JPH01180526A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory image quality scarcely having an uneven contrast in the whole area of an image display area by placing a dummy picture element group in the outside peripheral part of a display use picture element group and driving a liquid crystal existing thereon by a dummy signal being different from a video display signal. CONSTITUTION:At the outside of a display use picture element group 6, a dummy picture element group 7 of a picture element electrode group of vertical six columns and horizontal five rows is placed. In this state, an AC dummy signal is always applied continuously to a dummy picture element, and a liquid crystal on said picture element does not hold charge but always driven by an AC signal. In such a way, when the dummy picture element group 7 is driven by the AC signal, an uneven contrast is generated in a boundary of the dummy picture element group 7 and the display picture element group 6 after many hours, but since a transformation of a liquid crystal state in the boundary part is smooth, comparing with the case the outside periphery of the display picture element group 6 is a non-driving area, the uneven contrast is not generated for an extremely long period of time. In such a way, unevenness of the contrast can be prevented, and the display quality of the liquid crystal display device can be improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to the structure of a liquid crystal image display device.

[Conventional technology]

The structure of a conventional liquid crystal image display device, as shown in FIG. 2, is such that all the pixel electrodes arranged in a matrix are used as pixels for displaying an image.

[Problem to be solved by the invention]

However, in the prior art described above, the liquid crystal 4 present between the image display area 6 and the sealing material 30 is not driven, while the liquid crystal 4 present in the display pixel group 6 (image display area) is constantly driven. Therefore, the smooth transition of the liquid crystal circuit is not performed at the boundary between the liquid crystal that is not constantly driven and the liquid crystal that is constantly driven. Therefore, the driving state of the liquid crystal at the boundary portion changes compared to the driving state of the liquid crystal inside the image display area 6 which is sufficiently far away from the boundary portion.

On display, the contrast characteristics change at the periphery of the image display area 6 compared to the inside.

This situation is shown in FIG. It can be seen that the contrast characteristic 13 at the periphery of the image display area is shifted in the direction requiring more applied voltage compared to the contrast characteristic 12 at the center of the image display area, that is, the normal contrast characteristic 12. Figure 3 shows the characteristics of a method (normally black) in which the light transmittance is low when no voltage is applied, and the light transmittance gradually increases as the voltage is applied. In a section where the image is displayed using the normally black method, the peripheral area will be darker than the center area. Therefore, in the case of a method (/-Marie white) in which the light transmittance is high when no voltage is applied, the peripheral area becomes brighter than the center area. In either case, there is a problem in that contrast unevenness occurs between the periphery and the center, resulting in a significant deterioration in image quality.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its object is to provide a liquid crystal image display device that can obtain good image quality with little contrast unevenness over the entire image display area.

[Means to solve the problem]

In the liquid crystal image display device of the present invention, a pixel substrate in which pixel electrodes are arranged in a matrix and a counter substrate are held in parallel using a sealing material. i! In a liquid crystal image display device in which a liquid crystal is sealed between two substrates, a pixel electrode group not used for image display (dummy pixel group) is placed on the outer periphery of a pixel electrode group used for image display (display pixel group). and the liquid crystal present on the dummy pixel group is driven by an AC/DC or pulsating current signal (dummy signal) different from the drive signal (video display signal) for the liquid crystal present on the display pixel group. It is characterized by

〔Example〕

Embodiments of the present invention will be described below based on the drawings. 1st
Figure (a) shows a liquid crystal image display device according to the present invention, and outside the display pixel group 6 of the conventional liquid crystal image display device shown in FIG. row pixel i
A dummy pixel group 7 is formed by arranging a pole group. Further, FIG. 1(b) is a timing chart of a drive signal (video display signal) applied to one pixel in the display pixel group 6, and FIG. 1(c) is a timing chart of one pixel in the dummy pixel group 7. 5 is a timing chart of drive signals applied to pixels. Figure 4 (
λ) shows the change 10 in the voltage of the liquid crystal present on a pixel when the signal 8 (video display signal) in FIG. 1(b) is applied to that pixel. The figure shows that after a signal is applied to a pixel in the first frame, the liquid crystal on the same pixel gradually attenuates due to its own storage capacitance, but when the next signal is applied in the second frame, The previously applied signal voltage continues to be held until the signal voltage is applied. FIG. 4(b) shows a change in the voltage of the liquid crystal present on a pixel when the signal 9 (dummy signal) of FIG. 1(C) is applied to that pixel. As shown in the figure, an alternating current signal is constantly applied to the pixel, and therefore the liquid crystal on the pixel does not hold any charge and is always driven by the alternating current signal.

