JPH1010495A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal device which can widen the driving margin even when liquid crystals with asymmetrical threshold characteristic are used. SOLUTION: An DC voltage impressing means 10 impresses a weak DC voltage component on an information signal to be impressed on a matrix of the information electrode group 3a formed on a pair of opposing substrates. An impressed voltage adjusting means 12 controls the DC voltage impressing means 10 to adjust the magnitude of the DC voltage component. Thereby the magnitude of the synthesized signal of the scan signal and the information signal is adjusted and the asymmetricity of switching of the liquid crystal is resolved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device using a liquid crystal having a bistable characteristic, and more particularly to a device for driving a liquid crystal having an asymmetric switching threshold.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal device has a nematic liquid crystal,
Various materials such as smectic liquid crystal and polymer dispersed liquid crystal are used. When driving these liquid crystals, the liquid crystal is sandwiched between a pair of substrates 1a facing each other as shown in FIG. 13, while each pixel 100 is configured in a matrix type, and information of each pixel 100 is transmitted to an information signal line. Driving is performed by supplying the scanning signal of each line supplied from the scanning line 102 from the scanning line 102.

In FIG. 1, reference numeral 1 denotes a liquid crystal display panel; 101, a scanning line driver for selecting each scanning line 102 and outputting a driving waveform to the selected scanning line 102 at a predetermined timing; Information line 1 according to
The information line driver outputs a predetermined drive waveform at a predetermined timing.

A liquid crystal device having bistability as a conventional liquid crystal is disclosed in both Clark and Lagerwall in Japanese Patent Application Laid-Open No. 56-1980.
No. 07216, and U.S. Pat. No. 4,362,924.

Here, a ferroelectric liquid crystal having a chiral smectic C phase (SmC *) or an H phase (SmH *) is generally used as such a bistable liquid crystal. In these two states, the liquid crystal exhibits a so-called bistable state of a first optically stable state and a second optically stable state in response to an applied electric field, and the state when no voltage is applied. , That is, stability. In addition, since the response to a change in the electric field is quick, wide use in fields such as a high-speed and storage-type display device is expected.

On the other hand, in a liquid crystal display panel using the ferroelectric liquid crystal element, for example, a stripe electrode group is provided inside a pair of substrates, and the substrates are combined so that the stripe electrodes are orthogonal to each other. To form a matrix electrode. In the case of such a display device, for example, JP-A-59-193
Nos. 426, 59-193427 and 60-
The driving method disclosed in Japanese Patent Application Laid-Open Nos. 156046 and 60-156047 can be applied.

[0007]

By the way, in a liquid crystal device using such a ferroelectric liquid crystal, the bistable state of the ferroelectric liquid crystal is destroyed due to the substrate structure, aging, etc. Optical switching characteristics (drive threshold characteristics) may be asymmetric.

For example, FIG. 14 is a view showing a model of the orientation state of liquid crystal when the properties of the surface of the opposite substrate are different. In FIG. 14, reference numerals 701 and 707 denote glass substrates and 702 and 70, respectively.
Reference numeral 6 denotes a transparent electrode made of ITO or the like, 703 a rubbed polymer film having a horizontal alignment function, 704 a ferroelectric liquid crystal layer, and 705 a vertical alignment material.

708, 709, and 710 are front views of cones characterizing liquid crystal molecules in the chiral smectic layer, 708a and 709a show two stable states in uniform alignment, and 710a shows a splay alignment state An example is shown. Here for convenience 708
The stable state of a is called U2, and the stable state of 709a is called U1.

Now, when a thin film of polyimide or the like is used as the polymer film 703, the arrows are oriented due to the electric interaction between the dipole moment of the liquid crystal molecules (the arrow drawn on the liquid crystal cone in the figure) and the polymer surface. Considering that the regulating force acts in a state facing the film side (referred to as an outward), the vertical alignment material 70
On the side of No. 5, the regulating force of the liquid crystal molecules toward the substrate is negligible, so that U2 (708 in the figure) in which the dipole moment of the liquid crystal is restricted on the alignment film side is more stable.

On the other hand, the state of U1 (709 in the figure) in which the arrow of the liquid crystal cone faces the inside of the liquid crystal (referred to as an inward) is opposite to the regulating force on the surface of the alignment film, and therefore is inferior to U2. It is stable.

