JPH03284792A - Liquid crystal driving device and method for driving liquid crystal panel - Google Patents

Abstract

PURPOSE:To prevent picture quality from being deteriorated and to obtain a proper display image by comparing a signal voltage value to be impressed to liquid crystal with a prescribed voltage and restricting the signal voltage value in accordance with the compared result. CONSTITUTION:An input video signal voltage is adjusted to a prescribed amplitude Vb - Va an amplitude voltage adjusting means 1. A voltage level corresponding to a value most similar to black out of video signal levels is adjusted from the prescribed value Va to Vb by a DC level adjusting means 2. A contour emphasizing means 3 applies contour emphasizing processing to the adjusted signal, a comparing means 4 compares the video signal voltage with the prescribed voltage value Va and a signal level control means 5 restricts the signal voltage to a signal having DC level higher than the Va. A liquid crystal driving means 6 impresses the video signal voltage to a liquid crystal panel 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal drive device for displaying an image on a liquid crystal display panel and a method for driving the liquid crystal panel.

Jurai's technology In recent years, as television receivers have become larger, more precise, and brighter, LCDs have the characteristics of being small, lightweight, and low power consumption, and are becoming increasingly popular in pocket-type TVs and projection-type TVs. It is attracting attention and has been commercialized as a television.

FIG. 7 shows the operation of a standard twisted nematic mode liquid crystal transmission display.

In FIG. 5, 71 is a deflection plate, 72 is a glass plate, and 73
74 is a transparent electrode, and 74 is a liquid crystal molecule, in which (a) shows the off state and (b) shows the on state.

As shown in FIG. 5, when the voltage applied between the two transparent electrodes 73 is in the OFF state, the incident light is deflected by 90 degrees by the liquid crystal molecules, and when the voltage applied between the two transparent electrodes 73 is in the ON state, the incident light is deflected by the liquid crystal molecules. is transmitted without being deflected.

Therefore, if the polarization directions of the two deflection plates 71 are orthogonal, the light is transmitted in the off state and blocked in the on state (hereinafter referred to as
(referred to as normally white mode).

Conversely, if the polarization directions of the two deflection plates 71 are parallel, the light is blocked in the off state and transmitted in the on state (hereinafter referred to as normally black mode).

Through the above-described operations, an optical image corresponding to the video signal voltage is formed on the liquid crystal panel.

Below, we will discuss the case where the liquid crystal is used in transmissive, normally black mode.

FIG. 2 shows an example of a characteristic diagram regarding the light transmittance with respect to the applied voltage of the liquid crystal.

In FIG. 2(a), if the applied voltage is less than Va, there is a problem that proper image display cannot be performed because the light transmittance does not increase as the applied voltage increases. .

A conventional liquid crystal driving device and a method for driving a liquid crystal panel to solve this problem will be described.

FIG. 6 is a block diagram of a conventional liquid crystal driving device.

In FIG. 6, 1 is an amplitude voltage adjusting means, 2 is a DC level adjusting means, 6 is a liquid crystal driving means for AC driving the liquid crystal, and 7 is a liquid crystal panel.

A conventional method for driving a liquid crystal panel will be described using FIG. 2(a) and FIG. 6.

In FIG. 6, the amplitude of the input video signal voltage is adjusted by the amplitude voltage adjusting means 1 according to the voltage range number of Vb-Va in FIG. 2(a). Furthermore, the display level corresponding to the blackest color in the video signal is adjusted by the DC level adjusting means 2 in FIG. 6 to the level of Va in FIG. 2 (al). The liquid crystal driving means 6 shown in FIG. 6 outputs signals necessary for AC driving the liquid crystal and applies them to the liquid crystal of the liquid crystal panel 7.

As described above, an appropriate display image was obtained by using the video signal voltage only within the dynamic range from Va to vb in FIG. 2(a).

Problems to be Solved by the Invention However, in the above configuration, when the video signal voltage is processed to emphasize the contour, even if the applied voltage decreases due to the added contour correction amount, the light transmittance decreases. There was a problem that proper display could not be performed because of the increase in the amount of data.

Generally, it is known that the apparent sharpness of an image can be increased by emphasizing contours that have relatively large changes in the image.

FIG. 7 shows an example of a video signal waveform with its outline emphasized.

In FIG. 7, (a) shows an input signal waveform, and (b) shows a video signal waveform with its outline emphasized.

By the way, in FIG. 2(a), when the applied voltage is in the range of Vc to Va, the light transmittance begins to decrease as the applied voltage increases.

