JPH10268849A - Driving method for active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce flowing and trailing of an image on a screen at the time of high-speed driving. SOLUTION: A voltage V is applied to a liquid crystal in a period Tw corresponding to a selection period and a following nonselection prod (hold period) in one frame period Tf. Then, the voltage applied to the liquid crystal is held at 0 in a reset period Tr which is in the one frame period Tf and before the selection period of a next frame begins. Consequently, the liquid crystal in an array state when the voltage V is applied shifts to an array state of approximately 0 in transmissivity. Thereby the influence of the array state of liquid crystal molecules in the last frame is eliminated at the time of driving in the next frame, and flowing and trailing of an image can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for driving an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art As an active matrix type liquid crystal display device of this kind, a TFT is used.
2. Description of the Related Art A liquid crystal display device using a three-terminal switching element represented by (thin film semiconductor) or a two-terminal switching element represented by MIM (metal-insulation-metal) as a pixel switch is known.

In recent years, when the number of pixels in one line increases in order to display a high-definition image, it is necessary to drive a sampling switch for sampling data on a data line at a high speed. In particular, in recent years, there has been a tendency to mount a drive circuit on an active matrix substrate. For example, when an amorphous silicon TFT or a polysilicon TFT is used as a pixel switch, a sampling switch connected to the source of the TFT must be manufactured using the same TFT. I have no choice.

Since the channel layer of this type of TFT is made of amorphous silicon or polysilicon, it has lower mobility and is inferior in high-speed response as compared with a MOS transistor using single crystal silicon as a channel layer.

[0005] Then, the potential of the data signal line (source line) connected to the source of the TFT which is a pixel switch does not follow the original data voltage depending on the response of the sampling switch. In particular, in this type of liquid crystal display driving, since the polarity of the voltage applied to the liquid crystal is inverted with reference to the potential of the counter substrate, the value of the voltage charged and discharged to the source line increases, and the above tendency becomes more remarkable. .

To improve this, there is a method in which the source line is precharged to a predetermined precharge potential before the sampling period. Thus, the absolute value of the voltage charged / discharged to reach the data potential at the source line during the sampling period can be reduced, and the above problem can be solved.

As the next problem, there is a problem that the image quality is deteriorated depending on the time for the response of the liquid crystal to relax until a predetermined transmittance or reflectance is obtained according to the voltage applied during the selection period. That is, when attention is paid to the behavior of the liquid crystal molecules of a certain pixel, the liquid crystal molecules are applied in the selection period of the next frame from the arrangement state of the liquid crystal molecules based on the voltage applied in the selection period of the previous frame (one screen scanning period). A response relaxation time is required before a transition to the alignment state of the liquid crystal molecules based on the voltage.
Therefore, phenomena such as image flow and stringing occur on the screen over the response relaxation time. These phenomena are
The improvement cannot be achieved by the source line precharge method, and there is no choice but to select a liquid crystal having a short response relaxation time.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to reduce phenomena such as image flow and stringing on a screen, which occur depending on the relaxation time of liquid crystal molecules, to improve image quality. An object of the present invention is to provide a driving method of an active matrix type liquid crystal display device which can be improved.

[0009]

According to a first aspect of the present invention, there is provided an active matrix substrate in which a pixel electrode and a switching element connected thereto are formed for each pixel, and an opposing substrate facing each of the pixel electrodes. A method of driving an active matrix liquid crystal display device, comprising: a counter substrate on which electrodes are formed; and a liquid crystal sealed between the active matrix substrate and the counter substrate. The scanning signal supplied to the scanning signal line connected to the switching element is 1
During the frame period, the display device has a selection period, a non-selection period, and a reset period, and in the selection period, turns on the switching element at each pixel position connected to the scanning signal line, Applying a predetermined data voltage to the liquid crystal for each pixel, turning off the switching element at each pixel position connected to the scanning signal line during the non-selection period, and applying the data voltage to the liquid crystal during the selection period. Holding the applied data voltage, turning on the switching element at each pixel position connected to the scanning signal line during the reset period, and applying a voltage lower than a threshold value of the liquid crystal to the liquid crystal. It is characterized by applying.

