Architectures for sharing of current sources in an implantable medical device

A group select matrix is added to an implantable stimulator device to allow current sources to be dedicated to particular groups of electrodes at a given time. The group select matrix can time multiplex the current sources to the different groups of electrodes to allow therapy pulses to be delivered at the various groups of electrodes in an interleaved fashion. Each of the groups of electrodes may be confined to a particular electrode array implantable at a particular non-overlapping location in a patient's body. A switch matrix can be used in conjunction with the group select matrix to provide further flexibility to couple the current sources to any of the electrodes.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devices, and more particularly to improved current source architectures for an implantable neurostimulator.

BACKGROUND

Implantable neurostimulator devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc.

FIGS. 1A and 1Bshows a traditional Implantable Pulse Generator (IPG)100, which includes a biocompatible device case30formed of a conductive material such as titanium for example. The case30typically holds the circuitry and a battery necessary for the IPG100to function, although IPGs can also be powered via external RF energy and without a battery. The IPG100includes in this simple example an electrode array102containing a linear arrangement of electrodes106. The electrodes106are carried on a flexible body108, which also houses the individual electrode leads112coupled to each electrode. In the illustrated embodiment, there are eight electrodes on array102, labeled E1-E8, although the number of electrodes is application specific and therefore can vary. Array102couples to case30using a lead connector38, which is fixed in a non-conductive header material36such as epoxy for example. As is well known, the array102is implanted in an appropriate location in a patient to provide suitable simulative therapy, and is coupled through the patient's tissue to the IPG100, which may be implanted somewhat distant from the location of the array.

As shown inFIG. 1B, the IPG100typically includes an electronic substrate assembly14including a printed circuit board (PCB)16, along with various electronic components20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB16. Two coils (more generally, antennas) are generally present in the IPG100: a telemetry coil13used to transcutaneously transmit/receive data to/from an external controller (not shown); and a charging coil18for transcutaneously charging or recharging the IPG's battery26using an external charger (also not shown).

A portion of circuitry20in the IPG100is dedicated to the provision of therapeutic currents to the electrodes106. Such currents are typically provided by current sources150, as shown inFIGS. 2A and 2B. In many current-source based architectures, some number of current sources150are associated with a particular number of electrodes106. For example, inFIG. 2A, it is seen that N electrodes E1-ENare supported by N dedicated current sources1501-150N. In this example, and as is known, the current sources150are programmable (programming signals not shown) to provide a current of a certain magnitude and polarity to provide a particular therapeutic current to the patient. For example, if source1502is programmed to source a 5 mA current, and source1503is programmed to sink a 5 mA current, then 5 mA of current would flow from anode E2to cathode E3through the patient's tissue, R, hopefully with good therapeutic effect. Typically such current is allowed to flow for a duration, thus defining a current pulse, and such current pulses are typically applied to the patient with a given frequency. If the therapeutic effect is not good for the patient, the electrodes chosen for stimulation, the magnitude of the current they provide, their polarities, their durations, or their frequencies could be changed.

(FIG. 2Ashows that each of the electrodes is tied to a decoupling capacitor. As is well known, decoupling capacitors promote safety by prevent the direct injection of current form the IPG100into the patient. For simplicity, decoupling capacitors are not shown in subsequent drawings, even though they are typically present in practical implementations).

FIG. 2Bshows another example current source architecture using a switch matrix160. In this architecture, the switch matrix160is used to route current from any of the sources150Pto any of the electrodes EN. For example, if source1052is programmed to source a 5 mA current, and source1051is programmed to sink a 5 mA current, and if source1502is coupled to electrode E2by the switch matrix160, and if source1501is connected to electrode E3by the switch matrix160, then 5 mA of current would flow from anode E2to cathode E3through the patient's tissue, R. In this example, because any of the current sources150can be connected to any of the electrodes, it is not strictly required that the number of electrodes (N) and the number of current sources (P) be the same. In fact, because it would perhaps be rare to activate all N electrodes at once, it may be sensible to make P less than N, to reduce the number of sources150in the IPG architecture. This however may not be the case, and the number of sources and electrodes could be equal (P=N). Although not shown, it should be understood that switch matrix160would contains P×N switches, and as many control signals (C1,1-CP,N), to controllably interconnect all of the sources150Pto any of the N electrodes. Further details of a suitable switch matrix can be found in U.S. Patent Pub. U.S. Patent Publication 2007/0038250, which is incorporated herein by reference.

