JP2013098785A - Duplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact duplexer that has a matching circuit comprising lumped constant elements.SOLUTION: The duplexer includes: an input terminal 102; a first output terminal 116; a second output terminal 118; a first filter 110 arranged between the input terminal and the first output terminal; a second filter 112 arranged between the input terminal and the second output terminal; and a first matching circuit 100 arranged between the input terminal and the first and second filters. The matching circuit includes: a first capacitor 106 comprising a set of capacitor electrodes and having one of the capacitor electrodes connected to the first filter; a second capacitor 108 comprising a set of capacitor electrodes, and having one of the capacitor electrodes connected to the second filter and the other of the capacitor electrodes connected to the other of the capacitor electrodes of the first capacitor; a first inductor 104 arranged between a junction 148 of the first and second capacitors and the input terminal; and a ground circuit 130 comprising reactance elements arranged between the junction and a ground.

Description

  The present invention relates to a duplexer, and more particularly to a duplexer composed of passive elements.

  Multiband-compatible mobile phones capable of making calls and transmitting / receiving data using a plurality of communication methods have become widespread. A multi-band mobile phone includes a duplexer that separates a multi-band signal on which signals of a plurality of frequency bands are superimposed for each frequency band.

  A duplexer typically includes a plurality of bandpass filters having unique passbands. When a plurality of bandpass filters are connected, the input impedance is out of the matching state, so that the loss of the signal in the passband increases. Therefore, when a plurality of bandpass filters are connected, a matching circuit that matches the input impedance in the passband of each bandpass filter is disposed in front of these bandpass filters.

  The matching circuit is roughly classified into a distributed constant type matching circuit configured using distributed constant lines and a lumped constant type matching circuit configured using lumped constant elements. For example, Japanese Unexamined Patent Application Publication No. 2007-266897 (Patent Document 1) discloses a distributed constant type matching circuit configured by connecting a plurality of distributed constant lines in multiple stages. Since the amount of phase shift in the distributed constant type matching circuit is determined by the electrical length of the distributed constant line, the size of the distributed constant type matching circuit is inevitably increased according to the amount of phase shift. On the other hand, Japanese Unexamined Patent Application Publication No. 2010-527192 (Patent Document 2) discloses a lumped constant type matching circuit formed by combining lumped element elements. A lumped constant matching circuit is easy to downsize, but no method has been established to determine the arrangement and value of elements that achieve impedance matching. difficult.

JP 2007-266897 A JP 2010-527192 A

  Various embodiments of the present invention provide a small duplexer having a matching circuit comprised of lumped elements. Other problems will be understood from the following detailed description and the accompanying drawings.

  A duplexer according to an embodiment of the present invention includes an input terminal to which a reception signal from an antenna is input, a first output terminal, a second output terminal, and between the input terminal and the first output terminal. A first filter that passes a signal in a first pass band, and is arranged between the input terminal and the second output terminal, and has a second pass band that is different from the first pass band. A second filter for passing a signal; and a first matching circuit disposed between the input terminal and the first and second filters. In one embodiment, the matching circuit comprises a set of capacitor electrodes, one capacitor electrode comprising a first capacitor connected to the first filter, and a set of capacitor electrodes, wherein one capacitor electrode is the above-described capacitor electrode. A second capacitor connected to the second filter and having the other capacitor electrode connected to the other capacitor electrode of the first filter; and between a connection point of the first and second capacitors and the input terminal. A first inductor disposed; and a ground circuit including a reactance element disposed between a connection point of the first and second capacitors and the ground.

  According to various embodiments of the present invention, a small duplexer having a matching circuit made up of lumped elements is provided.

1 is a circuit diagram showing a duplexer according to an embodiment of the present invention. The schematic diagram explaining the impedance matching of the diplexer which concerns on one Embodiment of this invention Smith chart showing input impedance of diplexer according to one embodiment of the present invention The graph showing the attenuation characteristic of the diplexer which concerns on one Embodiment of this invention The graph showing the attenuation characteristic of the diplexer which concerns on one Embodiment of this invention Smith chart showing input impedance of duplexer according to one embodiment of the present invention The graph showing the attenuation characteristic of the duplexer which concerns on one Embodiment of this invention The graph showing the attenuation characteristic of the duplexer which concerns on one Embodiment of this invention The graph showing the attenuation characteristic of the duplexer which concerns on one Embodiment of this invention

  Various embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a duplexer 10 according to an embodiment of the present invention. The duplexer 10 according to an embodiment of the present invention separates a multiband signal input from an antenna (not shown) via an input terminal 102 into signals of individual frequency bands, and the separated signals are output to the output terminals 116, Output from 118 and 120 to the subsequent circuit. The duplexer 10 is used, for example, as a front end module of a mobile phone.

