Contact detection of physiological sensors

Abstract

The present disclosure relates to contact detection of physiological sensors. A device includes sensing circuitry, excitation circuitry, and processing circuitry. The sensing circuitry is configured to sense a physiological signal. The sensing circuitry includes first sensing circuitry configured to sense a first electrode and second sensing circuitry configured to sense a second electrode. The excitation circuitry is configured to drive an excitation signal on the first electrode. The processing circuitry is coupled to the sensing circuitry. The processing circuitry is programmed to, during measurement of the physiological signal using one or more signals measured by the first sensing circuitry and using one or more signals measured by the second sensing circuitry: in accordance with a determination that a first signal of the one or more signals measured by the first sensing circuitry fails to satisfy one or more criteria in response to the excitation signal, stop measurement of the physiological signal.

Description

[0001] This application is a divisional application of the invention patent application with application number 201910858666.3, application date September 11, 2019, entitled "Contact Detection of Physiological Sensors". Technical Field

[0002] This disclosure relates in its entirety to systems and methods for processing physiological signals, and more specifically, to detecting contact with one or more electrodes of a physiological sensor. Background Technology

[0003] Electrocardiogram (ECG) waveforms can be generated based on the electrical activity of the heart during each heartbeat. Waveforms can be recorded from multiple electrical leads attached to various areas of the patient's body. For example, a 12-lead ECG system may have one set of ten measuring electrodes placed on the patient's chest and another set of ten attached to the patient's limbs. The measuring electrodes used for ECG data acquisition may include conductive or electrolytic gels (e.g., Ag / AgCl gel) to provide a continuous conductive path between the skin and the electrodes. Such "wet" electrodes can reduce impedance at the electrode-skin interface, thus facilitating the acquisition of low-noise ECG signals. All measuring electrodes can be connected to a device, and signals from the measuring electrodes can be transmitted to the device for storage, processing, and / or display. Devices with multiple "wet" electrodes coupled to the user's chest and limbs are invasive, potentially difficult for laypeople to operate, and the resulting ECG waveforms may be difficult to interpret. Therefore, ECG measurement and analysis may limit the use of ECG devices to medical settings or to use by healthcare professionals.

[0004] One method for measuring ECG signals is using dry electrodes, which typically contact two areas of the patient on opposite sides of the heart (e.g., on each of the user's hands). On mobile devices (e.g., wearable devices), ECG electrodes can be placed on the device so that the user can contact both electrodes. Reliable contact may be required to generate accurate ECG waveforms. Summary of the Invention

[0005] This disclosure relates to apparatus and methods for using a mobile or wearable device to detect contact between a user and one or more electrodes for measuring physiological signals (e.g., ECG signals) in order to process and / or display them on the mobile or wearable device. The mobile or wearable device may include one or more measuring electrodes, one or more reference electrodes, and processing circuitry coupled to the electrodes. In some examples, the device may include excitation circuitry. The excitation circuitry may drive an excitation signal on one of the measuring electrodes. In some examples, the processing circuitry may detect a signal generated by the excitation signal and determine, based on the detected signal, whether a user is in contact with the one or more measuring electrodes. In some examples, upon determining that a user is in contact with the one or more measuring electrodes, the processing circuitry may measure the user's physiological signals.

[0006] In some examples, the excitation circuitry may drive a first excitation signal on one electrode (e.g., a first measuring electrode) and a second excitation signal on a second electrode (e.g., a first reference electrode). In some examples, the processing circuitry may detect one or more signals generated by the first and second excitation signals and determine, based on the one or more detected signals, whether a user is in contact with the one or more electrodes. In some examples, upon determining that a user is in contact with the one or more electrodes, the processing circuitry may measure a physiological signal of the user. In some examples, while measuring a user's physiological signal, analog circuitry may drive one or more electrodes to determine whether the user remains in contact with the one or more electrodes during the measurement of the user's physiological signal. Attached Figure Description

[0007] Figures 1A to 1B An exemplary system is shown that includes a physiological sensor and wherein contact detection according to an example of this disclosure is implemented.

[0008] Figure 2 A block diagram of an exemplary computing system is shown, illustrating a specific implementation of physiological signal processing according to an example of this disclosure.

[0009] Figures 3A to 3B An exemplary system for measuring physiological signals according to an example of this disclosure is shown.

[0010] Figures 4A to 4B An exemplary system for measuring physiological signals, according to an example of this disclosure, is shown.

[0011] Figures 5A to 5B An exemplary system for measuring physiological signals and for contact detection, according to an example of this disclosure, is shown.

[0012] Figure 6 An exemplary system for measuring physiological signals, according to an example of this disclosure, is shown.

[0013] Figure 7 An exemplary process for detecting physiological signals, including contact detection and / or saturation detection, according to examples of this disclosure is shown.

[0014] Figure 8 An exemplary process for detecting physiological signals, including contact detection and / or saturation detection, according to examples of this disclosure is shown.

[0015] Figure 9 An exemplary system for measuring physiological signals and for contact detection on multiple electrodes, according to an example of this disclosure, is shown.

[0016] Figure 10 An exemplary signal processing for contact detection is shown according to an example of this disclosure.

[0017] Figure 11 An exemplary process for detecting physiological signals, including contact detection, is shown according to an example of this disclosure.

[0018] Figure 12 An exemplary system for measuring physiological signals and for contact detection on multiple electrodes, according to an example of this disclosure, is shown. Detailed Implementation

[0019] Cross-reference to related applications

[0020] This patent application claims U.S. Provisional Application No. 62 / 729,590, filed September 11, 2018; U.S. Non-Provisional Application No. 16 / 565,090, filed September 9, 2019; and U.S. Non-Provisional Application No. 16 / 565,127, filed September 9, 2019, the contents of which are incorporated herein by reference in their entirety for all purposes.

[0021] In the following description of the examples, reference will be made to the accompanying drawings, which form part of the following description, and specific examples that can be implemented are shown by way of example in the drawings. It should be understood that other examples and structural changes may be used without departing from the scope of the disclosed examples.

[0022] This disclosure relates to apparatus and methods for using a mobile or wearable device to detect contact between a user and one or more electrodes for measuring physiological signals (e.g., ECG signals) in order to process and / or display them on the mobile or wearable device. The mobile or wearable device may include one or more measuring electrodes, one or more reference electrodes, and processing circuitry coupled to the electrodes. In some examples, the device may include excitation circuitry. The excitation circuitry may drive an excitation signal on one of the measuring electrodes. In some examples, the processing circuitry may detect a signal generated by the excitation signal and determine, based on the detected signal, whether a user is in contact with the one or more measuring electrodes. In some examples, upon determining that a user is in contact with the one or more measuring electrodes, the processing circuitry may measure the user's physiological signals.

[0023] In some examples, the excitation circuitry may drive a first excitation signal on one electrode (e.g., a first measuring electrode) and a second excitation signal on a second electrode (e.g., a first reference electrode). In some examples, the processing circuitry may detect one or more signals generated by the first and second excitation signals and determine, based on the one or more detected signals, whether a user is in contact with the one or more electrodes. In some examples, upon determining that a user is in contact with the one or more electrodes, the processing circuitry may measure a physiological signal of the user. In some examples, while measuring a user's physiological signal, analog circuitry may drive one or more of the electrodes to determine whether the user remains in contact with the one or more electrodes during the measurement of the user's physiological signal.

[0024] Figures 1A to 1B An exemplary system is shown that includes a physiological sensor and wherein contact detection according to an example of this disclosure is implemented. Figure 1A An exemplary wearable device 150 (e.g., a watch) is shown, which includes an integrated touchscreen 152 and a physiological sensor 160 (e.g., an ECG sensing system including one or more measuring electrodes, one or more reference electrodes, and processing circuitry coupled to the electrodes). The wearable device 150 can be attached to a user using a strip 154 ​​or any other suitable fastener. Figure 1BAn exemplary view of the back of a wearable device 150 is shown, including electrodes 166A to 166C of a physiological sensor 160. The physiological sensor 160 may include: an electrode 166C implemented in the crown 162 of the wearable device 150, an electrode implemented in a button 164 of the wearable device 150 (not shown), an electrode 166A on the back of the wearable device 150, and / or an electrode 166B on the back of the wearable device 150. In some examples, the physiological sensor 160 may include a measuring electrode (e.g., electrode 166C in the crown 162), a first reference electrode (e.g., electrode 166A on the back of the wearable device 150), and a second ground reference electrode (e.g., electrode 166B on the back of the wearable device 150). In some examples, in addition to or instead of the measuring electrode 166C in the crown 162, the physiological sensor 160 may also include a measuring electrode in the button 164. In some examples, the physiological sensor 160 may include more than one measuring electrode and more than two reference electrodes. It should be understood that the aforementioned physiological sensors can be implemented in other wearable and non-wearable devices, including dedicated devices for acquiring and / or processing physiological signals (e.g., ECG signals). It should be understood that although mobile device 136 and wearable device 150 include touchscreens, the display of the physiological signals described herein can be performed on a touch-sensitive or non-touch-sensitive display of a device including physiological sensor 160, on a touch-sensitive or non-touch-sensitive display of a separate device, or on a separate display. Furthermore, it should be understood that although this disclosure focuses primarily on ECG signals, it is also applicable to other physiological signals.

[0025] In some examples, the electrodes of the physiological sensor 160 may be dry electrodes, which may be measuring electrodes configured to contact the skin surface and capable of obtaining accurate signals without the use of conductive or electrolytic gels. In some variations, one or more reference electrodes may be located on a wrist-worn device (such as a bracelet, wristband, or watch) such that the reference electrodes can contact the skin in the wrist region, while one or more measuring electrodes may be configured to contact a second, different skin region (e.g., the fingers of the hand opposite the wrist on which the wrist-worn device is worn). In some examples, the measuring electrodes may be located on a component separate from the reference electrodes. In some examples, some or all of the measuring electrodes may be located on the wrist or finger cot, fingertip cap, a second wrist-worn device, an area of ​​the wrist-worn device that may be different from the location of the reference electrodes, etc. In some examples, one or more electrodes (e.g., reference electrodes or measuring electrodes) may be integrated with the input mechanism of the device (e.g., a rotatable input device, a pressable input device, or a pressable and rotatable input device), such as... Figure 1B As shown. One or more electrical signals measured at one or more measuring (and / or reference) electrodes can be measured and processed, as described in more detail herein.

[0026] Figure 2 A block diagram of an exemplary computing system 200 is shown, illustrating a specific implementation of physiological signal processing according to an example of this disclosure. The computing system 200 may be included in, for example, a wearable device 150 or any mobile or non-mobile computing device, wearable or non-wearable computing device for physiological signal analysis and / or display. The computing system 200 may include: one or more physiological sensors 202 (e.g., ECG sensors) including one or more electrodes to measure electrical signals (e.g., ECG signals) from a person contacting the ECG sensor electrodes; a data buffer 204 (or other volatile or non-volatile memory or storage device) for temporarily (or permanently) storing physiological signals from the physiological sensors 202; a digital signal processor (DSP) 206 for analyzing and processing physiological signals; a host processor 208; a program memory 210; and a touchscreen 212 for performing display operations (e.g., displaying real-time ECG signals). In some examples, the touchscreen 212 may be replaced by a non-touch-sensitive display.

[0027] The host processor 208 can be connected to program memory 210 (e.g., a non-transitory computer-readable storage medium) to execute instructions stored in program memory 210. The host processor 208 can, for example, provide control and data signals to generate display images on the touchscreen 212, such as display images of a user interface (UI). The host processor 208 can also receive outputs from the DSP 206 (e.g., ECG signals) and perform actions based on those outputs (e.g., displaying ECG signals, playing sounds, providing haptic feedback, etc.). The host processor 208 can also receive outputs (touch inputs) from the touchscreen 212 (or a touch controller, not shown). Touch input can be used by a computer program stored in program memory 210 to perform actions, including but not limited to: moving objects such as cursors or pointers, scrolling or panning, adjusting control settings, opening files or documents, viewing menus, making selections, executing commands, operating peripherals connected to the host device, answering telephone calls, making telephone calls, terminating telephone calls, changing volume or audio settings, storing information related to telephone communication (such as addresses, frequently dialed numbers, received calls, missed calls), logging onto a computer or computer network, allowing authorized individuals access to restricted areas of a computer or computer network, loading user profiles associated with the user's preferred computer desktop layout, allowing access to web page content, launching specific programs, encrypting or decrypting messages, etc. The host processor 220 may also perform additional functions that may not be related to touch processing and display.

