JPS58123587A - Liquid crystal video display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Currently, liquid crystal displays are becoming the main type of flat display in many fields. A new and attractive application field for liquid crystal displays is liquid crystal video displays. Video displays are already commercially available as liquid crystal displays such as watches, clocks, etc.
counter.

Compared to displays for calculators, games, etc., the amount of information that must be displayed at once is orders of magnitude larger, and there are many problems in displaying that information quickly and reliably. It also requires some ingenuity.

Now, as liquid crystal video displays that are close to the level of practical use, there are the quadruple matrix method and the active matrix method. Of these, the quadruple matrix method is a method that uses technology that is an extension of the conventional high-duty time-division drive TN, F]IiM panel technology, and although it is advantageous in terms of cost compared to the active matrix method, it The display quality, such as ratio and number of pixels, is poor.

There are currently two types of active matrix systems that have reached a practical level. Both MOs for switching
8) A silicon substrate with the function of an active element integrated with transistors is used on one side of the liquid crystal panel substrate, but the operating method of the liquid crystal used is different; one uses the DSM (dynamic scattering mode) method and the other uses the DSM (dynamic scattering mode) method. ()H (guest/host) method.

Among these, the GH method is superior in terms of reliability such as power consumption, wide viewing angle, and life span, and currently seems to be the most promising liquid crystal video display in terms of display quality. However, since the GH method uses an expensive silicon substrate, the cost of the liquid crystal panel inevitably increases.

In contrast to these methods, another method that is expected to be used in future liquid crystal video displays is an active matrix method using thin film transistors (TFTs) and TN (twisted nematic) type liquid crystals. This method surpasses the GH active matrix method using a silicon substrate in terms of spring cost, screen size, contrast ratio, etc. Unfortunately, however, the voltage-contrast ratio characteristics of current liquid crystal panels using the TN method are generally steeper than those of the GH method. The steep voltage-contrast ratio characteristic of this RU type liquid crystal panel works advantageously when performing time-division driving.However, in the active matrix method, this steep characteristic is not required, but rather this characteristic This is disadvantageous in that it is difficult to express the necessary intermediate gradations in image display.

The present invention relates to a liquid crystal video display having a driving method that does not have these drawbacks. In other words, the intermediate gradations necessary for image display are not expressed analogously by the color density of the smallest pixel that makes up the screen, as has been done in the past, but by Divide it into several smaller dots (for example, 25
g) It incorporates a transistor in each pixel to express the color depth of the smallest pixel as the ratio of the number of lit dots and non-lit dots included in that pixel, and digitally expresses intermediate gradations. be. Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a diagram illustrating the principle of a method for expressing intermediate gray scales in a liquid crystal video display according to the present invention. Conventionally, the ON state (::1 state where no light passes through). In order to express a state (intermediate gradation) between the states (state where light passes), it is common to use a state where the desired amount of light passes in an analog manner.

FIG. 2 explains this state using a voltage-contrast ratio characteristic diagram of a liquid crystal panel. Liquid crystal displays using the active matrix method have the advantage of good display quality because they can achieve virtually the same duty ratio as static drive, but it is difficult to express intermediate tones using conventional methods. As long as the second
It had to be driven in the area shown in Figure -■. However, this region (■) is an unstable region in which the contrast ratio fluctuates greatly due to changes in viewing angle, temperature, etc., and therefore good display quality cannot be obtained. In particular, a TN type liquid crystal panel has a steep voltage-contrast ratio characteristic, so the viewing angle dependence and temperature dependence become large.

FIGS. 3 and 4 are diagrams showing the viewing angle dependence and temperature dependence of the voltage-contrast ratio characteristics of the TN liquid crystal panel, and the above-mentioned points are clear from these figures. However, in contrast to this, the liquid crystal video display of the present invention is shown in FIG.
Since this area does not need to be used, it is possible to take advantage of the advantage of using an active matrix method that essentially performs static driving. Let me list some of the advantages below.

(1) Since only two states, the ON state and the OFF state, are used, a large voltage margin can be obtained. ('VON
The difference between VOFF and VOFF can be made large. ) (2) Therefore, the restrictions on the drive voltage may be loose.

(3) Low temperature dependence.

(4) Low viewing angle dependence.

(5) Fast response because no cumulative response effect is used (6)
For the same reason, liquid crystal cells are highly reliable.

()) Even when expressing intermediate gradations, if we focus on a single dot, either VON or VOFF is applied, so
The response speed is the same when fully ON and completely OFF.

As described above, the liquid crystal video display of the present invention can display images with good display quality such as quick response and wide viewing angle by taking advantage of the advantages of static drive.

Furthermore, since the liquid crystal video display of the present invention includes finer dots in the smallest lj element constituting the screen, the degree of integration of the liquid crystal panel substrate is increased. Therefore, it seems likely that larger devices will become practical.

[Brief explanation of the drawing]

Figure 4: Principle diagram of the method for expressing intermediate gradations Figure 2: Voltage-contrast ratio characteristic diagram of liquid crystal panel Figure 3: TI type liquid crystal panel Figure 4 shows the viewing angle dependence of the voltage-contrast ratio characteristics of a TN type liquid crystal panel.Applicant: Suwa Seikosha Co., Ltd. Figure 4 55

Claims (1)

[Claims] In a liquid crystal video display, the intermediate gradation required for image display is determined by dividing the smallest pixel that makes up the screen into smaller dots, and then determining the ratio of the number of lit and non-lit dots included in the smallest pixel. A liquid crystal video display characterized by expressing contrast ratio.