JPH10246879A - Liquid crystal display device and its adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically adjust a flicker into the best state without impeding display of an input video signal and requiring a screen outside the device. SOLUTION: A dummy pixel part 22 is provided around a video display pixel part 21 where the normal video signal of a liquid crystal panel 1 is displayed. Further, a photosensor 2 which detects a flicker is mounted on the dummy pixel part 22. At the dummy pixel part 22, an intermediate-color checked pattern is displayed as a pattern showing the flicker conspicuously. The photosensor 2 detects transmitted light exiting from the liquid crystal panel 1 and its detection signal is processed by a signal processing circuit 15. A common electrode potential generator 11 automatically adjusts the DC voltage applied to a common electrode 12 according to the output voltage from a voltage-control amplifier so that variation in the peak value detected by a peak holder 7 becomes minimum, in other words, the flicker is always minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which pixels are arranged in a matrix, and more particularly to a liquid crystal display device which automatically adjusts flicker to an optimum state and a method of adjusting the same.

[0002]

2. Description of the Related Art When driving a liquid crystal in a matrix display, if the potential of the common electrode deviates from a predetermined value due to variations in the liquid crystal element or the like, the absolute value of the voltage relative to the potential of the common electrode applied to the liquid crystal changes and a DC component is applied to the liquid crystal. In addition, it causes deterioration of the liquid crystal. Also, since the polarity is inverted in synchronization with the field period, if the potential of the common electrode deviates from a predetermined value, the brightness of the screen changes for each field,
As a result, it is known that flicker (change in luminance) occurs.

Therefore, various methods have been conventionally proposed as measures to reduce the flicker. As an example, an "liquid crystal display panel automatic adjustment device" (hereinafter referred to as "prior invention 1") described in JP-A-6-130920 and a "liquid crystal display device adjustment method" described in JP-A-7-72456. (Hereinafter referred to as Prior Invention 2) and the like.

In the prior art 1, the transmitted light emitted from the liquid crystal display panel is condensed and detected by an optical sensor, and the AC component of the detection signal is extracted during the flicker adjustment, while the DC component of the detection signal is extracted during the contrast adjustment. And automatically adjusts the trimmer provided on the liquid crystal display panel by a signal processing circuit, a control circuit, and a trimmer adjustment mechanism according to the AC component and the DC component, thereby improving flicker and contrast. It automatically adjusts to the state.

On the other hand, in the prior art 2, the same data is written positively in the first field and negatively written in the second field so that flicker is noticeable on the display of the liquid crystal display panel. Is detected, and the offset voltage of the selection pulse is adjusted so as to minimize flicker.

In addition, there is known a "common electrode voltage adjusting device" (hereinafter referred to as Prior Invention 3) described in JP-A-6-138842. As shown in FIG. 6, this common electrode voltage adjusting device detects flickers occurring in an image projected from a liquid crystal projector 61 onto a screen 62 and automatically adjusts the voltage of the common electrode.

[0007] The detection of flicker based on the image projected from the liquid crystal projector 61 is performed by a photodiode 63 provided on a screen 62, and the fluctuation of the current flowing depending on the flicker indicates the presence of flicker. After this variation is converted into a voltage by the current / voltage conversion circuit 64, the voltage is amplified by the amplification circuit 65, the output voltage is rectified by the rectification circuit 66, and the peak value is held by the peak hold circuit 67. Here, the magnitude of the peak value indicates the level of flicker. A / A
The data is converted into a digital value by the D conversion circuit 68 and output to the microcomputer 69. The DC level of the common electrode signal obtained by the counter electrode signal generation circuit 71 is controlled by the electronic volume 70. Therefore, the microcomputer 69 controls the electronic volume 70 and automatically adjusts the DC level of the common electrode so that the detected peak value is minimized, that is, flicker is minimized.

[0008]

SUMMARY OF THE INVENTION The above-mentioned prior inventions 1,
No. 2 is for detecting light transmitted from the video display area near the center, and thus has a problem that the photosensor partially obstructs the display of the input video signal. On the other hand, in the prior art 3, since the photodiode 63 is disposed on the screen 62, the screen 62, the photodiode 63, and a dark room for blocking external light are required in addition to the liquid crystal projector 61 as an apparatus. There was a problem. Further, application to a direct-view type liquid crystal display device having no screen is impossible. Furthermore, if the photodiode 63 near the screen is not always operating while the liquid crystal projector 61 is operating, it is not possible to compensate for the temperature with time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to prevent display of an input video signal, to eliminate the need for a screen external to the apparatus, and to optimize flicker. It is an object of the present invention to provide a liquid crystal display device which can be automatically adjusted to a proper state, and a method of adjusting the same.

