JP3337981B2 - Liquid crystal display - Google Patents

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 particularly suitable for displaying moving images such as televisions.

[0002]

2. Description of the Related Art Various materials such as a nematic liquid crystal, a smectic liquid crystal, and a polymer-dispersed liquid crystal are used as a liquid crystal for a liquid crystal display device.

Among these liquid crystals, a liquid crystal element of a TN (Twisted Nematic) mode using a nematic liquid crystal has a long response time of 50 to several hundreds ms in a half tone, within one frame period (60 Hz, 16.7 ms). Because the response does not end in, the phenomenon that the image flows and blurs when the image moves, so-called "moving video" becomes worse,
It is not suitable for displaying moving images on televisions and the like.

On the other hand, a liquid crystal device using a smectic liquid crystal having spontaneous polarization, or an OCB (optically compensating) using a bend alignment state of a nematic liquid crystal.
In a liquid crystal element of a saturated bend mode,
The response time is about 10 to 1000 times shorter than that of the conventional TN mode liquid crystal element, the response is possible in one frame period, and it is said that it is suitable for displaying moving images.

[0005]

However, in recent years,
It turned out that "shortening of the moving image" is not enough if the response time is short. "IEICE Technical Report" EID96-4 (199
6) p. 16, a continuous lighting type display device such as a conventional liquid crystal element (hereinafter, referred to as a “hold type display device”) is a pulse lighting type such as a CRT (hereinafter, referred to as a “non-hold type display device”). Device))
In principle, the image quality of a moving image (hereinafter, referred to as “moving image quality”) is poor. Therefore, also in the hold type display device, as described in the above-mentioned document, the moving image quality can be improved by setting a part of the continuous display for one frame period to a non-display state for a part of the period. I know that Also, the image quality can be improved by setting the display speed of one screen to 60 Hz, but to a higher frequency, for example, 120 Hz.

However, according to the present inventors, even when a non-display period is provided in the above-mentioned hold-type display device and a substantially non-hold display is performed, the moving image quality is improved by the response time of the liquid crystal and the response time of the backlight light source. It became clear that the problem that the degree of deterioration was different occurred. It has also been found that the degree of deterioration of the moving image quality varies depending on the pixel size, luminance, contrast, and the like of the display device.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to improve the quality of moving images in a liquid crystal display device. More specifically, it is an object of the present invention to provide a liquid crystal display device having improved moving image quality in accordance with the response time of liquid crystal. Further, a liquid crystal display device having improved moving image quality corresponding to pixel size, brightness, contrast, and the like. Is to provide.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a liquid crystal display device having a liquid crystal element having a plurality of pixels and a driving circuit for the liquid crystal element, wherein the liquid crystal is sandwiched between a pair of substrates. , One frame period is divided into a continuous first period and a second period, a first luminance is displayed in the first period, and a first luminance equal to or lower than the first luminance is displayed in the second period. 2 is displayed, and one frame period is _Fr ,
The ratio between the first period and one frame period is defined as the time aperture ratio T
_ap , when the maximum luminance is 100% and the minimum luminance is 0%,
Τ _{on is} a rising period during which the luminance reaches 0% to 90% when displaying 100% from the 0% display state, and τ is a period during which the luminance attenuates from 100% to 10% when displaying 0% from the 100% displaying state. when the _off, a liquid crystal display device which is characterized in that set to be _{T ap + (τ off -τ on} ) / 2F r = T s ≦ 0.6.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the operation of the liquid crystal display of the present invention will be described with reference to FIG. Assuming that the maximum luminance that can be displayed by the liquid crystal display device of the present invention is 100% and the minimum luminance is 0%, FIG.
It is a waveform showing the lapse of time of luminance when 00% display is performed and 0% display is performed in the second period. In FIG. 1, _Fr is one frame, _Fa is the first period, and _Fb is the second period.
Period.

In the present invention, as shown in FIG.
One frame is divided into a first period and a second period. In the first period, the first luminance is displayed, and in the second period, the second luminance equal to or lower than the first luminance is displayed. The first luminance is luminance according to predetermined image information. In the present invention, non-hold display is performed by providing a second period in which a second luminance equal to or lower than the first luminance is displayed.

The control from the first luminance to the second luminance is performed by a method of controlling the transmittance of the liquid crystal layer or a method of controlling the blinking of the backlight light source, as described later. Can be implemented. In any case, when the display luminance changes, a certain period of time is required until the display luminance reaches a predetermined luminance. Here, a rising period in which the display reaches 90% when the display is 100% from the 0% display state is τ _on , and a period in which the display is attenuated to the 10% display when the display is 0% from the 100% display state is τ _off .

The present inventors have found that the effect of improving moving image quality by non-hold display depends on the integrated value of luminance displayed within one frame period.

Since the waveform of FIG. 1A is approximated to the linear waveform of FIG. 1B, the integrated value of the luminance in one frame of FIG. 1A is obtained from the linear waveform of FIG. (Τ _on / 2) + (F _a −τ _on ) + (τ _off / 2) Here, substituting F _a = T _ap × F _r (T _ap is a time aperture ratio): = (τ _on / 2) + (T _ap × F _r −τ _on ) + (τ _off / 2) = T to normalize _{ap × F r + (τ off} -τ on) / 2 which one frame period F _r, a _{= T ap + (τ off -τ} on) / 2F r.

