WO2019237281A1

WO2019237281A1 - Ppg sensor, smart watch or bracelet

Info

Publication number: WO2019237281A1
Application number: PCT/CN2018/091071
Authority: WO
Inventors: 席毅; 孙士友; 贺彦国; 杨荣广
Original assignee: 华为技术有限公司
Priority date: 2018-06-13
Filing date: 2018-06-13
Publication date: 2019-12-19
Also published as: CN110913757B; CN110913757A

Abstract

Disclosed is a PPG sensor. The PPG comprises a first PD, a first LED and a second LED, wherein the distance between the first PD and the first LED is not equal to the distance between the first PD and the second LED. Thus, in the PPG sensor, two distances of different sizes between the PD and the LEDs can be formed. The two different distances between the PD and the LEDs can meet the requirements for the distances between the PD and the LEDs in different application scenarios, specifically, the PPG sensor can meet four application requirements: static heart rate measurement, dynamic heart rate measurement, wearing tightness detection and blood oxygen measurement. On this basis, further provided is a smart watch or a bracelet comprising the PPG sensor.

Description

A PPG sensor, smart watch or bracelet

Technical field

The present application relates to the field of wearable devices, and in particular, to a PPG (Photoplethysmograph) sensor and a smart watch or bracelet including the PPG sensor.

Background technique

PPG uses photoelectric plethysmography to detect human physiological parameters and is used in biomedicine.

PPG sensors include PD (photodiode, photodiode) and LED (Light Emitting Diode, light emitting diode), which include two types of transmission and reflection. PPG sensors applied to wearable devices are usually reflective. The working principle of the reflective PPG sensor is as follows: After the light emitted by the LED is reflected by the human blood and tissue, the PD receives the light reflected from the human blood and tissue, and detects the difference in the intensity of the reflected light absorbed by the human blood and tissue. To trace human physiological parameters.

With the development of smart watches or bracelets, PPG technology has become a standard feature of smart watches or bracelets. At present, PPG has the following applications on smart watches or bracelets: static heart rate measurement, dynamic heart rate measurement, wearing tightness detection, and blood oxygen measurement.

However, the above four different applications have different requirements for the layout of PD and LED. For example, the static heart rate measurement requires a small distance between PD and LED, while the tightness detection and blood oxygen measurement require a large distance between PD and LED, and The dynamic heart rate measurement requires that the distance between the PD and the LED be both large and small.

In the existing PPG sensors, the layout of PD and LED cannot meet the above four application requirements.

Summary of the Invention

In view of this, the first aspect of the present application provides a PPG sensor, so that the layout of the PD and LED can take into account the multiple application requirements of PPG on a smart watch or bracelet.

Based on the first aspect of the present application, the second aspect of the present application provides a smart watch or bracelet including the PPG sensor.

In order to solve the above technical problems, this application adopts the following technical solutions:

A first aspect of the present application provides a PPG sensor, including: a first PD, a first LED, and a second LED, wherein a distance between the first PD and the first LED and the first PD The distance from the second LED is not equal.

In the PPG sensor provided in the first aspect of the present application, a distance between two PDs and LEDs of different sizes can be formed. The distance between the two different PDs and LEDs can meet the requirements for the distance between PDs and LEDs in different application scenarios. For example, you can measure the static heart rate by measuring the reflected light intensity between a PD and an LED with a small distance, and you can wear a smart watch or bracelet by measuring the reflected light intensity between a PD and an LED with a large distance. Tightness detection and blood oxygen measurement can be used to measure the dynamic heart rate by measuring the reflected light intensity between the two different sizes of PD and LED. Therefore, the layout of the PD and the LED in the PPG sensor provided in the embodiment of the present application can meet the four application requirements of static heart rate measurement, dynamic heart rate measurement, wearing tightness detection, and blood oxygen measurement.

Based on the first aspect of the present application, in a first possible implementation manner, the first PD, the first LED, and the second LED are located on a straight line.

Based on the first aspect of the present application, in a second possible implementation manner, the first PD, the first LED, and the second LED are not on a straight line.

In a second possible implementation manner based on the first aspect of the present application, in a third possible implementation manner, the PPG sensor further includes a second PD, and the second PD and the first PD are distributed between The first PD, the second PD, and the first LED have the same distance on both sides of the straight line where the first LED and the second LED are located, and the first PD and the second PD The distance to the second LED is equal. A third possible implementation manner can improve the accuracy of PPG in measuring human physiological parameters and the tightness of the device.

