A Reconfigurable Capacitive Power Converter With Capacitance Redistribution for Indoor Light-Powered Batteryless Internet-of-Things Devices

In this article, a reconfigurable capacitive power converter with capacitance redistribution for indoor light-powered batteryless Internet-of-Things (IoT) devices is presented. The proposed converter is capable of redistributing the capacitance among two charge pump stages to efficiently utilize the harvested energy and further powering milliwatt-powered loading circuits occasionally. Moreover, the proposed converter is capable of storing and reusing the harvested energy to cope with the power demand under different operating modes. The first charge pump stage stores the excessive energy produced by a photovoltaic (PV) cell to the storage capacitor using a maximum power point tracking (MPPT) technique under low-output power demand, whereas the second stage provides a regulated 1.5-V output voltage. The variation of the PV input voltage (from 0.45 to 0.9 V) is compensated by employing a converter, whose power stage consists of 16 reconfigurable charge pump submodules with 1.5x and 2x conversion ratios and a digital low-dropout (DLDO) regulator. By implementing the proposed capacitance redistribution, the on-chip capacitance can be reduced by 46.7%. The proposed capacitive power converter is fabricated using a 0.18-μm CMOS process. The measured results show a peak-power conversion efficiency of 92.4%, 65.7%, and 69.5% for 1x, 1.5x, and 2x conversion ratios, respectively.