Dual feedback control system for implantable hearing instrument Number:7,522,738 from the United States Patent and Trademark Office (PTO) owispatent The invention is directed to an implanted microphone having reduced sensitivity to vibration. In this regard, the microphone differentiates between the desirable and undesirable vibration by utilizing at least one motion sensor to produce a motion signal when an implanted microphone is in motion. This motion signal is used to yield a microphone output signal that is less vibration sensitive. In a first arrangement, the motion signal may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. Specifically, the motion signal may be scaled to match the motion component of the microphone output such that upon removal of the motion signal from the microphone output, the remaining signal is an acoustic signal.<H implantable, instrument, Dual, feedback, c, 7522738.html, Patent, pto, 7522738

Title: Dual feedback control system for implantable hearing instrument

Abstract: The invention is directed to an implanted microphone having reduced sensitivity to vibration. In this regard, the microphone differentiates between the desirable and undesirable vibration by utilizing at least one motion sensor to produce a motion signal when an implanted microphone is in motion. This motion signal is used to yield a microphone output signal that is less vibration sensitive. In a first arrangement, the motion signal may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. Specifically, the motion signal may be scaled to match the motion component of the microphone output such that upon removal of the motion signal from the microphone output, the remaining signal is an acoustic signal.

Patent Number: 7,522,738 Issued on 04/21/2009 to Miller, III

Inventors: Miller, III; Scott Allan (Lafayette, CO)
Assignee: Otologics, LLC (Boulder, CO)

Appl. No.: 11/565,001

Filed: November 30, 2006

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
60740710	Nov., 2005

Current U.S. Class: 381/318 ; 381/312; 381/317

Current International Class: H04R 25/00 (20060101)

Field of Search: 381/312,315-318,320 600/25 607/55-57

References Cited [Referenced By]

U.S. Patent Documents


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Primary Examiner: Ni; Suhan
Attorney, Agent or Firm: Marsh Fischmann & Breyfogle LLP

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. .sctn.119 to U.S. Provisional Application U.S. Provisional 60/740,710 entitled "Active Vibration Attenuation For Implantable Microphone," having a filing date of Nov. 30, 2005.

Claims

The invention claimed is:

1. A system for reducing noise in a drive signal of an implantable hearing instrument, comprising: a microphone operative to receive sound and generate a microphone output signal; a first noise control system for generating a first cancellation signal, wherein said first cancellation signal is combinable with said microphone output signal to generate a first combined signal; a second noise control system for generating a second cancellation signal, wherein said second cancellation signal is combinable with said microphone output signal to generate a second combined signal; a controller, said controller being operative to select at least a portion of one of said first and second combined signals for at least one frequency band; and a signal processor connected to an output of said controller for processing at least signals selected by said controller to generate a drive signal for actuating an implantable auditory stimulation device.

2. The system of claim 1, wherein said microphone is adapted for subcutaneous positioning.

3. The system of claim 1, wherein said first noise control system comprises: a motion sensor operative to generate a motion sensor output signal indicative of motion; and a filter operative to filter said motion sensor output signal to generate said first cancellation signal.

4. The system of claim 3, wherein said filter matches at least one component of said motion sensor output signal to at least one corresponding component of said microphone output signal.

5. The system of claim 4, wherein said component comprises at least one of magnitude, phase and frequency.

6. The system of claim 3, wherein said filter comprises a digital filter.

7. The system of claim 6, wherein said digital filter comprises an IIR digital filter.

8. The system of claim 6, further comprising: an analog to digital converter for converting an analog output of said motion sensor to a digital motion signal, wherein said digital filter receives said digital motion signal.

9. The system of claim 3, further comprising: a first summation device for combining said first cancellation signal with said microphone output signal wherein combining comprises subtracting said first cancellation signal from said microphone output signal.

10. The system of claim 3, wherein said second noise control system comprises: a digital filter adapted to receive a digital output of said signal processor including said drive signal and match at least one component of said digital output to at least one corresponding component of said microphone output signal.

11. The system of claim 10, further comprising: a signal source for injecting a known signal into said digital output, wherein said known signal is present in said digital output and is present in said microphone output via a feedback path.

