JPH01246523A - Method of driving liquid crystal element - Google Patents

Abstract

PURPOSE:To decrease the degradation in the contrast of the liquid crystal element, the flickering thereof, etc., and to enable high-gradation display without having unequalness in the quantity of transmitted light by averting the continuous impression of the voltage pulses for selecting the display contents of the liquid crystal elements in the same polarity direction in the non-selection periods and providing an erasing period within the non-selection periods. CONSTITUTION:The signal electrode waveforms varying according to the display contents are impressed in the non-selection period t12, t22, t32, t42, but the continu ous impression or the continuous impression via zero of the voltage pulses of the same polarities like signal electrode waveforms 202a, 202b, does not arise. A pair of AC pulses + or -V4 of the absolute value larger than the saturation value of the liquid crystal element are impressed on the scanning electrodes in the non-selection periods t17, t27, t37 and t47. The element is off regardless of the contents of the selection periods in these periods. The degradation in the contrast of the element, the flickering thereof, etc., are thereby decreased and the high-gradation display without having the unequalness in the quantity of the transmitted light is thereby enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal element, and more particularly to a time-division driving method for a ferroelectric liquid crystal.

[Conventional technology]

Conventionally, as a method of driving a ferroelectric liquid crystal element, the patent application Sho G
The driving waveform was as described in No. o-021499. In the drive waveform (Fig. 3) presented in patent application No. Sho Eta-021499, the scanning electrode (301 in Fig. 3)
A first voltage pulse (V in FIG. 3) having a larger absolute value than the vertical phase of the liquid crystal for orienting the bistable liquid crystal to the first stable state between the selection groups tlo and t20, and this. A second voltage pulse (V in FIG. 3) with a smaller absolute value than the saturation voltage for orienting the liquid crystal to the second stable state with opposite polarity is applied, and the non-selection periods tll and t21 are zero volts. - The force signal electrode (302 in Fig. 3) has a third voltage pulse which, when combined with the second voltage pulse, can increase the saturation value of the liquid crystal at the second stable voltage pulse or higher. A voltage pulse (Vs in Fig. 3) or a fourth voltage pulse (V4 in Fig. 3) having an opposite polarity and equal DC component to the third voltage pulse to lower the liquid crystal threshold value on the same polarity side. ) is applied, and within a period corresponding to the first voltage pulse, the voltage pulses are of opposite polarity to the third and fourth voltage pulses, have equal DC components, and are combined with the first voltage pulse. This is a driving method in which a fifth (V in FIG. 3) voltage pulse is applied that is equal to or higher than the saturation value of the liquid crystal on the polarity side of the first voltage pulse. This driving method is configured such that when not selected, the average value of the DC component of the positive and negative voltage pulses on the liquid crystal is always zero below the threshold of the liquid crystal, regardless of the selected content and quantity of each pixel. , and the voltage pulse is not continuously applied in the same polarity direction for a period longer than twice the pulse width of the second voltage pulse. This driving method is characterized in that it prevents to some extent the phenomenon that the threshold value of the liquid crystal varies depending on the pulse width of the applied pulse and the change in the selection content of the liquid crystal due to the cumulative response effect.

Furthermore, as a method for displaying gradations in a ferroelectric liquid crystal element, the threshold voltage of the liquid crystal element is determined by pulses with different voltages depending on the gradation data, which is basically the same method as in the above-mentioned Japanese Patent Application No. 60-021499. Patent application No. 60-2283 filed by applying a voltage waveform that can be changed from to saturation voltage.
01 etc. are presented.

[Problem to be solved by the invention]

However, in the conventional driving method, as shown in FIG. 3, depending on the contents of each pixel, the voltage pulses applied during the non-selection period are applied in the same polarity direction. It is known that ferroelectric liquid crystals respond cumulatively, and when a voltage pulse of approximately twice the width is applied, the response may vary depending on the pixel selection due to the pulse width dependence. The operating margin becomes narrower, and optical characteristics, especially fluctuations in the amount of transmitted light level when selecting halftones, a decrease in contrast ratio, and flickering are likely to occur. Further, as shown in FIG. 3, the waveforms applied to the liquid crystal during the selection period have different DC components of positive and negative voltage pulses. It is well known that when a direct current component is applied to a liquid crystal element during operation, deterioration of the element is accelerated due to an electrochemical reaction, resulting in a shortened lifespan. Furthermore, in ferroelectric liquid crystals, when the magnitude of the voltage pulse applied to the element increases or decreases in a certain polarity direction, a hysteresis phenomenon may be observed in the corresponding optical response. This is undesirable because it causes fluctuations in the amount of transmitted light, especially when selecting intermediate tones.

The present invention is intended to solve the above-mentioned problems, and its purpose is to ensure that the voltage pulse width applied to the liquid crystal is always constant during the non-selection period regardless of the selection content, and that the DC components of the positive and negative voltage pulses By configuring so that the average value of is zero, deterioration of the liquid crystal element due to the DC component is prevented,
In addition, the present invention provides a time-division driving method that enables gradation display by providing an erasing period within the non-selection period and stabilizing the threshold characteristics in the subsequent selection period.

[Means to solve the problem]

In order to solve the above problems, the method for driving a liquid crystal element of the present invention provides a first voltage pulse whose absolute value is at least equal to or greater than the saturation value of the element on the scanning electrode within the selection period; A second voltage pulse with opposite polarity and an absolute value of which is greater than or equal to the threshold voltage of the element and less than the saturation value, and a third voltage pulse whose absolute value is less than or equal to the threshold voltage are applied to the signal electrode within the same selection period. The first, which is applied to the scan frf tll,
In synchronization with the second and third voltage pulses, a first voltage pulse whose absolute value is zero, and a second voltage pulse whose absolute value is less than or equal to the threshold voltage and whose polarity is opposite to that of the first voltage pulse on the scanning ffi pole and which is variable. 2 voltage pulses, a third voltage pulse of equal absolute value and opposite polarity to the second voltage pulse, or within the same selection period, a third voltage pulse of the same polarity as the second voltage pulse on the scanning electrode. A first voltage pulse whose absolute value is less than or equal to the threshold voltage and is variable, a second voltage pulse whose absolute value is opposite to that of the first voltage pulse and whose absolute value is equal, and a third voltage pulse whose absolute value is zero are applied. , On the other hand, during the non-selection period, a voltage pulse whose absolute value is zero or less than the threshold voltage of the liquid crystal element is applied to at least the signal electric picture, and the Zf ffl pressure pulse is applied at least to the first signal voltage in the same polarity direction. It is characterized in that the voltage pulse is not applied continuously with a length longer than the pulse width of the voltage pulse or continuously through zero.

〔Example〕

FIG. 1 is a schematic diagram showing an example of the configuration of a liquid crystal element in an embodiment of the present invention, FIG. 1(a) is a cross-sectional view, and FIG.
b) is a plan view. Transparent electrodes 23 and 24 made of indium oxide and tin oxide are provided on opposing surfaces of a pair of substrates 21 and 220 made of glass or plastic. The ffi poles are each formed in a stripe shape, are crossed at right angles, and are combined in a lattice shape. Here, 23.24
are a scanning electrode and a signal electrode, respectively. Furthermore, if necessary, apply S i O! on this electrode. After providing an insulating layer such as, for aligning the liquid crystal, an alignment film 25 made of an obliquely deposited film such as SiO or polyimide, nylon, polyethylene, silane, a pulling agent, etc. is provided, and the liquid crystal 26 is aligned by rubbing. let In addition, polarizing plates 27 and 28 are installed on the surfaces of the upper and lower substrates 21 and 22 where the electrodes 23 and 24 are not provided so that they are orthogonal to each other, and the polarization axis of one polarizing plate and the saturation of the ferroelectric liquid crystal are aligned. The long sleeve direction of the liquid crystal molecules was made to match when an electric field higher than the voltage was applied. FIGS. 2(a) and 2(b) show the driving waveform and optical response of the embodiment of the present invention. For convenience, this example will be explained using four gradation levels, and the erasing will be assumed when a pulse higher than the negative saturation voltage is applied.
The liquid crystal element becomes non-transparent and turns off in that state.
state. Further, when a pulse higher than the positive saturation voltage is applied, it is defined as a fully transparent state, and is defined as an ON state.

In FIGS. 2(a) and 2(b), 201a and 201b are scanning electrode waveforms, 202a and 202b are signal electrode waveforms, 203a,
203b is a composite waveform applied to the liquid crystal element;
4a, 204b are the corresponding optical responses. ,t. OFF selection frame at t4°, ON selection at t,. ,
T! . 2A and 2B show examples of drive waveforms and corresponding optical responses for halftone selection frames each having a different amount of transmitted light. During the selection period, 11 i ls js + and t
In step 4, first, the first voltage pulse (-
V+ 10V, )・tll, (-V, +V6)・t*5
1-V+' ss and -V, ·t4, are applied. Although the peak value of the first voltage pulse differs depending on the selection, the absolute value is greater than the saturation value in all cases, so
There is no color in the optical response. Then the second voltage pulse is oN
When selected, the voltage pulse (+Vj + Vs ) - ta J is higher than the saturation value in the other polarity direction, and when OFF is selected, the voltage pulse (+V! - Vl ) - tea is lower than the threshold voltage of the element.
is applied, and when selecting a halftone, (+Vt - va )・
A voltage pulse whose absolute value, such as ts 4 N (+v, +Vs)' tsa, is greater than the threshold voltage of the liquid crystal element and less than the saturation voltage is applied. Furthermore, at j+s and jt within the selection period, a third voltage pulse whose absolute value is zero or less than the threshold voltage is applied to tsssias. This third voltage pulse is the beginning of the selection period and non-selection period (signal waveform related to the selection period in the next scan electrode)
This is to prevent pulses of the same polarity from being applied continuously. −, non-selection period i + *, tx s,
For js is not applied continuously or continuously through zero.

