JPH0527711A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which is used as a display of OA and televisions, is fixed in chromaticity points in spite of a change in driving voltage level and can make exact color reproduction. CONSTITUTION:A control circuit 5 determines a brightness level from the R, G, B signals inputted thereto and sends a control signal to a matrix circuit 4. Matrix components are changed by the control signal in the matrix circuit 4 and the chromaticity point of a screen is moved according to the inputted brightness level. The liquid crystal display device which compensates the optically rotatory dispersion intrinsic to the liquid crystal device, is fixed in the chromaticity point in spite of a change in the driving voltage level of the liquid crystal and can make exact color reproduction is provided in such a case.

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 used as a display for OA equipment such as personal computers and word processors, and television receivers.

[0002]

2. Description of the Related Art In recent years, in the field of information equipment centering on computers and in the field of video equipment centering on televisions, video tape recorders, etc., there is an increasing demand for large-screen, thin display devices. As a display device of this type, a device using liquid crystal has recently been particularly attracting attention because it is easy to realize a thin, lightweight and large screen.

As a conventional liquid crystal display device, a twisted nematic (hereinafter referred to as TN) type liquid crystal is often used. The liquid crystal panel may be a simple matrix type liquid crystal or an active matrix type liquid crystal using a thin film transistor (hereinafter referred to as TFT). Active matrix type liquid crystal is easy to obtain high contrast, and is widely used. Hereinafter, the liquid crystal is a TN type liquid crystal and an active matrix type liquid crystal using a TFT will be described.

FIG. 3 shows an example of a block diagram of a conventional liquid crystal display device. In FIG. 3, reference numerals 1, 2, and 3 are input terminals to which color signal components of the video signal, that is, R, G, and B signals are input, 9 is a signal electrode drive circuit, 10 is a scan electrode drive circuit, and 11 is a TN type. It is a liquid crystal panel.

The operation of the conventional liquid crystal display device configured as described above will be described. First, the scan electrode driving circuit 10 includes a shift register, the output of which is output to the gates of the TFTs connected in parallel on the liquid crystal panel 11 in the horizontal direction. The output of the signal electrode drive circuit 9 is commonly connected to the drains or sources of the TFTs arranged vertically on the liquid crystal panel 11. The signal electrode drive circuit 9 includes a shift register and a transfer gate or a sample and hold circuit, and switches analog signals for one line in a dot-sequential manner or holds them for one line period. Corresponding to the waveform of the signal electrode, a gate pulse is applied to the scanning electrode for each line to turn on the switch of the TFT. A signal applied to the signal electrode drive circuit 9 is amplified and clamped by a signal processing circuit (not shown), then the phase is inverted, and the signal is output to the signal electrode drive circuit 9 through a buffer.

[0006]

In the TN liquid crystal used in such a conventional liquid crystal display device, the light transmittance depends on the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the cell gap d. Taking the voltage applied to the liquid crystal as a parameter,
The transmittance with respect to the wavelength of light has a relationship as shown in FIG. 4, for example, and the transmittance changes depending on the wavelength and also changes depending on the voltage. This is known as optical rotatory dispersion and is a phenomenon unique to liquid crystal devices.

Therefore, in the above-mentioned structure, when the driving voltage applied to the liquid crystal panel 11 is different, the chromaticity point of the displayed screen is different, so that accurate color reproduction cannot be performed. For example, even if white is displayed on the entire surface, the chromaticity point of white moves depending on the magnitude of the input level, so that the white balance is lost and there is a problem that coloring is performed according to the input level.

Further, a method of compensating for coloring by superposing a phase compensating plate on a liquid crystal panel has been proposed and put into practical use. FIG. 5 shows an example of a sectional view of a liquid crystal panel in which phase compensating plates are stacked. In FIG. 5, 21 is a phase compensating plate, 22 and 23 are glass substrates including transparent electrodes, 24 is a liquid crystal layer, and 25 and 26 are polarizing plates. The conventional liquid crystal panel 11 is composed of 22, 23, 24, 25 and 26.

