Examination Committee

Prof Dit Yan YEUNG, CSE/HKUST (Chairperson)
Prof Amine BERMAK, ECE/HKUST (Thesis Supervisor)
Prof Man Kay LAW, Faculty of Science and Technology, University of Macau (Thesis Co-supervisor)
Prof Khaled Nabil SALAMA, Computer, Electrical and Mathematical Science and Engineering Division, King Abdullah University of Science and Technology (External Examiner)
Prof Wing Hung KI, ECE/HKUST
Prof James SHE, ECE/HKUST
Prof Yi-Kuen LEE, MAE/HKUST 

Abstract

Electrical stimulator has been playing an important role in both disclosing secrets of the biological sensory system and recovering functions of various impaired sensory organs, such as ear, eye, and vestibular organ. Yet, improving the stimulation efficiency while ensuring system scalability and safety still remains a challenging research problem that needs to be resolved. In this thesis, we will focus on the design and development of a micro-stimulator system in terms of power efficiency, scalability, control overhead and safety.

To provide a systematic optimization strategy for designing micro-stimulator systems, a comprehensive system model that can evaluate the system behavior under wide input and output dynamic range operations specific to the application requirement is developed. System behaviors imperative to system level optimization, including the parasitic losses throughout the energy flow path, close-loop stability and transient performance are established and analyzed. A verification platform is also developed to validate the proposed model. Measurement results show that the system behavior well match the simulated ones.
 
To improve energy efficiency of existing micro-stimulator designs, an energy efficient multi-channel power-supply modulated micro-stimulator capable of energy recycling is proposed. The stimulation efficiency is enhanced by recycling the charge from electrodes during the cathodic stimulation phase.  A chip prototype fabricated in a standard 0.18-µm BCDLite CMOS process optimized using the proposed model is designed. Measurement results show that the stimulation efficiency is vastly improved over the conventional fixed-voltage supply-based stimulators. Fast reference tracking is achieved under wide stimulation conditions during the inter-phase transition. Improved stimulation safety is also ensured by the reduced heat generation across the current drivers and the intrinsic isolation of the power supply from the electrodes in case of device failure.
 
A digital pulse-skipping PWM quasi-PID (D-PS-PWM-QPID) controller and a global digital controller (GDC) are also proposed. By exploiting a column parallel topology, flexible stimulation with reduced control overhead, global power-supply modulation and real-time tissue-electrode impedance (TEI) monitoring for improved stimulation efficiency and safety can be simultaneously achieved. Validated by a 4-column chip prototype fabricated in a 0.18-µm CMOS process, a power consumption of 18 µW per column is accomplished, demonstrating a highly scalability micro-stimulator system with robust operation under large output power dynamic range and design parameter requirements