U.S. patent application number 12/425505 was filed with the patent office on 2010-10-21 for architectures for multi-electrode implantable stimulator devices having minimal numbers of decoupling capacitors.
This patent application is currently assigned to Boston Scientific Neuromodulation Corporation. Invention is credited to Rafael Carbunaru, Jordi Parramon.
Application Number | 20100268309 12/425505 |
Document ID | / |
Family ID | 42167532 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100268309 |
Kind Code |
A1 |
Parramon; Jordi ; et
al. |
October 21, 2010 |
Architectures for Multi-Electrode Implantable Stimulator Devices
Having Minimal Numbers of Decoupling Capacitors
Abstract
Architectures for implantable stimulators having N electrodes
are disclosed. The architectures contains X current sources, or
DACs. In a single anode/multiple cathode design, one of the
electrodes is designated as the anode, and up to X of the
electrodes can be designated as cathodes and independently
controlled by one of the X DACs, allowing complex patient therapy
and current steering between electrodes. The design uses at least X
decoupling capacitors: X capacitors in the X cathode paths, or one
in the anode path and X-1 in the X cathode paths. In a multiple
anode/multiple cathode design having X DACs, a total of X-1
decoupling capacitors are needed. Because the number of DACs X can
typically be much less than the total number of electrodes (N),
these architectures minimize the number of decoupling capacitors
which saves space, and ensures no DC current injection even during
current steering.
Inventors: |
Parramon; Jordi; (Valencia,
CA) ; Carbunaru; Rafael; (Valley Village,
CA) |
Correspondence
Address: |
Wong, Cabello, Lutsch, Rutherford & Brucculeri LLP
20333 SH 249, Suite 600
Houston
TX
77070
US
|
Assignee: |
Boston Scientific Neuromodulation
Corporation
Valencia
CA
|
Family ID: |
42167532 |
Appl. No.: |
12/425505 |
Filed: |
April 17, 2009 |
Current U.S.
Class: |
607/116 |
Current CPC
Class: |
A61N 1/3686 20130101;
A61N 1/37205 20130101; A61N 1/36125 20130101; A61N 1/05 20130101;
A61N 1/36185 20130101 |
Class at
Publication: |
607/116 |
International
Class: |
A61N 1/05 20060101
A61N001/05 |
Claims
1. An implantable medical device, comprising: a plurality of N
electrodes, wherein only one first of the electrodes is designated
as either a cathode or an anode having a first current path, and
wherein a second plurality of the other of the electrodes are
designatable as the other of cathodes or anodes each having a
second current path; a plurality of X current sources, each current
source being coupleable to one of the second electrodes, wherein X
is less than N; and a plurality of at least X capacitors, wherein
the at least X capacitors are placed in the first or second current
paths.
2. The device of claim 1, wherein the device comprises X+1
capacitors such that each of the first or second current paths
contains a capacitor.
3. The device of claim 1, wherein the device comprises only X
capacitors such that only one of the first or second current paths
contains no capacitor.
4. The device of claim 3, wherein the X capacitors are placed in
the second current paths such that only the first current path
contains no capacitor.
5. The device of claim 3, wherein X-1 of the capacitors are placed
in the second current paths and one of the capacitors is placed in
the first current path such that only one of the second current
paths contains no capacitor.
6. The device of claim 1, wherein the first electrode comprises an
anode, and wherein the second electrodes are designatable as
cathodes.
7. The device of claim 1, wherein the first electrode comprises a
cathode, and wherein the second electrodes are designatable as
anodes.
8. The device of claim 1, wherein the first electrode can be
selected from any of the N electrodes.
9. The device of claim 1, wherein the first electrode comprises a
dedicated one of the N electrodes.
10. A method for operating an implantable medical device having a
plurality of electrodes, comprising: simultaneously designating
only one first electrode as either a cathode or anode thereby
establishing a first current path, and a plurality of Y second
electrodes as the other of the cathodes or anodes thereby
establishing Y second current paths; and placing only Y capacitors
in the first or second current paths, wherein only one of the first
or second current paths contains no capacitor.
11. The method of claim 10, wherein the Y capacitors are placed in
the second current paths such that the first current path contains
no capacitor.
12. The method of claim 10, wherein Y-1 of the capacitors are
placed in the second current paths and one of the capacitors is
placed in the first current path such that only one of the second
current paths contains no capacitor.
13. The method of claim 10, wherein the first electrode is
designated as an anode, and wherein the second electrodes are
designated as cathodes.
14. The method of claim 10, wherein the first electrode is
designated as an cathode, and wherein the second electrodes are
designated as anodes.
15. The method of claim 10, wherein the first electrode can be
selected from any of the plurality of electrodes.
16. The method of claim 10, wherein the first electrode comprises a
dedicated one of the plurality of electrodes.
17. The method of claim 10, wherein the second electrodes are
designated by coupling each to a current source.
