CN116617562A

CN116617562A - Sensing Evoked Compound Action Potential (ECAP)

Info

Publication number: CN116617562A
Application number: CN202310144185.2A
Authority: CN
Inventors: R·A·科里; J·安德森; D·丁斯莫尔; K·哈格曼; S·斯坦斯拉斯基; T·史密斯; H·奥马尔
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2022-02-21
Filing date: 2023-02-21
Publication date: 2023-08-22

Abstract

A system for providing therapy to a patient includes a stimulus generation circuit, a sensing circuit, and a processing circuit. The processing circuit is configured to cause a first voltage on a first terminal to be stored in a first calibration capacitor and a second voltage on a second terminal to be stored in a second calibration capacitor. The processing circuit is configured to turn off the first calibration switch to prevent a change in a first voltage stored in the first calibration capacitor and turn off the second calibration switch to prevent a change in a second voltage stored in the second calibration capacitor; and determining, with the sensing circuit, a sensing signal based on the first voltage offset by the first calibration voltage stored by the first capacitor and based on the second voltage offset by the second calibration voltage stored by the second capacitor.

Description

Sensing Evoked Compound Action Potential (ECAP)

The present application claims the benefit of U.S. provisional patent application No. 63/268,305 filed on 21, 2, 2022, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates generally to electrical stimulation, and more particularly to control of electrical stimulation.

Background

The medical device may be external or implanted and may be used to deliver electrical stimulation to a patient via various tissue sites to treat various symptoms or conditions, such as chronic pain, tremor, parkinson's disease, epilepsy, urinary and urinary incontinence, sexual dysfunction, obesity, or gastroparesis. The medical device may deliver the electrical stimulation therapy via one or more leads that include electrodes that are positioned near a target location associated with the brain, spinal cord, pelvic nerve, peripheral nerve, or gastrointestinal tract of the patient. Stimulation near the spinal cord, near the sacral nerve, in the brain, and near the peripheral nerve are commonly referred to as Spinal Cord Stimulation (SCS), sacral Neuromodulation (SNM), deep Brain Stimulation (DBS), and Peripheral Nerve Stimulation (PNS), respectively. Electrical stimulation typically results in the generation of Evoked Compound Action Potentials (ECAPs) by nerves within the patient.

Disclosure of Invention

Generally, the systems, devices, and techniques described herein are used to calibrate sensing circuitry for generating sensing signals, such as evoked action potential (ECAP) signals or brain resonance signals (e.g., ERNA), to help provide electrical stimulation therapy to a patient. ECAP signal may refer to a measure of the response of neural tissue to a stimulus. For example, in response to a stimulus, the nerve generates an ECAP signal, and a parameter (such as an amplitude value) of the ECAP signal may be a function of the degree of response of the nerve to the stimulus. The medical device may adjust the amount of stimulation based on the sensed ECAP signal, thereby providing a more effective treatment.

In one example, a system for providing therapy to a patient includes: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a first voltage on a first terminal and to sense a second voltage on a second terminal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit. The processing circuit is configured to cause the first voltage on the first terminal to be stored in a first calibration capacitor and the second voltage on the second terminal to be stored in a second calibration capacitor when the electrical stimulus is not provided by the stimulus generating circuit. The processing circuit is further configured to switch off a first calibration switch to prevent a change in the first voltage stored in the first calibration capacitor and switch off a second calibration switch to prevent a change in the second voltage stored in the second calibration capacitor after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor and when the stimulus generating circuit provides the electrical stimulus. The processing circuit is configured to determine a sense signal with the sense circuit based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off and when the stimulus generating circuit is not providing the electrical stimulus. The processing circuit is configured to provide therapy to the patient based on the sensing signal with a stimulus generation circuit.

In another example, a method includes: when the stimulus generating circuit does not provide electrical stimulus, causing, by the processing circuit, a first voltage on a first terminal of the sensing circuit to be stored in a first calibration capacitor and a second voltage on a second terminal of the sensing circuit to be stored in a second calibration capacitor; and after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, cutting off a first calibration switch by the processing circuit to prevent the first voltage stored in the first calibration capacitor from changing, and cutting off a second calibration switch by the processing circuit to prevent the second voltage stored in the second calibration capacitor from changing. The method further comprises: determining, by the processing circuit, a sense signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the electrical stimulus is not provided by the stimulus generating circuit; and causing, by the processing circuit, the stimulus generation circuit to deliver therapy to the patient based on the sensing signal.

In one example, a medical device includes: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a first voltage on a first terminal and to sense a second voltage on a second terminal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit. The processing circuit is configured to cause the first voltage on the first terminal to be stored in a first calibration capacitor and the second voltage on the second terminal to be stored in a second calibration capacitor when the electrical stimulus is not provided by the stimulus generating circuit; and after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch to prevent the second voltage stored in the second calibration capacitor from changing. The processing circuit is further configured to: determining, with the sensing circuit, a sensing signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the stimulus generating circuit does not provide the electrical stimulus; and causing the stimulus generation circuit to deliver therapy to the patient based on the sensing signal.

In another example, a system for providing therapy to a patient includes: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a sensing signal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit. The system further includes an amplifier circuit configured to: receiving the sense signal from the sense circuit; amplifying the sense signal using a transconductance amplifier to generate a first amplified sense signal; and preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus. The amplifier circuit is further configured to allow the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generation circuit does not provide the electrical stimulus, and to amplify the first amplified sense signal using the second stage amplifier to generate a second amplified sense signal. The processing circuit is configured to cause the stimulus generation circuit to deliver the therapy based on the second amplified sense signal.

In one example, a system for providing therapy to a patient includes: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a sensing signal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit. The processing circuit is configured to receive the sense signal from the sensing circuit and amplify the sense signal using a transconductance amplifier to generate a first amplified sense signal. The processing circuit is further configured to prevent the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generation circuit provides the electrical stimulus. The processing circuit is further configured to allow the first amplified sense signal to be received at the input of the second stage amplifier when the electrical stimulus is not provided by the stimulus generating circuit. The processing circuit is further configured to amplify the first amplified sense signal using the second stage amplifier to generate a second amplified signal. The processing circuit is configured to cause the stimulus generation circuit to deliver the therapy based on the second amplified sense signal.

This summary is intended to provide an overview of the subject matter described in this disclosure. This summary is not intended to provide an exclusive or exhaustive explanation of the systems, devices, and methods described in detail in the following figures and description. Further details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques will be apparent from the description and drawings, and from the claims.

Drawings

Fig. 1 is a conceptual diagram illustrating an example system including an Implantable Medical Device (IMD) in accordance with the techniques of this disclosure.

Fig. 2 is a block diagram of the example IMD of fig. 1 in accordance with one or more techniques of the present disclosure.

Fig. 3 is a conceptual diagram illustrating an example circuit of the IMD of fig. 1 according to one or more techniques of this disclosure.

Fig. 4 is a conceptual diagram illustrating an example analog circuit for determining a sensor signal according to one or more techniques of this disclosure.

Fig. 5 is a conceptual diagram illustrating an example digital circuit for determining a sensor signal according to one or more techniques of this disclosure.

Fig. 6 is a conceptual diagram illustrating an example digital circuit for determining a sensor signal according to one or more techniques of this disclosure.

Fig. 7 is a circuit diagram illustrating an example stimulation operational state in accordance with one or more techniques of the present disclosure.

Fig. 8 is a circuit diagram illustrating an example active charging operating state in accordance with one or more techniques of the present disclosure.

Fig. 9 is a circuit diagram illustrating an example passive charging operating state in accordance with one or more techniques of the present disclosure.

Fig. 10 is a waveform timing diagram illustrating an example operational state in accordance with one or more techniques of the present disclosure.

Fig. 11A and 11B are circuit diagrams illustrating examples of sensing circuitry during an auto-zero operating state in accordance with one or more techniques of the present disclosure.

Fig. 12 is a circuit diagram illustrating an example of a sensing circuit during a blocking operational state in accordance with one or more techniques of the present disclosure.

Fig. 13 is a circuit diagram illustrating an example of a sensing circuit during a signal acquisition operating state in accordance with one or more techniques of the present disclosure.

Fig. 14 is a circuit diagram illustrating an example transconductance amplifier according to one or more techniques of the present disclosure.

Fig. 15A and 15B are polar zero plan views illustrating examples of extracting a sense signal from a digitized waveform in accordance with one or more techniques of the present disclosure.

Fig. 16 is a plot illustrating an example sense signal in accordance with one or more techniques of the present disclosure.

Fig. 17 is a flowchart illustrating example operations of a sensing circuit for calibrating the IMD of fig. 1 in accordance with one or more techniques of the present disclosure.

Fig. 18 is a flow diagram illustrating an example operation of an amplifier circuit in accordance with one or more techniques of the present disclosure.

FIG. 19 is a flowchart illustrating example operations of feature extraction in accordance with one or more techniques of the present disclosure.

Fig. 20 is a flowchart illustrating example operations for providing therapy based on a sensing signal in accordance with one or more techniques of the present disclosure.

Detailed Description

The present disclosure describes examples of medical devices, systems, and techniques for calibrating sensing circuitry of a medical device configured to provide electrical stimulation therapy. Electrical stimulation therapy is typically delivered to a target tissue of a patient (e.g., nerve or muscle of the spinal cord) via two or more electrodes. The two or more electrodes may deliver control pulses configured to elicit an Evoked Compound Action Potential (ECAP) signal from nerve tissue of the patient, or deliver notification pulses configured to deliver therapy to the patient. In this disclosure, a "control pulse" may be a stimulation pulse used to trigger an ECAP signal. The control pulses may provide a therapeutic effect, but need not provide a therapeutic effect. The "notification pulse" may be a stimulation pulse that provides a therapeutic effect. The notification pulse may be "notified" in the sense that a parameter (e.g., amplitude, pulse width, or frequency) of the notification pulse may be based on sensing an ECAP signal generated as a result of the control pulse. The notification pulse may be considered to provide a management therapy or a controlled therapy. The administration therapy or controlled therapy may indicate that the stimulation pulses are for effective therapy.

The clinician and/or patient may select parameters of the electrical stimulation therapy (e.g., electrode combination, voltage amplitude, current amplitude, pulse width, or pulse frequency) to alleviate various symptoms, such as pain, neurological disorders, muscular disorders, and the like. In addition, parameters of the electrical stimulation therapy (e.g., notification pulses) may be adjusted in response to the measured ECAP. To accurately measure ECAP and provide more effective treatment, sensing circuitry configured to sense ECAP may be effectively calibrated.

The present disclosure describes an amplifier (e.g., a biological amplifier) and processing circuitry to measure amplitude values of Evoked Compound Action Potentials (ECAPs) of the human spinal cord. Such low power systems may use medical devices (e.g., implantable devices) that do not have a significant DC pathway to the body to detect very small signals (e.g., 10 μvpp (0-4.5 kHz)) within a short time (e.g., less than 200 us) after a large stimulus (e.g., about 10V), which may help to maximize patient safety. The measured amplitude value may be related to the amount of tissue captured by the electrical stimulation (which may vary with body position and other factors) to achieve optimal therapeutic level control.

Fig. 1 is a conceptual diagram illustrating an example system 100 including an IMD110 in accordance with the techniques of this disclosure. While the techniques described in this disclosure are generally applicable to a variety of medical devices including external devices and IMDs, for purposes of illustration, application of such techniques to IMDs, and more particularly, to implantable electrical stimulators (e.g., neurostimulators) will be described. More specifically, for purposes of illustration, the present disclosure will relate to implantable SCS systems, but are not limited to other types of medical devices or other therapeutic applications of medical devices.

As shown in fig. 1, system 100 includes IMD110, leads 108A and 108B, and an external programmer 150 shown with patient 102 (which is a human patient). In the example of fig. 1, IMD110 is an implantable electrical stimulator configured to generate and deliver electrical stimulation therapy to patient 102 via one or more of electrodes 132A and/or 132B (collectively, "electrodes 132") of leads 108A and/or 108B (collectively, "leads 108"), e.g., for alleviating chronic pain or other symptoms. In other examples, IMD110 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 the IMD110 may use to determine the posture state assumed by the patient 102 and/or to determine how to adjust one or more parameters defining the stimulation therapy. The control pulse may provide a therapeutic effect, but in one or more examples the control pulse may not provide a therapeutic effect. IMD110 may be configured to deliver notification pulses to provide a therapeutic effect. The notification pulse may be "notified" in that a parameter of the notification pulse may be based on an ECAP signal generated by the delivery of the control pulse. The notification pulse may be considered to provide controlled therapy. The management therapy may indicate that the stimulation pulses are for effective therapy. The control pulse may be "controlled" in that delivery of the control pulse is used to control the parameters of the notification pulse.

