Pulse wave detection device, pulse wave detection system, and pulse wave detection method

Abstract

To enhance accuracy of pulse wave detection.SOLUTION: A pulse wave detection system includes: a light reception element for receiving light including reflection light reflected on a living body; a conversion circuit for converting a current generated in the light reception element to a voltage; a first amplification circuit for amplifying a voltage signal output from the conversion circuit; a removal circuit for removing at least part of a direct current component of the voltage signal amplified by the first amplification circuit; a second amplification circuit for amplifying the voltage signal in which at least part of the direct current component is removed in the removal circuit; and a detection unit for detecting a pulse wave of the living body using the output of the second amplification circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a pulse wave detection device and the like that detects the pulse wave of a subject. [Background technology]

[0002] Pulse wave detection devices that detect pulse waves are known. For example, Patent Document 1 describes a terminal device that can be worn on a living body, which includes a light-emitting element, a light-receiving element that receives light from the light-emitting element and converts it into a current corresponding to the intensity of the received light, a current-voltage conversion circuit to which a current obtained by subtracting a predetermined amount from the current flowing through the light-receiving element is input, an amplifier circuit that amplifies the output voltage of the current-voltage conversion circuit, and a microcomputer that detects the pulse based on a signal from the amplifier circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-105338 Summary of the Invention [Problem to be solved by the invention]

[0004] When the change in current generated by the light receiving element is minute, it is difficult to detect the change in current. It is also not easy to detect a pulse wave from such a change in current. Furthermore, the accuracy of the detected pulse wave is not high. Therefore, it would be desirable to be able to detect a pulse wave with high accuracy even from a slight change in current. [Means for solving the problem]

[0005] A pulse wave detection system according to one embodiment of the present disclosure includes a photodetector that receives light including light reflected from a living body, a conversion circuit that converts a current generated by the photodetector into a voltage signal, a first amplifier circuit that amplifies the voltage signal output from the conversion circuit, a removal circuit that removes at least a portion of the DC component of the voltage signal amplified by the first amplifier circuit, a second amplifier circuit that amplifies the voltage signal from which at least a portion of the DC component has been removed in the removal circuit, and a detection unit that detects the pulse wave of the living body using the output of the second amplifier circuit. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, the pulse wave of a living body can be detected with high accuracy. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a functional block diagram showing a configuration of a main part of a pulse wave detection system according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram for explaining how a voltage signal is processed in each circuit in the pulse wave detection system. [Figure 3] FIG. 10 is a diagram showing an example of a pulse wave detection system implemented in a wristwatch format. [Figure 4] 2 is a schematic diagram showing a first substrate included in the pulse wave detection system as viewed from the side where it is attached to a subject. FIG. [Figure 5] 4 is a diagram schematically showing the relationship between the position of the first substrate and the radial artery of a subject when the pulse wave detection system is attached to the subject. FIG. [Figure 6] 10 is a diagram showing the relationship between a cross section of the first substrate cut along a line including the light emitting element and the light receiving element and the radial artery. FIG. [Figure 7] 4A and 4B are diagrams for explaining a light emission pattern of a light emitting element. [Figure 8] 1 is a cross-sectional view showing an example of an arrangement structure of a light-emitting element and a light-receiving element. [Figure 9] 4 is a flowchart showing a processing flow in the pulse wave detection system. [Figure 10]1 is a functional block diagram showing a configuration of a main part of a pulse wave detection system according to a first embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] An embodiment of the present disclosure will be described in detail below. A pulse wave detection system 1 according to the present disclosure is, for example, a wristwatch-type device worn on a subject's wrist to detect the subject's pulse wave. More specifically, the pulse wave detection system 1 detects pulse waves by detecting changes in the volume of the subject's blood vessels, such as the radial artery, from changes in reflected light from the subject's blood vessels. The following description will discuss a case in which the pulse wave detection system 1 receives light including light reflected from the subject's blood vessels. However, the pulse wave detection system 1 may be any device capable of receiving light reflected from a living body. In addition to a wristwatch-type system, the pulse wave detection system 1 may also be, for example, a ring-type system, an armband-type system, a neckband-type system, or a legband-type system. Furthermore, the pulse wave detection system 1 may have a portion that can be attached to the subject's measurement site with an adhesive or the like.

[0009] By detecting the pulse wave of a subject using the pulse wave detection system 1, it is possible to derive and estimate not only the pulse wave but also various other biological information of the subject. For example, it is possible to estimate the subject's blood glucose indicators (blood glucose level, glucose metabolism state, etc.) from changes in the pulse wave. It is also possible to estimate the subject's vascular age and degree of arteriosclerosis. Furthermore, it is possible to estimate pulse wave velocity and blood pressure by combining the pulse wave with an electrocardiogram. It is also possible to estimate vascular endothelial function and the risk of heart disease, cerebrovascular disease, etc.

[0010] Fig. 1 shows a functional block diagram of a pulse wave detection system 1 according to the present disclosure. As shown in Fig. 1, the pulse wave detection system 1 includes a first substrate 10 and a second substrate 20. The first substrate 10 includes a light-emitting element 11, a light-receiving element 12, a conversion circuit 13, and a first amplifier circuit 14. The second substrate 20 includes a removal circuit 21, a second amplifier circuit 22, a detection unit 23, and an element control unit 24.

