KR940007504B1 - Driving method of ferroelectric liquid crystal display device - Google Patents

Abstract

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Description

Driving method of ferroelectric liquid crystal display device

1 is a cross-sectional view showing the structure of a liquid crystal panel of a ferroelectric liquid crystal display device.

2 is a perspective view showing the distribution of the electrode in FIG.

3 is a graph showing the relationship between voltage and light transmittance applied in a ferroelectric liquid crystal panel.

4 is a waveform diagram for driving a ferroelectric liquid crystal display element in the related art.

5 is a waveform diagram for driving a ferroelectric liquid crystal display device according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric liquid crystal display device, and more particularly, to a waveform applied to each drive electrode distributed in a liquid crystal panel for displaying an image in a ferroelectric liquid crystal panel.

First, the general structure of the liquid crystal panel of the ferroelectric liquid crystal display device will be described with reference to FIG.

1 is a cross-sectional view showing a structure of a general ferroelectric liquid crystal panel, a glass substrate serving as a substrate for protecting the liquid crystal and forming a transparent electrode on the upper plate and the lower plate, and vertical electrodes and transverse electrodes are distributed therein, respectively. The alignment film which can orientate a liquid crystal in a fixed direction is apply | coated inside, and the liquid crystal is inject | poured in it. 1 is a structure of a general liquid crystal panel as well as ferroelectric. The vertical electrode and the horizontal electrode are also called a common electrode and a segment electrode in a liquid crystal display device. The general distribution of each electrode in the liquid crystal panel will be described with reference to FIG.

2 shows the distribution of the electrodes in the liquid crystal panel. In general, electrodes called COM electrodes and SEGMENT electrodes are located on both sides of the liquid crystal, and the direction in which the COM and SEGMENT electrodes are arranged is perpendicular to each other. It can be seen that the intersection of can drive the mattress and the potential applied to the liquid crystal is a potential difference applied to the COM electrode and the SEGMENT electrode. At this time, before looking at the waveform applied to the liquid crystal will be briefly described the type and its properties.

In general, liquid crystals used in liquid crystal display devices include TN, STN, FLC, and the like.

TN is an abbreviation of Twist Nematic and has a structure in which the arrangement of liquid crystals is twisted so that the incident light is constantly redirected and the response speed is approximately 50-60 ms. STN is an abbreviation of Super Nematic Twist, and the twist angle of the liquid crystal in the TN is deepened. The response characteristic is slower than that of TN, resulting in a value of 100 to 300 ms. FLC is an abbreviation of Ferroelectric Liquid Crystal, which has a better response than the STN, and has a value of 5 ~ 20 ~. It has a bistable state and changes its state according to the applied voltage. There is a function of memory to keep until.

3 shows the relationship between the voltage applied to the ferroelectric liquid crystal panel and the light transmittance. The ferroelectric liquid crystal has two stable states and the threshold voltages Vth1 and Vth2 which start the transition to the two stable states and two It can be seen that there are saturation voltages Vsat1 and Vsat2, which are transitions to the stable state, and exhibit hysteretic characteristics. That is, when the absolute value is applied below the saturation voltage to the ferroelectric liquid crystal, the stable state does not transition.

4 is a waveform diagram applied to each electrode of a ferroelectric liquid crystal panel according to the properties of the ferroelectric liquid crystal as described above in the prior art, where a is a waveform applied to a COM electrode. Is applied and if the data is different from the previous data, the corresponding data waveform of "1" is applied. b represents a waveform applied to the SEGMENT electrode. The waveform is applied according to data to be displayed. c shows the voltage applied to the ferroelectric liquid crystal panel when the signal waveform is formed as described above on the COM electrode and the SEGMENT electrode, and the order in which the saturation voltage of the waveform is applied varies according to data.

In the related art, when the image is displayed by applying a voltage having the above-described waveform to the ferroelectric liquid crystal panel, the response speed is high, but there is a disadvantage that contrast is inferior.

Accordingly, an object of the present invention is to provide a method for driving the liquid crystal panel in order to improve contrast when displaying an image with a ferroelectric liquid crystal panel.

In order to achieve the above object, a method of driving a ferroelectric liquid crystal display device includes a first state of data when a voltage level has a relation of -V < -V2 < V1 < 0 < V1 < V2 < When the scan signal is applied during the screen display period, the voltage level is sequentially converted to -V, -V2, V2, V, and the voltage level is alternately converted to -V1, V1 for the remaining period. When the AC waveform is applied to the liquid crystal panel and the second state of data is to be displayed, the voltage level is sequentially changed to V, V2, -V2, -V during the period during which the scanning signal is applied during the screen display period, and the remaining period Is characterized in that an AC waveform whose voltage levels are alternately converted to -V1, V1 is applied to the liquid crystal panel.

The present invention will be described in detail with reference to FIG.

First, when data is not displayed, the waveform applied to the ferroelectric liquid crystal panel is an alternating current waveform in which the voltage level is alternately changed between -V1 and V1. This is to prevent deterioration of the liquid crystal display device. At this time, the absolute value of the voltage level of -V1 and V1 is less than the absolute value of the threshold voltage level of the ferroelectric liquid crystal, and the voltage level applied when the waveform is applied to the COM electrode and the SEGMENT electrode in order to apply the waveform to the liquid crystal panel. It can be seen that the alternating current waveform is alternately changed to V2 and V1 and the alternating current waveform is alternately converted to V and 0. At this time, each voltage level has a relationship of 0 <V1 <V2 <V.

