Monolithic optical position encoder with on-chip photodiodes

A system that combines light sensors and analog and digital parts on the same CMOS chip has been fabricated. The optical and electrical properties of various photodiodes, which are fully compatible with a standard CMOS technology, are discussed. The current comparators use CMOS-compatible lateral bipolar transistors. The optical encoder also comprises a signal processor for code conversion, a serial or parallel output, and a self-test function. A 14-channel circuit which senses light signals at 880 nm with a power of 0.3-3 mW/cm² has been fabricated. Response time is shorter than 1 μs at all illumination levels. This circuit operates in the temperature range -55 to +125°C. Its current consumption is 8 mA at 5 V