JPS58179826A - Driving method of liquid crystal display - Google Patents

Abstract

PURPOSE:To prevent the variation in contrast, to increase the degree of multiplexing and to enable the display of medium contrast, by suppressing the fluctuation in the effective voltage of a liquid crystal layer. CONSTITUTION:A signal electrode signal SIGN has the same potential as the potential of a scanning electrode signal SCAN for the same time as a selection period before the selection period of each scanning electrode and the signal SIGN and a waveform V (Mn, N) of the voltage applied on picture elements are obtained with respect to the case (a) in which only the picture elements (M, N) turn on and all the picture elements on the same signal electrode are off, the case (b) in which only one picture element is alternately on and off, and the case (c) in which all the picture elements on the same electrode are on. Potentials LV1-LVN, LVC are formed by the resistance division having analog switches 111, 112 at both ends and the output of the switch 111 is the peak value VD of the driving voltage at ''0'' of 32Hz and the min. value GND at ''1''. The output of the switch 112 is reverse thereto. As a result, each potential is an alternating wave having 32Hz period and the fluctuation in the effective voltage of the liquid crystal layer is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a liquid crystal display device that uses an element having nonlinear characteristics. Refers to nonlinear elements, varistor elements, metal-insulator-metal (MlM) elements, diode elements, discharge tube elements, etc., which have nonlinear characteristics such as high resistance in the low voltage region and low resistance in the high voltage region. ◎ Figure 1 shows an example of the voltage-current characteristics.e Compared to ordinary liquid crystal displays, liquid crystal displays that have a nonlinear element on at least one side have extremely high multiplicity when performing multiplex drive. It is possible to increase the number to
, resistance (PLO) 2, nonlinear element isotsukuda 1 capacitance (C!M
L)3. Consists of equivalent resistance (Rap) 4 ・'BNL exhibits the nonlinear characteristics shown in Figure 1 ・Figure 3 shows multiplicity of 64 (1/64 duty ratio), 11
This is an example of a drive waveform for the voltage averaging method of the 5-bias method. Scan period. The scanning electrode 5 and the scanning electrode signal are called 80AN17, and the subscript indicates the selection order of the scanning electrode within the frame period.The signal electrode 6 and the signal electrical contact signal are called B, G, and the subscript is In the S-GN in Figure 3, which shows differentiation by position, the pixels (M, N) are out of light, and the pixels on the other 5 IGNs are non-lighting signals.
In synchronization with the y-th scanning electrode signal EIOANM, a selection potential is taken during a t scanning period, that is, a selection period of 80 ANM,
During the selection period of other scan electrodes, the non-selection potential is maintained.

At this time, the voltage V (M, N) applied to the pixel (M, N)
80ANM-8IGN.

The solid line in FIG. 4 shows the voltage waveform V)II- of the non-linear element and the liquid crystal layer when V(M, N) shown in FIG. 3 is applied to the non-linear element and the liquid crystal pixel in FIG. Voltage wave/shape vTJo
In addition, the broken line shows VNL, Vl, and O in the following case when non-linear coercive voltage is applied.V)11-
When enters the low resistance region, most of the driving voltage is applied to the liquid crystal layer, and the liquid crystal layer is charged.The time constant at this time is the second
From the equivalent circuit shown in the figure, the change in aVLo given by PLO+FINL, first, OLO and O
The voltage is divided by the capacitance due to NL, and then Bt
, assuming that the resistance change of the nonlinear element approaches the voltage divided by O and RNL between 0 and infinity,
The 51st kl (a) is schematically shown.

If the resistance of the 0 nonlinear element shown in (b) is 0, a current of 1 flows transiently as shown in (a), charging the OLO. When entering the zero-order non-selection period in which all voltages are applied to the liquid crystal layer, most of the current 1 that becomes FHiL and flows transiently flows through the PLO as shown in (b). The approximate time constant is given by τ-(OIIa+0aL)xRr,a. Generally, the FtLO of the liquid crystal used in field-effect liquid crystal display devices is thick, and it is quite possible to set τ to about the scanning period. In the case of non-selection as shown by the broken line, ij and VNh do not go into the low resistance region even when they are at their peak, so the liquid crystal layer is not charged and VLO remains at a low voltage. As understood from M41J+, the effective value ratio of the non-selected VLO is larger than the simple voltage averaging method, and considering that the contrast of the liquid crystal display depends on the effective value, multiplex driving with a higher multiplicity is required. I hope it will be realized.

