SYSTEM AND METHODS FOR EXTRACTING CORRELATION CURVES FOR AN ORGANIC LIGHT EMITTING DEVICE

• US 20140015824A1
• Filed: 09/16/2013
• Published: 01/16/2014
• Est. Priority Date: 02/04/2010
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza, Jaffari, Javid, Nathan, Arokia
• Granted Patent: US 9,430,958 B2
• Time in Patent Office: Days
• US Class Current: 345/212
• CPC Class Codes: G09G 2300/0413 Details of dummy pixels or dummy lines in flat panels
• 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• 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 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements

Abstract

A system and method for determining and applying characterization correlation curves for aging effects on an organic light organic light emitting device (OLED) based pixel is disclosed. A first stress condition is applied to a reference pixel having a drive transistor and an OLED. An output voltage based on a reference current is measured periodically to determine an electrical characteristic of the reference pixel under the first predetermined stress condition. The luminance of the reference pixel is measured periodically to determine an optical characteristic of the reference pixel. A characterization correlation curve corresponding to the first stress condition including the determined electrical and optical characteristic of the reference pixel is stored. Characterization correlation curves for other predetermined stress conditions are also stored based on application of the predetermined stress conditions on other reference pixels. The stress condition of an active pixel is determined and a compensation voltage is determined by correlating the stress condition of the active pixel with the curves of the predetermined stress conditions.

Claims

1. A method for determining a characterization correlation curve for aging compensation for an organic light emitting device (OLED) based pixel in a display comprising:

applying a first stress condition to a reference device;

storing a baseline optical characteristic and a baseline electrical characteristic of the reference device;

periodically measuring an output voltage based on a reference current to determine an electrical characteristic of the reference device;

periodically measuring the luminance of the reference pixel to determine an optical characteristic of the reference device;

determining a characterization correlation curve corresponding to the first stress condition based on the baseline optical and electrical characteristics and the determined electrical and optical characteristics of the reference device; and

storing the characterization correlation curve corresponding to the first stress condition.

2. The method of claim 1, wherein the reference device is a pixel including an OLED and a drive transistor, and the baseline electrical characteristic is determined from measuring a property of the drive transistor and the OLED.

3. The method of claim 2, further comprising:

applying the first stress condition to a plurality of reference pixels each having a drive transistor and an OLED;

periodically measuring an output voltage based on a reference current to determine an electrical characteristic of each of the reference pixels;

periodically measuring the luminance of each of the reference pixels to determine an optical characteristic of each of the reference pixels; and

averaging the electrical and optical characteristics of each of the plurality of reference pixels to determine the characterization correlation curve.

5. The method of claim 1, further comprising:

applying a second stress condition to a second reference pixel having an OLED;

storing a baseline optical characteristic and a baseline electrical characteristic of the second reference pixel;

periodically measuring an output voltage based on a reference current to determine an electrical characteristic of the second reference pixel;

periodically measuring the luminance of the reference pixel to determine an optical characteristic of the second reference pixel;

determining a second characterization correlation curve corresponding to the second stress condition based on the baseline optical and electrical characteristics and the determined electrical and optical characteristic of the second reference pixel; and

storing the second characterization correlation curve corresponding to the second stress condition.

6. The method of claim 5, further comprising:

determining a stress condition on an active pixel on a display, the stress condition falling between the first and second stress condition;

determining a compensation factor as a function of the first and second characterization correlation curves corresponding to the first and second reference pixels; and

modifying a programming voltage by the compensation factor to the active pixel to compensate for aging effects.

7. The method of claim 6, wherein the compensation factor is determined based on a previous determined stress condition on the active pixel multiplied by an average compensation factor, the average compensation factor being a function of the difference between the first and second characterization correlation curves.

12. The method of claim 1, wherein the baseline optical characteristic and the baseline electrical characteristic of the reference device are measured from the reference device immediately after fabrication of the reference device.

13. The method of claim 1, wherein the baseline optical characteristic and the baseline electrical characteristic of the reference device are determined from periodic measurement of a base device.

15. The method of claim 1, wherein the luminance characteristic is measured by a photo sensor in proximity to the reference pixel.

4. (canceled)

8-11. -11. (canceled)

14. (canceled)

16. A display system for compensating of aging effects, the display system comprising:

a plurality of active pixels displaying an image, the active pixels each including a drive transistor and an organic light emitting diode (OLED);

a memory storing a first characterization correlation curve for a first predetermined stress condition and a second characterization correlation curve for a second predetermined stress condition; and

a controller coupled to the plurality of active pixels, the controller determining a stress condition on one of the active pixels, the stress condition falling between the first and second predetermined stress conditions, and determining a compensation factor to apply to a programming voltage based on the characterization correlation curves of the first and second stress conditions.

17. The display system of claim 16, further comprising:

a first reference pixel including a drive transistor and an OLED;

a second reference pixel including a drive transistor and an OLED; and

wherein the first characterization correlation curve is determined based on electrical and optical characteristics determined from the first reference pixel under the first stress condition and the second characterization correlation curve determined based on electrical and optical characteristics determined from the second reference pixel under the second stress condition

21. The display system of claim 16, wherein the compensation factor is determined by dynamic moving averaging by adjusting the coefficient as a function of the age of the active pixel.

22. The display system of claim 16, wherein the compensation factor is determined by the compensation factor determined at a previous time period and the electrical change from the current stress condition applied to the predetermined characterization correlation curves.

18-20. -20. (canceled)

23. A method of determining a characterization correlation curve for an OLED device in a display, the method comprising:

storing a first characterization correlation curve based on a first group of reference pixels at a predetermined high stress condition;

storing a second characterization correlation curve based on a second group of reference pixels at a predetermined low stress condition;

determining a stress level of an active pixel falling between the high and low stress conditions;

determining a compensation factor based on the stress on the active pixel, the compensation factor based on the stress on the active pixel and the first and second characterization correlation curve; and

adjusting a programming voltage to the active pixel based on the characterization correlation curve.

24. The method of claim 23, wherein the first characterization correlation curve is determined based on averaging the characteristics of the first group of reference pixels.

25. The method of claim 23, wherein the compensation factor is determined based on a previous determined stress condition on the active pixel multiplied by an average compensation factor, the average compensation factor being a function of the difference between the first and second characterization correlation curves.

26. The method of claim 23, wherein the average compensation factor is increased as a function of time.

27. The method of claim 23, wherein the compensation factor is determined based on a previously determined compensation factor.

28. A display system for compensating for aging effects, the display system comprising:

a plurality of active pixels displaying an image, the active pixels each including a drive transistor and an organic light emitting diode (OLED);

a memory storing a first characterization correlation curve for a first predetermined stress condition and a second characterization correlation curve for a second predetermined stress condition; and

a controller coupled to the plurality of active pixels, the controller

determining a stress condition of a selected one of the active pixels, the stress condition falling between the first and second predetermined stress conditions, and

determining a compensation factor to apply to a programming voltage for said selected active pixel, based on a weighted moving average of said first and second characterization correlation curves of said first and second predetermined stress conditions.

29. The display system of claim 28 in which said stress condition for an active pixel at a time t_i is St(t_i)=(St(t_i−

1)*k_avg+L(t_i))/(k_avg+1), where St(t<sub>i−

1</sub>) is the stress condition at a previous time, k_avg is a moving average constant, L(t_i) is the measured luminance of the active pixel at time t_i.

30. The display system of claim 28 which includes determining the two predetermined stress conditions closest to said determined stress condition of said selected one of the active pixels and attendant characteristic data obtained from said reference pixels at said closest two predetermined stress conditions