Dwayne Reid wrote:
> You can make most op-amps stable even with gain less than -1 by
> increasing the noise gain of the op-amp.

Actually it's gains above -1 that are usually the problem, at least for
opamps generally tuned for stability.  Specifically gains between -1 and +1
are the issue.  Lower gain magnitudes decrease stability.

> In other words, you add a
> gain-set resistor from the (-) input to ground.  As long as the noise
> gain exceeds the minimum gain required for stability, the op-amp
> remains stable even is the input gain is less than that minimum.

That is unpredictable since you're relying on characteristics of the opamp
as they differ from a ideal amp.  The usual way to increase stability is to
add capacitance between the output and the (-) input.  Some opamps,
particularly old one, have extra "compensation" pins for adding the
capacitor, but those are rare nowadays.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.