In the present invention, T _ap + (τ _off −
τ _on ) / 2F _r = T _s ≦ 0.6. That is, 100%
In the display state, by setting the integral value of the display time including the response time in one frame period to be equal to or less than a certain threshold value (0.6), the moving image quality according to the response time such as τ _on and τ _off is improved. Can be achieved. More preferably, T _s ≦ 0.45.

In the present invention, the lower limit of T _s may be as close as possible to 0 as far as the improvement of moving picture quality is concerned, but the lower limit is about 0.05 in consideration of the brightness of the displayed image.

In the present invention, since the moving image quality is improved by limiting the integral value, τ _off is equal to or less than the second period. In other words, it is desirable that the minimum value of the second luminance in the second period is 10% or less, and it is preferable that the display can be sufficiently attenuated to 0%.

In the present invention, as will be described later, a method for controlling the second luminance by changing the transmittance of the liquid crystal layer,
A method of controlling the second luminance by blinking the backlight light source is adopted. In the case of the former, in the case of a reflective liquid crystal display device, a constant light is irradiated, and in the case of a transmissive liquid crystal display device, the backlight light source is continuously lit, and the transmittance of the liquid crystal layer is appropriately adjusted. Is changed to control the luminance. Therefore, in the first period, a predetermined voltage is applied to the liquid crystal layer so that the liquid crystal layer of each pixel has a transmittance corresponding to the image information, and in the second period, the predetermined voltage is applied to the liquid crystal layer in the first period. The voltage applied to the liquid crystal layer is changed so that the transmittance is equal to or lower than the transmittance. Therefore, in this configuration, when the maximum transmittance of the liquid crystal layer is 100% and the minimum transmittance is 0%, the above τ _on is 100% from the 0% transmittance state.
% Transmission when transferred to the transmission rate is rising period to reach 90% from 0%, the tau _off is 10% transmittance is 100% when the transition to 0% transmittance and 100% transmittance state This is the period of decay.

On the other hand, when the second luminance is controlled by blinking of the backlight light source, the first period is a lighting period,
A second period is a non-lighting period, and a predetermined voltage is applied to the liquid crystal layer using the second period of the previous frame so that the liquid crystal layer of each pixel has a transmittance according to image information. The backlight according to the image information is displayed by turning on the backlight light source in the first period of the frame following the frame. Subsequently, by turning off the backlight light source in the second period of the frame, the luminance is set to be equal to or less than the first luminance. Therefore, in this configuration, the above τ _on
Is a rising period in which the luminance of the light source reaches 90% from 0% when the backlight light source is turned on from the non-lighting state, and τ _off is the luminance of the light source when the light source is turned _off from the lighted state. This is a period in which the frequency decreases from 100% to 10%.

Next, as described above, the degree of deterioration of the moving image quality differs depending on the pixel size, luminance, and contrast. First, for the pixel size, and the length of the lateral direction of the display unit pixel and Sz (m), it is preferable that the _{T s × Sz / (300 ×} 10 -6) ≦ 0.6. Preferably, a _{T s × Sz / (300 ×} 10 -6) ≦ 0.5.

The speed of the displayed image increases as the pixel size increases, and the quality of the moving image deteriorates almost proportionally as the display speed increases. This tendency is substantially similar to the relationship between T _s and video quality, and holds independently. Therefore, the moving image quality can be defined by the product of these. Visually, the quality of the moving image is greatly affected in the horizontal direction, and thus may be defined by the pixel size in the horizontal direction. Here, the display unit pixel is a minimum unit related to display, and in the case of gray scale display between white and black, one pixel of the minimum unit capable of changing the transmittance is one display unit pixel, and R (red) ), G (green), B (blue)
In the case of performing full-color display by a color or a four-color display obtained by adding W (white) thereto, the pixels of the three or four colors are set as one display unit pixel. The distance between the centers of gravity of the unit pixels is defined as Sz, and the length in the horizontal direction is defined as Sz.

Next, the luminance on the display screen is expressed as Br (cd)
/ M ² ), it is preferable to satisfy T _s × log (Br) ≦ 1.3. Desirably, T _s × log (Br) ≦ 1.0.

According to the characteristics of the human eye, luminance is perceived almost logarithmically. Therefore, as the luminance increases, the quality of the moving image deteriorates almost in proportion. This tendency is independent of the relationship between T _s and the quality of the moving image, and the product of these can define the quality of the moving image.

Further, _assuming that the contrast is Cr, it is preferable that T _s × log (Cr) ≦ 1.2. Desirably, T _s × log (Cr) ≦ 0.9.

According to the characteristics of the human eye, the contrast is also perceived almost logarithmically like the luminance. Therefore, as the contrast increases, the quality of the moving image deteriorates almost in proportion. This tendency is independent of the relationship between T _s and the quality of the moving image, and the product of these can define the quality of the moving image.

Next, the liquid crystal display device of the present invention will be described with reference to a specific configuration example.

