Heart rate sensor with high aspect ratio photodetector element

Abstract

The present application relates to a heart rate sensor having a high aspect ratio photodetector element. A heart rate sensor including a high aspect ratio photodetector element is discussed herein. Such a high aspect ratio photodetector element provides improved signal strength to power consumption performance for a heart rate sensor incorporating such a photodetector element, compared to a heart rate sensor incorporating, for example, a square photodetector element.

Description

Technical Field

[0001] The present invention relates to a heart rate sensor. More particularly, the present invention relates to a heart rate sensor having a photodetector element. Background Art

[0002] Heart rate can be measured using any of a variety of different sensors, including, for example, electrode-based sensors such as EKG sensors and optical sensors such as photoplethysmography (PPG) sensors. A PPG sensor typically includes a light source and a photodetector placed near a person's skin. The light source and photodetector are typically arranged so that light from the light source cannot directly reach the photodetector. However, when a PPG sensor is placed near a person's skin, light from the light source can diffuse into the person's flesh and then be emitted back from the person's flesh so that the light can be detected by the photodetector. The amount of this light emitted from the person's flesh can change as a function of heart rate because the amount of blood present in the flesh changes as a function of heart rate, and the amount of light emitted from the person's flesh, in turn, changes as a function of the amount of blood present.

[0003] Fitbit, the assignee of this application, manufactures wearable health monitoring devices, some of which (e.g., Charge HR TM and Surge TM ) and a PPG sensor consisting of two high brightness green light emitting diodes (LEDs) approximately 8 mm apart and a 2 mm square photodetector element located between the LEDs. Various other companies making wearable fitness monitoring devices utilize similar architectures. For example, the Motorola Moto 360 TM Same, BasisPeak TM And there are two green LEDs with a square photodetector element located in the middle of the two green LEDs.

[0004] FIG. 1 depicts a simplified representation of a prior art wristband-type wearable health monitor 100 incorporating a PPG sensor. In this example, the wearable health monitor 100 includes a housing 104 with two strips 102 attached; the strips 102 can be used to fasten the housing 104 to a person's forearm in much the same manner as a watch (in fact, many such devices can also incorporate timekeeping functionality). In this example, the PPG sensor includes two light sources 108, with a photodetector element 112 interposed between the two light sources 108 on a back side 128 of the housing 104; in this example, the photodetector element 112 has a photosensitive area with a square aspect ratio. When the wearable health monitor 100 is worn by a person in a manner similar to a wristwatch, the back side 128 can be pressed against the person's skin, allowing the light sources 108 to illuminate the person's skin. The photodetector element 112 can then measure the amount of that light that is then emitted back from the person's skin. Control logic (not depicted) within housing 104 may then calculate the person's heart rate based on the fluctuations in the amount of light measured by photodetector elements 112 . Summary of the invention

[0005] Details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from the description, drawings, and claims. Note that the relative dimensions of the following figures are not necessarily drawn to scale unless specifically indicated as drawings drawn to scale.

[0006] In some implementations, an apparatus may be provided having a light source and one or more discrete photodetector elements. Each photodetector element may have a first edge having a first length, and may also have a first width along a direction perpendicular to the first edge. The apparatus may also include control logic that may be communicatively connected to the light source and each photodetector element and configured to cause the light source to emit light, obtain one or more measured light intensity measurements from the one or more photodetector elements, and determine a heart rate measurement based at least in part on the one or more light intensity measurements. In such implementations, the ratio of the first length to the first width of each photodetector may be substantially between 2:1 and 5:1.

[0007] In some such implementations, the first edge of each photodetector element can be perpendicular or transverse to an axis radiating outward from the center of the light source.

[0008] In some embodiments of the apparatus, the light source can include a plurality of light emitting devices.

[0009] In some such implementations, the plurality of light emitting devices may include at least two light emitting devices that primarily emit light of different wavelengths. In some further or alternative such implementations, there may be a plurality of photodetector elements arranged in a pattern, and the plurality of light emitting devices may be clustered at a central point of the pattern of photodetector elements. In some such implementations, each photodetector element in the pattern may be equidistant from the center of the light source and / or evenly spaced within the pattern.

[0010] In some implementations of the apparatus, the ratio of the first length to the first width of each photodetector element may be substantially between 2: 1 and 3.5: 1. In some other implementations of the apparatus, the ratio of the first length to the first width of each photodetector element may be substantially between 3.5: 1 and 5: 1.

[0011] In some implementations of the device, each photodetector element may have a first length between 1 mm and 5 mm and a first width between 0.5 mm and 2 mm, wherein the ratio of the first length to the first width is substantially between 2:1 and 5:1, and each such photodetector element may be positioned so that an edge of the photodetector element closest to the light source is at a distance between 1 mm and 4 mm from the light source.

[0012] In some implementations of the apparatus, there may be a pattern of photodetector elements comprising three or four photodetector elements equally spaced around the light source.

[0013] In some embodiments of the device, the device may also include a housing having a back side that includes one or more transparent window areas through which light can pass into the device. In such embodiments, each photodetector element is positioned so that the photodetector element overlaps a corresponding one of the one or more transparent window areas, and the housing may be configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0014] In some such implementations of the apparatus, the back surface may include a thin window, and the window region may be a subregion of the window defined by the photodetector elements. In some other or additional such implementations, each photodetector element may be offset from the corresponding transparent window region by a corresponding gap in a direction normal to the photodetector element, and the gap may be free of an optical light guide.

[0015] In some implementations of the apparatus, each photodetector element has, in addition to the first edge, an arcuate second edge opposite the first edge. The arcuate second edge may have a maximum distance from the first edge when measured in a direction perpendicular to the first edge that is equal to the first width.

[0016] In some embodiments, a device may be provided that includes a first light source and a second light source and a photodetector element inserted between the first light source and the second light source. The device may also include control logic that is communicatively connected to the first and second light sources and the photodetector element and is configured to cause the first light source and the second light source to emit light, obtain a measured light intensity measurement from the photodetector element, and determine a heart rate measurement based at least in part on the light intensity measurement. In such embodiments, the photodetector element may be rectangular in shape, have a first edge having a first length, and have a second edge having a second length that is perpendicular to the first edge. Furthermore, in such embodiments, the ratio of the first length to the second length may be substantially between 2:1 and 5:1.

[0017] In some such implementations, the first edge of each photodetector element can be perpendicular or transverse to an axis spanning between the center of the first light source and the center of the second light source.

[0018] In some other or additional such implementations, the device may include a housing having a back side, the back side including a transparent window region overlapping the photodetector element and two further window regions each associated with a different one of the first light source and the second light source and allowing light from the associated light source to pass through the back side. In such implementations, the first light source and the second light source may be the only light sources in the device configured to emit light through the back side, and the housing may be configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0019] In some implementations of the apparatus, the photodetector element can be equidistant from the first light source and the second light source.

[0020] In some implementations, an apparatus may be provided that includes a light source and one or more photodetectors, each photodetector having a photosensitive area. In such implementations, at least 90% of the photosensitive area of ​​the photodetector is defined by a first dimension along a first axis and a second dimension along a second axis perpendicular to the first axis. In such implementations, the apparatus may also include control logic that is communicatively connected to the light source and each photodetector and is configured to cause the light source to emit light, obtain one or more measured light intensity measurements from the one or more photodetectors, and determine a heart rate measurement based at least in part on the one or more light intensity measurements. In such implementations, the ratio of the first dimension to the second dimension may be substantially between 2:1 and 5:1.

[0021] In some embodiments of the apparatus, the light source may include a plurality of light emitting devices. In some such embodiments, the plurality of light emitting devices may include at least two light emitting devices that primarily emit light of different wavelengths. In some further or alternative such embodiments, there may be a plurality of photodetector elements arranged in a pattern, and the plurality of light emitting devices may be gathered at a central point of the pattern of photodetector elements. In some such embodiments, each photodetector element in the pattern may be equidistant from the center of the light source and / or evenly spaced within the pattern.

[0022] In some implementations of the apparatus, the ratio of the first length to the first width of each photodetector element may be substantially between 2: 1 and 3.5: 1. In some other implementations of the apparatus, the ratio of the first length to the first width of each photodetector element may be substantially between 3.5: 1 and 5: 1.

[0023] In some implementations of the device, each photodetector element may have a first length between 1 mm and 5 mm and a first width between 0.5 mm and 2 mm, wherein the ratio of the first length to the first width is substantially between 2:1 and 5:1, and each such photodetector element may be positioned so that an edge of the photodetector element closest to the light source is at a distance between 1 mm and 4 mm from the light source.

[0024] In some implementations of the apparatus, there may be a pattern of photodetector elements comprising three or four photodetector elements equally spaced around the light source.

[0025] In some embodiments of the device, the device may also include a housing having a back side that includes one or more transparent window areas through which light can pass into the device. In such embodiments, each photodetector element is positioned so that the photodetector element overlaps a corresponding one of the one or more transparent window areas, and the housing may be configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0026] In some such implementations of the apparatus, the back surface may include a thin window, and the window region may be a subregion of the window defined by the photodetector elements. In some other or additional such implementations, each photodetector element may be offset from the corresponding transparent window region by a corresponding gap in a direction normal to the photodetector element, and the gap may be free of an optical light guide.

[0027] In some implementations, an apparatus may be provided that includes a light source and at least one photodetector element. The apparatus may also include control logic that is communicatively connected to the light source and each photodetector element and is configured to cause the light source to emit light, obtain at least one measured light intensity measurement from the at least one photodetector element, and determine a heart rate measurement based at least in part on the at least one light intensity measurement. In such implementations, the at least one photodetector element may be directed toward at least substantially a portion of a center of the light source. Angle, where r i is the measurement of the distance from the center of the light source to the photodetector elements, at least 80% of the photodetector elements covering the region centered on the center of the light source and defined by r i and r o The defined ring region, and r o R i No larger than 2 mm.

