AMPLIFICATION USING CONTACT DETECTION

Abstract

Embodiments are directed to methods, devices, and systems for determining and applying a gain match to detected electrical signals. The methods may include operating a device to determine that a user is wearing the portable electronic device and applying a test signal to a detection electrode of the portable device. An input impedance for the detection electrode can be determined using the test signal. The input impedance and a base impedance can be used to determine a gain match. An electrical signal from the user can be measured using the detection electrode, and the gain match can be applied to the electrical signal. A physiological parameter of the user can be determined using the measured electrical signal to which the gain match has been applied.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a non-provisional application and claims the benefit of U.S. Provisional Patent Application No. 63 / 534,459, filed August 24, 2023, the contents of which are incorporated herein by reference as if fully disclosed herein, pursuant to 35 USC 119(e). AREA

[0002] The described embodiments generally relate to devices and methods for processing physiological signals, and more particularly, the present embodiments relate to adapting physiological signals based on contact metrics of one or more electrodes with a user. BACKGROUND

[0003] Electrodes can be used as part of electronic devices to measure a user's electrical potentials. For example, electrocardiogram (ECG) measurements may use electrodes in contact with a user's body to measure a user's electrical heart activity over one or more cardiac cycles. Similarly, electromyography (EMG) and electroencephalography (EEG) may use electrodes to measure muscle and brain activity, respectively. Electrodes may contact a user at different locations on their body, and a pair of electrodes may each measure an electrical signal at different locations on the user. The measured signals from the different electrodes can be used to determine an electrical potential difference.During an ECG measurement, the electrical potential difference can be analyzed over one or more cardiac cycles to obtain information about the electrical function of the user's heart.

[0004] Conventional electrodes, also called "wet electrodes," contain an electrically conductive gel to facilitate the conduction of current from the skin. Electrodes can be integrated into wearable devices such as a smartwatch, which can be used to continuously or periodically monitor a user's electrical cardiac activity. In wearable devices such as a smartwatch, it may be desirable to use "dry electrodes," which do not require electrically conductive gel. Dry electrodes can result in greater signal attenuation of the electrical signals from the user's skin. SUMMARY

[0005] Embodiments relate to methods for electrode sensing on a portable electronic device. The methods may include, in response to determining that a user is wearing the portable electronic device, applying, using contact detection circuitry, a test signal to the sensing electrode; and determining, using contact detection circuitry, an input impedance for the sensing electrode using the test signal. The methods may include determining a gain adjustment using the input impedance and a baseline impedance; and measuring, using physiological sensing circuitry, an electrical signal of the user using the sensing electrode.The methods may include applying, using the physiological sensing circuit, the gain adjustment to the measured electrical signal and determining a physiological parameter of the user using the measured electrical signal to which the gain adjustment was applied.

[0006] Embodiments also relate to methods for electrode gain calibration of sense electrode signals on a portable electronic device. The methods may include isolating a contact detection circuit from a physiological detection circuit. While the contact detection circuit is isolated from the physiological detection circuit, a first test signal may be applied to a sense electrode of the portable electronic device. The methods may include determining a first input impedance for the sense electrode using the first test signal. The contact detection circuit may be connected to the physiological detection circuit. The methods may include applying a second test signal to the sense electrode while the contact detection circuit is connected to the physiological detection circuit.A second input impedance may be determined for the sensing electrode using the second test signal. The methods may include determining a gain adjustment using the first input impedance and the second input impedance, measuring a user's electrical signal using the sensing electrode, and determining a user's physiological parameter by applying the gain adjustment to the measured electrical signal.

[0007] Embodiments further include a system for electrode sensing on a portable electronic device. The system may include: a housing configured to be coupled to a user; a sense electrode coupled to the housing and configured to contact the user; and a processor. The processor may be configured to, in response to determining that the user is wearing the portable electronic device, cause a test signal to be applied to the sense electrode and, using the test signal, determine an input impedance for the sense electrode.The processor may determine a gain adjustment using the input impedance and a base impedance, measure an electrical signal of the user using the sensing electrode, and determine a physiological parameter of the user by applying the gain adjustment to the measured electrical signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The disclosure will be readily understood from the following detailed description taken in conjunction with the accompanying drawings, in which like reference numerals designate like structural elements and in which: Fig. 1A shows a front view of an exemplary electronic device that can be used to perform physiological measurements as described herein; Fig. 1B shows a rear view of an exemplary electronic device that can be used to perform physiological measurements as described herein; Fig. 2 shows an exemplary block diagram for an electronic device that can be used to perform physiological measurements as described herein; Fig. 3 shows an exemplary gain adjustment circuit that may be used to perform physiological measurements as described herein; Fig. 4 shows an exemplary contact detection circuit that may be used to perform physiological measurements as described herein; Fig. 5 shows an exemplary process for performing physiological measurements using a gain adjustment circuit; Fig. 6 shows an exemplary gain calibration circuit that can be used to perform physiological measurements as described herein; and Fig. Figure 7 shows an exemplary process for performing physiological measurements using a gain calibration circuit.

[0009] It should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations and positional relationships illustrated therebetween in the accompanying figures are merely intended to facilitate an understanding of the various embodiments described herein and, accordingly, are not necessarily presented or illustrated to scale and are not intended to indicate any preference or requirement for any illustrated embodiment to the exclusion of embodiments described by reference thereto. DETAILED DESCRIPTION

[0010] Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to a preferred embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the described embodiments as defined by the appended claims.

[0011] The embodiments disclosed herein relate to devices, systems, and methods for improving the accuracy of physiological measurements, particularly physiological measurements using electrodes that contact a user's skin. The devices and systems described herein may include electrodes that can sense electrical signals from and / or apply electrical signals to a user's skin surface. The devices and systems may include one or more circuits that help improve the accuracy of electrical measurements by determining and applying a gain adjustment to the electrical signals sensed by one or more electrodes.For example, the devices and systems may perform electrocardiogram (ECG) measurements, which may include using one or more electrodes to sense electrical cardiac signals of a user and applying a gain adjustment to the sensed electrical cardiac signals.

[0012] In some cases, the interface between the user and the electrode may have a high electrical impedance, which can attenuate the signals detected by an electrode. For example, when dry electrodes are used to measure electrical signals from the user, the contact between the dry electrode and the user's skin may have a high input impedance. As used herein, the term "dry electrode" refers to electrodes that do not use a gel or other liquid material to provide a conductive path between the skin and an electrode. In some cases, the input impedance can cause signal attenuation, resulting in physiological measurements (e.g., ECG measurements) that fail to meet at least one accuracy and / or reliability criterion.For example, a physiological parameter such as an ECG measurement determined from a severely attenuated signal may fail to meet a defined accuracy and / or reliability criterion. This means that the device may determine that the signal quality is too low to provide an accurate ECG measurement for the user.

