Extending ambient light cancellation range for optical sensing

Abstract

In some embodiments, a system for performing ambient noise cancellation includes an optical system including an optical emitter configured to emit light, an optical detector, and optical circuitry in electrical communication with the optical detector. The optical system can be configured to collect a charge imbalance with the integrating capacitor and receive an optical signal from the detector wherein the optical signal comprises a signal of interest component and a noise component. The optical system can be configured to subtract a first portion of the noise component from the optical signal by discharging the charge imbalance from the integrating capacitor, and subtract a second portion of the noise component from the optical signal by delivering a current from the current source, the current based directly or indirectly on time taken for the integrating capacitor voltage to reach the reference voltage level, thereby substantially isolating the signal of interest component.

Description

Aty Ref. No. A0012441W001EXTENDING AMBIENT LIGHT CANCELLATION RANGE FOR OPTICAL SENSING

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 724,863, filed November 25, 2024, the entire content of which is incorporated herein by reference.TECHICAL FIELD

[0002] The present technology relates to devices, systems, and methods for extending ambient light cancellation range for optical sensing.BACKGROUND

[0003] Many medical devices (e.g., pulse oximeters) utilize photoplethysmography (PPG), an optical technique that can be used to detect volumetric changes in blood in peripheral circulation. For example, PPG can be used to detect blood volume changes in the microvascular bed of tissue. PPG can, for example, provide quantification of physiological metrics such as blood pressure, heart rate, and blood oxygenation levels.

[0004] In general, PPG involves operation of an optical emitter-detector pair, where the emitter is a light source that illuminates tissue of interest, and the detector operates in a reflectance mode to measure the amount of that light that is reflected or otherwise transmitted to the detector. Some PPG devices are external (e.g., wearable), while some PPG devices are implantable in a patient.SUMMARY

[0005] The subject technology is illustrated, for example, according to various aspects described below, including with reference to FIGS. 1-11. Various examples of aspects of the subject technology are described as numbered clauses (1, 2, 3, etc.) for convenience. These are provided as examples and do not limit the subject technology.1. An optical system comprising: an optical emitter configured to emit light; an optical detector; andAtly Ref. No. A0012441W001 optical circuitry in electrical communication with the optical detector and comprising an integrating capacitor, a current source, and a timer, the timer configured to monitor time taken for an integrating capacitor voltage to reach a reference voltage level, wherein the optical system is configured to: collect a charge imbalance with the integrating capacitor; receive an optical signal from the detector, wherein the optical signal comprises a signal of interest component and a noise component; subtract a first portion of the noise component from the optical signal by discharging the charge imbalance from the integrating capacitor; and subtract a second portion of the noise component from the optical signal by delivering a current from the current source, the current based directly or indirectly on time taken for the integrating capacitor voltage to reach the reference voltage level, thereby substantially isolating the signal of interest component. The optical system of clause 1, wherein the optical circuitry is configured to limit the integrating capacitor to be no greater than a saturation voltage of the integrating capacitor. The optical system of clause 1 or 2, wherein the optical circuitry is configured to limit the integrating capacitor to be no greater than the reference voltage, wherein the reference voltage is less than the saturation voltage. The optical system of any one of clauses 1-3, wherein the current source comprises a current digital to analog converter. A medical device configured to be implanted in a patient, wherein the implantable medical device comprises the optical system of any one of clauses 1-4. The medical device of clause 5, wherein the medical device comprises an insertable cardiac monitor comprising a power source and one or more electrodes.Atty Ref. No. A0012441W001 The optical system of clause 6, wherein the insertable cardiac monitor is configured to be implanted subcutaneously in the patient. The medical device of clause 6 or 7, wherein the insertable cardiac monitor has a volume of about 1.5 cubic centimeters or less. A method of operating an optical system comprising an emitter and a detector, the method comprising: receiving an optical signal from the detector, wherein the optical signal comprises a signal of interest component and a noise component; developing a capacitor voltage across an integrating capacitor in electrical communication with the detector; canceling a first portion of the noise component from the optical signal by discharging the integrating capacitor of the capacitor voltage; and canceling a second portion of the noise component from the optical signal by delivering a current based directly or indirectly on a rate of change of the capacitor voltage during development of the capacitor voltage, thereby substantially isolating the signal of interest component. The method of clause 9, wherein receiving the optical signal from the detector is performed over a sensing period, and wherein developing the capacitor voltage across the integrating capacitor is performed while the emitter is inactive, prior to the sensing period. The method of clause 9 or 10, wherein receiving the optical signal from the detector is performed over a sensing period having a duration of Tsense, wherein a controller controls a current source to deliver the current based directly or indirectly on the rate of change of the capacitor voltage, and wherein the controller uses delta-sigma modulation at an oversampling frequency, wherein the oversampling frequency is an integer multiple of 1 / T sense-Atly Ref. No. A0012441W001 The method of any one of clauses 9-11, wherein the optical signal from the detector comprises a photoplethysmography (PPG) signal. The method of any one of clauses 9-12, wherein canceling a first portion of the noise component from the optical signal comprises switching a configuration of the integrating capacitor from a first polarity to a second polarity. The method of any one of clauses 9-13, wherein the current delivered while canceling the second portion of the noise component of the optical signal (Iamb, can) is a function of a duration of a sensing period (T sense), a duration of a saturation period (Tsat), and a calibration current (Icai), calculated as: Iamb,can =xIcal.The method of any one of clauses 9-14, further comprising controlling the emitter to emit light while canceling the first and second portions of the noise component from the optical signal. The method of any one of clauses 9-15, wherein canceling the first and second portions of the noise component from the optical signal are performed continuously and automatically. An optical system, the optical system comprising: an optical emitter configured to emit light; an optical detector; and optical circuitry in electrical communication with the optical detector and comprising an integrating capacitor, a capacitor swapping mechanism, a timer, and a current source, wherein the capacitor swapping mechanism is configured to switch a configuration of the integrating capacitor, and wherein the timer is configured to measure time remaining in a first sensing period after the integrating capacitor has reached a reference voltage, wherein the optical system is configured to: during the first sensing period, receive a first optical signal from the detector, and develop a charge imbalance on the integrating capacitor in a firstAty Ref. No. A0012441W001 configuration, the charge imbalance developing until a capacitor voltage reaches the reference voltage; switch the integrating capacitor to a second configuration via the capacitor swapping mechanism; during a second sensing period, receive a second optical signal from the detector, wherein the second optical signal comprises a signal of interest component and a noise component, the noise component comprises a first noise component and a second noise component; deliver a first cancellation current based on the charge imbalance on the integrating capacitor to cancel the first noise component; deliver via the current source a second cancellation current based on the time remaining in the first sensing period after the integrating capacitor reached the reference voltage to cancel the second noise component, thereby substantially isolating the signal of interest component.18. The optical system of clause 17, wherein the optical emitter only emits light during the second sensing period.19. The optical system of clause 17 or 18, wherein the second cancellation current is delivered through a negative feedback loop.20. The optical system of any one of clauses 17-19, further comprising a controller, wherein the controller comprises a processor and a memory, and wherein the time remaining in the first sensing period after the integrating capacitor reached the reference voltage is stored in the memory.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure.Atty Ref. No. A0012441W001

[0007] FIG. 1 is an illustrative conceptual diagram of an example optical device, in accordance with the present technology.

[0008] FIG. 2 is an illustrative schematic of example circuitry for processing signals from an optical sensor, in accordance with the present technology.

[0009] FIG. 3A is an illustrative schematic of an example embodiment of an implantable medical device, in accordance with the present technology.

[0010] FIG. 3B is a conceptual diagram of an example embodiment of an implantable medical device, in accordance with the present technology.

[0011] FIG. 4 is an illustrative schematic of a cardiac monitoring system including an implantable medical device placed in a patient, in accordance with the present technology.

[0012] FIG. 5 is a conceptual perspective schematic diagram of an example embodiment of an implantable medical device, according to various examples described in this disclosure.

[0013] FIG. 6A is an illustrative schematic of example circuitry of an optical sensor arrangement for canceling an ambient light portion of an optical signal using an integrating capacitor, in accordance with the present technology.

[0014] FIG. 6B is a timing diagram of the example circuitry shown in FIG. 6A, in accordance with the present technology.

[0015] FIG. 7 is a graphical representation of voltage over time for an integrating capacitor during a period of ambient light sensing, in accordance with the present technology.

[0016] FIG. 8A is an illustrative schematic of example circuitry of an optical sensor arrangement for canceling an ambient light portion of an optical signal using an integrating capacitor, a timer, and a current source, in accordance with the present technology.

[0017] FIG. 8B is a timing diagram of the example circuitry shown in FIG. 8A, in accordance with the present technology.

[0018] FIG. 9 is a flowchart of an example method to determine a cancellation current corresponding to ambient light, in accordance with the present technology.Atty Ref. No. A0012441W001

[0019] FIG. 10 is a flowchart of an example method to cancel portions of a noise component from an optical signal, in accordance with the present technology.

[0020] FIG. 11 is a flowchart of an example method to cancel components of an optical signal.DETAILED DESCRIPTION

[0021] Sensor signals often exist within a milieu of ambient noise. For example, optical signals, such as those of photoplethysmography (PPG), are accompanied by ambient light that can create noise in the signals. Ambient light can come from myriad sources such as a rising sun, a fluorescent lightbulb, or a television. In many applications in which an optical signal is sensed, ambient light can be excluded from the signal through physical and / or optomechanical techniques. For example, in a bedside application such as clinical pulse oximetry, an enclosure can block a substantial amount of environmental light from reaching an optical sensor arrangement that measures light absorption to determine blood oxygenation. In a wearable application such as a fitness tracker and / or smartwatch, a snug fit between the optical sensor arrangement and the portion of the body to be sensed can ensure minimal ambient light noise infiltrates the optical signal of interest. In some applications, however, shielding an optical sensor arrangement from ambient light is not practical and / or feasible. One example application includes optical sensing done within an implantable medical device. Implantable medical devices (such as insertable cardiac monitors) are disposed within human bodies and often cannot be easily reoriented or repositioned. For some implantable devices, for example subcutaneous devices, a portion of the optical sensor arrangement (e.g., one or more detectors) faces outward toward the skin and thus light that makes it through the skin in the region of the optical sensor arrangement falls directly onto that portion of the optical sensor arrangement, thereby creating a large ambient light interference, which can overwhelm the signal of interest. While some ambient light can be partially blocked through physical techniques (e.g., covering the skin with an opaque material such as cloth, or using an opaque housing), other signal conditioning processes may be needed to cancel a portion of the optical signal associated with noise of the ambient light.

[0022] In some applications, energy can be expended to condition a signal. For example, an optical sensor arrangement comprising an emitter and a detector to sense anAtly Ref. No. A0012441W001 optical signal can increase the intensity of light emitted by the emitter by using more energy, so that the optical signal detected by the detector comprises a greater portion of light from the emitter than light from the surrounding environment (e.g., ambient light). However, because implantable medical devices typically rely on small batteries which may not have ready access to recharging, implantable medical devices have limited power budget to use conditioning signals. As such, when a PPG device is implanted in a patient, optical signals obtained with a detector in the PPG device may be subject to noise from external, ambient light sources that can interfere with detection of the signals of interest; however, when implanted in the patient, PPG devices often lack the energy capacity to increase dynamic range to improve signal quality.

[0023] The present technology relates to devices, systems, and methods to improve signal conditioning by extending a cancellation range to eliminate a portion of the signal associated with the ambient environment, using minimal energy through passive techniques or active techniques or both. While these and other technical advantages and improvements are described herein in relation to subcutaneous devices, it will be understood that at least some of technical advantages and improvements are applicable to other devices. For example, various methods and arrangements presented herein result in approaches that enable optical signal processing with lower power expenditure; the technical advantage of reduced power expenditure may be desirable in virtually any other device such as, for example, a wearable optical sensor or a bedside monitor.

[0024] The present technology relates to devices, systems, and methods for performing optical sensing. Some embodiments of the present technology, for example, are directed to systems and methods for cancelling ambient noise in optical sensing. Specific details of several embodiments of the technology are described below with reference to FIGS. 1-11.

[0025] The techniques described herein may be used in various optical sensing devices configured to generate an optical signal using one or more optical emitters and one or more optical detectors. For example, FIG. 1 is an illustrative schematic of an example optical sensing device 100, which includes an optical sensor arrangement 110, electrical circuitry 120, and a power source 130.Atly Ref. No. A0012441W001I. Optical sensing devices and systems

[0026] The optical sensor arrangement 110 may include an emitter set of one or more emitters and a detector set of one or more detectors. The emitter set and the detector set may, in some embodiments, be located under an optically transparent surface (e.g., sapphire, glass, ceramic) of the optical sensing device, so as to allow passage of light out of and into the optical sensing device 100. Each emitter may be configured, when activated, to emit light at a desired wavelength suitable for optical signal measurements, such as photoplethysmography (PGG). For example, an emitter in the optical sensor arrangement 110 may be configured to emit light at a red wavelength (e.g., 640 nanometers (nm)-660 nm, or about 660 nm), a green wavelength (e.g., 530 nm-550 nm, or about 550 nm), or an infrared wavelength (e.g., 880 nm-940 nm, or about 940 nm). In some embodiments, light emitted from an active emitter may be filtered with one or more suitable filters in the optical pathway between the emitter and a corresponding detector in an emitter-detector pair being used to generate an optical signal (e.g., a PPG signal). Such filter(s) may block wavelengths that are not of interest for illuminating tissue, and pass through wavelengths that are of interest for illuminating tissue. For example, the filter(s) may include one or more suitable low-pass filters, high-pass filters, bandpass filters, or bandstop filters. The filter(s) may be coupled to an output side of the emitter or otherwise located in the optical pathway between the emitter and the detector. The emitter set may include any suitable type of light source, including, for example, a light-emitting diode (LED). Furthermore, each detector in the detector set may be configured to detect light that is emitted from an emitter and reflected off tissue of interest, where an optical signal such as a PPG signal may be derived from measurements of the reflected light. For example, a detector in the optical sensor arrangement 110 may include a photodiode. Various example configurations of the optical sensor arrangement 110 are described in further detail below.

