Gain adjustment using contact detection

Abstract

The invention relates to gain adjustment using contact detection. More specifically, embodiments relate to methods, devices, and systems for determining and applying a gain adjustment to a sensed electrical signal. The methods may include operating a device to determine that a user is wearing a wearable electronic device and applying a test signal to a sensing electrode of the wearable device. The test signal may be used to determine an input impedance of the sensing electrode. The input impedance and the baseline impedance may be used to determine a gain adjustment. An electrical signal of the user may be measured using the sensing electrode, and the gain adjustment may be applied to the electrical signal. A physiological parameter of the user may be determined using the measured electrical signal to which the gain adjustment has been applied.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is a non-provisional application of U.S. Provisional Patent Application No. 63 / 534,459 filed on August 24, 2023, and claims the benefit of that U.S. Provisional Patent Application under 35 U.S.C. 119(e), the contents of which are incorporated herein by reference as if fully disclosed herein. Technical Field

[0003] The described embodiments generally relate to apparatus and methods for processing physiological signals, and more particularly, the present embodiments relate to adjusting the physiological signals based on a measure of contact of one or more electrodes with a user. Background Art

[0004] Electrodes may be used as part of an electronic device to measure the electrical potential of a user. For example, an electrocardiogram (ECG) measurement may use electrodes contacting the user's body to measure the user's cardiac electrical activity over one or more cardiac cycles. Similarly, electromyograms (EMG) and electroencephalograms (EEG) may use electrodes to measure muscle and brain activity, respectively. Electrodes may contact the user at different parts of the user's body, and a pair of electrodes may each measure electrical signals at different locations on the user, and the measured signals from the different electrodes may be used to determine a potential difference. In an ECG measurement, the potential difference over one or more cardiac cycles may be analyzed to obtain information about the electrical function of the user's heart.

[0005] Conventional electrodes, which may be referred to as "wet electrodes," include a conductive gel to facilitate electrical conduction from the skin. The electrodes may be incorporated into a wearable device, such as a smartwatch, which may be used to continuously or periodically monitor a user's cardiac electrical activity. It may be desirable to utilize "dry electrodes" in wearable devices, such as smartwatches, that do not require a conductive gel. Dry electrodes may result in greater signal attenuation of electrical signals from the user's skin. Summary of the invention

[0006] Embodiments relate to methods for electrode sensing at a wearable electronic device. The method may include, in response to determining that a user is wearing the wearable electronic device: applying a test signal to a sensing electrode using a contact detection circuit; and using the contact detection circuit, determining an input impedance of the sensing electrode using the test signal. The method may include: determining a gain adjustment using the input impedance and a baseline impedance; and using a physiological sensing circuit, measuring an electrical signal of the user using the sensing electrode. The method may include: applying a gain adjustment to the measured electrical signal using the physiological sensing circuit; and determining a physiological parameter of the user using the measured electrical signal to which the gain adjustment is applied.

[0007] Embodiments also relate to a method for performing electrode gain calibration on a sensing electrode signal at a wearable electronic device. The method may include isolating a contact detection circuit from a physiological sensing circuit. When the contact detection circuit is isolated from the physiological sensing circuit, a first test signal may be applied to a sensing electrode of the wearable electronic device. The method may include determining a first input impedance of the sensing electrode using the first test signal. The contact detection circuit may be connected to the physiological sensing circuit. The method may include applying a second test signal to the sensing electrode when the contact detection circuit is connected to the physiological sensing circuit. A second input impedance may be determined for the sensing electrode using the second test signal. The method may include: determining a gain adjustment using the first input impedance and the second input impedance; measuring an electrical signal of a user using the sensing electrode; and determining a physiological parameter of the user by applying the gain adjustment to the measured electrical signal.

[0008] Embodiments further include a system for performing electrode sensing at a wearable electronic device. The system may include: a housing configured to be coupled to a user; a sensing electrode coupled to the housing and configured to contact the user; and a processor. The processor may be configured to: cause a test signal to be applied to the sensing electrode in response to determining that the user is wearing the wearable electronic device; and use the test signal to determine an input impedance of the sensing electrode. The processor may determine a gain adjustment using the input impedance and the baseline 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

[0009] The present disclosure will be readily understood through the following detailed description in conjunction with the accompanying drawings, in which like reference numerals represent like structural elements, and in which:

[0010] Figure 1A shows a front view of an example electronic device that can be used to perform physiological measurements as described herein;

[0011] Figure 1B shows a rear view of an example electronic device that may be used to perform physiological measurements as described herein;

[0012] Figure 2 shows an example block diagram of an electronic device that may be used to perform physiological measurements as described herein;

[0013] Figure 3 An example gain adjustment circuit that can be used to perform physiological measurements as described herein is shown;

[0014] Figure 4 An example contact detection circuit that can be used to perform physiological measurements as described herein is shown;

[0015] Figure 5An example process for performing physiological measurements using a gain adjustment circuit is shown;

[0016] Figure 6 An example gain calibration circuit that can be used to perform physiological measurements as described herein is shown; and

[0017] Figure 7 An example process for performing physiological measurements using a gain calibration circuit is shown.

[0018] It should be understood that the proportions and sizes (relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, spacings, and positional relationships presented therebetween are provided in the accompanying drawings solely to facilitate understanding of the various embodiments described herein and therefore may not necessarily be presented or illustrated to measure and are not intended to indicate any preference or requirement for the illustrated embodiments to exclude the embodiments described in conjunction therewith. DETAILED DESCRIPTION

[0019] Reference will now be made in detail to the representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to a preferred embodiment. On the contrary, the following description is intended to cover substitutions, modifications and equivalents that may be included within the spirit and scope of the described embodiments defined by the appended claims.

[0020] Embodiments disclosed herein relate to devices, systems, and methods for improving the accuracy of physiological measurements and, in particular, physiological measurements made using electrodes in contact with a user's skin. The devices and systems described herein may include electrodes that can sense electrical signals from a user's skin surface 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 a gain adjustment and applying the gain adjustment to electrical signals sensed by one or more electrodes. For example, the devices and systems may perform an electrocardiogram (ECG) measurement that may include sensing a user's cardiac electrical signals using one or more electrodes and applying a gain adjustment to the sensed cardiac electrical signals.

