阅读说明：本技术 分波器 (Branching filter ) 是由 大久保功太 于 2020-08-10 设计创作，主要内容包括：本发明提供一种能够抑制带通滤波器的通过特性的劣化的分波器。分波器具备：带通滤波器,在第1端子与连接于天线的公共端子之间,使给定的频带的信号通过；以及带阻滤波器,在第2端子与公共端子之间,使给定的频带的信号衰减,带阻滤波器具备：多个谐振器,串联连接在第2端子与公共端子之间的线路,多个谐振器包含：第1谐振器,谐振频率最低；以及第2谐振器,设置在比第1谐振器靠公共端子侧。(The invention provides a branching filter capable of suppressing deterioration of the pass characteristic of a band-pass filter. A branching filter is provided with: a band-pass filter for passing a signal of a predetermined frequency band between the 1 st terminal and a common terminal connected to the antenna; and a band rejection filter that attenuates a signal of a predetermined frequency band between the 2 nd terminal and the common terminal, the band rejection filter including: a plurality of resonators connected in series to a line between the 2 nd terminal and the common terminal, the plurality of resonators including: 1 st resonator, the resonance frequency is lowest; and a 2 nd resonator provided on the common terminal side of the 1 st resonator.)

1. A branching filter is provided with:

a band-pass filter for passing a signal of a predetermined frequency band between the 1 st terminal and a common terminal connected to the antenna; and

a band-stop filter attenuating signals of the given frequency band between a 2 nd terminal and the common terminal,

the band elimination filter is provided with:

a plurality of resonators connected in series on a line between the 2 nd terminal and the common terminal,

the plurality of resonators includes:

1 st resonator, the resonance frequency is lowest; and

and a 2 nd resonator provided on the common terminal side of the 1 st resonator.

2. The wave splitter according to claim 1,

the band-pass filter includes a 3 rd resonator disposed in a series arm and a 4 th resonator disposed in a parallel arm between the 1 st terminal and the common terminal,

the anti-resonance frequencies of the plurality of resonators are each higher than the resonance frequency of the 4 th resonator and lower than the anti-resonance frequency of the 3 rd resonator.

3. The wave splitter according to claim 1 or 2,

the plurality of resonators includes:

the 5 th resonator has the largest capacitance value; and

and a 6 th resonator provided closer to the common terminal than the 5 th resonator.

4. The wave splitter according to any one of claims 1 to 3,

the 1 st resonator and the 2 nd resonator are disposed adjacent to each other,

the band elimination filter is also provided with:

and a 1 st inductor having one end connected to a connection point between the 1 st resonator and the 2 nd resonator and the other end to which a reference potential is supplied.

5. The wave splitter of claim 4,

the band elimination filter is also provided with:

a 2 nd inductor connected in series with the 2 nd resonator between the 2 nd resonator and the common terminal,

an inductance value of the 1 st inductor is greater than an inductance value of the 2 nd inductor.

6. The wave splitter according to any one of claims 1 to 4,

the band elimination filter is also provided with:

a 2 nd inductor and a 3 rd inductor connected in series to a line between the 2 nd terminal and the common terminal,

the band-pass filter further includes:

a 4 th inductor connected in series to a line between the 1 st terminal and the common terminal,

the 3 rd inductor is disposed closer to the 2 nd inductor than the 4 th inductor.

7. The wave splitter according to any one of claims 1 to 5,

the band elimination filter is also provided with:

a 3 rd inductor connected in series to a line between the 2 nd terminal and the common terminal,

the band-pass filter further includes:

a 4 th inductor connected in series to a line between the 1 st terminal and the common terminal,

the branching filter further includes:

a 5 th inductor connected in series to a line between a connection point of the band pass filter and the band reject filter and the common terminal,

the 3 rd inductor is disposed closer to the 5 th inductor than the 4 th inductor.

Technical Field

The present invention relates to a branching filter.

Background

In mobile communication devices such as mobile phones, so-called carrier aggregation is required to simultaneously transmit and receive signals of a plurality of frequency bands different from each other. In carrier aggregation, for example, a splitter for separating a reception signal received by one antenna according to a frequency band is connected to the antenna. For example, patent document 1 listed below discloses a multiplexer including a band-pass filter for passing a signal in a predetermined frequency band and a band-stop filter for attenuating a signal in the predetermined frequency band.

