JPH0310216A - Method for driving liquid crystal device - Google Patents

Abstract

PURPOSE:To obtain an attractive gradational display by employing the driving method for the liquid crystal device which selects (m) out of (n) frames and setting (n) larger than 1.25Xthe total number of gradations. CONSTITUTION:The value of the driving method for the liquid crystal device which selects (m) out of (n) frames (n >= total number of gradations) so that an effective voltage applied to picture elements is an effective voltage corre sponding to the gradation level of display picture elements is set larger than 1.25Xthe total number of gradations. Namely, n>1.25Xthe number of gradations and the difference in the number of frames which are selected between adjacent gradation levels at a part where variation in transmissivity is small is set to >=2 to increase the difference in the effective voltage applied to picture elements. Consequently, display characteristics are prevented from decreasing and the attractive gradational display is obtained.

Description

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

[Conventional technology]

A conventional method for driving a liquid crystal device is shown in FIGS. 3(a) to 3(g).

In Fig. 3(g), x1, x2, and x3 are signal electrodes, respectively.
Yl, ¥2, and Y3 are respectively scan electrodes, intersections of the scan electrodes and signal electrodes, the hatched ones are selected pixels, the ones without diagonal lines are unselected pixels, VXI, VX2,
VX3 is the voltage waveform applied to each signal electrode, V
Yl, VY2, VY3 are voltage waveforms applied to the respective scanning electrodes, VO is the reference voltage, VO+VY is the scanning voltage,
VO-VY is a selection voltage.

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 VO. Among the pixels on the scanning electrode \1, the one at the intersection with the signal electrode Xi is the selected pixel, and the selection voltage vo-vx
are applied, x2, x30] Those at the intersection are non-selected pixels and the non-selected voltage Vo+x is applied. Since the difference between the voltage of the scanning electrode and the voltage of the signal electrode is applied to each pixel,
A voltage vy+vx is applied to the intersection between x2 and Yl and a voltage VY-VX is applied to the intersection between x2 and Yl and x3 and Yl. Also, at this time, the voltages of Y2 and ¥3 are Vo, so ¥2 and Y
VX or -Vx is applied to the pixel above 3.

In the next selection period, ¥2 is selected and the above operation is performed for Y2, and thereafter similar scanning is sequentially performed for each scanning electrode.

That is, vy+vx is applied to the selected pixel during the selection period, VY-VX is applied to the non-selected pixel, and -Vx is applied during the non-selection period.
Alternatively, x is applied, so the effective value of the voltage applied to the selected pixel becomes higher than the effective value of the non-selected pixel, and a display appears.

Furthermore, as a method for performing gradation display in such a driving method, for example, in the case of 8-gradation display, gradation level 3 is set based on C'7 frame (the larger the gradation level value, the more applied to the pixel. ), when performing k gradation display such that out of 7 frames, there are 2 selected frames and 5 non-selected frames, (k
-1) By mixing selected frames and non-selected frames within the frame as a reference, the value of the effective voltage applied to the pixel is changed to provide an intermediate display between selected and non-selected.

[Problems to be Solved by the Invention] FIG. 1 shows the relationship between the effective voltage value and the transmittance when a voltage is applied to a general liquid crystal device. As is clear from this, in the vicinity where the applied voltage exceeds the threshold (2, 1
The change in transmittance is small (near Vl-1), but after that the change becomes large (21~22■), and then becomes small again (2
2).

Therefore, in the prior art described above, when performing k-gradation display,
(k-1) Since gradation is performed using the frame as a reference, the difference in effective voltage applied to pixels between adjacent gradation levels is equal, and gradation is achieved in areas where the effective voltage is low and where the change in transmittance is small. This has the problem that it becomes difficult to distinguish the tone level or the tone level in a high part.

The present invention is intended to solve these problems, and its purpose is to prevent deterioration of display characteristics due to the above-mentioned reasons and provide a gradation display with good appearance.

[Means for Solving the Problems] A method for driving a liquid crystal device of the present invention includes sandwiching a liquid crystal layer between a substrate having a scanning electrode and a substrate having a signal electrode, and displaying a liquid crystal layer in a portion where the scanning electrode and the signal electrode overlap. When performing gradation display of a liquid crystal device that forms pixels, scanning voltages are sequentially applied to the scanning electrodes, and the signal voltage waveforms applied to the signal electrodes at the display pixels that exist at the intersections of the signal electrode and the scanning electrode Set m frames in n frames (n≧total number of gradations) to a selected state so that the effective voltage of the composite waveform of the scanning voltage waveforms applied to the scanning electrodes becomes an effective voltage corresponding to the gradation level of the display pixel. In the method for driving a liquid crystal device, the value of n is set to 1.25.
It is characterized in that X (total number of gradations)<n.

[Function] The condition under which the gradation display is most visible at -1Ki is 1'(k), where the transmittance of the liquid crystal device at the gradation level is T(k).
-T (k-1) =T (k-1) -
T (k2)=...=T (2) −"I' (
1). Therefore, the value of n mentioned above is set to n>1
．． '25 By increasing the voltage difference and determining the number of frames in the selected state at each gradation level so as to satisfy the above conditions, a good-looking gradation display can be obtained.

