JPS61248093A - Liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

2. Prior Art As a conventional liquid crystal display device, for example, Japanese Patent Application Laid-Open No. 55-12
It is shown in Publication No. 919.

Figure 3 shows the configuration of one picture element arranged in an X-Y matrix, where 1 is a thin film transistor (hereinafter abbreviated as TPT), which is a switching element for applying a signal voltage to the liquid crystal, 2 is a liquid crystal cell, and 3 is an auxiliary capacitor for holding a signal applied to the liquid crystal cell. 4 is a signal electrode that supplies a signal, 5 is a scanning electrode that supplies a signal for operating the TPT, and 6 is a counter electrode that applies a voltage to the liquid crystal cell. FIG. 4 shows an equivalent circuit for one picture element corresponding to FIG. 3, and 7 shows an equivalent circuit of the TFTl shown in FIG. 3. 7& is an equal current source when the TPT is in the ON state, and 7b is an equivalent resistance when the TPT is in the OFF state. 8
is the liquid crystal cell capacity.

Conventionally, the LCD TV screen drive system scans one screen sequentially from the first scanning line to the last scanning line in 1/60 seconds (hereinafter referred to as 1 field). There is. FIG. 5 shows the drive waveform of the first line of the screen,
a is the waveform of a gate pulse with a period of 1 field, pulse width TG, and height VG; b is a waveform of a gate pulse with a period of 1 field and a height of VS for each field centered on VC in order to drive the liquid crystal with AC. The waveform C of the signal with the polarity inverted is a certain voltage VC, which is the voltage applied to the counter electrode 6 shown in FIG. d is the voltage applied to the auxiliary capacitor 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 row of the screen in comparison with the drive waveform of the first row of the screen shown in FIG. 5, and a shown in FIG. 6 is the waveform of the gate pulse;
b is the signal waveform, 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, a constant voltage V (H shown in FIG. 5C) is applied to the counter electrode 6 shown in FIG. 3, and the signal waveform shown in FIG. The voltage is applied to the signal electrode 4 shown in FIG.

By applying the gate pulse waveform shown in FIG. 6a to the scanning electrode 5 shown in FIG. 3, the TF shown in FIG.
The equivalent circuit 7 of T 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. When the effective voltage shown is applied to the liquid crystal cell 2 shown in FIG. 3, the luminance is shown in accordance with the magnitude of the signal waveform shown in FIG. 5 and the signal waveform shown in FIG. 6. .

Problems to be Solved by the Invention However, in the above configuration, the problem shown in FIG.
There is a difference in the timing at which TFTl turns ON within one field, as shown in FIG. 6a and FIG. 6. That is, in the drive waveform on the first line of the screen shown in FIG.
Over most of the period of one field. Since the waveform shown in 9d and the waveform shown in b have the same polarity, there is almost no discharge of the charges accumulated in the liquid crystal cell capacitor 8 and the auxiliary capacitor 3 shown in FIG. In the drive waveform in the last row, immediately after charging the liquid crystal cell capacitor 8 and the auxiliary capacitor 3 shown in FIG. 4, the polarity of the signal shown in FIG. A large potential difference is generated between both ends of the resistor 7b, and the amount of discharge 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 shaded area in FIG. 6 d decreases. do. Therefore, the effective voltage applied to the liquid crystal cell 2 shown in FIG. 3 decreases toward the bottom of the screen, resulting in a problem in that brightness changes between the top and bottom of the screen.

In view of the above, an object of the present invention is to provide a liquid crystal display device that reduces changes in brightness between the upper and lower portions of the 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 a signal supplied to a signal voltage to a liquid crystal cell.

Operation The present invention aims to reduce the change in screen brightness by reducing the effective voltage applied to the liquid crystal cell at the top of the screen and increasing it at the bottom of the screen using the above-described configuration.

Embodiment FIG. 1 shows a driving waveform for the first row of the screen of a liquid crystal display device according to an embodiment of the present invention.

