Managing electrical charge for neural sensing

Abstract

A system for providing stimulation therapy to a patient includes stimulation generation circuitry, sensing circuitry, and processing circuitry. In one example, the processing circuitry may be configured to control the stimulation generation circuitry to generate at least one stimulation pulse via a stimulation electrode combination, control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period, control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period, control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period, and control the sensing circuitry to measure an electric signal during at least a second portion of the passive recharge blanking period.

Description

MANAGING ELECTRICAL CHARGE FOR NEURAL SENSINGCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 625,819, filed January 26, 2024, which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This disclosure generally relates to electrical stimulation, and more specifically, control of electrical stimulation.BACKGROUND

[0003] Medical devices may be external or implanted and may be used to deliver electrical stimulation to patients via various tissue sites to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson’s disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. A medical device may deliver electrical stimulation therapy via one or more leads that include electrodes located proximate to target locations associated with the brain, the spinal cord, pelvic nerves, peripheral nerves, or the gastrointestinal tract of a patient. Stimulation proximate the spinal cord, proximate the sacral nerve, within the brain, and proximate peripheral nerves are often referred to as spinal cord stimulation (SCS), sacral neuromodulation (SNM), deep brain stimulation (DBS), and peripheral nerve stimulation (PNS), respectively. Electrical stimulation often results in an evoked compound action potential (ECAP) from nerves within the patient.SUMMARY

[0004] In general, systems, devices, and techniques are described herein for managing poststimulus recharge and physiological signal measurement during delivery of stimulation therapy. Between stimulation pulses, the system may recharge, or charge balance, any remaining electrical charge at electrodes due to the delivery of one or more electrical stimulation pulses. The system may control circuitry to enable passive recharge at certain times between stimulation pulses in order to reduce any remaining charge at the electrodes. The system may also manage the timing of this passive recharge to reduce any effect the passive recharge may have on thesensing of physiological signals (e.g., ECAP signals or other types of electrical signals) from the patient. For example, the system may blank, or stop, passive recharging in order to measure physiological signals. In addition, the system may settle the measurement circuitry to a charge state during this, or a different, passive recharge blanking period in order to reduce measurement inaccuracies that may be caused by passive recharging.

[0005] In one example, a system includes stimulation generation circuitry configured to generate electrical stimulation pulses via a stimulation electrode combination of a plurality of electrodes; sensing circuitry configured to measure an electric signal via a sense electrode combination of the plurality of electrodes; switching circuitry; and processing circuitry configured to: control the stimulation generation circuitry to generate at least one stimulation pulse via the stimulation electrode combination; control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and control the sensing circuitry to measure the electric signal during at least a second portion of the passive recharge blanking period.

[0006] In another example, a method includes controlling, by processing circuitry, stimulation generation circuitry to generate at least one stimulation pulse via a stimulation electrode combination, wherein the stimulation generation circuitry is configured to generate electrical stimulation pulses via the stimulation electrode combination of a plurality of electrodes; controlling, by the processing circuitry, switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; controlling, by the processing circuitry, the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; controlling, by the processing circuitry, the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and controlling, by the processing circuitry, sensing circuitry to measure an electric signal during at least a second portion of the passive recharge blanking period, wherein the sensing circuitry is configured to measure the electric signal via a sense electrode combination of the plurality of electrodes.

[0007] In another example, a computer-readable storage medium comprising instructions that, when executed by processing circuitry, causes the processing circuitry to: control stimulation generation circuitry to generate at least one stimulation pulse via a stimulation electrode combination, wherein the stimulation generation circuitry configured to generate electrical stimulation pulses via the stimulation electrode combination of a plurality of electrodes; control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and control sensing circuitry to measure the electric signal during at least a second portion of the passive recharge blanking period, wherein the sensing circuitry is configured to measure the electric signal via a sense electrode combination of the plurality of electrodes.

[0008] The summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the systems, device, and methods described in detail within the accompanying drawings and description below. Further details of one or more examples of this disclosure are set forth in the accompanying drawings and in the description below. Other features, objects, and advantages of the techniques will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a conceptual diagram illustrating an example system that includes an implantable medical device (IMD) according to the techniques of the disclosure.

[0010] FIG. 2 is a block diagram of the example IMD of FIG. 1 , in accordance with one or more techniques of this disclosure.

[0011] FIG. 3 is a conceptual diagram illustrating an example circuit for the IMD of FIG. 1, in accordance with one or more techniques of this disclosure.

[0012] FIG. 4 is a conceptual diagram illustrating an example analog circuit for determining a sensor signal, in accordance with one or more techniques of this disclosure.

[0013] FIG. 5 is a circuit diagram illustrating an example stimulus state of operation, in accordance with one or more techniques of this disclosure.

[0014] FIG. 6 is a circuit diagram illustrating an example active recharge state of operation, in accordance with one or more techniques of this disclosure.

[0015] FIG. 7 is a circuit diagram illustrating an example passive recharge state of operation, in accordance with one or more techniques of this disclosure.

[0016] FIG. 8 is a waveform timing diagram illustrating example states of operation.

[0017] FIG. 9 is a waveform timing diagram illustrating an example in which the system settles measurement circuitry and measures signals during a passive recharge blanking period.

[0018] FIG. 10 is a waveform timing diagram illustrating an example in which the system settles measurement circuitry and measures signals during a passive recharge blanking period.

[0019] FIG. 11 is a waveform timing diagram illustrating an example in which the system settles measurement circuitry and measures signals during a passive recharge period.

[0020] FIG. 12 is a waveform timing diagram illustrating an example in which the system settles measurement circuitry after measuring signals.

[0021] FIG. 13 is a waveform timing diagram illustrating an example in which the system measure signals after passive recharge and prior to settling measurement circuitry.

[0022] FIG. 14 is a flow chart of an example technique for settling measurement circuitry and measuring signals during a passive recharge blanking period.

[0023] FIG. 15 is a flow charge of an example technique for adjusting offset values for measurement circuitry based on timing or order of stimulation pulses.DETAILED DESCRIPTION

[0024] The disclosure describes examples of medical devices, systems, and techniques for managing post-stimulus recharge and physiological signal measurement during delivery of stimulation therapy. These techniques may enable calibration of, and accruable measurements using, sensing circuitry of medical devices configured to provide electrical stimulation therapy. Electrical stimulation therapy is typically delivered to a target tissue (e.g., nerves of the spinal cord or muscle) of a patient via two or more electrodes. In some examples, a system may deliver stimulation therapy and also sense physiological signals. These physiological signals may beintrinsic (e.g., occurring without stimulation but possibly altered by stimulation) or elicited (e.g., physiological signals evoked by the delivered stimulus).

[0025] In some examples, the system may utilize two or more electrodes to deliver pulses configured to elicit evoked signals, such as ECAP signals and / or CMAP signals. In some examples, these pulses configured to elicit signals may be referred to as control pulses configured to elicit ECAP signal from nerve tissue of a patient. The system may also deliver informed pulses which may be configured to provide therapy to the patient. In this disclosure, “control pulses” may be stimulation pulses that are configured to elicit the ECAP signal. The control pulses may provide therapeutic effect, but need not necessarily provide therapeutic effect. “Informed pulses” may be stimulation pulses that provide therapeutic effect. Informed pulses may be “informed” in the sense that the parameters of the informed pulses (e.g., an amplitude, a pulse width, or a frequency) may be based on the sensing of the ECAP signal that was generated due to the control pulses. The informed pulses may be considered as providing governing therapy or governed therapy. Governing therapy or governed therapy may indicate that the stimulation pulses are for effective therapy. Using this control pulse and informed pulse strategy, the system may be configured to sense ECAP signals (or other evoked signals) after control pulses instead of after informed pulses. Put another way, the system may not be configured to even attempt to detect an evoked signal after an informed signal, but the informed signal may still elicit an evoked signal. In other examples, the system may attempt to sense ECAP signals elicited by the same type of pulses that are modulated according to the sensed ECAP signals.

[0026] Parameters of the electrical stimulation therapy (e.g., an electrode combination, a voltage amplitude, a current amplitude, a pulse width, or a pulse frequency) may be selected by a clinician and / or the patient to provide relief from various symptoms, such as pain, nervous system disorders, muscle disorders, etc. In addition, parameters of the electrical stimulation therapy (e.g., informed pulses) may be adjusted in response to a measured ECAP, for example. However, there are challenges to sensing electrical signals from the patient, such as ECAP signals.

[0027] For example, there are various sources of noise that can influence measured signals. One source of noise can be the stimulus (or pulse) itself by residual electrical charge that is stored at the electrode interface and can overlap with the evoked neural response to be sensed.These are fast-changing charges that can be reduced using signal filtering or other timing changes by the system. Other sources of noise can be from outside of the stimulation and sensing system. This outside noise can be from various muscles of the body (e.g., skeletal muscle contractions or cardiac activity) or external sources (e.g., electromagnetic interference from lights, computers, microwave ovens, etc.). Outside noise can be accounted for using techniques such common mode rejection, spatial or time separation from the noise source, or signal filtering techniques. Additional sources of noise can include post-stimulus electrode interface offsets (e.g., slowly changing charge relative to a sensing window duration) and poststimulus recharge current from passive recharging of electrodes (e.g., balancing any remaining charge from electrodes via passively draining charge). Although these post-stimulus electrode interface offsets and post-stimulus recharge currents may introduce small errors in physiological signal measurement, these small errors may be significant when measuring relatively small physiological signals such as evoked signals (e.g., ECAPs), local field potentials, or other smaller electrical signals. Inaccurate signal measurement may lead to less effective therapy when those inaccurate signals are used as feedback for adjusting subsequent stimulation therapy.

[0028] As described herein, various systems and techniques may be employed in order to reduce the effect of noise such as post-stimulus electrode interface offsets and post-stimulus recharge currents on measured physiological signals. For example, to reduce the effects from the post-stimulus recharge currents, the system can employ passive recharge blanking during the process of measuring (e.g., sensing) physiological signals. This passive recharge blanking may include the system disconnecting the stimulus interface, including passive recharge circuitry, from the electrode interface configured for sensing. In some examples, this disconnection may include the controlling of switches to prevent current from flowing from stimulation electrodes to sensing electrodes. In another example, to reduce effects from post-stimulus electrode interface offsets, the system may adjust or even remove a voltage offset that is applied to measured signal to account for voltages that may not be equal the biological steady state voltage (e.g., an auto-zero function). These techniques may be employed separately or together as part of the process for managing noise during a single stimulation cycle or as a part of on-going stimulation cycles.

[0029] The systems and devices described herein can accurately measure ECAP and provide more effective therapy, sensing circuitry configured to sense ECAP may be effectivelycalibrated. However, there can be challenges to effectively calibrating the sensing circuitry (such as calibrating measurement circuitry included with the sensing circuitry). In some examples, a medical device (e.g., an implantable medical device (IMD)) can include an amplifier (e.g., a bio-amplifier) and processing circuitry to measure an amplitude value of an evoked compound action potential (ECAP) of the human spinal cord. This low power system can detect very small signals (e.g., 10 pVpp (0 - 4.5 kHz)), very shortly (e.g., less than 200 us) after a large stimuli (e.g., about 10 V) using a medical device (e.g., an implantable device) that has no appreciable DC pathway to the body, which may help to maximize patient safety. The measured amplitude values may correlate to the amount of tissue captured by electrical stimulus, which varies with body position and other factors, allowing for optimal therapy level control. The timing of this measurement may be controlled with respect to other device functions, such as delivering stimulation and providing active and / or passive recharge, in order to further reduce noise and increase accurate ECAP signal measurement.

[0030] FIG. 1 is a conceptual diagram illustrating an example system 100 that includes an IMD 110 according to the techniques of the disclosure. Although the techniques described in this disclosure are generally applicable to a variety of medical devices including external devices and IMDs, application of such techniques to IMDs and, more particularly, implantable electrical stimulators (e.g., neurostimulators) will be described for purposes of illustration. More particularly, the disclosure will refer to an implantable SCS system for purposes of illustration, but without limitation as to other types of medical devices or other therapeutic applications of medical devices. For example, other therapies may include pelvic floor related stimulation (e.g., sacral nerve stimulation or tibial nerve stimulation), peripheral nerve stimulation, deep brain stimulation, etc.