[0028] In some such embodiments, the angle subtended by at least one photodetector element at the center of the light source may be substantially at most

[0029] In some implementations, an apparatus may be provided that includes a light source configured to primarily emit light having a wavelength in the range of 500 nm to 600 nm and a photodetector element having a central opening. The apparatus may also include control logic communicatively connected to the light source and the photodetector element and configured to cause the light source to emit light, obtain a measured light intensity measurement from the photodetector element, and determine a heart rate measurement based at least in part on the light intensity measurement. In such implementations, the light source may be positioned to emit light through the central opening of the photodetector element, and the photodetector element may have a) a periphery defined by a first boundary and b) a second boundary defining the central opening.

[0030] In some such implementations, the first boundary and the second boundary can form a ring, the first boundary can be radially offset from the second boundary by a first distance, and the ratio of the circumference of the second boundary to the first distance can be between 9.5:1 and 11.5:1.

[0031] In some other or additional such implementations, the first boundary and the second boundary may form a ring, the first boundary may have a diameter between 3 mm and 5.5 mm, and the second boundary may have a diameter between 1 mm and 2.5 mm.

[0032] In some implementations of the apparatus, the second boundary can be a regular polygon of N sides each having a second length, and for each of the N sides of the second boundary, the first boundary can be offset from the side of the second boundary by a first distance along a reference axis originating at a center of the light source and passing through a midpoint of the side of the second boundary. In such implementations, for each of the N sides, the ratio of the second length to the first distance can be between 2:1 and 5:1.

[0033] In some implementations of the apparatus, each photodetector element has a first length between 1 mm and 5 mm and a first width between 0.5 mm and 2 mm, wherein the ratio of the first length to the first width is substantially between 2:1 and 5:1, and is positioned such that an edge of the photodetector element closest to the light source is at a distance between 1 mm and 4 mm from the light source.

[0034] In some implementations of the apparatus, the pattern of photodetector elements includes three photodetector elements equally spaced around the light source.

[0035] In some implementations of the apparatus, the pattern of photodetector elements includes four photodetector elements equally spaced around the light source.

[0036] In some embodiments of the device, the device further includes a housing having a back side, the back side including one or more transparent window areas through which light can pass into the device, wherein: each photodetector element is positioned so that the photodetector element overlaps with a corresponding one of the one or more transparent window areas, and the housing is configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0037] In some implementations of the apparatus, the back surface includes a thin window, and the window region is a sub-region of the window defined by the photodetector elements.

[0038] In some implementations of the apparatus, each photodetector element is offset from a corresponding transparent window region by a corresponding gap in a direction normal to the photodetector element, and the gap is free of an optical light guide.

[0039] In some embodiments of the device, each photodetector element has, in addition to the first edge, an arched second edge opposite the first edge, wherein the arched second edge has a maximum distance from the first edge when measured in a direction perpendicular to the first edge that is equal to the first width.

[0040] In some embodiments of the device, the device includes: a first light source; a second light source; a photodetector element inserted between the first light source and the second light source; and control logic, which is communicatively connected to the first light source, the second light source and the photodetector element and is configured to: cause the first light source and the second light source to emit light, obtain a measured light intensity measurement from the photodetector element and determine a heart rate measurement based at least in part on the light intensity measurement, wherein: the photodetector element is rectangular in shape, has a first edge with a first length, and has a second edge with a second length perpendicular to the first edge, and the ratio of the first length to the second length is approximately between 2:1 and 5:1.

[0041] In some implementations of the apparatus, a first edge of each photodetector element is perpendicular to an axis spanning between a center of the first light source and a center of the second light source.

[0042] In some implementations of the apparatus, a first edge of each photodetector element is transverse to an axis spanning between a center of the first light source and a center of the second light source.

[0043] In some embodiments of the device, the device further includes a housing having a back side, the back side including a transparent window area overlapping the photodetector element and two further window areas, each associated with a different one of the first light source and the second light source and allowing light from the associated light source to pass through the back side, wherein: the first light source and the second light source are the only light sources in the device configured to emit light through the back side, and the housing is configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0044] In some implementations of the apparatus, the photodetector element is equidistant from the first light source and the second light source.

[0045] In some embodiments of the device, the device includes: a light source; one or more photodetectors, each photodetector having a photosensitive area, wherein at least 90% of the photosensitive area is defined by a first dimension along a first axis and a second dimension along a second axis perpendicular to the first axis; and control logic, which is communicatively connected to the light source and each photodetector and is configured to: cause the light source to emit light, obtain one or more measured light intensity measurements from the one or more photodetectors, and determine a heart rate measurement based at least in part on the one or more light intensity measurements, wherein for each photodetector: the ratio of the first dimension to the second dimension is approximately between 2:1 and 5:1.

[0046] In some embodiments of the apparatus, the light source comprises a plurality of light emitting devices.

[0047] In some embodiments of the apparatus, the plurality of light emitting devices comprises at least two light emitting devices that primarily emit light of different wavelengths.

[0048] In some implementations of the apparatus, the one or more photodetectors include a plurality of photodetectors arranged in a pattern, and the plurality of light emitting devices are concentrated at a central point of the pattern of photodetector elements.

[0049] In some implementations of the apparatus, a ratio of the first dimension to the second dimension of each photodetector is substantially between 2:1 and 3.5:1.

[0050] In some implementations of the apparatus, a ratio of the first size to the second size of each photodetector is substantially between 3.5:1 and 5:1.

[0051] In some implementations of the apparatus, the one or more photodetectors include a plurality of photodetectors arranged in a pattern, and a center of a photosensitive area of ​​each photodetector in the pattern is equidistant from a center of the light source.

[0052] In some embodiments of the apparatus, the photodetectors in the pattern are uniformly spaced.

[0053] In some embodiments of the device, a first dimension associated with each photodetector is between 3 mm and 5 mm and a second dimension associated with each photodetector is between 1 mm and 2 mm, consistent with which a ratio of the first dimension to the second dimension is between 2:1 and 5:1, and each photodetector is positioned such that an edge of a photosensitive area of ​​the photodetector closest to the light source is between 1 mm and 4 mm from a center of the light source.

[0054] In some implementations of the apparatus, the pattern of photodetectors includes three photodetectors equally spaced around the light source.

[0055] In some implementations of the apparatus, the pattern of photodetectors includes four photodetectors equally spaced around the light source.

[0056] In some embodiments of the device, the device further includes: a housing having a back side, the back side including one or more thin transparent window areas, wherein: each photodetector is positioned so that a photosensitive area of ​​the photodetector overlaps with a corresponding one in the transparent window area, and the housing is configured so that when the device is worn by a person, the back side is adjacent to the skin of the person wearing the device.

[0057] In some implementations of the apparatus, the back side includes a thin window, and the window region is a subregion of the window defined by the photosensitive regions of the one or more photodetectors.

[0058] In some implementations of the apparatus, the photosensitive region of each photodetector is offset from the corresponding transparent window region by a corresponding gap in a direction normal to the photodetector, and the gap is free of an optical light guide.

[0059] In some embodiments of the device, the device includes: a light source; at least one photodetector element; and control logic, the control logic being communicatively connected to the light source and each photodetector element and configured to: cause the light source to emit light, obtain at least one measured light intensity measurement from the at least one photodetector element, and determine a heart rate measurement based at least in part on the at least one light intensity measurement, wherein: at least one photodetector element is directed toward at least a portion of a portion of a center of the light source; Angle, where: r i is the measurement of the distance from the center of the light source to the photodetector elements, at least 80% of the photodetector elements covering the region centered on the center of the light source and defined by r i and r o The defined ring region, and r o R i No larger than 2 mm.

[0060] In some embodiments of the apparatus, the angle subtended by at least one photodetector element at the center of the light source is substantially at most

[0061] These and other embodiments are described in further detail with reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Various implementations disclosed herein are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

[0063] FIG. 1 depicts a simplified representation of a prior art wristband-type wearable health monitor incorporating a PPG sensor.

[0064] Figure 2 Depicted is a simplified representation of a wristband-type wearable health monitor incorporating a PPG sensor using non-square photodetector elements, according to an example implementation.

[0065] Figure 3 is a theoretical plot of emitted light intensity and detected light intensity for an example PPG sensor for obtaining heart rate information from a person's body, according to an example implementation.

[0066] Figure 4 Depicts a grayscale plot of measured AC power intensity of light emitted from a rectangular area measuring approximately 4.5 mm wide by 5 mm high on a person's arm near the wrist, according to an example implementation.

[0067] Figure 5 Describes an example implementation scheme Figure 4 The same light intensity image map of FIG. 1 is shown in FIG. 1 , but the pattern increases the outline of the high aspect ratio photodetector elements.

[0068] Figure 6 Depicted is a simulation of the AC intensity or power of light emanating from a 16 mm by 16 mm skin zone due to light impinging into the skin at the center of the zone, according to an example embodiment.

[0069] Figure 7 Describes the measurable AC optical power according to example implementations Figure 6 Plot of the variation in aspect ratio of the simulated photodetector footprint shown in .

[0070] Figure 8 Describes the measurable AC optical power according to example implementations Figure 6 A plot of the variation in aspect ratio of the simulated photodetector footprint shown in , but with the edge of the photodetector closest to the center of the light source offset from the center of the light source by 2.6 mm instead of 1.65 mm.

[0071] Fig. 9 A diagram depicting a rectilinear high aspect ratio ("HAR") photodetector element according to an example implementation.

[0072] Fig.10 Diagram depicting a HAR photodetector element that is generally rectangular but possessing some non-rectangular aspects, according to an example implementation.

