阅读说明：本技术 滤波器装置、高频前端电路、以及通信装置 (Filter device, high-frequency front-end circuit, and communication device ) 是由 野阪浩司 于 2018-11-07 设计创作，主要内容包括：降低滤波器装置的通带的插入损耗。本发明的一个实施方式涉及的滤波器装置(1)具备第1端子(T1)及第2端子(T2)、和第1滤波器(FLT1)及第2滤波器(FLT2)。第1滤波器(FLT1)及第2滤波器(FLT2)在第1端子(T1)与第2端子(T2)之间并联地配置。第1滤波器(FLT1)包含多个串联臂谐振器。多个串联臂谐振器串联地配置在从第1端子(T1)经由第1滤波器(FLT1)到达第2端子(T2)的路径。多个串联臂谐振器包含第1串联臂谐振器(s11)及第2串联臂谐振器(s12)。在将各串联臂谐振器的反谐振频率与谐振频率之差除以谐振频率而得到的值定义为相对带宽的情况下,第1串联臂谐振器(s11)的第1相对带宽与第2串联臂谐振器(s12)的第2相对带宽不同。(The insertion loss of the pass band of the filter arrangement is reduced. A filter device (1) according to one embodiment of the present invention includes a 1 st terminal (T1) and a 2 nd terminal (T2), and a 1 st filter (FLT1) and a 2 nd filter (FLT 2). The 1 st filter (FLT1) and the 2 nd filter (FLT2) are arranged in parallel between the 1 st terminal (T1) and the 2 nd terminal (T2). The 1 st filter (FLT1) includes a plurality of series-arm resonators. The plurality of series-arm resonators are arranged in series on a path from the 1 st terminal (T1) to the 2 nd terminal (T2) via the 1 st filter (FLT 1). The plurality of series-arm resonators include a 1 st series-arm resonator (s11) and a 2 nd series-arm resonator (s 12). When a value obtained by dividing the difference between the anti-resonance frequency and the resonance frequency of each series-arm resonator by the resonance frequency is defined as a relative bandwidth, the 1 st relative bandwidth of the 1 st series-arm resonator (s11) is different from the 2 nd relative bandwidth of the 2 nd series-arm resonator (s 12).)

1. A filter arrangement having a pass band of 1, wherein,

the filter device includes:

a 1 st terminal and a 2 nd terminal; and

a 1 st filter and a 2 nd filter arranged in parallel between the 1 st terminal and the 2 nd terminal,

the 1 st pass band includes at least a portion of a 2 nd pass band of the 1 st filter and at least a portion of a 3 rd pass band of the 2 nd filter,

the 2 nd pass band is narrower than the 1 st pass band,

the 3 rd pass band is narrower than the 1 st pass band,

the center frequency of the 3 rd pass band is higher than the center frequency of the 2 nd pass band,

the 1 st filter includes a plurality of series-arm resonators arranged in series on a path from the 1 st terminal to the 2 nd terminal via the 1 st filter,

the plurality of series-arm resonators include a 1 st series-arm resonator and a 2 nd series-arm resonator,

when a value obtained by dividing a difference between an anti-resonance frequency and a resonance frequency of each series arm resonator by the resonance frequency is defined as a relative bandwidth, a 1 st relative bandwidth of the 1 st series arm resonator is different from a 2 nd relative bandwidth of the 2 nd series arm resonator.

2. The filter arrangement of claim 1,

the plurality of series-arm resonators also includes a 3 rd series-arm resonator,

the plurality of series arm resonators are arranged in series with the 1 st series arm resonator and the 3 rd series arm resonator as both ends in a path from the 1 st terminal to the 2 nd terminal via the 1 st filter,

a 3 rd relative bandwidth of the 3 rd series arm resonator is different from the 2 nd relative bandwidth.

3. The filter arrangement of claim 2,

said 1 st relative bandwidth is greater than said 2 nd relative bandwidth,

the 3 rd relative bandwidth is larger than the 2 nd relative bandwidth.

