HK1252467B - Remote control of power or polarity selection for a neural stimulator - Google Patents

Description

Remote control for power or polarity selection of neurostimulators

This application is a divisional application of patent application 201280037814.1, filed on July 30, 2012, with the invention name “Remote control for power or polarity selection of a neurostimulator”.

Cross-reference to related applications

This application claims the benefit of U.S. Provisional Patent Application No. 61/513,397, filed July 29, 2011, and PCT Application No. PCT/US2012/023029, filed January 27, 2012, both of which are hereby incorporated by reference in their entireties.

Technical Field

This specification relates to implanted neurostimulators.

Background Art

Neuromodulation of neural tissue in the body by electrical stimulation has become an important type of treatment for chronic disease conditions, such as chronic pain, problems with movement initiation and control, involuntary movements, dystonia, incontinence, sexual disorders, vascular insufficiency, cardiac arrhythmias, and the like. Electrical stimulation of the spine and nerve tracts detached from the spinal cord was the first approved neuromodulation treatment and has been commercially available since the 1970s. Implanted electrodes are used to deliver pulsating currents of controllable frequency, pulse width, and amplitude. Two or more electrodes are in contact with neurons, primarily axons, and are able to selectively activate varying diameters of axons, with positive therapeutic effects. A variety of therapeutic in vivo electrical stimulation techniques are used to treat neurological conditions, utilizing implanted neurostimulators in the spine or surrounding areas, including the dorsal horn, dorsal root ganglion, dorsal root, dorsal column fibers, and peripheral nerve tracts detached from the dorsal column or brain, such as the vagus nerve, occipital nerve, trigeminal nerve, hypoglossal nerve, sacral nerve, and coccygeal nerve.

Summary of the Invention

In one aspect, an implantable neurostimulator includes one or more electrodes, at least one antenna, and one or more circuits connected to the at least one antenna. The one or more electrodes are configured to apply one or more electrical pulses to stimulable tissue. The antenna is configured to receive one or more input signals containing polarity assignment information and electrical energy, the polarity assignment information specifying a polarity for each electrode. The one or more circuits are configured to control an electrode interface so that the electrode has a polarity specified by the polarity assignment information; create one or more electrical pulses using the electrical energy contained in the input signal; and supply the one or more electrical pulses to the one or more electrodes through the electrode interface so that the one or more electrodes apply the one or more electrical pulses to the stimulable tissue according to the polarity specified by the polarity assignment information.

Embodiments of this and other aspects may include the following features. The polarity specified by the polarity assignment information may include negative polarity, positive polarity, or neutral polarity. The electrical pulse includes a cathode portion and an anode portion. The electrode interface may include a polarity routing switching network. The polarity routing switching network may include a first input portion that receives the cathode portion of the electrical pulse and a second input portion that receives the anode portion of the electrical pulse. The polarity routing switching network may be configured to route the cathode portion to an electrode with a negative polarity, route the anode portion to an electrode with a positive polarity, and disconnect the electrode with a neutral polarity from the electrical pulse.

The one or more circuits may include a register having an output coupled to a selection input of the polarity routing switching network. The register may be configured to store the polarity assignment information and transmit the stored polarity assignment information from the register output to the selection input of the polarity routing switching network to control the polarity routing switching network to route the cathode portion to the electrode having a negative polarity, route the anode portion to the electrode having a positive polarity, and disconnect the electrode having a neutral polarity from the electrical pulse.

One or more circuits include a power-on reset circuit and a capacitor, wherein the capacitor can store charge using a portion of the electrical energy contained in one or more input signals, and wherein the capacitor can be configured to energize the power-on reset circuit to reset register contents when the implanted neurostimulator consumes power.

The at least one antenna may be configured to transmit one or more stimulation feedback signals to an independent antenna via electrical radiation coupling. The one or more circuits may be configured to generate the stimulation feedback signals. The stimulation feedback signals may indicate one or more parameters associated with one or more electrical pulses applied to the stimulable tissue by the one or more electrodes. The parameters may include power delivered to the tissue and impedance at the tissue.

The one or more circuits may include a current sensor configured to sense an amount of current delivered to the tissue and a voltage sensor configured to sense a voltage delivered to the tissue. The current sensor may include a resistor placed in series with an anode branch of the polarity routing switching network and may deliver an anode portion of an electrical pulse through the anode branch. The current sensor and the voltage sensor are coupled to an analog-controlled carrier modulator configured to transmit the sensed current and voltage to a separate antenna.

The at least one antenna may include a first antenna and a second antenna. The first antenna may be configured to receive an input signal containing electrical energy. The second antenna may be configured to transmit a stimulation feedback signal to an independent antenna through electrical radiation coupling. The second antenna may further be configured to receive an input signal containing polarity assignment information. The transmission frequency of the second antenna may be higher than the resonant frequency of the first antenna. The transmission frequency of the second antenna may be a second harmonic of the resonant frequency of the first antenna. The transmission frequency and the resonant frequency may be in the range of approximately 300 MHz to approximately 6 GHz. The length of the at least one antenna may be between approximately 0.1 mm and approximately 7 cm, and the width may be between approximately 0.1 mm and approximately 3 mm. The at least one antenna may be a dipole antenna.

The one or more circuits may additionally include a rectifier circuit configured to rectify an input signal received by the first antenna to generate the one or more electrical pulses. The rectifier circuit may be coupled to an RC timer to shape the one or more electrical pulses. The rectifier circuit may include at least one full-wave bridge rectifier. The full-wave bridge rectifier may include a plurality of diodes, each of which may be less than 100 microns in length.

In another aspect, the system includes an RF pulse generator module. The RF pulse generator module includes an antenna module and one or more circuits coupled to the antenna module.

The antenna module is configured to send one or more input signals to at least one antenna in the implantable neurostimulator through electrical radiation coupling. The one or more input signals contain electrical energy and polarity assignment information, and the polarity assignment information specifies the polarity assignment of one or more electrodes in the implantable neurostimulator. The implantable neurostimulator is configured to control the electrode interface so that the electrode has a polarity specified by the polarity assignment information; use the electrical energy contained in the input signal to create one or more electrical pulses suitable for stimulating neural tissue; and supply the one or more electrical pulses to the one or more electrodes through the electrode interface so that the one or more electrodes apply the one or more electrical pulses to the neural tissue using the polarity specified by the polarity assignment information. The antenna module is further configured to receive one or more signals from the at least one antenna in the implantable neurostimulator through electrical radiation coupling.

The one or more circuits are configured to generate the one or more input signals and send the one or more input signals to the antenna module; extract a stimulation feedback signal from the one or more signals received by the antenna module, wherein the stimulation feedback signal is sent by the implantable neurostimulator and indicates one or more parameters of the one or more electrical pulses; and adjust the parameters of the input signal based on the stimulation feedback signal.

Implementations of this and other aspects may include the following features: The antenna module may be configured to transmit the portion of the input signal containing electrical energy using a different carrier frequency than the portion of the input signal containing information encoding polarity assignments of one or more electrodes.

The antenna module may include a first antenna and a second antenna, wherein the first antenna is configured to operate at a first frequency to transmit an input signal containing electrical energy, and the second antenna is configured to operate at a second frequency to receive one or more signals from the at least one antenna of the implantable neurostimulator. For example, the second frequency may be a second harmonic frequency of the first frequency.

Embodiments may be inherently low-cost compared to existing implantable neuromodulation systems, and this may lead to wider adoption of neuromodulation therapy for patients in need and reduce overall costs to the healthcare system.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 depicts a high-level diagram of an example wireless neurostimulation system.

FIG2 depicts a detailed diagram of an example wireless neural stimulation system.

3 is a flow chart illustrating an example of the operation of a wireless neurostimulator system.

4 depicts a flow chart illustrating an example of operation of the system when the current level at the electrode is above a threshold limit.

FIG. 5 is a graph showing an example of a signal that may be used to detect an impedance mismatch.

6 is a diagram illustrating an example of signals that may be employed during operation of a wireless neurostimulator system.

7 is a flow chart illustrating a process by which a user controls an implantable wireless neurostimulator via an external programmer in an open-loop feedback system.

FIG8 is another exemplary flow chart of a process in which a user controls a wireless stimulator by using upper and lower limits of current amplitude.

9 is yet another example flow chart of a process for a user to control a wireless neurostimulator via pre-programmed parameter settings.

10 is another example flow chart of a process for an RF pulse generator module in a low battery state.

11 is another example flow chart of a process by which a manufacturer's representative programs control of an implanted wireless neurostimulator.

FIG. 12 is a circuit diagram illustrating an example of a wireless neural stimulator.

FIG. 13 is a circuit diagram illustrating another example of a wireless neural stimulator.

14 is a block diagram illustrating an example of control and feedback functionality of a wireless implantable neurostimulator.

15 is a schematic diagram illustrating an example of a wireless implantable neurostimulator having components that implement control and feedback functions.

FIG. 16 shows an example of a pulse waveform as seen at the power management circuit of a wireless implantable neurostimulator.

FIG. 17 is a schematic diagram of an example of a polarity routing switching network.

18A and 18B show examples of waveforms and corresponding spectra, respectively, generated by a rectifier circuit of a wireless neural stimulator.

19 is a flow chart illustrating an example of the operation of control and feedback functions of a wireless implantable neurostimulator.

DETAILED DESCRIPTION

In various embodiments, the neurostimulation system can be used to deliver electrical stimulation to targeted neural tissue by powering a passively implanted stimulator using remote radiofrequency (RF) energy without cables or inductive coupling. For example, the targeted neural tissue can be in the spinal column, including the spinothalamic tract, dorsal horn, dorsal root ganglion, dorsal root, dorsal column fibers and peripheral nerve tracts that detach from the dorsal column or brainstem, as well as any cranial nerve, abdominal, thoracic or trigeminal ganglion nerves, nerve tracts of the cerebral cortex, deep brain, and any sensory or motor nerve.

For example, in some embodiments, a neurostimulation system can include a controller module (such as an RF pulse generator module) and a passively implanted neurostimulator comprising one or more dipole antennas, one or more circuits, and one or more electrodes in contact with or close to the targeted neural tissue for stimulation. The RF pulse generator module can include an antenna and can be configured to transfer energy from the module antenna to the implanted antenna. The one or more circuits of the implanted neurostimulator can be configured to use the transferred energy to generate electrical pulses suitable for neurostimulation and supply the electrical pulses to the electrodes, thereby applying pulses to the neural tissue. For example, one or more circuits can include a wave conditioning circuit that rectifies a received RF signal (e.g., using a diode rectifier), converts the RF energy into a low-frequency signal suitable for stimulating neural tissue, and provides the resulting waveform to the electrode array. The one or more circuits of the implanted neurostimulator can also include a circuit for transmitting information back to the RF pulse generator module to facilitate a feedback control mechanism for stimulation parameter control. For example, an implanted neurostimulator may send a stimulation feedback signal to the RF pulse generator module that indicates parameters of the electrical pulses, and the RF pulse generator module may employ the stimulation feedback signal to adjust parameters of signals sent to the neurostimulator.

