Patent ID: 7732754

Claim:
An optical encoder, comprising: a light emitter element configured to emit a collimated beam of light; an optical encoder disk having a plurality of apertures disposed therethrough and configured to rotate substantially in a plane and in a first direction, and a light detector comprising at least first and second photodetectors positioned along the first direction on a first vertical portion thereof and at least one reference photodetector positioned on a second vertical portion thereof, the second vertical portion being vertically offset from the first vertical portion; wherein the light detector faces the light emitter, the optical encoder disk is disposed and configured to rotate between the light emitter and the light detector such that the collimated light beam is directed substantially in the plane and shines through the apertures onto the first and second vertical portions of the light detector as the disk rotates, the first and second photodetectors are configured to generate, in response to the collimated beam being incident thereon, first and second output signals about 90 degrees out of phase respecting one another, and the reference photodetector is configured to generate, in response to the collimated beam being incident thereon, a third output signal about 45 degrees out of phase respecting the first output signal and the second output signal, the optical encoder further comprising a circuit configured to receive the third output signal and employ the third output signal to correct at least one of a first amplitude corresponding to the first output signal and a second amplitude corresponding to the second output signal.