Circuits for implantable devices

Abstract

An integrated circuit comprises: a radio frequency (RF) to direct current (DC) rectifier circuit coupled to one or more antennas on a wirelessly powered implantable device, the rectifier circuit being configured to: rectify an input RF signal received from an external controller at the one or more antennas and through electrical radiation coupling; and extract DC power and configuration data from the input RF signal; a logic control circuit connected to the rectifier circuit and a drive circuit, the logic control circuit being configured to: generate current for the drive circuit using only the extracted DC power; set polarity state information for each electrode according to the extracted configuration data; and a drive circuit coupled to one or more electrodes, the drive circuit comprising a current mirror and being configured to: direct stimulation current to each electrode via the current mirror only from the generated current.

Description

[0001] This application is a divisional application. The original application was a patent application submitted to the China Patent Office on February 28, 2017 (the international application date is July 10, 2015), with application number 201580046708.3, and the name of the invention is “Circuit for implantable devices”.

[0002] Related Applications

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 022,768, filed on July 10, 2014, which is hereby incorporated by reference in its entirety. Technical Field

[0004] The present application relates generally to implantable stimulators. Background Art

[0005] Modulation of excitable tissues in the body through electrical stimulation has become an important treatment modality for patients with chronic disabling diseases, such as chronic pain, problems with movement initiation and control, involuntary movements, vascular insufficiency, and irregular heartbeats. A variety of therapeutic in vivo electrical stimulation technologies are available to treat these diseases. For example, devices can be used to deliver stimulation signals to excitable tissues, record vital signs, perform pacing or defibrillation procedures, record action potential activity of target tissues, control drug release from long-acting sustained-release capsules or drug pump units, or interface with the auditory system for hearing assistance. Typically, such devices utilize a subcutaneous battery-operated implantable pulse generator (IPG) to provide power or other charge storage mechanism. Summary of the invention

[0006] In one aspect, some embodiments provide an integrated circuit for a wirelessly powered implantable device, the device being implanted in a patient, the circuit comprising: a radio frequency (RF) to direct current (DC) rectifier circuit coupled to one or more antennas on the wirelessly powered implantable device, the rectifier circuit being configured to: rectify an input RF signal received from an external controller at one or more antennas and through electrical radiation coupling; and extract DC electrical power and configuration data from the input RF signal; a drive circuit coupled to one or more electrodes, configured to: direct a stimulation current to each electrode according to the extracted configuration data to regulate neural tissue in the patient; and a logic control circuit connected to the rectifier circuit and the drive circuit, the logic control circuit being configured to: generate a current for the drive circuit using the extracted DC electrical power alone; set polarity state information for each electrode according to the extracted configuration data; and a drive circuit coupled to one or more electrodes, the drive circuit comprising a current mirror and configured to: direct a stimulation current from the generated current to each electrode via the current mirror alone to regulate neural tissue in the patient.

[0007] Embodiments may include one or more of the following features. The drive circuit may include: a current source digital-to-analog circuit (DAC) and a current sink digital-to-analog circuit (DAC), the current source DAC and the current sink DAC being complementary to each other and both being mirrored to each electrode via a current mirror, wherein the stimulation current may be determined by a current mirror ratio, and wherein the configuration data may include the current mirror ratio. The current mirror ratio may be matched to the number of electrodes.

[0008] The drive circuit may include a switch bank configured to control the polarity state of each electrode. The drive circuit may include a variable shunt resistor adapted to reduce ripple on the electrode connected thereto just after the stimulation current ends.

[0009] The integrated circuit may further include a discharge delay timer for delaying the start of a capacitor coupled to each of the electrodes.

[0010] The integrated circuit may further include: a power-on reset (PoR) circuit for maintaining default state information of each electrode and default parameters of stimulation current of each electrode, the PoR circuit being configured to be triggered by a rising edge and turned off by a falling edge.

[0011] The integrated circuit may also include: one or more address control bits configurable as a logical address of an implantable device that is wirelessly powered by the extracted electrical power. The integrated circuit may also include a diode bridge.

[0012] The rectifying circuit may be coupled to a differential antenna on the wirelessly powered implantable device. The rectifying circuit may include an amplitude modulation (AM) detection circuit for extracting electrical power and configuration data from the input signal.

[0013] The logic control circuit may include: a state machine for recording state information of each electrode based on the extracted configuration data, the configuration data including the polarity setting of each electrode. The logic control circuit may also be configured to set the polarity state of each electrode during the duration of the communication initialization pulse. The logic control circuit may include a timer circuit for controlling the duration of the current generated for the drive circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A high-level diagram depicts an example of a wireless stimulation system.

[0015] Figure 2 A detailed diagram depicting an example of a wireless stimulation system.

[0016] Figure 3 is a flow chart illustrating an example of the operation of a wireless stimulation system.

[0017] Figure 4 is a circuit diagram illustrating an example of a wireless implantable stimulator device.

[0018] Figure 5 is a circuit diagram of another example of a wireless implantable stimulator device.

[0019] Figure 6 is a block diagram illustrating an example of control and feedback functionality of a wireless implantable stimulator device.

[0020] Figure 7 is a schematic diagram of an example of a wireless implantable stimulator device having components for implementing control and feedback functions.

[0021] Figure 8 is a schematic diagram of an example of a polarity routing switch network.

[0022] Fig.9A is a diagram of an exemplary microwave field stimulator (MFS) operating with a wireless implantable stimulator device.

[0023] Fig. 9B is a diagram of another exemplary MFS operating with a wireless implantable stimulator device.

[0024] Fig.10 is a detailed diagram of an exemplary MFS.

[0025] Fig.11is a flow chart illustrating an exemplary process for an MFS to transmit polarity setting information to a wireless implantable stimulator device.

[0026] Fig.12 is another flow chart illustrating an exemplary process by which an MFS receives and processes telemetry feedback signals to make adjustments to subsequent transmissions.

[0027] Fig.13 is a schematic diagram of an exemplary embodiment of power, signal, and control flow on a wireless implantable stimulator device.

[0028] Fig.14 is a diagram of an exemplary application specific integrated circuit (ASIC) for implantable use.

[0029] Fig.15 Shows Fig.14 An exemplary sequence during operation of an ASIC chip is shown.

[0030] Fig.16A Shows Fig.14 Exemplary current steering features of an ASIC chip are shown.

[0031] Fig. 16B Exemplary waveforms simulated based on the depicted ASIC chip model are shown.

[0032] Fig.17 Exemplary waveforms at various points in an ASIC chip with current steering features are shown.

[0033] Like reference numbers are used in the various drawings to indicate like elements. DETAILED DESCRIPTION

[0034] In various embodiments, the disclosed systems and methods are used to apply one or more electrical pulses to target excitable tissue (e.g., nerves) to treat chronic pain, inflammation, arthritis, sleep apnea, seizures, incontinence, cancer-related pain, incontinence, movement initiation and control problems, involuntary movements, vascular insufficiency, arrhythmia, obesity, diabetes, craniofacial pain (e.g., migraine or cluster headaches), and other conditions. In certain embodiments, a device can be used to send electrical energy to target neural tissue by powering a passive implantable wireless stimulator device using remote radio frequency (RF) energy without cables or inductive coupling. The target nerves can include, but are not limited to, the spinal cord and surrounding areas, including the dorsal horn of the spinal cord, the dorsal root ganglia of the spinal nerves, the exiting nerve roots, ganglia, dorsal column fibers of the spinal cord, and peripheral nerve bundles that leave the dorsal column of the spinal cord and the brain, for example, the vagus nerve, occipital nerve, trigeminal nerve, hypoglossal nerve, sacral nerve, coccygeal nerve, etc.

[0035] The wireless stimulation system may include an implantable stimulator device having one or more electrodes and one or more conductive antennas (e.g., dipole or patch antennas) and internal circuitry for frequency, waveform, and power correction. The system may also include an external controller and antenna for transmitting radio frequency or microwave energy from an external source to the implantable stimulator device, providing power without cables and without inductive coupling.

[0036] In various embodiments, the wireless implantable stimulator device is wirelessly powered (thus requiring no wired connection) and contains the circuitry required to receive pulse instructions from a source external to the body. For example, various embodiments employ an internal dipole (or other) antenna configuration to receive RF power via electrical radiation coupling. This allows such a device to generate current capable of stimulating a nerve bundle without a physical connection to an implantable pulse generator (IPG) or the use of an inductive coil.

[0037] According to some embodiments, the wireless implantable stimulator device includes an application specific integrated circuit (ASIC) chip for interacting with an external controller and electrodes contained in the device. The ASIC chip can obtain RF power from the received input signal sent from the external controller to power the wireless implantable stimulator device including the ASIC chip. The ASIC chip can also extract waveform parameters from the received input signal and use this information to create electrical pulses for stimulating excitable tissues through electrodes. Specifically, the ASIC chip includes a current steering feature to evenly reflect current to each electrode while maintaining a compact chip size. In addition, the ASIC chip can extract polarity setting information from the received input signal and use this information to set the polarity of the electrode interface.

[0038] Further description of exemplary wireless systems for providing neural stimulation to a patient may be found in commonly assigned, co-pending published PCT applications PCT / US2012 / 23029, filed January 28, 2011, PCT / US2012 / 32200, filed April 11, 2011, PCT / US2012 / 48903, filed January 28, 2011, PCT / US2012 / 50633, filed August 12, 2011, and PCT / US2012 / 55746, filed September 15, 2011, the entire disclosures of which are incorporated herein by reference.

[0039] Figure 11 depicts a high-level diagram of an example of a wireless stimulation system. The wireless stimulation system may include four main components, namely, 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 implantable wireless stimulator device 114. The programmer module 102 may be a computer device, such as a smartphone, running a program that supports the wireless connection 104 (e.g., ) software application. The application enables the user to view system status and diagnostics, change various parameters, increase / decrease the desired stimulation amplitude of the electrode pulses, and adjust the feedback sensitivity of the RF pulse generator module 106, among other functions.

[0040] The RF pulse generator module 106 may include communication electronics supporting the wireless connection 104, stimulation circuitry, and a battery to power 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 the tissue to create an electric field that powers the implantable wireless stimulator device 114. The TX antenna 110 communicates with the implantable wireless stimulator device 114 via an RF interface. For example, the TX antenna 110 radiates an RF transmission signal that is modulated and encoded by the RF pulse generator module 110. The implantable wireless stimulator device of the module 114 includes one or more antennas, such as a dipole antenna, to receive and transmit via the RF interface 112. Specifically, the coupling mechanism between the antenna 110 and one or more antennas on the implantable wireless stimulation device of the module 114 utilizes electrical radiation coupling rather than inductive coupling. In other words, the coupling is performed via an electric field rather than a magnetic field.

[0041] Through this electrical radiation coupling, the TX antenna 110 is able to provide an input signal to the implantable wireless stimulator device 114. The input signal contains energy and may contain information encoding a stimulation waveform to be applied at the electrodes of the implantable wireless stimulator device 114. In some embodiments, the power level of the input signal directly determines the applied amplitude (e.g., power, current, or voltage) of one or more electrical pulses created using the electrical energy contained in the input signal. Within the implantable wireless stimulator device 114 are components for demodulating the RF transmission signal and electrodes for delivering stimulation to surrounding neuronal tissue.

[0042] The RF pulse generator module 106 can be implanted subcutaneously or can be worn outside the body. When outside 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 the implantable wireless stimulator device 114. In either event, the receiver circuit inside the wireless stimulator device 114 (or the cylindrical wireless implantable stimulator device 1400 shown in Figure 14) can capture the energy radiated by the TX antenna 110 and convert the energy into an electrical waveform. The receiver circuit can also modify the waveform to create an electrical pulse suitable for stimulating neural tissue.

