A Class-E Power Amplifier With Wideband FSK Modulation for Inductive Power and Data Transmission to Medical Implants

Abstract

An inductive link, driven by a Class-E power amplifier (PA), is the most widely used method to transfer power to medical implants. Frequency-shift keying (FSK) is a robust data modulation scheme with negligible sensitivity to amplitude noise and movements of the transmitter and receiver coils of an inductive link. However, implementing FSK modulation on a Class-E PA has been a daunting task as high-Q Class-E PAs used for remote powering are narrowband circuits, while high data rate FSK modulation demands a wideband amplifier. In this paper, we propose a Class-E PA which uses wideband FSK modulation to transfer power and data to a medical implant. In the proposed circuit, the PA is effectively switched between two load networks that keep the amplifier tuned at both carrier frequencies used for data modulation. Using this approach and with carrier frequencies of 2 and 4 MHz, we have implemented a wireless power and data transfer link which can transmit data at a rate of 1 Mbps and with a bit error rate of 10−5. The power transfer efficiency and the power delivered to the load, with a 7.1- $\mu \text{H}$ transmitter coil and a 1.2- $\mu \text{H}$ receiver coil, separated by a 6-mm air gap, were measured to be 25% and 126 mW, respectively.