[0028] It should be noted that one or more functions described herein, including contact detection, saturation detection, and / or processing of physiological signals, may be executed by firmware stored in memory (e.g., in DSP 206) and by one or more processors (in DSP 206), or stored in program memory 210 and executed by host processor 208. The firmware may also be stored and / or delivered to any non-transitory computer-readable storage medium for use or in combination with an instruction execution system, apparatus, or device, such as a computer-based system, a processor-included system, or other system that can retrieve and execute instructions from and execute instructions from the instruction execution system, apparatus, or device. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding signals) that can contain or store programs for use or in combination with an instruction execution system, apparatus, or device. Computer-readable storage media may include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, portable computer disks (magnetic), random access memory (RAM) (magnetic), read-only memory (ROM) (magnetic), erasable programmable read-only memory (EPROM) (magnetic), portable optical discs such as CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash memory cards, secure digital cards, USB storage devices, memory sticks, etc.

[0029] This firmware can also be propagated in any transmission medium for use or in conjunction with an instruction execution system, apparatus, or device, such as a computer-based system, a processor-based system, or other system capable of retrieving and executing instructions from and with an instruction execution system, apparatus, or device. In the context of this document, "transmission medium" can be any medium through which a program can be transmitted, propagated, or transferred for use or in conjunction with an instruction execution system, apparatus, or device. Transmission media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, or infrared wired or wireless transmission media.

[0030] It should be understood that the computing system 200 is not limited to Figure 2 The components and configuration of the computing system 200 may include additional or additional components (or omit components) in various configurations according to various examples. For example, an analog-to-digital converter (ADC) may be added between the physiological sensor 202 and the DSP 206 to convert the signal to the analog domain, or the touchscreen 212 may be omitted, and the analysis and processing of the generated ECG signals or other information may be relayed to another device (e.g., a tablet, laptop, smartphone, computer, server, etc.) via a wired or wireless connection. This other device may include a display or other feedback mechanism for outputting a visual representation of data or other notifications or information. Furthermore, the components of the computing system 200 may be included in a single device or distributed among multiple devices.

[0031] Returning to physiological sensor 202, the mobile device or wearable device (or other device) may include one or more measuring electrodes and one or more reference electrodes. Physiological sensor 202 may communicate with DSP 206 to acquire physiological signals and send the signals to DSP 206. In some examples, physiological signals may be acquired by data buffer 204, and DSP 206 may acquire buffered samples of physiological waveforms (e.g., 3-second samples, 5-second samples, 10-second samples, 30-second samples, 60-second samples). In some examples, data buffer 204 may be implemented as part of DSP 206. It should be understood that although a DSP has been described, other processing circuitry may be used to implement the analysis and processing described herein, including microprocessors, central processing units (CPUs), programmable logic devices (PLDs), etc.

[0032] Although examples and applications of contact detection and processing devices and methods are described in the context of generating a complete ECG waveform, it should be understood that the same or similar devices and methods can be used to collect and process data from multiple measuring electrodes, and may or may not generate an ECG waveform. For example, signals from physiological sensor 202 can facilitate the monitoring of certain cardiac characteristics (e.g., heart rate, arrhythmias, changes due to medication or surgery, pacemaker function, heart size, etc.) and / or ECG waveform characteristics of the DSP and / or the user (e.g., timing, intervals, and composites of certain waves) without generating a complete ECG waveform. In some examples, the controller can generate a subset of the ECG waveform (e.g., one or more of the P wave, QRS complex, PR interval, T wave, and U wave). Furthermore, examples of this disclosure include contact detection and processing devices and methods configured for other types of physiological signal measurements, including but not limited to EEG and EMG measurements or optical determination of heart rate.

[0033] Figures 3A to 3B An exemplary system for measuring physiological signals (e.g., ECG waveforms) according to an example of this disclosure is shown. Figure 3AIn this embodiment, wearable device 150 can be worn on a user's wrist. In some examples, reference electrodes 166A and 166B on the back of wearable device 150 can contact the user's wrist when worn. In some examples, wearable device 150 can measure physiological signals when the user contacts measuring electrodes 166C on the crown 162 of wearable device 150 with a finger 304 (e.g., a finger of the hand opposite the wrist of the wrist-worn device). Physiological signal 302 can be measured in response to contact between finger 304 and measuring electrode 166C (and contact between wrist and reference electrodes 166A and 166B). In some examples, due to reliable contact with measuring electrode 166C (and reliable contact with reference electrodes 166A and / or 166B), the measured physiological signal 302 can be a clinically accurate waveform (e.g., meeting clinically accurate waveform specifications). Figure 3B The illustration shows user contact between finger 304 and the housing of wearable device 150, rather than crown 162. In some examples, a physiological signal 312 is acquired due to the coupling between the housing of wearable device 150 and measuring electrode 166C. In some examples, physiological signal 312 may have a similar morphology to physiological signal 302, but physiological signal 312 may be attenuated compared to physiological signal 302 (e.g., attenuated by 5%, 10%, 20%, etc.). In some examples, physiological signal 312 may be unstable, noisy, and / or its amplitude and attenuation may vary nondeterministically. In some examples, the measured physiological signal 312 may not be a clinically accurate waveform (e.g., does not meet the specifications for a clinically accurate waveform) and may be difficult to interpret or lead to misinterpretation of the physiological signal (e.g., compared to physiological signal 302). As described herein, contact detection can be used to avoid generating and / or presenting a waveform like physiological signal 312 to the user.

[0034] Figures 4A to 4B An exemplary system for measuring physiological signals, according to an example of this disclosure, is shown. Figure 4AIn this embodiment, circuitry 400 may include processor 430 (e.g., corresponding to DSP 206 and / or host processor 208), analog front-end 420, measurement electrode 402 (e.g., corresponding to measurement electrode 166C), reference electrode 404, and ground electrode 406 (e.g., corresponding to reference electrodes 166A and 166B). In some examples, circuitry 400 resides on a mobile device (e.g., wearable device 150). In some examples, analog front-end 420 includes amplifier 422 and analog-to-digital converter (ADC) 424. Amplifier 422 may be a differential amplifier coupled to measurement electrode 402 (e.g., at the inverting input or the non-inverting input) and reference electrode 404 (e.g., at the non-inverting input or the inverting input). In some examples, ground electrode 406 may be coupled to analog front-end 420 to provide a shared ground reference between circuitry 400 and ground electrode 406 (e.g., ground electrode 406 may provide a system ground reference voltage). In some examples, circuit 400 may include networks 412, 414, and 416 along signal paths along measuring electrode 402, reference electrode 404, and ground electrode 406, respectively. In some examples, networks 412, 414, and 416 may include circuit components (e.g., resistors, capacitors, inductors, and / or diodes) and / or may include impedances inherent in circuit 400 (e.g., routing impedance, parasitic impedance, etc.). In some examples, networks 412, 414, and 416 may provide electrostatic discharge (ESD) protection for circuit 400 and / or provide safety by limiting or preventing current from being applied to the user's skin and / or preventing accidental or unintentional external signals from entering the device and causing damage. In some examples, amplifier 422 may output an amplified differential signal, and analog-to-digital converter 424 may convert the amplified differential signal into a digital signal. In some examples, amplifier 422 may output an amplified single-ended output. In some examples, the output of analog-to-digital converter 424 may be a multi-bit signal (e.g., 8-bit, 12-bit, 24-bit, etc.) coupled to processor 430. The multi-bit signal may be transmitted serially or in parallel from analog front-end 420 to processor 430. In some examples, analog-to-digital converter 424 may be a differential analog-to-digital converter and converts differential analog inputs to digital outputs. In some examples, analog-to-digital converter 424 may be single-ended and converts single-ended analog inputs to digital outputs. In some examples, differential amplifier 422 may be implemented using two single-ended amplifiers, and ADC 424 may be implemented using two ADCs (each ADC connected to the output of one of the single-ended amplifiers).

[0035] In some examples, a user may wear a wearable device including circuitry 400. In such examples, a reference electrode 404 and a ground electrode 406 may contact the user's wrist. When the user touches a measuring electrode 402 (e.g., electrode 166C on the crown 162 of the wearable device 150), the measuring electrode 402 may receive physiological signals from the user. Figure 4A In this context, the user is represented as physiological signal source 401. In some examples, when the user touches measuring electrode 402, a path can be created via physiological signal source 401 from measuring electrode 402 and reference electrode 404 and / or ground electrode 406 (e.g., from the user's finger across the user's chest to the user's wrist wearing the wearable device and to reference electrode 404 and / or ground electrode 406). In some examples, contacting measuring electrode 402 can cause circuitry 400 to measure physiological signals from physiological signal source 401 (e.g., such as...). Figure 3A As shown and referenced Figure 3A The above).

[0036] Figure 4B An exemplary circuit diagram is shown, in which the user of the device contacts the outer shell of the wearable device rather than the measurement electrodes. Figure 4B In this context, circuit 450 may include the same components as circuit 400, and its description is omitted for brevity. In some examples, when a user touches the housing of the wearable device, an alternative path can be created via physiological signal source 451 from reference electrode 404 (e.g., electrode 166A connected to the user's wrist) and ground electrode 406 (e.g., the housing of the wearable device may be grounded to system ground via ground electrode 406). In some examples, the alternative path may allow physiological signal source 451 to inject a physiological signal between reference electrode 404 and ground electrode 406. In some examples, the physiological signal may cause amplifier 422 to detect and amplify the physiological signal. In such examples, processor 430 may misinterpret the signal from the physiological sensor as an appropriate physiological signal. However, as referenced above... Figure 3B The resulting physiological signals may be attenuated, unstable, or in other words, unreliable.

[0037] Figures 5A to 5B An exemplary system for measuring physiological signals and for contact detection, according to an example of this disclosure, is shown. For ease of description, Figures 5A to 5B The focus is on the measuring electrodes, reference electrodes, and analog circuitry used for measuring physiological signals and for contact detection; processing circuitry and a ground reference electrode are not shown. Figure 5AIn this circuit, circuit 500 may include an analog front-end 520, a measurement electrode 502 (e.g., corresponding to measurement electrode 166C), and a reference electrode 504 (e.g., corresponding to reference electrode 166A and / or reference electrode 166B). Analog front-end 520 may include an amplifier 522 (e.g., similar to amplifier 422), an analog-to-digital converter 528 (e.g., similar to ADC 424), buffers 524 and 526, and test signal circuitry. In some examples, buffers 524 and 526 may provide an impedance matching interface for the electrodes (e.g., matching the impedance of a user's body in contact with the corresponding electrode). In some examples, buffers 524 and 526 may be designed to accommodate large input impedances 512, 514 between the electrode and buffers 524 and 526. In some examples, buffers 524 and 526 may be designed to reduce noise or interference from an input network that directs input to amplifier 522.

[0038] In some examples, the test signal circuitry (e.g., excitation circuitry) may include a test signal generator 530 and a capacitor 538. In some examples, the test signal generator 530 may be a square wave generator, a clock generator, a periodic signal generator, or other suitable signal generator. In some examples, the test signal generator may include a digital-to-analog converter (DAC) to convert a digital signal into an analog excitation signal. The test signal 531 (e.g., excitation signal) generated by the test signal generator 530 may be a square wave, sine wave, trapezoidal wave, sawtooth wave, or any other suitable periodic oscillation, non-oscillating, or non-periodic (e.g., pseudo-noise) waveform. In some examples as described herein, regardless of the waveform, the test signal may be known or predetermined by the system to enable the detection of the resulting measurement test signal. The test signal 531 may be capacitively coupled to the measurement electrode 502 via the capacitor 538. In some examples, the test signal generator 530 may be controlled by a processor (e.g., DSP 206, host processor 208, processor 430). In some examples, the processor may change the frequency and / or amplitude of the test signal 531 and / or enable and disable the test signal generator 530. In some examples, the test signal generator 530 may be the clock output of the processor 430.

