JPH05119746A - Matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent an afterimage phenomenon due to a structural alternation of the smectic layer of the display device which uses antiferroelectric liquid crystal and to decrease the number of voltage levels required to drive display picture elements. CONSTITUTION:The matrix type liquid crystal display device is equipped with a liquid crystal cell 1 which has (n) row electrodes Y1-Yn and (m) column electrodes X1-Xm and also has (m)X(n) display picture elements formed by charging the antiferroelectric liquid crystal having one antiferroelectric state and two ferroelectric states according to an applied voltage, matrix driving means 22-24 applied with a 1st driving signal which turns ON optional picture elements on one row electrode by switching the ferroelectric states of the liquid crystal and a 2nd driving signal which turns OFF the remaining picture elements on the same row electrode (into antiferroelectric state), and a means which applies a DC voltage having a voltage corresponding to the nearly center value of a specific voltage range of one polarity between the (n) row electrodes Y1-Yn and (m) column electrodes X1-Xm after the 1st and 2nd driving voltages are applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal display device provided with a liquid crystal cell for forming display pixels of nm and a scan driving means, and more particularly to an antiferroelectric liquid crystal. And a matrix type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device utilizing an electric field induced phase transition generated in an antiferroelectric liquid crystal is described in detail in JP-A-2-153322. According to it, the electric field induced phase transition observed in this type of liquid crystal is, for example, when observed between crossed Nicols, as electro-optical characteristics, (1) double hysteresis characteristic of voltage-transmittance, (2) direct current threshold value and (3) It exhibits a high-speed response, and if these characteristics are effectively used, it is possible to use a conventional nematic liquid crystal or JP-A-56-107216.
It is stated that a high quality liquid crystal display device can be realized as compared with the liquid crystal display device using the ferroelectric liquid crystal described. A matrix driving method that effectively utilizes the characteristics of antiferroelectric liquid crystal is disclosed in JP-A-2-230117 or JP-A-2-230117.
-173724. According to the driving method proposed there, it is possible to obtain a high-contrast display in which the characteristics of the antiferroelectric liquid crystal are fully utilized.

[0003]

However, the liquid crystal display device using the antiferroelectric liquid crystal described above also has the following problems. That is, one of them is that an afterimage is generated due to the structural change of the smectic layer when the same display is performed for a long time. For this reason, there is a restriction that only a specific one can be applied as the alignment control film for aligning the liquid crystal molecules. Another problem is that, according to the principle of alternating-current driving the liquid crystal, the hysteresis loop in the positive voltage range and the hysteresis loop in the negative voltage range are alternately used in time to drive. In this case, in order to drive one display pixel, at least five or more kinds of voltages must be input to the scanning electrodes and at least three or more voltages must be selected and input to the signal electrodes in a timely manner. This means that it is not possible to increase the degree of integration of drive ICs for driving the liquid crystal display device, and eventually the cost of the liquid crystal display device increases.

Therefore, an object of the present invention is to provide a matrix driving method for preventing the afterimage caused by the structural change of the smectic layer and for reducing the number of voltage levels necessary for driving the display pixel.

[0005]

In order to achieve the above-mentioned object, the present invention adopts the technical constitution as described below. That is, at least one antiferroelectric state and two ferroelectric states with respect to voltage application are provided between both electrode substrates in which n row electrodes and m column electrodes are arranged in parallel so as to face each other in a lattice row. Between the n row electrode and the m column electrode and the liquid crystal cell in which mn display pixels are formed by enclosing an antiferroelectric liquid crystal that is stably formed with each other. Of the display pixels, a first drive signal for ON-displaying an arbitrary pixel on the selected row electrode and a second drive signal for OFF-displaying the remaining pixels on the selected row electrode are provided. In the same way, each row electrode is
In a matrix type liquid crystal display device equipped with a matrix drive means for selectively scanning every / n time, two ferroelectric liquid crystals which can be controlled by the applied voltage as the antiferroelectric liquid crystal and the antiferroelectric state and the direction of the electric field are used. Dielectric states can be switched to each other, and the light transmittance of the antiferroelectric liquid crystal has at least a hysteresis sufficient for matrix driving in accordance with increase or decrease of the applied voltage within a predetermined voltage. A ferroelectric liquid crystal is adopted, and the driving means is formed as an AC-changing bipolar pulse that switches between two ferroelectric states as a first driving signal, and an anti-ferroelectric state is used as the second driving signal. It is formed as a bipolar pulse that changes in an alternating current with a voltage in a range where switching to the ferroelectric state is not performed, and the first and second drive signals are formed. Wherein n a DC signal having a connection to a voltage corresponding to substantially the center of one predetermined voltage range in polarity
The one-screen display is completed by applying it between the row electrodes of the strips and the column electrodes of the strips of m, and after that, or the above operation is repeated a plurality of times, the driving means drives the first and second drives. A voltage in which the voltage polarities of the signals and the DC signals following them are all opposite polarity is applied between the n-row electrode and the m-row column electrode by the same operation as described above. It is a matrix type liquid crystal display device.

