JPH0843796A - Driving method for liquid crystal display element and driving device therefor - Google Patents

Abstract

PURPOSE:To provide a driving method for a liquid crystal display element capable of realizing a uniform display with decreased flickering and driving device therefor. CONSTITUTION:This driving device is composed of a control circuit 13 which generates scanning data and signal data, a polarity signal generating circuit 14 which generates polarity signal inverted at every frame period, a scanning electrode driving circuit 15 which impresses the scanning data as scanning voltages and holding voltages to the scanning electrodes in the positive or negative polarity meeting the polarities of the selection period of the polarity signals and a signal electrode driving circuit 16 which impresses the signal data as selection voltages and non-selection voltages to the signal electrodes in the positive or negative polarity meeting the polarity signals. The scanning voltage of one pulse meeting the scanning data is applied on the scanning electrodes in the one line selection period according to the polarity signals, and in succession, the holding voltage having the same polarity as the polarity of the scanning voltage is applied before the next selection period. The polarity of the selection voltage or non-selection voltage meeting the signal data applied on the signal electrodes according to the polarity signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method and a driving device for a liquid crystal display element. More specifically, the present invention relates to a driving method and a driving apparatus for a liquid crystal display device using switching between tristable states of an antiferroelectric liquid crystal that causes a phase transition to a ferroelectric liquid crystal by an electric field.

[0002]

2. Description of the Related Art Switching between tristable states of an antiferroelectric liquid crystal is performed by a conventional surface-stabilized ferroelectric liquid crystal (hereinafter referred to as "SSF").
It is expected to be one of the methods for solving some of the essential problems of "LC"), and active research is underway [A. D. L. Chandani et. a
l. : Jpn. J. Appl. Phys. , 2
7, L729 (1988), A.S. D. L. Chand
ani et. al. : Jpn. J. Appl.
Phys. 28, L1265 (1988), or N.P. Yamamoto et. al. : Japan Society for the Promotion of Science, Organic Materials for Information Science, 142nd Committee, 58th Joint Research Group, P7-12 (1993), etc.].

The characteristics of the switching between the tristable states are as follows. (1) The antiferroelectric-ferroelectric phase transition caused by voltage application has a steep threshold characteristic with respect to a DC voltage (see FIG. 8).

(2) Since the antiferroelectric-ferroelectric phase transition is accompanied by a wide optical hysteresis, if a bias voltage is applied after selecting the antiferroelectric phase or the ferroelectric phase, The selected state can be retained (see FIG. 8).

(3) Two orientation states in the electric field induced ferroelectric phase can be made optically equivalent. (4) Since it is possible to prevent bias of charges in the liquid crystal layer,
It is possible to eliminate the change with time of electro-optical characteristics as seen in SSFLC.

By using these characteristics, it is possible to perform time division driving in the simple matrix without limitation of the duty ratio. As an example of a driving method known to date, there is a method of applying a driving voltage as shown in FIGS. 4 and 5 [M. Yamawaki e
t. al. : Digest of Japan Dis
play '89, p26 (1989), etc.]. In FIG. 4, V _t and V _d are voltage waveforms applied to the striation electrode and the signal electrode, respectively, and V _LC is a composite waveform applied to the liquid crystal layer. In this driving method, a frame F (+) to which a positive voltage is applied and a subsequent frame F (-) to which a negative voltage is applied are paired.
Further, in FIG. 5, (a) is a voltage waveform applied to each of the strip electrodes, (b) is a voltage waveform applied to each signal electrode, and (c) is a composite waveform applied to the liquid crystal layer. is there. Further, (d) shows a change in light transmittance with respect to the drive waveform.

