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LMX2595: EVM board performance not matching when using external source

Kannan Sockalingam
Intellectual 1965 points

Part Number: LMX2595

Working with a customer and am having issues getting the LM2595EVM eval board to get good phase noise results when using a clean 10 MHz Wenzel reference.  He has  tried multiple frequencies to no avail. He is able to get much better results using the 100 MHz TI reference pro but still has several spurs. Everything is configured with the default settings. Checked other E2E posts and does not seem to be the same issue as this.

Using 10 MHz Wenzel reference:

 Post

Ti Reference Pro 100 MHz:

  • 0
    TI__Guru** 119950 points

    Hi Kannan,

    The spurs appear below 10kHz, so this is most likely due to power supply or other external means. The board itself does not have anything that will generate these spurs.

  • 0 in reply to Noel Fung
    Prodigy 30 points

    Hi Noel,

    I am using an Agilent linear benchtop power supply and I have tried using an LDO in between with extremely low spectral noise density( this was recommended in a TI app note that I found) and saw near identical results. I have also tried testing with the DUT fully enclosed in a shielded environment. Are you sure its not potentially a setting or feedback loop issue?

  • 0 in reply to David Webster
    TI__Guru** 119950 points

    Hi David,

    If you were using the default software and hardware setting of the EVM, yes, I am sure this issue is caused by external means. We have been selling this EVM for a couples of year, unless there is a manufacturing false, we never see this kind of spurs before.

    Looks to me that the spurs are the harmonics of a 1xx Hz signal, if you can make a plot in spectrum analyzer mode, we should be able to count the spurs easier.