Interference suppression in tissue stimulation prostheses

Abstract

Techniques for suppressing electrical interference caused by a feedback path between an output channel and an input channel of an implantable medical device are presented herein. In particular, the output channel carries a stimulation signal that can pass through the feedback path and appear in the input channel, thereby causing interference with any input signal carried by the input channel. The implantable medical device is configured to determine a characteristic of the feedback and then use the feedback characteristic to generate a feedback compensation signal applied to the input channel.

Description

Technical Field

[0001] The present invention generally relates to interference suppression in tissue stimulation prostheses. Background Art

[0002] Implantable medical device systems including one or more implantable components have provided a wide range of therapeutic benefits to recipients in recent decades. Over the years, the types of implantable medical device systems and the range of functions performed have increased. For example, many implantable medical device systems now typically include one or more instruments, devices, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in the recipient. These functional components perform diagnosis, prevention, monitoring, treatment or management of disease or injury or its symptoms, or study, replace or modify anatomical structures or physiological processes.

[0003] There are several types of implantable medical devices that work by delivering electrical stimulation (electrical current stimulation) to the recipient's nerves, muscles, or other tissue fibers. These implantable medical devices, sometimes referred to herein as implantable tissue stimulation prostheses, typically deliver electrical current stimulation to compensate for the recipient's deficiencies. For example, tissue stimulation hearing / hearing prostheses are typically proposed when the recipient experiences sensorineural hearing loss due to, for example, the absence or destruction of cochlear hair cells that convert auditory signals into nerve impulses, or when the recipient experiences sensorineural hearing loss due to damage to the auditory nerve. Summary of the invention

[0004] In one aspect, a method is provided. The method includes: detecting the presence of one or more feedback paths between an output channel and an input channel of an implantable medical device, wherein the one or more feedback paths enable feedback to occur in the input channel, the feedback comprising a portion of a stimulation signal on the output channel; determining a feedback transfer function associated with the one or more feedback paths; and based on the feedback transfer function, eliminating feedback that occurs in the input channel in response to delivery of the stimulation signal via the output channel.

[0005] In one aspect, a method is provided. The method includes: detecting the presence of at least one feedback path between an output channel and an input channel of an implantable medical device; generating a model of the at least one feedback path; delivering a stimulation signal to a recipient of the implantable medical device via the output channel, wherein the stimulation signal is delivered at a stimulation frequency; and using the stimulation frequency of the stimulation signal and the model of the one or more feedback paths to identify feedback occurring at the input channel in response to the delivery of the stimulation signal.

[0006] In another aspect, a tissue stimulation prosthesis is provided. The tissue stimulation prosthesis includes: at least one input channel, the at least one input channel including an implantable sensor and one or more associated conductors; at least one output channel, the at least one output channel including a stimulation component and one or more associated conductors; and an interference suppression module configured to: detect feedback generated by the at least one output channel via at least one feedback path on the at least one input channel, and determine a real-time feedback compensation to be applied at the at least one input channel, wherein the application of the real-time feedback compensation is configured to eliminate the feedback at the at least one input channel.

[0007] In another aspect, an implantable medical device method is provided. The implantable medical device includes at least one input channel and at least one output channel configured to carry an input signal and a stimulation signal, respectively, and the method includes: detecting feedback from the at least one output channel via one or more feedback paths at the at least one input channel, wherein the feedback includes a portion of the stimulation signal; determining feedback compensation to be applied at the at least one input channel, wherein the application of the feedback compensation is configured to eliminate feedback from at least one of the one or more output channels; and applying the feedback compensation at the at least one input channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments of the present invention are described herein with reference to the accompanying drawings, in which:

[0009] Figure 1A is a schematic diagram showing a cochlear implant according to some embodiments presented herein;

[0010] Figure 1B yes Figure 1A A block diagram of a cochlear implant;

[0011] Figure 2A is a schematic diagram illustrating interference suppression operation of a cochlear implant according to certain embodiments presented herein;

[0012] Figure 2B is a schematic diagram illustrating interference suppression operation of a cochlear implant according to certain embodiments presented herein;

[0013] Figure 3 is a schematic diagram illustrating determination of compensation filter weights according to certain embodiments presented herein;

[0014] Figure 4A is a flow chart of an interference suppression method according to certain embodiments proposed herein; and

[0015] Figure 4Bis a flow chart of another interference suppression method according to certain embodiments presented herein. DETAILED DESCRIPTION

[0016] Embodiments of the present invention generally relate to techniques for suppressing interference caused by a feedback path between an output channel and an input channel of an implantable medical device. In particular, the output channel carries a stimulation signal that can pass through the feedback path and appear in the input channel as feedback (i.e., interference at the input channel). The implantable medical device is configured to determine a characteristic of the feedback and then use the feedback characteristic to generate a feedback compensation signal applied to the input channel.

[0017] For ease of explanation only, the technology presented herein is described primarily with reference to one type of implantable tissue stimulation prosthesis, namely a cochlear implant. However, it should be understood that the technology presented herein can be used for other implantable tissue stimulation prostheses, including, for example, auditory brainstem stimulators, implantable pacemakers, defibrillators, functional electrical stimulation devices, analgesic stimulators, visual prostheses, other neural or neuromuscular stimulators, etc.

[0018] Figure 1A is a schematic diagram of an exemplary cochlear implant 100 configured to implement an embodiment of the present invention, and Figure 1B is a block diagram of a cochlear implant 100. For ease of description, Figure 1A and 1B .