[0006]

In the matrix type liquid crystal display device of the present invention having the structure as described above, it is effectively utilized that the antiferroelectric liquid crystal has the light transmittance-voltage characteristic as described above. By setting the voltages and polarities of the first and second drive signal waveform shapes and the DC signals subsequent to these drive signals so as to be in a predetermined state, hysteresis and reverse polarity in one polarity predetermined voltage range are obtained. When matrix driving is performed by alternately utilizing the hysteresis in a predetermined voltage range in time, each display pixel similar to the conventional one by reversing only the voltage polarities of the first and second drive signals and the DC signal subsequent thereto. ON display and OFF display of can be realized. In this case, it is necessary to select and input four kinds of voltages to the n row electrodes and two kinds of voltages to the m column electrodes in a timely manner, and the number of voltage levels required for driving is And less. Further, since the liquid crystal is directly switched from one ferroelectric state to the other ferroelectric state by the first driving signal, an afterimage due to a change in the smectic layer structure can be prevented.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete configuration example of a matrix type liquid crystal display device according to the present invention and its driving method will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a specific example of a matrix type liquid crystal display device according to the present invention, and FIG. 2 is a sectional view showing a constitutional example of a liquid crystal cell 10 used in the present invention. n row electrodes (Y1, Y2 ... Yn) and m row electrodes (X
1. (X2 ... Xm) are arranged side by side so as to face each other in a grid pattern, and at least one antiferroelectric state and two ferroelectric states are mutually opposed to each other when a voltage is applied. The liquid crystal cell 10 in which the antiferroelectric liquid crystal 13 that is stably formed is encapsulated to form mn display pixels, the n row electrodes and the m column electrodes constitute the liquid crystal panel 1. A first drive signal for ON-displaying an arbitrary pixel on one selected row electrode among the mn display pixels and an OFF-display for the remaining pixels on the selected row electrode between the electrodes. A matrix type liquid crystal display device comprising matrix driving means (22, 23, 24) for selectively scanning each row electrode at intervals of 1 / n of one screen display time so as to apply two driving signals. , The anti-ferroelectric liquid crystals are A dielectric state and two ferroelectric states that can be controlled by the direction of the electric field can be switched to each other, and the light of the antiferroelectric liquid crystal can be changed according to the increase or decrease of the applied voltage within a predetermined voltage. An antiferroelectric liquid crystal 13 having a transmittance of at least sufficient hysteresis for matrix driving is adopted, and the driving means generates an AC-variable bipolar pulse for switching between two ferroelectric states as a first driving signal. Means to
Further, a means for generating a bipolar pulse that changes in an alternating manner with a voltage in a range in which switching from the antiferroelectric state to the ferroelectric state is not performed as the second drive signal, and further, the first drive signal.
And a DC signal having a voltage substantially corresponding to the center of a predetermined voltage range of one polarity is applied between the n-row electrode and the m-row column electrode after the second drive signal. Means are provided and the output signals from the respective means are combined to complete one-screen display.

After that, or after the signal generating operation by each means is repeated a plurality of times, the drive means makes the voltage polarities of the first and second drive signals and the DC signal following them have all opposite polarities. And a polarity different from the voltage polarity in the previous operation between the n-row electrode and the m-row column electrode by the same operation as described above. It is a matrix type liquid crystal display device configured to be applied with a voltage.

