PATENT DOCUMENT

Publication Number: US-12072288-B2
Application Number: US-202218084342-A
Country: US
Kind Code: B2

Title: Multiple light paths architecture and obscuration methods for signal and perfusion index optimization

Abstract:
A photoplethysmographic (PPG) device is disclosed. The PPG device can include one or more light emitters and one or more light sensors to generate the multiple light paths for measuring a PPG signal and perfusion indices of a user. The multiple light paths between each pair of light emitters and light detectors can include different separation distances to generate both an accurate PPG signal and a perfusion index value to accommodate a variety of users and usage conditions. In some examples, the multiple light paths can include the same separation distances for noise cancellation due to artifacts resulting from, for example, tilt and/or pull of the device, a user&#39;s hair, a user&#39;s skin pigmentation, and/or motion. The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the optical components and associated wiring from being visible to a user&#39;s eye.

Claims:
The invention claimed is: 
     
       1. A wearable electronic device comprising:
 a first window; 
 a first light sensor positioned behind the first window; 
 a second window; 
 a second light sensor positioned behind the second window; 
 a third window; 
 a first emitter positioned behind and off-center with respect to the third window; 
 a second emitter positioned behind the third window; and 
 a first Fresnel lens positioned between the first emitter and the third window and comprising:
 a first zone that is positioned above the first emitter and configured to collimate light emitted by the first emitter; and 
 a second zone that is positioned above the second emitter and includes ridges that act to obscure components underlying the second zone. 
 
 
     
     
       2. The wearable electronic device of  claim 1 , wherein:
 the first light sensor is centered within the first window; and 
 the second light sensor is centered within the second window. 
 
     
     
       3. The wearable electronic device of  claim 1 , further comprising:
 a second Fresnel lens positioned between the first window and the first light sensor. 
 
     
     
       4. The wearable electronic device of  claim 1 , wherein the first emitter and the second emitter have different emission wavelengths. 
     
     
       5. The wearable electronic device of  claim 4 , wherein the first emitter is a green LED. 
     
     
       6. The wearable electronic device of  claim 5 , wherein the second emitter is an infrared LED. 
     
     
       7. The wearable electronic device of  claim 1 , comprising a third light sensor positioned behind the first window. 
     
     
       8. The wearable electronic device of  claim 7 , comprising a fourth light sensor positioned behind the second window. 
     
     
       9. A wearable electronic device comprising:
 a first window; 
 a first light sensor positioned behind the first window; 
 a second window; 
 a second light sensor positioned behind the second window; 
 a third window; 
 a first emitter positioned behind the third window; 
 a second emitter positioned behind the third window; 
 a first Fresnel lens positioned between the first emitter and the third window and comprising:
 a first zone that is positioned above the first emitter and configured to collimate light emitted by the first emitter; and 
 a second zone that is positioned above the second emitter and includes ridges that act to obscure components underlying the second zone; and 
 
 a second Fresnel lens positioned between the first light sensor and the first window. 
 
     
     
       10. The wearable electronic device of  claim 9 , wherein:
 the first light sensor is centered within the first window; and 
 the second light sensor is centered within the second window. 
 
     
     
       11. The wearable electronic device of  claim 9 , wherein the first emitter and the second emitter have different emission wavelengths. 
     
     
       12. The wearable electronic device of  claim 11 , wherein the first emitter is a green LED. 
     
     
       13. The wearable electronic device of  claim 12 , wherein the second emitter is an infrared LED. 
     
     
       14. The wearable electronic device of  claim 9 , comprising a third light sensor positioned behind the first window. 
     
     
       15. The wearable electronic device of  claim 14 , comprising a fourth light sensor positioned behind the second window. 
     
     
       16. A method of determining physiological information of a user, the method comprising:
 at a device having: 
 a first window; 
 a first light sensor positioned behind the first window; 
 a second window; 
 a second light sensor positioned behind the second window; 
 a third window; 
 a first emitter positioned behind and off-center with respect to the third window; 
 a second emitter positioned behind the third window; and 
 a first Fresnel lens positioned between the first emitter and the third window and comprising:
 a first zone that is positioned above the first emitter and configured to collimate light emitted by the first emitter; and 
 a second zone that is positioned above the second emitter and includes ridges that act to obscure components underlying the second zone: 
 
 emitting first light from the first emitter; 
 receiving a first portion of the emitted first light by the first light sensor, wherein the first light sensor is located a first separation distance from the first emitter; 
 receiving a second portion of the emitted first light by the second light sensor, wherein:
 the second light sensor is located a second separation distance from the first emitter; and 
 the first separation distance is less than the second separation distance; and 
 
 determining the physiological information using the received first portion of the emitted first light and the received second portion of the emitted first light. 
 
     
     
       17. The method of  claim 16  comprising:
 emitting second light from the second emitter; 
 receiving a first portion of the emitted second light by the second light sensor, and 
 receiving a second portion of the emitted second light by the first light sensor, 
 wherein determining the physiological information comprises determining the physiological information using the received first portion of the emitted second light and the received second portion of the emitted second light. 
 
     
     
       18. The method of  claim 17 , comprising:
 generating first signals from the received first portion of the emitted first light and the received first portion of the emitted second light; 
 generating second signals from the received second portion of the emitted first light and the received second portion of the emitted second light; and 
 selecting between the first signals and the second signals based on the user&#39;s skin type. 
 
     
     
       19. The method of  claim 17 , further comprising:
 generating first signals from the received first portion of the emitted first light and the received first portion of the emitted second light; 
 generating second signals from the received second portion of the emitted first light and the received second portion of the emitted second light; and 
 selecting between the first signals and the second signals based on a usage condition. 
 