[0031] As shown in FIG. 1, system 100 includes an IMD 110, leads 108A and 108B, and external programmer 150 shown in conjunction with a patient 102, who is a human patient. In the example of FIG. 1, IMD 110 is an implantable electrical stimulator that is configured to generate and deliver electrical stimulation therapy to patient 102 via one or more electrodes of electrodes 132A and / or 132B (collectively, “electrodes 132”) of leads 108A and / or 108B (collectively, “leads 108”), e.g., for relief of chronic pain or other symptoms. In other examples, IMD 110 may be coupled to a single lead carrying multiple electrodes or more than two leads each carrying multiple electrodes. In some examples, the stimulation signals, or pulses (e.g.,control pulses), may be configured to elicit detectable ECAP signals that IMD 110 may use to determine the posture state occupied by patient 102 and / or determine how to adjust one or more parameters that define stimulation therapy. The control pulses may provide therapeutic effect, but in one or more examples, the control pulses may not provide therapeutic effect. IMD 110 may be configured to delivered informed pulses for providing therapeutic effect. The informed pulses may be “informed” because the parameters of the informed pulses may be based on the ECAP signal generated from the delivery of control pulses. The informed pulses may be considered as providing governed therapy. Governing therapy may indicate that the stimulation pulses are for effective therapy. The control pulses may be “control” because the delivery of the control pulses is used to control the parameters for the informed pulses. Although control and informed pulses are generally described herein, the techniques may be similarly applied to any types of stimulation pulses or patterns of pulses within which physiological signals, such as ECAP signals, may be sensed and / or measured.

[0032] IMD 110 may be a chronic electrical stimulator that remains implanted within patient 102 for weeks, months, or even years. In other examples, IMD 110 may be a temporary, or trial, stimulator used to screen or evaluate the efficacy of electrical stimulation for chronic therapy. In one example, IMD 110 is implanted within patient 102. In some examples, a medical device, configured to perform techniques similar to IMD 110, may be an external device coupled to percutaneously implanted leads. In some examples, IMD 110 uses one or more leads, while in other examples, IMD 110 is leadless.

[0033] IMD 110 may be constructed of any polymer, metal, or composite material sufficient to house the components of IMD 110 (e.g., components illustrated in FIG. 2) within patient 102. In this example, IMD 110 may be constructed with a biocompatible housing, such as titanium or stainless steel, or a polymeric material such as silicone, polyurethane, or a liquid crystal polymer, and surgically implanted at a site in patient 102 near the pelvis, abdomen, or buttocks. In other examples, IMD 110 may be implanted within other suitable sites within patient 102, which may depend, for example, on the target site within patient 102 for the delivery of electrical stimulation therapy. The outer housing of IMD 110 may be configured to provide a hermetic seal for components, such as a rechargeable or non-rechargeable power source. In addition, in some examples, the outer housing of IMD 110 is selected from a material that facilitates receiving energy to charge the rechargeable power source.

[0034] Electrical stimulation energy, which may be constant current or constant voltagebased pulses, for example, is delivered from IMD 110 to one or more target tissue sites of patient 102 via one or more electrodes 132 of implantable leads 108. In the example of FIG. 1, leads 108 carry electrodes 132 that are placed adjacent to the target tissue of spinal cord 106. One or more of electrodes 132 may be disposed at a distal tip of a lead 108 and / or at other positions at intermediate points along the lead. Leads 108 may be implanted and coupled to IMD 110. Electrodes 132 may transfer electrical stimulation generated by an electrical stimulation generator in IMD 110 to tissue of patient 102. Although leads 108 may each be a single lead, lead 108 may include a lead extension or other segments that may aid in implantation or positioning of lead 108. In some examples, IMD 110 may be a leadless stimulator with one or more arrays of electrodes arranged on a housing of the stimulator rather than leads that extend from the housing. In addition, in some examples, system 100 may include one lead or more than two leads, each coupled to IMD 110 and directed to similar or different target tissue sites.

[0035] Electrodes 132 of leads 108 may be electrode pads on a paddle lead, circular (e.g., ring) electrodes surrounding the body of the lead, conformable electrodes, cuff electrodes, segmented electrodes (e.g., electrodes disposed at different circumferential positions around the lead instead of a continuous ring electrode), any combination thereof (e.g., ring electrodes and segmented electrodes) or any other type of electrodes capable of forming unipolar, bipolar or multipolar electrode combinations for therapy. Ring electrodes arranged at different axial positions at the distal ends of lead 108 will be described for purposes of illustration.

[0036] The deployment of electrodes 132 via leads 108 is described for purposes of illustration, but arrays of electrodes 132 may be deployed in different ways. For example, a housing associated with a leadless stimulator may carry arrays of electrodes 132, e.g., rows and / or columns (or other patterns), to which shifting operations may be applied. Such electrodes 132 may be arranged as surface electrodes, ring electrodes, or protrusions. As a further alternative, electrode arrays may be formed by rows and / or columns of electrodes 132 on one or more paddle leads. In some examples, electrode arrays include electrode segments, which are arranged at respective positions around a periphery of a lead, e.g., arranged in the form of one or more segmented rings around a circumference of a cylindrical lead. In other examples, one or more of leads 108 are linear leads having 8 ring electrodes along the axial length of the lead. Inanother example, electrodes 132 are segmented rings arranged in a linear fashion along the axial length of the lead and at the periphery of the lead.

[0037] The stimulation parameter set of a stimulation program that defines the stimulation pulses of electrical stimulation therapy by IMD 110 through the electrodes of leads 108 may include information identifying which electrodes 132 have been selected for delivery of stimulation according to a stimulation program, the polarities of the selected electrodes 132, e.g., an electrode combination for the program, a voltage amplitude, a current amplitude, a pulse frequency, a pulse width, or a pulse shape of stimulation delivered by electrodes 132. These stimulation parameters values that make up the stimulation parameter set that defines pulses may be predetermined parameter values defined by a user and / or automatically determined by system 100 based on one or more factors or user input. Informed pulses may be defined by a set of informed stimulation parameter values and control pulses may be defined by a set of control stimulation parameter values.

[0038] Although FIG. 1 is directed to SCS therapy, e.g., used to treat pain, in other examples system 100 may be configured to treat any other condition that may benefit from electrical stimulation therapy. In some examples, system 100 may be configured to provide multimodal stimulation using prime stimulation and base stimulation together. In some examples, system 100 may be used to treat tremor, Parkinson’s disease, epilepsy, a pelvic floor disorder (e.g., urinary incontinence or other bladder dysfunction, fecal incontinence, pelvic pain, bowel dysfunction, or sexual dysfunction), obesity, gastroparesis, or psychiatric disorders (e.g., depression, mania, obsessive compulsive disorder, anxiety disorders, and the like). In this manner, system 100 may be configured to provide therapy taking the form of spinal cord stimulation(SCS), deep brain stimulation (DBS), peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), cortical stimulation (CS), pelvic floor stimulation, gastrointestinal stimulation, or any other stimulation therapy capable of treating a condition of patient 102.

[0039] In some examples, lead 108 includes one or more sensors configured to allow IMD 110 to monitor one or more parameters of patient 102, such as patient activity, pressure, temperature, or other characteristics. The one or more sensors may be provided in addition to, or in place of, therapy delivery by lead 108. Rather than or in addition to lead 108 including such sensors, IMD 110 may include such sensors.

[0040] IMD 110 may be configured to deliver electrical stimulation therapy (e.g., informed pulses and / or control pulses in the form of a prime pulse train and base pulse train, respectively) to patient 102 via selected combinations of electrodes 132 carried by one or both of leads 108, alone or in combination with an electrode carried by or defined by an outer housing of IMD 110. The target tissue for the electrical stimulation therapy may be any tissue affected by electrical stimulation, which may be in the form of electrical stimulation pulses or continuous waveforms. In some examples, the target tissue includes nerves, smooth muscle, or skeletal muscle. In the example illustrated by FIG. 1, the target tissue is tissue proximate spinal cord 106, such as within an intrathecal space or epidural space of spinal cord 106, or, in some examples, adjacent nerves that branch off spinal cord 106.

[0041] Leads 108 may be introduced into spinal cord 106 in via any suitable region, such as the thoracic, cervical, or lumbar regions. Stimulation of spinal cord 106 may, for example, prevent pain signals from traveling through spinal cord 106 and to the brain of patient 102. Patient 102 may perceive the interruption of pain signals as a reduction in pain and, therefore, efficacious therapy results. In other examples, stimulation of spinal cord 106 may produce paresthesia which may be reduce the perception of pain by patient 102, and thus, provide efficacious therapy results. In some examples, stimulation of spinal cord 106 or other anatomical structures associated with the spinal cord (e.g., nerves and cells associated with the nervous system) may provide relief from symptoms that may not produce paresthesia. For example, IMD 110 may deliver stimulation with intensities (e.g., amplitude values and / or pulse width values) below a sensory or perception threshold (e.g., sub-threshold stimulation) that reduces pain without paresthesia. In multimodal stimulation, for example, IMD 110 may deliver one pulse train at a higher frequency via one electrode combination and a second pulse train on an interleaved basis with a lower frequency via a second electrode combination, where both pulse trains are delivered at a sub-threshold intensity.

[0042] IMD 110 may be configured to generate and deliver electrical stimulation therapy to a target stimulation site within patient 102 via electrodes 132 of leads 108 to patient 102 according to one or more therapy stimulation programs. A therapy stimulation program may generally define informed pulses, but may also define control pulses if the control pulses also contribute to a therapeutic effect. A therapy stimulation program may define values for one or more parameters (e.g., a parameter set) that define an aspect of the therapy delivered by IMD 110according to that program. For example, a therapy stimulation program that controls delivery of stimulation by IMD 110 in the form of pulses may define a voltage, a current, a pulse width, a pulse rate (e.g., a pulse frequency), an electrode combination, or a pulse shape for stimulation pulses delivered by IMD 110 according to that program. In some examples, one or more therapy stimulation programs define multiple different pulse trains that have different parameter values (e.g., different pulse frequencies, amplitude values, pulse widths, and / or electrode combinations) but are delivered on an interleaved basis to together provide a therapy for the patient.

[0043] Furthermore, IMD 110 may be configured to deliver control stimulation to patient 102 via a combination of electrodes 132 of leads 108, alone or in combination with an electrode carried by or defined by an outer housing of IMD 110 in order to detect ECAP signals (e.g., pulses configured to elicit ECAP signals when IMD 110 is configured to sense the ECAP signals from those pulses). The tissue targeted by the stimulation may be the same or similar tissue targeted by the electrical stimulation therapy, but IMD 110 may deliver stimulation pulses for ECAP signal detection via the same, at least some of the same, or different electrodes of electrodes 132. Because control stimulation pulses can be delivered in an interleaved manner with informed pulses (e.g., when the pulses configured to contribute to therapy interfere with the detection of ECAP signals or pulse sweeps intended for posture state detection via ECAP signals do not correspond to pulses intended for therapy purposes), a clinician and / or user may select any desired electrode 132 combination for informed pulses (i.e., governed therapy). Like the electrical stimulation therapy, the control stimulation may be in the form of electrical stimulation pulses or continuous waveforms.

[0044] For example, each control stimulation pulse may include a balanced, bi-phasic square pulse that employs an active recharge phase. However, in other examples, the control stimulation pulses may include a monophasic pulse followed by a passive recharge phase. In other examples, a control pulse may include an imbalanced bi-phasic portion and a passive recharge portion. Although not necessary, a bi-phasic control pulse may include an interphase interval between the positive and negative phase to promote propagation of the nerve impulse in response to the first phase of the bi-phasic pulse. The control stimulation may be delivered without interrupting the delivery of the electrical stimulation informed pulses, such as during the window between consecutive informed pulses. The control pulses may elicit an ECAP signal from the tissue, and IMD 110 may be configured to sense the ECAP signal (if elicited) via two ormore electrodes 132 on leads 108. In cases where the control stimulation pulses are applied to spinal cord 106, the signal may be sensed by IMD 110 from spinal cord 106.

[0045] A user, such as a clinician or patient 102, may interact with a user interface of an external programmer 150 to program IMD 110. Programming of IMD 110 may refer generally to the generation and transfer of commands, programs, or other information to control the operation of IMD 110. In this manner, IMD 110 may receive the transferred commands and programs from external programmer 150 to control stimulation, such as stimulation pulses that provide electrical stimulation therapy. For example, external programmer 150 may transmit therapy stimulation programs, stimulation parameter adjustments, therapy stimulation program selections, posture states, user input, or other information to control the operation of IMD 110, e.g., by wireless telemetry or wired connection.

[0046] In some examples, external programmer 150 may be characterized as a physician or clinician programmer if it is primarily intended for use by a physician or clinician. In other cases, external programmer 150 may be characterized as a patient programmer if it is primarily intended for use by a patient. A patient programmer may be generally accessible to patient 102 and, in many cases, may be a portable device that may accompany patient 102 throughout the patient’s daily routine. For example, a patient programmer may receive input from patient 102 when the patient wishes to terminate or change electrical stimulation therapy, or when a patient perceives stimulation being delivered. In general, a physician or clinician programmer may support selection and generation of programs by a clinician for use by IMD 110, whereas a patient programmer may support adjustment and selection of such programs by a patient during ordinary use. In other examples, external programmer 150 may include, or be part of, an external charging device that recharges a power source of IMD 110. In this way, a user may program and charge IMD 110 using one device, or multiple devices.

