JP5503764B2 - Filters, duplexers, communication modules - Google Patents

Description

  The present disclosure relates to filters. Moreover, it is related with the duplexer provided with the filter, and the communication module.

  Due to the rapid spread of wireless devices such as mobile phone terminals, the demand for high-frequency filters is rapidly expanding. In particular, there is a strong demand for an elastic wave filter having a small size and high steepness.

  In recent years, the sophistication of wireless systems has progressed rapidly, and the required specifications for high-frequency filters have become very complex. For example, the transmission filter and the reception filter included in the duplexer have low loss in the pass band and high suppression in the other band (the reception filter band relative to the transmission filter band and the transmission filter band relative to the reception filter band). Is preferred.

  In general, a filter mounted on a mobile phone terminal or the like often has multiple stages of resonators connected to ensure a wide passband. For example, patent literature discloses an example of a ladder filter.

  JP 2004-15397 A

  However, in the above-described conventional configuration, if the number of ladder filters is increased in order to increase the number of attenuation poles in the suppression band, the loss in the pass band is increased.

  Further, in the configuration in which the inductor is connected to the parallel resonator, it is difficult to arrange the attenuation pole in the frequency band that needs the most suppression.

  Therefore, an object of the present invention is to provide a low-loss filter that can dispose an attenuation pole at an appropriate frequency position. Moreover, it aims at providing the duplexer and communication module provided with such a filter.

  The filter disclosed in the present application is a filter including a plurality of series resonators connected in series to a signal line and a plurality of parallel resonators connected in parallel to the signal line, At least two parallel resonators are connected in parallel to a signal line between the two series resonators, and inductors are respectively connected in series to the two parallel resonators, and the inductors have different inductances.

  According to the disclosure of the present application, the attenuation pole can be arranged at an appropriate frequency position in the high frequency band, and sufficient suppression of unnecessary bands can be realized. Further, since the number of attenuation poles can be increased without significantly increasing the number of filter stages, it is possible to reduce passband loss.

Circuit diagram of connecting the resonators S in series with the input terminal T _in and an output terminal T _out Circuit diagram of connecting the resonator P in parallel between the input terminal T _in and an output terminal T _out Characteristic diagram showing frequency characteristics of resonator S and resonator P 1A is a circuit diagram in which the resonator S shown in FIG. 1A is arranged on the series arm and the resonator P shown in FIG. 1B is arranged on the parallel arm. Characteristic diagram showing frequency characteristics of filter shown in FIG. 2A Circuit diagram showing the configuration of the ladder filter Circuit diagram showing the configuration of the ladder filter Circuit diagram of filter with inductance connected to parallel resonator Characteristic diagram showing frequency characteristics of filter shown in FIG. 4A Circuit diagram of filter with inductance connected to parallel resonator Characteristic diagram showing frequency characteristics of filter shown in FIG. 4A Circuit diagram showing a modification of a conventional filter Circuit diagram showing a modification of a conventional filter Circuit diagram showing a modification of a conventional filter Characteristic diagram showing frequency characteristics of filter shown in FIG. 6A The circuit diagram which shows the 1st structure of the filter of this Embodiment The circuit diagram which shows the 2nd structure of the filter of this Embodiment The circuit diagram which shows the modification of the filter of this Embodiment The circuit diagram which shows the modification of the filter of this Embodiment The circuit diagram which shows the modification of the filter of this Embodiment Circuit diagram with circuit constants added to a conventional filter (filter shown in FIG. 6A) Circuit diagram in which circuit constants are added to the filter of the present embodiment (filter shown in FIG. 10C) FIG. 11B is a characteristic diagram showing the frequency characteristics of the filter shown in FIG. 11B. 12 is a characteristic diagram showing the frequency characteristics shown in FIG. 12 and the frequency characteristics of the conventional filter shown in FIG. 11A. Enlarged view of portion Z in FIG. Enlarged view of portion Y in FIG. 14A The schematic diagram which shows an example of the chip layout of the surface acoustic wave filter (SAW filter) which employ | adopted the filter of this Embodiment Plan view of printed circuit board on which filter chip shown in FIG. 15A can be mounted The schematic diagram which shows an example of the chip layout of the piezoelectric thin film resonator filter (FBAR filter) which employ | adopted the filter of this Embodiment FIG. 16A is a plan view of a printed circuit board on which the filter chip shown in FIG. 16A can be mounted. Block diagram of a duplexer provided with a filter according to the present embodiment RF module block diagram Lattice filter circuit diagram

  The filter according to the embodiment of the present invention can take the following aspects based on the above configuration.