The matrix type liquid crystal display device of the present invention will be described more specifically. First, FIG. 1 is a schematic configuration diagram showing the overall configuration of the liquid crystal display device of the present embodiment. As shown in the figure, the liquid crystal display device of this embodiment has a liquid crystal panel 1 in which an antiferroelectric liquid crystal is sealed, and column electrodes X1, X2, ... Xm of the liquid crystal panel 1 based on a video signal input from the outside. The liquid crystal panel 1 is driven by applying a voltage to the row electrodes Y1, Y2, ..., Yn, and a control device 4 for displaying an image according to a video signal on the liquid crystal panel 1 is constituted.

Here, the liquid crystal panel 1 is, as shown in FIG.
The antiferroelectric liquid crystal 13 is sealed between the two electrode substrates 11 and 12, and is manufactured as follows. That is, first, the electrode substrate 11 is a transparent glass plate 11 as shown in FIG.
ITO (indium tin o) along the inner surface of a
x)) or tin oxide, and the conductive films 11b are vertically spaced apart from each other, so that the n row electrodes Y1 to Yn shown in FIG.
Are formed so as to project in parallel to each other in the left-right direction. Further, the electrode substrate 12 is subjected to the same processing as the electrode substrate 11,
The m row column electrodes X1 to Xm shown in FIG. 1 are each row electrodes Y1.
To Yn are formed so as to be orthogonal to each other.
It should be noted that the row electrodes Y1 to Yn and the column electrodes X1 to Xm form m × n display pixels G1, G2, ... G (m−n) on the liquid crystal panel 1 as shown in FIG. ..

Polymer films 16 and 17 are attached to the inner surfaces of the conductive films 11a and 11b, respectively. Polymer film 16,1
At least one of the surfaces of 7 has liquid crystal molecules 13a.
However, the rubbing process is performed so as to be parallel to the upper and lower substrates and aligned in the direction perpendicular to the normal P. Instead of the polymer films 16 and 17, a thin film of an inorganic material such as an oblique vapor deposition film of silicon oxide may be attached to the inner surfaces of the conductive films 11a and 11b.

Next, the antiferroelectric liquid crystal 1 in the liquid crystal cell 10
In encapsulating 3, the rubbing orientation of the polymer films 16 and 17 is parallel to the conductive films 11b and 12b (that is, the normal line P).
The electrode substrates 11 and 12 are combined in parallel so that they are perpendicular to each other. After that, the antiferroelectric liquid crystal 13 such as 4- (1-
Trifluoromethylheptoxycarbonylphenyl)-
4'-octyloxycarbonylphenyl-4-carboxylate is heated to be an isotropic liquid, which is injected between the electrode substrates 11 and 12 by utilizing a capillary phenomenon, and then,
The entire liquid crystal cell 10 is gradually cooled at about 1 ° C. per minute and cooled to an antiferroelectric liquid crystal phase (SmCA · phase).

As a result of such cooling, the antiferroelectric liquid crystal 13 having a layered structure is oriented along the rubbing direction of the polymer films 16 and 17. This state is a stable state that is quenched (first stable state) when observed under orthogonal Nicols, but a recent study by Chandani et al. {Jpn.J.Appl.Phys.Vol.28, (1989).
p.1261} revealed that the structure has an antiferroelectric structure in which polarization is canceled between layers.

In the liquid crystal cell 10 manufactured as described above, the polarizing plates 14 and 15 are arranged so that their polarization axes are orthogonal to each other.
The liquid crystal is attached so as to match the extinction position when no electric field is applied to the liquid crystal. In the liquid crystal panel 1 having the above configuration, when an electric field is applied between the electrode substrates 11 and 12 in the direction from the electrode substrates 11 to 12, liquid crystal molecules 13 are generated.
Since the permanent dipole moment of a is aligned with the electric field direction, an array change occurs (that is, an electric field-induced antiferroelectric phase-ferroelectric phase transition), and the extinction position shifts by an angle θ. At this time, due to the birefringence of the liquid crystal, the extinction state (dark state) is changed to the bright state where light is transmitted. When an electric field in the opposite direction to the above is applied, a bright state is obtained by the same principle, but the direction in which the extinction position shifts is −θ, which is the opposite direction to the above. When the voltage-transmittance characteristic when a triangular wave voltage was applied to the liquid crystal 13 was confirmed, the sufficient hysteresis characteristic shown in FIG. 3 was obtained.

