Please help About this circuit! -Multiplier?

Discussion in 'General Electronics Chat' started by Zara Engineer, Apr 6, 2015.

  1. Zara Engineer

    Thread Starter Member

    Feb 6, 2015
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    Hello

    I found this circuit in an old book , I've drawn the circuit .

    [​IMG]

    With :
    - F : clock signal 100 Hz
    - M is a DC signal from -5 to +5

    The author said that the result is M*F.

    Please let me know

    thanks in advance
    Zara
     
  2. Zara Engineer

    Thread Starter Member

    Feb 6, 2015
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    sorry this is the image
     
  3. DickCappels

    Moderator

    Aug 21, 2008
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    Please use a more description title next time.

    It is a balanced modulator provided that you switch the non-inverting input to ground with your carrier F. This causes the circuit to switch between inverting and not inverting the signal as a function of the state of F.

    Among other things, the swich can be a transistor if the base drive swings far enough below ground so that the collector-base junction does not become forward biased, with a MOSFET provided the capacitance is not to high, it can be a transmission gate (such 74HC4066) or a microcontroller out pin switched between being high impedance and ground if the signal is only a few hundred millivolts.

    R2 and R3 should be equal.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I have used that circuit as a synchronous detector (also known as a synchronous demodulator). Typically, you set the gain of the opamp to alternate between +1 and -1 as a function of the "carrier", which is a square wave with a 50% duty cycle.
     
  5. Zara Engineer

    Thread Starter Member

    Feb 6, 2015
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    Hi guys
    thanks for help
    and sorry for mysterious title :)
    but until now, i didn't understand by equation how can we have an output equal to F*M ? or F*Vin

    I tried to put per example M = 0 ;
    F = V+ = V-
    that's mean that (0-F)/R2 = (F-Vout) /R3;

    R2 = R3 = R;
    => Vout = 2 * F; ??
    and about you it's F*M=F*0 = 0 ;

    Please let me know what's the equation of output ! and an example please .
    Thanks in advance.
    Zara
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    F is equal to + or -C, where C is a constant, like 1 or 1.345. It is not a true multiplier where C can be varied dynamically. (C cannot be a function of time)
     
  7. Zara Engineer

    Thread Starter Member

    Feb 6, 2015
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    Hello Mike

    Ok let's suppose the F clock is between -1 and +1 .

    how to conclude the equation of the output in function of M and F.
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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  9. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    And I use the analogue in the digital realm for digital synchronous detection.
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Here is how to implement that function using an opamp. The switch shown is usually replaced with a FET. Note that the switch is closed when V(F)>0V; and is open when V(F)<=0V.

    Can you see how the switch reconfigures the opamp so that its gain goes from +1 to -1?

    186s.gif
     
  11. Zara Engineer

    Thread Starter Member

    Feb 6, 2015
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    Hello Mike

    thank you very much for your patience and doing the simulation for me .

    it was very helpful.
     
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