SiLabs’ application note: Output buffer options for Si53X/55X/57X/59X XO/VCXO devices (PDF!)
The Si53x/55x/57x/59x XO/VCXO devices can be ordered with one of four different output buffer types: CMOS, LVPECL, LVDS, or CML. Each output type has its own particular benefits and disadvantages. This document describes each buffer type, proper biasing and termination schemes, and related technical trade-offs.
from Dangerous Prototypes http://ift.tt/1pVrSGu