Patent ID: 6903784
Filing Date: 2005-06-07
Classification: G02F,G04G

Abstract:
1. A display assembly with two superposed contrast inversion display devices, the assembly including: a first display device; and a second active display device having a double structure, one structure being formed by a first contrast inversion display device provided by a twisted nematic liquid crystal dot matrix display cell or by a digit twisted nematic liquid crystal display cell, the liquid crystals of the one structure being confined in a space delimited by two transparent substrates and having two switching states, and the other structure being formed by a second contrast inversion display device provided by a twisted nematic liquid crystal optical valve, the liquid crystals of the other structure being confined in a space delimited by two transparent substrates and having at least two switching states and control means allowing an appropriate voltage to be selectively applied to the display cell and optionally to all or part of the valve to cause each liquid crystal to switch from one state to another, wherein the second active display includes only two polarisers such that a first absorbent or reflective front polariser is arranged at the front of the display cell and in that a second back polariser, crossed with the front polariser or parallel thereto, is arranged at the back of the valve so that when the display cell is switched to display at least one item of data, the total or partial switching of the valve, from one state to another, inverts the contrast of the data displayed from a light appearance to a dark appearance or vice versa, wherein the first display device has a dark shade and the back polariser is a reflective polariser, and wherein the first contrast inversion display device and the second contrast inversion display device are superposed; wherein the back polariser is crossed with the front polariser, the display cell and the optical valve both have positive anisotropy or both have negative anisotropy, and wherein the at least two switching states comprise: a first switching state wherein the display cell is switched OFF and the optical valve is switched OFF, and the first display device is hidden by a mirror mask; a second switching state wherein the display cell is switched ON and the optical valve is switched OFF so a portion of the first display device is seen through a transparent window and the display cell shows data in the dark shade on a light background; a third switching state wherein the display cell is switched OFF and the optical valve is switched ON so that only the first display device is seen; and a fourth switching state wherein the display cell is switched ON and the optical valve is switched ON so the first display device is seen and the display cell shows data in a light color on a dark background.