According to the first aspect of the present invention, before the selection period of the next frame is started for each pixel position connected to the same scanning signal line (one line), the position of each pixel position on that line is started. A reset period is provided for the alignment state of the liquid crystal molecules so that the transmittance of the pixel becomes substantially zero.
In this reset period, the switching element connected to the scanning signal line is turned on again via the scanning signal line. In this state, a voltage lower than the threshold value of the liquid crystal is applied to the liquid crystal at each pixel position via a plurality of data signal lines. For this reason, the liquid crystal molecules at each pixel position are shifted from the alignment state in which the transmittance is unique to each pixel to the alignment state in which the transmittance is almost zero. This reduces or prevents the influence of the alignment state of the liquid crystal molecules in the previous frame during driving in the next frame, and thus can prevent image flow and stringing.

According to a second aspect of the present invention, in the first aspect, during the reset period, the potential of the pixel electrode is set substantially equal to the potential of the counter electrode.

In this case, the voltage applied to the liquid crystal during the reset period becomes substantially zero, and during the reset period before driving in the next frame, the liquid crystal molecules at each pixel position are set to an alignment state with a transmittance of zero. .

According to a third aspect of the present invention, in the first or second aspect, during the reset period, molecules of the liquid crystal to which the data voltage is applied are in a stable state after a voltage less than the threshold is applied. The response relaxation time is set to be equal to or longer than the response relaxation time until the response is relaxed.

Thus, the liquid crystal molecules can be relaxed to the alignment state where the transmittance is almost zero during the reset period.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the data voltage applied to the liquid crystal during the selection period is set within one frame period having the selection period to which the data voltage is applied. A gradation display is performed by setting the time integration value of the transmittance change of the transmitted light passing through the liquid crystal to be different.

According to the fourth aspect of the present invention, instead of the conventional voltage setting based on the transmittance, the voltage is set based on a value obtained by time-integrating a change in the transmittance within one frame. It is possible to perform gradation display while using.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, each of the pixel electrodes is formed of a light-reflective electrode, the liquid crystal has a negative dielectric anisotropy, A first alignment film that is not rubbed is formed so as to make the molecules of the liquid crystal molecules stand perpendicular to the active matrix substrate, and the liquid crystal molecules form an alignment film that makes the molecules of the liquid crystal stand perpendicular to the counter substrate. A second alignment film formed by rubbing so as to have a predetermined pretilt angle is formed, and display driving is performed by controlling birefringence of the liquid crystal molecules by applying a voltage.

According to the fifth aspect of the present invention, since the first alignment film on the active matrix substrate side is not rubbed, an electric field less than the threshold value of the liquid crystal is applied to the liquid crystal molecules on the active matrix substrate side. In the state that was done,
The substrates are arranged so that their major axes are perpendicular to the substrates. Since only the second alignment film on the opposite substrate side has been subjected to the rubbing treatment, the liquid crystal molecules on the opposite substrate side have a long axis relative to the substrate when an electric field less than the threshold value of the liquid crystal is applied. Are arranged so as to have a predetermined pretilt angle.

Here, birefringence effect is generated only by liquid crystal molecules having a pretilt angle, and birefringence effect is not generated by liquid crystal molecules in a vertical state, with respect to light vertically incident on the substrate.

In the present invention, since only the liquid crystal molecules on the counter substrate side have a pretilt angle, the average tilt angle of the liquid crystal molecules arranged in tandem in the cell gap direction becomes small, and an electric field less than the threshold value of the liquid crystal is reduced. The influence of the birefringence effect in the applied state is small, and even if light passes through the liquid crystal layer twice, the total birefringence effect can be reduced. For this reason, for example, at the time of off-operation in which an electric field less than the threshold value of the liquid crystal is applied, light leakage due to the birefringence effect can be reduced, and the difference in brightness between on and off can be increased to increase the contrast ratio.

Further, since the rubbing treatment is not performed on the first alignment film on the active matrix substrate side, light scattering at the time of reflection on the pixel electrode is reduced, and thereby an improvement in the contrast ratio can be expected.

