Driving method for a liquid crystal panel

What is claimed is:

1. A method for driving a liquid crystal display device for producing a tone pattern, said display device including a plurality of signal electrodes overlapping a plurality of scanning electrodes and a plurality of display dots arranged in a matrix of rows and columns in which each display dot corresponds to the overlapping of one of the plurality of signal electrodes with one of the plurality of scanning electrodes, said method including driving each display dot into a lit or non-lit display state during each frame of an at least two frame cycle based on a scanning waveform and signal waveform being applied to the associated scanning electrode and signal electrode, respectively, and further comprising the steps of:

placing in the same display state all display dots producing the tone pattern which are associated with the same scanning electrode during one frame of the cycle; and

concurrently adjusting the scanning waveform applied to each scanning electrode during said one frame based on the tone pattern.

2. The method of claim 1, wherein the steps of claim 1 are repeated for each frame of the cycle.

3. The method of claim 1, wherein the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each cycle.

4. The method of claim 3, wherein the cycle includes a first frame and a second frame and further including applying the first voltage group to the scanning electrodes during a first portion of the first frame and a last portion of the second frame and the second voltage group during the last portion of the first frame and the first portion of the second frame.

5. The method of claim 4, further including applying the scanning waveform during an additional cycle which includes a third frame and a fourth frame wherein the second voltage group is applied to the scanning electrodes during the first portion of the third frame and the last portion of the fourth frame and th first voltage group is applied to the scanning electrodes during the last portion of the third frame and the first portion of the fourth frame.

6. The method of claim 5, wherein the cycle and additional cycles are alternately repeated.

7. The method of claim 1, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

8. The method of claim 3, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

9. The method of claim 8, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

10. The method of claim 1, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

11. The method of claim 10, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

12. The method of claim 11, wherein the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each cycle and which are polarity inversions of each other and wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

13. The method of claim 2, wherein the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each cycle.

14. The method of claim 13, wherein the cycle includes a first frame and a second frame and further including applying the first voltage group to the scanning electrodes during the first portion of the first frame and the last portion of the second frame and the second voltage group during the last portion of the first frame and the first portion of the second frame.

15. The method of claim 14, further including applying the scanning waveform during an additional cycle which includes a third frame and a fourth frame wherein the second voltage group is applied to the scanning electrodes during the first portion of the third frame and the last portion of the fourth frame and the first voltage group is applied to the scanning electrodes during the last portion of the third frame and the first portion of the fourth frame.

16. The method of claim 15, wherein the cycle and additional cycles are alternately repeated.

17. The method of claim 2, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

18. The method of claim 4, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

19. The method of claim 18, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

20. The method of claim 5, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

21. The method of claim 20, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

22. The method of claim 6, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

23. The method of claim 22, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

24. The method of claim 3, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

25. The method of claim 24, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

26. The method of claim 25, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

27. The method of claim 4, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

28. The method of claim 27, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

29. The method of claim 28, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

30. The method of claim 5, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

F=(Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

31. The method of claim 30, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

32. The method of claim 31, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

33. The method of claim 3, wherein the first voltage group is a polarity inversion of the second voltage group.

34. The method of claim 7, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

35. The method of claim 6, wherein the first voltage group is a polarity inversion of the second voltage group.

36. The method of claim 7, wherein the first voltage group is a polarity inversion of the second voltage group.

37. The method of claim 9, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

38. The method of claim 37, wherein the first voltage group is a polarity inversion of the second voltage group.

39. The method of claim 16, wherein the first voltage group is a polarity inversion of the second voltage group.

40. The method of claim 39, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

41. The method of claim 23, wherein the first voltage group is a polarity inversion of the second voltage group.

42. The method of claim 41, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

43. The method of claim 32, wherein the first voltage group is a polarity inversion of the second voltage group.

44. The method of claim 43, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

45. A method for driving a liquid crystal display device for producing a tone pattern, said display device including a plurality of signal electrodes overlapping a plurality of scanning electrodes and a plurality of display dots arranged in a matrix of rows and columns in which each display dot corresponds to the overlapping of one of the plurality of signal electrodes with one of the plurality of scanning electrodes, said method including driving each display dot into a lit or non-lit display state during each frame of an at least two frame cycle based on a scanning waveform and signal waveform being applied to the associated scanning electrode and signal electrode, respectively, and further comprising the steps of:

placing all display dots which produce the tone pattern in the lit state for the same duration of time during the cycle; and

concurrently adjusting the scanning waveform applied to each scanning electrode during the cycle based on the tone pattern;

wherein different groups of display dots which produce the tone pattern are placed in the non-lit display state at different portions of the cycle.