The purpose of the present invention is to provide a more complete multiplex driving method for a non-linear element liquid crystal display device. 6. Although non-linear element liquid crystal display devices are capable of increasing the display capacity, in multiplex driving using the conventional voltage average fhi method, the signal electrodes during non-selection periods are The signal causes a fluctuation in the effective voltage applied to the liquid crystal layer. Figure 6(a), (
b), (c), on the same signal line, (a) 1 pixel ON,
Other pixels are OFF.

(b) Alternately ON, 0IFF, ((RI[ii%0N(
The pixel applied voltage V (M, N) in the case of 7"1 winter is shown by the broken line, and the voltage VLa applied to the liquid crystal layer is shown by the solid line. vr.

Letting the effective voltages of Ka, Eb, and Kc be clearly Ka)
It can be seen that Eb>Ec. This means that it is affected by the ON and OFF states of other pixels on the same signal electrode. Therefore, in the conventional method, the minimum value of the ON effective voltage is set larger than the saturation voltage of the liquid crystal, and the OFF effective voltage is The maximum value of the voltage must be smaller than the threshold voltage of the liquid crystal.Of course, the characteristics of the nonlinear element are also strictly required, and when displaying halftones with an intermediate effective voltage, is more susceptible to the influence of other pixels.This invention solves the drawbacks of this invention.It suppresses fluctuations in effective voltage, prevents variations in contrast, increases multiplicity, and enables intermediate VT4 display. Next, according to an embodiment, suppression of fluctuations in effective voltage according to the present invention will be described. Figure 7 is an example of the drive waveform of the present invention - the same as the example of the voltage averaging method described above. (1/64 duty, 115 bias wave) - Unlike the normal voltage averaging method, a time is set before or after the selection time of each scan to make the potential applied to the scan electrode and the signal electrode the same value. In one embodiment, before the selection time of each scan electrode, the same time as the selection time is set as the equivalent time. Compared to this, the selection time of the scan electrodes is relatively halved, and the signal electrode signal represented by -8IGN, which is apparently equal to every other scan electrode signal with a duty of 17128, is selected before the selection period of each scan electrode. For the same time as the period, the potential is the same as that of the scanning electrode signal - As a result, if only the pixels (M, N) are ON and all other pixels on the same signal electrode are OFF (a), - for each pixel Turn on alternately.

In the case of OFF (b), all pixels on the same signal electrode are ON
In case (c), as shown in Fig. 7, the signal electrode signal S/GN and the pixel applied voltage waveform V (M, N) are obtained. In Fig. 8, V (M, N) shown by the broken line is applied. The voltage waveforms applied to the liquid crystal layer during the cold state are shown as solid lines in the same order as in Figure 7.Comparing this with the case of the normal voltage average fP method shown in Figure 6, It can be seen that the VLO waveforms in Figure 8 depict mutually equal discharge waveforms, if minute fluctuations are ignored - thus, the present invention suppresses fluctuations in the effective voltage of the liquid crystal layer. In other words, there is almost no difference in effective value between the VLO ON waveform and OFF waveform, and the multiplicity can be increased n! ! There are 64 examples and 31 [
Multiplex driving with a multiplicity of 128 is substantially similar to multiplex driving with a multiplicity of 128, but in the case of a non-linear element liquid crystal display device, the capacitance of the liquid crystal layer can be increased by setting a sufficient value within the scanning electrode selection period. There is no problem as long as it is the time when cLa is charged. - Halftone display using the conventional voltage averaging method is generally performed as follows.Each l1i of one signal electrode signal
6gA1 subdivides the scan electrode selection period corresponding to the FII element and changes the duty ratio within the selection period.For example, if you want to display 16 gray levels, the duty ratio will change in 16 ways.Other scans The duty ratio of the electrode is
Since it takes a long time for the effective value to change within one frame period, a voltage with an effective value corresponding to the gradation is applied to each pixel. However, the selection potential and non-selection potential are If you try to display a halftone with the middle potential of the other scanning electrodes, the selection of the middle value of the other scanning electrodes will affect the change in the effective value within one frame period, and the independence of each pixel will cause the selection of the halftone to be impossible. Expressed as deceased. In non-linear element liquid crystal display devices, the above-mentioned situation is completely different. Next, we will discuss halftone control in the present invention.
The figure shows an example of a driving waveform for displaying halftones according to the present invention. This is also based on the aforementioned driving method of the 1164 duty, i15 bias method. The signal electrode signal is applied to each scanning electrode selection period. Setting the intermediate potential between the selection potential and the non-selection potential, 18 gradations are set in 11, and there are 6 intermediate potentials, the 1st floor is completely OFF and the 8th floor is completely ON. Pixel (M, N
) is the 61st Sli tone (a), the second and fifth tone are repeated, (M@N) is the second tone (b), and all pixels are the fourth tone ( Regarding c), the signal electrode signal S/GN and the pixel applied voltage waveform (M, N) shown in FIG. 9 are obtained.

Figure 10 shows the voltage waveform applied to the liquid crystal layer when V (M, N) is applied, which is shown as a broken line, and the solid line shows the waveform of the voltage applied to the liquid crystal layer when V (M, N) is applied. If ignored, it can be seen that the discharge waveform is drawn according to the gradation. The changes in the waveform that appear at o V (M, N) and due to the influence of the communicating pixels are all due to the high resistance region of the nonlinear element, VLO is no longer affected. - The method of displaying halftones by changing the duty ratio, which is used in the normal voltage averaging method, is inappropriate for non-linear elements. The reason is that the length of the scanning electrode selection period does not have much effect on the charging of the liquid crystal layer (3LO) within a certain time constant, but it becomes difficult to control because it forces the charging of the liquid crystal layer (3LO). Although it is not impossible to set the time selection period, it is not preferable in that case because minute variations in the time constant have a large influence.

Next, the process of forming the drive waveform according to the embodiment of the present invention 1liKW!
□ This is the simplest example of the configuration using commercially available MOEI/Engine 9, etc., and other configurations are of course possible.

The explanation will be divided into Figs. 12 and 15, but it is assumed that the signal named So-and-so Fitz is a nine fundamental rectangular wave with a frequency indicated by a numerical value, and all of them have the same falling timing. , Fig. 11 is a power supply circuit for a drive circle, in which the potentials LVI, LVs, .''-, LV are determined by resistor division with analog switches 111 and 112 at both ends.
s, LvN, LV (forms 3.Analog switch - Commercially available PcA/CD4053 etc. can be used. -The output of the analog switch 111 is 32Hz9''O1
1 is the peak value of the drive voltage VD, and 1' is the lowest value G.
The output of the ND toru one analog switch 112 is the opposite. As a result, each potential is an alternating current turtle with a period of 32 Hz. LVO is the selection potential of the scanning electrode signal, and the LVM LV is the selection potential, and LV is the complete selection potential of the signal connection, and LV is the complete non-selection potential.
, ~L V v is the intermediate torso selection potential, and the example of the resistance value in Figure 0 assumes a 115 bias, 2, and equal intervals between the intermediate tone potentials, and other values are also possible. . In some cases, the halftone potentials may be set at staggered intervals.

FIG. 12 shows the scanning electrode signal S CA N s ~80 A
A deco-'+1'-121ij is a circuit for forming the Nas, and is composed of a 6-bit to 64-bit decoder 121 and an analog switch 122.It can be created using five commercially available CD4514s and an inverter circuit, and the analog switch 1
22 commercially available CD4055s can be created with 22 pieces. The input signal of the decoder is 2048Hz, 10
24Hz, 512Hz.

