JPH0713130A - Driving method of ferroelectric liquid crystal panel - Google Patents

Abstract

PURPOSE:To make a uniform display even on the ferroelectric liquid crystal display panel which is large area by impressing a selection voltage and a nonselection voltage which satisfy specific conditions. CONSTITUTION:The ferroelectric liquid crystal panel 31, where matrix electrodes are arranged, has scanning lines 33 and data lines 33 wired crossing each other, and ferroelectric liquid crystal is arranged between the scanning lines 32 and data lines 33 at respective intersections. The nonselection voltage Vor/N is impressed to unselected pixels while the selection voltage Vor satisfying a relation Vsat<maVon<(N/(N-2))Vthmi is impressed to selected pixels, where Vsat<ma> is the maximum value among saturation voltages at the respective positions of the ferroelectric liquid crystal panel 31 and Vthmi is the minimum value of a threshold voltage. Thus, the driving voltage and a bias ratio N are properly selected to make a high-contrast display even on a liquid crystal panel which has a distribution of threshold characteristics, so that the uniform display can be made even on the large-area ferroelectric liquid crystal panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method for a ferroelectric liquid crystal panel, and more particularly to a driving method for providing an optimized driving voltage and bias ratio.

[0002]

2. Description of the Related Art Conventionally, the use of a liquid crystal element having bistability has been disclosed by both Clark and Lagerwall in JP-A-56-10.
7216, U.S. Pat. No. 4,367,924, and the like. Bistable liquid crystals are generally chiral smectic C phase (SmC *) or H phase (Sm
A ferroelectric liquid crystal having H *) is used, and in these states, one of a first optical stable state and a second optical stable state in response to an applied electric field, and an electric field It is expected to be widely used in the field of high-speed and memory-type display devices, which has the property of maintaining its state when no voltage is applied, that is, bistability, and has a quick response to changes in the electric field.

On the other hand, many methods for driving a liquid crystal element using such a ferroelectric liquid crystal have been proposed, for example, JP-A-60-31121 and JP-A-62-2.
Japanese Patent No. 78539 discloses driving conditions that give an optimum bias ratio. In particular, JP-A-62-278
Japanese Laid-Open Patent Publication No. 539 discloses a method of setting a bias value that allows matrix driving and gives the maximum contrast based on the relationship between the threshold characteristic of the liquid crystal element and the driving pulse.

[0004]

By the way, the above-mentioned driving method is premised on that the entire liquid crystal element is uniform and the threshold characteristics are also uniform. However, there are problems that the image quality cannot be displayed on the entire screen or the display is nonuniform in the above driving method.

Therefore, an object of the present invention is to provide a driving method for a ferroelectric liquid crystal panel, which solves the above-mentioned problems by driving by applying an optimized driving voltage and bias ratio. .

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is provided between a matrix electrode including a plurality of scanning electrodes and a plurality of information electrodes, and the scanning electrodes and the information electrodes. In a ferroelectric liquid crystal panel provided with a disposed ferroelectric liquid crystal, the maximum value of the saturation voltage at each position of the ferroelectric liquid crystal panel is Vsat ^ma, and the minimum value of the threshold voltage is Vth ^mi . If Vsat ^ma <Vop <
A selection voltage Vop satisfying the relationship of {N / (N-2)} Vth ^mi is applied to the selected pixel, and a non-selection voltage Vop / N.
Is applied to non-selected pixels.

In this case, the selection voltage Vop is Vop = V
sat ^ma + δVop (where 0 <δVop <Vth ^mi ), and the bias ratio N is {(N−2) / N} <Vth ^mi /
It is characterized in that it is a maximum value of two significant figures satisfying the relation of Vop.

[0008]

When the selection voltage Vop and the non-selection voltage Vop / N satisfying the above conditions are applied on the basis of the above structure, uniform display is possible even with a large area ferroelectric liquid crystal panel.

[0009]

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

First, the structure of a ferroelectric liquid crystal panel in which matrix electrodes are arranged will be described with reference to FIG.

In this ferroelectric liquid crystal panel 31, scanning lines 32, ... And data lines 33, ... Are arranged so as to intersect with each other, and the scanning lines 32 and data lines 33 at each intersection.
Ferroelectric liquid crystal is arranged between and. Further, reference numeral 34 in the drawing denotes a scanning circuit, reference numeral 35 denotes a scanning side drive voltage generation circuit, reference numeral 36 denotes a signal side drive voltage generation circuit, reference numeral 37 denotes a line memory, and reference numeral 38 denotes a shift register. Respectively.

