JP2003270669A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OCB (optically compensated bend) type liquid crystal display device which performs satisfactory image display by properly setting a driving frequency and a black insertion rate. <P>SOLUTION: The black insertion rate and the driving frequency are specified on the basis of relation between the driving frequency and a critical black insertion rate being a minimum required black insertion rate for preventing the alignment state of a liquid crystal from changing from bend alignment to splay alignment, and display operation is performed with the specified black insertion rate and driving frequency. The driving frequency is properly switched, and the black insertion rate is changed in accordance with the switching. The driving frequency is switched in accordance with, for example, change in the temperature of a liquid crystal layer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used for a liquid crystal television, a liquid crystal monitor and the like, and particularly to a feel sequential color (FSC) suitable for displaying moving images.
Type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device has rapidly spread as an image display device from the viewpoint of space saving. As such a liquid crystal display device, a TN (Twisted Nematic)
A liquid crystal display device (hereinafter, referred to as a TN type liquid crystal display device) using a liquid crystal of (4) mode is generally used. However, the TN type liquid crystal display device is not suitable for displaying a moving image because of its slow response time of tens of ms, and has a problem that the viewing angle is narrow. Therefore, various attempts have been made for the purpose of improving the response speed of the liquid crystal, widening the viewing angle, and the like.

As one of such attempts, in order to provide a liquid crystal display device having a high-speed response suitable for displaying moving images,
A liquid crystal display device using an OCB (Optically Compensated Bend) mode liquid crystal (hereinafter, referred to as OCB type liquid crystal display device) has been proposed (monthly display 2001).
(See pages 18 to 23 of the monthly issue).

In such an OCB type liquid crystal display device, transparent electrodes as voltage applying means are formed respectively.
It has a liquid crystal panel composed of a single substrate and a liquid crystal layer sandwiched between these substrates. Alignment films are respectively formed on the transparent electrodes, and the alignment films are subjected to alignment treatment so as to align the nematic liquid crystals in parallel and in the same direction. Further, a retardation plate for compensating the retardation of the liquid crystal layer is provided.

The OCB type liquid crystal display device constructed as described above is characterized in that the alignment state of the liquid crystal is changed from the splay alignment to the bend alignment by applying a voltage, and an image is displayed in this bend alignment state. OC like this
In the case of a B type liquid crystal display device, the response time of the liquid crystal is several ms and T
Since it is remarkably shorter than that of the N-type liquid crystal display device, it is suitable for displaying moving images. Further, the liquid crystal in the bend alignment state is inclined in the opposite directions on the upper and lower surfaces of the glass substrate, so that optical compensation is performed. As a result, the viewing angle can be expanded.

However, even if the response speed of the liquid crystal is improved in this way, the liquid crystal display device is a hold-type display device, so that a blur of an image occurs at the time of displaying a moving image.

As a method of bringing the hold type display device closer to the impulse type display device, it is conceivable to intermittently turn on the backlight as disclosed in Japanese Patent Laid-Open No. 1-82019. However, in reality, since the OCB-mode liquid crystal has a dielectric anisotropy, a change in capacitance occurs, and as a result, a problem that an image (ghost) that should not be displayed is observed occurs. .

With respect to this problem, Japanese Patent No. 3229250
In the gazette, cyclic resetting drive (Cy
clic Resetting Drive (CR drive) has been proposed.
FIG. 10 is an explanatory diagram showing an example of a signal writing operation in CR driving. Note that the gate line is 48 in FIG.
The case where there are 0 rows is illustrated.

As shown in FIG. 10, in one period of one frame period, the video signal Data is sequentially written from the gate line of the first row to the gate line of the 480th row, and the reset signal BL is similarly set in another period. And write sequentially. Here, when the reset signal BL is a black signal for black display, intermittent display can be performed without intermittently lighting the backlight. Further, since the video signal Data is always written by being sandwiched between the reset signals BL, the ghost due to the change in the electric capacitance as described above is not observed. Furthermore, "liquid crystal" 1999
As described on pages 99 to 106 of Vol. 3, No. 3 of the year, even when a voltage below the critical voltage at which the alignment state of the liquid crystal transitions from bend alignment to splay alignment is periodically applied, 1 It has been confirmed that the transition from the bend alignment to the splay alignment (hereinafter referred to as splay transition) does not occur if the ratio of the period in which the reset signal BL is held in each pixel in the frame period is high to some extent. Normally, the reset signal BL is a black signal, so CR driving may be called black insertion driving. Hereinafter, the CR driving is referred to as black insertion driving, and the ratio of the period in which the reset signal BL is held in each pixel to one frame period is referred to as the black insertion rate.

It is considered that the black insertion FSC system can be realized by utilizing the high speed response of the OCB type liquid crystal display device, and the development thereof is underway. The technology related to FSC is described in, for example, the monthly display January 2001 issue, pages 24 to 29.

[0011]

By the way, in the black insertion drive, when the black insertion rate is increased, the light transmittance of the liquid crystal display panel is reduced accordingly.

FIG. 11 is a timing chart showing an example of the display operation of the FSC liquid crystal display device.
Shows the change in the voltage waveforms of the video signal and the black signal and the transmittance of the liquid crystal display panel 10 when the driving frequency is 180 Hz and the black insertion rate is 25%.
(C) shows a change in the voltage waveform of the video signal and the transmittance of the liquid crystal display panel 10 when the black signal is not written and the black insertion rate is 25%. The changes in the voltage waveforms of the video signal and the black signal and the change in the transmittance of the liquid crystal display panel 10 when the insertion rate is 25% are shown.

Comparing FIG. 11A and FIG. 11B, the liquid crystal display panel when the black signal is written (FIG. 5A) is more than when the black signal is not written (FIG. 5B). 10
It can be seen that the transmittance of is decreased. In addition, FIG.
When (a) and (c) are compared, the driving frequency is 360H.
In the case of z, the transmittance is lower than that in the case where the driving frequency is 180 Hz. This is because the response speed of the liquid crystal is limited.

