The design and the realisation of a photodiode array to be used for decoding the code wheel of an 13 bits absolute rotary encoder is reported. ODAE, contains two photodiode arrays placed orthogonal to each other, readout and control electronics as well as a serial interface for calibration. light generated by a high performance optical emitter pass through a glass wheel on which the digital code, representing the position, is impressed. ODAE is placed beyond the wheel and converts the dark and bright pattern into a digital output. The chip has been fabricated in a 1.2um CMOS process and measured 9170um x 3440u
