PATENT DOCUMENT

Publication Number: US-12164027-B1
Application Number: US-202017020659-A
Country: US
Kind Code: B1

Title: Multi-pathway distance measurements for optical sensors

Abstract:
Disclosed herein are electronic devices, detectors, systems, and methods for estimating a distance to an exterior object. Light pulses from an emitter on the electronic device or detector are received by at least one pair of light detectors positioned at different distances from the emitter. One or more ratios of strengths of signals of the light detectors are used to determine the object&#39;s distance. The ratios may be compared to a proximity curve to obtain the object&#39;s distance. If the ratio exceeds a critical distance value, a determination may be made that the exterior object has been separated from the electronic device. Wearable electronic devices, such as smart watches, may use the detectors, systems, and methods to determine if a user is wearing the electronic device.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing; 
 a first light emitter operable to emit light outward from or through the housing; 
 a second light emitter operable to emit light outward from or through the housing, wherein the first light emitter and the second light emitter are positioned to lie on an axis across a backside of the housing; 
 a first light detector positioned within the housing at a first separation distance from the first light emitter and configured to receive light emitted by at least one of the first light emitter or the second light emitter; 
 a second light detector positioned within the housing at a second separation distance from the first light emitter and configured to receive light emitted by at least one of the first light emitter or the second light emitter, wherein the second separation distance is different from the first separation distance; and 
 a processor configured to estimate an object distance by:
 determining a first signal strength of the first light detector; 
 determining a second signal strength of the second light detector; and 
 using a ratio of the first signal strength and the second signal strength to estimate the object distance; wherein: 
 
 the object distance is a distance from the electronic device to an object; and 
 the first light detector and the second light detector are positioned on a first side of the axis. 
 
     
     
       2. The electronic device of  claim 1 , wherein:
 the second separation distance is less than the first separation distance. 
 
     
     
       3. The electronic device of  claim 1 , wherein the first separation distance is less than the second separation distance. 
     
     
       4. The electronic device of  claim 1 , wherein, in the event that the processor estimates that the object distance is less than a critical distance, selecting a corresponding operational state of the electronic device. 
     
     
       5. The electronic device of  claim 1 , wherein:
 the electronic device is an electronic watch; and 
 the object is a limb of a person wearing the electronic watch. 
 
     
     
       6. The electronic device of  claim 1 , wherein:
 the electronic device further comprises:
 a third light detector positioned within the housing at the first separation distance from the second light emitter; and 
 a fourth light detector positioned within the housing at the second separation distance from the second light emitter. 
 
 
     
     
       7. The electronic device of  claim 6 , wherein the first light emitter and the second light emitter emit light at different times. 
     
     
       8. The electronic device of  claim 6 , wherein:
 the third light detector and the fourth light detector are positioned on a second side of the axis. 
 
     
     
       9. The electronic device of  claim 6 , wherein:
 the object distance is a first object distance; and 
 the processor is further configured to:
 determine a third signal strength of the third light detector; 
 determine a fourth signal strength of the fourth light detector; and 
 use the third signal strength and the fourth signal strength to estimate a second object distance. 
 
 
     
     
       10. The electronic device of  claim 9 , wherein the processor determines a tilt of the object relative to the electronic device based on:
 the ratio of the first signal strength to the second signal strength; and 
 a ratio of the third signal strength to the fourth signal strength. 
 
     
     
       11. An electronic device, comprising:
 a housing; 
 a first light emitter operable to emit light outward from or through the housing; 
 a second light emitter operable to emit light outward from or through the housing, wherein the first light emitter and the second light emitter are positioned to lie on an axis across a backside of the housing; 
 a first pair of light detectors positioned on a first side of the axis and configured to receive light emitted by at least one of the first light emitter or the second light emitter; 
 a second pair of light detectors positioned on a second side of the axis and configured to receive light emitted by at least one of the first light emitter or the second light emitter; and 
 a processor operably connected to the first and second light emitters and the first and second pairs of light detectors; wherein: 
 the processor estimates a first object distance from the electronic device to an object exterior to the electronic device at least partially by determining a ratio of signal strengths of the first pair of light detectors; and 
 the processor estimates a second object distance from the electronic device to the object exterior to the electronic device at least partially by determining a ratio of signal strengths of the second pair of light detectors. 
 
     
     
       12. The electronic device of  claim 11 , wherein:
 the first pair of light detectors comprises:
 a first light detector separated from the first light emitter by a first separation distance; and 
 a second light detector separated from the first light emitter by a second separation distance; wherein: 
 
 the ratio of signal strengths of the first pair of light detectors varies with:
 the first separation distance; 
 the second separation distance; and 
 the first object distance. 
 
 
     
     
       13. The electronic device of  claim 11 , wherein:
 the light from the first light emitter and the light from the second light emitter have the same wavelength. 
 
     
     
       14. The electronic device of  claim 13 , wherein:
 the signal strengths of the first pair of light detectors are based on an amount of light emitted by the first light emitter and received by the first pair of light detectors; and 
 the signal strengths of the second pair of light detectors are based on an amount of light emitted by the second light emitter and received by the second pair of light detectors. 
 
     
     
       15. The electronic device of  claim 11 , wherein the processor uses the first object distance and the second object distance to determine a tilt of the housing with respect to the object. 
     
     
       16. A method of operating an electronic device comprising a first light emitter and a second light emitter positioned on an axis across a backside of a housing, the method comprising:
 estimating that an object exterior to the electronic device is within a critical distance of the electronic device by:
 emitting, from at least one of the first light emitter or the second light emitter, an emitted light outward from or through the housing of the electronic device; 
 determining a first signal strength produced by a first light detector that varies with a portion of the emitted light reflected from the object and received by the first light detector, wherein the first light detector is positioned on a first side of the axis; 
 determining a second signal strength produced by a second light detector that varies with another portion of the emitted light reflected from the object and received by the second light detector, wherein the second light detector is positioned on the first side of the axis; 
 determining a ratio of the first signal strength and the second signal strength; 
 determining that the object is within the critical distance when the ratio is less than a critical distance value; and 
 enabling an operation of the electronic device when the object is within the critical distance. 
 
 
     
     
       17. The method of  claim 16 , further comprising disabling the operation of the electronic device when the processor determines that the object is not within the critical distance. 
     
     
       18. The method of  claim 16 , wherein:
 the ratio is a first ratio; 
 the first light detector is positioned a first separation distance from the first light emitter; 
 the second light detector is positioned a second separation distance from the first light emitter; 
 the second separation distance is greater than the first separation distance; and 
 the method further comprises
 determining a strength of a third signal of a third light detector that is positioned on a second side of the axis; 
 determining a strength of a fourth signal of a fourth light detector that is positioned on the second side of the axis; 
 determining a second ratio of the strength of the third signal and the strength of the fourth signal; and 
 determining that the object is within the critical distance when the second ratio is less than the critical distance value. 
 
 
     
     
       19. The method of  claim 18 , further comprising estimating a tilt or offset of the electronic device relative to the object based on the first and second ratios. 
     
     
       20. The method of  claim 16 , wherein:
 the first signal strength is one of a maximum signal strength, a minimum signal strength, an average signal strength, or a highest confidence signal strength of the light received by the first light detector; and 
 the second signal strength is one of a maximum signal strength, a minimum signal strength, an average signal strength, or a highest confidence signal strength of the light received by the second light detector.

