Liquid crystal display device

Claim 1

An electro-optic liquid crystal matrix display device comprising: two parallel supporting plates, patterns of strip-shaped electrodes crossing each other on facing surfaces of said supporting plates to form a matrix of display elements at said crossings, a layer of cholesteric liquid crystal between said facing surfaces and having a positive dielectric anisotropy, wherein said layer has at least one of a substantially transparent planar-conical texture or a light-scattering focal-conical texture below a first field strength E 1 , a transparent homeotropic-nematic texture above a second field strength E 2 , and at least one of a light-scattering focal-conical texture or a transparent homeotropic-nematic texture at field strengths between E 1 and E 2 , such that said liquid crystal exhibits hysteresis upon application of voltage to said device, wherein said liquid crystal has a negative dielectric anisotropy above a critical frequency of said electric field, such that said liquid crystal combines hysteresis with dielectric anisotrophy inversion, means for applying an electric field at a frequency below said critical frequency over each display element to provide said transparent homeotropic-nematic texture in said display elements, means for applying display signals to at least selected display elements to provide said light-scattering focal-conical texture in said selected display elements, wherein non-selected display elements remain in said transparent homeotropic-nematic texture, and means for applying an electric field at a frequency above said critical frequency over said non-selected display elements to provide said transparent planar-conical texture in said non-selected display elements, said selected display elements remaining in said light-scattering focal-conical texture.