JP4719388B2 - Liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device driven by a multiple line simultaneous selection method (multiline addressing method: MLA method).
[0002]
[Prior art]
FIG. 4 is a block diagram illustrating a configuration example of a conventional liquid crystal display device. In the liquid crystal display device, the scanning electrodes become transparent electrode 3 _{a (hereinafter,} simply referred to as scan electrodes 3 _a.) 2 and _a transparent substrate formed, the transparent electrode 3 _{b (hereinafter} to be signal electrodes, merely the signal electrode 3 _b and referred.) and the transparent substrate 2 _b formed are superposed. The transparent substrates 2 _a and 2 _b are overlapped so that the scanning electrode 3 _a and the signal electrode 3 _b are almost orthogonal to each other. A peripheral sealing material (not shown) is provided on each side of the portion where the transparent substrates 2 _a and 2 _b overlap, and the liquid crystal is disposed in a space formed by the transparent substrates 2 _a and 2 _b and the peripheral sealing material. . In addition, _a polarizing plate (not shown) is disposed on each of the transparent substrates 2 _a and 2 _b . The scanning drive circuit 9 and the signal drive circuit 10 apply a voltage to the electrodes 3 _a and 3 _b to change the liquid crystal state of each pixel.
[0003]
Usually, when using a STN (Super-Twisted Nematic) liquid crystal, each of the scanning electrodes 3 _a is parallel to the scanning direction will give a scanning signal to the scanning electrodes 3 _a, the vertical direction of the image displayed on the liquid crystal display device It is often arranged to become. That often the scan electrodes 3 _a itself is arranged such that the vertical direction at right angles with the displayed image.
[0004]
In the transparent substrates 2 _a and 2 _b , an alignment film (not shown) is formed on the surface on which the scanning electrode 3 _a and the signal electrode 3 _b are formed. The alignment films formed on the transparent substrates 2 _a and 2 _b are each rubbed in a certain direction. FIG. 5 is an explanatory diagram of rubbing. Here is described a case of applying a rubbing on the transparent substrate 2 _a as an example, the same applies to the case where rubbing the transparent substrate 2 _b. The rubbing is performed by rubbing the transparent substrate 2 _a on which the alignment film is formed with _a rubbing cloth 280. When the rubbing cloth 280 rubs in the direction of the arrow 283 on the transparent substrate _2a , the direction is referred to as a rubbing direction. By rubbing, the liquid crystal molecules 281 in contact with the alignment film (not shown) are aligned in the rubbing direction 282. Further, as shown in FIG. 5, the liquid crystal molecules 281 are aligned so that the head of the rubbing direction rises (pretilt angle).
[0005]
FIG. 6 is an explanatory diagram illustrating an example of the rubbing direction. However, the transparent electrode is not shown in FIG. The observer side substrate rubbing direction 211 is a rubbing direction of the alignment film provided on the observer side substrate. The back substrate rubbing direction 212 is the rubbing direction of the alignment film provided on the other substrate. In order to cause twist in the direction of the liquid crystal molecules in contact with the alignment films on both substrates, the observer side substrate rubbing direction 211 and the back substrate rubbing direction 212 are directed in different directions as shown in FIG. The twist angle of the liquid crystal molecules in contact with the alignment films on both substrates is, for example, 240 °. An axis 213 shown in FIG. 6 is an axis that bisects the angle formed by the observer-side substrate rubbing direction 211 and the back substrate rubbing direction 212.
[0006]
FIG. 7 is an explanatory diagram showing the relationship between the image displayed on the liquid crystal display device and the direction of the axis 213. In the example shown in FIG. 7, the character “A” is a display image. Hereinafter, in the figure, the horizontal direction of the display image is indicated by a broken line, and the vertical direction of the display image is indicated by a dashed line. The display image is easy to see when the observer looks into the liquid crystal display device from a direction that is 90 ° away from the axis 213. Therefore, conventionally, the axis 213 and the horizontal direction 301 (the direction indicated by the broken line) of the display image are parallel to each other so that the viewer can easily observe the display image (for example, the letter “A”) from the correct direction. Had been rubbed.
