differential apmplifier problem

[jutek]

hello

could you tell me what max gain i can achieve from circuit like this in the picture but with PMOS as the inputs and NMOS as a load?

i'm trying to simulate that with different currents and W/L ratios but the max i've achieved is 10V/V

What is incorrect? my expectations or calculations?

regards

 

[nxing]

probably 10 is the correct number. the gain is Gm(nmos)/Gm(pmos).

 

[beckchm]

the gain is not big

because the output pmos is diode connect.

so the output resistance is small

 

[jutek]

probably 10 is the correct number. the gain is Gm(nmos)/Gm(pmos).

so, if i want to build 2 stage opamp i have to use another input stage to have much more gain?

regards

 

[holddreams]

you can refer Allen's book ,chapter 6,Cmos operational amplifiers.