JPH07181445A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the display grade of a liquid crystal display device of a simple matrix type by eliminating the nonuniformity of display occurring in the distortion, etc., of the voltages impressed to liquid crystals. CONSTITUTION:The effective voltage values to be impressed between third electrodes 104 and signal electrodes 102 are changed in such a direction where the voltages impressed to the liquid crystals on the signal electrodes 102 are made uniform with each other according to the display contents of pixel 103 groups on the individual signal electrodes 102. Namely, such voltages that the effective values of the voltages impressed to the liquid crystals on the signal electrodes 102 having many on pixels on the same signal electrodes 102 and the effective values of the voltages impressed to the liquid crystals on the signal electrodes 102 having many off pixels separate from the signal electrodes 102 are made uniform are impressed to the third electrodes 102. As a result, the display unequalness of the screen occurring in the variation in the voltage impressed to the liquid crystals between plural pieces of the signal electrodes 102 is lessened or eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and in particular, it eliminates display nonuniformity caused by distortion of a liquid crystal applied voltage between display electrodes which are arranged to intersect and face each other, thereby improving display quality. The present invention relates to an improved liquid crystal display device.

[0002]

2. Description of the Related Art In a so-called simple matrix type liquid crystal display device, a strip made of a transparent conductive film such as ITO (Indium Tin Oxide) is provided on each surface of a transparent insulating substrate such as two glass substrates facing each other. Using a plurality of electrodes arranged in parallel in a row as an electrode group, two glass substrates on which these electrodes are formed are arranged at intervals and face each other so that the electrode groups intersect. Then, a liquid crystal layer is enclosed and sandwiched between these electrodes to form a liquid crystal cell.

Of the two electrodes facing each other, a scanning voltage (scanning pulse) having a scanning selection potential is applied line-sequentially to the scanning electrodes, and an image is applied to the signal electrodes on the opposite side. A video signal voltage for controlling lighting / non-lighting of each pixel for display is applied.
When the applied voltage is superposed on the liquid crystal layer, the liquid crystal layer responds to light / non-light each to form an image on the screen of the liquid crystal panel.

In such a conventional liquid crystal display device, since application of a DC voltage to the liquid crystal layer promotes deterioration of the liquid crystal (due to liquid crystal decomposition or the like), driving is generally performed using an AC voltage waveform. In reality, the frame inversion method is used in which the polarity of the drive voltage is inverted every frame.

However, in such a conventional liquid crystal display device, there is a problem in that display unevenness on the screen often occurs, for example, depending on a display image (display pattern), a shadow having a tail is generated in the image.

It is considered that the causes of such display unevenness are influenced by the internal resistance of each electrode and the capacitance of the liquid crystal cell. That is, since the liquid crystal display element has a characteristic as a CR circuit due to C _LC of the liquid crystal layer and internal resistance R of the electrode in terms of an equivalent circuit, this corresponds to the voltage waveform applied to the scan electrode or the signal electrode. On the other hand, it acts like a low-pass filter. Therefore, the voltage waveform applied to the electrode is distorted as it propagates on the electrode. Further, for example, the video signal voltage applied to the signal electrode appears as noise such as a spike wave shape on the scan electrode due to capacitive coupling with the scan electrode via the liquid crystal. This also occurs for the waveform from the scan electrode to the voltage of the signal electrode due to capacitive coupling through the liquid crystal layer.

The degree of distortion of the voltage waveform applied to each electrode and generation of noise depends on each display pattern. For example, in a pattern in which fine stripes are continuous, that is, in a pattern in which ON / OFF is frequently repeated, the frequency of the video signal voltage waveform becomes extremely high, and the influence of waveform distortion and noise is further increased. On the contrary, in the case of an image such as white display or black display over substantially the entire surface, the frequency of the signal voltage waveform is not so high, and therefore the influence of waveform distortion and noise is not so large.

In order to solve such a problem, in order to make the frequency of the signal voltage waveform uniform, the period of polarity reversal is shortened to a period shorter than one frame, and an alternating current is applied to each scan electrode N line. An N-line inversion method based on the optimization has been proposed.

However, display unevenness still occurs even when driven by the N-line inversion method.
Along with the recent demand for larger screens and multi-gradation gradation display, it has become a more significant problem.

ON / ON is one of the main causes for causing such a problem and making it difficult to solve.
The change in the capacitance of the liquid crystal display cell due to the OFF state can be mentioned. Liquid crystals used in liquid crystal display devices generally have dielectric anisotropy, and when a voltage above the threshold is applied, the liquid crystal molecules are arranged so that the axis with the larger dielectric constant is parallel to the electric field. Changes. Needless to say, liquid crystal display devices generally use this phenomenon for display. Therefore, the ON pixel has a larger capacitance than the OFF pixel, and the larger the capacitance is, the larger the distortion of the waveform becomes. Therefore, for example, an electrode having a large number of ON pixels to which a display pattern (signal voltage) is applied is The waveform will be distorted and the effective voltage will decrease. On the contrary, when the number of OFF pixels is large, the effective voltage does not drop so much,
The variation in waveform distortion between the ON pixel and the OFF pixel becomes large.

As described above, since the fluctuation of the video signal voltage on the signal electrode largely depends on the display pattern (display image), it causes display unevenness depending on each display pattern, and the N-line inversion method is the fundamental cause. Cannot be solved in a simple way. On the contrary, since the inversion period is further shortened, there is a problem that the display unevenness becomes more apparent than in the case of the conventional frame inversion.

It is considered that such a fluctuation of the voltage on the signal electrode can be reduced as the capacitance of the liquid crystal layer is reduced and the internal resistance of the electrode is reduced. However, the electrodes of the liquid crystal display cell need to be formed thin and have a small width in order to secure light transmittance and the number of pixels, and in order to secure transparency, a relatively large internal resistance such as ITO is required. to must be used a transparent conductive film, a very difficult to reduce the internal resistance, and for also the capacitance of the liquid crystal, the principle of operation of a liquid crystal display device, thereby reducing the liquid crystal capacitance C _LC It is not possible. Therefore, it has been difficult to solve the above problems by reducing the internal resistance of the electrodes and the capacitance of the liquid crystal layer.

[0013]

As described above, in the conventional liquid crystal display device, the applied voltage is transmitted on the electrodes due to the internal resistance of the electrodes of the liquid crystal display cell and the capacitance of the liquid crystal layer. There is a problem that noise is generated due to distortion or induction between the counter electrodes, and the display quality is degraded.

The present invention has been made to solve such a problem, and an object thereof is to simply drive a liquid crystal layer by applying a voltage to both electrodes in which a scanning electrode and a signal electrode are arranged to face each other. A liquid crystal display device of a matrix type or the like is to realize a liquid crystal display device having improved display quality by eliminating the occurrence of display nonuniformity due to distortion of applied voltage or the like.

[0015]

In the liquid crystal display device of the present invention, a plurality of scanning electrodes arranged on a first substrate are arranged so as to face the scanning electrodes with a gap therebetween. A plurality of signal electrodes arranged on the second substrate, a liquid crystal layer sandwiched in a gap between the scanning electrodes and the signal electrodes, and a scanning electrode driving circuit for applying a voltage to the scanning electrodes, In a liquid crystal display device having a signal electrode drive circuit for applying a voltage to the signal electrode, the sum of effective values of the liquid crystal applied voltage for each of the plurality of signal electrodes is connected to the third electrode, and A liquid crystal display device, comprising: a third electrode drive circuit that applies a voltage to the third electrode, the voltage varying in a direction in which the signal electrodes are made uniform.

[0016]

In the liquid crystal display device of the present invention, the effective voltage value applied between the third electrode and the signal electrode is set between the signal electrodes according to the display content of the pixel group on each signal electrode. The voltage applied to the liquid crystal is changed so as to be uniform. That is, the effective value of the liquid crystal applied voltage on the signal electrode having many ON pixels on the same signal electrode and the effective value of the liquid crystal applied voltage on the signal electrode having many OFF pixels on the signal electrode different from the signal electrode. Is applied to the third electrode. This makes it possible to reduce or eliminate display unevenness on the screen due to variations in the voltage applied to the liquid crystal between a plurality of signal electrodes.

[0017]

Embodiments of the liquid crystal display device of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing a main part of a structure of a liquid crystal display device of the present invention. This liquid crystal display device includes a liquid crystal display element 1, a scan electrode drive circuit 2 for applying a scan voltage to the liquid crystal display element 1, a signal electrode drive circuit 3 for applying a signal voltage, and a third electrode drive means 4. The power supply circuit 5 constitutes a main part of the power supply circuit 5.

The liquid crystal display element 1 uses two transparent insulating substrates such as glass substrates, and a transparent conductive film made of ITO (Indium Tin Oxide) as a material is formed on the opposing surface sides of the substrates. A plurality of electrode groups arranged in parallel are formed. The opposing electrode groups, that is, the scanning electrode group and the signal electrode group are formed so as to intersect in a substantially orthogonal direction with a gap. ing. A liquid crystal layer is sandwiched between the electrodes facing each other, and a pixel portion is formed at each portion where the electrodes facing each other intersect. As the liquid crystal layer, a super twisted nematic (STN) type liquid crystal was used in this embodiment. In the figure, the electrode group arranged so that the longitudinal direction is horizontal is the scanning electrode 1.
01, the electrode group formed so as to be orthogonal thereto is the signal electrode 102. Pixel 10 for each of these intersections
3 is formed. The pixels 103 are formed in a matrix as shown in the figure. In FIG. 1, each such pixel 103 is represented in a matrix. For example, 2 row and third column of pixels 103 are written as a _23.

A third electrode 104 is formed on a substrate on which the scanning electrodes 101 are arranged in a row, substantially parallel to a position adjacent to the endmost row of the scanning electrodes 101. Therefore, the third electrode 104 is arranged so as to be orthogonal to the signal electrode 102 and to face the signal electrode 102 with a gap. The third electrode 104 forms an electric capacity 105 by using a liquid crystal layer as a dielectric at each intersection with each signal electrode 102.

The panel size of the liquid crystal display element 1 is approximately A4.
Obviously, the number of pixels (dots) is 640 × 480 dots. That is, the scanning electrode 101 has 480 electrodes and the signal electrode 1
The number of electrodes of 02 is 640.

Each scan electrode 101 is connected to the scan electrode drive circuit 2, and each signal electrode 102 is connected.
Are connected to the signal electrode drive circuit 3, respectively.

The third electrode 104 is connected to the third electrode driving means 4.

The third electrode driving means 4 applies a voltage that changes the average value of the liquid crystal applied voltage between the plurality of signal electrodes 102 so as to be uniform.
4 is applied.

The scan electrode driving circuit 2 is a shift register 2
01, frame inversion circuit 202 and drive circuit array 2
The main part is constituted by 03, and one scanning selection voltage (scanning pulse) is line-sequentially applied to each scanning electrode in one frame period. In the scanning non-selection period, for example, a DC voltage is applied. While the scan selection voltage is applied to one scan electrode 101, the scan non-selection potential is held for the other scan electrodes 101 in the remaining scan selection period.

On the other hand, the signal electrode drive circuit 3 includes a shift register 301, a latch circuit 302, and a frame inversion circuit 30.
3 and the drive circuit array 304 form the main part. The video signal information input to the shift register 301 is serial-parallel converted via the latch circuit 302 and the like, and the signal information is introduced to the frame inversion circuit 303 and further to the drive circuit array 304 to form a video signal voltage waveform. . Then, a video signal voltage is applied in parallel to each electrode of the signal electrode 102. That is, in the pixel 103, for example, when a _ij is turned on (ON), the selection potential is applied, and when it is turned off (OFF), the non-selection potential is applied. In this way, the liquid crystal display element 1
Is driven.

The power supply circuit 5 is a power supply circuit for supplying a potential used to form a voltage waveform applied to each scan electrode 101 and each signal electrode 102 to each of the scan electrode drive circuit 2 and the signal electrode drive circuit 3. is there. The power supply potential supplied from the power supply circuit 5 is supplied to the drive circuit array 203 of the scan electrode drive circuit 2 and the drive circuit array 304 of the signal electrode drive circuit 3. And the drive circuit array 20
In 3, the supplied potential is switched and applied in a predetermined cycle to the corresponding scan electrode 101 for each scan selection period in a scanning manner. Also for the drive circuit array 304, a potential selected according to signal information of lighting or non-lighting is switched from the supplied power potential and applied to each predetermined signal electrode 102.

The third electrode driving means 4 is a counter circuit 401 for generating a square wave from a latch signal and a clock signal.
And frame inversion circuit 402 and drive circuit array 40
The main part is composed of 3 and, and the applied voltage having the waveform as shown in FIG. 2 is applied to the third electrode 104.

Next, the third electrode 104, which is the main part of the technique according to the present invention, the waveform of the applied voltage applied to the third electrode 104 from the third electrode driving means 4 and its operation will be described. explain. Here, in order to make the explanation easy to understand, as shown in FIG. 3, the number of pixels related to display is 2 rows × 3 columns.
A case of a liquid crystal display device having 6 pixels will be described as an example. It goes without saying that the operation of the present invention described with reference to FIG. 3 is also applied to the case where the number of electrodes is the number of liquid crystal display elements actually used such as the above-mentioned liquid crystal display element 1.

In FIG. 3, each signal electrode 102 is associated with two pixels for display. Further, three pixels relating to display are involved in each scan electrode 101. The third electrode 104 is arranged to face each signal electrode 102 so as to intersect with each other at substantially right angles, and the electric capacitance 105 is provided at each intersection with each signal electrode 102.
Is formed.

In FIG. 3, the leftmost first signal electrode 1
Pixels 103a ₁ , 1 associated with the signal electrode X _1, which is 02.
Both 03a ₂ are in the ON state. At this time, the electric capacitance 105 at the intersection of the third electrode 104 and the signal electrode X ₁
The effective value of the voltage applied to a corresponds to the OFF state.

Two pixels 103b ₁ and b associated with the signal electrode X ₂ which is the second (middle column) signal electrode 102
Regarding No. ₂ , both are in the OFF state. At this time,
The voltage applied to the electric capacitance 105b at the intersection of the signal electrode X ₂ and the third electrode 104 corresponds to the ON state.

Signal electrode X which is the third signal electrode 102
Pixels 103c ₁ and c ₂ involved in ₃ are pixels 103c ₁
Is on, and the pixel 103c ₂ is off. At this time, the voltage applied to the electric capacity 105c at the intersection of the _third electrode 104 and the signal electrode X ₃ corresponds to an intermediate state between the ON state and the OFF state.

Each electric capacity 105a, electric capacity 105b,
The voltage of the waveform having an amplitude offset to the ON side or the OFF side with respect to the reference voltage as shown in FIG. 4 with respect to the third electrode 104 so that the effective value of the electric capacitance 105c is in such a state. Is applied. As a result, the sum of the effective value of the liquid crystal application voltage of the pixel 103 group on each signal electrode 102 and the effective value of the voltage applied to the electric capacity 105 is X ₁ , X ₂ , and X ₃ between the signal electrodes. Will be averaged. As a result, display unevenness can be reduced or eliminated over the entire screen.

That is, each pixel related to image display Pixel 1
03a ₁ , pixel 103a ₂ , pixel 103b ₁ , ... Pixel 1
03c ₂ has different effective values of the liquid crystal applied voltage between the ON state and the OFF state, but the signal electrodes X ₁ and X
₂ and X ₃ , the sum of the effective values of the liquid crystal applied voltage is the electric capacity 105a + the pixel 103a for X _1.
1 + pixel 103a ₂ and electric capacity 105b for X ₂
For + pixel 103b ₁ + pixel 103b ₂ and X ₃ , the capacitance 105c + pixel 103c ₁ + pixel 103c _{2 is obtained} , and the sum of these values is almost uniform for X ₁ , X ₂ and X ₃ . . Therefore, the degree and distribution of the dullness and distortion of the applied voltage are made substantially uniform between X ₁ , X ₂ and X ₃ , so that the non-uniformity of the displayed image can be reduced or eliminated.

FIG. 4 shows an example of an applied voltage waveform used in the liquid crystal display device of FIG. 3 according to the present invention.

The signal voltage Vx and the scanning voltage Vy are superimposed and applied to the liquid crystal layer of each pixel 103. Further, the voltage of the signal voltage Vx and the voltage Vc applied to the third electrode 104 are superimposed and applied to the electric capacitances 105a, 105b, and 105c at the intersections of the signal electrodes 102 and the third electrode 104, respectively. To be done. For example, a square wave shown as Vc in FIG. 4, that is, a square wave voltage having a half period of the signal voltage waveform, and the wave height is offset with respect to the reference potential as shown in the figure. By applying the waveform voltage, it is possible to make the liquid crystal application voltages (sum of each) of X ₁ , X ₂ and X ₃ uniform. The area of the hatched portion in FIG. 4 is the effective value of the liquid crystal applied voltage. As is clear from the figure, the sum of the applied voltages on X _{1 and that} on X ₂ and that on X ₃ are almost equal.

FIG. 2 shows an example in which the operation of the present invention as described above is applied to an actual liquid crystal drive voltage waveform. The shaded area in FIG. 2 indicates the effective value of the liquid crystal applied voltage, as in FIG. As can be clearly seen from FIG. 2, the effective value of the applied voltage for each signal electrode is made uniform.

A video signal such as a test pattern was input to the liquid crystal display device according to the present invention as described above to cause display, and the display quality was visually verified.

The scanning electrode driving circuit 2 and the signal electrode driving circuit 3 are specifically T9822 and T98 manufactured by Toshiba, respectively.
21 (liquid crystal driver IC) was used. This driver I
C is connected on the substrate of the liquid crystal display element 1 by the TAB method.

Then, the duty ratio 1/480 and the bias ratio 1 /
23. At the frame frequency of 70 Hz, when multiplex driving was performed using the N line inversion method, uniform and good image display with little display unevenness depending on the display pattern was obtained.

(Embodiment 2) The material of the third electrode 104 in the above-mentioned first embodiment is a material having a lower internal resistance than that of the transparent conductive film ITO used in the first embodiment.
That is, when the film was changed to an aluminum film, the display unevenness on the screen was eliminated more effectively than in the case of the first embodiment, and a better display image could be obtained.

Thus, the third electrode 10 according to the present invention
Unlike the other scanning electrodes 101 and signal electrodes 102, 4 does not need to be transparent because it does not directly participate in lighting / non-lighting of pixels on the screen. Therefore, not only a transparent conductive film such as ITO, but also a metal material having a lower internal resistance can be preferably used. At this time, the third electrode 104 should be formed so as to be hidden in a portion of the screen that does not interfere with image display, such as a peripheral portion of the screen or a region hidden by the bezel of the liquid crystal display panel. Is preferred.

In the first and the present embodiments, only one third electrode 104 is formed and used, but in addition to this, a plurality of third electrodes 104 are formed to eliminate display unevenness. It goes without saying that the necessary electric capacity may be obtained.

Further, in FIG. 2 and FIG. 3 described above,
As the voltage waveform applied to the third electrode 104, a voltage waveform having a half cycle of the liquid crystal applied voltage for display is used, but it goes without saying that the voltage waveform is not limited to this.

It is needless to say that the amplitude of the voltage may be set so that effective averaging of the effective value voltage can be realized.

