Patent Description:
Medical devices having one or more implantable components, generally referred to herein as implantable medical devices, have provided a wide range of therapeutic benefits to recipients over recent decades. In particular, partially or fully-implantable medical devices such as hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc), implantable pacemakers, defibrillators, functional electrical stimulation devices, and other implantable medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions for a number of years.

The types of implantable medical devices and the ranges of functions performed thereby have increased over the years. For example, many implantable medical devices now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease/injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and/or data received from external devices that are part of, or operate in conjunction with, the implantable medical device. <CIT> relates to active implantable medical devices comprising an antenna and a band diplexer connected to said antenna. <CIT> is generally related to far field radiative powering of implantable medical devices. Both documents disclose the features in the preamble of claim <NUM>.

In one aspect an implantable medical device is provided. The implantable medical device comprises: a multi-band loop antenna; implant electronics; a near-field receiver circuit coupled to the loop antenna and the implant electronics and configured to receive, via the loop antenna, near-field signals from one or more devices positioned external to a body of a recipient and to provide the near-field signals to the implant electronics; and a far-field receiver circuit coupled to the loop antenna and the implant electronics and configured to receive, via the loop antenna, far-field signals from at least one device positioned external to the body of the recipient and to provide the far-field signals to the implant electronics.

In another aspect an implantable medical device is provided. The implantable medical device comprises: implant electronics; an implantable loop antenna; a transformer having a primary side connected to the loop antenna and a secondary side connected to the implant electronics, wherein the transformer is configured to receive, via the loop antenna, radio-frequency (RF) signals in the near-field; and an isolation coupler having a primary side connected to the implantable loop antenna and a second side connected to the implant electronics, wherein the isolation coupler is configured to receive, via the loop antenna, RF signals in the far-field, wherein the transformer and the isolation coupler are connected in parallel with one another.

In another aspect an implantable medical device is provided. The implantable medical device comprises: implant electronics; an implantable loop antenna configured to receive both near-field radio-frequency (RF) signals and far-field RF signals from one or more devices positioned external to a body of a recipient; a transformer disposed between the implant electronics and the loop antenna and configured to provide the near-field RF signals to the implant electronics; an isolation coupler disposed between the implant electronics and the loop antenna and configured to provide the far-field RF signals to the implant electronics; and first and second capacitors connected in series with a primary side of the isolation coupler, and wherein the first and second capacitors are disposed on opposing sides of the primary side of the isolation coupler.

In another aspect an implantable medical device is provided. The implantable medical device comprises: a loop antenna; a near-field receiver circuit coupled to the loop antenna and configured to receive, via the loop antenna, near-field signals from one or more devices positioned external to a body of a recipient; and a far-field receiver circuit coupled to the loop antenna and configured to receive, via the loop antenna, far-field signals from at least one device positioned external to the body of the recipient, wherein the near-field receiver circuit and the far-field receiver circuit are configured to operate in differential mode directly from the loop antenna to receive both the near-field signals and the far-field signals, respectively.

Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:.

Embodiments presented herein are generally directed to implantable medical devices that are configured for both near-field communication and far-field communication via the same implantable loop antenna. More specifically, the implantable medical devices include implant electronics that are independently coupled to the loop antenna via a transformer and an isolation coupler. The transformer is configured to provide near-field data and/or power signals (generally and collectively referred to herein as "near-field signals") received at the loop antenna to the implant electronics, while the isolation coupler is configured to provide far-field data signals ("far-field signals") received at the loop antenna to the implant electronics.

There are a number of different types of implantable medical devices in which embodiments presented herein may be implemented. However, merely for ease of illustration, the techniques presented herein are primarily described with reference to one type of implantable medical device, namely a cochlear implant. It is to be appreciated that the techniques presented herein may be used in any other partially or fully implantable medical device now known or later developed, including other auditory prostheses, such as auditory brainstem stimulators, electro-acoustic hearing prostheses, middle ear prostheses, direct cochlear stimulators, bimodal hearing prostheses, etc. and/or other types of medical devices, such as pain relief implants, pacemakers, etc..

