WO2024256924A1

WO2024256924A1 - Implant and methods for automatic measurement and control of stimulation currents

Info

Publication number: WO2024256924A1
Application number: PCT/IB2024/055511
Authority: WO
Inventors: Kostas Ioannis Tsampazis; Adrian Robert Cryer; Andrew Keith SALDANHA; Chor Beng CHOO; Padraig HURLEY; Helmut Christian Eder
Original assignee: Cochlear Ltd
Current assignee: Cochlear Ltd
Priority date: 2023-06-12
Filing date: 2024-06-05
Publication date: 2024-12-19
Anticipated expiration: 2025-12-12

Abstract

Presented herein are systems and methods for closed-loop control of an implantable medical device with multiple current sources, and systems and methods for the detection and remediation of imbalanced stimulation currents. More specifically, in accordance with the embodiments presented herein, an implantable medical device with multiple current sources is configured to measure the current flow through the body (e.g., body tissue and/or body fluid) of the recipient, and automatically control, in real-time, the stimulation currents (e.g., substantially immediately make corrections with respect to the injected/sourced current and/or sunk current) to prevent pain and/or harm to the recipient.

Description

IMPLANT AND METHODS FOR AUTOMATIC MEASUREMENT AND CONTROL OF STIMULATION CURRENTS

BACKGROUND

Field of the Invention

[oooi] The present invention relates generally to implant devices with multiple current sources, and in particular, implant devices with multipolar stimulation capabilities.

Related Art

[0002] Medical devices have provided a wide range of therapeutic benefits to recipients over recent decades. Medical devices can include internal or implantable components/devices, external or wearable components/devices, or combinations thereof (e.g., a device having an external component communicating with an implantable component). Medical devices, such as traditional hearing aids, partially or fully-implantable hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc.), pacemakers, defibrillators, functional electrical stimulation devices, and other medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions and/or recipient monitoring for a number of years.

[0003] The types of medical devices and the ranges of functions performed thereby have increased over the years. For example, many medical devices, sometimes referred to as “implantable medical devices,” now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease/injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and/or data received from external devices that are part of, or operate in conjunction with, implantable components.

SUMMARY

[0004] In one aspect, a first method is provided that comprises: delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes; measuring, via measurement circuitry of the implantable medical device, current flow through the body of the recipient in response to the one or more stimulation signals; and controlling, via control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the measured current flow.

[0005] In another aspect, an implantable medical device is provided that comprises: a stimulation unit configured to deliver one or more stimulation signals to a recipient of the implantable medical device via one or more stimulation electrodes configured to be implanted in the recipient; measurement circuitry configured to measure current flow through the body of the recipient in response to the one or more stimulation signals; and control circuitry configured to adjust a current level of at least one of the one or more stimulation signals delivered to the recipient based on the measured current flow.

[0006] In another aspect, a second method is provided that comprises: delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes; detecting, using measurement circuitry of the implantable medical device, a current imbalance based on a measured current flow through the body of the recipient in response to the one or more stimulation signals; and adjusting, using control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the detected current imbalance.

[0007] In another aspect, a method is provided. The method comprises: delivering one or more stimulating pulses to tissue of a recipient via one or more stimulation electrodes of an implantable medical device; storing charge resulting from the delivery of the one or more stimulating pulses in one or more implantable capacitors; and using the charge stored in the one or more implantable capacitors to deliver one or more charge balancing pulses via the one or more electrodes.

[0008] In another aspect, an implantable medical device is provided. The implantable medical device comprises: a plurality of electrodes configured to be implanted in a recipient; a plurality of current sources ; a plurality of capacitors associated with each of the plurality of electrodes; a plurality of shorting switches; and control circuitry configured to: activate one or more of the plurality of current sources to deliver one or more stimulation pulses to the recipient via one or more of the plurality of electrodes, wherein charge resulting from the delivery of the one or more stimulation pulses is stored in one or more of the plurality of capacitors; and actuate one or more of the switches to short-circuit the one or more stimulation electrodes to deliver, via the one or more electrodes, the charge stored in the one or more capacitors as one or more charge balancing pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:

[0010] FIG. 1A is a schematic diagram illustrating a cochlear implant system with which aspects of the systems and methods presented herein can be implemented;

[ooii] FIG. IB is a side view of a recipient wearing a sound processing unit of the cochlear implant system of FIG. 1A;

[0012] FIG. 1C is a schematic view of components of the cochlear implant system of FIG. 1 A;

[0013] FIG. ID is a block diagram of the cochlear implant system of FIG. 1A;

[0014] FIG. IE is a schematic diagram illustrating a computing device with which aspects of the systems and methods presented herein can be implemented;

[0015] FIG. 2A is a diagram depicting an implant for automatic measurement and control of multipolar stimulation currents, according to a first example implementation.

[0016] FIG. 2B is a diagram depicting automatic measurement and detection of imbalanced stimulation currents, and control of the stimulation currents;

[0017] FIG. 2C shows examples of imbalanced stimulation current due to amplitude variations (AIs) or due to phase duration variations (AT);

[0018] FIGs. 2D and 2E are diagrams depicting diagnostic tests for measuring accuracy and calibration of the implant;

[0019] FIG. 2F is a diagram depicting detection and measurement of leakage current (if any) flowing through the body;

[0020] FIG. 3A is a diagram depicting an implant for automatic measurement and control of multipolar stimulation currents, according to a second example implementation;

[0021] FIGs. 3B and 3C depict an example of multipolar stimulation on the stimulation electrodes (ICEs 1 to 5) with a charge balanced stimulation pulse and unequal (non-equal) phase durations (Tphi TPIU); [0022] FIG. 3D is a circuit diagram depicting an example of a balanced Phase 1 (Istim(phl)) during multipolar stimulation;

[0023] FIG. 3E is a circuit diagram depicting an example of an interphase gap (IPG) after balanced Phase 1 during multipolar stimulation;

[0024] FIG. 3F is a circuit diagram depicting an example of a balanced Phase 2 (Istim(ph2)) during multipolar stimulation;

[0025] FIG. 3G is a graph that shows the voltages (Uci to Ucs) over each of the measurement capacitors (Cl to C5) that are associated with the stimulation electrodes (ICEs 1 to 5) when the stimulation charge is balanced;

[0026] FIG. 3H is a circuit diagram depicting an example of an imbalanced Phase 1 (limb(phl)) during multipolar stimulation;

[0027] FIG. 31 is a graph that shows the voltages over the measurement capacitors (Cl, C2, C3, C4 and C5) associated with the stimulation electrodes (ICEs 1, 2, 3, 4 and 5), and over the measurement capacitor (CECE) associated with the return electrode (ECE2), when the stimulation is charge imbalanced due to current amplitude (Is + AIs);

[0028] FIG. 3 J is a graph that shows the voltages over the measurement capacitors (Cl, C2, C3, C4 and C5) associated with the stimulation electrodes (ICEs 1, 2, 3, 4 and 5), and over the measurement capacitor (CECE) associated with the return electrode (ECE2), when the stimulation charge is imbalanced due to current phase duration (T + AT);

[0029] FIG. 4A is a diagram depicting an implant for automatic measurement and control of monophasic stimulation currents, according to a third example implementation;

[0030] FIG. 4B is a circuit diagram depicting an example of a positive charge Istim(phl) (Phase 1 stimulation) generated by the current sources;

[0031] FIG. 4C is a circuit diagram depicting an example of a capacitive discharge Idisch(ph2) (Phase 2 short circuit) involving short-circuited stimulation electrodes and discharging of the blocking capacitors (Cb) and the measurement capacitors (Cm);

[0032] FIG. 4D is a circuit diagram depicting an example of a corrective pulse Icorrective(ph2) (Phase 2 corrective pulse) that is generated to balance the charge;

[0033] FIG. 4E is a graph that shows a series of Phase 1 stimulation pulses, inter-phase gaps and Phase 2 short-circuits, along with a Phase 2 corrective pulse to balance the charge; [0034] FIG. 4F is a diagram illustrating an example of controlling (maximizing) power efficiency using a voltage threshold (Uth);

[0035] FIG. 4G is a diagram illustrating an example of controlling (maximizing) stimulation rate using a time duration threshold (TDth);

[0036] FIG. 5 is a flowchart of an example method for automatic measurement and control of stimulation currents, according to an example embodiment;

[0037] FIG. 6 is a flowchart of an example method for measurement of stimulation currents and calibration of current sources, according to an example embodiment;

[0038] FIG. 7 is a flowchart of an example method for automatic measurement and adjustment of stimulation currents, according to an example embodiment;

[0039] FIG. 8 is a flowchart of an example method for automatic measurement and control of stimulation currents, according to an example embodiment; and

[0040] FIG. 9 is a schematic diagram illustrating a vestibular stimulator system with which aspects of the embodiments presented herein can be implemented.

DETAILED DESCRIPTION

Overview

[0041] Presented herein are systems and methods for closed-loop control of an implantable medical device with multiple current sources, and systems and methods for the detection and remediation of imbalanced stimulation currents. More specifically, in accordance with the embodiments presented herein, an implantable medical device with multiple current sources is configured to measure the current flow through the body (e.g., body tissue and/or body fluid) of the recipient, and automatically control, in real-time, the stimulation currents (e.g., substantially immediately make corrections with respect to the injected/sourced current and/or sunk current) to prevent pain and/or harm to the recipient. That is, using the embodiments described herein, an implantable medical device can be configured to implement automatic measurement and control of stimulation currents, including but not limited to multipolar stimulation currents for devices with multipolar stimulation capabilities (e.g., self-diagnostic, self-controlled multipolar stimulation implant system that is capable of detecting asymmetries or other anomalies). [0042] As described further below, the embodiments described herein can include: (1) measuring stimulation currents flowing through the body of the recipient from the electrodes in real time during stimulation, (2) detecting imbalance s/overstimulation (using the measurement to make a decision and take an appropriate protective action), and (3) controlling the current sources (e.g., adjust stimulation current sources, stop stimulation, correct for imbalance, correct for overstimulation, etc.) in order to compensate for (eliminate, prevent, avoid) such imbalance or overstimulation during the stimulation. Although some example embodiments described herein can involve multipolar stimulation, specifically, it is noted the embodiments described herein can be applied for any kind of stimulation (e.g., multipolar, monopolar, monophasic, bipolar, etc.), and example embodiments are not limited to any particular type of stimulation.

[0043] According to one aspect, an implantable medical device has a configuration that incorporates one or more measurement capacitor(s) on one or more electrodes to enable measurement of current sourced or sunk, resulting in a potential analysis and/or adjustment of real-time current (e.g., if needed to balance the charge/current). For example, the current flow through an area of the body is measured over one or more series capacitors on the one or more electrodes. This measurement also allows the implantable medical device to detect any faults (e.g., including decoding errors that cause imbalanced stimulation or overstimulation) in real time, and automatically stop the stimulation when the charge/current delivered reaches the threshold (C) level, thus preventing overstimulation and painful perception/sensation (i.e., by limiting and/or compensating the extra/imbalanced charge).

[0044] Conventional implantable medical devices, such as cochlear implants, can deliver current in multiple phases, which include a first phase (Phase 1) comprises of a stimulation pulse a second phase (Phase 2) comprised of a charge balancing pulse. However, conventional implantable medical devices do not have ability to measure and control the current/charge during the charge balancing phase (Phase 2). In addition, conventional implantable medical devices use current source(s) for both the stimulation pulse (Phase 1) and the charge balancing pulse (Phase 2), which results in current/power consumption from during both phases (Phase 1 and Phase 2). Certain embodiments presented herein are directed to systems and methods for substantially reducing (potentially eliminating) the use of current source(s) for Phase 2.

[0045] More specifically, certain embodiments are directed to a multipolar monophasic stimulation method in which the stimulation pulse(s) (Phase 1) is/are generated by multiple current sources, where each current source is associated to a relevant electrode. However, in accordance with embodiments presented herein, the charge balancing pulses (Phase 2) are generated by the voltages built up (during Phase 1) over the series electrode capacitors of the stimulation electrodes, when the stimulation electrodes are short circuited. The short circuit of the stimulation electrodes creates a current path for the electrodes’ capacitors to discharging through the body. As a result, there is no current/power consumption from the during Phase 2 (during the discharging of the electrodes’ capacitors). The charge balancing currents are continuously measured to detect/identify when the charge (injected during Phase 1) is balanced. If required, a short corrective pulse (during Phase 2) can be generated by the relevant current sources to discharge the capacitors before their full discharge through the short-circuited stimulation electrodes. By using corrective pulses during Phase 2, an adaptive/variable stimulation rate can be achieved. These corrective pulses can be generated any time during Phase 2, thus the stimulation rate can vary as per the set threshold level(s) or MAP.