[0043] In some embodiments, the RF pulse generator module 106 is capable of remotely controlling stimulation parameters (i.e., parameters of the electrical pulses applied to the neural tissue) and monitoring feedback from the wireless stimulator device 114 based on the RF signal received from the implantable wireless stimulator device 114. The feedback detection algorithm implemented by the RF pulse generator module 106 is capable of monitoring data wirelessly transmitted by the implantable wireless stimulator device 114, which includes information about the energy received by the implantable wireless stimulator device 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 disease, the system can be tuned to provide an optimal amount of stimulation or inhibition to the neural fibers through electrical stimulation. A closed-loop feedback control method can be used, in which the output signal from the implantable wireless stimulator device 114 is monitored and used to determine the appropriate neural stimulation current level for maintaining effective neuronal activation, or in some cases, the patient can manually adjust the output signal through an open-loop control method.

[0044] Figure 2 Detailed diagram of an example of a wireless stimulation system is depicted. As shown, the programming module 102 may include a user input system 221 and a communication subsystem 208. The user input system 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 (e.g., Bluetooth or Wi-Fi) and receive data from the module 106.

[0045] For example, a programmer module 102 that can be used for multiple users (e.g., 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 can include pulse amplitude, pulse frequency, and pulse width within the ranges shown in Table 1. In this context, the term pulse refers to the phase of the waveform that directly produces stimulation to the tissue, and similar control can be performed on the parameters of the charge balance phase (described below). The patient and / or clinician can also optionally control the overall duration and mode of treatment.

[0046] Stimulation parameters Table 1

[0047] Pulse amplitude: 0 to 20mA

[0048] Pulse frequency: 0 to 10000 Hz

[0049] Pulse width: 0 to 2ms

[0050] The RF pulse generator module 106 may be initially programmed to meet the specific parameter settings for each individual patient during the initial implantation process. Because medical disease or the body itself can change over time, the ability to readjust parameter settings may be beneficial in ensuring continued effectiveness of neuromodulation therapy.

[0051] Programmer module 102 may be functionally a smart device and associated applications. The smart device hardware may include CPU 206 and may serve as a carrier for manipulating touch screen inputs on a graphical user interface (GUI) 204 to process and store data.

[0052] RF pulse generator module 106 may be connected to external TX antenna 110 via wired connection 108. Alternatively, both the antenna and RF pulse generator are located subcutaneously (not shown).

[0053] The signal sent by the RF pulse generator module 106 to the implantable wireless stimulator device 114 may include both 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 that receives feedback signals from the implantable wireless stimulator device 114. For this purpose, the RF pulse generator module 106 may include microelectronic devices or other circuits for manipulating the generation of signals transmitted to the device 114 and manipulating feedback signals (e.g., those from the stimulator device 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.

[0054] Controller subsystem 214 may include a CPU 230 that handles data processing, a memory subsystem 228 (e.g., local memory), a communication subsystem 234 that communicates with programmer module 102 (including receiving stimulation parameters from the programmer module), a pulse generator circuit 236, and a digital / analog (D / A) converter 232.

[0055] The patient and / or clinician can control stimulation parameter settings using the controller subsystem 214 (e.g., by controlling the parameters of the signal sent by the RF pulse generator module 106 to the stimulator device 114). These parameter settings can affect, for example, the power, current level, or shape of one or more electrical pulses. Programming of stimulation parameters can be performed using the programming module 102 described above to set the repetition rate, pulse width, amplitude, and waveform of the receive (RX) antenna 238, which is typically a dipole antenna (although other types may also be used), that transmits RF energy to the implantable wireless stimulation device 214. The clinician may choose to lock and / or hide certain settings within the programmer interface, thereby limiting the patient's ability to view or adjust certain parameters, as adjustment of certain parameters may require detailed medical knowledge of neurophysiology, neuroanatomy, neuromodulation protocols, and electrical stimulation safety limitations.

[0056] The controller subsystem 214 may 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 may use the parameters stored in the local memory to control the pulse generator circuit 236 to generate a stimulation waveform modulated by the high frequency oscillator 218 in the range of 300 MHz to 8 GHz (preferably between about 700 MHz and 5.8 GHz, and more preferably between about 800 MHz and 1.3 GHz). The resulting RF signal may then be amplified by the RF amplifier 226 and sent to the TX antenna 110 through the RF switch 223 to reach the RX antenna 238 through the depth of the tissue.

[0057] In some embodiments, the RF signal transmitted by the TX antenna 110 may simply be a power transmission signal used by the wireless stimulation device module 114 to generate electrical pulses. In other embodiments, a telemetry signal may also be transmitted to the wireless stimulator device 114 to send instructions regarding various operations of the wireless stimulator device 114. The telemetry signal may be transmitted by modulation of a carrier signal (through the skin if external, or through other body tissue if the pulse generator module 106 is implanted subcutaneously). The carrier signal (high frequency signal) is modulated with the telemetry signal, which is coupled to the implanted antenna 238 and does not interfere with the input received on the same stimulator device for powering the device. In one embodiment, the telemetry signal and the power signal are combined into one signal, wherein the RF power signal is modulated with the RF telemetry signal, thereby directly powering the wireless stimulation device via the received telemetry signal; a separate subsystem in the wireless stimulation device utilizes the power contained in the signal and interprets the data content of the signal.

[0058] The RF switch 223 can be a multi-purpose device, such as a bidirectional coupler, which transmits relatively high amplitude and very short duration RF pulses to the TX antenna 110 with minimal insertion loss, while simultaneously providing two low-level outputs to the feedback subsystem 212; one output transmits a forward power signal to the feedback subsystem 212, wherein the forward power signal is an attenuated form of the RF pulse sent to the TX antenna 110, and the other output transmits a reverse power signal to different ports of the feedback subsystem 212, wherein the reverse power is an attenuated form of the RF energy reflected from the TX antenna 110.

[0059] During the on cycle time (when the RF signal is transmitted to the wireless stimulator device 114), the RF switch 223 is set to send a positive power signal to the feedback subsystem. During the off cycle time (when the RF signal is not transmitted to the wireless stimulator device 114), the RF switch 223 can be changed to a receive mode in which reflected RF energy and / or RF signals from the wireless stimulator device 114 are received for analysis in the feedback subsystem 212.

[0060] The feedback subsystem 212 of the RF pulse generator module 106 may include receiving circuitry to receive and extract telemetry signals or other feedback signals from the wireless stimulator device 114 and / or reflected RF energy from a signal 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.

[0061] Feedback subsystem 212 receives the forward power signal and converts the high frequency AC signal to a DC level that can be sampled and sent to controller subsystem 214. In this way, the characteristics of the generated RF pulses can be compared to reference signals within controller subsystem 214. If there is an inconsistency (error) in any parameter, then controller subsystem 214 can make adjustments to the output to RF pulse generator 106. The nature of the adjustment can be, for example, proportional to the calculated error. Controller subsystem 214 can introduce additional inputs and constraints to its adjustment scheme, such as the signal amplitude of the reverse power and any predetermined maximum or minimum values ​​for various pulse parameters.

[0062] The reverse power signal can be used to detect fault conditions in the RF power delivery system. In an ideal situation, when the TX antenna 110 has a perfectly matched impedance to the tissue in contact with it, the electromagnetic waves generated by the RF pulse generator 106 are transmitted from the TX antenna 100 unimpeded into the body tissue. However, in real-world applications, there may be a large degree of variation in the user's body shape, the type of clothing worn, and the positioning of the antenna 110 relative to the body surface. Since the impedance of the antenna 110 depends on the relative permittivity of the underlying tissue and any intervening materials, and also depends on the total separation distance between the antenna and the skin, there may be an impedance mismatch at the interface of the TX antenna 110 and the body surface in any given application. When such a mismatch occurs, the electromagnetic waves sent from the RF pulse generator 106 are partially reflected at the interface, and the reflected energy propagates backward through the antenna feed.

[0063] The dual directional coupler RF switch 223 can prevent the reflected RF energy from propagating back to the amplifier 226, and can attenuate the reflected RF signal, and then 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, which can be sampled and sent to the controller subsystem 214. Thereafter, the controller subsystem 214 can 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 level of the forward power can indicate the severity of the impedance mismatch.

[0064] To sense the impedance mismatch condition, the controller subsystem 214 can measure the reflected power ratio in real time, and based on a preset threshold of the measurement, the controller subsystem 214 can modify the level of RF power generated by the RF pulse generator 106. For example, for moderate levels of reflected power, the course of action can be that the controller subsystem 214 increases the amplitude of the RF power sent to the TX antenna 110, such as required to compensate for the slightly deviated but still acceptable coupling of the TX antenna to the body. For higher reflected power ratios, the course of action can be to prevent the RF pulse generator 106 from operating and set a fault code to indicate that the TX antenna 110 is poorly or not coupled to the body. This type of reflected power fault condition may also be generated by a poor or disconnected connection to the TX antenna. In either case, it may be desirable to stop RF transmission when the reflected power ratio exceeds a defined threshold, because the internally reflected power may cause undesirable heating of internal components, and the fault condition means that the system cannot deliver sufficient power to the implantable wireless stimulation device and thus cannot provide therapy to the user.

[0065] The controller 242 of the wireless stimulator device 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 for enabling or disabling the waveform that generates the corresponding RF burst pulses necessary for transmission to the external (or remotely implanted) pulse generator module 106, the telemetry signal from the wireless stimulator device 114 can be coupled to the modulated signal on the dipole antenna 238. The antenna 238 can be connected to an electrode 254 in contact with the tissue to provide a return path for the transmitted signal. An A / D (not shown) converter can be used to convert the stored data into a serialized pattern that can be transmitted from the internal antenna 238 of the wireless stimulator device 114 on the pulse modulated signal.

[0066] The telemetry signal from the implantable wireless stimulator device 114 may include stimulation parameters, such as the amplitude of the power or current delivered to the tissue from the electrode. The feedback signal may be transmitted to the RF pulse generator module 116 to indicate the stimulation intensity at the nerve bundle by coupling the signal to the implantable RX antenna 238 that radiates the telemetry signal to the external (or remote implantable) RF pulse generator module 106. The feedback signal may include either or both of the carrier signal modulated by analog and digital telemetry pulses. Data such as the measured characteristics of the stimulation pulse parameters and stimulator performance may be stored in an internal memory device within the implantable stimulator device 114 and sent on the telemetry signal. The frequency of the carrier signal may be in the range of 300MHz to 8GHz (preferably between about 700MHz and 5.8GHz, and more preferably between about 800MHz and 1.3GHz).

[0067] In the feedback subsystem 212, the telemetry signal may be downmodulated using a demodulator 222 and digitized by processing through an analog-to-digital (A / D) converter 220. The digital telemetry signal may then be sent to a CPU 230 with embedded code to convert the signal into a corresponding current measurement in the tissue based on the amplitude of the received signal with the aid of a reprogramming option. The CPU 230 of the controller subsystem 214 may compare the reported stimulation parameters with those stored in the local memory 228 to verify that the wireless stimulator device 114 delivered the specified stimulation to the tissue. For example, if the wireless stimulation device reports a current below a specified value, the power level from the RF pulse generator module 106 may be increased so that the implanted wireless stimulator device 114 will have more power available for stimulation. The implanted wireless stimulator device 114 may generate telemetry data in real time at a rate of, for example, 8K bits / second. All feedback data received from the implantable stimulator device 114 may be recorded as quickly as possible and sampled for storage for retrieval by a remote monitoring system accessible to a healthcare professional for trend and statistical correlation analysis.

