RU2786614C1 - Method and device for measuring heart rate with suppression of motion artifacts - Google Patents

Abstract

FIELD: heart rate measurement.

SUBSTANCE: group of inventions relates to methods and devices for measuring heart rate, as well as to wearable heart rate measuring devices containing such measuring devices. The heart rate measuring device contains a light source, photodetectors, a conversion unit and a computing unit. The photodetectors in each pair of photodetectors are connected counter-parallel. The light source and photodetectors form a balanced optical circuit. The conversion unit contains a transimpedance amplifier (TIA) and an ADC. At the same time, a part of the body is illuminated with coherent light. The light scattered by the tissues of the body area and blood particles is detected. The frequency component of motion artifacts in the analog difference signal of the photocurrent is eliminated by subtracting the analog signal of the photocurrent detected by one photodetector from a pair of photodetectors from the analog signal of the photocurrent detected by another photodetector from a pair of photodetectors. The analog difference signal of the photocurrent is converted by TIA into an analog voltage difference signal. An analog voltage difference signal is converted by ADC into a digital difference signal. The envelope of the digital difference signal is computed. The heart rate is calculated from the peaks of the calculated envelope of the digital difference signal.

EFFECT: present invention enables to simplify the design and reduce the size of the device, which does not require rigid fixation on the human body, is achieved due to the absence of sensors measuring the movement of the measuring device relative to the part of the body on which it is fixed, which also simplifies signal processing, since there is no need to process motion sensor signals to eliminate motion artifacts. The present invention enables to calculate the heart rate.

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Description

BACKGROUND OF THE INVENTION

The field of technology to which the invention belongs

[0001] The present invention relates generally to heart rate measurement using wearable devices, and more particularly to a motion artifact suppression heart rate measurement method and a motion artifact suppression heart rate measurement device that can be incorporated into various wearable devices, such as smart watches, fitness bracelets, etc.

Description of the Prior Art

[0002] There are devices for measuring heart rate based on photoplethysmography (PPG) or electrocardiography (ECG), which provide an accurate measurement in a stationary state of a person. There are also PPG or ECG based heart rate measurement devices built into wearable devices that provide measurement while the person is moving. However, the wearable device's heart rate measurement while the person is moving can be inaccurate due to motion artifacts caused by the movement of the device relative to the body part of the person wearing the wearable device. Motion artifacts introduce distortions into the measurement signal and the measurement result is inaccurate. In the present wearable devices, to eliminate the influence of motion artifacts, either a rigid fixation of the device on the body is used, or the wearable devices additionally contain sensors that measure motion, and motion artifacts are compensated based on the measurements of these sensors.

[0003] Rigid fixation of the heart rate measurement device on the body causes the inconvenience of wearing this device, and additional sensors and circuits to compensate for motion artifacts increase the size and weight of the device, in addition, complicate the design of the device and complicate signal processing.

[0004] In the prior art, technical solutions for measuring heart rate are known.

[0005] US Patent US4476875A, issued 10/16/1984 and entitled "METHOD AND APPARATUS FOR MEASURING FLOW MOTIONS IN A FLUID", proposes a solution in which a body area is illuminated with monochromatic laser light, light scattered from particles in the liquid and from any surrounding stationary structures is transmitted separately to two separate photodetectors. From the output signal of each photodetector, a signal is output containing beat frequency components resulting from interference between light components received by the photodetector that have different frequencies due to the Doppler frequency shift of the light scattered by the moving particles. The two signals obtained in this way from the output signals of the two photodetectors are subtracted from each other, and the signal resulting from this subtraction is used as a measure of the movement of the flow in the liquid. In this technical solution, not the photodetectors themselves are included in the differential circuit, but the device blocks, including amplifiers and analog filters. Such a solution increases the requirements for the elements of the electrical circuit, such as the linearity and stability of amplifiers, the identity of the electrical characteristics of all elements included in the differential circuit. In addition, a balanced arrangement of photodetectors relative to the light source is not disclosed, i.e. equality of distances from the light source to each photodetector and equality of photodetector parameters, such as sensitivity, detection area, etc. This solution uses optical fiber and many signal processing units, so this solution is large and heavy and is intended for stationary measurements and is not suitable for embedding in wearable devices.

