Driving system for active-matrix displays

1. A method of using raw grayscale image data, representing images to be displayed in successive frames, to drive a display having pixels that include a drive transistor and an organic light emitting device, said method comprising:

dividing each frame into at least first sub-frames and second sub-frames;

converting the raw grayscale values for each frame to first sub-frame grayscale values and second sub-frame grayscale values for the first sub-frames and second sub-frames, respectively; and

supplying each pixel with a drive current during said first sub-frames and said second sub-frames, said drive current being based on said first sub-frame grayscale values and said second sub-frame grayscale values, respectively, wherein

said drive current is higher in said first sub-frame than in said second sub-frame for raw grayscale values in a first preselected range, and non-zero or higher in said second sub-frame than in said first sub-frame for raw grayscale values in a second preselected range;

the raw grayscale values for each frame are converted to said first sub-frame grayscale values and said second sub-frame grayscale values for the first sub-frames and the second sub-frames, respectively, such that, with an increase of the raw grayscale values from zero,

the first sub-frame grayscale values are increased grayscale values while the second sub-frame grayscale values are maintained at zero, until a first threshold value for the first sub-frame grayscale values is reached, and

after said first threshold value is reached, the second sub-frame grayscale values begin to increase from zero while the first sub-frame grayscale values remain at said first threshold value or decrease with respect thereto,

wherein when the raw grayscale value increases to a value that causes the second sub-frame grayscale value to increase above said second threshold value, the second sub-frame grayscale value continues to increase while the first sub-frame grayscale value is decreased by the same amount.

2. The method of claim 1 in which the first and second sub-frame grayscale values are preselected to produce a pixel luminance during that frame that has a predetermined gamma relationship to said raw grayscale value for that frame.

3. The method of claim 1 in which said display is an active matrix display and said pixels in said active matrix display are OLED pixels.

4. The method of claim 1 wherein

the first preselected range is a grayscale range lower than the second preselected range, and

a duration of the first sub-frame is shorter than a duration of the second sub-frame.

5. An apparatus for using raw grayscale image data representing images to be displayed in successive frames, to drive a display having an array of pixels that each include a drive transistor and an organic light emitting device, multiple select lines coupled to said array for delivering signals that select when each pixel is to be driven, and multiple data lines for delivering drive signals to the selected pixels, said apparatus comprising:

a source driver coupled to said data lines and including a processing circuit ( 112 ) for receiving said raw grayscale image data and adapted to divide each frame into at least first and second sub-frames, and

convert the raw grayscale values for each frame to first and second sub-frame grayscale values for the first and second sub-frames, respectively,

supply each pixel with a drive current during said first and second sub-frames that is based on the first and second sub-frame grayscale values, respectively, wherein said drive current is

higher in said first sub-frame than in said second sub-frame for raw grayscale values in a first preselected range, and

non-zero or higher in said second sub-frame than in said first sub-frame for raw grayscale values in a second preselected range,

characterized in that

the raw grayscale values for each frame are converted to said first and second sub-frame grayscale values for the first and second sub-frames, respectively, such that, with an increase of the raw grayscale values from zero,

the first sub-frame grayscale values are increased grayscale values while the second sub-frame grayscale values are maintained to zero, until a first threshold value for the first sub-frame grayscale values is reached, and

after said first threshold value is reached, the second sub-frame grayscale values begin to increase from zero while the first sub-frame grayscale values remain at said first threshold value or decrease with respect thereto,

wherein when the raw grayscale value increases to a value that causes the second sub-frame grayscale value to increase above said second threshold value, the second sub-frame grayscale value continues to increase while the first sub-frame grayscale value is decreased by the same amount.

6. The apparatus of claim 5 in which said display is an active matrix display.

7. The apparatus of claim 6 in which said pixels in said active matrix display are OLED pixels.

8. The apparatus of claim 5 in which first and second sub-frame grayscale values are preselected to produce a pixel luminance during that frame that has a predetermined gamma relationship to said raw grayscale value for that frame.

9. The apparatus of claim 5 wherein

the first preselected range is a grayscale range lower than the second preselected range, and

a duration of the first sub-frame is shorter than a duration of the second sub-frame.