@Stefan Schippers how to run stability in xschem? @Piyush Dwivedi

see test_ac.sch:

xschem test_ac.sch

break the loop at the lower terminal of the feedback resistor, insert a "pass only DC" filter, restore the broken feedback loop loading condition, apply a voltage source with 0V dc and AC 1 0" signal on M4 gate, remove any other AC signal from voltage sources, (suggestion: do not use weird characters for node names, remove the + in Vin+) The vout is the open loop transfer function. Plot magnitude and phase and you get the phase margin (180 - phase shift when gain is 1).