Modulator Circuit

Discussion in 'General Electronics Chat' started by robby991, May 31, 2008.

  1. robby991

    Thread Starter Active Member

    Dec 17, 2007
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    Hello I have a question regarding generation of an ASK signal. I saw this simple circuit which generates a ASK signal using a NAND gate and I don't understand how it works. It consists of 2 circuits, one which generates the data signal frequency and the other which generates the carrier frequency, then they are both fed into a 2 input NAND which produces an output ASK signal (specifically OOK). How does this NAND work to generate ASK? I don't understand this at all. Thoughts?? Thanks for your help.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. robby991

    Thread Starter Active Member

    Dec 17, 2007
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    Ohhh I see. So the the logic gate is used to modulate the data signal f(t) and carrier frequency sin(x). So to acheive the ASK modulated carrier signal ASK = f(t)sin(x), an AND gate will be used to perform the multiplication of carrier and data signal, right? Is there any reason why this particular circuit uses NAND gate? I am a little confused on this.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    It only works for the ON/OFF variety of modulation. The carrier is present only when the data is HIGH. Same principle as Morse signaling.
     
  5. robby991

    Thread Starter Active Member

    Dec 17, 2007
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    The AND gate makes sense to me, if the modulating wave (digital signal) is high, and the carrier signal is high, then the and gate would produce a high signal, else a low. Using a NAND gate would be the opposite, so the modulated result wouldn't have teh same shape as the modulating wave. Am I seeing this wrong?
     
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