Optical encoder with automatic gain circuit

The invention provides for a device and method for automatically setting the gain of an output circuit in an optical encoder. Still further embodiments of optical encoders combine the code wheel misalignment and automatic gain control features. An optical encoder, including: a light emitter configured to emit a collimated beam of light; a code wheel provided with a plurality of apertures. A light detector includes at least first and second photo-detectors positioned along the first direction on a first vertical portion and at least a first automatic gain control photo-detector positioned on a second vertical portion. The light detector faces the light emitter and the code wheel is configured to rotate between the light-emitting element and the light detector such that the collimated light beam is directed substantially in the plane through the apertures onto the first and second vertical portions as the wheel rotates. The first and second photo-detectors generate first and second output signals, and the first automatic gain control photo-detector is configured to generate, in response to the second portion of the collimated beam being incident thereon, a third output signal provided to a circuit configured to receive the third output signal and compare same to a reference voltage using the comparator. The output of the comparator provides is used to set the gain of the automatic gain circuit.