Source: https://patents.google.com/patent/US9675809B2/en
Timestamp: 2018-07-18 09:19:17
Document Index: 407040588

Matched Legal Cases: ['Application No. 61', 'art 15', 'art 15', 'Application No. 15189806', '§ 1', 'Application No. 2841406']

US9675809B2 - Circuit, system and method for far-field radiative powering of an implantable medical device - Google Patents
Circuit, system and method for far-field radiative powering of an implantable medical device Download PDF
US9675809B2
US9675809B2 US13901874 US201313901874A US9675809B2 US 9675809 B2 US9675809 B2 US 9675809B2 US 13901874 US13901874 US 13901874 US 201313901874 A US201313901874 A US 201313901874A US 9675809 B2 US9675809 B2 US 9675809B2
US13901874
US20130253612A1 (en )
An isolated circuit including a RF input configured to receive a far field radiative powering signal and a rectified voltage output configured to provide a rectified voltage based on the received far field radiative powering signal. The isolated circuit also includes a first power assembly comprising a first impedance coupled to the RF input where the first impedance is provided, at least in part, by activating a first switch in response to the rectified voltage satisfying a first voltage threshold. The isolated circuit also includes a second power assembly comprising a second impedance coupled to the RF input where the second impedance is provided, at least in part, by activating the first switch and a second switch in response to the rectified voltage satisfying the first voltage threshold and a second voltage threshold, respectively.
This application claims priority to U.S. Provisional Application No. 61/665,687, filed on Jun. 28, 2012, entitled “Tuning A Matching Network To A Non-Linear Varying Rectifier Load For Far-Field Radiative Powering.” This application is also a continuation in part of U.S. Ser. No. 13/433,907, filed on Mar. 29, 2012, entitled “Far Field Radiative Powering Of Implantable Medical Therapy Delivery Devices,”; U.S. Ser. No. 13/434,119, filed on Mar. 29, 2012, entitled “Implantable Nerve Wrap For Nerve Stimulation Configured For Far Field Radiative Powering,”; and U.S. Ser. No. 13/434,240, filed on Mar. 29, 2012, entitled “Powering Of An Implantable Medical Therapy Delivery Device Using Far Field Radiative Powering At Multiple Frequencies,”, all of which claim priority to U.S. Ser. No. 61/507,992, filed on Jul. 14, 2011, entitled “Ultra-Miniature Leadless Pulse Generator For Implantation Next To The Vagus Nerve In The Neck,”, all of which are hereby incorporated by reference in their entirety.
The present disclosure is generally related to far field radiative powering and/or charging of implantable devices.
In a particular embodiment, an implantable medical device may include a first antenna configured to receive a first far field radiative signal in a first frequency band and may include a second antenna configured to receive a second far field radiative signal in a second frequency band. The implantable medical device may also include a voltage rectifier configured to rectify the received first far field radiative signal and the received second far field radiative signal to provide a rectified voltage signal. The implantable medical device may further include a charge storage element operative to receive the rectified voltage signal and to store charge responsive to the rectified voltage signal. The implantable medical device may also include a therapy delivery unit powered by the charge storage element. The therapy delivery unit may be operative to deliver a therapy to a patient.
In a particular embodiment, a method includes receiving a first far field radiative signal and a second far field radiative signal at an implantable medical device. The method may include rectifying the received first far field radiative signal and the received second far field radiative signal to provide a voltage. The method may also include charging a charge storage element of the implantable medical device responsive to the voltage. The method may further include providing a therapy to a patient using a therapy delivery unit of the implantable medical device. The therapy delivery may receive power from the charge storage element.
In a particular embodiment, an implantable medical device may include a multiband antenna configured to receive a first far field radiative signal in a first frequency band and to receive a second far field radiative signal in a second frequency band. The implantable medical device may also include a voltage rectifier configured to rectify the first far field radiative signal and the second radiative received by the multiband antenna to provide a rectified voltage signal. The implantable medical device may further include a charge storage element operative to receive the rectified voltage signal and to store charge responsive to the rectified voltage signal. The implantable medical device may also include a therapy delivery unit powered by the charge storage element. The therapy delivery unit may be operative to deliver a therapy to a patient.
In a particular embodiment, a system includes a first external transmitter configured to transmit a first far field radiative signal and a second external transmitter configured to transmit a second far field radiative signal. The system includes an implantable medical device configured to receive the first far field radiative signal and the second far field radiative signal. The implantable medical device may include a charge storage element that is operative to store a charge responsive to the received first far field radiative signal and the received second far field radiative signal. The implantable medical device may include a pulse generator powered by the charge storage element. The pulse generator may be operative to generate an electrical stimulation signal to stimulate a target tissue of a patient.
In a particular embodiment, an isolated circuit may include a RF input configured to receive a far field radiative powering signal and a rectified voltage output configured to provide a rectified voltage based on the received far field radiative powering signal. The isolated circuit also includes a first power assembly comprising a first impedance coupled to the RF input. The first impedance may be provided, at least in part, by activating a first switch in response to the rectified voltage satisfying a first voltage threshold. The isolated circuit also includes a second power assembly comprising a second impedance coupled to the RF input. The second impedance may be provided, at least in part, by activating the first switch and a second switch in response to the rectified voltage satisfying the first voltage threshold and a second voltage threshold, respectively.
In a particular embodiment, an implantable medical device may include an antenna, and a matching network coupled to the antenna where the antenna and the matching network together are configured to receive a far field radiative powering signal. The matching network may be configured to provide a matching impedance to the antenna. The implantable medical device may also include a voltage rectifier coupled to the matching network. The voltage rectifier may be configured to rectify the received far field radiative powering signal and to output a rectified voltage based on the received far field radiative powering signal. The implantable medical device may further include an impedance feedback circuit configured to adjust the matching impedance of the matching network based on the rectified voltage.
In a particular embodiment, and antenna assembly may include a receiving element configured to receive a far field powering signal and a load coupled to the receiving element, the load having a load impedance that varies non-linearly with variations in the far field powering signal. The load may include a matching network coupled to the receiving element and a voltage rectifier coupled to the matching network, where the voltage rectifier may be configured to output a rectified voltage based on the received far field radiative powering signal. The antenna assembly may also include an impedance feedback circuit configured to receive the rectified voltage from the voltage rectifier. The impedance feedback circuit may be configured to activate a first switch when the rectified voltage reaches a first rectified voltage threshold and to activate a second switch when the rectified voltage reaches a second rectified voltage threshold. The first switch may be configured to couple a first impedance to the load to adjust the load impedance when the first switch is activated and the second switch may be configured to couple a second impedance to the load to adjust the load impedance when the second switch is activated.
FIG. 10 is a diagram illustrating energy transfer using far field radiative signals for power generation with different amplitudes and on-times;
FIG. 11 is flow chart of a particular embodiment of a method of powering an implantable medical device using a far field transmitter;
FIG. 12 is a block diagram of another particular embodiment of a system including an implantable medical device and a far field transmitter, the implantable medical device including a first embodiment of an impedance matched far field radiative powering circuit;
FIG. 13 is a circuit diagram of a second embodiment of an impedance matched far field radiative powering circuit of an implantable medical device;
FIG. 14 is a circuit diagram of a third embodiment of an impedance matched far field radiative powering circuit of an implantable medical device;
FIG. 15 is a circuit diagram of a fourth embodiment of an impedance matched far field radiative powering circuit of an implantable medical device;
FIG. 16 is a circuit diagram of a fifth embodiment of an impedance matched far field radiative powering circuit of an implantable medical device;
FIG. 17 is a circuit diagram of a sixth embodiment of an impedance matched far field radiative powering circuit of an implantable medical device; and
FIG. 18 is flow chart of a particular embodiment of a method of tuning a matching network to a load that includes a non-linearly varying impedance.
