Methods and systems for frequency adjustment to optimize charging of implantable neurostimulator

1. A neurostimulation system for delivering one or more electrical pulses to a target region within a patient's body, the neurostimulation system comprising:

an implantable neurostimulator comprising:

a hermetic housing having an external surface that is configured to be implanted within a body of a patient, the housing comprising a ceramic transmission region; and

a charging circuit configured to receive power through the ceramic region of the hermetic housing; and

a charger for coupling with an implantable neurostimulator, the charger comprising:

a resonant circuit, wherein the resonant circuit is configurable to a plurality of natural frequencies; and

a processor coupled to the resonant circuit to control the natural frequency of the resonant circuit according to stored data identifying a previously determined natural frequency of the charging circuit of the implantable neurostimulator.

2. The neurostimulation system of claim 1 , wherein the processor is configured to control the natural frequency of the resonant circuit according to characterization data identifying a natural frequency of the charging circuit of the implantable neurostimulator.

3. The neurostimulation system of claim 2 , wherein the characterization data is uniquely associated with the implantable neurostimulator, and wherein the characterization data is stored in a database in memory at the charger.

4. The neurostimulation system of claim 3 , wherein the characterization data is received at the charger from the implantable neurostimulator when the charger is coupled with the implantable neurostimulator.

5. The neurostimulation system of claim 3 , wherein the characterization data is generated by the charger when the database does not contain characterization data for the implantable neurostimulator.

6. The neurostimulation system of claim 5 , wherein generating the characterization data comprises:

controlling the natural frequency of the resonant circuit to iteratively cycle through a plurality of natural frequencies of the resonant circuit;

iteratively receiving data from the implantable neurostimulator indicative of a level of matching between the plurality of natural frequencies of the resonant circuit and a natural frequency of the charging circuit of the implantable neurostimulator; and

identifying one of the plurality of natural frequencies as the natural frequency of the charging circuit of the implantable neurostimulator.

7. The neurostimulation system of claim 6 , wherein the identified one of the plurality of natural frequencies is the one of the plurality of natural frequencies that best matches the natural frequency of the charging circuit of the implantable neurostimulator.

8. The neurostimulation system of claim 7 , wherein the identified one of the plurality of natural frequencies is the one of the plurality of natural frequencies that best matches the natural frequency of the charging circuit of the implantable neurostimulator over a statistically significant number of iterations.

9. The neurostimulation system of claim 7 , wherein the identified one of the plurality of natural frequencies is a default natural frequency.

10. A method for coupling a charger with an implantable neurostimulator for delivering one or more electrical pulses to a target region within a patient's body, the method comprising:

powering a resonant circuit of a charger with a driver coupled to a power source, the driver powering the resonant circuit at a driving frequency, wherein the resonant circuit is configurable to a plurality of natural frequencies;

determining a first natural frequency of the resonant circuit;

retrieving stored characterization data, wherein the characterization data identifies a previously determined natural frequency of a resonant circuit of the implantable neurostimulator; and

changing the natural frequency of the resonant circuit from the first natural frequency to a second natural frequency with control signals generated by a processor according to the characterization data.

11. The method of claim 10 , wherein determining the natural frequency of the resonant circuit of the charger comprises at least one of: determining the driving frequency of the driver; or detecting ringing of the resonant circuit.

12. The method of claim 11 , wherein the resonant circuit comprises:

an inductor;

a first capacitor coupled in series to the inductor; and

a plurality of capacitors switchably coupleable to the inductor, wherein the plurality of capacitors are each configured to be in parallel with the first capacitor when switchably coupled to the inductor.

13. The method of claim 12 , wherein the plurality of capacitors comprises three capacitors.

14. The method of claim 13 , wherein each of the plurality of capacitors is switchably coupleable to the inductor via a transistor.

15. The method of claim 14 , wherein changing the natural frequency of the resonant circuit of the charger from the first natural frequency to a second natural frequency comprises:

identifying a first switch configuration of the resonant circuit resulting in the first natural frequency;

identifying a second switch configuration of the resonant circuit resulting in the second natural frequency; and

generating a control signal to control at least one of: opening of at least one switch in the resonant circuit to disconnect at least one of the plurality of capacitors from the inductor; or closing of at least one switch in the resonant circuit to connect at least one of the plurality of capacitors from the inductor.

16. The method of claim 11 , wherein changing the natural frequency of the resonant circuit of the charger from the first natural frequency to a second natural frequency comprises:

identifying a first inductance of an inductor in the resonant circuit resulting in the first natural frequency;

identifying a second inductance of the inductor in the resonant circuit resulting in the second natural frequency; and

generating a control signal to change the inductance of the inductor from the first inductance to the second inductance.

17. The method of claim 10 , wherein the characterization data is retrieved from a database in memory at the charger.

18. The method of claim 10 , wherein the characterization data is generated by the charger.

19. The method of claim 18 , wherein generating the characterization data comprises:

controlling the natural frequency of the resonant circuit to iteratively cycle through a plurality of natural frequencies of the resonant circuit;

iteratively receiving data from the implantable neurostimulator indicative of a level of matching between the plurality of natural frequencies of the resonant circuit and a natural frequency of the resonant circuit of the implantable neurostimulator; and

identifying one of the plurality of natural frequencies as the natural frequency of the resonant circuit of the implantable neurostimulator.