Multi-element pixel electrode circuits for electro-optic displays and methods for driving them - Patents.com

Abstract

An electro-optic display includes a first sub-pixel electrode and a second sub-pixel electrode associated with a display pixel, and an electrophoretic display medium disposed between the common electrode and the first and second sub-pixel electrodes. The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel. The display controller circuit is capable of applying waveforms to the display pixel by applying one or more time-dependent voltages between the common electrode and the first sub-pixel electrode through the first transistor, the one or more time-dependent voltages being applied to the first sub-pixel electrode. The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and the second sub-pixel electrode.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 481,964, filed January 27, 2023, the entire contents of which are incorporated herein by reference. Additionally, the entire contents of any patents, published applications, or other published works referenced herein are incorporated by reference in their entirety.

[0002] FIELD OF THE INVENTION The present invention relates to a method of driving a bistable electro-optic display in accordance with environmental conditions and an apparatus for use in such a method. In particular, the present invention relates to a method of driving a bistable electro-optic display in accordance with a temperature compensation scheme and a display pixel circuit for use in such a method. [Background technology]

[0003] Generally characterized by the movement of particles through an applied electric field, electrophoretic display media are highly reflective, can be made bistable, can be scaled to large areas, and consume very little power. Encapsulated electrophoretic displays also allow the displays to be printed. These properties allow encapsulated electrophoretic display media to be used in many applications where traditional electronic displays are not suitable, such as flexible displays.

[0004] It is often desirable to measure and analyze certain environmental factors that may adversely affect display performance so that a response event or action can then be taken. For example, the electrical properties of an encapsulated electrophoretic display medium may vary in response to environmental factors such as temperature. It has been observed that temperature-induced display artifacts such as lateral coupling and blooming are typically most pronounced during periods of high temperature, when the impedance of the front plane laminate or "FPL" is reduced and the voltage waveform applied to the electrodes of one display pixel is most likely to undesirably affect the optical state of neighboring display pixels.

[0005] In some situations, it may be desirable to modify the manner in which drive waveforms are applied to display pixels in response to changes in the electrical properties of the polymeric material comprising the encapsulated electrophoretic display medium in order to achieve reproducible optical states in the display. It is therefore desirable to implement a temperature-compensated drive scheme in response to and measuring environmental factors such as temperature that can affect the performance of an electrophoretic display. Summary of the Invention [Means for solving the problem]

[0006] Conventional solutions originate from liquid crystal display technology and are therefore based on the assumption that temperature compensation can be achieved simply by adjusting the voltage applied to the display pixels. However, electrophoretic displays have unique characteristics in different temperature ranges that cannot be addressed by voltage adjustment alone.

[0007] Other conventional solutions attempt to compensate for some of the undesirable display artifacts by using display pixel electrodes divided into multiple portions, each of which can be driven independently of the others. However, doing so can more than double the number of elements in the pixel array that must be individually addressed during display updates. Such solutions therefore require extensive modifications to the display controller circuitry and its corresponding software.

[0008] Thus, the invention described herein overcomes the shortcomings of the prior art by providing an inventive multi-element display pixel electrode layout that does not require a complete redesign of the display controller circuitry and corresponding software. Further, the invention described herein provides a display pixel drive circuit that can mitigate performance variations in electrophoretic displays that occur due to changes in ambient temperature. In addition, the invention described herein includes a temperature compensation method that uses all or a portion of the display pixel electrodes to drive each pixel.

[0009] In one aspect, the invention features an electro-optic display including first and second sub-pixel electrodes associated with a display pixel and an electrophoretic display medium disposed between a common electrode and the first and second sub-pixel electrodes. The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel. The display controller circuit is capable of applying waveforms to the display pixel by applying one or more time-dependent voltages between the common electrode and the first sub-pixel electrode through the first transistor, the one or more time-dependent voltages being applied to the first sub-pixel electrode. The electro-optic display also includes a second transistor in electrical communication with the first and second sub-pixel electrodes. A first enable signal activates the second transistor, placing the first and second sub-pixel electrodes in electrical communication.

[0010] In some embodiments, the electro-optic display includes a temperature sensor disposed proximate to the electrophoretic display medium. In some embodiments, the first enable signal activates the second transistor based on a measurement of ambient temperature from the temperature sensor. In some embodiments, the temperature sensor controls the first enable signal to activate the second transistor based on the measurement of ambient temperature.

[0011] In some embodiments, the electro-optic display includes a third transistor in electrical communication with the second subpixel electrode and the common electrode. In some embodiments, a second enable signal activates the third transistor to drain residual charge from the second subpixel electrode. In some embodiments, the second enable signal is controlled by a row select signal associated with a display pixel in a row that is not one of the display pixels in the row.

[0012] In some embodiments, the electro-optic display includes a physical gap between the first sub-pixel electrode and the second sub-pixel electrode, hi some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second sub-pixel electrodes.

[0013] In some embodiments, the electro-optic display includes a third transistor in electrical communication with the common electrode and a fourth transistor, the fourth transistor in electrical communication with the second sub-pixel electrode. In some embodiments, the first enable signal deactivates the fourth transistor when the second transistor is activated. In some embodiments, the second enable signal activates the third transistor to drain residual charge from the second sub-pixel electrode. In some embodiments, the second enable signal is controlled by a row select signal associated with a display pixel in a row, the display pixel being not one of the display pixels in the row.

[0014] In another aspect, the invention features an electro-optic display including first and second sub-pixel electrodes associated with a display pixel and an electrophoretic display medium disposed or electrically coupled between a common electrode and the first and second sub-pixel electrodes. The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel. The display controller circuit is capable of applying waveforms to the display pixel by applying one or more time-dependent voltages between the common electrode and the first sub-pixel electrode through the first transistor, the one or more time-dependent voltages being applied to the first sub-pixel electrode. The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and a third transistor. The third transistor is in electrical communication with the second sub-pixel electrode, and a row select signal associated with the display pixel activates the first and second transistors, placing the first sub-pixel electrode in electrical communication with the third transistor.

[0015] In some embodiments, the electro-optic display further includes a temperature sensor disposed proximate to the electrophoretic display medium. In some embodiments, a second enable signal activates the third transistor. In some embodiments, the second enable signal is pulsed at a predetermined rate when the first transistor and the second transistor are activated. In some embodiments, the third transistor is activated for a portion of the time that the first transistor and the second transistor are activated.

[0016] In some embodiments, the electro-optic display includes a physical gap between the first sub-pixel electrode and the second sub-pixel electrode, hi some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second sub-pixel electrodes.

[0017] These and other aspects of the present invention will become apparent in light of the following description. [Brief explanation of the drawings]

[0018] Additional details of one or more embodiments of the subject matter described herein are set forth in the accompanying drawings and description below. Other features, aspects, and advantages of the subject matter will become apparent from the description contained herein and the accompanying drawings. The drawings are not necessarily to scale, and elements of similar structure are generally annotated with like reference numerals throughout the drawings for illustrative purposes. However, the specific characteristics and functions of elements in different embodiments may not be the same. Furthermore, the drawings are intended only to facilitate explanation of the subject matter. The drawings do not depict every aspect of the described embodiments and do not limit the scope of the disclosure or claims.

[0019] [Figure 1] FIG. 1 is a circuit diagram illustrating an electrophoretic display in accordance with the subject matter described herein.

[0020] [Figure 2] FIG. 2 shows a circuit model of an electro-optic imaging layer in accordance with the subject matter described herein.

[0021] [Figure 3] FIG. 3 is a graph showing a plot of impedance versus temperature for an example front plane laminate or "FPL" in accordance with the subject matter described herein.

[0022] [Figure 4] FIG. 4 is a schematic diagram of an example layout of four display pixel electrodes of a conventional display, where each display pixel electrode comprises a single conductive pad or contact in accordance with the subject matter described herein.

[0023] [Figure 5] FIG. 5 is a schematic diagram of an example layout of four display pixel electrodes, each divided into multiple sub-pixel electrodes, in accordance with the subject matter described herein.

[0024] [Figure 6] FIG. 6 is a schematic diagram of an example layout of four display pixel electrodes, each divided into multiple sub-pixel electrodes, in accordance with the subject matter described herein.

[0025] [Figure 7] FIG. 7 is a schematic diagram of an exemplary pixel including a display pixel drive circuit in accordance with the subject matter described herein.

[0026] [Figure 8] FIG. 8 is a schematic diagram of an exemplary pixel comprising a display pixel drive circuit in accordance with the subject matter described herein.

[0027] [Figure 9]FIG. 9 is a schematic diagram of an exemplary pixel including a display pixel drive circuit in accordance with the subject matter described herein.

[0028] [Figure 10] FIG. 10 is a schematic diagram of an exemplary pixel comprising a display pixel drive circuit in accordance with the subject matter described herein.

