WO2015098240A1 - Filter device and duplexer - Google Patents

Abstract

Provided is a filer device which is capable of improving the attenuation characteristics outside the passband. This filter device (1) is provided with: a ladder filter (20) that is connected between an antenna-side signal terminal (11) and a transmission-side signal terminal (12) and comprises series arm resonators (S1-S4) and parallel arm resonators (P1-P4); an inductor (L1) that is connected between the antenna-side signal terminal (11) and the ladder filter (20); an inductor (L2) that is connected between the ladder filter (20) and the transmission-side signal terminal (12); and an inductor (L3) that is connected between the parallel arm resonators (P1-P3) and a ground potential. The amount of inductive coupling between the inductor (L1) and the inductor (L2) is smaller than the amount of inductive coupling between the inductor (L1) and the inductor (L3), and is also smaller than the amount of inductive coupling between the inductor (L2) and the inductor (L3).

Description

Filter device and duplexer

The present invention relates to a filter device and a duplexer, and particularly to a filter device and a duplexer provided with an inductor.

Conventionally, filter devices using elastic waves such as surface acoustic waves and boundary acoustic waves are mounted on communication devices such as mobile phones. Japanese Patent No. 4905614 (Patent Document 1) discloses an inductor connected between an antenna terminal and ground, an inductor connected between a parallel arm resonator of a ladder-type surface acoustic wave filter and ground, and a series arm. A duplexer is proposed having an inductor connected in series. Japanese Unexamined Patent Application Publication No. 2007-174100 (Patent Document 2) proposes a duplexer including a phase matching circuit inserted between an antenna terminal, a reception filter, and a transmission filter, and an expansion coil connected to the transmission filter. Has been.

Japanese Patent No. 4905614 JP 2007-174100 A

In filter devices, it is desired to further improve the attenuation characteristics outside the passband. In this respect, the techniques described in Patent Documents 1 and 2 still have room for improvement.

The present invention has been made in view of the above problems, and a main object thereof is to provide a filter device that can improve attenuation characteristics outside the passband.

The filter device according to the present invention includes a first signal terminal, a second signal terminal, a ladder filter, a first inductor, a second inductor, and a third inductor. The ladder filter is connected between the first signal terminal and the second signal terminal. The ladder type filter has a series arm resonator and a parallel arm resonator. The first inductor is connected between the first signal terminal and the ladder filter. The second inductor is connected between the ladder filter and the second signal terminal. The third inductor is connected between the parallel arm resonator and the ground potential. The amount of inductive coupling between the first inductor and the second inductor is smaller than the amount of inductive coupling between the first inductor and the third inductor, and the second inductor and the third inductor It is smaller than the amount of inductive coupling between.

Preferably, in the above filter device, the distance between the first inductor and the second inductor is larger than the distance between the first inductor and the third inductor, and the second inductor and the third inductor. Greater than the distance between the inductor.

Preferably, in the above filter device, the ladder filter has a plurality of parallel arm resonators, and the third inductor is connected between the plurality of parallel arm resonators and a ground potential.

Preferably, in the filter device, the first inductor is connected between a connection point between the first signal terminal and the ladder filter and a ground potential.

Preferably, in the filter device, the second inductor is connected in series between the ladder filter and the second signal terminal.

The duplexer according to the present invention includes the filter device according to any one of the above aspects, a third signal terminal, and another filter unit. The other filter unit is connected between the connection point between the first signal terminal and the ladder filter and the third signal terminal.

According to the filter device of the present invention, it is possible to improve attenuation characteristics outside the passband.

