JP2002098939A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of high-speed driving. SOLUTION: In the liquid crystal display device provided with a liquid crystal layer, capable of bending alignment, a display screen displaying an image by using light transmitted through a bend aligned liquid crystal layer and a liquid crystal voltage applying means for applying a liquid crystal voltage Vp' to the liquid crystal layer, corresponding to luminance information for each field of image information consisting of continuous fields and successively displaying the image, corresponding to the field of the image information on the display screen through changing of the transmittance of the light, by applying the liquid crystal voltage Vp'; and the liquid crystal voltage applying means applies the liquid crystal voltage Vp' whose intensity is varied so as to be voltage Vp corresponding to the luminous information, until the liquid crystal voltage is applied in the post-field, when the luminous information is varied between pre- and post-fields.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a device capable of high-speed driving.

[0002]

2. Description of the Related Art Conventionally, a TN type liquid crystal display device has been generally used as a liquid crystal display device. However, since the response speed of the TN type liquid crystal display device is slow, an OCB type display device has been studied as a liquid crystal display device capable of high-speed response.
For details of the OCB type liquid crystal display device, refer to “IEICE Technical Report EDI98-144, page 199”.

In the OCB type liquid crystal display device, liquid crystal is sandwiched between substrates, and a transparent electrode is formed on the inner surface of the substrate. Before the power is turned on, the alignment state of the liquid crystal is in a state called splay alignment. When the power of the liquid crystal display device is turned on, a relatively large voltage is applied to the transparent electrode in a short time to change the alignment of the liquid crystal to a bend alignment state. Performing display using this bend alignment state is a feature of the OCB type liquid crystal display mode, which enables a high-speed response.

[0004]

The problem of the HOLD type display device is that "The 142nd Committee for Organic Materials for Information Science, the 71st Meeting of the A Group (Liquid Crystal Materials), the 62nd Meeting of the B Group (Intelligent Organic Materials)". Research Meeting Joint Study Group Material November 20, 1998 Japan Society for the Promotion of Science 1-5
Page ", and C
A technique for realizing a moving image corresponding to RT has been suggested. Among these techniques, the simplest one is to write a screen at high speed and periodically insert a black screen. In this specification, the method of performing the screen writing time in a short time in such a manner is collectively referred to as “high-speed driving”.

[0005] However, although the OCB type liquid crystal display device can provide a high-speed response, there is a problem that it has not yet been able to sufficiently cope with the above-mentioned high-speed driving.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its object to provide a liquid crystal display device which can be driven at high speed.

[0007]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention comprises a liquid crystal layer capable of bend alignment, and a display for displaying an image by light transmitted through the liquid crystal layer in bend alignment. A screen, and a liquid crystal voltage applying unit that applies a liquid crystal voltage to the liquid crystal layer in accordance with luminance information of each field of image information composed of continuous fields,
In a liquid crystal display device which sequentially displays images corresponding to the fields of the image information on the display screen by changing the transmittance of the light by applying the liquid crystal voltage, the liquid crystal voltage applying means includes: When the luminance information changes between the two, the liquid crystal voltage whose magnitude changes so as to become a voltage corresponding to the luminance information before application in the next field is applied (claim 1).

With this configuration, a voltage different from the voltage corresponding to the luminance information of the image information is transiently applied to the liquid crystal, whereby the speed of the change in the transmittance of the liquid crystal in the OCB liquid crystal mode, that is, the response speed, is reduced. Can be controlled.

In this case, when the luminance information changes so as to increase the corresponding liquid crystal voltage, the liquid crystal voltage applying means increases the liquid crystal voltage so that the voltage becomes excessively large and then becomes a size corresponding to the luminance information. In the case where the changing liquid crystal voltage is applied and the luminance information changes so that the corresponding liquid crystal voltage decreases, the liquid crystal voltage that changes to become a magnitude corresponding to the luminance information after becoming too small. It may be applied (claim 2).

With this configuration, the transient voltage promotes a change in the transmittance of the liquid crystal, so that the response speed of the liquid crystal can be increased. In addition, since the amount of change in the amount of transmitted light with respect to the change in the dielectric constant of the liquid crystal is large in the OCB liquid crystal mode, the response speed is markedly higher than that in the conventional OCB liquid crystal mode due to the synergistic effect of this effect and the application of the transient voltage. Speed up. Therefore, it is possible to cope with “high-speed driving”.

Further, the liquid crystal voltage may change from an excessively large or small state to converge to a voltage corresponding to the luminance information.

With this configuration, the liquid crystal voltage is easily settled to a voltage corresponding to the luminance information of the image information.

The display screen is composed of a plurality of pixels, and the liquid crystal voltage applying means applies a pixel voltage to the liquid crystal layers of all the pixels sequentially in accordance with luminance information for each pixel in the field. It may be constituted by applying means (claim 4).

With this configuration, a configuration in which the liquid crystal voltage is changed can be applied to a liquid crystal display device in which the display screen is composed of a plurality of pixels.

In this case, the plurality of pixels are formed in a matrix, and the gate driving means sequentially scans the plurality of pixels through a gate electrode for each row or column. Source driving means for applying a base voltage based on luminance information of a pixel of image information through a source electrode,
And compensating voltage applying means for applying a compensating voltage to the liquid crystal layer of the pixel after the scanning through capacitive coupling so as to be superimposed on the base voltage, wherein the base voltage and the compensating voltage are used as the pixel voltage. The source driving means and the compensation voltage applying means may constitute the pixel voltage applying means so that the magnitude is changed by a change in capacitance (claim 5).

With such a configuration, a constant base voltage is applied from the source driving means to which a voltage can be applied only during scanning by the gate driving means, and a capacitive coupling is established in a period after scanning in which the pixel voltage is to be changed. The compensation voltage is superimposed on the base voltage using the voltage, and the voltage changes so as to be a voltage corresponding to the luminance information of the pixel due to a change in the liquid crystal capacitance of the pixel. Is automatically applied. Therefore, the configuration for applying the transient voltage is simplified.

In this case, the capacitive coupling may be formed between the pixel electrode and the gate electrode on the preceding stage in the scanning direction.

With this configuration, the compensation voltage can be applied by using the gate electrode, so that the configuration of the compensation voltage applying means is simplified.

In this case, the compensation voltage may be applied by the gate driving means applying a potential change to the preceding gate electrode.

In the above case, the capacitive coupling may be formed between the pixel electrode and a dedicated capacitance line.

In this case, the compensation voltage may be applied by giving a potential change to the capacitance line.

In the above case, the liquid crystal voltage applying means may supply a voltage based on luminance information for each field of the image information from a voltage supply source for supplying the liquid crystal voltage only through a signal line for applying the voltage to the liquid crystal layer. (Claim 10).

With this configuration, the waveform of the transient voltage can be easily controlled.

In this case, the voltage supply source is means for storing image information of successive fields, means for deriving a change in luminance information between the fields of the stored image information, and Means for generating a compensation voltage corresponding to the change in the brightness information, and a base voltage based on the brightness information of the subsequent field, and superimposing the compensation voltage on the base voltage and outputting this as the liquid crystal voltage. And a liquid crystal voltage supply unit.
1).

In the above case, the ratio of the image information writing period, which is the period for sequentially writing the image information of one field to all the pixels, in the field period, which is the period for writing the image information of one field at a constant period, is shown. 90%
It may be less than (claim 12).

With this configuration, it is possible to insert a black screen in the field period to improve the cutoff of moving image display.

In this case, the image information writing period is 1
It may be shorter than 6.6 ms (claim 13).

With this configuration, it is possible to obtain a liquid crystal display device in which a black screen is inserted to improve the sharpness of the moving image display in the generally employed moving image display method with a field frequency of 60 Hz.

In the above case, the ratio of the image information writing period to the field period may be smaller than half.

With this configuration, in this case, the image information writing period may be shorter than 8 ms.

With such a configuration, it becomes possible to cope with "double speed drive", and it becomes possible to display a sharp moving image by inserting a black screen in a generally adopted moving image display method with a field frequency of 60 Hz. In applications such as televisions and monitors, a liquid crystal display device that is practical with respect to response speed can be obtained.

In the above case, the pixel voltage applying means applies a pixel voltage for displaying a substantially black screen on the display screen during a period other than the image information writing period of the field period. (Claim 16).

With this configuration, it is possible to improve disconnection of moving image display.

In the above case, a light source for supplying light transmitted through the liquid crystal layer, and control means for controlling the light source so as to turn on during the image information writing period of the field period and turn off during the remaining period. (Embodiment 17).

With such a configuration, the screen at the time of display becomes dark while the light source is turned off, so that it is possible to improve the disconnection of the moving image display.

In the above case, the ratio of the capacitance for capacitive coupling to the liquid crystal capacitance of the pixel may be 0.7 or more.

With such a configuration, the change in the pixel voltage due to the change in the liquid crystal capacitance becomes large, so that the transient voltage can be increased. Therefore, the response speed of the liquid crystal can be increased.

In this case, the ratio of the capacitance for capacitive coupling to the liquid crystal capacitance of the pixel may be 1 or more.

