Composite filter device

Abstract

The present invention provides a transmission filter circuit and a composite filter device capable of suppressing third-order intermodulation distortion. The transmission filter circuit comprises: an input terminal to which a transmission signal is supplied; an output terminal connected to an antenna; a plurality of series arm resonators connected in series in a line between the input terminal and the output terminal, and including a first series arm resonator closest to the output terminal and a second series arm resonator second from the output terminal; and a parallel arm resonator, one end of which is connected to a connection point between the first series arm resonator and the second series arm resonator, and the other end of which is supplied with a reference potential, and the resonance frequency of the first series arm resonator is higher than the resonance frequency of the second series arm resonator.

Description

Technical Field

[0001] The present invention relates to a transmission filter circuit and a composite filter device. Background Art

[0002] In mobile communication devices such as cellular phones, a common antenna is sometimes used for transmitting a transmission signal and receiving a reception signal in order to miniaturize the terminal. A duplexer that separates the transmission signal and the reception signal is connected to such an antenna. As an example of a duplexer, for example, the following patent document 1 discloses a ladder filter circuit, that is, by connecting a plurality of resonators having inherent resonant frequencies and anti-resonant frequencies in a ladder shape, a signal of a given frequency band is passed, and signals of other frequency bands are attenuated.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2016 / 088680

[0006] In the resonator, for example, a third-order intermodulation distortion may be generated based on the transmission signal and the interfering wave due to the mixing of the transmission signal with an interfering wave having a frequency close to the frequency of the transmission signal. For example, when the reception band is higher than the transmission band, the third-order intermodulation distortion appears in the reception band, and thus the third-order intermodulation distortion becomes noise for the reception band, which may cause deterioration of the reception sensitivity.

[0007] Regarding this point, for example, in the ladder filter circuit disclosed in Patent Document 1, third-order intermodulation distortion is not considered. Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a transmission filter circuit and a composite filter device capable of suppressing third-order intermodulation distortion.

[0010] Technical solutions to solve problems

[0011] To achieve such an object, a transmission filter circuit according to one aspect of the present invention comprises: an input terminal to which a transmission signal is supplied; an output terminal connected to an antenna; a plurality of series arm resonators connected in series in a line between the input terminal and the output terminal, including a first series arm resonator closest to the output terminal and a second series arm resonator which is second from the output terminal; and a parallel arm resonator having one end connected to a connection point between the first series arm resonator and the second series arm resonator and having the other end supplied with a reference potential, wherein a resonant frequency of the first series arm resonator is higher than a resonant frequency of the second series arm resonator.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide a transmission filter circuit and a composite filter device capable of suppressing third-order intermodulation distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing a configuration example of a front-end circuit including a transmission filter circuit according to the first embodiment of the present invention.

[0015] Figure 2 This is a diagram for explaining third-order intermodulation distortion that may occur in a resonator.

[0016] Figure 3 : is a graph showing impedance characteristics in resonators having different resonance frequencies from each other.

[0017] Figure 4 It is a graph showing simulation results of third-order intermodulation distortion generated in the transmission filter circuits according to the first embodiment of the present invention and the comparative example.

[0018] Figure 5 It is a graph showing simulation results of attenuation characteristics in the transmission filter circuit according to the first embodiment of the present invention and the comparative example.

[0019] Figure 6 It is a diagram showing a configuration example of a front-end circuit including a transmission filter circuit according to a second embodiment of the present invention.

[0020] Figure 7 It is a graph showing simulation results of third-order intermodulation distortion generated in the transmission filter circuits according to the first embodiment and the second embodiment of the present invention.

[0021] Figure 8 It is a graph showing simulation results of third-order intermodulation distortion generated in the transmission filter circuits according to the first modification example and the comparative example of the present invention.

[0022] Fig. 9It is a graph showing simulation results of attenuation characteristics in the transmission filter circuit according to the first modification example of the present invention and the comparative example.

[0023] Description of Reference Numerals

[0024] 100, 100A: front-end circuit;

[0025] 10, 10A: Transmit filter circuit;

[0026] 20: receiving filter circuit;

[0027] 30: Antenna;

[0028] T1, T2: input terminals;

[0029] T3, T4: output terminals;

[0030] T5: Antenna terminal;

[0031] U1: line;

[0032] S1~S4, S2a, S2b: series arm resonator;

[0033] P1~P3: Parallel arm resonator. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are attached to the same elements, and repeated descriptions are omitted.

