Patent Publication Number: US-11388531-B2

Title: Smoothing power consumption of an active medical device

Description:
The present application is a Continuation application of U.S. patent application Ser. No. 14/886,683, filed Oct. 19, 2015, which is a Continuation application of U.S. patent application Ser. No. 13/301,946, filed Nov. 22, 2011, now U.S. Pat. No. 9,167,361, the entire contents of these applications being incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to power-consuming medical devices, and more particularly, to smoothing power consumption of such devices. 
     Related Art 
     Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Sensorineural hearing loss is due to the absence or destruction of the hair cells in the cochlea which transduce sound signals into nerve impulses. Various hearing prostheses are commercially available to provide individuals suffering from sensorineural hearing loss with the ability to perceive sound. For example, cochlear implants use an electrode array implanted in the cochlea to bypass the mechanisms of the ear. More specifically, an electrical stimulus is delivered to the auditory nerve via the electrode array, thereby causing a hearing percept. 
     Conductive hearing loss occurs when the normal mechanical pathways that provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicular chain or ear canal. Individuals suffering from conductive hearing loss may retain some form of residual hearing because the hair cells in the cochlea may remain undamaged. 
     Individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Hearing aids rely on principles of air conduction to transmit acoustic signals to the cochlea. In particular, a hearing aid typically uses a component positioned in the recipient&#39;s ear canal to amplify sound received by the device. This amplified sound reaches the cochlea causing motion of the perilymph and stimulation of the auditory nerve. 
     In contrast to hearing aids, certain types of hearing prostheses commonly referred to as bone conduction devices, convert a received sound into mechanical vibrations. The vibrations are transferred through the skull to the cochlea causing generation of nerve impulses, which result in the perception of the received sound. Bone conduction devices may be a suitable alternative for individuals who cannot derive sufficient benefit from acoustic hearing aids, cochlear implants, etc. 
     SUMMARY 
     According to one aspect of the present invention, there is an active medical device, comprising: an input receiver configured to receive a frequency-varying input signal; and a functional component that reacts to the input signal and consumes power at a rate dependant on the frequency of the input signal to which the functional component reacts, wherein the device is configured to adjust one or more portions of the input signal where the functional component consumes power at a rate that is greater than that of other portions of the input signal. 
     According to another aspect of the invention, there is an active medical device comprising: a functional component that has a parameter-dependent power consumption profile; and a power-smoothing circuit configured to determine an intensity level of a frequency-varying input signal, and to adjust, based on the intensity level, a parameter referenced by the functional component upon which the parameter-dependent power consumption profile depends so as to selectively reduce power consumption of the functional component, wherein the functional component is operably responsive to the adjusted parameter. 
     According to another aspect of the invention, there is a method of reducing power consumption of an active medical device including a functional component reactive to an input signal, comprising receiving the input signal, filtering the input signal to attenuate frequencies for which the functional component consumes power at a rate that is greater than that of other frequencies, and providing the filtered input signal to the functional component such that the functional component reacts to the input signal. 
     According to another aspect of the invention, there is a method of operating a hearing prosthesis, comprising receiving an acoustic signal having intensity level components, generating a signal, representative of the received acoustic signal, having corresponding intensity level components, evaluating the intensity level components of the input signal, and adjusting an operating parameter of the hearing prosthesis based on the intensity level, and evoking a hearing percept based on the received acoustic signal with the hearing prosthesis at the adjusted operating parameter so as to evoke the hearing percept utilizing a reduced amount of power as compared to evoking a hearing percept based on the received acoustic signal with the hearing prosthesis without adjustment of the operating parameter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments of the present invention are described herein with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a transcutaneous bone conduction device in which embodiments of the present invention may be implemented; 
         FIG. 1A  illustrates an example of an active medical device according to an embodiment of the present invention; 
         FIG. 1B  illustrates another example of an active medical device according to an embodiment of the present invention; 
         FIG. 1C  is a block diagram of a bone conduction device according to an embodiment of the present invention; 
         FIG. 1D  illustrates a power smoothing circuit that includes one or more filters according to an embodiment of the present invention; 
         FIG. 1E  illustrates a power smoothing circuit that includes a level controller according to an exemplary embodiment of the present invention; 
         FIG. 1F  illustrates a power smoothing circuit that includes the one or more filters and the level controller according to an embodiment of the present invention; 
         FIG. 2  is a plot of a frequency response of an exemplary stimulation transducer illustrated in  FIG. 1C ; 
         FIG. 3  is a plot of power consumed by the exemplary stimulation transducer having the frequency response illustrated in  FIG. 2 ; 
         FIG. 4  is a high-level circuit diagram of an embodiment of the transducer driver circuit illustrated in  FIG. 1C ; 
         FIG. 5  is a plot of a loudness:pulse-width (PW) mapping, according to an embodiment of the present invention; 
         FIG. 6  is a plot of a loudness:k G  mapping, according to an embodiment of the present invention; 
         FIG. 7A  illustrates an embodiment of the RF modulator illustrated in  FIG. 1C , for which the adjusted operating parameter is the voltage V kk ; 
         FIG. 7B  illustrates an embodiment of the RF modulator illustrated in  FIG. 1C , for which the adjusted operating parameter is a digital modulation parameter, namely, a pulse-width control signal (PW_CTRL); 
         FIG. 8  is a block diagram of a bone conduction device according to another embodiment of the present invention; 
         FIG. 9A  is a flowchart of an embodiment of a method of smoothing power consumption of an active medical device; 
         FIG. 9B  is a flowchart of an example method of smoothing power consumption of an AMD according to an embodiment of the present invention; and 
         FIG. 10  is a plot of a loudness:voltage V LL  mapping according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present invention are generally directed to reducing a rate of power consumption of a medical device, such as a bone conduction device. In one exemplary embodiment, the device consumes power at a rate that is dependant on the frequency of a frequency-varying input signal to which a functional component of the device reacts. In another exemplary embodiment, the device consumes power at a higher rate than may be necessary to attain sufficient efficacious performance. Exemplary embodiments described herein are presented in connection with a specific type of active medical device, namely a hearing prosthesis that processes received audio signals, and more specifically, a bone conduction device that mechanically stimulates the recipient to cause a hearing percept. Some embodiments of the present invention may be implemented in other hearing prostheses as well as other medical devices that react to or otherwise process frequency-varying input signals, as will now be briefly described. 
