JP2002122842A - Antiferroelectric liquid crystal display and method of driving the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type antiferroelectric liquid crystal display without deteriorating display quality, and to provide a method of driving the display. SOLUTION: In the reflection type antiferroelectric liquid crystal display, which is constituted so that an antiferroelectric liquid crystal 12 is filled between a transparent plate 10A in which a polarizer 13 is arranged on its outer surface and an alignment layer 11A is arranged on its inner surface side and a reflection surface opposite to the inner surface of the transparent plate 10A and the polarizing axis of the polarizer 13 is inclined in the direction opposite to the tilt direction of the antiferroelectric liquid crystal 12 during voltage application with respect to an alignment direction of the alignment layer 11A, then the writing and erasing of data are performed in respective pixels by selectively applying signal voltage to a plurality of signal electrodes while successively switching a selecting mode, a non-selecting mode and an erasing mode by a plurality of prescribed number of scanning electrodes in a definite order by a simple matrix driving method, the display is made to be in a sticking prevention mode, by which the antiferroelectric liquid crystal is made to be a ferroelectric state, by applying the voltage having polarity opposite to that of the selecting mode before the respective scanning electrodes are set to be in the erasing mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antiferroelectric liquid crystal display configured as a reflection type and a driving method thereof.

[0002]

BACKGROUND OF THE INVENTION Antiferroelectric liquid crystals have a remarkably fast response speed as compared with STN liquid crystals, and are suitable for displaying moving images. Further, the antiferroelectric liquid crystal has the advantages that the viewing angle is as wide as ± 60 °, the visibility of the display is good, and the light utilization is relatively high at 25% and the efficiency is high.
In the field of next-generation mobile phones and mobile devices, since the amount of transmitted data is expected to increase dramatically, displays using anti-ferroelectric liquid crystals with a large response speed as described above will be used in next-generation mobile phones. Or mobile video display.

A transmissive display inherently illuminates and consumes a large amount of power, whereas a reflective display uses external light and therefore inherently has no illumination. Not required. For this reason, the reflective type requires less power consumption than the transmissive type, and from this viewpoint, the reflective type is more suitable as a display device for a mobile phone or a mobile.

However, the practical use of transmissive antiferroelectric liquid crystal displays has just begun. For this reason, it is desired to configure the antiferroelectric liquid crystal display as a reflection type. In this case, it is possible to prevent the display quality from deteriorating, that is, to achieve a certain level of contrast,
It is also required to prevent image sticking.

[0005] The present invention has been made under such circumstances, and without deteriorating the display quality.
It is an object of the present invention to provide a reflection type antiferroelectric liquid crystal display and a driving method thereof.

[0006]

DISCLOSURE OF THE INVENTION The present invention employs the following technical means to solve the above-mentioned problems.

That is, the antiferroelectric liquid crystal display provided by the first aspect of the present invention includes a transparent plate having a polarizing plate disposed on an outer surface and an alignment film disposed on an inner surface.
An antiferroelectric liquid crystal is filled between the reflection surface facing the inner surface of the transparent plate, and the polarization axis of the polarizing plate is applied to the orientation direction of the alignment film when a voltage of the antiferroelectric liquid crystal is applied. It has a configuration that is tilted in the direction opposite to the tilt direction, and uses a simple matrix driving method to sequentially switch a plurality of scan electrodes between a selection mode, a non-selection mode, and an erase mode in a fixed order by a predetermined number. A reflective antiferroelectric device further comprising control means for performing writing and erasing on a plurality of pixels constituted by the antiferroelectric liquid crystal by selectively applying a signal voltage to the plurality of signal electrodes. Prior to setting each of the scanning electrodes to the erasing mode, the control means applies a voltage having a polarity opposite to that of the selection mode or the non-selection mode, and sets the scanning electrode to a high resistance. It is characterized by being configured so as to burn prevention mode to ferroelectric state conductive liquid.

Further, according to a second aspect of the present invention, a polarizing plate is disposed on an outer surface side and an alignment film is disposed on an inner surface side, and a reflecting surface facing the inner surface of the transparent plate is disposed between the transparent plate. It has a configuration in which an antiferroelectric liquid crystal is filled, and a polarization axis of the polarizing plate is inclined in a direction opposite to a tilt direction when a voltage is applied to the antiferroelectric liquid crystal with respect to an alignment direction of the alignment film. For a reflection type anti-ferroelectric liquid crystal display, a plurality of signal electrodes are switched by a predetermined number of scan electrodes in a fixed order in a selected order, a non-selection mode, and an erase mode by a simple matrix driving method. And selectively driving a plurality of pixels composed of antiferroelectric liquid crystal by applying a signal voltage to the plurality of pixels. Setting Before the selection mode or the non-selection mode, the anti-ferroelectric property is set to an anti-burning mode in which the antiferroelectric liquid crystal is brought into a ferroelectric state by applying a voltage having a polarity opposite to that of the nonselection mode. A method for driving a liquid crystal display is provided.

By the way, in a pair of polarizing plates (crossed Nicols) in which the polarizing axes are orthogonally arranged, light transmission when a uniaxial birefringent plate (antiferroelectric liquid crystal) is sandwiched between these polarizing plates. The rate is expressed by the following equation.

