JPH0279816A - Method for driving matrix type ferromagnetic liquid crystal panel - Google Patents

Abstract

PURPOSE:To suppress the reduction of contrast due to the array of signal waveforms and to improve the contrast by impressing a pair of positive and negative data pulses to a fixed potential to set up a 2nd stable state or impressing the fixed potential to hold a 1st stable state so as to turn on/off the signals. CONSTITUTION:A signal waveform to be impressed to a signal electrode 72 is turned on/off by impressing a pair of pulses having pulse width less than 1/2 of a selection period and having mutually symmetrical amplitude to a fixed potential in the case of setting up the 2nd stable state or setting up the fixed potential in the case of holding the 1st stable state. Even when the signal data are repeatedly turned on/off, the practical pulse width of a non-selection period is not duplicated. Consequently, the initial state written in the selection period can be effectively held during the period of the non-selection period, so that the display contrast can be improved.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for driving a matrix type liquid crystal panel using ferroelectric liquid crystal, and in particular to a method for driving a matrix type liquid crystal panel using a ferroelectric liquid crystal. Related to driving methods for liquid crystal panels.

[Conventional technology]

In recent years, matrix-type liquid crystal panels have become larger and denser, and in order to achieve even higher density, research is underway on matrix-type liquid crystal panels that utilize the memory properties, high-speed response, and wide viewing angle characteristics of ferroelectric liquid crystals. has been done. However, the operating principle of this ferroelectric liquid crystal panel differs from the voltage effective value drive of ordinary nematic liquid crystals, and is determined by the positive and negative polarity of the pulse, its voltage, application time, and whether or not a high-frequency voltage is applied. However, recently, a number of methods for driving ferroelectric liquid crystal panels have been proposed.

Driving methods for matrix type ferroelectric liquid crystal panels include a driving method with a slight modification of the conventional voltage averaging method, as disclosed in Japanese Patent Laid-Open No. 61-94026, and a driving method as disclosed in Japanese Patent Laid-Open No. 61-24672.
There is a driving method that utilizes the AC stabilization effect, as disclosed in Japanese Patent No. 1. The AC stabilization effect will be explained using FIG. 6.

FIG. 6 (bJ is an optical characteristic diagram when the driving waveform shown in FIG. 6 [a) is applied to a liquid crystal panel holding a ferroelectric liquid crystal having negative dielectric anisotropy. The applied waveform consists of a low frequency of several hundred Hz to several thousand Hz and a high frequency of several hundred Hz, and has an interval T.
1 and section T2, the low frequency phase is inverted. Section T
1 m and section T 2 m are only the low frequency of voltage VD,
In the section Tlb and the section T2b, a high frequency wave with one voltage 1 is superimposed on the low frequency wave.

The ferroelectric liquid crystal panel operates only at low frequencies due to the interaction P,.E between the spontaneous polarization P1 of the liquid crystal and the electrolyte E, and the direction of operation is determined by the positive or negative polarity of the pulse. Here, when a positive pulse is applied, the color is white, and when a negative pulse is applied, the color is black. Therefore, if the low frequency voltage VD is increased to some extent, the section T1. and section T2. The optical properties change from white to black and from black to white, respectively. The threshold voltage at this time is generally inversely proportional to the pulse width,
The wider the pulse width, the lower the value.

On the other hand, when a high frequency is applied to the extent that the liquid crystal molecules cannot respond, in a ferroelectric liquid crystal panel with negative dielectric anisotropy, the liquid crystal molecules move parallel to the substrate surface of the liquid crystal panel in proportion to the effective value of the high frequency voltage. If a force is generated that tends to become The voltage va c is made sufficiently thick (then, the previous state is maintained and the interval 'l'1b
In the interval T2b, black is retained, and in the interval T2b, white is retained. By utilizing this effect, even ferroelectric liquid crystal panels that do not have good bistability can achieve bistable properties, making it possible to create liquid crystal panels with high contrast.
This is called the stabilizing effect.

A method of matrix driving using this AC stabilizing effect is disclosed in Japanese Patent Laid-Open No. 61-246721. This driving method will be explained using FIGS. 5 and 7.

