blue111 wrote on May 27th, 2020, 8:55pm:I see. I haven't seen it for a long time and did not recognize it.
blue111 wrote on May 27th, 2020, 8:55pm:Which standard AC test ? I am pretty sure that my current test setup presents some problem.
I am also suspicious about your AC testbench. Maybe you wrote it, but for AC testbench you use a single voltage source in the feedback loop as suggested on YouTube of LTSpice tutorial. Long time ago I tried to set such testbench and I remember I had problems. I do not remember what those problems were exactly.
I would propose the old, known AC testbench, that is, breaking the loop and inserting capacitor and resistor/inductor. See attached picture from
https://payhip.com/b/5Srt ("Preview" in top right corner).
[
https://payhip.com/b/5Srt - "Preview" in top right corner]
"The easiest way to obtain the AC characteristic is to
break the loop using a large inductor and to connect a large capacitor to the negative input as
presented in Fig. 1.24:
The large inductor behaves as a very big resistance for AC signals. The large capacitor
keeps the bias on the negative input and ensures that any AC signal that leaks through the
inductor is shorted to the ground.
Some simulators enable to use a resistor instead of the inductor. In such case, a designer
specifies one resistance value that is seen in AC simulation and another one for all the other
simulations. The advantage of this solution over the inductor usage is the fact that the inductor
represents a different “resistance” value (electrical reactance to be specific) for different
frequencies. The higher the frequency, the higher the inductor's reactance. Hence, the inductor
is more leaky for lower frequencies and the AC characteristic may look a little bit strange
when very low frequencies are desired to be observed. On the contrary, the resistor keeps only
one resistance value across all frequency range."
Last remark: I see that you try to compensate your opamp using two paths: M14 and M22. Is that intentional?