Power and data transfer in hearing prostheses

Embodiments presented herein are generally directed to techniques for separately transferring power and data from an external device to an implantable component of a partially or fully implantable medical device. The separated power and data transfer techniques use a single external coil and a single implantable coil. The external coil is part of an external resonant circuit, while the implantable coil is part of an implantable resonant circuit. The external coil is configured to transcutaneously transfer power and data to the implantable coil using separate (different) power and data time slots. At least one of the external or internal resonant circuit is substantially more damped during the data time slot than during the power time slot.

BACKGROUND

Field of the Invention

The present invention relates generally to hearing prostheses, and more particularly, to power and data transfer in hearing prostheses.

Related Art

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 life saving 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 components perform diagnosis, prevention, monitoring, treatment or management of a disease or injury or symptom thereof, or to investigate, replace or modify of the anatomy or of a physiological process. Many of these functional components utilize power and/or data received from external components that are part of, or operate in conjunction with, the implantable medical device.

SUMMARY

In one aspect presented herein, an implantable medical device is provided. The implantable medical device comprises an implantable resonant circuit comprising an implantable coil, and an external resonant circuit comprising an external coil configured to transcutaneously transfer power and data to the implantable coil using separate power and data time slots. At least one of the external or implantable resonant circuit is substantially more damped during the data time slots than during the power time slots.

In another aspect presented herein, an external transmitter circuit is provided. The external transmitter circuit comprises an external resonant circuit comprising an external coil and one or more driver bridges configured to cause the external coil to transfer power and data to an implantable receiver circuit using separate power and data time slots. The quality factor of the external resonant circuit is lower during the data slots than during the power time slots.

In another aspect presented herein, an apparatus is provided. The apparatus comprises an implantable resonant circuit comprising an implantable coil, an external resonantcircuit comprising an external coil forming a transcutaneous power and data link with the implantable coil, and at least one driver bridge configured to drive the external coil so as to separately transfer power and data to the implantable coil. Operational characteristics of at least one of the implantable resonant circuit or the external resonant circuit are dynamically adjusted during transfer of data to the implantable coil.

In another aspect presented herein, a method for transmitting power from an external transmitter circuit to an implantable receiver circuit is provided. The external transmitter circuit comprises an external resonant circuit that includes an external coil, while the implantable receiver circuit comprise an implantable resonant circuit that includes an implantable coil. The method comprises driving the external resonant circuit with one or more driver bridges during a power time slot to cause the external coil to transfer power to the implantable receiver circuit. The method further comprises driving the external resonant circuit with one or more driver bridges during a data time slot to cause the external coil to transfer data to the implantable receiver circuit. The power and data time slots are different time slots and the external resonant circuit is driven such that the quality factor of the external resonant circuit is lower during the data slot than during the power time slot.

DETAILED DESCRIPTION

Embodiments presented herein are generally directed to techniques for separately transferring power and data from an external device to an implantable component of a partially or fully implantable medical device. The separated power and data transfer techniques use a single external coil and a single implantable coil. The external coil is part of an external resonant circuit, while the implantable coil is part of an implantable resonant circuit. The external coil is configured to transcutaneously transfer power and data to the implantable coil using separate (different) power and data time slots. At least one of the external or internal resonant circuit is substantially more damped during the data time slot than during the power time slot. In certain embodiments, the external and internal resonant circuits are resonsant tank circuits.

Embodiments of the present invention are described herein primarily in connection with one type of implantable medical devices, namely partially implantable hearing prostheses comprising an external component and an internal (implantable component). Hearing prostheses include, but are not limited to, auditory brain stimulators, cochlear implants (also commonly referred to as cochlear implant devices, cochlear prostheses, and the like; simply “cochlear implants” herein), bone conduction devices, and mechanical stimulators. It is to be appreciated that embodiments of the present invention may be implemented in any partially or fully implantable medical device now known or later developed.

FIG. 1is a perspective view of an exemplary cochlear implant100configured to implement separated power and data transfer techniques in accordance with embodiments presented herein. The cochlear implant100includes an external component142and an internal or implantable component144. The external component142is directly or indirectly attached to the body of the recipient and typically comprises one or more sound input elements124(e.g., microphones, telecoils, etc.) for detecting sound, a sound processor134, a power source (not shown), an external coil130and, generally, a magnet (not shown) fixed relative to the external coil130. The sound processor134processes electrical signals generated by a sound input element124that is positioned, in the depicted embodiment, by auricle110of the recipient. The sound processor134provides the processed signals to a transmitter circuit configured to drive (activate) external coil130.

As used herein, an “external component” refers to one or more elements or devices that are part of, or operate in conjunction with, the implantable medical device. In other words, an external component may form part of the implantable medical device or may be a separate device that operates with an implantable medical device.