1 is a schematic circuit diagram of a filter device according to an embodiment of the present invention. It is a typical top view which shows arrangement | positioning of a filter chip and an inductor. It is a 1st graph which shows the relationship between the inductive coupling between inductors and an isolation characteristic. It is a 2nd graph which shows the relationship between the inductive coupling between inductors and an isolation characteristic. It is a 3rd graph which shows the relationship between the inductive coupling between inductors and an isolation characteristic. It is a 4th graph which shows the relationship between the inductive coupling between inductors and an isolation characteristic. It is a 5th graph which shows the relationship between the inductive coupling between inductors, and an isolation characteristic. It is a 6th graph which shows the relationship between the inductive coupling between inductors, and an isolation characteristic. It is a graph which shows the isolation characteristic of embodiment which carries out the inductive coupling of the inductor connected to the several parallel arm resonator. It is a graph which shows the isolation characteristic of the 1st comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 2nd comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 3rd comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 4th comparative example with respect to embodiment shown in FIG. It is a graph which shows the passage characteristic of the ladder type filter which inductively couples between inductors. It is a graph which shows the passage characteristic of the 1st comparative example with respect to embodiment shown in FIG. It is a graph which shows the passage characteristic of the 2nd comparative example with respect to embodiment shown in FIG. It is a graph which shows the passage characteristic of the 3rd comparative example with respect to the embodiment shown in FIG. It is a graph which shows the passage characteristic of the 4th comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of embodiment which carries out the inductive coupling of the inductor connected to one parallel arm resonator. It is a graph which shows the isolation characteristic of the 1st comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 2nd comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 3rd comparative example with respect to embodiment shown in FIG. It is a graph which shows the isolation characteristic of the 4th comparative example with respect to embodiment shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the embodiments described below, the same or corresponding parts are denoted by the same reference symbols, and the description thereof may not be repeated. Further, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the following embodiments, each component is not necessarily essential for the present invention unless otherwise specified.

(Embodiment 1)
FIG. 1 is a schematic circuit diagram of a filter device 1 according to an embodiment of the present invention. First, a filter device 1 to which the idea of the present invention can be applied and a duplexer including the filter device 1 will be described as an example.

The filter device 1 shown in FIG. 1 includes an antenna side signal terminal 11 as a first signal terminal, a transmission side signal terminal 12 as a second signal terminal, and a transmission side filter unit. The antenna side signal terminal 11 is connected to the antenna 50. The transmission-side filter unit is connected between the antenna-side signal terminal 11 and the transmission-side signal terminal 12. The transmission-side filter unit is an unbalanced elastic wave filter that outputs an unbalanced signal to the antenna-side signal terminal 11. Specifically, the transmission-side filter unit is configured by a ladder filter 20.

The ladder filter 20 has a series arm 21 connecting the antenna side signal terminal 11 and the transmission side signal terminal 12. Series arm resonators S1 to S4 are connected to the series arm 21 in series. The ladder filter 20 also has parallel arms 22-25. The parallel arm 22 is connected to a connection point provided between the series arm resonators S <b> 1 and S <b> 2 of the series arm 21. The parallel arm 23 is connected to a connection point provided between the series arm resonators S2 and S3 of the series arm 21. The parallel arm 24 is connected to a connection point provided between the series arm resonators S3 and S4 of the series arm 21.

The parallel arm 22 has a parallel arm resonator P1 connected in series. A parallel arm resonator P2 is connected to the parallel arm 23 in series. A parallel arm resonator P3 is connected to the parallel arm 24 in series. A parallel arm resonator P4 is connected to the parallel arm 25 in series.

Connection points 15 and 16 are provided between the antenna-side signal terminal 11 and the ladder filter 20. An inductor L1, which is a first inductor, is connected in series between the connection point 16 and the ground potential. Between the ladder filter 20 and the transmission-side signal terminal 12, an inductor L2, which is a second inductor, is connected in series. The parallel arm 25 is connected between a connection point provided between the series arm resonator S4 and the inductor L2 and the ground potential. The inductors L1 and L2 are impedance matching inductors, and are also inductors for configuring a sub route for increasing the attenuation amount in the reception-side frequency band of the ladder-type filter 20.