[0007]
As a driving method of the liquid crystal display device illustrated in FIG. 4, a line-sequential selection method (for example, APT: Alto Pleshko Technique or improved IAPT: Improved APT), an MLA method for simultaneously selecting a plurality of scanning electrodes, or the like is used. It has been. Hereinafter, the scanning electrodes simultaneously selected by the MLA method are referred to as subgroups.
[0008]
In the MLA method, a voltage pulse voltage group (selection pulse group) applied to each scan electrode can be represented by a matrix of L rows and K columns. Hereinafter, this matrix is referred to as a selection matrix (A). L is the number of simultaneous selections. The voltage pulse voltage group is represented as a vector group orthogonal to each other. Therefore, a matrix including these vectors as elements is an orthogonal matrix. Each row vector in each matrix is orthogonal to each other. In the orthogonal matrix, each row corresponds to each line of the liquid crystal display device. For example, the element in the first row of the selection matrix (A) is applied to the first line among the L selection lines. That is, the selection pulse is applied to the first scan electrode in the order of the elements in the first column and the elements in the second column. Thus, the selection pulses corresponding to the respective columns from the first column to the Kth column are sequentially applied to the L selection lines. In addition, a frequency in which a period during which selection pulses corresponding to all columns of the selection matrix are applied to all subgroups is defined as one cycle is defined as a frame frequency.
[0009]
[Problems to be solved by the invention]
In the liquid crystal display device, the vertical length of the screen may be longer than the horizontal length. Here, the vertical direction of the screen is a direction that coincides with the vertical direction of the display image when display is performed in a normal manner, and the horizontal direction is a direction that coincides with the horizontal direction of the display image. Such elongated screen is realized by increasing the number of scanning electrodes 3 _a shown in FIG. However, increasing the scanning electrodes 3 _a, increases the duty number.
[0010]
Conventionally, in order to prevent an increase in the number of duties, when realizing a vertically long screen, each electrode is arranged so that the horizontal direction of the screen (the horizontal direction of the display image) and the scanning direction of the scanning electrodes are parallel to each other. In this case, the scanning electrodes 3 _a itself is arranged so as to be horizontal and perpendicular of the display image, the signal electrodes 3 _b itself is positioned in the vertical direction at right angles with the displayed image. FIG. 8 is a block diagram showing a configuration example of such a liquid crystal display device. A direction 301 (a direction indicated by a broken line) in FIG. 8 is a horizontal direction of the display screen. The direction 301 is parallel to the scanning direction of the scanning electrodes 3 _a, forms a respective scan electrodes 3 _a itself perpendicular. A direction 302 (a direction indicated by an alternate long and short dash line) is a vertical direction of the display screen, and this direction 302 is perpendicular to each signal electrode _3b itself. In such a liquid crystal display device, if L is the number of simultaneous selections, the selection matrix is represented as a matrix of K rows and L columns.
[0011]
Also in the liquid crystal display device shown in FIG. 8, the rubbing is performed so that the axis 213 and the horizontal direction 301 of the display image are parallel to each other. That is, the shaft 213, and the scanning direction of the scanning electrodes 3 _a were rubbed in parallel. However, when such rubbing is performed, streaks appear on the display screen in a liquid crystal display device driven by the MLA method. The streaks occur along the scan electrodes at both ends of each subgroup and appear in the subgroup period. Therefore, it appears as the scanning electrodes 3 _a parallel streaks. Note that such a streak does not occur in a driving method in which scanning electrodes are selected one by one, such as APT and IAPT.
[0012]
An object of the present invention is to provide a liquid crystal display device in which the electrodes are arranged so that the scanning direction of the scanning electrodes and the horizontal direction of the display image are parallel, and no streaks are generated even when driven by the MLA method.
[0013]
[Means for Solving the Problems]
A liquid crystal display device according to the present invention includes a substrate provided with a plurality of scan electrodes, a scan electrode side alignment film, a substrate provided with a plurality of signal electrodes, a signal electrode side alignment film, a scan electrode side alignment film, A liquid crystal layer disposed between the signal electrode side alignment film and a plurality of scanning electrodes selected as a subgroup at a time and driving the liquid crystal layer, The scanning electrode is arranged so that the scanning direction of the scanning electrode is substantially parallel to the horizontal direction of the display image, and the boundary between adjacent subgroups is substantially orthogonal to the horizontal direction of the display image. In the alignment film and the signal electrode side alignment film, the direction of the axis that bisects the angle formed by the alignment direction of the scan electrode side alignment film and the alignment direction of the signal electrode side alignment film is 30 to 150 ° with respect to the scan direction of the scan electrode . Or an angle of 210-330 ° It is arranged so that it may form.
[0014]
If Hodokose rubbing as their, when driven with a frame frequency 80Hz or more, can prevent the occurrence of streaks.
[0015]
In addition, the scan electrode side alignment film and the signal electrode side alignment film have an axis direction that bisects the angle formed by the alignment direction of the scan electrode side alignment film and the alignment direction of the signal electrode side alignment film. And 45-135 [deg.] Or 225-315 [deg.]. If rubbing is performed in such a manner, generation of streaks can be prevented even when the frame frequency is lowered to 60 Hz.
Further, the length in the vertical direction of the screen may be longer than the length in the horizontal direction of the screen.
[0016]
The alignment film is, for example, a rubbing alignment film.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a liquid crystal display device used in this embodiment. Scan electrode _{3 a} is formed on the transparent substrate _{2 a,} the signal electrode _{3 b} is formed on the transparent electrode _{2 b.}
Each scanning electrode 3 _a is arranged so that the scanning direction of the scanning electrode 3 _a and the horizontal direction 301 (direction indicated by a broken line) of the display image are parallel to each other. Accordingly, the scanning electrodes 3 _a itself forms a horizontal 301 at right angles with the display image, the signal electrodes 3 _b itself forms a vertical direction 302 and (the direction indicated by a dashed line) perpendicular of the displayed image.
[0018]
On the surface scanning electrodes 3 _a of the transparent substrate 2 _a is present, (not shown.) Scan electrode side orientation film is formed, on the surface there is a signal electrode 3 _b of the transparent substrate 2 _b, the signal electrode side An alignment film (not shown) is formed. Each of the scanning electrode side alignment film and the signal electrode side alignment film is provided with alignment means. In this configuration example, a rubbing alignment film is used as the alignment film. At this time, the substrate rubbing direction 211 on the observer side and the rubbing direction 212 on the back substrate are directed in different directions, and rubbing is performed so that the liquid crystal molecules in contact with the alignment films of both the substrates 2 _a and 2 _b are twisted. The The twist angle of the liquid crystal molecules is, for example, 240 °. Further, in the rubbing, the direction of the axis 213 that bisects the angle formed by the observer side substrate rubbing direction 211 and the back substrate rubbing direction 212 is 30 to 150 ° or 210 to 330 with the scanning direction of the scanning electrode 3 _a. It is given to make a °. In particular, the shaft 213, is preferably subjected to rubbing so as to form a scanning electrode _{3 a} in the scanning direction and 45 to 135 °, or two hundred and twenty-five to three hundred fifteen °. In Figure 1, an example of a case where the direction of the axis 213, the scanning direction of the scanning electrodes 3 _a forms a 90 °.
[0019]
In the present example shows a case where the transparent substrate 2 _b are disposed on the viewer's side, both of the transparent substrate 2 _a, 2 _b may be disposed on the viewer's side. Therefore, the rubbing direction of the alignment film on the scan electrode side and the rubbing direction of the alignment film on the signal electrode side may be either the observer side substrate rubbing direction 211 or the back substrate rubbing direction 212.
[0020]
In addition, as a liquid crystal alignment means, there is a method of aligning liquid crystal without rubbing, such as photo-alignment and oblique vapor deposition. In this case, although not generally called a rubbing direction, the direction in which the liquid crystal molecules are raised (pretilt) is defined as the alignment direction. Therefore, the present invention can be applied even when a method such as photo-alignment or oblique vapor deposition is used in addition to rubbing alignment. Hereinafter, the case of rubbing alignment will be described.
[0021]
The transparent substrates 2 _a and 2 _b are overlapped so that the scanning electrode 3 _a and the signal electrode 3 _b are almost orthogonal to each other. A peripheral sealing material (not shown) is provided on each side where the transparent substrates 2 _a and 2 _b overlap, and a liquid crystal is disposed in a space formed by the transparent substrates 2 _a and 2 _b and the peripheral sealing material. In addition, _a polarizing plate (not shown) is disposed on each of the transparent substrates 2 _a and 2 _b .
[0022]
The liquid crystal display device shown in FIG. 1 is driven by the MLA method. Therefore, the scanning electrode 3 _a is selected plurality of collectively, a predetermined voltage is applied between the selection period. FIG. 2 is a block diagram illustrating a configuration example of a liquid crystal driving device that drives a liquid crystal display device by the MLA method. In FIG. 2, the liquid crystal driving device 20 inputs image data 100 and a control signal 101, outputs a data signal 104 to the signal driving circuit 10, and performs necessary control for the signal driving circuit 10 and the scanning driving circuit 9. The signal 108 is output. The control signal 101 includes a dot clock signal, a vertical synchronization signal, a horizontal synchronization signal, a data enable signal indicating a valid period of image data, and the like.
The liquid crystal drive device 20 is also provided with a scan electrode selection pattern generator that supplies a scan electrode selection pattern signal based on an orthogonal matrix to the scan drive circuit 9, but this is not shown in FIG.
[0023]
Image data 100 having a gradation signal input to the liquid crystal driving device 20 is input to the gradation processing circuit 11. The gradation processing circuit 11 converts the input image data 100 into gradation data 102 indicating the gradation level for each display frame and writes it into the frame memory 12. The frame memory 12 holds the written gradation data until it is read a plurality of times for simultaneous selection driving (MLA driving) of a plurality of lines.
[0024]
The MLA arithmetic circuit 13 reads the gradation data 103 from the frame memory 12, performs a multiple line simultaneous selection arithmetic process, and generates a voltage pattern applied to the signal electrode _3b . The voltage pattern is output as a data signal 104 to the signal driving circuit 10. A scan electrode selection pattern signal from the scan electrode selection pattern generator is output to the scan drive circuit 9. The timing control circuit 15 generates control signals 105, 106, and 107 necessary for each circuit block and a control signal 108 for the signal driving circuit 10 and the scanning driving circuit 9.
The signal driving circuit 10 applies a liquid crystal driving voltage to the signal electrode 3 _b according to the data signal 104. The scan driving circuit 9 applies a predetermined voltage to the scanning electrode 3 _a in accordance with the scanning electrode selection pattern signals.
[0025]
As the horizontal scan electrodes 3 _a of the scanning direction and the display image becomes parallel in terms of placing the scanning electrodes 3 _a, the direction and the scanning electrodes 3 _a scanning direction angle between the axis 213 (hereinafter, theta ) Was changed, and the occurrence of muscles was confirmed. The confirmation result is shown below.
[0026]
The liquid crystal display device was driven by the MLA method by setting the duty ratio to 1/164 and the number of scanning electrodes to be selected simultaneously to four. Further, the voltage polarity reversal period was set to 13, and driving was performed by reversing the polarity of the voltage applied to the scan electrode and the signal electrode every 13 selection periods.
When the frame frequency was 80 Hz, no streaks occurred in the liquid crystal display device in which θ ≧ 30 °. Further, generation of streaks was confirmed in the liquid crystal display device in which θ <30 °.
Further, when the frame frequency was 60 Hz, no streaks occurred in the liquid crystal display device in which θ ≧ 45 °. Further, generation of streaks was confirmed in the liquid crystal display device in which θ <45 °.
Even if the scanning direction of the scanning electrodes 3 _a Conversely, there was no change in the check result. That is, the scanning electrodes 3 _a, be scanned from left to right, be scanned from right to left, occurrence of streaks did not change.
