JPS63212921A - Method for driving liquid crystal display device - Google Patents

Abstract

PURPOSE:To decrease the number of pulses as a whole by applying 1st-3rd voltages to liquid crystal cells in 1st-3rd periods and commonly using plural scanning electrodes in the 1st period. CONSTITUTION:For example, the 1st voltage V1 is commonly applied to the liquid crystal cells (a)-(c) belonging to a scanning electrode group in the 1st period t1 so that the liquid crystal cells (a)-(c) are maintained in a bright state. The scanning electrodes are sequentially selected in the 2nd period t2 and the 2nd voltage V2 is applied to the cells according to display information so that the bright state is changed to a dark state or the bright state is maintained. The 3rd voltage V3 is applied to the cells to negate the DC voltage component in the next 3rd period t3. The ensuing scanning electrode groups are thereafter selected and the above-mentioned operations are repeated. For example, the voltages shown by Va, Vb, Vc are applied to the liquid crystal cells (a), (b), (c) and are applied as the voltages of +V thereto to change the state to the bright state, then the 2nd voltages are applied thereto to maintain the bright state or to change the same to the dark state; thereafter, the 3rd voltages are applied to negate the DC voltage components. The number of pulses is, therefore, decreased and the electric power consumption is reduced.

Description

[Detailed Description of the Invention] [Summary] In a liquid crystal cell of a liquid crystal display device using ferroelectric liquid crystal, a first
applying first to third voltages according to the third to third periods;
By using the first period in common for a plurality of scan electrodes, the overall time is even shorter than the driving method in which three types of voltages are sequentially applied to one scan electrode within one scan period. It is designed to be able to drive the display.

(Industrial Application Field) The present invention relates to a method for driving a liquid crystal display device that can drive a liquid crystal display device using ferroelectric liquid crystal at high speed.

Chiral smectic C liquid crystal exhibits ferroelectricity, and constitutes a liquid crystal display device in which it is oriented in a direction parallel to the surface of a glass substrate through appropriate alignment treatment, and when a positive or negative voltage is applied, it becomes parallel to the surface. If it is oriented in another direction and a voltage of opposite polarity is applied, it will return to its original state. Therefore,
By sandwiching the polarizer between two polarizers, changes in molecular orientation can be converted into changes in optical properties, providing a bright and dark display function. A liquid crystal display device using this ferroelectric liquid crystal is
Since it has a memory function, it is possible to obtain a constant contrast that does not depend on the number of scanning lines, and it is possible to increase the capacity of the display screen.

[Prior Art] A liquid crystal display device using ferroelectric liquid crystal is also shown in, for example, US Pat. No. 4,367,924. In such a liquid crystal display device, as shown in FIG.
Scanning electrodes Y, , Y2 and data electrodes x, , x2 are arranged facing each other at right angles, and a ferroelectric liquid crystal is interposed between them,
When displaying liquid crystal cells a, b, c, and d at the intersections of these, with liquid crystal cells a and d in a dark state and liquid crystal cells b and c in a bright state, conventionally, the driving method shown in FIG. 6 has been used. was.

In FIG. 6, vx, , vx2 are data electrodes XI+X
The voltages applied to 2, VY, vyz are the scanning electrodes Y, , Y
The voltages applied to 2, Va and Vb indicate the voltages applied to liquid crystal cells a and b, and 2 is a voltage higher than the dark value voltage that changes the liquid crystal cell to a bright or dark state.

For example, as shown in Figure 7, the voltage transmittance characteristic of a liquid crystal cell is such that by applying a positive voltage higher than the dark value voltage mentioned above, the transmittance increases and becomes a bright state, and a negative polarity voltage It has a hysteresis characteristic in which the transmittance decreases and a dark state occurs by applying .

In addition, in the display explanatory diagram of FIG. 5, since it is a 2×2 matrix display device, ■frame F is 2 scanning periods TI
, T2. Also, each scanning period TI, T2
are divided into t1 to t4, respectively.