IMD110 may be a chronic electrical stimulator that remains implanted in patient 102 for weeks, months, or even years. In other examples, IMD110 may be a temporary or trial stimulator for screening or evaluating the efficacy of electrical stimulation for chronic therapy. In one example, IMD110 is implanted within patient 102. In some examples, a medical device configured to perform techniques similar to IMD110 may be an external device coupled to a percutaneously implanted lead. In some examples, IMD110 uses one or more leads, while in other examples, IMD110 is leadless.

IMD110 may be constructed of any polymer, metal, or composite material sufficient to house the components of IMD110 (e.g., the components shown in fig. 2) within patient 102. In this example, IMD110 may be constructed from a biocompatible housing (such as titanium or stainless steel) or a polymeric material (such as silicone, polyurethane, or liquid crystal polymer) and surgically implanted in a location near the pelvis, abdomen, or buttocks of patient 102. In other examples, IMD110 may be implanted within other suitable locations within patient 102, which may depend on, for example, the target location within patient 102 where electrical stimulation therapy needs to be delivered. The housing of IMD110 may be configured to provide an airtight seal for components such as a rechargeable or non-rechargeable power source. Additionally, in some examples, the housing of IMD110 is selected from a material that facilitates receiving energy to charge a rechargeable power source.

For example, electrical stimulation energy (which may be constant current or constant voltage based pulses) is delivered from IMD 110 to one or more target tissue sites of patient 102 via one or more electrodes 132 of implantable lead 108. In the example of fig. 1, the lead 108 carries an electrode 132 that is placed near the spinal cord 106 of the target tissue. One or more of the electrodes 132 may be disposed at the distal end of the lead 108 and/or at other locations along the mid-point of the lead. Leads 108 may be implanted and coupled to IMD 110. The electrodes 132 may deliver electrical stimulation generated by an electrical stimulation generator in the IMD 110 to tissue of the patient 102. Although the leads 108 may each be a single lead, the leads 108 may include lead extensions or other segments that may facilitate implantation or positioning of the leads 108. In some examples, IMD 110 may be a leadless stimulator with one or more electrode arrays disposed on a stimulator housing rather than on leads extending from the housing. Additionally, in some examples, system 100 may include one lead or more than two leads, each coupled to IMD 110 and directed to a similar or different target tissue site.

The electrodes 132 of the lead 108 may be electrode pads on a paddle lead, circular (e.g., ring) electrodes around the lead body, conformable electrodes, cuff electrodes, segmented electrodes (e.g., electrodes disposed at different circumferential locations on the lead instead of a continuous ring electrode), any combination thereof (e.g., ring electrodes and segmented electrodes), or any other type of electrode capable of forming a monopolar, bipolar or multipolar electrode combination for treatment. Ring electrodes disposed at different axial locations at the distal end of lead 108 will be described for illustrative purposes.

The deployment of the electrodes 132 via the leads 108 is described for illustration purposes, but the array of electrodes 132 may be deployed in different ways. For example, a housing associated with a leadless stimulator may carry an array of electrodes 132, e.g., in the form of rows and/or columns (or other patterns), to which a shifting operation may be applied. Such electrodes 132 may be arranged as surface electrodes, ring electrodes or protrusions. Alternatively, the electrode array may be formed by rows and/or columns of electrodes 132 on one or more paddle leads. In some examples, the electrode array includes electrode segments disposed at respective locations on the periphery of the lead, for example, in the form of one or more segmented rings disposed on the circumference of a cylindrical lead. In other examples, the one or more leads 108 are linear leads with 8 ring electrodes along the axial length of the leads. In another example, the electrode 132 is a segmented ring disposed in a linear fashion along the axial length of the lead and at the periphery of the lead.

The stimulation parameter set of the stimulation program (which defines the stimulation pulses of the electrical stimulation therapy by the electrodes of lead 108) may include information identifying which electrodes 132 have been selected for delivering stimulation according to the stimulation program, the polarity of the selected electrodes 132 (i.e., the combination of electrodes used for the program), the voltage amplitude, current amplitude, pulse frequency, pulse width, or pulse shape of the stimulation delivered by electrodes 132. These stimulation parameter values that make up the stimulation parameter set that defines the pulses may be predetermined parameter values that are user-defined and/or automatically determined by the system 100 based on one or more factors or user inputs. The notification pulse may be defined by a set of notification stimulation parameter values and the control pulse may be defined by a set of control stimulation parameter values.

Although fig. 1 relates to SCS therapy, for example, for treating pain, in other examples, system 100 may be configured to treat any other condition that may benefit from electrical stimulation therapy. In some examples, the system 100 may be configured to use the initial stimulus and the base stimulus together to provide a multi-modal stimulus. In some examples, the system 100 may be used to treat tremor, parkinson's disease, epilepsy, pelvic floor disorders (e.g., urinary or other bladder dysfunction, fecal incontinence, pelvic pain, bowel dysfunction or sexual dysfunction), obesity, gastroparesis, or mental disorders (e.g., depression, mania, obsessive-compulsive disorder, anxiety, etc.). In this manner, the system 100 may be configured to provide therapy in 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 the patient 102.

In some examples, the leads 108 include one or more sensors configured to allow the IMD 110 to monitor one or more parameters of the patient 102, such as patient activity, pressure, temperature, or other characteristics. One or more sensors may be provided to supplement or replace therapy delivery by lead 108. Instead of, or in addition to, lead 108 including such a sensor, IMD 110 may include such a sensor.

IMD 110 may be configured to deliver electrical stimulation therapy (e.g., notification pulses and/or control pulses in the form of an initial pulse train and a basic pulse train, respectively) to patient 102 via a selected combination of electrodes 132 carried by one or both leads 108, alone or in combination with electrodes carried or defined by the housing of IMD 110. The target tissue for the electro-stimulation therapy may be any tissue affected by an electro-stimulation, which may be in the form of an electro-stimulation pulse or a continuous waveform. In some examples, the target tissue includes nerves, smooth muscle, or skeletal muscle. In the example shown in fig. 1, the target tissue is tissue near the spinal cord 106, such as within the intrathecal or epidural space of the spinal cord 106, or in some examples, adjacent nerves branching off from the spinal cord 106.

The lead 108 may be introduced into the spinal cord 106 via any suitable area, such as the thoracic, cervical, or lumbar areas. Stimulation of the spinal cord 106 may, for example, prevent pain signals from propagating through the spinal cord 106 and reaching the brain of the patient 102. The patient 102 may perceive the interruption of the pain signal as a reduction in pain and thus as an effective therapeutic result. In other examples, stimulation of the spinal cord 106 may produce paresthesia, which may reduce the perception of pain by the patient 102 and thus provide effective therapeutic results. In some examples, stimulation of the spinal cord 106 or other anatomical structures associated with the spinal cord (e.g., nerves and cells associated with the nervous system) may alleviate symptoms that may not produce paresthesia. For example, IMD110 may deliver stimulation having an intensity (e.g., amplitude value and/or pulse width value) below a sensory or perception threshold (e.g., subthreshold stimulation) that reduces pain without producing paresthesia. For example, in multi-modal stimulation, IMD110 may deliver one burst at a higher frequency via one electrode combination and a second burst at a lower frequency interleaved via a second electrode combination, where both bursts are delivered at sub-threshold intensities.

IMD 110 may be configured to generate and deliver electrical stimulation therapy to a target stimulation site within patient 102 via electrodes 132 of lead 108 to patient 102 according to one or more therapy stimulation procedures. The therapeutic stimulation program may typically define a notification pulse, but a control pulse may also be defined if the control pulse also contributes to the therapeutic effect. The therapy stimulation program may define values for one or more parameters (e.g., parameter sets) that define an aspect of the therapy delivered by IMD 110 in accordance with the program. For example, a therapeutic stimulation program that controls IMD 110 to deliver stimulation in the form of pulses may define the voltage, current, pulse width, pulse rate (e.g., pulse frequency), electrode combination, or pulse shape of stimulation pulses delivered by IMD 110 according to the program. In some examples, one or more therapeutic stimulation programs define a plurality of different pulse trains having different parameter values (e.g., different pulse frequencies, amplitude values, pulse widths, and/or electrode combinations) but delivered interlaced to together provide therapy to the patient.

Further, IMD 110 may be configured to deliver control stimulation (e.g., control pulses and/or notification pulses) to patient 102 via a combination of electrodes 132 of leads 108, alone or in combination with electrodes carried or defined by the housing of IMD 110, in order to detect ECAP signals. The tissue targeted for stimulation may be the same or similar tissue targeted for electrical stimulation therapy, but IMD 110 may deliver stimulation pulses via the same electrodes, at least some of the same electrodes, or different electrodes of electrodes 132 for ECAP signal detection. Because the control stimulation pulses may be delivered in an interleaved manner with the notification pulses (e.g., when pulses configured to facilitate treatment interfere with detection of ECAP signals or pulse sweeps intended for posture state detection via ECAP signals do not correspond to pulses intended for therapeutic purposes), a clinician and/or user may select any desired combination of electrodes 132 for the notification pulses (i.e., controlled treatment). As with electrical stimulation therapy, the control stimulus may be in the form of electrical stimulation pulses or continuous waveforms.

For example, each control stimulus pulse may comprise a balanced biphasic square wave pulse employing an active charging phase. However, in other examples, the control stimulation pulses may include monophasic pulses followed by passive charging phases. In other examples, the control pulse may include an unbalanced biphasic portion and a passive charging portion. Although not required, the biphasic control pulse may include an inter-phase spacing between the positive and negative phases to facilitate propagation of nerve impulses in response to the first phase of the biphasic pulse. The control stimulus may be delivered without interrupting the delivery of the electrical stimulus notification pulse, such as during a window between successive notification pulses. The control pulse may induce an ECAP signal from tissue, and IMD 110 may sense the ECAP signal via two or more electrodes 132 on lead 108. Where a control stimulation pulse is applied to the spinal cord 106, the IMD 110 may sense signals from the spinal cord 106.

A user (e.g., a clinician or patient 102) may interact with a user interface of an external programmer 150 to program IMD 110. Programming IMD 110 may generally refer to generating and transmitting commands, programs, or other information for controlling the operation of IMD 110. In this manner, IMD 110 may receive transmitted 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 inputs, or other information for controlling operation of IMD 110, e.g., via wireless telemetry or a wired connection.

In some examples, if the external programmer 150 is primarily intended for use by a physician or clinician, it may be characterized as a physician or clinician programmer. In other cases, if the external programmer 150 is primarily intended for use by a patient, it may be characterized as a patient programmer. The patient programmer is generally accessible to the patient 102 and in many cases it may be a portable device that can accompany the patient 102 throughout the patient's daily life. For example, the patient programmer may receive input from the patient 102 when the patient wishes to terminate or alter the electrical stimulation therapy, or when the patient perceives that stimulation is being delivered. In general, a physician or clinician programmer may support a clinician in selecting and generating programs for use by the IMD 110, while a patient programmer may support a patient in adjusting and selecting these programs during normal use. In other examples, external programmer 150 may include or be part of an external charging device that charges a power supply of IMD 110. In this manner, a user may program and charge IMD 110 using a device or devices.

As described herein, information may be transferred between external programmer 150 and IMD 110. Accordingly, 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, radio Frequency (RF) telemetry and inductive coupling, although other techniques are also contemplated. In some examples, external programmer 150 includes a communication head that may be placed near the patient's body near the IMD 110 implantation site to improve the quality or security of communication between IMD 110 and external programmer 150. Communication between external programmer 150 and IMD 110 may occur during or separate from power transfer.