[0068] The remotely programmable RF signal sequence received by the internal antenna can be conditioned into a waveform that is controlled by the control subsystem 242 within the implantable wireless stimulator device 114 and sent to the appropriate electrodes 254 placed proximate to the tissue to be stimulated. For example, the RF signal transmitted by the RF pulse generator module 106 can be received by the RX antenna 238 and processed by circuitry within the implantable wireless stimulator device 114 (e.g., waveform conditioning circuitry 240) to convert it into electrical pulses that are applied to the electrodes 254 through the electrode interface 252. In some embodiments, the implantable wireless stimulator device 114 includes two to sixteen electrodes 254.

[0069] The waveform conditioning circuit 240 may include a rectifier 244 that rectifies the signal received via the RX antenna 238. The rectified signal may be fed to a controller 242 to receive 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 such that the one or more electrical pulses produce a substantially zero net charge at one or more electrodes (i.e., the pulses are charge balanced). The charge balanced pulses are transmitted through a current limiter 248 to an electrode interface 252, which applies the pulses to an electrode 254 as appropriate.

[0070] The current limiter 248 ensures that the current level of the pulse applied to the electrode 254 does not exceed the 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 this case, it may be particularly advantageous to include a current limiter 248 for preventing excessive current or charge from being delivered through the electrode, although the current limiter 248 may also be used in other embodiments other than this case. In general, for a given electrode with a surface area of ​​several square millimeters, the charge of each phase should be limited for safety reasons (wherein the charge delivered by the stimulation phase is the integral of the current). However, in some cases, a limit may be imposed on the current 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 limiter 248 acts as a charge limiter that limits the characteristics of the electrical pulse (e.g., current or duration) so that the charge of each phase remains below a threshold level (usually a safe charge limit).

[0071] Assuming that the implantable wireless stimulator device 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 "cut" the stimulation phase so that the total charge of the phase is maintained within safe limits. The current limiter 248 can be a passive current limiting component that cuts off the signal to the electrode 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 tissue damaging current levels.

[0072] A curtailment event can trigger a current limiter feedback control mode. A curtailment 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 communicated 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 completely cutting off the power. In this way, if the implantable wireless stimulator device 114 reports that it is receiving too much RF power, the pulse generator 106 can reduce the RF power delivered to the body.

[0073] The controller 250 of the stimulator 205 can communicate with the electrode interface 252 to control various aspects of the electrode settings and pulses applied to the electrodes 254. The electrode interface 252 can act as a multiplexer and control the polarity and switching of each of the electrodes 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 work through the assigned communication sent wirelessly with parameter instructions (the controller 250 is used to set the electrode interface 252 as appropriate). It may be advantageous from a physiological perspective to assign (for example) one or two electrodes as stimulation electrodes and assign all the remaining electrodes as return electrodes.

[0074] Moreover, in some embodiments, for a given stimulation pulse, the controller 250 can control the electrode interface 252 to arbitrarily distribute the current between designated stimulation electrodes (or according to instructions from the pulse generator module 106). Such control over electrode distribution and current control can be advantageous because, in practice, the electrodes 254 can be spatially distributed along various neural structures, and by strategically selecting stimulation electrode locations and the ratio of currents designated for each location, the cumulative current distribution in the tissue can be modified to selectively activate specific neural targets. This current steering strategy can improve the treatment effect on the patient.

[0075] In another embodiment, the timing of the stimulation can be arbitrarily manipulated. A given stimulation waveform can be started at time T_start and ended at time T_final, and the timing can be synchronized across all stimulation and return electrodes; in addition, the repetition frequency of the stimulation cycle can be synchronized for all electrodes. However, the controller 250 can control the electrode interface 252 independently or in response to instructions from the pulse generator 106 to specify one or more subsets of electrodes for delivering stimulation waveforms with asynchronous start and stop times, and the repetition frequency of each stimulation cycle can be arbitrarily and independently specified.

[0076] For example, a stimulator having eight electrodes may be configured to have a subset called set A consisting of five electrodes and a subset called set B consisting of three electrodes. Set A may be configured to use two of the electrodes as stimulation electrodes and the rest as return electrodes. Set B may be configured to have only one stimulation electrode. Thereafter, the controller 250 may specify that set A delivers a stimulation phase with a current of 3 mA for a duration of 200 us, followed by a charge balance phase of 400 us. The stimulation cycle may be specified to repeat at a rate of 60 cycles / second. Thereafter, for set B, the controller 250 may specify a stimulation phase with a current of 1 mA for a duration of 500 us, followed by a charge balance phase of 800 us. The repetition rate of the stimulation cycle of set B may be set independently of set A, for example, it may be specified to be 25 cycles / second. Alternatively, if the controller 250 was configured to match the repetition rate of set B to the repetition rate of set A, then for this case the controller 250 can specify the relative start times of the stimulation cycles to be coincident in time or arbitrarily offset by a delay interval relative to each other.

[0077] In some embodiments, the controller 250 can arbitrarily set the shape of the stimulation waveform amplitude, 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 this type of 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, has a constant amplitude during the duration of the stimulation, and then returns to the baseline very steeply. Alternatively or in addition, the controller 250 can increase or decrease the level of current at any time during the stimulation phase or during the charge balance phase. Thus, in some embodiments, the controller 250 can deliver a stimulation waveform of arbitrary shape, such as a triangular pulse, a sine pulse, or a Gaussian pulse. Similarly, the charge balance phase can be arbitrarily amplitude shaped, and similarly, the lead anode pulse (before the stimulation phase) can also be amplitude shaped.

[0078] As described above, the wireless stimulator device 114 may include a charge balancing component 246. Generally, for constant current stimulation pulses, the pulses should be charge balanced by making the amount of cathode current equal to the amount of anode current, which is often referred to as biphasic stimulation. Charge density is the amount of current multiplied by the duration of current application, which is usually expressed in units of uC / cm 2 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 the charge density should be less than 30uC / cm 2 Generally acceptable. The biphasic stimulation current pulses ensure that no net charge is present at the electrodes after each stimulation cycle and electrochemical process, and the biphasic stimulation current pulses are balanced to prevent the presence of a net direct current. The wireless stimulator device 114 can be designed to ensure that the stimulation waveform produced has a net zero 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.

[0079] The stimulation pulse can have a negative voltage or current, which is called the cathode phase of the waveform. The stimulation electrode can have both a cathode phase and an anode phase at different times during the stimulation cycle. An electrode that delivers a negative current with an amplitude sufficient 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 elsewhere in the tissue, at a 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.

[0080] In some embodiments, the charge balancing component 246 uses a blocking capacitor placed in series with the stimulation electrode and the body tissue between the point where stimulation is generated in the stimulator circuit and the point where stimulation is 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 in the stimulator circuit before the electrode selection point. The RC network can block direct current (DC), but it can also prevent low-frequency alternating current (AC) from being transmitted to the tissue. The series RC network essentially blocks signals below a certain frequency, which is usually referred to as the cutoff frequency. In one embodiment, the design of the stimulator system can ensure that the cutoff frequency does not exceed the fundamental frequency of the stimulation waveform. In the embodiment disclosed in the text, the value of the charge balancing capacitor of the wireless stimulator can be selected based on the measured series resistance of each electrode and the tissue environment in which the stimulator is implanted. By selecting a specific capacitance value, the cutoff frequency of the RC network in this embodiment is at or below the fundamental frequency of the stimulation pulse.

[0081] In other embodiments, the cutoff frequency may be selected to be at or above the fundamental frequency of the stimulation, in which case the stimulation waveform, referred to as the drive waveform, created before the charge balancing capacitor may be designed to be non-fixed, 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 to 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 passing through the charge balancing capacitor is modified. The shape of the stimulation waveform may be modified in this way to create a physiologically advantageous stimulation.

[0082] In some embodiments, the wireless stimulator device 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 stimulator device 114, thus eliminating the need for any energy storage within the stimulator itself. In this embodiment, the stimulator circuit can modify the envelope of the drive waveform and can communicate it directly to the charge balancing capacitor and / or electrode selection stage.

[0083] In some embodiments, the implantable wireless stimulator device 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 (e.g., a negative ongoing rectangular pulse), the pulse includes a physiological stimulation phase, and the charge balancing capacitor is polarized (charged) during this phase. After the drive pulse is completed, the charge balancing function is performed solely by the passive discharge of the charge balancing capacitor, wherein the charge balancing capacitor has its charge dissipated through the tissue, and the charge has an 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 a passive discharge phase, the capacitor can be allowed to discharge almost completely before the next stimulation pulse begins.

[0084] In terms of multi-phase drive waveforms, the wireless stimulator can perform internal switching to transmit negative ongoing or positive ongoing pulses (phases) to the charge balancing capacitor. These pulses can be delivered in any order, 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 the opposite phase can be placed before the stimulation phase. Prior to the stimulation of the phase with opposite polarity, it can (for example) have the advantage of reducing the amplitude of the stimulation phase required to excite the tissue.

[0085] In some embodiments, the amplitude and timing of the stimulation phase and the charge balance phase are controlled by the amplitude and timing of the RF pulses from the RF pulse generator module 106, in other words, the control can be managed internally by the onboard circuitry (e.g., the controller 250) of the wireless stimulator device 114. With respect to onboard control, the amplitude and timing can be specified or modified by data commands transmitted from the pulse generator module 106.

[0086] Figure 3 is a flow chart illustrating an example of the operation of a wireless neural stimulation system. In block 302, a wireless stimulator device 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 placed (e.g., close to the patient) in a manner that causes the TX antenna 110 to be electrically radiatively coupled to the implanted RX antenna 238 of the wireless stimulator device 114. In some embodiments, both the antenna 110 and the RF pulse generator 106 are located subcutaneously. In other embodiments, the antenna 110 and the RF pulse generator 106 are located outside the patient's body. In this case, the TX antenna 110 can be directly coupled to the patient's skin.

[0087] Energy from the RF pulse generator is radiated from the antenna 110 through the tissue to the implantable wireless stimulator device 114, as shown in block 304. In block 301, the radiated energy can be controlled by patient / clinician parameter inputs. In some cases, the parameter settings can be adjusted in an open-loop manner by the patient or clinician who adjusts the parameter inputs to the system in block 301.

[0088] The implantable wireless stimulator device 114 uses the received energy to generate electrical pulses to be applied to the neural tissue through the electrodes 238. For example, the wireless stimulator device 114 may include circuitry that rectifies the received RF energy and conditions the waveform so that the energy delivered to the electrodes for stimulation of the target nerve or tissue is charge balanced, as shown in block 306. The implantable wireless stimulator device 114 communicates with the pulse generator 106 by sending telemetry signals using the antenna 238, as shown in block 308. 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 has been reached, or the magnitude of the current provided to the tissue from the electrodes.

[0089] In block 310, the RF pulse generator 106 detects the received telemetry signal and amplifies, filters and modulates the received telemetry signal using the amplifier 226, the filter 224 and the demodulator 222, respectively. Afterwards, the A / D converter 230 digitizes the generated analog signal, as shown in 312. The digital telemetry signal is sent to the CPU 230, which determines whether the parameters of the signal sent to the wireless stimulator device 114 need to be adjusted based on the digital telemetry signal. For example, in block 314, the CPU 230 compares the information of the digital signal with the lookup table, which can indicate the appropriate change of the stimulation parameters. For example, the indicated change can be a change in the current level of the pulse applied to the electrode. As a result, the CPU can change the output power of the signal sent to the wireless stimulator device 114 to adjust the current applied by the electrode 254, as shown in block 316.

