JPH0310217A - Method for driving liquid crystal device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for driving a liquid crystal device.

[Prior Art] A conventional method for driving a liquid crystal device is shown in FIGS. 4(a) to (1). In Figure 4 (1), x1, x2, x3, x4 are signal electrodes, Y], ¥2, Y-3 are signal electrodes, respectively, and scanning electrodes and signal types (the circles at the intersections of the squares are indicated In each pixel, the number inside the circle indicates the gradation level, and the larger the number, the higher the effective value of the voltage waveform applied to the display pixel, and four-gradation display is performed. ) to (g), VX2, VX3, and VX4 are the voltage waveforms applied to the signal electrodes, respectively, and VYI in FIGS. 4(a) to (c),
VY2 and VY3 are voltage waveforms applied to the scanning electrodes, respectively, and 0 indicates the base '4BYIl pressure.

When scan electrode ¥1 is selected, scan voltage vo+vy is applied to scan electrode )′], and scan voltage vo+vy is applied to scan electrode Y2. Y3 remains as ■0. The pixel located at the intersection of the pixel on the scanning electrode \1 and the signal electrode x1 has a gradation level of 1, and vo+vx is applied to the signal electrode. The pixel at the intersection with the signal electrode x 2 has a gradation level of 2, and during the period of 2t, it is vo+
vx is applied, and then vo-vx is applied for a period of t.

The pixel at the intersection with the signal electrode x3 has a gradation level of 3, and vo+vx is applied for a period of t, and then vo-vx is applied for a period of 2t. The pixel at the intersection with the signal electrode x4 has a gradation level of 4, and the signal electrode has vo-vx
is applied. Since the difference between the voltage of the scanning electrode and the voltage of the signal electrode is applied to each pixel, the intersection of ×1 and ¥1 has v
y-vx is the intersection of x2 and ¥1, and for fortune-telling, the period of 2t is V
YVX is then vy+vx during period t, ×3 and Y
The intersection of l has VY-VX for a period of t, and then 2t
(7) The period is vy+vx, and the intersection of ×4 and Y] is V
'1' + V X ps is applied. Further, at this time, since the voltage of ¥2 and ¥3 is VO, vx or -Vx is applied to the second pixel of ¥2 and Y3.

In the next selection period, ¥2 will be selected and the following operations will be performed for ¥2.
Then, similar operations are performed for each scanning electrode in sequence.

In other words, in the selection period, the pixel at the gradation level is VY-
VX is vy- for a period of 2L for pixels at gradation level 2.
vx, then Ll for a period of t: V'I'+■x, and for a pixel at gradation level 3, VY-VX for a period of t.
After that, during the 2t period, vy+vx is applied to the pixel at gradation level 4, and 1■× or VX is applied during the non-selection period, so the voltage waveform applied to the pixel depending on the gradation level A difference appears in the effective value of , and gradation is displayed.

In this way, the relationship between the gradation level and the time during which the selection voltage is applied to the signal electrode in the selection period is 0 at gradation level l, t at gradation level 2, 2t at gradation level 3, and 2t at gradation level 4. Generally, the difference in the time during which the selection voltage is applied to the signal electrode (hereinafter referred to as gradation pulse width) between adjacent gradation levels is at equal intervals, such as 3t for gradation levels. In order to make the display easier to read, the gradation increments are not spaced at equal intervals, and the relationship between the gradation level and the time during which the selection voltage is applied to the signal electrode during the selection period is expressed as, for example, gradation level 1.
0 for gradation level 2, 12t for gradation level 3, 1 for gradation level 3
．． A method has also been proposed in which the gradation level is 8t, and the gradation level 4 is 3t.

[Problem to be Solved by the Invention 1] However, in the prior art described above, even if the difference in gradation pulse width is eliminated at equal intervals in order to make the gradation display easier to see, for example, when the temperature changes, the steepness of the liquid crystal changes. There is a problem in that the gradation display becomes difficult to see due to reasons such as changes in the gradation.

The present invention is intended to solve these problems, and its purpose is to prevent the deterioration of the appearance of the gradation display due to the above-mentioned reasons, and to provide an easy-to-read gradation display regardless of the temperature. be.