[0027] The electrical circuitry 110 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for operating the optical sensor arrangement 110 (e.g., activating the emitter(s) in the emitter set) and / or generating a signal (e.g., a PPG signal). For example, the electrical circuitry 120 may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or other analog signal conditioning circuits.Atly Ref. No. A0012441W001

[0028] The electrical circuitry 120 and / or other portions of the optical sensing device 100 may also include digital circuits, e.g., switches, logic gates, multiplexers, diodes, transistors, combinational or sequential logic circuits, state machines, digital filters, integrated circuits, one or more processors 124 (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices 126, or any other suitable components or combination thereof that provide the described functionality. For example, in some embodiments, the optical signal is analyzed (e.g., by the one or more processors 124) to obtain one or more various physiological metrics of the patient, such as blood volume, blood flow, blood pressure, heart rate, blood oxygenation, tissue perfusion, and / or the like. Rates of change and / or comparisons against threshold values for the one or more various physiological metrics of the patient can also be analyzed (e.g., by one or more processors).

[0029] In some embodiments, the electrical circuitry 120 includes and / or is coupled to additional circuitry that provides for analog-to-digital conversion of at least one signal (e.g., a voltage signal, a current signal). In some embodiments, the electrical circuitry 120 includes and / or is coupled to additional circuitry that provides for digital-to-analog conversion of at least one signal (e.g., a control signal, a current signal).

[0030] The power source 130 provides power to electrical circuitry 120, the optical sensor arrangement 110, as well as to any other components that require power. Power source 130 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries.

[0031] The electrical circuitry 120 may include optical circuitry 128 configured for processing one or more sensor outputs from the detector set. The optical circuitry 128 may comprise, for example, an integrator amplifier that transforms a signal from an optical detector to a voltage signal that can be delivered to one or more components in the electrical circuitry 120. The optical circuitry 128 can be electrically and / or operatively coupled to the optical sensor arrangement 110 and / or the power source 130.

[0032] FIG. 2 is an illustrative schematic of an example circuit 200 for processing signals from an optical sensor. FIG. 2 shows a representative example of an integrator amplifier circuit 200 configured to translate a current (IN) from a sensor (e.g., an optical detector) into a voltage waveform (VOUT) measurable by an analog-to-digital converter.Atty Ref. No. A0012441W001More specifically, the circuit 200 includes an integrating capacitor (CINT) configured to integrate the detector current (IN) over a suitable integration time. In some embodiments, the integrating capacitor (CINT) is a non-polarized capacitor (e.g., a ceramic capacitor, a film capacitor, a paper capacitor). In some embodiments, the integrating capacitor is a polarized capacitor (e.g., an electrolytic capacitor). Though only as a single integrating capacitor (CINT) in FIG. 2, one of skill in the art will be appreciated that two or more capacitors could be used, such as two or more capacitors in series, two or more capacitors in parallel, three or more capacitors in a series-parallel combination, three or more capacitors in a delta-wye combination, etc.

[0033] In some embodiments of the present technology, a value associated with the detector current integrated over a period of time can be stored as a charge imbalance in the circuit 200 (e.g., as a voltage across the integrating capacitor (CINT)) and / or elsewhere (e.g. a component of the electrical circuitry 120). The capacitor may have a fixed or variable capacitance value, and the integration time may be fixed or adjustable. Thus, in some embodiments, the capacitance value and / or the integration time may be adjusted (e.g., via other components of electrical circuitry 120) to vary the gain and / or attenuation factor of the detector signal. Furthermore, the capacitance value and / or integration time may be measured (e.g., a timer can measure the integration time of the capacitor) and the measured value can be used to adjust one or more parameters of one or more components comprising the optical sensing device. For example, a magnitude of current delivered by the optical sensing device can be increased inversely with integration time of the capacitor. In some embodiments, a calibration current used to cancel a portion of an optical signal associated with ambient light is scaled to a ratio of time taken to saturate the capacitor (e.g., reach a maximal voltage across the capacitor) and the time taken to sense the ambient light.

[0034] In some embodiments, a switch (e.g., a reset switch) is in parallel with the integrating capacitor so as to facilitate discharging accumulated charges from the integrating capacitor (e.g., by shorting the capacitor). In some embodiments, one or more switches (e.g., float switches) are in series with the integrating capacitor so as to facilitate electrical isolation of the capacitor from other circuit elements. The integrating capacitor being electrically isolated from other circuit elements enables charge stored across the capacitor to be selectively engaged before, during, and / or after a sensing period. For example, during a first period of time, the integrating capacitor coupled in series to one or more switches isAtly Ref. No. A0012441W001 connected to the integrator amplifier and accumulates charge and during a second period of time, the one or more switches electrically disconnect the integrating capacitor from the integrator amplifier and stops accumulating charge. In some embodiments, during a third period of time, the capacitor can be reconnected to the integrator amplifier via the one or more switches and thereby cause charges stored through the capacitor to interact with the optical circuitry 200 (e.g., to condition a signal from the optical sensor).

[0035] Additionally or alternatively, the signal current of the detector may be sampled for more time (e.g., as controlled by other components of electrical circuitry 120), which may result in an increase of the gain and signal-to-noise ratio (SNR) of the optical signal, with the tradeoff of a lower available sampling rate. Further details regarding optical circuitry of the present technology are shown and described herein (e.g., in connection with FIGS. 6A-6B and 8A-8B).

[0036] In some embodiments, the techniques described herein for extending an ambient light cancellation range of optical sensing can be performed with respect to generating a PPG signal with an implantable device such as an implantable medical device. FIG. 3A is a conceptual diagram of an example of an implantable medical device (IMD) 300 (also referred to herein as a “cardiac monitoring device”) for detecting a bradycardia / asystole event, according to another embodiment of the present disclosure. Implantable medical device 300 is an example of optical sensing device 100. In the example shown in FIG. 3 A, implantable medical device 300 may be embodied as a monitoring device having housing 302, a first (e.g., proximal) electrode 304, and a second (e.g., distal) electrode 306. Housing 302 may further comprise a first major surface 308, a second major surface 310, a first (e.g., proximal) end 312, and a second (e.g., distal) end 314. Housing 302 encloses electronic circuitry 350 and power source 352 (shown in FIG. 3B) located inside the implantable medical device 300 and protects the circuitry contained therein from body fluids. Electrical feedthroughs provide electrical connection of electrodes 304 and 306.

[0037] In some embodiments such as that shown in FIG. 3A, implantable medical device 300 is defined by a length L, a width W and thickness or depth D. The implantable medical device 300 may be in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D. In some embodiments, the geometry of the implantable medical device 300 (for example, a width WAtly Ref. No. A0012441W001 greater than the depth D) may be selected to allow the implantable medical device 300 to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insert. For example, the device shown in FIG. 3 A may include radial asymmetries (notably, the rectangular shape) along the longitudinal axis that maintains the device in the proper orientation following insertion. For example, in some embodiments the spacing between the proximal electrode 304 and distal electrode 306 may range from 30 millimeters (mm) to 55 mm, 35 mm to 55 mm, and from 40 mm to 55 mm and may be any range or individual spacing from 25 mm to 60 mm. In addition, implantable medical device 300 may have a length L that ranges from 30 mm to about 70 mm. In other embodiments, the length L may range from 40 mm to 60 mm, 45 mm to 60 mm and may be any length or range of lengths between about 30 mm and about 70 mm. In addition, the width W of major surface 308 may range from 3 mm to 10 mm and may be any single or range of widths between 3 mm and 10 mm. In some embodiments, the thickness of depth D of the implantable medical device 300 may range from 2 mm to 9 mm. For example, the depth D of the insertable cardiac monitor 300 may range from 2 mm to 5 mm and may be any single or range of depths from 2 mm to 9 mm. In addition, implantable medical device 300 according to an example embodiment of the present invention has a geometry and size designed for ease of implant and patient comfort. Embodiments of the implantable medical device 300 described in this disclosure may have a volume of three cubic centimeters (cm) or less, 1.5 cubic cm or less or any volume between three and 1.5 cubic centimeters.

[0038] In the example shown in FIG. 3A, once inserted within the patient, the first major surface 308 faces outward, toward the skin of the patient while the second major surface 310 is located opposite the first major surface 308. In addition, in the example shown in FIG. 3 A, proximal end 312 and distal end 314 are rounded to reduce discomfort and irritation to surrounding tissue once inserted under the skin of the patient. Implantable medical device 300, including instrument and method for inserting monitor 300 is described, for example, in U.S. Patent Publication No. 2014 / 0276928, incorporated herein by reference in its entirety.

[0039] In some embodiments, the device 300 may include an optical sensor arrangement configured to detect light. The optical sensor arrangement may be under an optically transparent region enabling pass through of light to the optical sensor arrangement. For example, in some embodiments, a portion of the first major surface 308 is opticallyAtly Ref. No. A0012441W001 transparent to enable pass through of optical signals such as light into and out of the device 300 while housing 302 is hermetically sealed. The portion of the first major surface 308 which is optically transparent may comprise an aperture 362 with an optical window 364 that allows at least a portion of a visible light spectrum and / or a near-visible light spectrum (e.g., infrared light or ultraviolet light) to pass through to an optical sensor arrangement 360 (e.g., optical sensor arrangement 360 described herein with respect to FIG. 3B). In some examples, the optically transparent region (e.g., window) comprises an optically clear material such as sapphire, glass, and / or plastic. In some examples, the optical window 364 may be formed of the same material as the housing 302 and / or the first major surface 308. Additionally or alternatively, the second major surface 310 can comprise an optical window (e.g., the optical window 364). Though shown as having a circular area, the aperture 362 of the optical window 364 may be of any shape (e.g., triangular, rectangular, polygonal, curvilinear). In some examples, the optical window 364 comprises the entire first major surface 308 and / or other surface of the housing 302. In some examples, the first major surface 308 and / or any other suitable surface of the device 300 is optically transparent (e.g., the first major surface 308 comprises transparent sapphire).

[0040] In some embodiments a proximal electrode 304 and a distal electrode 306 are used to sense cardiac signals for determining a cardiac event (e.g., bradycardia or asystole event) such as EGM signals, intra-thoracically or extra-thoracically, which may be sub-muscularly or subcutaneously. EGM signals may be stored in a memory of the implantable medical device 300, and EGM data may be transmitted via integrated antenna 322 to another medical device, which may be another implantable device or an external device.

[0041] In the example embodiment shown in FIG. 3A, proximal electrode 304 is in close proximity to the proximal end 312 and distal electrode 306 is in close proximity to distal end 314. In this embodiment, distal electrode 306 is not limited to a flattened, outward facing surface, but may extend from first major surface 308 around rounded edges 316 and onto the second major surface 310 so that the electrode 306 has a three-dimensional curved configuration. In the example embodiment shown in FIG. 3A, proximal electrode 304 is located on first major surface 308 and is substantially flat, outward facing. However, in other embodiments, proximal electrode 304 may utilize the three-dimensional curved configuration similar to that of distal electrode 306, providing a three-dimensional proximalAtty Ref. No. A0012441W001 electrode (not shown in this embodiment). Additionally or alternatively, in other embodiments, distal electrode 306 may utilize a substantially flat, outward facing electrode located on first major surface 308 similar to that shown with respect to proximal electrode 304. The various electrode configurations allow for configurations in which proximal electrode 304 and distal electrode 306 are located on both first major surface 308 and second major surface 310. In other configurations, such as that shown in FIG. 3 A, only one of proximal electrode 304 and distal electrode 306 is located on both major surfaces 308 and 310, and in still other configurations both proximal electrode 304 and distal electrode 306 are located on one of the first major surface 308 or the second major surface 310 (e.g., proximal electrode 304 located on first major surface 308 while distal electrode 306 is located on second major surface 310). In some embodiments, the implantable medical device 300 may include electrodes on both major surface 308 and 310 at or near the proximal and distal ends of the device, such that a total of at least four electrodes are included on implantable medical device 300. Electrodes 304 and 306 may be formed of a plurality of different types of biocompatible conductive material (e.g. stainless steel, titanium, platinum, iridium, or alloys thereof), and / or may utilize one or more coatings such as titanium nitride or fractal titanium nitride.

[0042] In the example shown in FIG. 3 A, proximal end 312 includes a header assembly 320 that includes one or more of proximal electrode 304, an integrated antenna 322, anti-migration projections 324, and / or suture hole 326. The integrated antenna 322 may be located on the same major surface (e.g., first major surface 308) as proximal electrode 304 and may also included as part of header assembly 320. Integrated antenna 322 allows implantable medical device 300 to transmit and / or receive data. In some embodiments, integrated antenna 322 may be formed on the opposite major surface as proximal electrode 304, or may be incorporated within the housing 322 of implantable medical device 300. In the example embodiment shown in FIG. 3A, anti-migration projections 324 are located adjacent to integrated antenna 322 and protrude away from first major surface 308 to prevent longitudinal movement of the device, though may be arranged on any suitable surface of the implantable medical device 300. In the example embodiment shown in FIG. 3A, antimigration projections 324 include a plurality (e.g., nine) small bumps or protrusions extending away from first major surface 308; however, anti-migration projections 324 may additionally or alternatively be located on the opposite major surface as proximal electrodeAtty Ref. No. A0012441W001304 and / or integrated antenna 322. As shown in FIG. 3A, the suture hole 326, which may be used to help secure the implantable medical device 300 in the patient to prevent movement following insertion of the implantable medical device 300, may be located adjacent to proximal electrode 304, though one or more suture holes 326 may additionally or alternatively be located in any other suitable location. In some embodiments, the header assembly 320 is a molded header assembly made from a polymeric or plastic material, which may be integrated or separable from the main portion of implantable medical device 300.

