A Self-Sustaining Integrated CMOS Regulator for Solar and HF RFID Energy Harvesting Systems

This paper presents a self-sustaining integrated regulator for ultralow power two-input energy harvesting systems. The energy sources include photovoltaic panels and high frequency radio-frequency identification tags. An input-powered charge pump utilizing dynamic charge transfer switches with tunable voltages at the bottom of the pumping capacitors is proposed. No external pulse signal is required. An output-powered digitally controlled dc-dc switching converter with a low-complexity oversampling analog-to-digital converter is also proposed to analyze the error signal between the dc-dc switching converter output and the reference voltage. In order to avoid limit-cycle oscillation, a digital sigma-delta modulator is adopted to increase the equivalent resolution of the digital pulsewidth modulator. The system is completely implemented and fully integrated in a standard 0.18-μm CMOS process with a die area of 2.1 mm
²
. The system output voltage is successfully regulated at 1 V and the measured maximum end-to-end conversion efficiency is ~57%, when the loading current is 65 μA.