A 12-μW to 1.1-mW AIM Piezoelectric Energy Harvester for Time-Varying Vibrations With 450-nA

Continuing advancements in low power VLSI systems have enabled the use of self-powered wireless sensor nodes (WSNs) for many industrial applications. To alleviate WSN battery maintenance requirements, piezoelectric devices are implemented to harvest vibration energy. However, significant challenges remain unresolved with regard to harvesting from time-varying vibrations in environments where harvestable energy is unpredictable. This paper presents a new integrated piezoelectric energy harvesting system. An adaptive impedance matching maximum power point tracking technique is proposed to improve harvesting efficiency. An adaptive on-time dc-dc controller with pulse skipping modulation is also employed. To retain reasonable efficiency in such low power applications, the controller is designed with ultralow power analog circuits and zero bias current dynamic circuits, with a total quiescent current of only 450 nA. The design is fabricated and verified on a 0.25-μm CMOS process. It is capable of harvesting time-varying piezoelectric energy ranging of 12 μW to 1.1 mW. In comparison with quasi-resistive impedance matching, a harvesting improvement of more than two times is achieved. Thanks to the low power design effort, it achieves greater than 70% efficiency from 80 μW to 1.1 mW.