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Help design analog multiplier to use as AM modulator

Discussion in 'Electronics Homework Help' started by aaaahmed, Mar 18, 2013.

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  1. aaaahmed

    aaaahmed

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    Mar 17, 2013
    hiii there !! plz anyone can help me?? i am trying to design analog multiplier to use as AM modulator for communication system using op-amp with multisim
     
  2. shrtrnd

    shrtrnd

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    Jan 15, 2010
    What's 'multisim'?
     
  3. aaaahmed

    aaaahmed

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    Mar 17, 2013
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Are we talking about audio modulation here?

    Chris
     
  5. aaaahmed

    aaaahmed

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    Mar 17, 2013
    Yes sir I need to get an output which is multiplication of the message signal with (low frequency) by the carrier signal with (high frequency)
    Output= m (t) . c(t)
     

    Attached Files:

    • AM.jpg
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    Last edited by a moderator: Mar 20, 2013
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    That is rather... no, ... it's extremely odd. AM is always impressed on the finals for a very good reason. If you inject it prior to carrier multiplication, which is usually operated class B or C, the audio will be garbage when it gets to the finals. Even if the multipliers were operated class A the audio would still be garbage after the first multiplication.

    Chris
     
  7. aaaahmed

    aaaahmed

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    Mar 17, 2013
    Sorry sir in fact I did not understand your intention
     
    Last edited by a moderator: Mar 20, 2013
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    AM prior to the multipliers or non class A (effective) stages will generate copious levels of spurious signals across the RF spectrum. It will not endear you to your governing communications agency either. In the old days, prior to cable and sat TV, it would have your neighbors gunning for you because missing a segment of the Lone Ranger was unthinkable!

    Chris

    Edit: Oops, I see your in Iraq. You may have to Google the Lone Ranger. ;)
     
    Last edited: Mar 19, 2013
  9. aaaahmed

    aaaahmed

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    Mar 17, 2013
    Thank you sir for your information but still I have to complete my design it is required from me by my supervisor do you have any idea about this design using op-amp??
     
    Last edited by a moderator: Mar 20, 2013
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    We need more information. What is fo? Is it modulated by voice?

    Chris
     
  11. Laplace

    Laplace

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    Apr 4, 2010
    Try googling "Gilbert cell amplitude modulator". It might give you some ideas.
     
  12. aaaahmed

    aaaahmed

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    Mar 17, 2013
    I will use a software for simulation to design a schematic consists of op-amp,,, I try to multiply message signal and carrier I want to get the result and compare it with amplitude modulation source result which already exist in the software I must get approximately the same answer from my designed circuit and the AM source,,,, no sir I will not apply voice I will use a signal of low frequency from a function generator in the software that I use
     
    Last edited by a moderator: Mar 20, 2013
  13. aaaahmed

    aaaahmed

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    Mar 17, 2013
    thank you Laplace but i need to use op-amp not transistors
     
    Last edited by a moderator: Mar 20, 2013
  14. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    Well I can see that we're talking about a different animal here (Balanced Mixer) and not a classic AM envelope and a totally different application than I thought. That said I would be remiss if I didn't comment that this is sounding more like home work with each post from the OP.

    Tread with caution mates. <<< I'm morphing into an Aussie . :D

    Chris
     
  16. duke37

    duke37

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    Jan 9, 2011
    Horrowitz and Hill give a circuit (p98 in my copy) of an operational amplifier with a gain of +1 or -1.
    It is a virtual earth amplifier with the + input conncted either to the input or ground.

    This gives a balanced modulator but frequency response will be limited.
     
  17. Laplace

    Laplace

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    Apr 4, 2010
    If you are limited to the op-amp as your only active element, then the attached technical paper (first 2 pages) may be of interest. It shows how to make an analog multiplier using only op-amps.
     

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