With this configuration, the transient voltage can be increased, and the liquid crystal response speed can be increased.

In the above case, the maximum level and the minimum level of the pixel voltage corresponding to the upper and lower limit levels of the luminance information of the image information are determined with respect to the dielectric constant of the liquid crystal layer below the maximum level. The ratio of the dielectric constant of the liquid crystal layer may be 1.2 or more.

With this configuration, the change in the liquid crystal capacitance when the luminance information of the image information changes is large, so that the liquid crystal response speed can be increased.

In this case, the ratio of the permittivity may be 1.4 or more.

With this configuration, the response speed of the liquid crystal can be further increased.

In the above case, the liquid crystal layer may have a dielectric anisotropy of 6.5 or more.

With this configuration, when the luminance information of the image information changes, the change in the dielectric constant of the liquid crystal increases in accordance with the magnitude of the dielectric anisotropy. "High-speed driving" becomes possible.

In this case, the liquid crystal layer may have an anisotropy of dielectric constant of 7.7 or more.

With this configuration, the response speed of the liquid crystal is further increased.

Also, the liquid crystal display device according to the present invention comprises a liquid crystal layer capable of bend alignment, a display screen including a plurality of pixels for displaying an image by light transmitted through the liquid crystal layer in bend alignment, and Pixel voltage applying means for sequentially applying a pixel voltage to the liquid crystal layers of all the pixels in accordance with the luminance information of each pixel, wherein the image information is obtained by changing the transmittance of the light by applying the pixel voltage. In the liquid crystal display device for displaying an image corresponding to the above on the display screen,
The pixel voltage applying means forms the pixel voltage together with the voltage applied to the liquid crystal layer of the pixel at the time of the sequential application, and sprays from the bend alignment of the liquid crystal layer through capacitive coupling after the sequential application. An offset voltage for preventing a reverse transition to the alignment may be applied to the pixel (claim 24).

With this configuration, the offset voltage can be applied without being limited by the charging capacity of the liquid crystal panel as in the case where the offset voltage is applied by changing the counter electrode. In addition, by configuring the pixel voltage to change transiently, the offset voltage can be applied using CC driving, so that the speed can be remarkably increased and the configuration for applying the offset voltage is simplified. Liquid crystal display device can be obtained.

In this case, there is provided a gate driving means for sequentially scanning the plurality of pixels through a gate electrode, and the pixel voltage applying means is provided in the liquid crystal layer of the scanned pixel based on the luminance information of the pixel of the image information. Source driving means for applying a reference voltage through a source electrode, and offset voltage applying means for applying an offset voltage so as to form the pixel voltage together with the base voltage through capacitive coupling to the pixel after the scanning, The coupling may be formed between the pixel electrode and the gate electrode on the preceding stage in the scanning direction.

With this configuration, the offset voltage can be applied by using the gate electrode, so that the configuration of the offset voltage applying means is simplified.

The capacitive coupling may be formed between the pixel electrode and a dedicated capacitance line.

Further, the offset voltage may be 1 V or more.

With this configuration, it is possible to prevent reverse transition from bend alignment to splay alignment in a general OCB type liquid crystal panel.

Further, the offset voltage may be higher than a reverse transition voltage of the liquid crystal layer from bend alignment to splay alignment (claim 28).

With this configuration, it is possible to prevent reverse transition from the bend alignment to the splay alignment.

Further, a substantially black screen may be displayed on the display screen within a field period which is a cycle of writing image information of one field at a constant cycle.

With this configuration, the required offset voltage can be reduced, and the break of moving image display can be improved.

The display screen may be substantially rectangular and have a diagonal length of 10 inches or more.

With such a configuration, in the liquid crystal display device of this size, it is advantageous to apply the offset voltage by the configuration of the present invention, so that the effect of the present invention is great.

In this case, the length of the diagonal may be 15 inches or more.

With this configuration, in the liquid crystal display device of this size, the offset voltage can be applied substantially only by the configuration of the present invention, so that the effect of the present invention is remarkable.

Further, the liquid crystal display device according to the present invention comprises a liquid crystal layer capable of transition to bend alignment, a display screen including a plurality of pixels for displaying an image by light transmitted through the liquid crystal layer in bend alignment, A liquid crystal display device comprising a voltage application unit, wherein the liquid crystal layer of the pixel has a capacitance, wherein the liquid crystal layer of the pixel has a capacitance by changing an transmittance of the light by applying the pixel voltage to display an image corresponding to the image information on the display screen. The transition to the bend alignment is performed by using a voltage applied to the liquid crystal layer of the pixel through the coupling (claim 32).

With this configuration, in addition to the voltage applied by the normal pixel voltage applying means, the voltage applied through the capacitive coupling can be used as the transfer voltage, so that the liquid crystal can be transferred in a shorter time. Can be.

In this case, prior to the transition operation, a pause period in which no voltage is applied to the liquid crystal layer of the pixel may be provided.

With this configuration, since no voltage is applied to the liquid crystal layer before the transition operation, the transition can be performed satisfactorily.

In this case, there is provided a gate driving means for sequentially scanning the plurality of pixels through a gate electrode, and the pixel voltage applying means controls the liquid crystal layer of the scanned pixel based on the luminance information of the pixel of the image information. Source driving means for applying a reference voltage through a source electrode, and accumulation voltage applying means for applying an accumulation voltage to form the pixel voltage together with the base voltage through the capacitive coupling to the pixel after the scanning, The accumulated voltage may be used to transfer the liquid crystal layer of the pixel to the bend alignment (claim 34).

With such a configuration, since the magnitude of the pixel voltage is changed transiently, the accumulated voltage by CC driving can be used as a part of the transition voltage, so that the speed can be remarkably increased. And a liquid crystal display device capable of shortening the transition time.

In this case, the capacitive coupling may be formed between the pixel electrode and the gate electrode on the preceding stage in the scanning direction.

With this configuration, the stacked voltage can be applied by using the gate electrode, so that the structure of the stacked voltage applying means is simplified.

In the above case, the capacitive coupling may be formed between the pixel electrode and a dedicated capacitance line.

In the above case, the gate driving means as the stacked voltage applying means may apply the stacked voltage to each pixel while sequentially scanning all the pixels during the transition. Item 37).

With such a configuration, the gate driving means can be operated in the same mode as during display even at the time of transition.

In this case, the source drive means outputs the base voltage having a voltage value for AC transfer, and the gate drive means is provided for each of the pixels during the idle period. The switching element outputs a gate signal having two voltage levels that are turned on and off at the time of the scanning and at other times, and at the time of the transition,
In addition to the two voltage levels, a gate signal having two voltage levels to which the stacked voltage having a polarity corresponding to the polarity of the base voltage can be applied immediately after the scanning may be output. Item 38).

With such a configuration, the accumulated voltage can be applied to the liquid crystal of the pixel at the time of transition, but the accumulated voltage can be prevented from being generated during the idle period, whereby the transition can be performed satisfactorily and in a short time. It can be performed.

The source driving means may output the base voltage having a DC transition voltage value, and the gate driving means may include a switching circuit provided for each pixel during the idle period. The element outputs a gate signal having two voltage levels that are turned on and off at the time of the scan and at other times, respectively. During the transition period, in addition to the two voltage levels, the gate signal is output immediately after the scan. It may output a gate signal having one voltage level to which the stacked voltage having the same polarity as the base voltage can be applied (claim 39).

With this configuration, since a stacked voltage of one polarity is generated, the stacked voltage can be generated efficiently.

The liquid crystal display device according to the present invention has a TN
A liquid crystal layer of a mode, a display screen for displaying an image by light transmitted through the liquid crystal layer, and a liquid crystal for applying a liquid crystal voltage to the liquid crystal layer according to luminance information for each field of image information composed of continuous fields. A voltage application unit, wherein the liquid crystal display device sequentially displays images corresponding to the image information fields on the display screen by changing the transmittance of the light by applying the liquid crystal voltage. When the luminance information changes between the successive fields, apply the liquid crystal voltage whose magnitude changes so as to be a voltage corresponding to the luminance information before application in the next field, and When the luminance information changes so that the corresponding liquid crystal voltage increases, the luminance information changes to become a size corresponding to the luminance information after becoming excessive. When the above-mentioned luminance information changes so that the corresponding liquid crystal voltage decreases, the liquid crystal voltage which becomes too small and then changes so as to have a magnitude corresponding to the luminance information is applied. The thickness of the liquid crystal layer is 3 μm or less (claim). With such a configuration, the response speed of the liquid crystal is increased by an amount corresponding to the increase in the electric field generated in the liquid crystal layer, and as a result,
It is possible to support "double speed drive", and it is possible to display a sharp moving image by inserting a black screen in a generally adopted moving image display method with a field frequency of 60 Hz. A practical liquid crystal display device can be obtained with respect to the response speed.

[0079]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view schematically showing a configuration of the liquid crystal display device of FIG. 1, and FIG. FIG. 4 is a plan view schematically showing a configuration of a pixel of the liquid crystal display element, FIG. 4 is a sectional view showing a configuration of an auxiliary capacitance electrode, and FIG. 5 is a circuit diagram showing an equivalent circuit of the pixel.