FIG. 2 is a plan view schematically showing the configuration of one embodiment of the liquid crystal display device of the present invention. In the figure, 1 is a pixel electrode, 2 is a TFT (thin film transistor), 3 is a scanning signal line, 4 is an information signal line, 5 is a scanning signal application circuit, and 6 is an information signal application circuit. This embodiment is a preferred configuration example of the present invention, and is an active matrix type device including an active element for each pixel. In the present embodiment, as shown in FIG. 2, a plurality of pixel electrodes 1 are arranged in a matrix, the gate electrode of a TFT 2 arranged for each pixel electrode 1 is used as a scanning signal line 3, and the source electrode is used as an information signal line. 4, a scanning signal applying circuit 5 sequentially applies a scanning selection signal (ON signal of the TFT 2) to each scanning signal line 3, and a predetermined signal from the information signal applying circuit 6 is synchronized with the scanning selection signal. An information signal having gradation information is applied to write to the pixel electrode 1 on the selected line, and a predetermined voltage is applied to the liquid crystal layer to perform display.

FIG. 3 is a sectional view schematically showing a configuration example of one pixel of the liquid crystal element of the liquid crystal display device of FIG. In the figure, 1
1 is a substrate, 12 is a gate electrode, 13 is a gate insulating film, 1
4 is a semiconductor layer, 15 is an ohmic contact layer, 16 is an insulating layer, 17 is a source electrode, 18 is a drain electrode, 19
Is a passivation film, 20 is a storage capacitor electrode, 21 is an alignment film, 22 is a substrate, 23 is a common electrode, 24 is an alignment film, 2
5 is a liquid crystal.

In the liquid crystal device shown in FIG. 3, a transparent substrate such as glass or plastic is usually used as the substrate 11 in the case of the transmission type, and an opaque substrate such as a silicon substrate is used in the case of the reflection type. In some cases. Pixel electrode 1
And the common electrode 23 is made of ITO in the case of the transmission type.
A transparent conductive material is used, but in the case of a reflective type, the pixel electrode 1 may be formed of a highly reflective metal and also serve as a reflector. As the semiconductor layer 14, amorphous (a-) Si is generally used, and in addition, polycrystalline (p-) Si is used.
Are also preferably used. Further, as the ohmic contact layer 15, for example, an n ⁺ a-Si layer or the like is used. As the gate insulating film 13, silicon nitride (Si
N _x ) and the like are used. Further, a metal such as Al is generally used for the gate electrode 12, the source electrode 17, the drain electrode 18, the storage capacitor electrode 20, the wiring, and the like. When the storage capacitor electrode 20 has a large area, a transparent conductive material such as ITO may be used. For the insulating layer 16 and the passivation film 19, an insulating film such as silicon nitride is preferably used. The alignment films 21 and 24 are appropriately selected depending on the liquid crystal and mode to be used. For example, for horizontal alignment of smectic liquid crystal, a rubbed polymer film such as polyimide or polyamide is used.

As the liquid crystal, a smectic liquid crystal having spontaneous polarization, for example, an antiferroelectric liquid crystal (TA) having no threshold value is used.
By using FLC), good gradation display can be performed. As shown in FIG. 8, TAFLC is an antiferroelectric liquid crystal whose transmittance continuously changes with a change in applied voltage and has no clear threshold value. Therefore, the transmittance can be continuously changed by controlling the voltage applied to the liquid crystal.

In addition, a nematic liquid crystal may be replaced with an OCB.
Mode can be used. The OCB mode is a mode in which a liquid crystal molecule has a pretilt angle at an interface with a substrate, and a liquid crystal molecule in a central portion of the liquid crystal layer in a normal direction of the substrate is in a bend alignment state. .
In the OCB mode, horizontal alignment films are formed on the upper and lower substrates and arranged so that the rubbing directions are parallel or substantially parallel to each other, so that the liquid crystal molecules have a pretilt angle at the interface with the substrate and have the rubbing direction. A splay orientation is set in parallel to the direction (average rubbing direction when the rubbing direction intersects the upper and lower substrates). When a predetermined bend voltage is applied to the liquid crystal layer in this state, the liquid crystal molecules in the center of the liquid crystal layer in the direction normal to the substrate are oriented parallel to the normal, and are sequentially positioned at the interface with the substrate as approaching the substrate. Bend alignment approaching the pretilt angle of the liquid crystal molecules to be formed.
This bend alignment can be maintained by a holding voltage lower than the bend voltage. When a predetermined voltage higher than the holding voltage is applied to the liquid crystal layer, the liquid crystal molecules in most of the liquid crystal layer excluding the vicinity of the interface with the substrate. It is oriented parallel to the substrate normal direction. Since the response time between the alignment and the bend alignment is fast and an intermediate state can be obtained, gradation display can be performed by changing the applied voltage with the holding voltage on the low voltage side.

In the present invention, in addition to the OCB mode, a conventional TN mode, an antiferroelectric liquid crystal exhibiting three-state stability, a DHF (Deformed Helix F)
erroelectric liquid crystal or the like can be used as appropriate.

In the case of using the TN mode or the OCB mode, any of the normally black mode and the normally white mode can be preferably implemented. In the case of a nematic liquid crystal, in the case of the normally white mode, τ _off becomes smaller than τ _on , so that the moving image quality is improved.

In the above embodiment, a TFT is used as an active element, but a two-terminal element such as an MIM can be used.

FIG. 4 is a schematic sectional view of a case where the liquid crystal display device of the present invention is of a transmission type. In the figure, 31 is a liquid crystal element, 32 and 33 are polarizing plates, 34 is a driving circuit of the liquid crystal element 31, and 35 is a backlight light source. In the present invention, when the second luminance is controlled by controlling the transmittance of the liquid crystal layer, any of a transmission type and a reflection type can be configured. In the case of the transmission type, a backlight light source is used. Since the light source is used continuously, a white light source usually used for a liquid crystal display device can be used. on the other hand,
In the case where the second luminance according to the present invention is controlled by blinking the backlight light source, a backlight light source that is limited to the transmission type and that can accurately control blinking is required.