     
     
       20. The method of  claim 16 , wherein the first emitter and the second emitter have different emission wavelengths.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/144,958, filed Sep. 27, 2018, which is a continuation of U.S. patent application Ser. No. 14/569,235, filed Dec. 12, 2014, now U.S. Pat. No. 10,215,698, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Patent Application No. 62/044,515, filed Sep. 2, 2014, the contents of which are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD 
     This relates generally to a device that measures a photoplethysmographic (PPG) signal, and, more particularly, to architectures for multiple light paths and obscuration methods for PPG signal and perfusion index optimization. 
     BACKGROUND 
     A photoplethysmographic (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). In a basic form, PPG systems can employ a light source or light emitter that injects light into the user&#39;s tissue and a light detector to receive light that reflects and/or scatters and exits the tissue. The received light includes light with an amplitude that is modulated as a result of pulsatile blood flow (i.e., “signal”) and parasitic, non-signal light with an amplitude that can be modulated (i.e., “noise” or “artifacts”) and/or unmodulated (i.e., DC). Noise can be introduced by, for example tilt and/or pull of the device relative to the user&#39;s tissue, hair, and/or motion. 
     For a given light emitter and light detector, the PPG pulsatile signal (i.e., detected light modulated by pulsatile blood flow) can decrease as the separation distance between the light emitter and light detector increases. On the other hand, perfusion index (i.e., the ratio of pulsatile signal amplitude versus DC light amplitude) can increase as the separation distance between the light emitter and light detector increases. Higher perfusion index tends to result in better rejection of noise due to motion (i.e., rejection of motion artifacts). Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index (e.g., motion performance). That is, a trade-off can exist, making it difficult to optimize separation distance for particular user skin/tissue types and usage conditions. 
     Additionally, the PPG system can include several light emitters, light detectors, components, and associated wiring that may be visible to a user&#39;s eye, making the PPG system aesthetically unappealing. 
     SUMMARY 
     This relates to a PPG device configured with an architecture suitable for multiple light paths. The architecture can include one or more light emitters and one or more light sensors to generate the multiple light paths for measuring a PPG signal and a perfusion index of a user. The multiple light paths (i.e., the optical paths formed between each pair of light emitter and light detector) can include different locations and/or emitter-to-detector separation distances to generate both an accurate PPG signal and perfusion index value to accommodate a variety of users and a variety of usage conditions. In some examples, the multiple light paths can include different path locations, but the same separation distances along each path. In other examples, the multiple light paths can include overlapping, co-linear paths (i.e., along the same line) but with different emitter-to-detector separation distances along each path. In other examples, the multiple light paths can include different path locations and different emitter-to-detector separation distances along each path. In such examples, the particular configuration of the multiple light paths can be optimized for cancellation of noise due to artifacts resulting from, for example, tilt and/or pull of the device, a user&#39;s hair, a user&#39;s skin pigmentation, and/or motion. The PPG device can further include one or more lenses and/or reflectors to increase the signal strength and/or and to obscure the light emitters, light sensors, and associated wiring from being visible to a user&#39;s eye. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 1 C  illustrate systems in which examples of the disclosure can be implemented. 
         FIG.  2    illustrates an exemplary PPG signal. 
         FIG.  3 A  illustrates a top view and  FIG.  3 B  illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for determining a heart rate signal. 
         FIG.  3 C  illustrates a flow diagram for canceling or reducing noise from a measured PPG signal. 
         FIG.  4 A  illustrates a top view and  FIG.  4 B  illustrates a cross-sectional view of an exemplary device with two light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  5 A  illustrates multiple light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  5 B  illustrates a plot of PPG signal strength and perfusion index values for multiple light paths with different separation distances according to examples of the disclosure. 
         FIG.  6 A  illustrates a top view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  6 B  illustrates a table of exemplary path lengths, relative PPG signal levels, and relative perfusion index values for an exemplary electronic device employing multiple light paths according to examples of the disclosure. 
         FIG.  6 C  illustrates a cross-sectional view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure. 
         FIGS.  6 D- 6 F  illustrate cross-sectional views of exemplary electronic devices employing multiple light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  7 A  illustrates a top view of an exemplary electronic device with eight light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  7 B  illustrates a table of light emitter/sensor paths and separation distances for an exemplary electronic device with eight light paths and four separation distances according to examples of the disclosure. 
         FIG.  7 C  illustrates a plot of PPG signal strength and perfusion index values for an exemplary architecture with eight light paths and four separation distances according to examples of the disclosure. 
         FIGS.  7 D- 7 F  illustrate cross-sectional views of exemplary electronic devices employing one or more light paths for determining a heart rate signal according to examples of the disclosure. 
         FIG.  8    illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a PPG signal according to examples of the disclosure. 
         FIG.  9    illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to 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 examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, 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 in order to not obscure some of the aspects and/or features described or referenced herein. 
     Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
     A photoplethysmographic (PPG) signal can be measured by PPG systems 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&#39;s tissue that can result from fluctuations in the amount or volume of blood or blood oxygen contained in a vasculature of the user. In a basic form, PPG systems can employ a light source or light emitter that injects light into the user&#39;s tissue and a light detector to receive light that reflects and/or scatters and exits the tissue. The PPG signal is the amplitude of the reflected and/or scattered light that is modulated with volumetric change in blood volume in the tissue. However, the PPG signal may be compromised by noise due to artifacts. Artifacts resulting from, for example, tilt and/or pull of the device relative to the user&#39;s tissue, hair, and/or motion can introduce noise into the signal. For example, the amplitude of reflected light can modulate due to the motion of the user&#39;s hair. As a result, the amplitude modulation of the reflected light caused by hair motion can be erroneously interpreted as a result of pulsatile blood flow. 
     This disclosure relates to a multiple light paths architecture and obscuration methods for PPG signal and perfusion index optimization. The architecture can include one or more light emitters and one or more light sensors to generate the multiple light paths to measure a PPG signal and a perfusion index of a user. The multiple light paths can include different locations and/or separation distances between light emitters and light detectors to generate both an accurate PPG signal and perfusion index value to accommodate a variety of users and a variety of usage conditions. In some examples, the multiple light paths can include different path locations, but the same emitter-to-detector separation distances along each path. In some examples, the multiple light paths can include overlapping, co-linear paths (i.e., along the same line), but with different emitter-to-separation distances along each other. In some examples, the multiple light paths can include different path locations and different emitter-to-detector separation distances along each path. In such examples, the particular configuration of the multiple light paths is optimized for noise cancellation due to artifacts such as tilt and/or pull of the device, a user&#39;s hair, a user&#39;s skin pigmentation, and/or motion. In some examples, the device can include one or more lenses and/or reflectors to increase the signal strength and/or to obscure the light emitters, light sensors, and associated wiring from being visible to a user&#39;s eye. 
     Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. In other instances, well-known process steps have been described in detail in order to avoid unnecessarily obscuring the described examples. Other applications are possible, such that the following examples should not be taken as limiting. 
       FIGS.  1 A- 1 C  illustrate systems in which examples of the disclosure can be implemented.  FIG.  1 A  illustrates an exemplary mobile telephone  136  that can include a touch screen  124 .  FIG.  1 B  illustrates an exemplary media player  140  that can include a touch screen  126 .  FIG.  1 C  illustrates an exemplary wearable device  144  that can include a touch screen  128  and can be attached to a user using a strap  146 . The systems of  FIGS.  1 A- 1 C  can utilize the multiple light path architectures and obscuration methods as will be disclosed. 
       FIG.  2    illustrates an exemplary PPG signal. A user&#39;s PPG signal absent of artifacts is illustrated as signal  210 . However, movement of the body of the user can cause the skin and vasculature to expand and contract, introducing noise to the signal. Additionally, a user&#39;s hair and/or tissue can change the amplitude of light reflected and the amplitude of light absorbed. A user&#39;s PPG signal with artifacts is illustrated as signal  220 . Without extraction of noise, signal  220  can be misinterpreted. 
     Signal  210  can include light information with an amplitude that is modulated as a result of pulsatile 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 can be the ratio of received modulated light (ML) to unmodulated light (UML) (i.e., ratio of blood flow modulated signal to static, parasitic DC signal) and can give extra information regarding the user&#39;s physiological state. The modulated light (ML) can be the peak-to-valley value of signal  210 , and unmodulated light (UML) can be the zero-to-average (using average  212 ) value of signal  210 . As shown in  FIG.  2   , the perfusion index can be equal to the ratio of ML to UML. 
     Both the PPG signal and perfusion index can be related to an accurate measurement of physiological signals such as heart rate. However, the PPG signal can include noise from modulated light resulting from, for example, motion of the user&#39;s tissue and/or the PPG device. Higher perfusion index (e.g., higher pulsatile signal and/or lower parasitic DC) can result in better rejection of such motion noise. Additionally, the intensity of a PPG signal relative to 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 PPG signal and perfusion index can be used to determine physiological signals for a variety of users and a variety of usage conditions. 
       FIG.  3 A  illustrates a top view and  FIG.  3 B  illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for determining a heart rate signal. A light sensor  304  can be located with a light emitter  306  on a surface of device  300 . Additionally, another light sensor  314  can be located or paired with light emitter  316  on a surface of device  300 . Device  300  can be situated such that light sensors  304  and  314  and light emitters  306  and  316  are proximate to a skin  320  of a user. For example, device  300  can be held in a user&#39;s hand or strapped to a user&#39;s wrist, among other possibilities. 
     Light emitter  306  can generate light  322 . Light  322  can be incident on skin  320  and can reflect back to be detected by light sensor  304 . A portion of light  322  can be absorbed by skin  320 , vasculature, and/or blood, and a portion of light (i.e., light  332 ) can be reflected back to light sensor  304  located or paired with light emitter  306 . Similarly, light emitter  316  can generate light  324 . Light  324  can be incident on skin  320  and can reflect back to be detected by light sensor  314 . A portion of light  324  can be absorbed by skin  320 , vasculature, and/or blood, and a portion of light (i.e., light  334 ) can be reflected back to light sensor  314  located with light emitter  316 . Light  332  and  334  can include information or signals such as a heart rate signal (i.e., PPG signal) due to a blood pulse wave  326 . Due to a distance between light sensors  304  and  314  along the direction of the blood pulse wave  326 , signal  332  can include a heart rate signal, whereas signal  334  can include a time-shifted heart rate signal. A difference between signal  332  and signal  334  can depend on the distance between light sensors  304  and  314  and the velocity of blood pulse wave  326 . 
     Signals  332  and  334  can include noise  312  due to artifacts resulting from, for example, tilt and/or pull of device  300  relative to skin  320 , a user&#39;s hair, and/or a user&#39;s motion. One way to account for noise  312  can be to locate light sensors  304  and  314  far enough such that noise in signals  332  and  334  may be uncorrelated, but close enough together that PPG signal is corrected in signals  332  and  334 . The noise can be mitigated by scaling, multiplying, dividing, adding, and/or subtracting signals  332  and  334 . 
       FIG.  3 C  illustrates a flow diagram for canceling or reducing noise from a measured PPG signal. Process  350  can include light emitted from one or more light emitters  306  and  316  (step  352 ) located on a surface of device  300 . Light information  332  can be received by light sensor  304  (step  354 ), and light information  334  can be received by light sensor  314  (step  356 ). In some examples, light information  332  and  334  can indicate an amount of light from light emitters  306  and  316  that has been reflected and/or scattered by skin  320 , blood, and/or vasculature of the user. In some examples, light information  332  and  334  can indicate an amount of light that has been absorbed by skin  320 , blood, and/or vasculature of the user. 
