Temperature-compensation in electro-optic displays

Abstract

To provide temperature-compensation in electro-optic displays.SOLUTION: An electro-optic display includes a display stack having a layer of electro-optic material between a common electrode and an array of pixel electrodes, each associated with a display pixel. A display controller circuit is in electrical communication with the display stack, and is capable of applying waveforms to each display pixel by applying one or more time-dependent voltages between the common electrode and each pixel electrode. A temperature sensor in communication with the display controller circuit is positioned proximate to the display stack.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 315,265, filed March 1, 2022, 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 herein by reference in their entirety.

[0002] The present invention relates to electro-optic display devices, and more particularly to display controllers for driving electro-optic displays. [Background technology]

[0003] Particle-based electrophoretic displays, or EPDs, have been the subject of intense research and development for several years. In such displays, a plurality of charged particles (sometimes referred to as pigment particles) move through a fluid under the influence of an electric field. The electric field is typically provided by a conductive film or a transistor, such as a field-effect transistor. Electrophoretic displays have good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared to liquid crystal displays. Currently, electrophoretic displays can be found in everyday products such as e-books (e-readers), mobile phones and mobile phone covers, smart cards, signs, watches, shelf labels, and flash drives.

[0004] During operation, EPD performance can change with changes in temperature. Therefore, there is a need to adjust EPD operation according to temperature conditions to achieve optimal display performance. Summary of the Invention [Means for solving the problem]

[0005] The present invention provides an electro-optic display and associated method for optimizing EPD performance according to measured temperature conditions.

[0006] In one aspect, the invention features an electro-optic display including a display stack including a layer of electro-optic material disposed between a common electrode and an array of pixel electrodes, each pixel electrode associated with a display pixel. The electro-optic display also includes a display controller circuit in electrical communication with the display stack. The display controller circuit is capable of applying a waveform to each display pixel by applying one or more time-dependent voltages between the common electrode and each pixel electrode of the array of pixel electrodes. The electro-optic display also includes a temperature sensor in communication with the display controller circuit. The temperature sensor is positioned proximate to the display stack. The electro-optic display also includes a first plurality of look-up tables in communication with the display controller circuit. The first plurality of look-up tables includes waveform shape data representing a plurality of shapes of waveforms that the display controller circuit can apply to each display pixel to transition each display pixel from an initial optical state to a final optical state. The electro-optic display also includes a second plurality of look-up tables in communication with the display controller circuit. The second plurality of look-up tables includes voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuit can apply to each display pixel to transition each display pixel from its initial optical state to its final optical state.

[0007] In some embodiments, each lookup table of the first plurality of lookup tables corresponds to one range of the first plurality of temperature ranges. In some embodiments, each range of the first plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display. In some embodiments, each lookup table of the second plurality of lookup tables corresponds to one range of the second plurality of temperature ranges. In some embodiments, each range of the second plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display.

[0008] In some embodiments, the display controller circuit is configured to receive a temperature signal representative of a temperature measured proximate to the display stack, select waveform shape data from a lookup table of a first plurality of lookup tables based on the temperature measured proximate to the display stack, select voltage amplitude data from a lookup table of a second plurality of lookup tables based on the temperature measured proximate to the display stack, and apply a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data.

[0009] In some embodiments, the temperature measured proximate the display stack is within a first plurality of temperature ranges, and the lookup table of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. In some embodiments, the temperature measured proximate the display stack is within a second plurality of temperature ranges, and the lookup table of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges.

[0010] In some embodiments, the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuit can apply to each display pixel to transition each display pixel from its initial optical state to its final optical state. In some embodiments, each range of the first plurality of temperature ranges is wider than each range of the second plurality of temperature ranges.

[0011] In another aspect, the invention features a method for driving an electro-optic display. The method includes providing a display stack including a layer of electro-optic material disposed between a common electrode and an array of pixel electrodes, each pixel electrode associated with a display pixel. The method also includes providing a display controller circuit in electrical communication with the display stack. The display controller circuit is capable of applying a waveform to each display pixel by applying one or more time-dependent voltages between the common electrode and each pixel electrode of the array of pixel electrodes. The method also includes providing a temperature sensor in communication with the display controller circuit. The temperature sensor is positioned proximate to the display stack. The method also includes providing a first plurality of lookup tables in communication with the display controller circuit. The first plurality of lookup tables includes waveform shape data representing a plurality of shapes of waveforms that the display controller circuit can apply to each display pixel to transition each display pixel from an initial optical state to a final optical state. The method also includes providing a second plurality of lookup tables in communication with the display controller circuit. The second plurality of lookup tables includes voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuit can apply to each display pixel to transition each display pixel from its initial optical state to its final optical state. The method also includes receiving a temperature signal representing a temperature measured proximate to the display stack. The method also includes selecting waveform shape data from a lookup table of the first plurality of lookup tables based on the temperature measured proximate to the display stack, and selecting voltage amplitude data from a lookup table of the second plurality of lookup tables based on the temperature measured proximate to the display stack. The method includes applying a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data.