[0027]
As shown in FIG. 3A, the axis 213 has a line-symmetric positional relationship between θ = x ° and θ = 180 ° -x °. Further, as shown in FIG. 3B, the axes 213 in the case of θ = 360 ° -x ° and in the case of θ = 180 ° + x ° are respectively in the case of θ = x ° and θ = 180 ° -x °. The axis 213 is in a line-symmetrical positional relationship.
Therefore, if streaks occur when θ <30 °, streaks also occur when 150 ° <θ <210 ° and θ> 330 °, and 30 ° ≦ θ ≦ 150 ° and 210 ° ≦ θ. In the range of ≦ 330 °, no streak occurs. Similarly, if streaks occur when θ <45 °, streaks also occur when 135 ° <θ <225 ° and θ> 315 °, and 45 ° ≦ θ ≦ 135 ° and 225 ° ≦ In the range of θ ≦ 315 °, no streak occurs.
[0028]
Therefore, when the frame frequency is 80 Hz, generation of streaks can be prevented by rubbing so that 30 ° ≦ θ ≦ 150 ° or 210 ° ≦ θ ≦ 330 °. Further, when the frame frequency is 60 Hz, the generation of streaks can be prevented by performing rubbing so that 45 ° ≦ θ ≦ 135 ° or 225 ° ≦ θ ≦ 315 °.
[0029]
Also, it can be seen from this result that the range of θ that can prevent the generation of streaks narrows as the frame frequency decreases. If rubbing is performed so that 30 ° ≦ θ ≦ 150 ° or 210 ° ≦ θ ≦ 330 °, no streaking occurs even when the frame frequency is driven to 80 Hz or higher. When the frame frequency is lowered to 60 Hz, rubbing is preferably performed so that 45 ° ≦ θ ≦ 135 ° or 225 ° ≦ θ ≦ 315 °.
[0030]
According to the present invention, even when the horizontal 301 of the scanning electrodes 3 _a of the scanning direction and the display image is to place the respective scanning electrodes 3 _a so as to be parallel, the viewer-side substrate rubbing direction 211 back substrate the direction of the axis 213 which bisects the angle between the rubbing direction 212 and the scanning direction of the scanning electrodes 3 _a is because rubbing to form a predetermined angle range, it is possible to prevent the occurrence of streaks, display quality A good screen can be realized.
[0031]
Further, the behavior of the liquid crystal of the pixel corresponding to one scan electrode was compared between θ = 90 ° and θ = 0 °. Here, when a voltage having the same drive waveform is applied to one scan electrode and the adjacent scan electrode, the transmitted light intensity of the pixel corresponding to the one scan electrode and the voltage at which the liquid crystal state of the pixel transitions ( Hereinafter, this is referred to as _Vth ). In this confirmation, black is displayed when the drive waveform is applied, and white is displayed when the drive waveform is not applied.
[0032]
For theta = 90 °, check the V _th and the transmitted light intensity for the following three aspects were compared V _th and the transmitted light intensity of each aspect. As a first aspect, the same drive waveform is applied in the same phase to one scan electrode and the adjacent scan electrode. As a second aspect, the same drive waveform is applied to the adjacent scan electrode one selection period earlier than the drive waveform is applied to one scan electrode. That is, the same drive waveform was applied by selecting the next scan electrode and then one scan electrode in this order. As a third aspect, a drive waveform is applied to one scan electrode, and the same drive waveform is applied to an adjacent scan electrode with a delay of one selection period. That is, the same drive waveform was applied by selecting one scan electrode and then the next scan electrode in this order. Regarding the first to third aspects, when comparing the magnitudes of _Vth and transmitted light intensity with respect to one scanning electrode, there is a change in _Vth and transmitted light intensity in each of the first, second, and third aspects. There wasn't.
[0033]
Similarly, when θ = 0 °, _Vth and transmitted light intensity were compared for the first, second, and third embodiments. V _th is the largest V _th in the second embodiment, the following, a first embodiment, V _th in the order of the third embodiment was smaller. Also, the transmitted light intensity was the highest in the second mode, and was decreased in the order of the first mode and the third mode.
