JP4944497B2 - Display device - Google Patents

Description

  The present invention relates to a display device having a removable memory display panel, and more particularly to a display device configured to write an image on the display panel in a state where the memory display panel is detachably connected to a base unit.

  2. Description of the Related Art Conventionally, as a non-luminous display device, there is a particle movement type display device that performs display based on moving particles by applying a voltage. As an example of such a particle movement type display device, an electrophoretic phenomenon in which an electrophoretic particle moves by a Coulomb force when an electric field is applied to a dispersion liquid in which the electrophoretic particle is dispersed in an insulating liquid is used. An electrophoretic display device may be mentioned.

  As one of such electrophoretic display devices, one having a configuration in which a dispersion liquid composed of a colored insulating liquid and a plurality of charged electrophoretic particles is sealed between two electrodes is known. When a voltage is applied between these electrodes, the charged electrophoretic particles are attracted to either one of the electrodes depending on the direction of the electric field (electric field). You will see the color of the particles.

  In such an electrophoretic display device, the charged electrophoretic particles attracted to the electrodes maintain their spatial state even when the electric field in the pixel is zero, and are displayed according to the spatial state of the charged electrophoretic particles. A display image can be held. In other words, this electrophoretic display device has a memory property, and therefore requires a power source only at the time of display rewriting, so that it is effective for low power consumption.

  By the way, the following methods are known as driving methods of electrophoretic display devices utilizing such memory characteristics. That is, in the reset operation period, a reset voltage is written to each pixel electrode. In the next writing operation period, each pixel electrode has a constant voltage for a period corresponding to the gradation value indicated by the image data, or for a voltage corresponding to the gradation value indicated by the image data for a certain period. This is a driving method applied to. In this driving method, the spatial distribution state of the electrophoretic particles is fixed during the display image holding operation period after the display state substantially reaches a desired gradation level. Therefore, the potential difference between the pixel electrode and the common electrode is set to zero so that the electric field received by the electrophoretic particles is zero (see Patent Documents 1 and 2).

  However, as such a holding operation, when the potential difference between the pixel electrode and the common electrode is suddenly reduced to zero, a counter electric field (reverse electric field) having a polarity opposite to the writing voltage may be generated in the dispersion layer. Here, when the threshold characteristics of the charged electrophoretic particles are insufficient, the charged electrophoretic particles move due to the counter-electric field, and a desired display state cannot be maintained, so that there is a problem that the memory property is hindered.

  Residual DC is considered as one of the causes. Here, in the electrophoretic display device, regions having different electrical time constants exist in the electrophoretic display element, and charges are accumulated at the interface between the regions, so that a DC component is generated. This DC component is generally called residual DC. If this residual DC accumulates, even if the applied voltage to the pixel electrode is set to 0 V, a counter electric field having a polarity opposite to the applied voltage may be generated in the dispersion liquid. Since the migrating particles are rewritten under the influence of the counter electric field, the image is not sufficiently retained.

  Therefore, in the past, when the display image is held, the absolute value of the potential difference between the pixel electrode and the common electrode is not abruptly reduced to zero, but is gradually reduced within a certain period of time. The DC is reduced, thereby suppressing the generation of the counter electric field as much as possible.

  Next, this operation will be described with reference to FIG. Here, a typical case is assumed, and the display image holding operation is performed after the display state substantially reaches a desired gradation level and the writing operation to all the pixels is completed. FIG. 3 is a timing chart showing the voltage applied to the pixel and the optical response in the conventional electrophoretic display device.

  In FIG. 3A, the horizontal axis is the time axis, the vertical axis is the voltage axis, the solid line is an example of a voltage applied from the outside to a certain pixel of the electrophoretic display device, and the broken line indicates the dispersion liquid at that time. Shows the effective voltage actually applied. FIG. 3B shows the optical response at that time. In FIG. 3, A indicates a reset operation period, B indicates a write operation period, and C indicates a holding operation period. Note that the period before the reset operation period A indicates the display state performed last time.

  First, in the reset operation period A after the time t0 reaches the time t1, the reset voltage Vr is applied to reset the previous display. Next, in the writing operation period B after reaching the time t2, by applying the writing voltage Vw, the TFT element in the electrophoretic display element is driven to display a desired gradation level on the pixel.

  Here, the gradation level is controlled by pulse width modulation or amplitude modulation of the write voltage Vw. Note that the gradation level can be controlled by the length of the write voltage Vw when performing pulse width modulation, and by the magnitude of the write voltage Vw when performing voltage amplitude modulation.