[0012] In some embodiments, each lookup table of the first plurality of lookup tables corresponds to one range of the first plurality of temperature ranges. In some embodiments, each range of the first plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display. In some embodiments, each lookup table of the second plurality of lookup tables corresponds to one range of the second plurality of temperature ranges. In some embodiments, each range of the second plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display.

[0013] In some embodiments, the temperature measured proximate the display stack is within a first plurality of temperature ranges, and the lookup table of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. In some embodiments, the temperature measured proximate the display stack is within a second plurality of temperature ranges, and the lookup table of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges.

[0014] In some embodiments, the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuit can apply to each display pixel to transition each display pixel from its initial optical state to its final optical state.

[0015] In some embodiments, each range in the first plurality of temperature ranges is wider than each range in the second plurality of temperature ranges.

[0016] In some embodiments, the method includes determining a DC balance pulse to apply to each display pixel based on a waveform applied to each display pixel based on selected waveform shape data and voltage amplitude data. The present invention provides, for example, the following. (Item 1) 1. An electro-optic display, comprising: a display stack comprising a layer of electro-optic material disposed between a common electrode and an array of pixel electrodes, each pixel electrode being associated with a display pixel; a display controller circuit in electrical communication with the display stack, the display controller circuit capable of applying a waveform to each display pixel by applying one or more time-dependent voltages between the common electrode and each pixel electrode of the array of pixel electrodes; a temperature sensor in communication with the display controller circuit, the temperature sensor being positioned proximate to the display stack; a first plurality of lookup tables in communication with the display controller circuit, the first plurality of lookup tables containing waveform shape data representing a plurality of shapes of waveforms that the display controller circuit can apply to each display pixel to transition each display pixel from an initial optical state to a final optical state; a second plurality of lookup tables in communication with the display controller circuit, the second plurality of lookup tables containing voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuit can apply to each display pixel to transition the initial optical state of each display pixel to the final optical state; An electro-optical display comprising: (Item 2) Item 1. The electro-optic display of item 1, wherein each lookup table of the first plurality of lookup tables corresponds to one range of a first plurality of temperature ranges. (Item 3) 3. The electro-optic display of claim 2, wherein each range of the first plurality of temperature ranges is a subset of an operating temperature range of the electro-optic display. (Item 4) Item 3. An electro-optic display as described in item 2, wherein each lookup table of the second plurality of lookup tables corresponds to one range of a second plurality of temperature ranges. (Item 5) Item 5. An electro-optic display as described in item 4, wherein each range of the second plurality of temperature ranges is a subset of an operating temperature range of the electro-optic display. (Item 6) The display controller circuit receiving a temperature signal representative of a temperature measured proximate the display stack; selecting waveform shape data from a lookup table of the first plurality of lookup tables based on the temperature measured proximate to the display stack; selecting voltage amplitude data from a lookup table of the second plurality of lookup tables based on the temperature measured proximate the display stack; applying a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data; Item 5. An electro-optic display according to item 4, configured to perform (Item 7) 7. The electro-optic display of claim 6, wherein the temperature measured proximate to the display stack is within a range of the first plurality of temperature ranges, and a lookup table of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. (Item 8) 7. The electro-optic display of claim 6, wherein the temperature measured proximate to the display stack is within a range of the second plurality of temperature ranges, and a lookup table of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges. (Item 9) Item 1. The electro-optical display of item 1, wherein the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuit can apply to each display pixel to transition the initial optical state of each display pixel to the final optical state. (Item 10) Item 5. An electro-optic display as described in item 4, wherein each range of the first plurality of temperature ranges is wider than each range of the second plurality of temperature ranges. (Item 11) 1. A method for driving an electro-optic display, said method comprising: providing a display stack comprising a layer of electro-optic material disposed between a common electrode and an array of pixel electrodes, each pixel electrode being associated with a display pixel; providing a display controller circuit in electrical communication with the display stack, the display controller circuit capable of applying a waveform to each display pixel by applying one or more time-dependent voltages between the common electrode and each pixel electrode of the array of pixel electrodes; providing a temperature sensor in communication with the display controller circuitry, the temperature sensor being positioned proximate to the display stack; providing a first plurality of lookup tables in communication with the display controller circuit, the first plurality of lookup tables containing waveform shape data representing a plurality of shapes of waveforms that the display controller circuit can apply to each display pixel to transition each display pixel from an initial optical state to a final optical state; providing a second plurality of lookup tables in communication with the display controller circuit, the second plurality of lookup tables containing voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuit can apply to each display pixel to transition the initial optical state of each display pixel to the final optical state; receiving a temperature signal representative of a temperature measured proximate the display stack; selecting waveform shape data from a lookup table of the first plurality of lookup tables based on the temperature measured proximate to the display stack; selecting voltage amplitude data from a lookup table of the second plurality of lookup tables based on the temperature measured proximate the display stack; applying a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data; A method comprising: (Item 12) Item 12. The method of item 11, wherein each lookup table of the first plurality of lookup tables corresponds to one range of a first plurality of temperature ranges. (Item 13) Item 13. The method of item 12, wherein each range of the first plurality of temperature ranges is a subset of an operating temperature range of the electro-optic display. (Item 14) Item 13. The method of item 12, wherein each lookup table of the second plurality of lookup tables corresponds to one range of a second plurality of temperature ranges. (Item 15) Item 15. The method of item 14, wherein each range of the second plurality of temperature ranges is a subset of an operating temperature range of the electro-optic display. (Item 16) Item 12. The method of item 11, wherein the temperature measured proximate the display stack is within a range of the first plurality of temperature ranges, and a lookup table of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. (Item 17) Item 12. The method of item 11, wherein the temperature measured proximate the display stack is within the second plurality of temperature ranges, and a lookup table of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges. (Item 18) Item 12. The method of item 11, wherein the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuit can apply to each display pixel to transition the initial optical state of each display pixel to the final optical state. (Item 19) Item 15. The method of item 14, wherein each range of the first plurality of temperature ranges is wider than each range of the second plurality of temperature ranges. (Item 20) Item 12. The method of item 11, further comprising determining a DC balance pulse to apply to each display pixel based on the waveform applied to each display pixel based on the selected waveform shape data and voltage amplitude data. [Brief explanation of the drawings]

