JPH0362688A - liquid crystal display device - 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 The present invention relates to an image display system for a matrix type liquid crystal television, and more particularly to an image display system for a liquid crystal television in which the resolution of a displayed image is 6 times lower than the resolution of a television video signal.

Liquid crystals have been put into practical use as light-receiving display materials due to their electro-optic effect. Here, we will discuss methods for distributing signals to display bodies in accordance with the characteristics of liquid crystals when displaying images, especially video signals for television, regardless of differences in display characteristics due to liquid crystal materials. It is. FIG. 1 shows the display response characteristics of the liquid crystal to applied voltage.

FIG. 1A shows a voltage waveform applied between two electrodes sandwiching a liquid crystal.

Figure 1B shows the degree to which the liquid crystal changes optically in response to the applied voltage.The vertical axis of waveform B is the display contrast.In Figure 1, l is the rising response of the liquid crystal, and 2 is the falling response. In addition, although there are differences depending on the material of the liquid crystal, for voltage waveforms that are the same over time, such as alternating signals or pulse signals of the same frequency, the display contrast of the liquid crystal is generally proportional to the effective value of the applied voltage. Change proportionally.

Figure 2 shows an example of the configuration of a liquid crystal display panel, and shows a cross-sectional view of the panel. In Figure 6, 3 is glass, 4 is a common transparent electrode such as Nesa film,
5 is a liquid crystal, 6 is a plate facing the glass 3 and sandwiching the liquid crystal 5,
In this case, a circuit for driving the liquid crystal is included. As an example, 6 is made of a silicon crystal wafer. Reference numeral 7 denotes an electrode made of aluminum or the like, which together with the transparent electrode 4 on the glass 3 applies a voltage to the liquid crystal. 8, 9, and 10 correspond to each part of a transistor provided for each display pixel, 8 is a source, 9 is a gate, and 10 is a drain. The drain 10 is coupled to the electrode 7. Although the liquid crystal display panel according to the present invention is not limited to the configuration shown in FIG. 2, the following description will be made using FIG. 2 as an example.

FIG. 3 is an example of a liquid crystal drive circuit for the panel of FIG. 2. 13 is a video signal input, 11 is a synchronization signal separated from the video signal, and 12 is a circuit that generates a timing clock to be sent from the synchronization signal 11 to the liquid crystal display drive circuits 14 and 15. 14 is a data line drive circuit that samples the video signal 13 for each data line 19 and outputs it to each data line.

Reference numeral 15 denotes a gate line drive circuit for sequentially scanning the gate lines 18, and each main circuit is constituted by a shift register. 16 is a liquid crystal pixel, 17 is connected in series to the liquid crystal pixel, and is turned on and off according to the output of the gate line drive circuit 15.
The transistor is turned off and selectively applies the video signal output to the data line 19 by the data line drive circuit 14 to the electrode of each pixel 16. 20 represents the entire liquid crystal display screen (within the broken line), indicating that the screen is displayed in a matrix.

FIG. 4 shows a method of interlaced scanning in the screen configuration of a television video signal.

The rectangular frame in FIG. 4 represents the entire so-called television display screen. Each diagonally drawn line within the frame represents a horizontal scanning line, and the image within the frame is scanned and displayed for each scanning line, thereby displaying one screen of images as a whole. Scan line a, to a. Up to 6 are scanned according to the sequential numbers, 262.5 in the first half and 262.5 in the second half.
Books are arranged every other book on the same screen. The scanning direction is
This is done from left to right on the screen as shown by the arrow. At this time, the screen consisting of 252.5 lines in the first half is called the first field, the screen consisting of 262.5 lines in the second half is called the second field, and the screen consisting of 525 lines in both is called one frame. . In the case of television video signals, the first field,
The scanning time for both the second field was approximately 16.7m5e. ,
1 frame scanning time is approximately 33.3 m5ec.

FIG. 5 is an example showing sample points of a video signal corresponding to each matrix pixel when displaying video on a conventional matrix type liquid crystal display panel. FIG. 5 is an example in which the number of horizontal scanning lines is reduced to one-third.

In the figure, a. to a sat shows a portion of the scanning line in FIG. R,,R,,R,,R4,Rs
, Re , Rt , Ra and L+, Lg, L, , L, respectively represent a portion of the vertical and horizontal rows of the liquid crystal display matrix, so each pixel in the liquid crystal display has R+,
Ra, Rz,... and Ll, Lx, Ls,...
. . , and the video signal is sampled at the circle marked at each intersection in FIG. 5 and applied to the electrode of the corresponding pixel. At this time, the time required to display one screen on the liquid crystal display panel is about 33.3 m1ee, which is the same as the original video signal. Horizontal scanning in Figure 5! Ia
-0, as+s * As a method to reduce the number of scanning lines in a matrix type display panel where video signals such as ash4 and ass are not sampled and are not required on the liquid crystal display screen, it is possible to reduce the number of scanning lines by 2 1/3, 1/3.
1/4 and 1/5 are possible, and in addition to the method of setting sample points as shown in FIG. 5, there are also methods such as sampling only the first field and not sampling during the second field. However, in these methods, as mentioned above,
Among the original signals, some scanning lines are not applied to the liquid crystal display at all and are not displayed.Furthermore, due to the following reasons, the drive cycle time of each pixel is too long, which increases the circuit load. A peripheral circuit for one pixel in FIG. 3 is shown in FIG.