[0035] Figure 1 1 is a diagram showing a configuration example of a front-end circuit including a transmission filter circuit according to a first embodiment of the present invention. The front-end circuit 100 according to this embodiment is used in a mobile communication device such as a cellular phone, for example.

[0036] like Figure 1 As shown, the front end circuit 100 includes, for example, a transmission filter circuit 10, a reception filter circuit 20, input terminals T1, T2, and output terminals T3, T4. The front end circuit 100 is connected to the antenna 30 via the antenna terminal T5.

[0037] When a mobile communication device transmits and receives a radio frequency (RF) signal via an antenna 30, a transmission filter circuit 10 and a reception filter circuit 20 form a splitter that separates a transmission signal from a reception signal. The splitter may be, for example, a composite filter device that has a plurality of filter circuits and separates signals of a plurality of frequency bands. The composite filter device may include, for example, a duplexer that combines two filter circuits, a triplexer that combines three filter circuits, a quadplexer that combines four filter circuits, or an octaplexer that combines eight filter circuits. In the present embodiment, a duplexer including two filter circuits (a transmission filter circuit 10 and a reception filter circuit 20) is used as an example for description.

[0038] The transmission filter circuit 10 is supplied with a transmission signal output from a transmission circuit (not shown) via the input terminal T1. The transmission filter circuit 10 has the function of passing a signal of a given frequency band from the input terminal T1 to the output terminal T3 and attenuating signals of other frequency bands. The transmission signal that has passed through the transmission filter circuit 10 is transmitted from the antenna 30 to the base station via the output terminal T3 and the antenna terminal T5. In addition, the output terminal T3 and the antenna terminal T5 may be replaced by the antenna terminal T5 serving as the output terminal T3 instead of being independently provided. In addition, the transmission signal is a signal with a lower frequency than the reception signal described later.

[0039] The transmission filter circuit 10 in this embodiment is a ladder filter in which a plurality of resonators are connected in series and in parallel. Specifically, the transmission filter circuit 10 has four series arm resonators S1 to S4 and three parallel arm resonators P1 to P3. The number of these resonators is an example and is not limited thereto. The elements of the series arm resonators S1 to S4 and the parallel arm resonators P1 to P3 are not particularly limited, and for example, they may be filters such as surface acoustic wave (SAW: Surface Acoustic Wave) filters, piezoelectric thin film resonators, or bulk acoustic wave (BAW: Bulk Acoustic Wave) filters, etc.

[0040] The four series arm resonators S1 to S4 are connected in series to the line U1 connecting the input terminal T1 and the output terminal T3 in the order close to the antenna 30. The three parallel arm resonators P1 to P3 are connected in parallel to branch from the line U1 in the order close to the antenna 30. One end of the three parallel arm resonators P1 to P3 is connected to the connection point of the series arm resonator S1 and the series arm resonator S2, the connection point of the series arm resonator S2 and the series arm resonator S3, and the connection point of the series arm resonator S3 and the series arm resonator S4, respectively, and a reference potential (for example, a ground potential) is supplied to the other end.

[0041] The reception filter circuit 20 is supplied with a reception signal received by the antenna 30 from the base station via the antenna terminal T5 and the input terminal T2. The reception filter circuit 20 has the function of passing a signal of a given frequency band from the input terminal T2 to the output terminal T4 and attenuating signals of other frequency bands. The reception signal that has passed through the reception filter circuit 20 is supplied to the reception circuit (not shown) via the output terminal T4. In addition, the input terminal T2 and the antenna terminal T5 may be provided separately, and the antenna terminal T5 may also serve as the input terminal T2.

[0042] exist Figure 1 , as an example of the reception filter circuit 20, a structure in which a plurality of resonators are connected in a ladder shape is shown in the same manner as the transmission filter circuit 10. This structure is the same as the transmission filter circuit 10, so a detailed description is omitted. In addition, the structure of the reception filter circuit 20 is not limited to this, and for example, a structure including a longitudinal coupling type resonator may also be used.