Returning to the example ofFIG. 1, the implantable component144comprises an implant body105, a lead region108, and an elongate stimulating assembly118. The implant body105comprises a stimulator unit120, an implantable (internal) coil136, and an internal receiver/transceiver unit132, sometimes referred to herein as transceiver unit132. The transceiver unit132is connected to the internal coil136and, generally, a magnet (not shown) fixed relative to the internal coil136. Internal transceiver unit132and stimulator unit120are sometimes collectively referred to herein as a stimulator/transceiver unit120.

Implantable coil136is typically a wire antenna coil comprised of multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire. The electrical insulation of implantable coil136is provided by a flexible silicone molding. In use, transceiver unit132may be positioned in a recess of the temporal bone of the recipient.

The magnets in the external component142and implantable component144facilitate the operational alignment of the external coil130with the implantable coil136. The operational alignment of the coils enables the external coil130to transmit/receive power and data to the implantable coil136. As described further below, the external component142is configured to transmit electrical signals (i.e., power and data) from external coil130to implantable coil136using separate time slots over a radio frequency (RF) link.

Elongate stimulating assembly118is implanted in cochlea140and includes a contact array146comprising a plurality of stimulating contacts148. Stimulating assembly118extends through cochleostomy122and has a proximal end connected to stimulator unit120via lead region108that extends through mastoid bone119. Lead region108couples the stimulating assembly118to implant body105and, more particularly, stimulator/transceiver unit120. The stimulating contacts148may be electrical contacts, optical contacts, or a combination of optical and electrical contacts.

As noted above, a transcutaneous RF link is provided to transfer power and data from external component142to implantable component144. Certain conventional transcutaneous RF links use an amplitude modulated signal where the data and the power are transferred simultaneously (i.e., at the same time) over the same RF coil for extraction by the implantable component. In other words, the data signals are embedded in the power signals for simultaneous transmission from the external coil to the implantable coil. RF links that simultaneously transmit power and data are sometimes referred to as combined power and data links.

Other conventional arrangements use time multiplexing of pure power and data signals on separate RF links from different power and data transmitters. More specifically, in such arrangements a first RF link is created between a first external coil and an implantable coil. This first RF link is used solely for data transmission. Additionally, a second RF link is created between a second (different) external coil and the implantable coil. This second RF link is used solely for power transmission. A time multiplexing scheme is implemented such that either the first RF link or the second RF link is activated and at one time in order to avoid interference between the power and data signals. In other words, these arrangements use a first RF link (and first external coil) that is dedicated to data transmission and a second RF link (and second external coil) that is dedicated to power transmission where the first and second links are alternatively activated.

Presented herein are separated power and data transfer techniques in which a single transcutaneous RF link is used to separately transfer power and data from an external component to an implantable component. In accordance with the separated power and data transfer techniques, transfer of power and data occur during separate (different) time slots using the same external coil130(i.e., a shared external coil for both data and power). For example, a single transmission sequence/frame may be split into a power time slot (block) and a data time slot (block) and repeated. All of the power towards the implantable component144is transferred during the power time slot.

In order to enable use of a single shared external coil for power and data transmission during different time slots, the operational characteristics of one or both of an external transmitter (or transceiver) or an implantable receiver (or transceiver) are dynamically adjusted between the power and data slots. More specifically, the implantable receiver includes an implantable resonant circuit (e.g., an implantable resonant tank circuit) comprising an implantable coil, while the external transmitter includes an external resonant circuit (e.g., an external resonant tank circuit) comprising an external coil configured to transcutaneously transfer power and data to the implantable coil using the separate power and data time slots. At least one of the external or internal resonant circuit is substantially more damped during the data time slot than during the power time slot. That is, the quality factor (Q) of one or both of the external circuit or the internal resonant circuit is reduced during data transmission (relative to the quality factor of one or both of the external circuit or the internal resonant circuit during power transmission).

For ease of illustrations, embodiments will be primarily described herein with reference to the use of external and implantable resonsant tank circuits. It is to be appreciated that embodiments may include other types of external and/or implantable resonant circuits.

As noted, the techniques presented herein involve switching between power transfer for some fraction of the frame, and then data transfer for another part of the frame. By decoupling the data from the power, the RF link can be optimized for efficient power transfer during the power time slots and then independently optimized for data transfer. For example, a very high quality factor may be used to optimize the power transfer efficiency during the power time slots. However, when switching to the data transfer mode, the internal or external tank circuit is dampened (and optionally detuned) to improve data integrity.

FIG. 2Ais a schematic diagram illustrating a transmitter circuit220configured to separately transfer power and data signals from an external component of an implantable component via a single external coil222. In the embodiment ofFIG. 2A, the external coil222is part of an external resonant tank circuit225that also comprises capacitor242(capacitor C1) and capacitor244(capacitor C2). In practice, external coil222has an inductive component (LHPC)246and some small copper losses represented as the series resistive component (RHPC)248.

