JPH0718993B2 - Driving method for ferroelectric liquid crystal panel - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a ferroelectric liquid crystal panel, which is effective for use in video equipment, information equipment and the like.

2. Description of the Related Art In recent years, in the field of information equipment centered on computers and in the field of video equipment centered on televisions, video tape recorders (VTRs), etc., thin optical shutters used for printers and large-screen thin display devices have been developed. Demand is rising. As an optical shutter and a display device of this kind, ones using liquid crystal have been attracting attention, and recently, a matrix type display device and an optical shutter using a ferroelectric liquid crystal material for the liquid crystal have been put into practical use.

Since this type of liquid crystal panel using ferroelectric liquid crystal has a fast response to an electric field and has a memory property, even if it is driven by multiplex, there is almost no reduction in contrast, and a display with good display quality or high speed Suitable for optical shutter.

Hereinafter, a liquid crystal panel using a conventional ferroelectric liquid crystal will be described with reference to the drawings.

FIG. 4 is a graph showing a driving voltage waveform for driving a liquid crystal panel using a conventional ferroelectric liquid crystal. In FIG. 4, each waveform shows a voltage waveform applied to an ON pixel and an OFF pixel, and V ₁ is a pulse voltage having a peak value higher than a threshold value required to invert the ferroelectric liquid crystal, and V _{1 2} is a pulse voltage whose peak value is lower than the above threshold value.

The operation of the conventional liquid crystal panel when the above driving waveform is applied will be described below. First, the write voltage is applied during the period T _W1 in the first field, but is turned off during the first half of the period T _W1.
A voltage is applied, and a negative ON voltage is applied in the latter half to turn on the pixel. During the period TH, an AC signal below the threshold is applied, so the liquid crystal maintains the ON state. Since the _peak value of the voltage applied during the period T _W2 is V ₂ , the liquid crystal is not inverted and the ON state is maintained. Then, in the second field the erase voltage is applied to the period T _W2, the first half of the period T _W2 applies a ON voltage is applied to OFF voltage in the second half. That is, a writing voltage is applied to pixels to be turned on in the first field, an erase voltage is applied to pixels to be turned off in the second field, and one frame is completed in two fields. The liquid crystal panel can be driven by repeating the above operation. In the first half of the periods T _W1 and T _W2 , the voltage of the opposite polarity of the signal required for writing or erasing is applied. This is to prevent the deterioration of the liquid crystal due to the application of the DC electric field. This is so that each field can be exchanged.

[“Application of chiral smectic see liquid crystal to time division large area display”, SID 85 digest. (An Application of Chiral Smectic-C Liquid Cr
ystal to a Multiplexed Large-Area Display.SID85DIG
EST)] FIG. 5 is an equivalent circuit between the terminals of the drive electrodes of the liquid crystal panel, where 21 is the electrode resistance, 22 and 23 are the alignment film resistance and capacitance, and 24 and 25 are the liquid crystal resistance and capacitance, respectively. . As is clear from FIG. 5, the actual voltage applied to the liquid crystal layer is the voltage across the resistor 24 or the capacitor 25. Since the resistance value of the electrode resistance 21 increases as the distance from the drive terminal increases, the effective pulse width and peak value of the voltage applied to the liquid crystal increase as shown in FIG. 6 in the pixels farther from the supply point of the drive voltage. Both decrease. In particular, when the liquid crystal is a ferroelectric liquid crystal, this effect becomes larger because the capacitance 25 of the liquid crystal is larger than that of a normal TN liquid crystal.

Problems to be Solved by the Invention In the case of a ferroelectric liquid crystal, since liquid crystal molecules are inverted and used as an optical switch, it is necessary to apply a voltage having a predetermined peak value until the liquid crystal molecules are inverted. Therefore, in the above-described conventional driving method, a driving voltage having a sufficient pulse width is applied to a pixel distant from the supply point of the driving voltage so that the pixel can operate stably even when the effective pulse width of the applied voltage is reduced. Therefore, there is a problem that the number of scanning electrodes cannot be increased when the scanning speed becomes slow and the scanning frame time is constant. In addition, since a voltage with a sufficient pulse width is applied to pixels near the drive voltage supply point even when the pixel is not selected, liquid crystal molecules respond even if the voltage is below the threshold, and it is difficult to maintain the ON or OFF state. It also had the problem of becoming stable.

Therefore, in the present invention, in the matrix type liquid crystal pulse,
It is an object of the present invention to provide an effective driving method capable of increasing the number of scanning electrodes without impairing operational stability.

Means for Solving the Problems And the technical means of the present invention for solving the above problems constitutes a liquid crystal panel in which a ferroelectric liquid crystal is sandwiched between a scanning electrode group and a signal electrode group, The selection period of the scanning electrodes facing the portion of the signal electrode group near the supply point of the drive voltage is set shorter than the selection period of the scanning electrodes facing the portion of the signal electrode group farther than the supply point of the drive voltage. .

That is, in a portion requiring a driving voltage with a long panel width, the selection period of the scan electrode and the signal electrode corresponding to that portion is lengthened, and conversely, in a portion that operates sufficiently with a driving voltage with a short pulse width, The selection period of the corresponding scan electrode and signal electrode is shortened.