As the phase compensating plate 21, there are one using a plastic film and one using another liquid crystal panel. Although the one using a plastic film is low in cost, it is difficult to completely compensate the optical rotatory dispersion. The liquid crystal panel 11 is used as the phase compensator 21.
It is theoretically possible to completely compensate the optical rotatory dispersion by compensating the optical rotatory dispersion by stacking another liquid crystal panel with the same liquid crystal material and cell gap and reversing the optical rotatory direction. The cost is also high, and due to manufacturing variations, the actual panel does not always sufficiently compensate the optical rotatory dispersion.

In view of the above points, an object of the present invention is to provide a liquid crystal display device in which the chromaticity point is constant even if the drive voltage level changes and accurate color reproduction is possible.

[0011]

In order to achieve the above object, a liquid crystal display device of the present invention uses a liquid crystal as a sum of values obtained by multiplying each color signal component value by each coefficient and inputting each color signal component of a video signal. A liquid crystal display device having a matrix circuit for outputting a driving color signal is provided with a control circuit for changing the matrix component of the matrix circuit, that is, the above-mentioned coefficient according to each color signal component value.

Further, the control circuit controls so that the chromaticity point of the screen displayed on the liquid crystal panel does not change even if the input level of the color signal component changes.

[0013]

In the liquid crystal display device of the present invention having the above structure, the matrix component of the matrix circuit can be changed by the control circuit, so that the color reproducibility of the screen displayed on the liquid crystal panel can be adjusted. Therefore, by setting the control circuit so that the matrix component is changed according to the input level change of the color signal component, it is possible to correct the color reproducibility when the input level change changes. In particular, stable color reproduction can be realized by performing control by the control circuit so as to correct so-called optical rotatory dispersion in which the relationship between wavelength and transmittance changes depending on the voltage value applied to the liquid crystal panel.

[0014]

1 shows an example of a block diagram of a liquid crystal display device according to a first embodiment of the present invention. As shown in FIG. 1, components 1, 2, 3, 9, 10, and 11 are the same as those in FIG. 3, 4 is a matrix circuit, 5 is a control circuit, and 6, 7 and 8 are input terminals 1 and 2, respectively. 3 is an output corresponding to the input of 3.

The operation of the liquid crystal display device of this embodiment constructed as described above will be described below. In FIG. 1, R, G, and B signals, which are color signal components of a video signal, are input to input terminals 1, 2, and 3, respectively. The control circuit 5 obtains the luminance signal level value from the input R, G, B signals. Brightness signal level value is Y, input R, G, B
If the signal level values are R _IN , G _IN , and B _IN , respectively,
Y is represented by the following equation.

[0016] _{Y = r · R IN + g} · G IN + b · B IN
(R, g, b: constant) A control signal is applied from the control circuit 5 to the matrix circuit 4 based on the value of Y. The matrix circuit 4 converts the R, G, and B signals by the control signal as in the following equation.

R _OUT = a ₁₁ · R _IN + a ₁₂ · G _IN + a ₁₃ · B _IN G _OUT = a ₂₁ · R _IN + a ₂₂ · G _IN + a ₂₃ · B _IN B _OUT = a ₃₁ · R _IN + a ₃₂ · G _IN + a ₃₃ · B _IN Here, the values of the coefficients a ₁₁ , a ₁₂ , ..., A ₃₃ change depending on the control signal. The R _OUT , G _OUT , and B _OUT thus obtained at the outputs 6, 7, and 8 are input to the signal electrode drive circuit 9. In other words, other signal components are added to the R, G, and B signals according to the input luminance level, and the chromaticity point of the displayed screen moves. Therefore, if the coefficients a ₁₁ , a ₁₂ , ..., A ₃₃ which are the matrix components are set so as to correct the wavelength-transmittance characteristic of the liquid crystal panel 11,
The optical rotatory dispersion can be compensated.

