Source: http://www.google.com/patents/US6961047?ie=ISO-8859-1&dq=6076065
Timestamp: 2015-05-07 07:59:43
Document Index: 230131632

Matched Legal Cases: ['art 340', 'art 350', 'art 411', 'art 412', 'art 412', 'art 411']

Patent US6961047 - Method and circuit for driving electrophoretic display, electrophoretic ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method for driving an active matrix electrophoretic display is provided. In a resetting period Tr, reset data Drest is supplied to a data line drive circuit and a reset voltage is applied to each pixel electrode. Next in a writing period, an image data is supplied to a data line drive circuit and a...http://www.google.com/patents/US6961047?utm_source=gb-gplus-sharePatent US6961047 - Method and circuit for driving electrophoretic display, electrophoretic display and electronic device using sameAdvanced Patent SearchPublication numberUS6961047 B2Publication typeGrantApplication numberUS 10/849,878Publication dateNov 1, 2005Filing dateMay 21, 2004Priority dateJun 22, 2000Fee statusPaidAlso published asUS6762744, US20020005832, US20040212870Publication number10849878, 849878, US 6961047 B2, US 6961047B2, US-B2-6961047, US6961047 B2, US6961047B2InventorsMakoto KataseOriginal AssigneeSeiko Epson CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (24), Non-Patent Citations (2), Referenced by (10), Classifications (23), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetMethod and circuit for driving electrophoretic display, electrophoretic display and electronic device using same
US 6961047 B2Abstract
1. A method for driving an electrophoretic display, the display comprising:
a plurality of data lines; a plurality of scanning lines, each of which intersects said data lines; a common electrode; a plurality of pixel electrodes, with one of said plurality of pixel electrodes being provided at one of each of said intersections of said data lines and said scanning lines, each of said pixel electrodes being provided in opposing spaced relation to said common electrode; a plurality of dispersal systems including a fluid in which pigment particles are suspended, with each of said dispersal systems being provided between said common electrode and one of said pixel electrodes; and a plurality of switching elements, with one of each of said switching elements being provided at a corresponding one of each of said intersections of said data lines and said scanning lines, with an on/off control terminal being connected to one of said scanning lines passing through one of said intersections; and with one of said data lines passing through one of said intersections, being connected to one of said pixel electrodes provided at each of one said intersections; and the method comprising: controlling an image displayed by employing said scanning lines and said data lines, each of said voltages being applied within a set period of a single scanning field, in which all of said scanning lines are once scanned; and within said period of a single scanning field, applying a common voltage to a said pixel electrode; selecting a scanning line sequentially; applying a voltage to a selected scanning line, to turn on all switching elements connected to said selected scanning lines; applying a plurality of pixel voltages to a plurality of said data lines for a set time, to generate electrostatic fields to cause said pigment particles to migrate to positions corresponding to desired gradations of an image displayed; and after applying said pixel voltages to said data lines, applying a plurality of brake voltages to said data lines for a set time, to create electrostatic fields in each of said dispersal systems, each of said brake voltages determined based on fluid resistance of said pigment particles and a respective one of said desired gradations; applying a voltage to said sequentially selected scanning lines, to turn off all of said switching elements connected to said sequentially selected scanning line. 2. The method of claim 1, wherein resetting operation is performed during a period of said scanning field and writing operation is performed during a period of a different scanning field, said resetting and writing operations performed alternately, and
the method further comprising the steps of: in said period for said resetting operation, applying a reset voltage to said plurality of data lines, to create an electrostatic field in each of said dispersal systems, to initialize said pigment particles; and in said period for said rewriting operation, applying to said selected data lines a plurality of voltages corresponding to said desired gradations. 3. The method of claim 2, wherein when a displayed image is switched, said pixel voltage and said reset voltage are applied to only those pixel electrodes corresponding to pixels, the gradation of which pixels change following switching of an image displayed.