12. The system of claim 10, wherein said digital filter comprises and IIR filter.

13. The system of claim 10, wherein said digital filter comprises and adaptive digital filter.

14. The system of claim 1, wherein said controller performs a binary selection of said first and second combined signals, wherein only one of said first and second combined signals is selected for said at least one frequency band.

15. The system of claim 1, wherein said controller is operative to select a portion of each of said first and second combined signals for said at least one frequency band.

16. The system of claim 15, further comprising: a summation device for combining selected portions of said first and second combined signals, wherein said signal processor receives a blend of said first and second combined signals.

17. The system of claim 1, wherein said controller is operative to select at least a portion of one of said first and second combined signals for a plurality of different frequency bands.

18. The system of claim 1,wherein said controller selects said at least a portion of one of said first and second combined signals based on a noise level associated with each of said first and second combined signals.

19. The system of claim 1, wherein said controller selects one of said first and second combined signals based on which of said first and second combined signals has a lower power level.

20. The system of claim 1, wherein said implantable auditory stimulation device comprises a mechanical actuator for mechanically stimulating an auditory component of a patient.

21. The system of claim 1, further comprising: a digital to analog converter for converting said drive signal to an analog signal prior to receipt of said drive signal by said implantable auditory stimulation device.

22. A method for reducing noise in a drive signal of an implantable hearing instrument, comprising: producing a first cancellation signal associated with motion of an implanted microphone; producing a second cancellation signal indicative of feedback received by said implanted microphone from operation of an implanted auditory stimulation device, combining said first and second cancellation signals to an output signal of said implanted microphone to generate a first and second cancelled microphone output signals, respectively; selecting at least a portion of one of said first and second cancelled microphone signals for at least one frequency band; and utilizing at least said portion of selected signal to generate a digital drive signal for use in actuating an implantable auditory stimulation device.

23. The method of claim 22, wherein producing said first cancellation signal comprises: manipulating an output of a motion sensor such that at least one component of said motion sensor output substantially matches a corresponding component of said microphone output.

24. The method of claim 23, wherein manipulating comprises filtering said output of said motion sensor using a digital filter.

25. The method of claim 23, further comprising: analog-to-digital converting said output of said motion sensor.

26. The method of claim 22, wherein producing said second cancellation signals comprises: manipulating digital drive signal such that at least one component of a resulting signal substantially matches a corresponding component of said microphone output.

27. The method of claim 26, wherein said resulting signals comprises said second cancellation signal.

28. The method of claim 26, further comprising injecting a known signal into said digital drive signal, wherein said at least one component comprises said known signal.

29. The method of claim 26, wherein manipulating comprises filtering said output of said motion sensor using a digital filter.

30. The method of claim 22, wherein selecting comprises performing a binary selection, wherein only one of said first and second cancelled microphone signals is selected for said at least on frequency band.

31. The method of claim 22, wherein selecting comprises selecting at least a portion of one of said first and second cancelled microphone signals for a plurality of frequency bands.

32. The method of claim 22, wherein selecting comprises: selecting at least a portion of each of said first and second cancelled microphone signals for at least one frequency band; and blending selection portions of said first and second cancelled microphone signals, wherein a resulting blended signal is utilized to generate said digital drive signal.

33. The system of claim 22, wherein selecting comprises selecting said at least a portion of one of said first and second cancelled microphone signals based on a noise level associated with each of said first and second combined signals.

34. The system of claim 22, selecting comprises selecting one of said first and second cancelled microphone signals based on which of said first and second cancelled microphone signals has a lower power level.

35. The method of claim 22, further comprising: digital-to-analog converting said digital drive signal to generate an analog drive signal, wherein said analog drive signal is utilized for actuating said auditory stimulation device.

36. A system for reducing noise in a drive signal of an implantable hearing instrument wherein an implantable processor receives an input signal originating from an implantable microphone and generates said drive signal for actuating an implantable auditory stimulation device, comprising: a microphone operative to receive sound and generate a microphone output, said microphone being adapted for subcutaneous positioning; a motion sensor for generating a motion signal indicative of motion of said microphone; a first digital filter adapted to receive said motion signal and generate a filtered motion signal that models a response of said microphone to motion; a first summation device for combining said microphone output and said filtered motion signal to generate a first compensated microphone signal; a second digital filter adapted to receive said drive signal and generate a feedback signal that models a response of said microphone to operation of said implantable auditory stimulation device; a second summation device for combining said microphone output and said feedback signal to generate a second compensated microphone signal; and a controller operative to select at least a portion of one of said first and second compensated microphone signals for at least one frequency band and provide such selected portions to a signal processor for use in generating drive signals for actuating said implantable auditory stimulation device.