[0073] Fig.11 Depicts a circuit similar to FIG. 1 except for a rectangular cutout along a first edge according to an example embodiment. Fig.10 A diagram of a HAR photodetector element.

[0074] Fig.12 Depicts a device similar to FIG. 1 except that the active area is generally rectangular but has a "peninsula" protruding outward from the rectangular area according to an example embodiment. Fig. 9 A diagram of a HAR photodetector element.

[0075] Fig.13 A diagram depicting a HAR photodetector element that is arched in shape, according to an example implementation.

[0076] Figures 14 to 17 Several examples of implementations with multiple HAR photodetector elements are depicted according to several example implementations.

[0077] Fig.18Describes how the Fig.15 An example of a PPG sensor photodetector layout using multiple light emitting devices in the light source is shown in .

[0078] Fig.19 Depicted are an example light source and surrounding annular region according to an example implementation.

[0079] Fig. 20 Depicts a curve from an arbitrary inner radius r according to an example embodiment. i Plot the fraction of the light intensity emitted outside the inner radius r i Falling on the inner radius r i and within the boundaries of the annular region as indicated as the annular width along the x-axis.

[0080] Fig.21 Depicts the light source, HAR photodetector, and various reference annotations.

[0081] Figures 22 to 24 Depicted are cross sections of simplified representations of various PPG sensors according to various example implementations.

[0082] Fig.25 Depicted is an example of a ring-shaped photodetector element with a light source in the middle according to an example implementation.

[0083] Fig.26 Depicted is an example of a polygonal photodetector element with a light source in the middle according to an example implementation.

[0084] Fig. 27 Depicted is a high-level block diagram of a PPG sensor according to an example implementation. DETAILED DESCRIPTION

[0085] The present invention relates to PPG sensors, and more particularly to PPG sensors designed for use with wearable biometric monitoring devices (also referred to herein as "biometric tracking devices," "biometric tracking modules," "wearable health monitors," etc.). The inventors have determined that the use of non-square photodetector elements in PPG sensors can provide significant performance improvements over conventional PPG designs that typically utilize square photodetector elements. The inventors have also determined that such performance improvements can be obtained, if desired, while still maintaining essentially the same power consumption as square photodetector elements in conventional PPG designs.

[0086] Figure 2Depicted is a simplified representation of a wristband-type wearable health monitor 200 incorporating a PPG sensor using non-square photodetector elements, according to an example implementation of the concepts achieved by the inventors and discussed below. In this example, the wearable health monitor 200 shares many components common to the prior art wearable health monitor 100, including control logic, housing 104 and strap 102, back surface 128, and two light sources 108. However, the wearable health monitor 200 features photodetector elements 212 having non-square active areas in place of photodetector elements 112.

[0087] As discussed above, a PPG sensor operates by shining light into a person's skin. This light diffuses through the person's flesh, and a portion of this light is then emitted back from the person's skin in close proximity to where the light is introduced into the flesh; the amount of light emitted back from the person's flesh decays as the distance from the light source increases. This effect can be seen when a bright penlight or other concentrated light source is held against the skin; the flesh around the area where the light source contacts the skin will turn red or orange due to the diffused light. Although imperceptible to the human eye, the amount of this light emitted from the person's skin will fluctuate in sync with the person's heart rate. When a person's heart beats, the person's blood vessels expand and contract in sync with the heart as the heart pulsates, exerting pressure on the person's blood, which in turn causes the circulatory pressure in the person's blood vessels to increase. When the blood vessels expand, they allow more blood to flow into the vessels, which causes the amount of blood present in a given area of ​​the person's flesh to fluctuate in rhythm with the person's heart rate. This in turn causes the amount of light emitted from the light source and back from the flesh to fluctuate. The heart rate can then be determined by measuring the amount of light emitted from the human body via the diffusion mechanism described above. This measured light may have two components - a component that remains constant (i.e., light that is typically emitted from the skin and is independent of the heart rate) and a component that fluctuates with the heart rate. The light that remains constant may be referred to herein as "DC" because it may be considered to be similar in some respects to direct current (because it remains relatively constant over time). The fluctuating light may be referred to herein as "AC" because it may be considered to be similar to alternating current (because it fluctuates relatively regularly over time). A typical heart rate may range from 50 beats per minute (BPM) to 200 bpm, and the AC component of the light may have a frequency that maps to the heart rate frequency.

[0088] In general, the magnitude of the AC component of the detected light (which may be referred to herein as "AC optical power" or more generally simply as "light intensity") may be much smaller than the DC component because a large amount of light that diffuses into a person's skin and is then emitted will still be emitted regardless of changes in the amount of blood present due to the heartbeat. However, the AC component is of primary interest because it indicates heart rate.

[0089] Figure 3is a theoretical plot of emitted light intensity and detected light intensity of an example PPG sensor that obtains heart rate information from a person's body according to an example implementation. It should be understood that Figure 3 The drawings are not necessarily to scale and do not depict actual data; they are merely intended to aid the reader in understanding the difference between the AC and DC components of the detected optical signal. Figure 3 , the horizontal axis indicates time, and the vertical axis indicates light intensity. As can be seen, light is emitted into the flesh of a person at a constant value 350 in this example. The light emitted from the person's skin is then measured by a photodetector element; this measured light intensity is depicted as data trace 348. Data trace 348 can be split into a DC component 346 that does not fluctuate with time and an AC component 344 that fluctuates with time.

[0090] As described above, a conventional PPG sensor may include a square photodetector element located near a light source (or in many cases, near two or more light sources). The inventors have determined that this arrangement is inefficient in terms of signal collection that varies in terms of potential power consumption. For example, a photodetector typically includes a single photosensitive lateral area (e.g., an area parallel to the top surface of the photodetector die that provides an output signal indicative of the total amount of light incident on the photosensitive unit at any given moment). The amount of power consumed by such a photodetector is directly related to the size of the photosensitive area of ​​the photodetector. The inventors have determined that for square photodetector elements, a very large percentage of the photodetector elements may be located in locations where very low amounts of AC light are emitted compared to locations where other portions of the photodetector elements are located. This effect is discussed in more detail with respect to some of the figures set forth below.

[0091] Figure 4 Depicted is a grayscale plot of measured AC power intensity of light emitted from a rectangular area measuring approximately 4.5 mm wide by 5 mm high on a person's arm near the wrist, according to an example embodiment. Light source 408 is located at X=0 mm and Y=0 mm and shines light into the person's arm; the intensity of the light emitted back is reflected in the shadows in the image (the maximum and minimum light intensities appear similar due to the limitations of using black and white ink - it should be understood that the light intensity is greatest at the left side of the image and then drops to the lowest intensity at the right edge of the image). Figure 4 The light source used in the experiment is a 1.9 mm diameter green wavelength LED, but the illumination beam it produces is concentrated in an area smaller than 1.9 mm in diameter. Figure 4 is based on actual image data acquired for a human subject; thus, it contains various defects, such as hair, that cause asymmetry in the detected light intensity. The light source used in this example emits light mainly in the range of 515 mm to 545 mm, ie, mainly green light.

[0092] The rectangular area has been divided into twelve rectangular grids; the number in each grid indicates the fraction of the total AC light intensity within the total grid area that is attributable to that particular grid (also called the "power fraction"). Thus, the grid in the lower left corner gets 20% of the total AC light intensity or power emitted from the total twelve grids, while the grid immediately to the right of the grid gets only 9% of the total AC light intensity or power within the area.

[0093] Figure 4 Also depicted is the footprint 442 of a typical square photodetector element spaced approximately 2.5 mm from the center of the light source. As used herein, the terms "photodetector element," "active area," "active zone," "photosensitive area," and "footprint" (with respect to a photodetector) all refer to the same portion of a photodetector, i.e., the area of ​​the photodetector that can actually detect light incident on the photodetector. It should be understood that a photodetector may also include other components outside the active area, such as interconnects, circuits, application specific integrated circuits (ASICs), etc. that interact with the photodetector element to provide power or generate a signal output. These other components are not considered part of the photodetector element. Thus, a photodetector with a 2 mm by 2 mm square photodetector element (which has a 1 mm by 2 mm ASIC located near one edge of the photodetector element) may have an overall size of 3 mm by 2 mm (which would be rectangular), but the photodetector element of the photodetector would not be rectangular because the ASIC is not part of the photodetector element. It should also be understood that references herein to a "square" photodetector refer to a photodetector having a square photodetector element, regardless of the aspect ratio that the entire photodetector has. Similarly, references herein to a "rectangular" or "non-square" photodetector should be understood to refer to a photodetector having rectangular or non-square photodetector elements, respectively, regardless of whether the photodetector has an overall square shape.

[0094] Due to the aspect ratio and positioning of the square photodetector element, more than half of the active area is only able to measure light from the rightmost six grids, which represent only 14% of the available AC power in the total grid area. The square photodetector element will not even collect all of the available light from the rightmost six grids, because it fully overlaps only one of the rightmost six grids - only a portion of the light emitted from the remaining five of the rightmost six grids will be available for collection by the square photodetector element. As shown, the square photodetector element may only be able to measure about 20% of the available light intensity emitted across all twelve grids.

[0095] Even if the square photodetector elements are shifted to the left so that the edge closest to the light source is located approximately 1.85 mm from the center of the light source, approximately 40% of the square photodetector elements will still only be able to measure light from the six rightmost grids. In this case, the square photodetector elements can collect roughly 50% of the AC optical power available in 12 grids.

