Implantable CMOS neuro-stimulus chip for visual prosthesis

A prototype chip with 2×2 pixels for implanting in blind patients affected by outer retinal degeneration is presented in this paper. This visual prosthesis 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, converting the illumination on the eyes into 3-bit resolution bi-phasic current pulses. On-chip charge cancellation modules are used to discharge each electrode site for tissue safety. The prototype chip is designed and fabricated in 0.18-μm N-well CMOS (complementary metal oxide semiconductor) 1P6M Mix-signal process, with a ±2.5 V dual voltage supply. The functionality of the fabricated chip is demonstrated on anesthetized rabbits. Neural responses in visual cortex are successfully evoked by the neuro-stimulus chip through an on-board trigger interface and flexible electrode.