Also, the first on the active matrix substrate side
If the alignment film is not subjected to the rubbing treatment, it is possible to prevent electrostatic breakdown of the element due to static electricity generated during the rubbing treatment.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described.

The present invention will be described as follows based on the experimental results shown in FIG. FIG. 1 shows a voltage waveform applied to the liquid crystal and a light transmittance characteristic of the liquid crystal that changes according to the voltage waveform. This experiment was performed by repeatedly applying a voltage to one pixel of liquid crystal sealed between a pair of substrates by a polarity inversion driving method. Therefore, in the experiment, TFT was used as the pixel electrode.
The voltage was directly applied to both ends of the liquid crystal without connecting the switching element. Note that the period Tf in FIG. 1 corresponds to one frame in active matrix driving. The period Tw in FIG. 1 corresponds to a selection period and a subsequent non-selection period (holding period) in active matrix driving. The period Tr in FIG. 1 is a reset period added in the present invention.

In the experiment of FIG. 1, Tf = 16.7 m
s and Tr were set to 5.2 ms. The length of this period Tf corresponds to the length of one frame at the time of 60 Hz drive used in the conventional active matrix drive. In addition, the period Tr was set to a longer time because the response relaxation time of the liquid crystal molecules used in this experiment was 5.0 ms.

As is clear from the experiment shown in FIG.
The voltage V or -V (the absolute value of V is larger than the threshold voltage Vth of the liquid crystal) is applied to the liquid crystal over a period of time. In the active matrix drive, a voltage V is applied to the liquid crystal by turning on all pixel switches connected to one scanning signal line for a selection period and supplying a data voltage to a data signal line during the selection period. . Thereafter, all the pixel switches connected to the one scanning signal line are turned off. The subsequent period is a non-selection period, but the voltage V supplied during the selection period is continuously applied to the liquid crystal, and the display state is maintained.

In the present invention, the period Tr before the next selection period
Then, the same voltage is applied to each of the pair of substrates, and the voltage applied to the liquid crystal eventually becomes zero. Then, as shown in FIG. 1, the relaxation is started so that the transmittance of the pixel becomes 0, and the relaxation ends within the period Tr. Thus, before the selection period in the next frame, the state of the liquid crystal molecules in the previous frame is always canceled.

Therefore, when a voltage is applied to the liquid crystal during the selection period of the next frame, the liquid crystal molecules do not start to shift from the arrangement state of the liquid crystal molecules in the previous frame, but are shown in FIG. As described above, the transition is started from the state where the transmittance is always 0. For this reason, phenomena such as image flow and stringing on the screen are prevented.

Next, a case where a gradation display is performed using the driving principle of FIG. 1 will be described. FIG. 2 shows a case where gradation display is performed by changing the voltage applied to the liquid crystal in the second frame.

According to the present invention, the voltage applied to the liquid crystal molecules in the case of performing the gradation display is obtained by integrating the change in the transmittance of the pixel, which changes within one frame period Tf, with the time of one frame period Tf. The value is set based on the value (in FIG. 2, the area corresponding to the time integration value when the transmittance is the maximum is S). As a result of changing the voltage Vvar applied to the liquid crystal of a certain pixel in the second frame of FIG. 2, this time integration value changes as shown in FIG.

According to the experiment of the present inventors, the applied voltage Vva
The relationship between r and the time integral was as follows.

Applied voltage (V) <3.2 3.90 4.05 4.30 4.60 Time integration value 0 S / 8 S / 4 S / 2 S As a result, five gradations can be displayed. Was.

As described above, in the present invention, the applied voltage for gradation display is determined based on the time integration value of the transmittance change characteristic of the liquid crystal within one frame period, so that the transmission as in the prior art is performed. Appropriate gray scale display driving could be performed as compared with the method of determining the applied voltage based on the ratio.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a sectional view of the liquid crystal display panel, and FIG. 4 is a schematic plan view of the active matrix substrate 10. As shown in FIG. 3, the liquid crystal display panel has a liquid crystal layer 200 in which liquid crystal is sealed between the active matrix substrate 10 and the counter substrate 100.