When the transmittance is low as described above, it becomes impossible to secure the brightness required for good display. Therefore, in order to obtain the maximum transmittance, it is necessary to set the minimum black insertion rate (hereinafter referred to as the critical black insertion rate) within a range in which splay transition does not occur.

As a result of diligent studies, the present inventors have found that the critical black insertion rate remarkably depends on the driving frequency and has a peak in a specific driving frequency range.

The present invention has been made in view of such findings, and an object thereof is to provide a liquid crystal display device suitable for displaying moving images by performing black insertion at an appropriate critical black insertion rate according to the driving frequency. To do.

[0017]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention comprises a liquid crystal layer in which liquid crystals having bend alignment are arranged when displaying an image, A liquid crystal display device having at least one retardation plate for compensating the retardation of the liquid crystal layer, for maintaining a video signal and the state of the bend alignment for each frame period according to a predetermined driving frequency. Of the bend alignment maintaining signal of the liquid crystal display element at a predetermined ratio, by changing the retardation of the liquid crystal layer according to the video signal and the bend alignment maintaining signal of the display light of the liquid crystal display element. A liquid crystal display device that performs display by changing the transmittance is characterized by including a control unit that switches the drive frequency to control the operation of the liquid crystal display element. To.

According to this structure, the splay transition can be avoided by appropriately switching the drive frequency, and good image display can be stably performed.

In the liquid crystal display device according to the present invention, the control means may control the operation of the liquid crystal display element by changing the ratio according to the switched driving frequency.

According to this structure, the bend alignment maintaining signal can be written in the liquid crystal display element at an appropriate ratio according to the driving frequency, so that the splay transition can be avoided and a good image display can be achieved. It becomes possible to carry out stably.

In the liquid crystal display device according to the invention, the liquid crystal display element includes a plurality of gate lines and a plurality of source lines arranged to intersect with each other, a gate driver for outputting a scanning signal to the gate lines, A bend orientation maintaining driver that outputs the video signal and the bend orientation maintaining signal to the source line, pixel electrodes arranged in a matrix, and pixel electrodes provided corresponding to each of the pixel electrodes, and supplied through the gate line. The video signal and the bend orientation maintaining signal supplied via the source line are supplied to the pixel electrode by switching between conduction / non-conduction between the pixel electrode and the source line according to the scanning signal. An array substrate having a writable switching element, a counter substrate facing the array substrate, and provided on the counter substrate, It may be provided a counter electrode for driving the liquid crystal by generating an electric potential difference between the serial pixel electrode.

As a result, it is possible to realize an active matrix type liquid crystal display device which can stably display a good image.

Further, in the liquid crystal display device according to the invention, an illuminating device having light sources for emitting red, green and blue color lights respectively, and the illuminating device for causing the light sources to emit each color light in a time division manner. It is also possible to further include a lighting device control means for controlling, and the control means may synchronously control the gate driver, the source driver, and the lighting device control means.

As a result, it is possible to realize an FSC liquid crystal display device capable of avoiding splay transition and reducing color breakage.

In the liquid crystal display device according to the invention, the liquid crystal display element includes a plurality of gate lines and a plurality of source lines arranged so as to intersect with each other, a gate driver for outputting a scanning signal to the gate lines, A source driver that outputs the video signal to the source line, a bend alignment sustaining driver that outputs the bend alignment sustaining signal to the source line, pixel electrodes arranged in a matrix, and the pixel electrodes are provided in correspondence with each other. The video signal and the video signal supplied via the source line by switching between conduction / non-conduction between the pixel electrode and the source line according to a scanning signal supplied via the gate line. An array substrate having a switching element capable of writing a bend orientation maintenance signal to the pixel electrode, and a pair facing the array substrate. A substrate provided on the counter substrate,
A counter electrode that drives the liquid crystal by generating a potential difference between the pixel electrode and the pixel electrode may be provided.

By providing the bend orientation maintaining driver for supplying the bend orientation maintaining signal in this way, the source driver does not need to supply the bend orientation maintaining signal, so that the load on the source driver can be reduced.

Further, in the liquid crystal display device according to the present invention, an illuminating device having light sources for emitting red, green, and blue color lights respectively, and the illuminating device for causing the light sources to emit the color lights in a time-division manner. It is also possible to further include a lighting device control means for controlling, and the control means may synchronously control the gate driver, the source driver, the bend orientation maintaining driver, and the lighting device control means.

Further, in the liquid crystal display device according to the present invention, the drive frequency may be n (n is an integer of 1 or more) times the frame frequency. Further, the frame frequency may be 60 Hz. Furthermore, n may be 4 or 6. The value of n will be determined according to the performance of the liquid crystal display element (for example, the slew rate of the source driver and the response speed of the liquid crystal).

Further, in the liquid crystal display device according to the present invention, a temperature sensor for measuring the temperature of the liquid crystal layer or the vicinity of the liquid crystal layer is further provided, and the control means has a drive frequency according to a measurement result of the temperature sensor. May be switched. Thereby, the display operation can be performed at an appropriate drive frequency according to the temperature of the liquid crystal layer.

In the liquid crystal display device according to the invention, the control means may switch the drive frequency when the temperature of the liquid crystal layer or the vicinity of the liquid crystal layer is a predetermined temperature. Here, the predetermined temperature is 40 ° C.
The temperature may be 60 ° C. or lower.

In the liquid crystal display device according to the present invention, the control means sets the drive frequency to 180 Hz when the temperature of the liquid crystal layer is lower than a predetermined temperature, and the temperature of the liquid crystal layer is equal to or higher than the predetermined temperature. In this case, the drive frequency may be 360 Hz.

In the liquid crystal display device according to the invention, the bend alignment maintaining signal may be a signal for displaying black.

In the liquid crystal display device according to the present invention, the ratio of the bend alignment maintaining signal is 10% or more and 30% or more.
It may be as follows.

In the liquid crystal display device according to the present invention, the liquid crystal layer may have a thickness of 2 μm or more and 4 μm or less.

In the liquid crystal display device according to the present invention, the product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer at room temperature for light having a wavelength of 589 nm has a product Δnd of 0.5 μm or more. It may be 8 μm or less.