[0010]

(Equation 1)

In the above equation (1), Ψ is the tilt angle of the liquid crystal molecules (long axis direction) with respect to the polarization axis when voltage is applied, Δ
n is the refractive index anisotropy of the liquid crystal molecules, d is the optical path length in the liquid crystal, and λ is the wavelength of light.

As can be seen from the above equation (1), in an antiferroelectric liquid crystal display in which the polarization axes are orthogonal, sin
Assuming that the term ² (πΔnd / λ) is optimized, the closer the tilt angle of the liquid crystal molecules is to 45 °, the greater the light transmittance and the maximum at 45 °.

On the other hand, in the reflection type antiferroelectric liquid crystal display, only one polarizing plate is required. Therefore, when this is replaced with a transmission type, a pair of polarizing plates are arranged so that the polarization axes are parallel. This is equivalent to one in which a polarizing plate is arranged. For this reason, the light transmittance of the reflection type antiferroelectric liquid crystal display is given by the following equation (2) in which the term of sin ^{2 2}置 き 換 え is replaced with cos ² 2Ψ in the above equation (1). In other words, the closer the tilt angle of the liquid crystal molecules is to 45 °, the smaller the light transmittance becomes, and the light transmittance becomes minimum at 45 °. In the reflection type, since the optical path length of the light traveling through the liquid crystal is twice the cell gap, sin ² (π
The cell gap for optimizing the term (Δnd / λ) is
It is half that of an antiferroelectric liquid crystal display configured as a transmission type.

[0014]

(Equation 2)

The maximum tilt angle of the antiferroelectric liquid crystal that has been discovered and synthesized at the time of voltage application is 31.2 °, and in a configuration in which the polarization axis and the alignment direction match, the above equation (2) is used. The tilt angle に お け る at the time of voltage application is 3 at the maximum.
1.2 °. Therefore, when an antiferroelectric liquid crystal display is configured as a reflection type, the minimum light transmittance is 0%.
And the contrast becomes worse because black display cannot be performed properly. For example, when the tilt angle Ψ is 3
In the case of 1.2 °, the minimum light transmittance is 21.5%, and the contrast at this time is 5 or less.

In the antiferroelectric liquid crystal display of the present invention, the polarization axis of the polarizing plate is in the direction opposite to the tilt direction when a voltage is applied to the antiferroelectric liquid crystal (ferroelectric state) with respect to the alignment direction of the alignment film. . For this reason, even if the maximum tilt angle of the liquid crystal molecule itself is smaller than 45 °, the apparent tilt angle with respect to the polarization axis can be 45 ° or an angle close thereto. as a result,
Black display in the selection mode or the non-selection mode can be appropriately performed, and the contrast can be improved.

On the other hand, in the antiferroelectric liquid crystal display having the above structure, it is possible to make the apparent tilt angle close to 45 ° when a voltage is applied. Even in the ferroelectric state, as a result of inclining the polarization axis from the orientation direction, the apparent tilt angle in the ferroelectric state becomes far from 45 °, and black display cannot be performed properly. In other words, as a result of inclining the polarization axis, the symmetry at the time of applying a voltage at each polarity is lost, and only one polarity can properly perform black display. Then, in fact, the ferroelectric state of the other polarity is not used, and burn-in is likely to occur.

On the other hand, in the present invention, for example, a voltage having a polarity opposite to that of the selected mode or the non-selected mode is applied by the control means and the ferroelectric state (burn-in prevention mode) is applied.
Is achieved. In this way, the selection mode and the non-selection mode are achieved by one polarity, and the burn-in prevention mode is achieved by the other polarity. As a result, the ferroelectric state of both polarities is used, and the burn-in is appropriately prevented. .

As described above, in the present invention, the anti-ferroelectric liquid crystal display can be configured to be of a reflection type without deteriorating the display quality by improving the contrast by preventing the image sticking by optimizing the black display. become able to.

In a preferred embodiment, the erasing mode is such that the antiferroelectric liquid crystal starts to change from an antiferroelectric state to a ferroelectric state having a polarity opposite to that of the burn-in prevention mode for a target pixel. This is performed by applying a voltage having a value equivalent or substantially equivalent to one threshold voltage.

In the antiferroelectric liquid crystal, when returning from the ferroelectric state to the antiferroelectric state, if a voltage having a reverse polarity such that writing is not performed is positively applied, such a voltage is applied. It is possible to increase the above-mentioned return speed as compared with the case where there is no return. According to the above configuration, when the antiferroelectric liquid crystal is switched from the ferroelectric state to the erasing mode by the burn-in prevention mode, the voltage applied to the liquid crystal has the opposite polarity. As a result, the image can be erased quickly. The antiferroelectric liquid crystal has a property that the return speed from the antiferroelectric state to the ferroelectric state is greatly affected by the temperature and becomes slow at a low temperature. According to the above configuration,
Even under the use condition at a low temperature, it is suitable to quickly complete the writing / erasing process of the pixel. Also, the first
Since the threshold voltage has the maximum absolute value at which the antiferroelectric state can be maintained, if the applied voltage in the erase mode is equivalent to the first threshold, each pixel is written in the select mode with good responsiveness. Will be able to do.