Also, j+t, jt within the non-selection period? , js and j+7, a pair of AC pulses ±V4 whose absolute value is larger than the saturation value of the liquid crystal element is applied to the scanning fin, and during this period, the element does not flash to the contents of the selection period and is in an OFF state. . This is to stabilize the threshold characteristics of the liquid crystal element by unifying the state before the selection period, and to prevent fluctuations in the transmitted light amount level especially when selecting halftones. Within the non-selection period t+ a N ty a , ts s ,
ta a are the selection periods t l I and ta l respectively
, t, I, ta This is a period to remove the DC component occurring within 1, and Vs-t18, Vs・tti, Vs"tx
a, Vs·t4g (IV, l:lV, -V, I) is applied in a polar direction that cancels the DC component.

Using the above method, the device shown in FIG.
It was assembled as 8-2.2 μm. The liquid crystal is ZLI-3775 manufactured by Merck. f'A C5-10
18, etc., and in each case, an element capable of good gradation display was obtained. The contrast ratio in the 0N10FF state was also as good as 1:30 or more. Furthermore, although a specific example of four gradations is shown in this embodiment, display of at least 16 gradations is possible by modulating the voltage of the signal electrode waveform.

〔Effect of the invention〕

As described above, according to the driving method of the present invention, voltage pulses for selecting the display content of the liquid crystal element are not continuously applied in the same polarity direction at least within the non-selection period, so that pulse width dependence is reduced. A wide margin can be obtained, and deterioration in contrast and flickering of the element can be reduced. In addition, by providing an erasure period within the non-selected 1111 period,
The element +7>La value characteristics are stabilized, and high gradation display without unevenness in the amount of transmitted light is possible. Furthermore, by reducing the average value of the DC component applied to the liquid crystal element to zero, deterioration of the element due to the DC component can be prevented. The present invention can be applied to liquid crystal televisions, various display devices, liquid crystal light valves, polarizers, and the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of a liquid crystal element in an embodiment of the present invention, FIG. 1(a) is a cross-sectional view, and FIG.
b) is a plan view. FIGS. 2(a) and 2(b) are diagrams showing drive waveforms and optical responses in an example of the present invention. FIG. 3 is a diagram showing conventional drive waveforms. 21...Lower substrate 22...Upper substrate 23...Scanning electrode 24...Signal electrode 25...Alignment film 26...Liquid crystal 27.28...Polarizing plate 29...Sealing agent 201 a120 l b, 301-...Scanning electrode waveform 202 a s 202 b s 302...Signal m ti 71t shape 203a12o3b13o3...
・Synthetic waveforms 204a, 204b...Optical response of liquid crystal element and above Applicant Seiko Epson Corporation 1st (a-) 7th approval (b) 2nth) 2nd (J (b) M force diagram

Claims (3)

[Claims] (1) In a method for driving a liquid crystal element in which a ferroelectric liquid crystal is sandwiched between substrates with electrode surfaces of a substrate having a scanning electrode and a substrate having a signal electrode facing each other, at least a first voltage pulse whose absolute value is greater than or equal to the saturation value of the element; a second voltage pulse whose absolute value is opposite in polarity to the first voltage pulse and whose absolute value is greater than or equal to the threshold voltage of the element and less than or equal to the saturation value; A third voltage pulse equal to or lower than the threshold voltage is applied to the signal electrode within the same selection period in synchronization with the first, second, and third voltage pulses applied to the scanning electrode.
A first voltage pulse having an absolute value of zero, a second voltage pulse having a polarity opposite to the first voltage pulse on the scanning electrode and having an absolute value equal to or less than a threshold voltage and variable, a second voltage pulse and an absolute value. A third voltage pulse of equal and opposite polarity is applied, or within the same selection period, a first voltage pulse of the same polarity as the second voltage pulse on the scanning electrode and whose absolute value is less than or equal to the threshold voltage and is variable. , a second voltage pulse with opposite polarity and equal absolute value to the first voltage pulse, and a third voltage pulse with an absolute value of zero, while during the non-selection period, at least on the signal electrode. A voltage pulse whose absolute value is zero or less than the threshold voltage of the liquid crystal element is applied, and the voltage pulse is continuous or passes through zero with a length equal to or longer than the pulse width of the first voltage pulse in at least the same polarity direction. A method for driving a liquid crystal element, characterized in that the voltage is not applied continuously. (2) In the method for driving the liquid crystal element, a voltage pulse equal to the difference in absolute value between the first voltage pulse and the second voltage pulse is applied in the polarity direction to eliminate the DC component within the selection period within the non-selection period. 2. The method of driving a liquid crystal element according to claim 1, further comprising applying a voltage pulse. (3) In the above method for driving a liquid crystal element, at least one pair of voltage pulses whose absolute value is greater than the saturation voltage of the liquid crystal element and whose polarity changes alternately is applied to the scanning electrode during the non-selection period. A method for driving a liquid crystal element according to claim 1, characterized in that: