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LMX2594: phase noise measurement using LMX2594EVM evaluation board

Sam Lo
Prodigy 20 points

Part Number: LMX2594
Other Parts Discussed in Thread: PLLATINUMSIM-SW

Hi all,

Would you be able to help me to understand my phase noise measurement results done using the LMX2594EVM evaluation board? The first figure below shows my phase noise measurement using an external single ended 10 MHz TCXO reference (should be high quality), which is divided to 1 MHz phase detector frequency. The evaluation board is configured to output at 9.8 GHz. What could be causing the significant difference between the values I can find in the datasheet and the values I am measuring? The second figure shows the settings I used in the evaluation software.

The third figure presents the results I got using the on-board 100 MHz reference oscillator doubled to 200 MHz phase detector frequency. The datasheet and my measurement agree a bit better, but there is still a large difference that starts to grow below 100 kHz. Again, what could cause the large difference between my measurement and the values from datasheet?

You can find the equipment I used in the measurements listed in the table under the figures.

Best regards.

  • 0
    TI__Mastermind 28031 points

    Sam,

    This is exactly what I would expect.

    In your case, the big change is that you have reduced the phase detector frequency from 100 MHz to 1 MHz.  This increases the PLL_N value by a factor of 100, which reduces the loop bandwidth.  This is the main effect that you are seeing.   Our PLLatinum Sim tool (ti.com/PLLATINUMSIM-SW) tool can model this effect.

    Now if you compare the on-board XO to the datasheet plot, the difference is that the datasheet plot was done with a 100 MHz Wenzel oscillator, which is better performance  than the XO that comes on this board.

    Regards,
    Dean

  • 0 in reply to Dean Banerjee
    Prodigy 20 points

    Hi Dan,

    thanks for your help. I thought my results could be something to expect, but I wanted to confirm with you. As a side note, if you have time, could you recommend literature where I could find information for example on this loop bandwidth reduction effect?

    Regards,

    Sampo