[0011] The light-emitting element 11 is an element that emits light, such as an LED (Light Emitting Diode). There may be one or more light-emitting elements 11, which are arranged on the first substrate 10 so as to emit light toward the subject when the subject wears the pulse wave detection system 1.

[0012] When a plurality of light-emitting elements 11 are arranged, each light-emitting element 11 may emit light at a different timing. If the plurality of light-emitting elements 11 emit light at different timings, it is possible to recognize whether the light received by the light-receiving element 12 is light emitted from a desired light-emitting element 11. This allows only the light emitted from the desired light-emitting element 11 to be the target of detection and judgment.

[0013] The light receiving element 12 is an element, such as a photodiode, that generates a current according to the intensity of the received light. One or more light receiving elements 12 are arranged on the first substrate 10 so as to receive light including light reflected from a living subject.

[0014] The conversion circuit 13 is a circuit that converts a current into a voltage, and converts the current generated by the light receiving element 12 into a voltage signal.

[0015] The first amplifier circuit 14 is a circuit that amplifies the voltage signal converted by the conversion circuit 13.

[0016] Removal circuit 21 is a circuit that removes at least a portion of the direct current (DC) component in the voltage signal amplified by first amplifier circuit 14. Removal circuit 21, for example, references the minimum value of the AC component of the voltage signal output from first amplifier circuit 14 for a predetermined time before removal, and performs removal using a value smaller than this minimum value. This allows the DC component to be removed while leaving the AC component, which is the pulse wave component, and therefore increases the accuracy of pulse wave detection.

[0017] The second amplifier circuit 22 is a circuit that amplifies the voltage signal from which at least a part of the DC component has been removed by the removal circuit 21.

[0018] The detection unit 23 uses the voltage signal amplified by the second amplifier circuit 22 to detect the pulse wave of the subject.

[0019] The element control unit 24 controls the light emission of the light-emitting elements 11 and the light reception of the light-receiving elements 12. The control of light emission is, for example, control of the timing of light emission. If there are multiple light-emitting elements 11, it is control of the order in which each of the light-emitting elements 11 emits light, the timing of light emission, etc. The control of light reception is, for example, control of the timing of light reception synchronized with the timing of light emission of the light-emitting elements 11. If there are multiple light-receiving elements 12, it is control so that light is received by the light-receiving element 12 corresponding to the light-emitting element 11 that emitted light.

[0020] As described above, in pulse wave detection system 1, light receiving element 12, conversion circuit 13, and first amplifier circuit 14 are provided on first substrate 10, and second amplifier circuit 22 is provided on second substrate 20, which is different from first substrate 10. This allows first substrate 10 to generate a voltage signal with high noise resistance with a small configuration and transmit it to the second substrate. This increases the degree of freedom in design, for example, by placing first substrate 10 near the subject's blood vessels and second substrate 20 at a desired position.

[0021] 2, it will be described how the voltage signal converted in the conversion circuit 13 is processed in the first amplifier circuit 14, the removal circuit 21, and the second amplifier circuit 22. Fig. 2 is a diagram for explaining how the voltage signal is processed in each circuit.

[0022] In FIG. 2, 201 indicates a voltage signal converted by the conversion circuit 13. The horizontal axis of 201 indicates time, and the vertical axis indicates voltage. When this voltage signal indicated by 201 is amplified by the first amplifier circuit 14, an amplified voltage signal is generated as indicated by 202 in FIG. 2. The amplified voltage signal is sent to the second board 20, and the DC component indicated by 203 in FIG. 2 is removed by the removal circuit 21, resulting in a voltage signal indicated by 204 in FIG. 2. The voltage signal from which the DC component has been removed by the removal circuit 21 is amplified again by the second amplifier circuit 22 as indicated by 205 in FIG. 2. This generates a signal in which the changing portion of the voltage signal is amplified. The detection unit 23 detects the pulse wave using this signal in which the changing portion of the voltage signal is amplified. This allows the subject's pulse wave to be detected with high accuracy.

[0023] Fig. 3 shows an example of a wristwatch-type pulse wave detection system 1. Reference numeral 301 in Fig. 3 is a diagram showing an overview of the pulse wave detection system 1. Reference numeral 302 in Fig. 3 is a diagram showing the circuit board portion of the pulse wave detection system 1 in an unfolded state.

[0024] 3, when pulse wave detection system 1 is implemented as a wristwatch, first substrate 10 is disposed in first portion 311, which corresponds to the band of the wristwatch, and second substrate 20 is disposed in second portion 312, which corresponds to the case of the wristwatch. More specifically, first substrate 10 is disposed on the palm side of first portion 311 of the wristwatch.

[0025] First substrate 10 is disposed in first portion 311, which corresponds to the band of a wristwatch, and may be a flexible printed circuit board. This allows first substrate 10 to be easily disposed in first portion 311, making it easy to make pulse wave detection system 1 a wearable device such as a wristwatch.

[0026] Furthermore, because first substrate 10 is disposed in first portion 311, which faces the palm when worn, there is a distance of at least several centimeters between first substrate 10 and second substrate 20, which is disposed in the case portion. Therefore, distance dSA between light receiving element 12 disposed within first substrate 10 and conversion circuit 13 and first amplifier circuit 14 corresponding to light receiving element 12 is shorter than distance dSB between first substrate 10 and second substrate 20. Furthermore, because first amplifier circuit 14 is disposed on first substrate 10 and second amplifier circuit 22 is disposed on second substrate 20, it can be said that distance dSA is shorter than the distance between first amplifier circuit 14 and second amplifier circuit 22.