[0043] FIG. 5 is a conceptual perspective schematic diagram of an implantable medical device 500 (IMD 500), according to various examples described in this disclosure. IMD 500 may be a leadless, subcutaneously implantable monitoring device including a proximal electrode 502A located at proximal end 504, a distal electrode 502B located at distal end 506 (collectively “electrodes 502”), a housing 508, electrical circuitry, an optical sensor arrangement 510 (comprising, for example optical sensor(s)), an integrated antenna 512, and a power source. In particular, electrical circuitry is coupled to proximal electrode 502B and distal electrode 502A to sense cardiac signals and monitor events. Electrical circuitry may also be connected to transmit and receive communications via integrated antenna 512. The power source can provide power to electrical circuitry, as well as to any other components that require power. The power source may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. In some examples, electrical circuitry includes processing circuitry and a storage device, such as memory (e.g., as shown in FIG. 3B), the memory being operatively coupled to the processing circuitry and configured to store data and / or instructions.

[0044] Electrical circuitry may be configured to receive one or more electrophysiological signals such as an electromyography (EMG) signal, an electrocardiography (ECG) signal, an electroencephalography (EEG) signal, and / or any biopotential-based signal. In the example shown in FIG. 5, electrical circuitry may receive one or more electrophysiological signals (e.g., raw EGM or EMG signals) monitored by the proximal electrode 502A and distal electrode 502B and raw optical signals monitored by the optical sensor arrangement 510. Electrical circuitry may include components / modules for converting the raw EGM signal to a processed EGM signal that can be analyzed to detect sense events and for converting the raw optical signals to calibrated processed optical signal(s) that can be analyzed to detect sense events. Although not shown, electrical circuitryAtty Ref. No. A0012441W001 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for analyzing optical signal(s) to determine a health condition status of a patient. For example, the electrical circuitry may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or other analog signal conditioning circuits. The modules may also include digital circuits, e.g., digital filters, combinational or sequential logic circuits, state machines, integrated circuits, a processor (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices, or any other suitable components or combination thereof that provide the described functionality.

[0045] In one example, electrical circuitry includes a sensing unit for monitoring the EGM signal detected by the respective proximal 502A and distal electrodes 502B and light signals received by the optical sensor arrangement 510, respectively. In one example, electrical circuitry includes processing circuitry that is utilized to receive information regarding sensed events and implements one or more algorithms for determining a health condition status of a patient. In addition, the analog voltage signals received from the electrodes 502 may be passed to analog-to-digital (A / D) converters included in the electrical circuitry and stored in a memory unit included as part of electrical circuitry for subsequent analysis with firmware executed by the processor included as part of electrical circuitry.

[0046] Some embodiments of the IMD 500 (e.g., examples shown in FIGS. 3 A, 3B, and 5) include a container 514 and an insulative cover 516. In some examples, the insulative cover 516 may include an optical window, the optical window transparent to at least a portion of a visible light spectrum and / or a near-visible light spectrum (e.g., infrared light or ultraviolet light). In some examples, the optical window comprises an optically clear material such as sapphire, glass, and / or plastic. In some examples, the optical window may be formed of the same material as insulative cover 516. In some examples, the optical window may be a portion of insulative cover 516. In some examples, the optical window comprises the entire insulative cover 516. In some examples, the insulative cover 516 is optically transparent (e.g., the insulative cover 516 comprises transparent sapphire). The proximal electrode 502A and the distal electrode 502B may be formed or placed on an outer surface of cover 516. The electrical circuitry may be formed or placed on an inner surface of cover 516, or within container 514. In some examples, the antenna 512 is formed or placed on the inner surface of cover 516. In other examples, antenna 512 is formed or placedAty Ref. No. A0012441W001 on the outer surface of cover 516, and in other examples, antenna 512 may be formed or placed at least partially on the inner surface and partially on the outer surface of cover 516. In some examples, insulative cover 516 may be positioned over an open container 15 such that container 514 and cover 516 form housing 20 and enclose electrical circuitry (and in some cases antenna 512) and protect the circuitries from fluids such as body fluids. For example, the housing 508 may be a hermetically-sealed housing configured for subcutaneous implantation within a patient, wherein at least the power source, memory, and processing circuitry are within the hermetically-sealed case, and in some examples, the optical sensor arrangement 510 are within the hermetically-sealed case.

[0047] The electrical circuitry may be formed on the inner side of insulative cover 516, such as by using flip-chip or wire bond integrated circuit packaging technology. Insulative cover 516 may be flipped onto a container 514. When flipped and placed onto container 514, the components of IMD 500 formed on the inner side of insulative cover 516 may be positioned in a gap defined by container 514. The electrodes 502 and the antenna 512 (when placed or formed on the outer surface of cover 516) may be electrically connected to sensing circuitry and communication circuitry, respectively, e.g., through one or more vias formed through insulative cover 516. The insulative cover 516 may be formed of sapphire (i.e., corundum), glass, and / or any other suitable insulating material. The container 514 may be formed from any suitable material configured to house electrical circuitry, support and mate with cover 516 to isolate electrical circuitry from contact with tissue and / or fluids of a patient, and to be implantable within the patient. In some examples, container 514 may house power source (e.g., a battery). In some examples, container 514 may also be electrically conductive. For example, container 514 may be formed from titanium or any other suitable material (e.g., a biocompatible material). Electrodes 502 may be formed from any of stainless steel, titanium, platinum, iridium, or alloys thereof. In addition, electrodes 502 may be coated with a material such as titanium nitride or fractal titanium nitride, although other suitable materials and coatings for such electrodes may be used.

[0048] In some embodiments, the IMD 500 is defined by a length L, a width W and thickness or depth D and is in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D, as illustrated in FIG. 5. In one example, the geometry of the IMD 500 - in particular a width W greater thanAtty Ref. No. A0012441W001 the depth D - is selected to allow the IMD 500 to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insert. For example, the IMD 500 may include a radial asymmetry (notably, a rectangular shape) along the longitudinal axis that maintains the device in the proper orientation following insertion. For example, in one example the spacing between the proximal electrode 502A and the distal electrode 502B may range from 30 millimeters (mm) to 55 mm, 35 mm to 55 mm, and from 40 mm to 55 mm and may be any range or individual spacing from 25 mm to 60 mm. In another example the spacing between the proximal electrode 502A and the distal electrode 502B may range from 15 mm to 30 mm, 17 mm to 28 mm, and from 20 mm to 28 mm and may be any range or individual spacing from 12 mm to 30 mm. In addition, the IMD 500 may have a length L that ranges from 30 mm to about 70 mm. In other embodiments, the length L may range from 40 mm to 60 mm, 45 mm to 60 mm and may be any length or range of lengths between about 30 mm and about 70 mm. In some examples, the IMD 500 may have a length L that ranges from 15 mm to about 35 mm, or from 20 mm to 30 mm, 22 mm to 30 mm and may be any length or range of lengths between about 15 mm and about 35 mm. In addition, the width W of a major surface of the IMD 500, e.g., insulative cover 516 in the example shown in FIG. 5, may range from 3 mm to 10 mm and may be any single or range of widths between 3 mm and 10 mm, or may range from 1.5 mm to 5 mm and may be any single or range of width between 1.5 mm and 5 mm. The thickness of depth D of the IMD 500 may range from 2 mm to 9 mm, or from 1.5 mm to 4.5 mm. In other embodiments, the depth D of the IMD 500 may range from 2 mm to 5 mm and may be any single or range of depths from 2 mm to 9 mm, or may range from 1 mm to 2.5 mm and may be any single or range of depths from 1 mm to 4.5 mm. In addition, IMD 500 according to an example of the present invention has a geometry and size designed for ease of implant and patient comfort. Examples of the IMD 500 described in this disclosure may have a volume of 3 cubic centimeters (cm) or less, 1.5 cubic cm or less or any volume between 3 and 1.5 cubic centimeters, or may have a volume of 1.5 cubic centimeters (cm) or less, 0.75 cubic cm or less or any volume between 1.5 and 0.75 cubic centimeters.

[0049] FIG. 3B is a functional schematic diagram of an implantable medical device, such as implantable medical device 300 as shown in FIG. 3 A in accordance with the present technology. Although the reference numbers refer to implantable medical device 300, it should be understood that other implantable medical devices (e.g., IMD 500) can includeAtly Ref. No. A0012441W001 one or more components similar to that described below. Implantable medical device 300 includes housing 302, proximal electrode 304 located at proximal end 312, distal electrode 306 located at distal end 314, integrated antenna 322, electrical circuitry 350 (which is an example of electrical circuitry 120), and power source 352 (which is an example of power source 130). In some embodiments, the implantable medical device 300 includes an optical sensor arrangement 360 (an example of optical sensor arrangement 110) comprising an emitter set of one or more optical light emitters and a detector set of one or more optical light detectors. The optical sensor arrangement 360 may, for example, be configured to provide a photoplethysmography (PPG) signal using the emitter and detector sets.

[0050] The optical sensor arrangement 360 can be configured to sense through one or more surfaces of the implantable medical device 300 (e.g., first major surface 308, second major surface 310, a surface of the header assembly 320). In some embodiments, one or more portions of the one or more surfaces comprise a material that is optically transparent to at least some wavelengths of light. For example, the one or more portions of the one or more surfaces through which the optical sensor arrangement 360 senses can be transparent to a red wavelength, transparent to a green wavelength, and / or transparent to an infrared wavelength. In some embodiments, the one or more portions of the one or more surfaces are optically transparent to visible light (e.g., electromagnetic radiation with a wavelength from approximately 380 nm to approximately 780 nm). The orientation of the optical sensor arrangement 360 with response to a patient is based on the implantation of the implantable medical device 300. For example, in some embodiments (e.g., embodiments wherein the optical sensor arrangement 360 senses through the first major surface 308), the optical sensor arrangement 360 is directed away from a center of the patient (e.g., oriented distally) when the implantable medical device 300 is implanted within the patient, and thus is exposed to a maximal amount of ambient light.

[0051] Fidelity of ambient light sensing can correlate to factors outside the optical sensor arrangement 360, such as physical activity of a patient and the environment surrounding the patient. Sensing from the optical sensor arrangement 360 can be affected when the patient moves vigorously and / or when then patient is in an environment of intense and / or rapidly varying ambient light. In some embodiments, the optical sensor arrangement 360 is configured to sense in response to sensor data (e.g., motion data, optical data). For example, in some embodiments, a motion sensor (e.g., an accelerometer) senses physicalAty Ref. No. A0012441W001 activity of the patient and while the patient is below a first motion threshold as sensed by the motion sensor (e.g., when the patient is resting, when the patient remains still), electrical circuitry 350 directs (e.g., via optical circuitry 358) the optical sensor arrangement 360 to sense. In some embodiments, the motion sensor senses the patient is above a second motion threshold (e.g., the patient is moving vigorously) and the electrical circuitry 350 directs the optical sensor arrangement 360 not to sense. In some embodiments, the optical sensor arrangement 360 senses for a first period of time to determine whether optical data is suitable for the optical sensor arrangement 360 to sense at a second period of time (e.g., immediately after, continuously until another condition is met) or whether the optical sensor arrangement 360 should sense at a third period of time (e.g., after a duration of time such as 1 minute).

[0052] The electrical circuitry 350 may be coupled to the optical sensor arrangement 360 to sense optical signals (e.g., via the optical circuitry 358) corresponding to PPG and / or ambient light. The electrical circuitry 350 may be coupled to the proximal electrode 304 and the distal electrode 306 to sense cardiac signals and monitor events (e.g., arrythmia, etc.). The electrical circuitry 350 is also connected to transmit and receive communications via integrated antenna 322. The power source 352 provides power to electrical circuitry 350, as well as to any other components that require power. Power source 352 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The implantable medical device 300 as shown in FIGS. 3A and 3B may be a monitoring-only device. However, in other examples, implantable medical device 300 may further provide therapy delivery capabilities.

[0053] The electrical circuitry 350 is configured to receive multiple signal types. For example, the electrical circuitry 350 can receive raw EGM signals monitored by proximal electrode 304 and distal electrode 306 and / or PPG signals monitored by the optical sensor arrangement 360. Electrical circuitry 350 may also include components / modules for converting a raw signal (e.g., EGM, PPG) to a processed signal that can be analyzed to detect sense events. Although not shown, electrical circuitry 350 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for analyzing EGM and / or PPG signals to detect / verify bradycardia and / or asystole events. For example, the electrical circuitry 350 may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or otherAtty Ref. No. A0012441W001 analog signal conditioning circuits. The modules may also include digital circuits, e.g., digital filters, combinational or sequential logic circuits, state machines, integrated circuits, one or more processors 354 (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices 356, or any other suitable components or combination thereof that provide the described functionality.

[0054] In some embodiments, electrical circuitry 350 may include a sensing unit for monitoring signals detected (e.g., by the proximal electrode 304 and distal electrode 306, by the optical sensor arrangement 360), and at least one sensing channel that utilizes an algorithm for identifying events in the signal (e.g., the EGM signal, the PPG signal). For example, sensed events (e.g., R-waves) are utilized to detect one or more cardiac episodes. In some embodiments, electrical circuitry 350 includes a processor configured to receive information regarding the sensed events and implements one or more algorithms for determining whether a particular one or more events have occurred. In addition, the analog voltage signals received from electrodes 304 and 306 and / or the optical sensor arrangement 360 may be passed to analog-to-digital (A / D) converters (ADC) included in the electrical circuitry 350, and stored in a memory unit 356 included as part of electrical circuitry 350 for subsequent analysis with firmware executed by the processor(s) 354 included as part of electrical circuitry 350.

[0055] Electrical circuitry 350 may control implantable medical device 300 functions and process signals received from electrodes 304 and 306 (e.g., EGM signals) and / or the optical sensor arrangement 360 (e.g., optical signals) according to programmed signal analysis routines or algorithms. The implantable medical device 300 may include optical circuitry 358 to facilitate optical signal detection, processing, and / or control. The implantable medical device 300 may include other optional sensors (not shown) for monitoring physiological signals, such as an activity sensor, pressure sensor, oxygen sensor, accelerometer, and / or other sensor used to monitor a patient. These may also be provided to electrical circuitry 350 for processing.

[0056] Electrical circuitry 350 may similarly control monitoring time intervals and sampling rates according to a particular clinical application. In addition, electrical circuitry may include state machines or other sequential logic circuitry to control device functions and need not be implemented exclusively as a microprocessor. For example, electricalAtty Ref. No. A0012441W001 circuitry 350 may include timers utilized to detect asystole events as described in more detail below.