The display principle of this driving method will be described below with reference to FIGS. 6 and 7. FIG. 6 is a conceptual diagram of the liquid crystal display element, and FIG. 7 is a sectional view of the liquid crystal display element. The optical axis OA in the antiferroelectric phase is orthogonal to the smectic phase. As shown in FIG. 7, the transparent electrodes 4 and 5 and the liquid crystal alignment films 9 and 10 are formed.
The cell formed by sandwiching the liquid crystal layer 6 between the two glass substrates 1 and 2 provided with the polarizing plates 11 and 1 whose polarization axes are orthogonal to each other.
If the optical axis OA is installed between the two so as to be parallel to one of the polarization axes, the liquid crystal display element will be in the dark state (OFF state). Then, even if the voltage waveform in the frame F ′ (+) or F ′ (−) of FIG. 4 is applied to the liquid crystal layer in this state, this voltage is | V _W2 | <| V (A−F) t | ( In the case of (see FIG. 8), since the change in light transmittance is slight, the OFF state can be maintained. On the other hand, frame F in FIG.
When a voltage waveform of (+) or F (-) is applied to the liquid crystal layer, if this voltage is | V _W1 |> | V (A−F) s | (see FIG. 8), the liquid crystal responds and the A ferroelectric phase (+) having an axis OF (+) and a spontaneous polarization Ps (+), and an optical axis OF.
Ferroelectric phase (-) having (-) and spontaneous polarization Ps (-)
Transfer to. In this case, the optical axis OA forms an angle θ with the polarization axis.
Since (+) or θ (−) is formed, the liquid crystal display element is in a bright state (ON state). Further, since the angles θ (+) and θ (−) are equal, both can be treated as optically equivalent.

[0008]

However, the above-mentioned conventional driving method has the following problems. That is, since the polarity of the holding voltage _Vb is inverted at the end of the frame (FIGS. 4 and 5A), there is a difference in the ON-state luminance depending on the order of the scanning electrodes selected in the frame (FIGS. 5 (d)). As a result, a luminance gradient occurs on the display screen, and a uniform display cannot be obtained. Further, since the one-line selection period is twice the pulse width or the erase period is provided (FIGS. 4 and 5), it takes a long time to write one screen, resulting in a display with a lot of flicker. .

In order to solve the above-mentioned problems in the prior art, the present invention makes full use of the characteristic of tri-stable state switching of antiferroelectric liquid crystal and realizes a uniform display with little flicker. It is an object to provide a driving method and a driving device.

[0010]

In order to achieve the above-mentioned object, a method of driving a liquid crystal display element according to the present invention comprises: a substrate having scan electrodes and a substrate having signal electrodes; For the liquid crystal display element that sandwiches the antiferroelectric liquid crystal exhibiting one orientation state that undergoes phase transition to the ferroelectric liquid crystal exhibiting two orientation states depending on the polarity of the voltage, the arrangement of the liquid crystal molecules is selected during the selection period. If the orientation to be selected is a ferroelectric liquid crystal, a voltage pulse whose absolute value is greater than or equal to a threshold value is applied, and if the orientation to be selected is an antiferroelectric liquid crystal, a voltage pulse whose absolute value is less than or equal to a threshold value is applied to the liquid crystal layer, and unselected. A method of driving a liquid crystal display device, in which a voltage pulse group of the same polarity is applied so as to maintain the alignment state selected in the selection period, and scanning is performed in one line selection period in accordance with a polarity signal inverted every frame period. Depending on the data The scanning voltage of 1 pulse is applied to the scanning electrodes, a holding voltage having the same polarity as the scanning voltage successively and applying to the next selection period.

Further, in the configuration of the driving method of the present invention, it is preferable to apply a selection voltage or a non-selection voltage having a positive or negative polarity according to the polarity of the selection period of the polarity signal to the signal electrode.

Further, according to the structure of the driving device of the liquid crystal display element according to the present invention, two alignment states are set between the substrates having the scanning electrodes and the substrate having the signal electrodes with the electrode surfaces facing each other depending on the polarity of the voltage. A driving device for a liquid crystal display element, which sandwiches an antiferroelectric liquid crystal exhibiting one orientation state that undergoes a phase transition to the ferroelectric liquid crystal shown in the figure, and scan data for causing the liquid crystal display element to perform a desired display and A control circuit that generates signal data, a polarity signal generation circuit that generates a polarity signal that is inverted every frame period, and the scan electrode with positive or negative polarity depending on the polarity of the selection period of the polarity signal. And a scan electrode drive circuit for applying a scan voltage and a holding voltage.