[0019] exist Figure 1A 1 and 2 show a recipient's outer ear 101, middle ear 102, and inner ear 103. In a fully functional human hearing anatomy, the outer ear 101 includes an auricle 105 and an ear canal 106. Acoustic signals 107 (sometimes referred to herein as sound or sound waves) are collected by the auricle 105 and directed into and through the ear canal 106. Disposed across the distal end of the ear canal 106 is an eardrum 104, which vibrates in response to the acoustic signals (i.e., sound waves) 107. This vibration is coupled to the oval window or elliptical window 110 through three bones of the middle ear 102 (collectively referred to as the ossicular chain or ossicles 111 and including the malleus 112, the incus 113, and the stapes 114). The ossicles 111 of the middle ear 102 serve to filter and amplify the acoustic signals 107, causing the oval window 110 to vibrate. Such vibrations generate fluid motion waves within the cochlea 116, which in turn activate hair cells (not shown) arranged inside the cochlea 116. Activation of these hair cells results in the transmission of appropriate nerve impulses through the spiral ganglion cells and the auditory nerve 118 to the brain (not shown), where they are perceived as sound.

[0020] As mentioned above, sensorineural hearing loss may be due to the loss or destruction of the cochlear hair cells that convert sound signals into nerve impulses. One treatment for this type of hearing loss is a cochlear implant, such as Figure 1A and 1B A cochlear implant 100 is shown in FIG. 1 , which bypasses the cochlear hair cells and delivers stimulation (eg, electrical stimulation) directly to the cochlear nerve cells.

[0021] exist Figure 1A and 1B In the illustrative embodiment of the present invention, cochlear implant 100 is a fully implantable cochlear implant, meaning that all components of the cochlear implant are configured to be implanted beneath the recipient's skin / tissue 115. Because all components of cochlear implant 100 are implantable, the cochlear implant operates, at least for a limited period of time, without the need for external devices. The external device can be used, for example, to charge the internal power source (battery) of cochlear implant 100.

[0022] Cochlear implant 100 includes an implant body or main module 120, a lead region 122, and an elongated intra-cochlear stimulation assembly 124. Implant body 120 includes a sealed housing 129 in which radio frequency (RF) interface circuitry 132 (sometimes referred to as a transceiver unit), at least one rechargeable battery 134, an interference suppression module 135, a signal processor 136, and a stimulator unit 138 are disposed. Housing 129 serves as a protective barrier between the electrical components within the housing (e.g., RF interface circuitry 132, battery 134, etc.) and the recipient's tissues and bodily fluids. For ease of description, the housing 129 is a sealed housing 129 in which a radio frequency (RF) interface circuitry 132 (sometimes referred to as a transceiver unit), at least one rechargeable battery 134, an interference suppression module 135, a signal processor 136, and a stimulator unit 138 are disposed. Figure 1B The electrical connections between the components within the housing 129 are omitted.

[0023] Implant body 120 also includes one or more electrical components located outside (externally) of housing 129. The electrical components located externally of housing 129 include internal / implantable coil 130, implantable sensors / transducers 140(A) and 140(B), and elongated intra-cochlear stimulation assembly 124.

[0024] RF interface circuit 132 is connected to implantable coil 130, and typically, a magnet (not shown) is fixed relative to implantable coil 130. Implantable coil 130 is typically a wire antenna coil composed of multiple turns of electrically insulated single or multiple strands of platinum or gold wire. Typically, implantable coil 130 and RF interface circuit 132 enable power and / or data to be transmitted from an external device to cochlear implant 100. However, it should be understood that various types of energy transmission, such as infrared (IR), electromagnetic, capacitive, and inductive transmission, can be used to transmit power and / or data from an external device to cochlear implant 100, and thus, Figure 1B Only one exemplary arrangement is shown.

[0025] The elongated stimulation assembly 124 is configured to be at least partially implanted in the cochlea 116 and extends through an opening (e.g., cochleostomy 146, oval window 110, round window 113, etc.) in the cochlea 116. The stimulation assembly 124 has a proximal end that is connected to the stimulator unit 138 via a lead region 122 that extends through the mastoid bone 119. The lead region 122 couples the stimulation assembly 124 to the implant body 120, and more particularly, to the stimulator unit 138.

[0026] The stimulation assembly 124 includes a plurality of longitudinally spaced intracochlear electrical stimulation contacts (electrodes) 142 that can be selectively used to deliver electrical current to the cochlea 116. The stimulation contacts 142 collectively form an intracochlear contact / electrode array 144 that is arranged at the cochlea 116. Figure 1B The example shown includes twenty-two (22) stimulation contacts, labeled contacts 142(1)-142(22). Figure 1B The use of twenty-two stimulation contacts is shown, but it should be understood that different numbers, arrangements, etc. of intra-cochlear contacts may be used in alternative embodiments.

[0027] exist Figure 1A and 1B Also shown are two reference contacts 142(23) and 142(24). Reference contacts 142(23) and 142(24) are located outside of the cochlea 116 and can also be used to deliver current to a recipient. Because reference contacts 142(23) and 142(24) are located outside of the cochlea 116, the reference contacts are sometimes referred to as extracochlear electrodes (ECEs).

[0028] As described above, cochlear implant 100 includes two implantable sensors 140(A) and 140(B). Figure 1BIn an illustrative embodiment of the present invention, implantable sensor 140(A) is a "sound" sensor / transducer (e.g., an implantable microphone) that is primarily configured to detect / receive external sounds, while implantable sensor 140(B) is a "vibration" sensor (e.g., another implantable microphone or accelerometer that is configured to be more sensitive to body noise than to external acoustic signals) that is primarily configured to detect / receive body noise. As used herein, body noise (BN) is undesirable sounds generated by the body that are primarily propagated as vibrations, such as breathing, scratching, rubbing, noise associated with head movement, chewing, etc. Self-speech (OV) (i.e., when the recipient speaks) is a special case of body noise because the sound is transmitted through air conduction and bone conduction (i.e., skull vibrations). In some self-speech instances, most of these sounds are transmitted through the skull and produce accelerations at the implantable sensor. For ease of description, the embodiments presented herein will be described primarily with reference to using implantable microphone 140(A) as a sound sensor and using accelerometer 140(B) as a vibration sensor. However, it should be understood that these specific embodiments are non-limiting and that embodiments of the present invention may be used with different types of implantable sensors.

