Andrew Beckett
Senior Fellow
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Life, don't talk to me about Life...
Posts: 1742
Bracknell, UK
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With the analog design environment (aka AnalogArtist) this is easily achieved. You can either use the stb (stability) analysis added in the IC50 release, which will measure the phaseMargin and gainMargin (and loop gain) of a loop - the loop can stay closed; you just need to put an iprobe in the loop, and then point the stb analysis at that iprobe. Or you can use one of the traditional methods (ac analysis of the amp in open loop, probably getting the operating point from a closed loop simulation, using the spt1switch etc component in analogLib to open/close in different analyses; or using Middlebrook's method) - and use the phaseMargin function in the calculator.
Having got your appropriate output expression ready for a single point, then do a parametric sweep of the load capacitance (make it a design variable). What ADE will do is plot any scalar value against the swept variable, giving you what you want.
This isn't an absolutely detailed step by step answer, because that would take quite a lot of time, and probably I'd need to do it to make sure I got the description spot on - I'm assuming you have a reasonable idea how to use the tools.
Regards,
Andrew.
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