In a preferred embodiment, the time of each of the erasing modes is set to a value corresponding to a plurality of steps in which a plurality of scanning electrodes other than the scanning electrodes set in the erasing mode are sequentially set to the selection mode. And

According to this driving method, the erase mode time of each scan electrode can be made longer than the select mode time assigned to one scan electrode. That is,
As the erase mode time, it is possible to secure a necessary and sufficient period for returning the antiferroelectric liquid crystal in the ferroelectric state to the antiferroelectric state. As described above, the antiferroelectric liquid crystal has a low return speed from the ferroelectric state to the antiferroelectric state under a low temperature condition. On the other hand, as described above, if the erase mode time can be extended,
During the erasing mode time, the liquid crystal can be appropriately returned from the ferroelectric state to the antiferroelectric state, and the subsequent writing to the pixel can be performed appropriately. Therefore, even if the selection mode time allocated to one scanning electrode of the antiferroelectric liquid crystal display is shortened by increasing the image display capacity of the antiferroelectric liquid crystal display, regardless of this, In addition, the writing and erasing processing of the pixel can be appropriately performed, and an appropriate image display can be performed.

In a preferred embodiment, after setting any one of the plurality of scanning electrodes to the erasing mode, the scanning electrode is set to the selection mode.

According to this driving method, since the erasing mode is set immediately before each of the scanning electrodes is set to the selection mode, it is possible to immediately write to the pixels after the erasing process. Become.

The light transmittance of the antiferroelectric liquid crystal in the selection mode need not always be maximized, and the gradation may be expressed for each pixel by appropriately adjusting the transmittance. The following two methods are used for gradation expression. In the first method, the value of the voltage applied to the antiferroelectric liquid crystal in the area corresponding to the pixel is changed to the first threshold value and the antiferroelectric liquid crystal completely transitions from the antiferroelectric liquid crystal to the ferroelectric state. While applying a voltage having an intermediate value with respect to the second threshold value,
This is a method performed according to the magnitude of the value. In the second method, the voltage applied to the antiferroelectric liquid crystal is set to a voltage equal to or higher than the second threshold, and the application time is set to a time during which the antiferroelectric liquid crystal cannot completely respond. (Pulse width).

[0027] Other advantages and features of the present invention will become more apparent from the following description of embodiments of the present invention.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings. here,
FIG. 1 is a cross-sectional view of an example of a structure of a reflection type antiferroelectric liquid crystal display A (configured for monochrome display) according to the present invention along an alignment direction. FIG. 2 is a perspective plan view of the display. FIG. 3 is a schematic perspective view showing main components of the display in an exploded state, and FIG. 4 is an explanatory view of the operation principle of a liquid crystal layer of the display.

The antiferroelectric liquid crystal display A shown in FIGS. 1 to 3 is configured as a reflection type.
As the driving method, a simple matrix method is adopted. The antiferroelectric liquid crystal display A includes a liquid crystal panel 1 and two types of drivers 2A and 2B.

As is apparent from FIG. 1, the liquid crystal panel 1 has a pair of transparent plates 10A and 10B and alignment films 11A and 11A.
11B, a liquid crystal layer 12, and a polarizing plate 13.

The transparent plates 10A and 10B are rectangular as shown in FIG. 3 and made of a transparent glass or resin film. As described above, a plurality of signal electrodes 14 and a plurality of scanning electrodes 15 are formed.

Each signal electrode 14 is formed of an ITO film or the like, and is formed as a strip-shaped transparent electrode extending in a certain direction as well shown in FIG. 2, and they are arranged in parallel in the width direction. One end 14a in the longitudinal direction of each signal electrode 14 is a terminal for connecting with the driver 2B.

Each scanning electrode 15 is made of aluminum or the like, and is formed as a reflective electrode extending perpendicular to each signal electrode 14 as well shown in FIG.
They are arranged in parallel to the direction in which the signal electrodes 14 extend. One end 15a of each scanning electrode 15 in the longitudinal direction is a terminal for connecting with the driver 2A.
Note that the surface of each scanning electrode 15 has a light reflecting function, and the surface constitutes a reflecting surface according to the present invention.

The alignment films 11A and 11B orient the liquid crystal molecules in a certain direction, and as shown in FIG.
And as shown in FIG. 3, the alignment directions of the alignment films 11A and 11B coincide with each other.

As shown in FIG. 1, the liquid crystal layer 12 includes an antiferroelectric liquid crystal (smectic liquid crystal) between a pair of transparent plates 10A and 10B (more precisely, between alignment films 11A and 11B). It is formed by encapsulation. This antiferroelectric liquid crystal has a layer structure in molecular arrangement as shown in FIG. 1 and schematically shown in FIG.
In the state where no voltage is applied to the liquid crystal layer 12, that is, when no electric field is applied to the antiferroelectric liquid crystal, FIG.
As shown in (2), the layers are arranged such that the directions of spontaneous polarization of adjacent layers are opposite to each other with respect to the normal direction of the layers. At this time, as a whole, the spontaneous polarizations cancel each other, the optical axis as a whole coincides with the orientation direction, and no apparent tilt angle occurs. On the other hand, when a voltage exceeding a predetermined threshold is applied, as shown in FIGS. 4 (II) and (III), the direction of spontaneous polarization is aligned with the direction of the electric field, and the liquid crystal molecules are at a predetermined angle with respect to the alignment direction. By tilting, for example, it becomes the first or second ferroelectric state.