[0006] International patent application WO 2007/122375A1, published Nov. 01, 2007 and titled "PHOTOPLETHYSMOGRAPHY", proposes a photoplethysmography device that includes a light source for illuminating a target object. The modulator controls the light source so that the output intensity changes depending on the modulation signal at the modulation frequency. The detector receives light from a target and generates an electrical output depending on the intensity of the light received. A demodulator with a local oscillator receives the output of the detector and produces a demodulated output, which is the modulation signal. The demodulator is insensitive to any phase difference between the modulation signal and the demodulator oscillator. From the demodulated output signal, a signal is generated that characterizes the volume of blood as a function of time and/or blood composition. Multiple demodulators may be provided to receive signals from multiple light sources at different wavelengths or from an array of detectors. The plethysmograph can operate in transmission or reflection mode. In reflection mode, the device can use the green part of the optical spectrum and polarizing filters. This technical solution is intended for measurements in a stationary state, since it does not eliminate motion artifacts that distort the measurement signal. In addition, the photoplethysmography device is not suitable for embedding in wearable devices due to the complexity of the design of the device and the inability to compensate for motion artifacts.

[0007] US Patent US10849513B2, issued 12/01/2020 and entitled "SENSING AT LEAST ONE BIOLOGICAL PARAMETER, E.G., HEART RATE OR HEART RATE VARIABILITY OF A SUBJECT", proposes a device for determining at least one biological parameter (for example, heart rate , changes in heart rate) of the subject, and the device includes a contact surface configured to be brought into contact with the skin surface of the subject. The device contains at least one light source for illuminating the skin surface through the contact surface along the optical axis of the light source with illumination including at least one wavelength, and at least one detector for detecting the response of said illumination at least at the said wavelength, from the skin surface through the contact surface along the optical axis of the detector and the supply of signals configured to determine the said biological parameter based on it, while the said optical illumination axis forms an acute contact angle with the said contact surface. This device does not compensate for motion artifacts and requires rigid fixation on the body area.

[0008] US Patent Application US20100298657A1 published 11/25/2010 entitled "METHOD FOR CONTINUOUSLY MONITORING A PATIENT USING A BODY-WORN DEVICE AND ASSOCIATED SYSTEM FOR ALARMS/ALERTS" proposes a body-worn monitor that measures a patient's vital signs (e.g. , blood pressure, SpO2, heart rate, respiratory rate and temperature) and at the same time characterizes the state of his activity (for example, rest, walking, cramps, falling). The body-worn monitor processes this information to minimize the distortion of vital signs by movement-related artifacts. The software environment generates alerts based on thresholds that are either predefined or determined in real time. The design further includes a set of "heuristic" rules that take into account the patient's activity and movement state and process vital signs accordingly. These rules, for example, indicate that a walking patient is likely to be breathing and having a regular pulse, even if their motion-corrupted vitals indicate otherwise. This technical solution includes several motion-detecting sensors to compensate for the movement of a part of the human body. And also it requires additional complex calculations to compensate for the movement of a part of the human body.

[0009] Current devices for measuring heart rate have the following disadvantages. Known devices for measuring heart rate are either designed to measure in a stationary state, or require a rigid fixation of the device on the body, or have a complex design with additional sensors that detect the movement of a part of the human body.

[0010] There is a need for a measurement device capable of providing accurate heart rate measurement even under heavy traffic conditions without rigid fixation of the measurement device on the body, small size, simple structure, and without complex signal processing. The present invention has been made to overcome the disadvantages described above and to provide the advantages described below.

SUMMARY OF THE INVENTION

[0011] The aim of the present invention is to simplify the design, reduce the size and simplify the signal processing of a heart rate measurement device with motion artifact suppression that does not require a rigid fixation on the human body, and which can be embedded in various wearable devices, for example, smart watches, fitness bracelet, etc.

[0012] One aspect of the present invention provides a method for measuring heart rate, comprising the steps of: illuminating a body area with coherent light emitted from a light source; detecting light scattered by the tissues of the body area and blood particles, at least one pair of photodetectors, wherein the photodetectors in each pair of photodetectors are connected in anti-parallel, and the light source and photodetectors form a balanced optical circuit; removing a frequency component from motion artifacts in the analog photocurrent difference signal by subtracting the analog photocurrent signal detected by one photodetector of the pair of photodetectors from the analog photocurrent signal detected by the other photodetector of the pair of photodetectors; convert transimpedance amplifier (TIU) analog differential photocurrent signal into an analog differential voltage signal; converting the analog-to-digital converter (ADC) analog voltage difference signal into a digital difference signal; calculating the envelope of the digital difference signal; and calculating the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0013] Another aspect of the present invention provides a device for measuring heart rate, comprising: a light source configured to illuminate a portion of the body with coherent light; at least one pair of photodetectors configured to detect light scattered by the tissues of the body area and blood particles, while the photodetectors in each pair of photodetectors are connected in anti-parallel, and the light source and photodetectors form a balanced optical circuit to eliminate the frequency component from motion artifacts in an analog photocurrent difference signal by subtracting an analog photocurrent signal detected by one photodetector of the photodetector pair from an analog photocurrent signal detected by another photodetector of the photodetector pair; a conversion unit containing a transimpedance amplifier (TIA) and an analog-to-digital converter (ADC) and configured to convert the analog photocurrent difference signal into an analog voltage difference signal using the TIA and convert the analog voltage difference signal into a digital difference signal using the ADC; a computing unit configured to calculate the envelope of the digital difference signal, and calculate the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0014] In one additional aspect, the apparatus comprises two pairs of photodetectors, wherein the two pairs of photodetectors are connected in parallel to produce a summed analog photocurrent difference signal, wherein the conversion unit is configured to convert the summed analog photocurrent difference signal into a summed analog voltage difference signal using the TIA and converting the summed analog voltage difference signal into a digital difference signal using the ADC.

[0015] In another additional aspect, the device comprises more than two pairs of photodetectors, with more than two pairs of photodetectors connected in parallel to obtain a summed analog photocurrent difference signal.

[0016] In another additional aspect, the device further comprises a converging lens in front of the light source and each photodetector.

[0017] Yet another aspect of the present invention provides a wearable heart rate monitor comprising a heart rate monitor according to any embodiment.

[0018] Another aspect of the present invention provides a method for measuring heart rate, comprising the steps of: illuminating a body area with coherent light emitted by a light source; light scattered by the tissues of the body area and blood particles is detected by a plurality of photodetectors, consisting of the first subset of photodetectors connected in one direction, and the second subset of photodetectors connected in the second direction, opposite to the first direction, at least one photodetector is connected to a separate conversion unit, containing a transimpedance amplifier (TIU) and an analog-to-digital converter (ADC), and a light source and photodetectors form a balanced optical circuit; converting the TIA analog photocurrent signals detected by the photodetectors into analog voltage signals; convert the ADC analog voltage signals into digital signals; removing a frequency component from motion artifacts in the digital difference signal by subtracting the digital signals derived from the analog photocurrent signals of the first subset of photodetectors from the digital signals derived from the analog photocurrent signals of the second subset of photodetectors; calculating the envelope of the digital difference signal; and calculating the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0019] Another aspect of the present invention provides a device for measuring heart rate, comprising: a light source configured to illuminate a portion of the body with coherent light; a plurality of photodetectors, consisting of a first subset of photodetectors connected in one direction and a second subset of photodetectors connected in a second direction opposite to the first direction, and a light source and photodetectors form a balanced optical scheme, wherein the plurality of photodetectors is configured to detect light scattered by tissues body area and blood particles; at least two conversion units, each of which contains a transimpedance amplifier (TIA) and an analog-to-digital converter (ADC), while each conversion unit is connected to at least one photodetector, each conversion unit is configured to convert an analog photocurrent signal detected at least one photodetector, into an analog voltage signal using a TIA and converting the analog voltage signal into a digital signal using an ADC; a computing unit configured to eliminate the frequency component from motion artifacts in the digital difference signal by subtracting digital signals obtained by at least one conversion unit from analog photocurrent signals detected by the first subset of photodetectors from digital signals obtained by at least one conversion unit from analog photocurrent signals detected by the second subset of photodetectors, calculating the envelope of the digital difference signal, and calculating the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0020] In one additional aspect, the device includes a first parallel connection of the first subset of photodetectors; and a second parallel connection from the second subset of photodetectors, wherein one conversion unit is connected to the first parallel connection and the other conversion unit is connected to the second parallel connection.

[0021] In another additional aspect, the device further comprises a converging lens in front of the light source and each photodetector.

[0022] Yet another aspect of the present invention provides a wearable heart rate monitor comprising a heart rate monitor according to any embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other aspects, features and advantages of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 schematically illustrates a heart rate detection process.

[0025] FIG. 2 is a schematic illustration of a balanced optical design.

[0026] FIG. 3 illustrates analog signals detected by photodetectors.

[0027] FIG. 4 illustrates an analog difference signal.

[0028] FIG. 5 illustrates a digital difference signal and its envelope.

[0029] FIG. 6 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0030] FIG. 7 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0031] FIG. 8 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0032] FIG. 9 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0033] FIG. 10 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0034] FIG. 11 is a block diagram of a heart rate measuring apparatus according to an embodiment of the present invention.

[0035] FIG. 12 is a flowchart of a heart rate measurement method according to an embodiment of the present invention.

[0036] FIG. 13 is a flowchart of a heart rate measurement method according to an embodiment of the present invention.

[0037] In the following description, unless otherwise indicated, the same reference numbers are used for the same elements when they are shown in different drawings, and their parallel description is not given.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0038] The following description with reference to the accompanying drawings is provided to facilitate a thorough understanding of various embodiments of the present invention as defined by the claims and their equivalents. The description includes various specific details to facilitate such understanding, but these details should be considered exemplary only. Accordingly, those skilled in the art will find that various variations and modifications of the various embodiments described herein can be made without departing from the scope of the present invention. In addition, descriptions of well-known functions and constructions may be omitted for the sake of clarity and brevity.

[0039] The terms and language used in the following description and claims are not limited to bibliographical meanings, but are simply used by the creator of the present invention to provide a clear and consistent understanding of the present invention. Accordingly, it will be clear to those skilled in the art that the following description of various embodiments of the present invention is provided for purposes of illustration only.

[0040] It should be understood that the singular forms include plurality, unless the context clearly indicates otherwise.

[0041] Additionally, it should be understood that the terms "comprises", "comprising", "includes" and / or "including", when used in this application, means the presence of the set forth features, values, operations, elements and/or components, but do not exclude the presence or addition of one or more other features, values, operations, elements, components and/or groups thereof.

[0042] FIG. 1 illustrates the photoplethysmography process used to measure heart rate in the present invention. The light source 101 illuminates the body area with coherent light, and at least two photodetectors 102 detect light scattered by the tissues of the body area and blood particles. The intensity of the detected light, and, consequently, the magnitude of the photodetector signal, is proportional to the change in blood volume in the studied area of the body during contraction and relaxation of the heart muscle. The more blood in the vessel, i.e., the more erythrocytes in it that scatter light, the stronger the light is reflected from them and the greater the value of the photodetector signal. In FIG. 1, only two photodetectors 102 are shown, however, the present invention is not limited to two photodetectors 102, and the heart rate measuring apparatus of the present invention may include more than two photodetectors 102.

[0043] In the present invention, it is preferable to use a small-sized coherent light source, such as a laser LED, as the light source 101. However, the present invention is not limited to a laser LED, the light source 101 may be any coherent light source that is sized to be embedded into a wearable device such as a smart watch, fitness bracelet, etc.

[0044] The photodetectors 102 can be any photodetectors operating in the photodiode mode, the output of which is a current signal. Two or more photodetectors 102 are connected back-to-back to provide a differential circuit for connecting photodetectors 102. Light source 101 and photodetectors 102 form a balanced optical circuit.

[0045] FIG. 2 schematically illustrates a balanced optical design. The balanced optical design is the arrangement of the photodetectors 102 at equal distances from the light source 101, as shown by the dotted circle in FIG. 2 and the photodetectors 102 have the same parameters such as sensitivity, detection area, and so on. For example, the photodetectors 102 may be arranged symmetrically with respect to the light source 101. The symmetrical arrangement of the photodetectors 102 can better eliminate motion artifacts that occur in different directions of movement of the device 100 relative to the area of the body in which the measurement is made. However, the invention is not limited to the symmetrical arrangement of the photodetectors 102 relative to the light source 101, the main condition is the location of the photodetectors 102 at the same distance from the light source 101. such as sensitivity, detection area, etc., provides signals from all photodetectors 102 with the same frequency component from motion artifacts.

[0046] FIG. 3-5 schematically illustrate the signals from photodetectors 102 before and after conversion.

[0047] FIG. 3 illustrates analog signals detected by photodetectors 102. For ease of explanation, FIG. 3 shows only two analog signals from two photodetectors 102 connected in anti-parallel. One analog signal is shown as a solid curved line, and the other analog signal is shown as a dotted curved line. However, the number of signals in the present invention may be equal to the number of photodetectors 102. The frequency component from motion artifacts in the signals of photodetectors 102 is indicated by a dashed curved line. The frequency component from motion artifacts is introduced into the signals of the photodetectors 102 due to the movement of the heart rate measurement device relative to the area of the body in which the heart rate measurement is performed. The oscillation frequency of the frequency component from motion artifacts of the signals of the photodetectors 102 is set by the frequency of movement of the heart rate measurement device 100 relative to the area of the body in which the heart rate measurement is performed. To simplify the illustration of the analog signals detected by the photodetectors 102, the frequency component from motion artifacts is shown as a smooth curved line. However, in reality, the frequency component from motion artifacts has a variable frequency of oscillation depending on the frequency of movement of the device 100 for measuring heart rate relative to the area of the body in which the measurement of heart rate is performed, since the movements of the device 100 can occur in different directions and at different frequencies. In different parts of the detected signal, the frequency component from motion artifacts can have an oscillation frequency the same as the heart rate, higher or lower than the heart rate. Therefore, the frequency component from motion artifacts cannot be eliminated by filtering the detected signal. The detection level is indicated by a dash-dotted straight line. The detection level is set in advance so as to take into account all heartbeats, for example, when performing a measurement without moving the heart rate measuring device relative to the body area, i.e. when the frequency component from motion artifacts is not introduced into the photodetector signals. As shown in the middle portion of the photodetector waveform 102, not all heart beats are detected due to the influence of the frequency component from motion artifacts.

[0048] FIG. 4 illustrates the analog difference signal obtained by subtracting the signals of the photodetectors 102 due to the connection of the photodetectors 102 in a differential circuit. The difference signal is shown as a solid curved line. Since photodetectors 102 and light source 101 form a balanced optical circuit, the frequency component from motion artifacts in all photodetector 102 signals will be the same and will be reduced when the signals are subtracted, as shown by the dotted straight line passing through the value 0 on the vertical axis of the graph. Therefore, the effect of motion artifacts is eliminated, and all heartbeats can be detected at the detection level indicated by the dashed straight line.

[0049] FIG. 5 illustrates a digital difference signal and its envelope. To improve the accuracy of heart beat detection, the analog photocurrent difference signal of the photodetectors 102 is converted into an analog voltage difference signal to increase the signal-to-noise ratio, and the analog voltage difference signal is converted into a digital difference signal. The envelope of the digital difference signal is then calculated, for example, using a Gilbert transform, a digital low-pass filter, etc. The envelope is shown as a dashed curved line. Any known method for calculating the envelope of a digital signal can be used in the present invention. Methods for calculating the envelope of a digital signal are known in the art and therefore their description is omitted. The detection level is indicated by a dash-dotted straight line. The heart rate is calculated from the peaks in the digital difference envelope that reach or exceed the detection level. The horizontal axis in the graph represents time in seconds and therefore it is possible to count the number of peaks that reach or exceed the detection level over time, i.e. calculate heart rate. For example, in FIG. 5 shows 3 peaks in 3 seconds, hence the heart rate shown in FIG. 5 is 60 heartbeats per minute.

[0050] FIG. 3-5 illustrate just one of the signal processing orders in the present invention. In the present invention, it is also possible to first convert the analog photocurrent signals detected by the photodetectors 102 into analog voltage signals, convert the analog voltage signals into digital signals, and then obtain a digital difference signal by subtracting the digital signals and calculate its envelope.

[0051] Hereinafter, various embodiments of the present invention are described in more detail with reference to the accompanying drawings.

[0052] In FIG. 12 shows a flowchart of a heart rate measurement method 200 according to an embodiment of the present invention.

[0053] In step S201, the body area is illuminated with coherent light emitted from the light source 101.

[0054] In step S202, light from the light source 101 scattered by the tissues of the body site and blood particles is detected by at least one pair of photodetectors 102. The photodetectors 102 in each pair of photodetectors are connected back-to-back. The light source 101 and photodetectors 102 form a balanced optical circuit.

[0055] In step S203, the frequency component from motion artifacts in the analog photocurrent difference signal is eliminated by subtracting the analog photocurrent signal detected by one photodetector 102 of the pair of photodetectors 102 from the analog photocurrent signal detected by the other photodetector 102 of the pair of photodetectors 102.

[0056] In step S204, the analog photocurrent difference signal obtained in step S203 is converted into an analog voltage difference signal by a transimpedance amplifier (TIA).

