CN110913757B

CN110913757B - PPG sensor, intelligent watch or bracelet

Info

Publication number: CN110913757B
Application number: CN201880047076.6A
Authority: CN
Inventors: 席毅; 孙士友; 贺彦国; 杨荣广
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2018-06-13
Filing date: 2018-06-13
Publication date: 2021-07-09
Anticipated expiration: 2038-06-13
Also published as: CN110913757A; WO2019237281A1

Abstract

The embodiment of the application discloses PPG sensor, this PPG includes first PD, first LED and second LED, wherein, the distance between first PD and the first LED and the distance between first PD and the second LED are not equal. As such, in the PPG sensor, the distance between two PDs and LEDs of different sizes may be formed. The distance between these two different PDs and LED can satisfy the requirement to distance between PD and the LED under the different application scenes, specifically, this PPG sensor can compromise four kinds of application demands such as static heart rate measurement, dynamic heart rate measurement, wear elasticity detection and blood oxygen measurement. Based on this, this application embodiment still provides a smart watch or bracelet including this PPG sensor.

Description

PPG sensor, intelligent watch or bracelet

Technical Field

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

Background

PPG is used for detecting human physiological parameters by utilizing a photoplethysmography technology and is applied to biomedicine.

PPG sensors include PD (photo Diode) and LED (Light Emitting Diode), which are two types of transmissive and reflective, and are generally reflective for application on wearable devices. The working principle of the reflection type PPG sensor is as follows: the light emitted by the LED is reflected by the blood and the tissue of the human body, and then the PD receives the light reflected by the blood and the tissue of the human body, and the physiological parameters of the human body are traced by detecting the difference of the intensity of the reflected light absorbed by the blood and the tissue of the human body.

With the development of smart watches or bracelets, PPG technology has become the standard matching function of smart watches or bracelets. The current PPG mainly has following application on intelligent wrist-watch or bracelet: static heart rate measurement, dynamic heart rate measurement, wear tightness detection, and blood oxygen measurement.

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

In the existing PPG sensor, the layout of PD and LED cannot meet the above 4 application requirements.

Disclosure of Invention

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

Based on the first aspect of this application, this application's second aspect provides a smart watch or bracelet that contains this PPG sensor.

In order to solve the technical problem, the following technical scheme is adopted in the application:

a first aspect of the application provides a PPG sensor, comprising: the LED light source 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.

In the PPG sensor provided in the first aspect of the present application, the distances between two PDs and LEDs of different sizes may be formed. The distance between the two different PDs and the LED can meet the requirement on the distance between the PD and the LED under different application scenes. For example, the detection of the static heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the smaller distance, the wearing tightness detection and the blood oxygen measurement of the smart watch or the bracelet can be realized by measuring the intensity of the reflected light between the PD and the LED with the larger distance, and the detection of the dynamic heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the two different sizes. Therefore, the layout of PD and LED in the PPG sensor provided by the embodiment of the application can give consideration to four application requirements such as 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, where the second PD and the first PD are distributed on two sides of a straight line where the first LED and the second LED are located, distances between the first PD, the second PD, and the first LED are equal, and distances between the first PD, the second PD, and the second LED are equal. The third possible implementation mode can improve the accuracy of the PPG in measuring the human physiological parameters and the wearing tightness of the equipment.

In a third possible implementation manner based on the first aspect of the present application, in a fourth possible implementation manner, 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 second LED, and the second PD are distributed at the vertex of the 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 positioned on an extension line of a connecting line of the second LED and the first LED, and the distance between the first PD and the second LED is equal to the distance between the first PD and the third LED;

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

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

In a fifth possible implementation manner based on the first aspect of the present application, in a sixth possible implementation manner, 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 a vertex of the 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 at least one of green light, red light, and infrared light.

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

A second aspect of the application provides a smart watch or bracelet, comprising: the novel PPG sensor comprises a machine body and a wearing belt, wherein a PPG sensor is arranged in the machine body, and the PPG sensor is the PPG sensor.