18. An implantable medical device, comprising: a plurality of N
electrodes, wherein at least one first electrode is designatable as
either a cathode or an anode having a first current path, and
wherein at least one second electrodes is designatable as the other
of cathodes or anodes having a second current path; a plurality of
J anode current sources, each anode current source being coupleable
to one of the first electrodes; and a plurality of I cathode
current sources, each cathode current source being coupleable to
one of the second electrodes; and a plurality of at least J+I-1
capacitors, wherein the at least J+I-1 capacitors are placed in the
first and second current paths.
19. The device of claim 18, wherein J is less than N and wherein I
is less than N.
20. The device of claim 18, wherein the device comprises J+I
capacitors such that each of the first or second current paths
contains a capacitor.
21. The device of claim 18, wherein the device comprises only J+I-1
capacitors such that only one of the first or second current paths
contains no capacitor.
22. The device of claim 18, wherein the at least one first
electrode is designatable as an anode, and wherein the at least one
second electrode is designatable as a cathodes.
23. The device of claim 18, wherein the at least one first
electrode can be selected from any of the N electrodes.
24. The device of claim 18, wherein each of the J anode current
sources are coupleable to any of the first electrodes by a switch
matrix, and wherein each of the I cathode current sources are
coupleable to any of the second electrodes by a switch matrix.
25. The device of claim 18, wherein the J anode current sources are
coupled to a compliance voltage, and wherein the I cathode current
sources are coupled to a reference voltage.
26. The device of claim 18, wherein J equals I.
27. An implantable medical device, comprising: a plurality of N
electrodes, wherein at least one first electrode is designatable as
either a cathode or an anode having a first current path, and
wherein at least one second electrodes is designatable as the other
of cathodes or anodes having a second current path; a plurality of
X current sources, each current source being programmable as either
a anode current source coupleable to one of the first electrodes,
or as a cathode current source coupleable to one of the second
electrodes; a plurality only X-1 capacitors, wherein the X-1
capacitors are placed in the first and second current paths such
that only one of the first or second current paths contains no
capacitor.
28. The device of claim 27, wherein X is less than N.
29. The device of claim 27, wherein the at least one first
electrode is designatable as an anode, and wherein the at least one
second electrode is designatable as a cathodes.
30. The device of claim 27, wherein the at least one first
electrode can be selected from any of the N electrodes.
31. The device of claim 27, wherein each of the X current sources
are coupleable to any of the N electrodes by a switch matrix.
32. A method for operating an implantable medical device having a
plurality of electrodes, comprising: simultaneously designating at
least one P first electrode as either a cathode or anode thereby
establishing P first current paths, and a plurality of Q second
electrodes as the other of the cathodes or anodes thereby
establishing Q second current paths; placing only P+Q-1 capacitors
in the first or second current paths, wherein only one of the first
or second current paths contains no capacitor.
33. The method of claim 32, wherein the P first electrodes and the
Q second electrodes can be selected from any of the plurality of
electrodes.
34. The method of claim 32, wherein each of the P first electrodes
are coupled to a first current source of a first polarity and
wherein each of the Q second electrodes are coupled to a second
current source of a second polarity opposite the first
polarity.
35. The method of claim 32, wherein the first current sources are
coupled to a compliance voltage, and wherein the second current
sources are coupled to a reference voltage.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to multi-electrode
implantable stimulator devices.
BACKGROUND
[0002] Implantable stimulation devices generate and deliver
electrical stimuli to 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,
occipital nerve stimulators to treat migraine headaches, and other
neural stimulators to treat urinary incontinence, sleep apnea,
shoulder sublaxation, etc. Implantable stimulation devices may
comprise a microstimulator device of the type disclosed in U.S.
Patent Application Publication 2008/0097529, or a spinal cord
stimulator of the type disclosed in U.S. Patent Application
Publication 2007/0135868, or other forms.
[0003] Microstimulator devices typically comprise a small,
generally-cylindrical housing which carries electrodes for
producing a desired electric stimulation current. Devices of this
type are implanted proximate to the target tissue to allow the
stimulation current to stimulate the target tissue to provide
therapy. A microstimulator's case is usually on the order of a few
millimeters in diameter by several millimeters to a few centimeters
in length, and usually includes or carries stimulating electrodes
intended to contact the patient's tissue. However, a
microstimulator may also or instead have electrodes coupled to the
body of the device via a lead or leads.
[0004] Some microstimulators 2 in the prior art contain only one
two electrodes, such as is shown in FIG. 1, and are thus referred
to as "bi-electrode" microstimulators. An example of a bi-electrode
microstimulator device includes the Bion.RTM. device made by Boston
Scientific Neuromodulation Corporation of Valencia, Calif. A single
anode electrode, Eanode, sources current into a resistance R, i.e.,
the user's tissue. The return path for the current is provided by a
single cathode electrode, Ecathode. Either of the anode or cathode
electrodes could comprise the case of the device, or other
conductive part of the case. Current flows by operation of a
current source 20, which typically comprises a Digital-to-Analog
Converter, or "DAC" 20, which is programmable to provide a desired
therapeutic current, Iout, to the patient's tissue R. Such current
Iout is typically pulsed as shown in the bottom of FIG. 1, and can
have a frequency and duty cycle suitable for the patient.
