From: Walter Harley
Subject: Re: linear power supply noise questions
Date: 13 Nov 2002 04:22:25 GMT
X-Newsreader: MicroPlanet Gravity v2.30
In article <firstname.lastname@example.org>,
> The best way, if you want _really_ low noise, is to use a circuit like
> shown at http://www.wenzel.com/documents/finesse.html.
That's a neat idea! When I first looked at the circuit I thought it was
sensing the voltage drop across the series resistor, which would have
meant that there was positive feedback actively impairing the load
regulation. But I see that's not the case; the series resistor is there
just so that there's something to shunt "against," and the sense input
is simply the high-pass-filtered supply rail, not the voltage drop. But
the load regulation will still be impaired by however much the series
resistor is, correct? Or perhaps by slightly less, since there's
actually a little bit of negative feedback due to the bias being taken
after the series resistor (the more the gain, the less the negative
feedback, if I understand).
In my own case, the net effect would still be kind of bad, since my
output signal would then show up on the power supply line and cause
asymmetric gain reduction as noted by another poster; considerably more
so than at present because of the much-higher source impedance of the
supply with this system. Still, I might be able to use this idea
elsewhere. Seems like very clever engineering.