JP2002196305A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of displaying a high-quality picture in which an afterimage phenomenon is not generated even when the power source of the device is turned OFF. SOLUTION: This display device is a liquid crystal display device in which plural video signal wirings and plural scan signal wirings are arranged in a matrix shape on the substrate on one side and first switching elements are arranged respectively at positions where the video signal wirings and the scan signal wirings intersect and the video signal wiring and a pixel electrode are connected by controlling the scan signal wiring via the first switching element and also a common electrode wiring is arranged in parallel with the scan signal wiring and the common electrode wiring and the pixel electrode forms a capacity and the device has second switching elements connecting video signal wirings and the pixel electrode by controlling the common electrode wiring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device having improved display quality. In particular, the present invention relates to a liquid crystal display device that eliminates the afterimage phenomenon that occurs when the power is turned off.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device, a plurality of video signal wirings and a plurality of scanning signal wirings are arranged in a matrix on one substrate of a liquid crystal display element composed of two electrode substrates. A switching element is arranged at each of the positions where the video signal wiring and the scanning signal wiring intersect, and the scanning signal wiring is controlled via the switching element to charge and discharge the video signal wiring and to be stored in the pixel electrode. Change the amount of charge. Then, by controlling the voltage between the counter electrode formed on the other substrate and the direction of the liquid crystal molecules, the polarization direction of light and the transmission of light are controlled.

FIG. 2 shows an equivalent circuit diagram of a conventional liquid crystal display device. FIG. 2 shows only one pixel electrode portion of the liquid crystal display element. In FIG. 2, 1a and 1b are video signal wirings, 2 is a scanning signal wiring, 3 is a common electrode wiring, 4 is a switching element, 6 is a liquid crystal, 7 is a capacitance between a pixel electrode and a common electrode wiring, and 8 is the other. A counter electrode 9 serving as a substrate electrode is a pixel electrode. The liquid crystal 6 is schematically shown.

In FIG. 2, when the liquid crystal 6 is driven by using a liquid crystal display device, a video signal is written to the pixel electrode 9 as needed by the control of the switching element 4 by the scanning signal wiring 2, and the common electrode Electric charges are held in a capacitor 7 between the wiring 3 and a liquid crystal 6 between the counter electrode 8.
When a voltage is applied to the image, an image is displayed.

[0005]

However, in the conventional liquid crystal display device, when the power supply of the liquid crystal display device is turned off and the driving of the liquid crystal 6 is stopped, the scanning signal wiring 2 for controlling the switching element 4 and the common electrode wiring 3 are formed. Is 0 V (GN
D). In this case, the electric charge accumulated in the pixel electrode 9 is discharged through the switching element 4 and disappears. However, the off characteristic of the switching element 4 is set so as to prevent leakage during a normal display operation. Generally, it has a very high resistance, and its discharge may require a time of several tens of seconds. Therefore,
Even after the power is turned off, the residual charge often causes an afterimage on the screen, which hinders improvement in display quality.

Therefore, the afterimage phenomenon that occurs when the power supply of the liquid crystal display device is turned off is substantially determined by the off characteristic of the switching element 4 formed in the liquid crystal display element used in the liquid crystal display device. There is a problem that the latent characteristics remain in the liquid crystal display device.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device capable of displaying a high-quality image without causing an afterimage even when the power is turned off. .

[0008]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a plurality of video signal wirings and a plurality of scanning signal wirings arranged in a matrix on one substrate. A first switching element is disposed at a position where the signal wiring and the scanning signal wiring intersect, and the video signal wiring and the pixel electrode are connected by controlling the scanning signal wiring via the first switching element, and the scanning signal is provided. A liquid crystal display device in which a common electrode wiring is arranged in parallel with the wiring, and the common electrode wiring and the pixel electrode form a capacitor, the liquid crystal display device including a second switching element connecting the video signal wiring and the pixel electrode. And

With this configuration, it is possible to connect a plurality of second switching elements separately from the switching elements for driving the liquid crystal normally, and to increase the leakage current when the power is turned off, so that the pixel electrodes can be driven in a shorter time. Can be eliminated, and the afterimage phenomenon when the power is turned off can be eliminated.

Further, in the liquid crystal display device according to the present invention, during normal use, it is necessary that a potential set to turn off the second switching element is applied to the common electrode wiring. This is in order not to hinder normal operation of the liquid crystal display device in a normal state.

Further, in the liquid crystal display device according to the present invention, it is preferable that the potential applied to the common electrode wiring is lower than the potential of the scanning signal wiring applied when the first switching element is turned off. This is for further increasing the leakage current in the second switching element.

Further, in the liquid crystal display device according to the present invention, it is preferable that the second switching element is formed by a thin film transistor. Further, in the liquid crystal display device according to the present invention, when the thin film transistor formed as the second switching element has a gate potential equal to the source potential or the drain potential, a current flows between the source electrode and the drain electrode. Is preferable. This is because the leak current when the power is turned off can be further increased, so that the charge accumulated in the pixel electrode can be eliminated in a shorter time.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an equivalent circuit diagram of a liquid crystal display device according to an embodiment of the present invention. FIG. 1 shows only one pixel electrode portion of the liquid crystal display element.

In FIG. 1, 1a and 1b are video signal wirings, 2 is a scanning signal wiring, 3 is a common electrode wiring, 4 is a switching element used in a normal display operation, 5a and 5b.
Is a second switching element different from the switching element 4 used in a normal display operation, 6 is a liquid crystal, 7 is a capacitance between a pixel electrode and a common electrode wiring, and 8 is an electrode on the other substrate. The electrode 9 is a pixel electrode. The liquid crystal 6
Is schematically shown.