Further, in the configuration of the driving apparatus of the present invention, a signal electrode driving circuit for applying the signal data to the signal electrodes as a selection voltage and a non-selection voltage with a positive or negative polarity according to the polarity signal is provided. preferable.

[0014]

According to the structure of the driving method of the present invention, a scanning voltage of one pulse corresponding to scanning data is applied to the scanning electrodes during one line selection period in accordance with a polarity signal that is inverted every frame period, and scanning is subsequently performed. Since the holding voltage having the same polarity as the voltage is applied until the next selection period,
A scanning voltage whose polarity is inverted every frame period can be applied to the scanning electrodes. Therefore, any scan electrode can be used in the same manner from the selection period to the next selection period, so that there is no difference in the brightness in the ON state. As a result, the display screen does not have a brightness gradient, and uniform display can be realized.

According to a preferred configuration of the driving method of the present invention, a selection voltage or a non-selection voltage having a positive or negative polarity according to the polarity of the selection period of the polarity signal is applied to the signal electrode. Since the polarity of the voltage applied to the pixel can be inverted during the selection period, one screen can be displayed in a time corresponding to the product of the pulse width and the number of scanning lines required to invert the antiferroelectric phase to the ferroelectric phase. Can write. Therefore, writing can be performed in a shorter time than in the conventional driving method, and beautiful display with less flicker can be realized.

Further, according to the structure of the driving device of the present invention, the control circuit for generating the scan data and the signal data for causing the liquid crystal display element to perform a desired display, and the polarity signal for inverting each frame period are generated. And a scan electrode drive circuit for applying the scan data to the scan electrodes as a scan voltage and a holding voltage with a positive or negative polarity according to the polarity of the selection period of the polarity signal. A polarity signal generating circuit generates a polarity signal which is inverted every frame period, and a scan electrode driving circuit applies a scan voltage having a positive or negative polarity according to the polarity of the polarity signal in the selection period to the scan electrodes. You can That is, the polarity of the scanning voltage can be inverted every frame period, and the holding voltage having the same polarity as the scanning voltage can be applied after the scanning voltage from the selection period to the next selection period. Therefore, any scan electrode can be used in the same manner from the selection period to the next selection period, so that there is no difference in the brightness in the ON state. Therefore,
When the liquid crystal display element is driven by using the present driving device, the display screen does not have a brightness gradient, and thus uniform display can be realized.

Further, in the configuration of the driving apparatus of the present invention, it is preferable to provide a signal electrode driving circuit for applying the signal data to the signal electrode as a selection voltage or a non-selection voltage with a positive or negative polarity according to the polarity signal. According to the configuration, since the signal electrode drive circuit can apply the selection voltage and the non-selection voltage having the positive or negative polarity according to the polarity of the selection period of the polarity signal to the signal electrode, it is applied to the pixel during the selection period. The polarity of the voltage can be reversed. Therefore, one screen can be written in a time corresponding to the product of the pulse width and the number of scanning lines required to invert the antiferroelectric phase to the ferroelectric phase. Can be done at. Therefore, by driving the liquid crystal display element using the present driving device, beautiful display with little flicker can be realized.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. As a sample, a liquid crystal display device having a structure as shown in FIG. 7 was used. In producing this sample, first, the insulating films 7 and 8 are formed on the transparent electrodes 4 and 5, and the polyimide film is formed on the insulating films 7 and 8 and the rubbing treatment is performed to perform the uniaxial orientation treatment. Alignment films 9 and 10
And Next, a panel was formed so that the rubbing directions were parallel or antiparallel by the substrates facing each other, and the gap was set to 1.7 μm. Then, the liquid crystal material 4- (1-methylheptyloxycarbo) is formed on the panel.
nyl) phenyl4'-octyloxybiph
enyl-4-carboxylate (MHPOB
C) was heated enclosed by keeping the environmental temperature to the temperature range of the antiferroelectric chiral smectic C phase (SmC _A ^* phase) to form a liquid crystal layer 6. Incidentally, in FIG. 7, 1, 2
Is a glass substrate, 3 is a spacer material, and 11 and 12 are polarizing plates. Further, one of the transparent electrodes 4 and 5 is used as a scanning electrode and the other is used as a signal electrode.

