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 accomplish es both nondestructive output and programmable positive or negative se nsitivity. Despite its simple structure, this VSPD array realizes prog rammable focal plane image processing by employing between-pixel curre nt 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 circu it has been optimized by SPICE simulation. Using a 2-mu m n-MOS proces s 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 i ncorporates 256 x 256 pixels, 16 parallel output ports, and a random a ccess function. The photosensitivity is 0.8 mu A/lx for a 1-ms accumul ation time. We demonstrate image capture in video mode and edge extrac tion mode, and light spot tracing using pattern matching in conjunctio n with the random access function.