[0057] In step S205, the analog voltage difference signal obtained in step S204 is converted into a digital difference signal by an analog-to-digital converter (ADC).

[0058] In step S206, the envelope of the digital difference signal obtained in step S205 is calculated.

[0059] In step S207, the heart rate is calculated from the peaks of the envelope of the digital difference signal calculated in step S206.

[0060] FIG. 6-8 show block diagrams of embodiments of a heart rate measurement device 100 that performs a heart rate measurement method 200 . The device 100 includes a light source 101, at least one pair of photodetectors 102, a conversion unit 103, and a computation unit 104.

[0061] The light source 101 illuminates the area of the body where heart rate measurement is performed with coherent light.

[0062] In one embodiment, shown in FIG. 6, device 100 may include one pair of photodetectors 102. In another embodiment, shown in FIG. 7, device 100 may include two pairs of photodetectors 102. In yet another embodiment, shown in FIG. 8, device 100 may include more than two pairs of photodetectors 102.

[0063] At least one pair of photodetectors 102 detects light from light source 101 scattered by body site tissues and blood particles. The photodetectors 102 in each pair of photodetectors 102 are connected back-to-back. The light source 101 and photodetectors 102 form a balanced optical circuit. The balanced optical scheme, due to the location of photodetectors 102 at the same distance from the light source 101 and the same parameters of all photodetectors 102, such as sensitivity, detection area, etc., provides signals from all photodetectors 102 with the same frequency component from artifacts movement. By connecting the photodetectors 102 in back-to-back, i. e. in a differential circuit, a pair of photodetectors 102 outputs an analog photocurrent difference signal by subtracting the analog photocurrent signal detected by one photodetector 102 of a pair of photodetectors 102 from the analog photocurrent signal detected by another photodetector 102 of a pair of photodetectors 102. Since the signals from all photodetectors 102 have the same the same frequency component from motion artifacts, then subtracting the signals eliminates the frequency component from motion artifacts in the analog differential photocurrent signal.

[0064] The conversion unit 103 includes a transimpedance amplifier (TIA) and an analog-to-digital converter (ADC). The TIA converts the analog photocurrent difference signal into an analog voltage difference signal. The ADC converts the analog differential voltage signal into a digital differential signal.

[0065] The calculation unit 104 calculates the envelope of the digital difference signal and calculates the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0066] If the device 100 includes two or more pairs of photodetectors 102, as shown in the embodiments of FIG. 7 and 8, pairs of photodetectors 102 are connected in parallel to produce a summed analog photocurrent difference signal. The converting unit 103 converts the summed analog photocurrent difference signal into a summed analog voltage difference signal with a TIA, and converts the summed analog voltage difference signal into a digital difference signal with an ADC.

[0067] FIG. 11 partially shows another embodiment of the device 100, in which the device 100 of all of the above embodiments may further include a converging lens 105 in front of the light source 101 and each photodetector 102. Converging lenses 105 allow you to get a stronger signal and increase the signal-to-noise ratio of the processed signals.

[0068] The device 100 of all of the above embodiments may be embedded in a wearable heart rate device such as a smart watch, a fitness bracelet, etc.

[0069] FIG. 13 shows a flowchart of a heart rate measurement method 300 according to an embodiment of the present invention.

[0070] In step S301, the body area is illuminated with coherent light emitted from the light source 101.

[0071] In step S302, light from the light source 101 scattered by the tissues of the body site and blood particles is detected by a plurality of photodetectors 102. The plurality of photodetectors 102 consists of a first subset of photodetectors 102 connected in one direction and a second subset of photodetectors 102 connected in a second direction , opposite to the first direction, i.e. the first subset of photodetectors 102 and the second subset of photodetectors 102 form a differential circuit. At least one photodetector 102 is connected to a separate conversion unit 103 containing a TIA and an ADC. The light source 101 and photodetectors 102 form a balanced optical circuit.

[0072] In step S303, the analog photocurrent signals detected by the photodetectors 102 convert the TIA into analog voltage signals.

[0073] In step S304, the analog voltage signals are converted by the ADC to digital signals.

[0074] In step S305, the frequency component from motion artifacts in the digital difference signal is eliminated by subtracting the digital signals obtained in steps S303 and S304 from the analog photocurrent signals of the first subset of photodetectors 102 from the digital signals obtained in steps S303 and S304 from the analog photocurrent signals a second subset of photodetectors 102.

