specified 250mV typical but I also want to know min and max voltage for lvds
Generally, the min input amplitude sensitivity for an LVDS receiver is 500 mVpp
differential, and it is typically 800 mVpp differential.
The datasheet specification for Input Sensitivity means that AD9518-4 is fine
with 1/2 of that 500 mVpp amplitude. Thus, the specification of 250 mVpp
differential or 125 mVpp per leg.