JPH1124045A - Active matrix type liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving method for liquid crystal which can decrease problems such as the deterioration in display quality and the shortening of the life of the liquid crystal by adjusting a counter electrode to an optimum counter electrode at any time even if there is a partial rise in temperature or variation in the environmental temperature. SOLUTION: When a built in a set of a light source, a personal computer, etc., the surface distribution of heat applied to a liquid crystal layer and its extent are checked, parts of the counter electrode on the liquid crystal layer which are greatly affected by the light source and not affected are divided into three parts such as a counter electrode 13, a counter electrode 14, and a counter electrode 15, whose temperatures are measured by a temperature sense part to supply optimum counter voltages to the respective counter electrodes according to the temperatures. Consequently, the liquid crystal layer can be driven with alternating currents without DC components at almost all of the parts to suppress the deterioration in display quality, the shortening of the life of the liquid crystal, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active matrix type liquid crystal display device which provides an image in combination with a liquid crystal and a driving method thereof.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in many fields, taking advantage of their features such as thinness and light weight. Among them, a so-called active matrix type liquid crystal display device in which a switching element is arranged for each pixel can provide a high-quality image in addition to the above-described features.
Attention has been paid to display devices for A-devices and AV devices.

FIG. 4 shows a structure of a general active matrix type liquid crystal display device. FIG. 4 shows two substrates 1 and 2 sandwiching a liquid crystal, a light guide plate 11 and a light source 12 provided behind these substrates, and a gate drive circuit 9, a source drive circuit 10, and a control circuit provided therearound. 17 is a plan view.

A gate bus line 6 and a source bus line 7 are formed as signal lines at high density on the surface of one of the substrates 2 which is in contact with the liquid crystal, and are orthogonal to each other and electrically insulated from each other. Have been. In the vicinity of each intersection, a TFT element 5 and a pixel electrode 4 are provided in a region surrounded by the gate bus line 6 and the source bus line 7, respectively.
The source bus line 7 and the pixel electrode 4 are electrically connected.

Although not shown, a capacitance wiring is formed in parallel with the gate bus line and so as to overlap the pixel electrode. In some cases, the pixel electrode is overlapped with a next-stage gate bus line without forming the capacitor wiring. Hereinafter, the former structure is referred to as Cs-on-Com
The latter structure is called a Cs-on-Gate structure.
Called structure.

[0006] On the surface of the other substrate 1 which is in contact with the liquid crystal, a counter electrode 8 provided opposite to the pixel electrode 4 is provided on the entire surface. Is bonded with a sealant (not shown), and liquid crystal is injected into the gap.
It is sealed. The liquid crystal injected between the substrates 1 and 2 is oriented so that the liquid crystal molecules are twisted by about 90 degrees between the substrates 1 and 2 by the regulating force of an alignment film (not shown) formed on the inner surfaces of the substrates 1 and 2. doing.

Further, a gate drive circuit 9 and a source drive circuit 10 for controlling voltages applied to the gate bus line 6 and the source bus line 7 are provided around the substrate 2, and these are connected to a control circuit 17. Have been. The control circuit 17 includes a power supply, a clock signal, and an HS (not shown).
A YN signal, a VSYN signal, and the like are input, and a desired voltage is applied to each of the gate drive circuit 9, the source drive circuit 10, and the counter electrode 8.

On the back side of the substrate 2, at least a light source 12 and a light radiated from the light source 12 uniformly irradiate the liquid crystal layer with light, and the light amount is constant. An illumination device having a light guide plate 11 controlled so as to be provided. Generally, the light guide plate 11 is a transparent or translucent one made of an acrylic resin or the like, and the light source 12 is a straight tube fluorescent lamp for realizing a thin liquid crystal display device.

Although not shown, a polarizing plate is attached to each of the substrates 1 and 2. The polarizing plates are arranged such that their polarization axes are parallel or orthogonal.

FIG. 6 is an equivalent circuit diagram of the gate bus line 6, the source bus line 7, the TFT element 5, the pixel electrode 4, and the capacitor wiring 38 formed on the substrate 2. In FIG. 6, G, S and D are TFTs, respectively.
A gate electrode, a source electrode, and a drain electrode of the element 5 are shown, and are connected to the gate bus line 6, the source bus line 7, and the pixel electrode 4, respectively. Clc is a liquid crystal capacitance formed between the pixel electrode 4 and the counter electrode 8,
Ccs is an auxiliary capacitance formed between the pixel electrode 4 and the capacitance wiring 38, and Cgd is a parasitic capacitance formed between the gate electrode G and the drain electrode D of the TFT element 5.