The transmitter circuit220comprises a driver bridge240. In certain embodiments, the driver bridge240is a full H-bridge driver. In other embodiments, the driver bridge240is a half H-bridge driver. The driver bridge240includes an input250that receives an input signal231(FIG. 2B) via a data input line252. The driver bridge240also comprises a first output254and a second output256(differential output). The first output254is connected to capacitor242(which is connected to external coil222) via a series circuit257. The series circuit257comprises a resistor258(R1) in series with an inductor260(L1). The second output256is connected to capacitor244(which is also connected to external coil222) via a series circuit261. The series circuit261comprises resistor262(R2) in series with an inductor264(L2). In an alternative arrangement the driver may only contain a single output (Half H-bridge or single push-pull) connected to a single series circuit comprising a resistor (R1) in series with an inductor260(L1).

The first output254and the second output256of driver bridge240are also connected to the capacitors242and244, respectively, via a switch266. When the switch266is closed, the first output254is directly connected to capacitor242so as to bypass series circuit257(i.e., bypass resistor258and inductor260). Similarly, when the switch266is closed, the second output256is directly connected to capacitor244so as to bypass series circuit261(i.e., bypass resistor262and inductor264). The switch266may be closed in response to an enable power signal233(FIG. 2B) received via enable power line268.

As noted above, power and data are transmitted during non-overlapping and separate (i.e., different) time slots.FIG. 2Billustrates a power time slot235and a data time slot237where On-Off keying (OOK) is used to transmit both the power and the data. In OOK, the signal may be either a “1” (i.e., a pulse of energy is present) or a “0” (i.e., no pulse of energy is present). In certain examples, five (5) cycles or pulses may represent a ‘1’ cell and the absence of energy during five (5) cycles may represent a ‘0’ cell. Energy is taken from the ‘1’ cells. As shown inFIG. 2B, during the power time slot235, the input signal231is all ‘1s,’ but switches between ‘1s’ and ‘0s’ during the data time slot237. The switching between 1s’ and ‘0s’ during the data time slot237is a digital code that is decoded at the implantable component.

The enable power signal233is a pulse waveform that also alternatives between a value of ‘1’ and ‘0.’ During the power time slot235, the enable power signal233has a value of ‘1’ so as to close the switch266. This causes the outputs254and256of the driver bridge240to be directly connected to the capacitors242and244, respectively, so as to bypass the series circuits257(R1and L1) and261(R2and L2).

Assuming for ease of illustration that the driver bridge240and the switch266are ideal, the resonance frequency of the external resonant tank circuit225during the power time slot (fres_power_timeslot) is defined below in Equation 1.

In the arrangement where the switch266is closed, the quality factor (Q) of the resonant tank circuit225during the power time slot (Qext_power_timeslot) is defined below in Equation 2.

Maximum power efficiency is obtained when the quality factor of the external resonant tank circuit225during the power time slot is maximized or RHPCis minimized. In order to maximum the quality factor of the external tank circuit during power transfer, the switch266is closed during the power time slots235so that signals provided by driver bridge240bypass the series circuits257(R1and L1) and261(R2and L2), thereby ensuring that the quality factor and of the external resonant tank circuit225is not affected (reduced) by the series circuits257and261.

Additionally, the external coil current is maximized when the resonant frequency of the resonant tank circuit225during the power time slot is substantially equal or close to the operating frequency (f0) of the external coil222(i.e., drive more current through the external coil while maintaining the driver at the same voltage). Therefore, the frequency of the external resonant tank circuit225is set (via tuning of capacitors242and244) to be close or equal to the operating frequency to maximize the power efficiency of the transcutaneous link. During the transcutaneous power transfer, the closure of the switch266during the power time slots235(so that signals provided by driver bridge240bypass the series circuits257(R1and L1) and261(R2and L2) ensures that the resonant frequency of the external resonant tank circuit225is not affected by the series circuits257and261.

During the data time slots, the switch266is opened so that the series circuits257(R1and L1) and261(R2and L2) are placed in series between the driver bridge240and the external coil222. Placing the series circuits257and261between the driver bridge240and the external coil222causes a drop in the quality factor of the resonant tank circuit225, the external coil current, and the resonance frequency. In this case, the resonance frequency of the external resonant tank circuit225during the data time slot (fres_data_timeslot) is defined below in Equation 4.

Additionally, in the arrangement where the switch266is open, the quality factor of the resonant tank circuit225during the data time slot (Qext_data_timeslot) is defined below in Equation 5.