As shown in FIG. 4, the active matrix substrate 10 has drive circuit areas 14A and 14B and a liquid crystal display area 16 on a transparent glass substrate 12, for example. The liquid crystal display area 16 has a plurality of scanning signal lines 20 and a plurality of data signal lines 22 orthogonal to the scanning signal lines 20. A thin film semiconductor (TFT) switch 24 is formed near each intersection of these lines 20 and 22 respectively. The gate of the TFT switch 24 is connected to the scanning signal line 20, the source is connected to the data signal line 22, and the drain is connected to a pixel electrode 46 described later. The pixel electrode 46 and the common electrode 106 formed on the opposite substrate 100
The liquid crystal layer 200 is disposed between the two, and a voltage difference between the pixel electrode 46 and the common electrode 106 is applied to the liquid crystal layer 200 of each pixel.

A TFT switch 24 having a polysilicon channel layer is formed on the active matrix substrate 10 by utilizing a low-temperature polysilicon forming method. As shown in FIG. 3, on a glass substrate 12 SiO ₂
A film 30 is formed. Irradiating the amorphous silicon layer formed on the SiO ₂ film 30 with a laser beam,
A polysilicon layer is formed on the SiO ₂ film 30. By performing the subsequent photolithography process, the island-shaped polysilicon layer 32 shown in FIG. 3 is formed. A gate oxide film 34 and a gate 36 are formed thereon, and the polysilicon layer 3 is self-aligned using the gate 36.
By introducing an impurity into 2, a source 32A and a drain 32B are formed. Further, after forming the first interlayer insulating film 38, wiring layers 40 and 42 are formed. Then, after forming the second interlayer insulating film 44, the pixel electrode 46 is formed.
Here, the TFT switch 24 shown in FIG.
A, a drain 32B, a channel layer 32C therebetween, a gate insulating film 34 and a gate 36. Also,
The scanning signal line 20 shown in FIG. 4 is formed by forming the wiring layer 40 of FIG. 3 in one direction, and the data signal line 22 shown in FIG. It is formed by extending in the direction orthogonal to the existing direction.

In this embodiment, the pixel electrode 46 is made of, for example, Al to form a reflective liquid crystal display panel.
Is formed of a light-reflective material such as a metal represented by.

On the surface of the active matrix substrate 10, a vertical alignment film (first alignment film) 50 for vertically aligning liquid crystal molecules is formed. And this vertical alignment film 5
0 is not rubbed.

Next, the counter substrate 100 will be described.
As shown in FIG. 3, the lower surface of the glass
A transparent electrode (common electrode) 106 is formed. On the common electrode 106, the above-described vertical alignment layer 50 is formed.
Vertical alignment layer (second alignment film) 108 made of the same material as
Is formed, and the vertical alignment layer 108 is rubbed to give a pretilt angle to the liquid crystal molecules.

Next, referring to FIG. 5 and FIG.
0 will be described. 5 and 6 schematically show the vertical cross section of the liquid crystal layer 200. FIG. 5 shows the case where the electric field E applied to the liquid crystal layer 200 is zero (for example, when the display is black in the off state and the display is black). 2) shows the arrangement of the liquid crystal molecules 202. FIG. 6 shows the arrangement of the liquid crystal molecules 202 when the electric field E> Vth (for example, when the display is white in the ON state).

As shown in FIG. 5, in the off state,
The initial tilt angle θp of the liquid crystal molecules 202 on the counter substrate 100 side with respect to the counter substrate 100 is set as a pretilt angle by the rubbing process described above. This pretilt angle θp is 85 ° or more, preferably 89 ° or more. The pretilt angle θp is used to determine the direction in which the liquid crystal molecules 202 fall when a voltage is applied to both ends of the liquid crystal layer 200. This pretilt angle θp is
It is preferable that the angle is close to 90 ° for the reason described later.

As shown in FIG. 3, in the off state,
The liquid crystal molecules 202 on the active matrix substrate 10 side
It is in a state of standing perpendicular to the substrate 10.