[0039] In some examples, the analog front end 520 may include an impedance network 536. In some examples, the impedance network 536 may be one or more discrete capacitors and / or one or more discrete resistors. In some examples, the impedance network 536 may represent parasitic impedance in the system. In some examples, the impedance network 536 may be one or more capacitors (including corresponding parasitic impedances). In some examples, capacitor 538 and impedance network 536 form a voltage divider grounded via path 534, and the test signal 531 generated by test signal generator 530 can be divided by the voltage divider. Buffer 524 can measure the node between capacitor 538 and impedance network 536. The resulting measurement test signal can be used to detect contact on measurement electrode 502.

[0040] In some examples, the amplitude of the measured test signal (e.g., voltage level) may depend on the load the test signal experiences. For example, the resulting measured test signal may attenuate when a user touches measuring electrode 502. Figure 5A As shown, contact between the user (e.g., a finger) and the measuring electrode 502 can form a path 532 for the test signal 531. In some examples, path 532 can be formed to system ground via a physiological signal source 501 (e.g., the user's body) through a grounding electrode (e.g., grounding electrode 406 contacting the user's wrist). In some examples, the user can contact the measuring electrode 502 with a first finger (e.g., index finger) and the device housing with a second finger (e.g., thumb). In this case, path 532 of the test signal 531 can be formed to system ground via the physiological signal source 501 (e.g., the user's body) and the finger touching the device housing (e.g., the device housing may be grounded to system ground). Therefore, path 532 can form an impedance in parallel with path 534 (through impedance network 536) and change the load experienced by the test signal 531. In such examples, the resulting measurement test signal 540 attenuated at buffer 524 can be attenuated. In contrast, when the user is not touching the measuring electrode 502 (or is touching the housing), the resulting measurement test signal may not be attenuated (or may be attenuated less). Figure 5BAs shown, path 532 may not be formed to system ground if there is no contact on measuring electrode 502. If test signal 540 does not reach system ground via path 532, the resulting measurement test signal 542 may not attenuate (or may attenuate less) compared to the expected attenuation of the voltage divider of capacitor 538 and impedance network 536. Comparing the amplitudes of the resulting measurement test signals 540 and 542, the measurement test signal 540 corresponding to contact on measuring electrode 502 may attenuate more than the measurement test signal 542. In some examples, test signal 531 may travel through path 532, through physiological signal source 501, and into reference electrode 504, and may be detected by buffer 526. In some examples, the test signal detected by buffer 526 may be sufficient to determine that the user is in contact with measuring electrode 502. In some examples, differential measurements may be performed on the resulting signal detected by buffer 526 and the resulting signal detected by buffer 524 to determine the amplitude level of the resulting test signal. In some examples, a single-ended measurement can be performed to determine the amplitude of the resulting test signal (e.g., without using reference electrode 504 and buffer 526).

[0041] In some examples, the response of test signal 531 to a load may depend on the frequency of test signal 531 and the corresponding impedance of the signal path. In some examples, the frequency of test signal 531 may be varied to determine the load of the signal path at the corresponding frequency (e.g., to determine the quality of the skin-electrode connection as a function of the test signal frequency). In some examples, the initialization process may be used to select a frequency for distinguishing when measuring electrode 502 is in contact and when it is not (e.g., the frequency of test signal 531, which causes an observable change in the amplitude of the resulting test signal). In some examples, test signal 531 may include multiple frequencies simultaneously (e.g., test signal 531 may include multiple frequency components). In such examples, the reactance of the system to different frequencies may be determined at once.

[0042] A threshold amplitude (e.g., voltage level) can be used to determine whether the measuring electrode 502 is in contact. When the measured test signal is less than the threshold amplitude, the system (e.g., DSP 206, host processor 208, processor 430) can determine that the measuring electrode is in contact (e.g., there is sufficient skin-electrode coupling for high-quality physiological measurements). When the measured test signal is greater than or equal to the threshold amplitude, the system can determine that the measuring electrode is not in contact (or in contact with the housing, or there is insufficient skin-electrode coupling for high-quality physiological measurements). The threshold amplitude can be set, for example, based on empirical studies of the expected range of load impedance from the skin-electrode coupling. Additionally, the threshold amplitude can be set based on other factors, including the accuracy of the resulting waveform and the desired sensitivity (e.g., regarding positive and negative identification). As described herein, detecting contact with the measuring electrode can be used to distinguish reliable measured physiological signals (e.g., physiological signal 302) from unreliable measured physiological signals. In some examples, the system may provide a notification to the user to contact the measuring electrode to begin measuring a physiological signal. In some examples, as described herein, contact detection may be used as a trigger for initiating physiological signal measurement and / or as a trigger for ending physiological signal measurement. In some examples, contact detection can be used to assign confidence to physiological signals during a measurement session. In some examples, initiating a physiological signal measurement may include acquiring the physiological signal (e.g., via data buffer 204 and / or DSP 206), storing the physiological signal (e.g., in program memory 210), and / or displaying the physiological signal on a display. In some examples, when the system determines that the measuring electrode is not in contact, the system may abandon the measurement of the physiological signal (e.g., shut down the circuit, discard the physiological signal measurement, or in other words, not process the input signal). In some examples, when the system determines that the measuring electrode is not in contact, the system may still measure the physiological signal, but with a low confidence value indicating low quality of the physiological signal (e.g., it may be unreliable for one or more intended uses). In some examples, the low confidence may be represented in a binary manner (e.g., a low confidence / low quality flag may be set). In some examples, the confidence may 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 may be unreliable or of low quality (e.g., displaying the physiological signal with a visual indicator, displaying a notification and / or any other visual feedback on the device’s display, and / or audio feedback and / or tactile feedback and / or any other suitable feedback mechanism).

[0043] In some examples, when a user touches the measuring electrode 502, a physiological signal from the physiological signal source 501 can enter the circuit 500. In some examples, the physiological signal can be mixed with or otherwise added to the test signal 531 generated by the test signal generator 530. In some examples, the frequency of the test signal 531 can be higher than the frequency of the physiological signal. For example, the spectrum of the physiological signal can be between 0.5 Hz and 40 Hz, and the frequency of the test signal 531 can be 100 Hz, 135 Hz, 200 Hz, 250 Hz, 400 Hz, 500 Hz, 600 Hz, or any other suitable frequency above 40 Hz. In some examples, the spectrum of the physiological signal can be between 0 Hz and 150 Hz, and the frequency of the test signal 531 can be 500 Hz, 600 Hz, or any other suitable frequency above 150 Hz. In some examples, the amplitude of the test signal 531 can be smaller than the amplitude of the physiological signal. In such examples, the physiological signal can act as the carrier of the test signal 531 (e.g., in a manner similar to amplitude modulation). In some implementations, filters (e.g., high-pass or band-pass filters) may be used to filter physiological signals and compare test signals (e.g., test signal 540) with thresholds to determine whether the measuring electrode 502 has been contacted.

[0044] In some examples, the test signal generator 530 may stop generating the test signal 531 after contact with the measuring electrode 502 is confirmed. In such examples, stopping test signal generation saves power and / or reduces or eliminates the need for filtering the test signal from the physiological signal. In some examples, the test signal generator 530 continues to provide the test signal 531 even after contact with the measuring electrode 502 is confirmed. In such examples, a filter (e.g., a low-pass filter or a band-pass filter) may be used to filter the test signal 531 and leave the physiological signal for measurement and / or processing. In some examples, continuing to generate the test signal 531 allows the system (e.g., DSP 206, host processor 208, processor 430) to continue determining that the user is in contact with the measuring electrode 502. In some examples, the system may determine that contact has stopped when the user of the device stops contact with the measuring electrode 502 and stop measuring and / or processing the physiological signal. In some examples, the system may provide the user with notification regarding the termination of contact with the measuring electrode during a physiological signal measurement session. In some examples, test signal generation may be periodically restarted to determine whether the measurement electrode 502 has been contacted. In some examples, contact detection may be continuous (e.g., test signals may be generated continuously), periodic (e.g., generated once per second, once per minute, once per hour), or may be triggered to generate (e.g., launching a physiological signal application, starting a physiological signal measurement session, and determining that a wearable device is being worn, etc.).

[0045] Although Figures 5A to 5B The integration of test signal circuitry and physiological signal measurement circuitry is illustrated, but it should be understood that the test signal circuitry can be implemented in different ways. For example, the test signal circuitry may include amplifiers or other front-end circuitry (e.g., separate from amplifier 524, amplifier 522, etc.) to perform the functions of measuring test signals and performing contact detection. In some examples (e.g., as...) Figure 12 As shown), separate signal paths can 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, implementing contact detection and physiological sensing separately allows optimization of the contact detection circuitry for the frequency, signal range, and / or signal accuracy of the test signal for contact detection, and optimization of the circuitry for the frequency, signal range, and / or signal accuracy for physiological sensing. In some examples, switching circuitry can be provided to couple the test signal circuitry (e.g., a test signal generator and a measurement amplifier) ​​to the measurement electrode during contact detection and to decouple the measurement electrode from the test signal circuitry during physiological signal measurement. In some examples, the test signal circuitry can be integrated with saturation detection circuitry, as described below. Additionally, although in Figures 5A to 5B The test signal 531 is shown as a discrete source, but it can be generated by a processor (e.g., DSP 206, host processor 208). In some examples, the same processor may also be coupled to receive the measured test signal from the output of buffer 524 or another buffer or amplifier circuit.

[0046] Furthermore, despite Figures 5A to 5B The diagram illustrates the integration of test signal circuitry into the signal path of measurement electrode 502; however, it should be understood that similar test signal circuitry can be integrated into the signal path of reference electrode 504, thereby achieving a similar result (e.g., as shown in the diagram). Figure 12 (As shown) detects the contact between the user (e.g., wrist) and the reference electrode 504. Additionally, although... Figures 5A to 5B A measuring electrode 502 and a reference electrode 504 are shown, but in some examples, the system may have multiple measuring electrodes and / or multiple reference electrodes, and similar test signal circuitry may be integrated with some or all of these electrodes.

[0047] Figure 6An exemplary system for measuring physiological signals (and for contact detection and / or saturation detection) according to examples of this disclosure is shown. In some examples, circuit 600 may be similar to circuit 500 (including impedance networks 612 and 614 corresponding to impedance networks 512 and 514, amplifier 622 corresponding to amplifier 522, ADC 628 corresponding to ADC 528, buffers 624 and 626 corresponding to buffers 524 and 526, and test signal circuitry including test signal generator 631 corresponding to test signal generator 530 and capacitor 538 and capacitor 637, and impedance network 635 corresponding to impedance network 536), but analog front end 620 includes saturation detection circuitry 630. In some examples, saturation detection circuitry 630 includes buffers 634 and 636, multiplexer 632, and analog-to-digital converter 638. In some examples, buffers 634 and 636 are coupled to route signals from measuring electrode 602 and reference electrode 604 to multiplexer 632, respectively. In some examples, multiplexer 632 multiplexes signals between selecting signals from measuring electrode 602 for passage through processor 650 and selecting signals from reference electrode 604 for passage through processor 650. In some examples, processor 650 can control the multiplexing of multiplexer 632. In some examples, analog-to-digital converter 638 converts the analog signal from multiplexer 632 into a digital signal. In some examples, the digital signal is then input to processor 650. In some examples, the digital output of analog-to-digital converter 638 can be a multi-bit signal (e.g., 4-bit, 6-bit, 8-bit, 10-bit, 12-bit, etc.). In some examples, the digital output of analog-to-digital converter 638 can have fewer bits than analog-to-digital converter 628 because the accuracy of saturation measurements used for saturation detection can be lower than the accuracy of measurements used for measuring physiological signals. In some examples, instead of time-multiplexing the signal measurement for saturation detection, multiplexer 632 can be omitted, and each of buffers 634 and 636 can be coupled to its own ADC (not shown). In some examples, saturation detection circuitry 630 can measure signals from measurement electrode 602 and reference electrode 604 to (e.g., at processor 650) determine whether the corresponding measurement circuitry is saturated. For example, the input signal (e.g., a physiological signal from a user, or other non-physiological signal) may have an amplitude exceeding the dynamic range supported by the electrode or buffer. In some examples, if the input signal has saturated the measurement circuitry (e.g., buffers 624 and / or 626), the resulting signal may be distorted (e.g., clipped) or otherwise transformed and may not be usable for reliable measurements. When one or both inputs are saturated, the device may abandon the measurement of physiological signals (e.g., shut down some or all of the circuitry, such as amplifier 622, ADC 628, etc.) or in other words, not process or store the input signal.

