Electro-optical device for the display of dark symbols composed of separately selectable display segments against a bright background and a means for addressing this device
An electro-optical display for the display of dark symbols against a bright background, wherein except for fine separation lines the front and rear cell plates are almost entirely covered with isolated electrode elements. The regions of overlap between these various front and rear electrode elements define the areas of the selectable display segments. The display employs an electro-optic media requiring no polarizers, for example, cholesteric liquid crystals to which has been added pleochroic dyes, or electrophoretic suspensions. The display device is addressed through the application of appropriate signals to the electrodes so that a vanishingly small potential difference lies across the liquid crystal layer in the region of the selected display segments which remain dark. In all the other regions of the display, however, there exists a potential difference which is larger than the transition voltage of the electro-optical medium, and these regions therefore appear as a bright background. The addressing is preferably carried out using unipolar pulsed signals which are applied to the electrode elements of the front and rear cell plates, with those electrodes corresponding to optically selected display segments receiving signals having the same phase and amplitude.
A color liquid crystal display device wherein a nematic liquid crystal to which a dichroic dye and an optically active substance have been added is used as the liquid crystal layer and the amount of said optically active substance added is so selected as to fall in a range making steep the threshold voltage characteristics of the liquid crystal.
