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TIDA-01021: LMK04828, LMX2594

vic zap
Intellectual 740 points
Part Number: TIDA-01021
Other Parts Discussed in Thread: LMK04828, LMK00304, LMX2594, LMK61E2

Hi!

I have some questions on TIDA-01021 (Multichannel JESD204B 15-GHz Clocking Reference Design).
In the design you use OSCout output of the LMK04828 buffered with LMK00304 to feed OSCin inputs of the two LMX2594 devices. Why don't you use DCLKoutX outputs of the LMK04828 to directly clock OSCin inputs of the LMX2594? It eliminates the need to use the LMK00304 buffer which adds vague propagation delay and certain noise to reference clocks which are used by LMX2594.

Regards, Vic.

  • 0
    TI__Expert 5120 points
    Vic, hello and thank you for your interest in Texas Instruments and TI Designs. Your query has been forwarded to our Industrial Test & Measurement team in India. As is is already the weekend there, they will respond to your within the next 1-2 business days.

    Best Regards,

    John Fullilove
    Texas Instruments
    TI Designs
  • 0 in reply to JohnFullilove
    Intellectual 740 points
    Thanks a lot, John!

    Best regards, Vic.
  • 0
    TI__Genius 12550 points

    Hi,

    In this design, LMK04828 works in PLL mode to generate FPGA clocks and SYSREFs. Hence, it adds the PLL noise to the DCLKout signals and that is not clean reference signal to LMX2594s for their best performance.

    OSCin signal of LMX2594s are the buffered output of LMK04828 and LMK00304 coming from LMK61E2, those are with constant delay and adds negligible noise.

    TIDA-01021 reference design also has a provision of DCLKout signal to OSCin of LMX2594. This configuration can be implemented when LMK04828 used in distribution mode with high performance external clock input and it doesn't add noise. Here, LMK00304 will be bypass.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    Intellectual 740 points
    Ok, thanks, Ajeet!

    As i've seen, LMK00304 has four differential outputs. Would it be better to buffer LMK61E2 output with LMK00304 first and then provide references from LMK00304 outputs to LMK04828 and LMX2594s, thus excluding LMK04828 from the LMX2594s' reference path?

    Best regards,
    Vic.
  • 0 in reply to vic zap
    TI__Genius 12550 points
    Hi,
    Yes, there is a possibility to place a LMK00304 between LMK04828 & OSCin signal (From LMK61E2 / VCXO / Ext Reference) and provide a reference signals to LMK04828 and LMX2594s.
    But this design has a various options, which doesn't fit the LMK00304 as above:
    1. In dual loop configuration mode of LMK04828, if an external reference wants to lock with on-board VCXO in PLL1, LMK00304 unnecessary comes in between LMK04828 and OSCin signal.
    2. Provided the option for bypass/remove the LMK00304 and distribute the OSCin of LMX2594s in a power division mode using R262/R263/etc.. Not tested yet.

    Thanks!
    Regards,
    Ajeet Pal
  • 0 in reply to Ajeet Pal
    Intellectual 740 points

    Ok, thank you very much, Ajeet, for your answers!

    Best regards,

    Vic.