JPH09265077A - Anti-ferroelectric liquid crystal element drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fix power consumption in a liquid crystal panel, to reduce a load for a power source circuit and to stably perform multiplex drive by fixing a frame frequency to any value of a specified value or above regardless of a temp. SOLUTION: Scan electrode waveforms a1 -an applied corresponding to (n) pieces of respective scan electrodes apply respectively a scan voltage Vr according to a polar signal inverted at every frame period in a selection period, and thereafter, apply a hold voltage Vb of the same polarity as the scan voltage Vr until the next selection period, and then, apply a reset voltage. For fixing the selection period, a pulse showing a rest phase is provided in one selection period, and the frame frequency is fixed. By fixing the frame frequency to any value of 30Hz or above, preferably 60Hz or above regardless of the temp., the change of the power consumption in the liquid crystal panel caused by a high temp. is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an antiferroelectric liquid crystal device utilizing three-state switching of an antiferroelectric liquid crystal that undergoes a phase transition to a ferroelectric liquid crystal by an electric field.

[0002]

2. Description of the Related Art Switching between three states of an antiferroelectric liquid crystal is expected as one of the methods for solving some of the essential problems found in the conventional surface-stabilized ferroelectric liquid crystal (SSFLC). Active research is underway. (ADL
Chandani et. Al.: Jpn. J. Appl. Phys., 27, L729 (19
88), ADLChandani et. Al.: Jpn. J. Appl. Phys.,
28, L1265 (1988) or N. Yamamoto et. Al .: Japan Society for the Promotion of Science, Organic Materials for Information Science, 142th Committee, 58th Joint Study Group, P7-12, (1993), etc. ) The switching between the three states has the following features.

(1) The antiferroelectric-ferroelectric phase transition caused by voltage application has a steep threshold characteristic with respect to a DC voltage, as shown in FIG. (2) As shown in FIG. 8, since the antiferroelectric-ferroelectric phase transition has a wide optical hysteresis, the bias voltage is applied and held after selecting the antiferroelectric phase or the ferroelectric phase. This allows the selected state to be retained.

(3) Two orientation states in an electric field induced ferroelectric phase can be made optically equivalent. (4) Since the bias of the charges in the liquid crystal layer can be prevented, S
There is no change over time in electro-optical characteristics like SFLC.

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 the driving method known to date, M. Yamawaki e, which drives the scanning electrodes and the signal electrodes by using the driving signals having the respective waveforms shown in FIG.
t. al .: Digest of Japan Display '89, p26 (1989).

In FIGS. 4A and 4B, a
_{1, a 2, ···, a} n and _{b 1, b 2, ···,} b n
Are the voltage waveforms applied to the runoff electrode and the signal electrode, respectively, and FIG. 9 shows the voltage waveform applied to the liquid crystal layer obtained from the difference between them. In this driving method, a frame F (+) to which a positive voltage is applied and a subsequent negative frame F (−) are paired.

The display principle of this driving method will be described with reference to FIG. In FIG. 6, the optical axis OA in the antiferroelectric phase is orthogonal to the smectic layer. A cell having a liquid crystal layer 6 sandwiched between two glass substrates 1 and 2 provided with transparent electrodes 4 and 5 and liquid crystal alignment films 9 and 10 as shown in FIG. When installed so that the optical axis OA is parallel to any of the polarization axes between 12, the element is in a dark state (provisionally referred to as an OFF state).

In this state, even if the voltage waveform in the frame F '(+) or F' (-) shown in FIG. 9 is applied, as shown in FIG. 8, | V _w2 | <| V (A- F)
_{If t} |, the change in light transmittance is slight and the OFF state can be maintained. On the other hand, the frame F shown in FIG.
When a voltage waveform at (+) or F (-) is applied, as shown in FIG. 8, | V _w1 |> | V (A−F) _s |
If the liquid crystal response, each of the optical axes OF (+) and OF (-), the spontaneous polarization P _s (+) and P _s (-)
With a ferroelectric phase (+) and a ferroelectric phase (-).
Since the optical axis forms an angle θ (+) or θ (−) with the polarization axis, a bright state (provisionally referred to as an ON state) is obtained.

Here, since the angles θ (+) and θ (−) are equal, they can be treated as optically equivalent.

