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EP-4736156-A1 - TIME-SHIFTED WAVEFORMS FOR MULTI-PARTICLE ELECTROPHORETIC DISPLAYS PROVIDING LOW-FLASH IMAGE UPDATES

EP4736156A1EP 4736156 A1EP4736156 A1EP 4736156A1EP-4736156-A1

Abstract

Electrophoretic displays with multi-particle electrophoretic media and improved methods for driving such multi-particle electrophoretic media, especially using active matrix backplanes and controllers. Larger look-up tables are used, which include a plurality of time-shifted waveforms for each color transition. The controller can thus easily cause a phase shift in the color flashes across the display, which ultimate diminishes or removes the perception that the device is "flashing" during an update from a first image to a second image.. The methods are generalizable to any electrophoretic display using waveforms, and are particularly well-suited for newer multi-particle electrophoretic displays capable of producing four or more colors at each pixel.

Inventors

  • SIM, Teck Ping
  • LADAVAC, KOSTA
  • BEN-DOV, YUVAL

Assignees

  • E Ink Corporation

Dates

Publication Date
20260506
Application Date
20240625

Claims (10)

  1. 1. An electrophoretic display comprising: a light-transmissive electrode; an active matrix backplane comprising a plurality of rows of pixel electrodes, each pixel electrode being coupled to a thin-film transistor comprising a gate line and a source line; an electrophoretic medium disposed between the light-transmissive electrode and the active matrix backplane, wherein the electrophoretic medium includes at least three different types of charged pigment particles; a controller coupled to a plurality of gate lines, each gate line being coupled to the thin- film transistors of one of the plurality of rows of pixel electrodes, and the controller being coupled to a plurality of source lines, the controller further being configured to address the pixel electrodes in a row-by-row fashion by providing both a gate voltage and a source voltage to each thin-film transistor; and non-transitory memory coupled to the controller and comprising a look-up table, wherein for a transition between a first color and a second color, the look-up table includes a first waveform for causing the electrophoretic medium to transition between the first color and the second color, and a second waveform for causing the electrophoretic medium to transition between the first color and the second color, wherein the first and second waveforms are identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses, but wherein the first and second waveforms are time-shifted by at least 1ms, the controller performing the following steps when updating the display between the first image and the second image: receiving the first waveform from the look up table; providing the first waveform to a first row of pixel electrodes; receiving the second waveform from the look up table; and providing the second waveform to a second row of pixel electrodes adjacent the first row of pixel electrodes.
  2. 2. The electrophoretic display of claim 1, wherein the look-up table further comprises a third waveform for causing the electrophoretic medium to transition between the first color and the second color, wherein the first, second, and third waveforms are identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses, but wherein the first and second and third waveforms are time-shifted by at least 5ms from each other, and the controller further performs the step of receiving the third waveform from the look-up table and providing the third waveform to a third row of pixel electrodes adjacent to the second row of electrodes, wherein the second row of electrodes are between the first row of electrodes and the third row of electrodes.
  3. 3. The electrophoretic display of claims 1 or 2, wherein the look-up table further comprises a fourth waveform for causing the electrophoretic medium to transition between the first color and a third color, wherein the third waveform is not identical with respect to a number of voltage pulses and a polarity and magnitude of each of the voltage pulses of the first and second waveforms, but wherein the first and second and third waveforms are time-shifted by at least 1ms from each other.
  4. 4. The electrophoretic display of any of claims 1 to 3, wherein the first waveform and the second waveform are time-shifted by at least 5ms, optionally at least 10ms, optionally time shifted by between 12ms and 20ms.
  5. 5. The electrophoretic display of any of claims 1 to 3, wherein the first waveform and the second waveform are time-shifted by a frame, wherein a frame is the time required to address every pixel in the active matrix backplane one time when addressing the active matrix backplane in a row-by-row fashion.
  6. 6. The electrophoretic display of any of the proceeding claims, wherein the magnitudes of the voltage pulses are between -15 V and +15V, or between -24V and +24V.
  7. 7. The electrophoretic display of any of the proceeding claims, wherein the electrophoretic medium includes a reflective white particle and at least one subtractive color particle or a reflective white particle and at least one reflective color particle.
  8. 8. The electrophoretic display of any of the proceeding claims, wherein the electrophoretic medium includes a fourth type of electrophoretic particle.
  9. 9. The electrophoretic display of claim 8, wherein two of the types of particles are negatively charged and two of the types of particles are positively charged, or wherein one of the types of particles is negatively charged and three of the types of particles are positively charged, or wherein three of the types of particles are negatively charged and one of the types of particles is positively charged.
  10. 10. The electrophoretic display of any of the proceeding claims wherein the electrophoretic medium is encapsulated in microcapsules or microcells.

