C what I mean wrote:

Negative output resistance from an amplifier?
.. please explain..

OK, it's negative slope resistance, of course...
Amp produces a certain voltage unloaded. Draw current by connecting a
load to it: the output voltage increases slightly.

It's done by measuring the output current with a current sensing
resistor and feeding a signal proportional to the output current back
*positively*, mixed with the usual negative voltage feedback.

As long as the positive resistance of the load exceeds the negative
resistance designed into the amplifier, so the sum of the two
resistances (effectively in series) is positive, this is stable.

--
Anahata
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