In a third possible implementation manner based on the first aspect of the present application, in a fourth possible implementation manner, the layouts of the first PD, the first LED, the second LED, and the second PD are rectangular And the first PD, the first LED, the second LED, and the second PD are distributed on vertices of a rectangle.

In a second possible implementation manner based on the first aspect of the present application, in a fifth possible implementation manner, the PPG sensor further includes a third LED and a second PD,

The third LED is located on an extension line connecting the second LED and the first LED, and a distance between the first PD and the second LED is equal to the first PD and the third LED the distance between;

The second PD is located at a position where the first PD is symmetrical with respect to a connection line between the first LED and the second LED.

The fifth possible implementation manner can further improve the accuracy of the PPG in measuring the physiological parameters of the human body and the tightness of the device.

In a fifth possible implementation manner based on the first aspect of the present application, in a sixth possible implementation manner, the layouts of the first PD, the second LED, the third LED, and the second PD are parallel A quadrangle, and the first PD, the second LED, the first LED, and the second PD are distributed on vertices of a parallelogram.

In a sixth possible implementation manner based on the first aspect of the present application, in a seventh possible implementation manner, the parallelogram is a square or a rhombus.

Based on the first aspect of the present application and any one of the foregoing possible implementation manners, in an eighth possible implementation manner, the first LED and the second LED can emit green light, red light, and infrared light At least one kind of light.

In a sixth or seventh possible implementation manner based on the first aspect of the present application, in a ninth possible implementation manner, the third LED can emit at least one of green light, red light, and infrared light Kind of light.

A second aspect of the present application provides a smart watch or bracelet, which includes a body and a wearing belt, wherein a PPG sensor is provided in the body, and the PPG sensor is the PPG sensor according to any one of claims 1-10. .

The effect of the smart watch or bracelet provided in the second aspect of the application corresponds to the PPG sensor provided in the first aspect described above.

Compared with the prior art, the present application has the following beneficial effects:

Based on the above technical solutions, it can be known that the PPG sensor provided in this application includes a first PD, a first LED, and a second LED, wherein a distance between the first PD and the first LED and a distance between the first PD and the second LED The distance varies. In this way, in this PPG sensor, the distance between two PDs and LEDs of different sizes can be formed. The distance between the two different PDs and LEDs can meet the requirements for the distance between PDs and LEDs in different application scenarios. For example, you can measure the static heart rate by measuring the reflected light intensity between a PD and an LED with a small distance, and you can wear a smart watch or bracelet by measuring the reflected light intensity between a PD and an LED with a large distance. Tightness detection and blood oxygen measurement can be used to measure the dynamic heart rate by measuring the reflected light intensity between the two different sizes of PD and LED. Therefore, the layout of the PD and the LED in the PPG sensor provided in the embodiment of the present application can meet the four application requirements of static heart rate measurement, dynamic heart rate measurement, wearing tightness detection, and blood oxygen measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic diagram of a PD and LED layout structure in a PPG sensor in the prior art;

2 is a schematic diagram of a PD and LED layout structure in another PPG sensor in the prior art;

FIG. 3 is a schematic diagram of a tightness detection principle provided by an embodiment of the present application; FIG.

4 to 7 are schematic diagrams of a PD and LED layout structure in a PPG sensor according to an embodiment of the present application;

8 is a schematic diagram of a layout structure of PDs and LEDs in another PPG sensor according to an embodiment of the present application;

FIG. 9 is a schematic diagram of a layout structure of PDs and LEDs in another PPG sensor according to an embodiment of the present application.

detailed description

In an existing PPG sensor, the layout of the PD and LED inside is shown in FIG. 1. The PPG sensor includes one PD 11 and three LEDs 12-14. Among them, PD 11 is located in the middle, and LEDs 12-14 are placed on three sides of the PD. The distance between the three LEDs 12-14 and PD 11 is equal. The PPG sensor can only measure static heart rate and dynamic heart rate when tightly worn. If you measure the dynamic heart rate when wearing loose, the accuracy of the dynamic heart rate will be seriously reduced.

In another existing PPG sensor, the layout of the internal PD and LED is shown in Figure 2. The PPG sensor includes a three-in-one LED 21 in the middle and three PDs 22-24 on the three sides of the LED 21. The distances between the three PDs 22-24 and the LED 21 are equal. The cost of PD is usually more than twice the cost of LEDs. Therefore, the use of 3 PDs in this PPG sensor will lead to a higher cost of the whole machine, and the PPG sensor is used for blood oxygen measurement and dynamic heart rate measurement when loosely worn. Are less accurate. Among them, the three-in-one LED 21 is an LED device capable of emitting green, red, and infrared light.

