WO2012011309A1

WO2012011309A1 - Demultiplexer

Info

Publication number: WO2012011309A1
Application number: PCT/JP2011/060815
Authority: WO
Inventors: 心平大島
Original assignee: 太陽誘電株式会社
Priority date: 2010-07-21
Filing date: 2011-05-11
Publication date: 2012-01-26
Also published as: JP2012028896A

Abstract

The disclosed demultiplexer is provided with: a first demultiplexing circuit including a first filter which allows the passage of signals of a first pass band and a second filter which allows the passage of signals of a second pass band; and a second demultiplexing circuit including a third filter which allows the passage of signals of a third pass band, to the outside of the frequency band which includes the first and second pass bands. The first demultiplexing circuit comprises a first distributed constant line which makes the input impedance of the first demultiplexing circuit a high impedance in at least a frequency band corresponding to the third pass band, and a first matching circuit which is formed from a lumped parameter element; the first demultiplexing circuit comprises a first distributed constant line which makes the input impedance of the first demultiplexing circuit a high impedance in a frequency band corresponding to the third pass band; and the second demultiplexing circuit comprises a second distributed constant line which makes the input impedance of the second demultiplexing circuit a high impedance close to infinity in at least a frequency band which includes the first and second pass bands.

Description

Duplexer

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

A multiband mobile phone capable of making a call and transmitting / receiving data using a plurality of communication methods is used by many users. 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. As the number of communication systems used increases, a duplexer that can separate more frequency components is desired.

There is a disclosed example of a duplexer that separates a received signal into three or more frequency bands. For example, a duplexer described in Japanese Patent Application Laid-Open No. 2007-266897 (Patent Document 1) includes three or more SAW filters having different pass bands, and a plurality of SAW filters are provided between each SAW filter and an input terminal. Are distributed in multiple stages. Also known is a method of separating a received signal into three or more frequency components by using an SP3T (single-pole, triple-throw) switch.

It is desirable that the high frequency circuit constituting the duplexer has a small insertion loss in the pass band and a high attenuation in the stop band.

JP 2007-266897 A

Various embodiments of the present invention provide a duplexer that can separate multiband signals into three or more frequency bands by passive elements and is easy to design.

Other problems will be understood from the following detailed description and the accompanying drawings.

A duplexer according to an embodiment of the present invention is disposed between an input terminal for receiving a received signal from an antenna, and the input terminal and the first output terminal, and passes a signal in a first passband. A first demultiplexing circuit including: a first filter that causes the first filter to pass; and a second filter that is disposed between the input terminal and the second output terminal and that passes a signal in a second passband. A third filter disposed between the terminal and the third output terminal and passing a signal in a third passband outside the frequency band including the first and second passbands. A second branching circuit. In one embodiment of the present invention, the first demultiplexing circuit includes: a first distributed constant line that sets an input impedance of the first demultiplexing circuit to a high impedance at least in a frequency band corresponding to the third passband; The input impedance of the first filter is set to a high impedance in a frequency band corresponding to the second pass band, and the input impedance of the second filter is set to the first pass band. And a first matching circuit having a high impedance in a corresponding frequency band. In one embodiment of the present invention, the second demultiplexing circuit has a second distributed constant that makes the input impedance of the second demultiplexing circuit high impedance in a frequency band including at least the first and second passbands. Has a track.

According to various embodiments of the present invention, a duplexer that can separate a multiband signal into three or more frequency bands by a passive element and is easy to design is provided.

1 is a circuit diagram showing a duplexer according to an embodiment of the present invention. Circuit diagram showing a duplexer according to another embodiment of the present invention. Circuit diagram showing a duplexer according to another embodiment of the present invention. 1 is an equivalent circuit diagram of a duplexer according to an embodiment of the present 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 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 Smith chart for explaining phase rotation by distributed constant line according to an embodiment of the present invention Smith chart for explaining phase rotation by distributed constant line according to an embodiment of the present 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 100 according to an embodiment of the present invention. The duplexer 100 according to an embodiment of the present invention separates a multiband signal input from an antenna (not shown) through an input terminal 102 into signals of individual frequency bands, and the separated signals are output to the

output terminals

116 and 118. , 120 to the subsequent circuit. The duplexer 100 is used in, for example, a mobile phone.

Between the input terminal 102 and the

output terminals

116 and 118, a high frequency side branching circuit 140 for transmitting a high frequency side signal among the input signals is provided, and between the input terminal 102 and the output terminal 120, an input is provided. A low frequency side branching circuit 160 for transmitting a low frequency side signal among the signals is provided. The high frequency side branching circuit 140 includes, for example, a SAW filter 110 having a pass band of 2110-2170 MHz and a SAW filter 112 having a pass band of 1930-1990 MHz. Further, the low frequency side branching circuit 160 includes a SAW filter 114 having a pass band of 869 to 894 MHz. 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.

