Alpha-numerical display device

Abstract: In an alpha-numerical display the segments are split up into (interconnected) sub-segments in such a way that characters can always be displayed in a manner analogous to that for a matrix display. This provides the advantages of a great freedom of choice of characters with a drive mode (1:n multiplexing, n ≦ 4) yielding a large viewing angle and a high contrast.

Description: The invention relates to an alpha-numerical display device comprising an electro-optical material sandwiched between a first supporting plate having at least one electrode and a second supporting plate having a set comprising seven rows and five columns of character elements formed by generally polygonal electrode segments in which an electrode segment of the second row is interconnected to a corresponding electrode segment of the third row and in which an electrode segment of the fifth row is interconnected to a corresponding electrode segment of the sixth row. In United States Patent no. 3,781,864 a liquid crystal display device is shown with a counterelectrode on the one supporting plate and 7 electrode segments for each character on the other supporting plate, and it describes the drive mode for such a display device. Substantially only numerals are shown while using the so-called direct drive method. In this drive method a segment to be visualized is continuously driven, while the polarity of the drive voltage is periodically changed so as to prevent degradation of the liquid crystal. Therefore, a separate connection is required for each electrode segment. It has been possible to reduce the number of required connections in such display devices by splitting up the undivided counter electrode into two or more parts and by ensuring the drive mode by way of multiplex drive (1:2 multiplexing, 1:3 or 1:4 multiplexing). Notably at a higher multiplex degree (5 or more) this leads to a more complicated drive mode as well as to a lower effective drive voltage across the picture segments to be driven. Notably when using liquid crystalline material as an electro-optical medium, such a lower effective voltage leads to a decrease of the viewing angle. The contrast also deteriorates at a multiplex degree of more than 4. Another drawback of the device of US-A-3.781.864 is the limited variation of the characterers to be displayed due to the limited number and particular shape and position of the electrode elements, each being formed by a particular electrode segment. This is much less the case if the characters are composed of elements arranged in accordance with a matrix, for example, n rows and m columns defining nxm character elements. As n and m increase, the characters can be fixed more accurately. However, this requires a complicated drive circuit (1: n multiplexing), while the effective voltage may even further decrease due to the lower duty cycle (1/n) (n is generally high, for example, n ≧ 8). A display device with a set of seven rows and five columns of character elements arranged in a matrix is known from European patent application number EP-A-164.152. The matrix is formed by generally square electrode segments which are mutually interconnected to form commonly adressable electrode sections in order to reduce the required number of connections. As such, each segment of the second row is interconnected to a corresponding electrode segment of the third row and each electrode segment of the fifth row is interconnected to a corresponding electrode segment of the sixth row. Although three- or even fourfold multiplexing is used in this known device to reduce the number of electical connections, it still requires 15 respectively 10 electrode lines in total for each character to be displayed. It is one of the objects of the invention to provide a display device of the type described in the opening paragraph in which the advantages of a drive mode using a low multiplex degree (up to 1:4) and a display device based on the matrix principle are combined as much as possible in order to realize a relatively small number of required electical connections already at a comparatively low degree of multiplexing. To this end a display device according to the invention is characterized in that each corner element of said set comprises two triangular electrode segments separated along the diagonal direction, in that one of said triangular segments is connected to two or more mutually interconnected segments of the same column and in that the other triangular segment is connected to two or more mutually interconnected segments in the next two rows lying in the adjacent column. The second supporting plate preferably has at least twelve electrode sections and their square-shaped, rectangular or parallelogram-shaped electrode segments occupy the majority of the character elements. The division of the electrode into (a large number of) segments gives the device a matrix structure which allows a wide range of characters to be displayed, while a convenient division of the segments over electrode sections together with a suitable form of the segments offers a considerable reduction of the required number of electrical connections already at a comparatively low degree of multiplexing. The use of a low multiplex degree yields a large viewing angle and a high contrast. Incidentally, a display device with different forms of electrode segments is in itself known from European patent application number 255.158. In this known device however, hardly none of the electrode segments is mutually interconnected to another electrode segment to form a commonly addreassable electrode section. As a result as much as 41 electrode connections are required for each character to be displayed. The invention will now be described in greater detail by way of example with reference to the accompanying drawings in which Fig. 1 shows diagrammatically the distribution according to the invention of a plurality of electrode segments over a number of electrode sections, while Fig. 2 shows a matrix of character elements, and Fig. 3 shows the display of a plurality of alphanumerical characters by means of a display device according to the invention. Fig. 1 shows diagrammatically the division of the electrode sections 1, 2, 3, ...., 12 on one of the supporting plates of a display device. The device also comprises a second supporting plate having one or more counterelectrodes (at most 4), while an electro-optical material, for example, a liquid crystalline medium is present between the two supporting plates. The boundaries of the different electrode sections 1, 2, 3, ...., 12 are denoted by means of broken lines in Fig. 1. According to the invention the electrode sections comprise mutually interconnected electrode segments 21, 22, 23, which electrode segments are formed in such a way that they occupy substantially entirely one of the character elements 30 on their own or together with other electrode segments in a matrix of character elements 30, as is shown in Fig. 2. For example, electrode section 1 comprises three substantially square-shaped electrode segments 21 in this embodiment, which electrode segments correspond to the character elements 30 ab , 30 ac , 30 ad in Fig. 2. Electrode section 2 comprises four substantially square-shaped electrode segments 21, which substantially entirely cover the character elements 30 bc , 30 cc , 30 ec and 30 fc , as well as a connection track 15 which connects the electrode segments 21 associated with the character elements 30 cc and 30 ec , and a triangular electrode segment 22 which together with a triangular electrode segment 22 associated with electrode section 10 substantially entirely covers the character element 30 dc . Electrode section 3 comprises a triangular electrode segment 22 which together with a triangular electrode segment 22 associated with electrode section 4 substantially entirely covers the character element 30 ae . Furthermore, the electrode section 3 comprises two pentagonal electrode segments 23 at the location of the character elements 30 bd , 30 cd , while electrode section 4 further comprises two substantially square-shaped electrode segments 21 at the location of the character elements 30 be and 30 ce . Similarly, electrode section 5 comprises three substantially square-shaped electrode segments 21 and a triangular electrode segment 22 which together with a triangular electrode segment 22 of electrode section 6 again substantially entirely covers the character element 30 ge , while electrode section 6 further comprises two pentagonal electrode segments 23. Electrode section 7 comprises three substantially square-shaped electrode segments 21. The electrode sections 8 and 9 can be described similarly as the electrode sections 3 and 4. In addition to the mentioned triangular electrode segment 22, the electrode section 10 comprises two substantially square-shaped electrode segments 21. The electrode sections 11 and 12 may be described similarly as the electrode sections 5 and 6. In the above-described configuration with twelve electrode sections the substantially square-shaped electrode segments occupy the majority of the character elements 30 (22 out of 35 character elements). The electrode sections have connection conductors 13 for external connections. If desired, the electrode section 2 may be connected at two ends, which is shown diagrammatically by means of the dot-and-dash line 14. Since the electrode sections can be driven directly or with a low multiplex degree (by means of a selection circuit which is not further described), a large viewing angle and a high contrast is obtained when using a liquid crystal display device. A satisfactory display of alpha-numerical characters can be simultaneously obtained by means of the sub-division into electrode segments. A plurality of characters has been shown in Fig. 3 for the purpose of illustration. Another division with fifteen electrode sections is shown in Fig. 4. The electrode sections 1, 3, 4, 5, 6, 7, 8, 9, 11 and 12 are comparable to those in Fig. 1. Instead of the electrode sections 2, 10, the device according to Fig. 4 now has electrode sections 16, 17, 18 each comprising one electrode segment and occupying the character elements 30 db , 30 dc and 30 dd as well as the electrode sections 19 and 20. Each electrode section 19, 20 comprises two square-shaped electrode segments 21 at the location of the character elements 30 bc , 30 cc and 30 ec , 30 fc , respectively. For the purpose of illustration, Fig. 5 shows a plurality of characters displayed by means of a distribution of electrode segments over electrode sections according to Fig. 4. The invention is of course not limited to the examples shown, but only by the appendent claims. Many other shapes, notably of the electrode segments 21, are possible, for example, rectangular or parallelogram shapes. Different distributions of the electrode segments over the electrode sections are alternatively possible.

