what is the effect of adding current buffer in the op-amp?

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priyanka.aj

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I m designing a 2-stage miller op-amp. here in this op-amp M3-M4 are working as a current buffer. what is the effect of this current buffer on the amplifier gain? how does it affects the current distibution in the circuit? say if an o/p current of I8=800nA is flowing in the circuit then the current in the input pair of op-amp wud be I1=I2=200nA, I7=400nA, I9=800nA(without using current buffer).

Here i m attaching the circuit diagram of my op-amp.


 

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priyanka.aj said:
... M3-M4 are working as a current buffer. what is the effect of this current buffer on the amplifier gain?
Click to expand...

Actually it's a Cascode Stage -- the combination of a common gate (M3-M4) and a common source stage (M5-M6). Due to higher output resistance at the common drains, this topology provides larger differential gain compared to simple (non-cascoded) load transistors, see any book about analog CMOS design.

This has no influence on current distribution.
 
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