JP3247524B2 - Antiferroelectric liquid crystal panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an antiferroelectric liquid crystal panel such as a liquid crystal display panel having a matrix of pixels and a liquid crystal optical shutter array, using an antiferroelectric liquid crystal as a liquid crystal layer. is there.

[0002]

2. Description of the Related Art A liquid crystal panel using an antiferroelectric liquid crystal,
Since Japanese Patent Application Laid-Open No. 2-173724 of Nippondenso Co., Ltd. and Showa Shell Sekiyu KK, it has been reported that a wide viewing angle, a high-speed response, a good multiplex characteristic, and the like have been reported. Research is being done energetically.

FIG. 3 is a configuration diagram of a liquid crystal display panel when an antiferroelectric liquid crystal is used as a display. Between the polarizing plates 31a and 31b matched to the cross Nicol,
The liquid crystal cell 32 is placed so that the polarization axis of either polarizing plate (polarization axis a or polarization axis b) is parallel to the major axis of the molecule when no voltage is applied, and black is applied when no voltage is applied. Sometimes white is displayed.

In such a cell configuration, when a pulse voltage is applied to a liquid crystal cell, a change in transmittance with respect to the pulse voltage is plotted on a graph to form a loop as shown in FIG. When a pulse voltage is applied and the voltage value is increased, the voltage value at which the transmittance starts to change is V1, the voltage value at which the transmittance is saturated is V2, and when the voltage value is decreased, the transmittance is V1. The voltage value at which the voltage starts to decrease is defined as V5. Further, when a pulse voltage having a polarity opposite to the voltage value is applied and the absolute value is increased, the voltage value at which the transmittance starts to change is V3,
The voltage at which the transmittance is saturated is V4, and the voltage at which the transmittance starts to decrease when the absolute value of the voltage is reduced is V6.
And FIG. 4 shows that the second stable state (ferroelectric liquid crystal state) is selected when a certain pulse wave is applied to the liquid crystal molecules, and when the voltage value exceeds a certain threshold value, the second stable state (ferroelectric liquid crystal state) is selected. The third stable state (ferroelectric liquid crystal state) is selected depending on the polarity of the liquid crystal. In the second and third stable states, when the absolute value of the voltage becomes lower than a certain threshold, the first stable state is selected. In a stable state (antiferroelectric liquid crystal state).

[0005] Various methods have been proposed as a method of time division driving. FIG. 5 shows one method of driving a conventional matrix liquid crystal element. In this figure, the voltage waveform of the scanning electrode and the signal electrode applied to one pixel on the matrix and the combined voltage waveform (which is the voltage applied to the pixel) which is the difference between the two are shown on the same time axis. Changes are also shown. In this driving method, writing is performed in two scanning periods in order to write one screen. In the first scanning period and the second scanning period, the voltage values of the respective waveforms are symmetrical with respect to 0V. In this way, we are aiming for exchange. 5A shows a voltage waveform when the ON state (white display) is set, and FIG. 5B shows a voltage waveform and a transmitted light amount at the time when the OFF state (black display) is set.

The signal applied to the scanning electrode during the selection period has two phases as shown in FIG. 5, and the first phase pulse is turned off (anti-ferroelectric liquid crystal state) regardless of the signal electrode waveform. A reset pulse Vr having a voltage of 0V for the second phase is a select pulse constituting a select pulse necessary for switching liquid crystal molecules in the composite waveform.
Pulse Vs.

In the signal electrode waveform, a two-phase ON waveform and an OFF waveform are arbitrarily arranged according to the display state of the pixel on the same signal electrode. During the signal electrode waveform selection period,
When an ON state is set for a pixel, an ON waveform is applied as shown in FIG. 5A, and when an OFF state is set, an OFF waveform is similarly set as shown in FIG. 5B.
(A) and (b) show the case where the ON waveform is continuously applied to the signal electrode waveform after the selection period and the case where the OFF waveform is continuously applied, respectively.

In the composite voltage waveform, the absolute value of the applied voltage is small in the first phase of the selection period, and the voltage is reset to the OFF state (antiferroelectric liquid crystal state). The second phase is a select pulse VS for setting a display state. When the signal electrode waveform exceeds a threshold voltage (V2 or V4) for setting a ferroelectric liquid crystal state as shown in FIG. Is set to an ON state (ferroelectric liquid crystal state) and a white display is established. When the threshold voltage is not exceeded as shown in FIG. The display becomes black.