The coefficient a ₁₁ of the component of the matrix circuit 4,
As a specific example of changing a ₁₂ , ..., A ₃₃ , an element whose resistance value changes with voltage, such as an FET, can be used. In addition, the matrix circuit 4 includes RAM and R
A memory device such as OM can also be used. At this time, an AD converter and a DA converter are required.

Next, a second embodiment is shown in FIG. 9 _R, 9 _G, 9 _B as components, as shown in FIG. 2 are each R, G, the signal electrode driving circuit for the B signal, 10 _R,
10 _G and 10 _B are scan electrode driving circuits for R, G, and B signals, and 11 _R , 11 _G , and 11 _B are R and _G , respectively.
This is a liquid crystal panel that displays G and B signals, and is otherwise similar to FIG. Also in FIG. 2, the matrix circuit 4 converts the R, G, and B signals by the control signal as in the above equation. Other signal components are added to the R, G, and B signals in accordance with the input brightness level, and the chromaticity point of the displayed screen moves. Therefore, the matrix component coefficients a ₁₁ , a ₁₂ ,
.., a ₃₃ are set so as to correct the wavelength-transmittance characteristics of the liquid crystal panels 11 _R , 11 _G , and 11 _B , optical rotation dispersion can be compensated. FIG. 2 shows an example in which three liquid crystal panels are used as light valves and enlarged projection is performed. In the case of magnified projection, the optical rotation dispersion is particularly noticeable, so that the effect of the present invention is great.

As described above, according to this embodiment, the matrix circuit having the component whose value changes according to the input luminance level is used, and the R, G, and B signals are different from each other according to the input luminance level. By adding the signal component and moving the chromaticity point of the displayed screen, it is possible to compensate the optical rotatory dispersion characteristic of the liquid crystal device.

Further, it is obvious that the same effect can be obtained when the phase compensating plate is superposed on the liquid crystal panel and when the present invention is corrected for the total wavelength-transmittance characteristic including the phase compensating plate.

Although the liquid crystal panel 11 is the TN liquid crystal in the first and second embodiments, it may be a liquid crystal of another mode, and an active matrix type liquid crystal other than the TFT or a simple matrix type liquid crystal may be used. Needless to say, it may be used. Further, the matrix circuit may be a digital circuit or an analog circuit.

[0023]

As is apparent from the above description, in the liquid crystal display device of the present invention, each color signal component processing by the matrix circuit is changed to the liquid crystal device by changing the component ratio according to the input fluctuation by the control circuit. It is possible to provide a liquid crystal display device that compensates for the inherent optical rotatory dispersion, has a constant chromaticity point even when the drive voltage level of the liquid crystal changes, and enables accurate color reproduction. Further, when the phase compensator is used, more accurate color reproduction can be achieved, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional liquid crystal display device.

FIG. 4 is a graph showing the relationship between the wavelength and the transmittance of a liquid crystal panel.

FIG. 5 is a cross-sectional view of a liquid crystal panel in which a conventional phase compensating plate is overlapped.

[Explanation of symbols]

1, 2, 3 input terminals 4 matrix circuit 5 control circuit 9 Signal electrode drive circuit 10 Scan electrode drive circuit 11 LCD panel

Claims (3)

[Claims] 1. A control circuit for inputting each color signal component of a video signal, and a matrix circuit for inputting each color signal component, multiplying each color signal component value by a coefficient, and outputting each color signal as a sum thereof. A liquid crystal drive circuit driven by the output of the matrix circuit and a liquid crystal panel driven by the liquid crystal drive circuit are provided, and the control circuit changes the coefficient of the matrix circuit according to each color component value. Liquid crystal display device. 2. The control circuit changes the coefficient of the matrix circuit so as to keep the chromaticity point of the screen displayed by the liquid crystal panel constant with respect to the variation of the input level of the color signal components. Liquid crystal display device. 3. A liquid crystal display device according to claim 1, wherein a phase compensating plate connected to a liquid crystal driving circuit is superposed on the liquid crystal panel.