Programmable gain CMOS photodetector array for a non-diffractive beam optical encoder II

In previous papers presented at EAMTA2011 and EAMTA2012 our group introduced the design of a customized photodetector array for a non-diffractive beam optical encoder implemented in a standard 0.5 μm channel length CMOS process. That design included a single programmable gain system that was multiplexed between all the photodiodes, thus it was not a fully functional design, but a proof of concept. In this work we present a new version of the chip endowed with an independent programmable gain system for each of the eight photodiodes that allows weighting the photocurrent generated by each pixel by a programmable factor between 0 and 63. The output of the chip is the concurrent sum of the eight weighted photocurrents, being in this way an appropriate signal to be used in a real design. In this new version of the chip a problem related to the sensitivity that was present in the previous design is solved. By means of experimental measurements the performance of the chip is studied for light intensities varying over two decades and gain factors varying between 0 and 63.