HK40110401A - Temperature compensation in electro-optic displays - Google Patents

Description

Temperature compensation in electro-optic displays

Cross-references 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. Furthermore, the entire contents of any patent, published application, or other published work referenced herein are incorporated herein by reference.

Technical Field

The present invention relates to an electro-optical display device, and more specifically, to a display controller for driving an electro-optical display.

Background Technology

Particle-based electrophoretic displays (EPDs) have been a subject of in-depth research and development for many years. In these displays, multiple charged particles (sometimes called pigment particles) move through a fluid under the influence of an electric field. This electric field is typically provided by a conductive film or a transistor (such as a field-effect transistor). Compared to liquid crystal displays (LCDs), electrophoretic displays offer superior brightness and contrast, wider viewing angles, bistable operation, and lower power consumption. Currently, electrophoretic displays are used in everyday products such as e-books (electronic readers), mobile phones and phone cases, smart cards, signage, watches, shelf labels, and flash drives.

During operation, the performance of the EPD varies with temperature. Therefore, it is necessary to adjust the operation of the EPD according to temperature conditions to achieve optimal display performance.

Summary of the Invention

This invention provides an electro-optic display and a related method for optimizing EPD performance based on measured temperature conditions.

In one aspect, the present invention features an electro-optic display comprising a display stack including an electro-optic material layer disposed between a common electrode and a pixel electrode array, wherein each pixel electrode is associated with a display pixel. The electro-optic display also includes display controller circuitry in electrical communication with the display stack. The display controller circuitry 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 pixel electrode array. The electro-optic display also includes a temperature sensor in communication with the display controller circuitry. The temperature sensor is located near the display stack. The electro-optic display also includes a first plurality of lookup tables in communication with the display controller circuitry. The first plurality of lookup tables include waveform shape data representing a plurality of waveform shapes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state. The electro-optic display also includes a second plurality of lookup tables in communication with the display controller circuitry. The second plurality of lookup tables include voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state.

In some embodiments, each lookup table in the first plurality of lookup tables corresponds to a range in the first plurality of temperature ranges. In some embodiments, each range in the first plurality of temperature ranges is a subset of the operating temperature range of the electro-optical display. In some embodiments, each lookup table in the second plurality of lookup tables corresponds to a range in the second plurality of temperature ranges. In some embodiments, each range in the second plurality of temperature ranges is a subset of the operating temperature range of the electro-optical display.

In some embodiments, the display controller circuit is configured to: receive a temperature signal representing a temperature measured near the display stack; select waveform shape data from a lookup table in a first plurality of lookup tables based on the temperature measured near the display stack; select voltage amplitude data from a lookup table in a second plurality of lookup tables based on the temperature measured near the display stack; and apply a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data.

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

In some embodiments, the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuitry can apply to each display pixel to transition an initial optical state to a final optical state for each display pixel. In some embodiments, each of the first plurality of temperature ranges is wider than each of the second plurality of temperature ranges.

On the other hand, the present invention provides a method for driving an electro-optic display. The method includes providing a display stack including an electro-optic material layer disposed between a common electrode and a pixel electrode array, wherein each pixel electrode is associated with a display pixel. The method also includes providing display controller circuitry in electrical communication with the display stack. The display controller circuitry 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 pixel electrode array. The method also includes providing a temperature sensor in communication with the display controller circuitry. The temperature sensor is located near the display stack. The method further includes providing a first plurality of lookup tables in communication with the display controller circuitry. The first plurality of lookup tables include waveform shape data representing a plurality of waveform shapes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state. The method also includes providing a second plurality of lookup tables in communication with the display controller circuitry. The second plurality of lookup tables include voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state. The method also includes receiving a temperature signal representing a temperature measured near the display stack. The method also includes selecting waveform shape data from a lookup table in a first plurality of lookup tables based on a temperature measured near the display stack, and selecting voltage amplitude data from a lookup table in a second plurality of lookup tables based on a temperature measured near the display stack. The method includes applying a waveform to each display pixel based on the selected waveform shape data and voltage amplitude data.

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

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

In some embodiments, the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuitry can apply to each display pixel to transform the initial optical state of each display pixel into a final optical state.

In some embodiments, each of the first plurality of temperature ranges is wider than each of the second plurality of temperature ranges.

In some embodiments, the method includes determining a DC balancing pulse applied to each display pixel based on the waveform applied to each display pixel, based on selected waveform shape data and voltage amplitude data.

Attached Figure Description

Various aspects and embodiments of this application are described with reference to the following accompanying drawings. It should be understood that the drawings are not necessarily drawn to scale. Furthermore, the drawings are intended only to facilitate the description of the subject matter. The drawings do not illustrate every aspect of the described embodiments and do not limit the scope of this disclosure or the claims.

Figure 1 shows an electrophoresis display based on the subject matter disclosed herein.

Figure 2 shows the equivalent circuit of the electrophoretic display shown in Figure 1 according to the subject matter disclosed herein.

Figure 3 illustrates an active matrix circuit based on the subject matter disclosed herein.

Figure 4 is a block diagram of an exemplary conventional electrophoresis display.

Figure 5 is an exemplary waveform diagram illustrating a conventional three-, four-, five-, or more-particle EPD system configured to drive display pixels in red, according to the subject matter described herein.