[0017] Various aspects and embodiments of the present application are described with reference to the following figures. It should be understood that the figures are not necessarily drawn to scale. Furthermore, the figures are intended only to facilitate explanation of the present subject matter. The figures do not depict every aspect of the described embodiments and do not limit the scope of the disclosure or claims.

[0018] [Figure 1] FIG. 1 illustrates an electrophoretic display in accordance with the presently disclosed subject matter.

[0019] [Figure 2] FIG. 2 illustrates an equivalent circuit of the electrophoretic display presented in FIG. 1 in accordance with the presently disclosed subject matter.

[0020] [Figure 3] FIG. 3 illustrates an active matrix circuit in accordance with the subject matter disclosed herein.

[0021] [Figure 4] FIG. 4 is a block diagram of an exemplary conventional electrophoretic display.

[0022] [Figure 5] FIG. 5 is an example waveform diagram showing waveforms configured to drive display pixels to a red color for a conventional three, four, five, or more particle EDP system in accordance with the subject matter described herein.

[0023] [Figure 6] FIG. 6 is a block diagram of an exemplary electrophoretic display in accordance with the subject matter described herein. DETAILED DESCRIPTION OF THE INVENTION

[0024] Detailed Description As indicated above, the subject matter presented herein provides methods and means for reducing charge buildup in electrophoretic display media and improving electro-optic display performance.

[0025] 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 that differ in at least one optical property, and that is changed from its first display state to its second display state by the application of an electric field to the material. The optical property is typically color perceptible to the human eye, but may 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.

[0026] The term “gray state” is used herein in its conventional sense in the imaging arts to refer to a state intermediate between two extreme pixel optical states, 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 in which the extreme states are white and dark blue, such that the intermediate “gray state” is actually light blue. In fact, as already noted, 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 their two extreme optical states, with no intervening gray states.

[0027] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to displays 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 addressing pulse to assume either its first or second display state, that state will persist after the addressing pulse is terminated for at least several times, e.g., at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Pat. No. 7,170,670 shows 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, but for convenience, the term "bistable" may be used herein to encompass both bistable and multistable displays.

[0028] 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.

[0029] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation have recently been published describing encapsulated electrophoretic media. Such encapsulated media comprise a multiplicity of small capsules, each of which itself comprises an internal phase containing electrophoretically mobile particles suspended in a liquid suspension medium, and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held within a polymer binder, forming a coherent layer positioned between two electrodes. The technologies described in these patents and applications include the following:

[0030] (a) Electrophoretic particles, fluids, and fluid additives (see, e.g., U.S. Pat. Nos. 7,002,728 and 7,679,814)

[0031] (b) Capsules, binders, and encapsulation processes (see, e.g., U.S. Patent Nos. 6,922,276 and 7,411,719)

[0032] (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)

[0033] (d) Methods for filling and sealing microcells (see, e.g., U.S. Patent Nos. 7,144,942 and 7,715,088)

[0034] (e) Films and subassemblies containing electro-optical materials (see, e.g., U.S. Patent Nos. 6,982,178 and 7,839,564)

[0035] (f) Backplanes, adhesive layers, other auxiliary layers, and methods used within displays [ka] [ka]

[0036] (g) Color formation and color control (see, e.g., U.S. Patent Nos. 7,075,502 and 7,839,564)

[0037] (h) Methods for driving displays (see, e.g., U.S. Patent Nos. 7,012,600 and 7,453,445)

[0038] (i) Display applications (see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348)

[0039] (j) Non-electrophoretic displays, such as those described in U.S. Pat. No. 6,241,921, and U.S. Patent Application Publication Nos. 2015 / 0277160, and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0040] All of the above patents and patent applications are incorporated herein by reference in their entirety.

[0041] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium may be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display 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 a polymer-dispersed electrophoretic display may be considered capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet. See, for example, the aforementioned 2002 / 0131147. Therefore, for purposes of this application, such polymer-dispersed electrophoretic media are considered a subspecies of encapsulated electrophoretic media.

