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PLL Phase Coherence

Bob Haagensen
Intellectual 370 points
Other Parts Discussed in Thread: LMX2582

Does TI have any PLL's in its portfolio which exhibit Phase Coherence at the output? Ie, start at F1, switch to another freq - F2 - , and then return to F1 and find yourself at the same phase position as when you left? And if so, can it be extended to more than 2 frequencies? I know that the recently-announced LMX2582 has an output phase adjustment capability but I don't know if that accomplishes the same thing. This is for an application in the 2.4 GHz ISM band.

thank you

Bob H

  • 0
    TI__Mastermind 28530 points
    I've assigned this question to one of the LMX apps engineers. Please stand by.
    I'm thinking we only have "frequency coherence."
  • 0
    TI__Mastermind 27581 points
    Bob,
    As the PLL is based on phase, it can coherent, but there are three things that can throw a monkey wrench:
    1. PLL R divider. If this is not one, then you can get multiple input phases
    2. VCO divider. This creates multiple phase possibilities.
    3. Fraction that is not zero. This creates multiple possible states.

    SOme devices get zero phase by putting the N divider in the feedback path. On the LMX2582, be aware that although it has phase adjust, it does not have phase sync and the initial phase is typically not deterministic, altough it can be programatically adjusted.

    I am talking about single-output PLLs here and when it works, it works for all frequencies.

    Regards,
    Dean