FIG1 depicts a high-level diagram of an example neurostimulation system. The neurostimulation system may include four main components: a programmer module 102, an RF pulse generator module 106, a transmit (TX) antenna 110 (e.g., a patch antenna, a slot antenna, or a dipole antenna), and an implanted wireless neurostimulator 114. The programmer module 102 may be a computer device (such as a smartphone) running a software application that supports a wireless connection 104, such as a RFID reader. The application enables a user to view system status and diagnostics, change various parameters, increase/decrease the desired stimulation amplitude of electrode pulses, and adjust the feedback sensitivity of the RF pulse generator module 106, among other functions.

The RF pulse generator module 106 can include communication electronics supporting the wireless connection 104, stimulation circuitry, and a battery for powering the generator electronics. In some embodiments, the RF pulse generator module 106 includes a TX antenna embedded in its package form factor, while in other embodiments, the TX antenna is connected to the RF pulse generator module 106 via a wired connection 108 or a wireless connection (not shown). The TX antenna 110 can be directly coupled to tissue to create an electric field that powers the implanted neurostimulator module 114. The TX antenna 110 communicates with the implanted neurostimulator module 114 via an RF interface. For example, the TX antenna 110 radiates an RF transmit signal modulated and encoded by the RF pulse generator module 110. The implanted wireless neurostimulator module 114 includes one or more antennas, such as dipole antennas, to receive and transmit via the RF interface 112. Specifically, the coupling mechanism between the antenna 110 and the one or more antennas on the implanted neurostimulator module 114 is electrical radiation coupling rather than inductive coupling. In other words, the coupling occurs via an electric field rather than a magnetic field.

Through this electrical radiation coupling, the TX antenna 110 is able to provide an input signal to the implanted neurostimulator module 114. The input signal contains energy and may contain information encoding a stimulation waveform to be applied at the electrodes of the implanted neurostimulator module 114. In some embodiments, the power level of the input signal directly determines the amplitude (e.g., power, current, or voltage) of the application of one or more electrical pulses created using the electrical energy contained in the input signal. Within the implanted wireless neurostimulator 114 are components for demodulating the RF transmit signal, as well as electrodes that deliver stimulation to the surrounding neural tissue.

The RF pulse generator module 106 can be implanted subcutaneously or can be worn externally to the body. When external to the body, the RF generator module 106 can be incorporated into a belt or harness design to allow electrical radiation coupling through the skin and underlying tissue to transfer power and/or control parameters to an implanted neurostimulator module 114, which can be a passive stimulator. In either event, receiver circuitry within the neurostimulator module 114 can capture the energy radiated by the TX antenna 110 and convert that energy into an electrical waveform. The receiver circuitry can also modify the waveform to create electrical pulses suitable for stimulating neural tissue, and the pulses can be delivered to the tissue via electrode pads.

In some embodiments, the RF pulse generator module 106 can remotely control stimulation parameters (i.e., the parameters of the electrical pulses applied to the neural tissue) and monitor feedback from the wireless neurostimulator module 114 based on the RF signal received from the implanted wireless neurostimulator module 114. A feedback detection algorithm implemented by the RF pulse generator module 106 can monitor data wirelessly transmitted from the implanted wireless neurostimulator module 114, including information about the energy being received by the implanted wireless neurostimulator module 114 from the RF pulse generator and information about the stimulation waveform being delivered to the electrode pads. In order to provide effective treatment for a given medical condition, the system can be tuned to provide an optimal amount of excitation or inhibition to the neural fibers through electrical stimulation. A closed-loop feedback control approach can be used in which the output signal from the implanted wireless neurostimulator module 114 is monitored and used to determine an appropriate level of neural stimulation current for maintaining effective neural activation, or in some cases, the patient can manually adjust the output signal in an open-loop control approach.

FIG2 depicts a detailed diagram of an example of a neurostimulation system. As shown, the programming module 102 may include a user input subsystem 221 and a communication subsystem 208. The user input subsystem 221 may allow a user to adjust various parameter settings in the form of an instruction set (in some cases, in an open-loop manner). The communication subsystem 208 may transmit these instruction sets (and other information) to the RF pulse generator module 106 via a wireless connection 104 (such as Bluetooth or Wi-Fi), and receive data from the module 106.

For example, a programmer module 102 that can be used by multiple users (such as a patient's control unit or a clinician's programmer unit) can be used to send stimulation parameters to the RF pulse generator module 106. The stimulation parameters that can be controlled may include pulse amplitude, pulse frequency, and pulse width in the ranges shown in Table 1. In this document, the term "pulse" refers to the phase of the waveform that directly produces stimulation to the tissue; the parameter of the charge balance phase (described below) can similarly be controlled. The patient and/or clinician can also optionally control the total duration and pattern of treatment.

The implantable neurostimulator module 114 or RF pulse generator module 106 is initially programmed to meet specific parameter settings for each individual patient during the initial implantation process. As medical conditions or the body itself change over time, the ability to readjust parameter settings can be beneficial to ensure continued efficacy of the neuromodulation therapy.

The programmer module 102 may be functionally a smart device and associated applications. The smart device hardware may include a CPU 206 and be used as an intermediary to handle touch screen input on a graphical user interface (GUI) 204 to process and store data.

RF pulse generator module 106 may be connected to an external TX antenna 110 via a wired connection 108. Alternatively, both the antenna and RF pulse generator are located subcutaneously (not shown).

The signals sent by the RF pulse generator module 106 to the implanted stimulator 114 may include power and parameter setting properties regarding the stimulation waveform, amplitude, pulse width, and frequency. The RF pulse generator module 106 may also act as a wireless receiving unit to receive feedback signals from the implanted stimulator module 114. To this end, the RF pulse generator module 106 may include microelectronics or other circuitry to handle the generation of signals transmitted to the stimulator module 114 and to handle feedback signals, such as those from the stimulator module 114. For example, the RF pulse generator module 106 may include a controller subsystem 214, a high frequency oscillator 218, an RF amplifier 216, an RF switch, and a feedback subsystem 212.

The controller subsystem 214 may include a CPU 230 for handling data processing, a memory subsystem 228 (such as local memory), a communication subsystem 234 for communicating with the programmer module 102 (including receiving stimulation parameters from the programmer module), a pulse generator circuit 236, and a digital/analog (D/A) converter 232.

The controller subsystem 214 can be used by the patient and/or clinician to control stimulation parameter settings (e.g., by controlling parameters of a signal sent from the RF pulse generator module 106 to the neurostimulator module 114). For example, these parameter settings can affect the power, current level, or shape of one or more electrical pulses. As described above, programming of the stimulation parameters can be performed using the programming module 102 to set the repetition rate, pulse width, amplitude, and waveform that will be transmitted via RF energy to a receive (RX) antenna 238 in the wirelessly implanted neurostimulator module 114, which is typically a dipole antenna (although other types may be used). Because adjusting specific parameters may require detailed medical knowledge of neurophysiology, neuroanatomy, neuromodulation protocols, and electrical stimulation safety limits, the clinician can have the option of locking and/or hiding specific settings within the programmer interface, thereby limiting the patient's ability to view or adjust specific parameters.

The controller subsystem 214 can store the received parameter settings in the local memory subsystem 228 until the parameter settings are modified by new input data received from the programming module 102. The CPU 206 can use the parameters stored in the local memory to control the pulse generator circuit 236 to generate a stimulation waveform modulated in the range of 300 MHz to 8 GHz by the high-frequency oscillator 218. The resulting RF signal can then be amplified by the RF amplifier and then sent to the TX antenna 110 through the RF switch 223 to penetrate the depth of the tissue to reach the RX antenna 238.

In some embodiments, the RF signal transmitted by the TX antenna 110 can simply be a power transmission signal used by the stimulator module 114 to generate electrical pulses. In other embodiments, a telemetry signal can also be transmitted to the stimulator module 114 to send instructions regarding various operations of the stimulator module 114. The telemetry signal can be sent by modulating a carrier signal (if external, through the skin, or, if the pulse generator module 106 is implanted subcutaneously, through other body tissue). The telemetry signal is used to modulate the carrier signal (high frequency signal) that is coupled to the implanted antenna 238 and does not interfere with the input received on the same lead for powering the implant. In one embodiment, the telemetry signal and the power signal are combined into one signal, wherein the RF telemetry signal is used to modulate the RF power signal, and thus the implanted stimulator is powered directly by the received telemetry signal; independent subsystems in the stimulator utilize the power contained in the signal and interpret the data content of the signal.

The RF switch 223 can be a multifunctional device (such as a bidirectional coupler) that passes high amplitude, very short duration RF pulses to the TX antenna 110 with minimal insertion loss while providing two low-level outputs to the feedback subsystem 212; one output delivers a forward power signal to the feedback subsystem 212, where the forward power signal is an attenuated version of the RF pulse sent to the TX antenna 110, and the other output delivers a reverse power signal to a different port of the feedback subsystem 212, where the reverse power is an attenuated version of the RF energy reflected from the TX antenna 110.

During on-cycle time (when RF signals are being transmitted to the stimulator 114), the RF switch 223 is configured to send forward power to the feedback subsystem. During off-cycle time (when RF signals are not being transmitted to the stimulator module 114), the RF switch 223 can be switched to a receive mode in which RF energy and/or RF signals reflected from the stimulator module 114 are received for analysis in the feedback subsystem 212.

The feedback subsystem 212 of the RF pulse generator module 106 may include receiving circuitry to receive and extract telemetry or other feedback signals from the stimulator 114 and/or RF energy reflected from signals transmitted by the TX antenna 110. The feedback subsystem may include an amplifier 226, a filter 224, a demodulator 222, and an A/D converter 220.

Feedback subsystem 212 receives the forward power signal and converts this high-frequency AC signal to a DC level, which can be sampled and sent to controller subsystem 214. In this way, the characteristics of the generated RF pulses can be compared with reference signals within controller subsystem 214. If there is an inconsistency (error) in any parameter, controller subsystem 214 can adjust the output to RF pulse generator 106. For example, the nature of the adjustment can be proportional to the calculated error. Controller subsystem 214 can incorporate additional inputs and constraints into its regulation scheme, such as the signal amplitude of the reverse power and any predetermined maximum or minimum values for various pulse parameters.

The reverse power signal can be used to detect fault conditions in the RF power delivery system. Under ideal conditions, when the TX antenna 110 has an impedance that perfectly matches the tissue it contacts, the electromagnetic waves generated by the RF pulse generator 106 are transmitted unimpeded from the TX antenna 110 into the body tissue. However, in actual applications, there is a large degree of variation in the user's body type, the type of clothing worn, and the positioning of the antenna 110 relative to the body surface. Because the impedance of the antenna 110 depends on the relative permittivity of the underlying tissue and any intervening materials, as well as the total separation distance between the antenna and the skin, in any given application, there will be an impedance mismatch at the interface between the TX antenna 110 and the body surface. When such a mismatch occurs, the electromagnetic waves transmitted from the RF pulse generator 106 are partially reflected at the interface, and this reflected energy propagates back through the antenna feed.