Description

FIELD OF THE INVENTION

The present invention relates to implanted hearing instruments, and more particularly, to the reduction of undesired signals from an output of an implanted microphone.

BACKGROUND OF THE INVENTION

In the class of hearing aid systems generally referred to as implantable hearing instruments, some or all of various hearing augmentation componentry is positioned subcutaneously on, within, or proximate to a patient's skull, typically at locations proximate the mastoid process. In this regard, implantable hearing instruments may be generally divided into two sub-classes, namely semi-implantable and fully implantable. In a semi-implantable hearing instrument, one or more components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components such as a transducer. In a fully implantable hearing instrument, typically all of the components, e.g., the microphone, signal processor, and transducer, are located subcutaneously. In either arrangement, an implantable transducer is utilized to stimulate a component of the patient's auditory system (e.g., ossicles and/or the cochlea).

By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to interface with and stimulate the ossicular chain of the patient via physical engagement. (See e.g., U.S. Pat. No. 5,702,342). In this regard, one or more bones of the ossicular chain are made to mechanically vibrate, which causes the ossicular chain to stimulate the cochlea through its natural input, the so-called oval window.

As may be appreciated, a hearing instrument that proposes to utilize an implanted microphone will require that the microphone be positioned at a location that facilitates the receipt of acoustic signals. For such purposes, an implantable microphone may be positioned (e.g., in a surgical procedure) between a patient's skull and skin, for example, at a location rearward and upward of a patient's ear (e.g., in the mastoid region).

For a wearer a hearing instrument including an implanted microphone (e.g., middle ear transducer or cochlear implant stimulation systems), the skin and tissue covering the microphone diaphragm may increase the vibration sensitivity of the instrument to the point where body sounds (e.g., chewing) and the wearer's own voice, conveyed via bone conduction, may saturate internal amplifier stages and thus lead to distortion. Also, in systems employing a middle ear stimulation transducer, the system may produce feedback by picking up and amplifying vibration caused by the stimulation transducer.

Certain proposed methods intended to mitigate vibration sensitivity may potentially also have an undesired effect on sensitivity to airborne sound as conducted through the skin. It is therefore desirable to have a means of reducing system response to vibration (e.g., caused by biological sources and/or feedback), without affecting sound sensitivity. It is also desired not to introduce excessive noise during the process of reducing the system response to vibration. These are the goals of the present invention.

SUMMARY OF THE INVENTION

In order to achieve this goal, it is necessary to differentiate between the desirable case, caused by outside sound, of the skin moving relative to an inertial (non accelerating) implant housing, and the undesirable case, caused by bone vibration, of an implant housing and skin being accelerated by motion of the underlying bone, which will result in the inertia of the overlying skin exerting a force on the microphone diaphragm.

According to one aspect of the invention, differentiation between the desirable and undesirable cases is achieved by utilizing at least one motion sensor to produce a signal when an implanted microphone is in motion. Such a sensor may be, without limitation, an acceleration sensor and/or a velocity sensor. In any case, the signal is indicative movement of the implanted microphone diaphragm. In turn, this signal is used to yield a microphone output signal that is less vibration sensitive. The motion sensor(s) may be interconnected to an implantable support member for co-movement therewith. For example, such support member may be a part of an implantable microphone or part of an implantable capsule to which the implantable microphone is mounted.

In a first arrangement, the implantable microphone may comprise a microphone housing, an external diaphragm disposed across an aperture of the housing, and a microphone transducer interconnected to the microphone housing and operable to provide an output signal responsive to movement of the diaphragm. Such output signal may be supplied to an implantable stimulation transducer for middle ear, inner ear and/or cochlear implant stimulation. In this arrangement, the motion sensor(s) may be interconnected to the microphone housing and/or the microphone transducer for co-movement therewith. An example of a middle ear stimulation transducer arrangement is described in U.S. Pat. No. 6,491,622, hereby incorporated by reference.

