JPH03269508A - Method for driving plzt display element - Google Patents

Abstract

PURPOSE:To decrease residual transmitted light and to make improvement in the contrast of display image by impressing the reverse voltage of a prescribed value on electrodes for a prescribed period of time and erasing the residual polarization of a picture element part at the time of switching the display of the picture element from ON to OFF. CONSTITUTION:The reverse voltage is impressed for a prescribed period of time between the electrodes constituting the picture element of a PLZT (transparent creamic) substrate at the time of switching the display of the picture element from ON to OFF. The light trans mittance of the picture element is decreased to approximately zero by the impression of this reverse voltage and, therefore, the voltage to turn the display of the picture element to OFF is thereafter impressed between the electrodes but since the residual transmitted light is already not generated in this picture element part, the light transmittance during the time of the OFF is maintained at approximately zero. The light transmittance of the picture element part does not immediately fall to the zero and there is the residual transmitted light when this reverse voltage is impressed and, therefore, the influence to be exerted on the contrast of the display image is small. The residual polarization of the picture element is erased in such a manner and the residual transmitted light is eliminated when the display of this picture element is turned to OFF and, therefore, the contrast of the display is improve when the PLZT substrate is used as the optical display element.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention utilizes the birefringence of PLZT (transparent ceramic) and relates to a method for driving a PLZT display element used as an optical shutter or a display device. A PLZT that prevents residual polarization from occurring in the pixel when a predetermined voltage is applied between the electrodes that make up the pixel and the light transmittance is controlled to turn on and off the display of that pixel.
The present invention relates to a method for driving a display element.

[Conventional example] In recent years, transparent ceramic PL made by adding La to PZT has been developed.
ZT (PbO, LaO, ZrO, -TiO) is about to be used in optical shutters and display devices. When using this PLZT as a device element, it is necessary to form electrodes 2 on a PLZT substrate 1 and apply a predetermined voltage (V P ) between the electrodes 2, as shown in FIG. 5, for example. Therefore, normally, when turning on the display of the pixel 3 formed between the electrodes 2, a predetermined voltage Vo (>O) is applied between the electrodes 2, and the light transmittance of the pixel 3 is increased. do. Conversely, when the display of the pixel 3 is turned off, zero voltage is applied between the electrodes 2 to reduce the light transmittance of the pixel 3 portion.

[Problems to be Solved by the Invention] By the way, as shown in the characteristic curve diagram of applied voltage versus light transmittance in FIG. 6, the display ON/OFF characteristics of the PLZT substrate 1 generally have hysteresis characteristics. Therefore, when the display of the pixel 3 is switched from ON to OFF, that is, even when zero voltage is applied between the electrodes 2, the light transmittance of the pixel 3 does not become completely zero, but reaches the predetermined value TR ((TD) becomes.

That is, this is because residual polarization occurs in the pixel 3, and therefore, there is a problem that residual transmitted light occurs in the pixel 3.

Therefore, when the above-mentioned PLZT substrate 1 is used as an optical display element, especially when displaying a moving image on the optical display device, the time required to turn on and off each pixel is shortened, and moreover, turning on and off may not be repeated. As a result, the contrast of the displayed image is further reduced, which hinders the use of the optical display element as a display device.

As shown in the characteristic curve diagram of FIG.
It was created in view of the above problem, noting that if a predetermined value of reverse voltage is applied between the electrodes, there will be no residual transmitted light to the pixels due to the electrodes, and its purpose is to eliminate the residual polarization occurring in the pixel portions It is an object of the present invention to provide a method for driving a PLZT display element that can reduce residual transmitted light and improve the contrast of a displayed image.

[Means for Solving the Problem] In order to achieve the above object, the present invention applies a predetermined voltage between electrodes forming the pixel when turning on and off the display of the pixel formed on the PLZT substrate, In a method for driving a PLZT display element to control its light transmittance, when switching the display of the pixel from ON to OFF, a reverse voltage of a predetermined value is applied to the electrode for a predetermined time,
The gist is that the residual polarization in the pixel portion is erased.

Further, in the present invention, when switching the display of the pixel from ON to OFF, the time during which the display is ON is shorter than the time during which the display is OFF, and the time difference is used as the time during which the reverse voltage is applied to the electrode. .