[0047] As described herein, information may be transmitted between external programmer 150 and IMD 110. Therefore, IMD 110 and external programmer 150 may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, radiofrequency (RF) telemetry and inductive coupling, but other techniques are also contemplated. In some examples, external programmer 150 includes a communication head that may be placed proximate to the patient’s body near the IMD 110 implant site to improve the quality or security of communication between IMD 110 and externalprogrammer 150. Communication between external programmer 150 and IMD 110 may occur during power transmission or separate from power transmission.

[0048] In some examples, IMD 110, in response to commands from external programmer 150, may deliver electrical stimulation therapy (e.g., informed pulses and / or control pulses) according to a plurality of therapy stimulation programs to a target tissue site of the spinal cord 106 of patient 102 via electrodes 132 on leads 108. In some examples, IMD 110 may modify therapy stimulation programs as therapy needs of patient 102 evolve over time. For example, the modification of the therapy stimulation programs may cause the adjustment of at least one parameter of the plurality of stimulation pulses. When patient 102 receives the same therapy for an extended period, the efficacy of the therapy may be reduced. In some cases, parameters of the plurality of stimulation pulses may be automatically (e.g., without user input) updated, for example, by IMD 110, external programmer 150 or another device or cloud system.

[0049] Efficacy of electrical stimulation therapy may be indicated by one or more features (e.g., an amplitude value between one or more peaks or an area under the curve of one or more peaks) of an action potential that is evoked by a control pulse delivered by IMD 110 (i.e., a characteristic value of the ECAP signal). Electrical stimulation therapy delivery by leads 108 of IMD 110 may cause neurons within the target tissue to evoke a compound action potential that travels up and down the target tissue, eventually arriving at sensing electrodes of IMD 110 (e.g., electrodes of electrodes 132 that are assigned for sensing). For instance, stimulation may elicit at least one ECAP signal, and ECAP responsive to stimulation may also be a surrogate for the effectiveness of the therapy. The amount of action potential (e.g., number of neurons propagating action potential signals) that are evoked may be based on the various parameters of electrical stimulation pulses such as an amplitude value, a pulse width, a frequency, or a pulse shape (e.g., slew rate at the beginning and / or end of the pulse). The slew rate may define the rate of change of the voltage amplitude value and / or current amplitude value of the control pulse at the beginning and / or end of each control pulse or each phase within the pulse. For example, a very high slew rate indicates a steep or even near vertical edge of the pulse, and a low slew rate indicates a longer ramp up (or ramp down) in the amplitude value of the control pulse. In some examples, these parameters contribute to an intensity of the electrical stimulation. In addition, a characteristic of the ECAP signal (e.g., an amplitude value) may change based on the distancebetween the stimulation electrodes and the nerves subject to the electrical field produced by the delivered control pulses.

[0050] Some example techniques for adjusting stimulation parameter values for stimulation pulses (e.g., informed pulses and / or control pulses that may or may not contribute to therapy for the patient) are based on comparing the value of a characteristic of a measured ECAP signal to a target ECAP characteristic value. In response to delivering a control pulse defined by a set of stimulation parameter values, IMD 110, via two or more electrodes interposed on leads 108, senses electrical potential of tissue of the spinal cord 106 of patient 102 to measure the electrical activity of the tissue. IMD 110 senses ECAP from the target tissue of patient 102, e.g., with electrodes on one or more leads 108 and associated sense circuitry. In some examples, IMD 110 may receive a sensor signal indicative of the ECAP from one or more sensors, e.g., one or more electrodes and circuitry, internal or external to patient 102. Such an example signal may include a sensor signal indicating an ECAP of the tissue of patient 102. Examples of the one or more sensors include one or more sensors configured to measure a compound action potential of patient 102, or a physiological effect indicative of a compound action potential. For example, to measure a physiological effect of a compound action potential, the one or more sensors may be an accelerometer, a pressure sensor, a bending sensor, a sensor configured to detect a posture of patient 102, or a sensor configured to detect a respiratory function of patient 102. In some examples, external programmer 150 may receive a sensor signal indicating a compound action potential in the target tissue of patient 102 and may transmit a notification of the sensor signal to IMD 110.

[0051] In the example of FIG. 1, IMD 110 is described as performing a plurality of processing and computing functions. However, external programmer 150 instead may perform one, several, or all of these functions. In this example, IMD 110 functions to relay sensed signals to external programmer 150 for analysis, and external programmer 150 transmits instructions to IMD 110 to adjust the one or more parameters defining the electrical stimulation therapy based on analysis of the sensed signals. For example, IMD 110 may relay the sensed signal indicative of an ECAP to external programmer 150. External programmer 150 may compare the parameter value of the ECAP to the target ECAP characteristic value, and in response to the comparison, external programmer 150 may instruct IMD 110 to adjust one ormore stimulation parameter that defines the electrical stimulation informed pulses and, in some examples, control pulses, delivered to patient 102.

[0052] In some examples, system 100 may change the target ECAP characteristic value and / or growth rate(s) over a period of time, such as according to a change to a stimulation threshold (e.g., a perception threshold or detection threshold specific for the patient). System 100 may be programmed to change the target ECAP characteristic in order to adjust the intensity of informed pulses (e.g., governed therapy) to provide varying sensations to the patient (e.g., increase or decrease the volume of neural activation). Although system 100 may change the target ECAP characteristic value, received ECAP signals may be used by system 100 to adjust one or more parameter values of the informed pulses and / or control pulses in order to meet the target ECAP characteristic value.

[0053] One or more devices within system 100, such as, for example, IMD 110 and / or external programmer 150, may perform various functions as described herein. For example, IMD 110 may include stimulation generation circuitry configured to deliver electrical stimulation, sensing circuitry configured to sense a plurality ECAP signals, and processing circuitry. The processing circuitry may be configured to control the stimulation generation circuitry to deliver a plurality of electrical stimulation pulses (e.g., one or more control pulses) having different amplitude values and control the sensing circuitry to detect, after delivery of each electrical stimulation pulse of the plurality of electrical stimulation pulses, a respective ECAP signal of the plurality of ECAP signals.

[0054] In some examples, reference may be made to one or more electrodes of IMD 110 “delivering” therapy. In these instances, stimulation generation circuitry of IMD 110 may be connected to one or more electrodes 132 and configured to deliver the therapy “using” or “on” one or more electrodes 132. In some examples described herein, reference may be made to one or more electrodes 132 of IMD 110 “sensing” ECAP signals. In these instances, sensing circuitry of IMD 110 may be connected to one or more electrodes 132 and configured to sense the ECAP signals “using” or “on” one or more electrodes 132. A different set (e.g., pair) of one or more electrodes 132 may be used for delivering therapy than a set (e.g., pair) of one or more electrodes 132 may be used for sensing ECAP signals. While the above refers to ECAP signals, similar techniques may be used for other sensing signals. In some examples, reference may be made to certain recharge states (e.g., active recharge or passive recharge) as “on” one or moreelectrodes 132 of IMD 110. In these instances, circuitry connected to one or more electrodes 132 may be “in” the certain recharge state.

[0055] In the example of FIG. 1, IMD 110 is described as performing a plurality of processing and computing functions. However, external programmer 150 instead may perform one, several, or all of these functions. In this example, IMD 110 may relay sensed signals to external programmer 150 for analysis and external programmer 150 may transmit instructions to IMD 110 to adjust the one or more parameters defining the electrical stimulation signal based on analysis of the sensed signals. For example, IMD 110 may relay the sensed signal indicative of an ECAP to external programmer 150. External programmer 150 may compare the parameter value of the ECAP to the target ECAP characteristic value, and in response to the comparison, external programmer 150 may instruct IMD 110 to adjust one or more parameters that define the electrical stimulation signal.

[0056] Although electrical stimulation is generally described herein in the form of electrical stimulation pulses, electrical stimulation may be delivered in non-pulse form in other examples. For example, electrical stimulation may be delivered as a signal having various waveform shapes, frequencies, and amplitude values. Therefore, electrical stimulation in the form of a nonpulse signal may be a continuous signal that may have a sinusoidal waveform or other continuous waveform.

[0057] In some examples, sensing circuitry of IMD 110 may be coupled to control electrodes of one or more electrodes 132 and governing electrodes of one or more electrodes 132. The control electrodes may be configured to deliver control pulses to patient tissue that elicit ECAP signals from the tissue of patient 102. The governing electrodes may be configured to deliver governed therapy (e.g., informed pulses) to patient tissue that provide therapy to patient 102. The sensing circuitry may include one or more amplifiers configured to amplify ECAP signals within the circuitry for more accurate sensing of the ECAP signals. The sensing circuitry may also include processing circuitry configured to enter an active recharge state on the control electrodes and, subsequent to entering an active recharge state, enter a passive recharge state on the control electrodes. The active recharge state and passive recharge state are explained with more specificity below. The processing circuitry may also be configured to calibrate, or autozero the operational amplifier of sensing circuitry while the control electrodes are in the passive recharge state.

[0058] FIG. 2 is a block diagram of the example IMD of FIG. 1. IMD 200 may be an example of IMD 110 of FIG. 1. In the example shown in FIG. 2, IMD 200 includes stimulation generation circuitry 204, sensing circuitry 206, processing circuitry 208, sensor 210, telemetry circuitry 212, power source 214, and memory 216. Each of these circuits may be or include programmable or fixed function circuitry can perform the functions attributed to respective circuitry. For example, processing circuitry 208 may include fixed-function or programmable circuitry, stimulation generation circuitry 204 may include circuitry can generate electrical stimulation signals such as pulses or continuous waveforms on one or more channels, sensing circuitry 206 may include sensing circuitry for sensing signals, and telemetry circuitry 212 may include telemetry circuitry for transmission and reception of signals. Memory 216 may store computer-readable instructions that, when executed by processing circuitry 208, cause IMD 200 to perform various functions described herein. Memory 216 may be a storage device or other non-transitory medium.

[0059] In the example shown in FIG. 2, memory 216 may store patient data 218, which may include anything related to the patient such as one or more patient postures, an activity level, or a combination of patient posture and activity level. Memory 216 may store stimulation parameter settings 220 within memory 216 or separate areas within memory 216. Each stored stimulation parameter setting 220 defines values for one or more sets of electrical stimulation parameters (e.g., an informed stimulation parameter set and a control stimulation parameter set, or parameters for other pulse trains). Stimulation parameter settings 220 may also include additional information such as instructions regarding delivery of electrical stimulation signals based on stimulation parameter relationship data, which can include relationships between two or more stimulation parameters based upon data from electrical stimulation signals delivered to patient 102 or data transmitted from external programmer 104. The stimulation parameter relationship data may include measurable aspects associated with stimulation, such as an ECAP characteristic value. In some examples, stimulation parameter settings 220 may also include instructions regarding the timing of various phases of a stimulation and measurement cycle, such as when to provide passive recharge, when to blank passive recharge, when to settle measurement circuitry, and when to measure physiological signals using sensing circuitry 206 (which may include measurement circuitry configured to measure one or more aspects of the physiological signal, such as voltage over time).

[0060] Accordingly, in some examples, stimulation generation circuitry 204 may generate electrical stimulation signals (e.g., informed pulses and / or control pulses) in accordance with the electrical stimulation parameters noted above. Other ranges of stimulation parameter values may also be useful and may depend on the target stimulation site within patient 102. While stimulation pulses are described, stimulation signals may be of any form, such as continuoustime signals (e.g., sine waves or cosine waves) or the like.

[0061] Sensing circuitry 206 may be configured to monitor signals from any combination of electrodes 232, 234. In some examples, sensing circuitry 206 includes one or more amplifiers, filters, and analog-to-digital converters. Sensing circuitry 206 may be used to sense physiological signals, such as ECAP. In some examples, sensing circuitry 206 detects ECAP from a particular combination of electrodes 232, 234. In some examples, the particular combination of electrodes for sensing ECAP includes different electrodes than a set of electrodes 232, 234 used to deliver control stimulation pulses and / or informed stimulation pulses. In some examples, the particular combination of electrodes used for sensing ECAP includes at least one of the same electrodes as a set of electrodes used to deliver informed and / or control stimulation pulses to patient 102. Sensing circuitry 206 may provide signals to an analog-to-digital converter (ADC), for conversion into a digital signal for processing, analysis, storage, or output by processing circuitry 208. Although not shown in FIG. 2, IMD 200 may also include switching circuitry and / or other electrical components that control the flow of current between electrodes, between electrodes and stimulation generation circuitry 204, between stimulation generation circuitry 204 and sensing circuitry 206, and / or between electrodes and sensing circuitry 206. Processing circuitry 208 may directly or indirectly control the switching circuitry.