  SAW filters 110, 112, and 114 are arranged in parallel between the input terminal 102 and the output terminals 116, 118, and 120. Each of the SAW filters 110, 112, 114 has a unique pass band. For example, the pass band of the SAW filter 112 can be set to 2110-2170 MHz, which is the band I reception band of UMTS (Universal Mobile Telecommunications System). Further, the pass band of the SAW filter 110 is 1930-1990 MHz, which is a reception band of Band II of UMTS, and the pass band of the SAW filter 114 is 1574-1576 MHz assigned to the L1 band of GPS (Global Positioning System). It can be. In the present specification, the pass bands of the SAW filters 110, 112, and 114 may be referred to as “first pass band”, “second pass band”, and “third pass band”, respectively. In one embodiment, signals in frequency bands corresponding to the first to third passbands are superimposed on the multiband signal received from the antenna. A signal in a frequency band other than the frequency band corresponding to the first to third passbands may be superimposed on the multiband signal.

  A matching circuit 100 is disposed between the input terminal 102 and the SAW filters 110 and 112. The matching circuit 100 is configured by combining a capacitor and an inductor, which are lumped element type reactance elements. In one embodiment, the matching circuit 100 includes a capacitor 106 connected in front of the SAW filter 110 (on the input terminal 102 side), a capacitor 108 connected in front of the SAW filter 112, and a connection between the capacitor 106 and the capacitor 108. The inductor 104 is disposed between the point 148 and the input terminal 102, and the ground circuit 130 is disposed between the connection point 148 and the ground. A high-pass filter type matching circuit 140 is disposed between the input terminal 102 and the SAW filter 114. The ground circuit 130 includes a capacitor 132 and an inductor 134. For example, the capacitor 132 is disposed closer to the inductor 104 than the inductor 134. The capacitor 132 and the inductor 134 are arranged so that one of them is grounded. The high-pass filter type matching circuit 140 is a known high-pass filter including a set of capacitors 142 and 144 connected in series and an inductor 146 disposed between the connection point of these capacitors and the ground.

  As described above, the duplexer 10 constitutes a third branching circuit in which the second branching circuit (diplexer) 150 including the SAW filters 110 and 112 and the circuit including the SAW filter 114 are arranged in parallel.

  In the matching circuit 100, as described above, the capacitor 106 and the inductor 104 are inserted in series between the input terminal 102 and the SAW filter 110, and the inductor 134 and the capacitor 132 are inserted in parallel. Similarly, a capacitor 108 and an inductor 104 are inserted in series between the input terminal 102 and the SAW filter 112, and an inductor 134 and a capacitor 132 are inserted in parallel. By these reactance elements, the impedance of the pass band is matched with the reference impedance, and the signal outside the pass band (here, the signal of the third pass band) is suppressed.

  The element values of the capacitors 106, 108, 132 and the inductors 104, 134 are determined based on whether the combined input impedance of the diplexer including the SAW filters 110, 112 in the duplexer 10 is the input terminal 102 or the output in the first and second passbands. It is determined so as to match the characteristic impedance (usually 50Ω) of the external circuit connected to the terminals 116 and 118 and to have a high impedance close to infinity in the third passband. In one embodiment, the element value of the inductor 104 is determined to offset the change in reactance due to the capacitors 106 and 108 being inserted in series, respectively. Specifically, the element value of the inductor 104 is such that the reactance value in the first pass band is substantially the same as the reactance value in the first pass band of the capacitor 106 and has an absolute value different from that of the second value. The reactance value in the pass band is determined so that the absolute value is substantially the same as the reactance value in the second pass band of the capacitor 108 and the polarity is different. The element value of the ground circuit 130 is determined so as to cancel the change in susceptance caused by connecting the SAW filter 110 and the SAW filter 112 in parallel. Specifically, the element value of the ground circuit 130 is the first pass band when the combined susceptance value in the first pass band is the filter 112 provided with the capacitor 108 viewed from the connection point 148 side to the output terminal 118 side. The input susceptance value and the absolute value of the first filter 110 in the second pass band of the first filter 110 provided with the capacitor 106 are seen from the connection point 148 side to the output terminal 116 side. In addition, the input susceptance value and the absolute value in the second pass band are set to be substantially the same and different in polarity.