It can be known from the above that the existing PPG sensors cannot be compatible with the four application requirements of static heart rate, dynamic heart rate (in the tightly worn state and the loosely worn state), wearing tightness detection, and blood oxygen detection.

In order to make the PPG sensor compatible with the four application requirements of static heart rate, dynamic heart rate (tight fit, loose fit), tight fit detection, and blood oxygen detection, a PPG sensor is provided in this application. The PPG sensor can be compatible with four application requirements: static heart rate, dynamic heart rate (in the tightly worn state and in the loosely worn state), wearing tightness detection, and blood oxygen detection.

Before introducing the PPG sensor provided in this application, the working principle of the PPG system is first introduced.

The PPG system uses the light reflected from human tissue received by the PD to detect functions such as blood oxygen or heart rate. Most of the reflected light is direct current (DC), and a small part is an alternating current (AC) signal due to pulse pulses. The composition of the DC signal is complex, with both external ambient light and reflected light from the skin and tissues. In fact, AC signals are the key signals used to detect blood oxygen or heart rate. Therefore, how to obtain a larger AC signal and increase the ratio of the AC signal to the DC signal is an important factor in system design. The study found that as the distance between PD and LED increases, the AC / DC ratio of each wavelength (called the modulation depth) also increases. In short, the larger the distance between the PD and the LED, the easier it is to obtain an effective AC signal.

However, the greater the distance between the PD and the LED, the more the skin absorbs light. Studies have shown that the light efficiency increases exponentially with the distance between the LED and the PD. In order to control power consumption, the distance between the LED and the PD needs to be reduced.

In summary, in order to obtain an effective AC signal and reduce power consumption, a reasonable distance between the PD and the LED needs to be selected.

In addition, the present application also studies the distance between the PD and the LED required by the above four applications. The findings are as follows:

1. Static heart rate measurement:

Only pay attention to the AC component in the PPG signal, and require the AC to be as large as possible. Studies have shown that green light (525nm) has a high absorption rate in the skin. Green light loss increases exponentially with the distance between PD and LED. In order to reduce power consumption, the distance between PD and LED is required to be as close as possible.

2. Dynamic heart rate measurement:

Motion noise in dynamic heart rate is very high. Using a single optical path, it is difficult to eliminate motion noise. Multiple signals are needed for blind source analysis. Therefore, in order to achieve dynamic heart rate measurement, the distance between PD and LED is required to be close.

3. Wear tightness detection:

As shown in Figure 3, when the user wears a watch / band, the signal between LED2-LED3 will be different and the signal between LED1-LED4 will be different when the watch is loose. The distance between the two LEDs and the skin is also larger, the difference between the signals is larger, and the feature values are easy to extract. Therefore, in order to detect the wearing tightness of a smart watch / band, the distance between the PD and the LED is required to be long.

4, blood oxygen measurement:

Requires a higher perfusion rate (AC / DC), requires light to penetrate deeper into the skin, and the layout requires that the distance from the LED to the PD be as far as possible.

Based on the above research results, we know that in order to make PPG compatible with the above four application requirements, the distance between the PD and the LED must be large and small. Based on this, this application provides a PPG sensor. The PPG sensor includes a first PD, a first LED, and a second LED. The distance between the first PD and the first LED and the first PD and the second LED. The distance varies. In this way, in this PPG sensor, the distance between two PDs and LEDs of different sizes can be formed. The distance between the two different PDs and LEDs can meet the requirements for the distance between PDs and LEDs in different application scenarios. For example, you can measure the static heart rate by measuring the reflected light intensity between a PD and an LED with a small distance, and you can wear a smart watch or bracelet by measuring the reflected light intensity between a PD and an LED with a large distance. Tightness detection and blood oxygen measurement can be used to measure the dynamic heart rate by measuring the reflected light intensity between the two different sizes of PD and LED. Therefore, the layout of the PD and the LED in the PPG sensor provided in the embodiment of the present application can meet the four application requirements of static heart rate measurement, dynamic heart rate measurement, wearing tightness detection, and blood oxygen measurement.

The specific implementation of the PPG sensor provided in the embodiments of the present application will be described in detail below with reference to the drawings.

