U.S. patent application number 11/404476 was filed with the patent office on 2006-10-26 for system and method for providing a waveform for stimulating biological tissue.
Invention is credited to Nagi Hatoum.
Application Number | 20060239482 11/404476 |
Document ID | / |
Family ID | 37054501 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060239482 |
Kind Code |
A1 |
Hatoum; Nagi |
October 26, 2006 |
System and method for providing a waveform for stimulating
biological tissue
Abstract
An implantable programmable stimulator system that includes
memory that stores waveform data for at least on waveform. A
playback system provides at least one output waveform based on the
waveform data.
Inventors: |
Hatoum; Nagi; (Cleveland
Heights, OH) |
Correspondence
Address: |
TODD N. HATHAWAY
119 N. COMMERCIAL ST. #620
BELLINGHAM
WA
98225
US
|
Family ID: |
37054501 |
Appl. No.: |
11/404476 |
Filed: |
April 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60671011 |
Apr 13, 2005 |
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Current U.S.
Class: |
381/312 |
Current CPC
Class: |
A61N 1/37229 20130101;
A61N 1/025 20130101 |
Class at
Publication: |
381/312 |
International
Class: |
H04R 25/00 20060101
H04R025/00 |
Claims
1. An implantable programmable stimulator system comprising: memory
that stores waveform data for at least one waveform; and a playback
system that provides at least one output waveform based on the
waveform data.
2. The system of claim 1, wherein the waveform data comprises
non-parametric waveform data corresponding to at least a fraction
of a period of the at least one waveform.
3. The system of claim 1, wherein the waveform data further
comprises waveform data for a plurality of different waveforms, the
playback system providing the output waveform based on the waveform
data selected for at least one of the plurality of different
waveforms.
4. The system of claim 3, wherein the playback system is configured
to construct the output waveform by combining at least two of the
plurality of different waveforms stored in the memory.
5. The system of claim 1, wherein the waveform data is encoded
according to a CODEC, the playback system being operative to decode
the waveform data according to the CODEC to provide the output
waveform.
6. The system of claim 1, further comprising an amplifier that
provides an amplified output signal corresponding to the output
waveform.
7. The system of claim 6, wherein the amplifier comprises a
switching amplifier that provides the amplified output signal as a
pulse-width-modulated signal.
8. The system of claim 6, further comprising at least one electrode
that emits an electrical stimulation signal having desired waveform
characteristics according to the amplified output signal.
9. The system of claim 8, further comprising feedback from an
output of the amplifier to the playback system; the feedback
providing the playback system with information about at least one
of the electrical stimulation signal emitted by the at least one
electrode or a characteristic of the electrode.
10. The system of claim 1, wherein the playback system is at least
one of programmed and configured to manipulate the output waveform
to vary at least one parameter of the output waveform.
11. The system of claim 1, further comprising a receiver that
receives an input signal that comprises the at least one waveform,
the waveform data being stored in the memory according to the input
signal to enable the playback system to provide the output waveform
with a least a portion of the at least one waveform.
12. The system of claim 11, further comprising an external
transmitter that provides the input signal according to at least
one communication mode.
13. The system of claim 12, further comprising a waveform generator
that provides the external transmitter with the at least one
waveform, the external transmitter providing the input signal to
program the memory with the waveform data for the at least one
waveform.
14. The system of claim 13, wherein the waveform generator is
programmed with at least one biological recorded waveform, the
waveform generator providing the at least one biological recorded
waveform to the external transmitter, the input signal provided by
the external transmitter comprising the at least one biological
recorded waveform.
15. The system of claim 12, wherein the memory and the playback
system form part of a single integrated circuit that is separate
from the external transmitter.
16. The system of claim 1, wherein the playback system is
configured to provide at least one selected waveform from the
memory according to a defined schedule.
17. The system of claim 1, wherein the playback system is
configured to provide at least one of selected waveform from the
memory in response to a stimulus.
18. The system of claim 1, wherein the memory stores waveform data
for a plurality of waveforms, at least one of the plurality
waveforms comprising a biological waveform recorded from a
biological subject.
19. An implantable pulse generator, comprising: memory that stores
a waveform representation for each of a plurality of waveforms; and
a playback system configured to retrieve at least one of the stored
waveform representations from the memory and to provide at least
one corresponding output waveform signal; and at least one
amplifier that amplifies the at least one corresponding output
waveform signal to provide at least one corresponding amplified
output waveform signal.
