A DISPLAY DEVICE AND A TELEPHONE SET COMPRISING SUCH A DISPLAY DEVICE

Abstract: Display device (for example, an LCD) in which connections between an IC (6) and an external electronic circuit (21) consist of satisfactorily conducting tracks, for example, gold tracks extending on a separate connection component (14). This connection component may be made of, for example, a flexible material and can be clamped.

Description: A DISPLAY DEVICE AND A TELEPHONE SET COMPRISING SUCH A DISPLAY DEVICE The invention relates to a display device comprising a display panel with a supporting plate which supports an IC, and an external electronic circuit arranged outside the supporting plate, in which electrically conducting connections extend between the IC and the external electronic circuit. Usually, the electrically conducting connections between the IC and the external electronic circuit are established by means of ITO (indium tin oxide) tracks on the supporting plate, which lead from the connections of the IC to electrically conducting wires connected to the external electronic circuit. However, if in the display panel a voltage is used which is much higher than the power supply voltage, it appears that the up-transformation, which is effected in the IC, does not always function properly. The invention is based on the recognition that this is caused by the fact that the ITO tracks have a much higher resistance than metal tracks, such as copper tracks. It is an object of the invention to reduce the electrical resistance of the tracks establishing electrically conducting connections between the IC of a display device and the external electronic circuit. To this end, the display device according to the invention is characterized in that the display device is provided with a separate connection component on which electrically conducting tracks extend which have a lower electrical resistance than ITO tracks and connect the IC connections to the external electronic circuit. By reducing the electrical resistance, the up-transformation of the voltage in the IC of the panel functions much better. The separate connection component on which the electrically conducting tracks extend is preferably made of a flexible material so that it can be clamped into a cavity or between two flat plates. The clamping yields a satisfactory physical contact between the connection component with the conducting tracks and the ITO tracks on the glass, which enhances the electrical contact. Moreover, possible unevennesses in the glass will not readily interrupt the contact, because flexible material is compliant with the unevennesses to some extent. When using a clamping connection component, it is also possible to replace this connection component in a simple manner, if it were to exhibit defects. A preferred flexible material is an elastomer. This type of material is readily available. The connection component preferably has the shape of a role, having one substantially flat side and one rounded side. It is easy to print trades on the rounded side. The trades will not break, when being present on a rounded surface with no edges. Because of the presence of one flat side it is possible to have the two ends of each track on the rounded side end substantially parallel to each other. This enhances the contact between the trades and the panel, when the connection part B clamped in. The conducting tracks on the connection component may be, for example, carbon tracks which have a low resistance and are inexpensive because carbon is an inexpensive material. The conducting tracks on the connection component are preferably gold tracks. Gold has a very low specific electrical resistance as compared with other metals and can easily be provided on a flexible material. Moreover, it is soft so that the tracks on an elastic connection component will not readily break. The invention may be used, for example in an LCD (liquid crystal display) having a chip-on-glass construction. An LCD comprises, inter alia, a display panel with two glass plates enclosing a very thin layer of LCD liquid and electrodes. In a chip-on- glass construction, an IC (or more ICs) is not secured on the PCB (printed circuit board) at the rear side of the LCD, but on a projecting edge of one of the glass plates of the display panel. Thus, an integrated display is obtained in which all connections between the IC and the LCD are completely isolated from their surroundings. The ITO electrode patterns which are present on both glass plates are extended with connection tracks to the IC. Tracks are also made from the IC to external connectors. These may be, for example clamps which are secured to the edge of the glass, with a conducting adhesive in between. These clamps can then be connected by means of electrically conducting wires to tracks on the PCB. These LCDs may be used, for example, on a telephone set for giving information, such as the number called, or the name of the person called. Many connections are required if much information is to be given on the small screen. To avoid space problems, multiplexing is necessary. If there are 4 rows of 8 pixels each in the display matrix, then the multiplex rate is 32. At such a high multiplex rate, the voltage applied to the liquid should sometimes be a factor of 4/5 higher than that of the power supply. Consequently, the voltage must be up-transformed. The ITO tracks on glass which are currently used have a high ohmic value as compared with copper tracks. The circuit for up- transformation, which is incorporated in the IC, thus does not always function properly. A solution is the use of gold tracks which extend on an elastomer connection component to be built in. Gold has a much lower specific electrical resistance than ITO. Moreover, the use of such a connection component leads to a shorter length of the gold tracks and thus to a smaller electrical resistance of the gold tracks. The tracks may therefore be thinner and narrower than the ITO tracks. Consequently, and also because there are no longer any clamps required for the roll construction, the tracks may be located closer together. The connections between the gold tracks and the IC connections may be constituted by short ITO tracks. Since the ITO tracks are so short, the high resistance of the ITO no longer has such a great influence. In a preferred embodiment of the invention, a track extending from the IC to the connection component is in contact with a plurality of conducting tracks on this connection component. Then there is less risk of failure of the electrical contact as compared with the situation in which there is only one connection. The risk that all connections have a failing electrical contact is smaller than the risk that the electrical contact of one connection fails, if there is only one connection. Moreover, a satisfactory contact can still be maintained if the connection component is displaced to some extent. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 is a diagrammatic cross-section of an embodiment of a conventional LCD having a chip-on-glass construction. Fig. 2 is a diagrammatic bottom view of an embodiment of a display panel of a conventional LCD having a chip-on-glass construction as shown in Fig. 1. Fig. 3 is a diagrammatic bottom view of an embodiment of a display panel of a conventional LCD having a chip-on-glass construction, other than that shown in Figs. 1 and 2. Fig. 4 is a diagrammatic cross-section of an embodiment of an LCD having a chip-on-glass construction according to the invention. Fig. 5 is a diagrammatic bottom view of an embodiment of a display panel of an LCD having a chip-on-glass construction according to the invention, as shown in Fig. 4. Fig. 6 shows an ITO track and a part of the gold tracks on the elastomer connection component. Fig. 7 is a diagrammatic, perspective elevational view of an embodiment of an elastomer connection component provided with gold tracks. Fig. 8 is a diagrammatic, perspective elevational view of the same embodiment of the connection component as in Fig. 7, viewed from a different side. For the sake of clarity, identical reference numerals are used in the Figures for the same types of components. Fig. 1 is a diagrammatic cross-section of an embodiment of a conventional LCD having a chip-on-glass construction. The LCD comprises a display panel (19) with two glass plates (1, 2) enclosing a very thin layer (of, for example several tens of microns thickness) of LCD liquid (3). One of the plates (1) projects with respect to the other (2). The projecting part is provided with an IC (6) whose connection points are connected in an electrically conducting manner to electrodes between the glass plates (1, 2) via ITO tracks (8). There are also connection points between the IC (6), via ITO tracks (7), to metal clamps (9) which are secured to the edge of the glass by means of a conducting adhesive between the metal clamps and the glass. Metal connection wires (10) extend from these metal clamps (9) to a PCB (12). When the connection wire is connected to a track on the PCB surface remote from the LCD, then the wire extends through the PCB to the surface remote from the LCD, where the wire is secured by means of solder (11) to a connection point of a track of the external electronic circuit (21) on the PCB (12). This is shown in the drawing. When a wire is connected to a track at the PCB side facing the LCD, then the wire does not extend through the PCB. A wire may also be connected to a track within the PCB. Polarizers (4, 5) are provided at the two sides of the glass plate assembly of the LCD. The display panel is accommodated in an insulating element (13) which may be made of, for example, a given type of synthetic resin material. The cross-section shown is diagrammatic and does not extend throughout the same plane. The IC (6) does not need to be located in the same plane as the combination of clamp (9), connection (10) and soldering point (11). Fig. 2 is a diagrammatic bottom view of an embodiment of a display panel (19) of a conventional LCD having a chip-on-glass construction as shown in Fig. 1. ITO tracks (8) extend from the IC (6) to electrodes between the glass plates, the lower plate (2) of which is shown in the drawing. ITO tracks (7) also extend from the IC (6) to metal clamps (9). For the sake of clarity, not all ITO tracks are shown. The Figure shows how the metal clamps (9) occupy a large part of the edge of the glass, which part is longer than the longest side of the IC (6), so that the ITO tracks connecting the metal clamps (9) to the connections of the IC (6) cannot extend straight and parallel and are thus longer than in the case where they would extend straight and parallel. Fig. 3 is a diagrammatic bottom view of an embodiment of a display panel (19) of a conventional LCD having a chip-on-glass construction, other than that shown in Figs. 1 and 2. ITO tracks (8) extend from the IC (6) to electrodes between the glass plates, the lower plate (2) of which is shown in this Figure. ITO tracks (7) also extend from the IC (6) to metal clamps (9). The Figure shows that, similarly as in Fig. 2, the metal clamps occupy a large part of the edge of the glass. Similarly as in Fig. 2, the ITO tracks are long. Due to the large resistance of ITO tracks, problems occur when the voltage in the IC is up-transformed. For the sake of clarity, not all ITO tracks are shown. Fig. 4 is a diagrammatic cross-section of an embodiment of an LCD having a chip-on-glass construction according to the invention. The LCD has glass plates (1, 2), polarizers (4, 5), an IC (6), ITO tracks (7, 8), a PCB (12), an insulating element (13), a connection component (14) of elastomer (16) with gold tracks (17) and a connection point (15) with a track on the PCB (12). The gold tracks (17) on the connection component (14) constitute the connection between the IC (6) and the tracks on the PCB (12). The Figure shows how a gold track is connected to an ITO track (7) and a track of the external electronic circuit (21) at the PCB side remote from the LCD. A metallized aperture (20) is present which is in contact with the gold track (17) at the location of the connection point (15) and constitutes an electrically conducting connection between a gold track (17) and a track associated with the external electronic circuit (21) on the PCB (12). When the