JPH08338983A - Display device - Google Patents

Abstract

PURPOSE: To provide a display device capable of securing the range of a driving condition (a driving margin) where a satisfactory display can be obtained over a long period. CONSTITUTION: This device is provided with a display element 101 in which ferroelectric liquid crystal is arranged between matrix electrodes constituted of a scanning electrode group and a information electrode group, and a driving control circuit 110 changing the driving condition by referring one of information other than picture data. Then, the driving condition is changed by changing the form of the driving waveform to be impressed on the scanning electrode group and the information electrode group in accordance with the total operating time of the display device. While the total operating time is short, an electric field is continuously impressed on the display element 101, and when the total operating time becomes long, a period when the electric field is not impressed on the element is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for displaying characters and images, and more particularly to a display device for displaying in two stable states indicated by a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element for displaying image information by filling a liquid crystal compound between a scanning electrode group and an information electrode group of a matrix electrode to form a large number of pixels is well known. Among them, a ferroelectric liquid crystal element having bistability and having a fast response to an electric field is expected as a high-speed and memory type display element, for example, Japanese Patent Laid-Open No. 56-107216.
It has been proposed in the Japanese publication.

Generally, in order to align a ferroelectric liquid crystal, a horizontally oriented polymer film such as polyimide (PI) or polyamide (PA) is formed on the surface of a substrate, and a pair of substrates subjected to a rubbing treatment in substantially the same direction is used. To use.

FIG. 6 shows a liquid crystal orientation model. 60 in the figure
1, 607 is a glass substrate, 602 and 606 are transparent electrodes such as ITO, 603 and 605 are polymer films having a horizontal alignment treatment capability subjected to rubbing treatment, 604 is a ferroelectric liquid crystal layer, and 608, 603 and 610 are chiral. The cone which characterizes the alignment state of the liquid crystal molecules in the smectic phase is viewed from the front, 608 and 609 indicate two stable states in the uniform alignment, and 610 indicates an example of the splay alignment state.

Here, for convenience, the stable state of 608 is set to U1,6.
The stable state of 09 is called U2. Seen from above the board is shown in FIG.
As described above, the two stable states U1 and U2 have inclinations of −θ and + θ with respect to the rubbing direction. Then, the axis of the polarizer is previously arranged at + θ (or −θ), and a voltage is applied between the upper and lower substrates to orient the film in either of the U1 and U2 states to determine the brightness of the display.

That is, in order for the ferroelectric liquid crystal element to exhibit desired electro-optical characteristics, the liquid crystal between the substrates is in an alignment state in which two stable states are switched in a stable and reproducible manner, and It is necessary that the alignment state is uniform over the entire pixel or display screen.

A large number of driving methods for matrix driving this ferroelectric liquid crystal element have been proposed so far.
For example, a practical driving method is disclosed in Japanese Patent Laid-Open No. 2-281233. FIG. 8 shows an example of a conventional drive waveform. In the figure, A is a scanning selection signal, B is a scanning non-selection signal, C is an information signal for bright display, and D is an information signal for dark display.

[0008]

By the way, in the conventional display device using the ferroelectric liquid crystal, when left in the stable state of one for a long time, the display device is caused by the interaction at the interface between the substrate and the liquid crystal layer. However, there is a problem that the threshold characteristic changes.

The driving method disclosed in Japanese Unexamined Patent Publication No. 2-281233 has a structure shown in FIG.
This is a method of constantly applying a voltage in accordance with the information signals shown in C and D. However, when a pulse having a continuous width of ΔT is applied in this way, fluctuation of liquid crystal molecules at the time of non-selection of scanning becomes large,
It can be said that there is a possibility that a part of the pixel is reversed and a good display cannot be maintained.

In view of the above problems of the prior art, it is an object of the present invention to provide a display device capable of ensuring a range of driving conditions (driving margin) capable of good display for a long period of time.

[0011]

In order to achieve the above object, a display device of the present invention comprises a display element in which a ferroelectric liquid crystal is arranged between matrix electrodes composed of a scanning electrode group and an information electrode group, And a drive control circuit for changing the drive condition by referring to one piece of information other than the image data.

