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LMX2571EVM: The spurious of LMX2571 in frequency switching

user5109674
Prodigy 20 points
Part Number: LMX2571EVM
Other Parts Discussed in Thread: LMX2571, CODELOADER

Hello,

         I want to generate two cycles frequency with LMX2571 EVM, 235MHz and 280MHz. Register values are configured by default, then  alternant switch register R0 to achieve frequency switching in BurstMode of CodeLoader 4. The Switching Period is 30ms, and both frequencies are correct.

         However, there is a lot of spurious near the center frequency. The spectrum of two frequencies is shown in the figures.

Why the spurious frequency is so much.

  • 0
    TI__Guru* 89540 points
    Hi There,

    I think one of the reasons is you have put the spectrum analyzer in Free Run trigger mode while the input is a burst signal (switching every 30ms). Try setup the spectrum analyzer into external trigger mode, you should not see the false spurs.
  • 0 in reply to Noel Fung
    Prodigy 20 points

    Thanks Noel Fung for spending time on reading my post....

           I measured it with a more precise spectrum analyzer, as shown in the figure .the results show that there is a large spurs in the instantaneous of frequency switching.

    1.I don't know if this kind of spurs will have any effect on actual use?

    2.Do I need to take some measures to improve it since this happens are  attributed to  the spectrum trigger mode?