Patent Grant
8749477
1. Technical Field
The present invention relates to a method of driving an electrophoretic display device, an electrophoretic display device, and an electronic apparatus.
2. Related Art
In electrophoretic display devices of this type, an image is displayed by applying an electric potential difference between a pixel electrode and a common electrode that face each other with electrophoretic elements including electrophoretic particles interposed therebetween so as to move the electrophoretic particles (for example, see 2002-116733). In addition, the electrophoretic display devices of this type have a memory characteristic for conserving a displayed image even in a state that no electric potential difference is applied between the pixel electrode and the common electrode.
In addition, the electrophoretic display devices of this type can display images each having three gray scale levels or more. For example, in a case where the electrophoretic display device has the electrophoretic element including a plurality of white particles and a plurality of black particles that are charged with different charges as the electrophoretic particles, first, an electric potential difference is applied between the pixel electrodes and the common electrodes for representing a whole black display (that is, the black particles are attracted to the common electrodes of all the pixels, and the white particles are attracted to the pixel electrodes of all the pixels). Then, by applying an electric potential difference between the pixel electrode and the common electrode such that the black particles are attracted to the pixel electrode side and the white particles are attracted to the common electrode side only for a time period corresponding to the gray scale level of each pixel, a gray image can be displayed.
However, in the electrophoretic display devices of this type, when a predetermined time elapses after the image is displayed, a part of the electrophoretic particles collected in each electrode diffuses. Accordingly, for example, the reflectance of a part, which is to be displayed in a white color by the white particles, of the displayed image may decrease, and the reflectance of a part, which is to be displayed in a black color by the black particles, of the displayed image may increase. Therefore, there is a problem that the contrast of the displayed image may decrease. Accordingly, for example, in JP-A-3-213827, in order to improve the decreased contrast, technology for performing a refresh operation at each interval of 10 minutes to several tens of hours has been disclosed.
The above-described refresh operation is an operation for improving the contrast that has decreased due to diffusion of a part of the electrophoretic particles at a time when ten minutes or more elapses from display of the image. However, additionally, inventors of the invention and the like found a kickback phenomenon in which the contrast decreases in several seconds right after the image is displayed (that is, right after the image is written). Thus, for example, in the above-described case where an image having three gray scale levels or more is displayed by initially applying an electric potential difference between the pixel electrodes and the common electrodes for displaying the whole black display, and then, by applying electric potentials between the pixel electrodes and the common electrodes in accordance with the gray scale levels of the pixels, a technical problem that the contrast may decrease due to the kickback phenomenon in addition to the decrease in the contrast due to the diffusion of a part of the electrophoretic particles may occur.
An advantage of some aspects of the invention is that it provides a method of driving an electrophoretic display device and an electrophoretic display device that are capable of displaying a high-quality image by improving the contrast thereof and an electronic apparatus having the electrophoretic display device.
According to a first aspect of the invention, there is provided a method of driving an electrophoretic display device having a display unit including a plurality of pixels in which electrophoretic elements each including electrophoretic particles are disposed between a pixel electrode and a common electrode that face each other. The method includes: forming a gray scale image in the display unit by applying a voltage between the pixel electrode and the common electrode of each of the plurality of pixels in accordance with image data that has three or more gray scale levels; having the pixel electrode and the common electrode in a high-impedance state to be electrically cut off only for a predetermined period after the forming of the gray scale image; applying a first pulse voltage that has a same polarity as the voltage applied in accordance with the image data having a highest gray scale level in the forming of the gray scale image between the pixel electrode and the common electrode of a pixel of the plurality of pixels to which the voltage is applied in accordance with the image data having the highest gray scale level after the having the pixel electrode and the common electrode in the high-impedance state; and applying a second pulse voltage that has a same polarity as the voltage applied in accordance with the image data having a lowest gray scale level in the forming of the gray scale image between the pixel electrode and the common electrode of a pixel of the plurality of pixels to which the voltage is applied in accordance with the image data having the lowest gray scale level after the having the pixel electrode and the common electrode in the high impedance state.
According to the above-described method of driving the electrophoretic display device, by applying a voltage between the pixel electrode and the common electrode of each pixel of the plurality of pixels included in the display unit of the electrophoretic display device, the electrophoretic particles included in the electrophoretic element disposed between the pixel electrode and the common electrode are moved between the pixel electrode and the common electrode so as to display an image in the display unit. In particular, inside the electrophoretic element that is, for example, a microcapsule, as the electrophoretic particles, for example, a plurality of white particles negatively charged and a plurality of black particles positively charged are included. According to a voltage applied between the pixel electrode and the common electrode, one group between the plurality of white particles negatively charged and the plurality of black particles positively charged is moved (that is, electrophoresis) to the pixel electrode side, and the other group is moved to the common electrode side. Thereby, an image is displayed on the common electrode side.
