JPH0412072B2 - - Google Patents

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 lower than the resolution of a television video signal.

Liquid crystals have been put to practical use as light-receiving display bodies due to their electro-optic effect. Here, we will discuss methods for distributing signals to display bodies in accordance with the characteristics of general liquid crystals when displaying images, especially video signals for television, regardless of the differences in display characteristics depending on the material of the liquid crystal. 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.

FIG. 1B shows the degree to which the liquid crystal optically changes depending on the applied voltage, and the vertical axis of waveform B represents the display contrast. In the figure, 1 indicates the rising response of the liquid crystal, and 2 indicates the falling response. Additionally, although there are differences depending on the material of the liquid crystal, for voltage waveforms that are the same over time, for example, alternating signals or pulse signals of the same frequency, the display contrast of the liquid crystal will generally vary with respect to the effective value of the applied voltage. Change proportionally.

FIG. 2 shows an example of the structure of a liquid crystal display panel, and shows a panel sectional view. In the figure, 3 is a glass, 4 is a common transparent electrode such as a Nesa film, 5 is a liquid crystal, and 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 mounted. As an example, assume that 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. Drain 10 is coupled to electrode 7. Although the liquid crystal display panel according to the present invention is not limited to the configuration shown in FIG.
The following explanation 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 to the liquid crystal display drive circuits 14 and 15 from the synchronization signal 11. 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 a transistor that is connected in series to the liquid crystal pixel and turns ON and OFF according to the output of the gate line drive circuit 15; the video signal is output to the data line 19 by the data line drive circuit 14; each pixel 16
selectively applied to the electrodes. Reference numeral 20 indicates the entire liquid crystal display screen section (inside the broken line area), 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. scanning line a ₁
The images from A to _A525 are scanned sequentially according to the numbers, and the first half 262.5 lines and the second half 262.5 lines are arranged every other line on the same screen. The scanning direction is from left to right on the screen as indicated 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. For television video signals, the scanning time for both the first and second fields is approximately 16.7 m _se
c , the scanning time for one frame is approximately 33.3 m _sec .

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 ₅₀ to a ₃₁₇ indicate a portion of the scanning line in FIG. 4. R ₁ , R ₂ , R ₃ , R ₄ , R ₅ ,
R ₆ , R ₇ , R ₈ and L ₁ , L ₂ , L ₃ , L ₄ represent portions of the vertical and horizontal rows of the liquid crystal display matrix, respectively. Therefore, each pixel in the liquid crystal display has R ₁ , R ₂ ,
Located at the intersection of R ₃ , ... and L ₁ , L ₂ , L ₃ , ...,
The video signal is sampled from the circle marked at each intersection in FIG. 5, and is 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 _msec , the same as the original video signal. Horizontal scanning line a ₅₀ in FIG.
Video signals such as a ₃₁₃ , a ₃₁₄ , and a ₅₂ are not sampled and do not appear on the liquid crystal display screen at all. In a matrix display panel, the number of scanning lines can be reduced by one-half, one-third, one-fourth, one-fifth, etc. of the original signal, as shown in Figure 5. In addition to the method of setting points, 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, some scanning lines are generated in the original signal that are not applied to the liquid crystal display at all. Furthermore, for 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 the leakage resistance between the circuit board 6 and the drain electrode 10, and 23 indicates the leakage resistance between the two electrodes sandwiching the liquid crystal. 21 is a capacitor provided in parallel with the liquid crystal. Although the leakage resistances 22 and 23 are extremely large, if the liquid crystal pixels are set small in order to improve image quality, the capacitance between the pixel electrodes becomes small. For example, the capacity of a 10μ thick liquid crystal is 1
The resistance value is about 1×10 ^-10 F per cm ² , and the resistance value is FE
It is about 10 ⁹ Ω for a type liquid crystal, and 10 ⁶ Ω for a DSM type liquid crystal.
If the pixel size is 100μ square, the capacitance is 1×
10 ^-14 F, resistance 10 ¹³ Ω, and 10 ¹⁰ Ω, respectively. Therefore, the time constant of the liquid crystal pixel is 1×10 ^-1 _sec for the FE type.
The DSM type takes about 1×10 ^-4 _sec . The in-circuit leakage resistance is mainly due to the leakage from the transistor 17, and when light enters from the outside, the effective leakage resistance value further becomes smaller due to the photovoltaic effect. For this reason, a capacitor 21 is provided in parallel with the liquid crystal 16. Since the frame period of the video signal is 33.3m _sec , the third
In the circuit shown in the figure, the cycle at which display signals are newly distributed and applied to each pixel is also 33.3 m _sec , and the voltage applied to each pixel must be maintained sufficiently during this period, so the self-constant number of pixels including the circuit is 33.3 m _sec. must be sufficiently larger. The capacitor 21 is inserted in parallel with the liquid crystal for the above reasons. The capacitor 21 is added to the capacity of the liquid crystal display itself, increasing the power consumption of the 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, for liquid crystal displays,
Characters such as numbers were mainly displayed, and the signal level was only a binary level display of 1 or 0. Therefore, by configuring a complementary output circuit and reversing the polarity of the signal at regular intervals, it was effectively possible to display direct current. The components are zero except for circuit variations. When displaying a moving image with gradation, the signal level at a specific position within the screen changes frame by frame and is unspecified. Therefore, it was unthinkable to eliminate the DC component using conventional circuit systems.