4. The filter arrangement according to claim 2 or 3,

at least one of the electrostatic capacitance of the 1 st series arm resonator and the electrostatic capacitance of the 3 rd series arm resonator is smaller than the electrostatic capacitance of the 2 nd series arm resonator.

5. The filter arrangement according to any one of claims 2 to 4,

the 1 st series arm resonator, the 2 nd series arm resonator, and the 3 rd series arm resonator each include at least one elastic wave resonator, and at least one of the number of elastic wave resonators included in the 1 st series arm resonator and the number of elastic wave resonators included in the 3 rd series arm resonator is larger than the number of elastic wave resonators included in the 2 nd series arm resonator.

6. A filter arrangement having a pass band of 1, wherein,

the filter device includes:

a 1 st terminal and a 2 nd terminal; and

a 1 st filter and a 2 nd filter arranged in parallel between the 1 st terminal and the 2 nd terminal,

the 1 st pass band includes at least a portion of a 2 nd pass band of the 1 st filter and at least a portion of a 3 rd pass band of the 2 nd filter,

the 2 nd pass band is narrower than the 1 st pass band,

the 3 rd pass band is narrower than the 1 st pass band,

the center frequency of the 3 rd pass band is higher than the center frequency of the 2 nd pass band,

the 2 nd filter includes:

a 1 st parallel arm resonator disposed between a ground point and a 1 st connection point on a path from the 1 st terminal to the 2 nd terminal via the 2 nd filter; and

a 2 nd parallel arm resonator arranged between the ground point and a 2 nd connection point different from the 1 st connection point on a path from the 1 st terminal to the 2 nd terminal via the 2 nd filter,

when a value obtained by dividing a difference between an anti-resonance frequency and a resonance frequency of each parallel arm resonator by the resonance frequency is defined as a relative bandwidth, a 4 th relative bandwidth of the 1 st parallel arm resonator is different from a 5 th relative bandwidth of the 2 nd parallel arm resonator.

7. The filter arrangement of claim 6,

the 2 nd filter includes:

a filter circuit including the 1 st and 2 nd parallel arm resonators;

a 1 st phase shifter disposed on a path between the filter circuit and the 1 st terminal; and

a 2 nd phase shifter disposed on a path between the filter circuit and the 2 nd terminal,

the 1 st phase shifter and the 2 nd phase shifter are configured to increase an impedance of the 2 nd filter in the 2 nd pass band.

8. The filter arrangement according to any one of claims 1 to 7,

further comprises a 2 nd switch, a 3 rd switch, a 4 th switch and a 5 th switch,

the 2 nd switch, the 1 st filter, and the 3 rd switch are connected in series in this order between the 1 st terminal and the 2 nd terminal,

the 4 th switch, the 2 nd filter, and the 5 th switch are connected in series in this order between the 1 st terminal and the 2 nd terminal,

the 2 nd switch, the 1 st filter, and the 3 rd switch connected in series and the 4 th switch, the 2 nd filter, and the 5 th switch connected in series are connected in parallel between the 1 st terminal and the 2 nd terminal.

9. The filter arrangement according to any one of claims 1 to 7,

further provided with:

a 3 rd terminal; and

a 2 nd switch and a 3 rd switch,

the 2 nd filter and the 2 nd switch are connected in series in this order between the 1 st terminal and the 2 nd terminal,

the 1 st filter and the 2 nd filter connected in series and the 2 nd switch are connected in parallel between the 1 st terminal and the 2 nd terminal,

the 3 rd switch is connected between the 3 rd terminal and a 3 rd connection point of the 2 nd filter and the 2 nd switch,

the 2 nd pass band and the 3 rd pass band do not overlap.