Description:
FIELD 
     The present disclosure generally relates to optical distance measuring devices, electronic devices that include such optical distance measuring devices, and methods of their operation. 
     BACKGROUND 
     Electronic devices are commonplace in today&#39;s society. Example electronic devices include smart watches, wearable health sensing devices, cell phones, tablet computers, personal digital assistants, and the like. More particularly, wearable devices include electronic devices such as electronic watches, smart watches, smart phones, health monitoring devices, fitness monitoring devices, audio playback devices, and so on. 
     Such devices may have one or more sensors or sensor systems that detect when an object exterior to the electronic device is within a certain distance. For example, a smart phone may have detectors that can aid in determining that the smart phone is horizontally placed on or near a flat surface, such as a charging mat. Other examples include smart watches or wearable health monitors that have sensors to detect that they are positioned on or near a user&#39;s body. 
     Such devices may use detection of proximity of an exterior object to enable or disable one or more functions. For example, a smart watch or a wearable health monitor may use proximity detection as part of a determination that it is on a user&#39;s body, and then enable or start monitoring, authentication, or sensing operations. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     Disclosed herein are electronic devices, systems, and methods of their operation. Such electronic devices may include optical or light-based components for estimating distance to, or detecting proximity to, an exterior object. 
     More specifically, described herein is an electronic device, comprising: a housing; a light emitter operable to emit light outward from or through the housing; a first light detector positioned within the housing at a first separation distance from the light emitter; a second light detector positioned within the housing at a second separation distance from the light emitter, the second separation distance different from the first separation distance; and a processor configured to estimate an object distance by: determining a first signal strength of the first light detector; determining a second signal strength of the second light detector; and using the first signal strength and the second signal strength to estimate the object distance; wherein: the object distance is a distance from the electronic device to an object. 
     Also described herein is an electronic device, comprising: a housing; a light emitter operable to emit light outward from or through the housing; a first pair of light detectors positioned on a first side of an axis on which the light emitter lies; a second pair of light detectors positioned on a second side of the axis; and a processor operably connected to the light emitter and the first and second pairs of light detectors; wherein: the processor estimates a first object distance from the electronic device to an object exterior to the electronic device at least partially by determining a ratio of signal strengths of the first pair of light detectors; and the processor estimates a second object distance from the electronic device to the object exterior to the electronic device at least partially by determining a ratio of signal strengths of the second pair of light detectors. 
     The present disclosure also describes a method of operating an electronic device, comprising: estimating that an object exterior to the electronic device is within a critical distance of the electronic device by: emitting, from a light emitter, an emitted light outward from or through a housing of the electronic device; determining a first signal strength produced by a first light detector that varies with a portion of the emitted light reflected from the object and received by the first light detector; determining a second signal strength that varies with another portion of the emitted light reflected from the object and received by the second light detector; determining a ratio of the first signal strength and the second signal strength; determining that the object is within the critical distance when the ratio is less than a critical distance value; and enabling an operation of the electronic device when the object is within the critical distance. 
     These and other embodiments are more fully described in the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. 
         FIG.  1 A  is a functional block diagram of certain components of a device or system, according to an embodiment. 
         FIG.  1 B  is an electrical connection block diagram of certain components of an electronic device or system, according to an embodiment. 
         FIG.  2 A  illustrates a plan view of a housing of an electronic device with light transmitters and light detectors, according to an embodiment. 
         FIG.  2 B  illustrates a plan view of a housing of an electronic device with light transmitters and light detectors, according to an embodiment. 
         FIG.  3    illustrates a plan view of a housing of an electronic device with light transmitters and light detectors, according to an embodiment. 
         FIG.  4    illustrates a perspective view of a housing of an electronic device with light transmitters and light detectors, according to an embodiment. 
         FIG.  5    illustrates a side view of an electronic device in proximity to an exterior object, according to an embodiment. 
         FIGS.  6 A-B  illustrate proximity curves, according to an embodiment. 
         FIG.  7    is a flow chart of a method of operating an electronic device, according to an embodiment. 
         FIG.  8    is a flow chart of a method of operating an electronic device, according to an embodiment. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The embodiments described herein are directed to electronic devices, light or optical distance estimating or measuring components or systems for electronic devices, and methods of operation of such electronic devices or components or systems. In some embodiments, the electronic devices are configured to be worn on, or in proximity to, a user. Examples of such wearable electronic devices include a smart watch, a smart phone, a health monitoring device, or another wearable device. Such wearable electronic devices may benefit from detecting whether they are being worn by a user. Such a detection may be based on an estimated proximity of the electronic device to an exterior object, such as a user&#39;s wrist, arm, leg, or other position. Even electronic devices not primarily designed to be worn may benefit from detection of a proximity to an exterior object. Accordingly, embodiments described herein may detect or estimate a distance between an electronic device and an object external to the electronic device. 
     Typically, distance estimations are performed by emitting light from an emitter of an electronic device toward an object being sensed, receiving emitted light that has been reflected from the object at a first and a second light detector, and using the signal strength of the light received at the first detector and the signal strength of the light received at the second detector to calculate a ratio of signal strengths. This ratio may then be correlated to a distance between the electronic device and the object. It should be appreciated that the emitter emits light of a certain wavelength and the light detectors detect light of that wavelength. Some embodiments may employ or incorporate light detectors that are sensitive substantially only to the wavelength(s) emitted by the light emitter(s), while other may incorporate or employ light detectors that sense a wider range of wavelengths. In embodiments with light detects that sense wider range of wavelengths than are outputted by the light emitter, techniques (such as dark channel subtraction, modulation/demodulation, and the like) or filters (including coatings) may be used to separate emitted light from ambient light. This ensures the light detectors receive and are sensitive to a signal (e.g., light) from the emitter rather than ambient light. 
     Expanding on this example, the first light detector is positioned a first separation distance from the emitter and the second light detector is positioned a second separation distance from the emitter. The first separation distance may be shorter than the second separation distance, such that light travels further from the emitter, to the object, and to the second light detector than light traveling from the emitter, to the object, and to the first light detector. Accordingly, the first light detector may be referred to herein as a “short length” light detector while the second light detector is referred to as a “long length” light detector. Similarly, the routing of the light from the emitter to a light detector may be referred to as a “light path.” 
     Generally, there are two separate distances that affect an amount of light from an emitter that is received by a light detector. First is the separation distance between the emitter and the detector, as discussed above. The further the detector is physically located from the emitter, the less light the detector receives from the emitter. Given a fixed distance between an electronic device and an object being sensed, a short length light detector will almost always receive more light from an emitter than will a long length light detector. Thus, presuming the electronic device is not tilted or offset from the object being sensed, a signal strength at the short length light detector will almost always exceed a signal strength at the long length light detector at any given moment. 
     More emitted light is typically received at the short length light detector than at the long length light detector, insofar as less light is lost to scattering, diffusion, absorption, and the like. It may be appreciated that a signal strength of the light received at the short length detector is greater than a signal strength of light received at the long length detector as a result. Likewise, the signal strength of a signal generated by the short length detector is correspondingly greater than the signal strength of a signal generated by the long length detector. 
     The second distance that affects the amount of light from an emitter that is received by a light detector is the distance between the electronic device and the object reflecting light from the emitter (e.g., the object being sensed). This may be referred to as the “object distance.” As the object distance increases, less light is received by a light detector since the light path increases. That is, light emitted by the emitter travels further to impinge on the object, as well as further to return to the detector. Longer light paths mean more light is scattered away from the detector. Thus, as the object distance increases, the signal strength for a detector usually decreases. 
     The electronic device may generate a ratio of the long length detector&#39;s signal strength to the short length detector&#39;s signal strength. As the object distance increases, this ratio approaches one. Likewise, as the object distance decreases, this ratio approaches zero. Put another way, the further the emitter/electronic device is from the object, the closer the signal strength of both light detectors becomes as the light paths to each detector near the same value. Likewise, as the emitter (and thus the electronic device) approaches the object, the object distance decreases and relative differences in the short and long light paths become greater. 