In the off state, the light incident on the liquid crystal layer 200 reaches the pixel electrode 46 in principle without twisting the polarization direction. Further, the reflected light reflected by the pixel electrode 46 is emitted again through the liquid crystal layer 200, but also emitted at this time without a twist in the polarization direction in principle. The emitted light whose polarization state does not change is not guided to the screen by, for example, a polarizing beam splitter described later, and becomes black on the display screen.

As shown in FIG. 5, when a voltage higher than the threshold voltage Vth of the liquid crystal is applied to both ends of the liquid crystal layer 200,
Liquid crystal molecules 2 which were perpendicular to substrates 10 and 100
02 will be defeated. Then, the polarization direction of the incident light incident on the liquid crystal layer 200 is twisted, for example, by 45 °.
Further, the incident light is reflected by the pixel electrode 46, and when the reflected light passes through the liquid crystal layer 200 again, the polarization direction of the reflected light is further twisted by 45 °. As a result, light whose polarization direction is twisted by 90 ° is emitted, and this is guided to the screen by the polarization beam splitter described later, and becomes white on the display screen.

Next, the above-described display principle will be described based on the liquid crystal molecules 202.
An explanation will be given based on the electric field control birefringence (ECB) effect of controlling the birefringence of an object by an applied electric field.

Light that vibrates in a direction perpendicular to the long axis of the liquid crystal molecules 202 is called an ordinary ray, and the refractive index for the ordinary ray is represented by no. On the other hand, light that vibrates parallel to the long axis of the liquid crystal molecules 202 is called an extraordinary ray, and the refractive index for the extraordinary ray is represented by ne.

The refractive index anisotropy (or birefringence) Δn is n
It is expressed by the difference between e and no. Here, the light incident along the major axis direction of the liquid crystal molecules 202 has a refraction characteristic equivalent to ordinary light, and does not cause birefringence. When a voltage higher than the threshold value Vth is applied to the liquid crystal layer 200, the liquid crystal molecules 202 tilt in a direction perpendicular to the direction of the electric field, and birefringence occurs. That is, since the refractive index no for the ordinary ray and the refractive index ne for the extraordinary ray are different, the incident ray is divided into ordinary rays and extraordinary rays, and travels through the liquid crystal layer 202.

In this embodiment, the refractive index anisotropy Δn = n
A liquid crystal having a positive e-no is used. The dielectric constant of the liquid crystal molecule 202 in the major axis direction is expressed as εe, the dielectric constant in a direction orthogonal to the major axis direction is expressed as εo, and the dielectric anisotropy Δε is expressed as Δε = εe−εo. Is done. In the present embodiment, a liquid crystal having a negative dielectric anisotropy Δε is used.

Here, as shown in FIG.
2 falls at an angle θ with respect to the substrate radiation L,
In this case, a condition for shifting the polarization direction by 90 ° is obtained.

FIG. 8 is an enlarged projection view showing a state where the liquid crystal molecules in the on and off states shown in FIG. 7 are projected on one substrate.

In FIG. 8, the refractive indices of the liquid crystal molecules 202 with respect to the light vibrating in the X and Y directions are nx,
When ny is set, nx = no to ne (where nx changes depending on the angle θ in FIG. 5 that changes depending on the voltage applied to the liquid crystal), and ny = no.

The wavelength of the incident light is λo,
If the wavelengths of the light oscillating in the Y direction are λx and λy, then λx = λo / nx λy = λo / ny.

Using the angle θ in FIG. 7, nx−ny = (ne−no) sin θ. Here, in order for the phase difference between the light oscillating in the x direction and the light oscillating in the y direction to be an integral multiple of π (= 180 °) and to rotate the polarization direction of the incident light by 90 °, the substrate 1
Assuming that the cell gap between 0 and 100 is d, the phase difference = (nx−ny) d = (m + ／) λo where m = 0, 1, 2,. Therefore, the liquid crystal material,
If a cell gap or the like is selected, the liquid crystal can be turned on and off.

Next, in the above-mentioned reflection type liquid crystal display panel,
A case where the driving method shown in FIG. 1 is performed will be described.

