JPH06258613A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element which makes a gradational display with superior reproducibility by suppressing the movement of a domain wall by improving its driving method. CONSTITUTION:When gradational information is displayed by selecting and writing the same pixel in the same frame, a plus and a minus bipolar pulse of the same type are used for at least 2nd and succeeding write waveforms. Namely, when one pixel on one scanning line is written plural times, a voltage pulse which is of the same type with a 1st write pulse, but opposite in polarity is applied precedently for 2nd and succeeding writing operation and then a write pulse is applied to write the pixel. For example, a compensating pulse 2' is applied. Once the compensating pulse 2' is applied, the domain wall moves like it expands momentarily or stably to the point of a white domain C'' as shown by an arrow. This movement causes no substantial unnecessary increase of a black domain (unnecessary decrease of a white domain) even when a next pulse is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a computer terminal,
The present invention relates to a liquid crystal display device used for a display device used in a television receiver, a word processor, a typewriter, a light valve of a projector, a viewfinder of a video camera recorder, and the like.

[0002]

2. Description of the Related Art Known liquid crystal display elements include those using twisted nematic (TN) liquid crystals, guest-host type ones, and those using smectic (Sm) liquid crystals.

These liquid crystals are arranged between a pair of substrates, and the light transmittance changes according to the applied voltage. Therefore, the applied electric field strength varies depending on the substrate distance, that is, the thickness of the liquid crystal layer.

Clark and Lagerwol
(Lagerwall) is Applied Physi
cs Letters Vol. 36, No. 11 (1980)
Published June 1, 2012) 899-901, JP-A-56-1
07216, U.S. Pat. No. 4,367,924
In detailed documents, U.S. Pat. No. 4,563,059, etc.
Surface-stabilized ferroelectric liquid crystal (Surface-stabil)
sized ferroelectric liquid
 Bistable ferroelectric liquid crystal device by
Revealed. This bistable ferroelectric liquid crystal device
Chiral smectic C phase (SmC *), H phase
(SmH *) Shape of helical arrangement structure of liquid crystal molecules in etc.
Pair of groups set at intervals small enough to control
A liquid crystal is placed between the plates and organized by multiple liquid crystal molecules.
Realized by arranging vertical molecular layers arranged in one direction
Was done.

Further, such a ferroelectric liquid crystal (FLC)
For a display element using, US Pat. No. 4,639,
No. 089, U.S. Pat. No. 4,655,561, and U.S. Pat. No. 4,681,404, the two inner surfaces are kept with a cell gap of about 1 to 3 μm. It is known that a ferroelectric liquid crystal is injected into a liquid crystal cell formed by facing glass substrates on which transparent electrodes are formed and subjected to an alignment treatment.

The characteristics of the above-mentioned display device using the ferroelectric liquid crystal are that the ferroelectric liquid crystal has spontaneous polarization so that the coupling force between the external electric field and the spontaneous polarization can be used for switching, and that the length of the ferroelectric liquid crystal molecule is long. The axial direction has a one-to-one correspondence with the polarization direction of the spontaneous polarization, so that switching can be performed depending on the polarity of the external electric field. That is, in the state of the chiral smectic phase, one of the first optical stable state and the second optical stable state is taken in response to the applied electric field, and when the electric field is not applied, the state is changed. It has a property of maintaining, that is, bistability, and has a rapid response to a change in an electric field, and is expected to be widely used in the fields of high-speed and memory type display devices and the like.

As described above, since the ferroelectric liquid crystal is generally a chiral smectic liquid crystal (SmC *, SmH *), the long axis of the liquid crystal molecules is twisted in the bulk state. Twisting of the long axis of the liquid crystal molecule can be eliminated by putting it in the cell having the cell gap of the second position (P213-P234 N.A. CLARK).
et al, MCLC, 1983, Vol 94).

A liquid crystal display device having a display panel formed of such a ferroelectric liquid crystal element is obtained by using a multiplexing driving method described in, for example, US Pat. No. 4,655,561 to Kamibe et al. An image can be formed on the display screen of large-capacity pixels. The liquid crystal display device described above can be used for display screens of word processors, personal computers, micro printers, televisions and the like.