[0013] The embodiments described herein include systems, devices, and methods for determining and applying a gain adjustment to measured physiological signals of a user. In some cases, the system may determine a gain adjustment using system calibration data and user-specific calibration data. The system calibration data may represent general characteristics of the system itself, which may include the baseline impedance data for one or more electrodes. User-specific calibration data may relate to the quality of electrode contact with a user and may include impedance data determined from a test signal applied to an electrode while the electrodes are in contact with the user.The system calibration data for a sensing electrode may be determined before a user wears a device or during a user's first use of the device, for example, as part of a manufacturing process, and stored by the system. The system calibration data may be obtained, for example, by applying a first test signal to the sensing electrode and using a contact detection circuit to determine a baseline impedance for the sensing electrode. The first test signal may be applied using any suitable method and does not necessarily have to mimic a user's biological conditions. For example, the first test signal may be applied using a test probe, and the determined baseline impedance may be lower than an expected impedance due to contact with a user.The user-specific calibration data may be obtained by determining that a user is wearing the electronic device, applying a second test signal to the user using the contact detection circuit, and determining a second input impedance based on the contact of the sensing electrode with the user. In some cases, the user-specific calibration data may be determined using contact detection methods and hardware described in U.S. Patent Application Publication No. 2020 / 0077955, the contents of which are incorporated herein by reference.

[0014] The determined gain adjustment can be used to increase the power and / or amplitude of the signals measured by the sensing electrode. For example, the sensing electrode can be operated to measure a user's electrical cardiac signals and determine one or more ECG parameters of a user. The device can apply the determined gain adjustment to the measured cardiac signals to increase the power and / or amplitude of the measured cardiac signals. The device can determine the one or more ECG parameters by applying the gain adjustment to the measured cardiac signals.

[0015] In some cases, the device may determine whether to apply a gain adjustment to a measured physiological signal. For example, a wearable device may determine whether the user-specified calibration data and / or the determined gain meet at least one criterion. The criterion may be an impedance threshold that defines an impedance range within which a gain adjustment is applied. In response to meeting the at least one criterion (e.g., an impedance based on the contact of the sensing electrode with the user is within the impedance range), the wearable device applies the gain adjustment to the measured physiological signal. In response to not meeting the at least one criterion (e.g.,an impedance based on the contact of the sensing electrode with the user is not within the impedance range), the wearable device does not apply the gain adjustment to the measured physiological signal.

[0016] In some cases, the systems and / or devices may include multiple sensing electrodes and determine a gain adjustment for each of the electrodes. For example, the system may determine and apply a first gain adjustment for electrical signals measured by a first sensing electrode and determine and apply a second gain adjustment for electrical signals measured by a second sensing electrode.

[0017] The embodiments described herein also include systems, devices, and methods for determining and applying gain adjustment to account for impedance changes and / or other changes in one or more circuits that cause attenuation of the measured physiological signals of a user. The devices of the system may include contact detection circuitry operable to characterize contact of the sensing electrode with a user (e.g., determining an input impedance based on the contact of the sensing electrode with the user) and physiological detection circuitry operable to measure electrical signals of a user. The systems and / or devices may be operable to isolate the contact detection circuitry from the physiological detection circuitry.A first test signal can be applied to a sensing electrode while the physiological sensing circuit is isolated from the contact detection circuit. A first impedance can be determined for the sensing electrode, which can correspond to an impedance of the contact detection circuit. The contact detection circuit can be connected to the physiological sensing electrode, and a second test signal can be applied to the sensing electrode. A second impedance can be determined for the sensing electrode and can correspond to an impedance of the contact detection circuit and the physiological sensing circuit.A gain adjustment may be determined from the first and second impedances, and the determined gain adjustment may be applied to measured electrical signals of the user to compensate for attenuation or other signal degradation due to the contact detection circuitry and / or the physiological sensing circuitry.

[0018] These and other embodiments are described below with reference to Fig. 1-7. However, it will be readily apparent to those skilled in the art that the detailed description given herein with respect to these figures is for illustrative purposes only and should not be considered limiting.

[0019] Fig. 1A shows a front view of an exemplary electronic device 100, and Fig. 1B shows a rear view of the exemplary electronic device 100 that can be used to perform physiological measurements as described herein. The electronic device 100 is depicted as a wristwatch, although this is only one embodiment of an electronic device, and the concepts discussed herein may be equally or analogously applied to other electronic devices, including mobile phones (e.g., smartphones), tablet computers, notebooks, head-mounted displays, headphones, earbuds, digital media players (e.g., MP3 players), wearable wristbands, rings, or the like.

[0020] The device 100 includes a housing 102 and a band 104 coupled to the housing. The housing 102 may at least partially define an interior volume in which components of the device 100 may be positioned. The housing 102 may also define one or more exterior surfaces of the device, such as all or a portion of one or more side surfaces, a back surface, a front surface, and the like. The housing 102 may be formed from any suitable material, such as metal (e.g., aluminum, steel, titanium, or the like), ceramic, polymer, glass, or the like.

[0021] The band 104 can secure the device 100 to a user, such as to the user's arm or wrist. The device 100 can include battery charging components within the device 100 that can receive power, charge a battery of the device 100, and / or provide direct power to operate the device 100 regardless of the battery's charge level (e.g., bypassing the battery of the device 100). The device 100 can include a magnet, such as a permanent magnet, that magnetically couples to a magnet (e.g., a permanent magnet, electromagnet) or a magnetic material (e.g., a ferromagnetic material such as iron, steel, or the like) in a charging dock (e.g., to facilitate wireless charging of the device 100).

[0022] The electronic device 100 may include a display 106. The display 106 may be positioned at least partially within the housing 102. The display 106 may define an output region in which graphical outputs are displayed. Graphical outputs may include graphical user interfaces, user interface elements (e.g., buttons, sliders, etc.), text, lists, photographs, videos, or the like. In some cases, the display 106 may output a graphical user interface with one or more graphical objects that display information collected or derived from one or more sensors. For example, the display 106 may output one or more physiological parameters, such as ECG parameters measured for a user.

[0023] The display 106 may include or be associated with touch sensors and / or force sensors that extend along the output area of ​​the display and that may utilize any suitable sensing elements and / or sensing techniques.

[0024] Using touch sensors, the electronic device 100 can detect touch inputs applied to the cover, including detecting locations of the touch inputs, movements of the touch inputs (e.g., the speed, direction, or other parameters a gesture applied to the cover may generate), or the like. Using force sensors, the electronic device 100 can detect amounts or magnitudes of force associated with touch events applied to the cover. The touch and / or force sensors can detect various types of user inputs for controlling or modifying the operation of the electronic device 100, including taps, swipes, multi-finger inputs, single- or multi-finger touch gestures, presses, and the like.