[0010]

In order to achieve the above object, a method for adjusting a liquid crystal display device according to the present invention is a method for displaying a normal video signal of a liquid crystal panel in a liquid crystal display device in which pixels are arranged in a matrix. A dummy pixel section is provided around the image display pixel section, and a photo sensor is mounted on the dummy pixel section. The transmitted light emitted from the liquid crystal panel is detected by the photo sensor, and the potential of the common electrode is automatically determined based on the result. And the flicker is adjusted to an optimum state. Further, in the method for adjusting a liquid crystal display device according to the present invention, the three primary colors 3
It is characterized in that flicker adjustment of one liquid crystal panel is performed. In addition, the liquid crystal display device according to the present invention includes a video display pixel portion in which pixels are arranged in a matrix and displays a video signal, and a dummy pixel which is provided around the video display pixel portion and displays a pattern in which flicker is noticeable. And a photo sensor is provided in the dummy pixel portion, the transmitted light emitted from the liquid crystal panel is detected by the photo sensor, and the potential of the common electrode is automatically adjusted based on the result to optimize the flicker. It is characterized in that it is adjusted to a proper state. In addition, the liquid crystal display device according to the present invention includes a video display pixel portion in which pixels are arranged in a matrix and displaying a video signal, and a dummy pixel provided around the video display pixel portion and displaying a pattern in which flicker is remarkably observed. A liquid crystal panel having a portion, a photosensor arranged in the dummy pixel portion to detect transmitted light emitted from the liquid crystal panel, a current / voltage converter for converting an output current from the photosensor into a voltage, A rectifier that rectifies the output from the current / voltage converter, a peak holder that holds the peak value of the signal rectified by the rectifier, and a comparison that compares the output from this peak holder with the peak value one vertical cycle earlier. And a common electrode potential generator that generates a voltage according to the signal from the comparator and optimizes flicker in addition to the common electrode of the liquid crystal panel. Further characterized, the liquid crystal display device according to the present invention is characterized in that visible on the dummy pixel unit is a halftone dot checkerboard pattern.

In the present invention, since the photo sensor is disposed in the dummy pixel portion provided around the video display pixel portion, it does not hinder display of the input video signal. Further, the photo sensor detects flicker generated when the flicker detection signal is written to the dummy pixel portion, converts the detected flicker into a quantitative electric signal, and inputs the electric signal to the comparator. Then, the comparator performs a comparison operation with a quantitative electric signal in an optimal state,
The common electrode potential generator controls the potential of the common electrode of the liquid crystal panel according to the output to minimize the flicker level, in other words, to set the common electrode potential to an optimum value.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a block diagram showing an embodiment of a liquid crystal display device in which the present invention is applied to a projection type liquid crystal projector, FIG. 2 is a diagram for explaining the structure of the liquid crystal display device, and FIG. FIG. 4 is a diagram for explaining a write signal to the dummy pixel portion in the embodiment, FIG. 4 is a diagram for explaining a method of generating a checkered signal to be written in the dummy pixel portion in the embodiment of the present invention,
FIG. 5 is a diagram showing waveforms in the signal processing circuit.

In FIG. 1, reference numeral 1 denotes a liquid crystal panel incorporated in a liquid crystal projector. The liquid crystal panel 1 used here includes an image display pixel portion 21 for displaying a normal image, and a dummy pixel portion 22 provided around the image display pixel portion 21 and which is normally shielded from light and is not projected and displayed. It has a special structure in which the photo sensor 2 is arranged on the back side of the dummy pixel section 22, and is different from the above-described prior arts 1, 2, and 3 in this point. Writing to each of the video display pixel portion 21 and the dummy pixel portion 22 of the liquid crystal panel 1 is performed simultaneously by the input video signal 23. The photo sensor 2 attached to the back surface of the dummy pixel unit 22 detects the light intensity of the signal written to the dummy pixel unit 22,
As a result, a signal depending on the flicker of the video is output to the signal processing circuit 15. Here, the image displayed on the dummy pixel section 22 is a pattern in which flicker is remarkable, for example, a halftone checkered pattern shown in FIG.

In FIG. 2, a liquid crystal display device used in the present invention comprises a video display pixel section 21 and a dummy pixel section 22.
, And a three-layer structure of an upper mold 24 and a lower mold 26 that shield light other than the image display pixel portion 21. The upper mold 24 is provided with a light incident detection hole 25 for detecting flicker due to a write signal to the dummy pixel section 22. The photosensor 2 is built in the lower mold 26, and the light intensity including the flicker component that enters from the detection hole 25 on the upper mold 24 and passes through the dummy pixel portion 22 on the liquid crystal panel 1 is changed by the photosensor 2. Is detected by Detection hole 2
5 and the incident light passing through the dummy pixel portion 22 are shielded by the lower mold 26. As a result, the liquid crystal projector device using the liquid crystal display device having this structure does not adversely affect the image display by the image display pixel unit 21 at all. It should be noted that a polarizing plate in a light incident direction or a light emitting direction with respect to the liquid crystal panel 1 is not necessary for the description of the present invention, and is omitted in the drawings.

