JPH10123482A - Active matrix type liquid crystal display device and its driving system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method in which the large increase in the signal amplitudes normally required in a conventional column reversal driving system is no longer required in a lateral electric field display system and the cross talk phenomenon, that is the problem in the picture quality improvement, is resolved by the power driving having smaller display signal amplitudes and a low power consumption. SOLUTION: In a lateral electric field system active matrix type liquid crystal display device, additional capacitances 106 are formed between either one of the scanning wirings of the front or the back stages of a scanning electrode wiring 101 against each pixel electrode 104 and the front and back stage formations of these capacitances are alternatively crossed for every signal wirings 102 which are adjacent to each other. The polarity of the potential applied to the wirings 102 is reversed for every signal wirings that are adjacent to each other and during an on-period of a switching element 105, the signal wiring potential is transmitted to an pixel electrode 104 and during an off-period, the wiring 101, which forms the capacitance 106, is applied with the modulation potential which changes its polarity to the polarity direction of the signal wiring potential transmitted to the electrode 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active matrix type liquid crystal display device using a thin film transistor as a switching element and a driving method thereof.

[0002]

2. Description of the Related Art Liquid crystal display devices are applied in a wide range of fields such as viewfinders of video cameras, pocket TVs, high-definition projection TVs, and personal computers. In particular, a thin film transistor (Thin Film Transistor:
An active matrix type liquid crystal display device using a TFT (hereinafter abbreviated as TFT) has a great feature that a high contrast is maintained even when a large-capacity display is performed, and has been actively developed and commercialized.

In the above active matrix type liquid crystal display device, a widely used liquid crystal display mode is a TN (Twisted Nematic) type NW (Normally).
White) mode. In the TN mode, a panel having a structure in which liquid crystal molecules are twisted by about 90 ° between electrode substrates sandwiching a liquid crystal layer is sandwiched between two polarizing plates. NW
In the mode, the polarization axes of the two polarizing plates are orthogonal to each other,
One polarizing plate is arranged so that its polarization axis is parallel or perpendicular to the long axis direction of the liquid crystal molecules in contact with one substrate. In this case, white display is performed when no voltage is applied or a voltage equal to or lower than the threshold voltage, and when a voltage higher than that is applied, the light transmittance is gradually reduced to black display. Such display characteristics are obtained because, when a voltage is applied to the liquid crystal panel, the liquid crystal molecules try to align in the direction of the electric field while untwisting the twisted structure. This is because the polarization state changes and the light transmittance is modulated. However, even in the same molecular alignment state, the polarization state of the transmitted light changes depending on the incident direction of the light incident on the liquid crystal panel, so that the light transmittance differs depending on the incident direction. That is, the characteristics of the liquid crystal panel have a viewing angle dependency. The above-described viewing angle dependence characteristic of the TN method is particularly large-screen liquid crystal displays that have been actively developed in recent years.
This is a serious problem in image characteristics.

As one means for solving this problem, T
Instead of applying an electric field in the direction perpendicular to the substrate as in the N-type liquid crystal display system, the direction of the electric field applied to the liquid crystal is made substantially parallel to the substrate, and the direction of the liquid crystal molecules is controlled within the plane of the substrate. , A so-called lateral electric field method has been proposed in Japanese Patent Publication No. 63-21907 and Japanese Patent Application Laid-Open No. 7-36058. FIG. 3 shows a schematic diagram of a basic pixel configuration of a horizontal electric field method. In FIG. 3, reference numeral 302 denotes a counter substrate. 303, 304 and 305 are glass substrates 3 respectively.
1 shows a signal electrode wiring, a common electrode wiring, and a scanning electrode wiring formed on the same. Reference numeral 306 denotes a switching element formed corresponding to the pixel electrode 307. The liquid crystal is disposed between the glass substrate 301 and the counter substrate 302. The liquid crystal molecules are switched from the signal electrode wiring 303 to the switching element 3.
06, the pixel voltage supplied to the pixel electrode 307 via
The modulation is performed by a horizontal electric field generated by the voltage supplied to the common electrode 304. As described above, the present method is a method in which liquid crystal molecules are switched in the plane of the substrate, and therefore, it is known that a very excellent viewing angle characteristic can be realized in principle.