20. The implantable pulse generator of claim 19, further comprising
a receiver that receives a signal corresponding to at least one
waveform according to a predetermined communication mode, the
memory storing at least some of the stored waveform representations
based on the signal received by the receiver.
21. The implantable pulse generator of claim 19, wherein the
playback system is configured to retrieve and play back at least
one selected waveform from the memory in response to a stimulus,
such that the output waveform signal provided by the playback
system comprises the at least one selected waveform.
22. The implantable pulse generator of claim 19, wherein the
playback system is configured to retrieve and play back at least
one selected waveform from the memory according to a schedule, such
that the output waveform signal provided by the playback system
comprises the at least one selected waveform.
23. The implantable pulse generator of claim 19, wherein the memory
and the playback system form part of a single integrated
circuit.
24. The implantable pulse generator of claim 19, further comprises
at least one electrode that is electrically connected with the at
least one amplifier, the at least one electrode emitting an
electrical stimulation signal having waveform characteristics
according to the corresponding amplified output waveform
signal.
25. The implantable pulse generator of claim 24, further comprising
feedback connected to provide the playback system with information
about at least one of the electrical stimulation signal emitted by
the at least one electrode or a characteristic of the
electrode.
26. The implantable pulse generator of claim 19, wherein the
playback system is configured to construct the at least one
corresponding output waveform signal by combining at least two of
the plurality of waveform representations stored in the memory.
27. The implantable pulse generator of claim 19, wherein the
playback system is at least one of programmed and configured to
manipulate at least one of the plurality of waveforms is retrieved
from the memory so as to vary at least one parameter of the
corresponding output waveform signal.
28. The implantable pulse generator of claim 18, further comprising
a receiver that receives an input signal that is provided according
to at least one communication mode, at least one waveform
representation being stored in the memory according to the input
signal.
29. The implantable pulse generator of claim 28, further comprising
an external transmitter that provides the input signal according to
the at least one communication mode.
30. The implantable pulse generator of claim 29, further comprising
a waveform generator that provides the external transmitter with at
least one of the plurality of waveforms, the external transmitter
providing the input signal to program the memory with the waveform
representation for the at least one of the plurality of waveforms
provided by the waveform generator.
31. The implantable pulse generator of claim 30, wherein the
waveform generator is programmed with waveforms recorded from a
biological subject, the at least one of the plurality of waveforms
provided by the waveform generator comprising at least one of the
biological recorded waveforms.
32. The implantable pulse generator of claim 19, wherein the memory
stores a plurality of waveforms, at least one of the plurality
waveforms stored in the memory comprising a biological waveform
recorded from a biological subject.
33. The implantable pulse generator of claim 19, wherein the
plurality waveforms are stored in the memory as digital data and
the playback system provides the at corresponding output waveform
signal as a digital output waveform signal, the implantable pulse
generator further comprising a digital-to-analog converter that
converts the digital output waveform signal to a corresponding
analog output waveform signal, the amplifier comprising analog
amplifier that amplifies the analog output waveform signal to
provide the at least one corresponding amplified output waveform
signal.
34. A method for providing a waveform for stimulation of biological
tissue, the method comprising: storing non-parametric waveform data
corresponding to a plurality of recorded waveforms in memory
located in an implantable pulse generator; retrieving at least one
of the plurality of waveforms from the memory; and providing an
output waveform from playback circuitry located in the implantable
pulse generator, the output waveform corresponding to the at least
one of the plurality of waveforms retrieved from the memory.
35. The method of claim 34, further comprising: implanting the
implantable pulse generator in a patient's body, at least one
electrode connected to receive the output waveform, the at least
one electrode delivering at least one electrical stimulus to
targeted biological tissue with waveform characteristics according
to the output waveform provided from the playback circuitry.
36. The method of claim 34, wherein the at least one waveform that
is retrieved from memory includes at least one waveform recorded
from a biological subject.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/671,011, which was filed Apr. 13, 2005,
and entitled SYSTEM AND METHOD FOR PROVIDING A WAVEFORM FOR
STIMULATING BIOLOGICAL TISSUE, the entire contents of which is
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to a system and
method for providing a waveform for stimulating biological
tissue.