  Next, in the holding operation period C after reaching time t3, display holding is performed by controlling the potential of the electrodes in order to make the electric field acting on the electrophoretic particles zero. At this time, the potential difference between the pixel electrode and the common electrode is gradually attenuated within a certain period in order to prevent the electric field from effectively becoming zero due to the residual DC. As a method for gradually attenuating the applied write voltage Vw in this way, there is the following method. That is, a method in which the applied voltage is gradually attenuated each time a voltage is applied to the pixel in each field using a plurality of fields, or the applied voltage is gradually attenuated by turning off the TFT element. It is a way to go.

  By such a holding operation, the optical response is held constant in the holding operation period C shown in FIG. 3B and the period thereafter. In this way, the generation of the counter electric field is suppressed as much as possible, and the holding characteristics are improved.

JP 2002-116733 A JP 2002-116734 A

  However, in an electrophoretic display device having a display panel unit that can be removed from the base unit, such as electronic paper, the user can easily attenuate the absolute value of the potential difference between the pixel electrode and the common electrode. The display panel unit may be removed from the display. In this case, simultaneously with the removal, the electric field in the pixel suddenly becomes zero, so that the display state may be disturbed.

In addition, while the image is being written, the user may remove the display panel unit. In this case as well, the display state is disturbed because the electric field in the pixel suddenly becomes zero simultaneously with the removal. There is a possibility .

  Therefore, the present invention has been made in view of the above circumstances, and provides a display device that can prevent a distorted image from being displayed even when the display panel unit is removed from the base unit during image writing or the like. It is intended.

The present invention is capable of detachably connecting a display panel unit having a memory display panel, and writing the image to the memory display panel in a state of being connected to the display panel unit. The display panel unit includes: a detection unit that detects that the display panel unit has been removed from the base unit; and a removal detection unit that removes the display panel unit. When There is sensed, have a, and a control means for controlling said memory type display panel, said removal detection means, said display panel unit timing reset operation period has been removed from the base unit, the writing operation period And the holding operation period, the control means When the result of the determination by the removal detection means is the reset operation period or the write operation period, an entire white writing process or an entire black writing process is executed, and the determination result by the removal detection means is In the holding operation period, a process of maintaining the display state immediately before the display panel unit is removed after the removal is performed .

  According to the present invention, even when the display panel unit is removed from the base unit during image writing or the like, when the removal detection unit detects the removal, the predetermined specific display drive is executed by the control unit. The As a result, it is possible to reliably prevent a problem that a disordered image is displayed on the removed memory display panel.

<Implementation form>
Hereinafter, the implementation form Ru engaged to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram schematically showing an electrophoretic display device as an embodiment of a display device having a removable memory display panel according to the present invention.

  As shown in FIG. 1, the electrophoretic display device includes a mother unit 6 and a display panel unit 14 that is detachably connected to the mother unit 6. The mother unit 6 includes a graphic memory (RAM) 1, a central processing unit (CPU) 2, a graphic controller (GC) 3, a panel control unit 4, and a power supply 5. The display panel unit 14 includes a data line driving circuit 8, a scanning line driving circuit 9, an electrophoretic display panel 10 as a memory display panel, a removal detection circuit 11 as a removal detection means, an auxiliary control unit 12 as a control means, and An auxiliary power supply 13 is provided.

  On the base unit 6 side, the graphic controller 3 transmits the image data of the graphic memory 1 to the panel control unit 4 according to the information transfer clock based on the command of the central processing unit 2. The panel control unit 4 generates a control signal such as a field synchronization signal, a horizontal synchronization signal, a data capture clock, and display data based on the image data from the graphic controller 3, and a data line driving circuit 8 and a scanning line driving circuit 9 Forward to.

  Then, the data line driving circuit 8 and the scanning line driving circuit 9 output a driving voltage to the electrophoretic display panel 10 according to the control signal and display data received from the panel control unit 4 to perform display. The power supply 5 supplies power to each part constituting the system.

  On the display panel unit 14 side, the removal detection circuit 11 is a circuit that electrically detects that the display panel unit 14 has been removed from the base unit 6, and the information is transmitted to the auxiliary control unit 12.

  The auxiliary control unit 12 receives information from the removal detection circuit 11 and starts control of the electrophoretic display panel 10 immediately after the display panel unit 14 is removed. At this time, the auxiliary power supply 13 supplies power for operating the auxiliary control unit 12, the data line driving circuit 8, and the scanning line driving circuit 9 for a certain period.

  The electrophoretic display panel 10 supplies the drive voltage to (applies to) the pixel electrode as the first electrode and the common electrode as the second electrode. The charged electrophoretic particles dispersed in are moved. As a result, an image is displayed on the electrophoretic display element 21 (see FIG. 2) per pixel made of the electrophoretic display element. The electrophoretic display panel 10 includes a plurality of electrophoretic display elements 21 (see FIG. 2) per pixel.

  Next, the circuit configuration of one pixel in the electrophoretic display panel 10 will be described with reference to FIG. 2 is a diagram schematically showing a circuit configuration of one of a plurality of pixels having the same configuration in the electrophoretic display panel 10.

  In FIG. 2, a plurality of gate lines (scanning lines) 23 and source lines (data lines) 24 are arranged in a matrix, but FIG. 2 shows an excerpt of one of them. . As shown in the figure, an active matrix driving display thin film transistor 22 (hereinafter referred to as TFT 22) is connected to the intersection of the gate line 23 and the source line 24. A pixel 27 is connected to the TFT 22.

  The pixel 27 has a pixel electrode 21 a connected to the drain electrode 22 a of the TFT 22, and has an electrophoretic display element 21 and an auxiliary capacitor 25, and the electrophoretic display element 21 is connected in common to the common electrode 26 and has a voltage. Vcom is applied. The auxiliary capacitor 25 is connected in parallel to the electrophoretic display element 21, one end of the electrode is connected to the drain electrode 22 a of the TFT 22, and the other end is connected to the common electrode 26. Further, the gate electrode 22 b of the TFT 22 is connected to the gate line 23, and the source electrode 22 c of the TFT 22 is connected to the source line 24.

  Here, in such a circuit configuration, when a certain gate line 23 becomes active in accordance with the drive voltage output from the scanning line drive circuit 9, all TFTs 22 connected to the gate line 23 are turned on. At this time, the drive voltage output from the data line drive circuit 8 is applied to the pixel 27 via the TFT 22. A plurality of gate lines 23 are sequentially scanned, and a drive voltage is applied to the source line 24 correspondingly, whereby a desired drive voltage is applied to the electrophoretic display element 21 of each pixel 27 and display is performed. .

  Next, the operation of the electrophoretic display panel 10 used in this embodiment will be described with reference to FIG. 3 described above.

  First, the voltage Vr is applied during the reset operation period A to the electrophoretic display element 21 for each pixel of the electrophoretic display panel 10 which is written and held at a certain grayscale level, and the grayscale level is set to black. Reset to. Thereafter, in the writing operation period B, the voltage Vw is applied between the pixel electrode 21a and the common electrode 26 to obtain a desired gradation level. Thereafter, in the holding operation period C, the potential difference between the pixel electrode 21a and the common electrode 26 is gradually attenuated within a certain period. Thereafter, a rest period is shown, and the display state is maintained with the electric field in the electrophoretic display element 21 per pixel being zero.

  Next, driving when the user removes the display panel unit 14 from the base unit 6 will be described.

Here, the timing when the user removes the display panel unit 14 from the base unit 6 is assumed to be as follows.
(1) Reset operation period A
(2) Write operation period B
(3) Holding operation period C
(4) Periods other than these periods A, B, and C

  Hereinafter, driving at each of the timings 1 to 4 will be described.

[Timing 1]
When the display panel unit 14 is detached from the base unit 6 at the timing of the reset operation period A, the removal detection circuit 11 detects that it has been removed and transmits the information to the auxiliary control unit 12. Further, the removal detection circuit 11 determines that it is the reset operation period A based on the signal indicating the reset operation period output from the panel control unit 4 immediately before the removal, and transmits the information to the auxiliary control unit 12.

  Accordingly, the auxiliary control unit 12 receives the information and drives to write the entire white (or the entire black) on the electrophoretic display panel 10. In this case, all the output stages of the scanning line driving circuit 9 are set to a high state, and the TFTs 22 of the electrophoretic display elements 21 for all the pixels of the electrophoretic display panel 10 are turned on. Then, write all white (or all black). At this time, the auxiliary power source 13 only needs to supply power for a certain period of time when the electrophoretic display panel 10 is written in white (or black). As described above, even when the reset is not completed because the user removed the display unit 14 from the mother unit 6 during the reset operation period A, it is possible to avoid displaying a distorted image. .