     Broadly speaking, active medical devices (AMDs) consume power. Some exemplary embodiments detailed herein are directed to strategies to reduce power consumption of a given AMD by adopting techniques to operate the AMD in a more energy-efficient manner based on specific characteristics of the given AMD. In some exemplary embodiments, certain frequencies within an input signal upon which operation of the AMD is based are identified as contributing more to the AMD&#39;s power consumption than other frequencies. In such embodiments, the input signal is filtered to selectively reduce (including eliminate) at least one of the more power intensive frequency components. In some exemplary embodiments, certain features of the input signal upon which operation of the AMD is based may indicate conditions for which a less than full operational capability can be sufficient in order to obtain sufficiently efficacious performance of the AMD. In such embodiments, there may be selective adjustment of one or more parameters of the AMD to temporarily adopt less than full operational capability, thereby reducing power consumption, while still providing sufficiently effective performance. Hereinafter, this is sometimes referred to as leveling. 
     Additional details of the above embodiments and other embodiments will be described in greater detail below. Prior to this, an exemplary medical device with which embodiments disclosed herein and variations thereof may be utilized will be briefly discussed. 
       FIG. 1  is a perspective view of a transcutaneous bone conduction device  1100  in which embodiments of the present invention may be implemented. As shown, the recipient has an outer ear  1101 , a middle ear  1102  and an inner ear  1103 . Elements of outer ear  1101 , middle ear  1102  and inner ear  1103  are described below, followed by a description of bone conduction device  1100 . 
     In a fully functional human hearing anatomy, outer ear  1101  comprises an auricle  1105  and an ear canal  1106 . A sound wave or acoustic pressure  1107  is collected by auricle  1105  and channeled into and through ear canal  1106 . Disposed across the distal end of ear canal  1106  is a tympanic membrane  1104  which vibrates in response to acoustic wave  1107 . This vibration is coupled to oval window or fenestra ovalis  1110  through three bones of middle ear  1102 , collectively referred to as the ossicles  1111  and comprising the malleus  1112 , the incus  1113  and the stapes  1114 . The ossicles  1111  of middle ear  1102  serve to filter and amplify acoustic wave  1107 , causing oval window  1110  to vibrate. Such vibration sets up waves of fluid motion within cochlea  1139 . Such fluid motion, in turn, activates hair cells (not shown) that line the inside of cochlea  1139 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells and auditory nerve  1116  to the brain (not shown), where they are perceived as sound. 
       FIG. 1  also illustrates the positioning of bone conduction device  1100  relative to outer ear  1101 , middle ear  1102  and inner ear  1103  of a recipient of device  1100 . As shown, bone conduction device  1100  is positioned behind outer ear  1101  of the recipient. It is noted that in other embodiments, the bone conduction device  1100  may be located at other positions on the skull. Bone conduction device  1100  comprises an external component  1140  and implantable component  1150 . External component  1150  is located beneath skin  1132 , and partially or fully below adipose tissue  1128  and/or muscle tissue  1128 . The bone conduction device  1100  includes a sound input element  1126  to receive sound signals. Sound input element  1126  may comprise, for example, a microphone, telecoil, etc. In an exemplary embodiment, sound input element  1126  may be located, for example, on or in bone conduction device  1100 , on a cable or tube extending from bone conduction device  1100 , etc. Alternatively, sound input element  1126  may be subcutaneously implanted in the recipient, or positioned in the recipient&#39;s ear. Sound input element  1126  may also be a component that receives an electronic signal indicative of sound, such as, for example, from an external audio device. For example, sound input element  1126  may receive a sound signal in the form of an electrical signal from an MP3 player electronically connected to sound input element  1126 . 
     Bone conduction device  1100  comprises a sound processor (not shown), an actuator (also not shown) and/or various other operational components. In operation, sound input device  1126  converts received sounds into electrical signals. These electrical signals are utilized by the sound processor to generate control signals that cause the actuator to vibrate. In other words, the actuator converts the electrical signals into mechanical vibrations for delivery to the recipient&#39;s skull. 
     In accordance with embodiments of the present invention, a fixation system  1162  may be used to secure implantable component  1150  to skull  1136 . As described below, fixation system  1162  may include an implant at least partially embedded in the skull  1136 . 
     In one arrangement of  FIG. 1 , bone conduction device  1100  is an active transcutaneous bone conduction device where at least one active component, such as the actuator, is implanted beneath the recipient&#39;s skin  1132  and is thus part of the implantable component  1150 . As described below, in such an arrangement, external component  1140  may comprise a sound processor and transmitter, while implantable component  1150  may comprise a signal receiver and/or various other electronic circuits/devices. 
     In another arrangement of  FIG. 1 , bone conduction device  1100  is a passive transcutaneous bone conduction device. That is, no active components, such as the actuator, are implanted beneath the recipient&#39;s skin  1132 . In such an arrangement, the active actuator is located in external component  1140 , and implantable component  1150  includes a movable component as will be discussed in greater detail below. The movable component of the implantable component  1150  vibrates in response to vibration transmitted through the skin, mechanically and/or via a magnetic field, that are generated by an external magnetic plate. 
     In a variation of the arrangement of  FIG. 1 , bone conduction device  1100  is a percutaneous bone conduction device in that the active component is located in external component  1140 . External component  1140  is connected to the skull via an abutment that penetrates the skin of the recipient and a bone screw (or bone fixture) screwed into the skull  136  such that vibrations generated by the external component  1140  are communicated to the skull  136 . 