[0005] A current source or DAC could also be coupled to the anode.
However, as shown, the anode is coupled to a compliance voltage,
V+, of sufficient strength to provide the current, Iout, programmed
into the DAC 20. This compliance voltage can be generated from a
battery voltage, Vbat, provided by a battery 12 in the
microstimulator 2. A DC-DC converter 22 is used to boost Vbat to
the desired compliance voltage V+, and is controlled by a V+
monitor and adjust circuitry 18. Because such circuitry for
compliance voltage generation is well known, and not directly
germane to the issues presented by this disclosure, further
elaboration is not provided.
[0006] Also shown in FIG. 1 is the provision of decoupling or
blocking capacitors 42 and 44 hardwired to the anode and cathode
respectively. As is well known, such decoupling capacitors only
allow the passage of AC components of the current provided by the
DAC 20, and thus prevent the DC injection of current into the
patient's tissue R (Idc=0). Preventing DC current injection into
the tissue is desired for safety: when the DC component of the
current is removed, the possibility of current building up in the
patient's tissue is minimized.
[0007] Although two decoupling capacitors 42 and 44 are shown in
FIG. 1, only one is needed to prevent DC current injection, which
one capacitor is coupled to the DAC 20. Thus, when the DAC 20
appears on the cathode side of the current path, only a cathode
capacitor 44 is needed, as shown in FIG. 2. Likewise, were the DAC
20 on the anode side of the current path, only an anode capacitor
42 would be needed (not shown in FIG. 2). Using only one decoupling
capacitor 42 or 44 is preferred because the decoupling capacitors
tend to be rather large in comparison to the rest of the circuitry
within the microstimulator 2, and hence take up significant room in
the case. Reducing the number of decoupling capacitors therefore
allows the microstimulator 2 to be made smaller, which simplifies
the implanting procedure and conveniences the patient.
[0008] Bi-electrode microstimulators 2 benefit from simplicity.
Because of their small size, such microstimulators 2 can be
implanted at site requiring patient therapy, and without leads to
carry the therapeutic current away from the body as mentioned
previously. However, such bi-electrode microstimulators lack
therapeutic flexibility: once implanted, the single cathode/anode
combination will only recruit nerves in their immediate proximity,
which generally cannot be changed unless the position of the device
is manipulated in a patient's tissue.
[0009] To improve therapeutic flexibility, microstimulators having
more than two electrodes have been proposed, and such devices are
referred to herein as "multi-electrode" microstimulators to
differentiate them from bi-electrode microstimulators discussed
above. When increasing the number of electrodes in this fashion,
the electrodes can be selectively activated once the device is
implanted, providing the opportunity to manipulate therapy without
having to manipulate the position of the device.
[0010] Exemplary multi-electrode microstimulators 4, 6, and 8 are
shown in FIGS. 3A-3C respectively, and are disclosed in the '529
Publication referenced above. As its name suggests, the
multi-electrode microstimulator comprises a plurality of
electrodes, which electrodes may be located on the case in various
manners, such as on two sides of the case as shown in the pictures
at the bottom right of FIGS. 3A-3C. In this and subsequent
examples, it should be noted that any of the electrodes can
comprise the implant's case, or conductive portions thereof.
[0011] In the embodiment of FIG. 3A, there is provided a dedicated
anode electrode, Eanode. By contrast, one of E1cathode-Encathode is
selectable as the cathode via cathode switches 62.sub.1-62.sub.n.
Selecting a particular cathode by closing its corresponding cathode
switch couples that cathode to the DAC 20. For example, FIG. 3A
shows the circuit that is completed when E1cathode is selected.
Notice that this design employs a single decoupling capacitor 42 in
the anode path.
[0012] Also shown in FIG. 3A are recovery switches 64 and
66.sub.1-66.sub.n. As explained in the above-referenced '529
Publication, the recovery switches 64 and 66.sub.1-66.sub.n are
activated at some point after provision of a stimulation pulse, and
have the goal of recovering any remaining charge left on the
decoupling capacitor 44 and in the patient's tissue. Thus, after a
stimulation pulse, the recovery switch 64 and at least one of
switches 66.sub.1-66.sub.n are closed. Closure of these switches
places the same reference voltage on each plate of the decoupling
capacitor 302, thus removing any stored charge. In one embodiment,
for convenience, the reference voltage used is the battery voltage,
Vbat, of the battery in the microstimulator 4, although any other
reference potential could be used. Thus, during recovery, Vbat is
placed on the left plate of capacitor 44 via recovery switch 64,
and is likewise placed on the right plate (through the patient's
tissue, R) via one or all of the recovery switches
66.sub.1-66.sub.n. As recovery is discussed in further detail in
the '529 Publication, and it is not directly germane to this
disclosure, it is not further discussed.