[Failure to solve the problem]

A method for driving a liquid crystal device according to the present invention includes a liquid crystal device sandwiching a liquid crystal layer between a substrate having a scanning electrode and a substrate having a signal electrode, and forming a display pixel in a portion where the scanning electrode and the signal electrode overlap. When performing display, scanning voltages are sequentially applied to the scanning electrodes, and the signal voltage waveform applied to the signal electrode and the scanning voltage waveform applied to the scanning electrode are While the scanning voltage is being applied, the potential of the signal voltage waveform applied to the signal electrode is changed between the selected voltage and the non-selected voltage so that the effective voltage of the composite waveform becomes an effective voltage corresponding to the gradation level of the display pixel. The method for driving a liquid crystal device is characterized in that the ratio of the time during which a selection voltage is applied to the signal electrode at each gradation level and the time during which a non-selection voltage is applied is changed depending on the temperature.

[For use] In the case of n-gradation display, the condition under which the β tone display is most easily visible on the shell is T (n) -T (n- ]) =T(n-1)
-T (n-2) =.=T (2) This is when T(1) is satisfied. Therefore, if a driving method is used in which the difference in gradation pulse width changes so as to satisfy this condition even when the temperature changes, a gradation display that is always easy to see can be obtained.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Example 1 Figures 1(a) to (c) are diagrams showing the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in this example. FIG. 1(1) is when the temperature is 20°C, and FIG. 1(c) is when the temperature is OoC. When this liquid crystal device was driven at a bias ratio of 13.1/200 duty and one selection period of 70 IIS e c, the effective voltage at which the contrast ratio was maximized at 20°C was Von = 2.20.
0v, Voff2.052v. Also, at this time, the effective voltage value at each gradation level that satisfies the condition that the gradation display is most legible is, in the case of 8 gradation display, V (8) = 2.200v (=Von)V (7) =
2.189V v (6)=2.178V V (5)=2. 167v V (4)=2. 153v V (3)=2. 137v V (2)=2. 1 14v V (1)=2. It was 052v (=Voff).

Also, the effective FE value of each gradation level where the gradation display is most legible when the contrast ratio is maximum at 0°C is V (8) = 2.300v (=Von) V (7) =
2.291v V (6) = 2.282v V (5) = 2.272v V (4) = 2.258v V (3) = 2.241v V (2) = 2.215v V (1) = 2. 145v (=Voff) When the contrast ratio is maximum at 40°C, the effective voltage value of each gradation level at which the gradation display is most legible is: ■ (8) V (7) = 2 V (6) = 2 V (5 )=2 V (4)=2 V (3)=2 V (2)=1 V (1)=1.

Here, △V (n) = (V (n)/ (V (
8) −V (1) ), △V(7) at each temperature
The relationship between △v (1) is △V (7) = 94 at 0°C.
．． 2% △V (6) = 88.4% △V (5) = 83.9% △V (4) = 72.9% △V (3) = 61.9% △V (2) = 45. 2% At 20℃, △V (7) V (1)) Von) 080v (068V 055 v 41v 27v 12v 991 v 940v (=Voff) 6% 2 △V (6) = 85. 1% △V (5 ) = 77, 7% △V (4) = 68. 2% △V (3) = 57. 4% △V (2) = 41., 9% At 40℃, △V (7) = 91. 4 % △V (6) = 82.1% △V (5) = 72 1% △V (4) = 62.1% △V (3) = 51.4% △V (2) = 36.4% Here, for each temperature, △V (1) = O%, △V (8) =
It is 1oo%.

Based on this value, the temperature was set in steps of 10°C] and the selection period was divided into 64 to determine the gradation pulse width. The gradation pulse width at each gradation level (gradation pulse width at gradation level n is t
(written as (n)) is 5° when one selection period is 64t.
Below C LJ t (7) = 60t t (6) = 56t t (5) - 52t t (4) = 46t t (3) = 39t t (2) = 28t Above 5°C and below 15°C , t (7) = 60t t (6) = 56t t (5) = 51t t (4) = 45t \ t (3) = 38t t (2) = 27t If it is 1560 or more and less than 25°C, t (7 )=59t t (6)=54t t (5)=49t t (4)=43t t (3)=36t t (2)=26t At temperatures above 25℃ and below 35℃, t(7)=59t t (6 ) = 54t t (5) = 48t t (4) = 42t t (3) = 35t t (2) = 25t At temperatures above 35°C, t (7) = 58t j (6) = 521: t (5) = 46t t(4) = 40t t (3) = 33t t (2J = 23t).

