ADF4155 reference input

I am using a ADF4155 synthesizer. For the reference I have a crystal oscillator with a CMOS 3.3 V output.

Is it correct to connect (ac coupled) directly the oscillator to REFIN+, in single-ended ? Do I need a filter ?

Is it good in term of phase noise, spurious, etc. ?

Would it be better to add a transformer and then go differential (ac coupled) to REFIN+, REFIN- ?