The polarizing plate 13 transmits only light that vibrates in a specific direction, and is provided on the outward surface of the transparent plate 10A as well shown in FIG. Polarizing plate 13
The polarization axis of the alignment film 11 as shown in FIG.
It is inclined in the direction opposite to the tilt direction when a voltage is applied (for example, in the first ferroelectric state (FIG. 4 (II))) with respect to the orientation directions of A and 11B. As described above, the tilt angle of the polarization axis is set such that the sum of the tilt angle of the antiferroelectric liquid crystal in the first ferroelectric state (FIG. 4 (II)) is 45 ° or a value close thereto. And the maximum tilt angle is 31.2
When using an antiferroelectric liquid crystal at an angle of 13.8 °, it is most preferably set to 13.8 °. When the tilt angle of the polarization axis is set to 13.8 ° in this way, the tilt angle in the second ferroelectric state (FIG. 4 (III)) is 17.4 °.

Antiferroelectric Liquid Crystal Display A Having the Above Structure
In FIG. 2, a portion where the signal electrode 14 and the scanning electrode 15 intersect corresponds to a pixel for liquid crystal display as indicated by a reference symbol G in FIG. 2, and such pixels G are arranged in a matrix. In the antiferroelectric liquid crystal display A in which the orientation direction and the polarization axis direction have the above-described relationship, each pixel G
The relationship between the voltage applied to (the liquid crystal layer 12) and the light transmittance is as shown in FIG. FIG. 3B also shows a case where the polarization axis is not inclined with respect to the orientation direction in the antiferroelectric liquid crystal display configured as a reflection type. Then, in order to facilitate understanding of the technical significance of the present invention, the relationship between the applied voltage and the light transmittance when the polarization axis is not inclined with respect to the orientation direction will be described first.

In a configuration in which the polarization axis is not inclined with respect to the alignment direction, if no voltage is applied to the liquid crystal layer 12 (pixel G), the liquid crystal of the pixel G becomes as shown in FIG. It is in an antiferroelectric state. As can be seen from the above equation (2), this state can be obtained by focusing only on the relationship with the tilt angle.
As shown in FIG. 5B, the light transmittance I becomes maximum. From this state, when applied to the pixel G is a positive first threshold value V ₁ or more voltage, starting to tilt part of the liquid crystal molecules in accordance with the electric field direction, shown in FIG. 5 (b) Thus, the light transmittance gradually decreases. And the applied voltage is positive
If the threshold V ₂ or more, a shown in FIG. 4 (II) 1
The ferroelectric state is established, and the light transmittance is minimized as shown in FIG. As described above, in the configuration in which the polarization axis coincides with the alignment direction, since the maximum tilt angle of the currently discovered and synthesized liquid crystal molecules is 31.2 °, the minimum light transmittance is:
For example, when it is 21.5% or more, black display cannot be performed properly, and the contrast becomes 5 or less.

The antiferroelectric liquid crystal has a hysteresis between the tilt (response speed) of liquid crystal molecules by applying a voltage and the return (response speed) of the liquid crystal by releasing the voltage. Therefore, the first ferroelectric state (Fig. 4 (II)), if we reduce the applied voltage, the applied voltage, than the third threshold value V ₃ further smaller positive than the positive second threshold value V ₂ When the voltage is also smaller, some liquid crystal molecules start to return, and the state shifts from the first ferroelectric state (FIG. 4 (II)) to the anti-ferroelectric state (FIG. 4 (I)). It becomes smaller than the threshold value V _4,
It is completely in an antiferroelectric state. In this process, the light transmittance gradually changes from the minimum value to the maximum value.

In a configuration in which the polarization axis matches the orientation direction,
The tilt angle with respect to the polarization axis in the first and second ferroelectric states is the same between when a positive voltage is applied and when a negative voltage is applied. In this case, the behavior is completely opposite to the case where the applied voltage is increased as shown in FIG. As described above, when the polarization axis is not inclined with respect to the alignment direction, there is symmetry between the applied voltage and the light transmittance between the case where the positive voltage is applied and the case where the negative voltage is applied. .

On the other hand, the polarization axis is inclined with respect to the orientation direction, and the apparent maximum tilt angle with respect to the polarization axis is 4 °.
In the configuration of 5 °, as a result of the polarization axis being inclined from the alignment direction, as shown in FIG. 5A, the light transmission symmetry between the case where a positive voltage is applied and the case where a negative voltage is applied is obtained. Sex disappears. The specific contents will be described as follows.

When a voltage equal to or more than the second positive threshold value V ₂ is applied so that the apparent tilt angle of the liquid crystal molecules with respect to the polarization axis becomes 45 °, the liquid crystal of the pixel G becomes as shown in FIG. In the first ferroelectric state. At this time, as is clear from the above equation (2), the term of cos ² 2Ψ becomes zero, and the light transmittance I also becomes zero. A first ferroelectric state, if we applied voltage is made smaller than the positive second threshold value V _2, the positive first ferroelectric state to a third threshold value by hysteresis with respect to anti-ferroelectric liquid crystal applied voltage Will be maintained. If a positive third applied voltage than a threshold V ₃ decreases, the liquid crystal molecules begin to return, by applying a positive voltage lower than the fourth threshold value V _4, as shown in FIG. 4 (I) anti The ferroelectric state is set. This antiferroelectric state is a state in which the light transmittance is at or near the maximum.