In the liquid crystal display device according to the invention, the bulk viscosity of the liquid crystal may be 60 mPa · s or less.

Further, in the liquid crystal display device according to the present invention, the liquid crystal display element may be configured such that the response time of the liquid crystal when the black display is changed to the white display is 2.2 ms or less. .

In the liquid crystal display device according to the present invention, the voltage applied to the liquid crystal display element in the case of black display may be 4.5 V or more and 7.5 V or less.

Further, in the liquid crystal display device according to the present invention, the liquid crystal may be a cyano-containing liquid crystal. Here, the cyano content of the liquid crystal may be 5% or more and 20% or less.

Further, the liquid crystal display device according to the present invention has a liquid crystal layer in which liquid crystals having a bend alignment are arranged when displaying an image, and at least one liquid crystal layer for compensating the retardation of the liquid crystal layer. A liquid crystal display element having a phase difference plate, and a liquid crystal display device having a predetermined ratio of a video signal and a bend alignment maintaining signal for maintaining the bend alignment state for each frame period according to a predetermined drive frequency. In a liquid crystal display device that performs display by writing on a display element and changing the retardation of the liquid crystal layer according to the video signal and the bend orientation maintenance signal to change the transmittance of the display light of the liquid crystal display element. , The relationship between the ratio and the transmittance at a plurality of drive frequencies is obtained in advance, and the transmittance specified based on the obtained result is the maximum. Characterized in that it comprises a control means for controlling the operation of the liquid crystal display device in become the driving frequency. As a result, good image display can be performed while maintaining the bend orientation.

Further, the liquid crystal display device according to the present invention has a liquid crystal layer in which liquid crystals having a bend alignment are arranged when displaying an image, and at least one sheet for compensating the retardation of the liquid crystal layer. A liquid crystal display element having a phase difference plate, and a liquid crystal display device having a predetermined ratio of a video signal and a bend alignment maintaining signal for maintaining the bend alignment state for each frame period according to a predetermined drive frequency. In a liquid crystal display device that performs display by writing on a display element and changing the retardation of the liquid crystal layer according to the video signal and the bend orientation maintenance signal to change the transmittance of the display light of the liquid crystal display element. ,
Control means for controlling the operation of the liquid crystal display element at a drive frequency at which the ratio specified based on the calculated result is the lowest, with the relationship between the ratio and the transmittance at a plurality of drive frequencies being obtained in advance. It is characterized by including. As a result, good image display can be performed while maintaining the bend orientation.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a sectional view schematically showing the constitution of a liquid crystal display device of the present invention according to Embodiment 1, and FIG. 2 shows the constitution of a liquid crystal cell provided in the liquid crystal display device. It is sectional drawing which shows typically. Further, FIG. 3 is a cross-sectional view schematically showing an alignment state of liquid crystals injected into a liquid crystal layer included in the liquid crystal display device. In the figure, for convenience of description, the X direction is the upward direction of the liquid crystal display device 100.

As shown in FIG. 1, the liquid crystal display device 100
Includes a liquid crystal display element (liquid crystal display panel) 10, and the liquid crystal display panel 10 is configured by sequentially laminating a retardation plate 11 and a polarizing plate 13 on both sides of a liquid crystal cell 12. In addition, the liquid crystal cell 12 is, as shown in FIG.
A plurality of substrates, that is, the upper substrate 102 and the lower substrate 103
Is equipped with. The upper substrate 102 and the lower substrate 103 are
The upper substrate 102 and the lower substrate 103 are arranged so as to face each other with the spacer 9 interposed therebetween in order to hold the cell gap CG.
The liquid crystal layer 4 is formed by injecting the liquid crystal 26 into the gap formed between the liquid crystal layer 4 and the liquid crystal layer 4.

The upper substrate 102 is formed by stacking the transparent electrode 2 and the alignment film 3 in this order on the lower surface of the glass substrate 1. On the other hand, the lower substrate 103 is formed by stacking the transparent electrode 7 and the alignment film 6 in this order on the upper surface of the glass substrate 8.

The alignment films 3 and 6 described above are subjected to an alignment treatment such as a known rubbing treatment so that the liquid crystal 26 is aligned in parallel and in the same direction.

The liquid crystal display panel 10 thus configured
Applies a predetermined voltage between the transparent electrode 2 and the transparent electrode 7 to change the alignment state of the liquid crystal 26 from the splay alignment (FIG. 3A) to the bend alignment (FIG. 3B). An image is displayed by this bend orientation state. That is, it is a so-called OCB mode liquid crystal display panel.

Further, in this liquid crystal display panel 10, a relatively low voltage (0 V or more and 2 V or more is applied between the transparent electrode 2 and the transparent electrode 7).
White display is performed when a voltage of about V or less) is applied, and black display is performed when a relatively high voltage (about 4.5 V or more and 7.5 V or less) is applied. That is, it is a so-called normally white mode liquid crystal display panel. The liquid crystal display panel 10 has a response time (transmission rising time) of the liquid crystal 26 of 2.0 ms in the case of transition from black display to white display, and a liquid crystal 2 in the case of transition from white display to black display.
6 response time (transmission fall time) is 0.2 ms
Is designed to be. Therefore, the display operation is performed by dividing one frame period into a plurality of subframe periods.
The configuration is compatible with the SC system. Therefore, for example, the driving frequency 360 which is 6 times the frame frequency 60 Hz
The liquid crystal 26 can sufficiently respond even at Hz.

Here, the voltage value at the time of black display is set to 4.5 V or more and 7.5 V or less while maintaining a high transmittance during the white display by the design of the retardation plate 11. Is set to. Since this voltage value is equivalent to that of the conventional TN type liquid crystal display device, it can be said to be preferable from the viewpoint of manufacturing cost of the liquid crystal display panel.

Liquid crystal display panel 1 constructed as described above
A backlight 20 is arranged below 0. The backlight 20 includes a light guide plate 22 made of a transparent rectangular synthetic resin plate, a light source 21 disposed near one end face 22a of the light guide plate 22 so as to face the end face 22a, and below the light guide plate 22. It is configured to include a reflection plate 23 arranged and a diffusion sheet 24 provided on the upper surface of the light guide plate 22.

