Ppg detection circuit and biometric detection system

Abstract

The application discloses a PPG detection circuit and a biological feature detection system. The PPG detection circuit is used to sense the blood oxygen saturation of a to-be-detected object and generate a blood oxygen saturation sensing value and a confidence result. The PPG detection circuit comprises a driver, a light receiver, a sensing data module and a confidence module. The driver is used to drive a light emitter to emit a plurality of light pulses to the to-be-detected object, wherein the plurality of light pulses generate a plurality of reflected light pulses after irradiating the to-be-detected object, and the light receiver receives the plurality of reflected light pulses and generates a first pulse wave signal. The sensing data module is used to obtain the blood oxygen saturation sensing value according to the first pulse wave signal. The confidence module is used to obtain the confidence result according to the first pulse wave signal. The confidence module comprises a feature calculation module and an interval judgment module. The feature calculation module is used to obtain a feature value according to the change of the first pulse wave signal in the time domain. The interval judgment module is used to obtain the confidence result according to the relative size relationship between the feature value and first and second thresholds.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of blood oxygen detection, and particularly relate to a PPG detection circuit and a biological feature detection system. BACKGROUND

[0002] Nowadays, with the popularity of wearable devices such as watches, bracelets, earphones, etc., in addition to basic functions such as counting steps, timing, positioning, etc., wearable devices can also detect biological features of the wearer, such as heart rate, blood oxygen saturation, etc., so as to record physiological feature changes of the wearer and monitor the health status of the wearer in real time.

[0003] When the signal quality is good, the detection accuracy of blood oxygen saturation is relatively high, but the detection result of blood oxygen saturation is still affected by other factors, especially in the wearing state, the pressure between the wearable device and the detection part of the wearer has a great influence on the detection result of blood oxygen saturation. For example, when the wearer wears the wearable device with different tightness, the pressure between the wearable device and the detection part is different, and the detection result of blood oxygen saturation will have a large deviation. SUMMARY

[0004] One of the purposes of the present application is to disclose a PPG detection circuit and a biological feature detection system to improve the accuracy of blood oxygen saturation detection.

[0005] In a first aspect, an embodiment of the present application discloses a PPG detection circuit coupled to a light emitter and a light receiver, for sensing blood oxygen saturation of a to-be-detected object and generating a blood oxygen saturation sensing value and a confidence result corresponding to the blood oxygen saturation sensing value, the PPG detection circuit comprising: a driver for driving the light emitter to emit a plurality of light pulses to the to-be-detected object, wherein the plurality of light pulses generate a plurality of reflected light pulses after irradiating the to-be-detected object, and the light receiver receives the plurality of reflected light pulses and generates a first pulse wave signal; a sensing data module for obtaining the blood oxygen saturation sensing value according to the first pulse wave signal; and a confidence module for obtaining the confidence result according to the first pulse wave signal, wherein the confidence module comprises: a feature calculation module for obtaining a feature value according to the change of the first pulse wave signal in the time domain; and an interval judgment module for obtaining the confidence result according to the relative size relationship between the feature value and first and second threshold values.

[0006] In an optional implementation, when an electronic device in which the PPG detection circuit is located is worn on the to-be-detected object, pressure is applied to blood vessels of the to-be-detected object, and the feature value is related to the size of the pressure.

[0007] In an alternative embodiment, the feature calculation module comprises: a second derivative module for performing second derivative on the first pulse wave signal to generate a second derivative signal; an amplitude extraction module for extracting a negative minimum value of the second derivative signal of the first pulse wave signal as a first amplitude, and extracting a positive maximum value of the second derivative signal of the first pulse wave signal as a second amplitude; and a ratio calculation module for calculating a ratio of the second amplitude to the first amplitude as the feature value.

[0008] In an alternative embodiment, the pressure is positively correlated with the feature value.

[0009] In an alternative embodiment, the feature calculation module further comprises: a band-pass filter module for performing band-pass filtering on the first pulse wave signal to generate a band-pass filtered signal, and the second derivative module performs second derivative on the band-pass filtered signal to generate the second derivative signal.

