JPH0766250B2 - Liquid crystal display - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which each pixel arranged in an XY matrix is driven by a switching element.

2. Description of the Related Art As a conventional liquid crystal display device, for example, JP-A-55-12919
It is shown in the publication.

FIG. 3 shows the structure of one picture element arranged in an XY matrix, where 1 is a thin film transistor (hereinafter abbreviated as TFT) which is a switching element for applying a signal voltage to the liquid crystal. Is a liquid crystal cell, and 3 is an auxiliary capacitance for holding a signal applied to the liquid crystal cell. Reference numeral 4 is a signal electrode for supplying a signal, 5 is a scanning electrode for supplying a signal for operating the TFT, and 6 is a counter electrode for applying a voltage to the liquid crystal cell. FIG. 4 shows an equivalent circuit of one picture element corresponding to FIG. 3, and 7 shows an equivalent circuit of the TFT ₁ shown in FIG. 7a is the equivalent current source when the TFT is on, 7b is the TFT
Equivalent resistance in the OFF state. Reference numeral 8 is a liquid crystal cell capacity.

Conventionally, the liquid crystal television screen drive system uses 1/60 seconds (hereinafter, one screen from the scanning line of the first row to the scanning line of the last row on one screen).
It is sequentially scanned and displayed in one field). FIG. 5 shows a driving waveform on the first line of the screen, where a is a waveform of a gate pulse having a period of 1 field, a pulse width T _G and a height V _G , and b is for driving the liquid crystal by AC driving. , 1 cycle 1 field, the signal is a high _{V S} around the _{V C}
The waveform of the signal whose polarity is inverted for each field, c is a constant voltage V _C , which is the voltage applied to the counter electrode 6 shown in FIG. d is the voltage applied to the auxiliary capacitance 3 shown in FIG. 3, and the area of the shaded area is the effective voltage applied to the liquid crystal cell 2 shown in FIG. FIG. 6 shows the drive waveform of the last line of the screen with respect to the drive waveform of the first line of the screen shown in FIG. 5, where a in FIG. 6 is the waveform of the gate pulse, b is the waveform of the signal, c is the voltage applied to the counter electrode, and d is the effective voltage applied to the liquid crystal cell.

In the conventional liquid crystal display device configured as described above, the constant voltage V _C shown in FIG. 5c is applied to the counter electrode 6 shown in FIG. 3, and the signal waveform shown in FIG. It is applied to the signal electrode 4 shown in FIG. By applying the waveform of the gate pulse shown in FIG. 5a to the scan electrode 5 shown in FIG. 3, the equivalent circuit 7 of the TFT shown in FIG. 4 is turned on and the liquid crystal cell capacitor 8 shown in FIG. A signal is supplied to the auxiliary capacitor 3 shown in FIG. 3, and the hatched portion in FIG.
The effective voltage shown by the shaded area is applied to the liquid crystal cell 2 shown in FIG. 3, and the signal waveform shown in FIG.
The luminance is shown according to the magnitude of the waveform of the signal shown in FIG.

Problems to be Solved by the Invention However, with the above configuration, the TFT ₁ shown in FIG.
There is a difference as shown in FIG. 5a and FIG. 6a in the timing at which is turned on in one field. That is, in the drive waveform in the first row of the screen shown in FIG. 5, the waveform shown in d and the waveform shown in b have the same polarity over most of the period of one field, so that the liquid crystal cell capacitor 8 shown in FIG. Also, there is almost no discharge of the electric charge accumulated in the auxiliary capacitance 3.
On the other hand, in the drive waveform on the last line of the screen shown in FIG.
Immediately after the liquid crystal cell capacitor 8 and the auxiliary capacitor 3 shown in the figure are charged with electric charges, the polarity of the signal shown in FIG. 6b is immediately inverted, and a large potential difference is present across the equivalent resistance 7b in the TFT OFF state shown in FIG. Occurs, the discharge amount of the charges charged in the liquid crystal cell capacitor 8 and the auxiliary capacitor 3 shown in FIG. 4 increases, and the effective voltage shown by the hatched portion in FIG. 6d decreases. Therefore, the third
The effective voltage applied to the liquid crystal cell 2 shown in the figure decreases as it goes to the lower part of the screen, and there is a problem that the luminance changes between the upper part and the lower part of the screen.

The present invention has been made in view of the above points, and an object thereof is to provide a liquid crystal display device that reduces a change in luminance at the upper and lower portions of a screen.

