JP2002090709A - Antiferroelectric liquid crystal display and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image sticking on an antiferroelectric liquid crystal display without causing any trouble such as a flicker. SOLUTION: While every specific number of scanning electrodes 15 of the antiferroelectric liquid crystal display (A) employing a simple matrix driving system are sequentially switched among a select mode, a non-select mode, and an erasure mode in certain order, a signal voltage is selectively applied to signal electrodes 14 to write and erase pixels composed of antiferroelectric liquid crystal. In addition to the mentioned three modes, a sticking prevention mode wherein a voltage higher than a certain value is applied to the respective scanning electrodes 15 so as to set in a ferroelectric state the antiferroelectric liquid crystal constituting the pixels corresponding to the respective scanning electrodes 15 is available as a driving mode of each scanning electrode 15, and the driving mode before each scanning electrode 15 is set in the erasure mode is set to the sticking prevention mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an antiferroelectric liquid crystal display and a driving method thereof.

[0002]

2. Description of the Related Art Antiferroelectric liquid crystals have a remarkably fast response time 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 factor 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, which have a high response speed as described above, will be used in next-generation mobile phones. And mobile video display.

Since the relationship between the light transmittance of an antiferroelectric liquid crystal display and the applied voltage is essential for understanding the present invention, FIG. 6 shows the relationship between the light transmittance and the applied voltage for a transmission type display. Show. FIG. 7 shows a schematic structure of the molecular arrangement of the antiferroelectric liquid crystal corresponding to FIG. The liquid crystal molecules have dipoles in a direction orthogonal to the long axis direction and have birefringence in which the refractive indices are different between the long axis direction and the short axis direction. As shown in FIG. 6, the antiferroelectric liquid crystal is
The antiferroelectric state is maintained until the voltage exceeds the saturation voltage Vsat from the state of no electric field. In this antiferroelectric state, FIG.
As shown in (I), the layers adjacent to each other are oriented so that the directions of spontaneous polarization are opposite to each other with respect to the layer normal. At this time, as a whole, the spontaneous polarizations cancel each other. Since the polarizing axes of the two polarizing plates on the light incident side and the light emitting side provided in the liquid crystal display are in directions perpendicular to each other, in the above-described antiferroelectric state, the apparent tilt of the liquid crystal molecules is apparent. The angle is 0 ° and no light passes through this liquid crystal display.

On the other hand, when the voltage applied to the antiferroelectric liquid crystal exceeds the saturation voltage Vsat, the liquid crystal enters a ferroelectric state. In this ferroelectric state, as shown in FIGS. 7 (II) and (III),
The liquid crystal molecules are tilted by a predetermined angle in the same direction for each layer, and light passes through the liquid crystal display with a predetermined transmittance. This characteristic has a hysteresis property, and the ferroelectric state is maintained and a predetermined transmittance is maintained until the applied voltage becomes lower than the threshold voltage Vth. Further, the above characteristics can be obtained regardless of whether the applied voltage is positive or negative.

As a driving method of the antiferroelectric liquid crystal display, a simple matrix method can be adopted similarly to the STN liquid crystal display, and an image can be displayed by a line sequential method. However, in the antiferroelectric liquid crystal display, there are three types of driving modes of the scanning electrode: a selection mode (writing mode), a non-selection mode, and an erasing mode. The selection mode is a mode for writing to a pixel formed of an antiferroelectric liquid crystal, and the writing is performed by bringing the antiferroelectric liquid crystal into a ferroelectric state. The non-selection mode is a mode for maintaining the writing state of the pixel. The erasing mode is a mode for erasing writing of a pixel,
The erasure is performed by returning the liquid crystal to an antiferroelectric state. When an antiferroelectric liquid crystal display having such three types of driving modes is driven by a line-sequential system, a plurality of scanning electrodes (horizontal electrodes, common electrodes) are selected, for example, one by one in a fixed order, and non-selected. A signal voltage is selectively applied to a plurality of signal electrodes (vertical electrodes, segment electrodes) while switching to each mode of selection and erasing.