In the figure, 22 indicates a leakage resistance bone between the circuit board 6 and the drain electrode 10, and 23 indicates a leakage resistance between two electrodes sandwiching the liquid crystal. 21 is a capacitor provided in parallel with the liquid crystal.

Although the leakage resistance of 22.23 is extremely large, if the liquid crystal pixels are set small to improve image quality, the capacitance between the pixel electrodes will be reduced.For example, the capacitance of a 10μ thick liquid crystal is lXl0- ”F, and the resistance value at this time is 109Ω for FE type liquid crystal and 106Ω for DSM type liquid crystal.
If the 0 pixel size, which is approximately
The leakage resistance within the circuit, which is about 1×10-'gec in the 10-'mac and DSM types, is mainly due to the leakage of the transistor 17, and when light enters from the outside, the effective leakage resistance increases due to the photovoltaic effect. The value becomes even smaller. For this reason,
A capacitor 21 is provided in parallel with the liquid crystal 16. Since the frame period of the video signal is 33.3 ms*c, the period at which the display signal is newly distributed and applied to each pixel in the circuit shown in FIG. 3 is also 33,3 m,,e, and the voltage applied to each pixel is The time constant of the pixel including the circuit must be sufficiently larger than 33.3 m5ec because it must be maintained sufficiently during this time.The capacitor 21 is inserted in parallel with the liquid crystal for the above reason. The capacitor 21 is added to the capacity of the liquid crystal display itself, increasing the power consumption of one display panel.

In addition, liquid crystals are a mixture of organic compounds, and are known to show deterioration phenomena when driven with a steady DC voltage. Therefore, AC voltage driving is desirable, and it is said that it is better to reduce the DC component as much as possible. ing. Conventionally, liquid crystal displays mainly display characters such as numbers, and the signal level is 1 or 0.
(Since only the I! level was displayed, if a complementary output circuit is configured and the polarity of the signal is reversed at regular intervals, the DC component will effectively be zero except for circuit variations, resulting in a moving image with 0 gradation. When displaying , the signal level at a specific position within the screen changes frame by frame and is unspecified.

Therefore, it has not been possible to eliminate the DC component using conventional circuit systems.

The present invention aims to improve these drawbacks of the conventional methods, by reducing the capacitance of the capacitor 21 or eliminating it, thereby lowering the power consumption of the panel and making use of the original low power characteristics of a liquid crystal display. By compensating for the deterioration in image quality that occurs when the number of scanning lines of the video signal is reduced, and by bringing the screen response speed closer to the speed of the video signal of the original video signal, high-quality television images can be displayed on the LCD. It is intended to be played back on a display panel.

The method of the present invention will be explained below in sequence. Fig. 7 shows sample points of a video signal according to the present invention and a part of the configuration of a display by a liquid crystal panel. a@Q
, as+, a@x is the horizontal scanning line of the first field, a
s+a+as+a+8m+4 is the horizontal scanning line of the second field. I2+, R-*, and β indicate a part of the horizontal pixel arrangement in the matrix pixel configuration of the liquid crystal display panel; similarly, r+*r
x - r z * r 4 indicates the - part of the vertical pixel arrangement among the matrix pixels in the liquid crystal display panel, 24
．． The rectangle 25 indicates two pixels arranged in a pixel column 1° apart. In contrast to the conventional video signal sampling method shown in FIG. 5, in the present invention, the dots marked with circles on each scanning line in FIG. 7 are sampled and displayed. That is, when sampling and displaying a signal at a point corresponding to a corresponding pixel from a television video signal, for example, for pixel 24 in the liquid crystal display screen, the signal on the scanning line allO in the first field of the video signal is sampled and displayed. Sample the signal at point 27 and then scan line a in the second field.
By sampling the signal at point 26 on m+2, the first
27 signals are displayed in the field, and 26 signals are displayed in the second field. The other pixels perform display in the same manner. As a result, the pixels on line 2 in the liquid crystal display panel cause the video signal to be displayed on scanning line a. and a3+
The image on i is repeatedly displayed every field, and all other scanned areas are also displayed every half frame. Therefore, even if the number of pixel lines in the liquid crystal display panel becomes half of the original number of television signal scanning lines, images on all scanning lines can be displayed by the liquid crystal. . More precisely, an image is displayed according to the effective voltage waveform of the first field signal level and the second field signal level that are repeatedly applied to each pixel in accordance with the response characteristics of the liquid crystal shown in Figure 1. As a whole, the first field screen and the second field screen are superimposed and the averaged screen is displayed on the LCD panel with zero image quality.