<FIG> is block diagram of an exemplary cochlear implant system <NUM> in which embodiments presented herein are implemented. The cochlear implant system <NUM> comprises a cochlear implant <NUM>, an external charging device (external charger) <NUM>, a first external device <NUM>, and a second external device <NUM>. As described further below, the external charger <NUM> and the first external device <NUM> are devices configured for near-field communication, while the second external device <NUM> is a device configured for far-field communication.

In general, the electromagnetic field surrounding a transmitting antenna can be broken into a near-field region/portion (the near-field) and a far-field region (the far-field). The boundary between the two regions is only generally defined and it depends on the dominant wavelength (λ) emitted by the antenna. The near-field and the far-field have different energies. The near-field is primarily magnetic in nature, while the far-field has both electric and magnetic components. Therefore, as used herein, near-field communication refers to short-range wireless connectivity that uses magnetic field induction to enable power and/or data communication between devices that are in close proximity to one another. In contrast, far-field communication refers to long-range wireless connectivity in the electromagnetic field region dominated by electric or magnetic fields with electric dipole characteristics.

In the example arrangement of <FIG>, cochlear implant <NUM> is a totally implantable cochlear implant where all components of the cochlear implant are configured to be implanted under the skin/tissue <NUM> of a recipient. Because all components are implantable, cochlear implant <NUM> operates, for at least a finite period of time, without the presence of any external devices/components, such as external charger <NUM>, external device <NUM>, and/or external device <NUM>.

Cochlear implant <NUM> includes an implant body (main module) <NUM>, a lead region <NUM>, and an elongate intra-cochlear stimulating assembly <NUM>. The implant body <NUM> generally comprises a hermetically-sealed housing <NUM> in which one or more implantable sound inputs <NUM>, multi-band radio frequency (RF) interface circuitry <NUM> and implant electronics <NUM> are located. The implant electronics <NUM> include, among other elements, a stimulator unit (stimulation electronics) <NUM>, one or more processors, such as a sound processor <NUM> and a data extractor component or data processor <NUM>, an implant controller <NUM> (i.e., battery and power management component or battery processor), and a rechargeable battery <NUM>. The one or more implantable more implantable sound inputs <NUM> may comprise, for example, one or more microphones, accelerometers, telecoils, etc..

The implant body <NUM> also includes an implantable multi-band loop (coil) antenna <NUM> that is located external to the housing <NUM>. The multi-band loop antenna <NUM> is electrically connected to the multi-band RF interface circuitry <NUM> within the housing <NUM> via a hermetic feedthrough (not shown in <FIG>). Multi-band loop antenna <NUM> is a wire antenna coil comprised of multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire. The electrical insulation of multi-band loop antenna <NUM> is provided by a flexible molding (e.g., silicone molding), which is not shown in <FIG>. In certain arrangements, a permanent magnet is fixed relative to the multi-band loop antenna <NUM>. The permanent magnet helps to retain and align an external component by interacting with another magnet in an external device.

Elongate stimulating assembly <NUM> is configured to be at least partially implanted in the recipient's cochlea (not shown) and includes a plurality of longitudinally spaced intra-cochlear electrical stimulating contacts (electrodes) <NUM> that collectively form a contact array <NUM> for delivery of electrical stimulation (current) to the recipient's cochlea. Stimulating assembly <NUM> extends through an opening in the cochlea (e.g., cochleostomy, the round window, etc.) and has a proximal end connected to the stimulator unit <NUM> via the lead region <NUM> and a hermetic feedthrough (not shown in <FIG>). Lead region <NUM> includes one or more conductors (wires) that electrically couple the electrodes <NUM> to the stimulator unit <NUM>.

The one or more implantable sound inputs <NUM> are configured to detect/receive input sound signals that are provided to the sound processor <NUM>. The sound processor <NUM> is configured to execute sound processing and coding to convert the received sound signals into output signals for use by the stimulator unit <NUM> in delivering electrical stimulation (current) to the recipient via electrodes <NUM>. In this way, cochlear implant <NUM> electrically stimulates the recipient's auditory nerve cells, bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity, in a manner that causes the recipient to perceive one or more components of the received sound signals.