In a second arrangement, the implanted microphone may be supportably interconnected within an opening of an implant capsule, wherein the external diaphragm is located to receive incident acoustic waves and a microphone transducer is hermetically sealed within the implant capsule. In this arrangement, the motion sensor(s) may be interconnected to the implant capsule for co-movement therewith. Such implant capsule may also hermetically house other componentry (e.g., processor and/or circuit componentry, a rechargeable energy source and storage device, etc.) and may provide one or more signal terminal(s) for electrical interconnection (e.g., via one or more cables) with an implantable stimulation transducer for middle ear or cochlear implant stimulation.

In either arrangement, the motion sensor(s) may be positioned such that an axis of sensitivity of the sensor is aligned with a principal direction of movement of the microphone diaphragm. Such a principal direction of movement may be substantially normal to a surface (e.g., a planar surface) defined by the diaphragm. Such alignment of the motion sensor may allow for enhanced detection of undesired movement between the diaphragm and overlying tissue (e.g., skin). More preferably, such an axis of sensitivity may extend through the center of mass of the microphone. This may allow for more accurately identifying movement of the microphone as an assembly. Accordingly, the center of mass of the microphone assembly and motion sensor(s) may be located on a common axis that may also be directed normal to the principal direction of movement of the microphone diaphragm. In an arrangement where a plurality of motion sensor(s) is employed, the sensors may be positioned so that their centroid or combinative center of mass is located on such a common axis.

In another aspect utilizing a motion sensor to yield a microphone output signal that is less vibration sensitive, the output of the motion sensor may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. For example, the motion sensor output may be appropriately scaled, phase shifted and/or frequency-shaped to match a difference in frequency response between the motion sensor output and the microphone transducer output, then subtracted from the microphone transducer output to yield a net, improved audio signal employable for driving a middle ear transducer, an inner ear transducer and/or a cochlear implant stimulation system.

In order to scale, frequency-shape and/or phase shift the motion sensor output, a variety of signal processing/filtering methods may be utilized. Mechanical feedback from an implanted transducer and other undesired signals, for example, those caused by biological sources, may be determined or estimated to adjust the phase/scale of the motion output signal. Such determined and/or estimated signals may be utilized to generate an output signal having a reduced response to the feedback and/or undesired signals. For instance, mechanical feedback may be determined by injecting a known signal into the system and measuring a feedback response at the motion sensor and microphone. By comparing the input signal and the feedback response a maximum gain for a transfer function of the system may be determined. Such signals may be injected to the system at the factory to determine factory settings. Further such signals may be injected after implant, e.g., upon activation of the hearing instrument. In any case, by measuring the feedback response using the motion sensor and removing the motion sensor response from the microphone response, the effects of such feedback may be reduced or substantially eliminated from the resulting net output.

By utilizing a filter to scale, frequency-shape and/or shift a motion sensor output response to mechanical feedback caused by an inserted signal, the magnitude and phase of the motion sensor response may be made to substantially match the microphone output response to the same mechanical feedback. Accordingly, by removing the `filtered` motion sensor response from the microphone output response, the effects of mechanical feedback in the resulting net output may be substantially reduced. By generating a filter to manipulate the motion sensor output response to substantially match the microphone output response to mechanical feedback (e.g., caused by a known inserted signal), the filter may also be operative to manipulate the motion sensor output response to other undesired signals such as biological noise.

According to one aspect of the invention, a method and apparatus (i.e., utility) for generating a system model to match the output response of a motion sensor to the output response of a microphone is provided. The utility includes inserting a known signal into an implanted hearing device in order to actuate an auditory stimulation mechanism of the implanted hearing device. This may entail initiating the operation of an actuator/transducer. Operation of the auditory stimulation mechanism may generate vibrations that may be transmitted back to an implanted microphone via a tissue path (e.g., bone and/or soft tissue). These vibrations or `mechanical feedback` are represented in the output response of the implanted microphone. Likewise, a motion sensor also receives the vibrations and generates an output response. The output responses of the implanted microphone and motion sensor are then sampled to generate a system model that is operative to match the motion sensor output response to the microphone output response. Once such a system model is generated, the system model may be implemented for use in subsequent operation of the implanted hearing device. That is, the matched response of the motion sensor may be removed from the output response of the implanted microphone to produce a net output response having reduced response to undesired signals (e.g., noise).

