JP2003270616A - Method of driving liquid crystal element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the voltage-transmittance characteristic of a chiral smectic liquid crystal from being varied when continuously driving a liquid crystal panel. <P>SOLUTION: In the case that what is called a one-side V-shaped liquid crystal (namely, a liquid crystal which has liquid crystal molecules largely tilted at the time of application of a first driving voltage having one polarity and has liquid crystal molecules scarcely tilted at the time of application of a second driving voltage having the other polarity), the second driving voltage is corrected on the basis of data in Figure 1 when the first driving voltage and the second driving voltage are successively applied. Thus a DC component is not stored in the liquid crystal panel to suppress the variance of liquid crystal characteristics (namely, the voltage-transmittance characteristic of the chiral smectic liquid crystal), which is accompanied with the storage. <P>COPYRIGHT: (C)2003,JPO

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 a liquid crystal element used in flat panel displays, projection displays and the like.

[0002]

2. Description of the Related Art Conventionally, a TFT (Thin Film T
A typical liquid crystal mode of a nematic liquid crystal display element that is widely used as a display element using an active element such as a transistor is, for example, M. Schatt and W. Helfrich, Applied. Phys
ics Letters Vol. 18, No. 4, (Published February 15, 1971), pages 127-128, Twisted Nematic.
tic) mode is widely used. On the other hand, recently
In-plane switching (In
A liquid crystal display using a -Plane Switching mode or a Vertical Alignment mode has been announced, and viewing angle characteristics, which have been a drawback of conventional liquid crystal displays, have been improved. As described above, there are several liquid crystal modes for use in the TFT display element using such nematic liquid crystal, and in any of these modes, the response speed of the liquid crystal is several tens of milliseconds or more. late,
Further improvement in response speed is required.

In order to improve the response speed of such a conventional nematic liquid crystal element, several liquid crystal modes using a liquid crystal exhibiting a chiral smectic phase have been proposed in recent years. For example, "short-pitch type ferroelectric liquid crystal", "polymer stable ferroelectric liquid crystal", "threshold antiferroelectric liquid crystal", etc. have been proposed, but they have not yet been put to practical use. It has been reported that a high-speed response of sub-millisecond or less can be realized.

On the other hand, we have disclosed in Japanese Unexamined Patent Publication No. 2000-338464.
Element described in Japanese Patent Publication (hereinafter referred to as "Prior Application 1")
Has invented and proposed. In the invention, for example, an isotropic liquid phase (ISO.)-Cholesteric phase from the high temperature side
Focusing on the material of the phase series showing the (Ch) -chiral smectic C phase or the isotropic liquid phase (ISO.)-Chiral smectic C phase, the mono-stabilization is performed at a position inside the edge of the virtual cone. There is. And for example,
At the time of the Ch-SmC * phase transition or at the isotropic phase-SmC * phase transition, a positive or negative DC voltage is applied between the pair of substrates to uniformize the layer direction in one direction, thereby A high-brightness liquid crystal element that is capable of high-speed response and gradation control and is excellent in moving image quality can be realized with high mass productivity. The element of the prior application can reduce the spontaneous polarization value as compared with the above-mentioned various smectic liquid crystal modes, and therefore is an element that is well matched with an active element such as a TFT.

Similarly, we have disclosed in Japanese Unexamined Patent Publication No. 2000-01007.
The device described in Japanese Patent Laid-Open No. 6 (hereinafter referred to as “Prior application 2”) is invented and proposed. In the present invention, for example, a phase series material showing an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase or an isotropic liquid phase (ISO.)-Chiral smectic C phase from the high temperature side. Paying attention to, the mono-stabilization is performed at the position of the virtual cone edge. And, for example, Ch-
When the SmC * phase transition or the isotropic phase-SmC * phase transition, a positive or negative DC voltage is applied between the pair of substrates.
As a result, the layer direction is made uniform in one direction, which enables high-speed response and gradation control, and realizes a high-brightness liquid crystal element excellent in moving image quality with high mass productivity. In addition, the element of the prior application 2 can realize stable halftone display with small hysteresis, and can reduce the spontaneous polarization value as compared with the other various smectic liquid crystal modes described above, so that matching with an active element such as a TFT is performed. Is a good element.

Further, we have disclosed in Japanese Patent Laid-Open No. 2000-275685.
Device described in Japanese Patent Publication (hereinafter referred to as "Prior Application 3")
Has invented and proposed. In the invention, prior application 1 or 2
As a method of controlling the orientation, an element in which a stripe-shaped orientation state is formed by appropriately adjusting the orientation regulating force and thereby high contrast can be realized.

As described above, a chiral smectic liquid crystal, in particular, the liquid crystal elements of the prior applications 1 to 3 were used in the sense that the problems relating to the response speed, which were conventionally held in the TFT liquid crystal display using the nematic liquid crystal, can be solved. Liquid crystal display devices are expected to be realized.

