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Open Access Publications from the University of California

Bioelectronic Circuits and Systems Design for Epi-Retinal and Neural Prostheses

  • Author(s): LO, YI-KAI
  • Advisor(s): Liu, Wentai
  • et al.

Over the past decades, neural prostheses have been developed and used to restore lost functions of individuals in order to improve the quality of human life. However, the functionalities of those commercial prosthetic devices are often limited by its bioelectronics. A well-known example is the FDA-approved 60-channel retinal implant (Argus II). Patient with retinal implant are only allowed to perform simple tasks, such as navigating in a room and reading large character, but 1000+ channel are further required for the patients to do facial recognition or reading, necessitating advanced design for the implant's bioelectronics.

In this dissertation, we present the circuits and systems design of a fully functionally integrated 1024-channel mixed-mode and mixed-voltage system-on-a-chip (SoC) for epi-retinal and neural prostheses. This SoC is designed and fabricated in TSMC 0.18 �m high-voltage 32 V CMOS process and occupies a chip area of 5.7 mm� 6.6 mm. Fully integrated high-efficient power telemetry was implemented to provide multiple supply voltages simultaneously to power the SoC. Data telemetry based on differential phase shift keying (DPSK) with a novel noise reduction scheme supports a data rate of 2 Mb/s at a bit-error-rate of 2�10-7. The 1024-channel stimulator array meets an output compliance voltage of �10 V and provides flexible stimulation waveforms. Using this SoC, a unique retinal implant bench-top test system is set up with real-time visual verification. We have further performed in-vitro experiment conducted in artificial vitreous humor to investigate stimulation waveforms for better visual resolution.

A versatile multi-channel neural stimulator was further designed and implemented based on the SoC. The stimulator has integrated residual charge cancellation function to prevent neural damage, and a unique technique to measure bio-impedance based on large signal analysis. In our in-vivo experiment, a hind-limb paralyzed rat with spinal cord transection and implanted chronic epidural electrodes has been shown to regain stepping and standing abilities using stimulus provided by the SoC. The proposed stimulator has also been shown effective to stimulate segments of both denervated and normal intestine of rats to regain motor function and to induce intestine contraction.

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