Figure 6 is a block diagram of an exemplary electrophoresis display according to the subject matter described herein.

Detailed Implementation

As described above, the subject matter presented in this paper provides a method and means for reducing the charge accumulated in electrophoretic display media and improving the performance of electro-optical displays.

The term "electro-optic" used in this document for materials or displays is used in its conventional meaning in the field of imaging, referring to a material having first and second display states that differ in at least one optical property, which is changed from its first display state to its second display state by applying an electric field to the material. While the optical property is typically color perceptible to the human eye, it can be another optical property, such as light transmission, reflection, emission, or, in the case of a display used for machine reading, a false color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

The term "grayscale state" is used here in its conventional sense in the field of imaging, referring to the state between two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, several EInk patents and published applications cited below describe electrophoretic displays where the extreme states are white and dark blue, so the intermediate "grayscale state" is actually light blue. In fact, as mentioned earlier, a change in optical state may not be a change in color at all. The terms "black" and "white" can be used below to refer to the two extreme optical states of a display and should be understood to generally include extreme optical states of black and white in a non-strict sense, such as the white and dark blue states mentioned above. The term "monochrome" can be used below to refer to a driving scheme that drives pixels only to their two extreme optical states without intermediate grayscale states.

As used herein, the terms “bistable” and “bistable” have their conventional meaning in the art, referring to a display comprising display elements having first and second display states that differ in at least one optical characteristic, and such that after any given element is driven to present its first or second display state by means of an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. As shown in U.S. Patent No. 7,170,670, some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, as are some other types of electro-optical displays. This type of display is properly referred to as “multistable” rather than bistable, although for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

The term "impulse" as used in this paper is in its conventional meaning, referring to the integral of voltage with respect to time. However, some bistable electro-optic dielectrics act as charge transducers, and for such dielectrics, an alternative definition of impulse can be used, namely the integral of current over time (which equals the total applied charge). The appropriate definition of impulse should be used depending on whether the dielectric acts as a voltage-time impulse transducer or a charge-impulse transducer.

Recently published patents and applications, assigned to or under the names of MIT and EInk Corporation, describe encapsulated electrophoretic media. Such encapsulated media comprise a plurality of small capsules, each capsule containing an inner phase comprising electrophoretically moving particles suspended in a fluid suspension medium, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held within a polymer binder to form an binder layer located between two electrodes. The techniques described in these patents and applications include:

(a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

(b) Capsules, adhesives, and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719;

(c) Microporous structures, wall materials, and methods for forming micropores; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

(d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

(e) Thin films and sub-assemblies containing electro-optic materials; see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564;

(f) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, U.S. Patent Nos. D485,294; 6,124,851; 6,130,773; 6,177,921; 6,232,950; 6,252,564; 6,312,304; 6,312,971; 6,376,828; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,480,182; 6,498,114; 6,506,438; 6,518,949; 6,521,489; 6,535,197; 6,545,291; 6,639,578; 6,6 57,772; 6,664,944; 6,680,725; 6,683,333; 6,724,519; 6,750,473; 6,816,147; 6,819,471; 6,825,068; 6,831,769; 6,842,167; 6,842,279; 6,842, 657; 6,865,010; 6,873,452; 6,909,532; 6,967,640; 6,980,196; 7,012,735; 7,030,412; 7,075,703; 7,106,296; 7,110,163; 7,116,318; 7,148,128; 7,167,155；7,173,752；7,176,880；7,190,008；7,206,119；7,223,672；7,230,751；7,256,766；7,259,744；7,280,094；7,301,693；7,304,780；7,3 27,511；7,347,957；7,349,148；7,352,353；7,365,394；7,365,733；7,382,363；7,388,572；7,401,758；7,442,587；7,492,497；7,535,624；7,551,3 46；7,554,712；7,583,427；7,598,173；7,605,799；7,636,191；7,649,674；7,667,886；7,672,040；7,688,497；7,733,335；7,785,988；7,830,592；7 843,626；7,859,637；7,880,958；7,893,435；7,898,717；7,905,977；7,957,053；7,986,450；8,009,344；8,027,081；8,049,947；8,072,675；8,077 ,141；8,089,453；8,120,836；8,159,636；8,208,193；8,237,892；8,238,021；8,362,488；8,373,211；8,389,381；8,395,836；8,437,069；8,441,41 4; 8,456,589; 8,498,042; 8,514,168; 8,547,628; 8,576,162; 8,610,988; 8,714,780; 8,728,266; 8,743,077; 8,754,859; 8,797,258; 8,797,633; 8, 797,636; 8,830,560; 8,891,155; 8,969,886; 9,147,364; 9,025,234; 9,025,238; 9,030,374; 9,140,952; 9,152,003; 9,152,004; 9,201,279; 9,223,164; 9,285,648; and 9,310,661; and U.S. Patent Application Publication Nos. 2002/0060321; 2004/0008179; 2004/0085619; 2004/0105036; 2004/0112525; 2005/0122306; 2005/0122 563; 2006/0215106; 2006/0255322; 2007/0052757; 2007/0097489; 2007/0109219; 2008/0061300; 2008/0149271; 2009/0122389; 2009/0315044; 20 10/0177396; 2011/0140744; 2011/0187683; 2011/0187689; 2011/0292319; 2013/0250397; 2013/0278900; 2014/0078024; 2014/0139501; 2014/0192 000; 2014/0210701; 2014/0300837; 2014/0368753; 2014/0376164; 2015/0171112; 2015/0205178; 2015/0226986; 2015/0227018; 2015/0228666; 2015/0261057; 2015/0356927; 2015/0378235; 2016/077375; 2016/0103380; and 2016/0187759; and International Application Publication No. WO00/38000; European Patent Nos. 1,099,207B1 and 1,145,072B1;