Although cochlear implant <NUM> is totally implantable and able to operate without the presence of any external devices, there are times when the presence of one or more external devices are useful. As such, in the example of <FIG>, the cochlear implant <NUM> is able to operate with external charger <NUM>, first external device <NUM>, and/or second external device <NUM>. In general, the external charger <NUM> is configured to deliver charging power to the cochlear implant <NUM> via a communication link <NUM>, while the device <NUM> is configured to send data to, possibly exchange data with, and/or possibly send power to, the cochlear implant <NUM> via a communication link <NUM>. The second device <NUM> is configured to send data to, and possibly exchange data with, the cochlear implant <NUM> via a communication link <NUM>. As noted above, the external charger <NUM> and the first data device <NUM> are devices configured for near-field communication. The signals sent via communication links <NUM> and <NUM> are magnetic induction power and/or data signals sent on/at one or more frequencies in the near-field. Also as noted, the second device <NUM> is a device configured for far-field communication. The signals sent via communication link <NUM> are data signals sent at one or more frequencies within the far-field. That is, the communication links <NUM> and <NUM> are near-field wireless communication links, while communication link <NUM> is a far-field wireless communication link.

The external charger <NUM> and the device <NUM> may each have a number of different forms. For example, the external charger <NUM> may comprise a headpiece coil wired to a battery pack, a headpiece power charger in the shape of a button, a charging headband, a pillow charger, etc. The device <NUM> may comprise, for example, a behind-the-ear (BTE) processor, an off-the-ear headpiece (i.e., a button processor), etc. The device <NUM> may comprise, for example, a remote control unit, a fitting system, a computing device (e.g., mobile phone, tablet computer, etc.), etc. It is to be appreciated that these examples are illustrative and that an implantable medical device in accordance with embodiments presented herein may communicate with a number of different types of external devices in both die near-field and the far-field.

As noted above, the cochlear implant <NUM> comprises the multi-band loop antenna <NUM> and that the multi-band RF interface circuitry <NUM>. The multi-band RF interface circuitry <NUM> is configured such that the multi-band loop antenna <NUM> may be used to receive both near-field signals and far-field signals, potentially at the same time. Stated differently, the multi-band RF interface circuitry <NUM> enables the multi-band loop antenna <NUM> to receive the charging power from the external charger <NUM>, receive power and/or data from first device <NUM>, and receive data from second device <NUM>. As a result, the multi-band RF interface circuitry <NUM> is configured to generate two outputs, shown in <FIG> as output <NUM>(<NUM>) and output <NUM>(<NUM>) that can each be provided to the implant electronics <NUM>. Output <NUM>(<NUM>) represents received near-field signals (i.e., signals received from the external charger <NUM> via inductive link <NUM> or signals received from the first device <NUM> via inductive link <NUM>) and, as such, is sometimes referred to herein as a "near-field output. " Output <NUM>(<NUM>) represents received far-field signals (i.e., signals received from the second data device <NUM> via link <NUM>) and, as such, is sometimes referred to herein as a "far-field output. " As described elsewhere herein, the arrangement of the multi-band RF interface circuitry <NUM> enables the cochlear implant to generate near-field output <NUM>(<NUM>) and far-field output <NUM>(<NUM>) simultaneously (i.e., the multi-band loop antenna <NUM> may operate to simultaneously receive both near-field and far-field signals from different external devices).

The near-field and the far-field signals may each be sent at a number of different frequencies. For example, the near-field output <NUM>(<NUM>) may comprise signals at approximately <NUM> Megahertz (MHz), at approximately <NUM>, at approximately <NUM>, at approximately <NUM>, etc. The far-field output <NUM>(<NUM>) may comprise signals above <NUM>, more preferably well above <NUM> (e.g. on the order of a few Gigahertz (GHz)). For example, the far-field output <NUM>(<NUM>) may be signals in the very high frequency (VHF) range, signals in the ultra high frequency (UHF) range, or a higher frequency range. For ease of illustration, certain embodiments presented herein will be primarily described with reference to use of the multi-band loop antenna <NUM> and the multi-band RF interface circuitry <NUM> to receive signals at specific frequencies, namely at approximately <NUM> via inductive link <NUM>, approximately <NUM> via inductive link <NUM>, and approximately <NUM> via link <NUM>. However, it is to be appreciated that these specific frequencies are illustrative and that the techniques presented herein may be used with other circuitry configured to receive different frequencies.