In one arrangement, the system model is generated using the ratios of the microphone and motion sensor output responses over a desired frequency range. For instance, a plurality of the ratios of the output responses may be determined over a desired frequency range. These ratios may then be utilized to create a mathematical model for adjusting the motion sensor output response to match the microphone output response for a desired frequency range. For instance, a mathematical function may be fit to the ratios of the output responses over a desired frequency range and this function may be implemented as a filter (e.g., a digital filter). The order of such a mathematical function may be selected to provide a desired degree of correlation between the function and the ratio of output responses. In any case, use of a second order or greater function may allow for non-linear adjustment of the motion sensor output response based on frequency. That is, the motion sensor output response may receive different scaling, frequency-shaping and/or phase shifting at different frequencies.

Variations exist in the implementation of such a system model. For instance, time domain samples or frequency domain samples of the microphone and motion sensor output responses may be utilized. In any case, upon generating a ratio of responses over a desired frequency range, a mathematical function may be fit to the ratio of responses and, if acceptable, implemented as a filter. Multiple known processes for fitting a function to such data exist. In one arrangement, the function comprises an IIR filter function. In such an arrangement, any appropriate method may be utilized selected coefficients for the IIR filter. Of note, when utilizing an IIR filter, the method may further entail monitoring the output values of the filter to identify instability. Upon identification of such instability, the filter coefficients may be reset to a predetermined starting value and/or reset to zero. Further, will be appreciated the multiple sets of filter coefficients may be established for a single IIR filter. In this regard, different filter coefficients may be utilized for different operating conditions. In such an arrangement, the filter may be adaptive to switch between or/or extrapolate between different coefficient sets.

Once a filter is established for matching the output response of the motion sensor to the output response of the microphone, the filtered motion sensor output may be combined with the microphone output response. This may result in the generation of a net output response of the microphone that has a reduced sensitivity to mechanical feedback as well as other sources of noise acting on both the microphone and a motion sensor.

One or more or all of the steps above may be performed by an internal processor of the implanted hearing instrument. In another arrangement, a portion of the steps may be performed external to the patient. For instance, the output responses of the microphone and the motion sensors may be transmitted (e.g., transcutaneously or via hard wiring) to an external processor (e.g., a PC) such that the modeling/generation of the system model may be performed external to the patient. Further, the system model may be validated prior to implementation within an implanted hearing instrument. If the system model performs adequately (exceeds one or more predetermined thresholds), the system model may be transmitted to the implanted hearing instrument (e.g., for storage in permanent/semi-permanent memory).

According to another aspect of the invention, a system and method (i.e., utility) are provided for use in an implantable hearing system. The method includes measuring first and second output responses of an implanted microphone and a motion sensor, respectively. The output responses are measured in response to a common stimulation. Ratio information is then generated that is associated with ratios of the first and second output responses. The ratio information may then be utilized to generate a relationship model of the first and second output responses. This model may be implemented as a filter to adjust subsequent output responses of at least one of the implanted microphone and/or the motion sensor.

Variations exist in the subject aspect. For instance, generating ratio information may include generating a plurality of time-based ratios and/or transforming the output responses of the implanted microphone and motion sensor to generate frequency domain output responses. According, such frequency domain responses may be utilized to generate ratio information. Typically, at least two ratios and more preferably a plurality of ratios of the first and second output responses (e.g., over a plurality of desired frequency ranges) are utilized to generate the ratio information associated with the first and second output responses.

Producing a model may include utilizing individual ratios for individual frequency bands or, producing a function that (e.g., a nonlinear function) substantially matches the ratio information over a desired frequency range. In one arrangement, this includes fitting a digital filter function to the ratio information over a predetermined frequency range. In such an arrangement, multiple sets of filter coefficients may be selected for the digital filter function. For instance, a first set of coefficients may correspond to a first relationship model of the first and second output responses to a first common stimulation. A second set of coefficients may correspond to a second relationship model of the first and second output responses to a second different common stimulation. The method may further including selectively switching between different sets of filter coefficients based on current operating parameters of the hearing system.