A driving method of the active matrix type liquid crystal display device having such a configuration will be described below. First, when a predetermined voltage is sequentially applied to each gate bus line 6 from the gate drive circuit 9, the gate electrode G of the TFT element 5 connected to the gate bus line 6 is applied.
Is applied through the gate bus line 6 to the
The element 5 is turned on. At this time, when a desired voltage is applied from the source drive circuit 10 to each pixel electrode 4 connected to the TFT element 5 which has been turned on via the source bus line 7, the source electrode S and the drain of the TFT element 5 The voltage is transmitted to the pixel electrodes 4 through the electrodes D, and a desired voltage can be applied to each pixel electrode 4.
The alignment direction of liquid crystal molecules between the pixel electrode 4 and the counter electrode 8 can be controlled.

Since the characteristics of the liquid crystal deteriorate when a constant DC voltage is applied for a long time, the potential difference between the pixel electrode 4 and the counter electrode 8 is constant, but the direction of the potential is reversed. , AC drive.

With such a configuration, the light emitted from the light source 12 is incident on the liquid crystal layer on the pixel electrode 4 through the polarizing plate (not shown) attached to the substrate 2 via the light guide plate 11, A polarizing plate (not shown) that is twisted along the alignment direction of the liquid crystal molecules changed by the potential difference generated between each pixel electrode 4 and the counter electrode 8 and is attached to the substrate 1
Through. At this time, since the amount of transmitted light changes in accordance with the change in the alignment direction of the liquid crystal molecules, display is performed using this.

In general, it is known that the potential applied to the liquid crystal layer shifts by a potential called a pull-in voltage after writing the voltage on the pixel electrode 4. Usually, the potential of the pull-in voltage is considered in consideration of the value of the pull-in voltage. The voltage applied to the counter electrode 8 is determined. Note that the pull-in voltage δV is equal to the parasitic capacitance Cg.
d, the liquid crystal capacitance Clc, the auxiliary capacitance Ccs, and the voltage Vgon for turning on the gate electrode G of the TFT element 5 and the voltage Vgoff for turning off the gate electrode G are expressed as follows.

[0015]

(Equation 1)

[0016]

However, when the above-described liquid crystal display device is incorporated in a set of a personal computer or the like, the temperature of the liquid crystal panel partially increases due to the heat generated from the light source 12, and as a result, Since temperature variations occur as a whole, the drop-in voltage δV1 in the vicinity of the light source 12 of the liquid crystal panel is different from the drop-in voltage δV2 in the central portion of the liquid crystal panel due to a change in the liquid crystal capacitance Clc or a change in the parasitic capacitance Cgd of the TFT element 5. Was different.

Therefore, as shown in FIG. 5, if the voltage applied to the counter electrode 8 is adjusted to the voltage applied to the liquid crystal layer in the central portion of the liquid crystal panel, the light source 12
In the vicinity, it is not possible to eliminate the DC component of the voltage applied to the liquid crystal layer.
Not only does display quality such as flicker and burn-in deteriorate, but also the life of the liquid crystal decreases.

Even if the voltage applied to the counter electrode 8 is adjusted to the voltage applied to the liquid crystal layer near the light source 12 of the liquid crystal panel, the DC voltage of the The components cannot be eliminated, and the same problem occurs. This means
Cs-on-Common structure also has Cs-on-
This is a problem commonly occurring in the gate structure.

In Japanese Patent Application Laid-Open No. Hei 8-201779, measures against display unevenness due to a change in optical characteristics of a liquid crystal display element due to the influence of heat of a light source are described.
The present invention relates to a simple matrix type liquid crystal display device, and generally cannot solve a problem associated with a fluctuation in the pull-in voltage δV in an active matrix type liquid crystal display device having a counter electrode formed on the entire surface.

In the active matrix type liquid crystal display device, a structure in which a counter electrode is divided is disclosed in
Japanese Patent Application Laid-Open No. 224235 discloses a method for compensating for a decrease in display quality due to a change in the parasitic capacitance Cgd for each exposure region with the boundary of the exposure pattern as a boundary. It cannot compensate for the deterioration of display quality due to the change.

