Integrated Auto-Reconfigurable Power-Supply Network With Multidirectional Energy Transfer for Self-Reliant Energy-Harvesting Applications

This paper presents an integrated, auto-reconfigurable power-supply network to enhance system lifetime and efficiency in self-reliant energy-harvesting applications. Carbon nanotube (CNT) supercapacitors are employed as both energy storage devices and power sources, thereby achieving multidirectional energy exchange. By leveraging advanced semiconductor processes, a low-volume, cost-effective single-inductor multiple-output (SIMO) power management unit (PMU) is developed, which connects all the supercapacitors into an autonomous power-supply network. The PMU enables reversible power flows, shorter power-delivery paths, and effective energy reutilization, which enhances the reliability and flexibility of the system. The use of CNT supercapacitors features small form factor and high energy/power density, making them highly attractive for power-constrained devices. A prototype of the PMU is fabricated with a 0.35-mu m N-well CMOS process, with a chip area of approximately 4.3 mm(2). The PMU interconnects 3-CNT supercapacitors in the power-supply network, and operates from 1.5 to 3 V. The measured peak energy-transfer efficiency is 85.03%. The supercapacitors deliver an energy density of 6.2 Wh/kg, at a high power density of 79 kW/kg and exhibit excellent stability of 98.5% retention, at a current density of 50 A/g.