[0021] In some cases, the user-electrode interface may have a high electrical impedance, which may attenuate the signal sensed by the electrode. For example, when a dry electrode is used to measure the user's electrical signal, 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 an electrode that does not use a gel or other liquid material to form a conductive path between the skin and the electrode. In some cases, the input impedance may cause signal attenuation, which results in physiological measurements (e.g., ECG measurements) that do not meet at least one specific accuracy and / or reliability standard. For example, physiological parameters such as ECG measurements determined from highly attenuated signals may not meet defined accuracy and / or reliability standards. That is, the device may determine that the quality of the signal is too low to accurately determine the ECG measurement for the user.

[0022] Embodiments described herein include systems, devices, and methods for determining a gain adjustment and applying the gain adjustment to a user's measured physiological signal. In some cases, the system may determine the gain adjustment using system calibration data and user-specific calibration data. The system calibration data may represent general properties of the system itself, which may include baseline impedance data for one or more electrodes. The user-specific calibration data may relate to the quality of contact with the user's electrodes, and may include impedance data determined from a test signal applied to the electrodes when the electrodes are in contact with the user. The system calibration data for the sensing electrodes may be determined, for example, as part of a manufacturing process before the user wears the device or during initial use of the device by the user, and stored by the system. The system calibration data may be obtained, for example, by applying a first test signal to the sensing electrodes and using a contact detection circuit to determine the baseline impedance of the sensing electrodes. The first test signal may be applied using any suitable method, and does not necessarily need to simulate the biological conditions of the user. For example, a first test signal may be applied using a test probe, and the determined baseline impedance may be lower than the expected impedance due to contact with the user. The user-specific calibration data may be obtained by determining that the user is wearing the electronic device and applying a second test signal to the user using a contact detection circuit and determining a second input impedance based on contact of the sensing electrodes with the user. In some cases, user-specific calibration data may be determined using the contact detection process and hardware discussed in U.S. Patent Application Publication No. 2020 / 0077955, the contents of which are incorporated herein by reference.

[0023] The determined gain adjustment may be used to increase the power and / or amplitude of the signal measured by the sensing electrodes. For example, the sensing electrodes may be operated to measure a user's cardiac electrical signal and determine one or more ECG parameters of the user. The device may apply the determined gain adjustment to the measured cardiac signal to increase the power and / or amplitude of the measured cardiac signal. The device may determine one or more ECG parameters by applying the gain adjustment to the measured cardiac signal.

[0024] In some cases, the device may determine whether to apply a gain adjustment to the measured physiological signal. For example, the wearable device may determine whether the user-specific calibration data and / or the determined gain meets at least one criterion. The criterion may be an impedance threshold that defines an impedance range for applying the gain adjustment. In response to meeting at least one criterion (e.g., the impedance based on the contact of the sensing electrode with the user is within the impedance range), the wearable device applies a gain adjustment to the measured physiological signal. In response to not meeting at least one criterion (e.g., the impedance based on the contact of the sensing electrode with the user is not within the impedance range), the wearable device does not apply a gain adjustment to the measured physiological signal.

[0025] In some cases, the system and / or device may include multiple sensing electrodes and determine a gain adjustment for each of the electrodes. For example, the system may determine a first gain adjustment and apply the first gain adjustment to an electrical signal measured by a first sensing electrode, and determine a second gain adjustment and apply the second gain adjustment to an electrical signal measured by a second sensing electrode.

[0026] Embodiments described herein also include systems, devices, and methods for determining and applying gain adjustments to account for impedance changes and / or other changes in one or more circuits that cause attenuation of a user's measured physiological signal. System devices may include a contact detection circuit and a physiological sensing circuit, the contact detection circuit being used to characterize contact between a sensing electrode and a user (e.g., determining an input impedance based on contact between the sensing electrode and the user), the physiological sensing circuit being used to measure the user's electrical signal. The system and / or device may be operated to isolate the contact detection circuit from the physiological sensing circuit. A first test signal may be applied to the sensing electrode while isolating the physiological detection circuit from the contact detection circuit. A first impedance of the sensing electrode may be determined, which may correspond to the impedance of the contact detection circuit. The contact detection circuit may be connected to the physiological sensing circuit, and a second test signal may be applied to the sensing electrode. A second impedance may be determined for the sensing electrode and may correspond to the impedance of the contact detection circuit and the physiological sensing circuit. A gain adjustment may be determined from the first impedance and the second impedance, and the determined gain adjustment may be applied to the user's measured electrical signal to compensate for attenuation or other signal degradation caused by the contact detection circuit and / or the physiological sensing circuit.

[0027] Refer to Figures 1 to Figure 7 However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for illustration purposes only and should not be construed as limiting.

[0028] Figure 1A A front view of an example electronic device 100 is shown, and Figure 1BA rear view of an example electronic device 100 is shown that can be used to perform physiological measurements as described herein. The electronic device 100 is depicted as a watch, but this is only one example embodiment of an electronic device, and the concepts discussed herein can also be applied similarly or by analogy to other electronic devices, including mobile phones (e.g., smartphones), tablet computers, laptop computers, head-mounted displays, headphones, earbuds, digital media players (e.g., mp3 players), wearable bands, rings, etc.

[0029] Device 100 includes housing 102 and a band 104 coupled to the housing. Housing 102 may at least partially define an interior volume in which components of device 100 may be positioned. 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 rear surface, a front surface, etc. Housing 102 may be formed of any suitable material, such as metal (e.g., aluminum, steel, titanium, etc.), ceramic, polymer, glass, etc.

[0030] Band 104 may attach device 100 to a user, such as to an arm or wrist of the user. Device 100 may include a battery charging component within device 100 that may receive power, charge a battery of device 100, and / or provide direct power to operate device 100 regardless of the charge state of the battery (e.g., bypassing the battery of device 100). Device 100 may include a magnet, such as a permanent magnet, that magnetically couples to a magnet (e.g., a permanent magnet, an electromagnet) or a magnetic material (e.g., a ferromagnetic material such as iron, steel, etc.) in a charging dock (e.g., to facilitate wireless charging of device 100).