The frequency band of 2110-2170 MHz corresponding to this first pass band is a band allocated for reception of band I of UMTS (Universal Mobile Telecommunications System), and a frequency of 1930-1990 MHz corresponding to the second pass band The band is a band allocated for reception of UMTS band II. In addition, 869 to 894 MHz corresponding to the third pass band is a band allocated for reception of the band V of UMTS. A signal in a frequency band corresponding to the first to third passbands is 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.

The high-frequency side branching circuit 140 includes a matching circuit 108 including one or a plurality of lumped constant type reactance elements in front of the

SAW filters

110 and 112, and the distributed constant line 104 between the matching circuit 108 and the input terminal 102. Is provided. The low frequency side branching circuit 160 includes a distributed constant line 106 between the input terminal 102 and the SAW filter 114.

The distributed constant line 104 has a line length L1, and the distributed constant line 106 has a line length L2. The distributed

constant lines

104 and 106 delay the phase of the passing signal by the amount of phase shift corresponding to each line length. The line length L1 of the distributed constant line 104 is determined so that the input impedance of the high frequency side branching circuit 140 viewed from the input terminal 102 side becomes a high impedance close to infinity in a frequency band corresponding to the third pass band. . Thereby, it is possible to prevent the signal in the third passband from leaking to the high frequency side branching circuit 140.

On the other hand, the line length L2 of the distributed constant line 106 has a high impedance close to infinity in the frequency band including the first and second passbands when the input impedance of the low frequency side branching circuit 160 viewed from the input terminal 102 side. It is decided to become. In one embodiment, the line length L2 is such that the input impedance of the low frequency side branching circuit 160 viewed from the input terminal 102 side is 2170 MHz which is the high frequency end of the first pass band and the low frequency end of the second pass band. In the frequency band between (that is, the frequency band from 1930 MHz to 2170 MHz), the impedance is determined to be close to infinity. Since the center frequencies of band I and band II are 2140 MHz and 1960 MHz, respectively, and are close to each other, the input impedance of the low frequency side branching circuit 160 is set to the respective frequency bands of band I and band II by the distributed constant line 106. The phase of the received signal can be rotated so as to have a high impedance close to infinity. Thereby, it is possible to prevent the signals in the first and second passbands from leaking to the low frequency side branching circuit 160.

Subsequent to the

SAW filters

110 and 112, or in addition to these SAW filters, a SAW filter having a pass band different from the first and second pass bands is provided as

SAW filters

110 and 112 at the subsequent stage of the distributed constant line 104. Can be connected in parallel. It is desirable that the plurality of SAW filters connected to the subsequent stage of the distributed constant line 104 have their passbands in close proximity to each other. For example, a SAW filter whose pass band is a frequency band of 1805 to 1880 MHz assigned to UMTS band III can be connected to the subsequent stage of the distributed constant line 104. Since the center frequency of band III of UMTS is 1847.5 MHz, the center frequencies of band I, band II, and band III are distributed within 300 MHz. Therefore, the line length L2 of the distributed constant line 106 can be set to an appropriate length by connecting a SAW filter having a pass band in any of the frequency bands of bands I, II, and III to the subsequent stage of the distributed constant line 104. Thus, the phase of the received signal can be rotated so that the impedance of the low frequency side branching circuit 160 viewed from the input terminal 102 side becomes a high impedance that is close to infinity in each frequency band of the bands I, II, and III. it can.

As described above, a signal passing through the low frequency side branch circuit 160 by the distributed constant line 104 is prevented from leaking to the high frequency side branch circuit 140, and also passes through the high frequency side branch circuit 140 by the distributed constant line 106. Since the signal can be prevented from leaking to the low frequency side branching circuit 160, occurrence of insertion loss in the pass band can be reduced.