Next, the waveform applied when the panel is driven will be described with reference to FIG.

A waveform S _{S in} FIG. 2A shows a selective scanning waveform applied to a selected scanning line, and a waveform S _N is a non-selective scanning waveform applied to an unselected scanning line, Further, the waveform I _S represents the selection information waveform (black) applied to the selected data line, and the waveform I _N represents the non-selection information signal (white) applied to the unselected data line. Further, the waveform (I _S -S _S ) and the waveform (I _N -S _S ) indicate voltage waveforms applied to the pixels on the selected scanning line, and of these waveforms (I _S -S _S ). The pixel to which is applied has a black display state, and the pixel to which the waveform (I _N -S _S ) is applied has a white display state. further,
In these waveforms, symbols P1, P2, and P3 indicate a selection pulse, a half-selection pulse, and a non-selection pulse, respectively. In the following description, P1 = V _S + V _I = Vop P2 = V _S −V _I = Let V _H P3 = V _I. On the other hand, when the bias ratio is N, Vop = NV _I ... (1) Therefore, when the voltage value V _H of the half-selected pulse is expressed by this bias ratio N, V _H = {(N−2) / N} Vop (2) Furthermore, FIG. 2B shows a time-series waveform when the display shown in FIG. 3 is performed with the drive waveform shown in FIG.

Next, the relationship between these values and the electro-optical characteristics of the ferroelectric liquid crystal panel will be described with reference to FIG. FIG. 1 shows threshold characteristics at two points described later in the FLC panel shown in FIG. In this figure, the horizontal axis represents the applied voltage and corresponds to the above-mentioned Vop, and the vertical axis represents the transmittance for each voltage value on an arbitrary scale. The waveform applied when measuring this characteristic can be a bipolar pulse or the composite waveform (I ₂ -S ₁ ) shown in FIG. 2B, and the pulse width matches the pulse width of the drive waveform. I am letting you.

This characteristic generally varies depending on the temperature distribution in the cell, the cell thickness distribution, etc., but in FIG. 1, the characteristic curve at the point where the threshold characteristic is on the low voltage side in the cell is B, and the characteristic curve is the highest. A characteristic curve at a portion on the voltage side is A, threshold voltages in each curve are Vth ^mi and Vth ^ma , and saturation voltages are Vsat ^mi and Vsat ^ma . In order to display a normal image on the entire panel having such a distribution of threshold characteristics (that is, to enable matrix driving), the voltage value Vop of the selection pulse and the half-selection pulse described above are used. It is necessary to impose the following driving conditions on the voltage value V _H of

That is, Vop ≧ Vsat ^ma (3) V _H ≦ Vth ^mi (4) From equations (4) and (2), Vop ≦ {N / (N−2)} Vth ^mi ... (5) From equations (5) and (3), Vsat ^ma ≤ Vop ≤ {N / (N-2)} Vth ^mi (6) The threshold characteristics of the panel, the selection voltage and the bias are calculated by the equation (6). A ratio relationship is established.

Next, the setting of the selection voltage and the bias ratio will be described. Here, as a matter of course, it is desirable that the selection voltage be low and that the bias ratio be large. That is, if the bias ratio is large, the non-selection voltage value becomes smaller than that in the equation (1), the response of the liquid crystal molecules at the time of non-selection becomes small, and the contrast becomes high as a result. From the above, it is possible to set each voltage value as follows, for example.

Vop = Vsat ^ma , _VH = Vth ^mi (7) The setting by the equation (7) is certainly the condition that the drive can be performed with the highest contrast, but it is not suitable for the actual drive of the panel. That is, the entire panel is practically driven under the extreme conditions such as the equation (7) due to the temperature change of the entire panel, the minute voltage fluctuation of the IC circuit, the deformation of the pulse due to the wiring resistance and the like. Is extremely difficult. From the above, in the present invention, the selection voltage Vop can be set as follows.

Vop = Vsat ^ma + δVop (8) where 0 <δVop <Vth ^mi, where δVop in the equation (8) is set by the size and temperature of the panel. Further, the bias ratio N is in the range of {(N-2) / N} <Vth ^mi / Vop (9) from the equation (5) with respect to Vop determined by the equation (8). It is a condition for being able to do it. As described above, it is desirable that N be as large as possible in order to increase the contrast. Therefore, the maximum value of N that satisfies the expression (9) can be set, but N is not always
Does not have to be an integer. However, even if N is set to a value that is too small, the change in display characteristics is small, so
It is appropriate that the number of significant digits is characteristically about 2 significant digits. The inventor conducted a driving experiment by the method described below in order to confirm the effect of the present embodiment.