The bidirectional coupler RF switch 223 can prevent the reflected RF energy from propagating back into the amplifier 226, and can attenuate the reflected RF signal and send the attenuated signal as a reverse power signal to the feedback subsystem 212. The feedback subsystem 212 can convert the high-frequency AC signal to a DC level, sample the DC level, and send it to the controller subsystem 214. The controller subsystem 214 can then calculate the ratio of the amplitude of the reverse power signal to the amplitude of the forward power signal. The ratio of the amplitude of the reverse power signal to the amplitude of the forward power signal can indicate the severity of the impedance mismatch.

To sense impedance mismatch conditions, the controller subsystem 214 can measure the reflected power ratio in real time and, based on a preset threshold for this measurement, modify the level of RF power generated by the RF pulse generator 106. For example, to achieve a moderate level of reflected power, the course of action can be for the controller subsystem 214 to increase the amplitude of the RF power sent to the TX antenna 110, as this may be necessary to compensate for slightly suboptimal but acceptable TX antenna coupling to the body. To achieve a higher reflected power ratio, the course of action can be to prevent the RF pulse generator 106 from operating and set a fault code indicating that the TX antenna 110 has little or no coupling to the body. This type of reflected power fault condition can also be generated by a poor or disconnected connection to the TX antenna. In either case, since internal reflected power can cause unnecessary heating of internal components, and this fault condition means that the system is unable to deliver sufficient power to the implanted wireless neurostimulator and, therefore, unable to provide therapy to the user, it may be desirable to cease RF transmission when the reflected power ratio rises above a defined threshold.

The controller 242 of the stimulator 114 can transmit information signals (such as telemetry signals) through the antenna 238 to communicate with the RF pulse generator module 106 during its receive cycle. For example, during the on and off states of the transistor circuit, the telemetry signal from the stimulator 114 can be coupled to the modulated signal on the dipole antenna 238 to enable or disable the waveform that generates the corresponding RF burst required for transmission to the external (or remotely implanted) pulse generator module 106. The antenna 238 can be connected to the electrode 254 in contact with the tissue to provide a return path for the transmitted signal. An A/D converter (not shown) can be used to convert the stored data into a serialized pattern that can be transmitted from the internal antenna 238 of the neurostimulator on a pulse modulated signal.

The telemetry signal from the implanted wireless neurostimulator module 114 can include stimulation parameters, such as the power or amplitude of the current delivered to the tissue from the electrode. A feedback signal can be transmitted to the RF pulse generator module 116 to indicate the intensity of the stimulation at the nerve bundle by coupling the signal to the implanted RX antenna 238, which radiates the telemetry signal to the external (or remotely implanted) RF pulse generator module 106. The feedback signal can include either or both of a carrier signal modulated by analog and digital telemetry pulses. Data such as stimulation pulse parameters and measured stimulator performance characteristics can be stored in an internal memory device within the implanted neurostimulator 114 and sent on the telemetry signal. The frequency of the carrier signal can be in the range of 300 MHz to 8 GHz.

In the feedback subsystem 212, the telemetry signal can be down-modulated using a demodulator 222 and digitized by processing through an analog-to-digital (A/D) converter 220. The digital telemetry signal can then be routed to a CPU 230 having embedded code, which can optionally be reprogrammed to convert the signal into a corresponding current measurement in the tissue based on the amplitude of the received signal. The CPU 230 of the controller subsystem 214 can compare the reported stimulation parameters with those stored in the local memory 228 to verify that the stimulator 114 is delivering the specified stimulation to the tissue. For example, if the stimulator reports a current below a specified value, the power level from the RF pulse generator module 106 can be increased so that the implanted neurostimulator 114 will have more available power for stimulation. The implanted neurostimulator 114 can generate telemetry data in real time (e.g., at a rate of 8k bits per second). All feedback data received from the implanted neurostimulator module 114 can be recorded with reference to time and sampled for storage and retrieval from a remote monitoring system accessible to a healthcare professional for trends and statistical correlations.

The sequence of remotely programmable RF signals received by the internal antenna 238 can be conditioned into a waveform that is controlled by the control subsystem 242 within the implantable stimulator 114 and routed to the appropriate electrodes 254 placed near the tissue to be stimulated. For example, the RF signal transmitted from the RF pulse generator module 106 can be received by the RX antenna 238 and processed by circuitry such as the waveform conditioning circuit 240 within the implanted wireless neurostimulator module 114 to convert it into electrical pulses that are applied to the electrodes 254 via the electrode interface 252. In some embodiments, the implanted stimulator 114 includes between two and sixteen electrodes 254.

The waveform conditioning circuit 240 may include a rectifier 244 that rectifies the signal received by the RX antenna 238. The rectified signal may be fed to the controller 250 for receiving encoded instructions from the RF pulse generator module 106. The rectifier signal may also be fed to a charge balancing component 246 that is configured to create one or more electrical pulses based on the one or more electrical pulses resulting in a substantially zero net charge at one or more electrodes (i.e., the pulses are charge balanced). The charge-balanced pulses are delivered through a current limiter 248 to an electrode interface 252 that appropriately applies the pulses to electrodes 254.

The current limiter 248 ensures that the current level of the pulses applied to the electrode 254 does not exceed a threshold current level. In some embodiments, the amplitude (e.g., current level, voltage level, or power level) of the received RF pulse directly determines the amplitude of the stimulation. In such cases, it can be particularly beneficial to include the current limiter 248 to prevent excessive current or charge from being delivered through the electrode, but the current limiter 248 can be used in other embodiments where this is not the case. Typically, for a given electrode having a surface area of several square millimeters, it is the charge per phase that should be limited for safety reasons (where the charge delivered by the stimulation phase is the integral of the current). However, in some cases, the current can be limited instead, where the maximum current multiplied by the maximum possible pulse duration is less than or equal to the maximum safe charge. More generally, the current limiter 248 acts as a charge limiter that limits the characteristics of the electrical pulse (e.g., current or duration) so that the charge per phase remains below a threshold level (typically, a safe charge limit).

In the event that the implanted wireless neurostimulator 114 receives a "strong" pulse of RF power sufficient to generate stimulation that would exceed a predetermined safe charge limit, the current limiter 248 can automatically limit or "clamp" the stimulation phase to maintain the total charge of that phase within safe limits. The current limiter 248 can be a passive current limiting component that cuts off the signal to the electrodes 254 once the safe current limit (threshold current level) is reached. Alternatively, or in addition, the current limiter 248 can communicate with the electrode interface 252 to shut down all electrodes 254 to prevent current levels that damage tissue.

The clamping event can trigger the current limiter feedback control mode. The clamping action can cause the controller to send a threshold power data signal to the pulse generator 106. The feedback subsystem 212 detects the threshold power signal and demodulates the signal into data that is transmitted to the controller subsystem 214. The controller subsystem 214 algorithm can act on this current limiting condition by specifically reducing the RF power generated by the RF pulse generator or by completely cutting off the power. In this way, if the implanted wireless neurostimulator 114 reports that it is receiving excessive RF power, the pulse generator 106 can reduce the RF power delivered to the body.

The controller 250 of the stimulator 205 can communicate with the electrode interface 252 to control various aspects of the electrode arrangement and the pulses applied to the electrodes 254. The electrode interface 252 can act as a multiplexer and control the polarity and switching of each electrode 254. For example, in some embodiments, the wireless stimulator 106 has multiple electrodes 254 in contact with the tissue, and for a given stimulation, the RF pulse generator module 106 can arbitrarily assign one or more electrodes to 1) act as stimulation electrodes, 2) act as return electrodes, or 3) not act as a function of the assigned electrodes by wirelessly communicating the assigned electrodes using parameter instructions that the controller 250 uses to appropriately set the electrode interface 252. For example, it may be physiologically advantageous to assign one or two electrodes as stimulation electrodes and all remaining electrodes as return electrodes.

Furthermore, in some embodiments, for a given stimulation pulse, the controller 250 can control the electrode interface 252 to divide the current arbitrarily (or according to instructions from the pulse generator module 106) between designated stimulation electrodes. Since, in practice, the electrodes 254 may be spatially distributed along various neural structures, and by strategically selecting stimulation electrode locations and specifying current ratios for each location, the overall current distribution in the tissue can be modified to selectively activate specific neural targets, such control over electrode allocation and current control can be advantageous. Such strategies for current steering can improve patient treatment outcomes.

In another embodiment, the time course of stimulation can be arbitrarily manipulated. A given stimulation waveform can start at time T_start and end at time T_final, and the time course can be synchronized across all stimulation and return electrodes; furthermore, the repetition rate of the stimulation cycle can be synchronized for all electrodes. However, the controller 250, independently or in response to instructions from the pulse generator 106, can control the electrode interface 252 to specify one or more subsets of electrodes to deliver stimulation waveforms with asynchronous start and stop times, and can arbitrarily and independently specify the repetition rate of each stimulation cycle.

For example, a stimulator with eight electrodes can be configured to have a subset of five electrodes (referred to as set A) and a subset of three electrodes (referred to as set B). Set A can be configured to use two of its electrodes as stimulation electrodes and the remaining electrodes as return electrodes. Set B can be configured to have exactly one stimulation electrode. The controller 250 can then specify that set A delivers a stimulation phase with a current of 3 mA for a duration of 200 μs, followed by a charge balancing phase of 400 μs. The stimulation cycle can be specified to repeat at a rate of 60 cycles per second. Thereafter, for set B, the controller 250 can specify that set A delivers a stimulation phase with a current of 1 mA for a duration of 500 μs, followed by a charge balancing phase of 800 μs. The repetition rate of the stimulation cycle for set B can be set independently of set A, for example, it can be specified at 25 cycles per second. Alternatively, if the controller 250 is configured to match the repetition rate for set B with the repetition rate for set A, in such a case, the controller 250 can specify the relative start times of the stimulation cycles to coincide in time or to be arbitrarily offset from each other by some delay interval.

In some embodiments, the controller 250 is capable of shaping the stimulation waveform amplitude arbitrarily, and can do so in response to instructions from the pulse generator 106. The stimulation phase can be delivered by a constant current source or a constant voltage source, and such control can generate a static characteristic waveform, for example, a constant current source generates a characteristic rectangular pulse in which the current waveform has a very steep rise, a constant amplitude for the duration of the stimulation, and then returns to the baseline very steeply. Alternatively, or additionally, the controller 250 is capable of increasing or decreasing the current level at any time during the stimulation phase and/or during the charge balancing phase. Thus, in some embodiments, the controller 250 is capable of delivering stimulation waveforms of arbitrary shapes, such as triangular pulses, sinusoidal pulses, or, for example, Gaussian pulses. Similarly, the charge balancing phase can be of arbitrary amplitude shape, and similarly, the leading edge anode pulse (preceding the stimulation phase) can also be amplitude shaped.