[0075] In step S306, the envelope of the digital difference signal obtained in step S305 is calculated.

[0076] In step S307, the heart rate is calculated from the peaks of the envelope of the digital difference signal calculated in step S306.

[0077] FIG. 9-10 show block diagrams of embodiments of a heart rate measurement device 100 that performs a heart rate measurement method 300 . The device 100 includes a light source 101, a plurality of photodetectors 102, at least two conversion units 103, and a computing unit 104.

[0078] The light source 101 illuminates the area of the body where heart rate measurement is performed with coherent light.

[0079] A plurality of photodetectors 102 detect light from the light source 101 scattered by body site tissues and blood particles. The plurality of photodetectors 102 consists of a first subset of photodetectors 102 connected in one direction and a second subset of photodetectors 102 connected in a second direction opposite to the first direction. The light source 101 and photodetectors 102 form a balanced optical circuit. The balanced optical scheme, due to the location of photodetectors 102 at the same distance from the light source 101 and the same parameters of all photodetectors 102, such as sensitivity, detection area, etc., provides signals from all photodetectors 102 with the same frequency component from artifacts movement.

[0080] Each of the at least two conversion units 103 includes a TIE and an ADC. Each conversion unit 103 is connected to at least one photodetector 102. Each conversion unit 103 converts the analog photocurrent signal detected by at least one photodetector 102 into an analog voltage signal using a TIA, and converts the analog voltage signal into a digital signal using an ADC.

[0081] The calculation unit 104 calculates a digital difference signal by subtracting the digital signals obtained by the at least one conversion unit 103 from the analog photocurrent signals detected by the first subset of the photodetectors 102 from the digital signals obtained by the at least one conversion unit 103 from the analog photocurrent signals detected by the second subset of photodetectors. Subtraction of digital signals removes the frequency component from motion artifacts in the digital difference signal because all signals have the same frequency component from motion artifacts. The calculation unit 104 calculates the envelope of the digital difference signal and calculates the heart rate from the peaks of the calculated envelope of the digital difference signal.

[0082] In one embodiment, shown in FIG. 9, in the device 100, the number of conversion units 103 is equal to the number of photodetectors 102. One conversion unit 103 is connected to one photodetector 102.

[0083] In another embodiment shown in FIG. 10, device 100 includes a first parallel connection from a first subset of photodetectors 102, a second parallel connection from a second subset of photodetectors 102, and two conversion units 103. One conversion unit 103 is connected to the first parallel connection of the first subset of photodetectors 102, and the other conversion unit 103 is connected to the second parallel connection of the second subset of photodetectors 102.

[0084] FIG. 11 partially shows another embodiment of the device 100, in which the device 100 of all of the above embodiments may further include a converging lens 105 in front of the light source 101 and each photodetector 102. Converging lenses 105 allow you to get a stronger signal and increase the signal-to-noise ratio of the processed signals.

[0085] The device 100 of all of the above embodiments may be embedded in a wearable heart rate device such as a smart watch, fitness bracelet, etc.

[0086] The above descriptions of embodiments of the invention are illustrative, and configuration and implementation modifications do not go beyond the scope of the present description. For example, while embodiments of the invention have been described generally in connection with Figures 6-13, the descriptions provided are exemplary. Although the subject matter has been described in terms of design features or methodological steps, it is to be understood that the subject matter defined by the appended claims is not necessarily limited to the specific features or steps described above. Moreover, the specific features and operations described above are disclosed as exemplary embodiments of the claims.

[0087] Accordingly, the scope of the embodiments is intended to be limited only by the following claims.

Claims (39)