Therefore, when switching between two stable states by an external electric field, the threshold voltage for switching from U1 to U2 and the threshold voltage for switching from U2 to U1 are different and asymmetric. Further, depending on the combination of the liquid crystal and the alignment film, switching from U2 to U1 does not occur, and the splay alignment of the alignment state from U2 to 710 may occur.

As described above, in a system in which the threshold value is asymmetric, the threshold value is increased or the crosstalk value is decreased. Therefore, the allowable range of the drive voltage pulse width or the amplitude in which the matrix drive can be performed, that is, the drive margin is narrowed, and the good drive margin is obtained. There is a problem that display cannot be performed.

The present invention has been made to solve the above problems, and has as its object to provide a liquid crystal device capable of widening a driving margin even when a liquid crystal having asymmetric threshold characteristics is used. Is what you do.

[0015]

According to the present invention, a scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and the scanning signal and the information signal are applied. In a liquid crystal device that performs switching of liquid crystal having bistable characteristics sandwiched between the substrates by a synthesized signal, a DC voltage applying unit that applies a weak DC voltage component to the information signal, and a DC voltage component of the applied DC voltage component. Applying voltage adjusting means for controlling the DC voltage applying means to adjust the magnitude, the applied voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the DC voltage component The magnitude of the combined signal is adjusted to eliminate the asymmetry of the switching threshold of the liquid crystal.

Further, according to the present invention, a scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and the scanning signal and the information signal are combined by a combined signal. In a liquid crystal device that performs switching of a liquid crystal having bistable characteristics sandwiched between substrates,
DC voltage application means for applying a weak DC voltage component to the scanning signal, and application voltage adjustment means for controlling the DC voltage application means to adjust the magnitude of the applied DC voltage component, The applied voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the DC voltage component to adjust the magnitude of the composite signal, thereby eliminating the asymmetry of the switching threshold of the liquid crystal. It is characterized by the following.

Further, according to the present invention, a scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and the scanning signal and the information signal are combined by the combined signal. In a liquid crystal device that performs switching of a liquid crystal having bistable characteristics sandwiched between substrates,
DC voltage application means for applying a weak DC voltage component to the composite signal, and application voltage adjustment means for controlling the DC voltage application means to adjust the magnitude of the applied DC voltage component, The voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the combined signal, thereby eliminating the asymmetry of the switching threshold of the liquid crystal.

Further, the present invention is characterized in that the magnitude of the applied DC voltage component ranges from 10 mV to 2 V.

Further, the present invention is characterized in that the liquid crystal is a ferroelectric liquid crystal.

Further, with this configuration, the DC voltage applying means applies a weak DC voltage component to the information signal applied to the information electrode group formed in a matrix on the pair of opposing substrates. . Then, by controlling the DC voltage applying means by the applied voltage adjusting means to adjust the magnitude of the DC voltage component, the magnitude of the combined signal of the scanning signal and the information signal is adjusted, and the switching threshold of the liquid crystal is adjusted. Eliminate asymmetry.

The DC voltage applying means applies a weak DC voltage component to the scanning signals applied to the scanning electrodes formed in a matrix on the pair of substrates facing each other. Then, by controlling the DC voltage applying means by the applied voltage adjusting means to adjust the magnitude of the DC voltage component, the magnitude of the combined signal is adjusted to eliminate the asymmetry of the switching threshold of the liquid crystal.

Further, by applying a weak DC voltage component to the composite signal by the DC voltage applying means and controlling the DC voltage applying means by the applied voltage adjusting means to adjust the magnitude of the DC voltage component, The magnitude of the composite signal is adjusted to eliminate the asymmetry of the switching threshold of the liquid crystal.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram of a liquid crystal device according to a first embodiment of the present invention. In FIG. 1, 1 is a liquid crystal display panel for displaying an image, 2 is a scanning line driver, and 3 is information A line driver 4, a scanning signal control circuit 5,
A drive control circuit having an information signal control circuit 6, a drive voltage generation circuit 7 for generating a drive voltage, and a graphic controller 8 having a VRAM 9 for storing image information.

