Low power optical measurements

1. A method of adjusting a power output level of a light source on a wearable device, comprising:

measuring, at a photodetector on the wearable device, a first photoplethysmography (PPG) signal derived from an ambient light source that is powered externally to the wearable device;

identifying one or more features of a morphology of the first PPG signal derived from the ambient light source based at least in part on measuring the first PPG signal, wherein the one or more features of the morphology comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof;

calculating, by the wearable device, a quality metric of the first PPG signal based at least in part on the one or more features of the morphology of the first PPG signal; and

adjusting, by the wearable device, the power output level of the light source powered by the wearable device based at least in part on the quality metric of the first PPG signal.

2. The method of claim 1 , further comprising:

measuring, at the photodetector on the wearable device, a second PPG signal derived from the light source powered by the wearable device; and

comparing, by the wearable device, the morphology of the first PPG signal and a morphology of the second PPG signal based at least in part on measuring the first PPG signal, wherein calculating the quality metric is based at least in part on comparing the morphology of the first PPG signal and the morphology of the second PPG signal, the morphology of the second PPG signal comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof.

3. The method of claim 1 , wherein calculating the quality metric further comprises:

calculating the pulse amplitude of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the pulse amplitude of the first PPG signal.

4. The method of claim 1 , wherein calculating the quality metric further comprises:

calculating the signal to noise ratio of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the signal to noise ratio of the first PPG signal.

5. The method of claim 1 , wherein calculating the quality metric further comprises:

calculating the systolic gradient of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the systolic gradient of the first PPG signal.

6. The method of claim 1 , further comprising:

determining that the quality metric of the first PPG signal satisfies a threshold based at least in part on calculating the quality metric; and

deactivating an ambient light cancellation technique based at least in part on determining that the quality metric satisfies the threshold.

7. The method of claim 6 , further comprising:

deactivating the light source powered by the wearable device based at least in part on determining that the quality metric satisfies the threshold, wherein adjusting the power output level is based at least in part on deactivating the light source powered by the wearable device.

8. The method of claim 1 , further comprising:

determining that the quality metric associated with the first PPG signal fails to satisfy a threshold based at least in part on calculating the quality metric; and

activating an ambient light cancellation technique based at least in part on determining that the quality metric fails to satisfy the threshold.

9. The method of claim 1 , further comprising:

determining that the quality metric associated with the first PPG signal fails to satisfy a threshold based at least in part on calculating the quality metric; and

deactivating an ambient light cancellation technique based at least in part on determining that the quality metric fails to satisfy the threshold.

10. The method of claim 9 , further comprising:

identifying movement of a user wearing the wearable device after deactivating the ambient light cancellation technique, wherein measuring the first PPG signal is based at least in part on identifying the movement by the user.

11. The method of claim 1 , wherein the power output level of the light source powered by the wearable device is adjusted to be less than a baseline power output level of the light source powered by the wearable device.

12. An apparatus, comprising:

a processor;

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

measure, at a photodetector on a wearable device, a first photoplethysmography (PPG) signal derived from an ambient light source that is powered externally to the wearable device;

identify one or more features of a morphology of the first PPG signal derived from the ambient light source based at least in part on measuring the first PPG signal, wherein the one or more features of the morphology comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof;

calculate, by the wearable device, a quality metric of the first PPG signal based at least in part on the one or more features of the morphology of the first PPG signal; and

adjust, by the wearable device, a power output level of a light source powered by the wearable device based at least in part on the quality metric of the first PPG signal.

13. The apparatus of claim 12 , wherein the instructions are further executable by the processor to cause the apparatus to:

measure, at the photodetector on a wearable device, a second PPG signal derived from a light source powered by the wearable device; and

compare, by the wearable device, the morphology of the first PPG signal and a morphology of the second PPG signal based at least in part on measuring the first PPG signal, wherein calculating the quality metric is based at least in part on comparing the morphology of the first PPG signal and the morphology of the second PPG signal, the morphology of the second PPG signal comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof.

14. The apparatus of claim 12 , wherein the instructions to calculate the quality metric are further executable by the processor to cause the apparatus to:

calculate the pulse amplitude of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the pulse amplitude of the first PPG signal.

15. The apparatus of claim 12 , wherein the instructions to calculate the quality metric are further executable by the processor to cause the apparatus to:

calculate the signal to noise ratio of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the signal to noise ratio of the first PPG signal.

16. The apparatus of claim 12 , wherein the instructions to calculate the quality metric are further executable by the processor to cause the apparatus to:

calculate the systolic gradient of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the systolic gradient of the first PPG signal.

17. A non-transitory computer-readable medium storing code, the code comprising instructions executable by a processor to:

measure, at a photodetector on a wearable device, a first photoplethysmography (PPG) signal derived from an ambient light source that is powered externally to the wearable device;

identify one or more features of a morphology of the first PPG signal derived from the ambient light source based at least in part on measuring the first PPG signal, wherein the one or more features of the morphology comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof;

calculate, by the wearable device, a quality metric of the first PPG signal based at least in part on the one or more features of the morphology of the first PPG signal; and

adjust, by the wearable device, a power output level of the light source powered by the wearable device based at least in part on the quality metric of the first PPG signal.

18. The non-transitory computer-readable medium of claim 17 , wherein the instructions are further executable by the processor to:

measure, at the photodetector on the wearable device, a second PPG signal derived from a light source powered by the wearable device; and

compare, by the wearable device, the morphology of the first PPG signal and a morphology of the second PPG signal based at least in part on measuring the first PPG signal, wherein calculating the quality metric is based at least in part on comparing the morphology of the first PPG signal and the morphology of the second PPG signal, the morphology of the second PPG signal comprises a pulse amplitude, a systolic gradient, a signal to noise ratio, or a combination thereof.

19. The non-transitory computer-readable medium of claim 17 , wherein the instructions to calculate the quality metric are further executable by the processor to:

calculate the pulse amplitude of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the pulse amplitude of the first PPG signal.

20. The non-transitory computer-readable medium of claim 17 , wherein the instructions to calculate the quality metric are further executable by the processor to:

calculate the signal to noise ratio of the first PPG signal based at least in part on measuring the first PPG signal, wherein adjusting the power output level is based at least in part on calculating the signal to noise ratio of the first PPG signal.