JPH06165087A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the easy-to-see liquid crystal display device with high picture quality by varying a response speed correction according to the content of picture. CONSTITUTION:In an input signal switching switch 3, the switching between a signal from a MUSE decoder 1 and a signal from an external input terminal 2 is selected according to the user's operation. The output of the switch 3 is inputted to a response speed correction circuit 4. In this case, the correction level of the response speed correction circuit 4 is controlled to take a control signal out from the MUSE decoder section 1. The response speed of the still picture part of the MUSE signal is made 'low', the response speed of an animation part is made 'middle', and the response speed is made 'high' in the external input signal processing when the MUSE signal is in pan, chilt processing, and at the time of scene changing. Thus, the noise elimination of the still picture part in the MUSE signal, a smooth display of animation part, and faithful display for pan, chilt, scene change, and base band signals can be executed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a display technique using a liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device is expected to be a display device next to a CRT because of its small size and light weight and the realization of a large projection screen when used as a light valve.

However, the response speed of an active matrix type liquid crystal panel using twisted nematic liquid crystal is about 30 to 60 milliseconds, and one field is about 17 milliseconds in NTSC or HDTV, so that a change in image for each field occurs. A phenomenon that cannot be followed, that is,
There are drawbacks such as slow response speed. This slow-moving image causes a moving image to appear blurred or, if the degree is poor, causes tailing, which is a major obstacle to achieving image quality that surpasses CRT.

As a method for increasing the response speed, it has been considered to thin the cell gap of liquid crystal, use a material having low viscosity, use it at high temperature, and the like. As an LCD for OA, it is at a satisfactory level with respect to the fast movement of the display of a bonding device such as a mouse cursor, but it is still insufficient for high quality display of television images, particularly high definition images. Therefore, means for correcting the slow response speed has been devised and announced along with the realization of a concrete circuit.

FIG. 2A shows an example in which this idea is applied to a high-definition receiver. 1 is MUSE
This is a decoder, and MUSE (multiple sub-Nyqui) that compresses the HDTV signal input from the antenna for transmission.
The st sampling encoding) signals as input, demodulates HDTV signals Y, P _R, P _B or the R, G, B. Reference numeral 2 is a high-definition signal input terminal for inputting a high-definition signal from a signal source such as a VTR or an optical disk. The input signal changeover switch 3 performs switching selection between the signal from the MUSE decoder 1 and the signal from the external input terminal 2 according to the user's operation.

The output of the input signal changeover switch 3 is input to the response speed correction circuit 4. This circuit generates a correction voltage larger than the amount of change according to the change of the input video signal, and promotes the change in the twist amount of the liquid crystal.
The purpose is to increase the response speed of the liquid crystal (LCD) panel 6. The output of the response speed correction circuit 4 is input to the LCD drive circuit 5. The LCD drive circuit 5 functions to make the video signal from the response speed correction circuit 4 correspond to the level and amplitude suitable for writing the liquid crystal.

Specifically, first, in a normally white liquid crystal for negative display, an input video signal is inverted. Second, it amplifies about 3 times. Thirdly, the voltage shifts to the high voltage side by about 2V. Fourthly, for the purpose of AC driving for the purpose of preventing deterioration of the liquid crystal, a certain voltage is inverted about every horizontal scanning period or every one vertical scanning period (see FIG. 2B). Fifth, since the liquid crystal panel 6 is a load having a relatively large capacity, current amplification is performed. The liquid crystal panel 6 is formed by sandwiching twisted nematic liquid crystal between two pieces of glass at intervals of several μ and twisted by 90 ° by an alignment film.

The liquid crystal panel 6 will be described with reference to FIG. Several hundred to several thousand signal line electrodes 61 and about 1,000 scanning electrodes 62 are provided orthogonally on one side of the glass, and active elements 63 such as thin film transistors (TFTs) are provided at the intersections thereof. Each TFT 63 displays an image by writing a potential corresponding to the image in a pixel 64 in which a liquid crystal is sandwiched by transparent electrodes. The signal line driver 65 includes a horizontal number of shift registers 651 and a sample hold unit 652. The sampling clock input to the shift register 651 shifts pixels from left to right one stage at a time, and at the same time, the sample hold unit 652 is moved to the left. Then, the input video signal is finely sampled and the pixel is held. After sampling to the right end at the end of one horizontal scanning period, the samples are simultaneously output to the signal line 61 and the pixel potential is applied to the drain of the TFT 63.