According to another aspect of the present invention, a system and method for use in an implantable hearing system is provided. The system and method (i.e., utility) includes measuring first and second outputs of an implanted microphone and a motion sensor, respectively, in response to the operation of an implanted auditory stimulation device. The first and second outputs are utilized to calibrate a digital filter such that transfer function of the digital filter may be utilized to adjust one of the first and second outputs to be substantially equal the other of the first and second outputs. Accordingly, the digital filter may be utilized to filter subsequent outputs for noise cancellation purposes.

In order to calibrate the digital filter, the frequency responses of the motion sensor and implanted microphone are measured in response to operation of an implanted auditory stimulation device. In this regard, the first output may measure a feedback transmitted through a first tissue path between an implanted auditory stimulation device and the implanted microphone while the second output may measure feedback transmitted through a second tissue path between the implanted auditory stimulation device and the motion sensor. In one arrangement, the first and second tissue paths may be substantially the same where the motion sensor and implanted microphone are substantially co-located.

In any case, once the digital filter is implemented to filter subsequent outputs of one of the motion sensor and the microphone output, the digital filter may generate filtered outputs. Accordingly, the filtered outputs may be combined with a non-filtered output to generate net outputs. Such net outputs may have reduced response to undesired signals.

According to another aspect of the present invention, a system and method (i.e., utility) is provided for use in an implantable hearing system. The method includes measuring first and second output responses of an implanted microphone and motion sensor, respectively, to a common stimulation source. First and second ratios of the first and second output response are generated for first and second frequency ranges, respectively. These first and second ratios are then utilized to adjust subsequent output responses of one of the motion sensor and implanted microphone for the first and second frequency ranges. In a further arrangement, a plurality of ratios of the first and second output responses is produced for plurality of frequency ranges. As may be appreciated, by increasing the number of frequency ranges, the output response of one of the implanted microphone and motion sensor may be better matched to the output of the other of the microphone and motion sensor. Such processing may be performed in a sub-band processing system.

According to another aspect of the present invention, an implantable hearing system that is operative to match an output response of a motion sensor to at least a portion of an output response of an implanted microphone is provided. The system includes a microphone that is adapted for subcutaneous positioning and which is operative to receive signals including motion/acceleration and acoustic components. The microphone is further operative to generate microphone output responses that include the motion/acceleration and acoustic components. The system further includes a motion sensor that is operative to receive signals including motion/acceleration components and generate motion sensor output responses. Such motion sensor output responses may be substantially free of acoustic components. The system further includes a digital filter that is adapted to utilize a ratio of the microphone output responses and motion sensor output responses to generate a transfer function. The digital filter is then operative to apply the transfer function to the motion sensor output and/or the microphone output responses to produce filtered output responses. A summation device is then utilized to combine filtered output responses to one of the microphone output response and the motion sensor output responses to generate net output responses. Finally, an implantable auditory stimulation device is operative to stimulate an auditory component of a patient in accordance with the net output response.

As may be appreciated, variations exist to the components of the present system. For instance, the system may include one or more A to D converters to convert analog output signals of the motion sensor and microphone to digital signals. Likewise, the system may include one or more D to A converters for converting digital output signals to analog drive signals that are operative to actuate the implantable auditory stimulation device. In one arrangement, the auditory stimulation device may be a mechanical actuator for physically stimulating an auditory component.

In another aspect of the present invention, an implantable hearing system and method (i.e., utility) utilizes first and second control systems or `control loops` for controlling the amount of noise (e.g., feedback and/or biological noise) in the output of the implanted microphone prior to processing. In this aspect, a first control loop includes a motion sensor for detecting acceleration within the system. An output response of this motion sensor may be removed from an output response to the microphone to reduce biological noise as well as mechanical feedback, which may be present due to the operation of an implanted auditory stimulation device. In this regard, the output response to the motion sensor may be filtered to adjust its magnitude and/or phase. However, this may result in amplification of electrical noise associated with the motion sensor. Accordingly, in quiet operating conditions a user of the implantable hearing system may experience enhanced noise due to amplification of electrical noise in the motion sensor output. To address this problem, the utility utilizes a second control loop. The second control loop utilizes a filter to match the digital output of a digital signal processor of the implanted hearing system to the mechanical feedback path. In this regard, the digital output of the digital signal processor is scaled and or phase shifted removed from the microphone output response and then reinserted into the digital signal processor. In this control loop, there is no electrical noise as all signals are digital. Accordingly, in quite operating conditions (e.g., low ambient noise environments) use of the second control loop may be preferred. However, the second control loop while being effective to reduce mechanical feedback within the microphone output response, it may be ineffective for removing other sources of noise (e.g., biological) in the microphone output response. Accordingly, it may be desirable in instances where other sources of noise exist to utilize the first control loop.