The ferroelectric liquid crystal element has two stable states as a light transmitting state and a light blocking state and is mainly used as a binary (white / black) display element, but it is also capable of multi-value display, that is, halftone display. One of the halftone display methods is to create an intermediate light transmission state by controlling the area ratio of bistable states in a pixel. Hereinafter, this method (area modulation method) will be described in detail.

FIG. 1 is a diagram schematically showing the relationship between the switching pulse amplitude and the transmittance of a ferroelectric liquid crystal device. A cell (device) that was initially in a completely light-blocking (black) state has a single polarity of one polarity. 6 is a graph in which the amount of transmitted light I after applying a pulse is plotted as a function of the amplitude V of a single shot pulse. When the pulse amplitude is less than or equal to the threshold value V _th (V <V _th ), the amount of transmitted light does not change, and the transmission state after the pulse application is the state before the application as shown in FIG. 2 (b). Does not change. When the pulse amplitude exceeds the threshold value (V _th <V <V _sat ), a part of the pixel transits to the other stable state, that is, the light transmission state shown in FIG. 7C, and shows an intermediate amount of transmitted light as a whole. When the pulse amplitude further increases and becomes equal to or higher than the saturation value V _sat (V _sat <V), all the pixels are in the light transmitting state as shown in FIG. That is, in the area modulation method, the voltage is pulse amplitude V is V _th <V <V
_The halftone is displayed by controlling to _sat .

However, according to such a simple driving method, since the relationship between the voltage and the amount of transmitted light in FIG. 1 also depends on the cell thickness and the temperature, if there is a cell thickness distribution or a temperature distribution in the display panel, There is a problem that different gradation levels are displayed for the applied pulse of the same voltage amplitude.

FIG. 3 is a diagram for explaining this.
2 is a graph showing the relationship between the voltage amplitude V and the transmitted light amount I as in FIG. 1, but shows two curves, a curve H and a curve L, which respectively represent the relationships at different temperatures, that is, at high temperature and low temperature. That is, in a display (display element) having a large display size, it is not uncommon for temperature distribution to occur in the same pulse (display section). Therefore, even if an attempt is made to display a halftone with a certain voltage V _ap , the temperature distribution shown in FIG. As shown, the halftone level varies over the range from I ₁ to I ₂ , and a uniform display cannot be obtained.

The inventor found that 19
U.S. application no. It is a "4-pulse method" filed as 681,993. This driving method, as shown in FIGS. 4 and 5, includes a plurality of pulses (A, B, and B in the figure) for the low threshold portion and the high threshold portion on the same scanning line in the pulse.
C and D) are finally applied to obtain the same inversion area ((D) in the figure).

The present inventors input different scanning signals to a plurality of scanning signal lines at the same time and select them to form a distribution of electric field intensity across a plurality of scanning lines to display a gradation. (Hereinafter referred to as the pixel shift method) in U.S. application No. Filed as No. 984,694.

The outline of the pixel shift method will be described below.

The liquid crystal cell that can be used is one in which the threshold value within one pixel has a distribution, as shown in an example in FIG. In the cell shown in FIG. 6, the FLC layer 55 between the electrodes is
Since the layer thickness of is changed, the switching threshold of FLC also has a distribution. When the voltage applied to such a pixel is increased, switching is performed in order from the portion having the smallest cell thickness.

This state is shown in FIG. 7 (a). Figure 7
In (a), T ₁ , T ₂ , and T ₃ indicate the temperatures of the observed portion in the panel. The switching threshold voltage of the FLC decreases as the temperature increases, and the relationship between the applied voltage and the light transmittance at the above three temperatures is shown by three curves.

Although there are other causes of the threshold value fluctuation than the temperature change, the mode of the present invention will be described mainly by using the temperature change for convenience of explanation.

As can be seen from FIG. 7A, when the entire pixel is first reset to the dark state and a voltage of V _i is applied to the pixel at the temperature T ₁ , the transmittance of X% can be obtained.
When the temperature rises to T ₂ or T ₃ , when the same voltage of V _i is applied to the pixel, the transmittance becomes 100%, and the gradation display cannot be performed properly. Figure 7 (c)
Shows the inversion state of the pixel after writing at each temperature. Under such a condition, the written gradation information is lost due to the temperature change, so that the application range as a display element is extremely limited.

