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LMX2594: VCO_PHASE_SYNC Issue

Doug Leonard
Prodigy 40 points
Part Number: LMX2594


Through testing with the LMX2594 EVM, I have encountered undesired behavior when VCO_PHASE_SYNC is enabled without CHDIV_DIV2.  In my setup I am attempting to generate 4.5 GHz with a 10 MHz reference, 10 MHz Fpd, 9 GHz VCO and the channel divider set to 2.  Because the channel divider is set to 2, TICS Pro is recommending that I disable CHDIV_DIV2 to save on power and improve far out spurs.  However, when I uncheck CHDIV_DIV2, the output shifts from 4.5 GHz to 7.475 GHz.  I have not been able to find any additional notes on CHDIV_DIV2 other than it enables the driver buffer when the channel divider is greater than 2.  Is this expected?  If so, I would recommend TICS Pro be updated to verify this requirement. 

Doug

  • 0
    TI__Mastermind 28021 points
    Doug,
    You may have an older version of TICSPro as I think that CHDIV_DIV2 has been renamed to SEG1_EN.

    In the case of SYNC, although you might be choosing to see just divide by 2, the SYNC feature uses divide by 4 in the feedback path. I have updated the TICSPro to reflect this.

    The divider has a divide by 2, followed by a divide by 2/3, followed by more divide.

    In all cases, the first divide by 2 is there. The second divide by 2/3 is used always for SYNC (unless both outputs are set to "VCO").

    Regards,
    Dean