In the scan period T1, the scan electrode Y is selected, and writing is performed on the liquid crystal cell a on the scan electrode YI to be in the dark state using the first period t1 and the second period t2, and the liquid crystal cell a is in the dark state. Writing is performed on the liquid crystal cell b to be set using the third period t3 and the fourth period t4. That is, in the first period t1, Ov,
Non-selected scan electrode Y2 has 3/4V, data electrode X has V,
A voltage of 1/2 V is applied to the data electrode
2 to 1/4■, data electrode X, to OV, data electrode X2
Apply 1/2v to .

As a result, liquid crystal cell a has vx, -vy.

A voltage of =Va is applied, +■ is applied during the first period t1 to change the state to a bright state, and then a voltage of 1 is applied during the second period t2 to change the state to a dark state. Also, VX in liquid crystal cell b
A voltage of z-VY,=Vb is applied, a voltage of +1/2v is applied in the first period t1, and a voltage of -1/2v is applied in the second period t2.
A voltage of 2V is applied, and since both are below the dark value voltage, the previous state is maintained.

In period t3 of writing 3, the selected scanning electrode Y.

■, 1/4■ to non-selected scan electrode Y2, data electrode Xl
1/2 V and OV are applied to the data electrode X2, and in the fourth period t4, 0V is applied to the selected scan electrode Y1, 3/4V is applied to the non-selected scan electrode Y2, and 1/2V is applied to the data electrode X. , a voltage of V is applied to the data electrode x2. As a result, a voltage of 1 1/2 ■ is applied to liquid crystal cell a during the third period t3 and +1/2 ■ during the fourth period t4, and the previous state is maintained, and to liquid crystal cell b, In the third period t3, a voltage of -■ is applied to change the state to a dark state, and in the next fourth period t4, a voltage of +■ is applied.
voltage is applied to change the state to bright.

In the next scanning period T2, the liquid crystal cell C is written in a bright state and the liquid crystal cell d is written in a dark state, and the relationship between the applied voltages is as follows.
This is opposite to the case of the scanning period T1, and as a result, the liquid crystal cells a and b have ±1/
A voltage of 4V is applied to maintain the previous state, 1■ is applied to the liquid crystal cell C during the third period t3, and +■ is applied during the fourth period t4 to bring the liquid crystal cell C into a bright state. +V is applied to d during the first period t1, and -V is applied during the second period t2.
V is applied to create a dark state.

As described above, writing in the dark state is performed during the first and second periods tl and t2, and during the third and fourth periods t3. At t4, bright state writing is performed, and the first and second periods t
1. The positive and negative voltages at t2 are equal, and the third and fourth
period t3. The applied voltage is selected so that the positive and negative voltages at t4 are equal, and the DC voltage component is canceled out.

Note that the polarity of the voltage for switching between the bright and dark states of the liquid crystal cell can be reversed to that described above.

The conventional example described above is a method of driving by dividing the l scanning period into four, but we have previously proposed a method of driving by dividing one scanning period into three. FIG. 8 is an explanatory diagram of this driving method, in which the same reference numerals as in FIG. 6 indicate the same parts, and in the first period t1, Ov is applied to the selected scanning electrode YI, and 3/4V is applied to the non-selected scanning electrode Y2. , a voltage of V1 is applied to the data electrode X, and a voltage of V is applied to the data electrode X2.
In the second period t2, a voltage of V is applied to the selected scan electrode Y1, a voltage of 1/4V is applied to the non-selected scan electrode Y2, a voltage of OV is applied to the data electrode X, and a voltage of 1/2V is applied to the data electrode X2. t
3, V is applied to the selected scan electrode Y1, and V is applied to the non-selected scan electrode Y.
2 to V, data electrode XI to V, data electrode X2 to 1/2
■Apply the voltage.