[Timing 2]
When the display unit 14 is removed from the base unit 6 at the timing of the writing operation period B, the removal detection circuit 11 detects that the display unit 14 has been removed, and transmits the information to the auxiliary control unit 12. Further, the removal detection circuit 11 determines that it is the writing operation period B based on the signal output from the panel control unit 4 immediately before the removal, and transmits the information to the auxiliary control unit 12. After that, similarly to the reset operation period A in the timing 1, the entire white (or the entire black) is driven to be written on the electrophoretic display panel 10. As described above, even when the writing is not completed because the user removed the display unit 14 from the base unit 6 during the writing operation period B, it is possible to avoid displaying a distorted image. .

As described above, the auxiliary control unit 12 performs the white display on the electrophoretic display panel 10 regardless of the display state immediately after the display panel unit 14 is detached from the base unit 6 after the display panel unit 14 is detached as the specific display drive set in advance. write narrowing process or entirely black writing process is executed.

  That is, the removal detection circuit 11 determines which of the reset operation period A, the write operation period B, and the holding operation period C is the timing at which the display panel unit 14 is removed from the base unit 6. When the result of determination by the removal detection circuit 11 is one of the reset operation period A and the write operation period B, the auxiliary control unit 12 executes the entire white writing process or the entire black writing process. The electrophoretic display panel 10 includes a plurality of TFTs 22 each including a source electrode 22c, a drain electrode 22a, and a gate electrode 22b for each pixel, and includes a common electrode 26 arranged with the drain electrode 22a through an electric capacitance. ing. Then, the auxiliary control unit 12 executes full white writing processing or full black writing by setting all the TFTs 22 to the same conductive state (that is, all on or all off) when executing the specific display drive. Can do.

[Timing 3]
When the display unit 14 is detached from the base unit 6 at the timing of the holding operation period C, the removal detection circuit 11 detects that the display unit 14 has been removed and transmits the information to the auxiliary control unit 12. Further, the removal detection circuit 11 determines that it is the holding operation period C based on the signal output from the panel control unit 4 immediately before the removal, and transmits the information to the auxiliary control unit 12. In response to the information, the auxiliary control unit 12 gradually changes the potential difference between the pixel electrode 21a and the common electrode 26 of each electrophoretic display element 21 per pixel of the electrophoretic display panel 10 within a certain period. Attenuate. In this case, all the output stages of the scanning line driving circuit 9 are set to the low state, and the TFTs 22 of the electrophoretic display elements 21 for all the pixels of the electrophoretic display panel 10 are turned off. Thus, the charge stored in the auxiliary capacitor 25 is gradually leaked. As described above, even if the user removes the display unit 14 from the mother unit 6 during the holding operation period C, the memory of the display image can be completed.

  As described above, the auxiliary control unit 12 performs the driving for maintaining the display state immediately before the display panel unit 14 is detached from the base unit 6 as the specific display driving set in advance.

  That is, the removal detection circuit 11 determines which of the reset operation period A, the write operation period B, and the holding operation period C is the timing at which the display panel unit 14 is removed from the base unit 6. When the result of determination by the removal detection circuit 11 is the holding operation period C, the auxiliary control unit 12 performs driving that maintains the display state immediately before the display panel unit 14 is removed after the removal. The electrophoretic display panel 10 includes a plurality of TFTs 22 each including a source electrode 22c, a drain electrode 22a, and a gate electrode 22b for each pixel, and includes a common electrode 26 arranged with the drain electrode 22a through an electric capacitance. ing. And the auxiliary control part 12 can maintain the display state immediately before removing the display panel unit 14 by removing all the TFTs 22 in the off state when executing the specific display driving.

  In this way, even when the display panel unit 14 is removed from the base unit 6 during image reset or writing, when the removal detection circuit 11 detects the removal, the predetermined specific display drive is auxiliary controlled. This is executed by the unit 12. For this reason, it is possible to reliably prevent a problem that a distorted image is displayed on the removed electrophoretic display panel 10.

[Timing 4]
When the display unit 14 is removed from the base unit 6 at a timing other than the reset operation period A, the write operation period B, and the holding operation period C, the electrophoretic display panel 10 has already completed display image memory. ,No problem. As described above, even when the user removes the display panel unit 14 from the base unit 6, it is possible to prevent a disordered image from being displayed.

