A Fully Integrated Maximum Power Tracking Combiner for Energy Harvesting IoT Applications

Modern Internet-of-Things (IoT) devices rely on energy harvesting to extend their battery life and create maintenance-free applications. However, energy from ambient sources is intermittent and unpredictable, which compromises the reliability of any system. Harvesting from multiple sources allows the collection of higher amounts of power, producing robust operation even in the presence of ambient variations. This paper describes the design of a fully integrated system that combines the energy delivered by four inputs. The proposed architecture applies a smart harvesting strategy based on the available power from the transducers. The two inputs with the most power are automatically selected and combined, while maximum power tracking is performed. If the other two sources still show some usable power, a two-way energy storage scheme allows their use to sustain the circuit's operation. The system is fabricated in a 0.13- $\mu$ m complementary metal–oxide–semiconductor (CMOS) technology. Experimental results demonstrate a peak tracking efficiency of 96 $\%$ . The power conversion efficiency has a maximum of 87.2 $\%$ at 198 $\mu$ W of output power and 72 $\%$ at 981 $\mu$ W.