The architecture ofFIG. 2B, like the architecture ofFIG. 2A, also comprises some number of current sources150(P) associated with a particular number of electrodes106(N). Other more complicated current architectures exist in the implantable stimulator art. See, e.g., the above-incorporated '250 Publication. But again generally such approaches all require some number of current sources150to be associated with a particular number of electrodes106.

The inventor considers the association of numbers of current sources and electrodes to be limiting because such architectures do not easily lend themselves to scaling. As implantable stimulator systems become more complicated, greater numbers of electrodes will provide patients more flexible therapeutic options. However, as the number of electrodes grows, so too must the number of current sources according to traditional approaches discussed above. This is considered undesirable by the inventor, because current source circuitry—even when embodied on an integrated circuit—is relatively large and complicated. Newer architectural approaches are thus believed necessary by the inventor to enable the growth of more complicated implantable stimulator systems, and such new architectures are presented herein.

DETAILED DESCRIPTION

FIG. 3shows a more complicated IPG200which contains a higher number of electrodes than that illustrated earlier, and which may be indicative of the future progress of IPG technology. In the example shown, there are three electrode arrays1021-1023, each containing eight electrodes, with electrodes E1-E8on array1021, E9-E16on array1022, and E17-E24on array1023. Each of the arrays102couples to the IPG200at a suitable lead connector381-383, which lead connectors can be arranged in the header36in any convenient fashion. It should be understood that this is merely an example, and that different numbers of arrays, and different numbers of electrodes on each array, could be used.

In this example, each of the arrays1021-1023comprises a group of electrodes that is implanted (or implantable) in a different location in a patient's body, thus allowing for the provision of complex stimulation patterns and/or stimulation across a wider portion of the patient's body. For example, in a therapy designed to alleviate sciatica, Location1for the Group1electrodes of array1021(E1-E8) might comprise the patient's right leg; Location2for the Group2electrodes of array1022(E9-E16) the left leg; and Location3for the Group3electrodes of array1023(E17-E24) the patient's spinal column. In a therapy designed to alleviate lower back pain, Location1of Group1might comprise the right side of a patient's spinal column; Location2of Group2the left side of the spinal column; and Location3of Group3a central location in the spinal column. Or each of Locations1-3may comprise different portions of a patient's brain in a deep brain stimulation example. The exact locations of each of the arrays, the number of electrodes in each array, and the particular therapies they provide, are not important to the concepts discussed herein. It is preferred that the Locations are non-overlapping in the patient's body.

As discussed in the Background section, conventional wisdom suggests that tripling the number of electrodes (from eight to 24 in this example) would require tripling the number of current sources in the IPG200used to support those electrodes. This is because conventional approaches associate a number of current sources with a particular number of electrodes, and hence the two would scale. As noted earlier, the inventor finds this unfortunate given the complexity and size of typical current course circuitry.

The present current source architecture diverges from this conventional approach by sharing current sources with an increased number of electrodes, such as is shown first inFIG. 4A. Consistent withFIG. 3, 24 total electrodes are supported by the current source circuitry ofFIG. 4A, comprising three arrays1021-1023(e.g., Groups) present in three different Locations in the body.FIG. 4Ais somewhat similar to the architecture ofFIG. 2Adiscussed earlier, in that there is a one-to-one correspondence of current sources150to electrodes within a given Group. For example, there are eight current sources150, and eight electrodes in each Group. New toFIG. 4Ais a group select matrix170. The group select matrix170allows current from the current sources150to be sent to particular electrodes in each of the Groups. For example, current source1501can send its current to electrode E1in Group1, to E9in Group2, and to E17in Group3. Current source1502can send its current to E2in Group1, to E10in Group2, and E18in Group3, etc.

Group control is enabled in this example by the use of three group control signals G1-G3. When G1is asserted, switches (e.g., transistors) in the group switch matrix170are closed to respectively route the current from each of the current sources1501-1508to Group1electrodes E1-E8. (Of course, not all of the current sources1501-1508may be programmed at a given moment to provide a current, and so current will not necessarily flow at an electrode E1-E8merely because of the assertion of G1). When G2is asserted, each of the current sources1501-1508are coupled to Group2electrodes E9-E16, and likewise when G3is asserted, each of the current sources1501-1508are coupled to Group3electrodes E17-E24. Although shown as switches, it should be understood that the group switch matrix170may also comprise a plurality of multiplexers.