[0029] For ease of explanation, the proposed technology is generally described herein with reference to microphone 140(A) and accelerometer 140(B). However, it should be understood that the implantable tissue stimulation prosthesis may also include other types of sensors, such as a pickup coil, a sensor for picking up neural signals (e.g., an electroencephalogram (EEG)), etc. Thus, microphone 140(A) and accelerometer 140(B) are merely examples of many different types of implantable sensors that may be affected by feedback from the output channel, as described elsewhere herein.

[0030] In operation, microphone 140(A) and accelerometer 140(B) detect input (sound / vibration) signals (e.g., external sounds and / or body noises) and convert the detected input signals into electrical signals. These electrical signals are received by signal processor 136, which is configured to perform signal processing and encoding to convert the electrical signals into processed signals representing the detected signals. The processed signals are then provided to stimulator unit 138, which is configured to utilize the processed signals to generate electrical stimulation signals, which are transmitted to the recipient's cochlea via one or more of the intracochlear stimulation contacts 142(1)-142(22) implanted in the recipient's cochlea 116. In this manner, cochlear implant 100 stimulates the recipient's auditory nerve cells, bypassing the missing or defective hair cells that normally convert acoustic vibrations into neural activity.

[0031] As described above, cochlear implant 100 includes one or more electrical components located in sealed housing 129, and one or more electrical components located outside of sealed housing 129. It is desirable to be able to achieve electrical connections between the various components outside of sealed housing 129 and the various components inside housing 129. Thus, cochlear implant 100 includes sealed feedthrough 150 that provides a physical electrical connection for transmitting signals between the electrical components outside of sealed housing 129 and the electrical components inside sealed housing 129. Figure 1B , conductors 152 extend from sealed feedthrough 150 to internal coil 130, microphone 140(A), accelerometer 140(B), reference contact 142(23), reference contact 142(24), and to each intracochlear stimulation contact 142(1)-142(22). For ease of illustration, Figure 1B Only a subset of the intracochlear stimulation contacts 142(1)-142(22) are shown, and correspondingly, only a subset of the conductors 152 extending to the intracochlear stimulation contacts 142(1)-142(22) are shown.

[0032] The term "input channel" is used herein to refer to the combination of a sound input component / device and associated conductors that connect the sound input component to another component (e.g., a feed-through). Figure 1A and 1B In an embodiment of the present invention, microphone 140(A) and accelerometer 140(B) are sound input components, each of which is associated with one or more conductors 152. Thus, cochlear implant 100 includes two input channels, referred to as input channel 156(1) and input channel 156(2). Input channel 156(1) includes microphone 140(A) and associated conductor 152, and input channel 156(2) includes accelerometer 140(B) and associated conductor 152. As described above, tissue stimulation prostheses according to embodiments presented herein may include additional or alternative input channels, including, for example, remote coils, sensors for picking up neural signals, and the like. Thus, input channels 156(1) and 156(2) are merely examples of a variety of different types of implantable channels that may be affected by feedback from output channels, as described elsewhere herein.

[0033] The term "output channel" is used herein to refer to the combination of a stimulation component / device and an associated conductor that connects the stimulation component to another component (e.g., a feed-through). Figure 1A and 1BIn an embodiment of the present invention, the intra-cochlear stimulation contacts 142(1)-142(22), the reference contacts 142(23) and the reference contacts 142(24) are stimulation components that are each associated with one or more conductors 152. Thus, the cochlear implant 100 includes twenty-four (24) output channels 158(1)-158(24). The cochlear implant 100 also includes twenty-four (24) outputs, namely, the intra-cochlear contacts 142(1)-142(22) and the extra-cochlear contacts 142(23)-142(24). Thus, the cochlear implant 100 includes twenty-four output channels 158(1)-158(24), wherein each output channel is formed by a corresponding contact 142(1)-142(24) and one or more associated conductors 152.

[0034] Prior to implantation, the housing 129, the internal coil 130, the feedthrough 150, and at least a portion of the conductor 152 proximate the feedthrough 150 may be overmolded / encapsulated with a silicone elastomer to create a uniform, conformable surface suitable for implantation. Figure 1A and 1B The encapsulation, which is omitted, substantially isolates the internal coil 130 and the conductors 152 proximate the feedthrough 150 from each other and from the implant environment. That is, the encapsulation is substantially resistant to the ingress of body fluids and has material properties that electrically isolate each conductor 152 and the internal coil 130.

[0035] A sealed feedthrough, such as sealed feedthrough 150, may be one of the most complex mechanical structures in an implantable medical device and is difficult to form correctly. Sealed feedthrough 150 includes an insulator 154 (e.g., formed of ceramic) and one or more conductors 153 (e.g., formed of platinum) extending through the insulator. Due to the requirements of the manufacturing process, conductor 153 extending through insulator 154 is non-insulated and may include or be connected to conductor 152. Therefore, at the outer surface of sealed feedthrough 150, only the applied encapsulation isolates conductor 152 or 153.

[0036] As described in detail above, cochlear implant 100 includes both an implanted sound input component (e.g., microphone 140(A) and accelerometer 140(B)) and an implanted stimulation component (e.g., intra-cochlear contacts 142(1)-142(22) and reference contacts 142(23)-142(24)). The sound input component is used to capture input signals (e.g., sound, body noise, etc.), which are in turn used by cochlear implant 100 to generate stimulation signals that can be used by the stimulation component to stimulate the recipient. That is, cochlear implant 100 is a fully implantable device that is configured to: (1) detect / receive sound from within the recipient, (2) process the sound, and (3) generate stimulation signals for delivery to the recipient to evoke perception of the acoustic signals. Thus, the use of an implantable sound input component provides the recipient with the ability to have a truly "invisible" prosthesis (i.e., the prosthesis is invisible to others due to the absence of external components).

