JP2001343956A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device of which the falling response speed is improved. SOLUTION: A liquid crystal panel indicates an extremum of transmissivity in a voltage-transmissivity characteristic at a voltage equal to or lower than a lowest gradation voltage. A driving circuit supplies a driving voltage, in which a gradation voltage corresponding to the input image signals of a beforehand determined present vertical interval is overshot, to a liquid crystal panel in accordance with the combination of the input image signals of one vertical interval before and the input image signals of the present vertical interval.

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, and more particularly, to a liquid crystal display suitably used for displaying moving images.

[0002]

2. Description of the Related Art Liquid crystal display devices include, for example, personal computers, word processors, amusement devices,
It is used in television devices and the like. Further, studies have been made to improve the response characteristics of the liquid crystal display device and obtain a high-quality moving image display.

Japanese Patent Application Laid-Open No. 4-288589 discloses a method for supplying a liquid crystal display section with an input image signal in which a high-frequency component is emphasized in advance in order to increase the response speed in halftone display and reduce afterimages. Discloses a liquid crystal display device in which the rise and fall of the liquid crystal are accelerated. Note that the “response speed” in the liquid crystal display device (liquid crystal panel) corresponds to the reciprocal of the time (response time) required for the alignment state of the liquid crystal layer to reach the alignment state corresponding to the applied voltage. FIG.
The configuration of the driving circuit of the liquid crystal display device will be described with reference to FIG.

The driving circuit of the liquid crystal display device includes an image storage circuit 61 for holding at least one field image of the input image signal S (t), an image signal held in the storage circuit 61 and the input image signal S (t). A time axis filter circuit 63 for detecting a level fluctuation of each picture element in the time axis direction from the signal S (t) and applying a high-frequency emphasis filter in the time axis direction. The input image signal S (t) is obtained by converting video signals into R, G,
Although the signal has been decomposed into B signals, the same processing is performed on the R, G, and B signals.
Only the channel is shown.

The input image signal S (t) is held in an image storage circuit 61 for storing image signals for at least one field. A differentiator 62 calculates a difference between corresponding picture element signals from the input image signal S (t) and the image storage circuit 61, and detects a change in signal level during one field. It has become. This difference device 62
Is input to the time axis filter circuit 63 together with the input image signal S (t).

The time axis filter circuit 63 outputs the difference signal Sd
A weighting circuit 66 for multiplying (t) by a weighting coefficient α corresponding to the response speed, a weighted difference signal and an input image signal S
(T).
The time axis filter circuit 63 is an adaptive filter circuit whose filter characteristics are changed according to the output of the level fluctuation detection circuit and the input level of each picture element of the input image signal. The input image signal S (t) is output by the time axis filter circuit 63.
Indicates that the high range in the time axis direction is emphasized.

The high-frequency emphasized signal obtained in this way is converted into an AC signal by a polarity inverting circuit 64, and the liquid crystal display 6
5 is supplied. The liquid crystal display section 65 is an active matrix type liquid crystal display section having a display electrode (also referred to as a picture element electrode) at each intersection of a plurality of data signal wirings and a plurality of scanning signal wirings crossing the data signal wirings. .

FIG. 13 is a signal waveform diagram showing how the response characteristics are improved by this drive circuit. In order to make the explanation easy to understand, it is assumed that the input image signal S (t) changes in a cycle of one field, and the figure shows a case where the signal level sharply changes in two fields. In this case, the change of the input image signal S (t) in the time axis direction, that is, the difference signal Sd (t) is, as shown in FIG.
When (t) changes positively, it becomes positive over one field, and when it changes negatively, it becomes negative over one field.

Basically, by adding the difference signal Sd (t) to the input image signal S (t), high frequency emphasis can be performed. Actually, since the relationship between the degree of change of the input image signal S (t) and the degree of change of the transmittance depends on the response speed of the liquid crystal layer, the weighting factor is corrected so as not to cause overshoot. Determine α. As a result, the high-frequency-corrected high-frequency correction signal Sc (t) as shown in FIG. 13 is input to the liquid crystal display unit, so that the optical response characteristics I (t) are obtained.
Is improved as shown by the solid line with respect to the conventional one shown by the broken line.

[0010]

However, when the driving circuit disclosed in the above publication is applied to a current liquid crystal display device, response characteristics of rising (change to a display state as the voltage applied to the liquid crystal layer rises) are increased. Can be improved, but the effect of improving the response characteristics of the fall (change to the display state due to the decrease in the voltage applied to the liquid crystal layer) is relatively small. The falling in the liquid crystal display device is intended to restore the alignment state of the liquid crystal molecules from the alignment state when a certain first voltage is applied to the alignment state when a second voltage lower than the first voltage is applied. The time required to reach the alignment state corresponding to the second voltage (fall response time) mainly depends on the restoring force acting between liquid crystal molecules. Therefore, the response speed (or response time) of the falling of the liquid crystal layer when the voltage applied to the liquid crystal layer decreases from the first voltage to the second voltage is generally equal to the magnitude of the second voltage (a certain first voltage). Voltage difference), the input image signal S
Even if (t) is emphasized, there is a problem that the effect of speeding up the falling response is small.

In particular, the voltage-transmittance (V-V) as shown in FIG.
T) Characteristics (The retardation in FIG. 5A of the present application is 260 nm)
Liquid crystal display device having a VT curve).
When the lowest gradation voltage (the lowest value of the gradation voltage) is set to a voltage at which the transmittance becomes the maximum, the falling response can be obtained even when an overshoot voltage (a voltage lower than the lowest gradation voltage) is applied. You can't be faster. This is because the alignment state of the liquid crystal molecules is substantially equal in the region of the voltage exhibiting the highest transmittance (the region where the VT curve is flat). The working restoring forces are substantially equal.

In the specification of the present application, “rise” and “fall” refer to the display state (or the alignment state of the liquid crystal layer) accompanying the “rise” and “decrease” of the voltage applied to the liquid crystal layer, respectively, as described above. Corresponding to the change. “Rise” is a change accompanying an increase in applied voltage, and corresponds to “decrease in luminance” in a normally white mode (hereinafter referred to as “NW mode”) and a normally black mode (hereinafter “NB mode”). ) Corresponds to “increase in luminance”. "Falling"
Is a change associated with a decrease in the applied voltage, and corresponds to “increase in luminance” in the NW mode, and corresponds to “decrease in luminance” in the NB mode. That is, "falling"
Is related to the relaxation phenomenon of the orientation of the liquid crystal layer (liquid crystal molecules).

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device having improved fall response characteristics.

[0014]

A liquid crystal display device according to the present invention comprises a liquid crystal panel having a liquid crystal layer and electrodes for applying a voltage to the liquid crystal layer, and a drive circuit for supplying a drive voltage to the liquid crystal panel. The liquid crystal panel exhibits an extreme value of transmittance at a voltage equal to or lower than the lowest gradation voltage in the voltage-transmittance characteristic, and the driving circuit controls the input image signal of the previous vertical period and the input image signal of the current vertical period. Depending on the combination of signals,
A predetermined drive voltage in which the gradation voltage corresponding to the input image signal in the current vertical period is overshot is supplied to the liquid crystal panel, thereby achieving the above object.

The difference in retardation between the state where no voltage is applied to the liquid crystal panel and the state where the highest gradation voltage is applied is 300 n.
m or more.

It is preferable that the liquid crystal panel is a transmission type liquid crystal panel, and the extreme value gives a maximum value of transmittance.

[0017] One vertical period of the input image signal is defined as one frame, and at least two fields of the drive voltage correspond to one frame of the input image signal, and the drive circuit operates at least the first of the drive voltage. In the field, a driving voltage in which a gradation voltage corresponding to the input image signal of the current field is overshot may be supplied to the liquid crystal panel.

The liquid crystal layer is preferably a homogeneous alignment type liquid crystal layer.