1. A method for measuring heart rate, comprising the steps of: illuminating (S201) the body portion with coherent light emitted from the light source; detecting (S202) the light scattered by the tissues of the body area and blood particles, at least one pair of photodetectors, while the photodetectors in each pair of photodetectors are connected back-to-back, and the light source and photodetectors form a balanced optical circuit; removing (S203) a frequency component from motion artifacts in the analog photocurrent difference signal by subtracting the analog photocurrent signal detected by one photodetector of the photodetector pair from the analog photocurrent signal detected by the other photodetector of the photodetector pair; converting (S204) a transimpedance amplifier (TIA) analog differential photocurrent signal into an analog differential voltage signal; converting (S205) analog-to-digital converter (ADC) analog voltage difference signal into a digital difference signal; calculate (S206) the envelope of the digital difference signal; and calculating (S207) the heart rate from the peaks of the calculated envelope of the digital difference signal. 2. Device for measuring heart rate, containing: a light source configured to illuminate the body area with coherent light; at least one pair of photodetectors configured to detect light scattered by the tissues of the body area and blood particles, while the photodetectors in each pair of photodetectors are connected in anti-parallel, and the light source and photodetectors form a balanced optical circuit to eliminate the frequency component from motion artifacts in an analog photocurrent difference signal by subtracting an analog photocurrent signal detected by one photodetector of the photodetector pair from an analog photocurrent signal detected by another photodetector of the photodetector pair; a conversion unit containing a transimpedance amplifier (TIA) and an analog-to-digital converter (ADC) and configured to convert the analog photocurrent difference signal into an analog voltage difference signal using the TIA and convert the analog voltage difference signal into a digital difference signal using the ADC; a computing unit configured to calculate the envelope of the digital difference signal and calculate the heart rate from the peaks of the calculated envelope of the digital difference signal. 3. The device according to claim 2, containing: two pairs of photodetectors, wherein two pairs of photodetectors are connected in parallel to obtain a summed analog photocurrent difference signal, wherein the conversion unit is configured to convert the summed analog difference signal of the photocurrent into a summed analog voltage difference signal using the TIA and convert the summed analog voltage difference signal into a digital difference signal using an ADC. 4. The device according to claim 3, containing: more than two pairs of photodetectors, more than two pairs of photodetectors connected in parallel to obtain a summed analog photocurrent difference signal. 5. The device according to any one of paragraphs. 2-4, further comprising a converging lens in front of the light source and each photodetector. 6. Wearable device for measuring heart rate, containing a device for measuring heart rate according to any one of paragraphs. 2-5. 7. A method for measuring heart rate, comprising the steps of: illuminating (S301) the body portion with coherent light emitted from the light source; detecting (S302) the light scattered by the tissues of the body area and blood particles by photodetectors forming the first subset of photodetectors connected in one direction and the second subset of photodetectors connected in the second direction opposite to the first direction, each conversion unit of at least two conversion units containing a transimpedance amplifier (TIU) and an analog-to-digital converter (ADC), connected to at least one photodetector from the same subset of photodetectors, and the light source and photodetectors form a balanced optical circuit; converting (S303) the TIA analog photocurrent signals detected by the photodetectors into analog voltage signals; converting (S304) the ADC analog voltage signals into digital signals; removing (S305) a frequency component from motion artifacts in the digital difference signal by subtracting the digital signals obtained from the analog photocurrent signals of the first subset of photodetectors from the digital signals obtained from the analog photocurrent signals of the second subset of photodetectors; calculate (S306) the envelope of the digital difference signal; and calculating (S307) the heart rate from the peaks of the calculated envelope of the digital difference signal. 8. Device for measuring heart rate, containing: a light source configured to illuminate the body area with coherent light; photodetectors forming the first subset of photodetectors connected in one direction, and the second subset of photodetectors connected in the second direction opposite to the first direction, and the light source and photodetectors form a balanced optical scheme, while the photodetectors are configured to detect light scattered by the tissues of the body area and blood particles; at least two conversion units, each of which contains a transimpedance amplifier (TIA) and an analog-to-digital converter (ADC), while each conversion unit is connected to at least one photodetector from the same subset of photodetectors, each conversion unit is made with the possibility of converting the analog signal of the photocurrent detected by at least one photodetector into an analog voltage signal using the TIA and converting the analog voltage signal into a digital signal using the ADC; a computing unit configured to eliminate the frequency component from motion artifacts in the digital difference signal by subtracting digital signals obtained by at least one conversion unit from analog photocurrent signals detected by the first subset of photodetectors from digital signals obtained by at least one conversion unit from analog photocurrent signals detected by the second subset of photodetectors, calculating the envelope of the digital difference signal, and calculating the heart rate from the peaks of the calculated envelope of the digital difference signal. 9. The device according to claim 8, containing: the first parallel connection of the first subset of photodetectors; and the second parallel connection from the second subset of photodetectors, wherein one conversion unit is connected to the first parallel connection and the other conversion unit is connected to the second parallel connection. 10. The device according to any one of paragraphs. 8, 9, further comprising a converging lens in front of the light source and each photodetector. 11. Wearable device for measuring heart rate, containing a device for measuring heart rate according to any one of paragraphs. 8-10.

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