That is, FIG. 3 shows the result of an experimental measurement of the relationship between the voltage applied between both electrodes of the liquid crystal cell 10 and the relative transmitted light intensity of the liquid crystal cell. Therefore, the horizontal axis of FIG. 3 represents the applied voltage, and the vertical axis represents the relative transmittance in which the relative transmitted light intensity is displayed in percentage. That is, when the threshold value of the relative transmittance is 90% or more,
If the threshold value of 10% or less is defined as a dark state, first, when the applied voltage is increased in the positive direction from the state where the liquid crystal cell is in the dark state at the applied voltage of 0 V, the electric field effect E and spontaneous emission of the liquid crystal are caused. The alignment of the molecules of the liquid crystal starts to change based on the polarization, and light transmission starts at the threshold voltage + V1, and when the saturation voltage exceeds + V2, the complete light transmittance becomes 100%.

That is, the threshold voltage is defined as the voltage at which the relative transmittance changes by 10% from the initial value, and the saturation voltage is defined as the voltage at which the relative transmittance changes by 90% from the initial value. The liquid crystal cell is switched from the dark state to the bright state while changing from the voltage of 1 to the voltage of the saturation voltage or more. On the contrary, when the applied voltage is decreased from + V2 or more, it does not show the same change as when the voltage is increased, but exhibits hysteresis as shown in FIG.

That is, when the voltage of the liquid crystal cell changes from the bright state to the threshold value + V3 or less, the molecules of the liquid crystal start to change, and the saturation voltage becomes + V4 or less, so that the liquid crystal cell becomes dark. Change to state. That is, when the applied voltage is changed from the threshold voltage to the saturation voltage, the liquid crystal cell is switched from the bright state to the dark state.

Such a state is the same when the applied voltage is a negative voltage, and the liquid crystal cell changes from a dark state to a bright state and from a bright state to a dark state, respectively. Threshold value -V1, -V3, and saturation voltage -V2,-
Each has V4. Therefore, the applied voltage is +/-
When the voltage is set to V1 or more, the liquid crystal cell is in a bright state, and when the applied voltage is set to +/- V3 or less, the liquid crystal cell is in a dark state.

If the voltage is applied between them, the state of the liquid crystal cell does not change, and the state immediately before that is maintained. Next, a device for driving the liquid crystal panel 1 will be described. The controller 4 for driving the liquid crystal panel 1 with the drive waveform of the present invention based on the line-sequential scanning method is shown in FIG.
As shown in FIG. 3, a frame memory 21 that captures and stores a video signal input from the outside as image data, and a control as a control unit that reads the image data from the frame memory 21 and generates and outputs various control signals such as clock signals. Receiving a control signal from the circuit 22 and the control circuit 22, each display pixel G is turned on or off.
Row driving means for applying a voltage {Va or -Va} for selecting a state and a voltage {Vo or -Vo} for holding the selected ON or OFF state to each of the row electrodes Y1 to Yn as a scanning signal. Drive circuit 2 as
3 and a column drive circuit 24 as column drive means for receiving a control signal from the control circuit 22 and applying a control voltage for controlling each display pixel to an ON or OFF state to each of the column electrodes X1 to Xm. It consists of

Further, the row drive circuit 23 includes the shift register 3
1, a data latch circuit 32, and a drive circuit 33, and the column drive circuit 24 includes a shift register 41, a data latch circuit 42, and a drive circuit 43. Here, the drive waveform of the present invention is shown in FIG. This drive waveform is composed of a first field driven by using the hysteresis in the positive voltage range and a second field driven by using the hysteresis in the negative voltage range of FIG.
Row electrodes (Y1 to Yn) and column electrodes (X1 to Xn, respectively)
m) consisting of eight basic signals applied to it. Figure 4 (a)
Is a group of scanning signals applied to the row electrodes (Y1 to Yn), FIG.
(B) is a group of control signals applied to the column electrodes (X1 to Xm). These are output from the control device 4 at appropriate times.

The detailed configuration and operation of the control device 4 will be described below. A row drive circuit 23 that receives a control signal from the control circuit 22 and outputs a scanning signal to the row electrodes Y1 to Yn will be described. First, as shown in FIG. 5, the control circuit 2 is provided in the shift register 31 of the row drive circuit 23.
2, 2 bits of data (hereinafter referred to as scanning signal data) D1 and D2 corresponding to four scanning signal levels of Va, Vo, -Va, and -Vo, and a clock signal CL1 synchronized with this data are input. And the shift register 31
6 sequentially fetches the scanning signal data D1 and D2 by this clock signal CL1 as shown in FIG. 6 (c).

