Driving System For Active-Matrix Displays

• US 20110069096A1
• Filed: 09/09/2010
• Published: 03/24/2011
• Est. Priority Date: 09/09/2009
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza, Gupta, Vasudha, Li, Kongning, Nathan, Arokia
• Granted Patent: US 9,093,019 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/2081 with combination of amplitude modulation and time modulation space and time error diffusion G09G3/2066
• CPC Class Codes: G09G 3/3225 using an active matrix

Abstract

A system is provided for 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. The system defines high and low ranges of raw grayscale image data, and determines whether the raw grayscale image data for each pixel falls within the high range or the low range. Raw grayscale image data that falls within the low range is converted to higher grayscale values, and the pixels are driven with currents corresponding to the higher grayscale values during time periods that are shorter than complete frame time periods. Raw grayscale image data that falls within the high range is converted to higher grayscale values, and the pixels are driven with currents corresponding to the higher grayscale values during time periods that are shorter than complete frame time periods and different from the time periods of the low range image data. When the raw grayscale image data is adjusted according to a preselected gamma curve before using that data to drive the pixels, the high and low ranges may be selected according to how well the gamma curve corrects the raw grayscale image data within the ranges.

Claims

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:

defining high and low ranges of raw grayscale image data,

determining whether the raw grayscale image data for each pixel falls within said high range or said low range,

converting raw grayscale image data that falls within said low range to higher grayscale values, and

driving said pixels with currents corresponding to said higher grayscale values during time periods that are shorter than complete frame time periods.

2. The method of claim 1 which includes driving said pixels with currents corresponding to said raw grayscale image data that falls within said high range during preselected time periods that are longer than the time periods during which said pixels are driven with currents corresponding to raw grayscale image data that falls within said low range.

3. The method of claim 1 which includes adjusting said raw grayscale image data according to a preselected gamma curve before using that data to drive said pixels, and selecting said high and low ranges according to how well said gamma curve corrects said raw grayscale image data within said ranges.

4. The method of claim 1 which includes a normal driving mode in which said pixels are driven with currents corresponding to said raw grayscale image data without converting any of the grayscale values to higher values, and a hybrid driving mode in which raw grayscale image data that falls within said low range is converted to higher grayscale values, and said pixels are driven with currents corresponding to said higher grayscale values during time periods that are shorter than a complete frame time period.

5. The method of claim 4 which includes selecting whether to operate in said normal driving mode or said hybrid driving mode.

6. The method of claim 1 in which a lookup table is used to convert said grayscale image data that falls within said low range to higher grayscale values.

7. The method of claim 1 in which said display is an AMOLED display.

8. The method of claim 1 in which said higher grayscale values contain an indicator that they have been converted from raw grayscale image data.

9. The method of claim 2 in which said preselected time periods in which said pixels are driven with currents corresponding to said raw grayscale image data that falls within said high range, are shorter than a complete frame time period.

10. The method of claim 9 which includes making gamma corrections of both said higher gray scale values converted from raw grayscale image data falling within said low range, and said raw grayscale image values falling within said high range, are made according to the same gamma correction curve.

11. The method of claim 9, wherein said array is organized in rows of pixels, each of the pixels in a row being simultaneously driven, wherein the time period of driving of said pixels in the row with currents corresponding to said raw grayscale image data does not overlap with the time period during which said pixels in the row are driven with currents corresponding to raw grayscale image data that falls within said low range

12. The method of claim 3, further comprising sensing ambient light around the display and wherein the overall luminance of the display is adjusted based on the sensed level of ambient light.

13. The method of claim 12, wherein preselection of the gamma curve is based on the sensed level of ambient light.

14. The method of claim 1, wherein a middle range of raw grayscale data is defined, the pixels with currents corresponding to said middle range of grayscale values being driven during a time period of the frame other than the time periods of the pixels with higher grayscale values.

15. 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 for receiving said raw grayscale image data, determining whether the raw grayscale image data for each pixel falls within a preselected high range or a preselected low range, and converting raw grayscale image data that falls within said low range to higher grayscale values,

a memory for storing said higher grayscale values corresponding to raw grayscale image data that falls within said low range, and raw grayscale image data that falls within said high range,

a gamma correction circuit for retrieving the data stored in said memory and making gamma corrections to that data,

a controller supplying control signals to said gamma correction circuit for controlling the timing of the retrieval of said data stored in said memory by said gamma correction circuit, and

a digital-to-analog converter for converting gamma-corrected data from said gamma correction circuit to corresponding analog signals for driving said pixels.

16. The apparatus of claim 15 in which said source driver supplies said pixels with currents corresponding to said higher grayscale values during time periods that are shorter than complete frame time periods.

17. The apparatus of claim 16 in which said source driver supplies said pixels with currents corresponding to said raw grayscale image data that falls within said high range, during preselected time periods that are longer than the time periods during which said pixels are driven with currents corresponding to said higher grayscale values converted from said raw grayscale image data that falls within said low range.

18. The apparatus of claim 15 in which said gamma correction circuit adjusts said raw grayscale image data and said higher grayscale values according to a preselected gamma curve before that data is used to drive said pixels.

19. The apparatus of claim 15 in which said processing circuit includes a switch for selecting either a normal driving mode in which said pixels are driven with currents corresponding to said raw grayscale image data without converting any of the grayscale values to higher values, and a hybrid driving mode in which raw grayscale image data that falls within said low range is converted to higher grayscale values, and said pixels are driven with currents corresponding to said higher grayscale values during time periods that are shorter than a complete frame time period.

20. The apparatus of claim 15 in which said processing circuit includes a lookup table to convert said grayscale image data that falls within said low range to higher grayscale values.

21. The apparatus of claim 15 in which said display is an AMOLED display.

22. The apparatus of claim 15 in which said higher grayscale values contain an indicator that they have been converted from raw grayscale image data.

23. The apparatus of claim 17 in which said preselected time periods in which said pixels are driven with currents corresponding to said raw grayscale image data that falls within said high range, are shorter than a complete frame time period.

24. The apparatus of claim 17 in which said gamma correction circuit makes gamma corrections of both said higher gray scale values converted from raw grayscale image data falling within said low range, and said raw grayscale image values falling within said high range, are made according to the same gamma correction curve.

25. The apparatus of claim 15, further comprising an ambient light sensor sensing ambient light around the display, the ambient light sensor coupled to the controller, wherein the controller adjusts the overall luminance of the array pixels based on the level of sensed ambient light.

26. The apparatus of claim 25, wherein the controller selects one of a plurality of gamma curves based on the level of sensed ambient light, the selected plurality of gamma curves being used by the gamma correction circuit to make the gamma corrections to that data.

27. The apparatus of claim 16, wherein the processing circuit determines whether each pixel falls within a preselected middle range of raw grayscale data, the pixels with currents corresponding to said middle range of grayscale values being driven during a time period of the frame other than the time periods of the pixels with higher grayscale values.