BACKGROUND
[0003] Various types of stimulators have been developed for a
variety of in-vivo applications. For example, a stimulator can be
employed for performing spinal cord stimulation, deep-brain
stimulation or for stimulation of other neurological paths, such as
for treatment of various disorders and diseases. Typically, each
stimulator includes a waveform generator that generates its own
waveform. For instance, a user defines the necessary parameters and
the stimulator constructs the waveform accordingly. Usually the
parameters include amplitude, frequency, phase symmetry and duty
cycle. The more complex the waveform, the more parameters are
necessary to describe the waveform.
[0004] Implantable stimulators are constrained by space and
typically cannot accommodate complex circuitry. Implantable
stimulators, therefore, usually trade off waveform complexity for
saving space. A simpler stimulator design also tends to consume
less power, which is also a significant consideration in
implantable devices. For example, power saving is important since
surgery is usually required to replace the battery. Furthermore,
simple stimulator designs are rugged and are generally less prone
to failure. Safety and low failure rate are important requirements
by the government regulator agencies for approving any medical
device.
SUMMARY
[0005] The present invention relates generally to a system and
method for providing a waveform for stimulating biological
tissue.
[0006] One embodiment of the present invention provides an
implantable programmable stimulator system that includes memory
that stores waveform data for at least one waveform. A playback
system provides at least one output waveform based on the waveform
data.
[0007] Another embodiment of the present invention provides an
implantable pulse generator (IPG). The IPG includes memory that
stores a waveform representation for each of a plurality of
waveforms. A playback system is configured to retrieve at least one
of the stored waveform representations from the memory and to
provide at least one corresponding output waveform signal. At least
one amplifier amplifies the corresponding output waveform signal to
provide a corresponding amplified output waveform signal.
[0008] Yet another embodiment provides a method for providing a
waveform for stimulation of biological tissue. The method includes
storing non-parametric waveform data corresponding to a plurality
of recorded waveforms in memory located in an implantable pulse
generator. At least one of the plurality of waveforms is retrieved
from the memory. An output waveform is provided from playback
circuitry located in the implantable pulse generator, the output
waveform corresponding to the at least one of the plurality of
waveforms retrieved from the memory.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 depicts an example of a block diagram for a
programmable stimulation system that can be implemented according
to an aspect of the present invention.
[0010] FIG. 2 depicts an example of yet another stimulation system
that can be implemented according to an aspect of the present
invention.
[0011] FIG. 3 depicts an example of a stimulation system with
external programming implemented according to an aspect of the
present invention.
DETAILED DESCRIPTION
[0012] The present invention relates to an implantable programmable
stimulation system that can provide an output waveform, such as for
use in stimulating biological tissue. The system includes memory
that stores waveform data that represents one or more waveforms.
The waveforms can be generated externally and provided to the
memory. The system also includes a playback system, which can be
similar to electronic digital or analog sound recording and
playback devices. The playback system provides an output waveform
based on the waveform data. For instance, one or more selected
waveforms can be selected and played back via the playback system
to provide an output waveform to an amplifier. The amplifier
amplifies the output waveform (e.g., using voltage or current
control) to stimulate the biological tissue electrically. For
example, the amplified output waveform can be provided to an
electrode implanted at a location for delivering the electrical
stimulus to targeted biological tissue (e.g., target sites within
organs such as the heart and brain/spinal cord, for example. The
output waveform can be adjusted or modified.
[0013] FIG. 1 depicts a stimulation system 10 that can be
implemented according to an aspect of the present invention. The
stimulation system 10 includes memory 12 that stores (or records)
waveform data corresponding to one or more waveforms. The waveform
data can be preprogrammed, such as prior to implantation, or the
waveform data can be programmed post-implantation of the system 10.
The waveform data can be stored in the memory 12 based on an INPUT
signal received by a communication system 14. The one or more
waveforms can be stored as one or more complete periods of the
waveform, which can be referred to as snippets. As described
herein, the waveform data that is stored in the memory 12
corresponds to one or more actual waveforms, which can be an analog
or digital representation of the waveform(s). This type of waveform
data that is stored in the memory 12 is referred to herein as
non-parametric waveform data.
