Abstract: A method and arrangement for resolution enhancement of a coordinate input device. The method includes the steps of receiving a predetermined number of light beams, which are generated from a light source and passed through a rotating grating disc, by a light detector; detecting the intensity of the light beams by the light detector so as to receive a continuous response voltage signal; converting the continues response voltage signal to a digital signal; and distinguishing the digital signal as at least three different detecting modes by a plurality of predetermined critical values for enhancing the resolution of the coordinate input device.