JPH0281585A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a high-quality picture with few flickers by providing a switching means to discharge charges accumulated in parastic capacity. CONSTITUTION:The charges accumulated in parasitic capacity CGS between the gate sources of a switching transistor(TR) Q1 for liquid crystal driving to be the main factor of DELTAV generation are discharged so as to made zero the difference DELTAV generated between a common electrode voltage VC and a mean value VPC of a picture element electrode voltage, and the flickers are decreased. That is, a switching means Q2 is provided between a picture element electrode 1 and a common electrode 2, a gate signal at timing different from that of the picture scanning gate signal to be supplied to a switching TR Q1 for the liquid cristal driving is added to the switching means Q2, the means Q2 is turned on, and the charges accumulated in the parastic capacity is discharged. Thus, the flickers can be decreased, and the liquid crystal display device with improved picture quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display device such as a liquid crystal television receiver, and particularly relates to an improvement of an active matrix type liquid crystal display device.

(Prior Art) Conventionally, a liquid crystal panel used in a liquid crystal display device such as a liquid crystal television receiver or a liquid crystal display is constructed as shown in FIG. That is, a liquid crystal 3 is arranged between a pixel electrode 1 and a common electrode 2 facing thereto, and a glass substrate 4 is placed on the pixel electrode side. A polarizing plate 5 is arranged, and a color filter 6 and a glass substrate 7 are arranged on the common electrode side. A polarizing plate 8 is arranged.

Further, the liquid crystal drive circuit is constructed as shown in FIG. 1 is a pixel electrode, 2 is a common electrode, 3 is a liquid crystal,
The liquid crystal 3 is equivalently represented by a liquid crystal content CLC and a liquid crystal resistance RLC, and a video signal vSC±VS is applied to the pixel electrode 1.
(However, ■SC is the average signal voltage value.

VS is a signal voltage) is applied from the signal line 9 through the drain and source of a switching transistor (for example, FET) Ql, and a screen scanning gate signal VGI is applied to its gate through the scanning line 10. There is. Further, a video signal holding sensor CS is arranged in parallel with the liquid crystal 3.

Incidentally, in a liquid crystal display device, AC voltage driving is used to protect the liquid crystal. That is, the polarity of the signal voltage VS is sequentially switched and applied to the signal line 9. Conventionally, the polarity is inverted for each field, which is the smallest medium level in which the polarity can be inverted.

FIG. 6(a) shows the change in the pixel electrode voltage vP in AC voltage driving, and FIG. 6(b) shows the luminance change (Noritsuka) in AC voltage driving.

As shown in FIG. 6(a), since there is a difference ΔV between the common electrode voltage VC and the average value vPC of the pixel electrode voltage, the common electrode voltage VC and the pixel electrode voltage VP (=VPC-)VS
) is vl or VP before and after polarity reversal. Therefore, as shown in FIG. 6(b), the screen fIli degree changes over time, which is perceived as a 301''Z flicker.

As shown in FIG. 7, the light transmittance of the liquid crystal is determined by the absolute value V (= l VP −Vc
This is because the transmission of light by the backlight differs from field to field since it is determined only by 1).

(Problems to be Solved by the Invention) As described above, conventional liquid crystal display devices have a problem in that when driven with an AC voltage, the screen brightness changes over time, which is perceived as flicker.

The present invention is intended to eliminate the above-mentioned problems, and an object of the present invention is to provide a liquid crystal display device that reduces flickers and improves screen quality.

[Structure of the Invention] (Means for Solving the Problems) Therefore, the present invention provides a common electrode voltage VC and a thread voltage ViA.
In order to make the difference △V between the voltage and the average voltage vPC zero, the parasitic capacitance CGS between the gate and source of the liquid crystal driving switch transistor Q1, which is the main cause of Δ■, is reduced to zero.
There is a method C that reduces flicker by discharging the charges accumulated in the screen. However, a switch means is provided between the pixel electrode and the common electrode, and this switch means is turned on by applying a gate signal having a timing different from that of the screen scanning gate signal supplied to the liquid crystal driving switch transistor. The device is characterized in that it is configured to discharge the charge accumulated in the parasitic capacitance.

