Avago Optical Encoders Boast Small Size, High Resolution

The AEDR 8400 series are the industry’s smallest reflective incremental optical encoders, according to Avago Technologies. The encoders combine this extremely small size—3.00 mm by 3.28 mm by 1.262 mm high—with a resolution of 254 lines per inch (LPI). The device features a count frequency of up to 15 kHz and an operating temperature range of -20 to +85 degrees C. It operates from a single 2.8-V (nominal) supply, drawing 12 mA (including 6 mA LED current), typical. The AEDR-8400’s lead-free packaging complies with the European Union’s directive for Restriction of Hazardous Substances (RoHS).

The encoders consist of an LED light source, a special photodetector IC with integrated electronics, and integrated optics. They can be used with a reflective code wheel to sense rotary position and velocity, or with a linear code strip to sense linear position and velocity. The devices provide two-channel digital outputs in quadrature, which provides both count and direction information. They are insensitive to axial play and maintain performance and accuracy over a wide variation in the gap between sensor and code wheel or strip.

The reflective optical encoders offer higher resolution than magnetic encoders, which typically are limited to approximately 150 LPI raw resolution. In motor control applications a lower resolution can cause torque ripple that increases motor vibration. Magnetic sensors also generate magnetic fields, which may call for magnetic shielding to prevent interference with nearby components.