a plurality of said scanning lines are selected simultaneously; and said reset voltage is applied to a plurality of said data lines, so that said reset voltage is applied simultaneously to said plurality of pixel electrodes to initialize said pigment particles. 5. The method of claim 1, wherein:
resetting operation is performed during a period of a scanning field and writing operation is performed during a period of next and different scanning field, in said period for said resetting operation, applying said reset voltage is applied to said plurality of pixel electrodes, to initialize said pigment particles; and in said period for said writing operation, a plurality of differential voltages are applied to said data lines, each of which differential voltages corresponds to a difference between a voltage corresponding to a gradation displayed in a previous writing operation, and a gradation to be displayed. 6. The method of claim 1, wherein:
the electrophoretic display includes a table for storing brake voltage data representing values of said brake voltages; and said brake voltage data is retrieved from said table based on image data used for switching a displayed image. 7. The method of claim 1, wherein:
the display further comprises a timer apparatus; and a displayed image is refreshed at a predetermined period of time. 8. A drive circuit for driving an electrophoretic display, the display comprising:
a plurality of data lines; a plurality of scanning lines, each of which intersects said data lines; a common electrode; a plurality of pixel electrodes, with one of said plurality of pixel electrodes being provided at one of each of said intersections of said data lines and said scanning lines, each of said pixel electrodes being provided in opposing spaced relation to said common electrode; a plurality of dispersal systems including a fluid in which pigment particles are suspended, with each of said dispersal systems being provided between said common electrode and one of said pixel electrodes; and a plurality of switching elements, with one of each of said switching elements being provided at a corresponding one of each of said intersections of said data lines and said scanning lines, with an on/off control terminal being connected to one of said scanning lines passing through one of said intersections; and with one of said data lines passing through one of said intersections, being connected to one of said pixel electrodes provided at each of one said intersections; the drive circuit comprising: an applying unit for applying said common voltage to said common electrode; a scanning drive unit for selecting a scanning line sequentially, applying a voltage to a selected scanning line, so as to turn on all of said switching elements which are connected to said sequentially selected scanning line during a certain period of time, and applying a voltage to said selected scanning line, so as to turn off all of said switching elements; and a data line drive unit for applying said common voltage to data lines, applying a plurality of pixel voltages to said data lines during a certain period of time, to migrate said pigment particles to positions corresponding to desired gradations, applying a plurality of brake voltages for braking said pigment particles to said data lines, each of said plurality brake voltages determined based on fluid resistance of said pigment particles and respective one of said desired gradations, and after said application of said brake voltages applying said common voltage to said data lines, said applications of said gradation voltages and brake voltages performed during a period in which a single scanning line is selected for applying a voltage to turn on all of said switching elements. 9. The drive circuit of claim 8, wherein:
resetting operation is performed during a period of a scanning field and writing operation is performed during a period of a different scanning field, said resetting and writing operations performed alternately; in said period for said resetting operation, said drive circuit applies a reset voltage to said plurality of data lines, to create an electrostatic field in each of said dispersal systems, to initialize said pigment particles; and in said period for said rewriting operation, said drive circuit applies to said selected data lines a plurality of voltages corresponding to said desired gradations. 10. The drive circuit of claim 8, wherein:
resetting operation is performed during a period of a scanning field and writing operation is performed during a period of next and different scanning field, in said period for said resetting operation, said drive circuit applies said reset voltage to said plurality of pixel electrodes, to initialize said pigment particles; and in said period for said writing operation, said drive circuit applies a plurality of differential voltages to said data lines, each of which differential voltages corresponds to a difference between a voltage corresponding to a gradation displayed in a previous writing operation, and a gradation to be displayed. 11. The method of claim 8, wherein:
a table for storing brake voltage data representing values of said brake voltages is provided with the display; and said brake voltage data is retrieved from said table based on image data used for switching a displayed image. 12. The method of claim 8, wherein:
the display further comprises a timer apparatus; and a displayed image is refreshed at a predetermined period of time. 13. An electrophoretic display, comprising:
