Composite filter and communication device

Abstract

In this composite filter, a first hybrid has first to fourth ports. A first filter is connected to the second port of the first hybrid and has a first passband. A second filter is connected to the third port and has a second passband that does not overlap the first passband. A third filter is connected to the fourth port and has the second passband. A resonator is connected to a reference potential unit while being branched off of a signal path from the first filter to the second port, and has a resonant frequency within the second passband. Alternatively, or in addition, a fourth filter is connected to a reference potential while being branched off of the signal path from the first filter to the second port, and passes a signal having a frequency within the second passband to the reference potential unit.

Description

Composite filter and communication device

[0001] The present disclosure relates to a composite filter having two or more filters, and a communication device having the composite filter.

[0002] Composite filters having two or more filters and a 90° hybrid coupler (hereinafter sometimes simply referred to as a "hybrid") connected to the two or more filters are known (see, for example, Patent Documents 1 and 2 listed below). The composite filters disclosed in Patent Documents 1 and 2 are configured as duplexers. In these duplexers, an antenna and a first filter, a second filter, and a third filter are connected to four ports of the hybrid, respectively. The first filter is, for example, a transmit filter. The second filter and the third filter are, for example, receive filters having the same passband.

[0003] International Publication No. 2009 / 078095

[0004] A composite filter according to one aspect of the present disclosure includes a first hybrid, a first filter, a second filter, a third filter, and a resonator. The first hybrid is configured as a 90° hybrid coupler. The 90° hybrid coupler has a first port, a second port, and a third port and a fourth port to which a signal input to the first port or the second port is distributed. The first filter is connected to the second port and has a first passband. The second filter is connected to the third port and has a second passband that does not overlap with the first passband. The third filter is connected to the fourth port and has the second passband. The resonator branches off from a signal path from the first filter to the second port and is connected to a reference potential section, and has a resonance frequency within the second passband.

[0005] A composite filter according to one aspect of the present disclosure includes a first hybrid, a first filter, a second filter, a third filter, and a fourth filter. The first hybrid is configured as a 90° hybrid coupler. The 90° hybrid coupler has a first port, a second port, and a third port and a fourth port to which a signal input to the first port or the second port is distributed. The first filter is connected to the second port and has a first passband. The second filter is connected to the third port and has a second passband that does not overlap with the first passband. The third filter is connected to the fourth port and has the second passband. The fourth filter branches off from the signal path from the first filter to the second port and is connected to a reference potential section, and passes signals having frequencies within the second passband to the reference potential section.

[0006] A communication device according to one aspect of the present disclosure includes any of the composite filters described above, an antenna connected to the first port, and integrated circuit elements connected to the first filter, the second filter, and the third filter on the electrically opposite side of the first hybrid.

[0007] Schematic diagrams showing the configurations of composite filters according to the first and second embodiments. Schematic diagrams showing the configuration of a portion of the composite filter according to the first embodiment. Schematic diagrams showing an example of the configuration of a resonator included in the composite filter according to the first embodiment. Schematic diagrams showing an example of the characteristics of a resonator included in the composite filter according to the first embodiment. A diagram showing nonlinear distortion in an example according to the first embodiment. Schematic diagrams showing the configuration of a portion of the composite filter according to the second embodiment. A diagram showing the transmission characteristics of an example according to the second embodiment. A diagram showing isolation in an example according to the second embodiment. A diagram showing nonlinear distortion flowing to a receiving terminal in an example according to the second embodiment. A diagram showing nonlinear distortion flowing to a reference potential section in an example according to the second embodiment. A schematic diagram showing the configuration of a composite filter according to a third embodiment. A plan view showing a schematic example of the configuration of a resonator included in the composite filter according to the embodiments. A block diagram showing an example of the configuration of a communication device including the composite filter according to the embodiments.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The drawings used in the following description are schematic. Therefore, for example, the dimensional ratios in the drawings do not necessarily correspond to the actual ones. Furthermore, the dimensional ratios may not match between drawings. Certain shapes and / or dimensions may be exaggerated, and details may be omitted. However, the above does not deny that the actual shapes and / or dimensions may be as shown in the drawings, or that features of shapes and / or dimensions may be extracted from the drawings.

[0009] In the description of multiple aspects, for later-described aspects, only the differences from previously described aspects will basically be described. Matters not specifically mentioned may be considered to be the same as previously described aspects or may be inferred from previously described aspects. Furthermore, for convenience, components that correspond to each other in multiple aspects may be given the same reference numerals even if there are differences. Conversely, for convenience, even if the components are the same, different reference numerals may be given. Furthermore, for convenience, in the description following the description of multiple aspects, only the reference numerals of previously described aspects may be used. However, unless a contradiction or the like arises, the reference numerals of previously described aspects may be replaced with the reference numerals of later described aspects.

[0010] In the present disclosure, when the phase of a signal is "shifted," the phase may be advanced or delayed. However, for convenience, when referring to the above, unless a contradiction arises, "shift" or the like will mean only one of the two terms commonly used for various components and various signals. For example, when it is said that the phase of a second signal is shifted by 90° relative to the phase of a first signal, and the phase of a fourth signal is shifted by 90° relative to the phase of a third signal, the former and latter shifts are both shifts in phase that are advanced by 90°, or both shifts in phase that are delayed by 90°.

[0011] In the present disclosure, the expression "electrically connected to the opposite side" is used. The "opposite side" refers to, for example, the "output side" relative to the input side, or the "input side" relative to the output side.

[0012] (Outline of the embodiment) FIG. 1 is a circuit diagram showing the configuration of a composite filter 1 according to the embodiment.

[0013] The composite filter 1 is configured as a duplexer and includes, for example, a transmission path 2T that filters a transmission signal from a transmission terminal 7 (first terminal) and outputs the filtered signal to an antenna terminal 5 (common terminal), and a reception path 2R that filters a reception signal from the antenna terminal 5 and outputs the filtered signal to a reception terminal 9 (second terminal).

[0014] The transmission path 2T has a transmission filter system 12 that is directly responsible for filtering the transmission signal. The transmission filter system 12 includes a transmission filter 13. The reception path 2R has a reception filter system 14 that is directly responsible for filtering the reception signal. The reception filter system 14 has reception filters 15A and 15B (hereinafter, the two may be simply referred to as reception filters 15 without distinguishing between them).

[0015] The transmit filter system 12 (transmit filter 13) passes signals in the transmit band (attenuates signals outside the transmit band). The receive filter system 14 (receive filter 15) passes signals in the receive band (attenuates signals outside the receive band). The transmit band and receive band are different frequency bands (they do not overlap). That is, the transmit filter 13 and receive filter 15 have pass bands that do not overlap. Note that the portion of the composite filter 1 that includes the transmit filter 13 and receive filter 15 and that directly contributes to filtering (excluding the hybrid, described below) is the portion that corresponds to a general duplexer (duplexer main body 3).

[0016] A first hybrid 17, which is a 90° hybrid coupler, is interposed between the antenna terminal 5, the transmitting filter 13, and the receiving filters 15A and 15B. The first hybrid 17 contributes to reducing nonlinear distortion (distorted signals), for example, as will be described later.

[0017] The first hybrid 17 has four ports 17a to 17d. To put it simply based on common technical knowledge, the relationship between the ports 17a to 17d is such that a signal input to port 17a or 17b is distributed to ports 17c and 17d. The antenna terminal 5 and the transmit filter 13 are connected to ports 17a and 17b, respectively, and the receive filters 15A and 15B are connected to ports 17c and 17d, respectively.

[0018] When a transmission signal is input to the transmission terminal 7 from outside the composite filter 1, the transmission signal is filtered by the transmission filter 13 and input to the first hybrid 17. The transmission signal input to the first hybrid 17 is split into two transmission signals that are 90° out of phase with each other and distributed to the two reception filters 15. Because the transmission band and the reception band do not overlap, the two distributed transmission signals are reflected by the two reception filters 15 and input again to the first hybrid 17. The two input transmission signals are made into in-phase signals by the first hybrid 17, combined, and output to the antenna terminal 5.

[0019] The composite filter 1 has a trap 24 that branches off from the signal path from the transmit filter 13 to the port 17b and is connected to the reference potential unit 11. The trap 24 is configured to allow signals having frequencies within the receive band to pass to the reference potential unit 11. For example, the trap 24 has a trap resonator 29T (FIG. 2) that has a resonant frequency in the receive band.

[0020] Therefore, nonlinear distortion (for example, PIM3: third-order passive intermodulation distortion) that occurs in the transmit filter 13 and has a frequency included in the receive band is allowed to escape to the reference potential section 11 by the trap 24. As a result, the probability that the nonlinear distortion passes through the receive filter 15 and flows to the receive terminal 9 is reduced.

[0021] In a typical duplexer that does not have the first hybrid 17, the transmit filter 13 and the receive filter 15 are both directly connected to the antenna terminal 5. Therefore, if a trap 24 is connected to the output side (antenna terminal 5 side) of the transmit filter 13, as in the composite filter 1, the signal that should flow from the antenna terminal 5 to the receive filter 15 also flows to the trap 24. Therefore, the trap 24 is something that would be unthinkable in a typical duplexer.

[0022] The above is an overview of the embodiments. The first and second embodiments, which will be described later, differ from each other in the specific configuration of the trap 24. The third embodiment differs from the first and second embodiments in its overall configuration, but is common to both in that the trap 24 reduces the likelihood that nonlinear distortion generated in the transmit filter 13 passes through the receive filter 15. Various embodiments according to the present disclosure will be described below, roughly in the following order: 1. First Embodiment 1.1. Composite Filter Configuration (Excluding Trap Configuration) (FIG. 1) 1.1.1. Filter 1.1.2. Hybrid 1.1.3. Termination Resistor 1.1.4. Others 1.2. Composite Filter Operation (Excluding Trap Operation) 1.2.1. Transmission of Transmit Signal 1.2.2. Transmission of Received Signal 1.2.3. Example of Nonlinear Distortion Reduction 1.3. Trap 1.3.1. Trap Configuration (FIG. 2) 1.3.2. 1. Example of the configuration of a resonator included in a trap (FIG. 3) 1.3.3. Example of the characteristics of a resonator included in a trap (FIG. 4) 1.4. Characteristics of a comparative example and an example (FIG. 5) 2. Second embodiment 2.1. Trap (FIG. 6) 2.2. Characteristics of a comparative example and an example (FIGS. 7A to 8B) 3. Third embodiment (FIG. 9) 4. Example of an acoustic wave resonator (FIG. 10) 5. Example of a communication device including a composite filter (FIG. 9) 6. Summary of embodiments

[0023] 1. First Embodiment A composite filter 1 according to a first embodiment will be described below. The composite filter 1 according to the first embodiment may be referred to as a composite filter 1A (reference numeral shown in FIG. 2).

