Method for measuring electrical properties of electro-optic displays.

Abstract

A method for driving an electro-optic display including an electro-optic material disposed between a common electrode and a backplane. The backplane includes an array of pixel electrodes, each coupled to a transistor. A display controller applies a waveform to the pixel electrodes. The method includes applying a first measurement waveform to a first portion of the pixel electrodes. During each frame of the first measurement waveform, an identical time-dependent voltage is applied to each pixel electrode of the first portion of the pixel electrodes. The method includes determining an impedance of the electro-optic material proximate the first portion of the pixel electrodes based on measurements of the current flowing through a current measurement circuit and the time-dependent voltage applied to each pixel electrode during the first measurement waveform, and selecting a drive waveform based on the impedance of the electro-optic material proximate the first portion of the pixel electrodes.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 293,947, filed December 27, 2021, and U.S. Provisional Patent Application No. 63 / 301,747, filed January 21, 2022. The entire contents of the foregoing provisional patent applications are incorporated herein by reference. Additionally, the entire contents of any patents, published applications, or other published works referenced herein are incorporated by reference in their entirety.

[0002] FIELD OF THE INVENTION The present invention relates to a method for measuring the electrical properties of an electro-optic display, and more particularly to a method for measuring the electrical properties of an active matrix electrophoretic display module. [Background technology]

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

[0004] One particular application for displaying a screen is an input device such as a touchscreen or keypad, or a writing tablet. In many cases, it is desirable to sense the state of the display in order to digitize the input. For example, measuring and analyzing certain properties of the display may allow for the detection of the location of the input. A responsive event or action may then be generated.

[0005] Additionally, the electrical properties of the encapsulated electrophoretic display media may vary in response to environmental factors such as temperature and humidity. In some situations, it may be desirable to compensate the drive waveform in response to changes in the electrical properties of the polymer material that comprises the encapsulated electrophoretic display media in order to achieve repeatable optical states in the display. Therefore, it is desirable to measure display parameters that affect the waveform compensation scheme. However, the use of external display sensors can increase the cost of the display and complicate the manufacturing process. In addition, external sensors may not accurately measure parameters inside the display. Summary of the Invention [Means for solving the problem]

[0006] (Summary of the Invention) Therefore, a need exists for efficiently and accurately measuring electrical properties of a display and applying waveforms to the display pixels according to the measured electrical properties.

[0007] Thus, in one aspect, the subject matter presented herein provides a method for driving an electro-optic display including a layer of electro-optic material disposed between a common electrode and a backplane. The backplane includes an array of pixel electrodes, each coupled to a pixel transistor. A display controller circuit applies a waveform to the array of pixel electrodes by applying one or more time-dependent voltages between the common electrode and the array of pixel electrodes via the pixel transistors. The driving method includes applying a first measurement waveform including one or more frames to a first portion of pixel electrodes of the array of pixel electrodes. During each frame of the first measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the first portion of pixel electrodes. The method also includes measuring a first current flowing through a current measurement circuit coupled between the common electrode and an output of the display controller circuit that applies the time-dependent voltage to the common electrode, and determining a first impedance of the electro-optic material proximate to the first portion of pixel electrodes based on the first current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes during the first measurement waveform. The method also includes selecting a first drive waveform for application to each pixel electrode in the first portion of the pixel electrodes based on a first impedance of an electro-optic material proximate the first portion of the pixel electrodes, and applying the first drive waveform to the first portion of the pixel electrodes, the first drive waveform comprising a time-dependent voltage sufficient to change the optical state of an electro-optic display proximate the first portion of the pixel electrodes.

[0008] In some embodiments, the current measurement circuit includes a resistive element and a differential voltage amplifier, a first input of the differential voltage amplifier connected to a first terminal of the resistive element, and a second input of the differential voltage amplifier connected to a second terminal of the resistive element.

[0009] In some embodiments, the time-dependent voltage applied to each pixel electrode in the first portion of pixel electrodes comprises a uniform voltage pulse. In some embodiments, the time-dependent voltage applied to each pixel electrode in the first portion of pixel electrodes comprises a first voltage pulse having a first polarity and a second voltage pulse having a second polarity opposite the first polarity.

[0010] In some embodiments, the first portion of the pixel electrodes comprises all of the pixel electrodes of the array of pixel electrodes, hi some embodiments, the first portion of the pixel electrodes includes pixel electrodes located proximate the periphery of the array of pixel electrodes.

[0011] In some embodiments, the method further includes applying a second measurement waveform comprising one or more frames to a second portion of pixel electrodes of the array of pixel electrodes, wherein during each frame of the second measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the second portion of pixel electrodes; measuring a second current flowing through a current measurement circuit; determining a second impedance of an electro-optic material proximate to the second portion of pixel electrodes based on the second current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes during the second measurement waveform; selecting a second drive waveform for application to each pixel electrode of the second portion of pixel electrodes based on the second impedance of the electro-optic material proximate to the second portion of pixel electrodes; and applying the second drive waveform to the second portion of pixel electrodes, wherein the second drive waveform comprises a time-dependent voltage sufficient to change the optical state of an electro-optic display proximate to the second portion of pixel electrodes.

[0012] In some embodiments, the first portion of pixel electrodes includes pixel electrodes from a first region of the array of pixel electrodes, and the second portion of pixel electrodes includes pixel electrodes from a second region of the array of pixel electrodes, wherein the first and second regions of pixel electrodes do not overlap. In some embodiments, the method further includes applying a zero volt waveform to the second portion of pixel electrodes while applying the first measurement waveform to the first portion of pixel electrodes, and applying a zero volt waveform to the first portion of pixel electrodes while applying the second measurement waveform to the second portion of pixel electrodes.