The cell structure 100 used in this experiment is shown in FIG.
2, a pair of substrates 101, 101 made of a glass plate, a plastic plate, or the like is provided, and a spacer 104 is interposed between these substrates.
Are held at predetermined intervals. Further, an adhesive 106 is applied around the substrate gap, and these substrates 10
1, 101 are bonded together, and the pair of substrates 101,
Sealing 101. Further, on the substrate 101, an electrode group (for example, a scanning voltage applying electrode group of a matrix electrode structure) including a plurality of transparent electrodes 102 is formed in a predetermined pattern such as a strip pattern. Further, an electrode group (for example, a signal voltage applying electrode group in the matrix electrode structure) including a plurality of transparent electrodes 102 'intersecting the transparent electrode 102 is formed on one substrate 101'. . Although not shown, either one of the transparent electrodes 102 and 102 'may be provided with an orientation control film or a protection film for preventing anti-shatter. Then, the phenylpyrimidine-based liquid crystal composition was injected into the cell structure assembled in this manner to prepare a liquid crystal display panel having a screen size of about A4 size. The phase transition process of this liquid crystal composition is as follows.

[0021]

[Outer 1] In this experiment, the threshold characteristics of the pixel A and the pixel B shown in FIG. 4 corresponded to the characteristic curves A and B in FIG. 1, respectively. That is, it is the pixel B that has the lowest threshold characteristic in the panel and the pixel A that has the highest threshold characteristic in the panel. To detect such a difference in the threshold characteristic in the panel, For example, it can be detected by gradually increasing the voltage value of the drive pulse and applying it to all the pixels, and by examining the pixel in which a predetermined image display is performed first and the pixel in which the predetermined image display is performed last.

Specifically, when positive and negative symmetrical bipolar pulses having a pulse width of 50 μs were used to obtain the threshold values and saturation values corresponding to FIG. 1 at room temperature, Vth ^mi = 13 respectively.
V, Vsat ^mi = 14V, Vth ^ma = 16V, Vsat ^ma = 1
It was 7V. Further, the selection voltage Vop is δVop = 5V (<
As Vth ^mi ), Vop = 22V. At this time, the right side of the equation (9) becomes Vth ^mi /Vop=0.59, and the maximum bias ratio N satisfying the equation (9) is N = 4.
It becomes 8.

The liquid crystal panel described above is driven by using the drive waveform shown in FIG. 2 with a drive voltage Vop = 22V and a bias ratio N = 4.
When driven as No. 8, a good image could be displayed.

[0024]

As described above, according to the present invention,
By selecting the drive voltage and bias ratio properly,
It is possible to perform high-contrast display even on a liquid crystal panel having a distribution of threshold characteristics. Further, even a large-area ferroelectric liquid crystal panel enables uniform display.

[Brief description of drawings]

FIG. 1 is a diagram showing threshold characteristics at two points in the panel shown in FIG.

FIG. 2 is a waveform diagram showing a waveform of a driving voltage used in the driving method according to the present invention.

FIG. 3 is a diagram showing a structure of a ferroelectric liquid crystal panel in which matrix electrodes are arranged.

FIG. 4 is a detailed view of FIG.

[Explanation of symbols]

 31 Ferroelectric Liquid Crystal Panel 32 Scanning Electrode (Scanning Line) 33 Information Electrode (Data Line) 101 Ferroelectric Liquid Crystal Panel (Cell Structure) 102 Scanning Electrode (Transparent Electrode) 102 'Information Electrode (Transparent Electrode) A, B Pixel Vop selection voltage N bias ratio

Claims (2)

[Claims] 1. A ferroelectric liquid crystal panel comprising: a matrix electrode composed of a plurality of scanning electrodes and a plurality of information electrodes; and a ferroelectric liquid crystal arranged between the scanning electrodes and the information electrodes. , Vsat ^ma <Vop <{N / (N-2)} Vth ^mi , where Vsat ^ma is the maximum value of the saturation voltage at each position of the ferroelectric liquid crystal panel and Vth ^mi is the minimum value of the threshold voltage. A method for driving a ferroelectric liquid crystal panel, characterized in that a selection voltage Vop satisfying the following relationship is applied to the selected pixel and a non-selection voltage Vop / N is applied to the non-selected pixel. 2. The selection voltage Vop is Vop = Vsat ^ma + δVop (where 0 <δVop <
Vth ^mi ), and the bias ratio N is a maximum value of two significant digits satisfying the relationship of {(N-2) / N} <Vth ^mi / Vop. Driving method for ferroelectric liquid crystal panel.