[0009]

However, the conventional driving method has a disadvantage that it is easily affected by a voltage value applied in a non-selection period immediately after a selection period. For example, FIG.
In the case of (B) of (B), the second phase of the selection period and the first phase of the non-selection period of the composite voltage waveform applied to the pixel have the same polarity, and the effective voltage of the voltage applied to the pixel is The value is the sum of the voltage value of the second phase in the selection period and the voltage value applied immediately after the selection period. When the absolute value becomes larger than the absolute value of the voltage value V1 or V3 at which the transmittance starts to change, and therefore does not become less than the desired transmitted light amount as shown in the transmitted light amount curve, and good display cannot be performed. was there. Therefore, the present invention provides a driving method capable of maintaining the state of being selected in the selection period, regardless of the combination of the signal electrode waveforms in the non-selection period, that is, regardless of the difference in the display pattern. It is an object of the present invention to provide a method of driving an antiferroelectric liquid crystal capable of performing high-quality display.

[0010]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
In the present invention, the composition applied to the antiferroelectric liquid crystal panel is
The voltage waveform includes a select pulse VS for switching the liquid crystal molecules to an arbitrary position in order for the antiferroelectric liquid crystal panel to perform a target display.
Is applied to the antiferroelectric liquid crystal panel after applying
A rest phase at which the combined voltage becomes 0 V is provided.

Also, a select pulse VS having a composite voltage waveform
For the 0V or select pulse VS to make reverse polarity pulse is applied immediately after the, select pulse
For select pulse applied to scan electrode side constituting VS
Immediately after the pulse Vs , an auxiliary pulse having a polarity opposite to that of the select pulse Vs is applied.

On the scanning electrode side, a select pulse
Immediately after Vs, polarity opposite to select pulse Vs
After applying the auxiliary pulse, which is the pulse of
And an auxiliary pulse having the same polarity as that of the
You.

[0013]

When the antiferroelectric liquid crystal is driven by a pulse wave, the liquid crystal molecules operate according to the magnitude of the product of the pulse height and the pulse width of the applied pulse wave. Therefore, in the two pulse waves A and B as shown in FIG. 6, the peak value of A is twice the peak value of B, and the pulse width of A is 1 of the pulse width of B.
When the pulse wave A and the pulse wave B are applied to the liquid crystal molecules at the time of / 2, the pulse wave of A and the pulse wave of B have the same value of the product of the pulse width and the peak value. Indicates a similar operation. When time-division driving of liquid crystal molecules is performed, the response of the liquid crystal molecules is controlled by the peak value of each applied pulse wave. However, when pulses of the same polarity are applied continuously, one pulse wave having the same value as the sum of the product of the pulse height and the pulse width of each continuously applied pulse wave appears. Performs the same operation as when.

By preventing a pulse having the same polarity as the select pulse from being applied immediately after the select pulse,
Each pulse can be used as a single pulse so that it does not become a composite pulse, and good display can be performed regardless of the display pattern.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the driving method according to the present invention will be described below in detail with reference to the drawings. However, the present invention is not limited to these embodiments. FIG. 7 is a diagram showing the cell configuration of the liquid crystal panel used in this embodiment. The liquid crystal panel used in the present embodiment is composed of a pair of glass substrates 73a and 73b having an antiferroelectric liquid crystal layer 76 having a thickness of about 2 μ, and is sealed with sealing materials 72a and 72b. Electrodes 74a and 74b are formed on the facing surface of the glass substrate, and polymer orientation films 75a and 75b are applied thereon, and rubbing is performed. Further, a first polarizing plate 71a is provided outside one of the glass substrates so that the polarizing axis of the polarizing plate and the rubbing axis are parallel to each other, and the first polarizing plate 71a is provided outside the other glass substrate. The second polarizing plate 71b is provided so that the polarization axis of the second polarizing plate 71b is different from that of the second polarizing plate by 90 °.

The voltage values of V1 to V6 depend on the liquid crystal composition used,
It differs depending on the cell gap thickness and the like. In the liquid crystal panel used this time, V1 = 22V, V2 = 30
V, V5 = 1V, V3 = -22V, V4 = -30V, V
6 = -1V.

