A Complete and Highly Flexible 256-Electrode Retinal Prosthesis Chip

This paper presents a highly flexible and complete 256-electrode retinal prosthesis chip, which is small and ready for packaging and implantation. The chip contains 256 separate programmable drivers each of which is dedicated to its own electrode for flexible stimulation. The stimulator possesses a wide range of stimulation features, supporting various stimulation strategies. Many safety features are included, such as ESD protection circuit at every electrode, real-time monitoring of voltage compliance and temperature, electrode self-locking in event of out-of-compliance, and electrode shorting after every stimulation pulse. The chip was fabricated in a 65 nm CMOS process. The electrode driver pitch is 150 μm, and total chip area is 8 mm. The chip has been extensively tested and all the requirements have been successfully verified. The measured DC current error for single driver stimulation with electrode shorting applied is 1 nA, which is well below the industrial safety limit of 25 nA.