a plurality of data lines; a plurality of scanning lines, each of which intersects said data lines; a common electrode; a plurality of pixel electrodes, with one of said plurality of pixel electrodes being provided at one of each of said intersections of said data lines and said scanning lines, each of said pixel electrodes being provided in opposing spaced relation to said common electrode; a plurality of dispersal systems including a fluid in which pigment particles are suspended, with each of said dispersal systems being provided between said common electrode and one of said pixel electrodes; and a display panel that includes a plurality of switching elements, with one of each of said switching elements being provided at a corresponding one of each of said intersections of said data lines and said scanning lines, with an on/off control terminal being connected to one of said scanning lines passing through one of said intersections; with one of said data lines passing through one of said intersections, being connected to one of said pixel electrodes provided at each of one said intersections; an applying unit for applying said common voltage to said common electrode; a scanning drive unit for selecting a scanning line sequentially, applying a voltage to a selected scanning line, so as to turn on all of said switching elements which are connected to said sequentially selected scanning line during a certain period of time, and applying a voltage to said selected scanning line, so as to turn off all of said switching elements; and a data line drive unit for applying said common voltage to data lines, applying a plurality of pixel voltages to said data lines during a certain period of time, to migrate said pigment particles to positions corresponding to desired gradations, applying a plurality of brake voltages for braking said pigment particles to said data lines, each of said brake voltages determined based on fluid resistance of said pigment particles and respective one of said desired gradations, and after said application of said brake voltages applying said common voltage to said data lines, said applications of said gradation voltages and brake voltages performed during a period in which a single scanning line is selected for applying a voltage to turn on all of said switching elements. 14. The electrophoretic display of claim 13, wherein said pigment particles reflect a certain color being displayed in said pixels and said fluid absorbs said color.
15. The electrophoretic display of claim 13, each of said plurality of said dispersal systems includes three subsets of dispersal systems, in each of the subsets red, blue, and green particles being contained, so as to display a colored image.
16. The electrophoretic display of claim 13, wherein said pigment particles are provided with differing properties.
17. An electronic device with which an electrophoretic display provided, the electrophoretic display, comprising:
a plurality of data lines; a plurality of scanning lines, each of which intersects said data lines; a common electrode; a plurality of pixel electrodes, with one of said plurality of pixel electrodes being provided at one of each of said intersections of said data lines and said scanning lines, each of said pixel electrodes being provided in opposing spaced relation to said common electrode; a plurality of dispersal systems including a fluid in which pigment particles are suspended, with each of said dispersal systems being provided between said common electrode and one of said pixel electrodes; a display panel that includes a plurality of switching elements, with one of each of said switching elements being provided at a corresponding one of each of said intersections of said data lines and said scanning lines, with an on/off control terminal being connected to one of said scanning lines passing through one of said intersections; with one of said data lines passing through one of said intersections, being connected to one of said pixel electrodes provided at each of one said intersections; an applying unit for applying said common voltage to said common electrode; a scanning drive unit for selecting a scanning line sequentially, applying a voltage to a selected scanning line, so as to turn on all of said switching elements which are connected to said sequentially selected scanning line during a certain period of time, and applying a voltage to said selected scanning line, so as to turn off all of said switching elements; and a data line drive unit for applying said common voltage to data lines, applying a plurality of pixel voltages to said data lines during a certain period of time, to migrate said pigment particles to positions corresponding to desired gradations, applying a brake voltage for braking said pigment particles to said data lines, said brake voltages determined based on fluid resistance of said pigment particles and said desired gradations, and after said application of said brake voltages applying said common voltage to said data lines, said applications of said gradation voltages and brake voltages performed during a period in which a single scanning line is selected for applying a voltage to turn on all of said switching elements. Description
This is a Division of application Ser. No. 09/884,092 filed Jun. 20, 2001 now U.S. Pat. No. 6,762,744. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety.
