I am trying to get an error out from this ADF4007 board for feedback (and I have a filter in place). For the sake of simplicity, I'm using:
RF in: 2GHz
RefIn: 125 MHz (which goes to 62.5 with the fixed R divider at 1/2)
Ndivider = 32
this is not a closed loop - just observing the error out (Vtune after filtering)
When the two signals are out of phase, I get 0V output. When I change the frequency by a small amount (a few Hz), I get pulsed output that looks like a dispersive error signal, at the rate of the frequency difference.
However, I was expecting a constant voltage output based on the phase difference. Is this the characteristic of PLLs - a pulsed error signal? I have been having trouble finding anything in journals about this - I have to understand it in order to finish the feedback.