JPH06235904A - Ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a ferroelectric liquid crystal display element capable of realizing a good-quality gradation display having little cross talk. CONSTITUTION:A liquid crystal display element is provided with ferroelectric liquid crystal between two electrode substrates arranged face to face, the pattern of the voltage signal applied to an information signal line is kept constant regardless of the writing gradation level for a fixed period immediately after the writing pulse voltage is applied to a liquid crystal layer, and a DC bias is applied when the pattern is applied to a scanning signal line for gradation display.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using a ferroelectric liquid crystal.

[0002]

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
And US Pat. No. 4,563,059, etc.
Ferroelectric liquid crystal (Surface-stabilize)
d ferroelectric liquid cr
reveal bistable ferroelectric liquid crystal device
I chose This bistable ferroelectric liquid crystal device has a bulk state
Chiral smectic C phase (SmC *), H phase (Sm
H *) Controls the formation of helical arrangement structure of liquid crystal molecules
Between a pair of substrates set to a distance small enough to control
A liquid crystal is placed and a suspension composed of multiple liquid crystal molecules.
It is realized by arranging straight molecular layers in one direction.
It was

Further, such a ferroelectric liquid crystal (FLC)
Japanese Patent Application Laid-Open No. 61-94023 discloses a display device using
As disclosed in Japanese patent publications, a liquid crystal cell formed by facing two glass substrates on which transparent electrodes are formed on the inner surfaces of the two inner surfaces while keeping a cell gap of about 1 to 3 μm and facing each other is used. It is known that a dielectric liquid crystal is injected.

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 liquid crystal molecule has a twisted major axis 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 used for a large-capacity pixel by using a multiplexing driving method described in, for example, US Pat. No. 4,655,561 to Kamibe et al. Images can be formed on the display screen. The liquid crystal display device described above can be used for a display screen of a word processor, a personal computer, a micro printer, a television, or 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 a multi-valued or halftone display is also possible. 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. 5 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-shielded (black) state has a single-shot single 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. 6B. 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 transmitted light amount 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. 5 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. 7 is a diagram for explaining this.
6 is a graph showing the relationship between the voltage amplitude V and the transmitted light amount I as in FIG. 5, but shows two curves H and L respectively showing the relationship at different temperatures, that is, high temperature and low temperature. That is, in a display (display element) having a large display size, it is not uncommon for a temperature distribution to occur within the same pulse (display section), and 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.

What has been devised there is the "four-pulse method" proposed by the present inventor in Japanese Patent Application No. 2-294384.
Is. In this driving method, as shown in FIGS. 8 and 9, a plurality of pulses (A, B, C, D in the figure) are applied for the low threshold portion and the high threshold portion on the same scanning line in the pulse. By doing so, the same inversion area is finally obtained ((D) in the figure).

The present inventor has further filed Japanese Patent Application No. 3-32054.
No. 2 proposes the "pixel shift method" in which the writing time is shorter than the "4 pulse method".

The pixel shift method is a method of inputting different scanning signals to a plurality of scanning signal lines at the same time and selecting them to form a distribution of electric field intensity across a plurality of scanning lines to display a gradation. .

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

A liquid crystal cell that can be used has a distribution of threshold values within one pixel, as shown in FIG. In the cell shown in FIG. 10, since the layer thickness of the FLC layer 55 between the electrodes changes, the FLC switching threshold 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. 11 (a). Figure 11
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 change 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. 11A, 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. Increases to T ₂ or T ₃ , the same V _i
When the above voltage is applied to the pixel, the transmittance becomes 100%, and the gradation display cannot be performed correctly. Figure 11
(C) shows the inverted state of the pixel after writing at each of the above temperatures. 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.
By displaying the pixel information across the two scanning signal lines S1 and S2, it is possible to perform stable gradation display with respect to temperature fluctuations.

The drive system will be described in detail below.