The matching circuit 108 includes a capacitor, an inductor, or a combination thereof, which is a lumped element type reactance element. The matching circuit 108 connects the input impedance of the SAW filter 110 to the characteristic impedance of the external circuit of the duplexer 100 (that is, the input terminal 102 or each of the

output terminals

116, 118, 120) in the first passband. In the second pass band, and the input impedance of the SAW filter 112 is matched with the characteristic impedance of the external circuit. The arrangement and element values of the reactance elements constituting the matching circuit 108 are set such that, for example, the impedance of the SAW filter 110 viewed from the distributed constant line 104 side is the characteristic impedance (typically 50Ω) of the transmission line in the first passband. While matching, the impedance is high in the frequency band corresponding to the second pass band, and the impedance of the SAW filter 112 viewed from the distributed constant line 104 side is high impedance in the frequency band corresponding to the first pass band. It is determined to match the characteristic impedance of the transmission line in the second passband. A method for matching the impedances of two parallel-connected SAW filters is well known to those skilled in the art, and those skilled in the art can use the Smith chart, the simulation device, the capacitors constituting the matching circuit 108 based on their own experience, etc. The element value and placement of the inductor can be determined.

In another embodiment, the input impedance of the SAW filter 110 has an inductive or capacitive first reactance component in the first passband, and the input impedance of the SAW filter 112 in the first passband is The arrangement and element values of the reactance elements constituting the matching circuit 108 are determined so as to be capacitive when the first reactance component is inductive and inductive when the first reactance component is capacitive. be able to. The matching circuit 108 has an inductive or capacitive second reactance component in which the input impedance of the SAW filter 112 is in the second pass band, and the input impedance in the second pass band of the SAW filter 110 is It can be configured to be capacitive when the second reactance component is inductive and to be inductive when the second reactance component is capacitive. By connecting the SAW filters 110 and 112 to the matching circuit 108 configured in this way, the input impedance in the first pass band of the SAW filter 110 is directed from the capacitive region toward the inductive region (or inductive). Rotated from the sex region to the capacitive region). As a result, the first reactance component approaches “0”, and impedance matching of the SAW filter 110 is realized with high accuracy. Similarly, the input impedance in the second passband of SAW filter 112 is rotated from the capacitive region to the inductive region (or from the inductive region to the capacitive region). As a result, the second reactance component approaches “0”, and impedance matching of the SAW filter 112 is realized with high accuracy. For example, Denys Orlenko, Novel High-rejection LTCC Diplexers for Dual-band WLAN
Applications, IEEE MTT-S Int. Microwave Symp. Dig., June 2005, pp. 727-730.

As described above, since signals in the first and second passbands do not leak to the low frequency side branching circuit 160, reactance included in the high frequency side branching circuit 160 when impedance matching of the SAW filters 110 and 112 is performed. The influence of the element (for example, the SAW filter 114) can be ignored. That is, the arrangement of reactance elements constituting the matching circuit 108 and the design of the element values can be performed independently from the high frequency side branching circuit 160. In addition, the distributed constant line 104 changes only the phase angle without changing the magnitude of the reflection coefficient of the received signal, and thus rotates the phase of the received signal without changing the matching state realized by the matching circuit 108. be able to. As described above, the design of the matching circuit 108 is facilitated because the design can be performed independently while ignoring the influence of the circuit elements other than the matching circuit 108. In addition, since the matching circuit 108 is composed of lumped constant elements, when the duplexer 100 is designed with a substrate having a relative dielectric constant of about an order of magnitude, it is demultiplexed as compared with the case where impedance matching is performed using only distributed constant lines. The shape of the device 100 can be reduced in size, and the insertion loss can be reduced.

FIG. 2 is a circuit diagram showing a duplexer 200 according to another embodiment of the present invention. Of the constituent elements of the duplexer 200, those substantially the same as the constituent elements of FIG. 1 are given the same reference numerals as the corresponding constituent elements of FIG. In the duplexer 200, a low frequency side branch circuit 260 that transmits a signal on the low frequency side of the input signal is provided between the input terminal 102 and the

output terminals

120 and 206. The low frequency side branching circuit 260 includes a SAW filter 114 and a SAW filter 204 connected to the subsequent stage of the distributed constant line 106, and a capacitor, an inductor, or the like is concentrated between the SAW filters 114 and 204 and the distributed constant line 106. And a matching circuit 202 made of a constant type reactance element. The signal that has passed through the SAW filter 204 is output from the output terminal 206 to a subsequent receiver.

The SAW filter 204 has a pass band at, for example, 925 to 960 MHz (hereinafter may be referred to as “fourth pass band”). 925 to 960 MHz corresponds to a frequency band allocated for reception of UMTS band VIII. This fourth pass band is located on the lower frequency side outside the frequency band including the first pass band 2110-2170 MHz and the second pass band 1930-1990 MHz (that is, the 1930-2170 MHz frequency band). Therefore, the SAW filter 204 is disposed in the low frequency side branching circuit 260 that transmits the low frequency side signal. Since the center frequency of the fourth passband is 942.5 MHz and is close to 881.5 MHz, which is the center frequency of the third passband, the third and second received signals are transmitted using the distributed constant line 104. Both frequency components corresponding to the pass band of 4 can be rotated to the high impedance side. The line length L1 of the distributed constant line 104 is such that the input impedance of the high frequency side branching circuit 140 viewed from the input terminal 102 side is a high impedance close to infinity in the frequency band including the third and fourth pass bands. It is determined as follows. For example, the line length L1 is such that the input impedance of the high frequency side branching circuit 140 viewed from the input terminal 102 side is 869 MHz which is the low frequency end of the third pass band and 960 MHz which is the high frequency end of the fourth pass band. In the frequency band between them (that is, the frequency band from 869 MHz to 960 MHz), the impedance is determined to be close to infinity.