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

Example 1 FIG. 1 shows the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in this example. The twist angle of the liquid crystal is 230 degrees.
Polyimide is used as an alignment film, and its surface is rubbed with cotton to align liquid crystal molecules.

This liquid crystal device has a bias ratio of 13.1/200d u t
y, when driven with one selection period of 70 JLsec, the effective voltage at which the contrast l-ratio is maximum is Von = 2.2
00v, Voff=2.052v. Also, in this case, when the gradation display does not meet the condition for the easiest viewing and the effective voltage value at each gradation level is 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) = 2.114v V C], ) = 2 There is .052v (=Voff),
The difference in effective voltage between each gradation level is V (8) −V
(7) 20.01. ]VV (7)-V (6)=0.
011VV (6) V (5)20.01. lVV
(5)-V (4)=O,O]4VV (4)
−V (3)=0. O]6VV (3)-V
(2)=0. 023VV (2)-V (1,
)=0. It becomes 062V. Here, V (k) is the effective voltage at the quantum level. Based on this value, the number of frames n is set to 12, and the number of frames that become selected at each gradation level is m (8) = 12 m (7) = 11 m (6) = 10 m (5) = 9 m (4 )=8 m(3)=7 m(2)=5 m(]i=0. Here, m(k) is the number of frames in the selected state when the gradation level is 1.

Table 1 shows the transmittance at each gradation level when using the driving method of this embodiment and the transmittance at each gradation level when using the conventional driving method, with gradation level 8 being 100.

Table 1 As is clear from this, in the conventional driving method, the difference in transmittance between gradation levels 8 and 7 is 26.9, and the difference between total gradation levels 7 and 6 is 234; The difference in transmittance between levels 2 and 1 is as small as 16, and the difference between gradation levels 3 and 2 is as small as 42, so it is difficult to distinguish between gradations in areas where the gradation levels are small. However, in the driving method of this embodiment, the maximum value of the difference in transmittance was 70, and the minimum value was 95, with little variation, making it very easy to distinguish the difference in gradation.

Example 2 FIG. 2 does not show the relationship between the effective value of the applied voltage and the transmittance of the liquid crystal device used in this example. The rice angle of the liquid crystal is 260 degrees, and the liquid crystal molecules are oriented by obliquely depositing SiO.

Bias ratio of this liquid crystal device] 3.1. / 200du
When driving with ty, one selection period of 70 μsec, the effective voltage at which the contrast ratio is maximum is Von=, 2.27
0v, Voff=2.1] It was 7v. In addition, at this time, the effective voltage value at each gradation level that satisfies the condition that it is easy to see even when the LLI scale table is not displayed is V (8) = 2.270v (=Von) V (7) =
2.258v V (6) = 2.248v V (5) = 2.239v V (4) = 2.229v V (3) = 2.2]4v V (2) = 2.188v V (1) = 2. J-] 7v (=Voff), and the difference in effective voltage between each gradation level is V (8) -V
(7)=0.012VV (7)-V (6)=0.
0IOVV (6) −V (5)=0.009VV
(5) -V (4)' =0. 0 ] OVV (
4)-V (3)=0.015VV (3)-V (2
)=0.026VV (2)-V (1)=0.071
It becomes V. Based on this value, the number of frames n is set to 13, and the number of frames that become selected at each gradation level is m(8) = 1
The following settings were made: 3 m (7) = 12 m (6) = 11 m (5) = 10 m (4) = 9 m (3) = 8 m (2) = 6 m (1) = 0.

Table 2 shows the transmittance at each gradation level when the driving method of this embodiment is used and the transmittance at each gradation level when the conventional driving method is used, with gradation level 8 being ]00.

Table 2 As is clear from this table, the difference in transmittance between gradation levels 8 and 7 in the conventional driving method, t, -J, is 30. ]
, li The difference between total gradation levels 7 and 6 is 283, while the difference in transmittance between gradation levels 2 and 1 is 20, and the difference between gradation levels 3 and 2 is 29, which is small. Differences in gradation are difficult to discern in small areas.However, with the driving method of this embodiment, the maximum value of the difference in transmittance is 18.5, and the minimum value is 76.
1 2 , and the variation in gradation became much easier to distinguish.

Embodiment 3 Although in Examples 1 and 2 above, 8-gradation display is performed, it is recognized that the effect of the present invention is similar in the case of 3 to 6411 tone. Furthermore, it is obvious that the same effect can be obtained when the gradation level exceeds 64.

[Effects of the Invention] As described above, the present invention provides an effective voltage applied to a pixel during n frames (n≧total number of gradations) so that the effective voltage applied to the pixel becomes an effective voltage corresponding to the total gradation level of the display pixel. In a method for driving a liquid crystal device in which m frames are selected, the value of n is set to 1.
．． By setting 25X (total number of gradations) <n, it is possible to obtain an attractive gradation display.

FIG. 3 is a diagram showing the relationship between the effective value of applied voltage and transmittance.

FIGS. 3(a) to 3(g) are diagrams showing a conventional method for driving a liquid crystal device.

I”d

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. During n frames (n≧
In a method of driving a liquid crystal device in which m frames are selected (total number of gradations), the value of n above is set to 1.25 x (total number of gradations).
A method for driving a liquid crystal device, characterized in that <n.