[0090] Thus, for example, the CPU 230 can adjust the parameters of the signal sent to the wireless stimulator device 114 every cycle to match the expected current amplitude setting programmed by the patient, as shown in block 318. The state of the stimulator system can be sampled in real time at a rate of 8K bits / second of telemetry data. All feedback data received from the wireless stimulator device 114 can be maintained as quickly as possible, and the feedback data can be sampled every minute for storage for download or upload to a remote monitoring system accessible to a healthcare professional for trend and statistical correlation analysis in block 318. If operating in an open loop, the stimulator system operation can be reduced to only the functional elements shown in blocks 302, 304, 306 and 308, and the patient uses his judgment rather than closed loop feedback from the implanted device to adjust the parameter settings.

[0091] Figure 4 4 is a circuit diagram showing an example of a wireless stimulator device 114. The example includes paired electrodes, including a cathode electrode 408 and an anode electrode 410, as shown. When energized, the charged electrodes create a volume conduction field of current density in the tissue. In this embodiment, wireless energy is received by a dipole antenna 238. At least four diodes are connected together to form a full-wave bridge rectifier 402 attached to the dipole antenna 238. Each diode up to 100 microns in length uses a junction potential to prevent negative current from the cathode to the anode from flowing through the device when the current does not exceed the reverse threshold. For neural stimulation transmitted through tissue via wireless power, the inherent low efficiency of lossy materials may bring about a low threshold voltage. In this embodiment, a zero bias diode rectifier causes a low output impedance of the device. Resistor 404 and smoothing capacitor 406 are placed across the output node of the bridge rectifier to discharge the electrode to the ground of the bridge anode. The rectifier bridge 402 includes two branches consisting of a diode pair connecting anode to anode and then cathode to cathode. Electrodes 408 and 410 are connected to the output of the charge balancing circuit 246 .

[0092] Figure 5 is a circuit diagram of another example of a wireless stimulator device 114 . Figure 5The example shown includes multi-electrode control, and full closed-loop control can be used. The wireless stimulation device includes an electrode array 254, wherein the polarity of the electrode can be assigned as a cathode or an anode, and for the electrode array 254, the electrode can be alternatively not powered with any energy. When powered, the charged electrode creates a volume conduction field of current density in the tissue. In this embodiment, wireless energy is received by the device through a dipole antenna 238. The electrode array 254 is controlled by an onboard controller circuit 242, and the controller circuit 242 sends appropriate bit information to the electrode interface 252 to set the polarity of each electrode in the array and the power supply to 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 supply status 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 .

[0093] 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 cathode to anode from flowing through the device when the current does not exceed the reverse threshold. For neural stimulation transmitted through tissue via wireless power, the inherent inefficiency of lossy materials may result in a low threshold voltage. In this embodiment, a zero-bias diode rectifier causes a low output impedance of the device. A resistor 404 and a smoothing capacitor 406 are placed across the output node of the bridge rectifier to discharge the electrode to the ground of the bridge anode. The rectifier bridge 402 can include two branches consisting of a diode pair that connects the anode to the anode and then connects the cathode to the cathode. The electrode polarity output, that is, both the cathode 408 and the anode 410 are connected to the output formed by the bridge connection. The charge balancing circuit 246 and the current limiting circuit 248 are placed in series with the output.

[0094] Figure 6 605 and feedback functions 630 of an implantable wireless stimulator device 600 (e.g., the device described above or below). An exemplary embodiment may be a wireless stimulator device module 114, as described above in connection with Figure 2 Control function 605 includes function 610 for polarity switching of electrodes and function 620 for power-on reset.

[0095] For example, the polarity switching function 610 can use a polarity routing switch network to assign polarity to the electrodes 254. The polarity assignment to the electrodes can be, for example, one of 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 implantable wireless stimulator device 600 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, the polarity of the electrodes 254 can be remotely controlled by the programmer through the programmer module 102, such as Figure 2 shown.

[0096] The power-on reset function 620 can reset the polarity allocation of each electrode immediately after each power-on event. As described in further detail below, the reset operation can cause the RF pulse generator module 106 to transmit polarity allocation information to the implantable wireless stimulator device 600. Once the polarity allocation information is received by the implantable wireless stimulator device 600, the polarity allocation information can be stored in a register stack or other short-term memory components. Thereafter, the polarity allocation information can be used to configure the polarity allocation of each electrode. If the polarity allocation information emitted in response to the reset is encoded to 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.

[0097] The feedback functionality 630 includes functionality 640 for monitoring the power delivered to the electrodes 254 and functionality 650 for making impedance diagnostics for the electrodes 254. For example, the delivered power functionality 640 may provide data encoding the amount of power delivered from the electrodes 254 to the excitable tissue, and the tissue impedance diagnostic functionality 650 may provide data encoding diagnostic information of tissue impedance. Tissue impedance is the electrical impedance of the tissue seen between the negative and positive electrodes when a stimulation current is being released between the negative and positive electrodes.

[0098] The feedback function 630 may additionally include a tissue depth estimation function 660 to provide an indication of the total tissue depth that an input radio frequency (RF) signal from a pulse generator module (e.g., RF pulse generator module 106) has penetrated before reaching an implanted antenna (e.g., RX antenna 238) within a wireless implantable stimulator device 600 (e.g., implantable wireless stimulator device 114). For example, a tissue depth estimate may 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 may indicate the attenuation caused by wave propagation through the tissue. For example, a second harmonic as described below may be received by the RF pulse generator 106 and used together with the power of the input signal transmitted by the RF pulse generator to determine tissue depth. The attenuation may be used to infer the total depth of the implantable wireless stimulator device 600 beneath the skin.

[0099] like Figure 1 and Figure 2 As shown, data from blocks 640 , 650 , and 660 may be transmitted to implantable RF pulse generator 106 , for example, via Tx antenna 110 .

[0100] Contact as above Figure 1 , Figure 2 , Figure 4 and Figure 5 As discussed, the implantable wireless stimulator device 600 can utilize a rectifier circuit to convert an input signal (having a carrier frequency in the range of about 300 MHz to about 8 GHz) into direct current (DC) power for driving the electrodes 254. Some embodiments can provide the ability to remotely adjust the DC power. Some embodiments can also provide different amounts of power to different electrodes, as discussed in further detail below.

[0101] Figure 7 is shown having a structure for implementing the above mentioned Figure 6Schematic diagram of an example of an implantable wireless stimulator device 700 with components for the control and feedback functions discussed. An RX antenna 705 receives an input signal. The RX antenna 705 can be embedded as a dipole, microstrip, folded dipole, or other antenna configuration other than a coil configuration, as described above. The input signal has a carrier frequency in the GHz range and contains electrical energy for powering the wireless implantable stimulator device 700 and for providing stimulation pulses to the electrodes 254. Once received by the antenna 705, the input signal is sent to a power management circuit 710. The power management circuit 710 is configured to rectify the input signal and convert it into DC power. For example, the power management circuit 710 may include a diode rectifier bridge, such as Figure 4 The diode rectifier bridge 402 shown in FIG. 4 is a DC power supply to the stimulation circuit 711 and the logic power circuit 713. The rectification can utilize one or more full-wave diode bridge rectifiers within the power management circuit 710. In one embodiment, a resistor can be placed across the output node of the bridge rectifier to discharge the electrode to the ground of the bridge anode, such as by Figure 7 As illustrated by the shunt resistor 404 in FIG.

[0102] Temporarily go to Figure 8 , a schematic diagram of an example of a polarity routing switch network 800 is shown. As discussed above, cathode (-) energy and anode energy are received at input 1 (block 722) and input 2 (block 723), respectively. The polarity routing switch network 800 couples one of its outputs to one of the electrodes 254, which may include a minimum of two electrodes and a maximum of sixteen electrodes. Eight electrodes are shown as an example in this embodiment.

[0103] The polarity routing switch network 800 is configured to connect each output individually to one of input 1 or input 2, or to disconnect the output from either of the inputs. This selects the polarity of each individual electrode in the electrode 254 as one of neutral (off), cathode (negative), or anode (positive). Each output is coupled to a corresponding three-state switch 830 to set the connection state of the output. Each three-state switch is controlled by one or more of the bits from the selection input 850. In some embodiments, the selection input 850 can assign more than one bit to each three-state switch. For example, two bits can encode the three-state information. Thus, the state of each output of the polarity routing switch device 800 can be controlled by information encoded in the bits stored in the register 732, which can be set by polarity assignment information received from the remote RF pulse generator module 106, as further described below.

[0104] Return to Figure 7, 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 718 can be placed in series with the anode branch 714. A current sensing circuit 719 senses the current across the resistor 718, and a voltage sensing circuit 720 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.

[0105] 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. Alternative circuits (not shown) can also be used in place of the sense resistor 718, depending on the implementation of the feature and whether the impedance and power feedback are measured separately or in combination.

[0106] The measurements from the current sensing circuit 719 and the voltage sensing circuit 720 can be sent to a voltage controlled oscillator (VCO) 733 or an equivalent circuit capable of converting from an analog signal source to a carrier signal for modulation. The VCO 733 can generate a digital signal having a carrier frequency. The carrier frequency can vary based on analog measurements such as voltage, differential of voltage, and power. The VCO 733 can also use amplitude modulation or phase shift keying to modulate the feedback information at the carrier frequency. The VCO or equivalent circuit can generally be referred to as an analog controlled carrier modulator. The modulator can transmit information encoding the sensed current or voltage back to the RF pulse generator 106.

[0107] Antenna 725 may transmit a modulated signal in, for example, a GHz frequency range back to RF pulse generator module 106. In some embodiments, antennas 705 and 725 may be the same physical antenna. In other embodiments, antennas 705 and 725 may be separate physical antennas. In separate antenna embodiments, antenna 725 may operate at a resonant frequency higher than the resonant frequency of antenna 705 to send stimulation feedback to RF pulse generator module 106. In some embodiments, antenna 725 may also operate at a higher resonant frequency to receive data encoding polarity assignment information from RF pulse generator module 106.

[0108] Antenna 725 may include a telemetry antenna 725, which may send received data (e.g., polarity assignment information) to stimulation feedback circuit 730. The encoded polarity assignment information may be in a frequency band in the GHz range. The received data may be demodulated by demodulation circuit 731 and then stored in register file 732. Register file 732 may be a volatile memory. Register file 732 may be an 8-channel memory bank, which may store (for example) a few bits of data for each channel to be assigned polarity. Some embodiments may not have a register file, while some embodiments may have a register file of up to 64 bits in size. The information encoded by these bits may be sent to polarity routing switch network 721 as a polarity selection signal, as indicated by arrow 734. The bit may encode the polarity assignment of each output of the polarity routing switch network as one of + (positive), - (negative) or 0 (neutral). Each output is connected to an electrode and the channel setting determines whether the electrode will be set to anode (positive), cathode (negative) or closed (neutral).

[0109] Returning to the power management circuit 710, in some embodiments, approximately 90% of the received energy is sent to the stimulation circuit 711, and less than 10% of the received energy is sent to the logic power circuit 713. The logic power circuit 713 can power control components for polarity and telemetry. In some embodiments, however, the power circuit 713 does not provide actual power to the electrodes for stimulating tissue. In certain embodiments, the energy leaving the logic power circuit 713 is sent to the capacitor circuit 716 to store a certain amount of readily available energy. The voltage of the charge stored in the capacitor circuit 716 can be labeled as Vdc. Next, this stored energy is used to power the power-on reset circuit 716, which is configured to send a reset signal at the power-on event. If the wireless implantable neural stimulator 700 loses power for a period of time (e.g., in the range of approximately 1 millisecond to more than 10 milliseconds), the contents of the register stack 732 and the polarity setting of the polarity routing switch network 721 can be reset to zero. For example, when the implantable wireless stimulation device 700 becomes less aligned with the RF pulse generator module 106, the implantable wireless stimulation device 700 may lose power. The power-on reset circuit 740 can use the stored energy to provide a reset signal, as shown by arrow 717. The reset signal can cause the stimulation feedback circuit 730 to notify the RF pulse generator module 106 of the loss of power. For example, the stimulation feedback circuit 730 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 power is returned to the wireless stimulation device 700. Thereafter, the RF pulse generator module 106 transmits one or more telemetry packets to the implantable wireless stimulation device. The telemetry packet contains polarity assignment information, which can be saved to the register stack 732 and can be sent to the polarity routing switch network 721. Thus, the polarity assignment information in the register file 732 may be recovered from the telemetry packet transmitted by the RF pulse generator module 106, and the polarity assignment of each output of the polarity routing switch network 721 may be updated accordingly based on the polarity assignment information.

