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LMX2594EVM: LMX2594 EVM integer boundary spurs

Ricardo Li
Intellectual 1045 points

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

Dears,

Our customer is using LMX2594 EVM, he want to output a 7000.02MHz signal. The TICS pro's config is as following:

While there are spurs signal at a frequency of 30kHz deviated from the central frequency. The customer suspected this is caused by integer boundary spurs. When he using a 120 MHz input signal, and config FPD =120 MHz, there will no spurs signal. 
Is this phenomenon normal?  If you have any comment please let me know.
Regards
Ricardo

  • 0
    TI__Expert 5370 points
    Dear Ricardo,,

    This is an excellent question.

    We call a spur at an offset corresponding to the difference between the integer frequency and actual desired output a integer Boundary spur (IBS). Using the reference multipler and divider, one can change that PFD frequency so the closest integer boundary is further out avoiding very small fraction and IBS.

    The input doubler in this device add very little noise. in fact will improve in band phase noise. The multiplier will add more noise but provide the ability to do clever frequency changes to the PFD for the exact purpose of avoiding IBS.

    Integer boundary spur can be be related also to the reference input (OSCIN) and hence would not be improved with use of that multiplier.

    I hope this helps.

    Regards
  • 0 in reply to Simon Damphousse
    TI__Intellectual 1045 points

    Hi Simon,

    Thank you for your help.

    Regards,

    Ricardo