Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-11-21
2001-11-13
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S082000, C455S083000, C455S159200, C333S129000, C333S101000, C330S126000
Reexamination Certificate
active
06317608
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an improved power amplifier matching in dual band mobile phones, in particular to a power amplifier output circuit for a dual band mobile radio unit according to the preamble of claim 1.
BACKGROUND OF INVENTION
Currently, mobile phones are operated predominantly with a single operating frequency.
FIG. 7
shows a realization of such a transmitter/receiver operation in a mobile phone being operated with a single operating frequency, e.g., with approximately 900 MHz for GSM, approximately 1800 MHz for DCS or approximately 1900 MHz for PCS. An antenna
100
being used to transmit signals and to receive signals is connected to a transmitter/receiver change over unit
102
. The transmitter/receiver change over unit
102
comprises a transmitter switch TX and a receiver switch RX. In the receiving mode, the transmitter switch TX is opened and the receiver switch RX is closed. To the contrary, in a transmitting mode the transmitter switch TX is closed and the receiver switch RX is opened.
In the transmitter mode, a power amplifier
104
outputs a transmitting signal in the pre-specified frequency band. Here, an impedance matching is carried out through an impedance matching circuit
106
such that the output of the power amplifier sees an impedance which in most cases is lower than the impedance of the following transmission branch, e.g., 50 &OHgr;.
However, the circuit design shown in
FIG. 7
more and more limits the increasing use of digital mobile telephony since the number of subscribers is continuously increasing while the number of transmitting frequencies and related transmission channels is limited. Although an increased transmitting frequency of, e.g., approximately 1800 MHz for DCS or approximately 1900 MHz for PCS in comparison to approximately 900 MHz for GSM enables an increased number of transmission channels, this is only possible at the expense of reduced working ranges for the transmitter stations.
Nevertheless, a combination of different technical advantages for the different approaches through provision of cellular dual band networks and dual band mobile phones adapted thereto seems to be promising, e.g., a combination of the GSM-frequency band with the DCS- or PCS-frequency band.
Heretofore, in U.S. Pat. No. 5,774,017 there is proposed a dual-band amplifier for wireless communication, in particular for operation at either the 800 MHz or the 1900 MHz band. The described dual band amplifier provides desired gain and input/output impedance. Switching impedance networks are used at the input and output of a power amplifier to provide matching input impedance and a desired output impedance for operation in two bands.
FIG. 8
shows another option of a corresponding power amplifier output circuit designed for the necessary transmission/receiving operation in a dual band mobile phone. This approach directly relies on the circuit design shown in FIG.
7
.
Here, the antenna
200
is connected to two transmitter/receiver change over units
202
and
204
. The sending/receiving change over unit
202
comprises a transmitter switch TXa and a receiver switch RXa for a first transmitter frequency. Further, the transmission/receiving change over unit
204
comprises a transmitter switch TXb and a receiver switch RXb for a second transmitter frequency. The different switches TXa, RXa, TXb, and RXb are operated in accordance with the different operation frequencies, respectively, as outlined above with respect to FIG.
7
. Further, a diplexer
206
is necessary to join the two transmission paths to the antenna
200
without losses. For the amplification of the transmitting signals in the frequency bands, there are provided related power amplifiers
214
and
216
. For these power amplifiers
214
and
216
an impedance matching is realized through impedance matching circuits
218
and
220
provided in each of the two transmission branches. Alternatively, the two power amplifiers
214
and
216
for the two transmitting frequencies can be substituted through a single power amplifier with two output terminals and a downstream impedance matching circuit.
This direct generalization of the single band transmitting/receiving circuit shown in
FIG. 7
leads to the advantage that the different transmission branches for both transmitting frequency bands are completely decoupled. However, while suitable impedance matching of the different transmitting frequency bands is achieved through the separated and fully decoupled provision of the impedance matching circuits this is only achieved with a high circuit complexity. On the one hand this leads to an increase in the production costs and on the other hand also the space requirements necessary for such a dual band transmitting/receiving change over unit constitute a barrier for the implementation thereof.
In view of the above, the object of the present invention is to achieve an improved matching of a power amplifier outputting transmitting signals in different transmitting frequency bands over a single output terminal to impedances of the different transmission branches in a dual band mobile phone.
According to the invention, this object is achieved through a power amplifier output circuit for a dual band mobile radio unit according to claim 1. The power amplifier output circuit comprises a first transmitter/receiver change over means for transmitting/receiving a first transmitting/receiving signal, the transmitter/receiver change over means being provided with an input terminal to which a first impedance matching means is connected, a second transmitter/receiver change over means for transmitting/receiving a second transmitting/receiving signal, a transmission branch change over means to selectively connect the first transmitter/receiver change over means or the second transmitter/receiver change over means to a power amplifier outputting transmitting signals in two frequency bands such that a second impedance matching means is provided between an output terminal of the power amplifier and the transmission branch change over means and the transmission branch change over means comprises at least two switching elements being connected in parallel in a branch connecting the power amplifier with the first transmitter/receiver change over means.
Therefore, for the present invention the stepwise approach to impedance matching in at least one transmission branch of the power amplifier output circuit is of importance as well as the simultaneous use of a plurality of switching elements connected in parallel. Both measures in functional relationship lead to a significant minimization of parasitic disturbances in the power amplifier output circuit. At the same time, there is also achieved a suitable impedance matching for the respective frequency bands and transmitting powers in both transmission branches.
Further, while the use of only a single impedance matching at the output of the power amplifier will not lead to an optimum impedance matching for both transmission branches according to the present invention this is achieved, firstly, through the first common impedance matching at the output of the power amplifier and, secondly, through a further impedance matching optimized for each transmitting frequency band, respectively. Further, since the common impedance matching is used for both. frequency bands the circuit complexity may be reduced significantly.
Still further, the present invention takes into account that the power absorption in parasitic elements of the transmission branch change over means increases when the disturbing real part of the impedance of the transmission branch change over means lies close to the output impedance of the power amplifier. E.g., the real part of output impedances of practically used power amplifiers lies in the range from approximately 5 to 6 &OHgr; while typical connecting resistances of different switching elements lie in the range of approximately 1 &OHgr;. In case switching elements are inserted in the transmission branch change over unit only after a firs
Burns Doane Swecker & Mathis L.L.P.
Perez-Gutierrez Rafael
Telefonaktiebolaget LM Ericsson
Trost William
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