Architecture tradeoffs in high density microstimulators for retinal prosthesis

Electrical stimulation of retinal neurons has been identified as a form of visual prosthesis to restore vision in blind patients affected by Retinitis Pigmentosa (RP) and Age-related Macular Degeneration (AMD) through several studies and experiments. This paper presents the different architectures of microstimulator for high density retinal prosthesis considering both the biomedical and circuit perspectives. The choices for the key aspects of the microstimulator - location of the chip in the eye, electrode configuration, method of stimulation, demultiplexing, stimulation sequence, and communication protocol - are discussed along with the associated tradeoffs for each of them. In addition, a 60-output microstimulator for an implantable retinal prosthesis to be used in future clinical trials, fabricated in 1.2-μm CMOS technology and its measurement results are presented. The chip consists of 60 independently programmable output drivers and a digital controller for managing run-time and configuration data.