Matching circuit 202 is composed of lumped constant elements, and matches the input impedance of SAW filter 114 with the characteristic impedance of the external circuit of duplexer 200 in the third pass band, and the input impedance of SAW filter 204 as the fourth pass. It is configured to match the characteristic impedance of the external circuit in the band. For example, the arrangement and the element values of the reactance elements constituting the matching circuit 202 match the impedance of the SAW filter 114 viewed from the distributed constant line 106 side with the characteristic impedance of the transmission line in a frequency band corresponding to the third pass band. In addition, the impedance of the SAW filter 204 viewed from the distributed constant line 106 side is set to high impedance in the frequency band corresponding to the third pass band and the fourth impedance is set to high impedance in the frequency band corresponding to the fourth pass band. It matches with the characteristic impedance of the transmission line in a frequency band corresponding to the passband of the transmission line.

In another embodiment, the arrangement and element values of the reactance elements constituting the matching circuit 202 are such that the input impedance of the SAW filter 114 has an inductive or capacitive third reactance component in the third passband, and The input impedance of the SAW filter 204 in the third passband is capacitive when the third reactance component is inductive and inductive when the third reactance component is capacitive. Determined. Further, the input impedance of the SAW filter 204 has an inductive or capacitive fourth reactance component in the fourth pass band, and the input impedance in the fourth pass band of the SAW filter 114 has a fourth reactance component. The matching circuit 202 can be configured to be capacitive when inductive and to be inductive when the fourth reactance component is capacitive. By connecting the SAW filters 114 and 204 to the matching circuit 202 configured in this way, the input impedance in the third pass band of the SAW filter 114 is directed from the capacitive region toward the inductive region (or inductive). Rotated from the sex region to the capacitive region). As a result, the third reactance component approaches “0”, and impedance matching of the SAW filter 114 is realized with high accuracy. Similarly, the input impedance in the fourth passband of SAW filter 204 is rotated from the capacitive region to the inductive region (or from the inductive region to the capacitive region). As a result, the fourth reactance component approaches “0”, and impedance matching of the SAW filter 204 is realized with high accuracy.

Next, the phase rotation of the received signal by the distributed

constant lines

104 and 106 will be described with reference to FIGS. 11 and 12. FIG. 11 is an example of a Smith chart for explaining phase rotation by the distributed constant line 104 of the duplexer 200, and shows the input impedance of the high frequency side branch circuit 140. FIG. 12 is an example of a Smith chart for explaining phase rotation by the distributed constant line 106 of the duplexer 200, and shows the input impedance of the low frequency side branch circuit 260. In these figures, markers M1, M2, M3, and M4 represent the center frequencies of the first, second, third, and fourth passbands, respectively. As shown in FIG. 11, by rotating the phase of the input signal by the phase rotation by the distributed constant line 104, the frequency band including M3 and M4 is rotated to the high impedance side close to infinity. The bands M1 and M2 are matched in the vicinity of the characteristic impedance of the transmission line by the matching circuit 108, and the matching state in M1 and M2 is not substantially affected by the phase rotation. As described above, the distributed constant line 104 rotates the phase of the received signal so that the input impedance of the high frequency side branching circuit 140 of the duplexer 200 is a high impedance close to infinity in the third and fourth passbands. Can be. Similarly, the phase of the input signal is rotated by the phase rotation of the distributed constant line 106, and the frequency band including M1 and M2 rotates to the high impedance side close to infinity as shown in FIG. As described above, the distributed constant line 106 can set the input impedance of the low frequency side branching circuit 260 of the duplexer 200 to a high impedance close to infinity in the first and second passbands.

As described above, since signals in the third and fourth passbands do not leak to the high frequency side branch circuit 140, reactance elements included in the high frequency side branch circuit 140 (reactance elements and SAW filters constituting the matching circuit 108). 110, 112, etc.) can be ignored and the matching circuit 202 can be designed. This facilitates the design of the matching circuit 202. This impedance matching is realized by appropriately determining the element values and arrangement of capacitors and inductors that are components of the matching circuit 202. The method of determining the element values and arrangement of capacitors and inductors is well known to those skilled in the art, as is the case with the matching circuit 108. Those skilled in the art can design the matching circuit 202 without undue trial and error. It can be performed.