  2A to 2F are schematic diagrams for explaining impedance matching of signals in the first and second passbands in the duplexer 10. FIG. 2A to 2F are Smith charts showing the input impedance of the SAW filter viewed from the input terminal 102 (common terminal) side and the input impedance of the diplexer 150 viewed from the input terminal 102 side. This is shown schematically. In FIG. 2, a marker m1 indicates an impedance at 2110 MHz, which is a low frequency end of the second pass band, and a marker m2 indicates an impedance at 2170 MHz, which is a high frequency end of the second pass band. The marker m3 indicates the impedance at 1930 MHz, which is the low frequency end of the first pass band, and the marker m5 indicates the impedance at 1990 MHz, which is the high frequency end of the first pass band. The marker m4 indicates the impedance at 1575 MHz that is the center frequency of the third passband.

  FIG. 2A shows the input impedance of the SAW filter 110 and the SAW filter 112 alone. As shown in the figure, the impedance of the SAW filter 112 is generally matched to 50Ω, which is the reference impedance, in the range of m1 to m2, which is the second passband, and is substantially in the capacitive region in the other bands. The impedance of the SAW filter 110 is matched to approximately 50Ω in the range of m3 to m5, which is the first pass band, and is substantially in the capacitive region in the other bands. It is known that the input impedance of a single SAW filter is not limited to the example of FIG. 2A and is capacitive in most frequency bands.

  As shown in FIG. 2B, capacitors 106 and 108 are provided in front of the SAW filters 110 and 112, respectively, in order to increase the out-of-band input impedance. As shown in the figure, the impedances of the SAW filters 110 and 112 are rotated counterclockwise on the equal resistance line in the Smith chart by the capacitors 106 and 108. Specifically, the capacitor 106 rotates frequency components other than the pass band of the SAW filter 110 to the high impedance side on the equal resistance line, and the capacitor 108 causes frequency components other than the pass band of the SAW filter 112 to move on the equal resistance line. Rotates to high impedance side. The capacitors 106 and 108 deviate from the reference impedance of the passband impedance, but the passband impedance is matched to the reference impedance by the phase rotation by the inductor 104 as described later.

  Next, as shown in FIG. 2C, when the SAW filters 110 and 112 are connected in parallel to form the diplexer 150 (the inductors 104 and 134 and the capacitor 132 are omitted), the connection point is viewed. The input impedance of the diplexer 150 is obtained by rotating the single input impedance of the SAW filters 110 and 112 clockwise along the isoconductance line. That is, by connecting the SAW filters 110 and 112 in parallel, a phase rotation effect equivalent to inserting a grounded capacitor in parallel can be obtained. The SAW filter 110 provided with the capacitor 106 shown in FIG. 2B functions as a grounded capacitor in the second pass band, and the SAW filter 112 provided with the capacitor 108 is grounded in the first pass band. This is because it functions as a capacitor.

  Next, as shown in FIG. 2D, an inductor 134 is inserted in parallel between the connection point 148 and the input terminal 102. By this inductor 134, the input impedance of the diplexer 150 rotates counterclockwise along the isoconductance line. As shown in the figure, this phase rotation causes the m4 frequency band signal corresponding to the third passband to rotate to the high impedance region and the first and second passbands to rotate in the vicinity of the reference impedance. Since this inductor is provided between the connection point 148 between the capacitor 106 and the capacitor 108 and the input terminal 102, the circuit can be reduced in size compared to the case where individual inductors are provided in front of the SAW filters 110 and 112, respectively. Can be

