JPS63287829A - Electrooptical device - Google Patents

Abstract

PURPOSE:To attain display of a picture high in definition by using plural pulses in one frame of period as selection signals supplied to respective gate lines. CONSTITUTION:In a time chart of the selection signals G and G', a picture signal 6 supplied to a drain line 6 connected to the drain of a thin film transistor 3, a picture element electric potential 7 equal to the potential of the lease of the thin film transistor 3 and a common electrode electric potential 8, the picture signal 6 is driven in terms of AC in the frame period T nearly setting the common electrode electric potential as a center. While the selection pulses G and G' are supplied to the gate of the thin film transistor 3, the picture element electric potential 7 gradually closes to the picture signal 6 and while the selection pulses G and G' are not supplied to the gate, it holds a certain electric potential. Since the selection pulses G and G' are short, the picture element electric potential 7 can not gradually close to the picture signal 6 with one pulse, so that it does with two pulses. If two pulses are insufficient, one more pulse is added. Thus, the display quality can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] In an active matrix electro-optical device using thin film transistors (hereinafter referred to as TPT), etc., electricity with good display quality that faithfully reproduces image signals for image display is used. The present invention relates to a driving method for making it possible to provide an optical device.

[Summary of the invention]

The present invention provides an active matrix device including:
In order to ensure the lifespan of electro-optical elements such as liquid crystals, the polarity of the potential applied to the pixel electrode is reversed at a fixed cycle (frame cycle) with respect to the common electrode, so the potential of the common electrode and the potential of the pixel electrode are The purpose of this invention is to solve the problem that when the absolute value of the difference is not equal between normal rotation and reverse rotation, a linker phenomenon occurs in which the screen display repeats brightness and darkness at a constant cycle.

To solve this problem, the selection pulse supplied to the gate line is applied multiple times to the same gate line, so that the absolute value of the difference in potential between the common electrode and the pixel electrode is the same for normal rotation and reverse rotation, thereby eliminating the flicker phenomenon. This makes it possible to realize electro-optical devices such as liquid crystal display devices and printer shutters with high display quality.

〔Example〕

Liquid crystal display devices used for video displays, lamp tops, personal computers, etc. are required to have large screens, high definition, and high quality images. An active matrix liquid crystal display device in which each pixel is provided with a thin film transistor for pixel selection is attracting attention as a device that satisfies these conditions.

FIG. 2 is a circuit diagram of an active matrix display device. Gate lines (row lines) 1 for selecting thin film transistors 3 arranged in the row direction and drain lines (column lines) 2 for supplying image signals are arranged in a matrix.
A pixel consisting of a thin film transistor 3, an image signal component capacitor N4, and a liquid crystal 5 is provided at each intersection of the drain line 2 and the drain line 2. Note 4. The a capacitor 4 is connected between the source of the thin film transistor 3 and the ground, and the liquid crystal 5 is connected between the source of the thin film transistor 3 and common electrodes facing each other via the liquid crystal.

To display the image, a selection signal for the thin film transistor 3 is sequentially supplied from the gate line 1 at the top of the screen to the gate line 1 at the bottom of the screen, and an image signal matching the timing of each gate line 1 is supplied to the drain line 2. This is done by applying a potential according to the image signal to the storage capacitor 4 and liquid crystal 5 within the pixel.

FIG. 3 is a time chart of the selection signal G supplied to the gate line 1. The selection signal for the n-th gate line 1 has a pulse width tejf shorter than -horizontal scanning time. Further, the selection signal of the n+1th gate line 1 is set so as not to overlap in time. Further, the selection signal for the n-th gate line 1 has only one pulse within one frame period.

By the way, the image signal consists of a component (corresponding to the threshold voltage of the liquid crystal) that is AC-driven with respect to the common electrode with a frame period T, and a true image signal component that has a smaller amplitude than the AC-driven component.

Therefore, in order to supply an image signal to the storage capacitor 4 and the liquid crystal 5, the source potential of the thin film transistor 3 must be the sum of a component that is AC driven at each frame period T and an image signal component for displaying approximately twice the gradation. only has to change.

