| Retinal prostheses have restored light perception to people who have poor or no vision as a consequence of retinal degeneration. However, the function of commercially available retinal prostheses are still confined to tasks of low visual complexity such as reading letters with large font sizes, mainly due to the limited number of electrodes in the implant. To advance the quality of visual perception for retinal implant recipients, a prosthesis with a higher number of electrodes is required.;In this dissertation we will discuss a unique prototyping system for retinal prostheses that has been engineered. The design requirements that are necessitated by the electrode increase are carefully analyzed. To reduce the data bandwidth requirement and increase the stimulation flexibility, a data transmission protocol aimed at thousand-channel prostheses is defined. This protocol supports variable length data packets and different data protection levels to accommodate a wide range of wireless transmission conditions.;Combining new circuits and the research results from our collaborators, two test chips are designed using Taiwan Semiconductor Manufacturing Company (TSMC) 0.18 mum high-voltage CMOS semiconductor technology. A digital controller featuring two-tier architecture, on-chip address generation, flexible scanning patterns, and regional stimulation are designed and implemented in both chips. Two approaches that target increasing the channel number in the space restricted implant are also developed: master-slave mode brings in more channels by adopting several identical chips in the system; output de-multiplexing lets four electrodes share one current driver using time-division multiplexing. Both chips are fabricated and tested.;A unique prototyping system is built for system-level verification. This system includes primary processing, dual-band power and data telemetry, 256-channel stimulator array, and output verification. End-to-end system validation and individual functional block characterization can be achieved with this prototype. In addition to the hardware implementation, custom-built software running on the computers also provides a good platform for testing new ideas before they are realized by the time-consuming IC fabrication process. Real-time visual feedback through the video displayed on the computer screen and the LED array make it easy to monitor and debug the system operation. This system serves as a great tool for bench-top testing and in-vitro experiments, and assists in the development toward the next generation of higher density retinal prostheses. |