     Based on light information  332  and light information  334 , a heart rate signal can be computed by canceling noise due to artifacts (step  358 ). For example, light information  334  can be multiplied by a scaling factor and added to light information  332  to obtain the heart rate signal. In some examples, heart rate signal can be computed by merely subtracting or dividing light information  334  from light information  332 . 
     In some examples, light information  332  and  334  can be difficult to determine due to a low signal intensity. To increase the signal intensity or signal strength, the distance between light sensors and light emitters can be reduced or minimized such that light travels the shortest distance. Generally, for a given light emitter and light sensor pair, the signal strength decreases with increasing separation distance between the light emitter and light sensor. On the other hand, the perfusion index generally increases with increasing separation distance between the light emitter and the light sensor. A higher perfusion index can correlate to better rejection of artifacts caused by, for example, motion. Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index (e.g., motion performance). That is, a trade-off can exist making it difficult to optimize separation distance for particular user skin/tissue types and usage conditions. 
     To alleviate the trade-off issue between signal strength and perfusion index, multiple light paths with various distances between light emitter(s) and light sensor(s) can be employed.  FIG.  4 A  illustrates a top view and  FIG.  4 B  illustrates a cross-sectional view of an exemplary device with two light paths for determining a heart rate signal according to examples of the disclosure. Device  400  can include light emitters  406  and  416  and a light sensor  404 . Light emitter  406  can have a separation distance  411  from light sensor  404 , and light emitter  416  can have a separation distance  413  from light sensor  404 . 
     Light  422  from light emitter  406  can be incident on skin  420  and can reflect back as light  432  to be detected by light sensor  404 . Similarly, light  424  from light emitter  416  can be incident on skin  420  and can reflect back as light  434  to be detected by light sensor  404 . Separation distance  411  can be small compared to separation distance  413 , and as a result, light information  432  can have a higher PPG signal strength than light information  434 . Light information  432  can be employed for applications requiring a higher PPG signal strength. Separation distance  413  can be large compared to separation distance  411 , and as a result, light information  434  can have a higher perfusion index than light information  432 . Light information  434  can be employed for applications requiring a high perfusion index (e.g., motion performance). Due to the different separation distances  411  and  413 , 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 particular user skin types and usage conditions (e.g., sedentary, active motion, etc.). 
       FIG.  5 A  illustrates multiple light paths for determining a heart rate signal according to examples of the disclosure. For enhanced measurement resolution, more than two light paths can be employed. Multiple light paths can be formed from a light emitter  506  and a plurality of light sensors such as light sensors  504 ,  514 ,  524 ,  534 , and  544 . Light sensor  504  can have a separation distance  511  from light emitter  506 . Light sensor  514  can have a separation distance  513  from light emitter  506 . Light sensor  524  can have a separation distance  515  from light emitter  506 . Light sensor  534  can have a separation distance  517  from light emitter  506 . Light sensor  544  can have a separation distance  519  from light emitter  506 . Separation distances  511 ,  513 ,  515 ,  517 , and  519  can be different values. 
       FIG.  5 B  illustrates a plot of PPG signal strength and perfusion index values for light emitter  506  and light sensors  504 ,  514 ,  524 ,  534 , and  544 . As shown, an intensity of the PPG signal or signal strength can decrease as the separation distance between a light emitter and a light sensor (i.e., separation distances  511 ,  513 ,  515 ,  517 , and  519 ) increases. On the other hand, the perfusion index value can increase as the separation distance between a light emitter and a light sensor increases. 
     Information obtained from the multiple light paths can be used both for applications requiring a high PPG signal strength and applications requiring a high perfusion index value. In some examples, information generated from all light paths can be utilized. In some examples, information generated from some, but not all light paths can be utilized. In some examples, the “active” light paths can be dynamically changed based on the application(s), available power, user type, and/or measurement resolution. 
       FIG.  6 A  illustrates a top view and  FIG.  6 C  illustrates a cross-sectional view of an exemplary electronic device employing multiple light paths for determining a heart rate signal according to examples of the disclosure. Device  600  can include light emitters  606  and  616  and light sensors  604  and  614  located on a surface of device  600 . Light sensors  604  and  614  can be symmetrically placed, while light emitters  606  and  616  can be asymmetrically placed. Optical isolation  644  can be disposed between light emitters  606  and  616  and light detectors  604  and  614 . In some examples, optical isolation  644  can be an opaque material to, for example, reduce parasitic DC light. 
     Light emitters  606  and  616  and light sensors  604  and  614  can be mounted on or touching 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 a same material as optical isolation  644 . 
     Device  600  can include windows  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 plane  648 , and windows  601  can be located within an 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 a wrist strap  646 . 
     Light emitters  606  and  616  and light detectors  604  and  614  can be arranged such that there are four light paths with four different separation distances. Light path  621  can be coupled to light emitter  606  and light sensor  604 . Light path  623  can be coupled to light emitter  606  and light sensor  614 . Light path  625  can be coupled to light emitter  616  and light sensor  614 . Light path  627  can be coupled to light emitter  616  and light sensor  604 . 
       FIG.  6 B  illustrates a table of exemplary path lengths, relative PPG signals levels, and relative perfusion index values for light paths  621 ,  623 ,  625 , and  627  of device  600  according to examples of the disclosure. As shown, relative PPG signal levels can have higher values for shorter path lengths. For example, light path  625  can have a higher PPG signal of 1.11 than light path  627  with a PPG signal of 0.31 due to the shorter path length (i.e., path length of light path  625  is 4.944 mm, whereas path length of light path  627  is 6.543 mm). For applications that require high PPG signal levels, device  600  can utilize information from light path  625  or light path  621 . However, relative perfusion index values can have higher values for longer path lengths. For example, light path  623  can have a higher perfusion index value of 1.23 than light path  621  with a perfusion index value of 1.10 due to the longer path length (e.g., path length of light path  623  is 5.915 mm, whereas path length of light path  621  is 5.444 mm). For applications that require high perfusion index values, device  600  can favor information from light path  623  over information from light path  621 . While  FIG.  6 B  illustrates exemplary values for path lengths  621 ,  623 ,  625 , and  627  along with exemplary PPG signal levels and perfusion index values, examples of the disclosure are not limited to these values. 
