A peak-to-peak voltage of 0.5V should be sufficient for the referecen clock input signal. However, the peak amplitude shall not be too high, especially if the input is a square wave where there will be more harmonics.
MAX2769C
Production
The MAX2769C is a next-generation Global Navigation Satellite System (GNSS) receiver covering L1/E1, B1, G1 bands for GPS, Galileo, BeiDou, and GLONASS...
Datasheet
MAX2769C on Analog.com
MAX2769B
Production
The MAX2769B is a next-generation Global Navigation Satellite System (GNSS) receiver covering GPS, GLONASS, Galileo, and Compass navigation satellite systems...
Datasheet
MAX2769B on Analog.com
A peak-to-peak voltage of 0.5V should be sufficient for the referecen clock input signal. However, the peak amplitude shall not be too high, especially if the input is a square wave where there will be more harmonics.