Abstract:
A cochlear implant is disclosed, comprising: a transcutaneous energy transfer circuit for transcutaneously transferring power across a recipient&#39;s skin; and a transcutaneous capacitive data link circuit for transcutaneously transferring data across the recipient&#39;s skin, wherein the transcutaneous energy transfer circuit and the transcutaneous capacitive data link circuit operate independently of each other. The transcutaneous capacitive data link circuit comprises: a first pair of capacitors each having an external electrode configured to be externally positioned on a recipient and an internal electrode configured to be internally positioned in the recipient; a first voltage driver having positive and negative terminals each connected to one of the external electrodes, and configured to generate a first voltage drive signal responsive to a first input control signal; and a first differential amplifier circuit connected to the internal electrodes, configured to generate a first output data signal representative of the first input control signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of International Application No. PCT/AU2005/001658, entitled “Transcutaneous Capacitive Data Link,” filed Oct. 28, 2005, which claims the priority of U.S. Provisional Application No. 60/622,602, entitled “Coupling Out Telemetry Data in a Transcutaneous Transfer System,” filed Oct. 28, 2004, and U.S. Provisional Application No. 60/522,512, entitled “Transcutaneous Capacitive Data Link,” filed Oct. 28, 2004. The entire disclosure and contents of the above applications are hereby incorporated by reference herein. 
     This application is related to U.S. patent application Ser. No. 10/883,809, now U.S. Pat. No. 7,171,273 issued on Jan. 30, 2007, Ser. No. 10/856,823, which is still pending, Ser. No. 10/333,676, now U.S. Pat. No. 7,502,653 issued on Mar. 10, 2009, Ser. No. 10/887,894, now U.S. Pat. No. 7,860,572 issue don Dec. 28, 2010, and Ser. No. 10/887,893, now U.S. Pat. No. 8,223,982 issued on Jun. 17, 2012, and U.S. Pat. Nos. 6,810,283, 6,751,505 and 6,700,982 which are hereby incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to transcutaneous transfer systems and, more particularly, to a transcutaneous capacitive data link. 
     2. Related Art 
     The use of implantable medical devices to provide therapy to individuals for various medical conditions has become more widespread as the advantages and benefits such devices provide become more widely appreciated and accepted throughout the population. In particular, devices such as hearing aids, implantable pacemakers, defibrillators, functional electrical stimulation devices such as cochlear prostheses, organ assist or replacement devices, and other medical devices, have been successful in performing life saving and/or lifestyle enhancement functions for a number of individuals. 
     Medical devices often include one or more sensors, processors, controllers or other functional electrical components that are permanently or temporarily implanted in a patient. Many such implantable devices require power and/or require communications with external systems that are part of or operate in conjunction with the medical device. One common approach to provide for the transcutaneous transfer of power and/or communications with an implantable component is via a transcutaneous transfer system. 
     One type of medical device that may include a transcutaneous transfer system is a Cochlear™ prosthesis (commonly referred to as Cochlear™ prosthetic devices, Cochlear™ implants, Cochlear™ devices, and the like; simply cochlear implant herein.) Cochlear implants provide the benefit of hearing to individuals suffering from severe to profound hearing loss. Hearing loss in such individuals is due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Cochlear implants essentially simulate the cochlear hair cells by directly delivering electrical stimulation to the auditory nerve fibers. This causes the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. 
     Conventional cochlear implants primarily include external components directly or indirectly attached to the body of the patient (sometimes referred to herein as the recipient), and internal components which are implanted in the patient. The external components typically comprise a microphone for detecting sounds, a speech processor that converts the detected sounds into a coded signal, a power source, and an external transmitter antenna coil. The internal components typically comprise an internal receiver antenna coil, a stimulator located within a recess of the temporal bone of the recipient, and an electrode array positioned in the recipient&#39;s cochlear. 