  Next, as shown in FIG. 2 (e), a capacitor 132 is inserted in parallel, adjusted to an equal resistance line of 50Ω in the first passband and the second passband, and the impedance of the third passband is set. By performing fine adjustment of the impedance by rotating in a region close to infinity, the signal in the third passband is further suppressed. When such a fine adjustment of impedance is performed using a capacitor, the element value of the capacitor can be set to a small value. When fine adjustment of the impedance is performed only by the inductor, a large element value is required. That is, by adjusting the characteristics using the two elements of the capacitor 132 and the inductor 134, the element value of the inductor 134 can be designed to a small value. Further, the inductor 134 is inserted mainly for the purpose of matching the pass band (first and second pass bands) with the reference impedance, so that only one element of the inductor 134 (that is, without using the capacitor 132). When the circuit is designed, there is a possibility that the input impedance in the stop band (third pass band) cannot be sufficiently increased. On the other hand, by designing a circuit using the two elements of the inductor 134 and the capacitor 132 and appropriately setting the respective element values, it is possible to achieve both a high stop band impedance and a matching pass band. . If the impedance of the third passband is adjusted to infinity by inserting the inductor 134, the capacitor 132 can be omitted.

  Next, as shown in FIG. 2F, the inductor 104 is inserted in series, and the input impedance of the diplexer 150 is rotated clockwise along the equal resistance line. Since the third passband is already located in a region close to infinity, even if the inductor 104 is inserted in series, the impedance in the third passband does not move from the infinity region.

  As described above, the impedance of the diplexer 150 rotates counterclockwise on the equal resistance line by the capacitors 106 and 108 inserted in series between the SAW filters 110 and 112 and the input terminal 102, respectively. The deviation from the reference impedance due to the phase rotation is canceled by inserting the inductor 104 in series between the connection point of the capacitors 106 and 108 and the input terminal 102. Therefore, the element values of inductor 104 and capacitors 106 and 108 are set so that the amount of phase shift rotation due to serial insertion of capacitors 106 and 108 and the amount of phase shift rotation due to serial insertion of inductor 104 are equal. For example, as described above, the reactance value of the inductor 104 is substantially the same as the reactance value in the first pass band of the capacitor 106 in the first pass band and has an absolute value that is substantially the same as the reactance value. The reactance value in the second pass band is determined so that the absolute value is substantially the same as the reactance value in the second pass band of the capacitor 108 and the polarity is different. Further, since the input impedance is rotated clockwise on the isoconductance line by connecting the capacitor 106 and the capacitor 108, the capacitor 132 and the inductor 134 are connected in parallel between the connection point and the input terminal 102. The phase rotation on the isoconductance line is canceled by inserting it into the. Therefore, the element values of the capacitor 132 and the inductor 134 are substantially equal in polarity to the susceptance value in the first pass band of the SAW filter 112 in which the combined susceptance value in the first pass band is provided with the capacitor 108. And the combined susceptance value in the second pass band is set so that the absolute value of the susceptance value in the second pass band of the SAW filter 110 provided with the capacitor 106 is substantially equal and the polarity is different. From such a viewpoint, in one embodiment, the capacitance values of the capacitors 106, 108, and 132 are 1.9 pF, 2.1 pF, and 0.25 pF, respectively, and the inductance values of the inductors 104 and 134 are 2.3 nH, 4 .4 nH.

  FIG. 3 is a Smith chart showing the simulation result of the input impedance viewed from the input terminal 102 of the diplexer 150 shown in FIG. In the simulation, the passbands of the SAW filters 110 and 112 are 1930-1990 MHz and 2110-2170 MHz, respectively, and the capacitance values of the capacitors 106, 108, and 132 are 1.9 pF, 2.1 pF, and 0.25 pF. , 134 are 2.3 nH and 4.4 nH, respectively. The impedance shown in FIG. 3 was measured by sweeping the frequency from 500 MHz to 3 GHz. As illustrated, the markers m1, m2, m3, and m5 corresponding to the first and second passbands are all distributed around 50Ω, and the marker m4 corresponding to the third passband is infinite. It was confirmed that it is located in a close high impedance region. Thus, the first and second passband signals are input to the SAW filters 110 and 112 with low loss, respectively, while the third passband signal does not reach the SAW filters 110 and 112.

