JPS61223793A - Driving of liquid crystal matrix display panel - 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 (Field of Industrial Application) The present invention relates to a method for driving a liquid crystal matrix display panel that can realize large-scale display with low power consumption and good contrast.

(Prior Art) Conventionally, in dot matrix display liquid crystal panels, twisted matic liquid crystals (hereinafter abbreviated as TN liquid crystals) have been widely driven by a voltage averaging method.

The voltage averaging method is based on the premise that the electro-optical properties of the TN liquid crystal depend on the effective value of the applied voltage, and that an alternating current voltage is applied to the liquid crystal, and that picture elements are applied during the half-selection period and the non-selection period. Under the restriction that the applied voltages are averaged, the ratio of the effective value voltages applied to the lit picture elements and the non-lit picture elements is maximized.

A driving method using the voltage averaging method will be explained. As shown in FIG. 3, the scanning electrodes 31 are line-sequentially selected at regular intervals, and a selection voltage is applied to the signal electrode 33 corresponding to the lit picture element 32 existing on one selected scanning electrode, and the selected voltage is applied to the non-lit picture element 32. By applying a non-selection voltage to each of the signal electrodes 33 corresponding to the signal electrodes 34, a difference is made between the voltages applied to the lit picture elements and the non-lit picture elements.

Scanning voltages and signal voltages during selection and non-selection periods in the voltage averaging method are shown in FIGS. 7(a) and 7(b). here,
R1 and R3 are scanning voltages during the selection period, R2 and R4 are scanning voltages during the non-selection period, CI and C3 are signal voltages during the selection period, and C2 and C4 are signal voltages during the non-selection period. All waveforms are square waves.

In the above driving method, when a=JN+l (N is the number of scanning electrodes), lit and non-lit picture elements are taken, and at this time, the highest display contrast is obtained.

(Special Publication No. 57-57718: P, M, ALT, P
, PLESHKO, IEEEETRANS ELECT
RON DEVICES, Vol, ED-21, Nn
2. Feb.

(Problem to be solved by the invention) According to our experiments, when the effective value of the voltage applied to the liquid crystal display panel is kept constant and its frequency is increased, the brightness of the liquid crystal display panel changes and The display brightness is close to that of the hour. The changes were significant above a few kilohertz. An example is shown in FIG. If the dielectric constant of the liquid crystal decreases as the frequency of the applied voltage increases, the above phenomenon will occur by itself, but it was confirmed that the liquid crystal used in the measurement was constant in the measurement frequency range.

Therefore, the electrical circuit characteristics of the liquid crystal display panel are considered to be the cause of the above phenomenon. FIG. 5 shows an equivalent circuit corresponding to a picture element portion of a liquid crystal display panel. When a voltage of V is applied across the picture element, the effective value voltage 9 applied to the liquid crystal layer is expressed as follows. Here, CL and RL are the capacitance 51 and resistance 52 of the liquid crystal layer, Ro is the series resistance 53 such as electrode resistance or alignment film, and ω=2πf, f is the frequency of the applied voltage.

From equation (1), as the frequency becomes higher, the effective value voltage (4) applied to the liquid crystal layer decreases. That is, the display brightness of the picture element approaches the brightness in the absence of an electric field.

By the way, in the voltage averaging method, the frequency corresponding to the selection period becomes several kilohertz when the number of scanning electrodes is about 100. Furthermore, since it is a rectangular wave, the contribution of harmonic components cannot be ignored. Therefore, as mentioned earlier, in actual liquid crystal display panels, voltage attenuation is large at high frequencies, so
The voltage averaging method in which the drive waveform includes harmonic components has the problem of voltage attenuation, which is disadvantageous in terms of power consumption.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method for driving a liquid crystal matrix display panel that can display a large-scale display with low power consumption and good contrast.

(Means for Solving the Problems) In order to solve the above problems, the method for driving the liquid crystal matrix display panel of the present invention uses variables as shown in the first table to represent the peak value of the voltage in each state. For example, Vira(t)=V'ct(t)=l:VaSinωt
(+ when i == 2, - when i == 2).

(Function) As described above, the present invention converts the drive waveform into a sine wave, thereby lowering the frequency compared to the drive waveform in the voltage averaging method using a rectangular wave.

Despite the electrical circuit nature of the liquid crystal display panel, which has a large attenuation of voltage at high frequencies (several kilohertz or higher),
The voltage applied to the liquid crystal layer will hardly be attenuated. This is an advantageous condition when considering power consumption.

Further, the maximum value of the effective value ratio of the voltage applied to the ON picture element and the OFF picture element according to this driving method and the scanning voltage value are the same as those of the voltage averaging method.

Duty 1/128. Fourier analysis of the voltage applied to the picture element when a = J128+1 was performed.

FIG. 6(a) shows the case of the voltage averaging method, and FIG. 6(b) shows the case of the driving method of the present invention. Obviously, the waveform of the driving method of the present invention has a lower frequency.

(Example) A method for driving a liquid crystal matrix display panel according to an example of the present invention will be described based on FIGS. 1 and 2.

