HK1219644B - Multiple light paths architecture and obscuration methods for signal and perfusion index optimization - Google Patents

Description

Multi-optical architecture and masking methods for signal and perfusion index optimization

Technical Field

The present invention generally relates to measuring photoplethysmographic (PPG) signals, and more particularly to an architecture for multiple optical paths and masking methods for PPG signals and perfusion index optimization.

Background Art

Photoplethysmography (PPG) signals can be measured by a PPG system to derive corresponding physiological signals (e.g., pulse rate). In a basic form, a PPG system can employ a light source or emitter that injects light into the user's tissue and a light detector that receives light that is reflected and/or scattered and leaves the tissue. The received light includes light whose amplitude is modulated due to pulsating blood flow (i.e., "signal") and parasitic, non-signal light whose amplitude can be modulated (i.e., "noise" or "artifacts") and/or unmodulated (i.e., DC). Noise can be introduced by, for example, tilting and/or pulling the device relative to the user's tissue, hair, and/or movement.

For a given light emitter and light detector, the PPG pulsation signal (i.e., the detected light modulated by pulsating blood flow) can decrease as the separation distance between the light emitter and the light detector increases. On the other hand, the perfusion index (i.e., the ratio of the pulsation signal amplitude to the DC light amplitude) can increase as the separation distance between the light emitter and the light detector increases. A higher perfusion index tends to result in better rejection of noise due to motion (i.e., rejection of motion artifacts). Therefore, a shorter separation distance between the light emitter and the light sensor can favor high PPG signal strength, while a longer separation distance can favor a high perfusion index (e.g., motion performance). That is, there is a trade-off that makes it difficult to optimize the separation distance for a specific user's skin/tissue type and usage conditions.

Furthermore, a PPG system may include several light emitters, light detectors, components, and associated wiring that are visible to the user's eyes, making the PPG system aesthetically pleasing.

Summary of the Invention

The present invention relates to a PPG device configured with an architecture suitable for multiple optical paths. The architecture may include one or more light emitters and one or more light sensors to generate multiple optical paths for measuring a user's PPG signal and perfusion index. The multiple optical paths (i.e., the optical paths formed between each pair of light emitters and light detectors) may include different positions and/or emitter-to-detector spacing distances to generate both accurate PPG signals and perfusion index values to accommodate a variety of users and usage conditions. In some examples, the multiple optical paths may include different path positions but the same spacing distance along each path. In other examples, the multiple optical paths may include overlapping, collinear paths (i.e., along the same line) but with different emitter-to-detector spacing distances along each path. In yet other examples, the multiple optical paths may include different path positions and different emitter-to-detector spacing distances along each path. In such examples, the specific configuration of the multiple optical paths can be optimized for noise cancellation due to artifacts, such as device tilt and/or pulling, user hair, skin pigmentation, and/or movement. The PPG device may also include one or more lenses and/or reflectors to increase signal strength and/or shield the light emitters, light sensors, and associated wiring from the user's eyes.

BRIEF DESCRIPTION OF THE DRAWINGS

1A-1C illustrate systems in which examples of the present disclosure may be implemented.

FIG2 shows an exemplary PPG signal.

3A illustrates a top view, and FIG. 3B illustrates a cross-sectional view, of an exemplary electronic device including a light sensor and a light emitter for determining a heart rate signal.

FIG3C shows a flow chart for canceling or reducing noise from a measured PPG signal.

4A illustrates a top view and FIG. 4B illustrates a cross-sectional view of an exemplary device having two optical paths for determining a heart rate signal according to an example of the present disclosure.

FIG. 5A illustrates multiple optical paths for determining a heart rate signal according to an example of the present disclosure.

5B shows a graph of PPG signal intensity and perfusion index values for multiple optical paths having different separation distances, according to an example of the present disclosure.

6A illustrates a top view of an exemplary electronic device employing multiple optical paths for determining a heart rate signal according to an example of the present disclosure.

6B illustrates a table of exemplary path lengths, relative PPG signal levels, and relative perfusion index values for an exemplary electronic device employing multiple optical paths according to examples of the present disclosure.

6C illustrates a cross-sectional view of an exemplary electronic device employing multiple optical paths for determining a heart rate signal according to an example of the present disclosure.

6D-6F illustrate cross-sectional views of exemplary electronic devices employing multiple optical paths for determining a heart rate signal according to examples of the present disclosure.

7A illustrates a top view of an exemplary electronic device having eight optical paths for determining a heart rate signal according to an example of the present disclosure.

7B shows a table of light emitter/sensor paths and separation distances for an exemplary electronic device having eight light paths and four separation distances according to examples of the present disclosure.

7C shows a graph of PPG signal strength and perfusion index values for an exemplary architecture having eight optical paths and four separation distances, according to examples of the present disclosure.

7D-7F illustrate cross-sectional views of exemplary electronic devices employing one or more optical paths for determining a heart rate signal according to examples of the present disclosure.

8 illustrates an exemplary block diagram of a computing system including a light emitter and a light sensor for measuring a PPG signal, according to an example of the present disclosure.

FIG. 9 illustrates an exemplary configuration in which a device is connected to a host according to examples of the present disclosure.

DETAILED DESCRIPTION

In the following description of the examples, reference is made to the accompanying drawings in which is shown by way of illustration specific examples that can be practiced. It should be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples.

Various techniques and process flow steps will be described in detail with reference to the examples illustrated in the accompanying drawings. In the following description, various details are set forth to provide a thorough understanding of one or more aspects and/or features described or referenced herein. However, it will be apparent to one skilled in the art that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail so as not to obscure some aspects and/or features described or referenced herein.

In addition, although process steps or method steps can be described in sequential order, such processes and methods can be configured to work in any suitable order. In other words, any order or sequence of steps that can be described in this disclosure does not indicate that the steps themselves need to be performed in that order. In addition, although some steps are described or implied as not occurring at the same time (for example, because one step is described after another step), they can be performed simultaneously. Moreover, the description of the process by its depiction in the accompanying drawings does not imply that the illustrated process excludes other variations and modifications thereto, does not imply that the illustrated process or any step thereof is necessary for one or more examples, and does not imply that the illustrated process is preferred.

