Current Management System for a Stimulation Output Stage of an Implantable Neurostimulation System

• US 20120071950A1
• Filed: 09/20/2010
• Published: 03/22/2012
• Est. Priority Date: 09/20/2010
• Status: Active Grant

• Current Assignee: Neuropace Inc.
• Original Assignee: Neuropace Inc.
• Inventors: Archer, Stephen T.
• Granted Patent: US 9,155,891 B2
• Time in Patent Office: Days
• US Class Current: 607/66
• CPC Class Codes: A61N 1/36125 Details of circuitry or electric components
• CPC Class Codes: A61N 1/3616 Voltage density or current density

Abstract

A current management system for use in the stimulation output stage of a neurostimulation system can be programmed to steer different amounts of current through different stimulation electrodes to vary how strongly the tissue adjacent each electrode is stimulated during a particular programmed stimulation episode. An stimulation electrode drive circuit associated with each electrode that is available for stimulation allows independent control of the flow of current through that electrode. A reference electrode is provided in the circuit to source or sink current as necessary to balance the currents going into and out of the patient, so that no stimulation electrode is required to serve that purpose. More specifically, by configuring the circuit to maintain a constant potential at the reference electrode (e.g., a potential that is approximately half way between a top and bottom voltage rail), the reference electrode will source or sink currents as necessary to cause the net current flow into the patient to be equal to the net current flowing out of the patient, thus satisfying Kirchhoff'"'"'s current law.

Claims

1. A current management system for the stimulation output stage of a neurostimulation system including a neurostimulator enclosed in a housing having an electrically conductive surface and a plurality of stimulation electrodes, the current management system comprising:

a stimulation electrode drive circuit for each of the plurality of stimulation electrodes, each stimulation electrode drive circuit adapted to allow current to be sourced or sunk through its associated stimulation electrode in accordance with the limits of top and bottom voltage rails and in accordance with programmed instructions provided to the electrode drive circuit by digital control and timing signals; and

a reference electrode drive circuit adapted to maintain the electrically conductive surface of the neurostimulator at a constant potential when any or all of the stimulation electrodes are sourcing or sinking current, so that the reference electrode will sink or source an amount of current equal to the total amount of current being source or sunk through the stimulation electrodes at any given time in a stimulation episode,

whereby each stimulation electrode is capable of sourcing and sinking current independently of any current being sourced or sunk through any other of the stimulation electrodes.

2. The current management system of claim 1 wherein all of the top rail voltage, the bottom rail voltage and the constant potential at which the reference electrode is to be maintained are programmable.

3. The current management system of claim 1 wherein none of the top voltage rail, the bottom voltage rail and the reference electrode constant potential is below ground potential.

4. The current management system of claim 1 wherein the top voltage rail is above ground potential and the bottom voltage rail is below ground potential.

5. The current management system of claim 1 wherein each stimulation electrode drive circuit has a current sink portion and a current source portion, and at least one feature that prevents the current sink portion from being enabled at the same time as the current source portion.

6. The current management system of claim 1 wherein each stimulation electrode drive circuit has a bias circuit to which the digital control and timing signals are input and from which a digital output and an analog output are derived, the digital output enabling the electrode drive circuit to source or sink current through its associated stimulation electrode, and the analog output setting the reference current for the electrode drive circuit to source or sink.

7. The current management system of claim 1 wherein the digital control and timing signals, in addition to conveying instructions to cause a stimulation electrode to source or sink current, further convey instructions to cause a stimulation electrode to function as a high impedance or a short circuit.

8. The current management system of claim 1 wherein each stimulation electrode drive circuit establishes a reference current for its associated stimulation electrode with a current mirror circuit.

9. The current management system of claim 1 further comprising a feature wherein a signal is generated whenever a programmed amount of current cannot be sourced or sunk through a stimulation electrode because the limits defined by the top and bottom voltage rails are exceeded.

10. The current management system of claim 1 further comprising a feature wherein the top and bottom voltage rails are automatically adjusted within predetermined not-to-exceed values whenever a programmed amount of current cannot be sourced or sunk through a stimulation electrode because the limits defined by the top and bottom voltage rails are exceeded.

11. The current management system of claim 1 wherein the voltages are derived from a power source for the neurostimulator.

