A self-oscillating detuning-insensitive class-E transmitter for implantable microsystems

This paper describes a low-cost, self-oscillating, detuning-in-sensitive, class-E driver for transcutaneous power and data transmission to implantable microsystems. A voltage feedback scheme using a fast comparator for zero-crossing detection and a CMOS start-up circuit were used to stabilize the class-E operation for various transmitter coil inductance values. This technique solves the common problem of mismatch between the switching frequency of the driving device and the resonant frequency of the load network, which can cause excessive power loss and damage to the active device. Data is transmitted by AM modulation of the carrier through switching the power supply between two levels. The transmitter uses a 9-V supply, consumes 212 mA, operates at 3.9 MHz, and has an efficiency of 71%. The efficiency is stable (< 2% change) against 13% variations in the inductance value of a pancake shaped transmitter coil. Index Terms-Biomedical microsystems, class-E transmitter, implantable electronics, inductive powering, transcutaneous links.