JPH05333819A - Liquid display device and method thereof - Google Patents

Abstract

PURPOSE:To optimize the driving method, to make characteristics of nonlinear elements in a display screen uniform, and to eliminate retained image and obtain high picture quality by supplying plural selection pulses in a selection period, and applying reverse data, generated by inverting the white and black of an original image signal to the nonlinear elements right before the original image signal is applied to the nonlinear elements. CONSTITUTION:The selection period is divided into three periods T1-T3 and a positive, a negative, and a positive signal are applied to pixels respectively. A signal with a duty ratio d3 which is applied in the period T3 is the original signal and a signal with a duty ratio d2 which is applied in T2 is the inverted signal of the d3 and satisfies d2+d3=1. In general, a current which is sufficient for rewriting flows to a nonlinear element when applying polarity-inverted pulses. so when the inverted signal and original signal are written successively twice, the polarity needs to be inverted in advance. A signal with a duty ratio d1 which is applied in T1 is made constant irrelevantly to image data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device using a non-linear element and a driving method thereof.

[0002]

2. Description of the Related Art As an example of a conventional driving method of an active matrix type liquid crystal display device using a non-linear element, "Nikkei Microdevice July 1987 No. 2" is cited.
5, p. 121-126, small lot, etc. " FIG. 2 is an example of the timing chart, 21 is a scanning signal waveform Yi, 22 is a data signal waveform Xi, and 23 is an applied waveform Yi-Xi to one pixel. This is an example of gradation display by the pulse width modulation method, but if the height of the data signal waveform 22 is changed according to the data, the pulse height modulation method is used. FIG. 3 shows an example of an equivalent circuit of the liquid crystal display device. Reference numeral 31 is a non-linear element, and 32 is a liquid crystal capacitor.

[0003]

However, the above-mentioned prior art has the following problems.

Generally, the stability and reliability of a thin film nonlinear element are extremely poor as compared with an ordinary diode formed on a single crystal semiconductor substrate. It is considered that this is because the crystallinity of the thin film is poor, so that there are many levels and that the state changes with continued application of electricity. Since the change in the characteristics of this element has a bias dependence, for example, when the same pattern is displayed for a long time, the same element characteristic distribution as the display pattern is created, and the pattern remains for a long time even after the pattern is erased. Cause This is called afterimage or image sticking, which is a fatal defect in data display.

The liquid crystal display driving method of the present invention solves such a problem, and an object thereof is to optimize the driving method of the liquid crystal display device so that the characteristics of the non-linear element in the display screen can be improved. The aim is to achieve high image quality without homogenization and image sticking.

[0006]

According to a method of driving a liquid crystal display device of the present invention, a plurality of selection pulses are given in a selection period, and the image signal is inverted in black and white immediately before applying the original image signal to the nonlinear element. The reverse data is applied to the non-linear element.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS This embodiment will be described below with reference to the drawings. FIG. 1 is an example of a timing chart showing drive waveforms of the liquid crystal display device of the present invention. 11 is a scanning signal waveform Yi, 12 is a data signal waveform Xi, and 13 is a waveform Yi− applied to one pixel.
Xi. FIG. 3 is an equivalent circuit of a pixel portion of an active matrix type LCD using a non-linear element, which shows a signal electrode X.
The nonlinear element 31 and the liquid crystal 32, which are arranged in series between the i and the scan electrode Yi, form one pixel, and the voltage Yi-Xi in FIG. 1 is applied to this pixel. In this example, gradation display is performed by the pulse width modulation method, and when the duty ratio is large, the voltage applied to the liquid crystal increases.
For example, with a normally white mode TN liquid crystal, a smaller duty ratio produces a brighter image and a larger duty ratio produces a darker image. A feature of the present invention is that a signal obtained by inverting the image signal is applied immediately before the original image signal is applied to the pixel. In FIG. 1, the selection period is divided into three periods T1, T2, and T3, and positive, negative, and positive polarity signals are applied to the pixels, respectively. Here, the signal having the duty ratio d3 applied at T3 is the original signal. The signal having the duty ratio d2 applied at T2 is an inverted signal of d3, and the relationship of d2 + d3 = 1 is established. In general, a non-linear element causes a sufficient current to rewrite data by applying a pulse whose polarity is inverted. Therefore, when writing an inversion signal and an original signal twice in succession, the polarity is inverted in advance. Need to be kept. This is the duty ratio d1 applied at T1 and is set to a constant value regardless of the image data.

When such a driving method is used, the current flowing through the non-linear element becomes constant regardless of the image data. Therefore, it is possible to avoid the image sticking and the afterimage caused by the change in the characteristics of the element according to the difference in the applied voltage. Although it is desirable to set the periods T2 and T3 to be the same here, the period T1 does not have to be the same as T2 and T3. Rather, it is possible to make a margin in the writing operation of the non-linear element by shortening T1 and lengthening the original signal writing time T2 and T3.