12. A stimulation output stage of a neurostimulation system that is at least partially implantable in the body of a human patient comprising:

a plurality of stimulation electrodes implantable in the patient so that each is adjacent or in the patient'"'"'s tissue wherein each stimulation electrode can be selectively engaged to perform any of the following functions at a given time during a stimulation episode;

source current into the patient;

sink current out of the patient;

present a high impedance; and

provide a short circuit to ground;

a reference electrode the electrically conductive surface area of which is at least an order of magnitude greater than the electrically conductive surface area of any of the plurality of stimulation electrodes;

digital control and timing signals sufficient to determine whether a stimulation electrode is used in a stimulation episode, what function the stimulation electrode performs at what time(s) during the stimulation episode and, if the function is to source or sink current, the amplitude of the current to be sourced or sunk;

for each stimulation electrode, a voltage reservoir associated with a stimulation electrode drive circuit adapted to respond to the digital control and timing signals and configurable to establish a reference current for the stimulation electrode when the stimulation is programmed to source or sink current; and

for the reference electrode, a constant reference voltage associated with a reference electrode drive circuit adapted to maintain the reference electrode at a constant voltage during the stimulation episode so that the reference electrode sinks or sources current to balance the current being sourced or sunk by the stimulation electrodes.

13. The stimulation output stage of claim 12 wherein the reference electrode comprises the electrically conductive surface area of the housing for an implantable neurostimulator.

14. The stimulation output stage of claim 12 wherein all of the voltages are at a potential between ground potential and a positive voltage.

15. The stimulation output stage of claim 12 wherein all of the voltages are at a potential between a negative voltage and a positive voltage.

16. The stimulation output stage of claim 12 wherein each stimulation electrode drive circuit comprises a bias circuit the inputs of which include the digital control and timing signals and the outputs of which include a digital output and an analog output corresponding to the reference current, the digital output determining whether a current sink portion or a current source portion of the stimulation electrode drive circuit is enabled, and the analog output determining the amplitude of any current the stimulation electrode drive circuit will cause to be sourced or sunk through its associated stimulation electrode.

17. The stimulation output stage of claim 12 wherein each stimulation electrode drive circuit is configured to generate a signal corresponding to the condition that occurs when a voltage reservoir associated with a stimulation electrode drive circuit and a stimulation electrode is not sufficient to permit a programmed amount of current to be sourced or sunk through the stimulation electrode.

18. The stimulation output stage of claim 12 wherein each stimulation electrode drive circuit comprises a current sink portion and a current source portion, the current sink portion is in operable communication with a first TILT circuit and the current source portion is in operable communication with a second TILT circuit, such that when the voltage reservoir associated with the stimulation electrode drive circuit and its associated stimulation electrode is not sufficient to sink a programmed amount of current through the stimulation electrode, the first TILT circuit will generate a TILT sink signal, and when the voltage reservoir associated with the stimulation electrode drive circuit and its associated stimulation electrode is not sufficient to source a programmed amount of current through the stimulation electrode, the second TILT circuit will generate a TILT source signal.

19. The stimulation output stage of claim 12 further comprising a feature that will automatically adjust the reservoir voltage within a predetermined range of voltages whenever the reservoir voltage is insufficient to allow a stimulation electrode drive circuit to source or sink a programmed amount of current through its associated stimulation electrode.

20. A method for steering the amount of current to be sourced or sunk to a patient through each of a plurality of stimulation electrodes under the control of a neurostimulator in a neurostimulation system comprising:

providing a stimulation electrode drive circuit for each stimulation electrode configurable to cause the associated stimulation electrode to perform one of four functions at any given time period in a stimulation episode, namely, sourcing current into the patient, sinking current out of the patient, presenting a high impedance, or providing a short circuit to ground;

providing programmed instructions in the form of digital control and timing signals to each electrode drive circuit to cause the associated stimulation to perform one or more of the four functions at selected time periods during the stimulation episode;

providing a voltage reservoir for the stimulation electrode drive circuits when the stimulation electrode drive circuits are programmed to source or sink currents;

providing a reference electrode drive circuit that maintains a housing of the neurostimulator at a constant reference voltage during the stimulation episode, causing the reference electrode to source or sink an amount of current equal to the total amount of current being sunk or sourced by the stimulation electrodes at each selected time period, thus allowing the current sourced or sunk through any one stimulation electrode to be independent of the amount of current being sourced or sunk through any other stimulation electrode at any given time period in the stimulation episode.

21. The method of claim 20 wherein the providing a stimulation electrode drive circuit for each stimulation electrode further comprises providing a bias circuit for each electrode drive circuit wherein the inputs to each bias circuit are the digital control and timing signals and the outputs of each bias circuit include a digital output to enable the electrode drive circuit to cause the stimulation electrode to source current, sink current, present a high impedance or short the electrode to ground and, when the electrode drive circuit is to cause the stimulation electrode to source current or to sink current, an analog output corresponding to the reference current for the sourcing or sinking function.

22. The method of claim 20 wherein the voltage reservoir is defined by top and bottom voltage rails and the top and bottom voltage rails and the constant reference voltage for the reference electrode are all programmable values.

23. The method of claim 22 further comprising automatically adjusting the voltage reservoir between predetermined limits whenever the reservoir voltage is insufficient to allow a stimulation electrode drive circuit to source or sink a programmed amount of current through its associated stimulation electrode.