阅读说明：本技术 滤波器装置、高频前端电路及通信装置 (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：滤波器装置(1)具备第一端子(T1)及第二端子(T2)、第一滤波器(FLT1)及第二滤波器(FLT2)。第一滤波器(FLT1)及第二滤波器(FLT2)并联配置在第一端子(T1)与第二端子(T2)之间。滤波器装置(1)的第一通带包括第一滤波器(FLT1)的第二通带的至少一部分。第一通带包括第二滤波器(FLT2)的第三通带的至少一部分。第二通带比第一通带窄。第三通带比第一通带窄。第三通带的中心频率比第二通带的中心频率高。第一滤波器(FLT1)包括多个弹性波谐振器(s1、s2、p1)和第一电容元件(Cp1)。第一电容元件(Cp1)与第一弹性波谐振器(p1)并联连接。(The filter device (1) is provided with a first terminal (T1) and a second terminal (T2), a first filter (FLT1), and a second filter (FLT 2). The first filter (FLT1) and the second filter (FLT2) are arranged in parallel between the first terminal (T1) and the second terminal (T2). The first pass band of the filter arrangement (1) comprises at least a part of the second pass band of the first filter (FLT 1). The first pass band includes at least a portion of a third pass band of a second filter (FLT 2). The second pass band is narrower than the first pass band. The third pass band is narrower than the first pass band. The third pass band has a center frequency that is higher than a center frequency of the second pass band. The first filter (FLT1) includes a plurality of elastic wave resonators (s1, s2, p1) and a first capacitive element (Cp 1). The first capacitance element (Cp1) is connected in parallel to the first elastic wave resonator (p 1).)

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

the filter device includes:

a first terminal and a second terminal; and

a first filter and a second filter arranged in parallel between the first terminal and the second terminal,

the first pass band comprising at least a portion of a second pass band of the first filter and at least a portion of a third pass band of the second filter,

the second pass band is narrower than the first pass band,

the third pass band is narrower than the first pass band,

the third pass band has a center frequency higher than a center frequency of the second pass band,

the first filter includes:

a plurality of elastic wave resonators; and

and a first capacitance element connected in parallel to a first elastic wave resonator included in the plurality of elastic wave resonators.

2. The filter arrangement of claim 1,

the first filter includes a parallel arm circuit connected between a ground point and a path from the first terminal to the second terminal via the first filter,

the parallel arm circuit includes the first elastic wave resonator and the first capacitance element.

3. The filter arrangement according to claim 1 or 2,

the first filter includes at least one series arm circuit arranged in a path from the first terminal to the second terminal via the first filter,

the at least one series arm circuit has the first elastic wave resonator and the first capacitance element.

4. The filter arrangement of claim 3,

the at least one series arm circuit comprises a first series arm circuit and a second series arm circuit,

the first series arm circuit includes the first elastic wave resonator and the first capacitance element,

the second series arm circuit includes a second elastic wave resonator and a second capacitance element connected in parallel to the second elastic wave resonator,

the at least one series arm circuit is configured with the first series arm circuit and the second series arm circuit as both ends in series in a path from the first terminal to the second terminal via the first filter.

5. The filter arrangement according to any one of claims 1 to 4,

the plurality of elastic wave resonators include a third elastic wave resonator to which a capacitive element is not connected in parallel,

when a value obtained by dividing a difference between an antiresonant frequency of an elastic wave resonator and a resonant frequency of the elastic wave resonator by the resonant frequency is defined as a relative bandwidth,

the relative frequency bandwidth of the first elastic wave resonator is larger than the relative frequency bandwidth of the third elastic wave resonator.

6. The filter arrangement according to any one of claims 1 to 5,

in the case where the electrostatic capacitance value per unit area is defined as the capacitance density,

the capacitance density of the first capacitance element is larger than the capacitance density of the first elastic wave resonator.

7. The filter arrangement according to any one of claims 1 to 6,

the first filter further comprises a first switch connected in series with the first capacitive element,

the first elastic wave resonator is connected in parallel to the first capacitor element and the first switch connected in series.