[Problem that the invention seeks to solve]

As mentioned above, in order to extend the lifespan of electro-optical elements such as liquid crystals, electro-optical devices that apply image signals to a common electrode by reversing the polarity every frame period are suitable for larger screens and higher definition screens. As the wiring resistance and parasitic capacitance of the gate line and the drain line increase, and - the horizontal scanning time decreases, - the ability to supply an accurate potential to the liquid crystal via the selected thin film transistor during the horizontal scanning time ( As a result, the display quality deteriorates, that is, the gradation display ability decreases, and flicker phenomena occur.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention makes the selection signal supplied to each gate line a plurality of pulses within one frame period, so that the selection signal is applied to an electro-optical element such as a liquid crystal via a thin film transistor. It is now possible to apply sufficiently accurate image signals.

[Effect]

Since sufficiently accurate image signals are applied to elements such as liquid crystals,
Decrease in gradation display ability and flicker phenomena caused by signal distortion are eliminated, and as a result, high-quality image display can be realized in large-screen, high-definition liquid crystal display devices and in electro-optical devices such as printer shutters.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. FIG. 1 is a time chart of selection signals G and G' supplied to the gate line 2 in the present invention. The selection signal G is
This is the same signal as before.

However, the selection signal G1 is a signal added in the present invention.

FIG. 4 shows the timing of the selection signals G, G', the image signal 6 supplied to the drain line 6 connected to the drain of the thin film transistor 3, the pixel potential 7 equal to the lease potential of the thin film transistor 3, and the common electrode potential 8.・It is a chart. The image signal 6 is AC driven with a frame period T approximately centered on the common electrode potential. The pixel potential 7 is
During the period when the selection pulses G, G'' are supplied to the gate of the thin film transistor 3, they asymptotically approach the image signal 6, and the selection pulses G,
A constant potential is maintained during a period when G' is not supplied to the gate. Selection pulse G.

Go has a short pulse width of less than one horizontal scanning time, so 1
Since the pixel potential 7 cannot asymptotically approach the image signal 6 with a pulse, two pulses are used in the example of FIG. 4. If two pulses are insufficient, just add more. By the way, the timings of the selection pulse G and the selection pulse G° are shifted by three times the horizontal scanning time. If the liquid crystal display device is a mosaic in which color filters of three colors (R, G, B) are arranged diagonally, the same color with a high correlation of the potential of the image signal 6 is displayed every three times the horizontal scanning time. This is to increase the writing efficiency of the potential of the image signal 6 to the pixel potential 7 by taking advantage of the fact that the potential of the image signal 6 is generated. Therefore, if the color filter is a vertical line, the selection pulse G and the selection pulse G
No interval is required between 1.

〔Effect of the invention〕

As explained above, this invention increases the number of selection pulses supplied to the gate line and appropriately controls the deterioration of gradation display ability and flicker phenomenon caused by insufficient writing of image signals to pixels. The present invention provides a drive circuit that can improve display quality by setting time intervals.

[Brief explanation of drawings]

Figure 1 is a time chart of selection pulses in the present invention, Figure 2 is a circuit diagram of a liquid crystal display device, Figure 3 is a time chart of conventional selection pulses, and Figure 4 is a time chart showing pixel operation. It is. 1... Gate line 2... Drain line 3.
...Thin film transistor 4...Storage capacity 5...Liquid crystal 6...Image signal 7...Pixel potential 8...Common electrode potential G, G"...More than selection signal

Claims (1)

[Claims] (1) Arrange gate lines and drain lines in a matrix,
In an electro-optical device in which an electro-optical element is sealed between a substrate provided with a pixel having a pixel selection transistor at each intersection thereof and a counter substrate having a common electrode facing the substrate, an analog signal is connected to the drain line. While supplying the video signal, in order to select each pixel, a selection pulse is sequentially supplied to the gate line from the top of the screen every horizontal scanning period, and prior to the selection pulse, a selection pulse similar to the selection pulse is applied to the gate line. An electro-optical device characterized in that it supplies a signal with a pulse width of .