It should be noted that, in the embodiment of the present application, the outline of the PPG sensor is described using a circle as an example. In fact, the outline of the PPG sensor can also be other shapes such as ellipse, strip, and the like.

Referring to FIG. 4, a PPG sensor provided by an embodiment of the present application includes a first PD 41, a first LED 42 and a second LED 43. The distance d1 between the first PD 41 and the first LED 42 and the first LED 42 The distance d2 between one PD 41 and the second LED 43 is not equal. As an example, d1 <d2.

In FIG. 4, the first PD 41, the first LED 42 and the second LED 43 are arranged laterally and are located on a straight line. As another optional implementation manner of the present application, as shown in FIG. 5, the first PD 41, the first LED 42 and the second LED 43 may also be arranged vertically and located on a straight line.

As another optional implementation manner of the present application, as shown in FIG. 6, the first PD 41, the first LED 42 and the second LED 43 may not be located on the same straight line. As a more specific example of the present application, as shown in FIG. 7, the layout of the first PD 41, the first LED 42 and the second LED 43 has a triangular distribution. As a more specific example, the layout of the three may be a right-angled triangle, where The first PD 41 is located on the right-angle vertex, and the lengths of the two right-angle sides are not equal.

In the embodiment of the present application, the first LED 42 and the second LED 43 may be LED devices capable of emitting at least one of green light (G), red light (R), and infrared light (IR). In order to make the light intensity meet the above four application requirements, as an optional method, the first LED 42 and the second LED 43 may be a green light (G) LED device, a green light and infrared light two-in-one LED device, and red light. Any one of a two-in-one LED device, green light, and red light (a three-in-one LED device that is infrared light).

In the PPG sensor shown in FIG. 4 to FIG. 7, in order to control the power consumption of the PPG, a path between the first PD 41 and the first LED 42 with a short distance can be used to measure the static heart rate.

The first PD 41, the second LED 42 and the second LED 43 are used for dynamic heart rate measurement. When the first LED 42 and the second LED 43 are three-in-one (G, R, and IR) LED devices, three short-distance light paths can be formed between the first PD 41 and the first LED 42. The first PD Three long-distance light paths can be formed between 41 and the second LED 43. Using these 6 light paths can effectively remove motion noise and achieve accurate measurement of dynamic heart rate.

The first PD 41 and the second LED 43 with a long distance are used to achieve tightness detection and blood oxygen detection.

The foregoing is a specific implementation manner of a PPG sensor provided by an embodiment of the present application. In this specific implementation, the distance between two PDs and LEDs of different sizes can be formed. The distance between the two different PDs and LEDs can meet the requirements for the distance between PDs and LEDs in different application scenarios. For example, the static heart rate can be detected by measuring the reflected light intensity between the first PD 41 and the first LED 42 with a small distance, and the distance between the first PD 41 and the second LED 42 with a large distance can be measured. The reflected light intensity realizes the tightness detection and blood oxygen measurement of the smart watch or bracelet. By measuring the reflected light intensity between the first PD 41 and the first LED 42 and the second LED 43, the dynamic heart rate can be detected. Therefore, the layout of the PD and the LED in the PPG sensor provided in the embodiment of the present application can meet the four application requirements of static heart rate measurement, dynamic heart rate measurement, wearing tightness detection, and blood oxygen measurement.

In order to improve the accuracy of the measurement results, the embodiment of the present application also provides another implementation manner of the PPG sensor. It should be noted that another implementation manner of the PPG sensor is improved based on the PPG sensor shown in FIG. 7.

Referring to FIG. 8, another implementation manner of the PPG sensor provided in the embodiment of the present application may include a first PD 41, a first LED 42 and a second LED 43, and may further include a second PD 81,

The second PD 81 and the first PD 41 are distributed on both sides of the straight line where the first LED 42 and the second LED 43 are located, and the distances between the first PD 41, the second PD 81, and the first LED 42 are equal. For a distance d1, the distances between the first PD 41, the second PD 81, and the second LED 42 are equal, and is set to a second distance d2, where d1 <d2. The layout of the PDs and LEDs in the PPG sensor can also be understood as: the distributions of the first PD 41, the first LED 42 and the second LED 43, and the second PD 81 in the PPG are parallelograms. The first PD 41, the first LED 42 and the second LED 43 and the second PD 81 are distributed on the vertices of the parallelogram.

As a specific example of the present application, the layouts of the first PD 41, the first LED 42, the second LED 43 and the second PD 81 are rectangular, wherein the first PD 41, the first LED 42, the second LED 43 and the second PD PD 81 is located on the vertex of the rectangle, and the LED and PD are located on non-adjacent vertices.

