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This paper presents a fully-integrated µW-level photovoltaic (PV) self-sustaining energy harvesting system proposed for smart nodes of Internet of Things (IOT) networks. A hysteresis regulation is designed to provide a constant 3.3 V output voltage for a host of applications, including powering sensors, signal processors, and wireless transmitters. Due to the stringent power budget in IOT scenarios, the power consumption of the harvesting system is optimized by multiple system and circuit level techniques. Firstly, the hill-climbing MPPT mechanism reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Secondly, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations. Thirdly, to execute the impedance tuning of MPPT, the capacitor value modulation (CVM) scheme is proposed instead of the conventional frequency modulation scheme, avoiding quiescent power consumption. Utilizing a commercial PV cell of 2.5 cm 2 , the proposed system provides 0-21 µW output power to the IOT smart nodes. Measured results showed that the PV harvesting system achieved both ultra-low power operation capability at 12 µW and a peak self-sustaining efficiency of 86%.

This paper presents a novel cost-effective automatic resonance tracking scheme with maximum power transfer (MPT) for piezoelectric transducers (PT). The conventional approaches compensate the PT with complex power factor correction schemes or drive it in resonance using intricate loops with limited operating range. The proposed tracking scheme is based on a band-pass filter (BPF) oscillator, exploiting the PT's intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system, where accurate PT displacement regulation over a wide range of loads is required. An amplitude control for a switching power stage was developed to regulate the output mechanical motion and provide different power levels for the specific surgical functions such as sealing and dissecting. A proportional-integral (PI) compensator was developed to ensure stable operation under various loading conditions. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin.

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