Self-aligning CMOS photodetector sensor for application on an NDB-based optical encoder

In this work, a complementary metal-oxide-semiconductor (CMOS) photodetector specifically designed to be used in a non-diffracting-beam (NDB) optical encoder is introduced. The sensor is aimed to address the critical alignment of the NDB-based optical encoder head and consists of a hexagonal array of photodiodes that can be interconnected among themselves. The photodiodes' interconnection is configured by means of static random access memory (SRAM) cells and transistors that operate as configurable connection switches between each photodiode and three of its neighbor photodiodes. This feature of the photodetector makes it possible to implement a search algorithm in order to find the photodiode where the NDB center impinges and then configure the appropriate detectivity pattern centered on that photodiode. It is shown that the new sensor design remarkably simplifies the alignment of the system.