This is due to the reasons described below.

It is generally known that liquid crystals have a characteristic of light transmittance depending on the product of the effective value of the refractive index anisotropy of the liquid crystal and the film thickness of the liquid crystal layer, and Figure 8 shows the refractive index anisotropy of the liquid crystal. An example of the characteristics of light transmittance with respect to the product of the effective value of and the thickness of the liquid crystal layer is shown.

In FIG. 8, Δn@ff is the effective value of the refractive index anisotropy of the liquid crystal, d is the thickness of the liquid crystal layer, and T is the light transmittance.

Now, if ΔnevrXd of the liquid crystal panel is nd in Figure 8, the refractive index anisotropy of the liquid crystal decreases as the applied voltage increases, so light transmission for the applied voltage shown in Figure 2) It becomes a characteristic of the rate.

Similarly, Δn and rrXd of the liquid crystal panel are nd in FIG.
2, the applied voltage is as shown in Fig. 2 (if the characteristic of light transmittance with respect to the applied voltage is shown in C1, and if Δnett×d of the liquid crystal panel is n d B in Fig. 8, then fa in Fig. 2). This is the characteristic of light transmittance for

Ideally, the light transmittance would increase as the applied voltage increases, as shown in Figure 2), but due to the manufacturing process of liquid crystal panels, it is difficult to maintain a constant thickness d of the liquid crystal layer. , when the thickness d of the liquid crystal layer becomes smaller than the ideal state, that is, when it becomes d2 in Fig. 8, the characteristics of light transmittance with respect to the applied voltage are as shown in Fig. 2 (C ), and even if a voltage value corresponding to black is applied, the amount of transmitted light is large, making it impossible to properly display black.

For this reason, generally the thickness of the liquid crystal layer is made slightly thicker, and the second
An appropriate display is obtained by setting Va in Figure (a) to the video signal voltage level that most corresponds to black, and limiting it to a range in which the light transmittance increases as the applied voltage increases.

Therefore, when the contour is emphasized with the above configuration, the light transmittance increases when the added contour correction amount is applied with a voltage equal to or less than Va in FIG. 2(a). This phenomenon of inversion of light transmittance occurs, making it impossible to obtain a proper display image.

Means for Solving the Problems In order to solve the above problems, the liquid crystal driving device and liquid crystal panel driving method of the present invention include a configuration in which the video signal voltage is limited to a predetermined voltage level and then applied to the liquid crystal. It is.

Effect of the Invention With the above-described configuration, the present invention has the above-mentioned structure, so that even when a video signal voltage lower than the pedicle level is generated in order to perform outline enhancement processing in a liquid crystal display, it is possible to eliminate the problem due to the inversion phenomenon of light transmittance. It becomes possible to provide an appropriate display image without deterioration of image quality.

EXAMPLE Hereinafter, a liquid crystal driving device and a method for driving a liquid crystal panel according to an example of the present invention will be described with reference to the drawings.

Note that this embodiment describes a case where the liquid crystal is used in a transmission type and normally black mode.

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

In FIG. 1, 1 is an amplitude voltage adjusting means, 2 is a DCC level adjusting means, 3 is an edge emphasizing means, 4 is a comparing means, 5 is a signal level limiting means, 6 is a liquid crystal driving means, and 7 is a liquid crystal panel.

The operation of the liquid crystal driving device configured as described above will be described below with reference to FIGS. 1 and 2.

The input video signal voltage is determined by the amplitude voltage adjustment means 1 in FIG.
The amplitude is adjusted to Vb-Va in FIG. 2(a). Further, the DC level adjusting means 2 in FIG. 1 adjusts the voltage level corresponding to the blackest color among the video signal levels to the level Va in FIG. 2(a). The video signal voltage whose amplitude and DC level have been adjusted from Va to Vb in FIG. 2(a) is subjected to contour enhancement processing by the contour enhancement means 3 in FIG. The comparison means 4 compares the video signal voltage subjected to the contour enhancement processing by the contour enhancement means 3 with the voltage shown in FIG.
), and the signal level limiting means 5 limits the input video signal voltage to a DC level signal higher than the voltage (iVa) in the input video signal voltage.

The video signal voltage limited by the signal level limiting means 5 outputs a signal necessary for AC driving the liquid crystal by the liquid crystal driving means 6, and is applied to the liquid crystal of the liquid crystal panel 7.