The present invention has been made in view of the above-described problems. Even when a partial rise in temperature occurs due to heat or the like generated from a light source, an optimum voltage is always applied to the counter electrode. Another object of the present invention is to provide an active matrix type liquid crystal display device and a driving method thereof, which can reduce the deterioration of display quality and the life of liquid crystal.

[0022]

According to a first aspect of the present invention, there is provided an active matrix type liquid crystal display device having a first substrate on which a plurality of signal lines, pixel electrodes and switching elements are formed, and a counter electrode. A liquid crystal panel in which a second substrate and a second substrate are arranged with their electrode surfaces facing each other, and a liquid crystal is sandwiched between the two substrates; and a control circuit for supplying a voltage for performing display on the liquid crystal panel And an illuminating device provided on the back surface of the liquid crystal panel, wherein the counter electrode formed on the second substrate has a plurality of portions extending in a direction parallel to a light source of the illuminating device. And a desired voltage is applied to each of the opposed electrodes.

Therefore, even when the temperature of the liquid crystal panel partially rises, the DC component of the voltage applied to the liquid crystal layer can be eliminated by applying the optimum counter electrode driving voltage to each counter electrode. Therefore, it is possible to prevent a decrease in display quality and a decrease in the life of the liquid crystal.

Further, the liquid crystal panel has temperature sensing means for detecting the temperature of each of the counter electrodes, and the control circuit has a temperature / voltage for converting the temperature sensed by the temperature sensing means into a voltage. As long as the liquid crystal panel includes a conversion unit and a common electrode driving unit that generates a desired common electrode driving voltage based on the converted voltage, even if the temperature of the panel changes during use of the liquid crystal panel, In each case, it becomes possible to apply an optimum counter electrode drive voltage to each counter electrode.

The counter electrode formed on the second substrate is:
The liquid crystal panel may be divided based on the in-plane distribution of heat applied to the liquid crystal depending on the usage environment. In this case, it is possible to further suppress the occurrence of temperature variation in each of the opposed electrodes.

Further, the opposed electrodes formed on the second substrate may be divided so that the in-plane resistance of each divided opposed electrode is equal. In this case, it is not necessary to generate the counter electrode drive voltage in consideration of the in-plane resistance value of each counter electrode.

According to a fifth aspect of the present invention, there is provided a method of driving an active matrix type liquid crystal display device having an opposing electrode divided into a plurality of portions in a direction parallel to a light source of a lighting device. A method of detecting a temperature near each of the opposed electrodes by a temperature sensing means provided on each of the opposed electrodes, and changing a voltage applied to each of the opposed electrodes based on the sensed temperature. Things.

As described above, it is possible to apply the optimum opposing electrode drive voltage corresponding to the temperature to each opposing electrode.
It is possible to prevent a decrease in display quality and a decrease in the life of the liquid crystal.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. FIG. 1 is a diagram showing an active matrix type liquid crystal display device of the present embodiment.
Is a substrate made of a light-transmitting insulating material such as glass.
Reference numerals 1 and 12 denote a light guide plate and a light source, respectively. 13,
Reference numerals 14 and 15 denote counter electrodes divided into a plurality of portions in a direction parallel to the light source 12, and reference numeral 25 denotes a control circuit. Since other configurations are the same as those of the conventional active matrix type liquid crystal display device shown in FIG.
The same reference numerals are given and the description is omitted.

FIG. 2 shows how the counter electrodes 13, 14, 15 and the control circuit 25 are connected. In FIG. 2, 2
0 is a temperature sensing unit composed of a thermocouple, a thermistor, etc.
It is provided around the display area so as not to hinder display. In the control circuit 25, a counter electrode control circuit 24 and a temperature / voltage conversion circuit 23 are provided.

Hereinafter, a specific driving method of the active matrix type liquid crystal display device of the present embodiment will be described.

First, when the liquid crystal display device is incorporated in a set of a personal computer or the like, the surface distribution and the degree of the heat applied to the liquid crystal layer from a light source or the like are examined in advance. Based on the result, for example, as shown in FIG. 1, the regions of the counter electrode on the liquid crystal layer which is significantly affected by heat and the region of the counter electrode which is not so are divided by the counter electrodes 13, 14 and 15. Into three parts. In the present embodiment, the counter electrode 1
Reference numerals 3 and 15 denote opposing electrodes on the liquid crystal layer that are significantly affected by heat, and opposing electrodes 14 are opposing electrodes on the liquid crystal layer that are not affected by heat.

