Power transfer circuit for implanted devices

• US 6,212,431 B1
• Filed: 08/18/1999
• Issued: 04/03/2001
• Est. Priority Date: 09/08/1998
• Status: Expired due to Term

• Current Assignee: Advanced Bionics AG (Sonova Holding AG)
• Original Assignee: Advanced Bionics Corporation (Sonova Holding AG)
• Inventors: Griffith, Glen A., Hahn, Tae W.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US09/376,881
• Time in Patent Office: 594 Days
• Field of Search: 607/61, 607/32, 607/33, 607/55, 607/56, 607/57
• US Class Current: 607/61
• CPC Class Codes: A61N 1/36038 Cochlear stimulation
• CPC Class Codes: A61N 1/3787 from an external energy source

Abstract

An external power transfer circuit (12) couples ac power having a fixed frequency into an implantable electrical circuit (14), e.g., an implantable tissue stimulator, while automatically maintaining optimum power transfer conditions. Optimum power transfer conditions exist when there is an impedance match between the external and implanted circuits. The external transfer circuit includes a directional coupler (42) and an impedance matching circuit (44). The directional coupler senses the forward power being transferred to the implant device, as well as the reverse power being reflected form the implant device (as a result of an impedance mismatch). The impedance matching circuit includes at least one variable element controlled by a control signal. The sensed reverse power is used as a feedback signal to automatically adjust the variable element in the impedance matching circuit, and hence the output impedance of the external power transfer circuit, so that it matches the input impedance of the implant device, despite variations that occur in the input impedance of the implant device due to variations in implant distance and implant load.

Claims

1. An external power coupling system for optimally coupling power to an implantable device at a fixed frequency, the implantable device having an input impedance that varies as a function of implant distance and implant load, the power coupling system comprising:

eternal driver means for generating an ac power signal at a fixed frequency;

an external coil for receiving the ac power signal and inductively coupling the ac power signal to the implantable device;

an impedance matching circuit interposed between the external coil and external driver means for setting an output impedance of the power coupling system, the impedance matching circuit having means for adjusting the output impedance as a function of a control signal;

directional coupler means coupled to the ac power signal for sensing reverse power;

signal processing means for generating the control signal as a function of the sensed reverse power, and applying the control signal to the impedance matching circuit so as to adjust the output impedance to match the input impedance of the implantable device.

2. The external power coupling system of claim 1 wherein the signal processing means comprises means for generating the control signal so that it causes the output impedance to increase to match an increase in the input impedance of the implantable device, and to decrease to match a decrease in the input impedance of the implantable device.

3. The external power coupling system of claim 1 wherein the impedance matching circuit includes at least one varactor that functions as a variable capacitor having a capacitance that varies as a function of a voltage applied thereto, the varactor comprising the means by which the output impedance of the power coupling system is adjusted.

4. The external power coupling system of claim 1 wherein the directional coupler means comprises a directional coupler circuit providing a forward power signal and a reverse power signal, and wherein the directional coupler circuit is interposed intermediate the external driver means and the impedance matching circuit.

5. The external power coupling system of claim 4 wherein the signal processing means comprises an analog circuit having means for comparing the forward power signal to the reverse power signal and generating a difference signal as a function of the difference therebetween, and means for integrating the difference signal to produce the control signal.

6. The external power coupling system of claim 4 wherein the signal processing means comprises a digital circuit having means for digitizing the reverse power signal to produce a digitized reverse power signal, digital signal processing (DSP) means for processing the digital reverse power signal in accordance with a prescribed processing program to produce a digitized control signal, and means for converting the digitized control signal to an analog control signal for application to the impedance matching circuit.

7. A power coupling circuit for optimally coupling power to an implantable stimulation device, the implantable stimulation device having an input impedance that varies as a function of implant distance and implant load, the power coupling circuit comprising

a transmission coil;

a driver circuit that generates an ac power signal, the ac power signal being applied to the transmission coil, where it is inductively coupled to the implantable stimulation device; and

an adjustable impedance matching system that automatically matches the impedance of the power coupling circuit to match the input impedance of the implant device.

8. The power coupling system of claim 7 wherein the adjustable impedance matching system comprises:

a sensor that senses variations in power directed to the transmission coil;

an impedance matching circuit interposed between the transmission coil and sensor, the impedance matching circuit having an output impedance;

means for adjusting the output impedance of the impedance matching circuit as a function of the sensed variations in the power directed to the transmission coil to match the output impedance to the input impedance of the implant device.

9. The power coupling system of claim 8 wherein the sensor senses reverse power reflected from the transmission coil, and wherein the means for adjusting the output impedance adjusts the output impedance until the sensed reverse power is reduced to a minimum value.

10. The power coupling system of claim 7 wherein the implantable stimulation device comprises an implantable cochlear stimulator (ICS), and wherein the power coupling circuit is included within an external headpiece used with the ICS.

11. The power coupling system of claim 7 wherein the means for adjusting the output impedance comprises an impedance matching circuit that includes at least one varactor diode that functions as a variable capacitor having a capacitance that varies as a function of a voltage applied thereto.

12. A method of optimally coupling power to an implantable stimulation device, the implantable stimulation device having an impedance that varies as a function of implant distance and implant load, the method comprising:

(a) generating an external ac power signal;

(b) applying the external ac power signal to an external transmission coil through an impedance matching circuit;

(c) inductively coupling the external transmission coil with an implanted coil included within the implantable stimulation device;

(d) sensing reverse power from the external transmission coil;

(e) adjusting the impedance of the impedance matching circuit in a direction that causes the sensed reverse power to go to a minimum value;

(f) coupling power into the implanted device while maintaining the impedance of the impedance matching circuit at that value which keeps the sensed reverse power at the minimum value of step (e).

13. The method of claim 12 wherein step (a) comprises generating an external ac power signal having a fixed frequency.

14. The method of claim 13 wherein step (a) comprises generating an external ac power signal having a fixed frequency of about 49 MHz.

15. The method of claim 13 wherein the impedance matching circuit includes a varactor element that provides a variable capacitance as a function of a voltage applied thereo, and wherein step (e) comprises adjusting the voltage applied to the varactor, wherein the capacitance provided by the varactor element varies, and wherein the impedance of the impedance matching circuit varies.