Electricity: circuit makers and breakers – Electric switch details – Cases and bases
Reexamination Certificate
1998-03-02
2001-03-27
Luebke, Renee (Department: 2833)
Electricity: circuit makers and breakers
Electric switch details
Cases and bases
C200S512000
Reexamination Certificate
active
06207912
ABSTRACT:
The present invention relates to a portable communication device, comprising an electronic circuit board arranged inside a housing, and a keypad, the individual keys of which are arranged, when depressed, to collapse a respective tactile dome on a domefoil interposed between the keypad and the circuit board, so as to establish electric contact with a respective contact point on the circuit board, said communication device being provided with means for protecting the circuit board from electrostatic discharge (ESD).
BACKGROUND
Portable communication devices are used in various applications to provide a means for remote communication between two parties. Common communication devices of this kind are for instance cellular telephones, cordless phones, paging devices, walkie-talkies, PDAs (Personal Digital Assistants), etc. Such devices comprise an apparatus housing, in which an electronic circuit board is arranged. The circuit board is provided with circuitry necessary for performing the operational communication tasks of the device, e.g. CPU, memory modules and radio circuits (amplifiers, local oscillators, filters, modulators, mixers, etc). Furthermore, the circuit board is often provided with LEDs (Light Emitting Diodes) or other devices for illuminating a keypad arranged in the housing.
Keypad-operated devices of the kind described above have to fulfill various requirements in order to provide a reliable communication service to the user of the device. Such requirements are for instance immunity to electrostatic discharge (ESD) as well as a sufficiently high degree of electromagnetic compatibility (EMC). When the user touches the keypad, there is an apparent risk of an electrostatic discharge between the user's fingertip and conductive elements, e.g. the electronic circuit board inside the device, and hence a keypad-operated communication device must be provided with ESD-protective means. Furthermore, the device must be shielded in a way that prevents the active parts of the communication device from interfering electromagnetically with surrounding electronic equipment. Such shielding must also protect the device from electromagnetic influences or disturbances caused by such surrounding electronic equipment.
FIG. 2
discloses a previously known keypad arrangement for a cellular telephone. A keypad
30
is made from e.g. rubber and comprises a set of individual keys
32
. Although not shown in the drawing each key
32
is labelled according to its dedicated purpose, for instance a digit “3” or a “*” sign. A domefoil
40
made from plastics or the like is interposed between the keypad
30
and an electronic circuit board
20
arranged inside the telephone housing. The domefoil
40
is provided with a plurality of tactile domes
42
, each of which is given a convex shape protruding or bulging from the domefoil
40
. One respective dome
42
is arranged beneath one respective key
32
in the keypad
30
.
The circuit board
20
is given a purely schematical appearance in FIG.
2
. The circuit board
20
comprises various electronic circuitry, such as radio transmitter/receiver circuits, amplifiers, filters, buffers, oscillators, mixers, one or several micro-processors, memory modules, etc., none of which are indicated in FIG.
2
. Furthermore, the circuit board
20
is provided with a set of contact points
22
, a respective one of which being arranged in vertical alignment with a respective pair of key
32
and dome
42
.
The functional operation of the keypad
30
is as follows. When a key
32
is depressed by a user, the back of the key will exert a force upon the underlying tactile dome
42
. The dome
42
will not be able to resist the force exerted by the key
32
but will collapse inwardly/downwardly and reach contact with the underlying contact point
22
. For this purpose the rear side of each dome
42
is made electrically conductive, for instance by providing each dome with a conductive layer, such as a silver or carbon compound. The collapsing dome establishes electric contact between a contact pair at the contact point
22
, the details of which are omitted in the drawing, since they are believed to be well-known per se to a man skilled in the art. The electric connection so established is immediately detected by a controller comprised on the circuit board.
Furthermore, the circuit board
20
is provided with illuminating means
24
realized as LEDs (Light Emitting Diodes), the purpose of which is to illuminate the keys
32
through respective openings
44
in the domefoil
40
. In
FIG. 2
one illuminating means
24
is arranged to illuminate four keys
32
surrounding the opening
44
. In addition to these openings the domefoil
40
is provided with various holes, openings or recesses
46
,
48
,
49
for various electronic components or mounting means arranged on the circuit board
20
.
In the prior art arrangement according to
FIG. 2
the rubber-based keypad sheet
32
serves as an ESD-protective means. Furthermore, the housing
12
shown in
FIG. 1
is provided on the inside thereof with a thin metallized layer functioning as a protection or a shielding against electromagnetic interference between the telephone
10
and surrounding electronic equipment. Although providing a sufficient protection against ESD as well as electromagnetic interference, the prior art arrangement according to
FIG. 2
is disadvantageous when it comes to cost considerations. Both the keypad rubber sheet
30
and the metallized layer inside the housing
10
and a non-negligable price penalty to the total cost for manufacturing the telephone
10
.
SUMMARY
It is an object of the present invention to provide a portable communication device with safe and inexpensive electrostatic discharge protection A further object of some embodiments is to provide the communication device with means protecting the device from electrostatic discharge (ESD) as well as assuring electromagnetic compatibility (EMC).
The objects of the invention are achieved for a portable communication device of the kind described above by protecting the circuit board inside the communication device from electrostatic discharge by means of a domefoil formed as a non-conductive sheet providing an air-tight and/or electrostatic seal between the keypad and the circuit board
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patent: 4636593 (1987-01-01), Novak et al.
patent: 4678880 (1987-07-01), Loizumi et al.
patent: 4809126 (1989-02-01), Burkman et al.
patent: 4916262 (1990-04-01), Jungels-Butler et al.
patent: 5063474 (1991-11-01), Igarashi
patent: 5335137 (1994-08-01), English et al.
patent: 5513078 (1996-04-01), Komrska et al.
patent: 5557079 (1996-09-01), Jackson et al.
patent: 5661279 (1997-08-01), Kenmochi
patent: 0 302 350 (1988-07-01), None
patent: 0 358 885 (1989-07-01), None
patent: 0 367 530 (1989-10-01), None
patent: 0 703 591 (1995-07-01), None
Burns Doane Swecker & Mathis L.L.P.
Luebke Renee
Telefonaktiebolaget LM Ericsson
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