It has been discovered that the data integrity improves when the external resonant tank circuit225is more dampened (i.e., has a lower quality factor) during data transmission. This is opposed to power transmission where, as noted above, maximum power efficiency is achieved when the quality factor of the resonant tank circuit is maximized. As such, in accordance with the techniques presented herein, the quality factor of the resonant tank circuit is maximized during power transmission, but is purposely lowered during data transmission (i.e., Qext_data_timeslot<Qext_power_timeslot). The dampened external resonant tank circuit225reduces the ringing effects during one or more ‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOK modulation at fo. The series resistors258and262operate to dampen the external resonant tank circuit225when connected in series between the between the driver bridge240and the external coil222.

It has also been discovered that the data integrity improves and that the external coil current drops during the data time slot when the external resonant tank circuit225is tuned lower than the operating frequency. The lower the tuning frequency of the external coil222is relative to the operating frequency, the higher the decrease in current flow through the external coil222when the driver bridge222is acting as a pulsating voltage source (e.g. Class-D driver bridge). As described further below, the decrease in the external coil current prevents interference of the implantable component load with the data recovery at the implantable component. In one example, the operating frequency of the external coil222is 5 megahertz (MHz) and the resonant frequency of the external resonant tank circuit225during data transmission (fres_data_timeslot) is set equal to 4.75 MHz). The series inductors260and264operate to reduce the resonant frequency of the external resonant tank circuit225when connected in series between the between the driver bridge240and the external coil222.

As shown inFIG. 2A, the resonance frequency and quality factor during the power time slot and the data time slot are dynamically adjusted through the use of the switch266.FIG. 3illustrates an alternative arrangement where a dedicated driver bridge, rather than a switch, is used to dynamically adjust the resonance frequency and quality factor of an external tank circuit.

More specifically,FIG. 3is a schematic diagram illustrating an external transmitter circuit320configured to separately transfer power and data signals to an implantable component via a single external coil322. In the embodiment ofFIG. 3, the external transmitter circuit320comprises a first driver bridge340(data driver bridge) and a second driver bridge341(power driver bridge). As described further below, the driver bridge340is enabled during the data time slot, but is deactivated during the power time slot. Similarly, the driver bridge341is enabled during the power time slot, but is deactivated during the data time slot. As such, the arrangement ofFIG. 3uses dedicated driver bridges for each of data and power transmission (i.e., the data and power signals have their own driver bridges and only a single driver bridge is enabled at a time).

In the embodiment ofFIG. 3, the external coil322is part of an external resonant tank circuit325that also comprises capacitor342(capacitor C1) and capacitor344(capacitor C2). In practice, external coil322has an inductive component (LHPC)346and some small copper losses represented as the series resistive component (RHPC)348.

The driver bridge340includes an input350that receives an input signal331via data input line352and an enable data input353that receives a enable data signal329via enable data signal line355. The driver bridge340also comprises a first output354and a second output356. The first output354is connected to capacitor342(which is connected to external coil322) via a series circuit357that comprises a resistor358(R1) in series with an inductor360(L1). The second output356is connected to capacitor344(which is also connected to external coil322) via a series circuit361that comprises resistor362(R2) in series with an inductor364(L2).

The driver bridge341includes an input369that receives a power signal327via power input line372and an enable power input373configured to receive an enable power signal327via enable power signal line375. The driver bridge341also comprises a first output374and a second output376. The first output374is directly connected to capacitor342(which is connected to external coil322) so as to bypass series circuit357. Similarly, the second output376is directly connected to capacitor344so as to bypass series circuit361.

The power signal327is a series of all ‘1’ values (consecutive power cycles), while the data input signal331switches between ‘1s’ and ‘0s’ (i.e., at 5 MHz a ‘1’ represents five (5) cycles or pulses during 1 μs and a ‘0’ represents a silence during 1 μs for a data rate of 1 Mbps). The enable power signal333is a logic signal that alternatives between a value of ‘1’ and ‘0.’ The enable data signal329is also a pulse waveform that alternatives between a value of ‘1’ and ‘0.’ The enable signal activates the respective driver at value ‘1’. However, the enable data signal329is the inverse of the enable power signal333(note WME: make this more visible inFIG. 3). That is, when the enable power signal333is ‘1,’ the enable data signal329is a ‘0’ value, and vice versa.

In the embodiment ofFIG. 3, power and data are transmitted during non-overlapping and separate (i.e., different) time slots using the separate driver bridges. During the data time slots, the enable data signal329is high so as to enable driver bridge340. As such, the outputs354and356, generated using data input signal331, are used to drive external coil322. At the same time, the enable power signal333is low so as to cause the outputs374and376of driver bridge341to be placed in a high impedance state.

As noted above, the first output354is connected to external coil322via series circuit357(R1and L1) and the second output356is connected to external coil322via series circuit361(R2and L2). As such, when driver bridge340is enabled, the external coil322is driven with signals that pass through series circuit357and series circuit361.