[0024] (1.1. Configuration of the Composite Filter (Excluding the Configuration of the Trap)) The above-mentioned FIG. 1 shows the configuration of the composite filter 1 according to the first and second embodiments. The outline of the composite filter 1 has already been described. In addition to the components already described, the composite filter 1 also has a second hybrid 19. The second hybrid 19 is interposed between the receiving terminal 9 and the receiving filters 15A and 15B. The composite filter 1 also has a termination resistor 23 connected to an unused port 19c of the second hybrid 19. Although not specifically shown, the composite filter 1 may have a matching circuit at an appropriate position. Below, the components of the composite filter 1 will be explained in order.

[0025] (1.1.1. Filter) The transmit filter 13 is a band-pass filter with a predetermined transmit band as its pass band. Similarly, the receive filter 15 is a band-pass filter with a predetermined receive band as its pass band. The transmit band and receive band may conform to, for example, various standards. Furthermore, the transmit band may include two or more transmit bands that conform to predetermined standards. The same applies to the receive band.

[0026] The receive filters 15A and 15B correspond to the same receive band. That is, the passbands of the receive filters 15A and 15B are substantially and / or design-wise identical. For example, the receive filters 15A and 15B have the same or similar configurations and substantially or design-wise identical characteristics. However, the receive filters 15A and 15B may be fine-tuned so that their passbands and / or characteristics are slightly different.

[0027] The specific configurations of the transmit filter 13 and the receive filter 15 may be various, for example, known configurations or applications of known configurations. For example, the transmit filter 13 and / or the receive filter 15 may be a piezoelectric filter including a piezoelectric element, a dielectric filter utilizing electromagnetic waves in a dielectric, an LC filter combining an inductor and a capacitor, or a combination of two or more of these. The piezoelectric filter may be, for example, an elastic wave filter utilizing elastic waves, or may be something other than an elastic wave filter (for example, one utilizing a piezoelectric vibrator).

[0028] The specific configuration of the acoustic wave filter is also arbitrary. For example, the acoustic wave filter may be a ladder-type filter in which acoustic wave resonators (FIG. 10) described later are connected in a ladder configuration, or a multimode filter (including a double-mode filter) in which IDT (Interdigital Transducer) electrodes 33 (FIG. 10) described later are arranged in the propagation direction of the acoustic waves. The acoustic wave may be, for example, a surface acoustic wave (SAW), a bulk acoustic wave (BAW), a boundary acoustic wave, or a plate wave (however, these acoustic waves are not necessarily distinguishable). A BAW may propagate in the direction of expansion of a piezoelectric layer (see the description of the piezoelectric substrate 31 described later) or in the thickness direction of the piezoelectric layer. In the description of the embodiments, unless otherwise specified, an example in which the transmit filter 13 and the receive filter 15 are configured by acoustic wave filters may be used.

[0029] (1.1.2. Hybrid) The first hybrid 17 has four ports 17a to 17d for inputting and / or outputting signals, and also functions as a distributor, a combiner, and a 90° phase shifter. The configuration of the first hybrid 17 may be, for example, a known configuration or an application of a known configuration. For example, although not specifically shown, the first hybrid 17 may be a distributed constant type or a lumped constant type. A branch-line coupler is well known as the first hybrid 17.

[0030] Ports 17a and 17b on the left side of Fig. 1 are electrically connected to ports 17c and 17d on the right side of Fig. 1. "Electrical connection" here means that a signal can flow. For example, a signal input to port 17a can be output from ports 17c and 17d.

[0031] For convenience, the description of this embodiment may be based on the positional relationship of the ports 17a to 17d in the diagram showing the first hybrid 17. However, the positional relationship of the four ports 17a to 17d on the diagram does not have to match the positional relationship of the four actual ports 17a to 17d.

[0032] A signal input to port 17a on the left side of Fig. 1 is distributed to ports 17c and 17d on the right side of Fig. 1. The distribution ratio (ratio of the intensities of the two distributed signals) is 1:1. The intensities may be, for example, voltage, current, and / or power. The phases of the two distributed signals are shifted by 90° from each other.

[0033] The phase of the signal before distribution (e.g., the signal input to port 17a) may be the same as the phase of one of the two signals after distribution (e.g., the signal output from port 17c). Also, unlike the above, the phase of the signal before distribution may be different from the phase of both of the two signals after distribution. However, for convenience, in the description of this embodiment, the phase of the signal before distribution may be described as if it were the same as the phase of one of the two signals after distribution. Specifically, the phase of the signals of ports (e.g., ports 17a and 17c) located at the same vertical position in FIG. 1 may be described as if they were the same.

[0034] Although the above explanation takes the case where a signal is input to port 17a as an example, the above operation is similar when signals are input to the other ports 17b to 17d. That is, a signal input to one of the two ports located on one side of the left and right in Fig. 1 is distributed at a distribution ratio of 1:1 and output from the two ports located on the other side of the left and right in Fig. 1. At this time, the phases of the two distributed signals are shifted by 90° from each other.

[0035] As described above, when a phase shift is mentioned, for convenience, it refers to either an advance or a delay, commonly for various components and various signals, etc. In the illustrations, it is assumed that a signal output from a port (e.g., 17d) that is located in a different position in the vertical direction in Fig. 1 from a port (e.g., 17a) to which the signal is input is shifted in phase by 90° with respect to a signal output from a port (e.g., 17c) that is located in the same position in the vertical direction in Fig. 1 as the port to which the signal is input (e.g., 17a).

[0036] Since a hybrid operating as described above is called a 90° hybrid, the relationship between the four ports of the first hybrid 17 can be determined from a description of only some of the ports. For example, assume that port 17d is described as a port from which a signal that is 90° out of phase with respect to the signal distributed from port 17a to port 17c is distributed from port 17a. From this description, it follows that port 17a and the remaining port 17b are located on the same horizontal side of FIG. 1 , with ports 17c and 17d located on the opposite side, and that port 17a and port 17c are located on the same vertical side of FIG. 1 , with ports 17b and 17d located on the opposite side. When the relationship between the four ports is described using the signal distributed from port 17a as described above, the first hybrid 17 does not necessarily need to be configured in such a way that the intended signal is actually input from port 17a. The same applies when using distribution from other ports.

[0037] Furthermore, for example, when there is no need to particularly distinguish between two ports (e.g., 17c and 17d) located on the same left-right side of FIG. 1 , a more concise explanation can be provided. For example, as described in the overview of the embodiment, assume that ports 17c and 17d are ports to which a signal input to port 17a or 17b is distributed. From this explanation, it follows that port 17a and the remaining port 17b are located on the same left-right side of FIG. 1 , and ports 17c and 17d are located on the opposite side. When the relationship between the four ports is described using a signal distributed from port 17a or 17b as described above, the first hybrid 17 does not need to be configured in such a way that the intended signal is actually input from port 17a or 17b. The same applies when describing the distribution from other ports.

[0038] When signals are input to ports 17a and 17b on the left side of FIG. 1 , each signal is distributed as described above, and the distributed signals are then combined. For example, the signal input to port 17a is the first signal, and the signal input to port 17b is the second signal. The signals obtained by distributing the first signal to ports 17c and 17d are the third and fourth signals. The fourth signal is 90° out of phase with the third signal. The signals obtained by distributing the second signal to ports 17c and 17d are the fifth and sixth signals. The fifth signal is 90° out of phase with the sixth signal. In this case, a signal obtained by combining the third and fifth signals is output to port 17c, and a signal obtained by combining the fourth and sixth signals is output to port 17d. While the example has been given of signals being input to the two ports 17a and 17b on the left side of FIG. 1 , the same applies to signals being input to the two ports 17c and 17d on the right side of FIG. 1 .

[0039] As described above, for example, there may be a phase difference between the first signal (input to port 17a) and the third signal (distributed to port 17c without phase shift), and there may be a phase difference between the second signal (input to port 17b) and the sixth signal (distributed to port 17d without phase shift). In this case, the two phase differences are the same. The two phase differences when the signals are in opposite directions are also the same as the two phase differences.

[0040] Although the first hybrid 17 has been described, the above description may be applied to the second hybrid 19 by replacing the term first hybrid 17 with the term second hybrid 19 and by replacing the terms ports 17a to 17d with the terms ports 19a to 19d. The specific configuration of the first hybrid 17 (e.g., the shape and dimensions of the conductors) and the specific configuration of the second hybrid 19 may be the same as or different from each other.

[0041] In the first hybrid 17, the connections between the ports 17a to 17d and the other elements (the antenna terminal 5, the transmit filter 13, and the two receive filters 15) are as already described. In the second hybrid 19, the port 19a is connected to the receive filter 15A. The port 19b is connected to the receive filter 15B. The port 19c is connected to the termination resistor 23 as already described. The port 19d is connected to the receive terminal 9.

[0042] (1.1.3. Termination Resistor) The termination resistor 23 has, for example, a predetermined resistance value, and connects the port 19c of the second hybrid 19 to the reference potential unit 11. This reduces, for example, the reflection of signals flowing from the ports 19a and / or 19b to the port 19c. The resistance value of the termination resistor 23 may be set appropriately depending on the impedance on the second hybrid 19 side relative to the termination resistor 23, but is generally 50Ω.

[0043] The termination resistor 23 may have various configurations, such as a known configuration or an application of a known configuration. For example, although not specifically shown, the termination resistor 23 may be a mounted, embedded, or built-in resistor located on a circuit board (e.g., a multilayer board) (not shown) included in the composite filter 1. The termination resistor 23 may also be a built-in resistor (e.g., a conductor pattern overlapping the upper surface 31a of a piezoelectric element 31b (described later)) located on a piezoelectric substrate 31 (described later). Unlike the example shown in the figure, the termination resistor 23 may also be provided outside the composite filter 1.

