Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1998-07-16
2001-11-27
Gandhi, Jayprakash N. (Department: 2846)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S737000, C361S753000, C361S800000, C174S034000, C206S071000
Reexamination Certificate
active
06324074
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is concerned with electromagnetic shielding in electronic devices, especially radio devices. The present invention has particular applicability to radiotelephone transceivers manufactured in the format of a PC card or PCMCIA card.
Electromagnetic signals are generated as a by-product during normal operation of an electrical circuit. Electromagnetic compatibility (EMC) is defined as the ability of a device to function properly in its intended electromagnetic environment and not be a source of unacceptable pollution to that environment. In some situations, shielding is required to provide electromagnetic compatibility between a sensitive or noisy part of the circuit and the rest of the circuit. One typical example is the isolation of a frequency synthesiser from the rest of the RF section in a cellular radiotelephone.
FIG. 1
shows a conventional approach to providing electromagnetic shielding in this situation.
Referring to
FIG. 1
, a radiotelephone housing
10
has located within it a printed circuit board
12
. The printed circuit board
12
carries surface mount components. Some of these components
14
, for example the frequency synthesiser, require shielding from other components
16
, for example the rest of the RF section
16
. To this end, a shield box
18
is used to enclose electromagnetically the components
14
and thus provide for EMC between the components
14
and the component
16
.
However, because of the mechanical tolerances required in the height of the shield box
18
, resulting from the manufacturing of the shield box
18
itself or the surface mount process, a gap must be designed for between the roof
18
a
of the shield box and the housing
10
. This space plus the thickness of the roof
18
a
of the shield box
18
equates to the cost in terms of height which this conventional approach to shielding incurs. The ‘height cost’ is illustrated in
FIG. 1
by double headed arrow h
1
.
The present invention is concerned with reducing the height cost which this conventional approach inevitably incurs.
BRIEF SUMMARY OF THE INVENTION
With this in mind, the present invention provides, in one aspect, a portable device comprising a housing; a circuit board located within the housing; and a shield member mounted at a first end on the circuit board so as to surround electronic components on the circuit board to be shielded, wherein the device is arranged such that a conductive portion of an exterior wall of the housing electromagnetically seals off the shield member at the other second end.
By virtue of these features, the need for a roof
18
a
to the shield box
18
in
FIG. 1
is eliminated. Consequently, the thickness of the roof
18
a
no longer counts towards the height cost of the shielding and the aforementioned design tolerances associated with it are thus reduced.
The height cost of the shielding associated with the present invention is less than that associated with the conventional approach in FIG.
1
. This means that either components having a higher maximum height can be used or the overall volume of the device reduced if components with the same maximum height are used.
In addition, the tubular shield member of the present invention is even simpler to manufacture than the shield box
18
.
Preferably, a gasket is located at the second end of the shield member to facilitate electromagnetic sealing. Alternatively, a conductive adhesive can be used to adhere the gasket to the shield member and thus provide ohmic contact therebetween.
Both of these embodiments of the invention enjoy the advantage that no special structural modification to the housing wall is required to implement them.
In other embodiments, a gasket can be used to mount the first end of the shield to the printed circuit board.
It will be appreciated that the height savings which are available when employing the present invention are particularly useful in connection with a PC card based product, such as the PCMCIA card based cellular transceiver which is described hereinafter, which is extremely constrained height/thickness -wise.
REFERENCES:
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patent: 4890199 (1989-12-01), Beutler
patent: 4912604 (1990-03-01), Vaisanen
patent: 4945633 (1990-08-01), Hakanen et al.
patent: 5006667 (1991-04-01), Lonka
patent: 5271056 (1993-12-01), Pesola et al.
patent: 5323299 (1994-06-01), Weber
patent: 5354951 (1994-10-01), Lange, Sr. et al.
patent: 5365410 (1994-11-01), Lonka
patent: 5392461 (1995-02-01), Yokoyama
patent: 5400949 (1995-03-01), Hirvonen et al.
patent: 5442521 (1995-08-01), Hirvonen et al.
patent: 5495399 (1996-02-01), Gore et al.
patent: 5603103 (1997-02-01), Halttunnen et al.
patent: 5687470 (1997-11-01), Halttunen et al.
patent: 5742004 (1998-04-01), Greco et al.
patent: 5742488 (1998-04-01), Lonka et al.
patent: 0 756 446 A1 (1997-01-01), None
Gandhi Jayprakash N.
Nokia Mobile Phones Ltd.
Perman & Green LLP
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