As the number of frequency components to be demultiplexed increases (that is, as the number of SAW filters increases), the design of matching circuits that match the impedances of these SAW filters becomes more complicated. On the other hand, according to the duplexer 200 according to the embodiment of the present invention, the signals in the first and second passbands are not leaked to the low frequency side branch circuit 160 and the third is added to the high frequency side branch circuit 140. Since the signal in the fourth passband does not leak, the matching circuit 108 can be designed independently from the low frequency side branching circuit 160, and the matching circuit 202 can be designed independently from the low frequency side branching circuit 160. This facilitates the design of the matching

circuits

108 and 202. As described above, the duplexer 200 according to the embodiment of the present invention can be easily designed for impedance matching as compared with the case where the impedances of the four SAW filters are matched only by the lumped constant element. it can.

FIG. 3 shows a duplexer 300 in another embodiment of the invention. Among the components of the duplexer 300, those substantially the same as the components of FIG. 1 or FIG. 2 are denoted by the same reference numerals as the corresponding components of FIG. 1 or FIG. To do. In the duplexer 300, a high frequency side branch circuit 340 that transmits a high frequency side signal among the input signals is provided between the input terminal 102 and the

output terminals

116, 118, and 306. The high frequency side branching circuit 340 includes a SAW filter 304 in parallel with the SAW filters 110 and 112 in the subsequent stage of the distributed constant line 104. The SAW filter 304 has a pass band at 1805 to 1880 MHz, for example (hereinafter, may be referred to as “fifth pass band”). 1805 to 1880 MHz is a frequency band assigned to UMTS band III as described above. The signal that has passed through the SAW filter 304 is output from the output terminal 306 to a subsequent receiver.

The high frequency side branching circuit 340 includes a matching circuit 302 formed of one or a plurality of lumped constant type reactance elements between the SAW filters 110, 112, and 304 and the distributed constant line 104. The arrangement and element values of the reactance elements constituting the matching circuit 302 are such that the input impedance of each SAW filter viewed from the distributed constant line 104 side matches the characteristic impedance of the transmission line in the passband of the own filter, and other SAW filters. It is determined to have a high impedance close to infinity in a frequency band corresponding to the pass band. Thereby, the impedance of the SAW filter 110 viewed from the distributed constant line 104 side becomes a high impedance close to infinity in the frequency band corresponding to the second and fifth passbands, and the SAW viewed from the distributed constant line 104 side. The impedance of the filter 112 becomes a high impedance close to infinity in frequency bands corresponding to the first and fifth pass bands. Further, the impedance of the SAW filter 304 viewed from the distributed constant line 104 side becomes a high impedance close to infinity in a frequency band corresponding to the first and second pass bands.

The line length L2 of the distributed constant line 106 is a high impedance that is close to infinity in the frequency band including the first, second, and fifth passbands when the input impedance of the low frequency side branching circuit 260 viewed from the input terminal 102 side. It is decided to become. Since the center frequencies of the first, second, and fifth passbands are distributed in a range within 300 MHz, the distributed constant line 106 makes these frequency components have a high impedance close to infinity. The phase of the received signal can be rotated so that For example, the line length L2 of the distributed constant line 106 is such that the impedance of the distributed constant line 106 viewed from the input terminal 102 side is 2170 MHz, which is the high frequency end of the first pass band, and the low frequency end of the fifth pass band. In the frequency band between 1805 MHz (that is, the frequency band from 1805 MHz to 2170 MHz), the impedance is determined to be close to infinity.

As described above, the duplexer 300 can separate the received multiband signal into five frequency bands by combining the distributed

constant lines

104 and 106, which are passive elements, and the matching

circuits

202 and 302.

It is more difficult to separate a received signal into five or more frequency bands using passive elements than the above-described separation into four frequency bands. For this reason, when the received signal is demultiplexed by 5, it is common to use an active element such as an SP3T (single-pole, triple-throw) switch. For example, a reception signal can be separated into five frequency components by connecting three SAW filters to the SP3T switch and combining it with two diplexers. The SP3T switch is configured to selectively supply a received signal to filters connected in parallel, and cannot supply signals to a plurality of filters at the same time. On the other hand, since the duplexer 300 according to an embodiment of the present invention demultiplexes the received signal with a passive element without using an active element such as an SP3T switch, the circuit reduces the power consumption and does not require a power supply. The configuration can be simplified. In addition, since all of the

filters

110, 112, and 304 of the duplexer 300 are always connected to the antenna, signals in three frequency bands included in the received signal can be output to the receiver at the same time. Furthermore, passive elements such as capacitors and inductors are less expensive than SP3T switches, which contributes to a reduction in the manufacturing cost of the duplexer.