[0042] Encapsulated electrophoretic displays typically do not suffer from the clustering and settling failure modes of conventional electrophoretic devices and offer additional advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (The use of the word "printing" is intended to include all forms of printing and coating, including, but not limited to, pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating, roll coatings such as knife-over-roll coating, forward and reverse roll coating, gravure coating, dip coating, spray coating, meniscus coating, spin coating, brush coating, air knife coating, silk screen printing processes, electrostatic printing processes, thermal printing processes, inkjet printing processes, and other similar techniques.) The resulting display can therefore be flexible. Furthermore, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.

[0043] 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, typically a polymer film. See, for example, International Application Publication No. WO 02 / 01281 and Published U.S. Application No. 2002 / 0075556 (both assigned to Sipix Imaging, Inc.).

[0044] The aforementioned types of electro-optic displays are bistable and are typically used in a reflective mode, although, as explained in some of the aforementioned patents and applications, such displays may be operated in a "shield mode," in which an electro-optic medium is used to modulate the transmission of light so that the display operates in a transmissive mode. Liquid crystals, including polymer-dispersed liquid crystals, are, of course, also electro-optic media, but are typically not bistable and operate in a transmissive mode. While certain embodiments of the inventions described below are limited to use with reflective displays, others may be used with both reflective and transmissive displays, including conventional liquid crystal displays.

[0045] Whether the display is reflective or transmissive, and whether the electro-optic medium used is bistable or not, to obtain a high-resolution display, each pixel of the display must be addressable without interference from neighboring pixels. One way to achieve this goal is to provide an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel, producing an "active matrix" display. The addressing or pixel electrode that addresses a pixel is connected to an appropriate voltage source through the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor; although this arrangement will be assumed in the following description, it is essentially arbitrary, and the pixel electrode can also be connected to the source of the transistor. Conventionally, in a high-resolution array, pixels are arranged in a two-dimensional array of rows and columns, such that any particular pixel is uniquely defined by the intersection of one defined row and one defined column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode. Again, the assignment of sources to rows and gates to columns is conventional, but essentially arbitrary and can be reversed as desired. The row electrodes are connected to a row driver, which essentially ensures that only one row is selected at any given moment; i.e., a voltage is applied to the selected row electrode to ensure that all transistors in the selected row are conductive, while voltages are applied to all other rows to ensure that all transistors in these unselected rows remain non-conductive. The column electrodes are connected to a column driver, which applies voltages to the various column electrodes selected to drive the pixels in the selected row to their desired optical states. (These voltages are conventionally relative to a common front electrode provided on the opposite side of the electro-optic medium from the non-linear array and extending across the entire display.)) After a preselected interval known as the "line address time," the selected row is deselected, the next row is selected, and the voltages on the column drivers are changed so that the next line of the display is written. This process is repeated so that the entire display is written in a row-by-row fashion.

[0046] Processes for manufacturing active matrix displays are well established. Thin film transistors, for example, can be fabricated using various deposition and photolithography techniques. The transistor includes a gate electrode, an insulating dielectric layer, a semiconductor layer, and source and drain electrodes. Application of a voltage to the gate electrode provides an electric field across the dielectric layer, which dramatically increases the source-drain conductivity of the semiconductor layer. This change allows electrical conduction between the source and drain electrodes. Typically, the gate electrode, source electrodes, and drain electrodes are patterned. Generally, the semiconductor layer is also patterned to minimize stray conduction (i.e., crosstalk) between neighboring circuit elements.

[0047] Liquid crystal displays generally employ amorphous silicon ("a-Si") thin-film transistors ("TFTs") as switching devices for display pixels. Such TFTs typically have a bottom-gate configuration. Within a pixel, a thin-film capacitor typically holds the charge transferred by the switching TFT. Electrophoretic displays can use similar TFTs with capacitors, although the function of the capacitors is somewhat different from that in liquid crystal displays (see the aforementioned co-pending application Ser. No. 09 / 565,413 and publications Nos. 2002 / 0106847 and 2002 / 0060321). Thin-film transistors can be fabricated to provide high performance. However, the fabrication process can result in significant costs.

[0048] In a TFT-addressed array, the pixel electrodes are charged through the TFTs during the line address time. During the line address time, the TFTs are switched to a conductive state by changing the applied gate voltage. For example, for an n-type TFT, the gate voltage is switched to a "high" state to switch the TFT into a conductive state.

[0049] Additionally, unwanted effects such as voltage shifts can be caused by crosstalk occurring between the data lines that supply drive waveforms to the display pixels and the pixel electrodes. Similar to the voltage shifts described above, crosstalk between the data lines and the pixel electrodes can be caused by capacitive coupling between the two even when the display pixels are not addressed (e.g., the associated pixel TFTs are depleted). Such crosstalk can result in undesirable voltage shifts, which can lead to optical artifacts such as image streaks.