As shown in FIG. 5, the data latch circuit 3
A clock signal CL2 having n cycles of the clock signal CL1 shown in FIG. 6C as one cycle is input from the control circuit 22 to the data latch circuit 32, and the data latch circuit 32 receives the clock signal CL2. Every time the scanning signal data D1 and D2 of all the row electrodes Y1 to Yn are fetched, the data is latched.

On the other hand, as shown in FIG. 5, the driving circuit 33 includes n analog switches 33al, 33a2, ... 33an and n level shifters 33bl, 33b2 ,. 33bn. Further, each of the analog switches 33al to 33an is supplied with four kinds of scanning signals, that is, Va, Vo, -Va, and -Vo, to be applied to each of the row electrodes Y1 to Yn from the outside. 33an has these 4
Four switch elements are provided so that one of the seed scanning signals can be selectively applied to the row electrodes Y1 to Yn. Then, the level shifters 33bl to 33bn level-shift the scanning signal data for each row electrode Y1 to Yn accumulated in the data latch circuit 32, and output drive signals to the corresponding analog switches 33al to 33an.
The scanning signals applied to the row electrodes Y1 to Yn by the analog switches 33al to 33an are made to correspond to the scanning signal data.

As described above, the row driving circuit 23 sequentially takes in the scanning signal data D1 and D2 for each row electrode Y1 to Yn output from the control circuit 22 by the clock signal CL1, and scan signal data D1 to all the row electrodes Y1 to Yn. , D2 (that is, clock signal CL2
Every one cycle), the voltage applied to each row electrode Y1 to Yn is changed corresponding to the scanning signal data.

On the other hand, the control circuit 22 is shown in FIG.
, The scanning signal data D1 and D2 are sequentially output from the first row electrode Y1 to the last row electrode Yn within one cycle of the clock signal CL2.
Of the scanning signal data D1 and D2 output per one cycle, the scanning signal data D1 and D2 other than the specific row electrode (hereinafter, referred to as the selection electrode) which is the target of display change has antiferroelectricity. The third voltage, which is the intermediate voltage of the hysteresis characteristics of liquid crystal
The voltage {Vo or -Vo} is set, and ON / OF of the display pixel is set only for the scanning signal data D1 and D2 of the selection electrode.
The first and second voltages Va or − which can switch the F state
Set Va.

The control circuit 22 is shown in FIG.
6, the selection electrodes are sequentially changed from the row electrode Y1 of the first row every two cycles of the clock signal CL2.
As shown in (a), scanning signal data D for the selected electrode
1 and D2 are respectively the first and second voltages −Va and Va in the first and second cycles of the clock signal CL2.
Are set respectively. In addition, the control circuit 22 applies the second voltage to the selection electrode and then outputs the next clock signal CL2.
By this, the polarity of the third voltage applied to the electrode is set to the same polarity as the polarity of the second voltage until the selection electrode is changed to another row electrode and the electrode becomes the selection electrode again. That is, as shown in FIG. 6A, if the second voltage of the selection electrode is a positive voltage, then the positive third voltage Vo is applied to that electrode, and the second voltage of the selection electrode is a negative voltage −. If it is Va, then the negative third voltage −Vo is applied to the electrode.

Further, the control circuit 22 executes control to change the applied voltage in order from the first row electrode Y1. The first row electrode Y1 to the last row electrode Yn.
Each time the control for (1) is finished, that is, every time when scanning of one screen of the liquid crystal panel 1 is finished, the polarity of the voltage applied to each row electrode Y1 to Yn is changed to a polarity different from the previous one. Next, receiving the control signal from the control circuit 22, the column electrode X
The column drive circuit 24 that applies a control voltage to 1 to Xm will be described.

As shown in FIG. 7, in the shift register 41 of the column driving circuit 24, m is formed from the control circuit 22 at the intersection of the above-mentioned selection electrode and each column electrode X1 to Xm.
ON / OFF data DG indicating whether each display pixel is turned on or off is sequentially input for each column electrode, and a clock signal CL3 is input in synchronization with the input timing. As shown in FIG. 8B, this O
The N / OFF data and the clock signal CL3 are input in a cycle of (1 / m), which is one cycle of the clock signal CL2, and the shift register 41 receives all the column electrodes per one cycle of the clock signal CL2 by the clock signal CL3. X1
Take in the ON / OFF data DG of Xm.

