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Signal Multiplication

by n0_3sc
Tags: multiplication, signal
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Feb9-08, 04:50 AM
P: 265
In engineering we're always taught block diagrams in communication systems, specifically multiplying two signals...
How exactly do you multiply 2 seperate signals electronically? What does the circuit diagram look like?
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Feb9-08, 11:52 AM
P: 321
You use a mixer. Block diagram of a mixer is a circle with an X inside. How does a inside of a mixer look like is another story.
Feb9-08, 06:07 PM
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PF Gold
f95toli's Avatar
P: 2,250
The simplest type of mixer is just a non-linear element of some sort, usually a diode.
Nowadays mixer can be quite comlicated but in old-style crystal radios you can even see the diode which in their case consists of a thin wire in contact with a semiconducting crystal, the voltage-current characteristics of the metal-semiconductor interface is non-linear and can therefore be used to down-convert the radio signal back to audio frequencies.

Feb9-08, 10:56 PM
P: 2,251
Signal Multiplication

a PWM chopper circuit, with an LPF, can multiply two signals at low frequencies. it's just a sorta variation of looking at the "mixer" or "non-linear element" way of doing it.

also, there used to be these things we called Analog Computers that had very high quality op-amps in them in blocks for integrators, abs(), exp(), and log(). with a exp() and log() blocks, you can accomplish multiplication of positive voltages ("one quadrant multiply"). to do 2-quadrant multiply, i think there is something called a Gilbert cell that does it and i think they've been put together in a manner to accomplish 4-quadrant multiply (where you don't care about the sign of either voltage getting multiplied).

check out,28...0%255F,00.html,28...0%255F,00.html,28...0%255F,00.html

you can get some pretty good app note and other information like that from Analog Devices. now they do a few different kick-*** DSPs (with warts) but when i was in college, they were purely analog.
Feb10-08, 01:51 AM
P: 265
How is a diode used to multiply them? I understand its a nonlinear element but is their an example circuit of how you would implement a diode and use it too multiply two seperate signals?
Feb10-08, 01:52 AM
P: 265
That pdf file was exactly what I wanted to see - thanks.

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