OLED display with aging compensation

1. An OLED display, comprising:

a) a plurality of light emitting elements divided into two or more groups, the light emitting elements having an output that changes with time or use;

b) a current measuring device for measuring the total current used by the display in response to a given input signal to produce a current signal; and

c) a controller for simultaneously activating all of the light emitting elements in a group by applying the given input signal, and responsive to the current signal for calculating a correction signal for the light emitting elements in the group and applying the correction signal to input image signals to produce corrected input image signals that compensate for the changes in the output of the light emitting elements of the group.

2. The OLED display claimed in claim 1 , wherein the output of the light emitting elements change with temperature, and further comprising a temperature sensor and wherein the controller is also responsive to the temperature to calculate the correction signal.

3. The OLED display claimed in claim 1 , wherein the display is a color display including an array of pixels, each pixel comprising a plurality of differently colored light emitting elements, and wherein the groups of light emitting elements are defined by the colors of light emitting elements.

4. The OLED display claimed in claim 1 , wherein the groups of light emitting elements are defined by their location on the display.

5. The OLED display claimed in claim 1 , wherein the groups of light emitting elements are defined by individual light emitting elements.

6. The OLED display claimed in claim 1 , wherein the controller sequentially activates the groups of light emitting elements and compensates for the changes in each group.

7. The OLED display claimed in claim 1 , wherein the controller activates the light emitting elements in a group at a plurality of different input image signal levels to calculate the correction signal.

8. A method of driving an OLED display having a plurality of light emitting elements having outputs that change with time or use, comprising the steps of:

a) dividing the light emitting elements into two or more groups;

b) measuring the total current used by a group of light emitting elements in response to a given input signal; and

c) calculating a correction signal based on the measured total current for the light emitting elements in the group and applying the correction signal to input image signals to produce corrected input image signals that compensate for the changes in the output of the light emitting elements of the group.

9. The method claimed in claim 8 , wherein the output of the light emitting elements changes with temperature and further comprising sensing the temperature of the display and using the temperature in calculating the correction signal.

10. The method claimed in claim 8 , wherein the display is a color display including an array of pixels, each pixel comprising a plurality of differently colored light emitting elements, and wherein the groups of light emitting elements are defined by the colors of light emitting elements.

11. The method claimed in claim 8 , wherein the groups of light emitting elements are defined by their location on the display.

12. The method claimed in claim 8 , wherein the groups of light emitting elements are defined by individual light emitting elements.

13. The method claimed in claim 8 , further comprising the steps of sequentially measuring the total current used by the groups of light emitting elements and calculating a correction signal for each group.

14. The method claimed in claim 8 , wherein the total current used by the group is measured at a plurality of different input image signal levels to calculate the correction signal.

15. The method claimed in claim 8 , wherein the method is performed at power-up.

16. The method claimed in claim 8 , wherein the method is performed at power-down.

17. The method claimed in claim 8 , wherein the method is performed periodically while the display is in use.

18. The method claimed in claim 8 , wherein the method is performed in response to a user signal.

19. The method claimed in claim 8 , wherein the correction signal is calculated as a function of the measured total current and a previously calculated correction signal.

20. The method claimed in claim 8 , wherein the correction signal is restricted to be monotonically increasing.

21. The method claimed in claim 8 , wherein a change in a calculated correction signal from a previously calculated correction signal is limited to a pre-determined maximum change.

22. The method claimed in claim 8 , wherein the correction signal is calculated to maintain a constant average luminance output for the display over its lifetime.

23. The method claimed in claim 8 , wherein the correction signal is calculated to maintain a decreasing level of luminance over the lifetime of the display, but at a rate slower than that of an uncorrected display.

24. The method claimed in claim 8 , wherein the correction signal is calculated to maintain a constant white point.

25. The method claimed in claim 8 , further comprising the step of providing an end-of-life signal when the calculated correction signal exceeds a predetermined level.

26. The method claimed in claim 8 , wherein an average correction signal is calculated as the average of a number of correction signal calculations taken over time.

27. The method claimed in claim 26 , wherein the average correction signal is applied to the input image signal after the number of correction signal calculations are taken.