[0010] In an alternative embodiment, when the feature value is less than the first threshold, the interval judgment module sets the confidence result as a first untrusted level; when the feature value is greater than the first threshold and less than the second threshold, the interval judgment module sets the confidence result as a trusted level; when the feature value is greater than the second threshold, the interval judgment module sets the confidence result as a second untrusted level; wherein the trusted level corresponds to a higher confidence than the first untrusted level, and the first untrusted level corresponds to a higher confidence than the second untrusted level.

[0011] In an alternative embodiment, the driver drives the light emitter to emit the multiple light pulses to the object to be detected, and part of the multiple light pulses have a first wavelength, and the first pulse wave signal is obtained from the multiple light pulses having the first wavelength.

[0012] In an alternative embodiment, the driver drives the light emitter to emit the multiple light pulses to the object to be detected, and part of the multiple light pulses have a second wavelength, and the light receiver receives the multiple reflected light pulses to further generate a second pulse wave signal, and the second pulse wave signal is obtained from the multiple light pulses having the second wavelength.

[0013] In an alternative embodiment, the confidence module further comprises: a signal selection module for selecting at least the first pulse wave signal from the first pulse wave signal and the second pulse wave signal and transmitting to the feature calculation module.

[0014] In an alternative implementation, one of the first wavelength and the second wavelength is 660 nanometers.

[0015] In an alternative implementation, the other of the first wavelength and the second wavelength is 940 nanometers.

[0016] In a second aspect, an embodiment of the present application provides a biological feature detection system, comprising the PPG detection circuit according to the first aspect or any possible implementation of the first aspect, a light emitter, and a light receiver.

[0017] The PPG detection circuit and the biological feature detection system provided by the embodiments of the present application can extract a characteristic value in a pulse wave signal, which can accurately reflect the pressure between a wearable device and a detection part of a wearer, and use the characteristic value to determine whether the tightness of the wearable device worn by the wearer is appropriate when the wearer performs blood oxygen saturation detection by means of the wearable device, and distinguish signals into high-confidence signals and low-confidence signals according to the wearing state, so as to reduce the influence of the tightness of the wearable device on the detection accuracy of the blood oxygen saturation, thereby improving the accuracy of the blood oxygen saturation detection result. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a schematic diagram of an embodiment of a biological feature detection system provided by the present application.

[0019] Figure 2 FIG. 3 is a schematic diagram of an embodiment of a confidence module of a biological feature detection system provided by the present application.

[0020] Figure 3 FIG. 4 is a schematic diagram of an embodiment of a feature calculation module of a confidence module of a biological feature detection system provided by the present application.

[0021] Figure 4 FIG. 5 is a schematic diagram of an embodiment of an electronic device to which the biological feature detection system provided by the present application is applied. DETAILED DESCRIPTION

[0022] When a biological feature detection system measures a pulse period or blood oxygen saturation by using a photoplethysmogram (PPG) method, the system irradiates human skin with light to detect the volume change of blood perfusion in the dermis and subcutaneous tissue. When the volume of blood perfusion changes, the amount of light absorption also changes, and thus a subcutaneous plethysmogram can be obtained from the measured intensity of reflected light to reflect the heart rate or blood oxygen saturation state.

[0023] Generally, when a wearable device integrated with a biometric detection system is worn on a human body, the wearing state will affect the signal quality of the detected biometric signal. For example, when a blood oxygen detection system is worn, the pressure applied by the blood oxygen detection system on the blood vessels (e.g., the pressure of the light path structure position adhering to the skin) will affect the signal quality. In particular, wearable devices are usually worn on the wrist rather than the fingers, but due to the distribution of capillary blood vessels on the wrist is far less rich and uniform than that on the fingers, and in addition, the wearing tightness (i.e., the wearing pressure) of each user's habit is different, so the wearing tightness (i.e., the wearing pressure) will seriously affect the signal quality and signal stability of the biometric signal. Therefore, it is very important to identify the wearing effect of the wearable device for the accuracy judgment of the biometric (such as blood oxygen saturation) detection.

[0024] The present application judges whether the wearing state is suitable through signal processing and algorithm without affecting the appearance of the product, and divides the signal into high-confidence signal and low-confidence signal according to the wearing state. Compared with similar products, it can help to improve the accuracy of wrist blood oxygen saturation detection and reduce the occurrence of pseudo-hypoxia, pseudo-hyperoxia, etc.