[0008]

The liquid crystal elements of the above-mentioned prior applications 1 to 3 are highly expected as a next-generation display because they are capable of high-speed response and gradation display, but they are driven continuously. In such a case, the liquid crystal characteristics (voltage −
The transmittance characteristic) gradually changes, and there is a problem that display burn-in occurs.

Therefore, it is an object of the present invention to provide a method of driving a liquid crystal element which suppresses such a change in voltage-transmittance characteristic.

[0010]

The invention according to claim 1 of the present application has been made in view of the above circumstances, and a pair of substrates arranged to face each other and a gap between these substrates are arranged. Ferroelectric liquid crystal, a pair of electrodes arranged so as to sandwich the ferroelectric liquid crystal in each pixel, and an active element arranged for each pixel in a state of being connected to one electrode. In a method of driving a liquid crystal element in which a voltage is applied to the ferroelectric liquid crystal through the active element and an electrode for each pixel, the ferroelectric liquid crystal has stable alignment when no voltage is applied. The liquid crystal has only one state, and the voltage applied to the ferroelectric liquid crystal is an AC voltage such that the integrated value of the positive and negative voltages has a DC component with respect to the ground potential.

In this case, the magnitude of the DC component may be a magnitude according to the internal voltage generated in the ferroelectric liquid crystal.

Further, the magnitude of the DC component may be a magnitude according to the display signal voltage applied to the ferroelectric liquid crystal.

Further, the magnitude of the direct current component may be a magnitude according to the environmental temperature at which the ferroelectric liquid crystal is driven.

Further, the DC component is generated by making the absolute value of the positive half-wave of the AC voltage different from the absolute value of the negative half-wave of the AC voltage. May be.

[0015]

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS.
An embodiment of the present invention will be described.

The change in the voltage-transmittance characteristic as described above is
This is also seen in the conventional SSFLC, and has been studied in various fields from the viewpoints of uneven distribution of impurity ions and changes in orientation. However, ferroelectric liquid crystal modes other than SSFLC, especially TFT drive type ferroelectrics. The fact is that the liquid crystal mode has hardly been studied.

Therefore, when the present inventor diligently studied the characteristic change in the monostable ferroelectric liquid crystal mode, T
When the FT drive is driven, the liquid crystal element is asymmetrically driven, and
It has been found that the cause is a bias (DC component) in the internal electric field due to an asymmetrical structure of the liquid crystal element, an asymmetry due to driving of the liquid crystal element, and the like. The present invention is for suppressing the accumulation of such a DC component.

By the way, the liquid crystal element P driven in the present embodiment, as shown in FIG. 2, has a pair of substrates 1a and 1b arranged so as to face each other with a predetermined gap therebetween,
The chiral smectic liquid crystal 2 arranged in the gap between the pair of substrates 1a and 1b, and the pair of electrodes 3 arranged so as to sandwich the chiral smectic liquid crystal 2 in each pixel.
a, 3b, and the pair of electrodes 3a, 3b
Driving is performed by applying a driving voltage to the chiral smectic liquid crystal 2 via the. In each pixel, the active element 4 may be connected to one of the electrodes (electrode 3b in the figure), and a polarizing plate may be arranged on at least one of the substrates 3a and 3b.

Here, as the chiral smectic liquid crystal 2, an isotropic liquid phase (ISO.)-Cholesteric phase (Ch) -chiral smectic C phase or an isotropic liquid phase (ISO.)-Chiral smectic from the high temperature side. It is preferable to use a liquid crystal exhibiting a C phase transition sequence.

This chiral smectic liquid crystal has a voltage-transmittance characteristic as shown in FIG. 3. * An alignment state in which the average molecular axes of liquid crystal molecules are mono-stabilized when a driving voltage is not applied. When a driving voltage of one polarity (hereinafter referred to as “first driving voltage”) is applied, the average molecular axis of the liquid crystal molecules is at an angle according to the magnitude of the first driving voltage. It is tilted from the mono-stabilized position to one side, and a driving voltage (hereinafter, referred to as “second driving voltage”) of other polarity (reverse polarity with respect to the one polarity; hereinafter the same) is applied. When applied, the average molecular axis of the liquid crystal molecules is at an angle corresponding to the magnitude of the second driving voltage from the mono-stabilized position to the other side (that is, when the first driving voltage is applied). LCD that tilts to the side opposite to the side that tilts to Te, * tilt angle when the second driving voltage is applied,
It is preferable to use a liquid crystal (so-called one-sided V-shaped liquid crystal) having a tilt angle smaller than the tilt angle when the first drive voltage is applied (almost 0).

That is, the one side V used in the present embodiment
The character liquid crystal has a clear threshold value and continuously changes its transmittance according to a driving voltage, and enables gradation display.

