[sdiy] decoupling caps again

Magnus Danielson magnus at rubidium.dyndns.org
Tue Sep 3 02:53:26 CEST 2013

On 09/02/2013 11:54 PM, Ian Fritz wrote:
> I agree with the first comment below the article.  I'm sure that most
> diy-ers have at least one decoupling cap where power enters the
> board.  That already makes our typical boards different from the
> author's experiment, where he was comparing to the case where there
> was no decoupling at all.
> Just because the author saw some oscillations in one particular
> circuit/layout doesn't mean you have to put decoupling caps on every
> chip.  The earlier studies, in fact, showed that a few caps here and
> there on an analog board are plenty.  This has always worked well for
> me.  In fact, I've never found a problem of any kind that could be
> fixed by adding more bypass caps.
Most op-amps running in linear mode would not benefit from bypass caps,
but their bandwidth might be a bit too high, so a feedback cap can keep
things clean.

My mind comes to comparators or other pushers of fairly steep slopes,
such as digital gates. Putting caps over them helps to keep the rest of
the board fairly quiet.

Feeding an analog design with caps as you would do for a digital design
is a bit excessive, agree.


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