JPH10253943A - Antiferroelectric liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a drive for preforming a satisfactory display uniformly on the whole of a panel, by providing a selection period impressing a voltage for determining a display state and a non-selection priod for holding the display state within a time when a light source continues the emitting of light. SOLUTION: Such a light source as to be able to radiating lights of plural colors continuously, is provided on the back of a liquid crystal display element. At the time when colors of the light source are changed, an arbitrary period is provided and voltages to be impressed on respective pixels are made zero V to reset antiferroelectric liquid crystal of pixels to an antiferroelectric state. This period is called as a reset period (Rs) and, succeedingly, a selection period (Se) impressing a voltage on respective pixels for determining display states and a non-selection period (NSe) impressing a voltage for holding the display states. Thus, unnecessary displays to be performed in the reset period are made not to be recognized and flicker can be suppressed by suppressing the number of resettings to a minimum while resetting all pixels simultaneously in this manner and by turning off the light source of the back of the panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel having a matrix of pixels, a liquid crystal light shutter array, etc. having an antiferroelectric liquid crystal as a liquid crystal layer and a light source capable of emitting a plurality of colors. The present invention relates to a method for driving a combined antiferroelectric liquid crystal display.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal cell is used as a shutter, and a light emitting element (eg, LED, CRT, etc.) is provided behind the shutter.
Has been announced to realize color display by the phenomenon of successive additive mixing. For example, Eurodispla
Philip Bos, T, presented at y'84
homaz Buzak Rolf Vatne et al.
-9 "4AFFull-Color Field-Seq
uential Color Display ”(1
984/9 / 18-20) and the like are cited as prior documents. This display method is different from a method in which segments of each color are dispersed in display pixels, such as a color filter,
The color display is performed by illuminating each color within a short time. The liquid crystal cell used may have the same configuration as the cell used for monochrome display. The light emitting element behind is, for example, R
Light of three primary colors of (red), G (green), and B (blue) is irradiated with the light for a certain period of time (T), and each light is irradiated in order (for example, in the order of R, G, and B). I will do it. The liquid crystal cell turns on and off each display pixel in synchronization with the time T. According to the desired display color information, the transmission state of the R, G, and B light is determined by turning on and off the pixels of the liquid crystal cell. Usually, since this T is very short, each color is not recognized as a single color, but is recognized by humans as a mixed color of the respective colors.

As a technique in which such a method is applied to a ferroelectric liquid crystal display device, Japanese Patent Application Laid-Open Nos. 63-85523, 63-85524, and 63-85
No. 523 is disclosed, but there is no disclosed invention as to a specific driving method when applied to an antiferroelectric liquid crystal display device. The antiferroelectric liquid crystal exhibits ferroelectricity when a sufficient electric field is applied, but its characteristics are significantly different from those of the ferroelectric liquid crystal when there is no influence from an external electric field or magnetic field. Therefore, in the driving method of the antiferroelectric liquid crystal display element, a unique driving method utilizing the characteristics is required. Next, a method of driving the antiferroelectric liquid crystal display device will be described in detail.

A liquid crystal display device using an antiferroelectric liquid crystal is disclosed in Japanese Patent Application Laid-Open No. 2-173724 of Nippon Denso Co., Ltd. and Showa Shell Sekiyu KK, having a wide viewing angle and capable of high-speed response. Since the report of good multiplex characteristics, etc., studies have been made vigorously.

FIG. 2 is a configuration diagram of a liquid crystal cell showing an arrangement of polarizing plates when an antiferroelectric liquid crystal is used as a liquid crystal display element. Between the polarizing plates 21a and b matched to the cross Nicol,
The liquid crystal cell 22 is placed so that the polarization axis of either polarizing plate and the major axis direction of the molecule in the absence of an electric field are substantially parallel, so that black can be displayed when no voltage is applied and white can be displayed when an electric field is applied. . When a voltage is applied to a liquid crystal cell having such a cell configuration, a change in transmittance with respect to the voltage is plotted on a graph, whereby a loop as shown in FIG. 3 can be drawn. When the voltage is applied and increased, the voltage value at which the transmittance starts to change is V1, the voltage value at which the change in the transmittance is saturated is V2, and when the voltage value is decreased, the transmittance starts to decrease. The voltage value is V5, and the voltage value at which the transmittance starts to change when the voltage of the opposite polarity is applied and its absolute value is increased is V5.
3. The voltage value at which the transmittance change is saturated is V4, and conversely, the voltage value at which the transmittance starts to change when the absolute value of the voltage is reduced is V6. From FIG. 3, the first ferroelectric state is selected when the voltage value is equal to or higher than the threshold value of the antiferroelectric liquid crystal molecules, and the second ferroelectric state changes depending on the polarity of the applied voltage. From these ferroelectric states, it can be seen that the antiferroelectric state is selected if the voltage value is below a certain threshold.

