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LMX2594EVM: Clock & timing forum

user1536466
Prodigy 10 points
Part Number: LMX2594EVM 
It is evaluated by LMX2594EVM + Reference PRO. 
Spurious occurs when in SYNC mode.
Please tell me what to do.

LMX2594EVM_Sync MODE.pdf
  • 0
    TI__Guru** 108480 points

    Hi There,

    without phase sync, the fractional spurs frequencies are multiple of 2MHz, they are almost eliminated by the MASH and loop filter. (from your plot, we can see very small spurs at 2MHz and 4MHz offset.)

    With phase sync, the includeddivide changes the spurs frequencies to multiple of 500kHz.and 1MHz. Please try if these spurs can be eliminated if you use PLL_DEN = 1000001. 

  • 0
    Prodigy 10 points

    Dear Fung,
    Spurious is inside. The frequency also cannot be set to 1877MHz.

    LMX2594EVM_Sync MODE_0625.pdf

    Best regards,

  • 0 in reply to user1536466
    TI__Guru** 108480 points

    Hi There,

    All right, the new PLL_DEN value randomized the spurs energy and as a result degrade phase noise, this is expected but the result in this case is not ideal. Let's try use a different MASH ORDER and/or adjust the PFD_DLY_SEL to see if we can improve the phase noise. I don't have a specific combination of PLL_DEN/MASH ORDER/PFD_DLY_SEL in mind, the optimum combination have to be figured out by trial-and-error.