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

the second filter includes:

an elastic wave filter;

a first phase shifter arranged in a path between the elastic wave filter and the first terminal; and

a second phase shifter arranged in a path between the elastic wave filter and the second terminal,

the first phase shifter and the second phase shifter are configured to increase an impedance of the second filter in the second pass band.

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

the filter device is also provided with a second switch, a third switch, a fourth switch and a fifth switch,

the second switch, the first filter, and the third switch are sequentially connected in series between the first terminal and the second terminal,

the fourth switch, the second filter, and the fifth switch are sequentially connected in series between the first terminal and the second terminal,

the second switch, the first filter, and the third switch connected in series are connected in parallel between the first terminal and the second terminal with the fourth switch, the second filter, and the fifth switch connected in series.

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

the filter device further includes:

a third terminal; and

a second switch and a third switch, wherein,

the second filter and the second switch are sequentially connected in series between the first terminal and the second terminal,

the first filter is connected in parallel with the second filter and the second switch connected in series between the first terminal and the second terminal,

the third switch is connected between the third terminal and a connection point of the second filter and the second switch,

the second pass band is non-overlapping with the third pass band.

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

the filter device further includes:

a third terminal; and

a second switch and a third switch, wherein,

the first filter and the second switch are sequentially connected in series between the first terminal and the third terminal,

the second filter is connected in parallel with the first filter and the second switch connected in series between the first terminal and the third terminal,

the third switch is connected between the second terminal and a connection point of the first filter and the second switch,

the second pass band is non-overlapping with the third pass band.

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

the filter arrangement of any one of claims 1 to 11; and

an amplifying circuit electrically connected to the filter device.

13. A communication device is provided with:

an RF signal processing circuit that processes a high-frequency signal transmitted and received by the antenna element; and

the high frequency front end circuit of claim 12, passing the high frequency signal 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 connected in parallel to achieve a wider 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 connected in parallel to widen the passband.

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

As in the wireless receiving circuit disclosed in patent document 1, the first filter and the second filter are connected in parallel to form a passband of the filter device. The center frequency of the pass band of the second filter is higher than the center frequency of the pass band of the first filter. That is, a band (low band side) lower than the center frequency in the pass band of the filter device is mainly formed by the first filter (low band side filter), and a band (high band side) higher than the center frequency in the pass band of the filter device is mainly formed by the second filter (high band side filter).

In the case where the first filter includes an elastic wave filter, the frequency of the pass band of the second filter may be higher than the anti-resonance frequency of the elastic wave resonators included in the first filter. In this case, the impedance of the elastic wave resonator becomes capacitive at the frequency of the passband of the second filter, and the elastic wave resonator functions as a capacitor.

However, in a frequency band higher than the antiresonance frequency of the acoustic wave resonator, a loss (bulk wave loss) due to a bulk wave generated inside the piezoelectric substrate of the acoustic wave resonator occurs. Therefore, the Q characteristic of the elastic wave resonator functioning as a capacitor deteriorates. As a result, the insertion loss of the filter device at the highest frequency (high-band end) of the passband of the filter device deteriorates.

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

Means for solving the problems

The filter device of an embodiment of the present invention has a first pass band. The filter device includes a first terminal, a second terminal, a first filter, and a second filter. The first filter and the second filter are arranged in parallel between the first terminal and the second terminal. The first pass band includes at least a portion of a second pass band of the first filter. The first pass band includes at least a portion of a third pass band of the second filter. The second pass band is narrower than the first pass band. The third pass band is narrower than the first pass band. The third pass band has a center frequency that is higher than a center frequency of the second pass band. The first filter includes a plurality of elastic wave resonators and a first capacitive element. The first capacitance element is connected in parallel to a first elastic wave resonator included in the plurality of elastic wave resonators.

Effects of the invention

According to the filter device of one embodiment of the present invention, the insertion loss at the high-band end of the pass band of the filter device can be reduced by the capacitor connected in parallel to the elastic wave resonator of the low-band side filter.

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 pass band of the filter device of fig. 1 and the pass bands of the low-band side filter and the high-band side filter.

Fig. 3 is a graph showing (a) frequency characteristics of absolute values of impedances and (b) a smith chart showing the frequency characteristics of impedances, of the elastic wave resonators included in the filter of fig. 1.