(g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564;

(h) A method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;

(i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348;

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

The entire contents of all the aforementioned patents and patent applications are incorporated herein by reference.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete electrophoretic droplets and a continuous phase of polymeric material, and the discrete electrophoretic droplets within such a polymer dispersion electrophoretic display can be considered as capsules or microcapsules, even if no discrete capsule membrane is associated with each individual droplet; see, for example, 2002/0131147 above. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subclass of encapsulated electrophoretic media.

Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoresis apparatus and offer further advantages, such as the ability to print or coat displays on a variety of flexible and rigid substrates (the term "printing" is used to encompass all forms of printing and coating, including but not limited to: pre-quantity coating, such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating, such as doctor blade roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; and other similar techniques). Therefore, the resulting display can be flexible. Furthermore, since the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

One related type of electrophoretic display is the so-called "micro-unit electrophoretic display." In a micro-unit electrophoretic display, charged particles and suspended fluid are not encapsulated in microcapsules, but rather retained within multiple cavities formed within a carrier medium (typically a polymer membrane). See, for example, International Application Publication No. WO02/01281 and published U.S. Application No. 2002/0075556, both assigned to Sipix Imaging, Inc.

The electro-optic displays of the types described above are bistable and are typically used in reflective mode, although, as described in some of the aforementioned patents and applications, such displays can operate in a "shutter mode," where the electro-optic medium is used to modulate the transmission of light, causing the display to operate in transmissive mode. Liquid crystals, including polymer-dispersed liquid crystals, are also electro-optic media, but are generally not bistable and operate in transmissive mode. Some embodiments of the invention described below are limited to use with reflective displays, while other embodiments can be used with both reflective and transmissive displays, including conventional liquid crystal displays.

Regardless of whether the display is reflective or transmissive, and regardless of whether the electro-optic medium used is bistable, to achieve a high-resolution display, each pixel of the display must be addressable without interference from adjacent pixels. One way to achieve this 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. The addressing or pixel electrode of a pixel is connected to an appropriate voltage source via the associated nonlinear element. Typically, when the nonlinear element is a transistor, the pixel electrode is connected to the drain of the transistor; this arrangement will be assumed in the following description, although it is inherently arbitrary, and the pixel electrode can be connected to the source of the transistor. Typically, 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 a specified row and a specified column. The sources of all transistors in each column are connected to a single column electrode, and the gates of all transistors in each row are connected to a single row electrode; again, assigning sources to rows and gates to columns is conventional but inherently arbitrary and can be reversed as needed. Row electrodes are connected to row drivers, which essentially ensure that only one row is selected at any given time. That is, a voltage is applied to the selected row electrode to ensure that all transistors in the selected row are turned on, while a voltage is applied to all other rows to ensure that all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply selected voltages to the individual column electrodes to drive the pixels in the selected row to their desired optical state (these voltages are associated with a common front electrode, which is typically located on the side of the electro-optical medium opposite the nonlinear array and extends across the entire display). After a preselection interval known as the "row addressing time," the selected row is deselected, the next row is selected, and the voltage on the column drivers is changed to write the next row to the display. This process is repeated, writing row by row across the entire display.

The processes used to fabricate active matrix displays are well-established. For example, thin-film transistors (TFTs) can be fabricated using various deposition and photolithography techniques. A transistor consists of a gate electrode, an insulating dielectric layer, a semiconductor layer, and source and drain electrodes. Applying a voltage to the gate electrode generates an electric field across the dielectric layer, significantly increasing the source-drain conductivity of the semiconductor layer. This change enables electrical conduction between the source and drain electrodes. Typically, the gate, source, and drain electrodes are patterned. The semiconductor layer is also typically patterned to minimize stray conduction (i.e., crosstalk) between adjacent circuit elements.

Liquid crystal displays (LCDs) typically employ amorphous silicon (“a-Si”) thin-film transistors (“TFTs”) as the switching devices for the display pixels. These 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 differs slightly from those in LCDs; see above-mentioned pending application serial numbers 09/565,413 and publication numbers 2002/0106847 and 2002/0060321. Thin-film transistors can be fabricated to provide high performance. However, the manufacturing process can result in significant costs.

In a TFT-addressable array, the pixel electrode is charged via the TFT during the row addressing time. During the row addressing time, the TFT is switched to the on state by changing the applied gate voltage. For example, for an n-type TFT, the gate voltage is switched to the "high" state to switch the TFT to the on state.