Disclosed implantable medical devices may be used to treat various conditions by applying treatment to one or more tissues of a patient's body. To illustrate, an implantable medical device may be used to target neural tissue by inducing efferent or afferent action potentials in the neural tissue or by blocking intrinsic efferent or afferent action potentials in the neural tissue. For example, the implantable medical device may be used to target a vagus or trigeminal nerve to treat one or more conditions, such as epilepsy or other seizure inducing conditions. In another example, the implantable medical device may target an optic nerve to treat a vision condition or to supplement or facilitate use of a visual prosthesis for sight restoration. In another example, the implantable medical device may target a hypoglossal nerve to treat one or more conditions, such as sleep apnea. Although the examples above each relate to cranial nerves, the implantable medical device may be used to target another nerve or set of nerves rather than or in addition to a cranial nerve. For example, the implantable medical device may be used to target a sacral nerve to treat one or more conditions, such as to facilitate bladder control. In another example, the implantable medical device may be used to target a phrenic nerve to treat one or more conditions, such as to facilitate diaphragm or respiration control. In another example, the implantable medical device may be used to target one or more nerves of the spinal cord to treat one or more conditions, such as to facilitate pain management. Further, in addition to or instead of targeting a neural tissue, the implantable medical device may be used to target other tissue of a patient's body. For example, the implantable medical device may be used to stimulate a muscle to induce muscle contraction. To illustrate, the implantable medical device may target a heart muscle to act as a pacemaker. Other examples of conditions that may be treated using an implantable medical device that is at least partially powered by far field radiative power include, but are not limited to, traumatic brain injury and depression.
Electromagnetic energy may be described as propagating through a near field region in which the magnetic fields are relatively strong, a far field region in which the magnetic fields are relatively weak, and a transition region between the near field region and the far field region. Although there is no generally accepted firm boundary between these regions, as used herein, and as illustrated in FIG. 9, the near field region refers to a region within about one wavelength of a source of the electromagnetic energy (e.g., a transmitting antenna), and the far field region refers to a region two wavelength or more from the source of the electromagnetic energy. Thus, a magnetic field is likely to be insignificant in the far field region. Conversely, the magnetic field may dominate in the near field region. Non-radiative mechanisms, such as inductive or capacitive coupling, operate over a relatively short distance and may be used to transfer energy in the near field region. Non-radiative mechanisms generally operate based on the principle that a circulating current can produce a magnetic field component which can induce an opposing current in a nearby structure. The magnetic field dissipates rapidly with distance. Near-field interactions can be extremely complex because they are reactive. That is, a transmit structure and transmitted electromagnetic fields react to receive structures and electromagnetic absorption in the vicinity. Approximate relationships descriptive of the near field region indicate that the near-field magnetic field strength decreases with the inverse-cube of distance and the near-field electric field decreases with the inverse-square, and thus, the power density in the near field region decreases as the inverse of the distance to the fifth power. Accordingly, for sufficient distances typically around a wavelength or greater) the power quickly reduces to negligible levels. In contrast, for far-field radiative power transfer, the receive structure and its absorption does not affect the transmitter structure or the power output from the transmitter structure. The electric and magnetic fields from far-field radiative power transfer are better understood and both are inversely proportional to the distance and thus, the power is inversely proportional to the distance squared in the far field region.
From a clinical perspective, using non-radiative energy transfer may place limitations on the mobility of the patient and may lead to user error in patient populations. For example, non-radiative energy transfer mechanisms operate over a relatively short range and therefore require relatively short distances between an implanted medical device and an external charging device, which may limit patient mobility. Further, power may only be efficiently transferred via a non-radiative mechanism when a receiving component of the implanted medical device has a particular orientation with respect to a transmitting component of the external charging device. Maintaining this orientation can be difficult when the patient is moving (even breathing), which may further limit the patient's mobility.
Far field radiative signals 104 may be used to transfer power over a greater distance using radiative mechanisms. For example, the far field radiative signals 104 may transmit energy through free space using electrical fields propagating between a broad-beam external antenna and an internal antenna of the implantable medical device 106. This arrangement may allow greater freedom of placement for the external device 108 with respect to the patient. To illustrate, the external device 108 may be worn by or carried by the patient or may be positioned near the patient. As an illustrative example, when the implantable medical device 106 is implanted in the neck of the patient, the external device 108 may be worn by the patient, such as near the patient's upper arm or around the patient's neck. In another illustrative example, the external device 108 may include or be included within a mounted or table top power source.
F ⁢ ⁢ S ⁢ ⁢ P ⁢ ⁢ L = ( 4 ⁢ π ⁢ ⁢ d ⁢ ⁢ f c ) 2 = ( 32 ⁢ ⁢ π ⁢ ⁢ d ) 2 = ( 10 , 000 ) Eqn . ⁢ ( 1 )
F ⁢ ⁢ S ⁢ ⁢ P ⁢ ⁢ L ⁡ ( dB ) = ⁢ 10 ⁢ log ⁡ ( 4 ⁢ π ⁢ ⁢ d ⁢ ⁢ f c ) 2 = ⁢ 10 ⁢ log ⁡ ( 32 ⁢ ⁢ π ⁢ ⁢ d ) 2 = ⁢ 10 ⁢ log ⁡ ( 10 , 000 ) = ⁢ 40 ⁢ ⁢ dB Eqn . ⁢ ( 2 )
In a near-field region where magnetic fields are relatively strong, power transferred via a non-radiative mechanism, such as magnetic fields used by an inductive coil, may dissipate with distance. Further, power transfer via non-radiative mechanisms that rely on near-field interactions may react to receive structures and electromagnetic absorption in the vicinity. Magnetic fields used by an inductive coil may have a power transfer efficiency that is inversely proportional to the third power of the distance between the inductive coil and the patient. In contrast, power transfer by far field interactions is inversely proportional to the square of the distance between a far field transmitter and a patient. Therefore, far field power transfer enables greater efficiency of transfer of power across a far field region such that a transmitter structure or power output from the transmitter structure are not affected by a receive structure and its electromagnetic absorption.
In a particular embodiment, the implantable medical device 506 may use backscatter to transmit data to the far field transmitter 102 or another device. For example, the implantable medical device 506 may modulate backscattered energy in a manner that may be detected by a device external to the patient, such as the far field transmitter 102. In a particular embodiment, such as when the far field transmitter 102 continuously provides power to the implantable medical device 506, third order backscatter may be used to send information from the implantable medical device 506 to an external device. For third order backscatter, nonlinear components of the implantable medical device 506 may be used to generate a third order frequency harmonic component when exposed to energy of a particular frequency. For example, one or more diodes may be used as non-linear components. In this example, the diodes may be separate components or diodes of the voltage rectifier/multiplier 112 may be used to generate the third order frequency harmonic component. The third order frequency harmonic components may be modulated or enhanced to enable generation of a frequency component that is far removed from a fundamental frequency of the far field radiative signal 104. For example, a high-Q resonant circuit which is resonant around the third order frequency can be used to enhance the generation of this third order frequency harmonic component from the non-linear component. In another implementation, a high-frequency/radio-frequency amplifier, that maybe narrowband around the third order frequency harmonic component, can be used alone or in conjunction with the tuned high-Q resonant circuit, to enhance and amplify the third order frequency harmonic component. Thus, an external receiver (of the far field transmitter 102 or of another device external to the patient) may be able to tune to the third order frequency component without being saturated by the fundamental frequency, because the third order frequency component is sufficiently removed from the fundamental frequency so that power transmission and data transmission can occur at the same time (e.g., without time division duplexing the power transmission and data transmission). Because nonlinear components of the implantable medical device 506 naturally generate third order harmonics, modulation of such components to send information from the implantable medical device 506 to the external device may use little or no additional power.
