se error at lower frequencies by adding an equal but opposite phase shift i= n the amplifier feedback loop." That's completely wrong and not at all the = basis for the phase correction. Anyone can see the feedback loop has phase = lag and not lead. Just goes to show that the engineer can be completely clu= eless and still succeed in getting a working product.
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sees a feedback phase shift that lags Vin, so it must introduce a phase lea= d to zero the error. So it is the error amp in the main amp that introduces= the lead and not the feedback path. So the idea is introduce a phase lag i= n the feedback to force the main amp to produce the compensating phase lead= .
esingle feedback loop function, the output is easily shown to be the mathema= tical inverse of the feedback function. Using the relation between reciproc= als of transforms of inverse time functions, you know a simple phase delay = at fixed frequency is exp(-j theta) with corresponding reciprocal/inverse e= xp( + j theta), then superimpose that on the reality of an imperfect OA and= you have your result.- Hide quoted text -
Thanks Fred, That works too. I'm perhaps more like Joel. I'd like an intuitive understanding of what's going on and only drill down into the math when needed.
George H.