Method and system for compensation of non-uniformities in light emitting device displays

• US 7,868,857 B2
• Filed: 04/12/2006
• Issued: 01/11/2011
• Est. Priority Date: 04/12/2005
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Nathan, Arokia, Alexander, Stefan, Huang, Rick I-Heng, Church, Corbin, Chaji, G. Reza, Servati, Peyman
• Primary Examiner(s): Awad; Amr
• Assistant Examiner(s): Shapiro; Leonid
• Application Number:
  US11/402,624
• Publication Number:
  US 20060273997A1
• Time in Patent Office: 1,735 Days
• Field of Search: 345 82- 83, 345/204, 345/690
• US Class Current: 345/82
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• 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 2320/0295 by monitoring each display 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 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 5/10 Intensity circuits

Abstract

A method and system for compensation of non-uniformities in light emitting device displays is provided. The system includes a module for estimating degradation of an entire pixel circuit based on measurement of a part of the pixel circuit. Based on the estimation, a correction factor is produced to correct non-uniformity of the display.

Claims

1. A system for compensating non-uniformities in a light emitting device display, comprising:

a driver for driving a pixel array having a plurality of pixel circuits in an illumination operation and in a degradation estimation operation, each pixel circuit comprising;

a capacitor;

a first transistor selected by a select line;

a second transistor coupled to a light emitting device; and

a third transistor and a fourth transistor coupled between a data line and a potential in series;

wherein each transistor has a gate terminal, the gate terminal of the first transistor and the gate terminal of the third transistor coupled to the select line, the gate terminal of the fourth transistor and the capacitor coupled to the gate terminal of the second transistor, the first transistor coupled to the data line and the gate terminal of the second transistor;

a measuring module for measuring current or voltage on the data line coupled to a first-pixel circuit in the degradation estimation operation; and

a modifying module for modifying pixel data, the pixel data being applied to the first pixel circuit or a second pixel circuit-in the pixel array in the illumination operation, including;

an estimating module for estimating a degradation of the first pixel circuit based on the measured current or voltage; and

a compensating module for correcting the pixel data based on the estimated degradation of the first pixel circuit.

2. A system according to claim 1, wherein the modifying module implements a constant algorithm for increasing luminance data applied to a degraded pixel circuit such that the luminance data of the degraded pixel circuit matches that of a non-degraded pixel circuit.

3. A system according to claim 1, wherein the modifying module implements a decreasing algorithm for decreasing luminance data applied to a non-degraded pixel circuit in the pixel array based on the estimated degradation such that the luminance data of the non-degraded pixel circuit matches that of a degraded pixel circuit in the pixel array.

4. A system according to claim 2, wherein at least one of the estimating module and the compensating module produces a correction factor in accordance with the constant algorithm.

5. A system according to claim 3, wherein at least one of the estimating module and the compensating module produces a correction factor in accordance with the decreasing algorithm.

6. A system according to claim 1, wherein the estimating module includes estimating the degradation of the first pixel circuit based on the measured current or voltage together with electrical data measured from the light emitting device, the electrical data being measured separately from the measurement of the current or voltage.

7. A system according to claim 1, wherein the measured current or voltage being associated with the transistor, the light emitting device, or combinations thereof.

8. A system according to claim 1, wherein the modifying module dynamically allocates a timing of the measurement, a timing of the correction, or a combination thereof.

9. A system according to claim 8, wherein the modifying module includes a memory for storing compensation data or the measurement.

10. A system according to claim 1, wherein the estimating module estimates the degradation of the first pixel circuit based on the measured current or voltage together with one or more additional measurement inputs, one or more empirical parameters or combinations thereof.

11. A system according to claim 10, wherein the one or more additional measurement inputs include at least one of voltage reading from one or more current-programming pixels, current reading from one or more voltage-programming pixel, measurement of an ambient light, humidity measurement, temperature measurement, mechanical stress measurement, environmental stress measurement, and feedback from test structures on the display.

