Parallel multiplexing--a solution of large scale stimulation needed by the retinal prostheses to maintain the...

Since retinal prosthesis has been able to stimulate a limited number of neurons (around 100) by the 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/mm2. We are far behind that target. The time required by biphasic stimulus, and sequential stimulation by multiplexing technique limits our ability to stimulate a large number of neurons, and maintain the persistence of vision. We have designed a stimulus circuit applying parallel multiplexing technique, which is capable of simultaneous stimulation of a large number of cells. This paper presents an implantable CMOS-based 5x5 array prosthesis to demonstrate that idea. This 5x5 array prosthesis is scalable to a larger array. It uses external clock for its timing making it suitable for any data rate. It has a programmable biphasic width controller (BWC), which can generate monophasic or biphasic current stimulus with or without interphase delay. The chip has been fabricated using 0.5 microm CMOS technology and tested.