10. The filter arrangement according to any one of claims 1 to 7,

further provided with:

a 3 rd terminal; and

a 2 nd switch and a 3 rd switch,

the 1 st filter and the 2 nd switch are connected in series in this order between the 1 st terminal and the 3 rd terminal,

the 2 nd filter and the 1 st filter and the 2 nd switch connected in series are connected in parallel between the 1 st terminal and the 3 rd terminal,

the 3 rd switch is connected between the 2 nd terminal and a 3 rd connection point of the 1 st filter and the 2 nd switch,

the 2 nd pass band and the 3 rd pass band do not overlap.

11. A high-frequency front-end circuit is provided with:

a filter arrangement as claimed in any one of claims 1 to 10; and

and the amplifying circuit is electrically connected with the filter device.

12. A communication device is provided with:

an RF signal processing circuit for processing the high frequency signal transmitted and received by the antenna element; and

the high frequency front end circuit of claim 11, the high frequency signal being communicated between the antenna element and the RF signal processing circuitry.

Technical Field

The invention relates to a filter device, a high-frequency front-end circuit, and a communication device.

Background

Conventionally, a filter device is known in which two filters having different pass bands are arranged in parallel to realize a wide pass band. For example, in a wireless receiving circuit disclosed in japanese patent application laid-open No. 2008-160629 (patent document 1), two bandpass filters having different passbands are arranged in parallel, and the passband is widened.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 2008-160629

Disclosure of Invention

Problems to be solved by the invention

The passband of the filter device is formed by arranging the 1 st filter and the 2 nd filter in parallel as in the wireless receiving circuit disclosed in patent document 1. The center frequency of the passband of the 2 nd filter is higher than the center frequency of the passband of the 1 st filter. That is, in the pass band of the filter device, a band (low frequency side) lower than the center frequency is mainly formed by the 1 st filter (low frequency side filter), and a band (high frequency side) higher than the center frequency is mainly formed by the 2 nd filter (high frequency side filter).

When the attenuation of the low-frequency side filter in the passband of the high-frequency side filter or the attenuation of the high-frequency side filter in the passband of the low-frequency side filter is small, the insertion loss in the passband of the filter device becomes large.

However, in the wireless receiving circuit disclosed in patent document 1, neither the high attenuation of the low-frequency side filter in the pass band of the high-frequency side filter nor the high attenuation of the high-frequency side filter in the pass band of the low-frequency side filter is considered.

The present invention has been made to solve the above-described problems, and an object thereof is to reduce the insertion loss of the passband of a filter device.

Means for solving the problems

A filter device according to an embodiment of the present invention has a 1 st pass band. The filter device includes a 1 st terminal and a 2 nd terminal, and a 1 st filter and a 2 nd filter. The 1 st filter and the 2 nd filter are arranged in parallel between the 1 st terminal and the 2 nd terminal. The 1 st pass band contains at least a portion of the 2 nd pass band of the 1 st filter. The 1 st pass band contains at least a portion of the 3 rd pass band of the 2 nd filter. The 2 nd pass band is narrower than the 1 st pass band. The 3 rd pass band is narrower than the 1 st pass band. The center frequency of the 3 rd pass band is higher than the center frequency of the 2 nd pass band. The 1 st filter includes a plurality of series-arm resonators. The plurality of series arm resonators are arranged in series on a path from the 1 st terminal to the 2 nd terminal via the 1 st filter. The plurality of series-arm resonators include a 1 st series-arm resonator and a 2 nd series-arm resonator. When a value obtained by dividing the difference between the anti-resonance frequency and the resonance frequency of each series arm resonator by the resonance frequency is defined as a relative bandwidth, the 1 st relative bandwidth of the 1 st series arm resonator is different from the 2 nd relative bandwidth of the 2 nd series arm resonator.

According to the filter device according to one embodiment of the present invention, the 1 st filter includes series-arm resonators having different relative bandwidths, so that the insertion loss at the high-frequency end of the passband of the filter device can be reduced.

