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

Claim 1

In an electro-optical display device for the display of dark symbols against a bright background, wherein a plurality of separately selectable display segments are formed by a transparent front electrode applied to the surface of a transparent front cell plate and a rear electrode applied to the surface of a rear cell plate between which is located an electro-optical medium formed by a guest-host liquid crystal mixture, in particular a cholesteric liquid crystal with at least one added pleochroic dye, said cholesteric liquid crystal exhibiting a transition voltage where the cholesteric liquid crystal phase transforms to a nematic phase, said front electrode composed of a plurality of electrode elements that are electrically insulated from each other, said rear electrode composed of at least two electrode elements that cover nearly the entire area of the rear cell plate except for fine separation lines which serve to insulate them from each other, said front and said rear electrode elements having conduction paths leading to them, said front electrode having narrow separation lines which serve to electrically insulate the electrode elements thereof from each other and whose dimensions are small compared to the dimensions of the displayed symbols, said front electrode, except for said narrow separation lines, covering nearly the entire area of the front cell plate, and wherein at least one section of the separation line on the front electrode coincides with at least one third of the circumference of at least one display segment of a display symbol and at least one section of the separation line on the rear electrode coincides with at least one third of the circumference of the same display segment, improved means for driving the front and rear electrodes corresponding to an optically selected display element, comprising: means for addressing the display device whereby selected electrode segments are displayed against said bright background, said addressing means comprising, first means for applying first unipolar addressing signals to the selected front and rear electrodes corresponding to the selected display segments of a desired symbol, said first addressing signal having the same amplitude, frequency, phase and waveform, and second means for applying second addressing signals to the front and rear electrodes corresponding to unselected display segments, said second signals producing a potential difference in every region of the display background larger than the transition voltage of the electro-optical medium.