I have a really complex circuit as shown:

  • M4,M7,M14,M15 all pmos
  • the others->nmos

I am asked to draw common/differential mode half circuit.

What I don't know: How to deal with M14, M15?

Which mode should I put them into consideration? How?

enter image description here

PS: M4, 7, 6, 9, their gates are all biased.


This is a degenerated amplifier, where the transistors M14 and M15 act as the degeneration resistors.

Are you sure that M14 and M15 are supposed to be PMOS? The gate of M14, which is connected to V1 (or the gate of M4), is higher than its source/drain --> it is off. This configuration usually has M14 and M15 in its triode region (using NMOS).


Is the gate of M15 intended to be connected to the source of M9, which I believe is the ground rail?

The half circuit concepts are only applicable to symmetric circuits. However, that connection makes the circuit non symmetric. It talso means v2 is connected to ground which doesn't make sense for an NMOS.

If we ignore that connection, in common mode, the drains of M6 and M9 would be at the same potential, and the transistors M14 and M15 would just get shorted out.


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