(Embodiment 1) FIG. 1 shows drive waveforms used in an embodiment of a method for driving a liquid crystal display element according to the present invention.
In FIG. 1, (a) is a scan electrode waveform, (b) is a signal electrode waveform, and (c) is a composite waveform of these. Also,
(D) shows the change in light transmittance with respect to the drive waveform. The scan electrode waveform (a) is applied with a scan voltage V _r of one pulse according to scan data in one line selection period in accordance with a polarity signal that is inverted every frame period, and then is held with the same polarity as the scan voltage V _r. The voltage _Vb is applied and held until the next selection period. With such a configuration of the scanning electrode waveform (a), the polarity of the selection waveform can be inverted every time it is selected. On the other hand, the signal electrode waveform (b) is such that the selection voltage / non-selection voltage V _s corresponding to the signal data of the display pattern is applied with its polarity inverted according to the polarity signal. Figure 2
Shows the relationship between the polarity signal and the scanning voltage, the selection voltage, and the non-selection voltage. Since the scanning electrode waveform (a) and the signal electrode waveform (b) are configured as described above, the polarity of the voltage applied to the pixel during the selection period can be inverted. The temperature of the liquid crystal display element is kept at 90 ° C., the pulse width is 80 μsec, the scanning voltage is V _r = 18 V, the holding voltage is V _b = 5 V, the selection voltage / non-selection voltage is V _s = 2.7 V, and the duty ratio is 1 /
When driven as 480 under the above conditions, the contrast ratio was 1:20.

Next, the displays when the driving method of the present invention and the conventional driving method are used will be compared. When the conventional driving method is used, since the polarity of the holding voltage _Vb is reversed at the end of the frame (FIGS. 4 and 5), it is turned on depending on the order of the scanning electrodes selected in the frame. There is a difference in brightness (FIG. 5 (d)). On the other hand, in the present invention, since the polarity of the scanning voltage is inverted every frame period, any scanning electrode can be used in the same manner from the selection period to the next selection period (FIG. 1A). ). As a result, O
There is no difference in brightness in the N state (Fig. 1 (d)),
Since there is no brightness gradient on the display screen, uniform display can be realized.

Next, the display speeds when the driving method of the present invention and the conventional driving method are used will be compared. When the conventional driving method is used, one line selection period is twice the pulse width or an erase period is provided (FIG. 4), so the writing time for one screen is 76.8 msec or more (2 × 80μ
sec × 480 + α). On the other hand, in the present invention, since the polarity of the voltage applied to the pixel is inverted during the selection period, it corresponds to the product of the pulse width and the number of scanning lines required to invert from the antiferroelectric phase to the ferroelectric phase. One screen can be written in time. Because the time required for relaxation from the ferroelectric phase to the antiferroelectric phase, which is the slowest inversion, is 42
This is because it is 0 μsec, and it is possible to surely relax within the frame time (80 μsec × 480 = 38.4 msec) without providing an erasing period. Therefore, the time required to write one screen is 38.4 msec, and it is possible to write in half the time required by the conventional method. As a result, a beautiful display with little flicker can be realized.