On the other hand, the applied voltage is set to a negative first threshold value -V₁Than
If the liquid crystal of pixel G changes from the antiferroelectric state,
The transition to the second ferroelectric state is started, and the applied voltage is a negative second threshold.
-V _TwoLiquid crystal molecules apply a negative voltage
The minimum light transmittance at the time of this is obtained. At this time, liquid crystal molecules
The apparent tilt angle is much smaller than 45 °
The maximum tilt angle of itself is 31.2 °, the tilt angle of the polarization axis is
If it is 13.8 °, it becomes 17.4 °. For this reason,
2 In the ferroelectric state, a part of light (for example, about 20 to 30%)
Is displayed in gray in the second ferroelectric state because
Therefore, black display cannot be performed properly.

In order to solve such a problem, the present invention employs the following driving method. That is, the liquid crystal state of the pixel G is set to the first ferroelectric state (FIG. 4 (II)) to perform black display, and the liquid crystal state of the pixel G is set to the antiferroelectric state (FIG. 4 (I)) to perform white display. Do. And the pixel G
The state of the liquid crystal is set to the second ferroelectric state (FIG. 4 (III)) to prevent the liquid crystal panel 1 from burning. By using all of the first ferroelectric state, the second ferroelectric state, and the antiferroelectric liquid crystal state, the tilt direction of the liquid crystal molecules is prevented from being biased in one direction. In addition, burn-in of the liquid crystal panel 1 can be appropriately suppressed.

As shown by the imaginary line in FIG. 5A, the voltage applied to the pixel G is changed between the first threshold V ₁ and the second threshold V _2.
In this case, various gradations between black and white may be expressed without completely setting the state of the liquid crystal to the first ferroelectric state. Of course, the voltage applied to the pixel G is equal to or higher than the second threshold value V _2, and the time (pulse width) for applying the voltage equal to or higher than the second threshold value V ₂ is completely equal to the first liquid crystal.
The time during which the ferroelectric state does not occur (the time during which no response can be completely obtained) may be used to express an intermediate gradation.

Next, the specific operation of the drivers 2A and 2B of the antiferroelectric liquid crystal display A will be described, and the operation of the antiferroelectric liquid crystal display A will be described.

In order to make the description of the present embodiment easy to understand, the plurality of scanning electrodes 15 shown in FIG. 2 are sequentially arranged from the upper side to the lower side in the order of the first scanning electrode, the second scanning electrode, and the third scanning electrode. Scan electrodes ... With respect to the plurality of signal electrodes 14, the one located at the left end among them is the first signal electrode.

In order to drive the antiferroelectric liquid crystal display A, as shown in FIG. 6, each of the plurality of scanning electrodes 15 is selected, for example, one by one in a certain order, in the non-selection mode, and in the burn-in. While switching between the prevention mode and the erase mode, a signal voltage is selectively applied to the plurality of signal electrodes 14. Thus, the value of the voltage applied to the liquid crystal of each pixel G is updated, for example, for each line. The procedure of voltage application in this case will be described below as an example of a voltage application mode to the fifth scanning electrode 15 and the first signal electrode 14 corresponding to one pixel G indicated by cross hatching in FIG. As can be seen from FIG. 6, the fifth scan electrode 15 is subjected to one burn-in prevention mode for one frame (for example, from the end of the previous selection mode to the next selection mode). , 4
One erase mode, one selection mode, and a predetermined number of non-selection modes appropriately set according to the number of scan electrodes 15 and the driving method are sequentially repeated.

First, as shown in FIG. 7A, a voltage smaller than, for example, the negative second threshold value -V ₂ (see FIG. 5) is applied to the pixel G for a predetermined time T, and The liquid crystal is placed in the second ferroelectric state (FIG. 4 (III)), and the burn-in prevention mode is performed.

Such a voltage application is expressed as a difference between the signal voltage of the signal electrode 14 and the scanning voltage of the scanning electrode 15. During the burn-in prevention mode of the fifth scan electrode 15, one of the other scan electrodes 15 is always in the selection mode (see FIG. 6), and writing to the pixel corresponding to the scan electrode 15 is performed. Have been done. Therefore, FIG.
As shown in (c), a signal voltage is applied to the first signal electrode 14 under the control of the driver 2B. In the burn-in prevention mode, regardless of the magnitude of the signal voltage applied to the first signal electrode 14, as shown in FIG. −V ₂ . As a means for achieving this, the scanning voltage in the burn-in prevention mode is set to a value larger than the absolute value of the scanning voltage in the selection mode described later.

The length of the time T in the burn-in prevention mode is, for example, the same as the time T (time for one step) of the selection mode assigned to one scan electrode 15 described later. In addition, not only the pixel G but also all of the antiferroelectric liquid crystals constituting each of the pixels for one line corresponding to the fifth scanning electrode 15 are in the second ferroelectric state (see FIG. 4 (III)).