       FIG. 1A  illustrates an example of an active medical device (AMD)  100 A, according to an embodiment of the present invention. The AMD  100 A may be a percutaneous bone conduction device in some exemplary embodiments, or a transcutaneous bone conduction device (active or passive) in other embodiments. The AMD  100 A includes a functional component  103 A (e.g., a transducer) and a power-smoothing circuit  110 A. The functional component  103 A has a frequency-dependent power consumption profile. This profile may be known, such as thorough empirical and/or analytical experimentation, for example, during a design stage and/or a manufacturing stage (e.g., as part of a quality-assurance phase thereof). The power-smoothing circuit  110 A receives an input signal having time-varying frequency components (e.g., an audio signal in a context of a hearing prosthesis) and filters the input signal so as to obtain the power consumption reduction. In an exemplary embodiment, the input signal is filtered according to the power consumption profile so as to selectively reduce one or more power intensive (‘power hungry’) frequency components in the input signal. In an exemplary embodiment, the reduced frequency components may be one or more frequency components for which consumption of power by the functional component  103 A has a relatively greater dependence. Reducing the frequency component(s) may have utility in that it may correspondingly reduce an amount of power consumed by the functional component. In an exemplary embodiment, the filtering characteristics of the AMD are identified at the design stage, while in other embodiments the filtering characteristics of the AMD are identified at the fabrication stage or after the fabrication stage. 
     Still with reference to  FIG. 1A , the functional component  103 A is disposed in relation to a recipient  153 A of the AMD  100 A, and provides stimulation to the recipient  153 A as indicated by arrow  151 A. For example, in an exemplary embodiment where the AMD is a hearing prosthesis, (e.g., a hearing prosthesis that directly stimulates cochlea  1139  mechanically), the transducer may be implanted in the recipient. In an embodiment where the AMD is a passive transcutaneous bone conduction device, the transducer may be held against the outer skin of the recipient adjacent an implanted component of the device. 
     An exemplary embodiment of the present invention includes a functional component having a frequency-dependent power consumption profile that includes one or more resonance peaks. In an exemplary embodiment, frequency component reduction is accomplished by filtering. Such filtering may be accomplished via the use of, for example, notch filtering. In an exemplary embodiment utilizing notch filtering, respective notch center frequencies correspond to respective resonance peaks. Still further by example, in some embodiments where the profile might indicate that power consumption increases with frequency, low pass filtering is utilized. 
     Some embodiments may be practiced utilizing filtering that varies based upon, for example, an energy level available from a battery (or other power storage device). (Such embodiments may be practiced in combination with other techniques detailed herein.) In some such exemplary embodiments, as the available energy level from the battery decreases, filtering is performed to a greater degree than at the higher energy level. Such filtering may be accomplished by, for example, utilizing notches that can be progressively deepened as the available energy level decreases. 
     In another exemplary embodiment, the notch filtering can be enhanced relative to a desired frequency band. Some such embodiments rely on the phenomenon that the location of a resonance peak in the frequency spectrum can impact the likelihood (e.g., make it relatively less likely or more likely) that the input signal will contain a significant intensity (e.g., power consuming intensity) at that frequency. By way of illustrative example, a band of frequencies may have significant intensities with regard to human speech. An exemplary embodiment may address this phenomenon by utilizing a notch filter in a manner such that if a resonance peak in the profile overlaps a significant frequency band, the corresponding notch in the filter is made deeper. This may be done because, in some embodiments, some input signals are more likely than not to have a significant intensity at the resonance frequency. 
       FIG. 1B  illustrates another example of an AMD  100 B, according to an embodiment of the present invention, which utilizes leveling to reduce power consumption. AMD  100 B includes a functional component  103 B and a power-smoothing circuit  110 B. Functional component  103 B is disposed relative to a recipient of AMD  100 B, as indicated by arrow  151 B. Functional component  103 B may have a substantially time-invariant parameter and a parameter-dependent power consumption profile. Power-smoothing circuit  110 B is configured to receive an input signal having time-varying frequency components, determine an intensity level of the input signal, and adjust the parameter based upon the intensity level so as to selectively reduce power consumption, as will now be further described. 
     In an exemplary embodiment where the AMD  100 B is a hearing prosthesis (e.g., of a type that has an internal module and an external module that communicate transcutaneously, such as a cochlear implant), the transducer is the functional component and the parameter is a modulation parameter (e.g., a pulse-width control signal “PW_CTRL”), which affects the transcutaneous coupling between the external and internal modules. The intensity of the input signal (in this exemplary embodiment, an audio signal), can be monitored so as to recognize relatively quieter conditions and/or relatively louder conditions and/or recognize a change from one such condition to another such condition. With respect to an embodiment that recognizes quieter conditions, once quieter conditions are so recognized, the value of PW_CTRL may be decreased so as to reduce a duty cycle of the wireless transmission system, and thereby reduce power consumption. 
       FIG. 1C  is a functional diagram of a bone conduction device  100 C having a power-smoothing circuit  100 C corresponding to the power-smoothing circuits of the embodiments of  FIG. 1A or 1B  or a combination thereof, as just detailed. Accordingly, the bone conduction device  100 C is a selective power-consumption-reducing active medical device (again, “AMD”). The AMD  100 C includes an external component in the form of an external module  102  and an implantable component in the form of an implantable module  104 . The implantable module  104  is illustrated as having been implanted within a body of a person suffering from hearing loss, as denoted by a layer of skin  106  separating the implantable module  104  from the external module  102 . Communication between the external module  102  and the implantable module  104  takes place transcutaneously via a radio frequency (RF) link  130  using, by way of example, a 5 MHz carrier frequency. Power and/or control signals can be transferred via the RF link  130  from the external module  102  to the implantable module  104 . 