[0005]

However, although the above-mentioned in-plane switching method has excellent viewing angle characteristics, the common electrode 304 and the pixel electrode 307 are structurally obstructed as shown in FIG.
Since the so-called liquid crystal capacitance between them becomes very small, the capacitance of the pixel in the pixel region becomes small. On the other hand, the parasitic capacitance (hereinafter referred to as Csp) between the signal electrode wiring and the pixel electrode and the pixel electrode potential due to the parasitic capacitance (hereinafter referred to as Cgd) generated between the gate and the drain of the switching element, that is, between the scanning electrode wiring and the pixel electrode. Becomes susceptible to distortion. In order to reduce this effect, generally, an additional capacitance (additional capacitance) is formed on the pixel electrode in the pixel region. However, the formation of the additional capacitance reduces the aperture ratio of the pixel region, and there is a practical limit. Therefore, this method is susceptible to the capacitively-coupled distortion of the pixel potential due to the parasitic capacitance described above, thereby causing a problem in display such as crosstalk. Crosstalk is a phenomenon in which areas on the screen that must originally have the same luminance have different luminances depending on the image pattern.
Large and high-definition liquid crystal displays have a very large problem in image quality. The cause of such crosstalk is
As described above, the parasitic capacitance Csp causes the potential of the pixel electrode to be distorted due to the change in the potential of the signal electrode wiring, and as a result, the originally desired liquid crystal applied voltage cannot be obtained. A conventionally well-known driving method in which the direction of the potential change of the signal electrode wiring is inverted for each signal electrode wiring, that is, the polarity of the voltage is inverted for each signal electrode wiring (hereinafter referred to as column inversion driving). According to the signal potentials of adjacent signal lines,
Although crosstalk is eliminated except for special image patterns in order to cancel distortions to the pixel electrodes, there is a major problem such as a large signal amplitude.

The present invention solves the above-mentioned conventional problems, and is a method for eliminating crosstalk which is a problem in image quality in the horizontal electric field display system, which is required in the conventional column inversion driving system. The present invention realizes a method of eliminating the crosstalk phenomenon by driving at a low voltage without a large increase in the signal amplitude.

[0007]

In order to achieve the above object, an active matrix type liquid crystal display device according to the present invention comprises:
In an in-plane switching type active matrix type liquid crystal display device, an additional capacitance is formed between each pixel electrode and one of the preceding or subsequent scanning lines of the scanning line corresponding to the switching element of each pixel electrode. Further, the formation of the additional capacitance with the preceding scanning wiring and the formation of the additional capacitance with the latter scanning wiring are alternately performed for each signal wiring adjacent to each other.

Next, in order to achieve the above object, a method of driving an active matrix type liquid crystal display device according to the present invention comprises the steps of: inverting the polarity of a potential applied to a signal wiring for each adjacent signal wiring; Transmitting the potential of the signal wiring to the pixel electrode, and setting the potential of the signal wiring transmitted to the pixel electrode to the scanning wiring in which an additional capacitance is formed between the switching element and the pixel electrode during the off period of the switching element. A modulation potential that changes in the same polarity direction as the polarity is applied.

Further, in the driving method of the active matrix type liquid crystal display device according to the present invention, the modulation potential of the scanning wiring applied to modulate the potential of the pixel electrode is applied before and after the selection period of the scanning wiring. Is preferred.

