Modulator circuit. Please, help!!!

Discussion in 'The Projects Forum' started by leilacoco, Feb 11, 2010.

  1. leilacoco

    Thread Starter New Member

    Nov 14, 2009
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    0
    Hello dear friends,

    does anyone knows which modulator circuit can I use to mix/modulate two signals: one low frequency analog signal and another one is pseaudorandom -1/+1 digital signal.
    Analog signal has maximum frequency - 100 Hz,
    digital signal has maximum frequency -300Hz.

    I was trying to use MC 1496, but it only worked for high frequency signals:mad:.

    Your advice would be highly appreciated. Thanks in advance.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Are you trying to invert the polarity of the sine wave in step with the digital signal, i.e. multiply the analog signal by +1 or -1? If so, go to the Analog Devices website and look for a "two quadrant multiplier".

    Or look at the attached circuit.
     
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    Last edited: Feb 11, 2010
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Can you provide us with a schematic of the MC1496 circuit so that we can look at it? The only thing that would limit this device from working at low frequency would be if ac coupling capacitors were used.

    hgmjr
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    You can make a pretty good two quadrant modulator with a pair of analog transmission gates (74HC4066) and an inverting opamp, or perhaps better than the 4066 would be a 2:1 mux such as the SN74cbt3253 or CD4051. Use the digital signal to select the analog signal or the inverted version. Simple.


    Here is an old experiment that used this type of modulator (1 kHz synchronous demodulator) Note that the modulator (acutally a demodualtor in this case; same circuit) uses two op amps and two transmission gates:
    http://cappels.org/dproj/syncdet/syncdet.html
     
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