[0013] The embodiment of FIG. 3B improves upon the embodiment of
FIG. 3A in that it allows the anode electrode to be selected as
well as the cathode electrode. Thus, the device contains N
electrodes, E1-En, any of which can comprise the anode or cathode
at any given time. As before, which electrode acts as the cathode
is determined by selecting a particular cathode switch
62.sub.1-62.sub.n. Which electrode acts as the anode is determined
by selecting a particular anode switch 68.sub.1-68.sub.n. For
example, FIG. 3B shows the circuit that is completed when E1 is
selected as the anode, and E2 is selected as the cathode. Notice
again that this design employs a single decoupling capacitor 42 in
the anode path, regardless of which electrode is selected as the
anode.
[0014] The embodiments of FIGS. 3A and 3B are similar in that the
singular decoupling capacitor 42 prevents DC current injection to
the patient's tissue R, i.e., Idc=0. As a result, these designs can
be regarded as generally safe for the reasons stated earlier.
Moreover, these designs are generally compact: most significantly,
they only require a single decoupling capacitor 42.
[0015] However, the designs of FIGS. 3A and 3B have a shortcoming
arising from their provision of a single DAC 20, namely the
inability to simultaneously and independently modify the current at
two or more different cathodes. Being able to so modify the current
at two (or more) different cathode electrodes is desired in one
example to "steer" current from one cathode to another. The concept
of current steering is addressed in U.S. Patent Application
Publication 2007/0239228, and so is only briefly explained here
with reference to FIG. 4. FIG. 4 presents an initial condition, in
which E2 has been designated as the anode, and E4 has been
designated as the cathode. As the net amount of current provided by
these electrodes must equal zero, E2 sources 10 mA, while E4 sinks
-10 mA. In the next condition, some of the sink current (-2 mA) has
been moved or "steered" from cathode electrode E4 to E3. Steering
in 2 mA increments continues until in the last condition, all of
the sink current (-10 mA) has been moved to cathode E3, while
original cathode E4 is now off. Anode current can be similarly
steered in some stimulators, but this is not shown. Being able to
steer the current in this fashion not only improves the complexity
of therapy that can be provided to the patient, but also allows for
safe and comfortable experimentation during fitting to determine
the best electrodes to activate for a particular patient. However,
the designs of FIGS. 3A and 3B cannot so steer the current at two
different cathodes simultaneously.
[0016] An embodiment disclosed in the above-referenced '529
Publication capable of current steering is shown in FIG. 3C. This
microstimulator 8 improves from the microstimulator 6 of FIG. 3B in
that each electrode E1-En has its own dedicated, and
independently-controllable, DAC 20.sub.1-20.sub.n. As a result,
more than one electrode can be selected as the cathode at any given
time via selection of two or more of the cathode selection switches
62.sub.1-62.sub.n, and the current sunk at each can be
independently controlled by the corresponding DACs
20.sub.1-20.sub.n, which enables current steering of the sort
depicted in FIG. 4.
[0017] Unfortunately, microstimulator 8 of FIG. 3C has a
shortcoming related to its provision of a single decoupling
capacitor 42, namely the possibility of direct DC current injection
into the patient's tissue R during current steering. This is
illustrated in FIG. 5. The first circuit shows the selection of Ex
as the anode, and only a single electrode Ey as the cathode. In
this condition, the decoupling capacitor 42 prevents DC current
injection through the entirety of the current path. However, the
second circuit shows the selection of electrodes Ey and Ez as
cathodes, such as might occur when some of the current at Ey is
steered to Ez. In this configuration, the decoupling capacitor 42
prevents DC current injection in the anode path Idc.sub.a=0.
However, no such decoupling capacitor appears in the cathode paths,
and therefore DACs 20y and 20z are not prevented from providing a
DC current through the patient's tissue. In short, while the design
of FIG. 3C allows for current steering, and might be relatively
compact by virtue of its single capacitor 42, it does not guarantee
an absence of direct DC current injection into each cathode
electrode.
[0018] FIG. 6 provides yet another design for a multi-electrode
implantable stimulator 10. This type of design is often used in a
spinal cord stimulator (SCS), such as that illustrated in the
above-referenced '868 application. An SCS 10 will typically have a
case which is coupled by leads to an electrode array. The electrode
array is implanted into the patient's spine, while the case is
implanted at a distant, less-critical location, such as in the
patient's buttocks. Because the case is not implanted right at the
location requiring stimulation, the case of the SCS 10 can
typically be larger than the various microstimulators illustrated
to this point.
[0019] As seen in FIG. 6, the SCS 10 has a plurality of electrodes
E1-En. Hardwired to each electrode are decoupling capacitors C1-Cn,
and coupled to each of these capacitors are DACs 20.sub.1-20.sub.n.
In this particular design, the DACs can be controlled to operate as
either current sources or current sinks, and thus their associated
electrodes can comprise anodes or cathodes. Shown in FIG. 6 is an
example in which DAC 20.sub.2 is active as a source thus
designating E2 as an anode, and DAC 20.sub.4 is active as a sink
thus designating E4 as a cathode. All other DACs, and their
associated electrodes, are inactive.