As shown in FIG. 1, the liquid crystal display device 1 comprises a liquid crystal display element (liquid crystal panel) 106, a backlight 18,
A display control circuit 19; display light is supplied from the backlight 18 to the liquid crystal display element 106; and the display control circuit 19 controls the liquid crystal display element 106 to transmit the display light in accordance with the video signal 14. By driving, an image corresponding to the video signal 14 is displayed on the liquid crystal display element 106.

The backlight 18 supplies display light from the light source 15 driven by the lighting circuit 16 to the liquid crystal display element 106 via a light guide plate (not shown).

The display control circuit 19 includes the display controller 1
3. It has a gate driver 11, a source driver 12, and a lighting controller 17. Display controller 13
Outputs a control signal to the gate driver 11, the source driver 12, and the illumination controller 17 in response to the video signal 14. The gate driver 11 sequentially scans (selects) pixels of the liquid crystal display element 106 for each gate electrode 2 by outputting a gate signal through the gate electrode 2 according to the control signal. The source driver 12 sequentially writes the source signal through the source electrode 3 to the scanned pixel by outputting the source signal in timing with the gate signal according to the control signal. As a result, the transmittance of each pixel for display light changes in accordance with the source signal, whereby an image corresponding to the video signal 14 is displayed on the liquid crystal display element 106. The lighting controller 17 controls the driving of the light source 15 by the lighting circuit 16 according to a control signal from the display controller 13.

As shown in FIG. 2, the liquid crystal display element 106
In this case, the counter substrate 101 and the counter substrate 101, which are formed of an active matrix type, are disposed so as to face each other.
A liquid crystal 103 is sandwiched between the FT substrate 102 and the two substrates 101 and 10.
A retardation plate 104 and a polarizing plate 105 are arranged outside of 2 in this order. A counter electrode 8 (see FIG. 4) is formed on the inner surface of the counter substrate 101, and an alignment film (not shown) is formed on the surface of the counter electrode 8. Referring also to FIG. 3, a gate electrode 2, a source electrode 3, a pixel electrode 6, and the like are formed on the inner surface of the TFT substrate 102, and an alignment film (not shown) is formed so as to cover these. I have.
Rubbing treatment is performed on the alignment films of both substrates 101 and 102 in directions parallel to each other. FIG. 2 shows a cross section parallel to the rubbing direction. A nematic liquid crystal is used as the liquid crystal. That is, the liquid crystal display element 106 employs the OCB liquid crystal mode. In the OCB liquid crystal mode, in the initial state where no voltage is applied, the liquid crystal is in a splay alignment in which molecules are arranged substantially in parallel, but when a relatively large voltage, for example, a voltage of about 25 V is applied, the liquid crystal is in a display state. Transition to bend orientation. FIG. 2 shows this bend alignment state.

As shown in FIG. 3, on the inner surface of the TFT substrate 102, a plurality of linear gate electrodes 2 and a plurality of linear source electrodes 3 are formed so as to be orthogonal to each other. , 3 are pixels 4
Is composed. Then, a region including a set of all the pixels 4 forms a display screen (not shown). Each pixel 4
Have pixel electrodes 6 formed therein, and each pixel 4 has a TF
A switching element 5 made of T (Thin film transistor) is formed. The switching element 5 has a source and a drain connected to the source electrode 3 and the pixel electrode 6, respectively, and a gate connected to the gate electrode 2. Gate signals are sequentially output from the upper side to the lower side in FIG. 3 to the gate electrodes 2, whereby the pixels connected to each gate electrode 2 are sequentially scanned for each gate electrode 2. Hereinafter, the order before and after this scanning order is referred to as a former stage and a latter stage. In each pixel 4, an auxiliary capacitance electrode 7 is provided so as to be capacitively coupled to the gate electrode 2 on the preceding stage.
It is connected to the pixel electrode 6. That is, the liquid crystal display element 10
6 is the so-called capacitive drive method (hereinafter referred to as CC drive)
Has been adopted. For details of the CC drive, see Japanese Patent Application Laid-Open No. 2-157815 or AM-LCD95 Di.
See page 59 of the gest of Technical papers. More specifically, as shown in FIG. 4, a gate electrode 2 is formed on a TFT substrate 102, and a TFT on which the gate electrode 2 is formed is formed.
An insulating layer 9 is formed to cover the surface of the FT substrate 102. Then, the pixel electrode 6 is formed so as to cover the portion of the insulating layer 9 located in the pixel, and the portion of the insulating layer 9 located on the gate electrode 2 and the edge of the pixel electrode 6 adjacent thereto are formed. An insulating layer 10 is formed to cover.
Then, the auxiliary capacitance electrode 7 is formed on the insulating layer 10,
The contact hole 41 is connected to the pixel electrode 6 on the subsequent stage. With such a structure, the pixel 4
As shown in FIG. 5, a switching element 5 is connected to the source electrode 3, a liquid crystal capacitor Clc is connected between the switching element 5 and the counter electrode 8, and the switching element 5 is connected to the gate of the preceding stage. The storage capacitor Cst is connected between the electrode 2. Note that Cgd indicates a stray capacitance between the pixel electrode 6 and the gate electrode 2.

Next, the operation of the liquid crystal display device 1 configured as described above will be described.

FIG. 6 is a graph showing the gate signal, the source signal, and the potential of the common electrode. FIG. 7 is a graph showing the relationship between the change in the gate signal and the change in the pixel voltage. FIG. 7B is a diagram showing a change in an even field.

As shown in FIGS. 1 and 6, the potential of the counter electrode (hereinafter referred to as the counter voltage) Vcom is set to be constant. On the other hand, the liquid crystal display element 106 is AC driven. That is, the source driver 12 outputs a source signal Ss that alternately takes a positive value and a negative value for each pixel connected to the same source electrode 3 with respect to the common voltage Vcom. The polarity of the source signal Ss with respect to the counter voltage Vcom is inverted for each screen, that is, for each field. In the present embodiment,
The counter voltage Vcom is set to 3V. Further, the amplitude (base voltage) Vs of the source signal Ss is set to 3v, and therefore, the source signal Ss alternately takes the values of 6v and 0v.

On the other hand, the gate driver 11 outputs the following gate signal Sg. That is, this gate signal Sg
Is Vgon in the writing period Ta, and in the stacking period Tp following the writing period Ta, Vge1 in the odd field, Vge2 in the even field, and the remaining period excluding the writing period Ta and the stacking period Tp
Vg0ff is set to Tr. Here, Vge1 is set to a voltage higher than Vg0ff by Vge (+), and Vge2 is set to a voltage lower than Vg0ff by Vge (−). Then, not only Vg2 but also Vge1 is set to a voltage at which the switching element 5 is turned off (high resistance state). Further, the stacking period Tp is set to a period slightly more than twice the writing period. In the present embodiment, Vgon of the gate signal Sg is a predetermined positive value, and Vgoff is −10.
v, Vge1 is -3v, Vge (+) is 7v, Vge2 is -18v, Vg
e (-) is set to -8v.

As a result, in an arbitrary pixel, FIG.
As shown in FIG. 7 and FIG. 7, in the writing period Ta, the switching element 5 is turned on (low resistance state), and the pixel electrode 6 is charged to the voltage Vs of the source signal Ss. Thereby, the source signal Ss is written to the pixel 4. Here, in the case of an odd field, the pixel voltage Vp 'changes from positive to negative here. In this case, as shown in FIG.
When the source signal Ss is written to the pixel 4, the voltage Vge1 is applied to the gate electrode 2 on the previous stage. Further, a voltage lower than a voltage originally applied to the liquid crystal (a set pixel voltage Vp described later) is applied to the pixel electrode 6. Next, when the period shifts to the stacking period Tp, the voltage of the gate electrode 3 in the corresponding stage falls to Vge2, whereby the switching element 5 is turned off. On the other hand, the voltage of the gate electrode 3 on the former stage drops to Vgoff. In other words, it decreases by Vge (+). Then, since the switching element 5 is in the cut-off state and the pixel electrode 6 is coupled to the preceding gate electrode 3 by the auxiliary capacitance Cst, the potential of the pixel electrode 6 also decreases in conjunction with the voltage of the gate electrode 3. . This amount of voltage change (hereinafter,
Vcc (referred to as a compensation voltage or a stacking voltage) takes a value as shown in an equation described later.

In the case of the even field, the pixel voltage Vp 'changes from negative to positive here. In this case, the source signal Ss is written to the pixel 4 as shown in FIG. At this time, a voltage of Vge2 is applied to the gate electrode 2 on the preceding stage. Next, when the period shifts to the stacking period Tp, the voltage of the gate electrode 3 of the stage falls to Vge1, whereby
The switching element 5 is turned off. On the other hand, the voltage of the gate electrode 3 on the front stage rises to Vgoff. That is, Vge (-)
Just go up. Then, the potential of the pixel electrode 6 increases by the compensation voltage Vcc in conjunction with the voltage of the gate electrode 3. The compensation voltage Vcc in this case and in the above case is represented by the following equation.

Vcc = Cst / (Cst + Cgd + Clc) × (Vge (+) or Vge (−)) Usually, a voltage anticipating the compensation voltage Vcc, that is, Vp ′ = Vs + Vcc is applied to the pixel electrode 6. Design.

Such a driving method of the liquid crystal display element is CC driving. It is known that the response speed of the TN liquid crystal is increased to some extent by using the CC driving. This is due to dielectric anisotropy.

Now, in any pixel, the transmittance of the liquid crystal display element (hereinafter simply referred to as transmittance) is 100% to 0%.
Consider the case where it changes up to Assume that the display mode is a normally white mode. Then, when the transmittance is 100%, the voltage applied to the liquid crystal is low,
Liquid crystal has a small dielectric constant. Conversely, when the transmittance is 0%, the voltage applied to the liquid crystal is high, and the dielectric constant is large.

Since the response of the liquid crystal molecules requires more time than the charging of the pixel electrode, a time delay occurs with respect to the charging of the pixel electrode (writing of the source signal).

The voltage Vp 'applied to the pixel electrode at the beginning of charging (to be exact, immediately after the end of the writing period) (hereinafter referred to as pixel voltage) is Vp' (initial value) = Vs + Cst / (Cst + Cgd + Clc (100)) × Vge
(+), Which is Vp '(saturation value) = Vs + Cst / (Cst + Cgd + Clc (0)) × Vge
Changes to (+).

Here, Clc (100) is the liquid crystal capacity when the transmittance is 100%, and Clc (0) is the liquid crystal capacity when the transmittance is 0%. In this liquid crystal capacity, there is a relationship of Clc (100) <Clc (0), and therefore, the relationship of Vp ′ (initial value)> Vp ′ (saturation value) is satisfied.

In this case, Vp ′ (saturation value) is the voltage that should be originally applied to the pixel electrode 6, ie, the set pixel voltage.
Vp. The set pixel voltage Vp is a voltage corresponding to luminance information (gradation) for each pixel of the video signal.

Here, the transmittance is from 100% to 0%.
%, The voltage applied to the liquid crystal changes from a low state to a high state. At this time, a high voltage such as Vp '(initial value) is applied to the liquid crystal at the beginning of charging, although transiently, and the response speed of the liquid crystal is increased by the transient high voltage. You.

Conversely, when the state changes from a dark state with a low transmittance to a relatively bright half-tone state with a relatively high transmittance, the voltage applied to the liquid crystal changes from a high state. Change to a relatively low state. However, in this case, Vp '(initial value) <Vp' (saturation value), so that
At the beginning of charging, a low voltage Vp '(initial value) is transiently applied to the liquid crystal. Therefore, also in this case, the response speed of the liquid crystal is increased.

Next, in order to further clarify the features of the present invention, the present invention employs a normal driving method (hereinafter, simply referred to as normal driving).
This will be described in contrast to

FIG. 8 is a circuit diagram showing an equivalent circuit of a pixel in normal driving, and FIG. 9 is a graph for explaining a change in transmittance of the pixel due to normal driving. FIG. (B) is a graph showing a change in pixel voltage, (c) is a graph showing a change in pixel voltage at the transition from the writing period to the holding period, and (d) is a graph showing a change in the dielectric constant of the liquid crystal in the pixel. (E) is a graph showing a change in transmittance of a pixel, FIG. 10 is a graph for explaining a change in transmittance of a pixel according to the present embodiment, (a) is a diagram showing a gate signal, (b) ) Is a graph showing a change in pixel voltage, (c) is a graph showing a change in the pixel voltage at the transition from the writing period to the holding period, (d) is a graph showing a change in the dielectric constant of the liquid crystal in the pixel, (e) 4) is a graph showing a change in transmittance of a pixel.

First, in normal driving, as shown in FIG.
The auxiliary capacitance electrode is provided so as to be capacitively coupled to a capacitance line (not shown), and the capacitance line is connected to the counter electrode 8. As a result, the equivalent circuit of the pixel has an auxiliary capacitance Cst connected in parallel with the liquid crystal capacitance Clc.

The normal driving operation will be described. Here, a case where the voltage (pixel voltage vp ′) applied to the liquid crystal rapidly changes from a high state to a low state will be described.
As shown in FIGS. 9A and 9C, when the gate signal is output to the pixel, the switching element becomes conductive in the writing period Ta in which the voltage shows a high value, and the pixel electrode becomes the voltage of the source signal. Charged. The writing period Ta is, for example, 20 μs, which is extremely short. But,
The response time of the liquid crystal molecules is a value on the order of several milliseconds even for the OCB mode liquid crystal, and is longer than the charging time. Since the dielectric constant of the liquid crystal changes according to the response of the liquid crystal molecules as described above, the response is also slow. Therefore, at the initial stage of charging, the voltage applied to the liquid crystal, that is, the pixel voltage Vp ′
Changes as shown in FIG. 9B, but the dielectric constant of the liquid crystal at this time remains high at the time of high voltage, as shown in FIG. 9D. Next, when the switching element enters the cutoff state and shifts to the holding period, the molecules of the liquid crystal respond,
Thereby, the dielectric constant changes. Due to this change in the dielectric constant, charge redistribution occurs, and the pixel voltage Vp ′ changes as shown in FIGS. 9 (b) and 9 (c). As a result, the pixel voltage Vp ′ becomes a value shifted from the set pixel voltage Vp. As a result, FIG.
As shown in (e), the transmittance gradually changes over one field period Tf and over many fields. That is, the response of the liquid crystal becomes slow. Here, the pixel voltage Vp ′ is represented by the following equation.

Vp ′ = (Cst + Clc (0)) / (Cst + Clc (100)) × Vp In other words, in normal driving, the pixel voltage Vp ′ is changed such that a change in the dielectric constant of the liquid crystal impairs the response of the liquid crystal. It was a configuration.

Therefore, in the present embodiment, the pixel voltage Vp 'is changed so that the change in the dielectric constant of the liquid crystal increases the response speed of the liquid crystal. That is, the point that the gate signal is pulse-shaped as shown in FIG. 10A is the same as that of the normal driving, but as shown in FIG. 10B, the initial state of the holding period Th immediately after the end of the writing period Ta is shown in FIG. The compensation voltage Vc
c is applied from the gate electrode to the pixel electrode via the storage capacitor Cst. At this time, the dielectric constant of the liquid crystal also changes gradually as shown in FIG.
As shown in (b), the compensation voltage Vcc changes.
The change in the compensation voltage Vcc accompanying the change in the dielectric constant acts to speed up the response of the liquid crystal. Therefore, as shown in FIG. 10 (e), the transmittance does not slow down the response but rather changes at such a speed as to temporarily overshoot. This also has the effect of emphasizing changes in transmittance. Thereby, the liquid crystal can finish the response within one screen, that is, within one field period Tf.

As described above, it is a feature of the present invention that the compensation voltage is applied in a direction of accelerating the response, and the application of the compensation voltage is automatically performed by using the change of the liquid crystal capacitance. That's it.

Next, the effects of the liquid crystal display device according to the present embodiment will be described. The OCB liquid crystal mode is characterized by high speed, but it is difficult to respond within one field in the normal driving even with the OCB liquid crystal mode. This is because there was an inhibitory effect due to the change in the dielectric constant as described above. Therefore, in the present invention, by combining the OCB liquid crystal mode and the CC driving, a response within one field period can be surely realized.

FIG. 11 is a graph showing the response speed between gradations of the liquid crystal display device, and FIG. 12 is the rise timing between gradations.
5A and 5B are tables showing e and Decay time, wherein FIG. 5A shows a table in the case of a normal driving OCB liquid crystal mode, and FIG.
Table showing the case of the CB liquid crystal mode.
9 is a table showing a case of a liquid crystal mode.

As shown in FIG. 12, in order to confirm the effect of the liquid crystal display device according to the present embodiment, a normally driven OC is used.
For the B liquid crystal mode, the CC driven OCB liquid crystal mode (this embodiment), and the CC driven TN liquid crystal mode, rise time and decay time between each gradation were measured. This measurement is performed at room temperature in the case of the OCB liquid crystal mode of the normal drive,
In the case of the OCB liquid crystal mode driven by CC and the TN liquid crystal mode driven by CC, the test was performed at 32 ° C. FIGS. 12 (a), (b),
In each table of (c), the upper right half shows Decay time (τd), and the lower left half shows Rise time (τr). Also,
Numerical values representing the levels of the respective gradations represent percentages when the black display level and the white display level are 100 for screen luminance. FIG. 11 is a graph showing the response speed with respect to the target gradation in order to make the measurement result easier to understand. Here, the target gradation means two gradations for which the response speed is calculated. The response speed means the sum of the rise time from one of the two gradations to the other and the decay time from the other to the other. In a liquid crystal display device, the response speed is usually represented by the sum of the rise time and the decay time. As a specific example, in the OCB liquid crystal mode of the normal drive (FIG. 12 (a)), when the target gradations are those of the 0 level and 25 levels (0−0 in FIG. 11).
25), and the response speed is 0.92 (τr) +
3.2 (τd) = 4.12 [ms].