[0006]

In the above antiferroelectric liquid crystal display, as described below,
It is known that image sticking occurs. That is, the orientation structure of the liquid crystal in the antiferroelectric liquid crystal panel is ideally a structure in which liquid crystal layers are arranged in a straight line between a pair of substrates 90 and 91 as shown in FIG. (Bookshelf structure). However, actually, as shown in FIG. 3B, the liquid crystal layer has a structure (chevron structure) that is bent in the shape of a square. The degree of bending of the liquid crystal layer in the chevron structure changes depending on the driving history of the liquid crystal panel.
For this reason, the degree of bending of the liquid crystal layer may increase as shown in FIG. In such a state, it becomes difficult to display an image with a predetermined brightness, and when the liquid crystal display screen is visually observed, the part appears to be burned in.

In order to prevent such a burn-in phenomenon, a high voltage may be applied to the liquid crystal. When a voltage equal to or higher than the saturation voltage is applied to the liquid crystal, the orientation structure of the liquid crystal can be made closer to the bookshelf structure during that time.
By doing so, the alignment structure of the liquid crystal after the application of the voltage is released has a structure in which the degree of bending in the shape of a "<" is small, and burn-in can be prevented.

However, in the prior art, no specific means has been proposed in order to appropriately realize a voltage application process for preventing burn-in. If a voltage is applied simultaneously to each of the plurality of scanning electrodes of the liquid crystal display for the purpose of preventing image burn-in, the entire display screen becomes, for example, pure white. Also, when a voltage is applied to only a part of the plurality of scanning electrodes, all of the pixels on the corresponding line become pure white, for example, which causes flicker (screen flicker).

The present invention has been conceived under such circumstances, and is an antiferroelectric liquid crystal capable of preventing an image burn-in phenomenon without causing a problem such as flicker. An object of the present invention is to provide a display driving method and an antiferroelectric liquid crystal display.

[0010]

DISCLOSURE OF THE INVENTION In order to solve the above problems, the present invention employs the following technical means.

A method of driving an antiferroelectric liquid crystal display provided by a first aspect of the present invention is a method of driving a plurality of scanning electrodes of an antiferroelectric liquid crystal display employing a simple matrix driving method by a predetermined number. By sequentially applying a signal voltage to a plurality of signal electrodes while sequentially switching to a selection mode, a non-selection mode, and an erasing mode in order, writing and erasing of a plurality of pixels constituted by an antiferroelectric liquid crystal can be performed. The method of driving an anti-ferroelectric liquid crystal display according to claim 1, wherein the driving modes of the scanning electrodes include, in addition to the three types of modes, an anti-ferroelectric liquid crystal display comprising a plurality of pixels corresponding to the scanning electrodes. There is a burn-in prevention mode in which a voltage of a fixed value or more is applied to each of the scanning electrodes so as to bring the crystalline liquid crystal into a ferroelectric state, and the scanning electrodes are erased A drive mode before setting the over-de, is characterized in that the prevention mode the sticking.

In the method of driving an antiferroelectric liquid crystal display according to the present invention, the following effects can be obtained.

First, the plurality of scanning electrodes are sequentially switched in a certain order in the order of the selection mode, the non-selection mode, the burn-in prevention mode, and the erasing mode.
Therefore, each scanning electrode is always set to the burn-in prevention mode at least once during the image display for one frame, and the image burn-in is appropriately prevented while a desired image is displayed. be able to.

Second, in displaying an image, for example, after one scan electrode is set to the burn-in prevention mode, the next one scan electrode is set to the burn-in prevention mode. Then, the plurality of scan electrodes are switched to the burn-in prevention mode by a predetermined number in a fixed order. In this case, the time required for the burn-in prevention mode for one scanning electrode can be extremely short. Therefore, even if the pixel corresponding to the scan electrode set in the burn-in prevention mode becomes white, for example,
This can be prevented from being recognized by the user's naked eyes, and the occurrence of flicker can be prevented.