Prior art documents

Patent document

Patent document 1: international publication No. 2018/030277

In such a multiplexer including a plurality of filters, the characteristics of one filter may affect the characteristics of another filter to degrade the pass characteristics of another filter, but this is not considered in patent document 1. Therefore, for example, depending on the design of the resonator provided in the band elimination filter, the pass characteristic of the band pass filter may be deteriorated.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of such circumstances, and an object thereof is to provide a demultiplexer capable of suppressing deterioration of the pass characteristic of a band pass filter.

Means for solving the problems

In order to achieve the above object, a demultiplexer according to one aspect of the present invention includes: a band-pass filter for passing a signal of a predetermined frequency band between the 1 st terminal and a common terminal connected to the antenna; and a band rejection filter that attenuates a signal of the predetermined frequency band between the 2 nd terminal and the common terminal, the band rejection filter including: a plurality of resonators connected in series to a line between the 2 nd terminal and the common terminal, the plurality of resonators including: 1 st resonator, the resonance frequency is lowest; and a 2 nd resonator provided on the common terminal side of the 1 st resonator.

Effects of the invention

According to the present invention, it is possible to provide a demultiplexer capable of suppressing deterioration of the pass characteristic of a band-pass filter.

Drawings

Fig. 1 is a diagram showing a configuration example of a communication device including a demultiplexer according to an embodiment of the present invention.

Fig. 2 is a diagram showing a configuration example of a branching filter according to an embodiment of the present invention and components related thereto.

Fig. 3 is a graph showing the simulation results of the attenuation characteristics of the resonators included in the band-pass filter and the band-stop filter.

Fig. 4A is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the conditions of the resonance frequency and the capacitance value of the resonator of the band stop filter are changed.

Fig. 4B is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the conditions of the resonance frequency and the capacitance value of the resonator of the band stop filter are changed.

Fig. 4C is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the conditions of the resonance frequency and the capacitance value of the resonator of the band stop filter are changed.

Fig. 4D is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the conditions of the resonance frequency and the capacitance value of the resonator of the band stop filter are changed.

Fig. 5A is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the condition of the inductor of the band stop filter is changed.

Fig. 5B is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the condition of the inductor of the band stop filter is changed.

Fig. 5C is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the condition of the inductor of the band stop filter is changed.

Fig. 5D is a graph showing a simulation result of the pass characteristic of the band pass filter in the case where the condition of the inductor of the band stop filter is changed.

Fig. 6 is a diagram showing an example of the layout of each inductor shown in fig. 2.

Fig. 7A is a graph showing a simulation result of the pass characteristic of the band-stop filter in the case where the layout of the inductors shown in fig. 2 is changed.

Fig. 7B is a graph showing a simulation result of the pass characteristic of the band-stop filter in the case where the layout of the inductors shown in fig. 2 is changed.

Description of the reference numerals

100: a communication device;

10: an antenna;

20. 20A: a wave splitter;

21. 21A: a band-pass filter;

22. 22A: a band-stop filter;

30: a switch;

40: a duplexer;

41. 42: a band-pass filter;

50: a power amplifier;

60. 61: a low noise amplifier;

70、71：RFIC；

300: a substrate;

t1, T2: a terminal;

t3: a common terminal;

L1-L5: an inductor;

u1, U2: a line;

S1-S6, P1-P3: a resonator is provided.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same elements are denoted by the same reference numerals, and redundant description thereof is omitted.

Fig. 1 is a diagram showing a configuration example of a communication device including a demultiplexer according to an embodiment of the present invention. The communication device according to the present embodiment is mounted in a mobile communication device such as a mobile phone, for example, and transmits and receives signals.

As shown in fig. 1, the communication device 100 includes, for example, an antenna 10, a demultiplexer 20, a switch 30, a duplexer 40, a power amplifier 50, low noise amplifiers 60 and 61, and RFICs 70 and 71.

The antenna 10 transmits and receives Radio Frequency (RF) signals to and from a base station, or receives signals from GPS (Global Positioning System) satellites.

The demultiplexer 20 has a function of separating a transmission signal transmitted from the antenna 10 and a reception signal received by the antenna 10 based on frequency. The demultiplexer 20 includes a band pass filter 21 and a band reject filter 22. The band-pass filter 21 is a filter that passes a signal of a predetermined frequency and attenuates a signal of a frequency other than the predetermined frequency. The band-stop filter 22 is a filter that attenuates signals at a given frequency and passes signals other than the given frequency.