(Embodiment 2) FIG. 3 shows a block diagram of an embodiment of a driving device for a liquid crystal display element according to the present invention. As shown in FIG. 3, the present driving device includes a control circuit 13 for generating scan data and signal data for causing a liquid crystal display element (antiferroelectric liquid crystal panel) 17 to perform a desired display, and an inversion for each frame period. And a scan electrode drive circuit for applying the scan data to the scan electrodes as a scan voltage and a hold voltage with a positive or negative polarity depending on the polarity of the polarity signal in the selection period. 15 and a signal electrode drive circuit 16 for applying the signal data to the signal electrodes as a selection voltage and a non-selection voltage with a positive or negative polarity according to the polarity signal. Since the present drive device is configured as described above, the polarity signal generation circuit 14 generates a polarity signal that is inverted every frame period, and the scan electrode drive circuit 15 generates a positive or negative polarity depending on the polarity of the polarity signal in the selection period. The scan voltage having the polarity of can be applied to the scan electrodes. That is, the polarity of the scanning voltage can be inverted every frame period, and the holding voltage having the same polarity as the scanning voltage can be applied after the scanning voltage from the selection period to the next selection period. Therefore, any scan electrode can be used in the same manner from the selection period to the next selection period (FIG. 1A), so that no difference occurs in the brightness in the ON state (FIG. 1 ( d)). Therefore, when the liquid crystal display element is driven by using the present driving device, the display screen does not have a brightness gradient, and uniform display can be realized. In addition, the signal electrode drive circuit 16
As a result, a selection voltage or a non-selection voltage having a positive or negative polarity depending on the polarity of the selection period of the polarity signal can be applied to the signal electrode, so that the polarity of the voltage applied to the pixel during the selection period can be inverted. . Therefore, one screen can be written in a short time for the same reason as in the first embodiment. Therefore, by driving the liquid crystal display element using the present driving device, beautiful display with little flicker can be realized.

[0023]

As described above, according to the driving method of the liquid crystal display element of the present invention, the scanning voltage of one pulse corresponding to the scanning data is applied during the one line selection period in accordance with the polarity signal inverted every frame period. Since the holding voltage having the same polarity as the scanning voltage is applied until the next selection period, the scanning voltage whose polarity is inverted every frame period can be applied to the scanning electrode. . Therefore, any scan electrode can be used in the same manner from the selection period to the next selection period, so that there is no difference in the brightness in the ON state. As a result, the display screen does not have a brightness gradient, and uniform display can be realized.

In addition, according to the preferable structure of the driving method of the present invention, a selection voltage or a non-selection voltage having a positive or negative polarity according to the polarity of the selection period of the polarity signal is applied to the signal electrode. Since the polarity of the voltage applied to the pixel can be inverted during the selection period, one screen can be displayed in a time corresponding to the product of the pulse width and the number of scanning lines required to invert the antiferroelectric phase to the ferroelectric phase. Can write. Therefore, writing can be performed in a shorter time than in the conventional driving method, and beautiful display with less flicker can be realized.

Further, according to the liquid crystal display element driving device of the present invention, a control circuit for generating scan data and signal data for causing the liquid crystal display element to perform a desired display, and a polarity signal which is inverted every frame period. And a scan electrode drive circuit that applies the scan data to the scan electrodes as a scan voltage and a hold voltage with a positive or negative polarity according to the polarity of the polarity signal in the selection period. Therefore, the polarity signal generation circuit generates a polarity signal that is inverted every frame period, and the scan electrode drive circuit applies a scan voltage having a positive or negative polarity according to the polarity of the selection period of the polarity signal to the scan electrodes. can do. That is, the polarity of the scanning voltage can be inverted every frame period, and the holding voltage having the same polarity as the scanning voltage can be applied after the scanning voltage from the selection period to the next selection period. Therefore, any scan electrode can be used in the same manner from the selection period to the next selection period, so that there is no difference in the brightness in the ON state.
Therefore, when the liquid crystal display element is driven by using the present driving device, the display screen does not have a brightness gradient, and uniform display can be realized.

Further, in the configuration of the driving device of the present invention, it is preferable to provide a signal electrode driving circuit for applying signal data to the signal electrodes as a selection voltage and a non-selection voltage with a positive or negative polarity according to the polarity signal. According to the configuration, since the signal electrode drive circuit can apply the selection voltage and the non-selection voltage having the positive or negative polarity according to the polarity of the selection period of the polarity signal to the signal electrode, it is applied to the pixel during the selection period. The polarity of the voltage can be reversed. Therefore, one screen can be written in a time corresponding to the product of the pulse width and the number of scanning lines required to invert the antiferroelectric phase to the ferroelectric phase. Can be done at. Therefore, by driving the liquid crystal display element using the present driving device, beautiful display with little flicker can be realized.