[0025] The electronic device 100 may also include one or more user inputs, such as a first input device 108 having a cap, a crown, a protruding portion, or one or more components or features disposed along a side surface of the housing 102. At least a portion of the first input device 108 (e.g., a crown body) may protrude from the housing 102 or otherwise be located outside the housing and define a generally circular shape or a circular outer surface. The outer surface of the first input device 108 may be textured, knurled, grooved, or otherwise include features that enhance the tactile feel of the first input device 108 and / or enable rotation detection.

[0026] The first input device 108 may enable a variety of possible interactions. For example, the first input device 108 may be rotated by a user (e.g., the crown may receive rotational inputs). Rotational inputs to the first input device 108 may zoom, scroll, rotate, or otherwise manipulate a user interface or other object displayed on the display 106, among other possible functions. The first input device 108 may also be translated or pressed by the user (e.g., in an axial direction). Translational or axial inputs may select highlighted objects or icons, cause a user interface to return to a previous menu or display, or enable or disable features, among other possible functions.

[0027] In some cases, the electronic device 100 may detect touch inputs or gestures applied to the first input device 108, such as a finger sliding along the body of the first input device 108 (which may occur when the first input device 108 is configured not to rotate) or a finger touching the body of the first input device 108. In such cases, sliding gestures may cause operations similar to the rotational inputs, and touches of a cap or crown may cause operations similar to the translational inputs. Rotational inputs herein include both rotational movements of the first input device 108 and sliding inputs that result when a user slides a finger or object along the surface of a crown in a manner similar to rotation (e.g., when the crown is fixed and / or does not rotate freely).

[0028] The electronic device 100 may also include other input devices, switches, buttons, or the like. For example, the electronic device 100 includes a second input device 110, which may be a button. The second input device 110 may be a movable button or a touch-sensitive area of ​​the housing 102. The button may control various aspects of the electronic device 100. For example, the button may be used to select icons, items, or other objects displayed on the display 106, enable or disable functions (e.g., silence an alarm or alert), or the like.

[0029] Fig. 1B shows a back surface of the device 100. The electronic device 100 may include one or more windows 112 (one of which is depicted) that transmit light through a portion of the housing 102. The one or more windows 112 may be coupled to the housing 102. The one or more windows 112 may include light-transmitting materials and be associated with internal sensor components that can be used to determine biometric information of a user, such as heart rate, blood oxygen concentration, and the like, as well as information such as a distance of the device from an object. The Fig. The particular arrangement of the one or more windows 112 in the housing 102 shown in Figure 1B is an example of such an arrangement, and other window arrangements (including different number, size, shape, and / or position of the windows) are also contemplated. As described herein, the window arrangement may be defined by or otherwise correspond to the arrangement of components in the integrated sensor housing.

[0030] The housing 102 may also include one or more electrodes 114a, 114b (collectively, electrodes 114). The electrodes 114 may enable input to biometric sensing circuitry or other sensing circuitry within the device 100. The electrodes 114 may be a conductive surface coupled to the biometric sensing circuitry via one or more components of the device 100. In some cases, one or more input devices (e.g., the first input device 108 and / or the second input device 110) may operate as an electrode used to apply electrical signals to and / or sense electrical signals from a user. The input devices may be conductively coupled to sensing circuitry within the housing 102.

[0031] Fig. Figure 2 shows an exemplary block diagram for an electronic device 200 that may be used to perform physiological measurements as described herein. The electronic device 200 may include a processor 202, one or more sensors 204, a memory 206, a display 208, an input / output (I / O) mechanism 210, and a power source 212.

[0032] The processor 202 may control some or all of the operations of the electronic device 200. The processor 202 may communicate either directly or indirectly with some or all of the components of the electronic device 200. For example, a system bus or other communication mechanism 216 may provide communication between the processor 202, the one or more sensors 204, the memory 206, the display 208, the input / output (I / O) mechanism 210, and the power source 212.

[0033] Processor 202 may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, processor 202 may be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of such devices. As described herein, the term "processor" is intended to encompass a single processor or processing unit, multiple processors, multiple processing units, or one or more other suitable computing elements.

[0034] It should be noted that the components of electronic device 200 may be controlled by multiple processors. For example, selected components of electronic device 200 (e.g., a sensor 204) may be controlled by a first processor, and other components of electronic device 200 (e.g., the I / O mechanism 210) may be controlled by a second processor, where the first and second processors may or may not be in communication with each other.

[0035] The electronic device 200 may also include one or more sensors 204 disposed virtually anywhere on the electronic device 200. The sensor(s) 204 may be configured to sense one or more types of parameters, such as, but not limited to, electrical signals, pressure, sound, light, touch, heat, motion, relative motion, biometric data (e.g., physiological parameters), and so on. For example, the sensor(s) 204 may include one or more electrodes (and corresponding circuitry), a pressure sensor, an auditory sensor, a thermal sensor, a position sensor, a light or optical sensor, an accelerometer, a pressure transducer, a gyroscope, a magnetometer, a health monitoring sensor, etc.Additionally, the one or more sensors 204 may utilize any suitable sensing technology, including, but not limited to, capacitive, ultrasonic, resistive, optical, ultrasonic, piezoelectric, and thermal sensing technology.

[0036] Memory 206 may store electronic data that may be used by the electronic device. For example, memory 206 may store electrical data or content, such as measured electrical signals, audio and video files, documents and applications, device settings and user preferences, timing signals, control signals, and data structures or databases. Memory 206 may be configured as any type of memory. For example only, memory 206 may be implemented as random-access memory, read-only memory, flash memory, removable storage, other types of storage devices, or combinations of such devices.

[0037] The electronic device 200 may also include a display 208. The display 208 may include a liquid crystal display (LCD), an organic light-emitting diode (OLED), a light-emitting diode (LED), or the like. If the display 208 is an LCD, the display 208 may also include a backlight component that can be controlled to provide different display brightness levels. If the display 208 is an OLED or LED display, the brightness of the display 208 may be controlled by modifying the electrical signals provided to display elements. The display 208 may correspond to any of the displays shown or described herein.

[0038] The I / O mechanism 210 can transmit data to or receive data from a user or other electronic device. An I / O mechanism 210 can include a display, a touch-sensing input surface, one or more buttons (e.g., a "Home" button of a graphical user interface), one or more cameras, one or more microphones or speakers, one or more ports, such as a microphone port, and / or a keyboard. Additionally or alternatively, an I / O device or port can transmit electronic signals over a communications network, such as a wireless and / or wired network connection. Examples of wireless and wired network connections include, but are not limited to, cellular, Wi-Fi, Bluetooth, IR, and Ethernet connections.

[0039] Power source 212 may be implemented with any device capable of providing power to electronic device 200. For example, power source 212 may be one or more batteries or rechargeable batteries. Additionally or alternatively, power source 212 may be a power connector or power cable that connects electronic device 200 to another power source, such as an electrical outlet.