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

Efficacy of the electrical stimulation therapy may be indicated by one or more characteristics of the action potential induced by the control pulse delivered by IMD 110 (e.g., an amplitude value between one or more peaks or an area under the curve of one or more peaks) (i.e., a characteristic value of the ECAP signal). Electrical stimulation therapy delivered through leads 108 of IMD 110 may cause neurons within the target tissue to induce composite action potentials that propagate up and down from the target tissue, ultimately reaching the sensing electrodes of IMD 110 (e.g., the electrodes assigned for sensing among electrodes 132). For example, stimulation may elicit at least one ECAP signal, and ECAP in response to stimulation may also be an alternative indicator of therapeutic effectiveness. The amount of action potential induced (e.g., the number of neurons that propagate the action potential signal) may be based on various parameters of the electrical stimulation pulse, such as amplitude value, pulse width, frequency, or 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 the current amplitude value of each control pulse at the beginning and/or end of each phase within each control pulse or pulse. For example, a very high slew rate indicates that the edges of the pulse are steep or even nearly vertical, while a low slew rate indicates that the amplitude value of the control pulse has a longer ramp up (or ramp down). In some examples, these parameters contribute to the intensity of the electrical stimulus. In addition, the characteristics (e.g., amplitude values) of the ECAP signal may vary based on the distance between the stimulation electrode and the nerve affected by the electric field generated by the delivered control pulse.

Some example techniques for adjusting stimulation parameter values of stimulation pulses (e.g., notification pulses and/or control pulses that may or may not contribute to patient treatment) are based on comparing measured characteristic values of ECAP signals to target ECAP characteristic values. In response to delivering a control pulse defined by a set of stimulation parameter values, IMD 110 senses the electrical potential of tissue of spinal cord 106 of patient 102 via two or more electrodes disposed on lead 108 to measure the electrical activity of the tissue. IMD 110 senses ECAP from target tissue of patient 102, for example, using electrodes on one or more leads 108 and associated sensing circuitry. In some examples, IMD 110 may receive sensor signals indicative of ECAP from one or more sensors (e.g., one or more electrodes and circuitry) internal or external to patient 102. Such example signals may include sensor signals indicative of ECAPs of tissue of the patient 102. Examples of the one or more sensors include one or more sensors configured to measure a composite action potential of the patient 102 or a physiological effect indicative of the composite action potential. For example, to measure the physiological effects of the composite action potential, the one or more sensors may be accelerometers, pressure sensors, bending sensors, sensors configured to detect the posture of the patient 102, or sensors configured to detect the respiratory function of the patient 102. In some examples, external programmer 150 may receive sensor signals indicative of composite action potentials in target tissue of patient 102 and may transmit notifications of the sensor signals to IMD 110.

In the example of fig. 1, IMD 110 is described as performing a number of processing and computing functions. However, the external programmer 150 may alternatively perform one, several, or all of these functions. In this example, IMD 110 is used to relay the sensed signals to external programmer 150 for analysis, and external programmer 150 transmits instructions to IMD 110 to adjust one or more parameters defining the electrical stimulation therapy based on the analysis of the sensed signals. For example, IMD 110 may relay the sensed signal indicative of ECAP to external programmer 150. External programmer 150 may compare the parameter values of the ECAP to the target ECAP characteristic values, and in response to the comparison, external programmer 150 may instruct IMD 110 to adjust one or more stimulation parameters defining the electrical stimulation notification pulses (and, in some examples, control pulses) delivered to patient 102.

In some examples, the system 100 may change the target ECAP characteristic value and/or the growth rate(s) over a period of time, such as in accordance with a change in the stimulation threshold (e.g., a patient-specific perception threshold or detection threshold). The system 100 may be programmed to change the target ECAP characteristic in order to adjust the intensity of the notification pulse (e.g., controlled therapy) to provide the patient with a different sensation (e.g., increase or decrease the amount of nerve activation). Although the system 100 may change the target ECAP characteristic value, the received ECAP signal may be used by the system 100 to adjust one or more parameter values of the notification pulse and/or the control pulse to meet the target ECAP characteristic value.

One or more devices within system 100, such as 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 of ECAP signals, and processing circuitry. The processing circuit may be configured to control the stimulus generation circuit to deliver a plurality of electrical stimulation pulses (e.g., one or more control pulses) having different amplitude values, and to control the sensing circuit to detect a respective ECAP signal of the plurality of ECAP signals after delivery of each of the plurality of electrical stimulation pulses.

In some examples, one or more electrodes of the IMD 110 that "deliver" therapy may be mentioned. In these cases, the stimulation generation circuitry of IMD 110 may be connected to one or more electrodes 132 and configured to "use" or "deliver therapy on" one or more electrodes 132. In some examples described herein, one or more electrodes 132 of the IMD 110 that "sense" ECAP signals may be mentioned. In these cases, the sensing circuitry of IMD 110 may be connected to one or more electrodes 132 and configured to "use" one or more electrodes 132 or "sense ECAP signals on" these electrodes. A set (e.g., a pair) of one or more electrodes 132 may be used to sense ECAP signals, while a different set (e.g., a pair) of one or more electrodes 132 may be used to deliver therapy. Although ECAP signals are mentioned above, similar techniques may be used for other sense signals. In some examples, certain states of charge (e.g., active charge or passive charge) may be referred to as being "on" one or more electrodes 132 of IMD 110. In these cases, the circuitry connected to one or more electrodes 132 may be "in" a particular state of charge.

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

Although electrical stimulation is generally described herein in terms of electrical stimulation pulses, electrical stimulation may be delivered in non-pulsed form in other examples. For example, electrical stimulation may be delivered as signals having various waveform shapes, frequencies, and amplitude values. Thus, the electrical stimulus in the form of a non-pulsed signal may be a continuous signal, possibly with a sinusoidal waveform or other continuous waveform.

In some examples, sensing circuitry of IMD 110 may be coupled to control electrodes of one or more electrodes 132 and to steering electrodes of one or more electrodes 132. The control electrode may be configured to deliver control pulses to the patient tissue that elicit ECAP signals from the tissue of the patient 102. The steering electrode may be configured to deliver controlled therapy (e.g., notification pulses) to patient tissue that provides therapy to patient 102. The sensing circuit may include one or more amplifiers configured to amplify the ECAP signal within the circuit to more accurately sense the ECAP signal. The sensing circuit may further include a processing circuit configured to enter an active state of charge on the control electrode and to enter a passive state of charge on the control electrode after entering the active state of charge. The active state of charge and the passive state of charge are explained in more detail below. The processing circuit may also be configured to calibrate or auto-zero the operational amplifier of the sensing circuit when the control electrode is in a passive state of charge.

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, sensors 210, telemetry circuitry 212, power source 214, and memory 216. Each of these circuits may be or include a circuit of programmable or fixed functionality, which may perform the functions attributed to the corresponding circuit. For example, the processing circuitry 208 may include fixed functionality or programmable circuitry, the stimulus generation circuitry 204 may include circuitry that may generate electrical stimulus signals, such as pulses or continuous waveforms, on one or more channels, the sensing circuitry 206 may include sensing circuitry for sensing signals, and the telemetry circuitry 212 may include telemetry circuitry for transmitting and receiving signals. Memory 216 may store computer readable instructions that, when executed by processing circuitry 208, cause IMD 200 to perform various functions described herein. The memory 216 may be a storage device or other non-transitory medium.

In the example shown in fig. 2, memory 216 may store patient data 218, which may include any data related to the patient, such as one or more patient postures, activity levels, or a combination of patient postures and activity levels. The memory 216 may store the stimulation parameter settings 220 within the memory 216 or within a separate area within the memory 216. Each stored stimulation parameter setting 220 defines values for one or more sets of electrical stimulation parameters (e.g., parameters that inform the set of stimulation parameters and control the set of stimulation parameters, or other bursts). The stimulation parameter settings 220 may also include additional information, such as instructions regarding delivering electrical stimulation signals based on stimulation parameter relationship data, which may include a relationship between two or more stimulation parameters based on data of electrical stimulation signals delivered to the patient 102 or data transmitted from the external programmer 104. The stimulus parameter relationship data can include measurable aspects associated with the stimulus, such as ECAP characteristic values.

Thus, in some examples, stimulation generation circuitry 204 may generate electrical stimulation signals (e.g., notification pulses and/or control pulses) in accordance with the electrical stimulation parameters described above. Other stimulation parameter value ranges may also be used, which may depend on the target stimulation site within the patient 102. Although stimulation pulses are described, the stimulation signals may have any form, such as continuous time signals (e.g., sine waves or cosine waves), and the like.

The sensing circuit 206 may be configured to monitor signals from any combination of the electrodes 232, 234. In some examples, the sensing circuit 206 includes one or more amplifiers, filters, and analog-to-digital converters. The sensing circuit 206 may be used to sense physiological signals, such as ECAP. In some examples, the sensing circuit 206 detects ECAP from a particular combination of electrodes 232, 234. In some examples, the particular electrode combination used to sense ECAP includes a different electrode than the set of electrodes 232, 234 used to deliver the control stimulation pulse and/or the notification stimulation pulse. In some examples, the particular electrode combination used to sense ECAP includes at least one of the same set of electrodes used to deliver notification and/or control stimulation pulses to the patient 102. The sensing circuit 206 may provide signals to an analog-to-digital converter (ADC) for conversion into digital signals for processing, analysis, storage, or output by the processing circuit 208.

The processing circuitry 208 may include any one or more of the following: a microprocessor, controller, digital Signal Processor (DSP), application Specific Integrated Circuit (ASIC), field Programmable Gate Array (FPGA), discrete logic, or any other processing circuit capable of providing the functionality attributed to processing circuit 208, which may be embodied herein as firmware, hardware, software, or any combination thereof. The processing circuitry 208 may control the stimulation generation circuitry 204 to generate electrical stimulation signals in accordance with the stimulation parameter settings 220 stored in the memory 216 to apply stimulation parameter values, such as pulse amplitude values, pulse width, pulse frequency, and/or waveform shape, for each electrical stimulation signal.

In the example of fig. 2, a set of electrodes 232 includes electrodes 232A, 232B, 232C, and 232D, and a 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. The processing circuitry 208 also controls the stimulus generation circuitry 204 to generate and apply electrical stimulus signals to selected combinations of the electrodes 232, 234. In some examples, the stimulation generation circuit 204 includes switching circuitry that can couple the stimulation signals to selected conductors within the leads 230, which in turn can deliver the stimulation signals across the selected electrodes 232, 234. Such a switching circuit may be a switching array, a switching matrix, a multiplexer, or any other type of switching circuit capable of selectively coupling stimulation energy to selected electrodes 232, 234 and selectively utilizing the selected electrodes 232, 234 to sense bioelectrical nerve signals (not shown in fig. 2) of the spinal cord of the patient.

As shown, the stimulus generation circuit 204 may not include a switching circuit. In these examples, the stimulus generation circuit 204 may include multiple pairs of voltage sources, current sources, voltage sinks, or current sinks connected to each electrode 232, 234 such that each pair of electrodes has a unique signal circuit. In other words, in these examples, each of the electrodes 232, 234 may be independently controlled via its own signal circuitry (e.g., via a regulated voltage source and sink or a combination of regulated current sources and sinks), as opposed to a switching signal between the electrodes 232, 234.

The electrodes 232, 234 on the respective leads 230 may be configured in a variety of different designs. For example, one or both leads 230 may include one or more electrodes at each longitudinal location along the length of the lead, such as one electrode at each location A, B, C, D at a different peripheral location on the periphery of the lead. In one example, the electrodes may be electrically coupled to the stimulation generation circuitry 204 via respective wires that are straight or coiled within the housing of the lead and extend to a connector at the proximal end of the lead. In another example, each electrode on the lead may be an electrode disposed on the film. The membrane may include a conductive trace for each electrode that extends the length of the membrane to the proximal connector. The film may then be wrapped (e.g., helically) around the inner member to form the leads 230. These and other configurations can be used to construct leads with complex electrode geometries.

Although in fig. 2 sensing circuitry 206 is embedded in a common housing with stimulation generation circuitry 204 and processing circuitry 208, in some examples sensing circuitry 206 may be in a different housing than IMD 200 and may communicate with processing circuitry 208 via wired or wireless communication techniques.

In some examples, one or more of electrodes 232 and 234 may be adapted to sense ECAP. For example, electrodes 232 and 234 may sense a voltage magnitude of a portion of the ECAP signal, where the sensed voltage magnitude is a characteristic of the ECAP signal.