Accordingly, the utility is operative to select between and/or blend the outputs of the first and second control loops based on current operating conditions in order to reduce noise perceived by a user of the implantable hearing system. In one arrangement, the utility is operative to select the control loop signal having a lower magnitude and hence the lower noise component. In further arrangements, such as sub-band processing arrangements, different control loops may be utilized for different frequency ranges. In this regard, the control loop that provides the best noise cancellation for a predetermined frequency range may be utilized.

In a further arrangement for removing undesired signals caused by biological sources, one or more adaptive filtering techniques may be utilized. As will be noted, biological signals are not generally constant over time. Accordingly, the system may use an adaptive algorithm to adjust an adaptive filter in order to remove undesired signals. Illustrative adaptive algorithms include, without limitation, stochastic gradient-based algorithms such as the least-mean-squares (LMS) and recursive algorithms such as recursive least-squares (RLS).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a fully implantable hearing instrument as implanted in a wearer's skull;

FIG. 2 is a schematic, cross-sectional illustration of one embodiment of the present invention.

FIG. 3 illustrates an ambient sound source, biological noise source and feedback noise source applied to an implanted microphone.

FIG. 4 illustrates signal injection in an implantable hearing aid for determining transducer feedback.

FIG. 5 is a schematic illustration of an implantable microphone incorporating a motion sensor.

FIG. 6 is a process flow sheet.

FIG. 7 is a plot of the ratios of the magnitudes of output responses of an implanted microphone and motion sensor.

FIG. 8 is a plot of the ratios of the phases of output responses of an implanted microphone and motion sensor.

FIG. 9 is a plot of cancelled and non-cancelled outputs of an implanted microphone.

FIG. 10 is a plot of available gains for cancelled and non-cancelled outputs of an implanted microphone.

FIG. 11 is a schematic illustration of an implantable microphone that incorporates two control loops for controlling undesired signals.

FIG. 12 illustrates use of an adaptive filter algorithm for noise cancellation.

FIG. 13 illustrates another embodiment of adaptive filter for removing noise arising from acceleration.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the present invention. In this regard, the following description of a hearing instrument is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention.

FIG. 1 illustrates one application of the present invention. As illustrated, the application comprises a fully implantable hearing instrument system. As will be appreciated, certain aspects of the present invention may be employed in conjunction with semi-implantable hearing instruments as well as fully implantable hearing instruments, and therefore the illustrated application is for purposes of illustration and not limitation.

In the illustrated system, a biocompatible implant capsule 100 is located subcutaneously on a patient's skull. The implant capsule 100 includes a signal receiver 118 (e.g., comprising a coil element) and a microphone diaphragm 12 that is positioned to receive acoustic signals through overlying tissue. The implant housing 100 may further be utilized to house a number of components of the fully implantable hearing instrument. For instance, the implant capsule 100 may house an energy storage device, a microphone transducer, and a signal processor. Various additional processing logic and/or circuitry components may also be included in the implant capsule 100 as a matter of design choice. Typically, a signal processor within the implant capsule 100 is electrically interconnected via wire 106 to a transducer 108.

The transducer 108 is supportably connected to a positioning system 110, which in turn, is connected to a bone anchor 116 mounted within the patient's mastoid process (e.g., via a hole drilled through the skull). The transducer 108 includes a connection apparatus 112 for connecting the transducer 108 to the ossicles 120 of the patient. In a connected state, the connection apparatus 112 provides a communication path for acoustic stimulation of the ossicles 120, e.g., through transmission of vibrations to the incus 122.

