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From: Jim Weir
Subject: Re: How does a mixer work?
Date: Thu, 17 Oct 2002 10:18:46 -0700
Organization: RST Engineering
References: <firstname.lastname@example.org> <email@example.com>
X-Newsreader: Forte Agent 1.91/32.564
SNIPrf_man_frTHIS@yahoo.com (Frank Raffaeli)
shared these priceless pearls of wisdom:
->It doesn't need a non-linear element.
That's an interesting heresy.
So far as I know, you put in two signals to a linear amplifier, you get two
signals and ONLY two signals out the other end modified in amplitude by the
tranfer characteristic of the amplifier.
Non-linear elements, like diodes
->or over-driven transistors can provide a simple way to derive a
->product component of two signals. For a nearly linear approach, look
->up "Gilbert cell mixer". This uses linear elements and current
->steering / sharing. An AC current with a DC bias is split between a
->differential pair and steered to one side or the other by altering the
->bias on the bases / gates of the pair.
Horsefeathers. A Gilbert cell mixer is a very excellent distortion mechanism
(read "non-linear" for distortion if you like) for producing sum and difference
products from input signals rather efficiently and cleanly.
So far as I am aware, there is no mechanism for generating sum and difference
products from two signals without some distortion mechanism.
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