Memory 216 may be configured to store information within IMD 200 during operation. Memory 216 may include a computer-readable storage medium or a computer-readable storage device. In some examples, memory 216 includes one or more of short-term memory or long-term memory. The memory 216 may include, for example, a Random Access Memory (RAM), dynamic Random Access Memory (DRAM), static Random Access Memory (SRAM), magnetic disk, optical disk, flash memory, or in the form of electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). In some examples, memory 216 is used to store data indicative of instructions executed by processing circuitry 208. As discussed herein, the memory 216 may store patient data 218, stimulation parameter settings 220, and control strategy data 224.

The sensor 210 may include one or more sensing elements that sense the value of the corresponding patient parameter. As described, electrodes 232 and 234 may be electrodes that sense ECAP values indicative of target stimulation intensities via sensing circuit 206. The sensors 210 may include one or more accelerometers, optical sensors, chemical sensors, temperature sensors, pressure sensors, or any other type of sensor. The sensor 210 may output patient parameter values that may be used as feedback to control the delivery of the electrical stimulation signal. IMD 200 may include additional sensors that are coupled within the housing of IMD 200 and/or via lead 108 or one of the other leads. Additionally, IMD 200 may wirelessly receive sensor signals from remote sensors, for example, via telemetry circuitry 212. In some examples, one or more of these remote sensors may be located outside the patient (e.g., carried on the outer surface of the skin, attached to clothing, or otherwise positioned outside the patient). In some examples, the signal from the sensor 210 may indicate a posture state (e.g., sleep, awake, sitting, standing, etc.), and the processing circuitry 208 may select the target and/or threshold ECAP characteristic value based on the indicated posture state.

Telemetry circuitry 212 supports wireless communication between IMD 200 and an external programmer (not shown in fig. 2) or another computing device under control of processing circuitry 208. Processing circuitry 208 of IMD 200 may receive values of various stimulation parameters (such as amplitude values and/or electrode combinations (e.g., for notification and/or control pulses)) from an external programmer via telemetry circuitry 212 as updates to the program. Updates to the stimulation parameter settings 220 and the input efficacy threshold settings 226 may be stored in the memory 216. Telemetry circuitry 212 in IMD 200, as well as telemetry circuitry in other devices and systems described herein (e.g., external programmers) may enable communication via Radio Frequency (RF) communication techniques. In addition, telemetry circuitry 212 may communicate with an external medical device programmer (not shown in fig. 2) via proximity inductive interactions of IMD 200 with the external programmer. The external programmer may be one example of external programmer 104 of fig. 1. Thus, telemetry circuitry 212 may send information to an external programmer continuously, at periodic intervals, or upon request by IMD110 or an external programmer.

Power supply 214 may deliver operating power to various components of IMD 200. The power source 214 may include a rechargeable or non-rechargeable battery, and a power generation circuit for generating operating power. Charging may be accomplished by a proximity inductive interaction between an external charger and an inductive charging coil within IMD 200. In other examples, a conventional primary cell may be used. In some examples, the processing circuitry 208 may monitor the remaining charge (e.g., voltage) of the power supply 214 and select stimulation parameter values that may deliver similarly effective therapies at lower power consumption levels when needed to extend the run time of the power supply 214.

The stimulation generation circuitry 204 of the IMD 200 may receive instructions via the telemetry circuitry 212 to deliver electrical stimulation to a target tissue site of the patient's spinal cord according to the stimulation parameter settings 220 via the plurality of electrode combinations of the electrodes 232, 234 of the lead 230 and/or the housing of the IMD 200. Each electrical stimulation signal may trigger an ECAP signal sensed by sensing circuitry 206 via electrodes 232 and 234. The processing circuitry 208 may receive information indicative of ECAP signals generated in response to the electrical stimulation signal(s) via the electrical signals sensed by the sensing circuitry 206 (e.g., values indicative of characteristics of ECAP in electrical units such as voltage or power). The stimulation parameter settings 220 may be updated according to ECAP recorded on the sensing circuit 206. While the above discussion relates to ECAP signals, some examples may be directed to other sense signals.

Fig. 3 is a conceptual diagram illustrating an example circuit 300 of the IMD of fig. 1 according to one or more techniques of this disclosure. In this example, the sensor circuit 307 of the sense chip 309 may be configured to detect a sense signal (e.g., ECAP signal). For example, the sensor circuit 307 may use a multiplexer 330 (also referred to herein as a "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 detail in fig. 4 and 10. The amplifier 334 may be configured to amplify the sense signal generated by the auto-zero circuit 332, examples of which are discussed with reference to fig. 5. The successive approximation register analog-to-digital converter 336 (also referred to herein as "SAR ADC 336") may represent the sensed signal as a digital value. The feature extraction and configurable flip-flop unit 338 may be configured to extract features (e.g., ECAP features) from the digitized sensing signals output by the SAR ADC336, examples of which are discussed with reference to fig. 15A, 15B, 16.

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. Any of the one or more electrodes 132 (e.g., 17 electrodes) may be selected at the device level as the sensing electrode pair 432. For unsensed channels, the MUX/blanking switches may remain open (e.g., NMOS gate grounded) always disconnecting them from the calibration capacitors 452, 453 (e.g., 2 shared 5.0nF capacitors). For purposes of example only, only selected pairs of sense electrodes 432 are shown in the following figures.

The sensing circuit 206 of fig. 2 may be configured to sense ECAP signals from patient tissue. The sensing circuit 206 may include the circuit 400 prior to output to the amplifier circuit 456, where the amplifier circuit 456 may be configured to amplify a sensing signal (e.g., ECAP signal) sensed by the sensing circuit 206. Circuit 400 may include electrode 432, feed-through capacitors 440, 441, ac coupling capacitor 442, ground circuits 444, 445, blanking circuit 446, calibration capacitors 452, 453, and auto-zero circuit 454. The ground circuits 444, 445 may provide a high impedance ground (e.g., battery ground) for the circuit 400 to ground.

Electrode 432 may be an example of electrodes 232, 234 of fig. 2 and may be coupled to circuit 400. For example, the electrode 432 may rest on patient tissue (e.g., spinal cord) of the patient 102. Electrode 432 may include a control electrode configured to deliver control pulses to patient tissue that elicit ECAP signals from patient tissue. Electrode 432 may also include a steering electrode configured to deliver controlled therapy (e.g., notification pulses) to patient tissue that provides therapy to patient 102. One or more electrodes 432 may collect ECAP signals from patient tissue and provide an electrical signal representative of an amplitude value of the ECAP signals to the sensing circuitry of circuit 400.

AC coupling capacitor 442 may prevent charge accumulated on electrode 432 from affecting the patient by holding charge while stimulation generation circuitry 204 of IMD 200 provides therapy to patient tissue. Blanking circuit 446 may block the sense signal during the stimulated and active charge states. For example, the first switches 449, 451 may be configured to switch off the calibration capacitors 452, 453, respectively, when the stimulus generating circuit 204 provides a stimulus and when the stimulus generating circuit 204 provides active recovery.

After entering the active state of charge, the stimulus generation circuit 204 can be configured to enter a passive state of charge on the control electrode. The active state of charge may use relatively large power consumption from the power source 214 of the IMD 200 to generate opposing currents. To conserve power to extend the life of IMD 200, at least a portion of the active state of charge in stimulation generation circuitry 204 may be replaced with a passive state of charge. When in a passive charge state, in this example, the switching elements 449, 451 may be configured to turn on the calibration capacitors 452, 453, respectively, when the stimulus generating circuit 204 is not providing a stimulus and during a signal acquisition state. Resistors 448, 450 may help limit the amount of current in circuit 400.

When operating in a passive state of charge, the processing circuit 208 may automatically zero the output to the amplifier circuit 456. Auto-zeroing the output may calibrate the sensing circuit 206 for detecting the sensing signal from the patient tissue. To auto-zero the output, the processing circuit 208 may close the calibration switches 460, 461 of the auto-zero circuit 454 to connect the output to ground. The offset that may be stored on the calibration capacitors 452, 453 during passive charging may be used to provide common mode rejection seen at the input of the amplifier circuit during the signal acquisition state, which may improve the accuracy of the sense signal (e.g., ECAP signal) generated during the signal acquisition state.

The processing circuitry 208 of the IMD 200 may cause the stimulation generation circuitry 204 to deliver controlled therapy to the patient on the guard electrodes after sensing the evoked compound action potential signals. For example, the processing circuitry 208 may be configured to cause the sensing circuitry 206 to sense a sensing signal (e.g., ECAP signal) during a passive state of charge. After sensing the sensing signals, the processing circuitry 208 may cause the stimulus generation circuitry 204 to deliver controlled therapy to patient tissue on the steering electrode based on the sensing signals.

Fig. 5 is a conceptual diagram illustrating an example digital circuit 500 for determining a sensor signal according to one or more techniques of this disclosure. In this example, the first amplifier stage 565 of the amplifier circuit 563 may pre-amplify a sense signal output by an analog circuit (e.g., analog circuit 400 of fig. 4).

As shown, the first amplifier stage 565 may include a transconductance amplifier (referred to herein as a "GMR amplifier"), which is discussed in further detail in fig. 14. As used herein, GMR may refer to transconductance (gm) times resistance (R). Transconductance (gm) may refer to the transconductance of an input stage that converts a differential voltage into a differential current (e.g., gm=iout/Vin). Iout then passes through a resistor "R", yielding vout=r×iout. Vout/vin=gm×r for these 2 steps. Thus, these circuits are referred to herein as "GMR" circuits.

The first amplifier stage 565 may comprise a direct GMR stage with a gain of 10, a low pass filter of 60kHz, a current consumption of 8.5 ua, a clamp applied to the internal nodes to quickly recover out of range conditions, and an offset injection of +/-30mV at the output of the stage (reference input +/-3 mV). The circuit 500 may include an alternative blanking timing circuit 566, which may provide a blanking function. For example, the alternative blanking timing circuit 566 may shut off the second amplifier stage 567 during the stimulated state and/or the active recovery state. In this example, the alternative blanking timing circuit 566 may turn on the second amplifier stage 567 during the passive state of charge. The alternative blanking timing circuit 566 may switch off the second amplifier stage 567 during the controlled therapy state.

The second amplifier stage 567 may be configured to auto-zero at the input and may comprise a direct GMR with a gain of 20. When the input exceeds a threshold voltage range (e.g., about +/-20 mV), the direct GMR level may become non-linear. The second amplifier stage 567 may include a tunable low pass filter of 7.5kHz. The second amplifier stage 567 may be configured to add a trimmable amount of capacitance at the output of the stage to change the pole from, for example, 60kHz to 7.5kHz. The gain of the second amplifier stage 567 may be 20 compared to the gain 10 of the first amplifier stage 565. The power usage of the second amplifier stage 567 may be less than the power usage of the first amplifier stage 565 because the first amplifier stage 565 amplifies noise by a factor of 10. Noise power is inversely proportional to the current in these stages. The second amplifier stage 567 may include a current of 2.75 μΑ.

The third amplifier stage 568 may be configured to auto-zero at the input and may include a linearized GMR having a gain of 2.85 to 20. The linearization GMR stage may apply an inner loop feedback technique to provide a linear transfer function for larger input signals.

The fourth amplifier stage 569 may be configured to auto-zero at the input, output voltages of 100mV to 1300mV, may include an S/H buffer with a gain of 1, and current of 1.5 μA. The output of the fourth amplifier stage 569 may be digitized by a SAR ADC 571. The fourth amplifier stage 569 may convert the high impedance input signal to a low impedance output signal. For example, the fourth amplifier stage 569 may rapidly load a 19pF sample and hold capacitor from ground with a signal voltage to sub-mV accuracy within about 5 μs. For example, the fourth amplifier stage 569 may include a cascaded source follower unity gain buffer.

Fig. 6 is a conceptual diagram illustrating an example digital circuit 600 for determining a sensor signal according to one or more techniques of this disclosure. In the example of fig. 6, circuit 600 may calculate a plurality (e.g., 1 to 4) of overlapping rolling sums (or averages) of waveforms (e.g., 1 to 31 waveforms) (670), which may reduce noise. The circuit 600 may then apply a Finite Impulse Response (FIR) filter, which may be configurable, odd, symmetrical, time-varying edge processing (671), for example, which may further reduce noise. The circuit 600 may perform a derivative of the output of step 670 to protect the artifact from the presence of additive linear artifacts (see step 1904 of fig. 19). The circuit 600 may select the average value, or derivative of the average value, directly from step 670 as the input to the FIR filter.

