JPS6275516A - Driving method for optical modulation switch - Google Patents

Abstract

PURPOSE:To increase an operation speed without impressing voltage with reverse polarity by holding an optical modulation substance indicating bistability between a scanning electrode group and a signal electrode group and impressing a turnover voltage only to a picture element for inverting the stable state to drive an optical modulation switch. CONSTITUTION:The stable state of the optical modulation substance can be inverted by impressing a positive or negative voltage more than a prescribed threshold for a prescribed period and the stable state can not be changed by the impression of a voltage less than the prescribed threshold. Scanning electrodes 1 and signal electrodes 2 are driven by a row driver 3 and a column driver 4 respectively and the state of inputted picture element data is read out from a memory 6 and compared with a reference value by a data comparator 7. When both the values coincide with each other as the compared result, the picture element is kept at the non-selected state, and if the picture element is different from the reference, a voltage for inverting the stable state is impressed to the picture element and the contents of the memory are simultaneously rewritten. The matrix-like optical modulation switch can be driven by repeating similar operation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for driving a display device and an optical shutter that are effective for use in video and information equipment.

2. Description of the Related Art In recent years, thin optical shutters used in printers and thin optical shutters for large screens have been developed in the field of information equipment, mainly computers, and video equipment, mainly televisions and video tape recorders (V, TR). Demand for display devices is increasing. As this type of optical shutter or display device, those using liquid crystals have been attracting attention, and recently, matrix-type display devices and optical shutters using ferroelectric liquid crystal materials as the liquid crystals have been put into practical use.

This type of liquid crystal optical switch utilizes the bistability of ferroelectric liquid crystal to electric fields to maintain a stable state through its memory effect during non-scanning periods during multiplex drive, thereby preventing a decrease in contrast. ing. It also has the feature of fast response to electric fields.

A conventional optical switch using a ferroelectric liquid crystal will be described below with reference to the drawings.

FIG. 3 is a graph showing applied voltage and optical transmittance of a liquid crystal used in a conventional liquid crystal optical switch.

As is clear from FIG. 3, the stable state can be reversed by applying a positive or negative voltage higher than a predetermined dark value for a predetermined time, and when a voltage lower than a predetermined dark value is applied, the stable state can be reversed. , the stable state remains unchanged.

FIG. 4 is a graph showing a driving voltage waveform for driving a conventional liquid crystal optical switch. In Figure 4, each waveform is ON
It shows the voltage waveforms applied to pixels and OFF pixels,
Vl is a pulse voltage with a peak value higher than the dark value necessary to reverse the stable state of the liquid crystal, and 2 is a pulse voltage with a peak value lower than the dark value.

The operation of a conventional liquid crystal optical switch when the above driving waveform is applied will be described below. First, in the first field, a write voltage is applied for a period Twl.
In the first half of TH, an OFF voltage is applied, and in the second half, a negative ON voltage is applied to turn the pixel into the ON state, and during the period TH, the ON state is maintained due to the memory effect. The voltage applied during period Tw2 has a peak value of ■2, so the stable state of the liquid crystal does not change and is ON.
State is preserved. Next, in the second field, an erase voltage is applied during period Tw2, but the first half of period Tw2 is
An N voltage is applied, and an OFF voltage is applied in the latter half. That is, in the first field, a write voltage is applied to pixels to be turned ON, in the second field, an erase voltage is applied to pixels to be turned OFF, and one frame is completed in two fields.

By repeating the above operations, the liquid crystal optical switch can be driven. In addition, in the first half of the periods Twl and Tw2, a voltage with the opposite polarity of the signal required for writing or erasing is applied, but this is to prevent deterioration of the liquid crystal due to the application of a DC electric field, and the applied voltage I try to communicate with others.

[“Application of chiral smectine liquid crystal to time-division large-area display”, Niss ID 85 Digest. (An Application of Chir
alSmectic-CLiquid Crystal
to a Multiplexed Large-Ar
ea Display, 5ID85DIGEST))
Problems to be Solved by the Invention Therefore, the above driving method has the problem that writing and erasing takes twice as long because it is necessary to apply a voltage of opposite polarity to alternating the applied voltage. Was. Therefore, liquid crystal optical switches are configured in a matrix, and one
If the frame time is constant, there is a problem in that the number of scanning electrodes in the matrix cannot be increased.

Therefore, the present invention provides an effective driving method for a matrix type optical switch that can obtain high contrast even when the number of scanning electrodes increases.

Means for Solving the Problems The technical means of the present invention for solving the above problems is to use a material that exhibits bistability due to an electric field as the optical modulation material, and to invert only the pixels whose stable state is to be reversed. It applies voltage. Furthermore, the stable state of the pixel is stored in a memory circuit, and a voltage is applied to the pixel with reference to this information.

Furthermore, by using a ferroelectric material as the optical modulation material, bistability can be easily imparted by an electric field. For example, when a liquid crystal material of Karasmectisoc C is sealed in a cell in which the interelectrode gap is sufficiently thinner than the chiral pinch of the liquid crystal, the chiral is unwound due to the wall effect, and the liquid crystal exhibits bistability due to the electric field. It becomes like this.

action The effect of this technical means is as follows.