The present invention aims to improve these drawbacks of the conventional methods, by reducing or eliminating the capacitance of the capacitor 21, reducing the power consumption of the panel, and making use of the original low power characteristics of a liquid crystal display. By ensuring that the image quality does not deteriorate when the number of scanning lines of the video signal is reduced, and by bringing the response speed of the screen closer to the speed of the original video signal, high-quality television images can be displayed on the LCD. The purpose is to reproduce it on a display panel.

The system of the present invention will be sequentially explained below.

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 ₅₀ , a ₅₁ , and a ₅₂ are horizontal scanning lines of the first field, and a ₃₁₂ , a ₃₁₃ , and a ₃₁₄ are horizontal scanning lines of the second field. l ₁ , l ₂ , and l ₃ indicate a part of the horizontal pixel arrangement in the matrix pixel configuration of the liquid crystal display panel. Similarly, r ₁ , r ₂ , r ₃ , r ₄ are
A part of the vertical pixel arrangement of the matrix pixels in the liquid crystal display panel is shown. Squares 24 and 25 indicate two pixels arranged on the _l1 pixel column. 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 a liquid crystal display screen, a signal on scanning line a ₅₀ in the first field of the video signal is sampled and displayed. sample the signal at point 27, and then sample the signal at point 26 on scan line a ₃₁₂ in the second field.
By sampling the signals, the first field displays 27 signals, and the second field displays 27 signals.
6 signal is displayed. Display is performed similarly for other pixels. As a result, the pixels on line _l1 in the liquid crystal display panel cause the video signal to
The images on A ₅₀ and A ₃₁₂ will be displayed repeatedly every field, and all other scanning lines will also be 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. Become. More precisely, according to the response characteristics of the liquid crystal shown in FIG. The screen of the first field and the screen of the second field are weighed as a whole, and an averaged screen is displayed on the liquid crystal panel. The image quality approaches the original video signal and is significantly improved compared to conventional methods. In particular, in the past, the scanning lines were simply
The mosaic-like harshness that occurs when only 1/2 of the image is erased is eliminated, and a soft image quality is obtained.

Also, the repetition period for writing signals to each pixel is
The period is one field unit, that is, half a frame, which is half of that of the conventional method. The value of the capacitor 21, which is provided to compensate for the leakage current of the circuit within each pixel and hold the signal applied to the liquid crystal, is therefore only half that of the conventional method, and the capacitance can be reduced within a small pixel size. The burden of installing a large capacitor 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 by 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 the time of one frame. , the poor response of the moving image screen due to the synergistic effect of the response delay of the liquid crystal itself and the time delay required for rewriting will be halved.

In particular, the display system of the present invention is effective when the number of vertical pixel arrays on the screen is set to an even number, such as half or quarter of the number of television video signal scanning lines. big. Also, regarding the above explanation,
Although the case of FIG. 3 has been taken as an example, the same effect can be expected even with another drive circuit system, and this is not beyond the scope of the present invention. For example, in a so-called dynamic driving method, a liquid crystal is sandwiched between a plate having electrode groups arranged in an X arrangement and a plate having electrode groups arranged in a Y arrangement perpendicular to this electrode group, and the liquid crystal is sequentially driven in a time-division manner. Similarly, driving corresponding to each field signal can be performed every half frame, and has the same feature.

In the present invention, furthermore, compared to the conventional method,
This provides more effective AC drive. As mentioned above, in the case of a moving image signal with 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 performed, and the DC component is considered to be substantially negligible. That is, the polarity of the video signal is inverted for each field and applied to each pixel. Since the signal of the first field and the signal of the second field interpolate each other to form one frame of video, 26 in FIG.
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 field and the second field are adjacent to each other, and are applied and displayed to the same pixel 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 the resolution of a stationary screen. This is because the two sample points are adjacent. Also, even if it is in a video, the sample rate is half that of sampling every frame.
By sampling in time units of . 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 video signal of the second field are applied to the same pixel.
The potential polarity of the signal applied to the pixel in the field is set to be symmetrical with respect to the potential of the common side 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 and selectively applied.

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 that accompanies direct current voltage driving of liquid crystal can be avoided in the most effective manner.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the response characteristics of liquid crystal to applied voltage, Fig. 2 is a diagram showing an example of a cross section of a liquid crystal display panel, Fig. 3 is a diagram showing an example of a drive circuit diagram, and Fig. 4 is a diagram showing an example of a drive circuit diagram.
Figure 5 shows the scanning lines on a television screen.
FIG. 6 is a diagram showing a conventional video sampling method for a liquid crystal panel, FIG. 6 is a diagram showing a part of the circuit of FIGS. 3 and 4, and FIG. 7 is a diagram showing a video sampling method according to the present invention. It is. 3...Glass, 4...Transparent electrode, 5...Liquid crystal,
6...Substrate, 7...Pixel electrode, 14, 15...Matrix electrode drive circuit, 16...Liquid crystal pixel, 2
4, 25...matrix pixel.

Claims (1)

[Claims] 1. A liquid crystal is sealed between a substrate on which a plurality of row signal lines are formed and a substrate on which a plurality of column signal lines are formed,
In a dynamic drive type liquid crystal display device in which the row signal lines and the column signal lines are arranged in a matrix, an odd field consisting of odd scanning line signals of an input video signal and an even field consisting of an even scanning line signal are interlaced scanned. A means is provided for applying a video signal of an odd field and a video signal of an even field that are adjacent and continuous to one of the liquid crystal drive electrodes in a superimposed manner among one frame video signals to be displayed, and the video signal of the odd field is A liquid crystal display device characterized in that the signal and the video signal of the even field are AC video signals having mutually different polarities, and the cycle of the AC video signal is the same as the frame cycle of the frame video signal.