The liquid crystal panel further includes a phase difference compensating element, and the phase difference compensating element has three main refractive indices na, nb, and nc of a refractive index ellipsoid in a relationship of na = nb> nc. The liquid crystal layer may be arranged so as to cancel at least a part of the retardation of the liquid crystal layer.

Hereinafter, the operation of the present invention will be described.

The liquid crystal panel provided in the liquid crystal display device of the present invention exhibits an extreme value of the transmittance at a voltage lower than the lowest gradation voltage in the voltage-transmittance characteristic, and the gradation voltage overshooted by the liquid crystal panel. Is applied. In general, a liquid crystal display device is driven by an alternating current.
The transmittance characteristic indicates the relationship between the absolute value of the voltage applied to the liquid crystal layer and the transmittance based on the potential of the counter electrode.

In the specification of the present application, the voltage applied to the liquid crystal layer for performing display in the liquid crystal display device is referred to as a gradation voltage Vg, and is, for example, 64 gradations from 0 gradation (black) to 63 gradation (white). In the case of performing the gray scale display, the gray scale voltage Vg for performing the 0 gray scale display is denoted by V0, and the gray scale voltage Vg for performing the 63 gray scale display is denoted by V63. In the case of the NW mode liquid crystal display device exemplified in the embodiment, V0 is the highest gradation voltage, and V63 is the lowest gradation voltage. On the other hand, NB
Conversely, in the mode liquid crystal display device, V0 is the lowest gradation voltage, and V63 is the highest gradation voltage.

In the following, a signal giving image information to be displayed on the liquid crystal display device is called an input image signal S, and a voltage applied to a picture element according to each input image signal S is called a gradation voltage Vg. Input image signal of 64 gradations (S0 to S6
3) respectively correspond to the gradation voltages (V0 to V63) on a one-to-one basis. The gray scale voltages Vg are set so that when the liquid crystal layer to which each gray scale voltage Vg is applied reaches a steady state, the transmittance (display state) corresponding to each input image signal S is obtained. The transmittance at this time is called a steady state transmittance. Of course, the values of the gradation voltages V0 to V63 may differ depending on the liquid crystal display device.

The liquid crystal display device is driven by, for example, interlace, divides one frame corresponding to one image into two fields, and applies a gradation voltage Vg corresponding to the input image signal S to the display unit for each field. Is done. Of course, one frame may be divided into three or more fields, and non-interlace driving may be performed. In the non-interlace driving, a gradation voltage Vg corresponding to the input image signal S is applied to the display unit for each frame. One field in the interlace driving or one frame in the non-interlace driving is herein referred to as one vertical period.

The overshoot voltage is obtained by comparing the input image signal S between the previous vertical period (the immediately preceding vertical period) and the current vertical period. When the voltage is lower than the gradation voltage Vg corresponding to the input image signal S in the vertical period, the voltage is lower than the gradation voltage Vg corresponding to the input image signal in the current vertical period,
Conversely, when the gray scale voltage corresponding to the input image signal S in the current vertical period is higher than the gray scale voltage Vg corresponding to the input image signal in the previous vertical period, it corresponds to the input image signal S in the current vertical period. It indicates a voltage higher than the gradation voltage Vg.

The comparison of the input image signal S for detecting the overshoot voltage is performed between the input image signal S of the previous vertical period and the input image signal S of the current vertical period for each of all the picture elements. Even in the case of interlace driving in which one frame of image information is divided into a plurality of fields, the input image signal S for the picture element one frame before or the input image signal S of the upper and lower lines is used as a complementary signal, and one vertical period Signals corresponding to all picture elements are provided therein. Then, these input image signals S of the previous field and the current field are compared.

The difference between the overshooted gradation voltage Vg and a predetermined gradation voltage (grayscale voltage corresponding to the input image signal S in the current vertical period) Vg is sometimes referred to as an overshoot amount. Also, the overshoot grayscale voltage Vg may be referred to as an overshoot voltage. The overshoot voltage may be another grayscale voltage Vg having a predetermined overshoot amount with respect to the predetermined grayscale voltage Vg, or a voltage dedicated to overshoot drive prepared in advance for overshoot drive. There may be. At least a voltage that overshoots the highest gradation voltage (the gradation voltage having the highest voltage value among the gradation voltages) and the lowest gradation voltage (the gradation voltage having the lowest voltage value among the gradation voltages). A dedicated voltage for overshoot driving on high voltage side and a dedicated voltage for overshoot driving on low voltage side are prepared.

The liquid crystal panel of the liquid crystal display device of the present invention has an extreme value of transmittance at a voltage lower than the lowest gradation voltage in the VT characteristic.

When the extreme value of the transmittance is taken at the lowest gray scale voltage, the lowest gray scale voltage is applied when a voltage in which the lowest gray scale voltage is overshot (voltage dedicated to low voltage side overshoot driving) is applied. (In the case of the NW mode, this is the maximum value of the transmittance used for display and the extreme value of the transmittance. In the case of the NB mode, the minimum value of the transmittance used for display , Which is the extreme value of the transmittance), and then the transmittance corresponding to the overshoot voltage (the transmittance is smaller in the case of the NW mode, and larger in the case of the NB mode). To reach.

If the lowest gradation voltage is set higher than the voltage at which the transmittance has an extreme value, the voltage at which the lowest gradation voltage overshoots (the voltage dedicated to overshoot driving on the low voltage side) is changed to the transmittance. When the voltage is set lower than the voltage at which the extreme value is taken and applied, the transmittance corresponding to the lowest gradation voltage (the maximum value of the transmittance used for display in the NW mode, and the NB mode Is the minimum value of the transmittance used for display), passes through the extreme value of the transmittance, and passes through the transmittance (NW) corresponding to the overshoot voltage.
In the case of the mode, the transmittance is smaller, and in the case of the NB mode, the transmittance is higher. ).

When the lowest gradation voltage is set higher than the voltage at which the transmittance has an extreme value, the voltage at which the lowest gradation voltage overshoots (the voltage dedicated to overshoot driving on the low voltage side) is changed to the transmittance. Is set to a voltage higher than the extreme value of
When this is applied, the transmittance corresponding to the lowest gradation voltage (the maximum value among the transmittances used for display in the case of the NW mode, and the transmittance among the transmittances used for display in the case of the NB mode) ), And then reaches a transmittance corresponding to the overshoot voltage (a larger transmittance in the case of the NW mode and a smaller transmittance in the case of the NB mode).

The response time required for the fall (up to the steady state) is almost the same both when the lowest gradation voltage is applied and when the overshoot voltage is applied. Can be shortened to reach the transmittance corresponding to the gray scale voltage. That is, in a liquid crystal panel that exhibits an extreme value of transmittance at a voltage equal to or lower than the lowest gradation voltage, the liquid crystal molecules of the liquid crystal layer when the lowest gradation voltage is applied are the same as the liquid crystal molecules when no voltage is applied. V-T characteristics exhibiting a constant transmittance (that is, having no extreme value) over a voltage range equal to or lower than the lowest gradation voltage since the alignment state is substantially different from that of the first embodiment. The change in transmittance over time becomes steeper than when the liquid crystal panel having the above is driven overshoot (see FIGS. 5A and 5B).

Therefore, according to the present invention, it is possible to improve the response characteristic at the time of falling of the liquid crystal display device as compared with the conventional overshoot drive. Even when a liquid crystal panel that does not exhibit an extreme value of the transmittance on the low voltage side is used, the lowest gradation voltage is set higher than the voltage at which the transmittance becomes the highest (NW mode) or the lowest (NB mode). By setting, the fall response characteristic can be improved, but there is a problem that the range of the transmittance that can be used for display is narrowed by the higher the minimum gradation voltage is set. On the other hand, in the liquid crystal display device of the present invention, since the lowest gradation voltage is set to be equal to or higher than the voltage at which the transmissivity indicates an extreme value (maximum (NW mode) or minimal (NB mode)), With the loss suppressed or prevented, the fall response speed can be improved.