Furthermore, crosstalk between the data lines providing the drive waveform to the display pixels and the pixel electrodes can cause undesirable effects such as voltage shift. Similar to voltage shift, capacitive coupling between the data lines and pixel electrodes can also cause crosstalk even when the display pixel is not addressed (e.g., the associated pixel TFT is depleted). Such crosstalk can lead to undesirable voltage shifts because it can cause optical artifacts such as image streaks.

In some cases, an electrophoretic display or EPD may comprise two substrates (e.g., plastic or glass) with a front planar laminate (FPL) situated between them. In some embodiments, the bottom of the top substrate may be coated with a transparent conductive material to serve as a conductive electrode (i.e., V _{_com} ). The top of the lower substrate may include an array of electrode elements (e.g., conductive electrodes for each display pixel). Semiconductor switches (such as thin-film transistors or TFTs) may be associated with each pixel electrode. Applying a bias voltage to the pixel electrode and the V _{_com} plane can cause an electro-optical conversion of the FPL. This optical conversion can serve as the basis for displaying text or graphic information on the EPD. To display the desired image, an appropriate voltage needs to be applied to each pixel electrode.

Figure 1 illustrates a schematic model of a display pixel 100 of an electro-optic display according to the subject matter described herein. Pixel 100 may include an imaging film 110. In some embodiments, the imaging film 110 may be an electrophoretic material layer and is essentially bistable. The electrophoretic material may include a plurality of charged colored pigment particles (e.g., black, white, yellow, or red) located in a fluid and capable of moving through the fluid under the influence of an electric field. In some embodiments, the imaging film 110 may be an electrophoretic membrane having microunits of charged pigment particles. In some embodiments, the imaging film 110 may include, but is not limited to, an encapsulated electrophoretic imaging membrane that may include, for example, charged pigment particles. It should be understood that the driving method presented below can be applied to any type of electrophoretic material (e.g., an encapsulated electrophoretic medium or a membrane having microunits).

In some embodiments, the imaging film 110 may be disposed between the front electrode 102 and the rear electrode or pixel electrode 104. The front electrode 102 may be formed between the imaging film and the front portion 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 of any suitable transparent material, including but not limited to indium tin oxide (“ITO”). The rear electrode 104 may be formed on the side of the imaging film 110 opposite to the front electrode 102. In some embodiments, a parasitic capacitance (not shown) may be formed between the front electrode 102 and the rear electrode 104.

Pixel 100 can be one of a plurality of pixels. The plurality of pixels can 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 a specified row and a specified column. In some embodiments, the pixel matrix can be an “active matrix” in which each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 can be coupled between a backplane electrode 104 and an addressing electrode 108. In some embodiments, the nonlinear element 120 can include diodes and/or transistors, including but not limited to MOSFETs or thin-film transistors (“TFTs”). The drain (or source) of the MOSFET or TFT may be coupled to the backplane electrode or pixel electrode 104, the source (or drain) of the MOSFET or TFT may be coupled to the address electrode 108, and the gate of the MOSFET or TFT may be coupled to the driver electrode 106, which is configured to control the activation and deactivation of the MOSFET or TFT (for simplicity, the terminal of the MOSFET or TFT coupled to the backplane electrode 104 will be referred to as the drain of the MOSFET or TFT, and the terminal of the MOSFET or TFT coupled to the address 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 the MOSFET or TFT may be interchanged).

In some embodiments of the active matrix, 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 a nonlinear element 120 of all pixels 100 in the selected row. The column electrodes may be connected to a column driver that can apply a voltage suitable for driving the pixel to a desired optical state on the addressing electrodes 106 of the selected (activated) pixel. The voltage applied to the addressing electrodes 108 may be relative to the voltage applied to the front panel electrodes 102 of the pixel (e.g., approximately zero volts). In some embodiments, the front panel electrodes 102 of all pixels in the active matrix may be coupled to a common electrode.

In some embodiments, the pixels 100 of the active matrix can be written row by row. For example, a row driver can select a row of pixels, and a column driver can apply a voltage to the pixel corresponding to the desired optical state of that row of pixels. After a pre-selected interval (referred to as the "row addressing time"), the selected row can be deselected, another row can be selected, and the voltage on the column driver can be changed to write another row of the display.

Figure 2 illustrates a circuit model of an electro-optic imaging layer 110 disposed between a front electrode 102 and a rear electrode 104 according to the subject matter described herein. Resistor 202 and capacitor 204 may represent the resistance and capacitance of the electro-optic imaging layer 110, the front electrode 102, and the rear electrode 104 (including any adhesive layers). Resistor 212 and capacitor 214 may represent the resistance and capacitance of the laminated adhesive layer. Capacitor 216 may represent the capacitance formed between the front electrode 102 and the rear electrode 104, for example, an interface contact region between layers, such as the interface between the imaging layer and the laminated adhesive layer and/or the interface between the laminated adhesive layer and the backplane electrode. The voltage Vi across the imaging film 110 of a pixel may include the residual voltage of the pixel. Figure 3 illustrates an exemplary active matrix for driving an electrophoretic display. In some embodiments, each display pixel of the electrophoretic display may be controlled by a thin-film transistor (TFT). The TFT may be turned on and off to receive a driving voltage, thereby modulating the optical state of the associated display pixel. To effectively control the driving of associated display pixels, each TFT 102 may be equipped with gate line signals, data line signals, V _com line signals, and a storage capacitor. In one embodiment, as shown in FIG1, the gate of each TFT 102 may be electrically coupled to a scan line, and the source or drain of a transistor may be connected to a data line, and the two terminals of the storage capacitor may be connected to the V _com line and the pixel electrode, respectively. In some embodiments, the V _com line grid at the bottom of the top substrate and the V _com line grid at the top of the bottom substrate may be connected to the same DC source.