     The external module  102  of  FIG. 1C  includes, by way of example, an audio transducer  108  (e.g., a microphone), a power-smoothing circuit  110 C that itself may include a digital signal processor (DSP), a power supply  112  (e.g., a battery), a radio frequency modulator  114 , and an external RF tank circuit  116 . The audio transducer  108  is operable to generate an audio signal representing acoustic content of a sound impinging upon the recipient. The external RF tank circuit  116  includes a coil  132  and a capacitor  134 . The RF modulator block  114  is configured to use, for example, digital modulation (e.g., On Off Keying (OOK) modulation) and to generate an RF signal. In  FIG. 1C , the external module  102  is depicted has having one housing (represented by the solid line surrounding the components, but it is noted that the components of the module maybe divided such that respective components are located in two or more housings. 
     As will be discussed in more detail below, the power smoothing circuit  110 C includes one or more filters  166 C, and/or a level controller  168 C. Because of the optional presence/absence of these components, these components are represented in dashed lines. 
     In embodiments having one or more filters  166 C, the filter(s) provide a filtered audio signal(s) to the RF modulator block  114 . If these filters are not present in a given embodiment, the power smoothing circuit  110 C may transfer an unfiltered audio signal(s) to the RF modulator  114 . In embodiments having the level controller  168 C, the level controller  168 C provides an automatic level control (ALC) signal to the RF modulator  114 . 
       FIG. 1D  illustrates a power smoothing circuit  110 D according to an embodiment of the present invention that includes one or more filters  166 C but does not include the level controller  168 C. Circuit  110 D may be used as circuit  110 C in external module  102 . As no level controller is included, the power smoothing circuit  110 B only outputs the filtered audio signal(s) without a control signal. 
       FIG. 1E  illustrates a power smoothing circuit  110 C according to an embodiment of the present invention that includes the level controller  168 C but does not include one or more filters  166 C. Circuit  110 E may be used as circuit  110 C in external module  102 . As no filter is included, the power smoothing circuit is  110 E outputs the ALC signal and the unfiltered audio signal(s). 
       FIG. 1F  illustrates a power smoothing circuit  110 F according to an embodiment of the present invention that includes one or more filters  166 C and the level controller  168 C, and accordingly outputs the filtered audio signal(s) and the ALC signal. Circuit  110 F may be used as circuit  110 C in external module  102 . 
     Referring back to  FIG. 1C , the implantable module  104  of  FIG. 1C  includes an internal RF tank circuit  118 , a power rectification circuit  120  that includes a rectifier  140 , an RF decoder and pulse generator  122 , a transducer driver circuit  126  (e.g., implemented via an application-specific integrated circuit (ASIC)), and an electromechanical stimulation transducer  128  that includes a piezoelectric actuator  142 . The rectification circuit  140  extracts power from the RF link  130 , and supplies the extracted power as a voltage V LL  to the RF decoder and pulse generator  122  and the transducer driver circuit  126 . The internal RF tank circuit  118  includes a coil  136  and a capacitor  138  connected in parallel. The transducer driver circuit  126  is, for example, a Class-D amplifier. The piezoelectric device actuator  142  is illustrated as including an anchor  144  or other fixation device, thereby permitting the piezoelectric device actuator  142  to be placed into vibrational communication with bone of the recipient (e.g., the skull). The stimulation transducer can be regarded as a capacitive load to the driver  126 . 
     The RF decoder and pulse generator  122  of  FIG. 1C  is configured to use a demodulation scheme that corresponds to the modulation scheme of the RF modulator block  114 . Accordingly, the RF decoder and pulse generator  122  is configured to use, for example, digital demodulation (e.g., OOK demodulation). In the exemplary embodiment of  FIG. 1C , the RF decoder and pulse generator  122  has been illustrated as including two functional blocks, namely an RF decoder  146  (e.g., an OOK decoder) and a pulse generator  148 . A simple OOK decoder includes, for example, a diode loaded to an RC parallel circuit. 
     The pulse generator  148  can be, for example, a pulse width modulator, pulse density modulator or a sigma-delta modulator. The pulse generator  148  produces two bit streams, P 1  and P 2 , with each bit stream being 1-bit wide. In an exemplary embodiment, the bit streams P 1  and P 2  are non-overlapping. The transducer driver circuit  126 , for example, can be driven directly with the two bit streams, P 1  and P 2 . 
       FIG. 2  depicts a graph including an exemplary plot  262  of the magnitude of a frequency response of the exemplary implantable module  104  of the embodiment of  FIG. 1C  described above. The plot  262  reflects use of an exemplary stimulation transducer  128  corresponding to, by way of example, a 2.2 uF twin mass piezoelectric actuator that has been connected to and hence driven by transducer driver circuit  126 . The plot  262  results from the transducer driver circuit  126  being provided with a voltage V LL  of 3 volts. The x-axis of the graph of  FIG. 3  represents frequency in units of Hertz (Hz) of the signal. The y-axis of the graph of  FIG. 3  represents an output force level (OFL) generated by the stimulation transducer  128 , and is denominated in units of dBμN, where dBμN=20*log (x/1 μN), and N is a Newton. In other words, a value of OFL for the stimulation transducer  128  at a given frequency describes a force that the stimulation transducer  128  will exert upon the bone into which it is implanted. In the plot  262 , resonance peaks can be observed at about 700 Hz and about 1750 Hz. 