[0037] Although the use of an implanted sound input component promotes the fully implantable nature of the implant, the applicant has discovered that there is the potential for a feedback path to be created between the output channel and the input channel, where "feedback" (i.e., a portion of the stimulation signal) will appear in the input channel. For example, a feedback path can be created between the stimulation component itself (e.g., contacts 142(1)-142(24)) and the sound input component itself (e.g., microphone 140(A) and accelerometer 140(B)) via the recipient's tissue / fluid. In other examples, fluid ingress (leakage) into the encapsulation at feedthrough 150 can result in a conductive path being created between conductors 152 / 153 connected to the sound input component and conductors 152 / 153 connected to the stimulation component (i.e., the silicone encapsulation provides high impedance insulation between the wires, but over time, body fluids can leak under the silicone outside the feedthrough and create a slight conductive path between the stimulator wire and the microphone / accelerometer wire). Typically, the stimulation signal on the output channel has an amplitude that is significantly greater than the amplitude of the input signal on the input channel. That is, the output channel carries a high voltage stimulation signal (e.g., on the order of up to 10 volts), while the input channel carries a low voltage input signal line (e.g., on the order of several volts). Due to this voltage difference, feedback (i.e., a portion of the high voltage stimulation signal that reaches one or more input channels through the feedback path) will cause electrical interference in one or more input channels. In some embodiments, this electrical interference can be perceived by the recipient as audible noise.

[0038] In some examples, it may not be possible to eliminate feedback between input and output channels. However, the applicants have also discovered that because the feedback and resulting electrical interference is a result of the stimulation signal generated by cochlear implant 100, knowledge of the stimulation signal can be used to suppress the electrical interference.

[0039] More specifically, in Figure 1A and 1B In the embodiment of the present invention, the cochlear implant 100 includes an interference suppression module 135 ( Figure 1B ). The interference suppression module 135 is configured to determine the presence of at least one feedback path between at least one output channel 158(1)-158(24) and at least one input channel 156(1)-156(2). For each output-input channel combination for which a feedback path exists, the interference suppression module 135 is configured to determine a "feedback transfer function" that characterizes the propagation of feedback transmitted between the corresponding output and input channels. The interference suppression module 135 is configured to subsequently use the feedback transfer function to generate a feedback compensation signal for application to the input channel. As further described below, in some embodiments, the feedback transfer function is used to determine the weights of a compensation filter that is applied to the corresponding output channel to generate a compensation signal for application to the input channel.

[0040] Figure 1B Any number of feedback paths 162 are shown to exist between the output channel 158 (22) and the input channel 156 (1). As described above, the interference suppression module 135 is configured to determine the existence of the feedback path 162 and determine the feedback transfer function of the feedback path 162 (i.e., for the output-input channel combination consisting of the output channel 158 (22) and the input channel 156 (1)). Using the feedback transfer function (i.e., the determined characteristics of the feedback path 162), the interference suppression module 135 is configured to calculate the weights of a "feedback compensation filter" that can be used to subsequently generate feedback compensation at the input channel 156 (1). That is, once the characteristics of the feedback path 162 are known, the interference suppression module 135 can generate an estimate of the feedback transmitted from the output channel 158 (22) to the input channel 156 (1) in real time. Given this estimate, interference suppression module 135 may determine feedback compensation for application at input channel 156(1), where the feedback compensation, when applied at input channel 156(1), will cancel feedback passed from output channel 158(22) to input channel 156(1).

[0041] Figure 2A and 2B 2 is a simplified schematic block diagram showing portions of two cochlear implants, referred to as cochlear implants 200(A) and 200(B), respectively, configured to perform interference suppression operations according to examples presented herein. For ease of description, Figure 2A and 2B A similar arrangement is shown including a single input channel 256 and a single output channel 258. However, as described elsewhere herein, certain embodiments of the invention may be implemented with a greater number of input channels and / or output channels.

[0042] The input channel 256 includes an implantable microphone 240 electrically connected to an analog-to-digital converter (ADC) 260 via an electrical path including conductor 252(1). The implantable microphone 240 generates an analog signal representative of the detected acoustic signal, and the ADC 260 converts the analog signal into a digital domain for use by the digital signal processor 236. The output channel 258 includes a stimulation contact 242 connected to the stimulator unit 238 via an electrical path including conductor 252(2). Typically, the output channel 258 carries the stimulation signal from the stimulator unit 238 for delivery to the recipient via the stimulation contact 242.

[0043] As described above, there is the potential for any number of feedback paths 262 to be created between the output channel 258 and the input channel 256 via, for example, the recipient's tissue, leakage at the feedthrough (e.g., a conductive path created between the conductors 252(1) and 252(2) due to fluid entering the package), etc. That is, a portion of the stimulation signal sent to the stimulation contact 262 via the output channel 258 will pass through the feedback path 262 and, therefore, will appear in the microphone signal on the input channel 256. The portion of the stimulation signal that passes through the feedback path 262 is referred to herein as "output feedback" or, more simply, "feedback." Feedback that passes through the feedback path 262 may create electrical interference at the input channel 256.

[0044] As described above, cochlear implants 200(A) and 200(B) each include ADC 260, which is configured to receive analog microphone signals via input channel 256. ADC 260 is configured to convert the analog microphone signals into digital microphone signals that are processed by digital signal processor 236. Figure 2A shows an example of performing interference suppression in the analog domain, while Figure 2B An example of performing interference suppression in the digital domain is shown.

[0045] First reference Figure 2A In a specific embodiment of the present invention, an interference suppression module 235 (A) is provided to suppress interference caused by the feedback path 262. The interference suppression module 235 (A) is configured to determine the existence of the feedback path 262 and determine a feedback transfer function 267 for the feedback path 262 (i.e., determine the output-input transfer function between the output channel 258 and the input channel 256). The feedback transfer function 267 represents the characteristics of the feedback path 262 (e.g., amplitude and phase).