By the way, in the liquid crystal element P as described above,
As shown by reference numeral 5 in FIG. 4, drive voltage supply means is connected,
Driving voltages R ₄₁ , R ₄₂ , G ₄₁ , G are applied to the electrodes 3a, 3b.
₄₂ , B ₄₁ , B ₄₂ may be supplied. The driving voltage supply means 5 stores: • data relating to the display gradation and the correction voltage component (for example, data indicated by “rst 30 degrees” in FIG. 1); The first drive voltage having a magnitude corresponding to the “write” is used for the correction voltage (the gradation is “output (re
set) ”), and the first driving voltage R ₄₁ , G having a magnitude corresponding to the display gradation.
₄₁ and B _41, and an absolute value obtained by adding a correction voltage component (that is, an offset amount corresponding to a display gradation level) to the absolute value of the first driving voltage so that a DC component is not accumulated in the liquid crystal element P. Second drive voltage R ₄₂ , G ₄₂ , B
₄₂ and ₄₂ are sequentially applied to the chiral smectic liquid crystal 2 through the electrodes 3a and 3b of the liquid crystal element P, respectively.

Further, as shown by reference numeral 6 in FIG.
By disposing the means in the liquid crystal element P, the temperature of the element can be detected.
And the drive voltage supply means 5 is ・ Different data regarding the relationship between display gradation and correction voltage
Multiple types of memory are stored for each element temperature (for example, in FIG.
"Rst 10 degrees" "rst 30 degrees" "rst 50 degrees"
Together with the three types of data shown), -Compensation under the element temperature detected by the temperature detection means 6
A positive voltage component is calculated from the first drive voltage, .Display gradation of "input (write)"
First drive voltage R₄₁, G ₄₁, B₄₁And the liquid crystal element
Of the first drive voltage so that no DC component is stored in
Corrected voltage is added to the logarithmic value (gradation becomes "output").
Second drive voltage having an absolute value of
R₄₂, G₄₂, B₄₂And are applied in sequence.
It is good.

Next, a method of driving the liquid crystal element according to this embodiment will be described.

The liquid crystal element P is driven by applying a voltage to the ferroelectric liquid crystal 2 via the active element 4 and the electrodes 3a and 3b for each pixel. The generated voltage is an AC voltage whose integrated value of positive and negative voltages has a DC component with respect to the ground potential. That is, the voltage applied to the ferroelectric liquid crystal 2 is an AC voltage, and its average value is such that no voltage is accumulated in the ferroelectric liquid crystal 2 (generated in the ferroelectric liquid crystal 2). The size depends on the internal voltage). The magnitude of the DC component may be a magnitude according to the display signal voltage applied to the ferroelectric liquid crystal 2. The magnitude of the DC component may be set according to the environmental temperature at which the ferroelectric liquid crystal is driven. The direct-current component is different from the absolute value of the half-wave on the positive side in the AC voltage (absolute value of the peak value) and the absolute value of the half-wave on the negative side in the AC voltage (absolute value of the peak value). It is better to cause it to occur. Here, the positive polarity side voltage refers to the voltage obtained by combining the positive polarity half-wave voltage with the voltage of the DC component (that is, the correction voltage), and the negative polarity side voltage is (the voltage of the DC component, that is, The voltage obtained by combining the negative voltage half-wave voltage with the correction voltage). The “half-wave on the positive polarity side” and the “half-wave on the negative polarity side” have the same application time and are symmetrical (same shape).

The driving of the above-mentioned liquid crystal element P (so-called asymmetrical driving) is performed by the driving voltage supply means 5 in the first
A drive voltage (that is, a drive voltage having a magnitude corresponding to the display gradation, which is used to display the image by largely tilting the liquid crystal 2) and the second drive voltage (that is, the second drive voltage thereof). Is an absolute value of the first drive voltage plus the correction voltage component, and is a voltage applied to prevent the direct current component from accumulating in the liquid crystal element P). The chiral smectic liquid crystal 2 may be sequentially applied through the pair of electrodes 3a and 3b. Since the one-sided V-shaped liquid crystal as described above is used in the present embodiment, the liquid crystal 2 is largely tilted (that is, displayed) while the second drive voltage is applied while the first drive voltage is applied. During this period, the liquid crystal 2 is tilted slightly (that is, almost not displayed).

Here, the correction voltage will be supplemented. As described above, the first drive voltage needs to have a magnitude corresponding to the display gradation, but when the absolute values of the first drive voltage and the second drive voltage applied sequentially are equal, A direct current component will be accumulated in the element. When the absolute values of the first drive voltage and the second drive voltage are made equal, it seems that the drive voltages cancel each other out and the direct current component does not accumulate, but in reality, it was caused by the spontaneous polarization of the ferroelectric liquid crystal. An internal voltage of the element is generated and this becomes a DC component. In the present embodiment, the second drive voltage (absolute value) is generated by adding a correction voltage component to the first drive voltage (absolute value) so that such a DC component is not accumulated. That is, the asymmetrical drive voltage value is such that the voltage value applied to the inside of the liquid crystal element including the liquid crystal layer and the alignment film is effectively the write field period (the period for applying the first drive voltage) during actual use, An offset (adjusting the reset field period, adjusting the write field period, and varying the counter potential) is applied as much as possible to be equal to the reset field period (the period in which the second drive voltage is applied).