[0020] Because the SCS 10 has individually-controllable DACs
dedicated to each of the electrodes, current can readily be steered
between the two electrodes. That is, two or more of the electrodes
can act as cathodes (sinks) and/or two or more of the electrodes
can act as anodes (sources) at one time. Moreover, because each
electrode is hardwired to a decoupling capacitor C1-Cn, there is no
risk of direct DC current injection into the tissue R of the
patient, even during current steering.
[0021] The SCS 10 system therefore has many favorable functional
benefits. However, the requirement that each of the N electrodes be
hardwired to a dedicated decoupling capacitor means that N
decoupling capacitors must be provided. As mentioned before, these
capacitors can take up significant space in the case of the
implantable stimulator. This may not be as critical of a concern
where the implantable stimulator is an SCS 10 for example, because
as mentioned, that type of device can generally support a larger
case. However, where a small-sized microstimulator is concerned,
the requirement of N capacitors for each of the N electrodes is
prohibitive.
[0022] Accordingly, the inventor believes that the implantable
stimulator art, and particularly the multi-electrode
microstimulator art, would benefit from an architecture that would
minimize device size and ensure patient safety. Specifically
desirable would be a design that would minimize the number of
decoupling capacitors required, but which would still prevent DC
current injection even during current steering. Embodiments of such
a solution are provided herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1 and 2 illustrate the basic electrical components of
a bi-electrode microstimulator in accordance with the prior
art.
[0024] FIGS. 3A through 3C illustrate the basic electrical
components of multi-electrode microstimulators in accordance with
the prior art.
[0025] FIG. 4 illustrates the concept of current steering between
electrodes in a multi-electrode stimulator device.
[0026] FIG. 5 illustrates DC current injection while steering the
multi-electrode microstimulator of FIG. 3C.
[0027] FIG. 6 illustrates the basic electrical components of a
spinal cord stimulator in accordance with the prior art.
[0028] FIGS. 7A-7C illustrate a single anode/multiple cathode
stimulator having a minimal number of decoupling capacitors in
accordance with an embodiment of the invention.
[0029] FIGS. 8A-8D illustrate another single anode/multiple cathode
stimulator having a minimal number of decoupling capacitors in
accordance with an embodiment of the invention.
[0030] FIG. 9 illustrates a modification to the single
anode/multiple cathode stimulators having one additional decoupling
capacitor.
[0031] FIG. 10 illustrates implementation of the invention in a
single cathode/multiple anode configuration.
[0032] FIGS. 11A and 11B illustrate implementation of the invention
in a multiple anode/multiple cathode configuration having a minimal
number of decoupling capacitors.
[0033] FIG. 12 illustrates a modification to the multiple
anode/multiple cathode stimulator of FIG. 11A having one additional
decoupling capacitor.
[0034] FIG. 13 illustrates another implementation of the invention
in a multiple anode/multiple cathode configuration having a minimal
number of decoupling capacitors.
[0035] FIG. 14 illustrates a modification to the multiple
anode/multiple cathode stimulator of FIG. 13 having one additional
decoupling capacitor.
DETAILED DESCRIPTION
[0036] Architectures for implantable stimulators having N
electrodes are disclosed. The architectures contains X current
sources, or DACs. In a single anode/multiple cathode design, one of
the electrodes is designated as the anode, and up to X of the
electrodes can be designated as cathodes and independently
controlled by one of the X DACs, allowing complex patient therapy
and current steering between electrodes. The design uses at least X
decoupling capacitors: X capacitors in the X cathode paths, or one
in the anode path and X-1 in the X cathode paths. In a multiple
anode/multiple cathode design having X DACs, a total of X-1
decoupling capacitors are needed. Because the number of DACs X can
typically be much less than the total number of electrodes (N),
these architectures minimize the number of decoupling capacitors
which saves space, and ensures no DC current injection even during
current steering.
[0037] A first embodiment of an improved multi-electrode stimulator
100 is shown in FIGS. 7A and 7B, and a second embodiment 100' is
shown in FIGS. 8A and 8B. The stimulators 100 and 100' comprise
single anode/multiple cathode stimulators similar to
microstimulator 8 illustrated earlier in FIG. 3C. However,
stimulators 100 or 100' could also be employed in a spinal cord
stimulator 10 similar to that illustrated in FIG. 6, or in any
other implantable stimulator.
[0038] Stimulators 100 and 100' comprises N electrodes, E1-En. In
the configurations shown, any one of the electrodes can be
programmed as the anode, and one or more of the other electrodes
can be programmed as cathodes. As best shown in FIGS. 7B and 8B,
any of the electrodes E1-En can be programmed as the anode via
selection of its corresponding anode selection switch
68.sub.1-68.sub.n. However, it is not important to the invention
that the anode electrode be programmable. Instead, a dedicated
anode electrode, similar to microstimulator 4 shown in FIG. 3A,
could also be used.
[0039] Recovery switches 64 and 66a-66x are shown in FIGS. 7B and
8B for completeness. However, because the operation of such
recovery circuitry is essentially similar to that discussed
earlier, and is not required in embodiments of the invention, such
circuitry is not again discussed.