In the implementation of the above-mentioned PPG sensor, two PDs are provided. When the LED is a three-in-one LED device, a short-distance path between the six PDs and the LEDs can be formed (ie, the first PD 41 and the first LED 42). 3 paths between the second PD and 81 and the second LED 43) and 6 long-distance paths between the PD and the LED (that is, between the first PD 41 and the second LED 43 3 paths, and 3 paths between the second PD 81 and the first LED 42). In this way, the three paths between the first PD 41 and the first LED 42 and the three paths between the second PD 81 and the second LED 43 can be used to measure the static heart rate to achieve the effect of controlling power consumption. , Using the three pathways between the first PD 41 and the second LED 43 and the three pathways between the second PD 81 and the first LED 42 to achieve tightness detection and blood oxygen detection, and through the above 6 Two short-distance paths and six long-distance paths realize the measurement of dynamic heart rate to improve the accuracy of detection results.

In this way, the measurement of the physiological parameters of a person and the tightness of the wearing of the device by using multiple light intensities can reduce the error of the detection result and improve the accuracy of the detection result.

The above is another specific implementation manner of the PPG sensor provided in the embodiment of the present application. In this specific implementation manner, the static heart rate, dynamic heart rate, tightness of equipment wearing, and blood oxygen can be detected more accurately.

In addition, in order to further improve the accuracy of detecting the physiological parameters and the tightness of the device, this application also provides another implementation manner of the PPG sensor. Referring to FIG. 9, in addition to the first PD 41, the first LED 42 and the second LED 43 shown in FIG. 6, the PPG sensor provided in the embodiment of the present application may further include a second PD 91 and a third LED 92. The third LED 92 is located on an extension line connecting the second LED 43 and the first LED 42, and the distance between the first PD 41 and the second LED 43 is equal to the distance between the first PD 41 and the third LED 92 The second PD 91 is located at a position where the first PD 41 is symmetrical with respect to the connection between the first LED 42 and the second LED 43.

In this way, the distance between the second PD 91 and the first LED 42 is equal to the distance between the first PD 41 and the first LED 42, and the distance between the second PD 91 and the second LED 43 is the same as the first PD 41 and the second The distance between LED 43, the second PD 91 and the third LED 92 are equal to the first PD 41 and the third LED 92, and the distance between the first PD 41 and the second LED 43 and the third LED 92 equal.

Therefore, in the embodiment of the present application, the layouts of the first PD 41, the second LED 43, the second PD 91, and the third LED 92 may be parallelograms with equal sides and sides, and the first LED 42 is located in the parallelogram. center. As an example, the parallelogram may be a rhombus. As another example, the parallelogram may be a square.

In the embodiment of the present application, the third LED 92 can emit at least one of green light, red light, and infrared light. In order to improve the accuracy of the PPG sensor's detection of human physiological parameters and equipment wearing tightness, the third LED 92 can be a three-in-one LED device, that is, an LED device capable of emitting green, red, and infrared light. In order to reduce the cost of the PPG sensor, the third LED 92 may be an LED device that emits green light.

In the PPG device shown in FIG. 8, in order to improve the accuracy of detecting the physiological parameters of the PPG sensor and the wearing tightness of the device, the first LED 42, the second LED 43, and the third LED 92 may be green and red. Light and infrared light three-in-one LED device.

In the PPG sensor shown in FIG. 9, the distance between the first PD 41 and the first LED 42 is equal to the distance between the second PD 91 and the first LED 42, and the distance is the first distance d1. The distances between the first PD 41 and the second PD 91 are equal to the distance between the second LED 43 and the third LED 92, respectively. The distance is set to the second distance d2. According to mathematical knowledge, the first distance d1 is smaller than the second distance. d2. In order to reduce the power consumption of the PPG sensor, the first PD 41, the second PD 71, and the second LED 43 with the smallest distance between the PD and the LED can be used to measure the static heart rate.

In order to reduce motion noise and improve the accuracy of dynamic heart rate measurement, in the embodiment of the present application, the path between each LED and the PD can be fully used to measure the dynamic heart rate.

For example, when the first LED 42, the second LED 43, and the third LED 92 can all be three-in-one LED devices of green, red, and infrared light, 18 light paths can be formed in the PPG sensor, of which 12 There are 6 long-distance paths and 6 short-distance paths. Using these 18 light paths can effectively reduce motion noise and improve the accuracy of dynamic heart rate when loosely worn. It should be noted that in the method for specifically detecting the dynamic heart rate, the PPG will set different weights on the reflected light intensities on the 18 light paths, and then use the weighted average method to calculate the dynamic heart rate.