FIG. 5 shows a blinking circuit as an example of such a backlight light source. As a light source, a set of RGB LEDs is prepared and used as a white backlight light source. In the figure, 41 is a power supply, 42 is a transistor, 43a to 43g are LEDs,
44 is a waveform generator. LED 43a which is a monochromatic light source
43g are arranged in series, and in this example, 7 LEDs for each color, 21 LEDs in total are used. The gate voltage of the transistor 42 is adjusted by the waveform generator 44,
Control the current to D43a-43g. As RGB light source materials, for example, R is GaAlAs, G and B are GaN
Can be used. Thus, the response time is several μm
By using the LED of the order of as the light source, the lighting time of the backlight light source can be arbitrarily set.
In the present invention, it is also possible to use a cold cathode tube, a hot cathode tube, a halogen lamp, or the like, which is a fluorescent tube, in addition to the LED light source.

In the liquid crystal display device of the present invention, if the period according to the present invention can be set, the technology of the conventional liquid crystal display device other than the above-described configuration can be applied.

FIGS. 6 and 7 show examples of driving waveforms of the active matrix type liquid crystal element shown in FIG. This drive waveform is an example of a drive waveform of a liquid crystal element configured by using a TAFLC exhibiting a voltage-transmittance characteristic as shown in FIG. 8, and FIG. 6 controls the second luminance by changing the transmittance of the liquid crystal layer. FIG. 7 shows a case where the second luminance is controlled by blinking of the backlight light source. It will be described sequentially.

In FIG. 6, (a) to (c) show the scanning signal waveforms applied to the first, second, and third scanning signal lines, and (d) shows the information signal of the first column. (E) shows the waveform of the information signal applied to the line, (e) shows the voltage waveform applied to the liquid crystal of the pixel on the first line and the first column, and (f) shows the luminance at the pixel.

[0039] As shown in FIG. 6, in the first period F _a of the first frame, sequentially selects the lines, to the corresponding gate-on signal (reference voltage V _c of the pulse width T ₁ to the scanning signal lines of the line V _g ). In synchronization with this, the information signal which is set to V _s1 ~V _s2 applied to each of the information signal lines with respect to the reference voltage V _cs. A voltage having predetermined gradation information is applied to the pixel electrode of the selected pixel, and the luminance of the pixel rises. Then, in the second period F _b, select Similarly lines sequentially applies the information 0% luminance displayed in all pixels. As a result, in all the pixels, the luminance is attenuated sequentially for each line.

[0040] In this driving waveform, in response to the liquid crystal response time, F _a is set.

In FIG. 7, (a) to (c) represent 1
(D) is an information signal waveform applied to the first column of information signal lines, and (e) is a first signal line applied to the first, second, and last scanning signal lines. And a voltage waveform applied to the liquid crystal of the pixel in the first column, (f)
Represents the luminance of the backlight light source, and (g) represents the luminance of the pixels on the first line and the first column.

As shown in FIG. 7, prior to the first frame, lines are sequentially selected, and a gate-on signal (V _g with respect to the reference voltage V _c ) is applied to the corresponding scanning signal line. In synchronization with this, V _s1 to V s with respect to the reference voltage V _cs .
_The information signal set to _s2 is applied to each information signal line. A voltage having predetermined gradation information is applied to the pixel electrode of the selected pixel, and the liquid crystal of the pixel assumes a transmittance state according to the predetermined gradation information. At this point, the backlight light source is in a non-lighting state. After a period in which the liquid crystal completely switches, a first period F _a of the first frame is:
Turn on the backlight light source. Since the liquid crystal of each pixel is already in a corresponding transmittance state for displaying predetermined gradation information, the luminance of each pixel rises according to the rise of the luminance of the backlight light source, and the predetermined luminance is displayed. Subsequently, in the second period _Fb , by turning off the backlight light source, the brightness of each pixel is simultaneously reduced. The next frame is written using this non-lighting period. That is, the gate-on signal having a pulse width T ₁ sequentially applied to the scanning signal line, in synchronization therewith by applying a predetermined information signal to the information signal line, transmittance according to the liquid crystal of each pixel in the predetermined tone information State. Then, at a time T ₃ of the liquid crystal is completely switched, it starts first period in the second frame.

[0043] In this drive waveform, F _a is set corresponding to the response time of the backlight source.

[0044]

(Example 1) A liquid crystal display device having the structure shown in FIG. 2 and the sectional structure shown in FIG. 3 was formed by a conventional TFT manufacturing technique. The number of pixels is 160 × 120 pixels and one pixel is 30
An a-Si TFT having a size of 0 μm × 300 μm and an ON resistance of about 1 MΩ was provided for each pixel to shorten the selection period. As liquid crystal, TAFLC, bend-aligned OCB
Mode nematic liquid crystal (hereinafter referred to as “OCB”),
Twisted TN mode nematic liquid crystal (hereinafter referred to as “twisted”)
"TN") was used.