[0043] The passband of the transmission filter circuit 10 and the passband of the reception filter circuit 20 are not particularly limited, but are different frequency bands. For example, when the front-end circuit 100 transmits and receives the signal of Band 1 of the communication standard of LTE (Long Term Evolution), the passband of the transmission filter circuit 10 is 1920 MHz to 1980 MHz, which is the transmission frequency band of Band 1, and the passband of the reception filter circuit 20 is 2110 MHz to 2170 MHz, which is the reception frequency band of Band 1. In this case, the frequency of the passband of the reception filter circuit 20 is higher than that of the transmission filter circuit 10. In addition, the frequency band of the signal transmitted and received by the front-end circuit 100 is not limited thereto, and may also be other frequency bands including Band 8, Band 26, and Band 30. In addition, the frequency of the passband of the transmission filter circuit 10 may be higher than that of the reception filter circuit 20.

[0044] The components of the front-end circuit 100 described above may be formed as modules on the same chip or on different chips.

[0045] In the transmission filter circuit 10, in addition to the transmission signal supplied from the input terminal T1, an interference wave (so-called interference signal) having a frequency close to the transmission signal may be supplied from the antenna 30 via the antenna terminal T5, for example. In each resonator included in the transmission filter circuit 10, third-order intermodulation distortion may be generated based on these transmission signals and interference waves. Figure 2 The third-order intermodulation distortion is explained.

[0046] Figure 2 This is a diagram for explaining the third-order intermodulation distortion that may occur in a resonator. Generally speaking, if signals with relatively close frequencies f1 and f2 (f1 < f2) are supplied to the resonator, stress distributions caused by the signals of each frequency are generated in the resonator. Through these stress distributions, stress distributions of frequencies equivalent to the difference between the second harmonic of one frequency and the other frequency (2f1 - f2 and 2f2 - f1) are generated. This stress distribution is extracted by the electrodes of the resonator and thus appears as third-order intermodulation distortion.

[0047] For example, taking Band1 as an example, the frequency included in the transmission signal band Tx (1920 MHz to 1980 MHz) of the transmission signal supplied from the input terminal T1 to the transmission filter circuit 10 is set as f2, and the frequency of the interference wave supplied from the antenna 30 to the transmission filter circuit 10 is set as f1. Regarding the frequency f1 of the interference wave, for example, it is set to be slightly lower than f2 and is included in the frequency band 2Tx - Rx (1730 MHz to 1790 MHz) equivalent to the difference between the second harmonic of the transmission signal and the fundamental wave of the received signal.

[0048] At this time, the frequency (2f2 - f1) of the third-order intermodulation distortion generated by the transmission signal and the interference wave will overlap with the reception signal band Rx (2110 MHz to 2170 MHz) of Band1. Since this third-order intermodulation distortion can pass through the reception filter circuit 20, it becomes noise for the reception signal and may cause deterioration of the reception sensitivity.

[0049] Regarding this point, in the present embodiment, by designing the relationality of the resonance frequencies of the respective resonators included in the transmission filter circuit 10, this third-order intermodulation distortion is suppressed. Specifically, in the transmission filter circuit 10, it is designed such that the resonance frequency of the series-arm resonator S1 (the first series-arm resonator) closest to the output terminal T3 among the multiple series-arm resonators S1 to S4 is higher than the resonance frequency of the series-arm resonator S2 (the second series-arm resonator) that is the second from the output terminal T3. Additionally, for example, if the pitch of the comb-shaped electrodes (IDT: Interdigital Transducer) is set as λ and the sound velocity in the piezoelectric substrate constituting the SAW filter is set as v, the resonance frequency f r of the SAW filter can be represented by f r = v / λ [Hz]. Therefore, for example, by adjusting the pitch of the comb-shaped electrodes, the desired resonance frequency f r can be obtained.

[0050] Figure 3Graphs showing impedance characteristics in resonators having different resonant frequencies. In the graph shown in the same figure, the horizontal axis shows frequency and the vertical axis shows impedance.

[0051] The impedance characteristic 200 of a series resonator with a relatively high resonant frequency and the impedance characteristic 210 of a series resonator with a relatively low resonant frequency are compared. Both are designed so that the resonant frequency is located near the frequency band Tx of the transmitted signal. If we focus on the frequency band 2Tx-Rx that generates the interference wave of the third-order intermodulation distortion, as shown in Figure 3 As shown, the resonator with impedance characteristic 200 has higher impedance in this frequency band than the resonator with impedance characteristic 210. That is, a resonator with a high resonance frequency is less likely to allow interference waves to pass than a resonator with a low resonance frequency.