       FIG. 3  depicts a graph including an exemplary plot  364  of power consumed by the exemplary stimulation transducer  128  of the implantable module to which the frequency response plotted in  FIG. 3  corresponds. In the plot  364 , the x-axis represents signal frequency in units of Hertz (Hz), and the y-axis represents power consumed by the stimulation transducer  128  in units of milliwatts (mW). In correspondence to resonance peaks exhibited by the plot  262 , power consumption peaks can be observed in the plot  364  at about 700 Hz and about 1750 Hz. It is these power consumption peaks that are smoothed by the power-smoothing circuits utilizing filtering detailed herein in order to reduce the maximum instantaneous power consumption of the stimulation transducer  128 . Specifically, some embodiments include techniques usable with such embodiments that result in smoothing the power consumption of the stimulation transducer  128  (and thereby that of the implantable module  104 ). Such techniques may be considered as corresponding to techniques for reducing the maximum instantaneous power consumed by the stimulation transducer  128 . As will be understood from the embodiments of  FIGS. 1A, 1D and 1F , some such exemplary technique may be used in bone conduction device  100 C. Specifically, in embodiments of the bone conduction device  100 C that utilize the power-smoothing circuit  110 D of  FIG. 1D and 110F  of  FIG. 1F , such embodiments selectively filter the audio signal outputted from the audio transducer  108  so as to reduce the content of the signal at or about the frequencies corresponding to the resonance frequencies of the implantable module  104 . 
     With respect to bone conduction device  110 C, rather than provide a notch in the notch filter corresponding to the resonance peak observed at about 1750 Hz, a low pass filter (LPF) instead can be provided that is configured with a pass band below the approximately 1750 Hz resonance peak. Accordingly, another of the one or more active filters  166  of the DSP (again, an example implementation of the power smoothing circuit  110 A) is a low pass filter tuned to have a pass band below the approximately 1750 Hz resonance peak. 
     As noted above, the power smoothing circuit  110 C of bone conduction device  100 C can be implemented as a DSP such that the one or more filters  166  can be active filters. One of the active filters  166  can be configured as a notch filter with at least one notch corresponding to at least one of the one or more peaks in the frequency response (e.g., the peaks in plot  262 ), of the stimulation transducer  128  and/or implantable module  104 . More particularly, the magnitude of a given notch in the notch filter, in some embodiments, is inversely proportional to the magnitude of a corresponding resonance peaks in the frequency response (e.g., the plot  262 ). For example, a notch filter tuned to compensate for the peaks of the plot  262  of the frequency response would have at least a first notch centered at about 700 Hz and corresponding in magnitude inversely proportionally thereto, and/or may also have a second notch centered at about 1750 Hz. 
     Some embodiments utilizing leveling, that is, the selective adjustment of one or more parameters of the bone conduction device  100 C to temporarily adopt less than full operational capability, thereby reducing power consumption, while still providing effective performance, will now be described. As will be understood from the embodiments of  FIGS. 1B, 1C, 1E and 1F , some variations of bone conduction device  100 C utilize a power leveling controller. Specifically, in embodiments of the bone conduction device  100 C that utilize the power-smoothing circuit  110 E of  FIG. 1E and 110F  of  FIG. 1F , such embodiments automatically provide level control. Specifically, the level controller  168  of the power-smoothing circuits  110 E and  110 F recognizes a loudness level corresponding to relatively quiet acoustical conditions of the recipient&#39;s environment (as extrapolated from the output of transducer  108 ) and correspondingly adjusts one or more operating parameters of the bone conduction device  100 C based upon the loudness level so as to selectively reduce a level of power consumption by the transducer  128  of the implantable module  104 . Here, the one or more operating parameters of the bone conduction device  110 C are substantially time invariant and so do not directly represent or are otherwise directly correlated to acoustic content of sound impinging upon the recipient. Such operating parameters include, for example, a voltage V kk  used internally by the RF modulator  114 , a digital modulation parameter in the circumstance that the RF modulator  114  uses digital modulation, etc. 
     More specifically, some exemplary embodiments of the level controller  168  are configured to recognize relatively quiet acoustical conditions and then adjust (by selectively reducing) a pulse width of the OOK scheme used by the RF modulator  114 . This results in the level of the voltage V LL  provided to the transducer driver circuit  126  by the rectification circuit  120  being selectively reduced, resulting in power smoothing. 
     More particularly, the level controller  168  is configured to determine a loudness level based upon the audio signal from the audio transducer  108 . The level controller  168  can be configured with a first mapping, namely a loudness:pulse width PW mapping (e.g., in the form of a look-up table (LUT), an executable block of instructions, etc.) between loudness levels and values for the pulse width PW. The level controller  168  is further operable to index the loudness level into the first mapping and retrieve therefrom a corresponding value of the pulse width PW, and supply the same to the RF modulator  114 . 
     Before discussing further specific features of the exemplary leveling embodiments, details pertaining to the underlying features of the bone conduction device  110 C useful in conveying understanding of these specific features will now be discussed. Specifically, an exemplary circuit schematic of a transducer drive circuit will be described, followed by a discussion on conceptual principles underlying the use of leveling to smooth power consumption. 
       FIG. 4  illustrates an exemplary transducer driver circuit  126  of implantable module  104  of  FIG. 1C . 
     In  FIG. 4 , the transducer driver circuit  126  is a Class-D circuit that includes series connected first and second switches SW 1  and SW 2  arranged, for example, in a half H-bridge configuration. For example, the switch SW 1  can be a P-MOSFET  450  and the switch SW 2  can be an N-MOSFET  452 . A source of the P-MOSFET  450  is connected to the voltage V LL . A power storage device  458 , e.g., a capacitor, is connected between the voltage V LL  and ground. A drain of the P-MOSFET  450  is connected to a drain of the N-MOSFET  452  at a node  454 , and a source of the N-MOSFET  452  is connected to ground. The bit streams, P 1  and P 2 , from the pulse generator  148  are provided to the gates of the P-MOSFET  450  and the N-MOSFET  452 , respectively. Again, the bit streams, P 1  and P 2 , are non-overlapping, which is beneficial, e.g., in that they control the P-MOSFET  450  and the N-MOSFET  452  so as to avoid cross-conduction. 