FIG. 1 shows a first embodiment of the present invention. This shows a method of driving a liquid crystal matrix display panel. In the figure, 1 is a scanning electrode, and 2 is a signal electrode. The driving method is to sequentially select the scanning electrodes.

By applying a selection voltage to the signal electrode corresponding to the lit picture element 11 existing on the selected scan electrode, and applying a non-selection voltage to the signal electrode corresponding to the non-lit picture element 12,
Contrast is created by applying different voltages to lit and non-lit pixels. At this time, the voltage to be applied shall follow the relationship shown in FIG.

As described above, according to this embodiment, by making the drive waveform sinusoidal, the frequency of the waveform can be lowered, and voltage attenuation can be kept small.

In the above embodiment, AC voltage was applied to the liquid crystal by selecting all scanning electrodes twice line-sequentially, but as shown in FIGS. 2 and 9, AC voltage was applied to the liquid crystal within one selection period. The applied voltage may be changed to alternating current.

(Effects of the Invention) According to the present invention, by using a sine wave as the driving waveform and lowering the frequency of the waveform, the electric circuit property of the liquid crystal display panel is such that attenuation is large for voltages at high frequencies (several kilohertz or more). This has the effect of being able to apply an unattenuated voltage to each picture element without being affected by this.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention. A diagram explaining the operation of the driving method for a liquid crystal matrix display panel, FIG. 2 is a diagram explaining the operation of the driving method in the second embodiment of the present invention, and FIG. 3 is a diagram explaining the operation of the driving method of the conventional driving method. Figure 4 is a diagram explaining the operation of the method, and shows the brightness of the liquid crystal display panel (
Fig. 5 is an equivalent electric circuit diagram corresponding to a liquid crystal display panel, Fig. 6(a) is a diagram showing the frequency dependence (of applied voltage),
(b) is a diagram showing the Fourier amplitude of the drive voltage waveform, (a) is a diagram showing the conventional method (voltage averaging method), (
b) is a diagram corresponding to the driving method of the present invention, FIG. 7(a),
(b) is a diagram showing voltage waveforms, signal waveforms, and voltage waveforms applied to the liquid crystal in the voltage averaging method, and FIG. 8 is a diagram showing the scanning voltage, signal voltage, and voltage waveform applied to the liquid crystal in the first embodiment of the present invention. FIG. 9 is a diagram showing the scanning voltage, signal voltage, and voltage waveform applied to the liquid crystal in the second embodiment of the present invention. 1, 21.31... scanning electrode, 2, 22.33...
・Signal electrode, 11, 23, 32... lighting picture element,
12, 24, 34... Non-lighting picture element, 51... Electric capacity of liquid crystal layer, 52... Electric resistance of liquid crystal layer, 53...
・Electrode resistance. Patent Applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 1-11 ± Volume Electrode 2-11 Signal Electrical 11- Point Massage Element 12--1 non-A, it#, turtle! ! 2 Figure 3 Figure 4 Wavenumber (Hz) 5m Figure 6 (a) (b) 0m jK Number (Hz) 30720 7th ci
](a) (1)! Pressure average [Ken-no-den-dan] 1 Sugi Hosei/Signal wave post-tube 7
Figure (b) (2) Snow upper pL shape 8 where En is added to the liquid crystal Figure (2) Ti wave shape diagram where one force 0 is applied to the liquid crystal

Claims (3)

[Claims] (1) N scanning electrode groups aligned in one direction are formed on one of the opposing surfaces of a pair of substrates, M signal electrode groups are formed on the other side in a direction orthogonal to the said direction, and the substrate N having a liquid crystal layer therebetween and comprising a power supply circuit for driving both electrode groups.
In a liquid crystal matrix display panel with rows and M columns, when selecting the peak value of the voltage to be applied to the scanning electrode during a certain period τ, V
^i_r_a(t) (where i = 1, 2), when not selected, it is set to V^i_r_n(t), and when the peak value of the voltage applied to the signal electrode during the period is selected, it is set to V^i_c_s(t).
), when not selected, V^i_c_n(t), and the amplitude of the voltage applied to the lit picture element during the period is V_0Sin(
ωt) (here, 0≦t≦τ, ω=π/τ), and the subscript i is the voltage defined by 1 during the period (first period) until the scanning electrodes selected line-sequentially complete one cycle. Then, during the period (second period) until the selection of the scan electrode goes through one cycle, a voltage defined by the subscript i of 2 is applied, and the two periods are alternately repeated, The peak value of each voltage is V^i_r_a(t)=V^i_c_s(t)±V_0
SinωtV^i_r_n(t)=V^i_c_s(t
)±(V_0/a)SinωtV^i_c_n(t)=
V^i_c_s(t)±(2V_0/a) Sinωt(
A method for driving a liquid crystal matrix display panel, characterized in that a is a real number and the sign is + when i=1 and - when i=2. (2) A method for driving a liquid crystal matrix display panel according to claim (1), characterized in that a is set to a value near √N+1. (3) |V^1_c_s-V^2_c_s|=V_0S
The method for driving a liquid crystal matrix display panel according to claim 1, wherein inωt is set.