Third, since each scan electrode is switched to the erase mode after the burn-in prevention mode is set,
After the state in which writing to the pixel has been performed in the burn-in prevention mode is appropriately resolved in the subsequent erasing mode, the writing process to the pixel can be appropriately performed thereafter. As described above, in the present invention, a burn-in prevention mode is additionally provided as compared with the related art, but it is possible to prevent a problem that the image display function is impaired by this. .

In a preferred embodiment of the present invention, the selection mode is a mode in which a scanning voltage higher than a predetermined saturation voltage is applied to the scanning electrodes, and the non-selection mode is a mode in which the saturation voltage and the threshold voltage are applied. The erase mode is a mode in which a scan voltage less than the threshold voltage is applied to the scan electrode, and the burn-in prevention mode is the selection mode. In this mode, a scanning voltage having an absolute value higher than the applied voltage in the above is applied to the scanning electrode.

The value of the voltage actually applied to the antiferroelectric liquid crystal is a potential difference between the scanning voltage applied to the scanning electrode and the signal voltage applied to the signal electrode. Therefore, in the present invention, depending on how to apply a voltage to the signal electrode,
The contents of each of the selection mode, the non-selection mode, the burn-in prevention mode, and the erasing mode may be different from those described above.

In another preferred embodiment of the present invention, the scan voltage in the erase mode is opposite in polarity to the scan voltage in the burn-in prevention mode set immediately before the erase mode.

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 (the mode does not enter the selection mode) is positively applied, the It is possible to increase the above-described return speed as compared with a case where such a voltage application is not performed. According to the above configuration, when the anti-ferroelectric liquid crystal is switched from the ferroelectric state to the erasing mode in the burn-in prevention mode, the voltage applied to the liquid crystal has the opposite polarity. Increase the speed of returning to the dielectric state,
The image can be quickly erased.
Although the antiferroelectric liquid crystal rapidly changes from the antiferroelectric state to the ferroelectric state, the return speed from the ferroelectric state to the antiferroelectric state is greatly affected by the temperature, and when the temperature is low, Has the property of being slow. According to the above configuration,
This is suitable for quickly completing the write / erase process of the pixel under the use condition at a low temperature.

In another preferred embodiment of the present invention, the erase mode period of each of the scan electrodes is set such that a plurality of scan electrodes other than the scan electrodes set to the erase mode are sequentially set to the select mode. Period.

According to such a configuration, the erase mode period of each scan electrode can be made longer than the select mode period assigned to one scan electrode. That is, 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 the erasing mode period. 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 contrary,
As described above, if the erasing mode period can be lengthened, the liquid crystal can be appropriately returned from the ferroelectric state to the antiferroelectric state during this erasing mode period, and the subsequent writing to the pixel can be properly performed. It can be done. Therefore, even if the selection mode period assigned to one scan 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, it is possible to appropriately perform the erasing process of writing the pixel, and to perform an appropriate image display.

In another preferred embodiment of the present invention, when any one of the plurality of scanning electrodes is set to the selection mode, the selection mode is set after the scanning electrode. The other plurality of scan electrodes are set to the erase mode.

According to such a configuration, each of the scanning electrodes can be set to the erasing mode immediately before setting to the selection mode, and writing is immediately performed on the pixels after the erasing process. Becomes possible.

In the antiferroelectric liquid crystal display provided by the second aspect of the present invention, the antiferroelectric liquid crystal is sealed between a pair of substrates having a plurality of scanning electrodes and a plurality of signal electrodes. Thus, the liquid crystal panel in which a plurality of pixels are arranged in a matrix and the plurality of scanning electrodes of the liquid crystal panel are sequentially switched to a selection mode, a non-selection mode, and an erasing mode by a predetermined number in a fixed order. A control means for selectively applying a signal voltage to the plurality of signal electrodes to perform writing and erasing on the plurality of pixels. The driving modes of the scanning electrodes include, in addition to the three modes, an antiferroelectric liquid crystal constituting a plurality of pixels corresponding to the scanning electrodes in a ferroelectric state. There is a burn-in prevention mode for applying a voltage equal to or more than a predetermined value to each of the scan electrodes, and the control means sets the drive mode before setting each of the scan electrodes to the erase mode to the burn-in prevention mode. It is characterized by being constituted so that.