In FIG. 3, an input video signal 23 to the liquid crystal panel 1 provided with a dummy pixel section 22 used in the present invention is a normal video display signal 31 and a checkered pattern writing signal 32 to the dummy pixel section 22. Are superimposed signals.
In one vertical cycle 35, the video display period 33 is a write signal to the video display pixel unit 21 in FIG.
The checkered pattern write signal 32 in FIG. 4 is a write signal to the dummy pixel section 22 in FIG. Similarly, in one horizontal cycle 38, the video display period 36 is a write signal to the video display pixel unit 21 in FIG. 1, and the checkered pattern write signal during the flyback period 37 is a write signal to the dummy pixel unit 22 in FIG. is there. FIG. 4 shows a circuit configuration for realizing these signals.

In FIG. 4, an input signal discriminating circuit 41 discriminates the type of the input signal based on the cycle and width of the horizontal synchronizing signal 40 and the vertical synchronizing signal 39, and controls the signal output of the checkerboard signal generating circuit 42 following this. During the retrace period. Thereafter, the image display signal 31 is superimposed with the checkerboard write signal 32 by the addition circuit 43 during the flyback period, and output as the input image signal 23 to the liquid crystal panel 1. As a result, the flicker adjustment checkerboard signal is written into the dummy pixel section 22 provided around the video display pixel section 21 in FIG.

Next, the operation of the signal processing circuit will be described. The signal processing circuit 15, as shown in FIG.
It includes a voltage converter 3, an AC regenerator 4, an amplifier 5, a rectifier 6, a peak holder 7, a comparator 8, a low-pass filter 9, a voltage control amplifier 10, and a common electrode potential generator 11. The current output of the photo sensor 2 is converted into a voltage by the current / voltage converter 3. When a flickered image is detected by the photo senner 2, the current / voltage converter 3
Has a weak voltage waveform corresponding to the intensity of flicker as shown in FIG. Here, the horizontal axis is time, and the vertical axis is voltage. Then, the DC component is removed by the AC regenerator 4. The signal that has passed the AC regenerator 4 and has lost the DC component has the waveform shown in FIG. Further, the voltage is amplified by the amplifier 5 to obtain a waveform shown in FIG.

Next, the voltage amplified by the amplifier 5 is full-wave rectified by the rectifier 6, resulting in a waveform shown in FIG. The rectified voltage is input to the peak holder 7 so that a peak value is detected and held at every one vertical cycle 35, and becomes a DC component signal waveform shown in FIG. Here, the fluctuation of the peak value indicates the level of flicker. When the DC output from the peak holder 7 is input to the comparator 8, the DC output is compared with the value one vertical cycle before, and the difference is used as the output of the comparator 8 as one vertical cycle 35.
Low-pass filter 9 showing a time constant sufficiently larger than
To remove unnecessary high frequency components. The output from the filter 9 is amplified when input to the voltage control amplifier 10 and output to the common electrode potential generator 11. The common electrode potential generator 11 controls the common electrode 12 so that the fluctuation of the peak value detected by the peak holder 7 is minimized, in other words, the flicker is always minimized according to the output voltage from the voltage control amplifier 10. Adjust the DC voltage supplied to. The waveforms (a) to (e) shown in FIG.
The waveforms at the positions (a) to (e) in FIG. 1 are respectively shown.

In such a liquid crystal display device, the dummy pixel section 22 is formed around the image display pixel section 21 and the photosensor 2 for detecting flicker is disposed in the dummy pixel section 22. A good image can be obtained without affecting the display of the input image signal in the section 21 at all. Further, in the conventional liquid crystal projector shown in FIG. 6, it is necessary to dispose the photodiode 63 on the screen 62, but this is not necessary in the present invention.

In the above description, the case where flicker of, for example, a red primary color signal is detected by using one photo sensor 2 has been described. However, three independent three primary colors of red, green, and blue light are used. In a one-lens administration type liquid crystal projector device using a liquid crystal panel, one
It is possible to individually detect flicker of each color by arranging a total of three photosensors, or to detect using one photosensor after the three primary colors are combined. In that case, the light transmitted through the three liquid crystal panels and combined with the three colors enters the administration lens. The photo sensor is mounted immediately before the lens in the liquid crystal projector. 3
In order to determine which of the liquid crystal panels is the flicker component, it is possible to attach a color filter on the incident side of the photosensor and select this by a method such as rotation. Alternatively, there is a method in which a checkerboard pattern is not written into a dummy pixel portion of a liquid crystal panel for a color that is not selected, instead of using a color filter. According to these methods, independent control similar to the case where each liquid crystal panel has a dedicated photosensor can be performed with one photosensor.

