JPH05323343A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To evade waveform distortion due to a transient phenomenon of an applied waveform accompanying the switching of a driving voltage for effective voltage application and to obtain the display element of high quality by providing a segment electrode on a 1st substrate, an auxiliary electrode which is arranged on a 2nd substrate opposite the segment electrode, an insulating layer on the auxiliary electrode, and a common electrode on the insulating layer. CONSTITUTION:A capacitor CLC is composed of the segment electrode 2, an orientation film 3, a liquid crystal layer 7, an oriented film 6, and a common electrode 4. A capacitor CAD is composed of the common electrode 4, an insulating layer 9, and the auxiliary electrode 8 and electrically connected to the capacitor Cap in series. Further, a voltage VAD=CVLCXCLC/CAD) is applied to the capacitor CAD, so when the applied voltage is inverted in level, the directions of a displacement current ILC and a displacement current IAD are put in mutually opposite relation as to the common electrode 4. The voltage waveform distortion of the common electrode 4 is remarkably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duty-driven liquid crystal display device such as a matrix type LCD (liquid crystal display).

[0002]

2. Description of the Related Art When a matrix type LCD is driven by a voltage averaging method, a scanning voltage is sequentially applied to a plurality of scanning electrodes (common electrodes) laterally formed on one of a pair of substrates. Then, in synchronization with this, a signal voltage is applied to a plurality of signal electrodes (segment electrodes) vertically formed on the other substrate. As a result, the driving voltage, which is the difference voltage between the scanning voltage and the signal voltage, is applied to each pixel (pixel) corresponding to the intersection of the scanning electrode and the signal electrode, and the LCD
A desired character or figure is displayed on the screen.

In order to turn a pixel into an ON state (optically lit state), it is necessary to apply an effective voltage of Von = Vop / BIAS × ((BIAS ² + DUTY-1) / DUTY) ^1/2 (1). is there. Similarly, in order to put the pixel in the OFF state (optically non-illuminated state), Voff = Vop / BIAS × (((BIAS-2) ² + DUTY-1) / DUTY) ^1/2 (2) effective voltage Need to be applied.

In the above equations (1) and (2), Vop is a constant voltage preset according to the liquid crystal material, and BIAS
(Bias) is a value equal to (DUTY ^1/2 +1). DU
TY (duty) is set according to the total number of pixels of the LCD, for example, it is normally set to 200 when the LCD has pixels of 400 dots in the vertical direction, and 48
It is normally set to 240 if it has 0 dots of pixels.

By the way, a conventional liquid crystal display element is provided with a segment glass 11 having segment electrodes 12 ... And an alignment film 13 provided on the segment electrodes 12 ... As shown in FIG. Further, the liquid crystal display element includes a common electrode 15 and a common glass 15 having an alignment film 16 provided on the common electrode 14. The segment glass 11 and the common glass 15 are arranged so as to face each other with a predetermined distance therebetween, and a liquid crystal layer 17 is sandwiched between the two glasses.

Therefore, the liquid crystal display element is generally high in resistance and capacitive, and electrically bidirectional. As shown in FIG. 3, the equivalent circuit has a loop resistance R (R = R
₁ + R ₂ ) and a capacitor C are connected in series (forming a kind of low-pass filter). LCD
The actual loop resistance R of the panel is O of the segment LSI.
It is the sum of N resistance, segment ITO resistance, common ITO resistance, and ON resistance of common LSI. Further, the capacitor C includes the segment electrode 12 and the alignment film 1.
3, the liquid crystal layer 17, the alignment film 16, and the common electrode 14.

In the above driving method, the waveform of the driving voltage is distorted due to the inversion of the voltage levels of the scanning voltage and the signal voltage. This is due to the low pass filter
This is because the waveform distortion occurs due to the transient phenomenon of the applied waveform accompanying the switching of the driving voltage for applying the effective voltage. As a result, the effective voltage applied between the electrodes drops or rises, so that the brightness of each pixel of the display element also differs from the original brightness, causing so-called brightness unevenness (hereinafter referred to as shadowing). .. The liquid crystal display element responds to the effective value of the applied voltage in a region having no frequency dependence.

Now, the shadowing caused in the pixel by decreasing or increasing the effective voltage Von or Voff will be described below.