A common inductor L3 is connected between the parallel arm resonators P1, P2, P3 and the ground potential. The ladder filter 20 includes a plurality of parallel arm resonators P1, P2, and P3, and the inductor L3 is connected between the plurality of parallel arm resonators P1, P2, and P3 and a ground potential. . The inductor L3 is an inductor for increasing attenuation in a high frequency region by providing an attenuation pole at a desired frequency. The inductor L3 has a function as the third inductor in the first embodiment.

An inductor L4 is connected in series to the parallel arm 25 between the parallel arm resonator P4 and the ground potential.

The duplexer as an example of the acoustic wave filter shown in FIG. 1 includes the filter device 1 described above, a pair of balanced reception signal terminals 13a and 13b as third signal terminals, and reception as another filter unit. The side filter unit 30 is provided. The reception-side filter unit 30 is connected in series between the connection point 15 between the antenna-side signal terminal 11 and the ladder filter 20 and the pair of reception-side signal terminals 13a and 13b. The connection point 15 has a function as a connection point between the ladder-type filter 20 on the transmission side and the reception-side filter unit 30 on the reception side.

In the present embodiment, the reception-side filter unit 30 is configured by a balanced filter that outputs a balanced signal to the reception-side signal terminals 13a and 13b. Specifically, the reception-side filter unit 30 is configured by a longitudinally coupled resonator type acoustic wave filter. The reception-side filter unit 30 includes a surface acoustic wave resonator 31 and longitudinally coupled resonator type surface acoustic wave filter units 32 and 33. The longitudinally coupled resonator type surface acoustic wave filter units 32 and 33 are cascade-connected to each other and have a balance-unbalance conversion function.

The reception-side filter unit 30 may be configured by an unbalanced filter unit that outputs an unbalanced signal to the reception-side signal terminal. For example, the reception filter unit 30 may be configured by a ladder filter.

The filter chip 40 constitutes at least a part of the ladder filter 20 and the reception filter unit 30. Specifically, the filter chip 40 constitutes substantially the whole of the ladder filter 20 and the reception filter unit 30 excluding the inductor.

FIG. 2 is a schematic plan view showing the arrangement of the filter chip 40 and the inductors L1, L2, and L3. The filter chip 40 is flip-chip mounted on the main surface of the wiring board 60 via bonding members such as gold bumps and solder bumps. Inductors L1, L2, and L3 may each be formed of a chip inductor element and mounted on the main surface of wiring board 60. Alternatively, the inductors L1, L2, and L3 may be configured by an inductance component obtained by a wiring pattern formed on or inside the main surface of the wiring board 60. The filter chip 40 and the inductors L1, L2, and L3 are electrically connected by wiring.

Note that the inductors L1, L2, and L3 shown in FIG. 2 schematically show the arrangement of the inductors L1, L2, and L3 when viewed in the thickness direction of the wiring board 60. In FIG. 2, the outer shapes of the inductors L1, L2, and L3 are shown by solid lines. When the inductors L1, L2, and L3 are constituted by inductor chips, the outer shape shown in FIG. 2 is the outer shape of the inductor chip. On the other hand, when the inductors L1, L2, and L3 are formed by the wiring pattern inside the wiring board 60, the inductors L1, L2, and L3 do not actually appear on the main surface of the wiring board 60. Should.

2 shows a distance D1 between the inductor L1 and the inductor L2, a distance D2 between the inductor L1 and the inductor L3, and a distance D3 between the inductor L2 and the inductor L3. Referring to FIG. 2, distance D1 is larger than distance D2. The distance D1 is larger than the distance D3. Of the distances D1, D2 and D3, the inductors L1 to L3 are arranged so that the distance D1 takes the maximum value.

