A novel opto-electronics interface-circuit design for sensing applications

A new and practical opto-electronic sensor interface is presented. It consists of a transmitter and a receiver for sensors measuring optical attenuation. Emphasis is given to commonly-neglected background-noise-interference and dynamic-range-limitation problems. The design of the electronic circuitry allows sensors to operate in manufacturing environments. A modulated laser-diode, together with optical and electrical filtering, reduces the optical noise to less than a measurable level, even in extremely bright “light-infested” surroundings. In addition, a novel approach is introduced which substantially increases the sensor´s dynamic range. The power of the light-source is monitored in a dynamic intensity-control loop designed to perform “floating-point” measurements according to the attenuation in the optical path. The sensor acquires the combined dynamic ranges of the detector and light-source circuits