FIG. 7 is an explanatory diagram showing the structure of a matrix type ferroelectric liquid crystal panel, in which 71 is a scanning electrode group, 72 is a signal electrode group,
G21 and 031 are pixels used for explanation. In FIG. 5, S2 and 83 are voltage waveforms (hereinafter referred to as scanning waveforms) applied to the scanning electrodes in the second and third rows, respectively, and Dl
is the voltage waveform (hereinafter referred to as signal waveform) applied to the signal electrode of the first column, and G21 and G31 are the pixels G21 and G31, respectively.
This is the drive waveform applied to 31.

The scanning waveform consists of a selection period Ts and a non-selection period, and the selection period is a constant potential ■. is applied, and the non-selected section is fully AC
A high frequency of several hundred Hz is applied at a voltage Vat that provides a stabilizing effect. On the other hand, the signal waveform has potentials VO+V and Vo-V with a pulse width 1/2 of Ts. vo
It consists of one set of positive and negative low frequency pulses, and the pulse phases are reversed during on and off. By providing one positive and negative pair for vo, electrolysis of the liquid crystal due to residual DC components is prevented. Here, the pulse x applied to the pixel G21 is T
The first half of , is a black trap with a pulse of voltage -vD, and the second half is written in white with a pulse of voltage +v0.

Since high frequencies are superimposed in sections other than T8, the white state in the latter half of T8 is maintained.

In the pixel G31, on the other hand, the voltage in the latter half of T is written as black because it is -vD, and the sections other than TI also maintain black.

[Problem to be solved by the invention]

However, it is difficult to obtain a complete AC stabilizing effect due to the fact that the absolute value of the negative dielectric constant of the liquid crystal is not large enough or due to limitations on the driving voltage. However, if the number of scanning electrodes is large (if the non-selection period is long), the initial state of white or black cannot be maintained, and the display contrast will decrease.Especially, in the signal waveform,
When off-on-off is repeated, the pulse width of the signal waveform is effectively doubled, and the black-white reversal force is also almost doubled, which is greater than the force caused by the high-frequency voltage to make the liquid crystal parallel to the substrate. In other words, the initial state cannot be maintained and the display contrast sharply decreases. Therefore, display contrast unevenness occurs depending on how the signal waveforms are arranged.

An object of the present invention is to provide a driving method for a ferroelectric liquid crystal panel that utilizes the AC stabilization effect, which suppresses the reduction in contrast caused by the arrangement of signal waveforms, and provides high contrast and reduced display unevenness.

[Means to solve the problem]

The configuration of one frame of the scanning waveform according to the present invention includes a reset period in which a constant potential is brought into a first stable state by positive and negative sets of reset pulses, a selection period in which a constant potential is applied, and a high frequency of about Hz. The signal waveform consists of a non-selected period in which a voltage is applied, and the signal waveform is either applied with a set of positive and negative data pulses to a constant potential to achieve a second stable state, or to maintain the first stable state. Therefore, it is turned on and off by applying a constant potential.

Further, the scanning waveform is characterized in that when the N-th scanning electrode is in the selection period, one or more scanning electrodes such as the N+1-th line and the N+2-th line are in the reset period.

In addition, during the selection period of the scanning waveform, the period during which a constant potential is applied is set to 1/2 of the selection period, and the high-frequency voltage is applied during the remaining 1/2 period, and the reset pulse is converted to AC by multiple scans. It is also possible to do so. Here, alternating current means that the average voltage value of the positive and negative pulses is zero.

[Effect]

The signal waveform according to the present invention is turned on and off by applying a set of positive and negative data pulses to a constant potential, or by applying a constant potential, so that the signal data is turned on, off, on and off. Even if the drive is continuous, the actual pulse width in the non-selection period will not double as in the conventional driving method, so the initial state written in the selection period can be maintained well during the non-selection period. This improves display contrast.