[0027] To explain distance dSA and distance dSB in more detail, distance dSA is the distance between the center of light receiving element 12 and the center of the circuit portion including conversion circuit 13 and first amplifier circuit 14. Furthermore, in the case of a wristwatch type, distance dSB is the distance between first substrate 10 and second substrate 20 when the band portion of the wristwatch is unfolded on a plane. This is just one example, and distance dSB may also be the linear distance between first substrate 10 and second substrate 20 when worn.

[0028] As described above, the voltage signal is amplified by the first amplifier circuit 14 in the first substrate 10 and then sent from the first substrate 10 to the second substrate 20. Therefore, even if the first substrate 10 and the second substrate 20 are separated by at least several centimeters, a stable voltage signal can be transmitted.

[0029] Here, the first substrate 10 and the second substrate 20 may be electrically connected as long as a voltage signal can be transmitted from the first substrate 10 to the second substrate 20, but they do not have to be electrically connected. If they are electrically connected, the first substrate 10 and the second substrate 20 may be in direct contact via a connector or the like, or may be connected via wiring or the like. If they are not electrically connected, the voltage signal may be transmitted from the first substrate 10 to the second substrate 20 by a wireless device such as Bluetooth (registered trademark).

[0030] Next, the first substrate 10 will be described in detail with reference to FIG. 4. FIG. 4 is a schematic diagram showing the first substrate 10 as viewed from the side where it is attached to the subject. In the example shown in FIG. 4, four light-receiving elements 12 are arranged on a first line LA. Five light-emitting elements 11X are arranged on a second line LB, and five light-emitting elements 11Y are arranged on a third line LC. Here, the light-emitting elements 11 or the light-receiving elements 12 may be arranged so that at least a portion thereof is located on the first line LA, the second line LB, or the third line LC. The light-emitting elements 11 or the light-receiving elements 12 may also be arranged so that the center of gravity of the light-emitting elements 11 or the light-receiving elements 12 when viewed from the side where it is attached to the subject is located on the first line LA, the second line LB, or the third line LC. The light-emitting elements 11X and the light-emitting elements 11Y are assigned the symbols X and Y to distinguish their positions, but when there is no need to distinguish between them, they will simply be referred to as the light-emitting elements 11.

[0031] The first line LA, the second line LB, and the third line LC are different lines in the longitudinal direction of the band, which is the first portion 311. The first line LA, the second line LB, and the third line LC may be arranged so as not to intersect with each other within the range where the light-emitting element or the light-receiving element is located. The first line LA, the second line LB, and the third line LC may be arranged parallel to each other. The first line LA is located between the second line LB and the third line LC so that the light-emitting element 11 is located on either side of the light-receiving element 12. In other words, the second line LB and the third line LC are located so as to sandwich the first line LA.

[0032] The distance between the light emitting elements 11 arranged on either side of the light receiving element 12 may be, for example, 10 mm. The distance between the light emitting elements 11 and the light receiving element 12 may be, for example, greater than 3 mm and less than 6 mm.

[0033] By arranging the light emitting element 11 and the light receiving element 12 on different straight lines, it is possible to narrow the distance between the light receiving elements 12 and arrange the light receiving elements 12. This makes it possible to narrow the area where reflected light cannot be received.

[0034] Furthermore, by arranging the light emitting elements 11 so as to sandwich the light receiving element 12, the light emitted from the light emitting elements 11 can be efficiently received by the light receiving element 12.

[0035] Furthermore, the light-emitting elements 11 are arranged in a direction different from the direction perpendicular to the first straight line LA of the light-receiving elements 12. In other words, the light-emitting elements 11 are not arranged in the direction perpendicular to the first straight line LA of the light-receiving elements 12. This arrangement makes it possible to include a wide area as a measurable range with a combination of a small number of light-emitting elements 11 and light-receiving elements 12.

[0036] 5 and 6, the advantages of the above-described arrangement of light-emitting element 11 and light-receiving element 12 will be described. Fig. 5 is a diagram schematically showing the relationship between the position of first substrate 10 and the radial artery of the subject when pulse wave detection system 1 is worn on the subject.

[0037] 501 to 503 in Fig. 5 show states in which the position of the first substrate 10 is displaced in the circumferential direction of the subject's wrist. With 502 in Fig. 5 as a reference, 501 shows a state in which the first substrate 10 is displaced toward the thumb, and 503 shows a state in which the first substrate 10 is displaced toward the little finger.

[0038] When a subject wears wristwatch-type pulse wave detection system 1 on their wrist, the position of first substrate 10 is not necessarily always the same, and some deviation occurs in the circumferential direction of the subject's wrist.

[0039] Even if the position of the first substrate 10 is displaced in the circumferential direction of the subject's wrist, the light-emitting elements 11 are arranged so as to sandwich the radial artery of the subject, as shown by 501 to 503 in Fig. 5. The light-receiving element 12 is arranged between the light-emitting elements 11.

