An integrated 256-channel epiretinal prosthesis

This paper reports an integrated 256-channel epiretinal prosthesis integrated circuit (IC). This epiretinal prosthesis system consists of a power telemetry subsystem to deliver 100 mW power, a data telemetry subsystem to transfer 2 Mbps data, digital controllers to decode stimulation patterns, and a 256-channel stimulator to generate user programmable bi-phasic current stimuli. In this study, dual-band telemetry is adopted to achieve both high power efficiency and high data rate. Frequencies of 2 and 22 MHz are chosen for power and data carrier frequencies, respectively. A mixed-mode and multiple-voltage design is applied to the stimulator for withstanding a high-compliance voltage of ± 10 V at the output stage as well as for reducing the area of each pixel. To add flexibility to the stimulator, each pixel has a local digital controller, which enables the stimulator IC to generate 256 parallel stimulations with various pulse widths and amplitudes. The chip is fabricated in TSMC 0.18 μm 32 V CMOS process with 256 area pads constructed above the stimulus current drivers.