     Collectively, the external transmitter antenna coil and the internal receiver antenna coil form an inductively-coupled transcutaneous transfer system. The external transmitter antenna coil is usually positioned on the side of a recipient&#39;s head directly facing the implanted antenna coil to allow for the coupling of the coils to transfer energy and data between the external and internal antenna coils. Typically, the transfer of energy is controlled to effect the transmission of the coded sound signal and power from the external speech processor to the implanted stimulator unit, and to effect the transmission of telemetry data from the implanted stimulator unit to the external speech processor. 
     SUMMARY 
     According to one aspect of the present invention, a transcutaneous capacitive data link circuit is disclosed, the circuit comprising: a first pair of capacitors each having an external electrode configured to be externally positioned on a recipient and an internal electrode configured to be internally positioned in the recipient; a first voltage driver having positive and negative terminals each connected to one of the external electrodes, and configured to generate a first voltage drive signal responsive to a first input control signal; and a first differential amplifier circuit connected to the internal electrodes, configured to generate a first output data signal representative of the first input control signal. 
     According to another aspect of the present invention, a cochlear implant is disclosed, comprising: a transcutaneous energy transfer circuit for transcutaneously transferring power across a recipient&#39;s skin; and a transcutaneous capacitive data link circuit for transcutaneously transferring data across the recipient&#39;s skin, wherein the transcutaneous energy transfer circuit and the transcutaneous capacitive data link circuit operate independently of each other. 
     According to a further aspect of the present invention, a transcutaneous capacitive data link circuit is disclosed, comprising: a first pair of capacitors each having an external electrode configured to be externally positioned on a recipient and an internal electrode configured to be internally positioned in the recipient; first voltage driver means, having positive and negative terminals each connected to one of the external electrodes, for generating a first voltage drive signal responsive to a first input control signal; and first differential amplifier means connected to the internal electrodes, for generating a first output data signal representative of the first input control signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a perspective view of internal and external components of a cochlear implant system shown in their operational position on a recipient; 
         FIG. 2A  is a perspective view of an external transmitter unit and an internal receiver unit with external and internal electrodes shown juxtaposed to each other, in accordance with one embodiment of the present invention; and 
         FIG. 2B  is a simplified schematic diagram a capacitive data link in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are directed to the transcutaneous transfer of data using a capacitive link thereby providing for the low-power transmission of data across the skin of a patient without a galvanic connection. 
     Embodiments of the present invention are described below in connection with one embodiment of a hearing implant commonly referred to as a cochlear implant. As used herein, the term “cochlear implant” refers to any partially- or completely-implantable device that provides electrical stimulation and/or mechanical stimulation to a patient to improve and/or provide hearing sensations. It should be appreciated, however, that the present invention may be implemented in connection with other types of medical implants as well. 
     Cochlear implants use direct electrical stimulation of auditory nerve cells to bypass absent or defective hair cells that normally transducer acoustic vibrations into neural activity. Such devices generally use multi-contact electrodes inserted into the scala tympani of the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound. Such devices are also used to treat a smaller number of patients with bilateral degeneration of the auditory nerve. For such patients, a cochlear prosthetic device provides stimulation of the cochlear nucleus in the brainstem. 
     Exemplary cochlear implants in which embodiments of the present invention may be implemented include, but are not limited to, those systems described in U.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894 and 6,697,674, which are hereby incorporated by reference herein. A representative example of a cochlear implant is illustrated in  FIG. 1 .  FIG. 1  is a cut-away view of the relevant components of outer ear  101 , middle ear  102  and inner ear  103 , along with a perspective view of the components of a cochlear implant  100 . 