FIG. 4 is an equivalent circuit diagram of the duplexer 200. The matching circuit 108 includes a capacitor 402 disposed between the connection point P1 of the SAW filters 110 and 112 and the SAW filter 110, a capacitor 404 disposed between the connection point P1 and the SAW filter 112, and the capacitor 402.

Inductors

408 and 410 disposed between terminals on both sides and the ground, and an inductor 412 disposed between a connection point between the capacitor 404 and the SAW filter 112 and the ground, respectively. The element values of these capacitors and inductors are such that the impedance of each SAW filter viewed from the distributed constant line 104 side matches the characteristic impedance of the transmission line in the pass band of the own filter, and high impedance in the pass band of other SAW filters. It is determined to be. For example, the line length of the distributed constant line 104 is 22 mm, the capacitances of the

capacitors

402 and 404 are 3 pF and 4 pF, respectively, and the inductance values of the

inductors

408, 410 and 412 are 3.5 nH, 20 nH and 20 nH, respectively.

The matching circuit 202 includes a capacitor 414 disposed between the connection point P2 between the SAW filter 114 and the SAW filter 204 and the SAW filter 114, a capacitor 416 disposed between the connection point P2 and the SAW filter 204, An inductor 418 disposed between the connection point between the capacitor 414 and the SAW filter 114 and the ground, an inductor 420 disposed between the connection point between the connection point P2 and the capacitor 416 and the ground, and the capacitor 416 and the SAW. And an inductor 422 connected between a connection point with the filter 204 and the ground. The element values of these capacitors and inductors are such that the impedance of each SAW filter viewed from the distributed constant line 106 side matches the characteristic impedance of the transmission line in the passband of the own filter and is high impedance in the passband of other SAW filters. It is determined to be. For example, the line length of the distributed constant line 106 is 17.5 mm, the capacitances of the

capacitors

414 and 416 are 5 pF and 4 pF, respectively, and the inductance values of the

inductors

418, 420 and 422 are 18 nH, 20 nH and 18 nH, respectively.

FIG. 5 is a Smith chart showing the input impedance viewed from the input terminal 102 of the duplexer 200 shown in FIG. The impedance shown in FIG. 5 was measured by sweeping the frequency from 100 MHz to 6 GHz. As is apparent from FIG. 5, the markers m1-m4 corresponding to the first to fourth pass bands are all distributed in the vicinity of 50Ω, and the input impedance of the duplexer 200 is the first to fourth pass. It was confirmed that it matched with the characteristic impedance of the transmission line in each band.

6 to 9 are graphs showing the simulation results of the attenuation characteristics of the duplexer 200 shown in FIG. FIG. 10 is an enlarged graph showing a part of the simulation results shown in FIGS. These attenuation characteristics are simulated by incorporating the characteristics of the SAW filters 110, 112, 114, and 204 constituting the duplexer 200 into a circuit simulator, and synthesizing these characteristics with the passive elements that constitute the matching

circuits

108 and 202. It is the result. Each SAW filter is characterized by Agilent Technologies, Inc., headquartered in California, USA. Of PNA-L. 6 to 9, the horizontal axis represents the frequency in GHz, and the vertical axis represents the magnitude of the S parameter (S21) indicating the attenuation characteristic in dB. 6, the curve 601 represents the attenuation characteristic between the input terminal 102 and the output terminal 116, the curve 701 in FIG. 7 represents the attenuation characteristic between the input terminal 102 and the output terminal 118, and the curve 801 in FIG. The attenuation characteristic between the output terminals 120 is represented. In FIG. 9, a curve 901 represents the attenuation characteristic between the input terminal 102 and the output terminal 206.

As is apparent from FIGS. 6 and 10, the attenuation between the input terminal 102 and the output terminal 116 is sufficiently small to be approximately 2.5 dB or less at 2110-2170 MHz allocated to the band I of UMTS. Large enough in the band. 7 and 10, the attenuation amount between the input terminal 102 and the output terminal 118 is sufficiently small at about 3.5 dB or less at 1930-1990 MHz allocated to UMTS band II. Large enough in other bands. As is clear from FIGS. 8 and 10, the attenuation between the input terminal 102 and the output terminal 120 is sufficiently small at about 869 to 894 MHz allocated to the band V of UMTS, which is sufficiently small at about 2.5 dB or less. Large enough in the band. As is apparent from FIGS. 9 and 10, the attenuation between the input terminal 102 and the output terminal 206 is sufficiently small at about 925 to 960 MHz allocated to the UMTS band VIII and is approximately 2.5 dB or less. Large enough in the band.