The effect of the smart watch or bracelet that this application second aspect provided corresponds with the PPG sensor that the above-mentioned first aspect provided.

Compared with the prior art, the method has the following beneficial effects:

based on the above technical solution, the PPG sensor provided in the present application includes the first PD, the first LED, and the second LED, wherein a distance between the first PD and the first LED is different from a distance between the first PD and the second LED. As such, in the PPG sensor, the distance between two PDs and LEDs of different sizes may be formed. The distance between the two different PDs and the LED can meet the requirement on the distance between the PD and the LED under different application scenes. For example, the detection of the static heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the smaller distance, the wearing tightness detection and the blood oxygen measurement of the smart watch or the bracelet can be realized by measuring the intensity of the reflected light between the PD and the LED with the larger distance, and the detection of the dynamic heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the two different sizes. Therefore, the layout of PD and LED in the PPG sensor provided by the embodiment of the application can give consideration to four application requirements such as static heart rate measurement, dynamic heart rate measurement, wearing tightness detection and blood oxygen measurement.

Drawings

Fig. 1 is a schematic diagram of a layout structure of PDs and LEDs in a PPG sensor according to the prior art;

fig. 2 is a schematic diagram of another prior art arrangement of PDs and LEDs within a PPG sensor;

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

fig. 4 to 7 are schematic diagrams of layout structures of PDs and LEDs in a PPG sensor provided in an embodiment of the present application;

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

fig. 9 is a schematic diagram of a layout structure of PDs and LEDs in a PPG sensor provided in an embodiment of the present application.

Detailed Description

In a conventional PPG sensor, the layout of the PD and the LEDs inside the sensor is shown in fig. 1. The PPG sensor comprises 1 PD 11 and 3 LEDs 12-14, wherein the PD 11 is in the middle and the LEDs 12-14 are placed on three sides of the PD, respectively. The 3 LEDs 12-14 are all equidistant from the PD 11. The PPG sensor can only enable static heart rate measurements and dynamic heart rate measurements when worn tightly. If the wearing is loose, the accuracy of the dynamic heart rate can be seriously reduced when the dynamic heart rate is measured.

In another conventional PPG sensor, the layout of the PD and the LED inside the sensor is shown in fig. 2. Included in the PPG sensor are 1 triad of LEDs 21 in the middle and three PDs 22-24 on three sides of the LEDs 21. The 3 PDs 22-24 are all equidistant from the LED 21. The cost of PD is usually more than 2 times of the cost of LED, so in the PPG sensor, the use of 3 PDs will result in higher overall cost, and the accuracy of the PPG sensor for blood oxygen measurement and dynamic heart rate measurement when worn loosely is lower. Wherein the three-in-one LEDs 21 are LED devices that can emit green light, red light, and infrared light.

From the above, the existing PPG sensor cannot be compatible with 4 application requirements of static heart rate, dynamic heart rate (in a tight wearing state and a loose wearing state), wearing tightness detection, and blood oxygen detection.

In order to make the PPG sensor can be compatible with these 4 kinds of application demands of static heart rate, dynamic heart rate (tightly wear, loosely wear), wear elasticity detection, blood oxygen detection simultaneously, this application provides a PPG sensor. The PPG sensor can be compatible with 4 application requirements of static heart rate, dynamic heart rate (in a tight wearing state and a loose wearing state), tightness detection during wearing and blood oxygen detection.

Before introducing the PPG sensor provided herein, the working principle of the PPG system is first introduced.

The PPG system uses light received by the PD that is reflected from human tissue to detect blood oxygen or heart rate. The reflected light is mostly Direct Current (DC) and a small part is Alternating Current (AC) signal generated by pulse beat. The direct current signal has complex components, and not only has external ambient light, but also has light reflected by skin, tissues and the like. In fact, the ac signal is the key signal for detecting 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. It has been found that as the distance between the PD and the LED increases, the ac/dc ratio (referred to as the modulation depth) at each wavelength increases. In short, the greater 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 light is absorbed by the skin. Studies have shown that the light efficiency increases with the distance between the LED and the PD, exhibiting an exponential decay. 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 PD-to-LED distance needs to be selected.

In addition, the present application also makes studies on the distance between the PD and the LED required for the above four applications. The results of the study are as follows:

1. static heart rate measurement:

only the AC component of the PPG signal is of interest, requiring as large an AC as possible. Studies have shown high absorption in green (525nm) skin. The green light loss increases exponentially with the distance between the PD and the LED. For power consumption reduction, the distance between the PD and the LED is required to be as close as possible.

2. Dynamic heart rate measurement:

the motion noise in the dynamic heart rate is very high, and the motion noise is difficult to be eliminated completely by using a single light path, so that a plurality of paths of signals are required to be subjected to blind source analysis. Therefore, to achieve dynamic heart rate measurement, the distance between the PD and the LED is required to be far or close.

3. And (3) detecting the wearing tightness:

as shown in fig. 3, when the user wears the watch/bracelet loosely, the signals of the LEDs 2-3 are different, and the signals of the LEDs 1-4 are different; the distance between the LED1 and the LED4 to the PD is far, when the device is inclined, the distance between the two LEDs and the skin is larger, the difference between signals is larger, and the characteristic value is easy to extract. Therefore, for the wearing tightness detection of the smart watch/bracelet, the distance between the PD and the LED is required to be far.

4. Blood oxygen measurement:

higher perfusion rates (AC/DC) are required, light is required to penetrate deeper into the skin, and the LED is required to be as far from the PD as possible in layout.

Based on the above research results, the distance between PD and LED should be large and small in order to make PPG compatible with the above 4 application requirements. Based on this, the application provides a PPG sensor, this PPG sensor includes first PD, first LED and second LED inside, wherein, the distance between first PD and the first LED is different with the distance between first PD and the second LED. As such, in the PPG sensor, the distance between two PDs and LEDs of different sizes may be formed. The distance between the two different PDs and the LED can meet the requirement on the distance between the PD and the LED under different application scenes. For example, the detection of the static heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the smaller distance, the wearing tightness detection and the blood oxygen measurement of the smart watch or the bracelet can be realized by measuring the intensity of the reflected light between the PD and the LED with the larger distance, and the detection of the dynamic heart rate can be realized by measuring the intensity of the reflected light between the PD and the LED with the two different sizes. Therefore, the layout of PD and LED in the PPG sensor provided by the embodiment of the application can give consideration to four application requirements such as static heart rate measurement, dynamic heart rate measurement, wearing tightness detection and blood oxygen measurement.

Specific implementations of the PPG sensor provided in the embodiments of the present application are described in detail below with reference to the accompanying drawings.

Note that in the present embodiment, the outline of the PPG sensor is illustrated by taking a circle as an example. In fact, the outline of the PPG sensor may also be in other shapes, such as an oval shape, a long strip shape, and the like.

Referring to fig. 4, an embodiment of the present application provides a PPG sensor including: a first PD41, a first LED42 and a second LED43, wherein a distance d1 between the first PD41 and the first LED42 is not equal to a distance d2 between the first PD41 and the second LED 43. As an example, d1 < d 2.

In fig. 4, the first PD41, the first LED42, and the second LED43 are arranged laterally and on a straight line. As another alternative implementation of the present application, as shown in fig. 5, the first PD41, the first LED42, and the second LED43 may also be vertically arranged and located on a straight line.

As still another alternative implementation of the present application, as shown in fig. 6, the first PD41, the first LED42, and the second LED43 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 PD41, the first LED42, and the second LED43 is distributed in a triangle, and as a more specific example, the layout of the three may be in a right triangle, where the first PD41 is located at a right-angled vertex and the lengths of the two right-angled sides are not equal.

In the embodiment of the present application, the first LED42 and the second LED43 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 satisfy the above four application requirements, the first LED42 and the second LED43 may be any one of a green light (G) LED device, a green and infrared light two-in-one LED device, a red and infrared light two-in-one LED device, and a green light, a red light (and infrared light three-in-one LED device, as an alternative.

