Closed Loop Charger for an Implantable Medical Device System Employing Reflected Impedance Modulation

• US 20130096652A1
• Filed: 09/10/2012
• Published: 04/18/2013
• Est. Priority Date: 10/13/2011
• Status: Active Grant

• Current Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Inventors: Ozawa, Robert, Aghassian, Daniel
• Granted Patent: US 9,314,642 B2
• Time in Patent Office: Days
• US Class Current: 607/61
• CPC Class Codes: A61N 1/3787 from an external energy source

Abstract

The disclosed system for providing closed loop charging between an external charger and an implantable medical device such as an IPG involves the use of reflected impedance modulation, i.e., by measuring at the external charger reflections arising from modulating the impedance of the charging coil in the IPG. During charging, the charging coil in the IPG is periodically pulsed to modulate its impedance. The magnitude of the change in the coil voltage produced at the external charger ΔV as a result of these pulses is assessed and is used by the controller circuitry in the external charger as indicative of the coupling between the external charger and the IPG. The external charger adjusts its output power (e.g., Icharge) in accordance with the magnitude of ΔV, thus achieving closed loop charging without the need of telemetering coupling parameters from the IPG.

Claims

1. An external charger for an implantable medical device, comprising:

a coil for producing a magnetic field for providing power to the implantable medical device;

a detector for receiving an electrical parameter of the coil, wherein the detector determines at least a magnitude of a change in the electrical parameter, wherein the change is inducible by the implantable medical device; and

charging circuitry coupled to the coil, wherein the charging circuitry controls a strength of the magnetic field at least in accordance with the magnitude of the change.

2. The external charger of claim 1, wherein the detector determines at least the magnitude of the change by comparing it to a threshold.

3. The external charger of claim 1, wherein the detector comprises an A/D converter.

4. The external charger of claim 1, wherein the detector comprises control circuitry for the external charger.

5. The external charger of claim 1, further comprising a demodulator, wherein the demodulator determines data transmitted from the implantable medical device by demodulating the electrical parameter of the coil.

6. The external charger of claim 1, wherein the charging circuitry controls the strength of the magnetic field by controlling a AC current through the coil.

7. The external charger of claim 1, wherein the charging circuitry controls the strength of the magnetic field by comparing at least the magnitude of the change with coupling information accessible to the detector.

8. The external charger of claim 7, wherein the coupling information comprises calculated, simulation, or experimental data indicative of a relationship between a coupling parameter and at least a magnitude of a change in the electrical parameter.

9. The external charger of claim 1, wherein the detector further determines a magnitude of the electrical parameter, and wherein the charging circuitry controls the strength of the magnetic field at least in accordance with the magnitude of the change and the magnitude of the electrical parameter.

10. The external charger of claim 1, wherein the electrical parameter comprises voltage.

11. The external charger of claim 1, wherein the electrical parameter comprises current.

12. A system, comprising:

an implantable medical device, comprising;

a first coil for receiving a magnetic field for providing power to the implantable medical device; and

at least one switch for modulating an impedance of the first coil during receipt of the magnetic field; and

an external charger, comprising;

a second coil for producing the magnetic field;

a detector for receiving an electrical parameter of the second coil, wherein the detector determines at least a magnitude of a change in the electrical parameter caused by modulation of the impedance of the first coil; and

charging circuitry coupled to the coil, wherein the charging circuitry controls a strength of the magnetic field at least in accordance with the magnitude of the change.

13. The system of claim 12, wherein the implantable medical device comprises two switches, wherein each of the switches grounds an end of the first coil to modulate the impedance of the first coil.

14. The system of claim 12, wherein the at least one switch is coupled in series with the first coil.

15. The system of claim 12, wherein the at least one switch is periodically pulsed during receipt of the magnetic field.

16. The system of claim 12, wherein the implantable medical device further comprises a rechargeable battery, and wherein the magnetic field provides power to recharge the battery.

17. The external charger of claim 12, wherein the detector determines at least the magnitude of the change by comparing it to a threshold.

18. The external charger of claim 12, wherein the detector comprises an A/D converter.

19. The external charger of claim 12, wherein the detector comprises control circuitry for the external charger.

20. The external charger of claim 12, wherein the external charger further comprises a demodulator, wherein the at least one switch is responsive to data to be sent to the external charger, and wherein the demodulator demodulates the data during production of the magnetic field.

21. The external charger of claim 12, wherein the charging circuitry controls the strength of the magnetic field by controlling a AC current through the coil.

22. The external charger of claim 12, wherein the charging circuitry controls the strength of the magnetic field by comparing at least the magnitude of the change with coupling information accessible to the detector.

23. The external charger of claim 22, wherein the coupling information comprises calculated, simulation, or experimental data indicative of a relationship between a coupling parameter and at least a magnitude of a change in the electrical parameter.

24. The external charger of claim 12, wherein the detector further determines a magnitude of the electrical parameter, and wherein the charging circuitry controls the strength of the magnetic field at least in accordance with the magnitude of the change and the magnitude of the electrical parameter.

25. The external charger of claim 12, wherein the electrical parameter comprises voltage.

26. The external charger of claim 12, wherein the electrical parameter comprises current.

27. A method for providing power to an implantable medical device from an external charger, comprising:

providing a magnetic field from a second coil in an external charger;

modulating an impedance of a first coil in the implantable medical device while receiving the magnetic field from the external charger;

determining at least a magnitude of a change in an electrical parameter of the second coil in the external charger caused by modulating the impedance of the first coil; and

adjusting a strength of the magnetic field provided by the second coil in accordance with at least the magnitude of the change.

28. The method of claim 27, wherein the impedance of the first coil is modulated by shorting the first coil.

29. The method of claim 27, wherein the impedance of the first coil is modulated by opening the first coil.

30. The method of claim 27, wherein the impedance of the first coil is periodically modulated.

31. The method of claim 27, wherein modulating the impedance of the first coil transmits data to the external charger.

32. The method of claim 27, further comprising

determining at least a magnitude of the electrical parameter of the second coil in the external charger;

and

adjusting the strength of the magnetic field provided by the second coil in accordance with at least the magnitude of the change and the magnitude of the electrical parameter.

33. The method of claim 27, wherein the implantable medical device comprises a battery, and further comprising using the received magnetic field to recharge the battery.