[0044] (1.1.4. Others) The overall composite filter 1 may have any structural configuration. For example, the composite filter 1 may be configured as a single chip mounted on a circuit board. Alternatively, the composite filter 1 may be configured as part of a module having a circuit board and multiple chips mounted on the circuit board.

[0045] Furthermore, for example, one chip or part of a module serving as the composite filter 1 may be configured by mounting on a circuit board one or more chips that constitute the first hybrid 17, the second hybrid 19, the transmit filter 13, and the receive filter 15. In this embodiment, two or more of the transmit filter 13 and the receive filters 15A and 15B may be integrated into one chip, or parts of them may be integrated into one chip.

[0046] Furthermore, for example, a chip or part of a module serving as the composite filter 1 may be configured by mounting a chip having the transmit filter 13 and the receive filter 15 on a circuit board (e.g., a multilayer board) while incorporating the first hybrid 17 and the second hybrid 19 into the circuit board. The embedding may be by embedding the chip, or by building the hybrids into the circuit board using the conductors of the circuit board.

[0047] The antenna terminal 5, the transmitting terminal 7, the receiving terminal 9, and the reference potential section 11 may be included in the composite filter 1, or may be provided outside the composite filter 1. Furthermore, various terminals may not be provided, such as in a configuration in which an antenna built into a multilayer substrate and a first hybrid 17 built into the multilayer substrate are directly connected without intervening terminals, and the antenna terminal 5 is not provided.

[0048] The reference potential portion 11 is a portion (conductor) to which a reference potential is applied. More specifically, it may be, for example, a terminal to which the reference potential is applied, or a configuration other than a terminal (for example, a shield). A representative example of the reference potential is 0 V, but it is not limited to this.

[0049] In the drawings, the reference potential section 11 may be shown at multiple positions. The reference potential sections 11 shown at multiple positions may actually be different from each other, or may be considered to be shown separately from each other simply for convenience of illustration. Furthermore, two or more reference potential sections 11 as different from each other may or may not be connected to each other within the composite filter 1.

[0050] (1.2. Operation of the Composite Filter (Excluding Operation of the Trap)) The operation (function) of the composite filter will be described below. However, the function of the trap 24 will not be mentioned here.

[0051] (1.2.1. Transmission of Transmission Signal) We have already described the outline of the operation in which a signal (transmission signal) input from outside the composite filter 1 to the transmission terminal 7 is transmitted to the antenna terminal 5. More details are as follows.

[0052] The signal filtered by the transmit filter 13 and having a frequency within the passband of the transmit filter 13 is input to port 17b of the first hybrid 17. The signal input to port 17b is distributed to ports 17c and 17d. The phase of the signal distributed to port 17c is shifted by 90° from the phase of the signal distributed to port 17d.

[0053] The signal distributed to and output from port 17c has a frequency within the pass band (transmission band) of the transmission filter 13, and is therefore reflected by the reception filter 15A, which has a pass band (reception band) different from the transmission band. Therefore, the signal output from port 17c returns to port 17c. Similarly, the signal distributed to and output from port 17d is reflected by the reception filter 15B and returns to port 17d.

[0054] The signal returning to port 17c is distributed to ports 17a and 17b. At this time, the phase of the signal distributed to port 17b is shifted by 90° from the phase of the signal distributed to port 17a. Similarly, the signal returning to port 17d is distributed to ports 17a and 17b. At this time, the phase of the signal distributed to port 17a is shifted by 90° from the phase of the signal distributed to port 17b.

[0055] The signal that passes from the transmit filter 13 through ports 17b and 17c in this order, is reflected by the receive filter 15A, returns to port 17c and is transmitted to port 17a, and the signal that passes from the transmit filter 13 through ports 17b and 17d in this order, is reflected by the receive filter 15B, returns to port 17d and is transmitted to port 17a are both in phase because they have a phase shift of 90° once. Therefore, the two signals are combined and output from port 17a to the antenna terminal 5.

[0056] On the other hand, the signal that passes from the transmit filter 13 through ports 17b and 17d in this order, is reflected by the receive filter 15B, returns to port 17d, and is transmitted to port 17b does not have a 90° phase shift. Similarly, the signal that passes from the transmit filter 13 through ports 17b and 17c in this order, is reflected by the receive filter 15A, returns to port 17c, and is transmitted to port 17b has a 90° phase shift twice. Therefore, the two signals are out of phase with each other and cancel each other out, so they are not output from port 17b.

[0057] For convenience of explanation, it has been stated that the signal returned to port 17c or 17d is distributed to port 17b, but the fact that no signal is output from port 17b means that no signal is actually distributed to port 17b. In other words, ignoring insertion loss, the strength of the signal output to antenna terminal 5 is the same as the strength of the signal input to transmission terminal 7.

[0058] When focusing only on the first hybrid 17, there is no electrical continuity between the port 17b to which the transmit filter 13 is connected and the port 17a to which the antenna terminal 5 is connected. As described above, the signal from the transmit filter 13 is transmitted to the antenna terminal 5 by utilizing reflection at the receive filter 15. Even in this embodiment, for convenience, the transmit filter 13 may be expressed as being connected to the antenna terminal 5 via the first hybrid 17.

[0059] (1.2.2. Transmission of Received Signal) A signal (received signal) input from the antenna terminal 5 to port 17a of the first hybrid 17 is distributed to ports 17c and 17d. The phase of the signal distributed to port 17d is shifted by 90° from the phase of the signal distributed to port 17c.

[0060] The signal distributed to port 17c and output from port 17c passes through receiving filter 15A and is input to port 19a of second hybrid 19. The signal distributed to port 17d and output from port 17d passes through receiving filter 15B and is input to port 19b of second hybrid 19.

[0061] A signal input to port 19a is distributed to ports 19c and 19d. At this time, the phase of the signal distributed to port 19d is shifted by 90° from the phase of the signal distributed to port 19c. Similarly, a signal input to port 19b is distributed to ports 19c and 19d. At this time, the phase of the signal distributed to port 19c is shifted by 90° from the phase of the signal distributed to port 19d.

[0062] The signal transmitted from antenna terminal 5 to port 19d via ports 17a and 17c, receiving filter 15A, and port 19a in this order, and the signal transmitted from antenna terminal 5 to port 19d via ports 17a and 17d, receiving filter 15B, and port 19b in this order, are both in phase because they have a phase shift of 90° once. Therefore, the two signals are combined and output from port 19d to receiving terminal 9.

[0063] On the other hand, the signal transmitted from antenna terminal 5 to port 19c via ports 17a and 17c, receiving filter 15A, and port 19a in this order does not have a 90° phase shift. Also, the signal transmitted from antenna terminal 5 to port 19c via ports 17a and 17d, receiving filter 15B, and port 19b in this order has a 90° phase shift twice. Therefore, the two signals are out of phase and cancel each other out, so they are not output from port 19c.

[0064] For convenience of explanation, it has been stated that a signal input to port 19a or 19b is distributed to port 19c, but the fact that no signal is output from port 19c means that no signal is actually distributed to port 19c. In other words, ignoring insertion loss, the strength of the signal output to receiving terminal 9 is the same as the strength of the signal input to antenna terminal 5.

[0065] (1.2.3. Example of Reduction of Nonlinear Distortion) In the transmit filter 13 and / or the receive filter 15, nonlinear distortion (distorted signal) such as intermodulation distortion may occur due to its nonlinearity. An example of how nonlinear distortion is reduced by using a hybrid will be described. Note that the reduction of nonlinear distortion described here is due to the hybrid itself, not the trap 24.

[0066] It is assumed that two signals are input to the transmitting terminal 7 and that nonlinear distortion occurs in the transmitting filter 13. It is assumed that this nonlinear distortion has a frequency within the receiving band of the receiving filter 15 and can pass through the receiving filter 15.

[0067] The nonlinear distortion input from the transmit filter 13 to the port 17b is distributed to the ports 17c and 17d. The phase of the nonlinear distortion distributed to the port 17c is shifted by 90° from the phase of the nonlinear distortion distributed to the port 17d.

[0068] The nonlinear distortion distributed to port 17c and output from port 17c is input to port 19a of second hybrid 19 via receive filter 15A. The nonlinear distortion distributed to port 17d and output from port 17d is input to port 19b of second hybrid 19 via receive filter 15B.

[0069] Nonlinear distortion input to port 19a is distributed to ports 19c and 19d. At this time, the phase of the nonlinear distortion distributed to port 19d is shifted by 90° from the phase of the nonlinear distortion distributed to port 19c. Similarly, nonlinear distortion input to port 19b is distributed to ports 19c and 19d. At this time, the phase of the nonlinear distortion distributed to port 19c is shifted by 90° from the phase of the nonlinear distortion distributed to port 19d.

[0070] The nonlinear distortion propagated from the transmit filter 13 to port 19d via ports 17b and 17c, receive filter 15A, and port 19a in this order has a phase shift of 90° twice. The nonlinear distortion propagated from the transmit filter 13 to port 19d via ports 17b and 17d, receive filter 15B, and port 19b in this order does not have a phase shift of 90°. Therefore, the two nonlinear distortions are out of phase with each other, cancel each other out, and are not output from port 19d. In other words, the nonlinear distortion is not input to the receive terminal 9.

[0071] On the other hand, the nonlinear distortion transmitted from the transmit filter 13 to port 19c via ports 17b and 17c, receive filter 15A, and port 19a in this order, and the nonlinear distortion transmitted from the transmit filter 13 to port 19c via ports 17b and 17d, receive filter 15B, and port 19b in this order, are both in phase because they are shifted by 90 degrees once. Therefore, the two signals are combined and input from port 19c to the termination resistor 23. Consequently, the nonlinear distortion is released to the reference potential section 11 via the termination resistor 23.