By the way, in the above-mentioned driving (asymmetrical voltage driving), the direction and level of the DC component of the asymmetrical driving for generating the DC component should be applied so as to cancel the DC component generated inside the liquid crystal element in the symmetrical driving. It is good to That is, the first drive voltage and the second drive voltage (that is, a drive voltage having a polarity different from that of the first drive voltage and having a smaller tilt angle of liquid crystal molecules than when the first drive voltage is applied) If the absolute value remains the same, the DC component will be accumulated in the liquid crystal element for the above-mentioned reason. However, if the absolute value of the second drive voltage is reduced by the DC component, the DC component is accumulated in the liquid crystal element. Is suppressed.

In this case, the above-mentioned correction voltage component may be set to a value that increases proportionally to the information signal level input from the outside of the liquid crystal element with a certain threshold value. Further, in generating the second drive voltage, a display grayscale level is provided to compensate for a non-linear DC component generated in the liquid crystal element when an information signal is output to display all grayscales during symmetrical driving. It is advisable to apply a non-linear correction according to the above.

In the asymmetrical voltage control method according to the present embodiment, the γ-correction circuit (reference voltage correction circuit) mounted for compensating the voltage-transmittance characteristic of the liquid crystal element is used so that the γ-correction circuit performs the γ-correction in advance. Also, it is preferable to have a compensation table set to output a value subjected to asymmetrical drive voltage compensation and control the asymmetrical drive voltage.

Incidentally, FIG. 9 is a diagram showing the relationship between the first drive voltage (information signal input voltage) and the correction voltage component (applied DC component). That is, the specific first drive voltage (about 5.8 in the figure).
V) as a boundary, the polarity of the correction voltage changes. Hereinafter, the intersection of the characteristic curve C2 with the horizontal axis (axis where the applied DC component is 0V) is referred to as “zero crossing”, and the first drive voltage (information signal input voltage) at the time of zero crossing is referred to as “zero crossing voltage”. To do. In the case of a liquid crystal element having such characteristics, it is preferable to drive the first drive voltage as "a voltage equal to or lower than the zero cross voltage".

That is, the above-mentioned AC voltage is composed of the first drive voltage having a magnitude corresponding to the display gradation and the second drive voltage having a polarity different from that of the first drive voltage. The absolute value of is a value obtained by adding a correction voltage component to the absolute value of the first drive voltage, but in the liquid crystal element having the characteristic that the polarity of the optimum value of the correction voltage is switched according to the first drive voltage. The first drive voltage to be actually applied may be lower than the value when the polarities of the optimum values for the correction voltage are switched. The reason will be described below.

In the liquid crystal element having the characteristic of C2, when the first drive voltage is 6V, the correction voltage component is + 0.5V, so the second drive voltage to be applied is 6V + 0.5V = 6.5.
V, and when the first drive voltage is 6.5V, the second drive voltage is 8V or higher.

On the other hand, as is clear from FIG. 3, the change in the transmittance T with respect to the change in the first drive voltage is smaller in the high voltage region than in the low voltage region. Therefore,
In the liquid crystal element having the characteristic shown by reference numeral C2 in FIG.
When driving in a high voltage region near the zero-cross voltage, the first driving voltage must be greatly increased even if the transmittance is slightly increased. As is clear from the curve C2 in FIG. 9, the correction voltage component at this time must be largely changed even if the first drive voltage is slightly changed, and the second drive voltage is the first drive voltage. The voltage will be even higher than that. As a result, a driver IC having a high withstand voltage is required, and factors such as prevention of electrical shorts between the electrodes 3a and 3b, which increase costs, are significantly increased.

On the other hand, when the first driving voltage is set to a low voltage range of zero cross voltage or less, the transmittance can be largely changed with a relatively small change, and the correction voltage and the second driving voltage are also reduced. be able to.

Next, the effect of this embodiment will be described.

According to the present embodiment, it is possible to reduce the variation in the characteristics of the liquid crystal (voltage-transmittance characteristic) even when it is continuously driven, and suppress the occurrence of image sticking.

When the first drive voltage is set to a low voltage region below the zero cross voltage, a driver IC having a low withstand voltage can be used, and the electric short circuit of the electrodes 3a and 3b can be prevented by a simple structure. Therefore, the cost can be reduced accordingly.

[0039]

The present invention will be described in more detail below with reference to examples.