In certain embodiments, the multi-band loop antenna <NUM> and the multi-band RF interface circuitry <NUM> may be configured to support a combined power and data transfer, where the data transfer may be bi-directional, at one or more frequencies. For example, while operating at the <NUM> frequency, power and data can be modulated with one another (e.g., using on-off-keying (OOK)) or separated from one another and interleaved (e.g., time division multiple access (TDMA)) on inductive link <NUM>. As such, the near-field output <NUM>(<NUM>) may comprise data signals, power signals, modulated data and power, etc..

In the embodiments of <FIG>, the multi-band loop antenna <NUM> operates as a "loop" antenna while receiving/transmitting both near-field and far-field signals. As described further below, this is enabled by a transformer <NUM> to receive near-field signals detected at the antenna <NUM> and an isolation coupling circuit (isolation coupler) <NUM> to receive far-field signals detected at the antenna <NUM>. As used herein, a "loop" antenna refers to a closed circuit arrangement which, when used with another loop (e.g., operating as a coupler or a transformer without a magnetic core), allows the use of radio frequency (RF) signals to generate a differential output (whereas, in contrast, a single ended antenna uses common ground to close the loop).

In accordance with embodiments presented herein, the operation of multi-band loop antenna <NUM> as a loop antenna to receive both near-field and far-field signals maintains a strong RF signal level and isolates the implant electronics <NUM> from the antenna. Moreover, the differential output may improve the sensitivity of the coil and enable a better impedance matching by precisely controlling the differential output impedance.

<FIG> is schematic diagram illustrating one example arrangement for a multi-band loop antenna and multi-band RF interface circuitry in an implantable medical device, such as cochlear implant <NUM>, in accordance with embodiments presented herein. More specifically, shown is a portion of a cochlear implant <NUM> that includes, among other elements, a multi-band loop (coil) antenna <NUM> (represented by inductor L0), a near-field receiver circuit <NUM>, and a far-field receiver circuit <NUM>. The near-field receiver circuit <NUM> is coupled to the multi-band loop antenna <NUM> and is configured to generate a near-field output <NUM>(<NUM>) comprised of near-field signals received at the multi-band loop antenna <NUM>. The far-field receiver circuit <NUM> is also coupled to the multi-band loop antenna <NUM> and is configured to generate a far-field output <NUM>(<NUM>) comprised of far-field signals received at the multi-band loop antenna <NUM>. As noted, the outputs <NUM>(<NUM>) and <NUM>(<NUM>) are provided to implant electronics (not shown in <FIG>) of the cochlear implant <NUM>.

The near-field receiver circuit <NUM> comprises a transformer <NUM> without a magnetic core (i.e., an air transformer). The transformer <NUM> has a primary side (primary coil) <NUM> connected in series with the multi-band loop antenna <NUM> and a secondary side (secondary coil) <NUM> connected to the capacitor <NUM> (C1).

The far-field receiver circuit <NUM> comprises an isolation coupler <NUM>. The isolation coupler <NUM> is connected in series with the multi-band loop antenna <NUM> and is connected in parallel with the transformer <NUM>. In the embodiment of <FIG>, the inductance of the primary side of the coupler <NUM>, a first capacitor <NUM> (C2), and a second capacitor <NUM> (C3), which are connected between the isolation coupler <NUM> and the multi-band loop antenna <NUM>, form a high-pass filter <NUM> for signals received at the multi-band loop antenna <NUM>.