During the power time slots, the enable power signal333is high (i.e., a ‘1’ value) so as to enable driver bridge341. As such, the outputs374and376, generated using power signal327, are used to drive external coil322. At the same time, the enable data signal329is low (i.e., a ‘0’ value) so as to cause the outputs354and356of driver bridge340to be placed in a high impedance state.

As noted, maximum power efficiency is obtained when the quality factor of the external resonant tank circuit325during the power time slot is maximized or RHPCis minimized. Additionally, the external coil current is maximized when the resonant frequency of the resonant tank circuit325during the power time slot is substantially equal or close to the operating frequency (f0) of the external coil322. Therefore, during the power time slots, the bridge341is enabled to drive the external coil322with signals that pass directly from the outputs374and376to capacitors342and344, respectively. In this arrangement, the signals bypass the series circuits357(R1and L1) and361(R2and L2), thereby ensuring that the quality factor and resonant frequency of the external resonant tank circuit325are not affected by the series circuits357and361.

However, also as noted above, the data integrity improves when the external resonant tank circuit325is more dampened (i.e., has a lower quality factor) during data transmission. As such, during the data time slots, the driver bridge340is enabled so as to drive external coil322with signals that pass through the series circuit357(R1and L1) and series circuit361(R2and L2). That is, the series circuit357(R1and L1) and series circuit361(R2and L2) are placed in between the driver bridge340and the external coil322. Driving the external coil322via the series circuits357and361causes a drop in the quality factor of the resonant tank circuit325, the external coil current, and the resonance frequency of the resonant tank circuit. It should be noted that R1and R2may be an intrinsic part of the data driver bridge.

In summary ofFIG. 3, the quality factor of the resonant tank circuit325is maximized during power transmission, but is purposely lowered during data transmission (i.e., Qext_data_timeslot<Qext_power_timeslot). The dampened external resonant tank circuit325reduces the ringing effects during one or more ‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOK modulation at fo. The series resistors358and362operate to dampen the external resonant tank circuit325when connected in series between the between the driver bridge340and the external coil322.

FIG. 3also illustrates an implantable receiver circuit380configured to receive separate power and data signals transmitted by the external transmitter circuit320. The implantable receiver circuit380comprises an implantable coil382that is part of an implantable (internal) resonant tank circuit385that also comprises capacitor394(capacitor C4) and capacitor396(capacitor C5). In practice, implantable coil382has an inductive component (LIPC)377and some small copper losses represented as the series resistive component (RIPC)379. The implantable receiver circuit380also comprises a data output381, a load383(i.e., battery or other energy storage device), and an energy rectifier connected between the implantable coil382and the load383. In certain embodiments, the energy rectifier384is a diode.

The implantable receiver circuit380is described in relation to external transmitter circuit320. It is to be appreciated that the implantable receiver circuit380, or variants thereof, may be used with the other external transmitter circuits described herein.

Returning to the embodiment ofFIG. 3, it has also been discovered that the data integrity improves and that the current through external coil322drops when the external resonant tank circuit325is tuned lower than the operating frequency. The lower the tuning frequency of the external coil322is relative to the operating frequency, the higher the decrease in current flow through the external coil322when the driver bridge340is acting as a pulsating voltage source. In one example, the operating frequency of the external coil322is 5 MHz and the resonant frequency of the external resonant tank circuit325during data transmission (fres_data_timeslot) is set equal to 4.75 MHz). The series inductors360and364operate to reduce the resonant frequency of the external resonant tank circuit325when connected in series between the between the driver bridge340and the external coil322.

The decrease in the external coil current in response to the detuning of the resonant frequency prevents interference of the implantable component load383with the data recovery at the implantable receiver circuit380. More specifically, the detuning lowers the peak amplitude of the data signals so that the diode384is maintained in reverse polarization (i.e., non-conducting during data transmission), thereby preventing the load383from being seen at the data output381.

In certain embodiments, the driver bridge341is constructed as a full H-bridge driver, while the driver bridge340is a half H-bridge driver. The use of a half H-bridge driver lowers the peak amplitude of the data signal, thereby assisting in maintaining the diode384in reverse polarization. Fine adjustments to the received implant voltage level may also be accomplished by altering the pulse width of each RF cycle during the data and power time slot or adapting the driver bridge supply voltages.

FIG. 4is a diagram illustrating the signal observed at the implantable receiver circuit380during power time slots335and data time slots337. In the illustrative example ofFIG. 4, the power time slots335are approximately 0.5 milliseconds (ms) in length, while the data time slots are approximately 1.5 ms in length (i.e., the power time slots335occupy approximately ¼ of the time while the data time slots337occupy approximately ¾ of the time).

The implant voltage (VDD) at load383is represented inFIG. 4as dotted line386. As shown, during the power time slots335, the implantable receiver circuit380receives all ‘1’ signals. As a power time slot335ends and a subsequent data time slot335begins, ringing is observed at the implantable receiver circuit380. This ringing is a result of the high quality factor and efficiency of the external resonant tank circuit325during transmission of the power signals388. During the data time slots335, the ringing is eliminated by reducing the quality factor of the external resonant tank circuit325.