Therefore, as shown in FIG. 7D, by displaying the information of one pixel over the two scanning signal lines S1 and S2, it is possible to perform stable gradation display against temperature fluctuation. Become.

The driving method will be described in detail below.

Prepare a ferroelectric liquid crystal cell having a continuous threshold distribution in a pixel: Use a liquid crystal cell having a continuous cell thickness distribution in the pixel as shown in FIG. You can In addition, the applicant of the present invention has disclosed in Japanese Patent Laid-Open No. 63-186
A configuration having a potential gradient in the pixel or a configuration having a capacitance gradient as proposed in Japanese Patent No. 215 may be used.
In any case, by continuously distributing the threshold values in the pixel, the region (domain) corresponding to the bright state and the region (domain) corresponding to the dark state can be mixed in the pixel, and the domain of these domains can be mixed. The area ratio enables gradation display.

This method can be used even when the light quantity is modulated stepwise (for example, 16 gradations), but continuous light quantity change is necessary for analog gradation display.

Selecting two scanning signal lines at the same time: This operation will be described with reference to FIG. FIG. 8A shows
7 shows the transmittance-applied voltage characteristics when the pixels on two scanning signal lines are grouped together. In FIG. 8A, the transmittance of 0% to 100% is set as the display area of the pixel B on the scanning line 2,
The transmittance of 100% to 200% is shown as the display area of the pixel A on the scanning signal line 1. That is, since one scanning signal line constitutes one pixel, when two lines are simultaneously scanned, the transmittance is 200% when both the pixel A and the pixel B are in the light transmitting state. Here, two scanning signal lines are simultaneously selected for one gradation information, but an area having an area of one pixel is allocated to display one gradation information. This will be described with reference to FIG.

At the temperature T ₁ , the inputted gradation information is written in a range corresponding to 0% when the applied voltage V ₀ and ₁₀₀ % when the applied voltage V 100. As can be seen from the figure, at the temperature T ₁ , this range (pixel region) is entirely on the scanning signal line 2 (see the shaded portion in FIG. 8B). However, when the temperature rises from T ₁ to T ₂ , the threshold voltage of the liquid crystal drops,
When the same voltage is applied to the pixel, a region larger than that at the temperature T ₁ is inverted in the pixel.

In order to correct this, the pixel area at the temperature T ₂ is set across the scanning signal line 1 and the scanning signal line 2 (the shaded portion showing the case of the temperature T in FIG. 8B). .

Next, when the temperature further rises to T ₃ , the applied voltage is changed from V _{0 to} V _100, and the pixel region to be drawn is set only on the scanning signal line 1 (FIG. 8).
The shaded portion showing the case of the temperature T _{3 in} (b)).

As described above, by setting the pixel regions for gradation display depending on the temperature so as to be shifted on the two scanning signal lines, it is possible to maintain correct gradation display in the temperature range of T ₁ to T _3. become.

It is assumed that the scanning signals applied to the two scanning signal lines selected at the same time are different from each other: As described above, the threshold variation of the liquid crystal inversion due to the temperature change is 2
In order to compensate by simultaneously selecting two scanning signal lines, the scanning signals applied to the two selected scanning signal lines must be different from each other. This point will be described with reference to FIG. 7.

The scanning signals applied to the scanning signal lines 1 and 2 are set so that the thresholds of the pixels B on the scanning signal line 2 and the pixels A on the scanning signal line 1 continuously change. In FIG. 7B, the transmittance-voltage curve when the temperature is T ₁ indicates that the transmittance is displayed up to 100% in the region on the scanning signal line 2, and then 200% is scanned signal line. 1 is displayed in the upper area. In this way, the transmittance-voltage curve needs to be set continuously from the pixel B to the pixel A and with an equal gradient.