The light source 21 provided in the backlight 20 is an LED array in which LEDs emitting red, green and blue which are the three primary colors of light are sequentially and repeatedly arranged.

The LED is suitable as the light source 21 included in the backlight 20 of the liquid crystal display device of the present invention because it is easy to control blinking and the like, but the invention is not limited to this. For example, a cold cathode tube may be used as the light source 21 to achieve high brightness.

The backlight 20 constructed as described above
Then, the light emitted from the light source 21 enters the light guide plate 22 through the end face 22a. The incident light is multiply scattered inside the light guide plate 22 and emitted from the entire upper surface thereof. At this time, light that leaks below the light guide plate 22 and enters the reflection plate 23 is reflected by the reflection plate 23 and returned to the inside of the light guide plate 22.
The light emitted from the light guide plate 22 is diffused by the diffusion sheet 24, and the diffused light enters the liquid crystal display panel 10. As a result, the liquid crystal display panel 10 is entirely red,
The green or blue light is emitted uniformly.

FIG. 4 is a block diagram showing the structure of the liquid crystal display device 100 according to the first embodiment of the present invention. Referring also to FIGS. 1 and 2, the liquid crystal display panel 10 is
This is a well-known TFT (Thin Film Transistor) type display panel, and a counter substrate (not shown) having a counter electrode (not shown) formed on the inner surface, and a pixel electrode 39, a gate line 31, a source line 32 on the inner surface. And an array substrate (not shown) on which the TFTs 33 are formed so as to face each other with the liquid crystal layer 4 in between. Also, in the array substrate,
The gate lines 31 and the source lines 32 are arranged so as to alternate with each other, and the gate lines 31 and the source lines 32 are arranged.
A pixel electrode 39 and a TFT 33 are formed for each pixel partitioned by. The gate driver 34 drives the gate line 31 of the liquid crystal display panel 10, the source driver 35 drives the source line 32, and the black insertion driver 40 drives the gate driver 34 and the source driver 35.
And the black insertion driver 40 is controlled by the control circuit 36.

The liquid crystal display device 10 constructed as described above.
At 0, the control circuit 36 outputs a control signal to the backlight control circuit 37 in order to cause the LEDs emitting the respective colored lights to sequentially emit light in a predetermined cycle. Further, in order to perform display in synchronization with the light emission, the control circuit 36 also changes the video signal 38 input from the outside to a video signal for the field sequential color system (a time for displaying the video for each sub-frame period). A video signal compressed in the axial direction) is converted, and control signals are output to the gate driver 34 and the source driver 35 in accordance with the converted video signal. As a result, the gate driver 34 outputs the scanning signal corresponding to the voltage for turning on the TFT 33 to the gate line 31, thereby sequentially turning on the TFT 33 of each pixel, while the source driver 35 causes the source driver 35 to turn on the source in accordance with the timing. Video signals are sequentially written to the pixel electrode 39 of each pixel through the line 32.

More specifically, the gate driver 34 is
By outputting the above-mentioned scanning signal to the gate line 31 of the first row, the TFT 33 connected to the gate line 31 of the first row is turned on. And in this way TFT3
When 3 is turned on, the video signal output from the source driver 35 to each source line 32 is written in the pixel electrode 39 of the pixel in the first row.

Next, the gate driver 34 operates the TFT 33.
A signal corresponding to the voltage for turning off the gate is output to the gate line 31 of the first row to turn off the TFT 33 connected to the gate line 31 of the first row. At the same time, the gate driver 34 outputs the scanning signal to the gate line 31 of the second row to turn on the TFT 33 connected to the gate line 31 of the second row. Then, as in the case of the first row, the video signal output from the source driver 35 to each source line 32 is written in the pixel electrode 39 of the pixel of the second row.

By operating in the same manner thereafter, video signals are sequentially written in the pixel electrodes 39 of the pixels in each row. As a result, a potential difference is generated between the counter electrode and the pixel electrode 39, the liquid crystal 26 is driven, and the transmittance of light emitted from the backlight 20 changes. As a result, an image corresponding to the image signal 38 appears in the eyes of the observer.

In addition to the video signal, a black signal as a reset signal is written in each sub-frame period.
The control circuit 36 outputs control signals to the gate driver 34 and the black insertion driver 40, respectively, according to the black insertion ratio set as described later. As a result, the gate driver 34 outputs a scanning signal to the gate line 31 to sequentially turn on the TFT 33 of each pixel, while the black insertion driver 40 synchronizes the black signal through the source line 32 to the pixel of each pixel at the timing. Writing is sequentially performed on the electrodes 39.

As described above, the source driver may supply both the video signal and the black signal without providing the black insertion driver 40. However, with such a configuration, when displaying images with a drive frequency of 360 Hz, the source driver is set to a normal 60 Hz.
It is necessary to operate at 12 times the driving speed. On the other hand, if the configuration is such that the black insertion driver 40 is provided as in the present embodiment, it suffices to operate the source driver 35 and the black insertion driver 40 at 6 times speed, respectively, thus reducing the load on each driver. can do. In addition,
Needless to say, the source driver may supply both the video signal and the black signal if the liquid crystal display panel has a small number of pixels and the source driver can operate at 12 × speed. It is also effective to reduce the operating frequency of the source driver by dividing the display screen into upper and lower parts.

Although the black signal is used as the reset signal in this embodiment, the reset signal does not necessarily have to be the black signal if there is a period in which all the three color light sources 21 are turned off. . However, if there is no period for turning off all the three color light sources 21 as described above, so-called black floating occurs unless the black signal is used as the reset signal. Here, when the black signal is not used as the reset signal after the period is provided, the storage capacitance line is arranged in parallel with the gate line 31, and the reset signal is collectively set by using the storage capacitance line and the counter electrode. It is desirable to write.

Next, the setting of the black insertion rate in this embodiment will be described.

