JPH06208343A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device capable of realizing the image display of an uniform and high contrast-ratio while realizing the low consumption of a power by avoiding the boosting of a scanning voltage and a display signal voltage, CONSTITUTION:In this device, the write-in of a liquid crystal impression voltage VLC from the beginning of a scanning selection period of time until a sufficient value making a pixel 'ON'-state is obtained is performed quickly in a short time since a preliminary voltage is charged to liquid crystal layers 15 of the pixel while avoiding the ON state of the pixel before the beginning of the scanning selection period of time by impressing the voltage of a voltage level V5 less than the scanning selection voltage level V3 during at least one scanning selection time just before one scanning selection period of time by a scanning electrode driving circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using a non-linear element as an active element for switching a pixel portion.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as information processing devices such as word processors and personal computers, and display devices such as televisions and projection televisions. Liquid crystal display devices for such applications can be roughly classified into two types, a simple matrix type and an active matrix type.

The simple matrix method is widely used because it has a simple structure and a manufacturing method with high yield has already been established. In addition, the ST having a steep electro-optical threshold characteristic of the liquid crystal itself is particularly suitable for displaying large-capacity image information in information processing devices and high-definition televisions.
A liquid crystal display device using N (Super Twisted Nematic) type liquid crystal is used.

However, in such an STN type liquid crystal display device, the effective value of the liquid crystal applied voltage between the display portion (on-pixel) and the non-display portion (off-pixel) is driven by the optimum bias method or the like. Since the voltage cannot be higher than a specific voltage and the electro-optical threshold value characteristic of the STN liquid crystal itself is steep as described above, the contrast between the display portion (on-pixel) and the non-display portion (off-pixel) is high. Ratio is the number of scanning lines
It is not sufficient even in the case of a matrix display of about 200 lines, and the contrast ratio is fatally low in a large-scale display with 500 or more scanning lines.
In addition, the response speed is as slow as about 100 ms to 300 ms, and there is a problem that it is unsuitable for applications such as a display terminal of a VGA-compatible computer.

In place of the simple matrix type liquid crystal display device having such drawbacks, a so-called active matrix type liquid crystal display device having a switching element for directly switching control of application of a drive voltage to each pixel has been developed. Has been done. In this active matrix type liquid crystal display device, T is mainly used as a switching element.
FT (Thin Film Transistor) is adopted, and it has features such as good viewing angle characteristics, fast response speed, and high contrast. Various materials such as cadmium selenide, tellurium, single crystal silicon, and amorphous silicon have been proposed as semiconductor materials for forming the TFT.

However, in the active matrix type liquid crystal display device using such a TFT, the manufacturing cost is high because the TFT or the like requiring a complicated microfabrication process must be formed over a large area without defects. There is an inconvenience that it is not easy to apply to a large display panel.

Therefore, there has been proposed an active matrix type liquid crystal display device using a non-linear element such as a diode having a non-linear current-voltage characteristic as a switching element replacing a TFT which requires such a complicated microfabrication process. Some are put to practical use. Examples of such a non-linear element include a diode type element, a varistor using zinc oxide, and an MIM (Metal-insulator-) that holds an insulator between two electrodes made of metal.
There are a metal type and a type in which a semiconductive layer is sandwiched between two electrodes made of metal (MSI).

In particular, in the case of using the MIM element, when the liquid crystal applied voltage is applied between the electrodes which are opposed to each other with the liquid crystal layer interposed therebetween, the charging is performed with a small time constant and the liquid crystal applied voltage is not applied. , Is discharged with a large time constant. Therefore, if the display signal voltage exceeds the threshold voltage of the MIM element in the scan selection period, the voltage is written in the equivalent capacitance (liquid crystal capacitance CLC) of the liquid crystal layer of the corresponding pixel even in a short period, and the voltage once written is a simple matrix type. As described above, it is held for a sufficient time even in the scan non-selection period without being rapidly reduced. As a result, it is possible to increase the ratio of the effective value of the liquid crystal applied voltage of the ON pixel to the effective value of the liquid crystal applied voltage of the OFF pixel, as compared with the case of the simple matrix type liquid crystal display device, and thus display with a high contrast ratio is performed. Can be realized.

[0009]

However, there is a problem that the display performance of a two-terminal type liquid crystal display device represented by a liquid crystal display device using such an MIM element largely depends on a driving method. That is, the liquid crystal display device is normally driven by frame inversion, but in the frame inversion drive,
The ratio of the polarities of the voltages written to the pixels in the scanning non-selection period is different between when only one pixel on one signal line is displayed and when all pixels are displayed. As a result, the effective value of the voltage applied to the liquid crystal (temporal average of the voltage held in the liquid crystal layer) varies. As a result, there is a problem in that the display quality deteriorates due to variations in contrast between display patterns or display positions.

