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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Historical question: negative feedback and the op amp
References: <3DD25F72.5793B8D5@webaccess.net> <6PuA9.5701$XF5.firstname.lastname@example.org> <3DD27F3D.667A4D75@webaccess.net> <3DD2FD36.8877972F@webaccess.net> <3DD3A4A5.688DDDDD@webaccess.net>
Date: Fri, 15 Nov 2002 03:00:07 GMT
NNTP-Posting-Date: Thu, 14 Nov 2002 19:00:07 PST
> "Chuck Simmons" wrote in message
> > However, let's take up the control of dynamical systems and see why an
> > FIR, in general, will not work.
> On the other hand, the speed of a control loop containing an IIR or FIR
> filter is another matter. Assuming that an FIR filter could be used to
> control the system under consideration, the additional latency of a
> pipelined FIR introduces even more delay in the loop, which decreases
> stability even further.
This part of the thread was inspired by ideas set forth that negative
feedback in particular can somehow be replaced by digital systems of
arbitray precision and speed. In other words, the idea of the
operational amplifier is dead or soon will be. Of course some digital
methods of replacing traditional opamp circuits (and others) were bound
to come up. However, I sort of think in terms of feedback because I do
control work. I started working in my present area which is servos for
CD drives and DVD drives. I was actually asked to consult for this
project because of my very strong opinions about mixed signal chips for
control. I agreed and we developed a unique architecture and I set about
writing code for the chip that, as it happened, I was not to see for two
years. Working without any specifications at all on what my controllers
were to control, I made all kinds of SWAGs and presented the company
with several thousand lines of code that I claimed met or exceeded the
design goals. I really thought about how I would solve the problems with
opamps because this thinking defined the equations of a fairly
generalized controller that I could quickly adjust just like I would an
opamp controller designed for a poorly specified plant. Knobs everywhere
was what I had in mind.
When you replace opamps with digital devices, it is important to keep
track of both the advantages of the digital devices as well as the
disadvantages. There is a trade-off there. I dead bugged an opamp on a
board just a few days ago because I needed it.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com
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