The amount of inductive coupling between each of the inductors L1 to L3 is proportional to the coupling coefficient k. The coupling coefficient k increases as the distance between each of the inductors L1 to L3 decreases. Therefore, the inductive coupling amount between the inductor L1 and the inductor L2 is smaller than the inductive coupling amount between the inductor L1 and the inductor L3. In addition, the amount of inductive coupling between the inductor L1 and the inductor L2 is smaller than the amount of inductive coupling between the inductor L2 and the inductor L3.

The inductor L3 connected between the plurality of parallel arm resonators P1 to P3 and the ground potential is generally compared with the inductor L4 connected between one parallel arm resonator P4 and the ground potential. Since the inductance value is larger, inductive coupling is easier. Therefore, as described above, it is desirable to define the magnitude relationship of the inductive coupling amount between the inductor L3 and the inductors L1 and L2.

Hereinafter, inductive coupling between the inductors L1, L2, and L3 will be described. FIG. 3 is a first graph showing the relationship between inductive coupling between inductors and isolation characteristics. FIG. 4 is a second graph showing the relationship between inductive coupling between inductors and isolation characteristics. FIG. 5 is a third graph showing the relationship between inductive coupling between inductors and isolation characteristics. 3 to 5, the isolation characteristics when the inductors L1 and L3, the inductors L2 and L3, and the inductors L1 and L2 are coupled with a coupling coefficient k = ± 0.1 in the duplexer shown in FIG. The simulation results are shown.

Here, the sign of the coupling coefficient k is determined as follows. With respect to two inductors that are inductively coupled to each other, when the magnetic flux generated by the current flowing through one inductor and the magnetic flux generated by the current flowing through the other inductor mutually strengthen each other, the sign of the coupling coefficient k is positive and weakened. Negative if matching.

FIG. 3 shows the relationship between the inductive coupling between the inductor L1 and the inductor L3 and the isolation characteristics. As shown in FIG. 3, when the inductor L1 and the inductor L3 are coupled with a coupling coefficient k = −0.1, the isolation in the Rx band is improved. From this result, it can be seen that inductive coupling between the inductor L1 and the inductor L3 is desirable in order to obtain good isolation characteristics.

FIG. 4 shows the relationship between the inductive coupling between the inductor L2 and the inductor L3 and the isolation characteristics. As shown in FIG. 4, when coupling is performed with a coupling coefficient k = −0.1 between the inductor L2 and the inductor L3, the isolation in the Rx band is improved. From this result, it can be seen that inductive coupling between the inductor L2 and the inductor L3 is desirable in order to obtain good isolation characteristics.

FIG. 5 shows the relationship between the inductive coupling between the inductor L1 and the inductor L2 and the isolation characteristics. As shown in FIG. 5, when the inductor L1 and the inductor L2 are inductively coupled, the isolation is deteriorated both in the case of the coupling coefficient k = + 0.1 and in the case of the coupling coefficient k = −0.1. is doing. From this result, it can be seen that it is preferable not to inductively couple the inductor L1 and the inductor L2 in order to obtain good isolation characteristics.

FIG. 6 is a fourth graph showing the relationship between inductive coupling between inductors and isolation characteristics. FIG. 7 is a fifth graph showing the relationship between inductive coupling between inductors and isolation characteristics. 6 and 7 illustrate examples in which the inductive coupling between the inductors L1 and L3 and the inductive coupling between the inductors L2 and L3 are combined in the duplexer illustrated in FIG.

FIG. 6 shows a case where the inductors L1 and L3 are inductively coupled with the coupling coefficient k = −0.1 and the inductors L2 and L3 are not inductively coupled (k = 0) and the coupling coefficient k = −0. The isolation characteristics of the case of inductive coupling at 1 are illustrated. FIG. 7 shows the case where the inductors L1 and L3 are not inductively coupled in the state where the inductors L2 and L3 are inductively coupled with the coupling coefficient k = −0.1 (k = 0) and the coupling coefficient k = −0. The isolation characteristics of the case of inductive coupling at 1 are illustrated.