Assume electrode E13is to output 5 mA of current while electrode E12is to receive that 5 mA of current. In this example, source1505is programmed to source 5 mA worth of current, source1504is programmed to sink 5 mA of current, and group control signal G2is asserted.

With this architecture, there is no need to scale the number of current sources; for example, the number of current sources150in this example equals eight, even though 24 electrodes are supported. A fourth group of electrodes (e.g., E25-E32) could also be supported by these same eight current sources, etc. This is of great benefit, and conserves current source resources with the IPG200.

FIG. 4Bshows another current source architecture employing a group select matrix170. The architecture ofFIG. 4Bis somewhat similar to the architecture ofFIG. 2Bdiscussed earlier in that it uses a switch matrix160to associate P current sources1501-150Pwith a number of switch matrix outputs equal to the number of electrodes (N=8) in each Group. The switch matrix160thus allows the current of any of the current sources1501-150Pto be presented at any of the switch matrix160outputs, and the group select matrix170then routes those outputs to particular electrodes in the selected group.

Assume again that electrode E13is to output 5 mA of current while electrode E12is to receive that 5 mA of current. In this example, any of the P sources can be chosen to source and sink the current; assume that source1501will source the current, while source1502will sink the current. Electrode control signals C1,5and C2,4are asserted to close the necessary switches (not shown) in the switch matrix160to respectively connect source1501to the fifth switch matrix output, and source1502to the fourth switch matrix output. Then group control signal G2is asserted to respectively route those switch matrix outputs to electrodes E13and E12.

FIG. 5shows examples of therapies that can be enabled using the current source architectures ofFIG. 4A or 4B. As before, three arrays of electrodes, defining three Groups, are used to provide therapy to three different Locations in the patient. Assume that the therapies appropriate at each of these Locations have already been determined. For example, assume that at Location1it has been determined to source current from electrode E3and to sink that current from electrodes E2and E4, and to do so at particular magnitudes and durations tdwhich are unimportant for purposes of this example. Assume further that such therapy is to be provided at a frequency of f as shown. Assume further that at Location2it has been determined to sink current from electrode E11and to source that current from electrodes E10and E12, again at a frequency of f. Assume still further that at Location3it has been determined to source current from electrode E18and to sink that current from electrode E19, again at a frequency of f.

If the architecture ofFIG. 4Ais used, such therapy can be delivered as shown inFIG. 5. As shown, the therapies at each of the Locations are interleaved, so that the various therapies are non-overlapping. This allows the current sources150to be shared and activated in a time-multiplexed fashion, first being dedicated to provision of therapy at Location1, then Location2, then Location3, and back to Location1again, etc. Assume that the architecture ofFIG. 4Ais used, in which there is a one-to-one correspondence of current sources1501-1508to electrodes within a given Group, i.e., at a particular Location. In this instance, current sources1502-1504are used to provide the therapy to electrodes E2-E4in Group1/Location1. Notice that group control signal G1is asserted during this time as shown inFIG. 5. Then later, for example, after a recovery period t as discussed further below, these same current sources1502-1504are used to provide therapy to electrodes E10-E12in Group2/Location2, but this time with group control signal G2asserted. Again after another recovery period, two of these three same current sources1502-1503are used to provide the therapy to electrodes E18and E19in Group3/Location3, but this time with group control signal G3asserted. To summarize, by interleaving the therapy pulses at the different Groups/Locations, the current sources150can be shared and do not have to be increased in number to support the increased number of electrodes.

As is well known, stimulation pulses such as those shown inFIG. 5would normally be followed by pulses of opposite polarity at the activated electrodes, and even thereafter additional steps may be taken to reduce the build-up of injected charge or to prepare for the provision of the next stimulation pulse. Such portions of time may be referred to generally as a recovery phase, and are shown inFIG. 5as taking place during a time period trp. It is preferable to not issue a next stimulation pulse until the preceding recovery phase is completed. The details of what occurs during the recovery phases are not shown inFIG. 5for simplicity.

The extent to which therapies at different Locations can be interleaved will depend on several factors, such as the frequency f of simulation, the duration of the stimulation pulses td, and the duration of the recovery periods trp. For interleaving and sharing of current sources to occur as shown, these various timing periods should not be in conflict so that access to the current sources can be time multiplexed.