Therefore, a voltage of +V is applied to the liquid crystal cell a (see FIG. 5) during the first period t1, as shown by Va, to bring it into a bright state, and a voltage of 1 is applied during the next second period t2. is applied and becomes a dark state. Also, in liquid crystal cell b, as shown by vb,
A voltage of +V is applied during the first period t1, resulting in a bright state, and during the second and third periods t2. A voltage of 1/2 V is applied at t3 to maintain the bright state. That is, the first period t
After writing a bright state to 1, it is determined in the second period t2 whether to maintain the bright state or change to the dark state, and in the third period t3, a voltage is applied to cancel the DC voltage component. It is applied.

[Problem that the invention seeks to solve]

In the conventional driving method shown in FIG. 6, one scanning period is divided into four parts, so the response speed of the liquid crystal is equal to or higher than one-fourth of one scanning period. This is required. Furthermore, the liquid crystal panel is equivalent to a matrix circuit consisting of the resistance R of the scanning electrode and the data electrode, and the capacitance C of the liquid crystal cell. Therefore, as the number of pulses in one scanning period increases, that is, the frequency increases. If it becomes higher, the power consumption due to charging and discharging the capacitance C will increase.

On the other hand, since the driving method shown in FIG. 8 divides one scanning period into three, the response speed of the liquid crystal is 3/4 of that shown in FIG. This is a good thing; if the response speed is the same, high-speed scanning becomes possible, making it easy to increase the size. Furthermore, since the number of pulses in one scanning period is three, the frequency can be lowered, thereby reducing power consumption.

However, this is not sufficient to meet the demands for larger display devices and lower power consumption, and the present invention aims to further reduce the overall number of pulses.

[Means for solving problems]

The method for driving a liquid crystal display device of the present invention basically divides one scanning period into three, and scans are performed for a plurality of scanning electrodes, and will be explained with reference to FIG.

It has a plurality of scan electrodes and data electrodes arranged orthogonally with a ferroelectric liquid crystal in between, and by sequentially selecting the scan electrodes and applying a data voltage according to display information to the data electrodes, the scan electrodes and the data In a method of driving a liquid crystal display device that selects and displays a liquid crystal cell between an electrode, a first voltage v1 (
or -V1) is applied; a second period t2 is during which a second voltage Vz (or -v2) is applied to put the liquid crystal cell in a dark state (or bright state); A third period t3 during which a third voltage (3) is applied to cancel the DC voltage component is set within one scanning period T, a plurality of scanning electrodes are grouped, and the scanning electrode groups are sequentially selected; For the liquid crystal cell belonging to the selected scanning electrode group,
The first voltage V+ (or -V
1) is applied in common, then the scan electrodes in the scan electrode group are sequentially selected, and the liquid crystal cells belonging to the selected scan electrodes are subjected to the second and third periods t2. Second and third voltage vz at t3, V3 (or -v2.V3)
is applied.

[Effect]

A plurality of scan electrodes are grouped, and a first voltage V+ in a first period t1 is applied to a liquid crystal cell belonging to the scan electrode group.
(or -V1) is applied in common, and the liquid crystal cells belonging to that scanning electrode group are temporarily changed to the bright state (or dark state H),
In the next second period t2, the scan electrodes in the scan electrode group are sequentially selected and the second voltage Vz is applied according to the display information.
(or -Vz) to change the bright state (or dark state) to dark state B (or bright state), or apply a voltage below the dark value voltage to change the bright state (or dark state B). In the next third period t3, a third voltage V3 (or -V3) for canceling the DC voltage component is applied to reduce the DC voltage component applied to the liquid crystal cell belonging to the selected scan electrode. After canceling out, the next scanning electrode is selected and the second and third periods t2. When the second and third voltages are applied at t3 and the sequential selection of scan electrodes in the scan electrode group is completed,
The next scanning electrode group is selected and the above operation is repeated.

Therefore, the voltages shown as Va, Vb, and Vc are applied to the liquid crystal cells a, b, and c, and the liquid crystal cells belonging to the selected scan electrode group are temporarily changed to the bright state by the voltages of 10 and 10. A second voltage is applied to a selected scan electrode in the scan electrode group to control whether to maintain a bright state or change to a dark state, and then a DC voltage component is applied to the selected scan electrode. A voltage is applied to cancel the

As a result, if the number of scanning electrodes is N and the number of scanning electrodes in a scanning electrode group is n, then the number of pulses in one frame is (2n
+1)N/n. On the other hand, in a method in which one scanning period is simply divided into three and driven, the number of pulses in one frame is 3N, so for example, as shown in the figure, n
=3, the number of pulses within one frame can be reduced to 7/9.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, and the liquid crystal panel 1 includes a glass substrate on which scanning electrodes Y, to Ym are formed,
A glass substrate on which data electrodes X+-Xn are formed are placed facing each other with a ferroelectric liquid crystal interposed therebetween, and a -
h indicates a liquid crystal cell.

The drive circuit 2 is supplied with voltages YVa-YVd from the power supply circuit 4, and is manually supplied with a clock signal YCLK, scanning data YDATA, and period signal VFR as control signals, and applies pulse voltages to the scanning electrodes Y, to Ym. It is something to do. Further, the drive circuit 3 receives the voltage XVa-XV from the power supply circuit 5.
d is applied, and a clock signal XCLK,
The display data XDATA and the period signal XFR are input, and a data voltage corresponding to the display data XDATA for one scanning line is applied to the data electrodes X+''Xn.

FIG. 3 is an explanatory diagram of the operation of the embodiment of the present invention, and shows a case where two scanning electrodes are grouped in a 2×4 matrix type liquid crystal display device. In the same figure, ite, VX,, vx2
is the voltage applied to the data electrodes x, , x2, VY, ~■Y
4 is the voltage applied to the electrode Y, ~Y4, V a −y V
d indicates the voltage applied to liquid crystal cells a to d. Also■
is the voltage above the threshold voltage for changing the state of the liquid crystal cell,
F is one frame period, Tl and T2 are scanning periods, tl is the first period, t21. t22 is the second period, t31. t3
2 indicates the third period.

In the scan period TI, scan electrodes Y, Y2 become a selected scan electrode group, scan electrodes Y 3 + Y 4 become a non-select scan electrode group, and in the next scan period T2, scan electrodes Y l r
Y2 is a non-selected scan electrode group, and scan electrodes Y3+Y4 are a selected scan electrode group. In the first period t of the scanning period T1, the data electrodes x, , x2 are set to V, and the scanning electrodes Y1 . A voltage of 0 is applied to Y2, and a voltage of V is applied to scan electrodes Y3+Y4 of the non-selected scan electrode group. As a result, a voltage of +V is commonly applied to the liquid crystal cells a, b, c, and d belonging to the selected scanning electrode group, and the liquid crystal cells are changed to a bright state. At this time, liquid crystal cell e belonging to the non-selected scanning electrode group,
f.

The voltages applied to g and h are 0.

In the next period t21, data electrode XI is set to 0, data electrode
2 to 1/2v, scanning electrode Y1 to v1 scanning electrode Y2 to Y4
A voltage of 1/4v is applied to each. Thereby,
A voltage of -V is applied to the liquid crystal cell a belonging to the selected scan electrode Y, changing from a bright state to a dark state, and a voltage of 11/2 V is applied to the liquid crystal cell b.

A voltage of 1/4 V is applied to the liquid crystal cell c, and a voltage of +1/4 V is applied to the liquid crystal cell d, and since each voltage is below the threshold voltage, the previous state is maintained.

In the next period t31, V is applied to data electrode XI, and data electrode
2 to 1/2V, scanning electrode Y IL V s゛ scanning electrode Y
Apply a voltage of 3/4v to 2 to Y4. Thereby,
0 for liquid crystal cell a belonging to selected scan electrode Y1, liquid crystal cell b
A voltage of 1/2v is applied to the first period t1 and the second period t1.
The voltage difference between the voltages applied during period t21 and t21 is applied, and the DC voltage component is canceled out. Further, a voltage of 1/4 V is applied to the liquid crystal cell C, and a voltage of +1/4 V is applied to the liquid crystal cell d.

