JPH10104578A - Driving method of active matrix liquid crystal display - Google Patents

Abstract

(57) [Problem] To improve the viewing angle characteristics of a liquid crystal panel by eliminating the grayscale inversion with respect to the deterioration of the viewing angle characteristics of the liquid crystal panel due to the grayscale inversion. SOLUTION: A plurality of different optical characteristics are provided in one display pixel in a time-division manner by a new driving method of a liquid crystal panel, and averaging is performed to eliminate a grayscale inversion region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an active matrix liquid crystal display using a thin film transistor (TFT).

[0002]

2. Description of the Related Art A display using an active matrix type display substrate using TFTs has been actively studied because higher image quality can be obtained as compared with a simple matrix type display device.

FIG. 7 is a perspective view schematically showing a liquid crystal panel of a conventional active matrix type liquid crystal display device. Reference numeral 1 denotes a scanning line (gate bus), 2 denotes a data line (source or drain electrode), 3 denotes a source or drain electrode, and a liquid crystal driving picture element electrode 4 electrically connected to the source or drain electrode. Here, the TFT portion is a portion of 5.
In a normal transmission type liquid crystal display device, since it is necessary to transmit light from a back light source, this pixel electrode must be a transparent conductive film. The above elements are formed by repeatedly forming a thin film and selectively etching the substrate 6 on the array side. Reference numeral 7 denotes a transparent conductive film serving as a counter electrode. When color display is performed on the liquid crystal panel, display can be performed by forming a color filter on each pixel of the counter substrate 8. In such a liquid crystal panel, when the voltage applied to the liquid crystal layer is changed by driving the TFT in accordance with the image signal, the transmittance of the liquid crystal panel changes accordingly to display an image. Next, a driving method of the active matrix type liquid crystal display panel will be described. FIG. 8 shows an equivalent circuit of an active matrix type liquid crystal display panel.

An image signal is applied to lines A1, A2,. This line includes TFTs Q11, Q12... Q1m, Q2 at intersections with the scanning lines B1, B2.
1, Q22... Q2m, Qn1, Qn2. Further, a gate electrode of the TFT is connected to the scanning line. TFT
Are connected to the counter electrode T through a liquid crystal cell. Drive pulses Φ1 and Φ2 on the scan line
... Φm are sequentially applied to the gate electrode to turn on the TFT, and a television signal is written to each pixel electrode through the source electrode. This state is maintained until the scanning pulse is applied to the gate electrode of the TFT in the next field. Thus, the display of the television image is performed.

FIG. 5 shows a temporal change of a signal waveform in a driving method (hereinafter referred to as a capacitive coupling driving method) disclosed in Japanese Patent Application Laid-Open No. 02-157815, which is one of the methods for driving this liquid crystal display device. As the scanning signal Vg, a voltage Von for turning on the switching element, a voltage Voff for turning on the switching element, compensation voltages Ve + and Ve−.
Are used. The compensation voltages Ve + and Ve- are applied alternately for each scanning line or auxiliary capacitance line. The signal potential Vs and the liquid crystal voltage Vlc applied to the pixel are calculated by (Equation 1) and (Equation 2) using the above-mentioned potential.

Vlc + = Vs ++ Cst / Ctot * Ve− (Equation 1) Vlc− = Vs− + Cst / Ctot * Ve + (Equation 2) The polarity of the liquid crystal pixel voltage Vlc and the signal voltage Vs changes for each field. Vs + and Vlc indicate the case where the signal voltage and the pixel electrode potential are higher than the opposing potential Vc.
+, And the lower case was defined as Vs- and Vlc-.

[0007]

FIG. 9 (a) shows a voltage-transmittance curve of a liquid crystal panel when this capacitive coupling drive is performed.
(Normally white mode) is shown in FIG. FIG. 9 (b) shows, as the angle parameters for evaluating the viewing angle characteristics of the liquid crystal panel, the expected angle θ in the vertical direction and the estimated angle φ in the horizontal direction of the panel. The horizontal axis of FIG. 9A is the applied voltage, and the vertical axis is the transmittance of the liquid crystal panel.
The estimated downward angle θ with respect to the liquid crystal panel shown in FIG. As shown in FIG. 9 (a), the slope of the voltage-transmittance curve becomes gentler as θ increases, and when the slope becomes a certain slope or more, contrary to the normal transmittance change, the pixel changes as shown by the dotted line in the figure. When the applied voltage increases, a region where the transmittance increases occurs at a low transmittance. This region is called a grayscale inversion region, and causes deterioration of the viewing angle characteristics of the liquid crystal panel.