[Function] Since the above method is used, the display of pixels on the PLZT board can be turned on.
When switching from to OFF, a reverse voltage is applied for a predetermined period of time between the electrodes forming the pixel. That is, as is clear from the characteristic curve diagram of applied voltage vs. light transmittance in FIG. 6, the light transmittance of the pixel becomes approximately zero due to the application of the reverse voltage. Although the light is applied between the electrodes, since no residual transmitted light has already occurred in the pixel portion, the open light transmittance in the OFF state is maintained at approximately zero.

In addition, the application time of the above-mentioned reverse voltage is included in the time for turning on the display of the pixel, and the time for turning on the display is shortened by that much, but when the reverse voltage is applied, the light transmittance of the pixel portion immediately decreases. Since the light does not become zero and there is residual transmitted light, even if there is an effect on the contrast of the displayed image, it is small. Conversely, when the display is turned off, the brightness of the displayed image is improved if the residual transmitted light is approximately zero.

[Embodiment] Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 to 4. In addition, in the figure, the same parts as in FIG. 5 are given the same reference numerals, and redundant explanation will be omitted.

As shown in FIGS. 1 and 2, when the display of a pixel 3 formed on a PLZT substrate 1 is turned ON or OFF, the voltage applied between the electrodes 2 of the pixel 3 is
It is set to VD during the time N, and set to zero (GND) during the time when the display is turned off, but as is clear from the figure,
Only when switching the display from ON to OFF, the applied pressure is -v5 for a predetermined period of time. Note that, as shown in FIG. 6, the pixel 3 has a voltage of ■. When is applied between the electrodes 2, its light transmittance becomes large and the light is transmitted sufficiently to turn on the display), and -VE voltage is applied between the electrodes 2.
When GND is applied between the electrodes 2 for a predetermined period of time, the light transmittance becomes approximately zero (the display is turned off).

Further, the time during which the reverse voltage of -VH is applied between the electrodes 2 is included in the time during which the display is turned on, for example.

Although the length is shortened by that much, the residual transmitted light of the three pixels is not completely eliminated during this time, and a certain amount of light is transmitted.

By the way, in the method for driving the PLZT display element described above, when attempting to actually apply a voltage between the electrodes 2 of the PLZT substrate l, the driving circuit requires a negative power supply, etc.
Moreover, the circuit configuration becomes complicated.

Therefore, for example, by using the drive circuit shown in FIG. 3, the reverse voltage shown in FIG.
The voltages are made to correspond to VD10V, respectively.

In this figure, the drive circuit has a control voltage V! (Vcl)
An npn-type switching transistor 4 that is turned on and off by a signal of control voltage Vz (Vc2), an npn-type switching transistor 5 that is turned on and off by a signal of control voltage Vz (Vc2), and when both switching transistors 4 and 5 are in an OFF state. The emitter follower-connected transistor 6 is turned on, and is turned off when only the switching transistor 4 is in the on state, and the emitter voltage becomes equal to the base voltage when only the switching transistor 5 is in the on state. Note that the resistors 7 and 8 are set so that when only the switching transistor 5 is in the ON state, the base voltage of the transistor 6 is approximately 6. Further, the voltage source that generates the voltage VD and the voltage source that generates the voltage VE are connected in series, and the voltage source that generates the voltage VD and the voltage source that generates the voltage VE are connected in series.
A voltage D +v is connected between the collector and emitter of a transistor 6, one of the electrodes 2 is connected to the emitter of the transistor 6, and the other is connected to a power source of voltage VE.

Therefore, switching transistors 4 and 5 are both O
In the FF state, the emitter voltage of the transistor 6 is VD + vE, so that the voltage VD is applied to one of the electrodes 2 of the PLZT substrate 1 with respect to the voltage V. Moreover, when only the switching transistor 4 is in the ON state,
Since the base of the transistor 6 becomes GND, the transistor 6 is turned off, and GND is applied to one of the electrodes 2 with respect to the voltage VE. Furthermore, when only the switching transistor 5 is in the ON state,
Since the base voltage of the transistor 6 is set to approximately V9 voltage by the resistors 7 and 8, approximately vE voltage is applied to one of the electrodes 2 with respect to voltage VE.

The driving method applied to the above driving circuit will be explained in detail with reference to the time chart of FIG.

First, the signal of the control voltage V z (V c 2 ) is at the "H" level when the display of the pixel 3 is turned off, and is at the "L" level when the display is turned on (as shown in the figure). (shown in (c)). In addition, as shown in FIG. 3(b), the signal of the control voltage V□ (Vcl) is
Only when switching the display of pixel 3 from ON to OFF.
The control voltage v2 is at an "H" level, and its "HP+" level period is included in the "L" level period of the control voltage v2 signal.