[0050] In some cases, an electrophoretic display, or EPD, may include two substrates (e.g., plastic or glass) with a front plane laminate, or FPL, positioned between the two substrates. In some embodiments, the bottom portion of the top substrate is provided with a conductive electrode (i.e., V com The upper portion of the lower substrate may be coated with a transparent conductive material to act as a transparent conductive layer (plane). The upper portion of the lower substrate may include an array of electrode elements (e.g., a conductive electrode for each display pixel). A semiconductor switch, such as a thin film transistor, or TFT, may be associated with each of these pixel electrodes. The pixel electrodes and V com Application of a bias voltage to the plane can result in electro-optical conversion of the FPL. This optical conversion can be used as the basis for displaying text or graphic information on the EPD. To display the desired image, an appropriate voltage must be applied to each pixel electrode.

[0051] FIG. 1 illustrates a schematic model of a display pixel 100 of an electro-optic display according to the subject matter presented herein. Pixel 100 may include an imaging film 110. In some embodiments, imaging film 110 is a layer of electrophoretic material and may be inherently bistable. The electrophoretic material may include a plurality of charged colored pigment particles (e.g., black, white, yellow, or red) disposed in a fluid and capable of moving through the fluid under the influence of an electric field. In some embodiments, imaging film 110 may be an electrophoretic film having microcells with charged pigment particles. In some embodiments, imaging film 110 may include, for example, but not limited to, an encapsulated electrophoretic imaging film, which may include charged pigment particles. It should be understood that the driving methods presented below may be employed for either type of electrophoretic material (e.g., an encapsulated electrophoretic medium or a film with microcells).

[0052] In some embodiments, the imaging film 110 may be disposed between the front electrode 102 and the back or pixel 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 and light-transmitting. 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 on the opposite side of the imaging film 110 from 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.

[0053] 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 back plate electrode 104 and the addressing electrode 108. In some embodiments, the nonlinear element 120 may include a diode and / or a transistor, including, but not limited to, a MOSFET or thin film transistor (“TFT”). The drain (or source) of the MOSFET or TFT may be coupled to the back plate or pixel electrode 104, the source (or drain) of the MOSFET or TFT may be coupled to the addressing electrode 108, and the gate of the MOSFET or TFT may be coupled to a driver electrode 106 configured to control activation and deactivation of the MOSFET or TFT. (For simplicity, the terminal of the MOSFET or TFT that is coupled to the back plate electrode 104 will be referred to as the drain of the MOSFET or TFT, and the terminal of the MOSFET or TFT that is coupled to the addressing electrode 108 will be referred to as the source of the MOSFET or TFT. However, those skilled in the art will recognize that in some embodiments, the source and drain of a MOSFET or TFT may be interchanged.)

[0054] In some active matrix embodiments, the addressing 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 that can 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 that can apply a suitable voltage to the addressing electrodes 106 of the selected (activated) pixel to drive the pixel to a desired optical state. The voltage applied to the addressing electrodes 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.

[0055] In some embodiments, the active matrix pixels 100 may be written in a row-by-row manner. For example, a row of pixels may be selected by a row driver, and voltages corresponding to the desired optical state for the row of pixels may be applied to the pixels by a column driver. After a preselected interval known as a "line address time," the selected row may be deselected, another row may be selected, and the voltages on the column drivers may be changed so that another line of the display is written.

[0056] FIG. 2 illustrates a circuit model of the electro-optic imaging layer 110 disposed between the front electrode 102 and the 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 form at an interlayer contact area between the front electrode 102 and the back electrode 104, e.g., the interface between the imaging layer and the lamination adhesive layer and / or the lamination adhesive layer and the backplane electrode. The voltage V i across the imaging film 110 of a pixel may include the pixel's residual voltage. FIG. 3 illustrates an exemplary active matrix for driving an electrophoretic display. In some embodiments, each display pixel of an electrophoretic display may be controlled by a thin-film transistor (TFT). The TFTs receive drive voltages and may be turned on and off to modulate the optical state of an associated display pixel. To effectively control the drive of its associated display pixel, each TFT 102 receives a gate line signal, a data line signal, and a V com In one embodiment, as shown in FIG. 1, the gate of each TFT 102 may be electrically coupled to a scan line, the source or drain of the transistor may be connected to a data line, and the two terminals of the storage capacitor may be connected to V com In some embodiments, the V on the bottom portion of the top substrate may be connected to the pixel lines and pixel electrodes. com and V on the top portion of the bottom substrate com The line grids may be connected to the same DC source.

[0057] 4 is a block diagram of an exemplary conventional electrophoretic display 400. Electrophoretic display 400 includes display controller circuitry 480, a display stack 490, lookup tables 440a-440j (collectively referred to as lookup tables 440 or LUTs 440), and a temperature sensor 485.

[0058] Display stack 490 includes an array of display pixels arranged in an active matrix, as described above in connection with Figures 1-3. Those skilled in the art will understand that other display configurations are within the scope of this disclosure. (Electrophoretic displays and the structure of their component parts, pigments, adhesives, electrode materials, etc. are described in many patents and patent applications published by E Ink Corporation, such as U.S. Patent 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.)