Reference numeral 66 denotes a scanning line driver, which shifts down one stage by a clock applied every horizontal scanning period and outputs a gate pulse to the scanning electrode 62. The TFT 63 is turned on by this gate pulse, and the video signal for each pixel written from the signal line driver 65 to the signal line 61 is written to the pixel 64. The configuration of the response speed correction circuit 4 will be described with reference to FIG.

Reference numeral 41 is an A / D converter, which samples an input video signal at a clock of several tens MHz (for example, 74 MHz) and quantizes it into a digital signal of about 10 bits. The output of the A / D converter 41 is the frame memory 42,
It is supplied to the subtractor 43, the correction voltage generators 45 and 46, and the adder 48. The frame memory 42 is a memory of about 20 Mbits, stores the input data for one frame period, and outputs the oldest data in order. The subtractor 43 is A /
The video data from the D converter 41 and the video data one frame before are subtracted. The output of the subtractor 43 is input to the correction voltage generators 45 and 46 and the code detector 44. The sign detector 44 detects the sign of whether the output of the subtractor 43 is positive or negative. The correction voltage generators 45 and 46 are A
The pixel voltage of the difference between the current video signal pixel voltage from the / D converter 41 and the image signal pixel voltage of one frame before from the subtractor 43 is output. This output is for outputting the effect of accelerating the response speed of the liquid crystal, and outputs a signal larger than the amount of change. The correction voltage generator 45 is for outputting effective data when the pixel voltage is increased, and the correction voltage generator 46 is for outputting effective data when the pixel voltage is decreased.

The changeover switch 47 switches either the pixel correction signal from the increasing side correction signal generator 45 or the decreasing side correction signal generator 46 according to the output result of the code detector 44. That is, when the output of the subtractor 43 is positive, the output of the increasing side correction signal generator 45 is selected, and when it is negative, the output of the phenomenon side correction signal generator 45 is selected. Switch 47
Is output to the adder 48, where the current video pixel voltage from the A / D converter 41 and the correction signal are added and output. The output of the adder 48 is the D / A converter 4
9, the input video signal is converted into an analog signal and output.

Next, the operation and effect of the response speed correction circuit 4 will be described with reference to FIGS. In each figure, the vertical axis represents the signal potential and the liquid crystal transmittance V, the horizontal axis represents the time T, and one scale on the time axis represents one frame. Further, for the sake of easy understanding of the description, the case of a normally black (positive display) mode liquid crystal will be described, but a similar operation is performed even in a normally white (negative display), only the transmissivity is reversed.

FIG. 3B is an explanatory diagram of the operation when there is no correction circuit, and the circles show the pixel write potential for each frame. This example shows a case where the first two frames are changed to 2V black and the third and subsequent frames are changed to 4V white. If the transmittance of the liquid crystal follows the changes in the pixel potential as shown by the solid line, the display of the moving image (when there is a change in the potential for each pixel) is not blurred and the image is easy to see. However, in an actual twisted nematic liquid crystal, it takes 2 to 3 frames for the change in transmittance to follow the change in pixel potential as indicated by the dotted line.

FIG. 3C is an explanatory diagram when the response speed correction circuit 4 is used. The case where the input signal is the same as in FIG. In the first two frames, a black voltage of 2V changes to a white of 4V in the third frame. Here, a voltage of 5V, which is higher than the originally desired 4V, is applied to the liquid crystal.
This is because the output of the subtractor 43 in FIG.
(= 4-2) and increasing side correction signal generator (α _on ) 45
Outputs 1 V and the changeover switch 47 selects it, and the adder 48 adds the same to the video signal to obtain 5 V. In the next frame, the output of the subtractor 43 becomes 0V and the correction signal generator also outputs 0V, so the input 4V is output as it is. In this way, a signal larger than the increase is added only when the signal level increases, so that the change in the transmittance of the liquid crystal becomes faster as indicated by the dotted line in the figure.