In the case of multiplex driving, a selection period, a non-selection period, and a reset period are set during one frame period. In the selection period, all the TFT switches 24 connected to the scanning signal line 20 are turned on via a certain scanning signal line 20. In this state, a predetermined data voltage is applied to the liquid crystal of each pixel via the plurality of data signal lines 22. As a result, the liquid crystal molecules of each pixel start to relax from the arrangement state of the transmittance of 0 to the arrangement state of the transmittance corresponding to the data voltage. In the subsequent non-selection period, even if the TFT switch 24 is turned off, the data voltage is continuously applied to the liquid crystal, so that the liquid crystal molecules of each pixel maintain the alignment state according to the data voltage. The driving so far is illustrated in a period Tw in FIG.

In the present invention, before the selection period Tf of the next frame is started for the same pixel as described above, the transmittance of the pixels on one line of the liquid crystal in the liquid crystal becomes zero, as shown in FIG.
The reset period Tr shown in FIG. In this reset period Tr, all the TFT switches connected to the scanning signal line via the scanning signal line 20 via the one scanning signal line 20 are turned on again. In this state, the voltage of each pixel electrode 46 connected to the data signal lines 22 is set to be the same as the voltage of the common electrode 106 via the plurality of data signal lines 22. As a result, the voltage applied to the liquid crystal of each pixel becomes zero. For this reason, the liquid crystal molecules of each pixel start to relax from the alignment state where the transmittance is unique to each pixel to the alignment state where the transmittance is zero.

When a liquid crystal material having a response relaxation time of 5.0 ms is used, the reset period Tr is longer than 5.2.
ms is set. Therefore, within the reset period Tr,
The alignment state of the liquid crystal molecules of each pixel is forcibly set to a state of zero transmittance. For this reason, at the time of driving in the next frame, the influence of the arrangement state of the liquid crystal molecules in the previous frame is eliminated, and the flow of images and stringing can be prevented.

FIG. 9 is a schematic explanatory view of an apparatus for measuring the intensity of projection light using the liquid crystal display panel as a reflection type light valve. In FIG. 9, light beams whose polarization planes are orthogonal to each other are referred to as P waves and S waves, respectively.

The P-wave having a certain polarization plane emitted from the light source 300 goes straight through the polarization beam splitter 302 and enters the reflection type liquid crystal display panel 304. This panel 30
When a certain pixel 4 is in an off state, since no birefringence occurs, the polarization plane of the P wave is not rotated, and reflected light is emitted from the panel 304 while maintaining the polarization plane. Since the reflected light of the P wave travels straight again through the polarization beam splitter 302, it does not go to the photodetector 308 via the projection lens 306. Therefore, except for the light leakage based on the pretilt angle θp described later, the projection light intensity is not detected by the photodetector 308.

On the other hand, when a certain pixel of panel 304 is in the ON state, when the P wave passes through liquid crystal layer 200 twice,
Each produces a birefringence effect and its plane of polarization is rotated 90 °. Therefore, the S wave whose polarization plane of the P wave is rotated by 90 ° is emitted from panel 304. The reflected light of the S wave is bent by the polarization beam splitter 302 and travels to the photodetector 308 via the projection lens 306. Therefore, the light intensity of the projection light is detected by the light detector 308.

Next, the light intensity detected by the photodetector 308 in the off state will be described.

In the off state shown in FIG. 4, the liquid crystal molecules 202 on the counter substrate 10 are inclined by a pretilt angle. Therefore, the plane of polarization of the P wave is slightly rotated by the birefringence in the liquid crystal molecules 202 having this pretilt angle. In the case of the reflection type liquid crystal display panel 304, since light passes through the liquid crystal layer 200 twice, the polarization plane of the P wave is rotated by the liquid crystal molecules 202 having a pretilt angle at the time of incidence and reflection, respectively. As a result, a small amount of the S-wave component is emitted from the panel 304, and is incident on the photodetector 30 via the polarizing beam splitter 302 and the projection lens 306.