[0029] [Figure 11] FIG. 11 is a signal timing diagram illustrating drive signals for three pixels having a display pixel drive circuit in accordance with the subject matter described herein.

[0030] [Figure 12] FIG. 12 is a block diagram of an exemplary electrophoretic display in accordance with the subject matter described herein. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention relates to display pixel circuits and methods of driving electro-optic displays, particularly bistable electro-optic displays, and apparatus for use in such methods. More particularly, the present invention relates to driving methods that may enable reduced "afterimage" and edge effects, and low flashing in such displays. The present invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays in which one or more types of electrically charged particles are present in a fluid and are caused to move through the fluid under the influence of an electric field, changing the appearance of the display.

[0032] The term "electro-optic," as applied to a material or display, is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states in which at least one optical property differs, and which can be changed from its first display state to its second display state by application of an electric field to the material. The optical property is typically color perceptible to the human eye, but it can also be another optical property, such as optical transmittance, reflectance, luminescence, or, in the case of displays intended for machine-reading, pseudocolor in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.

[0033] The term “gray state” is used herein in its conventional sense in the imaging arts to refer to a state intermediate between two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between these two extreme states. For example, several of the E Ink patents and published applications referenced below describe electrophoretic displays whose extreme states are white and dark blue, so that an intermediate “gray state” would actually be light blue. In fact, as already mentioned, a change in optical state may not be a change in color at all. The terms “black” and “white” may be used hereinafter to refer to the two extreme optical states of a display and should generally be understood to include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term “monochrome” may be used hereinafter to refer to a drive scheme that drives pixels to only those two extreme optical states, with no intervening gray states.

[0034] Some electro-optic materials are solid in the sense that the material has a solid exterior surface, but the material can, and often does, have an interior liquid- or gas-filled space. Such displays that use solid electro-optic materials may hereinafter be referred to for convenience as "solid electro-optic displays." Thus, the term "solid electro-optic display" includes rotating dichroic member displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

[0035] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to a display having display elements with first and second display states that differ in at least one optical property, such that after any given element is driven with a finite-duration address pulse to exhibit either its first or second display state, that state will persist after the address pulse is terminated for at least several times, e.g., at least four times, the minimum duration of the address pulse required to change the state of the display element. U.S. Patent No. 7,170,670 indicates that some grayscale-capable particle-based electrophoretic displays are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for several other types of electro-optic displays. Displays of this type are properly referred to as "multistable" rather than bistable, although for convenience the term "bistable" may be used herein to include both bistable and multistable displays.

[0036] The term "impulse" is used herein in its conventional sense of the integral of voltage with respect to time. However, some bistable electro-optic media act as charge transducers, and when using such media, an alternative definition of impulse may be used: the integral of current over time (equal to the total charge applied). The appropriate definition of impulse should be used depending on whether the medium acts as a voltage-time impulse transducer or a charge impulse transducer.

[0037] Much of the discussion below will focus on methods for driving one or more pixels of an electro-optic display through a transition from an initial gray level to a final gray level (which may or may not be different from the initial gray level). The term “waveform” will be used to describe the overall voltage versus time curve used to effect a transition from one particular initial gray level to a particular final gray level. Typically, such a waveform comprises multiple waveform elements, and when these elements are essentially rectangular (i.e., when a given element comprises the application of a constant voltage for a period of time), the element may be referred to as a “pulse” or “drive pulse.” The term “drive scheme” refers to a set of waveforms sufficient to effect all possible transitions between gray levels for a particular display. A display may utilize more than one drive scheme; for example, the aforementioned U.S. Patent No. 7,012,600 teaches that a drive scheme may need to be modified depending on parameters such as the temperature of the display or the time it has been operating during its lifetime, and thus a display may be provided with multiple different drive schemes to be used at different temperatures, etc. A set of drive schemes used in this manner may be referred to as a “set of related drive schemes.” As described in some of the aforementioned MEDEOD applications, it is also possible to use two or more drive schemes simultaneously in different areas of the same display, and a set of drive schemes used in this manner may be referred to as a "set of simultaneous drive schemes."

[0038] Several types of electro-optic displays are known. One type of electro-optic display is the rotating dichroic member type, as described in, for example, U.S. Patent Nos. 5,808,783, 5,777,782, 5,760,761, 6,054,071, 6,055,091, 6,097,531, 6,128,124, 6,137,467, and 6,147,791. (This type of display is often referred to as a "rotating dichroic ball" display, but in some of the above-mentioned patents, the rotating member is not spherical, so the term "rotating dichroic member" is preferred as it is more accurate.) Such displays use a large number of small bodies (typically spherical or cylindrical) having two or more segments with different optical properties and an internal dipole. These bodies are suspended within liquid-filled vacuoles in a matrix, and the vacuoles are filled with liquid so that the bodies are free to rotate. The appearance of the display can be changed by applying an electric field to it, thus rotating the bodies to various positions and varying the position of segments of the bodies as seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0039] Another type of electro-optic display uses an electrochromic medium, e.g., in the form of a nanochromic film, which comprises electrodes formed at least in part from a semiconducting metal oxide and a plurality of dye molecules attached to the electrodes that can reverse their color change (see, e.g., O'Regan, B., et al., Nature 1991, 353, 737 and Wood, D., Information Display, 18(3), 24 (March 2002)). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Pat. Nos. 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0040] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, R.A., et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such electrowetting displays can be made bistable.

[0041] One type of electro-optic display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which a plurality of charged particles move through a fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared to liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle, resulting in an inadequate usable lifespan for these displays.

[0042] As described above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is liquid, but electrophoretic media can also be produced using gaseous fluids (see, for example, Kitamura, T., et al., "Electrical toner movement for electronic paper-like display," IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y., et al., "Toner display using insulative particles charged triboelectrically," IDW Japan, 2001, Paper AMD4-4). See also U.S. Patent Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media are believed to be susceptible to the same types of problems as liquid-based electrophoretic media due to particle settling when used in an orientation that allows such settling, for example, in a sign where the medium is positioned in a vertical plane. In fact, particle settling is believed to be a more serious problem with gas-based electrophoretic media than with liquid-based electrophoretic media. This is because the lower viscosity of the gaseous suspending fluid compared to the viscosity of a liquid allows for faster settling of the electrophoretic particles.

[0043] Numerous patents and applications assigned to (or in the name of) the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise a multitude of small capsules, each of which itself comprises an internal phase containing electrophoretically movable particles in a fluid medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder that forms a coherent layer positioned between two electrodes. Techniques described in these patents and applications include the following:

[0044] (a) electrophoretic particles, fluids, and fluid additives (see, e.g., U.S. Patent Nos. 7,002,728 and 7,679,814);

[0045] (b) capsules, binders, and encapsulation processes (see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719);

[0046] (c) microcell structures, wall materials, and methods of forming the microcells (see, e.g., U.S. Patent Nos. 7,072,095 and 9,279,906);

[0047] (d) methods of filling and sealing microcells (see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088);

[0048] (e) films and subassemblies containing electro-optical materials (see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564);

[0049] (f) backplanes, adhesive layers and other auxiliary layers and methods used in displays (see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624);

[0050] (g) color formation and color control (see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564);

[0051] (h) display applications (see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348);

[0052] (i) non-electrophoretic displays, such as those described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160, as well as non-display applications of encapsulation and microcell technology (see, e.g., U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710);

[0053] (j) Methods of driving displays (e.g., U.S. Patent Nos. 5,930,026, 6,445,489, 6,504,524, 6,512,354, 6,531,997, 6,753,999, 6,825,970, 6,900,851, 6,995,550, 7,012,600, 7,023,420, 7,034,783, 7,061,166, 7,061,662, 7,116,466, 7,119,772, 7,177,066, 7,193,625, 7,202,84 No. 7, No. 7,242,514, No. 7,259,744, No. 7,304,787, No. 7,312,794, No. 7,327,511 , No. 7,408,699, No. 7,453,445, No. 7,492,339, No. 7,528,822, No. 7,545,358, No. 7 , No. 583,251, No. 7,602,374, No. 7,612,760, No. 7,679,599, No. 7,679,813, No. 7,6 No. 83,606, No. 7,688,297, No. 7,729,039, No. 7,733,311, No. 7,733,335, No. 7,787, No. 169, No. 7,859,742, No. 7,952,557, No. 7,956,841, No. 7,982,479, No. 7,999,78 No. 7, No. 8,077,141, No. 8,125,501, No. 8,139,050, No. 8,174,490, No. 8,243,013, No. 8,274,472, No. 8,289,250, No. 8,300,006, No. 8,305,341, No. 8,314,784, No. 8 ,373,649, No.8,384,658, No.8,456,414, No.8,462,102, No.8,537,105, No.8,55 No. 8,783, No. 8,558,785, No. 8,558,786, No. 8,558,855, No. 8,576,164, No. 8,576, No. 259, No. 8,593,396, No. 8,605,032, No. 8,643,595, No. 8,665,206, No. 8,681,191 No. 8,730,153, No. 8,810,525, No. 8,928,562, No. 8,928,641, No. 8,976,444, No. 9,013,394, No. 9,019,197, No. 9,019,198, No. 9,019,318, No. 9,082,352, No. 9,Nos. 171,508, 9,218,773, 9,224,338, 9,224,342, 9,224,344, 9,230,492, 9,251,736, 9,262,973, 9,269,311, 9,299,294, 9,373,289, 9,390,066, 9,390,661, and 9,412,314, and U.S. Patent Application Publication Nos. 2003 / 0102858, 2004 / 0246562, 2005 / 0253777, 2007 / 0070032, 2007 / 0076289, 2007 / 0091418, 2007 / 0103427, 2007 / 0176912, 2007 / 0296452, 2008 / 0024429, 2008 / 0024482, 2008 / 0136774, 2008 / 0169821, 2008 / 0218471, No. 2008 / 0291129, No. 2008 / 0303780, No. 2009 / 0174651, No. 2009 / 0195568, No. 2009 / 0322721, No. 2010 / 0194733, No. 2010 / 0194789, No. 2010 / 02 20121, 2010 / 0265561, 2010 / 0283804, 2011 / 0063314, 2011 / 0175875, 2011 / 0193840, 2011 / 0193841, 2011 / 0199671, 2 No. 011 / 0221740, No. 2012 / 0001957, No. 2012 / 0098740, No. 2013 / 0063333, No. 2013 / 0194250, No. 2013 / 0249782, No. 2013 / 0321278, No. 2014 / 0009 No. 817, No. 2014 / 0085355, No. 2014 / 0204012, No. 2014 / 0218277, No. 2014 / 0240210, No. 2014 / 0240373, No. 2014 / 0253425, No. 2014 / 0292830, No. 201 (See Nos. 2014 / 0333685, 2014 / 0340734, 2015 / 0070744, 2015 / 0097877, 2015 / 0109283, 2015 / 0213749, 2015 / 0213765, 2015 / 0221257, 2015 / 0262255, 2016 / 0071465, 2016 / 0078820, 2016 / 0093253, 2016 / 0140910, and 2016 / 0180777).

[0054] Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium may be replaced by a continuous phase, thus producing so-called polymer-dispersed electrophoretic displays, in which the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic fluid and a continuous phase of polymer material, and that the discrete droplets of electrophoretic fluid in such polymer-dispersed electrophoretic displays may be considered capsules or microcapsules, even though no discrete capsule membrane is associated with each individual droplet (see, e.g., aforementioned 2002 / 0131147). Therefore, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0055] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, the charged particles and suspending fluid are not encapsulated in microcapsules, but instead are held within a plurality of cavities formed in a carrier medium, e.g., a polymer film. See, e.g., International Application Publication No. WO 02 / 01281 and Published U.S. Application No. 2002 / 0075556 (both assigned to Sipix Imaging, Inc.).

[0056] Many of the aforementioned E Ink and MIT patents and applications also contemplate microcell electrophoretic displays and polymer-dispersed electrophoretic displays. The term "encapsulated electrophoretic displays" can refer to any such display type, which may also be collectively described as "microcavity electrophoretic displays" to generalize to the entire wall configuration.

[0057] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, R.A., et al., "Video-Speed ​​Electronic Paper Based on Electrowetting," Nature, 425, 383-385 (2003). Co-pending application Ser. No. 10 / 711,802, filed Oct. 6, 2004, shows that such electrowetting displays can be made bistable.

[0058] Other types of electro-optic materials may also be used, most notably bistable ferroelectric liquid crystal displays (FLCs), which are known in the art and exhibit remnant voltage behavior.

[0059] Although electrophoretic media can be opaque (e.g., in many electrophoretic media, because the particles substantially block the transmission of visible light through the display) and operate in a reflective mode, some electrophoretic displays can be made to operate in a so-called "obscured mode," in which one display state is substantially opaque and one is light transmissive. See, for example, U.S. Patent Nos. 6,130,774 and 6,172,798, and U.S. Patent Nos. 5,872,552, 6,144,361, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays (similar to electrophoretic displays but relying on variations in electric field strength) can operate in a similar mode (see U.S. Patent No. 4,418,346). Other types of electro-optic displays may also be capable of operating in a obscured mode.

[0060] High-resolution displays may include individual pixels that are addressable without interference from neighboring pixels. One way to achieve such pixels is to provide an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel, to produce an "active matrix" display. An address or display pixel electrode that addresses a display pixel is connected to an appropriate voltage source through the associated nonlinear element. When the nonlinear element is a transistor, the display pixel electrode may be connected to the drain of the transistor; although this arrangement will be assumed in the following description, it is essentially arbitrary; the display pixel electrode may also be connected to the source of the transistor. In high-resolution arrays, pixels may be arranged in a two-dimensional array of rows and columns, whereby any particular pixel is uniquely defined by the intersection of a defined row and a defined column. The sources of all transistors in each column may be connected to a single column electrode, while the gates of all transistors in each row may be connected to a single row electrode; again, the assignment of sources to rows and gates to columns may be reversed as desired.

[0061] The display can be written in a row-by-row manner. The row electrodes are connected to row drivers, which may apply voltages to selected row electrodes to ensure that all transistors in a selected row are conductive, while applying voltages to all other rows to ensure that all transistors in those unselected rows remain non-conductive, etc. The column electrodes are connected to column drivers, which apply selected voltages to various column electrodes to drive pixels in a selected row to their desired optical states. (These voltages are relative to a common front electrode, which may be provided opposite a nonlinear array of electro-optic medium and span the entire display.) As is known in the art, voltage is relative and is the magnitude of the difference in charge between two points. One voltage value is relative to another voltage value. For example, zero voltage (“0V”) refers to having no voltage difference relative to another voltage. ) After a preselected interval known as the "line address time," the selected row is deselected, another row is selected, and the voltages on the column drivers are changed so that the next line of the display is written.

[0062] However, in use, certain waveforms can cause a remnant voltage to be induced in the pixels of an electro-optic display. The term "remnant voltage" is sometimes also used as a convenient term to refer to the overall phenomenon. However, the basis for the switching behavior of impulse-driven electro-optic displays is the application of a voltage impulse (the integral of voltage over time) across the electro-optic medium. The remnant voltage may reach a peak value shortly after application of the drive pulse and then decay substantially exponentially. The persistence of the remnant voltage for a significant period of time applies a "remnant impulse" to the electro-optic medium, and although not strictly speaking a remnant voltage, this remnant impulse may be responsible for the effects on the optical state of the electro-optic display that are usually considered to be caused by remnant voltage. This remnant voltage can produce several unwanted optical effects and is generally undesirable.

[0063] As presented herein, a "shift" in optical state associated with an address pulse refers to the situation where the initial application of a particular address pulse to an electro-optic display results in a first optical state (e.g., a first gray tone), and a subsequent application of the same address pulse to the electro-optic display results in a second optical state (e.g., a second gray tone). A remnant voltage can cause a shift in optical state because the voltage applied to a pixel of the electro-optic display during application of the address pulse comprises the sum of the remnant voltage and the voltage of the address pulse.

[0064] "Drift" in the optical state of a display over time refers to the situation where the optical state of an electro-optic display changes while the display is at rest (e.g., during periods when no address pulses are applied to the display). Residual voltages can cause drift in the optical state because the optical state of a pixel can depend on the remnant voltage of the pixel, and the remnant voltage of a pixel can decay over time.

[0065] As discussed above, "persistence" refers to the situation where, after an electro-optic display has been rewritten, a trace of the previous image is still visible.

[0066] "Edge persistence" is another type of persistence in which the contours (edges) of portions of a previous image remain visible. This type of artifact is caused by inter-pixel effects such as so-called "blooming." For example, in both monochrome and color systems, the electric field generated by a display pixel electrode tends to affect an area of ​​the electro-optic medium wider than that of the display pixel electrode itself, thereby effectively causing the optical state of one pixel to extend into portions of the area of ​​an adjacent pixel. Furthermore, in some cases, driving adjacent pixels results in a final optical state in the area between those pixels that differs from the optical state achieved by either of the adjacent pixels themselves. This final optical state in the area between adjacent pixels is caused by the electric field experienced in the inter-pixel region, which is the average of the electric fields applied to the adjacent pixels. It has been found that edge persistence can be reduced by driving electro-optic displays with a DC unbalanced waveform. However, as discussed above, a DC unbalanced waveform can cause residual voltage.

