An Integrated Concurrent Multiple-Input Self-Startup Energy Harvesting Capacitive-Based DC Adder Combiner

This paper introduces a switched-capacitor dc combiner suitable for energy harvesting applications. Since the dc voltage is small, addition of the voltages from different sources can boost the final output voltage with self-startup capability. This approach is valid for any number of dc voltage sources. To prove the energy harvesting principle, three sources are selected. The design of the three-input dc combiner, with no closed-loop controller, is fabricated in 0.13-μm CMOS technology and the chip area is 1.5 × 1.5 mm
²
. With integrated tunable thyristor-based differential oscillators, the chip can combine power from all three inputs. Manual frequency modulation is used to deliver the maximum power to the load. The system has proven to be functional even if one or two of the sources is/are weak or not available. Finally, for indoor conditions, the power from three different solar cells is combined where 70 μW is harvested with an open-circuit voltage of 1.4 V and the short-circuit current of 160 μA.