[0057] Electrical circuitry 350 communicates with integrated antenna 322 (shown in FIG. 3 A) or other communication to transmit electrical signal data, e.g. EGM signal data, stored in memory or received from electrical circuitry 350 in real time. Antenna 322 may be configured to transmit and receive communication signals via inductive coupling, electromagnetic coupling, tissue conductance, Near Field Communication (NFC), Radio Frequency Identification (RFID), BLUETOOTH®, WiFi, or other proprietary or nonproprietary wireless telemetry communication schemes.

[0058] The electrical circuitry 350 may include a communication module including the integrated antenna 322, so as to enable the implantable medical device 300 to communicate with one or more external devices located external to the device 300. For example, as shown in FIG. 4, a cardiac monitoring system 400 may include an implantable medical device 10 (e.g., of which implantable medical device 300 and implantable medical device 500 are examples), which may include a communication module for communicating with a programmer 410. The programmer 410 may include a user interface that presents information to and receives input from a user. In some embodiments, the programmer 410 may include, for example, a suitable computing device such as a tablet, a smartphone, desktop computer, laptop computer, and / or the like. It should be noted that the user may also interact with programmer remotely via a networked computing device. As further shown in FIG. 4, in some embodiments, the implantable medical device 10 and / or the programmer 410 may be configured to transfer and / or receive information (e.g., cardiac data, such as EGM data and / or cardiac episode-related information derived from the EGM data) to and / or from a secondary memory storage device 420, such as over a wired or wireless network.

[0059] A user, such as a physician, technician, surgeon, electrophysiologist, other clinician, or patient, interacts with the programmer to communicate with implantable medical device 10. For example, the user may interact with the programmer to retrieve physiological or diagnostic information from the implantable medical device 10. A user may also interact with the programmer to program the implantable medical device 10, e.g., select values for operational parameters of the implantable medical device 10. For example, theAtly Ref. No. A0012441W001 user may use the programmer to retrieve information from the implantable medical device 10 regarding the rhythm of a patient heart, trends therein over time, or arrhythmic episodes. In some embodiments, alerts regarding device status (e.g., health state) and / or regarding type(s) of cardiac episode(s) detection may be provided to the patient or a clinician through the programmer 410, though they may be provided in any suitable manner (e.g., personal smartphone, other computing device, pushed through to an electronic medical record, etc.). The implantable medical device 10 and the programmer may communicate via wireless communication using any techniques known in the art.

[0060] In some embodiments, the implantable medical device 10 can be placed subcutaneously in a patient near or over the patient’s heart. For example, in some embodiments the implantable medical device 10 can be placed in a subcutaneous pocket located over an intercostal space (e.g., over the 4thintercostal space), and positioned at a desirable angle and / or displacement relative to the patient’s sternum (e.g., between about 0 and 45 degrees relative to the sternum, about 2 cm from the left edge of the sternum). Once inserted, the implantable medical device 300 may go through suitable setup and / or calibration processes.

[0061] In some examples, the implantable medical device 10 is implanted outside of a thoracic cavity of a patient (e.g., subcutaneously in a pectoral location). The implantable medical device 10 may be positioned near the sternum near or just below the level of the heart of the patient, e.g., at least partially within the cardiac silhouette. In some embodiments, the implantable medical device 10 includes a plurality of electrodes and is configured to sense a cardiac electrogram (EGM) via the plurality of electrodes, as well as other physiological signals and / or parameters via the optical sensor arrangement 360. In some examples, the implantable medical device 10 takes the form of an insertable cardiac monitor (ICM) such as the RevealLINQ™ or LINQ II™ ICM, or other ICM similar to, e.g., a version or modification of the RevealLINQ™ or LINQ II™ ICM. Although described primarily in the context of examples in which implantable medical device 10 is an ICM, in various examples, the implantable medical device 10 may represent a cardiac monitor, a defibrillator, a cardiac resynchronization pacer / defibrillator, a pacemaker, an implantable pressure sensor, a neurostimulator, or any other implantable or external medical device.Atty Ref. No. A0012441W001

[0062] Depiction of different features as modules is intended to highlight different functional aspects and does not necessarily imply that such modules must be realized by separate hardware or software components. Rather, functionality associated with one or more modules may be performed by separate hardware, firmware and / or software components, or integrated within common hardware, firmware and / or software components.

[0063] Furthermore, it should be understood that the systems and methods described herein in accordance with the present technology are not limited to the implantable medical devices 300, 500 described herein with respect to FIGS. 3A, 3B and 5. Rather, the systems and methods described herein in accordance with the present technology may additionally or alternatively be used in conjunction with other implantable medical device, in conjunction with other cardiac monitoring devices (e.g., other leadless cardiac monitoring devices, cardiac monitoring devices with leads, etc.), and / or in conjunction with other optical sensing devices (e.g., a wearable device measuring PPG).II. Ambient light cancellation

[0064] FIG. 6A is an illustrative schematic of example optical circuitry 600 associated with an optical sensor arrangement 610, where the optical circuitry 600 is configured to cancel an ambient light portion of an optical signal. In some embodiments, for example, the optical sensor arrangement 610 may be of any type described herein (e.g., optical sensor arrangement 110, optical sensor arrangement 360). The optical circuitry 600 is an example of optical circuitry described herein (e.g., optical circuitry 128, optical circuitry 358). The optical circuitry described herein (e.g., optical circuitry 128, optical circuitry 358, optical circuitry 600) can be incorporated in an implantable medical device (e.g., an implantable medical device such as implantable medical device 10, implantable medical device 300, implantable medical device 500, an insertable cardiac monitor). As shown in FIG. 6A, the optical sensor arrangement 610 can comprise at least one emitter 604 and at least one detector 606. The emitter 604 can comprise an associated emitter current source 608 and a light source 612 (e.g., an LED). The detector 606 can comprise an associated detector current source 614 and a light detector 616 (e.g., a photodiode, a phototransistor). Although the emitter current source 608 and detector current source 614 are shown in FIG. 6A as distinct entities, in some embodiments a single current source can comprise the emitter current source 608 and the detector current source 614. The opticalAtly Ref. No. A0012441W001 sensor arrangement 610 can be electrically and / or otherwise operatively coupled to the optical circuitry 600. In some embodiments, the optical circuitry 600 comprises an amplifier 618, an integrating capacitor 602 electrically connected to the amplifier 618, and a capacitor swapping mechanism 620 and a reset switch 622 electrically coupled to the integrating capacitor 602. The capacitor swapping mechanism 620 is configured to change the polarity of the integrating capacitor 602 from a first polarity to a second polarity in order to discharge an accumulated charge imbalance and the reset switch 622 is configured to return the integrating capacitor 602 to a nominal state (e.g., an uncharged state). The optical circuitry 600 may be electrically and / or otherwise operatively coupled to other components of electrical circuitry. For example, the optical circuitry 600 can be coupled to an analog-to- digital converter (ADC) 624 that converts an analog signal (e.g., a signal associated with measured light) to a digital signal usable by a processor 626 (e.g., by sampling a signal at a sampling frequency).

[0065] In some embodiments, optical circuitry 600 may comprise an integrating capacitor 602. In some embodiments, the integrating capacitor 602 can have a capacitance that is between 10 pF and 100 pF. In some embodiments, the integrating capacitor 602 has a capacitance that is less than 150 pF. The integrating capacitor 602 may have a fixed or variable capacitance value, and the integration time (e.g., the ambient light sensing time period) may be fixed or adjustable. Thus, in some embodiments, the capacitance value and / or the integration time may be adjusted (e.g., via other components of electrical circuitry 120) to vary the gain and / or attenuation factor of a detector signal (e.g., an optical signal received by the detector 616).

[0066] In some embodiments, during a first period of time (e.g., during a period of ambient light sensing), the integrating capacitor 602 is connected in a first configuration defining a first polarity, and during a second period of time (e.g., during a period of canceling an ambient light signal), the integrating capacitor 602 is connected in a second configuration defining a second polarity. The second polarity can be opposite the first polarity. The first period of time may be the same duration as the second period of time or the first period of time may be a different duration than the second period of time (e.g., the first period of time may be longer than the second period of time, the first period of time may be shorter than the second period of time). The first period of time and / or the second period of time can have a duration that is between 15 microseconds and 150 microseconds.Atly Ref. No. A0012441W001In some embodiments, the first period of time and / or the second period of time can be around 1 millisecond. In other embodiments, the first period of time and / or the second period of time is less than 1 millisecond. In some embodiments, the first period of time and / or the second period of time is approximately 100 microseconds. The duration of the first period of time and / or the second period of time can be modified based on one or more factors. For example, in some embodiments, the duration of the first period of time and / or the second period of time can be shortened to decrease power usage and increase a lifespan of the device. In some embodiments, the duration of the first period of time and / or the second period of time can be lengthened to increase sensitivity to a signal collected during the first period of time and / or the second period of time. A measurement period can comprise the first period of time and the second period of time. The measurement period can be repeated at a repetition frequency. The repetition frequency can be constant or it can vary. For example, in some embodiments, the repetition frequency of the measurement period can be about 128 Hz. In some embodiments, the repetition frequency of the measurement period can be from about 8 Hz to about 1024 Hz. In some embodiments, the repetition frequency of the measurement period is based on sensor data. For example, in some embodiments, the repetition frequency of the measurement period is increased in response to a physiological event (e.g., increased heart rate, decreased physical motion, changing blood pressure). The repetition frequency of the measurement period can also be modified based on other factors, such as power usage by the device and / or user input.

[0067] In some embodiments, the integrating capacitor 602 is connected in the first configuration with the first polarity as the optical sensor arrangement 610 senses ambient light only (e.g., while the emitter light source 612 is off, or inactive), causing the integrating capacitor 602 to store a charge imbalance as a current is delivered by the detector 606 over the first period of time in response to the ambient light. The integrating capacitor 602 is then connected in the second configuration with the second polarity (e.g., via the capacitor swapping mechanism 620) as the optical sensor arrangement 610 senses ambient light and light from the emitter light source 612 (e.g., while the emitter light source 612 is on, or active). The charge imbalance stored on the integrating capacitor 602 delivers a current equal to the current delivered during the first period of time in response to the ambient light only. Since the integrating capacitor 602 is in the second configuration with the second polarity (e.g., an opposite polarity relative to the first polarity), the stored charge imbalanceAtly Ref. No. A0012441W001 current acts against a detector current comprising both ambient light and emitter light signals. Thus, the processed signal that remains during the second period of time comprises substantially only that produced in response to the emitter light source 612. This signal conditioning technique can be thought of as primarily passive since the energy used to condition the signal is from a charge imbalance stored on the integrating capacitor 602 developed in response to a background noise signal (e.g., ambient light) present in both the first period of time and the second period of time, with energy stored in the first period of time used to countervail energy from the second period of time.

[0068] FIG. 6B illustrates an example timing diagram of operation of the example circuitry shown in FIG. 6A. The time-logic representation of FIG. 6B shows a state of an optical sensing device including a state of the amplifier 618 ("Amplifier ON"), a state of ambient light sensing ("Ambient light sensing"), a state of the light source 612 such as an LED ("LED ON"), a state of the capacitor swapping mechanism 620 ("Capacitor swap"), a state of the reset switch 622 ("Capacitor reset"), and the state of a current source 606 such as a current DAC ("DC subtraction DAC").

[0069] A first phase of the ambient light cancellation method begins at time T1 when an ambient light sensing period begins. Prior to the initiation of the first phase of the ambient light cancellation method (e.g., just before Tl), the amplifier 618 is powered on. Once the first phase of the ambient light cancellation method begins, the integrating capacitor 602 begins to store a charge imbalance. The integrating 602 capacitor accumulates a charge imbalance (e.g., develops an electrical potential) until time T2 when the ambient light sensing period ends. From time T2 to time T3, the capacitor swapping mechanism 620 switches the integrating capacitor 602 from a first configuration with a first polarity to a second configuration with a second polarity. The duration from time Tl to time T2 can be from about 15 microseconds to about 150 microseconds. The duration from time T2 to time T3 is very short (e.g., <1 microsecond, <5% of the duration from time Tl to time T2).

[0070] A second phase of the ambient light cancellation method begins once the capacitor swapping mechanism 620 has switched the configuration of the integrating capacitor 602 (e.g., at time T3). Once the capacitor swapping mechanism 620 has switched the configuration of the integrating capacitor 602 (e.g., from a first configuration to a second configuration), the light source 612 (e.g., an LED) is turned on (e.g., at time T3). In someAtly Ref. No. A0012441W001 embodiments, once the capacitor swapping mechanism 620 has switched the configuration of the integrating capacitor 602, a current source 606 (e.g., the detector current source) turns on and thereby conditions a signal (e.g., by subtracting out a DC component). In some embodiments, the light source 612 remains on for a time equal to the duration of the ambient light sensing period that preceded it (e.g., about equal to the time from about time T1 to about the time T2). During this period of time, the charge imbalance stored on the integrating capacitor 602 can be delivered throughout the optical circuitry 600, and in so doing, eliminate from the signal a contribution corresponding to ambient light, leaving only a signal derived from an emitter signal.

[0071] A third phase of the ambient light cancellation method begins when the integrating capacitor 602 is reset (e.g., by a reset switch 622) at time T4. The integrating capacitor 602 can be reset for example by shorting the integrating capacitor 602. A reset period, such as from time T4 to time T5, can be sufficient to remove substantially all remaining residual charge on the integrating capacitor 602. Once the integrating capacitor 602 has been reset to a nominal state, the capacitor swapping mechanism 620 switches the integrating capacitor 602 from the second configuration with the second polarity to the first configuration with the first polarity from time T6 to time T7. In some embodiments, the amplifier 618 is turned off at time T7 and remains off until just before the next period of ambient light sensing.

[0072] A measurement period comprising the first phase, the second phase, and the third phase of the ambient light cancellation method can be repeated with a repetition frequency. The repetition frequency can be constant or the repetition frequency can vary (e.g., in response to sensor data). In some embodiments, the repetition frequency of the measurement period can be about 128 Hz. In some embodiments, the repetition frequency of the measurement period can be from about 8 Hz to about 1024 Hz. In some embodiments, the repetition frequency of the measurement period can change from one measurement period to another.