As noted, the receiver circuits <NUM> and <NUM> are used to receive near-field and far-field signals, respectively, via the multi-band loop antenna <NUM>. The receiver circuits <NUM> and <NUM> operate in differential mode directly from the multi-band loop antenna <NUM> to receive the signals. In addition, as noted, due to the physical arrangement of the receiver circuits <NUM> and <NUM>, the multi-band loop antenna <NUM> operates as a loop antenna to receive both the near-field and the far-field signals.

As noted above, the far-field receiver circuit <NUM> comprises isolation coupler <NUM> that is connected in series with the multi-band loop antenna <NUM>. The isolation coupler <NUM> may be implemented in a number of different manners, but generally includes a first (primary) side (not shown in <FIG>) that closes the antenna loop and a second (secondary) side (also not shown in <FIG>) that is electrically isolated from the first side. The second side of the isolation coupler <NUM> generates the far-field output <NUM>(<NUM>) that is provided to the implant electronics, while also electrically isolating the implant electronics from direct current (DC) at the primary side connected to the multi-band loop antenna <NUM>.

As noted, in the embodiment of <FIG>, the capacitors <NUM>, <NUM>, and the inductance of the primary side of the coupler <NUM> operate as a high-pass filter <NUM> that blocks the near-field signals. In addition, local ground is not required at the first side of the isolation coupler <NUM>.

As noted, isolation coupler <NUM>, as well other isolation couplers in accordance with embodiments presented herein, may be implemented in a number of different manners. <FIG> is a schematic diagram illustrating one example arrangement for isolation coupler <NUM>, in accordance with embodiments presented herein. In this embodiment, the isolation coupler <NUM> is a directional coupler and is referred to herein as directional coupler <NUM>.

Directional coupler <NUM> comprises an input port <NUM>, an output port <NUM>, and a coupled port <NUM>. The input port <NUM> is connected to the positive terminal <NUM>(<NUM>) of a multi-band loop antenna <NUM> via capacitor <NUM>, while output port <NUM> is connected to the negative terminal <NUM>(<NUM>) of the multi-band loop antenna <NUM> via capacitor <NUM>. The capacitors <NUM> and <NUM>, along with the inductance of the primary side of the coupler <NUM>, form a high-pass filter <NUM> for signals received at the multi-band loop antenna <NUM>. The multi-band loop antenna <NUM>, capacitor <NUM>, and capacitor <NUM> are substantially similar to multi-band loop antenna <NUM>, capacitor <NUM>, and capacitor <NUM>, respectively, described above with reference to <FIG>. The coupled port <NUM> is connected to implant electronics <NUM> which may be substantially similar to implant electronics <NUM> of <FIG>.

As shown, the directional coupler <NUM> also comprises two coupled transmission lines <NUM>(<NUM>) and <NUM>(<NUM>). Transmission line <NUM>(<NUM>) is connected between input port <NUM> and output port <NUM>, while transmission line <NUM>(<NUM>) is connected between coupled port <NUM> and an internal load <NUM>. In certain examples, transmission line <NUM>(<NUM>) is referred to as a "mainline" or "primary side" of the coupler <NUM>, while transmission line <NUM>(<NUM>) is referred to as a "coupled line" or "secondary side" of the coupler <NUM>. Each of the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) have an associated inductance and can be created using a number of different technologies, such as stripline technology, microstrip technology, etc..

The transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) are physically separated from one another and, as such, provide direct current isolation there between. However, at least a segment of each of the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) are positioned sufficiently close together such that energy passing through transmission line <NUM>(<NUM>) is coupled to transmission line <NUM>(<NUM>). That is, due to the relative positioning of the two coupled transmission lines <NUM>(<NUM>) and <NUM>(<NUM>), a defined amount of the electromagnetic power in transmission line <NUM>(<NUM>) passes to transmission line <NUM>(<NUM>) and, accordingly, to the coupled port <NUM> and the implant electronics <NUM>.

In <FIG>, arrows <NUM> illustrate the flow of current from multi-band loop antenna <NUM> through transmission line <NUM>(<NUM>). Arrow <NUM> illustrates the coupled current that flows through transmission line <NUM>(<NUM>) to coupled port <NUM>. As shown, transmission line <NUM>(<NUM>) closes the multi band loop antenna <NUM> while, due to the physical separation of the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>), the implant electronics <NUM> are isolated (protected) from direct current at the multi-band loop antenna <NUM>.