  That is, in the filter, the plurality of series resonators and the plurality of parallel resonators may be connected in a ladder shape.

  In the filter, the plurality of series resonators and the plurality of parallel resonators may be connected in a lattice form.

  In the filter, a plurality of parallel resonators including parallel resonators to which inductors having different inductances are connected can be grounded through one inductor.

(Embodiment)
[1. (Principle of filter etc.)
As described above, the filter is required to have a low loss in the pass band and high suppression in the suppression band. Furthermore, in recent years, for example, high suppression at higher harmonics (second harmonic and third harmonic) of the passband may be required to prevent cross modulation. In addition, for example, in order to prevent interference with a wireless system such as a wireless local area network (LAN) or Bluetooth (registered trademark), there is a demand for suppression in these use frequency bands.

  Ladder filters are widely used as a technique for realizing a low-loss high-frequency filter. The ladder filter is a high-frequency filter configured by connecting two resonators having different resonance frequencies in a ladder shape. The principle of the filter will be described with reference to FIGS. 1A to 1C.

Figure 1A is a circuit connecting a resonator S in series with the input terminal T _in and an output terminal T _out. Figure 1B is a circuit connecting a resonator P in parallel between the input terminal T _in and an output terminal T _out. The resonator S shown in FIG. 1A has a resonance frequency f _rs and an anti-resonance frequency f _as . The resonator P shown in FIG. 1B has a resonance frequency f _rp and an anti-resonance frequency f _ap . FIG. 1C shows the resonance characteristics of the resonator S and the resonator P. FIG.

2A shows a circuit diagram in which the resonator S shown in FIG. 1A is arranged on the series arm and the resonator P shown in FIG. 1B is arranged on the parallel arm. When having substantially the same value and the resonance frequency f _rs of the anti-resonance frequency f _ap and resonators S of the resonator P in FIG. 2A, it is possible to realize a filter characteristic shown in FIG. 2B. That is, the pass band is between the resonance frequency f _rp of the resonator P and the anti-resonance frequency f _as of the resonator S, and the lower side than the resonance frequency f _rp and the higher side than the anti-resonance frequency f _as are attenuated. A bandpass filter can be realized.

  In general, a filter mounted on a mobile phone terminal or the like often has a multistage connection of resonators shown in FIG. 2A in order to ensure a wider passband than that shown in FIG. 2B. As a filter for connecting resonators in multiple stages, there is a ladder filter in which a pair of ladder circuits are connected in multiple stages.

  FIG. 3A shows an example of a ladder filter. As shown in FIG. 3A, when ladder filters are connected in multiple stages, adjacent ladder circuits are connected in a mirror-inverted form in order to prevent reflection between the stages. In the following description, the resonator connected to the series arm is referred to as a series resonator, and the resonator connected to the parallel arm is referred to as a parallel resonator.

  When the resonators are connected in multiple stages as shown in FIG. 3A, the same kind of parallel resonators are connected in the parallel arm and the place where the same kind of series resonator is connected in the series arm as shown in the broken line frame in the figure. And there is a place. Since these similar types of resonators can be capacitively combined as one resonator as shown in FIG. 3B, the chip size can be reduced. Note that Patent Document 1 discloses an example of a ladder filter shown in FIG. 3B.

  In the ladder filter shown in FIG. 3B, a configuration in which an inductor is connected to the parallel resonator has been proposed in order to realize high suppression in the harmonics (second harmonic and third harmonic) of the passband as described above. Since the resonator functions as a capacitor outside the frequency band in which the resonance operation is performed, the parallel resonator to which the inductor is connected functions as an LC resonator outside the frequency band in which the resonance operation is performed.

  FIG. 4A shows a filter in which an inductor is connected to a parallel resonator. As shown in FIG. 4A, when inductors L1 and L2 having inductances H1 and H2 are connected in series to two parallel resonators P11 and P12 having a capacitance Cp, a frequency f1 outside the passband as shown in FIG. 4B. , F2 an attenuation pole is generated. The frequencies f1 and f2 of the attenuation pole can be calculated based on the following mathematical formula. In the following formula, Cp is the capacitance of the parallel resonator.

f1 = 1 / {2π (H1 · Cp) ^1/2 }
f2 = 1 / {2π (H2 · Cp) ^1/2 }
As described above, the number of attenuation poles can be increased by adding parallel resonators and connecting inductors in series with the parallel resonators.