[0052] Although the interference wave mixed into the transmission filter circuit 10 from the antenna 30 is attenuated to some extent in the process of passing through the plurality of resonators included in the transmission filter circuit 10, the level of the interference wave mixed into the resonator closest to the output terminal T3 (that is, closest to the antenna 30) is the highest. Therefore, by setting the resonance frequency of the series arm resonator S1 closest to the output terminal T3 higher than the resonance frequency of the series arm resonator S2 which is the second from the output terminal T3, it becomes easy to suppress the invasion of the interference wave.

[0053] Figure 4 It is a graph showing the simulation results of the third-order intermodulation distortion generated in the transmission filter circuit involved in the first embodiment of the present invention and the comparative example. The so-called comparative example is a structure in which the resonant frequency of the series arm resonator closest to the output terminal is lower than the resonant frequency of the second series arm resonator from the output terminal. In this simulation, as an example, it is assumed that the transmission filter circuit 10 constitutes a duplexer corresponding to Band30 (transmission band: 2305MHz~2315MHz, reception band: 2350MHz~2360MHz). The resonant frequency of each resonator is shown in the following Table 1 (unit: MHz). Figure 4 In the graph shown, the horizontal axis shows the frequency of the signal (MHz), and the vertical axis shows the third-order intermodulation distortion (IMD: Intermodulation Distortion) (dBm).

[0054] [Table 1]

[0055]

[0056] according to Figure 4 It can be seen that in the reception frequency band of Band 30, 2350 MHz to 2360 MHz, the transmission filter circuit 10 according to the present embodiment reduces the third-order intermodulation distortion by about 4 dB to 6 dB compared with the comparative example.

[0057] Figure 5 is a graph showing simulation results of attenuation characteristics in the transmission filter circuit according to the first embodiment of the present invention and the comparative example. Figure 4 The simulation shown is the same. Figure 5 In the graph shown, the horizontal axis shows the frequency (MHz) of the signal, and the vertical axis shows the attenuation characteristics (dB) of the signal. Attenuation characteristics 300 and 310 are graphs showing the results of the first embodiment and the comparative example in 10 dB units (see the scale of the vertical axis on the left), and attenuation characteristics 320 and 330 are graphs showing the results of the first embodiment and the comparative example in 1 dB units (see the scale of the vertical axis on the right). Boundary lines M1 to M4 respectively show the lower limit value and the upper limit value of the transmission band in Band 30, and the lower limit value and the upper limit value of the reception band.

[0058] according to Figure 5 In the transmission filter circuit 10 involved in this embodiment, in the transmission frequency band to be passed, slight loss is observed, especially on the high frequency side, compared with the comparative example, but there is no significant change in characteristics. In this way, if the resonance frequency of the series arm resonator closest to the output terminal is made higher than the resonance frequency of the second series arm resonator from the output terminal, the insertion loss in the passband may deteriorate, so this structure is usually not adopted. However, if Figure 5 As shown, the inventors of the present invention have found through simulation that even with this structure, the degradation of insertion loss is not enough to affect the transmission of signals. In addition, in the transmission filter circuit 10 involved in this embodiment, although the attenuation level in the reception frequency band to be attenuated is slightly worse than that of the comparative example, it is not enough to significantly deteriorate the reception performance.

[0059] As described above, in the transmission filter circuit 10 according to the present embodiment, the resonance frequency of the series arm resonator S1 closest to the output terminal T3 is higher than the resonance frequency of the series arm resonator S2 which is the second from the output terminal T3. As a result, the interference wave which causes the generation of the third-order intermodulation distortion can be greatly attenuated in the series arm resonator closest to the output terminal T3. Therefore, the third-order intermodulation distortion can be suppressed.

[0060] Here, for example, the following method can also be considered, that is, by dividing the series arm resonator closest to the output terminal, the third-order intermodulation distortion is reduced. The so-called dividing of the series arm resonator means that a plurality of series arm resonators are arranged between adjacent parallel arm resonators, and the characteristics of the plurality of series arm resonators synthesized are consistent with the characteristics of the series arm resonator before the division. It can be considered that by dividing the series arm resonator, the energy density in each resonator is reduced, so the third-order intermodulation distortion is reduced. However, the series arm resonator closest to the output terminal generally has a relatively large capacitance value, so the increase in circuit area caused by dividing the series arm resonator becomes a problem. In this regard, according to the present embodiment, compared with the structure in which the series arm resonator closest to the output terminal is divided, the third-order intermodulation distortion can be suppressed while suppressing the increase in circuit area.