     The node  454  in  FIG. 4  also is connected to a first end of a ‘high-Q’ inductor  456 . In  FIG. 2 , the stimulation transducer  128  is modeled as a series connection of a resistor  459 , R Pz , and a capacitor  460 , C Pz . A second end of the inductor  456  is connected to a first end of a resistor  459 . A second end of the resistor  459  is connected to the capacitor  460 , and a second end of the capacitor  460  is connected to ground. The inductor  456  is provided to facilitate ‘energy recovery’ of energy that otherwise would be lost during the process of energizing the stimulation transducer  128 . Again, the stimulation transducer  128  is capacitive (as illustrated by the capacitor  460 ), thereby making the energizing process behave similarly to that of charging the capacitor  460 . 
     If the stimulation transducer  128  is modeled to include capacitor  460 , the rate at which the transducer driver circuit  126  can charge the capacitor  460  is dq(t)=i(t)dt. At higher frequencies of the audio signal (again, provided by the audio transducer  108 , and upon which the control signals fed to the transducer driver circuit  126  are based), the rate of charging the capacitor  460  correspondingly increases, which may result in commensurately higher peak currents to remove or add charge more quickly from or to the plates of the capacitor  460 . Consequently, greater amounts of power are consumed in relation to higher audio frequencies. 
     Operational characteristics of the transducer driver circuit  126  also present opportunities to selectively smooth its power consumption, and thereby that of the implantable module  104 . The P-MOSFET  450  and the N-MOSFET  452  exhibit parasitic capacitances (e.g., gate capacitances). Also, conductive paths in the ASIC exhibit parasitic capacitances. Each such capacitance is regarded as a type of power consumption generally referred to as a switching loss, P SW-loss . Switching losses can be characterized as follows.
 
 P   SW-loss =( C   PD   +C   Layout )· V   LL   2   ·f   SW  [Watts]  Equation 1
 
     In Equation 1, C PD  represents a power dissipation capacitance and is a virtual capacitance value given by the manufacturer of an ASIC. More particularly, C PD  is a capacitance that consolidates most if not all parasitic capacitances of the switches SW 1  and SW 2 . Also, C Layout  represents an aggregate layout capacitance (including the capacitances of IC paths, PCB tracks, etc.). Note that C Layout  excludes the capacitance of the stimulation transducer, C Pz . For a Class-D amplifier, V LL  is a supply voltage. Lastly, f SW  represents the switching frequency. 
     In view of Equation 1, it can be seen that there is dependence of the switching losses upon the magnitude of the voltage V LL , namely P SW-loss =f(V LL   2 ) in some embodiments of the present invention. If the voltage V LL  can be selectively decreased, then significant reductions in the switching losses can be achieved for such embodiments because the switching losses are proportional to the square of the voltage V LL , namely P SW-loss =f(V LL   2 ). 
     As noted above, in some exemplary embodiments, the level controller  168  is configured to recognize relatively quiet acoustical conditions of the recipient&#39;s environment and correspondingly adjust one or more operating parameters of the AMD  100  (e.g., bone conduction device  100 C). The operating parameters that are adjusted are substantially time invariant parameters that are not used by the AMD to directly represent acoustic content of sound impinging upon the recipient. Such parameters include, for example, a voltage V kk  used internally by the RF modulator  114 , a digital modulation parameter in the circumstance that the RF modulator  114  uses digital modulation, etc. Such adjustment results in power smoothing, as will be described below. 
     As noted above, the RF modulator block  114  can be configured to use the OOK (On-Off Keying) type of digital modulation. A more particular example of such operating parameters is the pulse width used by the OOK modulation scheme. In an exemplary OOK modulation scheme, a binary value of one is represented by the presence of a carrier wave, i.e., the presence of pulses, during an interval representing a value of a bit (hereinafter, “bit interval”). By contrast, a binary value of zero is represented by the absence of the carrier wave, i.e., the absence of pulses, during the bit time interval. So long as the width of the pulses is sufficient to permit their recognition as pulses, the value for the width of the pulses can be varied. 
     Another way of viewing the width of the pulses in the OOK carrier is as a duty cycle. For a given number of pulses, greater values for the width of the pulses achieve greater duty cycles. In contrast, smaller values for the width of the pulses achieve smaller duty cycles. It is to be recalled that the rectification circuit  140  extracts power from the RF link  130 , and supplies the extracted power to the RF decoder and pulse generator  122  and the transducer driver circuit  126 . By selectively reducing the pulse width of the OOK carrier, the amount of power extracted by the rectification circuit  140 , and therefore the value of the resultant voltage V LL , can be selectively reduced, and so the power consumed by the transducer driver circuit  126  can be selectively reduced. 
     An example of a loudness:PW-mapping, according to an embodiment of the present invention, is illustrated in  FIG. 5  as a plot  570  of loudness (x-axis) versus pulse width PW (y-axis). The plot  570  has a piecewise discontinuous staircase shape. Other configurations of the first mapping are contemplated. For relatively quieter conditions, the first mapping might yield the lower or middle value depicted in  FIG. 5  for the pulse width PW. In contrast to the relatively quiet acoustical conditions, there will be relatively noisy conditions in which the level controller  168  either does not selectively reduce a value of the voltage V LL  supplied to the transducer driver circuit  126 , or reduces the voltage V LL  only slightly. 
     Under relatively noisy conditions, the level controller  168  also may apply a default value of a gain k G  that is applied to the audio signal from the audio transducer, where the default value k DEF  is, e.g., zero gain or relatively little gain. Under the quiet conditions for which the level controller  168  selectively reduces the voltage V LL , it may be desirable also to correspondingly increase the gain k G  applied to the audio signal from the audio transducer  108 . 
     Accordingly, the level controller  168  can be configured with a second mapping, namely a loudness:k G  mapping (e.g., in the form of another look-up table (LUT), another executable block of instructions, etc.) between loudness levels and values of the gain k G . 