[0046] There are a number of different types of devices in/with which embodiments of the present invention can be implemented. Merely for ease of description, the embodiments presented herein are primarily described with reference to a specific device in the form of a cochlear implant system. However, it is to be appreciated that the embodiments presented herein can also be partially or fully implemented by any of a number of different types of devices, including hearing devices, implantable medical devices, consumer electronic devices (e.g., mobile phones), wearable devices (e.g., smart watches, etc.), etc. As used herein, the term “hearing device” is to be broadly construed as any device that acts on an actual or potential auditory perception of an individual, including to improve perception of sound signals, to reduce perception of sound signals, etc. In particular, a hearing device can deliver sound signals to a user in any form, including in the form of acoustical stimulation, mechanical stimulation, electrical stimulation, etc., and/or can operate to suppress all or some sound signals. As such, a hearing device can be a device for use by a hearing -impaired person (e.g., hearing aids, middle ear auditory prostheses, bone conduction devices, direct acoustic stimulators, electro-acoustic hearing prostheses, auditory brainstem stimulators, bimodal hearing prostheses, bilateral hearing prostheses, dedicated tinnitus therapy devices, tinnitus therapy device systems, combinations or variations thereof, etc.), a device for use by a person with normal hearing (e.g., consumer devices that provide audio streaming, consumer headphones, earphones, and other listening devices), a hearing protection device, etc. In other examples, the embodiments presented herein can be implemented by, or used in conjunction with, various implantable medical devices, such as vestibular devices (e.g., vestibular implants), visual devices (i.e., bionic eyes), sensors, pacemakers, drug delivery systems, defibrillators, functional electrical stimulation devices, catheters, seizure devices (e.g., devices for monitoring and/or treating epileptic events), sleep apnea devices, electroporation devices, etc.

[0047] FIGs. 1A-1D illustrates an example cochlear implant system 102 with which aspects of the embodiments presented herein can be implemented. The cochlear implant system 102 comprises an external component 104 that is configured to be directly or indirectly attached to the body of the user, and an intemal/implantable component 112 that is configured to be implanted in or worn on the head of the user. In the examples of FIGs. 1A-1D, the implantable component 112 is sometimes referred to as a “cochlear implant.” FIG. 1A illustrates the cochlear implant 112 implanted in the head 154 of a user, while FIG. IB is a schematic drawing of the external component 104 worn on the head 154 of the user. FIG. 1C is another schematic view of the cochlear implant system 102, while FIG. ID illustrates further details of the cochlear implant system 102. For ease of description, FIGs. 1A-1D will generally be described together.

[0048] In the examples of FIGs. 1A-1D, the external component 104 comprises a sound processing unit 106, an external coil 108, and generally, a magnet fixed relative to the external coil 108. The cochlear implant 112 includes an implantable coil 114, an implant body 134, and an elongate stimulating assembly 116 configured to be implanted in the user’s cochlea. In one example, the sound processing unit 106 is an off-the-ear (OTE) sound processing unit, sometimes referred to herein as an OTE component, that is configured to send data and power to the implantable component 112. In general, an OTE sound processing unit is a component having a generally cylindrically shaped housing 111 and which is configured to be magnetically coupled to the user’s head 154 (e.g., includes an integrated external magnet 150 configured to be magnetically coupled to an intemal/implantable magnet 152 in the implantable component 112). The OTE sound processing unit 106 also includes an integrated external (headpiece) coil 108 (the external coil 108) that is configured to be inductively coupled to the implantable coil 114.

[0049] It is to be appreciated that the OTE sound processing unit 106 is merely illustrative of the external devices that could operate with implantable component 112. For example, in alternative examples, the external component 104 can comprise a behind-the-ear (BTE) sound processing unit configured to be attached to, and worn adjacent to, the recipient’s ear. In general, a BTE sound processing unit comprises a housing that is shaped to be worn on the outer ear of the user and is connected to the separate external coil assembly via a cable, where the external coil assembly is configured to be magnetically and inductively coupled to the implantable coil 114. It is also to be appreciated that alternative external components could be located in the user’s ear canal, worn on the body, etc.

[0050] Although the cochlear implant system 102 includes the sound processing unit 106 and the cochlear implant 112, as described below, the cochlear implant 112 can operate independently from the sound processing unit 106, for at least a period, to stimulate the user. For example, the cochlear implant 112 can operate in a first general mode, sometimes referred to as an “external hearing mode,” in which the sound processing unit 106 captures sound signals which are then used as the basis for delivering stimulation signals to the user. The cochlear implant 112 can also operate in a second general mode, sometimes referred as an “invisible hearing” mode, in which the sound processing unit 106 is unable to provide sound signals to the cochlear implant 112 (e.g., the sound processing unit 106 is not present, the sound processing unit 106 is powered-off, the sound processing unit 106 is malfunctioning, etc.). As such, in the invisible hearing mode, the cochlear implant 112 captures sound signals itself via implantable sound sensors and then uses those sound signals as the basis for delivering stimulation signals to the user. Further details regarding operation of the cochlear implant 112 in the external hearing mode are provided below, followed by details regarding operation of the cochlear implant 112 in the invisible hearing mode. It is to be appreciated that reference to the external hearing mode and the invisible hearing mode is merely illustrative and that the cochlear implant 112 could also operate in alternative modes.

[0051] In FIGs. 1A and 1C, the cochlear implant system 102 is shown with an external device 110, configured to implement aspects of the embodiments presented. The external device 110, which is shown in greater detail in FIG. 1 E, is a computing device, such as a personal computer (e.g., laptop, desktop, tablet), a mobile phone (e.g., smartphone), remote control unit, etc. The external device 110 and the cochlear implant system 102 (e.g., sound processing unit 106 or the cochlear implant 112) wirelessly communicate via a bi-directional communication link 126. The bi-directional communication link 126 can comprise, for example, a short-range communication, such as Bluetooth link, Bluetooth Low Energy (BLE) link, a proprietary link, etc.

[0052] Returning to the example of FIGs. 1A-1D, the sound processing unit 106 of the external component 104 also comprises one or more input devices configured to capture and/or receive input signals (e.g., sound or data signals) at the sound processing unit 106. The one or more input devices include, for example, one or more sound input devices 118 (e.g., one or more external microphones, audio input ports, telecoils, etc.), one or more auxiliary input devices 128 (e.g., audio ports, such as a Direct Audio Input (DAI), data ports, such as a Universal Serial Bus (USB) port, cable port, etc.), and a short-range wireless transmitter/receiver (wireless transceiver) 120 (e.g., for communication with the external device 110), each located in, on or near the sound processing unit 106. However, it is to be appreciated that one or more input devices can include additional types of input devices and/or less input devices (e.g., the short- range wireless transceiver 120 and/or one or more auxiliary input devices 128 could be omitted).

[0053] The sound processing unit 106 also comprises the external coil 108, a charging coil 130, a closely-coupled radio frequency transmitter/receiver (RF transceiver) 122, at least one rechargeable battery 132, and an external sound processing module 124. The external sound processing module 124 can be configured to perform a number of operations and can be formed by one or more processors (e.g., one or more Digital Signal Processors (DSPs), one or more uC cores, etc.), firmware, software, etc. arranged to perform the operations. That is, the external sound processing module 124 can be implemented as firmware elements, partially or fully implemented with digital logic gates in one or more application-specific integrated circuits (ASICs), partially or fully in software, etc. It is to be appreciated that these elements (e.g., functional operations) of the external sound processing module 124 could also or alternatively be implemented/performed as part of the implantable sound processing module 158, as part of the external device 110, etc.

[0054] Returning to the example of FIGs. 1A-1D, the implantable component 112 comprises an implant body (main module) 134, a lead region 136, and the intra-cochlear stimulating assembly 116, all configured to be implanted under the skin (tissue) 115 of the user. The implant body 134 generally comprises a hermetically-sealed housing 138 that includes, in certain examples, at least one power source 125 (e.g., one or more batteries, one or more capacitors, etc.), in which RF interface circuitry 140 and a stimulator unit 142 are disposed. The implant body 134 also includes the intemal/implantable coil 114 that is generally external to the housing 138, but which is connected to the RF interface circuitry 140 via a hermetic feedthrough (not shown in FIG. ID).

[0055] As noted, stimulating assembly 116 is configured to be at least partially implanted in the user’s cochlea. Stimulating assembly 116 includes a plurality of longitudinally spaced intra-cochlear electrical stimulating contacts (electrodes) 144 that collectively form a contact array (electrode array) 146 for delivery of electrical stimulation (current) to the recipient’s cochlea. Stimulating assembly 116 extends through an opening in the recipient’s cochlea (e.g., cochleostomy, the round window, etc.) and has a proximal end connected to stimulator unit 142 via lead region 136 and a hermetic feedthrough (not shown in FIG. ID). Lead region 136 includes a plurality of conductors (wires) that electrically couple the electrodes 144 to the stimulator unit 142. The implantable component 112 also includes an electrode outside of the cochlea, sometimes referred to as the extra-cochlear electrode (ECE) 139.

[0056] As noted, the cochlear implant system 102 includes the external coil 108 and the implantable coil 114. The external magnet 150 is fixed relative to the external coil 108 and the intemal/implantable magnet 152 is fixed relative to the implantable coil 114. The external magnet 150 and the intemal/implantable magnet 152 fixed relative to the external coil 108 and the intemal/implantable coil 114, respectively, facilitate the operational alignment of the external coil 108 with the implantable coil 114. This operational alignment of the coils enables the external component 104 to transmit data and power to the implantable component 112 via a closely-coupled wireless link 148 formed between the external coil 108 with the implantable coil 114. In certain examples, the closely-coupled wireless link 148 is a radio frequency (RF) link. However, various other types of energy transfer, such as infrared (IR), electromagnetic, capacitive and inductive transfer, can be used to transfer the power and/or data from an external component to an implantable component and, as such, FIG. ID illustrates only one example arrangement.

[0057] As noted above, sound processing unit 106 includes the external sound processing module 124. The external sound processing module 124 is configured to process the received input audio signals (received at one or more of the input devices, such as sound input devices 118 and/or auxiliary input devices 128), and convert the received input audio signals into output control signals for use in stimulating a first ear of a recipient or user (i.e., the external sound processing module 124 is configured to perform sound processing on input signals received at the sound processing unit 106). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in the external sound processing module 124 are configured to execute sound processing logic in memory to convert the received input audio signals into output control signals (stimulation signals) that represent electrical stimulation for delivery to the recipient.

[0058] As noted, FIG. ID illustrates an embodiment in which the external sound processing module 124 in the sound processing unit 106 generates the output control signals. In an alternative embodiment, the sound processing unit 106 can send less processed information (e.g., audio data) to the implantable component 112 and the sound processing operations (e.g., conversion of input sounds to output control signals 156) can be performed by a processor within the implantable component 112.

[0059] In FIG. ID, according to an example embodiment, output control signals (stimulation signals) are provided to the RF transceiver 122, which transcutaneously transfers the output control signals (e.g., in an encoded manner) to the implantable component 112 via external coil 108 and implantable coil 114. That is, the output control signals (stimulation signals) are received at the RF interface circuitry 140 via implantable coil 114 and provided to the stimulator unit 142. The stimulator unit 142 comprises a plurality of current sources that ae configured to utilize the output control signals to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea via one or more of the stimulating contacts (electrodes) 144. In this way, cochlear implant system 102 electrically stimulates the user’s auditory nerve cells, bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity, in a manner that causes the recipient to perceive one or more components of the input audio signals (the received sound signals).