[0013] In another aspect, the subject matter presented herein provides a method for driving an electro-optic display including a layer of electro-optic material disposed between a common electrode and a backplane. The backplane includes an array of pixel electrodes, each coupled to a pixel transistor. A display controller circuit applies a waveform to the array of pixel electrodes by applying one or more time-dependent voltages between the common electrode and the array of pixel electrodes via the pixel transistors. The driving method includes activating pixel transistors associated with a first portion of pixel electrodes of the array of pixel electrodes in parallel and applying a first voltage to the first portion of the pixel electrodes. The driving method also includes injecting a measurement waveform from a signal generating circuit through a current measuring circuit coupled between the signal generating circuit and the common electrode, and measuring a first current flowing through the current measuring circuit based on the measurement waveform. The driving method also includes determining a first impedance of the electro-optic material proximate to the first portion of the pixel electrodes based on the first current flowing through the current measuring circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the first measurement waveform. The method for driving also includes selecting a first drive waveform for application to each pixel electrode of the first portion of pixel electrodes based on a first impedance of an electro-optic material proximate the first portion of the pixel electrodes, and applying the first drive waveform to the first portion of the pixel electrodes, the first drive waveform comprising a time-dependent voltage sufficient to change the optical state of an electro-optic display proximate the first portion of the pixel electrodes.

[0014] In some embodiments, the current measurement circuit includes a resistive element and a differential voltage amplifier, a first input of the differential voltage amplifier connected to a first terminal of the resistive element, and a second input of the differential voltage amplifier connected to a second terminal of the resistive element.

[0015] In some embodiments, the measurement waveform comprises a periodic rectangular or sinusoidal voltage waveform. In some embodiments, the measurement waveform comprises a voltage having an amplitude insufficient to change the optical state of the electro-optic display. In some embodiments, the measurement waveform comprises an oscillating voltage waveform having multiple frequencies.

[0016] In another aspect, the subject matter presented herein provides a method for driving an electro-optic display including an electrophoretic display medium disposed between a first common electrode and an array of pixel electrodes, each pixel electrode coupled to a first terminal of a storage capacitor and a second terminal of each storage capacitor coupled to a second common electrode. A display controller circuit is configured to apply time-dependent voltages to the first common electrode and the second common electrode independently of each other. The driving method includes concurrently activating pixel transistors associated with first portions of the pixel electrodes. The driving method also includes toggling a first switch to disconnect the first common electrode from the display controller circuit and connect the first common electrode to a first terminal of an impedance measurement circuit, and toggling a second switch to disconnect the second common electrode from the display controller circuit and connect the second common electrode to a second terminal of the impedance measurement circuit. The driving method also includes injecting a measurement waveform voltage from the impedance measurement circuit into the first common electrode, the measurement waveform including a time-dependent voltage. The driving method also includes measuring a first current flowing through an impedance measurement circuit based on the measurement waveform, and determining a first impedance of the electro-optic material proximate to the first portion of the pixel electrodes based on the first current flowing through the impedance measurement circuit and a time-varying voltage applied to the first common electrode during the measurement waveform. The driving method also includes selecting a first drive waveform to apply to each pixel electrode of the first portion of the pixel electrodes based on the first impedance of the electro-optic material proximate to the first portion of the pixel electrodes. The driving method also includes toggling a first switch to disconnect the first common electrode from the impedance measurement circuit and connect the first common electrode to the display controller circuit, and toggling a second switch to disconnect the second common electrode from the impedance measurement circuit and connect the second common electrode to the display controller circuit.The method for driving also includes applying a first drive waveform to a first portion of the pixel electrode, the first drive waveform comprising a time-varying voltage sufficient to change the optical state of an electro-optic display proximate the first portion of the pixel electrode.

[0017] In some embodiments, the measurement waveform comprises a periodic rectangular or sinusoidal voltage waveform. In some embodiments, the measurement waveform comprises a voltage having an amplitude insufficient to change the optical state of an electro-optic display proximate the first portion of the pixel electrode. In some embodiments, the measurement waveform comprises a voltage having an amplitude less than 1 volt. In some embodiments, the measurement waveform comprises an oscillating voltage waveform having multiple frequencies.

