It's my understanding that phase and gain margins are used to see how much margin there is for the stability of a circuit. In other words, how much gain or phase would need to change in order to make the circuit unstable.
However, I don't think I've ever heard of using Monte-Carlo analysis to determine a stability metric. This approach would seem to me to have merit in that it would examine the actual variation of the components to look at the effects, rather than just some generic notion of margin.
On the other hand, I suspect that a generic margin has merit in the sense that it could capture parameters that are difficult to model (i.e., opamp open-loop gain).
So my question is why Monte-Carlo analysis isn't used for stability analysis?
Best Answer
Ideally you need both analyses. They do different things and both are used together.
Gain and phase margin not only show that a system is stable (e.g. a yes/no answer), but also how stable it is -- e.g. is there ringing or overshoot; how long does it take to settle.
Having some margin does also allow for (unanalyzed) variability in the system without it becoming actually unstable, but without MC analysis, this is often a judgement call, and may not have clear limits.
So in the end, for full confidence, you need MC analysis applied to gain/phase margin analysis.