<Embodiment 1> FIG. 1 is a diagram showing a drive voltage waveform and a corresponding amount of transmitted light according to a first embodiment of the drive method of the present invention. In this figure, the voltage waveform applied to the scanning electrode and the voltage waveform applied to the signal electrode, and a composite voltage waveform (which is the voltage applied to the pixel) which is the difference between the two are shown on the same time axis, and the change in the amount of transmitted light at that time is shown. Are also shown. In this driving method, writing is performed in two scanning periods in order to write one screen, and the first scanning period and the second scanning period are
The voltage values of the respective waveforms have a symmetrical relationship with each other with respect to 0 V, thereby achieving AC. The pulse width is 100 μs and the selection period is composed of two phases. (A) is for setting ON state (white display).
(B) shows the voltage waveform when the OFF state (black display) is set and the amount of transmitted light at that time. Also,
(A) and (b) show the case where the ON waveform is applied to the signal electrode waveform immediately after the selection period and the case where the OFF waveform is applied, respectively.

In the scan electrode waveform, the pulse of the first phase in the selection period is a reset pulse Vr of voltage 0V for turning off (antiferroelectric liquid crystal state) regardless of the signal electrode waveform, and the second phase is Select pulse of voltage required to switch liquid crystal molecules in composite waveform
This is a select pulse pulse Vs constituting VS. In the first embodiment, two-phase auxiliary pulses are provided immediately after the selection period. Select the first phase of the auxiliary pulse
The polarity is opposite to that of the pulse Vs, and the peak value is the same as the peak value of the signal electrode waveform.

As the signal electrode waveform, a two-phase ON waveform and an OFF waveform are arbitrarily arranged according to the display state of the pixel on the same signal electrode. During the signal electrode waveform selection period,
When setting the ON state to the pixel, the ON state shown in FIG.
When the waveform is applied and the OFF state is set, the OFF waveform is applied similarly as shown in FIG. The ON waveform and the OFF waveform have voltage values opposite to 0 V in the first scanning period and the second scanning period, respectively.

In the composite voltage waveform, in the first phase of the selection period, the absolute value of the applied voltage is small and reset to the OFF state (anti-ferroelectric liquid crystal state). The second phase is a select pulse VS for setting a display state, which is determined by a signal electrode waveform (ON waveform or OFF waveform).
When the voltage exceeds the threshold voltage (V2 or V4) for setting the ferroelectric liquid crystal state as shown in FIG.
State (ferroelectric liquid crystal state) and white display,
If the threshold voltage is not exceeded as shown in FIG.
The FF state (antiferroelectric liquid crystal state) is maintained, and black display is performed. In the first phase immediately after the selection period, when the ON waveform is applied to the signal electrode side (A), the pulse has a polarity opposite to that of the select pulse VS, and when the OFF waveform is applied to the signal electrode side (B), The pulse is 0 V, and a pulse having the same polarity as the select pulse VS is not applied.

All the pulses in the non-selection period are between the voltages V1 and V3 at which the transmittance starts to change. Therefore, as shown in the change in the amount of transmitted light, the state selected by the select pulse in all cases remains after that. Is held. That is, good display can be performed regardless of what display is performed.

The effect can be obtained even if the peak value of the pulse of the first phase of the auxiliary pulse is not the same as the peak value of the signal electrode waveform. However, it is preferable that the peak value be equal to or greater than the peak value of the signal electrode waveform.

Further, the second phase-th pulse of the auxiliary pulse in the scanning electrode waveform is a function to reduce the DC component of the voltage applied to the pixel, the select pulse to the second phase th
And the same polarity as the scanning pulse Vs.

<Embodiment 2> FIG. 2 is a diagram showing a drive voltage waveform and a corresponding amount of transmitted light according to a second embodiment of the drive method of the present invention. FIG. 2 is a view similar to FIG. 1 except that only the drive voltage waveform is changed in accordance with the second embodiment. The pulse width is 100 μs and the selection period is composed of three phases.

In the scanning electrode waveform, the pulse of the first phase in the selection period is a reset pulse Vr of voltage 0V for turning off (antiferroelectric liquid crystal state) regardless of the signal electrode waveform, and the second phase is Select pulse of voltage required to switch liquid crystal molecules in composite waveform
This is a select pulse pulse Vs constituting VS. In the second embodiment, the pulse for the select pulse is shifted to the third phase.
A rest phase is provided to prevent a pulse from being applied immediately after the loss Vs.

In the signal electrode waveform, a three-phase ON waveform and an OFF waveform are arbitrarily arranged according to the display state of the pixel on the same signal electrode. During the signal electrode waveform selection period,
When setting the ON state to the pixel, the ON state shown in FIG.
When the waveform is applied and the OFF state is set, the OFF waveform is applied similarly as shown in FIG. The ON waveform and the OFF waveform have voltage values opposite to 0 V in the first scanning period and the second scanning period, respectively. Also in the signal electrode waveform, the third phase of the selection period is a rest phase with a voltage value of 0V.

