JP2002297079A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device, capable of lowering a voltage to be applied to signal wirings between a driving circuit and pixels in a display device, in which relatively high voltage is needed for driving pixels. SOLUTION: This display device is provided, with plural segments #1 to #7 and an AC power source 3 for supplying a first drive voltage to respective segments; each segment has a voltage converting circuit, including at least a voltage transformer 6 which receives the first driving voltage and boosts it to a second driving voltage higher than it and pixels 4, to which the second driving voltage is applied. In this device, since the drive voltage is boosted locally in each segment, the voltage to be applied from the AC power source 3 to wirings to each segment can be suppressed low. As a result, since voltage drops generated in these wirings are reduced, deterioration in the display characteristics is prevented, and also power loss is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device,
More specifically, the present invention relates to a display device in which a voltage applied to a signal wiring between a driving circuit and a pixel is reduced.

[0002]

2. Description of the Related Art Conventionally, an electrophoretic display device utilizing an electrophoretic phenomenon has been known. In the electrophoretic display device, a medium and electrophoretic particles having a positive or negative charge are sealed therein, and by applying an electric field to the electrophoretic particles, the electrophoretic particles are collected on the display surface side of the display panel. Alternatively, it is possible to move away from the display surface side of the display panel, thereby displaying a desired image.

In order to drive such an electrophoretic display device,
In general, a high voltage of about 10 V to several hundreds of V is required. Therefore, a drive circuit for driving each pixel is provided with a booster circuit for boosting a power supply voltage, and a drive voltage generated by the booster circuit is provided. Is generally given to each pixel.

[0004]

However, in such an electrophoretic display device, a high drive voltage of about 10 V to several hundred V boosted by the boost circuit is applied to the signal wiring from the drive circuit to each pixel. From that
The voltage drop that occurs in such wiring becomes very large. For this reason, not only does the voltage actually applied to the pixels drop significantly, deteriorating the display characteristics,
There is a problem that the loss due to the voltage drop is very large.

In addition, since the amount of the voltage drop differs depending on the wiring length from the driving circuit to each pixel, there is a problem that the driving voltage applied to each pixel varies, which may cause display unevenness. .

[0006] Such a problem occurs not only in an electrophoretic display device but also in a display device requiring a relatively high voltage for driving a pixel. Therefore, a relatively high voltage is required for driving a pixel. In the required display device,
There has been a demand for a method capable of reducing a voltage applied to a signal wiring between a driving circuit and a pixel.

Accordingly, an object of the present invention is to provide a display device which requires a relatively high voltage for driving a pixel and which can reduce a voltage applied to a signal line between a driving circuit and the pixel. To provide.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
A plurality of segments, and voltage supply means for supplying a first drive voltage to each of the segments, wherein each of the segments receives the first drive voltage and supplies the second drive voltage to a second drive voltage higher than the first drive voltage. And a pixel to which the second drive voltage is applied.

According to the present invention, since the drive voltage is locally boosted in each segment, the voltage applied from the voltage supply means to the wiring to each segment can be suppressed low. As a result, the voltage drop that occurs in such wiring is reduced, deterioration of display characteristics is prevented, and loss is also reduced.

[0010] In a preferred embodiment of the present invention, the boosting means comprises a piezoelectric transformer.

[0011] In a further preferred aspect of the present invention, the voltage conversion circuit further includes a rectifier circuit.

[0012] In a further preferred aspect of the present invention, the rectifier circuit is a diode bridge circuit.

[0013] In another preferred embodiment of the present invention, the rectifier circuit is a transistor bridge circuit.

[0014] In a further preferred aspect of the present invention, the voltage conversion circuit further includes a smoothing capacitor.

In a further preferred aspect of the present invention, the pixel is an electrophoretic display device comprising a lower electrode, an upper electrode, and an electrophoretic layer provided between the lower electrode and the upper electrode. .

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A preferred embodiment of the present invention will be described in detail.

