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LMX2594PSEVM: CAN'T ACHIEVE LINEAR PHASE SHIFT AFTER PHASE SYNC

Primoz Smogavec
Prodigy 10 points
Part Number: LMX2594PSEVM
Other Parts Discussed in Thread: LMX2820, LMX2572

Hello,

I am using LMX2594PSEVM together with TicsPro software. I am trying to synhronize the outputs and then perform a 20 linear phase shifts of 18° with one of the synths. The synchronization part works as expected. All 8 DIP switches as turned ON during this stage. After synchronization 4 of the DIP swithces (SYNTH1) are turned OFF. Here MASH_SEED_EN is enabled. At this stage I am trying to perform a phase shift of 18° by writing 200 to MASH_SEED which should corespond to 18°. The phase shifts, but the shift seems to be random. Below i have attahced screenshot of my TicsPro settings. Am i missing something?

Best regards,

Primoz

  • 0
    TI__Mastermind 23791 points

    Hi Primoz, 
    According to DS equation - you should have a 18 degree phase shift at the outputs respective to the input. 
    Given your VCO frequency is below 10 GHz, try making recommendations: 

    Regards, 

    Vicente 

  • 0 in reply to vicente flores prado
    Prodigy 10 points

    Hi Vicente,

    Thank you for the answer. Is there maybe a document that describes these additional constraints? All the recommendations mentioned here are already applied.

    Regards,

    Primož

  • 0 in reply to Primoz Smogavec
    Prodigy 10 points

    Here's an example writing the value of 200 into MASH_SEED 20 times. The anticipated outcome is a series of 18-degree shifts, totaling 360 degrees. However, this is what i get:

    www.youtube.com/watch

  • 0 in reply to Primoz Smogavec
    TI__Guru* 98160 points

    Hi Primoz,

    As specified in the datasheet, there is limitation in phase adjustment when PHASE_SYNC is enabled and VCO frequency is below 10GHz. We don't have a solution to this limitation. FYI, you can try, make vco=12GHz and chdiv=24. This is not a valid configuration because chdiv should not be greater than 8 when vco is greater than 11.5GHz. This configuration still work on my board and I can get 18deg phase change consistently.

    If you need 500Mhz output, phase sync and consistent phase adjustment, you can use LMX2572 (low power series) or LMX2820 (high performance series).