[0067] In summary, remnant voltage as a phenomenon can manifest itself in various ways as image retention or visual artifacts, the severity of which can vary with the time elapsed between image updates. Remnant voltage can also create DC imbalances, reducing the final display life. The effects of remnant voltage can therefore be detrimental to the quality of electrophoretic or other electro-optical devices, and it is desirable to minimize both the remnant voltage itself and the sensitivity of the device's optical state to the effects of remnant voltage. Thus, discharging the remnant voltage in an electro-optical display can improve the quality of the displayed image, even in situations where the remnant voltage is already low.

[0068] 1 shows a schematic diagram of a pixel 100 of an electrophoretic display or EPD in accordance with the presently presented subject matter. Pixel 100 may include an imaging film 110. In some embodiments, imaging film 110 may be bistable. In some embodiments, imaging film 110 may include, for example, but not limited to, an encapsulated electrophoretic imaging film that may include charged pigment particles.

[0069] The imaging film 110 may be disposed between the front electrode 102 and the back electrode 104. The front electrode 102 may be formed between the imaging film and the front surface of the display. In some embodiments, the front electrode 102 may be transparent. In some embodiments, the front electrode 102 may be formed from any suitable transparent material, including, but not limited to, indium tin oxide (ITO). The back electrode 104 may be formed opposite the front electrode 102. In some embodiments, a parasitic capacitance (not shown) may be formed between the front electrode 102 and the back electrode 104.

[0070] Pixel 100 may be one of a plurality of pixels. The plurality of pixels may be arranged in a two-dimensional array of rows and columns to form a matrix such that any particular pixel is uniquely defined by the intersection of one defined row and one defined column. In some embodiments, the matrix of pixels may be an “active matrix” in which each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 may be coupled between the backplate electrode 104 and the address electrode 108. In some embodiments, the nonlinear element 120 may include a diode and / or a transistor, including, but not limited to, a MOSFET. The drain (or source) of the MOSFET may be coupled to the backplate electrode 104, the source (or drain) of the MOSFET may be coupled to the address electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106 configured to control activation and deactivation of the MOSFET. (For simplicity, the terminal of the MOSFET that is coupled to backplate electrode 104 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET that is coupled to address electrode 108 will be referred to as the source of the MOSFET. However, those skilled in the art will recognize that in some embodiments, the source and drain of a MOSFET may be swapped.)

[0071] In some active matrix embodiments, the address electrodes 108 of all pixels in each column may be connected to the same column electrode, and the driver electrodes 106 of all pixels in each row may be connected to the same row electrode. The row electrodes may be connected to a row driver, which may select one or more rows of pixels by applying a voltage to the selected row electrode sufficient to activate the nonlinear elements 120 of all pixels 100 in the selected row. The column electrodes may be connected to a column driver, which may apply an appropriate voltage to the address electrode 106 of the selected (activated) pixel to drive the pixel to a desired optical state. The voltage applied to the address electrode 108 may be relative to the voltage applied to the pixel's front plate electrode 102 (e.g., a voltage of about zero volts). In some embodiments, the front plate electrodes 102 of all pixels in the active matrix may be coupled to a common electrode.

[0072] In some embodiments, the active matrix pixels 100 can be written in a row-by-row manner. For example, a row of pixels can be selected by a row driver, and voltages corresponding to the desired optical state for the row of pixels can be applied to the pixels by a column driver. After a preselected interval known as a "line address time," the selected row can be deselected, another row can be selected, and the voltages on the column drivers can be changed so that another row of the display is written.

[0073] 2 shows a circuit model of an electro-optic imaging layer 110 disposed between a front electrode 102 and a back electrode 104 in accordance with the subject matter presented herein. Resistor 202 and capacitor 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, front electrode 102, and back electrode 104, including any adhesive layers. Resistor 212 and capacitor 214 may represent the resistance and capacitance of a lamination adhesive layer. Capacitor 216 may represent capacitance that may arise between the front electrode 102 and back electrode 104 (e.g., at an interfacial contact area between layers, such as the interface between the imaging layer and a lamination adhesive layer and / or the interface between a lamination adhesive layer and a backplane electrode). The voltage Vi across the imaging film 110 of a pixel may include the residual voltage of the pixel.

[0074] It has been observed that the performance of electrophoretic displays can vary according to environmental conditions. For example, variations in the impedance of an FPL can be related to variations in temperature. Figure 3 is a graph 300 showing a plot 305 of impedance versus temperature for an exemplary front plane laminate. In particular, graph 300 shows impedance in MΩcm at 10 Hz on the y-axis. 2 FPL impedance in units Z real 3 shows a plot 305 of FPL impedance versus temperature in degrees Celsius on the x-axis. As illustrated by graph 300, FPL impedance decreases as temperature increases. It should be understood that the FPLs referred to herein can include, but are not limited to, light-transmitting conductive layers, layers of electro-optic medium, and adhesive layers of an electrophoretic display.

[0075] Conventionally, for electrophoretic displays including a plurality of display pixels or a matrix thereof, there is only one display pixel electrode associated with each display pixel. For example, as described above, each display pixel of an active matrix is ​​typically associated with a separate transistor configured to drive the display pixel by applying one or more voltages to the display pixel electrode, which comprises a single conductive pad or contact. Figure 4 is a schematic diagram 400 of an exemplary layout of four display pixel electrodes (display pixel electrode 401, display pixel electrode 402, display pixel electrode 403, and display pixel electrode 404) of a conventional display, where each display pixel electrode comprises a single conductive pad or contact.

[0076] As shown in Figure 4, display pixel electrode 401 is maintained at a distance 430 from laterally adjacent display pixel electrode 402. Although not explicitly referenced in Figure 4, display pixel electrode 403 is also maintained at a distance 430 from laterally adjacent display pixel electrode 404. Furthermore, display pixel electrode 401 is maintained at a distance 431 from vertically adjacent display pixel electrode 403. Although not explicitly referenced in Figure 4, display pixel electrode 402 is also maintained at a distance 431 from vertically adjacent display pixel electrode 404. In some embodiments, distance 430 and distance 431 are substantially equal.

[0077] Electrophoretic displays may include circuitry for estimating the impedance of the FPL based on one or more measurements of ambient temperature. Conventional solutions attempt to mitigate undesirable optical artifacts by simply adjusting the voltage applied to the display pixels in response to temperature measurements. Conventional solutions are not suitable for electrophoretic displays, which have unique characteristics in different temperature ranges that cannot be compensated for using voltage adjustment alone. Other conventional solutions utilize display pixel electrodes subdivided into multiple segments, which can be individually addressed by a display controller. However, such solutions more than double the number of elements in the pixel array that must be managed and controlled during display updates, thus adding complexity and requiring extensive modifications to conventional display controller circuitry (integrated circuits and printed circuit board routing) and its corresponding software. Furthermore, using such solutions for electrophoretic displays can lead to panel degradation due to mismatches in kickback voltages associated with each drive element.

[0078] Thus, as described in detail below with reference to Figures 5-12, the invention described herein overcomes the shortcomings of the prior art by providing an inventive multi-element display pixel electrode layout and associated drive circuitry that does not require a complete redesign of the display controller circuitry and corresponding software.

[0079] 5 is a schematic diagram 500 of an example layout of four display pixel electrodes (display pixel electrode 501, display pixel electrode 502, display pixel electrode 503, and display pixel electrode 504), each divided into multiple sub-pixel electrodes. As shown in FIG. 5, display pixel electrode 501 includes a solid rectangular sub-pixel electrode 501a (e.g., a first sub-pixel electrode) at its center surrounded by a hollow rectangular sub-pixel electrode 501b (e.g., a second sub-pixel electrode). There is a gap 532 (e.g., a physical gap) between the edge of sub-pixel electrode 501a and the inner edge of sub-pixel electrode 501b (e.g., a physical gap between adjacent edges). For example, subpixel electrode 501a and subpixel electrode 501b may each be a conductive pad or contact formed on a substrate or backplane such that their edges are kept some distance apart (e.g., 0.5 mil to 1 mil, 1 mil to 2 mil, 2 mil to 5 mil, 5 mil to 50 mil, 1 mm to 5 mm). In some embodiments, gap 532 is a uniform distance around the periphery of subpixel electrode 501a. In some embodiments, the length of gap 532 varies between the horizontal direction (e.g., the physical gap in the horizontal direction) and the vertical direction (e.g., the physical gap in the vertical direction).

[0080] As shown in Figure 5, subpixel electrode 501b is spaced a distance 530 from laterally adjacent subpixel electrode 502b. Although not explicitly shown in Figure 5, subpixel electrode 503b is also spaced a distance 530 from laterally adjacent subpixel electrode 504b. Furthermore, subpixel electrode 501b is spaced a distance 531 from vertically adjacent subpixel electrode 503b. Although not explicitly shown in Figure 5, subpixel electrode 502b is also spaced a distance 531 from vertically adjacent subpixel electrode 504b. In some embodiments, distance 530 and distance 531 are substantially equal.

