An artificial retina chip with current-mode focal plane image processing functions

This paper describes an artificial retina chip consisting of an array of Variable Sensitivity Photo-Detector cells (VSPD's) which accomplishes both nondestructive output and programmable positive or negative sensitivity. Despite its simple structure, this VSPD array realizes programmable focal plane image processing by employing between-pixel current mode calculations, together with a novel addressing method in which filtering is executed by varying the addressing pattern generated by a scanning unit. The n-MOS VSPD pixel which we have designed consists of a pn photodiode and an n-MOS differential amplifier; the VSPD circuit has been optimized by SPICE simulation. Using a 2-mu m n-MOS process gives a pixel size of 35 (H) x 26 (V) mu m(2) with a photodiode fill factor of 25%. The artificial retina chip which has been fabricated incorporates 256 x 256 pixels, 16 parallel output ports, and a random access function. The photosensitivity is 0.8 mu A/lx for a 1-ms accumulation time. We demonstrate image capture in video mode and edge extraction mode, and light spot tracing using pattern matching in conjunction with the random access function.