Generally, the heat applied to the liquid crystal display device is most affected by the heat generated from the light source. Therefore, it is preferable that the counter electrode is divided in a direction parallel to the light source 12. In addition, these counter electrodes 13, 14, 15
In order to prevent the space between the opposing electrodes from overlapping with the pixel electrodes, the width of each of the opposing electrodes 13, 14, 15 needs to correspond to an integer number of rows of the pixel electrodes. For example, when the number of gate bus lines is 480, the surface distribution and the degree of heat applied to the liquid crystal layer from a light source or the like are examined in advance, and it is desirable that the width of each counter electrode is 1: 6: 1. Here, the counter electrodes 13 and 15 have a width corresponding to 60 rows of the pixel electrodes, and the counter electrode 14 has a width corresponding to 360 rows of the pixel electrodes.

Then, at the time of actual driving, the temperature changed by the light source 12 and the use environment is measured by the temperature sensing unit 20, and a temperature signal is generated for each of the counter electrodes 13, 14, and 15. Next, the temperature signal is converted to a temperature / voltage conversion circuit 23 provided corresponding to each counter electrode.
Thus, the signal is converted into a level control signal for each counter electrode.

Further, based on the converted level control signals, the opposing electrode control circuit 24 generates an opposing electrode driving voltage that is optimal for each opposing electrode, and converts each opposing electrode driving voltage to the corresponding opposing electrode 13. , 14, and 15 are applied. In FIG. 2, there is no notation on the counter electrode 15, but the control method is the same as that of the other counter electrodes.

In this case, the counter electrode 13 and the counter electrode 14
FIG. 3 shows the voltage actually applied to the upper liquid crystal. As shown in FIG. 3, the pull-in voltage generated after the voltage writing of the pixel electrode 4 is caused by a change in the liquid crystal capacitance Clc and a change in the parasitic capacitance Cgd in the corresponding portion due to a difference in temperature between the opposing electrodes 13 and 14. Since the opposing electrode drive voltage applied to the opposing electrodes 13 and 14 is adjusted in accordance with δV1 and δV2, the DC component of the voltage applied to the liquid crystal layer can be eliminated.

As described above, in the active matrix type liquid crystal display device of the present embodiment, a plurality of opposing electrodes are provided in a direction parallel to the light source in correspondence with a portion which is largely affected by heat from the light source and a portion which is not. Since it is divided into
Appropriate voltage can be applied to each of the opposed electrodes independently, so that a reduction in display quality and a reduction in the life of the liquid crystal can be suppressed.

The temperature sensing unit 2 corresponds to each counter electrode.
Since 0 is provided and the voltage applied to the counter electrode is adjusted according to the temperature detected by the temperature sensing unit, it is possible to cope with a change in temperature that occurs during use of the liquid crystal display device.

In the description of this embodiment, FIG.
Although one temperature sensing unit 20 is set for each of the opposed electrodes as shown in (1), in practice, the temperature sensing units 20 are provided at several places for one opposed electrode in order to eliminate measurement errors. Is also good. The counter electrode may be divided into four or more parts.

(Embodiment 2) Another embodiment of the present invention will be described below. In the first embodiment described above,
Since the counter electrode is divided into a region that is significantly affected by heat and a region that is not so affected, the area of each counter electrode may differ depending on the case, and the in-plane resistance value may differ for each counter electrode. In such a case, it is necessary to set the counter electrode drive voltage applied to each counter electrode in consideration of the in-plane resistance value of each counter electrode.

For this reason, in the liquid crystal display device shown in the first embodiment, for example, when the number of gate bus lines is 480, the counter electrodes are equally divided into eight so that each counter electrode has a width of 60 rows of pixel electrodes. Electrodes 13, 1 in the form
If the opposing electrodes on both sides are used as 5 and the other 6 opposing electrodes are used as the opposing electrode 14, the opposing electrode driving voltage applied to each opposing electrode needs to consider the variation in the in-plane resistance value of each opposing electrode. Therefore, the counter electrode control circuit 24 in the control circuit 25 can be easily designed.

[0042]

As described above, in the active matrix type liquid crystal display device of the present invention, the counter electrode formed on the second substrate is divided into a plurality of portions in a direction parallel to the light source of the illumination device. Since a desired voltage is applied to each of the counter electrodes, even when the temperature of the liquid crystal panel partially rises, by applying an optimum counter electrode driving voltage to each of the counter electrodes, In addition, since the DC component of the voltage applied to the liquid crystal layer can be eliminated, there is an effect that the deterioration of the display quality and the life of the liquid crystal can be prevented.

