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LMK04828BEVM: multiple harmonics problem

Kailyn Chen
Genius 9560 points
Part Number: LMK04828BEVM

Hello，

Our customer used LMK04828EM and find the signal quality is poor and appeared harmonics as following, he didn't used continuous SYSREF.

Could you please help to analyze？

Best regards

Kailyn 

  • 0
    TI__Genius 12560 points

    Hi Kailyn,

    How are they measuring the harmonics of LMK04828EVM? Based on above config setting, they should have fundamental output at 122.88MHz frequency.

    As the output is square wave, there should be harmonics components present at 122.88M*2, 122.88M*3, 122.88M*4, etc... those are not visible in the spectrum.

    I would be suggesting to do the test using spectrum analyzer and see the performance.

    If they are running any specific config, would be great to share, we can validate in our setup.

    Thanks!

    Regards,

    Ajeet Pal

  • 0 in reply to Ajeet Pal
    TI__Genius 9560 points

    Hi Pal,

    Yes, he used the EVM board.  His configuration is as the above TICSpro configuration which I shared.

    So he is wonder why the EVM has such harmonics.

    Best regards

    Kailyn 

  • 0 in reply to Kailyn Chen
    TI__Genius 12560 points

    Hi Kailyn,

    Below is the measured spectrum on the LMK04828EVM with the default configuration. Here, you could see the output without any other spurs/sub-harmonics.

    I am not sure, how they are seeing the spectrum. As mentioned, ask customer to test the clock out using the spectrum analyzer and see the performance.

    Thanks!

    Regards,

    Ajeet Pal