FIG. 1 is a circuit diagram of a display device 1 according to a preferred embodiment of the present invention. As shown in FIG. 2, the display device 1 according to the present embodiment is a seven-segment display device including segments # 1 to # 7, and can display numbers from 0 to 9.

As shown in FIG. 1, the display device 1 according to the present embodiment includes a segment # 1 to a segment # 7,
A control circuit 2 for controlling the display state of the segments # 1 to # 7 and an AC power supply 3 for generating an AC voltage of 1 V are provided. The segments # 1 to # 7 are provided with pixels 4-1 to 4-7, respectively. , Switches 5-1 to 5-7, piezoelectric transformers 6-1 to 6-7, diode bridge circuits 7-1 to 7-7, and smoothing capacitors 8-1 to 8-7.

The pixels 4-1 to 4-7 are pixels utilizing the phenomenon of electrophoresis. As described in detail below, each pixel 4-1 to 4-1
4-7, when a voltage of +10 V or more is applied between both electrodes, the state becomes "lit state", and when the voltage is not applied, the state becomes "off state" naturally.

The switches 5-1 to 5-7 receive control signals 9-1 to 9-7 supplied by the control circuit 2, respectively, and their conduction / non-conduction are controlled. In the present embodiment, each of the switches 5-1 to 5-7 becomes conductive when the corresponding control signal 9-1 to 9-7 is at a high level,
If the corresponding control signals 9-1 to 9-7 are at a low level, a non-conductive state is established.

Each of the piezoelectric transformers 6-1 to 6-7 has input terminals a and b and an output terminal c.
Is applied between the output terminal c and the input terminal b.
A voltage is generated by boosting this voltage. As such a piezoelectric transformer, a piezoelectric ceramic such as zirconate titanate can be used.

Diode bridge circuits 7-1 to 7-7
Are circuits that receive output voltages from the piezoelectric transformers 6-1 to 6-7 and rectify the output voltages, and the output voltages have pulsating waveforms.

The smoothing capacitors 8-1 to 8-7 receive output voltages from the diode bridge circuits 7-1 to 7-7 and smooth the same, respectively. The smoothed voltage is supplied between both electrodes of the pixels 4-1 to 4-7.

As described above, the piezoelectric transformer 6, the diode bridge circuit 7, and the smoothing capacitor 8 function as a voltage conversion circuit that boosts the AC voltage supplied from the AC power supply 3 and smoothes the voltage.

FIG. 3 is a schematic sectional view schematically showing the structure of the pixels 4-1 to 4-7.

As shown in FIG. 3, pixels 4-1 to 4-
Reference numeral 7 denotes a lower film 10, an upper film 11, a lower electrode 12 formed on the lower film 10, an upper electrode 13 formed on the upper film 11, and a gap between the lower electrode 12 and the upper electrode 13. Electrophoresis layer 1 enclosed in
4 is provided.

The electrophoretic layer 14 includes an electrically neutral medium and negatively charged electrophoretic particles. As will be described later, a dye is added to the medium, thereby giving a different brightness, color, and the like from the electrophoretic particles. The material of the medium contained in the electrophoretic layer 14 has a low solubility for electrophoretic particles, a high solubility for dyes, can stably dissolve or disperse dyes and electrophoretic particles, does not contain ions, and does not contain ions. It is desirable to use an insulating material that does not cause any problem. In particular,
Saturated hydrocarbons such as hexane, decane, hexadecane, and kerosene; aromatic hydrocarbons such as toluene, xylene, and trimethylbenzene; halogenated fluorine-based hydrocarbons such as trichlorotrifluoroethane, dibromotetrafluoroethane, and tetrachloroethylene; and fluorine-based solvents Can be mentioned. Note that these liquids can be used as a mixture. In this embodiment, when no voltage is applied between the lower electrode 12 and the upper electrode 13, the electrophoretic particles move toward the lower electrode 12 by gravity.
The medium has a slightly lower viscosity.