In the PPG sensors shown in fig. 4 to 7, in order to control the power consumption of the PPG, the measurement of the static heart rate may be achieved using the path between the first PD41 and the first LED42, which are at a smaller distance.

Dynamic heart rate measurement is achieved with a first PD41, a second LED42 and a second LED 43. When the first LED42 and the second LED43 are a three-in-one (G, R and IR) LED device, 3 short-distance optical paths may be formed between the first PD41 and the first LED42, and 3 long-distance optical paths may be formed between the first PD41 and the second LED 43. The 6 optical paths can effectively remove motion noise and realize accurate measurement of the dynamic heart rate.

Wearing tightness detection and blood oxygen detection are realized by the first PD41 and the second LED43 which are far away.

The above is a specific implementation manner of the PPG sensor provided in the embodiment of the present application. In this particular implementation, two distances between the PD and the LED of different sizes may be formed. The distance between the two different PDs and the LED can meet the requirement on the distance between the PD and the LED under different application scenes. For example, the detection of the static heart rate may be realized by measuring the intensity of the reflected light between the first PD41 and the first LED42 with a small distance, the wearing tightness detection and blood oxygen measurement of the smart watch or the bracelet may be realized by measuring the intensity of the reflected light between the first PD41 and the second LED42 with a large distance, and the detection of the dynamic heart rate may be realized by measuring the intensities of the reflected light between the first PD41 and the first LED42 and the second LED 43. Therefore, the layout of PD and LED in the PPG sensor provided by the embodiment of the application can give consideration to four application requirements such as static heart rate measurement, dynamic heart rate measurement, wearing tightness detection and blood oxygen measurement.

In order to improve the accuracy of the measurement result, the embodiment of the present application further provides another implementation manner of the PPG sensor. It should be noted that another implementation of the PPG sensor is improved on the basis of the PPG sensor shown in fig. 7.

Referring to fig. 8, another implementation of the PPG sensor provided in the embodiment of the present application includes: the first PD41, the first LED42, and the second LED43 may further include: the second PD81 is provided with a second PD,

the second PDs 81 and the first PDs 41 are distributed on two sides of a straight line where the first LED42 and the second LED43 are located, distances among the first PD41, the second PD81 and the first LED42 are equal and are set as a first distance d1, and distances among the first PD41, the second PD81 and the second LED42 are equal and are set as a second distance d2, wherein d1 < d 2. The layout of the PD and the LEDs in the PPG sensor may also be understood as follows: the distribution of the first PD41, the first LED42, the second LED43, and the second PD81 in the PPG is a parallelogram. The first PD41, the first LED42, the second LED43, and the second PD81 are distributed on the vertices of the parallelogram.

As a specific example of the present application, the layout of the first PD41, the first LED42, the second LED43, and the second PD81 is rectangular, wherein the first PD41, the first LED42, the second LED43, and the second PD81 are located at the vertex of the rectangle, and the LED and the PD are located at the non-adjacent vertex.

In the above implementation of the PPG sensor, two PDs are provided, and when the LEDs are a three-in-one LED device, a short distance path between 6 PDs and the LEDs (i.e. 3 paths between the first PD41 and the first LED42, and 3 paths between the second PD81 and the second LED 43) and a long distance path between 6 PDs and the LEDs (i.e. 3 paths between the first PD41 and the second LED43, and 3 paths between the second PD81 and the first LED 42) can be formed. In this way, the measurement of the static heart rate can be realized by using 3 paths between the first PD41 and the first LED42 and 3 paths between the second PD81 and the second LED43 to achieve the effect of controlling power consumption, the detection of the wearing tightness and the detection of blood oxygen can be realized by using 3 paths between the first PD41 and the second LED43 and 3 paths between the second PD81 and the first LED42, and the measurement of the dynamic heart rate can be realized by using the 6 short-distance paths and the 6 long-distance paths, so as to improve the accuracy of the detection result.

