External battery power source for implanted medical devices

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.

What is claimed is:  
     
         1 . A battery powered external power source for powering an implanted medical device having a receiver coil, of the type that inductively couples energy to the receiver coil through the skin of a patient, wherein the power source includes 
 a first battery operated power supply and a second battery operated power supply    an FPGA powered by the first battery operated power supply    a class D amplifier powered by the second battery operated power supply    a local oscillator providing an input signal to the FPGA and    an antenna driven by the class D amplifier to inductively couple energy to the receiver coil,    wherein the FPGA produces a modulation controlled pulse of RF frequency energy as an input for amplification by said amplifier to drive the antenna.    
     
     
         2 . The battery powered external power source of  claim 1 , wherein the class D amplifier is coupled via holdup capacitors to the second power supply.  
     
     
         3 . The battery powered external power source of  claim 1 , wherein the external antenna is sized to have a larger diameter than a receiver coil of the implanted medical device, and is tuned to resonate at the resonant frequency of the antenna of the receiver coil.  
     
     
         4 . The battery powered external power source of  claim 1 , wherein said first and second power supplies are switching power supplies having different switching frequencies.  
     
     
         5 . The battery powered external power source of  claim 1 , wherein said class D amplifier operates at a transmission frequency above several megahertz.  
     
     
         6 . A battery powered external power source for powering an implanted medical device having a receiver coil, of the type that inductively couples energy to the receiver coil through the skin of a patient, wherein the power source includes 
 first means including a battery or battery pack for providing electrical power    an FPGA powered by the first means    a class D amplifier controlled by the FPGA, and    a switching power supply for powering the class D amplifier    wherein the FPGA controls the switching power supply and class D amplifier to apply current pulses to an antenna for inductively coupling energy to the receiver coil in accordance with a desired pulse regimen.    
     
     
         7 . The battery powered external power source of  claim 6 , wherein the first means includes an auto power-down circuit having a power line enabled by said FPGA for selectively drawing battery power during operation and conserving the battery upon completion of a pulse regimen, such that only user operation can turn the power line ON, while either user operation or an FPGA generated signal turns the power line OFF.  
     
     
         8 . The battery powered external power source of  claim 6 , wherein the first means includes a switched power supply having a first switching frequency, and the switching power supply powering the amplifier has a second switching frequency different from said first frequency.  
     
     
         9 . The battery powered external power source of  claim 6 , wherein the antenna is tuned to a resonant frequency of about 5 MHz.  
     
     
         10 . The battery powered external power source of  claim 8 , wherein the antenna is tuned to a resonant frequency of about 5 MHz, and said first and second switching frequencies are lower than the resonant frequency.  
     
     
         11 . A battery-powered external power source having a signal generator coupled to a transmitting antenna for inductively coupling an rf signal to an implanted receiving coil of diameter d, and characterized in that the antenna has a diameter D such that d≦D≦7d.  
     
     
         12 . The battery-powered external power source of  claim 11 , further wherein the antenna is tuned to a resonant frequency of about 5 MHz.