As shown in FIGS. 6 and 7, by inductively coupling both the inductors L1 and L3 and between the inductors L2 and L3, the Rx band isolation is further improved as compared with the case where either one is inductively coupled. ing. Therefore, for example, the inductors cannot be arranged close to each other due to layout limitations, and the attenuation and isolation of the Rx band can be sufficiently obtained by only one of the coupling between the inductors L1 and L3 and the inductors L2 and L3. Even when there is not, sufficient Rx band attenuation and isolation can be obtained by utilizing the coupling between the inductors L1 and L3 and between the inductors L2 and L3.

FIG. 8 is a sixth graph showing the relationship between the inductive coupling between the inductors and the isolation characteristics. FIG. 8 illustrates the relationship between the distances D1, D2, and D3 between the inductors L1, L2, and L3 illustrated in FIG. 2 and the isolation characteristics in the duplexer illustrated in FIG.

In the graph (1) shown in FIG. 8, the distance D1 between the inductors L1 and L2 and the distance D2 between the inductors L1 and L3 are compared, the distance D1 is relatively small, and the distance D2 is relatively large. The Rx band isolation in the case is shown. In this case, the inductive coupling between the inductors L1 and L3 is small, and therefore the effect of improving the isolation by inductively coupling between the inductor L1 and the inductor L3 cannot be obtained. On the other hand, since the inductors L1 and L2 are inductively coupled, the isolation is deteriorated as described with reference to FIG.

In graph (2) shown in FIG. 8, the distance D2 between the inductors L1 and L3 and the distance D1 between the inductors L1 and L2 are compared, the distance D2 is relatively small, and the distance D1 is relatively large. The Rx band isolation in the case is shown. In this case, deterioration of isolation due to inductive coupling between the inductors L1 and L2 can be suppressed, and the inductors L1 and L3 are inductively coupled. Therefore, the isolation is improved as compared with the graph (1).

The graph (3) shown in FIG. 8 compares the distance D1 between the inductors L1 and L2, the distance D2 between the inductors L1 and L3, and the distance D3 between the inductors L2 and L3, and the distance D1 is greater than the distance D2. The Rx band isolation is shown when the distance D1 is made larger and the distance D1 is made larger than the distance D3. In this case, deterioration of isolation due to inductive coupling between the inductors L1 and L2 can be suppressed, and both the inductors L1 and L3 and between the inductors L2 and L3 are inductively coupled. Therefore, the isolation is further improved as compared with the graph (2).

As described above, the inductor L1 and the inductor L2 are disposed apart from each other, and the distance D1 between the inductors L1 and L2 is set larger than the distance D2 between the inductors L1 and L3 and the distance D3 between the inductors L2 and L3. , L2 is smaller than the inductive coupling between the inductors L1, L3 and between the inductors L2, L3. Thus, a route having the same amplitude and antiphase is provided between the input and output using the inductive coupling of the inductor between the input and output, the attenuation amount outside the pass band of the filter device 1 can be increased, and the out-of-band attenuation characteristic is improved. be able to. Further, in the duplexer in which the filter device 1 and the reception-side filter unit 30 are connected in parallel, the Rx band can be highly attenuated and the Rx band isolation can be improved.

FIG. 9 is a graph showing the isolation characteristics of the embodiment in which the inductor L3 connected to the plurality of parallel arm resonators P1 to P3 is inductively coupled. FIG. 10 is a graph showing the isolation characteristics of the first comparative example with respect to the embodiment shown in FIG. FIG. 11 is a graph showing the isolation characteristics of the second comparative example for the embodiment shown in FIG. FIG. 12 is a graph showing the isolation characteristics of the third comparative example for the embodiment shown in FIG. FIG. 13 is a graph showing the isolation characteristics of the fourth comparative example with respect to the embodiment shown in FIG.