[0062] Processing circuitry 208 may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or any other processing circuitry can provide the functions attributed to processing circuitry 208 herein may be embodied as firmware, hardware, software, or any combination thereof. Processing circuitry 208 may control stimulation generation circuitry 204 to generate electrical stimulation signals according to stimulation parameter settings 220 stored in memory 216 to apply stimulation parameter values, such as, for example, a pulse amplitude value, a pulse width, a pulse frequency, and / or a waveform shape of each of the electrical stimulation signals.

[0063] In the example of FIG. 2, set of electrodes 232 includes electrodes 232A, 232B, 232C, and 232D, and the set of electrodes 234 includes electrodes 234A, 234B, 234C, and 234D. In some examples, a single lead may include all eight electrodes 232 and 234 along a single axial length of the lead. Processing circuitry 208 also controls stimulation generation circuitry 204 to generate and apply the electrical stimulation signals to selected combinations of electrodes 232, 234. In some examples, stimulation generation circuitry 204 includes a switch circuit (which may be part of switching circuitry) that may couple stimulation signals to selected conductors within leads 230, which, in turn, may deliver the stimulation signals across selected electrodes 232, 234. Such a switch circuit may be a switch array, switch matrix, multiplexer, or any other type of switch circuitry can selectively couple stimulation energy to selected electrodes 232, 234 and to selectively sense bioelectrical neural signals of a spinal cord of the patient (not shown in FIG. 2) with selected electrodes 232, 234.

[0064] As shown, stimulation generation circuitry 204 may not include a switch circuit for channeling stimulation current to desired electrode combinations. In these examples, stimulation generation circuitry 204 may include a plurality of pairs of voltage sources, current sources, voltage sinks, or current sinks connected to each of electrodes 232, 234 such that each pair of electrodes has a unique signal circuit. In other words, in these examples, each of electrodes 232, 234 may be independently controlled via its own signal circuit (e.g., via a combination of a regulated voltage source and sink or regulated current source and sink), as opposed to switching signals between electrodes 232, 234. However, switching circuitry may still be in place to connect or disconnect each electrode with respective current sources from stimulation generation circuitry 204.

[0065] Electrodes 232, 234 on respective leads 230 may be constructed of a variety of different designs. For example, one or both of leads 230 may include one or more electrodes at each longitudinal location along the length of the lead, such as one electrode at different perimeter locations around the perimeter of the lead at each of the locations A, B, C, and D. In one example, the electrodes may be electrically coupled to stimulation generation circuitry 204 via respective wires that are straight or coiled within the housing of the lead and run to a connector at the proximal end of the lead. In another example, each of the electrodes of the lead may be electrodes deposited on a thin film. The thin film may include an electrically conductive trace for each electrode that runs the length of the thin film to a proximal end connector. Thethin film may then be wrapped (e.g., a helical wrap) around an internal member to form the lead 230. These and other constructions may be used to create a lead with a complex electrode geometry.

[0066] Although sensing circuitry 206 is incorporated into a common housing with stimulation generation circuitry 204 and processing circuitry 208 in FIG. 2, in some examples, sensing circuitry 206 may be in a separate housing from IMD 200 and may communicate with processing circuitry 208 via wired or wireless communication techniques.

[0067] In some examples, one or more of electrodes 232 and 234 may be suitable for sensing ECAP. For instance, electrodes 232 and 234 may sense the voltage amplitude of a portion of the ECAP signals, where the sensed voltage amplitude is a characteristic the ECAP signal.

[0068] Memory 216 may be configured to store information within IMD 200 during operation. Memory 216 may include a computer-readable storage medium or computer-readable storage device. In some examples, memory 216 includes one or more of a short-term memory or a long-term memory. Memory 216 may include, for example, random access memories (RAM), dynamic random-access memories (DRAM), static random-access memories (SRAM), magnetic discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable memories (EEPROM). In some examples, memory 216 is used to store data indicative of instructions for execution by processing circuitry 208. As discussed herein, memory 216 can store patient data 218, stimulation parameter settings 220, and control policy data 224.

[0069] Sensor 210 may include one or more sensing elements that sense values of a respective patient parameter. As described, electrodes 232 and 234 may be the electrodes that sense, via sensing circuitry 206, a value of the ECAP indicative of a target stimulation intensity. Sensor 210 may include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other types of sensors. Sensor 210 may output patient parameter values that may be used as feedback to control delivery of electrical stimulation signals. IMD 200 may include additional sensors within the housing of IMD 200 and / or coupled via one of leads 108 or other leads. In addition, IMD 200 may receive sensor signals wirelessly from remote sensors via telemetry circuitry 212, for example. In some examples, one or more of these remote sensors may be external to patient (e.g., carried on the external surface of the skin, attached to clothing, or otherwise positioned external to the patient).In some examples, signals from sensor 210 may indicate a posture state (e.g., sleeping, awake, sitting, standing, or the like), and processing circuitry 208 may select target and / or threshold ECAP characteristic values according to the indicated posture state.

[0070] Telemetry circuitry 212 supports wireless communication between IMD 200 and an external programmer (not shown in FIG. 2) or another computing device under the control of processing circuitry 208. Processing circuitry 208 of IMD 200 may receive, as updates to programs, values for various stimulation parameters such as an amplitude value and / or an electrode combination (e.g., for informed and / or control pulses), from the external programmer via telemetry circuitry 212. Updates to stimulation parameter settings 220 and input efficacy threshold settings 226 may be stored within memory 216. Telemetry circuitry 212 in IMD 200, as well as telemetry circuits in other devices and systems described herein, such as the external programmer, may accomplish communication by radiofrequency (RF) communication techniques. In addition, telemetry circuitry 212 may communicate with an external medical device programmer (not shown in FIG. 2) via proximal inductive interaction of IMD 200 with the external programmer. The external programmer may be one example of external programmer 104 of FIG. 1. Accordingly, telemetry circuitry 212 may send information to the external programmer on a continuous basis, at periodic intervals, or upon request from IMD 110 or the external programmer.

[0071] Power source 214 may deliver operating power to various components of IMD 200. Power source 214 may include a rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD 200. In other examples, traditional primary cell batteries may be used. In some examples, processing circuitry 208 may monitor the remaining charge (e.g., voltage) of power source 214 and select stimulation parameter values that may deliver similarly effective therapy at lower power consumption levels when needed to extend the operating time of power source 214.

[0072] Stimulation generation circuitry 204 of IMD 200 may receive, via telemetry circuitry 212, instructions to deliver electrical stimulation according to stimulation parameter settings 220 to a target tissue site of the spinal cord of the patient via a plurality of electrode combinations of electrodes 232, 234 of leads 230 and / or a housing of IMD 200. Each electrical stimulation signal may elicit an ECAP signal that is sensed by sensing circuitry 206 via electrodes 232 and 234. 1Processing circuitry 208 may receive, via an electrical signal sensed by sensing circuitry 206, information indicative of an ECAP signal (e.g., a numerical value indicating a characteristic of the ECAP in electrical units such as voltage or power) produced in response to the electrical stimulation signal(s). Stimulation parameter settings 220 may be updated according to the ECAP recorded at sensing circuitry 206. While the above discussion refers to an ECAP signal, some examples, may be directed to other sensing signals.

[0073] As described herein, an IMD, such as IMD 200, may be configured to perform various operations associated with delivering stimulation pulses and managing sensing circuitry to reduce different types of noise that may affect the accuracy of signal measurement. In one example, system 100, which may include an IMD such as IMD 110 or IMD 200, includes stimulation generation circuitry 204 configured to generate electrical stimulation pulses via a stimulation electrode combination of a plurality of electrodes 232, 234 and sensing circuitry 206 configured to measure an electric signal via a sense electrode combination of the plurality of electrodes 232, 234. IMD 200 may also include switching circuitry that includes one or more switches together or at different locations in the hardware that are controlled by a controller, such as processing circuitry 208. Processing circuitry 208 may be configured to control stimulation generation circuitry 204 to generate at least one stimulation pulse via the stimulation electrode combination and control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period.

[0074] Processing circuitry 208 may also control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period. In other words, processing circuitry 208 may control switching circuitry to stop passive recharge during the passive recharge blanking period. Processing circuitry 208 may also be configured to control the switching circuitry to settle sensing circuitry 206 during at least a first portion of the passive recharge blanking period. Settling the sensing circuitry 206 may enable an offset or other settling of the measurement circuitry to the ground or reference voltage of the device may increase the accuracy of the measurement of signals such as ECAP signals. In addition, processing circuitry 208 may be configured to control sensing circuitry 206 to measure the electric signal during at least a second portion of the passive recharge blanking period. In some examples, the passive recharge blanking period may include both the settling of sensing circuitry and measurement of signals inthat order or in reverse order. Passive recharge may be performed by IMD 200 before and / or after the passive recharge blanking period. This passive recharge blanking may be performed after delivery of biphasic (or triphasic or more than 3 phases) pulses and / or after delivery of a single phase stimulation pulse followed by only passive recharge instead of active recharge.

[0075] In some examples, processing circuitry 208 can be configured to apply an offset value to a measured value of the measured electrical signal. This offset value may be obtained by storing a voltage at a capacitor through which the voltage of the sensed signal will be obtained. Processing circuitry 208 may be configured to adjust this offset value based at least in part on a difference between an order of the stimulation pulse and the settle and a subsequent stimulation pulse and a subsequent settle period. For example, if the polarity of a stimulation pulse is changed between the settle period and subsequent measurement, the offset may not be reflective of the charge at the electrodes or measurement circuitry. This adjustment to the stored offset voltage may be performed in situations in which the offset is stored after or further in time from measurement.

[0076] As generally described herein, sensing circuitry 206 may be configured to sense ECAP signals. In other examples, sensing circuitry 206 may be configured to sense other evoked signals, such as evoked resonant neural activity (ERNA) signals in deep brain sensing. In other examples, sensing circuitry 206 may be configured to sense signals that are intrinsic, such as compound muscle action potentials (CMAP) signals, electromyograph (EMG) signals, local field potentials (LFP) signals, or any other type of electrical signals that can be sensed from the body. For example, ECAP signals may be used as feedback for spinal cord stimulation. In some examples, ECAP signals and / or CMAP signals may be used for incontinence therapy, such as tibial nerve or sacral nerve stimulation.

[0077] FIG. 3 is a conceptual diagram illustrating an example circuit 300 for the IMD of FIG. 1 , in accordance with one or more techniques of this disclosure. In this example, sensor circuitry 307 of sense chip 309 may be configured to detect a sense signal (e.g., an ECAP signal). For example, sensor circuitry 307 may use a multiplexer 330 (also referred to herein as “MUX 330”) to select a pair of electrodes. Auto-zero circuit 332 may be configured to perform auto-zero techniques, which are described in further details in FIGS. 4 and 8. Amplifier 334 may be configured to amplify the sense signal generated by auto-zero circuit 332. Successive- approximation-register analog-to-digital converter 336 (also referred to herein as “SAR ADC336”) may represent the sensing signal as a digital value. Feature extraction and configurable triggers unit 338 may be configured to extract features (e.g., ECAP features) from the digitized sensing signal output by SAR ADC 336.

[0078] FIG. 4 is a conceptual diagram illustrating an example analog circuit 400 for determining a sensor signal, in accordance with one or more techniques of this disclosure. Analog circuit 400 may be referred to as sensing circuitry in general, and may include measurement circuitry (e.g., amplifier circuitry 456 and auto-zero circuitry 454). Analog circuit 400 may be representative for two electrodes, but all electrodes, or only those electrodes that can be used for sensing, may have circuitry similar to analog circuit 400. Any of one or more electrodes 132 (e.g., 17 electrodes) at the device level can be selected as the sensing pair of electrodes 432. For the channels not being sensed, the MUX / Blanking switches (e.g., first switches 449 and 451) may be left open (e.g., NMOS gate at ground), always disconnecting them from calibration capacitors 452, 453 (e.g., the 2 shared 5.0 nF capacitors). First switches 449 and 451 may be described as part of switching circuitry because processing circuitry can control these switches to control the direction of current flow between electrodes and sensing circuitry (e.g., amplifier circuitry 456, calibration capacitors, and / or auto-zero circuitry 454). Only the selected sensing pair of electrodes 432 is shown in the below diagram for example purposes only. Specific values for various components, such as resistors and capacitors are shown for example purposes. However, other values (e.g., lower or higher) for some or all of these resistors and capacitors may be used in different examples.