Examples of the dye added to the medium include cyanine-based, phthalocyanine-based, naphthalocyanine-based, anthraquinone-based, azo-based, triphenylmethane-based, pyrylium or thiapyrylium salt-based, squarylium-based, and the like.
One or more kinds selected from croconium-based, metal complex dye-based, and the like, or a pigment appropriately selected according to the purpose can be used. The content of the dye is not particularly limited, and may be appropriately adjusted depending on the type, desired color, lightness, and the like.
About 10 to 10% by mass. In the following description,
The medium assumes a black color due to the added dye.

It is desirable that the electrophoretic particles are stably dispersed in a medium. Further, the particle size is preferably 0.05 μm to 7 μm. Within this range, the contrast is high and a sufficient response speed can be obtained when a voltage is applied.

Examples of the material of the electrophoretic particles include titanium oxide, zinc oxide, zirconium oxide, iron oxide, aluminum oxide, cadmium selenide, carbon black,
Inorganic pigments such as barium sulfate, lead chromate, zinc sulfide, cadmium sulfide, and calcium carbonate, or organic pigments such as phthalocyanine blue, phthalocyanine green, Hansa Yellow, Watching Red, and Diary Ride Yellow can be used. Among them, titanium oxide is preferable in order to obtain a high contrast ratio, and rutile type is particularly preferable. still,
In the following description, it is assumed that the electrophoretic particles have a white color.

The mixing ratio of the electrophoretic particles to the medium is not particularly limited as long as the electrophoretic properties of the electrophoretic particles are not hindered and the reflection of the medium can be sufficiently controlled. To 30% by mass is preferred.

The pixels 4-1 to 4- having the above structure
7, when a voltage of +10 V or more is applied between the lower electrode 12 and the upper electrode 13, the electrophoretic particles in the electrophoretic layer 14 constituting the pixel move to the upper electrode 13 side, and the “lighting state” Becomes As described above, in the present embodiment, since the medium included in the electrophoretic layer 14 is black and the electrophoretic particles are white, the pixels in the lighting state are black. On the other hand, if the voltage between the lower electrode 12 and the upper electrode 13 is less than +10 V, the electrophoretic particles in the electrophoretic layer 14 forming the pixel move to the lower electrode 12 side due to gravity, and the light turns off. Become. Pixels in the unlit state are white.

Next, the operation of the display device 1 according to this embodiment will be described.

In the display device 1 according to this embodiment, when any of the numbers 0 to 9 is displayed by the segments # 1 to # 7, the display device 1 should be turned on under the control of the control circuit 2. Control signal 9 corresponding to the segment
-1 to 9-7 are set to the high level, and the control signals 9-1 to 9-7 corresponding to the segments to be turned off are set to the low level.

Thus, the corresponding control signals 9-1 to 9
For segments where -7 is high,
An AC voltage of 1 V supplied from the AC power supply 3 is applied between the input terminal a and the input terminal b of the piezoelectric transformer 6, and the AC voltage is applied between the output terminal c and the input terminal b of the piezoelectric transformer 6. , And an AC voltage of 10 V appears. This voltage is
The light is rectified by the diode bridge circuit 7 and smoothed by the smoothing capacitor 8 and applied between the two electrodes of the pixel 4, whereby the corresponding pixel 4 is turned on.

On the other hand, in the segment where the corresponding control signals 9-1 to 9-7 are at the low level, no AC voltage is applied between the input terminal a and the input terminal b of the piezoelectric transformer 6, so that the piezoelectric voltage is not applied. No voltage appears between the output terminal c and the input terminal b of the transformer 6. Therefore, the voltage between both electrodes of the pixel becomes +10 V or less, and the corresponding pixel 4
Is turned off.

As described above, the display device 1 according to the present embodiment locally boosts the voltage in each of the segments # 1 to # 7.
The voltage applied to the wiring to 7 is kept low. As a result, the voltage drop that occurs in such wiring is reduced, deterioration of display characteristics is prevented, and loss is also reduced.

Next, another preferred embodiment of the present invention will be described.