[0060] As detailed above, in the external hearing mode the cochlear implant 112 receives processed sound signals from the sound processing unit 106. However, in the invisible hearing mode, the cochlear implant 112 is configured to capture and process sound signals for use in electrically stimulating the user’s auditory nerve cells. In particular, as shown in FIG. ID, an example embodiment of the cochlear implant 112 can include a plurality of implantable sound sensors 165(1), 165(2) that collectively form a sensor array 160, and an implantable sound processing module 158. Similar to the external sound processing module 124, the implantable sound processing module 158 can comprise, for example, one or more processors and a memory device (memory) that includes sound processing logic. The memory device can comprise any one or more of: Non-Volatile Memory (NVM), Ferroelectric Random Access Memory (FRAM), read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical/tangible memory storage devices. The one or more processors are, for example, microprocessors or microcontrollers that execute instructions for the sound processing logic stored in memory device.

[0061] In the invisible hearing mode, the implantable sound sensors 165(1), 165(2) of the sensor array 160 are configured to detect/capture input sound signals 166 (e.g., acoustic sound signals, vibrations, etc.), which are provided to the implantable sound processing module 158. The implantable sound processing module 158 is configured to convert received input sound signals 166 (received at one or more of the implantable sound sensors 165(1), 165(2)) into output control signals 156 for use in stimulating the first ear of a recipient or user (i.e., the implantable sound processing module 158 is configured to perform sound processing operations). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in implantable sound processing module 158 are configured to execute sound processing logic in memory to convert the received input sound signals 166 into output control signals 156 that are provided to the stimulator unit 142. The stimulator unit 142 (current sources) are configured to utilize the output control signals 156 to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea, thereby bypassing the absent or defective hair cells that normally transduce acoustic vibrations into neural activity.

[0062] It is to be appreciated that the above description of the so-called external hearing mode and the so-called invisible hearing mode are merely illustrative and that the cochlear implant system 102 could operate differently in different embodiments. For example, in one alternative implementation of the external hearing mode, the cochlear implant 112 could use signals captured by the sound input devices 118 and the implantable sound sensors 165(1), 165(2) of sensor array 160 in generating stimulation signals for delivery to the user.

[0063] As also illustrated in FIG. ID is measurement and control circuitry 170 (also referred to herein simply as control circuitry 170), which in this example is incorporated into the implant body 134 of the cochlear implant 112. The control circuitry 170 is configured to detect anomalous stimulation currents (e.g., imbalanced stimulation, overstimulation, or other faults), measure the anomalous stimulation currents, and control one or multiple current sources to correct or compensate the stimulation currents so as to prevent imbalanced stimulation, overstimulation, etc. The measurement and control circuitry 170 can include, for example, one or more measurement capacitors, one or more differential amplifiers connected with the one or more measurement capacitors, and a controller connected with the one or more differential amplifiers, wherein the controller is further connected with the stimulator unit 142 (which comprises a plurality of current sources and can also be referred to elsewhere herein as a “stimulation module”). Such components can be implemented in, for example, micro electromechanical systems (MEMS) or with other technology suitable for the particular application. As used elsewhere herein, the term “measurement circuitry” can refer to the one or more measurement capacitors, the one or more differential amplifiers, and their corresponding connections to other components, and the term “control circuitry” can refer to the controller and its corresponding connections to other components.

[0064] FIG. IE is a block diagram illustrating one example arrangement for an external computing device 110 configured to perform one or more operations in accordance with certain embodiments presented herein. As shown in FIG. IE, in its most basic configuration, the external computing device 110 includes at least one processing unit 183 and a memory 184. The processing unit 183 includes one or more hardware or software processors (e.g., Central Processing Units) that can obtain and execute instructions. The processing unit 183 can communicate with and control the performance of other components of the external computing device 110. The memory 184 is one or more software or hardware-based computer-readable storage media operable to store information accessible by the processing unit 183. The memory 184 can store, among other things, instructions executable by the processing unit 183 to implement applications or cause performance of operations described herein, as well as other data. The memory 184 can be volatile memory (e.g., RAM), non-volatile memory (e.g., ROM), or combinations thereof. The memory 184 can include transitory memory or non-transitory memory. The memory 184 can also include one or more removable or non-removable storage devices. In examples, the memory 184 can include random access memory (RAM), read only memory (ROM), EEPROM (Electronically-Erasable Programmable Read-Only Memory), flash memory, optical disc storage, magnetic storage, solid state storage, or any other memory media usable to store information for later access. By way of example, and not limitation, the memory 184 can include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media or combinations thereof. In certain embodiments, the memory 184 comprises logic 195 that, when executed, enables the processing unit 183 to perform aspects of the embodiments presented herein.

[0065] In the illustrated example of FIG. IE, the external computing device 110 further includes a network adapter 186, one or more input devices 187, and one or more output devices 188. The external computing device 110 can include other components, such as a system bus, component interfaces, a graphics system, a power source (e.g., a battery), among other components. The network adapter 186 is a component of the external computing device 110 that provides network access (e.g., access to at least one network 189). The network adapter 186 can provide wired or wireless network access and can support one or more of a variety of communication technologies and protocols, such as ETHERNET, cellular, BLUETOOTH, near-field communication, and RF (Radiofrequency), among others. The network adapter 186 can include one or more antennas and associated components configured for wireless communication according to one or more wireless communication technologies and protocols. The one or more input devices 187 are devices over which the external computing device 110 receives input from a user. The one or more input devices 187 can include physically- actuatable user-interface elements (e.g., buttons, switches, or dials), a keypad, keyboard, mouse, touchscreen, and voice input devices, among other input devices that can accept user input. The one or more output devices 188 are devices by which the computing device 110 is able to provide output to a user. The output devices 188 can include a display 190 (e.g., a liquid crystal display (LCD)) and one or more speakers 191, among other output devices for presentation of visual or audible information to the recipient, a clinician, an audiologist, or other user.

[0066] It is to be appreciated that the arrangement for the external computing device 110 shown in FIG. IE is merely illustrative and that aspects of the embodiments presented herein can be implemented at a number of different types of systems/devices including any combination of hardware, software, and/or firmware configured to perform the functions described herein. For example, the external computing device 110 can be a personal computer (e.g., a desktop or laptop computer), a hand-held device (e.g., a tablet computer), a mobile device (e.g., a smartphone), a surgical system, and/or any other electronic device having the capabilities to perform the associated operations described elsewhere herein.

[0067] For implantable medical devices with multiple current sources and, multipolar stimulation capabilities in particular, differences or variations between the injected/sourced current (“in” current) and the sunk current (“out” current) can cause harm to the recipient of the implantable medical device. In current implantable medical device systems, the conventional method used to detect imbalanced stimulation (imbalanced Phase 1 / Phase 2) is based on electrode potential measurement after Phase 2 of the stimulation. However, current cochlear implant systems are open-loop systems that do not have the capability to measure and control stimulation current(s) in real-time, in order to prevent overstimulation, imbalanced stimulation, unintended stimulation, etc. and keep the stimulation currents within the limits defined by the MAP.

[0068] As noted, the present disclosure describes a closed-loop implant system with multiple current sources that implements methods for real-time detection and correction of imbalanced stimulation. The implantable medical devices and methods described herein can implement automatic measurement and control of stimulation currents, including but not limited to multipolar stimulation currents for implantable medical devices with multipolar stimulation capabilities. The implantable medical device with multiple current sources can be a selfdiagnostic, self-controlled multipolar stimulation system that is capable of detecting asymmetries or other anomalies, measuring the current through the body, and automatically controlling stimulation currents (making corrections with respect to the injected/ source current and sunk current) to prevent pain and/or harm to the recipient. Since the method is based on the current measurement in real time, it is more sensitive, more accurate, more informative, safer, etc. than the conventional method involving electrode potential measurement after Phase 2 of the stimulation.

[0069] There are several possible reasons for imbalanced stimulation: (1) amplitude variations/differences between Phase 1 “sourced” and “sunk” currents, or between Phase 2 “sourced” and “sunk” currents (i.e., higher/lower current), (2) phase duration variations/differences between Phase 1 “sourced” and “sunk” currents, or between Phase 2 “sourced” and “sunk” currents (i.e., shorter/longer current), (3) time shifting between Phase 1 “sourced” and “sunk” currents, or between Phase 2 “sourced” and “sunk” currents, (4) amplitude variations/differences between Phase 1 and Phase 2 due to current leakage to Vdd or Vss (i.e., leakage at current source and/or current sink), or (5) some combination or all of the above. Using the embodiments described herein, the multipolar stimulation currents/current sources imbalances can be detected, the imbalanced current can be measured, an imbalance reason can be identified, and imbalanced stimulation can be prevented in real time by controlling the current sources (e.g., to adjust the stimulation current), if needed.

[0070] As further described below, an implantable medical device can have a configuration that incorporates one or more measurement capacitor(s) (e.g., on an extra-cochlear electrode (ECE), or on each of a plurality of intra-cochlear electrodes (ICEs) as well as the ECE) allows each current source to be measured, assessed, and adjusted and/or trimmed (if needed in order to balance the charge/current). The charge delivered to/from the body is measured over a series capacitor on the ECE (or series capacitors on each of the ICEs and the ECE), which is an ideal method to measure the charge/current accurately and in real time. Measuring the voltage over the measurement capacitor also allows the implantable medical device to detect any faults (e.g., including decoding errors that cause imbalanced stimulation or overstimulation) in real time, and automatically stop the stimulation when the charge/current delivered reaches the threshold (C) level, thus preventing overstimulation and painful perception/sensation (i.e., by limiting and/or compensating the extra/imbalanced charge).

[0071] A first example implementation of an implantable medical device and corresponding embodiments will now be described with reference to FIGs. 2A - 2F.

[0072] FIG. 2A is a diagram depicting an implantable medical device 212 for automatic measurement and control of stimulation currents (including but not limited to multipolar stimulation currents), according to an example embodiment. The first example implementation is based on measurement of the voltage over a measurement capacitor (C24m) connected at a return electrode (ECE2) in series with a DC blocking capacitor (C24b), as shown in FIG. 2A.

[0073] As shown in FIG. 2A, the implantable medical device 212 includes a stimulation module 242 (also refer to the stimulator unit 142 of FIG. ID) that is connected with a plurality of stimulating electrodes 244 (e.g., ICE1 to ICE22) and one or more return electrodes 239 (e.g., ECE1 and ECE2). Each of the stimulating electrodes 244 and the return electrodes 239 have a DC blocking capacitor 245 (generally referred to herein as “Cb”) connected in series therewith. The stimulation module 242 is configured to drive, as per the multipolar stimulation MAP, the individual current sources (e.g., one for each electrode).

[0074] The implantable medical device 212 of FIG. 2A further includes measurement and control circuitry 270 (also referred to herein as simply “control circuitry 270”) that is connected with the stimulation module 242. The control circuitry 270 can include a measurement capacitor 272 (generally referred to herein as “Cm,” and denoted as “C24m” in FIG. 2A) that is connected at the return electrode 239 (ECE2) in series with its DC blocking capacitor 245 (denoted as “C24b” in FIG. 2A). Additionally, the control circuitry 270 can include a multiplexer module 274 that connects each measurement capacitor 272 (Cm) to a respective differential amplifier, a differential amplifier module 276 connected with the multiplexer module 274, and a controller 278 that is connected with the differential amplifier module 276. As mentioned above, the term “measurement circuitry” as used herein can refer to the measurement capacitor 272 (Cm), the differential amplifier module 276, and their corresponding connections with other components, and the term “control circuitry” as used herein can refer to the controller 278 and its corresponding connections with other components.

[0075] The differential amplifier module 276 is configured to measure the voltage over the measurement capacitor 272 (Cm), and the controller 278 is configured to perform the current measurements, process the data (to determine whether imbalanced stimulation, overstimulation, or otherwise unintended stimulation is occurring), and control the stimulation module 242 to adjust the stimulation currents accordingly. The data processing performing by the controller 278 can involve calculation and comparison with a reference value, for example.

[0076] Although not shown in FIG. 2A, it is also possible to have a measurement capacitor (e.g., C23m) on the other return electrode (ECE1) as well, and to use it in the same way as the measurement capacitor 272 (C24m) on the return electrode 239 (ECE2), so the measurement/diagnostic capability of the control circuitry 270 is doubled. However, it is noted that the ECE2 and ECE1 measurement functions should not be used simultaneously.