Therefore, as shown in FIG. 9, the scanning signal line 1
The cell shapes of the upper pixel A and the pixel B on the scanning signal line 2 (see FIG.
Even if (b) is set to be equal, substantially the same display as in the case where continuous threshold characteristics are given to the pixels A and B (cell in FIG. 7B) is possible.

When gradation display is to be performed by the pixel shift method or the 4-pulse method, it is necessary to write one image information plural times. FIG. 5 described above is an example of the 4-pulse method, and the pulse (B), pulse (C), and pulse (D) are write pulses.

In order to perform proper gradation display by writing a plurality of times, "additivity of gradation density (reversal region)" is required. This will be described with reference to FIG. 10. When three pulses of the drive waveform shown in FIG. 10C are input to a cell having a threshold distribution in a pixel as shown in FIG. As shown in FIG. 10A, the pixel is erased by the first pulse (1), the pixel is reset in the black direction, and then the pulse (2) having the opposite polarity is applied to form the white domain up to the point c. Let Next, a pulse (3) is input to form a black domain up to point b. By doing so, the gradation density of this pixel is cb /, where the width from point a to point d is 1.
This is ad × 100 [%].

What is important in this operation is that the domain wall existing at the position c does not move when the black domain from the point a to the point b is formed (when the pulse (3) is applied). is there. However, according to the experiments performed by the present inventors, as shown in FIG. 10B, the domain wall formed in the pixel by the input of the pulse (3) is actually located at the position c ′ from the position c. The phenomenon of moving to the position was observed. This is considered to be a phenomenon that occurs because the threshold for domain wall movement is lower than the threshold for the generation of domain nuclei to the formation of domain walls. If there is a phenomenon as shown in FIG. 10B, it is not easy to perform gradation display with excellent reproducibility even if the 3-pulse method, 4-pulse method and pixel shift method described in the section of the prior art are performed. There wasn't.

Of course, attempts have been made to suppress the movement of the domain wall by improving the liquid crystal material, but sufficient characteristics have not yet been obtained.

[0036]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems and to provide a liquid crystal display device capable of performing gradation display excellent in reproducibility without using a special liquid crystal material. To provide.

Another object of the present invention is to provide a liquid crystal display device capable of performing gray scale display with excellent reproducibility by suppressing the movement of the domain wall by improving the driving method.

[0038]

SUMMARY OF THE INVENTION The present invention is a liquid crystal display for performing gradation display by sandwiching a liquid crystal between two electrode substrates arranged facing each other and forming pixels at intersections of upper and lower electrodes. In the element, when displaying the gradation information by selecting and writing the same pixel a plurality of times in the same frame, a liquid crystal display characterized in that the writing waveform at least from the second time onward is performed by positive and negative homopolar bipolar pulses. It is an element.

That is, when performing writing a plurality of times on at least one pixel on one scanning line, in the second and subsequent writing, after applying a voltage pulse of the same type and reverse polarity as the writing pulse in advance, writing is performed. Write by applying a pulse.

Here, the second time and thereafter means the time when writing is further performed in the pixel when the domain wall is already formed in the pixel. On the contrary, the first time is a case of writing when the domain wall is not formed in the pixel in all black or all white after reset.

In addition, the formation of the domain wall also means that an inversion region is partially formed in the pixel.

In the pulse of the above-described embodiment of the present invention, from another viewpoint, the positive and negative homomorphic bipolar pulse is used for the second and subsequent writing. Furthermore, it is necessary to set the preceding positive or negative pulse to the opposite polarity of the preceding applied pulse, for example.

When a domain wall already exists in a pixel, in order to form another domain wall so that the position of the domain wall is not moved, it is necessary to use a positive / negative symmetrical write waveform. By doing so, the additivity of the domain wall within the pixel is established, and it is applied not only to the 3-pulse method but also to the method of writing one pixel a plurality of times such as the pixel shift method and the 4-pulse method. Have a great effect.

The reason why such additivity holds is not completely clarified, but the idea is that the amount of movement of the domain wall already formed in the pixel in the second writing is reversed in advance in the opposite direction. It is to move it, but in reality, when the AC pulse as in the present invention is input, the movement of the domain wall itself does not occur.
The movement of the domain wall, the new formation of inversion nuclei,
It is possible that this is a complex process that includes the phenomenon of its disappearance.

