Reflective Encoders

Broadcom's reflective encoders combine an emitter and a detector in a single surface mount leadless package. When used with a codewheel or linear codestrip, the reflective encoder translates rotary or linear motion into digital outputs. The reflective encoder consists of three major components: a light emitting diode (LED) light source, a detector integrated circuit consisting of photodiodes and lens to focus light beam from the emitter as well as light falling on the detector.

The operation of the reflective encoder is based on the principle of optics where the detector photodiodes sense the absence or presence of light. The rotary/linear motion of an object being monitored is converted to equivalent light pattern via the use of codewheel/codestrip. The reflective area (window) of the codewheel (or codestrip) reflects light back to the photodetector IC, whereas no light is reflected by the non-reflective area (bar). An alternating light and dark patterns corresponding to the window and bar fall on the photodiodes as the codewheel rotates. The moving light pattern is exploited by the reflective encoder’s detector circuitry to produce digital outputs representing the rotation of the codewheel. When the codewheel is coupled to a motor, the reflective encoder outputs are then a direct representation of the motor rotation.