46. The method of claim 45, wherein the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each cycle.

47. The method of claim 46, wherein the cycle includes a first frame and a second frame and further including applying the first voltage group to the scanning electrodes during a first portion of the first frame and a last portion of the second frame and the second voltage group during the last portion of the first frame and the first portion of the second frame.

48. The method of claim 47, further including applying the scanning waveform during an additional cycle which includes a third frame and a fourth frame wherein the second voltage group is applied to the scanning electrodes during the first portion of the third frame and the last portion of the fourth frame and the first voltage group is applied to the scanning electrodes during the last portion of the third frame and the first portion o the fourth frame.

49. The method of claim 48, wherein the cycle and additional cycles ar alternately repeated.

50. The method of claim 45, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

51. The method of claim 50, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

52. The method of claim 45, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

53. The method of claim 52, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

54. The method of claim 53, wherein the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each cycle and which are polarity inversions of each other and wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

55. The method of claim 47, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

56. The method of claim 55, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

57. The method of claim 48, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

58. The method of claim 57, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

59. The method of claim 49, wherein the step of adjusting occurs when the voltage of the signal waveform changes.

60. The method of claim 59, wherein the step of adjusting also occurs when the scanning waveform changes from one voltage group to another voltage group.

61. The method of claim 46, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i+1 lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

62. The method of claim 61, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

63. The method of claim 62, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

64. The method of claim 47, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

F=(Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

65. The method of claim 64, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

66. The method of claim 65, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

67. The method of claim 48, wherein the step of adjusting is based on a value selected from a pair of parameters I and F, where:

I=Y.sub.i lit -Y.sub.i+1 lit

F=(Y.sub.i lit +Y.sub.i+1 lit)-X

where

Y.sub.i lit is the number of display dots currently lit on a selected scanning electrode

Y.sub.i+1 lit is the number of display dots to be lit on the next selected scanning electrode

X is the total number of signal electrodes.

68. The method of claim 67, wherein the step of adjusting includes adding compensating voltages to the scanning waveform, the compensating voltages being based on the magnitude and polarity of the value selected from the pair of parameters I and F.

69. The method of claim 68, wherein the value F is selected when the scanning waveform changes from one voltage group to another voltage group and the value of I is selected when the voltage of the signal waveform changes.

70. The method of claim 46, wherein the first voltage group is a polarity inversion of the second voltage group.

71. The method of claim 50, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

72. The method of claim 49, wherein the first voltage group is a polarity inversion of the second voltage group.

73. The method of claim 50, wherein the first voltage group is a polarity inversion of the second voltage group.

74. The method of claim 51, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

75. The method of claim 74, wherein the first voltage group is a polarity inversion of the second voltage group.

76. The method of claim 60, wherein the first voltage group is a polarity inversion of the second voltage group.

77. The method of claim 76, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

78. The method of claim 69, wherein the first voltage group is a polarity inversion of the second voltage group.

79. The method of claim 78, wherein the step of adjusting occurs when the voltage of the signal waveform changes from a lit to a non-lit level or from a non-lit to a lit level.

80. The method of claim 47, wherein the first portion and last portion of each frame are equal to half the frame.

81. The method of claim 48, wherein the first portion and last portion of each frame are equal to half the frame.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates generally to a driving method for a liquid crystal panel, and more particularly to a driving method for producing a substantially uniform tone pattern.

A conventional driving method, commonly referred to as the voltage averaging method, is generally employed for driving a matrix type liquid crystal panel. The voltage averaging method successively applies a selection voltage to each scanning electrode during each frame of a cycle (i.e. period). At the same time that a selection voltage is applied to a scanning electrode (i.e. a selected scanning electrode), a lighting voltage or a non-lighting voltage is applied to each of the signal electrodes. The selection of each scanning electrode and concurrent application of a lighting voltage or non-lighting voltage to each signal electrodes is repeated each frame. A display of lit and unlit dots (pixels) forming a desired pattern on the liquid crystal panel is produced. By providing two or more frames per period and a method for changing which of the dots is to be lit and unlit during each frame, a display with a desired tone (i.e., tone pattern/display) is produced. As used herein, a tone is considered to be a shade of grey that is neither white nor black.

Conventional driving methods also typically invert the polarity of the voltage applied across the liquid crystal panel from frame to frame to prevent application of a DC voltage to the liquid crystal panel.

In another conventional driving method, hereinafter referred to as a first driving method, the display dots associated with the same scanning electrode in forming the tone pattern during each frame are in the same lit or non-lit display state (i.e. the phases of the flickering cycles of each display dot associated with each signal electrode are equalized). The lighting or non-lighting of the display dots within the tone pattern is not based on the position of the signal electrodes. In yet another conventional driving method, hereinafter referred to as the second driving method, the adjacent display dots associated with the same scanning electrode are in different display states, that is, lit and non-lit. Each display dot in the second driving method is based on a position of a signal electrode. In particular, the display states of the display dots associated with a scanning electrode are varied based on the position of the corresponding signal electrodes.

Referring now to FIGS. 1(a) and 1(b), the display contents of a liquid crystal panel for a first frame and a second frame in accordance with the first driving method are illustrated, respectively. For exemplary purposes only, the liquid crystal panel includes a plurality of scanning electrodes Y1-Y10 and a plurality of signal electrodes X1 and X10. Each display dot is associated with the intersection (i.e. overlapping) of one of the plurality of scanning electrodes with one of the plurality of signal electrodes. A symbol .largecircle. represents a non-1 a mark symbol represents a lit display dot. Scanning electrodes Y1-Y10 are selected in ascending numerical order (i.e., Y1-Y10). FIGS. 1(a) and 1(b) illustrate a square using a half tone display positioned at the center of the liquid crystal panel.

The display dots corresponding to the odd numbered scanning electrodes (Y3, Y5, Y7) are not lit during the first frame (FIG. 1a) and lit during the second frame (FIG. 1(b)). The display dots corresponding to the even numbered scanning electrodes (Y4, Y6, Y8) are lit during the first frame and not lit during the second frame. Therefore flickering of the square display is not based on whether the signal electrodes are even numbered or odd numbered since all of the signal electrodes for a particular scanning electrode are of the same phase (i.e., lit or not lit). The first driving method therefore equalizes phases of flickering cycles of display dots generated by the scanning electrodes, for each scanning electrode, without regard to position of any signal electrode.

Referring next to FIGS. 4(a) and 4(b), the display contents of a liquid crystal panel for a first frame and a second frame in accordance with the second driving method is illustrated, respectively. Similar to FIGS. 1(a) and 1(b), the liquid crystal panel includes scanning electrodes Y1-Y10 and signal electrodes X1-X10.

In FIG. 4(a), the display dots produced by the odd numbered scanning electrodes (Y3, Y5, Y7) intersecting with the odd signal electrodes (X3, X5, X7) and the display dots produced by the even numbered scanning electrodes (Y4, Y6, Y8) intersecting with the signal electrodes (X4, X6, X8) are not lit in the first frame - and are lit in the second frame. Alternatively, FIG. 4(a) can be viewed as the display dots produced by the even numbered scanning electrodes (Y4, Y6,Y8) intersecting the odd numbered signal electrodes (X3, X5, X7) and the display dots produced by the odd numbered scanning electrodes (Y3, Y5, Y7) intersecting the even numbered signal electrodes (X4, X6, X8) being lit in the first frame and not lit in the second frame. Flickering of the display contents as shown in FIGS. 4(a) and 4(b) is based on the odd numbered and even numbered signal electrodes having different phases (i.e., out of phase with each other) per frame. In other words, the second driving method varies the phases of flickering cycles of the display dots generated by the scanning electrodes according to the position of the signal electrodes.

The unevenness of the display produced by the first driving method, which results in the aforementioned flicker, arises from crosstalk commonly referred to as zebra crosstalk (i.e., a zebra display pattern). Such unevenness is minimized by employing a driving method such as disclosed in Japanese Patent Application No. 63-159914. When the selected scanning electrode is successively changed, a nonuniformity in the display results. The nonuniformity is based on a parameter I, that is, the difference between the number of display dots currently lit on a selected scanning electrode (hereinafter referred to as the lighting dots) and the number of lighting dots currently lit in the scanning electrode to be selected next. That is, when the selected scanning electrode changes from the n-th scanning electrode to the n+1 th scanning electrode, and where the number of lighting dots on the n-th scanning electrode is Non and the number of lighting dots on the n+1 th scanning electrode is Mon, parameter I is equal to Non - Mon. When I is negative (-), a voltage with one or more spikes is generated on each scanning electrode. The spikes point in the side/direction of the lighting voltage. When parameter I is positive (+), a voltage with one or more spikes is generated in the non-lighting voltage direction/side based on the magnitude (i.e., absolute value) of parameter I. As can be readily appreciated, for relatively large values of parameter I which last for a relatively long period of time the level of the effective voltage applied to the display can vary significantly based on the voltage spikes. An appreciable increase in nonuniformity of the tone display results.