gold track is connected to a track on the PCB side facing the LCD, then this may be a direct connection. The gold track may be pressed against the track on the PCB. A connection between a gold track and a track within the PCB is alternatively possible. In that case, a metallized aperture may be provided which extends from the gold track through a part of the PCB. Fig. 5 is a diagrammatic bottom view of an embodiment of a display panel (19) of an LCD having a chip-on-glass construction according to the invention, as shown in Fig. 4. ITO tracks (8) extend from the IC (6) to electrodes between the glass plates, the lower plate (2) of which is shown in this Figure. ITO tracks (7) also extend from the IC (6) to the connection component (14). For the sake of clarity, not all ITO tracks are shown. The Figure shows that a smaller number of ITO tracks is required, inter alia because the ITO tracks (7) can now extend straight and parallel, but also because the elastomer connection component (14) can be accommodated in the display panel, yielding a short distance to the IC. An additional advantage is that the gold tracks on the elastomer may be very thin, because gold has a very low specific electrical resistance. The connection component (14) may be installed in such a way that a plurality of juxtaposed gold tracks is in contact with one and the same ITO track which is connected to a connection on the IC (6). When a number of the tracks in the center of this plurality of juxtaposed tracks is connected to a connection point on the PCB, there is a great certainty of an electrical connection between the connection point of the IC and the connection point, to be connected thereto, of the external electronic circuit. If the tracks are displaced, there will still be a connection. If a track does not provide an optimum connection, there will still be other tracks which do provide such a connection. Fig. 6 shows an ITO track (7) and a part of the gold tracks (17) on the connection component of elastomer (16). When the connection is made with the external electronic circuit by a number of tracks (18) in the midst of a larger group of tracks establishing contact with the ITO track (7), the ITO track and the elastomer connection component may be displaced to some extent relative to each other without interrupting the contact. Fig. 7 is a diagrammatic, perspective elevational view of an embodiment of a connection component (14) of elastomer (16) provided with gold tracks (17). For the sake of clarity, not all tracks are shown. Fig. 8 is a diagrammatic, perspective elevational view of the same embodiment of the connection component as in Fig. 7, viewed from a different side. For the sake of clarity, not all tracks are shown. The connection component may have a straight or a curved surface, so that the cross-section has an arch shape. In Figs. 7 and 8, the connection component is made of an elastomer and has a basket-handle arch shape throughout its length. The gold tracks are provided in a pattern of parallel stripes which extend throughout the circumference, except on at least a surface of the circumference. In Figs. 7 and 8, the curved surface is provided with tracks and the plane surface is not provided with tracks. In summary, the invention relates to a display device (for example, an LCD) in which connections between an IC and an external electronic circuit consist of satisfactorily conducting tracks, for example, gold tracks extending on a separate connection component. This connection component may be made of, for example a flexible material and can be fixed in position by clamping.

Claims: CLAIMS: 1. A display device comprising a display panel with a supporting plate which supports an IC (integrated circuit) and an external electronic circuit arranged outside the supporting plate, in which electrically conducting connections extend between the IC and the external electronic circuit, characterized in that the display panel is provided with a connection component on which electrically conducting tracks extend which have a lower specific electrical resistance than ITO tracks and connect the IC connections to the external electronic circuit. 2. A display device as claimed in Claim 1 , characterized in that the connection component is made of a flexible material. 3. A display device as claimed in Claim 2, characterized in that the flexible material is an elastomer. 4. A display device as claimed in Claim 1, 2 or 3, characterized in that the electrically conducting tracks are carbon tracks. 5. A display device as claimed in Claim 1 , 2 or 3, characterized in that the electrically conducting tracks are gold tracks. 6. A display device as claimed in Claim 1, 2, 3, 4 or 5, characterized in that the IC is arranged on the glass of a plate in the display panel. 7. A display device as claimed in Claim 6, characterized in that the connection between the control IC connections and the conducting tracks on the connection component is constituted by ITO tracks. 8. A display device as claimed in Claim 7, characterized in that an ITO track is in contact with a plurality of tracks on the connection component. 9. A telephone set, comprising a display device as claimed in claim 1. 10. A display panel with a supporting plate which supports an IC (Integrated circuit) in which electrically conducting connections extend between the IC and a place on the supporting plate which, when built-in in a display device, touches connections of an electronic circuit thereof, characterized in that the display panel is provided with a connection component on which electrically conducting trades extend which have a lower specific electrical resistance than ITO trades and connect the IC connections to the electronic circuit of the display device. 11. Display panel as claimed in Claim 10, characterized in that the connection component is made of a flexible material and in that the display panel comprises a cavity in which the connection component is clamped.

Inventors: SANGERS JOHANNES IDA MARIA MIC, SANGERS, JOHANNES, IDA, MARIA, MICHAEL
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1997
Main classification: G02F1
IPC codes: G02F1, G09F9, H05K3