I am starting to use the ADF4351 to generate a LO around 2.3GHz from a 26MHz clock input.
The loop bandwidth is around 10kHz.
ADIsimPLL give me these total phase noise values for 10k and 100k:
However, it is not what I am measuring (see attached file). At 100kHz, it is pretty good. I can observe a bump at 5kHz from the center frequency. The bump amplitude depends on the charge pump (CP) current value, smaller is the CP current higher is the peak.
I checked the 26MHz that is very clean. I tried to extend the loop bandwidth to 30kHz and the bump amplitude is still the same, just at a different frequency.
There is probably something with the filter that I am doing wrong but cannot figure out what, do you have some track that I should follow?