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Choice of Buffer after DDA for PGA

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deveshkm

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Hi,

I am designing a Programmable gain amplifier using DDA

DDA has NMOS input diff pairs
PGA uses variable feedback resistance (3k,9k,12k)


DDA is followed by single-ended OTA
Single-ended OTA is designed by using differential pair with current mirror load.

The open loop gain of SE - OTA is 40dB.
I have used it with unity-feedback.
In order to obtain optimal phase margin, I have utilized Miller compensation.
Is this a good option or should I use a different amplifier as buffer?


In open loop, DDA+buffer has a PM of 56 degrees.

Miller compensation is done using resistor 12.5k ohm and capacitor 2.2pF.

Is it possible to use any other OTA as buffer?
 


Thanks for responding.
Two stage miller opamp
First stage : simple ota
Expected gain is nearly Rf/R1
I have used a common source amplifier (with diode connected load) in second stage.

These are the results:

twostagemilleropamp_10pF.JPGmilleropamp_CL_1pF.JPG


For more gain, I would try to change the second stage to current source load.
 

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