Assuming that the capacitance of the liquid crystal display element is C and the loop resistance is R, the drop in effective voltage due to shadowing is (1- (1-1.5.C.R.N.F) ^{1 / 2} ) Proportional to Vop / BIAS. Note that N is the number of times the voltage level of the signal voltage is inverted (the number of times of segment direction inversion), and F is the inverse of the frame time (one screen scanning frequency).

Therefore, shadowing is prevented by setting the BIAS large or reducing the loop resistance R to suppress the decrease amount of the effective voltage.

[0011]

However, in the above conventional structure, two types of shadowing occur, as shown in FIG. One of them is a bar graph 21a extending vertically in the lower center of the LCD 20 in black (OFF state).
When displayed with, the brightness of the white (ON state) area 22a (including the framing pattern) on the extension of the bar graph 21a is
The brightness increases for the white areas 23, 23 on both sides of the bar graph 21a. The other one is to display the bar graphs 21b to 21e as shown in FIG.
Of the white (ON state) regions 22b to 22e (including the framed pattern) on the extension of the bar graphs 21b to 21e.
There is a problem that the brightness is reduced for the white areas 23, 23 on both sides of.

The cause of the former shadowing will be described below with reference to FIGS. 5 and 6.

A scanning voltage is sequentially applied to the scanning electrodes for each pulse of the scanning line shift clock signal 24 of FIG. 5A, and the level of the scanning voltage is an alternating signal 25 (FIG. 5).
It is inverted in a predetermined cycle based on (b). On the other hand, the scan line shift clock signal 2 is applied to each signal electrode.
4 is applied with a signal voltage (see FIG. 5 (c)),
The level of the signal voltage is also inverted based on the alternating signal, like the level of the scanning voltage.

In FIG. 5 (c), voltage levels V ₀ and V ₅ represent signal voltages (hereinafter referred to as lighting voltage) for turning on the pixel, and voltage levels V ₂ and V ₃ represent the pixel. The signal voltage (hereinafter, referred to as a non-lighting voltage) for turning off the LED is shown. The voltage levels V ₁ and V
Reference numeral ₄ is a scanning voltage applied to the unselected scanning electrodes (hereinafter, referred to as non-selection voltage).

When the AC signal 25 is inverted, both the scanning voltage level and the signal voltage level are inverted, so that all pixels are charged and discharged. At this time, as shown in FIG.
The waveform 27 of the non-selected voltage is significantly distorted by the transient phenomenon.

As shown in FIG. 4, when most of the pixels of the LCD 20 are in the ON state, the waveform 27 of the non-selection voltage is distorted to the lighting voltage side (the voltage level V ₀ side in the figure) (FIG. 6). reference). On the contrary, when most of the pixels of the LCD 20 are in the OFF state, the waveform of the non-selection voltage 27
Is distorted to the non-lighting voltage side (the voltage level V ₂ side in the figure) (see FIG. 6).

For this reason, the effective value of the driving voltage increases in the pixel on the signal electrode where the non-lighting voltage is applied for a long time like the region 22a. On the other hand, area 23.2
In the pixel on the signal electrode to which the lighting voltage is constantly applied as in No. 3, the effective value of the driving voltage is lowered. This causes a type of shadowing in which the brightness of the area 22a rises with respect to the areas 23 on both sides.

Such shadowing cannot be sufficiently dealt with by the conventional shadowing prevention method for increasing BIAS.

In the areas of the bar graphs 21b to 21e,
The lighting voltage and the non-lighting voltage are alternately applied to each scanning electrode or each signal electrode. Therefore,
In the regions 22b to 22e on this extension line, the waveform becomes blunt each time the drive voltage changes, and shadowing occurs in the direction in which the effective value decreases.

[0020]

The liquid crystal display element of the present invention is characterized by the following means in a liquid crystal display element in which liquid crystal is sandwiched between a first substrate and a second substrate.

That is, the liquid crystal display device includes a plurality of segment electrodes provided on the first substrate, an auxiliary electrode provided on the second substrate so as to face each of the segment electrodes. It includes an insulating layer provided on the auxiliary electrode and a common electrode provided on the insulating layer.