[0081] When used in conjunction with one of the display pixel drive circuits described in detail below, the multi-element display pixel electrode layout shown in FIG. 5 allows each hollow rectangular sub-pixel electrode to be selectively driven or taken out of the circuit independently from its associated solid rectangular sub-pixel electrode. For example, a hollow sub-pixel electrode can be selectively taken out of the circuit (e.g., floated, grounded, V COM ) so that the drive waveform applied to the pixel electrode is applied only to its central rectangular sub-pixel electrode. This effectively increases the distance between the electrodes applying voltage to the electro-optic imaging layer. In particular, when sub-pixel electrodes 501b and 502b are removed from the circuit, the lateral distance between pixel electrodes 501 and 502 effectively increases to distance 534, which is the distance between sub-pixel electrodes 501a and 502a. Similarly, when sub-pixel electrodes 501b and 503b are removed from the circuit, the vertical distance between display pixel electrodes 501 and 503 effectively increases to distance 535, which is the distance between sub-pixel electrodes 501a and 503a.

[0082] It has been observed that temperature-induced display artifacts such as lateral coupling and blooming are typically most pronounced during periods of high temperature, when the impedance of the FPL is reduced and a voltage waveform applied to the electrodes of one display pixel is most likely to undesirably affect the optical state of neighboring display pixels. The multi-element display pixel electrode layout of schematic diagram 500 and the pixel drive circuitry described below enable a drive scheme that can effectively compensate for variations in FPL temperature. For example, selectively removing some or all of the hollow subpixel electrodes from the circuitry during periods of high temperature, thereby increasing the distance between the driven portions of the display pixel electrodes, can reduce or eliminate temperature-induced display artifacts.

[0083] FIG. 6 is a schematic diagram 600 of an example layout of four display pixel electrodes (display pixel electrode 601, display pixel electrode 602, display pixel electrode 603, and display pixel electrode 604), in which each display pixel electrode is divided into multiple subpixel electrodes. As shown in FIG. 6, display pixel electrode 601 includes a rectangular subpixel electrode 601a (e.g., a first subpixel electrode) with an L-shaped subpixel electrode 601b (e.g., a second subpixel electrode) positioned adjacent to its left and bottom edges. There is a gap 632 between the edge of subpixel electrode 601a and the inner edge of subpixel electrode 601b. In some embodiments, gap 632 is a uniform distance along the entire inner edge of L-shaped subpixel electrode 601b. In some embodiments, the length of gap 632 varies between the horizontal and vertical directions. In some embodiments, the L-shaped subpixel electrode 601b is rotated 180 degrees clockwise and positioned adjacent to the right and bottom edge of the subpixel electrode 601a. ​​Those skilled in the art will appreciate that other subpixel electrode configurations are within the scope of the present disclosure.

[0084] As shown in Figure 6, subpixel electrode 601a is spaced a distance 630 from laterally adjacent subpixel electrode 602b. Although not shown in Figure 6, subpixel electrode 603a is also spaced a distance 630 from laterally adjacent subpixel electrode 604b. Furthermore, subpixel electrode 601b is spaced a distance 631 from vertically adjacent subpixel electrode 603a. Although not shown in Figure 6, subpixel electrode 602b is also spaced a distance 631 from vertically adjacent subpixel electrode 604a. In some embodiments, distance 630 and distance 631 are substantially equal.

[0085] The multi-element display pixel electrode layout of schematic 600 can also be used with pixel drive circuitry, described below, to implement a temperature-compensated drive scheme that reduces (or eliminates) temperature-induced display artifacts. Furthermore, the L-shaped subpixel electrode configuration simplifies the layout and fabrication of multiple display pixel electrodes and their associated drive circuitry. For example, because the L-shaped subpixel electrodes do not completely surround the corresponding rectangular subpixel electrodes, conductive traces can be routed to the rectangular subpixel electrodes without requiring vias to be drilled and conductively plated to connect to traces on different layers of the substrate or backplane. For similar reasons, the installation and routing of additional display pixel drive circuitry components is also simplified by this configuration.

[0086] As indicated above, the present disclosure includes several inventive display pixel drive circuits that can be used in conjunction with the multi-element display pixel electrode layouts described herein to implement temperature-compensated drive schemes for electro-optic displays. The configuration of each drive circuit varies depending on the preferred voltages and drive characteristics for the sub-pixel electrodes.

[0087] 7 is a schematic diagram of an example pixel 700 including a display pixel drive circuit in accordance with the subject matter described herein. As in a conventional display, the display pixel 700 includes a transistor 720 (e.g., a first transistor) that applies a voltage (e.g., a time-dependent voltage) present on an address electrode 708 to a display pixel electrode (in this case, subpixel electrode 701a) when a gate voltage sufficient to activate the transistor 720 is applied to a driver electrode 706. For example, the driver electrode 706 can be connected to row select circuitry of a display controller or driver. The voltage applied to the address electrode 708 is V COMor relative to the voltage applied to the front plate electrode 702 (e.g., a common electrode). The voltage applied to the front plate electrode 702 is typically a voltage of about zero volts, but is not so limited and can be a positive or negative voltage. A reservoir capacitor 750 (e.g., a first reservoir capacitor) maintains the voltage across the electro-optic medium 710 (e.g., an electrophoretic display medium) between updates.

[0088] As shown in FIG. 7 , unlike conventional pixel designs, display pixel 700 includes a transistor 740 (e.g., a second transistor) between subpixel electrode 701a (e.g., a first subpixel electrode) and subpixel electrode 701b (e.g., a second subpixel electrode), allowing display pixel 700 to operate in high and low temperature modes. For example, when the temperature is low, a voltage sufficient to activate transistor 720 is applied to enable signal 746 (e.g., a first enable signal), which drives the gate signal of transistor 740. Transistor 740 becomes conductive in the activated state, and subpixel electrode 701a and subpixel electrode 701b are then electrically connected. Therefore, a voltage applied to address electrode 708 is applied to both subpixel electrode 701a and subpixel electrode 701b. An additional reservoir capacitor 752 (eg, a second reservoir capacitor) also maintains the voltage across the electro-optic medium 710 between refreshes when transistor 740 is activated.

[0089] Conversely, when the temperature is high and the FPL impedance drops, enable signal 746 can be set to a low state to deactivate transistor 740, thereby placing subpixel electrode 701b in a high-impedance (e.g., floating, non-conductive) state and preventing the voltage applied to subpixel electrode 701a from also being applied to subpixel electrode 701b. As explained above, when using multi-element display pixel electrodes such as those shown in Figures 5 and 6, selectively removing subpixel electrode 701b from the circuit during periods of high temperature can increase the distance between the driven portions of the display pixel electrode and reduce or eliminate temperature-induced display artifacts.

[0090] 12 is a block diagram of an example electrophoretic display 1200 in accordance with the subject matter described herein. Electrophoretic display 1200 includes display controller circuitry 1280, a display stack 1290, and a temperature sensor 1285.

[0091] Display stack 1290 includes a front plate or common electrode 1222, an imaging film 1210, and an array of four display pixel electrodes, each divided into multiple subpixel electrodes: display pixel electrode 1201 includes subpixel electrode 1201a and subpixel electrode 1201b, display pixel electrode 1202 includes subpixel electrode 1202a and subpixel electrode 1202b, display pixel electrode 1203 includes subpixel electrode 1203a and subpixel electrode 1203b, and display pixel electrode 1204 includes subpixel electrode 1204a and subpixel electrode 1204b. The subpixel electrodes of each display pixel electrode shown in FIG. 12 are similar to those shown in FIG. 6, with one subpixel electrode rectangular and the other L-shaped. Those skilled in the art will understand that other subpixel electrode configurations are within the scope of this disclosure. Furthermore, those skilled in the art will appreciate that the present invention is not limited to electro-optic displays having four display pixel electrodes.

[0092] Common electrode 1222 can be formed from any suitable conductive transparent material, including, but not limited to, aluminum indium tin oxide (ITO). Imaging film 1210 can include, for example, but not limited to, an encapsulated electrophoretic imaging film, which may include charged pigment particles. Electrophoretic display 1200 is typically viewed from the side of common electrode 1222 opposite from the side of display pixel electrodes 1201-1204. However, the components of electrophoretic display 1200 can be selected such that electrophoretic display 1200 is viewable from the side of display pixel electrodes 1201-1204, or even from both.

[0093] Display stack 1290 also includes an adhesive layer 1240 between common electrode 1222 and imaging film 1210, and an adhesive layer 1241 between imaging film 1210 and display pixel electrodes 1201-1204. In some embodiments, the adhesive layer can include an integrated primer component to improve adhesion, or a separate primer layer (not shown in FIG. 12) can be used. (The structure and component parts, pigments, adhesives, electrode materials, etc. of electrophoretic displays are described in many patents and patent applications published by E Ink Corporation, such as U.S. Pat. Nos. 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564, all of which are incorporated herein by reference in their entireties.)