[0073] An initial measurement period with an initial first phase, an initial second phase, and an initial third phase can be followed by a subsequent measurement period with a subsequent first phase, a subsequent second phase, and a subsequent third phase. TheAtly Ref. No. A0012441W001 initial measurement period may have the same timing as the subsequent measurement or they may have different timings.

[0074] As shown in FIG. 6B, in some embodiments, the initial first phase begins with an initial ambient light sensing period starting at time T1 and a subsequent first phase begins with a subsequent ambient light sensing period starting at time Ti l. The initial first capacitor polarity switching occurs from time T2 to time T3, and a subsequent second capacitor polar switching occurs from time T12 to time T13. The initial and subsequent ambient light sensing periods can be substantially the same, for example, the duration between T1 and T2 and the duration between Ti l and T12 can be equal. In some embodiments, the duration between T1 and T3 and the duration between Ti l and T13 are the same. In some embodiments, the duration between T1 and T3 and the duration between T11 and T13 are different. For example, the duration of a subsequent ambient light sensing period may be less than the duration of an initial ambient light sensing period if ambient light is very intense and / or to conserve device energy.

[0075] The initial second phase of the ambient light cancellation method begins when the light source 612 is turned on at time T3 and a subsequent second phase begins when the light source 612 is turned on at time T13. The initial second phase lasts until T4 when the reset switch is engaged and the integrating capacitor 602 returned to a nominal state and the subsequent second phase lasts until T14 when the reset switch is engaged and the integrating capacitor 602 returned to a nominal state. In some embodiments, the duration of the initial second phase is equal to the duration of the initial first phase so that the charge imbalance stored on the integrating capacitor 602 accumulates and discharges over the same amount of time. In some embodiments, the duration of the subsequent second phase is equal to the duration of the subsequent first phase so that the charge imbalance stored on the integrating capacitor 602 accumulates and discharges over the same amount of time. In some embodiments, the duration of the initial second phase and the duration of the subsequent second phase can be the same. In some embodiments, the duration of the initial second phase and the duration of the subsequent second phase can be different.

[0076] The initial third phase of the ambient light cancellation method begins at timeT4 when the integrating capacitor 602 is reset, and a subsequent third phase begins at time T14 when the integrating capacitor 602 is reset (e.g., by the reset switch 622). An initialAtty Ref. No. A0012441W001 reset period from time T4 to time T5 may be the same as a subsequent reset period from time T14 to time T15 or they may be different. Once the integrating capacitor 602 has been reset, the capacitor swapping mechanism 620 switches the polarity of the integrating capacitor 602 from time T6 to time T7 in an initial second capacitor polarity switching period, and from time T16 to time T17 in a subsequent second capacitor polarity switching period.

[0077] In some situations of some embodiments, the integrating capacitor 602 meant to store a charge imbalance proportional to the intensity of ambient light can become saturated and unable to store a sufficient charge imbalance to represent the intensity of the ambient light. For example, when the ambient light is very intense (e.g., very bright), the charge imbalance stored on the integrating capacitor 602 (e.g., the voltage across the integrating capacitor 602) will tend toward charge imbalances (e.g., a voltage) beyond what the integrating capacitor 602 can provide. To avoid saturation, the measurement period can be shortened.

[0078] FIG. 7 is a graphical representation of voltage across an integrating capacitor over time during an ambient light sensing time period, Tsense, showing saturation of the integrating capacitor. The integrating capacitor can saturate under several circumstance, such as when the optical sensing device is exposed to intense light (e.g., outdoor light, bright indoor light), during longer measurement period durations (e.g., a longer measurement period may be used to more accurately measure a signal), and when ambient light intensity varies rapidly (e.g., a patient proximate a television screen). FIG. 7 shows the voltage across the integrating capacitor increases at a rate until a saturation voltage Vsat is reached at a time Tsat, after which point the saturated capacitor (solid line) maintains a constant voltage Vsat for the remainder of the ambient light sensing time period, Tsense. In the absence of a saturation limit, the voltage across the integrating capacitor would continue to increase at a rate (dashed line) until a maximum voltage Vmaxis reached at the end of the ambient light sensing time period T sense-

[0079] The rate at which the voltage develops across the integrating capacitor before saturation (e.g., <Tsat) can be used to model the rate at which voltage would have developed across the integrating capacitor after Tsat in the absence of a saturation limit. Modeling the rate at which the voltage develops across the integrating capacitor can include one or moreAtty Ref. No. A0012441W001 factors. For example, the rate at which the voltage develops across the integrating capacitor is in part dependent on the dielectric properties (e.g., capacitance) of the integrating capacitor, where larger capacitances tend to develop voltage across a capacitor at slower rates than smaller capacitances which tend to develop voltage across the capacitor at faster rates. Although shown in FIG. 7 as a linear relationship, the voltage that develops across the integrating capacitor may vary with time in other ways. For example, the rate at which voltage develops across the integrating capacitor can be linear, curvilinear, described by a polynomial, defined by a power function, a sinusoidal function, an exponential function, or any combination thereof. Moreover, while FIG. 7 shows a single ambient light sensing time period with a duration of time Tsense, it will be appreciated that other durations are possible and the ambient light sensing time duration can be varied from one ambient light sensing time period to the next. In some embodiments, the duration of the ambient light sensing time period Tsense can be from about 15 microseconds to about 150 microseconds.

[0080] In some situations, an integrating capacitor (e.g., with reference to FIGS. 6A and 6B, integrating capacitor 602) can become saturated and thereby limit the range of ambient noise cancellation that is attainable by switching the polarity of the integrating capacitor. Because the saturated integrating capacitor can only store a finite charge imbalance, it can only deliver up to a finite current over a given period of time. In some situations, this current delivered by the saturated integrated capacitor will not be sufficient to cancel a portion of a signal associated with noise (e.g., ambient light noise). For example, in situations in which an optical sensor arrangement is disposed in an environment of high intensity ambient light (e.g., outdoors) and / or highly variable ambient light (e.g., in front of a television screen, in front of a computer monitor, during physical activity), the current of an optical signal measured in the environment can be high and / or highly variable, due in part to an ambient light noise contribution to the optical signal. Other embodiments of the optical circuitry in accordance with the present technology can enable further ambient light noise cancellation (e.g., by extending a range of ambient light noise cancellation).

[0081] The optical circuitry 600 of FIG. 6A enables a passive technique of cancellation since the energy used to condition the signal comes from that stored in the integrating capacitor in response to sensing ambient energy (e.g., detecting ambient light). Other embodiments of the optical circuitry described herein (e.g., the optical circuitry of FIG. 8A, as described below) additionally or alternatively enable an active technique ofAtly Ref. No. A0012441W001 cancellation since a portion of the energy used to condition the signal comes from a source (e.g., a current source connected to a power source), which further improves ambient light noise cancellation by providing additional energy to extend the range of cancellation.

[0082] FIG. 8A is an illustrative schematic of example optical circuitry 800 of an optical sensor arrangement 810 for canceling an ambient light portion of an optical signal comprising an integrating capacitor 802, a timer 804 (e.g., a time-to-digital converter), and a current source (e.g., detector current source 806). The optical circuitry 800 is an example of optical circuitry described herein (e.g., optical circuitry 128, optical circuitry 358, optical circuitry 600). The optical circuitry described herein (e.g., optical circuitry 128, optical circuitry 358, optical circuitry 600, optical circuitry 800) can be incorporated in an implantable medical device (e.g., an implantable medical device such as implantable medical device 10, implantable medical device 300, implantable medical device 500, an insertable cardiac monitor). The optical sensor arrangement 810 may be of any type described herein (e.g., optical sensor arrangement 110, optical sensor arrangement 360, optical sensor arrangement 610). As shown in FIG. 8 A, in some embodiments of the present technology, the optical sensor arrangement 810 can comprise an emitter 808 and a detector 812. The emitter 808 can comprise an associated emitter current source 814 and a light source 816 (e.g., an LED). The detector 806 can comprise a detector current source 806 and a light detector 818 (e.g., a photodiode, a phototransistor). Although shown in FIG. 8 A as distinct entities, a single current source can comprise the emitter current source 814 and the detector current source 806. The optical sensor arrangement 810 can be electrically and / or operatively coupled to the optical circuitry 800. In some embodiments, the optical circuitry 800 comprises an amplifier 820, an integrating capacitor 802 electrically connected to the amplifier 820, one or more switches 822 to electrically isolate the integrating capacitor 802 (also known as float switches 822), and a capacitor swapping mechanism 824 and a reset switch 826 electrically coupled to the integrating capacitor 802. The capacitor swapping mechanism 824 is configured to change the polarity of the integrating capacitor 802 from a first polarity to a second polarity and the reset switch 826 is configured to return the integrating capacitor 802 to a nominal state (e.g., an uncharged state). Although shown in FIG. 8A as distinct, it will be appreciated that two or more elements can be combined into a single element capable of the structure and / or function of the two or more elements. For example, a single component can comprise the one or more switches 822 to electricallyAtty Ref. No. A0012441W001 isolate the integrating capacitor 802 and the capacitor swapping mechanism 824 to switch the configuration of the integrating capacitor 802. A process of switching the integrating capacitor from a first configuration to a second configuration via the capacitor swapping mechanism 824 of FIGS. 8A and 8B can, for example, be similar to that used by the capacitor swapping mechanism 620 of FIGS. 6A and 6B. The optical circuitry 800 may be electrically and / or operatively coupled to other components of electrical circuitry. For example, the optical circuitry 800 can be coupled to an analog-to-digital converter (ADC) 828 that converts an analog signal (e.g., a signal associated with measured light) to a digital signal usable by a processor 830 (e.g., by sampling a signal at a sampling frequency).

[0083] Although the optical circuitry 600 in FIG. 6A can enable ambient light cancellation, the optical circuitry 600 may be limited by the saturation of the integrating capacitor 602. Optical circuitry 800 in FIG. 8A includes additional operable components to extend the range of ambient light cancellation. As shown in FIG. 8A, in some embodiments of the present technology, an output of the amplifier 820 may be used as an input to a comparator 832. The comparator 832 may be set to a reference voltage level Vref such that when a level of the input exceeds the reference voltage level Vref, the comparator 832 trips (e.g., an output of the comparator 832 is true). In some embodiments, the reference voltage level Vref is set to about equal to a saturation voltage Vsat for the integrating capacitor 802. In some embodiments, the reference voltage level Vref is set to be less than the saturation voltage Vsat of the integration capacitor 802. For example, in some embodiments, the reference voltage level Vref is set to be about 95% of the magnitude of the saturation voltage Vsat. In some embodiments, the reference voltage level Vref is set to be about 99% of the magnitude of the saturation voltage Vsat. In some embodiments, Vsat is a value between about 3 V and about 7V, or between about 4V and about 6V, or about 5 V. Vref can, in some embodiment, be set to be between about 2.5V and about 6.5V, or between about 3.5V and about 5.5V, or between about 4.5V and about 4.9V, though can be any suitable value. The output of the comparator 832 can be tracked (e.g., by the processor 830) for each measurement period and / or across measurement periods. One or more timers 804 can mark when an ambient light sensing period begins, when the integrating capacitor 802 saturates (e.g., when the output of the comparator 832 is true), and when the ambient light sensing period ends. In some embodiments, the processor 830 utilizes data from the timer 804 to scale a calibration current (e.g., a current delivered by the detector current source 806).Atly Ref. No. A0012441W001

[0084] The integrating capacitor 802 may be of any type described herein (e.g., integrating capacitor 602). In some embodiments the integrating capacitor 802 has a capacitance between 10 pF and 100 pF. In some embodiments, the integrating capacitor 802 has a capacitance that is less than 150 pF. The integrating capacitor 802 may have a fixed or variable capacitance value, and the integration time (e.g., a first portion of an ambient light sensing time period) may be fixed or adjustable. Thus, in some embodiments, the capacitance value and / or the integration time may be adjusted to vary the gain and / or attenuation factor of a detector signal.

[0085] In some embodiments of the present technology, a measurement period of an optical sensing device comprises an ambient light sensing phase, an emitter light sensing phase, and a reset phase. The measurement period can be performed one or more times. In the embodiments in which the measurement period is performed more than once, the measurement period repetition frequency can be constant (e.g., approximately 128 Hz) or may vary (e.g., in response to sensor data, to conserve power, to improve signal fidelity).

[0086] The ambient light sensing phase comprises a first ambient light sensing phase in which a voltage across the integrating capacitor 802 is less than a reference voltage Vref (e.g., about equal to a saturation voltage of the integrating capacitor 802) and a second ambient light sensing phase in which a voltage across the integrating capacitor 802 is equal to or greater than the reference voltage Vref (e.g., approximately the saturation voltage of the integrating capacitor 802). At the end of the first ambient light sensing phase, one or more float switches 822 are thrown to electrically isolate the integrating capacitor 802. The timer 804 can determine the duration of the first ambient light sensing phase and / or the second ambient light sensing phase and the processor 830 can determine a relationship between the duration of the first ambient light sensing phase and the duration of the second light sensing phase, such as by taking a ratio of durations (e.g., a ratio of the duration of the first ambient light sensing phase to a total duration of the ambient light sensing phase). Between the ambient light sensing phase and the emitter light sensing phase, the integrating capacitor 802 is switched from a first configuration with a first polarity to a second configuration with a second polarity, the second polarity opposite the first polarity, and the one or more float switches thrown to electrically connect the integrating capacitor 802 across the amplifier 820.Atly Ref. No. A0012441W001

[0087] The emitter light sensing phase comprises activating an emitter light source 816 (e.g., turning on an LED) and detecting the emitter light with the detector 812 (e.g., via the light detector 818). During the emitter light sensing phase, the integrating capacitor 802 is electrically coupled to the amplifier 820 and current is delivered by the detector current source 806.