According to the antiferroelectric liquid crystal display having such a configuration, the same effect as obtained by the driving method of the antiferroelectric liquid crystal display provided by the first aspect of the present invention can be expected. .

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

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

FIGS. 1 and 2 show an example of an antiferroelectric liquid crystal display according to the present invention. The antiferroelectric liquid crystal display A of this embodiment is of a transmission type using a backlight (not shown), and its driving method is a simple matrix method. The antiferroelectric liquid crystal display A includes a liquid crystal panel 1 and two types of drivers 2A and 2A.
B.

As shown in FIG. 2, the liquid crystal panel 1 includes a pair of substrates 10A and 10B, a liquid crystal layer 11,
It comprises a pair of polarizing plates 12a and 12b. The substrates 10A and 10B are rectangular and made of a transparent glass or resin film. Substrates 10A, 10B
A plurality of signal electrodes 14 and a plurality of scanning electrodes 15 are formed on each of the inward faces. These are all formed as transparent electrodes made of an ITO film or the like. As is well shown in FIG.
Reference numeral 4 denotes a band extending in a certain direction, which is arranged in parallel in the short direction thereof (FIG. 1 is a perspective view showing the signal electrode 14 and the scanning electrode 15 by solid lines). One end 14a in the longitudinal direction of each signal electrode 14 is a terminal for connecting with the driver 2B. Multiple scanning electrodes 15
Are strip-shaped extending in a direction orthogonal to the signal electrodes 14, and are arranged in parallel with the direction in which the signal electrodes 14 extend.
One end 15a in the longitudinal direction of each scanning electrode 15 is connected to a driver 2A.
It is a terminal part for achieving connection with the terminal.

In FIG. 2, the liquid crystal layer 11 is formed by sealing an antiferroelectric liquid crystal between a pair of substrates 10A and 10B. The phase of this antiferroelectric liquid crystal is a smectic phase that exhibits ferroelectricity and antiferroelectricity,
It has the same characteristics as those described with reference to FIGS. In the liquid crystal layer 11, a portion where the scanning electrode 15 and the signal electrode 14 cross and face each other corresponds to a pixel for liquid crystal display, and the pixels are arranged in a matrix. The liquid crystal layer 11 is sandwiched between a pair of alignment films 13a and 13b covering the signal electrode 14 and the scanning electrode 15. These alignment films 13a and 13b are for aligning liquid crystal molecules in a certain direction, and they have a parallel alignment in which the alignment directions coincide with each other. The polarizing plates 12a and 12b are provided on the outward surfaces of the pair of substrates 10A and 10B, and the polarization axis of the polarizing plate 12b matches the alignment direction of the alignment films 13a and 13b. Polarizing plate 1
The polarization axis of 2a is orthogonal to the polarization axis of the polarizing plate 12b. The liquid crystal panel 1 is configured for monochrome display. However, by additionally providing an RGB color filter to the liquid crystal panel 1, a display capable of color display can be provided.

The driver 2A corresponds to a so-called horizontal driver or common driver. Driver 2
B corresponds to a so-called vertical driver or segment driver. These are all configured using one or more IC chips. Driver 2
A and 2B are tabs 3A having wiring portions 20a and 20b,
The terminal portions 15a of the scanning electrodes 15 and the terminal portions 14a of the signal electrodes 14 are electrically connected to each other via 3B. Of course, in the present invention, the driver 2
The means for connecting A and 2B is not limited to means using tabs 3A and 3B. For example, drivers 2A and 2B are directly mounted on the substrate of liquid crystal panel 1, and the drivers 2A and 2B are connected via a wiring pattern formed on the substrate. , 2B to each scanning electrode 15
Alternatively, it may be electrically connected to each signal electrode 14.

The drivers 2A and 2B are hard-wired to a CPU (not shown) and other external devices, and receive necessary power, data signals for display images, and other control signals. I have. Driver 2A, 2
B is configured to apply a scanning voltage to each scanning electrode 15 and a signal voltage to each signal electrode 14 so as to display a desired image in a line-sequential manner, as described later.