As described above, according to this embodiment, by providing means for limiting the voltage applied to the liquid crystal, the video signal voltage is
Even if a video signal voltage lower than the pedicle level is generated to enhance the outline, never apply a voltage value to the liquid crystal that would cause an inversion phenomenon in light transmittance.
It becomes possible to obtain an appropriate display image.

FIG. 3 shows a video signal waveform of a method for driving a liquid crystal panel according to an embodiment of the present invention.

In Fig. 3, (a) is the input signal waveform, (b) is the signal waveform with the contour emphasized, and (C) is the output signal waveform after signal level limitation, and Va and vb in the figure are Second
This corresponds to Va and vb in Figure (a). Input signal voltage (
In contrast to (a), in (b), the contour portion is emphasized, resulting in a voltage value of Va or less.

If a voltage value below Va is applied to the liquid crystal, the light transmittance characteristics of the liquid crystal with respect to the applied voltage will increase even if the applied voltage decreases, so the signal level should be limited to a signal level above Va. The output signal waveform (C) is obtained and applied to the liquid crystal.

As described above, according to this embodiment, by limiting the voltage applied to the liquid crystal and then applying it to the liquid crystal, the video signal voltage is lower than the pedestal level in order to perform edge enhancement processing. Even if this occurs, a voltage value that would cause an inversion phenomenon of light transmittance is not applied to the liquid crystal, making it possible to obtain an appropriate display image.

Furthermore, it is generally known that by amplifying the amplitude of a color signal relative to the amplitude of a luminance signal, the vividness of colors can be increased.

In this case, the red primary color signal and the green primary color signal.

When a voltage lower than the pedestal level is applied to the liquid crystal during matrix conversion into a blue primary color signal, a similar phenomenon of inversion of light transmittance occurs.

Therefore, in this embodiment, by amplifying the amplitude of the color signal with respect to the amplitude of the luminance signal, a voltage lower than the pedestal level will be present when matrix-converted into the red primary color signal, green primary color signal, and blue primary color signal. It is also effective in cases where

Although this embodiment deals with the case where the liquid crystal is used in normally black mode, it is also effective when used in normally white mode.

Furthermore, although liquid crystal is used as a transmissive display in this embodiment, it may also be used as a reflective display.

Figure 4 shows an example of the characteristics of the light transmittance with respect to the applied voltage of a reflective liquid crystal panel.If a voltage below Vd or an overpressure above Ve is applied, an inversion phenomenon of the light transmittance occurs. , means for limiting the video signal voltage to a voltage level above Vd and means for limiting the voltage level to a voltage level below Ve may be provided.

Effects of the Invention As described above, even if a voltage value that is not appropriate to be applied to the liquid crystal occurs due to processing such as emphasizing the outline, the present invention limits the level of the voltage value and then applies it to the liquid crystal. By applying the voltage, it is possible to obtain a proper display image without deterioration of image quality.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a liquid crystal driving device according to an embodiment of the present invention, 2rEJ is a characteristic diagram regarding light transmittance with respect to applied voltage of liquid crystal, and FIG. 3 is a drive of a liquid crystal panel according to an embodiment of the present invention. A video signal waveform diagram to which the method is applied; Figure 4 is a characteristic diagram of light transmittance versus applied voltage of a reflective liquid crystal panel;
The figure is an explanatory diagram of the operation of a standard twisted nematic mode liquid crystal, Figure 6 is a block diagram of a conventional liquid crystal driving device, Figure 7 is a video signal waveform diagram with the outline emphasized, and Figure 8 is a diagram showing the refractive index difference of the liquid crystal. FIG. 3 is a characteristic diagram of light transmittance versus the product of the effective value of orientation and the film thickness of a liquid crystal layer. 1... Amplitude voltage adjustment means, 2... DC
Level adjustment means, 3...Contour emphasis means, 4...
... Comparison means, 5 ... Signal level limiting means, 6 ... Liquid crystal drive means, 7 ... Liquid crystal panel.

Claims (2)

[Claims] (1) an active matrix liquid crystal display, a comparison means for comparing a signal voltage value applied to the liquid crystal of the active matrix liquid crystal panel with a predetermined voltage value;
A liquid crystal driving device characterized by comprising signal level limiting means for limiting the signal voltage value based on the comparison result of the comparing means. (2) In an active matrix liquid crystal display, after comparing the signal voltage value applied to the liquid crystal of the active matrix liquid crystal panel with a predetermined voltage value V and limiting it to a predetermined voltage range according to the comparison result, A method for driving a liquid crystal panel, comprising applying a voltage to the liquid crystal.