Fig. 4 is a circuit configuration diagram specifically showing the configuration of the low band side filter of fig. 1.

Fig. 5 is a diagram collectively showing the transmission characteristics of the low-band-side filter, the high-band-side filter, and the filter device according to embodiment 1.

Fig. 6 is a circuit configuration diagram of a filter device of a comparative example.

Fig. 7 is a diagram showing the pass characteristics of the filter devices of embodiment 1 and the comparative example, the reflection characteristics of the low-band side filter, and the reflection characteristics of the parallel arm circuit.

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

Fig. 9 is a circuit configuration diagram of a filter device according to embodiment 2.

Fig. 10 is a diagram collectively showing the transmission characteristics of the low-band-side filter, the high-band-side filter, and the filter device according to embodiment 2.

Fig. 11 is a diagram showing the pass characteristics of the filter devices of embodiment 2 and the comparative example, the reflection characteristics of the low-band side filter, and the reflection characteristics of the parallel arm circuit.

Fig. 12 is a diagram showing impedance characteristics of an elastic wave resonator (broken line) and impedance characteristics of a circuit including an elastic wave resonator and a capacitor connected in parallel (solid line).

Fig. 13 is a graph showing the relationship between the resonance frequency and the relative frequency bandwidth of the elastic wave resonator according to the embodiment.

Fig. 14 is a diagram showing the pass characteristics of the filter devices according to embodiments 2 and 3, the reflection characteristics of the low-band side filter, and the reflection characteristics of the series arm circuit.

Fig. 15 is an enlarged view of the pass characteristics in the range of 1.53GHz to 1.56GHz in fig. 14 (a).

Fig. 16 is a circuit configuration diagram of a filter device according to embodiment 4.

Fig. 17 is a diagram showing both the pass characteristics of the filter devices according to embodiments 3 and 4 and the reflection characteristics of the low-band side filter.

Fig. 18 is an enlarged view of the pass characteristics in the range of 1.53GHz to 1.56GHz in fig. 17 (a).

Fig. 19 is a circuit configuration diagram of a filter device according to a modification of embodiment 4.

Fig. 20 is a circuit configuration diagram of a filter device according to embodiment 5.

Fig. 21 is a diagram showing an example of a module configuration of the filter device of fig. 20.

Fig. 22 is a graph showing a pass characteristic of the filter device of fig. 20 together with a table showing the on state of each switch.

Fig. 23 is a configuration diagram of a communication device according to embodiment 6.

Fig. 24 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 (first filter), a filter FLT2 (second filter), an input/output terminal T1 (first terminal), and an input/output terminal T2 (second 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 filter FLT1 includes a plurality of elastic wave resonators. Filter FLT2 may include an elastic wave resonator or may include an LC resonant circuit. 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 a SM (solid Mounted) Resonator.

Fig. 2 is a diagram showing the relationship between the pass band PB1 (first pass band) and the pass bands PB2 (second pass band) and PB3 (third pass band) of the filter devices 1 and FLTs 1 and FLTs 2, respectively, in fig. 1. In fig. 2, frequencies Cf1 to Cf3 are the center frequencies of pass bands PB1 to PB3, respectively. The passband is an arbitrary continuous band in which the insertion loss falls within a range of not less than the minimum value of the insertion loss and not more than a 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. The band of the pass band PB1 lower than the center frequency Cf1 is mainly formed by the filter FLT1, and the band of the pass band PB1 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-band-side filter. The filter FLT2 is a filter forming the pass band PB3 and is referred to as a high-band-side filter.

In general, when a filter is configured using a parallel arm circuit having an elastic wave resonator and a series arm circuit having an elastic wave resonator, the impedance of the elastic wave resonator becomes capacitive in a frequency band higher than the anti-resonance frequency of the elastic wave resonator configuring the filter, and the elastic wave resonator functions as a capacitor. Here, in a frequency band higher than the antiresonant frequency, the reflection coefficient of the elastic wave resonator decreases compared to the reflection coefficient at the antiresonant frequency.