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 facilitate understanding of the description of the present embodiment, the plurality of scanning electrodes 15 shown in FIG. 1 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 electrode ... Multiple signal electrodes 14
For the first one of them
This is a signal electrode.

In order to drive the antiferroelectric liquid crystal display A, a plurality of scanning electrodes 15 are selected, for example, one by one in a fixed order, a non-selection mode, a burn-in prevention mode,
While switching to the erase mode, a plurality of signal electrodes 1
4 is selectively applied with a signal voltage. The procedure of voltage application in this case is described by the fifth scanning electrode 15 and the first signal electrode 1 corresponding to one pixel G indicated by cross hatching in FIG.
4 will be described below as an example of a voltage application mode.

First, the driver 2 is connected to the fifth scanning electrode 15.
Under the control of A, as indicated by reference numeral N1 in FIG.
A scanning voltage exceeding the saturation voltage Vsat (see FIG. 6) is applied, and the fifth scanning electrode 15 is set to the burn-in prevention mode for a predetermined time T1. The length of the time T1 is, for example, the same as the time T3 of the selection mode assigned to one scanning electrode 15 described later. This fifth scanning electrode 15
During the burn-in prevention mode, the other scan electrodes 15
Is always in the selection mode, and writing to the pixel corresponding to the scan electrode is performed. Therefore, as shown by reference numeral N1 'in FIG. 3B, a signal voltage for that purpose is applied to the first signal electrode 14 by 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 by the symbol N1 "in FIG.
The voltage applied to the pixel G (the potential difference between the fifth scanning electrode 15 and the first signal electrode 14) always exceeds the saturation voltage Vsat. 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.

In the above-described burn-in prevention mode,
Not only the pixel G, but also all of the antiferroelectric liquid crystal constituting each of the pixels for one line corresponding to the fifth scanning electrode 15 are brought into a ferroelectric state. Therefore, in this burn-in prevention mode, the alignment structure of the antiferroelectric liquid crystal corresponding to the fifth scanning electrode 15 can be made to be a structure close to the bookshelf structure shown in FIG. This allows
By preventing the orientation structure of the antiferroelectric liquid crystal from having the structure shown in FIG. 8C, image sticking can be prevented. When the fifth scanning electrode 15 is in the burn-in prevention mode and the antiferroelectric liquid crystal is in the ferroelectric state, as understood from the description in FIGS. 6 and 7, the pixel G transmits light. Thus, the pixels for one line corresponding to the fifth scanning electrode 15 are, for example, white. However, as described later, the white time is extremely short, and it is difficult to recognize this time with the naked eye.

Although the signal voltage shown in FIG. 3B is a pulse having positive and negative potentials, the present invention is not limited to this, and the signal voltage may be a signal voltage of only a positive potential or only a negative potential. Can also. Further, the value of the signal voltage does not need to be constant, and it is possible to give a shade 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 threshold voltage Vth (see FIG. 6) is applied to the fifth scanning electrode 15 under the control of the driver 2A, as indicated by reference numeral N2 in FIG.
, And the fifth scan electrode 15 is set in the erase mode for a predetermined time T2. The erasing mode time T2 is a time during which a plurality of scanning electrodes 15 different from the fifth scanning electrode 15 are sequentially switched to the selection mode, and specific values thereof will be described later. 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 as shown by the symbol N2 'in FIG. Is selectively applied with a signal voltage. In this erasing mode, the voltage applied to the pixel G does not exceed the threshold voltage Vth, as indicated by reference numeral N2 "in FIG. In the erasing mode, all of the antiferroelectric liquid crystals constituting each pixel of one line corresponding to the fifth scanning electrode 15 including the pixel G return from the ferroelectric state to the antiferroelectric state.

In this embodiment, the scanning voltage in the burn-in prevention mode indicated by reference numeral N1 in FIG. 3A is a negative voltage, whereas the scanning voltage in the erasing mode indicated by reference numeral N2 is a positive voltage. And its polarity is reversed.
By thus reversing the polarity of the scanning voltage, even when the antiferroelectric liquid crystal display A is used under a relatively low temperature condition, 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 msec at 0 ° C. . However, as described above, if the polarity of the scanning voltage in the erasing mode is opposite to the polarity of the scanning voltage in the immediately preceding burn-in prevention mode, for example, the ferroelectric state under the condition of 0 ° C. The time required to return to the antiferroelectric state from the above can be shortened to about 1 to several msec.