[0040] Fig. 3 shows an example gain adjustment circuit 300 that may be used to perform physiological measurements as described herein. The example gain adjustment circuit 300 may include a contact detection circuit (CD circuit) 302 and a physiological sensing circuit 304. In some cases, the example circuit 300 may be implemented in a single application-specific integrated circuit (ASIC). In other cases, the example gain adjustment circuit 300 may be implemented across multiple ASICs, and different components may be integrated on different ones of the multiple ASICs.

[0041] In some cases, the CD circuit 302 may be operated to determine a base input impedance, which may be performed at the factory (or as part of a device initialization procedure), and a second user input impedance, which is performed when a user touches an electrode 308. In other cases, the base input impedance may be determined using other techniques that do not require the use of the contact detection circuit, and the value of the base input impedance may be stored in the electronic device. An electrical signal from the CD circuit 302 may be applied to the input of the buffer 312 so that the CD circuit 302 can determine an input impedance for the electrical signal.The determined input impedance may include the contact impedance due to the impedance at the electrode 308 resulting from the electrode's contact with a user's skin surface and / or contact with a test electrode. The determined input impedance may also include a circuit impedance 310 due to the impedance of the detection circuit. An example circuit diagram for the contact detection circuit is shown in FIG. Fig. 4 shown.

[0042] The physiological sensing circuit 304 may include a buffer 312 that receives the detected electrical signal 306 from the electrode. The buffer 312 may include a voltage buffer amplifier used to transmit the sensed voltage from the sensing electrode 308 and the downstream circuitry until further processed by the circuit 300. The physiological sensing circuit 304 may also include an analog-to-digital converter (ADC) 314 that may receive the electrical signals from the buffer 312 and convert the analog signals into a digital signal. The digitized signals may be transmitted to a gain amplifier 316, which may increase the amplitude of the electrical signals.The gain amplifier 316 may be a digital gain amplifier that increases the amplitude of a digital signal received from the analog-to-digital converter.

[0043] The circuit 300 may include a digital signal processor 318 that may receive the impedances determined using the contact detection circuit 302 and / or the sensed and gain-adjusted electrical signals from the physiological sensing circuit 304. The digital signal processor 318 may perform one or more functions on the received signals, such as associating the signals with one or more measurement parameters and transmitting the signals to a host processor of the electronic device (e.g., the electronic device 100, 200), which may generate one or more outputs based on the received signals, as described herein.

[0044] Fig. Figure 4 shows an exemplary contact detection circuit 400 (e.g., contact detection circuit 302) that may be determined using an input impedance for an electrode, as described herein. The contact detection circuit may be an example of the system hardware discussed in U.S. Patent Application Publication No. 2020 / 0077955, the contents of which are incorporated herein by reference.

[0045] Fig. Figure 4 illustrates circuit components that may be implemented on one or more ASICs and / or using other hardware. Fig. 4 focuses on the electrode(s) and measurement circuitry that may be used to determine the input impedance; however, the contact detection circuitry and / or electronic device may also include other components, including processing circuitry and / or additional electrode(s) (e.g., a reference electrode).

[0046] Circuit 400 may include a first sense electrode 402 (e.g., corresponding to first electrode 114a), a second sense electrode 404, and a reference electrode 405 (e.g., corresponding to second electrode 114b). Circuit 400 may include buffers 406 and 408, gain amplifiers 407 and 409, and amplifier 410. Buffers 406 and 408 may provide impedance matching for electrodes 402 and 404. Buffers 406 and 408 may be configured to accommodate input impedances 412 and 414 resulting from contact of electrodes 402 and 404 with a user and / or from circuit 400. In some cases, buffers 406 and 408 are configured to reduce noise and / or interference for input to amplifier 410.In some cases, amplifier 410 may be coupled to an analog-to-digital converter, and the amplifier's outputs may be fed into the analog-to-digital converter. Additionally or alternatively, gain amplifiers 407 and 409 may be operated to provide gain adjustments to electrical signals before the signals are transmitted to amplifier 410, which may be configured as a differential amplifier.

[0047] The circuit 400 may also include a test signal generator 416, a capacitor 418, and an impedance network 420. The signal generator 416 may generate one or more test signals 422 used to determine an impedance of the sense electrode 402, which may result from contact of the sense electrode 402 with a user. The capacitor 418 and the impedance network 420 may form a voltage divider via path 419 to ground, and a test signal 422 generated by the test signal generator 416 may be divided by the voltage divider. The buffer 406 may measure a node between the capacitor 418 and the impedance network 420. A measured test signal 424 may be used to determine an input impedance for the sense electrode 402.

[0048] The amplitude (e.g., voltage level) of the measured test signal 424 may depend on the stress to which the test signal 422 is subjected. For example, if a user touches the sense electrode 402, the resulting test signal 422 may be attenuated. Contact between a user (e.g., a finger) and the sense electrode 402 may form a path 417 for the test signal 422. In some examples, the path 417 may be formed by a physiological signal source (e.g., the user's body) via a ground electrode (e.g., a ground electrode contacting the user) to system ground. In some examples, a user may contact the sense electrode 402 with a first part of their body (e.g., a finger) and the device housing with a second part of their body (e.g., their wrist). In such cases, the path 417 for the test signal 422 can be provided by a physiological signal source (e.g.A connection (e.g., the user's body) to system ground may be formed by the finger touching the device case (e.g., the device case may be grounded to system ground). Thus, path 417 may form an impedance parallel to path 419 (through impedance network 412) and change the stress experienced by test signal 422. In such examples, the resulting measured test signal 424 may be attenuated at buffer 406. Conversely, if a user does not touch sense electrode 402, the resulting measured test signal 424 may not be attenuated (or may be less attenuated).

[0049] The test signal 422 (e.g., stimulation signal) generated by the test signal generator 416 may be a square wave, a sine wave, a trapezoidal wave, a sawtooth wave, or any other suitable periodic, non-oscillating, or non-periodic (e.g., pseudo-noise signal) waveform. The test signal, regardless of the waveform, may be known or predetermined within the system to enable detection of the resulting measured test signal in some examples described herein. The test signal 422 may be capacitively or resistively coupled to the sense electrode 402 via the capacitor 418. In some examples, the test signal generator 416 may be controlled by a processor (e.g., a digital signal processor (DSP), host processor, or other processor). In some examples, the processor may change the frequency and / or amplitude of the test signal 422 and / or enable and disable the test signal generator 416.In some examples, the test signal generator 416 may be a clock output of a processor.

[0050] In some examples, the response of the test signal 422 to the load may depend on the frequency of the test signal 422 and the respective impedance of the signal paths. In some examples, the frequency of the test signal 422 may be varied to determine the loading of the signal paths at the respective frequency (e.g., the quality of the skin-electrode connection may be determined as a function of the test signal frequency). In some examples, an initialization process may be used to select a frequency that can distinguish when the sense electrode 402 is touched and when it is not (e.g., a frequency for the test signal 422 that results in a noticeable change in the resulting test signal amplitude). In some examples, the test signal 422 may include a plurality of frequencies simultaneously (e.g., the test signal 422 may include multiple frequency components).In such an example, the reactance of the system to different frequencies can be determined simultaneously.