FIG. 4 is a circuit diagram of a display device 20 according to another preferred embodiment of the present invention. The display device 20 according to the present embodiment is also a seven-segment display device including segments # 1 to # 7, as shown in FIG. 2, and can display numbers from 0 to 9.

As shown in FIG. 4, the display device 20 according to the present embodiment has segments # 1 to # 7.
And a control circuit 22 for controlling the display state of the segments # 1 to # 7, and an AC power supply 23 for generating an AC voltage of 1 V.
Each of the pixels 24-1 to 24-7 and the piezoelectric transformer 26
-1 to 26-7 and a transistor bridge circuit 27-1
27-7 and smoothing capacitors 28-1 to 28-7.

The pixels 24-1 to 24-7 are pixels utilizing the electrophoresis phenomenon. As described in detail below, each pixel 24
-1 to 24-7 are the pixels 4-1 to 4-1 according to the above embodiment.
Unlike 4-7, when a voltage of +10 V or more is applied between both electrodes, the state is turned on, and when a voltage of -10 V or more is applied between the electrodes, the state is turned off. When the voltage between the two electrodes is lower than the above voltage, the immediately preceding display state is maintained.

The piezoelectric transformers 26-1 to 26-7 have input terminals a and b and an output terminal c, respectively. When an AC voltage is applied between the input terminals a and b, the output terminals c and A boosted voltage is generated between the input terminal b. As such a piezoelectric transformer, a piezoelectric ceramic such as zirconate titanate can be used similarly to the piezoelectric transformers 6-1 to 6-7 according to the above embodiment.

Transistor bridge circuits 27-1 to 27
-7 is a circuit which receives the output voltage from each of the piezoelectric transformers 26-1 to 26-7 and rectifies the voltage. The transistors Q2 and Q3 are turned on, and the transistors Q1 and Q3 are turned on.
4 is off, the output voltage has a one-way pulsating waveform. Conversely, when the transistors Q1 and Q4 are on and the transistors Q2 and Q3 are off, the output voltage is A reverse pulsating waveform is obtained.

The smoothing capacitors 28-1 to 28-7 are circuits which receive output voltages from the transistor bridge circuits 27-1 to 27-7 and smooth the same, respectively. The smoothed voltage is supplied between the quantity electrodes of the pixels 24-1 to 24-7, respectively.

The control circuit 22 controls the control signals 29-1 to 29
-7 is a circuit for supplying -7 to segments # 1 to # 7, respectively. Each of the control signals 29-1 to 29-7 includes an on signal and an off signal, and the on signal is a transistor bridge circuit 27-1 to 27-7 in the corresponding segment.
Are commonly applied to the gate electrodes of the transistors Q2 and Q3, and the off signal is commonly applied to the gate electrodes of the transistors Q1 and Q4 configuring the transistor bridge circuits 27-1 to 27-7 in the corresponding segment.

FIG. 5 is a schematic sectional view schematically showing the structure of the pixels 24-1 to 24-7.

As shown in FIG. 5, the pixels 24-1 to 24-2
4-7, the lower film 30, the upper film 31,
A lower electrode 32 formed on the lower film 30; an upper electrode 33 formed on the upper film 31; a charge transport layer 34 that covers the lower electrode 32 and the upper electrode 33;
35, and an electrophoretic layer 36 enclosed between the charge transport layers 34, 35.

The electrophoretic layer 36 can be composed of components similar to those of the electrophoretic layer 14 used in the above-described embodiment.
The medium contained in is the movement of electrophoretic particles due to gravity,
It is preferable to have a viscosity such that condensation of the electrophoretic particles does not substantially occur.

The charge transport layers 34 and 35 are made of a P-type semiconductor. By interposing such charge transport layers, the display contents can be maintained for a longer time after the voltage is not applied. Becomes possible.