[0077] As shown in FIGs. 2B and 2C, the control circuitry 270 of the implantable medical device 212 allows for the detection and measurement of the imbalanced stimulation current flowing though the body in real time multipolar stimulation (e.g., via measurement capacitor 272, differential amplifier 276, and controller 278). In one example, the implantable medical device 212 can be configured to detect and measure an imbalance (Ucm) between the sourcing (“sourced”) current and the sinking (“sunk”) current due to their amplitude variations (AIs), as shown on the left side of FIG. 2C. In another example, the implantable medical device 212 can be configured to detect and measure an imbalance (Ucm) between the sourcing (“sourced”) current and the sinking (“sunk”) current due to their phase duration variations (AT), as shown on the right side of FIG. 2C.

[0078] In addition, the implantable medical device 212 can be configured to perform identification in real-time of the reason for the multipolar imbalanced stimulation, whether due to current amplitude variations (AIs), due to current phase duration variations (AT), due to time shifting between Phase 1 in and out currents or between Phase 2 in and out currents, due to current amplitude variations between Phase 1 and Phase 2 due to leakage to Vdd or Vss, or some combination thereof.

[0079] Further, referring again to the control circuitry 270 of FIGs. 2A and 2B, the controller 278 of the implantable medical device 212 can be configured to control the current sources in real-time during multipolar stimulation to, for example, prevent harm to the recipient due to imbalanced stimulation and/or overstimulation. Any imbalance between the injected/source current and the sinking current can be identified and measured over the measurement capacitor 272 (Cm) on the return electrode 239 (ECE). Once the imbalanced stimulation is detected and measured, corrections can be automatically implemented. For example, the controller 278 can adjust the current sources for injecting electrodes to make the difference/variation in the charge/current (limb) equal to zero.

[0080] According to one aspect, if imbalanced stimulation occurs during stimulation, it can be detected, the imbalanced current can be measured in real time, and a protective mechanism can be activated to prevent harm (by preventing imbalanced stimulation). According to another aspect, if a faulty condition occurs (e.g., decoding error resulting in imbalanced or overstimulation) during stimulation, it can be detected, the stimulation current on each electrode can be measured in real time, and the stimulation current can be automatically limited to the threshold (C) level for the particular electrode to prevent harm.

[0081] According to yet another aspect, diagnostic tests can be run automatically and regularly. For example, before any corrections are performed (e.g., by controlling the stimulation module 242 to adjust one or more current sources and corresponding stimulation currents), one or more diagnostic tests can be performed to confirm the current anomaly/imbalance and the related current source.

[0082] As shown in FIG. 2D, the implantable medical device 212 can allow for the measurement and/or calibration of the accuracy of the components of the measurement and control circuitry 270 itself (e.g., measurement capacitor 272, differential amplifier 276, etc.). This can be done in diagnostic mode, via monopolar stimulation with a global current source (GCS). The global current source (GCS) can be used to check/confirm the correct functioning of the measurement circuitry during monopolar stimulation.

[0083] As shown in FIG. 2E, the implantable medical device 212 can allow for the measurement of the amplitude/value of the stimulation current flowing though the body for each of a plurality of local current sources (CSx) and identification of the deviation (if any) from their production values. This can be done in diagnostic mode, via monopolar stimulation with each of the local current sources (CSx). All of the local current sources (CSx) can be checked one by one, such that each current source’s current is measured and compared with their reference value obtained at production during the trimming process. The measured current of each current source can or cannot have the correct value.

[0084] Additionally, a reference resistor 282 (Rm) that is switchable can also be used, as shown in FIG. 2E, whereby the implantable medical device 212 can measure the voltage drop over the reference resistor 282 (Rm) connected at the return electrode 239 (ECE) in series with the DC blocking capacitor 245 (CECE), such that confirmation can be performed in two ways, both for the current source (CSx) and for the measurement circuitry (e .g . , the measurement capacitor 272 (Cm)) itself.

[0085] In another example, the implantable medical device 212 can run a second check to confirm and measure the incorrect current value and the related current source. This can be done by running bipolar stimulation and performing voltage measurement over the measurement capacitor 272 (Cm) at the return electrode 239 (ECE). The difference between the incorrect current and the correct current will cause a current flow to/from the return electrode 239 (ECE).

[0086] Once the local current source (CSx) with the anomalous current is identified, corrections can be automatically implemented (i.e., to eliminate any current imbalance). In one example, the implantable medical device 212 can be configured to perform calibration/trimming of the local current sources CSx (if required), via the controller 278 controlling the stimulation module 242 to make corresponding adjustments.

[0087] Advantageously, the described measurement and control circuitry 270 (e.g., the measurement capacitor 272 (Cm), the differential amplifier module 276, and the controller 278) does not introduce error to the stimulation currents, as there can be a calibration of the measurement circuitry in production and/or in situ. In production, during trimming of the local current sources (CSx), the voltage drop over the related capacitor can be measured, so the related stimulation current (i.e., voltage over the capacitor (Is - Uc) for each local current source) can be identified and stored. Additionally or alternatively, the voltage drop over the related capacitor can be measured using the global current source (GCS), so the related stimulation current (i.e., voltage over the capacitor (Is - Uc)) for the GCS can be identified and stored.

[0088] Also, in situ measurements can be double checked in order to confirm the measurement result is correct. In situ, both of the above tests can be run to check and confirm the calibration. If a difference between the measured “sourced” and “sunk” currents/charge is identified during multipolar stimulation, then at the same time the same current/charge difference value can be measured across the measurement capacitor 272 (Cm) for the return electrode 239 (ECE). If the difference between the measured “sourced” and “sunk” currents/charge is not confirmed by a simultaneously measured current/charge difference value across the measurement capacitor 272 (Cm) for the return electrode 239 (ECE), then the control of the particular current source is not allowed and in situ calibration can be required. Accordingly, another advantage of the system and embodiments described herein is that the testing can be run as a real-time diagnostic. It can be run continually in the background or on a periodic basis, and it is fully flexible. Currently existing implementations are open-loop systems and cannot run diagnostics in real time.

[0089] Thus, the implantable medical device 212 and methods described herein enable calibration of the current source(s) by measuring the stimulation current flowing through the body, comparing the measured value with the set value, and adjusting/trimming the associated current source(s), if needed. The calibration can be performed automatically and at any time. A first calibration method can involve voltage measurement across a measurement capacitor 272 (Cm), and a second calibration method can involve voltage measurement across a reference resistor 282 (Rm). During the calibration procedure, protection from overstimulation can be activated if the current level reaches the threshold (C) level for the particular electrode.

[0090] As shown in FIG. 2F, the implantable medical device 212 can also allow for the detection and measurement of microphone leakage current (if any) flowing through the body. The leakage current (II) to the microphone can be detected by measuring the voltage (Ucm) across the measurement capacitor 272 (Cm), and hence measuring the charge/current accumulated over the measurement capacitor 272 (Cm) for the return electrode 239 (ECE), when no stimulation is applied. Likewise, this approach could also be applied to check for antenna (RF coil) leakage current (e.g., a short from coil to case or other “unintended” electrodes). This can be done in diagnostic mode, with no stimulation. If microphone leakage or antenna (RF coil) leakage occurs during stimulation, it can be detected, the leakage current can be measured in real-time, and a protective mechanism can be activated to prevent harm.

[0091] In one non-limiting illustrative example, this configuration allows the implantable medical device 212 to detect and measure imbalanced stimulation currents in multipolar stimulation (e.g., due to leakage to Vdd or Vss, decoding errors, etc.). Based on the measured imbalanced charge over the measurement capacitor 272 (Cm) on the return electrode 239 (ECE2 or ECE1), a correction or adjustment of the appropriate current source (CSx), and hence, the stimulation current, can be made to compensate or eliminate the leaky/imbalanced current.

[0092] Thus, in the first example implementation of FIG. 2A, the implantable medical device 212 with the measurement and control circuitry 270 can have a configuration with only one measurement capacitor 272 (Cm) connected in series with the DC blocking capacitor 245 for one of the return electrodes 239 (ECE2 or ECE1), and only one differential amplifier 276 connected to the measurement capacitor 272 (Cm). This configuration allows the implantable medical device 212 to: (1) check the accuracy of the measurement circuitry (e.g., the measurement capacitor 272 (Cm) and/or the differential amplifier 276) and perform calibration, if required, using the measurement capacitor 272 (Cm) on the return electrode 239 (ECE2 or ECE1), the global current source (GCS), a switchable reference resistor 282 (Rm), and predefined reference voltage values; (2) measure the stimulation current that flows through the body for any one of the local current sources (CSx), and detect anomalies using the measurement capacitor 272 (Cm) on the return electrode 239 (ECE2 or ECE1), each one of the local current sources (CSx), and pre-defined reference voltage values; (3) control (calibrate/trim) any one of the local current sources (CSx), if required, in order to maintain safe stimulation (and stimulation as per the MAP); and/or (4) detect current leakage from the microphone and from the antenna (RF coil).

[0093] A second example implementation of an implantable medical device and corresponding embodiments is described below with reference to FIGs. 3A - 3J. The examples shown in FIGs. 3B, 3C, 3G, 31, and 3J refer to multipolar stimulation on five electrodes. The examples shown in FIGs. 3D, 3E, 3F, and 3H refer to multipolar stimulation on three electrodes, for simplicity.

[0094] FIG. 3 A is a diagram depicting an implantable medical device 312 for automatic measurement and control of stimulation currents (including but not limited to multipolar stimulation currents), according to an example embodiment. The second example implementation is based on simultaneous measurement of the stimulation current flowing through multiple individual electrodes during multipolar stimulation, via measurement of the voltage over one or more of the respective measuring capacitors (CXm - one on each electrode ICE1 to ICE22 and ECE2/ECE1) connected in series with each DC blocking capacitor (CXb), as shown in FIG. 3A. This example embodiment allows for measurement of the charge/current for all, or at least a subset, of the stimulating electrodes (the ICEs) in addition to the return electrode (ECE), and control/adjustment of the parameters of the stimulation current separately for each individual electrode during multipolar stimulation (e.g., if required to balance the charge/current).

[0095] As shown in FIG. 3A, the implantable medical device 312 includes a stimulation module 342 (also refer to the stimulator unit 142 of FIG. ID) that is connected with a plurality of stimulating electrodes 344 (e.g., ICE1 to ICE22) and one or more return electrodes 339 (e.g., ECE2 and/or ECE1). Each of the stimulating electrodes 344 and the one or more return electrodes 339 have a DC blocking capacitor 345 (Cb) connected in series therewith. The stimulation module 342 is configured to drive, as per the multipolar stimulation MAP, the individual current sources (e.g., one for each electrode).

[0096] The implantable medical device 312 of FIG. 3A further includes measurement and control circuitry 370 (also referred to herein as simply “control circuitry 370”) that is connected with the stimulation module 342. The control circuitry 370 can include a plurality of measurement capacitors 372 (generally referred to herein as “Cm,” and denoted as “Clm” to “C22m” and “C24m” in FIG. 3A) that are connected at each of the stimulating electrodes 344 (ICE1 to ICE 22) and the return electrode 339 (ECE2) in series with their respective DC blocking capacitors 345 (generally referred to herein as “Cb,” and denoted as “Clb” to “C22b” and “C24b” in FIG. 3A). Additionally, the control circuitry 370 can include a multiplexer module 374 that connects each measurement capacitor 372 (Cm) to a respective differential amplifier, a differential amplifiers module 376 connected with the multiplexer module 374, and a controller 378 that is connected with the differential amplifiers module 376. As mentioned above, the term “measurement circuitry” can refer to the plurality of measurement capacitors 372 (Cm), the differential amplifiers module 376, and their corresponding connections with other components, and the term “control circuitry” can refer to the controller 378 and its corresponding connections with other components.

[0097] The differential amplifiers module 376 is configured to measure the voltage over each measurement capacitor 372 (Cm), and the controller 378 is configured to perform the stimulation currents measurements, process the data (to determine whether imbalanced stimulation, overstimulation, or otherwise unintended stimulation is occurring), and control the stimulation module 342 to adjust the stimulation currents accordingly. The data processing performing by the controller 378 can involve calculation and comparison with reference values, for example, in order to identify whether the correct electrodes (as per the multipolar MAP) are activated, the level of the stimulation current on each electrode is as per the multipolar MAP, the duration of each stimulation phase (pulse) on each electrode is as per the multipolar MAP, the multipolar stimulation is charge balanced, etc.

