From: firstname.lastname@example.org (Frank Miles)
Subject: Re: Historical question: negative feedback and the op amp
Date: 15 Nov 2002 18:23:52 GMT
Organization: University of Washington, Seattle
References: <email@example.com> <firstname.lastname@example.org>
In article <email@example.com>,
Tony Williams wrote:
>In article ,
> Frank Miles wrote:
>> In article <firstname.lastname@example.org>,
>> Tony Williams wrote:
>> > ..... He notes that Cin = Cf*(1+A), where A= gm*Rl.
>> > Note the "apparently". I don't have Terman's 1943
>> > book but have a 1950 Terman book, where he references
>> > back to his 1943 book in the footnotes.
>> Couldn't find any reference to sawtooth, ramp, or sweep
>> generators either. No Cin formula either -- there's
>> an equivalent circuit for a triode (without any
>> acknowledgement for what we know today as the Miller effect).
>> No similar equivalent is shown for the pentode.
> Thanks for looking. In Terman's 1952 book, (note the
> corrected date for the second edition), the footnote is
> alongside the formula, referencing his 1943 REH page 467,
> and a remark that Cf is large compared to the interelectrode
> capacitances which are neglected in the formula. So perhaps
> he was just referring to something basic about valves.
Aha! Thanks for the page#. There it is, right after the
'neutrodyne' analysis. He has a footnote to his brief discussion:
For derivation, see F.E.Terman, "Radio Engineering," 2nd
ed., p.232, McGraw-Hill, NY. See also J.M.Miller,
Dependence of the Input Impedance of a Three-electrode
Vacuum Tube upong the Load of the Plate Circuit, Bur.Standards
Sci. Paper 351: M. von Ardenne and W. Stoff, On the Values
and the Effects of Stray Capacities in Resistance-coupled
Amplifiers, Proc. I.R.E. Vol. 15, p. 895, Nov. 1927; E.L.
Chafee, Equivalent Circuits of an Electron Tube and the
Equivalent Input and Output Admittances, Proc. I.R.E. Vol.
17, p. 1633, Sep. 1929.
(John Woodgate -- you're right on the mark regarding Miller)
He goes on to relate the input capacitance to problems related to
tuned circuit implementations. And while he describes the reduction
in input impedance due to negative (voltage) feedback, I still see
no mention of integration in any form; no intentional negative
>> There is a lot of amazing stuff on effects of grid design,
>> electron optics in CRTs, and hosts of other stuff nobody
>> but specialists deal with any more.
> Since Terman was a prof it is probably a proper view
> of what an electronics engineer needed to be armed
> with 60 years ago..... the rate-of-change between
> then and now is frightening isn't it.
If more of it were downhill, it would make one helluva roller-
coaster ride. It's exciting, but there's a bit too much uphill
for those seeking easy thrills.