TAFLC has a spontaneous polarization at 30 ° C. of 15
0 nC / cm ² , tilt angle from rubbing direction is 30
And a liquid crystal having a dielectric constant of 5 and a voltage-transmittance characteristic shown in FIG. In the present liquid crystal, the response time of the liquid crystal varies depending on the applied voltage. FIG. 9 shows the change in the response time. FIG. 9 shows that the maximum transmittance is 100% and the minimum transmittance is 0%.
%, When displaying the transmittance shown on the horizontal axis from the transmittance 0%, the rise time reaching 90% of the transmittance,
The graph shows the time required for the transmittance to decrease to 10% when displaying the transmittance of 0% from the transmittance indicated on the horizontal axis. The measurement temperature is 25 ° C. As shown in FIG.
The response time of the LC is 1 ms or less.

OCB is "KN5027xx" manufactured by Chisso.
And the cell gap was 4 μm. Also in the present liquid crystal, the response time of the liquid crystal differs depending on the applied voltage. FIG. 10A shows the change in the response time. In FIG. 10A, similarly to FIG. 9, the maximum transmittance is 100% and the minimum transmittance is 0%.
When displaying the transmittance shown on the horizontal axis from the transmittance of 0%, the rise time reaching 90% of the transmittance and displaying the transmittance of 0% on the horizontal axis are shown. It shows the time required for the transmittance to decay to 10%. The measurement temperature was 25 ° C., and the display mode was a normally black mode.

Next, FIG. 10B shows the change of the response time in the normally white mode of the OCB. As described above, the relationship between the rise time and the decay time in the normally white mode is reversed from that in the normally black mode. Therefore, in the normally white mode, τ _off becomes smaller than τ _on , so that the moving image quality is improved.

As the TN, "KN5015" manufactured by Chisso was used, and the cell gap was 4.5 μm. Also in the present liquid crystal, the response time of the liquid crystal differs depending on the applied voltage. FIG. 11 shows the change in the response time. FIG. 11 is also similar to FIG.
When the maximum transmittance is 100% and the minimum transmittance is 0%,
When displaying the transmittance shown on the horizontal axis from the transmittance 0%,
The graph shows the rise time reaching 90% and the time required to attenuate the transmittance from 10% to 10% when displaying 0% transmittance from the transmittance shown on the horizontal axis. Measurement temperature is 25 ° C
The display mode was a normally black mode.

Using the above three types of liquid crystal display devices, FIGS.
As shown in FIG. 11, by utilizing the difference in response time (rise time, decay time) in halftone display, substantially different conditions of τ _off −τ _on are set in binary image display, and further described later. The temporal aperture ratio _Tap was changed as described above, and a subjective evaluation of moving image quality was performed under each condition. The transmittance condition of the liquid crystal element, the brightness of the backlight light source, and the like were adjusted so that the maximum brightness and the minimum brightness under each condition were equal.

As shown in FIG. 6, the driving waveform is basically such that the scanning signal lines are sequentially selected and a predetermined information signal is applied in synchronization with the selection. Assuming that V _c = 0 V and V _g = 36 V in the figure, for example, TAFLC
About _Vcs = 10V, _Vs1 = 16V, _Vs2 = 4
V, the voltage value of the information signal and the like of other liquid crystals were appropriately changed at the same timing. Further, any one frame and 16.8Ms, for other periods, for example T _a
= 8.4 ms, T _b = 8.4 ms, T ₁ = T ₂ = 70 μ
s, T _ap was reduced by shortening T ₁ , and T _ap was increased by increasing T ₁ .

The evaluation of the moving image quality was carried out at a display image speed of an average of about 12 ° / s, with a display luminance of 150 cd / m ² , a contrast of 100: 1, and a distance from the observer to the panel of 30 cm. Was. Figure 1 shows the results.
It is shown in FIG. In the figure, ○ indicates that the deterioration is not anxious, Δ indicates that the deterioration is a little anxious but can be endured as a display, and x indicates that the deterioration is anxious and cannot be endured as a display.

The solid line in FIG. 12 is T _ap + (τ _off −τ _on )
/ 2F _r = T _s = 0.6, and the dotted line indicates T _s = 0.45. As is clear from FIG. 12, when T _s ≦ 0.6, the effect of improving the moving image quality is recognized, and in particular, T _s ≦ 0.45
In this case, the quality of the moving image is improved to such an extent that deterioration is hardly noticed.

(Example 2) TAFLC used in Example 1
And a backlight light source having a blinking circuit shown in FIG. 5 was used. L of backlight light source
R of the ED uses GaAlAs, G and B use GaN, and the voltage of each color is about 14 V for R, about 25 V for G and B, and the maximum current value is 20 mA.

In the drive waveform of FIG. 7, V _c = 0 V, V
_g = 36V, _Vcs = 10V, _Vs1 = 16V, _Vs2 = 4V
And one frame is fixed at 16.8 ms. For each period, for example, F _a = 4.8 ms, F _b = 12 ms, T
₁ = 40 μm, T ₃ = 1 ms, and T _ap was reduced by increasing T ₁ and T ₃ , and T _ap was increased by shortening it. Further, the response times τ _on and τ _off of the backlight light source are adjusted by adjusting the blinking circuit, and different conditions of T _ap and τ _off −τ _on are set in the binary image display, and the video quality of each condition is improved. Subjective evaluation was performed. The transmittance condition of the liquid crystal panel, the brightness of the backlight light source, and the like were adjusted so that the maximum brightness and the minimum brightness under each condition were equal. The combination of T _ap and tau _{off-tau on} was set to be the same as in Example 1.