[0079] Sensing circuitry 206 of FIG. 2 may be configured to sense an ECAP signal from patient tissue. Sensing circuitry 206 may include circuit 400 (or part of analog circuit 400) prior to outputting to amplifier circuitry 456, where amplifier circuitry 456 may be configured to amplify a sensing signal (e.g., an ECAP signal) sensed by sensing circuitry 206. In some examples, sensing circuitry 206 includes some or all of analog circuitry 400 and amplifier circuitry 456. Circuit 400 may include electrodes 432, feedthrough capacitors 440, 441, AC coupling capacitors 442, grounding circuitry 444, 445, blanking circuitry 446, and auto-zero circuitry 454 (which may include calibration capacitors 452, 453). Grounding circuitry 444, 445 may provide a high impedance (e.g., loosely grounded) grounding of circuit 400 to ground (e.g., a battery ground or common mode Voltage). When switches 464 and 465 are open, the electrodes 432 may be referred to as “open-circuited” because they are loosely tied to thereference voltage (e.g., common mode Voltage) or ground via the high impedance connection. It is noted that this configuration may not be fully open-circuited because the high impedance connection is still available to pass current. Closing of switches 464 and 465 bypasses the high impedance 20 MOhm resistors and directly connects respective electrodes 432 directly to the ground or reference voltage. 20 MOhm resistors are just one example, but other resistors, such as an 80 MOhm resistor, could be used in other examples. Although the processing circuitry may control all of switches 464 and 465 together, processing circuitry may independently control any of the switches 464 and 465 for any electrodes in other examples. Switches 464 and 465 may also be referred to as part of the switching circuitry that is controlled by processing circuitry (or other component), which may also include switches such as first switches 449 and 451 in some examples.

[0080] Electrodes 432 may be examples of electrodes 232, 234 of FIG. 2 and may be coupled to circuit 400. For example, electrodes 432 may rest against the patient tissue (e.g., spinal cord) of patient 102. Electrodes 432 may include control electrodes configured to deliver a control pulse to the patient tissue that elicits an ECAP signal from patient tissue. Electrodes 432 may be configured to perform as governing electrodes configured to deliver governed therapy (e.g., informed pulses) to patient tissue that provides therapy to patient 102. One or more electrodes 432 may collect an ECAP signal from patient tissue and provide an electrical signal to the sensing circuitry of circuit 400 representing an amplitude value for the ECAP signal.

[0081] As the stimulation generation circuitry 204 of the IMD 200 provides therapy to patient tissue, AC coupling capacitors 442 may prevent accumulated charge on electrodes 432 from impacting the patient by holding the charge. During the stimulation state and the active recharge state, blanking circuitry 446 (e.g., which may be part of switch circuitry) can open first switches 449 and 451 to block current from affecting calibration capacitors 452, 453, auto-zero circuitry 454, and / or amplifier circuitry 456. For example, first switches 449, 451 may be configured to open and switch-out calibration capacitors 452, 453, respectively, when stimulation generation circuitry 204 provides stimulation, when stimulation generation circuitry 204 provides active recovery (e.g., active recharge phase of a pulse), and / or when passive recharge is being performed. The timing of these different switch operations and active and passive recharge are described in the various examples of FIGS. 8-13.

[0082] In some examples, subsequent to entering the active recharge state, stimulation generation circuitry 204 may be configured to enter a passive recharge state on the control electrodes (e.g., closing switches 464, 465 to drive stimulus electrodes to the reference voltage or ground). Active recharge states may use a relatively large power expenditure from power source 214 of IMD 200 to generate the opposing current. In order to conserve power for extending the life of IMD 200, at least a portion of the active recharge state in stimulation generation circuitry 204 may be replaced by a passive recharge period. While in the passive recharge state, in this example, switching elements 449, 451 may be configured to switch-in calibration capacitors 452, 453, respectively, when stimulation generation circuitry 204 does not provide stimulation and during a signal acquisition state. Resistors 448, 450 may help to limit an amount of electrical current of circuit 400 and / or provide electrostatic discharge (ESD) protection. In other examples, processing circuitry may blank passive recharge by opening switches 464, 465 before closing first switches 449, 451 to switch-in calibration capacitors 452, 453, settle measurement circuitry using auto-zero circuitry 454 (which can include calibration capacitors 452, 453), and / or measure sensed signals using amplifier circuitry 456. In some examples, blanking passive recharge may include opening switches 464, 465 on all electrodes. Passive recharge generally means closing switches 464, 465 for stimulation electrodes, but these switches may remain open on non-stimulation electrodes and sensing electrodes. In this manner, blanking passive recharge may involve the process of opening any closed switches 464, 465 for stimulation electrodes.

[0083] In some examples, while operating in the passive recharge state, processing circuitry 208 may auto-zero outputs to amplifier circuitry 456. Auto-zeroing the outputs to may calibrate the sensing circuitry 206 for detecting sensing signals from patient tissue. To auto-zero the outputs, processing circuitry 208 may close calibration switches 460, 461 of auto-zero circuitry 454 to connect the outputs to ground. Offsets may be stored on calibration capacitors 452, 453 during passive recharge may be used to provide common mode rejection seen at the input of amplifier circuitry during a signal acquisition state, which may improve the accuracy of a sensing signal (e.g., an ECAP signal) generated during the signal acquisition state. In some examples, processing circuitry 208 may adjust the offsets stored on calibration capacitors 452, 453 to account for changes in the charge at electrodes due to different polarity of stimulus pulses and / or the timing of the settling of measurement circuitry for which the stored offsets may be accurately represent the charge at the electrodes. In some cases, the process of adjusting thestored offsets may include injecting a current or voltage into the amplifier chain to correct the stored offset. This injection may be in the form of digital control to an analog correction feedback. In this manner, the amplifier circuitry may include an offset correction circuitry for analog correction. Alternatively, processing circuitry 208 may adjust the processed signal at a later time to make that adjustment.

[0084] Processing circuitry 208 of IMD 200 may cause stimulation generation circuitry 204 to deliver, using electrodes configured as governing electrodes, a governed therapy to the patient after sensing for the evoked compound action potential signal. For example, processing circuitry 208 may be configured to cause sensing circuitry 206 to sense, during the passive recharge state or during passive recharge blanking, for a sensing signal (e.g., an ECAP signal). Following sensing for the sensing signal, processing circuitry 208 may cause stimulation generation circuitry 204 to deliver a governed therapy to the patient tissue on the governing electrodes based on the sensing signal.

[0085] FIGS. 5-7 are example circuit diagrams of stimulus related circuits for delivering stimulation pulses, active recharge, and / or passive recharge. The circuitry of FIGS. 5-7 may partially overlap with some components described in FIG. 4 associated with sensing circuitry. FIG. 5 is a circuit diagram illustrating an example stimulus state of operation, in accordance with one or more techniques of this disclosure. The stimulus hardware of FIG. 5 is an example of an evoked compound action potential (ECAP) stimulus hardware. This stimulus hardware may be used to establish the relative voltage between device ground and the common body voltage, which may be important to ECAP sensing. In the example of FIG. 5, stimulation generation circuitry 204 may apply current 778 to perform a stimulation state operation, which results in a current being applied to patient 102 (779), which results in a total charge (780). The total charge Q may result in a residual voltage left on the 10 pF AC coupling capacitors of as a result of the initial condition on the capacitor and current applied through tissue.

[0086] In Fig. 7, Zbody represents the electrode body interface. The electrode body interface may be described as an ion double layer capacitor in parallel with an ion oxidation reduction pathway, which may be described by the Butler- Volmer equation. The ion double layer capacitor in parallel with the ion oxidation reduction pathway may be in series with an Ohmic body impedance. A further simplified model of the electrode body interface may be referred to as Randles circuit, which is a leaky capacitor in series with an ohmic body impedance.

[0087] FIG. 6 is a circuit diagram illustrating an example active recharge state of operation, in accordance with one or more techniques of this disclosure. In the example of FIG. 6, stimulation generation circuitry 204 may apply current 881 to perform an active recharge state operation (882). The current being applied to patient 102 may remove the charge on the 10 pF coupling capacitors that was added during stimulus, which may return the capacitors to the initial voltage (Vo). Note that an electrode combination may include two or more electrodes, with at least one electrode being a cathode and at least one electrode being an anode.

[0088] FIG. 7 is a circuit diagram illustrating an example passive recharge state of operation, in accordance with one or more techniques of this disclosure. Loop 986 may rapidly drain CPar (e.g., 1 to 200 ps or more) to make Vbody closer (or equal in some examples) to device ground (or reference voltage), which may help to improve an accuracy of a sensing state. As described herein, the system, such as processing circuitry 208 of IMD 200 may blank (or stop) passive recharge in order to perform certain operations related to measuring ECAP signals, such as setting measurement circuitry and / or measuring the sensed signal. This passive recharge blanking may be performed to reduce any effect that the movement of charge at electrodes may have on sensing circuitry. The total voltage difference between Vbody and Device VSS is the lOuF capacitor voltage and the electrode- interface voltage on double layer capacitors that are factored in the Zbody. In this manner, the total voltage may be across the device capacitors and electrode interface.

[0089] FIG. 8 is a waveform timing diagram illustrating one example technique for delivering pulses and measuring signals during operation. In the example of FIG. 8, processing circuitry 208 may operate in 4 states (or steps) of operation. The ordinate axis of FIG. 8 represents the signal from a ping electrode pair current 1086 and a governed therapy electrode pair current 1087 and the abscissas axis of FIG. 8 represents time.

[0090] In the auto-zero state 1090, processing circuitry 208 may obtain a “best” approximation of the differential and common mode offset that will be seen at the input of the amplifier during signal acquisition phase 1092 so that the differential and common mode offset can be cancelled. In some examples, processing circuitry 208 may apply further adjustments to the offset to account for various situations, such as injecting an offset correction to the amplifier chain downstream from the calibration capacitors that store the offset. In the blocking state 1091, processing circuitry 208 may be configured to recover quickly from the presence of a pingstimulus and active recharge (e.g., about 10 V) and be able to sense a sensing signal as low as 10 gVPP, as early as 200 ps after the ping stimulus, a factor of 1 million in voltage difference. For example, during blocking state 1091, sensing circuitry may be disconnected (or blanked) from electrodes. In the signal acquisition state 1092, processing circuitry 208 may be configured to acquire a sensing signal to measure an amplitude value (e.g., an ECAP amplitude value).Passive recharge may or may not be blanked during the acquisition and measurement of the sensing signal, as described in different examples of FIGS. 9-13.

[0091] In governed therapy stimulus state 1093, processing circuitry 208 may perform titrated therapy based on a feature of the sensing signal (e.g., an ECAP amplitude value). For example, during governed therapy stimulus state 1093, stimulation generation circuitry 204 may deliver stimulus according to FIGS. 5-7. Passive recharge of the governed (therapy) electrodes may not be the desired device state to perform an auto-zero. Instead, system 100 may be configured to the ping electrode passive recharge state (e.g., auto-zero state 1090).

[0092] FIGS. 9-13 describe various different techniques for performing operations associated with delivering stimulation signals and measuring signals from the patient. These operations will be described as being controlled by processing circuitry 208 of IMD 200, but other control circuitry and / or other devices (e.g., IMD 110 or a programmer) may at least partially perform some of these features in other examples. Circuitry of FIGS. 4-7 may also be described as being part of the operations described in FIGS. 9-13. The processes of FIGS. 9-13 are described for a single stimulation channel. However, these processes may be performed on multiple stimulation and / or sensing channels and, in some examples, stimulation, settling, delay, blanking, and measuring, may occur independently on different channels (e.g., partially or fully overlapping in time). In some examples, passive recharge blanking will be performed for both settling sensing circuity and measuring signals or passive recharge is active for both settling sensing circuity and measuring signals to match system states for both the settling and measuring operations.However, in other examples, passive recharge may be active for only one of settling or measuring, or passive recharge blanking may be active for only one of settling or measuring.

[0093] FIG. 9 is a waveform timing diagram 900 illustrating an example in which IMD 200 is configured to settle measurement circuitry and measure signals during a passive recharge blanking period 926. As shown in the example of FIG. 9, timing diagram 900 includes various steps or operations for IMD 200 in the process of delivering stimulation and measuring a signalduring stimulation-measurement cycle 912. Stimulation signal 902 is a representation of current delivered via stimulation electrodes during cycle 912. Various operations will be described, including steps such as stimulation, a post-stimulation delay, active recharge, post-active recharge delay, passive recharge, and passive recharge blanking. Stimulation generally includes the process of applying a stimulus to an electrode combination of stimulation electrodes. Active recharge generally includes the process of applying a stimulation pulse having an opposite polarity of the stimulation pulse to the stimulation electrodes to recover charge at the stimulation electrodes. Passive recharge may include closing switches (e.g., switches 464, 465) or otherwise driving the voltage of the stimulation electrodes to ground or reference voltage (e.g., common ground voltage). The post-stimulation delay, the post-active recharge delay, and passive recharge blanking may all include processing circuitry 208 controlling switch circuitry to open circuit (e.g., opening switches 464, 465) which may prevent charge from moving from the electrodes (which the exception of the electrodes still being loosely tied to reference voltage or ground via a high impedance connection, e.g., grounding circuitry 444, 445 of FIG. 4).