[0014] The communication system 14 can include a receiver that
receives the INPUT signal via one or more communication modes, such
as including radio frequency (RF), infrared (IR), direct contact
(e.g., electrically or optically conductive path), capacitive
coupling, and inductive coupling to name a few. The INPUT signal
further can be provided via more than one communication mode, such
as providing the INPUT signal as including one or more waveforms
via one mode and command information (e.g., scheduling and
programming information) via another mode. The communication system
14 can be capable of bi-directional communications, such as also
including a transmitter or transceiver circuitry. The transmitter
and receiver portions of the communication system 14 can employ the
same or different communication modes.
[0015] The memory 12 can be implemented as an analog memory, such
as is capable of storing an analog version of the waveform that is
received by the communication system 14. The memory can also be
implemented as digital memory that stores a digital representation
or sample of the input waveform or stores a digitally encoded
version of the waveform. For instance, the memory 12 can store the
sample waveform as a digital sample, such as using pulse code
modulation (PCM) or adaptive differential pulse code modulation
(ADPCM) or pulse width modulation (PWM), although other modulation
techniques can be utilized. The digital sample of the waveform
further may be stored in a compressed format according to one or
more CODECs (e.g., MP3, AAC, 3GPP, WAV, etc.), although compression
is not required. There are a multitude of varying standards that
can be grouped in three major forms of audio CODECs, including, for
example, direct audio coding, perceptual audio coding, and
synthesis coding, any one or more of which can be employed to store
a digital representation of waveforms in the memory 12.
[0016] A playback system 16 is configured to retrieve and play back
one or more waveforms according to selected waveform data stored in
the memory 12. The playback system 16 can be implemented as
hardware (e.g., one or more integrated circuits), software or a
combination or hardware and software. The implementation of the
playback system 16 can vary, for example, according to the type of
audio (analog or digital) that is stored in the memory 12. The
playback system 16, for example, can be programmed with one or more
audio CODECs that convert (or decode) the encoded waveform data
into a corresponding output waveform.
[0017] The playback system 16 can be implemented as an integrated
circuit 24, such as including a microcontroller or microprocessor.
For instance, suitable microcontroller integrated circuits (ICs)
are commercially available from Atmel Corporation of San Jose,
Calif. Such microcontroller ICs may include the memory 12
integrated into the IC 24, such as in the form or FLASH memory or
other programmable memory (electrically programmable read only
memory (EPROM)), or the memory 12 can be external to the IC 24.
[0018] The playback system 16 provides the output waveform to an
amplifier 18 that amplifies the output waveform. The playback
system 16 further can be configured to provide output waveforms to
one or more output channels, each output channel providing an
amplified output waveform corresponding to the waveform data stored
in the memory 12. One or more electrodes 20 can be coupled to each
of the channels for delivering electrical stimulation to biological
tissue located adjacent the electrode(s).
[0019] As an example, the playback system 16 can be configured to
select one or more waveforms from the memory 12 for providing a
corresponding output waveform. As mentioned above, a plurality of
different types of waveforms can be stored in the memory 12,
generally limited only by the size of the memory. The playback
system 16 thus can select and arrange one or more waveforms to
provide a desired output waveform pattern. Additionally, the
playback system 16 further can combine a plurality of different
waveforms into more complex composite output waveforms. It will be
appreciated that the ability of selecting from a plurality of
predefined stored waveforms affords the stimulation system enhanced
capabilities, as virtually any output waveform can be stored and
played back from the memory 12.
[0020] The design can be simplified even further by storing
waveforms of gradually changing parameters in the memory 12. For
example, a plurality of versions of the same waveform, but of
varying amplitude, can be stored in the memory 12 so as to
effectively eliminate the need for additional amplitude controlling
circuitry. Accordingly, if a greater or lesser amplitude may be
required for a given application, an appropriate different waveform
can be selected. The playback system 16 can also be programmed
and/or configured to manipulate one or more selected waveforms from
the memory 12, such as using digital or analog computation, to vary
parameters (e.g., amplitude, frequency, phase symmetry and/or duty
cycle) of the one or more selected waveforms. The corresponding
amplified output signal corresponds to an amplified version of the
selected waveform, including any such manipulations.
