METHOD AND APPARATUS FOR AVERAGED LUMINANCE AND UNIFORMITY CORRECTION IN AN AMOLED DISPLAY

• US 20070290958A1
• Filed: 06/16/2006
• Published: 12/20/2007
• Est. Priority Date: 06/16/2006
• Status: Abandoned Application

• Current Assignee: Global OLED Technology LLC (LG Display Co., Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Cok, Ronald S.
• Application Number:
  US11/424,645
• Publication Number:
  US 20070290958A1
• Time in Patent Office: Days
• US Class Current: 345/77
• 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 3/3225 using an active matrix

Abstract

A method for the correction of average luminance or luminance uniformity variations in an active-matrix OLED display, comprising:

• • a) providing an active-matrix OLED display;
  • b) determining at a first time a first offset voltage and a first gain relationship between the voltage and the current passing through one or more light-emitting elements;
  • c) receiving a signal for driving the light-emitting elements after step b), correcting the signal by employing the first offset voltage and gain relationship values to compute a linear correction for the light-emitting elements to form a corrected signal, and driving the display with the corrected signal;
  • d) determining at a time after the first time an updated offset voltage and an updated gain relationship between the voltage and the current passing through the light-emitting elements; and
  • e) receiving a signal for driving the one or more light-emitting elements after step d), correcting the signal by employing the updated offset voltage and gain relationship values to compute a linear correction for the light-emitting elements to form an updated corrected signal, and driving the display with the updated corrected signal.

Claims

1. A method for the correction of average luminance or luminance uniformity variations in an active-matrix OLED display, comprising:

a) providing an active-matrix OLED display having thin-film transistors driving one or more light-emitting elements responsive to a multi-valued input signal for causing the light-emitting elements to emit light at a plurality of luminance levels;

b) determining at a first time a first offset voltage at which at least one of the one or more light-emitting elements will not conduct more than a pre-determined minimum current and a first gain relationship between the voltage and the current passing through the at least one of the one or more light-emitting elements at voltages above the first offset voltage;

c) receiving a signal for driving the one or more light-emitting elements after step b), correcting the signal by employing the first offset voltage and gain relationship values to compute a linear correction for at least one of the one or more light-emitting elements to form a corrected signal, and driving the active-matrix OLED display with the corrected signal;

d) determining at a time after the first time an updated offset voltage at which at least one of the one or more light-emitting elements will not conduct more than a pre-determined minimum current and an updated gain relationship between the voltage and the current passing through the at least one of the one or more light-emitting elements at voltages above the updated offset voltage; and

e) receiving a signal for driving the one or more light-emitting elements after step d), correcting the signal by employing the updated offset voltage and gain relationship values to compute a linear correction for at least one of the one or more light-emitting elements to form an updated corrected signal, and driving the active-matrix OLED display with the updated corrected signal.

2. The method of claim 1, wherein the first offset voltage and first gain relationship are determined before the OLED display is sold to a customer, and the updated offset voltage and updated gain relationship are determined after the display is sold to a customer and put into use.

3. The method of claim 1, wherein steps e) and d) are repeated over time.

4. The method of claim 1, wherein the first and updated voltage offsets and gain relationships are determined by measuring the current used by one or more light-emitting element at a plurality of luminance levels.

5. The method of claim 4, further comprising measuring the luminance of the at least one light-emitting element at a plurality of luminance levels before the display is sold, and wherein the measured current and luminance values are employed to determine a relationship between the luminance and the current usage of the display, and the determined relationship is employed when computing the linear correction for at least one of the one or more light-emitting elements employed to form the updated corrected signal.

6. The method of claim 1, wherein the thin-film transistors of the active-matrix OLED display comprise amorphous silicon thin-film transistors.

7. The method of claim 1, wherein the signal correction is performed with an adder and/or a multiplier.

8. The method of claim 1, wherein the OLED display has more than one light-emitting element and the corrected signal improves the luminance uniformity of the OLED display.

9. The method of claim 1, wherein the OLED display ages over time and the updated corrected signal compensates for changes in OLED display luminance over time.

10. The method of claim 1, wherein the OLED display is a color display comprising light-emitting elements of multiple colors, and wherein first and updated voltage offsets and gain relationships are determined separately for each color of light-emitting element.

11. The method of claim 1, wherein the updated corrected signal employs a gain correction to maintain a constant current through the light-emitting element for a given input signal.

12. The method of claim 1, wherein the updated correction signal compensates for losses in efficiency of the light-emitting elements by employing a gain correction that is greater than the gain correction that would be necessary to match the current through the light-emitting element for a given input signal in accordance with the first gain relationship.

13. The method of claim 12, wherein the increase in the gain correction is based on a change in offset voltage between the first and updated measurements.

14. The method of claim 12, wherein the increase in the gain correction is based on a change in gain relationship between the first and updated measurements.

15. The method of claim 1, wherein the updated offset voltage and gain relationship are determined by measuring the current through at least one of the one or more light-emitting elements at only two signal values that result in two current values above the pre-determined minimum current, and the updated gain relationship is a single linear function.

16. The method of claim 1, wherein the updated offset voltage and gain relationship are determined by measuring the current through at least one of the one or more light-emitting elements at more than two signal values that result in current values above the pre-determined minimum current, and the measurements are combined to form an updated gain relationship comprising a plurality of linear functions.

17. An active-matrix OLED display, comprising:

a) an active-matrix OLED display having thin-film transistors driving one or more light-emitting elements responsive to a multi-valued input signal for causing the light-emitting elements to emit light at a plurality of brightness levels; and

b) a controller for (i) accessing a pre-determined first offset voltage at which at least one of the one or more light-emitting elements will not conduct more than a pre-determined minimum current and a pre-determined first gain relationship between the voltage and the current passing through the at least one of the one or more light-emitting elements at voltages above the first offset voltage;

(ii) receiving a signal for driving the one or more light-emitting elements, correcting the signal by employing the first offset voltage and gain relationship values to compute a linear correction for at least one of the one or more light-emitting elements to form a corrected signal, and driving the active-matrix OLED display with the corrected signal;

(iii) determining an updated offset voltage at which at least one of the one or more light-emitting elements will not conduct more than a pre-determined minimum current and an updated gain relationship between the voltage and the current passing through the at least one of the one or more light-emitting elements at voltages above the updated offset voltage; and

(iv) receiving a signal for driving the one or more light-emitting elements, correcting the signal by employing the updated offset voltage and gain relationship values to compute a linear correction for at least one of the one or more light-emitting elements to form an updated corrected signal, and driving the active-matrix OLED display with the updated corrected signal.

18. The OLED display of claim 17, wherein the thin-film transistors comprise amorphous silicon thin-film transistors.