JPH08179728A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To extend the period of polarity of a driving voltage applied to a display picture element and improve the quality of image by providing such a constitution that the polarity of a display signal applied to a signal electrode is reversed every plural vertical scanning period, and the polarity of a counter voltage applied to a counter electrode is reversed at the same timing as a scanning signal. CONSTITUTION: During n-vertical scanning periods which is an integer multiple of one period scanning period, a negative polarity voltage level (-Vsr ) of a signal voltage Vs1 is applied to a signal electrode 16. During the following n-vertical scanning period, the positive polarity voltage level (Vsr ) of the signal voltage Vs1 is written in the signal electrode 16. On the other hand, during the n-vertical scanning period, a negative polarity level (-Vcr ) of a counter voltage Vc1 is applied to a counter electrode 17, and during the following n- vertical scanning period, the positive polarity level (Vcr ) of the counter voltage Vc1 is written in the counter voltage 17. Thereafter, the polarity inversion of the signal voltage Vs1 and the counter voltage Vc1 is repeated. Consequently, the current generated by the picture element capacity and be suppressed low to reduce the current consumption at the polarity inversion.

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,
In particular, it relates to a matrix type liquid crystal display device having a switching transistor.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device, there is a matrix type liquid crystal display device in which a switching transistor is added to each picture element. This liquid crystal display device is capable of obtaining a high-contrast display without crosstalk due to the switching action of the transistor, and takes advantage of features such as thinness, light weight, and low power consumption, and OA (office automation) equipment such as a personal computer. It is used as a display device such as an AV (audiovisual) device such as a portable television.

FIG. 3 is a diagram showing the structure of this liquid crystal display device. In FIG. 3, reference numeral 100 denotes a liquid crystal display portion which constitutes an active matrix type liquid crystal display device. The liquid crystal display portion 100 is a display medium. It is composed of a liquid crystal layer (not shown) and first and second substrates 11 and 12 that sandwich the liquid crystal layer.

On the first substrate 11 of the liquid crystal display section 100, a plurality of display picture element electrodes 14 constituting display picture elements are arranged in a matrix of m rows and n columns, and the display picture element electrodes 14 are further arranged. A plurality of scanning electrodes 15 are arranged corresponding to each row of the signal electrodes 1 corresponding to each column of the display picture element electrodes 14.
A plurality of 6 are provided.

At a plurality of intersections of the scanning electrodes 15 and the signal electrodes 16, switching transistors 13 forming display picture elements are arranged, and each switching transistor 13 is connected to the corresponding signal electrode 16. It is connected between the display picture element electrodes 14 and is turned on / off by a scanning signal from the corresponding scanning electrode 15.

A counter electrode 17 is formed on the second substrate 12 constituting the liquid crystal display section 100 so as to face the display picture element electrode 14. Then, in a portion where the counter electrode 17 of the second substrate 12 and each display picture element electrode 14 of the first substrate 11 face each other via the liquid crystal layer 18,
A pixel capacity (capacitor C _LC ) is formed. In addition,
In FIG. 3, the liquid crystal layer 18 and the counter electrode 17 are schematically shown.

FIG. 4 shows the liquid crystal display unit 100,
A structure corresponding to one display picture element is shown as an equivalent circuit, and FIG. 5 shows a waveform of a drive voltage applied to the equivalent circuit. Note that FIG. 5 shows, as an example of the voltage waveform, a signal waveform when a uniform display contrast is obtained over the entire screen of the liquid crystal display unit.

Here, V _S is a signal voltage applied to the signal electrode 16, and a reference potential such as a white level or a black level is changed every vertical scanning period, and at the same time, its polarity is changed to a level (Vs
It is inverted between r) and the level (-Vsr). Also,
V _G is a scan signal applied to the scan electrode 15, V _c is a counter voltage applied to the counter electrode 17, and the counter voltage 17 is between the positive level (Vcr) and the negative level (−Vcr). The polarity is inverted at the same timing as V _S.

In this driving method, when the switching transistor 13 is turned on by the scanning signal V _G applied to the scanning electrode 15, the signal voltage V _S applied to the signal electrode 16 is applied to the counter electrode 17. the difference between the counter voltage V _C which are (V _S -V _C), the corresponding pixel capacitance C
_The liquid crystal layer 18 equivalent to _LC is charged, and the charge due to the charge is retained in the liquid crystal layer 18 until the switching transistor 13 is turned on next time.

Then, the switching transistor 13
Is turned on, the signal electrode 16 and the counter electrode 17
Is applied with a voltage of the opposite polarity to the previous scan, and the pixel capacitance C _LC is also charged to the opposite polarity.

As a result, the liquid crystal layer 18 has (V _S -V _C ).
The voltage is applied alternately with its polarity reversed every vertical scanning period, so that direct current voltage can be prevented from being applied to the liquid crystal molecules, and good display characteristics can be obtained. A driving method of this type is also described in, for example, Japanese Patent Publication No. 5-29916.

[0012]

However, according to the liquid crystal driving method by frame inversion as described above, in the liquid crystal display device of the VGA standard (640 × 480 dots), the time for one vertical scanning period is 16.7 μS, Further, the polarity of the signal voltage and the counter voltage is inverted every vertical scanning period, so the polarity inversion cycle is 30 Hz.

Therefore, the center of the counter voltage V _C , that is, the center value of the level (Vcr) and the level (-Vcr) is slightly different from the center of the signal voltage V _S , that is, the level (Vsr) and the level (-Vsr). Even if it deviates from the center value, there is a problem that the DC deviation of these signals becomes noticeable to the human eye as flicker.

As described above, the liquid crystal display device, which is characterized by low power consumption as a display device, has been increasingly used as a mobile terminal in recent years, and further low power consumption is required. . However, in the case of alternating-current driving the liquid crystal layer forming the display picture element, when the polarities of the signal electrode and the counter electrode are reversed, a current flows in the liquid crystal layer forming the display picture element due to the polarity reversal. However, this is contrary to the demand for low power consumption in the mobile terminal as described above.

The present invention has been made in order to solve such a problem, and makes it possible to display an image displayed by a liquid crystal in a good condition with no noticeable flicker, and at this time, the driving current of the display picture element is reduced. It is an object of the present invention to obtain a liquid crystal display device that can reduce consumption.

[0016]

A liquid crystal display device according to the present invention has first and second substrates sandwiching a liquid crystal layer. The first substrate corresponds to a plurality of display picture element electrodes arranged in a matrix, a plurality of signal electrodes arranged to correspond to each row of the display picture element electrodes, and a column of the display picture element electrodes. A plurality of scanning electrodes arranged in parallel with each other, arranged at each intersection of the signal electrode and the scanning electrode, and switching between the corresponding display pixel electrode and the signal electrode by the scanning signal so as to conduct or non-conduct. It has a transistor. The second substrate is arranged so as to face the first substrate, and has a counter electrode formed so as to face each of the display pixel electrodes. Then, in the present liquid crystal display device, the polarity of the display signal applied to the signal electrode is inverted every plural vertical scanning periods,
In addition, the polarity of the counter voltage applied to the counter electrode is inverted at the same timing as the scanning signal. Thereby, the above object is achieved.

In the liquid crystal display device according to the present invention, it is preferable that the amplitude of the polarity reversal of the counter voltage and the potential difference caused by the polarity reversal of the display signal are substantially equal to each other.

[0018]

In the present invention, the polarity of the display signal applied to the signal electrode is inverted every plural vertical scanning periods, and the polarity of the opposite voltage applied to the opposite electrode is inverted at the same timing as the scanning signal. Therefore, the polarity inversion cycle of the drive voltage applied to the display picture element becomes longer than that in one vertical scanning period.