In other words, since the present invention uses a material that exhibits bistable properties depending on an electric field as the optical modulation material, the contrast does not deteriorate significantly even if the number of scanning electrodes increases due to its memory effect, and the stable state of the optical modulation material remains unchanged. Since the voltage for inversion is applied only to the pixels that are to be inverted, the responsiveness of the optical switch can be further improved and the number of scanning electrodes can be increased.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

The optical modulation material in one embodiment of the present invention can be a material having voltage-optical transmittance characteristics as shown in FIG. As is clear from FIG. 3, the stable state can be reversed by applying a positive or negative voltage higher than a predetermined dark value for a predetermined time, and when a voltage lower than a predetermined dark value is applied, the stable state can be reversed. , the stable state remains unchanged. Ferroelectric materials are one of the materials exhibiting such characteristics, and materials exhibiting a chiral smectic C phase have a fast response speed and are easy to use. For example, +DORAMBC(+p-
A liquid crystal material called denyloxybenzylidene-p-acin 2-methylbutyl cinnamate) can be used.

FIG. 1 is a block diagram showing the configuration of an optical modulation switch in an embodiment of the optical modulation switch driving method of the present invention. In Fig. 1, 1 is a scanning electrode, 2 is a signal electrode, and 3 is a scanning electrode.
4 is a row driver, 4 is a column driver, 5 is a pixel, 6 is a memory, 7 is a data comparator for comparing the memory and input data, 8 is an input interface, and 9 is a control circuit.

The operation of the optical modulation switch in one embodiment of the present invention configured as above will be described below.

The scanning electrode 1 is connected to the signal electrode 2 by the row driver 3.
is driven by the column driver 4, and in response to input pixel data, the state of the pixel is first read from the memory 6 and compared by the data comparator 7. and,
If the comparison results are the same, the pixel is left in a non-selected state, and if the comparison results are different, a voltage is applied to the pixel to reverse the stable state, and the memory is also rewritten at the same time. By repeating the same operation, it is possible to drive a matrix of optical modulation switches.

FIG. 2 shows the voltages to be applied to each electrode and the voltages to be applied to each matrix pixel in an embodiment of the optical modulation switch driving method of the present invention.

In even-numbered fields, a voltage to put the pixel in the first stable state and a voltage to keep it in other states are applied to the signal electrode according to the comparison result with the contents of the memory, and in odd-numbered fields, the voltage to put the pixel in the second stable state is applied to the signal electrode. A voltage to be changed and a voltage to be maintained in another state are applied to the signal electrode according to the comparison result with the contents of the memory. On the other hand, a selection voltage whose polarity is inverted between even and odd fields is applied to the scanning electrodes.

By driving the optical modulation switch as described above,
Since the inversion voltage is applied only to the pixels whose stable state is to be inverted, the operating speed of the optical modulation switch can be increased.

Note that the driving voltage shown in FIG. 2 is only one example, and is not limited to this voltage, and the applied voltage for reversing each stable state is divided into two fields for driving. It is not limited to this. Furthermore, the optical modulating material is not limited to liquid crystal either.

Effects of the Invention The present invention uses an optical modulation material exhibiting bistability between a scanning electrode group and a signal electrode group, and applies an inversion voltage only to pixels whose stable state is to be inverted to drive an optical modulation switch. , there is no need to apply a voltage of opposite polarity to alternating current when the stable state is reversed, and the operating speed can be increased. Therefore, 1
When a matrix-like optical modulation switch with a constant frame time is constructed, the number of scanning electrodes can be doubled compared to the conventional method, and a large-area optical modulation switch can be constructed with high contrast. becomes possible. Furthermore, when the stable state is not reversed, it is not necessary to apply voltage most of the time, so that a ripple effect of reducing power consumption can also be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an optical modulation switch in an embodiment of the optical modulation switch D driving method of the present invention,
FIG. 2 is a relationship diagram showing the voltages to be applied to each electrode and the voltages to be applied to each matrix pixel in an embodiment of the optical modulation switch driving method of the present invention, and FIG. A graph showing the applied voltage and optical transmittance of a liquid crystal in one embodiment. FIG. 4 is a graph showing a driving waveform in one embodiment of a conventional liquid crystal optical switch. 1...Scanning electrode, 2...Signal electrode, 3
...Row driver, 4...Column driver, 5...Pixel, 6...Memory, 7
...Data comparator, 8...Input interface, 9...Control circuit. Agent's name: Patent attorney Toshio Nakao (1 person) Figure 2 Ikuno Field Figure 3 ↑ Time opening Figure 4 Twl THTw2Ts

Claims (4)

[Claims] (1) It has a scanning electrode group and a signal electrode group, and exhibits a bistable state due to an electric field between the scanning electrode group and the signal electrode group.
An optical modulation substance is held between the scanning electrode and the signal electrode to form a pixel, and by applying a first voltage to the pixel, the optical modulation substance is brought into the first state of the bistable state. By applying the second voltage, the second state of the bistable state is achieved, and the first or second voltage is applied only to the pixel whose stable state is to be reversed. A driving method for a featured optical modulation switch. (2) The optical modulation switch according to claim (1), wherein the stable state of each pixel is stored in a storage circuit, and a voltage is applied to each pixel with reference to the information in the storage circuit. driving method. (3) A method for driving an optical modulation switch according to claim (1) or (2), wherein the optical modulation substance is a ferroelectric substance. (4) The method for driving an optical modulation switch according to claim (3), wherein the ferroelectric substance exhibits a chiral smectic C phase.