About ADF41020

We are ready to design a optical PLL to lock the phase between two lasers. We get a beat signal which is the frequency difference between two lasers from a photodetector.We want to input this 9.2GHz beat signal  to the RFin port of ADF41020 chip.

Quenstion One: Do we need to convert the beat signal to a digital signal by a comparator before inputing it to ADF41020. Or dose  it have a comparator in the ADF41020?

Quenstion Two: We intend to use a signal generated by a function generator as the reference signal. What is the form of the reference signal should  be? Is it a sine wave or a square wave before entrying the ADF41020 chip?

Thanks very much. I'm looking forward to receive your response.