JP2616496B2 - Driving method of liquid crystal element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 temperature characteristics of a liquid crystal element using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art A conventional driving method for compensating temperature characteristics of a liquid crystal element using a ferroelectric liquid crystal is disclosed in, for example,
No. 125825.

[0003]

When a liquid crystal device using a ferroelectric liquid crystal is multiplex driven, the temperature dependence of its optical characteristics is very severe. For example, FIG. The change of the drive pulse width is shown.
The driving pulse width changes about 100 times in the temperature range of 0 to 40 ° C. FIG. 5 shows a change in driving voltage required by the temperature when the driving pulse width is fixed. The driving voltage changes about 20 times in a temperature range of 5 to 40 ° C. Therefore, when this liquid crystal element is multiplex-driven, there is a disadvantage that temperature compensation cannot be performed only by adjusting only the driving voltage or only the driving pulse width.

Further, when driving is performed at a constant driving voltage in a high temperature region, the pulse width must be very 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 driving circuit. And the optical characteristics of each pixel differ depending on the distance from the output terminal.

The above-mentioned conventional example does not address this point and does not clarify the problem.

[0006]

According to the present invention, there is provided a method for driving a liquid crystal element comprising a pair of substrates having electrodes on the inner surfaces of opposing substrates, wherein the liquid crystal has a memory property. Drive voltage and drive applied to liquid crystal
The pulse width is changed according to the temperature change, and the driving voltage is
Change so that it becomes smaller as the temperature rises and
The amount of change in the drive voltage with respect to
The drive pulse width changes so as to narrow as the temperature rises
And the amount of change in the drive pulse width with respect to temperature rise
It is characterized by being made smaller .

[0007]

[0008]

[0009]

[0010]

[0011]

According to the present invention, by increasing the drive pulse width in the low temperature region, it is possible to avoid an increase in the drive voltage, 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. It is possible to avoid a difference in optical characteristics between the pixels due to dulling of the applied waveform.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on specific examples.

REFERENCE EXAMPLE 1 640 × 400 dots and a pixel pitch of 0,0 using an optically polished soda glass substrate having a matrix-shaped transparent electrode formed by sputtering ITO having a sheet resistance of 30Ω / □.
A cell having a cell gap of 4 mm and a cell gap of 2 μm was formed, and a ferroelectric liquid crystal was injected to obtain a liquid crystal element.

FIG. 1 shows 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 the temperature. When the driving voltage Vp =
When driven at 25 V, at a temperature of 26 ° C. or less (at this time, the drive pulse width Pw was 80 μsec), a difference was observed in the optical characteristics between the pixel closest to the input terminal of the panel and the pixel farthest away. When the time constant of the pixel farthest from the input terminal was calculated, it was 35 μsec. Therefore, the drive voltage Vp is corrected by a circuit for detecting the temperature by the thermistor 10 as shown in FIG.
The drive voltage was adjusted to a maximum drive voltage of 25 V for the driver LSI in the temperature range of up to 26 ° C., and the drive voltage Vp was changed to 25 V to 5 V in the temperature range of 26 to 40 ° C.

Further, as shown in FIG.
A / D-converts the voltage at both ends of the circuit and changes the clock frequency by controlling the programmable oscillation circuit 15 so that the drive pulse width Pw is 65 ° C. at 5 to 26 ° C. as shown in FIG.
0 μsec, and 80 μsec at 26 ° C. to 40 ° C.
It was set to be constant at c.

As described above, by separately adjusting the drive voltage Vp and the drive pulse width Pw, the temperature characteristic of the drive circuit changes linearly as shown by the main line in FIG.

When the liquid crystal element was driven under such temperature compensation conditions, there was no problem in the temperature range of 20 to 40.degree. C., but at a temperature of 20.degree. When the temperature is lower than ° C., the scanning time of one pixel takes 0.3 sec or more, and the scanning itself becomes visible.