FIG. 5 is a graph showing the relationship between the critical black insertion rate and the driving frequency. In addition, this figure shows the critical black insertion rate and the driving frequency when the temperature of the liquid crystal layer 4 is 80 ° C., the cell gap CG is 2.6 μm, Δn of the liquid crystal 26 is about 0.25, and the bulk viscosity is 49 mPa · s. Exemplifies the relationship of In the present specification, Δn represents the refractive index anisotropy of liquid crystal at room temperature with respect to light having a wavelength of 589 nm.

Referring to FIG. 5, it can be seen that the critical black insertion rate has a peak when the driving frequency is 120 Hz. In the case of the FSC system, since one frame period is generally composed of sub-frame periods of three colors of red, green and blue, the frame frequency is 3 times the frequency of 60 Hz.
The display operation is often performed at 80 Hz. Thus, when the driving frequency is 180 Hz, the critical black insertion rate is about 30% due to the peak of the critical black insertion rate as described above. Further, it can be seen that when the driving frequency is 360 Hz, the influence of such a peak is almost eliminated and the critical black insertion rate becomes 15% or less. Thus, the critical black insertion rate has a remarkable dependence on the driving frequency.

FIG. 6 is a graph showing the relationship between the black insertion rate calculated based on the response time of the liquid crystal 26 and the relative luminance. In FIG. 6, 6a shows the relationship when the drive frequency is 180 Hz, and 6b shows the relationship when the drive frequency is 360 Hz.

As shown in FIG. 11, when the black insertion rate is the same, since the response speed of the liquid crystal is limited, the luminance at the driving frequency of 360 Hz is lower than that at the driving frequency of 180 Hz. To do. However, as shown in FIG. 5, in practice, the critical black insertion rate when the temperature of the liquid crystal layer is 80 ° C. is about 30% when the driving frequency is 180 Hz, whereas Frequency is 360
It is about 15% at Hz. Then, as shown in FIG. 6, when the driving frequency is 180 Hz and the black insertion is 30%, and when the driving frequency is 360 Hz and the black insertion rate is 15%.
The transmittance of the liquid crystal display panel is higher in the latter case when compared with the case. Therefore, the temperature of the liquid crystal layer 4 is 80 ° C.
In such a case, a better display can be realized by setting the drive frequency to 360 Hz.

Therefore, the liquid crystal display device 10 of the present embodiment
The control circuit 36 included in 0 has a driving frequency of 360 Hz
Then, the gate driver 3 is adjusted so that the black insertion rate becomes 15%.
4, the source driver 35, the black insertion driver 40, and the backlight control circuit 37 are controlled.

According to a study by the inventors, the critical black insertion rate is often 10% or more and 30% or less.

By the way, here, the driving frequency is 180H.
The case of z and the case of 360 Hz are compared, but the present invention is not limited to this. That is, the gist of the present invention is to measure the frequency dependence of the critical black insertion rate and the response time of the liquid crystal in advance, and show the relationship between the black insertion rate and the transmittance (or relative luminance) at the driving frequency to be compared. The purpose is to calculate, specify the drive frequency at which the maximum transmittance is obtained based on these, and display an image at the specified drive frequency. Therefore, for example, the drive frequency is 240
It is easily assumed that the case of Hz is the comparison target.

As described above, in the present embodiment, the driving frequency at which the maximum transmittance is obtained is specified under the constraint of the critical black insertion ratio, and the image is displayed at the specified driving frequency. This drive frequency does not always match the drive frequency at which the black insertion rate itself is the lowest. By the way, the critical black insertion rate depends on the frequency due to the influence of the flow of liquid crystal that occurs due to the transition of the alignment state of liquid crystal from splay alignment to bend alignment or from bend alignment to splay alignment. It is speculated that there is. If this assumption is correct, it is expected that the display becomes unstable when the liquid crystal flows. In such a case, it is desirable to make the black insertion rate as low as possible in order to stabilize the display. Therefore, it is possible to specify a driving frequency that minimizes the black insertion rate instead of the driving frequency that achieves the maximum transmittance as in the present embodiment, and perform image display at the specified driving frequency.

The present invention can be applied to a liquid crystal display panel provided with a color filter when the driving frequency is 60 Hz and the critical black insertion rate remarkably increases. FIG. 7 is a graph showing the relationship between the critical black insertion rate and the driving frequency in a liquid crystal display panel when the temperature of the liquid crystal layer is 80 ° C. and the cell gap is 4.5 μm. In FIG. 7, 7a shows the above relationship when the liquid crystal is a non-cyano containing liquid crystal, and 7b shows the above relationship when the liquid crystal is a 10% cyano containing liquid crystal.

As shown in FIG. 7, when the liquid crystal is a non-cyano containing liquid crystal, a critical black insertion rate of about 25% is required near the driving frequency of 60 Hz, but the driving frequency is 12%.
At 0 Hz or 180 Hz, the critical black insertion rate is lower than that. On the other hand, when the liquid crystal is a 10% cyano-containing liquid crystal,
The peak of the critical black insertion rate is shifted to the high frequency side, and it is possible to reduce the critical black insertion rate when the driving frequency is 60 Hz. Since the transmittance can be improved with the decrease in the critical black insertion ratio, it is preferable that the liquid crystal is a 10% cyano-containing liquid crystal. Increasing the cyano content can reduce the bulk viscosity of the liquid crystal, and as a result, improves the response speed of the liquid crystal, which is desirable, but reduces the reliability for long-term use. Therefore, it is considered preferable that the cyano content is 5% or more and 20% or less.

By narrowing the cell gap CG, it becomes possible to make the liquid crystal respond faster. According to a study by the inventors, it is desirable that the cell gap CG is 2 μm or more and 4 μm or less. However, if the cell gap CG is narrowed even though the refractive index anisotropy Δn of the liquid crystal is small, the modulation rate of the liquid crystal is lowered, and as a result, the transmittance is lowered. Therefore, the product Δnd of Δn and the value d of the cell gap CG is taken into consideration in consideration of the phase difference plate 11 designed based on the modulation rate of the liquid crystal, the voltage of the black signal, the viewing angle characteristics of the liquid crystal display panel, and the like. Must be set. According to the study by the inventors, when Δnd is 0.5 μm or more and 0.8 μm or less, a response that can sufficiently correspond to a high-speed display operation such as a driving frequency of 360 Hz while ensuring a high modulation rate. Speed can be realized.