In the next period t22, data electrode X has 1/2V, data electrode X2 has 0, scan electrode YI has 1/4V, scan electrode Y2
A voltage of V and a voltage of Y 3 + Y 4L 1 /4v is applied to the scanning electrode. As a result, a voltage of 11/2 V and 1 volt are applied to the liquid crystal cell C and the liquid crystal cell d belonging to the selected scan electrode Y2, respectively, and the liquid crystal cell d is changed to a dark state. Further, a voltage of +1/4 V and -1/4 V are applied to liquid crystal cell a and liquid crystal cell b belonging to non-selected scan electrode YI, and the previous state is maintained.

In the last period t32 of the scanning period Tl, 1/2V is applied to the data electrode XI, v is applied to the data electrode x2, and 3/4 is applied to the scanning electrode Y.
V, scan electrode Y2, V, scan electrode Y3. 3/4v to Y4
Apply a voltage of As a result, voltages of -1/4V, +1/4V, -1/2V, and O are applied to the liquid crystal cells a to d during periods t1, t21. t31. A voltage is applied to cancel the DC voltage component of the voltage applied at t22.

In the next scanning period T2, the scanning electrodes Y3 and Y4 become the selected scanning electrode group, and in the first period tl, the liquid crystal cell e+
+V is applied to f+g*h to bring it into a bright state, and in the next period t21, a voltage of 1 is applied to liquid crystal cell e belonging to the selected scan electrode Y3 to change it to a dark state, and liquid crystal cells r,
G and h maintain their previous states, and in the next period t31 a voltage is applied to cancel the DC voltage component of liquid crystal cells e and f, and in the next period t22, a voltage is applied to liquid crystal cell h belonging to the selected scan electrode Y4. 1) is applied to change the dark state to the liquid crystal cell e.

f and g maintain their previous states, and in the next period t32, a voltage is applied to cancel the DC voltage component of liquid crystal cells g and h.

During this scanning period T2, a voltage of +1/4V is applied to the liquid crystal cell aNd belonging to the non-selected scanning electrode group, and the previous state is maintained.

FIG. 4 is an explanatory diagram of control signals and power supply voltage, and
, XD2 is the display data XDATA, YD input to the drive circuit 3 (see FIG. 2), -YD4 is the scanning data YDATA input to the drive circuit 2, X V a −X V d is the power supply voltage applied from the power supply circuit 5 to the drive circuit 3, and Y
V a −Y V d indicates the power supply voltage applied from the power supply circuit 4 to the drive circuit 2, and each of them corresponds to the scanning period T in FIG.
l period t1. t21, t31. t22. An example of a waveform at t32 is shown. Note that the period signal VFR input to the drive circuit 2 is 1'' for each scanning period Tl and T2 in FIG. 3, although not shown.

It can be switched to "0".

In the first period t1, scanning data YDI, YD2
is 0'', scanning data YD3.YD.

is “1”, power supply voltage YVa is V, power supply voltage yvb~YV
d is O, and the scan electrode Yl is connected from the drive circuit 2.

O1 scanning electrode Y3. A voltage of V is applied to Y and Y, respectively. In addition, the display data XD, , XD2 are "1-", and the power supply voltage XVa is v1, and the power supply voltages XVb and XVc are 1/
2) The power supply voltage XVd is 0 and the period signal XFR is "1", so that the data electrodes XI+X from the drive circuit 3
A voltage of ■ is applied to 2. Therefore, as described above, the +■ voltage is commonly applied to the liquid crystal cells belonging to the selected scanning electrode group, and the bright state (or dark state B) is changed.