[0051] In some examples, a physiological signal from the user may enter circuitry 300 when a user contacts sense electrode 402. In some examples, initiating physiological signal measurements may include acquiring the physiological signal (e.g., by data buffer 316), storing the physiological signal (e.g., in memory), and / or displaying the physiological signal on a display of the device. In some examples, if the system determines that the sense electrode is not contacted, it may forgo measuring the physiological signal (e.g., by shutting down the circuitry, discarding the physiological signal measurements, or otherwise not processing incoming signals).In some examples, if the system detects that the sensing electrode is not contacted, it may still measure the physiological signal, but with a low confidence value, indicating that the physiological signal is of low quality (e.g., may not be reliable for one or more intended uses). In some examples, the low confidence may be represented binary (e.g., a low confidence / low quality flag may be set). In some examples, the confidence may be represented in another way (e.g., a probability) that is representative of the quality.In some examples, if the confidence is below a threshold or if the low confidence / low quality flag is set, a notification may be displayed to the user to indicate that the measured physiological signal measurement may be unreliable or of low quality (e.g., displaying the physiological signal with a visual indicator, displaying a notification on the device display, and / or other visual feedback, and / or audio feedback, and / or haptic feedback, and / or other suitable feedback mechanism).

[0052] Although Fig. While Figure 3 illustrates the integration of contact detection circuitry 302 with physiological sensing circuitry 304, it should be understood that the contact detection circuitry may be implemented in other ways. For example, the test signal circuitry may include an amplifier or other front-end circuitry (e.g., separate from amplifier 410, etc.) to perform the functions of measuring the test signal and performing contact detection. In some examples, separate signal paths may be used for contact detection and physiological sensing (e.g., without integrating the test signal circuitry with the physiological signal measurement circuitry).In some examples, the separate implementation of contact detection and physiological sensing may enable optimization of the circuitry for contact detection with respect to the frequencies, signal range, and / or signal accuracy of the test signal for contact detection and optimization of the circuitry with respect to the frequencies, signal range, and / or signal accuracy for physiological sensing. In some examples, switching circuitry may be provided to couple the test signal circuitry (e.g., test signal generator and sense amplifier) ​​to the sense electrode during contact detection and to decouple the sense electrode from the test signal circuitry during physiological signal measurement. In some examples, the test signal circuitry may be integrated into a saturation detection circuit. Although the test signal 422 in . Fig. 4 is illustrated as a discrete source, it may additionally be generated by a processor (e.g., DSP, host processor). In some examples, the same processor may also be coupled to receive the measured test signals from the output of buffer 406 and / or 408 or another buffer or amplifier circuit.

[0053] Although Fig. 3 and Fig. 4 illustrate the integration of the test signal circuit into the signal path of a sense electrode, additionally or alternatively, similar test signal circuits may be integrated into the signal path of other sense electrodes and / or a reference electrode (e.g., reference electrode 405). For example, in the embodiment described with reference to Fig. 4, the reference electrode 405 may be coupled to a ground circuit. However, in cases where contact detection is performed on the reference electrode 405, a different electrode may be coupled to the ground circuit, and the contact detection process may be applied to the reference electrode 405 using the same or a similar process for the sense electrode(s) 402, 404 as described herein. Determining a contact metric for the reference electrode 405 may occur at different times than determining a contact metric for a sense electrode.

[0054] Although Fig. 4 illustrates the sense electrodes 402, 404 and a reference electrode 405, in some examples the system may also include a plurality of sense electrodes and / or a plurality of reference electrodes, and similar test signal circuitry may be incorporated into some or all of these electrodes.

[0055] Fig. 5 shows an exemplary process 500 for performing physiological measurements to apply a gain adjustment to a physiological signal. The process may be performed using the circuits described herein (e.g., circuits 300 and 400 described with reference to Fig. 3 and Fig. 4).

[0056] At operation 502, process 500 may include determining a first contact metric for a sensing electrode. The first contact metric may be a baseline metric determined before a device is used to perform physiological measurements. In some cases, the first contact metric may be determined through a calibration procedure performed in a factory and / or prior to a user wearing the device.

[0057] Determining a first contact metric may include applying one or more test signals to the sense electrode and measuring an effect of the signal, for example, using circuits 300 and 400 described herein. In some cases, the test signal may be applied using a calibration probe that contacts the sense electrode (or other electrode(s)) on the device. The calibration probe may, for example, be contacted to the sense electrode and apply the test signal(s) to the sense electrode. Using the contact detection circuitry, the device may determine an impedance and / or another metric (e.g., the amplitude of the voltage signal) for the test signal.In other cases, the calibration probe may be configured to complete a circuit between the sense electrode, a reference electrode, and / or a ground electrode, and the contact detection circuit may apply the test signal to the circuit. The resulting test signal may be measured and used to determine an impedance metric for the calibration probe.

[0058] At operation 504, process 500 may include initiating a sensing session for a user. Initiating a sensing session may include the device determining that the device is being worn by a user and / or one or more electrodes contacting a user. In some cases, the device may use one or more sensors to determine that the user is wearing the device and / or contacting the electrode(s). For example, the device may operate the contact detection circuitry to apply a test signal to an electrode and measure the test signal, as described herein. The measured test signal may be used to determine whether the user is wearing the electronic device and / or whether sufficient contact exists between an electrode and the user.For example, if the user contacts an electrode, the measured test signal may be attenuated due to the user contact, and if the user does not touch the electrode, the test signal may not be attenuated (or may be attenuated less). In some cases, a threshold amplitude (e.g., the voltage level) may be used to determine whether a sensing electrode is contacting the user. For example, if the measured test signal is less than a threshold amplitude, the device may determine that the sensing electrode is contacted (e.g., that there is sufficient coupling between the skin and the electrode for accurate physiological measurements). If the measured test signal is greater than or equal to the threshold amplitude, the device may determine that the sensing electrode is not contacted (or that the coupling between the skin and the electrode is insufficient for accurate physiological measurements).

[0059] Additionally or alternatively, the device may use other sensors to determine whether the user is wearing the device and / or contacting the electrode. In some cases, the system may use temperature sensors, accelerometers, light sensors, humidity sensors, and so on. For example, the system may use a temperature sensor, which may include comparing the temperature measurements to one or more thresholds / ranges. For example, if the measured temperature is within a defined range, the system may determine that the device and / or the electrodes are in contact with the user, and if the measured temperature is outside the defined range, the system may determine that the device and / or the electrodes are not in contact with the user.In some cases, one or more temperature sensors can be positioned near an electrode, providing more precise determinations of contact. In other examples, light sensors can be positioned near an electrode (e.g., on a rear sensor assembly near the electrodes) and used to determine contact with the user. The light sensor can include light sources that emit light toward the user and photodetectors that receive a reflected portion of the emitted light. The received light can be evaluated to determine contact with the user.