It is to be noted that in the present invention, voltages are applied as required, via switching elements, to respective pixel electrodes, thereby creating a matrix in the electrophoretic display. In the method for driving the electrophoretic display of the present invention, each of the pixel electrodes is first subject to a preset uniform voltage applied by the common electrode. Scanning lines are then selected sequentially. Next, a voltage differential corresponding to a desired display update is applied via the switching elements to their respective pixel electrodes, whereby designated pigment particles are caused to migrate. To maintain a desired display state, a uniform voltage is applied to each of the pixel electrodes via respective switching elements, and, further, a break voltage is applied to counter inertial movement of the suspended pigment particles in each of the particle dispersion systems, and finally the switching elements are turned off.
FIG. 23 is a block diagram of the data line drive circuit 140B thereof;
Thus, in this embodiment, dispersal system 1 r corresponding to R color has red particles as the pigment particles 3 r and the dielectric fluid 2 r is a cyanogen color medium. The pigment particles 3 r are made of iron oxide, for example. The dispersal system 1 g corresponding to G color uses green particles as the pigment particles 3 g and the dielectric fluid 2 g is a magenta-color medium. The pigment particles 3 g are made of cobalt-green pigment particles, for example. The dispersal system 1 b corresponding to B color uses blue particles as the pigment particles 3 b and the dielectric fluid 2 b is a yellow medium. The pigment particles 3 b are made of cobalt-blue pigment particles, for example.
That is, the pigment particles 3 that correspond to each color to be displayed are used, while the dielectric fluid 2 of a certain color (the complementary color, in this embodiment) that absorbs the color to be displayed is used.
The opposing substrate 200, the common electrode 201, and the sealer 202 are transparent, enabling a user to see images displayed the opposing substrate 200. Thus, if pigment particles 3 migrate towards to the display-surface-side electrode, they will reflect light of a wavelength corresponding to the color to be displayed. On the other hand, when the pigment particles 3 migrate to the opposite-side electrode to the display surface, light of a wavelength corresponding to the color to be displayed is absorbed by the dielectric fluid 2. In this case, such light will not be visible to a user, and therefore no color will be visible. In the present invention, a strength of an electrostatic field applied to the dispersal system 1 determines how the pigment particles 3 are distributed in the direction of thickness of the dispersal system 3. The combined use of the pigment particles 3, the dielectric fluid 2 which absorbs light reflected by pigment particles 3, and controlling the dielectric field strength enables adjustment of light reflectance of a color. As a result, a strength of light reaching an observer can be controlled.
The reset data Drest is used for attracting pigment particles 3 to the pixel electrodes 104 so that their positions are initialized. In this embodiment, dielectric fluid 2 is dyed black and pigment particles 3 consist of titanium oxide, which has a whitish color, and for in this explanation will be described as having a positive charge. Timing generator 400 generates several timing signals synchronously with image D, described later for a scanning drive circuit 130 and data line drive circuit 140A.
Incident light from common electrode 201 is reflected by pigment particles 3 and this reflected light reaches observer's eye through common electrode 201. Incident and reflected light are absorbed in dielectric fluid 2 and the absorption rate is proportional to the optical path length. Hence a gradation recognized by an observer is determined by the positions of pigment particles 3. As mentioned above, since the positions of pigment particles 3 are determined by an applied voltage over a constant period, a desired gradation will be displayed.
To assist in control, pigment particles are provided with differing properties. These differences enable a statistical distribution to be achieved of positions of pigment particles. FIG. 5 shows an example of a relation between a voltage applied between a common and pixel electrodes and the gradation displayed. The time fame for voltage application is 50 milliseconds and the average voltage applied to migrate pigment particles 3 to common electrode 201 is 5 volts; and the standard deviation of the distribution is 0.2 volts normalized with 5 volts.
At this time, when the scanning signal Y1 becomes active (the H-level), TFTs 103 in the first line are switched on and the reset voltage Vrest is applied to each pixel electrode 104. After that, reset voltage Vrest is applied to each pixel electrode 104 of the second, third, . . . , mth lines. For exemple, at time tx, when the scanning line signal Y1 is made inactive, each TFT 103 in the first line is switched off so that the pixel electrodes 104 and data lines 102 are cut off. However capacity has been created in the system comprised of the pixel electrode 104, dispersal system 1 and the common electrode 201. Hence if each TFT 103 is switched off, the reset voltage Vrest is maintained between the pixel electrode 104 in the first horizontal line and the common electrode 201.