As a measure for solving such a problem, there is, for example, the technique disclosed in Japanese Patent Publication No. 62-6210. This divides one scan selection period of the scan electrode into at least a first scan period and a so-called fine scan selection period, and sets the scan voltage to the scan selection voltage level in one period and the scan non-scan period in the other period. Non-linear by a driving method in which the selection voltage level is set, and the display signal voltage is set to the display selection level or the display non-selection level corresponding to the image information in the first period, and is set to the inversion level of the first period in the second period. This is a technique of driving a liquid crystal display device using elements. According to such a driving method, it is possible to realize image display with a uniform contrast without actually depending on the display pattern.

However, in such a driving method,
Since the time to apply the scan pulse at the scan selection voltage level is only half the normal one scan selection period, which is short, the scan voltage and the display signal voltage must be set in order to ensure the writing of sufficient voltage for display. There is a problem that the liquid crystal applied voltage, which is the superimposed voltage of, must be increased. And in recent years, as mentioned above, the number of pixels has increased significantly,
Furthermore, since the one-scan selection period itself is shortened, this problem is becoming more difficult to solve.

The present invention has been made to solve such a problem, and its object is to realize low power consumption while avoiding increasing the scanning voltage and the display signal voltage.
An object of the present invention is to provide a liquid crystal display device capable of realizing uniform and high-contrast image display.

[0013]

A liquid crystal display device according to the present invention comprises a first substrate on which a scanning electrode is formed, a pixel electrode and a nonlinear element connected to the pixel electrode and having a non-linear electric resistance characteristic. A second substrate having a signal electrode connected to a non-linear element and arranged to face the first substrate;
A liquid crystal layer that is enclosed between the substrate and the second substrate and is sandwiched between the opposing scanning electrodes and pixel electrodes to form pixels, and scanning electrode driving means that applies a scanning voltage to the scanning electrodes. In a liquid crystal display device having a signal electrode driving means for applying a display signal voltage to the signal electrode, one scanning selection period of the scanning electrode is divided into at least a first period and a second period, and in one of the periods. The scan selection voltage level is set and the scan non-selection voltage level is set in the other period, and at least immediately before the one scan selection period.
The capacity of the liquid crystal layer of the pixel is reserved by avoiding turning on the pixel when the voltage is smaller than the scan selection voltage level and overlaps with the display signal voltage over one scan selection time. Scan electrode driving means for applying a scan voltage to the scan electrodes at a pre-charge voltage level for charging; and a display selection level or a display non-selection level corresponding to image information in the first period, and the second In the period, when the first period is the display selection level, the display non-selection level is set, and when the first period is the display non-selection level, the display selection level is set. And means.

Regarding the magnitude of the preliminary voltage level of the scanning voltage, for example, in the case of 1 / N bias driving, the lower limit is 1/3 of the scanning selection voltage level in the scanning selection period, and (N-3) ) / (N-1) is the upper limit. This is because if the magnitude of the preliminary voltage level is 1/3 or less of the scan selection voltage level in the scan selection period, there is no effect, and if it is (N−3) / (N−1) or more, no pixel is displayed as a non-display pixel. This is because there is a risk that a liquid crystal application voltage that turns on may be applied, which may cause shadows.

As the non-linear element, a diode element, a varistor element using zinc oxide, an MIM element in which an insulator is sandwiched between two electrodes made of metal, or two electrodes made of metal are used. It is possible to use an MSI element or the like in which a semiconductive layer is sandwiched.

[0016]

In the liquid crystal display device of the present invention, one scanning selection period is divided into at least two periods, for example, the first half is set to the scanning voltage of the scanning selection voltage level and the latter half is set to the scanning non-selection voltage level, while the first During the period, the display selection level or the display non-selection level is set according to the image information, and the second
In the period, the display pattern is applied by applying the display signal voltage that is the display non-selection level when the first period is the display selection level and the display selection level when the first period is the display non-selection level, to the display pattern. It is possible to suppress variations in the effective value of the liquid crystal applied voltage depending on the.

Further, immediately before such a scan selection period, by applying a scan voltage having a voltage level smaller than the scan selection voltage level to the scan electrodes for at least one scan selection time, before entering the scan selection period. Since the preliminary voltage is charged to the equivalent capacitance of the liquid crystal layer of the pixel while avoiding turning the pixel on, the holding voltage of the liquid crystal layer becomes a sufficient value for driving the pixel after entering the scan selection period. It is possible to quickly charge up to the equivalent capacity in a short time.

