JPH0823634B2 - Liquid crystal element driving method - Google Patents

Description

The present invention relates to a method for driving a liquid crystal element. More specifically, the present invention relates to a driving method for compensating the temperature characteristics of a liquid crystal element using a ferroelectric liquid crystal.

[Conventional technology]

A conventional driving method for compensating the temperature characteristics of a liquid crystal element using a ferroelectric liquid crystal is described in, for example, Japanese Patent Laid-Open No. 60-123825.

[Problems to be solved by the invention]

When a liquid crystal device using a ferroelectric liquid crystal is driven by multiplex, the temperature dependence of its optical characteristics is extremely severe,
For example, FIG. 2 shows the change of the drive pulse width necessary with the temperature when the drive voltage is constant. The drive pulse width changes about 100 times in the temperature range of 0 to 40 ° C. In addition, Fig. 3 shows the change in the drive voltage required with the temperature when the drive pulse width is constant.
Change twice. Therefore, in the case of performing multiplex driving of this liquid crystal element, there is a drawback that temperature compensation cannot be performed by adjusting only the driving voltage or only the driving pulse width.

In addition, when driving with a constant drive voltage in a high temperature region, the pulse width must be made extremely short, and the applied waveform becomes dull due to the influence of the wiring resistance of the liquid crystal element and the output impedance of the drive circuit. Another problem is that the optical characteristics of each pixel differ depending on the distance from the input terminal.

In the above-mentioned conventional example, this point was not touched and the problem was not clarified.

[Means for solving problems]

The method of driving a liquid crystal element according to the present invention is the method of driving a liquid crystal element, comprising a pair of substrates having a plurality of electrodes on opposing inner surfaces of a substrate, and a liquid crystal having a memory property sandwiched between the pair of substrates.
In the second temperature region, the driving voltage is constant and the driving pulse width is changed with respect to the temperature change to apply a voltage pulse to the liquid crystal. In the second temperature region, the driving pulse width is constant and the driving is performed with respect to the temperature change. It is characterized in that a voltage pulse whose voltage is changed is applied to the liquid crystal.

The second liquid crystal element driving method of the present invention is characterized in that the driving pulse width in the first temperature region becomes narrower as the temperature rises.

Further, the third driving method of the liquid crystal element of the present invention is characterized in that the driving voltage in the second temperature region decreases as the temperature rises.

Further, the fourth method of driving the liquid crystal element of the present invention is characterized in that the temperature of the first temperature range is lower than the temperature of the second temperature range.

[Action]

According to the present invention, by increasing the drive pulse width in the low temperature region, it is possible to prevent the drive voltage from rising, and in the high temperature region, the drive voltage is lowered, and at the same time, the lower limit of the drive pulse width is set to reduce the applied waveform. It is possible to prevent the difference in optical characteristics between the pixels due to the dullness.

〔Example〕

Details of the present invention will be described below based on specific examples.

Example 1 A cell having 640 × 400 dots, a pixel pitch of 0.4 mm, and a cell gap of 2 μm was formed by using two optically polished soda glass substrates on which ITO having a sheet resistance of 30 Ω / □ was sputtered and transparent electrodes in a matrix were formed. A ferroelectric liquid crystal was injected to prepare a liquid crystal element.

The relationship between the driving voltage Vp and the driving pulse width Pw required for the multiplex driving of the liquid crystal element with respect to temperature is shown by the thin line in FIG. When this liquid crystal element is driven with a drive voltage Vp = 25V, at a temperature of 26 ° C. (the drive pulse width Pw was 80 μsec at this time) and below, the optical distance between the pixel closest to the panel input terminal and the pixel farthest from There was a difference in the characteristics. The time constant of the pixel farthest from the input terminal was calculated to be 35 μsec. Therefore, as shown in FIG. 4, the circuit for detecting the temperature by the thermistor 10 corrects the drive voltage Vp. As shown in FIG. 5, in the temperature range of 5 to 26.degree. Maximum drive voltage of 25V, 26-40
The driving voltage Vp was adjusted to change from 25V to 5V in the temperature range of ℃. Also, as shown in FIG. 6, the thermistor
By converting the voltage across 13 from A / D by the A / D converter 14 and controlling the programmable oscillator circuit 15 to change the clock frequency, as shown in FIG. 26
The temperature was changed from 650 μsec to 80 μsec at ℃, and was kept constant at 80 μsec from 26 ℃ to 40 ℃.