Another embodiment of the present invention relates to a filter device having a pass band of 1. The filter device includes a 1 st terminal and a 2 nd terminal, and a 1 st filter and a 2 nd filter. The 1 st filter and the 2 nd filter are arranged in parallel between the 1 st terminal and the 2 nd terminal. The 1 st pass band contains at least a portion of the 2 nd pass band of the 1 st filter. The 1 st pass band contains at least a portion of the 3 rd pass band of the 2 nd filter. The 2 nd pass band is narrower than the 1 st pass band. The 3 rd pass band is narrower than the 1 st pass band. The center frequency of the 3 rd pass band is higher than the center frequency of the 2 nd pass band. The 2 nd filter includes a 1 st parallel arm resonator and a 2 nd parallel arm resonator. The 1 st parallel arm resonator is arranged between a ground point and a 1 st connection point on a path from the 1 st terminal to the 2 nd terminal via the 2 nd filter. The 2 nd parallel arm resonator is arranged between the ground point and a 2 nd connection point different from the 1 st connection point on a path from the 1 st terminal to the 2 nd terminal via the 2 nd filter. When a value obtained by dividing a difference between the anti-resonance frequency and the resonance frequency of each parallel arm resonator by the resonance frequency is defined as a relative bandwidth, the relative bandwidth of the 1 st parallel arm resonator is different from the relative bandwidth of the 2 nd parallel arm resonator.

According to the filter device according to the another embodiment of the present invention, the 2 nd filter includes the parallel arm resonators having different relative bandwidths, so that the insertion loss at the low frequency end of the pass band of the filter device can be reduced.

Effects of the invention

According to the filter device of the present invention, the insertion loss of the pass band of the filter device can be reduced.

Drawings

Fig. 1 is a circuit configuration diagram of a filter device according to an embodiment.

Fig. 2 is a diagram showing the relationship between the 1 st passband of the filter device of fig. 1 and the 2 nd passband and the 3 rd passband of the low-frequency side filter and the high-frequency side filter, respectively.

Fig. 3 is a graph showing a relationship between the resonance frequency and the relative bandwidth of the elastic wave resonator according to the embodiment.

Fig. 4 is a circuit configuration diagram specifically showing the configurations of the low-frequency side filter and the high-frequency side filter of fig. 1.

Fig. 5 is a diagram showing both the pass characteristic of the low-frequency side filter and the impedance characteristic of the resonator included in the low-frequency side filter in embodiment 1.

Fig. 6 is a diagram showing both the pass characteristic of the low-frequency side filter and the impedance characteristic of the resonator included in the low-frequency side filter in comparative example 1.

Fig. 7 is a diagram showing both the pass characteristics of the filter devices according to embodiment 1 and comparative example 1 and the pass characteristics of the low-frequency side filter.

Fig. 8 is a circuit configuration diagram of a filter device according to a modification of embodiment 1.

Fig. 9 is a diagram showing both the pass characteristic of the high-frequency side filter and the impedance characteristic of the resonator included in the high-frequency side filter in embodiment 2.

Fig. 10 is a diagram showing both the pass characteristic of the high-frequency side filter and the impedance characteristic of the resonator included in the high-frequency side filter in comparative example 1.

Fig. 11 is a diagram showing both the pass characteristics of the filter devices according to embodiment 2 and comparative example 1 and the pass characteristics of the high-frequency side filters.

Fig. 12 is a circuit configuration diagram of a filter device according to embodiment 3.

Fig. 13 is a diagram showing both the pass characteristics of the filter devices according to embodiment 3 and comparative example 2 and the pass characteristics of the low-frequency side filter.

Fig. 14 is a diagram showing both the pass characteristics of the filter devices according to embodiment 4 and comparative example 2 and the pass characteristics of the low-frequency side filter.

Fig. 15 is a diagram showing the change in impedance characteristics and reflection characteristics of an elastic wave resonator when the capacitance of the elastic wave resonator is changed.