The signal voltage shown in FIG. 7 (c) is a pulse having a positive potential, but the present invention is not limited to this. The signal voltage has a positive or negative potential or only a negative potential. Can be used as the signal voltage.
Further, the amplitude value of the signal voltage does not need to be constant, and it is possible to give a gradation of light and shade to the display image by changing the value, and such a configuration may be adopted.

After the burn-in prevention mode, the erase mode is performed. In this erase mode, as shown in FIG. 7B, the voltage applied to the fifth scan electrode 15 is set to zero under the control of the driver 2A, and this state is maintained for a predetermined time. The time in the erasing mode is a time in which a plurality of scanning electrodes 15 different from the fifth scanning electrode 15 are sequentially switched to the selection mode, and is, for example, four times (four steps) the time in the selection mode. Even during the erasing mode of the fifth scanning electrode 15, the other plurality of scanning electrodes 15 are sequentially switched to the selection mode, and the signal voltage is applied to the first signal electrode 14 as shown in FIG. Is selectively applied. In this erasing mode, regardless of the magnitude of the signal voltage, as shown in FIG.
Voltage applied is made so as not to exceed the first threshold voltage V ₁ of the positively. However, since the select mode is performed next erase mode, preferably keep a value closer to the applied voltage first threshold voltages V ₁ positive the erasing mode for the next selection mode.

In this erase mode, the pixel G
, All of the antiferroelectric liquid crystal constituting each pixel of one line corresponding to the fifth scan electrode 15 returns from the ferroelectric state to the antiferroelectric state.

In this embodiment, while the applied voltage in the burn-in prevention mode shown in FIG. 7A is a negative voltage, the applied voltage in the erase mode is a positive voltage, and its polarity is It is the opposite. By thus reversing the polarity of the applied voltage, even when the antiferroelectric liquid crystal display A is used under relatively low temperature conditions, the liquid crystal in the ferroelectric state is relatively changed to the antiferroelectric state. It is possible to return quickly. More specifically, the time required to return from the ferroelectric state to the antiferroelectric state is, for example, about 1 msec at 25 ° C., and about 10 m at 0 ° C.
msec. However, as described above, when the polarity of the scan voltage in the erase mode is set to the opposite polarity to the polarity of the scan voltage in the immediately before burn-in prevention mode, for example, under the condition of 0 ° C., the ferroelectric state changes. The time required to return to the antiferroelectric state can be shortened to about 1 to several msec.

After the erase mode, a selection mode is performed. Large The selection mode, as shown in FIG. 7 (a), in accordance with the gradation to be achieved, a positive first second threshold voltages V ₁ and the same degree of voltage and positive than the second threshold voltage V ₂ A voltage having a value between the voltage and the voltage is applied, and writing to the pixel G is performed. For example, when performing black display, the pixel G has a positive second
The same degree of voltage and the threshold voltage V ₂ is applied (see the first frame of FIG. 7 (a)), the liquid crystal of the pixel G is the first ferroelectric state (Fig. 4 (II)). On the other hand, when performing white display, a voltage approximately equal to the positive first threshold value V ₁ is applied to the pixel G (see the third frame in FIG. 7A), and the liquid crystal of the pixel G is in an antiferroelectric state. (FIG. 4I) is maintained. Further, when displaying an intermediate gray level between black and white, a voltage having a value between the first threshold voltage V ₁ and the second threshold voltage V ₂ corresponding to the gray level to be expressed is applied ( FIG. 7A shows the second frame. The value of the voltage applied to the pixel G is shown in FIG. 7C by applying a negative voltage to the fifth scan electrode 15 as shown in FIG. 7B under the control of the driver 2A and by controlling the driver 2B. As described above, the adjustment is performed by applying a signal voltage corresponding to the gradation to be expressed to the first signal electrode 14.

Thereafter, under the control of the driver 2A, no voltage is applied to the fifth scanning electrode 15 as shown in FIG. 7 (b), and under the control of the driver 2B, the first scanning electrode 15 as shown in FIG. 7 (c). the signal electrode 14 first threshold voltages V ₁ and the third threshold voltage V ₃ intermediate voltage first threshold voltages V ₁ the voltage applied to the pixel G by applying the values of the third threshold voltage V ₃ And maintain an intermediate value. This mode is a non-selection mode in which the state of the selection mode is maintained. During the non-selection mode, the ferroelectric state or the antiferroelectric state of the pixel G is maintained, and the pixel G
The state of writing to is maintained.

When the image display of the second frame is executed after the first frame for displaying the moving image is completed, as shown in FIG. A predetermined scanning voltage is applied in the same procedure as in the first frame, and the driving mode of the fifth scanning electrode 15 is sequentially switched to a burn-in prevention mode, an erasing mode, a selection mode, and a non-selection mode. Writing and erasing to the pixel G are performed.

The driver 2A performs the above-described scanning voltage application processing on each of the plurality of scanning electrodes 15. A specific procedure at that time will be described with reference to FIG. However, in the figure, the contents are simplified for easy understanding.