FIG. 11 is a schematic diagram showing an embodiment of the present invention, which can be easily understood by comparing with FIG. 10 described above.

In this example, the compensation pulse (2 ') is applied. It is known that when this compensation pulse (2 ′) is applied, the domain wall instantaneously or stably moves to expand the white domain to the point “c” ”as shown by the arrow in FIG. Therefore, even if the next pulse (3) is applied, the unnecessary increase of the black domain (the unnecessary decrease of the white domain) as shown in FIG. 10B does not substantially occur.

In order to produce such a phenomenon with good reproducibility, the compensation pulse (2 ') has the same pulse width and the same peak value (absolute value) as the pulse (3), but only the polarities are opposite. It is desirable to design it to be a pulse. Further, the pulses (1), (2), (2 '), and (3) may be continuously applied to each other, or may be discontinuous with a pause period provided therebetween.

Desirably, as shown in FIG. 11, the reset pulse (1) and the first write pulse (2) are continuous, and a rest period is provided between the pulse (2) and the compensation pulse (2 '). To provide. The effective value of each pulse is shown in FIG.
Reset pulse, first write pulse,
It is desirable to set the compensation pulse (or the second write pulse) in order.

As the liquid crystal material used in the present invention, a well-known ferroelectric liquid crystal is preferably used, but if it is an antiferroelectric liquid crystal or any other liquid crystal having an inversion threshold and capable of applying the area gradation method, A nematic liquid crystal or a cholesteric liquid crystal may be used.

FIG. 12 is a block diagram of the display device of the present invention, and FIG. 13 is a communication timing chart of image information used therein.

The operation will be described below with reference to the drawings.
The graphics controller 102 is configured by a scanning line driving circuit 104 and an information line driving circuit 105 for scanning line address information designating a scanning electrode and image information (PD0 to PD3) on a scanning line designated by the address information. Display driving circuit 104/1 of the liquid crystal display device 101
Transfer to 05. In the present embodiment, the image information having the scanning line address information and the display information is transferred through the same transmission line, so that the two types of information must be distinguished. The signal for this identification is AH / DL, and this AH / D
When the L signal is at the Hi level, it indicates scanning line address information, and when it is at the Lo level, it indicates display information.

The scanning line address information is used for the liquid crystal display device 10.
On the side of the drive control circuit 111 in No. 1, image information PD0 to PD0
After being extracted from the image information transferred as 3,
It is output to the scanning line driving circuit 104 at the timing of driving the designated scanning line. This scanning line address information is input to the decoder 106 in the scanning line driving circuit 104, and the designated scanning electrode of the display panel 103 is driven by the scanning signal generating circuit 107 via the decoder 106. On the other hand, the display information is guided to the shift register 108 in the information line driving circuit 105 and is shifted in units of 4 pixels by the transfer clock. When the shift register 108 completes the shift of one scanning line in the horizontal direction, the display information for 1280 pixels is transferred to the line memory 109 provided side by side and stored for one horizontal scanning period, and the information signal is generated. It is output from the circuit 110 to each information electrode as a display information signal.

Further, in this embodiment, since the driving of the display panel 103 in the liquid crystal display device 101 and the generation of the scanning line address information and the display information in the graphics controller 102 are performed asynchronously, the image information is transferred between the devices. It is necessary to synchronize (101/102).
The signal that controls this synchronization is SYNC, which is generated in the drive control circuit 111 in the liquid crystal display device 101 every horizontal scanning period. The graphics controller 102 side is always S
The YNC signal is monitored, and if the SYNC signal is at the Lo level, the image information is transferred. On the contrary, when it is at the Hi level, the transfer is not performed after the transfer of the image information for one horizontal scanning line is completed. That is, in FIG. 12, when the graphics controller 102 detects that the SYNC signal has become the Lo level, it immediately sets the AH / DL signal to the Hi level and starts the transfer of image information for one horizontal scanning line. The drive control circuit 111 in the liquid crystal display device 101 has a SYNC
The signal is set to Hi level during the image information transfer period. After the writing to the display panel 103 is completed after a predetermined one horizontal scanning period, the drive control circuit (FLCD controller) 1
11 can return the SYNC signal to the Lo level again and receive the image information of the next scanning line.

