Method and apparatus for uniformity compensation in an OLED display

1. A method of compensating the uniformity of an OLED device having a plurality of light-emitting elements, comprising the steps of:

a) providing an OLED display having one or more light-emitting elements, each light-emitting element comprising a first electrode and a second electrode and at least one light-emitting layer formed between the first and second electrodes responsive to a current passing through the first and second electrodes, driven by an external controller that drives a current to pass through the electrodes, and the light-emitting layer to emit light, in response to input intensity values;

b) measuring the performance of the one or more light-emitting elements or groups of elements at three or more different input intensity values;

c) calculating parameters a and b for each of the one or more light-emitting elements or groups of elements that minimize the sum, for each of the three or more input intensity values i, of a minimization function:

ƒ(y i ,i,(y i −g(y i ,i,a,b)) 2 )

where y i is the performance value of the light-emitting element or groups of elements in response to an input intensity value i, and g is a function that is a simplified representation of the performance of the one or more light-emitting elements or groups of elements;

d) forming a linear transformation function ƒ(i)=mi+k, where m and k depend upon the function g, and the parameters a and b;

f) receiving an input signal;

g) employing the linear transformation function to compensate the input signal; and

h) driving the OLED display with the compensated signal.

2. The method of claim 1 , wherein the minimization function equals the product of a weighting function w(y i ,i) and (y i −g(y i , i, a, b)) 2 .

3. The method of claim 2 , wherein the weighting function is larger for smaller values of i and smaller for larger values of i.

4. The method of claim 2 , wherein w(y i ,i) for any performance measurement y i is a scaling factor times the value at y i of the first derivative of a function converting y i to CIE standard L*, or is a scaling factor divided by the value at y i of a function converting y i to CIE standard L*.

5. The method of claim 4 , wherein the measured performance value is the light output, or the current used, of the one or more light-emitting elements or groups of elements.

6. The method of claim 2 , wherein the weight w(y i , i) for any performance measurement y i is a scaling factor times the value at y i of a continuous weighting function, having either:

a) two main regions: a region of rapid decrease with y i increase at low y i , and a region of very slow decrease with y i at high y i , and in which the transition from the first region to the second happens below 50% of the y i of a reference white; or

b) three main regions: a region of constant or increasing weight with y i increase at very low y i , a region of rapid decrease with y i increase at low y i , and a region of very slow decrease with y i increase at high y i ; and in which the transition from the first region to the second happens below 20% of a reference white, and the transition from the second region to the third happens below 50% of the y i of a reference white.

7. The method of claim 1 , wherein the minimization function equals ƒ(y i −(ax i +b)) 2 ), or ƒ(i, (y i −(ax i +b)) 2 ), or ƒ(y i , (y i −(ax i +b)) 2 ).

8. The method of claim 1 , wherein the function g is a power function.

9. The method of claim 1 , wherein the minimization function is non-linearly larger for larger values of y i −g(y i , i, a, b) and non-linearly smaller for smaller values of y i −g(y i , i, a, b).

10. The method of claim 1 , further comprising a plurality of active-matrix OLED devices and wherein the input intensity values selected are the same for each of the plurality of active-matrix OLED devices.

11. The method of claim 1 , further comprising a plurality of active-matrix OLED devices and wherein the input intensity values selected are different for each of at least two of plurality of active-matrix OLED devices.

12. The method of claim 1 , wherein the OLED display is a color display comprising light-emitting elements of multiple colors and a different linear transformation is determined for different colors of light-emitting elements.

13. The method of claim 1 , wherein the OLED display is a color display comprising light-emitting elements of multiple colors and wherein the white point of the display is adjusted by adjusting the linear transformation for each light-emitting element or group of light-emitting elements to modify the average brightness of the display for each color of light.

14. The method of claim 1 , wherein the linear transformation for each light-emitting element or group of elements is adjusted to modify the average brightness of the display.

15. The method of claim 1 , wherein the linear transformation for each light-emitting element or group of light-emitting elements is adjusted over time to compensate for decreasing display brightness.

16. The method of claim 1 , wherein the function g(y i , i, a, b) equals ai+b, and wherein m is the ratio of a desired gain divided by the value a and k is the desired y-intercept minus the value b, divided by the value a.

17. An OLED device having a plurality of light-emitting elements, comprising:

a) an OLED display having one or more light-emitting elements, each light-emitting element comprising a first and second electrodes and at least one light-emitting layer formed between the electrodes responsive to a current passing through the electrodes;

b) an external calibration controller causing a current to pass through the electrodes and the light-emitting layer;

c) wherein the external calibration controller calculates a linear compensation transformation function that compensates the light output of each of the plurality of light-emitting elements by:

i) measuring the performance of the one or more light-emitting elements or groups of elements at three or more different code values;

ii) calculating parameters a and b for each of the one or more light-emitting elements or groups of elements that minimize the sum, for each of the three or more input intensity values i, of a minimization function:

ƒ(y i ,i,(y i −g(y i ,i,a,b)) 2 )

where y i is the performance value of the light-emitting element or group of elements in response to an input intensity value i, and g is a function that is a simplified representation of the performance of the one or more light-emitting elements or groups of elements; and

iii) forming a liner transformation function ƒ(i)=mi+k, where m and k depend upon the function g, and the parameters a and b.

18. An OLED device having a plurality of light-emitting elements, comprising:

a) an OLED display having one or more light-emitting elements, each light-emitting element comprising a first and second electrodes and at least one light-emitting layer formed between the electrodes responsive to a current passing through the electrodes;

b) an external controller causing a current to pass through the electrodes and the light-emitting layer;

c) wherein the external controller receives an input signal and employs a linear compensation transformation function to compensate the input signal by multiplying each input signal value i by m and adding k; and drives an OLED display with the compensated signal, wherein the linear compensation transformation function is calculated by an external calibration controller that calculates a linear compensation transformation function that compensates the light output of each of the plurality of light-emitting elements by:

i) measuring the performance of the one or more light-emitting elements or groups of elements at three or more different code values;

ii) calculating the parameters a and b for each of the one or more light-emitting elements or groups of elements that minimize the sum, for each of the three or more input intensity values i, of a minimization function:

ƒ(y i ,i,(y i −g(y i ,i,a,b)) 2 )

where y i is the performance value of the light-emitting element or group of elements in response to an input intensity value i, and g is a function that is a simplified representation of the performance of the one or more light-emitting elements or groups of elements; and

iii) forming a liner transformation function ƒ(i)=mi+k, where m and k depend upon the function g, and the parameters a and b.

19. The OLED device of claim 18 , wherein the values m and k for each light-emitting element are stored together at single address locations of the lookup table.

20. The OLED device of claim 18 , wherein the values m for each light-emitting element are stored with a first number of bits and the values k are stored at a second number of bits, and wherein the first and second number of bits are different or are stored as a difference from a mean.