[0040] In the both of stimulators 100 and 100', there are X DACs
20a-20x, and X switch matrices 81a-x for coupling those DACs to any
of the electrodes E1-En. Each switch matrix 81 comprises N cathode
selection switches 62.sub.1-n to couple a given DAC 20 to any of
the N electrodes. For example, if it was desired to couple DAC 20b
to electrode E1, thus designating electrode E1 as a cathode, then
selection switch 62b.sub.1 in switch matrix 81b would be
selected.
[0041] Because there are X DACs 20a-20x, a maximum of X electrodes
can act as cathodes at any given time. (Actually, it is possible
that more than X electrodes can act as cathodes so long as some of
these cathodes share one of the DACs, but this possibility is not
further discussed). Moreover, the current at each of those X
cathode electrodes can be individually and simultaneously
controlled. It would normally be the case that X (the number of
DACs, or the maximum number of cathodes) is smaller than N (the
number of electrodes). This is true because it is generally only
desired to allow some subset of the electrodes (as opposed to all
electrodes) act as cathodes at a given time. For example, in a
microstimulator having N=8 electrodes, it might be desirable to at
most designate X=3 cathodes at one time. In an even simpler example
illustrated in FIG. 8D, which presents an implementation of
stimulator 100', there are N=4 electrodes and X=2 DACs. This allows
one electrode to operate as the anode, while at most two electrodes
can operates as cathodes. In any event, because of the use of X
individually-controllable DACs 20, current in the improved
stimulator 100 can be steered, such as was illustrated in FIG. 4.
As noted earlier, current steering is a useful feature in an
implantable stimulator.
[0042] Unlike the microstimulator 8 of FIG. 3C, such steering can
occur safely in stimulators 100 and 100' with no DC current
injection into the patient's tissue R. Even further, and unlike the
SCS 10 of FIG. 6, such safety is achieved by using a minimal number
of decoupling capacitors.
[0043] Specifically, in each of stimulators 100 and 100', only X
decoupling capacitors (i.e., equal to the number of DACs) are
required to ensure no DC current injection. In the improved
stimulator 100 of FIGS. 7A and 7B, there are no capacitors in the
anode path, and X capacitors 44a to 44x in the cathode paths. In
the improved stimulator 100' of FIGS. 8A and 8B, there is one
capacitor 42 in the anode path, and X-1 capacitors 44a to 44(x-1)
in the cathode paths. Again, because X is usually less than N, this
cuts the total number of decoupling capacitors down from N to X
when compared to the approach of FIG. 6 for example.
[0044] Even when only X total capacitors are used, the improved
stimulators 100 and 100' guarantee no DC current injection in any
path, even during current steering. This can be noticed from the
different scenarios illustrated in FIGS. 7C and 8C for stimulators
100 and 100' respectively.
[0045] Starting with stimulator 100 and FIG. 7C, Scenario I shows
selection of a single cathode electrode Ey using DAC 20a having a
decoupling capacitor 44a. In this case, the cathode capacitor 44a
prevents DC current injection at electrode Ey (Idc.sub.c1=0).
Because the sum of the DC currents must equal 0 at the common node
established by the patent's tissue R, then the current in the anode
path at electrode Ex (Idc.sub.a) must also equal 0, even though the
anode path lacks a capacitor.
[0046] Scenarios II and III include the selection of additional
cathode electrodes, such that, generically speaking, one anode and
Y cathodes are simultaneously designated as a given time. However,
because each of the cathode paths includes a capacitor, and hence
draws no DC current, then the current in the single anode path
(Idc.sub.a) must again equal 0.
[0047] In stimulator 100' of FIGS. 8A and 8B, because only X-1
decoupling capacitors are in the cathode current paths, one of the
DACs (e.g., 20x) is not coupled to a capacitor. However, because
stimulator 100' also includes a capacitor 42 in the anode path, the
lack of a capacitor in the one cathode path does not raise concerns
about DC current injection, even during current steering.
[0048] This can be noticed from the different scenarios illustrated
in FIG. 8C. Scenario I shows selection of a single cathode
electrode Ey using DAC 20a having a decoupling capacitor 44a. In
this case, both the anode capacitor 42 and the cathode capacitor
44a prevent DC current injection along the singular current path
established. Scenario II shows selection of a single cathode
electrode Ey using DAC 20x that does not have a decoupling
capacitor. In this case, the anode capacitor 42 prevents DC current
injection along the singular current path established.