[0010]

However, the conventional method of driving an antiferroelectric liquid crystal element as described above has the following problems.

According to the conventional method for driving an antiferroelectric liquid crystal element, when the temperature changes, the selection period is changed and the frame frequency is changed as the optimum pulse width of the antiferroelectric liquid crystal is changed. At high temperatures, the frame frequency becomes high when the drive pulse width becomes small, and the power consumption of the liquid crystal panel increases.

The power consumption of the liquid crystal panel is W, the duty ratio is Duty, the frame frequency is f, the capacity of the pixel to be driven is C, the drive voltage is V, and the proportional constant is k.
This is because it is represented by W = k × f × C × V × Duty. That is, this equation represents that the power consumption W of the liquid crystal panel increases as the frame frequency f increases.

Further, when the liquid crystal panel is an antiferroelectric liquid crystal panel, the gap C is usually narrower than that of the STN liquid crystal panel, so that the pixel capacitance C is large and the power consumption W of the liquid crystal panel is significantly increased.

As a result, the load on the power supply circuit increases, and there is a problem in that the multiplex drive utilizing the characteristics of the three-state switching cannot be stably performed.

The present invention solves the above-mentioned problems, and makes it possible to reduce the load on the power supply circuit by keeping the power consumption of the liquid crystal panel constant, and to make full use of the characteristics of three-state switching. Provided is a method for driving an antiferroelectric liquid crystal element capable of stably performing the above.

[0016]

In order to solve the above-mentioned problems, a method for driving an antiferroelectric liquid crystal device according to claim 1 of the present invention is directed to a substrate having a scanning electrode and an electrode of a substrate having a signal electrode. Depending on the polarity of the voltage between the two substrates facing each other, 2
An anti-ferroelectric liquid crystal device having a liquid crystal panel sandwiching anti-ferroelectric liquid crystal exhibiting one orientation state that undergoes a phase transition to a ferroelectric liquid crystal exhibiting one orientation state, wherein a scanning electrode at a certain address in the liquid crystal panel During the selection period of a certain frame, a voltage pulse having a positive polarity of the voltage pulse that finally determines the state of the liquid crystal is applied to the upper pixel, and the selection period of the next frame is continued from the selection period. During the non-selection period, the average potential is positive in the non-selection period, a voltage pulse group holding the liquid crystal state obtained in the selection period is applied, , The average potential is zero or negative, and a voltage pulse group in which the liquid crystal state is an antiferroelectric phase is applied, and finally the liquid crystal state is determined in the selection period following the non-selection period and the erase period. A voltage pulse in which the positive polarity of the pressure pulse is negative is applied, and at least a non-selection period and an erasing period are provided from this selection period to the selection period of the subsequent frame, and in this non-selection period, the average potential is A voltage pulse group that is negative and holds the liquid crystal state obtained in the selection period is applied, and during this erasing period, a voltage pulse group in which the average potential is zero or positive and the liquid crystal state is in the antiferroelectric phase is applied. However, the frequency of the frame is set to 30H regardless of the temperature.
The method is set to be constant at any value of z or more.

According to a second aspect of the present invention, there is provided a method of driving an antiferroelectric liquid crystal device, wherein the frame frequency of the first aspect is preferably 6
The method is made constant with any value of 0HZ or more. According to these methods, the frame frequency is kept constant at any value of 30 Hz or higher, preferably 60 Hz or higher irrespective of temperature, thereby suppressing a change in power consumption of the liquid crystal panel caused by a high temperature. .

A method of driving an antiferroelectric liquid crystal device according to a third aspect of the present invention detects the temperature of the liquid crystal panel according to the first or second aspect, and switches the number of pulses in the selection period according to the temperature.
The selection period is t for the selection period and Dut for the duty ratio.
It is assumed that y and the frame frequency are f, and the display is performed so as to be constant at a value represented by t = Duty / f.

According to this method, the selection period t has a constant width. According to a fourth aspect of the present invention, in the driving method of the antiferroelectric liquid crystal device according to the third aspect, the pulse width of the pulse synchronized with the signal according to the brightness of the display in the pulse of the selection period depending on the temperature is set to The optimum pulse width at that temperature is set to be the same, and the remaining time is set as a pause period of a signal irrelevant to the brightness of the display.