The same applies when the image changes from white to black, which will be described with reference to FIGS. 3 (d) and 3 (e). Similar to FIG. 3B, FIG. 3D is an operation explanatory diagram when there is no correction circuit. This example shows a case where the first two frames are changed to white of 4V and changed to black of 2V after the third frame. The transmittance of the liquid crystal does not follow the change of the pixel potential as connected by the solid line, and it takes 2-3 frames for the change of the transmittance to follow the change of the pixel potential as indicated by the dotted line.

FIG. 3 (e) is an explanatory diagram when the response speed correction circuit 4 is used as in FIG. 3 (d). The case where the input signal is the same as in FIG. The first 2 frames are 4
A white voltage of V changes to a black of 2V in the third frame. Here, a voltage of 1V, which is lower than 2V that is originally desired to be written, is applied to the liquid crystal. This is because the output of the subtractor 43 in FIG. 3A is -2 (= 2-4), the increasing side correction signal generator (α _off ) 46 outputs -1 V, and the changeover switch 47 selects it. Therefore, it is added to the video signal by the adder 48 and becomes 1V. In the next frame, the output of the subtractor 43 becomes 0V and the correction signal generator also outputs 0V, so the input 2V is output as it is. In this way, a signal smaller than the decrease is added only when the signal level decreases, so that the change in the transmittance of the liquid crystal becomes faster as indicated by the dotted line in the figure. By using the response speed correction circuit 4 based on the above principle, the blurring feeling of the moving image portion, which is a defect of the liquid crystal, is improved.

[0017]

As described with reference to FIG. 2, consider a case of displaying a high-definition image from the MUSE decoder.

In MUSE, in order to transmit a wide band high-definition image by satellite broadcasting for one channel, the band is compressed by different processing methods for a still image portion and a moving image portion. Briefly, in the still image portion, the original image is thinned out every four pixels and transmitted, and completed in four fields. Since the video part is created from the information thinned out to 1/4,
The resolution is lower than that of the still image part. Actually, since the processing is more complicated than this description, the resolution does not drop to 1/4, but the horizontal resolution of the still image portion is 650 TV.
In contrast to the number of books, that of the moving image portion is about 350 TV lines. This is because the human eye uses the principle that the resolution is low for moving objects.

Such a MUSE signal is transmitted to a cathode ray tube (CR
Some people point out that the motion of the video part is awkward when played back in T). When this image is displayed on the liquid crystal without any correction, the slow response speed is fortunate, and the moving image part is slightly blurred and easy to see.

However, when the response speed correction circuit 4 is used, the moving image portion is clearly displayed and the image becomes a CRT-like image, resulting in awkwardness. Then, it seems to be good to stop the response speed correction circuit 4 only when the MUSE signal is input, but when the contents of the image change greatly during the panning and tilting of the camera (scene change), the signal level of each pixel is large. Because it changes, it is blurred on the liquid crystal,
MUSE does still image processing, and I want to display it exactly on the LCD. As described above, it has been difficult to realize a liquid crystal display device with a response speed correction circuit that displays the MUSE signal in an easily viewable state.

Therefore, according to the present invention, the response speed of the still image portion of MUSE is low, and the moving image portion is medium speed.
Aiming at the realization of a device that has a high response speed in the processing of external input signals at the time of pan / tilt processing of signals and scene changes, noise removal of still image parts, smooth display of moving image parts, pan / tilt, scene It is an object of the present invention to provide a liquid crystal display device capable of realizing a faithful display for changes and baseband signals.

[0022]

The present invention makes it possible to control the correction level of a response speed correction circuit,
Take out the control signal from the decoder section and
The response speed of the still image part of the E signal is low, the response speed of the moving image part is medium speed, and the response speed is high for the external input signal processing during pan / tilt processing, scene change of the MUSE signal. To realize a configuration that allows you to set your preferences.

[0023]

According to the above means, noise removal of the still image portion in the MUSE signal, smooth display of the moving image portion, faithful display for pan, tilt, scene change and baseband signals are realized, and a high quality liquid crystal display is realized. Realize the device.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. 1 is M
The USE decoder is a MUSE (multiple sub) that compresses the high-definition signal input from the antenna for transmission.
As input -Nyquist sampling encoding) signals, demodulates HDTV signals Y, P _R, P _B or the R, G, B. Reference numeral 2 is a high-definition signal input terminal for inputting a high-definition signal from a signal source such as a VTR or an optical disk.