It approaches the original video signal and is significantly improved compared to conventional methods. In particular, the mosaic-like prickliness that conventionally occurs when only half of a scanning line is erased is eliminated, and a soft image quality can be obtained.

In addition, the repetition period for writing signals to each pixel is in l-field units, that is, half a frame period, which is different from the conventional method.
It becomes 1/1. A capacitor 21 provided to compensate for the leakage current of each pixel's own circuit and hold the signal applied to the liquid crystal.
Therefore, the value of 1/2 of the conventional method is sufficient,
The burden of providing a large capacitor within a small pixel size is halved. As a result, the output capacitance of the video amplifier for supplying video signals to the terminal 13 in the liquid crystal display panel can be satisfied with a smaller circuit than conventional amplifiers because the load capacitance of the pixels in the panel is halved, and the power consumption of the amplifier can be reduced. Can be reduced. Furthermore, since the screen displayed on the LCD panel is rewritten in units of half a frame of the original video signal across the entire screen, the responsiveness of the video screen is improved compared to the conventional case where rewriting takes one frame. This means that the poor response of the video screen due to the synergistic effect of the response delay itself and the time delay required for rewriting will be halved.

In particular, the display system according to the present invention reduces the number of vertical pixel arrays on the screen to half the number of television video signal scanning lines. Or the effect is great when set to 1 of an even number bone, such as 1/4, etc.
Also, regarding the above explanation.

Although the case of FIG. 3 has been taken as an example, the same effect can be expected even if another drive circuit system is used, and is not beyond the scope of the present invention. is sandwiched between a plate having electrode groups arranged in an It can be driven in accordance with field signals and has similar features.

The present invention also provides more effective AC drive compared to the conventional system. As mentioned above, in the case of a moving image signal with one gradation, the signal level is unstable, which is a problem with the conventional method.

In the present invention, attention is paid to the speed of the moving image, and the most effective AC driving method is used, and the DC component is considered to be substantially negligible. That is, the polarity of the video signal is inverted every field and applied to each pixel. Since the first field signal and the second field signal interlace each other and form l-frame video, the seventh
In the figure, 26 and 27 are located adjacent to each other within the same frame. Similarly, signals are sampled over the entire screen so that the sample points on the first and second fields are adjacent to each other, and are applied and displayed to the same pixels on the matrix liquid crystal panel. The difference between the signal in the first field and the signal in the second field applied to each pixel has the minimum relationship in terms of screen resolution in a still image. This is because the two sample points are adjacent. Also, by sampling in a time unit that is half the time of sampling every l frame during a video, the amount of displacement of the signal between the first field and the second field due to the movement of the image is This is approximately one-half of the amount of signal displacement between the first frame and the second frame. Therefore, in the present invention, the video signal of the first field and the video signal of the second field are applied to the same pixel, and at the same time, the signal applied to the pixel in the first field and the signal applied to the pixel in the second field are The potential polarity is set to be symmetrical with respect to the potential of the common electrode facing the pixel electrode with the liquid crystal in between. As a method for realizing this, for example, two types of video output amplifiers with opposite polarities of video signals may be provided, and their respective outputs may be switched in units of one field to selectively apply the video signals.

By inverting the signal polarity in this manner, the DC component of the signal applied to the liquid crystal becomes a value that can be effectively ignored, both in the long term and in the short term (one frame time). Thereby, the deterioration phenomenon caused by direct current voltage driving of the liquid crystal can be avoided in the most effective manner.

[Brief explanation of drawings]

Figure 1 is a diagram showing the response characteristics of liquid crystal to applied voltage, Figure 2 is a diagram showing an example of a cross section of a liquid crystal display panel, Figure 3 is a diagram showing an example of a drive circuit diagram, and Figure 4 is a diagram showing a television screen. Figure 5 is a diagram showing the above scanning line, Figure 5 is a diagram showing a conventional image sample method for a liquid crystal panel, Figure 6 is a diagram showing a part of the circuit of Figures 3 and 4, and Figure 7 is a diagram showing a method of sampling images to a conventional liquid crystal panel. Video sample method % formula% 15...Matrix electrode drive circuit...Liquid crystal pixel 25...Matrix pixel or more

Claims (2)

[Claims] (1) The first frame of the 1-frame video signal to be interlaced scanned
field video signal and second field video signal,
A liquid crystal television display system characterized by repeatedly applying voltage to the same pixel on the liquid crystal display screen. (2) The liquid crystal television display system according to claim (1), wherein the polarity of the video signal applied to the liquid crystal is different between the applied signal of the first field and the applied signal of the second field. (3) Claim (1) characterized in that the video signals are repeatedly applied to the same liquid crystal pixel as a pair of two adjacent horizontal scanning signals of the first field and the second field in a superimposed manner. LCD TV display method.