As a result, even if the liquid crystal applied voltage is not increased, it is possible to suppress the variation in the effective value of the liquid crystal applied voltage depending on the display pattern and realize a uniform image display with a high contrast ratio.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing the structure of the liquid crystal display device of the present invention, and FIG. 2 is an enlarged diagram showing the liquid crystal display panel used therein.

This liquid crystal display device includes a MIM type liquid crystal display panel 1, a scanning electrode driving circuit 3, and a signal electrode driving circuit 5.
Its main part is composed of and.

The MIM type liquid crystal display panel 1 includes the scanning electrodes 7
A pixel electrode 9 arranged opposite to the pixel electrode 9; a MIM element 11 connected to the pixel electrode 9 in parallel with each other; and a signal electrode 13 connected to the MIM element 11.
And a liquid crystal layer 15 sandwiched between the pixel electrode 9 and the scanning electrode 7. In terms of an equivalent circuit, each pixel forms a liquid crystal capacitor (C _LC ).

As shown in FIG. 2, T is placed on the glass substrate 17.
The signal electrode 13 made of a and the lower electrode 19 of the MIM element 11 are formed. An insulator 21 by anodic oxidation is formed on the upper surface of the lower electrode 19. Further, an upper electrode 23 is formed thereon, and the MIM element 11 having a nonlinear resistance value characteristic is formed. Then, the pixel electrode 9 is formed from a transparent conductive film such as ITO,
It is connected to the upper electrode 23 of the MIM element 11. An alignment film 25 is formed so as to cover almost the entire surface thereof, and a matrix array substrate 27 is formed. On the other hand, the scanning electrode 7 made of a transparent conductive film such as ITO is formed on the glass substrate 29 so as to face the matrix array substrate 27 so as to be orthogonal to the signal electrode 13 and face the pixel electrode 9. An alignment film 31 is formed so as to cover almost the entire surface thereof, and a counter substrate 33 is formed. The matrix array substrate 27 and the counter substrate 3
3 and 3 are opposed to each other with a gap (cell gap) of 5 μm, and the liquid crystal layer 15 is enclosed and sandwiched in the gap. And one pixel electrode 9 and MI connected to this
M element 11 and scanning electrode 7 facing this pixel electrode 9
And a liquid crystal layer 15 sandwiched between them forms one pixel. The liquid crystal display panel of this embodiment has a pixel number of 128 × 128 dots. The pixel size is 200μ
The size is m square.

FIG. 3 is a diagram showing the scanning voltage and the display signal voltage used in the liquid crystal display device of this embodiment. FIG. 3A shows a voltage waveform applied to the signal electrode 13 by the signal electrode drive circuit 5 when a display is selected (so-called pixel on-display), and FIG. 3B shows a voltage waveform when the display is not selected (so-called). 7 shows a voltage waveform when a pixel is displayed off. Further, in FIG. 3C, the scan electrode drive circuit 3 has the scan electrode 7
3 shows the voltage waveform of the scanning voltage applied to.

As shown in FIGS. 3 (a) and 3 (b), one scanning selection period (one line scanning period) is divided into at least a first period and a second period, and image information is converted into image information in the first period. Correspondingly, display selection level V1 or display non-selection level V
2 and the display signal voltage Vx in the second period is the display non-selection level V2 when the first period is the display selection level V1 and is the display selection level V1 when the first period is the display non-selection level V2. Is applied to the pixel electrode 9 via the signal electrode 13 by the signal electrode drive circuit 5. As a result, it is possible to suppress variations in the effective value of the liquid crystal applied voltage applied to each pixel on the same signal electrode during the scan non-selection period in one frame and make it approximately constant. It is possible to suppress variations in the contrast.

Moreover, as shown in FIG. 3C, the scan voltage is set to the preliminary voltage level V5 which is a voltage level smaller than the scan selection voltage level V3 for at least one scan selection time immediately before the scan selection period. The scan electrode drive circuit 3 applies the voltage to the scan electrodes 7. The scan voltage applied to the scan electrode 7 during the first period of the scan selection period is set to the scan selection voltage level V3, and the scan voltage applied to the scan electrode 7 during the second period of the scan selection period is not scanned. The selected voltage level is V4. By doing so, the liquid crystal layer 15 of the pixel is charged with the preliminary voltage while avoiding turning on the pixel before entering the scan selection period. Liquid crystal capacitance CLC until the holding voltage of the layer 15 reaches a value sufficient for pixel driving
Can be quickly charged in a short time.

In this way, even if the liquid crystal applied voltage (that is, the superimposed voltage of the scanning voltage and the display signal voltage) is not increased, the variation in the effective value of the liquid crystal applied voltage depending on the display pattern is suppressed and the high contrast ratio is achieved. A uniform image display can be realized.