  4 and 5 are graphs showing simulation results of the attenuation characteristics of the diplexer 150 shown in FIG. These attenuation characteristics are the result of simulating by combining the characteristics of the SAW filter 110 and the SAW filter 112 constituting the diplexer 150 into a circuit simulator and synthesizing these characteristics with the passive elements constituting the matching circuit 100. These SAW filter attenuation characteristics are available from Agilent Technologies, Inc., headquartered in California, USA. Of PNA-L. 4 and 5, the horizontal axis represents the frequency in GHz, and the vertical axis represents the magnitude of the S parameter indicating the attenuation characteristic in dB. A curve 401 in FIG. 4 represents the attenuation characteristic between the input terminal 102 and the output terminal 118, and a curve 501 in FIG. 5 represents the attenuation characteristic between the input terminal 102 and the output terminal 116.

  As is apparent from FIG. 4, the attenuation between the input terminal 102 and the output terminal 118 is sufficiently small at approximately 3dB or less at 2110-2170 MHz allocated to band I of UMTS, and sufficiently large in other bands. . Further, as is apparent from FIG. 5, the attenuation between the input terminal 102 and the output terminal 116 is sufficiently small at about 5.0 dB or less at 1930-1990 MHz allocated to the band II of UMTS. Big enough.

  FIG. 6 is a Smith chart showing the simulation result of the input impedance viewed from the input terminal 102 of the duplexer 10 shown in FIG. In the measurement, the passbands of the SAW filters 110, 112, and 114 were set to 1930-1990 MHz, 2110-2170 MHz, and 1574-1576 MHz, respectively. The element values of the reactance elements of the matching circuit 100 are set to the same values as in the simulation of FIG. 3, the capacitance value of the capacitor 142 is 4.4 pF, the capacitance value of the capacitor 144 is 2.2 pF, and the inductance of the inductor 146 The value was set to 6.2 nH, respectively. As shown in the figure, it was confirmed that all of the markers m1 to m5 corresponding to the first to third passbands are distributed in the vicinity of 50Ω.

  7 to 9 are graphs showing simulation results of the attenuation characteristics of the duplexer 10 shown in FIG. Similar to the graph of FIG. 5, these attenuation characteristics are the results of simulating by incorporating the circuit elements constituting the duplexer 10 into a circuit simulator. A curve 701 in FIG. 7 represents an attenuation characteristic between the input terminal 102 and the output terminal 118, a curve 801 in FIG. 8 represents an attenuation characteristic between the input terminal 102 and the output terminal 116, and a curve 901 in FIG. The attenuation characteristic between the output terminals 120 is represented.

  As apparent from the graphs of FIGS. 7 and 8, the attenuation between the input terminal 102 and the output terminal 118 and the attenuation between the input terminal 102 and the output terminal 116 are the same as the simulation results shown in FIGS. Each of 2110-2170 MHz and 1930-1990 MHz is sufficiently small, and is sufficiently large in other bands. As is clear from FIG. 9, the attenuation between the input terminal 102 and the output terminal 120 is sufficiently small in 1574 to 1576 MHz allocated to the GPS L1 band, and sufficiently large in other bands.

  As described above, the duplexer 10 according to the embodiment of the present invention can separate a multiband received signal on which signals of three different frequency bands are superimposed into signals of the respective frequency bands. The impedance matching of the duplexer 10 can be configured with five capacitors (capacitors 106, 108, 132, 142, 144) and three inductors (inductors 104, 134, 146). The number of reactance elements can be reduced as compared with the matching circuit used in the third branching circuit. For example, in the third branching circuit disclosed in Japanese Patent Application Laid-Open No. 2009-534871, seven capacitors and six inductors are used. Further, in the third demultiplexing circuit described in Japanese Patent Application Laid-Open No. 2010-527192 described above, five units, capacitors, and five inductors are used. The duplexer 10 according to the embodiment of the present invention can realize a duplexer that demultiplexes the received signal into 3 with a small number of elements, as compared with the conventional 3 demultiplexing circuit represented by these. Further, even when the element values of the capacitors 106 and 108 and the inductor 134 are set to relatively small values, the phase rotation necessary for suppressing the out-of-band signal can be sufficiently realized. Therefore, the capacitors 106 and 108 and the inductor 134 can be formed relatively small. As described above, since the duplexer 10 according to the embodiment of the present invention has a small number of inductors and can set the element value of the inductors to be small, the LTCC (low temperature co-fired ceramics) multilayer circuit board. Thus, when the duplexer 10 is realized, the size can be reduced as compared with a circuit having a large number of inductors or a circuit using an inductor having a large capacity. When the LTCC multilayer circuit board is fabricated, the capacitor 130 disposed between the inductor 104 and the inductor 134 is replaced with the parasitic capacitance of the lines and the planar electrodes constituting the inductor 104, the inductor 134, the capacitor 108, and the capacitor 106. Therefore, further downsizing is possible.