[0094] At the beginning of example cycle 912, processing circuitry 208 can control stimulation generation circuitry 204 provide stimulation 914 which includes stimulation pulse 904 during stimulation phase 916, followed by post-stimulation delay 918, and then followed by active recharge pulse 906 during active recharge phase 920. After active recharge pulse 920, processing circuitry 208 control the switch circuitry to open circuit the stimulation electrodes during post-active recharge delay 922. However, some electrical charge may still remain at the stimulation electrode interface. Therefore, processing circuitry 208 controls switch circuitry to perform passive recharge 924 by driving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445). Passive recharge 924 may provide various advantages for measuring signals, such as reducing the sensing artifact and / or reduce the post-stimulus common mode potential in the system.

[0095] Not all of the charge may be removed from the stimulation electrodes by the time processing circuitry 208 needs to sense or measure signals (e.g., ECAP signals). Since the passive recharge process may affect the measurement of signals, processing circuitry 208 may perform passive recharge blanking 926 during which processing circuitry 208 controls the switch circuitry to stop passive recharge (e.g., by opening switches 464, 465 of grounding circuitry 444, 445). In other words, charge recovery is disabled during passive recharge blanking 926. Duringpassive recharge blanking 926, processing circuitry 208 can setting the measurement circuitry during settling period 928 and then measure the sensed signal during measuring period 930. Processing circuitry 208 can settle the measurement circuitry (or sensing circuitry) via auto-zero circuitry 454 and calibration capacitors 452, 453. In this manner, the measurement circuitry can be settled to the steady state of the system such that the measurement of the signal is representative of the physiological signal instead of any noise or other factors associated with the system. Performing this settling process immediately prior to measuring the signal may reduce variations that could occur over time. However, the settling process can be performed at other times with respect to the measurement step (e.g., before or after, or with intervening processes), but processing circuitry 208 may provide an adjustment to the offset in certain situations to account for these variations in the steady state of the system. Processing circuitry 208 can control the sensing circuitry (e.g., some or all of analog circuitry 400 and / or amplifier circuitry 456), to measure the potential at the sensing electrodes by closing first switches 449, 451 and using amplifier circuitry 456 to measure the resulting voltage on the respective lines. In some examples, processing circuitry 208 may analyze the resulting offset in the sensing circuitry and feed it back via digital to analog feedback to provide the mechanism for fine offset adjustment.

[0096] There may be residual charge still remaining on the stimulation electrodes at the end of passive recharge blanking 926. Therefore, processing circuitry 208 may again control switch circuitry to perform passive recharge during passive recharge period 932 that may continue up until the next cycle which may begin at the next stimulation 934 which includes stimulation pulse 908 and active recharge pulse 910. Generally, processing circuitry 208 may perform passive recharge during any quiescent period of the stimulation-measurement cycle 912 in order to reduce possible charge at the stimulation electrodes (or any of the plurality of electrodes). In other examples, processing circuitry 208 may skip the second passive recharge period 932 if the first passive recharge period 924 is sufficient to remove all or most of the charge from stimulation electrodes. In some examples, processing circuitry 208 may control stimulation generation circuitry 204 to deliver additional stimulation pulses during the period of time between the end of passive recharge blanking 926 and the start of stimulation 934 if there is sufficient time to deliver those pulses and the therapy or measurement calls for such signals.

[0097] As shown in cycle 912, measuring period 930 occurs immediately after setting period 928. However, there may be a brief period of time between each period that is required forcircuitry to move switches or otherwise reconfigure one configuration (of the settling process) to another configuration (of the measuring process). Although settling period 928 is shown as occurring immediately prior to measuring period 930, settling period 928 may be provided after measuring period 930 and still within passive recharge blanking 926 in other examples. Generally, processing circuitry 208 may be configured to control IMD 200 to settle the sensing circuitry before measuring the signal, and it may provide most accurate results by settling the sensing circuitry as fast as possible. In some examples, settling period 928 may have a duration from 10 microseconds to 100 microseconds, but may be faster or slower in other examples.Settling period 928 may be shorter for fast acting signals such as ECAPs (e.g., within the 10-100 microsecond range), but longer signal responses such as CMAP signals may utilize longer settling periods.

[0098] As described with respect to the example of FIG. 9, an IMD, such as IMD 200, may be configured to perform various operations associated with delivering stimulation pulses and managing sensing circuitry to reduce different types of noise that may affect the accuracy of signal measurement. Processing circuitry 208 may be configured to control stimulation generation circuitry 204 to generate at least one stimulation pulse via the stimulation electrode combination and control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period (e.g., periods 924 and / or 932).

[0099] Processing circuitry 208 may also control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period 926 different from the passive recharge period 924, 932. In other words, processing circuitry 208 may control switching circuitry to stop passive recharge during the passive recharge blanking period 926. Processing circuitry 208 may also be configured to control the switching circuitry to settle sensing circuitry 206 during at least a first portion (e.g., settling period 928) of the passive recharge blanking period 926. In addition, processing circuitry 208 may be configured to control sensing circuitry 206 to measure the electric signal during at least a second portion (e.g., measuring period 930) of the passive recharge blanking period 926. In some examples, the passive recharge blanking period 926 may include both the settling of sensing circuitry and measurement of signals in that order or in reverse order. Passive recharge may be performed by IMD 200 before and / or after the passive recharge blanking period 926.Stimulation 914 is an example of a biphasic pulse. In other examples, stimulation having more than two phases (e.g., a triphasic pulse having two phases of one polarity and another phase with an opposite polarity). This passive recharge blanking 926 may be performed after delivery of biphasic pulses and / or after delivery of a single phase stimulation pulse followed by only passive recharge instead of active recharge.

[0100] As discussed herein, settling period 928 may include operations that include processing circuitry 208 controlling injection of an offset correction later in analog circuitry via digital to analog feedback or even storing an offset at a capacitor that is related to the steady state of the system, where the offset is applied to the measured value of the measured electrical signal. In some examples, processing circuitry 208 is configured to adjust the offset value (or the resulting measured signals) based at least in part on a difference between an order of the stimulation pulse and the settle and a subsequent stimulation pulse and a subsequent settle period. For example, if a stimulation pulse is delivered between the settling period and the subsequent measurement of the sensed signal, that stimulation pulse may affect the steady state of the system such that the stored offset does not accurately reflect the steady state of the system. As another example, switching the polarity of subsequent stimulation pulses can also affect the stored offset from the settling period. In these situations, processing circuitry 208 may adjust the offset value to account for these system changes. This adjustment may be based on empirical data from other patients of the specific patient. This adjustment may also be based on other system changes or even the measured signal being different beyond expectations that could be due to the stored offset that is inaccurate.

[0101] As shown in the example of timing diagram 900, processing circuitry 208 is configured to control the switching circuitry to settle the sensing circuitry 206 during the first portion (928) of the passive recharge blanking period 926 and immediately prior to the second period (930) of the passive recharge blanking period 926 during which processing circuitry 208 is configured to control sensing circuitry 206 to measure the electric signal. In other examples, the order of settling period 928 and measuring period 930 may be switched such that processing circuitry 208 is configured to control the switching circuitry to settle the sensing circuitry 206 during the first portion (928) of the passive recharge blanking period 926 that occurs after the second period (930) of the passive recharge blanking period 926 during which processing circuitry 208 is configured to control sensing circuitry 206 to measure the electric signal. Ineither case, the settling of the sensing circuitry and measurement of the signal may be performed completely within passive recharge blanking period 926.

[0102] The example of timing diagram 900 illustrates one example stimulation-measurement cycle 912. As part of cycle 912, processing circuitry 208 may perform a first action including controlling stimulation generation circuitry 204 to generate the at least one stimulation pulse via the stimulation electrode combination, the at least one stimulation pulse including a first stimulation pulse (904) of a first polarity followed by a second recharge pulse (906) having a second polarity opposite the first polarity. Processing circuitry 208 can then perform a second action, after the first action, including controlling the switching circuitry to disconnect the plurality of electrodes from stimulation generation circuitry 204 and sensing circuitry 206. Processing circuitry 208 can then perform a third action, after the second action, including controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination during the passive recharge period 924. Processing circuitry 208 can then perform a fourth action, after the third action, including controlling the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during passive recharge blanking period 926 and, during passive recharge blanking period 926, control the switching circuitry to settle sensing circuitry 206 during at least the first portion (928) of passive recharge blanking period 926 and control sensing circuitry 206 to measure the electric signal during at least the second portion (930) of the passive recharge blanking period.

[0103] FIG. 10 is a waveform timing diagram 1000 illustrating an example in which the system settles measurement circuitry and measures signals during a passive recharge blanking period 926. The technique of FIG. 10 is substantially similar to the technique of FIG. 9, but a single phase stimulation pulse 904 is delivered with only passive recharge instead of an active recharge phase.

[0104] As shown in the example of FIG. 10, timing diagram 1000 includes various steps or operations for IMD 200 in the process of delivering stimulation and measuring a signal during stimulation-measurement cycle 1012. At the beginning of example cycle 912, processing circuitry 208 can control stimulation generation circuitry 204 provide stimulation 1014 which includes only one stimulation pulse 904. Pulse 904 is followed by post-stimulation delay 1022 before processing circuitry 208 controls switch circuitry to perform passive recharge 1024 bydriving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445) as shown by recharge signal 1006.

[0105] Not all of the charge may be removed from the stimulation electrodes by the time processing circuitry 208 needs to sense or measure signals (e.g., ECAP signals). Since the passive recharge process may affect the measurement of signals, processing circuitry 208 may perform passive recharge blanking 926 during which processing circuitry 208 controls the switch circuitry to stop passive recharge (e.g., by opening switches 464, 465 of grounding circuitry 444, 445). In other words, charge recovery is disabled during passive recharge blanking 926. During passive recharge blanking 926, processing circuitry 208 can setting the measurement circuitry during settling period 928 and then measure the sensed signal during measuring period 930. Processing circuitry 208 can settle the measurement circuitry (or sensing circuitry) via auto-zero circuitry 454 and calibration capacitors 452, 453. In this manner, the measurement circuitry can be settled to the steady state of the system such that the measurement of the signal is representative of the physiological signal instead of any noise or other factors associated with the system. Performing this settling process immediately prior to measuring the signal may reduce variations that could occur over time. However, the settling process can be performed at other times with respect to the measurement step (e.g., before or after, or with intervening processes), but processing circuitry 208 may provide an adjustment to the offset in certain situations to account for these variations in the steady state of the system. Processing circuitry 208 can control the sensing circuitry (e.g., some or all of analog circuitry 400 and / or amplifier circuitry 456), to measure the potential at the sensing electrodes by closing first switches 449, 451 and using amplifier circuitry 456 to measure the resulting voltage on the respective lines.

[0106] There may be residual charge still remaining on the stimulation electrodes at the end of passive recharge blanking 926. Therefore, processing circuitry 208 may again control switch circuitry to perform passive recharge during passive recharge period 932 that may continue up until the next cycle which may begin at the next stimulation 1034 which includes stimulation pulse 908 and recharge signal 1010. Generally, processing circuitry 208 may perform passive recharge during any quiescent period of the stimulation-measurement cycle 1012 in order to reduce possible charge at the stimulation electrodes (or any of the plurality of electrodes). In other examples, processing circuitry 208 may skip the second passive recharge period 932 if the first passive recharge period 924 is sufficient to remove all or most of the charge fromstimulation electrodes. In some examples, processing circuitry 208 may control stimulation generation circuitry 204 to deliver additional stimulation pulses during the period of time between the end of passive recharge blanking 926 and the start of stimulation 1034 (e.g., within second passive recharge period 932) if there is sufficient time to deliver those pulses and the therapy or measurement calls for such signals.

[0107] As shown in FIG. 10, cycle 1012 includes stimulation 1014 having only a single stimulation pulse 904 which is a single phase pulse. Instead of using an active recharge phase, processing circuitry 208 is configured to recover charge at the stimulation electrode combination controlling the switching circuitry to perform passive recharge 1024 of at least the stimulation electrode combination instead of controlling the stimulation generation circuitry to generate an active recharge pulse for the delivered at least one stimulation pulse.