In the conventional time division driving method, scanning electrodes (X1, X2, X3,...) Are formed on a glass substrate as shown in FIG.
Xn) and signal electrodes (Y1, Y2, Y3... Y)
n), and a voltage is applied line by line to the scanning electrodes corresponding to the pixels (A11, Anm) located in a matrix where these oppose each other, and in synchronization with this, the signal electrodes are switched to the display state. A corresponding voltage waveform is applied, and a display is written according to a composite waveform of the voltage waveforms of the signal electrode and the scanning electrode. More specifically, in order to write one pixel, as shown in FIG. 5, a composite voltage waveform (Anm) of a voltage waveform applied to the scanning electrode (Xn) and a voltage waveform applied to the signal electrode (Ym), as shown in FIG. , The first or second ferroelectric state or the antiferroelectric state is selected in the selection period (Se), and the state is changed to the next non-selection period (NSe).
Was held at That is, the display is performed by holding the transmitted light amount (T) by the select pulse applied in the selection period (Se) in the subsequent non-selection period (NSe).

[0007]

Here, in the antiferroelectric liquid crystal display element, the antiferroelectric liquid crystal is brought into the first or second ferroelectric state or the antiferroelectric liquid crystal just before writing to the pixel. It is common to reset to a state.
For example, in FIG. 5, a reset period (Re) is provided immediately before the selection period (Se). During this period, a voltage equal to or lower than the threshold voltage is applied to the pixel, and the pixel is reset to the antiferroelectric state. As described above, by resetting the state of each pixel immediately before writing necessary information to the pixel, favorable display can be performed without being affected by the state at the time of previous writing. There are two major factors that may be affected by the previous write state. The first factor is the first or second ferroelectric state or antiferroelectric state. It is believed that this is due to the fact that the molecules of the antiferroelectric liquid crystal form different layer structures. In other words, it is presumed that if a voltage waveform necessary for the next writing is applied while the previous writing is being performed, the layer structure at the time of the previous writing is affected, which makes it difficult to change the layer structure. You. Therefore, if a reset period is not provided, a phenomenon occurs in which display characteristics such as contrast deteriorate. As a second factor, since the antiferroelectric liquid crystal takes various stable states, the state of molecules differs depending on the immediately preceding display state. Since the threshold when voltage is applied differs depending on the stable state of the molecules, if all molecules do not have the same stable state immediately before the selection period, all pixels will be displayed in the same display state with the applied voltage during the selection period. Control becomes difficult.

When the color display of the above-described successive addition method is actually driven, writing must be performed each time the light source of each color is turned on. In particular, when an antiferroelectric liquid crystal is used as a liquid crystal display element, it is desirable to provide a reset period as described above. However, if a reset period is provided every time each color is lit, one write operation is performed. A plurality of reset periods must be provided during the operation. In particular, in the case of the time-division driving described above, a reset period is provided each time lighting is performed for each color and each time a voltage is applied to each scanning electrode. Here, during the reset period, information other than the necessary writing is displayed. As the number of times of the reset period increases, an unnecessary display state is displayed and display quality is significantly impaired. Will happen.

Accordingly, the present invention provides a method for driving an antiferroelectric liquid crystal display using the successive additive mixing phenomenon, and further solves the above problems by providing an antiferroelectric liquid crystal display using the successive additive mixing method. It is an object of the present invention to provide an antiferroelectric liquid crystal display element using a driving method for uniformly and excellently displaying the entire panel in a non-volatile liquid crystal display panel.

[0010]

To achieve the above object, the present invention uses the following means.