     Given this relationship between signal strengths and both the separation distance and object distance, the electronic device may use the ratio of signal strengths to estimate distance. Further, a ratio of the two signal strengths is used because the ratio is dimensionless and so is not dependent on any particular quality of the object reflecting light. Thus, embodiments described herein may accurately measure or estimate a distance to two objects that have different light absorptive, diffusive, and/or scattering properties with the same degree of accuracy. 
     Certain embodiments described herein may use multiple pairs of light detectors to determine an object distance. In various embodiments, a light emitter positioned in or on a housing, including on a surface of the electronic device&#39;s housing, emits light outward from the electronic device. If the exterior object is near or proximate to the electronic device, such as within a certain range of object distances, the emitted light may reflect from the object both to a first pair of light detectors and to a second pair of light detectors. The first and second pairs of light detectors are positioned at different separation distances from the emitter, and thus have different light paths. The electronic device may measure signal strengths of the light received at each of the pairs of detectors and generate a ratio of the signal strength of the first pair of light detectors to the signal strength of the second pair of detectors. This ratio of signal strengths may be correlated with a distance of the exterior object from the electronic device, for example by relating the ratio to a proximity curve that correlates the ratio to a distance, or may otherwise be correlated to a distance. Further, because the signal strengths at or generated by each detector in the pair(s) of detectors is used to estimate distance to an object, the estimated object distance does not change as the reflective, absorptive, or scattering properties of the object change. 
     Additional and/or alternative embodiments may use more than two light detectors, more than two pairs of light detectors, and/or more than one light emitter. In the methods described, an electronic device using such object distance detection or measuring embodiments may alter an operational state based on the detections or measurements. 
     Further, a tilt, skew, offset, or other alignment of an electronic device may be determined by comparing signal strength ratios of multiple sets of light detectors, such as multiple pairs of light detectors. Since the detectors are generally coplanar and closer light detectors have higher signal strengths (as they receive more light reflected from an object), the relative signal strengths of the pairs of light detectors indicate the orientation of the electronic device&#39;s housing relative to the object. 
     Although embodiments discuss the use of signal strength ratios, it should be appreciated that other constructs may be employed in lieu of a ratio or signal strength. Certain embodiments may employ any suitable value, measurement, or characteristic of a signal (including frequency, wavelength, phase, and so on) in a distance estimation. Likewise, any suitable construct may be derived from such signal characteristics and used to estimate distance. A “construct” is a value derived by applying a mathematical function to one or more signal characteristics of one or more signals. Thus, a signal strength (e.g., amplitude) is a signal characteristic, while a ratio of signal strengths is a construct. Other constructs may include derivatives, integrals, rates, proportions, summations, squares, roots, or powers of other constructs, “constructs of constructs” (e.g., a derivative of a ratio) and so on. Additionally, a “signal strength ratio,” as used herein, may refer to a ratio of signal strengths that are measured or calculated at a single point in time, measured or calculated from an averaged or weighted set of signal strengths measured across a time period, or some particular measurement of signal strength (such as maximum signal strength, minimum signal strength, average signal strength, highest confidence signal strength, and so on). 
     These and other embodiments are discussed below with reference to  FIGS.  1 A- 8   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Further, the term “exemplary” does not mean that the described example is preferred or better than other examples. 
     In the following Figures, like reference numerals are used to designate similar or related components or features. However, it is not implied that such components or features are necessarily identical. Variations of those components or features, as would be known to one skilled in the art, are within the scope of the disclosure for the components or features having like reference numerals. 
       FIG.  1 A  shows a functional block diagram of an electronic device (or device)  100 . In some examples, the device  100  may be a wearable device, such as an electronic watch, smart watch, smart phone, health monitoring device, fitness monitoring device, or audio playback device that is wearable on a wrist of a user. The device  100  may also or alternatively be wearable on an ankle, arm, forehead, waist, or other body part, or may be positionable or attachable to another device (e.g., a seat cushion or bed). The device  100  may include one or more input devices  102 , one or more output devices  104 , and a processor  106 . As used herein, a “processor,” such as the processor  106 , may refer to any of a singular processor, a set of multiple processors, a microprocessor or microcontroller, a field programmable gate array, and/or another type of processor in combination with supporting circuitry. Broadly, the input device(s)  102  may detect various types of user input or sense various types of parameters, and the output device(s)  106  may provide various types of outputs. 
     In some cases, user input and/or parameters that are sensed by the input device(s)  102  may be used to control one or more settings, functions, or other aspects of the device  100 , or may be provided to a remote device. Particular examples of input devices  102  include light emitters and light detectors as discussed in the embodiments described below. In some cases, one or more of the output devices  104  may be configured to provide output that is dependent on, or manipulated in response to, the user input and/or parameters sensed by one or more of the input devices  102 . The outputs provided by one or more of the output devices  104  may also be responsive to, or initiated by, a program or application that is executed by the processor  106  and/or an associated companion device. The output devices  104  may include any suitable components for generating or communicating outputs. Examples of output devices  104  include audio output devices (e.g., speakers), visual output devices (e.g., lights, displays, or other electromagnetic radiation emitters), tactile output devices (e.g., haptic output devices), communication devices (e.g., wired or wireless communication devices), and so on, or some combination thereof. Each output device  104  may be configured to receive signals, data, or instructions from the processor  106  and/or one or more of the input devices  102 , and to provide one or more outputs dictated by the signals, data, or instructions. 
     The processor  106  may be operably coupled to the input devices  102  and the output devices  104 . The processor  106  may receive inputs (e.g., signals, statuses, and/or measurements) directly or indirectly from the input device(s)  102 , in response to user input and/or parameters sensed by the input device(s)  102 . In some cases, the processor  106  may interpret the inputs. In response to the inputs, or interpreted inputs, the processor  106  may maintain or alter one or more settings, functions, or aspects of the device  100  and, in some cases, the processor  106  may provide signals, data, or instructions to one or more of the output devices  104 . In some cases, the processor  106  may provide signals, data, or instructions to one or more of the output devices  104  independently of any input received from an input device  102 . A signal, data, or instruction provided to an output device  104  may cause the output device  104  to generate one or more outputs (e.g., an audio output, a visual output, a tactile output, one or more signals or instructions, and so on). Examples of suitable processors are discussed in more detail below with reference to  FIG.  1 B . 
       FIG.  1 B  shows an example electrical block diagram of an electronic device  110 , such as electrical device  100  and the electronic devices described in the embodiments below. The electronic device  110  may include an electronic display  112  (e.g., a light-emitting display), a processor  114 , a power source  116 , a memory  118  or storage device, a subsystem  120  of light emitters and light detectors, or an input/output (I/O) mechanism  122  (e.g., an input/output device, input/output port, or haptic input/output interface). The processor  114  may control some or all of the operations of the electronic device  110 . The processor  114  may communicate, either directly or indirectly, with some or all of the other components of the electronic device  110 . For example, a system bus or other communication mechanism  124  can provide communication between the electronic display  112 , the processor  114 , the power source  116 , the memory  118 , the subsystem  120  of light emitters and light detectors, and the I/O mechanism  122 . 
     The processor  114  may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions, whether such data or instructions are in the form of software or firmware or otherwise encoded. For example, the processor  114  may include a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a controller, or a combination of such devices. As described herein, the term “processor” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. It should be noted that the components of the electronic device  110  can be controlled by multiple processors. For example, select components of the electronic device  110  (e.g., subsystem  120  of light emitters and light detectors) may be controlled by a first processor and other components of the electronic device  110  (e.g., the electronic display  112 ) may be controlled by a second processor, where the first and second processors may or may not be in communication with each other. 
     The power source  116  can be implemented with any device capable of providing energy to the electronic device  110 . For example, the power source  116  may include one or more batteries or rechargeable batteries. Additionally or alternatively, the power source  116  may include a power connector or power cord that connects the electronic device  110  to another power source, such as a wall outlet. 
     The memory  118  may store electronic data that can be used by the electronic device  110 . For example, the memory  118  may store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing signals, control signals, and data structures or databases. The memory  118  may include any type of memory. By way of example only, the memory  118  may include random access memory, read-only memory, flash memory, removable memory, other types of storage elements, or combinations of such memory types. 