The compensating pulse of the present invention described with reference to FIG. 11 is generated in the scanning signal generating circuit 107 and the information signal generating circuit 1.
Compensation pulse generation circuits 120 and 121 provided in
Generated by. The circuit may be a circuit that includes a gate circuit and that opens and closes the gate at a predetermined timing to supply a reference voltage having the same peak value (absolute value) as the reference voltage of the second pulse but having the opposite polarity.

[0055]

【Example】

(Embodiment 1) FIG. 14 shows a cross section of a liquid crystal cell 101.
To configure the liquid crystal cell 101, the lower glass substrate 11
A UV curable resin 112 is applied in a predetermined shape on 1 and then cured by ultraviolet irradiation to change the cell thickness, and an ITO transparent electrode 113 is further provided thereon. Then, Ta ₂ O ₅ as an insulating layer is sputtered on the ITO transparent electrode 113, and then the alignment film 114 is manufactured by Toray LP-64.
(Product name) is applied to form the lower substrate. On the other hand, the upper glass substrate 111 is treated in the same manner as the lower substrate except that the UV curable resin 112 is not applied. Then, the alignment films of the upper and lower substrates are subjected to a rubbing treatment in a fixed direction to obtain lower substrates. The alignment film 114 of the upper and lower substrates 111 is subjected to an alignment treatment so that the alignment film 114 is rotated by about 10 ° in the right screw direction from the rubbing direction of the upper substrate to the rubbing direction of the lower substrate when viewed from the surface of the cell. . Then, a liquid crystal having the physical properties shown in Table 1 is used. The change in cell thickness is about 1.10 to 1.65 μm. The liquid crystal materials used are shown in Table 1.

[0056]

[Table 1]

In this example, the system shown in FIG. 12 supplies the signals shown in FIG. 15 to the display panel for display.

In FIG. 15, S1, S2 and S3 are scanning signals, (1) is a reset pulse, (2) is a first write pulse, (2 ') is a compensation pulse, and (3) is a second pulse. This is the write pulse for the first time. The minute pulse (5) added to the pulses (2 ′) and (3) is a compensation pulse, and is for suppressing the application of the DC voltage component.

I is an information signal, and the crest value (voltage) differs depending on the gradation step to be displayed.

S1-I is a composite voltage signal applied to the liquid crystal, (11) is reset, (12) is the first writing, (12 ') is compensation, and (13) is the second writing. , The signal component. As shown in FIG. 15, the signal component (1
2 ') and (13) differ only in polarity.

In FIG. 15, | V ₁ | = 20.0V,
_{| V 2 | = 17.2V, |} V i | = 3.4V~-3.4
V, dt ₁ = 40 μs, dt ₂ = 27 μs, dt ₃ = 1
3 μs, | V ₃ | = 4V. The modulation method of the information signal here is a voltage modulation method. (V _s + V _i ) is 1
0% is displayed at 3.8V, 100% is displayed at 20.6V, and a halftone is displayed at the intermediate voltage. S2-I is S
The composite signal for two lines is shown.

FIG. 16 shows the formation of domains when the cell of FIG. 14 is driven with the driving waveform of FIG. In FIG.
The cell thickness (thickness of the liquid crystal) of the portion α is set to about 1.65 μm, and the cell thickness of the portion β is set to about 1.1 μm. Therefore, the selection signal pulse (2) of FIG. Data is written in the white direction from the state where the entire surface is reset to the black state by the input, and the black domain of the α portion is formed as the remaining portion. After that, the second writing is generated from the β portion by the input of the selection signal pulse (3) in FIG. 15, but at this time, the domain wall formed by the first writing by selecting A does not move. Is desirable. When driven by the driving method of FIG. 15, the domain wall did not move when displaying any of the grayscale levels of. This means that good gradation display was realized by the driving method of FIG. However, Figure 17
When the drive waveform of the comparative example shown in (1) is used (the voltage setting range is the same as that of FIG. 15), the domain wall formed by the input of the selection signal pulse (2) (first write) is the selection signal pulse (3). ) Was changed by the input.