In the liquid crystal display device of this embodiment, the duty ratio was 1/450 and the bias ratio was 1/9. The preliminary voltage level V5 is the scan selection voltage level V during the scan selection period.
The voltage was set to 5/8 times the voltage of 3.

FIG. 4A is a waveform diagram showing a liquid crystal applied voltage applied to one pixel of the liquid crystal display device of this embodiment, and FIG. Hold voltage VLC held (that is, effective value of liquid crystal applied voltage)
It is a waveform diagram showing. As shown in FIG. 4, the liquid crystal layer 1
The holding voltage VLC of No. 5 can be reduced in variation in its value between the ON display and the OFF display even during the scan non-selection period.

As a result, as shown in the liquid crystal applied voltage / contrast characteristic curve of FIG. 5, in the case of the present embodiment shown by the solid line, the liquid crystal applied voltage giving the peak of the contrast ratio is shown by the broken line of the conventional MIM type. It was possible to reduce the voltage by about 2V as compared with the case of the liquid crystal display device.

The preliminary voltage level V of the above scanning voltage
In the present embodiment, the magnitude of 5 is 5/8 times the scan selection voltage level V3 (V5 = V3 * (5/8)), but the present invention is not limited to this value. Not limited. For example, in the case of 1 / N bias driving, it is desirable to set 1/3 of the scan selection voltage level V3 in the scan selection period as the lower limit and (N-3) / (N-1) as the upper limit.
This is because if the magnitude of the preliminary voltage level V5 is 1/3 or less of the scan selection voltage level V3 in the scan selection period, there is no effect, and if it is (N-3) / (N-1) or more, it is applied to the display non-selected pixels. This is because there is a possibility that a liquid crystal application voltage for turning on a pixel is applied, which may cause shadows. Also in this embodiment, since N = 9, the value of the above formula (N-3) / (N-1) is 6/8,
V5 is the above condition V3 × (⅓) ≦ V5 ≦ (N−
Needless to say, the value is set to satisfy 3) / (N-1).

Also, in this embodiment, MI is used as the non-linear element.
Although the example using the M element 11 is shown, the present invention is not limited to only the MIM element as the nonlinear element used. Besides, a diode element, a varistor element using zinc oxide, an MIM element, an MSI element having a semiconductive layer sandwiched between two electrodes made of metal, and the like can be used.

In addition, it goes without saying that various changes can be made to the material forming each part of the liquid crystal display device of the present invention without departing from the scope of the present invention.

[0034]

As is clear from the detailed description above, according to the present invention, an image having a uniform and high contrast ratio is realized while realizing low power consumption while avoiding increasing the scanning voltage and the display signal voltage. A liquid crystal display device that can realize display can be provided.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a structure of a liquid crystal display panel of the liquid crystal display device of the present invention.

FIG. 3 is a diagram showing an example of a scanning voltage waveform and a display signal voltage waveform of the liquid crystal display device of the present invention.

FIG. 4 is a diagram showing a liquid crystal applied voltage waveform and a holding voltage waveform of the liquid crystal display device of the present invention.

FIG. 5 is a diagram showing a liquid crystal applied voltage / contrast characteristic curve of a liquid crystal display device of the present invention in comparison with a case of a conventional liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display panel 3 ... Scan electrode drive circuit 5 ... Signal electrode drive circuit 7 ... Scan electrode 9 ... Pixel electrode 11 ... MIM element 13 ... Signal electrode 15 ... Liquid crystal layer

Claims (1)

[Claims] 1. A first substrate having scan electrodes formed thereon, a pixel electrode, a non-linear element connected to the pixel electrode and having non-linear electric resistance characteristics, and a signal electrode connected to the non-linear element. A pixel is formed by being sandwiched between a second substrate arranged to face the first substrate and the scanning electrode and the pixel electrode sealed between the first substrate and the second substrate and facing each other. In a liquid crystal display device having a liquid crystal layer, a scanning electrode driving unit that applies a scanning voltage to the scanning electrodes, and a signal electrode driving unit that applies a display signal voltage to the signal electrodes, one scanning selection period of the scanning electrodes is set. It is divided into at least the first period and the second period, and the scan selection voltage level is set in one of the periods and the scan non-selection voltage level is set in the other period, and at least one scan is selected immediately before the one scan selection period. A spare for precharging the capacitance of the liquid crystal layer of the pixel while avoiding turning on the pixel when the voltage level is smaller than the scan selection voltage level and overlapped with the display signal voltage over time. Scan electrode driving means for applying a scan voltage at a charge voltage level to the scan electrodes; a display selection level or a display non-selection level corresponding to image information in the first period, and the display period in the second period. Signal electrode driving means for applying a display signal voltage to the signal electrode when the first period is the display selection level and when the first period is the display non-selection level and when the first period is the display non-selection level. A liquid crystal display device comprising: