You may refer to Table 3-9 (Serial Input Data Specifications) of
LatticeECP3 Family data sheet.
The minimum and maximum voltage levels of LatticeECP3 SERDES inputs are
defined as input levels (VRX-IN) in LatticeECP3 data sheet. The minimum
input voltage can be as low as 0V. The maximum voltage is the smaller
one of 1.76V and VCCA+0.5V.