Radio frequency filter, multiplexer, radio frequency front end circuit, and communication apparatus

A filter (10) includes two capacitors (C1a and C1b) that are connected in series on a path connecting an input terminal (101a) and an output terminal (102a), an inductor (L2) that is connected in parallel with a series circuit including the two capacitors (C1a and C1b), and a parallel-arm resonator (P1) that is connected between the ground and a node (N) between the two capacitors (C1a and C1b) on the path.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a radio frequency filter, a multiplexer, a radio frequency front end circuit, and a communication apparatus.

Description of the Related Art

Ladder filters including acoustic wave resonators have been proposed (see, for example, Patent Document 1). As disclosed in Patent Document 1, with acoustic wave resonators arranged in a ladder shape, a filter having a sharp attenuation characteristic can be implemented.

Patent Document 1: Japanese Unexamined Patent Application Publication No. 10-335965

BRIEF SUMMARY OF THE DISCLOSURE

A pass band of a ladder filter is determined based on a band width between the resonant frequency and the anti-resonant frequency of each of a plurality of acoustic wave resonators forming the filter (called a resonant band width). That is, a pass band of the ladder filter is limited by the resonant band width of each of a plurality of acoustic wave resonators. For example, although a pass band wider than the resonant band width is desired, the pass band is limited by the resonant band width, and insertion loss in the pass band increases.

Thus, an object is to provide a radio frequency filter and the like with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator.

To achieve the above object, a radio frequency filter according to an aspect of the present disclosure includes two first impedance elements that are connected in series on a path connecting an input terminal and an output terminal, a second impedance element that is connected in parallel with a series circuit including the two first impedance elements, and a parallel-arm resonator that is connected between a ground and a node between the two first impedance elements on the path. Each of the first impedance elements is one of a capacitor and an inductor, and the second impedance element is the other one of the capacitor and the inductor.

A multiplexer according to an aspect of the present disclosure includes a plurality of filters each including a first filter and a second filter as the radio frequency filters described above. Input terminals or output terminals of the plurality of filters are connected to a common terminal.

A radio frequency front end circuit according to an aspect of the present disclosure includes the multiplexer described above, a switch that is connected directly or indirectly to the multiplexer, and an amplifying circuit that is connected directly or indirectly to the multiplexer.

A communication apparatus according to an aspect of the present disclosure includes an RF signal processing circuit that processes a radio frequency signal transmitted and received at an antenna element and the radio frequency front end circuit described above that transmits the radio frequency signal between the antenna element and the RF signal processing circuit.

According to the present disclosure, a radio frequency filter and the like with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator can be implemented.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, embodiments of the present disclosure will be explained in detail with reference to the drawings. The embodiments described herein illustrate either general or specific examples. Numerical values, shapes, materials, components, and arrangement and modes of connection of the components described in the embodiments are merely examples, and are not intended to limit the present disclosure. Components in the embodiments, except those described in the independent claims, will be explained as optional components. The sizes or the ratios between the sizes of the components illustrated in the drawings are not strictly correct. Furthermore, in the drawings, the same signs are assigned to substantially the same components, and redundant explanation may be omitted or simplified. Furthermore, in the embodiments described below, the term “being connected” not only represents being directly connected but also includes being electrically connected with other elements or the like interposed therebetween.

First Embodiment

Hereinafter, configurations and bandpass characteristics of a radio frequency filter and a multiplexer according to a first embodiment will be described with reference to Examples 1 to 6. Furthermore, configurations and bandpass characteristics of a radio frequency filter and a multiplexer to be compared with each of the Examples will be described with reference to Comparative Examples 1 to 4.

A configuration of a radio frequency filter according to the first embodiment that is common in the Examples will be described first, and then the Examples will be described. Hereinafter, a radio frequency filter will also be referred to as a filter.

A filter according to the first embodiment includes two first impedance elements that are connected in series on a path connecting an input terminal and an output terminal, a second impedance element that is connected in parallel with a series circuit including the two first impedance elements, and a parallel-arm resonator that is connected between the ground and a node between the two first impedance elements on the path. Each of the first impedance elements is one of a capacitor and an inductor, and the second impedance element is the other one of the capacitor and the inductor. That is, in the case where the first impedance elements are capacitors, the second impedance element is an inductor. In contrast, in the case where the first impedance elements are inductors, the second impedance element is a capacitor. With such a relationship between the first impedance elements and the second impedance element, the two first impedance elements and the second impedance element form an LC resonant circuit (specifically, an LC parallel resonant circuit). Furthermore, by appropriately setting element values (capacitance value and inductance value) of the two first impedance elements and the second impedance element, the LC resonant circuit may function as a high pass filter or a low pass filter.

A capacitor according to the present disclosure represents an element exhibiting capacitive characteristics over the entire band as an ideal element and does not include an acoustic wave resonator. This is because an acoustic wave resonator is an element exhibiting inductive characteristics in a band between the resonant frequency and the anti-resonant frequency and exhibiting capacitive characteristics in other bands, not an element exhibiting capacitive characteristics over the entire band.

Hereinafter, a filter assumed to have the configuration described above and a multiplexer that includes the filter will be described.

FIG. 1is a circuit configuration diagram of a filter10according to Example 1.

The capacitors C1aand C1bare two first impedance elements that are connected in series on a path connecting a terminal101aand a terminal102a. Hereinafter, in Examples and Comparative Examples, explanation will be provided by defining the terminal101aas an input terminal and defining the terminal102aas an output terminal. However, the terminal101amay be an output terminal, and the terminal102amay be an input terminal.

The inductor L2is a second impedance element that is connected in parallel with a series circuit including the capacitors C1aand C1b. Specifically, the inductor L2is connected between a connection point between the capacitor C1aand the terminal101aand a connection point between the capacitor C1band the terminal102a.

In the filter10, the capacitors C1aand C1band the inductor L2form an LC resonant circuit11. Also, in other Examples described below, two first impedance elements, each of which is one of a capacitor and an inductor, and a second impedance element, which is the other one of the capacitor and the inductor, form an LC resonant circuit. However, a broken line surrounding the first impedance elements and the second impedance element and the word “LC resonant circuit” will be omitted.

The parallel-arm resonator P1is an acoustic wave resonator that is connected between the ground and a node N between the capacitor C1aand the capacitor C1bon the path connecting the terminal101aand the terminal102a.

The acoustic wave resonator is a resonator using acoustic waves and may be, for example, a resonator using SAW (Surface Acoustic Wave), a resonator using BAW (Bulk Acoustic Wave), an FBAR (Film Bulk Acoustic Resonator), or the like. SAWs include boundary waves as well as surface acoustic waves. In this example, an acoustic wave resonator is represented by a SAW resonator. Accordingly, an acoustic wave resonator forming the filter10is configured including an IDT (InterDigital Transducer) electrode formed on a substrate having piezoelectricity. Thus, a compact and low-profile filter circuit with a sharp attenuation characteristic can be implemented. A substrate having piezoelectricity is a substrate having piezoelectricity at least on its surface. The substrate includes, for example, a multilayer body including a piezoelectric thin film on its surface, a film with an acoustic velocity different from that of the piezoelectric thin film, and a supporting substrate. Furthermore, the substrate may include, for example, a multilayer body including a supporting substrate with high acoustic velocity and a piezoelectric thin film formed on the supporting substrate with high acoustic velocity, a multilayer body including a supporting substrate with high acoustic velocity, a film with low acoustic velocity formed on the supporting substrate with high acoustic velocity, and a piezoelectric thin film formed on the film with low acoustic velocity, or a multilayer body including a supporting substrate, a film with high acoustic velocity formed on the supporting substrate, a film with low acoustic velocity formed on the film with high acoustic velocity, and a piezoelectric thin film formed on the film with low acoustic velocity. The entire substrate may have piezoelectricity. The same applies to acoustic wave resonators (series-arm resonator and parallel-arm resonator) described in Examples 2 to 6. Thus, such explanation will be omitted in Examples 2 to 6.

As illustrated inFIG. 1, the present disclosure is characterized in that the parallel-arm resonator P1is connected between the capacitors C1aand C1b(two first impedance elements) forming the LC resonant circuit11. Principles of this configuration will be explained with reference toFIGS. 2A to 4B.

FIGS. 2A to 4Bare diagrams for explaining the principles of the present disclosure.

FIG. 2Ais a diagram illustrating a filter (LC resonant circuit) that includes the capacitor C1band the inductor L2in a configuration of the filter10, in which the capacitor C1aand the parallel-arm resonator P1are removed.FIG. 2Bis a Smith chart indicating impedance characteristics of the filter illustrated inFIG. 2A.

In Smith charts ofFIGS. 2B, 3B, and 4Bindicating impedance characteristics, markers are provided near a lower frequency end and near a higher frequency end of a required pass band and near a lower frequency end and near a higher frequency end of a required attenuation band. Furthermore, frequency, size ρ of a reflection coefficient and phase θ, and impedance (a coefficient Z0represents, for example, 50Ω) at markers m* in the graph (* represents a numerical value subsequent to m in the graph) are illustrated on the right of the Smith charts indicating impedance characteristics. For example, the required pass band is from 2300 MHz (frequency at the marker m3) to 2690 MHz (frequency at the marker m4), and the required attenuation band is from 1710 MHz (frequency at the marker m1) to 1920 MHz (frequency at the marker m2).

For example, the filter illustrated inFIG. 2Afunctions as a high pass filter to achieve the required pass band and attenuation band. As illustrated inFIG. 2B, impedance near the lower frequency end and near the higher frequency end of the pass band is close to 50Ω, and impedance near the lower frequency end and near the higher frequency end of the attenuation band is close to open. On the Smith chart illustrated inFIG. 2B, a region near the lower frequency end and near the higher frequency end of the pass band (markers m3and m4) is surrounded by a broken-line circle, and a region near the lower frequency end and near the higher frequency end of the attenuation band (markers m1and m2) is surrounded by a dashed-dotted line circle.

The filter illustrated inFIG. 2Arepresents the LC resonant circuit including the capacitor C1band the inductor L2. Thus, it is difficult for the filter to achieve a sharp attenuation characteristic. However, by adding an acoustic wave resonator having a sharp attenuation pole, a sharp attenuation characteristic may be achieved.

FIG. 3Aillustrates a filter including the capacitor C1b, the inductor L2, and a parallel-arm resonator P1a. The filter is obtained by adding the parallel-arm resonator P1ato the configuration of the filter illustrated inFIG. 2A. The parallel-arm resonator P1ais connected between the ground and a node between the terminal101aand a connection point between the capacitor C1band the inductor L2, which are connected in parallel.

For example, the parallel-arm resonator P1ais a resonator with a resonant frequency of 2200 MHz and an anti-resonant frequency of 2500 MHz. Thus, the parallel-arm resonator P1aexhibits inductive characteristics in a resonant band width (from 2200 MHz to 2500 MHz) and exhibits capacitive characteristics in other bands.

FIG. 3Bis a Smith chart indicating impedance characteristics of the filter illustrated inFIG. 3A. InFIG. 3B, to indicate changes in the impedance characteristics caused by adding the parallel-arm resonator P1ato the filter illustrated inFIG. 2A, a dashed-dotted line circle is provided at the same position as the positions of the markers m1and m2illustrated inFIG. 2B, and a broken-line circle is provided at the same position as the positions of the markers m3and m4illustrated inFIG. 2B.

