Patent ID: 7511260

Claim:
An encoder device comprising: first through fourth photodiodes each having a rhombus shape and a length of X 1 in an X direction, the first through fourth photodiodes being disposed adjacent to each other in the X direction such that a line passing through a pair of opposing vertices of the rhombus shape of each of the first through fourth photodiodes is parallel to an X axis; a slit member that includes light transmitting sections and light shielding sections alternately arranged, and is movable in the X direction, each of the light transmitting sections and the light shielding sections having a length of 2Ã—X 1 in the X direction; and a logic circuit that generates a first detection signal and a second detection signal from output signals of the first through fourth photodiodes that have received lights passing through the light transmitting sections, a phase of the second detection signal being shifted by a Â¼ period of the first detection signal relative to the first detection signal.