OLED display with aging compensation

• US 20070103411A1
• Filed: 11/07/2005
• Published: 05/10/2007
• Est. Priority Date: 11/07/2005
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald, Leon, Felipe
• Granted Patent: US 8,207,914 B2
• Time in Patent Office: Days
• US Class Current: 345/82
• CPC Class Codes: G09G 2320/0285 using tables for spatial correction of display data
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0693 Calibration of display systems
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3225 using an active matrix

Abstract

A method of compensating image signals for driving an OLED display having a plurality of light-emitting elements having outputs that change with time or use, comprising the steps of: a) obtaining a measured or estimated first value of the current used by individual light-emitting elements in response to known image signals at a first time; b) specifying multiple groups of light-emitting elements at a second time, wherein at least one of the specified groups contains at least one light-emitting element common to another specified group; c) measuring total currents used by each of the specified groups in response to known image signals at a second time; d) forming an estimated second value of the current used by individual light-emitting elements based on the measured total currents, e) calculating correction values for individual light-emitting elements based on the difference between the first and second current values, and f) employing the correction values to compensate image signals for the changes in the output of the light-emitting elements and produce compensated image signals.

Claims

1. A method of compensating image signals for driving an OLED display having a plurality of light-emitting elements having outputs that change with time or use, comprising the steps of:

a) obtaining a measured or estimated first value of the current used by individual light-emitting elements in response to known image signals at a first time;

b) specifying multiple groups of light-emitting elements at a second time, wherein at least one of the specified groups contains at least one light-emitting element common to another specified group;

c) measuring total currents used by each of the specified groups in response to known image signals at a second time;

d) forming an estimated second value of the current used by individual light-emitting elements based on the measured total currents;

e) calculating correction values for individual light-emitting elements based on the difference between the first and second current values; and

f) employing the correction values to compensate image signals for the changes in the output of the light-emitting elements and produce compensated image signals.

2. The method of claim 1, wherein at least two of the specified groups are of different sizes.

3. The method of claim 1, wherein each of the groups overlap with another of the groups.

4. The method of claim 1, wherein the location of one of the groups is contained within another of the groups.

5. The method of claim 1, wherein the correction values are the same for each light-emitting element within at least one of the specified groups.

6. The method of claim 1, wherein the correction values are different for at least two light-emitting elements within at least one of the specified groups.

7. The method of claim 1, wherein the estimated second value of the current used by at least one individual light-emitting element is interpolated from the measured total currents.

8. The method of claim 7, wherein the interpolation is dependent on the location of the at least one light-emitting element within a specified group.

9. The method of claim 1, further comprising the step of iteratively specifying sub-groups within a specified group and measuring the total current used by at least one of the sub-groups.

10. The method of claim 9, further comprising the step of forming an estimate of the current used by individual light-emitting elements in the at least one sub-group based on the measured total current of the sub-group.

11. The method claimed in claim 1, wherein the total currents used by the specified groups are measured in response to a plurality of different known image signals to calculate a plurality of correction values for different image signals.

12. The method claimed in claim 1, wherein total currents used by the specified groups are measured at power-up, power-down, when the device is powered but idle, in response to a user signal, or periodically.

13. The method claimed in claim 1, wherein the method is repeated over time to obtain recalculated correction values, and the correction value for a light-emitting element is restricted to be monotonically increasing, limited to a predetermined maximum change, calculated to maintain a constant average luminance output for the light-emitting element over its lifetime, calculated to maintain a decreasing level of luminance over the lifetime of the light-emitting element but at a rate slower than that of an uncorrected light-emitting element, and/or calculated to maintain a constant white point for the light-emitting element.

14. The method claimed in claim 1, 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 values.

15. The method 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.

16. The method of claim 1, wherein the locations of the groups are defined by the usage of the OLED display.

17. The method of claim 1, wherein one or more of the specified groups comprises a sampled subset of a one- or two-dimensional array of light-emitting elements.

18. The method of claim 1, wherein the measured or estimated first value of the current used by individual light-emitting is obtained by specifying first multiple groups of light-emitting elements at a first time, measuring first total currents used by each of the first groups in response to known image signals at the first time, and forming a first estimated value of the current used by individual light-emitting elements based on the measured first total currents;

and wherein the estimated second value of the current used by individual light-emitting is obtained by specifying second multiple groups of light-emitting elements at the second time, wherein at least one of the specified second groups contains at least one light-emitting element common to another specified second group, measuring second total currents used by each of the second groups in response to known image signals at the second time, and forming the estimated second value of the current used by individual light-emitting elements based on the measured second total currents.

19. An OLED display having, comprising:

a) a plurality of light-emitting elements having outputs that change with time or use;

b) a current measuring device for sensing the total current used by the display to produce current signals; and

c) a controller for specifying multiple groups of light-emitting elements, wherein at least one of the specified groups contains at least one light-emitting element common to another specified group, for activating the specified groups of light-emitting elements in response to known image signals, and responsive to the current signals for calculating correction values for the light-emitting elements in each group, and for applying the correction values to image signals to produce compensated image signals that compensate for the changes in the output of the light-emitting elements of each group with time or use.

20. The OLED display claimed in claim 19, 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 values.