[0049] Scenarios III to V illustrates the selection of additional
cathode electrodes, such that, generically speaking, one anode and
Y cathodes are simultaneously designated as a given time. Scenarios
III and IV select two cathode electrodes Ey and Ez as cathodes,
which could be a permanent therapy setting for a given patient or
could be a temporary setting such as occurs during current steering
between electrodes. In Scenario III, DACs 20a and 20b are used,
each having a capacitor 44a and 44b. As capacitors are present in
the anode path and both cathode paths, it is elementary that no DC
current injection is possible. In scenario IV, DAC 20x, which lacks
a capacitor, is used, along with DAC 20b, which includes a
capacitor 44b. In this case, the DC current in the anode path is
Idc.sub.a=0 by virtue of anode capacitor 42. The DC current in the
cathode path established by DAC 20b is Idc.sub.c1=0 by virtue of
cathode capacitor 44b. Because the sum of the DC currents must
equal 0 at the common node established by the patent's tissue R,
the DC current in the cathode path established by DAC 20x
(Idc.sub.c2) is 0, even though that path lacks a decoupling
capacitor. Scenario V furthers this example by the addition of yet
another cathode path, but still the DC current in the cathode path
established by DAC 20x (Idc.sub.c3) is 0.
[0050] To summarize, in stimulator 100', the cathode path
established by DAC 20x need not contain a decoupling capacitor
because all other paths to the patient's tissue R, i.e., the anode
path and all other cathode paths, will contains a decoupling
capacitor. Therefore, the circuitry is guaranteed to have no DC
current injection into the patient's tissue, despite the lack of a
decoupling capacitor in DAC 20x's cathode path.
[0051] While there is a size benefit to using only X capacitors, it
should be noted that X+1 capacitors can also be used in another
embodiment, such as stimulator 100'' shown in FIG. 9. In this
embodiment, there is one capacitor 42 in the anode path, and X
capacitors 44a to 44x in the cathode paths. Although stimulator
100'' contains one additional capacitor when compared with
stimulators 100 and 100', it can still result in a smaller number
of capacitors than in previous approaches requiring N capacitors,
i.e., X+1 can still be significantly less than N. For example,
consider the example discussed earlier of a microstimulator having
N=8 electrodes with X=3 cathode electrodes activatable at one time.
Regardless of whether 3 (X) or 4 (X+1) capacitors are used, the
total number is still significantly less than 8 (N), resulting in
substantial space savings.
[0052] To this point in the disclosure, it has been assumed that
the improved stimulators 100 or 100' comprise a single
anode/multiple cathode design. However, and as shown in FIG. 10,
either of these embodiments can also be implemented in a multiple
anode/single cathode design. FIG. 10 shows a multiple anode/single
cathode stimulator 102 modeled after stimulator 100' having a
single cathode path capacitor 42 and X-1 anode path capacitors 42a
to 42(x-1). In this design, the circuitry has been modified to
include cathode switches 62.sub.1-62.sub.n, which allows any one of
the electrodes E1-En to function as the cathode or current sink.
Multiple anodes can be selected via anode selection switches
68a.sub.1 to 68x.sub.n, which in conjunction with DACs 20a-20x can
allow more than one electrode to act as an anode or current source
at one time. Regardless of the cathode chosen, decoupling capacitor
44 will remain in the cathode path. Notice again that DACs
20a-20(x-1) are coupled to decoupling capacitors 42a to 42(x-1),
while the anode path containing DAC 20x contains no decoupling
capacitor. However, for the same reasons discussed above, such
architecture still guarantees no DC current injection, and is safe
in this respect.
[0053] To this point in the disclosure, embodiments of the
invention have been illustrated in either single anode/multiple
cathode or multiple anode/single cathode configurations. However,
the invention is also extendable to a multiple anode/multiple
cathode configuration, such as is shown in stimulator 110 of FIG.
11A. As shown, separate DACs are provided to service both the
anodes and the cathodes. Specifically, NDACs 20a-20i comprise
current sinks and thus operate as cathode current sources, and are
coupleable via cathode selection switches 62 to designate any of
electrodes E1-En as cathodes. Likewise, PDACs 21a-21j comprise
opposite-polarity anode current sources, and are coupleable via
anode selection switches 68 to designate any of electrodes E1-En as
anodes. As one skilled in the art will appreciate, reference to "N"
or "P" DACs relates to the polarity of the devices preferably used
in the DAC circuitry, with PDACs generally comprising P-channel
transistors, and NDACs generally comprising N-channel transistors.
See, e.g., U.S. Patent Application Publication 2007/0038250. As
shown, there are I NDACs 20, and therefore (assuming no DAC
sharing), I of the electrodes can act as cathodes at any given
time. There are J PDACs 21, and therefore (again assuming no
sharing), J of the electrodes can act as anodes at a given time. In
this example, I+J=X, meaning (consistent with earlier examples)
that there are a total of X DACs 20 or 21 and a maximum of X
electrodes that can be active (I cathodes and J anodes) at one
time. In a sensible application, I and J could be equal.
[0054] Multiple anode/multiple cathode stimulator 110 comprises at
least X-1 decoupling capacitors. This means a decoupling capacitor
can be missing from any of the X NDACs 20 or PDACs 21 illustrated,
but as shown, the capacitor is missing from the anode path coupled
to the last PDAC 21j. Thus, in the illustrated example, there are I
cathode path capacitors, and J-1 anode path capacitors, for a total
of X-1 capacitors.