[0060] At operation 506, process 500 may include determining a second contact metric for a sensing electrode based on the electrode's contact with the user. In some cases, the sensing metric may be an impedance and / or a change in amplitude (e.g., voltage level) for electrical signals transmitted from the user's skin to the electrode. Determining the second contact metric may include applying a test signal to the sensing electrode and measuring the resulting test signal using the contact detection circuitry as described herein. The system may analyze the measured test signal to determine the contact metric, which may be an input impedance for electrical signals based on contact with the user.

[0061] At operation 508, process 500 may include measuring electrical signals from the user. For example, a physiological sensing circuit (e.g., physiological sensing circuit 304) may be used to measure electrical cardiac signals from a user's skin surface. The electrical cardiac signals may be sensed by one or more electrodes and transmitted to a buffer, where the signal may be converted to a digital signal. In some cases, a gain adjustment may be applied to the digital signal and the signal may be transmitted to a digital signal processor, which may further analyze it and / or transmit it to a host processor, which may cause the device to perform one or more functions based on the signal.For example, the digital signal processor and / or the host processor can generate an ECG output signal that indicates changes in the polarization of a user's heart. The device can display the ECG signal on a display. Additionally or alternatively, the DSP and / or the host processor (or the remote processor) can determine physiological metrics such as beat-to-beat timing, heart rate, heart rate variability, and / or identify conditions such as arrhythmia, tachycardia, bradycardia, heart valve conditions, and so on.

[0062] In some cases, the system may use the first contact metric and the second contact metric to adjust the user's measured electrical signals. For example, the first and second contact metrics may each include an impedance, and a ratio of the first input impedance and the second input impedance may be used to determine a gain adjustment that may be applied to the user's measured electrical signal. The gain adjustment may increase the amplitude of the measured electrical signal, which may improve the quality of the measured signal prior to signal analysis by the DSP and / or host processor.

[0063] In some cases, the system may determine and apply a gain adjustment for each measured electrical signal from a user. For example, in response to initiating an acquisition session, the system may determine a second contact metric that is used to determine a gain adjustment for measured signals. Accordingly, different gain adjustments may be applied during different acquisition sessions based on the contact of the electrode with the user. In other cases, the second contact metric may be checked and updated periodically or continuously during an acquisition session. Accordingly, the systems and devices herein may adapt as the contact (and impedance) between a user and an electrode changes.

[0064] In some cases, the system may apply a gain adjustment only if at least one impedance criterion is not met (path 501) to account for high signal attenuation. If at least one impedance criterion is met, the signal attenuation may be so low that the system can accurately determine the physiological parameters without applying a gain adjustment (path 503) to the measured electrical signals.

[0065] At operation 510, process 500 may include determining whether at least one impedance criterion is met. The at least one impedance criterion may be used to determine attenuation and / or quality of the sensed cardiac signal. Determining whether the at least one impedance criterion is met may include analyzing the second contact metric (e.g., determined at operation 506) and the first contact metric (e.g., determined at operation 502) to determine whether the impedance for the measured electrical signal (e.g., measured at operation 508) is of sufficient quality to determine physiological parameters for a user.

[0066] In some cases, the at least one impedance criterion may be a defined threshold, and the first and second contact metrics may be used to determine an impedance ratio. If the ratio is above the defined threshold, the system may determine that the second input impedance does not meet the at least one impedance criterion and may apply a gain adjustment to the measured electrical signals via path 501. If the ratio is below the defined threshold, the system may determine that the second input impedance meets at least one impedance criterion and may process the measured electrical signal without applying a gain adjustment via path 503.

[0067] At operation 512, in response to determining that the at least one impedance criterion is not met, the process 500 may include determining a gain adjustment using the first and second contact metrics. For example, the first and second contact metrics may each include an input impedance for the sensing electrode. The system may analyze the first and second input impedances to determine a change in impedance between the baseline impedance (e.g., the first input impedance determined during the baseline / calibration process at 502) and the second input impedance due to contact with a user. In some cases, the gain adjustment may be proportional to the difference between the first and second input impedances.

[0068] At operation 514, process 500 may include determining a physiological parameter of the user using the determined gain adjustment. For example, the determined gain adjustment may be a digital gain adjustment applied to the measured electrical signal after it has been converted to a digital signal. The gain adjustment may be applied to the signal before the signal is transmitted to the digital signal processor and / or a host processor. In other cases, the gain adjustment may be applied to the analog signal before the signal is converted to a digital signal (also referred to herein as an "analog gain adjustment").

[0069] In some cases, gain adjustment may include a combination of digital and analog gain adjustment. Because digital gain adjustment also amplifies all upstream noise, including circuit noise introduced as the measured electrical signal propagates through the system, it may be desirable in some cases to limit the magnitude of the digital gain adjustment. Accordingly, the system may apply both analog gain adjustment to the analog measured signal (e.g., by changing the gain of one or more amplifiers within the system) and digital gain adjustment to the measured signal after it has been converted to the digital signal.In this way, the analog gain adjustment forms a first portion of the specific gain adjustment, and the digital gain adjustment forms a second portion of the specific gain adjustment. While the analog gain adjustment can reduce the relative impact of noise in the downstream circuits, this can increase the system's power consumption. Accordingly, the relative amounts of the analog gain and the digital gain within the specific gain adjustment can be selected to achieve a balance between noise rejection and power consumption.For example, in some variations, the particular gain adjustment may include only a digital gain adjustment when the digital gain adjustment is below a threshold, and may include both a digital gain adjustment and an analog gain adjustment when the digital gain adjustment is at or above the threshold. In these cases, digital gain adjustments may be used for relatively small adjustments, and a combination of digital and analog gain adjustments may be used for relatively large adjustments.

[0070] At operation 516, in response to determining that the at least one impedance criterion is met, process 500 may include determining a physiological parameter of a user without applying a gain adjustment to the measured electrical signal, as described herein.

[0071] Although Fig. 5 illustrates an exemplary process for performing gain adjustment for a single electrode, it is understood that a similar test signal circuit may be integrated into the signal path of one or more additional electrodes on the device. Although Fig. 4 also illustrates two sense electrodes 402, 404 and one reference electrode 405, in some examples the system may include additional or fewer sense electrodes and / or a plurality of reference electrodes, and similar test signal circuitry may be integrated with some or all of these electrodes.

[0072] Fig. 6 shows an example gain calibration circuit 600 that may be used to perform physiological measurements as described herein. The example circuit 600 may be an example of the circuits described herein (e.g., gain adjustment circuit 300 and circuit 400) and may include a contact detection (CD) circuit 602 and a physiological sensing circuit 604, as described herein. In some cases, the example circuit 600 may be implemented in a single application-specific integrated circuit (ASIC). In other cases, the example circuit 600 may be implemented across multiple ASICs, and different components may be integrated on different ones of the multiple ASICs.

