METHOD AND APPARATUS FOR UNIFORMITY AND BRIGHTNESS CORRECTION IN AN OLED DISPLAY

• US 20050280615A1
• Filed: 06/16/2004
• Published: 12/22/2005
• Est. Priority Date: 06/16/2004
• Status: Active Grant

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald S., Ford, James H.
• Granted Patent: US 6,989,636 B2
• Time in Patent Office: Days
• US Class Current: 345/77
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• 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 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3216 using a passive matrix
• CPC Class Codes: G09G 3/3225 using an active matrix

Abstract

A method for the correction of brightness and uniformity variations in OLED displays, comprising: a) providing an OLED display having a plurality of light-emitting elements with a common power signal and local control signals; b) providing a digital input signal for displaying information on each light-emitting element, the signal having a first bit depth; c) transforming the digital input signal into a transformed digital signal having a second bit depth greater than the first bit depth; and d) correcting the transformed signal for one or more light-emitting elements of the display by applying a local correction factor to produce a corrected digital signal. In accordance with various embodiments, the present invention may provide the advantages of improved uniformity in a display that reduces the complexity of calculations, maintains a consistent bit-depth for all light-emitting elements, provides a pre-determined output brightness, improves the yields of the manufacturing process, and reduces the electronic circuitry needed to implement the uniformity calculations and transformations.

Claims

1. A method for the correction of brightness and uniformity variations in OLED displays, comprising:

a) providing an OLED display having a plurality of light-emitting elements with a common power signal and local control signals;

b) providing a digital input signal for displaying information on each light-emitting element, the signal having a first bit depth;

c) transforming the digital input signal into a transformed digital signal having a second bit depth greater than the first bit depth; and

d) correcting the transformed signal for one or more light-emitting elements of the display by applying a local correction factor to produce a corrected digital signal.

2. The method of claim 1, further comprising providing a global correction factor for all light-emitting elements and correcting the transformed signal by the global correction factor in combination with the local correction factor to produce the corrected digital signal.

3. The method of claim 2, wherein correction of the transformed signal is performed by integer scaling.

4. The method of claim 2, wherein the global and local corrections are performed with a combined correction factor to produce the corrected digital signal.

5. The method of claim 2, wherein the global and local corrections are performed with in separate steps with separate correction factors to produce the corrected digital signal.

6. The method of claim 2 further comprising the step of calculating the average brightness of the display with a nominal digital input signal and wherein the global correction factor is a multiplication factor equal to the desired brightness of the display at the nominal digital input signal divided by the average brightness of the display at the nominal digital input signal.

7. The method of claim 6 further comprising the step of calculating the local correction factor for a light-emitting element with the nominal digital input signal and wherein the local correction factor is a multiplication factor equal to the desired brightness of the light-emitting element at the nominal digital input signal divided by the brightness of the globally corrected light-emitting element at the nominal digital input signal.

8. The method of claim 1 further comprising the step of calculating the local correction factor for a light-emitting element with a nominal digital input signal and wherein the local correction factor is a multiplication factor equal to the desired brightness of the display at the nominal digital input signal divided by the brightness of the light-emitting element at the nominal digital input signal.

9. The method of claim 1 wherein the transformation is a multiplication of the digital input signal by a factor of two.

10. The method of claim 1 wherein the light-emitting elements are organized and controlled by rows and columns and a single, common local correction factor is applied to each light-emitting element in a row or column of light-emitting elements.

11. The method of claim 10 wherein the single, common local correction-factor applied to light-emitting element in a row or column of light-emitting elements is the average, maximum, or minimum of the local correction factors of the light-emitting elements in the row or column.

12. The method of claim 10 wherein a single, common row local correction factor is first applied to each light-emitting element in a row of light-emitting elements and a single, common local correction factor is then calculated and applied to each light-emitting element in a column of light-emitting elements.

13. The method of claim 10 wherein a single, common column local correction factor is first applied to each light-emitting element in a column of light-emitting elements and a single, common local correction factor is then calculated and applied to each light-emitting element in a row of light-emitting elements.

14. The method of claim 1 wherein a plurality of corrections are provided for each light-emitting element for a corresponding plurality of brightness levels.

15. The method of claim 14 wherein the corrections are scaling factors stored in a look-up value in a table.

16. The method of claim 1 wherein the OLED display is a color display comprising light emitting elements of multiple colors, and further comprising providing a separate global correction factor for all light-emitting elements of a common color and correcting the transformed signal for each light-emitting element by the common color global correction factor in combination with the local correction factor to produce the corrected digital signal.

17. The method of claim 1, further comprising converting the corrected digital signal to an analog signal, and providing a global correction factor for the analog signal.

18. The method of claim 17, wherein the OLED display is a color display comprising light emitting elements of multiple colors, and wherein separate global correction factors are provided for all light-emitting elements of a common color.

19. The method of claim 1, further comprising providing a global power correction factor for the common power signal.

20. The method of claim 19, further comprising adjusting the common power signal based on a relative lifetime of the device materials and an application requirement.

21. The method of claim 1 further comprising the step of providing a uniformity threshold below which the local correction is applied and above which the local correction is not applied.

22. The method of claim 21 wherein the uniformity threshold is selected based on a relative lifetime of the device materials and an application requirement.

23. The method of claim 1 further comprising the step of providing an acceptability threshold below which the local correction is not applied and above which the local correction is applied.

24. The method of claim 1 further comprising the step of sorting the corrected OLED displays based on a relative lifetime of the device materials and an application requirement.

25. The method of claim 1, wherein correction of the transformed signal is performed by integer scaling.

26. The method of claim 1 wherein the first bit depth is 8 bits.

27. The method of claim 26 wherein the second bit depth is 10 bits.

28. A method for the correction of brightness and uniformity variations in OLED devices and improving the manufacturing yields of OLED devices, comprising:

a) providing an OLED device having a plurality of light-emitting elements having a nominal lifetime and a nominal brightness at a nominal drive current density and one or more non-uniform light-emitting elements that do not produce the nominal brightness at the nominal drive current density;

b) providing an application for the OLED display having a required lifetime lower than the nominal OLED device lifetime; and

c) driving the one or more non-uniform light-emitting elements in the OLED device at a current density higher than the nominal drive current density so that the nominal brightness is achieved.