[0048] As described above, in some examples, the saturation detection circuit 630 can be used for contact detection (e.g., as referenced). Figure 12 The circuit used is similar to that shown in the saturation detection circuit 630 for contact detection. For example, when a test signal is applied by a test signal circuit, the resulting signal can be measured by a buffer 634 in the saturation detection circuit 630, converted into a digital signal by an ADC 638, and transmitted to a processor 650 based on the attenuation of the measured test signal for contact determination.

[0049] Figure 7 An exemplary process 700 for detecting physiological signals, including contact detection and / or saturation detection, according to an example of this disclosure is shown. Process 700 may be executed by one or more processors (e.g., DSP 206, host processor 208, processor 650, etc.) of a system programmed to perform process 700. At 702, an excitation signal may be driven onto a measuring electrode. In some examples, the excitation signal (e.g., test signal 531) may be coupled to a measuring electrode (e.g., similar to a reference electrode). Figures 5A to 5B The system is driven by an excitation circuit (e.g., a test signal circuit) of the described test signal circuit. At 704, the system can sense one or more signals measured by a first sensing circuit and a second sensing circuit (e.g., corresponding to amplifiers / buffers 524 and 526). In some examples, the first sensing circuit may receive one or more signals from a measuring electrode and / or an excitation circuit, and may include a buffer (e.g., corresponding to amplifier / buffer 524). In some examples, the one or more signals measured by the first sensing circuit include physiological signals injected via contact between the user and the measuring electrode. In some examples, the one or more signals measured by the first sensing circuit may include signals measured in response to an excitation signal (e.g., the resulting test signal 540 or 542). In some examples, the second sensing circuit may receive one or more signals from a reference electrode, and may include a buffer (e.g., corresponding to amplifier / buffer 526). In some examples, the one or more signals measured by the second sensing circuit may represent a reference voltage level of the user's body. In some examples, depending on the user's physiology and impedance, the one or more signals measured by the second sensing circuit may include physiological signals injected via user contact with the measuring electrode (e.g., thereby closing a circuit loop between the measuring electrode and the reference electrode, such as a reference electrode). Figures 4A to 5B The above).

[0050] At 706, based on one or more signals that meet one or more criteria measured by the first sensing circuit and the second sensing circuit (e.g., as determined by the processor 650), the system may measure a physiological signal at 714; or based on one or more signals that do not meet one or more criteria measured by the first sensing circuit and the second sensing circuit (e.g., as determined by the processor 650), the system may abandon the measurement of a physiological signal at 712. (See above reference.) Figures 5A to 5B The measurement of physiological signals may include acquiring physiological signals (e.g., via data buffer 204 and / or DSP 206), storing physiological signals (e.g., in program memory 210), and / or displaying physiological signals on a display (e.g., touchscreen 212). In some examples, abandoning the measurement of physiological signals may include shutting down circuitry, discarding any stored signal measurements, or in other words, not processing the input signal. In some examples, the system may provide the user of the device with a notification to contact the measuring electrodes to begin measuring physiological signals. In some examples, the notification may be a notification displayed on the device's display and / or any other visual feedback, and / or audio feedback and / or tactile feedback and / or any other suitable feedback mechanism. In some examples, the system may wait for a threshold amount of time for the signal to meet one or more criteria (e.g., waiting for the user to contact the measuring electrodes and / or waiting for the signal to no longer saturate). In some examples, the system may abandon the measurement of physiological signals after a timeout threshold.

[0051] In some examples, one or more criteria optionally include (708) a criterion requiring that a signal of one or more of the signals detected in response to an excitation signal (e.g., a measured test signal) is less than a threshold (e.g., satisfied under this condition). For example, contact with the measuring electrode can be indicated by a resulting measured test signal measured in response to a driving excitation signal falling below a threshold (corresponding to the resulting measured test signal 540). When a user contacts the measuring electrode, the system can measure a physiological signal introduced into the system (as another of one or more signals) via the user's contact with the measuring electrode. When the resulting measured test signal is not lower than a threshold (corresponding to the resulting measured test signal 542), the system can abandon the measurement of the physiological signal (as referenced above). Figures 5A to 5B The above).

[0052] In some examples, one or more criteria optionally include (710) a criterion requiring that the outputs of the first sensing circuit and the second sensing circuit be unsaturated (e.g., satisfied under this condition). In some examples, the saturation detection circuit may include circuitry coupled to the outputs of the first and second sensing circuits (e.g., saturation detection circuitry 630). In some examples, the saturation detection circuitry may include buffers (e.g., buffers 634, 636), multiplexers (e.g., multiplexer 632), and analog-to-digital converters (e.g., ADC 638) to convert signals from the buffers into digital signals. In some examples, the saturation detection circuitry and processor 650 may determine whether the outputs of the first and / or second sensing circuits are saturated. For example, the first / second sensing circuit may be determined to be saturated by processor 650 when the measured voltage is at the supply voltage of the first / second sensing circuit within a threshold time period. Otherwise, the first / second sensing circuit may be determined to be unsaturated. In some examples, whether the first or second sensing circuit is saturated may be determined based on other characteristics (e.g., the shape of the measured signal). In some examples, the system can measure physiological signals when the outputs of both the first and second sensing circuits are unsaturated. In some examples, the system can abandon the measurement of physiological signals when the output of one or both of the first and second sensing circuits is saturated. In some examples, one or more standards may include standards 708 and 710, or only one standard may be included, or standards other than 708 and 710 may be included. In some examples, contact and / or saturation detection may be performed continuously to indicate the quality of physiological signal measurement during physiological signal measurement. In some examples, contact and / or saturation detection may be used to terminate a physiological signal measurement session. In some examples, contact and / or saturation detection may be performed, and the result may be used to trigger a physiological signal measurement session.

[0053] Figure 8An exemplary process 800 for detecting physiological signals, including contact detection and / or saturation detection, according to an example of this disclosure is shown. Process 800 may be executed by one or more processors (e.g., DSP 206, host processor 208, processor 650, etc.) of a system programmed to perform process 800. At 802, the system may receive user input requesting physiological signal measurement. In some examples, the user input may be for the user to open an application for measuring or viewing physiological signals. In some examples, the user input may be a request to begin a physiological signal measurement session. The session may be a predefined time period (e.g., 10 seconds, 30 seconds, 1 minute, etc.) during which physiological signals can be measured. The session may begin with user input and end at the end of the duration. In some examples, the measured physiological signals may be analyzed, classified, stored, and / or displayed during the session. At 804, in response to the user request, the system may drive the measuring electrodes (e.g., corresponding to measuring electrode 166C, measuring electrode 402, measuring electrode 502) using excitation signals (similar to the discussion at 702 above). In some examples, the system can power on the physiological measurement circuitry in response to a user request. At 806, the system can measure a signal generated in response to an excitation signal. In some examples, the signal can be a resulting test signal (e.g., the resulting excitation signal) measurable by sensing circuitry. In some examples, the sensing circuitry can be a buffer (e.g., buffer 524) coupled to the excitation circuitry and the measuring electrodes. In some examples, the resulting test signal can be measured from the output of a differential amplifier (e.g., differential amplifier 522). In some examples, the signal generated in response to the excitation signal (e.g., the resulting test signal) can be a voltage division of the excitation signal (e.g., via a reference voltage). Figures 5A to 5B The voltage divider described may be filtered (e.g., high-pass or band-pass filtered) to exclude physiological signal measurements on the measuring electrodes. At 808, in response to a measured signal (e.g., the resulting test signal) being less than a threshold voltage (e.g., as determined by a processor such as processor 650), the system may initiate physiological signal measurement. In some examples, the signal may be less than the threshold voltage when the user touches the measuring electrodes. In some examples, initiating physiological signal measurement may include acquiring the physiological signal (e.g., via data buffer 204 and / or DSP 206), storing the physiological signal (e.g., in program memory 210), and / or displaying the physiological signal on a display. In some examples, the physiological signal may be acquired from the measuring electrodes via sensing circuitry (e.g., analog front-end 420, 520). In some examples, physiological signal measurement may be a differential measurement between the measuring electrode and a reference electrode. For example, a differential amplifier (e.g., 422, 522) may output a differential signal based on the physiological signal received on the measuring electrode and / or the reference electrode. In some examples, such as the reference... Figures 6 to 7The measurement of physiological signals can begin after it is determined that the outputs of the first sensing circuit and the second sensing circuit are not saturated.

[0054] At 810, the driving of the excitation signal on the measuring electrode may optionally be stopped. In some examples, the driving of the excitation signal may be stopped in response to a signal measured to be less than a threshold voltage. In some examples, step 810 is optional, and the excitation signal may continue to be driven on the measuring electrode. At 812, the system may optionally stop the measurement of the physiological signal in response to a signal measured to be greater than the threshold voltage. In some examples, after the excitation signal is driven on the measuring electrode and the measurement of the physiological signal has begun, the system may determine that the signal generated in response to the excitation signal is no longer less than the threshold voltage (e.g., greater than or equal to the threshold voltage). In some examples, the system may stop the measurement of the physiological signal when it determines that the signal is no longer less than the threshold voltage. In some examples, this may include pausing the measurement and providing the user with a notification (e.g., visual and / or audio and / or tactile feedback) to resume contact with the measuring electrode. In some examples, the pause in the measurement may time out and the measurement may be aborted after a threshold time. In some examples, the physiological signal measured so far may be discarded. In some examples, the cessation of physiological signal measurement may be triggered by determining that the measured signal no longer conforms to the characteristics of a physiological signal, or by determining that the measured signal is inconsistent with previously measured physiological signals (e.g., the signal has ended or the signal has been attenuated).

[0055] The above description focuses primarily on contact detection of a single electrode (e.g., measuring electrode 502 / 602). In some examples, contact detection can be performed on multiple electrodes via a first excitation signal on one driving electrode (e.g., the first measuring electrode) and a second excitation signal on a second electrode (e.g., the second measuring electrode or the first reference electrode). Contact detection on multiple electrodes can be used to improve the physiological signal detection performance of the system, including by ensuring proper contact on two electrodes in a manner similar to that described above for contact detection on a single measuring electrode 502 / 602. Figure 9An exemplary system for measuring physiological signals and for contact detection on multiple electrodes, according to an example of this disclosure, is shown. Circuit 900 may be similar to circuits 500 and 600. Circuit 900 may include a first electrode (e.g., a measuring electrode 902 corresponding to measuring electrode 502 / 602), a second electrode (e.g., a reference electrode 904 corresponding to reference electrode 504 / 604), impedance networks 912 and 914 (e.g., corresponding to impedance networks 512 / 612 and 514 / 614), analog front-end circuitry 920 (e.g., corresponding to analog front-end 520 or 620), and processor 950 (e.g., corresponding to processor 650). Analog front-end circuitry 920 may include buffers 924 and 926 (e.g., corresponding to buffers 524 / 624 and 526 / 626), a differential amplifier 922 (e.g., corresponding to amplifier 522 / 622), and an ADC 928 (e.g., corresponding to ADC 528 / 628). For ease of description, the saturation detection circuit 630 has been omitted, but it should be understood that saturation detection may also be included for saturation detection as described herein.

[0056] Circuit 900 may also include test signal circuitry. However, unlike the illustrations of circuits 500 and 600, the test signal circuitry may include circuitry that drives a first excitation signal on a first electrode and a second excitation signal (different from the first excitation signal) on a second electrode (different from the first electrode). For example, the test signal circuitry may include a test signal generator comprising a digital-to-analog converter (DAC) 942 configured to output two complementary excitation signals S1 and S2. For example, S1 and S2 may be sine waves of the same frequency with a 180-degree phase shift between S1 and S2. In some examples, DAC 942 may receive an oscillation signal and / or digital values ​​from a memory to generate voltage values ​​for the waveforms S1 and S2. The first excitation signal may be driven to the first electrode via capacitor 937, and the second excitation signal may be driven to the second electrode via capacitor 947.

