A Highly Efficient Reconfigurable Charge Pump Energy Harvester With Wide Harvesting Range and Two-Dimensional MPPT for Internet of Things

Abstract

A monolithic microwatt-level charge pump energy harvester is proposed for smart nodes of Internet of Things (IOT) networks. Due to the variation of the available voltage and power in IOT scenarios, the charge pump was optimized by the proposed architecture and circuit level innovations. First, a reconfigurable charge pump is introduced to provide the hybrid conversion ratios (CRs) as $1\frac {1}{3} \times$ up to $8 \times$ for minimizing the charge redistribution loss. Second, the reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional (2-D) MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened. Third, the constant-on-time (COT) scheme from the regulation part was reused with the proposed MPPT arbiter as a sensing approach, which eliminates the conventional power hungry current sensor. The proposed energy harvester is capable of harvesting various energy sources, such as a photovoltaic (PV) cell and a thermoelectric generator (TEG), with a wide input range from 0.45 to 3 V and a regulated 3.3 V output voltage for the IOT smart nodes. Measured results showed that the harvester achieved a flattened and improved PCE as high as 89% for ultra-low power operation capability below $50\,\upmu{\text {W}}$ .