[0072] Next, assume that nonlinear distortion occurs in receive filter 15 when a transmit signal that is input from outside to transmit terminal 7 and passes through transmit filter 13 and first hybrid 17 is reflected by receive filter 15. The phase relationship of the nonlinear distortion that occurs in receive filters 15A and 15B at this time is the same as the phase relationship of the nonlinear distortion that occurs in transmit filter 13 and propagates to receive filters 15A and 15B described above. Therefore, using the same principle as above, the nonlinear distortion is absorbed by termination resistor 23 (it is not input to receive terminal 9).

[0073] (1.3. Trap) As already mentioned, the trap 24 allows signals having frequencies included in the reception band to escape to the reference potential section 11. In other words, the provision of the trap 24 makes it relatively easier for signals having frequencies included in the reception band to flow to the reference potential section 11 compared to signals having frequencies outside the reception band (for example, within the transmission band). Various configurations are possible for achieving this effect. In the first embodiment, they are as follows.

[0074] 2 is a schematic diagram showing a part of the composite filter 1A according to the first embodiment (from the transmitting terminal 7 to the first hybrid 17). The trap 24 according to the first embodiment may be referred to as trap 24A.

[0075] In this figure, a ladder-type filter is illustrated as the transmit filter 13. That is, the transmit filter 13 has a plurality (or one) of series resonators 29S (series arms from another perspective) and a plurality (or one) of parallel resonators 29P (parallel arms from another perspective) connected in a ladder configuration. The plurality of series resonators 29S are connected in series from the input side (transmit terminal 7 side) to the output side (first hybrid 17 side). The plurality of parallel resonators 29P connect different positions on the signal path from the input side to the output side to the reference potential unit 11.

[0076] The composite filter 1A has a trap resonator 29T as the trap 24A. The trap resonator 29T is located between the first hybrid 17 side (output side) of the transmit filter 13 and the reference potential unit 11 (connected in series with the transmit filter 13 and the reference potential unit 11). The impedance (absolute value) of the trap resonator 29T becomes a minimum value at the resonant frequency. The resonant frequency of the trap resonator 29T is located within the receive band. Therefore, of the nonlinear distortion generated in the transmit filter 13, signals having frequencies included in the receive band (the resonant frequency of the trap resonator 29T and frequencies nearby) flow to the reference potential unit 11 via the trap resonator 29T.

[0077] In terms of the connection mode, the trap resonator 29T is similar to the parallel resonator 29P (the illustrated transmit filter 13 does not include this parallel resonator 29P) that is located closer to the output than all of the series resonators 29S. However, while the parallel resonator 29P of the transmit filter 13 has a resonant frequency in the transmit band, the trap resonator 29T has a resonant frequency in the receive band. In other words, the two have different characteristics.

[0078] Although not specifically shown, the trap 24 may have two or more trap resonators 29T connected in parallel. In this case, the resonant frequencies (and / or antiresonant frequencies) of the two or more trap resonators 29T may be the same or different from one another. In the following description, a trap resonator 29T consisting of a plurality of resonators (a plurality of split resonators 29Tb) connected in series may be described. The description of the resonant frequencies and antiresonant frequencies of the plurality of resonators connected in series may be applied to the resonant frequencies and antiresonant frequencies of a plurality of resonators connected in parallel, unless a contradiction occurs.

[0079] The trap resonator 29T may have any configuration. For example, the trap resonator 29T may be a resonator that utilizes the resonance of a piezoelectric material, a resonator that utilizes the resonance of a dielectric material, an LC resonant circuit that combines an inductor and a capacitor, or a combination of two or more of these. A resonator that utilizes a piezoelectric material may, for example, utilize an elastic wave, or may not utilize an elastic wave (e.g., utilizes a piezoelectric vibrator). The elastic wave may be, for example, a surface acoustic wave (SAW), a bare acoustic wave (BAW), a boundary acoustic wave, or a plate wave. In the description of the embodiments, unless otherwise specified, an example in which the trap resonator 29T is configured as an elastic wave resonator may be used.

[0080] (1.3.2. Example of the Configuration of the Resonator Included in the Trap) FIG. 3 is a schematic diagram showing an example of the configuration of the trap resonator 29T.

[0081] The trap resonator 29T in the illustrated example may be referred to as a trap resonator 29Ta. The trap resonator 29Ta has a plurality of split resonators 29Tb (four in the illustrated example) connected in series between the output side of the transmit filter 13 and the reference potential unit 11. Therefore, for example, the possibility of high pressure occurring locally in the trap resonator 29Ta can be reduced by pressure division. Note that, unlike the description here, each split resonator 29Tb may be regarded as an example of a trap resonator 29T.

[0082] Each split resonator 29Tb is configured by an acoustic wave resonator (details will be described in Section 4). In this case, the specific configuration of the split resonator 29Tb is arbitrary. For example, in the illustrated example, adjacent split resonators 29Tb share a part of the IDT electrode 33 (a bus bar described later) and a part of the reflector 35 (a bus bar described later). However, such sharing is not required.

[0083] Note that a resonator configured with multiple split resonators connected in series may also be applied to resonators other than the trap resonator 29T (for example, resonators of the transmit filter 13 and / or the receive filter 15). The multiple series resonators 29S and the multiple split resonators 29Tb have in common the fact that the resonators are connected in series with each other. Whether or not a split resonator is applied to the series resonator 29S can be determined based on the connection positions of one or more parallel resonators 29P with respect to a signal path including the series resonator 29S. In other words, when multiple resonators are included in one region (one series arm) of the signal path defined by one or more parallel resonators 29P, the multiple resonators are split resonators.

[0084] The resonant frequency of each split resonator 29Tb is located within the reception band. Consequently, the resonant frequency of the trap resonator 29Ta is also located within the reception band. When a resonator used in a ladder-type filter or the like is composed of multiple split resonators, the characteristics (e.g., resonant frequency) are usually approximately the same. In the trap resonator 29Ta, the characteristics of the split resonators 29Tb may be approximately the same, or may differ to the extent that they are not approximately the same.

[0085] The resonant frequencies of the multiple (some or all) split resonators 29Tb may be the same as each other or may be different from each other. In the latter embodiment, in the characteristics of the trap resonator 29Ta as a whole, the minimum value of the absolute value of the impedance (resonant point) may appear at multiple frequencies within the reception band or at a single frequency. In other words, the trap resonator 29Ta may have multiple resonant frequencies or may have a single resonant frequency. Note that the anti-resonant frequencies described below may also be the same as each other or different from each other in the multiple (some or all) split resonators 29Tb.

[0086] The number of split resonators 29Tb (the number of divisions of the trap resonator 29Ta) is arbitrary. For example, the number of divisions may be 2 to 6 (4 in the illustrated example). Also, for example, assume that the transmit filter 13 is a ladder-type filter. In this case, the number of divisions of the trap resonator 29Ta may be less than, equal to, or greater than the number of divisions of the series resonator 29S located closest to the output side of the transmit filter 13 and / or the number of divisions of the parallel resonator 29P located closest to the output side of the transmit filter 13. Note that an embodiment in which the number of divisions of the trap resonator 29Ta is greater than the number of divisions of the series resonator 29S and / or the parallel resonator 29P includes an embodiment in which the series resonator 29S and / or the parallel resonator 29P are not divided.

[0087] 4 is a diagram showing an example of the characteristics of the trap resonator 29T. The explanation here may naturally be applied to the trap resonator 29Ta, but may also be applied to each split resonator 29Tb as long as no contradiction occurs.

[0088] In Figure 4, the horizontal axis represents frequency f (Hz), with higher frequencies toward the right. The vertical axis on the left represents transmission characteristics (dB) (labeled "S21 (dB)" in the figure), with values ​​increasing toward the top of the figure (signals pass more easily). The vertical axis on the right represents the absolute value of impedance |Z| (Ω), with values ​​increasing toward the top of the figure.

[0089] The line LBT indicates the transmission characteristic of the transmit filter 13. The line LBR indicates the transmission characteristic of the receive filter 15. In the transmit filter 13, the value of the transmission characteristic is large in the transmit band BT. In the receive filter 15, the value of the transmission characteristic is large in the receive band BR. In the example shown in the figure, the receive band is located on the lower frequency side than the transmit band. However, the relationship between the two bands may be reversed. The pass bands (receive band and transmit band) may be defined as appropriate, but may be, for example, frequency bands in which the transmission characteristic is between -3 dB and 0 dB.

[0090] The line X1 indicates |Z| of the trap resonator 29T. The impedance characteristics of the trap resonator 29T, which is an acoustic wave resonator, include a resonance point X1r where |Z| is a minimum value and an anti-resonance point X1a where |Z| is a maximum value. The frequency at which the resonance point X1r appears is the resonance frequency fxr. The frequency at which the anti-resonance point X1a appears is the anti-resonance frequency fxa. In the illustrated example, the anti-resonance frequency fxa is located on the higher frequency side of the resonance frequency fxr (from another perspective, on the same side as the transmission band relative to the reception band). However, the relationship between the resonance frequency fxr and the anti-resonance frequency fxa (whether it is on the higher frequency side or not and / or on the same side as the transmission band or not) may be reversed.

[0091] The resonant frequency fxr may be located at any frequency within the reception band BR. For example, the resonant frequency fxr may be the frequency of nonlinear distortion (e.g., PIM3) included in the reception band, or a frequency near that frequency, or may be away from such a frequency. In an embodiment in which multiple resonance points appear due to multiple split resonators 29Tb, all of the resonant frequencies fxr may be located at or near the frequency of the nonlinear distortion, only some of the resonant frequencies fxr may be located at or near the frequency of the nonlinear distortion, or all of the resonant frequencies fxr may be away from the frequency of the nonlinear distortion.

[0092] Furthermore, for example, when the reception band BR is divided into thirds or fifths, the resonant frequency fxr may be located in the center band (as in the illustrated example), or in another band on the low frequency side or another band on the high frequency side. In an embodiment in which multiple resonance points appear due to multiple split resonators 29Tb, multiple (all) resonant frequencies fxr may fall within the center band when the reception band BR is divided into thirds or fifths, or may fall within another band on the low frequency side or another band on the high frequency side, or may be distributed over two or more bands or all bands. Furthermore, some resonant frequencies fxr may be located outside the reception band BR.