After the erasing mode, the control of the driver 2A controls the fifth operation as indicated by reference numeral N3 in FIG.
A scan voltage exceeding the saturation voltage Vsat (see FIG. 6) is applied to the scan electrode 15, and the fifth scan electrode 15 is turned on for a certain time T3.
Only select mode. At this time, the first signal electrode 14
Is a signal voltage P1 for setting the pixel G to black or white.
Is applied. If the signal voltage P1 is, for example, a voltage having the opposite polarity to the scanning voltage, the voltage applied to the liquid crystal of the pixel G exceeds the saturation voltage Vsat, as shown by a symbol N3 "in FIG. In this case, the liquid crystal enters a ferroelectric state, in which case the pixel G is, for example, white, and conversely, if the signal voltage P1 is of the same polarity as the scanning voltage, the liquid crystal of the pixel G The applied voltage is less than the saturation voltage Vsat, and the liquid crystal remains in an antiferroelectric state, in which case the pixel G is black, for example.

Thereafter, under the control of the driver 2A, a scanning voltage having an intermediate value between the threshold voltage Vth and the saturation voltage Vsat is applied to the fifth scanning electrode 15 for a predetermined time T4, as indicated by reference numeral N4 in FIG. And the fifth scanning electrode 15 is set to the non-selection mode. During the non-selection mode, the ferroelectric state or the non-ferroelectric state of the pixel G is maintained, and the writing state to the pixel G is maintained.

When the image display of the second frame is performed after the end of the first frame for displaying the moving image, as shown in FIG. A predetermined scanning voltage is applied in the same manner as in the case of the first frame, and the driving mode of the fifth scanning electrode 15 is switched to the burn-in prevention mode, the erasing mode, the selection mode, and the non-selection mode. However, the polarity of the scanning voltage in the second frame is opposite to the polarity of the scanning voltage in the first frame. As described above, if the polarity of the voltage applied to the liquid crystal is changed for each frame, the arrangement of the liquid crystal molecules is alternately switched to the modes shown in FIGS. 7 (II) and (III). This is effective in preventing image burn-in as seen in displays using ferroelectric liquid crystals.

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.

Further, 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 T1 of the burn-in prevention mode may be the same length of time as the assigned time, and if the time is extremely short as described above, all the pixels of one line corresponding to one scanning electrode 15 are white. However, it is difficult to recognize this 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, for example, white in the burn-in prevention mode, this writing is performed after the pixels are erased by the subsequent erase mode. Switch to selection 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 T2 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. Thus, 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, it is possible to appropriately perform such a return 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. However, 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 below msec.

The antiferroelectric liquid crystal display according to the present invention is not limited to the transmissive type but may be configured as a reflective type display. When configured as a reflective display, for example, as shown in FIG. 5, the scanning electrode 15 is made of an electrode capable of reflecting light, and the polarizing plate 12a, Substrate 10
A, and the light transmitted through the liquid crystal layer 11
(Refer to FIG. 1 schematically showing the layer structure of the liquid crystal layer 11). In this case, two polarizing plates are not used,
Only one polarizing plate 12a is used. In the case of this transmissive display, natural light or the liquid crystal panel 1
An image is displayed using a front light (not shown) arranged in front of A.

In the present invention, when sequentially switching the respective driving modes of the 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 front view showing an example of an antiferroelectric liquid crystal display according to the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

3A is a time chart for a scanning voltage, FIG. 3B is a time chart for a signal voltage, and FIG. 3C is applied to the liquid crystal as a total of the scanning voltage and the signal voltage. It is a time chart of a voltage.

FIG. 4 is a diagram showing a procedure for switching modes of a plurality of scanning electrodes.

FIG. 5 is a sectional view showing another example of the antiferroelectric liquid crystal display according to the present invention.