[0031] The electronic device 100 may include a display 106. The display 106 may be at least partially positioned within the housing 102. The display 106 may define an output area in which a graphical output is displayed. The graphical output may include a graphical user interface, user interface elements (e.g., buttons, sliders, etc.), text, lists, photos, videos, etc. In some cases, the display 106 may output a graphical user interface having one or more graphical objects that display information collected or obtained 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.

[0032] The display 106 may include or be associated with a touch sensor and / or force sensor that extends along the output area of ​​the display and may use any suitable sensing element and / or sensing technology. Using the touch sensor, the electronic device 100 may detect a touch input applied to the cover, including detecting the location of the touch input, the movement of the touch input (e.g., the speed, direction, or other parameters that a gesture applied to the cover may generate), etc. Using the force sensor, the electronic device 100 may detect the amount or magnitude of force associated with a touch event applied to the cover. The touch sensor and / or force sensor may detect various types of user input to control or modify the operation of the electronic device 100, including taps, swipes, multi-finger inputs, single-finger or multi-finger touch gestures, presses, etc.

[0033] The electronic device 100 may also include one or more user inputs, such as a first input device 108 having a cap, crown, raised portion, or component or feature positioned along a side surface of the housing 102. At least a portion of the first input device 108, such as a crown body, may protrude from the housing 102 or otherwise be located outside of the housing and may 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 have features that may improve the tactile feel of the first input device 108 and / or facilitate rotational sensing.

[0034] The first input device 108 can facilitate a variety of possible interactions. For example, the first input device 108 can be rotated by the user (e.g., the crown can receive the rotational input). The rotational input of the first input device 108 can zoom, scroll, rotate, or otherwise manipulate the user interface or other objects displayed on the display 106, as well as other possible functions. The first input device 108 can also be translated or pressed (e.g., axially) by the user. The translational or axial input can select a highlighted object or icon, return the user interface to a previous menu or display, or activate or deactivate a function, as well as other possible functions.

[0035] In some cases, the electronic device 100 may sense a touch input or gesture 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, the sliding gesture may cause an operation similar to a rotational input, and a touch on the top cover or crown may cause an operation similar to a translational input. As used herein, rotational input includes rotational movement of the first input device 108, as well as sliding input generated when a user slides a finger or object along the surface of the crown in a manner similar to rotation (e.g., where the crown is fixed and / or cannot rotate freely).

[0036] The electronic device 100 may also include other input devices, switches, buttons, etc. 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 an icon, item, or other object displayed on the display 106, to activate or deactivate a function (e.g., to silence an alarm or warning), etc.

[0037] Figure 1B The back side of the device 100 is shown. The electronic device 100 may include one or more windows 112 (one of which is shown) that allow light to pass 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 a light-transmissive material and be associated with an internal sensor component that can be used to determine biometric information of the user, such as heart rate, blood oxygen concentration, etc., as well as information such as the distance from the device to an object. Figure 1B The particular arrangement of one or more windows 112 in housing 102 shown in FIG. 1 is an example arrangement, and other window arrangements (including different numbers, sizes, shapes, and / or locations of windows) are also contemplated. As described herein, the window arrangement may be defined by or otherwise correspond to the arrangement of components in an integrated sensor package.

[0038] The housing 102 may also include one or more electrodes 114a, 114b (collectively referred to as electrodes 114). The electrodes 114 may facilitate input to a biometric sensing circuit or other sensing circuitry within the device 100. The electrodes 114 may be conductive surfaces that are conductively 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 electrodes for applying electrical signals to a user and / or sensing electrical signals from a user. The input devices may be conductively coupled to sensing circuitry within the housing 102.

[0039] Figure 2 An example block diagram 200 of an electronic device that may be used to perform physiological measurements as described herein is shown. 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.

[0040] The processor 202 may control some or all operations of the electronic device 200. The processor 202 may communicate, directly or indirectly, with some or all components of the electronic device 200. For example, a system bus or other communication mechanism 216 may provide communication between the 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.

[0041] 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 a combination of such devices. As used 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.

[0042] It should be noted that components of the electronic device 200 may be controlled by multiple processors. For example, selected components of the electronic device 200 (e.g., the sensor 204) may be controlled by a first processor and other components of the electronic device 200 (e.g., the I / O 210) may be controlled by a second processor, wherein the first processor and the second processor may or may not communicate with each other.

[0043] The electronic device 200 may also include one or more sensors 204 positioned substantially anywhere on the electronic device 200. The sensors 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, movement, relative motion, biometric data (e.g., biological parameters), etc. For example, the sensor 204 may include one or more electrodes (and corresponding circuits), pressure sensors, auditory sensors, thermal sensors, position sensors, light or optical sensors, accelerometers, pressure transducers, gyroscopes, magnetometers, health monitoring sensors, etc. In addition, 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 technologies.

[0044] Memory 206 can store electronic data that can be used by the electronic device. For example, memory 206 can store electronic data or content, such as, for example, measured electrical signals, audio files and video files, documents and applications, device settings and user preferences, timing signals, control signals, and data structures or databases. Memory 206 can be configured as any type of memory. By way of example only, memory 206 can be implemented as random access memory, read-only memory, flash memory, removable memory, other types of memory storage elements, or a combination of such devices.

[0045] 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) display, a light emitting diode (LED) display, and the like. If the display 208 is an LCD, the display 208 may also include a backlight component that can be controlled to provide variable display brightness levels. If the display 208 is an OLED or LED type display, the brightness of the display 208 may be controlled by modifying the electrical signals provided to the display elements. The display 208 may correspond to any display shown or described herein.

[0046] The I / O mechanism 210 may transmit data to a user or another electronic device and / or receive data from a user or another electronic device. The I / O mechanism 210 may include a display, a touch sensing input surface, one or more buttons (e.g., a graphical user interface "home" button), one or more cameras, one or more microphones or speakers, one or more ports such as a microphone port, and / or a keyboard. In addition or alternatively, the I / O device or port may send electrical signals via a communication network such as a wireless and / or wired network connection. Examples of wireless and wired network connections include, but are not limited to, cellular networks, Wi-Fi, Bluetooth, IR, and Ethernet connections.