Photoplethysmography (PPG) signals can be measured by a PPG system to derive corresponding physiological signals (e.g., pulse rate). Such PPG systems can be designed to be sensitive to changes in blood in a user's tissue, which can be due to fluctuations in the amount or volume of blood or blood oxygen contained in the user's blood vessels. In a basic form, a PPG system can employ a light source or emitter that injects light into the user's tissue and a light detector that receives light reflected and/or scattered from the tissue. The PPG signal is the amplitude of the reflected and/or scattered light modulated by volumetric changes in the blood volume in the tissue. However, PPG signals can be compromised by noise caused by artifacts. Artifacts such as tilting and/or pulling of the device relative to the user's tissue, hair, and/or movement can introduce noise into the signal. For example, the amplitude of the reflected light can be modulated by the movement of the user's hair. Consequently, the amplitude modulation of the reflected light caused by hair movement can be erroneously interpreted as the result of pulsating blood flow.

The present disclosure relates to a multi-light path architecture and masking methods for PPG signals and perfusion index optimization. The architecture may include one or more light emitters and one or more light sensors to generate multiple light paths for measuring a user's PPG signal and perfusion index. The multiple light paths may include different positions and/or emitter-to-detector separation distances to generate accurate PPG signals and perfusion index values for a variety of users and usage conditions. In some examples, the multiple light paths may include different path positions but have the same emitter-to-detector separation distance along each path. In some examples, the multiple light paths may include overlapping, collinear paths (i.e., along the same line) but have different emitter-to-detector separation distances along each path. In some examples, the multiple light paths may include different path positions and have different emitter-to-detector separation distances along each path. In such examples, the specific configuration of the multiple light paths may be optimized for noise cancellation due to artifacts such as tilting and/or pulling of the device, user hair, skin pigmentation, and/or motion. In some examples, the device may also include one or more lenses and/or reflectors to increase signal strength and/or shield the light emitter, light sensor, and associated wiring from the user's eyes.

Representative applications of the methods and apparatus according to the present disclosure are described in this section. These examples are provided solely to add context and aid in understanding the described examples. Thus, it will be apparent to those skilled in the art that the described examples may be practiced without some or all of these specific details. In other cases, well-known process steps have not been described in detail to avoid unnecessarily obscuring the described examples. Other applications are possible, such that the following examples should not be considered limiting.

Figures 1A-1C illustrate systems in which examples of the present disclosure may be implemented. Figure 1A illustrates an exemplary mobile phone 136 that may include a touch screen 124. Figure 1B illustrates an exemplary media player 140 that may include a touch screen 126. Figure 1C illustrates an exemplary wearable device 144 that may include a touch screen 128 and may be attached to a user via a strap 146. The systems of Figures 1A-1C may utilize a multi-optical path architecture and shielding methods to be disclosed.

FIG2 illustrates an exemplary PPG signal. A user's PPG signal without artifacts is illustrated as signal 210. However, the user's body movement can cause the skin and blood vessels to expand and contract, introducing noise into the signal. Furthermore, the user's hair and/or tissue can alter the amplitude of reflected and absorbed light. A user's PPG signal with artifacts is illustrated as signal 220. If the noise is not extracted, signal 220 can be misinterpreted.

Signal 210 may include optical information whose amplitude is modulated due to pulsating blood flow (i.e., "signal") and parasitic, unmodulated, non-signal light (i.e., DC). From the measured PPG signal 210, a perfusion index can be determined. The perfusion index may be the ratio of received modulated light (ML) to unmodulated light (UML) (i.e., the ratio of the blood flow modulated signal to the static, parasitic DC signal) and may provide precise information about the user's physiological state. The modulated light (ML) may be the peak-to-valley values of signal 210, while the unmodulated light (UML) may be the zero-average (using average 212) value of signal 210. As shown in FIG. 2 , the perfusion index may be equal to the ratio of ML to UML.

Both the PPG signal and the perfusion index are relevant to the accurate measurement of physiological signals such as heart rate. However, the PPG signal can include noise from the modulated light due to, for example, motion of the user's tissue and/or the PPG device. A higher perfusion index (e.g., a higher pulsatility signal and/or lower parasitic DC) results in better rejection of this motion noise. Furthermore, the strength of the PPG signal relative to the perfusion index can vary for different users. Some users may naturally have a high PPG signal but a weak perfusion index, or vice versa. Thus, the combination of the PPG signal and the perfusion index can be used to determine physiological signals for a variety of users and under various usage conditions.

FIG3A shows a top view of an exemplary electronic device including a light sensor and a light emitter for determining a heart rate signal, while FIG3B shows a cross-sectional view thereof. Light sensor 304 can be positioned on the surface of device 300 together with light emitter 306. In addition, another light sensor 314 can be positioned together with light emitter 316 or paired on the surface of device 300. Device 300 can be positioned so that light sensors 304 and 314 and light emitters 306 and 316 are close to the user's skin 320. Among other possibilities, device 300 can also be held in the user's hand or wrapped around the user's wrist, for example.

Light emitter 306 can generate light 322. Light 322 can be incident on skin 320 and reflected back to be detected by light sensor 304. A portion of light 322 can be absorbed by skin 320, blood vessels, and/or blood, and a portion of the light (i.e., light 332) can be reflected back to light sensor 304, which is co-located with or paired with light emitter 306. Similarly, light emitter 316 can generate light 324. Light 324 can be incident on skin 320 and reflected back to be detected by light sensor 314. A portion of light 324 can be absorbed by skin 320, blood vessels, and/or blood, and a portion of the light (i.e., light 334) can be reflected back to light sensor 314, which is co-located with light emitter 316. Lights 332 and 334 can include information or signals, such as a heart rate signal (i.e., a PPG signal) caused by blood pulse wave 326. Due to the distance between light sensors 304 and 314 along the direction of blood pulse wave 326, signal 332 may include a heart rate signal, while signal 334 may include a time-shifted heart rate signal. The difference between signal 332 and signal 334 may depend on the distance between light sensors 304 and 314 and the rate of blood pulse wave 326.