As described above, the insertion loss when the multiband signal on which the signals of the band I, band II, band V, and band VIII of UMTS are superimposed using the branching filter 300 is divided into four is determined by the branching filter of the mobile phone. As a small enough level. For comparison, according to a simulation performed by the present inventor using a duplexer including an SP3T switch, the insertion loss of each pass band is deteriorated by about 0.5 to 1.0 dB. Thus, it has been confirmed that the insertion loss is improved by the duplexer 200 according to the embodiment of the present invention.

The circuit configuration of the duplexer shown in FIGS. 1 to 3 can be changed as appropriate. For example, by arranging a sixth SAW filter in parallel with the SAW filters 114 and 204, the received signal can be demultiplexed into six frequency bands. The sixth SAW filter has a pass band on the low frequency side outside the frequency band including the pass bands of the SAW filters 110, 112, and 304, for example. In this case, the line length L1 of the distributed constant line 104 includes the third and fourth passbands and the passband of the sixth SAW filter when the input impedance of the high frequency side branch circuit 140 viewed from the input terminal 102 side. It is determined to have a high impedance close to infinity in the frequency band.

In addition, in each of the duplexers shown in FIGS. 1 to 3, the arrangement of the SAW filter can be changed as appropriate. In various embodiments of the present invention, each pass band of a SAW filter connected in parallel to one distributed constant line includes a frequency band including each pass band of a SAW filter connected in parallel to another distributed constant line. (That is, between the frequency at the lowest frequency side of the low frequency ends of the passbands of the plurality of SAW filters connected in parallel to other distributed constant lines and the frequency at the highest frequency side of the high frequency ends. The arrangement of each SAW filter is determined so as to be located on either the high frequency side or the low frequency side outside the frequency band. For example, in the duplexer 300 shown in FIG. 3, the frequency bands of the SAW filters 114 and 204 connected to the distributed constant line 106 are 869 to 894 MHz and 925 to 960 MHz, respectively. The passbands of the SAW filters 114 and 204 are both 1805 MHz including the passband of the SAW filter connected to the distributed constant line 104 (the lowest of the low frequency ends of the passbands of the SAW filter connected to the distributed constant line 104). It is outside the frequency band (low frequency side) sandwiched between 2170 MHz (the frequency on the high frequency side of the high frequency end of the pass band of the SAW filter connected to the distributed constant line 104). Similarly, the passbands of the SAW filters 110, 112, and 304 connected to the distributed constant line 104 are 2110-2170 MHz, 1930-1990 MHz, and 1805 to 1880 MHz, respectively. It is outside (high frequency side) the frequency band of 869 MHz to 960 MHz including the pass band of the filter. By arranging a plurality of SAW filters according to this rule, the impedance of the received signal is such that the impedance in each distributed constant line becomes high impedance in the frequency band including the respective pass bands of the SAW filters connected to the other distributed constant lines. The phase can be rotated, whereby the matching circuit provided in the subsequent stage of each distributed constant line can be designed independently. This rule regarding the arrangement of the SAW filter is also valid for the duplexer 100 and the duplexer 200 according to another embodiment of the present invention. And as long as this rule is satisfied, arrangement | positioning and the number of installation of each SAW filter may be changed suitably.

The embodiment of the present invention is not limited to the mode explicitly described above, and various changes can be made. For example, the SAW filters 110, 112, 114, 204, and 304 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 reduced in size by being built in an LTCC (low temperature co-fired ceramics) multilayer circuit board. In addition, various modifications can be made to the above-described embodiment without departing from the spirit of the present invention.