The evaluation of the moving image quality was carried out at a display image speed of about 12 ° / s on average, with a display luminance of 150 cd / m ² , a contrast of 100: 1, and a distance from the observer to the panel of 30 cm. Was.

As a result, if the conditions of τ _off -τ _on and T _ap are the same, the same evaluation as in the first embodiment is obtained, and T _s ≦ 0.6
If so, an effect of improving the video quality is recognized, and in particular, T _s ≦
It was found that when the ratio was 0.45, the moving image quality was improved to such an extent that the deterioration was hardly noticeable.

(Embodiment 3) A liquid crystal element of the embodiment 1 (160 × 120 pixels, pixel size 300 μm square) and a liquid crystal having the same structure as the liquid crystal element of the embodiment 1 and having a pixel number of 480 × 360, pixel size 100 μm square. a device was produced in example 1 and varying the T _ap and tau _{off-tau on} in the same manner, was investigated the effect of pixel size Sz (m) to the video quality.

The image was displayed as a binary image in the same manner as in Example 1, and the pixel size was adjusted by enlarging the elements of the above two types of pixel sizes and the display images displayed thereon. For example, in the case of an element having a pixel size of 300 μm square, display is performed by regarding 2 × 2 pixels as one pixel, so that the pixel size is substantially 600 μm square. The data rate of the moving image sent from the driver was the same for all pixel sizes. Therefore, the speed of the display image viewed by the observer increases as the pixel size increases.

Although the display image speed was changed variously,
The average was 12 ° / s with a pixel size of 300 μm square. The display condition of the liquid crystal display device is a display luminance of about 150 cd / m.
^{2. The} contrast was about 100: 1, and the distance from the observer to the panel was 30 cm.

FIG. 13 shows the results of the subjective evaluation. In the figure,
(A) T _ap = 0.2, (b) T _ap = 0.3, (c)
Is T _ap = 0.4, and (d) is T _ap = 0.5. In the figure, ○ indicates no concern for deterioration, Δ indicates a little concern for deterioration, ×
Indicates that deterioration is a concern.

The solid line in FIG. 13 is T _s × Sz / (300 ×
10 ⁻⁶ ) = 0.6, and the dotted line is T _s × Sz / (300 × 10
^-6 ) = 0.5. As is clear from FIG.
_{If s} × Sz / (300 × 10 ⁻⁶ ) ≦ 0.6, the effect of improving moving image quality is high, and in particular, T _s × Sz / (300 × 10 ⁻⁶ ).
^-6 ) If ≤0.5, the moving image quality is improved to such an extent that deterioration is hardly noticeable.

[0062] Among the liquid crystal element used in Example 4 Example 3, using those TAFLC, combining the same backlight source as in Example 2, T _ap in the same manner as in Example 2
And τ _off -τ _on to change the pixel size Sz
The effect of (m) was examined.

The image was displayed as a binary image as in Example 3, and the pixel size was adjusted as in Example 3 by enlarging the two types of elements and the display images displayed on them. The data rate of the moving image sent from the driver was the same for all pixel sizes. Therefore, the speed of the display image viewed by the observer increases as the pixel size increases.

Although the display image speed was changed variously,
The average was 12 ° / s with a pixel size of 300 μm square. The display condition of the liquid crystal display device is a display luminance of about 150 cd / m.
^{2. The} contrast was about 100: 1, and the distance from the observer to the panel was 30 cm.

As a result, if the conditions of τ _off -τ _on and T _ap are the same, the same evaluation as in Example 1 can be obtained, and T _s × Sz /
If (300 × 10 ⁻⁶ ) ≦ 0.6, the effect of improving the moving image quality is high, and in particular, T _s × Sz / (300 × 10 ⁻⁶ ) ≦ 0.
It was found that the moving image quality was improved to the extent that the deterioration was hardly noticeable if it was 5.

[0066] Using the liquid crystal display device of Example 5 Example 1, Example 1 and varying the T _ap and tau _{off-tau on} in the same manner, further changes the brightness or transmittance of the liquid crystal backlight source The brightness Br (cd / m
² ) The effects were examined. The image was the same binary display image as in Example 1.

Although the display image speed was changed variously,
The average was 12 ° / s. The display conditions of the liquid crystal display device are as follows:
The contrast was about 100: 1, and the distance from the observer to the panel was 30 cm.

FIG. 14 shows the results of the subjective evaluation. In the figure,
(A) T _ap = 0.2, (b) T _ap = 0.3, (c)
Is T _ap = 0.4, and (d) is T _ap = 0.5. In the figure, ○ indicates no concern for deterioration, Δ indicates a little concern for deterioration, ×
Indicates that deterioration is a concern.

The solid line in FIG. 14 is T _s × log (Br) =
1.3, the dotted line indicates T _s × log (Br) = 1.0.
As is clear from FIG. 14, T _s × log (Br) ≦
If the value is 1.3, the effect of improving the moving image quality is high, and in particular, T _s ×
If log (Br) ≦ 1.0, the moving image quality is improved to such an extent that the deterioration is hardly noticeable.

[0070] Using the liquid crystal display device of Example 6 Example 2, Example 2 and varying the T _ap and tau _{off-tau on} in the same manner, further changes the brightness or transmittance of the liquid crystal backlight source The brightness Br (cd / m
² ) The effects were examined. The image was the same binary display image as in Example 2.