     In a fully functional ear, outer ear  101  comprises an auricle  105  and an ear canal  106 . An acoustic pressure or sound wave  107  is collected by auricle  105  and channeled into and through ear canal  106 . Disposed across the distal end of ear cannel  106  is a tympanic membrane  109  which vibrates in response to acoustic wave  107 . This vibration is coupled to oval window or fenestra ovalis  110  through three bones of middle ear  102 , collectively referred to as the ossicles  111  and comprising the malleus  112 , the incus  113  and the stapes  114 . Bones  112 ,  113  and  114  of middle ear  102  serve to filter and amplify acoustic wave  107 , causing oval window  110  to articulate, or vibrate. Such vibration sets up waves of fluid motion within cochlea  116 . Such fluid motion, in turn, activates tiny hair cells (not shown) that line the inside of cochlea  116 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells (not shown) and auditory nerve  150  to the brain (not shown), where they are perceived as sound. In deaf persons, there is an absence or destruction of the hair cells. Cochlear implant  100  is needed to directly stimulate the ganglion cells to provide a hearing sensation to the recipient. 
       FIG. 1  also shows how a cochlear implant  100  is positioned in relation to outer ear  101 , middle ear  102  and inner ear  103 . Cochlear implant  100  comprises external component assembly  123  which is directly or indirectly attached to the body of the recipient, and an internal component assembly  124  which is temporarily or permanently implanted in the recipient. 
     External component assembly  123  comprises microphone  125  for detecting sound which is outputted to a BTE (Behind-The-Ear) speech processing unit  126  that generates coded signals and are provided to an external transmitter unit  128 , along with power from a power source such as a battery (not shown). External transmitter unit  128  comprises an external coil  130  and, preferably, a magnet (not shown) secured directly or indirectly to the external coil. 
     Internal component assembly  124  comprises an internal receiver unit  132  having an internal coil (not shown) that receives power and coded signals from external assembly  123 . Internal receiver unit  132  transmits the received power and coded signals to a stimulator unit  120  which applies the coded signal to an electrode assembly  144  disposed on the distal end of a carrier member  140 . Electrode carrier member  140  enters cochlea  116  at cochleostomy  122  such that one or more electrodes  142  of electrode assembly  144  are aligned with portions of cochlea  116 . 
     Cochlea  116  is tonotopically mapped with each region of the cochlea being responsive to acoustic and/or stimulus signals in a particular frequency range. To accommodate this property of cochlea  116 , electrodes  142  are each constructed and arranged to deliver appropriate stimulating signals to particular regions of cochlea  116 , each representing a different frequency component of a received audio signal. Signals generated by stimulator unit  120  are applied by the electrodes  142  of electrode array  144  to cochlea  116 , thereby stimulating the auditory nerve  150 . It should be appreciated that although in the embodiment shown in  FIG. 1  electrodes  142  are arranged in array  144 , other arrangements are possible. 
     As noted, cochlear implant  100  comprises an embodiment of a capacitive data link system of the present invention to transmit data between internal components  124  and external components  123 . A simplified schematic diagram of embodiments of such a capacitive data link system is depicted in  FIG. 2A  and  FIG. 2B . As shown in  FIG. 2A , a capacitive data link system  200  comprises external components  202  and internal components  204 . External components  204  are worn by the recipient, for example, integrated into speech processor  126  ( FIG. 1 ), or as a separately-worn unit connected to speech processor  126  by a cable. The operational connection to speech processor  126  is generally represented by line  203 . Internal components  204  are implanted in the recipient at a location in which a capacitive link may be established, as described herein. Internal components  204  are operatively coupled to stimulator unit  120  ( FIG. 1 ). The operational connection to stimulator unit  120  is generally represented by line  201 . 
     In this exemplary embodiment, capacitive data link system  200  comprises two capacitors  206 A and  206 B. Each capacitor  206  comprises two electrodes capacitively coupled across skin  208 . Specifically, external component assembly  202  comprises an external electrode  210 A and  210 B of capacitors  206 A and  206 B, respectively. External component assembly  202  also comprises a voltage driver  212  ( FIG. 2B ) which generates a biphasic voltage signal  214  to differentially drive external electrodes  210  of capacitors  206  as described herein. Voltage driver  212  is responsive to input control signals  230  generated by speech processing unit  126 . 
     Internal component assembly  204  comprises internal electrodes  216 A and  216 B of capacitors  206 A and  206 B, respectively. Each internal electrodes  216 A,  216 B is connected to one input of a differential amplifier  218  ( FIG. 2B ) through a resistive network  220 . Differential amplifier  218  generates an output data signal  222  which is received by stimulator unit  120  ( FIG. 1 ). Because changes in voltage drive signal  214  are reflected in output data signal  222 , speech processing unit  126  may transmit data to stimulator unit  120  by controlling voltage driver  212 . 
     It should be appreciated that the embodiment illustrated in  FIG. 2B  is a simplified schematic. For example, as one of ordinary skill in the art would appreciated, embodiments of internal component assembly  204  would typically include signal conditioning circuitry to convert output data signal  222  generated by differential amplifier  218  to a form suitable for use by stimulator unit  120  or other internal component  124  of system  100 . Such signal conditioning circuitry may include, for example, a comparator, pulse forming circuitry and related circuitry and/or other circuitry to amplify and shape output data signal  222  as required for the particular application. 
     Capacitors  206 A and  206 B each comprise oppositely-spaced electrodes  210 A/ 216 A and  210 B/ 216 B; that is, the opposing electrodes  210 ,  216  of each capacitor  206  are aligned with each other along an axis line substantially orthogonal to planes defined by the electrodes. Such transcutaneous alignment facilitates the capacitive coupling attained by each capacitor  206  during operation of capacitive data link system  200 . In the embodiment shown in  FIG. 2A , such alignment is attained by the use of magnets  228 A and  228 B. 
     External electrodes  210  are adjacent to and preferably not in contact with skin  208  of the recipient. Accordingly, external electrodes  210  may be encased in a housing formed of a suitable dielectric material. Such housing may provide a desired separation between external electrodes  210  and the recipient and, therefore, between external electrodes  210  and internal electrodes  216 . 
     Internal electrodes  216 , on the other hand, are galavanically isolated from the body of the recipient to maintain operational integrity of the device as well as to ensure the device is biocompatible. As such, internal capacitor electrodes  216  may be encapsulated in, for example, a silicon film. 
     External and internal electrodes  210 ,  216  may be formed of any conductive material and may have any dimensions suitable for a particular application. For example, in one embodiment, electrodes  210 ,  216  comprise a conductive material such as copper or platinum metal and are formed as a flexible coil or film. Thus, it should be appreciated that capacitors  206  can be implemented with any conductive material having any dimensions suitable for achieving a capacitive link given the particular patient and where on the patient the capacitor is located. It should also be appreciated that the materials used to form the external electrode of a capacitor  206  need not be the same as the materials used to form the internal electrode of that same capacitor  206 . 
     Preferably, external electrode  210  and internal electrode  216  of each electrode  206  have the substantially the same dimensions and surface area. In addition, in many embodiments, capacitors  206  are as large as possible to facilitate signal coupling, while taking into consideration the limits imposed on capacitor size due to the size of the recipient&#39;s head, the distance between opposing electrodes  210 ,  216  of each capacitor  206 , etc. In one embodiment, electrodes  210 ,  216  are rectangular and have a surface area of approximately 1 cm 3 . It should be appreciated, then, that the surface area and dimensions of electrodes  210 ,  216  may vary depending on the requirements of the particular application. 
     As one of ordinary skill in the art would appreciate, the capacitance of each capacitor  206  is determined by a number of factors such as the dimensions and spacing of its electrodes  210 ,  216 , and the material, here, skin and perhaps hair, between the electrodes of the capacitor. In some embodiments in which capacitors  206  are designed for use in connection with a cochlear implant system such as system  100  introduced above, the capacitance of each capacitor  206  is in the range of approximately 0.1 pf-0.5 pf. In alternative embodiments implemented in connection with the same or different application, the capacitance of each capacitor  206  may be different, and based on a variety of factors including the distance and material between electrodes  210 ,  216 . 