[0061] In addition, the order of the resonance frequencies of the four series arm resonators S1 to S4 is not particularly limited. In the present embodiment, for example, the order of the resonance frequencies is S3>S1>S2>S4. That is, the resonance frequency of the third series arm resonator S3 (the third series arm resonator) from the output terminal T3 is higher than the resonance frequency of the series arm resonator S1 closest to the output terminal T3. It can also be said that the transmission filter circuit 10 has the series arm resonator S3 with the highest resonance frequency on the input terminal T1 side of the second series arm resonator S2 from the output terminal T3. For example, when the interval between the transmission band and the reception band is relatively narrow and the relative bandwidth of the frequency band is small relative to the relative bandwidth of the resonator, as in Band 30, the impedance in the passband is likely to become inductive. Therefore, in the present embodiment, by making the resonance frequency of the series arm resonator S3 higher than the resonance frequencies of the other series arm resonators, the impedance in the passband is restored from inductive to capacitive, thereby preventing impedance mismatch. By achieving impedance matching, it is possible to suppress loss due to reflection of the signal, and to suppress degradation of insertion loss of the transmission filter circuit 10 .

[0062] In addition, although the above-mentioned embodiment shows an example in which the transmission filter circuit is applied to a duplexer, the structure to which the transmission filter circuit is applied is not limited to the duplexer, and a filter circuit formed on a chip different from the reception filter circuit may also be used. In this case, if the output terminal T3 of the transmission filter circuit 10 is connected to the input terminal of the reception filter circuit via the antenna terminal T5, third-order intermodulation distortion will also become a problem, so this embodiment also functions appropriately.

[0063] Figure 61 is a diagram showing a configuration example of a front-end circuit including a transmission filter circuit according to a second embodiment of the present invention. In the second embodiment, the description of matters common to the first embodiment is omitted, and only the differences are described. In particular, the same effects based on the same configuration will not be mentioned one by one in each embodiment.

[0064] like Figure 6 As shown, the front end circuit 100A according to the second embodiment differs in the configuration of the transmission filter circuit 10A from the above-described front end circuit 100. The transmission filter circuit 10A includes two divided series arm resonators S2a and S2b instead of the second series arm resonator S2 from the output terminal T3.

[0065] The resonator has a given electrostatic capacitance. When the series arm resonator is divided into two, for example, the capacitance of each resonator needs to be doubled in order to obtain the same capacitance value as before the division. Therefore, the total area of ​​the two divided elements becomes four times that before the division.

[0066] When the ladder circuit is designed according to the mirror impedance in the two-terminal pair circuit, the capacitance value of the series arm resonator S1 closest to the output terminal T3 becomes larger than the capacitance value of the second series arm resonator S2, for example, about twice. In this embodiment, by dividing the second series arm resonator S2 from the output terminal T3, the third-order intermodulation distortion can be further suppressed while suppressing the increase in the element area, compared with the structure in which the series arm resonator S1 closest to the output terminal T3 is divided.

[0067] In addition, the number of divisions of the series arm resonator S2 is not particularly limited, and it may not be two. In addition, in addition to or instead of the series arm resonator S2 that is the second from the output terminal T3, other series arm resonators may be divided. The series arm resonator S1 closest to the output terminal T3 may also be divided, as long as the number of divisions of the series arm resonator S2 that is the second from the output terminal T3 is greater than the number of divisions of the series arm resonator S1 closest to the output terminal T3.

[0068] Figure 7 1 is a graph showing simulation results of third-order intermodulation distortion generated in the transmission filter circuits according to the first and second embodiments of the present invention. Figure 4 The resonant frequencies of the resonators are shown in Table 2 below (in MHz). The resonant frequencies of the series arm resonators S2a and S2b in the second embodiment are both 2294 MHz. Figure 7In the graph shown, the horizontal axis shows the frequency of the signal (MHz), and the vertical axis shows the third-order intermodulation distortion (dBm).