A ferroelectric liquid crystal cell having a continuous threshold distribution within a pixel is prepared: The liquid crystal cell should be constructed such that the cell thickness within the pixel is continuously distributed as shown in FIG. You can In addition, the applicant of the present invention disclosed in Japanese Patent Laid-Open No. 63-18
A configuration having a potential gradient in a pixel or a configuration having a capacitance gradient as proposed in Japanese Patent No. 6215 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 simultaneously: This operation will be described with reference to FIG. Figure 12 (a)
Shows the transmittance-applied voltage characteristics when the pixels on the two scanning signal lines are grouped together. In FIG. 12 (a),
The transmittance of 0% to 100% is shown as the display area of the pixel B on the scanning line 2, and 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 temperature T ₁ ,
This range (pixel region) is entirely on the scanning signal line 2 (see the shaded portion in FIG. 12B). However, the temperature is T
_{When the} voltage is increased from ₁ to T ₂ , the threshold voltage of the liquid crystal is lowered, so that 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 over the scanning signal line 1 and the scanning signal line 2 (the shaded portion in FIG. 12B showing the case of the temperature T ₂ ). ).

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. 12). 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 from 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 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.

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. 11B, the transmittance-voltage curve when the temperature is T ₁ shows 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. 13, even if the cell shapes of the pixel A on the scanning signal line 1 and the pixel B on the scanning signal line 2 (see FIG. 13B) are set to be the same, the pixel A is substantially the same. , When a continuous threshold characteristic is given to the pixel B (see FIG. 11).
The same display as in (b) cell) is possible.

[0031]

When a voltage waveform as shown in FIG. 4A is applied to a cell having a threshold distribution in a pixel as shown in FIG. 10, an alternating current following the write pulse V ₁ is applied. When the pulse ± V ₂ is input, the writing gradation level due to the V ₁ pulse is changed.

The value of | V ₂ | has a pulse width of 40 μs (see FIG. 4).
In (a)), since it is below the inversion threshold, when the pulse of ± V ₂ is applied without the presence of V ₁ , only the state of being reset by V ₀ is displayed. V
_Even if V ₁ and V ₀ are the same due to the peak value of ₂ , the write level is affected (hereinafter, crosstalk)
In contrast, as shown in FIG. 4B, it can be seen that the crosstalk amount increases as the value of | V ₂ | increases. When | V ₂ | = 5V, the crosstalk amount is 20.
%, And therefore, when some AC signal is applied after the write pulse, the matrix electrode cells cannot be sequentially written and driven (FIG. 4C).

The characteristics of the liquid crystal element described here are the same as those used in the examples described later in terms of cell structure and materials. This crosstalk is considered to be due to the instability of the FLC immediately after switching.

Looking at the change in the light amount immediately after the switching of the FLC, as shown in FIG. 3A, the light amount changes for a certain period of time and then settles to a certain light amount level. Figure 3 (a) shows FLC
The change in the light intensity during switching is shown in the photo-mal, but it is about 200 before the optical response settles down.
It requires a time of μs (hereinafter, relaxation time).

When the relationship between the relaxation time and the crosstalk is examined by using the drive waveform as shown in FIG.
It becomes like (b).

In FIG. 3C, V _ON is a write waveform,
At V _E it is a reset pulse. The change in final transmittance is shown when a crosstalk pulse of ± V _C is applied after a lapse of time T after the rise of the V _ON pulse.

Even when fixed to | V ₀ | = 5V, the crosstalk amount varies depending on the value of T, and T ≧ relaxation time (20
Under the condition of 0 μs), the effect of ± V _C disappears.

When the drive waveform as shown in FIG. 14A is input, the crosstalk is generated depending on how many crosstalk pulses are input after the V _ON pulse. However, if the total number of pulses exceeds the relaxation time,
It can be seen that it no longer affects the amount of crosstalk. Figure 1
4 (b), it is almost constant when N ≧ 2, and is 2 when the time is changed.
It is about 00 μs. Therefore, when performing gradation display, processing of such a non-selection signal applied after the switching pulse becomes a serious problem. As one method, it is possible to prevent crosstalk by holding the non-selection signal for a time corresponding to the relaxation time after inputting without writing, but the one-line selection time becomes long, and other than the still image display. Since it is not suitable, there is a problem that it is not practical.

[0039]

According to the present invention, a write pulse voltage is applied to a liquid crystal layer in a liquid crystal display device in which a ferroelectric liquid crystal is sandwiched between two electrode substrates arranged to face each other. Immediately after that, the pattern of the voltage signal applied to the information signal line is made constant regardless of the writing gradation level, and DC is applied during applying the pattern to the scanning signal line.
It is characterized in that gradation display is performed by applying a bias.

