An environmental energy harvesting framework for sensor networks
Proceedings of the 2003 international symposium on Low power electronics and design
Energy Scavenging for Mobile and Wireless Electronics
IEEE Pervasive Computing
Energy-efficient platform designs for real-world wireless sensing applications
ICCAD '05 Proceedings of the 2005 IEEE/ACM International conference on Computer-aided design
Design and power management of energy harvesting embedded systems
Proceedings of the 2006 international symposium on Low power electronics and design
Indoor solar energy harvesting for sensor network router nodes
Microprocessors & Microsystems
Design of a solar-harvesting circuit for batteryless embedded systems
IEEE Transactions on Circuits and Systems Part I: Regular Papers
Design considerations of sub-mW indoor light energy harvesting for wireless sensor systems
ACM Journal on Emerging Technologies in Computing Systems (JETC)
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This paper presents a micro power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched capacitor (SC) voltage doubler circuit with maximum power point tracking (MPPT), and finally stored in a large capacitor. The MPPT fractional open circuit voltage (VOC) technique is implemented by an asynchronous state machine (ASM) that creates and dynamically adjusts the clock frequency of the step-up SC circuit, matching the input impedance of the SC circuit to the maximum power point condition of the PV cells. The ASM has a separate local power supply to make it robust against load variations. In order to reduce the area occupied by the SC circuit, while maintaining an acceptable efficiency value, the SC circuit uses MOSFET capacitors with a charge sharing scheme for the bottom plate parasitic capacitors. The circuit occupies an area of 0.31 mm2 in a 130 nm CMOS technology. The system was designed in order to work under realistic indoor light intensities. Experimental results show that the proposed system, using PV cells with an area of 14 cm2, is capable of starting-up from a 0 V condition, with an irradiance of only 0.32 W/m2. After starting-up, the system requires an irradiance of only 0.18 W/m2 (18 μW/cm2) to remain operating. The ASM circuit can operate correctly using a local power supply voltage of 453 mV, dissipating only 0.085 μW. These values are, to the best of the authors' knowledge, the lowest reported in the literature. The maximum efficiency of the SC converter is 70.3 % for an input power of 48 μW, which is comparable with reported values from circuits operating at similar power levels.