Mobile phone

Prior Art

0001The invention proceeds from the mobile phone in accordance with the generic class of the independent patent claims. Such a mobile phone is described in <patcit id="pcit0001" dnum="EP0859464A"><text>EP-A-0859464</text></patcit>.

0002It is already well known, that power amplifiers, which are used for radio transmitters in mobile phones must allow a precise control of the power level of the output radio frequency signal. Therefore, the output radio frequency signal has to be coupled from the output of the power amplifier into a control loop.

0003It is also already well known to use mobile phones for two frequency bands. The Motorola "Micro Tac 8900" mobile phone allows automatic shifting between the GSM 900 MHz and the GSM 1800 MHz frequency band. <patcit id="pcit0002" dnum="DE2607530C2"><text>DE 26 07 530 C2</text></patcit> discloses a radio transmitter/receiver operating in two frequency bands. The modulated oscillator signal of the two oscillators are supplied via an inductive coupler to an amplifier.

Advantages of the invention

0004The mobile phone having the characterizing features of the independent patent claims, has the advantage, that two or more control loops which are sharing the same loop control can use a common coupler for coupling the output signals of the control loops back into the control loops. Therefore, further couplers can be saved as well as combining filters or switches to connect an input port of the common loop control to different couplers. This saves space and costs.

0005In multiband mobile phones, common loop controls may be shared by control loops of voltage control oscillators generating signals at frequencies in different frequency bands. Such common loop controls are independent on frequencies.

0006The features of the dependent patent claim enable further improvements of the invention. A very simple realization of such a coupler consists in utilizing at least three adjacent transmission lines and to profit from the physical effect of coupling of alternating current between them. This also saves costs.

0007Further space can be saved by realizing the transmission lines as strip lines embedded into a printed circuit board. This configuration allows also the realization of a common coupler for more than two control loops.

0008A further advantage results by grounding the third one of the at least three transmission lines at a second end via a resistor, whereby the first end of the third one of the at least three transmission lines constitutes a common coupling port. Therefore, disturbing signals at an output port of the common coupler are not coupled to the common coupling port.

Drawings

0009An exemplary embodiment of the invention is shown in <figref idref="f0001">figure 2</figref> and explained in greater detail in the description below. <figref idref="f0001">Figure 1</figref> shows a block diagram of a mobile phone with a common loop control for the control loops of two power amplifiers for different frequency bands, <figref idref="f0001">figure 2</figref> a block diagram of an embodiment of the invention with a common loop control for the control loops of two voltage controlled oscillators for different frequency bands, <figref idref="f0002">figure 3</figref> a realization of a common coupler using three transmission lines embedded into a printed circuit board, <figref idref="f0002">figure 4</figref> a realization of a common coupler with three transmission lines on a surface of a printed circuit board and <figref idref="f0002">figure 5</figref> a realization for a common coupler with four transmission lines embedded into a printed circuit board.