That is, after the rising of the write pulse, the voltage waveform pattern applied to the pixel at a constant time is made uniform, and the average value V _{M of the} voltage levels applied to the pixel within that time is the reference level ( The potential difference between the upper and lower electrodes becomes 0).

When the polarity of the voltage pulse applied immediately after the write voltage is the same as the polarity of the write voltage, V _M is configured to have the opposite polarity to the write voltage and applied immediately after. polarity of the voltage pulse that is, when different from the polarity of the write voltage is configured to be the same as the polarity of the voltage writing polarity of the V _M.

Next, the operation of the present invention will be described.

Crosstalk is a disturbance of write information due to application of a voltage signal such as an information signal synchronized with subsequent scanning to an unstable alignment state after the fall of the voltage pulse in the FLC switching process.

Therefore, as shown in FIG. 3, the influence of the voltage signal applied after writing becomes smaller as the write pulse falls.

Therefore, in the present invention, the shape of the voltage waveform immediately after the write pulse is fixed irrespective of the write pulse voltage, and the voltage average within the time for fixing the voltage waveform is not set to 0, but a constant voltage. A voltage is applied to the liquid crystal layer so that it becomes V _H.

This voltage waveform fixing time is much shorter than the relaxation time at the time of switching the liquid crystal, and the alignment of the liquid crystal molecules can be stabilized.

[0047]

【Example】

Example 1 As a first example, a liquid crystal cell having a cross-sectional shape as shown in FIG. 10 was produced. In the figure, for the dusty shape of the lower substrate, make an original shape on the mold and apply it to the acrylic U
It was made by transferring it onto a glass substrate with V-curing resin 52.

On the sawtooth shape of the UV curable resin 52,
An ITO film is formed by sputtering as the stripe electrode 51,
Further, an alignment film LQ-1802 manufactured by Hitachi Chemical Co., Ltd. was formed as an alignment film 54 on the upper layer thereof to a thickness of about 300 Å.

The cell substrate on the opposite side has a stripe electrode 51.
The same alignment film is formed on the upper surface, and no uneven shape is provided.

The rubbing directions of the upper and lower substrates were parallel to each other, and the rubbing direction of the lower substrate was shifted by about 6 ° with respect to the rubbing direction of the upper substrate to form a cell. The cell thickness was controlled so that the thin portion had a thickness of about 1.10 μm and the thick portion had a thickness of about 1.64 μm. Further, the stripe electrode 51 of the lower substrate was patterned in a stripe shape along the ridges so that one side of the sawtooth shape becomes one pixel.

The width of the stripe electrode 51 was set to 300 μm, and the pixel size was set to a rectangle of 300 μm × 200 μm. The liquid crystal materials used are shown in Table 1.

[0052]

[Table 1] On the other hand, FIG. 2 is a block configuration diagram of the display device of the present invention, and FIG. 19 is a communication timing chart of image information.

The operation will be described below with reference to the drawings.
The graphics controller 102 displays the scanning line address information designating the scanning electrodes and the image information (PD0 to PD3) on the scanning lines designated by the address information on the display drive circuit (the scanning line drive circuit 104 and the information line) of the liquid crystal display device 101. It is configured by the driving circuit 105) and transferred to 104/105. In this embodiment, since the image information having the scanning line address information and the display information is transferred through the same transmission line,
The two types of information must be distinguished. The signal for this identification is AH / DL. When this AH / DL signal is at the Hi level, it indicates that it is scanning line address information, and when it is at the Lo level, it indicates that it is 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. 2, when the graphics controller 102 detects that the SYNC signal has become Lo level, it immediately sets the AH / DL signal to 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 sets the SYNC signal to the 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) 11
1 can return the SYNC signal to the Lo level again and receive the image information of the next scanning line.

FIG. 1 shows driving waveforms in the present invention. In the figure, | V _e | = 8.0 V, | V _s | = 17.0 V, | V
_i | = 3.0 V, ΔT = 40 μs, δ = 26 μs, t ₁
= 7 μs and t ₂ = 7 μs.