As shown in FIG. 1, when the liquid crystal 6 is driven by using the liquid crystal display device, a video signal is written into the pixel electrode 9 by controlling the switching element 4 by the scanning signal wiring 2 as needed. 7 between the common electrode wiring 3 and
And a voltage is applied to the liquid crystal 6 between itself and the counter electrode 8. At this time, the second switching elements 5a and 5b are always off.

Next, when the power supply of the liquid crystal display device is turned off and the driving of the liquid crystal 6 is stopped, the scanning signal wiring 2 for controlling the switching element 4 and the second switching elements 5a and 5
The potential of the common electrode wiring 3 for controlling b becomes 0 V (GND). In this case, the electric charge accumulated in the pixel electrode 9 is equal to the switching element 4 and the second switching elements 5a and 5a.
It is extinguished by discharging in accordance with the leakage characteristic at 0 V (GND) of b.

That is, when the power is off, not only the switching element 4 but also the second switching elements 5a and 5a
b, the charge held in the pixel electrode 9 is discharged, so that the discharge of the charge can be completed in a shorter time than in the conventional method in which the charge is discharged using only the switching element 4. It is possible to make it difficult to cause an afterimage phenomenon at the time of off.

Further, as a liquid crystal display device according to the present invention, a TFT (Thin Film Tran) using a thin film transistor is used.
sistor) -LCD. In this case, the configuration and operation are almost the same as those of the conventional example shown in FIG. 2, but are different in that switching elements 5a and 5b formed by thin film transistors are provided.

That is, for the switching elements 5a and 5b formed of thin film transistors, the gate electrode is connected to the common electrode wiring 3, the source or drain electrode is connected to the pixel electrode 9, and the other source or drain electrode is connected to the video signal wiring 1a. And 1b.

Further, since a voltage for turning off the switching elements 5a and 5b is always applied to the potential of the common electrode wiring 3, in a normal display state of the liquid crystal display device, the liquid crystal display device is completely the same as the conventional example. It is possible to perform the operation.

However, when the power is turned off, the electric charge held in the pixel electrode 9 can be discharged not only through the switching element 4 but also through the second switching elements 5a and 5b. The discharge can be completed in a shorter time than in the method of (1).

When the gate potential is equal to the source potential or the drain potential, the second switching elements 5a and 5b may be formed by a depression type thin film transistor in which a current flows between the source electrode and the drain electrode.

In this case, since the gate potential becomes equal to the source potential or the drain potential when the power is turned off, a current flows between the source electrode and the drain electrode, that is, between the pixel electrode 9 and the video signal lines 1a and 1b. Accordingly, it can be expected that the discharge time of the electric charge held in the pixel electrode 9 can be further reduced, and that the afterimage phenomenon does not occur.

As described above, according to the present embodiment, when the power supply of the liquid crystal display element is turned off, the electric charge held in the pixel electrode 9 can be discharged by a plurality of thin film transistors, or the leakage current at the time of extremely off. Since the voltage can be discharged by the depletion type thin film transistor having a large voltage, the voltage applied to the liquid crystal molecules, that is, the potential between the pixel potential 9 and the counter electrode 8 can be instantaneously equalized. Becomes possible.

[0025]

As described above, according to the liquid crystal display device of the present invention, when the power of the liquid crystal display element is turned off, the electric charge held in the pixel electrode 9 can be discharged from the plurality of thin film transistors. The voltage applied to the molecules, that is, the potential between the pixel potential 9 and the counter electrode 8 can be instantaneously made equal, and the afterimage when the liquid crystal display device is turned off can be eliminated.

[Brief description of the drawings]

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

FIG. 2 is an equivalent circuit diagram of a conventional liquid crystal display element.

[Explanation of symbols]

 1a, 1b video signal wiring 2 scanning signal wiring 3 common electrode wiring 4 switching element 5a, 5b second switching element 6 liquid crystal 7 capacitance between pixel electrode and common electrode wiring 8 counter electrode 9 pixel electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 29/786 H01L 29/78 614 5F110 F term (Reference) 2H092 JB22 JB31 JB64 JB65 NA01 PA06 2H093 NB07 NB11 NC09 NC11 NC18 NC35 NC36 NC90 ND12 5C006 AC11 AF33 AF51 AF52 BB16 BC06 FA34 5C080 AA10 BB05 DD09 DD30 EE28 FF11 JJ03 5C094 AA60 BA03 BA43 CA19 DB04 EA04 EA07 5F110 AA30 BB01

Claims (5)

[Claims] 1. A plurality of video signal wirings and a plurality of scanning signal wirings are arranged in a matrix on one substrate, and a first switching element is provided at each of intersections of the video signal wirings and the scanning signal wirings. The video signal wiring and the pixel electrode are connected by controlling the scanning signal wiring via the first switching element, and the common electrode wiring is disposed in parallel with the scanning signal wiring; A liquid crystal display device in which a wiring and the pixel electrode form a capacitor, comprising a second switching element that connects the video signal wiring and the pixel electrode. 2. The liquid crystal display device according to claim 1, wherein a potential set so as to turn off said second switching element is applied to said common electrode wiring during normal use. 3. The electric potential applied to the common electrode wiring,
3. The liquid crystal display device according to claim 2, wherein the potential is not higher than the potential of the scanning signal line applied when the first switching element is turned off. 4. The liquid crystal display device according to claim 1, wherein the second switching element is formed by a thin film transistor. 5. A depletion-type transistor in which a thin film transistor formed as the second switching element flows a current between a source electrode and a drain electrode when a gate potential is equal to a source potential or a drain potential. Item 5. A liquid crystal display device according to item 4.