Further, the liquid crystal panel has temperature sensing means for detecting the temperature of each of the counter electrodes, and the control circuit has a temperature / voltage for converting the temperature sensed by the temperature sensing means into a voltage. As long as the liquid crystal panel includes a conversion unit and a common electrode driving unit that generates a desired common electrode driving voltage based on the converted voltage, even if the temperature of the panel changes during use of the liquid crystal panel, In each case, an optimum counter electrode driving voltage can be applied to each counter electrode.

The counter electrode formed on the second substrate is
If the division is performed based on the in-plane distribution of the heat applied to the liquid crystal depending on the use environment of the liquid crystal panel, an effect that the temperature variation can be further suppressed in each of the opposed electrodes can be suppressed.

Further, if the opposing electrodes formed on the second substrate are divided so that the in-plane resistance of each of the divided opposing electrodes is equal, the in-plane resistance of each opposing electrode is reduced. It is no longer necessary to generate the counter electrode drive voltage
This has the effect of facilitating the design of the counter electrode driving means in the control circuit.

In the driving method of the active matrix type liquid crystal display device of the present invention, the temperature near each of the opposed electrodes is sensed by the temperature sensing means provided on each of the opposed electrodes, and each of the opposed electrodes is detected based on the sensed temperature. By changing the voltage applied to the electrodes, it is possible to apply an optimum opposing electrode drive voltage according to the temperature for each opposing electrode, thereby preventing a reduction in display quality and a reduction in the life of the liquid crystal. Play.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an active matrix type liquid crystal display device of the present invention.

FIG. 2 is an enlarged view of a counter electrode and a control circuit.

FIG. 3 is a waveform diagram of a liquid crystal applied voltage according to the driving method of the present invention.

FIG. 4 is a schematic view showing a conventional active matrix type liquid crystal display device.

FIG. 5 is a waveform diagram of a liquid crystal applied voltage according to a conventional driving method.

FIG. 6 is a peripheral circuit diagram of a TFT element.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 substrate 4 pixel electrode 5 TFT element 6 gate bus line 7 source bus line 8 counter electrode 9 gate drive circuit 10 source drive circuit 11 light guide plate 12 light source 13 counter electrode 14 counter electrode 15 counter electrode 17 control circuit 20 temperature sensing unit 23 temperature / voltage conversion circuit 24 counter electrode control circuit 25 control circuit 38 capacitance wiring

Claims (5)

[Claims] A first substrate on which a plurality of signal lines, pixel electrodes, and switching elements are formed, and a second substrate on which a counter electrode is formed, with their electrode surfaces facing each other; Active matrix type liquid crystal including a liquid crystal panel having liquid crystal sandwiched between two substrates, a control circuit for supplying a voltage for performing display on the liquid crystal panel, and a lighting device installed on the back of the liquid crystal panel In the display device, a counter electrode formed on the second substrate is divided into a plurality of portions in a direction parallel to a light source of the lighting device, and a desired voltage is applied to each of the counter electrodes. An active matrix type liquid crystal display device characterized by the above-mentioned. 2. The liquid crystal panel has a temperature sensor for detecting the temperature of each of the counter electrodes, and the control circuit has a temperature / voltage for converting the temperature sensed by the temperature sensor into a voltage. 2. The active matrix liquid crystal display device according to claim 1, further comprising a conversion unit, and a counter electrode driving unit that generates a desired counter electrode driving voltage based on the converted voltage. 3. The liquid crystal display according to claim 1, wherein the counter electrode formed on the second substrate is divided based on an in-plane distribution of heat applied to the liquid crystal depending on a use environment of the liquid crystal panel. An active matrix type liquid crystal display device as described above. 4. The device according to claim 1, wherein the opposing electrodes formed on the second substrate are divided such that the in-plane resistance values of the respective opposing electrodes are equal. Active matrix type liquid crystal display device. 5. A method for driving an active matrix type liquid crystal display device having an opposing electrode divided into a plurality of portions in a direction parallel to a light source of a lighting device, comprising: a temperature sensing means provided on each of the opposing electrodes. A method for driving an active matrix type liquid crystal display device, comprising: sensing a temperature in the vicinity of each counter electrode; and changing a voltage applied to each counter electrode based on the sensed temperature.