[0094] 12, the display stack 1290 can include one or more additional layers, as needed. As an example, the display pixel electrodes 1201-1204 can be a component of a backplane that includes a substrate layer on which the display pixel electrodes 1201-1204 are disposed. Additionally, the common electrode 1222 can be disposed on a substrate layer such as a poly(ethylene terephthalate) (PET) film, which is commercially available, for example, as "aluminized Mylar" ("Mylar" is a registered trademark of EI du Pont de Nemours & Company, Wilmington, DE).

[0095] Display controller circuitry 1280 represents the circuits and components that provide the supply voltages and control signals 1295 necessary to operate electrophoretic display 1200. For example, display controller circuitry 1280 may include power management circuitry for generating and supplying multiple voltages to display stack 1290, along with row and column drivers for addressing the array of display pixel electrodes and driving waveforms sufficient to change the optical state of imaging film 1210. In some embodiments, the transistors used to address and drive the display pixel electrodes are positioned in close proximity to the array of display pixel electrodes.

[0096] Display controller circuitry 1280 also controls the state of enable signal 1246, which corresponds to enable signal 746 described above in connection with Figure 7. Although not shown in Figure 12, display controller circuitry 1280 can also be configured to control the state of additional enable signals used in the embodiments described below in connection with Figures 8-10.

[0097] Those skilled in the art will understand that the display controller circuitry 1280 of the present invention can be implemented in several different physical forms and can utilize a variety of analog and digital components. For example, the display controller circuitry 1280 can include a general-purpose microprocessor along with appropriate peripheral components (e.g., one or more digital-to-analog converters (“DACs”)) to convert the digital output from the microprocessor to appropriate voltages for application to the pixels. Alternatively, the display controller circuitry 1280 can be implemented in an application-specific integrated circuit (“ASIC”) or a field-programmable gate array (“FPGA”). Those skilled in the art will understand that the display controller circuitry 1280 can include both processing components and power management circuitry.

[0098] In some embodiments, display controller circuitry 1280 includes a timing controller integrated circuit (“IC”) that receives incoming image data and outputs control signals to data collection and selection driver ICs (e.g., row and column driver ICs) to produce appropriate voltages at display pixel electrodes to display the desired image. In some embodiments, a host controller in communication with the display controller circuit requests updates from electrophoretic display 1200 and provides image data for updating to the display controller circuit. In some embodiments, display controller circuitry 1280 accepts image data through access to a memory buffer containing the image data, or receives signals from which the image data is extracted. In some embodiments, the memory buffer has a structure such as those described in U.S. Pat. No. 9,721,495. In some embodiments, display controller circuitry 1280 receives a serial signal containing information required to perform the calculations necessary to generate drive impulses (e.g., drive waveforms) to be applied to the electrophoretic medium during scanning of the pixel array.

[0099] Temperature sensor 1285 measures the temperature of the electrophoretic medium or its immediately adjacent environment and provides the temperature information to display controller circuitry 1280 via interface 1286. In some embodiments, temperature sensor 1285 is positioned within the encapsulating electrophoretic medium of imaging film 1210. In some embodiments, temperature sensor 1285 comprises multiple temperature sensors positioned at different physical locations around or within imaging film 1210.

[0100] Temperature sensor 1285 may be a sensor whose electrical properties, such as resistance or capacitance, change in response to variations in temperature. In some embodiments, temperature sensor 1285 comprises a thermocouple, a resistance temperature detector ("RTD"), and / or a thermistor (e.g., a negative temperature coefficient ("NTC") thermistor). In some embodiments, temperature sensor 1285 comprises a semiconductor-based integrated circuit for sensing temperature.

[0101] In some embodiments, interface 1286 is an integrated bus interface or similar bus interface that temperature sensor 1285 uses to communicate temperature information to display controller circuitry 1280. In some embodiments, interface 1286 is a signal that temperature sensor 1285 outputs to communicate the measured temperature. For example, interface 1286 can be a signal that temperature sensor 1285 is configured to drive high when the measured temperature exceeds a threshold. In some embodiments, electrophoretic display 1200 is configured such that temperature sensor 1285 controls the state of an enable signal without intervention from display controller circuitry 1280.

[0102] Referring to FIG. 12 in the context of the circuit shown in FIG. 7, when the temperature proximate the electrophoretic medium of imaging film 1210 is low, reducing the occurrence and effect of temperature-induced display artifacts, enable signal 1246 is driven to a state that activates a transistor (e.g., transistor 740 in FIG. 7) positioned between subpixel electrode 1201a and subpixel electrode 1201b, thereby electrically connecting them. Thus, any voltage applied to subpixel electrode 1201a is also applied to subpixel electrode 1201b. Similarly, enable signal 1246 activates a transistor positioned between subpixel electrodes 1202a and 1202b, a transistor positioned between subpixel electrodes 1203a and 1203b, and a transistor positioned between subpixel electrodes 1204a and 1204b, thereby electrically connecting each pair of subpixel electrodes, respectively. This configuration effectively increases the overall area of ​​each display pixel electrode and reduces the distance between adjacent display pixel electrodes.

[0103] Conversely, when the temperature proximate the electrophoretic medium is high and the occurrence and effects of temperature-induced display artifacts are most pronounced, enable signal 1246 is driven to a state that deactivates the transistor positioned between subpixel electrode 1201a and subpixel electrode 1201b (e.g., transistor 740 in FIG. 7), thereby electrically isolating them. Thus, the voltage applied to subpixel electrode 1201a is not applied to subpixel electrode 1201b. Similarly, enable signal 1246 deactivates the transistor positioned between subpixel electrodes 1202a and 1202b, the transistor positioned between subpixel electrodes 1203a and 1203b, and the transistor positioned between subpixel electrodes 1204a and 1204b, thereby electrically isolating each pair of subpixel electrodes. By effectively reducing the overall area of ​​each display pixel electrode and increasing the distance between adjacent display pixel electrodes, this configuration can reduce or eliminate temperature-induced display artifacts that would otherwise occur at high temperatures. Furthermore, a single enable signal is used to select either the high or low temperature drive scheme, thereby reducing the complexity of drive schemes that use sub-pixels.

[0104] In some embodiments, the array of display pixel electrodes is divided into subgroups (e.g., halves, quadrants, etc.), each comprising multiple display pixel electrodes, and there is an enable signal and temperature sensor associated with each subgroup. This allows each subgroup of display pixels to be operated in a low or high temperature mode independently of other subgroups. For example, a display used for applications such as outdoor signage may have a portion of its surface exposed to direct sunlight, while another portion of its surface is mostly shaded. In this case, if the temperature of the electrophoretic medium in the portion of the display exposed to direct sunlight rises above a threshold, the display pixels corresponding to that portion can be operated in a high temperature mode, while the display pixels corresponding to the shaded portion can be operated in a low temperature mode.

[0105] 7 illustrates an aspect of the invention featuring an electro-optic display including a first subpixel electrode and a second subpixel electrode associated with a display pixel, and an electrophoretic display medium disposed between a common electrode and the first and second subpixel electrodes. In some embodiments, the electro-optic display includes a physical gap between the first subpixel electrode and the second subpixel electrode. In some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second subpixel electrodes.

[0106] The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel. The display controller circuit is capable of applying waveforms to the display pixel by applying one or more time-dependent voltages between the common electrode and the first sub-pixel electrode via the first transistor, the one or more time-dependent voltages being applied to the first sub-pixel electrode. The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and the second sub-pixel electrode. A first enable signal activates the second transistor, placing the first sub-pixel electrode in electrical communication with the second sub-pixel electrode.

[0107] As described in connection with FIG. 12 , an electro-optic display can include a temperature sensor positioned proximate to a display pixel to measure the temperature of or near the electrophoretic display medium. In some embodiments, the first enable signal activates the second transistor based on a measurement of the ambient temperature from the temperature sensor. In some embodiments, the temperature sensor controls the first enable signal to activate the second transistor based on the measurement of the ambient temperature.

[0108] 8 is a schematic diagram of another exemplary pixel 800 including a display pixel drive circuit in accordance with the subject matter described herein. Pixel 800 is similar to pixel 700, but also includes a transistor 860 (e.g., a third transistor) between subpixel electrode 801b and front plate electrode 802.

[0109] This embodiment is configured such that the row select signal for a previous row of display pixels in the array controls the state of enable signal 866 (e.g., a second enable signal), which activates or deactivates transistor 860 by controlling the state of the gate signal for transistor 860. As a result, when transistor 840 is deactivated in the high temperature mode, instead of simply floating, subpixel electrode 801b is refreshed to the voltage applied to front plate electrode 802 during each frame immediately prior to updating the state of pixel 800.

