JPH0150916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an information holding device, and particularly to an information holding device that can output written information to an external device. Hereinafter, a liquid crystal device having a display function and an information holding device will be described as an example of an information holding device.

[Background of the invention]

Conventionally, as information holding devices, devices made of a smectic liquid crystal or the like and having a display function and an information holding function, and devices made of a ferroelectric material such as PLZT are known.

For example, liquid crystal devices are known that use various display principles such as nematic liquid crystal, cholesteric liquid crystal, or smectic liquid crystal, but in all of them, the alignment state of liquid crystal molecules is changed by some external field, and the resulting optical The display is achieved by utilizing changes in the physical properties.

As an example of these liquid crystal devices, U.S. Patent No.
No. 3796999 “Locally Erasable Thermo−
Optic・Smectic Liquid Crystal Storage
This paper provides an overview of the thermal writing type liquid crystal device shown in "Displays".

In this device, transparent electrodes 13 and 14 are provided inside two glass substrates 11 and 12 as shown in FIG. 1A, and a smectic liquid crystal 15 is sealed between them. A laser beam 16 emitted by an Ar (argon) laser or a YAG (yttrium aluminum garnet) laser is focused on such a display panel by a lens 17, and the display area 1 is focused.
The temperature of the smectic liquid crystal 15 of No. 8 is increased to temporarily bring it into an isotropic liquid crystal phase.

Thereafter, when the laser beam is removed and the liquid crystal is rapidly cooled to a smectic phase, the alignment direction of the liquid crystal molecules is disturbed and a region 19 exhibiting strong scattering properties is generated, as shown in FIG. 1b. Since this scattering state remains stable, arbitrary image information can be written.

Based on the display principle described above, thermal writing type liquid crystal devices write arbitrary image information on the liquid crystal element by scanning and modulating a laser beam, and can also achieve partial erasure by applying an electric field. It is excellent as. However, it did not have a function to read written image information, and was used only as a display device for inputting information signals as images.

Furthermore, other information holding devices have so far only had the function of displaying information, and could not be used as information output devices.

[Purpose of the invention]

An object of the present invention is to provide an information holding device in which pixels are arranged in an XY matrix, which is completely unaffected by current caused by crosstalk and can input and output information signals in a short time with a simple circuit. There is a particular thing.

[Summary of the invention]

The information holding device of the present invention that achieves the above object is characterized in that a plurality of one electrodes and a plurality of other electrodes are opposed to each other on opposing surfaces, and the opposing portion of the one electrode and the other electrode is the entire a pair of substrates formed to form a matrix, a dielectric held between the pair of substrates, means for changing the capacitance of the dielectric at any of the opposing portions, and any one of the above substrates; Means for applying a voltage with a constant voltage increase rate dv/dt to the electrodes, and sequentially detecting currents flowing through at least two other electrodes facing the one electrode during a period when the voltage is applied to the one electrode. The objective is to have the means to do so.

Here, a "dielectric material" is a material whose capacitance changes when an electric field, heat, etc. is applied, and which remains unchanged for a certain period of time even after the electric field, heat, etc. is removed, and is stored. For example, liquid crystals with a smectic phase, liquid crystals with a cholesteric phase, PLZT, etc. are used. Liquid crystals with a smectic phase are used, which allow information to be written at relatively low temperatures and have a long storage time. It is preferable to do so.

Further, "a voltage with a constant voltage increase rate dv/dt" includes a ramp voltage, a triangular wave voltage, etc., and it is desirable that the voltage value hardly changes the capacitance of the dielectric material.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail by taking a liquid crystal having a smectic phase as an example.

FIG. 2 shows an overall configuration diagram of a liquid crystal device according to an embodiment of the present invention. The image information writing means 21 writes image information such as characters and symbols to the liquid crystal panel 22 by changing the capacitance of the liquid crystal having a smectic phase, which serves as a dielectric in the opposing portion of one electrode and the other electrode of the substrate. It is a means of writing. The image information written on the liquid crystal panel 22 is based on the voltage increase rate applied to the liquid crystal in the area facing the electrodes.
The image information readout voltage generation circuit 20 generates a voltage with a constant dv/dt, and the image information detection circuit 23 detects the current flowing through the dielectric material in the opposing portion of the electrodes.The image information is read out by the image signal conversion circuit 24. sent to. The image information signal obtained here is taken into an external circuit 25 composed of, for example, a microprocessor (CPU).