Here, when the signals shown in (b) and (c) of the figure are input to the drive circuit, when both of these signals are at the dlL'' level, that is, when the display of the pixel 3 is turned on, the switching transistor 4, 5 are both in the OFF state, the voltage applied between the electrodes 2 of the pixel 3 becomes VD with respect to 5. That is, as is clear from FIG. 6, the light transmittance of the pixel 3 is The pixel 3 has a large TD, can sufficiently transmit light, and the display of the pixel 3 is turned on.

Subsequently, only the control voltage V□ (Vcl) signal is 11H.
At the P+ level, that is, when erasing the residual polarization of the pixel 3, only the switching transistor 4 is turned on, so that the voltage applied between the electrodes 2 becomes GND with respect to VE. That is, since a reverse voltage of -VE is applied between the electrodes 2, as is clear from FIG.
The light transmittance of pixel 3 becomes smaller than TR, and the pixel 3
The residual polarization of the area is eliminated.

Then, when only the signal of the control voltage V z (V c 2 ) is at II HP+ level, that is, the display of pixel 3 is O
When switched to FF, switching transistor 5
Since only one of the electrodes is in the ON state, the voltage applied between the electrodes 2 becomes approximately V6 compared to the voltage (6), that is, the potential difference between the electrodes 2 becomes zero. That is, as is clear from FIG. 6, the residual polarization in the third part of the pixel is erased, and its light transmittance becomes approximately zero, and the light transmittance is maintained at zero during the period of the above-mentioned signal at the high level. Therefore, the display of that pixel 3 is OFF.
become.

Note that when the display of pixel 3 is switched to ON, the voltage applied between the electrodes 2 becomes VD for ■6,
Since the light transmittance of the pixel 3 increases, the display of that pixel 3 is turned on. In this case, since the residual transmitted light has already disappeared when the display is turned off, there is no need to consider the residual transmitted light.

In this way, when switching the display of the pixel 3 formed on the PLZT substrate 1 from ON to OFF, a reverse voltage is applied between the electrodes 2 for a predetermined period of time to erase the residual polarization of the pixel 3. When the display is turned off, there is no residual transmitted light, that is, no light leakage. Therefore, when the above-mentioned PLZT substrate l is used with a PLZT display element, the contrast of the displayed image becomes good, and even if the display is turned ON and OFF repeatedly, the contrast does not deteriorate, so that the display of moving images etc. This makes it possible to use it as a variety of display devices.

[Effects of the Invention] As explained above, according to the method for driving a PLZT display element of the present invention, when switching the display of a pixel formed on a PLZT substrate from ON to OFF, a reverse voltage is applied between the electrodes, and the Since the residual polarization of a pixel is erased and the residual transmitted light is eliminated when the display of that pixel is turned off, when the above PLZT substrate is used as an optical display element, the contrast of the display can be significantly improved. This has the advantage that it can be used in various display devices.

[Brief explanation of drawings]

FIG. 1 and FIG. 4 show an embodiment of the present invention, and PL
FIG. 2 is a schematic partial perspective view of a PLZT substrate to which the above-mentioned method for driving a PLZT device element is applied;
FIG. 3 is a schematic circuit diagram of a drive circuit to which the above-mentioned PLZT device element driving method is applied, FIG. 5 is a schematic perspective view of a PLZT substrate, and FIG. 6 is an applied voltage pair of a display element using a PLZT substrate. It is a characteristic curve diagram showing light transmittance. In the figure, 1 is a PLZT substrate, 2 is an electrode, 3 is a pixel, 4°5
is a switching transistor, 6 is an emitter follower connection transistor, 7 and 8 are resistors, and VD and v5 are voltages. Figure 1

Claims (2)

[Claims] (1) Turn on and off the display of pixels formed on the PLZT substrate
In a method for driving a PLZT display element, in which a predetermined voltage is applied between electrodes constituting the pixel to control the light transmittance thereof, when switching the display of the pixel from ON to OFF, a predetermined value is applied to the electrodes. 1. A method for driving a PLZT display element, characterized in that a reverse voltage of 1 is applied for a predetermined period of time to erase residual polarization in the pixel portion. (2) When switching the display of the pixel from ON to OFF, the time during which the display is ON is shorter than the time during which the display is OFF, and the time difference is defined as the time during which the reverse voltage is applied to the electrodes. A method for driving a PLZT display element.