Further, in order to perform finer and more effective averaging of the effective value voltage, PWM (pulse width) control is performed as the voltage waveform applied to the third electrode 104, and not only the amplitude but also the pulse width is controlled. It may be controlled.

COMPARATIVE EXAMPLE First and second conventional liquid crystal display devices using the conventional liquid crystal display element which does not include the third electrode 104 and the third electrode driving means 4 in the first embodiment. When a test pattern similar to that of Example 2 was displayed, display unevenness depending on the display pattern was remarkable, the display screen was uncomfortable, and the display quality was degraded as compared with the above-mentioned examples.

As a voltage applied to the third electrode, it is theoretically preferable that the total sum of the effective values of the liquid crystal applied voltage of each signal electrode is completely equalized between all the signal electrodes. However, such perfect homogenization is difficult, and it can be said that such perfect homogenization is an excessive measure in practical use. Therefore, by appropriately setting the value and waveform of the voltage applied to the third electrode in consideration of the operating characteristics of the liquid crystal display element actually used, the degree of occurrence of display unevenness, etc., it is possible to improve the display quality. The necessary and sufficient effect of can be obtained.

Further, although the STN type liquid crystal display element is used as the liquid crystal display element 1 in the above embodiments, it is needless to say that the present invention is not limited to this. In addition to this, a liquid crystal display using a so-called multiplex driven liquid crystal display element such as a simple matrix type liquid crystal display element of another mode or an active matrix type liquid crystal display element using a two-terminal element (for example, a diode). The technique of the present invention can be widely applied to a device.

Further, in the above embodiment, the case where the square wave is applied to the third electrode 104 has been described for the sake of simplification of the description, but the waveform of the voltage applied to the third electrode 104 is as follows. Not only a square wave but also si
You may use the voltage of n (sine) wave and other waveforms.
Any waveform may be used as long as it is a voltage with which the sum of the effective values of the voltages finally applied to the pixels on the signal electrode is averaged.

Besides, without departing from the scope of the present invention, the material of each component of the above-mentioned liquid crystal display device, the specification of the liquid crystal layer, or the third electrode driving for outputting the above-mentioned voltage according to the present invention. It goes without saying that various modifications (variations) of the specific circuit structure of the means are possible.

[0053]

As described above in detail, according to the present invention, the nonuniformity of the display caused by the distortion of the applied voltage in the liquid crystal display device of the simple matrix type or the like is eliminated, The present invention relates to a liquid crystal display device having improved display quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a configuration of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing a drive voltage waveform used in a liquid crystal display device according to the present invention and a diagram showing an applied voltage waveform applied to a third electrode.

FIG. 3 is a diagram showing an operation of the liquid crystal display device according to the present invention.

FIG. 4 is a diagram showing an effective value of a liquid crystal applied voltage in the liquid crystal display device according to the present invention.

[Explanation of symbols]

 1 ... Liquid crystal display element 2 ... Scan electrode drive circuit 3 ... Signal electrode drive circuit 4 ... Third electrode drive means 5 ... Power supply circuit

Claims (1)

[Claims] 1. A plurality of scanning electrodes arranged on a first substrate and a plurality of scanning electrodes arranged on a second substrate so as to face the scanning electrodes with a gap therebetween. A signal electrode, a liquid crystal layer sandwiched in a gap between the scan electrode and the signal electrode, a scan electrode drive circuit for applying a voltage to the scan electrode, and a signal electrode drive circuit for applying a voltage to the signal electrode. A liquid crystal display device having a third electrode arranged on the second substrate in parallel with the scanning electrodes so as to cross and oppose each of the plurality of signal electrodes via a liquid crystal layer. And a voltage that is connected to the third electrode and that changes the sum of the effective values of the liquid crystal applied voltage for each of the plurality of signal electrodes in a direction that makes the plurality of signal electrodes uniform. Third electrode drive circuit applied to the third electrode The liquid crystal display device characterized by comprising and.