[0096] The inventors have determined that significant performance improvements can be achieved by deviating from the typical square (or near-square) aspect ratio used in photodetector elements of conventional PPG sensors. More specifically, the inventors have determined that the use of high aspect ratio photodetector elements can provide a significant increase in the amount of AC light that can be measured by the photodetector without incurring a significant power consumption penalty compared to a square photodetector having the same active area. As used herein, the term "high aspect ratio" (or "HAR") photodetector refers to a non-square photodetector in which the maximum first dimension along a first axis for at least 90% of the active area of ​​the photodetector element, which may be referred to herein as the "active area of ​​interest," is at least twice the maximum second dimension of the photodetector element along a second axis that is perpendicular or orthogonal to the first axis; the second axis being parallel to light rays emanating from the center of a light source used with the photodetector to form a PPG sensor, and the first axis being perpendicular to the light rays. The maximum first dimension may be considered to be the distance between two lines that are both parallel to light rays emanating from the center of the light source and that pass through opposite ends of the active area of ​​interest that are farthest from the light rays in a direction perpendicular to the light rays. The maximum second dimension may be considered to be the distance between two lines that are both perpendicular to light rays emitted from the center of the light source and pass through opposite ends of the active area of ​​interest farthest and closest to the center of the light source, respectively. The "maximum first dimension" may also be referred to herein and in the claims as the "height" or "length" of the HAR photodetector, and the "maximum second dimension" may also be referred to herein and in the claims as the "base" or "width" of the HAR photodetector.

[0097] It should be appreciated that while the examples discussed herein feature HAR photodetector elements having a long axis that is perpendicular to light rays extending outward from the PPG sensor light source, similar performance advantages can be achieved by utilizing similarly sized photodetector elements that are not strictly perpendicular (e.g., ±10° from perpendicular). More generally, the concepts discussed herein can be practiced using HAR photodetector elements that are arranged such that the long axis of such HAR photodetector elements is transverse to light rays radiating outward from the center of the light source.

[0098] Figure 5 Describes an example implementation scheme Figure 4The same light intensity image map of FIG. 1 , but the figure adds the outline of the high aspect ratio photodetector element. The HAR photodetector element outline shown has a height to width aspect ratio of approximately 2.8:1 and completely overlaps the leftmost six grids, which represent approximately 85% of the available AC power in the total grid area. Therefore, Figure 5 The light that the HAR photodetector element shown in is able to collect is Figure 4 The square photodetector element shown in FIG. 1 is able to collect nearly four times as much light. HAR photodetectors are able to provide such improved light collection capabilities while still having comparable Figure 4 For example, a square photodetector element may have a substantially similar active area to that of a square photodetector element. 2 The active area of ​​the HAR photodetector element may be approximately 7 mm 2 Therefore, the power consumed by the square photodetector and the HAR photodetector will be approximately equal because they have the same active area. Figure 5 In the example simulation shown in FIG, the HAR photodetector is coupled to a Figure 4 The conventional square photodetector implementation described in provides a 300% improvement in collected AC power while requiring virtually no additional power to achieve this improvement.

[0099] Figure 6 Depicted is a simulation of the AC intensity or power of light emitted within a 16 mm by 16 mm skin zone due to light impinging into the skin at the center of the zone, according to an example embodiment. Figure 6 , two photodetector active area footprints 642 are shown - one is a square photodetector footprint 652 and one is a HAR photodetector footprint 654. Both have a 7.5 mm 2 The area of ​​the Fitbit Charge HR TM and Surge TM The square photodetectors used in the product have an area of ​​the photosensitive area) and are positioned so that the edge closest to the light source is offset by 1.65 mm from the center of the light source. Figure 6 The density of stippling in the 650D provides an indication of relative intensity - the higher the density of stippling, the higher the light intensity (the center region is not stippled because this area is actually the area through which light passes to be introduced into the skin plus some buffer, and it is not suitable for obtaining light intensity measurements). As can be seen, the proportion of HAR photodetector footprint 654 overlapping with the higher density stippling / light intensity region is much higher than the proportion of square photodetector footprint 652 overlapping with the higher density stippling / light intensity region.

[0100] Figure 7Describes the measurable AC optical power according to example implementations Figure 6 . The vertical axis represents the AC optical power that can be measured by the photodetector, and the horizontal axis represents the aspect ratio of the photodetector; the vertical axis has been normalized so that a 1:1 aspect ratio photodetector provides a measurable AC optical power of 1. As can be seen, by utilizing a HAR photodetector (e.g., a photodetector having an aspect ratio of 2:1 or 3:1), the amount of AC light that can be measured by the HAR photodetector can be increased by up to 20% compared to a square photodetector. This is lower than the above description of the aspect ratio of the photodetector. Figure 5 The performance increase discussed is a performance increase, but it is still significant in terms of the power consumption efficiency of the PPG sensor. In the modeled case, the HAR photodetector with an aspect ratio between 3:1 and 4:1 provides the highest performance in this regard. As used herein, the term "between..." with respect to a range is used to indicate a range that includes the upper and lower limits of the range. Thus, in the above example, aspect ratios of 3:1 and 4:1 would be included in the range "between 3:1 and 4:1". This convention is used herein and in the claims. The same observations can be made about the use of "to" to describe an implied range, for example "a ratio of 3:1 to 4:1" would mean "between 3:1 and 4:1" and 3:1 and 4:1 would be included in this range.

[0101] Figure 8 Describes the measurable AC optical power according to example implementations Figure 6 , but the edge of the photodetector closest to the center of the light source is offset from the center of the light source by 2.6 mm instead of 1.65 mm. The vertical axis represents the AC optical power measurable by the photodetector, and the horizontal axis represents the aspect ratio of the photodetector; the vertical axis has been normalized so that a 1:1 aspect ratio photodetector provides a measurable AC optical power of 1. As can be seen, similar performance increases are observed when HAR photodetectors are used with further increased spacing from the light source, but the performance increases are slightly more pronounced, for example, up to ~27% performance increases for HAR photodetectors with aspect ratios of 3:1 to 5:1.

[0102] In view of the above, in some implementations, the PPG sensor may utilize one or more HAR photodetector elements having an aspect ratio between 2:1 and 5:1. In some implementations, the PPG sensor may utilize one or more HAR photodetector elements having an aspect ratio between 2:1 and 7:2, and in some other implementations, the PPG sensor may utilize one or more HAR photodetector elements having an aspect ratio between 7:2 and 5:1. It should be understood that the HAR photodetector elements may have ratios that fall substantially between the aspect ratios discussed herein, before and after this point, for example, the HAR photodetector elements may also have dimensions within ±0.1 mm of the dimensions that would satisfy such aspect ratios, or have aspect ratios within ±0.1 mm of such aspect ratios, for example, for a 2:1 to 5:1 aspect ratio range, a HAR photodetector element having an aspect ratio of 1.8:1 or 5.5:1 may be considered to have an aspect ratio substantially between the aspect ratios between 2:1 and 5:1.

[0103] HAR photodetectors can increase in effectiveness when arranged and sized according to one or more guidelines as discussed in more detail below.

[0104] As mentioned previously, the maximum first dimension of at least 90% of the active or photosensitive area of ​​the HAR photodetector along a first axis may be at least twice the maximum second dimension of the active or photosensitive area along a second axis that is perpendicular or orthogonal to the first axis; the second axis is parallel to light rays emitted from the center of a light source used with the photodetector to form a PPG sensor, and the first axis is perpendicular to the light rays. This concept is discussed in more detail below with reference to several figures.

[0105] Fig. 9 A diagram depicting a rectilinear HAR photodetector element 912 according to an example implementation. As can be seen, the active area of ​​the HAR photodetector element 912 is rectangular and has a first dimension 986 along an axis perpendicular to a ray 956 emanating from the center of the light source 908 and a second dimension 988 along an axis parallel to the ray 956; the first dimension 986 and the second dimension 988 are thus orthogonal to each other. In this case, the HAR photodetector element 912 has a form factor in which the active area as a whole has a first dimension 986 that is three times greater than the second dimension 988, i.e., 100% of the active or photosensitive area of ​​the HAR photodetector element 912 has a maximum first dimension that is at least twice (in this case, three times) the size of the maximum second dimension.

[0106] In this particular example, the HAR photodetector elements 912 are rectangular elements, which are the most efficient shape in terms of manufacturing yield because such photodetector elements can be made by simply cutting a semiconductor wafer having the necessary semiconductor elements for the photodetector elements in a rectangular grid in much the same manner as square photodetector elements are made (just with a different cutting pitch).

[0107] The HAR photodetectors as described herein may also be in HAR shapes other than simple rectangles.Several examples of such alternative photodetector elements are discussed in more detail below.

[0108] Fig.10 A diagram depicting a HAR photodetector element 1012 that is generally rectangular but has some non-rectangular aspects according to an example implementation. The HAR photodetector element 1012 may have a first edge closest to the light source 1008 and an arcuate second edge opposite the first edge. If the entire active area of ​​the HAR photodetector element 1012 is considered, it should be appreciated that the HAR photodetector element 1012 has an active area with a maximum first dimension 1090 and a maximum second dimension 1092, which is the same as the HAR photodetector element 912. Therefore, the depicted HAR photodetector element 1012 will also be considered to have an aspect ratio of 3:1.

[0109] Fig.11 Describes a similar Fig.10 FIG. 1 is a diagram of a HAR photodetector element 1112 having a rectangular cutout along a first edge. Although the active area of ​​this photodetector element is different from Fig. 9 and 10 photodetector element, but the active area of ​​the HAR photodetector element 1112 still has a maximum first dimension 1190 that is three times larger than the maximum second dimension 1192 of the active area.