As described above, the stimulator 114 may include a charge balancing component 246. Typically, for constant current stimulation pulses, the pulses should be charge balanced by making the amount of cathodic current equal to the amount of anodic current, which is often referred to as biphasic stimulation. Charge density is the amount of current multiplied by the duration for which it is applied, and is often expressed in units of μC/cm2. To avoid irreversible electrochemical reactions, such as pH changes, electrode dissolution, and tissue damage, no net charge should appear at the electrode-electrolyte interface, and a charge density of less than 30 μC/cm2 is often acceptable. Biphasic stimulation current pulses ensure that no net charge appears at the electrodes after each stimulation cycle, and that the electrochemical processes are balanced to prevent net direct current. The neurostimulator 114 can be designed to ensure that the resulting stimulation waveform has zero net charge. Charge-balanced stimulation is believed to have minimal damaging effects on tissue by reducing or eliminating electrochemical reaction products created at the electrode-tissue interface.

The stimulation pulse can have a negative voltage or current, which is called the cathode phase of the waveform. The stimulation electrode can have a cathode and anodal phase at different times during the stimulation cycle. The electrode that delivers a negative current with sufficient amplitude to stimulate adjacent neural tissue is called a "stimulation electrode". During the stimulation phase, the stimulation electrode acts as a current sink. One or more additional electrodes act as current sources, and these electrodes are called "return electrodes". The return electrode is placed at other locations in the tissue at a certain distance from the stimulation electrode. When the typical negative stimulation phase is delivered to the tissue at the stimulation electrode, the return electrode has a positive stimulation phase. During the subsequent charge balance phase, the polarity of each electrode is reversed.

In some embodiments, the charge balancing component 246 uses a blocking capacitor, which is placed in series electrical connection with the stimulation electrode and the body tissue between the stimulation generation point within the stimulator circuit and the stimulation point delivered to the tissue. In this way, a resistor-capacitor (RC) network can be formed. In a multi-electrode stimulator, a charge balancing capacitor can be used for each electrode, or a centralized capacitor can be used within the stimulator circuit before the electrode selection point. The RC network can block direct current (DC), however, it can also prevent low-frequency alternating current (AC) from flowing to the tissue. Below a certain frequency, the series RC network basically blocks the signal, which is generally referred to as the cutoff frequency, and in one embodiment, the design of the stimulator system can ensure that the cutoff frequency is not higher than the fundamental frequency of the stimulation waveform. In this embodiment of the invention, the wireless stimulator can have a charge balancing capacitor having a value selected based on the measured series resistance of the electrode and the tissue environment in which the stimulator is implanted. By selecting the specific capacitance value, the cutoff frequency of the RC network in this embodiment is at or below the fundamental frequency of the stimulation pulse.

In other embodiments, the cutoff frequency can be selected to be at or above the fundamental frequency of the stimulation, and in this scenario, the stimulation waveform created before the charge balancing capacitor (referred to as the drive waveform) can be designed to be unstable, wherein the envelope of the drive waveform is changed during the duration of the drive pulse. For example, in one embodiment, the initial amplitude of the drive waveform is set at an initial amplitude Vi, and the amplitude is increased during the duration of the pulse until it reaches a final value k*Vi. By varying the amplitude of the drive waveform over time, the shape of the stimulation waveform delivered through the charge balancing capacitor is also modified. The shape of the stimulation waveform can be modified in this way to create physiologically beneficial stimulation.

In some embodiments, the wireless neurostimulator module 114 can create a drive waveform envelope that follows the envelope of the RF pulse received by the receive dipole antenna 238. In this case, the RF pulse generator module 106 can directly control the envelope of the drive waveform within the wireless neurostimulator 114, and therefore no energy storage may be required within the stimulator itself. In such embodiments, the stimulator circuitry can modify the envelope of the drive waveform or pass it directly to the charge balancing capacitor and/or electrode selection stage.

In some embodiments, the implanted neurostimulator 114 can deliver a single-phase drive waveform to the charge balancing capacitor, or it can deliver a multi-phase drive waveform. In the case of a single-phase drive waveform, for example, a negative-going rectangular pulse, the pulse comprises a physiological stimulation phase, and during this phase, the charge balancing capacitor is polarized (charged). After the drive pulse is completed, the charge balancing function is performed only by the passive discharge of the charge balancing capacitor, wherein its charge is consumed by the tissue in the opposite polarity relative to the previous stimulation. In one embodiment, a resistor within the stimulator facilitates the discharge of the charge balancing capacitor. In some embodiments, using the passive discharge phase, the capacitor can be allowed to discharge virtually completely before starting a subsequent stimulation pulse.

In the case of a multiphase drive waveform, the wireless stimulator can perform internal switching to pass negative or positive pulses (phases) to the charge balancing capacitor. These pulses can be delivered in any sequence and with varying amplitudes and waveform shapes to achieve the desired physiological effect. For example, the stimulation phase can be followed by an actively driven charge balancing phase and/or preceded by an opposite phase. For example, a preceding stimulation with an opposite polarity phase can have the advantage of reducing the amplitude of the stimulation phase required to stimulate the tissue.

In some embodiments, the amplitude and timing of the stimulation and charge balancing phases are controlled by the amplitude and timing of the RF pulses from the RF pulse generator module 106, and in other cases, such control may be implemented internally by circuitry onboard the wireless stimulator 114, such as the controller 250. In the case of onboard control, the amplitude and timing may be specified or modified by data commands delivered from the pulse generator module 106.

FIG3 is a flow chart illustrating an example of the operation of a neurostimulator system. In block 302, a wireless neurostimulator 114 is implanted near a nerve bundle and coupled to the electric field generated by a TX antenna 110. That is, the pulse generator module 106 and the TX antenna 110 are positioned (e.g., near the patient) such that the TX antenna 110 is electrically radiatively coupled to the implanted RX antenna 238 of the neurostimulator 114. In some embodiments, the antenna 110 and the RF pulse generator 106 are both located subcutaneously. In other embodiments, the antenna 110 and the RF pulse generator 106 are located externally to the patient's body. In this case, the TX antenna 110 can be directly coupled to the patient's skin.

As shown in block 304, energy from the RF pulse generator is radiated from the antenna 110 through the tissue to the implanted wireless neurostimulator 114. The radiated energy can be controlled by the patient/clinician parameter input in block 301. In some examples, the parameter settings can be adjusted in an open-loop manner by the patient or clinician who adjusts the parameter input to the system in block 301.

The wireless implanted stimulator 114 uses the received energy to generate electrical pulses to be applied to the neural tissue via the electrodes 238. For example, as shown in block 306, the stimulator 114 may include circuitry to rectify the received RF energy and adjust the waveform, charge balance the energy delivered to the electrodes, and stimulate the target nerve or target tissue. As shown in block 308, the implanted stimulator 114 communicates with the pulse generator 106 using the antenna 238 to send telemetry signals. The telemetry signals may include information about the parameters of the electrical pulses applied to the electrodes, such as the impedance of the electrodes, whether a safe current limit is reached, or the magnitude of the current provided to the tissue from the electrodes.

In block 310, the RF pulse generator 106 detects, amplifies, filters, and modulates the received telemetry signal using amplifier 226, filter 224, and demodulator 222, respectively. As shown in block 312, the A/D converter 230 then digitizes the resulting analog signal. The digital telemetry signal is routed to the CPU 230, which determines, based on the digital telemetry signal, whether it is necessary to adjust the parameters of the signal sent to the stimulator 114. For example, in block 314, the CPU 230 compares the information in the digital signal with a lookup table, which may indicate an appropriate change in the stimulation parameters. For example, the indicated change may be a change in the current level of the pulse applied to the electrode. Thus, as shown in block 316, the CPU may change the output power of the signal sent to the stimulator 114 in order to adjust the current applied by the electrode 254.

Thus, for example, as shown in block 318, CPU 230 can adjust the parameters of the signal sent to stimulator 114 per cycle to match the desired current amplitude set by the patient's programming. The state of the stimulator system can be sampled in real time at a rate of 8k bits per second of telemetry data. All feedback data received from stimulator 114 can be maintained with reference to time, and all feedback data can be sampled per minute to be stored for downloading or uploading to a remote monitoring system accessible to a healthcare professional in block 318 to obtain trends and statistical correlations. If operated in an open-loop manner, the stimulator system operation can be reduced to the functional elements shown in only blocks 302, 304, 306, and 308, and the patient uses his or her judgment rather than closed-loop feedback from an implanted device to adjust the parameter settings.

FIG4 depicts a flow chart illustrating an example of the operation of the system when the current level at the electrode 254 is above a threshold limit. In some cases, as shown in block 402, the implanted wireless neurostimulator 114 may receive an input power signal having a current level above an established safety current limit. For example, as shown in block 404, the current limiter 248 may determine that the current is above an established tissue safety current limit in amperes. If the current limiter senses that the current is above the threshold, it may stop the high power signal from damaging surrounding tissue in contact with the electrode, as shown in block 406, as described above in conjunction with FIG2 .

As shown in block 408, the capacitor can store excess power. When the current limiter senses that the current is above a threshold, the controller 250 can use the available excess power to send a small 2-bit data burst back to the RF pulse generator 106, as shown in block 410. During the RF pulse generator's receive cycle, a 2-bit data burst can be transmitted via the implanted wireless neurostimulator's antenna 238, as shown in block 412. The RF pulse generator antenna 110 can receive the 2-bit data burst at a rate of 8 kbps during its receive cycle, as shown in block 414, and can transmit the data burst back to the RF pulse generator's feedback subsystem 212, which monitors all reverse power, as shown in block 416. The CPU 230 can analyze the signal from the feedback subsystem 212, as shown in block 418, and, if no data burst is present, no changes can be made to the stimulation parameters, as shown in block 420. If a data burst is present during the analysis, the CPU 230 can shut off all transmit power for one cycle, as shown in block 422.

As shown in block 424, if the data burst continues, RF pulse generator 106 may push a "Near Power Danger" notification to the application on programmer module 102. This near power danger notification occurs because the RF pulse generator has terminated its power transmission. This notification indicates that an unauthorized form of energy is powering the implant at a level above a safe level. As shown in block 426, the application may alert the user of the danger and warn the user to leave the immediate area to resume neuromodulation therapy. As shown in block 428, if the data burst ceases after one cycle, RF pulse generator 106 may slowly ramp up the transmit power in increments, for example, from 5% to 75% of the previous current amplitude level. The user can then manually adjust the current amplitude level to increase at their own risk. As shown in block 430, during the ramp-up period, RF pulse generator 106 may notify the application of its progress, and the application may notify the user of the unsafe power level and the system ramps back up.

FIG5 is a diagram showing an example of a signal that can be used to detect an impedance mismatch. As described above, a forward power signal and a reverse power signal can be used to detect an impedance mismatch. For example, an RF pulse 502 generated by an RF pulse generator can be transmitted to the TX antenna 110 via a device such as a bidirectional coupler. The TX antenna 110 then radiates the RF signal into the body, where the energy is received by the implanted wireless neurostimulator 114 and converted into pulses that stimulate the tissue. The coupler transmits an attenuated version of the RF signal, i.e., forward power 510, to the feedback subsystem 212. The feedback subsystem 212 demodulates the AC signal and calculates the amplitude of the forward RF power, and this data is transmitted to the controller subsystem 214. Similarly, the bidirectional coupler (or similar component) also receives the RF energy reflected back from the TX antenna 110 and transmits an attenuated version of the RF signal, i.e., reverse power 512, to the feedback subsystem 212. The feedback subsystem 212 demodulates the AC signal and calculates the magnitude of the reflected RF power, and this data is passed to the controller subsystem 214 .

