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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.25$</tex-math> </inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$180$</tex-math> </inline-formula> nm 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%.
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