[0098] Although not shown in FIG. 3A, it is also possible to have a measurement capacitor (e.g., C23m) on the other return electrode (ECE1) as well, and to use it in the same way as the measurement capacitor 372 (C24m) on the return electrode 339 (ECE2), so the measurement/diagnostic capability of the control circuitry 370 is doubled. However, it is noted that the ECE2 and ECE1 measurement functions should not be used simultaneously. [0099] The stimulation module 342 drives the individual current sources for each stimulating electrode 344. The stimulation currents generated by the current sources flow through each of the stimulating electrodes 344 (ICE1 to ICE22) and the return electrode 339 (e.g., ECE2), and through each measurement capacitor 372 (Clm to C22m, and C24m). The voltage (Ucim to Uc22m, and Uc24m) across each measurement capacitor 372 is proportional to the current flowing through it and is measured by a respective differential amplifier of the differential amplifiers module 376. The measured voltage (Ucim to Uc22m, and Uc24m) over each measurement capacitor 372 (Clm to C22m, and C24m) is processed by the controller 378, which controls the stimulation module 342 (e.g., to adjust one or more current sources and corresponding stimulation currents) accordingly in order to prevent overstimulation, imbalanced stimulation, unintended stimulation, etc.

[ooioo] An example of multipolar stimulation on stimulation electrodes 344 (ICEs 1 to 5) with a charge balanced stimulation pulse and unequal (non-equal) phase durations (Tphi Tpin) is shown in FIGs. 3B, 3C, and 3G. It is noted that the capacitors Cl to C5 in FIGs. 3B and 3C are measurement capacitors (Cm), and the DC blocking capacitors (Cb) are not shown for simplicity.

[ooioi] FIG. 3D is a circuit diagram depicting an example of a balanced Phase 1 (Istim(phl)) during multipolar stimulation. FIG. 3E is a circuit diagram depicting an example of an interphase gap (IPG) after balanced phase 1 during multipolar stimulation. In FIG. 3E, all electrodes are disconnected from their current source (all Sxcs switches are open circuit). FIG. 3F is a circuit diagram depicting an example of a balanced Phase 2 (Istim(ph2)) during multipolar stimulation.

[00102] FIG. 3G is a graph that shows the voltages (Uci to Ucs) over each of the measurement capacitors 372 (Cl to C5) that are associated with the stimulation electrodes 344 (ICEs 1 to 5) when the stimulation charge is balanced.

[00103] The measurement of Uc_x can be performed during the interphase gap (IPG, referring to FIG. 3E), and the stimulation current can be calculated as:

Ucx Ix = C -

T1

[00104] or the measurement of Uc_x can be performed during Phase 1 (Phi, refer to FIG. 3D) and Phase 2 (Ph2, refer to FIG. 3F), and the stimulation current can be calculated as: HUcx lx = C -

ATI (2)

[00105] For the example shown in FIGs. 3B and 3C, involving multipolar stimulation on five electrodes, the conditions for charge balanced stimulation are:

Tphl (13) = Tphl (II) = Tphl (12) = Tphl (14) = Tphl (15)

Tph2 (13) = Tph2 (II) = Tph2 (12) = Tph2 (14) = Tph2 (15)

[00106] As can be seen in FIGs. 3B and 3C, the stimulation currents have the following values:

For phase 1 (Phi): 13 = 1200uA, 12 = 14 = 400uA, Il = 15 = 200uA

1200uA = Z 200uA, 400uA, 400uA, 200uA

For phase 2 (Ph2): 13 = 600uA, 12 = 14 = 200uA, Il = 15 = lOOuA

600uA = Z lOOuA, 200uA, 200uA, lOOuA

[00107] As can be seen in FIG. 3G, the duration of the first stimulation pulse Tphl for all stimulation electrodes/currents Tphl(Ix) is the same:

Tphl(I3) = Tphl(Il) = Tphl(I2) = Tphl(I4) = Tphl(I5) = lOuS

[00108] and the duration of the second stimulation pulse Tph2 for all stimulation electrodes/currents Tph2(Ix) is the same:

Tph2(I3) = Tph2(Il) = Tph2(I2) = Tph2(I4) = Tph2(I5) = 20uS

[00109] The following equation is valid for the voltages (Ucx) over the measurement capacitors

372 (Cl, C2, C3, C4, and C5) at any time during stimulation (Phi, IPG, and Ph2):

[oono] FIG. 3H is a circuit diagram depicting an example of an imbalanced Phase 1 (limb(phl)) during multipolar stimulation.

[oom] FIG. 31 is a graph that shows the voltages over the measurement capacitors 372 (Cl, C2, C3, C4 and C5) associated with the stimulation electrodes 344 (ICEs 1, 2, 3, 4 and 5), and over the measurement capacitor 372 (CECE) associated with the return electrode 339 (ECE2), when the stimulation is charge imbalanced due to current amplitude (Is + AIs) - (also refer to the left side of FIG. 2C):

[00112] then

[00113] The imbalanced portion (AI3) of the current 13 cannot flow into the stimulation electrodes 344 (ICEs 1, 2, 4 and 5, due to the current sources of ICEs 1, 2, 4 and 5) and flows to the return electrode 339 (ECE2). It charges the measurement capacitor 372 (CECE) of the return electrode 339 (ECE2) to a voltage proportional to the value of AI3 current.

[00114] As can be seen from the graph of FIG. 31, the stimulation current 13 during phase 1 (Phi) has an increase (AI3) of 10% in amplitude:

13 + AI3 = 1200uA + 120uA = 1320uA.

[00115] Then the voltage over capacitor C3 at the end of phase 1 is:

Uc3 = 120m V + 12m V = 132mV.

[00116] The imbalanced portion (AI3) of the 13 current creates a voltage (UCECE) over the measurement capacitor 372 (CECE) of the return electrode 339 (ECE2). The value of the voltage UCECE at the end of Phase 1 is 12mV.

[00117] FIG. 3J is a graph that shows the voltages over the measurement capacitors 372 (Cl, C2, C3, C4 and C5) associated with the stimulation electrodes 344 (ICEs 1, 2, 3, 4 and 5), and over the measurement capacitor 372 (CECE) associated with the return electrode 339 (ECE2), when the stimulation charge is imbalanced due to current phase duration (T + AT) - (also refer to the right side of FIG. 2C).

[00118] As can be seen from the graph of FIG. 3J, the duration of Phase 1 (Phi) of the stimulation current 13 has an increase (AT) of 10% in duration:

Tphl(I3) + ATphl(I3) =10us +lus = l lus

Tphl (II) = Tphl (12) = Tphl (14) = TphI(I5) = lOus

[00119] SO

Tphl (13) Tphl (II) = Tphl (12) = Tphl (14) = TphI(I5)

[00120] then

[00121] The current 13 flowing during the ATph 1 (13) cannot flow into the stimulation electrodes 344 (ICEs 1, 2, 4 and 5, due to the current sources of ICEs 1, 2, 4 and 5) and flows to the return electrode 339 (ECE2). It charges the measurement capacitor 372 (CECE) of the return electrode 339 (ECE2) to a voltage proportional to the value of current 13 and the duration of ATphl(I3).

[00122] As the duration of phase 1 (Phi) of 13 current has an increase (ATphl(I3) of 10%, the voltage over capacitor C3 at the end of phase 1 is:

Uc3 = (13 x (Tphl + ATphl))/C3) = 132mV.

[00123] The 13 current flowing to the return electrode 339 (ECE2) during ATphl(I3) creates a voltage (UCECE) over the measurement capacitor 372 (CECE) of the return electrode 339 (ECE2). The value of the voltage UCECE at the end of Phase 1 is 12mV.

[00124] It is noted that the values of the currents and pulse durations in the paragraphs above and the related graphs are merely an illustrative example, and example embodiments are not limited thereto (i.e., different values are possible).

[00125] Thus, in the second example implementation of FIG. 3A, the implantable medical device 312 with the measurement and control circuitry 370 can have a configuration with a plurality of measurement capacitors 372 (Cm) connected in series with the DC blocking capacitor 245 for each of the stimulating electrodes 344 (ICE1 to ICE22), in addition to the measurement capacitor 372 (Cm) for the return electrode 339 (ECE2 or ECE1), and a plurality of differential amplifiers 276 connected to each of the plurality of measurement capacitors 372 (Cm), respectively. In addition to providing the same functional capabilities as the implantable medical device 212 of FIG. 2A, this configuration allows the implantable medical device 312 of FIG. 3A to detect, measure, and prevent imbalanced stimulation in real time during stimulation by: measuring the voltages (Ucm) over the measurement capacitors 372 (Cm) of the stimulating electrodes 344 (ICEs), or measuring the voltage (Ucm) over the measurement capacitor 372 (Cm) of the return electrode 339 (ECE2 or ECE1), or possibly both measurements simultaneously, and then controlling/driving (e.g., adjusting) the corresponding current sources (CSx) that are associated with the imbalanced stimulation.

[00126] Next, a third example implementation of an implantable medical device and corresponding methods are described below with reference to FIGs. 4A - 4G. As noted above, current cochlear implant systems do not have the capability to measure and control the current/charge during the charge balancing phase (Phase 2). Also, the current cochlear implant systems are using current source(s) for both Phase 1 (stimulation pulse) and Phase 2 (charge balancing pulse). However, there is a current that is used (i.e., power consumption) from the battery of the implant (or a sound processing unit coupled with the implant) during both Phase 1 and Phase 2. The third example implementation is intended to address these issues, as further described below.

[00127] FIG. 4A is a diagram depicting an implantable medical device 412 for automatic measurement and control of stimulation currents (including but not limited to multipolar monophasic stimulation or monopolar monophasic stimulation), according to an example embodiment. The third example implementation involves monophasic stimulation (Phase 1) and is based on the implantable medical device 312 of FIG. 3A but saves up to 50% of the power required in comparison to the currently used biphasic stimulation modes. The system and methods described below enable selective and dynamic electrode shorting, which can be done immediately after Phase 1 (monophasic stimulation) to balance the charge/current for the electrodes that have been activated. The charge/current accumulated in the electrode’s capacitor during Phase 1 is used for charge balancing (during Phase 2), which can help to save/increase battery life when using monophasic stimulation.

[00128] The implantable medical device 412 of FIG. 4A includes the same or similar components as the implantable medical device 312 of FIG. 3 A, with like numbers referring to like parts in both FIG. 4A and FIG. 3A, respectively. As such, a detailed description of the components shown in FIG. 4A that correspond to components already described above with reference to FIG. 3A will not be repeated again. The main distinction between the two Figures is that FIG. 4A further illustrates shorting switches 473 (e.g., switches SI through S22 for the ICE 1-22, and switches S23 to S24 for the ECE1 and ECE2) connected with the measurement capacitors 472 (Clm through C24m), and the shorting switches 473 can be selectively opened and closed according to the embodiments described herein. The shorting switches 473 (SI through S24) may be connected with, part of, or included in the stimulation module 442, although example embodiments are not limited thereto. The location of the shorting switches 473 as shown in FIG. 4A is intended to be conceptual and functional in nature and is not indicative of actual physical locations of the shorting switches 473, or any other component shown in the figures.

[00129] In the implantable medical device 412 of FIG. 4A, the associated blocking capacitors 445 (e.g., one or more of Clb through C22b) and measurement capacitors 472 (e.g., one or more of Clm through C22m) of the multiple electrodes 444 (e.g., one or more of ICE 1 through ICE22) that have been activated (Phase 1 stimulation) are charged to the level equal to the charge delivered (sourced/sinked) to/from the body. To save power, the current sources that are activated/used in Phase 1 are not activated/used to generate Phase 2 stimulation (with opposite polarity) to balance the charge/current delivered to the body. Instead, the associated capacitors (445, 472) can effectively be used as voltage sources to balance the charge/current. This can be done by shorting (immediately after Phase 1) the electrodes 444 that have been activated in Phase 1, via the shorting switches 473 (e.g., SI through S22). In certain examples, the charge balance for each electrode 444 can be monitored, so that the shorting time for each electrode can be minimized. All the other electrodes 444 are available and used for stimulation, except the discharging electrodes, which will be available again as soon as their charge is balanced (or as soon as required). Thus, instead of using Phase 1 and Phase 2 both generated by current source(s), the third example implementation uses Phase 1 (stimulation phase) generated by the current source(s), and Phase 2 (charge balancing phase) uses the charge accumulated during Phase 1.