In an optimal situation, when TX antenna 110 can be perfectly impedance-matched to the body, allowing RF energy to pass unimpeded across the interface of TX antenna 110 to the body, no RF energy is reflected at the interface. Therefore, in this optimal situation, reverse power 512 can have a magnitude close to zero, as shown by signal 504, and the ratio of reverse power 512 to forward power 510 is zero. In this environment, there is no error condition, and controller 214 sets a system message that operation is optimal.

In practice, the impedance match between the TX antenna 204 and the body may not be optimal, and some of the energy of the RF pulse 502 may be reflected from the interface between the TX antenna 110 and the body. This can occur, for example, if the TX antenna 110 is held slightly off the skin by a piece of clothing. This non-optimal antenna coupling causes a small portion of the forward RF energy to be reflected at the interface, as depicted by signal 506. In this case, the ratio of reverse power 512 to forward power 510 is small, but this small ratio means that most of the RF energy is still radiated from the TX antenna 110, so this condition is acceptable within the control algorithm. This determination of an acceptable reflection ratio can be made within the controller subsystem 214 based on preprogrammed thresholds, and the controller subsystem 214 can generate a low-priority alert that will be sent to the user interface. Furthermore, upon sensing the low reflection ratio condition, the controller subsystem 214 can modestly increase the amplitude of the RF pulse 502 to compensate for the modest loss in forward energy transfer to the implanted wireless neurostimulator 114.

During routine operational use, the TX antenna 110 may be accidentally completely removed from the body, in which case the coupling (if any) of the TX antenna to the body will be very poor. In this or other circumstances, a high proportion of the RF pulse energy is reflected from the TX antenna 110 as signal 508 and fed back into the RF power system. Similarly, this phenomenon can occur if the connection to the TX antenna is physically broken, in which case effectively 100% of the RF energy is reflected back from the point of breakage. In this case, the ratio of reverse power 512 to forward power 510 is very high, and the controller subsystem 214 will determine that the ratio has exceeded an acceptable threshold. In this case, the controller subsystem 214 can prevent the generation of any further RF pulses. The shutdown of the RF pulse generator module 106 can be reported to the user interface to inform the user that stimulation therapy cannot be delivered.

FIG6 is a diagram illustrating an example of signals that may be employed during operation of a neurostimulator system. According to some embodiments, the amplitude of an RF pulse 602 received by an implanted wireless neurostimulator 114 can directly control the amplitude of stimulation 630 delivered to tissue. The duration of an RF pulse 608 corresponds to the specified pulse width of stimulation 630. During normal operation, the RF pulse generator module 106 transmits an RF pulse waveform 602 into the body via the TX antenna 110, and the RF pulse waveform 608 may represent the corresponding RF pulse received by the implanted wireless neurostimulator 114. In this case, the received power has an amplitude suitable for generating a safe stimulation pulse 630. The stimulation pulse 630 is below the safety threshold 626, and no error condition exists. In another example, the attenuation between the TX antenna 110 and the implanted wireless neurostimulator 114 is unexpectedly reduced, for example due to a user repositioning the TX antenna 110. This reduced attenuation may result in an increase in the amplitude of the RF pulse waveform 612 received at the neurostimulator 114. Although an RF pulse 602 having the same amplitude as before is generated, the improved RF coupling between the TX antenna 110 and the implanted wireless neurostimulator 114 can result in a larger amplitude of the received RF pulse 612. In this case, the implanted wireless neurostimulator 114 can generate a larger stimulus 632 in response to the increase in the received RF pulse 612. However, in this example, the received power 612 can generate a stimulus 632 that exceeds a prudent safety limit for the tissue. In this case, the current limiter feedback control mode can operate to clamp the waveform of the stimulation pulse 632 so that the delivered stimulus remains within the predetermined safety limit 626. As described above, a clamp event 628 can be transmitted by the feedback subsystem 212, and the controller subsystem 214 can subsequently reduce the amplitude specified for the RF pulse. As a result, the subsequent RF pulse 604 is reduced in amplitude, and correspondingly, the amplitude of the received RF pulse 616 is reduced to an appropriate level (non-clamped level). In this way, if the implanted wireless neurostimulator 114 receives excessive RF power, the current limiter feedback control mode can operate to reduce the RF power delivered to the body.

In another example, the RF pulse waveform 606 depicts a higher amplitude RF pulse generated as a result of a user input to the user interface. In this environment, the RF pulse 620 received by the implanted wireless neurostimulator 14 increases in amplitude, and similarly, the current limiter feedback mode operates to prevent the stimulation 636 from exceeding the safety limit 626. Again, this clamp event 628 can be communicated via the feedback subsystem 212, and subsequently, the controller subsystem 214 can reduce the amplitude of the RF pulse, thereby overriding the user input. The reduced RF pulse 604 can produce a correspondingly smaller amplitude of the received waveform 616, and it may no longer be necessary to clamp the stimulation current to keep the current within safe limits. In this way, if the implanted wireless neurostimulator 114 reports that it is receiving excessive RF power, the current limiter feedback can reduce the RF power delivered to the body.

FIG7 is a flow chart illustrating a user's control of an implantable wireless neurostimulator via a programmer in an open-loop feedback system. In one embodiment of the system, a user has a wireless neurostimulator implanted in their body, an RF pulse generator 106 wirelessly transmits stimulation pulses of power to the stimulator 114, and an application on the programmer module 102 (e.g., a smart device) communicates with the RF pulse generator 106. In this embodiment, as shown in block 702, if the user wishes to observe the current status of the pulse generator in operation, the user may open the application, as shown in block 704. As shown in block 706, the application may interrogate the pulse generator using the Bluetooth protocol built into the smart device. As shown in block 708, the RF pulse generator 106 may authenticate the identity of the smart device and securely iterate the serialized patient-assigned application. The authentication process may utilize a unique key specific to the patient's RF pulse generator serial number. As shown in block 720, the application may be customized using the patient-specific unique key by a manufacturer's representative who has programmed the initial patient settings for the stimulation system. If the RF pulse generator denies authentication, as shown in block 718, it may inform the application that the code is invalid and, as shown in block 722, require authentication by an authorized individual using a security check from the device manufacturer, referred to as a "manufacturer's representative." In embodiments, only the manufacturer's representative has access to the security code required to change the RF pulse generator's unique ID stored by the application. If the RF pulse generator authentication system passes, as shown in block 710, the pulse generator module 106 returns all data recorded since the last synchronization. The application may then register the latest information, as shown in 712, and transmit the information to third parties in a secure manner. As shown in block 714, the application may maintain a database recording all system diagnostic results and values, changes to settings made by the user and the feedback system, and a global runtime history. As shown in block 716, the application may then display relevant data to the user, including battery capacity, current program parameters, runtime, pulse width, frequency, amplitude, and feedback system status.

FIG8 is another example flow chart illustrating a user controlling a wireless stimulator using upper and lower current amplitude limits. As shown in block 802, the user wishes to change the amplitude of the stimulation signal. As shown in block 704, the user may open the application, and as shown in block 804, the application may communicate with the RF pulse generator through the process described in FIG7 , successfully authenticate, and display the current status to the user. The application displays stimulation amplitude as the most common changeable interface option and two arrows that allow the user to adjust the current amplitude. As shown in block 806, the user may decide whether to increase or decrease the stimulation based on their pain level. As shown in block 808, if the user chooses to increase the current amplitude, the user may press the up arrow on the application screen. The application may include a safety maximum limiting algorithm. Therefore, as shown in block 810, if the application identifies a request to increase the current amplitude as exceeding a preset safety maximum, as shown in block 812, the application will display an error message and will not communicate with the RF pulse generator module 106. If the user presses the up arrow, as shown in block 808, and the current amplitude request does not exceed the maximum allowed current amplitude, as shown in block 814, the application will send a command to the RF pulse generator module 106 to increase the amplitude. As shown in block 816, the RF pulse generator module 106 may then attempt to increase the current amplitude of the stimulation. If the RF pulse generator successfully increases the current amplitude, as shown in block 818, the RF pulse generator module 106 may briefly vibrate to physically confirm to the user that the amplitude has been increased. As shown in block 820, the RF pulse generator module 106 can also send a confirmation of the amplitude increase back to the application, as shown in block 822, and the application may then display the updated current amplitude level.

If the user decides to decrease the current amplitude level in block 806, as shown in block 828, the user can press the down arrow on the app. If the current amplitude level is already zero, as shown in block 830, the app recognizes that the current amplitude cannot be decreased further and, as shown in block 832, displays an error message to the user without transmitting any data to the RF pulse generator. If the current amplitude level is not zero, as shown in block 834, the app can send instructions to the RF pulse generator module 106 to decrease the current amplitude level accordingly. The RF pulse generator can then attempt to decrease the current amplitude level stimulating the RF pulse generator module 106. If successful, as shown in block 842, the RF pulse generator module 106 can perform a short vibration to physically confirm to the user that the current amplitude level has been decreased. As shown in block 838, the RF pulse generator module 106 can send confirmation of the current amplitude level decrease back to the app. As shown in block 840, the app can then display the updated current amplitude level. If the current amplitude level fails to decrease or increase, the RF pulse generator module 106 can perform a series of short vibrations to alert the user and send an error message to the application, as shown in block 824. The application receives the error and can display the data for the user's benefit, as shown in block 826.

FIG9 is another example flow chart illustrating a process by which a user controls the wireless neurostimulator 114 using preprogrammed parameter settings. As indicated by block 902, the user wishes to change a parameter program. When the user is implanted with the wireless neurostimulator, or during a visit to a physician, a manufacturer's representative may determine and provide the patient/user with a preset program for the RF pulse generator, which has different stimulation parameters to be used to treat the user. The user can then switch between the various parameter programs as needed. As indicated by block 704, the user can open an application on their smart device, which first follows the process described in FIG7 , communicating with the RF pulse generator module 106, successfully authenticating, and displaying the current status of the RF pulse generator module 106, including the current program parameter settings, as indicated by block 812. In this embodiment, as indicated by block 904, the user can select the program they wish to use through the application's user interface. As indicated by block 906, the application can then access a library of preprogrammed parameters approved by the manufacturer's representative, allowing the user to switch between them as needed and in accordance with the manufacturer's representative's instructions. As shown in block 908, a table can be displayed to the user, with each row displaying the program's code name, as shown in block 910, and listing its basic parameter settings, as shown in block 912, including but not limited to: pulse width, frequency, cycle timing, pulse shape, duration, and feedback sensitivity. As shown in block 912, the user can then select the row containing the desired parameter preset program to use. As shown in block 916, the application can send a command to the RF pulse generator module 106 to change the parameter settings. The RF pulse generator module 106 can attempt to change the parameter settings 154. If the parameter settings are successfully changed, as shown in block 920, the RF pulse generator module 106 can perform a unique vibration pattern to physically confirm to the user that the parameter settings have been changed. Furthermore, as shown in block 922, the RF pulse generator module 106 can send confirmation back to the application that the parameter changes were successful, and the application can display the updated current program, as shown in block 924. If the parameter program change fails, as shown in block 926, the RF pulse generator module 106 may perform a series of short vibrations to alert the user and send an error message to the application, as shown in block 928, which receives the error and may display it to the user.

