Fully autonomous interface circuit for thermoelectric energy harvesting in wearable and IoT applications

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2018-9
Hamed, Osouli Tabrizi
IoT and wearable electronics are building blocks of the current and future monitoring technologies with numerous applications such as environmental monitoring, precision agriculture, healthcare, transportation and logistics, and smart buildings. Powering the IoT smart nodes is costly due to the existence of billions of these nodes in the technology roadmaps, and is not environmental friendly due to the use of chemical batteries with toxic substances. Eliminating batteries is therefore highly desirable. Fully integrated solutions with sufficient output power capacity for batteryless IoT applications are rarely targeted in the literature. In this thesis, a novel fully autonomous interface circuit for energy harvesting from thermoelectric devices is introduced, which provides considerably increased output power with maximum power point tracking capability at 1 V regulated voltage level. The circuit is composed of a DC-DC converter based on charge pump and LC-tank oscillator with a digital MPPT block, and an LDO regulator. A novel MPPT algorithm is proposed that refrains from disconnecting the circuit form the TEG, and is compatible with varying input and load conditions. Based on the measurement results, the circuit start-up voltage is as low as 170 mV. The output power attains 500 µW, which is the state of the art in the literature for a fully integrated design, and thus meets the real time demand of IoT nodes for sensing, signal processing and wireless data transmission in duty cycle mode and some GHz range. The peak efficiency based on post-layout simulations is 36%, which reduces to 20% due to fabrication mismatches. The discrepancies between simulations and measurements are fully characterized as part of the research, and are modeled to enable design improvements in the future. The MPPT algorithm reaches up to 98% accuracy when the internal resistance of the thermoelectric generator is between 30 Ω to 100 Ω, which is a typical range for a number of tiny TEGs in series.

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Citation Formats
O. T. Hamed, “Fully autonomous interface circuit for thermoelectric energy harvesting in wearable and IoT applications,” M.S. - Master of Science, Middle East Technical University, 2018.