[0018] In some embodiments, the first portion of pixel electrodes includes pixel electrodes located proximate the periphery of the array of pixel electrodes. The present specification also provides, for example, the following: (Item 1) 1. A method for driving an electro-optic display comprising a layer of electro-optic material disposed between a common electrode and a backplane, the backplane including an array of pixel electrodes, each pixel electrode coupled to a pixel transistor, and a display controller circuit applying waveforms to the array of pixel electrodes by applying one or more time-dependent voltages between the common electrode and the array of pixel electrodes via the pixel transistors, the method comprising: applying a first measurement waveform comprising one or more frames to a first portion of pixel electrodes of the array of pixel electrodes, wherein during each frame of the first measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the first portion of pixel electrodes; measuring a first current flowing through a current measurement circuit coupled between the common electrode and an output of the display controller circuit that applies a time-dependent voltage to the common electrode; determining a first impedance of the electro-optic material proximate to the first portion of the pixel electrodes based on the first current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the first measurement waveform; selecting a first drive waveform for application to each pixel electrode of the first portion of pixel electrodes based on the first impedance of the electro-optic material proximate to the first portion of the pixel electrodes; applying the first drive waveform to a first portion of the pixel electrode, the first drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the first portion of the pixel electrode; A method comprising: (Item 2) 2. The method according to claim 1, wherein the current measurement circuit comprises a resistive element and a differential voltage amplifier, a first input of the differential voltage amplifier being connected to a first terminal of the resistive element, and a second input of the differential voltage amplifier being connected to a second terminal of the resistive element. (Item 3) Item 10. The method of item 1, wherein the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes comprises a uniform voltage pulse. (Item 4) Item 10. The method of item 1, wherein the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes comprises a first voltage pulse having a first polarity and a second voltage pulse having a second polarity opposite to the first polarity. (Item 5) Item 10. The method of item 1, wherein the first portion of pixel electrodes comprises all of the pixel electrodes of the array of pixel electrodes. (Item 6) Item 10. The method of item 1, wherein the first portion of pixel electrodes comprises pixel electrodes located proximate to the periphery of the array of pixel electrodes. (Item 7) applying a second measurement waveform comprising one or more frames to a second portion of pixel electrodes of the array of pixel electrodes, wherein during each frame of the second measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the second portion of pixel electrodes; measuring a second current flowing through the current measurement circuit; determining a second impedance of the electro-optic material proximate to a second portion of the pixel electrodes based on the second current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the second measurement waveform; selecting a second drive waveform for application to each pixel electrode of the second portion of pixel electrodes based on the second impedance of the electro-optic material proximate to the second portion of pixel electrodes; applying the second drive waveform to a second portion of the pixel electrode, the second drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the second portion of the pixel electrode; Item 1, the method of claim 1 further comprising: (Item 8) 8. The method of claim 7, wherein the first portion of pixel electrodes comprises pixel electrodes from a first region of the array of pixel electrodes, and the second portion of pixel electrodes comprises pixel electrodes from a second region of the array of pixel electrodes, and the first and second regions of pixel electrodes do not overlap. (Item 9) applying a first measurement waveform to a first portion of the pixel electrodes while applying a zero volt waveform to a second portion of the pixel electrodes; applying a zero volt waveform to a first portion of the pixel electrodes while applying a second measurement waveform to a second portion of the pixel electrodes; 8. The method of claim 7, further comprising: (Item 10) 1. A method for driving an electro-optic display comprising a layer of electro-optic material disposed between a common electrode and a backplane, the backplane including an array of pixel electrodes, each pixel electrode coupled to a pixel transistor, and a display controller circuit applying waveforms to the array of pixel electrodes by applying one or more time-dependent voltages between the common electrode and the array of pixel electrodes via the pixel transistors, the method comprising: concurrently activating pixel transistors associated with a first portion of pixel electrodes of the array of pixel electrodes; applying a first voltage to a first portion of the pixel electrode; injecting a measurement waveform from the signal generating circuit through a current measuring circuit coupled between the signal generating circuit and the common electrode; measuring a first current flowing through the current measurement circuit based on the measured waveform; determining a first impedance of the electro-optic material proximate to the first portion of the pixel electrodes based on the first current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the first measurement waveform; selecting a first drive waveform for application to each pixel electrode of the first portion of pixel electrodes based on the first impedance of the electro-optic material proximate to the first portion of the pixel electrodes; applying the first drive waveform to a first portion of the pixel electrode, the first drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the first portion of the pixel electrode; A method comprising: (Item 11) 11. The method of claim 10, wherein the current measurement circuit comprises a resistive element and a differential voltage amplifier, a first input of the differential voltage amplifier connected to a first terminal of the resistive element, and a second input of the differential voltage amplifier connected to a second terminal of the resistive element. (Item 12) Item 11. The method of item 10, wherein the measurement waveform comprises a periodic rectangular or sinusoidal voltage waveform. (Item 13) Item 11. The method of item 10, wherein the measurement waveform comprises a voltage having an amplitude insufficient to change the optical state of the electro-optic display. (Item 14) Item 11. The method of item 10, wherein the measurement waveform comprises an oscillating voltage waveform having multiple frequencies. (Item 15) 1. A method for driving an electro-optic display, the electro-optic display comprising an electrophoretic display medium disposed between a first common electrode and an array of pixel electrodes, each pixel electrode coupled to a first terminal of a storage capacitor, a second terminal of each storage capacitor coupled to a second common electrode, and a display controller circuit configured to apply time-dependent voltages to the first common electrode and the second common electrode independently of each other, the method comprising: concurrently activating pixel transistors associated with a first portion of the pixel electrodes; toggling a first switch to disconnect the first common electrode from the display controller circuit and connect the first common electrode to a first terminal of an impedance measurement circuit; toggling a second switch to disconnect the second common electrode from the display controller circuit and connect the second common electrode to a second terminal of the impedance measurement circuit; injecting a measurement waveform voltage from the impedance measurement circuit into the first common electrode, the measurement waveform comprising a time-varying voltage; measuring a first current flowing through the impedance measurement circuit based on the measured waveform; determining a first impedance of the electro-optic material proximate to a first portion of the pixel electrode based on the first current flowing through the impedance measurement circuit and the time-dependent voltage applied to the first common electrode during the measurement waveform; selecting a first drive waveform for application to each pixel electrode of the first portion of pixel electrodes based on the first impedance of the electro-optic material proximate to the first portion of the pixel electrodes; toggling the first switch to disconnect the first common electrode from the impedance measurement circuitry and connect the first common electrode to the display controller circuitry; toggling the second switch to disconnect the second common electrode from the impedance measurement circuitry and connect the second common electrode to the display controller circuitry; applying the first drive waveform to a first portion of the pixel electrode, the first drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the first portion of the pixel electrode; A method comprising: (Item 16) Item 16. The method of item 15, wherein the measurement waveform comprises a periodic rectangular or sinusoidal voltage waveform. (Item 17) Item 16. The method of item 15, wherein the measurement waveform comprises a voltage having an amplitude insufficient to change the optical state of the electro-optic display adjacent to the first portion of the pixel electrode. (Item 18) Item 18. The method of item 17, wherein the measurement waveform comprises a voltage having an amplitude of less than 1 volt. (Item 19) Item 16. The method of item 15, wherein the measurement waveform comprises an oscillating voltage waveform having multiple frequencies. (Item 20) Item 16. The method of item 15, wherein the first portion of pixel electrodes comprises pixel electrodes located proximate to the periphery of the array of pixel electrodes. [Brief explanation of the drawings]