According to the above-described aspect of the invention, first, in the forming of the gray scale image, a gray scale image is formed in the display unit. For example, when a gray scale image having three gray scale levels including a black color, a gray color, and a white color is formed, in the forming of the gray scale image, for example, a voltage having a first polarity (that is, a voltage having a polarity for which the electric potential of the pixel electrode becomes higher than that of the common electrode) is applied first for a first predetermined period between the pixel electrodes and the common electrodes so as to represent the whole black display (that is, for the all pixels, the black particles are attracted to the common electrode and the white particles are attracted to the pixel electrode). Subsequently, for each pixel to display the gray color, a voltage having a second polarity that is opposite to the first polarity (that is, a voltage for which the electric potential of the pixel electrode is lower than that of the common electrode) is applied between the pixel electrode and the common electrode only for a second predetermined period, so that the black particles are attracted to the pixel electrode side and the white particles are attracted to the common electrode side. Subsequently, for each pixel to display the white color, a voltage having the second polarity is applied between the pixel electrode and the common electrode only for a third predetermined period that is longer than the second predetermined period. As described above, by applying voltages between the pixel electrodes and the common electrodes, for each pixel to display the black color, the black particles can be collected on the common electrode side and the white particles can be collected on the pixel electrode side, and accordingly, the black color can be displayed. On the other hand, for each pixel to display the white color, a state in which the white particles are collected on the common electrode side and the black particles are collected on the pixel electrode side can be formed, and thereby the white color can be displayed. In addition, for each pixel to display the gray color, a state in which the black particles are relatively attracted to the pixel electrode side and the white particles are relatively attracted to the common electrode side, compared to the pixel to display the black color (that is, a state that the white particles are relatively attracted to the pixel electrode side and the black particles are relatively attracted to the common electrode side, compared to the pixel to display the white color) can be formed, and thereby the gray color can be displayed. As a result, the gray scale image having three gray scale levels of the black color, the gray color, and the white color can be formed. The above-described first, second, and third predetermined periods are set in accordance with the gray scale level of the pixel data.
Subsequently, in the having of the pixel electrode and the common electrode in the high-impedance state, the pixel electrode and the common electrode are set to the high-impedance state to be electrically cut off only for a predetermined period, for example, that is equal to or longer than 200 ms and is equal to or shorter than 5 s.
According to this aspect of the invention, particularly, after the having of the pixel electrode and the common electrode in the high-impedance state, the applying of the first pulse voltage and the applying of the second pulse voltage are performed in the described order or in the order opposite to the described order.
In other words, in the applying of the first pulse voltage, between the pixel electrode and the common electrode of a pixel, to which a voltage is applied in accordance with image data of the highest gray scale level, of the plurality of pixels, a first pulse voltage having a same polarity as that of the voltage applied in accordance with the image data of the highest gray scale level in the forming of the gray scale image is applied. For example, between the pixel electrode and the common electrode of a pixel among the plurality of pixels to display the black color as the highest gray scale level, the first pulse voltage having a first polarity for which the electric potential of the pixel electrode becomes higher than that of the common electrode is applied once or a plurality of times. In addition, in the applying of the second pulse voltage, between the pixel electrode and the common electrode of a pixel, to which a voltage is applied in accordance with the image data having the lowest gray scale level, of the plurality of pixels, a second pulse voltage having a same polarity as that of the voltage applied in accordance with the image data having the lowest gray scale level in the forming of the gray scale image is applied. For example, between the pixel electrode and the common electrode of a pixel of the plurality of pixels to display the white color as the lowest gray scale level, the second pulse voltage having a second polarity for which the electric potential of the pixel electrode becomes lower than that of the common electrode is applied once or a plurality of times.
Accordingly, the contrast of the gray scale image displayed in the display unit in the forming of the gray scale image can be improved. In other words, right after the gray scale image is displayed in the forming of the gray scale image, the contrast of the gray scale image that may decrease due to the kickback phenomenon can be improved by the applying of the first and second pulse voltages. As a result, according to the method of driving the electrophoretic display device of this aspect of the invention, an image having the high quality can be displayed.
In addition, according to this aspect of the invention, particularly, the applying of the first and second pulse voltages are performed after the forming of the gray scale image is performed. Thus, the gray scale image can be displayed in a relatively short time, and accordingly, stress due to elapse of a long time until display of the image is not given or is scarcely given to an observer or a user who observes the gray scale image. In other words, after a state that most of the whole gray scale image can be recognized by an observer is formed by displaying the gray scale image in the display unit in the forming of the gray scale image, the contrast of the gray scale image can be improved by the applying of the first and second pulse voltages, and accordingly, the image having the high quality can be displayed without any stress given to the observer or with stress scarcely given to the observer.
As described above, according to the method of driving the electrophoretic display device of this aspect of the invention, the contrast can be improved, and thereby an image having the high quality can be displayed.
In the above-described method of driving the electrophoretic display device, the pixel electrode of a pixel of the plurality of pixels to which a voltage is applied in accordance with the image data having an intermediate gray scale level may be in a high-impedance state to be electrically cut off in the applying of the first pulse voltage and the applying of the second pulse voltage.
In such a case, application of an unnecessary voltage between the pixel electrode and the common electrode of a pixel to display the intermediate gray scale level that represents the gray color in a case where a gray scale image having three gray scale levels, for example, of the black color, the gray color, and the white color is formed can be prevented. In other words, adverse affect on the pixel to display the intermediate gray scale level caused by the first or second pulse voltage can be avoided.
In the above-described method of driving the electrophoretic display device, the pixel electrode and the common electrode of a pixel of the plurality of pixels to which the image data having the intermediate gray scale level is applied may be electrically synchronized with each other in the applying of the first pulse voltage and the applying of the second pulse voltage.
In such a case, the pixel electrode and the common electrode of the pixel to display the intermediate gray scale level can be set to a same electric potential. Accordingly, application of an unnecessary voltage between the pixel electrode and the common electrode of the pixel to display the intermediate gray scale level can be prevented.
In the above-described method of driving the electrophoretic display device, the electrophoretic display device may have a memory circuit including SRAMs that are electrically connected to the pixel electrodes of the plurality of pixels and can store image signals supplied to the pixel electrodes in accordance with supply of a power supplying voltage, and the first pulse voltage may be repeatedly applied a plurality of times and a power supplying voltage that is lower than the first pulse voltage is supplied to the memory circuit as the power supplying voltage in a period excluding a period in which the first pulse voltage is applied between the pixel electrode and the common electrode, in the applying of the first pulse voltage.
