A High-Efficiency ASK-Modulated Class-E Power and Data Transmitter for Medical Implants

Abstract

In this article, we propose an amplitude-shift keying (ASK) modulation technique for Class-E power transmitters used in the inductive power and data transfer links. The proposed modulation circuit consists of a capacitor and a transistor, which switch the load network of the Class-E transmitter between two states; in one state, the drain waveform of the Class-E transistor satisfies both zero-voltage switching (ZVS) and zero-voltage-derivative switching conditions, while in the other one, the waveform approximately satisfies the ZVS condition. Therefore, at both states, the dc-to-ac power conversion efficiency is high, but the transmitted power is different, which allows the implementation of ASK data modulation in the transmitter. We also present an analytical procedure to design the circuit for the desired output power and data modulation index (MI). We have verified the design procedure in both simulation and measurement. The implemented inductive link consists of a 2.4- <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> H transmitter coil and a 1.1- <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> H receiver coil, separated by a 10-mm air gap. With a carrier frequency of 10 MHz, the power transfer efficiency and the power delivered to load were measured to be 64.6% and 35 mW, respectively. With MI = 10%, the bit error rate for the data rates of 1 and 2 Mb/s was measured to be less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–8</sup> and 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–6</sup> , respectively.