A 500-nW-to-1-mW Input Power Inductive Boost Converter With MPPT for RF Energy Harvesting System
Gaurav Saini, Laxmeesha Somappa, Maryam Shojaei Baghini
Abstract
This article discusses a novel RF energy-harvesting system for available power as low as 500 nW. The system includes a main RF rectenna (antenna followed by rectifier) for energy harvesting, an auxiliary RF rectenna for power detection, and a boost converter along with its control circuit. For maximum power point tracking (MPPT), a particular reference voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V_{\text {ref}}}$ </tex-math></inline-formula> for a range of received RF power (from −11 to 3 dBm) is used to harvest maximum available power from the main rectenna by regulating its output voltage with the help of the boost converter. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V_{\text {ref}}}$ </tex-math></inline-formula> for MPPT is provided by the auxiliary RF rectenna and the power-detector circuit and depends on the RF power. The complete system is designed, simulated, fabricated, and tested in the 180-nm mixed-mode CMOS technology. Measured results show that the boost converter can track the maximum power point for the input available power ranging from 500 nW to 1 mW. The efficiency of the boost converter is a function of the available input power and the equivalent source resistance of the RF energy harvester. For an equivalent source resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1~\text {k}\Omega }$ </tex-math></inline-formula> , the maximum efficiency of the boost converter is 91.6% at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${165~\mu \text {W}}$ </tex-math></inline-formula> of the available input power. As a potential application, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta \Sigma }$ </tex-math></inline-formula> modulator designed in the 180-nm mixed-mode CMOS technology is powered by the proposed energy-harvesting system. The efficiency of the boost converter is approximately 76.6% while powering the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta \Sigma }$ </tex-math></inline-formula> modulator and 78.5% while powering the dc load at the RF 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">${-7\,\,\text {dBm}}$ </tex-math></inline-formula> .