Electroluminescent device aging compensation with reference subpixels

1. An electroluminescent (EL) device, comprising:

an illumination area comprising one or more primary EL emitters;

a reference area comprising a reference EL emitter;

a reference driver circuit configured to cause the reference EL emitter to emit light while the EL device is active;

a sensor configured to detect light emitted by the reference EL emitter;

a measurement unit configured to detect an aging-related electrical parameter of the reference EL emitter while the reference EL emitter is emitting light; and

a controller configured to:

receive an input signal for each primary EL emitter in the illumination area,

form a corrected input signal from each input signal using the detected light and the aging-related electrical parameter, and

apply the corrected input signals to the respective primary EL emitters in the illumination area,

wherein the reference driver circuit is further configured to cause the reference EL emitter to emit light at two levels, a measurement level and a fade level, at different times, and

wherein the measurement unit is further configured to take measurements of the reference EL emitter while the reference EL emitter emits light at the measurement level.

2. The EL device of claim 1 , wherein the controller is further configured to form corrected input signals which compensate for loss of efficiency of the respective primary EL emitters.

3. The EL device of claim 1 , wherein the sensor comprises:

a colorimeter, a spectrophotometer, or a spectroradiometer, for providing color data to the controller,

wherein the controller is further configured to form corrected input signals which compensate for chromaticity shift of the respective primary EL emitters due to aging.

4. The EL device of claim 1 , wherein the reference area further comprises:

a plurality of reference EL emitters;

a plurality of corresponding reference driver circuits configured to cause the respective reference EL emitters to emit light;

a plurality of corresponding sensors configured to detect light emitted by the respective reference EL emitters; and

a plurality of corresponding measurement units configured to detect respective aging-related electrical parameters of the respective reference EL emitters while the respective reference EL emitters are emitting light,

wherein the controller is further configured to use one or more of the plurality of detected light and aging-related electrical parameters to form a corrected input signal from each input signal.

5. The EL device of claim 1 , further comprising:

a temperature measurement unit configured to measure a temperature parameter related to the temperature of the reference EL emitter while the reference EL emitter is emitting light,

wherein the controller is further configured to use the measured temperature parameter to form the corrected input signals.

6. The EL device of claim 1 , wherein the fade level is greater than the measurement level.

7. The EL device of claim 1 , wherein:

each input signal controls a respective emission level of the corresponding primary EL emitter; and

the fade level is greater than the maximum of the respective emission levels.

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

a memory configured to store detected light measurements and corresponding aging-related electrical parameter measurements,

wherein the controller is further configured to use the values stored in the memory to form the corrected input signals.

9. The EL device of claim 1 , wherein:

the reference driver circuit is further configured to case the reference EL emitter to emit light successively at a plurality of measurement levels; and

respective measurements of the reference EL emitter are taken while it emits light at each measurement level.

10. The EL device of claim 1 , wherein the reference EL emitter and all primary EL emitters comprise a same size and composition.

11. The EL device of claim 1 , wherein the reference driver circuit is further configured to provide a test current to the reference EL emitter to cause the reference EL emitter to emit light.

12. The EL device of claim 1 , further comprising:

a timer configured to run while the EL device is active,

wherein the measurement unit is further configured to take measurements of the reference EL emitter at intervals determined by the timer.

13. The EL device of claim 1 , wherein a measurement of the reference EL emitter is taken while the EL device is in thermal equilibrium.

14. The EL device of claim 1 , wherein the measurement unit is further configured to take a measurement of the reference EL emitter while the EL device is active.

15. The EL device of claim 1 , further including a second reference area comprising a second reference EL emitter.

16. The EL device of claim 1 , wherein the EL device comprises an EL display.

17. The EL device of claim 1 , wherein the aging-related electrical parameter comprises a voltage or a current.

18. The EL device of claim 1 , wherein each primary EL emitter and reference EL emitter comprises an organic light-emitting diode emitter.