Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-10-25
2003-02-11
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C349S113000, C349S115000, C349S116000
Reexamination Certificate
active
06518944
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to liquid crystal display device which functions both as a cholesteric reflective flat-panel display and a solar cell assembly to provide electrical energy to power the display and associated electronics and, more particularly, to a liquid crystal display device including a passive matrix, bistable, cholesteric liquid crystal display having one or more solar cells disposed in alignment with the display and adjacent a substrate bounding a layer of cholesteric liquid crystal material, the one or more solar cells providing electrical energy to power display electronics.
BACKGROUND OF THE INVENTION
Typically, a reflective liquid crystal display comprises a single layer of liquid crystal material sandwiched between adjacent inner surfaces of generally planar substrates. In matrix type liquid crystal displays, on the inwardly facing surface of one of the substrates is disposed a set or array of parallel column electrode segments (column electrodes) and on an inwardly facing surface of the other of the substrates is a set or array of parallel row electrode segments (row electrodes), extending generally perpendicular to the column electrodes. The row and column electrode segments (also referred to as “row and column electrodes”) are spaced apart by the thin layer of liquid crystal material. Display picture elements or pixels are defined by regions of liquid crystal material adjacent the intersection of the row and column electrode segments.
Upon application of a suitable electric field, a pixel of a display will assume either a reflective or a non-reflective state. A pixel, P(xi,yj), formed at the overlapping or intersection of the ith row electrode segment and the jth column electrode segment is subject to an electric field resulting from the potential difference between a voltage applied to the ith row electrode segment and a voltage applied to the jth column electrode segment.
Recent advances in liquid crystal material research have resulted in the discovery of bistable cholesteric (also referred to as chiral nematic) liquid crystal display devices. Cholesteric liquid crystal display materials are able to maintain a given reflective state (reflective or nonreflective) without the need for the constant application of an electric field. In a reflective cholesteric liquid crystal display, the reflectivity of an image pixel depends upon the configuration or texture of the liquid crystal material (e.g., planar, focal conic, homeotropic configurations) defining the image pixel. Moreover, the state of the liquid crystal material may be changed upon imposing an appropriate electric field across the liquid crystal material for an appropriate period of time. This is accomplished by appropriately energizing the row and column electrodes defining an image pixel so as to generate an electric field having a desired magnitude (that is, a desired root mean square (rms) voltage) for a desired period of time. If the panel or substrate furthest from the viewer is painted with a black material, a pixel with a low reflectance or nonreflective state will appear as a black area to the viewer. A pixel in a high reflectance state will appear to the viewer as a visible colored area in the display.
Display driver circuitry is coupled to the vertical and horizontal electrodes. Operating under the control of a logic and control unit, the display driver circuitry energizes the row and column electrodes with appropriate voltage waveforms such that an appropriate voltage across each pixel is generated. The voltage across a pixel will either cause it to remain in its present state of reflectance or change its state of reflectance. The image generated by the display pixels may be modified by changing the state of selected pixels. In this way, text or image data can be presented for viewing on the display.
Certain prior art calculators and watches have included both a liquid crystal display and a solar cell assembly to provide electrical energy to the device electronics. However, in such devices, the display and the solar cell or cells have been disposed in different areas of the device, that is, the display area and the solar cell area do not overlap. This requires a device with a surface area large enough to accommodate both the solar cell area and the area of the display. This type of configuration is disadvantageous in small sized hand held devices were surface area is at a premium.
SUMMARY OF THE INVENTION
The present invention is directed to a cholesteric liquid crystal display utilizing a solar cell assembly as a power source for powering the display electronics. The display includes a front substrate, closest to a viewer, a back substrate and a thin layer of cholesteric liquid crystal material sandwiched therebetween. On an inner surface of the front substrate (that is, the surface of the substrate adjacent the liquid crystal material) is disposed a set or array of electrode segments and on an inner surface of the back substrate is a set or array of electrode segments, extending generally perpendicular to the column electrode array. In one configuration of the present invention, the display is a matrix display and one set of electrode segments comprises a set of parallel row electrode segments and the other set of electrode segments comprises a set of parallel column electrode segments. The row and the column electrode segments are substantially orthogonal. This arrangement of perpendicular row and column electrodes results in an orthogonal pattern of image pixels (orthogonal display). It should also be appreciated that the present invention is equally suited to providing power to other types of liquid crystal displays in addition to orthogonal displays such as, for example, segmented displays. While a segmented display also includes electrodes which may be fabricated in various shapes and disposed in orthogonal or non-orthogonal orientations to generate desired image configurations. For example, in a segmented liquid crystal display electrode segments may advantageously be disposed to create a seven segment numerical display. In other segmented displays, electrode segments of irregular shape may be used to generate an icon on the display. Moreover, it should additionally be appreciated that the concept of the present invention of using a solar cell assembly in a cholesteric liquid crystal display to provide power to display electronics is equally applicable to active matrix cholesteric liquid crystal displays in addition to passive matrix cholesteric liquid crystal displays. An actively driven matrix cholesteric liquid crystal display is one in which where each of the image pixels is driven individually by an active circuit component, e.g., a transistor. An active matrix Ch-LCD is disclosed in an article entitled “Amorphous Silicon Thin-Film Transistor Active-Matrix Reflective Cholesteric Liquid Crystal Display,” authored by J. Y. Nahm, T. Goda, B. H. Min, T. K. Chou, J. Kanicki, X. Y. Huang, N. Miller, V. Sergan, P. Bos and J. W. Doane and published in the Proceedings of the 18th International Display Research Conference, Seoul, Korea, September 1998, pages 979-982. The aforesaid active matrix Ch-LCD article is incorporated herein in its entirety by reference.
In one embodiment of an orthogonal Ch-LCD, display drive electronics include a set of row driver electronics electrically coupled to the row electrode segments that controls energization of all of the row electrodes and a set of column driver electronics electrically coupled to the column electrode segments that controls energization of all of the column electrode segments in the plurality of sets of column electrodes. The sets of row and column driver electronics constitute a single set of drive electronics.
The cholesteric or chiral nematic liquid crystal material is unique and advantageous in that it permits illumination incident on the display to pass through the liquid crystal material and impinge upon the solar cell. Typical nematic liquid crystal material displays such as twisted nematic (T
Davis Donald James
Doane J. William
Miller, IV Nick M.
Hjerpe Richard
Kent Displays, Inc.
Nguyen Frances
Watts Hoffmann Fisher & Heinke
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