Description

0010In <figref idref="f0001">figure 1</figref>, 25 designates a mobile phone for use in two separate frequency bands. Therefore, in a transmission path of the mobile phone 25 there is provided a first power amplifier 95 for amplifying signals at frequencies in a first frequency band and a second power amplifier 100 for amplifying signals at frequencies in a second frequency band. Preceeding transmission stages of the transmission path and other components of the mobile phone 25 e.g. for reception of signals are not shown in <figref idref="f0001">figure 1</figref>. The amplification of the first power amplifier 95 is controlled by a first control loop 5 and the amplification of the second power amplifier 100 is controlled by a second control loop 10. Therefore, an output 45 of the first power amplifier 95 is coupled back into the first control loop 5 and therefore represents an output port of the first control and therefore represents an output port of the first control loop 5. An output 50 of the second power amplifier 100 is coupled back into the second control loop 10 and therefore represents an output port of the second control loop 10. For coupling back the output signals of the first power amplifier 95 and the second power amplifier 100 into their corresponding control loop 5, 10, a common coupler 1 is used. A first input port 30 of the common coupler 1 is connected to the output port 45 of the first power amplifier 95 and a second input port 35 of the common coupler 1 is connected to the output port 50 of the second power amplifier 100. The first input port 30 is connected to a first end 81 of a first transmission line 60 and the second input port 35 is connected to a first end 91 of a second transmission line 65. The first transmission line 60, the second transmission line 65, and a third transmission line 70 in the middle between the first transmission line 60 and the second transmission line 65 are arranged parallel to each other. The first transmission line 60 and the second transmission line 65 are therefore arranged adjacent to the third transmission line 70. This arrangement of the three transmission lines 60, 65, 70 provides a coupling of a certain amount of signal power of the signals on the first transmission line 60 and the second transmission line 65 to the third transmission line 70. Supposing, that the first power amplifier 95 amplifies signals at frequencies in the GSM 900 MHz frequency band (GSM = Global System for Mobile Communications) and that the second power amplifier 100 amplifies signals at frequencies in the GSM 1800 MHz frequency band, the signals coupled from the first transmission line 60 and the second transmission line 65 to the third transmission line 70 are high frequency signals. As only one of the two power amplifiers 95, 100 is powered at a time, either signals from the first transmission line 60 or signals from the second transmission line 65 are coupled to the third transmission line 70. At a first end 101 of the third transmission line 70, the third transmission line 70 is connected to a common coupling port 40 of the common coupler 1. The common coupling port 40 is connected to an input 85 of a first common loop control 55 which receives the signals coupled from the first transmission line 60 or the second transmission line 65 to the third transmission line 70. The first common loop control 55 is shared by the first control loop 5 and the second control loop 10 and provides a control signal for the first power amplifier 95 and the second power amplifier 100. Only the power amplifier 95, 100, which is actually powered, may be controlled by the control signal of the first common loop control 55. As the first common loop control 55 controls the first power amplifier 95 and the second power amplifier 100 by use of an amplitude modulation technique, it is not frequency dependent and therefore can be utilized for the different frequency bands of both power amplifiers 95, 100.

0011A second end 82 of the first transmission line 60 is connected to a first output port 125 of the common coupler 1. A second end 92 of the second transmission line 65 is connected to a second output port 130 of the common coupler 1. A second end 102 of the third transmission line 70 is connected to ground via a first resistor 80. The output ports 125, 130 of the common coupler 1 are connectable to an antenna 135 via an antenna switch circuit 140, respectively.

0012In the described example, a system impedance of 50 Ω is chosen for the mobile phone 25. Therefore, the common coupler 1 has an input impedance of 50 Ω at its first input port 30, at its second input port 35, at its common coupling port 40, at its first output port 125 and at its second output port 130. The input impedance at the several ports is input impedance at a third output port 131 of the common coupler 1, which is connected to the second end 102 of the third transmission line 70, is also 50 Ω. The impedance of the antenna 135 is also 50 Ω. Therefore, a signal transmitted to the antenna 135 is not reflected from the antenna 135 back into the transmission path. If the antenna 135 changes its impedance e.g. by demolition, there will be a mismatch and a certain amount of the signal power transmitted to the antenna 135 will be reflected into the transmission path. Thereby, the first resistor 80 ensures, that the signal reflection of the antenna 135 is essentially not coupled to the first common coupling port 40 and so into the first common loop control 55, but to the first resistor 80. Therefore, the control of the amplification of the first power amplifier 95 and the second power amplifier 100 is not disturbed by signal reflection of a mismatched antenna 135.

