Thermoelectric Energy Harvesting Interface Circuit With Capacitive Bootstrapping Technique for Energy-Efficient IoT Devices

This paper presents a low-input-voltage (100 mV), low-output-voltage (500–600 mV) thermoelectric energy harvesting interface circuit for near-threshold energy-efficient Internet-of-Things (IoT) devices. The capacitive bootstrapping technique is used to generate a positive and negative bias pair for alleviating the significant conduction losses of power MOSFETs in a near-threshold operation. Internal bias voltages are automatically boosted to different levels as per the loading conditions to extend the output power range. The deployment of constant on-time digital pulse skip modulation with digital zero current detection (ZCD) achieves an ultralight load operation, and precluding a reverse current. The digital ZCD is capable of dynamically adjusting the off-time ( ${T}_{\mathrm {OFF}}$ ) of the power transistors, which vary according to the input and output voltage levels. The proposed step-up dc-dc power converter implemented using a 180 nm CMOS technology demonstrates a maximum conversion efficiency of 76.4% over a $1~{\mu }\text{W}$ – $500~{\mu }\text{W}$ load range, significantly evaluating the feasibility of the near-threshold interface circuit architecture for energy-efficient IoT devices.