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LMK04806: LMK04806 phase noise degradation

JH Shin
Mastermind 7115 points
Part Number: LMK04806

Hello,

My customer used the LMK04806 as high speed data converter clock gernerator.

They has an issue of the phase noise degradation of the  output clock 491.52MHz as shown below.

Please advise on the cause of the phase noise degradation and how to solve it.

Thank you.

JH

  • 0
    TI__Mastermind 29010 points

    JH,

    Can you please identify what, on this plot, constitutes the customer's claim of phase noise degradation?

    Do you have any other information from the customer, such as a frequency plan, register settings, schematic?

    Regards,

    Derek Payne

  • 0 in reply to Derek Payne
    Mastermind 7115 points

    Hello Derek,

    Is the performance of 491.52MHz normal in the output clock plot of LMK04806?

    I've received comments from another thread that the output clock phase noise could be an issue.

    Please refer to the link below.

    https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1024388/ads54j42-ads54j42-snr-performance-degradation

    Regards,

    JH

  • 0 in reply to JH Shin
    TI__Mastermind 29010 points

    Hi JH,

    Thanks for the context.

    It is difficult to assess phase noise performance using a spectrum analyzer, because of the variation in measured signal floor caused by setting to different resolution bandwidths and number of sample points. Ideally we would use something like a phase noise analyzer to measure the precise phase noise across the band of interest. I also know that some signal and spectrum analyzers have a phase noise measurement mode, though usually the noise floor is outclassed by other dedicated phase noise measurement systems.

    If the customer does not have a way to measure phase noise directly, they may want to try simulating the expected phase noise performance using PLLatinum Sim software. They can import their reference oscillator, PLL, and loop filter settings to check the phase noise contribution of each element of their system.

    If you can provide me with the customer's oscillator datasheet (assuming it has information about phase noise performance at several offsets), as well as the loop filter values being used for LMK04806, I could also help generate the PLLatinum Sim file. This may reveal more about where the customer's phase noise is originating. You can ask Rob Reeder to loop me in to the discussion.

    For now since it seems this conversation is headed to email, I'll mark the thread as resolved.

    Regards,

    Derek Payne