PLL functions as AM modulator

Discussion in 'Homework Help' started by penny07, Apr 24, 2014.

  1. penny07

    Thread Starter New Member

    May 25, 2013
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    Hi,anyone have any idea how to design the PLL(phase-locked loop)to function as AM modulator?
    Thanks:)
     
  2. t06afre

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    Are you trying to make a lock-in amplifier?
     
  3. penny07

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    May 25, 2013
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    erm...is AM modulator not AM demodulator...
     
    Last edited: Apr 24, 2014
  4. alfacliff

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    Dec 13, 2013
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    pll would not be proper for this, pll can do phase and frequencies, but not amplitudes. a pll could be used to generate the carrier for an am signal.
     
  5. Wendy

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    Mar 24, 2008
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    A Phase Locked Loop can be an FM modulator, an FM demodulator, and it can be an integral part of an AM demodulator, where it derives the carrier frequency (with great stability) and is heterodyned with the RF.

    There is no way I know of that it can be used to create the AM sideband (ie, vary the carrier frequency amplitude) to do what you want. This does not mean it is not possible, but PPL usually revolves around frequency synthesis and FM.

    If you come up with the answer to this I would be interested.
     
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  6. WBahn

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    Mar 31, 2012
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    What happens if you take a baseband signal such as the raw data signal and mix it with the carrier frequency coming out of the PLL? Doesn't that just translate the baseband signal to the carrier, thus producing sidebands that are replicas of the baseband signal? Isn't that AM?
     
  7. w2aew

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    Jan 3, 2012
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    In this case, the *mixer* is doing amplitude modulation, not the PLL. The OP asked if a PLL could function as an AM Modulator, which is no.
     
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  8. penny07

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    May 25, 2013
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    So,means that PLL only can be used in angle modulation? If I want to design frequency modulator by using LM567,any reference for the circuit design?
     
  9. penny07

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    May 25, 2013
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    Edit 1

    Is it possible to add certain components/different configuration of PLL to make it act as AM(amplitude modulation)? For example, using PLL to generate the carrier frequency and use other components to mix it up with the modulating signal to produce AM. Sorry for my insistence but my lecturer insisted that we have to do amplitude modulation and we are at our wits end on what to proceed.
     
  10. WBahn

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    Have you discussed your concerns with your lecturer?
     
  11. penny07

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    May 25, 2013
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    This is what my lecturer said:
    PLL can be used as modulator and demodulator but demodulator circuit will be more complex. We have done this design many times and it is common design of amplitude modulation by using PLL. So, there should not be a problem to design AM using PLL.
     
  12. WBahn

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    Was the PLL in the demodulator used to do anything more than provide a constant reference signal?
     
  13. penny07

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    May 25, 2013
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    But I'm doing AM modulator.
     
  14. WBahn

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    The lecturer said that you have done something many times. What is the something that you have done many times and how was the PLL used in that something?
     
  15. penny07

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    May 25, 2013
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    I have no idea on this.I think my lecturer means that she used the PLL as AM modulator in her research.
     
  16. WBahn

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    You said that she told you "we have done this design many times".

    Are you saying that you have no idea what she means by that? Does it really make any sense that she would say something like that to you about an assignment that she's given you if she was talking about what she has done in her research.

    Do you have class notes? Have you been going to class? What does your text have to say on it?
     
  17. w2aew

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    Jan 3, 2012
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    Some phase detector designs used in PLLs are basically mixers, so that piece of it could be used as an amplitude modulator. Of course this isn't universally true, it only applies to a limited set of phase detector designs. Maybe that is what she's referring to.
     
  18. shteii01

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  19. w2aew

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    Jan 3, 2012
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    Of course, *most* people would call that Phase Modulation (PM). But, if the professor is indeed calling AM = Angle Modulation, then we can conclude two things:
    1) Prof hasn't worked in the US where AM = Amplitude Modulation, and angle modulation is called Phase Modulation PM.
    2) If she wants PM, this is EASY with a PLL...
     
  20. vk6zgo

    Active Member

    Jul 21, 2012
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    You could produce a messy sort of AM by feeding an FM signal through a narrow Bandpass filter,but it would still have a lot of FM artifacts.

    AM demodulation with a PLL would be a type of Synchronous detector where the PLL would supply a stable carrier (locked to the incoming one) to a mixer.

    I'm wondering about some sort of phasing system---
    Some early FM modulators used balanced modulators & phase differences to achieve their ends.

    Perhaps the reverse is possible,but I'm only a furry old Tech---it's a bit outside my payscale!:D
     
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