Electronic instruments worn on the wrist taking a form similar to that of a wristwatch are already known. Specific examples of such electronic instruments answering the aforementioned definition are also known.
European Patent No. 1 274 150 A1 proposes, for example, a portable electronic instrument able to take the form of a wristwatch and a part of whose case can be made of an electrically conductive metal material, this electronic instrument also including an antenna for receiving satellite positioning signals. According to this solution, the electronic module does not lie directly in the electrically conductive part of the case, but inside an assembly made of plastic material, the electronic module being supplied with electric power by the electric power source in a conventional manner via conductive contact strips or flanges. It should also be noted that the antenna (a micro-strip—or patch antenna—including a radiating element separated from a ground plane by a dielectric) lies on an element forming a bezel fitted onto the case and made of a dielectric material.
The articles entitled (“GPS Watch—Une montre à quartz analogique équipée d'un récepteur GPS à très faible consommation” (European Chronometry Congress, CEC 2000, Session 7, Communication 19, Geneva, 28 and 29 Sep. 2000) and “GPS Watch—An analogue watch including a very low power GPS receiver” (ION GPS 2000 Conference, Salt Lake City, Utah, USA, Sep. 19-22, 2000) in the name of P.-A. Farine and consorts, Asulab S.A., also describe an electric instrument taking the form of a wristwatch including a case in which are housed an electric power source, an electronic module carrying in particular a micro-strip antenna and a satellite positioning receiver, as well as an analogue and digital display device. A part of the case, in this case a back cover-middle part, can also be made of an electrically conductive metal material, a non metal bezel being, however, fitted onto the top part of the instrument above the antenna. Like the solution disclosed in the aforementioned EP Patent No. 1 274 150 A1, the electronic module is powered by the electric power source via conductive contact strips or flanges. According to this solution, it should be noted that the micro-strip antenna lies directly on the printed circuit board of the electronic module where its ground plane is made.
In order to complete this list of the state of the art, European Patent No. 1 134 837 A1, which discloses a portable electronic instrument including a so-called inverted L antenna or inverted F antenna because of its particular profile, should also be cited. The ground plane of this antenna is made on the top face of the printed circuit board of the electronic module. Insofar as the lateral and top parts of the case are made in one piece as illustrated in this document, the configuration of the instrument necessarily requires the use of a dielectric material to make the case in which the electronic module is housed. The electronic module is again powered by the electric power source by conductive contact strips or flanges. It should also be stressed that the electronic instrument has a back cover made of metallic material, which is electrically connected to a determined electric potential, in this case the positive potential of the electric power source. It is mentioned that this electric connection has the advantage of allowing the surface of the antenna ground plane to be increased, in particular via the body of the person wearing the instrument, which leads to increased sensitivity of the antenna.
In the aforementioned examples, it should thus be noted that the electronic module is conventionally powered by the electric power source via a set of conductive contact strips or flanges, electrically connecting the two electric poles of the power source to the sets of conductive supply paths typically made on the printed circuit board of the electronic module.
When one wishes to design an electronic instrument of the aforementioned type and fit it with a case at least part of which is electrically conductive, for example metal, it is known that it is also desirable to fix the electric potential of this conductive part rather than leave it floating. The electric potential of this electrically conductive part is thus often fixed by an electric connection to one of the poles of the electric power source, for example to the ground potential or the other supply potential. This electric connection is achieved either by directly connecting the part concerned to the corresponding pole of the power source, or again via conductive contact strips or flanges. By way of example, the European Patent No. 1 134 837 A1 mentions that the connection of the metal back cover to the positive pole of the electric power source is achieved via contact strips.
The use of conductive contact strips or flanges to ensure the electric connection of the electronic module and/or a part of the case to the electric power source often constitutes a constraint, in particular when the portable instrument is being assembled. It is an object of the present invention to propose a solution simplifying to a certain extent the manufacture of these electric connections as well as the operations for assembling the instrument.
Within the scope of the more specific embodiment wherein the instrument incorporates an antenna fitted with a ground plane, a solution is sought for increasing the sensitivity of the antenna by enlarging its ground plane via a simplified electric connection, the enlargement being located substantially in the plane containing the ground plane of the antenna. Owing to this latter feature, improvement in the sensitivity of the antenna is better in the case of the present invention than in the case of the prior art.