High Resolution Implantable Microsystem and Probe Design for Retinal Prosthesis

By a retinal prosthesis, the researchers have been able to stimulate a limited number of neurons (around 100) by biphasic current stimulus to reproduce an image spatially by multiplexing technique. For functional restoration of sight (visual acuity 20/80), we are to stimulate at least 2500 neurons/mm(2). We are far behind that target. The time required by biphasic current stimulus, the sequential stimulation by multiplexing technique, and the conventional probes used for stimulation limits our ability to stimulate large number of neurons and maintains the persistence of vision. To address this problem, we have designed high resolution donut probes and used them in designing neural implant chip (NIC) applying parallel multiplexing technique, which helped us stimulate large number of neurons. This paper presents the design of a donut probe and an implantable CMOS-based 5x5 array NIC to demonstrate that idea. This 5x5 array NIC is scalable to any larger array. It uses external clock, which makes it suitable for any data rate. The programmable biphasic width controller (BWC) used in this design is capable of generating various kinds of stimulus for stimulation. NIC doesn’t need address to route the pixels, which reduces the data transmission overhead. 0.5 µm CMOS technology is used to fabricate NIC with donut probes. Test results verify our technique of increasing the resolution.