Self-calibrating optical transceiver system with reduced crosstalk sensitivity for through-display proximity sensing

1. An electronic device comprising:

an optical transceiver system for detecting proximity of an object external to the electronic device, the optical transceiver system comprising:

a light emitter configured to emit light toward the object;

a first photosensor configured to receive light emitted from the light emitter;

a second photosensor optically isolated from the first photosensor and the light emitter and configured to receive light emitted from the light emitter and reflected from the object;

a first temperature sensor thermally coupled to the light emitter;

a second temperature sensor thermally coupled to the second photosensor; and

a processor configured to:

apply a first field calibration by adjusting power output from the light emitter based on an output from the first photosensor;

apply a second field calibration by adjusting power output of the second photosensor based on at least one sensor output of the first temperature sensor or the second temperature sensor; and

apply a third field calibration of the optical transceiver system by filtering output of the second photosensor with a high-pass filter.

2. The electronic device of claim 1 , comprising:

a housing defining an interior cavity; and

a display within the interior cavity; wherein

the optical transceiver system is positioned within the interior cavity adjacent to the display.

3. The electronic device of claim 2 , wherein:

the display defines an active display area;

the optical transceiver system is positioned below the active display area; and

the light emitter is configured to emit light through the active display area.

4. The electronic device of claim 1 , wherein the optical transceiver system comprises:

a module enclosure defining:

a first barrel enclosing the light emitter and the first photosensor; and

a second barrel enclosing the second photosensor and optically isolated from the first barrel.

5. The electronic device of claim 4 , wherein the processor is enclosed, at least partially, by the module enclosure.

6. The electronic device of claim 4 , wherein:

the first barrel encloses the first temperature sensor; and

the second barrel encloses the second temperature sensor.

7. The electronic device of claim 6 , wherein:

the first barrel is capped by a first lens; and

the second barrel is capped by a second lens.

8. The electronic device of claim 1 , further comprising:

a digital-to-analog converter configured to convert a first digital value into a first analog signal driving the light emitter; and

an analog-to-digital converter configured to convert a second analog signal output from the second photosensor into a second digital value.

9. The electronic device of claim 8 , wherein:

the first field calibration comprises a first digital adjustment to the first digital value;

the second field calibration comprises a second digital adjustment to the second digital value; and

the third field calibration comprises a third digital adjustment to the second digital value.

10. The electronic device of claim 9 , wherein the processor is configured to:

access a first lookup table to determine the first digital adjustment;

access a second lookup table to determine the second digital adjustment; and

access a third lookup table to determine the third digital adjustment.

11. The electronic device of claim 10 , wherein:

the optical transceiver system comprises an application-specific integrated circuit comprising:

the processor; and

a memory operably coupled to the processor; and

the first lookup table, the second lookup table, and the third lookup table are stored in the memory of the application-specific integrated circuit.

12. The electronic device of claim 1 , wherein the processor is configured to:

apply the first field calibration by adjusting real-time power output from the light emitter based on power output from the first photosensor; and

apply the second field calibration by adjusting real-time power output of the second photosensor based on sensor output of the first temperature sensor and the second temperature sensor.

13. The electronic device of claim 1 , wherein:

the light emitter comprises a laser;

the first photosensor comprises a first photodiode; and

the second photosensor comprises a second photodiode.

14. The electronic device of claim 1 , wherein the processor is configured to apply the first field calibration by adjusting power output from the light emitter based on a wavelength of light detected by the first photosensor.

15. An optical proximity sensor system for determining proximity of an object to an external surface of a portable electronic device, the optical proximity sensor system comprising:

an enclosure defining a transmitter-side barrel and a receiver-side barrel;

a transmitter module within the transmitter-side barrel and configured to receive a first digital value, the transmitter module comprising:

a digital-to-analog converter configured to receive the first digital value and to output a current in proportion to the first digital value;

a light-emitting element configured to receive the current and, in response, to emit light out of the transmitter-side barrel;

a photodetector module configured to receive light emitted from the light-emitting element and, in response, output a second digital value used to bias the first digital value to control:

power output from the light-emitting element;

wavelength output from the light-emitting element; or

bandwidth output from the light-emitting element; and

a temperature sensor thermally coupled to the light-emitting element and configured to output a temperature value used to bias the first digital value to control:

power output from the light-emitting element;

wavelength output from the light-emitting element; or

bandwidth output from the light-emitting element; and

a receiver module within the receiver-side barrel and configured to receive light reflected from the object and, in response, output a third digital value corresponding to proximity of the object to the external surface.

16. The optical proximity sensor system of claim 15 , wherein:

the temperature sensor is a first temperature sensor;

the temperature value is a first temperature value; and

the receiver module comprises:

a photosensor configured to receive light reflected from the object;

an analog-to-digital converter operably coupled to the photosensor and configured to output the third digital value; and

a second temperature sensor thermally coupled to the photosensor and configured to output a second temperature value used to bias the third digital value.

17. The optical proximity sensor system of claim 15 , wherein the receiver module comprises a high-pass filter applied to the third digital value.

18. The optical proximity sensor system of claim 15 , wherein the temperature value is used to bias the first digital value by an amount selected from a lookup table.

19. A method of operating an optical proximity sensor system for a portable electronic device, the method comprising:

driving a light-emitting element with a current defined by a digital drive current value;

sampling a first temperature sensor thermally coupled to the light-emitting element to obtain a first temperature value;

biasing the digital drive current value based on the first temperature value;

sampling a first light sensor optically coupled to the light-emitting element to obtain a first light value;

biasing the digital drive current value based on the first light value;

sampling a second light sensor optically isolated from the light-emitting element to obtain a second light value;

sampling a second temperature sensor thermally coupled to the second light sensor to obtain a second temperature value;

biasing the second light value based on the second temperature value; and

providing, as output, the biased second light value.

20. The method of claim 19 , further comprising:

querying a first lookup table with the first temperature value to obtain a first thermal calibration value;

biasing the digital drive current value based on the first thermal calibration value;

querying a second lookup table with the first light value to obtain a first light calibration value;

biasing the digital drive current value based on the first light calibration value;

querying a third lookup table with the second light value to obtain a second light calibration value;

one, or both, of:

biasing the digital drive current value based on the second light calibration value; or

biasing the second light value based on the second light calibration value;

querying a third lookup table with the second temperature value to obtain a second thermal calibration value; and

biasing the second light value based on the second light calibration value.