[0047] The power supply 212 may be implemented using any device capable of providing energy to the electronic device 200. For example, the power supply 212 may be one or more batteries or rechargeable batteries. Additionally or alternatively, the power supply 212 may be a power connector or a power cord that connects the electronic device 200 to another power source such as a wall outlet.

[0048] Figure 3 An example gain adjustment circuit 300 is shown that can be used to perform physiological measurements as described herein. The example gain adjustment circuit 300 may include a contact detection (CD) circuit 302 and a physiological sensing circuit 304. In some cases, the example circuit 300 may be implemented on a single application specific integrated circuit (ASIC). In other cases, the example gain adjustment circuit 300 may be implemented across multiple ASICs, and various components may be integrated on different ASICs in the multiple ASICs.

[0049] In some cases, the CD circuit 302 can be operated to determine a baseline input impedance, which can be performed at the factory (or as part of the device startup process), and a second user input impedance, which is performed when the user contacts the electrode 308. In other cases, other techniques that do not require the use of a contact detection circuit can be used to determine the baseline input impedance, and the baseline input impedance value can be stored at the electronic device. The electrical signal from the CD circuit 302 can be applied to the input of the buffer 312 so that the CD circuit 302 can determine the input impedance of the electrical signal. The determined input impedance may include a contact impedance due to the impedance at the electrode 308, which is caused by the contact of the electrode with the user's skin surface and / or contact with the 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 of a contact detection circuit is shown in FIG. Figure 4 Shown in.

[0050] 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 that transmits the sensed voltage from the sensing electrode 308 and downstream circuits until the voltage is 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 signal from the buffer 312 and convert the analog signal into a digital signal. The digitized signal may be transmitted to a gain amplifier 316 that may increase the amplitude of the electrical signal. The gain amplifier 316 may be a digital gain amplifier that increases the amplitude of the digital signal received from the analog-to-digital converter.

[0051] The circuit 300 may include a digital signal processor 318 that may receive the impedance determined using the contact detection circuit 302 and / or the detected and gain-adjusted electrical signal from the physiological sensing circuit 304. The digital signal processor 318 may perform one or more functions on the received signal, such as correlating the signal with one or more measurement parameters, and transmit the signal to a host processor of an electronic device (e.g., electronic device 100, 200), which may generate one or more outputs based on the received signal, as described herein.

[0052] Figure 4 An example contact detection circuit 400 (e.g., contact detection circuit 302) that can be used to determine the input impedance of an electrode is shown, as described herein. The contact detection circuit can be an example of system hardware discussed in U.S. Patent Application Publication No. 2020 / 0077955, the contents of which are incorporated herein by reference.

[0053] Figure 4 Circuit components are illustrated that may be implemented on one or more ASICs and / or using other hardware. Figure 4 Focus is placed on electrodes and measurement circuitry that may be used to determine input impedance, however the contact detection circuit and / or electronics may include other components, including processing circuitry and / or additional electrodes (eg, reference electrodes).

[0054] Circuit 400 may include a first sensing electrode 402 (e.g., corresponding to first electrode 114a), a second sensing 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 generated by electrodes 402 and 404 in contact with a user and / or by circuit 400. In some cases, buffers 406 and 408 are configured to reduce noise and / or interference at the input to amplifier 410. In some cases, amplifier 410 may be coupled to an analog-to-digital converter, and the output from the amplifier may be fed into the analog-to-digital converter. Additionally or alternatively, gain amplifiers 407 and 409 may be operated to provide gain adjustment to the electrical signal before transmitting the signal to amplifier 410 (which may be configured as a differential amplifier).

[0055] Circuit 400 may also include a test signal generator 416, a capacitor 418, and an impedance network 420. Signal generator 416 may generate one or more test signals 422 for determining the impedance of sensing electrode 402, which may be generated by contact between sensing electrode 402 and a user. Capacitor 418 and impedance network 420 may form a voltage divider connected to ground via path 419, and the test signal 422 generated by test signal generator 416 may be divided by the voltage divider. Buffer 406 may measure the node between capacitor 418 and impedance network 420. The measured test signal 424 may be used to determine the input impedance of sensing electrode 402.

[0056] The amplitude (e.g., voltage level) of the measured test signal 424 may depend on the load experienced by the test signal 422. For example, when the user touches the sensing electrode 402, the resulting test signal 422 may be attenuated. The contact between the user (e.g., finger) and the sensing electrode 402 may form a path 417 for the test signal 422. In some examples, the path 417 may be formed to the system ground by a physiological signal source (e.g., the user's body) via a ground electrode (e.g., a ground electrode that contacts the user). In some examples, the user may contact the sensing electrode 402 with a first part of his body (e.g., a finger) and contact the housing of the device with a second part of his body (e.g., a wrist). In such cases, the path 417 for the test signal 422 may be formed to the system ground by the physiological signal source (e.g., the user's body) and by the finger touching the housing of the device (e.g., the housing of the device may be grounded to the system ground). Therefore, the path 417 may form an impedance in parallel with the path 419 (through the impedance network 412) and change the load experienced by the test signal 422. In such examples, the resulting measured test signal 424 may be attenuated at the buffer 406. In contrast, when the user is not touching the sense electrode 402, the resulting measured test signal 424 may not be attenuated (or may be attenuated less).

[0057] The test signal 422 (e.g., an excitation signal) generated by the test signal generator 416 can be a square wave, a sine wave, a trapezoidal wave, a sawtooth wave, or any other suitable periodic oscillating, non-oscillating, or non-periodic (e.g., a pseudo-noise signal) waveform. In some examples as described herein, regardless of the waveform, the test signal can be known or predetermined by the system to enable detection of the resulting measured test signal. The test signal 422 can be capacitively or resistively coupled to the sensing electrode 402 via the capacitor 418. In some examples, the test signal generator 416 can be controlled by a processor (e.g., a digital signal processor (DSP), a host processor, or other processor). In some examples, the processor can 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 can be a clock output of the processor.