In this example, circuit 600 may apply an interpolator (e.g., a 4x interpolator) that uses zero insertion (e.g., 3 zero insertions) per input data point, followed by a FIR quarter low pass, and implemented, for example, in a polyphase form to improve efficiency (672). The circuit 600 may perform additive linear artifact-invariant amplitude extraction (673), which will be described in further detail with reference to step 1908 of fig. 19, and generate a waveform observable register set (674). In this example, the circuit 600 may output a representation of the waveform to a Master Control Unit (MCU) (675) via a local mein force scalable programmable sensor bus (MEPS) bus transmitter using MEPS multiplexer (676). While the above examples use MEPS, some examples may use other buses. The circuit 600 may output a representation of the waveform using a MEPS transmitter (e.g., in a 25kHz clock mode in addition to the continuous mode of the w/100kHz clock) (677).

Fig. 7 is a circuit diagram illustrating an example stimulation operational state in accordance with one or more techniques of the present disclosure. The stimulation hardware of fig. 7 is an example of an electronically Evoked Compound Action Potential (ECAP) stimulation hardware. The stimulation hardware may be used to establish a relative voltage between device ground and common body voltages, which may be important for ECAP sensing. In the example of fig. 7, the stimulus generation circuit 204 can apply a current 778 to perform a stimulus state operation, which results in a voltage (e.g., +Δv+vo) being applied to the patient 102 (779), which results in a total charge Q (780). The total charge Q may result in a residual voltage of +Δv+vo and- Δv+vo being the initial conditions on the capacitor being left on the 10 μf AC coupling capacitor.

In FIG. 7, Z _body Representing an electrode body interface. The electrode body interface may be described as an ionic double layer capacitor in parallel with an ionic redox pathway, which may be described by the Butler-Fu Ermo (Butler-Volmer) equation. An ionic double layer capacitor in parallel with the ionic redox pathway may be in series with the ohmic body impedance. A further simplified model of the electrode body interface may be referred to as a randes circuit, which is a drain capacitor in series with an ohmic body impedance.

Fig. 8 is a circuit diagram illustrating an example active charging operating state in accordance with one or more techniques of the present disclosure. In the example of fig. 8, the stimulus generation circuit 204 may apply a current 881 to perform an active state of charge operation (882). The current applied to the patient 102 may remove the charge added to the 10 μf coupling capacitor during stimulation, which may return the capacitor to the initial voltage (Vo).

Fig. 9 is a circuit diagram illustrating an example passive charging operating state in accordance with one or more techniques of the present disclosure. Loop 986 may be depleted of C quickly _par (e.g., 10 μs) to make V _body Equal to device ground, this may help to improve the accuracy of the sensed state.

Fig. 10 is a waveform timing diagram illustrating an example operational state in accordance with one or more techniques of the present disclosure. In the example of fig. 10, the processing circuitry 208 may operate in 4 operating states. The ordinate axis of fig. 10 represents the ping electrode pair current 1086 and the controlled therapy electrode pair current 187, and the abscissa axis of fig. 10 represents time.

In the auto-zero state 1090, the processing circuit 208 may obtain a "best" approximation of the differential and common mode offsets that will be seen at the inputs of the amplifier during the signal acquisition stage 1092, such that the differential and common mode offsets may be cancelled. Details of the auto-zero state 1090 are described with reference to FIG. 11A and FIG. 11BDiscussed. In the blocking state 1091, the processing circuitry 208 may be configured to quickly recover from the presence of the ping stimulus and active charge (e.g., about 10V) and be able to sense as low as 10 μv as early as within 200 μs after the ping stimulus _pp Wherein the voltage difference is 100 tens of thousands times. Details of the blocking state 1091 are discussed with reference to fig. 12. In the signal acquisition state 1092, the processing circuitry 208 may be configured to acquire a sense signal to measure an amplitude value (e.g., ECAP amplitude value). Details of the signal acquisition state 1092 are discussed with reference to fig. 13.

In the controlled therapy stimulation state 1093, the processing circuitry 208 may perform titration therapy based on a characteristic of the sensing signal (e.g., ECAP amplitude values). For example, during the controlled therapy stimulation state 1093, the stimulation generation circuit 204 may deliver stimulation according to fig. 7-9. Passive charging of the controlled (therapeutic) electrode may not be the desired device state to perform auto-zeroing. Rather, the system 100 may be configured to ping the electrode in a passive state of charge (e.g., auto-zero state 1090).

Fig. 11A and 11B are circuit diagrams illustrating an example of a sensing circuit during an auto-zero operating state 1090 in accordance with one or more techniques of this disclosure. Counteracting the differential offset may facilitate viewing the sense signal, which may include 10 μV, with high resolution _pp (peak-to-peak voltage) to 300. Mu.V _pp Is a signal of (a). Canceling the common mode offset may be advantageous to maintain within the common mode input range of the high performance low voltage amplifier components. In addition, small variations in the common-mode input signal may create an offset that is caused by the finite common-mode rejection ratio of the amplifier. In this auto-zero state 1090, common and differential mode offsets at the sense amplifier inputs may be stored on auto-zero capacitors 1152 ("Cs, 1") and 1153 ("Cs, 2"), which may be examples of calibration capacitors 452, 453, respectively. During measurement, auto-zero capacitors 1152, 1153 may be placed in series with amplifier 1156, which may help cancel differential and/or common mode offsets. During the auto-zero state 1090, the auto-zero capacitors 1152, 1153 may store the signal acquisition state as close to the time as possible due to low frequency interference(e.g., 60Hz noise), which may maximize cancellation of differential and/or common mode offsets. In some examples, during the auto-zero state 1090, the auto-zero capacitors 1152, 1153 may store the inherent offset that the device expects to see in the subsequent signal acquisition state. Storing the inherent offset may be accomplished by placing the device (e.g., IMD 110) in the same configuration that would exist in the signal acquisition state when performing the auto-zero operation of auto-zero state 1090.

Fig. 11B shows passive charging of the ping electrode. In the configuration of FIG. 11B, two charge balance capacitors 1142 ("C _t,3 "AND" C _t,4 ", which may be an example of AC coupling capacitor 442 of fig. 4) is connected between device ground and human tissue through a ping electrode. The AC coupling capacitor 1142 may control the voltage (see fig. 9). The common mode voltage between device ground and common body voltage may be a non-zero voltage stored on these capacitors.

Returning to FIG. 11A, the common mode voltage seen at the input of amplifier 1156 may include a stored charge balance capacitor 1142 and a second pair of charge balance capacitors 1143 ("C") present between the body and the sense amplifier input _t,1 "AND" C _t,2 ", which may be an example of AC coupling capacitor 442 of fig. 4). The differential voltage seen at amplifier 1156 may be the differential voltage at the sense electrode interface and on charge balance capacitor 1143. The charge balance capacitor 1143 may be configured to use the electrode as a therapy electrode. The charge balance capacitor 1143 may help prevent DC current from flowing into the body of the patient 102 from causing tissue/electrode damage during treatment. The charge balance capacitor 1143 also prevents silicon from failing in the field to produce DC current, which may also lead to tissue damage of the patient 102. Since the system 100 can be highly configured for the selected electrodes, the sense and ping electrodes can be selected between 17 options at the device level. The offset measured by this auto-zero process is only an estimate.

FIG. 12 is a circuit diagram illustrating an example of a sensing circuit 1200 during a blocking operational state in accordance with one or more techniques of the present disclosure. Fig. 12 illustrates an example blanking operation. The blanking operation may include: the processing circuit 208 opens the switches 1249, 1251 to prevent the capacitors 1252, 1253 ("C) _s,1 "AND" C _s,2 ") change their voltages. Capacitor 1242 may be an example of AC coupling capacitor 442 of fig. 4 and/or a 10 μf capacitor in fig. 9. The blanking operation may help prevent the sense signal from being received by the second amplifier stage 1267.

The circuit 1200 may be configured to perform a blanking operation or clamp using the switches 1249, 1251 and a blanking operation using the blanking switches 1266, 1268. For example, the processing circuitry 208 may blank the input of the first amplifier stage 1265 (e.g., at the end of the blocking state 1091 of fig. 10) using the switches 1249, 1251 for a time other than active charging (e.g., at least 40 μs), and may blank the input of the second amplifier stage 1267 using the blanking switches 1266, 1268 for a time other than active charging (e.g., at least 60 μs), which may help allow the transient state of the received sense signal to reach steady state before propagating the received sense signal to a longer time constant stage downstream (e.g., the second amplifier stage 1267 or the second amplifier stage 1267 with one or more additional amplifier stages).

In some examples, the switches 1249, 1251 may be configured to clamp the sense signal only to the component safe voltage range. For example, the processing circuitry 208 may clamp the input of the first amplifier stage 1265 to a target voltage range (e.g., a component safe voltage range) using switches 1249, 1251. In this example, the processing circuitry 208 may use blanking switches 1266, 1268 to blank the input of the second amplifier stage 1267 (e.g., at the end of the blocking state 1091 of fig. 10) at times other than active charging (e.g., at least 60 μs), which may help allow transients of the received sense signal to reach steady state before propagating the received sense signal to a longer time constant stage downstream (e.g., the second amplifier stage 1267 or the second amplifier stage 1267 with one or more additional amplifier stages).

Fig. 13 is a circuit diagram illustrating an example of a sensing circuit 1300 during a signal acquisition operating state in accordance with one or more techniques of the present disclosure. During the signal acquisition state 1092, the sensing circuit 1300 may widen the band of the high pass filter (e.g., disable the high pass filter). For example, the sensing circuit 1300 may widen the passband by moving the high pass pole from 100Hz to 0 Hz. The frequency of the pole is fhp (Hz) =1/(2×pi×r×c). By opening the switch in series with the resistor, R becomes infinite and fhp (Hz) =0.

The benefit of disabling the high pass filter is not just to preserve all low frequency content of the target signal. The sensing circuit 1300 may exhibit offset jitter that cannot be controlled entirely by any of our offset control mechanisms. When the step offset passes through a cascade of 4 high pass filters (rather than an auto-zero process), the step response may result in a complex background signal that may be difficult to separate from the sensing signal (e.g., ECAP signal) and the resulting amplitude value that it is desired to extract. In contrast, it is much easier for IMD 110 to design a measurement of amplitude extraction that is not affected by flat background signals. For example, the peak-to-valley amplitude measurement is not affected by the offset as long as the offset is within the dynamic range of the amplifier.

The sensing circuit 1300 may help increase the Common Mode Rejection Ratio (CMRR) of the amplifier system during the signal acquisition state 1092, which may help avoid signal degradation caused by common mode interferents in the patient 102 body. The disconnection of the resistor of the ground circuit 1354 at the amplifier input may help to force the input impedance, which mainly corresponds to the capacitance of the differential pair at the amplifier input, to be extremely high. The input impedance at the body (which ranges from 30kΩ at low frequency to 1kΩ at high frequency and does not match) forms an impedance divider with the amplifier input impedance, which may reduce CMRR. If the resistor of the ground circuit 1354 is not cut off, the common mode rejection ratio of the system may be poor and the sense signal may not be measured. During signal acquisition state 1092, a second differential offset cancellation mechanism using a digital control loop may be applied.

In accordance with the techniques of this disclosure, injection circuit 1356 may be configured to provide a differential offset cancellation mechanism. The differential offset cancellation mechanism of injection circuit 1356 may help address situations where the offset between the auto-zero state (e.g., at the end of auto-zero state 1090) and after the ping pulse (e.g., at the end of the blocking state 1091) changes slowly. For example, when the patient 102 changes posture state (e.g., from supine to standing), the offset difference between the auto-zero state and after the ping pulse may change slowly. In this example, injection circuit 1356 may be configured to inject a differential offset to counteract changes in the body interface since auto-zero state 1090.

The injection circuit 1356 may be configured to inject a cancellation offset between the first stage amplifier 1365 and the second stage amplifier 1367. Injecting a cancellation offset between the first stage amplifier 1365 and the second stage amplifier 1367 may represent improved operation compared to systems where a slowly varying cancellation offset is injected before the first stage amplifier 1365 or after the second stage amplifier 1367. For example, when injection circuit 1356 injects a cancellation offset between first stage amplifier 1365 and second stage amplifier 1367, the fidelity requirements may be relaxed, for example, due to having a portion of the amplified signal from first stage amplifier 1365, as compared to a system in which a slowly varying cancellation offset is injected prior to first stage amplifier 1365. Furthermore, when injection circuit 1356 injects a cancellation offset after second stage amplifier 1367, the allowable range of amplifier stage 1367 may be exceeded.

