designing a gain boosted cascode amplifer. I am using a conventional two stage amplifier but with the gain boosting in the second stage. My aim is to get 80 dB gain with 50 MHz UGB. Can somebody help me in this.

Right now from my design I am getting 75 dB gain but I am having all sorts of problems in stability.

I am using 0.18um technology with Vdd=1.8V
 

You should read the classical artical from Class Bult

K. Bult and G. J. G. Geelen, “A Fast-Settling CMOS Opamp for SC Circuits with 90-dB DC Gain”, IEEE, Journal of Solid State Circuits, Vol. 25, no. 6 pp. 1379-1384, December 1990.

to set correctli the position of the poles of the gain boosting amplifier.

Bastos
 

That is the same paper I am using as one of my references. But it doesn't seem to work.
 

My main problem I suppose is trying to stack 4 transistors in 1.8 V.

Added after 6 minutes:

Oops I forgot to add this in my previous message. Can somebody help me with the stability analysis/pole-zeros/transfer function derivaiton of the gain boosted cascode circuit. There is an internal feedback loop in the basic circuit which as far as I can make out is creating all sorts of trouble.
 

Hi
If convenient, can you post what you have here? It's not readily understood what's meant by conventional two-stage amplifier?
I thought it's better so that it's easier for those who can help you.
 

ashish,
4 transistors in stack shd not be an issue with 1.8V supply..i m doing that with 1.2V..
infact u dont need 2 stages i guess..
UL ur ckt..
 

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