[0034]
If θ = 0 °, the transmitted light intensity of the pixels corresponding to the scan electrodes located at the boundary of the subgroup differs from the transmitted light intensity of the pixels corresponding to the other scan electrodes in the subgroup. For example, in the first line of the subgroup that is selected simultaneously with four lines, the adjacent line has been selected immediately before, so that the transmitted light intensity corresponding to the second mode is exhibited. The second line and the third line exhibit the transmitted light intensity corresponding to the first mode because the adjacent lines are selected at the same time. The fourth line exhibits the transmitted light intensity corresponding to the third aspect because the next line is selected next. In the conventional liquid crystal display device, since the transmitted light intensity of the pixels in the subgroup is different as described above, it is recognized that the observer has a streak.
[0035]
On the other hand, in the case of θ = 90 °, the same transmitted light intensity was exhibited regardless of whether or not adjacent scanning electrodes were simultaneously selected. Accordingly, the pixels corresponding to the scanning electrodes located at the boundary of the subgroup also show the same transmitted light intensity as the other pixels in the subgroup, and thus are not recognized as a streak by the observer. In the liquid crystal display device according to the present invention, the angle corresponding to each scanning electrode in the sub-group exhibits the same transmitted light intensity so that θ is an angle within a predetermined range, so that a streak is recognized. There is no.
[0036]
In addition, there is a method in which a part of lines simultaneously selected in the MLA method is a dummy line that is not actually displayed. By providing the dummy line, the number of levels of the voltage applied to the signal electrode can be reduced. Generation of streaks can also be prevented when such MLA driving is performed. For example, even if driving is performed by setting the number of simultaneously selected lines to 3 and providing one dummy line, generation of streaks can be prevented.
[0037]
【The invention's effect】
According to the present invention, the generation of muscles can be prevented. Further, even when a vertically long screen is used, the generation of streaks can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a liquid crystal display device according to the present invention.
FIG. 2 is a block diagram illustrating a configuration example of a liquid crystal driving device.
FIG. 3 is an explanatory diagram showing the orientation of an axis and a scanning electrode in the scanning direction.
FIG. 4 is a block diagram illustrating a configuration example of a conventional liquid crystal display device.
FIG. 5 is an explanatory diagram of rubbing.
FIG. 6 is an explanatory diagram showing an example of a rubbing direction.
FIG. 7 is an explanatory diagram showing a relationship between an image and a direction of an axis in a conventional example.
FIG. 8 is a block diagram showing a conventional liquid crystal display device.
[Explanation of symbols]
2 _a , 2 _b transparent substrate 3 _a , 3 _b transparent electrode 9 scanning drive circuit 10 signal drive circuit 211 observer side substrate rubbing direction 212 rear substrate rubbing direction 213 axis 301 horizontal direction of display image 302 vertical direction of display image

Claims (4)

Between a substrate provided with a plurality of scan electrodes, a scan electrode side alignment film, a substrate provided with a plurality of signal electrodes, a signal electrode side alignment film, and between the scan electrode side alignment film and the signal electrode side alignment film In the liquid crystal display device, the plurality of scan electrodes are collectively selected as a subgroup and the liquid crystal layer is driven.
The scanning electrode is arranged so that the scanning direction of the scanning electrode and the horizontal direction of the display image are substantially parallel,
The boundary between adjacent subgroups is made to be almost orthogonal to the horizontal direction of the display image,
In the scan electrode side alignment film and the signal electrode side alignment film, the direction of the axis that bisects the angle formed by the alignment direction of the scan electrode side alignment film and the alignment direction of the signal electrode side alignment film is 30 in the scan direction of the scan electrode. The liquid crystal display device is arranged so as to form an angle of ˜150 ° or 210-330 ° .   In the scan electrode side alignment film and the signal electrode side alignment film, the axis direction that bisects the angle formed by the alignment direction of the scan electrode side alignment film and the alignment direction of the signal electrode side alignment film is 45. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged to form an angle of ˜135 ° or 225 to 315 °. 3. The liquid crystal display device according to claim 1, wherein a vertical length of the screen is longer than a horizontal length of the screen .   The liquid crystal display device according to claim 1, wherein the alignment film is a rubbing alignment film.

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