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Signal Multiplication 
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#1
Feb908, 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? 


#2
Feb908, 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.



#3
Feb908, 06:07 PM

Sci Advisor
PF Gold
P: 2,259

The simplest type of mixer is just a nonlinear element of some sort, usually a diode.
Nowadays mixer can be quite comlicated but in oldstyle crystal radios you can even see the diode which in their case consists of a thin wire in contact with a semiconducting crystal, the voltagecurrent characteristics of the metalsemiconductor interface is nonlinear and can therefore be used to downconvert the radio signal back to audio frequencies. 


#4
Feb908, 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 "nonlinear element" way of doing it.
also, there used to be these things we called Analog Computers that had very high quality opamps 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 2quadrant 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 4quadrant multiply (where you don't care about the sign of either voltage getting multiplied). check out http://www.analog.com/en/subCat/0,28...0%255F,00.html http://www.analog.com/en/subCat/0,28...0%255F,00.html http://www.analog.com/en/subCat/0,28...0%255F,00.html http://www.analog.com/analog_root/st...omputation.pdf 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. 


#5
Feb1008, 01:51 AM

P: 265

f95toli:
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? 


#6
Feb1008, 01:52 AM

P: 265

rbj:
That pdf file was exactly what I wanted to see  thanks. 


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