The Internet of Things (IoT) is an emerging trend which is foreseen to bring about the next wave of the semiconductor industry boom. Due to the astronomical number of sensor nodes, battery maintenance should be minimized or eliminated. Energy harvesting is the key enabling technology to extend battery-life for IoT devices, or even make the devices entirely energy autonomous. The thermoelectric generator (TEG) that can convert thermal energy into electrical energy is among the most popular energy harvesting sources. However, the voltage generated by TEGs is typically unsuitable for powering electronic devices, and adding power management circuits to the energy harvesting system becomes the standard practice. However, the voltage and power generated by TEGs can vary in a wide range due to...[ Read more ]

The Internet of Things (IoT) is an emerging trend which is foreseen to bring about the next wave of the semiconductor industry boom. Due to the astronomical number of sensor nodes, battery maintenance should be minimized or eliminated. Energy harvesting is the key enabling technology to extend battery-life for IoT devices, or even make the devices entirely energy autonomous. The thermoelectric generator (TEG) that can convert thermal energy into electrical energy is among the most popular energy harvesting sources. However, the voltage generated by TEGs is typically unsuitable for powering electronic devices, and adding power management circuits to the energy harvesting system becomes the standard practice. However, the voltage and power generated by TEGs can vary in a wide range due to environmental changes. Therefore, highly efficient energy harvesting circuits and systems with wide harvesting range are in great demands.

Firstly, a novel thermoelectric energy harvesting system with a reconfigurable array of TEGs, which requires neither an inductor nor a flying capacitor, is proposed. The proposed architecture can accomplish maximum power point tracking (MPPT) and voltage conversion simultaneously via the reconfiguration of the TEG array, and can demonstrate significantly improved power conversion efficiency over the conventional switching converter and switched-capacitor architectures. Two systematical scaling approaches—powers-of-two scaling and maximum-factor scaling—are presented and analyzed to serve as the design guideline, catering for reconfigurable TEG arrays of different sizes. The 16-node and 12-node versions of the proposed system have been implemented in a standard 0.35-μm CMOS process. Measurement results verify the analysis and confirm that the proposed system can maintain a higher than 87% efficiency over a wide range of input voltage.

Secondly, an inductorless triple-output thermoelectric energy harvesting system based on a reconfigurable TEG array is presented. The TEG array in the proposed system can be dynamically reconfigured to achieve maximum power point tracking (MPPT) and voltage conversion (VC) for three outputs. Two regulated outputs and an energy recycling mechanism that can store excessive energy in the battery and supplement insufficient energy to the load are provided. An optimization method based on Lagrange multipliers is proposed to size the switches in the switch array and the areal cost can be reduced by 43%. To optimize the control overhead, the building blocks in the control stage are designed to operate in four different frequency domains. An adaptive frequency control scheme is applied to the regulation control loop, making the system able to maintain regulation over a wide power range while achieving 14-nA quiescent current. In addition, a fast wake-up response scheme is designed to cater for the requirement of some applications with duty-cycled operation. Experimental results show that a higher than 86% efficiency can be achieved over an input voltage range of 0.15–10.8 V and an output power range of 38 μW–200 mW with a 99% peak efficiency.