Figure 4 is a block diagram of an exemplary conventional electrophoresis display 400. The electrophoresis display 400 includes a display control circuit 480, a display stack 490, lookup tables 440a-440j (collectively referred to as lookup table 440 or LUT 440) and a temperature sensor 485.

Display stack 490 includes an array of display pixels arranged in an active matrix, as described above in conjunction with Figures 1-3. Those skilled in the art will understand that other display configurations are also within the scope of this disclosure (the structure and components of electrophoretic displays, pigments, binders, electrode materials, etc., are described in numerous patents and patent applications published by EInk Corporation, such as U.S. Patents 6,922,276, 7,002,728, 7,072,095, 7,116,318, 7,715,088, and 7,839,564, the entire contents of which are incorporated herein by reference).

Display controller circuitry 480 represents the circuitry and components that provide the power supply voltage and control signals 495 required to operate the electrophoretic display 400. For example, display controller circuitry 480 may include power management circuitry for generating and supplying multiple voltages to display stack 490, row and column drivers for addressing the pixel electrode array, and drive waveforms sufficient to change the optical state of display stack 490. In some embodiments, transistors for addressing and driving pixel electrodes are located near the pixel electrode array.

Those skilled in the art will recognize that the display controller circuit 480 of the present invention can be implemented in a variety of different physical forms and can utilize a variety of analog and digital components. For example, the display controller circuit 480 may include a general-purpose microprocessor and suitable peripheral components (e.g., one or more digital-to-analog converters "DACs") to convert the digital output from the microprocessor into an appropriate voltage for application to the pixels. Alternatively, the display controller circuit 480 may be implemented in an application-specific integrated circuit ("ASIC") or a field-programmable gate array ("FPGA"). Those skilled in the art will recognize that the display controller circuit 480 may include processing components and power management circuitry.

Lookup table 440 includes waveforms (a sequence of voltages applied over time) applied by display controller circuitry 480 to drive the display pixels of display stack 490 from one optical state to another. In some embodiments, each lookup table 440 includes a two-dimensional matrix, with one axis representing the initial state of the display pixel and the other axis representing the desired final state of the display pixel. Although LUT 440 is shown separately from display controller circuitry 480 in Figure 4, in some embodiments, LUT 440 is incorporated into display controller circuitry 480.

Typically, the entries in lookup table 440 include data representing the voltage impulses required to drive the display pixels from the initial optical state to the desired optical state. In practice, each entry defines the time-varying voltage waveform required to achieve the transition from the initial state to the final state and typically includes a series of integers representing the voltage to be applied to the display pixel electrodes during each frame of the frame sequence.

The entries in lookup table 440 can take many forms. In some embodiments, each element contains a single number. For example, an electro-optic display may use a high-precision voltage modulation drive circuit capable of outputting a variety of different voltages above and below a reference voltage, and simply applying the desired voltage to the display pixel for a standard predetermined time period. In such cases, each entry in lookup table 440 may simply be a signed integer specifying which voltage to apply to a given display pixel. In other cases, each element may include a series of numbers associated with different portions of a waveform. For example, some drive schemes use so-called single or double prepulse waveforms, and specifying such waveforms necessarily requires several numbers associated with different portions of the waveform.

In some embodiments, pulse length modulation is used to apply a predetermined voltage to the display pixel during a selected sub-scanning period (frame) within a plurality of sub-scanning cycles (frames) during a full scan (superframe). In such embodiments, the elements of lookup table 440 may have the form of a series of bits specifying whether the predetermined voltage should be applied during each sub-scanning cycle (frame) of the relevant transition.

Finally, as discussed in more detail below, the entries in lookup table 440 may be organized to include temperature compensation information. For example, entries in lookup table 440 may also include information indicating changes in the voltage level applied to the display pixels in response to a measured temperature change near display stack 490. In some embodiments, the temperature compensation information includes a numerical value indicating a specific voltage level applied to the display pixels during a given waveform. In some embodiments, the temperature compensation information includes a coefficient indicating that display controller circuitry 480 increases or decreases the voltage level applied to the display pixels during a specific waveform.

Those skilled in the art will recognize that the size of the lookup table 440 can vary depending on the display application. For example, if the display stack 490 includes a display capable of displaying 16 grayscale levels (e.g., a 4-bit display), the full grayscale lookup table would require 256 entries (16 initial states multiplied by 16 final states), while the lookup table for the monochrome area of the display would only require 4 entries.

