What's inside an analog 4-quadrant multiplier?

[Ken Smith]

In article <23heu01ckhch13qqf57hgi2qb6cppqvae6@4ax.com>,
John Larkin <john@spamless.usa> wrote:

On Thu, 13 Jan 2005 20:03:13 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

[...]
We may have to increase it anyway because you can do it electro-thermally.

It should be possible to multiply using a couple of tungsten filaments
as the nonlinear elements.

That is one of the many electro-thermal methods. You can also use the
fact that the power in a transistor is the product of voltage and current.
There are many thermistor methods too.

Certainly CdSe photocells. Or mosfets in their saturation region.

Somebody (Beckman maybe) used to sell a polychrystaline MOV-sort of
resistor that had an exponential i/v curve, sold specifically for
analog computation.

I think that we've got the number of methods up to something like 6 so
far.

Circuits involving SQUIDs produce outputs that are A*sin(B). If B is
small, this becomes A*B.

For small changes, the photcell signal in an atomic clock is the product
of the frequency offset and the lamp brightness.
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