Means for Solving the Problems The present invention is a liquid crystal display device configured to apply a signal voltage having the same phase as an AC drive signal supplied to a signal voltage to a liquid crystal cell.

Action The present invention is intended to reduce the change in the brightness of the screen by decreasing the effective voltage applied to the liquid crystal cell in the upper part of the screen and increasing the effective voltage in the lower part of the screen with the above-described structure.

Practical Example FIG. 1 shows a drive waveform on the first line of the screen of the liquid crystal display device according to one embodiment of the present invention. In this embodiment, the structure of one picture element of the liquid crystal display device is the same as that shown in FIG. In FIG. 1, the signals a, b and d are the same as the conventional signals shown in FIG. C shown in FIG. 1 is a waveform of a signal having the same phase as the waveform of the signal shown in b and an amplitude V _T centered on a certain voltage V _C. FIG. 2 shows a drive waveform on the last line of the screen in the present embodiment, which has the first structure.
It is the same as the figure.

The operation of the liquid crystal display device of the present embodiment configured so that the above-mentioned drive signals are applied will be described below.

The signal waveform shown in FIG. 1c is added to the counter electrode 6 shown in FIG. 3, and the signal waveform shown in FIG. 1b is applied to the signal electrode 4 shown in FIG. When the scanning electrode 5 shown in FIG. 3 receives the waveform of the gate pulse shown in FIG. 1a,
The equivalent circuit 7 of the TFT shown in FIG. 4 is turned on, and a signal is supplied to the liquid crystal cell capacitor 8 shown in FIG. 4 and the auxiliary capacitor 3 shown in FIG. Here, although the voltage applied to the counter electrode 6 shown in FIG. 3 changes, the voltage of the auxiliary capacitor 8 changes because of the auxiliary capacitor 8 having a capacity sufficiently larger than the liquid crystal cell capacity 8 shown in FIG. However, the effective voltage applied to the liquid crystal cell capacitor 8 shown in FIG. 4 depends only on the voltage applied to the counter electrode 6 shown in FIG. That is, the first
The effective voltage applied to the liquid crystal cell capacitor 8 shown in FIG. 4 is reduced by the signal shown in FIG. 4 as shown by the hatched portion in FIG. On the contrary, in FIG. 2, the shaded portion showing the effective voltage in FIG.

As described above, according to this embodiment, by applying the waveform as shown in FIG. 1c to the counter electrode 6 shown in FIG. 3, the effective voltage applied to the liquid crystal cell 2 shown in FIG. Decrease at the top and increase at the bottom of the screen, as shown in Figure 4.
It is possible to correct the luminance change in the upper and lower parts of the screen caused by the fact that the equivalent resistance 7b in the TFT OFF state is not sufficiently large.

EFFECTS OF THE INVENTION As described above, according to the present invention, the uniformity of the brightness of the screen is improved, the fine gradation of the video signal can be reproduced, and a good image can be displayed, and its practical effect is great. .

[Brief description of drawings]

FIG. 1 is a timing chart of drive waveforms on the first line of the screen of the liquid crystal display device in one embodiment of the present invention, and FIG. 2 is a timing diagram of drive waveforms on the last line of the screen as in FIG. Three
FIG. 4 is a configuration diagram of one picture element of the present invention and the conventional liquid crystal display device, FIG. 4 is the same as FIG. 3 and an equivalent circuit diagram of one picture element, and FIG. 5 is a screen of the conventional liquid crystal display device. The timing chart of the drive waveforms in the first row, and FIG. 6 is the timing chart of the drive waveforms in the last row of the screen as in FIG. 1 ... TFT, 2 ... Liquid crystal cell, 3 ... Auxiliary capacitance, 4 ...
Signal electrode, 5 ... Scan electrode, 6 ... Counter electrode.

Claims (1)

[Claims] 1. A plurality of bus wirings are arranged in an XX matrix, and an area defined by the bus wirings in the X and Y directions corresponds to a picture element, and each picture element is a switching element, a liquid crystal cell, and A liquid crystal cell having a capacitance sufficiently larger than that of the liquid crystal cell;
Is electrically connected to the first electrode of the storage capacitor, the bus wiring in the X direction is a scanning electrode for operating the switching element, and the bus wiring in the Y direction is the liquid crystal cell and the storage capacitor. And a signal electrode of a switching element for supplying a signal to the second electrode of the liquid crystal cell, and a signal voltage having the same phase as the AC drive signal supplied to the signal electrode is applied to the second electrode of the liquid crystal cell. .