MOTION ARTIFACT CANCELATION

• US 20160296173A1
• Filed: 12/30/2013
• Published: 10/13/2016
• Est. Priority Date: 12/30/2013
• Status: Abandoned Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: CULBERT, Daniel J.
• Application Number:
  US15/038,420
• Publication Number:
  US 20160296173A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/02444 Details of sensor A61B5/02427 takes precedence
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7475 User input or interface means, e.g. keyboard, pointing device, joystick

Abstract

A photoplethysmogram (PPG) signal may be obtained from a pulse oximeter, which employs a light emitter and a light sensor to measure the perfusion of blood to the skin of a user. However, the signal may be compromised by noise due to motion artifacts. That is, movement of the body of a user may cause the skin and vasculature to expand and contract, introducing noise to the signal. To address the presence of motion artifacts, examples of the present disclosure can receive light information from two light sensors situated in a line parallel to the direction of the blood pulse wave. The light information from each sensor may include the same noise signal, and thus subtracting one from the other can result in a heart rate signal where the noise has been canceled out. In some examples, a signal from one of the light sensors may be multiplied by a scaling factor before cancellation to account for response differences in each light sensor.

Claims

1. A method of an electronic device including one or more light emitters and a plurality of light sensors, the method comprising:

emitting light from the one or more light emitters;

receiving first light information from a first light sensor, the first light sensor optically coupled to one of the one or more light emitters;

receiving second light information from a second light sensor, the second light sensor optically coupled to one of the one or more light emitters, wherein the second light information includes time-shifted information; and

computing a heart rate signal wherein noise due to motion artifacts has been canceled by using the first and second light information.

2. The method of claim 1, wherein computing the heart rate signal includes:

scaling the second light information by a scaling factor; and

subtracting the scaled second light information from the first light information.

3. The method of claim 2, further comprising:

computing the scaling factor based on the first and second light information.

4. The method of claim 3, wherein computing the scaling factor is further based on a heart rate signal template.

5. The method of claim 1, wherein the computed heart rate signal is a differential of an actual heart rate signal.

6. The method of claim 1, wherein computing the heart rate signal includes subtracting the second light information from the first light information.

7. The method of claim 1, further comprising multiplying the computed heart rate signal by a scaling factor.

8. The method of claim 1, wherein both the first light information and the second light information contain the same noise due to motion artifacts.

9-16. -16. (canceled)

17. An electronic device, comprising:

a first light emitter configured to emit first light, the first light including first light information;

a second light emitter configured to emit second light, the second light including second light information, the second light information including time-shifted information;

a first light sensor configured to receive a reflection of the first light;

a second light sensor configured to receive a reflection of the second light; and

a processor configured to;

compute a heart rate signal using first and second light information, wherein noise due to motion artifacts has been canceled.

18. The electronic device of claim 17, wherein computing the heart rate signal includes:

scaling the second light information by a scaling factor; and

subtracting the scaled second light information from the first light information.

19. The electronic device of claim 18, the method further comprising:

computing the scaling factor based on the first and second light information.

20. The electronic device of claim 19, wherein computing the scaling factor is further based on a heart rate signal template.

21. The electronic device of claim 17, wherein the computed heart rate signal is a differential of an actual heart rate signal.

22. The electronic device of claim 17, wherein computing the heart rate signal includes subtracting the second light information from the first light information.

23. The electronic device of claim 17, the method further comprising multiplying the computed heart rate signal by a scaling factor.

24. The electronic device of claim 17, wherein both the first light information and the second light information contain the same noise due to motion artifacts.

25. The electronic device of claim 17, wherein the first and second light sensors are situated in a line parallel to a direction of a blood pulse wave included in the user.

26. The electronic device of claim 17, wherein the time-shifted information is based on a distance between the first and second light sensors and a blood pulse wave velocity.

27. The electronic device of claim 17, wherein a distance between the first and second light sensors is such that noise in the first light information is same as noise in the second light information.

28. The electronic device of claim 17, wherein one or more of the first and second light emitters are configured to emit one or more of infrared, green, amber, blue, and red light.