[0059] Display controller circuitry 480 represents the circuits and components that provide the supply voltages and control signals 495 necessary to operate electrophoretic display 400. For example, display controller circuitry 480 may include power management circuitry for generating and supplying multiple voltages to display stack 490, as well as row and column drivers for driving waveforms sufficient to address the array of pixel electrodes and change the optical state of display stack 490. In some embodiments, the transistors used to address and drive the pixel electrodes are positioned in proximity to the array of pixel electrodes.

[0060] Those skilled in the art will understand that the display controller circuitry 480 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 480 can include a general-purpose microprocessor in conjunction with appropriate peripheral components (e.g., one or more digital-to-analog converters, or "DACs") to convert the digital output from the microprocessor into appropriate voltages for application to the pixels. Alternatively, the display controller circuitry 480 can be implemented within 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 480 can include both processing components and power management circuitry.

[0061] Lookup tables 440 contain waveforms (sequences of voltages to be applied over time) that are applied by display controller circuitry 480 to drive display pixels of display stack 490 from one optical state to another. In some embodiments, lookup tables 440 each contain a two-dimensional matrix, with one axis of the matrix representing the initial state of the display pixel and the other axis representing the desired final state of the display pixel. Although LUTs 440 are shown in FIG. 4 as being separate from display controller circuitry 480, in some embodiments LUTs 440 are incorporated into display controller circuitry 480.

[0062] Generally, entries in lookup table 440 contain data representing voltage impulses required to drive display pixels in an initial optical state to a desired optical state. Each entry effectively defines the time-varying voltage waveform required to effect a transition from the initial state to the final state, and typically contains a series of integers representing the voltages to be applied to a display pixel electrode during each frame of a sequence of frames.

[0063] The entries in lookup table 440 may have a variety of forms. In some embodiments, each element includes a single number. For example, an electro-optic display may use precision voltage modulation driver circuitry capable of outputting a number of different voltages, both above and below a reference voltage, and simply apply the required voltage to a display pixel for a standard, predetermined period of time. In such cases, each entry in lookup table 440 may simply have the form of a signed integer that defines the voltage to be applied to a given display pixel. In other cases, each element may comprise a series of numbers associated with different portions of the waveform. For example, some drive schemes use so-called single or double pre-pulse waveforms, and defining such a waveform necessarily requires several numbers associated with different portions of the waveform.

[0064] In some embodiments, pulse length modulation is used to apply predetermined voltages to display pixels during selected ones of multiple partial scan periods (frames) during a full scan (superframe). In such embodiments, the elements of lookup table 440 may have the form of a series of bits that specify whether a predetermined voltage should be applied during each partial scan period (frame) of the associated transition.

[0065] Finally, as discussed in more detail below, the entries in lookup table 440 can be organized to include temperature compensation information. For example, lookup table 440 entries can also include information indicating changes in voltage levels to be applied to display pixels in response to measured changes in temperature proximate display stack 490. In some embodiments, the temperature compensation information includes a numerical value indicating a particular voltage level to be applied to a display pixel during a corresponding waveform. In some embodiments, the temperature compensation information includes a coefficient that indicates to display controller circuitry 480 to increase or decrease the voltage level applied to a display pixel during a particular waveform.

[0066] Those skilled in the art will appreciate that lookup table 440 may be different sizes depending on the display application. For example, if display stack 490 comprises a display capable of displaying 16 gray levels (e.g., a 4-bit display), a full grayscale lookup table would require 256 entries (16 initial states x 16 final states), while a lookup table for the monochrome area of ​​the display would require only four entries.

[0067] It has been found that the final optical state of a display pixel after application of a particular drive waveform may depend on its initial optical state, and also on one or more previous optical states of that display pixel at a particular time prior to the initial state. Thus, in some embodiments, lookup table 440 includes additional information about one or more previous optical states of each display pixel. However, depending on the number of previous states stored, lookup table 440 can become very large. To take an extreme example, a lookup table 440 may store 256 (2 8 ) gray levels. The required four-dimensional lookup table has 2 entries. If each entry requires, for example, 64 bits (8 bytes), the total size of the lookup table would be approximately 32 GBytes. While storing this amount of data does not pose any problem for a desktop computer, it may present a problem in portable devices such as e-readers.

[0068] In some embodiments, the display controller circuitry 480 includes a timing controller (“Tcon”) integrated circuit (“IC”) that receives incoming image data, outputs control signals to data collectors, and selects driver ICs (e.g., row and column driver ICs) to produce the appropriate waveforms and voltages at the pixel electrodes to display the desired image. For example, when an image update is occurring, the display controller circuitry 480 compares the currently displayed image with the next image to be displayed. Based on the comparison, the Tcon references the lookup table 440 to find the appropriate waveforms and voltage potentials for each pixel in the display stack 490. More specifically, when driving from a current image to the next image, a driving waveform and voltage level is selected from the lookup table for each pixel depending on the color state of that pixel in the two successive images. For example, for a pixel that is in a white state in the current image and will be in a level 5 gray state in the next image, the Tcon selects the waveform and voltage level that will cause the color change.

