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ADF4350  phase noise problem

Question asked by zxl1234567890 on Apr 8, 2013
Latest reply on May 7, 2013 by icollins

hi all

    Can anyone help me to explain why different PFD can cause the different result ?

    As the attached two files show,the phase noise @10kHz in the 8M.jpg is good (about -90dBc/Hz) , while its poor in the 8.4M.jpg (only about -70dBc/Hz).

   The output frequency bothe is 2690MHz.

  The PFD is 8MHz in the 8M.jpg and channel space is 100KHz (because there‘s a 50kHz spur been showed , so this spur is normal.)

   The PFD is 8.4MHz in the 8.4M.jpg and channel space is 400kHz. (but there's a high noise at about 10kHz , this is abnormal.)

    Other registers for the two PFD freq are the same , expect the R0 (due to freq must be the same).