An 86% Efficiency 12 µW Self-Sustaining PV Energy Harvesting System With Hysteresis Regulation and Time-Domain MPPT for IOT Smart Nodes

This paper presents a fully-integrated μW-level photovoltaic (PV) self-sustaining energy harvesting system proposed for smart nodes of Internet of Things (IOT) networks. A hysteresis regulation is designed to provide a constant 3.3 V output voltage for a host of applications, including poweringsensors, signal processors, and wireless transmitters. Due to the stringent power budget in IOT scenarios, the power consumption of the harvesting system is optimized by multiple system and circuit level techniques. Firstly, the hill-climbing MPPT mechanism reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits.

Secondly, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations. Thirdly, to execute the impedance tuning of MPPT, the capacitor value modulation (CVM) scheme is proposed instead of the conventional frequency modulation scheme, avoiding quiescent power consumption. Utilizing a commercial PV cell of 2.5 cm 2 , the proposed system provides 0-21 μW output power to the IOT smart nodes. Measured results showed that the PV harvesting system achieved both ultra-low power operation capability at 12 μW and a peak self-sustaining efficiency of 86%.