Referring once again to FIGS. 1(a) and 1(b), the first and second frames which are respectively represented by FIGS. 1(a) and 1(b), represents one cycle (period). The first driving method shown in FIGS. 1(a) and 1(b) requires that all of the display dots within the tone pattern associated with one of the scanning electrodes Y3-Y8 be lit or maintained not lit during each frame. A large value of parameter I results. For example, parameter I equals a value of 6 when the selected scanning electrode is changed from Y4-Y5. A relatively large nonuniform tone display is produced.

As shown in FIGS. 4(a) and 4(b), parameter I using the second driving method is minimized. For example, when the selecting scanning electrode is changed from Y4-Y5, parameter I has a value 0. Production of a nonuniform tone display is substantially avoided. More particularly, when a scanning electrode is selected the charge and discharge rates of the electric charges of the display dots associated with odd numbered signal electrodes is equalized by the charge and discharge rates of the electric charges of display dots associated with the even numbered signal electrodes.

The second driving method nevertheless produces a non-uniform tone display when used to drive a multicolor liquid crystal panel having a filter of three or more colors. Such a panel requires that the electrodes be disposed relatively close to each other. Consequently, an element providing a driving waveform to the panel must be connected to more than one signal electrode. For example, the element is connected alternately to opposite ends (i.e., upper and lower ends) of the signal electrodes to reduce the number of connections of different electrical elements to the signal electrodes. Assembly of a liquid crystal panel based on such connections to the signal electrodes contributes to a nonuniform tone display when using the second driving method.

More particularly, a driving waveform would be applied to the odd numbered signal electrodes (X1, X3, X5, X7, X9) from the top of the panel and to the even numbered signal electrodes (X2, X4, X6, X8, X10) from the bottom of the panel. Application of the driving waveforms to the upper and lower ends of the signal electrodes based on their position in the liquid crystal panel can result in higher charge and discharge rates of the display dots associated with the odd numbered signal electrodes as compared to the charge and discharge rates of the display dots associated with the even numbered signal electrodes. A difference in the charge and discharge rates between the display dots associated with the odd and even numbered signal electrodes results.

The lower charge and discharge rates of the display dots associated with even numbered signal electrodes is based on the significant level of attenuation to the driving waveform. This attenuation is based on the driving waveform being supplied to the lower end of each even numbered signal electrode as compared to the upper end of each odd numbered signal electrode. The magnitude of the driving waveform supplied to the even numbered signal electrodes is attenuated by their resistance and the impedance of other components in the panel. The driving waveform supplied to the odd numbered signal electrodes, however, is slightly, if at all, attenuated since the driving waveform need not travel along the length of the signal electrode before reaching the display dot. The substantial difference in the magnitude of the driving waveform based on the position of the signal electrode produces a relatively large difference in the charge and discharge rates of the display dots associated with the odd numbered and even numbered signal electrodes leading to a nonuniform display when using the second driving method.

In yet another method for driving a liquid crystal panel disclosed in Japanese Patent Application No. 63-159914 and commonly referred to as inversion stringing, a nonuniform tone display can occur. In this method, the polarity of the voltage applied across the liquid crystal panel is inverted when switching from one selected scanning electrode to the next selected scanning electrode. The shape of the waveform undergoing such inversion can change and is based on a parameter F. Parameter F is equal to the difference between the sum of the number of lighting dots on the current selected scanning electrode and the number of lighting dots on the next selected scanning electrode and the number of display dots on a scanning electrode (i.e., the number of signal electrodes).