[0108] FIG. 11 is a waveform timing diagram 1100 illustrating an example in which the system settles measurement circuitry and measures signals during a passive recharge period 1124. The technique of FIG. 11 is substantially similar to the technique of FIG. 9, but without using a passive recharge blanking period for settling and measuring sensing circuitry 206. FIG. 11 is a waveform timing diagram 1100 illustrating an example in which IMD 200 is configured to settle measurement circuitry and measure signals during a passive recharge period 1124. As shown in the example of FIG. 11, timing diagram 100 includes various steps or operations for IMD 200 in the process of delivering stimulation and measuring a signal during stimulationmeasurement cycle 1112.

[0109] At the beginning of example cycle 1112, processing circuitry 208 can control stimulation generation circuitry 204 provide stimulation 1114 which includes stimulation pulse 904 during stimulation phase 916, followed by post-stimulation delay 918, and then followed by active recharge pulse 906 during active recharge phase 920. After active recharge pulse 920, processing circuitry 208 control the switch circuitry to open circuit the stimulation electrodes during post-active recharge delay 922. However, some electrical charge may still remain at the stimulation electrode interface. Therefore, processing circuitry 208 controls switch circuitry to perform passive recharge 1124 by driving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445).

[0110] During passive recharge period 1124, processing circuitry 208 can settle the measurement circuitry during settling period 1128 and then measure the sensed signal duringmeasuring period 1130. As discussed herein, settling the sensing circuitry and measuring the sensed signal during passive recharge period 1124 can cause variations in the measured signal due to changing of charge the electrode interface. However, processing circuitry 208 may still perform these processes during passive recharge period 1124 in situations in which the remaining charge is minimal, the sensed signal has a larger signal to noise ratio, or there is no time available to stop passive recharge before the next stimulation 1134. Since settling period 1128 is performed immediately before measuring period 1130 and most of the charge has been passively recovered by the time measuring period 1130 begins, any remaining passive recharge may have a relatively small effect on the measurement of the signal, such as the ECAP signal elicited by stimulation 1114. During period 1140, processing circuitry 208 may control stimulation generation circuitry 204 to provide additional stimulation pulses or perform other functions as desired.

[0111] FIG. 12 is a waveform timing diagram 1200 illustrating an example in which the system settles measurement circuitry after measuring signals. The process of FIG. 12 is similar to the process of FIG. 9, but FIG. 12 illustrates when the system may settle sensing circuitry after measuring a signal within the same stimulation-measurement cycle 1212. This settling period 1228 may be performed immediately prior to the next stimulation cycle (e.g., stimulation 934).

[0112] As shown in the example of FIG. 12, timing diagram 1200 includes various steps or operations for IMD 200 in the process of delivering stimulation and measuring a signal during stimulation-measurement cycle 1212. At the beginning of example cycle 1212, processing circuitry 208 can control stimulation generation circuitry 204 provide stimulation 914 which includes stimulation pulse 904 during stimulation phase 916, followed by post-stimulation delay 918, and then followed by active recharge pulse 906 during active recharge phase 920. After active recharge pulse 920, processing circuitry 208 control the switch circuitry to open circuit the stimulation electrodes during post-active recharge delay 922. However, some electrical charge may still remain at the stimulation electrode interface. Therefore, processing circuitry 208 controls switch circuitry to perform passive recharge 924 by driving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445).

[0113] Not all of the charge may be removed from the stimulation electrodes by the time processing circuitry 208 needs to sense or measure signals (e.g., ECAP signals). Since thepassive recharge process may affect the measurement of signals, processing circuitry 208 may perform passive recharge blanking 926 during which processing circuitry 208 controls the switch circuitry to stop passive recharge (e.g., by opening switches 464, 465 of grounding circuitry 444, 445). In other words, charge recovery is disabled during passive recharge blanking 926. During passive recharge blanking 926, processing circuitry 208 can control the sensing circuitry (e.g., some or all of analog circuitry 400 and / or amplifier circuitry 456), to measure the potential at the sensing electrodes by closing first switches 449, 451 and using amplifier circuitry 456 to measure the resulting voltage on the respective lines during measuring period 1230.

[0114] There may be residual charge still remaining on the stimulation electrodes at the end of passive recharge blanking 926. Therefore, processing circuitry 208 may again control switch circuitry to perform passive recharge during passive recharge period 1232 that may continue up until the next cycle which may begin at the next stimulation 934 which includes stimulation pulse 908 and active recharge pulse 910. Generally, processing circuitry 208 may perform passive recharge during any quiescent period of the stimulation-measurement cycle 1212 in order to reduce possible charge at the stimulation electrodes (or any of the plurality of electrodes). In other examples, processing circuitry 208 may skip the second passive recharge period 1232 if the first passive recharge period 924 is sufficient to remove all or most of the charge from stimulation electrodes. In some examples, processing circuitry 208 may control stimulation generation circuitry 204 to deliver additional stimulation pulses during the period of time between the end of passive recharge blanking 926 and the start of stimulation 934 if there is sufficient time to deliver those pulses and the therapy or measurement calls for such signals.

[0115] At the end of cycle 1212, processing circuitry 208 can perform the settling operation for sensing circuitry 206 during settling period 1228 (which may be similar to settling period 928). By performing the settling operation immediately prior to stimulation 934 of the next cycle, stimulation pulses are delivered using the stimulation electrodes between the settling operation and the next measurement period. In this manner, the offset stored during settling period 1228 may not be completely accurate to represent the charge of the system at the next measurement opportunity. Processing circuitry 208 may adjust the offset to account for this charge that may be present on the electrode interface as a result of the stimulation delivery. In some examples, settling period 1228 may have a duration from 10 microseconds to 100 microseconds, but may be faster or slower in other examples. Settling period 1228 may beshorter for fast acting signals such as ECAPs (e.g., within the 10-100 microsecond range), but longer signal responses such as CMAP signals may utilize longer settling periods.

[0116] FIG. 13 is a waveform timing diagram 1300 illustrating an example in which the system measure signals after passive recharge and prior to settling measurement circuitry. The technique of FIG. 13 is substantially similar to the technique of FIGS. 9 and 11, but without using a passive recharge blanking period for settling and measuring sensing circuitry 206. FIG. 13 is a waveform timing diagram 1300 illustrating an example in which IMD 200 is configured to settle measurement circuitry and measure signals during a passive recharge period 1324. As shown in the example of FIG. 13, timing diagram 100 includes various steps or operations for IMD 200 in the process of delivering stimulation and measuring a signal during stimulationmeasurement cycle 1312.

[0117] At the beginning of example cycle 1312, processing circuitry 208 can control stimulation generation circuitry 204 provide stimulation 914 which includes stimulation pulse 904 during stimulation phase 916, followed by post-stimulation delay 918, and then followed by active recharge pulse 906 during active recharge phase 920. After active recharge pulse 920, processing circuitry 208 control the switch circuitry to open circuit the stimulation electrodes during post-active recharge delay 922. However, some electrical charge may still remain at the stimulation electrode interface. Therefore, processing circuitry 208 controls switch circuitry to perform passive recharge 1324 by driving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445).

[0118] Most of the charge may be removed from the stimulation electrodes during period 1332 at the initial period of passive recharge 1324. After period 1332, circuitry 208 can control the sensing circuitry (e.g., some or all of analog circuitry 400 and / or amplifier circuitry 456), to measure the potential at the sensing electrodes by closing first switches 449, 451 and using amplifier circuitry 456 to measure the resulting voltage on the respective lines during measuring period 1330. If there is any charge remaining on the stimulation electrodes during measuring period 1330, it may continue to be removed during measurement, but that charge may be minimal.

[0119] After passive recharge 1324 is complete, processing circuitry 208 may control stimulation generation circuitry 204 to deliver additional stimulation pulses, perform further measurements (and possibly even settling operations), or perform any other operations duringperiod 1350. Passive recharge is typically no longer be active during period 1350. At the end of cycle 1312, processing circuitry 208 can perform the settling operation for sensing circuitry 206 during settling period 1328 (which may be similar to settling period 928). By performing the settling operation immediately prior to stimulation 934 of the next cycle, stimulation pulses are delivered using the stimulation electrodes between the settling operation and the next measurement period. In this manner, the offset stored during settling period 1328 may not be completely accurate to represent the charge of the system at the next measurement opportunity. Processing circuitry 208 may adjust the offset to account for this charge that may be present on the electrode interface as a result of the stimulation delivery. In some examples, settling period 1328 may have a duration from 10 microseconds to 100 microseconds, but may be faster or slower in other examples. Settling period 1328 may be shorter for fast acting signals such as ECAPs (e.g., within the 10-100 microsecond range), but longer signal responses such as CMAP signals may utilize longer settling periods. In other examples, processing circuitry 208 may perform the settling operation for sensing circuitry 206 during settling period 1328 and period 1350 in order to provide a longer period of time to settle the sensing circuitry to the steady state of the system.

[0120] FIG. 14 is a flow chart of an example technique for settling measurement circuitry and measuring signals during a passive recharge blanking period. The process of FIG. 14 may be representative of FIG. 9, but may be applicable to other variations of a stimulationmeasurement cycle as described herein. Processing circuitry 208 and components of IMD 200 are described herein with respect to FIG. 14, but other circuitry and / or devices may perform similar processes in other examples.

[0121] In the example of FIG. 14, processing circuitry 208 can control stimulation generation circuitry 204 to deliver one or more stimulation pulses (1402). These stimulation pulses may include one or more stimulus pulses and, in some examples, an active recharge phase to recover charge at the electrodes. Processing circuitry 208 can then impose a delay before passive recharge, where the delay includes controlling the switch circuitry to open circuit the stimulation electrodes (1404). Then, processing circuitry 208 controls switch circuitry to perform passive recharge by driving the voltage of the stimulation electrodes to ground or the reference voltage (e.g., via switches 464, 465 of grounding circuitry 444, 445) (1406). Passive recharge is performed to remove most, or all, of the remaining charge on the electrode interface to reducethat charge from interfering with the accurate measurement of physiological signals, such as ECAP signals.

[0122] Since the passive recharge process may affect the measurement of signals, processing circuitry 208 may perform passive recharge blanking (1408). To blank the passive recharge, processing circuitry 208 may control the switch circuitry to stop passive recharge (e.g., by opening switches 464, 465 of grounding circuitry 444, 445). In other words, charge recovery is disabled during passive recharge blanking. During passive recharge blanking, processing circuitry 208 can settle the measurement circuitry during a settling period and then measure the sensed signal during a measuring period (1410). In other examples, processing circuitry 208 may perform the measurement prior to settling the sensing circuitry. After measurement, processing circuitry 208 can then terminate the passive recharge blanking and resume passive recharge to remove any remaining charge at the stimulation and / or measurement electrodes (1412). Processing circuitry 208 may then deliver additional stimulation pulses in another stimulation-measurement cycle or deliver one or more other stimulation pulses (such as informed pulses based on the measurement of an ECAP signal) before returning to delivering stimulation pulses in step 1402.

[0123] FIG. 15 is a flow charge of an example technique for adjusting offset values for measurement circuitry based on timing or order of stimulation pulses. The process of FIG. 15 may be performed by processing circuitry 208 and components of IMD 200, but other circuitry and / or devices may perform similar processes in other examples.

[0124] In the example of FIG. 15, processing circuitry 208 controls stimulation generation circuitry 204 to deliver one or more stimulation pulses (1502). This stimulation may include one, two, or more phases, and active and / or passive recharge may be performed after the stimulation. Processing circuitry 208 may determine the type of adjustment that needs to be applied to the stored offset in sensing circuitry 206. For example, the offset may be a voltage representative the charge in the system when stable, and may be stored by one or more capacitors such as capacitor 452 or 453 of analog circuit 400 of FIG. 4. Depending on the operation of the system after the settling is performed and the offset is stored and before measurement of a sensed signal, the stored offset may need to be adjusted to account for this activity. For example, if measurement occurs immediately after the offset is stored during the settling period, processing circuitry 208 may not be programed to apply any adjustment to the stored offset.

[0125] If the polarity of the stimulation pulse(s) or order of different pulse polarity has changed from the previous pulse(s) or from the previous stimulation-measurement cycle (“YES” branch of block 1504), processing circuitry 208 may adjust the offset for the measurement circuitry (1506). The magnitude of the adjustment to the offset may be determined based on system information related to the residual charge that is typically remaining on the electrode interface as a difference from the previous different pulse configuration. This adjustment magnitude may be empirically determined or modeled and may be stored in memory for retrieval. If the timing of the measurement and settling periods has changed from the previous stimulation-measurement cycle (“YES” branch of block 1508), processing circuitry 208 may adjust the offset for the measurement circuitry (1510). In some examples, processing circuitry 208 may perform both adjustments from steps 1506 and 1510 if applicable. This double adjustment may create a larger adjustment, or the adjustments may partially or fully reduce each other. The measurement and settling timing can refer to separation of each period in time or changing the order of the measurement and settling process from the previous stimulationmeasurement cycle. The magnitude of the adjustment to the offset based on the timing may be determined based on system information related to the residual charge that is typically remaining on the electrode interface as a difference from the previous timing. This adjustment magnitude may be empirically determined or modeled and may be stored in memory for retrieval.