       FIGS.  6 D- 6 F  illustrate cross-sectional views of exemplary electronic devices employing multiple light paths for determining a heart rate signal according to examples of the disclosure. As shown in  FIG.  6 D , optical isolation  654  can be designed to improve mechanical stability of device  600  by providing a larger surface area (than optical isolation  644  of  FIG.  6 C ) for windows  601  to rest on and/or adhere to. While optical isolation  654  can provide a larger surface area for windows  601 , the light may have to travel a longer distance through skin  620 , and as a result, the signal intensity may be reduced. Either the signal quality can be compromised or device  600  can compensate by increasing the power (i.e., battery power consumption) of light emitted from light emitter  606 . A lower signal intensity or a higher battery power consumption can degrade the user&#39;s experience. 
     One way to overcome the issues with lower signal intensity and higher power consumption can be illustrated in  FIG.  6 E . Device  600  can include lens  609  coupled to light emitter  606  and/or lens  605  coupled to light sensor  604 . Lens  609  can be any type of lens such as a Fresnel lens or image displacement film (IDF) that steers the light over the optical isolation  644 . Lens  605  can be any type of lens such as an IDF or a brightness enhancement film (BEF) that shifts the light into an optical receiving area of light sensor  604 . Lens  609  can direct light emitted from light emitter  606  closer to lens  605 , and lens  605  can direct light to closer light sensor  604 . By employing lenses  609  and/or  605 , light may not have to travel a longer distance through skin  620 , and as a result, the signal intensity can be recovered. 
     In some examples, device  600  can include a reflector  607 , in addition to or alternatively to lens  609  and  605 , as shown in  FIG.  6 F . Reflector  607  can be formed from 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 . Such light in the architectures illustrated in  FIGS.  6 D- 6 E  could be lost or absorbed by optical isolation  654 . However, in the architecture illustrated in  FIG.  6 F , reflector  607  can prevent light loss by reflecting the light back to skin  620 , and the light could 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 . 
       FIG.  7 A  illustrates a top view of an exemplary electronic device with multiple light paths for determining a heart rate signal according to examples of the disclosure. Device  700  can include a plurality of light emitters  706  and  716  and a plurality of light sensors  704 ,  714 ,  724 , and  734  located on a surface of device  700 . Optical isolation  744  can be disposed between light emitters  706  and  716  and light sensors  704 ,  714 ,  724 , and  734  to prevent light mixing. Component mounting plane  748  can be mounted behind light emitters  706  and  716  and light sensors  704 ,  714 ,  724 , and  734 . Windows such as window  701  can be located in front of light emitters  706  and  716  and light sensors  704 ,  714 ,  724 , and  734  for protection. The plurality of light emitters  706  and  716 , plurality of light detectors  704 ,  714 ,  724 , and  734 , optical isolation  744 , component mounting plane  748 , and windows  701  can be located within an opening  703  of housing  710 . In some examples, device  700  can be a wearable device such as a wristwatch, and housing  710  can be coupled to a wrist strap  746 . 
     Although  FIG.  7 A  illustrates two light emitters and four light sensors, any number of light emitters and light sensors can be employed. In some examples, light sensors  704  and  724  can be a single light sensor partitioned into two or more separate sensing regions. Similarly, light sensors  714  and  734  can be a single light sensor partitioned into two or more separate sensing regions. In some examples, optical isolation  744  and/or component mounting plane  748  can be an opaque material. In some examples, one or more of optical isolation  744 , component mounting plane  748 , and housing  710  can be a same material. 
     Light emitters  706  and  716  and light sensors  704 ,  714 ,  724 , and  734  can be arranged such 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 placed such that the separation distances of light paths  721  and  729  (i.e., separation distance d 1 ) are the same, the separation distances of light paths  727  and  735  (i.e., separation distance d 2 ) are the same, the separation distances of light paths  723  and  731  (i.e., separation distance d 3 ) are the same, and the separation distances of light paths  725  and  733  (i.e., separation distance d 4 ) are the same. In some examples, two or more of the light paths can be overlapping light paths. In some examples, two or more of the light paths can be non-overlapping light paths. In some examples, two or more light paths can be co-located light paths. In some examples, two or more light paths can be non-co-located light paths. 
     An advantage to the multiple light-path architecture illustrated in  FIG.  7 A  can be signal optimization. There can be non-overlapping lights paths such that if there is signal loss in one light path, other light paths can be used for signal redundancy. That is, the device can ensure the existence of a signal by having light paths that collectively span a larger total area. The architecture can mitigate against the risk of having only one light path where signal is either very low or non-existent. A very low or non-existent signal can render a light path ineffective due to, for example, a user&#39;s particular physiology where a “quiet” no-signal (or low signal) spot exists. For example, light path  729  can be used for signal redundancy when there is signal loss in light path  721 . 
       FIG.  7 B  illustrates a table of light emitter/sensor paths and separation distances for an exemplary electronic device with eight light paths and four separation distances according to examples of the disclosure.  FIG.  7 C  illustrates a plot of PPG signal strength and perfusion index values for an exemplary architecture with eight light paths and four separation distances according to examples of the disclosure. As shown, an intensity of the PPG signal can decrease as the separation distance between a light emitter and a light sensor (i.e., separation distances d 1 , d 2 , d 3 , and d 4 ) increases. On the other hand, the perfusion index value can increase as the separation distance between a light emitter and a light sensor increases. 
     By configuring the light sensors and light emitters such that multiple light paths have a same separation distance, noise due to artifacts such as motion, user hair and user skin can be canceled or reduced. For example, light path  721  and light path  729  can be two different light paths with a same separation distance d 1 . Due to the separation distance being the same for both light paths, the PPG signal should be the same. However, light path  721  can reflect off a different area of the user&#39;s skin, vasculature, and blood than light path  729 . Due to the asymmetry of the human skin, vasculature, and blood, light information from light path  721  can be different than light information from light path  729 . For example, a user&#39;s skin pigmentation in light path  721  can be different than the user&#39;s skin pigmentation in light path  729 , leading to a different signal for light path  721  and light path  729 . Such differences in light information can be used to cancel or reduce noise and/or enhance pulsatile signal quality to determine an accurate PPG signal. 
     In some examples, light emitters  706  and  716  can be different light sources. Exemplary light sources can include, but are not limited to, light emitting diodes (LEDs), incandescent lights, and fluorescent lights. In some examples, light emitters  706  and  716  can have different emission wavelengths. For example, light emitter  706  can be a green LED and light emitter  716  can be an infrared (IR) LED. A user&#39;s blood can effectively absorb light from a green light source, and thus, the light path coupled to light emitter  706  with the shortest separation distance (i.e., light path  721 ) can be used for a high PPG signal when a user is sedentary, for example. An IR light source can effectively travel further distances through a user&#39;s skin than other light sources and as a result, can consume less power. A light path coupled to light emitter  716  (i.e., light paths  727 ,  729 ,  731 , and  733 ) can be used when device  700  is operating in a low power mode, for example. In some examples, light emitters  706  and  716  can have different emission intensities. 
       FIGS.  7 D- 7 F  illustrate cross-sectional views of exemplary electronic devices employing one or more light paths for determining a heart rate signal according to examples of the disclosure. Device  700  can include window  701  located in front of a component such as light emitter  706  of  FIG.  7 D  and light sensor  704  of  FIG.  7 E . Window  701  may be transparent, and as a result, the internal components of device  700  may be visible to a user. Since device  700  can include several components and associated wiring, it can be desirable to obscure the components and prevent internal components from being visible to a user&#39;s eye. In addition to obscuring the internal components, it may be desirable that the light emitted from light emitter  706  retains its optical power, collection efficiency, beam shape, and collection area so that the intensity of light is unaffected. 
     To obscure internal components, a lens such as a Fresnel lens  707  can be located between window  701  and light emitter  706 , as shown in  FIG.  7 D . Fresnel lens  707  can have two regions: an optical center  709  and a cosmetic zone  711 . Optical center  709  can be placed in substantially a same area or location as light emitter  706  to collimate the emitted light into a smaller beam size. Cosmetic zone  711  can be located in areas outside of optical center  709 . The ridges of the cosmetic zone  709  can act to obscure the underlying internal components. 
     To obscure light sensor  704 , a lens such as Fresnel lens  713  can be located between window  701  and light sensor  704 , as shown in  FIG.  7 E . Because light sensor  704  can be a large-area photodiode, shaping of the light field may not be needed, so Fresnel lens  713  may not require an optical center. Instead, Fresnel lens  713  may have one region comprising ridges configured for a cosmetic zone. 
     The ridge shapes of Fresnel lenses  707  and  713  can be altered to improve obscuration, especially in cosmetic zones. For example, deep and sharp sawtooth patterns can be used for high obscuration needs. Other types of ridge shapes can include rounded cylindrical ridges, asymmetric shapes, and wavy shapes (i.e., ridges that move in and out). 
     In some examples, the Fresnel lens  707  illustrated in  FIG.  7 D  can be used additionally or alternatively for light collimation. By collimating light, the optical signal efficiency can be improved. Without a lens or similar collimating optical element, emitter light can be directed at an angle away from the light sensor and can be lost. Additionally or alternatively, light can be directed at an angle toward the light sensor, but the angle may be shallow. The shallow angle may prevent the light from penetrating deep enough to reach the signal layers in the skin. This light may contribute only to parasitic, non-signal light. The Fresnel lens  707  can redirect light to directions that otherwise may be lost or enter into the tissue at shallow angles. Such redirected light can be collected instead of being lost and/or can mitigate against parasitic non-signal light, resulting in improved optical signal efficiency. 
     In some examples, a diffusing agent can be used. Diffusing agent  719  can be surrounding, touching, and/or covering one or more components of light emitter  706 . In some examples, diffusing agent  719  can be a resin or epoxy that encapsulates the dies or components and/or wire bonds. Diffusing agent  719  can be used to adjust the angle of the light emitted from light emitter  706 . For example, the angle of light emitted from a light emitter without a diffusing agent can be 5° wider than the angle of light emitter from light emitter  706  encapsulated by diffusing agent  719 . By narrowing the beam of light emitted, more light can be collected by the lens and/or window resulting in a larger amount of detected light by the light sensor. 
     In some examples, diffusing agent  719  can have an increased reflectivity for the wavelength or color of emitted light from light emitter  706 . For example, if light emitter  706  emits green light, diffusing agent  719  can be made of white TiO 2  material to increase the amount of green light reflected back toward the skin. This way, light that would have otherwise been lost can be recycled back and detected by the light detector. 
       FIG.  8    illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a PPG signal according to examples of the disclosure. Computing system  800  can correspond to any of the computing devices illustrated in  FIGS.  1 A- 1 C . Computing system  800  can include a processor  810  configured to execute instructions and to carry out operations associated with computing system  800 . For example, using instructions retrieved from memory, processor  810  can control the reception and manipulation of input and output data between components of computing system  800 . Processor  810  can be a single-chip processor or can be implemented with multiple components. 
     In some examples, processor  810  together with an operating system can operate to execute computer code and produce and use data. The computer code and data can reside within a program storage block  802  that can be operatively coupled to processor  810 . Program storage block  802  can generally provide a place to hold data that is being used by computing system  800 . Program storage block  802  can be any non-transitory computer-readable storage medium, and can store, for example, history and/or pattern data relating to PPG signal 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 , hard disk drive  808  and/or the like. The computer code and data could also reside on a removable storage medium and loaded or installed onto the computing system  800  when needed. Removable storage mediums include, for example, CD-RM, DVD-ROM, Universal Serial Bus (USB), Secure Digital (SD), Compact Flash (CF), Memory Stick, Multi-Media Card (MMC) and a network component. 
