Display device

• US 20050231449A1
• Filed: 04/07/2005
• Published: 10/20/2005
• Est. Priority Date: 04/15/2004
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Miyagawa, Keisuke
• Granted Patent: US 7,460,137 B2
• Time in Patent Office: Days
• US Class Current: 345/77
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

A display device where the power consumption of a display panel can be reduced by controlling a display time rate. The display device includes a gray scale control circuit for controlling the display time rate of a pixel of a display means based on an output of a display time rate table that outputs a gray scale control signal for reducing the display time rate of a pixel when the average gray scale of a video signal of one frame obtained by an one frame average gray scale calculator exceeds a certain value. A display time of a pixel is controlled by erasing a video signal written to a pixel of the display means based on an output signal of the display time rate table. When an image with a high average gray scale is displayed, the luminance of the entire screen increases and power consumption increases. However, power consumption can be suppressed to a certain value by decreasing the display time rate when the average gray scale of a video signal of one frame exceeds a certain value.

Claims

1. A display device comprising:

an average gray scale calculator obtaining an average gray scale of a video signal of one frame;

a display time rate table outputting a gray scale control signal for reducing a display time rate of a pixel based on the average gray scale; and

a display unit having the pixel,

wherein a gray scale of the pixel is controlled based on the gray scale control signal.

5. The display device according to claim 1, wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds a certain value.

9. The display device according to claim 1,

wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds a certain value, and

wherein the video signal written to the pixel is erased based on the magnification signal.

15. The display device according to claim 1, wherein the pixel comprises an EL element arranged in matrix.

21. The display device according to claim 1, wherein the pixel comprises a liquid crystal element arranged in matrix.

29. The display device according to claim 1, wherein the video signal of one frame is divided into a plurality of subframes, and the display time rate is controlled in each of the plurality of subframes to perform time division gray scale display.

33. The display device according to claim 1, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

2. A display device comprising:

an average gray scale calculator obtaining an average gray scale of a video signal of one frame;

a display time rate table outputting a gray scale control signal for reducing a display time rate of a pixel based on the average gray scale; and

a display unit having the pixel,

wherein a gray scale of the pixel is controlled based on the gray scale control signal, and

wherein the gray scale of the pixel is controlled by erasing the video signal written to the pixel.

6. The display device according to claim 2, wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds a certain value.

10. The display device according to claim 2,

wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds a certain value, and

wherein the video signal written to the pixel is erased based on the magnification signal.

16. The display device according to claim 2, wherein the pixel comprises an EL element arranged in matrix.

22. The display device according to claim 2, wherein the pixel comprises a liquid crystal element arranged in matrix.

30. The display device according to claim 2, wherein the video signal of one frame is divided into a plurality of subframes, and the display time rate is controlled in each of the plurality of subframes to perform time division gray scale display.

34. The display device according to claim 2, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

3. A display device comprising:

an average gray scale calculator obtaining an average gray scale of a video signal of one frame;

a display time rate table outputting a gray scale control signal for reducing a display time rate of a pixel when the average gray scale exceeds a certain value; and

a display unit having the pixel,

wherein a gray scale of the pixel is controlled based on the gray scale control signal.

7. The display device according to claim 3, wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds the certain value.

11. The display device according to claim 3,

wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds the certain value, and

wherein the video signal written to the pixel is erased based on the magnification signal.

17. The display device according to claim 3, wherein the pixel comprises an EL element arranged in matrix.

23. The display device according to claim 3, wherein the pixel comprises a liquid crystal element arranged in matrix.

31. The display device according to claim 3, wherein the video signal of one frame is divided into a plurality of subframes, and the display time rate is controlled in each of the plurality of subframes to perform time division gray scale display.

35. The display device according to claim 3, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

4. A display device comprising:

an average gray scale calculator obtaining an average gray scale of a video signal of one frame;

a display time rate table outputting a gray scale control signal for reducing a display time rate of a pixel when the average gray scale exceeds a certain value; and

a display unit having the pixel,

wherein a gray scale of the pixel is controlled based on the gray scale control signal, and

wherein the gray scale of the pixel is controlled by erasing the video signal written to the pixel.

8. The display device according to claim 4, wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds the certain value.

12. The display device according to claim 4,

wherein the display time rate table generates a magnification signal for reducing the display time rate when the average gray scale exceeds the certain value, and

wherein the video signal written to the pixel is erased based on the magnification signal.

18. The display device according to claim 4, wherein the pixel comprises an EL element arranged in matrix.

24. The display device according to claim 4, wherein the pixel comprises a liquid crystal element arranged in matrix.

32. The display device according to claim 4, wherein the video signal of one frame is divided into a plurality of subframes, and the display time rate is controlled in each of the plurality of subframes to perform time division gray scale display.

36. The display device according to claim 4, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

13. A display device comprising:

an A/D converter for converting an analog video signal into a digital video signal and outputting the digital video signal;

a data controller for taking and processing the digital video signal and outputting the digital video signal to a display unit;

an average gray scale calculator obtaining an average gray scale by averaging a gray scale of each pixel over an entire screen of one frame based on the digital video signal from the A/D converter and for outputting an average gray scale signal;

a display time rate table outputting a magnification signal for reducing a display time rate when the average gray scale exceeds a certain value in accordance with the average gray scale signal; and

a timing signal generator generating an erase start signal for erasing the digital video signal written to the each pixel of the display unit in accordance with the magnification signal.

