The Periodic Stability analysis (pstb) does not give you the loop gain in each phase. It gives you the time-averaged loop gain over the whole period, which is what you really want. If you want the loop gain in a particular phase, you could run a transient, set up a stb analysis, and then specify the acnames and actimes parameters of the tran analysis to measure the loop gain at the times where each loop is closed. However, that is probably not what you want... pstb is more likely to be useful. Similarly, Periodic AC (pac) gives you the time-averaged small-signal response to a small signal input over the period. A couple of corrections from the document you referenced (there may be others, I just scanned it quickly): The iprobe does not "break" the loop. The loop remains closed at all times, which is the point of these analyses. It is the perturbation/measurement point for the loop gain You should no longer use cmdmprobe to measure differential and common-mode stability. Instead there is a superior component, diffstbprobe which copes with the loops not being balanced (i.e. if there is common-mode to differential-mode leakage or vice versa) and also allows the choice of whether you are measuring common mode or differential mode to be made on the analysis form, rather than on the component itself. Regards, Andrew.
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