The image information stored in the VRAM 9 is transferred as data from the graphic controller 8 to the drive control circuit 4 in accordance with a transfer clock.
Thereafter, this data is input to the scanning signal control circuit 5 and the information signal circuit 6, and is converted into scanning signal address data and display data, respectively.

Further, the scanning line driver 2 and the information line driver 3 output a scanning signal waveform and an information signal waveform to the scanning electrode group 2a and the information electrode group 3a, respectively, according to the scanning signal address data and the display data. ing. The drive voltage generation circuit 7 generates a drive voltage to which a DC voltage component input from the information signal voltage control circuit 10 described later is applied, and applies the drive voltage to the information electrode group 3a.

On the other hand, FIG. 2 shows an example of each scanning signal waveform and information signal waveform outputted from the scanning line driver 2 and the information line driver 3. In the scanning signal shown in FIG. V1 is the voltage of the erase pulse Pe,
V2 indicates the voltage of the write pulse Pw, V5 indicates the voltage Pa of the auxiliary pulse, and Vc indicates the voltage during the non-selection period of the scanning signal.

In the information signal shown in FIG. 2B, V3 and V4 indicate the voltages of the information signal indicating "black" or "white", respectively. Here, in the present embodiment, V1 = −V2 = V3 × 2, V3 = −V4, V
It is assumed that c = 0 and V5 = V3 × 1.1. V3 may be in the range of 2V to 10V.

FIG. 3 shows a composite waveform of the scanning signal and the information signal, and the write pulse voltage Vw in the composite voltage is V2 + V3. Here, when a positive pulse Pp is applied as shown in FIG. 4, the liquid crystal LC switches in a counterclockwise direction (from right to left in FIG. 4) (hereinafter, switching in this direction is an L-direction switch). ). When a negative pulse Pn is applied, switching is performed in a clockwise direction (from left to right in the figure) (hereinafter, switching in this direction is referred to as an R-direction switch).

Here, the liquid crystal which performs such a switching operation is formed by using a compound as shown in FIG.
This is a liquid crystal composition having ferroelectricity, which is formed at a weight ratio of / B1 / B2 / B3 / C = 80/3/3/4/5. The spontaneous polarization of this composition at 25 ° C. was 26 nC / cm.
^{2. At} 20 ° C, the layer inclination angle δ is 0 ° and the tilt angle is 27 °
It is. By using the ferroelectric liquid crystal as described above, the speed of the material itself can be increased, and higher-speed display can be performed.

In the liquid crystal display panel 1, a polarizing plate (not shown) is arranged in a crossed Nicols state. The axis of the polarizing plate is made to coincide with the optical axis of the liquid crystal orientation when an erasing pulse voltage is applied. (The direction of the polarizing plate is different in the R and L direction switches). Thereby, the write pulse voltage V
If w is greater than the threshold voltage Vth of the liquid crystal, the liquid crystal switches, and the transmittance increases.

Now, in the liquid crystal display panel 1 using this liquid crystal, each threshold value Vt of the R and L direction switches is set.
hR and VthL are asymmetric, and the relationship is Vth
Assuming that R>Vw> VthL, when a write pulse voltage Vw as shown in FIG. 3 is applied, FIG.
As shown in FIG. 6, Vw> VthL, writing is performed in the L-direction switch, and the transmittance Tr increases. However, in the R-direction switch, VthR> Vth as shown in FIG.
Since it is w, writing is not performed, and the transmittance Tr rises momentarily but immediately falls.

However, when a slight DC voltage component Vd1 is applied to the negative polarity side of the composite waveform as shown in FIG. 7, this DC voltage component Vd1 causes a rotation torque in the negative direction to the liquid crystal molecules. Even an R-direction switch that does not switch to the maximum can be switched as shown in FIG. 7B.

However, when a small DC voltage component Vd1 is applied, the L-direction switch can continue to be switched as shown in FIG. 7A, but when a larger DC voltage component Vd2 is applied, the rotation is reduced. Since the torque becomes too large, writing cannot be performed with the L-direction switch as shown in FIG. The R-direction switch can perform switching as shown in FIG. 8B even when such a large DC voltage component Vd2 is applied.

FIG. 9 shows the relationship between the DC voltage component and the threshold voltages of the switches in the R and L directions. That is, by applying a small DC voltage component, the threshold value can be relatively lowered in the R-direction switch, and the write pulse voltage Vw as shown in FIG.
Switching can be performed even when is applied. on the other hand,
In the L-direction switch, the threshold value is relatively increased by applying a DC voltage component, so that even if switching was possible up to that time, switching cannot be performed.