     The electronic device  110  may also include a subsystem  120  of light emitters and light detectors, potentially positioned almost anywhere on the electronic device  110 . In some cases, the subsystem  120  may include one or more electromagnetic radiation emitters and detectors, positioned and/or configured as described with reference to any of  FIGS.  2 A- 8   . 
     The I/O mechanism  122  may transmit or receive data from a user or another electronic device. The I/O mechanism  122  may include the electronic display  112 , a touch sensing input mechanism (such as a touch-sensitive display, button, or portion of a housing), a crown, one or more buttons (e.g., a graphical user interface “home” button), one or more cameras (including an under-display camera), one or more microphones or speakers, one or more ports, such as a microphone port, and/or a keyboard, all of which are optional. Additionally or alternatively, the I/O mechanism  122  may transmit electronic signals via a communications interface, such as a wireless, wired, and/or optical communications interface. Examples of wireless and wired communications interfaces include, but are not limited to, cellular and Wi-Fi communications interfaces. 
       FIG.  2 A  shows a plan view of a housing  201  of an electronic device  200 . The housing  201  may be define an exterior (including a back side) of a smart watch, a wearable health monitor that attaches to a user, a smart phone, or another electronic device. The back side of the electronic device  200  is shown in the plan view as a rectangle, but other shapes are possible. The electronic device  200  includes various optical and other components that it may use to determine proximity of an exterior object or estimate the object distance. 
     The electronic device  200 , as shown, includes a first light emitter  202 . The light emitter  202  may be a light emitting diode, a laser diode, or another component able to emit light. The light emitter  202  may be an infrared laser diode, though this is not required in the embodiments. The wavelength or spectral range of the light emitted by the first light emitter  202  may be fixed or variable, such as depending on a received input or control signal. The light emitter  202  may be able to emit light, which may be triggered by received input or control signals, such as from the processor  106 , and may be emitted sequentially, and may have a variable duration and duty cycle. The light emitter may be positioned at, in, or proximate to the housing  201  so as to emit light in a certain direction outward from the electronic device  200 . In some embodiments, the light emitter  202  may be a laser emitter, and may be mounted in a movable fixture, such as a piezoelectric or piezo-resistive fixture, that allows the emitted laser light to be steered. 
     In some embodiments, the light emitters (and/or the detectors discussed below) may be positioned within the housing  201  or beneath a cover attached to, or forming part of, the housing. This cover may be formed from glass, sapphire, plastic, crystal, or the like. Either or both of the housing or such an element may be optically transparent in a visible spectrum, or may be partly transparent at infrared, ultraviolet, and/or other wavelengths while being visibly opaque. In some examples, the housing or cover (or other suitable element) may be optically and/or infrared transparent but covered with an optical and/or infrared barrier, such as a coating or ink. This barrier may define one or more windows through which light may enter or exit the housing  201  or cover. As one non-limiting example, the barrier may define a window over one or more emitters as discussed herein, thus permitting light to exit the emitter and the device  400 . It should be appreciated that the window may be fully defined by the barrier or may be defined by cooperation between the barrier and the housing of cover on which the barrier is deposited (e.g., the housing or cover may be thinned, raised, stepped, or otherwise configured to facilitate light transmission therethrough or provide a demarcation for the barrier), although this is not necessary. Although this description is given with respect to  FIG.  2 A , it should be appreciated that it is equally applicable to all embodiments discussed herein, specifically including those of  FIGS.  2 B- 5   . 
     The electronic device  200  also includes two pairs of light detectors: the first pair  204   a  and  204   b , and the second pair  208   a  and  208   b . Each of the four light detectors  204   a ,  204   b ,  208   a , and  208   b  may be implemented using known photon or light detection technologies, such as CMOS photodetectors, photodiodes, or another technology. The four light detectors  204   a ,  204   b ,  208   a , and  208   b  may be implemented with different technologies. The four light detectors  204   a ,  204   b ,  208   a , and  208   b  may be positioned proximate to the housing  201 , such as by being coplanar with the housing  201  of the electronic device  200 , or may be positioned within the housing  201 . In some cases, a glass, sapphire, or crystal cover or element may define a portion of, or may be affixed to or over, the housing  201 . The four light detectors  204   a ,  204   b ,  208   a , and  208   b  may detect light having a specific wavelength or within a specific wavelength range, and may generate a signal having a signal strength that varies with an amount of light that is emitted by the emitter and detected or received by the light detector. Put another way, the signal strength may increase as more emitted light is received by a light detector  204   a ,  204   b ,  208   a ,  208   b  and decrease as less emitted light is received by a light detector. One or more of the four light detectors  204   a ,  204   b ,  208   a , and  208   b  may be positioned so as to preferentially detect light entering from within a limited solid angle, such as light entering from the direction of the light emitter  202 . In some embodiments, the light detectors receive light through the housing  201 , a back cover, or the like. Further, although the light detectors are visible in  FIGS.  2 A- 2 B , they may be hidden from view not only by the housing or cover, but also by an ink or coating that is visually opaque but passes light in the wavelengths emitted by the light emitters  202 . 
     Signals (such as voltage or current signals) produced by any of the four light detectors  204   a ,  204   b ,  208   a , and  208   b  in response to detection of light, and their relative signal strengths, may be received and processed by control electronics within the electronic device  200 , such as the processor  106 . It should be appreciated that the signal strengths used to determine a ratio, and thus a distance to an object (e.g., an object distance), may be either a signal strength of light received by a light detector or a signal strength of a signal generated by a light detector in response to receiving light. In some embodiments, constructs other than ratios may be used. 
     One or more of the four light detectors  204   a ,  204   b ,  208   a , and  208   b  may have filters at, or in the housing  201  to remove or reduce impinging light outside the wavelength range of light emitted by the light emitter  202 . These filters may be in addition to the coating described above, or the coating may function as such a filter. 
     The first pair of light detectors  204   a  and  204   b  are positioned in or on the housing  201  at different respective separation distances  206   a  and  206   b  from the light emitter  202 . In the embodiment shown, the separation distance  206   a  is less than the separation distance  206   b  (e.g., the separation distance  206  is a short length and the separation distance  206   b  is a long length). The first pair of light detectors  204   a  and  204   b  need not be collinear with the light emitter  202 , though they may be. Similarly, the second pair of light detectors  208   a  and  208   b  are positioned in or on the housing  201  at different respective separation distances  210   a  and  210   b  from the light emitter  202 . In the embodiment shown, the separation distance  210   a  is a short length while the separation distance  210   b  is a long length. Again, the second pair of light detectors  208   a  and  208   b  need not be collinear with the light emitter  202 , though they may be. In the embodiment shown, the separation distance  206   a  is equal (or nearly equal) to the separation distance  210   a , and the separation distance  206   b  is equal (or nearly equal) to the separation distance  210   b , but this is not required. When a detector or emitter is described as “in or on the housing,” it should be appreciated this encompasses such detectors or emitters being in or on an element attached to the housing, such as a cover or crystal, as well. 
     The electronic device  200  may include a second light emitter  212  positioned on or proximate to the housing  201 . The second light emitter  212  may emit light having the same, a similar, or a different wavelength or wavelength spectrum than that of the light emitted by the first light emitter  202 . The first and second light emitters may emit light at different times, such that the light detectors  204   a ,  204   b ,  208   a ,  208   b  receive light from only one emitter at any given time; in embodiments where the first and second light emitters emit light having the same wavelength(s), such time multiplexing may be employed to ensure that light detectors receive light from only one emitter at any given instant (although this is not necessary). Alternately, the first and second emitters may emit light having different wavelengths simultaneously, and the light detectors may be configured to detect both wavelengths separately (or some detectors may detect light from the first emitter and some may detect light from the second emitter). 
     In the embodiment shown in  FIGS.  2 A-B , the light emitter  202  and light emitter  212  lie on an axis (vertical in the orientation shown in  FIG.  2 A ). In the embodiment shown, the first pair of light detectors  204   a ,  204   b  are on a first side (left) of the axis, with the second pair of light detectors  208   a ,  208   b  on the opposite side (right) of the axis. By splitting the light detectors into pairs, with each pair on an opposing side of the axis, the embodiment may compare signal strength ratios (or other constructs) between pairs of detectors. That is, the signal strength ratio of each signal generated by a first pair of light detectors  204   a ,  204   b  may be compared against the signal strength ratio of each signal generated by a second pair of light detectors  208   a ,  208   b.    
     Generally, as separation distances  206   a ,  206   b ,  210   a ,  210   b  increase, the corresponding path length increases, light impinging on a light detector  204   a ,  204   b ,  208   a ,  208   b  decreases and so the signal strength of a light detector will decrease. Likewise, as a separation distance decreases between an emitter and light detector, the detector receives more of the emitted light and so signal strength increases. Accordingly, short separation distances (and short path lengths) yield higher signal strength from a light detector while long separation distances (and long path lengths) yield lower signal strength from the light detector. 