Incidentally, the active matrix substrate 10
If the liquid crystal molecules 202 in the vicinity thereof are kept in a vertical state without performing the rubbing treatment on the alignment film 50, the liquid crystal molecules 202 on the active matrix substrate 10 side do not have the pretilt angle θp, and the rotation of the polarization plane here ( Phase difference) does not occur. Therefore, the light intensity detected by the photodetector 308 at the time of off can be made smaller than that obtained by rubbing the alignment layers 50 and 108 on the substrates 10 and 100 together.

As a result, the difference in brightness between the off state and the on state is increased, and the contrast can be increased.

Here, assuming that the supplementary angle of the angle θ in FIG. 6 is θ ′, the phase difference R generated by the liquid crystal molecules 202 is represented by R = d × Δncos θ ′.

The sum of the phase differences generated in the liquid crystal molecules 202 having the tilt angle θ ′ affects the generation of the S-wave component emitted from the liquid crystal display panel when the liquid crystal display panel is turned off. Without processing, the liquid crystal molecules 202 on the substrate 10 do not have a pretilt angle, so that the average tilt angle of the liquid crystal molecules in the column direction can be reduced. As a result, it is possible to reduce the generation of the S-wave component due to the tilt angle of the liquid crystal molecules 202 in the off state, and improve the contrast.

In order to reduce the phase difference R, it can be seen from the above equation of the phase difference R that the pretilt angle θp corresponding to the angle θ which is the complement of θ ′ should approach 90 °. .

FIG. 10 is a schematic explanatory view of a projector using three liquid crystal display panels described above. In FIG. 10, a light source device 4 including a light source 402 and a reflecting mirror 404
The light emitted from 00 is bent by the polarizing beam splitter prism 410 and guided to the dichroic prism 420. The dichroic prism 420 distributes the incident light in three directions: straight traveling, left refraction, and right refraction. This 3
In the direction, three liquid crystal display panels 430, 440, and 450 having the above-described configuration used as light valves are arranged.

Each of the liquid crystal display panels 430, 440, 4
The reflected light from 50 is incident on the polarizing beam splitter prism 410 via the dichroic prism 420. The P-wave component of the reflected light described in FIG. 9 is bent at a right angle by the polarizing beam splitter prism 410 and returned to the light source device 400. The S-wave component of the reflected light described with reference to FIG. 9 travels straight through the polarizing beam splitter prism 410 and is guided to the screen 470 via the projection lens 460. Thus, a color image is projected on the screen 470.

At this time, according to the present invention, when the pixels of each of the liquid crystal display panels 430, 440, and 450 are driven off, the emission of the S-wave component is reduced as described above. The contrast of the color image projected on 470 can be improved.

The active matrix type liquid crystal display panel to which the present invention is applied is not limited to the one using a polysilicon TFT, but may be an amorphous silicon TFT. These three-terminal switching elements are used. Alternatively, a two-terminal element represented by MIM (metal-insulation-metal) can be used.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, the present invention is not necessarily limited to the one using the reflection type liquid crystal display panel, but has the same effect in the transmission type. Further, an electronic device using a liquid crystal display device to which the present invention is applied is not limited to a projector, and can be applied to a liquid crystal television, a personal computer, and the like that require high-speed driving.

[0073]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As the liquid crystal material of the liquid crystal layer 200, E.I. Mer
CK ZLI-4318 was used. This liquid crystal has a refractive index anisotropy Δn = 0.1243 and a dielectric anisotropy Δε = −.
2.0. Alignment film 5 formed on substrates 10 and 100
0-108, SE-75 manufactured by Nissan Chemical Industries, Ltd.
11 L was used. Then, only the alignment film 108 was rubbed. In addition, the cell gap d between the substrates 10 and 100
= 3.5 μm.

At this time, 5 as shown in the above numerical values
A gradation display was realized. At this time, the contrast ratio is 7
It was 00-800.

[0075]

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing experimental data showing a driving principle of the present invention, showing a voltage applied to a liquid crystal and a transmittance at that time.

FIG. 2 is a characteristic diagram showing experimental data of gradation display driving of the present invention, showing a voltage applied to a liquid crystal and a transmittance at that time.

FIG. 3 is a schematic sectional view showing an example of the liquid crystal display panel of the present invention.