The implantable medical device 806 also includes sensor circuitry 816. The sensing circuitry 816 may be powered by a charge storage element of the IMD power and control circuitry 618. The sensor circuitry 816 may be configured to receive a stimulus and to generate a digital or analog output corresponding to the stimulus. The stimulus may be electrical, optical, magnetic, chemical or physical. For example, the stimulus may correspond to or be indicative of presence or concentration of a chemical, such as a chemical that occurs naturally within a patient's body (e.g., a neurotransmitter, a hormone, blood oxygen, a metabolic product, etc.) or a foreign chemical (e.g., a medication). In another example, the stimulus may correspond to or be indicative of presence or other characteristics of an electrical signal, such as a naturally occurring electrical signal (e.g., an endogenous action potential) or an induced electrical signal (e.g., an induced action potential). In yet another example, the stimulus may correspond to or be indicative of presence or other characteristics of a physical function or parameter, such as a movement of the body or a portion of the body, respiratory rate, pulse rate, blood pressure, body temperature, etc.
In a particular embodiment, the implantable medical device 806 does not include a therapy delivery unit and is only used to gather and transmit sensed data from the patient's body. Thus, the far field radiative signals 802 may be used to power an implantable medical device that is a sensor or is primarily used as a sensor.
In addition to being designed for efficient power transfer, the implantable medical device 106, 206, 306, 406, 506, 606, 706, 806 may be designed to reduce power consumed to provide therapy. For example, parameters of the therapy may also be controlled (e.g., by the control unit 320) or configured to reduce power consumption. To illustrate, a strength duration curve of nerve fibers to be stimulated may be consider to enable reduced power consumption. The strength duration curve is a relationship between current and pulse width of a therapeutic signal. When applying stimulation to a nerve fiber using the therapeutic signal, as the duration of stimulus decreases, the applied current has to increase to bring the nerve fiber to a threshold potential. The current and pulse width of the therapeutic signal may be selected to efficiently provide energy to the nerve fiber.
Although only one implantable medical device is shown in each of FIGS. 1-9, a far field transmitter may be used to provide power to more than one implantable medical device at a time. For example, a patient may have two or more implantable medical devices that receive at least a portion of their operating power from the far field transmitter. With inductive power coupling, as opposed to far field radiative power transfer, power coupling is targeted to a relatively small area. Accordingly, it may be difficult or impossible to use inductive coupling to provide power to implantable medical devices at different locations of a patient's body (e.g., one proximate a left vagus nerve and one proximate a right vagus nerve) with a single external inductive powering unit. However, using far field radiative signals enables providing power to such implantable medical devices using a single far field transmitter even though the implantable medical devices are remotely located from one another.
Additionally or in the alternative, a single implantable medical device 106, 206, 306, 406, 506, 606, 706, 806 (and possibly one or more other implantable medical devices) may be supplied with at least a portion of its operating power from two or more far field transmitters 102. For example, a first far field transmitter may supply power to the implantable medical device 106, 206, 306, 406, 506, 606, 706, 806 when the patient is at a first location (e.g., a first room of the patient's home) and a second far field transmitter may supply power to the implantable medical device 106, 206, 306, 406, 506, 606, 706, 806 when the patient is at a second location (e.g., in a second room of the patient's home).
Efficiency of the power transfer may also be improved by designing or tuning the antenna using an accurate 3D high-frequency electromagnetic model and an accurate human RF phantom. For example, a trial-and-error type procedure in which multiple different antenna types and geometries are tested (e.g., a simulation using an optimization search heuristic with the 3D high-frequency electromagnetic model and the human RF phantom) may be used to select a suitable antenna design. Additionally, simulation or physical testing may be used to tune the antenna. For example, resonance frequency seeking may be used to tune a resonant frequency of the antenna to provide efficient power transfer. Further, the antenna and matching network may be actively or passively tuned to provide efficient power transfer. To illustrate, the antenna may be tuned using a varactor that is arranged to change an effective electrical length of the antenna. In another example, a varactor, one or more inductors, one or more capacitors, or a combination thereof may be used to tune the matching network.
As illustrated in FIG. 9, and as described above, a distance, d, 916 between the far field transmitter 902 and an antenna 908 of the implantable medical device 906 may be greater than twice a wavelength, .lamda., 918 of the far field radiative signals 904. In the embodiment illustrated in FIG. 9, the far field radiative signals 904 are pulsed. That is, the far field radiative signals 904 have on-times 910 during which electromagnetic waves are generated, and off-times 914 during which no electromagnetic waves are generated. During a particular on-time 910, a burst 912 of energy may be transmitted. As used herein, the frequency of the far field radiative signals 904 refers to a frequency of electromagnetic waves of the burst 912. Relative timing of the on-times 910 and off-times 914 is referred to herein with reference to a duty cycle of the far field radiative signals 904. The pulsed far field radiative signals 904 may have an average transmission power of 1 watt or less. The pulsed far field radiative signals 904 may have a duty cycle of 10% or less, 5% or less, 2% or less, 1% or less, 0.5% or less, 0.266% or less, or 0.2% or less. Each burst 912 of the pulsed far field radiative signals 904 may deliver 100 milliwatts or less of power at the antenna 908. For example, each burst 912 may deliver 50 milliwatts or less, 30 milliwatts or less, 20 milliwatts or less, 10 milliwatts or less, 5 milliwatts or less, or 1 milliwatt or less of power at the antenna 908. During operation, an average input power at the antenna 908 may be 53 microwatts or less and the implantable medical device 906 may have a power conversion efficiency of 11.3 percent or less.
Additionally, Schottky diodes are non-linear components that operate more efficiently the further they are forward biased. The non-linear characteristics of Schottky diodes can be described by a relationship of current to forward bias:
I≈I 0 ·e V F /(nV T ) Eqn (3)
Where I is current that the diode can pass (diode current), h is reverse bias saturation current, n is a number that depends on a substrate of the Schottky diodes (e.g., about 1-2 for silicon) and VT is thermal voltage which is about 26 mV for room temperature, VF is the forward bias voltage. Thus, as the forward bias voltage, VF, increases, the current that the diode can pass, I, increases exponentially. Considering Ohm's Law, V=IR, or R=V/I, as the voltage increase linearly, the resistance/impedance will decrease exponentially. Thus, the rectifier/multiplier circuit will “impede” the current/power flowing through it less as the forward bias voltage is increased. Stated another way, the diodes behave more like shorts as the forward bias voltage increases, thereby increasing the overall efficiency of the diodes.