In such a case, in the applying of the first pulse voltage, in a period excluding a period in which the first pulse voltage is applied between the pixel electrode and the common electrode, a power supplying voltage lower than the first pulse voltage is supplied to the memory circuit including the SRAM (Static Random Access Memory) as the power supplying voltage. Accordingly, by supplying an image signal to the memory circuit once in the applying of the first pulse voltage, the image signal can be maintained to be stored in the memory circuit. Thus, supply of the image signal to the memory circuit a plurality of times in the applying of the first pulse voltage can be avoided, and thereby power consumption needed for supplying the image signal to each pixel can be reduced. The power consumption needed for supplying an image signal to each pixel is larger than power consumption needed for supplying the power supplying voltage that is lower than the first pulse voltage to the memory circuit.
In the above-described method of driving the electrophoretic display device, the electrophoretic display device may be configured to have a memory circuit including SRAMs that are electrically connected to the pixel electrodes of the plurality of pixels and can store image signals supplied to the pixel electrodes in accordance with supply of a power supplying voltage, and the second pulse voltage may be repeatedly applied a plurality of times and a voltage that is lower than the second pulse voltage is supplied to the memory circuit as the power supplying voltage in a period excluding a period in which the second pulse voltage is applied between the pixel electrode and the common electrode, in the applying of the second pulse voltage.
In such a case, in the applying of the second pulse voltage, in a period excluding a period in which the second pulse voltage is applied between the pixel electrode and the common electrode, a power supplying voltage lower than the second pulse voltage is supplied to the memory circuit including the SRAM as the power supplying voltage. Accordingly, by supplying an image signal to the memory circuit once in the applying of the second pulse voltage, the image signal can be maintained to be stored in the memory circuit. Thus, supply of the image signal to the memory circuit a plurality of times in the applying of the second pulse voltage can be avoided, and thereby power consumption needed for supplying the image signal to each pixel can be reduced. The power consumption needed for supplying an image signal to each pixel is larger than power consumption needed for supplying the power supplying voltage that is lower than the second pulse voltage to the memory circuit.
According to a second aspect of the invention, there is provided an electrophoretic display device that is driven by the above-described method (including the various forms).
According to the above-described electrophoretic display device, the electrophoretic display device is driven by using the above-described method of driving the electrophoretic display device, a high-contrast image having the high quality can be displayed.
According to a third aspect of the invention, there is provided an electronic apparatus including the above-described electrophoretic display device (including the various forms).
According to the above-described electronic apparatus, the above-described electrophoretic display device is included. Therefore, various electronic apparatuses such as a wrist watch, an electronic paper sheet, an electronic notebook, a cellular phone, and a mobile audio instrument capable of displaying a high contrast image having the high quality can be implemented.
The operation and other advantages of the invention will be disclosed in the following description of exemplary embodiments.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings.
An electrophoretic display device according to a first embodiment of the invention will now be described with reference to
First, the whole configuration of the electrophoretic display device according to this embodiment will be described with reference to
As shown in
In the display unit 3, pixels 20 of m rows×n columns are arranged in a matrix shape (in a two-dimensional plane). In addition, in the display unit 3, m scanning lines 40 (that is, scanning lines Y1, Y2, . . . , Ym) and n data lines 50 (that is, data lines X1, X2, . . . , Xn) are disposed to intersect each other. In particular, m scanning lines 40 extend in the row direction (that is, direction X), and n data lines 50 extend in the column direction (that is, direction Y). In addition, the pixels 20 are disposed in correspondence with intersections of the m scanning lines 40 and the n data lines 50.
The controller 10 controls operations of the scanning line driving circuit 60, the data line driving circuit 70, the power supply circuit 210, and the common electric potential supplying circuit 220. The controller 10, for example, supplies timing signals such as a clock signal and a start pulse to each circuit.
The scanning line driving circuit 60 sequentially supplies scanning signals in pulses to the scanning lines Y1, Y2, . . . , Ym based on a timing signal that is supplied from the controller 10.
The data line driving circuit 70 supplies image signals to the data lines X1, X2, . . . , Xn based on a timing signal that is supplied from the controller 10. The image signals have binary levels including a high electric potential level (hereinafter, referred to as a “high level”, for example, 5 V) and a low electric potential level (hereinafter, referred to as a low level, for example, 0 V).
The power supply circuit 210 supplies a high power supplying electric potential VEP to a high-electric potential power line 91, supplies a low power supplying electric potential Vss to a low-electric potential power line 92, supplies a first electric potential S1 to a first control line 94, and supplies a second electric potential S2 to a second control line 95. Although not shown in the figure, the high-electric potential power line 91, the low-electric potential power line 92, the first control line 94, and the second control line 95 are electrically connected to the power supply circuit 210 through electrical switches.
The common electric potential supplying circuit 220 supplies a common electric potential Vcom to a common electric potential line 93. Although not shown in the figure, the common electric potential line 93 is electrically connected to the common electric potential supplying circuit 220 through an electrical switch.
In addition, various signals are input to or output from the controller 10, the scanning line driving circuit 60, the data line driving circuit 70, the power supply circuit 210, and the common electric potential supplying circuit 220. However, a description for transmission of signals that is not directly related to this embodiment is omitted here.
As shown in
The pixel switching transistor 24 is configured by an N-type transistor. The gate of the pixel switching transistor 24 is electrically connected to the scanning line 40, the source of the pixel switching transistor is electrically connected to the data line 50, and the drain of the pixel switching transistor is electrically connected to an input terminal N1 of the memory circuit 25. The pixel switching transistor 24 outputs an image signal that is supplied from the data line driving circuit 70 (see
The memory circuit 25 includes inverter circuits 25a and 25b and is configured by an SRAM.