[0046] Using the feedback transfer function 267, the interference suppression module 235 (A) is configured to generate an analog compensation filter 265 (A) that models the feedback path voltage in response to the current stimulus. The analog compensation filter 265 (A) is configured to apply analog compensation (e.g., a voltage signal) to the analog microphone signal in the input channel 256, and the analog compensation is configured to offset the portion of the stimulus signal that passes through the feedback path 262 and appears in the input channel. Thus, the interference suppression module 235 (A) and / or the analog compensation filter 265 (A) include hardware (e.g., resistors, buffers, amplifiers, etc.) that generates a voltage that is combined with (e.g., subtracted or added to) the analog microphone signal. As shown, the analog compensation is applied in the analog domain (i.e., before the ADC 260).

[0047] Next reference Figure 2B In the specific embodiment of FIG. 2 , an interference suppression module 235 (B) is provided to suppress interference caused by the feedback path 262. Figure 2A In an embodiment of the present invention, the interference suppression module 235(B) is configured to determine the presence of the feedback path 262 and determine a feedback transfer function 267 for the feedback path 262. Using the feedback transfer function 267, the interference suppression module 235(B) is configured to generate a digital compensation filter 265(B) that models the feedback path voltage in response to the current stimulus. The digital compensation filter 265(B) is configured to apply digital compensation to the digital microphone signal in the input channel 256, the digital compensation being configured to cancel the portion of the stimulus signal that passes through the feedback path 262 and appears in the input channel. Figure 2B In , digital compensation is applied by the digital signal processor 236 in the digital domain (ie, after the ADC 260).

[0048] on the whole, Figure 2A and 2B Two different techniques for applying feedback compensation are shown, which are configured to cancel the portion of the stimulation signal that passes through the feedback path 262 (ie, in the analog or digital domain). Figure 2A and 2B In both examples, feedback compensation is generated based on a feedback transfer function 267 , which generally represents one or more characteristics of the feedback path 262 , and the stimulation signal carried / delivered on the output channel 258 .

[0049] More specifically, signal processor 236 is configured to perform signal processing and encoding to convert electrical signals received from microphone 240 into processed signals 268 that are generally representative of target sounds detected by implantable microphone 240. Stimulator unit 238 is configured to receive processed signals 268 from signal processor 236 and utilize processed signals 268 to generate electrical stimulation signals that are delivered to the cochlea of ​​a recipient via output channel 258 (i.e., via wire 252(2) and contact 242).

[0050] exist Figure 2A and 2B In the example of , the processed signal 268 is not only delivered to the stimulator unit 238, but also delivered to the interference suppression modules 235(A) and 235(B). The interference suppression modules 235(A) and 235(B) can use the information included in the processed signal 268 and the feedback transfer function 267 to determine the real-time feedback compensation to be applied to the input channel 256 via the filter 265(A) or 265(B).

[0051] The feedback transfer function 267 can be generated / created in a variety of different ways, as described below. Figure 2B 256. In some examples, when there is no audio signal from microphone 240, feedback transfer function 267 is generated based on one or more measurements at input channel 256. More specifically, in one example, interference suppression module 235(B) identifies low input periods at input channel 256 (e.g., periods when implantable microphone 240 is turned off and / or periods when acoustic / vibration input is low). During the low input periods, interference suppression module 235(B) causes test stimuli to be delivered to the recipient via output channel 258. In some examples, to reduce interference to the recipient, the test stimuli may be delivered to the recipient below the recipient's hearing threshold (e.g., at a level that does not cause auditory perception by the recipient).

[0052] When the test stimulus is delivered, the interference suppression module 235(B) performs one or more measurements at the input channel 256 to determine a feedback signal (e.g., voltage) in the input channel. As described above, because the test stimulus is delivered during a period of low sound / vibration input, the signal at the input channel can be attributed to feedback through the feedback path 262. The interference suppression module 235(B) knows the properties of the test stimulus (e.g., frequency), and knowing this, the interference suppression module 235(B) can determine the feedback transfer function 267. As described above, the feedback transfer function 267 generally represents the amplitude and phase changes that occur due to the feedback path 262, which can vary over the stimulus frequency.

[0053] It should be understood that the above techniques for determining feedback transfer function 267 are illustrative and other techniques may be utilized according to embodiments presented herein. For example, in additional embodiments, feedback transfer function 267 may be determined by monitoring input channel 256 over a period of time without waiting for a silent period.

[0054] In such an embodiment, the input channel data obtained from the input channel 256 during the period can be analyzed in view of the stimulation signal delivered via the output channel 258 during the period to determine how the stimulation signal affected the input during the period. That is, knowledge of the stimulation signal during the period can be used to determine how the input channel 256 is affected by the feedback from the output channel 258. This can be determined because the feedback is inherently related to the stimulation rate, not the input signal, and can therefore be detected. It is also unlikely that an acoustic input signal with the same characteristics will coexist with the feedback signal.

[0055] Additionally, the feedback transfer function 267 may be estimated and updated periodically, continuously, etc. However, in practice, it is likely that the period will be limited to the time when the known signal is associated with the feedback, rather than being mixed with a similar actual input signal.

[0056] Once the feedback transfer function 267 is calculated by the interference suppression module 235(B), the interference suppression module 235(B) may use the feedback transfer function 267 in real time to compensate for feedback passing through the feedback path 262. That is, the feedback compensation filter 265(B) represents predetermined characteristics of the feedback, which may be used together with knowledge of the properties of the stimulation signal (e.g., the frequency of the stimulation signal) to generate and deliver a compensation signal.

[0057] Several techniques for calculating the feedback transfer function 267 and the associated compensation filter design are described above. In some embodiments, the feedback transfer function 267 and the associated digital compensation filter 265 (B) may be adjusted based on iterative measurements of the feedback received at the input channel 256. This may be accomplished using, for example, an adaptive least mean square (LMS) technique. An example of such an arrangement is shown in FIG. Figure 3 Shown in.