It has been found that after applying a specific driving waveform, the final optical state of a display pixel can depend on the initial optical state, or it can depend on one or more previous optical states of the display pixel at a specific time prior to the initial state. Therefore, in some embodiments, lookup table 440 includes additional information about one or more previous optical states for each display pixel. However, depending on the number of previous states stored, lookup table 440 can become very large. To give an extreme example, consider a display with 256 (2 ^{^8} ) grayscale levels, using an algorithm that considers the initial, final, and two previous display pixel states. The necessary four-dimensional lookup table would have 232 entries. If each entry requires, for example, 64 bits (8 bytes), the total size of the lookup table would be approximately 32 GB. While storing this amount of data is not a problem for desktop computers, it could pose a problem for portable devices such as e-readers.

In some embodiments, the display controller circuit 480 includes a timing controller (“Tcon”) integrated circuit (“IC”) that accepts incoming image data and outputs control signals to a data set and selects driver ICs (e.g., row and column driver ICs) to generate appropriate waveforms and voltages at pixel electrodes to display the desired image. For example, when performing an image update, the display controller circuit 480 compares the currently displayed image with the next image to be displayed. Based on the comparison, Tcon consults a lookup table 440 to find the appropriate waveform and voltage potential for each pixel in the display stack 490. More specifically, when driving from the current image to the next image, a driving waveform and voltage level are selected from the lookup table for each pixel depending on the color state of the two consecutive images of that pixel. For example, for a pixel that is white in the current image but will be in a level 5 grayscale state in the next image, Tcon selects the waveform and voltage level that will affect the color change.

In some embodiments, a host controller communicating with display controller circuitry requests an update to the electrophoretic display 400 and provides image data for the update to the display controller circuitry. In some embodiments, display controller circuitry 480 receives image data by accessing a memory buffer containing the image data, or receives a signal from which image data is extracted. In some embodiments, the memory buffer has a structure such as that described in U.S. Patent No. 9,721,495. In some embodiments, display controller circuitry 480 receives a serial signal containing information required to perform necessary calculations to generate a drive impulse (e.g., a drive waveform) to be applied to the electrophoretic medium during pixel array scanning.

Once the drive waveform and voltage are selected from lookup table 440, they are applied to the display pixels of display stack 490 to drive the current image to the next image. The drive waveform is sent to display stack 490 frame by frame.

Temperature sensor 485 measures the temperature of the electrophoretic medium or the environment adjacent to it and provides temperature information to display controller circuitry 480 via interface 486. In some embodiments, temperature sensor 485 is located within the encapsulated electrophoretic medium of display stack 490. In some embodiments, temperature sensor 485 includes multiple temperature sensors located at different physical locations around or inside display stack 490.

Temperature sensor 485 may be a sensor that changes its electrical properties (e.g., resistance or capacitance) in response to temperature fluctuations. 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.

In some embodiments, interface 486 is a serial or multi-signal/parallel bus interface used by temperature sensor 485 to transmit temperature information to display controller circuitry 480. For example, interface 486 may be 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.).

The optical performance of an EPD can be affected by changes in ambient temperature. Therefore, an EPD module (such as an electrophoretic display 400) may include one or more temperature sensors 485 to acquire information about the temperature at one or more locations on the EPD module (typically near the electrophoretic medium). The temperature sensors 485 send the temperature information to a timing controller associated with the display controller circuitry 480.

In a conventional EPD module, Tcon can be configured to select a waveform set from LUT440, optimized to most accurately achieve the desired optical variations for a specific measurement temperature or temperature range. For example, for a given temperature range of 0 to 50 degrees Celsius, LUT440 can be divided into a group of ten LUTs, LUT440a-440j, each storing drive waveform and voltage level information configured to cover a 5-degree Celsius temperature range. For instance, LUT440a may include drive waveform and voltage level information optimized for driving display pixels when the measurement temperature is in the 0 to 4 degree Celsius range. Similarly, LUT440b may include drive waveform and voltage level information optimized for driving display pixels when the measurement temperature is in the 5 to 9 degree Celsius range, and so on, with LUT440j including drive waveform and voltage level information optimized for driving display pixels when the measurement temperature is in the 45 to 50 degree Celsius range. As mentioned above, LUT440j actually stores drive waveform and voltage level information for a 6-degree Celsius temperature range. However, electrophoretic displays tend to exhibit greater performance variations at lower temperatures, at the cost of lower accuracy at higher temperatures.

It has been observed that the voltage level required to achieve optimal EPD performance can vary significantly within a 5-degree Celsius range when a drive waveform is applied to the display pixels of the EPD. Therefore, the conventional configuration of using a single LUT to store the drive waveform and voltage level within a 5-degree Celsius range is insufficient for optimizing display performance. As mentioned above, the size of each LUT can be increased, or additional LUTs can be added to increase the temperature granularity of the information stored in each LUT. However, increasing the number of LUTs to cover a wider temperature range requires allocating more memory within the flash memory, one-time programmable memory, or OTP of the electrophoretic display 400. Since these memories are typically components of the EPD module, increasing the number of LUTs also undesirably increases the cost of the EPD module.

According to embodiments of the present invention, instead of adding more LUTs to store drive waveform and voltage level information to cover additional temperature ranges, the voltage value of the applied waveform can be modified.

Referring now to Figure 5, an exemplary waveform diagram 500 is shown, illustrating a waveform configured to drive a display pixel in red for a conventional three-, four-, five-, or more particle EPD system. As shown, waveform 500 includes a DC balancing pulse portion 404, a vibration and reset portion 406, and a smaller positive voltage portion 402 (also referred to herein as VPOS_low 402).