Therefore, there is a deviation between the center potential of the scanning signal for which the polarity inversion is performed, that is, the center potential of the potential difference caused by the polarity inversion of the scanning signal, and the center potential of the amplitude of the opposing voltage for which the polarity inversion is performed. Even if it occurs, the change in the brightness level on the display screen caused by the polarity reversal has a long cycle, which is difficult for human eyes to perceive as flicker. As a result, the display image by the liquid crystal can be made excellent without flicker.

Further, as described above, since the cycle of polarity reversal of the drive voltage applied to the display picture element is lengthened, the number of times of generation of current due to the polarity reversal in the liquid crystal layer of the display picture element can be reduced. It is possible to reduce the consumption of the drive current in the picture element.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a diagram for explaining a liquid crystal display device according to an embodiment of the present invention, which is applied to an equivalent circuit (see FIG. 4) corresponding to one display pixel constituting the liquid crystal display device. The waveform of the drive voltage is shown. The liquid crystal display device of this embodiment also has a structure shown in FIG. 3 as a liquid crystal display section.

In the figure, V _S1 is the liquid crystal display unit 100.
(See FIG. 3) is a waveform of a signal voltage applied to the signal electrode 16 that causes polarity inversion for each of a plurality of vertical scanning periods (n vertical scanning periods) longer than one vertical scanning period. In this case, a uniform display contrast can be obtained over the entire surface. V _G1 is the scanning electrode 15
The scanning signal V _C1 applied to the counter electrode 17 is a counter signal applied to the counter electrode 17 and its polarity is inverted in synchronization with the polarity inversion of the signal voltage V _S1 .

In this case, in the n vertical scanning period (the period from t1 to t2) which is an integral multiple of one period scanning period, the signal electrode 16 has a negative voltage level (-Vsr) of the signal voltage V _S1.
Is applied, the positive voltage level (Vsr) of the signal voltage V _S is written in the signal electrode 16 in the next n vertical scanning period (the period from t2 to t3).

On the other hand, the n vertical scanning period (from t1 to t2)
Until the next n), the negative polarity level (-Vcr) of the counter voltage V _C1 is applied to the counter electrode 17, and the next n
In the vertical scanning period (the period from t2 to t3), the counter electrode 1
The positive level (Vcr) of the counter voltage V _C1 is written in 7. After that, the polarity inversion of the signal voltage V _S1 and the counter voltage V _C1 is repeatedly performed.

Further, in the present embodiment, the amplitude in the polarity reversal of the counter voltage and the potential difference generated based on the polarity reversal of the display signal are substantially matched.

Next, the function and effect will be described.

FIG. 2 shows the signal voltage V _S1 having the above waveform.
And an example of a change in polarity appearing on the display screen (panel) of the liquid crystal display unit in the driving state by the counter voltage V _c1 .

In the first vertical scanning period immediately after the power is turned on, positive polarity data (Vsr-Vcr> 0) is written in each pixel as shown in the screen Da. The writing of the positive polarity data signal continues after (n-1) vertical scanning periods until the n-th vertical scanning period.

Then, in the (n + 1) th vertical scanning period, the screen Db in the case where the positive polarity data is written in the display pixel in the nth vertical scanning period is the negative polarity of the display pixel. The screen Dc is obtained when the sex data (Vsr-Vcr <0) is written. The writing of the negative polarity data signal continues after the (n-1) th vertical scanning period until the 2nth vertical scanning period.

After that, in the (2n + 1) th vertical scanning period, the screen Dd when the negative polarity data is written in the display pixel in the 2nth vertical scanning period is as follows.
Screen D when positive polarity data is written in the display pixel
It becomes e.

In this way, the signal voltage V _S1 and the counter voltage V _C1
It is possible to prevent the application of a DC voltage to the display picture element by repeatedly reversing the polarity of No. 2 and to increase the polarity of the signal voltage and the counter voltage. There are fewer change points. For example, the polarity inversion cycle 2n is about 3 minutes.