(Embodiment 1) In this embodiment, an active matrix type panel shown in FIGS. 2 and 6 is used as a liquid crystal panel (liquid crystal element) P, and the liquid crystal 2 has a voltage-transmittance characteristic shown in FIG. One sided V-shaped liquid crystal was used. Reference numeral 4 in FIG. 2 indicates a TFT (thin film transistor) as an active element arranged in each pixel, reference numeral 25 indicates an insulating film, reference numerals 26a and 26b indicate an orientation control film, and reference numeral 27 holds. A capacitance electrode is shown. Further, reference numerals S ₁ , S ₂ , S ₃ , ... In FIG. 6 denote information signal lines connected to the source electrode of the TFT 4, and reference numerals G ₁ , G ₂ , G ₃ ,.
Indicates a scanning signal line connected to the gate electrode of the TFT 4, reference numeral 20 indicates a scanning signal line drive circuit for scanning each scanning signal line G ₁ , G ₂ , G ₃ , ..., Reference numeral 21 indicates each An information signal line drive circuit for supplying a source voltage to the information signal lines S ₁ , S ₂ , S ₃ , ... And this liquid crystal panel P
As shown in FIG. 4, the A / D converters 31R, 31G, 3
A liquid crystal device was configured by connecting 1B, γ correction circuits 32R, 32G, 32B, an offset data generation circuit (driving voltage supply means) 5, and the like.

In the liquid crystal panel P, when the scanning signal line driving circuit 20 sequentially scans the scanning signal lines G ₁ , G ₂ , G ₃ , ..., The TFT 4 is turned on by applying a gate voltage to the gate electrode. Becomes The information signal voltage corresponding to the display data is applied to the source electrode of the TFT 4 from the information signal line drive circuit 21 via each of the information signal lines S ₁ , S ₂ , S ₃ , so as to be synchronized with the scanning timing. (Source voltage) is applied.

Next, a method of driving the liquid crystal panel will be described with reference to FIG.

When driving the above-mentioned liquid crystal panel P
Is the display gradation of each pixel in each frame period.
Display signal of positive polarity (first drive voltage)
R₄₁, G ₄₁, B₄₁And the negative electrode with the correction voltage added
Reset signal (second drive voltage) R₄₂, G₄₂, B
₄₂And were sequentially applied.

Now, the red image input to the input terminal 30R
Image signal (hereinafter referred to as "R signal") R ₁Is an A / D converter
Digital signal R at 31R_TwoIs converted into the γ correction circuit 3
After being corrected by 2R, the offset data generation circuit 5
Sent to. This offset data generation circuit 5 is shown in FIG.
The offset data table that stores the data shown in
And a γ correction circuit connected to the memory 33.
R signal R from 32R _ThreeTo .Display signal R stored in memory 33₄₁When, .Corrected reset signal R₄₂And divide it into
Has become. For example, the offset data generation circuit 5
Forced R signal R_ThreeWhen the gradation level of is 255
If .Display signal R₄₁Has its gradation level (that is, 25
5 gradation level signal is used, ・ Reset signal R₄₂The data shown in FIG.
Signal corrected on the basis of "degree" (ie input (wri
Since te) has 255 gradations, the output (reset) is
215 gradations are used).

A green image signal (hereinafter referred to as "G signal") is input to the input terminal 30G, and the input terminal 30B
A blue image signal (hereinafter referred to as “B signal”) is input to the A / D converter 31.
The G, 31B, γ correction circuits 32G, 32B, and the offset data generation circuit 5 perform the same processing as the R signal, and display signals R ₄₁ , G for these RGB signals.
₄₁ , B ₄₁ and reset signals R ₄₂ , G ₄₂ , B ₄₂
Is input to the liquid crystal panel P and converted into an analog signal by the driver IC thereof.

By the way, the sync signal F-Sync inputted to the input terminal 30F is sync-separated by the offset data generating circuit 5, and the liquid crystal panel P and the light source unit 34 are also separated.
The display signal and the reset signal converted into analog signals as described above are synchronized with the synchronization signal F-S.
It will be sequentially sent to each pixel based on the timing of ync. In addition, the light source unit 34 uses the synchronization signal F-S.
The light is turned on based on the sync., so that the image on the liquid crystal panel is recognized as a full-color image.

FIG. 7 shows the DC component application amount at the input level of the information signal in the system in which the voltage-transmittance characteristic of the liquid crystal panel is stable when the asymmetrical driving is performed using the V-shaped liquid crystal on one side. It is a figure. That is, FIG. 7 shows the relationship between the gradation (horizontal axis) to which a display signal is applied for display and the DC component (vertical axis) to be corrected in the reset signal for each panel temperature. Such data is stored in the offset data generation circuit 5.

Then, at a temperature of 10 ° C., the liquid crystal panel P
A gradation image of a predetermined pattern (display signal for each area is −5
The image sticking phenomenon was observed at all gradation areas by conducting a seizure endurance test by continuously displaying for 5 hours a display in which each gradation was displayed in steps of 0.5V from V to + 5V). Was not done. In addition, 10 ℃ in Figure
A correction voltage component (DC component) is calculated from the data in accordance with the display gradation of the area, and the reset voltage is determined for each area by adding the correction voltage component to the display signal. Such a seizure endurance test was also conducted at panel temperatures of 30 ° C. and 50 ° C. (in that case, 3 in FIG.
(0 ° C correction data and 50 ° C correction data were used)
However, in any case, the display burn-in phenomenon was not observed at all.

