The present invention concerns an electro-optical passive timepiece display comprising a first display cell, a second display cell superposed on said first display cell and located in a different plane therefrom, said first cell comprising analog time indication means and said second cell comprising an alphanumeric or digital indicator.
A watch possessing a double superposed liquid crystal display cell is already known from the state of the art which shows in one position of a manual display control the hour, minute, second and date and in the other position of said control the display of the monthly calender. An examination of this timepiece shows that utilisation of liquid crystal display permits the obtaining of an information display density clearly greater than with a standard classical hands display. Continual efforts are being made to increase this density but often with the detriment of an unacceptable readibility. One may thus not reduce the dimensions of digits, signs or symbols below a certain lower limit, and in the same manner one may not squeeze together beyond a certain limit these digits or signs. Under such conditions one might considerably increase the display surface but this solution leads immediately to an excessive overall dimension.
U.S. Pat. No. 4,095,405 describes an LCD digital display of a single layer wherein the date indication is located in the center of the dial of the watch. In addition to the fact that such an arrangement necessitates the utilisation of hands of rather short length, thereby poorly reproducing the hands of the mechanical watch, it does not enable increasing the information density so as to be able to add to the watch a chronograph function showing tenths or even hundredths of a second for instance.
To overcome such difficulties it has already been proposed to provide a double layer display superposed as mentioned above. In one example thereof each LCD cell is enclosed in sandwich form between two very thin glass retainers, the units thereby obtained being fastened one under the other by means of an optical glue or another type of glue located outside the field of vision. In an other example each cell is placed on opposite sides of a glass layer, the unit thus formed being sandwiched between two further glasses. In the one example as in the other, each of the cells thus formed provides information which may be alternately displayed on the one or the other of the displays, through operation of the manual control for instance, or else simultaneously on both displays. If the information thus displayed is simultaneous, two cases may occur according to whether the information is superimposed or not. If a choice is made for an analog display of time information by electro-optical methods, and for the other display a digital indication of the date, there will obviously necessarily arise situations in which one type of information is concealed by the other information as would be the case for a mechanical watch or electro-mechanical watch. Thus, it is known in examples of realisation of the type of cells mentioned above that when two activated zones are superimposed result will be suppressed, this leading to non-excited zones and thereby rendering difficult the reading of the information.