With this configuration and method, it is possible to apply a modulation signal potential that changes in the same direction with respect to a signal potential that has been inverted for each signal wiring and applied from the scanning wiring via the additional capacitor. The signal amplitude of the signal wiring can be suppressed small, and low voltage driving can be realized while eliminating the crosstalk phenomenon.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic plan view showing a pixel region for four pixels of a thin film transistor array substrate used in an active matrix liquid crystal display device according to an embodiment of the present invention. In the drawing, reference numeral 101 denotes a scanning electrode wiring, and 103 denotes a common electrode wiring. In the present embodiment, the two electrode wirings 101 and 103 are formed in the same plane, and a metal thin film containing aluminum as a main component. Was formed, and the shape shown in the figure was formed by photolithography. The metal material to be used is not particularly limited to an aluminum-based metal, and a single-layer film or a multilayer film may be used. Next, after stacking an anodic oxide layer of the above aluminum film and silicon nitride (SiNx) as an insulating film and amorphous silicon as a semiconductor layer, two layers of aluminum / titanium (Al / Ti) deposited by a sputtering method are deposited. After that, the signal electrode wiring 102 and the pixel electrode wiring 104 were pattern-formed together with the semiconductor layer by dry etching. Reference numeral 105 denotes a thin film transistor which is a switching element.
In the present embodiment, the line width of the pixel electrode wiring 104 and the common electrode wiring 103 is 5 μm. The pixel electrode wiring 10
In No. 4, an additional capacitor 106 was formed between itself and the scanning electrode wiring 101. The additional capacitance 106 is formed between the corresponding scan electrode wiring 101 and the scan electrode wiring one line before or after the corresponding scan electrode wiring 101, and the formation position is alternately arranged for each adjacent signal electrode wiring 102. .

Next, the drive signal waveform of the present invention applied to the active matrix type liquid crystal display device shown in FIG. 1 and its operation will be described with reference to FIG. 20
Reference numerals 1 and 202 denote driving waveforms applied to the scanning electrode wiring 101 and the signal electrode wiring 102, respectively. 203
Represents a driving waveform supplied to the common electrode wiring 103. Reference numeral 204 in FIG. 2 denotes a voltage waveform of the pixel electrode 104 in the pixel in which the additional capacitance is formed between the scan electrode line and the previous line,
For example, FIG. 1 shows a voltage waveform of the pixel electrode 104 of the upper left liquid crystal cell among the four liquid crystal cells, and 205 denotes the voltage of the pixel electrode 104 in a pixel formed between the pixel electrode 104 and the scanning electrode wiring 101 one line later. 1 shows a waveform, for example, a voltage waveform of a pixel electrode of a lower right liquid crystal cell among four liquid crystal cells in FIG.

Here, the potential 204 of the pixel electrode 104 in which the additional capacitance 106 is formed on the scanning electrode wiring one line before is modulated as follows. First, the polarity of the signal potential applied to the signal electrode wiring 102 is inverted for each adjacent signal electrode wiring electrode 102. Next, the switching element 105
Is turned on, the signal potential is supplied from the signal electrode wiring 102 to the pixel electrode 104, and then, in a state where the switching element 105 is turned off, the modulation voltage due to the voltage change component of the scanning electrode wiring 101 one line before is supplied. Is additional capacity 10
6 is superimposed on the pixel electrode 104. At 204, the polarity of the applied signal voltage is positive and the polarity of the modulation voltage is also positive. On the other hand, the potential of the pixel electrode 104 in which the additional capacitance 106 is formed on the scanning electrode wiring 101 one line later shown in 205 is supplied from the signal electrode wiring 102 while the switching element is on, as described above. Then, with the switching element turned off,
A modulation voltage due to a voltage change component of the scanning electrode wiring 101 one line behind is superimposed on the pixel electrode 104 via the additional capacitance. In 205, the polarity of the applied signal voltage is negative, and the polarity of the modulation voltage is also in the negative direction.

As described above, the polarity of the signal potential is inverted for each adjacent signal electrode wiring, and each scanning electrode wiring 1
Since the voltage modulation direction to the pixel electrode 104 at 01 is controlled so that the polarity is the same as the polarity of the applied signal potential, the parasitic effect of Csd, which is a major problem in image quality in the horizontal electric field display mode, is obtained. Pixel voltage distortion due to capacitance can be compensated, a wide-field, high-quality image without crosstalk can be realized, and a modulation signal is superimposed from the scanning electrode wiring. Since the voltage applied to the liquid crystal can be increased while keeping the amplitude small, low power consumption can be realized.