[0088] The current delivered by the detector current source 806 (e.g., during the emitter light sensing phase) can comprise a cancellation current. One or more values associated with the cancellation current (e.g., a magnitude, a waveform) can be delivered via a feedback loop 834 connecting (e.g., coupling with electrical communication) the processor 830 and the detector 812 (e.g., to the detector current source 806) so that the cancellation current may counteract a current associated with the detector 812 (e.g., during the emitter light sensing phase). In some embodiments, the feedback loop 834 is a negative feedback loop. In some embodiments, the feedback loop 834 facilitates a control method (e.g., in a control loop) such as proportional control, integral control, derivative control, fuzzy logic control, model predictive control, and / or combinations thereof. The current delivered can be a direct current (DC) or an alternating current (AC) or a combination. In some embodiments, the current delivered by the detector current source 806 can comprise two or more components, such as a first DC component (e.g., to cancel an offset to a signal) and a second DC component (e.g., to cancel an ambient light contribution to a signal). The magnitude of the current delivered by the detector current source 806 can be based in part on a duration of time during an ambient light sensing phase. For example, the processor 830 can calculate a ratio of the time duration to saturate the integrating capacitor 802 (e.g., the first ambient light sensing phase) to the total time duration for the ambient light sensing phase (e.g., comprising both the first ambient light sensing phase and the second ambient light sensing phase). Based on the ratio, a portion of the current delivered by the detector current source 806 (e.g., a second DC component) can be scaled to a calibration current. For example, in some embodiments current delivered by the detector current source 806 to cancel an ambient light contribution is calculated aswhere an ambient light cancellation current, Iamb, can, is a function of the calibration current Lai, the duration of the first ambient light sensing phase Tsat, and the total duration of theAtly Ref. No. A0012441W001 light sensing phase Tsense. In some embodiments, current is delivered by the detector current source 806 as long as the emitter light source 816 is on. In those embodiments in which Tsat < Tsense, a time remaining after the first light sensing phase will be equal to the difference between Tsense and Tsat (e.g., the time remaining is equal to Tsat subtracted from Tsense).

[0089] In some embodiments, the magnitude of the calibration current Icaiis equal to the magnitude of the current required to cause the integrating capacitor 802 to saturate (e.g., reach Vsat) at the end of the ambient light sensing period (e.g., at Tsense). The magnitude of the calibration current can be proportional (e.g., linearly correlated) to the rate at which voltage across the integrating capacitor 802 develops during time, Tsense. In some embodiments, the cancellation current is based on a ratio of the time remaining after saturation (e.g., the difference between Tsense and Tsat) to the total duration of the ambient light sensing period (e.g., Tsense) scales the calibration current, such that when the time remaining after saturation is equal to 10% of the total duration of the ambient light sensing period, the cancellation current is 10% of the magnitude of calibration current, when the time remaining after saturation is equal to 50% of the total duration of the ambient light sensing period, the cancellation current is 50% of the magnitude of calibration current, and when the time remaining after saturation is equal to 90% of the total duration of the ambient light sensing period, the cancellation current is 90% of the magnitude of calibration current.

[0090] The reset phase comprises the reset switch 826 resetting the integrating capacitor 802 to a nominal state (e.g., an uncharged state). At the end of the reset phase, the integrating capacitor 802 is switched from the second configuration with the second polarity to the first configuration with the first polarity. At the end of the reset phase, the integrating capacitor 802 is electrically connected to the amplifier 820.

[0091] When the integrating capacitor 802 is connected in the first configuration with the first polarity (e.g., as the optical sensor arrangement 810 senses ambient light only and the emitter light source 814 is off), the integrating capacitor 802 stores a charge imbalance as a current is delivered by the detector 812 over the duration of the ambient light sensing phase. When the integrating capacitor 802 is connected in the second configuration (e.g., via the capacitor swapping mechanism 824) with the second polarity (e.g., as the optical sensor arrangement 810 senses ambient light and light from the emitter light source 816 (e.g., the emitter light source 816 is on), the charge imbalance stored on the integratingAtly Ref. No. A0012441W001 capacitor 802 delivers a current equal to the current delivered during the ambient light sensing phase and acts against a detector current comprising both ambient light and emitter light signals. Moreover, if the integrating capacitor 802 were to saturate during the ambient light sensing phase, the timer 804 can determine when that occurs, and the processor 830 can direct the detector current source 806 to deliver ambient light cancellation current (e.g., in the manner described above). Thus, this signal conditioning technique can be thought of as comprising both passive and active conditioning. The passive conditioning of the signal comprising energy used to condition the signal coming from a charge imbalance stored on the integrating capacitor 802 developed in response to a background noise signal (e.g., ambient light) present in both the ambient light sensing phase and the emitter light sensing phase, with energy stored in the ambient light sensing phase used to countervail energy from the emitter light sensing phase. The active conditioning of the signal comprising energy from the detector current source 806 delivered in response to the saturation of the integrating capacitor 802 (e.g., the time taken to saturate the integrating capacitor 802). In some embodiments, a contribution corresponding to ambient light is cancelled from a signal (e.g., a PPG signal) using passive conditioning to cancel a first portion of the signal and using active conditioning to cancel a second portion of the signal, wherein with the first portion and the second portion of the signal cancelled, what remains of the signal is associated primarily with signal detected (e.g., by the light detector 818) from the emitter 808 (e.g., measured when the light source 816 is on).

[0092] FIG. 8B illustrates a timing diagram of the example circuitry shown in FIG. 8A. The time-logic representation of FIG. 8B shows a state of an optical sensing device including a state of the amplifier ("Amplifier ON"), a state of the ambient light sensing ("Ambient light sensing"), a state of the comparator ("Comparator output"), a state of the integrating capacitor isolation ("Capacitor float"), a state of the emitter light source ("LED ON"), a state of the capacitor swapping mechanism ("Capacitor swap"), a state of the reset switch ("Capacitor reset"), and a state of the detector current source ("DC + Ambient subtraction DAC").

[0093] A first phase of the ambient light cancellation method begins at time T1 when an ambient light sensing period begins. The ambient light sensing period has a duration that can be fixed or it can vary (e.g., from about 15 microseconds to about 150 microseconds). Prior to the initiation of the first phase of the ambient light cancellation method (e.g., justAtly Ref. No. A0012441W001 before Tl), the amplifier 820 is powered on. Once the first phase of the ambient light cancellation method begins, the integrating capacitor 802 begins to store a charge imbalance (e.g., develop a voltage across the capacitor 802). The integrating capacitor 802 accumulates charge imbalance until time T2 when the integrating capacitor 802 becomes saturated or nearly saturated. The comparator 832 can be configured to determine when the integrating capacitor 802 has been saturated. The output of the comparator 832 can be connected to the timer 804 to determine time taken to saturate the integrating capacitor 802.

[0094] In some embodiments, a first input of the comparator 832 is connected to the output of the amplifier 820 and a second input of the comparator 832 is held at a reference voltage Vref equal to or nearly equal to a saturation limit (e.g., a saturation voltage) of the integrating capacitor 802, such that the comparator 832 trips (e.g., its output becomes true) when the voltage across the integrating capacitor 802 is about equal to or greater than Vref. The output of the comparator 832 is connected a timer (e.g., the timer 804), which can record the time at which saturation occurs (e.g., relative to the start of the ambient light sensing period). The length of time taken to saturate the integrating capacitor 802 can be temporarily stored (e.g., in the optical circuitry 800, in the processor 830) and its value can be used at another point in the ambient light cancellation method (e.g., to control a current source while the emitter light source 816 is on).

[0095] One or more float switches 822 are configured to electrically isolate the integrating capacitor 802 based on the output of the comparator 832. For example, in some embodiments, when the integrating capacitor 802 has saturated (e.g., the comparator 832 monitoring the integrating capacitor 802 voltage trips) one or more float switches 822 are directed (e.g., by optical circuitry 800, by processor 830) to electrically isolate the integrating capacitor 802 (e.g., by electrically disconnecting the capacitor 802 from the optical circuitry 800).

[0096] In some embodiments, a first phase of the ambient light sensing period begins when the integrating capacitor 802 starts to accumulate charge imbalance (e.g., at time Tl) and ends when the integrating capacitor 802 has saturated (e.g., at time T2) and a second phase of the ambient light sensing begins when the integrating capacitor 802 has been electrically isolated from the amplifier 820 (e.g., at about time T2) and ends at the conclusion of the duration of the ambient light sensing period (e.g., at time T3). The timeAtly Ref. No. A0012441W001 duration of the first phase of the ambient light sensing period (e.g., from T1 to T2) is approximately equal to the saturation time, Tsat, of the integrating capacitor 802 in response to a current developed by the optical sensor arrangement 810 under ambient light conditions only (e.g., the emitter light source 816 is off). The time duration of the second phase of the ambient light sensing period (e.g., from about time T2 to T3) is approximately equal to the difference between the total ambient light sensing period, Tsense, and the saturation time, Tsat. The time duration of either the first or the second phase of the ambient light sensing period can be used to scale a cancellation current (e.g., a portion of current delivered by the detector current source 806). For example, in some embodiments, the cancellation current is equal to a calibration current, Icai, scaled to a ratio of the time difference between the total ambient light sensing period, Tsense, and the saturation time, Tsat, and the total time duration of the ambient light sensing period, T sense-

[0097] At the conclusion of the duration of the ambient light sensing period (e.g., at about time T3), the one or more float switches 822 electrically couple the integrating capacitor 802 to the amplifier 820 (e.g., by electrically connecting the capacitor 802 to the optical circuitry 800). Furthermore, after the conclusion of the duration of the ambient light sensing period, the capacitor swapping mechanism 824 switches the integrating capacitor 802 from a first configuration with a first polarity to a second configuration with a second polarity (e.g., by about time T4). The second polarity can be opposite the first polarity such that given a first direction of a current, the first polarity would tend to cause the integrating capacitor 802 to increase its charge imbalance and the second polarity would tend to cause the integrating capacitor 802 to decrease its charge imbalance.

[0098] A second phase of the ambient light cancellation method begins after the capacitor swapping mechanism 822 has switched the configuration of the integrating capacitor 802 from the first configuration with the first polarity to the second configuration with the second polarity (e.g., by about time T4). The emitter light source 816 turns on at this time (e.g., at time T4). The detector 812 detects a light signal via the light detector 816. In some embodiments, the emitter light source 816 remains on for a time equal to the duration of the ambient light sensing period that preceded it (e.g., equal to Tsense, about equal to a duration from about T1 to about T3).Atly Ref. No. A0012441W001

[0099] During the second phase of the ambient light cancellation method, the light signal comprises both an ambient light signal and an emitter light signal. By switching the configuration of the integrating capacitor 802 from the first polarity to the second polarity, a portion of the light signal corresponding to a first portion of the ambient light signal (e.g., referring to FIG. 7, the solid line portion of the voltage up to Vsat) can be cancelled. A second portion of the ambient light signal (e.g., referring to FIG. 7, the dashed line portion of the voltage between Vsat and Vmax) can be cancelled by applying a cancellation current via the detector current source 806. In some embodiments, the cancellation current is scaled to a calibration current previously determined (e.g., via a calibration process). In some embodiments, the cancellation current is scaled to a ratio of the saturation time Tsat (e.g., from about T1 to about T2) and the total duration of the ambient light sensing period Tsense (e.g., from about T1 to about T3). For example, the cancellation current can be equal to the difference between Tsense and Tsat divided by Tsense, scaled the calibration current. By canceling the first portion of the ambient light signal and the second portion of the ambient light signal, the light signal that remains after conditioning comprises a signal derived from the emitter light signal.

[0100] The second phase of the ambient light cancellation method can comprise passive technique(s) and / or active technique(s) by which to cancel one or more portions of the ambient light signal. In some embodiments, canceling the first portion of the ambient light signal is achieved primarily through passive technique(s). For example, the first portion of the ambient light signal can be cancelled during the second phase of the ambient light cancellation method by using energy stored on the integrating capacitor 802 during the first phase of the ambient light cancellation method. In some embodiments, canceling the second portion of the ambient light signal is achieved primarily through active technique(s). For example, the second portion of the ambient light signal can be cancelled during the second phase of the ambient light cancellation method by using energy from a current source (e.g., the detector current source 806), wherein the magnitude of the current delivered is based in part on the time taken (e.g., as measured by the timer 804) to saturate the integrating capacitor 802.

[0101] A third phase of the ambient light cancellation method begins when the integrating capacitor 802 is reset (E.g., by a reset switch 826) at time T5. The integrating capacitor 802 can be reset for example by shorting the integrating capacitor 802. A resetAtly Ref. No. A0012441W001 period, such as from time T5 to time T6, can be sufficient to remove substantially all remaining residual charge on the integrating capacitor 802. Once the integrating capacitor 802 has been reset to a nominal state, the capacitor swapping mechanism 822 switches the integrating capacitor 802 from the second configuration with the second polarity to the first configuration with the first polarity from time T7 to time T8. In some embodiments, the amplifier 820 is turned off at a time T8 and remains off until just before the next period of ambient light sensing.

[0102] A measurement period comprising the first phase, the second phase, and the third phase of the ambient light cancellation method can be repeated with a repetition frequency. The repetition frequency can be constant or the repetition frequency can vary (e.g., in response to sensor data). In some embodiments, the repetition frequency of the measurement period can be about 128 Hz. In some embodiments, the repetition frequency of the measurement period can be from about 8 Hz to about 1024 Hz. In some embodiments, the repetition frequency of the measurement period can change from one measurement period to another.

[0103] An initial measurement period with an initial first phase, an initial second phase, and an initial third phase can be followed by a subsequent measurement period with a subsequent first phase, a subsequent second phase, and a subsequent third phase. The initial measurement period may have the same timing as the subsequent measurement or they may have different timings.

[0104] As shown in FIG. 8B, in some embodiments, the initial first phase begins with an initial ambient light sensing period starting at time T1 and a subsequent first phase begins with a subsequent ambient light sensing period starting at time Ti l. In the embodiment shown, the initial saturation time (at time T2) takes longer to occur than the subsequent saturation time (at time T12). This can happen, for example, when the ambient light intensity during the initial measurement period is less than the ambient light intensity during the subsequent measurement period. After saturation of the integrating capacitor 802, the comparator 832 trips (e.g., initially at time T2, subsequently at T12), and the one or more float switches 822 electrically isolate the integrating capacitor 802 from the amplifier 820. Once tripped, the comparator 832 can remain tripped for the remainder of the ambient light sensing period (e.g., as seen in the initial first phase from time T2 to about time T3) or itAtly Ref. No. A0012441W001 can remain tripped for a portion of the remainder of the ambient light sensing period (e.g., as seen in the subsequent first phase from time T12 to about time T13).