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

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

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

[0022] [Figure 4A] FIG. 4A shows two plots of exemplary impedance measurements implemented on three exemplary display modules in accordance with the subject matter described herein.

[0023] [Figure 4B] FIG. 4B is a plot showing afterimage performance during different graytone transitions in accordance with the subject matter described herein.

[0024] [Figure 5] FIG. 5 illustrates a diagram of an embodiment of an electrophoretic display in accordance with the subject matter described herein.

[0025] [Figure 6] FIG. 6 illustrates a diagram of an embodiment of an electrophoretic display in accordance with the subject matter described herein.

[0026] [Figure 7] FIG. 7 illustrates a diagram of an embodiment of an electrophoretic display in accordance with the subject matter described herein.

[0027] [Figure 8] FIG. 8 shows a set of impedance measurements from an exemplary active matrix display module using the methods described herein.

[0028] [Figure 9] FIG. 9 illustrates a diagram of an embodiment of an electrophoretic display in accordance with the subject matter described herein.

[0029] [Figure 10] FIG. 10 illustrates an exemplary signal sequence for enabling impedance measurements as described herein.

[0030] [Figure 11] FIG. 11 illustrates a diagram of an embodiment of an electrophoretic display in accordance with the subject matter described herein. DETAILED DESCRIPTION OF THE INVENTION

[0031] (Detailed Description of the Invention) The present invention relates to a method for driving electro-optic displays, particularly bistable electro-optic displays, and to an apparatus for use in such a method. More particularly, the present invention relates to a driving method that may enable the reduction of "afterimages" and edge effects in such displays, as well as the reduction of flashing. The present invention is particularly, but not exclusively, intended for use with particle-based electrophoretic displays, in which one or more types of electrically charged particles are present in a fluid and are moved through the fluid under the influence of an electric field, changing the appearance of the display.

[0032] The term "electro-optic," as applied to a material or display, is used herein in its conventional sense in the imaging arts to refer to a material having first and second display states 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 it 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.

[0033] The term “gray state” is used herein in its conventional sense in the imaging arts to refer to a state intermediate between two extreme 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.

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

[0035] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to 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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0053] (j) Methods for driving displays (e.g., U.S. Patent Nos. 5,930,026, 6,445,489, 6,504,524, 6,512,354, 6,531,997, 6,753,999, 6,825,970, 6,900,851, 6,995,550, 7,012,600, 7,023,420, 7,034,783, 7,061,166, 7,061,662, 7,116,466, 7,119,772, 7,177,066, 7,193,625, 7,222,224, 7,222,226, 7,222,228 ... No. 02,847, No. 7,242,514, No. 7,259,744, No. 7,304,787, No. 7,312,794, No. 7,327 ,511, No. 7,408,699, No. 7,453,445, No. 7,492,339, No. 7,528,822, No. 7,545,3 No. 58, No. 7,583,251, No. 7,602,374, No. 7,612,760, No. 7,679,599, No. 7,679,813 No. 7,683,606, No. 7,688,297, No. 7,729,039, No. 7,733,311, No. 7,733,335, No. No. 7,787,169, No. 7,859,742, No. 7,952,557, No. 7,956,841, No. 7,982,479, No. 7, No. 999,787, No. 8,077,141, No. 8,125,501, No. 8,139,050, No. 8,174,490, No. 8,24 No. 3,013, No. 8,274,472, No. 8,289,250, No. 8,300,006, No. 8,305,341, No. 8,314, No. 784, No. 8,373,649, No. 8,384,658, No. 8,456,414, No. 8,462,102, No. 8,537,105 No. 8,558,783, No. 8,558,785, No. 8,558,786, No. 8,558,855, No. 8,576,164, No. 8,576,259, No. 8,593,396, No. 8,605,032, No. 8,643,595, No. 8,665,206, No. 8 ,681,191, No.8,730,153, No.8,810,525, No.8,928,562, No.8,928,641, No.8,9 No. 76,444, No. 9,013,394, No. 9,019,197, No. 9,019,198, No. 9,019,318, No. 9,082,Nos. 352, 9,171,508, 9,218,773, 9,224,338, 9,224,342, 9,224,344, 9,230,492, 9,251,736, 9,262,973, 9,269,311, 9,299,294, 9,373,289, 9,390,066, 9,390,661, and 9,412,314, and U.S. Patent Application Publication Nos. 2003 / 0102858, 2004 / 0246562, 2005 / 0253777, 2007 / 0070032, 2007 / 0076289, 2007 / 0091418, 2007 / 0103427, 2007 / 0176912, 2007 / 0296452, 2008 / 0024429, 2008 / 0024482, 2008 / 0136774, 2008 / 0169821, 2008 / 0218471, No. 2008 / 0291129, No. 2008 / 0303780, No. 2009 / 0174651, No. 2009 / 0195568, No. 2009 / 0322721, No. 2010 / 0194733, No. 2010 / 0194789, No. 2010 / 02 20121, 2010 / 0265561, 2010 / 0283804, 2011 / 0063314, 2011 / 0175875, 2011 / 0193840, 2011 / 0193841, 2011 / 0199671, 2 No. 011 / 0221740, No. 2012 / 0001957, No. 2012 / 0098740, No. 2013 / 0063333, No. 2013 / 0194250, No. 2013 / 0249782, No. 2013 / 0321278, No. 2014 / 0009 No. 817, No. 2014 / 0085355, No. 2014 / 0204012, No. 2014 / 0218277, No. 2014 / 0240210, No. 2014 / 0240373, No. 2014 / 0253425, No. 2014 / 0292830, No. 201 (See Nos. 4 / 0293398, 2014 / 0333685, 2014 / 0340734, 2015 / 0070744, 2015 / 0097877, 2015 / 0109283, 2015 / 0213749, 2015 / 0213765, 2015 / 0221257, 2015 / 0262255, 2016 / 0071465, 2016 / 0078820, 2016 / 0093253, 2016 / 0140910, and 2016 / 0180777).