In the above-described embodiment, an example in which the present invention is applied to a liquid crystal display device of a projection type liquid crystal projector device has been described. However, the present invention is not limited to this, and is applied to, for example, a direct-view type liquid crystal display device requiring a backlight. Can also be applied.

[0022]

As described above, the liquid crystal display device and the method of adjusting the same according to the present invention provide a video display pixel section for displaying a normal video signal of a liquid crystal panel in a liquid crystal display device having pixels arranged in a matrix. A dummy pixel section is provided around the pixel, a photo sensor is mounted on the dummy pixel section, the transmitted light emitted from the liquid crystal panel is detected by the photo sensor, and the potential of the common electrode is automatically adjusted based on the detection result to reduce flicker. Adjustment to the optimum condition automatically adjusts flicker due to individual differences between panels to the optimum condition, and also automatically follows changes over time due to factors such as temperature, improving image quality and panel life. Can be done.

Further, according to the present invention, when the present invention is applied to a projection type liquid crystal projector without hindering display of an input video signal, all operations are completed by a liquid crystal panel and peripheral circuits inside the set, so that a screen, a photo sensor Or, a system construction such as a luminance meter becomes unnecessary. Further, the present invention can be applied to a direct-view type liquid crystal display device which requires a backlight as well as the projection type.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a liquid crystal display device in which the present invention is applied to a projection type liquid crystal projector device.

FIG. 2 is a diagram for explaining a structure of the liquid crystal display device.

FIG. 3 is a diagram for explaining a write signal to a dummy pixel unit according to the embodiment of the present invention.

FIG. 4 is a diagram for explaining a method of generating a checkered signal written to a dummy pixel unit according to the embodiment of the present invention.

FIG. 5 is a diagram showing a waveform in the signal processing circuit.

FIG. 6 is a block diagram showing a conventional example of a common electrode voltage adjusting device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel, 2 ... Photosensor, 3 ... Current / voltage converter, 4 ... AC regenerator, 5 ... Amplifier, 6 ... Rectifier, 7 ...
Peak holder, 8 ... comparator, 9 ... low-pass filter,
10: voltage controlled amplifier, 11: common electrode potential generator, 1
2 common electrode, 15 signal processing circuit, 21 video display pixel section, 22 dummy pixel section, 23 input video signal.

Claims (5)

[Claims] In a liquid crystal display device having pixels arranged in a matrix, a dummy pixel portion is provided around a video display pixel portion for displaying a normal video signal of a liquid crystal panel, and a photo sensor is mounted on the dummy pixel portion. The photosensor detects transmitted light emitted from the liquid crystal panel, and automatically adjusts the potential of the common electrode based on the detection result to adjust flicker to an optimum state. 2. The method for adjusting a liquid crystal display device according to claim 1, wherein flicker adjustment of three liquid crystal panels of three primary colors is performed by one photosensor. 3. A liquid crystal panel having a video display pixel portion in which pixels are arranged in a matrix and displaying a video signal, and a dummy pixel portion provided around the video display pixel portion and displaying a pattern in which flicker appears remarkably. A photo sensor is provided in the dummy pixel portion, the transmitted light emitted from the liquid crystal panel is detected by the photo sensor, and the potential of the common electrode is automatically adjusted based on the result to adjust the flicker to an optimal state. A liquid crystal display device characterized by the above-mentioned. 4. A liquid crystal comprising: a video display pixel portion in which pixels are arranged in a matrix form to display a video signal; and a dummy pixel portion provided around the video display pixel portion and displaying a pattern in which flicker appears remarkably. A panel, a photosensor arranged in the dummy pixel portion for detecting transmitted light emitted from the liquid crystal panel, a current / voltage converter for converting an output current from the photosensor into a voltage, and a current / voltage converter. Rectifier for rectifying the output of the rectifier, a peak holder for holding the peak value of the signal rectified by the rectifier, a comparator for comparing the output from the peak holder with the peak value one vertical cycle earlier, and the comparator And a common electrode potential generator for generating a voltage corresponding to a signal from the common electrode and for setting a flicker in an optimum state in addition to the common electrode of the liquid crystal panel. apparatus. 5. The liquid crystal display device according to claim 4, wherein the pattern displayed in the dummy pixel portion is a halftone dot checkerboard pattern.