Among them, the 12 long-distance paths are as follows:

Second LED 43 (G / RED / IR)-first PD 41, 3 long-distance paths;

Second LED 43 (G / RED / IR) —Second PD 91, 3 long-distance paths;

Third LED 92 (G / RED / IR) —the first PD 41, 3 long-distance paths;

Third LED 92 (G / RED / IR) —Second PD 91, 3 long-distance paths.

Among them, in the 12 long-distance paths, the green, red, and infrared light paths of each LED are used.

The six short-distance paths are as follows:

First LED 42 (G / RED / IR) —First PD 41, 3 short-distance paths;

First LED 42 (G / RED / IR) —Second PD 91, 3 short-distance paths.

Among them, in the six long-distance paths, the green, red, and infrared light paths of each LED are utilized.

In addition, in order to improve the accuracy of the device wearing tightness detection, the signal difference between the above 12 long-distance paths can be used to detect the device wearing tightness detection.

In order to effectively extract the blood oxygen signal, the following eight long-distance pathways can be used for blood oxygen test.

Second LED 43 (RED / IR) —First PD 41, 2 long-distance paths;

Second LED 43 (RED / IR) —Second PD 91, 2 long-distance paths;

Third LED 92 (RED / IR) —the first PD 41, 2 long-distance paths;

Third LED 92 (RED / IR) —Second PD 91, 2 long-distance paths.

Among them, in the eight long-distance paths, the red and infrared light paths of each LED are used.

The above is another specific implementation manner of the PPG sensor provided in the embodiment of the present application. In this specific implementation manner, the static heart rate, dynamic heart rate, tightness of equipment wearing, and blood oxygen can be detected more accurately. Moreover, this specific implementation can control PPG power consumption and support 24-hour continuous heart rate testing.

The above is the specific implementation of the PPG sensor provided in the embodiment of the present application. Based on the specific implementation of the PPG sensor, the embodiment of the present application also provides a smart bracelet or watch.

The smart bracelet or watch includes a body and a wearing belt, and a PPG sensor is arranged in the body. The PPG sensor is the PPG sensor described in any one of the above specific implementation manners.

The foregoing is a specific implementation manner of the embodiment of the present application.

Claims

A PPG sensor, comprising: a first PD, a first LED, and a second LED, wherein a distance between the first PD and the first LED and a distance between the first PD and the first LED The distance between the two LEDs is not equal.
The PPG sensor according to claim 1, wherein the first PD, the first LED, and the second LED are located on a straight line.
The PPG sensor according to claim 1, wherein the first PD, the first LED, and the second LED are not on a straight line.
The PPG sensor according to claim 3, wherein the PPG sensor further comprises a second PD, and the second PD and the first PD are distributed on a straight line where the first LED and the second LED are located On both sides, the distances between the first PD, the second PD, and the first LED are equal, and the distances between the first PD, the second PD, and the second LED are equal.
The PPG sensor according to claim 4, wherein the layout of the first PD, the first LED, the second LED, and the second PD is rectangular, and the first PD, the first LED, the first PD, The two LEDs and the second PD are distributed on the vertices of the rectangle.
The PPG sensor according to claim 3, wherein the PPG sensor further comprises: a third LED and a second PD,

The third LED is located on an extension line connecting the second LED and the first LED, and a distance between the first PD and the second LED is equal to the first PD and the third LED the distance between;

The second PD is located at a position where the first PD is symmetrical with respect to a connection line between the first LED and the second LED.
The PPG sensor according to claim 6, wherein the layout of the first PD, the second LED, the third LED, and the second PD is a parallelogram, and the first PD, the second LED, The first LED and the second PD are distributed on vertexes of a parallelogram.
The PPG sensor according to claim 7, wherein the parallelogram is a square or a rhombus.
The PPG sensor according to any one of claims 1 to 8, wherein the first LED and the second LED are capable of emitting at least one of green light, red light, and infrared light.
The PPG sensor according to any one of claims 7-8, wherein the third LED is capable of emitting at least one of green light, red light, and infrared light.
A smart watch or bracelet, comprising: a body and a wearing band, a PPG sensor is disposed in the body, and the PPG sensor is the PPG sensor according to any one of claims 1-10.