In the present embodiment, the passband, which is the frequency band passed by the band pass filter 21, overlaps with the attenuation band, which is the frequency band attenuated by the band stop filter 22. For example, when it is desired to extract a GPS reception signal from various signals received by the antenna 10, the passband of the band-pass filter 21 and the attenuation band of the band-stop filter 22 are set to frequencies of the GPS reception signal. Thus, the received GPS signal passes through the band pass filter 21, and the other received signals pass through the band rejection filter 22. In this manner, the demultiplexer 20 can extract signals of a specific frequency from signals of various frequencies. The type of the extracted signal is not limited to GPS.

The reception signal having passed through the band pass filter 21 is supplied to the low noise amplifier 60. The reception signal having passed through the band elimination filter 22 is supplied to the switch 30. Further, the band elimination filter 22 is supplied with the transmission signal from the switch 30. The detailed structure of the demultiplexer 20 will be described later.

The switch 30 supplies the reception signal supplied from the band elimination filter 22 to any duplexer based on the communication standard and the frequency band. Although the duplexer 40 is shown as an example in fig. 1, a plurality of duplexers may be connected to the switch 30, or a demultiplexer and a receiver may be connected instead of the duplexer. The switch 30 supplies the transmission signal supplied from each duplexer to the band elimination filter 22. The communication device 100 may not include the switch 30.

The duplexer 40 has a function of separating the reception signal supplied from the switch 30 and the transmission signal supplied from the power amplifier 50 based on the frequency. The duplexer 40 includes, for example, two band pass filters 41 and 42. One band-pass filter 41 passes signals of a reception band, and the other band-pass filter 42 passes signals of a transmission band. This can suppress mutual leakage between the transmission signal and the reception signal.

The power amplifier 50 amplifies the power of the transmission signal generated in the RFIC71 and supplies the amplified power to the duplexer 40.

The low noise amplifier 60 amplifies the power of the reception signal supplied from the demultiplexer 20 and supplies the amplified power to the RFIC 70.

The low noise amplifier 61 amplifies the power of the reception signal supplied from the duplexer 40 and supplies the amplified power to the RFIC 71.

The RFIC70 is an integrated circuit that processes a given signal (for example, a reception signal of GPS) extracted by the demultiplexer 20. The RFIC71 is an integrated circuit that processes signals other than the given signal, i.e., signals contained within the pass band of the band stop filter 22 (e.g., the received signal of a cellular telephone). Although fig. 1 shows an example in which the RFIC70 and the RFIC71 are formed of different ICs, part or all of the functions may be formed of one chip.

Each of the components included in the communication device 100 may be formed as a module on the same chip or may be formed on different chips. For example, the communication device 100 may not include the antenna 10, and in this case, the antenna 10 may be connected to the communication device 100. Next, the structure of the branching filter 20 will be described in more detail.

Fig. 2 is a diagram showing a configuration example of a branching filter according to an embodiment of the present invention and components related thereto.

As shown in fig. 2, the demultiplexer 20A according to the present embodiment includes a band-pass filter 21A and a band-stop filter 22A. The band-pass filter 21A outputs a reception signal supplied from the antenna 10 via the common terminal T3 from the terminal T1 (1 st terminal). The band-elimination filter 22A outputs the reception signal supplied from the antenna 10 via the common terminal T3 from the terminal T2 (2 nd terminal), and outputs the transmission signal supplied from the switch 30 via the terminal T2 from the common terminal T3. Although the band-pass filter 21A passes the reception signal in the present embodiment, the transmission signal may be passed instead of or in addition to this.

The band-pass filter 21A is a ladder filter in which a plurality of resonators are arranged in a series arm and a parallel arm. Specifically, the band-pass filter 21A includes four resonators S1 to S4, three resonators P1 to P3, and an inductor L2. The numbers of resonators and inductors are examples, and are not limited to these.

The elements of the resonators S1 to S4 and the resonators P1 to P3 are not particularly limited, and examples thereof include a Surface Acoustic Wave (SAW) filter, a filter such as a piezoelectric thin film resonator, and a Bulk Acoustic Wave (BAW) filter. The same applies to resonators S5 and S6 described below.