[0093] The value of the antiresonant frequency fxa of the trap resonator 29T is arbitrary. For example, the antiresonant frequency fxa may be located within the reception band BR or outside the reception band BR (as shown in the example). In the latter case, the frequency difference between the antiresonant frequency fxa and the reception band BR (the end on the antiresonant frequency fxa side) is also arbitrary. For example, the frequency difference may be equal to or less than half the bandwidth of the reception band BR, equal to or more than half, or equal to or more than one time. When multiple antiresonant points appear due to multiple split resonators 29Tb, the aspect of whether the antiresonant frequency fxa is located inside or outside the reception band BR as described above may be the same for all antiresonant frequencies fxa, or may differ between some of the antiresonant frequencies fxa.

[0094] Furthermore, for example, in a configuration in which the anti-resonance frequency fxa is located outside the reception band BR and the side on which the anti-resonance frequency fxa is located relative to the reception band BR is the same side (the higher frequency side in the illustrated example) as the side on which the transmission band BT is located relative to the reception band BR, the anti-resonance frequency fxa may be located within the transmission band BT (in the illustrated example), or may be located outside the transmission band BT (on the reception band BR side or the opposite side). In a configuration in which multiple anti-resonance points appear, all of the anti-resonance frequencies fxa may be located within the transmission band BT, some of the anti-resonance frequencies fxa may be located within the transmission band BT, or all of the anti-resonance frequencies fxa may be located outside the transmission band BT.

[0095] In an embodiment in which the anti-resonance frequency fxa is located within the transmission band BT, when the transmission band BT is divided into thirds or fifths, the anti-resonance frequency fxa may be located in the center band (as in the illustrated example), or in another band on the low-frequency side or another band on the high-frequency side. Also, in an embodiment in which multiple anti-resonance points appear due to multiple split resonators 29Tb, multiple (for example, all) anti-resonance frequencies fxa may fall within the center band when the transmission band BT is divided into thirds or fifths, or may fall within another band on the low-frequency side or another band on the high-frequency side, or may be distributed over two or more bands or all bands.

[0096] 4 also shows the impedance characteristics of the series resonator 29S and the parallel resonator 29P to provide a better understanding of the impedance characteristics of the trap resonator 29T. Here, an example is taken in which the transmit filter 13 and the receive filter 15 are each configured as a ladder filter.

[0097] The line LTS indicates |Z| of the series resonator 29S of the transmit filter 13. The line LTP indicates |Z| of the parallel resonator 29P of the transmit filter 13. Similar to the trap resonator 29T, these resonators also have resonance points TSr and TPr and anti-resonance points TSa and TPa. Each resonator is configured so that the resonant frequency of the series resonator 29S (the frequency of the resonance point TSr) and the anti-resonant frequency of the parallel resonator 29P (the frequency of the anti-resonance point TPa) generally coincide with each other. This forms a ladder-type filter (transmit filter 13) whose passband (transmission band BT) is slightly narrower than the frequency band from the resonant frequency of the parallel resonator 29P (the frequency of the resonance point TPr) to the anti-resonant frequency of the series resonator 29S (the frequency of the anti-resonance point TSa).

[0098] The same applies to the receive filter 15. That is, a line LRS indicates |Z| of the series resonator 29S of the receive filter 15. A line LRP indicates |Z| of the parallel resonator 29P of the receive filter 15. These resonators also have resonance points RSr and RPr and anti-resonance points RSa and RPa. Each resonator is configured so that the resonant frequency of the series resonator 29S (the frequency of the resonance point RSr) and the anti-resonant frequency of the parallel resonator 29P (the frequency of the anti-resonance point RPa) generally match. This forms a ladder-type filter (receive filter 15) whose passband (receive band BR) is slightly narrower than the frequency band from the resonant frequency of the parallel resonator 29P (the frequency of the resonance point RPr) to the anti-resonant frequency of the series resonator 29S (the frequency of the anti-resonance point RSa).

[0099] As described above, the connection relationship of the trap resonator 29T is the same as or similar to the connection relationship of the parallel resonator 29P of the transmit filter 13. However, the resonant frequency fxr of the trap resonator 29T is located in the receive band BR, whereas the resonant frequency (frequency of the resonant point TPr) of the parallel resonator 29P of the transmit filter 13 is located in the transmit band BT (its center).

[0100] In the series resonator 29S or the parallel resonator 29P, the frequency difference between the resonant frequency fxr and the antiresonant frequency fxa (referred to as Δf in this paragraph) is generally slightly larger than half the bandwidth of the passband. There is no such restriction for the trap resonator 29T. In the illustrated example, Δf is larger than the Δf of the series resonator 29S or the parallel resonator 29P. The specific magnitude is arbitrary, but the former may be set to be at least twice the Δf of the latter, for example. Unlike the illustrated example, the Δf of the trap resonator 29T may be equal to or smaller than the Δf of the series resonator 29S or the parallel resonator 29P.

[0101] (1.4. Characteristics of Comparative Examples and Examples) With respect to the first embodiment, the characteristics of the PIM 3 in the composite filters according to the comparative examples and examples will be shown.

[0102] Here, we considered a situation in which two signals having frequencies (f1 or f2) within the transmission band were input to the transmission filter 13, resulting in a PIM3 having a frequency of 2f1-f2. We also assumed various values ​​for f1 and f2 and investigated the PIM3 level. Specifically, we set f1 = 1805 + X (MHz), f2 = 1852.5 + X (MHz), and 2f1-f2 = 1757.5 + X (MHz). Various values ​​(MHz) greater than or equal to 0 were set for X. In the comparative example, an inductor was provided instead of the trap resonator 29T in the embodiment (composite filter 1A).

[0103] 5 is a diagram showing the PIM 3 of the composite filter 1A according to the comparative example and the example. In this diagram, the horizontal axis represents the frequency 2f1-f2 (MHz) of the PIM 3. The vertical axis represents the level (dBc) of the PIM 3 flowing to the receiving terminal 9.

[0104] Line L1 shows the PIM3 value obtained by experiment for the comparative example, line L2 shows the PIM3 value obtained by simulation calculation for the comparative example, and line L3 shows the PIM3 value obtained by simulation calculation for the example.

[0105] As shown in Fig. 5, the PIM3 is reduced in the example compared to the comparative example. As described in Section 1.2.3, the composite filter 1A is configured to be able to reduce nonlinear distortion by the first hybrid 17 and the second hybrid 19. Even in such a configuration, it was confirmed that the trap resonator 29T can further reduce nonlinear distortion.

[0106] (2. Second Embodiment) The composite filter 1 according to the second embodiment will be described below. The composite filter 1 according to the second embodiment may be referred to as a composite filter 1B (reference numeral shown in FIG. 6). The composite filter 1B differs from the composite filter 1A of the first embodiment in the configuration of the trap 24. Specifically, this is as follows.

[0107] (2.1. Trap) Fig. 6 is a schematic diagram showing a part of a composite filter 1B according to a second embodiment, and corresponds to Fig. 2 of the first embodiment. The trap 24 according to the second embodiment may be referred to as trap 24B.

[0108] The trap 24B has a trap filter 51 located between the output side (first hybrid 17 side) of the transmit filter 13 and the reference potential unit 11. The trap filter 51 passes signals having frequencies within the receive band. This allows signals having frequencies included in the receive band to escape to the reference potential unit 11.

[0109] The trap filter 51 may be of any suitable type, such as a band-pass filter, a low-pass filter, or a high-pass filter. In the description of the embodiments, unless otherwise specified, a band-pass filter is used. For example, the pass band of the band-pass filter at least partially overlaps with at least a portion of the receive band, but does not entirely overlap with the transmit band. Because the pass band of the transmit filter 13 and the pass band of the trap filter 51 do not overlap, the combination of the transmit filter 13 and the trap filter 51 can be considered as a branching filter 55 (duplexer or diplexer).

[0110] The trap 24B may have other appropriate components in addition to the trap filter 51. For example, the trap 24B may have a termination resistor 53 between the trap filter 51 and the reference potential section 11. Although not particularly shown, the trap 24B may have a matching circuit (not shown) at an appropriate position (however, this may be considered as part of the trap filter 51).

[0111] The trap filter 51 may have any configuration. The descriptions of the configurations of the transmit filter 13 and the receive filter 15 may be applied to the trap filter 51. To be clear, the trap filter 51 may include, for example, a piezoelectric filter, a dielectric filter, and / or an LC filter. The piezoelectric filter may include an acoustic wave filter. The acoustic wave filter may be, for example, a ladder filter and / or a multimode filter. The type of acoustic wave is arbitrary. Furthermore, in an actually fabricated composite filter 1B, the type of configuration of the trap filter 51 as described above may be the same as or different from that of the other filters (13 and 15). In FIG. 6 , a ladder filter is illustrated as the trap filter 51. The descriptions of the ladder filter described above may be applied to the trap filter 51, unless a contradiction arises.

[0112] The pass band of the trap filter 51 (band-pass filter) may be set arbitrarily, as long as at least a portion of it overlaps at least a portion of the reception band and does not overlap the transmission band. Specifically, for example, the pass band of the trap filter 51 may match the reception band (they may overlap entirely), may be a portion of the reception band, may be wider than the reception band and include the entire reception band, or may have a portion of the low-frequency side or high-frequency side overlap with a portion of the high-frequency side of the reception band.

[0113] Furthermore, for example, in an aspect in which the overlapping range between the trap filter 51 and the reception band is a part of the reception band, the width of the overlapping range may be less than half, or may be equal to or greater than half, or may be equal to or greater than two-thirds of the width of the reception band. Furthermore, when the reception band is divided into thirds or fifths, the overlapping range may include the central band, or may include one or more bands on the low frequency side or one or more bands on the high frequency side, with or without including the central band.

[0114] When the pass band and the receive band of the trap filter 51 are roughly the same, the configuration of the trap filter 51 may be the same as or different from the configuration of the receive filter 15. As described above, the trap filter 51 and the transmit filter 13 can be regarded as a duplexer 55, and a configuration (e.g., a chip) actually fabricated as the duplexer 55 may be used in the composite filter 1B.

