[SI-LIST] Re: Power supply noise
- From: steve weir <weirsp@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Sun, 01 Dec 2002 17:16:10 -0800
Martin,
Somewhat ironically, Mike's work points to emulation of the brute force
methods that the Wenzel paper tries to avoid. Mike analyzed the problems
caused by inadequate gain in the one transistor approach in the Wenzel
paper. Wenzel fixed that with the op-amp version. The op-amp version has
enough gain so that the matching is as good as the four resistors: source
series, emitter, and the two feedback resistors.
The neat subtlety about Wenzel's op-amp circuit is that it inherently
limits. So it attacks the AC noise without as much settling time penalty
as Mike's suggestions. A diode limiter around the 300K feedback resistor
should help further. A key point by Wenzel is that it is the noise we want
to remove, and the noise is a small fraction of the DC output voltage.
If you favor Mike's filtered voltage follower approach, it is adaptable
with tight DC voltage regulation using an LT1575. The LT1575 is a follower
controller in an SO-8, that includes current sensing, shutdown, and a lot
of bandwidth. To suppress the reference noise, you would defeat the high
frequency response by changing the compensation network components, and
then insert a low-pass network in series with the external N-FET gate.
Another way to go about Mike's AC shunt or follower approaches is to make
the filter response switchable. At power-on, who cares about a few mv of
noise? After basic voltage stabilization, the filter LF cutoff can be
switched much lower to kill off shot noise and other artifacts.
Regards,
Steve.
At 03:59 PM 12/1/2002 -0800, Martin Euredjian wrote:
>Something I got off list:
>
>
> > -----Original Message-----
> > From: Mike Monett [mailto:add.automation@xxxxxxxxxxxx]
> > Sent: Sunday, December 01, 2002 2:12 AM
> > To: Martin Euredjian
> > Subject: Wenzel Finesse Power Supply Noise
> >
> >
> > Hi Martin,
> >
> > I saw your post in the SI-LIST. I get the summaries so I can only reply
> > via email, but you could copy this message to the others if you like.
> >
> > I'm working on low noise power supplies for a uhf varactor vco
> > synthesizer and studied the techniques Wenzel describes. I wrote a
> > summary of my findings that may be of interest. It's at
> >
> > http://www3.sympatico.ca/add.automation/spice/ripple.htm
> >
> > Best Regards,
> >
> > Michael R. Monett
> >
>
>
>
>
>
>
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