[0069] In some embodiments, a host controller, in communication with the display controller circuitry, requests updates to electrophoretic display 400 and provides image data for updates to the display controller circuitry. In some embodiments, display controller circuitry 480 receives 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 that described in U.S. Pat. No. 9,721,495. In some embodiments, display controller circuitry 480 receives a serial signal containing information required to perform the calculations necessary to generate drive impulses (e.g., drive waveforms) for application to an electrophoretic medium during scanning of a pixel array.

[0070] Once the drive waveforms and voltages are selected from LUT 440, they are applied to the display pixels of display stack 490 to drive the current image to the next image. Drive waveforms are sent to display stack 490 every frame.

[0071] Temperature sensor 485 measures the temperature of the electrophoretic medium or the environment immediately adjacent thereto and provides the temperature information to display controller circuitry 480 via interface 486. In some embodiments, temperature sensor 485 is positioned within the encapsulating electrophoretic medium of display stack 490. In some embodiments, temperature sensor 485 comprises multiple temperature sensors positioned at different physical locations around or within display stack 490.

[0072] Temperature sensor 485 can be a sensor across which an electrical property, such as a resistance or capacitance, changes in response to an increase or decrease in temperature. In some embodiments, temperature sensor 485 includes a thermocouple, a resistance temperature detector ("RTD"), and / or a thermistor (e.g., a negative temperature coefficient ("NTC") thermistor). In some embodiments, temperature sensor 485 includes a semiconductor-based integrated circuit for sensing temperature.

[0073] In some embodiments, interface 486 is a serial or multi-signal / parallel bus interface that temperature sensor 485 uses to communicate temperature information to display controller circuitry 480. For example, interface 486 can be a signal connected to a general purpose input / output (GPIO) of display controller circuitry 480. In some embodiments, interface 486 is a low pin count peripheral interface (e.g., Inter-Integrated Circuit (I2C), Serial Peripheral Interface (SPI), Controller Area Network (CAN) bus, etc.).

[0074] The optical performance of an EPD can be affected by fluctuations in ambient temperature. Therefore, an EPD module such as electrophoretic display 400 typically includes one or more temperature sensors 485 to obtain information about the temperature at one or more locations of the EPD module proximate the electrophoretic medium. Temperature sensor 485 transmits the temperature information to a timing controller associated with display controller circuitry 480.

[0075] In a conventional EPD module, Tcon can be configured to select a set of waveforms from LUT 440 that is optimized to most accurately produce the desired optical change for a particular measured temperature or temperature range. For example, for a given temperature range of 0° to 50° Celsius, LUT 440 can be divided into ten LUT sets, i.e., LUTs 440a-440j, each storing drive waveform and voltage level information configured to cover a temperature range of 5° Celsius. For example, LUT 440a can contain drive waveform and voltage level information optimized for driving display pixels when the measured temperature is within the range of 0° to 4° Celsius. Similarly, LUT 440b can contain drive waveform and voltage level information optimized for driving display pixels when the measured temperature is within the range of 5° to 9° Celsius, and so on. LUT 440j can contain drive waveform and voltage level information optimized for driving display pixels when the measured temperature is within the range of 45° to 50° Celsius. As explained, LUT 440j actually stores drive waveform and voltage level information for a temperature range of 6 degrees Celsius. However, electrophoretic displays tend to have more variation in performance at lower temperatures, so a trade-off is made: having less precision at higher temperatures.

[0076] It has been observed that the voltage levels of the drive waveforms required to achieve optimal EPD performance when applied to the display pixels of an EPD can vary significantly within a 5-degree Celsius range. Therefore, conventional configurations that use one LUT to store drive waveforms and voltage levels over a 5-degree Celsius range may be insufficient to optimize display performance. As described above, the size of each LUT can be increased, or additional LUTs can be added to improve the temperature granularity of the information stored in each LUT. However, increasing the number of LUTs to cover additional temperature ranges requires a larger memory allocation within the electrophoretic display 400's flash memory or one-time programmable memory, or OTP. Because these memories are generally components of the EPD module, increasing the size of the number of LUTs also undesirably increases the cost of the EPD module.

[0077] According to an embodiment of the present invention, instead of adding more LUTs to store drive waveform and voltage level information to cover additional temperature ranges, the voltage values ​​of the applied waveform can instead be modified.

[0078] 5, illustrated is an example waveform diagram 500 showing a waveform configured to drive a display pixel to a red color for a conventional 3, 4, 5, or more particle EPD system. As shown, waveform 500 includes a DC balance pulse portion 404, a shake and reset portion 406, and a smaller positive voltage portion 402 (also referred to herein as VPOS_low 402).

[0079] The shake and reset section 406 is used to separate the charged ink particles from each other, bring them into a mixed state within the display fluid, and then drive the particles to a known state prior to driving the display pixel to a desired optical state.