In the embodiment shown in FIG. 9, as shown in FIG. 1, the inductor L 1 is connected between the connection point 16 and the ground potential, and the inductor L 2 is connected in series between the ladder filter 20 and the transmission side signal terminal 12. It is connected to the. In addition, the inductors L1 and L3 and the inductors L2 and L3 are inductively coupled. In the first comparative example shown in FIG. 10, the connections of the inductors L1 and L2 are the same as those in the embodiment shown in FIG. 9, except that the inductors L1 and L3 and the inductors L2 and L3 are not inductively coupled. This is different from the embodiment shown in FIG.

The simulation results shown in FIGS. 9 and 10 are compared, and both the inductors L1 and L3 and the inductors L2 and L3 are inductively coupled to attenuate in the stop band on the high frequency side outside the pass band of the filter device 1. It has been shown that the characteristics can be improved and sufficient attenuation and isolation of the Rx band can be obtained in the duplexer having the Rx band in the high-side stop band outside the pass band of the filter device 1.

The second comparative example shown in FIG. 11 differs from the embodiment shown in FIG. 9 in that the inductor L1 is connected in series. In the second comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG. At this time, the isolation in the pass band of Rx is 10 dB better in FIG. 11 than in FIG. 10 where the inductors L1 and L3 and the inductors L2 and L3 are not inductively coupled.

The third comparative example shown in FIG. 12 differs from the embodiment shown in FIG. 9 in that the inductor L2 is connected in parallel. In the third comparative example, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. The inductor L2 is connected between the other connection point and the ground potential. At this time, the isolation in the passband of Rx is 12 dB better in FIG. 12 than in FIG. 10 where the inductors L1 and L3 and the inductors L2 and L3 are not inductively coupled.

The fourth comparative example shown in FIG. 13 is different from the embodiment shown in FIG. 9 in that the inductor L1 is connected in series and the inductor L2 is connected in parallel. In the fourth comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG. Further, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. 1 and the transmission-side signal terminal 12, and the inductor L <b> 2 is separated from the connection point. Between the connection point and the ground potential. At this time, the isolation in the passband of Rx is 10 dB better in FIG. 13 than in FIG. 10 where the inductors L1 and L3 and the inductors L2 and L3 are not inductively coupled.

The simulation results of the embodiment shown in FIG. 9 and the comparative examples shown in FIGS. 11 to 13 are compared. In the embodiment shown in FIG. 9 in which the inductor L1 is connected in parallel and the inductor L2 is connected in series, the filter device 1 passes through. It was shown that the out-of-band attenuation characteristics can be improved most, and that the duplexer has the best isolation.

(Embodiment 2)
FIG. 14 is a graph showing pass characteristics of the ladder filter 20 that inductively couples the inductors L1, L2, and L3. FIG. 15 is a graph showing pass characteristics of the first comparative example for the embodiment shown in FIG. FIG. 16 is a graph showing pass characteristics of the second comparative example for the embodiment shown in FIG. FIG. 17 is a graph showing pass characteristics of the third comparative example for the embodiment shown in FIG. FIG. 18 is a graph showing pass characteristics of a fourth comparative example with respect to the embodiment shown in FIG.

FIG. 14 illustrates the pass characteristic of the filter device 1 including the ladder filter 20 in which the configuration from the connection point 15 to the reception-side signal terminals 13a and 13b is deleted from the configuration of the duplexer illustrated in FIG. ing. The inductor L1 is connected between the connection point 16 and the ground potential, and the inductor L2 is connected in series between the ladder type filter 20 and the transmission side signal terminal 12. In addition, the inductors L1 and L3 and the inductors L2 and L3 are inductively coupled.

In the first comparative example shown in FIG. 15, the connections of the inductors L1 and L2 are the same as those in the embodiment shown in FIG. 14, except that the inductors L1 and L3 and the inductors L2 and L3 are not inductively coupled. 14 is different from the embodiment shown in FIG.

14 and 15 is compared, and the inductive coupling between the inductors L1 and L3 and the inductors L2 and L3 improves the attenuation characteristics on the high frequency side outside the passband of the filter device 1. It was shown that it can.