Fig. 16 is a diagram showing impedance characteristics and reflection characteristics of the series-arm resonators of embodiment 3 and embodiment 4 together.

Fig. 17 is a diagram showing impedance characteristics and reflection characteristics of the series-arm resonators of embodiment 3 and embodiment 4 together.

Fig. 18 is a diagram showing the reflection characteristics of the low-frequency side filter of embodiment 3 and the reflection characteristics of the low-frequency side filter of embodiment 4.

Fig. 19 is a diagram showing both the pass characteristics of the filter devices according to embodiments 3 and 4 and the pass characteristics of the low-frequency side filters.

Fig. 20 is a circuit configuration diagram of a filter device according to a modification of embodiment 4.

Fig. 21 is a circuit configuration diagram of a filter device according to embodiment 5.

Fig. 22 is a diagram showing an example of a block configuration of the filter device of fig. 21.

Fig. 23 is a graph showing a pass characteristic of the filter device of fig. 21 together with a table showing the on state of each switch.

Fig. 24 is a configuration diagram of a communication device according to embodiment 6.

Fig. 25 is a circuit configuration diagram of a filter device according to a modification of embodiment 6.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and description thereof will not be repeated in principle.

Fig. 1 is a circuit configuration diagram of a filter device 1 according to an embodiment. As shown in fig. 1, the filter device 1 includes a filter FLT1 (1 st filter), a filter FLT2 (2 nd filter), an input/output terminal T1 (1 st terminal), and an input/output terminal T2 (2 nd terminal). The filters FLT1 and FLT2 are connected in parallel between the input-output terminals T1 and T2. Specifically, one terminal of the filter FLT1 is connected to the input-output terminal T1, and the other terminal of the filter FLT1 is connected to the input-output terminal T2. One terminal of the filter FLT2 is connected to the input/output terminal T1, and the other terminal of the filter FLT2 is connected to the input/output terminal T2.

The filters FLT1 and FLT2 each include an elastic wave resonator as a series-arm resonator and a parallel-arm resonator. The elastic Wave Resonator is, for example, a Surface Acoustic Wave (SAW) Resonator, a Bulk Acoustic Wave (BAW) Resonator, a FBAR (Film Bulk Acoustic Wave) Resonator, or an SM (solid state Mounted) Resonator. In embodiment 1, the high-frequency side filter FLT2 may be an LC filter formed of an LC resonant circuit.

Fig. 2 is a diagram showing the relationship of the pass band PB1 (pass band 1) of the filter device 1 of fig. 1, and the pass bands PB2 (pass band 2) and PB3 (pass band 3) of the filters FLT1 and FLT2, respectively. In fig. 2, frequencies Cf1 to Cf3 are center frequencies of pass bands PB1 to PB3, respectively. The passband is an arbitrary continuous band in which the range of the insertion loss is not less than the minimum value of the insertion loss and not more than the value obtained by adding 3dB to the minimum value.

As shown in FIG. 2, passband PB1 includes a portion of passband PB2 and a portion of passband PB 3. Passband PB2 is narrower than passband PB 1. Passband PB3 is narrower than passband PB 1. The center frequency Cf3 of the passband PB3 is higher than the center frequency Cf2 of the passband PB 2. Within the pass band PB1, a band lower than the center frequency Cf1 is mainly formed by the filter FLT1, and a band higher than the center frequency Cf1 is mainly formed by the filter FLT 2. The filter FLT1 is a filter forming the pass band PB2, and is referred to as a low-frequency side filter. The filter FLT2 is a filter forming the pass band PB3 and is referred to as a high-frequency side filter.

In the pass band PB3, the larger the attenuation amount of the filter FLT1 is, the smaller the signal consumed in the filter FLT1 is, and the larger the signal passing through the filter FLT2 is. As a result, the insertion loss of the filter device 1 at the highest frequency (high frequency end) of the pass band PB1 is reduced.

