Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1998-12-21
2001-04-24
Vo, Nguyen T. (Department: 2682)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S082000, C455S083000, C333S017300, C333S035000
Reexamination Certificate
active
06223022
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a mobile radio telephone comprising at least a transmitter output stage, at least an antenna and at least an impedance matching network inserted between transmitter output stage and antenna, which matching network has a transformation factor for adjusting a transmitter load impedance to match with an antenna input impedance.
The invention further relates to a transmitter including at least a transmitter output stage, at least an antenna and at least an impedance matching network inserted between transmitter output stage and antenna which matching network has a transformation factor for adjusting a transmitter load impedance to match with an antenna input impedance.
BACKGROUND OF THE INVENTION
From disclosure DE 42 22 190 A1 is known such a radio telephone comprising an antenna switch for alternately operating in the transmitting and receiving states. For adjustment purposes is then arranged a &lgr;/4 waveguide between transmitter output stage (
31
) and antenna (
1
). As a result, the special transformation properties for the initial and terminal resistance Z
A
and Z
E
respectively, of the &lgr;/4 waveguide can be used. The terminal resistance Z
E
of a &lgr;/4 waveguide is transformed on the input of the &lgr;/4 waveguide in dependence on its wave resistance Z. By means of the parameters of the waveguide range such as geometric dimensions and material constants (&egr;,&mgr;), the wave resistance Z can be set for the wavelength &lgr; to be used. The transformation of the resistance is generally effected in accordance with the relation Z
A
=Z
2
/Z
E
. In the transmitting state, the &lgr;/4 waveguide (
32
) connected to the transmitter output stage (
31
) transforms the antenna impedance in accordance with the requirements of the transmitter output stage (
31
). In this manner, the transmitter output stage (
31
) in the transmitting state is adjusted to match with the antenna (
1
) and the output power of the transmitter output stage (
31
) is fully passed on to the antenna (
1
). As a result of, inter alia, possibilities to change the wave resistance Z, a suitable transformation factor may be set. The second &lgr;/4 waveguide (
32
) may be discarded for the transformation of the resistance when the wave resistance of the waveguide is set equal to the antenna resistance (see above, transformation equation).
The load impedance of a power amplifier in a transmitter output stage is adjusted to match with the input of an antenna to achieve a maximum efficiency of the transmitter output stage (ratio of the power fed to the antenna to the overall power used). An adjustment by means of a state-of-the-art &lgr;/4 waveguide, however, provides a good efficiency (fixed transformation factor) only for an operating state with a certain output power P
A
and supply power U
B
of the power amplifier. In mobile radio telephones, for example, for mobile radio in accordance with the GSM standard, however, various levels are determined for the output power, which are to be exactly set by means of a power control in dependence on the transmission properties. Furthermore, the supply voltage U
B
varies in accordance with a discharge curve for the battery used. Consequently, as against the adjusted operating state, for example, with an increased supply voltage U
B
and regulated output power P
A
, the efficiency drops because the voltage U
A
on the output of the transmitter output stage remains constant. This also provides that the current I
A
on the output retains the regulated constant value, so that the efficiency diminishes strongly. All in all, often only a reduced efficiency of the transmitter output stage is achieved. This is a considerable disadvantage, especially for battery-operated mobile radio telephones because of the consequent shortened service life.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide a mobile radio telephone that has improved the efficiency of the transmitter output stage in different operating states.
The object is achieved in that at least two impedance transformers in the impedance matching network form at least two transformation factors by alternatively connecting them in parallel. In this manner, at least two different load impedances may be set for the transmitter output stage, whereas even more transformation factors are conceivable by suitable circuit formations. The arrangement in the impedance matching network may be adapted in a highly flexible manner to requirements especially by means of software-controlled switches, without the necessity to make changes in the hardware. This provides that a proper efficiency of the transmitter output stage can be achieved in different operating states, because the transmitter output stage has a load impedance from which the voltage amplitude develops that is the highest possible for the set transmitter power.
A preferred embodiment of the invention is that at least two &lgr;/4 waveguides form the impedance transformers. The &lgr;/4 waveguides may be arranged as coaxial conductors or as microstrips. Also a copy of a &lgr;/4 waveguide by means of an LC network that has the respective transmission properties may be used.
In an advantageous further embodiment, a first &lgr;/4 waveguide in the impedance matching network is coupled, on the one hand, to the output of the transmitter output stage and, on the other hand, to the input of the antenna and a second &lgr;/4 waveguide is coupled, on the one hand, to the output of the transmitter output stage and, on the other hand, to at least one switch which establishes in a first position the connection to a ground terminal and in a second position to the input of the antenna. The switch may be formed by a PIN-diode high-frequency switch or a bistable mechanical relay. With such an arrangement, the control of the switches may be taken over by software, so that a fast and flexible control of the impedance matching network is possible. Furthermore, by arranging the switch on the side of the antenna, it is avoided that large losses arise in the switch. Since this side is high-ohmic, there is only a small current flowing in the transmitter output stage compared to the maximum transmitting current.
Besides, the object of the invention is further achieved by a transmitter in which at least two impedance transformers in the impedance matching network form at least two transformation factors by alternatively connecting them in parallel.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 5654679 (1997-08-01), Mavretic
patent: 5678199 (1997-10-01), Birth et al.
patent: 4222190A1 (1994-01-01), None
Birth Winfrid
Burdenski Ralf
Wunsch Christian
Halajian Dicran
Moore James K.
U.S. Philips Corporation
Vo Nguyen T.
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