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Signal Multiplication

  1. Feb 9, 2008 #1
    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. jcsd
  3. Feb 9, 2008 #2
    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.
  4. Feb 9, 2008 #3


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    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.
  5. Feb 9, 2008 #4


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    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



    you can get some pretty good app note and other information like that from Analog Devices. now they do a few different kick-ass DSPs (with warts) but when i was in college, they were purely analog.
  6. Feb 10, 2008 #5
    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?
  7. Feb 10, 2008 #6
    That pdf file was exactly what I wanted to see - thanks.
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