[0110] Fig.12 Describes a similar Fig. 91294 , but the active area of ​​the HAR photodetector element 1212 is generally rectangular but has a "peninsula" protruding outward from the rectangular area. In this case, if 100% of the active area of ​​the photodetector is considered, then the maximum first dimension 1290 and the maximum second dimension 1292' would be technically the same, which would result in an aspect ratio of 1:1. However, if the active area of ​​the peninsula is omitted, then the remaining 90% (indicated by the diagonal cross-hatching) of the active area of ​​the photodetector element 1212 (e.g., the active area of ​​interest 1294) has a maximum first dimension 1290 that is three times larger than the maximum second dimension 1292. Therefore, this photodetector element 1212 can be considered a HAR photodetector element under the conditions described herein.

[0111] Fig.13 A diagram depicting a HAR photodetector element 1312 that is arcuate in shape, according to an example implementation. In this case, the HAR photodetector element 1312 has an active area with a maximum first dimension that is also three times larger than a maximum second dimension.

[0112] For the sake of clarity, Figures 9 to 13 All instances of photodetector elements shown in can be classified as HAR photodetector elements because at least 90% of the active or photosensitive area of ​​each of such photodetector elements has a maximum first dimension along a first axis, wherein the first axis is perpendicular to light rays emanating from the center of the light source of the PPG sensor, that is at least twice as large as a maximum second dimension of the active or photosensitive area along a second axis that is perpendicular or orthogonal to the first axis. Of course, there are other shapes and instances of photodetector elements that can be considered HAR photodetector elements, which is commensurate with the above discussion.

[0113] Generally speaking, while only one light source and one photodetector element are required to construct a PPG sensor, the inclusion of multiple light sources or light emitting devices and / or multiple photodetector elements may provide increased sensitivity, but at the expense of increased power consumption.

[0114] If multiple light emitting devices are used, they may be spaced apart from one another or may be closely grouped, for example, as shown in FIGS. 1 and 2 . In some embodiments, all such light sources may be of the same type. However, in some other embodiments, different types of light sources may be used for some or all of the light sources. For example, it may be desirable to utilize LEDs that emit primarily light in the green spectrum for the purpose of detecting heart rate, as fluctuations in light emitted back from a person's skin may be more pronounced in the green spectrum. At the same time, photoplethysmography techniques may also be used to measure other physiological parameters besides heart rate, such as blood oxygen levels. In such cases, it may be desirable to utilize LEDs that emit primarily light in the red or infrared spectrum for such purposes. Thus, it may be desirable to include separate light emitting devices that are each capable of emitting light of a different wavelength; each light emitting device may be used to supply light for a different type of photoplethysmographic measurement. In some embodiments, these light emitting devices or light sources may be distributed throughout the PPG sensor face - for example, Figure 2 The light source 108 on the left side may be a green wavelength LED, and Figure 2 The light source 108 on the right side of the diagram may be a red or infrared wavelength LED. In some other embodiments, the light emitting devices may be clustered closely together (e.g., one or two millimeters or less from each other); in such embodiments, the clustered light emitting devices may be considered a single light source with a center point that is, for example, associated with the centroid of the light intensity distribution of the cluster of light emitting devices when all light emitting devices in the cluster emit light simultaneously, or associated with the average position of all light emitting devices in the cluster. For a light source having a single light emitting device, the center of the light source is understood to correspond to a point that is typically associated with the centroid of the light intensity distribution of the light emitting device (e.g., typically the center of an LED). It should be understood that the term "light-emitting device" as used herein refers to a single discrete light-emitting device (e.g., a single LED or laser diode), and the term "light source" as used herein refers to one or more light-emitting devices that are generally viewed as a unit, which are (for example) closely enough together that an observer would not be able to discern gaps between light-emitting devices in a group of light-emitting devices when all of the light-emitting devices in the group are illuminated simultaneously and the observer is approximately 2 feet to 3 feet away from the light-emitting devices (this assumes that the light-emitting devices emit light in a spectrum visible to the observer; for light-emitting devices that emit light in a non-visible spectrum (e.g., infrared), this assessment may be based on whether gaps between such light-emitting devices would be visible at a distance of 2 feet to 3 feet if such light-emitting devices instead emitted visible light).

[0115] A conventional PPG sensor featuring a square photodetector element such as the example shown in FIG. 1 may utilize two light sources surrounding the photodetector element so that the Figure 4 The apparent drop in lighting intensity in this arrangement is Figure 4The light intensity at the left edge of the delineated area may be mirrored along the right edge of the delineated area, resulting in a valley of lower intensity light adjacent to the middle of the square photodetector, but increased light intensity may be seen at the left and right edges of the square photodetector. However, this requires powering two LEDs instead of one, effectively doubling the power consumption attributable to the light source.

[0116] The inventors have determined that in some cases, utilizing HAR photodetector elements may provide a technique for achieving increased sensor performance that is more power efficient than conventional approaches that include multiple light sources because the HAR photodetector elements and a single light source may achieve performance that is comparable to or better than the performance of a square photodetector with multiple light sources - thereby avoiding the use of additional light sources (and the additional power consumption that would result).

[0117] The inventors have also determined that in some cases further increases in PPG sensor performance can be obtained by arranging multiple HAR photodetectors in an array or pattern around a light source. Because the same light source can provide light to multiple HAR photodetectors, there is little or no additional power consumption attributable to the light source in such embodiments compared to embodiments with only one photodetector element. The use of such HAR photodetector elements can also increase the signal-to-ambient noise ratio of the PPG sensor.

[0118] Figures 14 to 16 Several examples of implementations with multiple HAR photodetectors are depicted according to example implementations. Fig.14 In FIG. 1 , two HAR photodetector elements 1412 are shown, wherein a light source 1408 is inserted between the two HAR photodetector elements 1412. Fig.15 , three HAR photodetector elements 1512 are shown in a circular array centered on light source 1508. Similarly, in Fig.16 , four HAR photodetector elements 1612 are arranged in a circular array around light source 1608. The HAR photodetector elements in such a pattern or array need not be equally spaced, e.g. Fig.14 , 15 As shown in the embodiment of Figure 16. For example, an array of three elements can be obtained by Fig.16 The array shown in FIG. 1 is formed by removing one of the photodetector elements 1612. The photodetector elements within this pattern or array need not all be of the same size and shape. For example, Fig.16 The upper and lower photodetector elements 1612 in FIG. 1 may have an aspect ratio of 5:1, and Fig.16 The left and right HAR photodetector elements 1612 in FIG. 1 may have an aspect ratio of 3:1 (which is the actual aspect ratio depicted). Fig.17Another example arrangement of photodetector elements is depicted. Fig.17 In the embodiment of the present invention, the upper and lower HAR photodetector elements 1612 may have an aspect ratio of 2:1, and the left and right HAR photodetector elements 1612 may have an aspect ratio of 3:1; in some such implementations, the shorter photodetector elements (e.g., the photodetector elements 1712 of the 2:1 aspect ratio in the depicted example) may be positioned so that the midpoints of their shorter edges are positioned substantially along a line spanning the short edges of the longer photodetector elements (e.g., the photodetector elements 1712 of the 3:1 aspect ratio in the depicted example). In some PPG implementations involving multiple HAR photodetector elements, the HAR photodetector elements may occupy more than 50% of the annular area around the light source having an annular width of 1 mm.

[0119] Fig.18 Describes how the Fig.15 , but using multiple light emitting devices in the light source. As previously discussed herein, the PPG sensor may utilize one or more light sources, each of which may include one or more light emitting devices. As can be seen, the light source 1808 includes two light emitting devices 1810, which may be (for example) surface mounted LEDs, one emitting primarily green wavelength light and the other emitting primarily red wavelength light. The two light emitting devices 1810 may define a center point 1866 located between them and may be considered in combination to form the light source 1808. It should be understood that the light emitting devices 1810 may be operated individually and cannot be powered on at the same time during actual use. Therefore, the array of photodetector elements 1812 may not appear to be centered on the center of any one of the light emitting devices 1810 when the light emitting devices 1810 are turned on, but nevertheless, the array of photodetector elements 1812 may be considered to be centered on the light source 1808.

[0120] The inventors have further determined that in at least some embodiments, the HAR photodetector element can be sized so that its width, or a second maximum dimension of at least 90% of the active area of ​​the HAR photodetector element, is between approximately 0.5 mm and 1 mm; in some of these embodiments there may be some deviation from this range, such as a HAR photodetector element in which this dimension is in the range between 0.45 mm and 1.1 mm.

[0121] In general, the light intensity of light from a PPG light source emitted from a person's skin decreases in an axially symmetric manner as the distance from the center of the light source increases (this assumes a single light source PPG sensor). Therefore, the light source may be surrounded by multiple concentric, annular zones, each corresponding to a different average light intensity. The inventors analyzed the characteristics of such annular zones and determined that regardless of the inner radius of a particular annular zone, approximately 80% of the available power or intensity of the emitted light available outside the inner radius of the annular zone occurs within 1 mm of the inner radius. Therefore, a particular annular zone with an annular width of approximately 1 mm will result in approximately 80% of the light intensity / power available outside the inner radius of the annular zone. For clarity, the "annular width" (w) of an annular zone is equal to the outer radius (r o ) minus the inner radius of the annular region (r i ). Fig.19 It is explained in Fig.19 A light source 1908 and a surrounding annular region 1958 are shown according to an example embodiment; the inner radius r of the annular region 1958 is indicated. i , outer radius r o And ring width. Fig. 20 Depicts a curve from an arbitrary inner radius r according to an example embodiment. i Plot the fraction of the light intensity emitted outside the inner radius r i Falling on the inner radius r i and within the boundaries of an annular region of annular width as indicated along the x-axis. As can be seen, approximately 80% of the available light intensity falls within the inner radius r i Outside and inside radius r of 1mm i Within.

[0122] The inventors determined that, given the high concentration of emitted light intensity within this 1 mm area, sizing the HAR photodetector to have a width of approximately 1 mm or less or such that the second dimension cited above is approximately 1 mm or less may provide enhanced performance in a PPG sensor in some implementations.

[0123] In some implementations, the HAR photodetector elements may be sized and arranged to satisfy certain geometric constraints. For example, in some implementations, the size of the HAR photodetector elements may be subject to the following constraints regarding Fig.21 Certain geometric relationship constraints are further described. Fig.21 Depicts the light source, HAR photodetector, and various reference annotations. Fig.21 , the HAR photodetector element 2112 is shown positioned a distance r from the light source 2108. i . With an inner radius r i and outer radius r oThe annular region 2158 may be centered on the light source 2108. Generally, in such embodiments, for the annular region 2158, r i With r o The difference between them can be less than or equal to 2 mm. i With r o In addition to the relationship between , as shown, the HAR photodetector element 2112 can subtend an angle θ at the center of the light source. In such cases, the HAR photodetector can be sized so that a) there is at least 80% overlap between the annular region 2158 and the HAR photodetector element 2112 (overlapping at Fig.21 2158); in this example, approximately 86% of the HAR photodetector 2112 overlaps the annular region 2158), and b) the angle θ is at least:

[0124]

[0125] In some further implementations, the HAR photodetector 2112 may be further sized such that the angle θ is no greater than:

[0126]

[0127] Figures 22 to 24 Depicted are cross sections of simplified representations of various PPG sensors according to various example implementations. Figures 22 to 24 Similar components in each of the are indicated by a numerical designator having the last two digits in common and may be referred to only with respect to Fig. 22 described once; however, this description can also apply to Fig.23 and 24 The corresponding components in .

[0128] exist Fig. 222208. In the embodiment shown in FIG. 2208, a substrate 2272 supports two HAR photodetector elements 2212 located on either side of a light source 2208. A window 2278 is offset from the substrate 2272. In this embodiment, the window 2278 is made of a translucent or transparent material (e.g., clear acrylic) with an in-mold label 2276 embedded therein. The in-mold label 2276 may be black or otherwise rendered opaque to light to prevent light (except through the window area 2226) from entering or leaving the PPG sensor through the window 2278. In other embodiments, other masking techniques such as spray paint or a screen printing mask applied to the window 2278 may be used. Regardless of which technique is used, either the in-mold label 2276 or the masking may prevent stray light from other light sources (e.g., ambient light) from reaching the HAR photodetector elements 2212 and affecting the heart rate signal obtained by the PPG sensor. The window 2278 may be secured against the person's skin (e.g., by being secured in place with a strap) when obtaining a heart rate measurement to allow light from the light source 2208 to shine through its associated window region 2226 and into the person's skin, where the light then diffuses into the surrounding flesh and is then emitted back from the person's skin and into the HAR photodetector element 2212 through its associated window region 2226.

[0129] To reduce the likelihood that light from the light source 2208 will reach any of the HAR photodetector elements 2212 without first diffusing through the person's skin, the light source 2208 may be separated from the HAR photodetector elements 2212 within the PPG sensor by a wall 2274, which may or may not extend to the window 2278. In some implementations, an adhesive gap filler (e.g., black silicone) may be used to bridge any gap between the wall 2274 and the window 2278. In some implementations, a gap 2280 may exist between the window 2278 and the HAR photodetector element 2212, but in other implementations, this gap may be eliminated and the HAR photodetector element 2212 may abut the window 2278. The wall 2274 may prevent light from the light source 2208 from reaching the HAR photodetector element 2212 by following a path that is entirely within the housing of the PPG sensor. As can be seen, the window regions 2226 through which light passes to the HAR photodetector elements 2212 each overlap with its corresponding HAR photodetector element 2212. In the depicted example, the window regions 2226 and their corresponding HAR photodetector elements 2212 are coextensive with each other, but in other implementations, the window regions 2226 may be smaller or larger than their corresponding HAR photodetector elements 2212, for example, to accommodate assembly tolerance mismatches.

[0130] Fig.23Depicts a window similar to FIG. 2374 except that window 2378 does not include any masking (e.g., in the form of an in-mold label (e.g., in-mold label 2276)). Fig. 22 PPG sensor implementation of the PPG sensor. Fig.23 In FIG. 23, wall 2374 also extends closer to window 2378. Fig.23 , window 2378 is optically transparent throughout the described span.

[0131] Fig.24 Describes a method similar to FIG. 2 except that continuous windows 2278 and 2328 have been replaced with discrete window 2478. Fig. 22 and 23 2478. In this implementation, each window 2478 may have its own window area 2426 that overlaps a different one of the light source 2408 or the HAR photodetector element 2412. In such an implementation, the windows 2478 may be glued or otherwise fixed in place within the frame of the supply wall 2474. Alternatively, the windows 2478 may be formed by filling the recesses formed by the wall 2474 and other surrounding structures with a transparent flowable material, such as an epoxy, and then allowing the flowable material to cure and harden. In such an implementation, the gap 2480 may not exist because the flowable material may encapsulate the HAR photodetector element 2412.

[0132] Regardless of the particular manner in which the window region 2226, 2326, or 2426 is provided, the window region overlaps the HAR photodetector element such that light entering the PPG sensor via the window region generally takes a direct route to the HAR photodetector element as compared to a route that involves forcing the light to travel in a direction parallel to the window (as may be done using various types of transparent light guides). The phrase "optical light guide" as used herein with respect to a PPG sensor refers to a particular type of optical structure that redirects or transmits light entering a first region of a surface through a surface such that most of the light is transmitted in a direction generally transverse to the surface to an area overlapping a second region of the surface that is offset from the first region along the surface. As the term is used herein, an optical light guide is not to be confused with other optical structures (e.g., a microlens array or lens that may be placed over a HAR photodetector element to improve collection efficiency, an optical window that may refract light passing through the window slightly but not transmit or redirect the light in a significant manner in a direction transverse to the surface, an optical filter that may filter only certain wavelengths of light, etc.). In some embodiments of the PPG sensor discussed herein, an optical light guide is not required because the HAR photodetector element generally overlaps the window region.

[0133] The above concepts have been discussed primarily with respect to light sources that emit green light (e.g., wavelengths in the range of 500nm to 550nm), but it is expected that the photodetector element concepts discussed herein may achieve similar performance using light sources that primarily emit light in the range of 500nm to 600nm (including yellow light and some bright orange light). Light sources that emit light in the green spectrum are particularly well suited for photoplethysmography techniques for measuring heart rate. In contrast, other photoplethysmography techniques, such as techniques for measuring blood oxygen levels, may be most effective using light of significantly different wavelengths, such as in the red wavelength (e.g., 660nm) or in the infrared spectrum. The aspect ratios and dimensional values ​​discussed herein are tailored based on the green / yellow spectrum and are not suitable for use in other spectrums, such as the red or infrared spectrum.

[0134] While the concepts discussed herein are believed to be applicable to photodetectors of various different sizes, the concepts are particularly applicable to PPG implementations for wearable health monitoring devices. In general, such devices, which are typically designed to be worn as a bracelet or wristband, have a small housing with a limited area that comes into contact with a person's skin. Therefore, in such implementations, there are practical limits on how the light sources and photodetector elements of the PPG sensor can be arranged and sized. In general, the light sources and photodetector elements of such implementations can be arranged so that the photodetector elements are positioned so that the edge closest to the light source is positioned between 1 mm and 4 mm from the center or edge of the light source. However, it should be understood that the implementations discussed herein can be used in products that achieve closer or farther spacings from the center of the light source (e.g., closer than 1 mm or farther than 4 mm).

[0135] In some implementations, a HAR photodetector element that may be used in a PPG may be positioned such that an edge of a light source closest to the PPG sensor is offset from a center of the light source by between 1 mm and 4 mm and may be sized such that it has a maximum first dimension that is approximately between 1 mm and 5 mm and a maximum second dimension that is approximately between 0.05 mm and 2 mm, while conforming to an aspect ratio of the maximum first dimension to the maximum second dimension that is approximately between 2:1 and 5:1.

[0136] Although the photodetector elements can be positioned so that their closest edges are more than 4 mm from the center of the light source, doing so may prove counterproductive because a higher intensity light source may be required to ensure that enough light is spread across the increased distance to obtain a sufficiently strong signal at the photodetector. Because a higher intensity light source will generally consume additional power, this tradeoff may be undesirable in the context of a wearable health monitor.

[0137] In addition to the HAR photodetectors discussed herein, performance increases relative to square photodetector based PPG for heart rate measurement may be achieved by using non-HAR and non-square photodetector elements that typically surround a light source and have a central opening in the middle of the light source for the light source to shine through. In general, such photodetector elements may have a periphery defined by a first boundary and a second boundary within the first boundary defining a central opening. Fig.25 and 26 Two example implementations of such a PPG sensor are depicted.

[0138] Fig.25 An example of an annular photodetector element 2512 with a light source 2508 in the middle is depicted according to an example implementation. The annular photodetector element 2512 may have a periphery defined by a first boundary 2532 and a central opening defined by a second boundary 2534; the first boundary 2532 and the second boundary 2534 may be offset from each other by a first distance 2584 along the radius of the annular region. The light source 2508 may be a green wavelength light source that primarily emits light in wavelengths between 500 nm and 550 nm or between 500 nm and 600 nm. This photodetector element 2512 may be sized such that the ratio of the perimeter of the second boundary 2534 to the first distance 2584 is between 9.5:1 and 11.5:1. In some implementations, the annular photodetector element 2512 may be sized such that the first boundary has a diameter between 3 mm and 5.5 mm, and the second boundary has a diameter between 1 mm and 2.5 mm. Such parameters are believed to provide good light focusing performance when used with green wavelength light for heart rate measurement purposes.

[0139] Fig.26 An example of a polygonal photodetector element 2612 with a light source 2608 in the middle is depicted according to an example embodiment. Like the annular photodetector element 2512, the polygonal photodetector element 2612 may have a periphery defined by a first boundary 2632 and a central opening defined by a second boundary 2634. However, in this case, both the first boundary 2632 and the second boundary 2634 are polygonal in nature, such as hexagonal. Other polygonal shapes may be used in other implementations, such as triangular shapes, square shapes, pentagonal shapes, heptagonal shapes, octagonal shapes, etc., i.e., N-gons. The edges of the first boundary 2632 and the second boundary 2634 may be offset from each other by a first distance 2684 along an axis perpendicular to the edges. In such implementations, each side of the polygon forming the second boundary 2634 may have a second length 2682, and the ratio of the second length 2682 to the first distance 2684 may be between 2:1 and 5:1. These parameters are believed to provide good light focusing performance when used with green wavelength light for heart rate measurement purposes.

[0140] It should be understood that references to "control logic" herein refer to hardware and / or software that can be used to provide certain functionality, such as controlling when the light source of the PPG is turned on or off, controlling the intensity of the illumination light source, collecting data from one or more photodetectors, and analyzing at least the data collected from the one or more photodetectors to determine a measurement of a person's heart rate. The control logic may include, for example, one or more processors and a memory storing computer executable instructions for controlling the one or more processors to provide this functionality. The control logic may also include various circuit elements that can provide aspects of this functionality without the need for computer executable instructions stored in memory. In some implementations, the control logic may be provided, at least in part, by an application specific integrated circuit (ASIC).

[0141] Fig. 27 Depicts a high-level block diagram of a PPG sensor according to an example implementation. Fig. 27 27, control logic 2706 is shown, which includes a processor 2768 and a memory 2770 operatively coupled to each other. The control logic is operatively coupled to the light source 2708 and the photodetector element 2712. The control logic 2706 can thus cause the light source 2708 to emit light at a desired time, and can receive a signal from the photodetector element 2712 indicating the amount of detected light.

[0142] Many inventions are described and illustrated herein. Although certain embodiments, features, attributes and advantages of the present invention have been described and illustrated, it should be understood that many other and different and / or similar embodiments, features, attributes and advantages of the present invention become apparent from the description and illustration. Thus, the above embodiments of the present invention are merely exemplary. The above embodiments of the present invention are not intended to be exhaustive or to limit the present invention to the precise form, technology, material and / or configuration disclosed. In the context of the present invention, many modifications and variations are feasible. It should be understood that other embodiments can be utilized and operational changes can be made without departing from the scope of the present invention. Thus, the scope of the present invention is not limited to the above description alone, because the description of the above embodiments is presented for the purpose of illustration and description.

[0143] In particular, it should be appreciated that any of the implementations discussed above with respect to a single photodetector element separated from the light source may also be implemented using multiple photodetector elements arranged around the light source, as discussed with respect to various other implementations discussed herein.

[0144] In addition, it should be understood that the use of the term "substantially" herein should be understood to indicate an amount of ±10%, unless otherwise limited with respect to a particular context, with respect to a numerical quantity or other quantifiable relationship (e.g., perpendicularity or parallelism). Thus, for example, lines that are substantially perpendicular to each other may be at an angle of between 81° and 99° to each other. In a further example, a dimension that is substantially between 1 mm and 3 mm may be, for example, in the range from 0.9 mm to 3.3 mm. In another example, an angle that is substantially in the range of 1.1 radians may be between 0.9 radians and 1.21 radians.

[0145] Importantly, the present invention is not limited to any single aspect or embodiment, nor to any combination and / or permutation of such aspects and / or embodiments. Furthermore, each of the aspects of the present invention and / or embodiments thereof may be employed alone or in combination with one or more of the other aspects and / or embodiments of the present invention. For the sake of brevity, many of the permutations and combinations will not be discussed and / or described separately herein.

Claims

1. A device comprising: light source; a plurality of discrete photodetector elements arranged in a pattern, each photodetector element in the pattern being equidistant from a center of the light source, each photodetector element having: a first edge having a first length, a first width along a direction perpendicular to the first edge; and control logic communicatively coupled to the light source and each photodetector element and configured to: causing the light source to emit light, obtaining one or more measured light intensity measurements from the plurality of photodetector elements, and A heart rate measurement is determined based at least in part on the one or more light intensity measurements, wherein: the first width is between 0.5 mm and 2 mm, and a ratio of the first length of each photodetector to the first width is between 3:1 and 5:1, and wherein each photodetector element is positioned so that an edge of the photodetector element closest to the light source is between 1 mm and 4 mm away from the light source.

2. The apparatus according to claim 1, wherein: The first edge of each photodetector element is perpendicular to an axis radiating outward from a center of the light source.

3. The apparatus according to claim 1, wherein: The first edge of each photodetector element is transverse to an axis radiating outward from a center of the light source.

4. The apparatus according to any one of claims 1 to 3, wherein: The light source includes a plurality of light emitting devices.

5. The apparatus according to claim 4, wherein: The plurality of light emitting devices include at least two light emitting devices that primarily emit light of different wavelengths.

6. The apparatus of claim 4, wherein: The plurality of light emitting devices are concentrated at a center point of the pattern of the plurality of photodetector elements.

7. The apparatus of any one of claims 1-3, wherein the ratio of the first length to the first width of each photodetector element is between 3:1 to 3.5:

1.

8. The apparatus of any one of claims 1-3, wherein the ratio of the first length to the first width of each photodetector element is between 3.5:1 to 5:

1.

9. The apparatus of claim 1, wherein the plurality of photodetector elements are uniformly spaced within the pattern.

10. The apparatus of any one of claims 1 to 3, wherein the first length is between 1 mm and 5 mm.

11. The apparatus of claim 6, wherein the pattern of the plurality of photodetector elements comprises three photodetector elements equally spaced about the light source.

12. The apparatus according to any one of claims 1 to 3, further comprising: A housing having a back surface, the back surface including one or more transparent window areas through which light can pass into the device, wherein: Each photodetector element is positioned such that the photodetector element overlaps a corresponding one of the one or more transparent window regions, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

13. The apparatus of claim 12, wherein: The back surface includes a thin window, and The window region is a sub-region of the window defined by the plurality of photodetector elements.

14. The apparatus of claim 12, wherein: Each photodetector element is offset from the corresponding transparent window region by a corresponding gap along a direction normal to the photodetector element, and The gap is free of an optical light guide.

15. An apparatus according to any one of claims 1 to 3, wherein each photodetector element has, in addition to the first edge, an arched second edge opposite to the first edge, wherein when measured in a direction perpendicular to the first edge, the arched second edge has a maximum distance from the first edge, and the maximum distance is equal to the first width.

16. An apparatus comprising: The first light source; Second light source; a photodetector element interposed between the first light source and the second light source, wherein the photodetector element is equidistant from the first light source and the second light source; and control logic communicatively coupled to the first light source, the second light source, and the photodetector element and configured to: causing the first light source and the second light source to emit light, obtaining a measured light intensity measurement from the photodetector element; and determining a heart rate measurement based at least in part on the light intensity measurement, in: The photodetector element is rectangular in shape, the photodetector element has a first edge with a first length, and has a second edge perpendicular to the first edge with a second length, the second length being between 0.5 mm and 2 mm, The ratio of the first length to the second length is between 3:1 and 5:1, and The photodetector elements are positioned such that an edge of the photodetector element closest to the first light source is at a distance of between 1 mm and 4 mm from the first light source or an edge of the photodetector element closest to the second light source is at a distance of between 1 mm and 4 mm from the second light source.

17. The apparatus of claim 16, wherein: The first edge of the photodetector element is perpendicular to an axis spanning between a center of the first light source and a center of the second light source.

18. The apparatus of claim 16, wherein: The first edge of the photodetector element is transverse to an axis spanning between a center of the first light source and a center of the second light source.

19. The apparatus according to any one of claims 16 to 18, further comprising: a housing having a back side, the back side including a transparent window region overlapping the photodetector element and two further window regions, the two further window regions each being associated with a different one of the first light source and the second light source and allowing light from the associated light source to pass through the back side, wherein: The first light source and the second light source are the only light sources in the apparatus configured to emit light through the back surface, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

20. An apparatus comprising: light source; a plurality of photodetectors arranged in a pattern, each photodetector having a photosensitive area, wherein a center of the photosensitive area of ​​each photodetector in the pattern is equidistant from a center of the light source, and wherein at least 90% of the photosensitive area is defined by a first dimension along a first axis and a second dimension along a second axis perpendicular to the first axis; and control logic communicatively coupled to the light source and each photodetector and configured to: causing the light source to emit light, obtaining one or more measured light intensity measurements from the plurality of photodetectors, and A heart rate measurement is determined based at least in part on the one or more light intensity measurements, wherein for each photodetector: The second dimension associated with each photodetector is between 1 mm and 2 mm, and The ratio of the first size to the second size is between 3:1 and 5:

1.

21. The apparatus of claim 20, wherein: The light source includes a plurality of light emitting devices, and The plurality of light emitting devices include at least two light emitting devices that primarily emit light of different wavelengths.

22. Apparatus according to claim 20 or 21, wherein: The light source is located at a center point of the pattern of the photodetector.

23. The apparatus of claim 20 or 21, wherein a ratio of the first size to the second size of each photodetector is between 3:1 and 3.5:

1.

24. The apparatus of claim 20 or 21, wherein a ratio of the first size to the second size of each photodetector is between 3.5:1 and 5:

1.

25. The apparatus of claim 20, wherein: The first dimension associated with each photodetector is between 3 mm and 5 mm, the ratio of the first dimension to the second dimension is between 3:1 and 5:1, and Each photodetector is positioned so that an edge of the photosensitive area of ​​the photodetector closest to the light source is a distance between 1 mm and 4 mm from the center of the light source.

