Disclosed is an electric visual display. More particularly, an electric paper display using a thin film transistor active matrix array and integrated addressing logic to control the output of the display is disclosed useful, for example, as point of purchase signs.
Traditional signs have been based upon printed materials, paper, plastic, metal, etc., and are, therefore, not programmable. Accordingly, they are not easily changed. In an attempt to overcome this problem, electronically programmable and/or controllable signs have been in existence for many years. For example, liquid crystal diode (LCD) displays, cathode ray tube (CRT) displays, and other electrically-addressable displays will display an image in response to applied electric signals or fields. However, such signs typically require a large amount of electricity, since they must provide illumination in order to be visible to a viewer.
Electric writeable media, including twisting-cylinder and rotary ball displays, such as those described in U.S. Pat. Nos. 4,126,854 and 4,143,103 to Sheridon, incorporated herein by reference in their entirety, have been developed to overcome the problems with previous programmable signs. Twisting-cylinder displays, rotary-ball displays and related displays have numerous advantages over conventional displays, such as LCDs and CRTs, since they are suitable for viewing in ambient light, they retain an image indefinitely in the absence of an applied electric field, and they can be made to be very lightweight and/or flexible. For further advantages of such displays, see U.S. Pat. No. 5,389,945 to Sheridon, incorporated herein by reference in its entirety. Such displays are referred to herein as “electric paper” displays. An example of such a display is a SmartPaper™ display from Gyricon LLC.
Another type of electric writeable media is known as an electronic ink display, such as the one described in U.S. Pat. No. 6,518,949 to Drzaic, which is incorporated herein by reference. An electronic ink display includes at least one capsule filled with a plurality of particles, made of a material such as titania, and a dyed suspending fluid. When a direct-current electric field of an appropriate polarity is applied across the capsule, the particles move to a viewed surface of the display and scatter light. When the applied electric field is reversed, the particles move to the rear surface of the display and the viewed surface of the display then appears dark.
Yet another type of electric writeable media, also described in U.S. Pat. No. 6,518,949 to Drzaic, includes a first set of particles and a second set of particles in a capsule. The first set of particles and the second set of particles have contrasting optical properties, such as contrasting colors, and can have, for example, differing electrophoretic properties. The capsule also contains a substantially clear fluid. The capsule has electrodes disposed adjacent to it connected to a voltage source, which may provide an alternating-current field or a direct-current field to the capsule. Upon application of an electric field across the electrodes, the first set of particles moves toward a first electrode, while the second set of particles moves toward a second electrode. If the electric field is reversed, the first set of particles moves toward the second electrode and the second set of particles moves toward the first electrode. Other examples of writeable media include liquid crystal diode displays, encapsulated electrophoretic displays, and other displays.
Electric paper displays respond slowly to changes in applied voltage. However, electric paper displays are also generally addressed infrequently. Recent developments in electric paper displays are permitting operation at voltage thresholds of approximately 40V. Current electric displays are driven with crystal silicon integrated circuits in separate packages. Such integrated circuits are costly and increase the size of the display. As a result, new technologies for supplying threshold voltages are being explored.
A thin film transistor (TFT) active matrix array is composed of an array of TFTs. A TFT is a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) implemented using thin film technology. A TFT uses thin films, which may be made of for example, amorphous silicon (a-Si), polycrystalline silicon (p-Si), or which may be an organic material, and a glass substrate. Current flows between the source and drain of a TFT when a voltage is applied to its gate. Thus, by connecting the gate of a TFT to the power rail of the TFT active matrix array, a TFT is turned on (at a positive voltage). If the gate of a TFT is connected to the ground rail, the TFT is turned off (at zero voltage).
Active matrix liquid crystal displays are a well-established technology. The gate voltage swing is typically from −10 V to +15 V, and the data voltage swing is typically ±10V. However, the transistors are capable of withstanding substantially greater voltages. For example, it is reasonable to expect that a transistor with a gate nitride thickness of 300 nm will have a breakdown voltage of more than 50V. Moreover, threshold voltage shifts that are induced by a high gate voltage are insignificant if the transistor is not turned on for a large percentage of time.
Addressing logic has previously been constructed for active matrix liquid crystal display arrays. However, such designs require logic to compensate for threshold drifts of critical transistors.
A need exists for methods and systems of controlling a display that use electric paper and thin film transistor active matrix technologies to provide low power operation and/or pixel-addressability without the need for additional logic to compensate for transistor threshold drifts.