Fig. 3 is a graph showing (a) frequency characteristics of absolute values of impedances and (b) a smith chart showing the frequency characteristics of impedances, in the elastic wave resonator included in the filter FLT1 of fig. 1. In fig. 3, frequencies fr and fa represent the resonance frequency and the antiresonance frequency of the elastic wave resonator, respectively. The frequency Hf1 is a frequency at the high-band end of the stop band in the elastic wave resonator higher than the anti-resonance frequency fa.

As shown in fig. 3 (a), the impedance of the elastic wave resonator becomes extremely small at the resonance frequency fr and extremely large at the antiresonance frequency fa. As shown in fig. 3 (b), the impedance of the elastic wave resonator is located at a point where the real component and the imaginary component become very small at the resonance frequency fr and at a point where the real component or the imaginary component becomes very large at the antiresonance frequency fa. When the frequency is higher than the anti-resonance frequency fa, the impedance of the elastic wave resonator moves clockwise on the smith chart, and becomes a capacitive impedance.

Here, as described above, the reflection coefficient of the elastic wave resonator is smaller than the reflection coefficient at the anti-resonance frequency fa at a frequency higher than the frequency Hf1 at the high-band end as the stop band of the elastic wave resonator. This is because the bulk wave in the elastic wave resonator leaks to the outside of the elastic wave resonator, and the reflection loss increases, thereby deteriorating the Q characteristic of the elastic wave resonator (leakage loss). As a result, the insertion loss of the filter device 1 at the high-band end of the pass band PB1 deteriorates.

In contrast, in the embodiment, the capacitor is connected in parallel to the elastic wave resonator included in the low-band-side filter. In a frequency band higher than the anti-resonance frequency fa of the elastic wave resonator, the Q characteristic of the capacitor is not deteriorated. Since the applied power is distributed to the elastic wave resonator and the capacitor, the bulk wave loss in the elastic wave resonator is reduced, and the Q characteristic of a circuit including the elastic wave resonator and the capacitor connected in parallel is improved. As a result, the insertion loss at the high-band end of the pass band of the filter device of the embodiment can be reduced.

In embodiments 1 to 4, the structure of the low-band side filter of the filter device of the embodiment will be specifically described. Hereinafter, the parallel arm circuit is a circuit disposed between a connection point on a path connecting the first input/output terminal and the second input/output terminal and the ground. The series arm circuit is a circuit disposed between the first input/output terminal or the second input/output terminal and a connection point on the path to which the parallel arm circuit is connected, or a circuit disposed between a connection point on the path to which the parallel arm circuit is connected and another connection point on the path to which another parallel arm circuit is connected. The series arm circuit and the parallel arm circuit may be formed of one elastic wave resonator or one reactance element (for example, an inductor or a capacitor). Each of the series arm circuit and the parallel arm circuit may include a plurality of elastic wave resonators divided in series or in parallel.

[ embodiment 1]

In embodiment 1, a case where a capacitor is connected in parallel to an elastic wave resonator included in a parallel arm circuit will be described.

Fig. 4 is a circuit configuration diagram specifically showing the configuration of the filter FLT1 of fig. 1. As shown in fig. 4, the filter FLT1 includes series-arm resonators s1, s2, a parallel-arm resonator p1 (first elastic wave resonator), and a capacitor Cp1 (first capacitive element).

The series-arm resonators s1 and s2 are connected in series between the input-output terminals T1 and T2. The series-arm resonators s1 and s2 form a series-arm circuit, respectively. The parallel-arm resonator p1 is connected in parallel with the capacitor Cp1 between the ground point and the connection point of the series-arm resonators s1 and s 2. The parallel arm resonator p1 and the capacitor Cp1 form a parallel arm circuit pc 1.

Table 1 below shows the resonance frequency fr, the anti-resonance frequency fa, the relative bandwidth BWR, and the capacitance of each of the series-arm resonators s1 and s2, the parallel-arm resonator p1, and the parallel-arm circuit pc1 in embodiment 1. For the capacitor Cp1, only electrostatic capacitance is shown. The relative bandwidth BWR is a value obtained by dividing the difference between the antiresonant frequency fa and the resonant frequency fr by the resonant frequency fr as a percentage.