Pixels 24-1 and 24-2 having such a structure
4-7 is +10 between the lower electrode 32 and the upper electrode 33.
When a voltage equal to or higher than V is applied, the electrophoretic particles in the electrophoretic layer 36 constituting the pixel move to the upper electrode 33 side and enter a “lighting state”. Also in the present embodiment, since the medium included in the electrophoretic layer 36 is black and the electrophoretic particles are white, the pixels in the lighting state are black. On the other hand, when a voltage of −10 V or more is applied between the lower electrode 32 and the upper electrode 33, the electrophoretic particles in the electrophoretic layer 36 constituting the pixel move to the lower electrode 32 side and “turn off”. Becomes Pixels in the unlit state are white.

Next, the operation of the display device 20 according to this embodiment will be described.

In the display device 20 according to this embodiment, when any one of the numbers 0 to 9 is displayed by the segments # 1 to # 7, the display device 20 should be turned on under the control of the control circuit 22. The on signal of the control signal corresponding to the segment is set to the high level, the off signal is set to the low level, while the on signal of the control signal corresponding to the segment to be turned off is set to the low level, and the off signal is set to the high level.

As a result, in the segment where the on signal of the corresponding control signal is at the high level and the off signal is at the low level, the transistors Q2 and Q3 of the transistor bridge circuit 27 are turned on, and the transistors Q1 and Q4 are turned off. As a result, the AC voltage between the output terminal c and the input terminal b of the piezoelectric transformer 26 is rectified in one direction, and is rectified by the smoothing capacitor 28.
It is applied between both electrodes of the pixel 24. Thereby, the corresponding pixel 24 is turned on.

On the other hand, in the segment where the corresponding control signal on signal is at low level and the off signal is at high level, the transistors Q1 and Q4 of the transistor bridge circuit 27 are turned on, and the transistor Q1 is turned on.
2 and Q3 are turned off, so that the AC voltage between the output terminal c and the input terminal b of the piezoelectric transformer 26 is rectified in the opposite direction,
This is smoothed by the smoothing capacitor 28 and the pixel 2
4 is applied between both electrodes. Thereby, the corresponding pixel 24 is turned off.

The contents displayed by the segments # 1 to # 7 in this manner correspond to the control signals 29-1 to 29-7.
Are kept low by setting both the on signal and the off signal to low level, and turning off all the transistors Q1 to Q4 constituting the transistor bridge circuits 27-1 to 27-7.

As described above, the display device 20 according to the present embodiment also locally boosts the voltage in each of the segments # 1 to # 7.
The voltage applied to the wiring to # 7 is kept low. As a result, the voltage drop that occurs in such wiring is reduced, deterioration of display characteristics is prevented, and loss is also reduced.

Further, in this embodiment, since the rectification is performed using the transistors Q1 to Q4 in each of the segments # 1 to # 7, the voltage applied between both electrodes of the pixels 24-1 to 24-7 is reduced. The direction can be reversed, so that each of the pixels 24-1 to 24-7 can be driven not only in a lighted state but also in a light-off state. in this way,
In the present embodiment, each of the pixels 24-1 to 24-7 can be driven not only in a lighting state but also in an extinguished state. Therefore, in a state where no pixel is driven, the display state is changed to the immediately preceding display state. It is possible to maintain the state.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the invention described in the claims, which are also included in the scope of the present invention. It goes without saying that it is a thing.

For example, each of the above embodiments is an example in which the present invention is applied to a seven-segment display device. However, the scope of the present invention is not limited to a seven-segment display device, and other types of display devices are applicable. For example, the invention can be applied to a matrix type display device.

In each of the above embodiments, the present invention is applied to an electrophoretic display device. However, the scope of the present invention is not limited to the electrophoretic display device.
Any display device that requires a relatively high voltage to drive the pixel can be applied to other types of display devices.