FIG10 is another example flow chart of a process for a low battery condition in the RF pulse generator module 106. In this embodiment, as shown in block 1002, the remaining battery power level of the RF pulse generator module is identified as low. As shown in block 1004, the RF pulse generator module 106 periodically queries the power supply battery subsystem 210 for its current power level, and the RF pulse generator microprocessor queries the battery whether its remaining power level is below a threshold. If the remaining battery power level is above the threshold, as shown in block 1006, the RF pulse generator module 106 may store the current battery status to be sent to the application during the next synchronization. If the remaining battery power level is below the threshold, as shown in block 1008, the RF pulse generator module 106 may push a low battery notification to the application. As shown in block 1010, the RF pulse generator module 106 may continue to perform a short vibration sequence to alert the user of a problem and send a notification to the application. If the application continues to receive no confirmation of the notification, as shown in block 1010, the RF pulse generator may continue to perform short vibration pulses to notify the user. If the app successfully receives the notification, as shown in block 1012, it may display the notification and may request user confirmation. For example, if one minute passes without dismissing the notification message on the app, as shown in block 1014, the app notifies the RF pulse generator module 106 of the lack of manual confirmation, and the RF pulse generator module 106 may initiate a vibration pulse to notify the user, as shown in block 1010. If the user dismisses the notification, as shown in block 1016, the app may display a passive notification to switch batteries. If a predetermined amount of time, such as five minutes, passes without switching batteries, as shown in block 1014, the app may notify the RF pulse generator module 106 of the lack of manual confirmation, and the RF pulse generator module 106 may initiate a vibration pulse, as shown in block 1010. If the RF pulse generator module battery is switched, as shown in block 1018, the RF pulse generator module 106 restarts and interrogates the battery to assess remaining power. If the remaining battery power is below the threshold, as shown in block 1008, the cycle may begin again with the RF pulse generator module 106 sending a notification to the application. If the remaining battery power is above the threshold, as shown in block 1020, the RF pulse generator module 106 may send a notification to the application indicating that the battery change was successful. The application may then communicate with the RF pulse generator module 106 and display the current system status, as shown in block 1022.

FIG11 is another example flow chart of a process for a manufacturer's representative to program an implanted wireless neurostimulator. In this embodiment, as shown in block 1102, a user desires a manufacturer's representative to set up a personalized parameter program from a remote location other than the user's location for the user to use as needed. The manufacturer's representative is able to access the user-set parameter program via a secure web-based service. As shown in block 1104, the manufacturer's representative can securely log into the manufacturer's web service on a device connected to the Internet. If the manufacturer's representative is registering a user for the first time in their care area, as shown in block 1106, they enter basic patient information, the unique ID of the RF pulse generator, and the unique ID of the program application. Once a new or existing manufacturer's representative user has been registered, as shown in block 1108, the manufacturer's representative accesses the user's profile. As shown in block 1110, the manufacturer's representative is able to view a list of currently assigned parameter programs for the specific user. As shown in block 1112, this list may include previously active and retired parameter preset programs. As shown in block 1114, the manufacturer's representative can activate/deactivate the preset parameter program by checking the box adjacent to the appropriate row displayed in the table. The manufacturer's representative can then submit and save the assigned new preset parameter program, as shown in block 1116. The user's programmer application can receive the new preset parameter program the next time it synchronizes with the manufacturer's database.

FIG12 is a circuit diagram illustrating an example of a wireless neural stimulator (such as stimulator 114). This example includes paired electrodes, including a cathode electrode 1208 and an anode electrode 1210, as shown. When energized, the charged electrodes create a volume conduction field of current density within the tissue. In this embodiment, wireless energy is received via a dipole antenna 238. At least four diodes are connected together to form a full-wave bridge rectifier 1202 attached to the dipole antenna 238. Each diode, up to 100 microns in length, uses a junction potential to prevent negative current from flowing from the cathode to the anode from passing through the device when the current does not exceed a reverse threshold. For neural stimulation via wireless power transmitted through tissue, the naturally low efficiency of lossy materials can result in a low threshold voltage. In this embodiment, a zero-bias diode rectifier results in a low output impedance for the device. A resistor 1204 and a smoothing capacitor 1206 are placed between the output nodes of the bridge rectifier to discharge the electrodes to the ground of the bridge anode. The rectifier bridge 1202 includes two branches of a diode pair, connecting anode to cathode and then cathode to cathode. Electrodes 1208 and 1210 are connected to the output of the charge balancing circuit 246.

FIG13 is a circuit diagram showing another example of a wireless neural stimulator (such as stimulator 114). The example shown in FIG13 includes multiple electrode controls and can adopt fully closed-loop control. The stimulator includes an electrode array 254, wherein the polarity of the electrode can be specified as a cathode or anode, and for this purpose, it is possible to alternately not supply any energy to the electrode. When energized, the charged electrode creates a volume conduction field of current density within the tissue. In this embodiment, wireless energy is received by the device via a dipole antenna 238. The electrode array 254 is controlled by an onboard controller circuit 242, which sends appropriate bit information to the electrode interface 252 to set the polarity of each electrode in the array and to power each individual electrode. Not powering a specific electrode will set the electrode in a functional off position. In another embodiment (not shown), the amount of current sent to each electrode is also controlled by the controller 242. The controller current, polarity, and power state parameter data shown as controller outputs are sent back to the antenna 238 for telemetry transmission back to the pulse generator module 106. The controller 242 also includes current monitoring functionality and sets a bit register counter so that the status of the total current drawn can be sent back to the pulse generator module 106 .

At least four diodes can be connected together to form a full-wave bridge rectifier 302 attached to the dipole antenna 238. Each diode, up to 100 microns in length, uses a junction potential to prevent negative current from flowing from the cathode to the anode from passing through the device unless the current exceeds a reverse threshold. For neural stimulation via wireless power transmitted through tissue, the natural inefficiency of lossy materials can result in a low threshold voltage. In this embodiment, the zero-bias diode rectifier results in a low output impedance for the device. Resistor 1204 and smoothing capacitor 1206 are placed between the output nodes of the bridge rectifier to discharge the electrode to ground at the bridge anode. The rectifier bridge 1202 can include two branches of a diode pair, connecting the anode to the cathode, and then connecting the cathode to the cathode. The electrode polarity output, cathode 1208 and anode 1210, are both connected to the output formed by the bridge connection. Charge balancing circuit 246 and current limiting circuit 248 are placed in series with the output.

14 is a block diagram illustrating an example of control functionality 1405 and feedback functionality 1430 of a wireless implantable neurostimulator 1400, such as those described above or below. As discussed above in conjunction with FIG2 , an example embodiment of the implantable neurostimulator 1400 may be an implanted neurostimulator module 114. The control functionality 1405 includes functionality 1410 for polarity switching of electrodes and functionality 1420 for power-on reset.

For example, the polarity switching function 1410 can use a polarity routing switching network to assign polarity to the electrodes 254. For example, the polarity assigned to the electrodes can be one of the following: cathode (negative polarity), anode (positive polarity), or neutral (off) polarity. The polarity assignment information for each of the electrodes 254 can be included in the input signal received by the wireless implantable neurostimulator 1400 from the RF pulse generator module 106 via the Rx antenna 238. Since the programmer module 102 can control the RF pulse generator module 106, as shown in FIG2, the polarity of the electrodes 254 can be remotely controlled by the programmer through the programmer module 102.

The power-on reset function 1420 can reset the polarity assignment of each electrode immediately upon each power-on event. As described in more detail below, this reset operation can cause the RF pulse generator module 106 to transmit polarity assignment information to the wireless implantable neurostimulator 1400. Once the polarity assignment information is received by the wireless implantable neurostimulator 1400, the polarity assignment information can be stored in a register file or other short-term memory component. Thereafter, the polarity assignment information can be used to configure the polarity assignment of each electrode. If the polarity assignment information transmitted in response to the reset encodes the same polarity state as before the power-on event, the polarity state of each electrode can be maintained before and after each power-on event.

Feedback functionality 1430 includes functionality 1440 for monitoring power delivered to electrodes 254 and functionality 1450 for making impedance diagnostics for electrodes 254. For example, delivered power functionality 1440 may provide data encoding the amount of power delivered from electrodes 254 to stimulatable tissue, and tissue impedance diagnostic functionality 1450 may provide data encoding diagnostic information about tissue impedance. Tissue impedance is the electrical impedance of tissue seen between the negative and positive electrodes when stimulation current is delivered between the negative and positive electrodes.

The feedback functionality 1430 can additionally include a tissue depth estimation functionality 1460 to provide data indicating the overall tissue depth that an input radio frequency (RF) signal from a pulse generator module (e.g., the RF pulse generator module 106) has penetrated before reaching an implanted antenna (e.g., the RX antenna 238) within the wireless implantable neurostimulator 1400 (e.g., the implanted neurostimulator module 114). For example, a tissue depth estimate can be provided by comparing the power of the received input signal to the power of the RF pulses transmitted by the RF pulse generator 106. The ratio of the power of the received input signal to the power of the RF pulses transmitted by the RF pulse generator 106 can indicate the attenuation caused by wave propagation through the tissue. For example, a second harmonic, as described below, can be received by the RF pulse generator 106 and used with the power of the input signal transmitted by the RF pulse generator to determine tissue depth. The attenuation can be used to infer the overall depth of the wireless implantable neurostimulator 1400 beneath the skin.

1 and 2 , data from blocks 1440 , 1450 , and 1460 may be transmitted to the RF pulse generator 106 via, for example, the Tx antenna 110 .

As discussed above in conjunction with Figures 1, 2, 12, and 13, the wireless implantable neurostimulator 1400 can utilize a rectifier circuit to convert an input signal (e.g., having a carrier frequency in the range of about 800 MHz to about 6 GHz) into direct current (DC) power to drive the electrodes 254. Some embodiments can provide the ability to remotely adjust the DC power. As described in more detail below, some embodiments can also provide different amounts of power to different electrodes.

FIG15 is a schematic diagram illustrating an example of a wireless implantable neurostimulator 1500 having components implementing control and feedback functions as discussed above in conjunction with FIG14 . An RX antenna 1505 receives an input signal. As described above, the RX antenna 1505 can be embedded as a dipole, microstrip, folded dipole, or other antenna configuration in addition to a coiled configuration. The input signal has a carrier frequency in the GHz range and contains electrical energy for powering the wireless implantable neurostimulator 1500 and providing stimulation pulses to the electrodes 254. Once received by the antenna 1505, the input signal is routed to a power management circuit 1510. The power management circuit 1510 is configured to rectify the input signal and convert it into a DC power supply. For example, the power management circuit 1510 may include a diode bridge rectifier, such as the diode bridge rectifier 1202 illustrated in FIG12 . The DC power supply provides power to the stimulation circuit 1511 and the logic power circuit 1513. Rectification may utilize one or more full-wave diode bridge rectifiers within the power management circuit 1510. In one embodiment, as illustrated by shunt register 1204 in FIG. 12 , a resistor may be placed between the output nodes of the bridge rectifier to discharge the electrode to ground at the anode of the bridge.