[0105] The initial and subsequent ambient light sensing periods can be substantially the same, for example, the duration between T1 and T3 and the duration between Ti l and T13 can be equal. In some embodiments, the duration between T1 and T4 and the duration between Ti l and T 14 are the same. In some embodiments, the duration between T1 and T4 and the duration between Ti l and T14 are different. For example, the duration of a subsequent ambient light sensing period may be less than the duration of an initial ambient light sensing period if ambient light is very intense and / or to conserve device energy.

[0106] After the ambient light sensing period has concluded, the configuration of the integrating capacitor 802 can be switched from that with the first polarity to that with the second polarity, occurring from time T3 to time T4 in the initial measurement period and occurring from time T13 to time T14 in the subsequent measurement period. The time duration of switching of the configuration of the integrating capacitor 802 can be very short compared to the ambient light sensing period (e.g., <5% of Tsense).

[0107] The initial second phase of the ambient light cancellation method begins when the emitter light source 816 is turned on at time T4 and a subsequent second phase begins when the emitter light source is turned on at time T14. In some embodiments, the duration of the initial and subsequent second phase is equal to the duration of the initial and subsequent first phase, respectively, so that the charge imbalance stored on the integrating capacitor 802 accumulates and discharges over the same amount of time, thereby canceling in the second phase a portion of the ambient light signal sensed in the first phase. In some embodiments, the duration of the initial second phase and the duration of the subsequent second phase can be the same. In some embodiments, the duration of the initial second phase and the duration of the subsequent second phase can be different.

[0108] The initial third phase of the ambient light cancellation method begins at time T5 when the integrating capacitor 802 is reset, and a subsequent third phase begins at time T15 when the integrating capacitor 802 is reset (e.g., by the reset switch 622). An initial reset period from time T5 to time T6 may be the same as a subsequent reset period from time T15 to time T16 or they may be different. Once the integrating capacitor 802 has been reset, the capacitor swapping mechanism 822 switches the polarity of the integratingAtly Ref. No. A0012441W001 capacitor 802 from time T7 to time T8 in an initial second capacitor polarity switching period, and from time T17 to time T18 in a subsequent second capacitor polarity switching period.III. Methods for canceling ambient light component of an optical signal

[0109] FIG. 9 shows a flowchart of an example method 900 to deliver a cancellation current corresponding to ambient light. The method 900 may be performed, for example, through the operation of optical circuitry similar to optical circuitry 800 described herein with respect to FIGS. 8 A and 8B. The method 900 to deliver a cancellation current corresponding to ambient light may be combined with any other method described herein. The method 900 comprises three phases: a calibration phase, an ambient light sensing phase, and an emitter light sensing phase.

[0110] The calibration phase of the method 900 begins with block 902 wherein a light detector (e.g., light detector 616, light detector 818) of an optical sensor arrangement is disconnected from an amplifier (e.g., an integrating amplifier). In block 904, current is injected into the amplifier using a current source (e.g., a detector current source). The current injected into the amplifier using the current source may begin at a first level to determine saturation of an integrating capacitor. Current can be increased from the first level (e.g., to a second level, to a third level, etc.) until the integrating capacitor reaches saturation at the very end of a time period corresponding to a duration of the ambient sensing phase (e.g., Tsense). Saturation of the integrating capacitor can be determined by connecting a comparator held at a reference voltage near the saturation voltage of the integrating capacitor to an output of the integrating amplifier. In block 906, a magnitude of a calibration current, Icai, is determined to be equal to that of the current level that causes the comparator to trip at a time equal to the duration of the ambient light sensing phase. In some embodiments, the value of the calibration current, Icai, is stored (e.g., in memory of electrical circuitry, in a processor, in optical circuitry). In some embodiments, the stored value of the calibration current, Icai, is retrieved (e.g., by a processor) to control one or more parameters the cancellation current. After the calibration phase, the light detector is connected to the amplifier as shown in block 908.

[0111] The ambient light sensing phase begins when ambient light is sensed via the light detector while an emitter light source is off. In the example method 900 of FIG. 9, theAtty Ref. No. A0012441W001 duration of the ambient light sensing phase is Tsense. In block 910, time elapsed during the ambient light sensing phase is measured. During the ambient light sensing phase, the integrating capacitor may become saturated (e.g., due to intensity of ambient light). Saturation of the integrating capacitor can be determined by the comparator held at a reference voltage near the saturation voltage of the integrating capacitor connected to an output of the integrating amplifier. The time at which the comparator trips can be determined, as in block 912, indicating a time Tsat in which the integrating capacitor is saturated.

[0112] As shown in block 914, once a saturation time Tsat has been determined, an ambient light cancellation current, mb.cm, can be calculated (e.g., by electrical circuitry, by a processor). In some embodiments, the ambient light cancellation current, Iamb,can, is determined by a ratio of the saturation time, Tsat, to the total duration of the ambient light sensing phase, Tsense. In some embodiments, the ratio of the saturation time, Tsat, to the total duration of the ambient light sensing phase, Tsense, is used to scale a calibration current, Icai, to determine the ambient light cancellation current, mb.cm. For example, in some embodiments, the ambient light cancellation current, Iamb,can, is equal to a product of the calibration current, Icai, and a ratio of time remaining after saturation (e.g., the difference of Tsense and Tsat) to the total duration of the ambient light sense phase, Tsense. A shorter saturation time Tsat indicates a larger current from the light detector which can be due to more intense ambient light during the ambient light sensing phase and thus can generate a larger ambient light cancellation current, Iamb,can. In some embodiments, the ambient light cancellation current is a function of the calibration current Icai, the duration of the first ambient light sensing phase Tsat, and the total duration of the light sensing phase Tsense, such that

[0113] In some embodiments, the ambient light cancellation current, Iamb,can, reaches a maximum value, Icaiwhen the integrating capacitor immediately saturates (e.g., Tsat is nearly zero) and is indirectly proportional to the ratio of the saturation time to the total duration of the ambient light sensing phase (e.g., Tsat / T sense). For example, when Tsat is 10% of Tsense, the ambient light cancellation current, Iamb,can, can be 90% of the magnitude of the calibration current, Icai, when Tsat is 50% of Tsense, the ambient light cancellation current, Iamb,can, can be 50% of the magnitude of the calibration current, Icai, and when Tsat is 90% ofAtty Ref. No. A0012441W001Tsense, the ambient light cancellation current, Iamb, can, can be 10% of the magnitude of the calibration current, Icai. In some embodiments, the ambient light cancellation current, Iamb, can, is linearly indirectly proportional to the ratio of the saturation time to the total duration of the ambient light sensing phase. In some embodiments, for example to compensate for other factors (e.g., dielectric properties of the integrating capacitor, environment temperature, a device state) the ambient light cancellation current, Iamb, can, is nonlinearly indirectly proportional to the ratio of the saturation time to the total duration of the ambient light sensing phase.

[0114] In some embodiments, the value of the ambient light cancellation current, Iamb, can, is stored (e.g., in memory of electrical circuitry, in a processor, in optical circuitry). In some embodiments, the stored value of the ambient light cancellation current, Iamb, can, is retrieved (e.g., by a processor). For example, in some embodiments, during a first measurement period the ambient light cancellation current, Iamb, can, is determined and its value is stored (e.g., in memory, in electrical circuitry), and during a second measurement period, the stored value of the ambient light cancellation current, Iamb, can, is retrieved and a current source delivers a current equivalent to the stored value.

[0115] The emitter light sensing phase begins after the ambient light sensing phase while the emitter light source is on. As in block 916, a cancellation current is delivered during the emitter light sensing phase. The cancellation current is delivered to condition an optical signal, wherein the optical signal comprises a signal of interest component and a noise component. The cancellation current can comprise one or more currents to cancel one or more noise components. For example, in some embodiments, the cancellation current comprises a first cancellation current and a second cancellation current. The first cancellation current can be, for example, current from discharging a capacitor (e.g., an integrating capacitor). The second cancellation current can be, for example, the ambient light cancellation current, Iamb, can, (e.g., delivered by the current source). The first cancellation current can cancel a first noise component and the second cancellation current can cancel a second noise component, thereby substantially isolating the signal of interest component of the optical signal.

[0116] FIG. 10 shows a flowchart of an example method 1000 to cancel portions of a noise component from an optical signal. The method 1000 may be performed, for example,Atly Ref. No. A0012441W001 through the operation of optical circuitry similar to optical circuitry 800 described herein with respect to FIGS. 8A and 8B. In some embodiments, the method 1000 is a method 1000 of operating an optical system comprising an emitter and a detector (e.g., for optical sensing). Such an optical system may, for example, be included in an implantable medical device (e.g., insertable cardiac monitor such as IMD 300, IMD 500, etc.). The method 1000 comprises receiving an optical signal (block 1002), developing a voltage across a capacitor (block 1004), canceling a first portion of the noise component from the optical signal by discharging the capacitor (block 1006), and canceling a second portion of the noise component from the signal by delivering current based on a rate of change of voltage across the capacitor (block 1008).

[0117] Receiving the optical signal (block 1002) can comprise receiving an optical signal that comprises a signal of interest component and a noise component. For example, the signal of interest component can comprise a physiological signal (e.g., an arterial signal, a blood pressure signal, a photoplethysmographic signal) indicative of an anatomical and / or physiological process (e.g., heart rate, respiratory rate, oxygenation level, blood volume). The noise component can comprise all other signal(s) received along with the signal of interest component, such as, for example, an ambient light signal from a surrounding environment. Receiving the optical signal (block 1002) can be performed over a sensing period with a duration, Tsense. In some embodiments, receiving (e.g., by the detector) the optical signal (block 1002) (e.g., during the sensing period) is performed while the emitter is inactive (e.g., not emitting light). The optical signal received while the emitter is inactive primarily comprises the noise component, while the signal of interest component is negligible and / or nonexistent. In some embodiments, while the emitter is inactive, the noise component reflects a contribution of an ambient light component present just before, during, and just after the sensing period. To sense a signal of interest component, in some embodiments, the emitter is activated, and the optical signal received while the emitter is active comprises the signal of interest component and the noise component. In some embodiments, receiving the optical signal (block 1002) comprises receiving a photoplethysmography (PPG) signal.

[0118] Developing the voltage across the capacitor (block 1004) can comprise holding the capacitor (e.g., an integrating capacitor) in a first configuration with a first polarity and allowing the capacitor to accumulate a charge imbalance in response to currentAtly Ref. No. A0012441W001(e.g., current from a detector, current from a current source). Developing the voltage across the capacitor (block 1004) can occur over the sensing period. For example, the capacitor in the first configuration with the first polarity can accumulate a charge imbalance proportional to a current delivered during the sensing period while the emitter is inactive. In some embodiments, the charge imbalance developed (e.g., the voltage across the capacitor) while the capacitor is electrically connected to the detector is proportional to an ambient light noise component. In some embodiments, the charge imbalance developed while the capacitor is electrically connected to the detector is equal to the first portion of the noise component.

[0119] In some embodiments, developing the voltage across the capacitor (block 1004) causes the capacitor to saturate or to nearly saturate (e.g., reach a reference voltage less than or about equal to a saturation voltage). In those embodiments in which developing the voltage across the capacitor (block 1004) causes the capacitor to saturate or to nearly saturate, a time within the sensing period at which the capacitor saturates or nearly saturates, Tsat, can be determined (e.g., by a comparator, by a timer). In some embodiments, the capacitor can be electrically isolated (e.g., electrically isolated from optical circuitry) once saturation or near saturation is determined.

[0120] Canceling a first portion of the noise component from the optical signal by discharging the capacitor (block 1006) can comprise switching the capacitor from the first configuration with the first polarity to a second configuration with a second polarity. In those embodiments in which the capacitor is electrically isolated after having developed a voltage across the capacitor (block 1004), the capacitor is electrically connected to the detector in the second configuration with the second polarity. By switching the capacitor from the first configuration with the first polarity to the second configuration with the second polarity, a current can be delivered by the capacitor equal to the current delivered to the capacitor during the sensing period while the capacitor is in electrical communication with the detector.

[0121] Canceling a second portion of the noise component from the optical signal by deliver current based on the rate of change of voltage across the capacitor (block 1008) can comprise determining a rate of change of voltage across the capacitor based the time within the sensing period at which the capacitor saturates or nearly saturates, Tsat. In someAtty Ref. No. A0012441W001 embodiments, determining a rate of change of voltage across the capacitor is based on a ratio of the time within the sensing period at which the capacitor saturates or nearly saturates, Tsat, and the duration of the sensing period in which the emitter is inactive, Tsense. For example, the current delivered can be a calibration current (e.g., a current found via method 900), Icai, scaled to the ratio, Tsat / TSense. In some embodiments, the current delivered while canceling the second portion of the noise component of the optical signal, Lmb.cm, is a function of the duration of the sensing period, Tsense, the time within the sensing period at which the capacitor saturates or nearly saturates, Tsat, and a calibration current, Icai, such that

[0122] In some embodiments, the emitter emits light while canceling the first and second portions of the noise component from the optical signal (blocks 1006 and 1008, respectively).