Aspects disclosed herein include
In embodiments there is illustrated:
In an embodiment, an electric display includes a plurality of multichromal media, a thin film transistor active matrix array including a plurality of thin film transistors each having a gate input and a data input, gate control logic coupled to the gate inputs of the thin film transistors, and data control logic coupled to the data inputs of the plurality of transistors. The plurality of thin film transistors may be arranged as one or more rows and one or more columns of thin film transistors, for example, at least one row and at least one column of thin film transistors. In an embodiment, the gate control logic includes a shift register and one or more output buffers. Each output buffer may be coupled to the shift register. In an embodiment, the data control logic includes a shift register, one or more latches coupled to the shift register, and one or more output buffers. Each output buffer may be coupled to one of the latches.
In an embodiment, the electric paper display using a thin film transistor (TFT) active matrix and an integrated addressing logic to control the output of the display is provided, in which a TFT active matrix array is similar to a dynamic random access memory (DRAM) array. In other words, each pixel may be at the intersection of horizontal and vertical address lines and may be addressed by enabling both lines. In one embodiment, when using TFT active matrix arrays with electric paper displays, a localized electric field used to rotate one or more rotatable elements within an electric paper display may be generated from each TFT. A rotatable element may be an anisotropic particle such as, for example, a ball, a cylinder or other particulate matter. The rotatable element may rotate when an electric field is applied across the element while the element is suspended in an electrophoretic substance. As such, an individual TFT may be used as an active switch for each picture element or pixel. Alternatively, multiple TFTs may be used to form a pixel where a first TFT controls rotatable elements of a first color, such as red, a second TFT controls rotatable elements of a second color, such as blue, and a third TFT controls rotatable elements of a third color, such as green. Each sub-pixel TFT may control one or more rotatable elements.
In an alternative embodiment, other multichromal media may be used in place of or in addition to the rotatable elements described above. Such multichromal media may include inks, dyes, pigments, pigment dispersions, dye solutions, multichromal rotatable elements, and other media that can display two or more colors depending on their orientation with respect to a viewer. Furthermore, multichromal media may include any combination of the above-listed exemplary substances or elements.
In the application of electric paper to point of purchase signs, the circuitry to control the sign may only be empowered for a very small portion of the day. For example, if a point of purchase sign were updated once a day, the sign may only be powered for about two minutes per day, or for about 0.14% of the time. If a threshold shift were to occur in a TFT during this time because a voltage surpassing the TFT gate breakdown voltage is supplied to the TFT, the TFT would return to its original state during the time that the circuit is not powered. As a result, control circuitry for a TFT active matrix array used in an electric paper display may be simplified by not accounting for voltage levels greater than the TFT gate breakdown voltage.
Generally, TFT active matrix arrays may be limited by the speed with which they may be updated. Since liquid crystal displays are generally refreshed at 60 Hz, the low mobility of the TFT active matrix array may be unable to provide a complete refresh to a liquid crystal display with a refresh cycle. In addition, as the size of the display increases, the load capacitance and, therefore, the transistor power up time increases as well. In contrast, the addressing speed required for electric paper displays is much slower than for an active matrix liquid crystal display. As a result a TFT active matrix array may be used in an electric paper display to perform the addressing logic of the pixel elements.
In addition, the control circuitry of an electric paper display would differ from active matrix liquid crystal displays in that the gate and data lines would each require only a two-level output. Although the addressing logic for gate lines in an electric paper display and in a liquid crystal display may be similar, the data lines in a liquid crystal display utilizes a range of output voltages to provide the grayscale capability of an LCD. In contrast, in electric paper displays the data lines may require only two states: on or off. In this embodiment, the circuitry may be vastly simplified.
Alternate embodiments may include different numbers of data drivers 101 ad/or gate drivers 106. In addition, different voltage levels may be used for the one or more gate drivers. For instance, where a color electric paper display is used, one or more gate drivers may be used for each color used for a pixel. The gate drivers for each sub-pixel color may be driven at different voltage levels so that only the rotatable elements corresponding to an appropriate color are updated at a given time.
In an alternate embodiment, more than one shift registers may replace the shift register 306 of
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
This application claims benefit of, under 35 U.S.C. §119(e), U.S. Provisional Application Ser. No. 60/570,938, filed May 13, 2004.
Number | Date | Country | |
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60570938 | May 2004 | US |