From: Tony Williams
Subject: Re: Historical question: negative feedback and the op amp
Date: Fri, 15 Nov 2002 16:50:06 +0000 (GMT)
References: <firstname.lastname@example.org> <3DD24CD4.ECD230B9@webaccess.net> <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: Fri, 15 Nov 2002 16:54:19 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article <email@example.com>,
Tony Williams wrote:
> 20? years later A.D Blumlein appears to have
> exploited the Miller-Effect to build the first
> feedback integrator.
I emailed the Robert Alexander, the author of
"The life and works of Alan Dower Blumlein"
and the owner of the website
which holds many retyped copies of Blumlein's patents.
He kindly sent back a fascinating reply, which is
quoted in full below.
Dear Mr Williams,
Many thanks for your e-mail. Blumlein did indeed invent such an
'Integrator' as that which you mention, and it pre-dates 1950 by some
The Patent in question is No. 580,527 first applied for on 5 June 1942.
This invention became known around the world as the Miller Integrator for a
couple of reasons. Firstly, 5 June 1942 was just two days before Alan
Blumlein was unfortunately killed in the crash of a Halifax bomber in which
he was testing a early version of H2S radar, and secondly, Blumlein, with
characteristic modesty, attributed much of the work to the American, John
Miller, who in 1919 had carried out a mathematical analysis of the triode
valve as an RF amplifier for the US Bureau of Standards.
Miller discovered that for tuned RF amplifiers, that if an anti-phase
signal was coupled back to the grid a neutralisation of the feedback
occured. For frequencies below resonance where the anode lead was
inductive, this feedback from the anode circuit to the grid circuit could
give rise to a component of negative input resistance. This negative
resistance was in parallel with the grid tuned circuit and, under
conditions of low damping a sustained oscillation could occur.
But Miller never truly solved the problem,as he was the first to admit. His
solution was crude and effect only over a certain frequency range. Blumlein
took the basic elements of the Miller Integrator and deliberately added an
external capacitor to the stray capacitance which initiated a whole series
of circuits using diodes as auxilliaries, including the celebrated
'phantastron' and 'sanatron'. He also extended the principle to the
integration of more than one voltage at a time, used later in analogue
Blumlein decided the principle had been discovered by John Miller, and that
the invention which he patented on 5 June 1942 should be called the Miller
Integrator though many of his colleagues disagreed and argued verciforacly
that it should be called the Blumlein Integrator. Had he not died in 1942,
this may well have come to pass, but as with many things with Alan
Blumlein he does not get the credit he is due. Needless to say, there is
hardly an amplifier in the world which does not have a small 'piece' of
Alan Blumlein in its circuit design.
I hope this helps you in your quest. I have not placed Patent No.580,527 on
my website in full yet, but with your interest, I shall endeavour to do in
the near future.
Robert Charles Alexander
P.S. please feel free to use my answer and explanation on the forum