FIG. 4 is a timing chart showing drive waveforms according to the second embodiment of the present invention. 41 is a scanning signal waveform Yi, 42 is a data signal waveform Xi, and 13 is an applied waveform Yi-Xi to one pixel. In this example, gradation display is performed by the pulse height modulation method, and when the amplitude of the data pulse Xi is large, the voltage applied to the liquid crystal increases. For example, with a normally white mode TN liquid crystal, a brighter image is obtained as the amplitude is smaller, and a darker image is obtained as the amplitude is larger. Also in this example, the selection period is divided into three periods T1, T2, and T3, and positive, negative, and positive polarity signals are applied to the pixels, respectively. Here, the signal applied at T3 is the original signal. The signal applied at T2 is an inverted signal of the original signal, and the sum of the two voltages is constant.
The signal applied at T1 has a constant magnitude regardless of the image data.

Similar to the example of FIG. 1, when such a driving method is used, the current flowing through the non-linear element becomes constant regardless of the image data. Therefore, it is possible to avoid the image sticking and the afterimage caused by the change in the characteristics of the element according to the difference in the applied voltage.

Next, a specific structure of the liquid crystal display device for realizing these driving methods will be described. FIG. 5 is a circuit block diagram of the liquid crystal display device. In this example, four line memories that store image data for one horizontal scanning period are used. First, the image signal amplified for driving the liquid crystal from the data input unit is sequentially input to the line memory 1 during the horizontal selection period. At this time, at the same time, the image data whose polarity has been inverted by the data inversion circuit is sequentially transferred to the line memory 2
Memorized in. Next, during the blanking period, the line memories 1 and 2 are synchronized with the pulse of the timing signal generating circuit.
Data are simultaneously sent to the line memories 3 and 4, respectively. The data driver first refreshes all selected non-linear elements during one horizontal scanning period, then outputs the inverted data fetched from the line memory 4, and finally outputs the original image data fetched from the line memory 3. To do. At this time, it goes without saying that the data driver and the scan driver are synchronized.

In this example, the memory circuit is provided outside the data driver, but it is easy to incorporate these circuits in the data driver. For example, two series of two-stage latches and buffers may be arranged for each output of the driver.

According to the present invention, a non-linear element is turned on by applying a selection pulse to a scanning line, such as a thin film diode made of a non-single crystal Si thin film or a compound semiconductor thin film, an MIM made of an insulator thin film and a metal thin film, a varistor or a thyristor. -Applicable to all active matrix liquid crystal display devices that are turned off.

[0014]

As described above, the liquid crystal display device and the driving method thereof according to the present invention can make the voltage applied to the non-linear element constant regardless of the image signal. Therefore, it is possible to completely eliminate afterimages and image sticking due to changes in the characteristics of the device. According to this method, only the drive waveform is changed while the structure of the device is the same as that of the conventional device, so that high image quality and high reliability of the liquid crystal display can be realized with almost no increase in cost.

[Brief description of drawings]

FIG. 1 is a timing chart showing drive waveforms of a liquid crystal display device.

FIG. 2 is a timing chart showing drive waveforms of a conventional liquid crystal display device.

FIG. 3 is an equivalent circuit diagram of a pixel portion of a liquid crystal display device.

FIG. 4 is a timing chart showing drive waveforms of a liquid crystal display device.

FIG. 5 is a circuit block diagram of a liquid crystal display device.

[Explanation of symbols]

 11, 21, 41 Scanning signal waveform 12, 22, 42 Data signal waveform 13, 23, 43 1 Waveform applied to one pixel 31, 51 Non-linear element 32, 52 Liquid crystal

Claims (3)

[Claims] 1. A signal comprising a plurality of scanning lines and a pixel electrode array on a first substrate, a non-linear element connecting the scanning lines to the pixel electrodes, and a plurality of transparent conductive films on a second substrate. A method of driving a liquid crystal display device, comprising electrodes, wherein liquid crystal is sandwiched in a space in which the first substrate and the second substrate face each other, and a plurality of selection pulses are applied in a selection period.
A method for driving a liquid crystal display device, characterized in that, immediately before an original image signal is applied to the non-linear element, reverse data obtained by inverting the image signal in black and white is applied to the non-linear element. 2. When three selection pulses are applied in positive / negative / positive or negative / positive / negative polarities in the selection period and application periods of the three selection pulses are T1, T2 and T3, respectively, T
2. The liquid crystal according to claim 1, wherein a certain signal is applied to the non-linear element at T2, reverse data obtained by inverting the original image signal in black and white is applied at T2, and the original image signal is applied to the non-linear element at T3. Driving method of display device. 3. A signal comprising a plurality of scanning lines and a pixel electrode array on a first substrate, a non-linear element connecting the scanning lines to the pixel electrodes, and a plurality of transparent conductive films on a second substrate. A liquid crystal display device comprising electrodes, wherein liquid crystal is sandwiched in a space in which the first substrate and the second substrate are opposed to each other, and a plurality of storage circuits for holding image data for at least one horizontal scanning period; A circuit that inverts data,
A liquid crystal display device comprising: a timing signal generating circuit for controlling the operation of the memory circuit; and a scanning circuit for generating a plurality of selection pulses in one horizontal scanning period in synchronization with the timing signal generating circuit.