Further, as shown in FIG. 7, the data latch circuit 4
2 is the clock signal CL2 from the control circuit 22.
And the field signal F1 indicating the polarity of the voltage applied to the selection electrode. Then, the data latch circuit 42 fetches the ON / OFF data DG of all the column electrodes X1 to Xm from the shift register 41 by the clock signal CL2, and also the ON / OFF data DG of each column electrode X1 to Xm based on the field signal F1. Is converted into control voltage data corresponding to the polarity of the voltage applied to the selected electrode and stored.

Here, the control circuit 22 changes the selection electrode, that is, every two cycles of the clock signal CL2.
The ON / OFF data DG for each column electrode is changed based on the image data read from the frame memory 21, and as shown in FIG.
When the F data DG represents the ON command of the display pixel,
In the data latch circuit 42, the field signal F1 is ON,
That is, if the polarity of the voltage applied to the selection electrode is positive, the control voltage data of the first cycle of the clock signal CL2 is + Vb,
Conversely, if the field signal F1 is OFF, that is, if the polarity of the voltage applied to the selection electrode is negative, the control voltage data of the first cycle of the clock signal CL2 is -Vb, The control voltage data of the second cycle is + V
Set to b.

Although not shown in the figure, the control circuit 2
When the ON / OFF data DG from 2 represents the OFF command of the display pixel, conversely to the above, if the field signal F1 is ON, that is, the polarity of the voltage applied to the selection electrode is positive, the clock The control voltage data of the first cycle of the signal CL2 is −Vb, the control voltage data of the second cycle is + Vb,
When the field signal F1 is OFF, that is, when the polarity of the voltage applied to the selection electrode is negative, the clock signal CL2
The control voltage data in the first cycle is set to + Vb, and the control voltage data in the second cycle is set to -Vb.

On the other hand, the drive circuit 43, as shown in FIG. 7, has m analog switches 43al, 43a2, ... 43an and n level shifters 43b1 provided corresponding to the respective column electrodes X1, X2, ... Xm. , 43b2, ... 43bn. Further, each analog switch 43a1, 43a2, ...
43an has two kinds of control voltages to be applied to the column electrodes X1, X2, ... Xm from the outside, that is, + Vb, −Vb.
Control voltage of each analog switch 43 is supplied.
43an are provided with two switch elements so that one of these three kinds of control voltages can be selectively applied to the column electrodes X1, X2, ... Xm.

The level shifters 43b1, 43b2, ...
43bn level-shifts the control voltage data for each column electrode X1 to Xm accumulated in the data latch circuit 42 and outputs a drive signal to the corresponding analog switch 43a1, 43a2, ...
A control voltage corresponding to the control voltage data from 1, 43a2, ... 43an is simultaneously applied to each column electrode X1 to Xm.

That is, to summarize the operation of the column driving circuit 24, first, the selection electrode to which the first voltage (−Va) → the second voltage (Va) is sequentially applied from the row driving circuit 23 for each cycle of the clock signal CL2. A display pixel formed by the selection electrode Yj and the column electrode Xi (i: 1 to m) when the polarity of the applied voltage of Yj (j: 1 to n) (that is, the second voltage (Va)) is positive. When G is turned on, the column drive circuit 24 causes the column electrode X
i + Vb for each cycle of the clock signal CL2 →
When applying −Vb and turning off the display pixel on the contrary,
The column driving circuit 24 applies −Vb → + Vb to the column electrode Xi for each cycle of the clock signal CL2.

When the polarity of the voltage applied to the selection electrode Yj is negative, the selection electrode Yj and the column electrode Xi (i: 1 to 1).
m), the column driving circuit 24 applies −Vb → + Vb to the column electrode Xi for each cycle of the clock signal CL2, and vice versa. When turning off, the column drive circuit 24 causes the column electrode Xi to be + for each cycle of the clock signal CL2.
Vb → −Vb is applied.

The operation of the antiferroelectric liquid crystal 13 according to the drive waveform of the present invention formed as described above will be described. Figure 9
FIG. 7 is a diagram schematically showing a part of a matrix pixel group G.
Here, the shaded pixels are (for example, (1, 2).) OF
The F display pixel and the others (for example, (1, 1)) are ON display pixels. The waveform applied to the ON display pixel is shown in FIG.
It shows in (a). Each voltage level has Vo in the hysteresis width (for example, V
(Defined by 1 ⁺ -V3 ⁺ ) The voltage values at the approximate center, Va and Vb, are
The following three conditions Va + Vb> V2 ⁺ ... (1) Va-Vb <V1 ⁺ ... (2) 2 * Vb <V1 ⁺ -V3 ⁺ ... (3) are set. And each pulse width t
Indicates the switching time when the voltage (Va + Vb) is applied to the antiferroelectric liquid crystal 13. At this time, the liquid crystal 13 changes to a bright state in which the extinction position is deviated by −θ at the first voltage − (Va + Vb) pulse in the selection period, and then changes to a bright state in which the extinction position is deviated at θ by the voltage (Va + Vb) pulse. To do. The voltage applied during the non-selection period (Vo
The bright state is held by + Vb) or (Vo-Vb). This relationship is exactly the same for voltages of opposite polarity.
The change in optical transmittance showing this state is shown in FIG.
Next, the waveform applied to the OFF display pixel is shown in FIG.
Shown in. With this voltage waveform, the liquid crystal that is originally in the OFF state (antiferroelectric state, that is, dark state) does not respond and remains in dark display. In addition, in the above ON-displayed waveform, the ON state (-θ
In the selected period, the voltage (Va-Vb), which does not change with the first pulse of voltage-(Va-Vb) but does not change to the bright state of + θ, continues with the opposite polarity.
Pulse causes the -θ bright state to be an antiferroelectric state (dark state)
Return to. FIG. 10 shows changes in optical transmittance showing this state.
It shows in (d).

As described above, the matrix liquid crystal cell 10 is dynamically driven by controlling the voltages of the row electrode side 4 level and the column electrode side 2 level, and high contrast display can be obtained. Further, the present driving method has the following advantages. The smectic layer of the antiferroelectric liquid crystal 13 shown in FIG. 3 has a chevron structure which is folded in a "<" shape as shown. This layer structure changes into a bookshelf structure in which the "<" shape extends when an electric field is applied to bring it into a ferroelectric state. This state is examined by the X-ray diffraction method in FIG. When the electric field is zero in FIG. 6A, the smectic layer has a “<” shape inclined by about 11 °. When an electric field is applied, it does not change at the voltage before it changes to the ferroelectric phase (FIG. 6 (b)), but it changes to a bookshelf structure with no tilt of the smectic layer at the voltage at which it changes to the ferroelectric phase (FIG. 2 (c)). ). When the electric field is set to zero again, it returns to a chevron structure with a smaller angle than the initial one. These facts are due to M. Johno et
al: Jpn.J.Appl.Phys., vol.28, (1989) L119 or Y.
Yamada et al: Jpn.J.Appl.Phys., Vol.29, (1990) pp17
It is reported in papers such as 57 to 1764. That is, the antiferroelectric liquid crystal 13 is accompanied by a layer structure change (called layer switching) when switching between an antiferroelectric state (dark display) and a ferroelectric state (bright display). According to our experiments, excessive layer switching causes an afterimage (development called image sticking) when the device is used as a display device. In the conventional driving method, since there is a period of zero voltage in the selection signal, the liquid crystal of the ON display pixel has, for example, a negative voltage ferroelectric state → an antiferroelectric state → a positive voltage ferroelectric state in each field cycle, or vice versa. The state of the route changes. Then, the layer switching is occurring accordingly. Then, for example, when a still image is displayed as in a computer terminal, there is excessive layer switching only in the liquid crystal of a specific pixel, that is, an ON display pixel, and the liquid crystal is turned OFF.
This means that layer switching does not occur in the liquid crystal of the display pixel. Therefore, this difference appears as a printed image.

However, in the driving method of the present invention, ON
Since the liquid crystal of the display pixel does not have the period of zero voltage, only the ferroelectric state of the negative voltage → the ferroelectric state of the positive voltage or the state change of the reverse path occurs every field period. That is, the polarity reversal occurs without passing through the antiferroelectric state. Therefore, this change does not cause layer switching. After all, according to the driving method of the present invention, the layer switching occurs only when the ON display and the OFF display are switched. Therefore, since there is no layer switching bias to the specific pixel as in the conventional driving method, image sticking can be prevented.

