JPH0331817A - Driving method for liquid crystal device - Google Patents

Abstract

PURPOSE:To attain an invariably legible gradational display even when a voltage value is varied by varying the ratio of a time of the application of a selected voltage to a signal electrode and a time of the application of a nonselected voltage according to a scanning voltage value, a selected voltage value, and a nonselected voltage value. CONSTITUTION:The output of a voltmeter 1 is inputted to a ROM 2 and a clock signal, on the other hand, is inputted to a counter 4 and converted into a waveform obtained by dividing one selected period by 64 and inputted to the ROM 2. The ROM 2 generates a signal waveform which determines a gradation pulse width with the signal of the counter 4 and the signal of an A/D converter. This waveform is sent to a driver IC for gradations through a flip- flop circuit 3 and a voltage waveform to be applied to a signal electrode is outputted according to the gradation level of a picture element. Therefore, the scanning voltage value, selected voltage, and nonselected voltage value are varied for control over transmissivity, the pulse width of gradations is set according to the voltage value and the legible gradational display is obtained.

Description

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

[Conventional technology] How to drive a conventional liquid crystal device? Figure J5 (L'L) ~ (h
). X1, X2 in FIG. 5(A). X5°x4 are signal electrodes, Yl, Y2. Is Y5 a signal electrode and a scanning electrode respectively? The circle at the intersection of the 1i pole and the signal electrode is a display pixel, and the number inside the circle indicates the level of protection, and the larger the number, the higher the effective value of the voltage waveform applied to the display pixel. A 4-gradation display is performed. Figure 5(d)-(
! 1) VXl, VX2. VX5. VX4 is the voltage waveform applied to the signal electrode, vyt, VY2 . VY5 is a voltage waveform applied to each scanning electrode, and VO indicates a reference voltage.

When scan', ll pole Y1 is selected, scan electrode Y1
A scanning voltage vO+vY is applied to Y2. Y3 is vO
It remains as it is. Of the pixels on the scanning electrode Y1, the signal electrode
The pixel at the intersection with 1 has a gradation level of 1, and vo+vx is applied to the signal electrode. The pixel at the intersection with the signal electrode x2 has a gradation level of 2, and in a period of 2t, v
o+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 in period t vo-1-vx, then 2t
vo-vx is applied during the period. The pixel at the intersection with the signal electrode X4 has a gradation level of 4, and the signal electrode has a v
o-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, VY-VX is applied to the intersection of Xl and Yl, vy-vX is applied to the intersection of x2 and Yl for a period of 2t, and thereafter , t, vy+vx is x
vy-vx is applied to the intersection of X4 and Yl(7) for a period of t, VY+VX is applied for a period of 2t, and vy+vx is applied to the intersection of X4 and Yl(7). Also, at this time, Y2, Y
3 is vO, so VX or -VX is applied to the pixels on Y2 and Y5.

In the next selection period, Y2 is selected and the above operation is performed for Y2, and thereafter, the same operation is sequentially performed for each scan 1if pole.

In other words, during the selection period, the pixel of gradation level 1 has VY-
VX to M tone 7+1/2 (4' to Q pixel!, 2
VY-VX for period t, then VY+ for period t
vx is VY-' for the pixel at gradation level 5 during period t.
After that, VY+VX is applied during the 2t period, VY+VX is applied to the pixel at gradation level 4, and -vx or VX is applied during the non-selection period, so the voltage applied to the pixel depends on the gradation level. Differences appear in the effective values of the waveforms, 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 1, t at gradation level 2, 2t at gradation level 5, 5'
At J tone level 4, the time during which the selection voltage is applied to the signal electrode between adjacent tone levels, such as 3t (hereinafter referred to as If
Generally, the differences in the f-level pulse width (referred to as f-level pulse width) are at equal intervals, but in order to make the gradation display easier to see, the gradation increments are not at equal intervals, and the difference between the signal electrodes at the gradation level and selection period is changed. For example, at gradation level 1, the time period during which the voltage is applied is 1.2t between O1 gradation levels.

A method has also been proposed in which t and at are used for gradation level 5 and 5t is used for gradation level 4.

[Kokukoku to be solved by the invention] However, in the above-mentioned conventional technology, even if the difference in gradation pulse width is not equal to f9J in order to make the gradation display easier to see, for example, changes in temperature or transmission of the liquid crystal device When the scanning voltage value or the selection voltage value and the non-selection voltage value are changed to adjust the ratio, there is a problem that the gradation display becomes distorted ((().

The present invention is intended to solve these problems, and its purpose is to prevent the appearance of gradation display from deteriorating due to the above-mentioned reasons, and to provide gradation display that is always easy to see.