In the pass band PB2, the larger the attenuation amount of the filter FLT2 is, the smaller the signal consumed in the filter FLT2 is, and the larger the signal passing through the filter FLT1 is. As a result, the insertion loss of the filter device 1 at the lowest frequency (low frequency end) of the pass band PB1 is reduced.

In the pass band PB3, the attenuation pole of the filter FLT1 is generated in the vicinity of the anti-resonance frequency of the series-arm resonator included in the filter FLT 1. Therefore, by providing the filter FLT1 with a plurality of series-arm resonators, a plurality of attenuation poles of the filter FLT1 in the vicinity of the pass band PB3 can be formed. Further, by increasing the frequency difference between the anti-resonance frequencies of the plurality of series-arm resonators in the filter FLT1, the frequency difference between the plurality of attenuation poles of the filter FLT1 in the vicinity of the passband PB3 can be increased, and the attenuation bandwidth can be widened. Therefore, the attenuation amount of the filter FLT1 in the pass band PB3 can be increased.

Further, in the pass band PB2, the attenuation pole of the filter FLT2 is generated in the vicinity of the resonance frequency of the parallel-arm resonator included in the filter FLT 2. Therefore, by providing the filter FLT2 with a plurality of parallel-arm resonators, a plurality of attenuation poles of the filter FLT2 in the vicinity of the passband PB2 can be formed. Further, by increasing the frequency difference between the resonance frequencies of the plurality of parallel-arm resonators in the filter FLT2, the frequency difference between the plurality of attenuation poles of the filter FLT2 in the vicinity of the passband PB2 can be increased, and the attenuation bandwidth can be widened. Therefore, the attenuation amount of the filter FLT2 in the pass band PB2 can be increased.

Further, the impedance of the elastic wave resonators constituting the series arm resonator and the parallel arm resonator becomes maximum at the anti-resonance frequency and minimum at the resonance frequency.

Therefore, in embodiment 1, the frequency difference between the two attenuation poles of the low-frequency side filter is increased in the pass band of the high-frequency side filter by including two series-arm resonators having different relative bandwidths in the plurality of series-arm resonators constituting the low-frequency side filter and shifting the anti-resonance frequency. As a result, the attenuation of the low-frequency side filter in the pass band of the high-frequency side filter becomes large, and the insertion loss at the high-frequency end of the pass band of the filter device can be reduced.

In embodiment 2, the frequency difference between the two attenuation poles of the high-frequency side filter is increased in the pass band of the low-frequency side filter by including two parallel-arm resonators having different relative bandwidths in the plurality of parallel-arm resonators constituting the high-frequency side filter and shifting the resonance frequencies. As a result, the attenuation of the high-frequency side filter in the pass band of the low-frequency side filter becomes large, and the insertion loss at the low-frequency end of the pass band of the filter device can be reduced.

In the embodiment, the relative bandwidth is a percentage (%) obtained by dividing the difference between the anti-resonance frequency and the resonance frequency of the series-arm resonator or the parallel-arm resonator by the resonance frequency.

Fig. 3 is a graph showing a relationship between the resonance frequency fr and the relative bandwidth BWR of a general elastic wave resonator. When the resonance frequency fr is changed, the relative bandwidth BWR changes. When a general filter device is configured using a plurality of elastic wave resonators, the frequency difference between the resonance frequencies fr of the plurality of elastic wave resonators is substantially 100MHz or less. As shown in fig. 3, when the resonance frequency fr is changed by 100MHz, the bandwidth BWR changes by about 0.7%. Therefore, hereinafter, when the difference between the two relative bandwidths is 0.8% or more, the two relative bandwidths are assumed to be different from each other. When the difference between the two relative bandwidths is less than 0.8%, the two relative bandwidths are equal to each other.