Injection circuit 1356 may be configured to generate a cancellation offset using a digital control loop. The digital control loop of fig. 13 may be designed to implement a discrete-time, single pole, high pass filter with configurable pole locations in the forward signal flow path. For example, injection circuit 1356 may be configured to generate a cancellation offset based on a set of waveforms (e.g., digital history waveforms). For example, injection circuit 1356 may be configured to generate a cancellation offset based on a set of waveforms received by SAR ADC 571 of fig. 5.

The processing circuitry 208 may be configured to determine a weighted set of digital history offsets for the waveform based on one or more previous sense signals that occurred prior to the sense signal. For example, the processing circuitry 208 may generate a respective weighted digital history offset for each waveform in a set of previous digital waveforms to generate a weighted digital history offset set of waveforms. Each respective weighted digital history offset may be associated with a different previous "ping pulse period". The ping pulse period may refer to the period of states 1090-1093 of fig. 10 in which the waveform is sensed during signal acquisition state 1092 using the auto-zero technique described herein during auto-zero state 1090.

For example, for a set of 3 previous ping pulse periods, the processing circuitry 208 may generate a first weighted digital history offset for the first digital waveform by multiplying an offset of the first digital waveform associated with a first previous ping pulse period occurring prior to the current ping pulse period by a first weight. In this example, the processing circuitry 208 may generate a second weighted digital history offset for the second digital waveform by multiplying the offset of the second digital waveform associated with a second previous ping pulse period occurring before the first previous ping pulse period by a second weight. The second weight may be less than the first weight. In this example, the processing circuitry 208 may generate a third weighted digital history offset for the third digital waveform by multiplying an offset of the third digital waveform associated with a third previous ping pulse period occurring before the second previous ping pulse period by a third weight. The third weight may be less than the second weight. Although the above example uses 3 history offsets, other examples may use 1 history offset, 2 history offsets, or more than 3 history offsets (e.g., 10 history offsets).

The injection circuit 1356 may be configured to generate a cancellation offset by applying closed-loop control feedback using a weighted set of digital historic offsets of the waveform. For example, the injection circuit 1356 may apply an integral controller (e.g., an I controller) to the weighted set of digital history offsets of the waveform to generate the cancellation offset.

Fig. 14 is a circuit diagram illustrating an example GMR amplifier 1400 in accordance with one or more techniques of the present disclosure. The GMR amplifier 1400 may be an example of the first amplifier stage 565 of fig. 5. The GMR amplifier 1400 may exhibit the following characteristics:

1) Low noise amplification is performed at minimum power.

2) Balance and high input impedance to achieve optimal system level CMRR.

3) Very high common mode and power supply rejection ratio.

4) The response speed recovered from the transient after the blocked state is very fast.

5) The controlled gain varies with temperature and process variations.

To achieve these goals, the design of fig. 14 does not use the more common bio-amplifier, low Noise Amplifier (LNA) approach that utilizes feedback. A common form of such a method is a Capacitive Feedback Network (CFN). This is because CFNs may consume a lot of additional power and may be slower in transient recovery after the blocking state. Instead, the GMR amplifier 1400 may use a sister approach of feedback, i.e., invariance, in which the process parameters and temperature are vanished from the forward transfer function by designing to cancel the terms in the numerator and denominator without using feedback. The method is directed to the objective of the first gain stage described above. After the first stage, the implementation is less important because the required power drops with the square of the gain of the target signal-to-noise-and-amplitude ratio. In this case, the gain square may be 100. The constant GMR method (gm (transconductance) r (resistance)) may be well suited for the first stage amplifier. The gain achievable by this circuit is limited but this limitation applies to analog offset injection control loops that require injection of an offset at the intermediate stage of amplification to avoid sensitivity of noise and fidelity to injection, avoid limitation of the dynamic range of the system, and not adversely affect the 5 targets described above for the input states.

The gain can be well controlled and is at least partially immune to process variations and temperature through the following analysis. In fact, the gain is controlled by the ratio of two resistors sharing the same process variation, and is related to the I sent to the amplifier _BIAS The scaling of the current is proportional. The signal-to-noise amplitude is observed to be proportional to the square root of the bias current sent to the different pairs. By properly selecting the ratio and current of the resistors, the required noise and gain can be determined independently. Thus, the GMR amplifier 1400 may have no feedback in the forward signal path, which would result in a slower and higher current system, but may be controlled by invariance techniques. Moreover, the input impedance of the GMR amplifier 1400 may be matched and very high.

Gain=9 _m R _out

But is provided with

In the case of a weak inversion, the first inversion,

in the case of a weak inversion, the first inversion,

thus (2)

Wherein M is ₁ Is a bias gain (e.g., I _BIAS * M), R _out Is a resistor 1409, and R _bias Is a resistor 1407.

Fig. 15A and 15B are polar zero plan views illustrating examples of extracting a sense signal from a digitized waveform in accordance with one or more techniques of the present disclosure. In fig. 15A, the additive linear artifact is depicted by 2 poles 1521 at 1 on the unit circle, which may represent a linear line (see fig. 16). In fig. 15B, any filtering operation with two zeros 1523 at one point on the unit circle removes the additive linear artifact of fig. 15A. Any resulting measurement may not be affected by the presence of artifacts. An example solution for the invariant filter may include f (Z) =flp (Z) (1-Z ^-n )(1-z ^-m ) Where 'n' =2 corresponds to the derivative (e.g., step 1904), and'm' corresponds to a much larger number, which is equal to the interval between the peaks and troughs of the derivative signal in time steps, which can be implemented in step 673 of fig. 6.

Two example principles of extracting ECAP amplitude values may include reducing noise and interferer content, and making the measurement immune to the presence of time-varying tissue inherent artifacts. Noise and interference can be reduced by: the bandwidth is limited using a digital low pass filter because the thermal noise power (e.g., the dominant noise source) may be proportional to the bandwidth and the waveforms are averaged because the uncorrelated noise power is reduced to 1/N, where N is the number of average waveforms. Artifacts at the body interface may be described as offset + line + decay exponent. In a sufficiently small measurement area, this is well approximated by a line with an offset. Such artifacts can vary with body position, time, and other factors. In order to make the measurement invariant (e.g., invariant with artifacts), the measurement may be immune to the presence of additive linear artifacts.

Fig. 16 is a plot illustrating an example sense signal 1601 in accordance with one or more techniques of the present disclosure. In the example of fig. 16, the processing circuit 208 may calculate the amplitude value of the sense signal (e.g., ECAP signal) as a maximum derivative 1607 between the peak P2 and the trough N1 and a minimum derivative 1605 between the peak P2 and the trough B2.

The low-pass properties in the low-pass derivative filter may be optimized for noise and artifact suppression and signal strength based on a very large human database prior to peak-to-valley measurement. A cascaded hardware implementation of a 1,0, -1 filter and an 11-tap symmetric FIR filter may result in a general form of a 13-tap antisymmetric filter, antisymmetric meaning that there is 1 zero at 1 on the unit circle. This general form may be configured to implement an optimal filter determined from the human database, i.e. an optimized low-pass derivative filter in series with the discrete time derivative, wherein the low pass allows content of about 4.5 kHz. The other zero at 1 on the unit circle of the measurement technique (in order to be unaffected by the additive linear artifact) may be implemented by a peak-to-trough operation.

Fig. 17 is a flowchart illustrating an example operation of a sensing circuit for calibrating IMD 110 in accordance with one or more techniques of the present disclosure. Fig. 17 is discussed in conjunction with fig. 1-16 for exemplary purposes only. When the stimulus generating circuit 204 is not providing electrical stimulus, the processing circuit 208 may cause a first voltage on the first terminal 458 to be stored in the first calibration capacitor 452 and a second voltage on the second terminal 459 to be stored in the second calibration capacitor 453 (1702).

After the first voltage is stored in the first calibration capacitor 452 and the second voltage is stored in the second calibration capacitor 453, and when the stimulus generating circuit 204 provides the electrical stimulus, the processing circuit 208 may turn off (e.g., open the switch or avoid creating a channel in the switching element) the first calibration switch 460 to prevent the first voltage stored in the first calibration capacitor 452 from changing and turn off the second calibration switch 461 to prevent the second voltage stored in the second calibration capacitor 453 from changing (1704). For example, the processing circuitry may open the calibration switches 460, 461 (e.g., the blocked state 1091 of fig. 10) during stimulation, which may help eliminate any path for charge variation on the calibration capacitors 452, 453. As further discussed in fig. 18, the first switches 449, 451 may block or clamp the stimulus signal (e.g., 10V) from being received at the input of the amplifier circuit 456 (e.g., the first stage amplifier 565 of fig. 5). The first switches 449, 451 may be open during stimulation (e.g., the blocking state 1091 of fig. 10), which may also help prevent the voltage stored in the calibration capacitors 452, 453 from changing.

After the electrical stimulus is blocked and when the stimulus generating circuit 204 is not providing the electrical stimulus, the processing circuit 208 may determine a sense signal using the sensing circuit 206 based on the first voltage on the first terminal 458 being offset by the first calibration voltage stored by the first calibration capacitor 452 and based on the second voltage on the second terminal 459 being offset by the second calibration voltage stored by the second calibration capacitor 453 (1706). The processing circuitry 208 may cause the stimulus generation circuitry 204 to deliver therapy to the patient 102 based on the sensing signal (1708).

Fig. 18 is a flow diagram illustrating an example operation of an amplifier circuit in accordance with one or more techniques of the present disclosure. Fig. 18 is discussed in conjunction with fig. 1-17 for exemplary purposes only. Switches 1249, 1251 may receive the sense signal (1800). The switches 1249, 1251 may block or clamp the received sense signal from being received by the first amplifier stage 1265 (1802). For example, the switches 1249, 1251 may block the received sense signal from being received by the first amplifier stage 1265 during the block state 1091. In some examples, switches 1249, 1251 may clamp the received sense signal to less than the component safe voltage range (e.g., during states 1090-1093).

The first amplifier stage 1265 may amplify the sense signal (1804), for example, using a GMR amplifier. When the stimulus generation circuit 204 provides electrical stimulus ("yes" of step 1806), the blanking switches 1266, 1268 may prevent the amplified sense signal from being received by the second amplifier stage 1267 (1808). For example, blanking switches 1266, 1268 may prevent the amplified sense signal from being received by the second amplifier stage 1267 while the first switching elements 1249, 1251 clamp the sense signal to a threshold voltage range, e.g., a component safety voltage range.

In some examples, the switches 1249, 1251 may blank the input of the first amplifier stage 1265 (e.g., at the end of the blocking state 1091 of fig. 10) at times other than active charging (e.g., at least 40 μs), and the blanking switches 1266, 1268 may blank the input of the second amplifier stage 1267 at times other than active charging (e.g., at least 60 μs). For example, the switches 1249, 1251 may be configured to block the sense signal after a first time delay from when the stimulus generation circuit 204 is no longer providing electrical stimulus. In this example, blanking switches 1266, 1268 may be configured to block the sense signal after a second time delay from when stimulus generating circuit 204 is no longer providing electrical stimulus, where the second time delay is different from the first time delay. The second time delay may be longer than the first time delay.

When the stimulus generation circuit 204 does not provide electrical stimulus ("no" of step 1806), at least the second amplifier stage 567 may generate a second amplified sense signal from the amplified sense signal using one or more amplifiers (1810). The processing circuitry 208 may cause the stimulus generation circuitry 204 to deliver therapy to the patient 102 based on the second amplified sensing signal (1812).

FIG. 19 is a flowchart illustrating example operations of feature extraction in accordance with one or more techniques of the present disclosure. Fig. 19 is discussed in conjunction with fig. 1-18 for exemplary purposes only. The processing circuitry 208 may generate waveforms based on the sense signals. For example, the processing circuit 208 may determine an average waveform from the amplified sense signal (1902). The processing circuitry 208 may perform a derivative operation on the average waveform, which provides a zero point at 1 on the unit circle (1904).