[0115] The trap filter 51, which is a low-pass filter, is used, for example, in an embodiment in which the reception band is lower than the transmission band, as shown in FIG. 4 . The cutoff frequency is, for example, spaced apart from the low-frequency end of the reception band toward the high-frequency end. This allows the low-pass filter to pass signals having frequencies included in at least a portion of the reception band. Furthermore, the cutoff frequency is, for example, set lower than the transmission band. This reduces the likelihood that signals having frequencies included in the transmission band will pass through the low-pass filter. The specific value of the cutoff frequency is arbitrary. For example, the cutoff frequency may be located lower or higher than the center frequency of the reception band, or may be located within the reception band or higher than the reception band.

[0116] The trap filter 51, which is a high-pass filter, is used, for example, in a configuration in which the reception band is higher than the transmission band, as opposed to the example shown in FIG. 4 . The cutoff frequency is, for example, spaced apart from the high-frequency end of the reception band toward the low-frequency end. This allows the high-pass filter to pass signals having frequencies included in at least a portion of the reception band. Furthermore, the cutoff frequency is, for example, set higher than the transmission band. This reduces the likelihood that signals having frequencies included in the transmission band will pass through the high-pass filter. The specific value of the cutoff frequency is arbitrary. For example, the cutoff frequency may be located higher or lower than the center frequency of the reception band, or may be located within the reception band or lower than the reception band.

[0117] As can be understood from the above description, when the trap filter 51 is a ladder-type filter, the series resonator 29S of the trap filter 51 connects the output side (first hybrid 17 side) of the transmit filter 13 and the reference potential unit 11 (more precisely, the termination resistor 53), and has a resonant frequency located in the receive band. Therefore, the series resonator 29S of the trap filter 51 may be regarded as a type of trap resonator 29T.

[0118] When the trap filter 51 is a longitudinally coupled multimode filter, the plurality of resonators (resonators 29 in FIG. 10 minus reflectors 35, as will be described later) of the trap filter 51 include at least one resonator that connects the output side of the transmit filter 13 to the reference potential section 11 (more precisely, the termination resistor 53), although this resonator has a resonant frequency in the receive band. Therefore, this resonator may also be considered as a type of trap resonator 29T.

[0119] In other embodiments, when the trap filter 51 connects the output side of the transmit filter 13 and the reference potential section 11 and has a resonator whose resonance frequency is located in the pass band, the resonator may be regarded as a type of trap resonator 29T.

[0120] The structure of the composite filter 1B may be variously configured, similar to the structure of the composite filter 1A. The description of the structures of the transmit filter 13 and the receive filter 15 may be used to describe the structure of the trap filter 51. To be clear, the trap filter 51 may be a chip mounted on a circuit board (e.g., a multilayer board), or may be built into the circuit board. Part or all of the trap filter 51 may be integrated into a single chip together with part or all of the other filters (13 and / or 15).

[0121] The explanation of the termination resistor 23 may be applied to the termination resistor 53, except for its specific connection destination. To be clear, the resistance value of the termination resistor 53 may be set appropriately depending on the impedance on the trap filter 51 side of the termination resistor 53, and is generally 50 Ω. The termination resistor 53 may be provided on the circuit board on which the filter (13, 15, and / or 51) is mounted, or on the piezoelectric substrate 31 (described later) that constitutes the filter. Furthermore, the termination resistor 53 may be configured as a mounted, embedded, or built-in resistor.

[0122] (2.2. Characteristics of Comparative Example and Example) The characteristics of the comparative example and example (composite filter 1B) for the second embodiment are shown below. The characteristics shown below were obtained by simulation calculation.

[0123] Here, as in the first embodiment, we considered a situation in which two signals having frequencies within the transmission band are input to the transmission filter 13, resulting in PIM3 of 2f1 - f2. Also, as in the first embodiment, we set f1 = 1805 + X (MHz), f2 = 1852.5 + X (MHz), and 2f1 - f2 = 1757.5 + X (MHz). However, Figures 7A and 7B show the characteristics when X is fixed to a predetermined value. Figures 8A and 8B show the characteristics when X is set to various values. In the comparative example, the trap 24B was eliminated from the composite filter 1B.

[0124] 7A is a diagram showing the transmission characteristics of the comparative example and the working example. The horizontal axis represents frequency f (GHz). The vertical axis represents transmission characteristics (dB). In this diagram, approximately 1.7 GHz to 1.8 GHz corresponds to the reception band. Approximately 1.8 GHz to 1.9 GHz corresponds to the transmission band.

[0125] Lines L5Tt and L5Tr show the characteristics of the comparative example. Lines L6Tt and L6Tr show the characteristics of the embodiment. Lines L5Tt and L6Tt show the transmission characteristics of the transmission path 2T. Since the two lines roughly overlap in the transmission band, symbols are assigned in the reception band. Lines L5Tr and L6Tr show the transmission characteristics of the reception path 2R. Since the two lines roughly overlap in the reception band, symbols are assigned in the transmission band.

[0126] As shown in this figure, the transmission characteristics of the transmission path 2T in the reception band (including the frequency of PIM3) are lower in the example than in the comparative example. In other words, the transmission path 2T of the example is less likely to pass signals in the reception band. This improves the characteristics of the composite filter 1B as a duplexer.

[0127] 7B is a diagram showing the isolation characteristics of the comparative example and the example. The horizontal axis represents frequency f (GHz). The vertical axis represents isolation (dB). Line L5I represents the characteristics of the comparative example. Line L6I represents the characteristics of the example.

[0128] As shown in this figure, the example has improved isolation compared to the comparative example at or near the frequency of PIM 3 (roughly 1.75 GHz to 1.76 GHz). In other words, the composite filter 1B has improved characteristics as a duplexer.

[0129] 8A is a diagram showing the characteristics of the PIM 3 of the comparative example and the working example. The horizontal axis represents the frequency 2f1-f2 (MHz) of the PIM 3 (expressed as "1757.5+X (MHz)"). The vertical axis represents the level (dBm) of the PIM 3 flowing to the receiving terminal 9. Line L5P represents the characteristics of the comparative example. Line L6P represents the characteristics of the working example.

[0130] As shown in this figure, the example reduces the PIM3 flowing to the receiving terminal 9 compared to the comparative example. Therefore, similar to the first embodiment, the composite filter 1B is originally configured to reduce nonlinear distortion, but it was confirmed that the trap filter 51 can further reduce nonlinear distortion.

[0131] 8B is a diagram showing the characteristics of the PIM3 of the comparative example and the working example. The horizontal axis is the same as in FIG. 8A. The vertical axis shows the level of the PIM3 output from the trap filter 51 to the reference potential unit 11 (denoted as "PIM3-T (dBm)"). The line in the diagram shows the characteristics of the working example.

[0132] 8A and 8B, it can be seen that there is a correlation between the level of PIM3 flowing to the receiving terminal 9 and the level of PIM3 flowing to the trap filter 51. In other words, it was confirmed that the reduction in PIM3 flowing to the receiving terminal 9 is due to the trap filter 51.

[0133] 3. Third Embodiment FIG. 9 is a circuit diagram showing the configuration of a composite filter 301 according to a third embodiment.

[0134] In short, the composite filter 301 has a configuration in which the second hybrid 19 is eliminated from the composite filter 1 of the first or second embodiment, receiving terminals 9A and 9B corresponding to the receiving filters 15A and 15B, respectively, are provided, and a 90° phase shifter 20 (hereinafter simply referred to as the “phase shifter 20”) is provided between the receiving filter 15B and the receiving terminal 9B. The configuration of the trap 24 may be the same as that of the first or second embodiment.

[0135] The operation related to the transmission of a transmission signal input to the transmitting terminal 7 from outside the composite filter 301 is the same as in the first embodiment. The operation related to the transmission of a reception signal input to the antenna terminal 5 from outside the composite filter 301 is the same as in the first embodiment until the signal passes through the receiving filters 15A and 15B. Thereafter, the phase of the reception signal that passes through the receiving filter 15B is shifted by 90° by the phase shifter 20. As a result, the phase of the reception signal that passes through the receiving filter 15B is shifted by 180° relative to the phase of the reception signal that passes through the receiving filter 15A, taking into account the phase shift caused by the first hybrid 17. As a result, the two reception signals are output from the two receiving terminals 9 (9A and 9B) as balanced signals that indicate the signal strengths based on the potential difference between them.

[0136] In the composite filter 301, the signal (e.g., nonlinear distortion) distributed from the transmit filter 13 to the receive filters 15A and 15B by the first hybrid 17 is finally converted into an in-phase signal by the phase shifter 20 and output to the receive terminals 9A and 9B. Therefore, in principle, the signal from the transmit filter 13 does not affect the potential difference of the balanced signal described in the previous paragraph. In other words, the nonlinear distortion output from the receive terminals 9A and 9B to the outside is substantially reduced.

[0137] (4. Examples of Elastic Wave Resonators) As described above, the trap resonator 29T (29Ta), the split resonator 29Tb, and the series resonators 29S and / or parallel resonators 29P constituting the filters (13, 15, and / or 51) may be elastic wave resonators. An example of an elastic wave resonator will be described below. Note that the above-described various resonators and elastic wave resonators are collectively referred to as resonators 29.

[0138] FIG. 10 is a plan view schematically showing the configuration of the resonator 29. As shown in FIG.

[0139] Although either direction of the resonator 29 may be considered to be the up or down direction, in the following description, for convenience, an orthogonal coordinate system consisting of the D1-axis, D2-axis, and D3-axis is attached to the drawings, and the +D3 side (the side facing the page) is considered to be the up direction, and terms such as the top surface or the bottom surface may be used. The D1-axis is defined to be parallel to the propagation direction of an elastic wave propagating along the top surface of the piezoelectric body (described later), the D2-axis is defined to be parallel to the top surface of the piezoelectric body and perpendicular to the D1-axis, and the D3-axis is defined to be perpendicular to the top surface of the piezoelectric body.

[0140] The resonator 29 is configured as a so-called one-port acoustic wave resonator. The resonator 29 receives a signal from one of two terminals 28, which are shown schematically on both the left and right sides of FIG. 10 , and outputs the signal from the other of the two terminals 28. In this case, the resonator 29 converts an electrical signal into an acoustic wave and an acoustic wave into an electrical signal. The terminal 28 may correspond to, for example, the antenna terminal 5, the transmitting terminal 7, the receiving terminal 9, or the reference potential unit 11.

