OLED luminance degradation compensation

• US 9,125,278 B2
• Filed: 10/11/2013
• Issued: 09/01/2015
• Est. Priority Date: 08/15/2006
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Chaji, Gholamreza
• Primary Examiner(s): A, Minh D
• Application Number:
  US14/052,146
• Publication Number:
  US 20140035488A1
• Time in Patent Office: 690 Days
• Field of Search: 3151691-1694, 345/204, 345 76- 81, 345/84
• US Class Current: 1/1
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 2320/0295 by monitoring each display 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 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/3283 in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H05B 45/60 Circuit arrangements for operating LEDs comprising organic material, e.g. for operating organic light-emitting diodes [OLED] or polymer light-emitting diodes [PLED]

Abstract

A system and method are disclosed for determining a pixel capacitance. The pixel capacitance is correlated to a pixel age to determine a current correction factor used for compensating the pixel drive current to account for luminance degradation of the pixel that results from the pixel aging.

Claims

1. A method of compensating for luminance degradation of a pixel having a luminescent device, the method comprising:

determining a luminance degradation resulting from aging of the pixel;

determining based on the determined luminance degradation a current correction factor;

compensating a drive current for the luminescent device based on the current correction factor; and

driving the luminescent device with the compensated drive current.

2. The method of claim 1, wherein the current correlation factor is an absolute amount of current to be added to the drive current.

3. The method of claim 1, wherein the current correction factor is a multiplier by which the drive current is multiplied in connection with the compensating.

4. The method of claim 1, wherein the current correction factor is retrieved from a lookup table that correlates desired luminance values with compensated driving currents, the lookup table being stored in a memory device.

5. The method of claim 1, wherein the luminance degradation is determined by a read block connected to the pixel by a switch, the read block reading a characteristic of the pixel or of the luminescent device when the switch is closed.

6. The method of claim 5, wherein the characteristic is a capacitance.

7. The method of claim 5, further comprising deducting a voltage caused by a leakage current caused by the read block so that the current correction factor is not influenced by the leakage current.

8. The method of claim 1, wherein the current correction factor is determined based on a plurality of current correction factors, wherein a first of the current correction factors is an age-related current correction factor related to the aging of the pixel and another of the current correction factors is a temperature-related correction factor relating to an environmental temperature.

9. A method of compensating a drive current of a pixel, the method comprising:

determining a combined correction factor that is based on an age-related correction factor and a non-age-related correction factor;

compensating a drive current for the pixel based on the combined correction factor; and

driving the pixel with the compensated drive current.

10. The method of claim 9, where the combined correction factor is a sum of the age-related correction factor and the non-age-related correction factor, the non-age-related correction factor being a temperature-related correction factor.

11. The method of claim 10, further comprising:

prior to the determining the combined correction factor, determining a luminance degradation of the pixel resulting from aging of the pixel;

determining, based on the determined luminance degradation, the age-related correction factor; and

determining, based on an operating environment temperature, the temperature-related correction factor.

12. The method of claim 11, wherein the pixel is an organic light emitting diode (OLED).

13. The method of claim 12, wherein the determining the luminance degradation of the pixel includes determining a capacitance of the OLED.

14. The method of claim 11, wherein the pixel is one of a plurality of pixels arranged in an array to form a display device.

15. The method of claim 11, further comprising updating the determined luminance degradation of the pixel more than once during a lifetime of the pixel so as to account for ongoing aging degradation during the lifetime of the pixel.

16. The method of claim 14, further comprising:

determining a capacitance of the pixel during a read operation of the display device, the pixel having been aged by use of the pixel to selectively emit light during a display operation of the display device;

determining a capacitance of a base pixel of the display during the read operation, the base pixel not having been used to selectively emit light during the display operation; and

the determining the luminance degradation of the pixel resulting from aging of the pixel comprises using a difference between the determined capacitance of the pixel and the determined capacitance of the base pixel.

17. The method of claim 16, wherein the pixel is an organic light emitting diode (OLED).