This state is shown in FIG. In FIG. 18, point α is a thick cell portion (about 1.65 μm), and point β is a thin cell portion (about 1.1 μm). The portion on α is written in the white direction (first writing) by the input of the selection signal (2) in FIG. 17 after resetting “black”,
It is a black domain wall generated as a result, after which the second writing is performed by the selection pulse (3) in FIG.

Here, focusing on the width of the domain wall on the α part in FIG. 18, the domain wall expands in the order of ,. This means that if the above-mentioned pixel shift method is applied, the information content on the next scanning line should shift to the scanning line according to the temperature change, but the shift amount cannot be controlled. . If the voltage applied to the pixel on the next scan line is high, the amount of fluctuation of the position of the domain wall already on the pixel becomes large, the linearity of the countability is lost, and the control becomes extremely difficult, or the gradation It also causes a drop in display accuracy.

In the above-described embodiment, the inversion threshold value within the pixel is provided with a gradient by providing the liquid crystal thickness (cell thickness) with a gradient. However, as another method, minute irregularities are formed in the pixel and the irregularities are formed. By giving a distribution to the arrangement density of, it is possible to create a threshold gradient equivalent to the case where the cell thickness has a gradient. Further, the domain expansion by the driving of the present invention is not limited to one-dimensional shape, and may be two-dimensional shape.

[0066]

As described above, by using the present invention, it is possible to avoid deterioration of gradation display accuracy due to writing a plurality of times in one pixel and realize excellent gradation display.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the relationship between voltage and transmittance in a conventional area modulation method.

FIG. 2 is a diagram showing a voltage and a light transmission state of a pixel in a conventional area modulation method.

FIG. 3 is a diagram showing a relationship at different temperatures in the relationship diagram of FIG.

FIG. 4 is an explanatory diagram of a conventional four-pulse driving method.

FIG. 5 is an explanatory diagram of a conventional four-pulse driving method.

FIG. 6 is a schematic cross-sectional view showing an example of a liquid crystal cell.

FIG. 7 is an explanatory diagram of a conventional pixel shift method.

FIG. 8 is an explanatory diagram of a conventional pixel shift method.

FIG. 9 is an explanatory diagram of a conventional pixel shift method.

FIG. 10 is a schematic diagram for explaining a display state of a pixel by a conventional 3-pulse method.

FIG. 11 is a schematic diagram for explaining a display state of a pixel according to the present invention.

FIG. 12 is a block diagram of a drive circuit applicable to the present invention.

13 is a timing chart for explaining the drive circuit of FIG.

FIG. 14 is a schematic view of a liquid crystal cell applicable to the present invention.

FIG. 15 is a diagram showing drive waveforms according to the first embodiment.

FIG. 16 is a schematic diagram showing an example of a display state according to the first embodiment of the present invention.

FIG. 17 is a diagram showing drive waveforms according to a comparative example.

FIG. 18 is a schematic diagram showing an example of a display state according to a comparative example.

Claims (4)

[Claims] 1. In a liquid crystal display element for performing gradation display by forming a pixel at an intersection of upper and lower electrodes by sandwiching a liquid crystal between two electrode substrates arranged facing each other, the same pixel is formed in the same frame. A liquid crystal display element, characterized in that, when gradation information is displayed by selecting and writing a plurality of times, at least the second and subsequent writing waveforms are performed with positive and negative same-type bipolar pulses. 2. The liquid crystal display element according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal. 3. A method of driving a liquid crystal display element, wherein a liquid crystal is sandwiched between two electrode substrates arranged to face each other and a pixel is formed at an intersection of upper and lower electrodes to perform gradation display, in the same frame. By selecting and writing the same pixel multiple times,
A method of driving a liquid crystal display device, wherein, when displaying gradation information, at least the second and subsequent write waveforms are performed with positive and negative same-type bipolar pulses. 4. The method of driving a liquid crystal display device according to claim 3, wherein the liquid crystal is a ferroelectric liquid crystal.