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LMX2594: LMX2594 Phase Coherence?

LL
Prodigy 190 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMX2491, LMX2492

In a ramped application, will the LMX2594 maintain phase coherence frequency to frequency?

What if two ICs are locked to a common reference, and both ramped manually and simultaneously, will the system maintain phase coherence?

Same question for the LMX2491.

If there is a difference in fractional vs. integer mode with respect to this phase coherent question, please comment as well.

  • 0
    TI__Mastermind 27721 points
    LL


    During the ramping, their phases should track.

    If the devices both start off in integer mode, I would expect them to be the same phase when the ramping stops.

    However, if the devices were in the fractional mode when not ramping, their phase could be randomized the the initial accumulator state "SEED".

    I assume that you are clocking the ramp manually.

    Just out of curiosity, can you share any details of what the need in your application is for this coherent ramping?

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Intellectual 270 points

    Dean,

    Presuming the initial relative phase was randomized, due to one or more devices starting in fractional mode, would the relative phase between the two synthesizers still remain constant (coherent) over the duration of the ramp?

    I'd be interested to know if the same behavior applies to the LMX2492 in fractional mode as well.  For that particular devices the phase accumulator may be reset at the start of each ramp, but now I'm curious to know if there's some additional 'seed' register.  Coherence is necessary for many radar and EW applications.

    Thanks,

    David

  • 0 in reply to David Langan
    TI__Mastermind 27721 points
    David,

    The LMX2594 involves frequency calibration and this could take a different amount of time for the two devices. So if there is any calibration involved, I think it would NOT be phase coherent. Furthermore, there is no trigger pin to guarantee the ramps start at exactly the same time, so again,this seems to be an issue having two coherent ramps with the LMX2594.

    For the LMX2492, there are two undisclosed engineering "SEED" registers, but the datasheet says to program to 0. Also, there is no SYNC pin to synchronize this.

    Regards,
    Dean
  • 0 in reply to Dean Banerjee
    Intellectual 270 points
    Thank you for the response Dean.