[Means for Solving the Problems] A method for driving a liquid crystal device of the present invention includes sandwiching a liquid crystal 1Δ between a substrate having a scanning electrode and a substrate having a signal electrode, and
The gradation display of the liquid crystal device in which display pixels are formed in the overlapped part of the scanning electrode and the signal electrode is performed in row 5 Lz', and the scanning voltage is sequentially applied to the scanning electrode, and the display existing at the intersection of the signal electrode and the scanning electrode is A neutral voltage is applied to the signal electrode so that the effective voltage of the composite waveform of the signal voltage waveform applied to the signal electrode in the pixel and the scanning voltage waveform applied to the scanning utility pole becomes an effective voltage corresponding to the gradation level of the display pixel. In a liquid crystal device driving method in which the potential of a signal voltage waveform is changed between a selection voltage and a non-selection voltage while a scanning voltage is applied, the time during which the selection voltage is applied to the signal electrode at each gray level and the non-selection voltage are A special feature characterized in that the ratio of the time during which the selection voltage is applied is changed in accordance with changes in the scanning voltage value, the selection voltage value and the non-selection voltage value. In the case of n-gradation display, if the transmittance of the liquid crystal device at gradation level n is T(n), then T (n) - T (n-1) = T (n-1)
-T (n-2) = ... = T (2) - T (1). Therefore, in order to adjust the temperature change and the transmittance of the C night device, the scanning voltage value or selection voltage value and If a driving method is used in which the difference in the pulse width of the gradation changes accordingly even when the non-selection voltage value is changed, 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) FIG. 1 is a diagram showing the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in this example.

This liquid crystal device has a bias ratio of 1 s, 1/200
auty, when driven with 70μ formula for one selection period, 20
The effective voltage at which the contrast ratio is maximum at °C is Von=2
．． 200V, Voff=2.0'52V. Also, at this time, the effective 11 pressure value at each gradation level is 8 ULI 1. i! In case of display, V(8)=2.200v(=Von) V(i2)=2189V V(6)=2.178v ■(5)=2,167v V(4)=2.155V V(5) "2.157v V(2)=2.114V V(1)"ZO52V(=Voff).

Also, when Von=2.180v, the effective voltage value of each floor and 14 levels where the gradation display is most visible is V (8) ”
Z 180 V (=V on )V(7)=2
．． 172v V(6) = 2.1 t53y V(5)"2.153v V(4)=2.14i v V(5)"2.126v V(2)=2.103v V(1)=:2 .033v (=Voff) Also, V o
When n, = 2.220 V, the effective voltage value of each gradation level where the gradation display is most visible is V(8) = 2.22
0v (Von) V (7) = 2.206 V V (6) = 2.194v V (5) = 2.182 V V (4): = 2.169 v V (5) = 2゜156v V ( 2):2.151V V(1)=2.070v(=voff) Also, Von=
The effective voltage value of each gradation level where the gradation display is most legible at 2°240v is V(8)=2.240v(=Von
) V(7)=2.250v ■(6)=2.216v V(5)=2.204v V(4)=2-192v V(5)=, 2.1 64v V(2)=2. 141 v V(1)=2.039v(=Voff)Here, ΔV(
n, )=(V(n) V(1))/(V(8)-V(
1)), ΔV(7) to ΔV(1) at each temperature
When Von=2°180v, the +A coefficient is as follows: ΔV (7) = 94.7S% ΔV (6) = 8E12% ΔV (5) = 8+, 3% ΔV (4) = 73.5% ΔV ( a) = 63.0% ΔV (2) = 47.6% When V on = 2.200 v, ΔV (7)
=92.6% ΔV (6) = 85. i% ΔV (5) = 77.7% ΔV(4) = 6a2% Δ'li' (3) = 57.4% ΔV(2) = 41.9% When VOn=2°220v, ΔV( 7)=9 (17% Δv (6)=82.7% ΔV(5)=74.6% ΔV(4)=6 6.0% ΔV(3)=55..3% Δv(2)= 4 [lL7% When Von=2.240v, ΔV(7)=93.4% ΔV (6) = 8 4.1% ΔV(5)=76.2% ΔV(4)=6a2% ΔV ( 3) = 4 9.7%ΔV (2
) = 3 4.4% Based on this value, the gradation pulse width was determined by dividing Won in steps of α1v and dividing one selection period into 64. The gradation pulse width at each gradation level (at gradation level n) The gradation pulse width of t(
n)) is Won when one selection period is 64t.
(At 2,185v, t(7) = 61t t(6) = 56t t (5) = 5 2 t t(4) = 47t t (5) = 4 0 t t (2) = 5 0 t 2. 185v≦Won (at 2,195v, t (7>
=6 0 t t(6)=55t t(5)=51t t(4)=45t t(3)=38t t(2)=27t L195v≦Van (at 2,205v, t(7)=59
t t (6) = 54t t (5) = 5 0 t t (a ) a44 t t (5) = 37t t (2) = 27t 2.205v≦Van (at 2,215v, t(7) = 5
9t t(6) = 54t t(5) =, a 9 t t (4) = 4 5t t(3) = 36t t (2) = 2 6 t 2-215v≦Won (t(7 at 2,225v) )=5
8t t(6)=53t t(5)=48t t(4)=42 t t(3)”5 5 t t(2):26t 2.225 v≦Won (at 2,255v, t(7)=
59t t(6)=5 4 t t(5)=48t t(4)"43t t(3)=54t t(2)=24t 2-235v≦Von, t(7)=-5Ot t(d) =54t t(5)=49t t(4)=44t t(3)=5 2 t t(2)=2 2 t .