FIG. 8 is a diagram showing the offset voltage level generated by the asymmetric information signal generated in this embodiment.

A voltage including an asymmetrical DC component as shown in FIG. 8 is output from the information signal line drive circuit 20 shown in FIG. 6 and applied to the source electrode of the TFT 4. The offset level was determined based on the experimental results shown in FIG.

A specific image (fixed pattern such as a black and white chart) in the asymmetric drive state shown in FIG.
Was continuously displayed for about 5 hours and a seizure durability test was conducted. As a result, the display burn-in phenomenon was not observed at all.
In other words, due to the asymmetrical drive as an external input, no DC component is generated inside the panel at all, and the fluctuation of the voltage-transmittance characteristic due to the generation of the DC component is completely eliminated, and it is possible to maintain a stable state. It is considered that the reliability against seizure is greatly improved.

(Embodiment 2) In this embodiment, an active matrix type liquid crystal panel P shown in FIGS. 2 and 6 is manufactured using the same one-sided V-shaped liquid crystal as in Embodiment 1, but as shown in FIG. A temperature sensor (temperature detecting means) 6 is arranged on the liquid crystal panel P so that the panel temperature can be detected, and the offset data generating circuit 5 has data (“rst10 degrees” in FIG. 1) corresponding to the panel temperature. "Rst30
3 types of data indicated by "degree" and "rst50 degree") are stored. Other configurations were the same as those in the first embodiment.

Next, a method of driving the liquid crystal panel will be described with reference to FIG.

When driving the above-mentioned liquid crystal panel P
Is the display gradation of each pixel in each frame period.
Display signal of positive polarity (first drive voltage)
R₄₁, G ₄₁, B₄₁And the panel temperature and correction voltage
Negative polarity reset signal (second drive voltage)
R₄₂, G₄₂, B₄₂And were sequentially applied.

Now, the red image input to the input terminal 30R
Image signal (hereinafter referred to as "R signal") R ₁Is an A / D converter
Digital signal R at 31R_TwoIs converted into the γ correction circuit 3
After being corrected by 2R, the offset data generation circuit 5
Sent to. This offset data generation circuit 5 is shown in FIG.
Data ("rst 10 degrees" "rst 30 degrees" "r
st of 50 degrees) stored in the office
Connected to memory 33
R signal R from the γ correction circuit 32R _ThreeTo .Display signal R stored in memory 33₄₁When, .Corrected reset signal R₄₂And divide it into
Has become. For example, the offset data generation circuit 5
Forced R signal R_ThreeWhen the gradation level of is 255
If .Display signal R₄₁Has its gradation level (that is, 25
5 gradation level signal is used, ・ Reset signal R₄₂Is corrected based on the data in Figure 1.
Signal is used. That is, ・ When the panel temperature is low, the curve "rst1" in FIG.
Based on the relationship of "0 degree", the reset data of gradation level 196
Is used, ・ When the panel temperature is high, the curve “rst5” in FIG.
Based on the relationship of "0 degree", the reset data of the gradation level 215
Is used, ・ If the panel temperature is neither high nor low,
Based on the relationship of the line “rst 30 degrees”, the gradation level 215
Reset data is used, and so on.

A green image signal (hereinafter referred to as "G signal") is input to the input terminal 30G, and the input terminal 30B
A blue image signal (hereinafter referred to as “B signal”) is input to the A / D converter 31.
The G, 31B, γ correction circuits 32G, 32B, and the offset data generation circuit 5 perform the same processing as the R signal, and display signals R ₄₁ , G for these RGB signals.
₄₁ , B ₄₁ and reset signals R ₄₂ , G ₄₂ , B ₄₂
Is input to the liquid crystal panel P and converted into an analog signal by the driver IC thereof.

By the way, the sync signal F-Sync input to the input terminal 30F is sync-separated by the offset data generating circuit 5, and the liquid crystal panel P and the light source unit 34 are also separated.
The display signal and the reset signal converted into analog signals as described above are synchronized with the synchronization signal F-S.
It will be sequentially sent to each pixel based on the timing of ync. In addition, the light source unit 34 uses the synchronization signal F-S.
The light is turned on based on the sync., so that the image on the liquid crystal panel is recognized as a full-color image.

In this embodiment as well, a black-and-white image having the same pattern as in Example 1 was continuously displayed for 5 hours to carry out a seizure durability test. The panel temperature was any of 10, 30, and 50 degrees. However, the display burn-in phenomenon was not observed at all. Therefore, the temperature characteristics of the liquid crystal element can be compensated by changing the level according to the usage environment and performing asymmetrical driving, and no DC component is generated inside the panel, and the voltage-transmittance characteristic It is considered that the shift is completely eliminated, and the reliability against image sticking is greatly improved within the ambient temperature at which the liquid crystal element can be driven.

Although three patterns of offset data tables are prepared in this embodiment, it is desirable to adjust the number of data tables to be used according to the temperature characteristic performance of the liquid crystal panel.

In addition, in the first and second embodiments, most of the asymmetrical drive data processing is performed outside the panel and further in the state of 256 digital signals which is the stage of image data. There is no problem even if the internal processing is performed, and further, a higher bit such as 10 bi
It is also possible to perform more precise control by processing as a t digital signal.

Lastly, in the present embodiment, the offset data generation is digitally processed, but analog processing can also be performed, and the reference voltage generation circuit performs the gamma correction processing of the liquid crystal and collectively corrects it. However, there is no problem, and it is necessary to use them properly depending on the specifications and cost of the product to be aimed for.

(Embodiment 3) In this embodiment, an active matrix type liquid crystal panel (liquid crystal element) P shown in FIG. 2 is used.
It was created. The details will be described below.

<Preparation of Liquid Crystal Composition> First, the following liquid crystal compounds were mixed in the weight ratios shown on the right side of each to prepare a liquid crystal composition LC.

[0064]

[Chemical 1] The physical property parameters of the liquid crystal composition LC are shown below.

[0065]                              86.3 61.2 -7.2 Phase transition temperature (° C.): ISO. → Ch → SmC^*  → Cry Spontaneous polarization (30 ° C.): Ps = 2.9 nC / cm^Two Cone angle (30 ° C): Θ = 23.3 ° (100Hz, ± 12.5V, substrate gap 1.4μm) SmC^*Helical pitch in phase (30 ℃): 20μm or more

<Production of Liquid Crystal Cell> A glass substrate having a thickness of 1.1 mm was used for the substrates 1a and 1b, and a transparent electrode 3 was used for them.
A and 3b were formed from ITO having a thickness of 700 liters. An RGB color filter (not shown) was formed on one glass substrate 1a. The screen size is 10.4 inches, and the number of pixels (that is, the number of pixels configured by RGB color pixels (sub-pixels)) is 800 (width) ×
It was set to 600 (vertical). At this time, the number of sub-pixels is 2
It was 400 (horizontal) × 600 (vertical), and the size of the opening of each sub-pixel was 75 μm (horizontal) × 230 μm (vertical).

Further, the active element 4 is formed of a-SiT.
FT was used, and a silicon nitride film was used as the gate insulating film 25 of the TFT 4.

The orientation control films 26a and 26b are formed of a polyimide film. Specifically, a commercially available alignment film for TFT (SE7992 manufactured by Nissan Chemical Co., Ltd.) is applied by a spin coating method so as to cover the transparent electrodes 3a and 3b, and then pre-dried at a temperature of 80 ° C. for 5 minutes. , 20 more
It was formed by heating and baking at a temperature of 0 ° C. for 1 hour, and the film thickness was set to 150 ° C. The orientation control films 26a and 26b were subjected to rubbing treatment (uniaxial orientation treatment) with a cotton cloth. For this rubbing process,
Using a rubbing roll having a diameter of 10 cm with a cotton cloth bonded to the outer peripheral surface, the pushing amount was 0.7 mm, the feed speed was 10 cm / sec, the rotation speed was 1000 rpm, and the feed frequency was 4 times. The rubbing direction at this time was set to be parallel to the source lines S ₁ , S ₂ , ... For both the upper and lower substrates.

Subsequently, the average grain size of 1.
5 μm silica beads (spacers) were scattered and bonded so that the rubbing treatment directions of the respective substrates were anti-parallel to each other to obtain cells having uniform substrate gaps.

The liquid crystal composition LC was injected into the cell manufactured by the above process at the temperature of the Ch phase, and the liquid crystal was cooled to a temperature showing the chiral smectic liquid crystal phase (however, the cooling rate was 1 ° C./min). , Liquid crystal is from Ch phase to SmC ^*
An offset voltage (DC voltage) of -1 V was applied as a voltage condition to be applied (within a temperature range of Tc-2 ° C to Tc + 2 ° C) at the time of phase transition to a phase. As a result, a liquid crystal panel (one-side V-shaped liquid crystal panel) having the characteristics shown in FIG. 3 (that is, asymmetrical voltage-transmittance characteristics) was obtained.

In the liquid crystal panel produced in this example, a characteristic curve showing the relationship between the information signal input voltage (first drive voltage) and the applied DC component (correction voltage) is as shown by reference numeral C2 in FIG. Something (that is, applied D at the boundary of about 5.8V)
The polarity of the C component changed). That is, it is possible to control the optimum offset condition by changing the voltage processing condition during the phase transition.