In particular, when the lowest gradation voltage is set to a voltage at which the transmittance shows an extreme value, there is no loss in transmittance. In order to enhance the effect of improving the response speed, it is preferable to set the lowest gradation voltage higher than the voltage at which the transmittance shows the extreme value. Even if the minimum gradation voltage is set in this way, the transmittance loss can be reduced as compared with the case where a liquid crystal panel that does not exhibit an extreme value on the low voltage side is used. This is because, in the liquid crystal display device of the present invention, the alignment state of the liquid crystal layer to which the voltage at which the transmittance takes an extreme value is substantially different from the alignment state of the liquid crystal layer when no voltage is applied. The reason for this is that, since the state can be relaxed, the relaxation phenomenon in the process from the extreme value of the transmittance to the transmittance in the state where no voltage is applied can be used for the fall response.

Of course, the response speed of the rise of the liquid crystal layer is
Since the higher the applied voltage value, the faster the response, the rising response characteristic is also improved by applying the overshoot voltage.

In the VT characteristic, a liquid crystal panel exhibiting an extreme value of transmittance at a voltage equal to or lower than the lowest gradation voltage is realized, for example, by adjusting its retardation.

In the specification of the present application, "the retardation of the liquid crystal panel" means the sum of the retardation of the liquid crystal layer when no voltage is applied and the retardation of the phase difference compensating element, unless otherwise specified. Of light incident perpendicularly to the display surface (parallel to the layer surface of the liquid crystal layer). Of course, in a configuration without the phase difference compensating element, the retardation of the liquid crystal panel is the retardation of the liquid crystal layer when no voltage is applied. The retardation of the liquid crystal layer is a value obtained by multiplying the difference (Δn) between the maximum refractive index and the minimum refractive index of the liquid crystal material by the thickness (d) of the liquid crystal layer.

In general, the retardation of a transmissive liquid crystal panel is reduced by about 2 by application of a gradation voltage.
It is set to change by 60 nm. That is, the difference between the retardations of the liquid crystal panel in the lowest gradation display state and the highest gradation display state is set to about 260 nm. This is determined in consideration of a high contrast ratio with respect to green light (wavelength: about 550 nm) having the highest luminous efficiency and display characteristics (viewing angle dependency) with respect to light of other colors. It is set in the range of about 250 nm to about 270 nm according to the specifications of the liquid crystal display device. In the following description, “about 260 nm” is used as a value representative of the set retardation value.

The retardation of the liquid crystal layer changes according to the voltage because the liquid crystal molecules change the alignment state in response to the voltage. However, in the liquid crystal layer, there is a liquid crystal layer anchored on the substrate surface (hereinafter, referred to as “anchoring layer”) whose alignment state does not change when a voltage is applied (voltage range used in normal display). The retardation of the anchoring layer is about 40 nm to about 80 nm. Therefore, in general, the retardation of the entire liquid crystal layer is a value obtained by adding the retardation of the anchoring layer to the above set value (about 260 nm) (about 300 nm to about 340 n).
m).

In some cases, a retardation compensating element (for example, a retardation plate or a retardation film) for compensating the retardation caused by the anchoring layer is provided. That is, a phase difference compensating element is provided such that the total retardation of the liquid crystal layer and the phase difference compensating element becomes the above set value (about 260 nm).

The difference in retardation between the non-voltage-applied state and the highest gradation voltage-applied state of the liquid crystal panel of the liquid crystal display device of the present invention (may be simply referred to as “liquid crystal panel retardation difference”) is 300 nm or more. It is preferred that By setting the retardation of the liquid crystal panel to change by 300 nm or more within the voltage range up to the highest gradation voltage, it is possible to secure about 260 nm as the range of the retardation used for display, and to set the lowest gradation. A VT characteristic that gives an extreme value of transmittance at a voltage equal to or lower than the voltage can be realized. Of course, in a configuration that emphasizes the response speed, the range of the retardation used for display may be narrowed.

Since the effect of improving the fall response characteristic according to the present invention is remarkably observed in the NW mode liquid crystal panel, it is preferable to apply the present invention to the NW mode liquid crystal display device. When the present invention is applied to an NB mode liquid crystal panel including a horizontal alignment type liquid crystal layer and using a phase difference compensating element, an extreme value (minimum value) of the transmittance appears on the black display side, Hard to be observed. In addition, in the vicinity of the extreme value on the black display side, since the retardation value is largely different only by a slight difference in the gradation voltage, it is difficult to compensate for the phase difference so as to display good black. When the present invention is applied to an NB mode liquid crystal panel having a vertical alignment type liquid crystal layer,
Since no extreme value of the transmittance is observed on the black display side, there is no effect of shortening the response time.

The parallel alignment (homogeneous alignment) type liquid crystal layer has a higher response speed than the twist alignment type liquid crystal layer and the vertical alignment type liquid crystal layer (for example, a response time of about 17 ms).
c) Therefore, by applying the present invention, the response speed can be further improved, and a liquid crystal display device having particularly excellent moving image display characteristics (for example, a response time of about 10 msec or less) can be realized.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display according to an embodiment of the present invention will be described with reference to the drawings. In the following, embodiments of the present invention will be described using an NW mode liquid crystal display device as an example, but the present invention is not limited to this.

(Retardation) The liquid crystal panel of the NW mode provided in the liquid crystal display device of the present embodiment exhibits the maximum value (and the maximum value) of the transmittance at the voltage lower than the lowest gradation voltage in the VT characteristic. The retardation has been adjusted. Typically, the liquid crystal panel is set so that the retardation changes by 300 nm or more by voltage application.

The reason will be described with reference to FIGS. 1, 2A and 2B.

Positive refractive anisotropy (Δn = n // − n⊥> 0)
FIG. 1 shows a VT curve of a liquid crystal panel provided with a parallel alignment type liquid crystal layer including a liquid crystal material having the following. FIG. 1 also shows VT curves of liquid crystal panels having different retardations. FIG. 2A shows a voltage-retardation curve of a liquid crystal panel having a retardation of 260 nm, and FIG. 2B shows a voltage-retardation curve of a liquid crystal panel having a retardation of 300 nm. The vertical axis of the graph showing the curve indicating the transmittance or the retardation that changes according to the applied voltage is indicated by a relative value (arbitrary unit) where the lowest value of the transmittance or the retardation is zero. Therefore, the transmittance or retardation shown in these graphs indicates the amount that changes with the change in the applied voltage.

The liquid crystal panel having various retardations shown in FIG. 1 can be obtained by changing the liquid crystal material having different Δn and changing the thickness d of the liquid crystal layer. In addition, the value of the retardation can be adjusted by using the phase difference compensating element.

First, the relationship between the alignment state of liquid crystal molecules and the retardation of the liquid crystal layer excluding the anchoring layer will be described. When a voltage is applied to the parallel alignment type liquid crystal layer, when the liquid crystal molecules rise (incline) with respect to the layer surface of the liquid crystal layer, the maximum refractive index for light incident perpendicularly to the liquid crystal layer becomes smaller than n // (minimum). (The refractive index remains unchanged at n）), so as shown in FIGS. 2A and 2B,
The retardation at the time of applying a voltage is reduced. Furthermore, increase the applied voltage (apply a voltage higher than the saturation voltage)
And the liquid crystal molecules are oriented perpendicular to the layer surface of the liquid crystal layer, so that both the maximum refractive index and the minimum refractive index of the liquid crystal layer are n⊥.
And the retardation becomes zero. However, since the anchoring layer exists in the actual liquid crystal layer, the retardation does not become zero. FIG. 2A and FIG. 2B are voltage-retardation curves of a liquid crystal panel provided with a phase difference compensating element for compensating for retardation due to the anchoring layer. Here, the retardation of the liquid crystal layer when 5 V is applied is cancelled.