During normal operation, ambient acoustic signals (i.e., ambient sound) impinge on patient tissue and are received transcutaneously at the microphone diaphragm 12. Upon receipt of the transcutaneous signals, a signal processor within the implant capsule 100 processes the signals to provide a processed audio drive signal via wire 106 to the transducer 108. As will be appreciated, the signal processor may utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on patient-specific fitting parameters. The audio drive signal causes the transducer 108 to transmit vibrations at acoustic frequencies to the connection apparatus 112 to effect the desired sound sensation via mechanical stimulation of the incus 122 of the patient.

Upon operation of the transducer 108, vibrations are applied to the incus 122, however, such vibrations are also applied to the bone anchor 116. The vibrations applied to the bone anchor are likewise conveyed to the skull of the patient from where they may be conducted to the implant capsule 100 and/or to tissue overlying the microphone 10.

Accordingly such vibrations may be applied to the microphone diaphragm 12 and thereby included in the output response of the microphone 10. Stated otherwise, mechanical feedback from operation of the transducer 108 may be received by the implanted microphone diaphragm 12 via a feedback loop formed through tissue of the patient. Further, application of vibrations to the incus 122 may also vibrate the eardrum thereby causing sound pressure waves, which may pass through the ear canal where they may be received by the implanted microphone diaphragm 12 as ambient sound. Further, biological sources may also cause vibration (e.g., biological noise) to be conducted to the implanted microphone through the tissue of the patient. Such biological sources may include, without limitation, vibration caused by speaking, chewing, movement of patient tissue over the implant microphone (e.g. caused by the patient turning their head), and the like.

FIG. 2 shows one embodiment of an implantable microphone 10 that utilizes a motion sensor 70 to reduce the effects of noise, including mechanical feedback and biological noise, in an output response of the implantable microphone 10. As shown, the microphone 10 is mounted within an opening of the implant capsule 100. The microphone 10 includes an external diaphragm 12 (e.g., a titanium membrane) and a housing having a surrounding support member 14 and fixedly interconnected support members 15, 16, which combinatively define a chamber 17 behind the diaphragm 12. The microphone 10 may further include a microphone transducer 18 that is supportably interconnected to support member 15 and interfaces with chamber 17, wherein the microphone transducer 18 provides an electrical output responsive to vibrations of the diaphragm 12. The microphone transducer 18 may be defined by any of a wide variety of electroacoustic transducers, including for example, capacitor arrangements (e.g., electret microphones) and electrodynamic arrangements.

One or more processor(s) and/or circuit component(s) 60 and an on-board energy storage device (not shown) may be supportably mounted to a circuit board 64 disposed within implant capsule 100. In the embodiment of FIG. 2, the circuit board is supportably interconnected via support(s) 66 to the implant capsule 100. The processor(s) and/or circuit component(s) 60 may process the output signal of microphone transducer 18 to provide a drive signal to an implanted transducer. The processor(s) and/or circuit component(s) 60 may be electrically interconnected with an implanted, inductive coil assembly (not shown), wherein an external coil assembly (i.e., selectively locatable outside a patient body) may be inductively coupled with the inductive coil assembly to recharge the on-board energy storage device and/or to provide program instructions to the processor(s), etc.

Vibrations transmitted through the skull of the patient cause vibration of the implant capsule 100 and microphone 10 relative to the skin that overlies the microphone diaphragm 12. Movement of the diaphragm 12 relative to the overlying skin may result in the exertion of a force on the diaphragm 12. The exerted force may cause undesired vibration of the diaphragm 12, which may be included in the electrical output of the transducer 18 as received sound. As noted above, two primary sources of skull borne vibration are feedback from the implanted transducer 108 and biological noise. In either case, the vibration from these sources may cause undesired movement of the microphone 10 and/or movement of tissue overlying the diaphragm 12.

To actively address such sources of vibration and the resulting undesired movement between the diaphragm 12 and overlying tissue, the present embodiment includes a motion sensor 70 that provides an output response proportional to the vibrational movement experienced by the implant capsule 100 and, hence, the microphone 10. Generally, the motion sensor 70 may be mounted anywhere within the implant capsule 100 and/or to the microphone 10 that allows the sensor 70 to provide an accurate representation of the vibration received by the implant capsule 100, microphone 10, and/or diaphragm 12. In a further arrangement (not shown), the motion sensor may be a separate