In FIG. 11, the characteristic of the OCB liquid crystal mode in the normal driving is shown by a curve B. As is clear from the curve B, the response speed of the normally driven OCB liquid crystal mode has to be said to be practically still low at the intermediate gradation. In other words, it is necessary to insert a black screen in order to cut out a moving image similar to that of a CRT. To that end, a video signal is written at a frequency higher than the normal field frequency of 60 Hz, and the black screen is displayed in an extra time. Need to be inserted. If possible, to get the required video breaks,
It is preferable that the insertion time of the black screen is at least half or more of one field period.
It is necessary to write a video signal at a frequency of 120 Hz.
For this purpose, it is necessary to realize a response speed of 8 ms or less. Further, if the liquid crystal display element is linked with a backlight or if it is desired to realize a high-speed response even at a low temperature, a higher speed is required. In this specification,
Writing a video signal at this 120 Hz frequency
In particular, it is called “double speed drive”.

On the other hand, in the normally driven OCB liquid crystal mode, the response speed between gray scales was 12.8 ms at the maximum. Therefore, although it is possible to partially support not only writing of a video signal at a normal field frequency of 60 Hz but also "high-speed driving", writing of a video signal at 120 Hz capable of displaying a sharp moving image, that is, , "Double speed drive" cannot be used at all, and cannot be put to practical use in applications such as televisions and monitors.

On the other hand, the characteristic of the OCB liquid crystal mode driven by the CC is shown by a curve A in FIG. 11, and as apparent from the curve A, the response speed between gradations is 6 m at the maximum.
s or less (exactly 5.4 ms or less). This response speed is less than half that of the normally driven OCB liquid crystal mode.
This was sufficiently shorter than 8 ms corresponding to a video signal writing period of the frequency z (hereinafter, referred to as an image information writing period). Therefore, the liquid crystal display device according to the present embodiment can perform not only “high-speed driving” but also “double-speed driving”, and as a result, the response speed can be sufficiently used in applications such as televisions and monitors. It has become. That is, for the first time, the liquid crystal display device according to the present embodiment enables practical moving image display at a response speed.

The characteristics of the TN liquid crystal mode of the normal drive which is widely used at present are shown by a curve C in FIG. 11. In this liquid crystal mode, it is possible to respond in a time equal to or shorter than a field period of a normal frequency of 60 Hz. The range of gray levels is extremely small, and it cannot sufficiently cope with not only "double speed driving" but also "high speed driving". Therefore, the response speed is insufficient for displaying a moving image.

FIG. 13 shows the rise time and the time between each gray level.
It is a three-dimensional graph which shows a decay time visually, (a) is a table | surface which shows the case of the OCB liquid crystal mode of CC drive, and (b) is a table which shows the case of the OCB liquid crystal mode of normal drive.

FIG. 13 shows the measurement of rise time and decay time between gradations in which the steps are made finer than those in the measurement of FIG. The level of each gradation is represented by a level in screen luminance when black display is set to 0 and white display is set to 255.

As is apparent from FIG.
The CB liquid crystal mode has a particularly high effect on the decay time, that is, the response time in the direction in which the liquid crystal is relaxed, as compared with the normally driven OCB liquid crystal mode. Also, C
In the C-drive OCB liquid crystal mode, the response time is about 3 ms or less between any gradations. When this is viewed from the response speed (τr + τd), it is 6 ms or less. Further, the difference between the gradations is much smaller than that in the normally driven OCB liquid crystal mode. This is because the largest compensation voltage is automatically applied to the pixel electrode at the time of the change from the black display level to the white display level, which has the slowest response. As described above, even when the steps of the gradation are finely divided, the liquid crystal display device according to the present embodiment can be applied to a television,
It has a response speed that is practical for applications such as monitors.

Next, the temperature characteristics of the liquid crystal display device according to the present embodiment will be described. In the OCB liquid crystal mode of CC driving, the low temperature limit at which “double speed driving” was possible was 10 ° C. However, the temperature of 10 ° C. refers to the temperature of the liquid crystal display element heated by a backlight or the like, and the environmental temperature in this case was 0 ° C. Therefore, the liquid crystal display device according to the present embodiment was able to achieve sufficiently good “double speed driving” even at room temperature or lower. It should be noted that the normally driven OCB
In the liquid crystal mode, the low temperature limit at which driving at a field frequency of 60 Hz is possible is 25 ° C., and at temperatures lower than that, even driving at a field frequency of 60 Hz was difficult.

Next, preferred conditions of the present embodiment will be described. As described above, the speeding up by the CC driving is brought about by the superposition of the compensation voltage Vcc and the change of the pixel voltage Vp ′ due to the dielectric anisotropy. Therefore, it is preferable that the anisotropy of the dielectric constant is large. In this embodiment mode, a liquid crystal material having a dielectric constant of 11 at all voltages, 5 at no voltage, 10 at black display voltage, and 7 at white display voltage is used. An important parameter in selecting this liquid crystal material is the ratio between the dielectric constant under a black display voltage and the dielectric constant under a white display voltage (hereinafter referred to as the dielectric ratio), and the larger the ratio, the more effective. In the present embodiment, a liquid crystal material having a dielectric ratio of 1.4 is used. If the dielectric ratio is 1.2 or more, the effect of increasing the speed is exhibited. If the dielectric ratio is 1.4 or more, it can be applied to "double speed driving" in which the frequency of the image information writing period is 120 Hz. The TN type liquid crystal usually has a dielectric ratio of 2 or more, but the OCB type liquid crystal is used in a state where molecules are considerably raised even in white display, so that the dielectric ratio becomes small. This is a great restriction on the choice of liquid crystal material. However, in the present embodiment, the improvement of the dielectric ratio was realized by selecting a liquid crystal material having a large dielectric anisotropy. The dielectric constant of the liquid crystal material used in this embodiment is ε vertical = 3.
7, ε parallel = 11.5. Therefore, dielectric anisotropy Δε = ε parallel−ε vertical = 7.8. Regarding the selection of the liquid crystal material, if Δε> 6.5 or more, the dielectric ratio becomes 1.2 or more, and the effect of speeding up appears, and Δε> 7.7.
If it is above, the dielectric ratio becomes 1.4 or more and "double speed drive"
Was applicable to

Another parameter that is important in CC driving is the ratio between the auxiliary capacitance Cst and the liquid crystal capacitance Clc.
The larger the Cst, the more effective. In the present embodiment, the capacitance ratio = Cst / Clc is set to 1. In order to achieve the effect of speeding up, it is preferable to set the capacitance ratio to 0.7 or more, and to apply to “double speed drive”, it is preferable to set it to 1 or more.

As described above, according to the present embodiment, the response time of the liquid crystal display device can be reduced to half or less of the conventional driving method. This is a very large effect from the empirical rule of the TN liquid crystal mode. This is probably because the amount of change in the amount of transmitted light with respect to the change in the dielectric constant of the liquid crystal is large in the OCB liquid crystal mode. In other words, the effect of the present embodiment is not simply the sum of the speed-up effect by the CC drive and the speed-up effect by the OCB liquid crystal mode, but the CC drive configuration and the above-described characteristics of the OCB liquid crystal mode match. This is considered to be due to the synergistic effect of the two. Further, it was confirmed that the effect of increasing the speed can be further improved by increasing the anisotropy of the dielectric constant.

Next, a modified example of this embodiment will be described. [Modification 1] The method of supplying the compensation voltage to the pixel electrode is not limited to the former-stage gate method. The compensation voltage may basically be supplied from an electrode capacitively coupled to the pixel electrode.

FIG. 14 is a plan view showing a configuration of a capacitance line according to this modification, and FIG. 15 is a cross-sectional view taken along line XV-XV in FIG. FIG.
As shown in FIG. 4, in this modification, an independent capacitance line 31 is formed on the inner surface of the TFT substrate 102 in parallel with the gate electrode 2. This capacitance line 31 is formed corresponding to each gate electrode 2. This capacitance line is formed on the TFT substrate 102 so as to be covered with the insulating layer 9 as shown in FIG.
The pixel electrode 6 is formed on the insulating layer 9. Therefore,
An auxiliary capacitance is formed between the pixel electrode 6 and a portion 31 a of the capacitance line 31 below the pixel electrode 6. And
Generally, a general capacitance line is connected to the counter electrode 8, but this capacitance line 31 is connected to a dedicated driver (not shown). This is because a predetermined voltage must be applied to the capacitance line 31 in synchronization with the scanning of the gate electrode 2, so that the capacitance line 31 needs to be driven independently. As a result, the number of drivers on the gate side increases, but by forming these drivers with polysilicon, the burden due to the increase in the number of drivers is reduced. Voltages corresponding to Vg (+) and Vg (-) applied to the former-stage gate electrode in FIG. 6 are applied to this capacitance line 31 by the dedicated driver at the same timing as in FIG. Thereby, the same effect as in the case of FIG. 6 can be obtained. [Modification 2] In the above configuration example, the compensation voltage is supplied from the capacitively-coupled gate electrode so that the compensation voltage is automatically superimposed. Since the application is performed in such a direction that the change in the transmittance of the display element is accelerated, this can be realized without using the above-described capacitive coupling. Therefore, in this modification, such a compensation voltage application circuit is configured.

FIG. 16 shows the configuration of a compensation voltage applying device according to this modification. In FIG. 16, the compensation voltage applying device 30
Is, for example, a plurality (here, two) of field memories
32, 33, in which image information for one screen (one field) before and after the video signal 14 is stored, respectively, and the difference calculation circuit 34 is used to store the pixels of the image information stored in the respective field memories 32, 33. The difference of the gradation (luminance information) is calculated, the compensation voltage generation circuit 35 generates a compensation voltage having a value corresponding to the difference of the gradation, and the source driver 12 calculates the gradation of the pixel of the video signal 14 in the subsequent field. A voltage (source signal) obtained by superimposing the compensation voltage on a reference voltage based on the tone (the voltage Vs of the source signal in FIG. 6) is supplied to the liquid crystal display element 106. At present, a large amount of calculation is required to calculate the difference in gray level of each pixel between fields, and it is difficult to achieve this in terms of calculation speed. However, in the near future, the miniaturization and speeding up of semiconductors will be advanced to such an extent that they can be processed in the controller chip, so that it will be possible to realize this configuration. [Modification 3] According to the present embodiment, it is possible to further increase the speed by setting the OCB liquid crystal mode of the CC drive, but in the present modification, a black screen is inserted in the field period in this configuration. It is a combination of configurations. With such a configuration, the break of the moving image, that is, the visibility is improved. Here, in this specification, the field period is 1
This means a cycle in which image information (here, a video signal) for a screen is written at a constant cycle. In the field period, a period in which image information for one screen is sequentially written to all pixels is referred to as an image information writing period. In the field period, a period during which a black screen is written is referred to as a black screen insertion period. The present modification is effective when the image information writing time is smaller than 90% of the field period.
For example, when the black screen insertion period is set to 10% or more of the field period, the liquid crystal hardly returns to the splay alignment, that is, there is an effect of preventing reverse transition. Further, when the image information writing period is set to be equal to or less than half of the field period, the remaining period can be set as the black screen insertion period, so that the visibility can be further improved. The voltage for displaying a black screen may be any of a voltage for black level or substantially black, and a voltage for black level or higher. [Modification 4] In this modification, the backlight is turned off during the black screen insertion period in the field period. Specifically, in the configuration of FIG. 1, the lighting controller 17 controls the lighting circuit 16 so as to turn off the light source 15 over the entire black screen insertion period. With such a configuration, it is possible to achieve both improvement in visibility by inserting a black screen and reduction in power consumption. [Modification 5] In this modification, a cell thickness is set to 3 μm or less in a liquid crystal display device of a TN liquid crystal mode driven by CC. With such a configuration, the electric field intensity generated in the liquid crystal increases as the cell thickness decreases, thereby enabling a high-speed response. In particular, when the cell thickness was 3 μm or less, “double speed driving” was possible as in the case of the OCB liquid crystal mode of CC driving. In this configuration, it is needless to say that the response speed can be further increased by selecting the liquid crystal material for the dielectric anisotropy and the dielectric ratio in the same manner as described above. Second Embodiment The CC drive used in the first embodiment has an advantage that the drive voltage can be optimized in addition to the high speed. Therefore, in the second embodiment of the present invention, an offset voltage is applied using this CC drive.

FIG. 17 is a pixel voltage-transmittance graph showing the setting of the offset voltage in the liquid crystal display device according to the present embodiment.

The overall configuration of the liquid crystal display according to the present embodiment is the same as that of the first embodiment. However, in the present embodiment, unlike the first embodiment, the compensation voltage shown in FIG.
The value of Vcc is set to a value that allows for the offset voltage. Here, the offset voltage refers to the bend-aligned liquid crystal as shown in FIG.
A voltage applied for the purpose of preventing reverse transition to splay alignment. In the present embodiment, this offset voltage is 2
v. Note that the electrode to be capacitively coupled may be a gate electrode or an independent capacitance line. This is the same as in the first embodiment. With such a configuration, the reverse transition of the liquid crystal can be prevented by using the CC driving, so that the configuration for preventing the reverse transition is simplified.

That is, in the OCB type liquid crystal display device, there is a problem that splay alignment occurs when the voltage is too low. For this reason, a driving method that does not lower the pixel voltage below a certain value is generally used. As a preferable example of such a driving method, for example, it is conceivable to apply an offset voltage by changing the potential of the counter electrode into an alternating rectangular wave shape.

However, this driving method is suitable for a small liquid crystal panel (liquid crystal display element), but is not suitable for a large liquid crystal panel. This is because the CR time constant during charging becomes too large because the capacity of the liquid crystal panel becomes too large. According to the results of the study by the present inventors, it was practically impossible to apply an offset voltage by the above-mentioned driving method to a liquid crystal panel of 10 inches or more. Further, in a liquid crystal panel of 15 inches or more, application of an offset voltage cannot be realized by a method other than the CC driving. Here, the “○” means that the length of the diagonal line of the substantially rectangular display screen of the liquid crystal panel is “○ inch”.

Therefore, an offset voltage is applied using CC driving as in the present embodiment.

Incidentally, in the OCB type liquid crystal display device, the voltage at which the transition to the splay alignment reversely depends on the pretilt angle. When the pretilt angle is 15 degrees, the reverse transition voltage is 1
v. According to the study of the present inventors, general OC
In a B-type liquid crystal panel, an offset voltage of 1 V or more was required. However, when a black screen is inserted in one field, a lower offset voltage is also good. That is, when a black screen is inserted, the bend alignment is maintained even if a low voltage is temporarily applied to the liquid crystal. However, this only lowers the critical voltage for reverse transition to the splay alignment, and it is still necessary to always apply the offset voltage. Note that the offset voltage in this case may be lower than 1 V. Embodiment 3 Embodiment 3 of the present invention uses CC driving for transition from splay alignment to bend alignment at the time of startup of a liquid crystal display device.

FIG. 18 is a graph showing the waveform of the counter voltage when the liquid crystal display device according to the present embodiment is started, and FIG.
7A is a graph showing waveforms of a counter voltage, a gate signal, and a source signal. FIG. 7A is a graph showing a waveform during a pause period, and FIG. 7B is a graph showing a waveform during a transition voltage application period. 18 and 19, the same symbols as those in FIG. 6 indicate the same or corresponding parts.

In the liquid crystal display device according to the present embodiment, the counter voltage, the gate signal, and the source signal are output with the following waveforms at the time of startup in the configuration of the first embodiment. Further, a driver for driving the counter electrode is provided.

As shown in FIG. 18, when the liquid crystal display device is started, a counter voltage Vcom having a low frequency AC waveform of 0.5 to 10 Hz is applied to the counter electrode over a predetermined transition period T3. . The counter voltage Vcom of this AC waveform has a pause period T1 having a value of 3v and a transition voltage application period having a value of -25v.
T2 has a waveform that is alternately repeated. Here, the reason for taking the value of 3v is to prevent a voltage from being applied to the liquid crystal, as described later.

Referring also to FIG. 19, gate signal Sg is output to the gate electrode even during the transition voltage application period. As the gate signal Sg, during the pause period T1, FIG.
As shown in FIG. 19A, a signal having two values of Vgon and Vgoff is output, and during the transition voltage application period T2, the same quaternary signal as that after the transition (see FIG. 6) is output as shown in FIG. Is done. Therefore, in the transition voltage application period T2, the accumulated voltage Vcc
Is applied to the pixel electrode, and +3-(− 2)
5) Although only the transition voltage of 28 V can be applied to the liquid crystal, a transition voltage of 30 V or more could be effectively applied to the liquid crystal. This means that the accumulated voltage Vcc is 2
This is because more than v occurred. Also, the gate signal Sg is Vge2
In the case of taking the value of, a particularly large accumulated voltage Vcc was generated, and a larger transition voltage could be applied accordingly. For this reason, it is desirable to output a signal having three values of Vgon, Vgoff, and Vge2 as the gate signal Sg during the transition voltage application period T2. However, in this case, the gate signal Sg
Is different from the waveform after the transition, so that another routine work is imposed on the gate driver.

On the other hand, during the idle period T1, the binary signal is output, for the following reason.
That is, it is desirable that no voltage is applied to the liquid crystal during the idle period T1 in order to perform the transition favorably. However, when the quaternary signal is output in the same manner as during the transition voltage application period T1, the accumulated voltage Vcc is applied to the liquid crystal by CC driving. Therefore, to prevent this stacked voltage Vcc from being generated,
The gate signal Sg in the idle period T1 is a binary signal as described above.

Further, the source signal Ss has the same voltage as the counter voltage Vcom at least during the idle period T1. This is to prevent a voltage from being applied to the liquid crystal during the idle period T1. In the present embodiment, during the transition period T3, both the rest period T1 and the transition voltage application period T2 are equal to 3 during the transition period T3.
v is a constant value.

In the present embodiment, the transfer can be sped up by the configuration described above. Specifically, the transition time, which was conventionally 3 seconds, could be reduced to 2 seconds.

The prior art is disclosed in Japanese Patent Application Laid-Open No. HEI 9-185.
No. 037 discloses a technique in which a gate voltage is always set to a high level to apply a transition voltage.
On the other hand, in the present embodiment, the scanning of the gate electrode is performed in the same manner as in the display state (after the transition), so that the accumulated voltage Vc
c is used effectively at the time of transfer, and transfer is performed efficiently.

Next, a modification of this embodiment will be described.
FIG. 20 is a graph showing waveforms of a counter voltage, a gate signal, a source signal, and a voltage of a pixel electrode according to the present modification.

In this modification, the source signal is
Both Ss and the counter voltage Vcom are 0 V, so that no voltage is applied to the liquid crystal. Then, in the transition voltage application period T2, the counter voltage Vcom is greatly shifted to −20 V on the negative side, and the source signal Ss is inverted on the positive side to +7 V. Further, the gate signal Sg is a ternary signal as shown in the enlarged view in the dotted line in FIG. 20, and therefore, the accumulated voltage Vcc by CC driving is applied to the pixel electrode.
As a result, in the pixel electrode, the accumulated voltage Vcc is accumulated on the voltage 7v of the source signal Ss, and the electric potential is + 10v. As a result, the pixel voltage became as high as 30 V, and this voltage could be applied to the liquid crystal. Further, since the gate signal Sg during the transition voltage application period T2 is a ternary signal, the stacked voltage Vcc of only one polarity is superimposed, and the stacked voltage Vcc is as large as about 3V. Note that the transition voltage application period T2 is set to 1 second here. Further, the gate signal Sg is a binary signal during the pause period T1, as in the above configuration example. In addition, suspension period
If the source electrode and the counter electrode have the same potential during T1, both potentials may change, but it is most stable to keep them constant.

In the first to third embodiments,
Although a layered electrode made of a conductive material was formed on the inner surface of the substrate as the electrode portion, the electrode portion in the present invention is not limited to this electrode. For example, between the electrode and the liquid crystal, an electric property variable body whose electric property is switched between insulating and conductive by irradiating light is arranged, and the electric property variable body and the electrode are arranged. The electrode unit may be configured by using.

[0141]

The present invention is embodied in the above-described embodiment and has an effect that a liquid crystal display device capable of high-speed driving can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view schematically showing a configuration of the liquid crystal display of FIG.

FIG. 3 is a plan view schematically showing a configuration of a pixel of the liquid crystal display device of FIG.

FIG. 4 is a cross-sectional view illustrating a configuration of an auxiliary capacitance electrode.

FIG. 5 is a circuit diagram showing an equivalent circuit of a pixel.

FIG. 6 is a graph showing a gate signal, a source signal, and a counter voltage.

7A and 7B are graphs showing a relationship between a change in a gate signal and a change in a pixel voltage, wherein FIG. 7A is a diagram showing a change in an odd field, and FIG. 7B is a diagram showing a change in an even field.

FIG. 8 is a circuit diagram showing an equivalent circuit of a pixel in normal driving.

9A and 9B are graphs for explaining a change in transmittance of a pixel due to normal driving, in which FIG. 9A shows a gate signal, and FIG.
Is a graph showing a change in pixel voltage, (c) is a graph showing a change in pixel voltage at the transition from the writing period to the holding period, (d) is a graph showing a change in the dielectric constant of the liquid crystal in the pixel, (e) 6 is a graph showing a change in transmittance of a pixel.

10A and 10B are graphs for explaining a change in transmittance of a pixel according to the first embodiment of the present invention, wherein FIG. 10A is a diagram illustrating a gate signal, FIG. 10B is a graph illustrating a change in pixel voltage, (c) is a graph showing a change in pixel voltage at the transition from the writing period to the holding period, (d) is a graph showing a change in the dielectric constant of the liquid crystal in the pixel, and (e) is a graph showing a change in the transmittance in the pixel. It is.

FIG. 11 is a graph showing a response speed between gradations of the liquid crystal display device.

12A and 12B are tables showing rise time and decay time between gradations, where FIG. 12A shows a table in the case of the OCB liquid crystal mode of the normal drive, and FIG. 12B shows a case of the OCB liquid crystal mode in the CC drive. Table (c) is a table showing the case of the TN liquid crystal mode driven by CC.

FIG. 13: Rise time and Decay time between each gradation
(A) is a table showing the case of the OCB liquid crystal mode of CC drive, and (b) is a stereograph of
9 is a table showing a case of a CB liquid crystal mode.

FIG. 14 is a plan view showing a configuration of a capacitance line according to a first modification of the first embodiment of the present invention.

15 is a sectional view taken along line XV-XV in FIG.

FIG. 16 is a block diagram showing a configuration of a compensation voltage applying device according to a second modification of the first embodiment of the present invention.

FIG. 17 is a pixel voltage-transmittance graph showing setting of an offset voltage in the liquid crystal display device according to Embodiment 2 of the present invention.

FIG. 18 is a graph showing a waveform of a counter voltage when the liquid crystal display device according to Embodiment 3 of the present invention is started.

FIGS. 19A and 19B are graphs showing waveforms of a counter voltage, a gate signal, and a source signal when the liquid crystal display device according to Embodiment 3 of the present invention is started, and FIG. (b) is a graph showing a waveform during a transition voltage application period.

FIG. 20 is a graph showing waveforms of a counter voltage, a gate signal, a source signal, and a voltage of a pixel electrode according to a modification of the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Gate electrode 3 Source electrode 4 Pixel 5 Switching element 6 Pixel electrode 7 Auxiliary capacitance electrode 8 Counter electrode 9 Insulating layer 10 Insulating layer 11 Gate driver 12 Source driver 13 Display controller 14 Video signal 15 Light source 16 Lighting circuit 17 Lighting controller 18 Backlight 19 Display control circuit 30 Stacked voltage application circuit 31 Capacitance line 32,33 Field memory 34 Difference calculation circuit 35 Compensation voltage generation circuit 41 Contact hole 101 Opposite substrate 102 TFT substrate 103 Liquid crystal 104 Phase difference plate 105 Polarizer 106 Liquid crystal display element Cgd Floating capacitance between pixel electrode and gate electrode Clc Liquid crystal capacitance Cst Auxiliary capacitance Sg Gate signal Ss Source signal T1 Transition voltage application period T2 Pause period T3 Transition period Ta Writing period Tf Field period Th Holding period Tp Stacking Period Tr Remaining period Vcc Stacked voltage (stacked voltage) Vcom The amplitude of pressure Vp set the pixel voltage Vp 'pixel voltage Vs source signal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Kawaguchi 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Machitori Watari 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Katsuyuki Arimoto 1006 Okadoma Kadoma, Kadoma City Osaka Pref. MA09 2H093 NA16 NC34 NC42 NC49 NC62 ND07 ND32 ND39 NF05 NF28 5C006 AC22 AC28 AF42 AF44 AF46 BB16 BC03 BC06 BC13 FA14 FA18 FA37 GA03 5C080 AA10 BB05 DD08 JJ02 JJ03 JJ04 JJ05 JJ06

Claims (40)