In an antiferroelectric liquid crystal display having an antiferroelectric liquid crystal display element and a light source capable of continuously emitting light of different colors, the light color of the light source changes. The light source does not emit any color during this arbitrary period, and the anti-ferroelectric liquid crystals of all pixels are simultaneously in this arbitrary period.
Reset to the same state of any one of the antiferroelectric state or the first ferroelectric state or the second ferroelectric state, and within a time period in which light of an arbitrary color of the light source is emitted,
It is characterized by having a selection period for applying a voltage for determining a display state of a pixel and a non-selection period for maintaining the display state.

Alternatively, in the first period of the period in which light of an arbitrary color is emitted from the light source, the antiferroelectric liquid crystals of all the pixels are simultaneously in the antiferroelectric state, the first ferroelectric state, or the second ferroelectric state. Reset period to the same state of any one of the ferroelectric states, during a period in which light of any color of the light source is emitting, a selection period for applying a voltage for determining the display state of the pixel, It has a non-selection period in which a display state is maintained.

Alternatively, in the last period during which light of an arbitrary color of the light source emits light, the antiferroelectric liquid crystals of all the pixels are simultaneously in the antiferroelectric state, the first ferroelectric state, or the second ferroelectric state. Reset period to the same state of any one of the ferroelectric states, during a period in which light of any color of the light source is emitting, a selection period for applying a voltage for determining the display state of the pixel, It is characterized by having a non-selection period for maintaining the display state.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a conventional liquid crystal display device in which an antiferroelectric liquid crystal is injected can be used as it is. In addition, a light source that can continuously emit a plurality of colors is provided as a backlight on the back surface of the liquid crystal display element. For example, LEDs that emit red (R), green (G), and blue (B) light are used in a planar arrangement. Hereinafter, a driving method when the R, G, and B light sources are used will be described. In order to execute a predetermined display on one pixel, the R, G, and B light sources are sequentially turned on for an arbitrary period of time, and the time during which R, G, and B are all turned on (one cycle)
However, this is a period necessary for writing necessary information to one pixel. In addition, the light source of each color lights up during a reset period for resetting the antiferroelectric liquid crystal, a selection period for applying a voltage for determining the display state of the pixel, and a non-selection period for holding the display state. Provided within any given time. That is, when the light sources of the three colors R, G, and B are used, the reset period, the selection period, and the non-selection period are repeatedly executed for each of R, G, and B lighting.

Here, in the present invention, when the color of light emitted from the light source is switched, an arbitrary period is provided, and the light source is turned off only during this period. During the arbitrary period, the antiferroelectric liquid crystal of all pixels is simultaneously turned on. Reset to the first or second ferroelectric state or antiferroelectric state. That is, the reset period is set to overlap with this arbitrary period. By simultaneously resetting all pixels at the same time, the number of times of resetting is minimized, and by turning off the light source on the back, unnecessary display performed during the reset period is not recognized, and good display is performed. It becomes possible.

The length of time required for resetting depends on the antiferroelectric liquid crystal material used. That is, depending on the antiferroelectric material to be used, the state of the antiferroelectric liquid crystal may not be completely changed unless the reset period is long. Here, in the case where such an antiferroelectric liquid crystal material is used, if the light source is turned off during the reset period, the turn-off time becomes long, and when the display is executed, it is recognized as flicker.

Therefore, in the present invention, a reset period is provided so that the antiferroelectric liquid crystals of all the pixels are simultaneously reset in the first period when the light source of a certain color starts to emit light. By resetting all the pixels at the same time as described above, the number of resets can be minimized. By providing the reset period at the beginning of the period during which the light source emits light, the selection period and the non-selection period Can be set continuously during the period when the light source of an arbitrary color is emitting light, so that the emission time of the light source can be lengthened while the necessary display is written, and a good display can be obtained. It becomes possible.

The same effect can be obtained by providing a reset period so that the antiferroelectric liquid crystals of all pixels are simultaneously reset in the last period in which a light source of a certain color emits light. Even if the reset period is set to the last period during which the light source emits light, it is possible to minimize the number of times of resetting by simultaneously resetting all pixels. In addition, the selection period and the non-selection period can be set continuously during a period in which the light source of an arbitrary color emits light, so that the light emission time of the light source can be lengthened while necessary display is written, and a good display can be obtained. Becomes possible.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 6 is a configuration diagram of a liquid crystal panel used in this embodiment. The liquid crystal panel used in this embodiment is a pair of glass substrates 53a and 53 having an antiferroelectric liquid crystal layer 56 having a thickness of about 2 μm.
b and sealing materials 52a and 52b for bonding two glasses. Electrodes (IT
O) 54a, 54b are formed, and alignment films 55a, 55b are applied thereon, and an alignment process is performed.
Further, a first polarizing plate 51a is provided outside one of the glass substrates so that the polarizing axis of the polarizing plate and the rubbing axis are parallel to each other, and the first polarizing plate 51a is provided outside the other glass substrate. The second polarizing plate 51b is provided so as to be different from the polarization axis by 90 °. An LED light source capable of displaying three colors (R, G, B) is provided as a backlight on the rear side of the liquid crystal display element. The backlight lights up in the order of R, G, B, and each lighting time is about 1
6.7 ms.