Therefore, the method can reduce the error of the detection result and improve the accuracy of the detection result by measuring the physiological parameters of the person and the wearing tightness of the equipment by utilizing the multi-path light intensity.

Above for another kind of concrete implementation of the PPG sensor that this application embodiment provided, in this concrete implementation, can detect static heart rate, dynamic heart rate, equipment wearing elasticity degree and blood oxygen comparatively accurately.

In addition, in order to further improve the accuracy of physiological parameters and equipment wearing tightness degree detection, the application also provides another implementation mode of the PPG sensor. Referring to fig. 9, the PPG sensor provided in the embodiment of the present application may further include, in addition to the first PD41, the first LED42, and the second LED43 shown in fig. 6: a second PD 91 and a third LED 92, the third LED 92 being located on an extension of a connecting line between the second LED43 and the first LED42, and a distance between the first PD41 and the second LED43 being equal to a distance between the first PD41 and the third LED 92; the second PD 91 is located at a position where the first PD41 is symmetrical with respect to the line connecting the first LED42 and the second LED 43.

In this way, the distance between the second PD 91 and the first LED42 is equal to the distance between the first PD41 and the first LED42, the distance between the second PD 91 and the second LED43 is equal to the distance between the first PD41 and the second LED43, the distance between the second PD 91 and the third LED 92 is equal to the distance between the first PD41 and the third LED 92, and the distance between the first PD41 and the second LED43 and the third LED 92 is equal to each other.

Therefore, in the embodiment of the present application, the layout of the first PD41, the second LED43, the second PD 91, and the third LED 92 may be a parallelogram with four sides having equal sides, and the first LED42 is located at the center of the parallelogram. As an example, the parallelogram may be a rhombus. As another example, the parallelogram may be square.

In the present embodiment, the third LED 92 is capable of emitting at least one of green light, red light, and infrared light. In order to improve the accuracy of the PPG sensor in detecting the degree of tightness of human physiological parameters and equipment wear, the third LEDs 92 may be three-in-one LED devices, i.e., LED devices capable of emitting green light, red light, and infrared light. 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 the PPG sensor in detecting the physiological parameters of a person and the degree of tightness of wearing the equipment, the first LED42, the second LED43, and the third LED 92 may all be LED devices combining green light, red light, and infrared light.

In the PPG sensor shown in fig. 9, the distance between the first PD41 and the first LED42 is equal to the distance between the second PD 91 and the first LED42, which is the first distance d 1. The first PD41 and the second PD 91 are equal to the second LED43 and the third LED 92, respectively, and the distance is set to be the second distance d2, and the first distance d1 is smaller than the second distance d2 according to mathematical knowledge. To reduce the power consumption of the PPG sensor, the static heart rate may be measured using the first PD41, the second PD71 and the second LED43 in combination, where the PD and LED distances are minimal.

In order to reduce the motion noise and improve the accuracy of the measurement of the dynamic heart rate, in the embodiment of the present application, the paths between the LEDs and the PD may be fully utilized to measure the dynamic heart rate.

For example, when first LED42, second LED43 and third LED 92 can be the trinity LED device of green glow, ruddiness and infrared light, can form 18 light paths in this PPG sensor, wherein, 12 long distance paths, 6 short distance paths, utilize this 18 light paths can effectively reduce the motion noise, improve the accuracy of wearing the dynamic heart rate when pine. It should be noted that in a specific method for detecting a dynamic heart rate, the PPG may set different weights to the reflected light intensities on the 18 light paths, and then calculate the dynamic heart rate by using a weighted average method.

Wherein, 12 long distance paths are respectively as follows:

second LED43 (G/RED/IR) -first PD41, 3 long distance vias;

second LED43 (G/RED/IR) -second PD 91, 3 long distance vias;

third LED 92(G/RED/IR) -first PD41, 3 long distance vias;

third LED 92(G/RED/IR) -second PD 91, 3 long distance vias.

Wherein the green, red and infrared light paths of each LED are utilized in the 12 long distance paths.