Signals 332 and 334 may include noise due to artifacts caused by tilting and/or pulling of the example device 300 relative to the skin 320, the user's hair, and/or the user's movement. One way to account for noise 312 may be to position light sensors 304 and 314 far enough apart that the noise in signals 332 and 334 may be uncorrelated, but close enough that the PPG signal is corrected in signals 332 and 334. Noise may be mitigated by scaling, multiplying, dividing, adding, and/or subtracting signals 332 and 334.

FIG3C illustrates a flow chart for canceling or reducing noise from a measured PPG signal. Process 350 may include emitting light from one or more light emitters 306 and 316 positioned on a surface of device 300 (step 352). Light information 332 may be received by light sensor 304 (step 354), and light information 334 may be received by light sensor 314 (step 356). In some examples, light information 332 and 334 may indicate the amount of light reflected and/or scattered by the user's skin 320, blood, and/or blood vessels from light emitters 306 and 316. In some examples, light information 332 and 334 may indicate the amount of light absorbed by the user's skin 320, blood, and/or blood vessels.

Based on light information 332 and light information 334, a heart rate signal can be calculated by canceling noise caused by artifacts (step 358). For example, light information 334 can be multiplied by a scaling factor and added to light information 332 to obtain a heart rate signal. In some examples, the heart rate signal can be calculated by simply subtracting or dividing light information 334 from light information 332.

In some instances, light information 332 and 334 may be difficult to determine due to low signal strength. To increase signal strength, the distance between the light sensor and the light emitter can be reduced or minimized so that the light travels the shortest distance. Generally speaking, for a given light emitter and light sensor pair, signal strength decreases with increasing separation distance between the light emitter and the light sensor. On the other hand, perfusion index generally increases with increasing separation distance between the light emitter and the light sensor. A higher perfusion index can be associated with better rejection of artifacts due to, for example, motion. Thus, a shorter separation distance between the light emitter and the light sensor may favor high PPG signal strength, while a longer separation distance may favor a high perfusion index (e.g., motion performance). That is, there is a trade-off that makes it difficult to optimize the separation distance for a specific user's skin/tissue type and usage conditions.

To mitigate the tradeoff between signal strength and perfusion index, multiple optical paths with various distances between the optical emitter(s) and the optical sensor(s) can be employed. FIG4A illustrates a top view of an exemplary device having two optical paths for determining a heart rate signal, while FIG4B illustrates a cross-sectional view thereof, according to an example of the present disclosure. Device 400 can include optical emitters 406 and 416 and optical sensor 404. Optical emitter 406 can have a separation distance 411 from optical sensor 404, and optical emitter 416 can have a separation distance 413 from optical sensor 404.

Light 422 from light emitter 406 may be incident on skin 420 and may be reflected back as light 432 to be detected by light sensor 404. Similarly, light 424 from light emitter 416 may be incident on skin 420 and may be reflected back as light 434 to be detected by light sensor 404. Separation distance 411 may be smaller than separation distance 413, and thus, light information 432 may have a higher PPG signal intensity than light information 434. Light information 432 may be used for applications requiring a higher PPG signal intensity. Separation distance 413 may be greater than separation distance 411, and thus, light information 434 may have a higher perfusion index than light information 432. Light information 434 may be used for applications requiring a high perfusion index (e.g., athletic performance). Due to the different separation distances 411 and 413, the light information 432 and 434 can provide various combinations of PPG signals and perfusion index values to allow the device to dynamically select light information for specific user skin types and usage conditions (e.g., sedentary, active activities, etc.).

FIG5A illustrates multiple optical paths for determining a heart rate signal according to an example of the present disclosure. For enhanced measurement resolution, more than two optical paths may be employed. The multiple optical paths may be comprised of a light emitter 506 and a plurality of light sensors, such as light sensors 504, 514, 524, 534, and 544. Light sensor 504 may have a spacing distance 511 from light emitter 506. Light sensor 514 may have a spacing distance 513 from light emitter 506. Light sensor 524 may have a spacing distance 515 from light emitter 506. Light sensor 534 may have a spacing distance 517 from light emitter 506. Light sensor 544 may have a spacing distance 519 from light emitter 506. Spacing distances 511, 513, 515, 517, and 519 may have different values.

5B shows a graph of PPG signal intensity and perfusion index values for light emitter 506 and light sensors 504, 514, 524, 534, and 544. As shown, the intensity of the PPG signal may decrease as the separation distance between the light emitter and the light sensor increases (i.e., separation distances 511, 513, 515, 517, and 519). On the other hand, the perfusion index value may increase as the separation distance between the light emitter and the light sensor increases.

Information obtained from multiple optical paths can be used for both applications requiring high PPG signal strength and applications requiring high perfusion index values. In some examples, information generated from all optical paths can be utilized. In some examples, information generated from some, but not all, optical paths can be utilized. In some examples, the "active" optical path can be dynamically changed based on the application(s), available power, user type, and/or measurement resolution.

FIG6A shows a top view of an exemplary electronic device that employs multiple optical paths for determining a heart rate signal according to an example of the present disclosure, while FIG6C shows a cross-sectional view thereof. Device 600 may include light emitters 606 and 616 and light sensors 604 and 614 positioned on a surface of device 600. Light sensors 604 and 614 may be positioned symmetrically, while light emitters 606 and 616 may be positioned asymmetrically. Optical isolation 644 may be disposed between light emitters 606 and 616 and light detectors 604 and 614. In some examples, optical isolation 644 may be an opaque material, for example, to reduce parasitic DC light.

Light emitters 606 and 616 and light sensors 604 and 614 can be mounted on or in contact with component mounting plane 648. In some examples, component mounting plane 648 can be made of an opaque material (e.g., flex). In some examples, component mounting plane 648 can be made of the same material as optical isolation 644.

Device 600 can include a window 601 to protect light emitters 606 and 616 and light sensors 604 and 614. Light emitters 606 and 616, light detectors 604 and 614, optical isolation 644, component mounting surface 648, and window 601 can be positioned in opening 603 of housing 610. In some examples, device 600 can be a wearable device such as a wristwatch, and housing 610 can be coupled to wristband 646.

