Heart rate sensor with high-aspect-ratio photodetector element

• US 9,775,548 B2
• Filed: 06/24/2016
• Issued: 10/03/2017
• Est. Priority Date: 05/28/2015
• Status: Active Grant

• Current Assignee: Fitbit, Inc. (Alphabet Inc.)
• Original Assignee: Fitbit, Inc. (Alphabet Inc.)
• Inventors: Sarantos, Chris H., Richards, Peter W.
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Liu, Chu Chuan (JJ)
• Application Number:
  US15/192,447
• Publication Number:
  US 20160345881A1
• Time in Patent Office: 466 Days
• Field of Search: 600310, 600322, 600323, 600324, 600340, 600473, 600476, 356 41
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 2562/04 Arrangements of multiple sensors of the same type
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/02427 Details of sensor
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Blood oxygenation sensors including high-aspect-ratio photodetector elements are discussed herein. Such high-aspect-ratio photodetector elements may provide improved signal-strength-to-power-consumption performance for blood oxygenation sensors incorporating such photodetector elements as compared with blood oxygenation sensors incorporating, for example, square photodetector elements.

Claims

1. An apparatus comprising:

a light source;

one or more discrete, high-aspect-ratio (HAR) photodetectors, each HAR photodetector having a die with a photosensitive area and configured to provide an output signal that indicates the total amount of light that is incident on the photosensitive area of the die of the HAR photodetector, the photosensitive area of each HAR photodetector having;

a first edge having a first length, and

a first width in a direction perpendicular to the first edge; and

control logic, the control logic communicatively connected with the light source and each HAR photodetector and configured to;

cause the light source to emit light,

obtain one or more measured light intensity measurements from the one or more HAR photodetectors based on the output signal from each HAR photodetector, and

determine a heart rate measurement based, at least in part, on the one or more light intensity measurements,

wherein;

the ratio of the first length to the first width of each photodetector element is substantially between 3;

1 to 5;

1,

the light source is mounted on a surface of a substrate, and

each photosensitive area faces away from the surface of the substrate on which the light source is mounted.

2. The apparatus of claim 1, wherein:

the first edge of the photosensitive area of each HAR photodetector, when viewed from a direction perpendicular to the substrate, is perpendicular to, and intersects with, a corresponding axis radiating out from a center of the light source and parallel to the substrate, and

the one or more HAR photodetectors and the light source are supported by the substrate.

3. The apparatus of claim 1, wherein:

the first edge of the photosensitive area of each HAR photodetector, when viewed from a direction perpendicular to the substrate, is transverse to, and intersects with, a corresponding axis radiating out from a center of the light source and parallel to the substrate, and

the one or more HAR photodetectors and the light source are supported by the substrate.

4. The apparatus of claim 1, wherein:

the light source includes a plurality of light-emitting devices.

5. The apparatus of claim 4, wherein:

the plurality of light-emitting devices includes at least two light-emitting devices that predominantly emit light of different wavelengths from one another.

6. The apparatus of claim 4, wherein:

there are a plurality of HAR photodetectors arranged in a pattern, and

the plurality of light-emitting devices is collocated at a center point of the pattern of HAR photodetectors.

7. The apparatus of claim 1, wherein the ratio of the first length to the first width of the photosensitive area of each HAR photodetector is substantially between 3:

1 to 3.5;

1.

8. The apparatus of claim 1, wherein the ratio of the first length to the first width of the photosensitive area of each photodetector is substantially between 3.5:

1 to 5;

1.

9. The apparatus of claim 1, wherein the photosensitive area 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, with the ratio of the first length to the first width substantially between 3;

1 to 5;

1, and

is positioned such that an edge of that HAR photodetector closest to the light source is between 1 mm and 4 mm from the light source.

10. The apparatus of claim 6, wherein the pattern of HAR photodetectors includes three photodetector elements that are equidistantly spaced about the light source.

11. The apparatus of claim 1, further comprising:

a housing having a back face that includes one or more transparent window regions through which light may enter the apparatus, wherein;

each HAR photodetector is positioned such that the photosensitive area of that HAR photodetector is overlapped by a corresponding one of the one or more transparent window regions, and

the housing is configured such that the back face is adjacent to the skin of a person wearing the apparatus when the apparatus is worn by that person.

12. The apparatus of claim 11, wherein:

the back face includes a thin window, and

the window regions are sub-regions of the window that are defined by the HAR photodetectors.

13. The apparatus of claim 11, wherein:

the photosensitive area of each HAR photodetector is offset from the corresponding transparent window region by a corresponding gap in a direction normal to the photosensitive area of that HAR photodetector, and

the gap is free of optical light guides.

14. The apparatus of claim 1, wherein the photosensitive area of each HAR photodetector has, in addition to the first edge, an arcuate second edge opposite the first edge, wherein:

the arcuate second edge is arcuate in a plane parallel to the photosensitive area of that HAR photodetector, and

the arcuate second edge has a maximum distance from the first edge, when measured along a direction perpendicular to the first edge, that is equal to the first width.

15. An apparatus comprising:

a first light source mounted on a surface of a substrate;

a second light source supported by the substrate;

a HAR photodetector interposed between the first light source and the second light source, having a die with a photosensitive area, and configured to provide an output signal that indicates the total amount of light that is incident on the photosensitive area of the die of the HAR photodetector; and

control logic, the control logic communicatively connected with the first light source, the second light source, and the HAR photodetector and configured to;

cause the first light source and the second light source to emit light,

obtain measured light intensity measurements from the HAR photodetector based on the output signal, and

determine a heart rate measurement based, at least in part, on the light intensity measurements,

wherein;

the photosensitive area faces away from the surface of the substrate on which the first light source is mounted,

the photosensitive area of the HAR photodetector is rectangular in shape, has a first edge with a first length, and has a second edge, perpendicular to the first edge, with a second length, and

the ratio of the first length to the second length is substantially between 3;

1 to 5;

1.

16. The apparatus of claim 15, wherein:

the first edge of the photosensitive area of the HAR photodetector element, when viewed from a direction perpendicular to the substrate, is perpendicular to, and intersects with, 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.

17. The apparatus of claim 15, wherein:

the first edge of the photosensitive area of the HAR photodetector, when viewed from a direction perpendicular to the substrate, is transverse to, and intersects with, 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.

18. The apparatus of claim 15, further comprising

a housing having a back face that includes a transparent window region that overlaps the photosensitive area of the HAR photodetector and two further window regions that are each associated with a different one of the first light source and the second light source and that allow light from the associated light source to pass through the back face, 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 face, and

the housing is configured such that the back face is adjacent to the skin of a person wearing the apparatus when the apparatus is worn by that person.

19. The apparatus of claim 15, wherein the HAR photodetector is equidistant from the first light source and the second light source.

20. An apparatus comprising:

a light source mounted on a surface of a substrate;

one or more high-aspect-ratio (HAR) photodetectors, each HAR photodetector having a die with a total photosensitive area, 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 is configured to provide an output signal that indicates the total amount of light that is incident on the total photosensitive area of the HAR photodetector; and

control logic, the control logic communicatively connected with the light source and each HAR photodetector and configured to;

cause the light source to emit light,

obtain one or more measured light intensity measurements from the one or more HAR photodetectors based on the output signal from each HAR photodetector, and

determine a heart rate measurement based, at least in part, on the one or more light intensity measurements, wherein, for each HAR photodetector;

the ratio of the first dimension to the second dimension is substantially between 3;

1 to 5;

1, and

the total photosensitive area faces away from the surface of the substrate on which the light source is mounted.

21. The apparatus of claim 20, wherein:

the light source includes a plurality of light-emitting devices, and

the plurality of light-emitting devices includes at least two light-emitting devices that predominantly emit light of different wavelengths from one another.

22. The apparatus of claim 20, wherein:

the one or more HAR photodetectors includes a plurality of HAR photodetectors arranged in a pattern, and

the light source is located at a center point of the pattern of HAR photodetectors.

23. The apparatus of claim 20, wherein the ratio of the first dimension to the second dimension of each HAR photodetector is substantially between 3:

1 to 3.5;

1.

24. The apparatus of claim 20, wherein the ratio of the first dimension to the second dimension of the photosensitive area of each HAR photodetector is substantially between 3.5:

1 to 5;

1.

25. The apparatus of claim 20, wherein:

the one or more HAR photodetectors includes a plurality of HAR photodetectors arranged in a pattern, and

the center of the total photosensitive area of each HAR photodetector in the pattern is equidistant from the center of the light source.

26. The apparatus of claim 25, wherein:

the first dimension associated with the photosensitive area of each HAR photodetector is between 3 mm and 5 mm and the second dimension associated with the photosensitive area of each HAR photodetector is between 1 mm and 2 mm, consistent with the ratio of the first dimension to the second dimension being between 3;

1 to 5;

1, and

each HAR photodetector is positioned such that an edge of the total photosensitive area for that HAR photodetector that is closest to the light source is between 1 mm and 4 mm from the center of the light source.

27. The apparatus of claim 26, wherein the pattern of HAR photodetectors includes four HAR photodetectors that are equidistantly spaced about the light source.

28. The apparatus of claim 20, further comprising:

a housing having a back face that includes one or more thin, transparent window regions, wherein;

each HAR photodetector is positioned such that the total photosensitive area of that HAR photodetector is overlapped by a corresponding one of the transparent window regions, and

the housing is configured such that the back face is adjacent to the skin of a person wearing the apparatus when the apparatus is worn by that person.

29. The apparatus of claim 28, wherein:

the back face includes a thin window, and

the window regions are sub-regions of the window that are defined by the total photosensitive areas of the one or more HAR photodetectors.

30. The apparatus of claim 28, wherein:

the total photosensitive area of each HAR photodetector is offset from the corresponding transparent window region by a corresponding gap in a direction normal to the total photosensitive area of that HAR photodetector, and

the gap is free of optical light guides.