A complete 256-electrode retinal prosthesis chip

This paper presents a complete 256-electrode retinal prosthesis chip, which is small and ready for packaging and implantation. It contains 256 separate programmable drivers dedicated to 256 electrodes for flexible stimulation. A 4-wire interface is employed for power and data transmission between the chip and a driving unit. Power and forward data are recovered from a 600 kHz differential signal, while backward data are sent at 100 kbps rate simultaneously. The stimulator possesses many stimulation features, supporting various stimulation strategies. Many safety features are included such as real-time monitoring of voltage compliance and temperature, electrode self-locking in the event of out-of-compliance, and ESD protection circuit at every electrode. The chip is fabricated in a 65 nm CMOS process. The electrode driver pitch is 150 µm, and total chip area is 8 mm2. The chip has been extensively tested and all the requirements have been successfully verified. The measured DC current error for single driver stimulation without electrode shorting is 20 nA. The average power consumption per electrode with typical stimulus pulse parameters and full-scale output current is 129 µW, inclusive of all standby power. The chip overall power efficiency is 70% with 23 mW of power delivered to load.