Impedance Matched, Far Field Radiative Powering of an Implantable Medical Device
Far field radiative signals to power or charge an implantable medical device may facilitate miniaturization of the implantable medical device by reducing on-board power storage requirements. Far field radiative powering, alone or in combination with miniaturization of the implantable medical device, may reduce the complexity of implant procedures, and may enable use of the implantable medical device in new areas of the body.
Several challenges exist in the field of far-field radiative powering. One of the challenges arises out of a loss in powering efficiency as the impedance of the load, which includes the rectifier circuit (or voltage rectifier), varies in a non-linear fashion. The impedance of the load may vary as a result of changes in the powering signal received. The changes in the powering signal may result from various factors, for example, a change in distance between the transmitter and receiver, physical obstructions between the transmitter and receiver including a change in transmission medium properties, interference from other signals, changes in orientation of the transmitter and receiver, fluctuations in the transmission power (e.g., if the transmitter is battery operated and the battery is close to depleted), or any other factor that may cause the powering signal seen at the receiver to vary from what the antenna and matching network were designed to receive. As the powering signal seen at the receiver causes the impedance of the load to vary from the value the circuit was designed for, the powering efficiency of the circuit decreases.
Challenges also exist in powering implantable medical devices. For example, some degree of efficiency may be lost as the impedance of the load of the implantable medical device circuitry changes. The impedance of the load, which includes a voltage rectifier circuit, may vary after implantation of the device and throughout use of the device. Upon implantation, the impedance seen by the antenna used to receive the power will change. The impedance seen by the antenna is affected by the dielectric properties of the antenna's surrounding environment. Since biological tissue has significantly different dielectric properties than air, the impedance seen by the antenna changes upon implantation. Throughout the use of the device, the implanted antenna may continue to experience some variations in seen impedance due to changes in the surrounding biological tissue.
The impedance of the load of the implantable medical device may also vary as a result of changes in the powering signal received, for example, due to the power level being sufficient enough to forward bias the diodes in the voltage rectifier circuit, and the corresponding non-linear impedance variation of those diodes or other nonlinear elements. Variations in the powering signal may result from various factors, for example but not limited to, a change in distance between an external transmitter antenna and internal receiver antenna, physical obstructions between the transmitter antenna and receiver antenna (e.g., a change in transmission medium properties), interference from other signals, changes in orientation of the transmitter and receiver antennas, fluctuations in the transmission power (e.g., if the transmitter is battery operated and the battery is close to depleted), or any other factor that may cause the powering signal seen at the receiver antenna to vary from what the receiver antenna is designed to receive. As the powering signal seen at the receiver antenna causes the impedance of the load to vary from the value the circuit was designed for, the powering efficiency of the circuit decreases.
Far field radiative powering applications may operate at very low power levels and some closed loop feedback systems for responding to impedance variations of the load may consume too much power to be practical for many applications.
A closed loop feedback system may be implemented to adjust the impedance of the load in response to variations in the received powering signal while consuming very little power. In one embodiment, a closed loop feedback system may include an antenna, a matching network, a rectifier circuit, other circuitry, circuitry to cause switches to turn on at predetermined voltage levels (V1-VN) of the output of the rectifier circuit, switches configured to couple impedance to the matching network, and impedances Z1-ZN. For example, one or more antennas may be coupled to a matching network and configured to receive a far field radiative powering signal. The output of the matching network may then be provided to the rectifier circuit input at VIN. The rectifier circuit may be a full-wave bridge rectifier and may use, for example, low threshold voltage diodes (e.g., Schottky diodes). The threshold voltage for the Schottky diodes may be about 0.4V or less. The output of the rectifier circuit VOUT may be provided to other circuitry, such as, but not limited to, a boost converter, a multiplier, a DC-to-DC converter, a charge storage element, a signal generator, and a control unit.
The output of the rectifier may also be fed to multiple circuits that cause switches to turn on when the output of the rectifier reaches one or more predetermined voltage levels. The circuits that cause the switches to turn on may be voltage dividers that provide switching voltages to switches. In some embodiments, the voltage dividers may use transistors having ratios to control the voltages provided to switches. The switches may be transistors and the switching voltage may be provided to the gates of the switch transistors.
The gate width and/or length of the transistors in the voltage dividers may be scaled to provide a different turn on voltages, or voltage thresholds, for the switch transistors. The transistors of the voltage divider may be provided in a diode configuration. In other embodiments, transistors of the same size may be added in parallel rather than scaling the gate width of a transistor to provide a different turn on voltage for each switch transistor. The transistors of the impedance divider may also be configured in series to create different turn on voltages. Configurations other than diode configured transistors may be used to provide different turn on or off voltages for the different switches, for example, off transistors, and/or sub-threshold transistors may be used. The voltage divider may also be implemented using linear components, such as resistors, non-linear components, or a combination thereof. In some embodiments, the closed loop (or varying impedance) feedback circuitry could use resistors controlling a bank of micro-electromechanical (MEMS) switching to couple and decoupled impedances to the matching network as the output of the rectifier circuit changes.
When the switch turns on, the impedance coupled in series with the switch, such as a capacitor, is connected to the matching network input and/or output to change the matching. The impedance may be a non-linear element, a linear element, or a combination thereof. For example, the impedance may include a diode, a transistor, a capacitor, an inductor, a resistor, or a combination thereof. The voltage levels V1-VN which cause the switches to open or close may be selected to vary linearly with respect to one another or non-linearly (e.g., in a logarithmic fashion or any other type of non-linear manner). The impedance values Z1-ZN may be selected to be approximately equal, may vary linearly with respect to one another, or may vary non-linearly. The matching network may be a Pi configuration, T configuration, L configuration, or any other type of matching network configuration.
A closed loop feedback system in accordance with embodiments of the present disclosure may be implemented to adjust the impedance of the load in response to variations in the received powering signal while consuming very little power.
In another embodiment, the matching network may be adjusted or tuned as a function of the received power using a feedback approach, and employ switches to switch on and off components to adjust the overall impedance of the matching network. The output of a voltage rectifier may be fed to multiple circuits that cause switches to close or open when the output of the voltage rectifier reaches one or more predetermined voltage levels. The circuits that cause the switches to close or open may be implemented, for example, as voltage dividers that provide switching voltages to switches. In some embodiments, voltage dividers may employ transistors having ratios to control the voltage provided to switches. The switches may be transistors and the switching voltage may be provided to the gates of the switch transistors.
Referring to FIG. 12, a block diagram is provided according to one embodiment of a far field powering system 1200 including an implantable medical device 1206 coupled to an external device 108. The external device 108 includes a far field transmitter 102 that powers the implantable medical device via far field radiative signal 104. The far field powering system 1200 may be similar to the systems of FIGS. 1-8, and includes an antenna 109, a matching network 110, a rectifier circuit (or voltage rectifier) 112, a charge store element 114 and a therapy delivery unit 116. The far field powering system 1200 may also include impedance feedback circuit 1211. An electrode 115 may also be coupled to the implantable medical device 1206 and the target tissue 130.
The far field powering system 1200 may be a closed loop feedback system that dynamically adjusts the impedance of the load seen at the antenna 109. The antenna 109, the matching network 110, the impedance feedback circuit 1211, the voltage rectifier 112, and the charge store element 114 of the implantable medical device 1206 are operatively connected to form the impedance (or load) matched far field radiative powering circuit 1207 (e.g., the impedance seen at the antenna). The implantable medical device 1206 employs the impedance feedback circuit 1211 to adjust the effective the impedance of the load seen at the antenna 109 of the implantable medical device 1206 in response to variations in the received far field radiative signal 104. These adjustments may be made while consuming little power.