FIG16 illustrates an example pulse waveform generated by the MFS sent to the power management circuit 1510 of the wireless implantable neurostimulator 1500. This can be a typical pulse waveform generated by the RF pulse generator module 106 and then delivered on a carrier frequency. The pulse amplitude is ramped in pulse width (duration), with values ranging from -9 dB to +6 dB. In certain embodiments, the ramp start and end power levels can be set to any range from 0 to 60 dB. The gain control is adjustable and can be an input parameter from the RF pulse generator module 106 to the stimulation power management circuit 1510. In some embodiments, as shown in FIG16 , the pulse width Pw can range from 100 to 300 microseconds (μs). In other embodiments not shown, the pulse width can range from approximately 5 microseconds (5 μs) to approximately 10 milliseconds (10 ms). As shown, the pulse frequency (rate) can range from approximately 5 Hz to 120 Hz. In some embodiments not shown, the pulse frequency can be less than 5 Hz and up to about 10,000 Hz.

Returning to FIG15, as discussed above, based on the received waveform, the stimulation circuit 1511 creates a stimulation waveform to be sent to the electrode 254 to stimulate the stimulable tissue. In some embodiments, the stimulation circuit 1511 can route the waveform to a pulse shaping resistor-capacitor (RC) timer 1512 to shape the waveform of each pulse as it travels. As illustrated in FIG12 and described above, an example RC timer can be a shunt resistor 1204 and a smoothing capacitor 1206. The pulse shaping RC timer 1512 can also be used, but is not limited to, to reverse the pulse to create a pre-anodic soak or provide a slow ramp in the waveform.

As discussed above, once the waveform has been shaped, cathodic energy (the energy emitted on the cathodic branch 1515 of the polarity routing switching network 1523) is routed through the passive charge balancing circuit 1518 to prevent the buildup of harmful chemicals at the electrode 254. The cathodic energy is then routed to input 1 of the polarity routing switching network 1521, block 1522. Anodic energy (the energy emitted on the anodic branch 1514 of the polarity routing switching network 1523) is then routed to input 2 of the polarity routing switching network 1521, block 1523. Polarity routing switching network 1521 then delivers stimulation energy in the form of cathodic energy, anodic energy, or no energy to each of the electrodes 254, according to the corresponding polarity assignment, which is controlled based on a set of bits stored in register file 1532. The bits stored in register file 1532 are output to the select input 1534 of the polarity routing switching network 1523, which causes input 1 or input 2 to be appropriately routed to the electrode.

Referring now to FIG17 , a schematic diagram of an example of a polarity routing switching network 1700 is shown. As discussed above, cathodic (-) energy and anodic energy are received at input 1 (block 1522) and input 2 (block 1523), respectively. Polarity routing switching network 1700 has one of its outputs coupled to an electrode in electrodes 254, which can include as few as two electrodes or as many as sixteen electrodes. In this embodiment, eight electrodes are shown as an example.

Polarity routing switch network 1700 is configured to individually connect each output to either input 1 or input 2, or disconnect the output from either input. This selects the polarity for each individual electrode 254 as one of the following: neutral (off), cathode (negative), or anode (positive). Each output is coupled to a corresponding three-state switch 1730 for setting the output's connection state. Each three-state switch is controlled by one or more bits from select input 1750. In some embodiments, select input 1750 can assign more than one bit to each three-state switch. For example, two bits can encode the three-state information. Thus, as further described below, the state of each output of polarity routing switch 1700 can be controlled by information encoded in bits stored in register 1532, which can be set by polarity assignment information received from remote RF pulse generator module 106.

Returning to FIG15 , power and impedance sensing circuits can be used to determine the power delivered to the tissue and the impedance of the tissue. For example, a sensing resistor 1518 can be placed in series with the anode branch 1514. A current sensing circuit 1519 senses the current across the resistor 1518, and a voltage sensing circuit 1520 senses the voltage across the resistor. The measured current and voltage can correspond to the actual current and voltage applied by the electrode to the tissue.

As described below, the measured current and voltage can be provided as feedback information to the RF pulse generator module 106. The power delivered to the tissue can be determined by integrating the product of the measured current and voltage over the duration of the waveform delivered to the electrode 254. Similarly, the impedance of the tissue can be determined based on the measured voltage applied to the electrode and the current applied to the tissue. Depending on the implementation of the feature and whether the impedance and power feedback are measured individually or combined, alternative circuits (not shown) can also be used instead of the sense resistor 1518.

The measurements from the current sensing circuit 1519 and the voltage sensing circuit 1520 can be routed to a voltage controlled oscillator (VCO) 1533 or an equivalent circuit capable of converting an analog signal source into a carrier signal for modulation. The VCO 1533 can generate a digital signal having a carrier frequency. The carrier frequency can vary based on the analog measurement results (e.g., voltage, differential of voltage, power, etc.). The VCO 1533 can also use amplitude modulation or phase shift keying to modulate the feedback information at the carrier frequency. The VCO or equivalent circuit can be collectively referred to as an analog controlled carrier modulator. The modulator can send information encoding the sensed current or voltage back to the RF pulse generator 106.

Antenna 1525 can transmit a modulated signal back to RF pulse generator module 106, for example, in the GHz frequency range. In some embodiments, antennas 1505 and 1525 can be the same physical antenna. In other embodiments, antennas 1505 and 1525 can be separate physical antennas. In separate antenna embodiments, antenna 1525 can operate at a resonant frequency higher than the resonant frequency of antenna 1505 to transmit stimulation feedback to RF pulse generator module 106. In some embodiments, antenna 1525 can also operate at a higher resonant frequency to receive data encoding polarity assignment information from RF pulse generator module 106.

Antenna 1525 may be a telemetry antenna 1525 that can route received data (such as polarity assignment information) to stimulation feedback circuit 1530. The encoded polarity assignment information may be in a frequency band in the GHz range. The received data may be demodulated by demodulation circuit 1531 and then stored in register file 1532. Register file 1532 may be a volatile memory. Register file 1532 may be an 8-channel memory bank capable of storing, for example, a few bits of data for each channel to be assigned a polarity. Some embodiments may not have a register file, while some embodiments may have a register file of up to 64 bits. As indicated by arrow 1534, the information encoded by these bits may be sent as a polarity select signal to polarity routing switch network 1521. These bits may encode the polarity assignment for each output of the polarity routing switch network as one of the following: + (positive), - (negative), or 0 (neutral). Each output is connected to an electrode, and the channel setting determines whether the electrode will be set as anode (positive), cathode (negative), or off (neutral).

Returning to the power management circuit 1510, in some embodiments, approximately 90% of the received energy is routed to the stimulation circuit 1511, and less than 10% of the received energy is routed to the logic power circuit 1513. The logic power circuit 1513 can power control components for polarity and telemetry. However, in some embodiments, the power circuit 1513 does not provide actual power to the electrodes for tissue stimulation. In certain embodiments, energy leaving the logic power circuit 1513 is sent to a capacitor circuit 1516 to store a certain amount of readily available energy. The voltage of the charge stored in the capacitor circuit 1516 can be represented as Vdc. This stored energy is then used to power the power-on reset circuit 1516, which is configured to send a reset signal upon a power-on event. If the wireless implantable neurostimulator 1500 consumes power for a certain period of time (e.g., in the range of approximately 1 millisecond to over 10 milliseconds), the contents of the register file 1532 and the polarity setting of the polarity routing switch network 1521 can be reset to zero. For example, the wireless implantable neurostimulator 1500 consumes power when it becomes misaligned with the RF pulse generator module 106. Using this stored energy, the power-on reset circuit 1540 can provide a reset signal as indicated by arrow 1517. The reset signal can cause the stimulation feedback circuit 1530 to notify the RF pulse generator module 106 about the power consumption. For example, the stimulation feedback circuit 1530 can transmit a telemetry feedback signal to the RF pulse generator module 106 as a status notification of the power outage. The telemetry feedback signal can be transmitted in response to the reset signal and immediately after the neurostimulator 1500 is powered on again. The RF pulse generator module 106 can then transmit one or more telemetry packets to the implantable wireless neurostimulator. The telemetry packets contain polarity assignment information, which can be saved in the register file 1532 and sent to the polarity routing switch network 1521. Therefore, the polarity assignment information in register file 1532 can be recovered from the telemetry data packet transmitted by RF pulse generator module 106, and the polarity assignment of each output section of polarity routing switch network 1521 can be updated accordingly based on the polarity assignment information.

The telemetry antenna 1525 can transmit a telemetry feedback signal back to the RF pulse generator module 106 at a frequency higher than the characteristic frequency of the RX antenna 1505. In one embodiment, the telemetry antenna 1525 can have an elevated resonant frequency that is the second harmonic of the characteristic frequency of the RX antenna 1505. For example, the second harmonic can be utilized to transmit power feedback information estimating the amount of power received by the electrode. This feedback information can then be used by the RF pulse generator 106 when determining any adjustments to the power level transmitted by the RF pulse generator 106. In a similar manner, second harmonic energy can be used to detect tissue depth. Second harmonic emissions can be detected by, for example, an external antenna on the RF pulse generator module 106 tuned to the second harmonic. As a general matter, the power management circuit 1510 can include a rectifier circuit, which is a nonlinear device capable of generating harmonic energy from an input signal. Harvesting such harmonic energy to transmit the telemetry feedback signal can improve the efficiency of the wireless implantable neurostimulator 1500. 18A and 18B and the following discussion demonstrate the feasibility of utilizing the second harmonic to transmit telemetry signals to the RF pulse generator module 106 .

Figures 18A and 18B show the example full-wave rectified sine wave and the corresponding spectrum, respectively. Specifically, a full-wave rectified 915MHz sine wave is being analyzed. In this example, the second harmonic of the 915MHz sine wave is the 1830MHz output harmonic. This harmonic can be attenuated by the amount of tissue that the harmonic needs to pass through before reaching the external harmonic receiver antenna. In general, an estimate of the power level during harmonic propagation can reveal the feasibility of this method. The estimate can take into account the power of the input signal received at the receiving antenna (e.g., at antenna 1505 and at 915MHz), the power of the second harmonic radiated from the rectified 915MHz waveform, the attenuation of the second harmonic propagating through the tissue medium, and an estimate of the coupling efficiency for the harmonic antenna. The average power emitted in watts can be estimated by equation 1:

P _t =PkDuC

P _r =(P _t /A _antenna )(1-{Г} ² )Lλ ² G _r η/4π (1)

Table 1 below lists the meaning of each symbol and the corresponding value used in the estimation.

Table 1. Parameters used in developing the received power equation.

