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From: tom@syssoft.com (Rodentia)
Newsgroups: sci.electronics
Subject: AGC Op Amps
Message-ID: <1991May3.042449.14290@syssoft.com>
Date: 3 May 91 04:24:49 GMT
Reply-To: tom@syssoft.com (Rodentia)
Organization: Systems & Software, Inc., Irvine, CA
Lines: 27

I am looking into using Automatic Gain Control (AGC) amplifiers to
scale the signal of an IR detector (photodiode or phototransistor)
to logic levels.  The only two parts that appear suitable are the
Motorola MC1490 and MC1350 wideband and IF opamps.

First, are there any other AGC amps out there?  Second, how do I
hook these babies up?  The example R and C values are only given
for 455KHz and 10.7MHz, and no equations are given to calculate
values centered around other frequencies.  There was an appnote
(AN-513), but apparently it is no longer distributed and existing
stock is to be destroyed (why would they do that?).

In general, how does one connect an opamp with two (differential)
outputs, and where one input (-) is suggested to be connected to
ground through a capacitor (would that be to allow the input to 
float at virtual ground?)?  Any good books on the subject?

OR... if you want to save me all the work, is there an appnote
or design for an entire IR digital receiver.  I know about the
sharp (and Radio Shack) GP series receivers, but they can't
go above a 5Kbit data rate (and that's even out of spec).
But I do like their relative insensitivity to distance.
-- 
Thomas Roden                                      | tom@syssoft.com
Systems and Software, Inc.                        | Voice: (714) 833-1700 x454 
"If the Beagle had sailed here, Darwin would have | FAX:   (714) 833-1900
come up with a different theory altogether." - me |