Here, for each temperature, t(8)=64t;, 1°(1)=
It is Ot.

FIG. 2 is a schematic diagram of a circuit for realizing this embodiment, and FIGS. 3(a) to 3(, J) are diagrams showing clock signals, waveforms for determining gradation pulse widths, and signal voltage waveforms.

1 2 In FIG. 2, ■ is a temperature sensor, and its output is input to the ROM 3 via the A/D converter 2.

On the other hand, the clock signal is input to the counter 5 in FIG. 2, converted into a waveform obtained by dividing one selection period into 64 as shown in FIG. 3(a), and sent to the ROM. In the ROM, the signal waveform ((b) in Figure 3) determines the gradation pulse width from the signal sent from the counter and the signal sent from the A/D converter.
))make. This waveform is a pulse waveform that rises at the beginning of the selection period and when the signal waveform at each gradation level changes from the selection voltage to the non-selection voltage. The waveform output from the ROM is sent to the gradation driver IC via the flip-flop circuit 4. The gradation driver IC outputs a voltage waveform applied to the signal electrode in accordance with the gradation level of the pixel. In Figure 3, (c) is gradation level 1, (d) is gradation level 2, (e) is gradation level 3, (f) is gradation level 4,
(g) is gradation level 5, (h) is gradation level 6, (1)
indicates the gradation level 7, and (j) indicates the voltage waveform applied to the signal electrode at the gradation level 8. The timing at which the voltage waveform applied to the signal electrode at gradation level 2 or 67 changes from a selection voltage to a non-selection voltage is the pulse rise of the signal waveform (Fig. 3(b)) that determines the gradation pulse width. ” at the same time.

In the conventional I-tone method, even if the pulse width of the gradation is set so that the gradation display becomes most visible at 20°C, as the temperature changes, the relationship between the effective voltage and the transmittance changes as shown in Figure 1. For example, when the temperature is 0° C., it is difficult to distinguish between gradation levels 6 and above, and when the temperature is 40° C., it is difficult to distinguish between gradation levels 3 and below. However, in this example, by setting the pulse width of the gradation according to the temperature, a gradation display that was always easy to see even when the temperature changed was obtained.

Example 2 In Example 1, 8-gradation display was performed, but it has been recognized that the same effect of the present invention can be obtained in the case of 3 to 64 gradations. Furthermore, it is obvious that the same effect can be obtained when the gradation level exceeds 64.

The temperature increments are also set to 10°C in Example 1, but this takes into account the temperature characteristics of the liquid crystal used. For example, if a liquid crystal whose characteristics are highly dependent on temperature is used, the increments may be made smaller and It is also possible to increase the size by using a liquid crystal with a small size.

[Effects of the Invention] As described above, the present invention changes the ratio of the time during which a selection voltage is applied to the signal electrode at each gradation level and the time during which a non-selection voltage is applied depending on the temperature. This has the effect that an easy-to-read gradation display can be obtained at all times.

Figure 4(a) Diagram showing the method.

(1) is a conventional LCD device drive 1...Temperature sensor 2...A/D converter 3.・ROM 4...Flip-flop 5...Counter

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) are diagrams showing the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in one embodiment of the present invention. FIG. 2 is a schematic diagram of a circuit for implementing one embodiment of the present invention. FIGS. 3(a) to 3(j) are diagrams showing fj clock signals, waveforms for determining gradation pulse widths, and voltage waveforms applied to signal electrodes.

Claims (1)

[Claims] When performing gradation display in a liquid crystal device in which a liquid crystal layer is sandwiched between a substrate having a scanning electrode and a substrate having a signal electrode, and display pixels are formed in a portion where the scanning electrode and the signal electrode overlap,
Scanning voltages are sequentially applied to the scanning electrodes, and the signal voltage waveform applied to the signal electrode and the scanning voltage waveform applied to the scanning electrode are changed at display pixels existing at the intersections of the signal electrode and the scanning electrode. The potential of the signal voltage waveform applied to the signal electrode is changed between the selection voltage and the non-selection voltage while the scanning voltage is applied so that the effective voltage of the composite waveform becomes an effective voltage corresponding to the gradation level of the display pixel. A method for driving a liquid crystal device, characterized in that the ratio of the time during which a selection voltage is applied to a signal electrode at each gradation level and the time during which a non-selection voltage is applied is changed depending on the temperature. Driving method.