EMISSION CONTROL IN AGED ACTIVE MATRIX OLED DISPLAY USING VOLTAGE RATIO OR CURRENT RATIO

1 . A method of determining compensation needed for reduced light efficiency in aged sub-pixels of an active matrix organic light-emitting diode (OLED) display, the method comprising:

aging a plurality of sections of sub-pixels of a first active matrix OLED display, the sections including at least a first section including aged sub-pixels and a second section including reference sub-pixels that are not aged;

applying a predetermined voltage across one or more of the aged sub-pixels and one or more of the reference sub-pixels;

determining a first current through said one or more of the aged sub-pixels and a second current through said one or more of the reference sub-pixels;

determining an age of said one or more of the aged sub-pixels based on the first current relative to the second current;

determining light emission characteristics of said one or more of the aged sub-pixels; and

determining corrections to be made to digital numbers indicative of desired brightness in said one or more of the aged sub-pixels based on mappings between the determined age and the determined light emission characteristics of said one or more of the aged sub-pixels.

2 . The method of claim 1 , wherein the plurality of sections of the sub-pixels are aged for a same predetermined period of time but with different amounts of current flowing through two or more of the sections of the sub-pixels to obtain different effective ages in said two or more of the sections of the sub-pixels of the OLED display.

3 . The method of claim 1 , wherein determining the first current includes measuring the first current through two or more of the aged sub-pixels and averaging the measured first current, and determining the second current includes measuring the second current through two or more of the reference sub-pixels and averaging the measured second current.

4 . The method of claim 1 , wherein each of the sub-pixels of the active matrix OLED display include a thin film transistor configured to drive an OLED of the sub-pixel, and current through the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

5 . The method of claim 1 , wherein the age of said one or more of the aged sub-pixels is determined based on a current ratio of the first current to the second current, the current ratio being less than one and being smaller as the sub-pixels have longer effective age.

6 . The method of claim 5 , further comprising storing a mapping between the current ratio and the age of the aged sub-pixel in a selection look-up table.

7 . The method of claim 1 , further comprising storing said corrections to be made to the digital numbers in one of a plurality of age curve look-up tables corresponding to the determined age of the aged sub-pixel, each age curve look-up table corresponding to a different age of the aged sub-pixel and mapping the digital numbers to said corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel, wherein one or more of the aged sub-pixels of the OLED display are assigned to use said one of the age curve look-up tables for correction of the digital numbers.

8 . The method of claim 7 , further comprising:

after a second active matrix OLED display is aged by actual use, applying the predetermined voltage across one of aged sub-pixels of the second active matrix OLED display and at least one of reference sub-pixels of the second active matrix OLED display;

determining a third current through said one of the aged sub-pixels of the second active matrix OLED display and a fourth current through said at least one of the reference sub-pixels of the second active matrix OLED display;

determining an age of said one of the aged sub-pixels of the second active matrix OLED display based on the third current relative to the fourth current;

selecting one of the age curve look-up tables to use for correction of the digital numbers indicative of desired brightness in said one of the aged sub-pixels of the second active matrix OLED display, based upon the determined age of said one of the aged sub-pixels of the second active matrix OLED display.

9 . The method of claim 8 , further comprising storing mappings between a sub-pixel number corresponding to said one of the aged sub-pixels of the second active matrix OLED display and an age curve look-up table number corresponding to the selected age curve look-up table in a correction look-up table.

10 . A method of determining compensation needed for reduced light efficiency in aged sub-pixels of an active matrix organic light-emitting diode (OLED) display, the method comprising:

aging a plurality of sections of sub-pixels of a first active matrix OLED display, the sections including at least a first section including aged sub-pixels and a second section including reference sub-pixels that are not aged;

determining a first voltage applied to one or more of the aged sub-pixels to generate a predetermined reference current through said one or more of the aged sub-pixels;

determining a second voltage applied to one or more of the reference sub-pixels to generate the same predetermined reference current through said one or more of the reference sub-pixels;

determining an age of said one or more of the aged sub-pixels based on the first voltage relative to the second voltage;

determining light emission characteristics of said one or more of the aged sub-pixels;

determining corrections to be made to digital numbers indicative of desired brightness in said one or more of the aged sub-pixels based on mappings between the determined age and the determined light emission characteristics of said one or more of the aged sub-pixels.

11 . The method of claim 10 , wherein the plurality of sections of the sub-pixels are aged for a same predetermined period of time but with different amounts of current flowing through two or more of the sections of the sub-pixels to obtain different effective ages in said two or more of the sections of the sub-pixels of the OLED display.

12 . The method of claim 10 , wherein determining the first voltage includes measuring the first voltage across two or more of the aged sub-pixels with the same predetermined reference current flowing through said two or more of the aged sub-pixels and averaging the measured first voltage, and determining the second voltage includes measuring the second voltage across two or more of the reference sub-pixels with the same predetermined reference current flowing through said two or more of the reference sub-pixels and averaging the measured second voltage.

