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June 9th 04, 02:15 AM

Avery Fineman ) writes:
In article ,
(The Eternal Squire) writes:

Has anyone ever implemented a gilbert cell mixer using valves instead
of FETs?
I'm considering this instead of using the increasingly rare and costly
heptode mixer.

To do this, one needs a minimum of three triodes, the top pair
being (essentially) a differential amplifier, the bottom being a
configured constant-current source replacing a moderately-
high common cathode resistor for the differential pair.

That's a LOT of circuit work where a single dual triode could
(and has) work just as well. Connect it as a differential pair
and put the signal in one side, the LO in the other.

Any valve that runs its control grid into the positive region is
going to be operating in a non-linear region and will therefore
"mix" well enough to do some heterodyning.

The name "Gilbert cell" got there in later integrated circuit
times to describe a particular arrangement of BJT junctions
to do mixing or AGC actions. Valve circuitry had other
names and worked for decades as mixers quite will without
fancy names. :-)

But the "Gilbert Cell" mixer also got by for a good long time without
the fancy name.

Nobody used the term in the early seventies when the MC1496 came along.
It was just a double balanced mixer. It was the late eighties when I
started hearing the term, in reference to the NE602, though suddenly
decades of the same circuit was suddenly a Gilbert Cell.

I know I mentioned this at one time in one of the newsgroups, and
there was an explanation, but I can't remember what it was.

Michael VE2BVW

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