As a result, it is possible to suppress the current generated in the pixel capacitance during the polarity reversal and reduce the power consumption. In addition, the polarity inversion cycle is set to 3
Since it is delayed by a minute, D of the signal voltage and the counter voltage
Even if there is a C shift, it is possible to obtain a good display image that is inconspicuous to human eyes as flicker.

Further, since the cycle of polarity reversal of the drive voltage applied to the display picture element is lengthened, the number of times of current generation due to the polarity reversal in the liquid crystal layer of the display picture element can be reduced, and thus the picture element The consumption of drive current can be reduced.

Further, in the present embodiment, the amplitude in the polarity reversal of the counter voltage and the potential difference caused by the polarity reversal of the display signal are made to substantially coincide with each other, so that the power consumption can be further reduced. it can.

[0036]

As described above, according to the liquid crystal display device of the present invention, the polarity of the display signal applied to the signal electrode is inverted every plural vertical scanning periods, and the counter voltage applied to the counter electrode is applied. Since the polarity is inverted at the same timing as the scanning signal, the period of polarity inversion of the drive voltage applied to the display picture element becomes long. Therefore, even if there is a deviation between the center potential of the scanning signal for which polarity inversion is performed and the center potential of the amplitude of the opposing voltage for which polarity inversion is performed, this voltage deviation causes The change in the luminance level has a long cycle, and is not easily noticed by the human eye as flicker, which has the effect of making the display image by the liquid crystal excellent without the flicker being noticeable.

Further, as described above, since the cycle of polarity reversal of the drive voltage applied to the display picture element becomes long, the number of times of current generation due to the polarity reversal in the liquid crystal layer of the display picture element can be reduced. This has the effect of reducing the consumption of the drive current in the picture element.

As a result, according to the present invention, it is possible to realize a liquid crystal display device which is extremely useful as a display device because it can obtain a good display with low power consumption and inconspicuous flicker.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a liquid crystal display device according to an embodiment of the present invention, showing a waveform of a drive voltage applied to an equivalent circuit corresponding to one display pixel included in the liquid crystal display device. ing.

FIG. 2 is a diagram showing an example of a polarity change that appears on a display screen (panel) of a liquid crystal display unit in a driving state with the signal voltage V _S1 and the counter voltage V _{C1 having the} waveforms shown in FIG. 1.

FIG. 3 is a diagram showing a schematic configuration of a liquid crystal display device of the related art and the present invention.

FIG. 4 is a diagram showing, as an equivalent circuit, a configuration corresponding to one display picture element, which constitutes the liquid crystal display device.

FIG. 5 is a diagram showing a waveform of a conventional drive voltage applied to the equivalent circuit.

[Explanation of symbols]

11 First Substrate 12 Second Substrate 13 Switching Transistor 14 Display Pixel Electrode 15 Scanning Electrode 16 Signal Electrode 17 Counter Electrode 18 Liquid Crystal Layer 100 Liquid Crystal Display Device Da-De Screen V _G1 Scanning Voltage V _S1 Signal Voltage V _C1 Counter Voltage

Claims (2)

[Claims] 1. A plurality of display picture element electrodes arranged in a matrix, a plurality of signal electrodes arranged corresponding to respective rows of the display picture element electrodes, and corresponding to respective columns of the display picture element electrodes. A plurality of scanning electrodes arranged and switching transistors arranged at respective intersections of the signal electrodes and the scanning electrodes for electrically connecting and disconnecting corresponding display pixel electrodes and signal electrodes by a scanning signal. A first substrate having, a second substrate arranged to face the first substrate and having a counter electrode formed to face each of the display pixel electrodes, and the first and second substrates A liquid crystal layer interposed therebetween, the polarity of the display signal applied to the signal electrode is inverted every plural vertical scanning periods, and the polarity of the counter voltage applied to the counter electrode is the scan signal. Liquid crystal display device configured to invert at the same timing Place. 2. The liquid crystal display device according to claim 1, wherein an amplitude in polarity reversal of the counter voltage and a potential difference generated based on polarity reversal of the display signal are substantially equal to each other.