An automatically compensated readout channel for rotary encoder systems

This paper presents a readout channel for high-performance rotary encoders. It includes a photodiode, which transduces light pulses into current signals, and the corresponding readout electronics, which produces the digital output related to the angular position information. Digitally programmable calibration is provided to compensate for spreads in the impinging light power. Care was taken to ensure thermal stability and minimize noise contributions of the readout electronics. These features improve the performance of the presently used absolute encoders and reduce the cost of the whole encoder system. Experimental evaluations on integrated prototypes demonstrated the correct operation of the circuit with an optical input power from 0.5 to 4.5 muW at a maximum frequency of 500 kHz.