The present applicant has described in detail the structure and operation of the liquid crystal panel 22 and the image information writing means 21 in Japanese Patent Application No. 58-29450. For this reason, the liquid crystal panel 2
2 and the image information writing means 21 will be briefly explained. A schematic cross-sectional view of the liquid crystal panel 22 is shown in FIG. 3, and a schematic plan view is shown in FIG. 4. The liquid crystal panel includes a pair of substrates 26 and 27 arranged in parallel with a plurality of Y electrodes 29 and a plurality of X electrodes 30 intersecting each other on opposing surfaces.
A gap of about 10 μm is created, and a liquid crystal 31 having a smectic phase is placed between the substrates and sealed with a spacer 28. Here, Y electrode 29, X electrode 3
The portion facing 0 becomes a pixel, forming a matrix as a whole.

FIG. 5 shows an optical characteristic diagram of the liquid crystal having the above-mentioned smectic phase. When a liquid crystal with a smectic phase is heated, it becomes an isotropic liquid phase (c
point) and becomes almost transparent. When a sufficient voltage is applied to the liquid crystal layer to cool the liquid crystal layer, the liquid crystal layer enters a smectic phase (point a), becomes almost transparent, and maintains this state.

On the other hand, when the voltage applied to the liquid crystal layer is set to 0V or around 0V, a smectic phase exhibiting scattering properties (point b) occurs, the brightness decreases, and this state is maintained thereafter.

Next, the image information writing means 21 will be explained. FIGS. 6 and 7 show means for writing image information by irradiating laser light onto a liquid crystal panel using liquid crystal having a smectic phase.

FIG. 6 shows a device equipped with a laser pen 33 that can focus laser light on an arbitrary position. The laser pen 33 is composed of an optical fiber that guides laser light from a light source and a condensing lens, or one in which a semiconductor laser 34 and a condensing lens 35 are integrated.

FIG. 7 shows another image information writing means, which includes a laser 36, a modulator 37 that modulates the laser beam, an X-direction deflector 38, a Y-direction deflector 38 that deflects the laser beam in any direction, It is composed of a lens 39 that focuses laser light onto the liquid crystal element surface.

FIG. 8 shows another embodiment of the image information writing means.

Here, among the pixels of the liquid crystal panel 46, the shaded pixels e ₁₂ , e ₁₃ , e ₂₁ , e 23 , e ₃₁ , and _{e 32 are} in the written state (scattered state), and the other pixels e ₁₁ , e ₂₂ , and e X electrode 44a when ₃₃ is in a non-writing state (transparent state)
44c and the voltages applied to the Y electrodes 43a to 43c are shown in FIG.

Next, the principle of a method for reading out image information will be explained.

Considering the pixels e ₁₁ to _{e 33} arranged in a matrix shown in FIG. 8 as a kind of capacitor, the liquid crystal panel 46 can be considered as a group of capacitors 48 as shown in FIG. 10.

At this time, each pixel is filled with a dielectric liquid crystal layer between the electrodes, so as mentioned above, the dielectric constant changes due to the different molecular orientation in the written state or non-written state. The capacitance varies depending on the difference.

Therefore, the capacitance _CW of a pixel in a written state is different from the capacitance _CNW of a pixel in a non-written state. As mentioned above, for example, when a liquid crystal material with positive dielectric anisotropy is used and vertically aligned in the non-written state, C _W <C _NW , and the ratio is C _NW /C _W =ε/1/3. (ε+2ε⊥)＞1 ...(1). The inventors measured the capacitance using a liquid crystal material with ε=12 and ε⊥=4.7, and found that C _NW /
It has been confirmed that C _W =1.48, which is close to the calculated value of 1.68 using equation (1).

As mentioned above, pixels in the written state and pixels in the non-written state have different capacitances, so
By electrically reading out the difference in capacitance, the written information can be recognized and output to an external device.

In FIG. 10, in order to read the capacitance of pixel e ₁₁ , a voltage increase rate (dv/dt) is applied to the Y electrode 50a.
applies a constant readout voltage v _R and detects a current i _S flowing into the X electrode 49a with the Y electrodes 50b, 50c and the X electrodes 49b, 49c at constant potential.

At this time, the relationship between the read voltage v _R and the current i _S is expressed as
As shown in the figure. The saturation value of electric constant i _S is the capacitance of pixel e ₁₁
C ₁₁ and read voltage v _R voltage increase rate (dv/dt=K)
Determined only by Therefore, information written in each pixel can be read out by determining the magnitude of the saturation value of the current i _S.

These details are provided in the patent application filed by the applicant in 1982.
29450, as stated in patent application No. 58-90716.

Next, an embodiment of the image information read voltage generation circuit 20, image information detection circuit 23, and image information signal conversion circuit 24 shown in FIG. 2 will be described.

FIG. 12 shows an embodiment according to the present invention. The Y electrodes 56a to 56c have resistivity, for example.
It is made of Cr with a resistance of 0.1Ω/□, a width of 0.2mm, and a length of 180mm.
It is formed from a transparent conductive film of 100Ω/□, width 0.2mm, and length 120mm. Y of liquid crystal matrix panel 55
One out of two analog switches 58a to 58c are connected to the electrodes 56a to 56c. and,
One terminal of each switch is grounded, and the other terminal is connected to the read voltage generation circuit 61. In addition,
The output signals V _L1 to V _L3 of each of the switches mentioned above are
The scanning signals CP ₁ to _{CP 3} from the vertical scanning circuit 60 provide the ground level or the read voltage v _R .

On the other hand, the X electrodes 57a to 57c have 1out of 2
analog switches 59a to 59c are connected.
Then, ground one terminal of each switch,
The other terminal is connected to the image information detection circuit 23.
Each of the switches described above is controlled by the scanning signals CL ₁ to _{CL 3} from the horizontal scanning circuit 65, and as a result, the current i _S1 flowing into the X electrodes 57a to 57c
~i _S3 is selectively input to the image information detection circuit.

FIG. 13 shows a specific example of the image information detection circuit 23 and the image information signal conversion circuit 24.

The image information detection circuit 23 includes switches 59a to 5
It is comprised of a current-voltage conversion circuit 66a that converts the current i _S0 selected by 9c into a voltage v _S , and a comparison circuit 67 that compares the voltage v _S with a reference voltage V _ref from a reference power supply 68.

Further, the image information signal conversion circuit 24 takes in D ₀ obtained by the comparison circuit 67 at the timing of the CPR signal, and outputs it as an image information signal D ₁ .

Therefore, the circuit operation in Figure 12 is shown in Figure 14 and Figure 1.
This will be explained in detail using FIG.

FIG. 14 schematically shows the relationship between the Y electrode voltages V _L1 to V _L3 and the horizontal switch scanning signals CL ₁ to _{CL 3} and CPR when reading out the capacitance of pixels e ₁₁ to _{e 33} . It is something that

The switches 58a to 58c control the Y electrode voltage.
V _L1 to V _L3 are the read voltage v _R with a peak value of 5 V, or
It becomes the ground level (0). At this time, it is assumed that the read voltage v _R that starts being applied from time t ₀ ' has a constant dv/dt.

As a result, the current flows through the X electrodes 57a to 57c.
i _S1 to _{i S3} (displacement currents) begin to flow, but at time t ₀ when these currents show a constant value, first, the scanning signal CL ₁ is set to "H" and only the current i _S1 is sent to the current-voltage conversion circuit. input. In this example, the time T ₁ from t ₀ ' to t ₀
is approximately 40-50μsec.

Next, the current i _S2 is inputted to the current-voltage conversion circuit 66 at time t ₁ and the current i _S3 is inputted to the current-voltage conversion circuit 66 at time t ₂ .
In this embodiment, the time T ₂ from t ₀ to t ₁ and from t ₁ to t ₂ is approximately 0.5 μsec.

Through the above operations, the capacitances of the pixels e ₁₁ to _{e 13} can be read. Further, this operation is repeated for each line.

In particular, the operation when reading out the capacitance of pixels e ₁₁ to _{e 33} will be explained in more detail using FIG. 15.

Now, let pixels e ₁₁ and e ₁₃ be in a writing state and pixel e ₁₂ be in a non-writing state. At this time, if the capacitances of pixels e ₁₁ to _{e 13} are respectively C ₁₁ , C ₁₂ , and C ₁₃ , then C ₁₁ = C ₁₃ , C ₁₁ <
C ₁₂ .

Therefore, the saturation value I _S1 (I _S3 ) of the currents _i S1 to i _S3 and
I _S2 becomes as follows.

I _S1 = dv/dtC ₁₁ , I _S2 = dv/dtC ₁₂ Since C ₁₁ < C ₁₂ in the previous equation, I _S1 < I _S2 .
Note that dv/dt is the voltage increase rate of the voltage V _L1 .

Therefore, from time t ₀ when the currents i _S1 to i _S3 are saturated,
Each current is sequentially selected by switches 59a to 59c and inputted to current-voltage conversion circuit 66.

As a result, the obtained detection voltage v _S and reference voltage V _fef
The comparator circuit 67 compares the output signal with
D ₀ is taken into the image information signal conversion circuit 24 at the timing of CPR.

Through the above operations, the information written in each pixel can be read out.

By the way, the saturation time _T1 until the currents i _S1 to i _S3 are saturated is determined by the resistance of the X electrode and the Y electrode and the capacitance of each pixel, but especially as the panel becomes larger, the saturation time T1 becomes shorter. ₁ becomes longer.

However, according to this embodiment, since the current flowing through each X electrode is sequentially selected in a short period of time from the time point _t0 when the current is saturated, it is possible to substantially shorten the readout time for one screen. It is particularly suitable for reading information from large panels.

FIG. 16 shows another embodiment according to the present invention.

1out of connected to liquid crystal matrix panel 69
2 switches 71, 73 and a vertical scanning circuit 70,
Read voltage generation circuit 72, current-voltage conversion circuit 6
6. The operations of the comparison circuit 67 and the image information signal conversion circuit 24 are the same as those of the respective circuits shown in FIG.

The feature of this embodiment is that the 1out of
2 switches are divided into M blocks, and a current-voltage conversion circuit 66, a comparison circuit 67, and an image information signal conversion circuit 24 are provided corresponding to each block.

As a result, information on M pixels can be read out simultaneously, so information on one screen can be read out in a shorter time.

〔Effect of the invention〕

According to the present invention, since information written on a large matrix panel can be read out using a simple circuit and in a short time, a highly reliable and highly functional display device can be constructed.

Furthermore, it is also useful as an input tablet for kanji input, etc., which requires high resolution and high speed.

[Brief explanation of drawings]

Figure 1 is a diagram showing a conventional liquid crystal display device, Figure 2 is a diagram showing a conventional liquid crystal display device;
The figure is a block diagram of the entire device according to an embodiment of the present invention, FIGS. 3 and 4 are structural diagrams of a liquid crystal panel used in an embodiment of the present invention, and FIG. 5 is a structural diagram of a liquid crystal panel used in an embodiment of the present invention. Temperature characteristic diagrams, FIGS. 6 to 9 are diagrams showing examples of writing image information, FIGS. 10 to 13 are diagrams showing examples of image information reading circuits, and FIGS. 14 and 15 are diagrams showing examples of image information writing. FIG. 16 is a diagram showing an embodiment of the image information reading operation, and FIG. 16 is a diagram showing another embodiment of the image information reading circuit. 49a-49c, 57a-57c...X electrode, 5
0a to 50c, 58a to 58c...Y electrodes.

Claims (1)

[Claims] 1. A pair of substrates in which a plurality of rows of one electrode and a plurality of columns of the other electrode face each other on opposing surfaces, and the opposing portions of the one electrode and the other electrode are formed in a matrix shape as a whole. a dielectric held between the pair of substrates, a means for changing the capacitance of any dielectric in the opposing portion of the one electrode and the other electrode, and applying a voltage to any one of the electrodes. means for applying a voltage with a constant rate of increase dv/dt;
After the displacement current flowing through the dielectric of the opposing portion saturates during the period in which the voltage is applied to the one electrode, the displacement current flowing through at least two rows of other electrodes facing the one electrode is sequentially detected. An information holding device comprising: means.