[Brief description of drawings]

FIG. 1 is a drive waveform diagram used in an example of a method for driving a liquid crystal display element according to the present invention.

FIG. 2 is a diagram showing a relationship between a polarity signal and a scanning voltage, a selection voltage, and a non-selection voltage.

FIG. 3 is a configuration diagram showing an embodiment of a driving device of a liquid crystal display element according to the present invention.

FIG. 4 is a drive waveform diagram in a conventional technique.

FIG. 5 is a diagram showing changes in light transmittance with respect to a drive waveform applied to a liquid crystal layer in a conventional drive method.

FIG. 6 is a conceptual diagram of a liquid crystal display element.

FIG. 7 is a cross-sectional view of a liquid crystal display element.

FIG. 8 is an electro-optical characteristic diagram of a liquid crystal display element.

[Explanation of Symbols] a ₁ , a ₂ , a ₃ , a _n , V _t electrode waveforms b ₁ , b ₂ , b ₃ , b _n , V _d signal electrode waveforms c ₁₁ , c ₁₃ , c ₂₂ , c _nn , V _LC composite waveform d ₁₁ , d ₁₃ , d ₂₂ , d _nn , transmittance V _r scanning voltage V _s selection voltage / non-selection voltage V _b holding voltage OA optical axis in antiferroelectric phase OF (+) ferroelectric phase (+) (Molecular orientation direction)
Optical axis OF (-) Ferroelectric phase (-) (Molecular orientation direction)
Optical axis 1, 2 Glass substrate 3 Spacer material 4, 5 Transparent electrode (ITO) 6 Liquid crystal phase 7, 8 Insulating layer (TiO ₃ ) 9, 10 Polyimide alignment film 11, 12 Polarizing plate

Claims (4)

[Claims] 1. A phase transition to a ferroelectric liquid crystal exhibiting two alignment states depending on the polarity of a voltage between a substrate having a scanning electrode and a substrate having a signal electrode facing each other.
For a liquid crystal display element that sandwiches an antiferroelectric liquid crystal that exhibits two alignment states, a voltage pulse whose absolute value is greater than or equal to a threshold value is applied during the selection period if the alignment that selects the alignment of liquid crystal molecules is a ferroelectric liquid crystal. If the selected orientation is an anti-ferroelectric liquid crystal, a voltage pulse whose absolute value is less than or equal to a threshold value is applied to the liquid crystal layer, while the same orientation is applied during the non-selection period so as to maintain the selected orientation state. A driving method of a liquid crystal display element applying a voltage pulse group of polarity, wherein a scanning voltage of 1 pulse corresponding to scanning data is applied to the scanning electrodes in a 1-line selection period in accordance with a polarity signal inverted every frame period, A method of driving a liquid crystal display device, characterized in that a holding voltage having the same polarity as the scanning voltage is applied continuously until the next selection period. 2. The method for driving a liquid crystal display element according to claim 1, wherein a selection voltage or a non-selection voltage having a positive or negative polarity according to the polarity of the selection period of the polarity signal is applied to the signal electrode. 3. A phase transition to a ferroelectric liquid crystal exhibiting two alignment states depending on the polarity of a voltage between a substrate having a scanning electrode and a substrate having a signal electrode facing each other.
A driving device for a liquid crystal display device, which sandwiches an antiferroelectric liquid crystal exhibiting two alignment states, a control circuit for generating scan data and signal data for causing the liquid crystal display device to perform a desired display, and a frame A polarity signal generation circuit that generates a polarity signal that is inverted every cycle, and a scan that applies the scan data to the scan electrodes as a scan voltage and a holding voltage with a positive or negative polarity according to the polarity of the selection period of the polarity signal. A drive device for a liquid crystal display device, comprising: an electrode drive circuit. 4. A drive device for a liquid crystal display device according to claim 3, further comprising a signal electrode drive circuit for applying signal data as a selection voltage and a non-selection voltage to the signal electrode with positive or negative polarity according to the polarity signal. .