[0040] 6 shows the relationship between the radial artery and a cross section of first substrate 10 taken along a line including light-emitting element 11 and light-receiving element 12, for example, line SA in FIG. 4. As shown by 601 to 603 in FIG. 6, if light-receiving element 12 is sandwiched between two light-emitting elements 11, reflected light of light emitted from light-emitting element 11 will be received by light-receiving element 12 no matter where the radial artery is located between the two light-emitting elements 11. This makes it possible to easily detect a pulse wave without requiring the subject to align the radial artery.

[0041] The conversion circuit 13 and the first amplifier circuit 14 are provided for each light-receiving element 12. The conversion circuit 13 and the first amplifier circuit 14 are disposed adjacent to the light-receiving element 12 in a direction perpendicular to the first line LA of the light-receiving element 12. Here, the first amplifier circuit 14 may be disposed so that at least a portion thereof is located in a direction perpendicular to the first line LA. The first amplifier circuit 14 may be disposed so that the center of gravity of the first amplifier circuit 14, as viewed from the side where it is worn on the subject, is located in a direction perpendicular to the first line LA. This arrangement allows the conversion circuit 13 and the first amplifier circuit 14 to be disposed near the light-receiving element 12 and reduces the installation space. Furthermore, the current signal output from the light-receiving element 12 can be converted into a voltage by the conversion circuit 13 before being affected by noise, etc., thereby reducing the influence of noise, etc. on the current signal.

[0042] Although the above description has been given with reference to an example in which there are a plurality of light-emitting elements 11, light-receiving elements 12, conversion circuits 13, and first amplifier circuits 14, there may be only one of each. Also, instead of the ten light-emitting elements 11 and four light-receiving elements 12, conversion circuits 13, and first amplifier circuits 14 shown in FIG. 4, there may be any number of two or more.

[0043] Although the light-emitting element 11 has been described as including the light-emitting element 11X arranged on the second straight line LB and the light-emitting element 11Y arranged on the third straight line LC, the light-emitting element 11 may be arranged on only one of the straight lines. That is, the combination of the light-emitting element 11 and the light-receiving element 12 may be including the light-emitting element 11X arranged on the second straight line LB and the light-receiving element 12X arranged on the first straight line LA, or including the light-emitting element 11Y arranged on the third straight line LC and the light-receiving element 12X arranged on the first straight line LA.

[0044] [Light Emitting Element Light Emitting Pattern] The light emission pattern of the light emitting element 11 will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining the light emission pattern of the light emitting element 11.

[0045] 7 shows light receiving element 12A as the light receiving element 12 of interest, and four light emitting elements 11A to 11D sandwiching light receiving element 12A. In this case, element control unit 24 may cause any two of the elements sandwiching light receiving element 12A, for example, light emitting element 11A and light emitting element 11D, or light emitting element 11B and light emitting element 11C, to emit light, or may cause all four light emitting elements 11A to 11D to emit light. Alternatively, any three of the elements sandwiching light receiving element 12A may be used.

[0046] When any two light-emitting elements sandwiching the light-receiving element 12A are made to emit light, for example, if the light-emitting element 11 is an LED, the light-emitting element 11 is made to emit light with a wavelength of 855 nm and a current of 120 mA supplied to the LED. When all four light-emitting elements 11A-D are made to emit light, the light-emitting elements 11A-D are made to emit light with a wavelength of 855 nm and a current of 60 mA supplied to the LED. When all four light-emitting elements 11A-D are made to emit light with a current of 60 mA supplied to the LED, the light-receiving element 12A can obtain the same output as when any two light-emitting elements sandwiching the light-receiving element 12A are made to emit light with a current of 120 mA supplied to the LED. In other words, the light-receiving element 12A can obtain the same output even when the input current is halved.

[0047] [Arrangement of Light-Emitting Element 11 and Light-Receiving Element 12] The light-emitting element 11 and the light-receiving element 12 may be arranged on the same plane on the first substrate 10 so that the light-emitting direction of the light-emitting element 11 and the light-receiving direction of the light-receiving element 12 are approximately the same, but this is not necessarily limited to this.

[0048] Fig. 8 shows an example of the arrangement structure of the light-emitting element 11 and the light-receiving element 12. As shown in Fig. 8, the arrangement structure of the light-emitting element 11 and the light-receiving element 12 may be such that the surface on which the light-emitting element 11 is arranged is different from the surface on which the light-receiving element 12 is arranged.

[0049] 8 shows an example of an arrangement structure of the light-emitting element 11 and the light-receiving element 12. In the example shown in 801, the light-receiving element 12 is arranged in a first recess 811 provided in the first substrate 10, and the light-emitting element 11 is arranged in a second recess 812 provided within the first recess 811. In other words, when the subject wears the pulse wave detection system 1, the light-receiving element 12 is arranged closer to the subject than the light-emitting element 11. More specifically, the light-receiving element 12 is arranged closer to the subject's radial artery than the light-emitting element 11. Specifically, the distance dY between the light-emitting element 11 and the skin of the subject's wrist where the light-emitting element 11 is worn in a direction perpendicular to the surface of the first substrate 10 is longer than the distance dX between the light-receiving element 12 and the skin of the subject's wrist where the light-emitting element 11 is worn (dY>dX).

