E-design
Advanced Member level 5
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Yes, I think the instability comes from this design not the OPAmp itself. E-design, your last figure doesn't show the loop gain, the DC gain of the open-loop system should be around 100dB for this system. So the phase margin is not that what you show, and probably your simulation is wrong.
1 Opamp is the best, most straightforward solution, I also recommend that.
Well today after work I decided to breadboard (hate these things) the circuit in the lab and test it. When I powered up and checked I could not see any obvious problems. I then simulated the circuit in another more trusted simulator to double check. The latest TINA release has some nasty bugs (often crash when plotting an AC response sweep) that the programmers are trying to sort out. It reported to expect 62 deg phase margin and 11 dB gain margin. I then thought, well, while it is on the bench and the FRA is free to check the actual figures. The FRA plotted 53 deg phase margin (taking into account that phase is a very sensitive measurement) and a corresponding 9.8 dB gain margin. Not bad for a horrible breadboard circuit. It is a bit peaky with square wave inputs but who knows all the effects caused by the breadboard itself.
The crossover is way too high (unless you want to do music) and should be knocked down at least a decade or so. I will play with it a bit more as time permits to see what I can improve.
I also checked the waveforms on our hi-res scope at full bandwidth and they look very clean.
I do like the circuit shown by Klaus!