Circuits and methods for selecting a mode of operation of a photoplethysmographic sensor

• US 9,730,644 B1
• Filed: 07/29/2016
• Issued: 08/15/2017
• Est. Priority Date: 07/29/2016
• Status: Active Grant

• Current Assignee: Fitbit, Inc. (Alphabet Inc.)
• Original Assignee: Fitbit, Inc. (Alphabet Inc.)
• Inventors: Wu, Anjian, Richards, Peter W., Yuen, Shelten Gee Jao
• Primary Examiner(s): Winakur, Eric
• Assistant Examiner(s): Liu, Chu Chuan (J J)
• Application Number:
  US15/223,678
• Time in Patent Office: 382 Days
• Field of Search: 600310-344, 600473, 600476, 356 41
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• 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 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• 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 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

Processing a photoplethysmographic (“PPG”) signal in a monitoring device that monitors a property of blood flow. A switching component is operated to select between at least a first light source when the mode selection signal specifies the first mode of operation and a second light source when a mode selection signal specifies the second mode of operation. A selected one of the first light source and the second light source, as selected by the switching component, is then operated. A first digital signal representing a detected light signal from the selected light source is obtained, and a second digital signal is generated from the first digital signal based at least in part on the selected mode of operation. The second digital signal is provided to a processor for use by the processor in measuring a property of blood flow.

Claims

1. A method for processing a detected light signal, comprising a photoplethysmographic (PPG) signal, in a monitoring device to measure properties of blood flow, the method comprising:

receiving a mode selection signal that specifies between at least a first mode of operation of the monitoring device and a second mode of operation of the monitoring device;

operating a switching component to select between at least a first light source when the mode selection signal specifies the first mode of operation and a second light source when the mode selection signal specifies the second mode of operation;

operating a selected one of the first light source and the second light source, as selected by the switching component, to generate a source light signal;

obtaining a first digital signal representing a detected light signal from the selected light source after the source light signal interacts with a skin tissue;

generating a second digital signal from the first digital signal based at least in part on the selected mode of operation;

providing the second digital signal to a processor, the processor measuring a selected one of the properties of blood flow in accordance with the selected mode of operation; and

generating an offset control signal from an estimation of a non-pulsatile component of the first digital signal,

wherein, in the first mode of operation;

(i) the offset control signal is set to zero;

or (ii) one or more components generating the offset control signal are disabled, and

wherein, in the second mode of operation, the second digital signal is generated by subtracting a voltage corresponding to the offset control signal from the detected light signal and applying a gain to the subtracted signal.

2. The method of claim 1, wherein the first mode of operation is a mode to measure a heart rate.

3. The method of claim 1, wherein the second mode of operation is a mode to measure a blood oxygenation level.

4. The method of claim 2, wherein the first light source is a light emitter operating in a green wavelength region.

5. The method of claim 3, wherein the second light source includes at least a first light emitter operating in a red wavelength region and at least a second light emitter operating in an infrared wavelength region.

6. The method of claim 1, the method further comprising:

generating, in the second mode of operation, a reconstructed signal calculated from the gain and one or more of;

(i) the first digital signal, and

(ii) the second digital signal and the offset control signal.

7. The method of claim 1, wherein generating the offset control signal includes:

selecting a value for the offset control signal such that the first digital signal adjusted by the gain and the offset control signal does not exceed a range threshold.

8. The method of claim 1, wherein generating the offset control signal includes:

selecting an initial value for the offset control signal;

determining that the first digital signal adjusted by the gain and the initial value of the offset control signal does exceed a range threshold;

selecting a subsequent value for the offset control signal; and

determining that the first digital signal adjusted by the gain and the subsequent value of the offset control signal does not exceed the range threshold.

9. The method of claim 6, further comprising:

constructing a digital representation over time of the detected light signal based on a series of reconstructed output signals.

10. The method of claim 9, wherein constructing the digital representation over time includes:

identifying, at a point in time, a value of the second digital signal and a value of the offset control signal; and

generating a digital representation of the detected light signal at the point in time using the value of the second digital signal, the value of the offset control signal and the gain.

11. The method of claim 1, wherein the method further comprises:

operating a detector switching component to switch between a plurality of photodetectors.

