A tri-mode fully-integrated capacitive voltage multiplier for photovoltaic energy harvesting

In this paper, a tri-mode fully-integrated capacitive voltage multiplier is proposed. The system provides power conversion efficiency over 60% within the loading current ranges from 60 μA to 160 μA. The input voltage (V_in) ranges from 0.45-0.7V to meet the output of photovoltaic cells, and the output voltage (V_out) is set as 1.2V. The proposed tri-mode operation combines doubler mode, tripler mode and boosting mode to cover wide input voltage range. The doubler mode is implemented by utilizing a single-stage charge pump (CP) circuit while the tripler mode is realized by connecting two CP stages in series. The boosting mode enlarges the gate swing of the second CP power stage to further reduce the conduction loss of the power transistors, which allows the system to operate at 0.45-V V_in. The regulation controller consists of the coarse/fine modulators and mode selection circuit. By applying the proposed regulation and reconfigurable techniques, the system is able to switch operating mode automatically as input voltage varies. To achieve low power and low voltage operation, all regulation systems are built by digital circuits. From simulation results, the peak power conversion efficiency of 89% is achieved at 100-μA output current.