Here, for each condition, t(8)=64t, t(1)=Ot
It is.

Figure 2 is a schematic diagram of the circuit for realizing this embodiment;
Figures <a> to ()) are diagrams showing clock signals, waveforms that determine the gradation pulse width, and signal voltage waveforms.

In FIG. 2, 1 is a voltmeter, and its output is input to ROM2. On the other hand, the clock signal is sent to counter 4 in Figure 2.
(Figure 3
)) and sent as ROMK. In the ROM, a signal waveform (sixth
Figure (b)) is created. This waveform is a pulse waveform that rises at the beginning of the selection period and when the signal waveform of each gray level L/bevel changes from the selection voltage to the non-selection voltage. Ro 1
The waveform output from A is sent to a gradation driver C via a friso-soflop circuit 5. Gradation driver I
At O, a voltage waveform applied to the signal electrode is output in accordance with the gradation level of the pixel. FIG. 3 <C> shows gradation level 1. 6th
Figure (d) shows gradation level 2. Figure 6 (g) is tone level 5
．． FIG. 6(f) shows gradation level 4. Figure 3 (y) is at gradation level 5.2g Figure 3 (A) is at gradation level 6, Figure 6 (i)
shows the voltage waveform applied to the signal electrode at gradation level 7, and FIG. 6() shows the voltage waveform applied to the signal electrode at gradation level 8. The voltage waveform applied to the signal electrode at gradation levels 2 to 7 is selected'1
The timing at which the voltage changes from the voltage to the non-selection voltage is at the same time as the rise of the pulse of the signal waveform (FIG. 3 (b)) that determines the gradation pulse width.

In the conventional gradation method, even if the gradation pulse width is determined so that the gradation display is most easily seen at Von = 2.220V, the V
When the value of On changes, the relationship between effective voltage and transmittance changes as shown in Figure 1, so even if V o n =
When V on = 2.240 V, it was difficult to distinguish between MFJ4 levels 6 and above, and when V on = 2.180 V, it was difficult to distinguish between gradation levels 6 and below. but,
In this example, by setting the gradation pulse width according to the TonO value, a gradation display that was always easy to see even when the vOn value changed (Example 2) In the above Example 1, the VanO value We set the gradation pulse width by focusing on VOn, but we also focused on temperature as well as VOn.
It is more effective to set the pulse width of the gradation depending on the relationship between the temperature and the temperature.

Further, FIG. 4 is a schematic diagram of a circuit for realizing this embodiment.

In the figure, the output of the voltmeter 1 is input to the ROM 2, and at the same time, the output of the temperature sensor 5 is also input to the ROM via the A/D*F) 456. On the other hand, as in the first embodiment, the clock signal is input to the counter 4 in FIG.
The waveform is converted into four divided waveforms and sent to the ROM. The ROM creates a signal waveform that determines the gradation pulse width from the signal sent from the counter, the signal sent from the voltmeter, and the signal sent from the A/D converter. The waveform output from the ROM passes through the flip-flop circuit 6 and is sent to B8.
The 6-gradation driver IC sent to the L'4 driver C outputs a voltage waveform to be applied to the signal electrode according to the gradation level of the pixel.

When such a driving method is used, there is an advantage that a gradation display that is always easy to see regardless of the temperature and the value of VOn can be obtained.

(Example 3) In the above-mentioned Example 1, 8-gradation display was performed, but it has been recognized that the effects of the present invention can be obtained even in the case of 3 to 64 gradations. It goes without saying that the same effect is obtained when the gradation level exceeds 64 (obviously).

The increments of Yon are also set to [LOlv in Example 1 above, but this takes into account the characteristics of the liquid crystal used. For example, when using a liquid crystal with a large steepness, the increments are made small; It is also possible to make it larger.

[Effects of the Invention] As described above, the present invention is capable of determining the ratio of the time when a selected voltage is applied to the signal electrode at each gray scale level and the time during which a non-selected voltage is applied to the scanning voltage value and the three selection voltage values. By changing it in accordance with the change in the difference between the voltage values and the non-selection voltage values, it is possible to obtain an easy-to-read gradation display regardless of the temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in Example 1 of the present invention. FIG. 2 is a schematic diagram of a circuit for realizing Embodiment 1 of the present invention. FIGS. 5(α) to 5()) are diagrams showing the clock signal, the waveforms that determine the gradation pulse width, and the voltage waveforms applied to the signal electrodes. FIG. 4 is a schematic diagram of a circuit for realizing the second embodiment.
α) to <h> are diagrams showing a conventional method of driving a liquid crystal device. 1... Voltmeter 2 ROM 3...7 lip 70 knob 4...
・・・Counter 5・・・・・・Temperature sensor

Claims (1)

[Claims] When performing gradation display of 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 the overlapping portion of the scanning electrode and the signal electrode,
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. In the method for driving a liquid crystal device, the ratio of the time during which a selection voltage is applied to the signal electrode at each gray scale level and the time during which a non-selection voltage is applied is determined by varying the scanning voltage value, the selection voltage value and the non-selection voltage value. A method for driving a liquid crystal device characterized by changing the selected voltage value as the value changes.