[0110] The addition of transistor 860 is beneficial because it drains residual charge that might otherwise remain on subpixel electrode 801b and lead to undesirable image artifacts such as blooming and shifts in the optical state of the display pixel. For example, subpixel electrode 801b can be driven to a voltage while the display is in a low-temperature mode in which transistor 840 is activated. Without transistor 860, if the display were to enter a high-temperature mode prior to its next update, transistor 840 would be deactivated and any charge remaining on subpixel electrode 801b would be stored by storage capacitor 852 (e.g., a second storage capacitor), leading to the image artifacts discussed above. Because transistor 860 is activated by enable signal 866 during every frame, residual charge is beneficially drained from subpixel electrode 801b; this configuration advantageously drains residual voltage regardless of which temperature mode the display is in.

[0111] 8 illustrates an aspect of the invention featuring an electro-optic display including a first subpixel electrode and a second subpixel electrode associated with a display pixel, and an electrophoretic display medium disposed between a common electrode and the first and second subpixel electrodes. In some embodiments, the electro-optic display includes a physical gap between the first subpixel electrode and the second subpixel electrode. In some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second subpixel electrodes.

[0112] The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel, the display controller circuit being capable of applying waveforms to the display pixel by applying, via the first transistor, one or more time-dependent voltages between the common electrode and the first sub-pixel electrode, the one or more time-dependent voltages being applied to the first sub-pixel electrode.

[0113] The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and the second sub-pixel electrode. A first enable signal activates the second transistor, placing the first sub-pixel electrode and the second sub-pixel electrode in electrical communication. The electro-optic display also includes a third transistor in electrical communication with the second sub-pixel electrode and the common electrode. In some embodiments, the second enable signal activates the third transistor, causing residual charge to drain from the second sub-pixel electrode. In some embodiments, the second enable signal is controlled by a row select signal associated with a display pixel in a row, where the display pixel is not one of the display pixels in the row.

[0114] 7, the electro-optic display illustrated in FIG. 8 may include a temperature sensor positioned proximate to the display pixel to measure the temperature of the electrophoretic display medium or its vicinity. In some embodiments, the first enable signal activates the second transistor based on a measurement of the ambient temperature from the temperature sensor. In some embodiments, the temperature sensor controls the first enable signal to activate the second transistor based on the measurement of the ambient temperature.

[0115] 9 is a schematic diagram of another exemplary pixel 900 including a display pixel drive circuit in accordance with the subject matter described herein. Pixel 900 is similar to pixel 800, but also includes a transistor 941 (e.g., a fourth transistor) between subpixel electrode 901b and transistor 941 (e.g., a third transistor). In this embodiment, an enable signal 946 (e.g., a first enable signal) drives the gate signals of both transistor 940 (e.g., a second transistor) and transistor 941, but the enable signal 946 is inverted in the gate signal of transistor 941 so that the state of transistor 941 is always opposite to the state of transistor 940. Those skilled in the art will understand that there is not necessarily a logic inverter circuit between the enable signal 946 and the gate signal of transistor 941. For example, in some embodiments, transistor 940 is an n-type transistor and transistor 941 is a p-type transistor.

[0116] During operation, when the display is in low-temperature mode, transistor 940 is activated and transistor 941 is deactivated. When the display enters high-temperature mode, the state of enable signal 946 toggles, causing transistor 940 to be deactivated while transistor 941 is then activated. Thus, subpixel electrode 901b is refreshed to the voltage applied to front plate electrode 902 only when the display is in high-temperature mode. Like display pixel 800, the row select signal for a previous row of display pixels in the array controls the state of enable signal 966, which activates or deactivates transistor 960; therefore, refreshing occurs during each frame just prior to updating the state of display pixel 900, when the previous row of display pixels is selected and enable signal 966 activates transistor 960. This solution is useful during high-temperature operation when the display controller's post-drive discharge routine is unable to drain residual charge from subpixel electrode 901b.

[0117] 9 illustrates an aspect of the invention featuring an electro-optic display including a first subpixel electrode and a second subpixel electrode associated with a display pixel, and an electrophoretic display medium disposed between a common electrode and the first and second subpixel electrodes. In some embodiments, the electro-optic display includes a physical gap between the first subpixel electrode and the second subpixel electrode. In some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second subpixel electrodes.

[0118] The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel, the display controller circuit being capable of applying waveforms to the display pixel by applying, via the first transistor, one or more time-dependent voltages between the common electrode and the first sub-pixel electrode, the one or more time-dependent voltages being applied to the first sub-pixel electrode.

[0119] The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and the second sub-pixel electrode. A first enable signal activates the second transistor, placing the first sub-pixel electrode and the second sub-pixel electrode in electrical communication. The electro-optic display also includes a third transistor in electrical communication with the common electrode and a fourth transistor, the fourth transistor in electrical communication with the second sub-pixel electrode. In some embodiments, the second enable signal activates the third transistor, causing residual charge to drain from the second sub-pixel electrode. In some embodiments, the first enable signal deactivates the fourth transistor when the second transistor is activated. In some embodiments, the second enable signal activates the third transistor, causing residual charge to drain from the second sub-pixel electrode. In some embodiments, the second enable signal is controlled by a row select signal associated with a display pixel in a row, the display pixel being a non-display pixel of the display pixels in the row.

[0120] 7 and 8, the electro-optic display illustrated in FIG. 9 may include temperature sensors positioned proximate to the display pixels to measure the temperature of the electrophoretic display medium or its vicinity. In some embodiments, the first enable signal activates the second transistor and deactivates the fourth transistor based on a measurement of the ambient temperature from the temperature sensor. In some embodiments, the temperature sensor controls the first enable signal to activate the second transistor and deactivate the fourth transistor based on a measurement of the ambient temperature.

[0121] 10 is a schematic diagram of another exemplary pixel 1000 including a display pixel drive circuit in accordance with the subject matter described herein. Display pixel 1000 includes many elements similar to other display pixels described herein, such as display pixel 800, but is configured to control the voltage of sub-pixel electrode 1001b within a range when the display is in a high temperature mode.

[0122] 10 , the upper terminals of subpixel electrode 1001b (e.g., the second subpixel electrode) and storage capacitor 1052 (e.g., the second storage capacitor) are not positioned between transistor 1040 (e.g., the second transistor) and transistor 1060 (e.g., the third transistor) as in the configuration of display pixel 800, but instead are connected at the far side of transistor 1060 such that they do not have any direct connection to transistor 1040. Furthermore, in the display pixel circuit of display pixel 1000, row select logic of a display controller connected to driver electrode 1006 controls the gate signals of transistor 1020 (e.g., the first transistor) and transistor 1040. Thus, the row select logic of a display controller connected to driver electrode 1006 functions similarly to an enable signal to transistor 1040 (e.g., a first enable signal similar to 746, 846, and 946 from FIGS. 7, 8, and 9, respectively). Thus, transistor 1040 is activated whenever transistor 1020 is activated, and the state of transistor 1060 controls whether the voltage applied to subpixel electrode 1001a (e.g., the first subpixel electrode) is also applied to subpixel electrode 1001b.

[0123] The configuration of display pixel 1000 allows the voltage applied to sub-pixel electrode 1001b to be controlled within a range by modulating the duty cycle and / or amplitude of enable signal 1066 (e.g., second enable signal). In some embodiments, enable signal 1066 can be operated similarly to a pulse-width modulation ("PWM") circuit. For example, enable signal 1066 can be pulsed between the gate-on and gate-off thresholds of transistor 1060, and the frequency and / or duration of the on and off periods can be controlled so that the voltage applied to sub-pixel electrode 1001b can be adjusted.

[0124] 10 thus illustrates an aspect of the invention featuring an electro-optic display including a first subpixel electrode and a second subpixel electrode associated with a display pixel, and an electrophoretic display medium disposed between (or electrically coupled to) a common electrode and the first and second subpixel electrodes. In some embodiments, the electro-optic display includes a physical gap between the first subpixel electrode and the second subpixel electrode. In some embodiments, the electro-optic display includes a physical gap between at least one adjacent edge of the first and second subpixel electrodes.

[0125] The electro-optic display also includes a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel, the display controller circuit being capable of applying waveforms to the display pixel by applying, via the first transistor, one or more time-dependent voltages between the common electrode and the first sub-pixel electrode, the one or more time-dependent voltages being applied to the first sub-pixel electrode.

[0126] The electro-optic display also includes a second transistor in electrical communication with the first sub-pixel electrode and a third transistor, the third transistor in electrical communication with the second sub-pixel electrode, and a row select signal associated with the display pixel activates the first transistor and the second transistor to place the first sub-pixel electrode in electrical communication with the third transistor.

[0127] In some embodiments, the electro-optic display further includes a temperature sensor disposed proximate to the electrophoretic display media and / or the display pixels. In some embodiments, a second enable signal activates the third transistor. In some embodiments, the second enable signal is pulsed at a predetermined rate when the first transistor and the second transistor are activated. In some embodiments, the third transistor is activated for a portion of the time that the first transistor and the second transistor are activated.