Further, in the display device according to each of the above embodiments, electrophoretic particles exhibiting white and a medium exhibiting black are used in the electrophoretic layers 14 and 36, but their brightness is reversed, that is, black. Electrophoretic particles and a white medium may be used. Furthermore, these may be not only white and black, but also other color combinations, for example, red and blue. In addition, it is not essential to use electrophoretic particles and media having different lightness for the electrophoretic layers 14 and 36,
The electrophoretic layers 14 and 36 may be configured by using two types of display particles having different lightness from each other and making one of the display particles positive or negative. further,
Electrophoretic layers 14 and 36 are formed by encapsulating a large number of such microcapsules in a predetermined color, for example, a black solution in which conductive particles having a different color, for example, white, are encapsulated. May be. Further, one side is made of a predetermined color, for example, a black conductive substance, and the other side is made of a different color, for example, a microcapsule made of a white insulating substance. The electrophoretic layers 14 and 36 may be configured by the following.

In the display device according to each of the above-described embodiments, the electrophoretic particles included in the electrophoretic layers 14 and 36 are negatively charged electrophoretic particles. The charge need not be negative, but may be positive. The particles to be electrophoresed need not be conductive particles, but may be insulating particles.

Further, in the electrophoretic display device according to each of the above-described embodiments, a separator may be provided to partition the inside of the electrophoretic layers 14 and 36 for each pixel, thereby forming a cell structure.

[0064]

As described above, in the present invention, since the drive voltage is locally boosted in each segment, the voltage applied from the voltage supply means to the wiring to each segment can be kept low. As a result, the voltage drop that occurs in such wiring is reduced, deterioration of display characteristics is prevented, and loss is also reduced.

[Brief description of the drawings]

FIG. 1 shows a display device 1 according to a preferred embodiment of the present invention.
FIG.

FIG. 2 is a schematic plan view showing an arrangement of segments # 1 to # 7 in the display device 1.

FIG. 3 is a schematic sectional view schematically showing a structure of pixels 4-1 to 4-7.

FIG. 4 is a circuit diagram of a display device 20 according to another preferred embodiment of the present invention.

FIG. 5 is a schematic sectional view schematically showing the structure of pixels 24-1 to 24-7.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Control circuit 3 AC power supply 4 Pixel 5 Switch 6 Piezoelectric transformer 7 Diode bridge circuit 8 Smoothing capacitor 9 Control signal 10 Lower film 11 Upper film 12 Lower electrode 13 Upper electrode 14 Electrophoretic layer 20 Display 22 Control circuit 23 AC Power supply 24 Pixel 26 Piezoelectric transformer 27 Transistor bridge circuit 28 Smoothing capacitor 29 Control signal 30 Lower film 31 Upper film 32 Lower electrode 33 Upper electrode 34, 35 Charge transport layer 36 Electrophoretic layer

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[Procedure amendment]

[Submission date] May 24, 2001 (2001.5.2)
4)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 3

FIG. 4

FIG. 5

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H02M 7/06 H02M 7/06 VF term (Reference) 5C080 AA13 BB02 DD05 EE28 FF03 JJ01 JJ03 JJ06 5H006 CA02 CA07 CB01 CC01 CC04 CC08

Claims (7)

[Claims] A plurality of segments; and a voltage supply unit for supplying a first drive voltage to each of the segments, wherein each of the segments receives the first drive voltage and supplies the first drive voltage to the first drive voltage. A display device, comprising: a voltage conversion circuit including at least boosting means for boosting to a higher second drive voltage; and a pixel to which the second drive voltage is applied. 2. The display device according to claim 1, wherein said step-up means comprises a piezoelectric transformer. 3. The display device according to claim 1, wherein the voltage conversion circuit further includes a rectifier circuit. 4. The display device according to claim 3, wherein the rectifier circuit is a diode bridge circuit. 5. The display device according to claim 3, wherein the rectifier circuit is a transistor bridge circuit. 6. The display device according to claim 3, wherein the voltage conversion circuit further includes a smoothing capacitor. 7. The pixel, comprising: a lower electrode; an upper electrode;
The display device according to claim 1, wherein the display device is an electrophoretic display element including an electrophoretic layer provided between the lower electrode and the upper electrode.