The vibration and reset section 406 is used to separate the charged ink particles from each other and to mix them in the display fluid, and then drive the particles to a known state before driving the display pixels to the desired optical state.

During VPOS_low 402, the positive amplitude of the waveform applied to the display pixel is less than the positive amplitude of the waveform applied during other periods (such as the vibration and reset portion 406). For example, as shown in FIG5, the positive amplitude of the waveform applied during VPOS_low 402 is approximately 7V, while the positive amplitude of the waveform applied during the vibration and reset portion 406 is approximately 15V. In some embodiments, the voltage applied during VPOS_low portion 402 is configured to provide optimal optical performance for displaying red (e.g., the highest red a* value). Although not shown in FIG5, in some embodiments, the negative amplitude of the waveform applied to the display pixel may be reduced during a period of driving the display pixel. In some embodiments, a negative voltage with an amplitude of approximately -7V is applied during the VNEG_low portion, while a negative voltage with an amplitude of approximately -15V is applied at other times when updating the display pixel.

In practice, the electrophoretic display can be configured to include not only lookup tables (LUTs) storing information describing waveforms used to cover multiple temperature ranges, but also LUTs storing voltage value information for the VPOS_low portion 502 (and/or the VNEG_low portion) for smaller temperature ranges. In one embodiment, the same number of LUTs as in Figure 4 (e.g., 10) can be used to store information about waveform shapes used in the temperature range of 0 to 50 degrees Celsius (e.g., a 5-degree range for each LUT), and additional LUTs can be included to store voltage level information, including smaller positive and/or negative voltage values, with the accuracy of a set of voltage level values increasing for each degree of temperature change.

Because multiple voltage values can be encoded into a small number of bits, the memory required to store voltage level values is significantly reduced. For example, only 3 bits can represent 2 ^{^3} or 8 unique voltage values. Therefore, despite the improved accuracy, only two additional LUTs are needed to store the voltage level information. For example, one additional LUT can store temperature voltage values in the range of 0 to 24 degrees Celsius, while another additional LUT can store temperature voltage values in the range of 25 to 50 degrees Celsius.

In this configuration, the Tcon can select waveform shape information for a first temperature range (e.g., 5 degrees Celsius) from one LUT and voltage value information with a granularity of 1 degree Celsius from another LUT. For example, when the electrophoretic display operates at a temperature of 23 degrees Celsius, the temperature sensor forwards temperature information to the Tcon associated with the display. The Tcon can select a waveform shape LUT specifying a temperature range of 20 to 25 degrees Celsius. Furthermore, the Tcon can select another LUT to retrieve voltage value information specified for 23 degrees Celsius, to combine with waveform shape information designed for the 20 to 25 degree Celsius range. This configuration advantageously allows for more precise fine-tuning of the waveform shape and voltage level applied to the display pixels at a specific temperature, achieving display performance superior to conventional solutions without significantly increasing the cost of the EPD module.

In some embodiments, Tcon may be further configured to calculate the DC balancing pulses required to maintain DC balance based on the applied waveform. Referring again to FIG5, waveform 500 may include a DC balancing pulse portion 504 configured to maintain the overall DC balance of waveform 500. In operation, applying a temperature-specific waveform shape and voltage level provided by a LUT may not be able to maintain overall DC balance. However, Tcon can maintain DC balance by calculating the required DC balancing pulses in real time or by retrieving DC balancing pulse information that has been predetermined and stored in the display controller circuitry.

Figure 6 is a block diagram of an electrophoretic display 600 according to the subject matter described herein. The electrophoretic display 600 includes many of the same components as the electrophoretic display 400 of Figure 4, but the LUT 640 of the electrophoretic display 600 is configured to separate waveform shape information from voltage level information.

It has been observed that higher accuracy of the voltage level applied to the display pixel at a specific temperature is more beneficial than higher accuracy of the applied waveform shape. Therefore, in the exemplary configuration shown in Figure 6, LUTs 640a-640e store information describing the waveform used in a temperature range of 0 to 50 degrees Celsius. For example, LUT 640a may include waveform shape information optimized for driving the display pixel when the measured temperature is in the range of 0 to 9 degrees Celsius. Similarly, LUT 640b may include waveform shape information optimized for driving the display pixel when the measured temperature is in the range of 10 to 19 degrees Celsius, and so on, with LUT 640e including waveform shape information optimized for driving the display pixel when the measured temperature is in the range of 40 to 50 degrees Celsius.

Furthermore, in the exemplary configuration shown in Figure 6, LUT640f and 640g store information describing voltage level information used within a temperature range of 0 to 50 degrees Celsius. For example, LUT640f may include voltage level information optimized for driving display pixels when the measured temperature is between 0 and 24 degrees Celsius, with a granularity of one set of voltage level information per degree Celsius. Similarly, LUT640g may include voltage level information optimized for driving display pixels when the measured temperature is between 25 and 50 degrees Celsius, also with a granularity of one set of voltage level information per degree Celsius.