0013An embodiment of the invention is shown according to <figref idref="f0001">figure 2</figref>. In <figref idref="f0001">figure 2</figref> same numerals designate same components as in <figref idref="f0001">figure 1. Figure 2</figref> shows a transmission stage of the mobile phone 25 preceeding the amplification stage shown in <figref idref="f0001">figure 1</figref>. In <figref idref="f0001">figure 2</figref>, the common coupler 1 is the same as described according to <figref idref="f0001">figure 1</figref>. The first output port 125 of the common coupler 1 is connected to the first power amplifier 95, the second output port 130 of the common coupler 1 is connected to the second power amplifier 100 and the third output port 131 of the common coupler 1 is connected to ground via a second resistor 81. The second resistor 81 has also a resistance of 50 Ω. The first input port 30 of the common coupler 1 is connected to an output 46 of a first voltage controlled oscillator 145. The second input port 35 of the common coupler 1 is connected to an output 51 of a second voltage controlled oscillator 150. The output 46 of ' the first voltage controlled oscillator 145 is an output port of the third control loop 15 and the output 51 of the second voltage controlled oscillator is an output output 51 of a second voltage controlled oscillator 150. The output 46 of the first voltage controlled oscillator 145 is an output port of the third control loop 15 and the output 51 of the second voltage controlled oscillator is an output port of the fourth control loop 20. The common coupling port 40 of the common coupler 1 is connected to an input 86 of a second common loop control 56. The second common loop control 56 is shared by a third control loop 15 and a fourth control loop 20. The third control loop 15 controls the oscillation frequency of the first voltage controlled oscillator 145 via a first phase detector 155. The fourth control loop 20 controls the oscillation frequency of the second voltage controlled oscillator 150 via a second phase detector 160. The first voltage controlled oscillator 145 provides frequencies in the first frequency band and the second voltage controlled oscillator provides frequencies in the second frequency band. Either the first or the second voltage controlled oscillator 145, 150 is powered at a time. Therefore, either signals on the first transmission line 60 or signals on the second transmission line 65 are coupled to the third transmission line 70 and therefore back into the corresponding control loop 15, 20. The second common loop control 56 therefore provides either a control signal for the first phase detector 155 or a control signal for the second phase detector 160. As the second common loop control 56 also provides control signals based on amplitude modulation, it is also independent of frequency and therefore can be used in both separated frequency bands and shared by the third and the fourth control loop 15, 20.

0014The function of the common coupler 1 is the same as described according to <figref idref="f0001">figure 1</figref>. Also, the common coupler 1 has an input impedance of 50 Ω at its first input port 30, at its second input port 35, at its common coupling port 40, at its first output port 125, at its second output port 130, and, because of the second resistor 81 of 50 Ω also at its third output port 131. Thereby, the system impedance of the embodiment of the invention according to <figref idref="f0001">figure 2</figref> is also chosen to 50 Ω and therefore corresponds to the system impedance of the system according to <figref idref="f0001">figure 1</figref>. As described above, according to the system shown in <figref idref="f0001">figure 1</figref>, the signal reflected from the amplification stage in <figref idref="f0001">figure 2</figref> with the two power amplifiers 95, 100 back to the common coupler 1 will bis essentially coupled to the second resistor 81, but not to the common coupling port 40 of the common coupler 1 and therefore not into the third or fourth control loop 15, 20. Therefore, the control of the first and the second voltage controlled oscillator 145, 150 is not disturbed by signals reflected from the amplification stage.

0015<figref idref="f0002">Figure 3</figref> shows the common coupler 1 in more detail. The three transmission lines 60, 65, 70 are thereby realized as striplines embedded into a first printed circuit board 120. The distance between the first transmission line 60 and the third transmission line 70 is designated by the numeral 105 and will further be called the first distance. The distance between the second transmission line 65 and the third transmission line 70 is designated by the numeral 110 and will further be called the second distance. The distance between the first transmission line 60 and the second transmission line 65 is designated by the numeral 115 and will further be called the third distance. The first distance 105 and the second distance 110 essentially correspond to each other and are small in comparison with the third distance 115. The first and the second distance 105, 110 is chosen such, that an amount of 10-18 dB is coupled out from the first transmission line 60 to the third transmission line 70 or from the second transmission line 65 to the third transmission line 70. The coupling from the first transmission line 60 or the second transmission line 65 to the third transmission line 70 is indicated in <figref idref="f0002">figure 3</figref> by arrows. There is also a signal coupling between the first and the second transmission line 60, 65. Because of the third distance 115 of more than the sum of the first and the second distance 105, 110, there will only be neglectable signal coupling between the first and the second transmission line 60, 65. The outcoupling of signals from the first transmission line 60 or from the second transmission line 65 results together with conventional transmission losses at a loss of signal power of about 0,2 - 0,5 dB on the corresponding transmission line 60, 65.

