A Sub-μA Quiescent Current Power Management System with SAR-based Adaptive MPPT for Piezoelectric Energy Harvesting

Abstract

We report on the design of a low quiescent current, high-efficiency power management circuit for piezoelectric (PZE) energy harvesting using a 180 nm CMOS process. The system includes: (i) an active bias-flip rectifier to convert the AC output of the PZE energy harvester to DC, (ii) an inductor-based DC-DC boost converter with maximum power point tracking (MPPT) to boost the rectified voltage to a higher pre-defined value, (iii) a constant current battery charging module for charging a small Li-ion rechargeable battery, which is used as the energy storage element. The MPPT is implemented by a successive approximation (SAR)-controlled digital to analog converter (DAC), which is used as the current reference for the constant current battery charging module. This proposed MPPT method can adaptively adjust to different PZE harvesters (size, output voltage). The active bias-flip rectifier has 99.2% power conversion efficiency (PCE) and can boost the total amount of energy harvested from conventional rectifiers by more than 4 times. The step-up converter has 90.6% PCE, and the charging module can output 0-12.8 μA under control of the 5-bit current DAC.