Method and apparatus for uniformity and brightness correction in an amoled display

• US 20080055209A1
• Filed: 08/30/2006
• Published: 03/06/2008
• Est. Priority Date: 08/30/2006
• Status: Abandoned Application

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald S.
• Application Number:
  US11/512,940
• Publication Number:
  US 20080055209A1
• Time in Patent Office: Days
• US Class Current: 345/77
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3225 using an active matrix

Abstract

A method for reducing brightness uniformity variations in an active-matrix OLED display employing amorphous silicon thin-film transistors, by providing an active-matrix OLED display having amorphous silicon thin-film transistors; and deriving a first correction value from a measured or estimated value of light-emitting element performance. Subsequently groups of light-emitting elements are identified, whereupon one or more representative light-emitting elements are selected. Remaining steps include measuring total representative current used by the representative light-emitting elements for each predetermined group of light-emitting element; deriving an estimated second correction value from the first correction value, or the measured or estimated value of light-emitting element performance, and the measured total representative currents for each individual light-emitting elements; and employing the estimated second correction value to correct image signals for the changes in the output of the light-emitting elements and produce compensated image signals.

Claims

1. A method for reducing brightness uniformity variations in an active-matrix OLED display employing amorphous silicon thin-film transistors, comprising the steps of:

a) providing an active-matrix OLED display having amorphous silicon thin-film transistors that drive a plurality of light-emitting elements responsive to an input signal that causes the light-emitting elements to emit light;

b) deriving a first correction value from a measured or estimated value of light-emitting element performance in response to known image signals at a first time;

c) identifying a plurality of predetermined groups of light-emitting elements, the plurality of predetermined light-emitting groups including all of the light-emitting elements in the OLED display, wherein each predetermined group of light-emitting elements includes more than one light-emitting element;

d) selecting one or more representative light-emitting elements for each predetermined group of light-emitting elements;

e) measuring total representative current used by the representative light-emitting elements for each predetermined group of light-emitting element in response to known image signals at a second time;

f) deriving an estimated second correction value from the first correction value, or the measured or estimated value of light-emitting element performance in response to known image signals at the first time, and the measured total representative currents for each individual light-emitting elements; and

g) employing the estimated second correction value to correct 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 the first correction value is derived before the OLED display is sold to a customer and the second correction value is derived after the display is sold to a customer and put into use.

3. The method of claim 1, wherein steps e) through g) are repeatable.

4. The method of claim 1, wherein the estimates for each light-emitting element are calculated by interpolating from the total representative current measurements for each predetermined group.

5. The method of claim 1, wherein a correction value for at least one light-emitting element is estimated by interpolating between correction values for other light-emitting elements.

6. The method of claim 1, wherein a single representative light-emitting element is selected.

7. The method of claim 1, wherein the representative light-emitting elements comprise all of the light-emitting elements in a group.

8. The method of claim 1, wherein the representative light-emitting elements comprise more than one but fewer than all of the light-emitting elements in a group.

9. The method of claim 8, wherein the representative light-emitting elements comprise a regular array of samples within a group.

10. The method of claim 1, wherein the performance or current measurement of the light-emitting elements is done at a plurality of luminance levels.

11. The method of claim 1, wherein the correction values for one or more of the light-emitting elements is calculated by interpolating the measured total representative current values.

12. The method of claim 1, wherein the OLED display luminance is held substantially constant.

13. The method of claim 1, further comprising the steps of re-determining the groups after the first correction value is derived and measuring the total representative current for each of the re-determined groups.

14. The method of claim 1, wherein the OLED display is a color display comprising light-emitting elements of multiple colors and wherein the measurements are done separately for each color of light-emitting element.

15. The method of claim 1, wherein the total representative current for each group is measured for a plurality of different input signal values and a plurality of correction values are estimated for each light-emitting element.

16. The method of claim 1, wherein different sets of representative light-emitting elements are specified for each group and different total representative currents are measured for each group and then combined to form a total representative current measurement.

17. An active-matrix OLED display, comprising:

a) an active-matrix OLED display having amorphous silicon thin-film transistors that drive a plurality of light-emitting elements responsive to an input signal that causes the light-emitting elements to emit light;

the light-emitting elements divided into a plurality of predetermined groups, each group comprising more than one light-emitting element and one or more representative light-emitting elements selected for each group of light-emitting elements; and

b) a controller coupled to the active-matrix OLED display that obtains a first correction value of current used by the light-emitting elements in response to known image signals at a first time; and

also that measures total representative current used by the representative light-emitting elements for each of the predetermined groups in response to known image signals at a second time.

18. The active matrix OLED display as claimed in claim 17, wherein the controller further comprises:

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

means for calculating correction values for individual light-emitting elements based on the difference between the first and second measurements; and

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