Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-03-08
2003-01-07
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S048000, C345S084000, C345S210000, C315S169300, C349S086000, C359S296000, C359S297000
Reexamination Certificate
active
06504524
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic displays and, in particular, to reducing the rate of deterioration of display material in such displays.
BACKGROUND OF THE INVENTION
Traditionally, electronic displays such as liquid crystal displays have been made by sandwiching an optoelectrically active material between two pieces of glass. In many cases each piece of glass has an etched, clear electrode structure formed using indium tin oxide. A first electrode structure controls all the segments of the display that may be addressed, that is, changed from one visual state to another. A second electrode, sometimes called a counter electrode, addresses all display segments as one large electrode, and is generally designed not to overlap any of the rear electrode wire connections that are not desired in the final image. Alternatively, the second electrode is also patterned to control specific segments of the displays.
Conventional liquid crystal displays are monostable, i. e., in the absence of any potential difference between the electrodes, the liquid crystal molecules assume random orientations, which renders the liquid crystal material non-transmissive of light, and indeed in such displays a given pixel is rendered non-transmissive simply by removing the potential difference between its associated electrode and the counter electrode, thereby allowing the molecules within this pixel to relax to random orientations. To maintain any given pixel in a transmissive state, it is necessary to drive the associated electrode substantially continuously.
Electrophoretic and other bistable displays have been the subject of intense research and development for a number of years. (The term “bistable” is used herein in its conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. The bistable characteristics of such displays are discussed in more detail below.) Such displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up electrophoretic displays tend to cluster and settle, resulting in inadequate service-life for these displays.
An encapsulated, electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates.
In electrophoretic and other bistable displays, it has been commonly observed that the display fails after some time. One of the reasons why such a display may fail is that the materials used to construct the display are damaged by repeated application of electrical addressing signals. In particular, the application of a signal of one volt over a distance of one micron (one micrometer), or ten microns results in field strengths applied to the capsule of one million volts per meter or one hundred thousand volts per meter, respectively. These are quite large field strengths.
SUMMARY OF THE INVENTION
The present invention provides a solution that overcomes these and other problems that are encountered in conventional addressing methods that have been used in the prior art to address bistable displays. This invention provides novel methods and apparatus for controlling and addressing such displays. Additionally, the invention discloses applications of these methods and materials on flexible substrates, which are useful in large-area, low cost, or high-durability applications.
In one aspect, the present invention relates to a method for addressing a bistable display element having first and second display states differing in at least one optical property. The method comprises (a) applying a first addressing signal to the display element that does not substantially change the display state of the display element; and (b) applying a second addressing signal to the display element that does change the display state of the display element.
Embodiments of this aspect of the invention have the following features. The display element can be an electrophoretic element, desirably an encapsulated electrophoretic display element. The electrophoretic display element may comprise a liquid and at least one particle disposed within this liquid and capable of moving therethrough on application of an electric field to the medium. Such an element may have a viewing surface and the liquid can have an optical property differing from that of the particle disposed therein so that the display element is in its first display state when the particle(s) lie(s) adjacent the viewing surface and in its second display state when the particle(s) is/are spaced from the viewing surface so that the liquid lies adjacent the viewing surface. Alternatively, the element may have a viewing surface and the liquid can have disposed therein at least one first particle having a first optical property and a first electrophoretic mobility and at least one second particle having a second optical property different from the first optical property and a second electrophoretic mobility different from the first electrophoretic mobility, so that the display element is in its first display state when the first particle(s) lie(s) adjacent the viewing surface and is in its second display state when the second particle(s) lie(s) adjacent the viewing surface.
The method can include the step of applying to the display element a first addressing signal having a first polarity, a first amplitude as a function of time, and a first duration, such that the first addressing signal does not substantially change the optical property displayed by the display element. The method can include the step of applying to the display element a second addressing signal having a second polarity opposite the first polarity, a second amplitude as a function of time, and a second duration such that the second addressing signal substantially changes the optical property displayed by the display element, and such that the sum of the first amplitude as a function of time integrated over the first duration and the second amplitude as a function of time integrated over the second duration is substantially zero. The method can include a first addressing signal and a second addressing signal represented by functions of time such that the sum of the first amplitude as a function of time integrated over the first duration and the second amplitude as a function of time integrated over the second duration is, in a preferred embodiment, smaller in absolute magnitude than 10 Volt-seconds; in a more preferred embodiment, smaller in absolute magnitude than 1 Volt-second; and in a still more preferred embodiment, smaller in absolute magnitude than 0.1 Volt-seconds. The aforementioned sum (expressed in volt-seconds) is, in a preferred embodiment, smaller in absolute magnitude than one-tenth of the maximum amplitude expressed in volts of the larger of the first and second amplitudes; in a more preferred embodiment, this sum is smaller in absolute magnitude than one one-hundredth of this maximum amplitude; and in a still more preferred embodiment, this sum is smaller in absolute magnitude than one one-thousandth of this maximum amplitude.
The method can include using first and second addressing signals of opposite polarity.
The method can include steps of applying first and second addressing pulses such that the second amplitu
Albert Jonathan D.
Comiskey Barrett
Drzaic Paul S.
Gates Holly
Kazlas Peter T.
E INK Corporation
Kovalick Vincent E.
Shalwala Bipin
LandOfFree
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