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

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

[0056] Many of the aforementioned E Ink and MIT patents and applications also discuss microcell electrophoretic displays and polymer-dispersed electrophoretic displays. The term "encapsulated electrophoretic displays" can refer to all such display types, which can also be collectively described as "microcavity electrophoretic displays" to generalize across wall morphologies.

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

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

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

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

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

[0062] Exemplary EPD

[0063] 1 shows a schematic diagram of a pixel 100 of an electrophoretic display or EPD in accordance with the subject matter presented herein. Pixel 100 may include an imaging film 110. In some embodiments, imaging film 110 may be bistable. In some embodiments, imaging film 110 may include, but is not limited to, an encapsulated electrophoretic imaging film, which may include, for example, charged pigment particles.

[0064] The imaging film 110 may be disposed between the front electrode 102 and the rear electrode 104. The front electrode 102 may be formed between the imaging film and the front surface of the display. In some embodiments, the front electrode 102 may be transparent. In some embodiments, the front electrode 102 may be formed from any suitable transparent material, including, but not limited to, indium tin oxide (ITO). The rear electrode 104 may be formed opposite the front electrode 102. In some embodiments, a parasitic capacitance (not shown) may be formed between the front electrode 102 and the rear electrode 104.

[0065] 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 case each pixel is associated with at least one nonlinear circuit element 120. The nonlinear circuit element 120 may be coupled between the backplane 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. The drain (or source) of the MOSFET may be coupled to the backplane electrode 104, the source (or drain) of the MOSFET may be coupled to the addressing electrode 108, and the gate of the MOSFET may be coupled to a driver electrode 106 configured to control the activation and deactivation of the MOSFET (for convenience, the terminal of the MOSFET that is coupled to the backplane electrode 104 will be referred to as the drain of the MOSFET, and the terminal of the MOSFET that is coupled to the addressing electrode 108 will be referred to as the source of the MOSFET. However, those skilled in the art will recognize that in some embodiments, the source and drain of the MOSFET may be interchanged).

[0066] 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, which may select one or more rows of pixels by applying a voltage to the selected row electrode sufficient to activate the nonlinear elements 120 of all pixels 100 in the selected row. The column electrodes may be connected to a column driver, which may apply a suitable voltage to the addressing electrodes 106 of the selected (activated) pixels to drive the pixels 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 plane electrode 102 (e.g., a voltage of about zero volts). In some embodiments, the front plane electrodes 102 of all pixels in the active matrix may be coupled to a common electrode.

[0067] 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.

[0068] FIG. 2 shows 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 disclosed herein. Resistor 202 and capacitor 204 represent the resistance and capacitance of the electro-optic imaging layer 110, the front electrode 102, and the back electrode 104, which may include any adhesive layers. Resistor 212 and capacitor 214 may represent the resistance and capacitance of the laminating adhesive layer. Capacitor 216 may represent capacitance that may form between the front electrode 102 and the back electrode 104, e.g., the interfacial contact area between layers, such as the interface between the imaging layer and the laminating adhesive layer and / or the laminating 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.

[0069] It has been observed that the performance of electrophoretic displays can vary depending on environmental conditions. For example, variations in the impedance of a front panel laminate ("FPL") can be correlated to variations in temperature. Thus, impedance measurements, such as measurements of the impedance of a front plane laminate, can provide useful insight into the operating characteristics of electrophoretic displays and their ink systems.

[0070] 3 is a graph 300 showing a plot 305 of impedance versus temperature for an exemplary front plane laminate. In particular, graph 300 shows impedance in MΩcm at 10 Hz on the Y-axis. 2 FPL impedance in units Z real 3 shows a plot 305 of temperature in degrees Celsius on the x-axis against FPL impedance. As illustrated by graph 300, FPL impedance decreases as temperature increases. It should be understood that the FPL referred to herein may include, but is not limited to, the light-transmissive conductive layer, the layer of electro-optic medium, and the adhesive layer of an electrophoretic display. In some embodiments, this impedance measurement information may be used in place of temperature measurements for waveform selection to optimize display performance.

