#### farhan89

##### Junior Member level 3

I am simulating differential pair with resistive load and another with active load with differential output, I have read onlone and razavi book that Active load improves CMRR and also differential gain, but reason for this is not mentioned. can anyone guide me why we replace load resistors with MOS loads ? advantages /disadvantages?

Also I have a question that in resistive load I am measuring common mode gain at differential out, I have used this equation

A_vcm=V_out/V_(in,cm) = (Δgm.RD)/(1+2gm.RSS )

is this equation correct for hand calculations ? If not which equation can I use for calculating common mode gain ?

Thanks!