Liquid crystal display device and method for driving the same

• US 20050062904A1
• Filed: 08/25/2004
• Published: 03/24/2005
• Est. Priority Date: 08/25/2003
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Shimoshikiryoh, Fumikazu
• Granted Patent: US 7,961,165 B2
• Time in Patent Office: Days
• US Class Current: 349/89
• CPC Class Codes: G09G 2300/0876 Supplementary capacities in pixels having special driving circuits and electrodes instead of being connected to common electrode or ground; Use of additional capacitively coupled compensation electrodes
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

A liquid crystal display device includes a plurality of pixels, each of which includes a liquid crystal capacitor made up of a liquid crystal layer and two electrodes to apply a voltage to the liquid crystal layer. While the device is conducting a display operation, an oscillation voltage, which oscillates a number of times within a single vertical scanning period, and a predetermined gray-scale voltage are applied to the liquid crystal capacitor of an arbitrary one of the pixels.

Claims

1. A liquid crystal display device comprising a plurality of pixels, each of which includes a liquid crystal capacitor made up of a liquid crystal layer and two electrodes to apply a voltage to the liquid crystal layer,

wherein while the device is conducting a display operation, an oscillation voltage, which oscillates a number of times within a single vertical scanning period, and a predetermined gray-scale voltage are applied to the liquid crystal capacitor of an arbitrary one of the pixels.

4. The liquid crystal display device of claim 1, wherein in each of the pixels, the two electrodes of the liquid crystal capacitor are a pixel electrode, which is provided for each said pixel, and a counter electrode, which applies a common counter voltage to all of the pixels, and

wherein the gray-scale voltage is applied to the pixel electrode and the oscillation voltage is applied to the counter electrode.

5. The liquid crystal display device claim 1, wherein each said pixel further includes a storage capacitor, and

wherein the liquid crystal capacitor includes a pixel electrode, which is provided for each said pixel, and a counter electrode, which is provided for all of the pixels in common, and

wherein the storage capacitor includes a first electrode, which is electrically connected to the pixel electrode, an insulating layer, and a second electrode, which faces the first electrode with the insulating layer interposed between the first and second electrodes, and

wherein the oscillation voltage is applied to the second electrode.

6. The liquid crystal display device of claim 5, wherein the pixels are arranged in columns and rows, and

wherein in an arbitrary vertical scanning period, the respective second electrodes of all pixels belonging to an arbitrary one of the rows are electrically connected together.

7. The liquid crystal display device of claim 6, wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row are substantially equal to each other.

8. The liquid crystal display device of claim 6, wherein the oscillation voltage includes a first oscillation voltage and a second oscillation voltage, which is different from the first oscillation voltage, and

wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row during the arbitrary vertical scanning period are either the first oscillation voltage or the second oscillation voltage.

9. The liquid crystal display device of claim 8, wherein in an arbitrary vertical scanning period, the first oscillation voltage is applied to the respective second electrodes of all pixels belonging to one of two mutually adjacent rows, and the second oscillation voltage is applied to the respective second electrodes of all pixels belonging to the other row.

10. The liquid crystal display device of claim 9, wherein the first and second oscillation voltages both have a period corresponding to two horizontal scanning periods, and have the same amplitude but a phase difference of 180 degrees.

11. The liquid crystal display device of claim 8, wherein in the arbitrary vertical scanning period, the oscillation voltage applied to the respective second electrodes of the pixels changes every m consecutive rows.

12. The liquid crystal display device of claim 11, wherein each of the periods of the oscillation voltage, which also changes every m consecutive rows, is m times as long as one horizontal scanning period and has the same amplitude.

13. The liquid crystal display device of claim 6, wherein the oscillation voltages applied to the respective second electrodes of the pixels during the arbitrary vertical scanning period are substantially equal to each other.

14. The liquid crystal display device of claim 13, wherein the oscillation voltages have a period corresponding to one horizontal scanning period.

15. The liquid crystal display device of claim 6, further comprising a TFT, which is provided for each said pixel, and a gate bus line and a source bus line, which are connected to each TFT, and

wherein the respective second electrodes of the pixels belonging to the arbitrary row are connected to the gate bus line associated with the row.

16. The liquid crystal display device of claim 6, wherein the pixels are arranged in columns and rows, and

wherein the liquid crystal display device further includes:

a TFT, which is provided for each said pixel;

a gate bus line and a source bus line, which are connected to each TFT; and

a plurality of CS bus lines, each of which connects together the respective second electrodes of pixels belonging to an associated one of the rows, and

wherein in the CS bus lines, there are an even number of electrically independent CS bus lines.