The modulation method of the information signal is a phase modulation method, and FIG. 15 shows the modulation method of the information signal.

The voltage waveform is from I (0%) to I (100%)
Until (each is an information signal for displaying information in parentheses), the pulse width of the portion A in the figure is variably modulated. The voltage signal with a width of δ is set to have write information. The modulation of the A part is (δ side pulse width) and (δ
And the pulse width on the opposite side) is 1 / γ: (1-1 /
γ) is set.

The reason for setting such a ratio is to make the inversion threshold value continuous in the pixels to which the scanning signal SA and the scanning signal SB are applied.

Here, the width of δ is 1 / γ of the selection time ΔT of the scanning signal SA. This constraint also exists to maintain the continuity of the threshold. Here, σ indicates a slope, ∂T / ∂λ, in which the vertical axis represents the transmittance (T) and the horizontal axis represents the modulation parameter (λ). Here, the modulation parameter will be described.

A graph of transmittance T [%]-modulation parameter (λ) is shown in FIG. In the case of adopting the modulation method as shown in FIG. 16, the scale of the horizontal axis is set to 1n, but this is for allowing the change of the threshold value of the liquid crystal due to the temperature change to appear as parallel movement on the graph.

In such a modulation method, the selection voltage waveform S
The change in A is a 14V rectangle [(b- in FIG. 16B).
1)] to a 20V rectangle [(b- in FIG. 16B).
3)].

By taking the time weighted by the voltage as the modulation parameter, the transmittance (T) -1n (modulation parameter, λ) characteristic becomes linear and the temperature change as shown in FIG. 16 (a). Translate by.

The following describes how to perform weighting. The pulse length of the portion of the peak value V ₁ is t ₁ (if it is divided into two, it is added) Peak value V
Pulse length of the _second portion of the t ₂

[0065]

[Equation 1] Here, t ₁ + t ₂ = 40 μs, V ₁ = 14 V, V ₂ = 2
V _h in 0V Figure 1 is a point according to the present invention. DC pulse V _h to the scanning signal line immediately after the first write (SA in Fig. 15)
Is applied.

The information signal waveform at this time corresponds to the section B in FIG. The information signal is also applied to the non-selected scanning lines, and if it has a DC component, the information signal itself causes crosstalk, so it is not necessary to set it so that the DC component does not build up. (The information signal waveform of FIG. 15 is set as such).

Further, the shapes of the information signal waveforms during the application time of V _h of the scanning signal are all the same. That is, in the section B of FIG. 15, a constant electric signal is supplied to the liquid crystal layer regardless of the information content.

When such a voltage is supplied between the liquid crystal layers,
As a result, the voltage V _h on the scanning signal is applied to the liquid crystal layer as a DC component. The crosstalk amount described above can be reduced by the shape of this fixed pulse (FIG. 15) (whether it has a negative polarity first) and the amount of V _h .

In this embodiment, since | V _i | = 3.0 V, the first write has a positive polarity, and when the leading pulse of the subsequent section in FIG. 15B has a negative polarity, V _h = + 0.4 V write has a negative polarity. When the leading pulse of the subsequent section in FIG. 15B has a positive polarity, V _h = −0.4 V is set.

The polarity of V _h is determined by the polarity of the B1 pulse in the section B of FIG. 15 (the other pulses in the section B following B1 have a pulse waveform dual to B1).

In either case, the polarity of the succeeding pulse is the same as or opposite to the polarity of the write pulse, depending on the direction in which the inversion of FLC is promoted or the direction in which it is prevented. When this is expressed in a table, the polarity of V _h is as follows.

[0072]

[Table 2] Next, as shown in FIG. 17, the voltage value of V _h is B in FIG.
It depends on the pulse peak value of the section, and in this example, | V _c | =
Since | V _i | = 3.0V, | V _h | = 0.4V is determined.

[0073] cross-talk and write voltage, has been described above that does not depend on the determined cell thickness by the ratio of the voltage V _c immediately after, the amount of writing you of V _h also does not depend on the cell thickness is determined only by the V _c.