100, 200, 300 Splitter 102

Input terminal

104, 106 Distributed

constant line

108, 202, 302

Matching circuit

110, 112, 114, 204, 304

SAW filter

116, 118, 120, 206, 306

Output terminal

140, 340 High frequency

Side demultiplexing circuit

160, 260 Low frequency

side demultiplexing circuit

402, 404, 414, 416

Capacitor

408, 410, 412, 418, 420, 422 Inductor

Claims

An input terminal for inputting a received signal from the antenna;
A first filter disposed between the input terminal and the first output terminal and configured to pass a signal in a first passband; and disposed between the input terminal and the second output terminal; A first filter that includes a second filter that passes a signal in the passband of
A third filter disposed between the input terminal and the third output terminal and passing a signal in a third pass band outside the frequency band including the first and second pass bands; A second branching circuit including:
With
The first branching circuit includes:
A first distributed constant line that sets an input impedance of the first branching circuit to a high impedance in a frequency band corresponding to at least the third passband;
It consists of a lumped constant element and matches the input impedance of the first filter with the characteristic impedance of the external circuit in the first passband and the input impedance of the second filter in the second passband, respectively. A first matching circuit,
Have
The second demultiplexing circuit includes a second distributed constant line that makes the input impedance of the second demultiplexing circuit high in a frequency band including at least the first and second passbands.
Duplexer.
The first matching circuit sets the input impedance of the first filter to a high impedance in a frequency band corresponding to the second pass band, and sets the input impedance of the second filter to the first pass band. The duplexer according to claim 1, wherein a high impedance is set in a frequency band corresponding to.
The input impedance of the first filter has an inductive or capacitive first reactance component in the first passband, and the input impedance of the second filter in the first passband is the The first matching circuit according to claim 1, wherein the first matching circuit is configured to be capacitive when the first reactance component is inductive and to be inductive when the first reactance component is capacitive. Duplexer.
The input impedance of the second filter has an inductive or capacitive second reactance component in the second passband, and the input impedance of the first filter in the second passband is 4. The first matching circuit is configured to be capacitive when the second reactance component is inductive and to be inductive when the second reactance component is capacitive. The duplexer described in 1.
The second branching circuit is
Between the second distributed constant line and the fourth output terminal, a fourth pass band is provided on the same side as the third pass band outside the frequency band including the first and second pass bands. A fourth filter;
A lumped-constant element that matches the input impedance of the third filter with the characteristic impedance in the third passband and the input impedance of the fourth filter in the fourth passband, respectively. Two matching circuits;
With
The first distributed constant line has a high impedance input impedance of the first branching circuit in a frequency band including the third and fourth passbands;
The duplexer according to any one of claims 1 to 4.
The second matching circuit sets the input impedance of the third filter to a high impedance in a frequency band corresponding to the fourth pass band, and sets the input impedance of the fourth filter to the third pass band. The duplexer according to claim 5, wherein a high impedance is set in a frequency band corresponding to.
The input impedance of the third filter has an inductive or capacitive third reactance component in the third passband, and the input impedance of the fourth filter in the third passband is The second matching circuit is configured to be capacitive when the third reactance component is inductive and to be inductive when the third reactance component is capacitive. Duplexer.
The input impedance of the fourth filter has an inductive or capacitive fourth reactance component in the fourth passband, and the input impedance of the third filter in the fourth passband is 8. The first matching circuit is configured to be capacitive when the fourth reactance component is inductive and to be inductive when the fourth reactance component is capacitive. The duplexer described in 1.
The first branching circuit is
Between the first matching circuit and the fifth output terminal, a fifth pass on the same side as the first and second passbands outside the frequency band including the third and fourth passbands. A fifth filter having a band;
The first matching circuit comprises:
The input impedance of the first filter is set to high impedance in each of frequency bands corresponding to the second and fifth passbands,
The input impedance of the second filter is set to high impedance in each of the frequency bands corresponding to the first and fifth passbands; and
The input impedance of the fifth filter is set to high impedance in each of the frequency bands corresponding to the first and second passbands,
The first distributed constant line has a high impedance input impedance of the first branching circuit in a frequency band including the third, fourth, and fifth passbands;
The duplexer according to any one of claims 5 to 8.
The duplexer according to claim 9, wherein each of the first to fifth filters is a surface acoustic wave filter.
The duplexer according to claim 9, wherein each of the first to fifth filters is a dielectric filter.
The first matching circuit comprises:
A first capacitor disposed between a connection point of the first and second filters and the first filter;
A second capacitor disposed between a connection point of the first and second filters and the second filter;
First and second inductors respectively disposed between terminals on both sides of the first capacitor and ground;
A third inductor disposed between a connection point between the second capacitor and the second filter and the ground;
The duplexer according to claim 1, further comprising:
The second matching circuit comprises:
A third capacitor disposed between a connection point of the third and fourth filters and the third filter;
A fourth capacitor disposed between a connection point of the third and fourth filters and the fourth filter;
A fourth inductor disposed between a connection point between the third capacitor and the third filter and the ground;
Fifth and sixth inductors respectively disposed between terminals on both sides of the fourth capacitor and ground;
The duplexer according to claim 5, further comprising:
A wireless communication device comprising the duplexer according to any one of claims 1 to 13.