Note: Descriptions are shown in the official language in which they were submitted.
WO 95119069 _ PCTILTS94/13946
POWER ADAPTER WITH INTEGRAL
RADIO FREQUENCY PORT
Field of the Invention
This invention relates to a power adapter for a portable device,
and more particularly to a power adapter having an integral radio
frequency port for communication equipment.
Background of the Invention
In portable battery-powered equipment, such as a cellular
telephone or other communication device, an external power supply is
usually provided so that the user can operate the equipment from
household current or vehicle power current in order to conserve batter~~
power. To operate the communication device inside a vehicle, power
adapters are commonly designed to fit into the cigarette lighter socket
2o provided in the vehicle. The other end of the power adapter plugs into an
external power input connector of the device, or includes what is
commonly known in the industry as a "battery eliminator" which replaces
a detachable battery coupled to the telephone or communication device.
When operating a cellular telephone or other communication
device within a vehicle, it is generally desirable to use an antenna
mounted external to the vehicle to improve the performance of the
telephone. Some telephones provide a radio frequency (RF) input/output
port in addition to the external power input port so that an external
antenna may be utilized. However, such a device requires two separate
so connectors. In other telephones, the external power input port and the RF
input/output port are combined within a single connector of the device.
However, such a device would typically require that either an external
power supply or external antenna be connected.
Accordingly, there is a need to provide a simple, single cable
vehicle power adapter which also provides RF input/output capability for
connection to an external vehicle antenna.
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Summary of the Invention
According to one aspect of the present invention a single-piece power adapter
assembly for coupling power and RF signals to a communication device is
provided. The
communication device has an integral antenna and an input connector. A first
connector
for coupling to a power source and having an RF port for coupling to an
external antenna,
is connected to one end of a cable. The cable has a second connector coupled
to the
other end. The second connector has a plurality of contacts for providing
power to the
communication device and for transmission of RF signals between the
communication
device and the external antenna when the second connector is inserted in the
input
connector, and the external antenna is connected to the RF port. Means for
selecting
either one of the integral antenna or the external antenna are also provided.
Brief Description of the Drawings
FIG. 1 is a perspective view of a power adapter having an integral RF port
according to the present invention.
FIG. 2 is a schematic diagram of the power adapter of FIG. 1.
FIG. 3 is a schematic diagram of a power adapter coupled between an external
antenna and a communication device having an internal antenna and circuitry
for
selecting either the internal antenna or the external antenna.
FIG. 4 is a block diagram of an alternate embodiment of a power adapter
according to the present invention having an external, user selectable switch
for selecting
which antenna is coupled to the transceiver of the communication device.
FIG. 5 is a schematic diagram of a connector 16 of a power adapter for
automatic
selection of an external antenna according to the present invention.
FIG. 6 is a schematic diagram of an alternate embodiment of a connector 16 of
a power adapter for automatic selection of an external antenna according to
the present
invention.
FIG. 7 is a schematic diagram of an antenna adapted to be coupled to the power
adapter of FIG. 2.
FIG. 8 is a schematic diagram of an antenna adapted to be coupled to the power
adapter of FIG. 2.
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Descr~tion of the Preferred Embodiments
The present invention provides a power adapter for coupling an
external antenna to a communication device by way of a cable which is
typically plugged into a cigarette lighter of a vehicle or some other power
source at one end, and an input connector of the communication device
at the other end. In particular, the present invention provides a simple,
single cable vehicle power adapter having a radio frequency (RF)
t o input/output port for connection to an external vehicle antenna.
According to certain aspects of the invention, the adapter can be
configured to have a variety of antenna selection mechanisms. For
example, the external antenna could be selected when the power
adapter is attached to the communication device. Alternatively, the
15 adapter could include an external switch for allowing the user to select
the desired antenna. Finally, the adapter could include a switch
associated with the RF port which automatically can cause the
communication device to select the external antenna when the external
antenna is connected to the adapter.
2o Turning first to FIG. 1, a perspective view of a power adapter
according to the present invention is shown. Power adapter 10 includes
a cigarette lighter adapter 11 which is commonly plugged into a cigarette
lighter of a vehicle to receive power from the vehicle's electrical system.
However, a source of power could also be supplied from a connector
25 other than the cigarette lighter. A cable 12 is coupled between cigarette
lighter adapter 11 and a connector 14. Connector 14 preferably is
inserted into a receptacle in the communication device adapted to
receive the connector. Alternatively, connector 14 could be associated
with a "battery eliminator" to replace a detachable battery which is
so coupled to the communication device to power the device. Finally, an
external RF port 16 which is preferably associated with cigarette lighter
adapter 11 is adapted to receive an antenna cable to transmit signals
between the device and an external antenna of the vehicle. An RF
transmission means is provided from external RF port 16 through cable
35 12 and connector 14 to the communication device.
