MIPSIMO: A Multi-Input Piezo-Adaptive Single-Inductor Multi-Output Energy Harvester Achieving Using a Shared Inductor With an Integrated Analog Computer Achieving 95% MPPT Efficiency

Abstract

This paper presents a multi-input piezo-adaptive single-inductor multi-output (MIPSIMO) architecture that harvests energy from up to three inputs while regulating up to three loads plus a battery all in a single power stage. The proposed power management unit performs load domain inductor switching to reduce switching losses by 3x and allows recycling of excess energy back to the battery for decoupled single-stage regulation, all while utilizing an adaptive ON-time PFM control method during battery utilization to free up inductor cycles as much as possible for harvesting. The proposed architecture implements a technique that performs multi-phase piezoelectric harvesting (PEH) charge flipping (CF) using the single shared inductor from the power stage together with four flying capacitors that reduce the required inductor size by 8x while achieving 90% flipping efficiency. In addition, a fully-integrated power-extraction analog computer is employed to enable real-time hill-climbing MPPT compatible with PEH sources. Fabricated in 180nm, the analog computer achieves a MPPT efficiency of 95% and the converter supports power range of 6μW to 60mW, and achieves a peak efficiency of 87%.