[0110] The telemetry antenna 725 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 705. In one embodiment, the telemetry antenna 725 can have an increased resonant frequency that is a second harmonic of the characteristic frequency of the RX antenna 705. For example, the second harmonic can be used to transmit power feedback information about an estimate of the amount of power received by the electrode. The RF pulse generator can then use the feedback information to determine adjustments to the power level to be transmitted by the RF pulse generator 106. In a similar manner, the second harmonic energy can be used to detect tissue depth. The second harmonic transmission can be detected by, for example, an external antenna on the RF pulse generator module 106 that is tuned to the second harmonic. As a general case, the power management circuit 710 can include a rectifier circuit, which is a nonlinear device capable of generating harmonic energy from an input signal. Harvesting this harmonic energy to transmit the telemetry feedback signal can improve the efficiency of the implantable wireless stimulator device 700.

[0111] Fig.9A is a diagram of an exemplary embodiment of a microwave field stimulator (MFS) 902 as part of a stimulation system utilizing an implantable wireless stimulator device 922. In this example, the MFS 902 is external to the patient's body and can be placed in close proximity to the implantable wireless stimulator device 922, for example within 3 feet. The RF pulse generator module 106 can be an exemplary embodiment of the MFS 902. The MFS 902 is generally referred to as a controller module. The implantable wireless stimulator device 922 is a passive device. The implantable wireless stimulator device 922 does not have its own independent power supply, but instead receives power for its operation from a transmission signal emitted by a TX antenna powered by the MFS 902.

[0112] In some embodiments, the MFS 902 can communicate with a programmer 912. The programmer 912 can be a mobile computing device, such as a laptop, a smart phone, a tablet, etc. The communication can be wired, for example, using a USB or FireWire cable. The communication can also be wireless, for example, using a Bluetooth protocol implemented by a transmitting Bluetooth module 904 that communicates with a host Bluetooth module 914 within the programmer 912.

[0113] Additionally, the MFS 902 can communicate with the wireless stimulator device 922 by transmitting a transmission signal via a Tx antenna 907 coupled to the amplifier 906. The transmission signal can propagate through the skin and underlying tissue to arrive at the RX antenna 923 of the wireless stimulator device 922. In some embodiments, the wireless stimulator device 922 can transmit a telemetry feedback signal back to the microwave field stimulator 902.

[0114] The microwave field stimulator 902 may include a microcontroller 908 configured to manage communications with a programmer 912 and generate an output signal. A modulator 909 may modulate an RF carrier signal using the output signal. The frequency of the carrier signal may be in the microwave range, for example, from about 300 MHz to about 8 GHz, preferably from about 800 MHz to 1.3 GHz. The modulated RF carrier signal may be amplified by an amplifier 906 to provide a transmission signal for transmission to a wireless stimulator device 922 via a TX antenna 907.

[0115] Fig. 9B 9 is a diagram of another example of an embodiment of a microwave field stimulator 902 as part of a stimulation system utilizing a wireless stimulator device 922. In this example, the microwave field stimulator 902 may be embedded within the patient, e.g., subcutaneously. The embedded microwave field stimulator 902 may receive power from a separate remote wireless battery charger 932.

[0116] Power may be transmitted from the wireless battery charger 932 to the embedded microwave field stimulator 902 at frequencies in the MHz or GHz range. The microwave field stimulator 902 should be embedded at a very shallow depth (e.g., less than 1 cm) subcutaneously, and alternative coupling methods may be used to transfer energy from the wireless battery charger 932 to the embedded MFS 902 in the most efficient manner known in the art.

[0117] In some embodiments, the microwave field stimulator 902 can be suitable for placement in the dura mater layer of the spine, on or near the dura mater of the spine, in tissue in close proximity to the spine, in tissue located near the dorsal horn of the spinal cord, in a dorsal root nerve center, in one or more of the dorsal roots, in spinal fibers, or in peripheral nerve bundles exiting the dorsal column of the spine.

[0118] In this embodiment, the microwave field stimulator 902 should transmit power and parameter signals to a passive Tx antenna also embedded under the skin, which should couple to the RX antenna within the wireless stimulator device 922. The power required in this embodiment is much lower because the TX antenna and RX antenna are already in the body tissue and therefore do not need to transmit signals through the skin.

[0119] Fig.10 is a detailed diagram of an exemplary microwave field stimulator 902. The microwave field stimulator 902 may include a microcontroller 908, a telemetry feedback module 1002, and a power management module 1004. The microwave field stimulator 902 has a two-way communication scheme with a programmer 912 and with a communication or telemetry antenna 1006. The microwave field stimulator 902 transmits output power and data signals through the TX antenna 1008.

[0120] The microcontroller 908 may include a storage device 1014, a Bluetooth interface 1013, a USB interface 1012, a power interface 1011, an analog-to-digital converter (ADC) 1016, and a digital-to-analog converter (DAC) 1015. An embodiment of the storage device 1014 may include a non-volatile memory, such as a static electrically erasable programmable read-only memory (SEEPROM) or a NAND flash memory. The storage device 1014 may store waveform parameter information for use by the microcontroller 908 to synchronize the output signal used by the modulator 909. The stimulation waveform may include a plurality of pulses. The waveform parameter information may include the shape, duration, amplitude, and pulse repetition frequency of each pulse. The storage device 1014 may additionally store polarity assignment information for each electrode of the wireless stimulator device 922. The Bluetooth interface 1013 and the USB interface 1012 interact with the Bluetooth module 1004 or the USB module, respectively, to communicate with the programmer 912.

[0121] The communication antenna 1006 and the TX antenna 1008 can be configured to various sizes and form factors, including, but not limited to, patch antennas, slot antennas, or dipole antennas, for example. In addition to being suitable for transmitting power to the implantable passive neurostimulator device 922, the TX antenna 1008 can also transmit a transmission signal to it. As described above, the modulator 909 can use the output signal generated by the microcontroller 908 to provide instructions for creating a modulated RF carrier signal. The RF carrier signal can be amplified by the amplifier 906 to generate a transmission signal. The directional coupler 1009 can be used to provide two-way coupling so that the forward power of the transmission signal stream emitted by the TX antenna 1008 and the reverse power of the reflected transmission can be picked up by the power detector 1022 of the telemetry feedback module 1002. In some embodiments, a separate communication antenna 1006 can act as a receiving antenna for receiving a telemetry feedback signal from the wireless stimulator device 922. In some configurations, the communication antenna can operate at a higher frequency band than the TX antenna 1008. For example, the communication antenna 1006 may have a characteristic frequency that is the second harmonic of the characteristic frequency of the TX antenna 1008, as discussed above.

[0122] In some embodiments, the microwave field stimulator 902 may additionally include a telemetry feedback module 902. In some embodiments, the telemetry feedback module 1002 may be directly coupled to the communication antenna 1006 to receive the telemetry feedback signal. The power detector 1022 may provide a reading of the forward power of the transmission signal and the reverse power of the portion of the transmission signal that is reflected during transmission. The telemetry signal, the forward power reading, and the reverse power reading may be amplified by a low noise amplifier (LNA) 1024 for further processing. For example, the telemetry module 902 may be configured to process the telemetry feedback signal by demodulating the telemetry feedback signal to extract the encoded information. This encoded information may include, for example, the state of the wireless stimulator device 922 and one or more electrical parameters associated with a specific channel (electrode) of the wireless stimulator device 922. Based on the decoded information, the telemetry feedback module 1002 may be used to calculate the expected operating characteristics of the wireless stimulator device 922.

[0123] Some embodiments of the MFS 902 may also include a power management module 1004. The power management module 1004 may manage various power sources of the MFS 902. Exemplary power sources include, but are not limited to, lithium-ion batteries or lithium polymer batteries. The power management module 1004 may provide several operating modes to conserve battery power. Exemplary operating modes may include, but are not limited to, normal mode, low power mode, sleep mode, deep sleep / hibernation mode, and off mode. The normal mode provides regulation of transmission signals to the wireless stimulator device 922 and the transmission of stimulation. In the normal mode, telemetry feedback signals are received and processed to monitor stimulation as usual. The low power mode also provides regulation of transmission signals to the electrodes of the wireless stimulation device and the transmission of stimulation. However, in this mode, the telemetry feedback signals may be ignored. More specifically, the telemetry feedback signals encoding the stimulation power may be ignored, thereby saving the overall power consumption of the MFS 902. In the sleep mode, the transceiver and amplifier 906 are turned off, and the microcontroller retains the last saved state in its memory. In deep sleep / hibernation mode, the transceiver and amplifier 906 are turned off, and the microcontroller is in power-off mode, but the power regulator is turned on. In shutdown mode, all transceivers, microcontrollers and regulators are turned off to obtain zero static power.

[0124] Fig.11Flowchart of an exemplary process for microwave field stimulator 902 to transmit polarity setting information to wireless stimulator device 922. Polarity assignment information is stored in non-volatile memory 1102 within microcontroller 908 of MFS 902. Polarity assignment information can be representative-specific and can be selected to meet the specific needs of a particular patient. Based on the polarity assignment information selected for a particular patient, microcontroller 908 executes a dedicated routine to assign polarity to each electrode of the electrode array. The particular patient has a wireless stimulation device as described above.

[0125] In some embodiments, the polarity assignment process includes sending a signal to the wireless stimulation device having an initial power-on portion followed by a configuration portion that encodes the polarity assignment. For example, the power-on portion may simply include an RF carrier signal. The initial power-on portion has a duration sufficient to power on the wireless stimulation device and allow the device to reset to a configuration mode. Once in the configuration mode, the device reads the encoded information in the configuration portion and sets the polarity of the electrodes as indicated by the encoded information.

[0126] Thus, in some embodiments, the microcontroller 908 turns on the modulator 909, thereby sending an unmodulated RF carrier to the wireless stimulator device 1104. After a set duration, the microcontroller 908 automatically starts transmitting information encoding the polarity assignment. In this scenario, the microcontroller 908 transmits the polarity setting without a handshake signal from the wireless stimulation device. Since the microwave field stimulator 902 operates in close proximity to the wireless stimulator device 922, signal degradation may not be severe enough to permit the use of a handshake signal to improve communication quality.

[0127] To transmit polarity information, the microcontroller 908 reads the polarity assignment information from the non-volatile memory and generates a digital signal 1106 encoding the polarity information. The digital signal encoding the polarity information can be converted to an analog signal, for example, by a digital-to-analog (DAC) converter 1112. The analog signal encoding the waveform can modulate a carrier signal at the modulator 909 to generate a configured portion of the transmission signal (1114). The configured portion of the transmission signal can be amplified by the power amplifier 906 to generate a signal to be sent through the antenna 907 (1116). Thereafter, the configured portion of the transmission signal is transmitted to the wireless stimulator device 922 (1118).

[0128] Once the configuration portion is transmitted to the wireless stimulation device, the microcontroller 908 initiates the stimulation portion of the transmission signal. Similar to the configuration portion, the microcontroller 908 generates a digital signal that encodes the stimulation waveform. The digital signal is converted to an analog signal using a DAC. The analog signal is then used to modulate a carrier signal at a modulator 909 to generate the stimulation portion of the transmission signal.