<FIG> is an example of a three (<NUM>) port directional coupler. It is to be appreciated that the use of a three port directional coupler is illustrative and that other directional couplers may be used in other embodiments. For example, <FIG> is a schematic diagram illustrating a four (<NUM>) port directional coupler <NUM> that can be used in accordance with embodiments presented herein. The directional coupler <NUM> is similar to the coupler <NUM> of <FIG> except that that both ends of the coupled line are coupled ports.

More specifically, directional coupler <NUM> comprises an input port <NUM>, an output port <NUM>, and a first coupled port <NUM>(<NUM>) and a second coupled port <NUM>(<NUM>). The first coupled port <NUM>(<NUM>) is sometimes referred to herein as a "forward coupled" port, while the second coupled port <NUM>(<NUM>) is sometimes referred to herein as a "reverse coupled" or "isolated" port. The input port <NUM> is connected to the positive terminal <NUM>(<NUM>) of a multi-band loop antenna <NUM> via capacitor <NUM>, while output port <NUM> is connected to the negative terminal <NUM>(<NUM>) of the multi-band loop antenna <NUM> via capacitor <NUM>. The capacitors <NUM> and <NUM>, along with the inductance of the primary side of the coupler <NUM>, form a high-pass filter <NUM> for signals received at the multi-band loop antenna <NUM>. The multi-band loop antenna <NUM>, capacitor <NUM>, and capacitor <NUM> are substantially similar to multi-band loop antenna <NUM>, capacitor <NUM><NUM>, and capacitor <NUM>, respectively, described above with reference to <FIG>. The coupled ports <NUM>(<NUM>) and <NUM>(<NUM>) are connected to implant electronics <NUM>, which may be substantially similar to implant electronics <NUM> of <FIG>. In certain examples, the reverse coupled port <NUM>(<NUM>) may be terminated with an external load (not shown in <FIG>).

As shown, the directional coupler <NUM> also comprises two coupled transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) that form the primary and secondary sides, respectively, of the coupler <NUM>. Transmission line <NUM>(<NUM>) is connected between input port <NUM> and output port <NUM>, while transmission line <NUM>(<NUM>) is connected between coupled ports <NUM>(<NUM>) and <NUM>(<NUM>). Similar to the above embodiments, the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) can be created using a number of different technologies (e.g., stripline technology, microstrip technology, etc.).

The transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) are physically separated from one another. However, at least a segment of each of the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>) are positioned sufficiently close together such that energy passing through transmission line <NUM>(<NUM>) is coupled to transmission line <NUM>(<NUM>). That is, due to the relative positioning of the two coupled transmission lines <NUM>(<NUM>) and <NUM>(<NUM>), a defined amount of the electromagnetic power in transmission line <NUM>(<NUM>) passes to transmission line <NUM>(<NUM>) and, accordingly, to the forward coupled port <NUM>(<NUM>) and the implant electronics <NUM>.

In <FIG>, arrows <NUM> illustrate the flow of current from multi-band loop antenna <NUM> through transmission line <NUM>(<NUM>). Arrow <NUM> illustrates the induced (coupled) current that flows through transmission line <NUM>(<NUM>) to forward coupled port <NUM>(<NUM>). As shown, transmission line <NUM>(<NUM>) closes die multi band loop antenna <NUM> while, due to die physical separation of the transmission lines <NUM>(<NUM>) and <NUM>(<NUM>), the implant electronics <NUM> are isolated (protected) from direct current at the multi-band loop antenna <NUM>.

<FIG> and <FIG> illustrate example arrangements for isolation couplers in accordance with embodiments presented herein. In the example arrangements of <FIG> and <FIG>, the coupling is via two transmission lines. In further embodiments, the transmission lines may be replaced by coils so as to form an air transformer (i.e., a transformer without a magnetic core). In certain embodiments, an isolation coupler may be implemented as a balun operating as an air transformer.

