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

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..

<FIG> shows a traditional Implantable Pulse Generator (IPG) <NUM>, which includes a biocompatible device case <NUM> formed of a conductive material such as titanium for example. The case <NUM> typically holds the circuitry and a battery necessary for the IPG <NUM> to function, although IPGs can also be powered via external RF energy and without a battery. The IPG <NUM> includes in this simple example an electrode array <NUM> containing a linear arrangement of electrodes <NUM>. The electrodes <NUM> are carried on a flexible body <NUM>, which also houses the individual electrode leads <NUM> coupled to each electrode. In the illustrated embodiment, there are eight electrodes on array <NUM>, labeled E<NUM>-E<NUM>, although the number of electrodes is application specific and therefore can vary. Array <NUM> couples to case <NUM> using a lead connector <NUM>, which is fixed in a nonconductive header material <NUM> such as epoxy for example. As is well known, the array <NUM> is implanted in an appropriate location in a patient to provide suitable simulative therapy, and is coupled through the patient's tissue to the IPG <NUM>, which may be implanted somewhat distant from the location of the array.

As shown in <FIG>, the IPG <NUM> typically includes an electronic substrate assembly <NUM> including a printed circuit board (PCB) <NUM>, along with various electronic components <NUM>, such as microprocessors, integrated circuits, and capacitors mounted to the PCB <NUM>. Two coils (more generally, antennas) are generally present in the IPG <NUM>: a telemetry coil <NUM> used to transcutaneously transmit/receive data to/from an external controller (not shown); and a charging coil <NUM> for transcutaneously charging or recharging the IPG's battery <NUM> using an external charger (also not shown).

A portion of circuitry <NUM> in the IPG <NUM> is dedicated to the provision of therapeutic currents to the electrodes <NUM>. Such currents are typically provided by current sources <NUM>, as shown in <FIG>. In many current-source based architectures, some number of current sources <NUM> are associated with a particular number of electrodes <NUM>. For example, in <FIG>, it is seen that N electrodes E<NUM>-EN are supported by N dedicated current sources <NUM><NUM>-<NUM>N. In this example, and as is known, the current sources <NUM> are 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 source <NUM><NUM> is programmed to source a <NUM> mA current, and source <NUM><NUM> is programmed to sink a <NUM> mA current, then <NUM> mA of current would flow from anode E<NUM> to cathode E<NUM> through 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> shows 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 IPG <NUM> into the patient. For simplicity, decoupling capacitors are not shown in subsequent drawings, even though they are typically present in practical implementations).

<FIG> shows another example current source architecture using a switch matrix <NUM>. In this architecture, the switch matrix <NUM> is used to route current from any of the sources <NUM>P to any of the electrodes EN. For example, if source <NUM><NUM> is programmed to source a <NUM> mA current, and source <NUM><NUM> is programmed to sink a <NUM> mA current, and if source <NUM><NUM> is coupled to electrode E2 by the switch matrix <NUM>, and if source <NUM><NUM> is connected to electrode E<NUM> by the switch matrix <NUM>, then <NUM> mA of current would flow from anode E<NUM> to cathode E<NUM> through the patient's tissue, R. In this example, because any of the current sources <NUM> can 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 sources <NUM> in 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 matrix <NUM> would contains PxN switches, and as many control signals (C<NUM>,<NUM>-CP,N), to controllably interconnect all of the sources <NUM>P to any of the N electrodes. Further details of a suitable switch matrix can be found in U. Patent Pub.

The architecture of <FIG>, like the architecture of <FIG>, also comprises some number of current sources <NUM> (P) associated with a particular number of electrodes <NUM> (N). Other more complicated current architectures exist in the implantable stimulator art. See, e.g., the above-incorporated '<NUM> Publication. But again generally such approaches all require some number of current sources <NUM> to be associated with a particular number of electrodes <NUM>.

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. <CIT>, <CIT> and <CIT> relate to an active electrode.