The processing circuitry 208 may FIR filter the average waveform after performing the derivative operation to generate a FIR filtered waveform, thereby reducing the noise bandwidth (1906). The FIR filter may mainly apply low-pass filtering. The processing circuitry 208 may apply a peak-to-valley operation to the FIR filtered waveform to measure an amplitude value (e.g., ECAP amplitude value) of the FIR filtered waveform, which provides a zero point at 1 on the unit circle such that the overall measurement is not affected by additive linear artifacts (1908). As shown in fig. 15B, the solution set of the invariant filter may include f (Z) =flp (Z) (1-Z ^-n )(1-z ^-m ) Where 'n' =2 corresponds to the derivative (e.g., step 1904), and'm' corresponds to a much larger number, which is equal to the interval between the peaks and troughs of the derivative signal in time steps (e.g., step 1908), which together are not affected by additive linear artifacts. That is, for example, (1-z) ^-m ) May correspond to subtracting the current value from the value of the previous m steps (e.g., step 1908). Artifacts may come from the body interface and may be described as offset + line + decay index. The processing circuitry 208 may cause the stimulus generation circuitry 204 to deliver therapy to the patient 102 based on the amplitude values (1910).

Fig. 20 is a flowchart illustrating example operations for providing therapy based on a sensing signal in accordance with one or more techniques of the present disclosure. For illustration purposes only, fig. 20 is discussed in conjunction with fig. 1-19. During the auto-zero state, the processing circuit 208 may cause a first voltage on the first terminal 458 to be stored in the first calibration capacitor 452 and a second voltage on the second terminal 459 to be stored in the second calibration capacitor 453 (2002). An example of the storage of the first voltage and the storage of the second voltage on the second terminal 459 is depicted in fig. 17.

During the blocking state, the blanking circuit 446 may block or clamp the sense signal (2004). For example, when the stimulus generation circuit 204 provides electrical stimulus, the blanking circuit 446 can block or clamp the electrical stimulus from being received at the amplifier circuit 456 (e.g., the input of the first amplifier stage 565 of fig. 5). In some examples, when the stimulus generation circuit 204 provides electrical stimulus, the alternative blanking timing circuit 566 can prevent the amplified sense signal from being received by the second amplifier stage 567. In some examples, during the blocking state, the processing circuit 208 may turn off the first calibration switch 460 to prevent a change in the first voltage stored on the first calibration capacitor 452 and turn off the second calibration switch 461 to prevent a change in the second voltage stored on the second calibration capacitor 453 (see fig. 17).

During a signal acquisition state, IMD 110 may generate a sensing signal using first calibration capacitor 452 and second calibration capacitor 453 (2006). For example, after the electrical stimulus is blocked and when the stimulus generating circuit 204 is not providing the electrical stimulus, the processing circuit 208 may generate a sense signal with the sensing circuit 206 that is offset by the first calibration voltage stored by the first calibration capacitor 452 based on the first voltage on the first terminal 458 and by the second calibration voltage stored by the second calibration capacitor 453 based on the second voltage on the second terminal 459.

During the signal acquisition state, IMD 110 may generate an amplified sense signal based on the sense signal using the GMR amplifier and the one or more amplifiers (2004). For example, the first amplifier stage 565 may amplify the sense signal using a GMR amplifier to generate a first amplified sense signal, and at least the second amplifier stage 567 may generate an amplified sense signal from the first amplified sense signal using one or more amplifiers (e.g., amplifier stages 565-569).

During the signal acquisition state, IMD 110 may generate characteristics based on the amplified sensing signal using an artifact filter (including a peak-to-valley function) with two zeros at 1 on the unit circle (2006). For example, the processing circuitry 208 may determine an average waveform from the amplified sense signal and may FIR filter the average waveform to generate a FIR filtered waveform, which may improve accuracy in determining the features. In this example, the processing circuitry 208 may filter out artifacts (e.g., artifacts from the body interface) by applying one zero at 1 on the unit circle using a derivative operation (e.g., step 1904) and another zero at 1 on the unit circle by applying a peak-to-trough operation (e.g., step 1908; see fig. 15A, 15B, 16).

During the controlled therapy state, the processing circuitry 208 may cause the stimulus generation circuitry 204 to deliver therapy to the patient 102 based on the amplitude values (2008). For example, the processing circuitry 208 may determine a set of stimulation parameters, such as one or more of an electrode combination, a voltage amplitude value or a current amplitude value, a pulse width, or a pulse frequency, based on the amplitude values (e.g., ECAP amplitude values). The amplitude value may represent a function of the degree of response of the nerve to the stimulus. In this example, the processing circuitry 208 may cause the stimulus generation circuitry 204 to provide the stimulus in accordance with the set of stimulus parameters.

The following examples are example systems, devices, and methods described herein.

Example 1: a system for providing therapy to a patient, the system comprising: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a first voltage on a first terminal and to sense a second voltage on a second terminal; and processing circuitry electrically connected to the sensing circuitry and the stimulus generation circuitry, the processing circuitry configured to: causing the first voltage on the first terminal to be stored in a first calibration capacitor and the second voltage on the second terminal to be stored in a second calibration capacitor when the stimulus generating circuit does not provide the electrical stimulus; after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch to prevent the second voltage stored in the second calibration capacitor from changing; determining, with the sensing circuit, a sensing signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the stimulus generating circuit does not provide the electrical stimulus; and causing the stimulus generation circuit to deliver the therapy to the patient based on the sensing signal.

Example 2: the system of example 1, further comprising an amplifier circuit configured to: receiving the sensing signal; amplifying the sense signal using a first stage amplifier and at least a second stage amplifier to generate an amplified sense signal; and wherein the processing circuitry is configured to cause the stimulus generation circuitry to deliver the therapy based on the amplified sense signal.

Example 3: the system of example 2, wherein to amplify, the first stage amplifier amplifies the sense signal to a first amplified sense signal for output to the second stage amplifier, and wherein the amplifier circuit further comprises a set of blanking switches configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 4: the system of example 3, further comprising a set of switches configured to: preventing the sense signal from being received at the input of the first stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the first stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 5: the system of example 4, wherein to prevent the sense signal from being received at the input of the first stage amplifier, the set of switches is configured to prevent the sense signal after a first time delay from when the stimulus generation circuit is no longer providing the electrical stimulus; and wherein to prevent the first amplified sense signal from being received at the input of the second stage amplifier, the set of blanking switches is configured to prevent the sense signal after a second time delay from when the stimulus generation circuit is no longer providing the electrical stimulus, wherein the second time delay is different from the first time delay.

Example 6: the system of example 5, wherein the second time delay is longer than the first time delay.

Example 7: the system of example 3, further comprising a set of blanking switches configured to clamp the voltage of the sense signal to a threshold voltage range.

Example 8: the system of example 7, wherein the threshold voltage range comprises a component safety voltage range.

Example 9: the system of any of examples 2-8, wherein the first stage amplifier comprises a transconductance amplifier.

Example 10: the system of any of examples 2-9, wherein the second amplifier stage is configured to auto-zero at an input and comprises a direct transconductance amplifier.

Example 11: the system of example 10, wherein the amplifier circuit includes a third amplifier stage configured to receive an output of the second amplifier stage and to auto-zero at an input, wherein the third amplifier stage includes a linearized transconductance amplifier.

Example 12: the system of example 11, wherein the amplifier circuit includes a fourth amplifier stage configured to receive an output of the third amplifier stage and to auto-zero at an input.

Example 13: the system of any of examples 9 to 12, wherein the processing circuit is further configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 14: the system of any of examples 2-13, further comprising an injection circuit configured to inject a cancellation offset between the first stage amplifier and the second stage amplifier.

Example 15: the system of example 14, wherein the injection circuit is further configured to generate the cancellation offset based on a weighted digital history offset set of waveforms.

Example 16: the system of example 15, wherein the processing circuit is configured to determine the weighted digital history offset set of waveforms based on one or more previous sense signals occurring prior to the sense signal.

Example 17: the system of any of examples 15-16, wherein the injection circuit is further configured to apply an integral controller to a weighted digital history offset set of the waveform to generate the cancellation offset.

Example 18: the system of any one of examples 1 to 17, wherein the processing circuit is configured to: generating a waveform based on the sense signal; performing a derivative operation on the waveform; after performing the derivative operation, applying a peak-to-valley operation to the waveform to determine an amplitude value; and causing the stimulus generation circuit to deliver the therapy based on the amplitude value.

Example 19: the system of example 18, wherein to perform the derivative operation, the processing circuit is configured to provide a zero point at 1 on a unit circle; and wherein, to perform the peak-to-valley operation, the processing circuitry is configured to provide a zero point at 1 on the unit circle.

Example 20: the system of any of examples 18 to 19, wherein to generate the waveform, the processing circuit is further configured to determine an average waveform from the sense signal and at least one other sense signal.

Example 21: the system of example 20, wherein the waveform is a Finite Impulse Response (FIR) filtered waveform, and wherein the processing circuit is further configured to: an FIR filter is applied to the average waveform to generate the FIR filtered waveform.

Example 22: the system of any of examples 18 to 21, wherein the magnitude value comprises an Evoked Compound Action Potential (ECAP) magnitude value.

Example 23: the system of any one of examples 1 to 22, wherein the sensing signal comprises an Evoked Compound Action Potential (ECAP) signal.

Example 24: the system of any one of examples 1 to 23, wherein the therapy comprises one or more of Spinal Cord Stimulation (SCS), deep Brain Stimulation (DBS), peripheral Nerve Stimulation (PNS), peripheral Nerve Field Stimulation (PNFS), cortical Stimulation (CS), pelvic floor stimulation, or gastrointestinal stimulation.

Example 25: the system of any one of examples 1 to 24, wherein the stimulus generation circuit, sensing circuit, memory, and processing circuit are disposed in a medical device.

Example 26: the system of any one of examples 1 to 25, wherein the medical device comprises an implantable medical device.

Example 27: a method, comprising: when the stimulus generating circuit does not provide electrical stimulus, causing, by the processing circuit, a first voltage on a first terminal of the sensing circuit to be stored in a first calibration capacitor and causing, by the processing circuit, a second voltage on a second terminal of the sensing circuit to be stored in a second calibration capacitor; after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch by the processing circuit to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch by the processing circuit to prevent the second voltage stored in the second calibration capacitor from changing; determining, by the processing circuit, a sense signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the electrical stimulus is not provided by the stimulus generating circuit; and causing, by the processing circuit, the stimulus generation circuit to deliver the therapy to the patient based on the sensing signal.

Example 28: a medical device, comprising: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a first voltage on a first terminal and to sense a second voltage on a second terminal; and processing circuitry electrically connected to the sensing circuitry and the stimulus generation circuitry, the processing circuitry configured to: causing the first voltage on the first terminal to be stored in a first calibration capacitor and the second voltage on the second terminal to be stored in a second calibration capacitor when the stimulus generating circuit does not provide the electrical stimulus; after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch to prevent the second voltage stored in the second calibration capacitor from changing; determining, with the sensing circuit, a sensing signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on a second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the stimulus generating circuit does not provide the electrical stimulus; and causing the stimulus generation circuit to deliver the therapy to the patient based on the sensing signal.

Example 29: the medical device of example 28, further comprising an amplifier circuit configured to: receiving the sensing signal; amplifying the sense signal using a first stage amplifier and at least a second stage amplifier to generate an amplified sense signal; and wherein the processing circuitry is configured to cause the stimulus generation circuitry to deliver the therapy based on the amplified sense signal.

Example 30: the medical device of example 29, wherein to amplify, the first stage amplifier amplifies the sense signal to a first amplified sense signal for output to the second stage amplifier, and wherein the amplifier circuit further comprises a set of blanking switches configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 31: the medical device of example 30, further comprising a set of switches configured to: preventing the sense signal from being received at the input of the first stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the first stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 32: the medical device of example 31, wherein to prevent the sense signal from being received at the input of the first stage amplifier, the set of switches is configured to prevent the sense signal after a first time delay from when the stimulus generation circuit is no longer providing the electrical stimulus; and wherein to prevent the first amplified sense signal from being received at the input of the second stage amplifier, the set of blanking switches is configured to prevent the sense signal after a second time delay from when the stimulus generation circuit is no longer providing the electrical stimulus, wherein the second time delay is different from the first time delay.

Example 33: the medical device of example 32, wherein the second time delay is longer than the first time delay.

Example 34: the medical device of example 30, further comprising a set of blanking switches configured to clamp a voltage of the sense signal to a threshold voltage range.

Example 35: the medical device of example 34, wherein the threshold voltage range includes a component safety voltage range.

