Hello.
First I'm new to this forum. Great pleasure to meet all of you
My question is:
I have an opamp (one stage with differential input and current mirror as a active load - the basic configuration). I wanted to measure the DC Open-Loop Gain, Closed-Loop Gain, PM & GM.
First I have made STB sim(with no C as a load at output): I put the opamp in the voltage follower configuration and in the loop i put a DC voltage source with 0 value as a probe. I have made the sim and the result for PM, for example, was PM=41.2deg.
Second I have made AC sim(with no C as a load at output): I put the opamp in the voltage follower configuration and in the loop i put an inductor L=1G H and a capacitor to ground C=1G F. I have made the sim and the result for PM, for example, was PM=-85.8deg.
Strange. So I applied a step at input and in the voltage follower configuration(same, with no C as a load at output) I looked at output to see the wave form, and the wave form looks like for a PM of around 40-45.
https://i.ibb.co/RpVf3Bj/STB-vs-AC-loop.pngI put the image below.
*in the image there are 3 simulation for both STB in the right and AC in the left, with 3 different values of output C as load.
All of them are different, hence offering different results.
* also in the image it can be seen the step response, looking almost like a PM around 45.
What is the explanation ?
STB and AC should show the same result or not ?