Next, the cause of this grayscale inversion will be described with reference to FIGS. 10 (a) and 10 (b). The display mode of an active matrix type liquid crystal panel is generally TN
Display in (twisted nematic) mode. This display mode has a structure in which the alignment directions of the liquid crystal of the array substrate and the counter substrate are twisted by 90 °. FIG. 10A shows an alignment state of liquid crystal molecules in the liquid crystal panel in a state where no voltage is applied, and FIG. 10B shows a state in which a voltage is applied. When no voltage is applied, the liquid crystal molecules are arranged in parallel with the array substrate and the counter substrate. In this state, as the voltage is applied, the liquid crystal molecules approach from the parallel direction to the vertical direction with respect to the substrate. When such a display is made, when the liquid crystal molecules are viewed with a certain inclination with respect to the radiation direction of the panel, when the applied voltage is higher than a certain applied voltage, the liquid crystal molecules are more oriented in the direction than the liquid crystal panel is viewed as the liquid crystal is vertically aligned. This is because in the tilt and normally white mode, light leakage due to tilt of liquid crystal molecules increases. A radar chart (FIG. 11) shows the grayscale inversion angle of the TFT liquid crystal panel in the conventional example. The line on the concentric circle indicates the same θ with respect to the normal direction, and indicates the angle at which the gradation inversion occurs when the panel is rotated from 0 ° to 360 ° φ while maintaining the θ. It is.
According to this, when the panel is viewed from below at φ = 0 ° (directly below the panel), gradation inversion occurs at an inclination of θ = 26 °.

[0009] The grayscale inversion causes the display quality of the liquid crystal panel to be largely deteriorated. In order to solve this problem, as disclosed in Japanese Patent Application Laid-Open No. Sho-64, by dividing one pixel into a plurality of regions and giving each pixel different optical characteristics, a liquid crystal having excellent gradation display characteristics is obtained. Although a method for obtaining a panel has been proposed, in this method, it is necessary to form each area, and therefore, a space is always required between each area, and by securing this space, the effective display area in the pixel is reduced. There are certain disadvantages.

[0010]

According to the present invention, with respect to the deterioration of the viewing angle characteristic of the liquid crystal panel due to the above-described grayscale inversion, Ve of the capacitive coupling drive is changed every several fields or within one vertical scanning period. Values Ve +, Ve-, and according to the temporal regularity, the central voltage Vec = (Ve ++ Ve-) / 2 between Ve + and Ve- is the same,
The width Vepp between Ve + and Ve − = (Ve + −Ve−)
/ 2 are applied with different voltages so that 1
By having a plurality of different optical characteristics in one display pixel, the optical characteristics of the liquid crystal are averaged in view angle,
This is to improve or reduce the viewing angle characteristics of the liquid crystal panel by reducing or eliminating the grayscale inversion region.

The reason why the gradation inversion angle of the liquid crystal panel is reduced or eliminated by the above driving will be described with reference to FIG. FIG. 1 shows a driving method in the present application. The driving conditions of the liquid crystal panel are set as follows. The polarity of the signal line is inverted every horizontal scanning time (1H time), and the amplitude is changed from 0 V to 5 V to change the brightness from white display to black display. Here, the value of the amplitude value Vepp = (Ve + −Ve −) / 2 of the compensation voltage is set to 5.5 V for a certain period, and then the amplitude value Vepp of the compensation voltage is set to 4.5 V for a certain period. A for the first time domain,
Let B be the next time domain. 1 and 2 show signal waveforms applied to each of these time regions. The voltage-transmittance characteristics in the time domain A when driven under the above conditions are shown by the dotted line in FIG.
The broken line in FIG. 5 shows the voltage-transmittance characteristics of the region B. In the capacitive coupling drive, the shift ΔV on the horizontal axis of each voltage-transmittance characteristic corresponds to the difference between the amplitude component Vepp of the compensation voltage and the auxiliary capacitance ratio Cs / Ct as shown in Expression 3. Thus, the transmittance change is shifted.

ΔV = Cs / Ct * [Vepp (time domain B) −Veppp (time domain A)] The voltage-transmittance characteristic of the liquid crystal panel obtained by time-dividing the voltage-transmittance characteristic of the pixel as described above is both characteristics. The voltage-transmittance characteristics at this time are shown by the solid line in FIG. The grayscale inversion area, which has occurred when θ is large, is reduced by averaging. Further, it is also possible to eliminate the grayscale inversion region by changing and optimizing the amplitude of the counter voltage between the two.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) The process of producing a liquid crystal panel is the same as the conventional process. Hereinafter, each set voltage in the present embodiment is shown.