Turning now to FIG. 2, a detailed schematic diagram of the power
adapter is shown. In particular, the power adapter is attached to external
CA 02156634 1999-02-26
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antenna 17 by way of a transmission line 18 (preferably a coaxial cable)
at a coaxial connector having an outer conductor 19 and an inner
conductor 20. Cigarette lighter adapter 11 preferably includes a
connector 16 which is also a coaxial connector. Connector 16 has an
outer conductor 21 and an inner conductor 22 which are coupled to a
transmission line 23 (preferably a coaxial cable) provided within cable
12. Transmission line 23 has an outer conductor 24 and an inner
conductor 25 which are coupled to a coaxial connector 26 having an
outer conductor 27 and an inner conductor 28. The power adapter 10 is
1 o coupled to a communication device, such as a cellular telephone, by way
of connector 26. Finally, cable 12 could include other lines 29, such as
power lines from cigarette lighter 11 to a communication device or data
signals from an electronic control module in the vehicle.
Turning now to FIG. 3, a detailed schematic diagram shows power
~ 5 adapter 10 connected between an external antenna and a
communication device 30. The power adapter is identical to the power
adapter of FIG. 2, except that a direct current (DC) blocking capacitor 35
and a resistor 37 have been included. While only a relevant portion of
the communication device circuitry for implementing this power adapter
2o is shown, it is understood that other circuitry is required for the
operation
of the communication device. In order to couple RF signals to the
external antenna connector 14 on the power adapter, the communication
device must contain an RF switch means for selectively routing RF
signals to either the phone's internal antenna or the external antenna
25 port. In particular, communication device 30 generally includes an
integral antenna 32 which is coupled to an RF switch 34 by a capacitor
36. The RF switch is coupled to the transceiver portion of the
communication device and selects which antenna is connected to the
transceiver. Preferably, the switch could couple the transceiver to an
3o external antenna when the power adapter is applied.
In order for the RF switch to couple RF signals to the external
antenna, the power adapter preferably provides a signal to
WO 95/19069 PCT/ITS94/13946
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communication device 30 indicating that the power adapter
is attached
and the external antenna should be used. The power adapter
contains
resistor 37 (preferably 10kS2) which is coupled to ground
to provide this
signal. White capacitor 35 and resistor 37 are shown proximal
to inner
S conductor 28 of coaxial connector 26, the blocking capacitor
could be
positioned at any location along the inner conductor 25
of transmission
line 23, and the resistor could be positioned at any location
to provide a
path to ground as long as it is on the side of the capacitor
closer to
coaxial connector 26. For example, the resistor and capacitor
could be
1 o positioned within cigarette lighter adapter 11. As will
be described in
detail below, when the path to ground is provided by the
resistor in the
power adapter, circuitry in the communication device will
couple the
transceiver of the communication device to its external
RF port 40 (and
therefore, the external antenna). The communication device
includes
15 bipolar junction transistors (BJTs) 44 and 46 to control
RF switch 34.
According to the present invention, transistor 44 is preferably
a NPN
transistor and transistor 46 is preferably a PNP transistor.
The circuit
further includes a resistor 48 having a first end coupled
to connector 40
and a second end coupled at a node 49 to a capacitor 50
coupled to
2o ground. Resistor 48 and capacitor 50 are also coupled at
node 49 to a
resistor 52 which is coupled to the base of transistor
44. A resistor 54 is
coupled between the base and the emitter of transistor
44 which is
coupled to a negative voltage, preferably minus 3.9 volts.
A resistor 56 is
also coupled between the collector of transistor 44 (at
switch control port
25 A) and the base of transistor 46. A resistor 58 is coupled
between the
base and the emitter of transistor 46, which is coupled
to a positive
voltage, preferably 4.75 volts. Finally, a resistor 60
is coupled between
the collector of transistor 46 (at switch control port
B) and a negative
voltage, preferably minus 3.9 volts. While the specific
transistor switching
so arrangement of FIG. 3 is one example of a circuit which
could be used to
_ switch between an internal and an external antenna, other
circuits could
be employed within the scope of the present invention.
For example,
metal oxide semiconductor (MOS) transistors or different
reference
potentials could be employed.
35 Having described the preferred structure of the switch
control
circuit, the operation of the circuit will now be described.
Resistor 37 of
the power adapter activates the RF switch 34 when the power
adapter is
WO 95!19069 PCT/US94/13946
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plugged into the external RF port of the transceiver at connector 40. In
particular, resistor 37 pulls the base of transistor 44 up to approximately 0
volts which turns on transistor 44, thus applying a negative voltage to RF
switch control port A. The base of transistor 46 is also pulled low by the
collector of transistor 44, thereby turning on transistor 46 to apply a
positive voltage to RF switch control port B. When a negative voltage is
applied to RF switch control port A and a positive voltage is applied to RF
switch control port B, RF signals are routed from the transceiver to the
external RF port 40 of the communication device 30.
