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PLL Lock detector

Discussion in 'Embedded' started by bokiteam, Mar 14, 2006.

  1. bokiteam

    bokiteam Guest

    Hi All,

    I have a register that name is "PLL Lock detector"

    I think it is a register representing the PLL locks the clock yet or
    not, am I right?

    and we use PLL to lock frequency, how other things know the PLL lock
    yet or not? detect its variation value?

    Thank you very much!

    bokiteam, Mar 14, 2006
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  2. bokiteam

    shoppa Guest

    What is commonly done is look at the output of a flip-flop phase
    comparator and if you're not in phase "most of the time" (subject to
    threshold), then you're not locked.

    When you're locked, the output of the phase comparator will be
    occasional blips of correction. When you're not in lock, you get the
    beat frequencies of the divided-down VCO with the reference.

    Many PLL chips use an off-chip capacitor to set the lock-detect
    threshold. While the capacitor is important in setting the threshold,
    this is not something that will help you measure phase noise 80dB down
    and 50Hz away from the fundamental :).

    Look at the NE565 or CD4046 datasheets for some info (and especially as
    you have no datasheets on your parts?)

    shoppa, Mar 14, 2006
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  3. bokiteam

    Boki Guest

    I think module provider can't provide enough information, because they
    are not chip designer.

    btw, thanks for your information, I will check it out.
    Boki, Mar 14, 2006
  4. bokiteam

    Ken Taylor Guest

    You need to read that register with something and provide a hardware
    signal if that's what the rest of your circuitry requires.

    Ken Taylor, Mar 14, 2006
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