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A platform architecture combining energy from solar, thermal, and vibration sources is presented. A dual-path architecture for energy harvesting is employed that has a peak efficiency improvement of 11%-13% over the traditional two-stage approach. The system implemented consists of a reconfigurable multi-input, multi-output switch matrix that combines energy from three distinct energy-harvesting sources-photovoltaic, thermoelectric, and piezoelectric. The system can handle input voltages from 20 mV to 5 V and is capable of extracting maximum power from individual harvesters all at the same time utilizing a single inductor. A proposed time-based power monitor is used for achieving maximum power point tracking for the photovoltaic harvester. This has a peak tracking efficiency of 96%. The peak efficiencies achieved with inductor sharing are 83%, 58%, and 79% for photovoltaic boost, thermoelectric boost, and piezoelectric buck-boost converters, respectively. The switch matrix and the control circuits are implemented on a 0.35-μm CMOS process.
Date of Publication: Sept. 2012