  On the other hand, when one inductor L3 is connected to the parallel resonators P11 and P12 as shown in FIG. 5A, an attenuation pole is generated at a frequency f3 outside the passband as shown in FIG. 5B.

  The filter shown in FIG. 4A can have several modifications as shown in FIGS. 6A to 6C. In any case, two attenuation poles are generated by an inductor in the high frequency band of the pass band, and the circuit is equivalent to FIG. 4A. It becomes.

  Here, if the number of ladder filters is increased in order to increase the number of attenuation poles, the loss in the passband is increased. Further, in the configuration in which the inductor is connected to the parallel resonator, it is difficult to arrange the attenuation pole in the frequency band that needs the most suppression.

For example, FIG. 7 is a diagram showing the frequency characteristics of the filter shown in FIG. 6A. As shown in FIG. 7, in the filter shown in FIG. 6A, the two attenuation poles generated in the high frequency band are between the Rx band and the Bluetooth (hereinafter referred to as BT) band (attenuation pole A), and twice the Tx. Between the wave and the Tx triple wave (attenuation pole B). These attenuation poles are required to be arranged in frequency bands (BT band, Tx second harmonic band, Tx third harmonic band) that most require suppression. In the following embodiment, attenuation is performed at an appropriate frequency position in the high frequency band. A pole can be arranged and a low-loss filter can be provided.

[2. Filter configuration
FIG. 8 is a circuit diagram of a first configuration of the filter according to the present embodiment. In the filter shown in FIG. 8, series resonators S11, S12, and S13 are connected to a series arm (signal line). In addition, parallel resonators P21 and P22 are connected in parallel with the series arm (signal line) between adjacent series resonators S11 and S12. Further, parallel resonators P23 and P24 are connected in parallel with the series arm between the adjacent series resonators S12 and S13. In addition, an inductor L11 is connected to the parallel resonator P21. In addition, an inductor L12 is connected to the parallel resonator P22. In addition, an inductor L13 is connected to the parallel resonator P23. In addition, an inductor L14 is connected to the parallel resonator P24. The inductors L11 to L14 have different inductances (values).

  In the filter shown in FIG. 8, the parallel resonators combined into one are divided in parallel, and inductors having different inductances are connected to the respective parallel resonators. With such a circuit configuration, it is possible to increase the number of attenuation poles without increasing the number of resonator stages. That is, the filter shown in FIG. 8 has the same number of resonator stages as the filter shown in FIG. 4A and has four stages, but can have four attenuation poles (the filter shown in FIG. 4A has four attenuation poles). 2 places).

  Note that the number of stages of the filter is one stage including one series resonator and one parallel resonator. For example, in the circuit shown in FIG. 4A, S11 and P11, S12 and P11, S13 and P12, and S14 and P12 are combined to realize a total of four stages of filters. On the other hand, in the circuit shown in FIG. 8, S11 and P21, S12 and P22, S13 and P23, and S14 and P24 form a set, thereby realizing a total of four stages of filters.

  FIG. 9 is a circuit diagram of a second configuration of the filter according to the present embodiment. The filter shown in FIG. 9 has series resonators S11, S12, and S13 connected to the series arm. Further, parallel resonators P21 and P22 are connected between the series resonators S11 and S12 in parallel with the series arm. A parallel resonator P23 is connected in parallel with the series arm between the series resonators S12 and S13. In addition, an inductor L11 is connected to the parallel resonator P21. In addition, an inductor L12 is connected to the parallel resonator P22. In addition, an inductor L13 is connected to the parallel resonator P23. The inductors L11 to L13 have different inductances.

  In the filter shown in FIG. 9, the parallel resonators combined into one are divided in parallel, and inductors having different inductances are connected to the respective parallel resonators. With such a circuit configuration, it is possible to add attenuation poles without increasing the number of resonator stages. That is, the filter shown in FIG. 9 has four resonator stages similar to the filter shown in FIG. 4A, etc., but can have three attenuation poles (in the filter shown in FIG. 4A, the attenuation poles are 2 places).