[Claims] 1. A liquid crystal layer capable of bend alignment, a display screen for displaying an image by light transmitted through the liquid crystal layer in bend alignment, and brightness information for each field of image information comprising a continuous field. Liquid crystal voltage applying means for applying a liquid crystal voltage to the liquid crystal layer, and changing the transmittance of the light by applying the liquid crystal voltage to sequentially display images corresponding to the image information fields on the display screen. In the liquid crystal display device, the liquid crystal voltage applying means has a size such that, when the luminance information changes between the preceding and succeeding fields, the voltage corresponds to the luminance information before application in the next field. A liquid crystal display device characterized by applying the changing liquid crystal voltage. 2. The liquid crystal voltage applying means, when the luminance information changes so that the corresponding liquid crystal voltage increases, changes the luminance information so that the magnitude becomes excessively large and then becomes the magnitude corresponding to the luminance information. When the luminance information changes so that the corresponding liquid crystal voltage decreases, a liquid crystal voltage that changes to become a magnitude corresponding to the luminance information after becoming too small is applied. Claim 1
The liquid crystal display device according to the above. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal voltage changes from an excessively large or small state to converge to a voltage corresponding to the luminance information. 4. The display screen comprises a plurality of pixels, and the liquid crystal voltage applying means applies a pixel voltage to all the liquid crystal layers of the pixels sequentially in accordance with luminance information for each pixel in the field. 3. The liquid crystal display device according to claim 2, comprising an application unit. 5. Gate driving means for sequentially scanning the plurality of pixels through a gate electrode, and source driving for applying a base voltage based on the luminance information of the pixel of the image information to a liquid crystal layer of the scanned pixel through a source electrode. Means, and a compensation voltage applying means for applying a compensation voltage to the pixel after the scanning through capacitive coupling so as to be superimposed on the base voltage, wherein the base voltage and the compensation voltage are used as the pixel voltage as the liquid crystal capacitance of the pixel. 5. The liquid crystal display device according to claim 4, wherein the magnitude is changed by the change of the voltage, and the source driving means and the compensation voltage applying means constitute the pixel voltage applying means. 6. The liquid crystal display device according to claim 5, wherein said capacitive coupling is formed between a pixel electrode and a gate electrode at a preceding stage in the scanning direction. 7. The liquid crystal display device according to claim 6, wherein the compensation voltage is applied when the gate driving means applies a potential change to a preceding gate electrode. 8. The liquid crystal display device according to claim 5, wherein said capacitive coupling is formed between a pixel electrode and a dedicated capacitance line. 9. The liquid crystal display device according to claim 8, wherein the compensation voltage is applied by giving a potential change to the capacitance line. 10. The liquid crystal voltage applying means comprises a voltage supply source for supplying the liquid crystal voltage only through a signal line for applying a voltage based on luminance information for each field of the image information to the liquid crystal layer. The liquid crystal display device as described in the above. 11. The voltage supply source includes means for storing image information of successive fields, means for deriving a change in luminance information between fields of the stored image information, and the derived voltage information. Means for generating a compensation voltage corresponding to a change in luminance information, and a liquid crystal for generating a base voltage based on the luminance information of the subsequent field, superimposing the compensation voltage on the base voltage, and outputting the same as the liquid crystal voltage The liquid crystal display device according to claim 10, further comprising a voltage supply unit. 12. An image information writing period in which one field of image information is sequentially written to all pixels in a field period which is a period in which one field of image information is written in a constant cycle is less than 90%. The liquid crystal display device according to claim 4. 13. The image information writing period is 16.6.
The liquid crystal display device according to claim 12, wherein the time is less than ms. 14. The liquid crystal display device according to claim 12, wherein a ratio of the image information writing period to the field period is less than half. 15. The liquid crystal display device according to claim 14, wherein the image information writing period is less than 8 ms. 16. The pixel voltage applying means for applying a pixel voltage for displaying a substantially black screen on the display screen during a period other than the image information writing period of the field period. 13. The liquid crystal display device according to 12. 17. An illuminating device comprising: a light source for supplying light transmitted through the liquid crystal layer; and control means for controlling the light source to be turned on during the image information writing period of the field period and turned off during the remaining period. The liquid crystal display device according to claim 12, comprising: 18. The liquid crystal display device according to claim 5, wherein a ratio of the capacitance for capacitive coupling to the liquid crystal capacitance of the pixel is 0.7 or more. 19. The liquid crystal display device according to claim 18, wherein a ratio of the capacitance for capacitance coupling to the liquid crystal capacitance of the pixel is 1 or more. 20. With respect to the maximum level and the minimum level of the pixel voltage corresponding to the upper and lower limit levels of the luminance information of the image information, the dielectric constant of the liquid crystal layer below the minimum level with respect to the dielectric constant of the liquid crystal layer below the maximum level The liquid crystal display device according to claim 5, wherein the ratio of the ratios is 1.2 or more. 21. The liquid crystal display device according to claim 20, wherein the ratio of the dielectric constant is 1.4 or more. 22. The liquid crystal display according to claim 5, wherein the liquid crystal layer has a dielectric anisotropy of 6.5 or more. 23. The liquid crystal display device according to claim 22, wherein the liquid crystal layer has a dielectric anisotropy of 7.7 or more. 24. A liquid crystal layer capable of bend alignment, a display screen composed of a plurality of pixels for displaying an image by light transmitted through the liquid crystal layer in bend alignment, and a luminance information for each pixel of image information. A pixel voltage applying means for sequentially applying a pixel voltage to the liquid crystal layers of all the pixels, and changing the transmittance of the light by applying the pixel voltage to display an image corresponding to the image information on the display screen. In the liquid crystal display device for displaying, the pixel voltage applying means forms the pixel voltage together with the voltage applied to the liquid crystal layer of the pixel at the time of the sequential application, and through the capacitive coupling after the sequential application, A liquid crystal display device, wherein an offset voltage for preventing a reverse transition from a bend alignment to a splay alignment of a liquid crystal layer is applied to the pixel. 25. A gate driving unit for sequentially scanning the plurality of pixels through a gate electrode, wherein the pixel voltage applying unit is configured to display, based on luminance information of the pixel of the image information, a liquid crystal layer of the scanned pixel. Source driving means for applying a base voltage through a source electrode, and offset voltage applying means for applying an offset voltage to the pixel after the scanning so as to form the pixel voltage together with the base voltage through the capacitive coupling to the pixel; 25. The liquid crystal display device according to claim 24, wherein the coupling is formed between the pixel electrode and a gate electrode on a preceding stage in the scanning direction. 26. The liquid crystal display device according to claim 24, wherein the capacitive coupling is formed between the pixel electrode and a dedicated capacitance line. 27. The liquid crystal display device according to claim 24, wherein the offset voltage is 1 V or more. 28. The liquid crystal display device according to claim 24, wherein the offset voltage exceeds a reverse transition voltage of the liquid crystal layer from bend alignment to splay alignment. 29. The liquid crystal display device according to claim 24, wherein a substantially black screen is displayed on the display screen during a field period which is a cycle of writing image information of one field at a constant cycle. 30. The liquid crystal display device according to claim 24, wherein the display screen is substantially rectangular and has a diagonal length of 10 inches or more. 31. The liquid crystal display device according to claim 30, wherein the length of the diagonal line is 15 inches or more. 32. A liquid crystal display device comprising: a liquid crystal layer capable of transitioning to a bend alignment; a display screen including a plurality of pixels for displaying an image by light transmitted through the bend-aligned liquid crystal layer; In a liquid crystal display device that displays an image corresponding to the image information on the display screen by changing the transmittance of the light by applying a voltage, the liquid crystal layer of the pixel is applied to the liquid crystal layer of the pixel through capacitive coupling. A liquid crystal display device, wherein transition to bend alignment is performed by using applied voltage. 33. The liquid crystal display device according to claim 32, further comprising a pause in which no voltage is applied to the liquid crystal layer of the pixel prior to the transition operation. 34. A gate driving unit for sequentially scanning the plurality of pixels through a gate electrode, wherein the pixel voltage applying unit is configured to control the liquid crystal layer of the scanned pixel based on luminance information of the pixel of the image information. Source driving means for applying a base voltage through a source electrode; and stacking voltage applying means for applying a stacking voltage to the pixel after the scanning so as to form the pixel voltage together with the base voltage through the capacitive coupling to the pixel; The liquid crystal display device according to claim 33, wherein the voltage is used for transition of the liquid crystal layer of the pixel to a bend alignment. 35. The liquid crystal display device according to claim 34, wherein the capacitive coupling is formed between a pixel electrode and a gate electrode on a preceding stage in the scanning direction. 36. The liquid crystal display device according to claim 32, wherein the capacitive coupling is formed between the pixel electrode and a dedicated capacitance line. 37. The liquid crystal display device according to claim 35, wherein said gate driving means as said accumulated voltage applying means applies said accumulated voltage to each pixel while sequentially scanning all pixels at said transition. 38. The source driving means for outputting the base voltage having an AC transition voltage value, wherein the gate driving means comprises a switching circuit provided for each of the pixels during the idle period. The device outputs a gate signal having two voltage levels that are turned on and off at the time of the scan and at other times, respectively, during the transition period,
38. A gate signal having two voltage levels capable of applying the accumulation voltage having a polarity corresponding to the polarity of the base voltage immediately after the scanning in addition to the two voltage levels. Liquid crystal display. 39. The apparatus according to claim 39, wherein the source driving means outputs the base voltage having a DC transition voltage value, and the gate driving means comprises a switching circuit provided for each of the pixels during the idle period. The device outputs a gate signal having two voltage levels that are turned on and off at the time of the scan and at other times, respectively, during the transition period,
38. The liquid crystal according to claim 37, wherein a gate signal having one voltage level capable of applying the stacked voltage having the same polarity as the base voltage immediately after the scanning is output in addition to the two voltage levels. Display device. 40. A TN mode liquid crystal layer, a display screen for displaying an image by light transmitted through the liquid crystal layer, and a liquid crystal voltage corresponding to luminance information for each field of image information composed of continuous fields. A liquid crystal voltage applying means for applying the liquid crystal layer to the liquid crystal layer, and changing the transmittance of the light by applying the liquid crystal voltage to sequentially display images corresponding to the fields of the image information on the display screen. The liquid crystal voltage applying means is configured such that, when the luminance information changes between the preceding and succeeding fields, the liquid crystal voltage has a magnitude that changes to a voltage corresponding to the luminance information before application in the next field. Is applied, and the luminance information changes so that the corresponding liquid crystal voltage increases. When the luminance information changes so that the corresponding liquid crystal voltage decreases, the magnitude of the luminance information becomes smaller and then becomes the magnitude corresponding to the luminance information. A liquid crystal display device for applying a changing liquid crystal voltage, wherein the thickness of the liquid crystal layer is 3 μm or less.