JPH0584883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a method for driving an active matrix type liquid crystal display device.

(b) Prior art An active matrix type liquid crystal display device is disclosed in Sanyo Electric Technical Report Vol. 16, No. 2, 1984, and its configuration is as shown in FIG.
An amorphous silicon (a-Si) TFT is formed on one line and a plurality of drain electrodes perpendicular to the lines and one amorphous silicon (a-Si) TFT is formed at the intersection of the lines and a pixel electrode is bonded to the substrate.A counter electrode faces the substrate, and a liquid crystal It is meant to hold the

Such a TFT has a gate electrode 2, an insulating film 9, an a-Si film 8, a drain electrode 1, a source electrode 7, The pixel electrodes 3 are sequentially formed.

However, in such a structure, the channel width W is small because the mobility of the a-Si film 8 of the TFT is small.
A method is used to increase the ON current and sufficiently charge the capacitance created by the pixel electrode and counter electrode.

(c) Problems to be solved by the invention However, in the structure described above, the overlapping area of the gate electrode 2 and the source electrode 7 becomes large.
The parasitic capacitance of the TFT shown at 10 in FIG. 5 increases. Therefore, the voltage charged in the capacitance formed by the counter electrode 6 and the pixel electrode 3 drops at the fall of the gate pulse, thereby increasing the DC component applied to the liquid crystal, which adversely affects the deterioration of the liquid crystal and the contrast.

In addition, the area of the overlapping portion of the gate electrode 2 and the source electrode 7 may be due to pattern deviation in photolithography.
Due to variations due to non-uniform side etching and large parasitic capacitance, the difference in voltage drop applied to the liquid crystal becomes large, which causes unevenness when displaying halftones, making it impossible to increase the gradation. Ta.

(d) Means for solving the problem In the method for driving a liquid crystal display device of the present invention, the rising timing of the gate pulse is advanced by one or several gate pulse times, and the pulse width is expanded while the falling timing of the pulse remains unchanged. It is.

(E) Effect According to the present invention, the capacitance created by the pixel electrode and the counter electrode, that is, the liquid crystal, starts to be charged before the timing of the gate pulse applied to the gate line is written to the corresponding pixel electrode, and the corresponding pixel electrode begins to be charged. Since the TFT is further charged at the timing of the gate pulse, the channel width of the TFT can be shortened, and the overlapping area of the gate electrode and source electrode can be reduced. This reduces deterioration of the liquid crystal, improves contrast, and enables high gradation.

(F) Embodiment FIG. 1 shows the gate pulses of the drive signal used in the drive method of the present invention by timing. Incidentally, FIG. 2 shows a conventional gate pulse for comparison.

Considering the deterioration of the liquid crystal, it is necessary to use AC drive. Therefore, in order to drive a liquid crystal TV, the drain signal is inverted for each field. Also, since one field is created in about 1/60 seconds, in the conventional gate pulse as shown in Fig. 2, if the number of gates is 250, the gate pulse width will be (1/60)/250 = 66.7 μS.
During that 66.7μS pulse width, the drain voltage is ±
When the voltage is 4V (inverted at 16.7mS per field), there is a voltage between the pixel electrode 3 and the opposing electrode 6 due to AC drive.
Requires 8V charging. If there is a charging rate of 80% with a certain channel width, in the conventional case, the voltage would be 8 x 0.8 = 6.4V, and 1.6V would be uncharged.

On the other hand, in the method of the present invention, if the pulse of the j+1th gate is turned on, the TFT is turned on at the jth writing time Wj, and the pixel is Electrode 3 is charged to a charging rate of 80%. Then, while the gate of this TFT remains ON, the next timing Wj+1 is reached and the signal that was originally input to that line is applied, but at this time, the original signal is of course the same sign as the previous video signal, so it was originally The potential difference between this signal and the previous one is only about 2V, and as a result, the gate is turned on.
During this time, considering the 80% charge rate for the original signal, it will be charged to a point where there is only a potential difference of 0.4V, which is 2 x 0.8 = 1.6V.

Therefore, in order to obtain the same charging voltage using the conventional method, it is necessary to lengthen the channel width, but in the present invention, there is no need to lengthen the channel width. As a result, in the present invention, the overlapping area between the gate and the source can be reduced, and the parasitic capacitance between the gate and the source can be reduced. Thereby, it is possible to prevent the voltage applied to the liquid crystal from becoming asymmetrical with respect to the opposite electrode, and it is possible to suppress a decrease in contrast, display unevenness in halftone display, and deterioration.

The above example shows that the gate is turned on one timing before, but the gate is turned on several timings ago.
The same goes for increasing the pulse width of the gate by turning it ON.

(G) Effects of the Invention The present invention enables driving with a drive signal whose pulse width is expanded by only the rising timing of the gate pulse without changing the falling timing of the gate pulse, or by several timings earlier, so that the signal can be changed from the previous video signal. Since the capacitance between the display electrode and the counter electrode can be charged, the charging capacity is improved compared to the conventional method, and therefore the channel width of the a-SiTFT can be shortened.
By shortening this channel width, TFT
The overlapping area of the gate electrode and source electrode is reduced, reducing parasitic capacitance, preventing liquid crystal deterioration, improving contrast, and achieving high gradation.

[Brief explanation of the drawing]

FIG. 1 is a timing diagram of a gate signal according to the method of driving a liquid crystal display device of the present invention, FIG. 2 is a timing diagram of a gate signal according to a conventional method, and FIGS.
1 and 5 are a partially cutaway perspective view, a plane pattern diagram of a main part, and a cross-sectional view of a liquid crystal display device, respectively. 1...Drain electrode, 2...Gate electrode, 3...
...Pixel electrode, 6...Counter electrode, 7...Source electrode, 8...A-Si film.

Claims (1)

[Claims] 1. A first substrate in which a plurality of gate lines and a plurality of drain lines intersect, a thin film transistor is provided at each intersection, and a pixel electrode is formed at the source of each thin film transistor, and a common electrode is provided on the entire surface. In a method for driving an active matrix type liquid crystal display device having a structure in which a liquid crystal material is sandwiched between a second substrate and a second substrate, the width of a gate pulse applied to a gate line is made longer than the writing time for one line. Further, a method for driving a liquid crystal display device, characterized in that the rising timing of the gate pulse is set at the rising timing of the gate pulse at least one time before the writing start timing to the pixel electrode.