In the composite voltage waveform, in the first phase of the selection period, the absolute value of the applied voltage is small and reset to the OFF state (antiferroelectric liquid crystal state). The second phase is a select pulse VS for setting a display state, which is determined by a signal electrode waveform (ON waveform or OFF waveform).
When the voltage exceeds the threshold voltage (V2 or V4) for setting the ferroelectric liquid crystal state as shown in FIG.
State (ferroelectric liquid crystal state) and white display,
If the threshold voltage is not exceeded as shown in FIG.
The FF state (antiferroelectric liquid crystal state) is maintained, and black display is performed. In the third phase of the selection period, the voltage is 0 V in both electrode waveforms, and thus the voltage is 0 V in the composite voltage waveform. Because of this pause phase, both the ON display and the OFF display are performed. No matter what kind of pulse is applied after the selection period, a pulse having the same polarity as the select pulse is not continuously applied in the composite voltage waveform applied to the pixel.

All the pulses in the non-selection period are between the voltages V1 and V3 at which the transmittance starts to change. Therefore, as shown in the change in the amount of transmitted light, the state selected by the select pulse in all cases remains after that. Is held. That is, good display can be performed regardless of what display is performed.

For this reason, as shown in the change in transmitted light amount, the state selected by the select pulse is maintained in all cases. That is, no matter what display is performed, a good display with high contrast can be performed.

[0030]

According to the driving method of the present invention, a pulse of the same polarity is not applied to the pixel immediately after the select pulse for selecting the display mode, so that the driving method can be performed irrespective of the display history regardless of the display history. Display can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a drive voltage waveform used in Example 1 of the present invention and a transmitted light amount corresponding thereto.

FIG. 2 is a diagram illustrating a drive voltage waveform used in a second embodiment of the present invention and a transmitted light amount corresponding thereto.

FIG. 3 is a panel configuration diagram of an antiferroelectric liquid crystal panel and a polarizing plate used in the present invention.

FIG. 4 is a diagram illustrating a hysteresis curve of an antiferroelectric liquid crystal panel.

FIG. 5 is a diagram showing a conventional driving method.

FIG. 6 is a diagram illustrating a pulse wave applied to a liquid crystal cell.

FIG. 7 is a cell configuration diagram of the antiferroelectric liquid crystal panel used in the present invention.

[Explanation of symbols]

 31a, 31b Polarizer 32 Liquid Crystal Cell 71a, 71b Polarizer 72a, 72b Seal 73a, 73b Glass Substrate 74a, 74b Electrode 75a, 75b Polymer Alignment Film 76 Antiferroelectric Liquid Crystal

Claims (4)

(57) [Claims] An antiferroelectric liquid crystal is sandwiched between a pair of substrates.
The anti-ferroelectric liquid crystal panel.
The composite voltage waveform applied to the panel is based on the antiferroelectric liquid crystal panel.
Equipped with a select pulse to set the display state of the
After applying the select pulse, the anti-ferroelectric liquid crystal
A rest phase where the combined voltage applied to the
An antiferroelectric liquid crystal panel characterized by the following. 2. An antiferroelectric liquid crystal panel has a scanning electrode and a signal electrode, and a voltage applied to the scanning electrode and the signal electrode.
Are set to 0V, and the combined voltage becomes 0V.
The antiferroelectric liquid crystal panel according to claim 1. 3. An antiferroelectric liquid crystal is sandwiched between a pair of substrates.
Anti-ferroelectric liquid crystal panel with scanning electrodes and signal electrodes
Wherein the scan electrode waveform applied to the scan electrode and the signal
The composite voltage waveform with the signal electrode waveform applied to the pole is
Select to set the display state of the dielectric liquid crystal panel
A pulse, and the scan electrode is provided with the select pulse.
Apply select pulse of scan electrode waveform to compose
Immediately after the selection pulse is applied.
Has an auxiliary pulse having a polarity opposite to that of the select pulse.
And the auxiliary pulse is applied to the scanning electrode.
Immediately after that, the same polarity as the select pulse
Characterized by applying a pulse to the scanning electrode.
Ferroelectric liquid crystal panel. 4. The auxiliary pulse applied to a scanning electrode
Is the same as the peak value of the signal electrode waveform applied to the signal electrode.
4. The method according to claim 3, wherein the peak value is greater than or equal to the peak value.
2. The antiferroelectric liquid crystal panel according to 1.