The four resonators S1 (3 rd resonators) to S4 are connected in series in the order of being closer to the antenna 10 on the line U1 connecting the common terminal T3 and the terminal T1. The three resonators P1 (4 th resonator) to P3 are connected in parallel in order of being close to the antenna 10 side, and branch from the line U1. One ends of the three resonators P1 to P3 are connected to a connection point of the resonator S1 and the resonator S2, a connection point of the resonator S2 and the resonator S3, and a connection point of the resonator S3 and the resonator S4, respectively, and the other ends are supplied with a reference potential (for example, ground potential).

The inductor L2 (the 4 th inductor) is connected in series with the resonator disposed in the series arm between the resonator S4 and the terminal T1.

The band elimination filter 22A is a structure in which a plurality of resonators are connected in series. Specifically, the band elimination filter 22A includes two resonators S5 and S6 and three inductors L3 to L5. The number of resonators and inductors is an example, and is not limited thereto.

The resonator S5 (2 nd resonator, 6 th resonator) and the resonator S6 (1 st resonator, 5 th resonator) are adjacently connected in series on a line U2 connecting the common terminal T3 and the terminal T2 in order of being close to the antenna 10 side.

An inductor L3 (2 nd inductor) is connected in series with the resonator S5 between the common terminal T3 and the resonator S5. One end of the inductor L4 (1 st inductor) is connected to a connection point of the resonator S5 and the resonator S6, and the other end is supplied with a reference potential (for example, ground potential) so as to branch from the line U2. An inductor L5 (3 rd inductor) is connected in series with the resonator S6 between the resonator S6 and the terminal T2.

The inductor L1 (5 th inductor) is connected in series in a line between the connection point a of the band-pass filter 21A and the band-stop filter 22A and the common terminal T3.

In the present embodiment, the passband and the bandwidth of the bandpass filter 21A are substantially the same as the attenuation band and the bandwidth of the bandstop filter 22A. Therefore, the resonators included in the filters satisfy the conditions of the resonance frequency and the antiresonance frequency shown in fig. 3.

Fig. 3 is a graph showing simulation results of attenuation characteristics of the resonators included in the bandpass filter and the band-stop filter shown in fig. 2. In the graph shown in the same figure, the horizontal axis shows frequency (MHz), and the vertical axis shows attenuation amount (dB) of the signal. Characteristic 200 shows the attenuation characteristic of resonator S1 of band-pass filter 21A. Characteristic 210 shows the attenuation characteristic of resonator P1 of band-pass filter 21A. Characteristic 220 shows the attenuation characteristics of resonator S5 of band stop filter 22A. Characteristic 230 shows the attenuation characteristics of resonator S6 of band reject filter 22A.

The resonators S1, S5, S6 are arranged in the series arm, and therefore, as shown in fig. 3, the signal is greatly attenuated at the anti-resonance frequency thereof. The resonator P1 is disposed in the parallel arm, and therefore the signal is greatly attenuated at its resonance frequency. In the present embodiment, the antiresonant frequencies of the resonator S5 and the resonator S6 of the band elimination filter 22A are arranged between the antiresonant frequency of the resonator S1 and the resonant frequency of the resonator P1 of the band-pass filter 21A. Thereby, the passband of the band-pass filter 21A and the attenuation band of the band-stop filter 22A overlap. In fig. 3, the resonator S1 and the resonator P1 are selected as examples of the resonators of the band pass filter 21A, but the anti-resonance frequency of the resonator included in the band rejection filter 22A may be higher than the resonance frequency of the resonator of any one of the parallel arms of the band pass filter 21A and lower than the anti-resonance frequency of the resonator of any one of the series arms.

Here, in a demultiplexer including a plurality of filters, the characteristics of one filter may affect the characteristics of another filter, and the transmission characteristics of another filter may be degraded. Therefore, for example, the pass characteristics of the band pass filter may be degraded by the design of the resonator provided in the band stop filter.

In this regard, in the present embodiment, the resonance frequency of the resonator S5 on the common terminal T3 side among the resonators provided in the band elimination filter 22A is set to be higher than the resonance frequency of the resonator S6 on the terminal T2 side. For example, assuming that the period of an Interdigital Transducer (IDT) is λ and the sound velocity in a piezoelectric substrate constituting a SAW filter is v, the resonance frequency f of the SAW filter is set to be λ_rCan be formed by_r＝v/λ[Hz]And (4) showing. Therefore, for example, when the resonator is a SAW filter, the desired resonance frequency f can be obtained by adjusting the period of the comb-shaped electrode_r。

The impedance on the bandpass filter 21A side viewed from the connection point a of the bandpass filter 21A and the band-stop filter 22A is Z1, and the impedance on the band-stop filter 22A side viewed from the connection point a is Z2. In general, it is designed that the impedance Z1 in the pass band of the band-pass filter 21A is, for example, 50 Ω, and the impedance Z2 in the attenuation band of the band-stop filter 22A becomes high impedance. Here, when the impedance Z2 is low, the signal tends to leak to the band elimination filter 22A side, which may cause deterioration in the pass characteristic of the band pass filter 21A and increase in the insertion loss of the band pass filter 21A.

In the present embodiment, the resonance frequency of the resonator S5 is higher than the resonance frequency of the resonator S6, and thus the impedance Z2 in the pass band of the band pass filter 21A becomes high. This reduces the signal leaking to the band elimination filter 22A side and increases the signal flowing to the band pass filter 21A side, and as a result, deterioration of the pass characteristic of the band pass filter 21A can be suppressed.

Further, although the resonators have a given electrostatic capacitance, in the band elimination filter 22A, the capacitance value of the resonator S5 is preferably smaller than that of the resonator S6. This makes the impedance Z2 in the pass band of the band-pass filter 21A higher, and can also suppress degradation of the pass characteristic of the band-pass filter 21A.

Fig. 4A to 4D are graphs showing simulation results of the pass characteristics of the band pass filter in the case where the conditions of the resonance frequency and the capacitance value of the resonators of the band stop filter shown in fig. 2 are changed. Specifically, in the present simulation, the relationship of the level of the resonance frequency of the resonators S5, S6 and the relationship of the magnitude of the capacitance value of the resonators S5, S6 were changed. Table 1 below shows the relationship between the resonance frequency and the capacitance value of the resonator S5 with respect to the resonator S6.

[ Table 1]

Capacitance/resonant frequency	Low (S5 < S6)	High (S5 > S6)
			Large (S5 > S6)	FIG. 4A	FIG. 4B
Small (S5 < S6)	FIG. 4C	FIG. 4D

In the present simulation, the passband of the band pass filter 21A is set to 1166.22 to 1186.68MHz, as an example. In the graph, the horizontal axis shows the frequency (MHz) of the signal, and the vertical axis shows the attenuation (dB) of the signal. In each graph, the upper graph on the paper surface shows the result of the passing characteristic in 10dB units (see the scale on the left vertical axis), and the lower graph on the paper surface shows the result of the passing characteristic in 1dB units (see the scale on the right vertical axis).

As is apparent from a comparison between fig. 4A and 4B, when the resonance frequency of the resonator S5 is higher than the resonance frequency of the resonator S6, the pass characteristic of the bandpass filter can be greatly improved. In fig. 4B, it is understood that the attenuation amounts of the signals are almost uniformly converged to about-2 to-1 dB in the pass band. Similarly, in comparison between fig. 4C and 4D, when the resonance frequency of the resonator S5 is higher than the resonance frequency of the resonator S6, the pass characteristic of the bandpass filter can be greatly improved.

As is clear from comparison between fig. 4B and 4D, when the capacitance value of the resonator S5 is smaller than the capacitance value of the resonator S6, the pass characteristic of the band pass filter is improved slightly, particularly on the high frequency band side. Similarly, in comparison between fig. 4A and 4C, when the capacitance value of the resonator S5 is smaller than the capacitance value of the resonator S6, the pass characteristic of the band pass filter is improved slightly particularly on the high frequency band side.

From the above simulation results, it can be said that the resonance frequency of the resonator S5 is preferably higher than the resonance frequency of the resonator S6, regardless of the magnitude relation of the capacitance values of the resonators S5, S6. It can be said that the capacitance value of the resonator S5 is preferably smaller than the capacitance value of the resonator S6, independently of the relationship between the resonance frequencies of the resonators S5 and S6. It can be said that the magnitude relation of the resonance frequency contributes more to the improvement of the pass characteristic of the band-pass filter than the magnitude relation of the capacitance value.

In the above-described embodiment, the band elimination filter 22A has two resonators S5 and S6, but the band elimination filter may have three or more resonators. When the band-stop filter includes three or more resonators, at least one resonator may be provided on the common terminal T3 side of the resonator having the lowest resonance frequency. At least one resonator may be provided on the common terminal T3 side of the resonator having the largest capacitance value.

Although the band elimination filter 22A has a structure in which one resonator is provided on each of both sides of the inductor L4 in the above-described embodiment, one or both of the resonators S5 and S6 may be divided. The term "divided resonator" means that a plurality of resonators connected in series are provided instead of one resonator, and the characteristic of the plurality of resonators combined matches the characteristic of the one resonator before division. When one or both of the resonators S5 and S6 are divided, it is preferable that all of the divided resonators satisfy the above-described relationship of the resonant frequencies. Further, it is preferable that the combined capacitance values of the divided resonators satisfy the above-described magnitude relation of the capacitance values.

Next, the inductor L4 included in the band stop filter 22A will be described. The band elimination filter 22A includes the inductor L4 between the resonator S5 and the resonator S6, and thus the impedance Z2 in the pass band of the band pass filter 21A is increased, whereby the pass characteristic of the band pass filter 21A can also be improved.

Fig. 5A to 5D are graphs showing simulation results of the pass characteristic of the band pass filter in the case where the condition of the inductor L4 of the band stop filter shown in fig. 2 is changed. Fig. 5A is a simulation result in a structure without an inductor equivalent to the inductor L4 of the band-stop filter 22A. Fig. 5B is a simulation result in a structure in which, instead of being connected to the connection point of the resonator S5 and the resonator S6, one end of an inductor equivalent to the inductor L4 of the band elimination filter 22A is connected to the connection point of the resonator S6 and the inductor L5. Fig. 5C is a simulation result in the case where the inductance value of the inductor L4 is smaller than the inductance value of the inductor L3 in the band elimination filter 22A. Fig. 5D is a simulation result in the case where the inductance value of the inductor L4 is larger than the inductance value of the inductor L3 in the band elimination filter 22A.

In addition, the resonator S5 is high in relation to the level of the resonance frequency of the resonators S5 and S6, and the resonator S5 is small in relation to the magnitude of the capacitance. The other conditions are the same as those in fig. 4A to 4D described above, and therefore, the description thereof is omitted.

As is clear from a comparison between fig. 5A and 5B, the band elimination filter includes an inductor branched from the line U2, and thus the pass characteristic in the vicinity of the center frequency of the pass band of the band pass filter is improved to a small extent.

As is clear from comparison between fig. 5B and 5C, the pass characteristic of the band-pass filter 21 is significantly improved when the inductor branching from the line U2 is located between the resonator S5 and the resonator S6, compared with the position of the inductor at the subsequent stage of the resonator S6.

As can be seen from comparison between fig. 5C and 5D, when the inductance value of inductor L4 is larger than the inductance value of inductor L3, the pass characteristic of band-pass filter 21 is further improved.

From the above simulation results, it can be said that the band elimination filter 22A according to the present embodiment further improves the pass characteristic of the band pass filter 21 by providing the inductor L4 having a larger inductance value than the inductor L3 between the resonator S5 and the resonator S6.

Fig. 6 is a diagram showing an example of the layout of each inductor shown in fig. 2. In fig. 6, only a part of the components of the demultiplexer 20A are shown, and the other components are not shown.

When the inductor included in the band pass filter 21A and the inductor included in the band stop filter 22A are built in one package, the inductor L5 is preferably arranged closer to the inductor L1 than to the inductor L2. In the example shown in fig. 6, a part of the inductor L1 and a part of the inductor L5 are formed substantially in parallel on the substrate 300. As described above, by disposing the inductor L1 and the inductor L5 close to each other, the two inductors are coupled to each other to generate mutual induction, and therefore, the pass characteristic of the band elimination filter 22A can be improved.

Fig. 7A and 7B are graphs showing simulation results of the pass characteristics of the band elimination filter shown in fig. 2. Fig. 7A shows the simulation result in the case where the inductor L1 and the inductor L5 are arranged relatively close to each other, and mutual induction occurs between the two. Fig. 7B shows the simulation result in the case where the inductor L1 and the inductor L5 are disposed relatively far apart, and no mutual induction occurs between the two. The horizontal axis in fig. 7A and 7B shows frequency (MHz), and the vertical axis shows attenuation (dB) in units of 1 dB.

As is clear from comparison between fig. 7A and 7B, when the distance between the inductor L1 and the inductor L5 is short, the attenuation is improved particularly in the region of 3000 to 5000 MHz. That is, the pass characteristic of the band elimination filter 22A is improved.

Although not shown in fig. 6, instead of being coupled to the inductor L1, the inductor L5 may be coupled to the inductor L3. That is, the inductor L5 may be disposed closer to the inductor L3 than the inductor L2. In this case, as well as the case of coupling with the inductor L1, the pass characteristic of the band-stop filter 22A can be improved.

The exemplary embodiments of the present invention have been described above. The demultiplexer 20A includes: a band-pass filter 21A for passing a signal of a predetermined frequency band between the 1 st terminal and a common terminal connected to the antenna; and a band rejection filter 22A that attenuates a signal of a predetermined frequency band between the 2 nd terminal and the common terminal, wherein the band rejection filter 22A includes a plurality of resonators connected in series to a line between the 2 nd terminal and the common terminal, and the plurality of resonators include a 1 st resonator having a lowest resonance frequency and a 2 nd resonator provided on the common terminal side of the 1 st resonator. Thereby, the impedance Z2 in the pass band of the band-pass filter 21A becomes higher, and hence the signal leaking to the band-stop filter 22A side decreases. Therefore, the signal flowing to the band pass filter 21A side increases, and deterioration of the pass characteristic of the band pass filter 21A can be suppressed.

In the demultiplexer 20A, the band-pass filter 21A may include a 3 rd resonator disposed in the series arm and a 4 th resonator disposed in the parallel arm between the 1 st terminal and the common terminal, and the anti-resonance frequencies of the plurality of resonators may be higher than the resonance frequency of the 4 th resonator and lower than the anti-resonance frequency of the 3 rd resonator. Thereby, the passband of the band-pass filter 21A and the attenuation band of the band-stop filter 22A overlap.

In the demultiplexer 20A, the plurality of resonators may include a 5 th resonator having the largest capacitance value and a 6 th resonator provided on the common terminal side of the 5 th resonator. This makes the impedance Z2 in the pass band of the band-pass filter 21A higher, and therefore can suppress deterioration of the pass characteristic of the band-pass filter 21A.

In the demultiplexer 20A, the 1 st resonator and the 2 nd resonator may be disposed adjacent to each other, and the band elimination filter may further include: and a 1 st inductor having one end connected to a connection point between the 1 st resonator and the 2 nd resonator and the other end to which a reference potential is supplied. This makes the impedance Z2 in the pass band of the band-pass filter 21A higher, and therefore can suppress deterioration of the pass characteristic of the band-pass filter 21A.

In the demultiplexer 20A, the band elimination filter 22A may further include: and a 2 nd inductor connected in series with the 2 nd resonator between the 2 nd resonator and the common terminal, wherein the inductance value of the 1 st inductor is larger than the inductance value of the 2 nd inductor. This further improves the pass characteristic of the band-pass filter 21A.

In the demultiplexer 20A, the band elimination filter 22A may further include: a 2 nd inductor and a 3 rd inductor connected in series to a line between the 2 nd terminal and the common terminal, the band pass filter 21A further including: and a 4 th inductor connected in series to a line between the 1 st terminal and the common terminal, wherein the 3 rd inductor is disposed closer to the 2 nd inductor than the 4 th inductor. Thereby, the 3 rd inductor and the 2 nd inductor are coupled to generate mutual induction, and thus the pass characteristic of the band elimination filter 22A can be improved.

In the demultiplexer 20A, the band elimination filter 22A may further include: a 3 rd inductor connected in series to a line between the 2 nd terminal and the common terminal, the band pass filter 21A further including: and a 4 th inductor connected in series to a line between the 1 st terminal and the common terminal, wherein the demultiplexer 20A further includes: and a 5 th inductor, a line connected in series between a connection point of the band pass filter and the band stop filter and the common terminal, the 3 rd inductor being disposed closer to the 5 th inductor than the 4 th inductor. Thereby, the 3 rd inductor and the 5 th inductor are coupled to generate mutual induction, and thus the pass characteristic of the band elimination filter 22A can be improved.

The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention can be modified or improved without departing from the gist thereof, and the present invention also includes equivalents thereof. That is, embodiments to which design changes are appropriately made by those skilled in the art to each embodiment as long as the features of the present invention are provided are also included in the scope of the present invention. For example, the elements and their arrangement, materials, conditions, shapes, dimensions, and the like included in the embodiments are not limited to the illustrated elements and their arrangement, materials, conditions, shapes, dimensions, and the like, and can be appropriately modified. Further, the elements included in the respective embodiments can be combined as long as the combination is technically feasible, and embodiments combining them are included in the scope of the present invention as long as the features of the present invention are included.