<FIG> shows a more complicated IPG <NUM> which 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 arrays <NUM><NUM>-<NUM><NUM>, each containing eight electrodes, with electrodes E<NUM>-E<NUM> on array <NUM><NUM>, E<NUM>-E<NUM> on array <NUM><NUM>, and E<NUM>-E<NUM> on array <NUM><NUM>. Each of the arrays <NUM> couples to the IPG <NUM> at a suitable lead connector <NUM><NUM>-<NUM><NUM>, which lead connectors can be arranged in the header <NUM> in 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 arrays <NUM><NUM>-<NUM><NUM> comprises 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, Location <NUM> for the Group <NUM> electrodes of array <NUM><NUM> (E<NUM>-E<NUM>) might comprise the patient's right leg; Location <NUM> for the Group <NUM> electrodes of array <NUM><NUM> (E<NUM>-E<NUM>) the left leg; and Location <NUM> for the Group <NUM> electrodes of array <NUM><NUM> (E<NUM>-E<NUM>) the patient's spinal column. In a therapy designed to alleviate lower back pain, Location <NUM> of Group <NUM> might comprise the right side of a patient's spinal column; Location <NUM> of Group <NUM> the left side of the spinal column; and Location <NUM> of Group <NUM> a central location in the spinal column. Or each of Locations <NUM>-<NUM> may 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 <NUM> in this example) would require tripling the number of current sources in the IPG <NUM> used 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 in <FIG>. Consistent with <FIG>, <NUM> total electrodes are supported by the current source circuitry of <FIG>, comprising three arrays <NUM><NUM>-<NUM><NUM> (e.g., Groups) present in three different Locations in the body. <FIG> is somewhat similar to the architecture of <FIG> discussed earlier, in that there is a one-to-one correspondence of current sources <NUM> to electrodes within a given Group. For example, there are eight current sources <NUM>, and eight electrodes in each Group. New to <FIG> is a group select matrix <NUM>. The group select matrix <NUM> allows current from the current sources <NUM> to be sent to particular electrodes in each of the Groups. For example, current source <NUM><NUM> can send its current to electrode E<NUM> in Group <NUM>, to E<NUM> in Group <NUM>, and to E<NUM> in Group <NUM>. Current source <NUM><NUM> can send its current to E<NUM> in Group <NUM>, to E<NUM> in Group <NUM>, and E<NUM> in Group <NUM>, etc..

Group control is enabled in this example by the use of three group control signals G1-G3. When G1 is asserted, switches (e.g., transistors) in the group switch matrix <NUM> are closed to respectively route the current from each of the current sources <NUM><NUM>-<NUM><NUM> to Group <NUM> electrodes E<NUM>-E<NUM>. (Of course, not all of the current sources <NUM><NUM>-<NUM><NUM> may be programmed at a given moment to provide a current, and so current will not necessarily flow at an electrode E<NUM>-E<NUM> merely because of the assertion of G1). When G2 is asserted, each of the current sources <NUM><NUM>-<NUM><NUM> are coupled to Group <NUM> electrodes E<NUM>-E<NUM>, and likewise when G3 is asserted, each of the current sources <NUM><NUM>-<NUM><NUM> are coupled to Group <NUM> electrodes E<NUM>-E<NUM>. Although shown as switches, it should be understood that the group switch matrix <NUM> may also comprise a plurality of multiplexers.

Assume electrode E<NUM> is to output <NUM> mA of current while electrode E<NUM> is to receive that <NUM> mA of current. In this example, source <NUM><NUM> is programmed to source <NUM> mA worth of current, source <NUM><NUM> is programmed to sink <NUM> mA of current, and group control signal G2 is asserted.

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

<FIG> shows another current source architecture employing a group select matrix <NUM>. The architecture of <FIG> is somewhat similar to the architecture of <FIG> discussed earlier in that it uses a switch matrix <NUM> to associate P current sources <NUM><NUM>-<NUM>P with a number of switch matrix outputs equal to the number of electrodes (N=<NUM>) in each Group. The switch matrix <NUM> thus allows the current of any of the current sources <NUM><NUM>-<NUM>P to be presented at any of the switch matrix <NUM> outputs, and the group select matrix <NUM> then routes those outputs to particular electrodes in the selected group.