1 o If the male connector 14 is removed from the external RF port 40 of
the communication device, the base of transistor 44 is pulled to the
emitter of transistor 44, effectively turning transistor 44 off to produce a
high voltage at control port A of RF switch 34. Transistor 46 is turned off
by the high voltage at its base, thus applying a negative voltage to RF
switch control port B of the RF switch. When a positive voltage is applied
to RF switch control port A and a negative voltage applied to control port
B, RF power will be routed from the receiver/transmitter to the integral
antenna of the transceiver.
According to another aspect of the invention, it is possible to
zo modify the design the power adapter to include a user-selectable switch
for determining whether or not RF signals should be coupled to the
external connector. In particular, FIG. 4 shows the power adapter with
resistor 37 and a user-selectable switch 70 for allowing RF power to be
coupled either to the portable's integral antenna or the external antenna
2s at the user's discretion. By closing switch 70, the circuitry in
communication device 30 is actuated as described above to route the RF
signals from transceiver 38 to external RF port 40 of the communication
device. If switch 70 is left open, the same effect of removing connector 14
from external port 40 of communication device 30 as described above
30 occurs and the RF signals will be coupled from transceiver 38 to integral
antenna 32. The adapter of FIG. 4 can be used with a communication
device having circuitry as shown in FIG. 3.
According to another aspect of the present invention, a connector
could be used wherein the RF signals are automatically coupled to the
ss external antenna when the external antenna is connected to the external
RF port power adapter. FIG. 5 shows the preferred connector 16 of
power adapter 10 for allowing automatic RF port selection. In particular,
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PCT/US94/13946
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the female mini-UHF antenna connector 22 is specifically designed with
a split center conductor socket, the two halves of which are normally
electrically isolated. One half of the socket is connected normally to inner
conductor 25 of transmission line 23. The other half of the socket is
connected to resistor 37 which is coupled to ground. When the user
plugs in a standard external antenna, two halves of the center conductor
socket are connected by the male end 20 of the external antenna plug.
This causes a connection to ground to be established through a resistor
37 which actuates the switch control circuitry of the communication
1 o device to couple RF signals to the external antenna as described above.
Accordingly, RF signals are automatically coupled to the external
antenna when the external antenna is connected.
Turning now to FIG. 6, an alternate embodiment of connector 16 of
power adapter 10 for allowing automatic RF port selection is shoran. In
15 the alternate embodiment, an additional contact 80 is integrally
associated with connector 16. Additional contact 80 is normally
electrically isolated from outer conductor 21 of connector 16. The
additional contact 80 is coupled to a resistor 37, the other end of which is
coupled to inner conductor 25 of transmission line 23. Between that
2o coupling point and inner conductor 22 of connector 16, there is also
disposed a DC blocking capacitor 35. When a standard coaxial antenna
is connected, outer conductor 19 of the connector for the external
antenna couples additional contact 80 to the outer conductor 21 of
connector 16, completing the path to ground through resistor 37, wherein
25 RF signals are automatically coupled to the external antenna. The
connectors of FIG. 5 and FIG. 6 allow the user to operate the power
adapter and utilize the integral antenna of the communication device if so
desired, by simply not connecting an external antenna.
Turning now to FIG. 7, a preferred external antenna 90 which
3o could be coupled to the power adapter of FIG. 2 is shown. In particular,
the antenna of FIG. 7 incorporates DC blocking capacitor 35 and resistor
37 which provides a path to ground. Therefore, when the external
antenna is connected, the communication device will automatically
couple RF signals through the adapter assembly to the external antenna
35 as described above. Antenna base 92 may incorporate a magnet or
window clip to attach the antenna to the vehicle.
Turning now to FIG. 8, an alternate embodiment of an external
WO 95/19069 PCT/US94/13946
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antenna to be coupled to the power adapter of FIG. 2 is shown. External
antenna 90 includes a loading coil 94 which acts as an autotransformer
to provide impedance matching between the antenna 17 and the
transmission line 18. Because of the construction of the loading coil, a
s direct current path to ground is provided which will cause the circuitry in
'
the communication device to couple RF signals through the adapter
assembly to the external antenna.
In summary, the present invention provides a simple device for
coupling both power and RF signals from a cigarette lighter adapter to a
o communication device by way of a single cable. Accordingly, the
invention simplifies the connection of an external antenna to a portable
cellular telephone employing such a power adapter. Also, the power
adapter can be configured to allow for the selection of the external
antenna by selectively employing an resistor in the adapter, or in the
1 s external antenna, to effect the coupling of RF signals to the external
antenna.
