A new power-processing circuit for an ultra-low-power autonomous sensor node based on a piezoelectric generator

This work presents power-processing electronics (PPE) for a piezoelectric generator, when system miniaturisation is an imperative. A new architecture is realised as an ASIC (Application Specific Integrated Circuit) in 3.3 V, 0.35 µm standard CMOS technology. Wireless sensor nodes, biomedical devices, and smart textiles are some of the applications where size is critical. Small size and high level of integration reduce the system cost and mass, thus creating new application areas. Designing a small generator (in MEMS technology, for instance) that will provide enough power, sufficient output voltage, and acceptable efficiency presents a significant challenge. Low generator output voltage (it can be significantly smaller than the rated supply voltage for the chosen CMOS technology), ultra-low generator power (in the microwatt range), and usage of integrated electronic components wherever possible, set hard requirements on the ASIC design. Conventional interface circuits, such as diode bridges, are not applicable in this case. In addition, the piezoelectric generator has a large output capacitance, which significantly affects the architecture of the following interface circuit and seriously deteriorates system performance for low voltages. Moreover, the value of the minimum input voltage required for system power-up is bigger, due to this serial capacitance. The task of PPE is to minimise this voltage, at the same time providing high power extraction efficiency.