Closed loop wireless power transmission for implantable medical devices

This paper describes a closed loop wireless inductive power transfer system for an implantable brain machine interface. The proposed system is designed to ensure optimal power transfer by an off-body unit, battery powered, to an in-body implanted unit while guarantying a minimum transmitted power level for proper operation and a maximum level to avoid brain tissue damage due to implanted electronics overheating. The closed loop ensures a minimum power of 20mW delivered to the implanted unit with a power amplifier measured power added efficiency of 69%. As part of the closed loop a microcontroller interprets a backscattered pulse train signal modulating a PWM signal duty cycle in order to control power amplifier drain bias voltage by using a PWM controlled DC/DC converter.