[0050] This structure reduces the risk that the light emitted from light-emitting element 11 will be directly received by light-receiving element 12. Furthermore, the light emitted from light-emitting element 11 can be directed at the living body in a more spread-out state, and even if the position of light-emitting element 11 is shifted from the position of the radial artery of the subject when pulse wave detection system 1 is worn on the subject, more light can be reflected by the radial artery.

[0051] 8, a structure may be adopted in which a reflector 821 that reflects light is arranged on a surrounding wall that faces away from the light-emitting direction of the light-emitting element 11. In other words, a structure may be adopted in which a reflector 821 is arranged on a wall of the second recess 812. By arranging the reflector 821 around the light-emitting element 11, the light emitted from the light-emitting element 11 can be efficiently irradiated toward the subject. Here, the reflector 821 may be arranged on a surrounding wall that faces away from the light-emitting direction of the light-emitting element 11. Furthermore, the surrounding wall that faces away from the light-emitting direction of the light-emitting element 11 may be made of the reflector 821.

[0052] The light emitting direction of the light emitting element and the light receiving direction of the light receiving element may be substantially the same, or alternatively, as shown in 803 in Fig. 8, the optical axis of the light emitting element 11 may be tilted toward the light receiving element 12. With the structure in which the optical axis of the light emitting element 11 is tilted toward the light receiving element 12, the reflected light of the light emitted from the light emitting element 11 can be more efficiently received by the light receiving element 12.

[0053] Furthermore, as shown in Figure 8, among the surrounding walls that are not in the light-emitting direction of the light-emitting element 11, the wall located near the light-receiving element 12 may be structured so that the distance to the light-receiving element 12 becomes closer when viewed from the side where it is worn on the subject as it moves away vertically from the surface on which the light-emitting element 11 is placed.

[0054] The first recess 811 may not be exposed, but may be covered with a cover. The cover may be made of a visible light blocking member that has a lower transmittance for visible light than for infrared light.

[0055] [Processing flow in pulse wave detection system 1] Next, the flow of processing in the pulse wave detection system 1 will be described with reference to Fig. 9. Fig. 9 is a flowchart showing the flow of processing in the pulse wave detection system 1.

[0056] As shown in FIG. 9, in pulse wave detection system 1, first, light receiving element 12 generates a current corresponding to light reflected from the subject (S101). Next, conversion circuit 13 converts the current generated in light receiving element 12 into a voltage signal (S102, conversion step). The voltage signal converted in conversion circuit 13 is amplified in first amplifier circuit 14 (S103, first amplification step). At least a portion of the DC component of the voltage signal amplified in first amplifier circuit 14 is removed in removal circuit 21 (S104, removal step). The voltage signal from which at least a portion of the DC component has been removed in removal circuit 21 is amplified again in second amplifier circuit 22 (S105, second amplification step).

[0057] Finally, the detection unit 23 detects the pulse wave of the subject using the voltage signal amplified by the second amplifier circuit 22 (S106, detection step).

[0058] The above is the flow of processing in the pulse wave detection system 1.

[0059] [Other configuration examples] In the above-described embodiment, the pulse wave detection system 1 includes the first board 10 and the second board 20, each performing its own processing. However, the present disclosure is not limited to this configuration and may be realized as a single pulse wave detection device including the light receiving element 12, the conversion circuit 13, the first amplifier circuit 14, the elimination circuit 21, the second amplifier circuit 22, and the detection unit 23. This allows the current generated by the light receiving element 12 to be converted into a voltage signal and then amplified, resulting in a voltage signal that is resistant to noise. The DC component is then removed by the elimination circuit 21, and the signal is further amplified by the second amplifier circuit 22, allowing for accurate detection of minute changes in the reflected light received by the light receiving element 12. This allows for accurate detection of minute changes in the light reflected by the blood of the living body, thereby enabling accurate detection of the living body's pulse wave.

[0060] [Embodiment 2] Other embodiments of the present disclosure will be described below. For convenience of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0061] The configuration of the main parts of a pulse wave detection system 1A according to this embodiment is shown in Fig. 10. Fig. 10 is a functional block diagram showing the configuration of the main parts of the pulse wave detection system 1A. In addition to the configuration of the pulse wave detection system 1 according to the first embodiment described above, the pulse wave detection system 1A includes a selection unit 25 on the second substrate 20.

[0062] The selector 25 acquires voltage signals output from the first amplifier circuits 14 for each of the plurality of light receiving elements 12 and selects, from the acquired voltage signals, voltage signals whose fluctuations in AC components satisfy a predetermined condition. At this time, the selector 25 may select voltage signals whose fluctuations in AC components during a predetermined time period before selection satisfy the predetermined condition. Examples of the predetermined condition include a condition that the fluctuation amount of the AC component is greater than a threshold value, or a condition that the fluctuation amount of the AC component is maximum. Specifically, the selector 25 may select voltage signals whose fluctuation amount of the AC component during a predetermined time period before selection is greater than a threshold value. Alternatively, the selector 25 may select voltage signals whose fluctuation amount of the AC component during a predetermined time period before selection is maximum. Here, "maximum fluctuation amount of the AC component" may mean that the fluctuation amount of the AC component is greater than the fluctuation amounts of the AC components of other voltage signals.