If the signal data sequence is on and on continuously, the fifth
Although this is the same as the conventional method shown in the figure, this arrangement provides the best contrast in the conventional driving method, whereas in the present invention, on the contrary, the arrangement results in the lowest contrast. That is, even when the contrast is the lowest in the present invention, it is the highest in the conventional example. During continuous off-off, the signal waveform always has a constant potential,
This is the state with the best contrast, but there is little difference in contrast from the on-on arrangement, and display unevenness is also improved.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. The liquid crystal used in this example was a mixture of ester-based ferroelectric liquid crystals, had negative dielectric anisotropy, and was aligned by a rubbing method, with a distance between the substrates of about 2 μm.

FIG. 7 schematically shows the structure of a matrix type ferroelectric liquid crystal panel. 71 is a scanning electrode group;
2 is a group of signal electrodes, and a ferroelectric liquid crystal is sandwiched between them. Here, for simplicity, when displaying in binary, pixels indicated by diagonal lines are turned on (black) and other pixels are turned off (white).

1 to 4 show drive waveforms of the present invention. 1 to 3 are examples in which the number of scanning electrodes is eight (1/8 duty), and FIG. 4 is an example in which the number of scanning electrodes is four.

S2 is the voltage waveform applied to the scan electrode in the second row, S3 is the voltage waveform applied to the scan electrode in the third row, S4 is the voltage waveform applied to the scan electrode in the fourth row, and Dl is the voltage waveform applied to the scan electrode in the first row. This is the voltage waveform of the signal electrode to be applied. G21 is pixel G2
The waveform applied to pixel G31 is in the off state, and the waveform applied to pixel G31 is in the on state.

FIG. 1 shows a first embodiment of the present invention, which is a driving method when the reset pulse width is equal to the selection period Ts and the reset pulse is applied to two lines simultaneously. The scanning waveform has reset periods Tri and Tr2 during which a reset pulse of voltage v1 is applied.
, one selection period in which writing is performed, and a non-selection period other than these periods, in which a constant potential v0 is applied, and in the non-selection period, a high frequency voltage vacO is applied at about [lz]. The pulse in the reset period Tr1 is for DC component correction, and the pulse in Tr2 is effective for resetting.

The signal waveform consists of an on waveform and an off waveform, and the on waveform is T
, the voltage is the width divided into two. It consists of one set of positive and negative pulses with respect to Vo, which also prevents residual DC components. The off waveform is equal to the selection potential vo of the scanning electrode.

Then, when S2 is the selection period T, the scanning waveform is S3
and 84 are applied with a reset pulse at the same time. ■Reset pulse. The polarity of the pulse applied to the pixel during the reset period Tr2 and the polarity of the on-signal pulse applied in the latter half of the selection period T@ are opposite, with the positive and negative order of the on-signal pulses being the same as that of the on-signal pulses. It is as it should be.

Generally, the operating threshold voltage of a ferroelectric liquid crystal is inversely proportional to the applied pulse width, and is therefore expressed as the product of voltage and pulse width. Here, ■. The description will be made assuming that the value of X T a /2 is sufficient for on-off operation. Here, for simplicity, V, =2V.

Then, in the reset period, it is uncertain whether the signal waveform is on or off, but regardless of which one is applied, the positive reset pulse applied to the pixel in the second half reset period Tr2 is 4vI)×T- /2, and is always set to white, which is the off state. Next, since the pixel G21 is off and no pulse is applied to the pixel during the selection period T1, it holds the reset white color. On the other hand, since the pixel G31 is on, a pulse is applied at Ts, and since the negative data pulse in the latter half exceeds the operating threshold voltage at VDXTs/2, it is inverted to black.

During the non-selection period, high-frequency voltage is applied to both pixels, so even if the data pulse exceeds the operating threshold voltage, they cannot operate due to the AC stabilization effect and maintain the state set during the selection period. . In addition, even if the signal waveform repeats on-off-on-off, the voltage applied to the pixel during the off signal is O■, so the actual pulse width of the low frequency component does not change, depending on the signal waveform arrangement. The state set during the selection period can be stably maintained during the non-selection period.

In this way, both black and white can be set in one frame, no DC component remains, and a display with high contrast and little unevenness can be performed without being affected much by the arrangement of signal waveforms. Note that here, Vm = 2Vn
However, v1≧■.

That's fine. v, = vD = i ov, and T m =
At 1 ms, the frequency of the high-frequency voltage applied during the non-selection period is from 20 ) Glz to 50 KELz, and V, c =
Good display was obtained at 30 to 50V.