[0073] The measurements performed by a gain adjustment circuit (e.g., gain adjustment circuit 300) may include a total impedance representing the combination of the electrode impedance (e.g., electrode impedance 308) and the circuit impedance (e.g., circuit impedance 310). When these impedances are measured together, the system may not be able to distinguish between changes in the electrode impedance (e.g., resulting from different types of contact with the electrode by the user) and the circuit impedance (e.g., resulting from wear, etc.).

[0074] The gain calibration circuit 600 can enable an electrode impedance 608 to be measured independently of the physiological sensing circuit 604. Furthermore, the gain calibration circuit 600 can measure the total input impedance to be measured (the combination of electrode impedance 608 and circuit impedance 610). Using the individual electrode impedance 608 and the total impedance, the system can determine the circuit impedance 610. Accordingly, the system can determine the electrode impedance 608 and the circuit impedance 610 independently and in real time, without requiring any initial calibration information. For example, the impedance of the circuit 600 can be determined in response to initiating a measurement session (e.g., prior to measuring a user's electrical signals) and / or when the electrodes are not contacting the user.

[0075] Circuit 600 may include a switch 620 that may isolate physiological sensing circuit 604 from contact detection circuit 602. The total impedance of gain calibration circuit 600 may include electrode impedance 608 and circuit impedance 610. The system / device may actuate switch 620 to selectively isolate contact detection circuit 602 from physiological sensing circuit 604 and couple physiological sensing circuit 604 to contact detection circuit 602.

[0076] Fig. Figure 7 shows an exemplary process 700 for performing physiological measurements using gain calibration. The process 700 may be performed using the circuitry described herein (e.g., the circuitry described with reference to Fig. 6 described circuit 600).

[0077] At operation 702, process 700 may include isolating a contact detection circuit (e.g., contact detection circuit 602) from a physiological sensing circuit (e.g., physiological sensing circuit 604). In some cases, a switch (e.g., switch 620) may be actuated to electrically isolate the physiological sensing circuit from the contact detection circuit. Once isolated, the contact detection circuit may be electrically coupled to a sense electrode, and the physiological sensing circuit may be isolated from the contact detection circuit.

[0078] At operation 704, process 700 may include determining a first impedance for the contact detection circuit. In some cases, the system may apply a test signal to a first node of the contact detection circuit and measure the resulting test signal at a second node of the contact detection circuit. The test signal may be altered (e.g., attenuated) due to the impedance of the contact detection circuit and / or contact of the electrode with a user (or other object), as described herein. The system may determine the first impedance based on analyzing differences between the test signal applied to the contact detection circuit and the measured test signal. In some cases, the differences may include a change in amplitude, a phase shift, or other change in the test signal.

[0079] At operation 706, process 700 may include electrically connecting the contact detection circuit and the physiological sensing circuit. The switch (e.g., switch 620) may be actuated to electrically connect the physiological sensing circuit to the contact detection circuit. Once connected, the physiological sensing circuit may be electrically coupled to the contact detection circuit and the sensing electrode.

[0080] At operation 708, process 700 may include determining a second impedance for the contact detection circuitry and the physiological sensing circuitry. The system may apply a test signal to a first node of the contact detection circuitry and measure the resulting test signal at a second node of the contact detection circuitry. The test signal may be altered (e.g., attenuated) due to the impedance of the contact detection circuitry, the impedance of the physiological detection circuitry, and / or contact of the electrode with a user (or other object), as described herein. The system may determine the second impedance based on analyzing differences between the test signal applied to the first node and the measured test signal. In some cases, the differences may include a change in amplitude, a phase shift, or other change in the test signal.

[0081] At operation 710, process 700 may include determining a gain adjustment using the first and second input impedances. For example, the system may analyze the first and second input impedances to determine whether the signal attenuation reaches an impedance threshold, which may be set by the system requirements. By comparing the electrode impedance 608 and the input impedance 610, it may be determined whether the signal attenuation reaches the impedance threshold. If the signal attenuation does not reach the impedance threshold, a gain adjustment may be made at 616. In some cases, the gain adjustment may be proportional to the difference between the first and second input impedances.

[0082] At operation 712, process 700 may include measuring a user's electrical signal. For example, a physiological sensing circuit (e.g., physiological sensing circuit 604) may be used to measure cardiac electrical signals from a user's skin surface. The cardiac electrical signals may be sensed by one or more electrodes and transmitted to a buffer, where the signal may be converted into a digital signal.

[0083] At operation 714, process 700 may include determining a physiological parameter of the user using the electrical signal and the gain adjustment. In some cases, a gain adjustment may be applied to the digital signal and the signal transmitted to a digital signal processor, which may further analyze it and / or transmitted to a host processor, which may cause the device to perform one or more functions based on the signal. For example, the digital signal processor and / or the host processor may generate an ECG output signal indicating changes in the polarization of a user's heart. The device may present the ECG signal on a display. Additionally or alternatively, the DSP and / or the host processor (or the remote processor) may determine physiological metrics, such asidentify beat-to-beat timing, heart rate, heart rate variability, and / or conditions such as arrhythmia, tachycardia, bradycardia, heart valve conditions, and so on.

[0084] This disclosure contemplates that entities responsible for the collection, analysis, disclosure, transmission, storage, or other use of such personal data will adhere to generally established privacy policies and / or practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or regulatory requirements for maintaining and protecting the confidentiality of personal data. These policies should be readily accessible to users and should be updated as the collection and / or use of data changes. Users' personal information should be collected for legitimate and meaningful uses by the entity and should not be shared or sold outside of those legitimate uses.Furthermore, such collection / disclosure should occur after obtaining the informed consent of users. Furthermore, such entities should consider taking all necessary steps to protect and secure access to such personal data and ensure that others who have access to the personal data adhere to their privacy policies and procedures. Furthermore, such entities may submit to third-party evaluation to confirm that they adhere to generally accepted privacy policies and practices. Furthermore, the policies and practices should be tailored to the particular types of personal data being collected and / or accessed and should comply with applicable laws and standards, including jurisdiction-specific considerations.For example, in the United States, the collection of or access to certain health information may be regulated by federal and / or state laws, such as the Health Insurance Portability and Accountability Act ("HIPAA"); whereas health information in other countries may be subject to different regulations and policies and should be treated accordingly. Therefore, different data protection practices should be followed for different types of personal information in each country.