For the electrodes installed on the glass substrate, the arrangement used in the conventional time-division driving method can be used as it is. In this embodiment, the arrangement of the scanning electrodes and the signal electrodes is adopted as shown in FIG. 4, and the number of the scanning electrodes is 100 and the number of the signal electrodes is 220.

(Embodiment 1) FIG. 1 shows a voltage driving waveform according to the present invention. The color of the light emitted from the backlight (light source) and the light emission period from the upper row, the composite voltage waveform applied to the pixels on the first row of scan electrodes in the next row, and the The next row shows the composite voltage waveform applied to the pixel on the third row of the scanning electrodes. An arbitrary period is provided when the color of the light source is switched. In this period, the voltage applied to each pixel is set to 0 V, and the antiferroelectric liquid crystal of the pixel is reset to the antiferroelectric state. This period is called a reset period (Rs). Following the reset period, a selection period (Se) in which a voltage for determining a display state is applied to each pixel, and a non-application period in which a voltage for maintaining the display state is applied to each pixel. The selection period (NSe) was set. By simultaneously resetting all pixels at the same time, minimizing the number of resets and turning off the light source on the back prevents unnecessary display performed during the reset period from being recognized and suppresses flickering. Was completed.

(Embodiment 2) FIG. 7 shows a voltage driving waveform according to another embodiment of the present invention. As in FIG. 1, the upper stage shows the color of the light emitted from the backlight (light source) and the emission period, the next stage shows the composite voltage waveform applied to the pixels on the scanning electrodes in the first row, and The composite voltage waveform applied to the pixels on the scanning electrodes in the third row is shown in the next row, and the composite voltage waveform applied to the pixels on the scanning electrodes in the third row is shown in the next row. A reset period (Rs) for simultaneously resetting the anti-ferroelectric liquid crystal of each pixel to the anti-ferroelectric state by setting the applied voltage to 0 V is provided in the first period in which the light source of a certain color starts to emit light, and then the selection period ( Se), a non-selection period (NSe) is provided continuously. By simultaneously resetting all the pixels in this manner, the number of resets can be minimized, flicker is suppressed, and the reset period is provided at the beginning of the period during which the light source emits light. The non-selection period can be set continuously to the period during which the backlight emits light. Therefore, the emission time of the backlight can be extended while necessary display is written, and the screen is bright and good display characteristics can be obtained.

(Embodiment 3) FIG. 8 shows a voltage driving waveform obtained by executing another embodiment of the present invention. As in FIG. 1, the upper stage shows the color of the light emitted from the backlight (light source) and the emission period, the next stage shows the composite voltage waveform applied to the pixels on the scanning electrodes in the first row, and The composite voltage waveform applied to the pixels on the scanning electrodes in the third row is shown in the next row, and the composite voltage waveform applied to the pixels on the scanning electrodes in the third row is shown in the next row. A reset period (Rs) for simultaneously resetting the antiferroelectric liquid crystal of each pixel to the antiferroelectric state by setting the applied voltage to 0 V is provided in the last period in which a light source of a certain color is emitting light, and is selected before that. The period (Se) and the non-selection period (NSe) are provided successively. By simultaneously resetting all the pixels in this manner, the number of resets can be minimized, flicker is suppressed, and the reset period is provided at the beginning of the period during which the light source emits light. The non-selection period can be set continuously to the period during which the backlight emits light. Therefore, the emission time of the backlight can be extended while necessary display is written, and the screen is bright and good display characteristics can be obtained.

Although the antiferroelectric liquid crystal is reset to the antiferroelectric state in the reset period in any of the embodiments, good display can be performed even when the antiferroelectric liquid crystal is reset to the first or second ferroelectric state. Characteristics were obtained.