[0141] The resonator 29 includes, for example, a piezoelectric substrate 31 (at least a part of its upper surface 31a), an IDT electrode 33 (excitation electrode) located on the upper surface 31a, and a pair of reflectors 35 located on both sides of the IDT electrode 33. A plurality of resonators 29 may be configured on one piezoelectric substrate 31. In other words, the piezoelectric substrate 31 may be shared by a plurality of resonators 29.

[0142] The piezoelectric substrate 31 has piezoelectricity at least in the region of the upper surface 31a where the resonator 29 is provided. The piezoelectric body 31b constituting at least the region of the piezoelectric substrate 31 where the resonator 29 is provided is made of, for example, a single crystal having piezoelectricity. Examples of materials constituting such a single crystal include lithium tantalate (LiTaO ３ ), lithium niobate (LiNbO ３ ) and quartz (SiO ２) can be mentioned. The cut angle, planar shape, and various dimensions can be set as appropriate. For example, the piezoelectric substrate 31 can be entirely made of a piezoelectric material (can be a piezoelectric substrate), can be a piezoelectric substrate and a support substrate bonded together, can be a support substrate on which a plurality of films are laminated and on which a piezoelectric layer is laminated, or can have a cavity between the piezoelectric layer and the support substrate.

[0143] The IDT electrode 33 and the reflector 35 are formed of layered conductors provided on the piezoelectric substrate 31. The IDT electrode 33 is formed of a so-called IDT electrode and has a pair of comb-tooth electrodes 37 (one of which is hatched for ease of visibility). Each comb-tooth electrode 37 has, for example, a bus bar 39, a plurality of electrode fingers 41 extending in parallel from the bus bar 39, and a plurality of dummy electrodes 43 protruding from the bus bar 39 between the plurality of electrode fingers 41. The pair of comb-tooth electrodes 37 are arranged so that the plurality of electrode fingers 41 interdigitate with (intersect with) each other.

[0144] The pair of reflectors 35 are located on both sides of the IDT electrode 33 in the propagation direction of the acoustic wave. Each reflector 35 may be, for example, in an electrically floating state or may be applied with a reference potential. Each reflector 35 is formed, for example, in a lattice shape. That is, the reflector 35 includes a pair of bus bars 45 facing each other and a plurality of strip electrodes 47 extending between the pair of bus bars 45.

[0145] When a voltage is applied to the pair of comb-tooth electrodes 37, the voltage is applied to the piezoelectric body 31 b by the multiple electrode fingers 41, causing the piezoelectric body 31 b to vibrate. That is, an elastic wave is excited. Of the elastic waves of various wavelengths that propagate in various directions, the elastic waves that propagate in the arrangement direction of the multiple electrode fingers 41 with the pitch p of the multiple electrode fingers 41 being approximately half the wavelength (λ / 2) tend to have large amplitudes because the multiple waves excited by the multiple electrode fingers 41 overlap in phase.

[0146] Furthermore, the elastic waves propagating through the piezoelectric body 31b are converted into electrical signals by the plurality of electrode fingers 41. At this time, similar to when elastic waves are excited, the intensity of the electrical signals converted from the elastic waves propagating in the arrangement direction of the plurality of electrode fingers 41, with the pitch p of the plurality of electrode fingers 41 being approximately half the wavelength (λ / 2), tends to be strong.

[0147] Due to the above-described actions (and other actions not described here), the resonator 29 functions as a resonator whose resonant frequency is the frequency of an elastic wave whose pitch p is approximately half the wavelength (λ / 2). The anti-resonant frequency is determined by the resonant frequency and the capacitance of the IDT electrode 33, etc. The pair of reflectors 35 contributes to confining the elastic wave.

[0148] A configuration in which the pair of reflectors 35 are removed from the resonator 29 (one-port resonator) is also a type of resonator. By arranging two or more IDT electrodes 33 (resonators excluding the pair of reflectors) between the pair of reflectors 35, a longitudinally coupled multimode filter is configured.

[0149] In a configuration in which a resonator using the IDT electrode 33 utilizes a BAW, the resonator may, for example, generate a BAW propagating in the D1 direction by the same action as described above, or may generate thickness-shear vibration by a different action from the above. In the latter case, the resonant frequency is relatively highly dependent on the thickness of the piezoelectric layer and relatively less dependent on the pitch p. Furthermore, even in a one-port resonator, the reflector 35 is not necessary.

[0150] 5. Example of a Communication Device Including a Composite Filter The composite filter may be used, for example, in a communication module and / or a communication device.

[0151] 11 is a block diagram showing the main parts of a communication device 151 as an example of using the composite filter 1. The communication device 151 has a module 171 and a housing 173 that houses the module 171. The module 171 performs wireless communication using radio waves and includes the composite filter 1. Here, only the transmit filter system 12 and the receive filter system 14 of the composite filter 1 are shown, and hybrids and other components are not shown.

[0152] In module 171, a transmission information signal TIS containing information to be transmitted is modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153 to generate a transmission signal TS. Unwanted components outside the transmission passband are removed from the transmission signal TS by a bandpass filter 155, amplified by an amplifier 157, and input to a composite filter 1 (transmission terminal 7). The composite filter 1 (transmission filter system 12) then removes unwanted components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from antenna terminal 5 to an antenna 159. The antenna 159 converts the input electrical signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

[0153] Furthermore, in module 171, a radio signal (radio wave) received by antenna 159 is converted by antenna 159 into an electrical signal (received signal RS) and input to composite filter 1 (antenna terminal 5). Composite filter 1 (receive filter system 14) removes unnecessary components outside the receive passband from the input received signal RS and outputs the signal from receive terminal 9 to amplifier 161. The output received signal RS is amplified by amplifier 161, and unnecessary components outside the receive passband are removed by bandpass filter 163. The received signal RS is then frequency-downshifted and demodulated by RF-IC 153 to generate received information signal RIS.

[0154] The transmit information signal TIS and the receive information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, such as analog audio signals or digitized audio signals. The passband of the radio signal may be set as appropriate. The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. Although the direct conversion method is illustrated, other appropriate circuit methods may be used, such as a double superheterodyne method. Furthermore, FIG. 11 schematically illustrates only the essential parts, and low-pass filters, isolators, etc. may be added at appropriate positions, and the positions of amplifiers, etc. may be changed.

[0155] The module 171 has, for example, components from the RF-IC 153 to the antenna 159 on the same circuit board. That is, the composite filter 1 is combined with other components to form a module. The composite filter 1 may be included in the communication device 151 without being modularized. Furthermore, the components exemplified as components of the module 171 may be located outside the module or may not be housed in the housing 173. For example, the antenna 159 may be exposed to the outside of the housing 173.

[0156] (6. Summary of the Embodiment) As described above, the composite filter 1 according to the embodiment includes the first hybrid 17, a first filter (e.g., the transmit filter 13), second and third filters (e.g., the receive filters 15A and 15B), and a resonator 29 of the trap 24 (e.g., the trap resonator 29T of the first embodiment or the series resonator 29S of the trap filter 51 of the second embodiment). The first hybrid 17 is configured as a 90° hybrid coupler having first and second ports (ports 17a and 17b) and third and fourth ports (ports 17c and 17d) to which a signal input to port 17a or port 17b is distributed. The first filter is connected to port 17b and has a first passband (e.g., a transmit band). The second filter is connected to port 17c and has a second passband (e.g., a receive band) that does not overlap with the first passband. The third filter is connected to port 17d and has a second passband. The resonator 29 branches off from the signal path from the first filter to the port 17b and is connected to the reference potential section 11, and has a resonance frequency within the second passband.

[0157] Therefore, for example, as described in the overview of the embodiment, it is possible to reduce the probability that nonlinear distortion generated in the transmit filter 13 passes through the receive filter 15. Since the composite filter 1 using the first hybrid 17 itself can reduce nonlinear distortion, the effect of reducing nonlinear distortion is further improved. The trap 24 is based on the premise that the flow of the receive signal from the antenna terminal 5 to the transmit filter 13 is basically prohibited by the first hybrid 17, and is difficult to conceive of in a duplexer that does not have the first hybrid 17.

[0158] The composite filter 1 may include a second hybrid 19. The second hybrid 19 may be configured as a 90° hybrid coupler having fifth and sixth ports (ports 19a and 19b) and seventh and eighth ports (ports 19c and 19d) to which a signal input to the fifth or sixth port is distributed. Port 19a may be connected to a second filter (e.g., receive filter 15A) on the electrically opposite side of the side to which the first hybrid 17 is connected. Port 19b may be connected to a third filter (e.g., receive filter 15B) on the electrically opposite side of the side to which the first hybrid 17 is connected.

[0159] In this case, as described above, at least a portion of the nonlinear distortions can be canceled out at port 19d. In the previous paragraph, it was stated that the signal input to port 19a or 19b is distributed to ports 19c and 19d. However, as already mentioned and as will be understood from the first and second embodiments, this expression is for convenience's sake. In other words, the intended signal does not necessarily need to be input to port 19a or 19b.

[0160] The resonator 29 of the trap 24 (for example, the trap resonator 29T of the first embodiment or the series resonator 29S of the trap filter 51 of the second embodiment) may have a plurality of split resonators 29Tb connected in series with each other between the second port (port 19b) of the first filter (for example, the transmit filter 13) and the reference potential unit 11.

[0161] In this case, as already described, the likelihood of a high voltage being locally applied to the trap resonator 29Ta can be reduced. As a result, the voltage resistance of the composite filter 1 is improved. Because the trap resonator 29Ta is located closer to the first hybrid 17 than the transmit filter 13, there is a higher likelihood that a high voltage will be applied from the first hybrid 17 compared to the resonator 29 in the transmit filter 13. This effectively improves the voltage resistance. When the split resonator 29Tb is applied to any of the multiple series resonators 29S of the trap filter 51 according to the second embodiment, voltage division by the series resonator 29S and voltage division by the split resonator 29Tb are performed, further improving the voltage resistance of the resonator 29. From another perspective, in the trap resonator 29T according to the first embodiment, the multiple split resonators 29Tb reduce the likelihood that the trap resonator 29T will be the first to experience dielectric breakdown within the composite filter 1 or increase the voltage at which dielectric breakdown first occurs, thereby improving the voltage resistance of the entire composite filter 1.

