| Stimulus amplifier or microstimulator is used in most biomedical implantable prosthesis device, since it establishes the interface between the electrical circuits and the tissue neuron. It is functionally the closest circuit to the tissue neurons. Open-loop system designs of voltage-mode and current-mode stimulus amplifiers had been reported in literatures. However, they have low accuracy on charge amount and charge-balance due to the nonlinear and time-variant electrode and tissue interface load. Power efficiency of current-mode stimulus amplifier is low and variable with different stimulus current and load. In this dissertation, a novel charge-metering stimulus amplifier is proposed for high performance neuron stimulation in the Biomimetic Microelectronic Systems. The charge-metering stimulus amplifier is the first stimulus amplifier with closed-loop control for high charge precision and small charge-imbalance. It is also the first charge-mode stimulus amplifier compared with existing voltage-mode and current-mode stimulus amplifier. A discrete-time charge-metering stimulus amplifier is designed with IBM CMOS 0.18um 7RF process. New circuit techniques like high-voltage isolation, half-clock sampling, and smart integration folding are used in the switched-capacitor circuits design. CMOS low power design techniques are applied in the design flow from system level to transistor level. Charge error of 1% and charge imbalance of 0.5% are proposed in the design. High power efficiency and maximum available stimulus current are achieved. The measured results from a fabricated prototype chip proved its functionality and performance. Further future work on sensor resistor calibration and high-voltage and low-voltage hybrid single chip solution are also discussed at the end of the dissertation. |
