An Adaptive Fully Integrated Wide-Range Power Management Unit With Fractional Charge Pump for Micro-Scale Energy Harvesting Applications

Abstract

This paper presents a fully integrated power management system suited for AC/DC micro-scale energy harvesting applications. The system employs a CMOS rectifier followed by a DC-DC charge pump (CP) and a capless low dropout regulator (LDO) to provide a regulated output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5 V$ </tex-math></inline-formula> . The proposed CP can provide a fractional voltage conversion ratio in a step of 0.25 to support wide AC/DC input range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4-1.5V$ </tex-math></inline-formula> in the DC mode and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.6-1.6V_{peak}$ </tex-math></inline-formula> in the AC mode. The system efficiency is optimized using real-time monitoring of the input current supplied to the CP. The proposed system is reconfigurable, with the aid of a finite state machine, to maximize end-to-end efficiency. This is achieved by adaptively optimizing the number of stages and switching frequency that provides the required output voltage. The proposed system is implemented in 180nm CMOS technology and utilizes a total on-chip flying capacitance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.4nF$ </tex-math></inline-formula> . Measurement results show that for DC operation, the system achieves a peak efficiency of 74% at a total output power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1mW$ </tex-math></inline-formula> . For AC operation, the system is designed with a rectifier peak efficiency of 84.2% and a total end-to-end efficiency of 58.6%.