[00130] An example of multipolar monophasic stimulation on stimulation electrodes 444 (e.g., ICEs 1 to 5) will now be described with reference to FIGs. 4B, 4C, 4D, and 4E.

[00131] FIG. 4B is a circuit diagram that shows a positive charge Istim(phl) (Phase 1 stimulation), generated by the current sources (e.g., CSICEX, CSICE(X-I), CSICE<X+I)). In FIG. 4B, each of the active stimulation electrodes 444 (ICE_x-i, ICE_X, and ICE_x+i) is connected to its relevant current source (CSICE(X-I), CSICEX, CSICE<X+I)) through corresponding switches (S(x-i)cs, Sxcs, and S<x+i)cs), respectively.

[00132] FIG. 4C is a circuit diagram that shows a capacitive discharge Idisch(ph2) (Phase 2 short circuit), involving short-circuited stimulation electrodes 444 and discharging of the blocking capacitors 445 (Cb) and the measurement capacitors 472 (Cm). In FIG. 4C, each of the stimulation electrodes 444 (ICEx-i, ICEx, and ICEx+i) is connected to a common rail through corresponding shorting switches 473 (S(x-i)SE, SXSE, and S(X+1)SE), respectively (i.e., short- circuited electrodes). That is, all of the current sources (CS) are disconnected from the electrodes 444 (i.e., all of the switches Scs are open circuit), and the measurement capacitors 472 (Cm) are short circuited to a common rail through shorting switches 473 (SSE) and are discharging through the rail and the body. [00133] FIG. 4D is a circuit diagram that shows a corrective pulse Icorrective(ph2) (Phase 2 corrective pulse), which is generated to balance the charge. If/when required, a corrective pulse (i.e., a Phase 2 corrective current) with a relatively short duration and small amplitude current can be generated by the related current sources to balance the charge. This corrective pulse Icorrective(ph2) can be generated if/when there is imbalance due to variations of the capacitors’ discharge time constant, for example.

[00134] In FIG. 4B, the stimulation pulses (Phase 1 charge) are generated by multiple current sources, where each current source is associated with a relevant stimulation electrode 444. In FIG. 4C, the charge balancing pulses (Phase 2 discharge/short-circuit) are generated by the voltages that were built up during Phase 1 over the series electrode capacitors (445, 472) of the stimulation electrodes 444 when the stimulation electrodes are short circuited, via the shorting switches 473 (SSE). The short circuit of the stimulation electrodes 444 creates a current path for the electrodes’ capacitors (445, 472) to discharge through the body. There is no current drawn (i.e., no power consumption) from the battery of the implant (or of a sound processing unit coupled with the implant) during the Phase 2 discharging of the electrodes’ capacitors (445, 472). The charge balancing currents are continuously measured (during the Phase 2 discharge/short-circuit) to detect/identify when the charge that was injected during Phase 1 is balanced. Then, if required, a short Phase 2 corrective pulse can be generated by the relevant current sources (CS) to discharge the blocking capacitors 445 (Cb) and the measurement capacitors 472 (Cm), before their full discharge through the short-circuited stimulation electrodes 444, as in FIG. 4D.

[00135] FIG. 4E is a diagram showing a series of Phase 1 stimulation pulses 481 (refer to FIG. 4B), inter-phase gaps 482 (IPGs), and short circuits 483 (refer to FIG. 4C), and a corrective pulse 484(3) (refer to FIG. 4D) to balance the charge. As shown in FIG. 4E, immediately following Phase 1, there is an inter-phase gap (IPG), in which all of the stimulation electrodes 444 are disconnected from their relevant current source(s) and from the common rail. The short circuit then comes after the IPG, followed by the next Phase 1 stimulation pulse, and so on.

[00136] The positive charge Istim(phl) (i.e., Phase 1 stimulation - see FIGs. 4B and 4E) and the capacitive discharge Idisch(ph2) (i.e., Phase 2 short circuit - see FIGs. 4C and 4E) can be automatically measured and controlled, if needed. If, during any given cycle, the discharging level 486 of the measurement capacitor 472 (e.g., Cm3 on ICE3) is detected to remain greater/higher than a threshold level 488 (T) prior to the next activation of the stimulation electrode 444 (e.g., ICE3), as shown by discharging level 486(3) in FIG. 4E, a corrective pulse 484(3) (i.e., a short/small Phase 2 corrective pulse Icorrective(ph2)) can be generated by the current source(s) to balance the charge/current during Phase 2, as shown in FIGs. 4D and 4E.

[00137] In certain embodiments, and as shown in FIG. 4E, immediately following the short Phase 2 corrective pulse 484(3), there can be another short inter-phase gap (e.g., IPG 485(3) in FIG. 4E), in which all of the stimulation electrodes 444 are disconnected from their relevant current source(s) and from the common rail, before and until the subsequent Phase 1 stimulation pulse begins. Following the subsequent Phase 1 stimulation pulse 481(4), and corresponding IPG (e.g., 482(4) in FIG. 4E) and Phase 2 short circuit 483(4), the discharging level 486(4) is now below the threshold level 488 (T) as shown in FIG. 4E, which indicates that the charge -balancing via the Phase 2 corrective pulse 484(3) according to the embodiments described herein was effective to balance the charge.

[00138] With series capacitors (445, 472) for each electrode 444 during Phase 1 stimulation, an equal amount of charge is stored in the series capacitor as is delivered to the recipient. By disconnecting the current sources and shorting the capacitors (445, 472) and allowing them to discharge into the recipient (via the shorting switches 473) the capacitors will charge-balance the stimulation without using more power from the implantable medical device (or its sound processing unit). As noted, this concept of charge recovery of stimulus pulses will lower the required power for an implantable medical device (such as the implantable medical device 412 of FIG. 4A) to provide stimulus, thereby providing longer battery life and less frequency charging, among various other advantages.

[00139] In addition, by using “corrective” Phase 2 stimulation pulses according to the embodiments described above, an adaptive/variable stimulation rate can also be achieved. Although the figures may show specific examples of the time at which the corrective Phase 2 pulses are generated during Phase 2, it is noted that the corrective Phase 2 pulses can be generated at any time during Phase 2, so that the stimulation rate can vary as per the set threshold level(s) or MAP. Examples of optimizing power consumption and/or optimizing stimulation rate utilizing thresholding embodiments will now be described with reference to FIGs. 4F and 4G.

[00140] FIG. 4F is a diagram illustrating an example of controlling (maximizing) power efficiency using a voltage threshold 498 (Uth). As shown in FIG. 4F, when the discharging level (e.g., 496(3)) is above a voltage threshold 498 (Uth), a short corrective pulse 494(4) (Icotr) can be generated to balance the charge. FIG. 4G is a diagram illustrating an example of controlling (maximizing) stimulation rate using a time duration threshold 499 (TDth). Likewise, as shown in FIG. 4G, when the discharging level (e.g., 496(6) and 496(9)) is above the voltage threshold 498 (Uth) at the end of the time duration threshold 499 (TDth), a short corrective pulse Icorr (e.g., 494(6) and 494(9)) can be generated to balance the charge. In certain examples, and as shown in FIG. 4G, the amplitude (current level) of the corrective pulse may vary depending on how much the voltage threshold 498 (Uth) is exceeded at the time of measuring the discharging level. For example, a relatively larger corrective pulse Icorr (e.g., 494(6)) can be generated to account for a larger deviation from the voltage threshold 498 (Uth) when the discharging level (e.g., 496(6)) is farther from the voltage threshold, or a relatively smaller corrective pulse Icorr (e.g., 494(9)) can be generated to account for a smaller deviation from the voltage threshold 498 (Uth) when the discharging level (e.g., 496(9)) is closer to the voltage threshold.

[00141] As noted, the charge injected “in” and taken “out” of the body is continuously measured over the electrode capacitor, and a corrective current pulse (Icorr) can be generated, if required, to balance the charge. The corrective current pulse is calculated and applied if the capacitor’s discharging voltage is higher than a voltage threshold 498 (Uth). The calculation of the amplitude of the corrective current pulse (Icorr) is based on the capacitor’s discharging voltage measured over the electrode capacitor at either: (1) a pre-determined time, prior to the next stimulation pulse (voltage threshold Uth, refer to FIG. 4F), or (2) the time duration threshold TDth (refer to FIG. 4G).

[00142] For a predefined duration (TCCP) of the corrective current pulse (e.g., TCCP = 5ps), and the measured voltage (Uc) over the electrode capacitor (CE) at a pre-determined time, prior to the next stimulation pulse (refer to FIG. 4F, Uc > Uth) or at the time duration threshold TDth, (refer to FIG. 4G, Uc > Uth), the amplitude of the corrective current pulse (Icorr) can be calculated as:

Icon = (Uc x CE) / TCCP

[00143] The stimulation rate can be controlled and adjusted by varying the voltage threshold 498 (Uth) and/or the time duration threshold 499 (TDth). By controlling/adjusting the level/value of the voltage threshold 498 (Uth), the power efficiency can be optimized (e.g., improved, increased, maximized, etc.). By controlling/adjusting the level/value of the time duration threshold 499 (TDth), the stimulation rate can be optimized (e.g., improved, increased, maximized, etc.).

[00144] Thus, an adaptive stimulation rate can be achieved by varying/adjusting the voltage threshold (Uth) and/or the time duration threshold (TDth). For example, the stimulation rate can be controlled by varying/adjusting the level/value of Uth and/or TDth in order to adapt the stimulation to the physiological condition of the nerves/tissue and to achieve optimum audio perception. The monophasic adaptive/dynamic stimulation rate can be controlled automatically by utilizing nerve responses as feedback for the quality of the audio perception. In some examples, the monophasic adaptive/dynamic stimulation rate can be controlled/adjusted manually by the patient with the use of an external device for communication with the implant.

[00145] In the implantable medical device 412 of FIG. 4A according to the third example implementation, the shorting switches 473 (SI through S22) are provided in addition to the extra measurement capacitors 472 (Cm) on each electrode 444 (ICE1 through ICE22). In addition to providing the same functional capabilities as the implantable medical device 212 of FIG. 2A described above according to the first example implementation and the implantable medical device 312 of FIG. 3A described above according to the second example implementation, the implantable medical device 412 of FIG. 4A is further configured to implement a novel stimulation algorithm using monophasic stimulation, and to control and optimize the discharge function for the monophasic stimulation mode.

[00146] According to the third example implementation of FIGs. 4A - 4G, imbalanced stimulation can be detected, measured and prevented in real time, during stimulation by measuring and controlling the current/charge that is injected to/taken from the body of the implant recipient. The device measures both the injected charge and the capacitive discharge current, and provides control to confirm the full discharge of the measurement capacitors (Cm) in multipolar stimulation is completed. If needed, a short/small “Phase 2 corrective pulse” can be generated to balance the charge. The device achieves similar Phase 2 duration for all electrodes’ capacitor discharging by measuring the discharging current and driving the associated current source accordingly (if required). The measurement and adjustment/control of the charge balancing current (the electrode capacitor discharge current) can be performed in real time, and the device and methods can improve power consumption efficiency and battery life (e.g., by up to 50%). The charge balancing current adjustment is achieved automatically, and as needed. Thus, the charge-balancing phase duration remains constant, regardless of any body impedance variations, for example. The device and methods also enables an adaptive stimulation rate that can be dynamically adjusted according to variations in the body impedance of the recipient, for example.

[00147] FIG. 5 is a flowchart of an example method 500 for automatic measurement and control of stimulation currents, according to an example embodiment. At 510, the method 500 includes delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes. At 520, the method 500 includes measuring, via measurement circuitry of the implantable medical device, current flow through the body of the recipient in response to the one or more stimulation signals. At 530, the method 500 includes controlling, via control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the measured current flow.