[0057] It should be understood that although S1 and S2 are described above as sine waves with a 180-degree phase shift, in some examples, the first excitation signal and / or the second excitation signal can be other waveforms (e.g., square wave, trapezoidal wave, sawtooth wave, or any other suitable wave), and / or the first and second excitation signals can have different phase relationships (e.g., a 90-degree phase shift or any other suitable phase shift). Additionally, in some examples, the frequencies of S1 and S2 can be the same or different (e.g., 1 kHz and 10 kHz). Finally, it should be understood that although the DAC 942 is shown as generating two excitation signals, other circuitry can also be used to generate excitation signals (two single-output DACs, or other test signal generators, such as those referenced above). Figures 5A to 5B Those mentioned above).

[0058] Circuit 900 may also include impedance networks 935 and 945 (e.g., similar to impedance networks 536 / 635), which can form a voltage divider with capacitors 937 and 947 for the two electrodes. The voltages of the corresponding excitation signals S1 and S2 can be divided by the corresponding voltage divider. In some examples, impedance networks 935 and 945 may include one or more discrete capacitors and / or one or more discrete resistors, and / or may represent the parasitic impedance of each electrode (modeling the electrode interface).

[0059] Buffer 924 measures the node between capacitor 937 and impedance network 935 corresponding to the first electrode (e.g., measuring electrode 902). Buffer 926 measures the node between capacitor 947 and impedance network 945 corresponding to the second electrode (e.g., reference electrode 904). The outputs of buffers 924 and 926 can be input to the two inputs of differential amplifier 922. The output of differential amplifier 922 can represent the combination of the voltage at the first electrode node and the voltage at the second electrode node. For example, due to the complementary nature of S1 and S2, the output of differential amplifier 922 can represent the sum of the voltages output by buffers 924 and 926 (subject to phase shift introduced by impedance changes due to electrical system and user contact with the electrodes). For other non-complementary excitation signals, the differential amplifier can still combine the outputs of buffers 924 and 926. In some examples, the resulting output from differential amplifier 922 can have a sinusoidal waveform. The analog output from differential amplifier 922 can be digitized by ADC 928, and the digitized value can be sent to processor 950 for contact detection (e.g., to compare with a reference). Figure 7 and Figure 8 (Similar to the aforementioned method). It should be understood that, although Figure 9 The circuit 900 shown illustrates a differential amplifier 922; however, it should be understood that in some examples, the differential amplifier 922 may be replaced by two single-ended amplifiers and two independent ADCs (e.g., using a combination of...). Figure 12 (Similar configuration shown in the independent contact detection circuit 1230).

[0060] For example, in a manner similar to that described above, contact between the user and the first electrode attenuates the output of buffer 924 (relative to the output without contact), and contact between the user and the second electrode attenuates the output of buffer 926 (relative to the output without contact). The composite signal output from amplifier 922 can be evaluated to determine whether it meets one or more criteria. These criteria may include a requirement that the composite signal detected in response to a first stimulus is less than a threshold (e.g., satisfied under this condition). When the composite digitized output of amplifier 922 is less than the threshold, processor 950 can determine appropriate contact between the user and both electrodes (e.g., contact sufficient to generate a threshold-quality physiological signal). When the composite digitized output of amplifier 922 is greater than the threshold, processor 950 can determine at least one inappropriate contact between the user and one of the electrodes (e.g., contact insufficient to generate a threshold-quality physiological signal). Since the composite digitized output is detected to be less than the threshold (corresponding to appropriate contact at both electrodes), the system can measure the physiological signal and / or continue measuring the physiological signal. If the detected composite digital output is greater than a threshold (corresponding to inappropriate contact at one or both electrodes), the system may abandon and / or stop measuring physiological signals (or discard the results or present a notification to the user, etc.), in a manner similar to that described in this paper for contact detection of a single measuring electrode.

[0061] As described herein, in some examples, the excitation signal for contact detection may be applied continuously, periodically, or in response to a trigger. In some examples, contact detection may be continuous to indicate the quality of physiological signal measurements during physiological signal measurement. In some examples, contact detection may be used to trigger and / or terminate a physiological signal measurement session. In some examples, contact detection may be used to distinguish between intended contact with the measuring electrode (e.g., on the coronal 162) and unintended contact with the measuring electrode (e.g., from the user's wrist). For example, contact between the coronal 162 and the user's wrist may be relatively intermittent (e.g., less than 3 to 5 seconds) compared to intended input for a physiological signal measurement that may require a threshold contact duration (e.g., greater than 10 seconds). Therefore, a session initiated due to unintended wrist contact may be terminated (and / or the session results may be discarded instead of showing inaccurate physiological signal measurements).

[0062] To perform contact detection continuously, in some examples, the excitation frequency may be selected outside the frequency band used for physiological signal measurement. For example, as described herein, in some examples, the frequency of the excitation signal may be higher than the frequency of the physiological signal. For example, the spectrum of the physiological signal may be less than 150 Hz, and the frequency of the excitation signal may be 500 Hz, 600 Hz, or any other suitable frequency higher than 150 Hz. Additionally, using a sine wave instead of a square wave for the excitation signal improves band separation (because a square wave includes frequency content across multiple frequency ranges).

[0063] As described above, the digitized output of the differential amplifier 922 can be processed for contact detection. In some examples, as mentioned above, contact detection can be based on the amplitude of the digitized output. In some examples, contact detection can be based on the impedance (including magnitude and phase) calculated from the digitized output. The latter can be used to detect additional information about the impedance. Figure 10 An exemplary signal processing block diagram 1000 for contact detection processing according to an example of this disclosure is shown. In some examples, the signal processing block diagram 1000 may be implemented in a digital signal processor or other processing circuitry (e.g., DSP 206, processor 650 / 950, etc.), including, for example, an application-specific integrated circuit, a programmable device (Field-Programmable Gate Array, Programmable Logic Device, etc.), or software executed by the processor. In some examples, the digital signal processing for contact detection may operate on the output from analog front-end circuitry 920.

[0064] Digital signal processing may include filter block 1002, in-phase and quadrature (IQ) demodulation block 1004, windowing block 1006, accumulation block 1008, and magnitude and / or phase detection block 1010. Filter block 1002 may optionally include a high-pass filter for removing high-frequency noise and / or a low-pass filter such as a decimation / anti-aliasing filter. In some examples, a band-pass filter may be used to remove high-frequency noise and low-frequency physiological signals. Although shown as filtering in the digital domain, it should be understood that in some specific implementations, filtering may be additionally or alternatively performed in the analog domain (e.g., via analog front-end circuitry 920). IQ demodulation block 1004 may include two mixers (e.g., signal multipliers) to mix the input to IQ demodulation block 1004 with the in-phase demodulated signal and the quadrature demodulated signal. For example, if excitation signals S1 and S2 correspond to an in-phase sine wave and a 180-degree out-of-phase sine wave (e.g., at the same frequency), the in-phase demodulation signal can be the same as S1, and the quadrature demodulation signal can be a 90-degree phase-shifted version of S1. In some examples, the demodulated signal applied to the mixer can be stored in and provided from memory (e.g., ROM 1020) to multiply a digital sine wave, which can be stored in ROM memory (e.g., in or accessible by DSP 204). In some examples, the in-phase demodulation signal can be a delayed version of the in-phase excitation signal (e.g., including a programmable delay added to account for differences propagating through the system). In some examples, the quadrature demodulation signal can also be adjusted by a phase delay (e.g., using a programmable delay). The I and Q components output by IQ demodulation block 1004 can be windowed using a window function at window block 1006. The window function applied at window block 1006 can include any suitable window, including rectangular, Taylor, triangular, Hamming, Hanning, Gaussian, Kaiser, etc. The windowed I and Q components can be accumulated by accumulator block 1008. The windowed and accumulated I and Q components can be used to calculate the magnitude and / or phase at magnitude and / or phase detection block 1010. As described herein, the magnitude output can be calculated as... And the phase can be calculated as Where I can represent the in-phase input of the vector value and / or phase detection block 1010, and Q can represent the quadrature input of the vector value and / or phase detection block 1010. As described herein, the magnitude can be proportional to the amplitude of the impedance and can be compared with a threshold to determine whether the user is making sufficient contact with the electrode.

[0065] It should be understood that Figure 10The signal processing described is exemplary, but variations may be made without departing from the scope of this disclosure. For example, in some examples, the magnitude may be used for contact detection, and phase calculation may not be necessary. Additionally or alternatively, some or all filtering may be moved to the analog domain. Additionally or alternatively, IQ demodulation may be implemented in the analog domain. Additionally or alternatively, windowing functionality may be implemented as part of the generation of the in-phase and quadrature demodulated signals (e.g., the demodulated signal stored in ROM 1020 may be windowed, or windowing functionality may be applied to the output of ROM 1020 before the IQ demodulation mixer). Additionally or alternatively, demodulation techniques other than IQ demodulation may be used.

[0066] In some examples, S1 and S2 can be excited at different frequencies, and execution can be performed for each excitation signal frequency. Figure 10 Signal processing. For example, a signal corresponding to the measuring electrode 902 excited by S1 at frequency f1 can be processed through... Figure 10 The signal is processed by signal processing designed to capture frequency content at or near f1 (e.g., to filter the frequency content at f2 in filter block 1002) to generate the magnitude and / or phase of the measuring electrode 902. A signal corresponding to the reference electrode 904 excited by S2 at frequency f2 (different from f1) can be similarly processed by... Figure 10 The signal processing is designed to capture frequency content at or near f2 (e.g., to filter out frequency content at f1 in filter block 1002) to generate the magnitude and / or phase of reference electrode 904. This processing can be time-multiplexed in processor 950 (applying different filters at filter block 1002, different demodulated signals at IQ demodulation block 1004, etc.), or processor 950 can include two signal processing channels to perform parallel processing (applying different filters at filter block 1002, different demodulated signals at IQ demodulation block, etc.).

[0067] Figure 11An exemplary process for detecting physiological signals, including contact detection, according to an example of this disclosure is illustrated. Process 1100 may be executed by one or more processors (e.g., DSP 206, host processor 208, processor 950, etc.) of a system programmed to perform process 1100. At 1105, the system (e.g., DAC 942 controlled by processor 950) may drive a first excitation signal (e.g., S1) on a first electrode (e.g., measuring electrode 902) and a second excitation signal (S2) on a second electrode (e.g., reference electrode 904). As described above, S1 and S2 may be different excitation signals. In some examples, S1 and S2 may be complementary excitation signals having the same frequency but 180 degrees out of phase. In some examples, the excitation may be continuous, periodic, or responsive to a trigger (e.g., requesting physiological signal measurement, opening an application for measuring or viewing physiological signals).

[0068] At 1110, the system (e.g., sensing circuitry) measures one or more signals generated in response to an excitation signal. In some examples, the sensing circuitry may include a first buffer coupled to a first electrode (e.g., buffer 924 coupled to measuring electrode 902) and a second buffer coupled to a second electrode (e.g., buffer 926 coupled to reference electrode 904). In some examples, the measurement may come from the output of a differential amplifier (e.g., differential amplifier 922). At 1115, the system (e.g., processor 950) estimates the contact at the first electrode (e.g., measuring electrode 902) and / or the second electrode (e.g., reference electrode 904). For example, the output of differential amplifier 922 may be processed (e.g., according to...) Figure 10 The system uses signal processing to determine the magnitude. When the magnitude is less than a threshold (e.g., as determined by a processor such as processor 950), the system can estimate the contact between the user and the first and second electrodes. Therefore, the system can begin or continue measuring the physiological signal. In some examples, beginning / continuing the measurement of the physiological signal may include acquiring the physiological signal (e.g., via data buffer 204 and / or DSP 206), storing the physiological signal (e.g., in program memory 210), and / or displaying the physiological signal on a display. In some examples, the physiological signal may be acquired from the measuring electrode and a reference electrode via sensing circuitry (e.g., analog front-end 920). In some examples, the physiological signal measurement may be a differential measurement between the measuring electrode and the reference electrode. For example, a differential amplifier (e.g., 922) may output a differential signal based on the physiological signal received on the measuring electrode and / or the reference electrode. In some examples, such as reference... Figures 6 to 7 The measurement of physiological signals can begin after it is determined that the outputs of the first sensing circuit and the second sensing circuit are not saturated.