Generally, when the retardation of the liquid crystal panel is about 260 nm (250 to 270 nm), the transmittance of the liquid crystal panel is set to be the highest. Therefore, when the retardation when no voltage is applied is about 260 nm or less (see the curves of 220 nm and 260 nm in FIG. 1), when the voltage is increased from the state where no voltage is applied, the transmittance gradually decreases monotonously. In contrast, the retardation when no voltage is applied exceeds about 260 nm (30 in FIG. 1).
In the case of 0 nm, 320 nm, 340 nm, and 380 nm, the transmittance increases gradually (until the retardation reaches about 260 nm) and then decreases due to the increase in voltage.

Since the retardation of the liquid crystal panel (the width that varies with the voltage) is 300 nm or more, the transmittance exhibits the highest value (maximum value) when the voltage applied to the liquid crystal layer is higher than 0 V, and the voltage exceeds this voltage. The minimum voltage of the gray scale voltage Vg (for example, V63) is set in the range of
By applying a voltage lower than this voltage as the overshoot voltage, overshoot on the low voltage side can be effectively performed.

(Overshoot drive dedicated voltage and gray scale voltage) In the NW mode, the minimum value of the gray scale voltage Vg of the liquid crystal display device according to the present invention is set to be equal to or higher than the voltage at which the steady transmittance becomes the highest. . The maximum value of the gradation voltage Vg is set to be equal to or lower than the voltage at which the steady transmittance becomes the lowest. In the case of the NB mode, the lowest value of the gradation voltage Vg is set to be equal to or higher than the voltage at which the steady transmittance becomes the lowest, and the highest value of the gradation voltage Vg is equal to or less than the voltage at which the steady transmittance becomes the highest. Is set to

The liquid crystal display device of the present invention is, for example, 300
Since there is a retardation difference of not less than nm, as shown in FIG. 1, the voltage at which the transmittance in the VT curve of the NW mode display device becomes the maximum is a voltage giving an extreme value, and therefore, the gradation voltage Vg Is set to a range that includes a voltage lower than the voltage that gives the extreme value, the transmittance is inverted, and as a result, inversion of the gradation is observed. To prevent this grayscale inversion, the lowest grayscale voltage is set to a voltage equal to or higher than the voltage that gives an extreme value. Also, of course,
The maximum value of the gradation voltage Vg is set so as not to exceed the withstand voltage of the driving circuit (driver, typically a driver IC).

In the liquid crystal display device of the present invention, an overshoot drive-dedicated voltage Vos is preset in addition to the gradation voltage Vg (V0 to V63). The overshoot drive dedicated voltage Vos includes Vos (L) on the lower voltage side than the grayscale voltage Vg and Vos (H) on the higher voltage side, and a plurality of different voltage values may be prepared. The overshoot drive-dedicated voltage Vos (H) on the high voltage side (the highest value in a plurality of cases) is set so as not to exceed the withstand voltage of the drive circuit. Furthermore, the overshoot drive dedicated voltage Vos and the gradation voltage Vg (V0 to 63) are set so that the number of bits does not exceed the number of bits of the drive circuit.

Next, the setting of the overshoot drive dedicated voltage Vos and the gradation voltage Vg will be specifically described with reference to FIG. FIG. 3 shows the relationship between the VT curve, the overshoot drive dedicated voltage Vos, and the gray scale voltage Vg. The gradation voltage Vg (V0 (black) to V63) is set in a range from a voltage at which the transmittance has the highest value to a voltage at which the transmittance has the lowest value. The overshoot drive-dedicated voltage Vos (L) on the low voltage side (for example, Vos (L) 1 to Vos (L) 32 of 32 gradations) is in a range of 0 V or more and less than V63 (the minimum value of the gradation voltage Vg). Is set by Overshoot drive dedicated voltage Vos (H) on the high voltage side (for example, 3
Vos (H) 1 to Vos (H) 32) of two gradations are V
The voltage is set in a range from a voltage higher than 0 (the maximum value of the gray scale voltage Vg) to a value not exceeding the withstand voltage of the drive circuit. The number of gradations of the gradation voltage Vg and the number of gradations of the overshoot drive dedicated voltage Vos can be arbitrarily set within a range not exceeding the number of bits of the driving circuit. The number of gradations of the overshoot drive dedicated voltage Vos (L) on the low voltage side may be different from the number of gradations of the overshoot drive dedicated voltage Vos (H) on the high voltage side.

The voltage applied when performing the overshoot drive is predetermined according to the change of the input image signal S, and one of the gray scale voltage Vg and the overshoot drive dedicated voltage Vos is used. .

For example, the gradation voltage Vg corresponding to the input image signal S of the current field is changed to the input image signal S of the previous field.
Is lower than the gray scale voltage Vg corresponding to the gray scale voltage Vg.
And overshoot drive dedicated voltage Vos on the low voltage side
A voltage on the lower voltage side than the gradation voltage Vg corresponding to the input image signal S of the current field selected from (L) is input to the liquid crystal panel. The voltage used for the overshoot drive is a predetermined time (for example, 16.7 ms) after applying the voltage of the current field.
Within ec), it is determined in advance to reach a steady-state transmittance corresponding to the input image signal S of the current field.
Alternatively, it is determined in advance so that the transmittance is such that the user does not feel uncomfortable.

The voltage used for overshoot drive is
Determined for the combination of the input image signal S of the previous field (for example, 64 gradations) and the input image signal S of the current field (64 gradations) (however, it is unnecessary for a combination having no change in gradation). Can be Depending on the response speed of the LCD panel,
There may be a combination of gradations that does not require overshoot drive. Further, the number of gradations of the overshoot drive-dedicated voltage Vos can be changed as appropriate.

(Circuit for Overshoot Drive) FIG. 4
The configuration of the driving circuit 10 in the liquid crystal display device according to the embodiment of the present invention will be described with reference to FIG.

The drive circuit 10 receives an externally input image signal S
, And supplies a driving voltage corresponding thereto to the liquid crystal panel 15. The drive circuit 10 includes an image storage circuit 11, a combination detection circuit 12, and an overshoot voltage detection circuit 1.
3 and a polarity inversion circuit 14.

The image storage circuit 11 holds at least one field image of the input image signal S. Of course, when one frame is not divided into a plurality of fields, the image storage circuit 11 stores at least one frame image. The combination detection circuit 12 compares the input image signal S of the current field with the input image signal S of the previous field held in the image storage circuit 11 and outputs a signal indicating the combination to the overshoot voltage detection circuit 13 I do. The overshoot voltage detection circuit 13 outputs a drive voltage corresponding to the combination detected by the combination detection circuit 12,
Grayscale voltage Vg and overshoot drive dedicated voltage Vo
s. The polarity inversion circuit 14 converts the drive voltage detected by the overshoot voltage detection circuit 13 into an AC signal, and supplies the AC signal to the liquid crystal panel (display unit) 15.

For the input / output signals of the respective circuits, the voltage used for the overshoot drive at the falling edge is set in advance to a gradation voltage Vg lower than the gradation voltage Vg corresponding to the input image signal S. Will be described.

First, the image storage circuit 11 holds the input image signal S one field before the input image signal S of the current field.

Next, the combination detection circuit 12 detects the combination of the current input image signal S and the input image signal S one field before stored in the image storage circuit 11 for each picture element. For example, for a picture element, the input image signal S20 of the previous field and the input image signal S4 of the current field
A combination (S20, S40) with 0 is detected.

The overshoot voltage detecting circuit 13 detects the combination (S20, S20) detected by the combination detecting circuit 12.
The predetermined gradation voltage V60 for S40)
(Corresponding to the input image signal S60) and supplies the grayscale voltage V60 to the polarity inversion circuit 14 as a drive voltage.
This operation is equivalent to converting the input image signal of the current field from S40 to S60. Combination detection circuit 1
In the process of detecting the grayscale voltage V60 as a predetermined overshoot voltage corresponding to the combination (S20, S40) detected by No. 2, for example,
It may be performed by using a look-up table method or by performing a predetermined operation.