The frequency at the marker m3, which is near the lower frequency end of the pass band, is 2300 MHz. Thus, by adding the parallel-arm resonator P1a, which exhibits inductive characteristics at the corresponding frequency, the position of the marker m3rotates anticlockwise (a direction represented by an arrow A) from the position of the broken-line circle. In contrast, the frequency at the marker m4, which is near the higher frequency end of the pass band, is 2690 MHz. Thus, by adding the parallel-arm resonator P1a, which exhibits capacitive characteristics at the corresponding frequency, the position of the marker m4rotates clockwise (a direction represented by an arrow B) from the position of the broken-line circle. As described above, the impedance at the frequency near the lower frequency end of the pass band and the impedance at the frequency near the higher frequency end of the pass band rotate in different directions. Thus, in a frequency range from 2300 MHz to 2690 MHz, which is the pass band, a region that deviates from the center (50Ω) of the Smith chart increases, and insertion loss in the pass band thus increases.

Furthermore, the frequency at the marker m1, which is near the lower frequency end of the attenuation band, is 1710 MHz, and the frequency at the marker m2, which is the higher frequency end of the attenuation band, is 1920 MHz. Thus, by adding the parallel-arm resonator P1a, which exhibits capacitive characteristics at these frequencies, the positions of the markers m1and m2rotate clockwise (a direction represented by an arrow C) from the position of the dashed-dotted line circle. As described above, a frequency range from 1710 MHz to 1920 MHz, which is the attenuation band, deviates from the open position of the Smith chart, and the attenuation characteristic thus degrades.

Accordingly, when an acoustic wave resonator is simply added, the bandpass characteristics degrade, and there is a need to devise a method for adding an acoustic wave resonator or the like. Thus, an inventor of the present application has found out that an acoustic wave resonator or the like is added, as illustrated inFIG. 4A.FIG. 4Ais a diagram illustrating a filter in which the capacitor C1ais connected in series with the capacitor C1bin the configuration of the filter illustrated inFIG. 2Aand the parallel-arm resonator P1is connected between the ground and the node between the capacitor C1aand the capacitor C1b. Excellent bandpass characteristics can be achieved by adding an acoustic wave resonator or the like as described above. A principle of a achieving excellent bandpass characteristics will be examined with reference toFIG. 4B.

FIG. 4Bis a Smith chart indicating impedance characteristics of the filter illustrated inFIG. 4A. InFIG. 4B, to indicate changes in the impedance characteristics caused by adding the capacitor C1aand the parallel-arm resonator P1(specifically, the capacitor C1aand the parallel-arm resonator P1are added in this order) to the filter illustrated inFIG. 2A, a dashed-dotted line circle is provided at the same position as the positions of the markers m1and m2illustrated inFIG. 2B, and a broken-line circle is provided at the same position as the positions of the markers m3and m4illustrated inFIG. 2B.

As with the parallel-arm resonator P1a, the parallel-arm resonator P1is a resonator with a resonant frequency of 2200 MHz and an anti-resonant frequency of 2500 MHz. Thus, the parallel-arm resonator P1exhibits inductive characteristics in the resonant band width (from 2200 MHz to 2500 MHz) and exhibits capacitive characteristics in other bands.

First, changes in impedance in the case where the capacitor C1ais connected in series with the capacitor C1bin the configuration of the filter illustrated inFIG. 2Awill be explained.

By connecting the capacitor C1a, which exhibits capacitive characteristics over the entire band as an ideal element, to the capacitor C1bin series, the position of each marker rotates anticlockwise. Specifically, the positions of the markers m3and m4rotate in the direction represented by the arrow A from the position of the broken-line circle and move close to the position of a dashed-two dotted line circle. The positions of the markers m1and m2rotate in the direction represented by the arrow B from the position of the dashed-dotted line circle. The positions of the markers m1and m2are originally located near an open position and do not move largely even when the capacitor C1ais added. Thus, the positions of the markers m1and m2after moving from the position of the dashed-dotted line circle are not illustrated, unlike the dashed-two dotted line circle.

Next, changes in the impedance in the case where the capacitor C1ais connected in series with the capacitor C1band then the parallel-arm resonator P1is connected between the capacitor C1aand the capacitor C1bwill be explained.

The frequency at the marker m3, which is near the lower frequency end of the pass band, is 2300 MHz. Thus, by adding the parallel-arm resonator P1, which exhibits inductive characteristics at the corresponding frequency, the position of the marker m3rotates anticlockwise (the direction represented by the arrow C) from the position of the dashed-two dotted line circle. In contrast, the frequency at the marker m4, which is near the higher frequency end of the pass band, is 2690 MHz. Thus, by adding the parallel-arm resonator P1, which exhibits capacitive characteristics at the corresponding frequency, the position of the marker m4rotates clockwise (a direction represented by an arrow D) from the position of the dashed-two dotted line circle. It is considered that, because the positions of the markers m3and m4that are located within the broken-line circle in the state of the filter illustrated inFIG. 2Aare rotated in the direction represented by the arrow A by the capacitor C1a, by rotating the markers m3and m4by the parallel-arm resonator P1from the position of the dashed-two dotted line circle after the rotation, the positions of the markers m3and m4are moved closer to the center of the Smith chart. Thus, an increase in the insertion loss in the pass band can be suppressed. The capacitance value of the capacitor C1a(that is, the amount of rotation in the direction represented by the arrow A) is adjusted such that the impedances at the markers m3and m4after addition of the parallel-arm resonator P1(that is, in the pass band) are located near the center of the Smith chart.

Furthermore, the frequency at the marker m1, which is near the lower frequency end of the attenuation band, is 1710 MHz, and the frequency at the marker m2, which is near the higher frequency end of the attenuation band, is 1920 MHz. Thus, by adding the parallel-arm resonator P1, which exhibits capacitive characteristics at these frequencies, the positions of the markers m1and m2rotate clockwise (a direction represented by an arrow E) from the position of the dashed-dotted line circle. Because the positions of the markers m1and m2that are located within the dashed-dotted line circle in the state of the filter illustrated inFIG. 2Aare rotated in the direction represented by the arrow B by the capacitor C1a, even if the markers m1and m2are rotated in the direction represented by the arrow E by the parallel-arm resonator P1from the position after the rotation, the markers m1and m2are not moved away from an open position of the Smith chart. Thus, degradation in the attenuation characteristics can be suppressed.

With the principles described above, it is considered that excellent bandpass characteristics can be achieved by connecting a parallel-arm resonator between the ground and a position between the two first impedance elements (in this example, the capacitors C1aand C1b) in the LC resonant circuit, which includes the two first impedance elements and the second impedance element (in this example, the inductor L2).

Bandpass Characteristics of Filter According to Example 1

Next, bandpass characteristics of the filter10according to Example 1 will be explained by comparing it with Comparative Examples 1 and 2.

FIG. 5is a circuit configuration diagram of a filter20according to Comparative Example 1.

The filter20according to Comparative Example 1 is different from the filter10according to Example 1 in the position where a parallel-arm resonator is connected. The other features are the same as those of the filter10, and explanation for those features will be omitted.

In the filter20, the parallel-arm resonator P1ais connected between the ground and a node between the terminal101aand the LC resonant circuit including the capacitors C1aand C1band the inductor L2. That is, in the filter20, the parallel-arm resonator P1ais not connected between the capacitor C1aand the capacitor C1b, unlike Example 1. The filter20has a configuration similar to that of the filter illustrated inFIG. 3A.

FIG. 6includes graphs indicating a comparison between the bandpass characteristics of the filter10according to Example 1 and the bandpass characteristics of the filter20according to Comparative Example 1. An upper graph inFIG. 6is obtained by enlarging a region around a broken-line circle in a lower graph. In other graphs indicating bandpass characteristics, the same applies to a part in which “enlarged” is provided next to a broken-line circle. InFIG. 6, solid lines represent the bandpass characteristics of the filter10according to Example 1, and broken lines represent the bandpass characteristics of the filter20according to Comparative Example 1. The graphs inFIG. 6indicate bandpass characteristics in the case where the filters10and20are designed to function as high pass filters.

The filters10and20each include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 6. Meanwhile, the filter10is able to suppress an increase in insertion loss in the pass band (from 2300 MHz to 2690 MHz), compared to the filter20. Specifically, at 2300 MHz, compared to the insertion loss of the filter20, which is 1.191 dB, the insertion loss of the filter10is as small as 0.838 dB. Furthermore, at 2690 MHz, compared to the insertion loss of the filter20, which is 4.216 dB, the insertion loss of the filter10is as small as 1.391 dB.

FIG. 7is a circuit configuration diagram of a filter20aaccording to Comparative Example 2.

The filter20aaccording to Comparative Example 2 includes series-arm resonators S10and S20, an inductor L20, and a parallel-arm resonator P10.

The series-arm resonators S10and S20are connected in series on a path connecting the terminal101aand the terminal102a.

The inductor L20is connected in parallel with a series circuit including the series-arm resonators S10and S20. Specifically, the inductor L20is connected between a connection point between the series-arm resonator S10and the terminal101aand a connection point between the series-arm resonator S20and the terminal102a.

The parallel-arm resonator P10is an acoustic wave resonator that is connected between the ground and a node between the series-arm resonator S10and the series-arm resonator S20on the path connecting the terminal101aand the terminal102a.

The filter20aaccording to Comparative Example 2 is different from the filter10according to Example 1 in that the series-arm resonators S10and S20are connected in place of the two capacitors C1aand C1band the filter is a ladder filter in which acoustic wave resonators are arranged in a ladder shape. Element parameters for the series-arm resonators S10and S20, the inductor L20, and the parallel-arm resonator P10are adjusted so that the filter20ahas a pass band equivalent to that of the filter10.

An acoustic wave resonator exhibits capacitive characteristics in a frequency region other than a band between the resonant frequency and the anti-resonant frequency and may also be used as a substitute for a capacitor. That is, a function of the filter10according to Example 1 may be implemented by the filter20aaccording to Comparative Example 2. However, a pass band of a ladder filter is limited by the resonant band width of each acoustic wave resonator. Thus, by taking Comparative Example 2 as a comparison target to be compared with Example 1, the degree of excellence of the bandpass characteristics of a filter according to the present disclosure compared to a ladder filter can be confirmed.

FIG. 8Aincludes graphs indicating a comparison between bandpass characteristics of the filter10(low pass filter) according to Example 1 and bandpass characteristics of the filter20a(low pass filter) according to Comparative Example 2. InFIG. 8A, solid lines represent the bandpass characteristics of the filter10according to Example 1, and broken lines represent the bandpass characteristics of the filter20aaccording to Comparative Example 2.

The filter10and the filter20aeach include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 8A. Meanwhile, the filter10is able to suppress an increase in insertion loss in the pass band, compared to the filter20a. Specifically, at 2200 MHz, compared to the insertion loss of the filter20a, which is 1.561 dB, the insertion loss of the filter10is as small as 0.792 dB.

FIG. 8Bincludes graphs indicating a comparison between bandpass characteristics of the filter10(high pass filter) according to Example 1 and bandpass characteristics of the filter20a(high pass filter) according to Comparative Example 2. InFIG. 8B, solid lines represent the bandpass characteristics of the filter10according to Example 1, and broken lines represent the bandpass characteristics of the filter20aaccording to Comparative Example 2.

The filter10and the filter20aeach include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 8B. Meanwhile, the filter10is able to suppress an increase in insertion loss in the pass band (from 2300 MHz to 2690 MHz), compared to the filter20a. Specifically, at 2300 MHz, compared to the insertion loss of the filter20a, which is 0.94 dB, the insertion loss of the filter10is as small as 0.922 dB. Furthermore, at 2690 MHz, compared to the insertion loss of the filter20a, which is 1.483 dB, the insertion loss of the filter10is as small as 1.1 dB.

As is clear from the above, the bandpass characteristics of the ladder filter including acoustic wave resonators in place of the capacitors C1aand C1bdegrade. That is, in the present disclosure, by not providing acoustic wave resonators in place of capacitors in an LC resonant circuit, degradation in the bandpass characteristics can be suppressed.

As described above, the filter10with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator (for example, 300 MHz etc.), unlike a ladder filter, can be implemented.

FIG. 9is a circuit configuration diagram of a filter10aaccording to Example 2.