[0063] Then, elimination circuit 21 removes at least a portion of the DC component from the voltage signal selected by selection unit 25. Thereafter, second amplifier circuit 22 amplifies the voltage signal from which at least a portion of the DC component has been removed by elimination circuit 21. Detection unit 23 uses the voltage signal amplified by second amplifier circuit 22 to detect the pulse wave.

[0064] In this way, by performing processing on second substrate 20 only on the voltage signal selected by selector 25, it is possible to reduce the amount of processing or the number of removal circuits 21 and second amplifier circuits 22. Furthermore, by selector 25 selecting a voltage signal whose AC component fluctuation amount is greater than the threshold value or a voltage signal whose AC component fluctuation amount is the largest, it is possible to improve the accuracy of pulse wave detection.

[0065] Furthermore, when the element control unit 24 causes the light-emitting element 11 to emit light intermittently, the selection unit 25 may perform the selection process in synchronization with the light-emitting timing of the light-emitting element 11. That is, the selection unit 25 may receive a signal indicating the light-emitting timing of the light-emitting element 11 from the element control unit 24, and perform the selection process in synchronization with the light-emitting timing indicated by the signal.

[0066] This prevents the selection unit 25 from performing the selection process at a timing when the light-emitting element 11 is not emitting light and the amount of fluctuation in the AC component of the voltage signal does not properly indicate a pulse wave, thereby enabling the selection unit 25 to select a voltage signal that allows proper pulse wave detection.

[0067] [Software implementation example] The functions of the pulse wave detection system 1 (1A) (hereinafter referred to as the "system") can be realized by a program that causes a computer to function as the system, and that causes a computer to function as each control circuit (conversion circuit 13, first amplifier circuit 14, removal circuit 21, second amplifier circuit 22) and control block (detection unit 23, element control unit 24, selection unit 25) of the system.

[0068] In this case, the system includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0069] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the system. In the latter case, the program may be supplied to the system via any wired or wireless transmission medium.

[0070] In addition, some or all of the functions of each of the control blocks can be realized by logic circuits. For example, integrated circuits in which logic circuits functioning as each of the control blocks are formed are also included in the scope of the present disclosure. In addition, the functions of each of the control circuits and control blocks can be realized by, for example, a quantum computer.

[0071] Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI may run on the control device or on another device (for example, an edge computer or a cloud server).

[0072] 〔summary〕 A pulse wave detection system according to a first aspect of the present disclosure includes a photodetector that receives light including light reflected from a living body, a conversion circuit that converts a current generated by the photodetector into a voltage signal, a first amplifier circuit that amplifies the voltage signal output from the conversion circuit, a removal circuit that removes at least a portion of the DC component of the voltage signal amplified by the first amplifier circuit, a second amplifier circuit that amplifies the voltage signal from which at least a portion of the DC component has been removed in the removal circuit, and a detection unit that detects the pulse wave of the living body using the output of the second amplifier circuit.

[0073] According to the above configuration, the current generated by the light receiving element is converted into a voltage signal and then amplified, resulting in a voltage signal that is resistant to noise. The DC component is then removed and the signal is further amplified, allowing for accurate detection of minute changes in the light reflected by the living body. This allows for accurate detection of minute changes in the light reflected by the blood of the living body, enabling accurate detection of the living body's pulse wave.

[0074] A pulse wave detection system according to a second aspect of the present disclosure is similar to the first aspect, except that the distance between the light receiving element and the first amplifier circuit is shorter than the distance between the first amplifier circuit and the second amplifier circuit. This configuration allows the signal output from the light receiving element to travel a long distance while being made more resistant to noise by the first amplifier circuit.

[0075] A pulse wave detection system according to a third aspect of the present disclosure is the same as that of the first or second aspect, except that the light receiving element, the conversion circuit, and the first amplifier circuit are provided on a first board, and the second amplifier circuit is provided on a second board different from the first board. This configuration allows the first board to generate a highly noise-resistant signal with a minimal configuration and transmit it to the second board. This allows for greater design freedom, such as by positioning the first board near a blood vessel and the second board at a desired location.

[0076] A pulse wave detection system according to Aspect 4 of the present disclosure is the pulse wave detection system of any one of Aspects 1 to 3, wherein the first substrate is a flexible printed circuit board. With this configuration, the first substrate can be easily placed near a blood vessel of a living body, making the pulse wave detection device wearable.

[0077] A pulse wave detection system according to aspect 5 of the present disclosure is any one of aspects 1 to 4, in which the light receiving element is multiple and the conversion circuit is provided for each light receiving element. According to this configuration, a current-voltage conversion circuit is provided for each light receiving element, so that the voltage conversion circuits can be disposed near each light receiving element. This allows the signal from the light receiving element to be converted to a voltage before being affected by noise, etc.

[0078] A pulse wave detection system according to a sixth aspect of the present disclosure is any of the first to fifth aspects, wherein the elimination circuit references the minimum value of the AC component of the voltage signal output from the first amplifier circuit during a predetermined time before elimination, and performs the elimination using a value smaller than the minimum value. This configuration allows the DC component to be removed while leaving the AC component (pulse wave component), thereby improving the accuracy of pulse wave detection.