12. A system according to claim 10, wherein the one or more empirical parameters include at least one of brightness loss in a light emitting device of the pixel circuit due to decreasing efficiency (Δ

L), a shift in the light emitting device diode voltage over time (Δ

Voled), dynamic effects of threshold shift, parameters related to performance of a pixel transistor including threshold, threshold shift, mobility (μ

), inter-pixel non-uniformity, DC bias voltages in the pixel circuit, changing gain of current-mirror based pixel circuits, short-term and long-term based shifts in pixel circuit performance, pixel-circuit operating voltage variation due to IR-drop and ground bounce.

13. A system according to claim 1, wherein the compensation module compensates for the non-uniformity due to process or construction inequality in the display, aging of one or more pixel circuits, or combinations thereof.

14. A system according to claim 1, wherein the compensating module includes grayscale compression module for implementing a gray scale compression algorithm on luminance data applied to the first or second pixel circuit to reserve grayscale values.

15. A system according to claim 14, wherein the gray scale compression algorithm module transforms the luminance data so as to use luminance values less than those of the original luminance data.

16. A system according to claim 1, wherein the transistors are thin-film-transistors.

17. A system according to claim 1, wherein the light emitting device is an organic light emitting device.

18. A system according to claim 1, wherein the fourth transistor in each pixel circuit is coupled to the light emitting diode and the second transistor.

19. A system according to claim 1, wherein the modifying module applying the pixel data to the first pixel circuit and the second pixel circuit in the pixel array in the illumination operation.

20. A method of compensating non-uniformities in a light emitting device display having a pixel array including a plurality of pixel circuits, each pixel circuit having:

a capacitor;

a first transistor selected by a select line;

a second transistor coupled to a light emitting device; and

a third transistor and a fourth transistor coupled between a data line and a potential in series;

wherein each transistor has a gate terminal, the gate terminal of the first transistor and the gate terminal of the third transistor coupled to the select line, the gate terminal of the fourth transistor and the capacitor coupled to the gate terminal of the second transistor, the first transistor coupled to the data line and the gate terminal of the second transistor;

the method of compensating comprising;

in a degradation estimation operation, operating on a first pixel circuit in the pixel array, including;

operating on the select line coupled to the first pixel circuit in a manner same as that of an illumination operation;

operating on the data line coupled to the first pixel circuit; and

measuring current or voltage on the data line coupled to the first pixel circuit;

estimating a degradation of the first pixel circuit based on the measured current or voltage; and

correcting pixel data applied to the first pixel circuit or a second pixel circuit in the pixel array in the illumination operation, based on the estimated degradation of the first pixel circuit.

21. A method according to claim 20, wherein the correcting step includes:

increasing luminance data to a degraded pixel circuit such that the luminance data of the degraded pixel circuit matches that of a non-degraded pixel circuit.

22. A method according to claim 20, wherein the correcting step includes:

decreasing luminance data to a non-degraded pixel circuit in the pixel array based on the estimated degradation such that the luminance data of the non-degraded pixel circuit matches that of a degraded pixel circuit in the pixel array.

23. A method according to claim 20, wherein the method further comprises:

measuring electrical data from the light emitting device, the electrical data being measured separately from the measurement of the current or voltage, and

the estimating step including the electrical data from the light emitting device when estimating the degradation of the first pixel circuit.

24. A method according to claim 20, wherein the the measured current or voltage being associated with the one or more the transistors, the light emitting device, or combinations thereof.

25. A method according to claim 20, further including the step of dynamically allocating a timing of the measurement, a timing of the correction, or a combined thereof.

26. A method according to claim 20, further including the step of compressing grayscales of luminance data applied to the first or second pixel circuit to reserve one or more grayscale values.

27. A method according to claim 26, wherein the compressing step includes the step of transforming the luminance data so as to use luminance values less than those of the original luminance data.

28. A method according to claim 20, wherein the correcting pixel data is applied to the first pixel circuit and the second pixel circuit in the pixel array in the illumunication based on the estimation of the first pixel circuit.