JPH1031203A - Driving method for anti-ferroelectric liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to perform a multi-level display independent of a flicker characteristic of human eyes by making a voltage applied to a pixel for a non-selection period a DC voltage threshold value of an anti- ferroelectric liquid crystal. SOLUTION: The anti-ferroelectroc liquid crystal display is constituted of a pair of glass substrates 22 holding an anti-ferroelectric liquid crystal layer 21 therebetween, and keeps a gap by a spacer 23, and cuts off the anti- ferroelectric liquid crystal payer 21 from the outside with seal material 24. Further, electrodes 25 being a scan electrode and a signal electrode are formed on the opposite surface of the glass substrates 22, and oriented films 26 are formed on them to be oriented. Further, polarizing plates 27 are set up on the outside of the glass substrates 22. At this time, a write-in period includes a selection period for applying a switching pulse for switching the state of the anti-ferroelectric liquid crystal and the non-selection period for holding the state of the anti-ferroelectric liquid crystal set for the selection period. Then, the voltage applied to the pixel for the non-selection period is made the DC voltage threshold value of the anti-ferroelectric liquid crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an antiferroelectric liquid crystal display, and more particularly to a method of driving an antiferroelectric liquid crystal display characterized by a gradation display method.

[0002]

2. Description of the Related Art Regarding the gradation display method of an antiferroelectric liquid crystal display, the 58th meeting of the 142nd Committee of Organic Materials for Information Science held by the Japan Society for the Promotion of Science held in November 1993 by Nippon Denso. There is a method presented under the title "Anti-ferroelectric liquid crystal display device" described in the materials of the Joint Study Group, which will be briefly described below.

FIG. 2 shows an example in which a driving method for gray scale display announced by Nippon Denso Co., Ltd. is implemented. In the figure, (a) shows the driving waveform, and (b) shows the optical response. In the driving waveform of FIG. 2A, one frame period is constituted by a selection period in which a bipolar pulse is applied and a non-selection period in which a holding voltage + V0 is applied, and driving is performed by inverting the voltage polarity for each frame. . In FIG. 2B, T1, T2, T3, T4, and T5 gradually increase the absolute values of the peak values of the bipolar pulse applied in the selection period of FIG. 2A to V1, V2, V3, V4, and V5. Optical response when FIG. 1 (b) T1, T
The average transmittance in one frame period of 2, T3, T4, and T5 is about 95%, 70%, 50%, 25%, and 5%, and the flicker characteristic of the human eye is about 30 Hz. Looking at the optical response, the average transmittance is recognized, and as a result, gradation display is possible.

However, in this driving method, the light transmittance gradually decreases after the voltage is applied, and gradation display is performed with the average transmittance during the non-selection period, and the flicker characteristics of human eyes are assumed. Therefore, the same image cannot be held for a long time, for example, several seconds. Therefore, the range of application as an optical device is limited.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of driving an antiferroelectric liquid crystal display which enables gradation display without relying on the flicker characteristics of the human eye.

Further, it is possible to hold an image displayed on the antiferroelectric liquid crystal display for a long time, for example, several seconds, and to completely convert the voltage waveform applied to the pixel of the antiferroelectric liquid crystal display to AC, The purpose is to prevent the deterioration of the liquid crystal.

[0007]

In order to achieve the above-mentioned object, according to the present invention, one display drive for a pixel includes at least one operation period, and at least one operation period involves writing to the pixel. Has a writing period for
In the writing period, a selection period in which a switching pulse for switching the state of the antiferroelectric liquid crystal is applied,
A non-selection period for maintaining a state of the antiferroelectric liquid crystal set in the selection period, and a voltage applied to the pixel in the non-selection period is set as a DC voltage threshold of the antiferroelectric liquid crystal.

In an antiferroelectric liquid crystal display in which an antiferroelectric liquid crystal is sandwiched between a pair of substrates each having a plurality of scanning electrodes and signal electrodes on opposing surfaces, and pixels are arranged in a matrix, non-selection of the scanning electrode is performed. The voltage applied during the period is set as the DC voltage threshold of the antiferroelectric liquid crystal.

Preferably, there is an image still period for applying a still voltage for stopping the written image immediately after the writing period, and the value of this still voltage is made to coincide with the DC voltage threshold.