Finally, the polarity inversion circuit 14 outputs the gradation voltage V
60 is converted into an AC signal and supplied to the liquid crystal panel 15.

Hereinafter, an operation of performing overshoot driving using the overshoot drive dedicated voltage Vos in the liquid crystal display device according to the embodiment of the present invention will be described.

For example, the overshoot voltage detection circuit 1
3 is 7 bits (64 gradation voltages Vg (V0 to V63)) corresponding to the input image signal S of 64 gradations (6 bits).
And 64 overshoot voltages Vos (high voltage side: V
os (H) 1 to Vos (H) 32, low voltage side: Vos
From (L) 1 to Vos (L) 32), a drive voltage for predetermined overshoot drive can be detected.

Specifically, for example, taking the falling edge as an example, the input image signal is shifted to S63 one field after S40.
And switch to The input image signal S40 is held in the image storage circuit 11. The combination detection circuit 12 outputs (S
40, S63). Then, the overshoot voltage detection circuit 13 determines the overshoot drive-dedicated voltage Vos predetermined to reach a steady transmittance corresponding to the input image signal S63 within one field, for example.
(L) 20 is detected and supplied to the polarity inversion circuit 14 as a drive voltage. The voltage Vos (L) 20 is supplied to the liquid crystal panel after being converted into an alternating current by the polarity inversion circuit 14.

In the above operation, the 6-bit digital input image signal S is converted by the overshoot voltage detection circuit 13 into the overshoot drive dedicated voltage Vos (64 gradations).
Is equivalent to being converted into a 7-bit digital input image signal S including

When there is no change in the input image signal S, the drive voltage does not overshoot. For example, when the combination detection circuit 12 detects (S40, S40),
The overshoot voltage detection circuit 13 uses the gradation voltage V40 corresponding to S40 as a drive voltage,
Output to

The object of the overshoot drive is not limited to the first field in which the input image signal S is switched. The overshoot drive may be executed not only for the first field but also for the next field and the next field. Such a driving method can be executed by combining appropriate circuits. When one frame is divided into a plurality of fields and driven, it is preferable to perform overshoot driving on the first field or all the fields. When overshoot driving is performed on a plurality of fields in one frame, the amount of overshoot used in each field (in other words, the amount of shift from a predetermined gradation voltage Vg) may be different from each other. For example, the overshoot drive for the second field may be performed with an overshoot amount smaller than the overshoot amount used for the overshoot drive for the first field.

(Transmittance Change When Overshoot Drive is Performed) Response characteristics when the liquid crystal display device of the embodiment according to the present invention is overshoot driven will be described with reference to FIGS. 5A and 5B.

FIG. 5A shows the VT curves of the liquid crystal display of this embodiment (liquid crystal panel with a retardation of 320 nm) and the liquid crystal display of the comparative example (liquid crystal panel with a retardation of 260 nm). The liquid crystal panel of the present embodiment has V
While the -T curve has an extreme value, the liquid crystal panel of the comparative example has no extreme value in the VT curve. In these two liquid crystal panels, the liquid crystal layers have the same thickness, the liquid crystal materials used have the same dielectric anisotropy (Δε) and viscosity, and have different Δn. Is used to adjust the retardation. These LCD panels are
The retardation starts to change substantially from the same voltage (Vth). When the applied voltage is gradually increased from the low voltage side,
The transmittance of the 260 nm liquid crystal panel monotonously decreases when it exceeds Vth, and the transmittance of the 320 nm liquid crystal panel becomes Vth
Once it rises, it rises once, goes through a local maximum, and monotonically decreases. The highest transmittance is T (c) for any liquid crystal panel.
And the steady transmittance for the applied voltage V (a) is T
(A).

FIG. 5B is a graph schematically showing a time change of the transmittance of the liquid crystal display device of the present embodiment. The time interval indicated by the broken line in FIG. 5B corresponds to one field, and from the first field of black display (lowest gradation: corresponding to S0),
The change of the white display (highest gradation: equivalent to S63) to the second field is shown. FIG. 5B shows a state where a steady state is reached at the same time ts. This is because, as described above, the fall in the liquid crystal display device is a phenomenon in which the orientation of the liquid crystal molecules is relaxed.

A curve L1 in FIG. 5B indicates a case where the voltage V (a), that is, the overshoot drive-dedicated voltage Vos on the low voltage side is applied to the liquid crystal panel having a retardation of 320 nm in the second field (the present invention). Is shown. On the other hand, the curve L2 has a retardation of 320.
The case where the lowest gradation voltage V (b) showing the same steady state transmittance as the case where the overshoot drive-dedicated voltage V (a) is applied to the liquid crystal panel of nm is applied. Here, for the sake of simplicity of comparison, the voltage indicating the same transmittance as the transmittance of the lowest gradation voltage V (b) is set as the overshoot drive dedicated voltage V (a). The setting of (a) is not limited to this.

As shown by the curve L1, when the overshoot drive-dedicated voltage V (a) on the low voltage side is applied, if one field is sufficiently long, the transmittance rises from the value of the first field. This decreases to approach the steady-state transmittance of the overshoot drive dedicated voltage V (a).

This is due to a change in retardation of the liquid crystal panel of the embodiment according to the present invention. The application of the overshoot drive voltage V (a) causes the liquid crystal molecules to fall, approaching a steady state. Naturally, the retardation of the liquid crystal layer rises and approaches a steady state corresponding to the applied overshoot drive voltage V (a). That is, the retardation rises, further rises through 260 nm, and the applied overshoot drive voltage V
It approaches steady retardation corresponding to (a). Generally, the maximum retardation is about 260n.
m, the transmittance increases first and then decreases, resulting in the transmittance change as described above (see FIG. 5A).

On the other hand, as shown by the curve L2, V (a)
Instead, when the lowest gradation voltage V (b) is simply applied (that is, when the overshoot drive is not performed), the transmittance increases from the value of the first field, and the lowest gradation voltage V (b) is obtained. ) Approaching the steady state transmittance. The liquid crystal molecules fall due to the application of the gradation voltage V (b) and approach a steady state. Naturally, the retardation rises and approaches the steady state of the applied V (b). In this case, since the retardation does not exceed about 260 nm (a retardation that gives an extreme value of the transmittance), the transmittance does not decrease.

The response characteristic when V (a) is applied to a liquid crystal panel having a retardation of 260 nm is represented by a curve L.
It changes almost the same as 2. Also, the retardation is 26
When a voltage (overshoot voltage) lower than V (a) (the lowest gradation voltage) is applied to the 0 nm liquid crystal panel, the response time is further shortened, but the response time is also slight and the curve A response curve steeper than L1 cannot be obtained.

As described above, as shown by the curve L1, when a voltage V (a) dedicated to overshoot driving is applied to a liquid crystal panel having a retardation of 300 nm or more, the transmittance in the second field increases. It can be seen that the steepness is high. According to the embodiment of the present invention, a response characteristic of falling is improved by utilizing such a steep change in transmittance, and a liquid crystal display device suitably used for displaying moving images is provided.

Next, as shown in FIG. 5C, the voltage (V (c)) showing the highest transmittance (T (c)) for the liquid crystal display device of the embodiment (the liquid crystal panel having a retardation of 320 nm). ) Will be described with reference to the response characteristics when the lowest gradation voltage is set and overshoot drive (voltage V (d) is applied). Liquid crystal panel having no extreme value in VT curve for comparison (liquid crystal panel with 260 nm retardation)
, The voltage (V) showing the highest transmittance (T (c))
The response characteristic when the lowest gradation voltage is set in (d)) and overshoot driving (voltage V (d ') is applied) will be described.