The inverter circuits 25a and 25b form a loop structure in which, to an input terminal of any one between the inverter circuits, an output terminal of the other is connected. In other words, the input terminal of the inverter circuit 25a and the output terminal of the inverter circuit 25b are electrically connected together, and the input terminal of the inverter circuit 25b and the output terminal of the inverter circuit 25a are electrically connected together. In addition, the input terminal of the inverter circuit 25a is configured as the input terminal N1 of the memory circuit 25, and the output terminal of the inverter circuit 25a is configured as an output terminal N2 of the memory circuit 25.
The inverter circuit 25a has an N-type transistor 25a1 and a P-type transistor 25a2. The gates of the N-type transistor 25a1 and the P-type transistor 25a2 are electrically connected to the input terminal N1 of the memory circuit 25. The source of the N-type transistor 25a1 is electrically connected to the low electric potential power line 92 to which the low power supplying electric potential Vss is supplied. In addition, the source of the P-type transistor 25a2 is electrically connected to the high potential power line 91 to which the high power supplying electric potential VEP is supplied. The drains of the N-type transistor 25a1 and the P-type transistor 25a2 are electrically connected to the output terminal N2 of the memory circuit 25.
The inverter circuit 25b has an N-type transistor 25b1 and a P-type transistor 25b2. The gates of the N-type transistor 25b1 and the P-type transistor 25b2 are electrically connected to the output terminal N2 of the memory circuit 25. The source of the N-type transistor 25b1 is electrically connected to the low electric potential power line 92 to which the low power supplying electric potential Vss is supplied. In addition, the source of the P-type transistor 25b2 is electrically connected to the high potential power line 91 to which the high power supplying electric potential VEP is supplied. The drains of the N-type transistor 25b1 and the P-type transistor 25b2 are electrically connected to the input terminal N1 of the memory circuit 25.
The memory circuit 25 outputs the low power supplying electric potential Vss from the output terminal N2 in a case where a high-level image signal is input to the input terminal N1 and outputs the high power supplying electric potential VEP from the output terminal N2 in a case where a low-level image signal is input to the input terminal N1. In other words, the memory circuit 25 outputs the low power supplying electric potential Vss or the high power supplying electric potential VEP depending on whether the input image signal is the high level or the low level. It may be paraphrased that the memory circuit 25 is configured to be able to store the input image signal as the low power supplying electric potential Vss or the high power supplying electric potential VEP.
The high electric potential power line 91 and the low electric potential power line 92 are configured to be supplied with the high power supplying electric potential VEP and the low power supplying electric potential Vss from the power supply circuit 210. The high electric potential power line 91 is electrically connected to the power supply circuit 210 through a switch 91s, and the low electric potential power line 92 is electrically connected to the power supply circuit 210 through a switch 92s. The switches 91s and 92s are configured to be switched between the ON state and the OFF state by the controller 10. As the switch 91s is in the ON state, the high electric potential power line 91 and the power supply circuit 210 are electrically connected together. On the other hand, as the switch 91s is in the OFF state, the high electric potential power line 91 is in a high-impedance state to be electrically cut off. In addition, as the switch 92s is in the ON state, the low electric potential power line 92 and the power supply circuit 210 are electrically connected together. On the other hand, as the switch 92s is in the OFF state, the low electric potential power line 92 is in the high-impedance state to be electrically cut off.
The switching circuit 110 includes a first transmission gate 111 and a second transmission gate 112.
The first transmission gate 111 has a P-type transistor 111p and an N-type transistor 111n. The sources of the P-type transistor 111p and the N-type transistor 111n are electrically connected to the first control line 94. In addition, the drains of the P-type transistor 111p and the N-type transistor 111n are electrically connected to a pixel electrode 21. The gate of the P-type transistor 111p is electrically connected to the input terminal N1 of the memory circuit 25, and the gate of the N-type transistor 111n is electrically connected to the output terminal N2 of the memory circuit 25.
The second transmission gate 112 has a P-type transistor 112p and an N-type transistor 112n. The sources of the P-type transistor 112p and the N-type transistor 112n are electrically connected to the second control line 95. In addition, the drains of the P-type transistor 112p and the N-type transistor 112n are electrically connected to the pixel electrode 21. The gate of the P-type transistor 112p is electrically connected to the output terminal N2 of the memory circuit 25, and the gate of the N-type transistor 112n is electrically connected to the input terminal N1 of the memory circuit 25.
The switching circuit 110 alternately selects any one control line between the first control line 94 and the second control line 95 in accordance with an image signal input to the memory circuit 25 and electrically connects the one control line to the pixel electrode 21.
In particular, when an image signal having a high level is input to the input terminal N1 of the memory circuit 25, the low power supplying electric potential Vss is output from the memory circuit 25 to the gates of the N-type transistor 111n and the P-type transistor 112p, and the high power supplying electric potential VEP is output to the gates of the P-type transistor 111p and the N-type transistor 112n. Accordingly, in such a case, only the P-type transistor 112p and the N-type transistor 112n that constitute the second transmission gate 112 are in the ON state, and the P-type transistor 111p and the N-type transistor 111n that constitute the first transmission gate 111 are in the OFF state. On the other hand, when an image signal having a low level is input to the input terminal N1 of the memory circuit 25, the high power supplying electric potential VEP is output from the memory circuit 25 to the gates of the N-type transistor 111n and the P-type transistor 112p, and the low power supplying electric potential Vss is output to the gates of the P-type transistor 111p and the N-type transistor 112n. Accordingly, in such a case, only the P-type transistor 111p and the N-type transistor 111n that constitute the first transmission gate 111 are in the ON state, and the P-type transistor 112p and the N-type transistor 112n that constitute the second transmission gate 112 are in the OFF state. In other words, when an image signal having the high level is input to the input terminal N1 of the memory circuit 25, only the second transmission gate 112 is in the ON state. On the other hand, when an image signal having the low level is input to the input terminal N1 of the memory circuit 25, only the first transmission gate 111 is in the ON state.