[0162] The resonator 29 of the trap 24 (for example, the trap resonator 29T of the first embodiment) may have an anti-resonant frequency within the first passband (for example, the transmission band).

[0163] In this case, for example, the probability that a signal to be output from the transmit filter 13 to the antenna terminal 5 will flow to the reference potential section 11 via the trap resonator 29T is reduced. That is, the probability that the insertion loss will decrease due to the trap 24 is reduced. Note that the anti-resonance frequency of the series resonator 29S (which can also be considered as a type of trap resonator 29T) of the trap filter 51 of the second embodiment is located slightly outside the receive band. This anti-resonance frequency is not located within the transmit band, for example.

[0164] The composite filter 1A (first embodiment) does not need to have a filter including the trap resonator 29T (the trap filter 51 of the second embodiment) between the second port (port 17b) of the first filter (e.g., the transmit filter 13) and the reference potential unit 11.

[0165] In this case, the configuration is simpler than, for example, the second embodiment. Therefore, for example, when the transmit filter 13 is an acoustic wave filter, the composite filter 1A according to the embodiment can be realized simply by adding electrodes (the IDT electrode 33 and a pair of reflectors 35) to the chip (the piezoelectric substrate 31) on which the transmit filter 13 is mounted. As a result, for example, the degree of freedom in structural design is improved. Note that although the trap resonator 29T of the first embodiment can also be considered a type of filter, this is not the case when referring to it as in the previous paragraph.

[0166] The composite filter 1B (second embodiment) may include a fourth filter (trap filter 51). The fourth filter may include a resonator 29 (e.g., a series resonator 29S) of the trap 24. The fourth filter also passes a signal having a frequency within a second pass band (e.g., a receive band) from the second port (port 17b) of the first filter (e.g., the transmit filter 13) to the reference potential unit 11.

[0167] In this case, compared to the first embodiment, for example, the trap 24 can trap not only nonlinear distortion at or near the resonant frequency of the resonator 29 but also nonlinear distortion within a relatively wide band, thereby making it possible to trap nonlinear distortion at frequencies other than those expected.

[0168] The fourth filter (trap filter 51) may include a bandpass filter having a third passband that includes at least a portion of the second passband (e.g., the receive band) and does not include the first passband (e.g., the transmit band).

[0169] In this case, for example, it is possible to reduce the possibility of trapping a transmission signal that should be output from the transmission filter 13 to the antenna terminal 5. Furthermore, for example, it is possible to use a chip fabricated as a duplexer 55 by combining the transmission filter 13 and the trap filter 51.

[0170] The entire third passband (the passband of the trap filter 51) may overlap the entire second passband (for example, the reception band).

[0171] In this case, for example, it is possible to trap nonlinear distortion over the entire receive band without excess or deficiency. This reduces the likelihood of trapping signals in the transmit band while reducing the nonlinear distortion input to the receive terminal 9 via the receive filter 15. Furthermore, it becomes possible to use the same configuration for the trap filter 51 and the receive filter 15, which is expected to improve productivity.

[0172] The composite filter 1B may have a terminating resistor 53 between the fourth filter (trap filter 51) and the reference potential section 11.

[0173] In this case, the likelihood that a signal (nonlinear distortion) that has passed through the trap filter 51 will be reflected on the output side (termination resistor 53 side) of the trap filter 51 is reduced. Taking a ladder-type filter as an example of the trap filter 51, it is originally assumed that a signal that passes through the parallel resonator 29P (a signal outside the pass band) will be released to the reference potential section 11. On the other hand, it is not assumed that a signal that passes through the series resonator 29S (a signal within the pass band) will flow to the reference potential section 11. Therefore, the provision of the termination resistor 53 makes it easier to utilize conventional filter designs.

[0174] From another perspective, the composite filter 1 according to the embodiment (e.g., the composite filter 1B according to the second embodiment) includes a first hybrid 17, a first filter (e.g., the transmit filter 13), second and third filters (e.g., the receive filters 15A and 15B), and a fourth filter (e.g., the trap filter 51). The first hybrid 17 is configured as a 90° hybrid coupler having first and second ports (ports 17a and 17b) and third and fourth ports (ports 17c and 17d) to which a signal input to port 17a or port 17b is distributed. The first filter is connected to port 17b and has a first passband (e.g., a transmit band). The second filter is connected to port 17c and has a second passband (e.g., a receive band) that does not overlap with the first passband. The third filter is connected to port 17d and has a second passband. The fourth filter branches off from the signal path from the first filter to the port 17b and is connected to the reference potential unit 11, and passes signals having frequencies within the second passband.

[0175] Therefore, for example, as described in the overview of the embodiment, it is possible to reduce the likelihood that nonlinear distortion generated in the transmit filter 13 will pass through the receive filter 15. In the composite filter 1 (1B) of the embodiment as described above, the resonator 29, which branches off from the signal path from the first filter (transmit filter 13) to the second port (port 17b), is connected to the reference potential unit 11, and has a resonant frequency in the second pass band (receive band), may not be provided. For example, the trap filter 51 may be a low-pass filter or high-pass filter that does not include a resonator and is composed of inductors, capacitors, etc., or may be a band-pass filter that is composed by lowering the cutoff frequency of a high-pass filter below the cutoff frequency of a low-pass filter.

[0176] The communication device 151 according to the embodiment may include a composite filter 1, an antenna 159 connected to a first port (port 17a), and an integrated circuit element (RF-IC 153) connected to the first filter, the second filter, and the third filter on the electrically opposite side of the first hybrid 17.

[0177] In this case, for example, the communication device 151 can utilize the effect of reducing nonlinear distortion in the composite filter 1. This in turn improves communication characteristics.

[0178] In the above embodiment, the transmit filter 13 is an example of a first filter. The receive filters 15A and 15B are examples of a second and a third filter, respectively. The trap resonator 29T or 29Ta, the split resonator 29Tb of the trap resonator 29Ta, and the series resonator 29S of the trap filter 51 are each an example of a resonator that connects the first filter and the reference potential unit. The trap filter 51 is an example of a fourth filter. The ports 17a to 17d and 19a to 19d are examples of first to eighth ports, respectively. The RF-IC 153 is an example of an integrated circuit element.

[0179] The technology according to the present disclosure is not limited to the above-described embodiment and may be implemented in various modes.

[0180] For example, the first filter may be a receive filter (the transmit terminal 7 may be a receive terminal), and the second and third filters may be two receive filters having receive bands (second pass bands) different from the receive band (first pass band) of the first filter. In this case, too, the likelihood that nonlinear distortion generated in the first filter will be input to the receive terminal 9 via the second and third filters is reduced. As can be understood from the above, the composite filter may be a diplexer instead of a duplexer.

[0181] Alternatively, for example, the first filter may be a receiving filter (the transmitting terminal 7 may be a receiving terminal), and the second and third filters may be transmitting filters (the receiving terminal 9 (or 9A and 9B) may be transmitting terminals). The trap 24 may have a resonant frequency and / or a passband in the transmitting band. In this case, too, the likelihood that nonlinear distortion occurring in any of the first to third filters will appear at any of the terminals is reduced.

[0182] Also, for example, the composite filter of the embodiment may be part of a multiplexer, such as a triplexer or a quadplexer.

[0183] 1, 1A, 1B, 301...composite filter, 11...reference potential section, 13...transmitting filter (first filter), 15, 15A, 15B...receiving filter (second filter, third filter), 17...first hybrid, 17a...port (first port), 17b...port (second port), 17c...port (third port), 17d...port (fourth port), 29...resonator, 29T, 29Ta...trap resonator (resonator), 29S...series resonator (resonator), 29Tb...split resonator (resonator), 51...trap filter (fourth filter).

Claims

1. A first hybrid composed of a 90° hybrid coupler having a first port, a second port, a third port, and a fourth port to which a signal input to the first port or the second port is distributed; A first filter connected to the second port and having a first passband; A second filter connected to the third port and having a second passband that does not overlap with the first passband; A third filter connected to the fourth port and having the second passband; A resonator branched from a signal path from the first filter to the second port and connected to a reference potential portion, the resonator having a resonance frequency within the second passband; A composite filter having the above.

2. Having a second hybrid composed of a 90° hybrid coupler having a fifth port, a sixth port, a seventh port, and an eighth port to which a signal input to the fifth port or the sixth port is distributed, The fifth port is connected to the side opposite to the side to which the first hybrid is connected with respect to the second filter electrically, The sixth port is connected to the side opposite to the side to which the first hybrid is connected with respect to the third filter electrically The composite filter according to claim 1.

3. The resonator has a plurality of divided resonators connected in series between the side of the second port of the first filter and the reference potential portion The composite filter according to claim 1.

4. The resonator has an anti-resonance frequency within the first passband The composite filter according to claim 1.

5. There is no filter including the resonator between the side of the second port of the first filter and the reference potential portion The composite filter according to claim 1.

6. Having a fourth filter including the resonator and passing a signal having a frequency within the second passband from the side of the second port of the first filter to the reference potential portion The composite filter according to claim 1.

7. A first hybrid composed of a 90° hybrid coupler having a first port, a second port, a third port, and a fourth port to which a signal input to the first port or the second port is distributed; A first filter connected to the second port and having a first passband; A second filter connected to the third port and having a second passband that does not overlap with the first passband; A third filter connected to the fourth port and having the second passband; A fourth filter branched from a signal path from the first filter to the second port and connected to a reference potential portion, and passing a signal having a frequency within the second passband to the reference potential portion; A composite filter having the above.

8. The fourth filter has a band-pass filter having a third passband that includes at least a part of the second passband and does not include the first passband. The composite filter according to claim 6.

9. The entire third passband overlaps with the entire second passband. The composite filter according to claim 8.

10. There is a terminating resistor between the fourth filter and the reference potential portion. The composite filter according to claim 6.

11. The composite filter according to any one of claims 1 to 10; An antenna connected to the first port; An integrated circuit element connected to the opposite side electrically to the first hybrids of the first filter, the second filter, and the third filter respectively; A communication device having the above.