According to this method, the selection period t can be set to a constant width, and an increase in power consumption of the liquid crystal panel caused by a constant frame frequency and high temperature can be suppressed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method of driving an antiferroelectric liquid crystal device showing an embodiment of the present invention will be described with reference to the drawings.

Here, as the sample, an insulating film was formed on the transparent electrode, and a polyimide film was formed on the transparent film, followed by rubbing treatment and uniaxial orientation treatment to obtain an orientation film. As for the structure of the device, as shown in FIG. 7, a liquid crystal panel was formed so that the rubbing directions were parallel or semi-parallel with the substrates facing each other, and the gap was 1.7 μm. The anti-ferroelectric liquid crystal material CS-4 manufactured by Chisso Corporation is used for the liquid crystal panel.
000 is heat-sealed and the ambient temperature is kept within the temperature range of the antiferroelectric chiral smectic C phase (SmCA * phase).

FIG. 1 shows each drive waveform in the method of driving the antiferroelectric liquid crystal element of this embodiment. Here, FIG.
1A shows a scanning electrode waveform, and FIG. 1B shows a signal electrode waveform.

In FIG. 1A, each of the n scanning electrodes is
Correspondingly applied scan electrode waveform a ₁ , A_Two , ...,
a_n Are inverted every frame period during the selection period.
Scanning voltage V according to the polarity signal_r And then
Scan voltage V until the selection period of _r Holding voltage V of the same polarity as_b 
And a reset voltage is applied. To do so
By, the polarity of the selected waveform is inverted every time it is selected.
be able to.

Further, in FIG. 1B, signal electrode waveforms b ₁ , b ₂ , ... Applied corresponding to each of the n signal electrodes.
, B _n are applied by inverting the polarities of the selection voltage / non-selection voltage V _s of the signal data of the display pattern according to the polarity signal.

FIG. 2 shows the relationship between the polarity signal and each signal having the scanning voltage V _r and the selection voltage / non-selection voltage V _s . In each of the above drive signals, the element temperature is set to 20 ° C
The pulse width τp was 75 μsec, the pulse width τr of the rest phase was 6 μsec, and the duty ratio was 1/200. The contrast ratio was 1:30 and the power consumption was 1.1 watts. At 40 ° C, the pulse width τp
Is 30 μs, that is, the resting phase period τr is 96 μs, the contrast ratio is 1:30 and the power consumption is 1.
Got 3 watts. The frame frequency at this time is fixed at 32 Hz, which is 30 Hz or higher, taking flicker into consideration.
The line selection period was 156 μsec.

Next, the driving method of the present embodiment based on each driving signal as shown in FIG. 3 and the driving method of the prior art will be compared. That is, even if the temperature rises to a high temperature, in the present embodiment, a pulse indicating a pause phase is provided within one selection period in order to keep the selection period constant unlike the prior art, and the time is changed depending on the temperature. This keeps the frame frequency constant. On the other hand, in the related art, when the temperature changes, the frame frequency changes according to the drive pulse. FIG. 5 shows the result of comparison of the above driving methods.

As shown in FIG. 5, when the driving pulse width is set to 75 μs at 20 ° C. and 30 μs at 40 ° C. according to the temperature and the conventional driving method is used, the same driving method as in the present embodiment is used. When driven under the conditions described above, the frame frequencies at the respective temperatures are 33.3 Hz and 83.4, respectively.
Hz, and the power consumption is 1.1 watts and 2.5, respectively.
Since the power consumption is watts, the power consumption increases remarkably with respect to the temperature rise as compared with the case of the driving method according to the present embodiment.

As can be seen from the comparison result shown in FIG. 5, by using the driving method according to the present embodiment, it is possible to easily suppress an increase in power consumption of the liquid crystal panel at a high temperature and to reduce the consumption of the liquid crystal panel. It is possible to reduce the load on the power supply circuit by keeping the electric power constant, and it is possible to stably perform the multiplex drive making full use of the characteristics of the three-state switching.

In the driving method of the present embodiment described above, the number of pulses applied according to the light and dark data of the display is 2 within one selection period, but the driving waveform is not limited to this. One pulse or three pulses may be used, and the effect of suppressing power consumption at high temperature did not change even with the number of each of these pulses.