Further, when Δnd is 0.5 μm or more and 0.8 μm or less as described above, the bulk viscosity is 60
It has been confirmed by the present inventors that when a liquid crystal of mPa · s or less is used, the response time of the liquid crystal at the time of transition from black display to white display in the normally white mode is 2.2 ms or less.

(Embodiment 2) Embodiment 2 exemplifies a liquid crystal display device which performs a display operation by appropriately switching a drive frequency. Note that the configuration of the liquid crystal display device of the present embodiment is the same as that of the first embodiment, so description thereof will be omitted. Therefore, description will be given below with reference to FIG.

The control circuit 36 included in the liquid crystal display device of the present embodiment switches the drive frequency appropriately and then, similarly to the case of the first embodiment, the gate driver 34, the source driver 35, the black insertion driver 40 and the back driver. The write control circuit 37 is controlled. In this case, considering the writing of the video signal and the black signal, it is preferable to adopt n times the frame frequency as the drive frequency. Here, in the case of a television receiver, the frame frequency is 60 Hz, and in the case of a monitor for a personal computer, a frame frequency of 75 Hz is also used.

Therefore, when the frame frequency is 60 Hz, when one frame period consists of three sub-frame periods of red, green and blue, 180 Hz which is three times the frame frequency is adopted as the drive frequency. . In addition to this, a sub-frame period of intermediate color or white as disclosed in JP-A-9-90916 and JP-A-8-101672 is provided, and at 240 Hz, which is four times the frame frequency, You may make it operate. Further, by providing two sub-frame periods of three colors of red, green and blue, one frame period can be 6
The number of subframe periods is 6 and the frame frequency is 6
It may be operated at 360 Hz, which is double.

By switching the driving frequency in this way, color breakup can be reduced. Here, color breakup is a phenomenon in which a color that does not actually exist is observed on the contour of an image, and LEDs are displayed in the order of red, green, and blue.
When the light is emitted, when the observer's eyes follow a moving object, the leading end of the object is observed red and the trailing end is also observed blue. In addition,
Details of color breakage are disclosed in JP-A-8-51633.

When the driving frequency is increased, the period in which a single color is perceived and the light emission interval of the LEDs of each color are shortened, so that color breakup is reduced. Therefore, for example, the control circuit 36 switches to a high driving frequency when displaying a moving image and switches to a low driving frequency when displaying a still image. Since the color breakup occurs only in the case of displaying a moving image, it becomes possible to stably display a good image. Further, the drive frequency may be switched according to the user's setting. This makes it possible to easily adjust the image quality.

When the drive frequency is switched as described above, the control circuit 36 included in the liquid crystal display device of the present embodiment sets the black determined according to the relationship between the drive frequency and the critical black insertion rate shown in FIG. The gate driver 34, the source driver 35, the black insertion driver 40, and the backlight control circuit 37 are controlled so that the display operation is performed at the insertion rate. For example, when the drive frequency is set to 180 Hz and the black insertion rate is set to 30% and the display operation is performed, when the drive frequency is switched to 360 Hz for the purpose of reducing color breakup, the black insertion rate is set to the drive frequency. The critical black insertion rate corresponding to 360 Hz is set to 15% to control each driver and the like. By operating in this way, it is possible to display an image at an appropriate black insertion rate according to the driving frequency. As a result, without causing spray transfer,
Good image display can be stably performed.

(Embodiment 3) FIG. 5 shows the frequency dependence of the critical black insertion rate when the temperature of the liquid crystal layer is 80 ° C., but the peak of the critical black insertion rate increases as the temperature of the liquid crystal layer rises. The position moves to the high frequency side. Thus, the frequency dependence of the critical black insertion rate changes depending on the temperature of the liquid crystal layer. Therefore, the third embodiment exemplifies a liquid crystal display device in which the driving frequency is switched according to the temperature of the liquid crystal layer and the black insertion rate is changed accordingly.

FIG. 8 is a graph showing the relationship between the temperature of the liquid crystal layer and the critical black insertion rate. FIG. 8 exemplifies the relationship when the driving frequency is 180 Hz.

As shown in FIG. 8, the temperature of the liquid crystal layer is 40 ° C.
When it becomes above, the critical black insertion rate remarkably increases. From this, it is understood that it is desirable to switch the drive frequency between the case where the temperature of the liquid crystal layer is lower than the predetermined temperature and the case where it is higher than the predetermined temperature. Here, the predetermined temperature is set to, for example, 40 ° C. or higher and 60 ° C. or lower, and when the temperature is lower than the predetermined temperature, the drive frequency is set to 180 Hz.
When the temperature is equal to or higher than the predetermined temperature, it is desirable to set the driving frequency to 360 Hz.

FIG. 9 is a block diagram showing the structure of the liquid crystal display device of the present invention according to the third embodiment. As shown in FIG. 9, the liquid crystal display device of this embodiment includes a temperature sensor 41, and the temperature sensor 41 is connected to the control circuit 36. The temperature sensor 41 is provided to detect the temperature of the liquid crystal layer. Therefore, it is desirable that the liquid crystal layer be provided so as to actually contact with the liquid crystal layer, but it may be provided at a position where at least the temperature of the liquid crystal layer can be detected. Alternatively, the temperature of the liquid crystal layer may be predicted by measuring the temperature in the vicinity of the liquid crystal layer. The temperature sensor 41 is composed of a pyroelectric sensor utilizing the pyroelectric effect, a thermocouple utilizing the thermoelectric effect, and the like. When it is composed of a thermocouple, it is preferably a K thermocouple.

The other configurations of the liquid crystal display device of the present embodiment are similar to those of the first embodiment, and therefore, the same reference numerals are given and the description thereof is omitted.