[0021] The amplifier 18 can be implemented as an analog amplifier
or a digital amplifier. For an analog version of the amplifier 18,
a digital-to-analog converter (not shown) can provide a
corresponding analog version of the output waveform and a linear
amplifier can, in turn, operate to amplify the analog output
waveform to a desired level. Power conditioning circuitry can be
utilized to provide a desired potential for use in generating the
amplified output waveform. Alternatively, the amplifier can be
implemented as a class D amplifier (or switched power supply),
although other amplifier topologies can also be used. By
implementing the amplifier as a class D amplifier, the amplifier 18
can run directly off a battery or other power supply efficiently
and be implemented using low-voltage components. Those skilled in
the art will appreciate various types of switching amplifier
topologies are that can be utilized in the system 10. Additionally,
the amplifier 18 can be configured to operate in a current mode or
a voltage mode control, such as to provide a desired current or
voltage.
[0022] The amplifier 18 can comprise a network of amplifiers
arranged to drive a plurality of loads (depicted as electrodes 20)
according to respective output waveforms provided by the playback
system 16. The electrode(s) 20 can be implanted in strategic
locations in the patient's tissue according to given application of
the stimulation system 10. For example, the electrode(s) can be
located within a patient's brain, spinal cord or other anatomic
locations. The anatomic locations can be in close proximity to the
playback system or at remote locations.
[0023] The system 10 can be implemented as an open loop system or a
closed loop system. For the example of a closed loop system, the
system 10 can also include feedback, indicated as dotted line 22.
The feedback 22 provides information about the stimulus being
applied to the electrode(s) and/or about a characteristic of the
electrode(s). As an example, the feedback 22 can provide an
electrical signal to the playback system 16, based on which an
indication of load impedance associated with the electrode(s) can
be determined.
[0024] The impedance characteristics can be utilized for a variety
of purposes. For instance, the impedance can be employed to
implement current control, such as by the playback system 16
selecting a predefined waveform from the memory 12 to maintain a
desired current level in the waveform that is provided to the
electrode(s) 20. Alternatively or additionally, the impedance
characteristics can be used as part of diagnostics, such as by
recording (or logging) impedance over extended periods of time and
evaluating a condition of the electrode(s). As another alternative,
the feedback 22 can be employed to ascertain high impedance
conditions (e.g., an open circuit) or a low impedance condition
(e.g., a short circuit). Those skilled in the art will understand
and appreciate various approaches that can be implemented to
provide the feedback 22. Additionally, various types of diagnostic
or operational controls can be implemented based on such
feedback.
[0025] Since the waveform is played back from non-parametric
waveform data that is stored in the memory 12, the system 10 can be
implemented in a cost efficient manner from commercially available
recording and playback circuitry. Additionally, because the
waveforms can be generated externally, provided to the system 10,
and stored in the memory 12, there is a greater degree of
flexibility in the types and complexity of waveforms that can be
stored in the memory. That is, the system 10 is not constrained by
limitations in the cost or size or complexity of a typical
parametric waveform generator. Additionally, the playback system 16
may further construct more complex waveforms by combining two or
more stored waveforms in a particular order (e.g., a pattern of
waveform trains). As an example, one or more of the waveforms
stored in the memory can include actual recorded impulses
(electrical waveforms), such as can be recorded from the patient in
which the stimulation system 10 is to be implanted, from a
different person or from a non-human animal subject.
[0026] FIG. 2 depicts an example of a programmable stimulation
system 50 that can be implemented according to an aspect of the
present invention. The system 50 comprises an implantable pulse
generator (IPG) 52 that is implanted in a patient's body 54, such
as implanted under the skin of the chest (e.g., below the
collarbone) or other anatomic location. In contrast to many
existing IPG designs, the IPG 52 is not required to generate a
pulse or waveform, but instead is configured to play back one or
more predefined waveforms. The IPG 52 includes an internal receiver
56 that can receive a signal from an external programmer 58, which
is located external to the body 54. The external programmer 58 can
communicate the signal to the receiver 56 using one or more
communications modes, such as described herein. In the example, of
FIG. 2, a connectionless communications mode is illustrated,
although a physical connection can be made to provide an electrical
or optical conductive medium for data communications.
[0027] A waveform generator 60 can provide one or more waveforms 62
to the external programmer 58 for transmission to the IPG 52. The
waveform generator 60 can include any type of device or system that
can generate the one or more waveforms 62, including a programmable
signal generator, a pulse generator, and a waveform synthesizer to
name a few. The waveform generator 60 further may be a PC-based
system or a stand alone system capable of generating one or more
desired waveforms. The waveform generator 60 can also be programmed
with biological, recorded waveforms, such as may have been measured
and recorded from the patient's body 54 or from any other
biological subject (e.g., human or other animal). For electrical
stimulation of the patient's brain, the waveform can be recorded as
electrical impulses measured from one or more anatomical regions of
a biological subject's brain. The waveform generator 60 thus can
provide the biological, recorded waveforms to the external
programmer 58.