Although the display image speed was changed variously,
The average was 12 ° / s. The display conditions of the liquid crystal display device are as follows:
The contrast was about 100: 1, and the distance from the observer to the panel was 30 cm.

As a result, if the conditions of τ _off -τ _on and T _ap are the same, the same evaluation as in the fifth embodiment can be obtained, and T _s × log
When (Br) ≦ 1.3, the effect of improving the moving image quality is high. In particular, when T _s × log (Br) ≦ 1.0, the moving image quality is improved to such an extent that the deterioration is hardly noticeable. Was.

[0073] (Example 7) using the liquid crystal display device of Example 1, Example 1 and varying the T _ap and tau _{off-tau on} in the same manner, further luminance and the transmittance of the liquid crystal of the backlight source, polarization The effect of contrast Cr on moving image quality was examined by changing the plate arrangement. The image was the same binary display image as in Example 1.

Although the display image speed was variously changed,
The average was 12 ° / s. The display conditions of the liquid crystal display device are as follows:
The display luminance was about 150 cd / m ² , and the distance from the observer to the panel was 30 cm.

FIG. 15 shows the results of the subjective evaluation. In the figure,
(A) T _ap = 0.2, (b) T _ap = 0.3, (c)
Is T _ap = 0.4, and (d) is T _ap = 0.5. In the figure, ○ indicates no concern for deterioration, Δ indicates a little concern for deterioration, ×
Indicates that deterioration is a concern.

The solid line in FIG. 15 is T _s × log (Cr) =
1.2, the dotted line indicates T _s × log (Cr) = 0.9.
As is clear from FIG. 15, T _s × log (Cr) ≦
If it is 1.2, the effect of improving the moving image quality is high, and in particular, T _s ×
If log (Cr) ≦ 0.9, the quality of the moving image is improved to such an extent that the deterioration is hardly noticeable.

[0077] (Example 8) using the liquid crystal display device of Example 2, Example 2 and similar to the T _ap changing the tau _{off-tau on} to further luminance and the transmittance of the liquid crystal of the backlight source, polarization By changing the board layout, the luminance Cr
The effect of was investigated. The image was the same binary display image as in Example 2.

Although the display image speed was variously changed,
The average was 12 ° / s. The display conditions of the liquid crystal display device are as follows:
The display luminance was about 150 cd / m ² , and the distance from the observer to the panel was 30 cm.

As a result, if the conditions of τ _off -τ _on and T _ap are the same, the same evaluation as in the seventh embodiment can be obtained, and T _s × log
If (Cr) ≦ 1.2, the effect of improving the quality of the moving image is high. In particular, if T _s × log (Cr) ≦ 0.9, the moving image quality is improved to such an extent that deterioration is hardly noticeable. Was.

[0080]

As described above, according to the present invention,
Since the moving image quality can be improved in accordance with the response speed of the liquid crystal and the response speed of the backlight light source, a good moving image quality of a certain level or more can be obtained. Furthermore, since the quality of the moving image can be improved in accordance with the pixel size, the display luminance, and the contrast, it is possible to always display a good moving image quality in response to a small design change. Therefore, the liquid crystal display device of the present invention can be preferably applied to a display device such as a television which mainly has a moving image quality.

[Brief description of the drawings]

FIG. 1 is a waveform diagram of luminance for explaining the operation of the present invention.

FIG. 2 is a schematic plan view of an embodiment of the liquid crystal display device of the present invention.

FIG. 3 is a schematic cross-sectional view of one pixel of one embodiment of the liquid crystal display device of the present invention.

FIG. 4 is a schematic cross-sectional view when the liquid crystal display device of the present invention is configured as a transmission type.

FIG. 5 is a blinking circuit diagram of a backlight light source that can be used in the present invention.

FIG. 6 is an example of a driving waveform of the liquid crystal display device of the present invention.

FIG. 7 is another example of a driving waveform of the liquid crystal display device of the present invention.

FIG. 8 is a diagram showing a voltage-transmittance characteristic of an antiferroelectric liquid crystal that can be used in the present invention.

FIG. 9 is a diagram showing a change in response time depending on an applied voltage of an antiferroelectric liquid crystal used in an example of the present invention.

FIG. 10 is a diagram showing a change in response time depending on an applied voltage of an OCB mode nematic liquid crystal used in an example of the present invention.

FIG. 11 is a diagram showing a change in response time depending on an applied voltage of a TN mode nematic liquid crystal used in an example of the present invention.

FIG. 12 is a diagram showing a subjective evaluation of moving image quality under conditions where τ _off −τ _on and T _ap are different in Example 1 of the present invention.

FIG. 13 is a diagram showing subjective evaluation of moving image quality under conditions where τ _off −τ _on and T _ap and the pixel size are different in Example 3 of the present invention.

FIG. 14 is a diagram illustrating subjective evaluation of moving image quality under conditions where τ _off −τ _on and T _ap and luminance are different in Example 5 of the present invention.

FIG. 15 is a diagram showing subjective evaluation of moving image quality under conditions where τ _off −τ _on and T _ap and contrast are different in Example 7 of the present invention.