     An example of a loudness:k G  mapping, according to an embodiment of the present invention, is illustrated in  FIG. 6  as a plot  674  of loudness (x-axis) versus gain k G  (y-axis). The plot  674  has a horizontal-S shape, and includes an inflection point  676 . The value of the inflection point  676  can be set such that loudness values below the inflection point are mapped to a greater degree to increased values of the gain k G , and loudness values above the inflection point are mapped to a lesser degree to increased values of the gain k G  up to a loudness value at which the value of the gain k G  is not further increased. The inflection point  676  can be set, for example, to coincide with an inflection point, if present, of plot  570 . 
       FIGS. 7A and 7B  illustrate exemplary embodiments of modulators  114  which react to the ALC signal output from the power-smoothing circuit  110 C to adjust non-acoustic content representational operating parameters to smooth power. Specifically,  FIG. 714A  depicts an exemplary RF modulator usable as modulator  114  in the embodiment of  FIG. 1C  for which the adjusted operating parameter is the voltage V kk . The RF modulator  714 A includes an RF modulator block  751 A that is either analog (e.g., amplitude modulation (AM), frequency modulation (FM), etc.) or digital (e.g., On-Off Keying (OOK) modulation, Amplitude Shift Keying (ASK) modulation, Frequency Shift Keying (FSK) modulation, Binary Phase Shift Keying (BPSK) modulation, Quadrature Phase Shift Keying (QPSK) modulation, etc.) and receives the audio signal (which can be either filtered or unfiltered). RF modulator  714 A further includes an RF driver voltage conditioner  755 A that provides a voltage V kk  and an RF driver circuit  753 A that is controlled by the voltage V kk  and operates upon a modulated output from the RF modulator  751 A to generate the RF signal. The ALC signal is provided as a control signal to the RF driver voltage conditioner  755 A, which then adjusts the voltage V kk  according to the ALC signal. The RF driver circuit  753 A adjusts the magnitude of the RF signal according to the voltage V kk . 
       FIG. 7B  illustrates another example of an RF modulator  714 B usable as modulator  114  in the embodiment of  FIG. 1C  for which the adjusted operating parameter is a digital modulation parameter (e.g., a pulse-width control signal PW_CTRL). 
     The RF modulator block  714 B includes a digital RF modulator  751 B that receives the audio signal (which can be either filtered or unfiltered), an RF driver voltage conditioner  755 B that provides the pulse-width control signal PW_CTRL to the digital RF modulator  751 B and an RF driver circuit  753 B that operates upon a modulated output from the RF modulator  751 B to generate the RF signal. The ALC signal is provided as a control signal to the RF driver voltage conditioner  755 B, which then adjusts the pulse-width control signal PW_CTRL according to the ALC signal. The digital RF modulator  751 B adjusts the width of the modulation pulses according to the pulse-width control signal PW_CTRL. 
     As noted above, the power-smoothing features detailed herein are usable in a variety of medical devices. In this regard, embodiments have been described in terms of an active transcutaneous bone conduction device  100 C with reference to  FIG. 1C . In an alternate embodiment, power smoothing may be implemented in a percutaneous bone conduction device. Specifically,  FIG. 8  illustrates an example of such a bone conduction device  800  having selective power-consumption-reduction. In  FIG. 8 , the percutaneous bone conduction device  800  includes a removable component  802  and a bone conduction implant  881  (which may comprise an abutment removably attached to a bone screw) fixed to an recipient&#39;s skull  882 . The abutment extends through the skin  106  and into the skull so that a the removable component  802  can be removably coupled to implant  881  via coupling  884 . 
     The removable component  802  of  FIG. 8  includes the audio transducer  108 , a power-smoothing circuit  810  that includes, for example, a digital signal processor (DSP), a power supply  812  (e.g., a battery); a driver voltage conditioner  886 , a pulse generator  848 , and a transducer driver circuit  826 . The implantable component further includes an electromechanical stimulation transducer  828  that includes a piezoelectric actuator  842 . Similar to the power smoothing circuit  110 F of  FIG. 1F , the power smoothing circuit  810  includes one or more filters  166 , and/or a level controller  868  (which is similar to the level controller  168 ). If present, the one or more filters  166  provide a filtered audio signal(s) to the pulse generator  848 , else the power smoothing circuit  810  simply transfers an unfiltered audio signal(s) to the pulse generator  848 . If present, the level controller  168  provides an automatic level control (ALC) signal to the driver voltage conditioner  886 . As there are several possible combinations, the one or more filters  166 , the level controller  868  and the ALC signal are illustrated using phantom lines. 
     In operation, the voltage conditioner  886  generates a voltage V LL  that is provided to the pulse generator  848  and the transducer driver circuit  826 . Similarly, the stimulation transducer  828  can be regarded as a capacitive load to the transducer driver circuit  826 . 
     As with pulse generator  148 , the pulse generator  848  can be a pulse width modulator, pulse density modulator or a sigma-delta modulator. The pulse generator  848  produces two bit streams, P 1  and P 2 , with each bit stream being 1-bit wide. It is to be observed that the bit streams P 1  and P 2  are non-overlapping. The transducer driver circuit  826 , for example, can be driven directly with the two bit streams, P 1  and P 2 . A simple OOK envelope detector can be made, e.g., using a diode loaded to an RC parallel circuit. 
     Similarly to the one or more operating parameters discussed above, operating parameters of the bone conduction device  800  include, for example, a level of the voltage V LL  provided to the transducer driver circuit  826 . Again, such parameters are parameters are substantially time invariant and not used by the AMD to directly represent acoustic content of sound impinging upon the recipient. Accordingly, like the level controller  168 , not only is the level controller  868  operable to recognize relatively quiet acoustical conditions, but it is further operable to then adjust (by selectively reducing) a level of the voltage V LL  provided to the transducer driver circuit  826 . 
     More particularly, the level controller  868  is operable to determine a loudness value based upon the audio signal from the audio transducer  108 . The level controller  868  is configured with a third mapping, namely a loudness:V LL  mapping (e.g., in the form of a look-up table, an executable block of instructions, etc.) between loudness levels and levels of the voltage V LL . The level controller  868  is further operable to index the loudness level into the third mapping and retrieve therefrom a corresponding value of the voltage V LL . 