Light emitters 606 and 616 and light detectors 604 and 614 can be arranged so that there are four optical paths with four different separation distances. Optical path 621 can be coupled to light emitter 606 and light sensor 604. Optical path 623 can be coupled to light emitter 606 and light sensor 614. Optical path 625 can be coupled to light emitter 616 and light sensor 614. Optical path 627 can be coupled to light emitter 616 and light sensor 604.

FIG6B shows a table of exemplary path lengths, relative PPG signal levels, and relative perfusion index values for four optical paths 621, 623, 625, and 627 of device 600, according to an example of the present disclosure. As shown, the relative PPG signal levels can have higher values for shorter path lengths. For example, due to the shorter path lengths (i.e., the path length of optical path 625 is 4.944 mm, while the path length of optical path 627 is 6.543 mm), optical path 625 can have a higher PPG signal of 1.11 compared to optical path 627, which has a PPG signal of 0.31. For applications requiring high PPG signal levels, device 600 can utilize information from either optical path 625 or optical path 621. However, the relative perfusion index values can have higher values for longer path lengths. For example, due to the longer path length (i.e., the path length of light path 623 is 5.915 mm, while the path length of light path 621 is 5.444 mm), light path 623 can have a higher perfusion index value of 1.23 compared to light path 621 having a perfusion index value of 1.10. For applications requiring a high perfusion index value, device 600 may favor information from light path 623 over information from light path 621. While FIG6B shows example values for path lengths 621, 623, 625, and 627, along with example PPG signal levels and perfusion index values, examples of the present disclosure are not limited to these values.

6D-6F show a cross-sectional view of an exemplary electronic device that uses multiple optical paths for determining heart rate signals according to an example of the present disclosure. As shown in FIG6D , optical isolation 654 can be designed to improve the mechanical stability of device 600 by providing (than the optical isolation 644 of FIG6C ) a larger surface area so that window 601 is placed thereon and/or attached thereto. Although optical isolation 654 can provide a larger surface area for window 601, light may have to travel a longer distance through skin 620, and therefore, signal strength will decrease. Either signal quality will be compromised, or device 600 can compensate by increasing the power (i.e., battery power consumption) of the light emitted from light emitter 606. Lower signal strength or higher battery power consumption can degrade the user's experience.

One approach to overcoming the issues of lower signal strength and higher battery power consumption can be illustrated in FIG6E . Device 600 can include lens 603 coupled to light emitter 606 and/or lens 605 coupled to light sensor 604. Lens 603 can be any type of lens, such as a Fresnel lens or an image shift film (IDF) that directs light across optical isolation 644. Lens 605 can be any type of lens, such as an IDF or a brightness enhancement film (BEF) that shifts light into the light receiving area of light sensor 604. Lens 603 can direct light emitted from light emitter 606 closer to lens 605, and lens 605 can direct light closer to light sensor 604. By employing lenses 603 and/or 605, light does not have to travel a longer distance through skin 620, and thus, signal strength can be restored.

In some examples, in addition to or in place of lenses 603 and 605, device 600 may also include a reflector 607, as shown in FIG6F . Reflector 607 can be made of any reflective material, such as a mirror or a white surface. Light emitted from light emitter 606 can reflect off the surface of skin 620 and be directed back to reflector 607. In the architecture shown in FIG6D-6E , this light would be lost or absorbed by optical isolation 654. However, in the architecture shown in FIG6F , reflector 607 can prevent light from being lost by reflecting light back onto the skin, and the light can then be reflected to light sensor 604. In some examples, optical isolation 654 can include any number of reflectors 607. In some examples, one or more windows 601 can include any number of reflectors 607.

7A shows a top view of an exemplary electronic device having eight optical paths for determining a heart rate signal according to an example of the present disclosure. Device 700 may include a plurality of light emitters 706 and 716 and a plurality of light sensors 704, 714, 724, and 734 positioned on a surface of device 700. Optical isolation 744 may be disposed between light emitters 706 and 716 and light sensors 704, 714, 724, and 734 to prevent light from mixing. A component mounting surface 748 may be mounted behind light emitters 706 and 716 and light sensors 704, 714, 724, and 734. For protection, a window such as window 701 may be positioned in front of light emitters 706 and 716 and light sensors 704, 714, 724, and 734. A plurality of light emitters 706 and 716, a plurality of light sensors 704, 714, 724, and 734, optical isolation 744, a component mounting surface 748, and a window 701 can be positioned in an opening 703 of a housing 710. In some examples, the device 700 can be a wearable device such as a wristwatch, and the housing 701 can be coupled to a wristband 746.

Although FIG7A shows two light emitters and four light sensors, any number of light emitters and light sensors may be used. In some examples, light sensors 704 and 724 may be a single light sensor divided into two or more separate sensing areas. Similarly, light sensors 714 and 734 may be a single light sensor divided into two or more separate sensing areas. In some examples, optical isolation 744 and/or component mounting plane 748 may be an opaque material. In some examples, one or more of optical isolation 744, component mounting plane 748, and housing 710 may be the same material.

Light emitters 706 and 716 and light sensors 704, 714, 724, and 734 can be arranged so that there are eight light paths with four different path lengths or separation distances. Light path 721 can be coupled to light emitter 706 and light sensor 704. Light path 723 can be coupled to light emitter 706 and light sensor 734. Light path 725 can be coupled to light emitter 706 and light sensor 714. Light path 727 can be coupled to light emitter 716 and light sensor 734. Light path 729 can be coupled to light emitter 716 and light sensor 714. Light path 731 can be coupled to light emitter 716 and light sensor 724. Light path 733 can be coupled to light emitter 716 and light sensor 704. Light path 735 can be coupled to light emitter 706 and light sensor 724.

Light emitters 706 and 716 and light sensors 704, 714, 724, and 734 can be positioned so that optical paths 721 and 729 are spaced the same distance apart (i.e., spacing distance d1), optical paths 727 and 735 are spaced the same distance apart (i.e., spacing distance d2), optical paths 723 and 731 are spaced the same distance apart (i.e., spacing distance d3), and optical paths 725 and 744 are spaced the same distance apart (i.e., spacing distance d4). In some examples, two or more optical paths may be overlapping optical paths. In some examples, two or more optical paths may be non-overlapping optical paths. In some examples, two or more optical paths may be co-located optical paths. In some examples, two or more optical paths may be non-co-located optical paths.