[0028] The external programmer 58 transmits a signal 59 to the
receiver 56 of the IPG 52 corresponding to the waveform 62 provided
by the generator 60. As discussed herein, the signal 59 transmitted
by the external programmer 58 can include (or encode) the actual
waveform 62 provided by the waveform generator 60 (e.g., an actual
biological, recorded waveform or a synthesized waveform). The
external programmer can transmit the signal 59 as including a
complete period, more than one period (e.g., snippets) or as a
fraction of a period of the desired waveform 62 in any
communications mode. The receiver 56, for example, can provide the
waveform to the memory as encoded waveform date, such as
corresponding to an encoding scheme implemented by the waveform
generator 60. Alternatively, the receiver 56 can demodulate/decode
an encoded received signal and provide a corresponding
demodulated/decoded signal 66 to the memory 64 so that the waveform
data corresponds to the one or more waveforms 62. Additionally
encoding may also be performed by the receiver 56 or other
circuitry (not shown) for providing encoded waveform date for
storing the waveform(s) 62 the memory 64.
[0029] The sample of the waveform 66 stored in the memory 64 can
correspond to an analog version of the waveform or a corresponding
digital (e.g., PCM) representation of the waveform. Those skilled
in the art will appreciate various different representations that
can be stored in the memory 64 based on the teachings contained
herein. It will further be understood that some or all of the
waveforms 66 stored in the memory 64 can be programmed prior to
implantation of the IPG 52 within the body 54.
[0030] After a desired number of one or more waveforms 66 have been
stored in the memory 64, such as during a program mode, playback
circuitry 68 can play back one or more selected waveforms 66 from
the memory 64. The playback circuitry 68 can play back a waveform
according to a defined play back schedule, which may be a periodic
or continuous schedule. Alternatively or additionally, the playback
circuitry 68 can be configured to play back on or more selected
waveforms in response to a stimulus, which stimulus can be
user-generated or provided by associated sensing circuitry (not
shown.)
[0031] The playback circuitry 68 can play back the one or more
selected waveforms by retrieving the selected waveform(s) from the
memory and providing the output waveform(s) to one or more
amplifiers 70. The amplifier 70 amplifies the output waveform to a
desired level to provide a corresponding amplified version of the
waveform. That is, the amplified waveform 72 can be substantially
the same as the waveform 62 generated by the waveform generator 60.
Alternatively, when the waveform 62 is stored as encoded date, the
amplified waveform 72 can correspond to a decoded version of the
waveform. Typically, a plurality of waveforms 66 are stored in the
memory 64 to provide a greater selection of available waveforms for
operating the IPG 52. The amplified waveform 72 can be provided to
one or more strategically placed electrodes or other implantable
devices capable of delivering an electrical stimulus to adjacent
biological tissue.
[0032] FIG. 3 depicts an example of part of a microprocessor based
stimulation system 100 that can be implemented according to an
aspect of the present invention. The system 100 includes a
microcontroller 102 that is programmed and/or configured to control
the system. The microcontroller 102 can communicate with an
external device via a data bus 104. The data bus 104 can provide
for bi-directional communication relative to the microcontroller
102. The communication my include input and/or output (I/O) data,
such as provided by a communications system (e.g., a transmitter or
receiver, not shown). The I/O data can be analog or digital data,
as the microcontroller 102 includes an analog-to-digital converter
106.
[0033] By way of example, the I/O data can include command data and
waveform data. The command data can include scheduling information
that controls operation of the system 100. For instance, the
scheduling information can identify which waveform(s) is to be
played, how many times the waveform is to be played (e.g., a fixed
number or continuously). The command data thus can be employed to
program one or more registers or other types of memory with program
instructions or operating parameters to control operation of the
system 100. The command data may also be utilized to enter a
programming or learning mode, such as during which waveform data
can be learned or programmed into the system 100. The command data
can also be provided as part of a diagnostic mode in which
information about system operation can be obtained from the system
100 as output data.