As described above, by adjusting the drive voltage Vp and the drive pulse width Pw separately, the temperature characteristic of the drive circuit of the present embodiment has the first temperature characteristic.
It changes linearly as shown by the thick line in the figure.

When the liquid crystal element was driven under such temperature compensation conditions, there was no problem in the temperature range of 20 to 40 ° C., but at a temperature of 20 ° C. or lower, flicker became conspicuous as the temperature decreased, and 10 ° C. In the following, the scanning time for one screen became 0.3 sec or more, and the scanning itself became visible.

(Example 2) A liquid crystal element in which a cell having the same configuration as that of Example 1 is used and a liquid crystal having a faster response than that of Example 1, that is, a response speed at 5 ° C of 400 µsec is injected is shown in Fig. 8. When driven by a drive circuit in which the temperature compensation characteristics change continuously, no flicker on the screen was visible in the temperature range of 5 to 40 ° C, and driving was possible without problems.

(Example 3) A cell having the same electrode configuration as in Examples 1 and 2, but having a sheet resistance of ITO varied from 15 to 80 Ω / □ was prototyped, and the liquid crystal used in Example 2 was injected. These liquid crystal elements
When driven by a drive circuit with a constant drive voltage Vp of 25V, 5
A liquid crystal element using ITO with a sheet resistance of 30Ω / □ or less could be driven without problems in the temperature range of -40 ℃, but a liquid crystal element with a sheet resistance higher than that showed a difference in optical characteristics due to pixels on the high temperature side. It was At 5 ° C., the relationship between the drive pulse width Pw in which the optical characteristics differ depending on the pixel and the maximum time constant τmax of each liquid crystal element was examined, and it was found that Pw = 3 × τmax.

This value is the case of the ferroelectric liquid crystal used in this example, and it will be different if other materials are used, but in practice it is desirable to be 2 to 4 times the time constant τmax. .

The temperature compensating circuit for the driving voltage Vp or the driving pulse width Pw is not limited by this embodiment, and for example, a circuit for oscillating blocking using thermistors 91 and 92 as shown in FIG. It may be used for detection to change the clock frequency and adjust the drive pulse width.
Generally, any circuit configuration may be used as long as it is used for the same purpose.

〔The invention's effect〕

According to the present invention, temperature compensation of a liquid crystal element using a ferroelectric liquid crystal can be performed without any practical problems.

[Brief description of drawings]

FIG. 1 is a diagram showing temperature characteristics of a drive voltage Vp and a drive pulse width Pw necessary for multiplex driving of a liquid crystal used in Embodiment 1 of the present invention, and a characteristic of a temperature compensation circuit thereof. FIG. 2 is a diagram showing a change in drive pulse width required with temperature when the drive voltage is kept constant. FIG. 3 is a diagram showing a change in driving voltage required with temperature when the driving pulse width is constant. FIG. 4 and FIG. 5 are diagrams respectively showing a correction circuit portion of the drive voltage Vp and its correction characteristic in the first embodiment of the present invention. FIG. 6 and FIG. 7 are diagrams showing a correction circuit portion of the drive pulse width Pw and its correction characteristic in the first embodiment of the present invention, respectively. FIG. 8 is a diagram showing temperature compensation characteristics of a circuit according to the second embodiment of the present invention. FIG. 9 is a diagram showing an example of another drive pulse width adjusting circuit that can be used in the present invention. 10,13,91,92 …… Thermistor for temperature detection 1 …… Zener diode 7,8,9 …… Resistor for voltage division

Claims (4)

[Claims] 1. A method of driving a liquid crystal element, comprising a pair of substrates having a plurality of electrodes on opposite inner surfaces of a substrate, and a liquid crystal having a memory property sandwiched between the substrates. To the liquid crystal, a voltage pulse having a drive pulse width changed is applied to the liquid crystal, and a voltage pulse having a constant drive pulse width in the second temperature region and having a drive voltage changed with respect to the temperature change is applied to the liquid crystal. A method for driving a liquid crystal element, characterized in that the voltage is applied. 2. The method of driving a liquid crystal element according to claim 1, wherein the driving pulse width in the first temperature region becomes narrower as the temperature rises. 3. The method of driving a liquid crystal element according to claim 1, wherein the driving voltage in the second temperature region decreases as the temperature rises. 4. The method of driving a liquid crystal element according to claim 1, wherein the temperature of the first temperature region is lower than the temperature of the second temperature region.