A SPAD-Based Optical Encoder

This paper reports on a proof-of-concept SPAD-based (Single Photon Avalanche Diode) optical encoder. The work aims at demonstrating the advantages of SPADs over photodiodes, which are typically used in the current optical position measuring systems. In addition to their high sensitivity and high speed, SPADs allow fully digital signal processing, offering a large system flexibility and scalability toward advanced CMOS technologies. Preliminary tests have been carried out using an array of 100 x 100 SPADs, coupled with an optical Gray-coded disk and a laser diode. Binary frame sequences were acquired and processed off-line through a lightweight algorithm to reproduce the disc code. The described algorithm aims at being integrated in the same chip of the sensor to speed up the signal processing chain, thus allowing high rotation speeds to be achieved. Experimental results are reported, together with future work and conclusions.