When the elastic wave resonator is a SAW resonator, the relative bandwidth of the elastic wave resonator can be changed by providing the 1 st adjustment film including an insulator or a dielectric between the comb-teeth electrode and the substrate having piezoelectricity and changing the film thickness of the 1 st adjustment film. In the case where the 1 st adjustment film is not provided, the relative bandwidth is the largest, and the relative bandwidth becomes smaller as the film thickness of the 1 st adjustment film is thicker. Further, by providing the 2 nd adjustment film including an insulator or a dielectric so as to cover the comb-teeth electrodes and changing the film thickness of the 2 nd adjustment film, the relative bandwidth of the SAW resonator can be changed. In the case where the 2 nd adjustment film is not provided, the relative bandwidth is the largest, and the relative bandwidth becomes smaller as the film thickness of the 2 nd adjustment film is thicker.

When the elastic wave resonator is a BAW resonator, the relative bandwidth can be changed by changing the material of the piezoelectric body between the opposing electrodes.

[ embodiment 1]

In embodiment 1, a case will be described in which two series-arm resonators having different relative bandwidths are included in a plurality of series-arm resonators constituting a low-frequency side filter. Fig. 4 is a circuit configuration diagram specifically illustrating the structures of the filters FLT1 and FLT2 of fig. 1. The circuit configurations of the filter device 100 according to comparative example 1 and the filter device 2 according to embodiment 2, which will be described later, are also the circuit configurations shown in fig. 4.

As shown in fig. 4, the filter FLT1 includes a plurality of series-arm resonators s11, s12 and parallel-arm resonator p 11. The series-arm resonator s11 (the 1 st series-arm resonator) and the series-arm resonator s12 (the 2 nd series-arm resonator) are connected in series between the input/output terminals T1 and T2. The parallel-arm resonator p11 is connected between the ground point and the connection point of the series-arm resonators s11 and s 12.

The filter FLT2 includes a phase shifter PS1 (1 st phase shifter), a phase shifter PS2 (2 nd phase shifter), and a filter circuit AS 1. The phase shifter PS1 is connected between the filter circuit AS1 and the input-output terminal T1. The phase shifter PS2 is connected between the filter circuit AS1 and the input-output terminal T2.

The filter circuit AS1 includes a series-arm resonator s21 and parallel-arm resonators p21, p 22. The series-arm resonator s21 is connected between the phase shifters PS1 and PS 2. The parallel-arm resonator p21 is connected between the ground point and the connection point of the phase shifter PS1 and the series-arm resonator s 21. The parallel-arm resonator p22 is connected between the ground point and the connection point of the phase shifter PS2 and the series-arm resonator s 21. The phase shifters PS1 and PS2 are configured to increase the impedance of the filter FLT2 in the pass band PB2 of the filter FLT 1.

Table 1 below shows the resonant frequency fr, the anti-resonant frequency fa, the relative bandwidth BWR, and the electrostatic capacitance of each of the series-arm resonators s11 and s12, the parallel-arm resonator p11, the series-arm resonator s21, and the parallel-arm resonators p21 and p22 in the filter device 1.

[ Table 1]

As shown in table 1, the difference between the resonance frequencies fr of the series-arm resonators s11 and s12 in the filter device 1 is 11MHz, and the difference between the anti-resonance frequencies fa is 40.8 MHz. The difference in the anti-resonance frequencies fa is about 4 times greater than the difference in the resonance frequencies fr. In the filter device 1, the anti-resonance frequencies fa of the series-arm resonators s11, s12 are mainly shifted, whereby the relative bandwidth BWR (1 st bandwidth) of the series-arm resonator s11 in the filter device 1 is made larger than the relative bandwidth BWR (2 nd bandwidth) of the series-arm resonator s 12.