12. A monitoring device for processing a detected light signal comprising a photoplethysmographic signal to measure properties of blood flow, the device comprising:

an interface to receive a mode selection instruction that specifies between at least a first mode of operation of the monitoring device and a second mode of operation of the monitoring device;

a switching component, responsive to the mode selection instruction, to generate a source light signal by enabling operation of at least a first light source when the mode selection instruction specifies the first mode of operation and at least a second light source when the mode selection instruction specifies the second mode of operation;

a light detection component, operated to obtain a first digital signal representing a detected light signal from the selected light source after a light signal of the selected light source interacts with a skin tissue;

a control circuit operated to generate a second digital signal from the first digital signal based at least in part on the mode selection instruction; and

one or more processors and a non-transitory, computer readable medium storing instructions, which are executed to;

cause the one or more processors to process the second digital signal to measure a selected one of the properties of blood flow in accordance with the selected mode of operation,

generate an offset control signal from an estimation of a non-pulsatile component of the first digital signal,

wherein, in the first mode of operation;

(i) the offset control signal is set to zero;

or (ii) one or more components generating the offset control signal are disabled, and

wherein, in the second mode of operation, the second digital signal is generated by subtracting a voltage corresponding to the offset control signal from the detected light signal and applying a gain to the subtracted signal.

13. The monitoring device of claim 12, wherein the first mode of operation is a mode to measure a heart rate.

14. The monitoring device of claim 12, wherein the second mode of operation is a mode to measure a blood oxygenation level.

15. The monitoring device of claim 13, wherein the first light source is a light emitter operating in a green wavelength region.

16. The monitoring device of claim 14, wherein the second light source includes at least a first light emitter operating in a red wavelength region and at least a second light emitter operating in an infrared wavelength region.

17. The monitoring device of claim 12, further comprising non-transitory computer readable instructions which, when executed, cause the one or more processors to:

generate, in the second mode of operation, a reconstructed signal calculated from the gain and one or more of;

(i) the first digital signal, and

(ii) the second digital signal and the offset control signal.

18. The monitoring device of claim 12, wherein generating the offset control signal includes non-transitory computer readable instructions which, when executed, cause the one or more processors to:

select a value for the offset control signal such that the first digital signal adjusted by the gain and the offset control signal does not exceed a range threshold.

19. The monitoring device of claim 12, wherein the instructions to generate the offset control signal further includes non-transitory computer readable instructions which, when executed, cause the one or more processors to:

select an initial value for the offset control signal;

determine that the first digital signal adjusted by the gain and the initial value of the offset control signal does exceed a range threshold;

select a subsequent value for the offset control signal; and

determine that the first digital signal adjusted by the gain and the subsequent value of the offset control signal does not exceed the range threshold.

20. The monitoring device of claim 17, further comprising non-transitory computer readable instructions which, when executed, cause the one or more processors to:

construct a digital representation over time of the detected light signal based on a series of reconstructed output signals.

21. The monitoring device of claim 20, wherein constructing the digital representation over time includes:

identify, at a point in time, a value of the second digital signal and a value of the offset control signal; and

generate a digital representation of the detected light signal at the point in time using the value of the second digital signal, the value of the offset control signal and the gain.

22. A non-transitory computer-readable medium storing executable instructions for processing a detected light signal comprising a photoplethysmographic signal in a monitoring device to measure properties of blood flow, the instructions, when executed, cause one or more processors to:

receive a signal selecting a mode of operation of the monitoring device;

operate a switching component to select a first light source in a first mode of operation and a second light source in a second mode of operation

operate a selected one of the first light source and the second light source to generate a source light signal;

obtain a first digital signal representing a detected light signal from the selected light source after the source light signal interacts with a skin tissue;

generate a second digital signal based at least in part on the selected mode of operation;

provide the second digital signal to a processor, the processor measuring a selected one of the properties of blood flow in accordance with the selected mode of operation; and

generating an offset control signal from an estimation of a non-pulsatile component of the first digital signal,

wherein, in the first mode of operation;

(i) the offset control signal is set to zero;

or (ii) one or more components generating the offset control signal are disabled, and

wherein, in the second mode of operation, the second digital signal is generated by subtracting a voltage corresponding to the offset control signal from the detected light signal and applying a gain to the subtracted signal.

23. The non-transitory computer-readable medium of claim 22, wherein a first mode of operation is a mode to measure a heart rate.

24. The non-transitory computer-readable medium of claim 22, wherein a first mode of operation is a mode to measure a blood oxygenation level.