The Implementation of Retinal Functions on CMOS ICs and Their Applications

In this talk, three main topics including the CMOS implementation of neuromorphic chips, focal-plane motion sensors, and implantable retinal chips for visual prostheses are addressed. A CMOS design methodology for implementing CMOS neuromorphic chips which imitate the ON brisk transient ganglion cell (GC) set of rabbits' retinas is presented in the first part. Retina is the most important preprocessor in visual system and comprised of five complex layers with at least 75 types of interacting neurons. The layer topology and model simulation of the retina are presented in figures and videos to probe into the profound retina system. Also the design and measurement results of the prototype retinal chip, which is the first monolithic CMOS chip realizing whole layer functions of the mammalian retina, are shown in Fig. 1. This biological model based neuromorphic chip makes feasible many potential applications of retinal chips on motion sensors, computer vision, retinal prosthesis, and biomedical devices. The design of focal-plane motion sensors is presented in the second part. A computational algorithm and chip architecture based on the modified directionally selective ganglion cell (DSGC) model are proposed. DSGC is a kind of retinal neuron that responses only to the stimulus moving in some specific directions. The biological measurement, the computational model, and the simulation result of the proposed system for motion computation are demonstrated. The prototype with the ability of image sensing and computation of motion direction and speed has been designed and fabricated as shown in Fig. 2. The detail design and results are given in the presentation. The last topic focuses on the implantable retinal chips for visual prostheses. Vision loss is a serious medical issue, where retinal diseases play major roles. Age-related macular degeneration (ARMD) and retinitis pigmentosa (RP) are the most important and difficult retinal disorders. However, there is no effective cure yet.