Vs = Vc = 2.5 V Von = 10 V Voff = −10 V Ve + = − 6 V Ve − = − 17 V Time domain A Ve + = − 7 V Ve − = − 16 V Time domain B.

In the first embodiment, as shown in FIG. 3, the time domain A and the time domain B appear alternately every two odd fields. In this case, it is of course possible to adjust the time ratio of the time-divided areas A and B so that the gradation inversion phenomenon is minimized. The grayscale inversion angle in the case of such driving is shown in a radar chart (FIG. 6). From this, it can be seen that when viewed from directly below the panel, no gradation inversion occurs. Thus, the display quality of the liquid crystal panel was significantly improved.

(Embodiment 2) A driving method according to Embodiment 2 will be described. FIG. 4 shows a driving waveform of the liquid crystal panel in the present embodiment. Each set voltage is shown.

Vs = Vc = 2.5 V Von = 10 V Voff = −10 V Ve + = − 6 V Ve − = − 17 V Time domain A Ve + = − 7 V Ve − = − 16 V Time domain B.

In the second embodiment, the time domain A and the time domain B change the amplitude of the compensation voltage during the off period within one field. In this case, it is of course possible to adjust the time ratio of the time-divided areas A and B so that the gradation inversion phenomenon is minimized. In this case as well, the improvement of the viewing angle characteristics has the same result as in the first embodiment, and
The display quality of the liquid crystal panel was greatly improved.

[0019]

As described above, the driving method of the liquid crystal display device of the present invention improves the viewing angle of the liquid crystal panel in the main viewing direction by providing a plurality of different optical characteristics in a time division manner in one pixel. Its technical significance can be very large.

[Brief description of the drawings]

FIG. 1 is a set driving voltage diagram of a liquid crystal panel in a time domain A according to Embodiment 1 of the present invention.

FIG. 2 is a set driving voltage diagram of a liquid crystal panel in a time domain B according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining a cycle between a time domain A and a time domain B according to the first embodiment of the present invention.

FIG. 4 is a set driving voltage diagram of a liquid crystal panel in time domain A and time domain B according to Embodiment 2 of the present invention.

FIG. 5 is a voltage-transmittance characteristic diagram in a time domain A and a time domain B.

FIG. 6 is a radar chart showing a grayscale inversion angle of the liquid crystal panel manufactured according to the first embodiment of the present invention.

FIG. 7 is a schematic view showing the structure of an active matrix type liquid crystal panel.

FIG. 8 is an equivalent circuit diagram of an active matrix type liquid crystal panel.

FIG. 9 is an angle dependence diagram of a voltage-transmittance characteristic of a liquid crystal panel having a conventional structure.

FIG. 10 is a diagram for explaining the reason why gradation inversion occurs.

FIG. 11 is a radar chart showing a gradation inversion angle of a liquid crystal panel having a conventional structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scan line (gate bus) 2 Data line (source electrode or drain electrode) 3 Source electrode or drain electrode 4 Pixel electrode 5 TFT part 6 Substrate 7 Transparent conductive film

Claims (3)

[Claims] 1. A pattern in which a pixel electrode made of a transparent conductive film for driving liquid crystal on an insulating substrate and a first conductive film called a gate electrode remain under a channel of the thin film transistor so as to form a scan electrode. A second conductive film called an image electrode of a liquid crystal panel and a source electrode or a drain electrode for transmitting an image signal is formed via an insulating layer, and a drain for connecting the pixel electrode to the TFT is formed. In an active matrix liquid crystal display composed of an electrode or a source electrode and composed of a counter electrode composed of a transparent electrode and holding a liquid crystal, an auxiliary capacitance formed by overlapping the pixel electrode with a part of an adjacent scanning electrode is provided. And a compensation voltage Ve is applied to the scan electrode during the off period of the scan electrode. Different values Ve +, V in the field
e−, and a voltage Vec = (Ve ++ Ve −) / at the center between Ve + and Ve− with time regularity.
2 is the same, but the width between Ve + and Ve−, Vepp =
A method of driving an active matrix liquid crystal display, wherein voltages different from (Ve + −Ve −) / 2 are applied. 2. The method of driving an active matrix liquid crystal display according to claim 1, wherein the temporal regularity is determined according to each vertical scanning period. 3. The driving method of an active matrix liquid crystal display according to claim 1, wherein the temporal regularity is determined according to each horizontal scanning period.