From this, when a DC voltage component having an appropriate polarity (broken line portion in the figure) is applied, threshold asymmetry can be compensated and symmetric threshold characteristics can be obtained. Note that the DC voltage component value (the portion indicated by ΔV in the figure) that makes this threshold characteristic symmetric varies greatly depending on the drive waveform, drive voltage, liquid crystal material, substrate configuration, and the like. According to the study of the present inventor, it has been found that the value ranges from 10 mV to 2 V.

Therefore, in the present embodiment, as shown in FIG. 1, a DC voltage applying means is a DC voltage applying means for applying a DC voltage component to the information signal to adjust the asymmetry of the polarity of the information signal voltage. A circuit 10 is provided.

Further, by adjusting the magnitude of the DC voltage component applied to the information signal by the information signal voltage control circuit 10, the magnitude of the composite signal of the scanning signal and the information signal is adjusted to switch the liquid crystal. An information signal voltage adjuster is provided as an applied voltage adjuster for eliminating asymmetry of the threshold. Note that this information signal voltage adjustment unit 12
It consists of knobs and levers so that manual operation is possible.

When a liquid crystal having an asymmetrical threshold characteristic is used and, for example, the screen flickers, the information signal voltage control unit 12 constituted by the knobs and levers is manually operated to control the information signal voltage control. The magnitude of the DC voltage applied to the drive voltage generation circuit 7 is adjusted by the circuit 10, and the information signal voltage applied to the information electrode group 3a is adjusted.

Here, for example, when -Vd is applied by the information signal voltage control circuit 10, for example, the information signal voltage is shifted by -Vd as shown in FIG. And
When the information signal voltage shifts by -Vd in this manner, the write pulse voltage Vw, which is a composite signal, also shifts in a direction to compensate for asymmetry, so that the asymmetric threshold characteristic of the liquid crystal can be eliminated. It should be noted that the DC voltage value can be reduced by such a configuration, and power consumption and the configuration of the power supply circuit can be simplified. In addition, by enabling the information signal voltage adjustment unit 12 to be manually operated, the screen can be easily adjusted.

In the first embodiment described above, the asymmetric threshold characteristic is eliminated by applying a DC voltage component to the information signal. However, the present invention is not limited to this. Alternatively, by applying a DC voltage component to the scanning signal, the asymmetric threshold characteristic can be eliminated.

FIG. 11 is a block diagram of such a liquid crystal device according to the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts.

In the figure, reference numeral 11 denotes a scanning signal voltage control circuit which is a DC voltage applying means for applying a weak DC voltage component to the scanning signal, and 13 adjusts the magnitude of the DC voltage component applied to the scanning signal. The scanning signal voltage adjusting unit 13 is an applied voltage adjusting unit that adjusts the magnitude of the combined signal to eliminate the asymmetry of the switching threshold of the liquid crystal. Note that the scanning signal voltage adjusting unit 13 is configured by a knob or a lever so that manual operation is possible.

When a liquid crystal having an asymmetrical threshold characteristic is used and, for example, the screen flickers, the scanning signal voltage control unit 13 constituted by the knobs and levers is manually operated to control the scanning signal voltage. The circuit 11 adjusts the magnitude of the DC voltage component applied to the drive voltage generation circuit 7 to adjust the information signal voltage applied to the scan electrode group 2a.

Here, assuming that, for example, -Vf is given by the scanning signal voltage control circuit 11, the information signal voltage becomes
The shift is performed by -Vf as shown in FIG. Then, by thus shifting the scanning signal voltage by -Vf,
Since the write pulse voltage also shifts in a direction to compensate for asymmetry, the asymmetric threshold characteristic of the liquid crystal can be eliminated. In addition, since DC asymmetry can be achieved only by applying DC to the scanning signal voltage Vc in the non-selection period, the configuration of the control circuit is simplified. Further, by enabling the scanning signal voltage adjusting unit 13 to be manually operated, the screen can be easily adjusted.

