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LMX2592EVM: Phase Noise Measurement

ikon
Genius 5355 points
Part Number: LMX2592EVM
Other Parts Discussed in Thread: LMX2594, LMX2592

Hi Support,

Customer have tested LMX2594 chip using LMX2592 EVB with on board 100MHz oscillator and loop filter  values are as per datasheet.

Below are the phase noise measurement at 14GHz . 

At 10KHz -94dBc/Hz

At 100KHz -97dBc/Hz.

Customer would like to use this chip if they can achieve results similar to datasheet which is -106dBc/Hz at 100KHz at 14GHz.

They have looked at the proposed clock sources but  those also have phase noise at 100KHz is -144dBC/Hz which turns to similar performance of  -97dBc/Hz at 14GHz.

Please help to advise the best solution.

Thanks.

  • 0
    TI__Expert 8505 points

    Hi Ikon,

    This is because of the 100MHz oscillator. To find out the contribution of the noise of the oscillator you have to scale it to the output frequency used.

    So since you are running at 14GHz, the scaled noise for example of -144dBC/Hz @ 100kHz offset, will be -144 + 20*log(14000M / 100M) = -144 + 41.5 = -102.5 dBC/Hz. Basically the input reference noise is the dominant noise source instead of the the LMX2594's PLL phase noise.

    For a visual explanation, see the attached slides showing the difference of using that 100MHz on board XO versus a very low noise 100MHz Wenzel Crystal (it has -156dBC/Hz @ 100kHz offset), to see what the input reference noise can do.

    6403.Input reference impact on phase noise.pptx

    Regards,

    Brian Wang