Next, the operation of the liquid crystal display device of this embodiment will be described.

The temperature sensor 41 described above converts the measured temperature into a voltage and then outputs it to the control circuit 36. In addition,
The output timing is arbitrary, and may be output continuously or at a predetermined cycle.

The control circuit 36 having received the output from the temperature sensor 41 in this manner determines whether the temperature of the liquid crystal layer 4 is lower than or equal to a predetermined temperature or higher. Here, the predetermined temperature is preferably 40 ° C. or higher and 60 ° C. or lower as described above.

When the control circuit 36 determines that the temperature of the liquid crystal layer 4 is lower than the predetermined temperature, the drive frequency is 180 Hz.
The gate driver 34, the source driver 35, the black insertion driver 40, and the backlight control circuit 37 are controlled so that the display operation is performed by.

On the other hand, when the control circuit 36 determines that the temperature of the liquid crystal layer 4 is equal to or higher than the predetermined temperature, the drive frequency 36
The gate driver 34, so that the display operation is performed at 0 Hz,
The source driver 35, the black insertion driver 40, and the backlight control circuit 37 are controlled.

By operating in this way, good image display can be stably performed without causing spray transfer.

[0092]

As described in detail above, according to the present invention,
Since the splay transition can be avoided by appropriately switching the drive frequency, good image display can be stably performed.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a configuration of a liquid crystal display device of the present invention according to a first embodiment.

FIG. 2 is a cross-sectional view schematically showing a configuration of a liquid crystal cell included in the liquid crystal display device of the present invention according to the first embodiment.

FIG. 3 is a cross-sectional view schematically showing an alignment state of liquid crystals injected into a liquid crystal layer included in the liquid crystal display device of the present invention according to the first embodiment.

FIG. 4 is a block diagram showing a configuration of a liquid crystal display device of the present invention according to the first embodiment.

FIG. 5 is a graph showing the relationship between the critical black insertion rate and the driving frequency.

FIG. 6 is a graph showing a relationship between a black insertion rate calculated based on a response time of liquid crystal and relative luminance.

FIG. 7 is a graph showing a relationship between a critical black insertion rate and a driving frequency.

FIG. 8 is a graph showing the relationship between the temperature of the liquid crystal layer and the critical black insertion rate.

FIG. 9 is a block diagram showing a configuration of a liquid crystal display device of the present invention according to a third embodiment.

FIG. 10 is an explanatory diagram showing an example of a signal writing operation in black insertion driving.

FIG. 11 is a timing chart showing an example of a display operation of a field sequential color liquid crystal display device, in which (a) shows a driving frequency of 180 Hz and a black insertion rate of 2;
The change of the voltage waveforms of the video signal and the black signal and the transmittance of the liquid crystal display panel 10 in the case of 5% is shown in (b) when the driving frequency is 180 Hz and the black insertion rate is 25%. (C) shows the voltage waveform of the video signal and the change of the transmittance of the liquid crystal display panel 10 when the writing is not performed, and the voltage waveform of the video signal and the black signal when the driving frequency is 360 Hz and the black insertion rate is 25%. Also, changes in the transmittance of the liquid crystal display panel 10 are shown.

[Explanation of symbols]

1 glass substrate 2 transparent electrode 3 Alignment film 4 Liquid crystal layer 6 Alignment film 7 Transparent electrode 8 glass substrates 9 spacers 10 Liquid crystal display panel 11 Phase plate 12 Liquid crystal cell 13 Polarizer 20 backlight 21 light source 22 Light guide plate 23 Reflector 24 Diffusion sheet 31 gate line 32 source line 33 TFT 34 Gate driver 35 Source Driver 36 Control circuit 37 Backlight control circuit 38 video signals 39 pixel electrodes 40 black insert driver 41 Temperature sensor 100 liquid crystal display 102 upper substrate 103 lower substrate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 612 G09G 3/20 612J 5C080 612U 621 621K 641 641J 641R 642 642L 642P 660 660 3 / 34V 3/34 34 J 3/36 3/36 F Term (reference) 2H088 HA01 HA08 HA16 HA28 JA04 JA05 JA11 KA07 MA20 2H090 JB02 LA09 LA16 MA00 2H091 FA11X FA11Z FA23Z FA41Z GA01 GA13 HA07 KA02 LA30 2H093 NC32 NC43 NC47 ND60A ANF22A006A01 NF05A01 NF05A01 NF05A01 NF05A01 NF05A01A NF05A01NF22 AF45 AF46 AF51 AF52 AF53 AF54 AF61 AF71 BA11 BB11 BB29 BC03 BC11 EA01 FA29 FA54 5C080 AA10 BB05 CC03 DD03 EE19 EE29 EE30 JJ02 JJ04 JJ05 JJ06

Claims (25)