In the above description, a case has been described in which a DC voltage is applied to the information signal and a DC voltage is applied to the scanning signal in order to apply a weak DC voltage component to the composite signal. The present invention is not limited to this, and may be configured to directly apply a weak DC voltage component to the composite signal.

[0047]

As described above, according to the present invention, the asymmetry can be compensated for by applying a weak DC voltage component to the liquid crystal having an asymmetric threshold characteristic, so that the driving margin of the driving margin can be reduced. A wide liquid crystal device can be provided. Further, by applying the DC voltage component, the write pulse voltage can also be shifted in a direction to compensate for asymmetry, so that the DC voltage value can be reduced and the power consumption can be reduced. The configuration of the power supply circuit can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram of a liquid crystal device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a scanning signal waveform and an information signal waveform of the liquid crystal device.

FIG. 3 is a diagram showing a composite waveform of the scanning signal waveform and the information signal waveform.

FIG. 4 is a diagram showing pulse polarities and switching directions of liquid crystal.

FIG. 5 is a diagram illustrating a compound constituting a liquid crystal of the liquid crystal device.

FIG. 6 is a diagram showing an optical response of a liquid crystal when the composite waveform is applied.

FIG. 7 is a diagram showing an optical response of a liquid crystal when a composite waveform to which Vd1 is added is applied.

FIG. 8 is a diagram showing an optical response of a liquid crystal when a composite waveform to which Vd2 is added is applied.

FIG. 9 is a diagram showing a relationship between a DC voltage component and a threshold voltage.

FIG. 10 is a view for explaining information signals generated by the first embodiment of the liquid crystal device.

FIG. 11 is a block diagram of a liquid crystal device according to a second embodiment of the present invention.

FIG. 12 is a diagram illustrating a scanning signal generated by the first embodiment of the liquid crystal device.

FIG. 13 illustrates a structure of a liquid crystal display unit of a conventional liquid crystal device.

FIG. 14 is a diagram showing threshold asymmetry of a conventional liquid crystal.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal display panel 1a substrate 2 scanning line driver 3 information line driver 7 driving voltage generation circuit 10 information signal voltage control circuit 11 scanning signal voltage control circuit 12 information signal voltage adjustment unit 13 scanning signal voltage adjustment unit 100 pixel

Claims (5)

[Claims] 1. A scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and a scanning signal and an information signal are sandwiched between the substrates by a composite signal of the scanning signal and the information signal. A liquid crystal device that performs switching of a liquid crystal having the obtained bistable characteristic, wherein: a DC voltage application unit that applies a weak DC voltage component to the information signal; and the DC that adjusts the magnitude of the applied DC voltage component. Applying voltage adjusting means for controlling voltage applying means, wherein the applied voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the DC voltage component to adjust the magnitude of the composite signal. And a liquid crystal device characterized by eliminating the asymmetry of the switching threshold of the liquid crystal. 2. A scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and a scanning signal and an information signal are sandwiched between the substrates by a composite signal of the scanning signal and the information signal. A liquid crystal device that performs switching of a liquid crystal having bistable characteristics, wherein a DC voltage applying unit that applies a weak DC voltage component to the scan signal; and the DC voltage is adjusted so as to adjust the magnitude of the applied DC voltage component. Applying voltage adjusting means for controlling voltage applying means, wherein the applied voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the DC voltage component to adjust the magnitude of the composite signal. And a liquid crystal device characterized by eliminating the asymmetry of the switching threshold of the liquid crystal. 3. A scanning signal and an information signal are respectively applied to a scanning electrode group and an information electrode group formed in a matrix on a pair of opposing substrates, and the scanning signal and the information signal are sandwiched between the substrates by a composite signal of the scanning signal and the information signal. A liquid crystal device that performs switching of a liquid crystal having bistable characteristics, wherein: a DC voltage application unit that applies a weak DC voltage component to the composite signal; and the DC that adjusts the magnitude of the applied DC voltage component. Applying voltage adjusting means for controlling voltage applying means, wherein the applied voltage adjusting means controls the DC voltage applying means to adjust the magnitude of the composite signal, so that the asymmetry of the switching threshold of the liquid crystal is changed. A liquid crystal device characterized by eliminating the above. 4. The liquid crystal device according to claim 1, wherein the magnitude of the applied DC voltage component ranges from 10 mV to 2 V. 5. The liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal.