A CMOS chip with active imaging and stimulation pixels for implantable retinal prosthesis

A prototype chip with 4×4 active pixels for implanting in blind patients affected by outer retinal degeneration is presented in this paper. This visual prosthesis chip consists of the imaging and stimulation pixels array, power recovery unit and data and clock receiver. The chip imitates the degenerated photoreceptor cells, senses the incident light and stimulates the remaining healthy layers of retina or optic nerve. Each pixel integrates photodiode and stimulus pulse generator, which converts the illumination on the eyes into bi-phasic current pulses with 4-bit amplitude resolution and 3-bit frequency resolution. On-Chip charge cancellation modules are used to discharge each electrode site for tissue safety. The power is recovered by on-chip shottky-diodes rectifier and low-dropout regulator through inductive electromagnetic coupling with a 4 MHz carrier. The data and clock receiver receives the modulated outside command data from power carrier and controls the imaging and stimulation pixels array. The prototype chip is designed and fabricated in 0.35-μm N-well CMOS (Complementary Metal Oxide Semiconductor) 2P4M Mix-signal process, with the chip area of 2.5×2.5 mm2.