[0010] The polarity of the voltage waveform applied to the pixel is inverted for one operation period or a plurality of operation periods, and the same display is displayed using two or more even operation periods. It is more preferable to carry out the conversion.

[0011]

FIG. 3 is a block diagram showing a cell structure of an antiferroelectric liquid crystal display used in the present invention. The antiferroelectric liquid crystal display used in the present invention has a pair of glass substrates 22 sandwiching an antiferroelectric liquid crystal layer 21 having a thickness of about 2 μm.
The gap is maintained by the spacer material 23, and the antiferroelectric liquid crystal layer 21 is shielded from the outside by the sealant 24. Further, an electrode 25 serving as a scanning electrode and a signal electrode is formed on the facing surface of the glass substrate 22, and an alignment film 26 is formed thereon to perform an alignment process. Further, a polarizing plate 27 is provided outside the glass substrate 22. The polarizing axis of one polarizing plate is parallel to the average long axis direction of the antiferroelectric liquid crystal molecules, and the polarizing axis of the other polarizing plate is perpendicular. .

When an AC voltage is applied to the liquid crystal cell sandwiching the antiferroelectric liquid crystal as described above, the relationship between the applied voltage and the light transmittance of the liquid crystal cell is a characteristic of the antiferroelectric liquid crystal with 0 V as the center of symmetry. It is known to draw a hysteresis carp. However, such a hysteresis curve appears when an AC voltage is applied to the liquid crystal cell, and the DC voltage VDC
When is applied, the optical response as shown in FIG. 4 is obtained. In FIG. 4, the applied DC voltage VDC is VD0, VD1, VD2,
The optical response at VD3, VD4, and VD5 is shown.
Each voltage value includes 0v <VD0 <VD1 <VD2 <VD3 <VD4 <V
There is a D5 relationship.

When the DC voltage value VDC ≧ VD1, the transmittance is always 100
%, But when VDC ≦ VDO, the light transmittance is near 0% regardless of the passage of time. In this way, there is a DC voltage whose light transmittance does not reach 100% irrespective of the passage of time and which is always near 0%. The maximum value of the DC voltage at which the light transmittance does not change near 0% is defined as the DC voltage threshold Vth.

[0014]

【Example】

(Embodiment 1) In driving an antiferroelectric liquid crystal display, the configuration of a scanning electrode side voltage waveform and a signal electrode side voltage waveform can take various forms as necessary, but the most important point in the present invention is as follows. Is a setting method of the holding voltage value. Therefore, in the first embodiment, in order to clarify the effect, an example according to the driving method of the prior art FIG. 2 will be described as an example, and the following description will be given. It does not do.

FIGS. 1 and 5 show a driving method to which the present invention is applied. As shown in FIG. 1, one display drive to the pixel includes at least one operation period, the operation period has one writing period, and one writing period includes a selection period and a non-selection period. .

FIG. 5A is a diagram showing a scan electrode side voltage waveform when a scan electrode and a signal electrode are provided on a substrate. In this embodiment, the selection period is two phases, and the time of one phase is t. For the scanning electrode side voltage waveform, a two-phase bipolar pulse having a peak value VS was applied during the selection period. This is hereinafter referred to as a select pulse. After applying the select pulse, the scan electrode side voltage waveform has the same polarity as the pulse of the second phase of the select pulse and the magnitude Vk during the non-selection period.
Is applied as a holding voltage. The non-selection period continues until a select pulse is applied to all the scan electrodes, and when the selection pulse ends, the process shifts to the second operation period. The scan electrode side voltage waveform in the second operation period is obtained by inverting the polarity of the scan electrode side voltage waveform in the first operation period.

FIG. 5B shows a signal electrode side voltage waveform. The signal electrode side voltage waveform is a symmetric bipolar pulse like the select pulse, and the signal electrode side voltage waveforms D1, D2, D3, D4, and D5 in the first operation period indicate the peak values of the second phase as Vdt1 and Vdt2. , Vdt3, Vdt4, Vdt5
It is what it was.

The signal electrode side voltage waveforms D1 ', D2', D3 ', D4', and D5 'in the second operation period have peak values at the second phase of -Vdt1, -Vdt2, -Vdt3, -Vdt4, -Vdt5. The signal electrode-side voltage waveforms D1, D2, D3, D4, and D5 in the first operation period are respectively inverted.

The voltage values Vs and Vdt1, Vdt2,
An example of setting of Vdt3, Vdt4, and Vdt5 will be described.

FIG. 1A shows a composite voltage waveform which is a difference between the scan electrode side voltage waveform in the first operation period and the signal electrode side voltage waveform applied only in the selection period. The holding voltage Vk is set to the aforementioned DC threshold value Vth. FIG. 1B is a diagram showing an optical response when the combined voltage waveform shown in FIG. 1A is applied to a liquid crystal pixel of an antiferroelectric liquid crystal display.

As shown in FIG. 1B, the holding voltage Vk
Is set to the DC threshold value Vth, the transmitted light amount in the halftone state is maintained for one operation period.

The optical responses T11 and T22 shown in FIG.
The peak values of the bipolar pulses generated in the selection period portion of the composite voltage waveform giving T33, T44, and T55 are V11, V22, V33, and V
44, V55, the voltage values VS, Vdt1, Vdt2, V
dt3, Vdt4 and Vdt5 are given by the following equations.

Vdt1 = V11−VS Equation (1) Vdt2 = V22−VS Equation (2) Vdt3 = V33−VS Equation (3) Vdt4 = V44−VS Equation (4) Vdt5 = V55−VS Equation (5) VS = (V11 + V55) / 2 Expression (6) However, Expression (6) is not a necessary condition, and may be set near this condition.

FIG. 6 shows scanning electrodes L1,
Voltage values Vk, Vs, Vdt1, Vdt2, Vdt3, Vdt4, Vdt applied to the liquid crystal pixels on L2, L3, L4, L5
5 shows an example of a composite voltage waveform in the first operation period in actual driving when 5 is set as described above. The second operation period is omitted.

FIG. 7 shows the optical response TL1, TL2, TL when the combined voltage waveform shown in FIG. 6 is applied to the liquid crystal pixels on the same signal electrode and on the scanning electrodes L1, L2, L3, L4, L5.
3, TL4 and TL5 are shown.

As shown in FIG. 6, during the actual driving, the voltage waveform on the signal electrode side is so-called random on the holding voltage during the non-selection period, and as shown in FIG. Of the optical response TL
1, TL2, TL3, TL4, and TL5 did not affect the image at all, only to the extent that they vibrated around the optical responses T11, T22, T33, T44, and T55 shown in FIG. 1B.

(Embodiment 2) FIG. 8 shows another embodiment of the drive used in the present invention. The first operation period is a reset period for uniformly returning the state of the antiferroelectric liquid crystal of the antiferroelectric liquid crystal display to the initial state, a writing period for writing an image including a selection period and a non-selection period, And an image stationary period for continuing to display the written image.

FIG. 8A is a diagram showing a scan electrode side voltage waveform used in this embodiment. In the scan electrode side voltage waveform, no voltage is applied during the reset period to bring all the antiferroelectric liquid crystals into an antiferroelectric state.

The selection period includes two phases, and the time length of one phase is t. During the selection period, a bipolar pulse having a peak value VS is applied. Hereinafter, the scan electrode voltage waveform during this selection period is referred to as a select pulse.

After a select pulse is applied to the scan electrode side voltage waveform, in a non-selection period, a DC voltage having the same polarity as the pulse of the second phase of the select pulse and a magnitude Vk is applied as a holding voltage. The non-selection period lasts until the selection pulse is applied to all the scanning electrodes, and when the selection pulse ends, the writing period ends and the image transitions to the image stationary period.

As for the scan electrode side voltage waveform in the image stationary period, the DC voltage of the magnitude Vk applied in the non-selection period of the writing period is continuously applied as the stationary voltage. The image still period is a period in which the image is literally kept displayed in a still state, and its length varies depending on the application. The inventor has confirmed that the length of this period can be on the order of tens of seconds. When the image still period ends, the first operation period ends. The description of the second operation period is omitted.

FIG. 8B shows a voltage waveform on the signal electrode side. During the writing period, 0 V is always applied, and during the writing period, the voltage waveforms D1, D2, D3, D4, and D5 are applied in synchronization with the select pulse according to image data. The voltage waveform on the signal electrode side during the writing period is a bipolar pulse having two phases, and the peak values Vdt1, Vdt2,
The setting of Vdt3, Vdt4, Vdt5 and Vs, Vk is performed as described in the first embodiment. Here, for the sake of convenience, the same notation of numerical values and the like will be used.