13 . The method of claim 10 , wherein each of the sub-pixels of the active matrix OLED display include a thin film transistor configured to drive an OLED of the sub-pixel, and voltage across the aged sub-pixel or the reference sub-pixel is measured with the thin film transistor biased in linear mode.

14 . The method of claim 10 , wherein the age of said one or more of the aged sub-pixels is determined based on a voltage ratio of the first voltage to the second voltage, the voltage ratio being greater than one and being larger as the sub-pixels have longer effective age.

15 . The method of claim 15 , further comprising storing a mapping between the voltage ratio and the age of the aged sub-pixel in a selection look-up table.

16 . The method of claim 10 , further comprising storing said corrections to be made to the digital numbers in one of a plurality of age curve look-up tables corresponding to the determined age of the aged sub-pixel, each age curve look-up table corresponding to a different age of the aged sub-pixel and mapping the digital numbers to said corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel, wherein one or more of the aged sub-pixels of the OLED display are assigned to use said one of the age curve look-up tables for correction of the digital numbers.

17 . The method of claim 16 , further comprising:

after a second active matrix OLED display is aged by actual use, determining a third voltage applied to one of aged sub-pixels of the second active matrix OLED display to generate the predetermined reference current through one of the aged sub-pixels of the second active matrix OLED display, and determining a fourth voltage applied to one or more of reference sub-pixels of the second active matrix OLED display to generate the same predetermined reference current through said one or more of the reference sub-pixels of the second active matrix OLED display;

determining an age of said one of the aged sub-pixels of the second active matrix OLED display based on the third voltage relative to the fourth voltage; and

selecting one of the age curve look-up tables to use for correction of the digital numbers indicative of desired brightness in said one of the aged sub-pixels of the second active matrix OLED display, based upon the determined age of said one of the aged sub-pixels of the second active matrix OLED display.

18 . The method of claim 17 , further comprising storing mappings between a sub-pixel number corresponding to said one of the aged sub-pixels of the second active matrix OLED display and an age curve look-up table number corresponding to the selected age curve look-up table in a correction look-up table.

19 . An active matrix organic light-emitting diode (OLED) display comprising:

a plurality of OLED elements arranged in a plurality of rows and a plurality of columns, each of the OLED elements corresponding to a sub-pixel of the OLED display; and

an active matrix drive circuit configured to drive current through the OLED elements, the active matrix drive circuit including:

a plurality of age curve look-up tables each corresponding to a different age of aged sub-pixels of the OLED display and mapping digital numbers to corrections to be made to the digital numbers for the corresponding age of the aged sub-pixel, one or more of the aged sub-pixels of the OLED display being assigned to use said one of the age curve look-up tables for correction of the digital numbers;

a correction look-up table storing mappings between each of the OLED sub-pixels and said assigned one of the age curve look-up tables; and

a selection look-up table storing mappings between ages of the sub-pixels of the OLED display and the age curve look-up tables, the ages of the sub-pixels represented by current ratios or voltage ratios associated with the sub-pixels of the OLED display, and wherein

the active matrix drive circuit is configured to receive the digital number indicative of a desired brightness of one of the aged sub-pixels and generate a corrected digital number for driving the OLED elements using the corrections to the digital numbers stored in the age curve look-up table assigned to said one of the aged sub-pixels.

20 . The active matrix organic light-emitting diode (OLED) display of claim 19 , wherein the active matrix drive circuit further comprises a calibration engine configured to:

apply a predetermined voltage across said one of the aged sub-pixels and at least one of the reference sub-pixels;

determine a first current through said one of the aged sub-pixels and a second current through said at least one of the reference sub-pixels;

determine an age of said one of the aged sub-pixels based on the first current relative to the second current; and

select one of the age curve look-up tables to use for correction of the digital numbers in said one of the aged sub-pixels for storage in the correction look-up table, based upon the determined age of said one of the aged sub-pixels.

21 . The active matrix organic light-emitting diode (OLED) display of claim 19 , wherein the active matrix drive circuit further comprises a calibration engine configured to:

determine a first voltage applied to said one of the aged sub-pixels to generate a predetermined reference current through said one of the aged sub-pixels, and determine a second voltage applied to one or more of reference sub-pixels that are un-aged to generate the same predetermined reference current through said one or more of the reference sub-pixels;

determine an age of said one of the aged sub-pixels based on the first voltage relative to the second voltage; and

select one of the age curve look-up tables to use for correction to the digital numbers in said one of the aged sub-pixel for storage in the correction look-up table, based upon the determined age of said one of the aged sub-pixels.

22 . The active matrix organic light-emitting diode (OLED) display of claim 19 , wherein the age curve look-up tables store mappings between the digital numbers and increases or decreases to be made to the digital numbers.

23 . The active matrix organic light-emitting diode (OLED) display of claim 19 , wherein the age curve look-up tables store mappings between the digital numbers and corrected digital numbers.