FIG. 5D shows that, for a liquid crystal panel having a retardation of 320 nm, the lowest gradation voltage is set to the voltage (V (c)) showing the highest transmittance (T (c)), and the overshoot drive ( A response curve L3 when the voltage V (d) is applied) and a response curve L4 when the lowest gradation voltage V (c) is applied without performing overshoot driving.

As is clear from the comparison between the curves L3 and L4 in FIG. 5D, in the liquid crystal panel with a retardation of 320 nm, when the lowest gradation voltage is set to the voltage V (c) at which the transmittance becomes the highest. Also, as in the case described above with reference to FIG. 5B, the overshoot voltage V
By applying (d), it is possible to improve the fall response characteristic. This is because, in the VT curve of a 320 nm liquid crystal panel, the point at which the highest transmittance is given is a maximum value, and the retardation further changes in a voltage range lower than V (c). This is because there is still room for relaxation. However, it is necessary to adjust the period during which the overshoot voltage V (d) is applied so that the transmittance does not decrease from the maximum value.

As described above, the response characteristic can be improved without sacrificing the transmittance by setting the lowest gradation voltage to the voltage V (c) at which the transmittance is the highest. However, as shown in FIG. 5B, the effect of improving the response characteristics is higher when the lowest gradation voltage is set to a voltage higher than the voltage at which the transmittance has an extreme value. Therefore, depending on the application of the liquid crystal display device, etc.,
The lowest gradation voltage may be set to a voltage equal to or higher than the voltage at which the transmittance indicates the maximum value.

On the other hand, as shown in FIG. 5C, in a liquid crystal panel having a retardation of 260 nm, when the voltage giving the maximum value of the transmittance is set to the lowest gradation voltage, only the overshoot driving less than the lowest gradation voltage is performed. Voltage V
Even if (d ′) is applied, the response characteristics cannot be improved. That is, both when the lowest gradation voltage V (d) is applied and when the overshoot voltage V (d ') is applied, the response curve is almost the same as the curve L4 in FIG. 5D. This is because, as described above, the alignment state of the liquid crystal molecules in the flat portion of the 260 nm curve is substantially the same,
This is because the restoring force is the same. Therefore, in order to improve the fall response characteristic of a liquid crystal panel having a retardation of 260 nm, a voltage (for example, V (c)) higher than the voltage at which the transmittance becomes the highest is set to the lowest gradation voltage, and the transmittance is made the lowest. Sacrifice, for the first time, high-speed response by overshoot drive (for example, application of V (d)) becomes possible.

As described above, according to the present embodiment, there is provided a liquid crystal display device which has improved response characteristics at the time of falling and is suitably used for displaying moving images.

In the above example, the case where the response speed of the liquid crystal layer is relatively fast, in which the steady-state transmittance corresponding to the applied voltage is obtained within one field, has been described. In a liquid crystal panel that requires a relatively long time (for example, two fields) to reach the rate, a predetermined display state (transmittance) cannot be realized with the response characteristic indicated by the curve L2. On the other hand, with the response characteristic of the curve L1, a predetermined display state can be realized in one field as shown in FIG. 6 in which the unit of the time axis in FIG. 5B is halved. Therefore, it is possible to prevent the moving image display from being blurred due to the overlap of the image of the previous field and the image of the current field.

Alternatively, when overshoot driving is performed on a liquid crystal panel having a liquid crystal layer having a relatively high response speed as shown in FIG. 5B, one field in FIG.
By dividing and applying the overshoot drive voltage V (a) to the first half field and applying V (b) corresponding to the predetermined gradation voltage Vg in the second half field, as shown in FIG. Response characteristics can also be obtained. That is, by doubling the frequency for supplying the driving voltage to the liquid crystal panel, it is possible to prevent the transmittance from decreasing once after increasing to a predetermined transmittance or more, as shown by the curve L1 in FIG. 5B. As shown in FIG. 6, a steep change in transmittance can be realized. As described above, if the response characteristic of the liquid crystal panel that can obtain a steady state transmittance corresponding to the applied voltage within one field without performing overshoot driving is further improved, the time during which the liquid crystal panel is in a predetermined display state (transmission Since the ratio (time integral value of the ratio) becomes longer, display quality (brightness, contrast ratio, etc.) can be improved.

As described above, according to the present invention, it is possible to obtain a high-speed response liquid crystal display device suitable for displaying moving images.

(Display Mode) The present invention can be applied to various liquid crystal display devices. However, as mentioned above,
The response characteristics of the liquid crystal panel depend on the response speed of the liquid crystal layer (liquid crystal material, alignment form, etc.). Therefore, by using a liquid crystal layer having a high response speed, a liquid crystal display device having higher speed and excellent moving image display characteristics can be obtained.

FIG. 7 schematically shows an NW mode transmission type liquid crystal panel 20 of an ECB (electric field controlled birefringence) mode using a parallel alignment (homogeneous alignment) type liquid crystal layer known as a liquid crystal mode having a high response speed. Is shown.

The liquid crystal panel 20 includes a liquid crystal cell 20a, a pair of polarizers 25 and 26 provided so as to sandwich the liquid crystal cell 20a, the polarizers 25 and 26, and the liquid crystal cell 2a.
0a are provided with phase difference compensating elements 23 and 24, respectively.

The liquid crystal cell 20a includes a pair of substrates 21 and 22.
And a liquid crystal layer 27 provided between them. Substrate 21
And 22 are a transparent substrate (for example, a glass substrate), a transparent electrode (not shown) for applying a voltage to the liquid crystal layer 27, and liquid crystal molecules 27a of the liquid crystal layer 27 provided on the surface of the liquid crystal layer 27 side. It has an alignment film (not shown) for defining the alignment direction. Of course, a color filter layer (not shown) may be further provided if necessary. The transparent electrode is formed using, for example, ITO (indium tin oxide).

The liquid crystal layer 27 is a parallel alignment type liquid crystal layer. When no voltage is applied, the liquid crystal molecules 27a in the liquid crystal layer 27 are substantially parallel to the layer surface of the liquid crystal layer 27 (parallel to the substrate surface) (pretilt angle difference). And the liquid crystal molecules 27a are substantially parallel to each other (not affected by the pretilt angle). The refractive index ellipsoid of the anchoring layer changes the layer surface (that is, the display surface) of the liquid crystal layer 27 to XY.
In the XYZ coordinate system as a plane, the axis is slightly tilted clockwise by a pretilt angle around the X axis.

The parallel alignment type liquid crystal layer is obtained by rubbing the alignment films provided on both sides of the liquid crystal layer 27 in an anti-parallel manner (see the arrow indicating the rubbing direction in FIG. 7). When rubbing treatment is performed on the alignment films provided on both sides of the liquid crystal layer in parallel, the liquid crystal molecules on one alignment film and the liquid crystal molecules on the other alignment film form an angle twice the pretilt angle. The liquid crystal molecules 27a are no longer parallel.

A pair of polarizers (for example, polarizing plates and polarizing films) 25 and 26 have their absorption axes (arrows in FIG. 7).
Are arranged at right angles to each other and at an angle of 45 degrees with the rubbing direction (the orientation direction of the liquid crystal molecules in the layer plane).

As shown in FIG. 7, the phase difference compensating elements (for example, phase difference plates and films) 23 and 24
The index ellipsoid (with principal axes a, b and c) is
In an XYZ coordinate system in which the layer surface of the liquid crystal layer 27 (that is, the display surface) is an XY plane, the liquid crystal layer 27 slightly rotates around an a-axis arranged in parallel with the X-axis. Here, the Y axis is set parallel (or antiparallel) to the rubbing direction, and the b axis of the refractive index ellipsoid is arranged so as to be inclined from the Y axis. That is, the major axis of the index ellipsoid (b
Axis) is inclined counterclockwise with respect to the X axis in the YZ plane. Phase compensation elements 23 and 2 thus arranged
4 is called a tilt type phase difference compensating element.