Assume again that electrode E<NUM> is to output <NUM> mA of current while electrode E<NUM> is to receive that <NUM> mA of current. In this example, any of the P sources can be chosen to source and sink the current; assume that source <NUM><NUM> will source the current, while source <NUM><NUM> will sink the current. Electrode control signals C<NUM>,<NUM> and C<NUM>,<NUM> are asserted to close the necessary switches (not shown) in the switch matrix <NUM> to respectively connect source <NUM><NUM> to the fifth switch matrix output, and source <NUM><NUM> to the fourth switch matrix output. Then group control signal G2 is asserted to respectively route those switch matrix outputs to electrodes E<NUM> and E<NUM>.

<FIG> shows examples of therapies that can be enabled using the current source architectures of <FIG> or <FIG>. 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 Location <NUM> it has been determined to source current from electrode E<NUM> and to sink that current from electrodes E<NUM> and E<NUM>, and to do so at particular magnitudes and durations td which 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 Location <NUM> it has been determined to sink current from electrode E<NUM> and to source that current from electrodes E<NUM> and E<NUM>, again at a frequency of f. Assume still further that at Location <NUM> it has been determined to source current from electrode E<NUM> and to sink that current from electrode E<NUM>, again at a frequency of f.

If the architecture of <FIG> is used, such therapy can be delivered as shown in <FIG>. As shown, the therapies at each of the Locations are interleaved, so that the various therapies are non-overlapping. This allows the current sources <NUM> to be shared and activated in a time-multiplexed fashion, first being dedicated to provision of therapy at Location <NUM>, then Location <NUM>, then Location <NUM>, and back to Location <NUM> again, etc. Assume that the architecture of <FIG> is used, in which there is a one-to-one correspondence of current sources <NUM><NUM>-<NUM><NUM> to electrodes within a given Group, i.e., at a particular Location. In this instance, current sources <NUM><NUM>-<NUM><NUM> are used to provide the therapy to electrodes E<NUM>-E<NUM> in Group <NUM>/Location1. Notice that group control signal G1 is asserted during this time as shown in <FIG>. Then later, for example, after a recovery period trp as discussed further below, these same current sources <NUM><NUM>-<NUM><NUM> are used to provide therapy to electrodes E<NUM>-E<NUM> in Group <NUM>/Location <NUM>, but this time with group control signal G2 asserted. Again after another recovery period, two of these three same current sources <NUM><NUM>-<NUM><NUM> are used to provide the therapy to electrodes E<NUM> and E<NUM> in Group <NUM>/Location <NUM>, but this time with group control signal G3 asserted. To summarize, by interleaving the therapy pulses at the different Groups/Locations, the current sources <NUM> can 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 in <FIG> would normally be followed by pulses of opposite polarity at the activated electrodes, and even thereafter additional steps may be taken to reduce the buildup 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 in <FIG> as 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 in <FIG> for 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 in <FIG>, it is seen that the frequency of the therapy provided to the electrodes in Group <NUM>/Location <NUM> is different (f<NUM>) from the frequency provided at the electrodes in Group <NUM>/Location <NUM> and Group <NUM>/Location <NUM> (f<NUM>). This at times crates periods of conflict, tc, where the Group <NUM>/Location <NUM> stimulation may overlap with stimulation in other Groups/Locations. For example, specifically shown in <FIG> is a conflict between Group <NUM>/Location <NUM> and Group <NUM>/Location <NUM>, where both of these Groups/Location would be calling for support from the same current sources <NUM><NUM>-<NUM><NUM>. In this circumstance, and assuming the conflict would not occur too often, the logic <NUM> in the IPG <NUM> (discussed below with reference to <FIG>) may decide to arbitrate the conflict by allowing only the Group <NUM>/Location <NUM> electrodes access to the desired current sources <NUM><NUM>-<NUM><NUM>. In other words, the Group <NUM>/Location <NUM> electrodes would simply not be pulsed during the conflict, as represented by dotted lies in <FIG>. 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 Group <NUM>/Location <NUM> at a first instance of conflict, Group <NUM>/Location <NUM> at a second instance of conflict, Group <NUM>/Location <NUM> at 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> shows the same conflict between Group <NUM>/Location <NUM> and Group <NUM>/Location <NUM> presented in <FIG>. However, here the logic <NUM> in the IPG resolves the conflict not by sharing current sources, but instead providing different current sources to Group <NUM>/Location <NUM> and Group <NUM>/Location <NUM>. 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 of <FIG> employing a switch matrix <NUM>. Recognizing the conflict, the logic <NUM> assigns current sources <NUM><NUM>, <NUM><NUM>, and <NUM><NUM> to electrodes E<NUM>, E<NUM>, and E<NUM> in Group <NUM>/Location <NUM>, rather than the current sources that might otherwise be expected (i.e., sources <NUM><NUM>-<NUM><NUM>) which are instead assigned to the electrodes in Group <NUM>/Location <NUM>. Note that during the conflict both group control signals G1 and G2 can be asserted. Note also that current sources <NUM><NUM>-<NUM><NUM> are also assigned to the electrodes in Group3/Location <NUM>, which is possible because there is no conflict between Group <NUM>/Location <NUM> and Group <NUM>/Location <NUM>.

