Abstract
This paper presents a fully-integrated µW-level photovoltaic (PV) self-sustainin g energy harvesting system pro- posed for smart nodes of Intern et of Things (IOT) networks. A hysteresis regulation is designed to provide a constant 3.3 V output voltage for a host of applications, including powering sensors, signal processors, and wireless tr ansmitters. 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 h ill-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-p erformance tradeoff of the hys- teresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achi eves high-performance and yet low-power operations. Thirdly, to execute the impedan ce tuning of MPPT, the capacitor value modulation (CVM) scheme is pro- posed instead of the conventional frequency modulation scheme, avoiding quiescent power consumption. Utilizi n gac o m m e r c i a l 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%.