     Computing system  800  can also include an input/output (I/O) controller  812  that can be operatively coupled to processor  810  or it may be a separate component as shown. I/O controller  812  can be configured to control interactions with one or more I/O devices. I/O controller  812  can operate by exchanging data between processor  810  and the I/O devices that desire to communicate with processor  810 . The I/O devices and I/O controller  812  can communicate through a data link. The data link can be a one way link or a two way link. In some cases, I/O devices can be connected to I/O controller  812  through wireless connections. By way of example, a data link can correspond to PS/2, USB, Firewire, IR, RF, Bluetooth or the like. 
     Computing system  800  can include a display device  824  that can be operatively coupled to processor  810 . Display device  824  can be a separate component (peripheral device) or can be integrated with processor  810  and program storage block  802  to form a desktop computer (all in one machine), a laptop, handheld or tablet computing device of the like. Display device  824  can be configured to display a graphical user interface (GUI) including perhaps a pointer or cursor as well as other information to the user. By way of example, display device  824  can 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) or the like. 
     Display device  824  can be coupled to display controller  826  that can be coupled to processor  810 . Processor  810  can send raw data to display controller  826 , and display controller  826  can send signals to display device  824 . Data can include voltage levels for a plurality of pixels in display device  824  to project an image. In some examples, processor  810  can be configured to process the raw data. 
     Computing system  800  can also include a touch screen  830  that can be operatively coupled to processor  810 . Touch screen  830  can be a combination of sensing device  832  and display device  824 , where the sensing device  832  can be a transparent panel that is positioned in front of display device  824  or integrated with display device  824 . In some cases, touch screen  830  can recognize touches and the position and magnitude of touches on its surface. Touch screen  830  can report the touches to processor  810 , and processor  810  can interpret the touches in accordance with its programming. For example, processor  810  can perform tap and event gesture parsing and can initiate a wake of the device or powering on one or more components in accordance with a particular touch. 
     Touch screen  830  can be coupled to a touch controller  840  that can acquire data from touch screen  830  and can supply the acquired data to processor  810 . In some cases, touch controller  840  can be configured to send raw data to processor  810 , and processor  810  processes the raw data. For example, processor  810  can receive data from touch controller  840  and can determine how to interpret the data. The data can include the coordinates of a touch as well as pressure exerted. In some examples, touch controller  840  can be configured to process raw data itself. That is, touch controller  840  can read signals from sensing points  834  located on sensing device  832  and turn them into data that the processor  810  can understand. 
     Touch controller  840  can include one or more microcontrollers such as microcontroller  842 , each of which can monitor one or more sensing points  834 . Microcontroller  842  can, for example, correspond to an application specific integrated circuit (ASIC), which works with firmware to monitor the signals from sensing device  832 , process the monitored signals, and report this information to processor  810 . 
     One or both display controller  826  and touch controller  840  can perform filtering and/or conversion processes. Filtering processes can be implemented to reduce a busy data stream to prevent processor  810  from being overloaded with redundant or non-essential data. The conversion processes can be implemented to adjust the raw data before sending or reporting them to processor  810 . 
     In some examples, sensing device  832  is based on capacitance. When two electrically conductive members come close to one another without actually touching, their electric fields can interact to form a capacitance. The first electrically conductive member can be one or more of the sensing points  834 , and the second electrically conductive member can be an object  890  such as a finger. As object  890  approaches the surface of touch screen  830 , a capacitance can form between object  890  and one or more sensing points  834  in close proximity to object  890 . By detecting changes in capacitance at each of the sensing points  834  and noting the position of sensing points  834 , touch controller  840  can recognize multiple objects, and determine the location, pressure, direction, speed and acceleration of object  890  as it moves across the touch screen  830 . For example, touch controller  840  can determine whether the sensed touch is a finger, tap, or an object covering the surface. 
     Sensing device  832  can be based on self-capacitance or mutual capacitance. In self-capacitance, each of the sensing points  834  can be provided by an individually charged electrode. As object  890  approaches the surface of the touch screen  830 , the object can capacitively couple to those electrodes in close proximity to object  890 , thereby stealing charge away from the electrodes. The amount of charge in each of the electrodes can be measured by the touch controller  840  to determine the position of one or more objects when they touch or hover over the touch screen  830 . In mutual capacitance, sensing device  832  can include a two layer grid of spatially separated lines or wires, although other configurations are possible. The upper layer can include lines in rows, while the lower layer can include lines in columns (e.g., orthogonal). Sensing points  834  can be provided at the intersections of the rows and columns. During operation, the rows can be charged, and the charge can capacitively couple from the rows to the columns. As object  890  approaches the surface of the touch screen  830 , object  890  can capacitively couple to the rows in close proximity to object  890 , thereby reducing the charge coupling between the rows and columns. The amount of charge in each of the columns can be measured by touch controller  840  to determine the position of multiple objects when they touch the touch screen  830 . 
     Computing system  800  can 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  proximate to skin  820  of a user. Light emitters  806  and  816  can be configured to generate light, and light sensor  804  can be configured to measure a light reflected or absorbed by skin  820 , vasculature, and/or blood of the user. Light sensor  804  can send measured raw data to processor  810 , and processor  810  can perform noise cancelation to determine the PPG signal and/or perfusion index. Processor  810  can dynamically activate light emitters and/or light sensors based on an application, user skin type, and usage conditions. In some examples, some light emitters and/or light sensors can be activated, while other light emitters and/or light sensors can be deactivated to conserve power, for example. In some examples, processor  810  can store the raw data and/or processed information in a ROM  818  or RAM  822  for historical tracking or for future diagnostic purposes. 