[0079] A pulse wave detection system according to a seventh aspect of the present disclosure is any one of the first to sixth aspects, wherein the light-receiving elements include a plurality of light-receiving elements, and the system includes a selector that acquires voltage signals output from the first amplifier circuits for each light-receiving element and selects, from the acquired voltage signals, voltage signals whose AC component fluctuations satisfy a predetermined condition, and the elimination circuit and the second amplifier circuit process the voltage signals selected by the selector. This configuration can reduce the number of elimination circuits and second amplifier circuits or the amount of processing. Furthermore, since a voltage signal whose AC component fluctuations, which indicates a pulse wave, are greater than a threshold, the accuracy of pulse wave detection can be improved.

[0080] A pulse wave detection system according to an eighth aspect of the present disclosure is the same as in the seventh aspect, wherein the selector selects the voltage signal with the largest fluctuation in AC component from among the acquired voltage signals. This configuration can reduce the number of removal circuits and second amplifier circuits, or the amount of processing. Furthermore, since the voltage signal with the largest fluctuation in AC component indicating the pulse wave is used, the accuracy of pulse wave detection can be improved.

[0081] A pulse wave detection system according to a ninth aspect of the present disclosure is the same as in the seventh or eighth aspect, further comprising a light-emitting element that emits light toward the living body, and the selector performs the selection at the timing when the light-emitting element emits light intermittently. With this configuration, the selection process is not performed when the light-emitting element is not emitting light and the amount of fluctuation in the AC component of the voltage signal does not properly indicate a pulse wave. Therefore, a voltage signal that can properly detect a pulse wave can be selected.

[0082] A pulse wave detection system according to aspect 10 of the present disclosure is any one of aspects 1 to 9, further comprising a light emitting element that emits light toward the living body. With this configuration, the pulse wave can be detected using light that is emitted from the system toward the living body and reflected by the living body.

[0083] A pulse wave detection system according to an eleventh aspect of the present disclosure is similar to the tenth aspect, except that the light-emitting elements are multiple and each emits light at a different timing. This configuration allows the system to determine whether the light received by the light-receiving element is emitted from a desired light-emitting element. This allows the system to detect and determine only the light emitted from the desired light-emitting element.

[0084] A pulse wave detection system according to a twelfth aspect of the present disclosure is the same as that of the tenth or eleventh aspect, in which the light receiving elements are arranged in a first straight line, and the light emitting elements are arranged in a second straight line different from the first straight line. This configuration allows the light receiving elements to be arranged with a narrower gap between them.

[0085] A pulse wave detection system according to aspect 13 of the present disclosure is any of aspects 10 to 12, wherein the light receiving elements are multiple and arranged on a first line, the light emitting elements are multiple and arranged on second and third lines different from the first line, and the first line is located between the second and third lines. With this configuration, the light emitting elements are arranged to sandwich the light receiving elements, so that light from the light emitting elements can be efficiently received by the light receiving elements.

[0086] A pulse wave detection system according to a fourteenth aspect of the present disclosure is any one of the tenth to thirteenth aspects, in which the light receiving elements are plural and arranged on a first straight line, the light emitting elements are plural and arranged so that one light receiving element is sandwiched between the light receiving element, and the light emitting elements are arranged in a direction different from the direction perpendicular to the first straight line of the light receiving elements. With this configuration, the number of combinations of light receiving elements and light emitting elements can be reduced, and a wider range can be measured.

[0087] A pulse wave detection system according to a fifteenth aspect of the present disclosure is the same as that of the fourteenth aspect, except that the conversion circuit and the first amplifier circuit are arranged in a direction perpendicular to the first straight line of the light receiving element. This configuration allows the current-voltage conversion circuit and the first amplifier circuit to be arranged near the light receiving element, and reduces the installation space.

[0088] A pulse wave detection system according to a sixteenth aspect of the present disclosure is any one of the tenth to fifteenth aspects, wherein the light receiving element is disposed in a first recess provided in a first substrate, and the light emitting element is disposed in a second recess provided within the first recess. This configuration reduces the risk that light emitted from the light emitting element will be directly received by the light receiving element.

[0089] A pulse wave detection system according to a seventeenth aspect of the present disclosure is any one of the tenth to sixteenth aspects, wherein the optical axis of the light-emitting element is tilted toward the light-receiving element. With this configuration, the light emitted from the light-emitting element can be efficiently received by the light-receiving element.

[0090] A pulse wave detection system according to an eighteenth aspect of the present disclosure is any one of the tenth to seventeenth aspects, wherein the light emitting element has a wall around it in a direction different from the light emitting direction, and the wall has a reflective material that reflects light. With this configuration, the light emitted from the light emitting element can be efficiently irradiated onto the living body.

[0091] A pulse wave detection device according to aspect 19 of the present disclosure includes a photodetector that receives light including light reflected from a living body, a conversion circuit that converts the current generated by the photodetector into a voltage signal, a first amplifier circuit that amplifies the voltage signal output from the conversion circuit, a removal circuit that removes at least a portion of the DC component of the voltage signal amplified by the first amplifier circuit, a second amplifier circuit that amplifies the voltage signal from which at least a portion of the DC component has been removed by the removal circuit, and a detection unit that detects the pulse wave of the living body using the output of the second amplifier circuit.