By introducing V _h in this way, 20%
The amount of crosstalk that had the above fluctuations could be reduced to several percent or less. When the waveforms after the section B in FIG. 15 are completely the same, the crosstalk amount can be set to 0.

As can be seen from the change of the crosstalk amount in FIG. 3, this is not perfect even if the B section is shorter than the relaxation time and the alignment state of the liquid crystal is stabilized, and the crosstalk of several% or less is obtained. The amount may remain.

[0076] In this example, it resulted in a 12% cross-talk when there is no V _h, by applying a V _h, even if the phase of the subsequent voltage waveform B section are different 180 °, 2% variation I was able to suppress it. In order to completely eliminate the effect of crosstalk, it is effective to use the waveform writing method shown in FIG. 1 and change the erasing direction for each frame for the same scanning line. According to this method, since crosstalk occurs in the opposite direction in two consecutive frames, there is no crosstalk in the average of two frames. However, if one pixel is written in two frames, one screen scanning frequency is 1/2. Is not desirable.

Therefore, by introducing V _h of the present invention, gradation display can be realized with an accuracy of several% or less in the first frame, so that display characteristics can be improved.

Although the effect of V _h is more remarkable as the section B is longer, the experimental result when V _h is applied during a half period (40 μs) of the section B of 40 × 2 = 80 μs in FIG. 4B. Is shown in FIG.

In FIG. 18, write pulse V _ON = 1
6V, pulse width ΔT = 40 μs, peak value of B section pulse is ± 5 v, pulse width ΔT ′ = 20 μs, and V _h was set to +0.96 V according to FIG. In FIG. 18, (II) is the light quantity when V _h is not applied, and (I) is the light quantity when the crosstalk pulse and V _h are not applied, and the crosstalk pulse ± 5 v and V _h = 0.96 V. The amount of light when applied simultaneously is shown. In (I), it can be seen that is exactly the same.

As described above, it was found that the crosstalk can be reduced by switching the FLC by designing the applied waveform immediately after switching.

[0081]

As described above, by using the present invention, it is possible to realize a high quality gradation display with less crosstalk.

[Brief description of drawings]

FIG. 1 is a diagram showing drive waveforms according to a first embodiment.

FIG. 2 is a drive circuit block diagram applicable to the present invention.

FIG. 3 is an explanatory diagram related to the problems of the present invention.

FIG. 4 is an explanatory diagram related to the problems of the present invention.

FIG. 5 is a diagram schematically showing the relationship between voltage and transmittance in a conventional area modulation method.

FIG. 6 is a diagram showing a voltage and a light transmission state of a pixel in a conventional area modulation method.

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

FIG. 8 is an explanatory diagram of a conventional 4-pulse driving method.

FIG. 9 is an explanatory diagram of a conventional 4-pulse driving method.

FIG. 10 is a schematic view of a liquid crystal cell applicable to the present invention.

FIG. 11 is an explanatory diagram of a conventional pixel shift method.

FIG. 12 is an explanatory diagram of a conventional pixel shift method.

FIG. 13 is an explanatory diagram of a conventional pixel shift method.

FIG. 14 is an explanatory diagram related to the problems of the present invention.

FIG. 15 is an explanatory diagram of an information signal waveform according to the first embodiment.

FIG. 16 is a graph showing the relationship between the transmittance and the modulation parameter according to the first embodiment.

FIG. 17 is a graph showing the relationship between V _h and the pulse crest value in section B according to the first embodiment.

FIG. 18 is a graph showing an experimental result when V _h is applied.

19 is a timing chart for explaining the drive circuit in FIG.

Claims (3)

[Claims] 1. In a liquid crystal display device comprising a ferroelectric liquid crystal sandwiched between two electrode substrates arranged opposite to each other, a write pulse voltage is applied to an information signal line for a certain period of time immediately after being applied to a liquid crystal layer. Ferroelectric liquid crystal display characterized in that the pattern of the voltage signal to be generated is made constant regardless of the writing gradation level, and gradation display is performed by applying a DC bias while applying the pattern to the scanning signal line. element. 2. The liquid crystal display device according to claim 1, wherein gradation display is performed by providing a threshold distribution in each pixel. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is driven by changing both the DC bias value applied to the scanning line and the voltage crest value applied to the information signal line.