< Reference embodiment>
Here, a reference embodiment in which the previous embodiment is partially modified will be described. That is, in the electrophoretic display device which is an example of the removable memory display device in the previous embodiment, for example, there is a user who wants to write full white (or full black) immediately after removal from the viewpoint of security. .

In this case, when detached at the timing 3 or timing 4 in the previous embodiment also, the same drive as the case that was removed at the timing 1 in the reset operation period A in the previous embodiment. As a result, immediately after the user removes the display panel unit 14 from the base unit 6, it is possible to rewrite the display panel to be completely white (or entirely black).

  That is, the auxiliary control unit 12 performs electrophoresis of the entire white (or the entire black) as a predetermined specific image (fixed image) immediately after the display panel unit 14 is removed from the base unit 6 as the specific display drive. It can be driven to write on the display panel 10. Also in this case, it is possible to reliably prevent a problem that a distorted image is displayed on the removed electrophoretic display panel 10.

In both embodiments, the graphic memory 1, the central processing unit 2, the graphic controller 3, the panel control unit 4, and the power source 5 are provided on the base unit 6 side, and the removal detection circuit 11, the auxiliary control unit 12, and the auxiliary power source 13 are provided. It was provided on the display panel unit 14 side. However, the present invention is not limited to the electrophoretic display device. For example, the display panel unit 14 includes a graphic memory 1, a central processing unit 2, a graphic controller 3, a panel control unit 4, a battery, and a removal detection circuit 11. Application to electrophoretic display devices is also possible. In that case, an image information transmission circuit, a charging circuit, and the like can be provided on the base unit 6 side.

In both the embodiments, the active matrix method using the TFT 22 is described as an example of the switching element connected to the electrophoretic display element 21 for each pixel of the electrophoretic display device. However, the present invention is not limited to an active matrix system using TFTs, but can be applied to an active matrix system using other switching elements such as TFD (Thin Film Diode), a segment system, and a simple matrix system.

  Furthermore, the present invention can be applied to both a vertically moving electrophoretic display device and a horizontally moving electrophoretic display device. The present invention can also be applied to an electrophoretic display device including an electrophoretic display element configured to enclose charged electrophoretic particles and a dispersion medium in each of a large number of microcapsules. The present invention is not limited to application to an electrophoretic display device. The present invention can also be applied to display devices having other display memory properties, such as toner display (Science Technical Report EID99-154, P7 (2000), Chiba Univ.), Gyricon (SID '77 Digest, p114, Xerox).

Block diagram schematically illustrating an electrophoretic display device which is an example of a display device in the implementation form engagement Ru in the present invention. Circuit diagram showing each pixel of the electrophoretic display device which is an example of a display device in engagement Ru implementation form the present invention. The timing chart figure which shows the applied voltage and optical response to the pixel of the conventional electrophoretic display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Graphic memory 2 Central processing unit 3 Graphic controller 4 Panel control part 5 Power supply 6 Base unit 8 Data line drive circuit 9 Scan line drive circuit 10 Memory display panel (electrophoretic display panel)
11 Removal detection means (detachment detection circuit)
12 Control means (auxiliary control unit)
13 Auxiliary power supply 14 Display panel unit 21 Electrophoretic display element 21
22 TFT
23 Gate line 24 Source line 25 Auxiliary capacitance

Claims (4)

A display panel unit having a memory type display panel, and a base unit capable of detachably connecting the display panel unit and writing an image on the memory type display panel in a state of being connected to the display panel unit; In a display device comprising:
The display panel unit is
Removal detecting means for detecting that the display panel unit has been removed from the base unit;
If removal of the display panel unit by said removal detection means is detected, have a, and a control means for controlling said memory type display panel,
The removal detection means determines whether the timing at which the display panel unit is removed from the base unit is a reset operation period, a write operation period, or a holding operation period,
When the result of the determination by the removal detection means is the reset operation period or the write operation period, the control means executes a full white write process or a full black write process, and the determination by the removal detection means If the result is the holding operation period, a process of maintaining the display state immediately before the display panel unit is removed after the removal is performed .
A display device characterized by that. The memory display panel includes an electrophoretic display element having a first electrode, a second electrode, and charged electrophoretic particles .
The display device according to claim 1, characterized in that. The control unit executes a process of reducing a potential difference between the first electrode and the second electrode within a certain period when the result of the determination by the removal detection unit is the holding operation period. ,
The display device according to claim 2, characterized in that. The display panel unit has a power source .
Display device according to any one of claims 1 to 3, characterized in that.

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