[0123] In some embodiments, the method 1000 is performed continuously and automatically. In some embodiments, the method 1000 may be performed in a calibration or setup procedure, such as upon implantation or initialization of the optical sensing device. Additionally or alternatively, the method 1000 may be performed intermittently or periodically at regular intervals, such synchronized to one or more physiological functions (e.g., heart beats, respiration). For example, the method may be performed approximately once per minute, once every 5 minutes, once every 10 minutes, once every 30 minutes, once every hour, or once every day, once every 5 cardiac cycles, once every 10 cardiac cycles, once every 30 cardiac cycles, once every 50 cardiac cycles, etc. Additionally or alternatively, the method 1000 may additionally or alternatively be performed in response to a trigger event, such as a user command (e.g., through a programmer such as programmer 410), detection of a change in position of the optical sensing device relative to the patient (e.g., device orientation such as a device rotating or flipping within a subcutaneous pocket in the patient tissue), detection of patient movement (e.g., detected by an accelerometer in the optical sensing device or associated secondary device), and / or change in detected ambient light (e.g., detected by a light sensor located on the optical sensing device, detected by a secondary external device with a light sensor in communication with the optical sensing system, etc.).Atly Ref. No. A0012441W001

[0124] In some embodiments, at least a subset of processes from the method 1000 are performed continuously and automatically. For example, canceling the first and second portions of the noise component (blocks 1006 and 1008, respectively) can be performed continuously and automatically. In some embodiments, a value associated with developing the voltage across the capacitor (block 1004) (e.g., the time taken to saturate or nearly saturate the capacitor) can be stored in memory and retrieved by a processor. In some embodiments, the stored value can be used to determine a magnitude of current delivered by the current source, for example, to cancel a portion of a noise component (e.g., current delivered in block 1008). The value stored in memory can be retrieved by the processor and the processor can the direct the current source (e.g., through a feedback loop) to deliver current of the magnitude determined.

[0125] In some embodiments, receiving an optical signal (block 1002) can comprise oversampling. Oversampling, a process of sampling a signal at a frequency much higher than a Nyquist rate for a signal of interest, can improve resolution and dynamic range of a system (e.g., an optical system).

[0126] Any analog-to-digital converter (e.g., ADC 624, ADC 828) or digital-to- analog converter (e.g., a current DAC) described herein can utilize oversampling, for example by sampling a signal and / or delivering a signal at a sampling frequency much higher than a frequency of interest from a signal of interest. Any ADC and / or DAC described herein can utilize delta-sigma modulation. In delta-sigma modulation, a quantizer reduces resolution of an input signal (e.g., an optical signal). Errors (e.g., differences between output and input) that occur are recorded by an integrator and an average output error is minimized by a feedback loop (e.g., a negative feedback loop). To allow for averaging the output, a modulator can sample high above the Nyquist rate. To demodulate, a lowpass filter can be used (e.g., to apply a weighted average) to the output. In some embodiments, delta-sigma modulation is performed at an oversampling frequency that is an integer multiple of the inverse of a sensing period (e.g., 1 / Tsense) to ensure that a noise component (e.g., a shaped quantization noise) is nullified through zeros that appear in a transfer function (e.g., a transfer function of the integrator, a sine filter) of a system (e.g., an optical system comprising an optical sensor arrangement).Atly Ref. No. A0012441W001

[0127] FIG. 11 shows a flowchart of an example method 1100 to cancel components of an optical signal. In some embodiments, the method 1100 is a method 1100 of operating an optical system comprising an emitter and a detector. The method 1100 comprises receiving a first optical signal from the detector while the emitter is off (block 1102), developing a charge imbalance on an integrating capacitor in electrical communication with the detector until a saturation limit is reached (block 1104), activating the emitter (block 1106), receiving a second optical signal from the detector (block 1108), canceling a first component of the second optical signal by deliver a current based on the charge imbalance on the integrating capacitor (block 1110), and canceling a second component of the second optical signal by delivering a current based on time taken for the charge imbalance on the integrating capacitor to reach the saturation limit (block 1112).

[0128] Receiving the first optical signal from the detector while the emitter is off (block 1102) can comprise an ambient sensing period of duration Tsense. With the emitter off, the first optical signal received primarily comprises an ambient light component based on ambient light of an environment surrounding the optical system. The ambient light can vary from negligible (e.g., the optical system is in a darkened room) to highly intense (e.g., the optical system has a detector oriented toward sunlight), and as such significantly contributes to the first optical signal.

[0129] During the ambient light sensing period, the integrating capacitor can be connected to the optical circuitry in a first configuration with a first polarity, thereby allowing the integrating capacitor to develop a charge imbalance in response to current (e.g., current from a detector due to ambient light). The charge imbalance develops on the integrating capacitor until a saturation limit (e.g., a capacitor limit, a reference voltage) is reached (block 1104). For example, when ambient light is significant (e.g., outdoors in daylight, in front of a television monitor), the charge imbalance will develop rapidly on the integrating capacitor and can reach the saturation limit before the end of the ambient light sensing period. If the saturation limit is reached (e.g., voltage across the integrating capacitor reaches a reference voltage), the time taken to reach the saturation limit can be determined (e.g., by a timer) and its value can be stored and used (e.g., by a processor) at another time (e.g., during an emitter light sensing period). In some embodiments, once the saturation limit is reached, the integrating capacitor is electrically isolated from the optical circuitry.Atly Ref. No. A0012441W001

[0130] An emitter light sensing period begins when the emitter is turned on (block 1106) so as to emit light detectable by the detector. The emitted light reflects off nearby material and / or transmits through nearby material (e.g., blood, tissue), the detector detects the reflected and / or transmitted light, and a second optical signal from the detector is received (block 1108) (e.g., by the optical circuitry). In some embodiments, the duration of the emitter light sensing period and the ambient light sensing phase are equal. By having ambient light and emitter light sensing periods of equal duration, the charge imbalance developed in response to a current during a first period (e.g., an ambient light sensing period) can cancel an equivalent current during a second period (e.g., an emitter light sensing period). In some embodiments, the duration of the emitter light sensing period and the ambient light sensing phase are approximately equal. In some embodiments, the duration of the emitter light sensing period and the ambient light sensing phase are different (e.g. the duration of the emitter light sensing period is greater than the duration of the ambient light sensing period, the duration of the ambient light sensing period is greater than the duration of the emitter light sensing period). In some embodiments, the optical system can utilize different sensing period durations, for example to optimize power management (e.g., minimize energy usage).

[0131] While receiving the second optical signal from the detector (block 1108), a first component of the second optical signal can be canceled by delivering a current based on the charge imbalance that developed on the integrating capacitor (block 1110) during the ambient light sensing period.

[0132] Canceling the first component of the second optical signal by delivering a current based on the charge imbalance on the integrating capacitor (block 1110) can comprise switching the integrating capacitor from the first configuration with the first polarity to a second configuration with a second polarity. In those embodiments in which the capacitor is electrically isolated after having developed a charge imbalance across the capacitor until a saturation is reached (block 1104), the capacitor is electrically connected to the detector in the second configuration with the second polarity. By switching the integrating capacitor from the first configuration with the first polarity to the second configuration with the second polarity, a current can be delivered by the integrating capacitor equal to the current delivered to the integrating capacitor during the ambient light sensing period while the integrating capacitor is in electrical communication with theAty Ref. No. A0012441W001 detector during the emitter light sensing period. In some embodiments, the charge imbalance developed on the integrating capacitor during a first period (e.g., an ambient light sensing period) is used to deliver current (e.g., charges at time rate) during a second period (e.g., an emitter light sensing period), thereby canceling a portion of an optical signal.

[0133] Canceling the second component of the second optical signal by delivering current based on the time taken for a charge imbalance on the integrating capacitor to reach the saturation limit (block 1112) can be controlled by a processor in electrical communication with a current source (e.g., a detector current source). The current delivered can be a modification of a calibration current (e.g., a previously determined current). The modification of the calibration current can be a scalar modification. In some embodiments, the current delivered is greater than a calibration current. For example, in some embodiments, the current delivered is as much as 2 times greater than the calibration current, the current delivered is as much as 2.5 times greater than the calibration current, the current delivered is as much as 3 times greater than the calibration current, the current delivered is as much as 4 times greater than the calibration current, the current delivered is as much as 8 times greater than the calibration current, or the current delivered is as much as 10 times greater than the calibration current. In some embodiments, the current delivered is a proportion of the calibration current. For example, in some embodiments, the current delivered is half as much as the calibration current, the current delivered is a third as much as the calibration current, the current delivered is a quarter as much as the calibration current, the current delivered is a tenth of the calibration current, or the current delivered is a hundredth of the calibration current.

[0134] In some embodiments, the first component of the optical signal and second component of the optical signal comprises a noise component that can be separated from a signal of interest component. In some embodiments, the signal of interest component comprises a physiological signal (e.g., an arterial signal, a blood pressure signal, a plethysmographic signal) indicative of an anatomical and / or physiological process (e.g., heart rate, respiratory rate, oxygenation level, blood volume). The noise component can comprise all other signal(s) received along with the signal of interest component, such as, for example, an ambient light signal from the surrounding environment. The noise component can comprise two or more noise components (e.g., the first component of the optical signal and the second component of the optical signal). One or more of the two orAty Ref. No. A0012441W001 more noise components can comprise a DC offset (e.g., a constant value noise), white noise (e.g., a heterogenous mixture of oscillations of myriad frequencies), signal outside a frequency range of interest, a drifting signal, or any combination thereof. For example, in some embodiments, the first component of the optical signal and second component of the optical signal each comprise a DC offset, with the first component of the optical signal proportional to the saturation limit of the integrating capacitor (e.g., about equal to Vsat in FIG. 7) and the second component of the optical signal proportional to the difference between a maximum voltage possible across the integrating capacitor without a saturation limit (e.g., about equal to Vmax in FIG. 7) and the saturation limit, thereby canceling a noise component proportional to the maximum voltage possible across the integrating capacitor without a saturation limit developed during the ambient light sensing period (e.g., delivering an accumulated charge about equal to the current delivered during the ambient sensing period).

[0135] In some embodiments, the method 1100 is performed continuously and automatically, such as in a manner described for method 1000. In some embodiments, at least a subset of processes from the method 1100 are performed continuously and automatically.Conclusion

[0136] Although many of the embodiments are described above with respect to systems, devices, and methods for performing ambient light cancellation for optical sensing with an implantable medical device (e.g., insertable cardiac monitor), the technology is applicable to other applications and / or other approaches, such as other implantable devices. Moreover, other embodiments in addition to those described herein are within the scope of the technology. Additionally, several other embodiments of the technology can have different configurations, components, or procedures than those described herein. A person of ordinary skill in the art, therefore, will accordingly understand that the technology can have other embodiments with additional elements, or the technology can have other embodiments without several of the features shown and described above with reference to FIGS. 1-11.

[0137] The descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Where the contextAtly Ref. No. A0012441W001 permits, singular or plural terms may also include the plural or singular term, respectively. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments.

[0138] As used herein, the terms “generally,” “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent embodiments in measured or calculated values that would be recognized by those of ordinary skill in the art.

[0139] Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term "comprising" is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and / or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.

Claims

Atly Ref. No. A0012441W001CLAIMSI / We claim:

1. An optical system, comprising: an optical emitter configured to emit light; an optical detector; and optical circuitry in electrical communication with the optical detector and comprising an integrating capacitor, a current source, and a timer, the timer configured to monitor time taken for an integrating capacitor voltage to reach a reference voltage level, wherein the optical system is configured to: collect a charge imbalance with the integrating capacitor; receive an optical signal from the detector, wherein the optical signal comprises a signal of interest component and a noise component; subtract a first portion of the noise component from the optical signal by discharging the charge imbalance from the integrating capacitor; and subtract a second portion of the noise component from the optical signal by delivering a current from the current source, the current based directly or indirectly on time taken for the integrating capacitor voltage to reach the reference voltage level, thereby substantially isolating the signal of interest component.

2. The optical system of claim 1, wherein the optical circuitry is configured to limit the integrating capacitor to be no greater than a saturation voltage of the integrating capacitor.

3. The optical system of claim 1 or 2, wherein the optical circuitry is configured to limit the integrating capacitor to be no greater than the reference voltage, wherein the reference voltage is less than the saturation voltage.

4. The optical system of any one of claims 1-3, wherein the current source comprises a current digital to analog converter.Atty Ref. No. A0012441W0015. A medical device configured to be implanted in a patient, wherein the implantable medical device comprises the optical system of any one of claims 1-4.

6. The medical device of claim 5, wherein the medical device comprises an insertable cardiac monitor comprising a power source and one or more electrodes.

7. The medical device of claim 5 or 6, wherein the insertable cardiac monitor is configured to be implanted subcutaneously in the patient.

8. A method of operating an optical system comprising an emitter and a detector, the method comprising: receiving an optical signal from the detector, wherein the optical signal comprises a signal of interest component and a noise component; developing a capacitor voltage across an integrating capacitor in electrical communication with the detector; canceling a first portion of the noise component from the optical signal by discharging the integrating capacitor of the capacitor voltage; and canceling a second portion of the noise component from the optical signal by delivering a current based directly or indirectly on a rate of change of the capacitor voltage during development of the capacitor voltage, thereby substantially isolating the signal of interest component.

9. The method of claim 8, wherein receiving the optical signal from the detector is performed over a sensing period, and wherein developing the capacitor voltage across the integrating capacitor is performed while the emitter is inactive, prior to the sensing period.

10. The method of claim 8 or 9, wherein receiving the optical signal from the detector is performed over a sensing period having a duration of Tsense, wherein a controller controls a current source to deliver the current based directly or indirectly on the rate of change of the capacitor voltage, and wherein the controller uses delta-sigma modulation at an oversampling frequency, wherein the oversampling frequency is an integer multiple of 1 / Tsense-Atly Ref. No. A0012441W00111. The method of any one of claims 8-10, wherein the optical signal from the detector comprises a photoplethysmography (PPG) signal.

12. The method of any one of claims 8-11, wherein canceling a first portion of the noise component from the optical signal comprises switching a configuration of the integrating capacitor from a first polarity to a second polarity.

13. The method of any one of claims 8-12, wherein the current delivered while canceling the second portion of the noise component of the optical signal (Iamb, can) is a function of a duration of a sensing period (T sense), a duration of a saturation period (Tsat), and a calibration current (Icai), calculated as: Iamb,can = x Icat.

14. The method of any one of claims 8-13, further comprising controlling the emitter to emit light while canceling the first and second portions of the noise component from the optical signal.

15. The method of any one of claims 8-14, wherein canceling the first and second portions of the noise component from the optical signal are performed continuously and automatically.

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