17. The liquid crystal display device of claim 6, wherein the voltage waveform of the oscillation voltage includes at least three potentials including two potentials that define maximum amplitude and another potential equal to an average potential.

18. The liquid crystal display device of claim 6, wherein supposing the storage capacitor has a capacitance CCS, the liquid crystal capacitor has a minimum capacitance CLC_min and an electro-optic characteristic of the liquid crystal layer has a threshold voltage Vth, the effective value of the oscillation voltage is at least one-tenth of, and at most equal to, Vth·

{(CCS+CLC_min)/CCS}.

19. The liquid crystal display device of claim 1, wherein the effective value of the oscillation voltage is at least one-tenth of, and at most equal to, the electro-optic threshold voltage Vth of the liquid crystal layer.

20. The liquid crystal display device of claim 1, wherein the oscillation voltage oscillates in a period that is an integral number of times as long as one horizontal scanning period.

21. The liquid crystal display device of claim 1, wherein the oscillation voltage oscillates in a period corresponding to one horizontal scanning period.

22. The liquid crystal display device of claim 1, wherein the liquid crystal display device conducts a display operation in normally black mode.

46. The liquid crystal display device of claim 7, wherein the oscillation voltage includes a first oscillation voltage and a second oscillation voltage, which is different from the first oscillation voltage, and

wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row during the arbitrary vertical scanning period are either the first oscillation voltage or the second oscillation voltage.

2. A liquid crystal display device comprising a plurality of pixels, each of which includes a liquid crystal capacitor made up of a liquid crystal layer and two electrodes to apply a voltage to the liquid crystal layer,

wherein in an arbitrary vertical scanning period, a predetermined gray-scale voltage is applied to one of the two electrodes of an arbitrary one of the pixels and an oscillation voltage, which oscillates a number of times within a single vertical scanning period, is applied to either the same electrode or the other electrode of the arbitrary pixel.

24. The liquid crystal display device of claim 2, wherein in each of the pixels, the two electrodes of the liquid crystal capacitor are a pixel electrode, which is provided for each said pixel, and a counter electrode, which applies a common counter voltage to all of the pixels, and

wherein the gray-scale voltage is applied to the pixel electrode and the oscillation voltage is applied to the counter electrode.

26. The liquid crystal display device claim 2, wherein each said pixel further includes a storage capacitor, and

wherein the liquid crystal capacitor includes a pixel electrode, which is provided for each said pixel, and a counter electrode, which is provided for all of the pixels in common, and

wherein the storage capacitor includes a first electrode, which is electrically connected to the pixel electrode, an insulating layer, and a second electrode, which faces the first electrode with the insulating layer interposed between the first and second electrodes, and

wherein the oscillation voltage is applied to the second electrode.

28. The liquid crystal display device of claim 26, wherein the pixels are arranged in columns and rows, and

wherein in an arbitrary vertical scanning period, the respective second electrodes of all pixels belonging to an arbitrary one of the rows are electrically connected together.

29. The liquid crystal display device of claim 28, wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row are substantially equal to each other.

30. The liquid crystal display device of claim 28, wherein the oscillation voltage includes a first oscillation voltage and a second oscillation voltage, which is different from the first oscillation voltage, and

wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row during the arbitrary vertical scanning period are either the first oscillation voltage or the second oscillation voltage.

34. The liquid crystal display device of claim 28, wherein the oscillation voltages applied to the respective second electrodes of the pixels during the arbitrary vertical scanning period are substantially equal to each other.

35. The liquid crystal display device of claim 34, wherein the oscillation voltages have a period corresponding to one horizontal scanning period.

36. The liquid crystal display device of claim 28, further comprising a TFT, which is provided for each said pixel, and a gate bus line and a source bus line, which are connected to each TFT, and

wherein the respective second electrodes of the pixels belonging to the arbitrary row are connected to the gate bus line associated with the row.

37. The liquid crystal display device of claim 28, wherein the pixels are arranged in columns and rows, and

wherein the liquid crystal display device further includes:

a TFT, which is provided for each said pixel;

a gate bus line and a source bus line, which are connected to each TFT; and

a plurality of CS bus lines, each of which connects together the respective second electrodes of pixels belonging to an associated one of the rows, and

wherein in the CS bus lines, there are an even number of electrically independent CS bus lines.

38. The liquid crystal display device of claim 28, wherein the voltage waveform of the oscillation voltage includes at least three potentials including two potentials that define maximum amplitude and another potential equal to an average potential.