As noted above, control of the various current source architectures disclosed herein can be achieved by suitably programmed logic circuitry <NUM>, as shown in <FIG>. Logic <NUM> in one example can comprise a microcontroller, as is common in an IPG. While the microcontroller <NUM> can implement many different IPG functions, as relevant here the microcontroller is responsible for processing one or more stimulation programs <NUM> dictating therapy for a patient, and for enabling the current sources and groups accordingly. In one embedment, the stimulation program <NUM> comprises 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 microcontroller <NUM> ultimately issues commands to the current source architecture at appropriate times, including enabling particular current sources <NUM>, and specifying the magnitude, polarity, and duration of the current pulses. Also ultimately issued by the microcontroller <NUM> are the group control signals (G1, G2, etc.), which are received at the group select matrix <NUM>. If the current source architecture employs a switching matrix <NUM> as shown and described in <FIG> for example, the microcontroller <NUM> can also issue the control signals for that matrix (C<NUM>,<NUM>-CP,N). To the extent that the stimulation program <NUM> presents a conflict, such as those discussed earlier with respect to <FIG> and <FIG>, special arbitration logic <NUM> may be used to resolve the conflict, such as by skipping certain stimulation pulses (<FIG>), rerouting alternative current sources <NUM> if possible (<FIG>), or in other ways.

To this point it has been assumed that Groups/Locations of electrodes correspond to particular arrays <NUM> coupled 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> shows a single electrode arrays having <NUM> electrodes, divided into three Groups of eight. Each of these Groups corresponds to a different Location for therapy, even though present on the same array <NUM>, and thus this type of electrode grouping arrangement can still benefit from the current source architectures described herein. For example, eight current sources <NUM> can be employed if the architecture of <FIG> is used, or P current sources if the architecture of <FIG> is used. <FIG> shows another example in which a plurality of arrays (<NUM><NUM> and <NUM><NUM>) 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 <NUM> electrodes present in <FIG> can be supported by eight current sources (<FIG>) or P current sources (<FIG>).

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.

Claim 1:
An implantable stimulator device (<NUM>; <NUM>), comprising:
a case (<NUM>);
a plurality of arrays (<NUM>) coupled to the case (<NUM>), wherein each array comprises a group of a plurality of electrodes (E1-E24) configured for implantation at a location in a patient;
a plurality of current sources (<NUM>) inside the case (<NUM>); and
a group selection matrix (<NUM>; <NUM>) inside the case (<NUM>) controllable by a plurality of group control signals each for coupling the plurality of current sources to a different selected group of the plurality of electrodes (E1-E24).