Further, in the driving method of the present embodiment described above, a frame frequency of 60 Hz or more is desirable in order to completely eliminate the flicker, and even in this case, the power consumption at high temperature increases. There was no change in the effect of suppressing.

[0032]

As described above, according to the present invention, the frame frequency is kept constant at any value of 30 Hz or more, preferably 60 Hz or more, regardless of the temperature.
It is possible to suppress a change in power consumption of the liquid crystal panel caused by a high temperature.

Further, the selection period t can be made to have a constant width. In addition, the selection period t can be set to a constant width, and an increase in power consumption of the liquid crystal panel caused by a constant frame frequency and high temperature can be suppressed.

As described above, the power consumption of the liquid crystal panel can be kept constant and the load on the power supply circuit can be reduced.
It is possible to stably perform multiplex drive that makes full use of the characteristics of state switching.

[Brief description of drawings]

FIG. 1 is a drive waveform diagram according to a driving method of an antiferroelectric liquid crystal element according to an embodiment of the present invention.

FIG. 2 is a comparison diagram of waveforms of drive signals of the same embodiment.

FIG. 3 is a comparison diagram of the drive waveform of the embodiment with a conventional drive waveform.

FIG. 4 is a drive waveform diagram according to a conventional drive method.

FIG. 5 is a comparison diagram of a driving method according to an embodiment of the present invention with a conventional driving method.

FIG. 6 is a conceptual diagram of an element used in the same embodiment.

FIG. 7 is a sectional view of a liquid crystal panel used in the same embodiment.

FIG. 8 is an explanatory diagram of electro-optical characteristics of the element used in the same embodiment.

FIG. 9 is a voltage waveform applied to a liquid crystal layer by a conventional driving method.

[Explanation of reference symbols] a ₁ , a ₂ , ..., A _n scan electrode waveform b ₁ , b ₂ , ..., b _n signal electrode waveform V _b holding voltage V _r scan voltage V _s selection voltage / non-selection voltage

Claims (4)

[Claims] 1. An alignment state that undergoes a phase transition to a ferroelectric liquid crystal exhibiting two alignment states depending on the polarity of voltage is provided between the substrates having the scanning electrodes and the substrate having the signal electrodes facing each other. In an antiferroelectric liquid crystal element having a liquid crystal panel sandwiching an antiferroelectric liquid crystal shown, for a pixel on a scanning electrode of a certain address in the liquid crystal panel,
During the selection period of a certain frame, a voltage pulse having a positive polarity of a voltage pulse that finally determines the state of the liquid crystal is applied, and at least a non-voltage pulse is applied from the selection period to the selection period of the next frame. Consisting of a selection period and an erasing period, the average potential is positive in the non-selection period, a voltage pulse group for holding the liquid crystal state obtained in the selection period is applied,
During the erasing period, a voltage pulse group in which the average potential is zero or negative and the liquid crystal state is an antiferroelectric phase is applied. The voltage pulse that determines the state of the voltage pulse is applied with a positive polarity is negative, and at least the non-selection period and the erase period are provided from this selection period to the selection period of the next frame. In, the average potential is negative, and a voltage pulse group that holds the liquid crystal state obtained in the selection period is applied. During this erasing period, the average potential is zero or positive, and the liquid crystal state becomes the antiferroelectric phase. A voltage pulse group is applied to change the frequency of the frame to 30 H regardless of temperature.
A method for driving an antiferroelectric liquid crystal element, characterized in that it is kept constant at any value of z or more. 2. The frame frequency is preferably 60 HZ
2. The method for driving an antiferroelectric liquid crystal element according to claim 1, wherein the value is made constant by any one of the above values. 3. The liquid crystal panel temperature is detected, and the number of pulses in the selection period is switched according to the temperature. The selection period is t = Duty / f, where t is the selection period, Duty ratio is Duty, and the frame frequency is f. The method for driving an antiferroelectric liquid crystal element according to claim 1 or 2, wherein the display is performed so that the value represented is constant. 4. The pulse width of the pulse synchronized with the signal according to the brightness of the display in the pulse of the selection period depending on the temperature is made to be the same as the optimum pulse width of the antiferroelectric liquid crystal at that temperature, and the remaining time is set. 4. The method for driving an antiferroelectric liquid crystal element according to claim 3, wherein is set as a pause period of a signal irrelevant to the brightness of the display.