Variable brightness and gain for optimizing signal acquisition
A physiological monitoring device controls an optical signal acquisition system within a number of discrete operating states, each providing values for controllable parameters such as illumination intensity for a light source and the gain for an optical detector. Using this technique, a small number of operating states may be defined, such as operating states that are known to work well within expected use scenarios. This approach advantageously facilitates optimal or near optimal operation across a range of most likely use cases while avoiding complex or continuous optimization problems. The list of operating states may further be prioritized so that a best operating state can be selected based on, e.g., signal quality or environmental conditions.
1. A method for operating a physiological monitoring device that uses an optical signal to determine a physiological signal, the method comprising:
providing a plurality of predetermined optical measurement states, each one of the plurality of predetermined optical measurement states characterized by at least a first discrete value for electronically controlling a brightness of a light source of the physiological monitoring device and a second discrete value for electronically controlling a gain of a light sensor of the physiological monitoring device, wherein the plurality of predetermined optical measurement states are ordered into a prioritized list according to preferred measurement states;
operating the light source according to the first discrete value for a current one of the predetermined optical measurement states;
operating the light sensor according to the second discrete value for the current one of the predetermined optical measurement states;
evaluating the physiological signal based on data from the light sensor; and
adjusting the predetermined optical measurement state in response to a detected condition.
2. The method of claim 1 wherein the prioritized list is ordered for monotonically increasing magnitudes of the first discrete value as a priority within the prioritized list increases to a more preferred measurement state.
3. The method of claim 1 wherein the prioritized list is ordered for monotonically increasing magnitudes of the second discrete value as a priority within the prioritized list increases to a more preferred measurement state.
4. The method of claim 1 wherein the light source includes one or more light emitting diodes.
5. The method of claim 1 wherein the detected condition includes a saturation of the light sensor, and wherein adjusting the predetermined optical measurement state includes decrementing to a lower priority state in response to the detected condition.
6. The method of claim 1 wherein the detected condition includes a decrease in a quality of the physiological signal, and wherein adjusting the predetermined optical measurement state includes incrementing to a higher priority state in response to the detected condition.
7. The method of claim 1 wherein the detected condition includes a removal and replacement of the physiological monitoring device on a user, and wherein adjusting the predetermined optical measurement state includes changing to a highest priority state in response to the detected condition.
8. The method of claim 1 wherein the detected condition includes an increase in ambient light, and wherein adjusting the predetermined optical measurement state includes incrementing to a higher priority state in response to the detected condition.
9. The method of claim 1 wherein the physiological monitoring device includes a wearable physiological monitoring device.
10. The method of claim 1 wherein the physiological monitoring device includes a photoplethysmography system for measuring a heart rate of a user.
11. A computer program product for operating a physiological monitoring device that uses an optical signal to determine a physiological signal, the computer program product comprising computer executable code embodied in a non-transitory compute readable medium that, when executing on the physiological monitoring device, performs the steps of:
storing a plurality of predetermined optical measurement states, each one of the plurality of predetermined optical measurement states characterized by at least a first discrete value for electronically controlling a brightness of a light source of the physiological monitoring device and a second discrete value for electronically controlling a gain of a light sensor of the physiological monitoring device, wherein the plurality of predetermined optical measurement states are ordered into a prioritized list according to preferred measurement states;
operating the light source according to the first discrete value for a current one of the predetermined optical measurement states;
operating the light sensor according to the second discrete value for the current one of the predetermined optical measurement states;
evaluating the physiological signal based on data from the light sensor; and
adjusting the predetermined optical measurement state in response to a detected condition.
12. The computer program product of claim 11 wherein the prioritized list is ordered for monotonically increasing magnitudes of the first discrete value as a priority within the prioritized list increases to a more preferred measurement state.
13. The computer program product of claim 11 wherein the prioritized list is ordered for monotonically increasing magnitudes of the second discrete value as a priority within the prioritized list increases to a more preferred measurement state.
14. The computer program product of claim 11 wherein the light source includes one or more light emitting diodes.
15. The computer program product of claim 11 wherein the detected condition includes a saturation of the light sensor, and wherein adjusting the predetermined optical measurement state includes decrementing to a lower priority state in response to the detected condition.
16. The computer program product of claim 11 wherein the detected condition includes a decrease in a quality of the physiological signal, and wherein adjusting the predetermined optical measurement state includes incrementing to a higher priority state in response to the detected condition.
17. The computer program product of claim 11 wherein the detected condition includes a removal and replacement of the physiological monitoring device on a user, and wherein adjusting the predetermined optical measurement state includes changing to a highest priority state in response to the detected condition.
18. The computer program product of claim 11 wherein the detected condition includes an increase in ambient light, and wherein adjusting the predetermined optical measurement state includes incrementing to a higher priority state in response to the detected condition.
19. The computer program product of claim 11 wherein the physiological monitoring device includes a wearable physiological monitoring device.
20. A wearable physiological monitoring system comprising:
a housing configured to be worn on a limb of a user;
a light source within the housing, the light source including one or more light emitting diodes;
a light sensor within the housing, the light sensor positioned to receive an optical signal from the light source through the limb of the user when placed for use;
a memory storing a plurality of predetermined optical measurement states, each one of the plurality of predetermined optical measurement states characterized by at least a first discrete value for electronically controlling a brightness of the light source and a second discrete value for electronically controlling a gain of the light, wherein the plurality of predetermined optical measurement states are ordered into a prioritized list according to preferred measurement states; and
a processor within the housing and coupled in a communicating relationship with the light source, the light sensor and the memory, the processor configured by executable code stored in the memory to perform the steps of operating the light source according to the first discrete value for a current one of the predetermined optical measurement states, operating the light sensor according to the second discrete value for the current one of the predetermined optical measurement states, evaluating a physiological signal based on data from the light sensor, and adjusting the predetermined optical measurement state in response to a detected condition.