[0058] In some examples, the response of test signal 422 to the load can depend on the frequency of test signal 422 and the corresponding impedance of the signal path. In some examples, the frequency of test signal 422 can be varied to determine the load of the signal path at the corresponding frequency (e.g., the quality of the skin-electrode connection as a function of the test signal frequency can be determined). In some examples, an initialization process can be used to select a frequency for distinguishing when sensing electrode 402 is contacted and when it is not contacted (e.g., the frequency of test signal 422 that results in an observable change in the resulting test signal amplitude). In some examples, test signal 422 can include multiple frequencies simultaneously (e.g., test signal 422 can include multiple frequency components). In such examples, the reactance of the system to different frequencies can be determined at once.

[0059] In some examples, when the user contacts the sensing electrode 402, a physiological signal from the user may enter the circuit 300. In some examples, starting the physiological signal measurement may include acquiring the physiological signal (e.g., via the data buffer 316), storing the physiological signal (e.g., in a memory), and / or displaying the physiological signal on a display of the device. In some examples, when the system determines that the sensing electrode is not contacted, the system may abandon measuring the physiological signal (e.g., closing the circuit, discarding the physiological signal measurement, or in other words not processing the input signal). In some examples, when the system determines that the sensing electrode is not contacted, the system may still measure the physiological signal, but with a low confidence value indicating that the quality of the physiological signal is low (e.g., it may be unreliable for one or more intended uses). In some examples, low confidence can be represented in a binary manner (e.g., a low confidence / low quality flag can be set). In some examples, confidence can be represented in another way that represents quality (e.g., probability). In some examples, when the confidence level is below a threshold or when a low confidence / low quality flag is set, a notification may be presented 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 a display of the device and / or any other visual feedback, and / or audio feedback and / or tactile feedback and / or any other suitable feedback mechanism).

[0060] although Figure 3The integration of the contact detection circuit 302 with the physiological sensing circuit 304 is illustrated, but it should be understood that the contact detection circuit can be implemented in different ways. For example, the test signal circuit may include an amplifier or other front-end circuit (e.g., separate from the amplifier 410, etc.) to perform the functions of measuring the test signal and performing contact detection. In some examples, separate signal paths can be used for contact detection and physiological sensing (e.g., without integrating the test signal circuit with the physiological signal measurement circuit). In some examples, implementing contact detection and physiological sensing separately can allow the contact detection circuit to be optimized for the frequency, signal range, and / or signal accuracy of the test signal for contact detection, as well as optimizing the circuit for the frequency, signal range, and / or signal accuracy of physiological sensing. In some examples, a switching circuit can be provided to couple the test signal circuit (e.g., a test signal generator and a measurement amplifier) ​​to the sensing electrode during contact detection, and to decouple the sensing electrode from the test signal circuit during physiological signal measurement. In some examples, the test signal circuit can be integrated with the saturation detection circuit. In addition, although in Figure 4 The test signal 422 is illustrated as a discrete source, but the test signal may be generated by a processor (e.g., a DSP, a host processor). In some examples, the same processor may also be coupled to receive the measured test signal from the output of buffer 406 and / or 408 or another buffer or amplifier circuit.

[0061] Additionally or alternatively, although Figure 3 and Figure 4 The example shows that the test signal circuit is integrated into the signal path of the sensing electrode, but similar test signal circuits can be integrated into the signal paths of other sensing electrodes and / or reference electrodes (e.g., reference electrode 405). Figure 4 In the described operation, the reference electrode 405 can be coupled to a ground circuit. However, in the case where contact detection is performed at the reference electrode 405, a different electrode can be coupled to a ground circuit, and the contact detection process can be applied to the reference electrode 405 using the same or similar process as described herein for the sensing electrodes 402, 404. Determining the contact metric for the reference electrode 405 can occur at a different time than determining the contact metric for the sensing electrodes.

[0062] In addition, although Figure 4 Sense electrodes 402, 404 and reference electrode 405 are illustrated, but in some examples, a system may have multiple sense electrodes and / or multiple reference electrodes, and similar test signal circuitry may be integrated with some or all of these electrodes.

[0063] Figure 5 An example process 500 for performing physiological measurements to apply gain adjustments to physiological signals is shown. Circuits described herein (e.g., with reference to Figure 3 and Figure 4 The process is performed using the circuits 300 and 400 described above.

[0064] At operation 502, process 500 may include determining a first contact metric of a sensing electrode. The first contact metric may be a baseline metric determined before the device is used to perform physiological measurements. In some cases, the first contact metric may be determined from a calibration process performed at the factory and / or before the user wears the device.

[0065] Determining the first contact metric may include, for example, applying one or more test signals to the sensing electrode using the circuits 300 and 400 described herein and measuring the effect of the signal. In some cases, the test signal may be applied using a calibration probe that contacts the sensing electrode (or other electrode) on the device. For example, the calibration probe may be contacted with the sensing electrode and the test signal may be applied to the sensing electrode. The device using the contact detection circuit may determine the impedance and / or other metrics (e.g., voltage signal amplitude) of the test signal. In other cases, the calibration probe may be configured to complete a circuit between the sensing electrode, the reference electrode, and / or the ground electrode, and the contact detection circuit may apply a test signal to the circuit. The resulting test signal may be measured and used to determine the impedance metric of the calibration probe.

[0066] At operation 504, process 500 may include initiating a sensing session for a user. Initiating a sensing session may include a device making a determination that the device is being worn by the user and / or that one or more electrodes are contacting the 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 electrodes. As described herein, for example, the device may operate a contact detection circuit to apply a test signal to the electrode and measure the test signal. The measured test signal may be used to determine whether the user is wearing the electronic device and / or whether there is sufficient contact between the electrode and the user. For example, when the user is contacting the electrode, the measured test signal may be attenuated due to the user contact, and when the user is not contacting the electrode, the test signal may not be attenuated (or may be less attenuated). In some cases, a threshold amplitude (e.g., a voltage level) may be used to determine whether the sensing electrode is contacting the user. For example, when the measured test signal is less than a threshold amplitude, the device may determine that the sensing electrode is contacted (e.g., there is sufficient skin-electrode coupling for accurate physiological measurements). When the measured test signal is greater than or equal to a threshold amplitude, the device may determine that the sensing electrodes are not contacted (or that there is insufficient skin-electrode coupling for accurate physiological measurements).