[0129] In other embodiments, after the microcontroller 908 recognizes a power-on reset signal transmitted by the neurostimulator, the microcontroller 908 initiates the polarity assignment protocol. The power-on reset signal can be extracted from a feedback signal received by the microcontroller 908 from the wireless stimulator device 922. The feedback signal is also called a handshake signal because it alerts the microwave field stimulator 902 of the ready state of the wireless stimulator device 922. In an example, the feedback signal can be demodulated and sampled into the digital domain before extracting the power-on reset signal in the digital domain.

[0130] Fig.12 is a flow chart illustrating an example of a process by which the microwave field stimulator 902 receives and processes telemetry feedback signals to make adjustments to subsequent transmissions.

[0131] In some embodiments, the microcontroller 908 polls the telemetry feedback module 1002 (1212). The polling is to determine whether a telemetry feedback signal has been received (1214). The telemetry feedback signal may include information that the MFS 902 can use to determine the power consumption utilized by the electrodes of the wireless stimulator device 922. This information can also be used to determine the operating characteristics of the combined system of the MFS 902 and the wireless stimulator device 922, such as the contact Fig.13 Information may also be recorded by the microwave field stimulator 902 so that the patient's response can be correlated with the treatment received over time. This correlation may reveal the patient's individual response to the most recent treatment received.

[0132] If the microcontroller 908 determines that the telemetry feedback module 1002 has not received the telemetry feedback signal, then the microcontroller 908 can continue to poll (1212). If the microcontroller 908 determines that the telemetry feedback module 1002 has received the telemetry feedback signal, then the microcontroller 908 can extract the information contained in the telemetry feedback signal to perform calculations (1216). The extraction can be performed by demodulating the telemetry feedback signal in the digital domain and sampling the demodulated signal. The calculations can reveal operating characteristics of the wireless stimulator device 922, including, for example, voltage or current levels associated with a particular electrode, power consumption of a particular electrode, and / or impedance of tissue stimulated by the electrode.

[0133] Thereafter, in some embodiments, the microcontroller 908 may store information extracted from the telemetry signals and the results of the calculations (1218). The stored data may be provided to a user via a programmer upon request (1220). The user may be a patient, a physician, or a manufacturer's representative. The data may be stored in a non-volatile memory, such as, for example, a NAND flash memory or an EEPROM.

[0134] In other embodiments, a power management scheme may be triggered 1222 by the microcontroller (908). Under the power management scheme, the microcontroller 908 may determine whether to adjust a parameter of a subsequent transmission (1224). The parameter may be an amplitude or a stimulation waveform shape. In one embodiment, the amplitude level may be adjusted based on a lookup table showing the relationship between the amplitude level and the corresponding power applied to the tissue by the electrodes. In one embodiment, the waveform shape may be pre-distorted to compensate for the frequency response of the microwave field stimulator 902 and the wireless stimulator device 922. The parameter may also be a carrier frequency of the transmission signal. For example, the carrier frequency of the transmission signal may be modified to provide fine tuning to improve transmission efficiency.

[0135] If the adjustment is implemented, the next transmitted transmission signal is adjusted accordingly. If the adjustment is not implemented, the microcontroller 908 can return to polling the telemetry feedback module 1002 for the telemetry feedback signal (1212).

[0136] In other embodiments, instead of polling the telemetry feedback module 1002, the microcontroller 908 may wait for an interrupt request from the telemetry feedback module 1002. The interrupt may be a software interrupt, for example, by an exception handler of an application. The interrupt may also be a hardware interrupt, for example, a hardware event, and may be handled by an exception handler of the underlying operating system.

[0137] Fig.131 is a schematic diagram of an exemplary embodiment of power, signal and control flow of the wireless stimulator device 922. The DC source 1302 obtains energy from the transmission signal received at the wireless stimulator device 922 during the initial power-on portion of the transmission signal when the RF power is ramped up. In one embodiment, the rectifier can rectify the received power-on portion to generate the DC source 1302, and the capacitor 1304 can store the charge from the rectified signal during the initial portion. When the stored charge reaches a certain voltage (e.g., a voltage sufficient or nearly sufficient to power the operation of the wireless stimulator device 922), the power-on reset circuit 1306 can be triggered to send a power-on reset signal to reset the components of the neural stimulator. The power-on reset signal can be sent to the circuit 1308 to reset, for example, digital registers, digital switches, digital logic, or other digital components such as the transmit and receive logic 1310. The digital components can also be associated with the control module 1312. For example, the control module 1312 can include the electrode control 252, the register stack 732, etc. The power-on reset may reset the digital logic so that the circuit 1308 starts operating from a known initial state.

[0138] In some embodiments, the power-on reset signal may then cause the FPGA circuit 1308 to transmit a power-on reset telemetry signal back to the MFS 902 to indicate that the implantable wireless stimulator device 922 is ready to receive the configuration portion of the transmission signal containing the polarity assignment information. For example, the control module 1312 may signal the RX / TX module 1310 to send the power-on reset telemetry signal to the telemetry antenna 1332 for transmission to the MFS 902.

[0139] In other embodiments, a power-on reset telemetry signal is not provided. As described above, due to the proximity between the MFS 902 and the implantable passive stimulator device 922, signal degradation caused by propagation losses may not be severe enough to permit implementation of a handshake signal from the implantable passive stimulator device 922 in response to the transmission signal. Additionally, the operating efficiency of the implantable passive neurostimulator device 922 may be another factor that may not favor implementation of a handshake signal.

[0140] Once the FPGA circuit 1308 has been reset to an initial state, the FPGA circuit 1308 transitions to a configuration mode configured to read the polarity assignment encoded on the received transmission signal during the configuration state. In some embodiments, the configuration portion of the transmission signal can arrive at the wireless stimulation device via the RX antenna 1334. The received transmission signal can provide an AC source 1314. The AC source 1314 can be at the carrier frequency of the transmission signal, for example, from about 300 MHz to about 8 GHz.

[0141] Thereafter, the control module 1312 may read the polarity assignment information and set the polarity of each electrode according to the polarity assignment information in the configuration portion of the received transmission signal through the analog multiplexing control 1316. The electrode interface 252 may be an example of an analog multiplexing control 1316, which may provide channels to corresponding electrodes of the implantable wireless stimulator device 922.

[0142] Once the polarity of each electrode is set by the analog multiplexing control 1316, the implantable wireless stimulator device 922 is ready to receive the stimulation waveform. Some embodiments may not use a handshake signal to indicate that the wireless stimulator device 922 is ready to receive the stimulation waveform. Instead, the transmission signal can automatically transition from the configuration portion to the stimulation portion. In other embodiments, the implantable wireless stimulator device 922 can provide a handshake signal to notify the MFS 902 that the implantable wireless stimulator device 922 is ready to receive the stimulation portion of the transmission signal. If a handshake signal is implemented, the handshake signal can be provided by the RX / TX module 1310 and transmitted through the telemetry antenna 1332.

[0143] In some embodiments, the stimulation portion of the transmission signal can also arrive at the implantable wireless stimulation device via the RX antenna 1334. The received transmission signal can provide an AC source 1314. The AC source 1314 can be at the carrier frequency of the transmission signal, for example, from about 300 MHz to about 8 GHz. The stimulation portion can be rectified and adjusted according to the discussion above to provide an extracted stimulation waveform. The extracted stimulation waveform can be applied to each electrode of the implantable wireless stimulator device 922. In some embodiments, the application of the stimulation waveform can occur simultaneously, that is, applied to each electrode at the same time. As discussed above, the polarity of each electrode has been set according to the polarity setting of the corresponding channel, and the stimulation waveform has been applied to each electrode.

[0144] In some embodiments, each channel of the analog multiplexing control 1316 is connected to a corresponding electrode and may have a reference resistor placed in series. Fig.13 Reference resistors 1322, 1324, 1326, and 1328 are shown connected in series with the matching channels. The analog multiplexing control 1316 may additionally include calibration resistors 1320 placed into separate and grounded channels. The calibration resistors 1320 are connected in parallel with a given electrode on a particular channel. The reference resistors 1322, 1324, 1326, and 1328 and the calibration resistors 1320 may also be referred to as sense resistors 718. These resistors may sense electrical parameters in a given channel, as discussed below.

[0145] In some configurations, the analog controlled carrier modulator may receive a differential voltage for determining the carrier frequency that should be generated. The generated carrier frequency may be proportional to the differential voltage. An exemplary analog controlled carrier modulator is VCO 733.

[0146] In one configuration, the carrier frequency may indicate an absolute voltage measured as a relative difference from a predetermined and known voltage. For example, the differential voltage may be the difference between the voltage across a reference resistor connected to the channel being measured and a standard voltage. The differential voltage may be the difference between the voltage across the calibration resistor 1320 and the standard voltage. An exemplary standard voltage may be ground.

[0147] In another configuration, the carrier frequency can reveal the impedance characteristics of a given channel. For example, the differential voltage can be the difference between the voltage at the electrode connected to the channel being measured and the voltage across the reference resistor in series. Due to the series connection, the comparison of the voltage across the reference resistor with the voltage at the electrode will indicate the impedance of the stimulated underlying tissue relative to the impedance of the reference resistor. Since the impedance of the reference resistor is known, the impedance of the stimulated underlying tissue can be inferred based on the carrier frequency obtained.

[0148] For example, the differential voltage can be the difference between the voltage at the calibration resistor and the voltage across the reference resistor. Since the calibration resistor is placed in parallel with a given channel, the voltage at the calibration resistor is substantially the same as the voltage at the given channel. Since the reference resistor is connected in series with the given channel, the voltage at the reference resistor is a portion of the voltage across the given channel. Thus, the difference between the voltage at the calibration resistor and the voltage across the reference resistor corresponds to the voltage drop at the electrode. Thus, the voltage at the electrode can be inferred based on the voltage difference.

[0149] In yet another configuration, the carrier frequency can provide a reading of the current. For example, if the voltage across the reference resistor 1322 has been measured, as discussed above, the current flowing through the reference resistor and the corresponding channel can be inferred by dividing the measured voltage by the impedance of the reference resistor 1322.

[0150] There may be many variations based on the examples specifically disclosed above. Each example and its variations may sense one or more electrical parameters simultaneously, and the simultaneously sensed electrical parameters may be used to drive an analog control modulator device. The resulting carrier frequency varies with the difference in the measurements produced simultaneously. The telemetry feedback signal may include a signal at the resulting carrier frequency.

[0151] The MFS 902 can determine carrier frequency changes by demodulating at a fixed frequency and measuring the phase shift accumulation caused by the carrier frequency changes. In general, a few cycles of the RF wave at the resulting carrier frequency may be sufficient to resolve the underlying carrier frequency changes. The determined changes can indicate the operating characteristics of the implantable wireless stimulator device 922. The operating characteristics can include impedance, power, voltage, current, etc. The operating characteristics can be associated with individual channels. Therefore, sensing and carrier frequency modulation can be channel-specific and can be applied to one channel at a given moment. Therefore, the telemetry feedback signal can be time-shared by the various channels of the implantable wireless stimulator device 922.

[0152] In one configuration, the controller module 1312 may select a particular channel in the time sharing scheme using the analog MUX 1318. The sensing information of the particular channel, for example, in the form of carrier frequency modulation, may be sent to the RX / TX module 1310. The RX / TX module 1310 may then transmit telemetry feedback encoding the sensing information of the particular channel to the MFS 902 via the telemetry antenna 1332.

