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ADF4371 with HMC1031/ADF4002, 20dB Phase Noise hit at 100Hz Foffset


I have an eval for the ADF4371 and I'm using an HMC1031 eval to lock the 100MHz ref to a precision 10MHz OCXO.  I am generating an 18GHz LO.  As seen here:

The problem here is measured PN at 100Hz offset.  With the on-board crystal reference PN @ 100Hz = -87dBc/Hz.  With HMC1031 PN @ 100Hz = -67dBc/Hz.

Notable design parameters:

- HMC1031 Loop BW set to 10Hz as outlined in the spec sheet page 12.

- 100MHz VCXO, CVHD-950, CMOS output

- The measure slew rate from the HMC1031/CVHD-950 better than on board 100MHz reference.

Thanks in advance!


Added other parts to title
[edited by: aandrews at 4:14 PM (GMT -4) on 24 Sep 2021]