AnsweredAssumed Answered

ADF4351 spurs

Question asked by zocco on Aug 28, 2016
Latest reply on Sep 6, 2016 by rbrennan


Im trying to learn/understand how this spurs get generated. So maybe someone here can try to explain.

I have ADF4351 with PDF=32MHz (max for frac-n mode). For example at 550.006MHz i get spurs every 4kHz.

In this example i have PFD=32MHz, INT=68, FRAC=3003, MOD=4000, OutDIV=4, channel spacing is 0,002MHz.

At same frequency 550,006, if i set R=2, so PFD=16MHz, INT=137, FRAC=1003, MOD=2000, they dissapear.

Is there any formula, i can calculate how they are generated or predict where i can expect them in whole frequency range with PFD=32MHz or any info on what kind of spurs are there and how are they generated inside of the chip?


Look at attached images. Last image is example at 550.002MHz with PDF=32MHz.

4kHz spurs at 550.006 with PDF=32MHzNo more spurs at 550.006 with PDF reduced to 16MHz, R=2


Similar as above at 550,002 with PDF=32MHz



Best regards,