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Phase locked loops?

  1. Dec 29, 2013 #1
    what is difference between coherent and non-coherent detection? and what is a PLL? secondly what is meant by 2*pi phase rotation? is it same as 2*pi phase shift? thanks in advance
  2. jcsd
  3. Dec 30, 2013 #2


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    Science Advisor

    PLL. By measuring the difference in phase between an oscillator and a signal carrier, the oscillator can be adjusted to lock onto the phase of the signal. http://en.wikipedia.org/wiki/Phase-locked_loop

    A coherent detector phase locks an oscillator to the carrier of the received signal. It then effectively multiplies the received signal by the oscillator to detect the modulated information. It retains the absolute phase of the modulation.

    A non-coherent detector does not track the signal carrier's phase. One example is an envelope detector for AM.

    Phase shift and phase rotation are effectively the same.
    A 2*Pi radian rotation is a 360° rotation, so it has no net effect.
    Modulation is often described as a “phasor” which is a directional vector. http://en.wikipedia.org/wiki/Phasor
  4. Dec 30, 2013 #3


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    Staff: Mentor

    Please check your PMs.

    Please do some reading on your own before asking overly broad questions here. We expect to see that you have put some effort into answering your questions. You have been given some great resources by Baluncore -- please read through the links, and then ask specific questions about that reading if you still have questions.
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