[0034] The waveform data can correspond to any number of one or
more sample waveforms, which can be stored in memory 108 of the
microcontroller 102. While the memory 108 is depicted as being
internal to the microcontroller 102, the memory could be external
to the microcontroller or be distributed partially within the
microcontroller and partially external. The memory 108 can be
implemented as programmable memory, such as including FLASH memory,
EPROM or other memory types. The memory 108 and other components of
the microcontroller 102 (as depicted in FIG. 3) can be accessed via
an internal bus 110.
[0035] The microcontroller 102 included a timing and control block
112 that controls an oscillator 114 to provide a corresponding
digital waveform to one or more associated port drivers 116. The
one or more port drivers 116 can receive more than one waveform
(e.g., via a register 118) from the oscillator 114, each of which
corresponds to one or more waveforms selected from the memory 108.
In the example of FIG. 3, it is assumed that the waveforms stored
in the memory 108 are digital waveforms, such as can be encoded
according to any desired CODEC. The one or more port drivers 116
provide a corresponding output waveform to an associated output
stage 120.
[0036] Each output stage 120 can include a digital-to-analog
converter and an amplifier that provides a respective amplified
output waveform. N output stages are utilized to provide N
corresponding amplified output waveforms, where N is a positive
integer (N.gtoreq.1). In the example of FIG. 3, each of the output
stages 120 includes a sigma delta demodulator 122 that demodulates
the encoded data provided by the port drivers 116 and converts the
digital representation to an analog signal. For instance, the
waveforms stored in the memory 108 can be encoded as 1-bit sigma
delta modulated signals, which allows for high resolution waveform
reproduction with low noise without required digital compression.
It is to be appreciated that other forms of demodulation, with or
without compression, can also be utilized in the system 100. Each
demodulator 122 provides a corresponding demodulated, analog output
signal to an associated amplified 124. Each amplified 124 can drive
an associated electrode with a corresponding amplified analog
output signal (the amplified output signals indicated as being
provided "to electrodes").
[0037] As an alternative, each output stage 120 can be configured
to directly convert the digital output waveforms provided by the
port drivers 116 to corresponding amplified analog signals. For
example, the port drivers 116 could provide the output waveforms as
PCM or PWM output waveforms. The output stages can include
associated amplifiers, such as implemented as class D or switching
amplifiers, which convert the digital output waveforms to
corresponding amplified analog output waveforms. Those skilled in
the art will understand and appreciate various types of switching
amplifier topologies that could be implemented to provide a
switching output signals based on such output waveforms. Thus, the
averaged (or low-pass filtered) amplified output signal for each
output stage represents a desired amplified output waveform. Those
skilled in the art will understand and appreciate various possible
amplifier topologies that can be utilized in the system 100 of FIG.
3 (as well as in the other approaches of FIGS. 1 and 2).
[0038] The system 100 can also employ feedback 130 for use in
impedance determination and charge balancing using the techniques
mentioned herein. For example, the feedback 130 can include an
analog indication of electrode voltages, which are provided to the
ADC 106 of the microcontroller 102 and converted to corresponding
digital signals. The microcontroller 102 thus can employ the
signals provided by the feedback information provided by the ADC to
implement desired controls (e.g., voltage control or current
control) or to implement diagnostic functions, such as described
herein.
[0039] Various feedback-schemes can be utilized to measure
impedance characteristics of a load (e.g., electrode) that is
associated with each of the respective output stages 120. The
impedance characteristics can be described according to a model of
an implanted electrode, such as may describe an
electrode-electrolyte interface that is expressed as a serial
capacitance and a serial resistance, together with a Faradic
resistance in parallel with the series resistance and capacitance.
Thus, the feedback scheme can be configured to measure the
electrode model parameters in real time. Possible feedback schemes
that could be implemented include a positive feedback scheme, a
current interrupt scheme or continuous impedance measurement using
small signal injections of multi-sinusoidal waveforms. Those
skilled in the art will understand and appreciate various types of
feedback schemes that can be utilized in accordance with the
present invention.
[0040] What have been described above are examples of the present
invention. It is, of course, not possible to describe every
conceivable combination of components or methodologies for purposes
of describing the present invention, but one of ordinary skill in
the art will recognize that many further combinations and
permutations of the present invention are possible. Accordingly,
the present invention is intended to embrace all such alterations,
modifications, and variations that fall within the spirit and scope
of the appended claims.
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