A 0.8-V 4096-Pixel CMOS Sense-and-Stimulus Imager for Retinal Prosthesis

This paper presents a 0.8-V CMOS imager with 4096 pixels and an integrated sense-and-stimulus (SAS) function for retinal prosthesis. The pixel consists of a photon-to-biphasic-current converter (sense) and a balanced current-mode stimulator (stimulus) to achieve a highly integrated and low-power solution for high-resolution vision recovery. Three operation modes, that is, test mode, programming (PG) mode, and implanted (IP) mode, have been implemented for various purposes. In test mode, the internal signals are multiplexed out serially for chip verification. In PG mode, the output pattern of the current stimulator array is programmable by external addresses for patterned electrical stimulus experiments of retina. In IP mode, the chip is fully functional with a minimized number of input/output as four optimized for in vivo operation. A prototype chip with a 64 × 64 SAS-pixel array, a 30 × 30 × μm² pixel size, and a 33.3% fill factor was designed and fabricated in Taiwan Semiconductor Manufacturing Company (TSMC) 0.18- μm CMOS image sensor technology. The proposed chip was operational under a wide supply range from 0.8 to 1.8 V. The measured conversion gains and maximal biphasic current amplitudes are 144 nA/lx (1.8 V), 21 nA/lx (0.8 V), ± 50 & μA (1.8 V), and ±10 & μA (0.8 V), respectively. The proposed SAS CMOS imager presents an integrated SAS solution for artificial retina with the highest array resolution of 4096 pixels and a low power consumption of 0.18 mW at 12.5 ft/s and a 0.8-V supply under 300-lx illumination.