[0128] Figure 11 is a signal timing diagram 1100 illustrating one possible implementation of drive signals for three display pixels having the configuration of display pixel 1000 from Figure 10. In this example, the three display pixels are from adjacent rows of an active matrix, with 10061 representing the state of the driver electrode of display pixel 10001 located in the first row that is activated during update, 10062 representing the state of the driver electrode of display pixel 10002 located in the second row that is activated during update, and 10063 representing the state of the driver electrode of display pixel 10003 located in the third row that is activated during update. Enable signal 1066 is a global signal that controls the activation and deactivation of transistor 10601 of display pixel 10001, transistor 10602 of display pixel 10002, and transistor 10603 of display pixel 10003.

[0129] When the measured ambient temperature is low enough that temperature-induced display artifacts such as lateral coupling and blooming are below the threshold at which they are typically most noticeable, enable signal 1066 is maintained in a high state during display updates, activating transistor 10602 and allowing the voltage applied to subpixel electrode 1001a2 to also be applied to subpixel electrode 1001b2. The state of enable signal 1066 in this low temperature mode is represented in FIG. 11 by "1066(low temperature)."

[0130] 11, enable signal 1066 is controlled in a high temperature mode, meaning that the measured ambient temperature is high enough that temperature-induced display artifacts are likely to occur if the display is driven such that the full voltage or charge applied to subpixel electrode 1001a2 is also applied to subpixel electrode 1001b2. The state of enable signal 1066 in this high temperature mode is represented in FIG. 11 by "1066(high temperature)."

[0131] As shown in Figure 11, at time tl, driver electrode 10061 is driven high to select the row of display pixels containing display pixel 10001 for updating.

[0132] At time t2, enable signal 1066 is toggled high to activate transistor 10601 and allow the voltage applied to subpixel electrode 1001a1 to be applied to subpixel electrode 1001b1 for a portion of the time that voltage is applied to subpixel electrode 1001a1.

[0133] At time t3, driver electrode 10061 is driven low to deselect the row of display pixels that includes display pixel 10001, and driver electrode 10062 is driven high to select the row of display pixels that includes display pixel 10002 for updating. Enable signal 1066 is also toggled low at time t3 to deactivate transistor 10601 and interrupt the connection between subpixel electrode 1001a1 and subpixel electrode 1001b1.

[0134] At time t4, enable signal 1066 is toggled high to activate transistor 10602 and allow the voltage applied to subpixel electrode 1001a2 to be applied to subpixel electrode 1001b2 for a portion of the time that voltage is applied to subpixel electrode 1001a2.

[0135] At time t5, driver electrode 10062 is driven low to deselect the row of display pixels containing display pixel 10002 for updating and driver electrode 10063 selects the row of display pixels containing display pixel 10003. Enable signal 1066 is also toggled low at time t5 to deactivate transistor 10602 and interrupt the connection between subpixel electrode 1001a2 and subpixel electrode 1001b2.

[0136] At time t6, enable signal 1066 is toggled high to activate transistor 10603 and allow the voltage applied to subpixel electrode 1001a3 to be applied to subpixel electrode 1001b3 for a portion of the time that voltage is applied to subpixel electrode 1001a3.

[0137] Finally, at time t7, driver electrode 10063 is driven low to deselect the row of display pixels that includes display pixel 10003. Enable signal 1066 is also toggled low at time t7, deactivating transistor 10603 and interrupting the connection between subpixel electrode 1001a3 and subpixel electrode 1001b3.

[0138] It can therefore be seen that the configuration of display pixel 1000 allows the impedance between sub-pixel electrode 1001a and sub-pixel electrode 1001b to be controlled by the duty cycle and / or voltage level of enable signal 1066, and thus the voltage difference between sub-pixel electrode 1001a and sub-pixel electrode 1001b can be fine-tuned and optimized.

[0139] This configuration provides additional options for implementing temperature-compensated drive schemes for electro-optic displays. For example, in low-temperature mode, enable signal 1066 can be set to provide a constant connection between each subpixel electrode 1001a and its respective subpixel electrode 1001b, maximizing the area of ​​each display pixel electrode that is energized and driving charged particles in the electrophoretic medium. When the display enters high-temperature mode, the voltage provided to subpixel electrode 1001b can be precisely adjusted so that the contrast ratio and update rate of the display are maintained without introducing the image artifacts discussed above.

[0140] Thus, as demonstrated herein, the multi-element display pixel electrode layout and display pixel drive circuitry of the present invention can mitigate performance variations in electrophoretic displays that arise due to changes in ambient temperature. It will be apparent to those skilled in the art that numerous changes and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the entirety of the foregoing description is to be interpreted in an illustrative sense, and not in a limiting sense.

[0141] The contents of all of the foregoing patents and applications are incorporated herein by reference in their entirety.

Claims

1. 1. An electro-optic display, comprising: a first sub-pixel electrode and a second sub-pixel electrode associated with the display pixel; an electrophoretic display medium disposed between a common electrode and the first and second sub-pixel electrodes; a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel, the display controller circuit capable of applying a waveform to the display pixel by applying, via the first transistor, one or more time-dependent voltages between the common electrode and the first sub-pixel electrode, the one or more time-dependent voltages being applied to the first sub-pixel electrode; a second transistor in electrical communication with the first sub-pixel electrode and the second sub-pixel electrode; Equipped with an electro-optic display, wherein a first enable signal activates the second transistor and places the first sub-pixel electrode in electrical communication with the second sub-pixel electrode;

2. 10. The electro-optic display of claim 1 further comprising a temperature sensor located proximate to the display pixel.

3. 3. The electro-optic display of claim 2, wherein the first enable signal activates the second transistor based on a measurement of ambient temperature from the temperature sensor.

4. 3. An electro-optic display as claimed in claim 2, wherein the temperature sensor controls the first enable signal to activate the second transistor based on a measurement of an ambient temperature.

5. 10. An electro-optic display according to claim 1, further comprising a third transistor in electrical communication with said second sub-pixel electrode and said common electrode.

6. 6. An electro-optic display as claimed in claim 5, wherein a second enable signal activates the third transistor to drain any residual charge from the second sub-pixel electrode.

7. 7. An electro-optic display according to claim 6, wherein the second enable signal is controlled by a row select signal associated with a row of display pixels that is not one of the row of display pixels.

8. 3. An electro-optic display according to claim 2, further comprising a third transistor in electrical communication with the common electrode and a fourth transistor, the fourth transistor in electrical communication with the second sub-pixel electrode.

9. 9. An electro-optic display as claimed in claim 8, wherein the first enable signal deactivates the fourth transistor when the second transistor is activated.

10. 10. An electro-optic display as claimed in claim 9, wherein a second enable signal activates the third transistor to drain any residual charge from the second sub-pixel electrode.

11. 11. An electro-optic display as claimed in claim 10, wherein the second enable signal is controlled by a row select signal associated with a row of display pixels that is not one of the row of display pixels.

12. 10. An electro-optic display as claimed in claim 1, further comprising a physical gap between the first sub-pixel electrode and the second sub-pixel electrode.

13. 10. An electro-optic display according to claim 1, further comprising a physical gap between at least one adjacent edge of the first and second sub-pixel electrodes.

14. 1. An electro-optic display, comprising: a first sub-pixel electrode and a second sub-pixel electrode associated with the display pixel; an electrophoretic display medium disposed between a common electrode and the first and second sub-pixel electrodes; a display controller circuit in electrical communication with the common electrode and a first transistor associated with the display pixel, the display controller circuit capable of applying a waveform to the display pixel by applying, via the first transistor, one or more time-dependent voltages between the common electrode and the first sub-pixel electrode, the one or more time-dependent voltages being applied to the first sub-pixel electrode; a second transistor in electrical communication with the first subpixel electrode and a third transistor; and Equipped with the third transistor is in electrical communication with the second sub-pixel electrode; an electro-optic display, wherein a row select signal associated with the display pixel activates the first transistor and the second transistor, placing the first sub-pixel electrode in electrical communication with the third transistor;

15. 15. The electro-optic display of claim 14, further comprising a temperature sensor positioned proximate to the electrophoretic display media.

16. 15. An electro-optic display as claimed in claim 14, wherein a second enable signal activates the third transistor.

17. 17. An electro-optic display as claimed in claim 16, wherein the second enable signal is pulsed at a predetermined rate when the first transistor and the second transistor are activated.

18. 17. An electro-optic display as claimed in claim 16, wherein the third transistor is activated for a portion of the time that the first and second transistors are activated.

19. 15. An electro-optic display as claimed in claim 14, further comprising a physical gap between the first sub-pixel electrode and the second sub-pixel electrode.

20. 15. An electro-optic display according to claim 14, further comprising a physical gap between at least one adjacent edge of the first and second sub-pixel electrodes.

Images