Subject: Re: Historical question: negative feedback and the op amp
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Date: Wed, 13 Nov 2002 16:09:38 GMT
NNTP-Posting-Date: Wed, 13 Nov 2002 11:09:38 EST
Organization: Cox Communications
"Jeroen" wrote in message
> "Mike" wrote in message
> > "Chuck Simmons" wrote in message
> > news:3DD25F72.5793B8D5@webaccess.net...
> > > Ban wrote:
> > > > digital circuits work with saturated transistors, no feedback there.
> > FIR
> > > > filter does not use feedback.
> > >
> > > I beg your pardon, in an FIR filter, what is the output term(s) doing
> > > the equation if not feedback?
> > Depends on the filter. In the filter Ban's thinking of, the output is a
> > function of the inputs, but not the ouput - it's strictly feedforward.
> > the more general digital filter structure, of course, there are
> > and feedback terms.
> In case of IIR filters, feedback reduces the number of calculations
> In this case feedback isn't a thing that slows things down.
Actually, it does slow down the maximum operating frequency. I can pipeline
an FIR filter almost without limit, and obtain very high clock frequencies.
In an IIR filter, the maximum operating frequency is often determined by the
feedback loop. In the general case, the feedback term has to be fully
calculated in one clock cycle.
-- Mike --