Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-06-20
2003-11-18
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S238000, C345S107000, C345S086000
Reexamination Certificate
active
06650462
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for driving an electrophoretic display which has dispersal systems comprised of pigment particles, a drive circuit for the display, and an electronic device in which the display is used.
BACKGROUND ART
Electrophoretic displays utilizing electrophoresis are classed as non-luminous devices. In electrophoresis, pigment particles migrate under the action of a Coulomb force which is generated when an electrostatic field is applied to a dielectric fluid in which the particles are dispersed.
In the conventional art, electrophoretic displays are known which consist of a pair of panels or substrates spaced apart in opposing relation, each of which is provided with an electrode. Between these electrodes a dyed dielectric fluid is provided. Differing voltages are applied via a switching element to the electrodes to generate an electrostatic field in the dielectric fluid, causing the electrically charged pigment particles to migrate in the direction of the applied field. Suspended in the fluid are particles having a pigment color different to the fluid in which they are suspended (hereinafter referred to simply as particles).
However, prior art electrophoretic displays suffer from a problem in that they afford poor viewing characteristics. The present invention has been made to overcome this problem, and provides for the first time an active matrix electrophoretic display, which display has superior viewing characteristics. As stated above, the object of the present invention is to provide an active matrix electrophoretic display. Also provided is a drive circuit integral to the device, and a method for driving the display by using the circuit.
DISCLOSURE OF INVENTION
The method of the present invention is applied to an electrophoretic display. The electrophoretic display comprises a first electrode, a plurality of second electrodes and a plurality of dispersal systems. The dispersal systems comprise a colored fluid in which pigment particles are suspended. A dispersal system is provided between the first electrode and each of one of the second electrodes. An electrostatic field is applied between the first and second electrodes for a predetermined time to cause the particles to migrate to a desired position corresponding to a color gradation of an image to be displayed.
In the method of the present invention, a constant voltage is applied for a set period of time which is calculated on the basis of a difference between a current average position of pigment particles and a subsequent desired position. By continually updating a voltage gradient using these position parameters, positions of pigment particles can be updated without the need for an initialization step. Since no initialization step is required, display updates can be affected rapidly. After applying the constant voltage to migrate particles to a desired position, the electrostatic field is removed and the particles become static, thereby providing desired display characteristics.
In the method and device of the present invention, to further improve display image characteristics, it is preferable for there to be variations in the properties of pigment particles employed. It should be further noted that when a voltage differential is cancelled between the 1st and a 2nd electrode by applying a constant voltage to make the pigment particles static, a capacitor formed by the 1st and 2nd electrode and the dispersal system functions to discharge an accumulated electric charge.
Furthermore, it is preferable before canceling a differential voltage between the electrodes to apply a differential voltage or brake voltage between the electrodes to brake movement of the particles. This is particularly important in the case that minimal fluid resistance acts against pigment particles, since, in such a case, there is significant inertial movement of particles and pronounced display fluctuations. This method enables to halt particles rapidly because the brake voltage is applied.
Since a direction of motion of a particle is determined by a direction of an applied electrostatic field, an applied brake voltage preferably has an opposite polarity to that of an initial voltage applied.
When applying a voltage between the 1st and 2nd electrodes, it is preferable that a time period for which the voltage is applied be measured against a reference time, so that in the event that the former time exceeds the latter, the voltage can be applied again, to prevent sedimentation or rising of pigment particles under gravity. In this way, display image characteristics provided by the method and device of the present invention can be maintained effectively.
A method of the present invention is employed in an electrophoretic display which comprises a plurality of data lines, a plurality of scanning lines each of which intersects each of the data lines, a common electrode, a plurality of pixel electrodes each of which is provided at each intersection spaced in opposing relation to the common electrode, a plurality of dispersal systems, each one of which comprises a colored fluid in which pigment particles are suspended, each of the systems being provided between the common electrode and one of the pixel electrodes, and a plurality of switching elements; with one of each of the switching elements being provided at a corresponding one of each of the intersections of the data lines and the scanning lines; with an on/off control terminal being connected to one of the scanning lines passing through one of the intersections; and with one of the data lines passing through one of the intersections, being connected to one of the pixel electrodes provided at each of one of the intersections.
The method comprises applying a predetermined common voltage to the first, common, electrode, selecting the scanning lines sequentially, applying a voltage during a predetermined time period to the selected scanning lines, to turn on all switching elements connected to the selected scanning lines, applying a constant voltage to each of the data lines for a set time period to migrate particles of each of corresponding pixels, and which are provided at the intersection of the data line and the selected scanning line, to attain a desired color gradation of an image to be displayed, and finally applying the common, first, voltage to the selected scanning lines.
It is to be noted that in the present invention, a constant voltage is applied as required, via switching elements, to respective pixel electrodes, over a set period of time, to attain a desired gradation of a displayed image. In addition, a common voltage is applied to the pixel electrodes to remove an electric charge accumulated between the electrodes, whereby an electrostatic field acting between the electrodes is removed, to fix a position of the particles, thereby creating a matrix in the electrophoretic display.
Furthermore, it is also possible to apply a brake voltage to a data line to brake particle motion before applying a common voltage to the data line, thus enabling particle movement to be halted rapidly. A method of the present invention is employed for an electrophoretic display which comprises a plurality of data lines, a plurality of scanning lines each of which intersects each of the data lines, a common electrode, a plurality of pixel electrodes each of which is provided at each intersection being spaced in opposing relation to the common electrode, a plurality of dispersal systems each one of which comprising a colored fluid in which pigment particles are suspended provided, each one of the systems being provided between the common electrode and one of the pixel electrodes, and a plurality of switching elements, with one of each of the switching elements being provided at a corresponding one of each of the intersections of the data lines and the scanning lines, with an on/off control terminal being connected to one of the scanning lines passing through one of the intersections; and with one of the data lines passing through one of the intersections, being c
Oliff & Berridg,e PLC
Schwartz Jordan M.
Seiko Epson Corporation
Thompson Tim
LandOfFree
Method and circuit for driving electrophoretic display and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and circuit for driving electrophoretic display and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and circuit for driving electrophoretic display and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3178605