[0069] [Table 2]

[0070]

[0071] according to Figure 7 It can be seen that in the reception frequency band of Band 30, 2350 MHz to 2360 MHz, the second embodiment further suppresses the third-order intermodulation distortion by about 5 dB to 8 dB compared with the first embodiment.

[0072] As a first variation that can be combined with the first and second embodiments described above, for example, the capacitance value of the series arm resonator S1 closest to the output terminal T3 may be smaller than the capacitance value of the series arm resonator S2 that is the second from the output terminal T3. If the capacitance value of the resonator is small, the impedance generally becomes higher. Since the capacitance value of the series arm resonator S1 closest to the output terminal T3 is relatively small, the impedance in the frequency band of the interference wave to be attenuated is increased, and it becomes easy to suppress the intrusion of the interference wave as in the first embodiment described above. In addition, as long as the combined capacitance value of the divided plurality of resonators satisfies the above-mentioned magnitude relationship when the series arm resonator S1 and the series arm resonator S2 are divided.

[0073] Figure 8 1 is a graph showing simulation results of third-order intermodulation distortion generated in the transmission filter circuit according to the first variant and the comparative example of the present invention. Figure 4 The first modification example is a configuration in which the resonant frequency of each resonator is the same as that of the comparative example, and the capacitance value of the series arm resonator S1 is smaller than the capacitance value of the series arm resonator S2.

[0074] according to Figure 8 It can be seen that in the reception frequency band of Band 30, 2350 MHz to 2360 MHz, the transmission filter circuit according to the present modification reduces the third-order intermodulation distortion by about 4 dB to 7 dB compared with the comparative example.

[0075] Fig. 9 is a graph showing simulation results of attenuation characteristics in the transmission filter circuit according to the first modification example and the comparative example of the present invention. Figure 8 The simulation is the same as in . Fig. 9In the curve diagram shown, attenuation characteristics 400 and 410 are curve diagrams showing the results of the first variant example and the comparative example in units of 10 dB (refer to the scale of the vertical axis on the left), and attenuation characteristics 420 and 430 are curve diagrams showing the results of the first variant example and the comparative example in units of 1 dB (refer to the scale of the vertical axis on the right).

[0076] according to Fig. 9 It can be seen that in the transmission filter circuit according to this modification, similarly to the first embodiment, a slight loss is observed in the transmission frequency band to be passed, particularly on the high frequency side, compared with the comparative example, but there is no significant change in characteristics.

[0077] By making the capacitance value of the series arm resonator S1 smaller than the capacitance value of the series arm resonator S2, third-order intermodulation distortion can also be suppressed. In this modification, the resonance frequency of the series arm resonator S1 and the resonance frequency of the series arm resonator S2 may be higher.

[0078] As a second variation that can be combined with the above-mentioned first embodiment, second embodiment, and first variation, for example, the capacitance value of the parallel arm resonator P1 closest to the output terminal T3 may be larger than the capacitance values ​​of the first and second series arm resonators S1 and S2 from the output terminal T3. If the capacitance value of the resonator is large, the impedance generally becomes lower. Since the capacitance value of the parallel arm resonator P1 is relatively large, the impedance in the frequency band of the interference wave to be attenuated is reduced, making it easier for the interference wave to flow to the ground. As a result, not only can the intrusion of the interference wave be further suppressed, but also the third-order intermodulation distortion can be suppressed.

[0079] Furthermore, the configurations described in the first and second modified examples, in which the third-order intermodulation distortion is suppressed by adjusting the capacitance value of the resonator, may be implemented without being combined with the first and second embodiments.

[0080] The above is a description of an exemplary embodiment of the present invention. The transmission filter circuit 10, 10A includes: an input terminal T1 to which a transmission signal is supplied; an output terminal T3 connected to the antenna 30; a plurality of series arm resonators connected in series to the line U1 between the input terminal T1 and the output terminal T3, including a first series arm resonator closest to the output terminal T3 and a second series arm resonator second from the output terminal T3; and a parallel arm resonator, one end of which is connected to the connection point of the first series arm resonator and the second series arm resonator, and the other end of which is supplied with a reference potential, and the resonance frequency of the first series arm resonator is higher than the resonance frequency of the second series arm resonator. As a result, the interference wave that causes the generation of the third-order intermodulation distortion can be greatly attenuated in the series arm resonator closest to the output terminal T3. Therefore, the third-order intermodulation distortion can be suppressed. For example, when the frequency band of the transmission signal is lower than the frequency band of the reception signal, the third-order intermodulation distortion generated in the frequency band of the reception signal can be suppressed.

