"putting a small shunt capacitance across the
    feedback resistor in an opamp circuit"

I don't think this quite qualifies ... there is
no intrinsic 'feedback' or 'reverse gain' (input
to output isolation problem) within the device,
rather the phase-gain margin over the frequency
range of device is such that in some circuit
configurations the "feedback" must compensate for
this phase shift with frequency ...

Neutralization does just that - 'neutralizes' that
feedback component which would otherwise exist.

I have an old tube RF amp in which the neutralization
can be adjusted with the power off - by measurement
of the S12 or reverse direction gain A/K/A isolation
figure from output to input - adjustment calls
for adjusting the tuning for a *minimum* or a null
in the signal from output to input using a signal
generator and spectrum analyzer/receiver.

Jim


----- Original Message -----
From: "Dave Dilatush" <dilatush@COMCAST.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, May 28, 2002 4:06 PM
Subject: Re: [EE]: Cascoded?


> Jim wrote...
>
> >Has the concept of "neutralization" (a means of
> >countering a finite figure for input-output
> >isolation or "reverse" gain) been lost on the
> >more recent, solid-state and IC generation?
>
> Nope.
>
> The term itself has fallen into disuse but the concept is very
> much alive, having broadened into a set of methods for
> stabilizing feedback loops.  For example, putting a small shunt
> capacitance across the feedback resistor in an opamp circuit
> (often necessary when the resistance is very large) to damp out
> high-frequency ringing in its step response is, in a sense,
> "neutralizing" the opamp's input capacitance since that
> capacitance is often a major contributor to the ringing.
>
> DD
>
>

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