Since each data line X1, . . . , Xn is generated through the D/A conversion of data Dc1, . . . , Dcn as shown in FIG. 7, the voltage of the data line signal Xj is, as shown in FIG. 10, equals to the gradation voltage Vij in the voltage applied period Tv from time T1 to time T2, while to the common voltage Vcom in the no-bias period Th from time t2 to time t3.
The scanning line signal Y1 supplied to the ith scanning line 101 is active during the period of the ith the horizontal scanning. Therefore, the TFT 103 which comprises the pixel Pij is switched on over that period and the data line signal Xj from time T1 to time tme T3 is applied to the pixel electrode 104. That is, in this embodiment, an operation that begins with applying the gradation voltage Vij to the pixel electrodes 104 and ends with applying the common voltage Vcom thereto is completed within a period of one horizontal line scanning.
In this embodiment, since the particles 3 are white and dielectric fluid 2 is black, the more pigment particle 3 is nearing to the common electrode 201, the higher the brightness Iij of the pixel Pij is. As a result, Iij is becomes higher gradually from time T1 as shown therein.
In the no-bias period Tb, since the common voltage Vcom is applied to the pixel electrode 104, the pixel electrode 104 and the common electrode 201 becomes equipotential at time T2. This means no electrostatic field is applied to pigment particles 3 from that time. If the fluid resistance of the dielectric fluidis, to some extent, large, the particles 3 stop moving at time T2 when no electrostatic field exists. This results in a constant value of brightness Iij from time T2 as shown therein.
If the value of the fluid resistance of the dielectric fluid 2 is small, the pigment particles 3 keep moving for a period due to their inertia. In this case, the image D which is compensated beforehand by taking the above effect into account is generated in the image signal processing circuit 300A.
In FIG. 7, at time T3, since the scanning line signal Y1 shifts from active to inactive, the TFT 103 of the pixel Pij is turned off. As mentioned above, in the no-bias period Tb, since the common voltage Vcom is applied to the pixel electrode 104, no electrostatic field is generated between the two electrodes. Therefore no electrostatic field is applied to the dispersal system 1 unless a new voltage is applied. This enables the position pigment particles 3 to be held, and thus a displayed image to be held.
In such a holding period Th, since there is no need to apply a voltage to pixel electrodes 104, and consequently neither the scanning line signal Y1, . . . , Ym nor the data line signal X1, . . . , Xn need be generated, thereby enabling a reduction in power consumption in this period as follows:
The third is to stop supplying the Y-clock YCK, the inverted Y-clock YCKB, the X-clock XCK, the inverted X-clock XCKB to the scanning line drive circuit 130, and the data lines driving circuit 140A. Since the scanning line drive circuit 130 and the data line drive circuit 140A is made of complementary TFTs as described above, power is consumed only when the current is fed therethrough, in other words, inversion of a logic level occurs. Consequently, stopping the supply to the clocks enables a reduction in power consumption.
As described above, while the selection circuit 144 (cf. FIG. 6) outputs the common voltage data Dcom during the no-bias timing signal Cb is in the H-level (active) and outputs the outputted data Db1, . . . , Dbn of the latch 143 during the no-bias timing signal Cb is in the low level. In other words, in the period which jth and j+1th scanning line 101 are selected, the reset voltage Vrest is supplied to all data lines 102, while in the other selected time of the scanning line 101, the common voltage Vcom is applied to all data lines 102.
Therefore while the common voltage Vcom is applied to the pixel electrodes 104 on from the first to the j−1th line and from the j+2th to the mth line, the reset voltage Vrest is applied to the pixel electrodes 104 of the jth and j+1th line, so that the pixels of the j th and j+1th lines are initialized. Since applying the common voltage Vcom to the pixel electrodes 104 generates no electrostatic field, the positions of pigment particles 3 in the pixels on from the first to the j−1th line and from the j+2 to the mth line don't change.