[Explanation of symbols]

 Reference Signs List 1 pixel electrode 2 TFT 3 scanning signal line 4 information signal line 5 scanning signal applying circuit 6 information signal applying circuit 11 substrate 12 gate electrode 13 gate insulating film 14 semiconductor layer 15 ohmic contact layer 16 insulating layer 17 source electrode 18 drain electrode 19 passivation Film 20 Storage capacitor electrode 21 Alignment film 22 Substrate 23 Common electrode 24 Alignment film 25 Liquid crystal 31 Liquid crystal element 32, 33 Polarizer 34 Drive circuit 35 Backlight light source 41 Power supply 42 Transistors 43a to 43g LED 44 Waveform generator

────────────────────────────────────────────────── (5) References JP-A-5-303078 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 570 G02F 1/133 535 G09G 3/36

Claims (20)

(57) [Claims] 1. A liquid crystal display device having a liquid crystal element having a plurality of pixels and a driving circuit for the liquid crystal element, wherein a liquid crystal is sandwiched between a pair of substrates, and one frame period is continuous in an arbitrary pixel. Dividing into a first period and a second period, the first luminance is displayed in the first period, and the first luminance is displayed in the second period.
Is displayed at a second luminance equal to or lower than the luminance of
_r , when the ratio between the first period and one frame period is the time aperture ratio T _ap , the maximum luminance is 100%, and the minimum luminance is 0%, the luminance becomes 0 when displaying 100% from the 0% display state. %
Τ _{on is} a rising period reaching from 90% to 90%, and brightness is from 100% to 10% when displaying 0% from 100% display state.
The liquid crystal display device is set so that T _ap + (τ _off −τ _on ) / 2F _r = T _s ≦ 0.6, where τ _off is the period of attenuation. 2. In the first period, a first luminance is displayed by setting the liquid crystal layer in a transmittance state corresponding to image information.
In the second period, a second luminance is displayed by setting the liquid crystal layer to a transmittance state equal to or lower than the first transmittance, and the maximum transmittance of the liquid crystal layer is set to 100% and the minimum transmittance is set to 0%. Sometimes, when τ _on transitions from 0% transmittance state to 100% transmittance, it is a rising period in which transmittance increases from 0% to 90%, and τ _off changes from 100% transmittance state to 0% transmittance. 2. The liquid crystal display device according to claim 1, wherein the transition is a period in which the transmittance attenuates from 100% to 10% during the transition. 3. The method according to claim 2, wherein said T _s is 0.45 or less.
The liquid crystal display device as described in the above. 4. The relationship between T _s and the horizontal length Sz (m) of a display unit pixel, wherein T _s × Sz / (300 × 10 ⁻⁶ ) ≦ 0.6. Liquid crystal display. 5. The liquid crystal display device according to claim 2, wherein the relationship between T _s and luminance Br (cd / m ² ) is T _s × log (Br) ≦ 1.3. 6. The liquid crystal display device according to claim 2, wherein the relationship between T _s and contrast Cr is T _s × log (Cr) ≦ 1.2. 7. The liquid crystal display device according to claim 2, wherein the liquid crystal element is an active matrix type liquid crystal element having an active element for each pixel. 8. The liquid crystal display according to claim 2, wherein the liquid crystal is a smectic liquid crystal having spontaneous polarization. 9. The liquid crystal is a nematic liquid crystal, wherein in the liquid crystal element, the liquid crystal has a pretilt angle at an interface with a substrate, and a liquid crystal molecule at a central portion of the liquid crystal layer in a normal direction of the substrate. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device takes a bend alignment state which is parallel to the normal direction. 10. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is a transmissive liquid crystal display device provided with a backlight light source, and the light source is used by being continuously turned on. 11. The liquid crystal display device according to claim 2, wherein the minimum value of the second luminance is 0%. 12. The liquid crystal display device includes a backlight light source, and in the first period, illuminates the light source and irradiates light from the light source to a liquid crystal layer in a transmittance state according to image information. The first luminance is displayed, and in the second period, the light source is turned off and the second luminance is displayed. When the τ _on is turned on from the non-lighting state, the luminance of the light source becomes lower. 0%
Is a rising period reaching 90% from the above, and the above τ _off
2. The liquid crystal display device according to claim 1, wherein when the light source is turned off from the lighted state, the brightness of the light source decreases from 100% to 10%. 13. The liquid crystal display device according to claim 12, wherein said T _s is 0.45 or less. 14. Display unit pixel and the T _s lateral relationship between the length Sz (m) _{is, T s × Sz / (300} × 10 -6) a ≦ 0.6 is according to claim 12, wherein Liquid crystal display. 15. The liquid crystal display device according to claim 12, wherein a relationship between the T _s and the brightness Br (cd / m ² ) is T _s × log (Br) ≦ 1.3. 16. The liquid crystal display device according to claim 12, wherein the relationship between T _s and contrast Cr is T _s × log (Cr) ≦ 1.2. 17. The liquid crystal display device according to claim 12, wherein the liquid crystal element is an active matrix type liquid crystal element having an active element for each pixel. 18. The liquid crystal display device according to claim 12, wherein the liquid crystal is a smectic liquid crystal having spontaneous polarization. 19. The liquid crystal is a nematic liquid crystal, wherein in the liquid crystal element, the liquid crystal has a pretilt angle at an interface with a substrate, and a liquid crystal molecule at a central portion of a liquid crystal layer in a normal direction of the substrate. Parallel to the normal direction,
13. The liquid crystal display device according to claim 12, which is in a bend alignment state. 20. The liquid crystal display device according to claim 12, wherein the minimum value of the second luminance is 0%.