Example 36: the medical device of any one of examples 29-35, wherein the first stage amplifier comprises a transconductance amplifier.

Example 37: the medical device of any of examples 29-36, wherein the second amplifier stage is configured to auto-zero at an input and comprises a direct transconductance amplifier.

Example 38: the medical device of example 37, wherein the amplifier circuit includes a third amplifier stage configured to receive an output of the second amplifier stage and to auto-zero at an input, wherein the third amplifier stage includes a linearized transconductance amplifier.

Example 39: the medical device of example 38, wherein the amplifier circuit includes a fourth amplifier stage configured to receive an output of the third amplifier stage and to auto-zero at an input.

Example 40: the medical device of any one of examples 36-39, wherein the processing circuitry is further configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 41: the medical device of any one of examples 29-40, further comprising an injection circuit configured to inject a cancellation offset between the first stage amplifier and the second stage amplifier.

Example 42: the medical device of example 41, wherein the injection circuit is further configured to generate the offset based on a weighted set of digital historical offsets of waveforms.

Example 43: the medical device of example 42, wherein the processing circuit is configured to determine the weighted digital history offset set of waveforms based on one or more previous sense signals occurring prior to the sense signal.

Example 44: the medical device of any one of examples 42-43, wherein the injection circuit is further configured to apply an integral controller to a weighted digital history offset set of the waveform to generate the offset.

Example 45: the medical device of any one of examples 28-44, wherein the processing circuitry is configured to: generating a waveform based on the sense signal; performing a derivative operation on the waveform; after performing the derivative operation, applying a peak-to-valley operation to the waveform to determine an amplitude value; and causing the stimulus generation circuit to deliver the therapy based on the amplitude value.

Example 46: the medical device of example 45, wherein to perform the derivative operation, the processing circuit is configured to provide a zero point at 1 on a unit circle; and wherein, to perform the peak-to-valley operation, the processing circuitry is configured to provide a zero point at 1 on the unit circle.

Example 47: the medical device of any one of examples 45-46, wherein to generate the waveform, the processing circuitry is further configured to determine an average waveform from the sense signal and at least one other sense signal.

Example 48: the medical device of example 47, wherein the waveform is a Finite Impulse Response (FIR) filtered waveform, and wherein the processing circuit is further configured to: an FIR filter is applied to the average waveform to generate the FIR filtered waveform.

Example 49: the medical device of any one of examples 45-48, wherein the amplitude value comprises an Evoked Compound Action Potential (ECAP) amplitude value.

Example 50: the medical device of any one of examples 28-49, wherein the sensing signal comprises an Evoked Compound Action Potential (ECAP) signal.

Example 51: the medical device of any one of examples 28-50, wherein the therapy includes one or more of Spinal Cord Stimulation (SCS), deep Brain Stimulation (DBS), peripheral Nerve Stimulation (PNS), peripheral Nerve Field Stimulation (PNFS), cortical Stimulation (CS), pelvic floor stimulation, or gastrointestinal stimulation.

Example 52: the medical device of any one of examples 28-51, wherein the medical device comprises an implantable medical device.

Example 53: a system for providing therapy to a patient, the system comprising: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a sensing signal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit; and an amplifier circuit configured to: receiving the sense signal from the sense circuit; amplifying the sense signal using a transconductance amplifier to generate a first amplified sense signal; preventing the first amplified sense signal from being received at the input of a second stage amplifier when the stimulus generating circuit provides the electrical stimulus; allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus; amplifying the first amplified sense signal using the second stage amplifier to generate a second amplified signal; and wherein the processing circuit is configured to cause the stimulus to deliver the therapy based on the second amplified sensing signal.

Example 54: the system of example 53, wherein the amplifier circuit further comprises a set of blanking switches configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 55: the system of example 54, further comprising a set of switches configured to: preventing the sense signal from being received at the input of the first stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the first stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 56: the system of example 55, wherein to prevent the sense signal from being received at the input of the first stage amplifier, the set of switches is configured to prevent the sense signal after a first time delay from when the stimulus generation circuit is no longer providing the electrical stimulus; and wherein to prevent the first amplified sense signal from being received at the input of the second stage amplifier, the set of blanking switches is configured to prevent the sense signal after a second time delay from when the stimulus generation circuit is no longer providing the electrical stimulus, wherein the second time delay is different from the first time delay.

Example 57: the system of example 56, wherein the second time delay is longer than the first time delay.

Example 58: the system of example 53, further comprising a set of blanking switches configured to clamp the voltage of the sense signal to a threshold voltage range.

Example 59: the system of example 58, wherein the threshold voltage range includes a component safety voltage range.

Example 60: a system for providing therapy to a patient, the system comprising: a stimulus generation circuit configured to provide electrical stimulus to the patient; a sensing circuit configured to sense a sensing signal; and a processing circuit electrically connected to the sensing circuit and the stimulus generation circuit, the processing circuit configured to: receiving the sense signal from the sense circuit; amplifying the sense signal using a transconductance amplifier to generate a first amplified sense signal; preventing the first amplified sense signal from being received at the input of a second stage amplifier when the stimulus generating circuit provides the electrical stimulus; allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus; amplifying the first amplified sense signal using the second stage amplifier to generate a second amplified signal; and wherein the processing circuit is configured to cause the stimulation generation therapy to deliver the therapy based on the second amplified sensing signal.

Example 61: the system of example 60, wherein the second amplifier stage is configured to auto-zero at the input and comprises a direct transconductance amplifier.

Example 62: the system of example 61, wherein the amplifier circuit comprises a third amplifier stage configured to receive an output of the second amplifier stage and to auto-zero at an input, wherein the third amplifier stage comprises a linearized transconductance amplifier.

Example 63: the system of example 62, wherein the amplifier circuit includes a fourth amplifier stage configured to receive the output of the third amplifier stage and to auto-zero at an input.

Example 64: the system of any one of examples 60 to 63, wherein the processing circuit is further configured to: preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and allowing the first amplified sense signal to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

Example 65: a method comprising performing the operations of any one of examples 1 to 64.

The techniques described in this disclosure may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, aspects of the described techniques may be implemented in one or more processors or processing circuits, 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 circuit" may generally refer to any of the foregoing logic circuits (alone or in combination with other logic circuits), or any other equivalent circuit. A control unit comprising hardware may also perform one or more techniques of this disclosure.

Such hardware, software, and firmware may be implemented within the same device or within different 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 different hardware or software components. Rather, functionality associated with one or more circuits or units may be performed by different hardware or software components or integrated within common or different hardware or software components.

The techniques described in this disclosure may also be embedded or encoded in a computer-readable medium, such as a computer-readable storage medium containing instructions, which may be described as a non-transitory medium. The instructions embedded or encoded in the computer-readable storage medium may cause a programmable processor, or other processor, to perform the method, for example, when the instructions are executed. The computer-readable storage medium may include Random Access Memory (RAM), such as Ferroelectric RAM (FRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, a hard disk, a CD-ROM, a floppy disk, a magnetic tape cartridge, magnetic media, optical media, or other computer-readable media.

Claims

1. A system for providing therapy to a patient, the system comprising:

a stimulus generation circuit configured to provide electrical stimulus to the patient;

a sensing circuit configured to sense a first voltage on a first terminal and to sense a second voltage on a second terminal; and

processing circuitry electrically connected to the sensing circuitry and the stimulus generation circuitry, the processing circuitry configured to:

Causing the first voltage on the first terminal to be stored in a first calibration capacitor and the second voltage on the second terminal to be stored in a second calibration capacitor when the stimulus generating circuit does not provide the electrical stimulus;

after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch to prevent the second voltage stored in the second calibration capacitor from changing;

determining, with the sensing circuit, a sensing signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the stimulus generating circuit does not provide the electrical stimulus; and

Causing the stimulus generation circuit to deliver the therapy to the patient based on the sensing signal.

2. The system of claim 1, further comprising an amplifier circuit configured to:

receiving the sensing signal;

amplifying the sense signal using a first stage amplifier and at least a second stage amplifier to generate an amplified sense signal; and is also provided with

Wherein the processing circuit is configured to cause the stimulus generation circuit to deliver the therapy based on the amplified sensing signal.

3. The system of claim 2, wherein to amplify, the first stage amplifier amplifies the sense signal to a first amplified sense signal for output to the second stage amplifier, and wherein the amplifier circuit further comprises a set of blanking switches configured to:

preventing the first amplified sense signal from being received at the input of the second stage amplifier when the stimulus generating circuit provides the electrical stimulus; and

the first amplified sense signal is allowed to be received at the input of the second stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

4. The system of claim 3, further comprising a set of switches configured to:

preventing the sense signal from being received at the input of the first stage amplifier when the stimulus generating circuit provides the electrical stimulus; and

the first amplified sense signal is allowed to be received at the input of the first stage amplifier when the stimulus generating circuit does not provide the electrical stimulus.

5. The system according to claim 4,

wherein, to prevent the sense signal from being received at the input of the first stage amplifier, the set of switches is configured to prevent the sense signal after a first time delay from when the stimulus generation circuit is no longer providing the electrical stimulus; and is also provided with

Wherein to prevent the first amplified sense signal from being received at the input of the second stage amplifier, the set of blanking switches is configured to prevent the sense signal after a second time delay from when the stimulus generation circuit is no longer providing the electrical stimulus, wherein the second time delay is different from the first time delay.

6. The system of claim 5, wherein the second time delay is longer than the first time delay.

7. The system of claim 3, further comprising a set of blanking switches configured to clamp the voltage of the sense signal to a threshold voltage range.

8. The system of claim 7, wherein the threshold voltage range comprises a component safety voltage range.

9. The system of claim 2, wherein the first stage amplifier comprises a transconductance amplifier.

10. The system of claim 2, wherein the second amplifier stage is configured to auto-zero at an input and comprises a direct transconductance amplifier.

11. The system of claim 10, wherein the amplifier circuit comprises a third amplifier stage configured to receive the output of the second amplifier stage and to auto-zero at an input, wherein the third amplifier stage comprises a linearized transconductance amplifier.

12. The system of claim 11, wherein the amplifier circuit comprises a fourth amplifier stage configured to receive an output of the third amplifier stage and to auto-zero at an input.

13. The system of claim 9, wherein the processing circuit is further configured to:

14. The system of claim 2, further comprising an injection circuit configured to inject a cancellation offset between the first stage amplifier and the second stage amplifier.

15. The system of claim 14, wherein the injection circuit is further configured to generate the cancellation offset based on a weighted set of digital historical offsets for waveforms.

16. The system of claim 15, wherein the processing circuit is configured to determine the weighted digital history offset set of waveforms based on one or more previous sense signals occurring prior to the sense signal.

17. The system of claim 15, wherein the injection circuit is further configured to apply an integral controller to a weighted set of digital historic offsets of the waveform to generate the cancellation offset.

18. The system of claim 1, wherein the processing circuit is configured to:

generating a waveform based on the sense signal;

performing a derivative operation on the waveform;

after performing the derivative operation, applying a peak-to-valley operation to the waveform to determine an amplitude value; and

causing the stimulus generation circuit to deliver the therapy based on the amplitude value.

19. A method, comprising:

when the stimulus generating circuit does not provide electrical stimulus, causing, by the processing circuit, a first voltage on a first terminal of the sensing circuit to be stored in a first calibration capacitor and causing, by the processing circuit, a second voltage on a second terminal of the sensing circuit to be stored in a second calibration capacitor;

after the first voltage is stored in the first calibration capacitor and the second voltage is stored in the second calibration capacitor, and when the stimulus generating circuit provides the electrical stimulus, switching off a first calibration switch by the processing circuit to prevent the first voltage stored in the first calibration capacitor from changing, and switching off a second calibration switch by the processing circuit to prevent the second voltage stored in the second calibration capacitor from changing;

Determining, by the processing circuit, a sense signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on the second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the electrical stimulus is not provided by the stimulus generating circuit; and

the stimulation generation circuit is caused by the processing circuit to deliver the therapy to the patient based on the sensing signal.

20. A medical device, comprising:

determining, with the sensing circuit, a sensing signal based on the first voltage on the first terminal being offset by a first calibration voltage stored by the first capacitor and based on a second voltage on the second terminal being offset by a second calibration voltage stored by the second capacitor while the first calibration switch is turned off and the second calibration switch is turned off, and when the stimulus generating circuit does not provide the electrical stimulus; and