19. The display device according to claim 13, wherein the each pixel comprises an EL element arranged in matrix.

25. The display device according to claim 13, wherein the each pixel comprises a liquid crystal element arranged in matrix.

37. The display device according to claim 13, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

14. A display device comprising:

an A/D converter for converting a analog video signal into a digital video signal and outputting the digital video signal;

a data controller for taking and processing the digital video signal, converting the digital video signal into the analog video signal, and outputting the analog video signal to a display unit;

an average gray scale calculator obtaining an average gray scale by averaging a gray scale of each pixel over an entire screen of one frame based on the digital video signal from the A/D converter and for outputting an average gray scale signal;

a display time rate table outputting a magnification signal for reducing a display time rate when the average gray scale exceeds a certain value in accordance with the average gray scale signal; and

a timing signal generator generating an erase start signal for erasing the analog video signal written to the each pixel of the display unit in accordance with the magnification signal.

20. The display device according to claim 14, wherein the each pixel comprises an EL element arranged in matrix.

26. The display device according to claim 14, wherein the each pixel comprises a liquid crystal element arranged in matrix.

38. The display device according to claim 14, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

27. A display device comprising:

an active matrix display unit comprising;

a source signal line driver circuit;

a first gate signal line driver circuit;

a second gate signal line driver circuit;

a pixel portion;

a plurality of source signal lines connected to the source signal line driver circuit;

a plurality of first gate signal lines connected to the first gate signal line driver circuit;

a plurality of second gate signal lines connected to the second gate signal line driver circuit; and

a power supply line,

wherein the pixel portion comprises a plurality of pixels,

wherein each of the pixels comprises a switching transistor, an EL driving transistor, an erasing transistor, and an EL element,

wherein a gate electrode of the switching transistor is connected to the first gate signal lines,

wherein one of a source region and a drain region of the switching transistor is connected to the source signal lines and the other is connected to a gate electrode of the EL driving transistor,

wherein a gate electrode of the erasing transistor is connected to the second gate signal lines,

wherein one of a source region and a drain region of the erasing transistor is connected to the power supply line and the other is connected to the gate electrode of the EL driving transistor,

wherein one of a source region and a drain region of the EL driving transistor is connected to the power supply line and the other is connected to the EL element, and

a gray scale control circuit comprising;

an A/D converter for converting an analog video signal into a digital video signal and outputting the digital video signal;

a data controller for taking and processing the digital video signal and outputting the digital video signal to the active matrix display unit;

an average gray scale calculator obtaining an average gray scale by averaging a gray scale of each of the pixels over the entire screen of one frame based on the digital video signal from the A/D converter and for outputting an average gray scale signal;

a display time rate table outputting a magnification signal for reducing a display time rate when the average gray scale exceeds a certain value in accordance with the average gray scale signal; and

a timing signal generator generating an erase start signal for erasing the digital video signal written to each of the pixels in accordance with the magnification signal,

wherein the digital video signal written to each of the pixels is erased by supplying the erase start signal to the second gate signal line driver circuit.

39. The display device according to claim 27, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

28. A display device comprising:

an active matrix display unit comprising;

a source signal line driver circuit;

a gate signal line driver circuit;

a pixel portion;

a plurality of source signal lines connected to the source signal line driver circuit;

a plurality of gate signal lines connected to the gate signal line driver circuit; and

a power supply line,

wherein the pixel portion comprises a plurality of pixels,

wherein each of the pixels comprises a switching transistor, an EL driving transistor, and an EL element,

wherein a gate electrode of the switching transistor is connected to the gate signal lines,

wherein one of a source region and a drain region of the switching transistor is connected to the source signal lines and the other is connected to a gate electrode of the EL driving transistor,

wherein one of a source region and a drain region of the EL driving transistor is connected to the power supply line and the other is connected to the EL element, and

a gray scale control circuit comprising;

an A/D converter for converting an analog video signal into a digital video signal and outputting the digital video signal;

a data controller for taking and processing the digital video signal, converting the digital video signal into the analog video signal, and outputting the analog video signal to the active matrix display unit;

an average gray scale calculator obtaining an average gray scale by averaging a gray scale of each of the pixels over the entire screen of one frame based on the digital video signal from the A/D converter and for outputting an average gray scale signal;

a display time rate table outputting a magnification signal for reducing a display time rate when the average gray scale exceeds a certain value in accordance with the average gray scale signal; and

a timing signal generator generating an erase start signal for erasing the analog video signal written to each of the pixels in accordance with the magnification signal,

wherein the analog video signal written to each of the pixels is erased by supplying the erase start signal to the gate signal line driver circuit.

40. The display device according to claim 28, wherein the display device is incorporated into an electronic apparatus selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook computer, a game machine, a portable information terminal, and an image reproducing device.

41. A display device comprising:

means for obtaining an average gray scale of a video signal of one frame;

a display time rate table outputting a gray scale control signal for reducing a display time rate of a pixel based on the average gray scale; and

a display unit having the pixel,

wherein a gray scale of the pixel is controlled based on the gray scale control signal.

42. A display device comprising:

an average gray scale calculator obtaining an average gray scale of a video signal of one frame,

wherein a display time rate of a pixel is controlled based on the average gray scale.

43. A driving method of a display device comprising the steps of:

controlling a display time rate of a pixel depending on an average gray scale of a video signal of one frame.