A Biofuel-Cell-Based Energy Harvester With 86% Peak Efficiency and 0.25-V Minimum Input Voltage Using Source-Adaptive MPPT

Abstract

This article presents an efficient cold-starting energy harvester system, fabricated in 65-nm CMOS. The proposed harvester uses no external electrical components and is compatible with biofuel-cell (BFC) voltage and power ranges. A power-efficient system architecture is proposed to keep the internal circuitry operating at 0.4 V while regulating the output voltage at 1 V using switched-capacitor dc–dc converters and a hysteretic controller. A startup enhancement block is presented to facilitate cold startup with any arbitrary input voltage. A real-time on-chip 2-D maximum power point tracking with source degradation tracing is also implemented to maintain power efficiency maximized over time. The system performs cold startup with a minimum input voltage of 0.39 V and continues its operation if the input voltage degrades to as low as 0.25 V. Peak power efficiency of 86% is achieved at 0.39 V of input voltage and 1.34 $\mu \text{W}$ of output power with 220 nW of average power consumption of the chip. The end-to-end power efficiency is kept above 70% for a wide range of loading powers from 1 to 12 $\mu \text{W}$ . The chip is integrated with a pair of lactate BFC electrodes with 2 mm of diameter on a prototype-printed circuit board (PCB). Integrated operation of the chip with the electrodes and a lactate solution is demonstrated.