(Function) The cause of the above ΔV is mainly the parasitic capacitance I between the gate and source of the switch transistor Q1 for driving the liquid crystal.
One example is CGS (see Figure 5). In other words, is there a charge on CGS? 5 If it is hit, CGS (VGS - ΔV)
-ΔV (O3+CLC) However, VGS is the gate-source dark voltage of the switching transistor Q1. From the above formula, ΔV=CGS-VGS/ (O3+CI-C+
CGS), and the voltage VG stored in CGS and this
Δ■ occurs based on S, causing flicker. According to the present invention, the charges accumulated in the CGS are discharged and Δ■
and flicker can be reduced.

Furthermore, since charges accumulated in other parasitic capacitances are also removed at the same time, the influence of parasitic capacitances 1i other than CGS can be eliminated by one.

(Example) The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a circuit diagram showing essential parts of a liquid crystal display device according to an embodiment of the present invention.

In this figure, the same parts as in Figure 5 are indicated by the same symbols.
It is shi. The difference from FIG. 5 is that a switching transistor (for example, FET) O2 for performing discharge is provided between the city electrode 1 and the common electrode 2 in both systems. Then, the switching transistor Q1 is connected to the goo i~ of the transistor Q2.
By adding and turning on the gate 54 Vcl, which has a different timing from the gate signal for double-sided scanning supplied to the
CGSk: Configured to discharge accumulated charges.

FIG. 2 shows an example of the timing of the above-mentioned gate signal VG2, and a signal having a faster timing than the screen scanning gate signal VGI is used as the gate signal VG2. This is to avoid discharging the charge in the video signal holding capacitor C8 by turning on the transistor Q2 just before the transistor Q1 is turned on and the video signal is stored in the pixel. . These Goo 1 to signals VG2 are generated by delaying the Goo 1 signal VGI for screen scanning of the previous pixel by a delay circuit C, or by using a circuit that combines a one-shot multivibrator with the previous VGI. C is created by supplying, etc.

FIG. 3 is a graph showing the effect of color modification of ΔV and Noritsuka according to the present invention. Figure 3 (a) (Average value of common electric power discharge month VC and drawing electrode ih pressure ■ PC
It shows the change over time. If there were no transistor Q2 as in the conventional case, the electric current Ij accumulated in the parasitic capacitance would result in Δ■ (which gradually increases with time) -b,
When discharging is performed by transistor Q2 as in the present invention,
Each time Q2 turns on, Δ is reduced to zero. Figure 3(b)
The change in the flicker value (degree of flicker) over time can be obtained depending on the presence or absence of the transistor Q2, and the present invention can obtain a significant flicker reduction result. Can be done.

[Effect of the Invention 1] As described above, according to the present invention, the charge accumulated in the parasitic capacitance can be removed, so that the shadow of the parasitic capacitance can be reduced, and a high-quality product with less flicker can be produced. Screens can be provided. Further, there is an advantage that the influence of non-uniformity of the liquid crystal material and parasitic capacitance of transistors other than the liquid crystal driving transistor can be eliminated.

[Brief explanation of the drawing]

FIG. 1 shows the main parts of a liquid crystal driving device according to an embodiment of the present invention.
2 is an explanatory diagram illustrating the timing of the gate signal that turns on the discharge switch l-run raster shown in FIG. 1; FIG. Figure 4 is a cross-sectional view schematically showing the structure of a liquid crystal panel, Figure 5 is a circuit diagram of a conventional liquid crystal drive circuit, Figure 6 is an explanatory diagram illustrating the principle of flicker generation by conventional AC voltage drive, and Figure 7. The figure is a graph showing the light transmittance of liquid crystal versus applied voltage. 1... Pixel electrode, 2... Common electrode, 3... Liquid crystal,
9...Signal line, 10...Scanning line, Ql...
- Switch transistor for liquid crystal drive, Q2...discharge switch 1 to transistor, VGI...gate signal for screen scanning, VO2...gate signal for Q2.

Claims (1)

[Claims] A liquid crystal layer is sandwiched between a pixel electrode and a common electrode opposite thereto,
In a liquid crystal display device in which a video signal is applied from a signal line to a pixel electrode through the drain and source of a switching transistor, and a screen scanning gate signal is applied from a scanning line to the gate thereof, the pixel electrode is common to the pixel electrode. A switch means provided between the electrodes and discharging the charge accumulated in the parasitic capacitance by turning on the switch means;
A liquid crystal display device comprising gate signal generating means for generating a gate signal having a timing different from the screen scanning gate signal and turning on the switch means.