[0025]

As has been described in the above embodiments, the present invention provides an antiferroelectric liquid crystal display for applying a color display using the successive addition phenomenon to sufficiently enhance the characteristics of the antiferroelectric liquid crystal. By providing a driving method that takes into account the above, it is possible to perform a favorable display in which flicker is suppressed when display is performed and the luminance of the entire panel is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a driving waveform according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an antiferroelectric liquid crystal cell and a polarizing plate of the present invention.

FIG. 3 is a diagram showing a hysteresis curve of the antiferroelectric liquid crystal display device of the present invention.

FIG. 4 is a diagram illustrating a matrix electrode.

FIG. 5 is a diagram showing a conventional driving method and the amount of transmitted light corresponding thereto.

FIG. 6 is a panel configuration diagram of the antiferroelectric liquid crystal panel of the present invention.

FIG. 7 is a diagram showing a drive waveform according to another embodiment of the present invention.

FIG. 8 is a diagram showing a drive waveform according to another embodiment of the present invention.

[Explanation of symbols]

 Rs reset period Se selection period NSe non-selection period 21a, 21b Polarizer 22 Liquid crystal cell X1 to Xn Scan electrode Y1 to Ym Signal electrode A11, Anm Pixel T Transmittance 51a, 51b Polarizer 52a, 52b Sealant 53a, 53b Glass substrate 54a, 54b Electrodes 55a, 55b Alignment film 56 Antiferroelectric liquid crystal

Claims (3)

[Claims] 1. An antiferroelectric liquid crystal display device in which an antiferroelectric liquid crystal is sandwiched between a pair of substrates having pixels in a matrix, and a light source capable of successively emitting light of different colors from each other. In the provided antiferroelectric liquid crystal display, the antiferroelectric liquid crystal is in a first ferroelectric state,
A second ferroelectric state that indicates a ferroelectric state when a voltage having a polarity opposite to that of the first ferroelectric state is applied; and an antiferroelectric state, in which the color of light from the light source changes. During this arbitrary period, the light source does not emit any color during this arbitrary period, and during this arbitrary period, the antiferroelectric liquid crystals of all pixels are simultaneously in the antiferroelectric state. Alternatively, the display state of the pixel is determined within the time period in which the light of an arbitrary color of the light source is emitted by being reset to the same one of the first ferroelectric state and the second ferroelectric state. Anti-ferroelectric liquid crystal display characterized by having a selection period in which a voltage is applied and a non-selection period for maintaining the display state. 2. An antiferroelectric liquid crystal display device in which an antiferroelectric liquid crystal is interposed between a pair of substrates having pixels in a matrix, and a light source capable of successively emitting light of different colors from each other. In the provided antiferroelectric liquid crystal display, the antiferroelectric liquid crystal is in a first ferroelectric state,
A second ferroelectric state that indicates a ferroelectric state when a voltage having a polarity opposite to that of the first ferroelectric state is applied, and an antiferroelectric state, and light of an arbitrary color of a light source In the first period of the light emitting period, the antiferroelectric liquid crystals of all the pixels are simultaneously in the antiferroelectric state, the first ferroelectric state, or the second ferroelectric state.
Reset period to the same state of any one of the ferroelectric states, during a period in which light of any color of the light source is emitting, a selection period for applying a voltage for determining the display state of the pixel, An antiferroelectric liquid crystal display having a non-selection period for maintaining a display state. 3. An antiferroelectric liquid crystal display device in which antiferroelectric liquid crystal is sandwiched between a pair of substrates having pixels in a matrix, and a light source capable of successively emitting light of different colors from each other. In the provided antiferroelectric liquid crystal display, the antiferroelectric liquid crystal is in a first ferroelectric state,
A second ferroelectric state that indicates a ferroelectric state when a voltage having a polarity opposite to that of the first ferroelectric state is applied, and an antiferroelectric state, and light of an arbitrary color of a light source In the last period of the light emitting period, the antiferroelectric liquid crystals of all pixels are simultaneously in the antiferroelectric state, the first ferroelectric state, or the second ferroelectric state.
Reset period to the same state of any one of the ferroelectric states, during a period in which light of any color of the light source is emitting, a selection period for applying a voltage for determining the display state of the pixel, An antiferroelectric liquid crystal display having a non-selection period for maintaining a display state.