Actually, the potential shown in FIG. 2 was applied to the liquid crystal panel having the TFT array structure shown in FIG. 1 to verify the effect of improving the characteristics. When a window-shaped pattern was displayed on the display screen and the potential waveform of the counter electrode was observed, no voltage oscillation component due to the signal electrode wiring potential was observed. Also, even when the actual display screen is visually observed,
Crosstalk has been completely eliminated.

[0016]

As described above, according to the active matrix type liquid crystal display device and the method of driving the same of the present invention, in an in-plane switching mode liquid crystal display device which can realize a wide viewing angle characteristic, adjacent signal The polarity of the signal potential is inverted for each electrode wiring, and the voltage modulation direction from each scanning electrode wiring to the pixel electrode can be controlled so that the polarity is the same as the polarity of the applied signal potential. Since the modulation voltage is superimposed on the wiring, a large applied voltage to the liquid crystal whose polarity is inverted for each signal electrode wiring can be obtained while the display signal amplitude is kept small. As a result, with low power consumption driving with a small display signal amplitude, adjacent signal line potentials cancel out distortion to the pixel electrode,
Cs which is a big problem in image quality in the horizontal electric field type display mode
Pixel voltage distortion due to the parasitic capacitance of d can be compensated, and a wide-field-of-view, high-quality image without crosstalk or the like can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a thin film transistor substrate of an active matrix type liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view of signal driving waveforms applied to the active matrix type liquid crystal display device according to the embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional in-plane switching mode liquid crystal display device.

[Explanation of symbols]

Reference Signs List 101 scanning electrode wiring 102 signal electrode wiring 103 common electrode wiring 104 pixel electrode wiring 105 thin film transistor element 106 additional capacitance section 201 scanning signal applied to scanning electrode wiring 202 scanning signal applied to signal electrode wiring 203 common electrode potential 204 previous stage The potential of the pixel electrode connected to the (n-1) scan electrode line via the additional capacitance 205 The potential of the pixel electrode connected to the subsequent (n + 1) scan electrode line via the additional capacitance

Claims (3)

[Claims] 1. A plurality of signal wirings and scanning wirings arranged in a matrix, at least one or more switching elements corresponding to respective intersections thereof, and a comb-shaped pixel electrode connected to the switching elements. An array substrate having a common electrode formed in engagement with the pixel electrode; a counter substrate disposed to face the array substrate; a liquid crystal layer sandwiched between the array substrate and the counter substrate; An active matrix type comprising two polarizing plates arranged outside a substrate, and generating an electric field between the pixel electrode and the common electrode that is substantially parallel to the two substrates to change the arrangement of liquid crystal molecules. In the liquid crystal device, an additional capacitance is provided between each of the pixel electrodes and one of the preceding or subsequent scanning lines of the scanning lines corresponding to the switching element of each pixel electrode. Wherein the formation of an additional capacitance between the first and second scanning lines and the formation of the additional capacitance between the first and second scanning lines are alternately performed for each signal line adjacent to each other. Matrix type liquid crystal display device. 2. A method for driving an active matrix type liquid crystal display device according to claim 1, wherein the polarity of the potential applied to the signal wiring is inverted for each adjacent signal wiring, and during the ON period of the switching element, The potential of the signal line is transmitted to the pixel electrode, and during the off period of the switching element,
An active matrix liquid crystal display characterized by applying a modulation potential that changes in the same polarity direction as the polarity of the potential of a signal line transmitted to the pixel electrode to a scanning line having an additional capacitance formed between the pixel electrode and the scanning line. How to drive the device. 3. The active matrix type according to claim 2, wherein the modulation potential of the scanning wiring applied to modulate the potential of the pixel electrode is applied before and after the selection period of the scanning wiring. A method for driving a liquid crystal display device.