Claims: An alpha-numerical display device comprising an electro-optical material sandwiched between a first supporting plate having at least one electrode and a second supporting plate having a set comprising seven rows and five columns of character elements (30 aa -30 ge ) formed by generally polygonal electrode segments (21-23) in which an electrode segment of the second row is interconnected to a corresponding electrode segment of the third row and in which an electrode segment of the fifth row is interconnected to a corresponding electrode segment of the sixth row, characterized in that each corner element (30 aa ,30 ae ,30 ga ,30 ge ) of said set comprises two triangular electrode segments (22) separated along the diagonal direction, in that one of said triangular segments is connected to two or more mutually interconnected segments of the same column and in that the other triangular segment is connected to two or more mutually interconnected segments in the next two rows lying in the adjacent column. An alpha-numerical display device as claimed in claim 1 characterized in that the other triangular segment is connected to two mutually interconnected segments in the next two rows and in the adjacent column, which each have a pentagonal shape (23) with one side substantially parallel to said diagonal direction. An alpha-numerical display device as claimed in claim 1 or 2 characterized in that the central character element (30 dc ) comprises two triangular electrode segments (22) separated along the diagonal direction, in that one of said two triangular segments is connected to the electrode segments in the adjacent columns lying within the same row (10) and in that the other of said two triangular segments is connected two the electrode segments in the next and in the previous two rows lying within the same column (2). An alpha-numerical display device as claimed in claim 1 or 2 characterized in that the central character element (30 dc ) and the adjacent character elements (30 db ,30 dd ) within the same row are each formed by a single electrode segment (16,17,18) which is separately connected.

Inventors: VAN ALMEN JACOBUS JOHANNES, VAN ALMEN, JACOBUS JOHANNES
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1990
Main classification: G09F9
IPC codes: G02F1, G09F9, G09G3