sheldon
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BobDyl,
Some additional comments/questions, 1) What is the gain and phase margin of the common-mode feedback loop? The differential characteristics look reasonable, but there is definitely an oscillation.
2) It is standard procedure to run both an ac analysis and a transient analysis to verify circuit stability. For example, circuits with positive feedback, inputs reversed, will often converge to a meta-stable state for dc op analysis and have good gain and phase margin. Running a transient simulation is useful in order to confirm the results of ac analysis.
3) While it is appropriate to use simulator settings to supress trapeziodal ringing, changing the simulator settings is not an appropriate method for reducing circuit oscillation. Circuit oscillations should be corrected by improve the circuits gain and phase margin.
Best Regards,
Sheldon
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