[Embodiment] A cell having the same configuration as that of the above-described first embodiment was used, and the response was faster than that of the first embodiment , that is, the response speed at 5 ° C. was 4
When the liquid crystal element in which the liquid crystal of 00 μsec was injected was driven by a drive circuit having a temperature compensation characteristic continuously changing as shown in FIG. 8, no flickering of the screen was observed in a temperature range of 5 to 40 ° C. I was able to drive.

Reference Example 2 A cell having the same electrode configuration as that of Reference Example 1 and Example was manufactured by changing the sheet resistance of ITO from 15 to 80 Ω / □, and the liquid crystal used in Example was injected. . When these liquid crystal elements were driven at a constant driving voltage Vp of 25 V, the driving voltage Vp was 5 to 5.
ITO with a sheet resistance of 30Ω / □ or less in a temperature range of 40 ° C
Although the liquid crystal element using the liquid crystal element could be driven without any problem, in the liquid crystal element having a higher sheet resistance, a difference in optical characteristics depending on the pixel was observed on the high temperature side.

At 5 ° C., the driving pulse width Pw at which the optical characteristics differ depending on the pixel and the maximum time constant m of each liquid crystal element
When the relationship with ax was examined, approximately Pw = 3 × rma
x.

This value is a value in the case of the ferroelectric liquid crystal used in the present embodiment. If another material is used, the value will be different, but practically it is 2 to 4 times the time constant rmax. It is desirable.

The circuit for temperature compensation of the drive voltage Vp or the drive pulse width Pw is not limited by this embodiment. For example, a circuit for performing blocking transmission using thermistors 91 and 92 as shown in FIG. May be used to change the clock frequency to adjust the drive pulse width. Usually, any configuration may be used as long as it is a circuit configuration used for the same purpose.

[0024]

According to the present invention, the following effects can be obtained by adopting the above configuration. That is, the temperature change
The drive voltage and drive pulse
More, the liquid crystal device driving at an optimum driving voltage and the driving pulse width
Can move.

[Brief description of the drawings]

FIG. 1 is a diagram showing characteristics of a driving voltage and a driving pulse width with respect to a temperature of a liquid crystal used in Reference Example 1 .

FIG. 2 is a diagram illustrating a change in a required driving pulse width with respect to a temperature when a driving voltage is fixed.

FIG. 3 is a diagram showing a change in drive voltage with respect to temperature required when a drive pulse width is fixed.

FIG. 4 is a diagram showing a drive voltage correction circuit portion used in Reference Example 1 .

FIG. 5 is a diagram showing a correction characteristic of a drive voltage with respect to a temperature in Reference Example 1 .

FIG. 6 is a diagram showing a drive pulse width correction circuit portion used in Reference Example 1 .

FIG. 7 is a diagram showing a correction characteristic of a drive pulse width with respect to a temperature in Reference Example 1 .

FIG. 8 is a diagram showing a temperature compensation characteristic of a circuit according to the embodiment of the present invention .

FIG. 9 is a diagram showing a drive pulse width adjustment circuit used in Reference Example 2 .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Zener diode 7 ... Resistor for voltage division 8 ... Resistor for voltage division 9 ... Resistor for voltage division 10 ... Thermistor for temperature detection 13 ... Thermistor for temperature detection 91 ... For temperature detection Thermistor 92 ・ ・ ・ Thermistor for temperature detection

Claims (1)

(57) [Claims] 1. A method of driving a liquid crystal element comprising a pair of substrates having electrodes on inner surfaces of opposed substrates, wherein a liquid crystal having a memory property is sandwiched between the substrates.
The driving voltage is changed according to the temperature rise.
And the drive against temperature rise.
The change amount of the dynamic voltage is increased, and the driving pulse width is
Change to narrow as temperature rises and temperature rise
A method for driving a liquid crystal element, wherein the amount of change in the driving pulse width with respect to (i) is reduced .