[0080] The positive amplitude of the waveform applied to the display pixels during VPOS_low 402 is less than the positive amplitude of the waveform applied during other periods, such as the shake and reset portion 406. For example, as shown in FIG. 5 , the positive amplitude of the waveform applied during VPOS_low 402 is approximately 7 V, while the positive amplitude of the waveform applied during the shake and reset portion 406 is approximately 15 V. In some embodiments, the voltage applied during VPOS_low portion 402 is configured to provide the best optical performance for displaying a red color (e.g., the highest red a* value). Although not shown in FIG. 5 , in some embodiments, the negative amplitude of the waveform applied to the display pixels can be shortened for a portion of the time the display pixels are driven. In some embodiments, a negative voltage having an amplitude of approximately −7 V is applied during the VNEG_low portion, while a negative voltage having an amplitude of approximately −15 V is applied at other times when the display pixels are being updated.

[0081] In practice, an electrophoretic display can be configured to not only include LUTs that store information describing waveforms spanning multiple temperature ranges, but also LUTs that store voltage value information for VPOS_low portion 502 (and / or VNEG_low portion) for even smaller temperature ranges. In one embodiment, the same number of LUTs (e.g., 10) as in FIG. 4 can be used to store information about waveform shapes for use over a temperature range of 0 to 50 degrees Celsius (e.g., a 5 degree range per LUT), and additional LUTs can be included to store voltage level information including smaller positive and / or negative voltage values, with improved precision in setting voltage level values ​​per 1 degree change in temperature.

[0082] Because some voltage values ​​can be encoded into a small number of bits, significantly less memory is required to store the voltage level values. As an example, even with only 3 bits, 2 3, i.e., eight unique voltage values ​​can be represented. Therefore, despite the increased accuracy, only two additional LUTs are required to store voltage level information. For example, one of the additional LUTs can store voltage value information for temperatures in the range of 0° to 24° Celsius, and the other additional LUT can store voltage value information for temperatures in the range of 25° to 50° Celsius.

[0083] In this configuration, the Tcon can select waveform shape information from one LUT for a first range of temperature values ​​(e.g., 5 degrees Celsius) and voltage value information with 1-degree Celsius granularity from another LUT. For example, when an electrophoretic display is operating at a temperature of 23 degrees Celsius, a temperature sensor transfers temperature information to a Tcon associated with the display. The Tcon can select one waveform shape LUT specified for a temperature range of 20-25 degrees Celsius. In addition, the Tcon can also select a LUT to retrieve voltage value information specified for 23 degrees Celsius to be combined with waveform shape information designed for the range of 20-25 degrees Celsius. This configuration advantageously enables more precise fine-tuning of waveform shapes and voltage levels applied to display pixels at specific temperatures, achieving superior display performance over conventional solutions without significantly increasing the cost of the EPD module.

[0084] In some embodiments, Tcon may be further configured to calculate the DC balance pulse required to maintain DC balance based on the applied waveform. Referring again to FIG. 5, waveform 500 may include a DC balance pulse portion 504 configured to keep waveform 500 generally DC-balanced. In operation, applying the temperature-specific waveform shape and voltage levels provided by the LUT may not maintain overall DC balance. However, Tcon can maintain DC balance by either calculating the required DC balance pulse in real time or by retrieving predetermined DC balance pulse information stored within the display controller circuitry.

[0085] Figure 6 is a block diagram of an electrophoretic display 600 in accordance with the subject matter described herein. Electrophoretic display 600 includes many of the same elements as electrophoretic display 400 of Figure 4, but LUT 640 of electrophoretic display 600 is configured to separate waveform shape information from voltage level information.

[0086] It has been observed that having more precision regarding the voltage levels applied to display pixels at a particular temperature has more beneficial effects than having more precision regarding the shape of the applied waveform. Thus, in the exemplary configuration shown in FIG. 6, LUTs 640a-640e store information describing waveforms for use over a temperature range of 0° to 50° Celsius. For example, LUT 640a may contain waveform shape information optimized for driving display pixels when the measured temperature is within a range of 0° to 9° Celsius. Similarly, LUT 640b may contain waveform shape information optimized for driving display pixels when the measured temperature is within a range of 10° to 19° Celsius, and so on, while LUT 640e contains waveform shape information optimized for driving display pixels when the measured temperature is within a range of 40° to 50° Celsius.

[0087] 6, LUTs 640f and 640g store information describing voltage level information for use over a temperature range of 0° to 50° Celsius. For example, LUT 640f may contain voltage level information, with a granularity of one set of voltage level information per degree of temperature, that is optimized for driving display pixels when the measured temperature is within the range of 0° to 24° Celsius. Similarly, LUT 640g may contain voltage level information, also with a granularity of one set of voltage level information per degree of temperature, that is optimized for driving display pixels when the measured temperature is within the range of 25° to 50° Celsius.

[0088] Thus, the configuration of electrophoretic display 600 requires less memory for the LUTs because only seven LUTs in total are used (five LUTs for storing waveform shape information and two LUTs for storing voltage level information). This configuration advantageously reduces the overall cost of the EPD module while still providing improved stability and performance of the EPD across a wide temperature range.

[0089] 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. Accordingly, the whole of the foregoing description is to be interpreted in an illustrative sense, and not in a restrictive sense.

Claims

[Claim 1] The invention described in this specification.

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