buddypoor
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To "complete the confusion" here is my summary:
Both, Tosei and Ken, are right - however, perhaps their contributions sound contradictionary, but they arenīt ! Phase as well as gain margins are defined only for the open loop system (of course, otherwise no input/output can be defined for loop gain). However, it is best and sometimes necessary to measure/simulate it in a closed loop configuration. For this purpose,Middlebrook has recommended a specific simulation topologie. For simple cases (when there is no severe load problem) you can simply place a series voltage source within the feedback path and let calculate Vout/Vin.
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