In the writing operation, writing is carried out in the manner as shown in FIG. 7, so that the image signal processing circuit 300A outputs the image data D to the line to be rewritten, while the common voltage data Dcom to the other lines. This enables rewriting only in the jth and j+1th lines.
The third method is that after a plurality of electrodes is reset, they are rewritten in the usual way. In the above second method, a reset operation is carried out line by line in such a way that first the jth line is reset then the j+1th line is reset and so on.
However, it is possible to reset simultaneously if a scanning line drive circuit which simultaneously select a plurality of scanning lines 101 to be rewritten. For example, as shown in FIG. 12, it is obvious that it is possible to reset simultaneously jth and j+1th line to be rewritten if the reset voltage Vrest is applied to the data lines 102 activating only the scanning line signal Yj and Yj+1. Writing is carried out in the usual way, as shown in FIG. 7 that the image signal processing circuit 300A outputs the image data D only in the line to be rewritten, then the common voltage data Dcom is outputted to the other lines. This method enables rewriting only in the jth and j+1 line.
First, the scanning line drive circuit is used which can rewrite simultaneously a plurality of the scanning lines 101 to be rewritten. The image signal processing circuit 300A outputs the data as the data of one line, which is the common voltage data Dcom for from the first to the c−1 th line and while is the reset data for from the cth to the Dth line and the common voltage data Dcom for from d+1th to the nth line. The no-bias timing signal remains to be inactive. This enables that the data lines signal from X1 to Xc−1 and from Xd+1 to Xn is set to the common voltage Vcom during the horizontal scanning, while the data lines signal from Xc to Xd is set to be the reset voltage Vrest. In the horizontal scanning period, the scanning line signal only from Ya to Yb can be set to active so as to reset the region R. In writing, the image signal processing circuit 300A outputs the image data D to the pixels corresponding to the region R, while the common voltage data Vcom to the others. Rewriting only of the region R is carried out in this way.
In the above embodiment, rewriting is carried out in a way that after a reset operation as shown in FIG. 16A is carried out, then a writing operation is carried out shown in FIG. 16B to renew a displayed image. In this case, the positions of the pigment particles 3 are initialized in displaying a subsequent image. In the case that dielectric fluid 2 is colored black and the pigment particles 3 are colored white, a black out occurs across the entire image. However, if a change in image is effected sufficiently rapidly, it will not be visible to the naked eye. Nevertheless there is a case that the resetting operation needs a long time according to physical property of the dispersal system 1, which results in the fact that change of the brightness in initializing the pigment particles 3 can be detected.
The brake voltage data Ds corresponds to the brake voltage Vs, which will be described later, and is used to brake pigment particles 3. As mentioned above, pigment particles 3 subject to inertial movement can be braked by utilizing a electrostatic field Coulomb force the direction of which is opposite to that of pigment particles 3. Since pigment particles 3 move in response to a gradation voltage for display of an image, it is necessary to apply an electrostatic field to them which is acting in an opposite direction, and the value of which is dependent on the kinetic energy of pigment particles 3, in other words, the gradation voltage V. Therefore, in this embodiment, taking into account fluid resistance of dielectric fluid 2 among other factors, the brake voltage data Ds corresponding to the values of the image data D is memorized in the table beforehand for reading.
As shown in FIG. 22, a selection part 340 outputs reset data in reset period Tr, while in the writing period, it outputs multiplex data Dm in which image data D and brake voltage data Ds are combined. If image data D consists of 6 bits and brake voltage data Ds is also 6 bits, the multiplex data Dm will be 12 bits, which means that 6 bits from the most significant bit (MSB) is the image data D and 6 bits from the latest significant bit (LSB) is the brake voltage data Ds.