For example, <FIG> is a simplified schematic diagram illustrating one arrangement for far-field receiver circuit <NUM>, referred to as far-field receiver circuit <NUM>, in which the isolation coupler is formed by a balun <NUM>. In this example, the balun <NUM> operates as an air transformer or directional coupler and comprises a primary side <NUM>(<NUM>) and a secondary side <NUM>(<NUM>). The primary and secondary sides <NUM>(<NUM>) and <NUM>(<NUM>) include coils <NUM>(<NUM>) and <NUM>(<NUM>), respectively.

The primary side <NUM>(<NUM>) of the balun <NUM> is connected between positive terminal <NUM>(<NUM>) of a multi-band loop antenna <NUM> via capacitor <NUM> and the negative terminal <NUM>(<NUM>) of the multi-band loop antenna <NUM> via capacitor <NUM>. The capacitors <NUM> and <NUM>, along with the inductance of the primary side of the coupler <NUM>, form a high-pass filter <NUM> for signals received at the multi-band loop antenna <NUM>. The multi-band loop antenna <NUM>, capacitor <NUM>, and capacitor <NUM> are substantially similar to multi-band loop antenna <NUM>, capacitor <NUM>, and capacitor <NUM>, respectively, described above with reference to <FIG>. The secondary side <NUM>(<NUM>) of the balun <NUM> is connected between a load <NUM> and implant electronics <NUM>, which may be substantially similar to implant electronics <NUM> of <FIG>.

The coils <NUM>(<NUM>) and <NUM>(<NUM>) are physically separated from one another but are positioned sufficiently close together such that energy passing through coil <NUM>(<NUM>) is coupled to coil <NUM>(<NUM>) and, as such, a defined amount of the electromagnetic power in <NUM>(<NUM>) passes to <NUM>(<NUM>) and the implant electronics <NUM>. In certain examples, some inductance and capacitance may be added in line with the coils <NUM>(<NUM>) and <NUM>(<NUM>) to balance the output. For ease of illustration, such additional inductance and capacitance have been omitted from <FIG>.

In <FIG>, arrows <NUM> illustrate the flow of current from multi-band loop antenna <NUM> through coil <NUM>(<NUM>). Arrow <NUM> illustrates the induced (coupled) current that flows through coil <NUM>(<NUM>). As shown, coil <NUM>(<NUM>) closes the multi band loop antenna <NUM> while, due to the physical separation of the coils <NUM>(<NUM>) and <NUM>(<NUM>)<NUM>), the implant electronics <NUM> are isolated (protected) from the multi-band loop antenna <NUM>. That is, balun <NUM> isolates the implant electronics <NUM> from direct current at the multi-band loop antenna <NUM>.

Although embodiments have been primarily described with reference to cochlear implants, it is to be appreciated that the techniques presented herein may be implemented in other implantable medical devices, such as other types of auditory prostheses.

It is to be appreciated that the embodiments presented herein are not mutually exclusive.

Claim 1:
An implantable medical device, comprising:
a multi-band loop antenna (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>);
implant electronics (<NUM>, <NUM>, <NUM>, <NUM>);
a near-field receiver circuit (<NUM>) coupled to the loop antenna (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the implant electronics (<NUM>, <NUM>, <NUM>, <NUM>) and configured to receive, via the loop antenna (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), near-field signals from one or more devices positioned external to a body of a recipient and to provide the near-field signals to the implant electronics (<NUM>, <NUM>, <NUM>, <NUM>); and
a far-field receiver circuit (<NUM>) coupled to the loop antenna (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and the implant electronics (<NUM>, <NUM>, <NUM>, <NUM>) and configured to receive, via the loop antenna (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), far-field signals from at least one device positioned external to the body of the recipient and to provide the far-field signals to the implant electronics (<NUM>, <NUM>, <NUM>, <NUM>),
characterized in that
the near-field receiver circuit (<NUM>) comprises a transformer (<NUM>) and the far-field receiver circuit (<NUM>) comprises an isolation coupler (<NUM>).