Description

TIME-SHIFTED WAVEFORMS FOR MULTI-PARTICLE ELECTROPHORETIC DISPLAYS PROVIDING LOW-FLASH IMAGE UPDATES RELATED APPLICATIONS [Para 1] This application claims priority to U.S. Provisional Application No. 63/523,484, filed June 27, 2023. All patents and publications disclosed herein are incorporated by reference in their entireties. BACKGROUND [Para 2] An electrophoretic display (EPD) changes color by modifying the position of one or more charged colored particles with respect to a light-transmissive viewing surface. Such electrophoretic displays are typically referred to as “electronic paper” or “ePaper” because the resulting display has high contrast and is sunlight-readable, much like ink on paper. Electrophoretic displays have enjoyed widespread adoption in eReaders because the electrophoretic displays provide a book-like reading experience, use little power, and allow a user to carry a library of hundreds of books in a lightweight handheld device. Such devices are increasingly being adapted to display out-of-home (OOH) digital content, such as shelf labels, outdoor advertisement and transportation signage. [Para 3] For many years, electrophoretic displays included only two types of charged color particles, black and white. (To be sure, “color” as used herein includes black and white.) The white particles are often of the light scattering type, and comprise, e.g., titanium dioxide, while the black particle are absorptive across the visible spectrum, and may comprise carbon black, or an absorptive metal oxide, such as copper chromite. In the simplest sense, a black and white electrophoretic display only requires a light-transmissive electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided the black particles move to the viewing surface. If the back electrode includes controllable regions (pixels) - either segmented electrodes or an active matrix of pixel electrodes controlled by transistors - a pattern can be made to appear electronically at the viewing surface. The pattern can be, for example, the text to a book. [Para 4] More recently, a variety of color option have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black white, yellow), and four color displays (black, white, red, yellow). Similar to the operation of black and white electrophoretic displays, electrophoretic displays with three or four reflective pigments operate similar to the simple black and white displays because the desired color particle is driven to the viewing surface. The driving schemes are far more complicated than only black and white, but in the end, the optical function of the particles is the same. [Para 5] Advanced Color electronic Paper (ACeP™) also includes four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, thereby allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing methods that have long been used in offset printing and ink-jet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the instance of ACeP, the relative positions of the cyan, yellow, magenta and white particles with respect to the viewing surface will determine the color at each pixel. While this type of electrophoretic display allows for thousands of colors at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometer-sized) pigments within a working space of about 10 to 20 micrometers in thickness. Obviously, variations in the position of the pigments will result in incorrect colors being displayed at a given pixel. Accordingly, exquisite voltage control is required for such a system. More details of this system are available in the following U.S. Patents, all of which are incorporated by reference in their entireties: U.S. Patent Nos. 9,361,836, 9,921,451, 10,276,109, 10,353,266, 10,467,984, 10,593,272, and 10,657,869. [Para 6] As described in the aforementioned patents, the waveforms (i.e., electric fields provided across the electrophoretic medium as a function of time) typically require substantial swings in voltage polarity in a short time. Because of this, in some instances, the colored electrophoretic display “flashes,” “flickers,” or “looks flashy” when switching between color images. This shortcoming is particularly pronounced when a full-color eReader is quickly switched (i.e., in less than 1 second) between full-color images. U.S. Patent No. 10,657,869 addressed a similar issue, however the ‘869 patent does not suggest to use look up tables to store offset waveforms, as described below. Other patents owned by E Ink Corporation, such a