  In addition, the filter in this Embodiment can be used as a filter corresponding to WCDMA_Band2 as an example. In WCDMA_Band2, three attenuation poles are required for the high frequency band (BT band, Tx second harmonic band, Tx third harmonic band). Therefore, the filter shown in FIG. 8 can correspond to WCDMA_Band2. Also, as shown in FIG. 9, even if one branch connecting the parallel resonator and the inductor is deleted, it is possible to cope with WCDMA_Band2.

  10A to 10C show a modification of the filter according to the present embodiment. In the filter shown in FIG. 10A, the inductor L11 is connected to the parallel resonator P21, the inductor L12 is connected to the parallel resonator P22, and the inductor L13 is connected to the inductors L11, L12 and the parallel resonator P23. At this time, the inductance of each inductor is set so that the combined inductance of the inductors L11 and L13, the combined inductance of the inductors L12 and L13, and the inductance of the inductor L13 do not have the same value.

  In the filter shown in FIG. 10B, the inductor L11 is connected to the parallel resonator P21, the inductor L12 is connected to the parallel resonator P23, and the inductor L13 is connected to the inductors L11, L12, and the parallel resonator P22. At this time, the inductance of each inductor is set so that the combined inductance of the inductors L11 and L13, the combined inductance of the inductors L12 and L13, and the inductance of the inductor L13 do not have the same value.

  In the filter shown in FIG. 10C, the inductor L11 is connected to the parallel resonator P21, the inductor L12 is connected to the parallel resonator P24, and the inductor L13 is connected to the inductors L11 and L12, and the parallel resonators P22 and P23. At this time, the inductance of each inductor is set so that the combined inductance of the inductors L11 and L13, the combined inductance of the inductors L12 and L13, and the inductance of the inductor L13 do not have the same value.

  Hereinafter, a comparison between the filter of FIG. 6A and the filter of FIG. 10C will be described.

  FIG. 11A is a diagram in which circuit constants are added to the filter shown in FIG. 6A. FIG. 11B is a diagram in which circuit constants are added to the filter of this embodiment (the filter shown in FIG. 10C). The circuit constants shown in FIG. 11B are, for example, a Tx second harmonic (3760 MHz) required suppression of 25 dB, a Tx third harmonic (5640 MHz) required suppression of 25 dB, and a BT band (2400 to 2500 MHz band) required suppression of 30 dB. Was set as follows.

  FIG. 12 shows the frequency characteristics of the filter having the circuit constant shown in FIG. 11B. As shown in FIG. 12, according to the filter of the present embodiment, attenuation poles can be formed at three locations, and each attenuation pole can be arranged in a frequency band that needs to be suppressed. That is, the attenuation pole A can be arranged near the BT band, the attenuation pole B can be arranged near the Tx second harmonic band (hereinafter referred to as 2Tx band), and the attenuation pole C is arranged in the Tx third harmonic band ( (Hereinafter referred to as 3Tx band).

  FIG. 13 shows the frequency characteristic (solid line in the figure) shown in FIG. 12 and the frequency characteristic (dashed line in the figure) of the filter having the circuit constant shown in FIG. 11A. As shown in FIG. 13, in the filter shown in FIG. 11A, the attenuation pole D is disposed between the Rx band and the BT band, and the attenuation pole E is disposed between the 2Tx band and the 3Tx band. However, sufficient suppression could not be obtained in the BT band, 2Tx band, and 3Tx band to be most suppressed. On the other hand, in the filter of FIG. 11B, the attenuation pole A is arranged near the BT band, the attenuation pole B is arranged near the 2Tx band, and the attenuation pole C is arranged near the 3Tx band. The desired frequency band can be suppressed.

  FIG. 14A is an enlarged view of the passband (Z portion) in FIG. FIG. 14B is an enlarged view of a Y portion in FIG. 14A. 14A and 14B, the solid line is the frequency characteristic in the filter shown in FIG. 11B, and the broken line is the frequency characteristic in the filter shown in FIG. 11A. As shown in FIGS. 14A and 14B, since the desired frequency band is suppressed by the attenuation pole in the high frequency band, the attenuation amount of the ladder filter itself can be set low. As a result, the loss in the passband can be greatly improved.

