JPH0451116A - Method for driving active matrix liquid crystal display panel - Google Patents

Abstract

PURPOSE:To obtain a picture of uniform and good quality without having unequal luminance by changing the low level of a gate pulse signal with the in- phase with a common signal by as much as the amplitude of the pulse of the common signal. CONSTITUTION:The offset level of the common signal impressed to a common electrode is set the same as the offset level of the amplitude generated in a pixel electrode and the amplitude V/20 thereof is set at 0.5V. The polarity of the common signal is inverted with each of frames. The level of +15v of the gate pulse signal is for turning on a thin-film transistor (TFTR) and the amplitude is supplied through the drain bus line via the TFTR to the pixcel electrode during the time of this +15V. The low levels -4V, -5V of the gate pulse signal maitain the TFTR in an off state and the video signal is held. The low level of the gate pulse signal changes with the in-phase by as much as the same amplitude in synchronization with the inversion of the common signal (a) in this case. The generation of the unequal luminance by each line is obviated in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving an active matrix liquid crystal display panel, and more particularly to a method for driving an active matrix liquid crystal display panel that eliminates the influence of field through due to capacitance between the gate and source of a thin film transistor.

[Conventional technology]

This type of active matrix liquid phase display panel is driven by applying an AC video signal to the drain bus line, applying a gate pulse signal to the gate bus line in line sequential scanning, and applying a common signal to the common electrode. However, in the conventional driving method, the low level of the gate pulse signal maintains the off state of the thin film transistor array and is a constant value.

FIG. 3 shows an equivalent circuit for one pixel of a liquid crystal display panel using thin film transistors as active elements.
By the video signal supplied from the vixel electrode 9a,
Charge is accumulated between the common electrodes b. FIG. 4 shows voltage waveforms at various parts, and FIG. 4(a) shows a gate pulse signal applied to the gate cross line. By applying a pulse equal to 1 duty, a voltage is generated at the vixel electrode 9a in FIG. 3, but this voltage is maintained in the off state of the thin film transistor (the low level of the signal in FIG. 4 (a>)). The polarity of the common signal applied to the common electrode 9b is reversed every frame as shown in FIG.
It changes as shown in Figure (b). This amount of change Δ■′ is
Since part of the charge is field-through due to the parasitic capacitance 10 of the thin film transistor shown in FIG. 3, the amount of change in the common signal is smaller than the amount of change Δ■. To illustrate the above, the potential between the vixel electrode and the common electrode is as shown in FIG. 4(d).

[Problem to be solved by the invention]

As described above, in the conventional driving method, a part of the charge escapes due to field-by-field inversion of the common signal, and the voltage between the vixel electrode and the common electrode decreases.

The time for this voltage to fall is the time after frame inversion until the voltage is applied between the gate electrodes, and therefore there is a large difference in the applied voltage between the upper and lower parts of the liquid crystal display panel. One way to reduce this problem is to reduce the parasitic capacitance, but there is a limit because reducing the parasitic capacitance increases the on-resistance of the thin film transistor.

[Means to solve the problem]

The present invention applies an AC video signal to the drain bus line of a liquid crystal display panel using a thin film transistor as an active element, applies a gate pulse signal to the gate bus line in line sequential scanning, and applies the AC video signal and the AC video signal to a common electrode. A method for driving an active matrix liquid crystal display panel in which a common signal of opposite phase is applied, characterized in that the low level of the gate pulse signal changes in phase with the common signal by the amplitude of the pulse of the common signal. shall be.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) to 1(d) schematically show electrical signal waveforms of the driving method according to the first embodiment of the present invention. A case will be described in which an amorphous silicon thin film transistor is used as the thin film transistor. Figure 1(a)
The common signal applied to the common electrode has the same offset level as the offset level of the video signal generated at the vixel electrode, and has an amplitude ΔV/2 of 0.5■. The polarity of the common signal is reversed every frame. The gate pulse signals (b), (c), and (d) are the first and i
It is applied to the th and last nth gate bus line. The +15V level of the gate pulse signal is for turning on the thin film transistor, and during this +15V time, the video signal is supplied to the vixel electrode via the thin film transistor through the drain bus line. The low level -4V, -5V of the gate pulse signal is to keep the thin film transistor in the off state, and as shown in the above-mentioned figure 0 where the supplied video signal is held, it synchronizes with the inversion of the common signal (a). The low level of the gate pulse signal changes by the same amplitude and in phase.

FIGS. 2(a) and 2(b) show voltage signal waveforms of a second embodiment of the present invention. In the first embodiment, the common signal is inverted for each frame, but in this embodiment, the common signal is inverted for each line. The polarity of the common signal (a) is inverted for each line, and the polarity is reversed for each frame. The low level of the first gate pulse signal (b) is the common signal (a>
changes in sync with. In the case of this embodiment as well, as in the first embodiment, there is no charge field-through every time the polarity of the common signal is reversed, so there is an effect that brightness unevenness from line to line does not occur.

〔Effect of the invention〕

As explained above, the present invention allows the low level of the pulse signal applied to the gate bus line to be changed in phase by the same width in synchronization with the common signal by the same width as the amplitude of the common signal applied to the common electrode. As a result, the potential of the vixel electrode between the common electrode and the gate electrode changes by the same width, and as a result, the voltage between the vixel electrode and the common electrode does not change. Therefore, since the same voltage is applied to the top and bottom of the liquid crystal display panel, it is possible to obtain a uniform, high-quality screen without uneven brightness.

[Brief explanation of drawings]

FIGS. 1(a) to 1(d) are diagrams showing drive signal waveforms for explaining the driving method of the first embodiment of the present invention, and FIG.
a) and (b) are diagrams showing drive signal waveforms of the second embodiment of the present invention, FIG. 3 is an equivalent circuit for one pixel of an active matrix liquid phase panel, and FIGS. d) is
FIG. 3 is a diagram showing waveforms for explaining a conventional driving method. 5... Thin film transistor, 6... Gate bus line, 7... Drain bus line, 8... Common electrode line, 9a... Vixel electrode, 9b... Common electrode, 1
0... Parasitic capacitance between gate and vixel.

Claims (1)

[Claims] An alternating current video signal is applied to the drain bus line of a liquid crystal display panel using a thin film transistor as an active element, a gate pulse signal is applied to the gate bus line in line sequential scanning, and a signal having a phase opposite to the alternating current video signal is applied to the common electrode. An active matrix liquid crystal display panel driving method in which a common signal is applied, wherein the low level of the gate pulse signal changes in phase with the common signal by an amount of the amplitude of the pulse of the common signal. driving method.