The advantage of the multi-optical path architecture shown in Figure 7A can be signal optimization. There can be non-overlapping optical paths so that if there is a signal loss in one optical path, the other optical paths can be used for signal redundancy. That is, by having optical paths that span a larger total area together, the device can ensure the presence of a signal. This architecture can alleviate the risk of having only one optical path in which the signal is either very low or non-existent. Due to, for example, a user's specific physiological structure in which a "quiet" no-signal (or low-signal) point exists, a very low or non-existent signal can make the optical path ineffective. For example, when there is a signal loss in optical path 721, optical path 729 can be used for signal redundancy.

FIG7B shows a table of light emitter/sensor paths and separation distances for an exemplary electronic device having eight light paths and four separation distances, according to an example of the present disclosure. FIG7C shows a graph of PPG signal intensity and perfusion index values for an exemplary system architecture having eight light paths and four separation distances, according to an example of the present disclosure. As shown, the PPG signal intensity decreases as the separation distance between the light emitter and the light sensor (i.e., separation distances d1, d2, d3, and d4) increases. On the other hand, the perfusion index value increases as the separation distance between the light emitter and the light sensor increases.

By configuring the light sensor and light emitter so that multiple light paths have the same separation distance, noise caused by factors such as motion, the user's hair, and the user's skin can be canceled or reduced. For example, light path 721 and light path 729 can be two different light paths with the same separation distance d1. Since the separation distance is the same for these two light paths, the PPG signals should be the same. However, light path 721 may reflect different areas of the user's skin, blood vessels, and blood compared to light path 729. Due to the asymmetry of human skin, blood vessels, and blood, the light information from light path 721 may differ from the light information from light path 729. For example, the pigmentation of the user's skin in light path 721 may differ from the pigmentation of the user's skin in light path 722, resulting in different signals for light path 721 and light path 729. This difference in light information can be used to cancel or reduce noise and/or enhance the quality of the pulsation signal to determine an accurate PPG signal.

In some examples, light emitters 706 and 716 may be different light sources. Example light sources include, but are not limited to, light emitting diodes (LEDs), incandescent lamps, and fluorescent lamps. In some examples, light emitters 706 and 716 may have different emission wavelengths. For example, light emitter 706 may be a green LED, while light emitter 716 may be an infrared (IR) LED. The user's blood can efficiently absorb light from a green light source, and therefore, for example, when the user is sedentary, the optical path coupled to light emitter 706 at the shortest separation distance (i.e., optical path 721) can be used for a high PPG signal. IR light sources can efficiently travel a greater distance through the user's skin than other light sources and therefore can consume less power. The optical paths coupled to light emitter 716 (i.e., optical paths 727, 729, 731, and 733) can be used, for example, when device 700 is operating in a low-power mode. In some examples, light emitters 706 and 716 may have different emission intensities.

7D-7F show cross-sectional views of an exemplary electronic device that employs one or more optical paths for determining a heart rate signal according to an example of the present disclosure. Device 700 may include a window 701 positioned in front of components such as light emitter 706 of FIG. 7D and light sensor 704 of FIG. 7E . Window 701 may be transparent, and therefore, the internal components of device 700 may be visible to the user. Since device 700 may include several components and associated wiring, it may be desirable to shield the components and prevent the internal components from being seen by the user's eyes. In addition to shielding the internal components, it may also be desirable that the light emitted from light emitter 706 maintain its optical power, collection efficiency, beam shape, and collection area so that the intensity of the light is not affected.

To shield internal components, a lens such as a Fresnel lens 707 can be positioned between window 701 and light emitter 706, as shown in FIG7D . Fresnel lens 707 can have two regions: an optical center 709 and a decorative region 711. Optical center 709 can be placed in substantially the same region or location as light emitter 706 to collimate the emitted light to a smaller beam size. Decorative region 711 can be positioned in an area outside of optical center 709. The ridges of decorative region 711 can be used to shield underlying internal components.

To shield light sensor 704, a lens such as Fresnel lens 713 can be positioned between window 701 and light sensor 704, as shown in FIG7E . Because light sensor 704 can be a large-area photodiode, light field shaping may not be required, and thus Fresnel lens 713 may not require an optical center. Instead, Fresnel lens 713 may have a region including ridges configured as a decorative area.

The ridge shape of Fresnel lenses 707 and 713 can be modified to improve shading, especially in decorative areas. For example, a deep, sharp sawtooth pattern can be used for high shading requirements. Other types of ridge shapes can include rounded cylindrical ridges, asymmetrical shapes, and wavy shapes (i.e., ridges that move in and out).

In some examples, the Fresnel lens 707 illustrated in FIG7D may additionally or alternatively be used for light aiming. By aiming the light, the efficiency of the light signal may be improved. Without a lens or similar aiming optical element, the transmitter light would be directed at an angle away from the light sensor and would be lost. Additionally or alternatively, the light may be directed at an angle toward the light sensor, but the angle may be shallow. A shallow angle may prevent the light from penetrating deep enough to reach the signal layer within the skin. Such light may only act on parasitic non-signal light. The Fresnel lens 707 may redirect the light in a direction that would otherwise be lost or enter the tissue at a shallow angle. Such redirected light may be collected rather than lost and/or may mitigate parasitic non-signal light, resulting in improved light signal efficiency.

In some examples, a diffusing agent may be used. Diffusing agent 719 may surround, contact, and/or cover one or more components of light emitter 706. In some examples, diffuser 719 may be a resin or epoxy that encapsulates the die or components and/or wire bonds. Diffusing agent 719 may be used to adjust the angle of light emitted from light emitter 706. For example, without the diffuser, the angle of light emitted from the light emitter may be 5° wider than the angle of light emitted from light emitter 706 encapsulated by diffuser 719. By narrowing the beam of emitted light, more light can be collected by the lens and/or window, resulting in a greater amount of light being detected by the light sensor.

