Towards a closed-loop transmitter system with integrated class-D amplifier for coupling-insensitive powering of implants

The efficiency of an inductive power transfer link is greatly affected by misalignment between the coils, caused by the patient's movement, after implantation. In this paper we present the preliminary design of a coupling-insensitive system with an integrated class-D transmitter, suitable for powering epidural stimulation implants. The operation of the system is based on closed-loop modulation of the power delivered to the implant, to compensate for losses of coupling between coils after implantation. An integrated transmitter with efficiencies above 90% was designed to operate between 1 MHz and 14 MHz. The circuit design employs 0.18-um high-voltage CMOS technology. Simulations are presented to verify the operation of the circuit.