The first control line 94 and the second control line 95 are configured to be supplied with the first electric potential S1 and the second electric potential S2 from the power supply circuit 210. The first control line 94 is electrically connected to the power supply circuit 210 through a switch 94s, and the second control line 95 is electrically connected to the power supply circuit 210 through a switch 95s. The switches 94s and 95s are configured to be switched between the ON state and the OFF state by the controller 10. As the switch 94s is in the ON state, the first control line 94 and the power supply circuit 210 are electrically connected together. In addition, as the switch 94s is in the OFF state, the first control line 94 is in the high-impedance state to be electrically cut off. As the switch 95s is in the ON state, the second control line 95 and the power supply circuit 210 are electrically connected together. In addition, as the switch 95s is in the OFF state, the second control line 95 is in the high-impedance state to be electrically cut off.
A pixel electrode 21 of each of the plurality of the pixels 20 is electrically connected to the control line 94 or 95 that is alternately selected in accordance with the image signal by the switching circuit 110. In such a case, the pixel electrode 21 of each of the plurality of the pixels 20 is supplied with the first electric potential S1 or the second electric potential S2 from the power supply circuit 210 based on the ON state or OFF state of the switch 94s or 95s or is in the high-impedance state.
In particular, in the pixel 20 to which the image signal having the low level is supplied, only the first transmission gate 111 is in the ON state. Accordingly, the pixel electrode 21 of the pixel 20 is electrically connected to the first control line 94 and is supplied with the first electric potential S1 from the power supply circuit 210 or is in the high-impedance state in accordance with the ON state or the OFF state of the switch 94s. On the other hand, in the pixel 20 to which the image signal having the high level is supplied, only the second transmission gate 112 is in the ON state. Accordingly, the pixel electrode 21 of the pixel 20 is electrically connected to the second control line 95 and is supplied with the second electric potential S2 from the power supply circuit 210 or is in the high-impedance state in accordance with the ON or OFF state of the switch 95s.
The pixel electrode 21 is disposed to face the common electrode 22 through the electrophoretic element 23.
The common electrode 22 is electrically connected to the common electric potential line 93 to which the common electric potential Vcom is supplied. The common electric potential line 93 is configured to be able to be supplied with the common electric potential Vcom from the common electric potential supplying circuit 220. The common electric potential line 93 is electrically connected to the common electric potential supplying circuit 220 through a switch 93s. The switch 93s is configured to be switched between the ON state and the OFF state by the controller 10. As the switch 93s is in the ON state, the common electric potential supplying circuit 220 is electrically connected to the common electric potential line 93. In addition, as the switch 93s is in the OFF state, the common electric potential line 93 is in the high-impedance state to be electrically cut off.
The electrophoretic element 23 is configured by a plurality of microcapsules that is formed to include electrophoretic particles.
Next, a detailed configuration of the display unit of the electrophoretic display device according to this embodiment will be described with reference to
As shown in
The component substrate 28 is a substrate that is formed of glass, plastic, or the like. On the component substrate 28, although not shown in the figure, a lamination structure in which the pixel switching transistor 24, the memory circuit 25, the switching circuit 110, the scanning lines 40, the data lines 50, the high-potential power line 91, the low-potential power line 92, the common electric potential line 93, the first control line 94, the second control line 95, and the like that have been described above with reference to
The opposing substrate 29 is a transparent substrate, for example, formed of glass, plastic, or the like. On a face of the opposing substrate 29 which faces the component substrate 28, the common electrode 22 is formed on the entire face so as to face a plurality of pixel electrodes 9a. The common electrode 22 is formed of a transparent conduction material such as magnesium silver (MgAg), indium tin oxide (ITO), or indium zinc oxide (IZO).
The electrophoretic element 23 is configured by a plurality of the microcapsules 80 that is formed to include electrophoretic particles. The electrophoretic element 23 is fixed between the component substrate 28 and the opposing substrate 29 by a binder 30, for example, formed of a resin or the like and an adhesive layer 31. In the electrophoretic display device 1 according to this embodiment, in the manufacturing process, an electrophoretic sheet in which the electrophoretic element 23 is fixed to the opposing substrate 29 side by a binder 30 in advance is bonded to a side of the separately-produced component substrate 28 on which the pixel electrode 21 and the like are formed through the adhesive layer 31.
The microcapsule 80 is pinched by the pixel electrode 21 and the common electrode 22. One or a plurality of the microcapsules is disposed within one pixel 20 (that is, for one pixel electrode 21).
As shown in
The coating film 85 serves as an outer shell of the microcapsule 80 and is formed of high-molecular resin such as acryl resin including polymethylmethacrylate, polyethylmethacrylate, or the like, urea resin, gum Arabic, or the like that has transparency.