In this embodiment, the configuration of one picture element of the liquid crystal display device is the same as that shown in FIG. 3. In FIG. 1, signals a, b, and d are the same as the conventional signals shown in FIG. C shown in FIG. 1 has the same phase as the waveform of the signal shown in b, and is a waveform of a signal having an amplitude vT centered at a certain voltage vc. FIG. 2 shows the driving waveform of the last row of the screen in this embodiment, and the configuration is the same as that in FIG. 1.

The operation of the liquid crystal display device of this embodiment, which is configured to receive the above drive signal, will be described below.

The signal waveform shown in FIG. 1C is applied to the counter electrode 6 shown in FIG. 3, and the signal waveform shown in FIG. 1 is applied to the signal electrode 4 shown in FIG. When the waveform of the gate pulse shown in FIG. 1a is applied to the scanning electrode 5 shown in FIG. 3,
The TPT equivalent circuit 7 shown in FIG. 4 is turned on, and a signal is supplied to the liquid crystal cell capacitor 8 shown in the same figure and the auxiliary capacitor 3 shown in FIG. 3. Here, the voltage applied to the counter electrode 6 shown in FIG. 3 changes, but since the auxiliary capacitor 8 has a sufficiently larger capacity than the liquid crystal cell capacitor 8 shown in FIG.
The voltage of the auxiliary capacitor 8 does not change, and 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. 3. That is,
The liquid crystal cell capacitance 8 shown in Fig. 4 is determined by the signal shown in Fig. 1 cK.
The effective voltage applied to the voltage decreases as shown by the shaded area in FIG. 1(d). Moreover, in FIG. 2, on the contrary, the shaded area indicating the small effective voltage in the figure increases.

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. T decreases at the top and increases at the bottom of the screen, as shown in Figure 4.
It is possible to correct the brightness change in the upper and lower portions of the screen caused by the equivalent resistance 7b not being sufficiently large in the PT OFF state.

As described in detail, according to the present invention, the uniformity of screen brightness is improved, fine gradation of video signals can be reproduced, and good images can be displayed, and its practical effects are significant. .

[Brief explanation of the drawing]

FIG. 1 is a timing diagram of the driving waveform at the first line of the screen of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a timing diagram of the driving waveform at the last line of the screen, which is similar to FIG. 3
The figure is a configuration diagram of one picture element of the present invention and a conventional liquid crystal display device, FIG. 4 is an equivalent circuit diagram of one picture element, similar to FIG. 3, and FIG. 6 is a screen diagram of a conventional liquid crystal display device. FIG. 6 is a timing diagram of the drive waveform in the first line, which is similar to FIG. 6, and is a timing diagram of the drive waveform in the last line of the screen. 1...TFT, 2...Liquid crystal cell, 3.
...Auxiliary capacitor, 4...Signal electrode, 6...
...Scanning electrode, 6...Counter electrode. Figure 1 Time JP-A Figure 2 B Current time Figure 3 1=, 7FT? ...Saichouturu 3..., Oke-suke-go-go 42. , iS4, i4, i4, Figure 7.
,,TF Dingyoi Gokukaiji, Figure 5 Captive Time

Claims (1)

[Claims] A plurality of bus wirings are arranged in an X-Y matrix, and the area divided by the bus wirings in the X and Y directions corresponds to a picture element, and each picture element has a switching element, a liquid crystal cell, and is sufficiently larger than the liquid crystal cell. A first electrode of the liquid crystal cell and a first electrode of the auxiliary capacitor are electrically connected to the switching element, and the bus wiring in the X direction operates the switching element. The bus wiring in the Y direction is a signal electrode of a switching element that supplies a signal to the liquid crystal cell and the auxiliary capacitor, and the second electrode of the liquid crystal cell is a scanning electrode for supplying a signal to the signal electrode. A liquid crystal display device characterized by applying a signal voltage having the same phase as a signal.