In some examples, diffuser 719 can have increased reflectivity for the wavelength or color of light emitted from light emitter 706. For example, if light emitter 706 emits green light, diffuser 719 can be made of a white _TiO2 material to increase the amount of green light reflected back toward the skin. In this way, light that would otherwise be lost can be recycled and detected by the light detector.

FIG8 illustrates an exemplary block diagram of a computing system including a light emitter and a light sensor for measuring a PPG signal, according to an example of the present disclosure. Computing system 800 may correspond to any of the computing devices illustrated in FIG1A-1C . Computing system 800 may include a processor 810 configured to execute instructions and perform operations associated with computing system 800. For example, using instructions retrieved from a memory, processor 810 may control the reception and manipulation of input and output data between components of computing system 800. Processor 810 may be a single-chip processor or may be implemented using multiple components.

In some examples, processor 810, along with an operating system, can operate to execute computer code and generate and use data. The computer code and data can reside in a program storage block 802 operatively coupled to processor 810. Program storage block 802 generally provides a place to store data being used by computing system 800. Program storage block 802 can be any non-transitory computer-readable storage medium and can store, for example, historical and/or pattern data regarding PPG signals and perfusion index values measured by one or more light sensors, such as light sensor 804. By way of example, program storage block 802 can include read-only memory (ROM) 818, random access memory (RAM) 822, a hard drive 808, and the like. The computer code and data can also reside on removable storage media and be loaded or installed into computing system 800 when needed. Removable storage media include, for example, CD-ROMs, DVD-ROMs, universal serial buses (USBs), secure digital (SD), compact flash (CF), memory sticks, multimedia cards (MMCs), and network components.

The computing system 800 may also include an input/output (I/O) controller 812 that is operably coupled to the processor 810 or may be a separate component as shown. The I/O controller 812 may be configured to control interaction with one or more I/O devices. The I/O controller 812 may operate by exchanging data between the processor 810 and the I/O devices that are desired to communicate with the processor 810. The I/O devices and the I/O controller 812 may communicate via a data link. The data link may be a unidirectional link or a bidirectional link. In some cases, the I/O devices may be connected to the I/O controller 812 via a wireless connection. For example, the data link may correspond to PS/2, USB, Firewire, IR, RF, Bluetooth, etc.

The computing system 800 may include a display device 824 operatively coupled to the processor 810. The display device 824 may be a separate component (peripheral device) or may be integrated with the processor 810 and the program storage block 802 to form a desktop computer (all-in-one computer), a laptop computer, a handheld or tablet computing device, etc. The display device 824 may be configured to display a graphical user interface (GUI) to a user, which may include a pointer or cursor and other information. By way of example, the display device 824 may be any type of display, including a liquid crystal display (LCD), an electroluminescent display (ELD), a field emission display (FED), a light emitting diode display (LED), an organic light emitting diode display (OLED), etc.

The display device 824 can be coupled to a display controller 826, which can be coupled to the processor 810. The processor 810 can send raw data to the display controller 826, and the display controller 826 can send signals to the display device 824. The data can include voltage levels for a plurality of pixels in the display device 824 to project an image. In some examples, the processor 810 can be configured to process the raw data.

The computing system 800 may also include a touch screen 830 operatively coupled to the processor 810. The touch screen 830 may be a combination of a sensing device 832 and a display device 824, wherein the sensing device 832 may be a transparent panel positioned in front of or integrated with the display device 824. In some cases, the touch screen 830 may recognize a touch on its surface as well as the location and size of the touch. The touch screen 830 may report the touch to the processor 810, and the processor 810 may interpret the touch according to its programming. For example, the processor 810 may perform tap and event gesture parsing, and may initiate a wake-up of the device or power one or more components based on a particular touch.

The touch screen 830 can be coupled to a touch controller 840, which can acquire data from the touch screen 830 and provide the acquired data to the processor 810. In some cases, the touch controller 840 can be configured to send raw data to the processor 810, and the processor 810 processes the raw data. For example, the processor 810 can receive data from the touch controller 840 and determine how to interpret the data. The data can include the coordinates of the touch and the pressure applied. In some examples, the touch controller 840 can be configured to process the raw data itself. That is, the touch controller 840 can read the signals from the sensing points 834 located on the sensing device 832 and convert them into data that the processor 810 can understand.

Touch controller 840 may include one or more microcontrollers, such as microcontroller 842, each of which may monitor one or more sensing points 834. Microcontroller 842 may, for example, correspond to an application specific integrated circuit (ASIC) that works with firmware to monitor signals from sensing device 832, process the monitored signals, and report this information to processor 810.

One or both of the display controller 826 and the touch controller 840 may perform filtering and/or conversion processes. The filtering process may be implemented to reduce the busy data flow to prevent the processor 810 from being overloaded with redundant or unnecessary data. The conversion process may be implemented to adjust the raw data before sending or reporting it to the processor 810.

In some examples, sensing device 832 is capacitance-based. When two conductive members are in close proximity to each other without actually touching, their electric fields interact to form a capacitance. The first conductive member can be one or more sensing points 834, and the second conductive member can be an object 890, such as a finger. When object 890 approaches the surface of touch screen 830, a capacitance can be formed between object 890 and one or more sensing points 834 in close proximity to object 890. By detecting changes in capacitance at each sensing point 834 and indicating the location of sensing point 834, touch controller 840 can identify multiple objects and determine the position, pressure, direction, speed, and acceleration of object 890 as it moves across touch screen 830. For example, touch controller 890 can determine whether a sensed touch is a finger, a tap, or an object covering the surface.

Sensing device 832 can be based on self-capacitance or mutual capacitance. In self-capacitance, each sensing point 834 can be provided by a separately charged electrode. When an object 890 approaches the surface of touch screen 830, the object can capacitively couple to those electrodes in close proximity to object 890, thereby stealing charge away from the electrodes. When one or more objects touch or hover over touch screen 830, the amount of charge in each electrode can be measured by touch controller 840 to determine the location of the one or more objects. In mutual capacitance, sensing device 832 can include a two-layer grid of spatially separated wires or conductors, but other configurations are possible. The upper layer can include wires in rows, while the lower layer can include wires in columns (e.g., orthogonal). Sensing points 834 can be provided at the intersection of rows and columns. During operation, the rows can be charged, and the charge can be capacitively coupled from the rows to the columns. When an object 890 approaches the surface of touch screen 830, the object 890 can capacitively couple to the rows immediately adjacent to the object 890, thereby reducing the charge coupling between the rows and columns. When multiple objects touch the touch screen 830 , the amount of charge in each column can be measured by the touch controller 840 to determine the positions of the multiple objects.