Fig. 5 is a diagram showing both the pass characteristics (frequency characteristics of insertion loss and attenuation) of the low-frequency side filter FLT1 and the impedance characteristics of the resonators s11, s12, and p11 included in the low-frequency side filter FLT1 in embodiment 1. Fig. 5 (a) is a diagram showing the pass characteristics of low-frequency side filter FLT1 in embodiment 1. Fig. 5 (b) is a diagram showing impedance characteristics of the series-arm resonators s11 and s12 and the parallel-arm resonator p11 included in the low-frequency side filter FLT1 in embodiment 1. The "pass characteristic of the filter" is a pass characteristic of the filter alone, and is a pass characteristic when the filter is separated from another circuit. The "impedance characteristic of the resonator" is an impedance characteristic of the resonator alone, and is an impedance characteristic when the resonator is separated from another circuit.

Referring to fig. 5 and table 1 together, as shown in fig. 5 (a), in the pass characteristic of the filter FLT1, attenuation poles are generated near the anti-resonance frequencies of the series-arm resonators s11 and s12 in the vicinity of the pass band PB 3. Since the anti-resonance frequencies of series-arm resonators s11 and s12 are shifted by 40.8MHz, the frequency band in which the attenuation pole is generated is also about the same as the difference between the anti-resonance frequencies of series-arm resonators s11 and s 12.

Next, the filter device 100 according to comparative example 1 will be described. The circuit configuration of the filter device 100 is the same as that shown in fig. 4. Table 2 below shows the resonant frequency fr, the anti-resonant frequency fa, the relative bandwidth BWR, and the electrostatic capacitance of each of the series-arm resonators s11 and s12, the parallel-arm resonator p11, the series-arm resonator s21, and the parallel-arm resonators p21 and p22 in the filter device 100.

[ Table 2]

As shown in table 2, in the filter device 100, since the resonance frequency fr and the anti-resonance frequency fa of the series-arm resonators s11 and s12 are substantially equal to each other, the relative bandwidth BWR of the series-arm resonator s11 is equal to the relative bandwidth BWR of the series-arm resonator s 12.

Fig. 6 is a diagram showing both the pass characteristic of the low frequency side filter FLT1 and the impedance characteristics of the resonators s11, s12, and p11 included in the low frequency side filter FLT1 in comparative example 1. Fig. 6 (a) is a diagram showing the pass characteristics of low-frequency side filter FLT1 in comparative example 1. Fig. 6 (b) is a diagram showing impedance characteristics of the series-arm resonators s11 and s12 and the parallel-arm resonator p21 included in the low-frequency side filter FLT1 in comparative example 1.

Referring to fig. 6 and table 2 together, as shown in fig. 6 (a), in the pass characteristic of the filter FLT1, attenuation poles are generated near the anti-resonance frequencies of the series-arm resonators s11 and s12 in the vicinity of the pass band PB 3. Since the anti-resonance frequencies of the series-arm resonators s11 and s12 are substantially the same, the attenuation pole is concentrated in a narrower frequency band than that of embodiment 1.

Next, embodiment 1 and comparative example 1 were compared. Fig. 7 is a diagram showing both the pass characteristics of the filter devices according to embodiment 1 and comparative example 1 and the pass characteristics of the low-frequency side filter. Fig. 7 (a) is a diagram showing both the pass characteristic of the filter device 1 (solid line) and the pass characteristic of the filter device 100 (broken line). Fig. 7 b is a diagram showing the pass characteristic (solid line) of the filter FLT1 in embodiment 1 shown in fig. 5 a and the pass characteristic (broken line) of the filter FLT1 in comparative example 1 shown in fig. 6 a.

As shown in fig. 7 (b), in embodiment 1, the frequency difference between the two attenuation poles of the filter FLT1 formed in the vicinity of the pass band PB3 is larger than that in comparative example 1, and the amount of attenuation in the pass band PB3 is large. Therefore, as shown in fig. 7 (a), the insertion loss of filter device 1 is smaller than the insertion loss of filter device 100 at the high-frequency end of passband PB 1.

[ modification of embodiment 1]