As shown in the drawing, in the first step, only the fifth scan electrode is in the burn-in prevention mode, and in the next second step, only the sixth scan electrode is in the burn-in prevention mode. Is done. Thereafter, similarly, each of the plurality of scan electrodes is switched to the burn-in prevention mode one by one in a fixed order. Therefore, when an image of one frame is displayed, all of the plurality of scan electrodes become 1
As a result, the image sticking prevention mode is set, and image sticking can be prevented for all pixels.

Since the scan electrodes 15 are switched one by one to the burn-in prevention mode, flicker can be prevented. For example, when the total number of the scanning electrodes 15 is 480 lines and a moving image of 30 frames / second is displayed, the allocation time for one scanning electrode is 0.0694 msec. The time T in the burn-in prevention mode may be the same length of time as the assigned time. In such a very short time, all the pixels of one line corresponding to one scanning electrode 15 are gray. Even if it is displayed, it is difficult to recognize it with the naked eye. Therefore, in the present embodiment, it is possible to prevent image burn-in while preventing flicker. The burn-in prevention mode is set immediately before the erase mode. Even if one line of pixels is written in gray by the burn-in prevention mode, for example,
This write operation is switched to the selection mode after being erased by the subsequent erase mode. Therefore, the original writing process for each pixel in the selection mode can be appropriately performed.

In the present embodiment, for example, in the second step, when the first scan electrode 15 is in the selection mode, the second scan electrode 15 to the fifth scan electrode 15
The four scanning electrodes 15 are collectively set to the erase mode. In the subsequent third step, while the second scan electrode 15 is set to the selection mode, the sixth scan electrode 1
5 is newly added to the erase mode, and the four scan electrodes 15 are also collectively set to the erase mode. Hereinafter, similarly, the four scanning electrodes 15 are always in the erasing mode.

According to such a procedure, each scanning electrode 15
Before the selection mode is set, the erase mode is always set to the four-step period (for example, when focusing on the fifth scan electrode 15 described above, the fifth scan electrode 15
Is maintained in the erase mode from the second step to the fifth step before is set to the selection mode). Therefore, it is possible to appropriately secure the time required for returning the antiferroelectric liquid crystal from the ferroelectric state to the antiferroelectric state. Needless to say, the time during which each scanning electrode 15 is in the erasing mode is not limited to the time during which the scanning electrodes 15 for four lines are switched to the selection mode, but can be longer.

For example, when the total number of the scanning electrodes 15 is 480 lines and a moving image of 30 frames / second is displayed, the time allocated to one scanning electrode 15 is 0.0.
694 msec has already been described.
On the other hand, in the present embodiment, for example, the time during which the scanning electrodes 15 for 15 lines are sequentially switched to the selection mode can be the erasing mode time for the scanning electrodes 15 for one line. Thereby, the time of the erasing mode of each scanning electrode 15 can be set to 1 msec or more. If it takes 1 msec for the liquid crystal to return from the ferroelectric state to the antiferroelectric state, such a return can be appropriately performed within the erasing mode time. As understood from the above, according to the present embodiment, the total number of the scanning electrodes 15 is increased in order to increase the display image capacity of the antiferroelectric liquid crystal display A. As a result, one scanning electrode Even if the assignment time of the selection mode is shortened, the erasure can be appropriately terminated before writing to the pixel, and an appropriate moving image can be displayed.

The contents of the present invention are not limited to the above embodiment.

In the above embodiment, the erase mode time of each scan electrode is set longer than the select mode time assigned to one scan electrode, but the present invention is not limited to this. In the present invention, the erase mode time of each scan electrode may be the same length as the select mode time. If the erase mode time is too long,
Since flicker becomes noticeable, set the erase mode time to 8
It is desirable to keep it to about msec or less.

In the present invention, when sequentially switching the respective driving modes of a plurality of scanning electrodes, it is not always necessary to switch the scanning electrodes one by one, but it is also possible to switch two scanning electrodes, for example. Further, in the present invention, an antiferroelectric liquid crystal display is employed in an STN liquid crystal display.
It is also possible to use a screen division drive system, and it is also possible to adopt such a two-screen division drive system and further apply the drive method according to the present invention repeatedly.

The specific structure of each part of the antiferroelectric liquid crystal display according to the present invention can be variously changed in design other than the above. Further, the specific procedure of the method of driving the antiferroelectric liquid crystal display according to the present invention can be variously changed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an embodiment of an antiferroelectric liquid crystal display according to the present invention.

FIG. 2 is a perspective plan view of an antiferroelectric liquid crystal display.

FIG. 3 is a schematic perspective view showing components of the antiferroelectric liquid crystal display shown in FIG. 1 in an exploded state.

FIG. 4 is an explanatory diagram of an operation of a liquid crystal layer of the antiferroelectric liquid crystal display according to the present invention.

FIG. 5 is a graph schematically showing a relationship between a voltage applied to a liquid crystal layer of an antiferroelectric liquid crystal display configured as a reflection type and a light transmittance of the display;
(A) shows the case where the polarization axis of the polarizing plate is inclined with respect to the orientation direction of the alignment film, and (b) shows the case where the polarization axis is not inclined.

FIG. 6 is a diagram showing a procedure for switching the mode of a scanning electrode.