In this case, the drive condition of the drive control circuit may be changed according to the change of the characteristic of the display device with time, or may be performed according to the total operating time of the display device. In this case, it is desirable to perform it by changing the shape of the drive waveform applied to the scanning electrode group and the information electrode group.

When the driving waveform is changed,
While the total operating time of the display device is short, an electric field is constantly applied to the display element, and a period during which the electric field is not applied to the display element when the total operating time becomes long, or according to the total operating time of the display element, The proportion occupied by the selection period within one horizontal scanning period may be different.

When the driving condition is changed by changing the shape of the driving waveform applied to the scanning electrode group and the information electrode group, the scanning selection signal applied to the scanning electrode group in the driving waveform is a selection pulse. And an erasing pulse arranged immediately before the selection pulse and an auxiliary pulse arranged immediately after the selection pulse, and the information signal applied to the information electrode group is a selection pulse and before and after the selection pulse while the total operating time is short. And the auxiliary pulse arranged before and after the selection pulse so that the auxiliary pulse is not continuous when the total operating time becomes long, and a pause provided between the auxiliary pulse and the auxiliary pulse. It is desirable to compose with the period.

The driving condition of the drive control circuit may be changed by changing the frame frequency.

[0016]

Since the present invention is constructed as described above,
The driving condition can be changed according to the total operating time of the display element, a driving margin can be secured for a long time, and fluctuations of liquid crystal molecules are reduced.

[0017]

EXAMPLE When the present inventor conducted an experiment on the relationship between an AC pulse and fluctuation, it was found that when the shape of the AC pulse in the non-selected state changes, the fluctuation degree of liquid crystal molecules also changes. In FIG. 9, a hemiform A is an AC waveform in which a positive polarity pulse α and a negative polarity pulse β having the same ΔT width as the waveform applied in the non-selected state in the conventional example are continuously and alternately applied, and the waveform B is the waveform A. , A waveform having a ½ ΔT rest period between the pulses α, and a waveform C, which has a half ΔT rest period between the pulses A of the waveform A, have the same effective value.

When the waveforms of A, B, and C are applied, the degree of fluctuation of liquid crystal molecules changes, and the state of U1 changes to U2.
It was found that when the polarity for reversing to the state is negative, the pulse β greatly fluctuates in the U1 state and the pulse α largely fluctuates in the U2 state.

Therefore, in consideration of reducing the number of times the pulse β is applied to the pixel in the U1 state at the time of non-selection of scanning, a pause period of 1/2 ΔT is inserted between the auxiliary pulses of the information signal. Then, bright display when scanning is not selected (U1 display in this case)
The pulse β is not applied even if the waveform of the information signal is continuous.

That is, if there is another pixel that displays the U1 state on the same information electrode, the number of times the pulse β is applied is reduced once per frame. If there are two other pixels that display the U1 state, the number decreases twice, and if there are three pixels, the number decreases three times. If all the pixels display the U1 state, the pulse β is not applied even once, and is used for the previous experiment. The waveform becomes the same as in FIG. 9C.

That is, although depending on the display pattern, the number of times the pulse β is applied is considerably smaller than that in the conventional example. Similarly, the number of times the pulse α is applied to the pixel in the U2 state is considerably reduced. By utilizing this, it is possible to suppress the fluctuation which has conventionally limited the drive margin and widen the drive margin.

The relationship between the width of the rest period and the drive margin is 1 /
As shown in FIG. 10, it was found that the width of the drive margin was saturated when the rest period was around 1/2 ΔT, as shown in FIG.

In this measurement, the temperature was 10 ° C. and the driving condition was V1.
= 14.3v, V2 = -14.3v, V3 = 5.7v,
V4 = -5.7v and V5 = 6.4v are set, and the range in which the display element 101 of the present embodiment, which will be described later, can display favorably is measured.