26. The apparatus of claim 25, wherein the pattern of photodetectors comprises four photodetectors equally spaced around the light source.

27. The apparatus according to claim 20 or 21, further comprising: A housing having a back surface, the back surface comprising one or more thin transparent window areas, wherein: Each photodetector is positioned so that the photosensitive area of ​​the photodetector overlaps a corresponding one of the transparent window regions, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

28. The apparatus of claim 27, wherein: The back surface includes a thin window, and The window region is a sub-region of the window defined by the photosensitive areas of the plurality of photodetectors.

29. The apparatus of claim 27, wherein: The photosensitive area of ​​each photodetector is offset from the corresponding transparent window area by a corresponding gap along a direction normal to the photodetector, and The gap is free of an optical light guide.

30. An apparatus comprising: light source; A plurality of discrete high aspect ratio (HAR) photodetectors arranged in a pattern, each HAR photodetector in the pattern having a photosensitive region and configured to provide an output signal indicative of an amount of light incident on the photosensitive region of the HAR photodetector, the photosensitive region of each HAR photodetector having: a first edge having a first length, a first width in a direction perpendicular to the first edge; and an arched second edge opposite to said first edge, wherein: The arcuate second edge is arcuate in a plane parallel to the photosensitive region of the HAR photodetector, and The arcuate second edge has a maximum distance from the first edge when measured in a direction perpendicular to the first edge, the maximum distance being equal to the first width; and control logic communicatively coupled to the light source and each HAR photodetector and configured to: causing the light source to emit light, obtaining one or more measured light intensity measurements from the plurality of HAR photodetectors based on the output signal from each HAR photodetector, and determining a heart rate measurement based at least in part on the one or more light intensity measurements, in: The first width is between 0.5 mm and 2 mm, a ratio of the first length to the first width of each photodetector element is between 3:1 and 5:1, The light source is mounted on the surface of the substrate, and Each photosensitive region faces away from the surface of the substrate on which the light source is mounted.

31. The apparatus of claim 30, wherein: When viewed from a direction perpendicular to the substrate, the first edge of the photosensitive area of ​​each HAR photodetector is perpendicular to and intersects a corresponding axis emanating from a center of the light source, and the first edge is parallel to the substrate, and The plurality of HAR photodetectors and the light source are supported by the substrate.

32. The apparatus of claim 30, wherein: When viewed from a direction perpendicular to the substrate, the first edge of the photosensitive area of ​​each HAR photodetector is transverse to and intersects a corresponding axis emanating from a center of the light source, and the first edge is parallel to the substrate, and The plurality of HAR photodetectors and the light source are supported by the substrate.

33. Apparatus according to any one of claims 30 to 32, wherein: The light source includes a plurality of light emitting devices.

34. The apparatus of claim 33, wherein: The plurality of light emitting devices include at least two light emitting devices that primarily emit light of different wavelengths from each other.

35. The apparatus of claim 33, wherein: The plurality of light emitting devices are concentrated at a center point of the pattern of the plurality of HAR photodetectors.

36. The apparatus of any one of claims 30 to 32, wherein a ratio of the first length to the first width of the photosensitive region of each HAR photodetector is between 3:1 to 3.5:

1.

37. The apparatus of any one of claims 30 to 32, wherein a ratio of the first length to the first width of the photosensitive region of each photodetector is between 3.5:1 to 5:

1.

38. The apparatus of any one of claims 30 to 32, wherein the photosensitive region of each HAR photodetector: has a first length between 1 mm and 5 mm and a first width between 0.5 mm and 2 mm, a ratio of the first length to the first width being between 3:1 and 5:1, and The edge of the HAR photodetector positioned closest to the light source is at a distance of between 1 mm and 4 mm from the light source.

39. The apparatus of claim 35, wherein the pattern of the plurality of HAR photodetectors comprises three photodetector elements equally spaced about the light source.

40. The apparatus of any one of claims 30 to 32, further comprising: A housing having a back surface, the back surface including one or more transparent window areas through which light can pass into the device, wherein: Each HAR photodetector is positioned such that the photosensitive area of ​​the HAR photodetector overlaps a corresponding one of the one or more transparent window regions, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

41. The apparatus of claim 40, wherein: The back surface includes a thin window, and The window region is a sub-region of the window defined by the plurality of HAR photodetectors.

42. The apparatus of claim 40, wherein: The photosensitive region of each HAR photodetector is offset from the corresponding transparent window region by a corresponding gap along a direction normal to the photosensitive region of the HAR photodetector, and The gap is free of an optical light guide.

43. An apparatus comprising: a first light source mounted on a surface of the substrate; a second light source supported by the substrate; a HAR photodetector interposed between the first light source and the second light source, wherein the HAR photodetector is equidistant from the first light source and the second light source, the HAR photodetector having a photosensitive area and configured to provide an output signal indicative of an amount of light incident on the photosensitive area of ​​the HAR photodetector; and control logic communicatively connected to the first light source, the second light source, and the HAR photodetector and configured to: causing the first light source and the second light source to emit light, obtaining a measured light intensity measurement from the HAR photodetector based on the output signal; and determining a heart rate measurement based at least in part on the light intensity measurement, in: The photosensitive region faces away from the surface of the substrate on which the first light source is mounted, The photosensitive region of the HAR photodetector is rectangular in shape, the photosensitive region having a first edge with a first length and having a second edge with a second length perpendicular to the first edge, The second length is between 0.5 mm and 2 mm, and A ratio of the first length to the second length is between 3:1 and 5:

1.

44. The apparatus of claim 43, wherein: When viewed from a direction perpendicular to the substrate, the first edge of the photosensitive area of ​​the HAR photodetector is perpendicular to and intersects a corresponding axis passing through a center of the first light source and a center of the second light source, and The HAR photodetector, the first light source, and the second light source are all supported by the substrate.

45. The apparatus of claim 43, wherein: The first edge of the photosensitive area of ​​the HAR photodetector is transverse to and intersects a corresponding axis passing through a center of the first light source and a center of the second light source when viewed from a direction perpendicular to the substrate, and The HAR photodetector, the first light source, and the second light source are all supported by the substrate.

46. ​​The apparatus of any one of claims 43 to 45, further comprising: a housing having a back side, the back side including a transparent window region overlapping the photosensitive area of ​​the HAR photodetector and two further window regions, the two further window regions each being associated with a different one of the first light source and the second light source and allowing light from the associated light source to pass through the back side, wherein: The first light source and the second light source are the only light sources in the apparatus configured to emit light through the back surface, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

47. An apparatus comprising: a light source mounted on a surface of the substrate; a plurality of high aspect ratio (HAR) photodetectors arranged in a pattern, each HAR photodetector in the pattern having a total photosensitive area, and a center of the total photosensitive area of ​​each HAR photodetector in the pattern being equidistant from a center of the light source, and wherein: At least 90% of the total photosensitive area is defined by a first dimension along a first axis and a second dimension along a second axis perpendicular to the first axis; and each HAR photodetector configured to provide an output signal indicative of a total amount of light incident on the total photosensitive area of ​​the HAR photodetector; and control logic communicatively coupled to the light source and each HAR photodetector and configured to: causing the light source to emit light, obtaining one or more measured light intensity measurements from the plurality of HAR photodetectors based on the output signal from each HAR photodetector, and A heart rate measurement is determined based at least in part on the one or more light intensity measurements, wherein for each HAR photodetector: the second dimension associated with the photosensitive area of ​​each HAR photodetector is between 1 mm and 2 mm, The ratio of the first size to the second size is between 3:1 and 5:1, and The total photosensitive area faces away from the surface of the substrate on which the light source is mounted.

48. The apparatus of claim 47, wherein: The light source includes a plurality of light emitting devices, and The plurality of light emitting devices include at least two light emitting devices that primarily emit light of different wavelengths from each other.

49. Apparatus according to claim 47 or 48, wherein: The light source is located at a center point of the pattern of the plurality of HAR photodetectors.

50. The apparatus of claim 47 or 48, wherein a ratio of the first size to the second size of each HAR photodetector is between 3:1 and 3.5:

1.

51. The apparatus of claim 47 or 48, wherein a ratio of the first size to the second size of the photosensitive area of ​​each HAR photodetector is between 3.5:1 and 5:

1.

52. The apparatus of claim 47, wherein: The first dimension associated with the photosensitive area of ​​each HAR photodetector is between 3 mm and 5 mm, the ratio of the first dimension to the second dimension is between 3:1 and 5:1, and Each HAR photodetector is positioned such that an edge of the total photosensitive area of ​​the HAR photodetector closest to the light source is a distance between 1 mm and 4 mm from the center of the light source.

53. The apparatus of claim 52, wherein the pattern of the plurality of HAR photodetectors comprises four HAR photodetectors equally spaced about the light source.

54. The apparatus of claim 47 or 48, further comprising: A housing having a back surface, the back surface comprising one or more thin transparent window areas, wherein: Each HAR photodetector is positioned such that the total photosensitive area of ​​the HAR photodetector overlaps a corresponding one of the transparent window regions, and The housing is configured so that when the device is worn by a person, the back surface is adjacent to the skin of the person wearing the device.

55. The apparatus of claim 54, wherein: The back surface includes a thin window, and The window region is a sub-region of the window defined by the total photosensitive area of ​​the plurality of HAR photodetectors.

56. The apparatus of claim 54, wherein: The total photosensitive area of ​​each HAR photodetector is offset from the corresponding transparent window area by a corresponding gap along a direction normal to the total photosensitive area of ​​the HAR photodetector, and The gap is free of an optical light guide.

Images