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From: "Ian Buckner"
Subject: Re: Diodes as collector load?
Date: Tue, 3 Sep 2002 09:38:33 +0100
Organization: Agilent Technologies
NNTP-Posting-Date: Tue, 3 Sep 2002 08:38:35 +0000 (UTC)
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"Chuck Simmons" wrote in message
> Jorge Omar wrote:
> > Hello,
> > Has someone seen diodes used as a collector load for a CE stage in
> > voltage noise, low level application?
> > Reason I'm asking that is 'cause I did such a circuit in 1975 or
> > as a preamplifier for a moving coil cartridge, but never saw
> > like it in print.
> > Just curious.
> > Jorge
> This sort of thing is done for logarithmic amplifiers and
> AGC's. The latter have the advantage of constant bandwidth. The idea
> useful for analog multipliers in general.
> ... The times have been,
> That, when the brains were out,
> the man would die. ... Macbeth
> Chuck Simmons email@example.com
I've used a diode as the feedback element in a fibre optic receiver.
modulation scheme was to use 2 light levels at a constant ratio, and
photodiode current passed through the feedback diode. This got me
instantaneous AGC and worked well over a large range (pun intended)
of receive signal levels. Getting a diode with low enough capacitance
At high levels the diode impedance is low, so the noise gets worse,
you don't care. At low levels the impedance increases so the noise
gets better (the diode is acting as the load for the photodiode).
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