Since it is preferable that the pause period is as short as possible in order to increase the frame period number, 1/2 ΔT is appropriate for the pause period from the viewpoint of both margin and speed. In addition,
Although the relationship between the width of the idle period and the drive margin may be finely divided and measured rigorously, it is desirable to set the ratio of the idle period to each pulse width to be a simple integer because of the configuration of the drive circuit. . The reason is that 1H is divided in order to output the drive waveform and the reference pulse of the drive circuit system is set so as to be an integral multiple of the selection pulse, the auxiliary pulse, or the idle period, so the pulse width ratio becomes too complicated. And the clock becomes very fast. As a result, it is necessary to make a circuit with a response speed faster than necessary, and to avoid cost increase.

FIG. 1 is a block diagram of a display device according to an embodiment of the present invention. Reference numeral 107 is a graphic controller, and the data transmitted from this is the drive circuit 105.
Through the scanning signal control circuit 104 and the information signal control circuit 1
It is input to 06 and converted into address data and display data, respectively.

In accordance with this address data, the scanning signal applying circuit 102 generates the scanning selection signal waveforms shown in FIGS. 4A and 5A and the scanning non-selection signal waveforms shown in FIGS. 4B and 5B, and the display element 101 consisting of 1280 × 1024 pixels. Applied to the scanning electrodes of. Further, the information signal applying circuit 103 generates the information signal waveforms shown in FIGS. 4C, 4D, 5C, and 5D according to the display data, and applies the information signal waveforms to the information electrodes of the display element 101. The operating time of this display device is the integration timer 108.
Then, a signal for waveform switching is generated when the recording time exceeds 10,000 hours.

The drive circuit 105 selects a drive waveform to be used based on this signal, and the scan signal application circuit 102 is selected through the scan signal control circuit 104 and the information signal control circuit 106.
And the waveform data is sent to the information signal applying circuit 103.

The scan signal applying circuit 102, the information signal applying circuit 103, the scan signal controlling circuit 104, the driving circuit 105, the integrating timer 108, etc. constitute a driving controlling circuit 110 according to the present invention.

FIG. 2 is a partially enlarged view of the display element 101. In FIG. 2, 201 is a scanning electrode, 202 is an information electrode, and 203 is an intersection of the scanning electrode 201 and the information electrode 202. A pixel as a display unit is shown.
FIG. 3 is a partial cross-sectional view of the display element 101. In the figure, 301 is an analyzer (polarizer), 303 is a polarizer (analyzer), and these are U2 for the display element 101.
They are arranged in crossed Nicols so that they are displayed dark when in the state. 302 and 308 are glass substrates, and 303 and 3
Reference numeral 07 is an insulating film, 304 and 306 are alignment films, 305 is a ferroelectric liquid crystal, and 310 is a sealing material.

The physical properties of the ferroelectric liquid crystal 305 are shown in Table 1 below.

[0031]

[Table 1] Note that the pixel of this embodiment can be used as a multicolor color display device by further dividing the pixel into three and disposing color filters in each.

FIG. 4 shows a drive waveform W1 initially used in the apparatus of FIG. 1, in which A is a scanning selection signal having a selection pulse of pulse width ΔT and a pulse width of 2.5 ΔT arranged immediately before the selection pulse. It is composed of an auxiliary pulse having a pulse width of 1 / 2ΔT arranged immediately after the erase pulse and the selection pulse. B is a scanning non-selection signal which is always 0 v, and C is an information signal for bright display, which is composed of a selection pulse having a pulse width ΔT and auxiliary pulses having a pulse width 1/2 ΔT arranged before and after the selection pulse. D is an information signal for dark display, and the polarity of the bright information signal C is inverted. In the figure, 1H indicates one horizontal scanning period, and ΔT indicates a selection period.

The display device of the present embodiment has a total operating time of 20
After 0 hours at room temperature, drive conditions V1 = 14.3v, V2
= -14.3v, V3 = 5.7v, V4 = -5.7v,
When driving was performed with V5 = 6.4 v and ΔT = 32.0 μs, good display was obtained over the entire surface of the display element 101.