The dispersion medium 81 is a medium that disperses the white particles 82 and the black particles 83 into the inside of the microcapsule 80 (that is, the inside of the coating film 85). As the dispersion medium 81, water; an alcohol-based solvent such as methanol, ethanol, isopropanol, butanol, octanol, or methyl cellosolve; a variety of esters such as acetic ethyl or acetic butyl; ketone such as acetone, methylethylketone, or methylisobutylketone; aliphatic hydrocarbon such as pentane, hexane, or octane; cycloaliphatic hydrocarbon such as cyclohexane or methylcyclohexane; aromatic hydrocarbon such as benzene, toluene, or benzene having a long-chain alkyl group including xylene, hexylbenzene, hebuthylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, dodecylbenzene, tridecylebenzene, or tetradecylbenzene; halogenated hydrocarbon such as methylene chloride, chloroform, carbon tetrachloride, or 1,2-dichloroethane; carboxylate; or other kinds of oils can be used in the form of a single material or a mixture. In addition, surfactant may be added to the above-described dispersion medium 81.
The white particles 82 are particles (polymer particles or colloids) made of white pigment such as titanium dioxide, zinc flower (zinc oxide), or antimony trioxide and, for example, are charged negatively.
The black particles 83 are particles (polymer particles or colloids) made of black pigment such as aniline black or carbon black and, for example, are charged positively.
Accordingly, the white particles 82 and the black particles 83 can move in the dispersion medium 81 due to an electric field that is generated by an electric potential difference between the pixel electrode 21 and the common electrode 22.
In addition, a charge control agent containing particles of an electrolyte, a surfactant, metal soap, a resin, rubber, oil, varnish, compound, or the like; a dispersant such as a titanium-coupling agent, an aluminum-coupling agent, and a silane-coupling agent; a lubricant; a stabilizing agent; or the like may be added to the above-described pigment, as is needed.
In
In addition, by changing the state of the distribution of the white particles 82 and the black particles 83 between the pixel electrode 21 and the common electrode 22, a gray color such as a light gray color, a gray color, or a dark gray color that corresponds to an intermediate gray scale level between the white color and the black color can be displayed. For example, after the black particles 83 are collected on the display face side of the microcapsule 80 and the white particles 82 are collected on the pixel electrode 21 side by applying a voltage between the pixel electrode 21 and the common electrode 22 such that the electric potential of the pixel electrode 21 becomes high relative to that of the common electrode, a voltage is applied between the pixel electrode 21 and the common electrode 22 such that the electric potential of the common electrode 22 becomes high relative to that of the pixel electrode 22 only for a predetermined period corresponding to an intermediate gray scale level to be represented, and thereby a predetermined amount of the white particles 82 are moved to the display face side of the microcapsule 80 and a predetermined amount of the black particles 83 are moved to the pixel electrode 21 side. As a result, a gray color that corresponds to an intermediate gray scale level between the white color and the black color can be displayed on the display face of the display unit 3.
In addition, by using pigment, for example, of a red color, a green color, a blue color, or the like instead of the pigment used for the white particles 82 or the black particles 83, the red color, the green color, the blue color, or the like can be displayed.
Next, a method of driving the electrophoretic display device according to this embodiment will be described with reference to
Hereinafter, for the convenience of description, a case where an image having five gray scale levels as shown in
As shown in
As shown in
As shown in
As shown in
As a result, after the black color writing step STB, the black color is displayed in all the pixels 20 of the display unit 3, and thereby a whole black image 510 (see
As shown in
As shown in
As shown in
As shown in
In particular, by supplying image signals having a low level to the pixels 20 disposed in the part R2, only the first transmission gates 111 (see
As a result, after the dark gray color writing step STDG, the color displayed by the pixels 20 disposed in the part R2 of the display unit 3 changes from the black color to the dark gray color, and the colors displayed by the pixels 20 disposed in the parts R1, R3, R4, and R5 of the display unit 3 are maintained to be the black colors. Accordingly, a gray scale image 520 (see
As shown in
In particular, by supplying image signals having a low level to the pixels 20 disposed in the part R3, only the first transmission gates 111 (see
Here, the gray color writing step STG is performed for a period longer than that of the dark gray color writing step STDG. In other words, a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R3 in the gray color writing step STG is set to be longer than a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R2 in the dark gray color writing step STDG. Accordingly, the pixels 20 disposed in the part R3 can display a gray color that has a gray scale level brighter than that of the dark gray color in the gray color writing step STG.
As a result, after the gray color writing step STG, the color displayed by the pixels 20 disposed in the part R3 of the display unit 3 changes from the black color to the gray color, the color displayed by the pixels 20 disposed in the parts R1, R4, and R5 of the display unit 3 is maintained to be the black color, and the color of the pixels 20 disposed in the part R2 of the display unit 3 is maintained to be the dark gray color. Accordingly, a gray scale image 530 (see
As shown in
In particular, by supplying image signals having a low level to the pixels 20 disposed in the part R4, only the first transmission gates 111 (see
Here, the light gray color writing step STLG is performed for a period longer than that of the gray color writing step STG. In other words, a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R4 in the light gray color writing step STLG is set to be longer than a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R3 in the gray color writing step STG. Accordingly, the pixels 20 disposed in the part R4 can display a light gray color that has a gray scale level brighter than that of the gray color in the light gray color writing step STLG.
As a result, after the light gray color writing step STLG, the color displayed by the pixels 20 disposed in the part R4 of the display unit 3 changes from the black color to the light gray color, the color displayed by the pixels 20 disposed in the parts R1 and R5 of the display unit 3 is maintained to be the black color, the color of the pixels 20 disposed in the part R2 of the display unit 3 are maintained to be the dark gray color, and the color of the pixels 20 disposed in the part R3 of the display unit 3 are maintained to be the gray color. Accordingly, a gray scale image 540 (see
As shown in
In particular, by supplying image signals having a low level to the pixels 20 disposed in the part R5, only the first transmission gates 111 (see
Here, the white color writing step STW is performed for a period longer than that of the light gray color writing step STLG. In other words, a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R5 in the white color writing step STW is set to be longer than a time period for which the voltages are applied between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the part R4 in the light white color writing step STLG. Accordingly, the pixels 20 disposed in the part R5 can display a white color that has a gray scale level brighter than that of the light white color in the white color writing step STW.