[0071] FIG. 4A shows two plots of exemplary impedance measurements performed on three exemplary display modules at 28° C. across different waveform frequencies; two of the modules, namely 1 and 3, have very similar impedances, while module 2 exhibits a different impedance than the other two.

[0072] FIG. 4B is a plot showing the persistence performance during different gray-tone transitions. For example, at 28° C., using the same driving waveforms as those used for FIG. 4A, there is a display capable of 16 4-bit gray levels, displayed from 1 (black) to 16 (white), with transitions (e.g., {GT1, GT2, ..., GT15}) → {GT1, GT2, ..., GT16}). The x-axis of this figure represents the different gray-tone transitions. As shown, the persistence performance of module 1 is very similar to module 3, while module 2 has significantly different persistence performance. The persistence results correlate with the impedance measurements shown in FIG. 4A. Therefore, it can be inferred that impedance measurements can be used as a measure of optical performance, and that modules with similar impedances will behave optically similarly and therefore can be driven similarly.

[0073] 5 illustrates a diagram of an electrophoretic display 500. In this embodiment, the output of controller 502 is synchronized source 506 and gate 508 line voltages to sequentially scan the display pixels. A DC voltage can be supplied to top plane 510 through Vcom 504 line during each update.

[0074] In practice, it may be desirable to use external instruments to access the pixel electrodes of an active matrix display and apply signals to measure electrical properties directly. Depending on the signal used as input, the electrical properties measured may include, but are not limited to, current, resistance, charge, capacitance, time constant, phase shift, magnitude, and frequency peak.

[0075] Referring now to FIG. 6 , one method for measuring electrical properties is to update the active-matrix display 600 using a known waveform while measuring the electrical response of the ink layer 602 through a common electrode. In this method, the voltage applied to all pixel electrodes during each frame is the same. Thus, at the end of each frame, a uniform electric field can be formed across the ink in the display area being updated. The electrical response measured through the common electrode can therefore reflect the average electrical properties of the updated area. For example, the pixels of an active-matrix backplane can be forced to a non-zero voltage while the current through the Vcom 604 line is measured. The current transients during and immediately after the voltage pulse on the backplane can reveal area-averaged electrical properties of the display 600, such as properties related to sheet resistance and sheet capacitance. In this configuration, the waveform is applied to the pixels by source and gate drivers in the controller, so this method can be used when the active-matrix display 400 is operating under normal scanning mode.

[0076] As shown in FIG. 6 , a current measurement circuit 606 can be inserted between the Vcom line 604 and the top plane electrode 608. In some embodiments, this current measurement circuit can include a small resistor (e.g., about 500 ohms) and a differential voltage amplifier with an input line applied across the resistor. In this configuration, the resistance of the resistor can be small enough so as not to substantially affect the operation of the display 600, but large enough to provide a voltage signal proportional to the current flowing through the Vcom line 604. In operation, when the display 600 is updated, waveforms and images are selected so that the same time-dependent voltage is applied to all pixels. This time-dependent voltage can be a simple voltage pulse, e.g., a uniform voltage applied for a finite length of time. In another embodiment, the time-dependent voltage can include two consecutive pulses of opposite amplitude. The current can be measured as a function of time across an entire display addressing event. The current can be averaged over a time period covering a portion of the latter half of each pulse. This value is proportional, in an approximation way, to the effective resistance or impedance of the display film. This effective impedance can be correlated to the electro-optical behavior of the display film and therefore can be used to select the appropriate waveform for updating in standard display operation. This measurement method provides the flexibility to perform selective area or local measurements, but does not affect the normal scanning operation of the display.

[0077] In another embodiment, a fraction of the display pixels can be driven while the current through the Vcom604 line is measured. In this configuration, the current transients provide an area-averaged electrical profile of the display, but are only averaged over the area of ​​the driven pixels. In this case, "driving" is defined such that the driven pixels receive a non-zero voltage while the remainder of the pixels are not driven, i.e., the undriven pixels receive a zero voltage bias. In this manner, the electrical profile of only the left half of the display 600 can be measured by applying a non-zero voltage to the pixels in only the left half of the display and measuring the current through the Vcom604 line. Of course, this example can be extended to measure the electrical profile of any sub-area of ​​the display by selecting pixels and receiving a non-zero voltage only within that area. This configuration can also be extended to drive a non-contiguous set of display pixels.

[0078] In operation, various waveforms can be employed to perform area-specific electrical measurements. A "waveform" is defined herein as a set of voltage lists for transitioning from one grayscale graytone to another grayscale graytone of the same or a different grayscale. In some embodiments, electrical properties measured within an area of ​​the display can be used as input to select an appropriate waveform to apply to that area of ​​the display. This can be done for multiple areas of the display, and various waveforms can be chosen to effect desired transitions in various regions of the display. For example, a complete waveform file can contain many temperature-appropriate waveforms designed to effect desired transitions across specific temperature zones, with one waveform for each temperature zone. In some embodiments, input from a temperature sensor can be used to select an appropriate waveform for the measured temperature. For example, a controller can take both temperature and area-specific electrical information as input. The area-specific electrical information can be used to provide information about temperature differences between various portions of the display, and the waveforms applied to various portions of the display can be shifted based on the electrical measurements. When the electrical measurements give an indication that a temperature difference exists between the left and right halves of the display, this information can be used to select two different waveforms, one for the left half and one for the right half of the display, based on an estimate of the temperature difference inferred from the region-specific electrical measurements. This concept can also be extended to select waveforms based solely on electrical measurements, i.e., a temperature sensor would not need to be used.