In the next period t21, the scanning data YD.

only is "1" and the others are 0, display data XD is "1", display data XD2 is 0'', period signal XFR
is “0”, power supply voltage YVa is ■, YVb-YVd is 1/
4V, and a voltage of 1.5V is applied to change the liquid crystal cell a in FIG. 2 to a dark state, and voltages below the dark value are applied to the other liquid crystal cells.

In the next period t31, the scanning data YD.

~YD41 and display data XD, , XD2 are for period t
21, the period signal XFR becomes "1". Also, the power supply voltage YVb-YVd is switched to 3/4 . Therefore, as shown at VY2 to VY4 in FIG. 3, a voltage of 3/4v is output.

Similarly, a voltage is applied from the drive circuit 2.3 to the scanning electrodes and the data electrodes to perform display according to the display information.

The above embodiment shows a case where two scan electrodes are grouped, but it is also possible to group more scan electrodes, and the data voltage and the scan voltage may be set as in the above embodiment. You can also select other waveforms.

〔Effect of the invention〕

As explained above, in the present invention, in the first period t1, after all the liquid crystal cells belonging to the scanning electrode group are brought into the gate-like state (or dark state) by the first voltage, the inside of the scanning electrode group is scan electrodes are selected in sequence, a second voltage is applied to determine whether or not to invert the state of the liquid crystal cell belonging to the selected scan electrode, and then a third voltage is applied to cancel the DC voltage component. For example, the number N of scanning electrodes is set to 400.
In the previously proposed method of driving by dividing one scanning period into three, the number of pulses of 3N-1200 is 1.
According to the present invention, when the number n of scanning electrodes in the scanning electrode group is 4, it is sufficient to apply 900 pulses within one frame, and the number of pulses is reduced to 75.
%. Therefore, it is possible to reduce power consumption, and it is also possible to reduce the response speed required of the ferroelectric liquid crystal. If the response speed of the ferroelectric liquid crystal is the same as the conventional one, it will be easy to increase the number of scanning electrodes and increase the size.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the operation of an embodiment of the present invention.
Fig. 4 is an explanatory diagram of control signals and power supply voltage, Fig. 5 is an explanatory diagram of the display, Fig. 6 is an explanatory diagram of the operation of the conventional example, Fig. 7 is a voltage transmittance characteristic curve diagram, and Fig. 8 is the previously proposed diagram. FIG. T is the scanning period, t1 to t3 are the first to third periods, V l
"" V3 is the first to third voltages, VaxVc is the applied voltage of the liquid crystal cells a"-c, l is the liquid crystal display panel, 2.
3 is a drive circuit, 4.5 is a power supply circuit, Y to Ym are scanning electrodes, X and -Xn are data electrodes, xcLK and YCLK are clock signals, XDATA is display data, and YDATA is scanning data.

Claims (1)

[Scope of Claims] A plurality of scan electrodes and data electrodes are arranged orthogonally with a ferroelectric liquid crystal in between, and the scan electrodes are sequentially selected and a data voltage is applied to the data electrodes in accordance with display information. In a method of driving a liquid crystal display device in which a liquid crystal cell between the scanning electrode and the data electrode is selectively displayed by applying a first voltage ( V
_1) (or -V_1) is applied (t1)
and a second period (t) in which a second voltage (V_2) (or -V_2) is applied to bring the liquid crystal cell into a dark state (or bright state).
2) and a third voltage (
A third period (t3) for applying V_3) is set within one scanning period (T), a group consisting of a plurality of scanning electrodes is sequentially selected, and the liquid crystal cells belonging to the scanning electrode group are A first voltage (V_1) (or -V_1) during a first period (t1) is commonly applied, scan electrodes in the scan electrode group are sequentially selected, and the liquid crystal belonging to the selected scan electrodes is The second and third voltages (for the cell) during the second and third periods (t2, t3) are applied to the cell.
A method for driving a liquid crystal display device, the method comprising applying V_2, V_3) (or -V_2, -V_3).