The inductors L1aand L1bare two first impedance elements that are connected in series on a path connecting the terminal101aand the terminal102a.

The capacitor C2is a second impedance element that is connected in parallel with a series circuit including the inductors L1aand L1b. Specifically, the capacitor C2is connected between a connection point between the inductor L1aand the terminal101aand a connection point between the inductor L1band the terminal102a. Example 2 is different from Example 1 in that the two first impedance elements are inductors and the second impedance element is a capacitor.

In the filter10a, the inductors L1aand L1band the capacitor C2form an LC resonant circuit.

The parallel-arm resonator P2is an acoustic wave resonator that is connected between the ground and a node between the inductor L1aand the inductor L1bon the path connecting the terminal101aand the terminal102a.

Bandpass Characteristics of Filter According to Example 2

Next, bandpass characteristics of the filter10aaccording to Example 2 will be explained by comparing it with Comparative Example 2.

FIG. 10Aincludes graphs indicating a comparison between bandpass characteristics of the filter10a(low pass filter) according to Example 2 and bandpass characteristics of the filter20a(low pass filter) according to Comparative Example 2. InFIG. 10A, solid lines represent the bandpass characteristics of the filter10aaccording to Example 2, and broken lines represent the bandpass characteristics of the filter20aaccording to Comparative Example 2.

The filter10aand the filter20aeach include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 10A. Meanwhile, the filter10ais able to suppress an increase in insertion loss in the pass band, compared to the filter20a. Specifically, at 2200 MHz, compared to the insertion loss of the filter20a, which is 1.561 dB, the insertion of the filter10ais as small as 0.825 dB.

FIG. 10Bincludes graphs indicating a comparison between bandpass characteristics of the filter10a(high pass filter) according to Example 2 and bandpass characteristics of the filter20a(high pass filter) according to Comparative Example 2. InFIG. 10B, solid lines represent the bandpass characteristics of the filter10aaccording to Example 2, and broken lines represent the bandpass characteristics of the filter20aaccording to Comparative Example 2.

The filter10aand the filter20aeach include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 10B. Meanwhile, the filter10ais able to suppress an increase in insertion loss in the pass band (from 2300 MHz to 2690 MHz), compared to the filter20a. Specifically, at 2300 MHz, compared to the insertion loss of the filter20a, which is 0.94 dB, the insertion loss of the filter10ais as small as 0.838 dB. At 2690 MHz, compared to the insertion loss of the filter20a, which is 1.483 dB, the insertion loss of the filter10ais as small as 1.391 dB.

As described above, the filter10athat has a sharp attenuation characteristic and a low-loss pass band can be implemented.

FIG. 11is a circuit configuration diagram of a filter10baccording to Example 3.

For example, the filters according to Examples 1 and 2 may further include a third impedance element that is connected in parallel with one of the two first impedance elements. In the case where the first impedance elements are inductors, the third impedance element is a capacitor. In the case where the first impedance elements are capacitors, the third impedance element is an inductor. Hereinafter, a filter in which inductors are provided as first impedance elements and a capacitor is provided as a third impedance element, specifically, the filter10bin which a capacitor C3is connected in parallel with the inductor L1a(first impedance element) according to Example 2, will be described as Example 3.

The filter10bincludes the capacitor C3, in addition to the configuration of the filter10aaccording to Example 2. The other features are the same as those in Example 2, and explanation for those features will be omitted.

The capacitor C3is connected in parallel with the inductor L1a. The capacitor C3may be connected in parallel with the inductor L1b, in place of the inductor L1a.

Bandpass Characteristics of Filter According to Example 3

Next, bandpass characteristics of the filter10baccording to Example 3 will be explained by comparing it with Comparative Example 2.

FIG. 12includes graphs indicating a comparison between bandpass characteristics of the filter10baccording to Example 3 and bandpass characteristics of the filter20aaccording to Comparative Example 2. InFIG. 12, solid lines represent the bandpass characteristics of the filter10baccording to Example 3, and broken lines represent the bandpass characteristics of the filter20aaccording to Comparative Example 2. The graphs inFIG. 12indicate bandpass characteristics in the case where the filters10band20aare designed to function as high pass filters.

The filters10band20aeach include an acoustic wave resonator and each have a sharp attenuation characteristic due to a sharp attenuation pole by the acoustic wave resonator, as illustrated inFIG. 12. Meanwhile, the filter10bis able to suppress an increase in insertion loss in the pass band (from 2300 MHz to 2690 MHz), compared to the filter20a. Specifically, at 2300 MHz, compared to the insertion loss of the filter20a, which is 0.94 dB, the insertion loss of the filter10ais as small as 0.907 dB, and at 2690 MHz, compared to the insertion loss of the filter20a, which is 1.483 dB, the insertion loss of the filter10ais as small as 1.314 dB. In Example 3, with provision of the capacitor C3, impedance near the higher frequency end of the pass band can made closer to 50Ω. Thus, at 2690 MHz, insertion loss can be reduced compared to Example 2.

As described above, the filter10bthat has a sharp attenuation characteristic and a low-loss pass band can be implemented.

Although detailed explanation will be omitted, by connecting an inductor in parallel with the capacitor C1a(first impedance element) according to Example 1, the filter10that has a sharp attenuation characteristic and a low-loss pass band can be implemented, as in Example 3.

The filters according to Examples 1 to 3 described above can be applied to multiplexers. Such multiplexers will be described in Examples 4 to 11. Specifically, the multiplexers according to Examples 4 to 11 each include a plurality of filters according to one or more of Examples 1 to 3. As described below in Examples 6, 9, and 10, a multiplexer may include a filter other than the plurality of filters (a third filter in Example 6, a low pass filter in Example 9, and a high pass filter in Example 10). Input terminals or output terminals of the plurality of filters are connected to a common terminal. The plurality of filters include at least a first filter and a second filter. An input terminal or an output terminal of the first filter and an input terminal or an output terminal of the second filter are connected to a common terminal. Hereinafter, in Examples and Comparative Examples, input terminals of the plurality of filters are connected to a common terminal. However, output terminals of the plurality of filters may be connected to a common terminal. In the case where a multiplexer includes a filter other than the plurality of filters, an input terminal or an output terminal of the filter other than the plurality of filters is also connected to the common terminal.

Furthermore, for example, each of the multiplexers according to Examples 4 to 11 may support so-called CA in which signals of a plurality of frequency bands corresponding to filters forming the multiplexer (filters whose input terminals or output terminals are connected to a common terminal in the multiplexer) are transmitted and received at the same time.

Furthermore, a plurality of frequency bands corresponding to the filters forming the multiplexer may be, for example, LTE (Long Term Evolution: 4G) Bands or NR (New Radio: 5G) Bands. Moreover, the plurality of frequency bands may be, for example, sub 6 GHz (n77 (3.3 GHz to 4.2 GHz), n78 (3.3 GHz to 3.8 GHz), n79 (4.4 GHz to 5.0 GHz), and 5.0 GHz to 7.125 GHz), as NR Bands. As a band from 5.0 GHz to 7.125 GHz, for example, Band 46 (5150 MHz to 5925 MHz), Band (5855 MHz to 5925 MHz), or the like is used. Furthermore, the plurality of frequency bands may be, for example, GPS (Global Positioning System) L5. Moreover, the plurality of frequency bands may include Wi-Fi® 5 GHz. For example, the 5 GHz band may range from 5150 MHz to 5725 MHz. For example, the pass band of each of the first filter and the second filter may include any one of the frequency bands mentioned above.

Furthermore, for example, a multiplexer may include at least two of a filter whose pass band includes 699 MHz to 960 MHz, a filter whose pass band includes 1.2 GHz, a filter whose pass band includes 1.4 GHz to 5 GHz, and a filter whose pass band includes 5 GHz to 7.125 GHz. Furthermore, for example, a multiplexer may include at least two of a filter whose pass band includes 699 MHz to 2.7 GHz, a filter whose pass band includes 3.3 GHz to 4.2 GHz, a filter whose pass band includes 4.4 GHz to 5 GHz, and a filter whose pass band includes 5 GHz to 7.125 GHz.

FIG. 13is a circuit configuration diagram of a multiplexer30according to Example 4.

A plurality of filters provided in the multiplexer30include a first filter and a second filter as two filters according to one or more of Examples 1 to 3. Specifically, the multiplexer30is a diplexer that includes two filters according to Example 1. In Example 4, the two filters according to Example 1 are referred to as filters10and10d. For example, the filter10dis the first filter, and the filter10is the second filter.

The capacitors C1cand C1dare two first impedance elements that are connected in series on the path connecting the terminal101aand the terminal102a.

The inductor L5is a second impedance element that is connected in parallel with a series circuit including the capacitors C1cand C1d. Specifically, the inductor L5is connected between a connection point between the capacitor C1cand the terminal101aand a connection point between the capacitor C1dand the terminal102a.

The parallel-arm resonator P3is an acoustic wave resonator that is connected between the ground and a node between the capacitors C1cand C1don the path connecting the terminal101aand the terminal102a.

As described above, the filter10dhas a configuration similar to that of the filter10according to Example 1.

The first impedance elements provided in the filter10dand the first impedance elements included in the filter10are capacitors.

A terminal101bis, for example, an input terminal, and a terminal102bis, for example, an output terminal. In the multiplexer30, the input terminal (terminal101a) of the filter10dand the input terminal (terminal101b) of the filter10are connected in common to a common terminal103. The common terminal103and each of the terminals101aand101bmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween.

For example, the filter10dis a high pass filter, and the filter10is a low pass filter. Furthermore, for example, the pass band of the filter10dis higher than the pass band of the filter10. Accordingly, the multiplexer30is able to handle two frequency bands. InFIG. 13, the description “High” provided next to the terminal102aof the filter10dand the description “Low” provided next to the terminal102bof the filter10indicate that the pass band of the filter10dis higher than the pass band of the filter10.

Bandpass Characteristics of Multiplexer According to Example 4

Next, bandpass characteristics of the multiplexer30according to Example 4 will be explained by comparing it with Comparative Example 3.

FIG. 14is a circuit configuration diagram of a multiplexer40according to Comparative Example 3.

The multiplexer40is a diplexer including two filters according to Comparative Example 2. In Comparative Example 3, the two filters according to Comparative Example 2 are referred to as filters20aand20b. The configuration of the filter20bis the same as that of the filter20a, and explanation for the configuration of the filter20bwill be omitted.

For example, the filter20ais a high pass filter, and the filter20bis a low pass filter. Furthermore, for example, the pass band of the filter20ais higher than the pass band of the filter20b. InFIG. 14, the description “High” provided next to the terminal102aof the filter20aand the description “Low” provided next to the terminal102bof the filter20bindicate that the pass band of the filter20ais higher than the pass band of the filter20b. Element values configuring the filter20aare set such that the pass band of the filter20ais equivalent to the pass band of the filter10d, and element values configuring the filter20bare set such that the pass band of the filter20bis equivalent to the pass band of the filter10.

FIG. 15includes graphs indicating a comparison between bandpass characteristics of the multiplexer30according to Example 4 and bandpass characteristics of the multiplexer40according to Comparative Example 3. InFIG. 15, solid lines represent the bandpass characteristics of the multiplexer30according to Example 4, and broken lines represent the bandpass characteristics of the multiplexer40according to Comparative Example 3. InFIG. 15, the description “High” is provided for the pass band of the filter10dforming the multiplexer30and the pass band of the filter20aforming the multiplexer40. Furthermore, the description “Low” is provided for the pass band of the filter10forming the multiplexer30and the pass band of the filter20bforming the multiplexer40.

The filters10dand20aeach include an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in a lower frequency end of the pass band indicated by “High” inFIG. 15due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filters10and20beach have an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in the higher frequency end of the pass band indicated by “Low” inFIG. 15due to a sharp attenuation pole by the acoustic wave resonator. Meanwhile, the multiplexer30is able to suppress an increase in insertion loss in the pass band, compared to the multiplexer40. Specifically, at 2200 MHz, compared to the insertion loss of the multiplexer40, which is 1.806 dB, the insertion loss of the multiplexer30is as small as 1.226 dB. Furthermore, at 2300 MHz, compared to the insertion loss of the multiplexer40, which is 1.778 dB, the insertion loss of the multiplexer30is as small as 1.217 dB, and at 2690 MHz, compared to the insertion loss of the multiplexer40, which is 1.02 dB, the insertion loss of the multiplexer30is as small as 0.788 dB.

As described above, the multiplexer30that has sharp attenuation characteristics and low-loss pass bands can be implemented.

Although the filter10d(the filter according to Example 1) is used as the first filter in this example, the filter10a(the filter according to Example 2) may be used as the first filter.

However, as in Example 4, by using capacitors as the first impedance elements provided in the filter10d(first filter) and the first impedance elements provided in the filter10(second filter), a multiplexer with low-loss pass bands compared to the case where the filter10ais used as the first filter can be implemented.

This is because Q values of inductors are lower than capacitors and using the filter10daccording to Example 1, which includes less inductors than the filter10aaccording to Example 2, reduces the total number of inductors with low Q values that are used in a multiplexer. That is, this is because the total number of capacitors with high Q values that are used in a multiplexer increases, and a reduction in the loss can thus be achieved.

FIG. 16is a circuit configuration diagram of a multiplexer30aaccording to Example 5.

The multiplexer30aincludes a filter10bin place of the filter10dof the multiplexer30according to Example 4. The other features are the same as those in Example 4, and explanation for those features will be omitted.

For example, the filter10bis a high pass filter, and the filter10is a low pass filter. Furthermore, for example, the pass band of the filter10bis higher than the pass band of the filter10. Accordingly, the multiplexer30ais able to handle two frequency bands. InFIG. 16, the description “High” provided next to the terminal102aof the filter10band the description “Low” provided next to the terminal102bof the filter10indicate that the pass band of the filter10bis higher than the pass band of the filter10.

Bandpass Characteristics of Multiplexer According to Example 5

FIG. 17includes graphs indicating a comparison between bandpass characteristics of the multiplexer30aaccording to Example 5 and bandpass characteristics of the multiplexer40according to Comparative Example 3. InFIG. 17, solid lines represent the bandpass characteristics of the multiplexer30aaccording to Example 5, and broken lines represent the bandpass characteristics of the multiplexer40according to Comparative Example 3. InFIG. 17, the description “High” is provided for the pass band of the filter10bforming the multiplexer30aand the pass band of the filter20aforming the multiplexer40. Furthermore, the description “Low” is provided for the pass band of the filter10forming the multiplexer30aand the pass band of the filter20bforming the multiplexer40.

The filters10band20aeach include an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in the lower frequency end of the pass band indicated by “High” inFIG. 17due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filters10and20beach include an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in the higher frequency end of the pass band indicated by “Low” inFIG. 17due to a sharp attenuation pole by the acoustic wave resonator. Meanwhile, the multiplexer30ais able to suppress an increase in insertion loss in the pass band, compared to the multiplexer40. Specifically, at 2200 MHz, compared to the insertion loss of the multiplexer40, which is 1.806 dB, the insertion loss of the multiplexer30ais as small as 1.05 dB. Furthermore, at 2300 MHz, compared to the insertion loss of the multiplexer40, which is 1.778 dB, the insertion loss of the multiplexer30is as small as 1.074 dB, and at 2690 MHz, compared to the insertion loss of the multiplexer40, which is 1.02 dB, the insertion loss of the multiplexer30is as small as 0.897 dB.

As described above, the multiplexer30athat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 18is a circuit configuration diagram of a multiplexer30baccording to Example 6.

A plurality of filters provided in the multiplexer30binclude a first filter and a second filter as two filters according to one or more of Examples 1 to 3. The multiplexer30bfurther includes a third filter whose input terminal or output terminal is connected to a common terminal. The third filter includes at least one series-arm resonator and at least one parallel-arm resonator. Specifically, the multiplexer30bis a triplexer including the filter10according to Example 1, the filter10baccording to Example 3, and a filter20c. For example, the filter10bis a first filter, the filter10is a second filter, and the filter20cis a third filter.

A terminal101cis, for example, an input terminal, and a terminal102cis, for example, an output terminal. In the multiplexer30b, an input terminal (terminal101a) of the filter10b, an input terminal (terminal101c) of the filter20c, and an input terminal (terminal101b) of the filter10are connected in common to the common terminal103. The common terminal103and each of the terminals101a,101b, and101cmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween.

For example, the filter10bis a high pass filter, the filter10is a low pass filter, and the filter20cis a band pass filter. Furthermore, for example, the pass band of the filter10bis higher than the pass band of the filter10, and the pass band of the filter20cis lower than the pass band of the filter10band higher than the pass band of the filter10. Accordingly, the multiplexer30bis able to handle three frequency bands. InFIG. 18, the description “High” provided next to the terminal102aof the filter10b, the description “Middle” provided next to the terminal102cof the filter20c, and the description “Low” provided next to the terminal102bof the filter10indicate that the pass band of the filter10bis higher than the pass band of the filter20cand the pass band of the filter20cis higher than the pass band of the filter10.

The filter20cincludes series-arm resonators S30and S40as at least one series-arm resonator and parallel-arm resonators P20and P30as at least one parallel-arm resonator. The series-arm resonators S30and S40are connected in series on a path connecting the terminal101cand the terminal102c. The parallel-arm resonator P20is connected between the ground and a node between the series-arm resonator S30and the series-arm resonator S40, and the parallel-arm resonator P30is connected between the ground and a node between the series-arm resonator S40and the terminal102c. The filter20cmay include one series-arm resonator or three or more series-arm resonators as at least one series-arm resonator and may include one parallel-arm resonator or three or more parallel-arm resonators as at least one parallel-arm resonator.

Bandpass Characteristics of Multiplexer According to Example 6

Next, bandpass characteristics of the multiplexer30baccording to Example 6 will be explained by comparing it with Comparative Example 4.

FIG. 19is a circuit configuration diagram of a multiplexer40aaccording to Comparative Example 4.

The multiplexer40ais a triplexer including two filters according to Comparative Example 2 and the filter20c. In this example, the two filters according to Comparative Example 2 are referred to as the filters20aand20b. Furthermore, the filter20caccording to Comparative Example 4 is the same as that in Example 6.

For example, the filter20ais a high pass filter, the filter20bis a low pass filter, and the filter20cis a band pass filter. Furthermore, for example, the pass band of the filter20ais higher than the pass band of the filter20b, and the pass band of the filter20cis lower than the pass band of the filter20aand higher than the pass band of the filter20b. InFIG. 19, the description “High” provided next to the terminal102aof the filter20a, the description “Middle” provided next to the terminal102cof the filter20c, and the description “Low” provided next to the terminal102bof the filter20bindicate that the pass band of the filter20ais higher than the pass band of the filter20cand the pass band of the filter20cis higher than the pass band of the filter20b. Element values configuring the filter20aare set such that the pass band of the filter20ais equivalent to the pass band of the filter10b, and element values configuring the filter20bare set such that the pass band of the filter20bis equivalent to the pass band of the filter10.

FIG. 20includes graphs indicating a comparison between bandpass characteristics of the multiplexer30baccording to Example 6 and bandpass characteristics of the multiplexer40aaccording to Comparative Example 4. InFIG. 20, solid lines represent the bandpass characteristics of the multiplexer30baccording to Example 6, and broken lines represent the bandpass characteristics of the multiplexer40aaccording to Comparative Example 4. InFIG. 20, the description “High” is provided for the pass band of the filter10bforming the multiplexer30band the pass band of the filter20aforming the multiplexer40a. Furthermore, the description “Middle” is provided for the pass bands of the filters20cforming the multiplexers30band40a. Furthermore, the description “Low” is provided for the pass band of the filter10forming the multiplexer30band the pass band of the filter20bforming the multiplexer40a.

The filters10band20aeach include an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in the lower frequency end of the pass band indicated by “High” inFIG. 20due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filters10and20beach include an acoustic wave resonator, and each of the multiplexers has a sharp attenuation characteristic in the higher frequency end of the pass band indicated by “Low” inFIG. 20due to a sharp attenuation pole by the acoustic wave resonator. Meanwhile, the multiplexer30bis able to suppress an increase in insertion loss in the pass band, compared to the multiplexer40a. Specifically, at 2200 MHz, compared to the insertion loss of the multiplexer40a, which is 1.488 dB, the insertion loss of the multiplexer30bis as small as 1.15 dB. Furthermore, at 2500 MHz, compared to the insertion loss of the multiplexer40a, which is 1.225 dB, the insertion loss of the multiplexer30bis as small as 1.074 dB.

As described above, the multiplexer30bthat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 21is a circuit configuration diagram of a multiplexer30caccording to Example 7.

A plurality of filters provided in the multiplexer30cinclude a first filter and a second filter as a combination of filters according to one or more of Examples 1 to 3. Specifically, the multiplexer30cis a diplexer including filters10eand10f, and each of the filters10eand10fis a combination of filters according to Examples 1 and 2. For example, the filter10fis a first filter, and the filter10eis a second filter.

The capacitors C1aand C1bare two first impedance elements that are connected in series on a path connecting the terminal101band the terminal102b.

The inductor L1ais a second impedance element that is connected in parallel with a series circuit including the capacitors C1aand C1b. Specifically, the inductor L1ais connected between a connection point between the capacitor C1aand the terminal101band a connection point between the capacitor C1band the inductor L1b.

The parallel-arm resonator P1is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1aand the capacitor C1bon the path connecting the terminal101band the terminal102b.

The inductor L10is an inductor that is connected between the node and the ground in series with the parallel-arm resonator P1.

A filter including the capacitors C1aand C1b, the inductor L1a, and the parallel-arm resonator P1in the filter10ehas a configuration similar to that of the filter10according to Example 1.

In Example 7, the inductor L1aalso serves as a first impedance element. This is because the inductors L1aand L1bare connected in series on the path connecting the terminal101band the terminal102band the inductors L1aand L1bserve as first impedance elements in the case where attention is paid to the inductors L1aand L1band the capacitor C2.

The capacitor C2is a second impedance element that is connected in parallel with a series circuit including the inductors L1aand L1b. Specifically, the capacitor C2is connected between a connection point between the inductor L1aand the terminal101band a connection point between the inductor L1band the terminal102b.

The parallel-arm resonator P2is an acoustic wave resonator that is connected between the ground and a node between the inductor L1aand the inductor L1bon the path connecting the terminal101band the terminal102b.

The inductor L11is an inductor that is connected between the node and the ground in series with the parallel-arm resonator P2.

A filter including the inductors L1aand L1b, the capacitor C2, and the parallel-arm resonator P2in the filter10ehas a configuration similar to that of the filter10aaccording to Example 2.

The capacitors C1cand C1dare two first impedance elements that are connected in series on a path connecting the terminal101aand the terminal102a.

The inductor L1cis a second impedance element that is connected in parallel with a series circuit including the capacitors C1cand C1d. Specifically, the inductor L1cis connected between a connection point between the capacitor C1cand the terminal101aand a connection point between the capacitor C1dand the inductor L1d.

The parallel-arm resonator P3is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1cand the capacitor C1don the path connecting the terminal101aand the terminal102a.

The inductor L12is an inductor that is connected between the node and the ground in series with the parallel-arm resonator P3.

A filter including the capacitors C1cand C1d, the inductor L1c, and the parallel-arm resonator P3in the filter10fhas a configuration similar to that of the filter10according to Example 1.

In Example 7, the inductor L1calso serves as a first impedance element. This is because the inductors L1cand L1dare connected in series on the path connecting the terminal101aand the terminal102aand the inductors L1cand L1dserve as first impedance elements in the case where attention is paid to the inductors L1cand L1dand the capacitor C4.

The capacitor C4is a second impedance element that is connected in parallel with a series circuit including the inductors L1cand L1d. Specifically, the capacitor C4is connected between a connection point between the inductor L1cand the terminal101aand a connection point between the inductor L1dand the terminal102a.

The parallel-arm resonator P4is an acoustic wave resonator that is connected between the ground and a node between the inductor L1cand the inductor L1don the path connecting the terminal101aand the terminal102a.

The inductor L13is an inductor that is connected between the node and the ground in series with the parallel-arm resonator P4.

A filter including the inductors L1cand L1d, the capacitor C4, and the parallel-arm resonator P4in the filter10fhas a configuration similar to that of the filter10aaccording to Example 2.

In the multiplexer30c, an input terminal (terminal101a) of the filter10fand an input terminal (terminal101b) of the filter10eare connected in common to the common terminal103. The common terminal103and each of the terminals101aand101bmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween.

For example, the filter10fis a high pass filter, and the filter10eis a low pass filter. Furthermore, for example, the pass band of the filter10fis higher than the pass band of the filter10e. Accordingly, the multiplexer30cis able to handle two frequency bands. InFIG. 21, the description “High” provided next to the terminal102aof the filter10fand the description “Low” provided next to the terminal102bof the filter10eindicate that the pass band of the filter10fis higher than the pass band of the filter10e.

Bandpass Characteristics of Multiplexer According to Example 7

Next, bandpass characteristics of the multiplexer30caccording to Example 7 will be explained.

FIG. 22is a graph indicating the bandpass characteristics of the multiplexer30caccording to Example 7. InFIG. 22, the description “High” is provided for the pass band of the filter10fforming the multiplexer30c, and the description “Low” is provided for the pass band of the filter10eforming the multiplexer30c.

The filter10fincludes an acoustic wave resonator, and the multiplexer30chas a sharp attenuation characteristic in a lower frequency end of the pass band indicated by “High” inFIG. 22due to a sharp attenuation pole by the acoustic wave resonator. The filter10ealso includes an acoustic wave resonator, and the multiplexer30chas a sharp attenuation characteristic in a higher frequency end of the pass band indicated by “Low” inFIG. 22due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, at 1430 MHz, 1880 MHz, 2200 MHz, 2300 MHz, and 2690 MHz, the insertion loss of the multiplexer30cis as small as 0.81 dB, 0.44 dB, 1.47 dB, 1.44 dB, and 1.15 dB, respectively.

As described above, the multiplexer30cthat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 23is a circuit configuration diagram of a multiplexer30daccording to Example 8.

A plurality of filters provided in the multiplexer30dincludes a first filter and a second filter as a combination of filters according to one or more of Examples 1 to 3. Specifically, the multiplexer30dis a diplexer including filters10gand10h, and each of the filters10gand10his a filter in which two filters that are similar to the filter10according to Example 1 are connected in series. For example, the filter10his a first filter, and the filter10gis a second filter.

The capacitors C1aand C1bare two first impedance elements that are connected in series on a path connecting the terminal101band the terminal102b.

The inductor L2is a second impedance element that is connected in parallel with a series circuit including the capacitors C1aand C1b. Specifically, the inductor L2is connected between a connection point between the capacitor C1aand the terminal101band a connection point between the capacitor C1band the capacitor Cle.

The parallel-arm resonator P1is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1aand the capacitor C1bon the path connecting the terminal101band the terminal102b.

A filter including the capacitors C1aand C1b, the inductor L2, and the parallel-arm resonator P1in the filter10ghas a configuration similar to that of the filter10according to Example 1.

The capacitors Cle and C1fare two first impedance elements that are connected in series on the path connecting the terminal101band the terminal102b.

The inductor L6is a second impedance element that is connected in parallel with a series circuit including the capacitors Cle and C1f. Specifically, the inductor L6is connected between a connection point between the capacitor Cle and the capacitor C1band a connection point between the capacitor C1fand the terminal102b.

The parallel-arm resonator P4is an acoustic wave resonator that is connected between the ground and a node between the capacitor Cle and the capacitor C1fon the path connecting the terminal101band the terminal102b.

The inductor L14is an inductor that is connected between the node and the ground in parallel with the parallel-arm resonator P4.

A filter including the capacitors Cle and C1f, the inductor L6, and the parallel-arm resonator P4in the filter10ghas a configuration similar to that of the filter10according to Example 1.

The capacitors C1cand C1dare two first impedance elements that are connected in series on a path connecting the terminal101aand the terminal102a.

The inductor L5is a second impedance element that is connected in parallel with a series circuit including the capacitors C1cand C1d. Specifically, the inductor L5is connected between a connection point between the capacitor C1cand the terminal101aand a connection point between the capacitor C1dand the capacitor C1g.

The parallel-arm resonator P3is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1cand the capacitor C1don the path connecting the terminal101aand the terminal102a.

A filter including the capacitors C1cand C1d, the inductor L5, and the parallel-arm resonator P3in the filter10hhas a configuration similar to that of the filter10according to Example 1.

The capacitors C1gand C1hare two first impedance elements that are connected in series on the path connecting the terminal101aand the terminal102a.

The inductor L7is a second impedance element that is connected in parallel with a series circuit including the capacitors C1gand C1h. Specifically, the inductor L7is connected between a connection point between the capacitor C1gand the capacitor C1dand a connection point between the capacitor C1hand the terminal102a.

The parallel-arm resonator P5is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1gand the capacitor C1hon the path connecting the terminal101aand the terminal102a.

The inductor L15is an inductor that is connected between the node and the ground in series with the parallel-arm resonator P5.

A filter including the capacitors C1gand C1h, the inductor L7, and the parallel-arm resonator P5in the filter10hhas a configuration similar to that of the filter10according to Example 1.

In the multiplexer30d, an input terminal (terminal101a) of the filter10hand an input terminal (terminal101b) of the filter10gare connected in common to the common terminal103. The common terminal103and each of the terminals101aand101bmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween.

For example, the filter10his a high pass filter, and the filter10gis a low pass filter. Furthermore, for example, the pass band of the filter10his higher than the pass band of the filter10g. Accordingly, the multiplexer30dis able to handle two frequency bands. InFIG. 23, the description “High” provided next to the terminal102aof the filter10hand the description “Low” provided next to the terminal102bof the filter10gindicate that the pass band of the filter10his higher than the pass band of the filter10g.

Bandpass Characteristics of Multiplexer According to Example 8

Next, bandpass characteristics of the multiplexer30daccording to Example 8 will be explained.

FIG. 24is a graph indicating the bandpass characteristics of the multiplexer30daccording to Example 8. InFIG. 24, the description “High” is provided for the pass band of the filter10hforming the multiplexer30d, and the description “Low” is provided for the pass band of the filter10gforming the multiplexer30d.

The filter10hincludes an acoustic wave resonator and the multiplexer30dhas a sharp attenuation characteristic in a lower frequency end of the pass band indicated by “High” inFIG. 24due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filter10galso includes an acoustic wave resonator, and the multiplexer30dhas a sharp attenuation characteristic in a higher frequency end of the pass band indicated by “Low” inFIG. 24due to a sharp attenuation pole by the acoustic wave resonator. At 1430 MHz, 1880 MHz, 2200 MHz, 2300 MHz, and 2690 MHz, the insertion loss of the multiplexer30dis as small as 0.89 dB, 0.51 dB, 1.21 dB, 1.21 dB, and 0.93 dB, respectively.

As described above, the multiplexer30dthat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 25is a circuit configuration diagram of a multiplexer30eaccording to Example 9.

A plurality of filters provided in the multiplexer30einclude a first filter and a second filter as a combination of filters according to one or more of Examples 1 to 3. The multiplexer30ealso includes a low pass filter whose input terminal or output terminal is connected to a common terminal. Specifically, the multiplexer30eis a triplexer including filters10g,10i, and20d, and each of the filters10gand10iis a filter in which two filters that are similar to the filter10according to Example 1 are connected in series. The filter20dis a low pass filter. For example, the filter10iis a first filter, and the filter10gis a second filter. The multiplexer30efurther includes a capacitor C6and an inductor L17.

The filter10ghas the same configuration as that described above in Example 8, and explanation for the filter10gwill be omitted.

The filter10iincludes a capacitor C5and an inductor L16, in addition to the configuration of the filter10hdescribed above in Example 8. The configuration of parts other than the capacitor C5and the inductor L16is the same as that of the filter10h, and explanation for those parts will be omitted.

The capacitor C5is a capacitor that is connected between the ground and a node between the capacitor C1dand the capacitor C1gon a path connecting the terminal101aand the terminal102a.

The inductor L16is an inductor that is connected between the ground and a node between the capacitor C1dand the capacitor C1gon the path connecting between the terminal101aand the terminal102a.

The capacitor C5and the inductor L16are connected in series.

The capacitor C7and the inductor L18are connected in parallel and form a parallel resonant circuit on a path connecting a terminal101cand a terminal102c.

The capacitor C9and the inductor L19are connected in parallel and form a parallel resonant circuit on the path connecting the terminal101cand the terminal102c.

The capacitor C8is a capacitor that is connected between the ground and a node between the capacitor C7and the capacitor C9on the path connecting the terminal101cand the terminal102c.

The capacitor C10is a capacitor that is connected between the ground and a node between the capacitor C9and terminal102con the path connecting the terminal101cand the terminal102c.

The capacitor C6is a capacitor that is provided on a path connecting the common terminal103and the terminal101a(terminal101b).

The inductor L17is an inductor that is connected between the ground and a node between the capacitor C6and the terminal101a(terminal101b) on the path connecting the common terminal103and the terminal101a(terminal101b).

For example, the capacitor C6and the inductor L17form a matching circuit.

In the multiplexer30e, an input terminal (terminal101a) of the filter10i, an input terminal (terminal101b) of the filter10g, and an input terminal (terminal101c) of the filter20dare connected in common to the common terminal103. The common terminal103and each of the terminals101a,101b, and101cmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween. InFIG. 25, an example in which the common terminal103and each of the terminals101aand101bare connected indirectly with other elements interposed therebetween is illustrated.

For example, the filter10iis a high pass filter, the filter10gis a band pass filter, and the filter20dis a low pass filter, as described above. Furthermore, for example, the pass band of the filter10iis higher than the pass band of the filter10g, and the pass band of the filter10gis higher than the pass band of the filter20d. Accordingly, the multiplexer30eis able to handle three frequency bands. InFIG. 25, the description “High” provided next to the terminal102aof the filter10i, the description “Middle” provided next to the terminal102bof the filter10g, and the description “Low” provided next to the terminal102cof the filter20dindicate that the pass band of the filter10iis higher than the pass band of the filter10gand the pass band of the filter10gis higher than the pass band of the filter20d.

Bandpass Characteristics of Multiplexer According to Example 9

Next, bandpass characteristics of the multiplexer30eaccording to Example 9 will be explained.

FIG. 26is a graph indicating the bandpass characteristics of the multiplexer30eaccording to Example 9. InFIG. 26, the description “High” is provided for the pass band of the filter10iforming the multiplexer30e, the description “Middle” is provided for the pass band of the filter10gforming the multiplexer30e, and the description “Low” is provided for the pass band of the filter20dforming the multiplexer30e.

The filter10iincludes an acoustic wave resonator, and the multiplexer30ehas a sharp attenuation characteristic in a lower frequency end of the pass band indicated by “High” inFIG. 26due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filter10gincludes an acoustic wave resonator, and the multiplexer30ehas a sharp attenuation characteristic in a higher frequency end of the pass band indicated by “Middle” inFIG. 26due to a sharp attenuation pole by the acoustic wave resonator. At 699 MHz, 960 MHz, 1430 MHz, 2200 MHz, 2300 MHz, and 2690 MHz, the insertion loss of the multiplexer30eis as small as 0.29 dB, 0.73 dB, 1.36 dB, 1.34 dB, 1.45 dB, and 1.45 dB, respectively.

As described above, the multiplexer30ethat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 27is a circuit configuration diagram of a multiplexer30faccording to Example 10.

A plurality of filters provided in the multiplexer30finclude a first filter and a second filter as a combination of filters according to one or more of Examples 1 to 3. The multiplexer30falso includes a high pass filter whose input terminal or output terminal is connected to a common terminal. Specifically, the multiplexer30fis a triplexer including filters10g,10i, and20e, and each of the filters10gand10iis a filter in which two filters that are similar to the filter10according to Example 1 are connected in series. The filter20eis a high pass filter. For example, the filter10iis a first filter, and the filter10gis a second filter. The multiplexer30ffurther includes a capacitor C11and an inductor L21.

The filter10ghas the same configuration as that described above in Example 8, and explanation for the configuration of the filter10gwill be omitted. The filter10ihas the same configuration as that described above in Example 9, and explanation for the configuration of the filter10iwill be omitted.

The capacitors C12and C14are connected in series on a path connecting the terminal101cand the terminal102c.

The capacitor C13is a capacitor that is connected between the ground and a node between the capacitor C12and the capacitor C14on the path connecting the terminal101cand the terminal102c.

The inductor L22is an inductor that is connected between the ground and the node between the capacitor C12and the capacitor C14on the path connecting the terminal101cand the terminal102c.

The capacitor C13and the inductor L22are connected in series.

The filter20emay not include the capacitor C13.

The inductor L21is an inductor that is connected on a path connecting the common terminal103and the terminal101a(terminal101b).

The capacitor C11is a capacitor that is connected between the ground and the node between the inductor L21and the terminal101a(terminal101b) on the path connecting the common terminal103and the terminal101a(terminal101b).

For example, the inductor L21and the capacitor C11form a matching circuit.

The multiplexer30fmay not include the inductor L21or the capacitor C11.

In the multiplexer30f, an input terminal (terminal101a) of the filter10i, an input terminal (terminal101b) of the filter10g, and an input terminal (terminal101c) of the filter20eare connected in common to the common terminal103. The common terminal103and each of the terminals101a,101b, and101cmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween. InFIG. 27, an example in which the common terminal103and each of the terminals101aand101bare connected indirectly with other elements interposed therebetween is illustrated.

For example, the filter10iis a band pass filter, the filter10gis a low pass filter, and the filter20eis a high pass filter, as described above. Furthermore, for example, the pass band of the filter20eis higher than the pass band of the filter10i, and the pass band of the filter10iis higher than the pass band of the filter10g. Accordingly, the multiplexer30fis able to handle three frequency bands. InFIG. 27, the description “Middle” provided next to the terminal102aof the filter10i, the description “Low” provided next to the terminal102bof the filter10g, and the description “High” provided next to the terminal102cof the filter20eindicate that the pass band of the filter20eis higher than the pass band of the filter10iand the pass band of the filter10iis higher than the pass band of the filter10g.

Illustration of the bandpass characteristics of the multiplexer30faccording to Example 10 is omitted. Because the multiplexer30fincludes the filters10gand10ieach including an acoustic wave resonator as in Example 9, the multiplexer30fthat has sharp attenuation characteristics and low-loss pass bands can be implemented.

FIG. 28is a circuit configuration diagram of a multiplexer30gaccording to Example 11.

A plurality of filters provided in the multiplexer30ginclude a first filter, a second filter, and a fourth filter as a combination of filters according to one or more of Examples 1 to 3. Specifically, the multiplexer30gis a triplexer including filters10g,10i, and10j, and each of the filters10g,10i,10jis a filter in which two filters that are similar to the filter10according to Example 1 are connected in series. For example, the filter10iis a first filter, the filter10gis a second filter, and the filter10jis a fourth filter.

The filter10ihas the same configuration as that described above in Example 9, and explanation for the configuration of the filter10iwill be omitted.

The filter10ghas the same configuration as that described above in Example 8 with the exception that the filter10gis connected between the terminal101cand the terminal102c, and explanation for the configuration of the filter10gwill be omitted.

The capacitors C1iand C1jare two first impedance elements that are connected in series on a path connecting the terminal101band the terminal102b.

The inductor L8is a second impedance element that is connected in parallel with a series circuit including the capacitors C1iand C1j. Specifically, the inductor L8is connected between a connection point between the capacitor C1iand the terminal101band a connection point between the capacitor C1jand the capacitor C1k.

The parallel-arm resonator P6is an acoustic wave resonator that is connected between the ground and a node between the capacitors C1iand C1jon the path connecting the terminal101band the terminal102b.

A filter including the capacitors C1iand C1j, the inductor L8, and the parallel-arm resonator P6in the filter10ghas a configuration similar to that of the filter10according to Example 1.

The capacitors C1kand C1lare two first impedance elements that are connected in series on the path connecting the terminal101band the terminal102b.

The inductor L9is a second impedance element that is connected in parallel with a series circuit including the capacitors C1kand C1l. Specifically, the inductor L9is connected between a connection point between the capacitor C1kand the capacitor C1jand a connection point between the capacitor C1land the terminal102b.

The parallel-arm resonator P7is an acoustic wave resonator that is connected between the ground and a node between the capacitor C1kand the capacitor C1lon the path connecting the terminal101band the terminal102b.

The inductor L23is an inductor that is connected between the node and the ground in parallel with the parallel-arm resonator P7.

A filter including the capacitors C1kand C1l, the inductor L9, and the parallel-arm resonator P7in the filter10jhas a configuration similar to that of the filter10according to Example 1.

In the multiplexer30g, an input terminal (terminal101a) of the filter10i, an input terminal (terminal101b) of the filter10j, and an input terminal (terminal101c) of the filter10gare connected in common to the common terminal103. The common terminal103and each of the terminals101a,101b, and101cmay be connected directly without any other elements interposed therebetween or connected indirectly with other elements interposed therebetween.

For example, the filter10iis a high pass filter, the filter10jis a band pass filter, and the filter10gis a low pass filter. Furthermore, for example, the pass band of the filter10iis higher than the pass band of the filter10j, and the pass band of the filter10jis higher than the pass band of the filter10g. Accordingly, the multiplexer30gis able to handle three frequency bands. InFIG. 28, the description “High” provided next to the terminal102aof the filter10i, the description “Middle” provided next to the terminal102bof the filter10j, and the description “Low” provided next to the terminal102cof the filter10gindicate that the pass band of the filter10iis higher than the pass band of the filter10jand the pass band of the filter10jis higher than the pass band of the filter10g.

Bandpass Characteristics of Multiplexer According to Example 11

Next, bandpass characteristics of the multiplexer30gaccording to Example 11 will be explained.

FIG. 29is a graph indicating the bandpass characteristics of the multiplexer30gaccording to Example 11. InFIG. 29, the description “High” is provided for the pass band of the filter10iforming the multiplexer30g, the description “Middle” is provided for the pass band of the filter10jforming the multiplexer30g, and the description “Low” is provided for the pass band of the filter10gforming the multiplexer30g.

The filter10iincludes an acoustic wave resonator, and the multiplexer30ghas a sharp attenuation characteristic in a lower frequency end of the pass band indicated by “High” inFIG. 29due to a sharp attenuation pole by the acoustic wave resonator. Furthermore, the filter10jincludes an acoustic wave resonator, and the multiplexer30ghas sharp attenuation characteristics in a higher frequency end and a lower frequency end of the pass band indicated by “Middle” inFIG. 29due to sharp attenuation poles by the acoustic wave resonator. Moreover, the filter10gincludes an acoustic wave resonator, and the multiplexer30ghas a sharp attenuation characteristic in a higher frequency end of the pass band indicated by “Low” inFIG. 29due to a sharp attenuation pole by the acoustic wave resonator. At 1430 MHz, 2200 MHz, 2300 MHz, 2400 MHz, 2500 MHz, and 2690 MHz, the insertion loss of the multiplexer30gis as small as 0.65 dB, 1.34 dB, 1.75 dB, 1.90 dB, 1.59 dB, and 1.25 dB, respectively.

As described above, the multiplexer30gthat has sharp attenuation characteristics and low-loss pass bands can be implemented.

An acoustic wave resonator is formed at a substrate having piezoelectricity. Thus, a plurality of acoustic wave resonators can be formed at a single substrate. That is, a plurality of acoustic wave resonators can be formed into one chip. Therefore, a reduction in size can be achieved.

However, in the case where a plurality of acoustic wave resonators are formed into one chip, countermeasures against harmonic waves (unwanted waves) corresponding to resonant frequencies of the individual acoustic wave resonators are required. Accordingly, productivity decreases, and cost increases.

Thus, acoustic wave resonators whose resonant frequencies are within the range of 200 MHz are formed into one chip. Accordingly, harmonic waves generated by acoustic wave resonators formed into one chip are within the range of 200 MHz, and countermeasures against harmonic waves located in close frequency bands can be easily implemented.

For example, the parallel-arm resonators P1and P3in the multiplexer30according to Example 4 may be formed into one chip. This will be explained below with reference toFIG. 30.

FIG. 30includes graphs for explaining a reason why resonators forming the multiplexer30according to Example 4 can be formed into one chip. An upper graph inFIG. 30indicates the bandpass characteristics of the multiplexer30, and a lower graph inFIG. 30indicates impedance characteristics of the parallel-arm resonators P1and P3forming the multiplexer30. In the upper graph, the description “High” is provided for the pass band of the filter10dforming the multiplexer30, and the description “Low” is provided for the pass band of the filter10forming the multiplexer30. On the vertical axis for the impedance characteristics, an upper side indicates a higher impedance.

An attenuation pole (Part A inFIG. 30) on the lower frequency side of the pass band of the filter10dcorresponds to the resonant frequency of the parallel-arm resonator P3, and an attenuation pole (Part B inFIG. 30) on the higher frequency side of the pass band of the filter10corresponds to the resonant frequency of the parallel-arm resonator P1. The resonant frequency of the parallel-arm resonator P1and the resonant frequency of the parallel-arm resonator P3are within the range of 200 MHz, as indicated in the lower graph inFIG. 30. Accordingly, even when the parallel-arm resonators P1and P3are formed into one chip, frequencies of harmonic waves generated by the parallel-arm resonators P1and P3are close to each other, and countermeasures against the harmonic waves can be implemented easily. Thus, the parallel-arm resonators P1and P3can be formed into one chip.

Furthermore, for example, resonators in the multiplexer30baccording to Example 6 can be formed into one chip. This will be explained below with reference toFIG. 31.

FIG. 31includes diagrams for explaining a reason why resonators forming the multiplexer30baccording to Example 6 can be formed into one chip. An upper graph inFIG. 31indicates the bandpass characteristics of the multiplexer30b, and a lower graph inFIG. 31indicates the impedance characteristics of the parallel-arm resonators P1, P2, P20, and P30and the series-arm resonators S30and S40forming the multiplexer30b. The description “High” is provided for the pass band of the filter10bforming the multiplexer30b, the description “Middle” is provided for the pass band of the filter20cforming the multiplexer30b, and the description “Low” is provided for the pass band of the filter10forming the multiplexer30b. On the vertical axis for the impedance characteristics, an upper side represents a higher impedance.

