From: John Woodgate
Subject: Re: Historical question: negative feedback and the op amp
Date: Wed, 13 Nov 2002 10:42:27 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Wed, 13 Nov 2002 13:04:38 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Peter O. Brackett
wrote (in )
about 'Historical question: negative feedback and the op amp', on Wed,
13 Nov 2002:
>"Mike" wrote in message
>> Harold Black came up with his negative feedback theory in 1927, yet the
>> first op-amp wasn't invented until the 1950s.
>> The op-amp seems like such a natural extension, once you know about
>> feedback. Why did it take so long for the op-amp to come along?
>> -- Mike --
>The Op-Amp *concept* requires "infinite gain" and back in those days, gain
>was definitely not cheap.
Well, that's not entirely true. You can get an awful lot of gain out of
two pentodes if the first one is operated under 'starvation' conditions
(RA = ra, approximately).
>I'm sure that if anyone were to have thought along those lines
>[approximately infiinite gain] back
>then, they would have stopped short because it would have seemed an absurd
>thought at the time.
>All good things have their time.
That's nearer the truth, I think. AFAIK, the op-amp concept came from
electronic analogue computing, and reliability was a big issue. It
wasn't until reliable semiconductors became available that the
requirement for millions of op-amps emerged, just about the same time as
they could be made as ICs.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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