When parameter F is negative (-), a rounding of the voltage waveform applied to the scanning electrode occurs based on the magnitude (i.e., absolute value) of the parameter F immediately after selection of a scanning electrode is made. When the parameter F is positive (+), one or more spikes in the voltage magnitude of the driving waveform applied to the signal electrodes occurs based on the magnitude (i.e., absolute value) of parameter F. The spikes rise in the direction (side) of the lighting voltage. The level of the effective voltage applied to the display dots due to the spikes in and rounding of the waveforms supplied to the scanning and signal electrodes can significantly vary (i.e., be greatly uneven) resulting in a nonuniform tone display.

The nonuniformity of tone display produced by the liquid crystal panel from these different driving methods leads to appreciable color degradation.

Accordingly, it is desirable to provide a driving method for a liquid crystal panel which produces a uniform tone display without appreciable color degradation. The driving method should correct for nonuniformity in the tone display produced by zebra crosstalk as well as nonuniformity produced at the time of polarity inversion of the driving waveforms.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the invention, a method for driving a liquid crystal display device for producing a substantially uniform tone pattern includes the steps of placing in the same display state all display dots which are associated with the same scanning electrode in producing the tone pattern during one frame of a cycle and concurrently adjusting the scanning waveform applied to each scanning electrode during the frame based on the tone pattern.

The method substantially eliminates the voltage disturbances which are typically in the form of voltage spikes or rounding of the driving waveforms so as to substantially eliminate any non-uniformity in the tone pattern. The placing of all display dots in the same display state and concurrent adjustment to the scanning waveform are repeated for each frame of the cycle.

The liquid crystal display device includes a plurality of signal electrodes overlapping a plurality of scanning electrodes. The plurality of display dots are arranged in a matrix of rows and columns. Each display dot corresponds to the overlapping of one of the plurality of signal electrodes with one of the plurality of scanning electrodes.

In one feature of the invention, the scanning waveform includes a first voltage group and a second voltage group which are alternately applied during each first cycle. In one embodiment of the invention the first cycle includes a first frame and a second frame. The first voltage group is applied to the scanning electrodes during the first portion of the first frame and the last portion of the second frame. The second voltage group is applied during the last portion of the first frame and the first portion of the second frame. An additional cycle which includes a third frame and a fourth frame applies the second voltage group to the scanning electrodes during the first portion of the third frame and the last portion of the fourth frame. The first voltage group is then applied to the scanning electrodes during the last portion of the third frame and the first portion of the fourth frame . The first and additional cycles are alternately applied. In accordance with one embodiment of the invention, the first and last portions of each frame are equal to one half of that frame.

In another feature of the invention, the adjustment to the scanning waveform occurs when the voltage of the signal waveform changes from a lit to non-lit or from a non-lit to lit level and when the scanning waveform changes from one voltage group to the other voltage group. The first voltage group and second voltage group of the scanning waveform are preferably polarity inversions of each other.

In yet another feature of the invention, the adjustment to the scanning waveform is based on a value selected from the pair of parameters I and F. In adjusting the scanning waveform, compensating (i.e. correcting) voltages are based on the magnitude and plurality of the value selected from the pair of parameters I and F. More particularly, the value of parameter F is selected when the scanning waveform changes from one voltage group to the other voltage group. The value of parameter I is selected when the voltage of the signal waveform changes. The correcting voltages are superposed on the driving waveform which is used to place the display dots associated with the same scanning electrode in the same display state during each frame.

In accordance with another aspect of the invention, a method for driving liquid crystal display for producing

a substantially uniform tone pattern includes the steps of placing all display dots which produce the tone pattern in the lit state for the same duration of time during the cycle; and concurrently adjusting the scanning waveform applied to each scanning electrode during the cycle based on the tone pattern; wherein different groups of display dots which produce the tone pattern are unlit at different portions of the cycle.

Accordingly, it is an object of the invention to provide an improved driving method for a liquid crystal panel which provides a substantially uniform tone display.

It is another object of the invention to provide an improved driving method for a liquid crystal panel which prevents nonuniformity from crosstalk produced by a zebra pattern display.

It is still another object of the invention to provide an improved driving method for a liquid crystal panel which prevents nonuniformity during polarity inversion of the driving waveforms.

Still other objects and advantages of the invention will, in part, be obvious and will, in part, be apparent from the specification.