Reference numeral 3 is an input signal changeover switch, and M
Switching between the signal from the USE decoder 1 and the signal from the external input terminal 2 is selected and derived according to the user's operation. The output of the switch 3 is input to the response speed correction circuit 4, and here, by generating a correction voltage larger than the change amount in accordance with the change of the input video signal, the change of the twist amount of the liquid crystal is promoted. The purpose is to increase the response speed of the liquid crystal panel 6. The output of the response speed correction circuit 4 is
It is input to the LCD drive circuit 5, and here it functions to make the video signal from the response speed correction circuit 4 correspond to the level and amplitude suitable for writing the liquid crystal. Specifically, firstly, the input video signal is inverted in the normally displayed normally white liquid crystal. Second, it amplifies about 3 times. Thirdly, the voltage shifts to the high voltage side by about 2V. Fourth, for the purpose of AC driving for the purpose of preventing deterioration of the liquid crystal, a certain voltage is inverted every horizontal scanning period or vertical scanning period. Fifth, since the liquid crystal panel has a relatively large load, current amplification is performed. The liquid crystal panel 6 is formed by sandwiching twisted nematic liquid crystal between two pieces of glass at intervals of several μ and twisted by 90 ° by an alignment film. The specific configuration is as described with reference to FIG.

Reference numeral 7 is a correction gain control circuit,
Internal control signal from MUSE decoder (1:
Still image, 2: moving image, 3: pan, tilt, 4: scene change, 4), 5: status signal indicating whether input is MUSE decoder or external input, 6: response speed according to user's favorite operation input This is a circuit for varying and controlling the correction level of the correction circuit 4. The detailed structure of the response speed correction circuit 4 is the same as that of FIG. The operation of the correction gain control circuit 7 will be further described.

When the input is the MUSE signal and (1) a still image, the function of the response speed correction circuit 4 is stopped to make the liquid crystal's original slow response speed, or the function of the response speed correction circuit 4 is reversed. To further slow down the response so that the noise reduce function works even for images with poor SN. Further, the line flicker becomes less noticeable in the interlaced signal, and the vertical resolution of the still image is also improved. The effect of this function can be changed by the user using a remote controller or the like.

Similarly, when the input is the MUSE signal (2) for a moving image, the response speed correction circuit 4 is set to a moderate effect so that the moving image portion is appropriately blurred. This eliminates the awkwardness of the moving image portion. Further, this condition can be changed by a remote controller or the like according to the preference of the user.

Furthermore, when the input is (3) pan and tilt of the MUSE signal, (4) scene change, and (5) external input, the response speed correction is maximized to maximize the liquid crystal characteristics such as blurring and tailing. Avoid the drawbacks of. Here as well, the response speed correction may be variable according to the preference of the user.

When a computer image such as a work station or a personal computer is connected to the external input and line flicker occurs in the case of interlace, it becomes difficult to see. Therefore, the response speed correction circuit 4 is disabled or the low speed mode is set. It may be done.

[0032]

As described above, according to the present invention,
Noise removal of still image part in MUSE signal, removal of line flicker, vertical resolution up, smooth display of moving image part, pan, tilt, high speed display faithful to scene change and baseband signal, easy to see,
This realizes a high-quality device, and this effect is an important additional function in an actual commercial set.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is a system explanatory diagram and an operation explanatory diagram and a liquid crystal panel configuration explanatory diagram for displaying an output of a MUSE decoder on a liquid crystal panel.

FIG. 3 is a specific circuit diagram and operation explanatory diagram of a response speed correction circuit.

[Explanation of symbols]

1 ... MUSE decoder part, 3 ... switch, 4 ... response speed correction circuit, 5 ... LCD drive circuit, 6 ... liquid crystal panel,
7 ... Correction gain control circuit.

Claims (1)

[Claims] 1. An image change part detection means for detecting a change amount of a signal potential of each pixel of an input video signal, and a ratio of the input video signal to the change amount detected by the image conversion part detection means. Video signal amplitude varying means for obtaining a corrected video signal by increasing / decreasing the potential, and a liquid crystal display panel drive circuit for converting the corrected video signal into a signal suitable for a liquid crystal panel and supplying the converted output video signal to the liquid crystal panel. A liquid crystal display device comprising: a means and a variable rate control means for increasing or decreasing a variable rate of the video signal amplitude varying means according to a property of the input video signal or an operation input.