The phase difference compensating elements 23 and 24 have a function of compensating for the retardation of the anchoring layer of the liquid crystal layer 27. Even if a voltage of, for example, 7 V is applied to the liquid crystal layer 27, the liquid crystal molecules anchored by the alignment film (not shown) maintain the alignment parallel to the layer surface of the liquid crystal layer 27, and thus the retardation of the liquid crystal layer 27 is suppressed. Does not become zero. This retardation is applied to the phase difference compensating elements 23 and 2
4 compensates (cancels).

As a typical example, it is assumed that the main refractive indices na, nb, and nc in each main axis direction are na = nb> nc. FIG.
As schematically shown in FIG.
Angle of the refractive index ellipsoid (angle formed by b axis with respect to Y axis)
Is 0 degree, the front retardation of the phase difference compensating elements 23 and 24 (in the normal direction of the display surface (parallel to the Z axis in the figure))
Is zero, but as the inclination angle increases, the retardation occurs and increases. That is, as shown in FIG.
When viewed from the normal direction of the display surface, it can be understood from the fact that the refractive index ellipsoid having a tilt angle of 0 degree looks like a perfect circle, but looks like an ellipse as the tilt angle increases.

Therefore, if the phase difference compensating elements 23 and 24 having the above-mentioned inclined refractive index ellipsoids are arranged so that the inclined direction (b-axis direction) and the rubbing direction are parallel or anti-parallel to each other, anchoring can be achieved. The retardation of the layer can be canceled by the front retardation of the phase difference compensating elements 23 and 24. Therefore, in the above example, 7V
The retardation of the liquid crystal layer 27 at the time of application of the voltage is canceled (the retardation of the liquid crystal panel 20 at the time of application of 7 V is made zero), and the transmittance is 0%, that is, black display can be realized.

The front retardation of the phase difference compensating elements 23 and 24 is based on the main refractive index, inclination angle,
It can be adjusted by the thickness. Phase difference compensating element 2
By changing the magnitudes of the front retardations 3 and 24, the magnitude of the retardation of the liquid crystal cell 20a to be canceled can be changed. Therefore, by canceling not only the retardation of the liquid crystal layer 27 due to the anchoring layer but also the retardation of the liquid crystal layer 27 when a certain voltage is applied, the range of the gradation voltage Vg can be adjusted arbitrarily. For example, as shown in FIG. 9, the main refractive index and the inclination angle of the refractive index ellipsoid were kept constant, and only the thickness d (the thickness in the normal direction of the display surface) of the phase difference compensating elements 23 and 24 was changed. 5 shows a VT curve of the liquid crystal panel 20 in this case. The transmittance is a transmittance in the normal direction of the display surface. Thus, it can be seen that the VT curve can be controlled by controlling the optical characteristics of the phase difference compensating elements 23 and 24. Of course, it is clear from the above description that the same effect can be obtained even if the inclination angle and the main refractive index of the refractive index ellipsoid are controlled.

The response time of the liquid crystal panel 20 (according to a conventional driving method without using overshoot driving) is 30 which is a typical response time of a conventional TN mode liquid crystal panel.
ms. The liquid crystal layer of the TN mode liquid crystal panel has a twisted alignment structure, whereas the homogeneous alignment has no twisted alignment structure. Therefore, it can be interpreted that the response time is short from the simplicity of the alignment structure.

Further, the transmitted light (display light) in the normal direction of the display surface and in the direction close to the display surface is diffused vertically in the liquid crystal panel 20 with respect to the line of sight of the observer. Optical elements that have an effect (for example,
By arranging a BEF film (manufactured by Sumitomo 3M Limited) on the display surface, it is possible to obtain a liquid crystal panel 20 having an extremely wide viewing angle, in which the display quality hardly changes even from all angles.

The liquid crystal display device 30 of the embodiment according to the present invention
Is schematically shown in FIG.

The liquid crystal display device 30 has the liquid crystal panel 20 shown in FIG. 7 and the drive circuit 10 shown in FIG. The liquid crystal display device 30 is an NW mode transmission type liquid crystal display device.

The liquid crystal panel 20 has a TFT substrate 21 and a color filter substrate (hereinafter, referred to as a “CF substrate”) 22.
And These are all manufactured by a known method. Although the liquid crystal display device 30 of the present invention is not limited to a TFT type liquid crystal display device, in order to realize a high response speed,
An active matrix type liquid crystal display device such as FT type or MIM is preferable.

In the TFT substrate 21, the glass substrate 3
A pixel electrode 32 made of ITO is formed on the substrate 1 and an alignment film 33 is formed on the surface of the pixel electrode 32 on the liquid crystal layer 27 side. In the CF substrate 22, a counter electrode (common electrode) 36 made of ITO is formed on a glass substrate 35, and the alignment film 3
7 are formed. The alignment films 33 and 37 are formed using, for example, polyvinyl alcohol or polyimide. The surfaces of the alignment films 33 and 37 are each rubbed in one direction. TFT substrate 21 and CF substrate 22
Are bonded so that their rubbing directions are antiparallel to each other, and then a nematic liquid crystal material having a positive dielectric anisotropy △ ε is injected to obtain a liquid crystal layer 27 of a parallel alignment type. The retardation of only the liquid crystal layer 27 is set to 400 nm. The liquid crystal layer 27 is sealed with a sealant 38.

The phase difference compensating elements 23 and 24 having a front retardation of 80 nm are attached to the outside of the TFT substrate 21 and the CF substrate 22 such that the rubbing direction and the slow axis of the phase difference compensating elements 23 and 24 are orthogonal to each other. . The retardation of the entire liquid crystal panel 20 including the retardation of the phase difference compensating elements 23 and 24 is 320
nm. The arrangement of the phase difference compensating elements 23 and 24 and the polarizers 25 and 26 is as described above with reference to FIG.

The liquid crystal display device 30 has the VT characteristic shown by the curve of 320 nm in FIG. 1, shows the highest transmittance (maximum value) at an applied voltage of about 2 V, and shows the transmittance when the applied voltage is further increased. The rate drops.

Next, a specific configuration of the drive circuit 10 will be described.

As the input image signal S, a 6-bit (64 gradation) progressive signal of 60 Hz per frame is used. The input image signal S is sequentially transmitted to the image storage circuit 1.
It is held at 1. Next, the combination detection circuit 12 stores, for each picture element, the current input image signal S and one in the image storage circuit.
The combination with the input image signal S one frame before held at 1 is detected at 120 Hz. Here, detection at 120 Hz is for performing double-speed writing described later. Since the input image signal S is 60 Hz per frame, it is converted to a double speed of 120 Hz at an appropriate place in the drive circuit 10.
Here, the conversion is performed by the combination detection circuit 12.

The overshoot voltage detection circuit 13
Bit (Low voltage side overshoot drive dedicated voltage: 0V
32 gradations between .about.2V, 64 gradations between gradation voltages 2.1V-5V, dedicated voltage for high voltage side overshoot drive:
A predetermined overshoot voltage corresponding to the combination detected by the combination detection circuit 12 is detected from the voltages of 32 tones between 5.1 V and 6.5 V). The overshoot voltage is a voltage of 120 Hz. This overshoot voltage is supplied to the polarity inversion circuit 14 and is converted into a 120 Hz AC voltage. This one
An AC voltage of 20 Hz is supplied to the liquid crystal panel 20. That is, the input image signal S of 60 Hz to the drive circuit 10 is output from the drive circuit 10 to the liquid crystal panel 20 as an image signal of 120 Hz. Therefore, one frame, 60
The input image signal S of 1 Hz is converted into two fields of an output image signal of 1 field / 120 Hz (referred to as "first and second subfields"), and is written to the liquid crystal panel 20 at double speed. .

