From: Allison J Parent <>
Date: Fri May 1 22:26:41 1998

<A question occurred to me today : Can you have an embedded analogue
<computer, and if so, how many op-amps are needed to have one?

Yes, and that's very common. None, a low pass filter(RC) performs a
function and can be considered analogue.

<I was looking at the service manual for my Micropolis 1203 hard disk, and
<I read the circuit description of the servo electronics. It's a fairly
<complicated array of op-amps, which combine integral and differential
<forms of the position error, positioner current, etc. I would claim that
<is an embedded analogue computer.

Valid claim, also a good example of a fairly complex function.

<On the other hand, I think it would be stretching the definition to call
<a simple op-amp wired as a voltage follower an analogue computer.

Correct. However often the buffer is between some function or follows one
so it's part of the analog system.

Other analog systems common to computers:

cassette IO (low pass filter on output) and complex filter/differentiator
edge/peak detectors for input. Some of the acients used PLLs for clock
recovery (KANSAS City is one).

Analog to digital conversion (quantification).
Digtial to analog conversion (filtering)

Disk/tape systems have several layers of analog function for data and

Received on Fri May 01 1998 - 22:26:41 BST

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