256Hz, 128Hz, 64Hz, and the inhibit input is 4094Hz - As a result, the output Ss ~ 5
Pulses of saK width m12e are output in sequence with a period of 64 Hz with the same time interval. These outputs are input as control signals 01 to Oa4 of the analog switch 122. Analog inputs LVM and LVO are selected [and the analog Outputs 01 to 0-4 - These are the scan W CAN, ~8 C! A N @4.

Figure 13 shows the circuit for forming the signal electrode signals 8IG1 to 8IG64 - The number of scanning electrodes and the number of signal electrodes are the same, but since the explanation is at the beginning, you can increase the number of signal electrodes 5et-t to 4 ◎Aralog switch 131, data output time 1 @
132, latch clock circuit 135.64 latch circuits 154.64 multiplexers from 135! l
131 commercially available analog switches 4053
can be created with three pieces, and analog human power L V l-L 'i
m, analog human power LVM, and f4096Tlz to output a power supply of 8mk with the same potential time as the scanning electrode signal.・Data output port-152 is not specified.・This is a ROM that stores image information.The recirculating circuit is a RAM. The self-clock circuit 135 may be a circuit or a circuit that digitizes and outputs a television video signal.The self-clock circuit 135 is a circuit that forms a clock signal that is launched in the latch circuit 164 in synchronization with the output content of the data output port W. , data output circuit 16
2. Latch times i'! '15
4ii City Q) a D It can be created with 4042, and one 3-bit output corresponds to each signal electrode.The content changes and outputs according to the selection time of the scanning electrode. The multiplexer 155 can be made with a commercially available CD4051 and has a length of 11J, and connects 8 types of analog inputs to the control signal C1.

This is an analog switch that selects and outputs one type according to a, , and c. As a result, each output becomes BNG'i ~
5IG64 With the circuit configuration described above, it is possible to drive a non-linear element liquid crystal display device with stable halftone display. Of course, this is just one example configuration, and it goes without saying that other configurations are also possible.According to the present invention, a non-linear element liquid crystal display device that can sufficiently control the contrast can be configured, so that television images can be 1-/

[Brief explanation of drawings]

Fig. 1 shows the V-1 characteristic of a typical non-linear element. Fig. 2 shows the valence circuit of a non-linear element liquid crystal display device. FIG. 3 shows driving waveforms of a liquid crystal display device using the conventional voltage averaging method.4 rgJ shows operating waveforms of a non-linear element liquid crystal display device. Figure 5 schematically shows the operating concept of a non-linear element liquid crystal display device - (1) when the non-linear element is turned on, (b) when it is turned off - Figure 6 shows the case when the non-linear element is turned off. The pixel applied voltage waveform of the liquid crystal display device is shown by a broken line, and the liquid crystal layer applied waveform is shown by a solid line. FIG. 7 shows the driving waveform according to the present invention. FIG. 8 shows the voltage waveform applied to the liquid crystal layer when the waveform in FIG. 7 is applied. FIG. 9 shows the voltage waveform applied to the liquid crystal layer when the waveform in FIG. 10 shows the voltage waveform applied to the liquid crystal layer when the waveform of FIG. 9 is applied. 12th
FIG. 13 shows the circuit configuration for forming the drive waveform in the implementation. ～Lunch 135～Multiplexer- Applicant: Reiwa Sayakosha Co., Ltd. Patent attorney: Muhitsu Mogami 2nd No. 4-(L3
(Ib>'-1" 11-7 (c >r-' (α) "-B Lj [b>"-: 111! (C) “-: 120th

Claims (1)

[Claims] 1. In the multiplex drive of a liquid crystal display device, each signal is processed by a normal voltage averaging method. At the intermediate potential between the selection potential and the non-selection potential,
A method for driving a liquid crystal display device characterized by setting a potential for a selected time of each scanning electrode and performing halftone display. 2. An element having nonlinear characteristics on at least one substrate that causes *vL of a liquid crystal display body. In a multiplex drive of a liquid crystal display device, a time is set before or after the selection time of each scanning electrode to make the potential applied to the scanning electrode and the signal electrode the same value. Display device driving method/