[0055] Even though a capacitor is missing from PDAC 21j's anode
path, the design is still guaranteed to allow no DC current
injection at any electrode, because once again, the presence of
capacitors in all other anode and cathode paths prevents this. The
scenario illustrated in FIG. 11B shows this, and based on similar
earlier illustrations, should be self explanatory. Generically,
assume P electrodes can be designated as anodes, including at least
electrode Ey coupled to PDAC 21j. Likewise, Q electrodes are
simultaneously designated as cathodes. The result is P+Q-1
capacitors in the various paths. However, there can be no DC
current injection into PDAC 21j's anode path despite the missing
capacitor. Therefore, the X-1 capacitors ensure no DC current
injection into the node formed by the patient's tissue R. Although
the capacitor is shown as missing in an anode path, the capacitor
may also be missing from one of the cathode paths to the same
effect.
[0056] Because only X-1 decoupling capacitors are required in the
stimulator 110 of FIG. 11A, and because X can normally be made
smaller than the total number of electrodes N, stimulator 110 can
be made smaller than approaches requires N decoupling capacitors
(see, e.g., FIG. 6). For example, consider a spinal cord stimulator
having N=16 electrodes, and which has three NDACs 20 and three
PDACs 21, meaning that a total of X=6 electrodes (I=3 anodes, J=3
cathodes) can be activated at any given time. Such a design would
require only X-1=5 decoupling capacitors instead of 16 as had been
typical in previous spinal cord stimulator designs.
[0057] FIG. 12 illustrates a modification to the embodiment of
stimulator 110 of FIG. 11A in which no decoupling capacitor is
missing from any of the anode or cathode paths. Although this
stimulator 110' requires one additional capacitor compared to
stimulator 110 (X versus X-1), it can still result in a substantial
reduction in the number of capacitors required. For example, and
continuing the example above, the number of capacitors in a spinal
cord stimulator could be cut from 16 to six for example.
[0058] FIG. 13 illustrates yet another multiple anode/multiple
cathode stimulator 120. In comparison to stimulator 110 of FIG. 11A
which was implemented using discrete NDACs and PDAC, stimulator 120
comprise X generic DACs 27a-x. DACs 27a-x are programmable to
operate either as cathode (sink) current sources or anode (source)
current sources, and therefore may comprise a combination of known
NDAC and PDAC circuitry. DACs 27a-x are coupleable to any of the N
electrodes by switch matrices 83a-x. Because the DACs 27a-x are
programmable to either sink or source current, the selection
switches 69 in each of the switch matrices 83 may be implementable
as transmission gates having both P and N channel transistors which
can pass the sourced or sunk current with equal efficiency. The X
DACs 27a-x permit X of the electrodes can act as cathodes or anodes
at any given time. More specifically, because there must be at
least one cathode and anode at any given time, there can be M
cathodes and X-M anodes active at any given time, which M is a
positive integer.
[0059] Like stimulator 110, multiple anode/multiple cathode
stimulator 120 comprises at least X-1 decoupling capacitors, as
shown in FIG. 13. This means a decoupling capacitor 45 can be
missing from any of the X DACs 27 illustrated, but as shown, the
capacitor is missing from the current path coupled DAC 27x. Even
though a capacitor is missing from DAC 27x's current path, the
design is still guaranteed to allow no DC current injection at any
electrode, because once again, the presence of capacitors in all
other current paths prevents this. To summarize, because the X-1
capacitors prevent DC current injection into the node formed by the
patient's tissue R, there can be no DC current injection into PDAC
27x's current path despite the missing capacitor. As with earlier
embodiments, because only X-1 decoupling capacitors are required,
stimulator 120 can generally be made smaller, etc.
[0060] FIG. 14 illustrates a modification to the embodiment of
stimulator 120 of FIG. 13 in which no decoupling capacitor is
missing from any of the current paths. Although this stimulator
120' requires one additional capacitor compared to stimulator 120
(X versus X-1), it can still result in a substantial reduction in
the number of capacitors required.
[0061] The disclosed stimulators improves upon the prior art.
Because they contains a smaller number of DACs (X) relative to the
number of electrodes (N), and accordingly contains a smaller number
of decoupling capacitors (either X-1, X, or X+1 depending on the
embodiment considered), the stimulator can be incorporated into a
relatively small case. This facilitates use as a multi-electrode
microstimulator for example, or allows a spinal cord stimulator
case to be made that much smaller. Moreover, the disclosed designs
guarantee no DC current injection, even during current steering,
i.e., during the simultaneous activation of more than one cathode
and/or more than one anode.
[0062] This disclosure has referred to "anodes" as being sources of
current and "cathodes" as sinks of current. However, because this
designation is relative, an "anode" can also refer to a sink of
current and a "cathode" can also refer to a source of current.
Therefore, as used herein, "anode" and "cathode" should simply be
understood as having opposite polarities.
[0063] While the invention herein disclosed has been described by
means of specific embodiments and applications thereof, numerous
modifications and variations could be made thereto by those skilled
in the art without departing from the literal and equivalent scope
of the invention set forth in the claims.
* * * * *