Two attenuation poles (Part A and Part B inFIG. 31) on the lower frequency side of the pass band of the filter20ccorrespond to the resonant frequencies of the parallel-arm resonators P30and P20, and an attenuation pole (Part C inFIG. 31) on the higher frequency side of the pass band of the filter10corresponds to the resonant frequency of the parallel-arm resonator P1. The resonant frequency of the parallel-arm resonator P30, the resonant frequency of the parallel-arm resonator P20, and the resonant frequency of the parallel-arm resonator P1are within the range of 200 MHz, as indicated in the lower graph inFIG. 31. Accordingly, even when the parallel-arm resonators P1, P20, and P30are formed into one chip, frequencies of harmonic waves generated by the parallel-arm resonators P1, P20, and P30are close to each other, and countermeasures against the harmonic waves can be implemented easily. Thus, the parallel-arm resonators P1, P20, and P30can be formed into one chip.

An attenuation pole (Part D inFIG. 31) on the lower frequency side of the pass band of the filter10bcorresponds to the resonant frequency of the parallel-arm resonator P2, and two attenuation poles (Part E and Part F inFIG. 31) on the higher frequency side of the pass band of the filter20ccorrespond to anti-resonant frequencies of the series-arm resonators S30and S40. The resonant frequency of the series-arm resonator S30, the resonant frequencies of the parallel-arm resonator P2, and the resonant frequency of the series-arm resonator S40are within the range of 200 MHz, as indicated in the lower graph inFIG. 31. Accordingly, even when the parallel-arm resonator P2and the series-arm resonators S30and S40are formed into one chip, frequencies of harmonic waves generated by the parallel-arm resonator P2and the series-arm resonators S30and S40are close to each other, and countermeasures against the harmonic waves can be implemented easily. Thus, the parallel-arm resonator P2and the series-arm resonators S30and S40can be formed into one chip.

Similarly, the resonant frequencies of the parallel-arm resonators P1, P2, P3, and P4in Example 7 are within the range of 200 MHz. Thus, the parallel-arm resonators P1, P2, P3, and P4can be formed into one chip.

Similarly, the resonant frequencies of the parallel-arm resonators P1, P3, P4, and P5in Example 8 are within the range of 200 MHz. Thus, the parallel-arm resonators P1, P3, P4, and P5can be formed into one chip.

Similarly, the resonant frequencies of the parallel-arm resonators P1, P3, P4, and P5in Example 9 are within the range of 200 MHz. Thus, the parallel-arm resonators P1, P3, P4, and P5can be formed into one chip.

Similarly, the resonant frequencies of the parallel-arm resonators P1, P3, P4, and P5in Example 10 are within the range of 200 MHz. Thus, the parallel-arm resonators P1, P3, P4, and P5can be formed into one chip.

Similarly, the resonant frequencies of the parallel-arm resonators P1, P4, and P6in Example 11 are within the range of 200 MHz. Thus, the parallel-arm resonators P1, P4, and P6can be formed into one chip. Furthermore, the resonant frequencies of the parallel-arm resonators P3, P5, and P7in Example 11 are within the range of 200 MHz. Thus, the parallel-arm resonators P3, P5, and P7can be formed into one chip.

The structure of a multiplexer in which a plurality of acoustic wave resonators are formed into one chip will be described below with reference toFIG. 32.

FIG. 32is a top view schematically illustrating the structure of the multiplexer30baccording to Example 6. InFIG. 32, the parallel-arm resonators P1, P2, P20, and P30and the series-arm resonators S30and S40that are actually formed of IDT electrodes or the like are schematically expressed as rectangles.

The multiplexer30bis implemented by, for example, a substrate60such as a mother board and substrates71and72having piezoelectricity mounted at the substrate60. As is clear fromFIG. 32, the substrate71and the substrate72are provided independently. For example, the substrates71and72may also be called chips. A state in which a plurality of components are formed into one chip represents a state in which the plurality of components are collectively arranged at a single substrate or the plurality of components are formed at a single substrate. A state in which the parallel-arm resonator P2and the series-arm resonators S30and S40are formed into one chip is indicated inFIG. 32by arranging the parallel-arm resonator P2and the series-arm resonators S30and S40, which are schematically illustrated as rectangles, collectively at the substrate71. Furthermore, a state in which the parallel-arm resonators P1, P20, and P30are formed into one chip is indicated inFIG. 32by arranging the parallel-arm resonators P1, P20and P30, which are schematically illustrated as rectangles, collectively at the substrate72.

Capacitors and inductors forming the multiplexer30bmay be formed of chip components or wiring patters or the like at a substrate and may be arranged or formed at any of the substrates60,71, and72. Thus, illustration for the capacitors and the inductors are omitted.

In the multiplexer30b, a combination of acoustic wave resonators formed into one chip is not limited to the above. For example, the parallel-arm resonator P2in the filter10band the series-arm resonators S30and S40and the parallel-arm resonators P20and P30in the filter20cmay be formed into one chip. Furthermore, for example, the series-arm resonators S30and S40and the parallel-arm resonators P20and P30in the filter20cand the parallel-arm resonator P1in the filter10may be formed into one chip. Moreover, the parallel-arm resonator P2in the filter10b, the series-arm resonators S30and S40and the parallel-arm resonators P20and P30in the filter20c, and the parallel-arm resonator P1in the filter10may be formed into one chip.

As described above, at least one of the parallel-arm resonator P2provided in the filter10band the parallel-arm resonator P1provided in the filter10and at least one of a series-arm resonator and a parallel-arm resonator provided in the filter20cmay be formed into one chip.

The configuration of a filter according to each of Examples may include other components.

For example, in each of Examples, a capacitor or an inductor may be connected in series with the capacitors C1aand C1bin the filter10, a capacitor or an inductor may be connected in parallel with the capacitors C1aand C1b, or a capacitor or an inductor may be connected in series with the inductor L2. Furthermore, for example, in each of Examples, a capacitor or an inductor may be connected in series with the inductors L1aand L1bin the filter10a, a capacitor or an inductor may be connected in parallel with the inductors L1aand L1b, or a capacitor or an inductor may be connected in series or parallel with the capacitor C2.

Furthermore, for example, in each of Examples, a capacitor or an inductor may be connected in series with the parallel-arm resonators P1and P2, or a capacitor or an inductor may be connected in parallel with the parallel-arm resonators P1and P2.

Furthermore, for example, in each of Examples, an impedance variable circuit may be connected, in series or parallel with the parallel-arm resonators P1and P2, between the ground and a node to which the parallel-arm resonators P1and P2are connected. The impedance variable circuit will be described below with reference toFIGS. 33 and 34. Explanation will be provided below by attention being paid to a filter according to Example 1. Similar effects can be achieved by applying the impedance variable circuit to the filters according to Examples 2 to 11.

FIG. 33is a circuit configuration diagram of a filter10caccording to a modification of Example 1.

The filter10cincludes an impedance variable circuit12, in addition to the configuration of the filter10according to Example 1. The other features of this modification are the same as those of Example 1. Thus, explanation for those features will be omitted.

The impedance variable circuit12is, for example, connected, in series with the parallel-arm resonator P1, between the ground and a node to which the parallel-arm resonator P1is connected. The impedance variable circuit12is a circuit for varying the impedance of a parallel arm (that is, a circuit in which the parallel-arm resonator P1and the impedance variable circuit12are connected in series) in the filter10c. The impedance variable circuit12is connected between the parallel-arm resonator P1and the ground. For example, however, the impedance variable circuit12may be connected between the node and the parallel-arm resonator P1.

The impedance variable circuit12includes an inductor L3, an inductor L4, and a switch SW. For example, the inductor L4is connected in series with the switch SW, and the inductor L3is connected in parallel with the series circuit.

The impedance variable circuit12is able to vary the impedance of the parallel arm, specifically, the frequency of an attenuation pole of the parallel arm, in accordance with ON and OFF of the switch SW. In accordance with the frequency of the attenuation pole of the parallel arm varying, the bandpass characteristics of the filter10calso vary.

FIG. 34is a graph indicating the bandpass characteristics of the filter10caccording to the modification of Example 1 when the switch SW is ON and OFF. InFIG. 34, a solid line represents the bandpass characteristics of the filter10cwhen the switch SW is OFF, and a broken line represents the bandpass characteristics of the filter10cwhen the switch SW is ON.

When the switch SW is ON, the impedance variable circuit12functions as a circuit in which the inductor L3and the inductor L4are connected in parallel, and due to the influence of the parallel circuit, the higher frequency end of the pass band of the filter20ccan be shifted toward higher frequencies, as illustrated inFIG. 34. In contrast, when the switch SW is OFF, the influence of the inductor L4becomes negligible in the impedance variable circuit12, and the higher frequency end of the pass band of the filter20ccan be shifted toward lower frequencies, as illustrated inFIG. 34.

The impedance variable circuit12does not necessarily have the circuit configuration illustrated inFIG. 33. The circuit configuration in which the switch SW may vary the number of inductors connected in parallel is provided. For example, however, a circuit configuration in which the switch SW may vary the number of inductors connected in series may be provided. Furthermore, for example, capacitors may be provided in place of the inductors L3and L4. Depending on the circuit configuration, the higher frequency end of the pass band of the filter20cmay be shifted or the lower frequency end of the pass band of the filter20cmay be shifted.

CONCLUSION

As described above, the radio frequency filter according to the first embodiment includes two first impedance elements that are connected in series on a path connecting an input terminal and an output terminal, a second impedance element that is connected in parallel with a series circuit including the two first impedance elements, and a parallel-arm resonator that is connected between the ground and a node between the two first impedance elements on the path. Each of the first impedance elements is one of a capacitor and an inductor, and the second impedance element is the other one of the capacitor and the inductor.

Accordingly, a low-loss pass band can be achieved compared to a case where a parallel-arm resonator is connected between the ground and a node between one of the two first impedance elements and an input terminal or an output terminal. Furthermore, a low-loss pass band can be achieved compared to a case where an acoustic wave resonator is provided in place of a capacitor as any of the two first impedance elements and the second impedance element. Furthermore, a sharp attenuation characteristic can be achieved by a parallel-arm resonator having a sharp attenuation pole. Accordingly, a radio frequency filter with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator can be implemented.

Furthermore, the radio frequency filter according to the first embodiment may further include a third impedance element that is connected in parallel with one of the two first impedance elements. In the case where the first impedance elements are inductors, the third impedance element may be a capacitor. In the case where the first impedance elements are capacitors, the third impedance element may be an inductor.

Accordingly, for example, by connecting the capacitor C3in parallel with the inductor L1aas the first impedance element, impedance can be made close to 50Ω in the vicinity of the higher frequency end of the pass band. Thus, insertion loss in the pass band can further be reduced.

Furthermore, the radio frequency filter according to the first embodiment may further include the impedance variable circuit12that is connected, in series or parallel with the parallel-arm resonator, between the ground and the node to which the parallel-arm resonator is connected.

Accordingly, with the impedance variable circuit12, a tunable filter whose pass band can be shifted can be implemented.

Furthermore, the multiplexer according to the first embodiment may include a plurality of filters each including the radio frequency filter according to the first embodiment, and input terminals or output terminals of the plurality of filters may be connected to the common terminal103.

Accordingly, a multiplexer with sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, the plurality of filters may include a first filter and a second filter. The first impedance elements provided in the first filter and the first impedance elements provided in the second filter may be capacitors.

Accordingly, for example, a diplexer that has sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, the multiplexer may further include a low pass filter whose input terminal or output terminal is connected to the common terminal. A pass band of the low pass filter may be lower than a pass band of the first filter and a pass band of the second filter.

Accordingly, for example, a triplexer that has sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, the multiplexer may further include a high pass filter whose input terminal or output terminal is connected to the common terminal, and a pass band of the high pass filter may be higher than a pass band of the first filter and a pass band of the second filter.

Accordingly, for example, a triplexer that has sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, parallel-arm resonators provided in the first filter and the second filter may be formed into one chip, and resonant frequencies of the parallel-arm resonators formed into one chip may be within the range of 200 MHz.

Accordingly, the size of the multiplexer may be reduced.