When estimating L, losses due to attenuation in the tissue, from the fundamental frequency (for the forward path to the implanted neurostimulator module 114) and the second harmonic (for the reverse path from the implanted neurostimulator module 114) may be considered. The plane wave attenuation is given by the following equation (2) and Table 2:

in

f = frequency

c = speed of light in a vacuum

ε _r = relative dielectric constant

σ = conductivity

ε ₀ = permittivity of vacuum (2)

Frequency (MHz) r S/m Napier/m Power loss 0.915e9 41.329 0.87169 25.030 0.606 1.83e9 38.823 1.1965 35.773 0.489

Table 2. Output power loss for 915 MHz and 1830 MHz harmonics at 1 cm depth.

The worst-case assumption for coupling harmonics to an external receiving antenna is that the power radiated by the implanted telemetry antenna (e.g., telemetry antenna 1625) at the harmonic frequency is completely absorbed by the external receiving antenna. This worst-case scenario can be modeled by the following equation (3) and Table 3:

_{Pnr ＝ PtLnLna ​}

in

n＝nth harmonic

_Pnr = nth harmonic antenna received power (W)

_Pt = total power received by the implant (W)

_Ln = power of the nth harmonic of the implant power (W)

_Lna = attenuation loss factor (3)

dBm 0.356 .2421 0.489 0.0422 16.3

Table 3. Total output power and received harmonic power for the 2nd harmonic.

In summary, using these developed equations, the reduction in power level is estimated to be approximately 10 dB. This includes the attenuation of a 915 MHz plane wave propagating through tissue from a depth of 1 cm to 6 cm. The average received power, Pr, is 0.356 W at 915 MHz. As obtained from SPICE simulations using a full-wave rectified 915 MHz sine wave, the power in the second harmonic (1830 MHz) is approximately -6.16 dB. The estimated value of 10 dB represents a 10-fold reduction, which is acceptable for field operations. Thus, the feasibility of utilizing the second harmonic to send telemetry feedback signals back to the RF pulse generator module 106 has been demonstrated.

19 is a flow chart illustrating an example of the operation of the control and feedback functions of a neurostimulator. The operations are described with respect to the wireless implantable neurostimulator 1500, although the operations may be performed by other variations of wireless implantable neurostimulators, such as the wireless implantable neurostimulators described above.

The RF pulse generator module 106 transmits one or more signals containing electrical energy (1900). In some embodiments, the RF pulse generator module 106 may also be referred to as a microwave field stimulator (MFS). The signal may be modulated in the microwave frequency range (e.g., from about 800 MHz to about 6 GHz).

An input signal containing electrical energy is received 1910 by the RX antenna 1505 of the neurostimulator 1500. As discussed above, the RX antenna 1505 may be embodied as a dipole, microstrip, folded dipole, or other antenna configurations in addition to a coiled configuration.

As shown in block 1911, the input signal is rectified and demodulated by the power management circuit 1510. Some embodiments may provide waveform shaping, and in this case, the rectified and demodulated signal is passed to a pulse shaping RC timer (1912). Charge balancing may be performed by the charge balancing circuit 1518 to provide a charge-balanced waveform (1913). The shaped and charge-balanced pulses are then routed to the electrodes 254 (1920), which deliver stimulation to the stimulatable tissue (1921).

At the same time, the current and voltage delivered to the tissue are measured using current sensor 1519 and voltage sensor 1520 (1914). These measurements are modulated and amplified (1915) and transmitted from telemetry antenna 1525 to RF pulse generator module 106 (1916). In some embodiments, telemetry antenna 1525 and RX antenna 1505 can utilize the same physical antenna embedded within neurostimulator 1500. RF pulse generator module 106 can use the measured current and voltage to determine the power delivered to the tissue and the impedance of the tissue.

For example, the RF pulse generator module 106 may store the received feedback information, such as information encoding the current and voltage. For example, the feedback information may be stored as current values in hardware memory on the RF pulse generator module 106. Based on the feedback information, the RF pulse generator module 106 may calculate the impedance value of the tissue based on the current and voltage delivered to the tissue.

In addition, the RF pulse generator module 106 can calculate the power delivered to the tissue based on the stored current and voltage (1950). The RF pulse generator module 106 can then determine whether the power level should be adjusted by comparing the calculated power with the desired power stored in, for example, a lookup table stored on the RF pulse generator module 106. For example, the lookup table can list the optimal amount of power that should be delivered to the tissue based on the position of the receive antenna 1505 on the neurostimulator 1500 relative to the position of the transmit antenna on the RF pulse generator module 106. This relative position can be determined based on the feedback information. The power measurement in the feedback information can then be correlated with the optimal value to determine whether a power level adjustment should be made to increase or decrease the amplitude of the stimulation of the power delivered to the electrode. The power level adjustment information can then enable the RF pulse generator module 106 to adjust the transmission parameters to provide the adjusted power to the RX antenna 1505.

In addition to the input signal containing electrical energy for stimulation, the RF pulse generator module 106 may transmit an input signal containing telemetry data (such as polarity assignment information) (1930). For example, upon power-up, the RF pulse generator module 106 may transmit data encoding the last electrode polarity setting for each electrode before the RF pulse generator module 106 is powered down. This data may be transmitted to the telemetry antenna 1525 as a digital data stream embedded on a carrier waveform. In some embodiments, the data stream may include telemetry data packets. The telemetry data packets are received from the RF pulse generator module 106 and subsequently demodulated by the demodulation circuit 1531. The polarity setting information in the telemetry data packets is stored in the register file 1532 (1932). The polarity of each electrode 254 is programmed (1933) according to the polarity setting information stored in the register file 1532. For example, the polarity of each electrode may be set to one of the following: anode (positive), cathode (negative), or neutral (off).

As discussed above, upon power-on reset, the polarity setting information is resent from the RF pulse generator module 106 to be stored in the register file 1532 (1932). This is indicated by the arrow from 1932 to 1916. The polarity setting information stored in the register file 1532 can then be used to program the polarity of each electrode 254 (1933). This feature allows the passive device to be reprogrammed remotely from the RF pulse generator module 106 at the beginning of each power session, thereby avoiding the need to maintain CMOS memory within the neurostimulator 1500.

A number of embodiments have been described. Nevertheless, it should be understood that various modifications can be made. Accordingly, other embodiments are within the scope of the following claims.

Claims (16)

1. A system for modulating neural tissue in a patient, comprising: An implantable neurostimulator includes one or more electrodes, at least one antenna, and an electrode interface; A radio frequency (RF) pulse generator module includes an antenna module configured to transmit an input signal via electrical radiation coupling to at least one antenna in an implantable neurostimulator. The input signal contains electrical energy and polarity assignment information specifying the polarity assignment of one or more electrodes in the implantable neurostimulator. The antenna module is further configured to transmit a first input signal containing the electrical energy and a second input signal containing the polarity assignment information to the implantable neurostimulator, wherein the first input signal has a different carrier frequency than the second input signal. The implantable neurostimulator is configured as follows: Control the electrode interface such that the one or more electrodes have the polarity assignment specified by the polarity assignment information; Using the electrical energy contained in the input signal, one or more electrical pulses suitable for modulating neural tissue are created; and The electrical pulses are supplied to the one or more electrodes through the electrode interface, such that the one or more electrodes apply the electrical pulses to the nerve tissue using the polarity assignment specified by the polarity assignment information. 2. The system of claim 1, wherein the implantable neurostimulator is configured to transmit a stimulation feedback signal indicative of one or more parameters of the electrical pulse to the antenna module of the radio frequency pulse generator module. 3. The system of claim 2, wherein the radio frequency pulse generator module includes one or more circuits coupled to the antenna module, and the one or more circuits are configured to receive the stimulus feedback signal and adjust parameters of the input signal based on the stimulus feedback signal. 4. The system of claim 2 or 3, wherein the antenna module includes a first antenna and a second antenna, the first antenna being configured to operate at a first frequency to transmit the first input signal, and the second antenna being configured to operate at a second frequency to receive the stimulation feedback signal from the at least one antenna of the implantable neurostimulator, wherein the second frequency of the second antenna is higher than the resonant frequency of the first antenna. 5. The system according to claim 4, wherein the second frequency of the second antenna is the second harmonic of the resonant frequency of the first antenna. 6. The system according to claim 4, wherein the second frequency and the resonant frequency are in the range of 300MHz to 6GHz. 7. The system of claim 1, wherein the at least one antenna of the implantable neurostimulator has a length between 0.1 mm and 7 cm and a width between 0.1 mm and 3 mm. 8. The system of claim 1, wherein the at least one antenna of the implantable neurostimulator is a dipole antenna. 9. The system according to claim 2, wherein: The polarity specified by the polarity assignment information includes negative polarity, positive polarity, or neutral polarity; The electrical pulse includes a cathode portion and an anode portion; and The electrode interface includes a polarity routing switching network, which includes a first input and a second input. The first input receives the cathode portion of the electrical pulse, and the second input receives the anode portion of the electrical pulse. The polarity routing switching network is configured to route the cathode portion to an electrode designated as negative polarity among the one or more electrodes, route the anode portion to an electrode designated as positive polarity among the one or more electrodes, and disconnect an electrode designated as neutral polarity among the one or more electrodes from the electrical pulse. 10. The system of claim 9, wherein the implantable neurostimulator comprises one or more circuits having a register having an output coupled to a selection input of the polarity routing switching network, wherein the register is configured to store the polarity assignment information and to send the stored polarity assignment information from the output of the register to the selection input of the polarity routing switching network to control the polarity routing switching network to route the cathode portion to an electrode of the one or more electrodes having a specified negative polarity, to route the anode portion to an electrode of the one or more electrodes having a specified positive polarity, and to disconnect an electrode of the one or more electrodes having a specified neutral polarity from the electrical pulse. 11. The system of claim 10, wherein the one or more circuits include a power-on reset circuit and a capacitor, wherein the capacitor uses a portion of the electrical energy contained in the input signal to store charge, and wherein the capacitor is configured to energize the power-on reset circuit when the implanted neurostimulator consumes power to reset the polarity assignment information stored in the register. 12. The system of claim 11, wherein the one or more parameters include the current and voltage of the electrical pulse, and the implantable neurostimulator includes a current sensor and a voltage sensor, the current sensor being configured to sense the amount of current in the electrical pulse, and the voltage sensor being configured to sense the voltage in the electrical pulse. 13. The system of claim 12, wherein the current sensor and the voltage sensor are coupled to a resistor, the resistor being positioned in series with the second input portion of the anode portion of the polarity routing network that receives the electrical pulse. 14. The system of claim 13, wherein the current sensor and the voltage sensor are coupled to an analog-controlled carrier modulator configured to transmit the sensed current and voltage to the antenna module. 15. The system of claim 1, wherein the implantable neurostimulator includes a rectifier circuit coupled to an RC timer, wherein the rectifier circuit is configured to rectify the first input signal received by the at least one antenna to generate the electrical pulse, and the RC timer is configured to shape the electrical pulse. 16. The system of claim 15, wherein the rectifier circuit comprises at least one full-wave bridge rectifier, wherein the full-wave bridge rectifier comprises a plurality of diodes, each diode having a length of less than 100 micrometers.