[0069] When a value exceeds a threshold (e.g., as determined by a processor such as processor 950), the system may estimate that the contact between the user and the first and / or second electrodes is weak or interrupted. In some examples, the measurement of the physiological signal may be stopped in response to a signal measured to be greater than the threshold voltage. In some examples, this may include pausing the measurement and providing the user with notification (e.g., visual and / or audio and / or tactile feedback) to restore contact with the electrodes. In some examples, the pause in measurement may time out and the measurement may be aborted after a threshold time. In some examples, the physiological signal measured up to this point may be discarded.

[0070] Although process 1100 is described as estimating contact with the first and / or second measuring electrodes, it should be understood that the system may take action (e.g., start / continue / stop / pause / discard physiological signal measurement) without estimating contact based on whether the measured signal value is greater than or less than a threshold. However, the threshold may be set such that signals below the threshold indicate contact on multiple electrodes (e.g., contact sufficient for threshold-quality physiological signal measurement), and signals above the threshold indicate interrupted or weak contact on one or more electrodes (e.g., contact insufficient for threshold-quality physiological signal measurement).

[0071] In some examples, S1 and S2 may be at different frequencies. In some such examples, the processing at 1115 may include estimating the contact at the first electrode (e.g., measuring electrode 902) and / or the contact at the second electrode (e.g., reference electrode 904), respectively. For example, the output of the differential amplifier 922 may be processed for different frequencies (e.g., according to...). Figure 10 The system uses signal processing to determine the magnitude of the electrodes (as described herein). When the magnitude is less than a threshold for the corresponding electrode (e.g., as determined by a processor such as processor 950), the system can estimate contact between the user and the corresponding electrode. When the magnitude is greater than a threshold for the corresponding electrode (e.g., as determined by a processor such as processor 950), the system can estimate poor or lack of contact between the user and the corresponding electrode. When appropriate contact is established for both electrodes (e.g., when both electrodes are less than the threshold), the system can begin or continue measuring the physiological signal. When the magnitude is greater than the threshold for either corresponding contact, the measurement of the physiological signal can be stopped. In some examples, this may include pausing the measurement and providing the user with notification (e.g., visual and / or audio and / or tactile feedback) to restore contact with the electrodes. In some examples, the notification provided to the user can be modified to provide the user with information about which contact is better to improve (e.g., instructing the user to improve the contact on the coronal 162 / measuring electrode 166C when the user has poor contact with the coronal, tightening the band 154 when the user has poor contact with the reference electrodes 166A / 166B, or instructing the user to perform both of the above actions when both have contact problems).

[0072] Figure 12 An exemplary system for measuring physiological signals and for contact detection on multiple electrodes, according to an example of this disclosure, is shown. Circuit 1200 may be similar to circuit 900 and includes a first electrode (e.g., measurement electrode 1202 corresponding to measurement electrode 902), a second electrode (e.g., reference electrode 1204 corresponding to reference electrode 904), impedance networks 1212 and 1214 (e.g., corresponding to impedance networks 912 and 914), analog front-end circuitry 1220 (e.g., corresponding to analog front-end 920), and processor 1250 (e.g., corresponding to processor 950). Analog front-end circuitry 1220 may include buffers 1224 and 1226 (e.g., corresponding to buffers 924 and 926), a differential amplifier 1222 (e.g., corresponding to amplifier 922), and an ADC 1228 (e.g., corresponding to ADC 928). Circuit 1200 may also include test signal circuitry (e.g., DAC 1242 corresponding to DAC 942, coupling capacitors 1237 and 1247 corresponding to capacitors 937 and 947, and impedance networks 1235 and 1245 corresponding to impedance networks 935 and 945).

[0073] Additionally, to perform contact detection (and / or impedance measurement) of multiple contacts independently, the analog front-end circuit 1220 may also include a separate contact detection circuit 1230. For ease of description, a saturation detection circuit has been omitted, but it should be understood that, as described herein, a saturation detection circuit may also be included for saturation detection (and in some examples, the same circuit may be used for both independent contact detection and saturation detection).

[0074] In some examples, the independent contact detection circuit 1230 may include buffers 1234 and 1236, a multiplexer 1232, and an analog-to-digital converter 1238. In some examples, buffers 1234 and 1236 are coupled to route signals from measuring electrode 1202 and reference electrode 1204 to multiplexer 1232, respectively. In some examples, multiplexer 1232 multiplexes a signal selected from measuring electrode 1202 for passage through processor 1250 and a signal selected from reference electrode 1204 for passage through processor 1250. In some examples, processor 1250 may control the multiplexing of multiplexer 1232. In some examples, analog-to-digital converter 1238 converts the analog signal from multiplexer 1232 into a digital signal. In some examples, the digital signal is then input to processor 1250. In some examples, the digital output of analog-to-digital converter 1238 may be a multi-bit signal (e.g., 4-bit, 6-bit, 8-bit, 10-bit, 12-bit, etc.). In some examples, the digital output of analog-to-digital converter 1238 may have fewer bits than that of analog-to-digital converter 1228 because the measurement accuracy for contact detection may be lower than that for measuring physiological signals. In some examples, instead of time-multiplexing the signal measurement for contact detection, multiplexer 1232 may be omitted, and each of buffers 1234 and 1236 may be coupled to its own ADC (not shown).

[0075] The signal from the independent contact detection circuit 1230 can be processed by the processor 1250. In some examples, a signal corresponding to the measuring electrode 1202 and the buffer 1234 can be processed by... Figure 10 The signal is processed by signal processing to generate the magnitude and / or phase shift of the measuring electrode 1202. In some examples, a signal corresponding to the reference electrode 1204 and the buffer 1236 can be similarly processed by... Figure 10 The signal processing is used to generate the magnitude and / or phase shift of the reference electrode 1204. This processing can be time-multiplexed in processor 1250, or processor 1250 can include two signal processing channels to perform parallel processing. The magnitude information of each electrode can be compared with a threshold (e.g., in a manner similar to that described herein for the differential output of differential amplifier 922) to determine / estimate whether each electrode is in contact. For example, contact between the user and the first electrode may attenuate the output of buffer 1224 (relative to the output without contact), and contact between the user and the second electrode may attenuate the output of buffer 1226 (relative to the output without contact).

[0076] Figure 12Individual processing allows for determination of whether a contact interruption (or poor contact) is detected at the first electrode (e.g., measuring electrode 1202) or the second electrode (e.g., reference electrode 1204) or both. In some examples, the notification provided to the user may be modified to provide the user with information about which contact is better to improve (e.g., instructing the user to improve contact on the coronal 162 / measuring electrode 166C when the user has poor contact with the coronal, tightening the band 154 when the user has poor contact with the reference electrodes 166A / 166B, or instructing the user to perform both of the above actions when both contact problems exist).

[0077] As described above, aspects of this technology include the collection and use of physiological information. This technology can be implemented in conjunction with technologies involving the collection of personal data related to a user's health and / or uniquely identifying or potentially used to contact or locate a specific person. Such personal data may include demographic data, date of birth, location-based data, telephone numbers, email addresses, home addresses, and data or records related to the user's health or health level (e.g., vital sign measurements, medication information, exercise information, etc.).

[0078] This disclosure recognizes that users' personal data (including physiological information, such as data generated and used by this technology) can be used to benefit users. For example, a user's heart rate can allow the user to track or otherwise gain insights about their health or health level.

[0079] This disclosure assumes that entities responsible for collecting, analyzing, disclosing, transmitting, storing, or otherwise using such personal data will comply with established privacy policies and / or privacy practices. Specifically, such entities should implement and adhere to privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy and security of personal data. Such policies should be easily accessible to users and should be updated as data collection and / or use change. Personal information from users should be collected for the entity's lawful and reasonable purposes and not shared or sold outside of these lawful uses. Furthermore, such collection / sharing should require the user's informed consent. In addition, such entities should consider taking any necessary steps to protect and safeguard access to such personal data and ensure that other persons with access to personal data comply with their privacy policies and processes. Additionally, such entities may be subject to third-party evaluations to demonstrate their compliance with widely accepted privacy policies and practices. These policies and practices may be tailored to geographic regions and / or the specific type and nature of the personal data collected and used.

[0080] Regardless of the foregoing, this disclosure also envisions implementation schemes that allow users to selectively block the collection, use, or access to personal data, including physiological information. For example, users may be able to disable hardware and / or software components that collect physiological information. Additionally, this disclosure anticipates providing hardware and / or software components to prevent or block access to collected personal data. Specifically, users may choose to remove, disable, or restrict access to certain health-related applications that collect their personal health or fitness data.

[0081] Therefore, based on the above description, some examples of this disclosure relate to a device. The device may include: a sensing circuit configured to sense physiological signals, the sensing circuit including a first sensing circuit configured to sense a first electrode and a second sensing circuit configured to sense a second electrode; an excitation circuit configured to drive an excitation signal on the first electrode; and a processing circuit coupled to the sensing circuit, the processing circuit being configured (e.g., programmed to): detect one or more signals measured by the first sensing circuit, wherein at least one of the one or more signals is measured by the first sensing circuit in response to the excitation signal; detect one or more signals measured by the second sensing circuit; measure the physiological signal based on the one or more signals measured by the first sensing circuit and the one or more signals measured by the second sensing circuit satisfying one or more criteria; and abandon the measurement of the physiological signal based on the one or more signals measured by the first sensing circuit and the one or more signals measured by the second sensing circuit failing to satisfy one or more criteria.

[0082] Additionally or alternatively, in some examples, one or more criteria may include a first criterion requiring that at least one signal measured in response to the excitation signal has an amplitude less than a threshold voltage. Additionally or alternatively, in some examples, the excitation circuit may include: a signal generator configured to generate the excitation signal; and a capacitor configured to couple the excitation signal to a first electrode. Additionally or alternatively, in some examples, the excitation signal may be a periodic oscillating signal. Additionally or alternatively, in some examples, the excitation signal may have a frequency greater than 40 Hz. Additionally or alternatively, in some examples, the excitation signal may have a frequency between 100 Hz and 600 Hz. Additionally or alternatively, in some examples, the sensing circuit may further include a differential analog-to-digital converter (ADC) configured to convert the differential analog output of a differential amplifier into a digital output. Additionally or alternatively, in some examples, the sensing circuit may also include two single-ended amplifiers and two single-ended analog-to-digital converters (ADCs) configured to convert the analog outputs of the two single-ended amplifiers into digital outputs. Additionally or alternatively, in some examples, the sensing circuit may further include a saturation detection circuit coupled to the output of the first sensing circuit and the output of the second sensing circuit, wherein the saturation detection circuit is configured to detect the saturation of the output of the first sensing circuit or the saturation of the output of the second sensing circuit.

[0083] Additionally or alternatively, in some examples, the saturation detection circuit may include: a first buffer coupled to the output of a first sensing circuit; a second buffer coupled to the output of a second sensing circuit; a multiplexer coupled to the first and second buffers, wherein the outputs of the first and second buffers are coupled to the multiplexer as inputs; and an analog-to-digital converter (ADC). Additionally or alternatively, in some examples, one or more criteria may include a second criterion requiring that the outputs of the first and second sensing circuits not be saturated. Additionally or alternatively, in some examples, the sensing circuit may also include a differential amplifier, wherein the output of the first sensing circuit is coupled to a first input (e.g., an inverting input) of the differential amplifier, and wherein the output of the second sensing circuit is coupled to a second input (e.g., a non-inverting input) of the differential amplifier.

[0084] Additionally or alternatively, in some examples, the processing circuit may be further configured to: stop driving the excitation signal based on at least one of one or more signals measured by the first sensing circuit in response to the excitation signal satisfying one or more criteria. Additionally or alternatively, in some examples, the processing circuit may be further configured to: determine, while measuring a physiological signal, that at least one of one or more signals measured by the first circuit in response to the excitation signal fails to satisfy one or more criteria; and stop measuring the physiological signal in response to determining that at least one of one or more signals measured by the first circuit in response to the excitation signal fails to satisfy one or more criteria. Additionally or alternatively, in some examples, the excitation circuit may drive the excitation signal on the first electrode while measuring the physiological signal. Additionally or alternatively, in some examples, measuring the physiological signal may include: filtering the one or more signals measured by the sensing circuit to remove at least one signal measured in response to the excitation signal from the one or more signals.