[0126] If there have been no changes to the polarity of pulses or timing of the measurement and settling periods, processing circuitry 208 may maintain the stored offset for the measurement circuitry (1512). In other words, no adjustment to the stored offset may be made. Using either the stored offset or the adjusted stored offset, processing circuitry can then measure the ECAP signal (or other type of signal) (1514). Processing circuitry 208 may continue to deliver additional stimulation pulses (1502).

[0127] The following examples are examples systems, devices, and methods described herein.

[0128] Example 1. A system comprising: stimulation generation circuitry configured to generate electrical stimulation pulses via a stimulation electrode combination of a plurality of electrodes; sensing circuitry configured to measure an electric signal via a sense electrode combination of the plurality of electrodes; switching circuitry; and processing circuitry configured to: control the stimulation generation circuitry to generate at least one stimulationpulse via the stimulation electrode combination; control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and control the sensing circuitry to measure the electric signal during at least a second portion of the passive recharge blanking period.

[0129] Example 2. The system of example 1, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period and immediately prior to the second period of the passive recharge blanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

[0130] Example 3. The system of any of examples 1 or 2, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period that occurs after the second period of the passive recharge blanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

[0131] Example 4. The system of any of examples 1 through 3, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry completely during the first portion of the passive recharge blanking period and control the sensing circuitry to measure the electric signal completely during the second portion of the passive recharge blanking period.

[0132] Example 5. The system of any of examples 1 through 4, wherein the processing circuitry is configured to control the switching circuitry to perform at least part of the passive recharge prior to the passive recharge blanking period and before subsequent stimulation pulse delivery.

[0133] Example 6. The system of example 5, wherein the processing circuitry is configured to control the switching circuitry to perform a second portion of the passive recharge after the passive recharge blanking period and before the subsequent stimulation pulse delivery.

[0134] Example 7. The system of any of examples 1 through 6, wherein the stimulation pulse is a single phase pulse, and wherein the processing circuitry is configured to recover chargeat the stimulation electrode combination controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination instead of controlling the stimulation generation circuitry to generate an active recharge pulse for the delivered at least one stimulation pulse.

[0135] Example 8. The system of any of examples 1 through 7, wherein the processing circuity is configured to perform a stimulation-measurement cycle comprising at least: a first action comprising controlling the stimulation generation circuitry to generate the at least one stimulation pulse via the stimulation electrode combination, the at least one stimulation pulse comprising a first stimulation pulse of a first polarity followed by a second recharge pulse having a second polarity opposite the first polarity; a second action, after the first action, comprising controlling the switching circuitry to disconnect the plurality of electrodes from the stimulation generation circuitry and the sensing circuitry; a third action, after the second action, comprising controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination during the passive recharge period; a fourth action, after the third action, comprising controlling the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during the passive recharge blanking period and, during the passive recharge blanking period: controlling the switching circuitry to settle the sensing circuitry during at least the first portion of the passive recharge blanking period; and controlling the sensing circuitry to measure the electric signal during at least the second portion of the passive recharge blanking period.

[0136] Example 9. The system of any of examples 1 through 8, wherein the stimulation pulse comprises a biphasic pulse or a triphasic pulse.

[0137] Example 10. The system of any of examples 1 through 9, wherein the processing circuitry is configured to apply an offset value to a measured value of the measured electrical signal, and wherein the processing circuitry is configured to adjust the offset value based at least in part on a different between an order of the stimulation pulse and the settle and a subsequent stimulation pulse and a subsequent settle period.

[0138] Example 11. The system of any of examples 1 through 10, wherein the sensing circuitry is configured to measure at least one of an evoked compound action potential (ECAP) signals, CMAP signal, or ERNA signal.

[0139] Example 12. The system of any of examples 1 through 11, further comprising an implantable medical device comprising the stimulation generation circuitry, the switching circuitry, the sensing circuitry, and the processing circuitry.

[0140] Example 13. A method comprising: controlling, by processing circuitry, stimulation generation circuitry to generate at least one stimulation pulse via a stimulation electrode combination, wherein the stimulation generation circuitry is configured to generate electrical stimulation pulses via the stimulation electrode combination of a plurality of electrodes; controlling, by the processing circuitry, switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; controlling, by the processing circuitry, the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; controlling, by the processing circuitry, the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and controlling, by the processing circuitry, sensing circuitry to measure an electric signal during at least a second portion of the passive recharge blanking period, wherein the sensing circuitry is configured to measure the electric signal via a sense electrode combination of the plurality of electrodes.

[0141] Example 14. The method of example 13, wherein controlling the switching circuitry to settle the sensing circuitry comprises controlling the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period and immediately prior to the second period of the passive recharge blanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

[0142] Example 15. The method of any of examples 13 or 14, wherein controlling the switching circuitry to settle the sensing circuitry comprises controlling the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period that occurs after the second period of the passive recharge blanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

[0143] Example 16. The method of any of examples 13 through 15, wherein controlling the switching circuitry to settle the sensing circuitry comprises controlling the switching circuitry to settle the sensing circuitry completely during the first portion of the passive recharge blankingperiod and control the sensing circuitry to measure the electric signal completely during the second portion of the passive recharge blanking period.

[0144] Example 17. The method of any of examples 13 through 16, wherein controlling the switching circuitry to perform at least part of the passive recharge comprises controlling the switching circuitry to perform at least part of the passive recharge prior to the passive recharge blanking period and before subsequent stimulation pulse delivery.

[0145] Example 18. The method of example 17, further comprising controlling the switching circuitry to perform a second portion of the passive recharge after the passive recharge blanking period and before the subsequent stimulation pulse delivery.

[0146] Example 19. The method of any of examples 13 through 18, wherein the stimulation pulse is a single phase pulse, and wherein the method comprises recovering charge at the stimulation electrode combination by controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination instead of controlling the stimulation generation circuitry to generate an active recharge pulse for the delivered at least one stimulation pulse.

[0147] Example 20. The method of any of examples 13 through 19, further comprising performing a stimulation-measurement cycle that comprises at least: a first action comprising controlling the stimulation generation circuitry to generate the at least one stimulation pulse via the stimulation electrode combination, the at least one stimulation pulse comprising a first stimulation pulse of a first polarity followed by a second recharge pulse having a second polarity opposite the first polarity; a second action, after the first action, comprising controlling the switching circuitry to disconnect the plurality of electrodes from the stimulation generation circuitry and the sensing circuitry; a third action, after the second action, comprising controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination during the passive recharge period; a fourth action, after the third action, comprising controlling the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during the passive recharge blanking period and, during the passive recharge blanking period: controlling the switching circuitry to settle the sensing circuitry during at least the first portion of the passive recharge blanking period; and controlling the sensing circuitry to measure the electric signal during at least the second portion of the passive recharge blanking period.

[0148] Example 21. The method of any of examples 13 through 20, wherein the stimulation pulse comprises a biphasic pulse or a triphasic pulse.

[0149] Example 22. The method of any of examples 13 through 21, further comprising: applying an offset value to a measured value of the measured electrical signal; and adjusting the offset value based at least in part on a different between an order of the stimulation pulse and the settle and a subsequent stimulation pulse and a subsequent settle period.

[0150] Example 23. The method of any of examples 13 through 22, wherein the sensing circuitry is configured to measure at least one of an evoked compound action potential (ECAP) signals, CMAP signal, or ERNA signal.

[0151] Example 24. A computer-readable storage medium comprising instructions that, when executed by processing circuitry, causes the processing circuitry to: control stimulation generation circuitry to generate at least one stimulation pulse via a stimulation electrode combination, wherein the stimulation generation circuitry configured to generate electrical stimulation pulses via the stimulation electrode combination of a plurality of electrodes; control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and control sensing circuitry to measure the electric signal during at least a second portion of the passive recharge blanking period, wherein the sensing circuitry is configured to measure the electric signal via a sense electrode combination of the plurality of electrodes.

[0152] The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the described techniques may be implemented within one or more processors or processing circuitry, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. A control unit including hardware may also perform one or more of the techniques of this disclosure.

[0153] Such hardware, software, and firmware may be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, circuits or components may be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as circuits or units is intended to highlight different functional aspects and does not necessarily imply that such circuits or units must be realized by separate hardware or software components. Rather, functionality associated with one or more circuits or units may be performed by separate hardware or software components or integrated within common or separate hardware or software components.

[0154] The techniques described in this disclosure may also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions that may be described as non-transitory media. Instructions embedded or encoded in a computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, e.g., when the instructions are executed. Computer readable storage media may include random access memory (RAM), such as, for example, ferroelectric RAM (FRAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a cassette, magnetic media, optical media, or other computer readable media.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: stimulation generation circuitry configured to generate electrical stimulation pulses via a stimulation electrode combination of a plurality of electrodes; sensing circuitry configured to measure an electric signal via a sense electrode combination of the plurality of electrodes; switching circuitry; and processing circuitry configured to: control the stimulation generation circuitry to generate at least one stimulation pulse via the stimulation electrode combination; control the switching circuitry to perform passive recharge of at least the stimulation electrode combination during a passive recharge period; control the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during a passive recharge blanking period different from the passive recharge period; control the switching circuitry to settle the sensing circuitry during at least a first portion of the passive recharge blanking period; and control the sensing circuitry to measure the electric signal during at least a second portion of the passive recharge blanking period.

2. The system of claim 1, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period and immediately prior to the second period of the passive recharge blanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

3. The system of any of claims 1 or 2, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry during the first portion of the passive recharge blanking period that occurs after the second period of the passive rechargeblanking period during which the processing circuitry is configured to control the sensing circuitry to measure the electric signal.

4. The system of any of claims 1 through 3, wherein the processing circuitry is configured to control the switching circuitry to settle the sensing circuitry completely during the first portion of the passive recharge blanking period and control the sensing circuitry to measure the electric signal completely during the second portion of the passive recharge blanking period.

5. The system of any of claims 1 through 4, wherein the processing circuitry is configured to control the switching circuitry to perform at least part of the passive recharge prior to the passive recharge blanking period and before subsequent stimulation pulse delivery.

6. The system of claim 5, wherein the processing circuitry is configured to control the switching circuitry to perform a second portion of the passive recharge after the passive recharge blanking period and before the subsequent stimulation pulse delivery.

7. The system of any of claims 1 through 6, wherein the stimulation pulse is a single phase pulse, and wherein the processing circuitry is configured to recover charge at the stimulation electrode combination controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination instead of controlling the stimulation generation circuitry to generate an active recharge pulse for the delivered at least one stimulation pulse.

8. The system of any of claims 1 through 7, wherein the processing circuity is configured to perform a stimulation-measurement cycle comprising at least: a first action comprising controlling the stimulation generation circuitry to generate the at least one stimulation pulse via the stimulation electrode combination, the at least one stimulation pulse comprising a first stimulation pulse of a first polarity followed by a second recharge pulse having a second polarity opposite the first polarity;a second action, after the first action, comprising controlling the switching circuitry to disconnect the plurality of electrodes from the stimulation generation circuitry and the sensing circuitry; a third action, after the second action, comprising controlling the switching circuitry to perform the passive recharge of at least the stimulation electrode combination during the passive recharge period; a fourth action, after the third action, comprising controlling the switching circuitry to prevent passive recharge of at least the stimulation electrode combination during the passive recharge blanking period and, during the passive recharge blanking period: controlling the switching circuitry to settle the sensing circuitry during at least the first portion of the passive recharge blanking period; and controlling the sensing circuitry to measure the electric signal during at least the second portion of the passive recharge blanking period.

9. The system of any of claims 1 through 8, wherein the stimulation pulse comprises a biphasic pulse or a triphasic pulse.

10. The system of any of claims 1 through 9, wherein the processing circuitry is configured to apply an offset value to a measured value of the measured electrical signal, and wherein the processing circuitry is configured to adjust the offset value based at least in part on a different between an order of the stimulation pulse and the settle and a subsequent stimulation pulse and a subsequent settle period.

11. The system of any of claims 1 through 10, wherein the sensing circuitry is configured to measure at least one of an evoked compound action potential (ECAP) signals, CMAP signal, or ERNA signal.

12. The system of any of claims 1 through 11, further comprising an implantable medical device comprising the stimulation generation circuitry, the switching circuitry, the sensing circuitry, and the processing circuitry.

13. The system of any of claims 1 through 12, further comprising one or more leads comprising the plurality of electrodes.

14. A computer-readable storage medium comprising instructions that, when executed by the processing circuitry, causes the processing circuitry to perform functions of any of claims 1 through 13.

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