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LMK61E2EVM: How to canncel the Xo Harmonic spur with the LMK61E2

kai You
Prodigy 10 points
Part Number: LMK61E2EVM

Hi,

I am trying to get the clock signal as much clear as the plot in the user Guide.  There is no big spur at least

But I only can get the clock Phase noise plot as below. All the setting is the default.

It seems that the spur comes from the Harmonic frequency  :   50MHz (XTAL) * 2 (PDF doubler)  / 32 ( Out_DIV) = 3.125MHz

3.125 MHz * 2= 6.25 MHz

3.125 MHz * 4 = 12.5 MHz

Do you have any idea about it ?

  • 0
    TI__Guru* 81400 points

    Hi Kai,

    The plot in the user guide has the spurs taken out. You are right, with 50MHz input and 156.25MHz output, multiples of 6.25MHz spurs are expected. In E5052, you can set it up to display spurs in dBc, this would make the phase noise plot looks much better.