[0085] Some examples of this disclosure relate to a method. The method may include receiving user input requesting a physiological signal measurement; driving a first measuring electrode using an excitation signal in response to receiving the user input; measuring one or more signals, wherein at least one of the one or more signals is measured in response to the excitation signal; performing the physiological signal measurement based on the one or more signals meeting one or more criteria, the one or more criteria including a criterion requiring at least one signal measured in response to the excitation signal to have an amplitude less than a threshold voltage; and abandoning the physiological signal measurement based on the one or more signals failing to meet the one or more criteria.

[0086] Additionally or alternatively, in some examples, the excitation signal may be a periodic oscillating signal. Additionally or alternatively, in some examples, the excitation signal may have a frequency greater than 40 Hz. Additionally or alternatively, in some examples, the excitation signal may have a frequency between 100 Hz and 600 Hz. Additionally or alternatively, in some examples, the method may further include detecting the saturation of the output of a first sensing circuit coupled to a first measuring electrode or the saturation of the output of a second sensing circuit coupled to a reference electrode. Additionally or alternatively, in some examples, one or more criteria include a criterion requiring that the outputs of the first sensing circuit and the outputs of the second sensing circuit not be saturated.

[0087] Additionally or alternatively, in some examples, the method may further include: stopping the use of an excitation signal to drive the first measuring electrode based on one or more signals satisfying one or more criteria. Additionally or alternatively, in some examples, the method may further include: determining, during the performance of a physiological signal measurement, that at least one of the one or more signals measured in response to the excitation signal has an amplitude not less than a threshold voltage; and stopping the performance of the physiological signal measurement in response to determining that at least one of the one or more signals measured in response to the excitation signal has an amplitude not less than the threshold voltage. Additionally or alternatively, in some examples, an excitation signal may be used to drive the first measuring electrode during the performance of the physiological signal measurement. Additionally or alternatively, in some examples, performing the physiological signal measurement may include: filtering one or more signals measured by a sensing circuit to remove at least one signal measured in response to the excitation signal from the one or more signals.

[0088] Some examples of this disclosure relate to a non-transitory computer-readable storage medium. This non-transitory computer-readable storage medium may store instructions that, when executed by a device including a first measuring electrode and one or more processing circuits, cause the one or more processing circuits to perform a method. In some examples, the method may include receiving user input requesting a physiological signal measurement; driving the first measuring electrode with an excitation signal in response to receiving the user input; measuring one or more signals, wherein at least one of the one or more signals is measured in response to the excitation signal; performing a physiological signal measurement based on the one or more signals satisfying one or more criteria, the one or more criteria including a criterion requiring at least one signal measured in response to the excitation signal to have an amplitude less than a threshold voltage; and abandoning the physiological signal measurement based on the one or more signals failing to satisfy the one or more criteria.

[0089] Additionally or alternatively, in some examples, the excitation signal may be a periodic oscillating signal. Additionally or alternatively, in some examples, the excitation signal may have a frequency greater than 40 Hz. Additionally or alternatively, in some examples, the excitation signal may have a frequency between 100 Hz and 600 Hz. Additionally or alternatively, in some examples, the method may further include detecting the saturation of the output of a first sensing circuit coupled to a first measuring electrode or the saturation of the output of a second sensing circuit coupled to a reference electrode. Additionally or alternatively, in some examples, one or more criteria include a criterion requiring that the outputs of the first sensing circuit and the outputs of the second sensing circuit not be saturated.

[0090] Additionally or alternatively, in some examples, the method may further include: stopping the driving of the first measuring electrode using an excitation signal based on one or more signals satisfying one or more criteria. Additionally or alternatively, in some examples, the method may further include: determining, during the performance of a physiological signal measurement, that at least one of the one or more signals measured in response to the excitation signal has an amplitude not less than a threshold voltage; and stopping the performance of the physiological signal measurement in response to determining that at least one of the one or more signals measured in response to the excitation signal has an amplitude not less than the threshold voltage. Additionally or alternatively, in some examples, the first measuring electrode may be driven using an excitation signal during the performance of a physiological signal measurement. Additionally or alternatively, in some examples, performing a physiological signal measurement may include: filtering one or more signals measured by a sensing circuit to remove at least one signal measured in response to the excitation signal from the one or more signals.

[0091] Some examples of this disclosure relate to a device. The device may include: a sensing circuit configured to sense physiological signals, the sensing circuit including a first sensing circuit configured to sense a first electrode and a second sensing circuit configured to sense a second electrode; an excitation circuit configured to drive a first excitation signal on the first electrode and a second excitation signal on the second electrode; and processing circuitry coupled to the sensing circuitry. The processing circuitry may be programmed to: measure the physiological signal based on one or more signals measured in response to the first and second excitation signals satisfying one or more criteria; and abandon the measurement of the physiological signal based on one or more signals measured in response to the first and second excitation signals failing to satisfy one or more criteria. Additionally or alternatively, in some examples, the sensing circuitry may also include a differential amplifier. The output of the first sensing circuitry may be coupled to a first input of the differential amplifier, and the output of the second sensing circuitry may be coupled to a second input of the differential amplifier. The one or more signals measured in response to the first and second excitation signals may be output by the output of the differential amplifier. Additionally or alternatively, in some examples, the one or more criteria may include a first criterion that can be satisfied when the one or more signals measured in response to the first and second excitation signals have an amplitude less than a threshold voltage. Additionally or alternatively, in some examples, one or more signals measured in response to the first excitation signal and the second excitation signal may include one or more first signals measured by the first sensing circuit and one or more second signals measured by the second sensing circuit. Additionally or alternatively, in some examples, one or more criteria may include a first criterion that can be satisfied when the amplitude of one or more first signals measured in response to the first excitation signal is less than a threshold voltage, and a second criterion that can be satisfied when the amplitude of one or more second signals measured in response to the second excitation signal is less than a threshold voltage. Additionally or alternatively, in some examples, the excitation circuit may include: a signal generator configured to generate the first excitation signal and the second excitation signal; a first capacitor configured to couple the first excitation signal to a first electrode; and a second capacitor configured to couple the second excitation signal to a second electrode. Additionally or alternatively, in some examples, the signal generator may include a digital-to-analog converter. Additionally or alternatively, in some examples, the first excitation signal may be a periodic oscillating signal having a first frequency and a first phase, and the second excitation signal may be a periodic oscillating signal having a first frequency and a second phase different from the first phase. Alternatively, in some examples, the first phase and the second phase may be separated by 180 degrees. Alternatively, in some examples, the first frequency may be greater than 150 Hz. Alternatively, in some examples, the first excitation signal and the second excitation signal may be driven simultaneously.Additionally or alternatively, in some examples, the first excitation signal and the second excitation signal may be driven at least partially simultaneously with the measured physiological signal. Additionally or alternatively, in some examples, the first excitation signal may be a periodic oscillating signal having a first frequency, and the second excitation signal may be a periodic oscillating signal having a second frequency different from the first frequency. Additionally or alternatively, in some examples, the first frequency and the second frequency may be greater than 150 Hz. Additionally or alternatively, in some examples, the processing circuitry may be further programmed to: determine, during the measurement of the physiological signal, that at least one of the one or more signals measured in response to the first excitation signal and the second excitation signal fails to meet one or more criteria; and in response to determining that at least one of the one or more signals measured by the first excitation signal and the second excitation signal fails to meet one or more criteria, stop the measurement of the physiological signal. Additionally or alternatively, in some examples, the measurement of the physiological signal may include: filtering the one or more signals measured by the sensing circuitry to remove the one or more signals measured in response to the first excitation signal and the second excitation signal from the one or more signals. Additionally or alternatively, in some examples, the processing circuitry may be further programmed to: filter one or more signals measured in response to the first excitation signal and the second excitation signal; demodulate one or more signals measured in response to the first excitation signal and the second excitation signal; window the one or more signals measured in response to the first excitation signal and the second excitation signal; and / or calculate the amplitude of the one or more signals measured in response to the first excitation signal and the second excitation signal. Additionally or alternatively, in some examples, the processing circuitry may be further programmed to: demodulate one or more signals measured in response to the first excitation signal and the second excitation signal with the first demodulated signal and the second demodulated signal, the second demodulated signal being 90 degrees out of phase with the first demodulated signal. The frequencies of the first excitation signal and the second excitation signal may be the same as the frequencies of the first demodulated signal and the second demodulated signal.

[0092] Some examples of this disclosure relate to a method. The method may include: driving a first excitation signal on a first electrode and a second excitation signal on a second electrode different from the first electrode; measuring one or more signals in response to the first and second excitation signals; measuring a physiological signal based on the one or more signals measured in response to the first and second excitation signals satisfying one or more criteria; and abandoning the measurement of the physiological signal based on the one or more signals measured in response to the first and second excitation signals failing to satisfy one or more criteria. Additionally or alternatively, in some examples, measuring one or more signals in response to the first and second excitation signals may include: measuring the first electrode using a first sensing circuit; and measuring the second electrode using a second sensing circuit. The one or more signals measured in response to the first and second excitation signals may be the output of a differential amplifier receiving the outputs of the first and second sensing circuits. Additionally or alternatively, in some examples, the one or more criteria may include a first criterion that can be satisfied when the one or more signals measured in response to the first and second excitation signals have an amplitude less than a threshold voltage. Additionally or alternatively, in some examples, one or more signals measured in response to the first excitation signal and the second excitation signal may include one or more first signals coupled to the first electrode measured by the first sensing circuit and one or more second signals coupled to the second electrode measured by the second sensing circuit. Additionally or alternatively, in some examples, one or more criteria may include a first criterion that can be satisfied when the amplitude of one or more first signals measured in response to the first excitation signal is less than a threshold voltage, and a second criterion that can be satisfied when the amplitude of one or more second signals measured in response to the second excitation signal is less than a threshold voltage. Additionally or alternatively, in some examples, driving the first excitation signal on the first electrode and the second excitation signal on the second electrode may include coupling the first excitation signal to the first electrode via a first capacitor and coupling the second excitation signal to the second electrode via a second capacitor. Additionally or alternatively, in some examples, the first excitation signal may be a periodic oscillating signal having a first frequency and a first phase, and the second excitation signal may be a periodic oscillating signal having a first frequency and a second phase different from the first phase. Additionally or alternatively, in some examples, the first phase and the second phase may be separated by 180 degrees. Additionally or alternatively, in some examples, the first frequency may be greater than 150 Hz. Additionally or alternatively, in some examples, the first excitation signal and the second excitation signal may be driven simultaneously. Additionally or alternatively, in some examples, the first excitation signal and the second excitation signal may be driven at least partially simultaneously with the measured physiological signal. Additionally or alternatively, in some examples, the first excitation signal may be a periodic oscillating signal having a first frequency, and the second excitation signal may be a periodic oscillating signal having a second frequency different from the first frequency.Additionally or alternatively, in some examples, the first frequency and the second frequency may be greater than 150 Hz. Additionally or alternatively, in some examples, the method may further include: determining, while measuring a physiological signal, that at least one of one or more signals measured in response to the first excitation signal and the second excitation signal fails to meet one or more criteria; and stopping the measurement of the physiological signal in response to determining that at least one of the one or more signals measured in response to the first excitation signal and the second excitation signal fails to meet one or more criteria. Additionally or alternatively, in some examples, measuring the physiological signal may include: filtering one or more signals measured by the sensing circuit to remove one or more signals measured in response to the first excitation signal and the second excitation signal. Additionally or alternatively, in some examples, the method may further include: filtering one or more signals measured in response to the first excitation signal and the second excitation signal; demodulating one or more signals measured in response to the first excitation signal and the second excitation signal; windowing one or more signals measured in response to the first excitation signal and the second excitation signal; and / or calculating the amplitude of one or more signals measured in response to the first excitation signal and the second excitation signal. Additionally or alternatively, in some examples, the method may further include: demodulating one or more signals measured in response to the first excitation signal and the second excitation signal with a first demodulated signal and a second demodulated signal, the second demodulated signal being 90 degrees out of phase with the first demodulated signal. The frequencies of the first excitation signal and the second excitation signal may be the same as the frequencies of the first demodulated signal and the second demodulated signal.

