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.