[00148] FIG. 6 is a flowchart of an example method 600 for measurement of stimulation currents and calibration of current sources, according to an example embodiment. At operation 610, the method 600 includes measuring accuracy of the measurement circuitry in a diagnostic mode for a global current source of the implantable medical device based on an amplitude of the measured current flow through the body of the recipient. At operation 620, the method 600 includes measuring accuracy of the measurement circuitry in a diagnostic mode for a plurality of local current sources of the implantable medical device based on a plurality of amplitudes of the measured current flow through the body of the recipient. At operation 630, the method 600 includes calibrating one or more of the plurality of local current sources of the implantable medical device based on a variation in values of the measured current flow through the body of the recipient for the one or more of the plurality of local current sources compared to target current values, respectively. In one example, the method 600 can include identifying whether one or more amplitudes of the measured current flow through the body of the recipient deviates from one or more target current values by more than a threshold amount, respectively.

[00149] FIG. 7 is a flowchart of an example method 700 for automatic measurement and adjustment of stimulation currents, according to an example embodiment. At operation 710, the method 700 includes delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes. At operation 720, the method 700 includes detecting, using measurement circuitry of the implantable medical device, a current imbalance based on a measured current flow through the body of the recipient in response to the one or more stimulation signals. At operation 730, the method 700 includes adjusting, using control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the detected current imbalance.

[00150] FIG. 8 is a flowchart of an example method 800 for automatic measurement and adjustment of stimulation currents of an implantable medical device, according to an example embodiment. At operation 810, the method 800 includes delivering one or more stimulating pulses to tissue of a recipient via one or more implantable stimulation electrodes. At 820, the method 800 includes storing charge resulting from the delivery of the one or more stimulating pulses in one or more capacitors. At 830, the method 800 includes using the charge stored in the one or more capacitors to deliver one or more charge balancing pulses via the one or more electrodes.

[00151] Thus, example embodiments described above provide a system and methods for automatic measurement and control of the delivered charge into/out of the body during multipolar stimulation. This allows for various problems related to the stimulation to be detected and solved (while current implant systems do not have such a fimction/capability). Currently, if a recipient has an uncomfortable or painful perception/sensation (due to faulty condition, decoding error, etc.), the recipient has to use a sound processor or magnet and manually reset the implant, and after that go to the clinic for further investigation. However, the devices and methods described herein can be configured to prevent uncomfortable or painful perception/sensation by limiting the charge delivered, can do this automatically without patient intervention, while allowing the stimulation to continue normally (i.e., a reset is not required). In the above-described examples, one or more additional measurement capacitor(s) Cm (e.g., connected in series with the DC blocking capacitor Cb for the ECE, or for each of the ICEs and the ECE) will allow the implantable medical device to be fully self-controlled due to the feedback/closed-loop configuration. This is a new function that the current implantable medical devices do not have. In the current implantable medical devices, the stimulation current/charge is not controllable in the manner described herein.

[00152] The example embodiments can be based on direct measurement of the charge/current, by measuring the voltage drop over a measurement capacitor (Cm) that is created by the stimulation current flowing through Cm. The charge/current delivered to/from the body of the recipient can be measured directly, any corresponding charge/current imbalance (limb) can be measured continuously and accurately in real-time during stimulation (e.g., during Phase 1 and/or during Phase 2). One or more current sources can be controlled (e.g., to adjust the stimulation currents) to compensate/correct for the detected charge/current imbalance in realtime during stimulation (e.g., during Phase 1 and/or during Phase 2). Notably, the measurement/detection and control/adjustment features described herein can be performed in real-time during the same phase (e.g., during the same single pulse of a stimulation signal) to actively prevent/avoid imbalanced stimulation or overstimulation, such that there is no need to wait until the end of Phase 2 to measure/detect a current imbalance and control/adjust current sources to address the current imbalance.

[00153] As explained above, implantable medical devices that are equipped with the measurement and control circuitry and corresponding methods described herein can provide several benefits and improvements over conventional implants and methods, including but not limited to:

[00154] (1) Protection from an undesirable current path through electrodes that are supposed to be “off’ during multipolar stimulation: The controller can check that the correct stimulation electrodes (ICEs), as per the MAP, are activated. If the controller detects electrodes that are not supposed to be activated, are activated, then the controller can disconnect them. The number of activated electrodes should be equal to the number of the set by the MAP stimulation electrodes.

[00155] (2) Protection from imbalanced stimulation: The controller can detect and measure the charge delivered, compare and calculate the charge balance, and correct the stimulation current parameters (if needed) so that the sum of the measured voltages over the measurement capacitors (Cm) of the stimulation electrodes becomes zero (Ucm = 0).

[00156] (3) Protection from overstimulation due to current amplitude differences/variations: The controller can check and measure the amplitude/level of the stimulation current on each stimulation electrode (ICEs), compare the measured value with the stimulation current value set by the MAP, and limit the amplitude/level of the stimulation current (if needed) so that it does not exceed a certain percentage of the set value (e.g., a 2% margin can be added to the current set value).

[00157] (4) Protection from overstimulation due to duration differences/variations: The controller can check and measure the duration of each stimulation phase on each stimulation electrode (ICEs), compare the measured value with the duration value set by the MAP, and correct/limit the duration (if needed). [00158] (5) Stimulation self-diagnostic/self-calibration functions: The controller can automatically measure the stimulation current (pulse amplitude), stimulation pulse duration (pulse width), interphase gap, etc.

[00159] As noted, the devices and methods described herein can be especially beneficial for multipolar stimulation, as the currents flowing through the body of the recipient can be continuously monitored in real time. However, examples embodiments are not limited to multipolar stimulation (or any particular type of stimulation or stimulation mode), and these methods can also be similarly applied for various other different types of stimulation or stimulation modes as well.

[00160] As previously described, the technology disclosed herein can be applied in any of a variety of circumstances and with a variety of different devices. Example devices that can benefit from technology disclosed herein are described in more detail in FIG. 9. The aspects of the present disclosure can be applied to other devices, such as neurostimulators, cardiac pacemakers, cardiac defibrillators, sleep apnea management stimulators, seizure therapy stimulators, tinnitus management stimulators, and vestibular stimulation devices, as well as other medical devices that deliver stimulation to tissue. Further, technology described herein can also be applied to consumer devices. These different systems and devices can benefit from the technology described herein.

[00161] FIG. 9 illustrates an example vestibular stimulator system 902, with which embodiments presented herein can be implemented. As shown, the vestibular stimulator system 902 comprises an implantable component (vestibular stimulator) 912 and an external device/component 904 (e.g., external processing device, battery charger, remote control, etc.). The external device 904 comprises a transceiver unit 960. As such, the external device 904 is configured to transfer data (and potentially power) to the vestibular stimulator 912.

[00162] The vestibular stimulator 912 comprises an implant body (main module) 934, a lead region 936, and a stimulating assembly 916, all configured to be implanted under the skin/tissue (tissue) 915 of the recipient. The implant body 934 generally comprises a hermetically-sealed housing 938 in which RF interface circuitry, one or more rechargeable batteries, one or more processors, and a stimulator unit are disposed. The implant body 934 also includes an intemal/implantable coil 914 that is generally external to the housing 938, but which is connected to the transceiver via a hermetic feedthrough (not shown). [00163] The stimulating assembly 916 comprises a plurality of electrodes 944(l)-(3) disposed in a carrier member (e.g., a flexible silicone body). In this specific example, the stimulating assembly 916 comprises three (3) stimulation electrodes, referred to as stimulation electrodes 944(1), 944(2), and 944(3). The stimulation electrodes 944(1), 944(2), and 944(3) function as an electrical interface for delivery of electrical stimulation signals to the recipient’s vestibular system.

[00164] The stimulating assembly 916 is configured such that a surgeon can implant the stimulating assembly adjacent the recipient’s otolith organs via, for example, the recipient’s oval window. It is to be appreciated that this specific embodiment with three stimulation electrodes is merely illustrative and that the methods presented herein can be used with stimulating assemblies having different numbers of stimulation electrodes, stimulating assemblies having different lengths, etc.

[00165] In operation, the vestibular stimulator 912, the external device 904, and/or another external device, can be configured to implement the methods presented herein. That is, the vestibular stimulator 912, possibly in combination with the external device 904 and/or another external device, can include an evoked biological response analysis system, as described elsewhere herein.

[00166] As should be appreciated, while particular uses of the technology have been illustrated and discussed above, the disclosed technology can be used with a variety of devices in accordance with many examples of the technology. The above discussion is not meant to suggest that the disclosed technology is only suitable for implementation within systems akin to that illustrated in the figures. In general, additional configurations can be used to practice the processes and systems herein and/or some aspects described can be excluded without departing from the processes and systems disclosed herein.

[00167] This disclosure described some aspects of the present technology with reference to the accompanying drawings, in which only some of the possible aspects were shown. Other aspects can, however, be embodied in many different forms and should not be construed as limited to the aspects set forth herein. Rather, these aspects were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible aspects to those skilled in the art.

[00168] As should be appreciated, the various aspects (e.g., portions, components, etc.) described with respect to the figures herein are not intended to limit the systems and processes to the particular aspects described. Accordingly, additional configurations can be used to practice the methods and systems herein and/or some aspects described can be excluded without departing from the methods and systems disclosed herein.

[00169] According to certain aspects, systems and non-transitory computer readable storage media are provided. The systems are configured with hardware configured to execute operations analogous to the methods of the present disclosure. The one or more non-transitory computer readable storage media comprise instructions that, when executed by one or more processors, cause the one or more processors to execute operations analogous to the methods of the present disclosure.

[00170] Similarly, where steps of a process are disclosed, those steps are described for purposes of illustrating the present methods and systems and are not intended to limit the disclosure to a particular sequence of steps. For example, the steps can be performed in differing order, two or more steps can be performed concurrently, additional steps can be performed, and disclosed steps can be excluded without departing from the present disclosure. Further, the disclosed processes can be repeated.

[00171] Although specific aspects were described herein, the scope of the technology is not limited to those specific aspects. One skilled in the art will recognize other aspects or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative aspects. The scope of the technology is defined by the following claims and any equivalents therein.

[00172] It is also to be appreciated that the embodiments presented herein are not mutually exclusive and that the various embodiments can be combined with another in any of a number of different manners.

Claims

CLAIMS What is claimed is:

1. A method comprising : delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes; measuring, via measurement circuitry of the implantable medical device, current flow through the body of the recipient in response to the one or more stimulation signals; and controlling, via control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the measured current flow.

2. The method of claim 1, wherein measuring the current flow through the body of the recipient via the measurement circuitry comprises: measuring an imbalanced current flow using a measurement capacitor connected between a stimulation unit of the implantable medical device and a return electrode, wherein the measurement capacitor is connected in series with a DC blocking capacitor on the return electrode.

3. The method of claim 1, wherein measuring the current flow through the body of the recipient via the measurement circuitry comprises: measuring an imbalanced current flow using one or more of a plurality of measurement capacitors, wherein each of the plurality of measurement capacitors is connected between a stimulation unit of the implantable medical device and a corresponding at least one of the one or more stimulation electrodes, wherein each of the plurality of measurement capacitors are connected in series with a DC blocking capacitor on the respective stimulation electrode.

4. The method of claim 1, 2, or 3, further comprising: determining that the current flow through the body of the recipient is imbalanced based on detecting an amplitude variation between corresponding sourcing and sinking currents.

5. The method of claim 1, 2, or 3, further comprising: determining that the current flow through the body of the recipient is imbalanced based on detecting a phase duration variation between corresponding sourcing and sinking currents.

6. The method of claim 1, 2, or 3, further comprising: detecting that the current flow through the body of the recipient is imbalanced; and identifying a reason for the current flow being imbalanced, wherein the identified reason is one of an amplitude variation between sourcing and sinking currents, a phase duration variation between the sourcing and sinking currents, time shifting between the sourcing and sinking currents, an amplitude variation between a first phase and a second phase of stimulation due to leakage, or a combination thereof.

7. The method of claim 1, 2, or 3, wherein controlling the at least one of the one or more current sources based on the measured current flow via the control circuitry comprises: automatically controlling the at least one of the one or more current sources in real time to prevent one or more of overstimulation, imbalanced stimulation, or unintended stimulation.

8. The method of claim 1, 2, or 3, wherein controlling the at least one of the one or more current sources based on the measured current flow via the controller comprises: automatically controlling the at least one of the one or more current sources in real time to maintain the current flow within limits defined by a mapping of the implantable medical device.