The 6 short-distance paths are respectively as follows:

first LED42 (G/RED/IR) -first PD41, 3 short distance paths;

first LED42 (G/RED/IR) -second PD 91, 3 short distance paths.

Wherein the green, red and infrared light paths of each LED are utilized in the 6 long distance paths.

In addition, in order to improve the accuracy of the detection of the degree of tightness of the equipment wearing, the detection of the degree of tightness of the equipment wearing can be detected by using the signal difference among the 12 long distance paths.

In order to effectively extract the blood oxygen signal, the blood oxygen test can be performed by using the following 8 long-distance channels,

second LED43 (RED/IR) -first PD41, 2 long distance vias;

second LED43 (RED/IR) -second PD 91, 2 long distance vias;

third LED 92(RED/IR) -first PD41, 2 long distance vias;

third LED 92(RED/IR) -second PD 91, 2 long distance vias.

Wherein in the 8 long distance paths, the red and infrared light paths of each LED are utilized.

Above is another concrete implementation of the PPG sensor that this application embodiment provided, in this concrete implementation, can detect static heart rate, dynamic heart rate, equipment wearing elasticity and blood oxygen more accurately. Moreover, this particular implementation can control PPG power consumption, supporting 24 hours continuous heart rate testing.

The above is a specific implementation manner of the PPG sensor provided in the embodiment of the present application. Based on this PPG sensor's concrete implementation, this application embodiment still provides an intelligent bracelet or wrist-watch.

This intelligence bracelet or wrist-watch includes the organism and wears the area, is provided with the PPG sensor in the organism, this PPG sensor be above-mentioned arbitrary specific implementation PPG sensor.

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

Claims

1. 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 is not equal to a distance between the first PD and the second LED; the distance between the first PD and the first LED is smaller than the distance between the first PD and the second LED, the path between the first PD and the first LED is used for realizing measurement of static heart rate, the path between the first PD, the first LED and the second LED is used for realizing measurement of dynamic heart rate, and the path between the first PD and the second LED is used for realizing wearing tightness detection and blood oxygen detection;

the first PD, the first LED, and the second LED are not in a straight line;

the PPG sensor further comprises a second PD, the second PD and the first PD are distributed on two sides of a straight line where the first LED and the second LED are located, the distance between the first PD and the first LED is equal to the distance between the second PD and the second LED, and the distance between the first PD and the second LED is equal to the distance between the second PD and the first LED.

2. The PPG sensor according to claim 1, 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 second LED and the second PD are distributed on the vertex of the rectangle.

3. The PPG sensor of claim 1 or 2 wherein the first and second LEDs are capable of emitting at least one of red and infrared light.

4. The PPG sensor according to claim 3, wherein the first LED and/or the second LED are LED devices capable of emitting green, red and infrared light.

5. 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 is not equal to a distance between the first PD and the second LED; the distance between the first PD and the first LED is smaller than the distance between the first PD and the second LED, the path between the first PD and the first LED is used for realizing measurement of static heart rate, the path between the first PD, the first LED and the second LED is used for realizing measurement of dynamic heart rate, and the path between the first PD and the second LED is used for realizing wearing tightness detection and blood oxygen detection;

the first PD, the first LED, and the second LED are not in a straight line;

the PPG sensor further comprises: a third LED and a second PD,

6. The PPG sensor according to claim 5, 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 third LED and the second PD are distributed on the vertex of the parallelogram.

7. The PPG sensor according to claim 6, wherein the parallelogram is a square or a diamond.

8. The PPG sensor according to any one of claims 5-7, wherein the first, second and third LEDs are capable of emitting at least one of red and infrared light.

9. The PPG sensor of claim 8, wherein the first LED, the second LED and/or the third LED are LED devices capable of emitting green light, red light and infrared light.

10. A smart watch or bracelet, comprising: a body and a wearing belt, wherein a PPG sensor is arranged in the body, and the PPG sensor is the PPG sensor as claimed in any one of claims 1-9.