In the case of displaying the first state of data, when the scan signal is applied during the screen display period when the voltage level is -V <-V2 <-V1 <0 <V1 <V2 <V, the voltage level is-. The waveforms are sequentially converted to V, -V2, V2 and V, and the waveforms of which voltage levels are alternately converted to -V1 and V1 are applied to the liquid crystal panel for the remaining period. In order to apply such a waveform to the ferroelectric liquid crystal panel, if the first electrode (COM electrode) has a voltage level of 0 &lt; V1 &lt; V2 &lt; When the scan signal is applied, the voltage level is sequentially converted to 0, V1, V2, and V, and for the remaining period, a voltage waveform in which the voltage level is alternately converted between V2 and V1 is applied to the second electrode (SEGMENT electrode). When the scan signal is applied during the arrow period when the voltage level is 0 &lt; V1 &lt; V2 &lt; V, the voltage level is sequentially converted to V, V, 0, 0 corresponding to the voltage level of the first electrode. During the remaining period, a voltage waveform whose voltage level is alternately converted to V, 0 is applied to the liquid crystal panel. At this time, the absolute value of the voltage level of V and -V is greater than or equal to the absolute value of the saturation voltage level of the ferroelectric liquid crystal and the absolute value of the voltage level of V1 and -V1 is less than or equal to the absolute value of the threshold voltage level of the ferroelectric liquid crystal.

In the case of displaying the second state of data, when the voltage level is related to -V &lt; -V2 &lt; V1 &lt; 0 &lt; V1 &lt; V2 &lt; The waveforms are sequentially changed to -V2 and -V, and the waveforms of which voltage levels are alternately converted to -V1 and V1 are applied to the liquid crystal panel in the remaining period. Looking at the waveform applied to each electrode in order to apply such a waveform to the ferroelectric liquid crystal display device, the scan signal during the screen display period is applied to the first electrode (COM electrode) when the voltage level is in the relation of 0 <V1 <V2 <V. In the period during which the voltage level is applied, the voltage waveform is sequentially changed to V, V2, V1, 0, and in the remaining period, a voltage waveform in which the voltage level is alternately converted to V2, V1 is applied and the screen display period is applied to the second electrode (SEGMENT electrode). In the period during which the scan signal is applied, the voltage level is sequentially changed to 0, V, V, 0 corresponding to the voltage level of the first electrode, and in the remaining period, a waveform in which the voltage level is alternately converted to V, 0 is applied. It is supposed to be. At this time, the absolute value of the voltage level of V and -V is greater than or equal to the absolute value of the saturation voltage level of the ferroelectric liquid crystal and the absolute value of the voltage level of V1 and -V1 is less than or equal to the absolute value of the threshold voltage level of the ferroelectric liquid crystal.

In the ferroelectric liquid crystal display device, the cell gap (CELL GAP) in the ferroelectric liquid crystal panel is compared with the case of displaying an image by applying a conventional voltage waveform and displaying the image by applying the voltage waveform according to the present invention to the liquid crystal panel. When the saturation voltage level of the applied voltage is 1.5 mu m, the frequency is 30 Hz, and the applied voltage is 15.2 V, the contrast ratio according to the prior art and the present invention shows a ratio of 1: 10.5. That is, the present invention can be seen that the effect of improving the contrast of the image is excellent.

Claims (4)

In a ferroelectric liquid crystal display device, a scan signal is applied during the screen display period when the first state of data is to be displayed when the voltage level has a relationship of -V &lt; -V2 &lt; -V1 &lt; 0 &lt; V1 &lt; V2 &lt; If the voltage level is changed to -V, -V2, V2, V in sequence, and the remaining voltage is applied to the liquid crystal panel with a waveform of alternating voltage levels -V1, V1 for the remaining period, and the second state of the data is applied. In the display period, the voltage level is sequentially changed to V, V2, -V2, -V during the period during which the scan signal is applied, and the waveform is alternately converted to -V1, V1 during the remaining period. A method of driving a ferroelectric liquid crystal display device, characterized in that applied to the liquid crystal panel. The method of driving a ferroelectric liquid crystal display device according to claim 1, wherein the voltage waveform applied to the liquid crystal panel is an alternating current signal alternately changed into -V1 and V1 during the screen display period in which no data is displayed. The electrode structure having a mesh structure for applying the voltage waveform as described above to the liquid crystal panel, wherein the voltage level is 0 &lt; V1 &lt; V2 &lt; V for the first electrode (COMMON electrode). In the case of displaying the first state of data when there is an error, when the scanning signal is applied during the screen display period, the voltage level is sequentially converted to 0, V1, V2, V, and the voltage level is V2, V1 for the remaining period. In the case of applying a voltage waveform that is alternately converted and to display the second state of data, the voltage level is sequentially changed to V, V2, V1, 0 during the period during which the scanning signal is applied during the screen display period. When a voltage waveform whose voltage levels are alternately converted to V2 and V1 is applied and the second electrode (SEGMENT electrode) has a voltage level of 0 &lt; V1 &lt; V2 &lt; V, the first state of data is to be displayed. Display period When a scan signal is applied, a voltage waveform in which the voltage level is sequentially converted to V, V, 0, 0 corresponding to the voltage level of the first electrode, and the voltage level is alternately converted to V, 0 for the remaining period. In the case of applying to the liquid crystal panel and displaying the second state of the data, in the period during which the scanning signal is applied during the screen display period, the voltage level is sequentially 0, V, V, 0 corresponding to the voltage level of the first electrode. And a waveform in which the voltage level is alternately converted into V, 0 in the remaining period. The method of claim 3, wherein an AC waveform in which the voltage level is alternately changed between V2 and V1 is applied to the first electrode and the voltage level is V and 0 to the second electrode. A method of driving a ferroelectric liquid crystal display device, characterized by applying an alternating current waveform that is alternately converted.