External transmitter for implanted medical device

Abstract

An external transmitter assembly for powering and controlling an implanted medical device, wherein a battery drives first and second power supplies that energize a modulation circuit and an amplifier, respectively, to apply programmed current pulses to a transmitting antenna. The second power supply is output limited and couples through holdup capacitors and a filter network to the amplifier, allowing momentary high current operation without affecting oscillator or modulation portions of the circuit. The transmitting antenna has a diameter greater than that of the implanted receiving antenna, and is adhered to the skin of the patient over the implanted device and is tuned by a trimmer element to resonate at the resonant frequency of the receiver and enhance energy coupling between the two coils A local oscillator operating at high frequency is divided down to form a clock, and the pulse-defining modulation circuit includes an FPGA that controls pulse shape and timing regimens for a defined neurologic treatment. The two power supplies have high switching frequencies that are different from each other and from the main transmitter operating frequency to minimize aliasing effects between the units. In addition an auto power-down circuit connects the battery to the power supplies. Upon user actuation of the main power switch, that circuit connects power to boot the FPGA, which then provides a switching enable gate signal; the auto circuit disconnects the battery when the state of the FPGA signal indicates a treatment cycle is over. The auto power down circuit draws little power, thus assuring that battery life is unimpaired if the user forgets to turn off the transmitter, or leaves it in a shut down state for extended periods of time.