That being said, modifications can be made in the disclosed technique to accommodate at least some potential conflicts. For example, as shown inFIG. 6A, it is seen that the frequency of the therapy provided to the electrodes in Group2/Location2is different (f2) from the frequency provided at the electrodes in Group1/Location1and Group3/Location3(f1). This at times crates periods of conflict, tc, where the Group2/Location2stimulation may overlap with stimulation in other Groups/Locations. For example, specifically shown inFIG. 6Ais a conflict between Group2/Location2and Group1/Location1, where both of these Groups/Location would be calling for support from the same current sources1502-1504. In this circumstance, and assuming the conflict would not occur too often, the logic250in the IPG200(discussed below with reference toFIG. 7) may decide to arbitrate the conflict by allowing only the Group1/Location1electrodes access to the desired current sources1502-1504. In other words, the Group2/Location2electrodes would simply not be pulsed during the conflict, as represented by dotted lies inFIG. 6A. Again, assuming such conflicts will not occur frequently, occasionally missing a stimulation pulse at a Group/Location should not materially affect patient therapy. Also, the downside to such therapy gaps can be alleviated by alternating the Groups/Locations being allowed access to the current sources during a conflict, e.g., by enabling Group1/Location1at a first instance of conflict, Group2/Location2at a second instance of conflict, Group1/Location1at a third instance of conflict, etc.

Conflicts of this type can also be resolved in different ways depending on the current source architecture used.FIG. 6Bshows the same conflict between Group1/Location1and Group2/Location2presented inFIG. 6A. However, here the logic250in the IPG resolves the conflict not by sharing current sources, but instead providing different current sources to Group1/Location1and Group2/Location2. Of course, this assumes a more flexible architecture is used in which current sources can be freely assigned to particular electrodes, such as the architecture ofFIG. 4Bemploying a switch matrix160. Recognizing the conflict, the logic250assigns current sources1501,1505, and1506to electrodes E10, E11, and E12in Group2/Location2, rather than the current sources that might otherwise be expected (i.e., sources1502-1504) which are instead assigned to the electrodes in Group1/Location1. Note that during the conflict both group control signals G1and G2can be asserted. Note also that current sources1502-1503are also assigned to the electrodes in Group3/Location3, which is possible because there is no conflict between Group1/Location1and Group3/Location3.

As noted above, control of the various current source architectures disclosed herein can be achieved by suitably programmed logic circuitry250, as shown inFIG. 7. Logic250in one example can comprise a microcontroller, as is common in an IPG. While the microcontroller250can implement many different IPG functions, as relevant here the microcontroller is responsible for processing one or more stimulation programs255dictating therapy for a patient, and for enabling the current sources and groups accordingly. In one embodiment, the stimulation program255comprises separate stimulation programs for each Group/Location, which specific programs may have been arrived at through a fitting procedure during which the patient expresses his preference for particular settings. As shown, the microcontroller250ultimately issues commands to the current source architecture at appropriate times, including enabling particular current sources150, and specifying the magnitude, polarity, and duration of the current pulses. Also ultimately issued by the microcontroller250are the group control signals (G1, G2, etc.), which are received at the group select matrix170. If the current source architecture employs a switching matrix160as shown and described inFIG. 4Bfor example, the microcontroller250can also issue the control signals for that matrix (C1,1-CP,N). To the extent that the stimulation program255presents a conflict, such as those discussed earlier with respect toFIGS. 6A and 6B, special arbitration logic260may be used to resolve the conflict, such as by skipping certain stimulation pulses (FIG. 6A), rerouting alternative current sources150if possible (FIG. 6B), or in other ways.

To this point it has been assumed that Groups/Locations of electrodes correspond to particular arrays102coupled to the IPG. But this is not necessarily the case, and groups of electrodes and their locations can be established in other ways. For example,FIG. 8Ashows a single electrode arrays having 24 electrodes, divided into three Groups of eight. Each of these Groups corresponds to a different Location for therapy, even though present on the same array102, and thus this type of electrode grouping arrangement can still benefit from the current source architectures described herein. For example, eight current sources150can be employed if the architecture ofFIG. 4Ais used, or P current sources if the architecture ofFIG. 4Bis used.FIG. 8Bshows another example in which a plurality of arrays (1021and1022) are treated as one Group of eight electrodes, even though such arrays would not be at exactly the same location in the patient. Nonetheless, the 24 electrodes present inFIG. 8Bcan be supported by eight current sources (FIG. 4A) or P current sources (FIG. 4B).

It should be understood that a “current source” comprises any type of power source capable of delivering a stimulation current to an electrode, such as a constant current source, a constant voltage source, or combinations of such sources.

A “microcontroller” should be understood as any suitable logic circuit, whether integrated or not, or whether implemented in hardware or software.