16 differs from the embodiment shown in FIG. 14 in that the inductor L1 is connected in series. In the second comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG.

The third comparative example shown in FIG. 17 differs from the embodiment shown in FIG. 14 in that the inductor L2 is connected in parallel. In the third comparative example, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. The inductor L2 is connected between the other connection point and the ground potential.

The fourth comparative example shown in FIG. 18 is different from the embodiment shown in FIG. 14 in that the inductor L1 is connected in series and the inductor L2 is connected in parallel. In the fourth comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG. Further, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. 1 and the transmission-side signal terminal 12, and the inductor L <b> 2 is separated from the connection point. Between the connection point and the ground potential.

The simulation results of the embodiment shown in FIG. 14 and the comparative examples shown in FIGS. 16 to 18 are compared. In the embodiment shown in FIG. 14 in which the inductor L1 is connected in parallel and the inductor L2 is connected in series, the filter device 1 passes through. It was shown that the attenuation characteristics on the high frequency side outside the band can be improved most.

(Embodiment 3)
FIG. 19 is a graph showing the isolation characteristics of an embodiment in which an inductor L4 connected to one parallel arm resonator P4 is inductively coupled. FIG. 20 is a graph showing the isolation characteristics of the first comparative example with respect to the embodiment shown in FIG. FIG. 21 is a graph showing the isolation characteristics of the second comparative example with respect to the embodiment shown in FIG. FIG. 22 is a graph showing the isolation characteristics of the third comparative example with respect to the embodiment shown in FIG. FIG. 23 is a graph showing the isolation characteristics of the fourth comparative example with respect to the embodiment shown in FIG.

In the third embodiment, an example in which an inductor L4 connected to the parallel arm 25 between the parallel arm resonator P4 and the ground potential and the inductors L1 and L2 are inductively coupled will be described. The inductor L4 has a function as the third inductor in the third embodiment.

In the embodiment shown in FIG. 19, as shown in FIG. 1, the inductor L1 is connected between the connection point 16 and the ground potential, and the inductor L2 is connected in series between the ladder filter 20 and the transmission side signal terminal 12. It is connected to the. In addition, the inductors L1 and L4 and the inductors L2 and L4 are inductively coupled. The distance between the inductors L1 and L2 is larger than the distance between the inductors L1 and L4 and the distance between the inductors L2 and L4. Thereby, the inductive coupling between the inductors L1 and L2 is smaller than the inductive coupling between the inductors L1 and L4 and between the inductors L2 and L4. When the inductors L1, L2, and L4 include winding portions made of a conductor having a winding axis in the normal direction of the main surface of the wiring board 60, the distance between the inductors is flat with respect to the main surface of the wiring board 60. The distance between the winding axes as seen can be used.

In the first comparative example shown in FIG. 20, the connections of the inductors L1 and L2 are the same as those in the embodiment shown in FIG. 19 except that the inductors L1 and L4 and the inductors L2 and L4 are not inductively coupled. This is different from the embodiment shown in FIG.

By comparing the simulation results shown in FIGS. 19 and 20 and inductively coupling both the inductors L1 and L4 and the inductors L2 and L4, the attenuation characteristics outside the passband of the filter device 1 can be improved. It was shown that sufficient Rx band attenuation and isolation can be obtained in the duplexer.

The second comparative example shown in FIG. 21 is different from the embodiment shown in FIG. 19 in that the inductor L1 is connected in series. In the second comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG.

The third comparative example shown in FIG. 22 is different from the embodiment shown in FIG. 19 in that the inductor L2 is connected in parallel. In the third comparative example, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. The inductor L2 is connected between the other connection point and the ground potential.