[ Table 1]

Fig. 5 is a diagram collectively showing the pass characteristics of the low-band-side filter FLT1, the high-band-side filter FLT2, and the filter device 1 according to embodiment 1. Fig. 5 (a) is a diagram showing the pass characteristics (frequency characteristics of insertion loss and attenuation) of low-band side filter FLT 1. Fig. 5 (b) is a diagram showing the pass characteristic of the high-band-side filter FLT 2. Fig. 5 (c) is a diagram showing the pass characteristics of the filter device 1 of fig. 4. 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 other circuits.

As shown in fig. 5 (a), the low-band-side filter FLT1 forms the low-band side of the passband PB1 of the filter device 1 and has a passband PB 2. As shown in fig. 5 (b), the high-band-side filter FLT2 forms the high-band side of the passband PB1 of the filter device 1 and has a passband PB 3.

Fig. 6 is a circuit configuration diagram of a filter device 900 of a comparative example. The filter device 900 has a structure in which the filters FLT1 and FLT2 of the filter device 1 in fig. 4 are replaced with filters FLT91 and FLT92, respectively. The series-arm resonators s1a, s2a and the parallel-arm resonator p1a included in the FLT91 correspond to the series-arm resonators s1, s2 and the parallel-arm resonator p1 in fig. 4, respectively, as objects of comparison. In the filter device 900, the capacitor is not connected in parallel to the parallel arm resonator p1 a. The filter arrangement 900, the filters FLT91, FLT92 are designed with pass-bands PB1, PB2, PB3, respectively. Table 2 below shows the resonance frequency fr, the antiresonance frequency fa, the relative bandwidth BWR, and the capacitance of each of the series-arm resonators s1a, s2a and the parallel-arm resonator p1a in embodiment 1.

[ Table 2]

Fig. 7 is a diagram showing the pass characteristics of the filter devices of embodiment 1 and the comparative example, the reflection characteristics of the low-band side filter, and the reflection characteristics of the parallel arm circuit. Fig. 7 (a) is a graph showing both the pass characteristic of the filter device 1 and the pass characteristic of the filter device 900 in the range of attenuation 0 to 5 dB. Fig. 7 (b) is a graph showing the reflection characteristics (frequency characteristics of reflection loss) of the filter FLT1 in fig. 4 and the reflection characteristics of the filter FLT91 in fig. 6. Fig. 7 (c) is a diagram showing the reflection characteristic of the parallel-arm circuit pc1 of the filter FLT1 of fig. 4 and the reflection characteristic of the parallel-arm resonator p1a of the filter FLT91 of fig. 6. The "reflection characteristic of the filter" refers to the reflection characteristic of the filter alone, and is a reflection characteristic when the filter is separated from other circuits. The "reflection characteristic of the parallel arm circuit" refers to a reflection characteristic of the parallel arm circuit alone, and is a reflection characteristic in the case where the parallel arm circuit is separated from other circuits.

In fig. 7 (a), a solid line shows the pass characteristic of the filter device 1, and a broken line shows the pass characteristic of the filter device 900. In fig. 7 (b), a solid line shows the reflection characteristic of the filter FLT1, and a broken line shows the reflection characteristic of the filter FLT 91. In fig. 7 (c), a solid line shows the reflection characteristic of the parallel arm circuit pc1, and a broken line shows the reflection characteristic of the parallel arm resonator p1 a.

As shown in fig. 7 (a), the insertion loss of filter device 1 is smaller than the insertion loss of filter device 900 at the high-band end of passband PB 1. As shown in fig. 7 (b), at the high-band end of the pass band PB1, the reflection loss of the filter FLT1 is smaller than the reflection loss of the filter FLT 91. As shown in fig. 7 (c), at the high-band end of the pass band PB1, the reflection loss of the parallel arm circuit pc1 is smaller than the reflection loss of the parallel arm resonator p1 a.

At the high-band end of the pass band PB1, the reflection characteristic of the filter FLT1 is lowered by lowering the reflection characteristic of the parallel arm circuit pc 1. As a result, the pass characteristic of the filter device 1 is reduced.

[ modification of embodiment 1]