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Fastest PLL settling time - ADF4351 on FMCOMMS1

Question asked by omkarpradhan on Apr 5, 2015
Latest reply on Apr 14, 2015 by rbrennan



I'm investigating if I can bring down the settling time of the ADf4351 PLL (on the FMCOMMS1) to the order of a few 10s of nanoseconds when staying within one band.


I'm trying to build an FMCW radar with this radio card.


I believe I can assume the band-select settling time to be a first time cost at the time of set-up. Then I'm trying to sweep the VCO frequency over (for e.g.) any one of the 45 MHz bands.


for exacmple, assume a sweep span of 40 MHz, at a 60nS interval. This means i'd need the VCO to settle within the 60 nS.


The default loop filters on the FMCOMMS1 revC seems to allow me a frequency lock settlign time of about 130 uS (according to ADIsimPLL).


Not sure what I can do to improve drasticaly upon this. The fastest that I have noted being designed by someone in this forum is for about 50 uS, by changing the loop filter component values.


Any and all help is much appreciated.