[0058] More specifically, Figure 3256 . The invention relates to a cochlear implant 200 (B) which is a schematic diagram illustrating the operation of the cochlear implant 200 (B) during the measurement of feedback between the output channel 258 and the input channel 256. In this example, the transfer function estimation (H') for the filter 265 (B) uses, for example, the above-described techniques. As shown, in this example, the interference suppression module 235 (B) includes an adaptive LMS filter 274, which is used to update the feedback transfer function 267 (H') during the measurement process. The feedback transfer function 267 is adjusted by minimizing the mean square error (e) of the signal. By minimizing the mean square error (e) of the signal, the adaptive LMS filter 274 estimates the transfer function between the signal Y and the signal X, which is the feedback of the feedback path 262 plus the digital-to-analog current conversion at the stimulator unit 238.

[0059] It should be appreciated that the use of LMS is one example technique for updating the compensation filter weights and that many other procedures for estimating the feedback path transfer function may be implemented in accordance with the embodiments presented herein.

[0060] For the sake of explanation, reference has been made to Figure 2A The above example is mainly described with reference to the interference suppression module 235 (A). It should be understood that similar operations can be implemented at the interference suppression module 235 (B) to generate weights for the feedback compensation filter 265 (B). However, due to Figure 2A and 2B While analog and digital compensation are shown separately, it should also be understood that feedback compensation filters 265 (A) and 265 (B) may be implemented differently and the corresponding compensation approach may be different in each analog and digital example.

[0061] In addition, also for ease of explanation, the above examples have been described with reference to a single output-input channel combination. In practice, an implantable hearing prosthesis or other implantable medical device may include multiple output channels and multiple input channels, and therefore include multiple output-input channel combinations. In some embodiments, as described above, for each output-input channel combination or at least for each output-input channel combination where one or more feedback paths exist, a different compensation filter may be generated, each compensation filter operating differently.

[0062] For example, returning a reference Figure 1A and 1B, the cochlear implant 100 includes two inputs, namely a microphone 140(A) and an accelerometer 140(B), both of which are implanted in the recipient and connected to the feedthrough via a wire 152. Thus, the cochlear implant 100 includes two input channels 156(1) and 156(2). The cochlear implant 100 also includes twenty-four (24) outputs, namely, intra-cochlear contacts 142(1)-142(22) and extra-cochlear contacts 142(23)-142(24). Thus, the cochlear implant 100 includes twenty-four output channels 158(1)-158(24), wherein each output channel is formed by a corresponding contact 142(1)-142(24) and a wire 152.

[0063] It is possible that feedback paths may be generated between any of the twenty-four output channels 158(1)-158(24) and any of the input channels 156(1) and 156(2), thus potentially resulting in up to forty-eight (48) output-input channel combinations and, therefore, up to forty-eight feedback path transfer functions. The interference suppression module 135 may perform the above-referenced Figure 2A , 2B The operations described in and / or 3 are used to generate feedback transfer functions and compensation filters for all or a subset of the forty-eight output-input channel combinations. In some examples, the generation of feedback transfer functions and filters for each of the plurality of output-input channel combinations may be a sequential (channel-by-channel) process as described above.

[0064] In certain embodiments, the compensation filters for multiple output-input channel combinations can be all different and specific to the associated output-input channel combinations. However, in other embodiments, the interference suppression module 135 can determine that multiple (e.g., subsets or all) of the forty-eight output-input channel combinations can have similar feedback paths with similar feedback transfer functions. In other words, through the measurement process, the interference suppression module 135 determines that each of the multiple output-input channel combinations produces similar amounts of feedback at the corresponding input channels. In these embodiments, since the feedback is similar for each output-input channel combination, the interference suppression module 135 can use the same compensation filter to generate compensation signals for all multiple output-input channel combinations.

[0065] As described elsewhere herein, feedback paths between output channels and input channels in an implantable hearing prosthesis or other implantable medical device may be the result of any of a number of different reasons (e.g., via the recipient's tissue / fluids, fluid entering the device's packaging, etc., or a combination thereof). However, it is also possible for implantable input and output channels to exist without a feedback path between them. Thus, in some embodiments, instantiation of a feedback compensation filter for an output-input channel combination may occur only after feedback is detected at the corresponding input channel. For example, again referring to Figure 1A and 1B In some embodiments, interference suppression module 135, signal processor 136, and / or another component of cochlear implant 100 may be configured to (e.g., periodically) monitor input channels 156(1) and 156(2) for possible feedback. Feedback from output channels 158(1)-158(24) may produce interference, which in some examples may be identified as a predetermined / known noise pattern in the input channels. Thus, in some embodiments, cochlear implant 100 is configured to (e.g., periodically) monitor input channels 156(1) and 156(2) for noise that may be attributable to (i.e., due to) feedback from one or more of output channels 158(1)-158(24).

[0066] In other embodiments, cochlear implant 100 may be configured to periodically (e.g., once a day, once a week, etc.) initiate a feedback evaluation process to determine if feedback exists between any output-input channel combinations. In these embodiments, cochlear implant 100 may (e.g., sequentially) evaluate each of the forty-eight output-input channel combinations to determine if feedback exists (e.g., cochlear implant 100 may perform the above referenced Figure 2A , 2B and / or the operations described in 3 to measure feedback at a given input channel 156(1) or 156(2), which is caused by a given output channel 158(1)-158(24)).

[0067] Once cochlear implant 100 determines that feedback may be present at one or more of input channels 156(1) or 156(2), cochlear implant 100 may initiate a process to determine which of output channels 158(1)-158(24) is the source of the feedback and, therefore, determine a feedback transfer function for the particular output-input channel combination, which in turn may be used as part of a feedback compensation filter for the particular output-input channel combination.

