An Area Efficient Thermal Energy Harvester with Reconfigurable Capacitor Charge Pump for IoT Applications

Abstract

Renewable energy sources are promising alternatives to a battery. Due to the varying power profile of renewable energy sources, an energy harvester needs the different power management techniques including boosting the small input voltage. The awareness of the demand, this thesis introduces an integrated energy harvester system targeting Internet of Things (IoT) sensor applications such as a wireless temperature sensor. The proposed design extracts energy from a thermal energy generator (TEG), and provides the regulated output voltage.

To ensure the maximum power extraction, the proposed energy harvester includes multiple circuit level techniques. First, the reconfigurable capacitor charge pump distributes on-chip capacitors to required step-up stages. This approach optimizes the silicon area by utilizing 100% on-chip capacitors regardless of a charge pump conversion gain. Second, the design is capable of 3 dimensional Maximum Power Point Tracking (MPPT), matching a source impedance to input impedance of an energy harvest source. Thus, the proposed energy harvester is able to extract power from a small form factor TEG, having low source impedance (1 Ω). With the increased matching range, up to 500 µW is available at the output for IoT applications.

Experimental results show an end-to-end power efficiency of 64% @ 1 V output voltage, and the input impedance matching range of 1 Ω–5 kΩ. The energy harvester was fabricated in 130 nm Complementary Metal-Oxide-Semiconductor (CMOS) standard technology, and occupies 0.835 mm².