Action The action of this technical means is as follows.

That is, in the present invention, the selection period of the scan electrodes and the signal electrodes is lengthened so that the drive voltage having a sufficient pulse width is applied only to the necessary places, and the selection period of the scan electrodes and the signal electrodes is set to the unnecessary places as much as possible. Since the length is short, the entire scanning time can be shortened, and the number of scanning electrodes can be increased by the shortening of the scanning time.

Embodiment One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an embodiment of the driving voltage of each scanning electrode showing the driving method of the ferroelectric liquid crystal panel of the present invention. Figure 1 is second
FIG. 2 shows drive waveforms when a 5 × 15 matrix liquid crystal panel as shown in FIG. 2 is driven. In FIG. 2, 1 to 5 are scan electrodes, 6 to 10 are signal electrodes, 11 is a scan electrode driver,
Reference numeral 12 is a signal electrode driver. As can be seen from FIG. 1, the selection period Ts of each scan electrode is sequentially changed for each scan electrode. In this case, the selection period of the scanning electrode 5 facing the portion farthest from the supply point of the drive voltage of the signal electrode group is set to be the longest to prevent the malfunction due to the electrode resistance of the signal electrode and drive the signal electrode group. The scanning period is shortened by minimizing the selection period of the scanning electrode 1 facing the portion near the voltage supply point.

FIG. 3 is a time chart of the drive voltage waveform of each signal electrode showing another embodiment of the driving method of the ferroelectric liquid crystal panel of the present invention. FIG. 3 also shows drive waveforms when a 5 × 15 matrix liquid crystal panel as shown in FIG. 2 is driven.
As can be seen from FIG. 3, the selection period Ts of each signal electrode is sequentially changed for each signal electrode. In this case, the signal electrode facing the portion farthest from the driving voltage supply point of the scan electrode group
The selection period of 10 is set to be the longest, operation failure due to the electrode resistance of the scan electrodes is prevented, and the selection period of the signal electrode 6 facing the portion near the drive voltage supply point of the scan electrode group is set to be the shortest. The pulse width of the voltage applied to the non-selected pixels is shortened to improve the stability of holding the ON or OFF state.

The liquid crystal used in each of the above-mentioned examples is a ferroelectric liquid crystal, but particularly a liquid crystal exhibiting a chiral smectic C phase has a high response speed and is likely to be fast. For example, + DOBAMBC (+ p-decyloxybenzylidene-p'-
A liquid crystal material such as asino 2-methylbutyl cinnamate) can be used.

The matrix panel shown in FIG. 2 is merely an example, and the present invention is not limited to this. The drive voltage waveforms of the scanning electrodes and the signal electrodes are also limited to those shown in FIGS. 1 and 3. Instead, the scanning electrodes and the signal electrodes may be driven so that the selection periods thereof are different from each other with a predetermined relationship.

EFFECTS OF THE INVENTION In the present invention, since the selection period of each scan electrode is made different, the drive voltage having the minimum required pulse width can be applied to each scan electrode, and the scanning time can be shortened while ensuring the stability of the operation. The effect that it can be obtained can be obtained. Therefore, the number of scan electrodes can be increased by the reduction of the scan time. Furthermore, since the selection period of each signal electrode is different, the pulse width of the voltage applied to the non-selected pixels can be minimized, and the stability of the ON and OFF state retention is improved. Is something that can be done.

[Brief description of drawings]

FIG. 1 is a timing chart showing drive voltage waveforms of respective scanning electrodes in an embodiment of a method for driving a ferroelectric liquid crystal panel of the present invention, and FIG. 2 is a configuration of a ferroelectric liquid crystal panel in an embodiment of the present invention. FIG. 3 is a schematic block diagram showing a driving voltage waveform of each signal electrode in another embodiment of the method for driving a ferroelectric liquid crystal panel of the present invention, and FIG. 4 is a driving voltage of a conventional liquid crystal panel. Waveform diagram, FIG. 5 is an equivalent circuit diagram of the liquid crystal panel, and FIG. 6 is a graph showing a voltage waveform actually applied to the liquid crystal layer when a drive voltage is applied to the liquid crystal panel. 1 to 5 ... scan electrodes, 6 to 10 ... signal electrodes, 11 ... scan electrode drivers, 12 ... signal electrode drivers.

Claims (3)

[Claims] 1. A liquid crystal panel in which a ferroelectric liquid crystal is sandwiched between a scan electrode group and a signal electrode group, and a scan electrode facing a portion near a drive voltage supply point of the signal electrode group is selected. A method of driving a ferroelectric liquid crystal panel, wherein a period is shorter than a selection period of a scanning electrode facing a portion farther from a supply point of the drive voltage of the signal electrode group. 2. The selection period of the signal electrode facing the portion of the scan electrode group near the supply point of the drive voltage is greater than the selection period of the signal electrode facing the portion of the scan electrode group farther than the supply point of the drive voltage. The method for driving a ferroelectric liquid crystal panel according to claim (1), wherein the method is also short. 3. A ferroelectric liquid crystal is chiral smectic C.
The method for driving a ferroelectric liquid crystal panel according to claim 1, wherein the ferroelectric liquid crystal panel exhibits a phase.