As described above, the peak amplitude of the data signals410is reduced from the peak amplitude of the power signals408. As shown inFIG. 4, the peak amplitude of the data signals410is reduced so as to stay below the implant voltage486so that the implant voltage is not observed during the data time slots337(i.e., so that the diode384remains in reverse polarization).

It is to be appreciated that the data time slots337may not be fully filled (i.e., the number of signals sent may depend on the amount of data that needs to be transferred from the external component to the implantable component). In certain embodiments, all or part of a data time slot337may be used for backlink telemetry where data is sent from the implantable component to the external component. As such, the external transmitter circuit320and the implantable receiver circuit380are, in practice, both transceiver circuits.

FIG. 5is a schematic diagram illustrating another external transmitter circuit520configured to separately transfer power and data signals to an implantable component via a single external coil522in accordance with embodiments presented herein. Similar to the embodiment ofFIG. 3, the external transmitter circuit520uses dedicated driver bridges for each of data and power transmission (i.e., the data and power signals have their own driver bridges and only a single driver bridge is enabled at a time). However, as described further below, the separate driver bridges are driven differently than as shown inFIG. 3.

In the embodiment ofFIG. 5, the external transmitter circuit520comprises a first driver bridge540(data driver bridge) and a second driver bridge541(power driver bridge) that are each separately connected to the external coil522. The external coil522is part of an external resonant tank circuit525that also comprises capacitor542(capacitor C1) and capacitor544(capacitor C2). In practice, external coil522has an inductive component (LHPC) 546 and some small copper losses represented as the series resistive component (RHPC)548.

The driver bridge540includes an input550that receives an input signal531via input signal line552and an enable input553that receives an enable signal529via enable signal line555. As described further below, the enable input553is an inverting input.

The driver bridge540also comprises a first output554and a second output556. The first output554is connected to capacitor542(which is connected to external coil522) via a series circuit557that comprises a resistor558(R1) in series with an inductor560(L1). The second output556is connected to capacitor544(which is also connected to external coil522) via a series circuit561that comprises resistor562(R2) in series with an inductor564(L2).

The driver bridge541includes an input569that receives the signal531via input line552. The driver bridge541also comprises an enable input573configured to receive the enable signal529via enable signal line555. In other words, the driver bridge541is connected to the same input signal line and the same enable signal as the driver bridge540. The driver bridge541also comprises a first output574and a second output576. The first output574is directly connected to capacitor542(which is connected to external coil522) so as to bypass series circuit557. Similarly, the second output576is directly connected to capacitor544so as to bypass series circuit561.

In the embodiment ofFIG. 5, power and data are transmitted during non-overlapping and separate (i.e., different) time slots using the separate driver bridges540and541. As shown, the input signal531is a series of all ‘1’ values or consecutive RF cycles during a power time slot535. However, during a data time slot537, the input signal531switches between ‘1s’ and ‘0s’ (i.e., is a digital code representing the OOK modulation). The enable signal529is a logic signal that alternatives between a value of ‘1’ and ‘0.’ The enable signal529has a vale of ‘1’ during the power time slots535and a value of ‘0’ during the data time slots537.

Additionally, during the power time slots, the enable signal529is high (i.e., a ‘1’ value) so as to enable driver bridge541. As such, the outputs574and576, generated using input signal531, are used to drive external coil522. As noted, the input553of driver bridge540is an inverting input. Therefore, when the enable signal529is high, the inverting input553will cause the driver bridge540to interpret the enable signal529as low (i.e., ‘0’ value). This causes the outputs554and556of driver bridge540to be placed in a high impedance state.

During the data time slots, the enable signal529is low so as to cause the outputs574and576of driver bridge541to be placed in a high impedance state. However, when the enable signal529is low, the inverting input553will cause the driver bridge540to interpret the enable signal529as a high value. As such, the outputs554and556, generated using input signal531, are used to drive external coil522.

As noted above, the first output554is connected to external coil522via series circuit557(R1and L1) and the second output556is connected to external coil522via series circuit561(R2and L2). As such, when driver bridge540is enabled, the external coil522is driven with signals that pass through series circuit557and series circuit561.

Maximum power efficiency is obtained when the quality factor of the external resonant tank circuit525during the power time slot is maximized or RHPCis minimized. Additionally, the external coil current is maximized when the resonant frequency of the resonant tank circuit525during the power time slot is substantially equal or close to the operating frequency (f0) of the external coil522. Therefore, as noted above, during the power time slots, the bridge541is enabled to drive the external coil522with signals that pass directly from the outputs574and576to capacitors542and544, respectively. In this arrangement, the signals bypass the series circuits557(R1and L1) and561(R2and L2), thereby ensuring that the quality factor and resonant frequency of the external resonant tank circuit525are not affected by the series circuits557and561.

However, the data integrity improves when the external resonant tank circuit525is more dampened (i.e., has a lower quality factor) during data transmission. As such, during the data time slots, the driver bridge350is enabled so as to drive external coil522with signals that pass through the series circuit557(R1and L1) and series circuit561(R2and L2). That is, the series circuit557(R1and L1) and series circuit561(R2and L2) are placed in between the driver bridge540and the external coil522. Driving the external coil522via the series circuits557and561causes a drop in (i.e., damp) the quality factor of the resonant tank circuit525, the external coil current, and the resonance frequency.

In summary ofFIG. 5, the quality factor of the resonant tank circuit525is maximized during power transmission, but is purposely lowered during data transmission (i.e., Qext_data_timeslot<Qext_power_timeslot). The dampened external resonant tank circuit525reduces the ringing effects during one or more ‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOK modulation at fo. The series resistors558and562operate to dampen the external resonant tank circuit525when connected in series between the between the driver bridge540and the external coil522.

Additionally, it has also been discovered that the external coil current drops during the data time slot when the external resonant tank circuit525is tuned lower than the operating frequency. The lower the tuning frequency of the external coil522is relative to the operating frequency, the higher the decrease in current flow through the external coil522when the driver bridge540is acting as a pulsating voltage source. As described elsewhere herein, the decrease in the external coil current prevents interference of the implantable component load with the data recovery at the implantable component. In one example, the operating frequency of the external coil522is 5 MHz and the resonant frequency of the external resonant tank circuit525during data transmission (fres_data_timeslot) is set equal to 4.75 MHz). The series inductors560and564operate to reduce the resonant frequency of the external resonant tank circuit525when connected in series between the between the driver bridge540and the external coil522.

FIG. 6is simplified schematic diagram illustrating another external transmitter circuit620configured to separately transfer power and data signals to an implantable component via a single external coil622in accordance with embodiments presented herein. Similar to the embodiment ofFIG. 5, the external transmitter circuit620uses dedicated driver bridges for each of data and power transmission. However, in the embodiment ofFIG. 6, two (2) bridges are dedicated for use during power time slots, while a single separate driver bridge is used during the data time slots.

The external transmitter circuit620comprises a data driver bridge640and two power driver bridges641(1) and641(2). The external coil622is part of an external resonant tank circuit625that comprises capacitors642(capacitors C1, C2, and C3). The driver bridges640,641(1), and641(2) receive an input signal531(described above with reference toFIG. 5) and an enable signal529(also described above with reference toFIG. 5). The enable signal529is inverted before reaching data bridge640. The driver bridge640may be a half H-bridge driver, while the driver bridges641(1) and641(2) may be full H-bridge drivers.

During the power time slot535(FIG. 5), the full H-bridge drivers641(1) and641(2) are activated and the outputs of the full H-bridge drivers are used to drive the external coil622. At the same time, due to the inversion of the enable signal529, the half H-bridge driver640is deactivated and the outputs of the half H-bridge driver are placed in a high impedance state. Placing the full H-bridge drivers641(1) and641(2) in parallel to operate simultaneously lowers the conductive losses at the output (relative to a single driver arrangement), thereby further increasing the quality factor of the tank circuit.

During the data time slot537(FIG. 5) the half H-bridge driver640is activated and the outputs of the half H-bridge driver are used to drive the external coil622. As shown inFIG. 6, a resistor658and an inductor660are connected between the outputs of the half H-bridge driver640and the external coil622. The positioning of the resistor658and an inductor660between the half H-bridge driver640and the external coil622during data transmission will (1) dampen the resonant tank circuit625as described above and (2) lower the signal level of the data pulses received by the implant resulting in a non-conducting energy rectifier as described above.

As noted, backlink telemetry is possible in accordance with embodiments presented herein.FIG. 6illustrates a switch605that is closed when data is received at the external transmitter circuit620from an implantable component. In essence, the switch605bypasses the unidirectional driver bridges640,641(1), and641(2) during backlink telemetry. Similar switches may be present in the embodiments ofFIGS. 2A, 3, 4, and 5, but have been omitted from those FIGS. for ease of illustration.

In summary ofFIG. 6, the quality factor of the resonant tank circuit625is maximized during power transmission because the outputs of the full H-bridge drivers641(1) and641(2) are directly connected to the resonant tank circuit625. However, the quality factor of the resonant tank circuit625is purposely lowered during data transmission. The dampened external resonant tank circuit625reduces the ringing effects during one or more ‘0’ cycle transitions after a sequence of ‘1’ cycles during use of OOK modulation at fo. The resistor658operates to dampen the external resonant tank circuit625when connected in series between the between the driver bridge640and the external coil622.

Additionally, the external resonant tank circuit625is tuned lower than the operating frequency. As described elsewhere herein, the decrease in the external coil current prevents interference of the implantable component load with the data recovery at the implantable component. In one example, the operating frequency of the external coil622is 5 MHz and the resonant frequency of the external resonant tank circuit625during data transmission (fres_data_timeslot) is set equal to 4.75 MHz). The inductor660operates to reduce the resonant frequency of the external resonant tank circuit625when connected in series between the between the driver bridge640and the external coil622.

Embodiments have been primarily described above with reference to adjustments to the operational characteristics of an external resonant tank circuit. However, it is to be appreciated that adjustments to the operational characteristics of an implantable (internal) resonant tank circuit may be made in addition to, or in place of, the above adjustments to an external resonant tank circuit during the separated power and data transfer techniques.

More specifically,FIG. 7illustrates an implantable receiver circuit780configured to receive separate power and data signals transmitted by an external transmitter circuit (not shown). The implantable receiver circuit780comprises an implantable coil782that is part of an implantable (internal) resonant tank circuit785that also comprises capacitor794(capacitor C4) and capacitor796(capacitor C5). In practice, implantable coil792has an inductive component (LIPC)777and some small copper losses represented as the series resistive component (RIPC)779. The implantable receiver circuit780also comprises a data output781, a load783(i.e., battery or other energy storage device) connected between a power terminal785and a ground terminal787, and an energy rectifier784connected between the implantable coil782and the load783. In certain embodiments, the energy rectifier784is a diode.

The implantable receiver circuit780also comprises a resistor798and a switch799connected in parallel to the capacitor794. During a data time slot (i.e., when data is received at the implantable coil782), the switch799is closed. When the switch799is closed, the resistor798is connected to the implantable resonant tank circuit785. The resistor798operates to dampen the implantable resonant tank circuit785. In other words, the resistor798functions to reduce the quality factor of the implantable resonant tank circuit785during data reception.

In certain embodiments, a method for transmitting power from an external transmitter circuit to an implantable receiver circuit is provided. The external transmitter circuit comprises an external resonant circuit that includes an external coil, while the implantable receiver circuit comprise an implantable resonant circuit that includes an implantable coil. The method comprises driving the external resonant circuit with one or more driver bridges during a power time slot to cause the external coil to transfer power to the implantable receiver circuit. The method further comprises driving the external resonant circuit with one or more driver bridges during a data time slot to cause the external coil to transfer data to the implantable receiver circuit. The power and data time slots are different time slots and the external resonant circuit is driven such that the quality factor of the external resonant circuit is lower during the data slot than during the power time slot. In certain examples, the external resonant circuit and the implantable resonant circuit are resonant tank circuits.

In certain examples, the method further comprises driving the external resonant circuit with one or more driver bridges during the data time slot such that a resonance frequency of the external resonant circuit is adjusted during the data time slot so as to be lower or higher than the resonant frequency of the external circuit during the power time slots. In further examples, the method further comprises driving the external resonant circuit with one or more driver bridges during the data time slot such that a peak amplitude of current used to drive the external coil during the data time slots is lower than a peak amplitude of current used to drive the external coil during the power time slots.

In other examples, the implantable receiver circuit comprises an energy rectifier and the method further comprises driving the external resonant circuit with one or more driver bridges during the data time slot such that the peak amplitude of current used to drive the external during the data time slot is such that the energy rectifier does not allow current to pass there through during the data time slots.

As noted above, presented herein are techniques to separately transfer power and data from an external device to an implantable component using a single external coil and a single implantable coil. The external coil is part of an external resonant tank circuit, while the implantable coil is part of an implantable resonant tank circuit. The external coil is configured to transcutaneously transfer power and data to the implantable coil using separate power and data time slots. At least one of the external or internal resonant tank circuit is substantially more damped during the data time slot than during the power time slot.

The techniques presented herein provide high efficiency power transfers (e.g., 40% efficiency over a 12 mm thick skin flap thickness) without affecting the data integrity. High efficiently power transfers may reduce the number of implantable batteries needed, increase autonomy of the implantable component, and enable use of implantable components with larger skin flaps

In certain embodiments, the data link can be considered as a Magnetic Induction (MI) radio system over, for example, 5 MHz and could accept data from the bilateral implant during the data time slot. Additionally, ringing effects are substantially eliminated during data transfer due to the damped external tank circuit. The techniques presented herein may also provide stable waveforms shapes during data time slots received by the implant and almost independent of coupling factor, implant load, data time slot duration or frame occupation.

In certain embodiments, the data link can support other modulation types. As amplitude ringing is a phenomena typically observed in OOK modulation other modulation types such as FSK or PSK may also suffer from excessive phase ringing or distortion due to insufficient dampening during the data time slot.