FIG. 2 shows a second embodiment of the present invention, and is an example of a driving waveform when the reset pulse width is halved in FIG. 1. Here again, if V, = 2VD, the pulse voltage in the second half reset period Tr2 changes depending on the signal waveform, and G21
Then, VD%G31 becomes 2vD, but both are ■. Since this is the case, it will be reset to white.

FIG. 3 shows a third embodiment of the present invention, in which a high frequency voltage similar to that in the non-selection period is applied to the first half of the selection period T- in FIG. 1 divided into two.

In G21, the AC stabilizing effect can also be obtained during the Ta period, which is preferable. Conversely, it is also possible to apply a high frequency in the latter half of the selection period Ts divided into two, but in that case, the polarity of the data pulse or the reset pulse must be reversed.

FIG. 4 shows a fourth embodiment of the present invention, in which the reset pulse during the reset period is set to a constant potential V in the first frame, which is the first scan. The drive waveform is positive for the second frame, and negative for the second frame, which is the second scan, when alternating current is applied between the two frames. The signal waveform is in the on-off state and the phase of the pulse is reversed in the first and second frames, but as in Fig. 1, it can be turned on and off in just one frame, and the DC component changes between two frames. None remain.

In all of the above embodiments, a reset pulse is applied to one or more scan electrodes such as the N+1st line when the Nth line scan electrode is in the selection period. If it is easy, there will be no need for the reset period and selection period to overlap, but since the data pulse width of the signal waveform will be reduced to less than T m / 4, it will be a problem to increase the voltage of the data pulse or double the time of one frame. Necessary and not very desirable.

〔Effect of the invention〕

By the driving method of the matrix-type ferroelectric liquid crystal panel of the present invention, the state of the pixel can be determined in one scan, and there is no residual DC component (no reduction in contrast due to differences in the arrangement of signal waveforms or display Because there is less unevenness, it is possible to display a large screen with high contrast and high image quality.

[Brief explanation of the drawing]

1, 2, 3, and 4 are waveform diagrams showing an example of the driving method of the present invention, FIG. 5 is a waveform diagram showing a conventional driving method, and FIG. , (b) is a driving waveform diagram and optical characteristic diagram of a ferroelectric liquid crystal element, and FIG. 7 is a schematic diagram of a ferroelectric liquid crystal panel. 71...Scanning electrode, 72...・Signal electrode. Fig. 1 Fig. 2 Fig. 6 Fig. 7

Claims (4)

[Claims] (1) Ferroelectric liquid crystal is sandwiched between a first substrate on which a plurality of scanning electrodes are formed and a second substrate on which a plurality of signal electrodes are formed, forming a matrix of pixels. In a method for driving a dielectric liquid crystal panel, the scanning waveform applied to each scanning electrode includes applying a set of reset pulses whose amplitudes are symmetrical with respect to a constant potential in order to bring the pixel into a first stable state. a reset period in which the constant potential is applied in order to bring the pixel into a second stable state in response to a display signal; The signal waveform applied to the signal electrode consists of a non-selected period in which a high-frequency electric field whose amplitude is symmetrical to A matrix type ferroelectric liquid crystal panel characterized in that the panel is a set of pulses having a width and whose amplitude is symmetrical with respect to the constant potential, and the constant potential is maintained when the first stable state is maintained. driving method. (2) The scanning waveform is characterized in that when the Nth line of the scanning electrode is in the selection period, one or more scanning electrode lines, such as the N+1st line and the N+2nd line, are in the reset period. driving method for matrix-type ferroelectric liquid crystal panels. (3) In the selection period of the scanning waveform, the period during which a constant potential is applied is 1/2 of the selection period, and the same high-frequency electric field as the non-selection period is applied to the remaining 1/2 period. 3. A method for driving a matrix type ferroelectric liquid crystal panel according to claim 1 or claim 2. (4) The matrix-type ferroelectric material according to claim 1, claim 2, or claim 3, wherein the pulse applied during the reset period in each scan electrode is changed to alternating current in multiple scans. Driving method for liquid crystal panels.