[0079] In one embodiment, the source driver 610 may be used to drive "drive pixels" at a voltage low enough that the electrical measurements do not significantly disturb the display image. In another embodiment, the electrical measurements may be performed using very short voltage pulses, so that the display image is effectively undisturbed during the electrical measurements. In yet another embodiment, the seam between two adjacent regions to which two distinct waveforms are applied may be "blurred" through a dither mask between the two regions, with the dither pattern determining which pixels receive which of the two waveforms. The dither is set to provide a gradient from one region where all pixels receive one waveform and an adjacent region where all pixels receive a second waveform, allowing a smooth transition within a local fraction of pixels to receive each of the two waveforms across the dithered region.

[0080] Thus, when a display has substantial temperature differences across its surface, a single waveform applied across the entire display gives undesirable performance; using the driving methods or schemes described herein allows a series of different waveforms to be applied to different segments of the display surface to compensate for temperature variations across the display surface.

[0081] Alternatively, referring now to FIG. 7 , an active matrix display 700 can be updated using an external source through a common electrode, and the electrical response of the ink 702 can be measured on the same Vcom line 704. A known voltage signal can be injected through the common electrode, while all pixel electrodes are connected to a known voltage, e.g., ground. To close the circuit loop, all TFTs in the active matrix are turned on simultaneously. In this configuration, all display electrodes can be treated as one single electrode covering the entire display area. More flexibility is gained in this method, since any signal can be applied to the common electrode without limitations due to scanning operation requirements. From the output of the signal generator 706 and the measured electrical response, the electrical properties of the electrophoretic layer can be inferred.

[0082] In use, for example, a low-amplitude voltage can be applied to the top plane 708 by the signal generator 706 shown in FIG. 7. This voltage can be low enough in amplitude so as not to disturb the optical state of the display to an extent that is noticeable to an unfamiliar observer, and large enough to allow a sufficient signal-to-noise ratio for the current measurement to provide reliable information. In some embodiments, voltages in the range of 10 to 100 mV can be used here. In another embodiment, an oscillating voltage, e.g., a 50 mV, 1 Hz square wave or sine wave, can be applied for a finite time. The in-phase portion of the current can be measured to provide a value that correlates to the effective resistance of the display. This effective resistance can then be correlated to the electro-optical behavior of the display film, and thereby used to select an appropriate waveform for updating during standard display operation. For example, if sine waves of different frequencies are applied to the top plane 708, the impedance of the display 700 can be calculated from the electrical response at each frequency.

[0083] 8 shows a set of impedance measurements from an exemplary active matrix display module using the methods described herein. The setup described herein provides flexibility in the types of input signals that can be used and the electrical properties that can be measured, and can be easily implemented to measure the entire display module.

[0084] Referring now to FIG. 9, in one embodiment, impedance measurements may be taken over the entire active matrix display area. In this configuration, the display's VCOM line, which typically supplies a common bias voltage to the display's front plane or top electrode and its transistor array, may be split into two lines. One line, VCOM_TFT 916, supplies bias voltage to the display's transistor network or active matrix of thin film transistors (TFTs), typically by supplying the bias voltage to the terminal of each pixel's reservoir capacitor opposite the terminal connected to the pixel electrode. The other line, VCOM_FPL 912, supplies bias voltage to the display's front plane or top electrode.

[0085] 9, this setup or configuration may include an active matrix display module 901 including a display controller circuit, which may consist of an active matrix display and source / gate drivers, an EPD controller 902, a power management integrated circuit (PMIC) 903 that controls the supply of high (i.e., VGH) and low (i.e., VGL) gate voltages, source voltages (VPOS and VNEG), both VCOM voltages, and a signal that may turn on all transistors of the active matrix (e.g., an XON signal), a host processing unit 904, a temperature sensor 905, and circuitry for performing impedance measurements 906. The circuitry may be configured to perform measurements at a single frequency or be able to sweep across different frequencies, and one or more switches 907, 908 are included to enable normal drive when closed and perform impedance measurements when open.

[0086] In some embodiments, to activate the impedance measurement, the gate high voltage or VGH is initially set to a voltage between 2 volts and 10 volts. A signal can then be sent to turn on all transistors in the active matrix. This signal, such as an XON signal, can be known in the art to perform such a task. The XON signal can be enabled either from the PMIC 903 or from a GPIO of the EPD controller 902. The impedance measurement circuit 906 can then be enabled by setting a signal (e.g., IMP-EN 910) to an appropriate voltage level. Once the impedance measurement circuit 906 is enabled, switches 907 and 908 can be set to an open state, thereby isolating the VCOM_FPL 912 line to the active matrix module 901. A sinusoidal voltage signal of a given frequency V can be sent to the VCOM_FPL line 912, allowing access to the top electrode of the display 901. The amplitude of this signal can be set small (e.g., less than 1 volt) so as not to excite nonlinearities in the ink system. Also, due to the small voltage amplitude of the signal, the optical effect is minimal and typically not noticeable to the viewer when the impedance measurement is active.

[0087] In some embodiments, when the XON signal and the VGH voltage are both on, access to all pixelated electrodes can be achieved through the ground line GND 914. The current drawn on the VCOM_FPL line 912 can also be measured in the impedance circuit 906. In this case, the voltage and current can be analyzed, and electrical properties such as phase shift can be obtained. In practice, the impedance measurement can be frequency f [Hz] dependent. For example, 5 to 10 cycles of measurement data may need to be first collected before the data can be analyzed. Therefore, a minimum measurement time of 5 / f [s] is required, which is at least 5 seconds at 1 Hz, while at 10 Hz, it may only be 0.5 seconds.