[0081] In the transmission filter circuit 10A, the number of divisions of the second series arm resonator is greater than the number of divisions of the first series arm resonator. This can further suppress third-order intermodulation distortion while suppressing an increase in element area, compared with a configuration in which the first series arm resonator closest to the output terminal T3 is divided.

[0082] In the transmission filter circuit 10, 10A, the plurality of series arm resonators further include a third series arm resonator provided on the input terminal T1 side relative to the second series arm resonator, and the resonance frequency of the third series arm resonator is higher than the resonance frequency of the first series arm resonator. As a result, the impedance in the passband of the transmission filter circuit 10 is restored from inductive to capacitive, and impedance matching can be achieved in the plurality of series arm resonators, so that the loss caused by the reflection of the signal can be suppressed, and the degradation of the insertion loss of the transmission filter circuit 10, 10A can be suppressed.

[0083] In the transmission filter circuits 10 and 10A, the capacitance value of the first series arm resonator may be smaller than the capacitance value of the second series arm resonator. This can significantly attenuate interference waves in the series arm resonator closest to the output terminal T3, thereby suppressing third-order intermodulation distortion.

[0084] In the transmission filter circuits 10 and 10A, the capacitance value of the parallel arm resonator is larger than the capacitance values ​​of the first series arm resonator and the second series arm resonator. As a result, the impedance of the parallel arm resonator in the frequency band of the interference wave to be attenuated is reduced, making it easier for the interference wave to flow to the ground. Therefore, not only can the intrusion of the interference wave be further suppressed, but also the third-order intermodulation distortion can be further suppressed.

[0085] Each embodiment described above is used to make the present invention easy to understand, and is not used to limit the interpretation of the present invention. The present invention can be changed or improved without departing from its purpose, and the present invention also includes its equivalent. That is, those skilled in the art appropriately apply the embodiment of design changes to each embodiment, as long as they have the features of the present invention, they are included in the scope of the present invention. For example, each element and its configuration, material, condition, shape, size, etc. possessed by each embodiment are not limited to the illustrated elements and their configuration, material, condition, shape, size, and can be appropriately changed. In addition, as long as it is technically feasible, each element possessed by each embodiment can be combined, and the embodiment in which they are combined is included in the scope of the present invention as long as it includes the features of the present invention.

Claims

1. A composite filter device, comprising: a transmit filter circuit; and Receive filter circuit, The transmission filter circuit comprises: A first input terminal is supplied with a transmission signal; The first output terminal is connected to the antenna; a plurality of series arm resonators connected in series in a line between the first input terminal and the first output terminal, and including a first series arm resonator closest to the first output terminal and a second series arm resonator second from the first output terminal; and The parallel arm resonator has one end connected to the connection point between the first series arm resonator and the second series arm resonator and the other end supplied with a reference potential. The resonant frequency of the first series arm resonator is higher than the resonant frequency of the second series arm resonator. The number of divisions of the second series arm resonator is greater than the number of divisions of the first series arm resonator. The receiving filter circuit comprises: a second input terminal connected to the antenna; and The second output terminal outputs a received signal.

2. The composite filter device according to claim 1, wherein: The plurality of series arm resonators further include a third series arm resonator provided on the first input terminal side relative to the second series arm resonator. A resonant frequency of the third series arm resonator is higher than a resonant frequency of the first series arm resonator.

3. The composite filter device according to claim 1 or 2, wherein: A capacitance value of the first series arm resonator is smaller than a capacitance value of the second series arm resonator.

4. The composite filter device according to claim 1 or 2, wherein: A capacitance value of the parallel arm resonator is larger than each capacitance value of the first series arm resonator and the second series arm resonator.

5. The composite filter device according to claim 3, wherein: A capacitance value of the parallel arm resonator is larger than each capacitance value of the first series arm resonator and the second series arm resonator.

6. The composite filter device according to claim 1 or 2, wherein: The frequency of the reception signal supplied to the reception filter circuit is higher than the frequency of the transmission signal.

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