     Further, in any given orientation, the signal strength ratio of one of the pairs of detectors will be less than the signal strength ratio of the other of the pair of detectors. Generally, the pair of detectors nearest an object will have the highest signal strength ratio, as the light travels a short distance both from the emitter to the object and when reflected from the object to the light detectors closest to the object. By comparing the signal strength ratios of the two pairs of detectors to one another, the electronic device may determine which pair of light detectors  204   a ,  204   b , or  208   a ,  208   b  is closest to the object. This, in turn, may be used to determine a tilt of the electronic device with respect to the object; the side of the electronic device on which the pair of light detectors having the highest signal strength ratio is located is closest to the object. Again and as referenced above, each pair of detectors is defined by its location on one side or another of an axis passing through the emitter (e.g., on which the emitter lies). 
     It should be appreciated that the signal strength ratio need not be a ratio of signal strengths measured at an instantaneous point in time. Rather, the ratio may be derived from signal strengths that are measured or calculated at a single point in time, measured or calculated from an averaged or weighted set of signal strengths measured across a period, or some particular measurement of signal strength (such as maximum signal strength, minimum signal strength, average signal strength, highest confidence signal strength, and so on). 
       FIG.  2 B  shows a plan view similar to that of  FIG.  2 A  for the electronic device  200 . In  FIG.  2 B  are shown the two respective separation distances  214   a  and  214   b  from a second light emitter  212  to the first pair of light detectors  204   a  and  204   b . In the embodiment shown, the separation distance  214   a  is greater than the distance  214   b . Similarly,  FIG.  2 B  shows the two respective separation distances  216   a  and  216   b  from the light emitter  212  to the second pair of light detectors  208   a  and  208   b . In the embodiment shown, the separation distance  216   a  is greater than the separation distance  216   b.    
     In some embodiments, the separation distance  214   a  may be equal to the separation distance  206   b  (e.g., both are short lengths), the separation distance  214   b  may equal the separation distance  206   a  (e.g., both are long lengths), the separation distance  216   a  may equal the separation distance  210   b  (again, both are long lengths), and the separation distance  216   b  may equal the separation distance  210   a  (again, both are short lengths). Herein, “equal” will mean equal to within a numerical tolerance appropriate for the scale of the embodiment. However, these equalities are not required: they may not be implemented in other embodiments. Signal strength ratios (or other constructs) may be calculated for each of the light detector pairs  204   a ,  204   b  and  208   a ,  208   b  with respect to light emitted by the second light emitter  212 . By comparing the signal strength ratio of a given pair of light detectors for light emitted by a first emitter  202  to that generated by light emitted by a second light emitter  212 , the electronic device  200  may determine which light emitter  202 ,  212  is closer to an object reflecting light. Accordingly, an embodiment may determine tilt of the electronic device, with respect to the object, about two axes. 
     While the embodiments described in relation to  FIGS.  2 A-B  have two light emitters  202  and  212 , other embodiments may use a single light emitter on the housing  201  of the electronic device  200 . Such single light emitter embodiments may use a single pair of light detectors, or two or more pairs of light detectors. The methods of operation of such alternative embodiments are related to the methods of operation discussed below, and will be apparent to one skilled in the art. 
       FIG.  3    shows a plan view of a surface of housing  301  of an electronic device  300 . The surface may be a backside of a smart watch, a wearable health monitor that attaches to a user, a smart phone, or another electronic device. The backside of the electronic device  300  is shown in the plan view as a rectangle, but other shapes are possible. The electronic device  300  includes various optical and other components that it may use to determine proximity of an exterior object or estimate an object distance separating the exterior object from the electronic device. The electronic device  300  may be the same as, or a variation of, the electronic device  200  described in relation to  FIGS.  2 A-B   
     The electronic device  300  includes a first pair of light emitters  202 ,  212  such as described in relation to  FIGS.  2 A-B . As shown, the first pair of light emitters  202 ,  212  are positioned oppositely along an axis  302 . The electronic device  300  also includes a first pair of light detectors  204   a ,  204   b  such as described in relation to  FIGS.  2 A-B , and a second pair of light detectors  208   a ,  208   b , such as described in relation to  FIGS.  2 A-B . In the configuration of the embodiment shown, the first pair of light detectors  204   a ,  204   b  is positioned on a first side of the axis  302 , and the second pair of light detectors  208   a ,  208   b  is positioned on a second side of the axis  302 . However, other embodiments may use other configurations. In the configuration shown, the first pair of light detectors  204   a ,  204   b  is positioned along a line segment approximately parallel to the axis  302 , and similarly the second pair of light detectors  208   a ,  208   b  is positioned along another line segment approximately parallel to the axis  302 . However, this is not required, and other embodiments may use different positioning configurations for the first and second pairs of light detectors. 
     The electronic device  300  also includes a third light emitter  304   a  and a fourth light emitter  304   b  positioned oppositely along a second axis  310 . In the configuration shown, the second axis  310  is horizontal and intersects the first, vertical axis  302  approximately perpendicularly. However, in other configurations the second axis  310  may intersect the first axis  302  at an angle different from a right angle. In the configuration shown, the second axis  310  approximately bisects each of the first and second light emitter pairs, so that the light detectors  204   a  and  208   a  are on a first (top) side of the axis  310 , and the light detectors  204   b  and  208   b  are on the opposite side of the second axis  310 . However, this configuration is not required. 
     In the configuration shown, the light emitter  304   a  has separation distance  306   a  to the light detector  204   a , and separation distance  306   b  to the light detector  208   a , which is greater than the separation distance  306   a . The light emitter  304   a  also has separation distance  306   c  to the light detector  204   b , and separation distance  306   d  to the light detector  208   b , which is greater than the separation distance  306   c . For the sake of simplicity, the separation distances between emitters and detectors are shown rather than the corresponding light paths. Light paths between emitters and detectors will in actuality be angled paths that reflect off an object to be sensed by the device  300 . This is shown, for example, in  FIG.  5   . 
     In the configuration shown, the light emitter  304   b  has separation distance  308   a  to the light detector  208   a , and separation distance  308   b  to the light detector  204   a , which is greater than the separation distance  308   a . The light emitter  304   b  also has separation distance  308   c  to the light detector  208   b , and separation distance  308   d  to the light detector  204   b , which is greater than the separation distance  308   a.    
     The operation of the emitters  304   a ,  304   b  and light detectors  204   a ,  204   b ,  208   a ,  208   b  is generally the same as described above with respect to  FIGS.  2 A- 2 B , and signal strength ratios for pairs of light emitters may be calculated in a similar fashion. Here, however, light detectors  204   a ,  208   a  may form a first pair while light detectors  204   b ,  208   b  form a second pair. This may permit the electronic device to determine and object distance, as well as tilt with respect to an object and about a second axis  310 . 
       FIG.  4    shows a perspective view of an exemplary electronic device  400  that incorporates the object distance measuring components described above (e.g., emitters and light detectors). In the example shown, the electronic device  400  is a smart watch, with the object distance measuring components emitting and receiving light through a backside of a housing  401 . The backside of the housing  401  may be defined by a cover that is attached to, and cooperates with, a shell or other element forming a portion of the backside and/or the sidewalls and/or at least a portion of a front of the housing. The smart watch  400  may be worn by a user, such as on a wrist, by using a watch band, whose ends  414   a ,  414   b  are shown attached to opposite edges of the smart watch  400 . The smart watch  400  may include one or more input or selection devices, such as a crown  411  or a button  410 . 
     When worn, the backside surface  401  may be positioned next to, and oriented toward, a user&#39;s wrist or arm. The object distance measuring components and their methods of operation may allow the smart watch  400  to change operational states or modes depending on a determined or estimated proximity of the smart watch  400  to the user&#39;s wrist or arm. An “operational state,” as used herein, may be an on-user mode, off-user mode, a power-on mode, a power-off mode, a mode in which full functionality of the electronic device is accessible, a mode in which limited or no functionality of the device is accessible, and so on. Certain example operational states are discussed more herein. 
     In the embodiment shown, the electronic device  400  includes the configuration of components described in relation to  FIGS.  2 A-B . More specifically, the electronic device  400  includes a first light emitter  402  and a second light emitter  412  defining an axis across the backside of the housing  401 . A first pair of light detectors  404   a ,  404   b  is positioned on a first side of the axis, and a second pair of light detectors  408   a ,  408   b  is positioned on an opposite side of the axis. 
     One skilled in the art may recognize that the electronic device  400  may alternatively include the configuration of components described in relation to  FIG.  3   , or may include a single light emitter and a single pair (or more) of light detectors. In another embodiment, two light emitters are positioned as in  FIG.  2 A . A single pair of light detectors is positioned between the two light emitters along an axis on which the two light emitters lie. By positioning the light detectors and light emitters in a straight line, the impact of ambient light on operation of the system may be reduced as compared to other embodiments. 