[0085] Notwithstanding the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of or access to personal data. That is, the present disclosure contemplates that hardware and / or software elements may be provided to prevent or block access to such personal data. For example, in the case of determining spatial parameters, the present technology may be configured to allow users to select whether to consent to ("opt in") or decline ("opt out") participation in the collection of personal data during registration for services or at any time thereafter.In addition to providing options to opt in or out, this disclosure contemplates providing notifications regarding access to or use of personal data. For example, a user may be notified when downloading an app that their personal data is being accessed and then reminded again shortly before the app accesses the personal data.

[0086] Furthermore, it is the intention of the present disclosure that personal data be managed and handled in a manner that minimizes the risks of accidental or unauthorized access or use. This risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and where necessary, including in certain health-related applications, data anonymization may be used to protect a user's privacy. De-identification may be supported, where appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of stored data (e.g., collecting location data at the location level rather than the address level), the manner in which data is stored (e.g.,aggregating data across users) and / or by other means.

[0087] Although the present disclosure broadly covers the use of personal information data to implement one or more of the various disclosed embodiments, the present disclosure also contemplates that the various embodiments may be implemented without the need for access to such personal information data. That is, the various embodiments of the present technology will not be rendered inoperable due to the absence of all or a portion of such personal information. For example, haptic outputs may be provided based on non-personal information data or a bare minimum amount of personal information, such as events or states on the device associated with a user, other non-personal information, or publicly available information.

[0088] The foregoing description utilized specific nomenclature for purposes of explanation in order to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to those skilled in the art that many modifications and variations are possible in light of the above teachings. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 63 / 534,459

[0001] US 2020 / 0077955 [0013, 0044]

Claims

[1] A method for electrode detection on a portable electronic device, the method comprising: in response to determining that a user is carrying the portable electronic device: Applying, using a contact detection circuit, a test signal to a sensing electrode; and Determining, using the contact detection circuit, an input impedance for the sensing electrode using the test signal; Determining a gain adjustment using the input impedance and a base impedance; Measuring, using a physiological sensing circuit, an electrical signal of the user using the sensing electrode; and Applying, using the physiological detection circuit, the gain adjustment to the measured electrical signal; and Determining a physiological parameter of the user using the measured electrical signal to which the gain adjustment was applied. [2] The method of claim 1, further comprising: in response to determining that the input impedance does not meet a criterion, determining the physiological parameter by applying the gain adjustment to the measured electrical signal; and in response to determining that the input impedance meets the criterion, determining the physiological parameter without applying the gain adjustment to the measured electrical signal. [3] The method of claim 1, further comprising, prior to applying the test signal, performing a calibration process that uses the contact detection circuit to determine the base impedance for the sense electrode. [4] The method of claim 3, wherein the physiological parameter is determined as part of a first acquisition session and further comprises: determining, by the portable electronic device, to initiate a second sensing session after completion of the first sensing session; in response to determining to initiate the second capture session: Applying a second test signal to the user; Measuring a second electrical signal from the user; Determining a second gain adjustment; and Determining a second physiological parameter of the user by applying the second gain adjustment to the measured second electrical signal. [5] The method of claim 1, wherein the test signal is a time-varying electrical signal. [6] The method of claim 1, wherein measuring the user's electrical signal comprises measuring a cardiac electrical signal of the user using the sensing electrode and at least one second electrode located on the portable electronic device. [7] The method of claim 6, wherein the sensing electrode contacts a first extremity of the user and the second electrode is configured to be contacted by a second extremity of the user when the portable electronic device is worn by the user. [8] The method of claim 1, wherein the sensing electrode is a dry electrode that contacts a skin surface of the user when the portable electronic device is worn by the user. [9] The method of claim 1, further comprising: in response to determining that the user is carrying the portable electronic device: Applying a second test signal to a second sensing electrode; and determining a second input impedance for the second sense electrode using the second test signal; determining a second gain adjustment using the second input impedance and the base impedance; Measuring a second electrical signal of the user using the second sensing electrode; and Determining the user's physiological parameter by applying the second gain adjustment to the measured second electrical signal. [10] A method for electrode gain calibration of sense electrode signals on a portable electronic device, the method comprising: Isolating a contact detection circuit from a physiological sensing circuit; applying, while the contact detection circuit is isolated from the physiological sensing circuit, a first test signal to a sensing electrode of the portable electronic device; Determining a first input impedance for the sense electrode using the first test signal; Connecting the contact detection circuit to the physiological sensing circuit; Applying a second test signal to the sensing electrode while the contact detection circuit is connected to the physiological sensing circuit; and Determining a second input impedance for the sense electrode using the second test signal; Determining a gain adjustment using the first input impedance and the second input impedance; and Measuring an electrical signal of a user using the sensing electrode; and Determining a user's physiological parameter by applying gain adjustment to the measured electrical signal. [11] The method of claim 10, further comprising: in response to determining that the gain adjustment does not meet a criterion, determining the physiological parameter by applying the gain adjustment to the measured electrical signal; and in response to determining that the gain adjustment meets the criterion, determining the physiological parameter without applying the gain adjustment to the measured electrical signal. [12] The method of claim 10, wherein measuring the user's electrical signal comprises measuring a cardiac electrical signal of the user using the sensing electrode. [13] The method of claim 10, further comprising converting the measured electrical signal into a digital signal, wherein applying the gain adjustment comprises applying a digital gain adjustment to the digital signal. [14] The method of claim 10, wherein the sensing electrode is a dry sensing electrode. [15] The method of claim 10, wherein the first test signal and the second test signal each include a time-varying electrical signal. [16] A system for electrode detection on a portable electronic device, the system comprising: a housing configured to be paired with a user; a sensing electrode coupled to the housing and configured to contact the user; and a processor configured to: in response to determining that the user is carrying the portable electronic device: Causing a test signal to be applied to the sensing electrode; and Determining an input impedance for the sensing electrode using the test signal; Determining a gain adjustment using the input impedance and a base impedance; Measuring an electrical signal of the user using the sensing electrode; and Determining a user's physiological parameter by applying gain adjustment to the measured electrical signal. [17] The system of claim 16, further comprising a second sensing electrode coupled to the housing, wherein: the sensing electrode is configured to contact a first extremity of the user; the second sensing electrode is configured to be contacted by a second extremity of the user; and the processor is configured to measure a second electrical signal from the user using the second sensing electrode; and Determining the physiological parameter using the second electrical signal. [18] The system of claim 17, wherein the processor is configured to: Determining a second gain adjustment for the second sensing electrode; and Determining the physiological parameter by applying the second gain adjustment to the measured second electrical signal. [19] The system of claim 16, wherein the processor is configured to: in response to determining that the input impedance meets a criterion, determining the physiological parameter by applying the gain adjustment to the measured electrical signal; and in response to determining that the input impedance does not meet the criterion, determining the physiological parameter without applying the gain adjustment to the measured electrical signal. [20] The system of claim 19, wherein: the criterion includes a defined impedance threshold; and determining that the input impedance satisfies the defined impedance threshold, comprising determining that a value of the input impedance is greater than the defined impedance threshold.

Images