A 6.78-MHz Wireless Power Transfer System With Inherent Wireless Phase Shift Control Without Feedback Data Sensing Coil

Abstract

This article presents a 6.78-MHz wireless power transfer (WPT) system with a differential class-D power amplifier (PA) for the transmitter (TX) and a delay-tuned rectifier for the receiver (RX). Besides the RX local voltage regulation, we propose a fully integrated TX global power regulation with wireless phase shift control without any extra off-chip components. Furthermore, the proposed system eliminates the feedback data-sensing coil used in prior arts, thus greatly improving the system integration level and reducing the circuit complexity. On the TX side, the global loop regulates the transmitted power through the duty cycle control of 1X/2X operation modes of the class-D PA to improve the system efficiency over a wide load range. On the RX side, we realize ac–dc power rectification and voltage regulation with a delay-tuned rectifier. The TX and RX chips fabricated in a standard 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m CMOS process used 3.3-V devices. Measured results show that the circuit can obtain a system efficiency improvement up to 14.2% at light load conditions, with the proposed wireless phase shift control regulating the TX global power. The peak end-to-end system efficiency is 77%, and the maximum output power is 0.9 W with a 3.3-V output voltage.