[0153] Some embodiments may include an application specific integrated circuit (ASIC) chip on a wireless stimulator device for processing input signals and docking with implantable electrodes. The ASIC chip can be coupled to an antenna to receive input signals from an external controller. The ASIC chip can obtain RF power from the received input signal to power the ASIC chip and the electrodes. The ASIC chip can also extract polarity setting information from the received input signal and use this information to set the polarity of the electrode interface. In addition, the ASIC chip can also extract waveform parameters from the received input signal and use this information to create electrical pulses for stimulating excitable tissues through electrodes. Specifically, the ASIC chip can include current steering features to evenly mirror current to each electrode while maintaining a compact chip size.

[0154] Fig.14 is a diagram of an example of an ASIC chip 1400 for implantable use. The chip 1400 can be fabricated using a 0.6um double poly process using high value resistors, Schottky diodes, and high voltage transistors. In some embodiments, the chip 1400 can be fabricated to have a width of 0.5mm to fit into, for example, an 18 gauge needle. In these embodiments, the chip 1400 can have an aspect ratio of up to 10 to 1. The chip 1400 can be coupled to, for example, four (4) or eight (8) platinum iridium electrodes that deliver electrical pulses to tissue.

[0155] Chip 1400 includes RF to DC rectifier circuit 1402, logic control circuit 1404 and drive circuit 1406. RF to DC rectifier circuit 1402 is coupled to differential antennas 1412A and 1412B. RF input signal can be received at the differential antenna and then rectified to detect its amplitude. The rectified signal can provide power for chip 1400. Thereafter, logic control circuit 1404 can extract waveform parameters from the amplitude-detected signal. Next, logic control circuit 1404 can generate electrical pulses based on the extracted waveform parameters and only on the extracted power. The generated electrical pulses can then be provided to drive circuit 1406, which includes a charge balancing circuit and a current mirror circuit. Drive circuit 1406 is coupled to electrode interfaces 1408A to 1408H, each of which is coupled to a corresponding electrical load 1409A to 1409H. The electrical pulses are then delivered to each electrode, i.e., 1410A to 1410H.

[0156] In this figure, a diode bridge circuit 1414 is included to provide full wave rectification to the input signal received in differential form from differential antennas 1412A and 1412B. Full wave rectification can utilize both the positive and negative portions of the RF input signal received at differential antennas 1412A and 1412B.

[0157] In some embodiments, a dipole antenna in a differential configuration can be embedded in a wireless implantable stimulator device. The dipole antenna receives power, serial communications, and stimulation waveforms from an external transmitter placed outside the patient's body. The dipole antenna is directly connected to a flexible circuit board embedded in the implantable stimulator device, the flexible circuit board containing discrete components and chip 1400. Chip 1400 can include a wireless serial command receiver with multiplexing capabilities of up to eight channels.

[0158] Rectification can provide power for the rest of chip 1400. In some cases, VDD circuit 1418 and ground circuit 1419 are coupled to capacitor C1 1420 to provide stored charge. The stored charge can generally power chip 1400. In some embodiments, a diode can be used to supply VDD logic power from Vrect. If chip 1400 is active and voltage VDD drops to below 1.8V, chip 1400 can enter "VDD low voltage recovery" mode. In this state, any / all high-side drivers will be temporarily rewritten to a high impedance state (Hi-Z), and all low-side drivers will be Hi-Z. Once VDD returns to a state above 3.0V and is in run mode, the driver will return to its previously programmed state.

[0159] The output from the rectifier circuit 1402 is coupled to the logic control circuit 1404. As shown, the logic control circuit 1404 may include a logic control / state machine 1422 and a timer / oscillator 1424. The logic control / state machine 1422 may be coupled to a channel selector 1426.

[0160] The received RF input signal may include waveform parameters of the electrical pulses for stimulating tissue.The received RF input signal may include polarity setting information for setting the interface of each electrode.

[0161] refer to Fig.15 , shows a sequence diagram during operation of chip 1400. Specifically, pulse sequence 1500 includes segments of pulses. Each segment may last for an epoch time (shown as T epoch ). Each segment may include two parts, an initial portion and a subsequent stimulation portion. In more detail, the initial portion refers to a portion that acquires the electrical power contained in the RF input signal and pumps the charge to the capacitor C1 1420. The initial portion may last for a period of time designated as Thigh. The initial portion may be referred to as communication initialization pulses 1502A and 1502B. The stimulation portion corresponds to portion 1504 and may include a serial message encoding waveform parameters of the electrical pulse and polarity setting information of the electrode interface. In some cases, portion 1504 may be present in the first segment of sequence 1500, which configures the electrical pulse and polarity settings. In the absence of a power-on reset event, once initialization is completed, the configuration information of the waveform parameters and polarity settings may be fixed.

[0162] Chip 1400 can allow for embedding serial messages between power surges. For example, a transmitter can initiate a communication by sending a 2 ms “communication initialization pulse” CIP (T high ), followed by a 2ms period of no power transmission (T msg -T high ) to start the serial communication message. In this example, data transmission can be followed by the 2 ms delay and at time T msg Start. Bit timing calibration can be performed by measuring the length of the header byte in the transmitted data stream.

[0163] In some embodiments, the serial data may use a format based on the IrDA SIR format. This encoding format sends out pulses where the bit to be sent is "0". No pulses may be sent during the bit time when the bit is set to "1". Each pulse may be as short as 3 / 16 of the bit time, but the width may be adjusted if necessary. This format may require less power, thus allowing serial data transmission to operate at lower baud rates.

[0164] In an exemplary serial data communication, data may be transmitted asynchronously as a byte with 1 start and 1 stop bit (e.g., an 8-n-1 format carries the same overhead as RS-232, which transmits 10 bits, but only 8 of the 10 bits carry data, and the other two bits are protocol overhead). The LSB may be the first data bit transmitted. This amounts to a total of 70 bits transmitted for 7 bytes of data. 10 of these bits are protocol overhead, and 60 of these bits may be used to carry data. In this example, there is no additional delay between bytes, and the data stream is continuous.

[0165] In this example, the serial baud rate is 19200. The serial message may have a fixed length of 7 bytes, including a header byte, five payload bytes, and a checksum byte. The payload bytes may generally encode the polarity setting of each electrode interface, the electrode driver for each electrode, the amplitude level of each electrode driver, etc. The checksum byte generally helps ensure message integrity.

[0166] The header byte is used to identify the start of a data message. In some embodiments, it can be preset to a value of OxAA. In these embodiments, the header byte can be discarded until the correct header byte is received. The header can also be used to calibrate the internal oscillator powered by the wireless energy stored on VDD. Some embodiments can provide a unique structure of on-off-on-off-on-off-on-off-on-off-on-off for a 10-bit sequence at regular (104μs between transmissions) intervals as a timing marker.

[0167] In some embodiments, the header may include the address of the selected electrode array. For example, bit 7 of byte 1 may be a lead address that distinguishes one of two possible electrode arrays to which the message refers. An electrode array may implement only messages that match its assigned lead address. If the lead of channel A receives a message intended for channel B, the state machine may reject the new message and retain the previously stored register contents. In this example, each electrode array may have an address of 0 or 1, which may be determined by strapping during lead manufacturing.

[0168] Return to Fig.14In some embodiments, the AM detector 1416 can output a logic zero when receiving RF power. In some embodiments, pre-amplification of low voltage data signals or limiting of high voltage data signals can extend the operating range of the AM detector 1416. Thus, signals of 100 mV or greater will be detected. The AM detector 1416 can decode a serial stream transmitted at 19200 baud. The AM detector 1416 input can be internal to the chip 1400 and has features for use at high frequencies (869-915 MHz).

[0169] The AM detector 1416 can generally process rectified signals within a nominal range between 50 mVpp and 15 Vpp supply levels (peak to peak). The AM detector 1416 can include a preamplifier to clamp higher swing signals without output collapse or folding down. The preamplifier should have sufficient gain and low offset to decode a 100 mVpp data signal.

[0170] AM detector 1416 can detect serial data encoded using IrDA (SIR) formatting. A serial data receiver can be included in the AM detector 1416, and data can be converted from a serial format to a parallel format. The operation of the serial data receiver hardware can be controlled by a clock signal that runs at a multiple of the data rate. In some embodiments, the receiver can test the state of the input signal on each clock pulse to search for a start bit. If the start bit is obviously valid, the bit marks the beginning of a new character. If not, the bit is considered to be a false pulse or a power pulse and is ignored. After waiting for an additional bit time, the state of the line is sampled again, and the time of the resulting level is recorded in the shift register.

[0171] After the required number of bit periods of the character length has elapsed, the contents of the shift register are made available to the receiving system.A serial data receiver has no timing system shared with the transmitter other than the communication signal.

[0172] The serial data receiver on chip 1400 can receive and buffer seven (7) eight-bit words. If the checksum match is successful, the data contained in the word will be used to program the control registers in the receiver IC LMI927. If the checksum match is unsuccessful, the data will be ignored and the receiver will continue to listen for valid data. If the received byte does not meet the IrDA (SIR) frame parameters, the serial data receiver will reset and prepare to receive a new word. This will allow the serial receiver to quickly reset after being erroneously activated due to receiving a false signal or stimulus power pulse. If any individual byte does not meet the timing parameters, the serial data receiver will not have to wait for all words to be fully received.

[0173] Chip 1400 may remain in an unconfigured state (all high-side outputs are high-Z, low-side outputs are in triode mode) until a valid serial data set is received. Note that in some implementations, the serial receiver may not function if the device lock bit is set.

[0174] The logic control / state machine 1422 may be synchronized by the timer / oscillator 1424. Synchronization may allow the logic control / state machine 1422 to extract and decode waveform parameters and polarity setting information from the portion 1504. Thereafter, the logic control / state machine 1422 may create one or more electrical pulses based on the waveform parameters. The logic control / state machine 1422 may also set the polarity of the electrode interfaces 1408A to 1408H based on the extracted polarity setting information.

[0175] The output of the logic control / state machine 1422 can be coupled to a drive circuit 1406 that includes features of charge balancing, shunt resistors, and current mirrors. Specifically, the drive circuit 1406 includes a shunt resistor controller 1430 configured to couple the shunt resistor to a switch network 1432. The coupling can enhance the default resistor 1431 through a delay controller 1433. The delay controller can insert a corresponding shunt resistor into the circuit including the stimulation electrode at the end of the electrical pulse to reduce the amount of leakage current.

[0176] Some embodiments may incorporate variable shunt resistors to control the discharge of stimulation pulses from the DC blocking resistor. In these embodiments, the initial serial command contains instructions for the setting values ​​of the shunt resistors. For example, the operator can select between four (4) different settings. The internal shunts are configured so that they are closed during the duration of the stimulation pulse and enabled after a pulse.

[0177] The enabling of the resistor may be delayed following the application of an electrical pulse. A timer is used to delay the start of the discharge of the DC blocking resistor. The timer may be initialized during the duration of a stimulation pulse and it begins its delay at the end of the stimulation pulse. The delay has a fixed duration and may be independent of the stimulation amplitude, repetition rate, and pulse width.

[0178] In some embodiments, stimulation electrical pulses are delivered to specific electrodes via a switching network 1432. To deliver electrical pulses of both polarities, the switching network is coupled to a current source DAC 1434A and a current sink DAC 1434B. As shown, the current source DAC 1434A includes a 7-bit dynamic range and is coupled to a rectified voltage Vrect 1417. In the case where the polarity of the connected electrode is set to positive, the current source DAC 1434A is called. Similarly, the current source DAC 1434A includes a 7-bit dynamic range. In the case where the polarity of the connected electrode is set to negative, the current sink DAC 1434B is called. The current source DAC 1434A and the current sink DAC 1434B are complementary. Both the current source DAC 1434A and the current sink DAC 1434B include a current mirror, which can be used to generate a copy of the current in one device (e.g., a device for generating voltage Vrect 1417) by replicating the current in another device (e.g., current source DAC 1434A or current sink DAC 1434B). The current mirror generally has a relatively high output resistance, which helps keep the output current constant regardless of the load conditions. Another feature of the current mirror is a relatively low input resistance, which helps keep the input current constant regardless of the driving conditions.