0016Another realization of the common coupler 1 is shown in <figref idref="f0002">figure 4</figref>. According to <figref idref="f0002">figure 4</figref>, the transmission lines 60, 65, 70 are realized as microstrips on a surface of a second printed circuit board 121. As the three transmission lines 60, 65, 70 according to <figref idref="f0002">figure 4</figref> are arranged on the surface of the second printed circuit board 121, the dielectric material between them would be air. In the arrangement of <figref idref="f0002">figure 3</figref>, the three transmission lines 60, 65, 70 are separated by substrate dielectric material, because they are embedded into the first printed circuit board 120. Because of the different dielectric material between the three transmission lines 60, 65, 70 according to the different realizations of the common coupler 1 in <figref idref="f0002">figure 3 and figure 4</figref>, the first distance 105, the second distance 110 and the third distance 115 may lightly differ for the microstrip arrangement according to <figref idref="f0002">figure 4</figref> in comparison with the stripline arrangement of <figref idref="f0002">figure 3</figref> to provide the above described amounts of signal coupling from the first transmission line 60 to the third transmission line 70 and from the second transmission line 65 to the third transmission line 70.

0017The microstrip arrangement according to <figref idref="f0002">figure 4</figref> provides also the third distance 115 greater than the sum of the first distance 105 and the second distance 110. The signal coupling from the first transmission line 60 to the third transmission line 70 or from the second transmission line 65 to the third transmission line 70 in <figref idref="f0002">figure 4</figref> is also indicated by arrows.

0018<figref idref="f0002">Figure 5</figref> shows a stripline arrangement of a second common coupler 165 with four transmission lines 60, 65, 70, 75. Thereby, the four transmission lines 60, 65, 70, 75 are embedded into a third printed circuit board 122. As described above, the third transmission line 70 provides a common coupling port. In the arrangement of <figref idref="f0002">figure 5</figref>, not only signals from the first transmission line 60 and the second transmission line 65 are coupled to the third transmission line 70 and its common coupling port but also signals from a fourth transmission line 75. This is indicated in <figref idref="f0002">figur5</figref> by arrows. The second common coupler 165 therefore may be shared by three control loops e.g. in a triple band phone utilizing three power amplifiers for three different frequency bands and three voltage controlled oscillators for the three different frequency bands. Thereby, the distance between the first transmission line 60 and the third transmission line 70, the distance between the second transmission line 65 and the third transmission line 70 and the distance between the fourth transmission line 75 and the third transmission line 70 are approximately equal and correspond essentially to the first distance 105 and the second distance 110 which advantageously also are chosen approximately equal according to <figref idref="f0002">figure 3 and figure 4</figref>. According to <figref idref="f0002">figure 5</figref>, the third transmission line 70 is placed in the middle between the first transmission line 60, the second transmission line 65, and the fourth transmission line 75. The first transmission line 60, the second transmission line 65 and the fourth transmission line 75 are arranged in such a way, that they have maximum distance between each other to prevent essential coupling of signal power between them. The third transmission line 70 is therefore e.g. placed in the center 170 of a circle 175 and the first transmission line 60, the second transmission line 65 and the fourth transmission line 75 are placed on that circle 175, having an angle distance of 120° between each other, respectively.

0019It is also possible, to arrange more than three transmission lines on the circle 175 to share the common coupler 1 between more than three control circuits e.g. for mobile phones 25 with more than three frequency bands. The angle distance between adjacent transmission lines on the circle 175 should always be appproximately equal to provide a maximum distance between the transmission lines on the circle 175 and therefore a minimum of signal coupling between the transmission lines on the circle 175. To prevent essential signal coupling between the transmission lines on the circle 175 it could be necessary to enlarge the radius of the circle 175 to provide more distance between adjacent transmission lines on the circle 175. Thereby, the radius of the circle 175 is limited by a predetermined minimum value of e.g. 10 dB for signal coupling from a transmission line on the circle 175 to the third transmission line 70 at the center 170 of the circle 175.

0020In all figures, same components are designated by the same numerals.

0021It is also possible, to realize the transmission lines as adjacent discrete cables mounted e.g. on a printed circuit board in an arrangement and with distances between each other according to an arrangement shown in <figref idref="f0002">figure 3, figure 4 or figure 5</figref>. Thereby, the cables could also be embedded into a common dielectric material.

0022In <figref idref="f0001">figure 1</figref>, the amount of signal power which is not coupled from the first transmission line 60 or the second transmission line 65 to the third transmission line 70 is transmitted via the antenna switching circuit 140 to the antenna 135. In <figref idref="f0001">figure 2</figref> the amount of signal powerwhich is not coupled from the first transmission line 60 or the second transmission line 65 to the third transmission line 70 is transmitted via the first power amplifier 95 or the second power amplifier 100 to following stages in the transmission path.