FIG. 9 shows scanning electrodes L1 and S1 on the same signal electrode.
Voltage values Vk, Vs, Vdt1, Vdt2, Vdt3, Vdt4, Vdt applied to the liquid crystal pixels on L2, L3, L4, L5
5 shows an example of a composite voltage waveform in the first operation period in actual driving when 5 is set as in the first embodiment. The second operation period is omitted.

FIG. 10 shows the composite voltage waveform shown in FIG. 9 on the same signal electrode and on the scanning electrodes L1, L2, L3, L4, L5.
Optical response TL1, TL2, T when applied to the upper liquid crystal pixel
L3, TL4, and TL5 are shown.

As shown in FIG. 9, during the actual driving, the voltage waveform on the signal electrode side is so-called random on the holding voltage during the non-selection period, and as shown in FIG. However, the antiferroelectric liquid crystal molecules do not fluctuate during the image stationary period, and maintain a constant transmitted light amount.

[0036]

As described above, the method according to the first embodiment makes it possible to display five gradations without depending on the flicker characteristics of the human eye, and further setting the signal-side electrode voltage waveform allows more gradation display. Will be possible. This is an effective means mainly for displaying moving images. Further, by employing the method of the second embodiment, multi-gradation display can be performed, and the display state can be maintained on the order of several tens of seconds. This is an effective means mainly for displaying a still image. Further, since the fluctuation of the liquid crystal molecules is eliminated in the still image state, the liquid crystal molecules are also effective as a spatial light modulator which requires the accuracy of the order of the wavelength of light.

[Brief description of the drawings]

FIG. 1 is a diagram showing a driving waveform and an optical response of the present invention.

FIG. 2 is a diagram showing a driving waveform and an optical response according to a conventional technique.

FIG. 3 is a configuration diagram illustrating a configuration of an antiferroelectric liquid crystal display.

FIG. 4 is a diagram showing light transmittance when a DC voltage is applied to an antiferroelectric liquid crystal display.

FIG. 5 is a waveform diagram showing a scan electrode side voltage waveform and a signal electrode side voltage waveform of the present invention.

FIG. 6 is a waveform diagram showing a composite voltage waveform according to the present invention.

FIG. 7 is a diagram showing an optical response according to the present invention.

FIG. 8 is a waveform diagram showing a scan electrode side voltage waveform and a signal electrode side voltage waveform of the present invention.

FIG. 9 is a waveform diagram showing a composite voltage waveform of the present invention.

FIG. 10 shows an optical response according to the present invention.

Claims (4)

[Claims] 1. A method of driving an antiferroelectric liquid crystal display having an antiferroelectric liquid crystal sandwiched between a pair of substrates and having pixels in a matrix, wherein one display drive for a pixel is performed by at least one display. It consists of an operation period, and one operation period has a writing period for writing to the pixel,
The writing period includes a selection period in which a switching pulse for switching the state of the antiferroelectric liquid crystal is applied and a non-selection period for maintaining the state of the antiferroelectric liquid crystal set in the selection period. And a voltage applied to the pixel during the non-selection period is a DC voltage threshold of the antiferroelectric liquid crystal. 2. A method of driving an antiferroelectric liquid crystal display having antiferroelectric liquid crystal sandwiched between a pair of substrates each having a plurality of scanning electrodes and signal electrodes on opposing surfaces and having pixels in a matrix. One display drive to a pixel includes at least one operation period, and one operation period has at least a writing period for writing to the pixel, and the writing period includes a state of the antiferroelectric liquid crystal. And a non-selection period for maintaining the state of the antiferroelectric liquid crystal set in the selection period, and a switching pulse is applied to the scan electrode during the non-selection period. Wherein the applied voltage is a DC voltage threshold of the antiferroelectric liquid crystal. 3. An image quiescent period for applying a quiescent voltage for immobilizing a written image immediately after the writing period, wherein the value of the quiescent voltage matches the DC voltage threshold of the antiferroelectric liquid crystal. 3. The method of driving an antiferroelectric liquid crystal display according to claim 1, wherein: 4. Inverting the polarity of a voltage waveform applied to a pixel for one operation period or a plurality of operation periods, and displaying the same display using two or more even operation periods. 4. The method for driving an antiferroelectric liquid crystal display according to claim 1, wherein