[0067] Additionally or alternatively, the device may use other sensors to determine whether the user is wearing the device and / or contacting the electrodes. In some cases, the system may use a temperature sensor, an accelerometer, a light sensor, a humidity sensor, and the like. For example, the system may use a temperature sensor that may include comparing the temperature measurement result with 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 electrode is in contact with the user, and if the measured temperature is outside the defined range, the system may determine that the device and / or electrode is not in contact with the user. In some cases, one or more temperature sensors may be positioned near the electrode, which may provide a more accurate contact determination. In other examples, a light sensor may be positioned near the electrode (e.g., on a rear sensor assembly near the electrode) and used to determine contact with the user. The light sensor may include a light emitter that emits light toward the user and a photodetector that receives a returned portion of the emitted light. The received light may be analyzed to determine contact with the user.

[0068] At operation 506, process 500 may include determining a second contact metric of the sensing electrode based on contact of the electrode with the user. In some cases, the sensing metric may be an impedance and / or amplitude (e.g., voltage level) change of an electrical signal transmitted from the user's skin and transmitted 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 a contact detection circuit, as described herein. The system may analyze the measured test signal to determine a contact metric, which may be an input impedance of the electrical signal based on contact with the user.

[0069] At operation 508, process 500 may include measuring the user's electrical signal. For example, a physiological sensing circuit (e.g., physiological sensing circuit 304) may be used to measure cardiac electrical signals from the user's skin surface. The cardiac electrical signal may be sensed by one or more electrodes, transferred to a buffer, where the signal may be converted into a digital signal. In some cases, a gain adjustment may be applied to the digital signal and the signal may be transferred to a digital signal processor, which may be further analyzed and / or transferred to a host processor, which may cause the device to perform one or more functions based on the signal. For example, a digital signal processor and / or a host processor may generate an ECG output signal showing a change in polarization of the user's heart. The device may display the ECG signal on a display. Additionally or alternatively, a DSP and / or a host processor (or a remote processor) may 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, etc.

[0070] In some cases, the system can use the first contact metric and the second contact metric to adjust the measured electrical signal of the user. For example, the first contact metric and the second contact metric can each include an impedance, and a ratio of the first input impedance to the second input impedance can be used to determine a gain adjustment that can be applied to the measured electrical signal from the user. The gain adjustment can increase the amplitude of the measured electrical signal, which can improve the quality of the measured signal before the signal is analyzed by the DSP and / or host processor.

[0071] In some cases, the system may determine a gain adjustment and apply the gain adjustment to each measured electrical signal from the user. For example, in response to initiating a sensing session, the system may determine a second contact metric that is used to determine a gain adjustment for the measured signal. Thus, different gain adjustments may be applied during different sensing sessions and based on electrode contact with the user. In other cases, the second contact metric may be periodically or continuously checked and updated during a sensing session. Thus, the systems and devices herein may adapt as the contact (and impedance) between the user and the electrode changes.

[0072] In some cases, the system may apply gain adjustment to account for high signal attenuation only when at least one impedance criterion is not met (path 501). If at least one impedance criterion is met, the signal attenuation may be low enough that the system can accurately determine the physiological parameter without applying gain adjustment to the measured electrical signal (path 503).

[0073] 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 the 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 of the measured electrical signal (e.g., measured at operation 508) is of sufficient quality to determine a physiological parameter of the user.

[0074] In some cases, at least one impedance criterion may be a defined threshold value, and the first contact metric and the second contact metric may be used to determine an impedance ratio. If the ratio is above the defined threshold value, 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 signal using path 501. If the ratio is below the defined threshold value, the system may determine that the second input impedance meets the at least one impedance criterion, and may process the measured electrical signal without applying a gain adjustment using path 503.

[0075] At operation 512, in response to determining that at least one impedance criterion is not met, process 500 may include determining a gain adjustment using the first contact metric and the second contact metric. For example, the first contact metric and the second contact metric may each include an input impedance of the sensing electrode. The system may analyze the first input impedance and the second input impedance to determine an impedance change due to contact with the user between a baseline impedance (e.g., the first input impedance determined during the baseline / calibration operation at 502) and the second input impedance. In some cases, the gain adjustment may be proportional to the difference between the first input impedance and the second input impedance.

[0076] 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 the measured electrical signal has been converted to a digital signal. The gain adjustment may be applied to the signal before passing the signal to a digital signal processor and / or a host processor. In other cases, the gain adjustment may be applied to the analog signal before converting the analog signal to a digital signal (also referred to herein as an "analog gain adjustment").

[0077] In some cases, the gain adjustment may include a combination of a digital gain adjustment and an analog gain adjustment. Because the digital gain adjustment will also amplify all upstream noise, including circuit noise introduced when the measured electrical signal is routed through the system, in some cases, it may be desirable to limit the magnitude of the digital gain adjustment. Therefore, the system may apply an analog gain adjustment to the analog measurement signal (e.g., by changing the gain of one or more amplifiers within the system) and apply both digital gain adjustments to the measured signal after the measured signal has been converted to a digital signal. In this way, the analog gain adjustment forms the first part of the determined gain adjustment and the digital gain adjustment forms the second part of the determined gain adjustment. The analog gain adjustment may reduce the relative impact of downstream circuit noise, but may increase the power consumption of the system. Therefore, the relative amount of analog gain and digital gain within the determined gain adjustment may be selected to balance noise reduction and power consumption. For example, in some variations, the determined gain adjustment may include only the digital gain adjustment when the digital gain adjustment is below a threshold level, and may include both the digital gain adjustment and the analog gain adjustment when the digital gain adjustment is at or above a threshold level. In these cases, digital gain adjustment may be used for relatively small adjustments, and a combination of digital gain adjustment and analog gain adjustment may be used for relatively large adjustments.

[0078] As described herein, at operation 516 , in response to determining that at least one impedance criterion is satisfied, process 500 may include determining a physiological parameter of the user without applying a gain adjustment to the measured electrical signal.

[0079] although Figure 5 An example process for performing gain adjustment for a single electrode is illustrated, but it should be understood that similar test signal circuitry may be integrated into the signal path of one or more additional electrodes on the device. Figure 4 Two sensing electrodes 402, 404 and one reference electrode 405 are illustrated, but in some examples, the system may have additional or fewer sensing electrodes and / or multiple reference electrodes, and similar test signal circuitry may be integrated with some or all of these electrodes.