Computing system 800 may also include one or more light emitters, such as light emitters 806 and 816, and one or more light sensors, such as light sensor 804, positioned near the user's skin 820. Light emitters 806 and 816 may be configured to generate light, and light sensor 804 may be configured to measure light reflected or absorbed by the user's skin 820, blood vessels, and/or blood. Light sensor 804 may send measured raw data to processor 810, which may perform noise cancellation to determine a PPG signal and/or perfusion index. Processor 810 may dynamically activate light emitters and/or light sensors based on the application, the type of user's skin, and usage conditions. In some examples, for example, some light emitters and/or light sensors may be activated while others may be deactivated to conserve power. In some examples, processor 810 may store raw data and/or processed information in ROM 818 or RAM 822 for historical tracking or future diagnostic purposes.

In some examples, (one or more) light sensors can measure light information, and the processor can determine a PPG signal and/or perfusion index from the reflected, scattered, or absorbed light. Processing of the light information can also be performed on the device. In some examples, processing of the light information does not need to be performed on the device itself. Figure 9 shows an exemplary configuration in which a device is connected to a host according to an example of the present disclosure. Host 910 can be any device external to device 900, including but not limited to any system shown in Figures 1A-1C, or a server. Device 900 can be connected to host 910 via a communication link 920. Communication link 920 can be any connection, including but not limited to a wireless connection and a wired connection. Exemplary wireless connections include Wi-Fi, Bluetooth, Wireless Direct, and infrared. Exemplary wired connections include Universal Serial Bus (USB), FireWire, Thunderbolt, or any connection that requires a physical cable.

In operation, rather than processing light information from the light sensor on device 900 itself, device 900 may send raw data 930 measured from the light sensor to host 910 via communication link 920. Host 910 may receive raw data 930 and process the light information. Processing the light information may include canceling or reducing any noise due to artifacts and determining physiological signals such as the user's heart rate. Host 910 may include algorithms or calibration procedures to account for differences in user characteristics that affect PPG signals and perfusion index. Furthermore, host 910 may include storage or memory for tracking PPG signal and perfusion index history for diagnostic purposes. Host 910 may send processing results 940 or related information back to device 900. Based on processing results 940, device 900 may notify the user or adjust its operation accordingly. By offloading the processing and/or storage of light information, device 900 may save space and power, thereby keeping device 900 small and lightweight, as space that might otherwise be required for processing logic may be freed up on the device.

In some examples, an electronic device is disclosed. The electronic device may include: one or more light emitters configured to generate multiple light paths, wherein at least two of the multiple light paths have a separation distance with a predetermined relationship; one or more light sensors configured to detect the at least two light paths with the predetermined relationship; and logic coupled to the one or more light sensors and configured to detect physiological signals from the at least two light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is the same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, the logic is further configured to generate a PPG signal and a perfusion index from the detected physiological signals. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is different separation distances. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is overlapping light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is non-overlapping light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is co-located light paths. Additionally or alternatively to one or more of the examples disclosed above, in other examples, the predetermined relationship is non-co-located optical paths. Additionally or alternatively to one or more of the examples disclosed above, in other examples, the logic unit is further configured to reduce noise in the multiple optical paths. Additionally or alternatively to one or more of the examples disclosed above, in other examples, the electronic device further includes one or more first lenses disposed on the one or more light emitters. Additionally or alternatively to one or more of the examples disclosed above, in other examples, at least one of the one or more first lenses is a Fresnel lens or an image-shifting film. Additionally or alternatively to one or more of the examples disclosed above, in other examples, at least one of the one or more first lenses includes an optical center positioned substantially at the same location as light emitted from the one or more light emitters. Additionally or alternatively to one or more of the examples disclosed above, in other examples, the electronic device further includes one or more second lenses disposed on the one or more light sensors. Additionally or alternatively to one or more of the examples disclosed above, in other examples, at least one of the one or more second lenses is an image-shifting film, a brightness-enhancing film, or a Fresnel lens. In addition or as an alternative to one or more of the examples disclosed above, in other examples, the electronic device further comprises: an optical isolator arranged between the one or more light emitters and the one or more light sensors; and a reflector arranged above at least one optical isolator, a window arranged on the one or more light emitters, and a window arranged on the one or more light sensors. In addition or as an alternative to one or more of the examples disclosed above, in other examples, at least one light sensor is divided into a plurality of sensing areas. In addition or as an alternative to one or more of the examples disclosed above, in other examples, at least two of the one or more light emitters emit light of different wavelengths. In addition or as an alternative to one or more of the examples disclosed above, in other examples, at least one light emitter is a green light emitting diode and at least one light emitter is an infrared light emitting diode.

In some examples, a method for forming an electronic device including one or more light emitters and one or more light sensors is disclosed. The method may include: emitting light from the one or more light emitters to generate a plurality of light paths, wherein at least two of the plurality of light paths have a separation distance with a predetermined relationship; receiving light from the one or more light sensors; and determining a physiological signal from the received light. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further includes dynamically selecting one or more light paths based on at least one of user characteristics and usage conditions. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the plurality of light paths have the same separation distance, and the method further includes canceling or reducing noise from at least two of the plurality of light paths having the same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the plurality of light paths include a first light path and a second light path, wherein the first light path has a first separation distance and the second light path has a second separation distance, and the first separation distance is shorter than the second separation distance, and the method further includes: determining a first physiological signal from the first light path; and determining a second physiological signal from the second light path. Additionally or alternatively to one or more examples disclosed above, in other examples, the first physiological signal indicates a photoplethysmographic signal and the second physiological signal indicates a perfusion index. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters include a first group of light emitters and a second group of light emitters, and the method further includes: dynamically activating the first group of light emitters; and dynamically deactivating the second group of light emitters.