[Claims] 1. A liquid crystal display having a liquid crystal layer in which liquid crystals in bend alignment are arranged when displaying an image, and at least one retardation plate for compensating retardation of the liquid crystal layer. An element, and according to a predetermined drive frequency, a video signal and a bend alignment maintaining signal for maintaining the state of the bend alignment are written in the liquid crystal display element at a predetermined ratio for each frame period, and the video signal and In a liquid crystal display device that performs display by changing the transmittance of light for display of the liquid crystal display element by changing the retardation of the liquid crystal layer in accordance with the bend orientation maintenance signal, the liquid crystal display is selected by switching the driving frequency. A liquid crystal display device comprising control means for controlling the operation of the element. 2. The liquid crystal display device according to claim 1, wherein the control unit controls the operation of the liquid crystal display element by changing the ratio according to the switched drive frequency. 3. The liquid crystal display device comprises: a plurality of gate lines and a plurality of source lines arranged to intersect with each other; a gate driver for outputting a scanning signal to the gate lines; A bend alignment sustaining driver that outputs a bend alignment sustaining signal, pixel electrodes arranged in a matrix, and the pixel electrodes that are provided corresponding to the pixel electrodes, respectively, according to a scanning signal supplied through the gate line. An array substrate having a switching element capable of writing the video signal and the bend orientation maintenance signal supplied through the source line to the pixel electrode by switching conduction / non-conduction between an electrode and the source line; , A counter substrate facing the array substrate and a counter electrode provided on the counter substrate to generate a potential difference between the pixel electrodes. The liquid crystal display device according to claim 1, further comprising: a counter electrode that drives the liquid crystal according to. 4. A lighting device having light sources for emitting red, green, and blue color lights respectively, and lighting device control means for controlling the lighting device so that the light sources emit the respective color lights in a time-division manner. The method further comprises: the control means synchronously controls the gate driver, the source driver, and the lighting device control means.
The liquid crystal display device according to item 1. 5. The liquid crystal display device includes a plurality of gate lines and a plurality of source lines arranged to intersect each other, a gate driver for outputting a scanning signal to the gate lines, and an output of the video signal to the source lines. Source driver, a bend orientation maintaining driver that outputs the bend orientation maintaining signal to the source line, pixel electrodes arranged in a matrix, and the pixel electrodes, which are provided in correspondence with each other and supplied through the gate line. Conduction between the pixel electrode and the source line according to a scanning signal
An array substrate having a switching element capable of writing the video signal and the bend orientation maintenance signal supplied to the pixel electrode by switching the non-conduction to the pixel electrode; and a counter substrate facing the array substrate. The liquid crystal display device according to claim 1, further comprising: a counter electrode which is provided on the counter substrate and drives the liquid crystal by generating a potential difference between the pixel electrode and the pixel electrode. 6. A lighting device having light sources for emitting red, green, and blue color lights respectively, and lighting device control means for controlling the lighting device so that the light sources emit the color lights in a time-division manner. The liquid crystal display device according to claim 5, further comprising: the control unit synchronously controlling the gate driver, the source driver, the bend alignment maintaining driver, and the lighting device control unit. 7. The driving frequency is n of a frame frequency.
The liquid crystal display device according to any one of claims 1 to 6, wherein (n is an integer of 1 or more) times. 8. The liquid crystal display device according to claim 7, wherein the frame frequency is 60 Hz. 9. The method according to claim 7, wherein n is 4.
The liquid crystal display device according to item 1. 10. The liquid crystal display device according to claim 7, wherein the n is 6. 11. The method according to claim 1, further comprising a temperature sensor that measures a temperature of the liquid crystal layer or a temperature in the vicinity of the liquid crystal layer, and the control unit switches a drive frequency according to a measurement result of the temperature sensor. The liquid crystal display device according to any one of 1 to 3 above. 12. The liquid crystal display device according to claim 11, wherein the control unit switches the drive frequency when the temperature of the liquid crystal layer or the vicinity of the liquid crystal layer is a predetermined temperature. 13. The liquid crystal display device according to claim 12, wherein the predetermined temperature is 40 ° C. or higher and 60 ° C. or lower. 14. The control means sets a drive frequency to 180 Hz when the temperature of the liquid crystal layer is lower than a predetermined temperature.
The liquid crystal display device according to claim 12 or 13, wherein the driving frequency is 360 Hz when the temperature of the liquid crystal layer is equal to or higher than a predetermined temperature. 15. The liquid crystal display device according to claim 1, wherein the bend alignment maintaining signal is a signal for black display. 16. A ratio of the bend orientation maintaining signal is 10
% Or more and 30% or less, The liquid crystal display device according to any one of claims 1 to 15. 17. The liquid crystal layer has a thickness of 2 μm or more and 4 μm or more.
The liquid crystal display device according to any one of claims 1 to 16, which is as follows. 18. The product Δnd of the refractive index anisotropy Δn of the liquid crystal and the thickness d of the liquid crystal layer at room temperature with respect to light having a wavelength of 589 nm is from 0.5 μm to 0.8 μm. Item 18. The liquid crystal display device according to any one of items 17. 19. The bulk viscosity of the liquid crystal is 60 mPa.
19. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a thickness of s or less. 20. In the liquid crystal display device, the response time of the liquid crystal when the black display is changed to the white display is 2.2.
20. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is configured to have a period of ms or less. 21. The liquid crystal display device according to claim 1, wherein an applied voltage to the liquid crystal display element in black display is 4.5 V or more and 7.5 V or less. 22. The liquid crystal display device according to claim 1, wherein the liquid crystal is a cyano-containing liquid crystal. 23. The cyano content of the liquid crystal is 5% or more 2
The liquid crystal display device according to claim 22, which is 0% or less. 24. A liquid crystal display having a liquid crystal layer in which liquid crystals in bend alignment are arranged when displaying an image, and at least one retardation plate for compensating retardation of the liquid crystal layer. An element, and according to a predetermined drive frequency, a video signal and a bend alignment maintaining signal for maintaining the state of the bend alignment are written in the liquid crystal display element at a predetermined ratio for each frame period, and the video signal and In a liquid crystal display device that performs display by changing the transmittance of light for display of the liquid crystal display element by changing the retardation of the liquid crystal layer according to the bend alignment maintenance signal, the ratio at a plurality of driving frequencies and The relationship with the transmittance is obtained in advance, and the liquid crystal display is obtained at the drive frequency that maximizes the transmittance specified based on the obtained result. The liquid crystal display device, characterized in that it comprises a control means for controlling the operation of the device. 25. A liquid crystal display having a liquid crystal layer in which liquid crystals in bend alignment are arranged when displaying an image and at least one retardation plate for compensating retardation of the liquid crystal layer. An element, according to a predetermined drive frequency, a video signal for each frame period and a bend alignment maintaining signal for maintaining the state of the bend alignment are written in the liquid crystal display element at a predetermined ratio, and the video signal and In a liquid crystal display device that performs display by changing the transmittance of light for display of the liquid crystal display element by changing the retardation of the liquid crystal layer according to the bend orientation maintenance signal, the ratio at a plurality of drive frequencies and The relationship with the transmittance is obtained in advance, and the liquid crystal display is displayed at the drive frequency at which the ratio specified based on the obtained result is the lowest. The liquid crystal display device, characterized in that it comprises a control means for controlling the operation of the child.