[0022]

According to the above construction, the segment electrode, the liquid crystal,
The first capacitor is formed by the common electrode.
Further, the second capacitor is formed by the common electrode, the insulating layer, and the auxiliary electrode. At this time, in order that the charges accumulated in the segment electrodes and the charges accumulated in the auxiliary electrodes have polarities different from each other, the first capacitor and the second capacitor have a voltage such that they are electrically connected in series. Each is applied.

A first displacement current flows from the segment electrode to the common electrode (or vice versa) according to the accumulated charge and the capacitance of the first capacitor. At the same time, depending on the accumulated charge and the capacitance of the second capacitor, from the common electrode to the auxiliary electrode (or vice versa).
The second displacement current flows in.

At this time, the first displacement current and the second displacement current flow in opposite directions to the common electrode. Therefore, the total current flowing through the common electrode decreases,
The voltage waveform distortion of the common electrode is remarkably improved. For example, the product of the capacitance of the first capacitor and the AC voltage applied to the first capacitor is made equal to the product of the capacitance of the second capacitor and the AC voltage applied to the second capacitor. Then, apparently no current flows through the common electrode, and the voltage waveform distortion of the common electrode disappears.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

Regarding the liquid crystal display element according to this embodiment, L
A CD (liquid crystal display element) panel will be described as an example. This LCD panel comprises a plurality of pixels (segments), and as shown in FIG. 1, comprises segment electrodes 2 ... And segment glass 1 (first substrate) having an alignment film 3 provided on the segment electrodes 2. ing. The total number of pixels of the LCD includes one having 400 dots in the vertical direction and one having 480 dots in the vertical direction.

Further, the above LCD panel has auxiliary electrodes 8
,, auxiliary electrode 8, an insulating layer 9 provided on the common electrode 4, a common electrode 4 provided on the insulating layer 9, and an alignment film 6 provided on the common electrode 4 (second substrate). I have it.

The auxiliary electrodes 8 are arranged so as to face the corresponding segment electrodes 2 ... The segment glass 1 and the common glass 5 are arranged so as to face each other with a predetermined distance therebetween,
A liquid crystal layer 7 is sandwiched between both glasses.

The LCD panel is capacitive and electrically bidirectional. Then, as shown in FIG. 1, the equivalent circuit corresponding to each pixel has a loop resistance R (R = R ₁
+ R ₂ ), the capacitor C _{LC of} each pixel, and the capacitor C _AD are electrically connected in series. The actual loop resistance R of the LCD panel is the sum of the ON resistance of the segment LSI, the segment ITO resistance, the common ITO resistance, the ON resistance of the common LSI, and the ON resistance of the auxiliary LSI.

The above-mentioned capacitor C _LC (whose electrostatic capacity is C _LC ) is formed by the segment electrode 2, the alignment film 3, the liquid crystal layer 7, the alignment film 6, and the common electrode 4. On the other hand, the above-mentioned capacitor C _AD (whose electrostatic capacity is C _AD ) is formed by the auxiliary electrode 8, the insulating layer 9, and the common electrode 4.

In the above structure, as shown in FIG.
Between the segment electrode 2 and the common electrode 4, the voltage V _LC = with the inversion of the scanning voltage level and the signal voltage level.
When Vop / BIAS is applied, the charge amount Q (= C _LC · V _LC ).
_Are accumulated in the capacitor C _LC (that is, + Q charges are accumulated in the segment electrode 2 and the common electrode 4
-Q charge is stored in). And the displacement current I _LC
Flow from the segment electrode 2 toward the common electrode 4.

Vop is a constant voltage preset according to the liquid crystal material, and BIAS is a value equal to (DUTY ^1/2 +1). Also, DUTY is set according to the total number of pixels of the LCD, and is usually 200 or 240.

At this time, between the common electrode 4 and the auxiliary electrode 8,
Along with the above inversion, the voltage V _AD (= V _LC × C _LC / C _AD )
Is applied. As a result, the same amount of charge as stored in the capacitor _{C LC Q (= C AD ·} V AD = C LC · V LC) is stored in the capacitor C _AD (that is, the common electrode 4 +
Along with the accumulation of Q charges, the auxiliary electrode 8 also accumulates -Q charges). Then, the displacement current I _AD flows from the common electrode 4 toward the auxiliary electrode 8.