[0088] 10, after an active update 1002, the IMP-EN switch may be switched on, as may the gate high voltage VGH, and an impedance measurement may be taken for the duration 1004 that VGH is turned on. It should be understood that impedance measurements using the methods described herein may be taken while the display is idling, in this case a full frequency scan may be performed.

[0089] In yet another embodiment, impedance measurements may be taken from unused areas of the module, for example, within a boundary area around the perimeter of the pixel array. In this case, referring now to FIG. 11 , direct access to the bottom electrode of the boundary area may be achieved through a boundary electrode line (e.g., boundary line 1130). In some embodiments, the high gate voltage and XON signal may not need to be activated, and measurements may be taken at any time. As shown in FIG. 11 , XON signal accessibility is no longer required, and measurements may be taken across boundary 1130 and the VCOM_FPL 1112 line.

[0090] In another embodiment, a dedicated area may be designed into the active matrix module for the purpose of impedance measurement.

[0091] The use of impedance measurements for waveform selection in accordance with the subject matter presented herein, instead of using temperature sensor measurements, has the advantage of achieving better performance on the display. This is due, at least in part, to the fact that impedance is a direct measurement of the ink system, as opposed to a separate temperature sensor within the device, which may only approximate the temperature experienced by the ink system therein. Impedance measurements can be used to quantify the aging of the display module. This information may be used to assist in the selection of an appropriate waveform for the load to compensate for module aging. When a database of waveforms is associated with different impedance data, it is possible to select the optimal waveform for a given time and module that can most closely match the device-level impedance information.

[0092] It will be apparent to those skilled in the art that numerous changes and modifications may 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 should be interpreted in an illustrative sense, and not in a restrictive sense.

Claims

1. 1. A method for driving an electro-optic display comprising a layer of electro-optic material disposed between a common electrode and a backplane, the backplane including an array of pixel electrodes, each pixel electrode coupled to a pixel transistor, and a display controller circuit applying waveforms to the array of pixel electrodes by applying one or more time-dependent voltages between the common electrode and the array of pixel electrodes via the pixel transistors, the method comprising: applying a first measurement waveform comprising one or more frames to a first portion of pixel electrodes of the array of pixel electrodes, wherein during each frame of the first measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the first portion of pixel electrodes; measuring a first current flowing through a current measurement circuit during a normal scanning mode, the current measurement circuit coupled between the common electrode and an output of the display controller circuit that applies a time-dependent voltage to the common electrode, the current measurement circuit comprising a resistive element and a differential voltage amplifier, a first input of the differential voltage amplifier connected to a first terminal of the resistive element and a second input of the differential voltage amplifier connected to a second terminal of the resistive element, the current measurement circuit interposed between a Vcom line of the display controller circuit and a top plane electrode of the common electrode; determining a first impedance of the electro-optic material proximate to the first portion of the pixel electrodes based on the first current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the first measurement waveform; selecting a first drive waveform for application to each pixel electrode in the first portion of the pixel electrodes based on the first impedance of the electro-optic material proximate to the first portion of the pixel electrodes; applying the first drive waveform to a first portion of the pixel electrode, the first drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the first portion of the pixel electrode; A method comprising:

2. The method of claim 1 , wherein the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes comprises a uniform voltage pulse.

3. 2. The method of claim 1 , wherein the time-dependent voltage applied to each pixel electrode of the first portion of pixel electrodes comprises a first voltage pulse having a first polarity and a second voltage pulse having a second polarity opposite to the first polarity.

4. The method of claim 1 , wherein the first portion of pixel electrodes comprises all of the pixel electrodes of the array of pixel electrodes.

5. The method of claim 1 , wherein the first portion of pixel electrodes comprises pixel electrodes located proximate to the periphery of the array of pixel electrodes.

6. applying a second measurement waveform comprising one or more frames to a second portion of pixel electrodes of the array of pixel electrodes, wherein during each frame of the second measurement waveform, the same time-dependent voltage is applied to each pixel electrode of the second portion of pixel electrodes; measuring a second current flowing through the current measurement circuit; determining a second impedance of the electro-optic material proximate a second portion of the pixel electrodes based on the second current flowing through the current measurement circuit and the time-dependent voltage applied to each pixel electrode of the first portion of the pixel electrodes during the second measurement waveform; selecting a second drive waveform for application to each pixel electrode in the second portion of pixel electrodes based on the second impedance of the electro-optic material proximate to the second portion of pixel electrodes; applying the second drive waveform to a second portion of the pixel electrode, the second drive waveform comprising a time-varying voltage sufficient to change the optical state of the electro-optic display adjacent the second portion of the pixel electrode; The method of claim 1 further comprising:

7. 7. The method of claim 6, wherein the first portion of pixel electrodes comprises pixel electrodes from a first region of the array of pixel electrodes, and the second portion of pixel electrodes comprises pixel electrodes from a second region of the array of pixel electrodes, and the first and second regions of pixel electrodes do not overlap.

8. applying a first measurement waveform to a first portion of the pixel electrodes while applying a zero volt waveform to a second portion of the pixel electrodes; applying a zero volt waveform to a first portion of the pixel electrodes while applying a second measurement waveform to a second portion of the pixel electrodes; The method of claim 6 further comprising:

Images