FIG. 5 shows a drive waveform W2 used after a long period of operation in the apparatus of FIG. In the figure, A is a scanning selection signal, which is composed of a selection pulse having a pulse width ΔT, an erase pulse having a pulse width of 2.5 ΔT arranged immediately before the selection pulse, and an auxiliary pulse having a pulse width of 1/2 ΔT arranged immediately after the selection pulse. To do. B is a scanning non-selection signal which is always 0 v, and C is an information signal for bright display. The selection pulse having a pulse width ΔT, the auxiliary pulse having a pulse width of 1/2 ΔT arranged before and after the selection pulse, and the auxiliary pulse are continuous. In order not to do so, it is composed of an auxiliary pulse and a pause period of a pulse width 1/2 ΔT provided between the auxiliary pulses. D is an information signal for dark display, and the polarity of the bright information signal C is inverted.

The display device of the present embodiment has a total operating time of 10
After 500 hours at room temperature, the driving condition was V1 = 14.3v,
V2 = -14.3v, V3 = 5.7v, V4 = -5.7
v, V5 = 6.4 v, and ΔT = 32.8 μs were set for driving. While operating for a long time, various displays are displayed on the display element 101, and the threshold characteristic, which was initially substantially uniform, also varies for each pixel. Since the threshold value of the entire display element is defined by the pixel having the highest threshold value, as a result, the threshold value after operating for a long time increases. For that reason, ΔT is increased by 0.8 μs. Then the frame frequency is 1
Although it was slowed down from 5.3 Hz to 11.9 Hz, good display could be performed over the front surface of the display element 101.

[0036]

As described above, according to the present invention,
It is possible to secure a driving margin for a long time,
Fluctuations of liquid crystal molecules are reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a display device according to the present invention.

FIG. 2 is an enlarged view of a display element.

FIG. 3 is a cross-sectional view of a display element.

FIG. 4 is a diagram showing drive waveforms in the present embodiment.

FIG. 5 is a diagram showing drive waveforms in the present embodiment.

FIG. 6 is a diagram showing an alignment model of liquid crystal.

FIG. 7 is a diagram showing a relationship between liquid crystal molecules and a polarizer.

FIG. 8 is a diagram showing a conventional drive waveform.

FIG. 9 is a diagram illustrating an AC pulse.

FIG. 10 is a diagram showing a relationship between an idle period and a drive margin.

[Explanation of symbols]

 101 display element 110 drive control circuit

Claims (8)

[Claims] 1. A display element in which a ferroelectric liquid crystal is arranged between a matrix electrode composed of a scan electrode group and an information electrode group, and drive control for changing drive conditions by referring to one piece of information other than image data. A display device including a circuit. 2. The change of the drive condition of the drive control circuit is
The display device according to claim 1, wherein the display device follows a change with time in characteristics of the display element. 3. The change of the drive condition of the drive control circuit is
The display device according to claim 1, wherein the display device is operated according to a total operating time of the display device. 4. The change of the drive condition of the drive control circuit is
The display device according to any one of claims 1 to 3, wherein the driving waveform applied to the scanning electrode group and the information electrode group is changed in shape. 5. The display device is constantly applied with an electric field during a short total operation time of the display device, and a period during which the display element is not applied with an extended total operation time is provided. Display device described. 6. The display device according to claim 3, wherein the proportion occupied by the selection period in one horizontal scanning period is changed according to the total operating time of the display device. 7. The scan selection signal applied to the scan electrode group among the drive waveforms comprises a selection pulse, an erase pulse arranged immediately before the selection pulse, and an auxiliary pulse arranged immediately after the selection pulse. The information signal applied to the electrode group is composed of a selection pulse and an auxiliary pulse arranged before and after the selection pulse while the total operation time is short, and is arranged before and after the selection pulse and the selection pulse when the total operation time becomes long. 5. The display device according to claim 4, wherein the display device comprises an auxiliary pulse and a rest period provided between the auxiliary pulse so that the auxiliary pulse is not continuous. 8. The change of the drive condition of the drive control circuit is:
2. The change in frame frequency according to claim 1.
The display device according to claim 1.