As a result, after the white color writing step STW, the color displayed by the pixels 20 disposed in the part R5 of the display unit 3 changes from the black color to the white color, the color displayed by the pixels 20 disposed in the parts R1 of the display unit 3 is maintained to be the black color, the color of the pixels 20 disposed in the part R2 of the display unit 3 is maintained to be the dark gray color, the color of the pixels 20 disposed in the part R3 of the display unit 3 is maintained to be the gray colors, and the color of the pixels 20 disposed in the part R4 of the display unit 3 is maintained to be the light gray color. Accordingly, a gray scale image 550 (see
As described above, in the image forming step ST10, by sequentially performing the black color writing step STB, the dark gray color writing step STDG, the gray color writing step STG, the light gray color writing step STLG, and the white color writing step STW, the gray scale image 550 of five gray scale levels including the black color, the dark gray color, the gray color, the light gray color, and the white color is displayed in the display unit 3 (in other words, the gray scale image 550 is formed in the display unit 3).
In this embodiment, in the image forming step ST10, first, the whole black image is displayed, and then image data of other gray scale levels is configured to be written. However, for example, after a whole white image is displayed, image data of other gray scale levels may be configured to be written.
As shown in
The period of the short interval step ST20, for example, is equal to or longer than 200 ms and is equal to or shorter than 5 s. For example, when the period of the short interval step ST20 is longer than 5 s, the reflectance for the black color displayed in a part R1 of the display unit 3 increases, and the reflectance for the white color displayed in a part R5 of the display unit 3 decreases. Accordingly, there is a possibility that the amount of a decrease in the contrast becomes too large. When the black auxiliary pulse inputting step ST30 and the white auxiliary pulse inputting step ST40 that will be described later are performed in the state that the contrast decreases too much as described above, there is a possibility that the change in the contrast (in other words, the change in the reflectance for the black color displayed in the part R1 and the change in the reflectance for the white color displayed in the part R5) is visually recognized by an observer, so that display is viewed to be slightly blinking (also referred to as flashing).
As shown in
As shown in
In particular, by supplying image signals having the low level to the pixels 20 disposed in the part R1, only the first transmission gates 111 (see
As a result, the reflectance for the black color displayed in the pixels 20 disposed in the part R1 of the display unit 3 that may increase due to a kickback phenomenon, which may occur right after the above-described black color writing step STB, can be lowered. In addition, in this embodiment, in the black auxiliary pulse inputting step ST30, the plurality of the black auxiliary pulse writing steps STpb is included, and accordingly, the reflectance for the black color displayed in the pixels 20 disposed in the part R1 of the display unit 3 can be lowered more assuredly.
In other words, as shown in
As shown in
As shown in
In particular, by supplying image signals having the low level to the pixels 20 disposed in the part R5, only the first transmission gates 111 (see
As a result, the reflectance for the white color displayed in the pixels 20 disposed in the part R5 of the display unit 3 that may decrease due to a kickback phenomenon, which may occur right after the above-described white color writing step STW, can increase. In addition, in this embodiment, in the white auxiliary pulse inputting step ST40, the plurality of the white auxiliary pulse writing steps STpw is included, and accordingly, the reflectance for the white color displayed in the pixels 20 disposed in the part R5 of the display unit 3 can increase more assuredly.
In other words, as shown in
As described above, according to the method of driving the electrophoretic display device of this embodiment, the reflectance for the black color displayed in the display unit 3 can decrease by performing the black auxiliary pulse inputting step ST30, and the reflectance for the white color displayed in the display unit 3 can increase by performing the white auxiliary pulse inputting step ST40. Accordingly, the contrast of the gray scale image displayed in the display unit 3 can be improved. As a result, a gray scale image having the high quality can be displayed.
In addition, according to this embodiment, in particular, the black auxiliary pulse inputting step ST30 and the white auxiliary pulse inputting step ST40 are performed within a relatively short time interval (for example, that is equal to or longer than 200 ms and is equal to or shorter than 5 s after the short interval step ST20) after the gray scale image 550 is displayed in the image forming step ST10. Accordingly, it can be suppressed or prevented that an image having the contrast decreased due to the kickback phenomenon, which may occur right after the image forming step ST10, is displayed more assuredly.
In addition, according to this embodiment, in particular, the black auxiliary pulse inputting step ST30 and the white auxiliary inputting step ST40 are performed after the image forming step ST10 is performed. Accordingly, the gray scale image 550 can be displayed in a relatively short time by performing the image forming step ST10, and thereby stress due to a long time interval until display of an image to an observer who watches the gray scale image displayed in the display unit 3 is scarcely or not given. In other words, by displaying the gray scale image 550 in the display unit 3 in the image forming step ST10, a state in which the observer can recognize almost the entirety of the gray scale image is formed. Thereafter, the contrast of the gray scale image can be improved by the black auxiliary pulse inputting step ST30 and the white auxiliary pulse inputting step ST40, and accordingly, an image with the high quality can be displayed with scarcely causing or without causing stress to the observer.
In the descriptions above, the low power supplying electric potential Vss has been described to be fixed to the low electric potential VL (for example, 0 V). However, the low power supplying electric potential Vss may be changed to be in the high-impedance state. In particular, in
Next, the temporal change of the reflectance of the display unit in a case where the above-described method of driving the electrophoretic display device is used will be described with reference
In
As shown in a part of the data DATA(B) which is surrounded by a dotted line C1 shown in
However, as shown in the data DATA(B) of
As shown in a part of the data DATA(W) of
However, as shown by the data DATA(W) in
As described above, according to the method of driving the electrophoretic display device according to this embodiment, the reflectance of the part R1 in which the black color is displayed can decrease by the black auxiliary pulse inputting step ST30. In addition, the reflectance of the part R5 in which the white color is displayed can increase by the white auxiliary pulse inputting step ST40. As a result, the contrast of the gray scale image displayed in the display unit 3 can be improved.
A method of driving an electrophoretic display device according to a second embodiment of the invention will be described with reference to
As shown in
As shown in
In particular, in
In addition, at that moment, according to this embodiment, particularly, the second electric potential S2 is maintained at the low electric potential VL by the power supply circuit 210 so as to be synchronized (or tuned) with the common electric potential Vcom. In other words, in the black auxiliary pulse inputting step ST30, the second electric potential S2 is alternately switched between the high-impedance state and the low electric potential VL with the same period as that of the common electric potential Vcom. Accordingly, in the black auxiliary pulse writing step STpb, the pixel electrodes 21 of the pixels 20 disposed in the parts R2, R3, R4, and R5 of the display unit 3 electrically connected to the second control line 95 are in synchronization with the common electric potential Vcom that is supplied to the common electrode 22 to be the low electric potential VL. As a result, application of an unnecessary voltage between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the parts R2, R3, R4, and R5 can be prevented.
In
In addition, at that moment, according to this embodiment, particularly, the second electric potential S2 is maintained at the high electric potential VH by the power supply circuit 210 so as to be synchronized (or tuned) with the common electric potential Vcom. In other words, in the white auxiliary pulse inputting step ST40, the second electric potential S2 is alternately switched between the high-impedance state and the high electric potential VH with the same period as that of the common electric potential Vcom. Accordingly, in the white auxiliary pulse writing step STpw, the pixel electrodes 21 of the pixels 20 disposed in the parts R1, R2, R3, and R4 of the display unit 3 electrically connected to the second control line 95 are in synchronization with the common electric potential Vcom that is supplied to the common electrode 22 to be the high electric potential VH. As a result, application of an unnecessary voltage between the pixel electrodes 21 and the common electrodes 22 of the pixels 20 disposed in the parts R1, R2, R3, and R4 can be prevented.
A method of driving an electrophoretic display device according to a third embodiment of the invention will be described with reference to
As shown in
As shown in
As shown in
Electronic Apparatus
Next, electronic apparatuses in which the above-described electrophoretic display device is used will be described with reference to
As shown in
As shown in
In the electronic paper sheet 1400 and the electronic notebook 1500 described above, the electrophoretic display device according to the above-described embodiment is included, and thereby display of a high-quality image can be performed with low power consumption.
In addition, in a display unit of an electronic apparatus such as a wrist watch, a cellular phone, or a mobile instrument, the electrophoretic display device according to the above-described embodiment can be used.
The invention is not limited to the above-described embodiments, and the embodiments may be appropriately changed without departing from the scope of the gist or idea of the invention which can be read from the Claims and descriptions here. Thus, a method of driving an electrophoretic display device and an electrophoretic device that have such changes therein, and an electronic apparatus that is configured to include the electrophoretic display device belongs to the technical scope of the invention.
The entire disclosure of Japanese Patent Application No. 2008-023029, filed Feb. 1, 2008 is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-023029 | Feb 2008 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6650462 | Katase | Nov 2003 | B2 |
| 7019889 | Katase | Mar 2006 | B2 |
| 7034783 | Gates et al. | Apr 2006 | B2 |
| 7359110 | Katase | Apr 2008 | B2 |
| 7542024 | Koyama | Jun 2009 | B2 |
| 7973761 | Yokoo et al. | Jul 2011 | B2 |
| 8098228 | Shimodaira et al. | Jan 2012 | B2 |
| 8294663 | Miyazaki | Oct 2012 | B2 |
| 20020021483 | Katase | Feb 2002 | A1 |
| 20030048370 | Koyama | Mar 2003 | A1 |
| 20060028427 | Katase | Feb 2006 | A1 |
| 20060209011 | Miyasaka | Sep 2006 | A1 |
| 20060244713 | Zhou et al. | Nov 2006 | A1 |
| 20070030243 | Ishii | Feb 2007 | A1 |
| 20070080928 | Ishii et al. | Apr 2007 | A1 |
| 20070120816 | Yokoo et al. | May 2007 | A1 |
| 20070176889 | Zhou et al. | Aug 2007 | A1 |
| 20080094388 | Yamazaki | Apr 2008 | A1 |
| 20080150887 | Kim et al. | Jun 2008 | A1 |
| 20080238867 | Maeda et al. | Oct 2008 | A1 |
| 20090128585 | Shimodaira | May 2009 | A1 |
| 20090237350 | Yamada | Sep 2009 | A1 |
| 20090237383 | Saito | Sep 2009 | A1 |
| 20110102481 | Miyasaka et al. | May 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 03-213827 | Sep 1991 | JP |
| 2002-116733 | Apr 2002 | JP |
| 2004-102054 | Apr 2004 | JP |
| 2006-267982 | Oct 2006 | JP |
| 2006-526801 | Nov 2006 | JP |
| 2007-041385 | Feb 2007 | JP |
| 2007-316594 | Dec 2007 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20090195566 A1 | Aug 2009 | US |
