Heart rate sensor with high-aspect-ratio photodetector element

• US 9,392,946 B1
• Filed: 05/28/2015
• Issued: 07/19/2016
• 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): Peng, Bo J
• Application Number:
  US14/724,750
• Time in Patent Office: 418 Days
• US Class Current: 1/1
• 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

Heart rate 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 heart rate sensors incorporating such photodetector elements as compared with heart rate sensors incorporating, for example, square photodetector elements.

Claims

1. An apparatus comprising:

a light source;

one or more discrete photodetector elements, each photodetector element 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 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,

wherein the ratio of the first length to the first width of each photodetector is substantially between 2;

1 to 5;

1.

2. The apparatus of claim 1, wherein:

the first edge of each photodetector element is perpendicular to an axis radiating out from a center of the light source.

3. The apparatus of claim 1, wherein:

the first edge of each photodetector element is transverse to an axis radiating out from a center of the light source.

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.

6. The apparatus of claim 4, wherein:

there are a plurality of photodetector elements arranged in a pattern, and

the plurality of light-emitting devices is collocated at a center point of the pattern of photodetector elements.

7. The apparatus of claim 6, wherein the ratio of the first length to the first width of each photodetector element is substantially between 2:

1 to 3.5;

1.

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

1 to 5;

1.

9. The apparatus of claim 1, wherein each photodetector element:

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 2;

1 to 5;

1, and

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

10. The apparatus of claim 9, wherein the pattern of photodetector elements 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 photodetector element is positioned such that that photodetector element 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 photodetector elements.

13. The apparatus of claim 11, wherein:

each photodetector element is offset from the corresponding transparent window region by a corresponding gap in a direction normal to the photodetector element, and

the gap is free of optical light guides.

14. The apparatus of claim 1, wherein each photodetector element has, in addition to the first edge, an arcuate second edge opposite the first edge, wherein 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;

a second light source;

a photodetector element interposed between the first light source and the second light source; and

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

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

obtain measured light intensity measurements from the photodetector element, and

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

wherein;

the photodetector element 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 2;

1 to 5;

1.

16. The apparatus of claim 15, wherein:

the 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.

17. The apparatus of claim 15, wherein:

the 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.

18. The apparatus of claim 15, further comprising

a housing having a back face that includes a transparent window region that overlaps the photodetector element 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 photodetector element is equidistant from the first light source and the second light source.

20. An apparatus comprising:

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, the control logic communicatively connected with the light source and each photodetector and 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 substantially between 2;

1 to 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 includes at least two light-emitting devices that predominantly emit light of different wavelengths.

22. The apparatus of claim 20, wherein:

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

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

23. The apparatus of claim 20, wherein the ratio of the first dimension to the second dimension of each photodetector is substantially between 2:

1 to 3.5;

1.

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

1 to 5;

1.

25. The apparatus of claim 20, wherein:

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

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

1 to 5;

1, and

each photodetector is positioned such that an edge of the photosensitive area for that 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 photodetectors includes four 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 photodetector is positioned such that the photosensitive area of that 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 photosensitive areas of the one or more photodetectors.

30. The apparatus of claim 28, wherein:

the photosensitive area 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 optical light guides.