9. The method of claim 1, 2, or 3, wherein controlling the at least one of the one or more current sources based on the measured current flow via the control circuitry comprises: automatically controlling the at least one of the one or more current sources in realtime to reduce a current level of one or more of the stimulation signals delivered to the recipient.

10. The method of claim 1, 2, or 3, wherein controlling the at least one of the one or more current sources based on the measured current flow via the controller comprises: automatically controlling the at least one of the one or more current sources in realtime to adjust a current level of at least one of the stimulation signals to offset a measured current imbalance.

11. The method of claim 1, 2, or 3, further comprising: measuring accuracy of the measurement circuitry in a diagnostic mode for a global current source of the implantable medical device based on an amplitude of the measured current flow through the body of the recipient; measuring accuracy of the measurement circuitry in a diagnostic mode for a plurality of local current sources of the implantable medical device based on a plurality of amplitudes of the measured current flow through the body of the recipient; and calibrating one or more of the plurality of local current sources of the implantable medical device based on a variation in values of the measured current flow through the body of the recipient for the one or more of the plurality of local current sources compared to target current values, respectively.

12. The method of claim 11, wherein measuring the accuracy of the measurement circuitry in the diagnostic mode for the plurality of local current sources of the implantable medical device comprises: identifying whether one or more amplitudes of the measured current flow through the body of the recipient deviates from one or more target current values by more than a threshold amount, respectively.

13. The method of claim 1, 2, or 3, wherein the implantable medical device includes a microphone, the method further comprising: detecting and measuring microphone leakage current flowing through the body of the recipient in a diagnostic mode.

14. The method of claim 1, 2, or 3, wherein the implantable medical device includes a coil antenna, the method further comprising: detecting and measuring coil antenna leakage current flowing through the body of the recipient in a diagnostic mode.

15. The method of claim 1, 2, or 3, wherein measuring the current flow through the body of the recipient via the measurement circuitry comprises: measuring, via differential amplifier circuitry connected between the measurement circuitry and the control circuitry, one or more voltages across one or more measurement capacitors during delivery of the one or more stimulation signals to the recipient; and processing the one or more voltages across the one or more measurement capacitors to obtain the measured current flow through the body of the recipient in response to the one or more stimulation signals.

16. An implantable medical device comprising: a stimulation unit configured to deliver one or more stimulation signals to a recipient of the implantable medical device via one or more stimulation electrodes configured to be implanted in the recipient; measurement circuitry configured to measure current flow through the body of the recipient in response to the one or more stimulation signals; and control circuitry configured to adjust a current level of at least one of the one or more stimulation signals delivered to the recipient based on the measured current flow.

17. The implantable medical device of claim 16, wherein the measurement circuitry comprises: a measurement capacitor connected between the stimulation unit and a return electrode, wherein the measurement capacitor is connected in series with a DC blocking capacitor on the return electrode; and a differential amplifier connected between the measurement capacitor and the control circuitry, wherein the differential amplifier is configured to measure a voltage across the measurement capacitor during delivery of the one or more stimulation signals to the recipient.

18. The implantable medical device of claim 17, wherein the control circuitry comprises: a controller configured to process the voltage across the measurement capacitor to obtain the measured current flow through the body of the recipient in response to the one or more stimulation signals.

19. The implantable medical device of claim 16, wherein the measurement circuitry further comprises: a plurality of measurement capacitors connected between the stimulation unit and a plurality of stimulation electrodes, wherein each of the plurality of measurement capacitors are connected in series with a DC blocking capacitor on the respective stimulation electrode; and a plurality of differential amplifiers connected between the plurality of measurement capacitors and the control circuitry, wherein the plurality of differential amplifiers are configured to measure one or more voltages across one or more of the plurality of measurement capacitors during delivery of the one or more stimulation signals to the recipient.

20. The implantable medical device of claim 19, wherein the control circuitry comprises: a controller configured to process the one or more voltages across the one or more of the plurality of measurement capacitors to obtain the measured current flow through the body of the recipient in response to the one or more stimulation signals.

21. The implantable medical device of claim 16, 17, 18, 19, or 20, wherein the control circuitry comprises: a controller configured to: detect that the current flow through the body of the recipient is imbalanced; and identify a reason for the current flow being imbalanced.

22. The implantable medical device of claim 21, wherein, to identify the reason for the current flow being imbalanced, the controller is configured to detect one or more of: an amplitude variation between corresponding sourcing and sinking currents, a phase duration variation between the corresponding sourcing and sinking currents, time shifting between the corresponding sourcing and sinking currents, or an amplitude variation between a first phase and a second phase of stimulation due to leakage.

23. The implantable medical device of claim 21, wherein the controller is configured to: automatically control the at least one of the one or more stimulation signals in realtime, based on the identified reason, to prevent one or more of overstimulation, imbalanced stimulation, or unintended stimulation.

24. The implantable medical device of claim 21, wherein the controller is configured to: automatically control the at least one of the one or more stimulation signals in realtime, based on the identified reason, to maintain the current flow within limits defined by a mapping of the implantable medical device.

25. The implantable medical device of claim 21, wherein the controller is configured to: automatically control the at least one of the one or more stimulation signals in realtime, based on the identified reason, to reduce a current level of one or more of the stimulation signals delivered to the recipient.

26. The implantable medical device of claim 21, wherein the controller is configured to: automatically control the at least one of the one or more stimulation signals in realtime, based on the identified reason, to adjust a current level of at least one of the stimulation signals delivered to the recipient in order to offset a measured current imbalance.

27. A method comprising: delivering, with one or more current sources configured to be implanted in a recipient of an implantable medical device, stimulation signals to the recipient via one or more stimulation electrodes; detecting, using measurement circuitry of the implantable medical device, a current imbalance based on a measured current flow through the body of the recipient in response to the one or more stimulation signals; and adjusting, using control circuitry of the implantable medical device, at least one of the one or more current sources in real-time based on the detected current imbalance.

28. The method of claim 27, wherein detecting the current imbalance using the measurement circuitry comprises: measuring, using one or more differential amplifiers of the measurement circuitry, current flow through the body of the recipient in response to the one or more stimulation signals based on measuring one or more voltages across one or more measurement capacitors of the measurement circuitry during delivery of the one or more stimulation signals to the recipient; and processing the one or more voltages across the one or more measurement capacitors to obtain the measured current flow through the body of the recipient in response to the one or more stimulation signals.

29. The method of claim 28, wherein detecting the current imbalance using the measurement circuitry comprises: determining that the measured current flow through the body of the recipient is imbalanced based on detecting a difference in amplitude between corresponding sourcing and sinking currents using the one or more differential amplifiers and a controller of the control circuitry.

30. The method of claim 28, wherein detecting the current imbalance using the measurement circuitry comprises: determining that the measured current flow through the body of the recipient is imbalanced based on detecting a difference in phase duration between corresponding sourcing and sinking currents using the one or more differential amplifiers and a controller of the control circuitry.

31. The method of claim 28, wherein adjusting the at least one of the one or more current sources using the control circuitry comprises: automatically controlling a stimulation unit of the implantable medical device, using a controller of the control circuitry, to adjust the at least one of the one or more current sources in real-time based on the measured current flow.

32. The method of claim 31, wherein automatically controlling the stimulation unit to adjust the at least one of the one or more current sources using the controller comprises at least one of: controlling the stimulation unit to adjust at least one of the one or more current sources in real-time to prevent one or more of overstimulation, imbalanced stimulation, or unintended stimulation; controlling the stimulation unit to adjust at least one of the one or more current sources in real-time to maintain the current flow within limits defined by a mapping of the implantable medical device; controlling the stimulation unit to adjust the at least one of the one or more current sources in real-time to reduce a current level of one or more of the stimulation signals delivered to the recipient; or controlling the stimulation unit to adjust the at least one of the one or more current sources in real-time to modify a current level of at least one of the stimulation signals in order to offset a measured current imbalance.

33. The method of claim 27, 28, 29, 30, 31, or 32, wherein detecting the current imbalance using the measurement circuitry comprises: measuring an imbalanced current flow through the body of the recipient using a measurement capacitor connected between a stimulation unit of the implantable medical device and a return electrode, wherein the measurement capacitor is connected in series with a DC blocking capacitor on the return electrode.

34. The method of claim 27, 28, 29, 30, 31, or 32, wherein detecting the current imbalance using the measurement circuitry comprises: measuring an imbalanced current flow through the body of the recipient using one or more of a plurality of measurement capacitors, wherein each of the plurality of measurement capacitors is connected between a stimulation unit of the implantable medical device and a corresponding at least one of the one or more stimulation electrodes, wherein each of the plurality of measurement capacitors are connected in series with a DC blocking capacitor on the respective stimulation electrode.

35. The method of claim 27, 28, 29, 30, 31, or 32, wherein the detecting and the adjusting occur during a same phase of delivering the stimulation signals to the recipient.

36. A method, comprising: delivering one or more stimulating pulses to tissue of a recipient via one or more stimulation electrodes of an implantable medical device; storing charge resulting from the delivery of the one or more stimulating pulses in one or more implantable capacitors; and using the charge stored in the one or more implantable capacitors to deliver one or more charge balancing pulses via the one or more electrodes.

37. The method of claim 36, wherein the charge stored in the one or more implantable capacitors is a result of voltages built up during delivery of the one or more stimulating pulses.

38. The method of claim 36 or 37, further comprising: measuring the charge delivered by the one or more stimulation pulses; and measuring the charge delivered by the one or more charge balancing pulses.

39. The method of claim 38, further comprising: determining, based on the measuring, when the charge delivered by the one or more stimulating pulses is balanced by the charge delivered by the one or more charge balancing pulses; and in response to determining the charge is balanced, stopping delivery of the one or more charge balancing pulses.

40. The method of claim 38, further comprising: determining, based on the measuring, when that the charge delivered by the one or more charge balancing pulses is insufficient to balance the charge delivered by the one or more stimulating pulses; and in response to determining that the charge delivered by the one or more charge balancing pulses is insufficient, delivering one or more corrective pulses from one or more current sources of the implantable medical device.

41. The method of claim 36, wherein using the charge stored in the one or more implantable capacitors to deliver one or more charge balancing pulses comprises: discharging the one or more implantable capacitors into the tissue of the recipient via the one or more stimulation electrodes.

42. An implantable medical device comprising: a plurality of electrodes configured to be implanted in a recipient; a plurality of current sources; a plurality of capacitors associated with each of the plurality of electrodes; a plurality of shorting switches; and control circuitry configured to: activate one or more of the plurality of current sources to deliver one or more stimulation pulses to the recipient via one or more of the plurality of electrodes, wherein charge resulting from the delivery of the one or more stimulation pulses is stored in one or more of the plurality of capacitors; and actuate one or more of the switches to short-circuit the one or more stimulation electrodes to deliver, via the one or more electrodes, the charge stored in the one or more capacitors as one or more charge balancing pulses.

43. The implantable medical device of claim 42, further comprising: measurement circuitry configured to measure the charge delivered by the one or more stimulation pulses and the charge delivered by the one or more charge balancing pulses.

44. The implantable medical device of claim 43, wherein the control circuitry is configured to: determine, based on the measuring, when the charge delivered by the one or more stimulating pulses is balanced by the charge delivered by the one or more charge balancing pulses; and in response to determining the charge is balanced, stop delivery of the one or more charge balancing pulses.

45. The implantable medical device of claim 43, wherein the control circuitry is configured to: determine, based on the measuring, when that the charge delivered by the one or more charge balancing pulses is insufficient to balance the charge delivered by the one or more stimulating pulses; and in response to determining that the charge delivered by the one or more charge balancing pulses is insufficient, delivering one or more corrective pulses from one or more current sources of the implantable medical device.

46. The implantable medical device of claim 43, wherein the control circuitry comprises: a plurality of measurement capacitors, wherein each measurement capacitor is connected between at least one of the plurality of current sources and one or more of the plurality of stimulation electrodes, wherein each of the measurement capacitors is connected in series with a DC blocking capacitor on each of the one or more stimulation electrodes, respectively; and a differential amplifier connected between each measurement capacitor and the control circuitry, wherein the differential amplifier is configured to measure a voltage across the measurement capacitors while the one or more stimulation electrodes are short-circuited, respectively.

47. The implantable medical device of claim 46, wherein the control circuitry comprises: a controller configured to process the voltage across the measurement capacitor for each of the one or more stimulation.