[0025] Figure 1 is a functional block diagram of an embodiment of a biometric detection system provided by the present application. The biometric detection system 100 includes a PPG detection circuit 102, a light emitter 104, and a light receiver 106. The PPG detection circuit 102 is coupled to the light emitter 104 and the light receiver 106, for controlling the light emitter 104 and the light receiver 106 to sense the blood oxygen saturation of a to-be-detected object 101 (such as a human wrist), and generate a blood oxygen saturation sensing value SR and a confidence result CR corresponding to the blood oxygen saturation sensing value SR. In some embodiments, the light emitter 104 can include a light source such as a light emitting diode (LED), a laser diode (LD), etc., and the light receiver 106 can include a photoelectric converter such as a photo-diode (PD), a photo-transistor, an avalanche photo-diode, a photomultiplier tube, or a photovoltaic cell, but the present application is not limited thereto.

[0026] The PPG detection circuit 102 comprises a driver 108, a sensing module 110, a confidence module 112, and an application module 114. The driver 108 is configured to send a driving signal TX to drive the light emitter 104 to generate incident light EL to the object 101 to be detected and form reflected light RL with blood oxygen saturation information. The light receiver 106 is configured to sense the reflected light RL to generate a receiving signal RX. In the embodiment, the incident light EL comprises a plurality of light pulses, and the reflected light RL comprises a plurality of reflected light pulses. The light receiver 106 can obtain a pulse wave signal P (included in the receiving signal RX) by sensing the reflected light RL. It should be understood that "a plurality of" in the embodiments of the present application means two or more.

[0027] The sensing data module 110 is configured to obtain a blood oxygen saturation sensing value SR according to the pulse wave signal P. The confidence module 112 is configured to obtain a confidence result CR according to the pulse wave signal P. The confidence result CR is used to represent the reliability of the blood oxygen saturation sensing value SR generated by the sensing data module 110 using the pulse wave signal P. For example, the confidence result CR can be used to assist the application module 114 to determine whether the blood oxygen saturation sensing value SR generated by the sensing data module 110 using the pulse wave signal P is reliable, so that the application module 114 can determine how to convey the blood oxygen saturation sensing value SR to the user based on the confidence result CR. For example, when the confidence result CR is high, the application module 114 directly provides the blood oxygen saturation sensing value SR to the user; when the confidence result CR is not high, the application module 114 provides the blood oxygen saturation sensing value SR to the user while adding a warning; when the confidence result CR is too low, the application module 114 does not provide the blood oxygen saturation sensing value SR to the user, but reminds the user to check whether the biometric detection system 100 is worn correctly. It should be noted that the present application does not limit how to apply the confidence result CR, and Figure 1 The application module 114 in the confidence module 112 can be unnecessary as long as the confidence result CR corresponding to the blood oxygen saturation sensing value SR can be generated, which belongs to the scope of protection of the present application.

[0028] Figure 2A schematic diagram of an embodiment of the confidence module of the biometric detection system provided in the present application is shown in FIG. 2. Specifically, the confidence module 112 includes a signal selection module 202, a feature calculation module 204, and an interval determination module 206. The signal selection module 202 is optional and will be described in more detail later. The feature calculation module 204 is configured to obtain a feature value based on the variation of the pulse wave signal P. In the present embodiment, the feature calculation module 204 obtains the feature value based on the variation of the pulse wave signal P in the time domain. As mentioned above, when the biometric detection system 100 is worn on the subject 101, the light emitter 104 and the light receiver 106 need to be in contact with the skin of the subject 101 and apply pressure to the blood vessels of the subject 101. The feature value calculated by the feature calculation module 204 is related to the magnitude of the pressure. Specifically, the magnitude of the pressure is positively correlated with the feature value.

[0029] For convenience of interpretation, the feature value can be roughly quantified before output. In the present embodiment, the interval determination module 206 is used to determine which interval the feature value falls into among a plurality of preset intervals, so as to give the final confidence result CR. For example, the confidence result CR can be obtained based on the relative size relationship between the feature value and the first threshold value and the second threshold value. Specifically, when the feature value is less than the first threshold value, the interval determination module 206 sets the confidence result CR as a first untrusted level. When the feature value is greater than the first threshold value and less than the second threshold value, the interval determination module 206 sets the confidence result CR as a trusted level. When the feature value is greater than the second threshold value, the interval determination module 206 sets the confidence result CR as a second untrusted level. The trusted level corresponds to a trustworthiness greater than that of the first untrusted level, and the first untrusted level corresponds to a trustworthiness greater than that of the second untrusted level. In some embodiments, the feature value can be directly used as the confidence result CR.

[0030] Figure 3A schematic diagram of an embodiment of a feature calculation module of a confidence module of a biometric detection system provided herein. The feature calculation module 204 comprises a band-pass filter module 302, a second-order differentiation module 304, an amplitude extraction module 306, and a ratio calculation module 308. The band-pass filter module 302 is configured to perform band-pass filtering on the pulse wave signal P to generate a band-pass filtered signal, so as to retain information within a target frequency band, facilitating subsequent operations. However, in some embodiments, the band-pass filter module 302 can be omitted. The second-order differentiation module 304 is configured to perform second-order differentiation on the band-pass filtered signal to generate a second-order differentiated signal. By performing second-order differentiation on the band-pass filtered signal in the time domain, information about the change in the slope of the waveform of the band-pass filtered signal in the time domain can be obtained, which can accurately reflect the pressure on the blood vessels of the user when the user performs blood oxygen detection by wearing the wearable device.

[0031] The amplitude extraction module 306 is configured to extract a feature parameter in the second-order differentiated signal as a feature value. In this embodiment, the amplitude extraction module 306 extracts a negative minimum value of the second-order differentiated signal as a first amplitude, and extracts a positive maximum value of the second-order differentiated signal as a second amplitude. The negative minimum value is the negative value with the largest absolute value. Then, the ratio calculation module 308 calculates the ratio of the second amplitude to the first amplitude as the feature value, because the ratio can be used to accurately determine the pressure on the blood vessels.

[0032] It should be noted that different wavelengths of light irradiated onto the skin of the subject 101 can penetrate to different depths below the skin, and thus the obtained pulse wave signals can have slight differences. In order to improve the sensing effect, the plurality of light pulses in the incident light EL can include light pulses of more than one wavelength, for example, first-type light pulses with a first wavelength and second-type light pulses with a second wavelength, and the received signal RX also correspondingly includes a first pulse wave signal PI sensed from the reflected light pulses of the first-type light pulses, and a second pulse wave signal P2 sensed from the reflected light pulses of the second-type light pulses. For example, the first-type light pulses are red light with a wavelength of 660 nanometers, and the second-type light pulses are infrared light with a wavelength of 940 nanometers. However, it should be noted that the present application is not limited thereto, and in some embodiments, the plurality of light pulses can only include light pulses of one wavelength; in some embodiments, the plurality of light pulses can also include green light, blue light, and / or yellow light.

[0033] When the received signal RX includes a plurality of pulse wave signals corresponding to a plurality of wavelengths, Figure 2The signal selection module 202 shown can be used to select at least one of the pulse wave signals to calculate the confidence result CR. For example, if the received signal RX includes the first pulse wave signal P1 and the second pulse wave signal P2 described above, the signal selection module 202 can select the first pulse wave signal P1 and / or the second pulse wave signal P2 to calculate the confidence result CR.

[0034] The PPG detection circuit 102 provided by the present application can be implemented by a chip, which can be a semiconductor chip implemented by different processes, and the light emitter 104 and the light receiver 106 can be arranged outside the chip where the PPG detection circuit 102 is located. However, the present application is not limited thereto, and in some embodiments, the light emitter 104 and the light receiver 106 can also be arranged in the chip where the PPG detection circuit is located.

[0035] Figure 4 An embodiment of the electronic device 400 including the biometric detection system 100 provided by the present application is shown. Referring to Figure 4 , the electronic device 400 includes the biometric detection system 100. The electronic device 400 can be a wearable electronic device or a mobile electronic device, such as a smart watch, a bracelet, a ring, or any other smart wearable device, or a smart phone, a tablet computer, or a notebook computer, etc.

[0036] In summary, the biometric detection system 100 provided by the present application can determine the conditions of pseudo-hypoxia, pseudo-hyperoxia, etc., and timely remind the user to check whether the wearing condition is normal, so as to avoid the improper tightness of the wearable device when the user wears it for blood oxygen saturation detection, which causes the low detection accuracy of the blood oxygen saturation, and thus helps to improve the accuracy of the blood oxygen saturation detection.

[0037] The terms used in the embodiments of the present application and the appended claims are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. For example, the singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0038] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A PPG detection circuit, characterized in that: The PPG detection circuit is coupled to the optical transmitter and the optical receiver to sense the blood oxygen saturation of the subject to be detected and generate a blood oxygen saturation sensing value and a confidence result corresponding to the blood oxygen saturation sensing value. The PPG detection circuit includes: a driver, configured to drive the light emitter to emit a plurality of light pulses to the object to be detected, wherein the plurality of light pulses generate a plurality of reflected light pulses after irradiating the object to be detected, and the light receiver receives the plurality of reflected light pulses and generates a first pulse wave signal; a sensing data module, configured to obtain the blood oxygen saturation sensing value according to the first pulse wave signal; and A confidence module, configured to obtain the confidence result based on the first pulse wave signal, wherein the confidence module includes: a feature calculation module, configured to obtain a feature value based on a time-domain change of the first pulse wave signal, wherein when the electronic device containing the PPG detection circuit is worn by the subject to be detected, pressure is applied to the blood vessels of the subject to be detected, and the feature value is related to the magnitude of the pressure, wherein the feature calculation module includes: A second-order differential module, configured to perform second-order differential on the first pulse wave signal to generate a second-order differential signal; an amplitude extraction module, configured to extract a negative minimum value of the second-order differential signal of the first pulse wave signal as a first amplitude, and to extract a positive maximum value of the second-order differential signal of the first pulse wave signal as a second amplitude; and a ratio calculation module, configured to calculate a ratio of the second amplitude to the first amplitude as the eigenvalue; and An interval judgment module is used to obtain the confidence result based on the relative size relationship between the characteristic value and the first threshold and the second threshold, wherein when the characteristic value is less than the first threshold, the interval judgment module sets the confidence result to a first untrustworthy level; when the characteristic value is greater than the first threshold and less than the second threshold, the interval judgment module sets the confidence result to a trustworthy level; when the characteristic value is greater than the second threshold, the interval judgment module sets the confidence result to a second untrustworthy level; wherein the credibility corresponding to the trustworthy level is greater than the credibility corresponding to the first untrustworthy level, and the credibility corresponding to the first untrustworthy level is greater than the credibility corresponding to the second untrustworthy level.

2. The PPG detection circuit according to claim 1, wherein: The magnitude of the pressure is positively correlated with the characteristic value.

3. The PPG detection circuit according to claim 1, wherein: The feature calculation module also includes: The bandpass filtering module is configured to perform bandpass filtering on the first pulse wave signal to generate a bandpass filtered signal, and the second-order differential module performs second-order differential on the bandpass filtered signal to generate the second-order differentiated signal.

4. The PPG detection circuit according to claim 1, wherein: Among the multiple light pulses emitted by the driver to the light emitter to the object to be detected, some of the light pulses have a first wavelength, and the first pulse wave signal is obtained from the multiple light pulses with the first wavelength.

5. The PPG detection circuit according to claim 4, wherein: Among the multiple light pulses emitted by the driver driving the light emitter to the object to be detected, some of the light pulses have a second wavelength, and the light receiver receives the multiple reflected light pulses and also generates a second pulse wave signal, which is obtained by the multiple light pulses having the second wavelength.

6. The PPG detection circuit according to claim 5, wherein: The confidence module also includes: A signal selection module is used to select at least the first pulse wave signal from the first pulse wave signal and the second pulse wave signal and transmit the signal to the feature calculation module.

7. The PPG detection circuit according to claim 5, wherein: One of the first wavelength and the second wavelength is 660 nanometers.

8. The PPG detection circuit according to claim 7, wherein: The other of the first wavelength and the second wavelength is 940 nanometers.

9. A biometric detection system, characterized in that: include: The PPG detection circuit according to any one of claims 1 to 8; Light transmitter; as well as Optical receiver.

Images