FIG. 6 is a graph showing a relationship between an applied voltage of an antiferroelectric liquid crystal and light transmittance.

FIG. 7 is an explanatory diagram schematically showing a change in molecular arrangement of an antiferroelectric liquid crystal.

FIGS. 8A to 8C are explanatory diagrams schematically showing an orientation structure of an antiferroelectric liquid crystal.

[Explanation of symbols]

 A Antiferroelectric liquid crystal display 1 Liquid crystal panel 2A, 2B Driver (control means) 10A, 10B Substrate 11 Liquid crystal layer 14 Signal electrode 15 Scanning electrode

Continued on the front page F term (reference) 2H088 EA67 JA20 MA04 MA13 2H093 NA12 NA51 NA61 NB29 ND10 ND12 NF20 5C006 AC15 AC22 BA12 BA13 BB12 FA23 FA34 5C080 AA10 BB05 DD06 DD08 DD09 DD18 FF12 JJ02 JJ04 JJ05 JJ06 JJ06

Claims (6)

[Claims] An antiferroelectric liquid crystal display adopting a simple matrix driving method switches a plurality of scanning electrodes in a predetermined order in a predetermined order to a selection mode, a non-selection mode, and an erasure mode while sequentially switching a plurality of signals. A method for driving an antiferroelectric liquid crystal display in which writing and erasing are performed on a plurality of pixels composed of antiferroelectric liquid crystal by selectively applying a signal voltage to the electrodes, comprising: The driving modes include, in addition to the above three modes, a voltage equal to or higher than a certain value to each of the scanning electrodes so that the antiferroelectric liquid crystal constituting a plurality of pixels corresponding to each of the scanning electrodes is brought into a ferroelectric state. And a drive mode before setting each of the scanning electrodes to the erase mode is set to the burn-in prevention mode. That, antiferroelectric method for driving a liquid crystal display. 2. The selection mode is a mode in which a scanning voltage equal to or higher than a predetermined saturation voltage is applied to the scanning electrodes. The non-selection mode uses a scanning voltage intermediate between the saturation voltage and a threshold voltage. The erase mode is a mode in which a scan voltage less than the threshold voltage is applied to the scan electrodes, and the burn-in prevention mode has an absolute value greater than the applied voltage in the selection mode. 2. The method of driving an antiferroelectric liquid crystal display according to claim 1, wherein the mode is a mode in which a high scanning voltage is applied to the scanning electrodes. 3. The antiferroelectric liquid crystal display according to claim 1, wherein a polarity of the scanning voltage in the erasing mode is opposite to a polarity of a scanning voltage in the burn-in prevention mode set immediately before the erasing mode. . 4. The erasing mode period of each of the scanning electrodes is a period in which a plurality of scanning electrodes other than the scanning electrodes set in the erasing mode are sequentially set to the selection mode. A method for driving an antiferroelectric liquid crystal display according to any one of the above. 5. When any one of the plurality of scan electrodes is set to the selection mode, the other plurality of scan electrodes scheduled to be set to the selection mode after the scan electrode are set to the erase mode. The method for driving an antiferroelectric liquid crystal display according to claim 4, wherein the setting is performed. 6. A liquid crystal in which a plurality of pixels are arranged in a matrix by filling an antiferroelectric liquid crystal between a pair of substrates having a plurality of scanning electrodes and a plurality of signal electrodes. And selectively applying a signal voltage to the plurality of signal electrodes while sequentially switching the plurality of scanning electrodes of the liquid crystal panel to a selection mode, a non-selection mode, and an erasing mode in a predetermined order by a predetermined number. And a control means for performing writing and erasing on the plurality of pixels. An anti-ferroelectric liquid crystal display comprising: In addition, burn-in prevention by applying a voltage equal to or more than a certain value to each of the scanning electrodes so that the antiferroelectric liquid crystal constituting the plurality of pixels corresponding to each of the scanning electrodes is brought into a ferroelectric state. An anti-ferroelectric property, wherein the control means is configured to set the drive mode before setting each of the scan electrodes to the erase mode to the burn-in prevention mode. LCD display.