Here, the drive circuit 10 receives the input image signal S
When (60 Hz) changes, the above-described overshoot voltage is output in the first subfield of 120 Hz, and in the second subfield, the grayscale voltage Vg corresponding to the input image signal S of the current frame (no overshoot).
Is set to be output to the liquid crystal panel 20.

FIG. 11 shows a liquid crystal display device 30 of the present embodiment.
(Solid line). FIG. 11 also shows, as a comparative example, response characteristics (broken line) when overshoot drive is not performed. FIG. 11 also shows the input image signal S, the voltage written to the liquid crystal panel 20 at double speed, and the voltage output to the liquid crystal panel of the comparative example when overshoot drive is not performed (no double speed drive is performed). Is shown.

As shown in FIG. 11, the input image signal (6
0 Hz) changes from the first field to the second field on the high gradation side (low voltage side), simply applying a predetermined gradation voltage, as indicated by a broken line, causes a predetermined change in the second field. The transmittance does not reach. On the other hand, when the overshoot drive is performed, a predetermined transmittance is reached in a half field (one subfield) as shown by a solid line. The effect of improving response characteristics according to the present invention is as follows.
This can be obtained even if the input image signal S of the field is a signal of the highest gradation.

Note that the response characteristic of the comparative example (broken line) shows a discontinuous change because the liquid crystal capacity is increased due to the change in the alignment of the liquid crystal during the period when the liquid crystal layer 27 holds the electric charge. As a result, the voltage applied to the liquid crystal layer 27 decreases.

In the description of the drive circuit 10, the embodiment of the present invention has been described with an example of a non-interlace drive type liquid crystal display device in which one frame corresponds to one vertical period. However, the present invention is not limited to this. The present invention can be applied to an interlace driving type liquid crystal display device in which one field corresponds to one vertical period.

[0119]

According to the present invention, a liquid crystal display device having an improved fall response speed is provided. In particular, by applying the present invention to a parallel alignment type liquid crystal layer, the response time can be reduced to about 10 msec.

Since the liquid crystal display device according to the present invention has a fast response speed, occurrence of image blurring due to an afterimage phenomenon in moving image display is prevented, and high quality moving image display is possible.

[Brief description of the drawings]

FIG. 1 is a graph showing a VT curve of a liquid crystal panel including a parallel alignment type liquid crystal layer including a liquid crystal material having a positive refractive anisotropy (Δn = n / −n⊥> 0).

FIG. 2A is a graph showing a voltage-retardation curve of a liquid crystal panel having a retardation of 260 nm.

FIG. 2B is a graph showing a voltage-retardation curve of a liquid crystal panel having a retardation of 300 nm.

FIG. 3 is a schematic diagram illustrating a relationship between a VT curve of a liquid crystal panel included in a liquid crystal display device according to an embodiment of the present invention and a voltage Vos dedicated to overshoot driving and a gradation voltage Vg.

FIG. 4 is a schematic diagram showing a configuration of a drive circuit 10 included in a liquid crystal display device according to an embodiment of the present invention.

FIG. 5A shows V of the liquid crystal display device (liquid crystal panel with a retardation of 320 nm) of the embodiment according to the present invention and the liquid crystal display device (liquid crystal panel with a retardation of 260 nm) of the comparative example.
4 is a graph showing a setting condition of a −T curve and a lowest gradation voltage.

FIG. 5B is a graph schematically showing a temporal change in transmittance of the liquid crystal display device of the embodiment according to the present invention.

FIG. 5C shows V of the liquid crystal display device (liquid crystal panel with a retardation of 320 nm) of the embodiment according to the present invention and the liquid crystal display device (liquid crystal panel with a retardation of 260 nm) of the comparative example.
4 is a graph showing a setting condition of a −T curve and a lowest gradation voltage.

FIG. 5D is a graph schematically showing a temporal change in transmittance of the liquid crystal display device of the embodiment according to the present invention.

FIG. 6 is a graph schematically showing a temporal change in transmittance of another liquid crystal display device of the embodiment.

FIG. 7 is a view schematically showing an NW mode transmission type liquid crystal panel using a parallel alignment type liquid crystal layer provided in the liquid crystal display device according to the embodiment of the present invention.

FIG. 8 is a diagram for explaining a function of a phase difference compensating element used in the embodiment.

FIG. 9 is a graph showing the effect of the thickness of the phase difference compensating element on the VT curve of the liquid crystal panel.

FIG. 10 is a diagram schematically showing a liquid crystal display device 30 according to an embodiment of the present invention.

FIG. 11 is a diagram for explaining the response characteristics of the liquid crystal display device 30 of the present embodiment, showing the input image signal S, the transmittance, and the voltage output to the liquid crystal panel together with a comparative example.

FIG. 12 is a schematic diagram illustrating a configuration of a driving circuit of a conventional liquid crystal display device.

13 is a signal waveform diagram showing how the response characteristics are improved by the drive circuit shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Drive circuit 11 Image storage circuit 12 Combination detection circuit 13 Overshoot voltage detection circuit 14 Polarity inversion circuit 15 Liquid crystal panel 20 Liquid crystal panel 20a Liquid crystal cell 21, 22 Substrate 23, 24 Phase difference compensation element 25, 26 Polarizer 27 Liquid crystal layer 27a Liquid crystal molecule 30 Liquid crystal display 31, 35 Glass substrate 32 Pixel electrode 33, 37 Alignment film 36 Counter electrode (common electrode) 38 Sealing material

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 621 G09G 3/20 621F 623 623C 623C 641 641C F-term (Reference) 2H090 LA06 MA02 MA10 MB01 2H091 FA11X FA11Z KA02 2H093 NA07 NA33 NA43 NC11 NC29 ND06 ND32 NF04 5C006 AA01 AC02 AC18 AC21 AC28 AF44 AF46 AF64 BB12 BC12 BF02 BF28 FA14 FA29 5C080 AA10 BB05 DD08 EE19 EE29 FF12 GG07 GG08 JJ02 JJ04 JJ05

Claims (6)

[Claims] A liquid crystal panel having a liquid crystal layer and an electrode for applying a voltage to the liquid crystal layer; and a drive circuit for supplying a drive voltage to the liquid crystal panel, wherein the liquid crystal panel has a voltage-transmittance characteristic. , Indicates an extreme value of the transmittance at a voltage equal to or lower than the lowest gradation voltage, and the driving circuit is determined in advance according to a combination of the input image signal of one vertical period before and the input image signal of the current vertical period, A liquid crystal display device for supplying a driving voltage, in which a gradation voltage corresponding to an input image signal in a current vertical period is overshot, to the liquid crystal panel. 2. A difference in retardation between a state where no voltage is applied to the liquid crystal panel and a state where a maximum gradation voltage is applied is 300.
The liquid crystal display device according to claim 1, wherein the thickness is at least nm. 3. The liquid crystal panel according to claim 1, wherein the liquid crystal panel is a transmissive liquid crystal panel, and the extreme value gives a maximum value of transmittance.
Or the liquid crystal display device according to 2. 4. A method according to claim 1, wherein one vertical period of the input image signal is defined as one frame, and at least two fields of the drive voltage correspond to one frame of the input image signal. 4. The liquid crystal display device according to claim 1, wherein, in a first field, a drive voltage in which a gradation voltage corresponding to an input image signal of a current field is overshot is supplied to the liquid crystal panel. 5. The liquid crystal display according to claim 1, wherein the liquid crystal layer is a homogeneous alignment type liquid crystal layer. 6. The liquid crystal panel further includes a phase difference compensating element, wherein the phase difference compensating element has a relation that three main refractive indices na, nb, and nc of an index ellipsoid satisfy na = nb> nc. 6. The liquid crystal display device according to claim 1, wherein the liquid crystal layer is arranged so as to cancel at least a part of the retardation of the liquid crystal layer.