Furthermore, the multiplexer may further include a third filter whose input terminal or output terminal is connected to the common terminal, the third filter may include at least one series-arm resonator and at least one parallel-arm resonator, and a pass band of the third filter may be lower than a pass band of the first filter and higher than a pass band of the second filter.

Accordingly, for example, a triplexer that has sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, at least one of the parallel-arm resonator provided in the first filter and the parallel-arm resonator provided in the second filter and at least one of the at least one series-arm resonator and the at least one parallel-arm resonator provided in the third filter may be formed into one chip, and resonant frequencies of the resonators formed into one chip may be within the range of 200 MHz.

Accordingly, the size of the multiplexer can be reduced.

Furthermore, the plurality of filters may further include a fourth filter. A pass band of the fourth filter may be lower than a pass band of the first filter and higher than a pass band of the second filter.

Accordingly, for example, a triplexer that has sharp attenuation characteristics and low-loss pass bands that are not limited by resonant band widths of acoustic wave resonators can be implemented.

Furthermore, at least one of the parallel-arm resonator provided in the first filter and the parallel-arm resonator provided in the second filter and the parallel-arm resonator provided in the fourth filter may be formed into one chip, and resonant frequencies of the resonators formed into one chip may be within the range of 200 MHz.

Accordingly, the size of the multiplexer can be reduced.

Furthermore, the multiplexer may include at least two of a filter with a pass band including 699 MHz to 960 MHz, a filter with a pass band including 1.2 GHz, a filter with a pass band including 1.4 GHz to 5 GHz, and a filter with a pass band including 5 GHz to 7.125 GHz.

Furthermore, the multiplexer may include at least two of a filter with a pass band including 699 MHz to 2.7 GHz, a filter with a pass band including 3.3 GHz to 4.2 GHz, a filter with a pass band including 4.4 GHz to 5 GHz, and a filter with a pass band including 5 GHz to 7.125 GHz.

Second Embodiment

The multiplexers described above according to Examples 4 to 11 in the first embodiment may be applied to a radio frequency front end circuit or a communication apparatus.

First, a radio frequency front end circuit that includes the multiplexer30described above in the first embodiment will be described with reference toFIG. 35.

FIG. 35is a circuit configuration diagram of a radio frequency front end circuit50according to a second embodiment. As illustrated inFIG. 35, the radio frequency front end circuit50is a reception-system front end circuit and includes the multiplexer30, switches31and32, filters21,22,23,24and25, and reception amplifiers41,42,43,44, and45. InFIG. 35, an antenna element ANT is illustrated. The antenna element ANT is a multiband antenna conforming to communication standards such as LTE, and transmits and receives radio frequency signals. The antenna element ANT and the radio frequency front end circuit50are arranged, for example, in a front end unit of a cellular phone with multimode/multiband capability.

As described above, the multiplexer30includes the filter10d(high pass filter) and the filter10(low pass filter).

The filter10is a low pass filter with a pass band of a low-band frequency range (for example, from 1427 MHz to 2200 MHz) and with an attenuation band of a high-band frequency range. The filter10dis a high pass filter with a pass band of a high-band frequency range (for example, from 2300 MHz to 2690 MHz) and with an attenuation band of a low-band frequency range. At least one of the filters10and10dmay be a tunable filter.

The switch31is a switch element that includes a common terminal and two selection terminals, and the common terminal is connected to the filter10. The switch31is a switch circuit of an SPDT type in which the common terminal may be connected to one of the two selection terminals.

The switch32is a switch element that includes a common terminal and three selection terminals, and the common terminal is connected to the filter10d. The switch32is a switch circuit of an SP3T type in which the common terminal may be connected to one of the three selection terminals.

The filter21is a band pass filter that is connected to a selection terminal of the switch31, and the pass band of the filter21is, for example, LTE Band 3 (reception band: from 1805 MHz to 1880 MHz). The filter22is a band pass filter that is connected to a selection terminal of the switch31, and the pass band of the filter22is, for example, LTE Band 1 (reception band: from 2110 MHz to 2170 MHz). The filter23is a band pass filter that is connected to a selection terminal of the switch32, and the pass band of the filter23is, for example, LTE Band 7 (reception band: from 2620 MHz to 2690 MHz). The filter24is a band pass filter that is connected to a selection terminal of the switch32, and the pass band of the filter24is, for example, LTE Band 40 (reception band: from 2300 MHz to 2400 MHz). The filter25is a band pass filter that is connected to a selection terminal of the switch32, and the pass band of the filter25is, for example, LTE Band 41 (reception band: from 2496 MHz to 2690 MHz).

The reception amplifier41is connected to the filter21, the reception amplifier42is connected to the filter22, the reception amplifier43is connected to the filter23, the reception amplifier44is connected to the filter24, and the reception amplifier45is connected to the filter25. Each of the reception amplifiers41to45is, for example, a low noise amplifier including a transistor or the like. The reception amplifiers41and42form an amplifying circuit46. The reception amplifiers43to45form an amplifying circuit47. Each of the amplifying circuits46and47may be composed of a reception amplifier. In this case, an SPDT switch is arranged between the amplifying circuit46and the filters21and22, and an SP3T switch is arranged between the amplifying circuit47and the filters23to25.

As described above, the radio frequency front end circuit50includes the multiplexer30according to the first embodiment, the switches31and32that are connected directly or indirectly to the multiplexer30, and the amplifying circuits46and47that are connected directly or indirectly to the multiplexer30.

With the configuration of the radio frequency front end circuit50described above that includes the multiplexer according to the first embodiment, a radio frequency front end circuit with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator can be implemented.

Next, a radio frequency front end circuit that includes the multiplexer30bdescribed above according to the first embodiment and a communication apparatus will be described with reference toFIG. 36.

FIG. 36is a circuit configuration diagram of a communication apparatus150according to the second embodiment.

As illustrated inFIG. 36, the communication apparatus150includes a radio frequency front end circuit130and an RF signal processing circuit (RFIC)140. InFIG. 36, an antenna element ANT is illustrated. The antenna element ANT may be built in the communication apparatus150.

The radio frequency front end circuit130is a circuit that transmits a radio frequency signal between the antenna element ANT and the RFIC140. Specifically, the radio frequency front end circuit130transmits a radio frequency signal (in this case, a radio frequency reception signal), which is received at the antenna element ANT, via a reception-side signal path to the RFIC140.

The radio frequency front end circuit130includes the multiplexer30baccording to the first embodiment, switches111to116, amplifying circuits121to123, and band pass filters (BPFs)161to168. The BPFs161and162form a duplexer, and the BPFs163and164form a duplexer.

As described above, the multiplexer30bincludes the filter10b(high pass filter), the filter20c(band pass filter), and the filter10(low pass filter).

The filter10is a low pass filter with a pass band of a low-band frequency range (for example, from 1427 MHz to 2200 MHz) and with an attenuation band of middle-band and high-band frequency ranges. The filter20cis a band pass filter with a pass band of a middle-band frequency range (for example, from 2300 MHz to 2400 MHz) and with an attenuation band of low-band and high-band frequency ranges. The filter10bis a high pass filter with a pass band of a high-band frequency range (for example, from 2496 MHz to 2690 MHz) and with an attenuation band of low-band and middle-band frequency ranges. At least one of the filters10,20c, and10bmay be a tunable filter.

The switches111to113are connected between the multiplexer30band the BPFs161to168and allow signal paths corresponding to low bands, middle bands, and high bands to be connected to the BPFs161to168in accordance with control signals from a controller (not illustrated inFIG. 36).

Specifically, a common terminal of the switch111is connected to the filter10b, and selection terminals of the switch111are connected to the BPFs161to164. A common terminal of the switch112is connected to the filter20c, and selection terminals of the switch112are connected to the BPFs165and166. A common terminal of the switch113is connected to the filter10, and selection terminals of the switch113are connected to the BPFs167and168.

The switches114to116are connected between the amplifying circuits121to123and the BPFs161to168and allow the BPFs161to168to be connected to the amplifying circuits121to123in accordance with control signals from a controller (not illustrated inFIG. 36).

Specifically, a common terminal of the switch114is connected to the amplifying circuit121, and selection terminals of the switch114are connected to the BPFs161to164. A common terminal of the switch115is connected to the amplifying circuit122, and selection terminals of the switch114are connected to the BPFs165and166. A common terminal of the switch116is connected to the amplifying circuit123, and selection terminals of the switch116are connected to the BPFs167and168.

The pass band (from 2496 MHz to 2690 MHz) of the filter10bincludes pass bands of the BPFs161to164. The pass band (from 2300 MHz to 2400 MHz) of the filter20cincludes pass bands of the BPFs165and166. The pass band (from 1427 MHz to 2200 MHz) of the filter10includes pass bands of the BPFs167and168.

The amplifying circuits121to123are, for example, low noise amplifiers that are connected to the multiplexer30bwith the switches111to116and the BPFs161to168interposed therebetween and electronically amplify radio frequency reception signals received at the antenna element ANT.

The RFIC140is an RF signal processing circuit that processes a radio frequency signal transmitted and received through the antenna element ANT. Specifically, the RFIC140performs signal processing, via down conversion or the like, on a radio frequency signal (in this case, a radio frequency reception signal) inputted via a reception-side signal path of the radio frequency front end circuit130through the antenna element ANT, and outputs the reception signal generated by the signal processing to a baseband signal processing circuit (not illustrated inFIG. 36).

The radio frequency front end circuit130may include a transmission-side signal path and may transmit a radio frequency signal (in this case, a radio frequency transmission signal) outputted from the RFIC140, via the transmission-side signal path to the antenna element ANT. In this case, the RFIC140may perform signal processing, via up conversion or the like, on a transmission signal inputted from the baseband signal processing circuit and output the radio frequency signal (in this case, a radio frequency transmission signal) generated by the signal processing to the transmission-side signal path of the radio frequency front end circuit130, and the amplifying circuits121to123may be power amplifiers that electronically amplify radio frequency transmission signals outputted from the RFIC140.

Although not illustrated inFIG. 36, the controller may be provided in the RFIC140, or the controller and a switch controlled by the controller may form a switch IC.

With the configuration of the radio frequency front end circuit130and the communication apparatus150described above that includes the multiplexer according to the first embodiment, a radio frequency front end circuit and a communication apparatus with a sharp attenuation characteristic and a low-loss pass band that is not limited by a resonant band width of an acoustic wave resonator can be implemented.

Other Embodiments

A radio frequency filter, a multiplexer, a radio frequency front end circuit, and a communication apparatus according to embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the embodiments described above. Other embodiments implemented by combining any components in the embodiments described above, modifications obtained by making various changes to the embodiments described above conceived by those skilled in the art without departing from the scope of the present disclosure, and various types of equipment in which a radio frequency filter, a multiplexer, a radio frequency front end circuit, and a communication apparatus according to the present disclosure are built may also be included in the present disclosure.

The number of acoustic wave resonators in the embodiments described above is not limited to one. A plurality of divided resonators obtained by dividing a resonator may be provided.

Furthermore, for example, an inductor or a capacitor may be connected between components in a radio frequency filter, a multiplexer, a radio frequency front end circuit, and a communication apparatus. The inductor may include a wiring inductor serving as wiring connecting the components.

Furthermore, in the embodiments described above, a multiplexer is used to demultiplex an input radio frequency signal. However, the multiplexer may be used to multiplex radio frequency signals.

Furthermore, in the embodiments described above, a plurality of filters provided in a multiplexer include two or more filters according to one or more of Examples 1 to 3. However, the plurality of filters may include at least one of the filters according to Examples 1 to 3.

Furthermore, in the embodiments described above, a diplexer including two filters or a triplexer including three filters is provided as a multiplexer. However, the multiplexer may include four or more filters.

Furthermore, in the second embodiment, a radio frequency front end circuit includes both a switch and an amplifying circuit. However, the radio frequency front end circuit may not include a switch or an amplifying circuit.