A High-Efficiency Dual-Antenna RF Energy Harvesting System Using Full-Energy Extraction With Improved Input Power Response

This paper presents a dual-antenna energy harvesting (EH) system using full-energy extraction (FEE) to reduce the buffer capacitor requirement and improve the input power response speed. Instead of using large buffer capacitors (in the order of $\mu \text{F}$ ) at the rectifier output, the proposed FEE technique can efficiently harvest the incoming 915MHz radio-frequency (RF) energy using only a 1-nF capacitor per channel, while reducing the operating frequency of the subsequent DC-DC converter for power loss minimization. The two most popular RF rectifiers are investigated to relax the energy extraction degradation due to impedance mismatch. The boost DC-DC converter combines the harvested energy from the dual-inputs through the FEE controller. Fabricated in standard 0.18- $\mu \text{m}$ CMOS and wire-bonded on an FR4 PCB, the dual-antenna EH system with the DC-DC converter operating typically at 6.25kHz demonstrates a measured peak system efficiency of 75.2% at an output power of $22.6~\mu \text{W}$ using only two 1-nF buffer capacitors at 1- $\mu \text{F}$ load. With a significant buffer size reduction than prior art at similar efficiency/power level, a short startup time of ~ 45ms is achieved when the output rises from 0 to 1 V at $15.5~\mu \text{W}$ total rectifier output power, corresponding to 90% startup time reduction over the conventional approach.