7A is a time chart of a voltage (signal voltage-scanning voltage) applied to the liquid crystal, FIG. 7B is a time chart of the scanning voltage, and FIG. 7C is a time chart of the signal voltage. It is.

[Explanation of symbols]

 A Antiferroelectric liquid crystal display 2A, 2B Driver (constituting control means) 10A Transparent plate 11A, 11B Alignment film 12 Liquid crystal layer 14 Signal electrode 15 Scanning electrode (constituting reflective surface) G pixel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // G09G 3/36 G02F 1/137 510 5C080 F term (reference) 2H088 EA02 GA04 JA20 KA15 KA17 MA02 MA20 2H090 KA15 LA09 MA06 MA10 2H091 FA08X FA08Z FD09 HA12 LA17 2H093 NA14 NA31 NA51 ND04 ND12 NE04 NF20 5C006 AA01 AA02 AA11 AA22 AC02 AC15 AC22 BA13 BB12 BC03 FA34 FA54 5C080 AA10 BB05 CC03 DD01 FF10 JJ02 KK04 JJ04 JJ04 JJ04 JJ04 JJ04 JJ02 JJ04 JJ04 JJ04

Claims (7)

[Claims] An antiferroelectric liquid crystal is filled between a transparent plate in which a polarizing plate is disposed on an outer surface side and an alignment film is disposed on an inner surface side, and a reflective surface facing the inner surface of the transparent plate, The polarizing plate has a configuration in which the polarization axis is inclined in the direction opposite to the tilt direction when the voltage of the antiferroelectric liquid crystal is applied with respect to the alignment direction of the alignment film, and by a simple matrix driving method. By selectively applying a signal voltage to a plurality of signal electrodes while sequentially switching a selection mode, a non-selection mode, and an erasing mode in a predetermined order by a plurality of scanning electrodes, the anti-ferroelectricity A reflective antiferroelectric liquid crystal display further comprising control means for writing and erasing a plurality of pixels constituted by liquid crystals, wherein the control means sets each of the scanning electrodes to the erasing mode. before The anti-ferroelectric liquid crystal is configured to be in a sticking prevention mode in which a voltage having a polarity opposite to that of the selection mode or the non-selection mode is applied to bring the antiferroelectric liquid crystal into a ferroelectric state. Dielectric liquid crystal display. 2. An antiferroelectric liquid crystal is filled between a transparent plate in which a polarizing plate is disposed on an outer surface side and an alignment film is disposed on an inner surface side, and a reflective surface facing the inner surface of the transparent plate. A reflective antiferroelectric liquid crystal display having a configuration in which the polarization axis of the polarizing plate is tilted in the direction opposite to the tilt direction when a voltage is applied to the antiferroelectric liquid crystal with respect to the alignment direction of the alignment film. On the other hand, by a simple matrix driving method, a predetermined number of scanning electrodes are sequentially switched in a predetermined order by a predetermined number, a selection mode, a non-selection mode, and an erasing mode. A method of driving by writing and erasing a plurality of pixels composed of antiferroelectric liquid crystal by applying the voltage, wherein each of the scanning electrodes is set to the selection mode or the erasing mode before the scanning electrode is set to the erasing mode. Characterized in that the anti-seizing mode by applying an opposite polarity voltage to the ferroelectric state the antiferroelectric liquid crystal and the non-selection mode, antiferroelectric method for driving a liquid crystal display. 3. The erase mode according to claim 1, wherein the antiferroelectric liquid crystal starts to change from the antiferroelectric liquid crystal state to a ferroelectric state having a polarity opposite to that of the burn-in prevention mode with respect to a target pixel.
3. The method of driving an antiferroelectric liquid crystal display according to claim 2, wherein the method is performed by applying a voltage having a value corresponding to or substantially equal to the threshold voltage. 4. The method according to claim 1, wherein the time of each of the erasing modes is a plurality of steps in which a plurality of scanning electrodes different from the scanning electrodes set in the erasing mode are sequentially set to a selection mode. 4. The method for driving an antiferroelectric liquid crystal display according to 2 or 3. 5. The anti-ferroelectric liquid crystal display according to claim 2, wherein, after setting one of the plurality of scan electrodes to the erase mode, the scan electrode is set to the select mode. Drive method. 6. The method according to claim 1, wherein the value of the voltage applied to the antiferroelectric liquid crystal in the region corresponding to the pixel is the first threshold value, and the antiferroelectric liquid crystal completely transitions from the antiferroelectric liquid crystal to the ferroelectric state. While applying a voltage having an intermediate value with respect to the second threshold value,
6. The driving method for an antiferroelectric liquid crystal display according to claim 3, wherein the gradation of each pixel is expressed according to the magnitude of the value. 7. An anti-ferroelectric liquid crystal in a region corresponding to the pixel, wherein the anti-ferroelectric liquid crystal can completely transition from the anti-ferroelectric state to the ferroelectric state. 4. The method according to claim 3, further comprising: applying a voltage equal to or more than two thresholds, setting the application time to a time during which the antiferroelectric liquid crystal cannot completely respond, and performing gradation expression of each pixel according to the magnitude of the time.
6. The method for driving an antiferroelectric liquid crystal display according to any one of items 5 to 5.