A 6.78-MHz Burst-Mode Controlled Inductive Wireless Power Transfer System for Biomedical Implants With Back-Channel Communication Eliminated Using Transmitter Q-Factor Detection

This article presents an analysis and design of high-efficiency, 6.78-MHz burst-mode controlled inductive wireless power transfer system (WPT) with no back-channel communication between a transmitter (TX) and a receiver (RX). Power is transmitted in bursts between the TX and the RX, and the duty cycle of the burst is controlled through load modulation to control power flow between the TX and the RX. Extra back-channel traditionally used for TX–RX communication to control power flow is avoided by using inherent load modulation properties of the WPT circuit. It is demonstrated that the quality factor of the TX can be detected to eliminate the back-channel communication. Furthermore, only an extra switch is added in the RX power stage in series with the load to regulate the output voltage. The proposed WPT circuit can regulate output voltage against distance variation of up to 3 cm using 3-cm-diameter TX and RX coils and a load variation from full load to no load. A 330-mW prototype circuit for use in medical implants is designed, built, and tested. The proposed research advances the state-of-the-art WPT systems for use in resource-constrained biomedical implants.