[0093] Some examples of this disclosure relate to a non-transitory computer-readable storage medium. This non-transitory computer-readable storage medium can store instructions that, when executed by a device including a first electrode, a second electrode, and one or more processing circuits, cause the one or more processing circuits to perform any of the methods described above.

[0094] While examples of this disclosure have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. It should be understood that such changes and modifications are considered to be included within the scope of the examples of this disclosure as defined by the appended claims.

Claims

1. A device comprising: sensing circuitry configured to sense a physiological signal, the sensing circuitry including first sensing circuitry configured to sense a first electrode and second sensing circuitry configured to sense a second electrode; stimulation circuitry electrically coupled to the first electrode and configured to drive a stimulation signal on the first electrode; and processing circuitry coupled to the sensing circuitry, the processing circuitry programmed to, during measurement of the physiological signal using one or more signals measured by the first sensing circuitry and using one or more signals measured by the second sensing circuitry: in accordance with a determination that a first signal, of the one or more signals measured by the first sensing circuitry, responsive to the stimulation signal fails to satisfy one or more criteria, cease measurement of the physiological signal.

2. The device of claim 1, the processing circuitry further programmed to, during measurement of the physiological signal: in accordance with a determination that the first signal, of the one or more signals measured by the first sensing circuitry, responsive to the stimulation signal satisfies the one or more criteria, continue measurement of the physiological signal.

3. The device of claim 2, wherein the processing circuitry is further programmed to: in accordance with a determination that the first signal, of the one or more signals measured by the first sensing circuitry, responsive to the stimulation signal satisfies the one or more criteria, cease driving of the stimulation signal.

4. The device of claim 1, wherein the one or more criteria include a first criterion that is satisfied when the first signal, of the one or more signals measured by the first sensing circuitry, responsive to the stimulation signal has an amplitude less than a threshold voltage.

5. The device of claim 1, wherein the stimulation circuitry includes: a signal generator configured to generate the stimulation signal; and a capacitor configured to couple the stimulation signal to the first electrode.

6. The device of claim 1, wherein the stimulation signal is a periodic oscillatory signal.

7. The device of claim 1, wherein the stimulation signal has a frequency greater than 150 Hz.

8. The device of claim 1, wherein the stimulation signal has a frequency between 400 Hz and 600 Hz.

9. The device of claim 1, wherein the sensing circuitry further includes a differential amplifier, wherein an output of the first sensing circuitry is coupled to a first input of the differential amplifier, and wherein an output of the second sensing circuitry is coupled to a second input of the differential amplifier.

10. The device of claim 9, wherein the sensing circuitry further includes a differential analog-to-digital converter (ADC) coupled to an output of the differential amplifier.

11. The device of claim 1, wherein the stimulation circuitry is configured to drive the stimulation signal on the first electrode during measurement of the physiological signal. the processing circuitry is further programmed to: ​ 12. The apparatus of claim 1, wherein, ​ filtering out, from the one or more signals measured by the first sensing circuit, the first signal of the one or more signals measured by the first sensing circuit that is responsive to the excitation signal.

13. A non-transitory computer-readable storage medium storing instructions that, when executed by a device comprising a first measurement electrode and processing circuitry, cause the device to: initiate measuring a physiological signal and driving the first measurement electrode with an excitation signal in accordance with a request to measure the physiological signal, the excitation signal being provided by excitation circuitry electrically coupled to the first measurement electrode, wherein measuring the physiological signal and driving the first measurement electrode with the excitation signal at least partially overlap in time; measure a plurality of signals, wherein a first signal of the plurality of signals is measured for the first measurement electrode in response to the excitation signal; and stop measuring the physiological signal in accordance with a determination that an amplitude of the first signal measured in response to the excitation signal is greater than a threshold voltage.

14. The non-transitory computer-readable storage medium of claim 13, wherein, the instructions, when executed by the device, further cause the device to: filter out, from the plurality of signals, the first signal of the plurality of signals that is responsive to the excitation signal.

15. The non-transitory computer-readable storage medium of claim 13, wherein, the instructions, when executed by the device, further cause the device to: stop driving the excitation signal in accordance with a determination that the amplitude of the first signal measured in response to the excitation signal is greater than the threshold voltage.

16. The non-transitory computer-readable storage medium of claim 13, wherein the excitation signal is a periodic oscillatory signal having a frequency greater than 40 Hz.

17. The non-transitory computer-readable storage medium of claim 13, wherein, the instructions, when executed by the device, further cause the device, during measuring the physiological signal: continue measuring the physiological signal in accordance with a determination that the amplitude of the first signal measured in response to the excitation signal is less than the threshold voltage.

18. A device comprising: excitation circuitry electrically coupled to a first electrode and a second electrode, the excitation circuitry configured to drive a first excitation signal on the first electrode and configured to drive a second excitation signal on the second electrode; sensing circuitry comprising a first sensing circuit configured to sense the first electrode and a second sensing circuit configured to sense the second electrode, wherein the sensing circuitry is configured to sense a physiological signal, the first sensing circuit is configured to measure a response of the first electrode to the first excitation signal, and the second sensing circuit is configured to measure a response of the second electrode to the second excitation signal; and processing circuitry coupled to the sensing circuitry, the processing circuitry programmed to: measure the physiological signal in accordance with one or more signals measured in the response to the first excitation signal and in the response to the second excitation signal satisfying one or more criteria; and abandon measuring the physiological signal in accordance with the one or more signals measured in the response to the first excitation signal and in the response to the second excitation signal not satisfying the one or more criteria.

19. The device of claim 18, wherein the sensing circuit further comprises a differential amplifier, wherein an output of the first sensing circuit is coupled to a first input of the differential amplifier and an output of the second sensing circuit is coupled to a second input of the differential amplifier, and wherein the one or more signals measured in response to the first excitation signal and in response to the second excitation signal are output by an output of the differential amplifier.

20. The device of claim 19, wherein the one or more criteria include a first criterion that is satisfied when the one or more signals measured in response to the first excitation signal and in response to the second excitation signal have an amplitude less than a threshold voltage.

21. The device of claim 18, wherein the one or more signals measured in response to the first excitation signal and in response to the second excitation signal include one or more first signals measured by the first sensing circuit and one or more second signals measured by the second sensing circuit.

22. The device of claim 21, wherein the one or more criteria include a first criterion and a second criterion, the first criterion is satisfied when the one or more first signals measured in response to the first excitation signal have an amplitude less than a threshold voltage, and the second criterion is satisfied when the one or more second signals measured in response to the second excitation signal have an amplitude less than the threshold voltage.

23. The device of claim 18, wherein the excitation circuit comprises: a signal generator configured to generate the first excitation signal and the second excitation signal; a first capacitor configured to couple the first excitation signal to the first electrode; and a second capacitor configured to couple the second excitation signal to the second electrode.

24. The device of claim 18, wherein the first excitation signal is a periodic oscillating signal having a first frequency and a first phase, and the second excitation signal is a periodic oscillating signal having the first frequency and a second phase different from the first phase.

25. The device of claim 24, wherein the first phase and the second phase are separated by 180 degrees.

26. The device of claim 18, wherein the first excitation signal and the second excitation signal are driven at least partially concurrently with measuring the physiological signal.

27. The device of claim 18, wherein the first excitation signal is a periodic oscillating signal having a first frequency, and the second excitation signal is a periodic oscillating signal having a second frequency different from the first frequency.

28. The device of claim 18, wherein the processing circuit is further programmed to: ​ during measurement of the physiological signal, determining that at least one of the one or more signals measured in response to the first excitation signal and in response to the second excitation signal fails to satisfy the one or more criteria; and in response to determining that the at least one of the one or more signals measured in response to the first excitation signal and in response to the second excitation signal fails to satisfy the one or more criteria, ceasing measurement of the physiological signal.

29. The device of claim 18, wherein measuring the physiological signal comprises: filtering one or more signals measured by the sensing circuit to remove one or more signals measured in response to the first excitation signal and in response to the second excitation signal from one or more signals measured by the sensing circuit.

30. The device of claim 18, wherein the processing circuit is further programmed to: filter the one or more signals measured in response to the first excitation signal and in response to the second excitation signal; demodulate the one or more signals measured in response to the first excitation signal and in response to the second excitation signal; window the one or more signals measured in response to the first excitation signal and in response to the second excitation signal; and calculate an amplitude of the one or more signals measured in response to the first excitation signal and in response to the second excitation signal.

31. The device of claim 18, wherein the processing circuit is further programmed to: demodulate the one or more signals measured in response to the first excitation signal and in response to the second excitation signal with a first demodulation signal and a second demodulation signal, the second demodulation signal being 90 degrees out of phase with the first demodulation signal; the first excitation signal and the second excitation signal having the same frequency as the first demodulation signal and the second demodulation signal. wherein 32. A method comprising: driving a first excitation signal on a first electrode and driving a second excitation signal on a second electrode different from the first electrode; measuring one or more signals by measuring the first electrode with a first sensing circuit in response to the first excitation signal and measuring the second electrode with a second sensing circuit in response to the second excitation signal; measuring a physiological signal using the first electrode and the second electrode in accordance with the one or more signals measured in response to the first excitation signal and the second excitation signal satisfying one or more criteria; and abandoning measurement of the physiological signal in accordance with the one or more signals measured in response to the first excitation signal and the second excitation signal failing to satisfy the one or more criteria.

33. The method of claim 32, wherein the one or more signals measured in response to the first excitation signal and the second excitation signal are outputs of a differential amplifier receiving outputs of the first sensing circuit and the second sensing circuit; and wherein the one or more criteria are based on a ratio of the one or more signals measured in response to the first excitation signal and the second excitation signal. ​ wherein The one or more criteria include a first criterion that is satisfied when the one or more signals measured in response to the first excitation signal and the second excitation signal have an amplitude that is less than a threshold voltage.

34. The method of claim 32, wherein the one or more signals measured in response to the first excitation signal and the second excitation signal include one or more first signals measured by the first sensing circuit coupled to the first electrode and one or more second signals measured by the second sensing circuit coupled to the second electrode; and wherein the one or more criteria include a first criterion that is satisfied when the one or more first signals measured in response to the first excitation signal have an amplitude that is less than a threshold voltage and a second criterion that is satisfied when the one or more second signals measured in response to the second excitation signal have an amplitude that is less than the threshold voltage.

35. The method of claim 32, wherein the first excitation signal is a periodic oscillating signal having a first frequency and a first phase, and the second excitation signal is a periodic oscillating signal having the first frequency and a second phase that is different than the first phase.

36. The method of claim 35, wherein the first phase and the second phase are separated by 180 degrees.

37. The method of claim 32, wherein the first excitation signal is a periodic oscillating signal having a first frequency, and the second excitation signal is a periodic oscillating signal having a second frequency that is different than the first frequency.

38. The method of claim 32, further comprising: determining, during the measuring of the physiological signal, that at least one of the one or more signals measured in response to the first excitation signal and the second excitation signal does not satisfy the one or more criteria; and in response to determining that the at least one of the one or more signals measured in response to the first excitation signal and the second excitation signal does not satisfy the one or more criteria, ceasing the measuring of the physiological signal.

39. The method of claim 32, wherein the measuring of the physiological signal includes: filtering one or more signals measured by a sensing circuit to remove the one or more signals measured in response to the first excitation signal and the second excitation signal from the one or more signals measured by the sensing circuit.

40. The method of claim 32, further comprising: filtering the one or more signals measured in response to the first excitation signal and the second excitation signal; demodulating the one or more signals measured in response to the first excitation signal and the second excitation signal; windowing the one or more signals measured in response to the first excitation signal and the second excitation signal; and computing an amplitude of the one or more signals measured in response to the first excitation signal and the second excitation signal. ​ 41. The method of claim 32, further comprising: demodulating the one or more signals measured in response to the first excitation signal and the second excitation signal with a first demodulation signal and a second demodulation signal, the second demodulation signal being 90 degrees out of phase with the first demodulation signal; wherein a frequency of the first excitation signal and the second excitation signal is the same as a frequency of the first demodulation signal and the second demodulation signal.

42. A non-transitory computer-readable storage medium storing instructions that, when executed by a device comprising a first electrode, a second electrode, and one or more processing circuits, cause the one or more processing circuits to perform the method of any of claims 32-41.

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