The invention accordingly comprises the several steps and the relation of one or more such steps with respect to each of the others thereof, which will be exemplified in the method hereinafter disclosed, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying in which:

FIGS. 1(a) and 1(b) illustrate diagrammatically the display contents of a liquid crystal panel in accordance with a first embodiment of the invention;

FIGS. 2(a) and (b) graphically illustrate a scanning voltage waveform and a signal voltage waveform during a first cycle in accordance with the invention, respectively;

FIGS. 2(c) and 2(d) graphically illustrate a scanning voltage waveform and a signal voltage waveform during a second cycle in accordance with the respectively;

FIGS. 3(a), 3(b) and 3(c) diagrammatically illustrate the display contents of a liquid crystal panel in accordance with a second embodiment of the invention;

FIGS. 4(a) and 4(b) illustrate the display contents of a liquid crystal panel in accordance with another driving method;

FIG. 5 is a block diagram of the liquid crystal display device constructed in accordance with the present invention;

FIG. 6 is a schematic diagram of a liquid crystal unit constructed in accordance with the invention;

FIG. 7 is a timing chart for the control signal and the data signal in accordance with the present invention;

FIG. 8 is a block diagram of a compensation circuit in accordance with the present invention;

FIG. 9 is a circuit diagram of the power circuit in accordance with the present invention;

FIG. 10 is a perspective view of a liquid crystal panel;

FIGS. 11(a)-11(c) are graphs of the driving waveforms applied to a signal electrode, scanning electrode and across a display dot of th of FIG. 10, respectively; and

FIG. 12 is a partially exploded view of the waveform of FIG. 11(b).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This application is a continuation-in-part of U.S. patent application Ser. No. 07/232,750 which discloses a number of driving method for maintaining a uniform tone display. While several of the methods disclosed in the parent application are disclosed herein, those methods not disclosed are incorporated herein by reference thereto.

In accordance with a first embodiment of the invention, FIGS. 1(a) and 1(b) illustrate the display patterns of a liquid crystal panel for a first frame and a second frame, respectively. The liquid crystal panel includes a plurality of scanning electrodes Y1-Y10 and a plurality of signal electrodes X1-X10. Preferably, scanning electrodes Y1-Y10 are formed on one of a pair of substrates. The gap between the pair of substrates is filled with a liquid crystal material. Signal electrodes X1-X10 are formed on the other substrate. For exemplary purposes only, only ten (10) scanning electrodes and ten (10) signal electrodes are included in the liquid crystal panel, it being understood that the liquid crystal panel typically includes far more scanning and signal electrodes.

Those portions of the panel where scanning electrodes Y1 -Y10 and signal electrodes X1-X10 intersect with each other function as the display dots (pixels). Each display dot marked as an O is a non-lighting dot. Each display dot mark as an .largecircle. is a lighting dot. The image in FIGS. 1(a) and 1(b) is a centrally positioned, half tone display of a square. The square is surrounded by scanning electrodes Y3-Y8 and signal electrodes X3 -X8. The display dots on odd numbered scanning electrodes (Y3, Y5, Y7) are not lit during the first frame and are lit during the second frame. The display dots on even numbered scanning electrodes (Y4, Y6, Y8) are lit during the first frame but not lit during the second frame. Display dots associated with the same scanning electrode flicker in phase with each other. The foregoing driving method, which produces two frames per period, equalizes the phases of the flickering cycles of the display dots generated by the scanning electrodes at each scanning electrode without regard to the position of the signal electrodes.

In accordance with the invention, a correction voltage is superposed on the driving waveform supplied to the scanning electrodes Y1-Y10 (hereinafter referred to as the scanning voltage waveform or scanning waveform) or on the driving waveform supplied to the signal electrodes Xl to X10 (hereinafter referred to as the signal voltage waveform or signal waveform). A method for producing correction voltages is disclosed in examples 1-6 of Japanese Patent Application No. 63-159914. In the present invention, a correction voltage in the driving waveform is (i.e., a correction method) provided by supplying a constant correction non-selecting voltage rather than the uncorrected non-selecting voltage for a period of time based on parameter I.

Referring now to FIGS. 2(a) and 2(b) when parameter I is negative (-) and the polarity of the selected scanning voltage is not inverted, the correction non-selecting voltages (V4U, V1L) provided on the non-lighting voltage side of the scanning waveform (i.e., which will not cause the display dot to be lit) are supplied to each scanning electrode instead of the uncorrected non-selecting voltage for a period of time based on the absolute value of parameter I. When parameter I is positive (+), the correction non-selecting voltages (V4L, V1U), whi