[0080] Figure 6 An example gain calibration circuit 600 that can be used to perform physiological measurements as described herein is shown. As described herein, the example circuit 600 can be an example of the circuits described herein (e.g., the gain adjustment circuit 300 and the circuit 400), and can include a contact detection (CD) circuit 602 and a physiological sensing circuit 604. In some cases, the example circuit 600 can be implemented on a single application specific integrated circuit (ASIC). In other cases, the example circuit 600 can be implemented across multiple ASICs, and various components can be integrated on different ASICs in the multiple ASICs.

[0081] The measurements performed by the gain adjustment circuit (e.g., gain adjustment circuit 300) may include a total impedance representing a combination of an electrode impedance (e.g., electrode impedance 308) and a circuit impedance (e.g., circuit impedance 310). When these impedances are measured together, the system may not be able to distinguish between changes in electrode impedance (e.g., caused by differences in how a user contacts the electrodes) and changes in circuit impedance (e.g., caused by wear, etc.).

[0082] The gain calibration circuit 600 can allow the electrode impedance 608 to be measured independently of the physiological sensing circuit 604. In addition, the gain calibration circuit 600 can measure the total input impedance to be measured (the combination of the electrode impedance 608 and the circuit impedance 610). Using the individual electrode impedances 608 and the total impedance, the system can determine the circuit impedance 610. Therefore, the system can independently determine the electrode impedance 608 and the circuit impedance 610 in real time without the need for initial calibration information. For example, the circuit 600 impedance can be determined in response to initiating a measurement session (e.g., before measuring the user's electrical signals) and / or when the electrodes are not in contact with the user.

[0083] The circuit 600 may include a switch 620 that may isolate the physiological sensing circuit 604 from the contact detection circuit 602. The total impedance of the gain calibration circuit 600 may include the electrode impedance 608 and the circuit impedance 610. The system / device may operate the switch 620 to selectively isolate the contact detection circuit 602 from the physiological sensing circuit 604 and couple the physiological sensing circuit 604 to the contact detection circuit 602.

[0084] Figure 7 An example process 700 for performing physiological measurements using gain calibration is shown. The circuits described herein (e.g., reference Figure 6 The process 700 may be performed using the circuit 600 described above.

[0085] 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 operated to electrically disconnect the physiological sensing circuit from the contact detection circuit. Once isolated, the contact detection circuit may be electrically coupled to the sensing electrode, and the physiological sensing circuit may be isolated from the contact detection circuit.

[0086] At operation 704, process 700 may include determining a first impedance of 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. As described herein, the test signal may change (e.g., attenuate) due to the impedance of the contact detection circuit and / or contact of the electrode with the user (or other object). The system may determine the first impedance based on analyzing a difference between the test signal applied to the contact detection circuit and the measured test signal. In some cases, the difference may include a change in amplitude, phase shift, or other changes to the test signal.

[0087] At operation 706, process 700 may include electrically connecting the contact detection circuit and the physiological sensing circuit. A switch (e.g., switch 620) may be operated 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.

[0088] At operation 708, process 700 may include determining a second impedance of the contact detection circuit and the physiological sensing circuit. 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. As described herein, the test signal may change (e.g., attenuate) due to the impedance of the contact detection circuit, the impedance of the physiological detection circuit, and / or contact of the electrode with the user (or other object). The system may determine the second impedance based on analyzing the difference between the test signal applied to the first node and the measured test signal. In some cases, the difference may include a change in amplitude, phase shift, or other changes to the test signal.

[0089] At operation 710, process 700 may include determining a gain adjustment using the first input impedance and the second input impedance. For example, the system may analyze the first input impedance and the second input impedance to determine whether the signal attenuation meets an impedance threshold, which may be set by system requirements. Determining whether the signal attenuation meets the impedance threshold may be determined by comparing the electrode impedance 608 and the input impedance 610. When the signal attenuation does not meet the impedance threshold, a gain adjustment may be applied at 616. In some cases, the gain adjustment may be proportional to the difference between the first input impedance and the second input impedance.

[0090] At operation 712, process 700 may include measuring an electrical signal of the user. For example, a physiological sensing circuit (e.g., physiological sensing circuit 604) may be used to measure cardiac electrical signals from the user's skin surface. The cardiac electrical signals may be sensed by one or more electrodes and transmitted to a buffer where the signals may be converted into digital signals.

[0091] At operation 714, process 700 may include using electrical signals and gain adjustments to determine a user's physiological parameters. In some cases, gain adjustments may be applied to digital signals and the signal may be passed to a digital signal processor, which may be further analyzed and / or passed to a host processor, which may cause the device to perform one or more functions based on the signal. For example, a digital signal processor and / or a host processor may generate an ECG output signal that shows a change in polarization of the user's heart. The device may display the ECG signal on a display. Additionally or alternatively, a DSP and / or a host processor (or a remote processor) may determine physiological metrics such as beat-to-beat timing, heart rate, heart rate variability, and / or identify conditions such as arrhythmias, tachycardia, bradycardia, heart valve conditions, and the like.

[0092] The disclosure anticipates that entities responsible for collecting, analyzing, disclosing, transmitting, storing or otherwise using such personal information data will comply with established privacy policies and / or privacy practices. Specifically, such entities should implement and adhere to the use of privacy policies and practices that are recognized as meeting or exceeding industry or government requirements for maintaining the privacy and security of personal information data. Such policies can be easily accessed by users and should be updated as the collection and / or use of data changes. Personal information from users should be collected for the legal and reasonable purposes of the entity and not shared or sold outside these legal uses. In addition, such collection / sharing should be performed after receiving the user's informed consent. Additionally, such entities should consider taking any necessary steps to protect and safeguard access to such personal information data and ensure that other entities with access to personal information data comply with their privacy policies and procedures. In addition, such entities can subject themselves to third-party assessments to prove that they comply with widely accepted privacy policies and practices. In addition, policies and practices should be adjusted to collect and / or access specific types of personal information data and apply to applicable laws and standards including specific considerations of jurisdiction. For example, in the United States, the collection or access of certain health data may be governed by federal and / or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA), while health data in other countries may be subject to other regulations and policies and should be handled accordingly. Therefore, different privacy practices should be maintained in each country for different types of personal data.

[0093] Regardless of the foregoing, the present disclosure also contemplates implementation schemes in which users selectively block the use or access of personal information data. That is, the present disclosure contemplates hardware elements and / or software elements to prevent or block access to such personal information data. For example, with respect to determining spatial parameters, the technology of the present invention may be configured to allow a user to choose to "opt in" or "opt out" to participate in the collection of personal information data at any time during or after registration for a service. In addition to providing "opt-in" and "opt-out" options, the present disclosure also contemplates providing notifications related to access or use of personal information. For example, a user may be notified that their personal information data will be accessed when downloading an application, and then be reminded again just before the personal information data is accessed by the application.

[0094] Furthermore, it is the intent of the present disclosure that personal information data should be managed and processed in a manner that minimizes the risk of unintentional or unauthorized access or use. Once the data is no longer needed, the risk can be minimized by limiting the collection of data and deleting the data. In addition, and when applicable, including in certain health-related applications, data de-identification can be used to protect the privacy of users. Where appropriate, de-identification can be facilitated by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or characteristics of stored data (e.g., collecting location data at a city level rather than an address level), controlling how data is stored (e.g., aggregating data across users), and / or other methods.

[0095] Thus, while 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 various embodiments may also be implemented without access to such personal information data. That is, the various embodiments of the present technology will not fail to function properly due to the lack of all or a portion of such personal information data. For example, tactile output may be provided based on non-personal information data or an absolute minimum amount of personal information (such as an event or state at a device associated with a user, other non-personal information, or publicly available information).

[0096] For the purpose of illustration, the foregoing description uses specific nomenclature to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that specific details are not required in order to practice the embodiments. Therefore, for the purpose of illustration and description, the foregoing description of the specific embodiments described herein is presented. They are not intended to be exhaustive or to limit the embodiments to the disclosed precise forms. It will be apparent to those of ordinary skill in the art that, in view of the above teachings, many modifications and variations are feasible.

Claims

1. A method for electrode sensing at a wearable electronic device, the method comprising: In response to determining that the user is wearing the wearable electronic device: applying a test signal to the sensing electrode using a contact detection circuit; as well as using the contact detection circuit, determining an input impedance of the sensing electrode using the test signal; determining a gain adjustment using the input impedance and a baseline impedance; Using a physiological sensing circuit, using the sensing electrodes to measure an electrical signal of the user; as well as applying the gain adjustment to the measured electrical signal using the physiological sensing circuit; as well as A physiological parameter of the user is determined using the measured electrical signal with the gain adjustment applied.

2. The method according to 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; as well as In response to determining that the input impedance satisfies the criterion, the physiological parameter is determined 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 using the contact detection circuit to determine the baseline impedance of the sensing electrode.

4. The method of claim 3, wherein the physiological parameter is determined as part of a first sensing session, and the method further comprises: After completing the first sensing session, the wearable electronic device determines to initiate a second sensing session; In response to determining to initiate the second sensing session: applying a second test signal to the user; measuring a second electrical signal of the user; determining a second gain adjustment; as well as A second physiological parameter of the user is determined by applying the second gain adjustment to the measured second electrical signal. The method of claim 1 , wherein the test signal is a time-varying electrical signal. 6 . The method of claim 1 , wherein measuring the electrical signal of the user comprises measuring a cardiac electrical signal of the user using the sensing electrode and at least a second electrode located on the wearable electronic device.

7. The method of claim 6, wherein the sensing electrode contacts a first limb of the user, and the second electrode is configured to contact a second limb of the user when the wearable 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 wearable electronic device is worn by the user.

9. The method according to claim 1, further comprising: In response to determining that the user is wearing the wearable electronic device: applying a second test signal to the second sensing electrode; as well as determining a second input impedance of the second sensing electrode using the second test signal; determining a second gain adjustment using the second input impedance and the baseline impedance; using the second sensing electrode to measure a second electrical signal of the user; as well as The physiological parameter of the user is determined by applying the second gain adjustment to the measured second electrical signal.

10. A method for performing electrode gain calibration on a sensing electrode signal at a wearable electronic device, the method comprising: isolating the contact detection circuit from the physiological sensing circuit; applying a first test signal to a sensing electrode of the wearable electronic device when the contact detection circuit is isolated from the physiological sensing circuit; determining a first input impedance of the sensing 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 when the contact detection circuit is connected to the physiological sensing circuit; as well as determining a second input impedance of the sensing electrode using the second test signal; determining a gain adjustment using the first input impedance and the second input impedance; as well as using the sensing electrodes to measure electrical signals of a user; as well as A physiological parameter of the user is determined by applying the gain adjustment to the measured electrical signal.

11. The method according to 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; as well as In response to determining that the gain adjustment satisfies the criterion, the physiological parameter is determined without applying the gain adjustment to the measured electrical signal. 12 . The method of claim 10 , wherein measuring the electrical signal of the user comprises measuring a cardiac electrical signal of the user using the sensing electrodes.

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. 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 comprise a time-varying electrical signal.

16. A system for electrode sensing at a wearable electronic device, the system comprising: a housing configured to be coupled to a user; a sensing electrode coupled to the housing and configured to contact the user; and A processor, the processor being configured to: In response to determining that the user is wearing the wearable electronic device: causing a test signal to be applied to the sensing electrode; and determining an input impedance of the sensing electrode using the test signal; determining a gain adjustment using the input impedance and a baseline impedance; measuring an electrical signal of the user using the sensing electrodes; as well as A physiological parameter of the user is determined by applying the 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 limb of the user; The second sensing electrode is configured to contact a second limb of the user; and The processor is configured to measure a second electrical signal of the user using the second sensing electrode; as well as The physiological parameter is determined 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 The physiological parameter is determined 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 satisfies 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, the physiological parameter is determined without applying the gain adjustment to the measured electrical signal.

20. The system of claim 19, wherein: The criteria include a defined impedance threshold; and Determining that the input impedance satisfies the defined impedance threshold includes determining that a value of the input impedance is greater than the defined impedance threshold.

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