Design of efficient CMOS rectifiers for integrated piezo-MEMS energy-harvesting power management systems

MEMS-based piezoelectric energy harvesters are promising energy sources for future self-powered medical implant devices, low-power wireless sensors, and a wide range of other emerging ultra-low-power applications. However, the small form factors and the low vibration frequencies can lead to very low (in μW range) harvester output power. This makes the design of integrated CMOS rectifiers a challenge, ultimately limiting the overall power efficiency of the entire power management system. This work investigates two different fully integrated rectifier topologies, i.e. voltage doublers and full bridges. Implemented in 0.35-μm, 0.18-μm, and 65-nm CMOS technologies, the two rectifier architectures are designed using active diodes and cross-coupled pairs. These are then evaluated and compared in terms of their power efficiency and voltage efficiency for typical piezoelectric transducers in such ultra-low-power applications which generate voltages between 0.27-1.2 V. Furthermore, analytical expressions for the rectifiers are verified against circuit simulation results, allowing a better understanding of their limitations.