As described above, according to the configuration of this embodiment,
Common electrode 4, the insulating layer 9, and the capacitor C _AD is formed by the auxiliary electrode 8, the capacitor C _LC and while being electrically connected in series, a voltage V _AD (= V in the capacitor C _{AD
Since LC} × C _LC / C _AD ) is applied, the direction of the displacement current I _{LC and} the direction of the displacement current I _AD are opposite to each other with respect to the common electrode 4 when the applied voltage level is inverted. Ideally, I _LC = I _AD , and at this time, the displacement current flowing to the common electrode 4 becomes zero.

For example, when C _LC = C _AD and V _LC = V _AD , the voltage waveform of the segment electrode 2 becomes as shown by the solid line in FIG. 2 (a), and the voltage waveform of the auxiliary electrode 8 is shown in FIG.
It becomes as shown by the solid line in (b). Therefore, the voltage waveform of the common electrode 4 at this time is as shown by the broken line in FIG.

Therefore, since the voltage waveform distortion of the common electrode 4 is remarkably improved, the waveform distortion caused by the transient phenomenon of the applied waveform accompanying the switching of the driving voltage for applying the effective voltage (in FIG. 4, the brightness of the region 22a). The shadowing of the type that rises with respect to the regions 23 on both sides is reduced. Therefore, a high quality liquid crystal display device can be provided.

Further, by reducing the resistance value of the auxiliary electrode 8, it is possible to reduce the shadowing of the type in which the brightness of the regions 22b to 22e in FIG. 4 is reduced with respect to the regions 23 and 23 on both sides. ..

Further, according to the configuration of this embodiment, since the capacitor C _LC and the capacitor C _AD are electrically connected in series, the pixel is adjusted by adjusting the ratio of the capacitances C _LC and C _AD. Since the apparent electrostatic capacity can be reduced, high-speed response can be achieved with low power, and various advantages can be enjoyed in manufacturing the element or in electrical rating.

[0039]

As described above, the liquid crystal display element of the present invention comprises a plurality of segment electrodes provided on the first substrate,
An auxiliary electrode provided on the second substrate so as to face each of the segment electrodes, an insulating layer provided on the auxiliary electrode, and a common electrode provided on the insulating layer. It is a configuration provided with.

Therefore, the waveform distortion due to the transient phenomenon of the applied waveform due to the switching of the driving voltage for applying the effective voltage is prevented without complicating the configuration and largely changing the driving method from the conventional one. It can be avoided. Therefore, each pixel is displayed with the brightness that should be originally displayed (shadowing is reduced), so that a high quality liquid crystal display device can be provided.

Further, by reducing the resistance value of the auxiliary electrode, it is possible to reduce the shadowing of a type in which the luminance of a certain region is lowered with respect to the regions on both sides.

Furthermore, since the apparent capacitance of each pixel can be reduced, various advantages can be obtained in manufacturing the device or in terms of electrical rating.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a liquid crystal display element of the present invention.

FIG. 2 is a waveform diagram showing an outline of a liquid crystal drive waveform of the above liquid crystal display element.

FIG. 3 is a cross-sectional view showing a configuration example of a conventional liquid crystal display element.

FIG. 4 is an explanatory diagram showing various types of shadowing that occur when a conventional liquid crystal display element is duty-driven.

5 is a waveform diagram for explaining the cause of the shadowing in FIG.

FIG. 6 is a partially enlarged view of the waveform of FIG. 5C when inverted.

[Explanation of symbols]

 1 segment glass (first substrate) 2 segment electrode 3 alignment film 4 common electrode 5 common glass (second substrate) 6 alignment film 7 liquid crystal layer 8 auxiliary electrode 9 insulating layer

Claims (1)

[Claims] 1. A liquid crystal display device in which a liquid crystal is sandwiched between a first substrate and a second substrate, wherein a plurality of segment electrodes provided on the first substrate and a plurality of segment electrodes provided on the second substrate. A liquid crystal display device comprising: an auxiliary electrode arranged to face the segment electrode, an insulating layer provided on the auxiliary electrode, and a common electrode provided on the insulating layer. ..