  The circuit configuration of the duplexer shown in FIGS. 1 to 3 can be changed as appropriate. For example, the passbands of the SAW filters 110, 112, and 114 described in this specification are examples, and filters having various passbands can be used. Further, instead of the SAW filters 110, 112, and 114, various filters such as a bulk acoustic wave filter (BAW filter) that have capacitive impedance outside the band can be used. FIG. 1 shows an example in which the received signal is demultiplexed into three. However, a circuit that demultiplexes the received signal into four or more signals can be realized by adding a filter such as a SAW filter in parallel. it can. Additional filters may be added in parallel with the SAW filters 110, 112 within the diplexer 150, and may be added in parallel with the SAW filter 114 outside the diplexer 150. When a filter is added in the diplexer 150, a capacitor is inserted in the same stage as the capacitors 106 and 108 before the added filter.

  Further, the SAW filters 110, 112, and 114 may be dielectric filters. The duplexer according to the present invention can be mounted on various wireless communication devices other than the mobile phone. The duplexer according to the present invention can be further reduced in size by being built in an LTCC (low temperature co-fired ceramics) multilayer circuit board.

  The embodiments of the present invention are not limited to the modes explicitly described above, and various modifications can be made to the above-described embodiments without departing from the spirit of the present invention.

  10 demultiplexer, 100, 140 matching circuit, 102 input terminal, 110, 112, 114 SAW filter, 116, 118, 120 output terminal, 130 ground circuit, 106, 108, 132, 142, 144 capacitor, 104, 134, 146 inductor

Claims (10)

An input terminal for receiving a signal received from the antenna;
A first output terminal;
A second output terminal;
A first filter disposed between the input terminal and the first output terminal and passing a signal in a first passband;
A second filter disposed between the input terminal and the second output terminal and passing a signal in a second passband different from the first passband;
A first matching circuit disposed between the input terminal and the first and second filters;
With
The first matching circuit comprises:
A first capacitor comprising a set of capacitor electrodes, one capacitor electrode connected to the first filter;
A second capacitor comprising a set of capacitor electrodes, wherein one capacitor electrode is connected to the second filter and the other capacitor electrode is connected to the other capacitor electrode of the first filter;
A first inductor disposed between a connection point of the first and second capacitors and the input terminal;
A ground circuit comprising a reactance element disposed between a connection point of the first and second capacitors and the ground;
A duplexer comprising:   2. The duplexer according to claim 1, wherein the ground circuit includes a second inductor disposed between a connection point of the first and second capacitors and the ground.   The duplexer according to claim 1 or 2, wherein the ground circuit includes a third capacitor disposed between a connection point of the first and second capacitors and the ground.   The reactance value of the first inductor in the first passband is substantially the same as the reactance value of the first capacitor in the first passband and has a different polarity. The duplexer described in the paragraph.   5. The reactance value of the first inductor in the second passband is substantially the same as the reactance value of the second capacitor in the second passband and has a different polarity. The duplexer described in the paragraph.   The susceptance value in the first pass band of the ground circuit is in the first pass band when the second filter provided with the second capacitor is viewed from the connection point side of the first capacitor and the second capacitor. The duplexer according to any one of claims 1 to 5, wherein the input susceptance value and the absolute value are substantially equal and have different polarities.   The susceptance value in the second pass band of the ground circuit is in the second pass band when the first filter provided with the first capacitor is viewed from the connection point side of the first capacitor and the second capacitor. The duplexer according to any one of claims 1 to 6, wherein the input susceptance value and the absolute value are substantially equal and have different polarities. A third output terminal;
A third filter disposed between the input terminal and the third output terminal and passing a signal in a third passband different from any of the first and second passbands;
The duplexer according to any one of claims 1 to 7, further comprising:   9. The duplexer according to claim 8, further comprising a high-pass filter type second matching circuit disposed between the input terminal and the third filter.   A wireless communication apparatus comprising the duplexer according to claim 1.

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