     In some examples, the light sensor(s) can measure light information and a processor can determine a PPG signal and/or perfusion index from the reflected, scattered, or absorbed light. Processing of the light information can be performed on the device as well. In some examples, processing of light information need not be performed on the device itself.  FIG.  9    illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure. Host  910  can be any device external to device  900  including, but not limited to, any of the systems illustrated in  FIGS.  1 A- 1 C  or a server. Device  900  can be connected to host  910  through communications link  920 . Communications 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 requiring a physical cable. 
     In operation, instead of processing light information from the light sensors on the device  900  itself, device  900  can send raw data  930  measured from the light sensors over communications link  920  to host  910 . Host  910  can receive raw data  930 , and host  910  can process the light information. Processing the light information can include canceling or reducing any noise due to artifacts and determining physiological signals such as a user&#39;s heart rate. Host  910  can include algorithms or calibration procedures to account for differences in a user&#39;s characteristics affecting PPG signal and perfusion index. Additionally, host  910  can include storage or memory for tracking a PPG signal and perfusion index history for diagnostic purposes. Host  910  can send the processed result  940  or related information back to device  900 . Based on the processed result  940 , device  900  can notify the user or adjust its operation accordingly. By offloading the processing and/or storage of the light information, device  900  can conserve space and power enabling device  900  to remain small and portable, as space that could otherwise be required for processing logic can be freed up on the device. 
     In some examples, an electronic device is disclosed. The electronic device may comprise: one or more light emitters configured to generate a plurality of light paths, wherein at least two of the plurality of light paths have separation distances with a predetermined relationship; one or more light sensors configured to detect the at least two light paths having the predetermined relationship; and logic coupled to the one or more light sensors and configured to detect a physiological signal from the at least two light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the predetermined relationship is a same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, the logic is further configured to generate PPG signals and perfusion signals from the detected physiological signal. 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, 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 examples disclosed above, in other examples, the predetermined relationship is non-co-located light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the logic is further configured to reduce noise in the plurality of light paths. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises one or more first lenses disposed on the one or more light emitters. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more first lenses is a Fresnel lens or an image displacement film. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more first lenses includes an optical center placed in substantially a same location as light emitted from the one or more light emitters. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises one or more second lenses disposed on the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the one or more second lenses is an image displacement film, a brightness enhancement film, or a Fresnel lens. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises: an optical isolation disposed between the one or more light emitters and the one or more light sensors; and a reflector disposed on at least one of the optical isolation, a window disposed on the one or more light emitters, and a window disposed on the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one light sensor is partitioned into a plurality of sensing regions. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the one or more light emitters emit light at different wavelengths. Additionally or alternatively to one or more 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 comprise: 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 separation distances 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 comprises dynamically selecting one or more light paths based on at least one of a user characteristic and a usage condition. Additionally or alternatively to one or more examples disclosed above, in other examples, at least two of the plurality of light paths have a same separation distance, the method further comprises canceling or reducing a noise from the at least two of the plurality of light paths with the same separation distance. Additionally or alternatively to one or more examples disclosed above, in other examples, the at least two of the plurality of light paths including 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, the method further comprises: 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 is indicative of a photoplethysmographic signal and the second physiological signal is indicative of a perfusion index. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters includes a first set of light emitters and a second set of light emitters, the method further comprising: dynamically activating the first set of light emitters; and dynamically deactivating the second set of light emitters. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20221219
Publication Date: 20240827
Grant Date: 20240827
Priority Date: 20140902
Inventors: HAN, Chin San
BLOCK, UEYN
LAND, BRIAN R.
KESTELLI, NEVZAT AKIN
ISIKMAN, SERHAN
WANG, ALBERT
SHI, JUSTIN
Assignee: APPLE INC
CPC Classifications: [{"code": "A61B2560/0475", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/02416", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/0059", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/0638", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/068", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/7203", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/55", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/026", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/7203", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2560/0475", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/02416", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/4738", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/02416", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/0059", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01N2201/068", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N2201/0638", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2560/0475", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/7203", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/02416", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01N21/55", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/0059", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01N21/4738", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 53773367