In this embodiment, the information signal input voltage for displaying an image is set to 5.8V or less.

According to this embodiment, since the information signal input voltage is as low as 5.8 V or less, the correction voltage and the reset voltage (second drive voltage) are also low. Therefore, the driver I
A low withstand voltage can be used for C, and an electrical short circuit of the electrode can be achieved with a simple structure, and the cost can be reduced accordingly.

[0074]

As described above, according to the present invention,
Even in the case of continuous driving, it is possible to reduce the variation in the characteristics of the liquid crystal (voltage-transmittance characteristic) and suppress the occurrence of image sticking.

Further, when the first drive voltage is set to a low voltage region of the zero cross voltage or less, the driver IC having a low withstand voltage can be used, and the electric short circuit of the electrodes can be prevented with a simple structure. Therefore, the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a display gradation and a gradation of a reset signal.

FIG. 2 is a sectional view showing the structure of a liquid crystal panel to which the present invention is applied and driven.

FIG. 3 is a characteristic diagram showing voltage-transmittance characteristics of a one-sided V-shaped liquid crystal.

FIG. 4 is a block diagram showing a structure of a liquid crystal device to which the present invention is applied and driven.

FIG. 5 is a block diagram showing a structure of a liquid crystal device to which the present invention is applied and driven.

FIG. 6 is a circuit diagram showing a structure of a liquid crystal panel to which the present invention is applied and driven.

FIG. 7 is a diagram showing a relationship between a display gradation and a correction voltage component.

FIG. 8 is a diagram showing a relationship between an information signal input voltage and an applied DC component.

FIG. 9 is a diagram showing a relationship between a first drive voltage (information signal input voltage) and a correction voltage component (applied DC component).

[Explanation of symbols]

1a, 1b Substrate 2 Chiral smectic liquid crystal 3a, 3b Electrode 4 TFT (active element) 5 Offset data generation circuit (driving voltage supply means) 6 Temperature sensor (temperature detection means) P Liquid crystal panel (liquid crystal element)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 621 G09G 3/20 621B 670 670K 3/36 3/36 (72) Inventor Hideo Mori Tokyo 3-30-2 Shimomaruko, Ota-ku Canon Inc. F-term (reference) 2H093 NA16 NA31 NC02 NC28 NC34 NC57 NC63 ND12 5C006 AA16 AA22 AC07 AC11 AC15 AC26 AF03 AF04 AF13 AF45 AF46 AF51 AF53 AF62 AF81 AF82 AF84 BA12 BB16 BC12 BC13 BC16 BF02 BF25 BF27 BF28 BF38 BF42 EC11 FA12 FA19 FA22 FA34 FA38 FA52 FA56 5C080 AA10 BB05 CC03 DD03 DD08 DD20 DD28 EE19 EE29 EE30 FF03 FF11 GG12 JJ02 JJ03 JJ05 JJ06 KK43

Claims (7)

[Claims] 1. A pair of substrates arranged to face each other, and a ferroelectric liquid crystal arranged in a gap between these substrates,
A liquid crystal element comprising: a pair of electrodes arranged so as to sandwich the ferroelectric liquid crystal in each pixel; and an active element arranged for each pixel in a state of being connected to one electrode, In a method of driving a liquid crystal element, in which a voltage is applied to the ferroelectric liquid crystal through the active element and an electrode for each, the ferroelectric liquid crystal is a liquid crystal having only one stable alignment state when no voltage is applied. A driving method of a liquid crystal element, wherein the voltage applied to the ferroelectric liquid crystal is an AC voltage whose integrated value of positive and negative voltages has a DC component with respect to the ground potential. 2. The magnitude of the DC component is a magnitude according to an internal voltage generated in the ferroelectric liquid crystal,
The method for driving a liquid crystal element according to claim 1, wherein 3. The method of driving a liquid crystal element according to claim 1, wherein the DC component has a magnitude corresponding to a display signal voltage applied to the ferroelectric liquid crystal. 4. The magnitude of the DC component is a magnitude according to an environmental temperature in which the ferroelectric liquid crystal is driven, according to claim 1. Driving method of liquid crystal element. 5. The direct current component is generated by making the absolute value of a positive half wave of the alternating voltage different from the absolute value of a negative half wave of the alternating voltage. The method for driving a liquid crystal element according to claim 1, wherein 6. The AC voltage comprises a first drive voltage having a magnitude corresponding to a display gradation and a second drive voltage having a polarity different from that of the first drive voltage. 6. The method for driving a liquid crystal element according to claim 1, wherein the absolute value is the absolute value of the first drive voltage plus a correction voltage component. 7. The liquid crystal element has a characteristic that the polarity of the optimum value of the correction voltage is switched according to the first drive voltage, and the first drive voltage actually applied to the liquid crystal element is the correction voltage. 7. The method for driving a liquid crystal element according to claim 6, wherein the polarity of the optimum value for the voltage is lower than the value when the polarity is switched.