FIG. 13 is a circuit diagram of a second embodiment of an impedance matched far field radiative powering circuit 1307 usable in an implantable medical device. The circuit 1307 includes a receiving element such as the antenna 109, the matching network 110, the voltage rectifier 112, circuitry 114′, and impedance feedback circuit 1311. The impedance feedback circuit 1311 may cause variable impedance devices to be switched in or out of the matching network 110 in response to voltage changes in the impedance matched far field radiative powering circuit 1307.
The circuit 1307 couples the antenna 109 to the matching network 110, as described above. The matching network 110 (variations of which are described below) is also coupled to the input (VIN) of the voltage rectifier 112 (as described above with respect to FIG. 1) and to the impedance feedback circuit 1311. The impedance feedback circuit 1311 is also coupled to the output (VOUT) of the voltage rectifier 112. The output of the voltage rectifier 112 is also coupled to the circuitry 114′.
In an embodiment, the impedance feedback circuit 1311 may be a bank of parallel variable impedance devices 1332 (e.g., switches, transistors, capacitors, voltage dividers, and/or other electrical devices) that switch in and out impedances to adjust the overall impedance of the matching network 110. In an embodiment, VOUT is provided from the voltage rectifier 112 to a bank of 1 through N of parallel variable impedance devices 1332. In the embodiment of FIG. 13, each variable impedance device 1332 includes a threshold detector 1334 that detects a designed voltage (VN), a transistor 1336 (a switch), and an impedance element 1338.
The voltage output (VOUT) of the voltage rectifier 112, as it rises or falls, causes one or more of the switches 1336 to individually close or open (sequentially, or simultaneously, depending on the configuration) when the output voltage of the voltage rectifier 112 reaches a voltage threshold for each threshold detector 1334. This relationship is set forth in the following equation (4):
VOUT=VN Eqn. (4)
Equation (4) is applied for 1 through N number of variable impedance devices 1332. When any of the threshold detectors 1334 detects a threshold crossing, the corresponding transistor 1336 switches in or out the impedance element 1338 in parallel with the matching network and the voltage rectifier 112. The variable impedance device 1332 may include various known circuit components or impedance devices (e.g., a resistor, inductor, capacitor, diode, transistor, or other circuit element) having an impedance value Z1-ZN for 1 through N number of variable impedance devices 1332.
When the voltage output VOUT of the voltage rectifier 112 reaches VN, where VN is the threshold voltage operable to trip the Nth threshold detector 1334 for any given threshold detector 1334 in the bank of variable impedance devices, the transistor 1336 electrically connects the impedance ZN of impedance device 1338 in parallel with the matching network 110 and the voltage rectifier 112, thereby adjusting the overall effective impedance of the circuit 1307. The number N of variable impedance devices 1338 may be determined based on the degree of tunability sufficient for matching the impedance of the voltage rectifier 112 to the antenna 109.
As shown in FIG. 13, the impedance feedback circuit 1311 may cause the transistor switches 1336 to open or close at predetermined voltage levels (V1-VN) of the output of the voltage rectifier 112. For example, threshold detectors 1334 may be configured to trip at voltages V1-VN, which would then switch in or out impedances Z1-ZN. The voltage levels V1-VN that cause the switches to open or close may be selected to vary linearly with respect to one another, or non-linearly. The impedance values Z1-ZN may be selected to be approximately equal, may vary linearly with respect to one another, or may vary non-linearly.
The threshold detectors 1334 may be configured to cause the transistor 1336 to switch on at a particular input voltage V1-VN. In an embodiment, the threshold detectors 1334 may cause the transistor switch 1336 to close when the voltage output of the voltage rectifier reaches one or more predetermined voltage levels. When each switch 1336 turns on, the impedance element 1338 coupled in series with the switch 1336 is connected to the matching network input and/or output to change the matching. The voltage output VOUT of the voltage rectifier 112 may be provided to the circuitry 114′. The voltage output VOUT of the voltage rectifier 112 may also be provided to the impedance feedback circuit 1311.
In the embodiment shown in FIG. 13, any number of variable impedance devices 1332 and/or switches 1336 (or other voltage dividers) could be selected from any type of electrical or mechanical switching device to couple and decouple impedance to the matching network 110. The impedance device 1332 may employ a non-linear element, a linear element, or a combination thereof. For example, the impedance of the impedance device 1332 may be a diode, a transistor, a capacitor, an inductor, a resistor, or a combination thereof.
The circuitry 114′ may be the charge storage element 114 and/or other circuitry, such as a boost converter, multiplier circuit, a DC-to-DC converter, a signal generator, a control unit, a feedback controller, step-up regulator, or the like. For example, the circuitry may include a boost converter positioned between the voltage rectifier 112 and charge storage element 114 to improve efficiency. If a boost converter is used, an effective input impedance for the boost converter may be taken into account when sizing the voltage threshold characteristics of the impedance feedback circuit 1311. The voltage feeding the threshold detectors 1334 can be taken either from the output of the voltage rectifier 112 or the boost converter output.
In some embodiments, the circuit 1307 (not including circuitry 114′) may be an isolated circuit in that no other inputs apart from the RF input(s) are provided to the circuit 1307. The isolated circuit may be used to power the circuitry 114′ where the circuitry may include a charge storage element that is charged by the circuit 1307. Various power assembly configurations may be used where each power assembly corresponds to different combinations of activated switches causing impedance devices associated with the activated switches to couple to the RF input. The switches are responsive to the output voltage of the rectifier circuit 112 and may each be activated at different voltage thresholds of the rectified voltage.
FIG. 14 is a circuit diagram of a third embodiment of an impedance (or load) matched far field radiative powering circuit 1407 of an implantable medical device. The circuit 1407 is the same as the circuit 1307 of FIG. 13, except that impedance feedback circuit 1411 and the matching network 110 have been relocated. In this embodiment, the impedance feedback circuit 1411 is in parallel with the matching network 110 and the voltage rectifier 112.
When the voltage output VOUT provided by the voltage rectifier 112 reaches VN, the threshold voltage operable to trip the Nth threshold detector 133, for any given detector 133 in the bank of variable impedance devices 1332, the transistor 1336 electrically connects the impedance ZN 1338 in parallel with the voltage rectifier 112 and the matching network 110, thereby adjusting the overall effective impedance of the circuit. As in FIG. 13, the output voltage (VOUT) of the voltage rectifier 112 may be provided to the circuitry 114′, as well as fed back to the impedance feedback circuit 1411. In a numerical example of a design in accordance with FIG. 14, the voltage turn-on ratio for each variable impedance device 1332, from right to left, may be twice the turn-on voltage for the most adjacent variable impedance device 1332.
FIG. 15 is a circuit diagram of a fourth embodiment of an impedance (or load) matched far field radiative powering circuit 1507 of an implantable medical device. This embodiment may be a variation of the circuit diagrams of FIGS. 13 and 14. As in FIG. 14, the output of the matching network 110 is also the input VIN to the voltage rectifier 112. In this embodiment, the impedance feedback circuit 1511 includes two banks 1515, 1516 of impedance devices 1332.
The impedance feedback circuit 1511 is present in two parallel branches, one bank 1515 of variable impedance devices 1332 is in parallel with the matching network 110, and a second bank 1516 of variable impedance devices 1332 is in parallel with the voltage rectifier 112. The first bank 1515 is connected in parallel to the antenna 109 and the matching network 110 as shown in FIG. 14. The first bank 1515 of the impedance devices 1332 is configured in the same way as the impedance feedback circuit 1311 of FIG. 13. The second bank 1516 of the impedance devices 1332 is configured in the same way as the first bank 1515, except that the second bank 1516 is connected in parallel to the VIN of the rectifier circuit 112.
As the input to the voltage rectifier 112 rises, the first bank 1515 of impedance devices 1332 of impedance feedback circuit 1511 that are in parallel with the matching network 110 are individually turned on and coupled to the input of the matching network. Likewise, as the output of the voltage rectifier 112 rises, the variable impedance devices 1332 of the second bank 1516 that are in parallel with the voltage rectifier 112 are individually turned on and coupled to the input of the voltage rectifier 112. As in FIG. 13, the output voltage of the voltage rectifier 112 may be provided to the circuitry 114′, and fed back to the impedance feedback circuit 1511. Placing a plurality of variable impedance devices 1332 in parallel with both the matching network 110 and the voltage rectifier 112 may offer a finer degree of tunability of the overall impedance of the load seen at the antenna 109.
FIG. 16 depicts a fifth embodiment of an impedance (or load) matched far field radiative powering circuit 1607 of an implantable medical device. This embodiment may include a bank of parallel capacitors that are switched in and out to adjust the overall impedance of the matching network. The circuit 1607 may be the same as the circuit 1307 of FIG. 13, except that the circuit 1607 employs a modified (or detailed) matching network 110′, impedance feedback circuit 1611 and a modified (or detailed) voltage rectifier 112′. The circuitry 114′ is not shown, but may also be provided. The feedback 1611 is coupled in parallel between the matching network 110′ and the voltage rectifier 112′. The impedance feedback circuit 1611 may provide impedance matching to a non-linear varying impedance of the rectifier for far-field radiative powering.
FIG. 16 depicts an example configuration of a matching network 110′ and an example configuration of a voltage rectifier 112′. The matching network 110′ is coupled to antenna 109, and includes an inductor 1619 with impedance Z and a capacitor 1620 with capacitance C in a matching configuration. The matching network 110′ may be in a variety of matching configurations, such as a Pi configuration, T configuration, L configuration, or any other type of matching network configuration. In some embodiments, the voltage rectifier 112′ may include diodes (e.g., Schottky diodes) 1623 and capacitors 1621 to convert the received far field power generating radiative signal into a DC voltage. Examples of rectifiers are described in U.S. Patent Publication, 2013/0018438, commonly assigned with the present disclosure, the entire contents of which is hereby incorporated by reference in its entirety.
In the embodiment of FIG. 16, the impedance feedback circuit 1611 includes a transistor bank threshold detector 1644 and an impedance switch circuit 1642. The impedance feedback circuit 1611 is positioned in parallel between the matching network 110′ and the VIN of the voltage rectifier 112′. The diode-connected transistors 1646 and 1648 may have pre-selected voltage turn-on ratios to control the voltage fed to the impedance switch circuit 1642. The impedance switch circuit 1642 may be used to control when the impedance, such as capacitor 1624, is put in parallel with the matching network 110′ and the voltage rectifier 112′.
The impedance switch circuits 1642 are depicted as being coupled to each of the transistor bank threshold detectors 1644. The voltage rectifier 112′ provides a voltage Vo+ (VOUT) to each of the transistor bank threshold detectors 1644. In some embodiments, an additional impedance switch circuit 1642 is provided at the end of the impedance feedback circuit 1611 without a transistor bank threshold detector 164 and is coupled to the output of the voltage rectifier 112′. A specific configuration is depicted in FIG. 16, however, N or N−1 number of transistor bank threshold detectors 1644 and N number of impedance switch circuits 1642 may be used.
When a switch transistor 1640 of the impedance switch circuit 1642 turns on (or is activated), a corresponding impedance, such as capacitor 1624, is coupled in series with the switch transistor 1640 and is connected to the matching network 110′ in parallel to adjust the impedance of the matching network 110′. Optionally, using low threshold voltage transistors for the switch transistors 1640 would extend the lower range limit. As shown, diode-connected transistors 1646 and 1648 can be used to create a high impedance inter-digitated layout, to ensure matching and a pre-determined voltage dividing ratio (e.g., ratio between diode-connected transistors 1646 and 1648) that controls the switch transistors 1640. For example, a gate width of each diode-connected transistor 1646 may be scaled to provide each transistor bank threshold detector 1644 with a different gate width ratio between diode-connected transistors 1646 and 1648. FIG. 16 shows a gate width scaling of 16, 8, 4, and 2 respectively for the transistor bank threshold detectors 1644 shown. Different scaling factors, schemes, dimensions, as so on, may be used to achieve any number of turn on voltages for the impedance switch circuits 1642. Using transistors for a voltage divider has the benefit of a relatively small layout area and lower power consumption during operation; however, other circuit elements may be used along with, or in place of transistors.
FIG. 17 is a circuit diagram of another embodiment of an impedance (or load) matched far field radiative powering circuit 1707 in an implantable medical device. The circuit 1707 is the same as the circuit 1607, except that the voltage rectifier 112 is depicted in a simplified form and circuitry 114′ is depicted as a charge storage device, such as a charge storage capacitor 1650. As demonstrated by this figure, the circuit 1707 may be used with any voltage rectifier.
In FIG. 17, the matching network 110′ may be coupled to a voltage rectifier 112 for far-field radiative powering, where the voltage rectifier 112 has a non-linear varying impedance. The antenna 109 couples to the matching network 110′ and impedance feedback circuit 1711. In some embodiments, a charge storage device, such as the charge storage capacitor 1650, may be connected to the output node of the voltage rectifier 112 for power storage. The impedance of the capacitor 1650 will change as the voltage on the top plate rises, and the impedance variation of the non-linear voltage rectifier 112 and capacitor 1650 can be simultaneously compensated for by this technique.
The impedance feedback circuit 1711 includes a transistor bank threshold detector 1641 and an impedance switch circuit 1642. Diode-connected transistors 1646 and 1648 may have pre-selected voltage turn-on ratios to control the voltage fed to the impedance switch circuit 1642. When the turn-on voltage threshold for each impedance switch circuit 1642 is reached, a corresponding impedance, such as a capacitor 1624, is put in parallel with the voltage rectifier 112 and the matching network 110′ to alter the impedance matching.
In some embodiments, the threshold detectors may use transistors or other devices as voltage dividers. The transistors may have ratios to control the voltages provided to switches. The switches may be transistors and the switching voltage may be provided to the gates of the switch transistors. The gate width and/or length of the transistors in the voltage dividers may be scaled to provide different threshold or turn on voltages for the switch transistors. The transistors of the voltage divider may be provided in a diode configuration. The impedances in the voltage divider may utilize the transistors in the sub-threshold region, which may further optimize the overall power.
In other embodiments, transistors of the same size may be added in parallel rather than scaling the gate width of a transistor to provide a different threshold voltage for each switch transistor. The transistors of the voltage divider may also be configured in series to create different threshold voltages. Configurations other than diode-configured transistors may be used to provide different threshold voltages for the different switches, for example, off transistors, and sub-threshold transistors may be used. The voltage divider may also be implemented using linear components, non-linear components, or a combination thereof. The impedance feedback circuitry may comprise circuits that cause the switches to close (or open). For example, the circuits that cause the switches to close (or open) may be voltage dividers that provide switching voltages to switches. Various combinations of the circuits, implantable medical device, and other features described herein may be used.
FIG. 18 is flow chart of a method 1800 of tuning a matching network to a load that includes a non-linear varying impedance of a voltage rectifier. The implantable medical device may correspond to any of the implantable medical devices of embodiments or variants described above. The method 1800 involves, receiving a far field radiative powering signal from an external device at an antenna, at 1840. The method further includes, rectifying the far field radiative powering signal at a voltage rectifier to provide a rectified voltage, the voltage rectifier comprising a non-linearly varying impedance, at 1842. The method further includes providing the rectified voltage to an impedance feedback circuit, at 1844, and selectively coupling one or more impedance devices from a bank of impedance devices to a matching network based on the rectified voltage satisfying one or more voltage thresholds, at 1846. The impedance selectively coupled to the matching network improves the impedance match of the antenna and matching network to the non-linearly varying impedance of the voltage rectifier, where the impedance of the voltage rectifier varies non-linearly with variations in the received far field radiative powering signal.
The method may also involve providing the rectified voltage to a charge storage element to charge the charge storage element and powering a therapy delivery unit configured to deliver a therapy to a target tissue of the patient. The method may be performed in any order and repeated as desired.
A method for adjusting the impedance of the matching network to non-linear variations in the voltage rectifier impedance may include, receiving a far field radiative powering signal at a matching network from an antenna coupled to the matching network, the matching network configured to provide a matching impedance to the antenna. The method further includes providing the far field radiative powering signal to a voltage rectifier coupled to the matching network, where the voltage rectifier is configured to output a rectified voltage. The method further includes adjusting the matching impedance of the matching network to a first matching impedance in response to the rectified voltage satisfying a first voltage threshold and adjusting the matching impedance of the matching network to a second matching impedance in response to the rectified voltage satisfying a second voltage threshold. Adjusting the matching impedance of the matching network to the first matching impedance in response to the rectified voltage satisfying the first voltage threshold may include activating a first switch when the rectified voltage is at the first voltage threshold to couple a first impedance to the matching network to adjust the matching impedance to the first matching impedance. Further, adjusting the matching impedance of the matching network to the second matching impedance in response to the rectified voltage satisfying the second voltage threshold may include activating the first switch and a second switch when the rectified voltage is at the second voltage threshold to couple the first impedance and a second impedance to the matching network, respectively, to adjust the matching impedance to the second matching impedance, where the second voltage threshold is higher than the first voltage threshold. In some embodiments, the first switch may be a first transistor and the second switch may be a second transistor.
In some embodiments, a first voltage divider may be coupled to the second transistor, where activating the second transistor may include dividing the rectified voltage at the first voltage divider to provide a first divided rectified voltage to the second transistor and activating the second transistor with the first divided rectified voltage, the first divided rectified voltage reaching a level to activate the second transistor when the rectified voltage is at, or above, the second voltage threshold.
The method may also include adjusting the matching impedance of the matching network to a third matching impedance in response to the rectified voltage satisfying a third voltage threshold, where adjusting the matching impedance of the matching network to the third matching impedance in response to the rectified voltage satisfying the third voltage threshold may include activating the first switch, the second switch, and a third switch when the rectified voltage is at the third voltage threshold to couple the first impedance, the second impedance, and a third impedance to the matching network, respectively, to adjust the matching impedance to the third matching impedance, wherein the third voltage threshold is higher than the second voltage threshold. In some embodiments, the third switch may be a third transistor and a second voltage divider may be coupled to the third transistor. In some embodiments, activating the third transistor may include dividing the rectified voltage at the second voltage divider to provide a second divided rectified voltage to the third transistor and activating the third transistor with the second divided rectified voltage, the second divided rectified voltage reaching a second level to activate the third transistor when the rectified voltage is at, or above, the third voltage threshold. The method may include any number of switches and corresponding impedances. In some embodiments, the voltage divider may include diode connected transistors.
While the present embodiments have been described with respect to implantable medical devices, applications of the present tunable matching network are envisioned to extend to other applications equally, including, but not limited to: any type of wireless sensor, powered in whole or in part (supplemental) by one or more far-field radiative signals; any type of wireless device that provides an open loop or closed loop action/response (e.g., switch, actuator, stimulator, signal generator); medical devices including implantable medical devices that employ a sensor for sensing any type of body parameter (e.g., pulse, blood pressure, respiration, action potentials, temperature), implantable medical devices that provide stimulation of any type of tissue including vagus nerve stimulation, cochlear implants, trigeminal nerve stimulation, deep brain stimulation; external medical devices; handheld devices including cell phones, smart phones, personal digital assistant (PDA), digital music players (e.g., MP3 players, iPod), portable audio electronics, vehicle media systems; powering handheld components while driving to extend life of components; providing powering in hostile environments and conditions sensors/actuators such as an engine or other vehicle system (e.g., tire pressure), drilling/exploration systems for natural gas and petroleum, aerospace applications (e.g., spacecraft, satellites); helicopter blade; smart dust or spy flies or other type of wireless powered miniature unmanned aerial vehicle (UAV); energy harvesting; and wireless powered lighting.
Embodiments disclosed herein enable efficiently providing power to an implantable medical device over a relatively long distance. Further, embodiments disclosed herein enable the implantable medical device to be relatively small since a charge storage element of the implantable medical device only needs to be large enough to store enough energy for a single treatment or relatively small number of treatments. Such embodiments may provide effective screening tools to determine whether a particular type of treatment will be effective for a particular patient. For example, vagus nerve stimulation is believed to be effective on about half of a particular candidate patient population. Currently methods of providing vagus nerve stimulation typically involve implanting a medical device in a patient's chest area and running leads under the patient's skin to electrodes implanted in the patient's neck. Since implantable medical devices described herein can be relatively small and may be directly coupled to electrodes, less invasive surgical procedures can be used to implant the implantable medical devices. Thus, these implantable medical devices may be used as screening tools to determine whether vagus nerve stimulation will be effective on a particular patient.
1. An isolated circuit comprising:
a RF input configured to receive a far field radiative powering signal;
a matching network configured to provide a matched impedance voltage of the RF input to other components of the isolated circuit;
a voltage rectifier configured to provide a rectified voltage based on the received far field radiative powering signal;
a first switching network comprising:
a first power assembly comprising a first impedance coupled between the RF input and the matching network, the first impedance provided, at least in part, by activating a first switch in response to the rectified voltage satisfying a first voltage threshold; and
a second power assembly comprising a second impedance coupled between the RF input and the matching network, the second impedance provided, at least in part, by activating the first switch and a second switch in response to the rectified voltage satisfying the first voltage threshold and a second voltage threshold, respectively; and
a second switching network comprising:
a third power assembly comprising a third impedance coupled between the matching network and the voltage rectifier, the third impedance provided, at least in part, by activating a third switch in response to the rectified voltage satisfying a third voltage threshold; and
a fourth power assembly comprising a fourth impedance coupled between the matching network and the voltage rectifier, the fourth impedance provided, at least in part, by activating the third switch and a fourth switch in response to the rectified voltage satisfying the third voltage threshold and a fourth voltage threshold, respectively.
2. The isolated circuit of claim 1, further comprising:
a first threshold detector coupled to the second switch, the first threshold detector configured to receive the rectified voltage and to activate the second switch when the rectified voltage increases to the second voltage threshold.
3. The isolated circuit of claim 2, wherein the first switch is a first transistor and the second switch is a second transistor.
4. The isolated circuit of claim 3, wherein the first threshold detector is a first voltage divider configured to divide the rectified voltage and to provide a first divided rectified voltage to the second transistor.
5. The isolated circuit of claim 4, wherein the first divided rectified voltage activates the second transistor when the rectified voltage is at, or above, the second voltage threshold.
6. The isolated circuit of claim 5, further comprising:
a fifth power assembly comprising a fifth impedance coupled between the RF input and the matching network, the fifth impedance provided, at least in part, by activating the first switch, the second switch, and a fifth switch in response to the rectified voltage satisfying the first voltage threshold, the second voltage threshold, and a fifth threshold, respectively; and
a second threshold detector coupled to the fifth switch, the second threshold detector configured to receive the rectified voltage and to activate the fifth switch when the rectified voltage increases to the fifth voltage threshold.
7. The isolated circuit of claim 6, wherein the fifth switch is a third transistor, wherein the second threshold detector is a second voltage divider configured to divide the rectified voltage and to provide a second divided rectified voltage to the third transistor.
8. The isolated circuit of claim 7, wherein the second divided rectified voltage activates the third transistor when the rectified voltage is at, or above, the fifth voltage threshold.
9. The isolated circuit of claim 8, wherein the first voltage divider comprises at least a first diode-connected transistor and a second diode-connected transistor, the first diode-connected transistor coupled to the rectified voltage output, the first diode connected transistor also coupled to the second transistor and the second diode connected transistor; and
wherein the second voltage divider comprises at least a third diode-connected transistor and a fourth diode-connected transistor, the third diode-connected transistor coupled to the rectified voltage output, the third diode-connected transistor also coupled to the third transistor and the fourth diode-connected transistor.
10. The isolated circuit of claim 9, wherein at least one dimension of the first diode-connected transistor is greater than that of the third diode-connected transistor.
11. The isolated circuit of claim 3, wherein rectified voltage is provided to the first transistor and activates the first transistor at the first voltage threshold.
12. The isolated circuit of claim 1, wherein the first impedance and the second impedance comprise a resistor, a capacitor, an inductor, a diode, a transistor, or a combination thereof.
a matching network coupled to the antenna, the antenna and the matching network together configured to receive a far field radiative powering signal, the matching network configured to provide a matching impedance of the antenna to other components of the implantable medical device;
a voltage rectifier coupled to the matching network, the voltage rectifier configured to rectify the received far field radiative powering signal and to output a rectified voltage based on the received far field radiative powering signal;
a first impedance feedback circuit configured to adjust the matching impedance of the matching network comprising:
a first switch coupled between the antenna and the matching network and a second switch coupled between the antenna and the matching network, the first switch configured to couple a first impedance between the antenna and the matching network when the first switch is activated in response to the rectified voltage satisfying a first voltage threshold, the second switch configured to couple a second impedance between the antenna and the matching network when the second switch is activated in response to the rectified voltage satisfying a second voltage threshold; and
a second impedance feedback circuit comprising:
a third switch coupled between the matching network and the voltage rectifier and a fourth switch coupled between the matching network and the voltage rectifier, the third switch configured to couple a third impedance between the matching network and the voltage rectifier when the third switch is activated in response to the rectified voltage satisfying a third voltage threshold, the fourth switch configured to couple a fourth impedance between the matching network and the voltage rectifier when the fourth switch is activated in response to the rectified voltage satisfying a fourth voltage threshold.
14. The implantable medical device of claim 13, wherein the first impedance feedback circuit further comprises a first threshold detector coupled to the second switch, the first threshold detector configured to receive the rectified voltage and to activate the second switch when the rectified voltage increases to the second voltage threshold.
15. The implantable medical device of claim 14, wherein the first switch is a first transistor and the second switch is a second transistor.
16. The implantable medical device of claim 15, wherein the first threshold detector is a first voltage divider configured to divide the rectified voltage and to provide a first divided rectified voltage to the second transistor, wherein the first divided rectified voltage activates the second transistor when the rectified voltage is at, or above, the second voltage threshold.
a receiving element configured to receive a far field powering signal;
a load coupled to the receiving element, the load having a load impedance that varies non-linearly with variations in the far field powering signal, the load comprising:
a matching network coupled to the receiving element;
a voltage rectifier coupled to the matching network, the voltage rectifier configured to output a rectified voltage based on the received far field radiative powering signal;
a first impedance feedback circuit coupled between the matching network and the voltage rectifier, the first impedance feedback circuit configured to activate a first switch when the rectified voltage reaches a first rectified voltage threshold and to activate a second switch when the rectified voltage reaches a second rectified voltage threshold, the first switch configured to couple a first impedance to the load to adjust the load impedance when the first switch is activated, the second switch is configured to couple a second impedance to the load to adjust the load impedance when the second switch is activated; and
a second impedance feedback circuit coupled between the receiving element and the matching network, the second impedance feedback circuit configured to activate a third switch when the rectified voltage reaches a third rectified voltage threshold and to activate a fourth switch when the rectified voltage reaches a fourth rectified voltage threshold, the third switch configured to couple a third impedance to the load to adjust the load impedance when the third switch is activated, the fourth switch is configured to couple a fourth impedance to the load to adjust the load impedance when the fourth switch is activated.
18. The antenna assembly of claim 17, wherein the first switch is a first transistor and the second switch is a second transistor, the impedance feedback circuit further comprising a first voltage divider configured to divide the rectified voltage and to provide a first divided rectified voltage to the second transistor, wherein the first divided rectified voltage activates the second transistor when the rectified voltage is at, or above, the second voltage threshold.
19. The antenna assembly of claim 18, wherein rectified voltage is provided to the first transistor and activates the first transistor at the first voltage threshold.
US13901874 2011-07-14 2013-05-24 Circuit, system and method for far-field radiative powering of an implantable medical device Active 2035-01-05 US9675809B2 (en)
US201161507992 true 2011-07-14 2011-07-14
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US201261665687 true 2012-06-28 2012-06-28
US13901874 US9675809B2 (en) 2011-07-14 2013-05-24 Circuit, system and method for far-field radiative powering of an implantable medical device
EP20130734265 EP2866889A1 (en) 2012-06-28 2013-06-21 Circuit, system and method for far-field radiative powering of an implantable medical device
PCT/US2013/047113 WO2014004316A1 (en) 2012-06-28 2013-06-21 Circuit, system and method for far-field radiative powering of an implantable medical device
US13433907 Continuation-In-Part US9492678B2 (en) 2011-07-14 2012-03-29 Far field radiative powering of implantable medical therapy delivery devices
US20130253612A1 true US20130253612A1 (en) 2013-09-26
US9675809B2 true US9675809B2 (en) 2017-06-13
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US13901874 Active 2035-01-05 US9675809B2 (en) 2011-07-14 2013-05-24 Circuit, system and method for far-field radiative powering of an implantable medical device
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US20130253612A1 (en) 2013-09-26 application
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