[0179] Chip 1400 may include a supervisory power-on reset (POR) circuit designed to hold the device in reset until the system voltage reaches an appropriate level and stabilizes. The POR circuit also operates as a protection against undervoltage conditions when the power supply voltage drops below the minimum operating level. The POR circuit design incorporates appropriate hysteresis between the reset and enable levels to prevent startup inrush current from causing the device to reset during normal operating power-up conditions. Under all power fluctuation conditions, including high-speed transients and slow-rate changing voltage conditions, the POR circuit performs as needed to maintain proper chip functionality. If necessary, the POR circuit can be combined with a watchdog timer tick event to ensure proper operation of chip 1400.

[0180] like Fig.14As shown, each electrode interface is coupled to a corresponding capacitor 1409A to 1409H. These capacitors are placed in series for the purpose of DC blocking. The capacitor is at the end of the signal chain before the stimulating electrical pulses are delivered to the electrodes. In some embodiments, the nominal serial capacitance at each electrode can be 3.0 / μF. Each capacitor is coupled in turn to a corresponding electrode 1410A to 1410H on an 8-electrode stimulator device. As noted, the chip 1400 can be coupled to 8 electrode outputs. Each electrode output can be set to sourcing, sinking or Hi-Z.

[0181] refer to Fig.16A , which shows an exemplary digital-to-analog current mirror for chip 1400. The example emphasizes the current mirror feature. In general, multiple DACs with current codes that can be individually addressed and controlled will increase the register space and design complexity of the ASIC and the die area. On the other hand, having fewer DACs than available channels may require coulomb counting to limit the current through each channel. In the case of having fewer DAC channels than electrodes, the current through each electrode may be increased due to fewer impedance channels.

[0182] In some embodiments, a single current steering DAC with a scaled-down least significant bit (LSB) current value is used to generate the main bias current. In these embodiments, no current is wasted in the current mirror. After the main bias current is generated, the DAC current is mirrored to each electrode using a current mirror ratio of 1:N. Here, mirroring to each electrode generally refers to connecting to each electrode via a current mirror. N can be selected based on the current steering DAC matching requirements. For example, N can be in the range of 10. The LSB size for each electrode can be 100uA. For 7 bits, the full dynamic range of the drive current can be up to 12.7mA.

[0183] Fig.16A The embodiment shown in shows a dual DAC scheme with a mirrored current source across eight (8) electrodes. In a 1:1 transistor mirror, transistor gate 1603A is a replica of transistor gate 1603B. Digital-to-analog conversion (DAC) circuit 1602A represents a push DAC and may correspond to a current sink. Meanwhile, DAC 1602B represents a pull DAC and may correspond to a current source. Logically, DAC 1602A and DAC 1602B may correspond to, respectively, Fig.14DAC 1434A and DAC 1434B are shown. To reduce current mirror mismatch and wasted current, an N-side current sink DAC is used for this application. In this configuration, complementary signals are used to enable each channel. Specifically, channel 0 is enabled by complementary transistors 1604A (for CH0 positive) and 1604B (for CH0 negative). Transistor gate 1604A is coupled to Vrect1417, while transistor gate 1604B is coupled to VDD 1418. Circuit 1605 represents the tissue load on channel 0 and the DC blocking resistor. In some embodiments, the tissue load of channel 0 may include a capacitive component in addition to a resistive component. Similarly, complementary transistors 1606A and 1606B represent the positive polarity arrangement and negative polarity arrangement of the tissue load 1607 for driving channel 1, respectively. This embodiment depicts an 8-side current sink DAC configuration, in which the current mirror reflection is replicated for each of the 8 channels coupled to the electrode leads. For example, a channel 7 drive arrangement is represented by complementary transistors 1608A and 1608B and tissue load 1608A, as shown in FIG. Fig.16A As shown. It is worth noting that in this N-side implementation, three states can be configured for each of the current sinks, namely, a controlled (mirror-reflected) current sink mode, a cut-off device (off mode), and an on device as a triode mode switch. As shown, each channel also includes an on switch. For example, channel 0 includes a CH0_ON switch, while channel 1 and channel 7 include CH1_ON and CH7_ON switches, respectively.

[0184] Based on this model, various electrical signal parameters can be modeled before manufacturing the ASIC chip. In one example, the stimulation waveform after rectification is labeled as Vstim. Fig. 16B The expected Vstim waveform (on channel 1) and the RF input signal (on channel 2) are shown. As demonstrated, a wide range of detailed performance can be simulated during the design phase.

[0185] Fig.17 1712 shows exemplary timing of the waveforms in the above embodiment. N The stimulus portion of the rectified RF input signal is seen on the left, while trace 1714A shows the switching 1714B shows the waveform seen on switch CH0_ON. The on resistance of the triode mode may not be important because it turns on during reverse discharge and does not turn on during stimulation mode.

[0186] The implemented current steering (one current source and eight current mirrors) can limit the charge per phase so that the electrical pulses for implementing stimulation can be applied within a safe range. In some embodiments, the external transmitter can specify limits on the serially written current levels for pulse width and amplitude. Using these specified (upper limit) parameters, the patient user is prevented from requesting unsafe per-phase charges because the patient user has limited parameter selection options. In these embodiments, the current DAC may not operate when there is no stimulation portion in the rectified RF input signal.

[0187] To avoid that a single electrode's sink or sink current exceeds the acceptable per-phase charge, a current control scheme can be used for both the high side and the low side. In a current-steering stimulation scheme, the high side is a single current source DAC connected to the Vrect voltage, and a current mirror is used for each electrode. The low side is a current sink DAC. Each current-steering DAC can include a 7-bit converter. Since the LSB corresponds to 100 μA, the maximum current can be limited to 12.7 mA per electrode. The main current reference for the DAC can be derived from Vrect. The following current mirror can be obtained from Vrect. A similar scheme can be used on the low side to prevent a single electrode from absorbing too much charge.

[0188] Several implementations have been described. However, it should be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.

Claims

1. A circuit for an implantable device to be wirelessly powered, the implantable device being implanted in a patient's body, the circuit comprising: A radio frequency to direct current rectifier circuit adapted to be coupled to one or more antennas on the wirelessly powered implantable device, the rectifier circuit being configured to: rectifying an input radio frequency signal received at the one or more antennas and from an external controller via non-inductive coupling; as well as extracting DC power and configuration data from the input RF signal; A logic control circuit is connected to the rectifier circuit and the drive circuit, and the logic control circuit is configured as follows: generating a current for the drive circuit using only the extracted DC power; According to the extracted configuration data, polarity state information is set for each electrode; The drive circuit is adapted to be coupled to one or more electrodes, the drive circuit comprising a current mirror and configured to: directing stimulation current from the generated current to each electrode via the current mirror to modulate neural tissue within the patient's body, The driving circuit further includes a shunt resistor controller, a switch network and a delay controller, wherein the shunt resistor controller is configured to couple the shunt resistor to the switch network so as to insert the shunt resistor into the circuit at the end of the electrical pulse delivered to the one or more electrodes through the delay controller.

2. The circuit according to claim 1, wherein The driving circuit comprises: a current source digital-to-analog circuit and a current sink digital-to-analog circuit, wherein the current source digital-to-analog circuit and the current sink digital-to-analog circuit are complementary to each other and both are suitable for being connected to each electrode via the current mirror, wherein the stimulation current is determined by a current mirror ratio, and wherein the configuration data comprises the current mirror ratio.

3. The circuit according to claim 2, wherein: The current mirror ratio is matched to the number of electrodes.

4. The circuit according to claim 1, wherein: The driving circuit includes a switch group configured to control the polarity state of each electrode.

5. The circuit according to claim 1, wherein: The driving circuit comprises: A variable shunt resistor is adapted to reduce ripple on the electrode connected thereto just after the stimulation current ends.

6. The circuit according to claim 1, further comprising: A discharge delay timer for delaying the start of discharge of a capacitor coupled to each of the electrodes.

7. The circuit according to claim 1, further comprising: One or more address control bits configurable as a logical address of the implantable device to be wirelessly powered by the extracted electrical energy.

8. The circuit according to claim 1, wherein: The rectifier circuit includes a diode bridge.

9. The circuit according to claim 1, wherein: The rectifying circuit is adapted to be coupled to a differential antenna on the wirelessly powered implantable device.

10. The circuit of claim 1, wherein: The rectifier circuit includes an amplitude modulation detection circuit for extracting power and configuration data from the input radio frequency signal.

11. The circuit according to claim 1, wherein: The logic control circuit includes a state machine that records state information of each electrode based on the extracted configuration data, the configuration data including a polarity setting of each electrode.

12. The circuit of claim 1, wherein: The logic control circuit is further configured to set a polarity state of each electrode during a communication initiation pulse of the input radio frequency signal.

13. The circuit of claim 1, wherein: The rectifier circuit is configured as follows: receiving a period of the input radio frequency signal at the one or more antennas, the period being divided into an initial portion and a subsequent stimulation portion; charging a capacitor using DC power extracted from the initial portion of the cycle of the input RF signal; The logic control circuit is configured as follows: extracting polarity state information for each electrode from the next stimulation portion of the cycle of the input radio frequency signal; and The driving circuit is configured as follows: After the stimulation portion, the current is applied to the electrode according to the polarity state information and using the charge stored in the capacitor.

14. A system for a wirelessly powered implantable device, comprising: A radio frequency to direct current rectifier circuit adapted to be coupled to one or more antennas on the wirelessly powered implantable device, the rectifier circuit being configured to: rectifying an input radio frequency signal received at the one or more antennas and from an external controller via non-inductive coupling; as well as extracting DC power and configuration data from the input RF signal; A logic control circuit is connected to the rectifier circuit and the drive circuit, and the logic control circuit is configured as follows: generating a current for the drive circuit using only the extracted DC power; According to the extracted configuration data, polarity state information is set for each electrode; The drive circuit is adapted to be coupled to one or more electrodes, the drive circuit comprising a current mirror and configured to: Directing stimulation current from the generated current to each electrode via the current mirror to modulate neural tissue within the patient's body, Wherein, the driving circuit also includes a shunt resistor controller, a switch network and a delay controller, and the shunt resistor controller is configured to couple the shunt resistor to the switch network so that the shunt resistor is inserted into the system at the end of the electrical pulse delivered to the one or more electrodes through the delay controller.

15. The system of claim 14, wherein: The driving circuit comprises: a current source digital-to-analog circuit and a current sink digital-to-analog circuit, wherein the current source digital-to-analog circuit and the current sink digital-to-analog circuit are complementary to each other and both are suitable for being connected to each electrode via the current mirror, wherein the stimulation current is determined by a current mirror ratio, and wherein the configuration data comprises the current mirror ratio.

16. The system of claim 15, wherein: The current mirror ratio is matched to the number of electrodes.

17. The system of claim 14, wherein: The driving circuit includes a switch group configured to control the polarity state of each electrode.

18. The system of claim 14, wherein: The driving circuit comprises: A variable shunt resistor is adapted to reduce ripple on the electrode connected thereto just after the stimulation current ends.

19. The system of claim 14, further comprising: A discharge delay timer for delaying the start of discharge of a capacitor coupled to each of the electrodes.

20. The system of claim 14, further comprising: One or more address control bits configurable as a logical address of the implantable device to be wirelessly powered by the extracted electrical energy.

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