The fourth comparative example shown in FIG. 23 differs from the embodiment shown in FIG. 19 in that the inductor L1 is connected in series and the inductor L2 is connected in parallel. In the fourth comparative example, the inductor L1 is connected in series between the antenna-side signal terminal 11 and the connection point 15 shown in FIG. Further, another connection point is provided between the connection point of the parallel arm 25 provided in the series arm 21 shown in FIG. 1 and the transmission-side signal terminal 12, and the inductor L <b> 2 is separated from the connection point. Between the connection point and the ground potential.

The simulation results of the embodiment shown in FIG. 19 and the comparative examples shown in FIGS. 21 to 23 are compared. In the embodiment shown in FIG. 19 in which the inductor L1 is connected in parallel and the inductor L2 is connected in series, the filter device 1 passes through. It was shown that the out-of-band attenuation characteristics can be improved most, and that the duplexer has the best isolation. Even when the inductor L4 connected to one parallel arm resonator P4 and the inductors L1, L2 are inductively coupled, the inductor L3 connected to the plurality of parallel arm resonators P1 to P3 and the inductors L1, L2 are connected. It has been clarified that the same kind of effect as that of the first embodiment inductively coupled is achieved.

In the above description, the magnitude relationship of the inductive coupling between the inductors is specified by specifying the magnitudes of the distances D1, D2, and D3 between the inductors L1, L2, and L3. However, the present invention is limited to this example. It is not a thing.

For example, the magnitude relationship of the inductive coupling between the inductors may be adjusted by reversing the winding direction of the windings constituting the inductors L1, L2, and L3. Further, for example, the magnitude relationship of the inductive coupling between the inductors may be adjusted by shifting the arrangement of the winding axes such that the central axes of the windings constituting the inductors L1, L2, and L3 are orthogonal to each other. Further, for example, the size relationship of inductive coupling between the inductors may be adjusted by making some inclusions functioning as electric field shields between the inductors L1, L2, and L3.

As described above, the embodiment of the present invention has been described. However, it should be considered that the embodiment disclosed this time is illustrative and not restrictive in all respects. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 filter device, 11 antenna side signal terminal, 12 transmission side signal terminal, 13a, 13b reception side signal terminal, 15, 16 connection point, 20 ladder type filter, 21 series arm, 22-25 parallel arm, 30 reception side filter section , 31 surface acoustic wave resonator, 32, 33 longitudinally coupled resonator type surface acoustic wave filter section, 40 filter chip, 50 antenna, 60 wiring board, D1, D2, D3 distance, L1-L4 inductor, P1-P4 parallel arm Resonator, S1-S4 series arm resonator.

Claims (6)

A first signal terminal;
A second signal terminal;
A ladder-type filter connected between the first signal terminal and the second signal terminal and having a series arm resonator and a parallel arm resonator;
A first inductor connected between the first signal terminal and the ladder filter;
A second inductor connected between the ladder filter and the second signal terminal;
A third inductor connected between the parallel arm resonator and a ground potential;
An inductive coupling amount between the first inductor and the second inductor is smaller than an inductive coupling amount between the first inductor and the third inductor, and the second inductor and The filter device, which is smaller than an inductive coupling amount with the third inductor. The distance between the first inductor and the second inductor is greater than the distance between the first inductor and the third inductor, and the second inductor and the third inductor The filter device according to claim 1, wherein the filter device is larger than a distance between the inductor and the inductor. The ladder filter has a plurality of the parallel arm resonators,
The filter device according to claim 1, wherein the third inductor is connected between the plurality of parallel arm resonators and a ground potential. 4. The first inductor according to claim 1, wherein the first inductor is connected between a connection point between the first signal terminal and the ladder filter and a ground potential. 5. Filter device. The filter device according to any one of claims 1 to 4, wherein the second inductor is connected in series between the ladder filter and the second signal terminal. A filter device according to any one of claims 1 to 5,
A third signal terminal;
A duplexer, comprising: a connection point between the first signal terminal and the ladder filter; and another filter unit connected between the third signal terminal.

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