[0039]

Since the matrix type liquid crystal display device according to the present invention adopts the above-mentioned technical structure, the matrix type liquid crystal display device having a high contrast capable of improving the degree of integration of the driving ICs. A liquid crystal display device is obtained, and in a display device using an antiferroelectric state liquid crystal, it is possible to prevent an afterimage caused by a structural change of a smectic layer and reduce the number of voltage levels required to drive a display pixel. Thus, it is possible to obtain a matrix type liquid crystal display device having a simplified drive circuit.

[Brief description of drawings]

FIG. 1 is an overall view showing a configuration of a specific example of a matrix type liquid crystal display device according to the present invention.

FIG. 2 is an enlarged schematic sectional view of a liquid crystal cell used in the present invention.

FIG. 3 is a diagram showing the relationship between the relative light transmittance and the applied voltage of the antiferroelectric liquid crystal used in the present invention.

FIG. 4 is a diagram showing an example of drive signal waveforms of a liquid crystal panel used in the present invention.

FIG. 5 is a block diagram showing a specific example of a row electrode driving circuit of a matrix type liquid crystal display device according to the present invention.

6 is a timing chart of each signal in the row electrode drive circuit shown in FIG.

FIG. 7 is a block diagram showing a specific example of a column electrode driving circuit of a matrix type liquid crystal display device according to the present invention.

8 is a timing chart of each signal in the column electrode drive circuit shown in FIG.

FIG. 9 is a partially enlarged view of row electrodes and column electrodes used in the matrix type liquid crystal display device according to the present invention.

FIG. 10 is a diagram for explaining a voltage signal waveform actually applied between both electrodes of a liquid crystal cell of a matrix type liquid crystal display device according to the present invention.

FIG. 11 is a diagram illustrating a change in the bookshelf structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 4 ... Control device 10 ... Liquid crystal cell 11 ... Electrode substrate 12 ... Electrode substrate 13 ... Antiferroelectric liquid crystal 14, 15 ... Polarizing plate 16, 17 ... Polymer film 21 ... Frame memory 22 ... Control circuit 23 ... Row electrode drive circuit 24 ... Column electrode drive circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuki Nobuaki 1-1, Showa-cho, Kariya city, Aichi prefecture Nihon Denso Co., Ltd. (72) Inventor Yuichiro Yamada 1-1-chome, Showa town, Kariya city, Aichi prefecture Sozo Co., Ltd.

Claims (1)

[Claims] 1. An n-row electrode and an m-row column electrode are arranged side by side so as to face each other in a grid, and at least one antiferroelectric state and two Between a liquid crystal cell in which anti-ferroelectric liquid crystal in which a ferroelectric state is stably formed is encapsulated to form mn display pixels, and between the n row electrodes and the m column electrodes, A first drive signal for ON-displaying an arbitrary pixel on the selected one row electrode among the mn display pixels and a second drive signal for OFF-displaying the remaining pixels on the selected row electrode. In a matrix type liquid crystal display device provided with a matrix driving means for selectively scanning each row electrode every 1 / n of one screen display time, the antiferroelectric liquid crystal is applied by an applied voltage. It can be controlled by the antiferroelectric state and the direction of the electric field 2 The two ferroelectric states can be switched to each other, and the light transmittance of the antiferroelectric liquid crystal exhibits at least a hysteresis sufficient for matrix driving in accordance with an increase or a decrease of the applied voltage within a predetermined voltage. The anti-ferroelectric liquid crystal is used, and the driving means is formed as an AC-changing bipolar pulse for switching between two ferroelectric states as the first driving signal, and the anti-ferroelectric as the second driving signal. Is formed as a bipolar pulse alternatingly changing with a voltage in a range in which switching from the state to the ferroelectric state is not performed, and is followed by a predetermined polarity in one polarity following the first and second drive signals. One screen display is completed by applying a DC signal having a voltage corresponding to approximately the center of the voltage range between the n row electrodes and the m column electrodes, and thereafter, or after the above operation. After a plurality of times, the driving means applies a voltage in which the voltage polarities of the first and second driving signals and the DC signal following them are all opposite to each other by the same operation as described above. Electrode and m
A matrix type liquid crystal display device, characterized in that it is configured to be applied between a row of column electrodes.