     An example of a loudness:V LL -mapping, according to an embodiment of the present invention, is illustrated in  FIG. 10  as a plot  1078  of loudness (x-axis) versus voltage V LL  (y-axis). The plot  1078  has a horizontal-S shape, and includes an inflection point  1080 . The value of the inflection point  1080  may be set such that loudness values below the inflection point are mapped to a greater degree to reduced values of the voltage V LL , and loudness values above the inflection point are mapped to a lesser degree to reduced values of the voltage V LL , up to a loudness value at which the value of the voltage V LL  is not further reduced. Some typical loudness values (in dB SPL) are: 20 dB for background noise in a television studio; 30 dB for a quiet bedroom at night; and 40 dB for a quiet library. The inflection point  1078  of the loudness:V LL  plot could be set, e.g., in the range of about 20 dB to about 40 dB. Other configurations of the third mapping are contemplated. 
     As with level controller  168 , the level controller  868  is similarly operable, under the quiet conditions for which the level controller  868  selectively reduces the voltage V LL , also to optionally and correspondingly increase the gain k G  applied to the audio signal from the audio transducer  108 . 
     Accordingly, the level controller  868  can be configured with the second mapping, similarly to the level controller  168 . 
     Various aspects of the present invention provide advantages over the Background Art. For example, the arrangement shown allows much of the circuit complexity to remain in the external module  102  with a simplified arrangement of the implantable module  104 . 
     The arrangements described herein may be used in a uni-directional system (i.e. power and data flow from the external module to the implantable module), thus allowing for further simplification of the implantable module. The various aspects of the present invention have been described with reference to specific embodiments. It will be appreciated however, that various variations and modifications may be made within the broadest scope of the principles described herein. 
     Some embodiments include methods of manufacturing and/or calibrating the AMD of  FIG. 1A . In this regard,  FIG. 9A  is a flowchart, according to an embodiment of the present invention, of an exemplary method  900  entailing smoothing power consumption of an AMD, e.g.,  100 A. In this embodiment, the AMD includes a functional component that has a frequency-dependent power consumption profile. Specifically, in  FIG. 9A , the method starts at block  902  and proceeds to block  903 , where the frequency-dependent power consumption profile for the functional component is determined. It is noted that profile determination can take place before (as mentioned above), during or after implantation. An exemplary embodiment includes methods by which profiles (e.g., frequency-dependent power consumption (FDPC) profiles) may be determined during or after implementation. For example, in an embodiment where the AMD is a hearing prosthesis (e.g., a middle-ear implant), the frequency-dependent power consumption profile can be determined during implantation, during the post-implantation fitting process, or thereafter. An exemplary embodiment utilizes the post-implantation determination of an FDPC described in U.S. patent application Ser. No. 13/106,335, filed May 12, 2011. As such, a delay between block  903  and a subsequent block  904  is variable depending upon the particular manner by which block  903  is implemented. From block  903 , flow proceeds to block  904 . 
     At block  904 , an input signal having time-varying frequency components (e.g., an audio signal) is received. From block  904 , the method proceeds to block  906 , which entails the step of filtering the input signal. 
     More particularly, at block  906 , the input signal is filtered according to the power consumption profile so as to selectively reduce one or more frequency components for which consumption of power by the functional component is relatively more dependent (i.e., one or more of the relatively more power intensive frequency components in the input signal). From block  906 , the method proceeds to block  908 , which entails the step of driving the functional component according to the filtered signal. From block  908 , the method proceeds to block  910 , which entails determining whether exit conditions have been satisfied (e.g., whether sufficient frequency component reduction has occurred to obtain desired power consumption reduction). If not, the method proceeds from block  910  back to block  906 . If exit conditions have been satisfied, the method proceeds from block  910  to block  912 , where the method ends. 
     It is further noted that this method may be practiced during normal use of the AMD. For example, the magnitude of the frequency reduction may be varied during normal use to further reduce power consumption. Such may be the case in the event of a batter with a very low charge, thus prolonging operation of the AMD for an additional period of time, however brief. 
     An exemplary embodiment includes a method executed by the AMD  100 B of  FIG. 1B . Specifically,  FIG. 9B  presents a flowchart according to an embodiment of the present invention representing an exemplary method  920  of smoothing power consumption of AMD  100 B. 
     In  FIG. 9B , the method starts at block  922  and proceeds to block  924 , where an input signal having time-varying frequency components (e.g., an audio signal), is received. From block  924 , the method proceeds to block  926 , where an intensity level (e.g., a loudness level), of the input signal is determined. The method then proceeds from block  926  to block  928 , where a parameter (e.g., pulse-width control signal, PW_CTRL as mentioned above) of the AMD, is adjusted based upon the loudness level of the input signal. The method then proceeds from block  928  to block  930 , where the functional component is driven according to the adjusted parameter. From block  930 , the method proceeds to block  932 , where a determination is made whether exit conditions have been satisfied (e.g., whether the parameter has been sufficiently adjusted to obtain sufficient/desired power consumption reduction). If exit conditions have not been satisfied, the method proceeds from block  932  and loops back up to block  926 . If exit conditions have been satisfied, the method proceeds from block  932  to block  934 , where the method ends. 
     It is noted that the just-described method may be practiced before or after implantation of the AMD. Its further noted that implantation includes attachment of an external component to the recipient that does not penetrate the skin. 
     Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include” and variations such as “comprising” and “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, operation, or other characteristic described in connection with the embodiment may be included in at least one implementation of the present invention. However, the appearance of the phrase “in one embodiment” or “in an embodiment” in various places in the specification does not necessarily refer to the same embodiment. It is further envisioned that a skilled person could use any or all of the above embodiments in any compatible combination or permutation. 
     It is to be understood that the detailed description and specific examples, while indicating embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the present invention includes all such modifications.