It is known from experience that if the liquid crystal does not hold any charge and is constantly driven by AC, contrast unevenness does not occur at the boundary with the non-driven area and at the center of the driven area. If a dummy pixel group is provided on the outer periphery of the 0 display lI pixel group and the dummy pixel group is driven with AC drive as described above, contrast unevenness will occur at the boundary between the dummy pixel group and the display pixel group for a long time. Although it occurs later, contrast unevenness does not occur for an extremely long period of time because the transition of the liquid crystal state at the boundary is smoother than when the outer periphery of the display pixel group is a non-driven region. Furthermore, when the dummy pixel group is driven with the same video display signal as the display pixel group, contrast unevenness occurs at the boundary between the dummy pixel group and the non-driven area on its outer periphery, and increases internally over time. It progresses toward the area of the display pixel group as well. When the same number of dummy pixel groups are provided, the time it takes for contrast unevenness to occur in the area of the display pixel group is longer than when the dummy pixel group is driven with AC as in the present invention. When driven with the same video display signal as the display element group, this is by far the longest, and therefore the lifespan of the liquid crystal image device can be greatly improved.

No matter what kind of alternating current signal is applied to the dummy pixel group, the effect will be exhibited as long as the liquid crystal does not retain charge.

Further, even if the liquid crystal retains the charge, the effect will be exhibited if the retention time is very short compared to the liquid crystal on the display pixel group. FIG. 5 shows an embodiment in that case. Figure 5(a)
is the signal applied to the display pixel group (video display signal), (b
) and (c) are examples of signals (dummy signals) applied to the dummy pixel group. (b) is a pulsating flow signal, and (C) is an alternating current pulse signal.

In the embodiment of the present invention, a dummy pixel group of 6 columns and 5 rows is provided, and although it is better to have a larger number, it is not necessary to use it unnecessarily because it greatly affects the screen size and cost of the liquid crystal display device. I can't afford to spend too much.

〔Effect of the invention〕

As described above, the present invention makes it possible to prevent contrast unevenness that occurs at the outer periphery of the display pixel group (image display area) of a liquid crystal image display device, which has been a problem in the past, and improves the display quality of the liquid crystal display device. This has the effect of significantly increasing lifespan.

[Brief explanation of the drawing]

FIG. 1(a) is a partial plan view showing an embodiment of the liquid crystal image display device of the present invention. FIG. 1(b) is an example of a timing chart of a video display signal of a liquid crystal image display device. FIG. 1(c) is an example of a timing chart of a dummy signal applied to a dummy pixel group of a liquid crystal image display device of the present invention. FIG. 2 is a partial plan view of a conventional liquid crystal image display device. FIG. 3 is a contrast characteristic diagram of the liquid crystal image display li fl. FIG. 4(a) is a diagram showing changes over time in the charge (voltage) of the liquid crystal when a video display signal is applied to the liquid crystal display device. FIG. 4(b) is a diagram showing the change over time in the charge (voltage) of the liquid crystal when a dummy signal is applied to the dummy pixel of the liquid crystal display device of the present invention. FIG. 5(a) is an example of a timing chart of a video display signal of a liquid crystal display device. FIG. 5(b) shows dummy pixels of the liquid crystal display device of the present invention,
An example of a timing chart of a dummy signal to be applied. FIG. 5(c) is an embodiment of a timing chart of a dummy signal applied to a dummy pixel of the liquid crystal display device of the present invention. FIG. 5(d) is an example of a timing chart of a dummy signal applied to a dummy pixel of the liquid crystal display device of the present invention. 0...Ground potential of liquid crystal 1...Pixel substrate 2...Counter substrate 3...Seal material 4...Liquid crystal 5...Pixel electrode 6...Display pixel group (image display area) 7...Dummy pixel group 8...Video display signal 9...Dummy signal 10...Charge of liquid crystal (i11 pressure) 11...Charge of liquid crystal (voltage) 12...Normal contrast Characteristic 13: Contrast characteristics of peripheral area Applicant: Seiko Epson Corporation Figure 1 Figure 3

Claims (1)

[Claims] In a liquid crystal display device in which a pixel substrate on which pixel electrodes are arranged in a matrix and a counter substrate are held in parallel using a sealing material, and a liquid crystal is sealed between the two substrates, a pixel electrode group used for pixel display ( A pixel electrode group (dummy pixel group) that is not used for image display is placed on the outer periphery of the display pixel group,
In addition, the liquid crystal present on the dummy pixel group receives a drive signal (video display signal) for the liquid crystal present on the display pixel group.
A liquid crystal display device characterized in that it is driven by an alternating current, direct current, or pulse wave signal (dummy signal) different from that of the liquid crystal display device.