Hello all, I am designing Miller OTA but there is a problem in the design always the transistor M5 off although in my calculation I ensure it is in sat could anyone help me what is the problem in these design steps?

How do you know the transistor is off? Did you run a simulation?

Yes after simulation

Did you close the loop in your simulation?

I run it as open loop to check first the DC operating point so I didn't proceed to closed loop

You can't simulate such a circuit open loop. Too much forward gain.

I simulated the same OTA with input pair NMOS and it works when I tried the PMOS input pair I faced this problem.

Then you were lucky. You had a perfectly balanced circuit. If you want to study your amplifier, close the loop, then study the performance. If you want to study the AC performance, then close the loop through a huge pole in the feedback. Put a huge inductor from the output to the minus input. Put a huge capacitor from the minus input to ground. Then you can see the AC performance in the open loop and the dc performance in the closed loop. This is how engineers in industry study closed loop systems, although there are multiple other methods to break the loop for AC.

ok, thanks sir.