Therefore, the configuration of the electrophoretic display 600 requires less memory for lookup tables, as only seven lookup tables are used in total (five for storing waveform shape information and two for storing voltage level information). This configuration helps reduce the overall cost of the EPD module while still providing EPD stability and performance over a wide temperature range.

Those skilled in the art will understand that various changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire description above should be interpreted in an illustrative rather than restrictive sense.

Claims (20)

1. An electro-optical display, comprising: The display stack includes an electro-optic material layer disposed between a common electrode and a pixel electrode array, wherein each pixel electrode is associated with a display pixel; The display controller circuit, which is electrically in communication with the display stack, 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 pixel electrode array; A temperature sensor that communicates with the display controller circuitry, wherein the temperature sensor is located near the display stack; A first plurality of lookup tables, communicating with the display controller circuitry, include waveform shape data representing a plurality of waveform shapes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state; and A second plurality of lookup tables, which communicate with the display controller circuitry, include voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuitry can apply to each display pixel to transform the initial optical state of each display pixel into the final optical state. 2. The electro-optical display according to claim 1, wherein each of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. 3. The electro-optic display according to claim 2, wherein each of the first plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display. 4. The electro-optical display according to claim 2, wherein each of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges. 5. The electro-optic display according to claim 4, wherein each of the second plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display. 6. The electro-optical display according to claim 4, wherein the display controller circuit is configured as follows: Receive a temperature signal representing the temperature measured near the display stack; Based on the temperature measured near the display stack, waveform shape data is selected from a lookup table in the first plurality of lookup tables; Based on the temperature measured near the display stack, voltage amplitude data is selected from a lookup table in the second plurality of lookup tables; and The waveform is applied to each display pixel based on the selected waveform shape data and voltage amplitude data. 7. The electro-optical display of claim 6, wherein the temperature measured near the display stack is within the range of the first plurality of temperature ranges, and the lookup table in the first plurality of lookup tables corresponds to the range of the first plurality of temperature ranges. 8. The electro-optical display of claim 6, wherein the temperature measured near the display stack is within the range of the second plurality of temperature ranges, and the lookup table in the second plurality of lookup tables corresponds to the range of the second plurality of temperature ranges. 9. The electro-optic display of claim 1, wherein the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes that the display controller circuitry can apply to each display pixel to transform the initial optical state of each display pixel into the final optical state. 10. The electro-optical display of claim 4, wherein each of the first plurality of temperature ranges is wider than each of the second plurality of temperature ranges. 11. A method for driving an electro-optic display, the method comprising: A display stack is provided, the display stack including an electro-optic material layer disposed between a common electrode and a pixel electrode array, wherein each pixel electrode is associated with a display pixel; A display controller circuit is provided that is electrically in communication with the display stack, the display controller circuit being 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 pixel electrode array; A temperature sensor is provided to communicate with the display controller circuitry, wherein the temperature sensor is located near the display stack; Provide a first plurality of lookup tables in communication with the display controller circuitry, the first plurality of lookup tables including waveform shape data, the waveform shape data representing a plurality of waveform shapes that the display controller circuitry can apply to each display pixel to transform an initial optical state of each display pixel into a final optical state; A second plurality of lookup tables are provided in communication with the display controller circuitry, the second plurality of lookup tables including voltage amplitude data, the voltage amplitude data representing a plurality of voltage amplitudes that the display controller circuitry can apply to each display pixel to transform the initial optical state of each display pixel into the final optical state; Receive a temperature signal representing the temperature measured near the display stack; Based on the temperature measured near the display stack, waveform shape data is selected from a lookup table in the first plurality of lookup tables; Based on the temperature measured near the display stack, voltage amplitude data is selected from a lookup table in the second plurality of lookup tables; and The waveform is applied to each display pixel based on the selected waveform shape data and voltage amplitude data. 12. The method of claim 11, wherein each of the first plurality of lookup tables corresponds to a range of the first plurality of temperature ranges. 13. The method of claim 12, wherein each of the first plurality of temperature ranges is a subset of the operating temperature range of the electro-optical display. 14. The method of claim 12, wherein each of the second plurality of lookup tables corresponds to a range of the second plurality of temperature ranges. 15. The method of claim 14, wherein each of the second plurality of temperature ranges is a subset of the operating temperature range of the electro-optic display. 16. The method of claim 11, wherein the temperature measured near the display stack is within the range of the first plurality of temperature ranges, and the lookup table in the first plurality of lookup tables corresponds to the range of the first plurality of temperature ranges. 17. The method of claim 11, wherein the temperature measured near the display stack is within the range of the second plurality of temperature ranges, and the lookup table in the second plurality of lookup tables corresponds to the range of the second plurality of temperature ranges. 18. The method of claim 11, wherein the voltage amplitude data includes voltage amplitude data representing at least four voltage amplitudes indicating that the display controller circuitry is capable of applying voltage amplitudes to each display pixel to transform the initial optical state of each display pixel into the final optical state. 19. The method of claim 14, wherein each of the first plurality of temperature ranges is wider than each of the second plurality of temperature ranges. 20. The method of claim 11, further comprising determining a DC balancing pulse applied to each display pixel based on the waveform applied to each display pixel, using selected waveform shape data and voltage amplitude data.