     In yet another embodiment, two light emitters are positioned adjacent to each other at one end of the electronic device. For example, light emitters may be positioned at one end of the back side surface of the housing, such that each is on an opposite side of a central axis (similar to an axis intersecting emitters  402 ,  412  of  FIG.  4   ). In such an embodiment, a single pair of light detectors may be positioned on the central axis. Each light emitter may emit its respective light at a non-right angle with respect to the central axis. 
     Any of the various configurations of light emitters and light detectors discussed above may be operated by the respective electronic device to determine if an exterior object is near or proximate to the electronic device, and/or to determine or estimate an object distance between the electronic device and the object. 
     As an overview, the determinations or estimations of object distances (and/or of tilts of an object with respect to the plane defined by the housing) are made by emitting light from at least one light emitter, and receiving respective reflections from the object at one (or more) pairs of light detectors. By using signal strengths corresponding to the amount of emitted light received at the light detectors, an object distance may be estimated. When the two light detectors are at different separation distances from the emitter, the path lengths traveled by light from the emitter to a respective light detector will be different and different amounts of light will be received by each of the light detectors, and different signal strengths will result. Thus, one of the light detectors will be a “short length” light detector as light travels a relatively short distance from the emitter, to the object, and back to this light detectors. A second light detector will be a “long length” detector as light travels a relatively long distance from the light emitter, to the object, and back to this second light detector. A ratio of signal strengths (either the “short length” light detector&#39;s signal strength divided by the “long length” light detector&#39;s signal strengths, or vice versa) may then be related to a proximity curve. 
     A proximity curve provides a relation from a value of the ratio to a value of an object distance, e.g., a distance between the electronic device and the exterior object. Such a proximity curve may be obtained either experimentally, or by geometric considerations. Further, a proximity curve may be implemented as a list of respective values of ratios and object distances, which may be implemented in the electronic device as a look-up table, with interpolation used for ratio values not in a list or table. In some embodiments, the proximity curve may include a critical distance value, which equates to a critical distance. The critical distance is the distance at which an electronic object may alter operations, states, functionality, power modes, or the like, as described herein. For example, when the electronic device is closer to the object than a critical distance, the electronic device may be in an “on-user” mode while the electronic device assumes an “off-user” mode when the distance between it and the object meets or exceeds the critical distance. On-user and off-user modes are described in more detail herein; generally (although not necessarily), full functionality of an electronic device is accessible to a user when the device is in the on-user state while limited or no functionality is accessible to the user when the device is in an off-user state. Alternatively, the proximity curve may be implemented as a function or algorithm, such as may be executed by a processor. Such a function may be obtained by a fit to a finite number of experimentally determined data points, or by geometric considerations. 
     When the ratio is compared to the proximity curve to obtain an object distance value, a determination may be made therefrom whether the object is within a critical distance of the electronic device. An operational state of the electronic device may then be adjusted depending on whether the exterior object is within the critical distance. For example, if the electronic device is operating under the assumption that it is away from or not on a user (e.g., not detecting heart beats, or locked from receiving user entries), and the object distance is then determined to be within the critical distance, the electronic device may initiate on-user operations (e.g., monitoring heart beasts, or initiating a logon operation). Alternatively, if the electronic device is operating under the assumption it is away from, or not positioned on, a user because the object distance is determined to be greater than the critical distance, the electronic device may maintain off-user status and respective operations. Analogous “maintain or change” operational decisions may occur if the electronic device is under the assumption that it is on a user or near the object. 
     As an additional operation, if a determination is made that the object is within the critical distance, the electronic device may perform a confirmation operation. For example, an initial determination made that the object is within the critical distance may be based on a ratio obtained from a first pair of light detectors. To verify this determination, the electronic device may use a ratio obtained from a second pair of light detectors, which may receive light from a second light emitter different from the light emitter used in the initial determination. The electronic device may enable (e.g., turn on) the second light emitter as part of the confirmation operation. Such a confirmation operation may be used in cases when the initial determination would cause the electronic device to alter its operational state. Similarly, if an initial determination is made that the object has moved (or is now) beyond the critical distance, the electronic device may confirm that initial distance determination using a second ratio based on the signal strengths of a second pair of light detectors, which also may be based on light from a second light emitter. As yet another example of a confirmation operation, the electronic device may form a second ratio using the initially used pair of light detectors but based on second signal strengths obtained from another light emitter, either from the initially used light emitter or from a second light emitter. 
     The electronic device may perform initial operations, such as calibration, with the light emitter(s) and light detectors. One calibration operation may use a measured scale factor for each optical path; e.g., at manufacture or periodically by a user, a calibration operation detects light from a standard reflective surface, and adjusts one or more scale factors for the signal strengths from the light detectors. 
     In operation, it may be that one or more signal strengths may be too low or too high to be considered reliable. In a first example, when the exterior object is in contact with the electronic device, little emitted light from one or more light emitters may not be received at the respective light detectors, such as due to complete absorption or surface irregularities of the exterior object, producing a too-low signal strength. In a second example, ambient light or another source of light may make one or more signal strengths noisy or close to or within a noise level. In a third example, a localized highly reflective area on the exterior object may cause the signal strength of the farther light to exceed that of the nearer light detector. 
     In these or other examples, the electronic device may determine that a ratio would not be reliable. The electronic device may then discard the ratio from use in determining whether the exterior object is within a critical distance. The electronic device may instead use a ratio of signal strengths from another pair of light detectors induced by light from another light emitter. Alternately, the electronic device may cause further emissions of light until a valid ratio is found. 
     Although embodiments are described herein as using a proximity curve to relate the signal strength ratio to the object distance, it should be understood that this is one sample way in which the signal strength ratio (or other construct) may be related or correlated to the object distance. Look-up tables or mathematical functions may be used in other embodiments and so the use of a proximity curve should be understood to be an example rather than a limitation. 
     Some embodiments may use more than one light emitter. For example, two light emitters may be positioned on or in the housing, as described above, and along an axis, with two pairs of light detectors configured as shown in  FIG.  2 A . The two light emitters may alternate to emit respective light. As each light is emitted, the respective light emitter may make its own determination or estimation of the object distance based on one or more signal strengths or ratios of signal strengths, as described herein. The two object distance estimates may be averaged, such as to reduce noise effects, or one may be discarded as an unreliable value (outside of an expected range). Further, it should be appreciated that, in embodiments employing two emitters, a single detector may receive light from each of the emitters at separate times; insofar as the signals received by the single light detector will vary, these signals may be used to determine a ratio and then estimate a distance to an object in a manner similar to that described herein with respect to embodiments having one emitter and multiple detectors. 
     In further methods, multiple light emitters may emit an alternating sequence of light (or may receive another triggering pattern for emissions from a processor), and for each light form a sequence of respective estimates of the object distance. This sequence of respective estimates of the object distance may be time-averaged (possibly with weights) to reduce the chance of spurious state changes. 
     In further methods, for embodiments with either a single light emitter or multiple light emitters, the light emitter(s) may emit a sequence of light pulses, with corresponding duty cycles. The light detectors may be enabled for reception only during each pulse emission period, or section thereof, to detect the pulse&#39;s reflections. The strengths of the light detectors&#39; corresponding signals may be time-averaged to reduce false state change operations. 
     As another option for an embodiment having multiple light emitters, such as for the configuration shown in  FIGS.  2 A-B , a first light emitter may emit light directed to a first pair of light detectors whose two light detectors are at two different separation distances from that first light emitter (e.g., in  FIG.  2 A  light emitter  202  is used with just light detectors  208   a  and  208   b ). A ratio of the signal strengths from just that pair of light detectors is used to obtain a first estimate of the object distance. Then, a second light emitter may emit another light directed to a second pair of light detectors whose two light detectors are also at two different separation distances from that second light emitter (e.g., in  FIG.  2 A , light emitter  212  is used with just light detectors  204   a  and  204   b ). A ratio of the signal strengths from just that second pair of light detectors is used to obtain a second estimate of the object distance. A difference in the estimates may be used to estimate a tilt, offset, or skew of the exterior object. 
     Still other embodiments may have a configuration that uses four light emitters, such as arranged in the “crossed-axis” configuration shown in  FIG.  3   . Each light emitter may emit, sequentially, a respective light. Respective estimates of an object distance may be made, such as by, for each light, using average signal strengths from multiple pairs of light detectors. The four estimates may be averaged (possibly with weights, such as based on signal strength), with possibly any outlier values discarded. Or, for each light, signal strengths from just as single pair of light detectors may be used to obtain separate estimates of object distances that may indicate tilt or orientation of the object. 
       FIG.  5    shows a cross-sectional view of an electronic device  500  and an exterior object  510  that is at an object distance OD  512  from the electronic device  500 . The electronic device  500  has a housing  501 , and may have an optional cover (such as a crystal or cover on a smart watch)  503 . The electronic device  500  includes a light emitter  502  positioned on the housing  501 , or proximate to the housing  501 , and able to emit light toward the object  510 . 
     The electronic device  500  also includes a first pair of light detectors: the first light detector  504   a  positioned on or proximate to the exterior of the housing  501  at a separation distance d 1    514   a  from the light emitter  502  and a second light detector  504   b  positioned on or proximate to the housing  501  at a separation distance d 2    514   b  from the light emitter  502 . Also, the electronic device  500  includes a second pair of light detectors: the light detectors  504   c  and  504   d , respectively at separation distances d 1    514   a  and  d   2    514   b . For simplicity, the pairs of light detectors are shown along parallel lines but this need not be the case. 
     Light emitted from the light emitter  502  may follow two light paths to be detected at the light detectors  504   a ,  504   b , and/or may also follow two analogous light paths to be detected at the light detectors  504   c ,  504   d . These light paths are generalized examples of how light may reach the emitters rather than specific, necessary paths. The first light path consists of the outward path section  506   a  and the reflected path section  506   b , extending from the point of reflection  506   d  to the light detector  504   a . At the point of reflection  506   d , light may be reflected or refracted in multiple directions such that some light is not received at (or does not impinge on) the light detector  504   a , as indicated by the reflections  506   c . The second light path consists of the outward path section  508   a  and the reflected path section  508   b , extending from the second point  508   d  to the light detector  504   b . At the point of reflection  508   d , some light may be reflected or refracted in multiple directions such that this light is not received at (or does not impinge on) the light detector  504   b , as indicated the reflection  508   c.    
     The two light paths will have different total travel distances (or “path lengths”). Given a stationary object, path lengths increase as separation distance increases. As the path lengths increase, more light is scattered from the object  510  and so is not received by the light detector. Accordingly, the signal strength of light at light detector  504   b  is less than that measured at light detector  504   a . Similarly, if the electronic device  500  is tilted as shown in  FIG.  5   , light detector  504   c  is further away from object  510  than is light detector  504   a  and light detector  504   d  is further away from object  510  than is detector  504   c . Thus, the first light detector pair (e.g., light detectors  504   a  and  504   b ) receives signals having higher strengths than does the second light detector pair (e.g., light detectors  504   c  and  504   d ). Put another way, each of the light detectors in the first light detector pair receive more light as compared to their counterparts in the second light detector pair. Thus, the signal strength ratio of the first light detector pair is greater than the signal strength ratio of the second light detector pair. This is true whether the signal strength is that of the light received by a light detector or the signal generated by a given light detector in response to receiving light, insofar as the signal strength of a generated signal is proportional to the amount of light received. Accordingly, the electronic device  500  may determine that it is tilted or offset in such a fashion that the light detectors  504   a ,  504   b  are closer to the object  510  than are the light detectors  504   c ,  504   d.    
       FIG.  6 A  shows a first graph  600  of a proximity curve  604  in which the horizontal axis  602   a  represents the object distance Dist (which is OD of  FIG.  5   ), and the vertical axis  602   b  represents the ratio value of the signal strength of the detector that is nearest the emitter (e.g., the short length detector) divided by a signal strength of the detectors that is furthest from the emitter (e.g., the long length detector). The proximity curve  604  may be obtained from a geometric analysis or from interpolation from experimentally measured values, as indicated by the discrete points  605 . 
     In the case that the ratio value is less than or equal to the critical distance value  608 , it may be determined that the object distance is less than or equal to a critical distance D crit    606  at which the electronic device may determine that the object is sufficiently close (for example, that a smart watch is being worn, or health monitor is attached to patient) for the electronic device to enter a corresponding operational state or mode. The “critical distance value” is a value of the ratio that corresponds to a critical distance. Accordingly and as used herein, the critical distance value is dimensionless (as is the ratio) and is not, itself, a measurement of distance but instead correlates to a critical distance. In some embodiments, the critical distance is a distance typically reached only when an electronic device has been removed from a wearer, and/or a distance at which certain functions of the electronic device do not operate, cease to become reliable, or otherwise are altered. The critical distance thus may be a distance that, when exceeded, causes the electronic device to change certain operations, functionalities, states, or the like. In certain embodiments, the critical distance may be approximately 10 centimeters, although this may vary between embodiments. 
     In some embodiments, the electronic device may use two critical distances: a near critical distance and a far critical distance. The electronic device may have three distinct operational states based on the two critical distance values. In a first situation, a determined object distance is less than the near critical distance, and so the electronic device may determine that is sufficiently close to the object to enable a first operational state (for example, a fully operational state). In a second situation, the determined object distance is greater than the far critical distance and so the electronic device may determine that it should enable a second operational state (for example, a powered-off state, a locked state, or the like). In a third situation, the determined object distance is greater than the near critical distance but less far the longer critical distance. In this this situation, the electronic device may be in a zone of uncertainty, where it may not be close enough to the object to enable the first operational state and not far enough from the object to enable the second operational state. In some embodiments, the electronic device may enable a third operational state when the determined object distance is greater than the near critical distance but less than the far critical distance. For example, the third operational state may provide limited functionality, may provide full functionality for a limited time, or may provide no functionality for a limited time. As another option, the electronic device may maintain its operational state for a limited time while it is in the zone of uncertainty rather than changing operational states. 
     The ratio value calculated by dividing the long length detector&#39;s signal strength by the short length detector&#39;s signal strength is always less than one, and the ratio (and thus proximity curve  604 ) approaches one as the value of Dist increases. As the value of Dist approaches 0, the ratio would, from geometric considerations, approach the limit ratio value  610   b  equal to d 1 /d 2  for d 1    514   a  and  d   2    514   b  as shown in  FIG.  5   . However, for such small values of Dist, such as below a limit value  610   a , the electronic device&#39;s measurements or determinations of the signal strengths may approach a constant, or may become indeterminate or invalid, insofar as the variation in signal strengths becomes extremely large. 
     Further, a tilt, skew, offset, or other alignment of an electronic device may be determined by comparing the relative signal strength ratios of different pairs of detectors and/or detectors within a pair. Since the detectors are generally coplanar and light detectors that are closer to an object have higher signal strengths (as they receive more light reflected from the object), the relative signal strengths of the light detectors indicate the orientation of the electronic device&#39;s housing relative to the object. “Tilt” generally refers to a condition where a surface of the electronic device through which light is emitted (an “emission surface”) extends at an angle from a surface of an object, or from a plane generally containing a surface of the object (an “object plane”). “Offset” refers to a condition where the emission surface of the electronic device is generally parallel to the object plane, but the emission surface is laterally offset from the object. “Skew” refers to a condition where the emission surface is both tilted and offset. 
       FIG.  6 B  shows a second graph  620  of an alternate proximity curve  624  in which the horizontal axis  622   a  represents the object distance Dist (which is OD of  FIG.  5   ), and the vertical axis  622   b  represents the ratio value of the signal strength of the shorter length detector to the signal strength of the longer length detector. The proximity curve  624  may be obtained from a geometric analysis or from interpolation from experimentally measured values. The ratio value of the long path length to the short path length is always greater than 1, and the ratio (and thus proximity curve  624 ) approaches 1 as the value of Dist decreases toward 1. As the value of Dist decreases toward 0, the ratio value will increase to a limit value  630  equal to d 2 /d 1 , for d 1    514   a  and  d   2    514   b  as shown in  FIG.  5   . As before, for such small values of Dist, the electronic device&#39;s measurements or determinations of the path lengths of the light&#39;s light paths may not be valid. 