39. The liquid crystal display device of claim 28, wherein supposing the storage capacitor has a capacitance CCS, the liquid crystal capacitor has a minimum capacitance CLC_min and an electro-optic characteristic of the liquid crystal layer has a threshold voltage Vth, the effective value of the oscillation voltage is at least one-tenth of, and at most equal to, Vth·

{(CCS+CLC_min)/CCS}.

3. A liquid crystal display device comprising:

a plurality of pixels, each of which includes a liquid crystal capacitor made up of a liquid crystal layer and two electrodes to apply a voltage to the liquid crystal layer;

a gray-scale voltage generator for generating a gray-scale voltage in accordance with a display signal;

a counter voltage generator for generating a counter voltage; and

an oscillation voltage generator for generating an oscillation voltage that oscillates a number of times within a single vertical scanning period,

wherein in an arbitrary vertical scanning period, the gray-scale voltage is applied to one of the two electrodes of an arbitrary one of the pixels, the counter voltage is applied to the other electrode of the arbitrary pixel, and the oscillation voltage is applied to either the one or the other electrode of the arbitrary pixel.

25. The liquid crystal display device of claim 3, wherein in each of the pixels, the two electrodes of the liquid crystal capacitor are a pixel electrode, which is provided for each said pixel, and a counter electrode, which applies a common counter voltage to all of the pixels, and

wherein the gray-scale voltage is applied to the pixel electrode and the oscillation voltage is applied to the counter electrode.

27. The liquid crystal display device claim 3, wherein each said pixel further includes a storage capacitor, and

wherein the liquid crystal capacitor includes a pixel electrode, which is provided for each said pixel, and a counter electrode, which is provided for all of the pixels in common, and

wherein the storage capacitor includes a first electrode, which is electrically connected to the pixel electrode, an insulating layer, and a second electrode, which faces the first electrode with the insulating layer interposed between the first and second electrodes, and

wherein the oscillation voltage is applied to the second electrode.

31. The liquid crystal display device of claim 27, wherein the pixels are arranged in columns and rows, and

wherein in an arbitrary vertical scanning period, the respective second electrodes of all pixels belonging to an arbitrary one of the rows are electrically connected together.

32. The liquid crystal display device of claim 31, wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row are substantially equal to each other.

33. The liquid crystal display device of claim 31, wherein the oscillation voltage includes a first oscillation voltage and a second oscillation voltage, which is different from the first oscillation voltage, and

wherein the oscillation voltages applied to the respective second electrodes of the pixels belonging to the arbitrary row during the arbitrary vertical scanning period are either the first oscillation voltage or the second oscillation voltage.

40. The liquid crystal display device of claim 31, wherein the oscillation voltages applied to the respective second electrodes of the pixels during the arbitrary vertical scanning period are substantially equal to each other.

41. The liquid crystal display device of claim 40, wherein the oscillation voltages have a period corresponding to one horizontal scanning period.

42. The liquid crystal display device of claim 31, further comprising a TFT, which is provided for each said pixel, and a gate bus line and a source bus line, which are connected to each TFT, and

wherein the respective second electrodes of the pixels belonging to the arbitrary row are connected to the gate bus line associated with the row.

43. The liquid crystal display device of claim 31, wherein the pixels are arranged in columns and rows, and

wherein the liquid crystal display device further includes:

a TFT, which is provided for each said pixel;

a gate bus line and a source bus line, which are connected to each TFT; and

a plurality of CS bus lines, each of which connects together the respective second electrodes of pixels belonging to an associated one of the rows, and

wherein in the CS bus lines, there are an even number of electrically independent CS bus lines.

44. The liquid crystal display device of claim 31, wherein the voltage waveform of the oscillation voltage includes at least three potentials including two potentials that define maximum amplitude and another potential equal to an average potential.

45. The liquid crystal display device of claim 31, wherein supposing the storage capacitor has a capacitance CCS, the liquid crystal capacitor has a minimum capacitance CLC_min and an electro-optic characteristic of the liquid crystal layer has a threshold voltage Vth, the effective value of the oscillation voltage is at least one-tenth of, and at most equal to, Vth·

{(CCS+CLC_min)/CCS}.

23. A method for driving a liquid crystal display device including a plurality of pixels, each of which includes a liquid crystal capacitor made up of a liquid crystal layer and two electrodes to create a potential difference in the liquid crystal layer, the method comprising the steps of:

applying an oscillation voltage, which oscillates in a period that is shorter than one vertical scanning period, to the liquid crystal capacitors of all of the pixels in an arbitrary vertical scanning period; and

applying gray-scale voltages, which are associated with the respective pixels, to the respective liquid crystal capacitors thereof while the oscillation voltage is being applied.