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From: "Mike Engelhardt"
Subject: Re: SPICE and amp stability
Date: 20 Nov 2002 16:19:13 GMT
Reply-To: "Mike Engelhardt"
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
> > Or is there some more correct way to determine the loop characteristics?
> You have to look at the *loop* gain. This is the open loop gain around
> the *feedback* path. This involves setting up a circuit such that the
> opamp has a closed loop for dc (or very, very low frequencies), but open
> loop for the main plot. This is so the amp will bias correctly. The
> easist way to see how this is done is to run my SuperSpice
This is a poor way of doing this. All you have to do insert a floating
AC voltage source in series with the feedback at in front of a high
impedance point of the circuit, typically the opamp input. Then do your
.AC analysis, and plot the ratio of complex voltages to either side of
the voltage source. This method also is a good one for bench use,
called either a frequency response analysis or Venable.
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