     As noted, external components  202  include a voltage driver  212 . Voltage driver  212  generates differential voltage signal  214  to generate an electric field change on internal electrodes  216  of capacitors  206 . Preferably voltage driver  212  generates a pulse waveform, although any biphasic waveform such as a sinusoidal waveform may be used to differentially drive capacitors  206 . In one embodiment, voltage driver  212  generates a 5 volt signal for the implemented TTL circuitry. It should be appreciated, however, that any suitable voltage signal generated by any voltage source now or later developed can be used in alternative embodiments. For example, in one alternative embodiment, voltage driver  212  generates a 3 volt signal. 
     In one embodiment, capacitive data link system  200  is powered, for example, by a battery. In such embodiments, the amplitude of voltage signal  214  may be limited. In alternative embodiments, a voltage signal  214  with relatively greater amplitude may be provided to support greater signal strength. As one of ordinary skill in the art would appreciate, such a voltage boost will likely consume additional power and, therefore require some trade-offs. 
     As noted, internal electrodes  216  of capacitors  206  are connected to respective inputs of a discrete differential amplifier  218  through a resistive network  220 . Differential amplifier  218  amplifies the difference in electric potential between the two inputs. In this way, common mode variations caused not by external sources are substantially isolated. Preferably, differential amplifier  218  is a transistor differential amplifier implementing JFETs due to its high input resistance and low input capacitance. As one of ordinary skill in the art would appreciate, differential amplifier  218  may be implemented in a variety of ways with a variety of components well known in the art. 
     Resistive network  220  is provided to adjust the input impedance of differential amplifier  218 . In one embodiment, resistors  224 A and  224 B are approximately 1 MOhm. It should be appreciated that the values of resistors  224  may be selected based on conventional design considerations well-known to those of ordinary skill in the art. In the above exemplary embodiment, the resulting differential voltage across the inputs of amplifier  218  is approximately 20 mV. Collectively, differential amplifier  218  and resistive network  220  are referred to herein as differential amplifier circuit  226 . 
     As understood by those of ordinary skill in the art, the current through capacitors  206  is determined by the rise time and the height of voltage signal  214  generated by voltage driver  212 . This also determines the amplitude of output data signal  222 . The current through capacitors  206  is also proportional to the size of electrodes  206 . As such, the voltage provided to the inputs of differential amplifier  218  is approximately proportional to its input impedance and this current. 
     It should also be appreciated that just a few embodiments of the present invention have been described herein. For example, although capacitive data link system  200  is herein described as having components that are internal or external to the patient, it should be understood that in another embodiment of the present invention, the capacitive data link system may be configured to also have components  202  internal to the patient, and having components  204  external to the patient, to permit bi-directional communication. A bi-directional half duplex data link may be achieved, for example, with the addition of a multiplexer and additional driver and receiver components. One advantage of such embodiments is that bi-directional communication of data can be achieved with low power usage. It should be appreciated that such bi-directional communication can be half-duplex or full-duplex. 
     The present invention advantageously allows for the functional separation of data and power transmission, enabling each to be optimally configured without concern for the potential adverse effects on the other type of transmission. In one embodiment of the present invention, the data rate is approximately 1 megabit per second, or 1 megahertz. It should be appreciated, however, that the data rate can be significantly higher or lower should a different data bandwidth be required. 
     One advantage of certain embodiments of the present invention is that high data transmission rates can be achieved with low power usage. In one embodiment for example, the transmission rate is 1 MHz. It should be appreciated, however, that the transmission rate is determined by a number of factors including, but not limited to, the skin and the hair that are located between the external and internal plates of each capacitor  206 . 
     Yet another advantage of certain embodiments of the present invention is that longer data streams can be achieved with low power usage, than is possible where energy and data transfers are transmitted through a combined means. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.