[0092] A pulse wave detection method according to aspect 20 of the present disclosure includes a conversion step of converting a current generated in a light receiving element that receives light including reflected light reflected from a living body into a voltage signal, a first amplification step of amplifying the voltage signal converted in the conversion step, a removal step of removing at least a portion of the DC component of the voltage signal amplified in the first amplification step, a second amplification step of amplifying the voltage signal from which at least a portion of the DC component has been removed in the removal step, and a detection step of detecting the pulse wave of the living body using the voltage signal amplified in the second amplification step.

[0093] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0094] 1. Pulse wave detection system 10 First board 11 Light-emitting element 12 Photodetector 13 Conversion circuit 14 First amplifier circuit 20 Second board 21 Elimination circuit 22 Second amplifier circuit 23 Detection unit 24 Element control unit 25 Selection section

Claims

1. a light receiving element that receives light including light reflected by a living body; a conversion circuit that converts the current generated by the light receiving element into a voltage signal; a first amplifier circuit that amplifies the voltage signal output from the conversion circuit; a removal circuit that removes at least a portion of the DC component of the voltage signal amplified by the first amplifier circuit; a second amplifier circuit that amplifies the voltage signal from which at least a portion of the DC component has been removed in the removal circuit; a detection unit that detects a pulse wave of the living body using the output of the second amplifier circuit.

2. The pulse wave detection system according to claim 1 , wherein the distance between the light receiving element and the first amplifier circuit is shorter than the distance between the first amplifier circuit and the second amplifier circuit.

3. the light receiving element, the conversion circuit, and the first amplifier circuit are provided on a first substrate; The pulse wave detection system according to claim 1 , wherein the second amplifier circuit is provided on a second board different from the first board.

4. The pulse wave detection system according to claim 3 , wherein the first substrate is a flexible printed circuit board.

5. the light receiving element is a plurality of elements, The pulse wave detection system according to claim 1 , wherein the conversion circuit is provided for each of the light receiving elements.

6. 2. The pulse wave detection system according to claim 1, wherein the elimination circuit references a minimum value of the AC component of the voltage signal output from the first amplifier circuit during a predetermined time before elimination, and performs the elimination using a value smaller than the minimum value.

7. the light receiving element is a plurality of elements, a selector for acquiring a voltage signal output from the first amplifier circuit for each of the light receiving elements and selecting, from among the acquired voltage signals, a voltage signal whose fluctuation in AC component satisfies a predetermined condition; The pulse wave detection system according to claim 1 , wherein the removal circuit and the second amplifier circuit perform processing on the voltage signal selected by the selector.

8. The pulse wave detection system according to claim 7 , wherein the selector selects the voltage signal with the greatest amount of fluctuation in AC component from among the acquired voltage signals.

9. Further comprising a light emitting element that emits light toward the living body, The pulse wave detection system according to claim 8 , wherein the selection unit performs the selection at the timing of light emission when the light emitting element emits light intermittently.

10. The pulse wave detection system according to claim 1 , further comprising a light emitting element that emits light toward the living body.

11. The pulse wave detection system according to claim 10 , wherein the light emitting element is a plurality of elements, and each of the light emitting elements emits light at a different timing.

12. The light receiving elements are plural and arranged on a first straight line, The light-emitting elements are plural and are arranged on a second straight line different from the first straight line. The pulse wave detection system according to claim 10.

13. The light receiving elements are plural and arranged on a first straight line, a plurality of the light-emitting elements are arranged on a second straight line and a third straight line different from the first straight line; The pulse wave detection system according to claim 10 , wherein the first straight line is located between the second straight line and the third straight line.

14. The light receiving elements are plural and arranged on a first straight line, The light-emitting element is a plurality of light-emitting elements, and the plurality of light-emitting elements are arranged for one light-receiving element so as to sandwich the light-receiving element, The pulse wave detection system according to claim 10 , wherein the light emitting element is arranged in a direction different from a direction perpendicular to the first straight line of the light receiving element.

15. The pulse wave detection system according to claim 14 , wherein the conversion circuit and the first amplifier circuit are arranged in a direction perpendicular to the first straight line of the light receiving element.

16. the light receiving element is disposed in a first recess provided in a first substrate; The pulse wave detection system according to claim 10 , wherein the light emitting element is disposed in a second recess provided within the first recess.

17. The pulse wave detection system according to claim 10 , wherein the optical axis of the light-emitting element is tilted toward the light-receiving element.

18. The pulse wave detection system according to claim 10 , wherein the light emitting element has a wall on a periphery opposite to the light emitting direction, the wall having a reflective material for reflecting light.

19. a light receiving element that receives light including light reflected by a living body; a conversion circuit that converts the current generated by the light receiving element into a voltage signal; a first amplifier circuit that amplifies the voltage signal output from the conversion circuit; a removal circuit that removes at least a portion of the DC component of the voltage signal amplified by the first amplifier circuit; a second amplifier circuit that amplifies the voltage signal from which at least a portion of the DC component has been removed by the removal circuit; a detection unit that detects the pulse wave of the living body using the output of the second amplifier circuit.

20. a conversion step of converting a current generated by a light receiving element that receives light including light reflected by a living body into a voltage signal; a first amplification step of amplifying the voltage signal converted in the conversion step; a removing step of removing at least a part of the DC component of the voltage signal amplified in the first amplifying step; a second amplifying step of amplifying the voltage signal from which at least a portion of the DC component has been removed in the removing step; a detecting step of detecting a pulse wave of the living body using the voltage signal amplified in the second amplifying step.

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