Although the disclosed embodiments have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. These changes and modifications should be understood to be included within the scope of the disclosed examples defined by the appended claims.

Claims (17)

1. An electronic device, comprising: Multiple optical emitters, configured to emit multiple beams of light, wherein: The first optical emitter of the plurality of optical emitters is configured to generate a first optical light that has traveled a first optical path and a second optical light that has traveled a second optical path, wherein the first optical path is in a different direction from the second optical path; The second optical emitter among the plurality of optical emitters is configured to generate a third optical light that has traveled a third optical path and a fourth optical light that has traveled a fourth optical path, wherein the third optical path is in a different direction from the fourth optical path; Multiple optical sensors are configured to detect multiple lights and generate multiple signals indicating the detected light, wherein: A first optical sensor among the plurality of optical sensors is positioned at a first interval distance from the first optical emitter and a second interval distance from the second optical emitter, wherein the first interval distance and the second interval distance are different, and wherein the first optical sensor is configured as follows: Detect the first light and generate a first signal indicating the detected first light, and Detect the fourth light and generate a fourth signal indicating the detected fourth light, and The second optical sensor among the plurality of optical sensors is positioned at a second interval distance from the first optical emitter and a first interval distance from the second optical emitter, wherein the second optical sensor is configured as follows: Detect the second light and generate a second signal indicating the detected second light, and The third light is detected and a third signal indicating the detected third light is generated. Among them, the first optical path, the second optical path, the third optical path, and the fourth optical path are non-overlapping. A plurality of first windows are arranged on the plurality of light emitters and a plurality of second windows are arranged on the plurality of light sensors, wherein each first window is configured to allow a corresponding light emitted from a corresponding light emitter of the plurality of light emitters to pass through, and A logic unit, coupled to the plurality of optical sensors and configured to determine a physiological signal from at least two of the detected optical signals. 2. The electronic device of claim 1, wherein the logic unit is further configured to generate a PPG signal and a perfusion index from one or more of the plurality of signals. 3. The electronic device of claim 1, wherein the logic unit is further configured to reduce noise in the plurality of signals. 4. The electronic device of claim 1, wherein at least two of the plurality of optical paths are co-located optical paths. 5. The electronic device of claim 1, wherein at least two of the plurality of optical paths are non-co-located optical paths. 6. The electronic device of claim 1, further comprising a plurality of first lenses disposed between the plurality of first windows and the plurality of light emitters, wherein at least one of the plurality of first lenses is a Fresnel lens or an image shifting film. 7. The electronic device of claim 6, wherein the first lens includes an optical center disposed at substantially the same position as light from a respective light emitter among the plurality of light emitters. 8. The electronic device of claim 1, further comprising a plurality of second lenses disposed between the plurality of second windows and the plurality of optical sensors, wherein at least one of the plurality of second lenses is an image shifting film, a brightness enhancement film, or a Fresnel lens. 9. The electronic device of claim 1, wherein at least one of the plurality of optical sensors is divided into a plurality of sensing regions. 10. The electronic device of claim 1, wherein at least one of the plurality of light emitters is a green light-emitting diode, and at least one of the plurality of light emitters is an infrared light-emitting diode. 11. The electronic device of claim 1, further comprising a diffusing agent covering at least one of the plurality of light emitters, wherein the diffusing agent comprises white _TiO2 . 12. A method for determining physiological signals from an electronic device, the electronic device comprising a plurality of light emitters, a plurality of light sensors, a plurality of first windows, a plurality of second windows, and a processor, the method comprising: Multiple beams are emitted from the plurality of light emitters, wherein: The first light of the plurality of lights is emitted from the first light emitter of the plurality of light emitters, and the first light travels along the first optical path; The second light of the plurality of lights is emitted from the first light emitter of the plurality of light emitters, and the second light travels along a second optical path, wherein the first optical path is in a different direction from the second optical path; The third light among the plurality of lights is emitted from the second light emitter among the plurality of light emitters, and the third light travels along a third optical path; The fourth light of the plurality of lights is emitted from the second light emitter of the plurality of light emitters, and the fourth light travels along a fourth optical path, wherein the third optical path is in a different direction from the fourth optical path; Allowing the plurality of light emitted by the plurality of light emitters to pass through the plurality of first windows; Allowing the plurality of light to be detected by the plurality of light sensors to pass through the plurality of second windows, wherein the plurality of first windows are separate from and different from the plurality of second windows; The plurality of light sensors are used to detect the plurality of light and generate a plurality of signals indicating the detected light, wherein: The first light is detected using a first optical sensor among the plurality of optical sensors, and a first signal indicating the detected first light is generated; The fourth light is detected using the first optical sensor, and a fourth signal indicating the detected fourth light is generated; Wherein, the first optical sensor is located at a first interval distance from the first optical transmitter and a second interval distance from the second optical transmitter, wherein the first interval distance and the second interval distance are different; The second light is detected using a second optical sensor among the plurality of optical sensors, and a second signal indicating the detected second light is generated; The third light is detected using the second light sensor, and a third signal indicating the detected third light is generated; The second optical sensor is positioned at a second interval distance from the first optical transmitter and at a first interval distance from the second optical transmitter. Among them, the first optical path, the second optical path, the third optical path, and the fourth optical path are non-overlapping; and The physiological signal is determined from at least two of the detected multiple lights. 13. The method of claim 12, further comprising dynamically selecting one or more of the plurality of lights based on at least one of user characteristics and usage conditions. 14. The method of claim 12, further comprising canceling or reducing noise from the plurality of signals. 15. The method of claim 12, further comprising: Determine a first physiological signal from the first signal; and The second physiological signal is determined from the second signal. 16. The method of claim 15, wherein the first physiological signal indicates a first photoplethysmography signal having a first associated perfusion index, and the second physiological signal indicates a second photoplethysmography signal having a second associated perfusion index. 17. The method of claim 12, wherein the plurality of optical emitters comprises a first group of optical emitters and a second group of optical emitters, the method further comprising: Dynamically activate the first group of light emitters; and The second group of optical emitters is dynamically deactivated.