     In the case that the ratio value of the long path length to the short path length is greater than or equal to the critical distance value  628 , it may be determined that the object distance is less than or equal to a critical distance D crit    626  at which the electronic device may determine that the object is sufficiently close for the electronic device to enter a corresponding operational state or mode. 
     The optical-based object distance determination methods described above (using at least one light emitter in conjunction with at least one pair of light detectors at different separation distances, or two pairs of light detectors that are grouped by their position relative to an axis passing through the emitter) may be used by wearable electronic devices in conjunction with other sensors for detecting proximity of a human user. Certain other types of proximity sensors, for example, may use or be based on detecting skin tones or colors, or amounts of light reflected from a person&#39;s skin, or the like. However, such other sensors may not adequately handle cases where a user has hirsute or tattooed arms, or prosthetic devices. Because they employ a dimensionless signal strength ratio-based distance determination, the embodiments described above can overcome such limitations. 
     Further embodiments may use multiple pairs of light emitters in conjunction with multiple pairs of light detectors, such as the embodiment of  FIG.  3   , to improve the accuracy of the object distance determinations, as well as potentially determining a tilt of the exterior object. When multiple light detectors are used and corresponding multiple estimates of the object distance based on relative signal strength ratios are then obtained, the multiple estimates may be averaged to improve accuracy. Also, obtaining multiple preliminary estimates of the object distance using multiple lights from multiple sensors can allow for indeterminate estimates to be disregarded. Hair, tattoos, and prosthetics may react differently than skin, for example, in an embodiment that estimates object distances based on absolute reflectance or values of light. Further, different skin pigmentations may alter absorption, reflection, and/or scattering and so may cause different readings even though the skin is at the same distance. For example, a hair follicle, or a dark tattoo, may block reflections along one of the two light paths described in relation to  FIG.  5   , so that one of the light detectors does not receive a reflection of the light (e.g., the light detector does not create a high enough output signal within an enabled detection period). In another example, a light detector may create a positive reception signal due to ambient light reception or due to noise. A distance determination based on such an erroneous signal may be too different from the remaining distance determinations produced using other light from other light emitters and received at other light detectors. By contrast, embodiments described herein rely on relative signal strengths of light detectors. Insofar as any variance or change in an object&#39;s surface will affect the signal at all detectors, the relative signal strengths (e.g., the ratio of signal strengths) remains unchanged. This is true whether the object reflecting light from an emitter to the detectors is skin or another substance. 
       FIG.  7    is a flow chart of a method  700  of operating an electronic device to detect proximity of an exterior object, and/or estimate whether the exterior object is within a critical distance. The method  700  may be used with the electronic devices as described above, or by other electronic devices. The method may be initiated by the electronic device on a fixed schedule or time intervals, by a user input, or by a signal from a sensor of the electronic device. 
     At block  702 , an electronic device estimates a distance to an exterior object (e.g., an object distance). This may be by the optical components and procedures discussed previously, or by other methods. 
     At block  704 , the estimate of the object distance is compared to a critical distance. The critical distance may be a fixed value stored by the electronic device, or may be an adaptively set value. 
     At block  706 , in the case that the estimated object distance is found to be more than the critical distance, the electronic device may enable or maintain an off-user mode. As an example, when the device enters an off-user mode, it may change its operation. Continuing this example, the device may lock, power down, sleep, disable certain functionality or the like, and may require a security check be passed before unlocking, waking, or restoring functionality. Such a security check may be entry of a valid passcode, receipt of a valid biometric identifier, or the like. Additionally or alternatively, certain features (e.g., one or more health monitoring functions, communication functions, display functions, and so on) may be disabled while the device is in an off-user mode. Similarly, user alerts may take a different form, may be enhanced, or may be disabled when the device is in an off-user mode and as compared to those user alerts when the device is in an on-user mode. As one example, a user alert may be a haptic alert when the device is in an on-user mode while the user alert may be a visual or audible alert when the device is in an off-user mode. 
     At block  708 , in the case that the estimated object distance is found to be less than the critical distance, the electronic device may enter an operational state that assumes the electronic device is on or near enough to the user. As an example, for a health monitor, in the on-user mode of operation various sensors (e.g., pulse, temperature, etc.) may be started and their respective measurements recorded and transmitted. As another example, a smart watch may enter a powered up state under the assumption that the exterior object is a user&#39;s wrist and that the smart watch is being worn by the user. As another example, a smart phone may determine that object is a table and so reduce power to an on-board camera pointed toward the table. In certain embodiments, the operational state may enable or maintain an on-user mode, where functionality and operation of the electronic device assumes, is based on, or otherwise functions as if the device is worn or held by a user. 
       FIG.  8    is a flow chart of a method  800  of operating an electronic device having a light emitter and at least one pair of light detectors to detect proximity of an exterior object, and/or estimate whether the exterior object is within a critical distance. The method  800  may be used with the electronic devices as described above, or by other electronic devices. The method may be initiated by the electronic device on a fixed schedule or time intervals, by a user input, or by a signal from a sensor of the electronic device. 
     At block  802 , a light emitter may be selected or enabled. A selection may be based on a change of state (e.g., a position change detected by an accelerometer, or a change in ambient light) of the electronic device, or on another basis, such as a rotation schedule between multiple light emitters. 
     At block  804 , the selected light emitter emits a light. The emitted light may be from a fixed direction outward from the electronic device, or variably directed outward in an expected direction of the exterior object. 
     At block  806 , a first estimate is made to obtain a first estimated object distance based on light emitted by the first emitter and the resulting ratio of signal strengths from a corresponding pair of light detectors. Also, a second estimate may be made of a second estimated object distance based on light emitted by a second emitter and a resulting ratio of signal strengths form a corresponding pair of light detectors. The general functions and methodology to make such estimates are discussed elsewhere herein. 
     At block  808 , a decision is made whether to make further estimates of object distances. A determination that such further estimates are to be made may occur when at least one of the first or second estimates at block  806  could not be determined. For example, one of the light detectors may not have received any reflected light. In another example, the method may use multiple light detector pairs for improved accuracy. As yet another option, further estimates of object distances may occur when a first estimate of an object distance is indeterminate. When it is determined that such further estimates are to be made, the method  800  returns to block  802  to select either another light emitter or use the current light emitter to repeat the operations of blocks  804  and  806 . 
     At block  810 , based on the various pairs of long and short lengths of light between the selected light emitter(s) and pairs of light detectors, a distance estimate is formed of a distance from the electronic device to an exterior object (or, more specifically, an exterior surface of an object). The object distance estimate may be a selection (for example, based on signal strengths) of a single object distance estimate of many, or as a weighted average of multiple object distance estimates. 
     At block  812 , the estimated distance from the electronic device to the object is compared to a critical value, and determined to be either greater than or equal to the critical value or less than the critical value. The critical value may be fixed or may be adaptively and/or dynamically adjusted. Also at block  812 , a determination may be made whether to confirm that estimated distance is greater or less than the critical distance. For example, if such an initial estimate is based on a single distance determination, or from multiple but conflicting determinations that the distance is less than the critical distance, the electronic device may return to block  802 . In the method  800 , the electronic device may return to block  802  and repeat the emission(s) of light and measurements of ratios of signal strengths, with possibly alternate light emitters and light detectors. Such a confirmation operation may be used if the initial estimated distance would cause a change of operational state of the electronic device. 
     At block  814 , in the case that the estimated object distance is greater than or equal to the critical value, the electronic device may enable or maintain an off-user mode. Such modes may be as described above for block  706  of method  700 . 
     At block  816 , in the case that the estimated object distance is less than the critical value, the electronic device enables an on-user operation mode. The electronic device may either transition to such a mode if not presently in it, or may remain in that mode if currently in that on-user mode. The on-user mode may refer to any of the operational modes or procedures discussed above for the various examples and embodiments. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20200914
Publication Date: 20241210
Grant Date: 20241210
Priority Date: 20200914
Inventors: DUAN, XIYU
ALLEC, NICHOLAS P.
BLOCK, UEYN L.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01S7/4808", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4863", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S7/4863", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4808", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01S7/4863", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S7/4808", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01S17/08", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 93796350