4 is a schematic plan view of an active matrix substrate of the liquid crystal display panel shown in FIG.

FIG. 5 is a schematic explanatory view showing an alignment state of liquid crystal molecules in an off state.

FIG. 6 is a schematic explanatory view showing an alignment state of liquid crystal molecules when turned on.

FIG. 7 is a schematic explanatory view showing the state of liquid crystal molecules at the time of ON and OFF.

FIG. 8 is a schematic explanatory view showing an enlarged state of projecting the liquid crystal molecules of FIG. 7 onto one substrate.

9 is a schematic explanatory view of a projection light intensity measuring device using the liquid crystal display panel of FIG. 3 as a reflection type light valve.

FIG. 10 is a schematic explanatory view of a projector using the liquid crystal display panel of FIG. 3 as R, G, B reflective light valves.

[Explanation of symbols]

Reference Signs List 10 active matrix substrate 12 glass substrate 14A, 14B drive circuit area 16 liquid crystal display area 20 scan signal line 22 data signal line 24 TFT switch 30 SiO ₂ film 32 polysilicon layer 32A source 32B drain 32C channel layer 34 gate insulating film 36 gate 38 First interlayer insulating film 40, 42 Wiring layer 44 Second interlayer insulating film 46 Pixel electrode 50 Vertical alignment film (first alignment film) 100 Opposite substrate 101 Glass substrate 106 Common electrode 108 Vertical alignment film (second alignment film) Reference Signs List 200 liquid crystal layer 202 liquid crystal molecules 300 light source 302 polarizing beam splitter 304 liquid crystal display panel 306 projection lens 308 projection light detector 400 light source device 410 polarizing beam splitter prism 420 dichroic prism 430, 440, 450 Panel 460 projection lens 470 screen

Claims (5)

[Claims] An active matrix substrate on which a pixel electrode and a switching element connected thereto are formed for each pixel; a counter substrate on which a counter electrode facing each of the pixel electrodes is formed; And a liquid crystal sealed between a matrix substrate and the counter substrate. A driving method for an active matrix type liquid crystal display device, comprising: a scanning signal line connected to the switching element at a plurality of pixel positions on one line; The supplied scanning signal is 1
During the frame period, the display device has a selection period, a non-selection period, and a reset period, and in the selection period, turns on the switching element at each pixel position connected to the scanning signal line, Applying a predetermined data voltage to the liquid crystal for each pixel, turning off the switching element at each pixel position connected to the scanning signal line during the non-selection period, and applying the data voltage to the liquid crystal during the selection period. Holding the applied data voltage, turning on the switching element at each pixel position connected to the scanning signal line during the reset period, and applying a voltage lower than a threshold value of the liquid crystal to the liquid crystal. A method for driving an active matrix type liquid crystal display device, characterized by applying a voltage. 2. The driving method of an active matrix liquid crystal display device according to claim 1, wherein during the reset period, the potential of the pixel electrode is set substantially equal to the potential of the counter electrode. 3. The reset period according to claim 1, wherein, during the reset period, molecules of the liquid crystal to which the data voltage is applied are relaxed to a stable state after a voltage less than the threshold is applied. A driving time of the active matrix type liquid crystal display device, wherein the driving time is set to be equal to or longer than the response relaxation time. 4. The liquid crystal display according to claim 1, wherein a data voltage applied to the pixel during the selection period passes through the liquid crystal within one frame period having the selection period to which the data voltage is applied. A method for driving an active matrix type liquid crystal display device, wherein gradation display is performed by setting the time integration value of transmittance change of transmitted light to be different. 5. The liquid crystal display device according to claim 1, wherein each of the pixel electrodes is formed of a light-reflective electrode, the liquid crystal has a negative dielectric anisotropy, and A first alignment film, which is not rubbed, is formed so as to be perpendicular to the matrix substrate, and the liquid crystal molecules have a predetermined pretilt angle. A driving method for an active matrix type liquid crystal display device, wherein a second alignment film formed by rubbing is formed so as to have a display, and a display is driven by controlling a birefringence of the liquid crystal molecules by applying a voltage.