[0068] Once the compensation filter is instantiated for an output-input channel combination, the filter can be periodically re-evaluated and adjusted as needed. This process can be similar to reference Figure 2A , 2B and / or the process described in 3 for determining initial filter weights. In some embodiments, the filter re-evaluation process may be performed periodically (e.g., once a day, once a week, etc.). In other embodiments, the filter re-evaluation process may be performed in response to a triggering event (e.g., detection of additional electrical interference (e.g., noise) at input channels 156(1)-156(2)).

[0069] In one exemplary embodiment utilizing an LMS adaptive filter, the LMS may be continuously updated even under conditions of acoustic input. This may be regulated and adaptation may be allowed only when conditions are favorable to do so (e.g., low acoustic input levels). In some such examples, one aspect is determining whether a signal is due to feedback or another acoustic input. As described above, this may be determined because feedback is inherently related to the stimulation rate, not the input signal, and therefore may be detected. It is also unlikely that an acoustic input signal with the same characteristics will coexist with the feedback signal.

[0070] Figure 4A 4 is a flow chart of a method 480 according to an embodiment presented herein. The method 480 begins at 482, where an implantable medical device detects the presence of one or more feedback paths between an output channel and an input channel of the implantable medical device, wherein the one or more feedback paths enable feedback to appear in the input channel, the feedback comprising a portion of the stimulation signal on the output channel. At 484, the implantable medical device determines a feedback transfer function associated with the one or more feedback paths. At 486, based on the feedback transfer function, the implantable medical device eliminates feedback that appears in the input channel in response to the delivery of the stimulation signal via the output channel.

[0071] Figure 4B 4 is a flow chart of a method 490 according to an embodiment presented herein. The method 490 begins at 492, where an implantable medical device detects the presence of at least one feedback path between an output channel and an input channel of the implantable medical device. At 494, the implantable medical device generates a model of the at least one feedback path. At 496, the implantable medical device delivers a stimulation signal to a recipient of the implantable medical device via the output channel, where the stimulation signal is delivered at a stimulation frequency. At 498, the implantable medical device uses the stimulation frequency of the stimulation signal and the model of the one or more feedback paths to identify feedback that occurs at the input channel in response to the delivery of the stimulation signal.

[0072] It should be understood that the embodiments presented herein are not mutually exclusive.

[0073] The invention described and claimed herein is not limited in scope by the specific preferred embodiments disclosed herein, because these embodiments are intended to be illustrative, rather than limiting several aspects of the present invention. Any equivalent embodiments are intended to be within the scope of the present invention. In fact, in addition to those shown and described herein, various modifications of the present invention will become apparent to those skilled in the art according to the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

Claims

1. A method for suppressing electrical interference, comprising: detecting the presence of one or more feedback paths between an output channel and an input channel of an implantable medical device, wherein the one or more feedback paths extend through tissue or fluid of a recipient and cause a portion of an electrical stimulation signal on the output channel to appear as electrical interference in the input channel; determining a feedback transfer function associated with the one or more feedback paths, wherein the feedback transfer function characterizes propagation of a portion of the electrical stimulation signal transmitted between an output channel and an input channel; and Electrical interference present in the input channel in response to delivery of the electrical stimulation signal via the output channel is cancelled based on the feedback transfer function.

2. The method according to claim 1, further comprising: delivering a first set of electrical stimulation signals via the output channel; as well as determining the frequency of the first set of electrical stimulation signals; Wherein eliminating electrical interference present in the input channel in response to delivery of the first set of electrical stimulation signals via the output channel comprises: generating one or more feedback compensations for the input channels using the stimulation frequencies of the first set of electrical stimulation signals; as well as The one or more feedback compensations are applied to cancel electrical interference present in the input channel due to the first set of electrical stimulation signals from the input channel.

3. The method of claim 1 , wherein determining a feedback transfer function associated with the one or more feedback paths comprises: delivering a test stimulus via the output channel during a period of low input at the input channel; as well as In response to delivering a test stimulus via the output channel, at least one measurement is performed at the input channel.

4. The method according to claim 3, further comprising: iteratively delivering a plurality of sets of test stimuli via the output channel; performing at least one additional measurement at the input channel in response to delivering each set of iterative test stimuli via the output channel; as well as The feedback transfer function is iteratively updated in response to each additional at least one measurement.

5. The method of claim 1 , wherein determining a feedback transfer function associated with the one or more feedback paths comprises: monitoring the input channel for a period of time to capture input channel data; as well as Input channel data captured during the period of time is analyzed in view of the stimulation signal delivered via the output channel during the period of time.

6. The method of claim 1 , wherein detecting the presence of one or more feedback paths between the output channel and the input channel comprises: The input channels are monitored for noise attributable to a portion of the electrical stimulation signal communicated between the corresponding output channel and the input channel.

7. The method of claim 6, wherein monitoring whether the input channel is noisy comprises: The input channel is monitored for the presence of one or more predetermined noise patterns.

8. The method of claim 1, wherein the implantable medical device comprises a plurality of output channels and a plurality of input channels, and wherein the method further comprises: detecting that a plurality of input channels are each affected by a set of one or more feedback paths extending from one or more of the plurality of output channels; as well as A feedback transfer function is determined for each set of feedback paths affecting one of the plurality of input channels.

9. The method of claim 1, wherein the implantable medical device is an implantable hearing prosthesis, and wherein the input channel comprises a sound input component and one or more associated conductors, and the output channel comprises a stimulation component and one or more associated conductors.

10. A method for suppressing electrical interference, comprising: detecting the presence of at least one feedback path between an output channel and an input channel of the implantable medical device extending through tissue or fluid of a recipient; generating a model of the at least one feedback path; delivering an electrical stimulation signal to a recipient of the implantable medical device via the output channel, wherein the electrical stimulation signal is delivered at a stimulation frequency; as well as Electrical disturbances occurring at the input channel in response to delivery of the electrical stimulation signal are identified using a stimulation frequency of the electrical stimulation signal and a model of the one or more feedback paths.