FIG. 24 shows a block diagram showing a detailed configuration of the selection circuit 144B and FIG. 25 shows the timing chart thereof. As shown in FIG. 24, the selection circuit 144B has n selection units from U1 to Un, each of which selects appropriate data from the image data D and the brake voltage data Ds, which is comprising the multiplex data Dm and the voltage data Ds, and outputs it, depending on the no-bias timing signal Cb and the stop timing signal Cb. The no-bias timing signal Cb becomes active (the H-level) only in the period in which the common voltage data Dcom is selected like in the fist embodiment described above, while the top timing signal Cs becomes active (in the H-level) only in the period in which the brake voltage data Ds is selected.
In the following, the pigment praticles' motions will be described in the pixel Pij. Having been done the reset operation before the writing operation begins, at time T1, all pigment praticles of the pixel Pij are positioned on the side of the pixel electrode 104. At this time when the voltage 104 Vij is applied to the pixel electrode 104, an electric field is generated which is in the direction of from the common electrode 201 from to the pixel electrode 104. Thus pigment praticles 3 start to migrate at time T1 and the brightness Iij is being gradually high.
A brake voltage generation part 350 has a table in which the brake voltage data Ds′ and a differential image data Dd whose values are correspondent to those of Ds′ are memorized. This means that the brake voltage data Dds is to be acquired by accessing the table and pointing to the differential image data Dd as the address. The table is configured with storage circuits such as RAMs and ROMs.
FIG. 28 shows a timing chart of the electrophoretic display in the writing operation. An ith line (ith scanning line) and a jth column (jth data line) are depicted but it is obvious that other pixels can bedealt with similarly. In the following, the pixel of the ith line and the jth column is represented by Pij, the differential voltage to be displayed in the pixel Pij is represented by Vdij and the brightness of Pij is represented by Iij. Suppose the gradation in Pij was 10% in the next previous period.
In the period of the ith horizontal scanning in the no-bias period Thf, when the scanning signal Yi becomes active, the common voltage Vcom is applied to pixel electrode 104. Therefore the voltage of pixel electrode 104 coincides with the common voltage Vcom at time T4.
It is preferable that the specific gravity of the dielectric fluid 2 and that of the pigment particles 3 which comprise the dispersal system 1 be equal. However, it is difficult to achieve complete parity of the respective specific gravities, due to restrictions of materials employed and variations therein. In such a case, when the dispersal system 1 is left in stasis for a long time once an image is displayed, the pigment particles 3 sink down or float up due to gravitational effect. In order to overcome this problem, it is preferable for a timer apparatus to be set in the timing generator 400 to rewrite the same image for a certain period. The timer apparatus 410 has a timer part 411 and a comparison part 412. The timer generates duration data Dt measuring time, in which the value of the duration data Dt is reset to �0� when either a writing start signal Ws which designates an ordinary writing, or a rewriting signal Ws′ becomes active. The comparison part 412 compares the duration data Dt with the predetermined reference time data Dref which designates the refresh period and, if they coincide, generates the rewriting signal Ws′ which is active during a preset period.
FIG. 38 is a timing chart of the timer apparatus 410. As shown, when the writing signal Ws becomes active, the duration data Dt of the timing part 411 is reset and measurement starts. When predetermined refresh period has passed, the duration data Dt and the reference time data Dref coincides, so that the rewriting signal Ws′ becomes active. The measurement of refreshing period starts when the writing signal Ws becomes active, or the rewriting signal Ws′ is active once the refresh period passes.
Electronic devices other than those shown in FIGS. 39 to 41 include a TV monitor, outdoor advertising board, traffic sign, view-finder type or monitor-direct-viewing type display of a vidoe tape recorder, car navigation device, pager, electronic note pad, electronic calculator, word processor, work station, TV telephone, POS terminal, devices having a touch panel, and others. Thus, the electrophoretic display panel according to each of the foregoing embodiments can be applied for use with such devices. Alternatively, an electro-optical apparatuses having such electrophoretic display panel can also be applied to such devices.
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