11. The method according to claim 10, further comprising: A real-time feedback compensation to be applied at at least one input channel is determined, wherein the application of the real-time feedback compensation is configured to cancel electrical interference at the at least one input channel.

12. The method of claim 10, wherein generating a model of the at least one feedback path comprises: delivering a test stimulus via the output channel during a period of low input at the input channel; as well as In response to delivering a test stimulus via the output channel, at least one measurement is performed at the input channel.

13. The method according to claim 12, further comprising: iteratively delivering a plurality of sets of test stimuli via the output channel; performing at least one additional measurement at the input channel in response to delivering each set of iterative test stimuli via the output channel; as well as The model of the at least one feedback path is iteratively updated in response to each additional at least one measurement.

14. The method of claim 10, wherein generating a model of the at least one feedback path comprises: monitoring the input channel for a period of time to capture input channel data; as well as Input channel data captured during the period of time is analyzed in view of the stimulation signal delivered via the output channel during the period of time.

15. A tissue stimulation prosthesis comprising: at least one input channel comprising an implantable sensor and one or more associated conductors configured to be implanted in a recipient; at least one output channel comprising a stimulation component and one or more associated conductors configured to be implanted in a recipient; as well as An interference suppression module, wherein the interference suppression module is configured to: detecting on the at least one input channel an electrical disturbance generated by the at least one output channel via at least one feedback path extending through tissue or fluid of a recipient, and A real-time feedback compensation to be applied at the at least one input channel is determined, wherein the application of the real-time feedback compensation is configured to cancel electrical interference at the at least one input channel.

16. A tissue stimulation prosthesis according to claim 15, wherein the interference suppression module is configured to determine one or more characteristics of the at least one feedback path, and wherein the interference suppression module is configured to determine the real-time feedback compensation based on one or more properties of the electrical stimulation signal to be delivered to the at least one output channel and based on one or more characteristics of the at least one feedback path.

17. A tissue stimulation prosthesis according to claim 16, wherein the interference suppression module is configured to use one or more characteristics of the at least one feedback path to generate in real time an estimate of a portion of the electrical stimulation signal transmitted via the at least one output channel that is transmitted from the at least one output channel to the at least one input channel in response to the transmission of the electrical stimulation signal via the at least one output channel.

18. The tissue stimulation prosthesis of claim 16, wherein to determine one or more characteristics of the at least one feedback path, the interference suppression module is configured to: delivering a test stimulus via the at least one output channel during a period of low input at the at least one input channel; and In response to delivering a test stimulus via the at least one output channel, at least one measurement is performed at the input channel.

19. The tissue stimulation prosthesis of claim 18, wherein the interference suppression module is configured to: iteratively delivering a plurality of sets of test stimuli via the at least one output channel; performing at least one additional measurement at the input channel in response to delivering each set of iterative test stimuli via the output channel; and In response to each additional at least one measurement, one or more characteristics of the at least one feedback path are iteratively updated.

20. The tissue stimulation prosthesis of claim 16, wherein to determine one or more characteristics of the at least one feedback path, the interference suppression module is configured to: monitoring the input channel for a period of time to capture input channel data; and Input channel data captured during the period of time is analyzed in view of the electrical stimulation signal delivered via the output channel during the period of time.

21. The tissue stimulation prosthesis of claim 15, wherein the stimulation component comprises stimulation contacts configured to deliver electrical stimulation to a recipient.

22. The tissue stimulation prosthesis of claim 15, wherein the implantable sensor comprises an implantable microphone.

23. An implantable medical device method, wherein the implantable medical device comprises at least one input channel and at least one output channel configured to carry an input signal and an electrical stimulation signal, respectively, the method comprising: delivering an electrical stimulation signal to a recipient of the implantable medical device via the at least one input channel; detecting at the at least one input channel an electrical disturbance resulting from delivering the electrical stimulation signal to the recipient via the at least one output channel by extending through tissue or fluid of the recipient, wherein the electrical disturbance comprises a portion of the electrical stimulation signal; determining a feedback compensation to be applied at the at least one input channel; as well as The feedback compensation is applied at the at least one input channel to eliminate electrical interference generated by delivering the electrical stimulation signal to the recipient.

24. The implantable medical device method of claim 23, wherein a portion of the electrical stimulation signal is passed from the at least one output channel to the at least one input channel via one or more feedback paths, wherein the method further comprises: determining a feedback transfer function associated with the one or more feedback paths, wherein the feedback transfer function characterizes propagation of a portion of the electrical stimulation signal passing between an output channel and an input channel; and The feedback compensation is determined based on the feedback transfer function and one or more properties of the electrical stimulation signal.

25. The implantable medical device method of claim 24, wherein determining a feedback transfer function associated with the one or more feedback paths comprises: delivering a test stimulus via the output channel during a period of low input at the input channel; as well as In response to delivering a test stimulus via the output channel, at least one measurement is performed at the input channel.

26. The implantable medical device method of claim 25, further comprising: iteratively delivering a plurality of sets of test stimuli via the output channel; performing at least one additional measurement at the input channel in response to delivering each set of iterative test stimuli via the output channel; as well as The feedback transfer function is iteratively updated in response to each additional at least one measurement.

27. The implantable medical device method of claim 24, wherein determining a feedback transfer function associated with the one or more feedback paths comprises: monitoring the input channel for a period of time to capture input channel data; as well as Input channel data captured during the period of time is analyzed in view of the stimulation signal delivered via the output channel during the period of time.

28. The implantable medical device method of claim 23, wherein detecting electrical interference from the at least one output channel via the one or more feedback paths comprises: The input channel is monitored for noise attributable to a portion of the electrical stimulation signal from the output channel.

29. The implantable medical device method of claim 28, wherein monitoring the input channel for noise comprises: The input channel is monitored for the presence of one or more predetermined noise patterns.

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