  FIG. 15A is an example of a chip layout of a surface acoustic wave filter (SAW filter) employing the filter of the present embodiment. FIG. 15B is a plan view of a printed circuit board on which the surface acoustic wave filter shown in FIG. 15A can be flip-bonded. The filter illustrated in FIG. 15A is an example of the chip layout of the filter illustrated in FIG. 10C. The filter illustrated in FIG. 15A is an example of a transmission filter chip mounted on a communication device or the like. In FIG. 15A, the bump electrode 11 is connected to the antenna terminal Ant shown in FIG. 15B. The bump electrode 12 is connected to a Tx terminal shown in FIG. 15B and is connected to a transmission circuit or a power amplifier. The bump electrode 13 is connected to the inductor L11 shown in FIG. 15B. The bump electrode 14 is connected to the inductor L12 shown in FIG. 15B. The bump electrode 15 is connected to the inductor L13 shown in FIG. 15B. The bump electrodes 11 to 15 are electrically connected to each other through the conductor pattern 16. A resonator is arranged on the conductor pattern 16 that connects the bump electrodes. Moreover, the inductors L11, L12, and L13 shown in FIG. 15B are formed of spiral coils.

In FIG. 15A, the resonators C _s11 and C _s12 correspond to the series resonator S11 in FIG. 10C. The resonators C _{s21 to} C _s23 correspond to the series resonator S12 in FIG. 10C. The resonators C _{s31 to} C _s33 correspond to the series resonator S13 in FIG. 10C. The resonators C _p11 and C _p12 correspond to the parallel resonator P21 in FIG. 10C. The resonators C _p21 and C _p22 correspond to the parallel resonator P22 in FIG. 10C. The resonator C _p3 corresponds to the parallel resonator P23 in FIG. 10C. The resonator C _p4 corresponds to the parallel resonator P24 in FIG. 10C.

  FIG. 16A is an example of a chip layout of a piezoelectric thin film resonator filter (FBAR filter) employing the filter of the present embodiment. FIG. 16B is a plan view of a printed circuit board on which the filter chip shown in FIG. 16A can be mounted. The filter illustrated in FIG. 16A is an example of the chip layout of the filter illustrated in FIG. 10C. The filter illustrated in FIG. 16A is an example of a transmission filter chip mounted on a communication device or the like. In FIG. 16A, the bump electrode 21 is connected to the antenna terminal Ant shown in FIG. 16B. The bump electrode 22 is connected to the Tx terminal shown in FIG. 16B and is connected to a transmission circuit or a power amplifier. The bump electrode 23 is connected to the inductor L11. The bump electrode 24 is connected to the inductor L12. The bump electrode 25 is connected to the inductor L13. The bump electrodes 21 to 25 are electrically connected to each other through a conductor pattern 26. A resonator is arranged on the conductor pattern 26 that connects the bump electrodes. In addition, inductors L11, L12, and L13 shown in FIG. 16B are formed of spiral coils.

In FIG. 16A, the resonator C _s1 corresponds to the series resonator S11 in FIG. 10C. The resonator C _s2 corresponds to the series resonator S12 in FIG. 10C. The resonators C _s11 and C _s12 correspond to the series resonator S13 in FIG. 10C. The resonator C _p1 corresponds to the parallel resonator P21 in FIG. 10C. The resonator C _p2 corresponds to the parallel resonator P22 in FIG. 10C. The resonator C _p3 corresponds to the parallel resonator P23 in FIG. 10C. The resonator C _p4 corresponds to the parallel resonator P24 in FIG. 10C.

[3. (Duplexer configuration)
FIG. 17 is a block diagram of a duplexer including the filter according to the present embodiment. As illustrated in FIG. 17, the duplexer 102 includes a reception filter 103 and a transmission filter 104. The duplexer 102 filters the reception signal input via the antenna 101 by the reception filter 103 and extracts the reception signal Rx in a desired frequency band. Further, the duplexer 102 filters the input transmission signal Tx by the transmission filter 104 and outputs it through the antenna 101.

  The circuit configuration of the transmission filter 104 can be, for example, FIG. 8, FIG. 9, FIG. 10A, FIG. 10B, or FIG. Thereby, the transmission filter 104 can be made to correspond to the specification of WCDMA_Band2, for example. As an example, the pass band of the transmission filter 104 can be 1850 MHz to 1910 MHz. The other band (reception filter pass band) is 1930 MHz to 1990 MHz. In this case, the Tx second harmonic can be 3760 MHz, and the Tx third harmonic can be 5640 MHz. Further, in order to prevent interference with a Bluetooth standard system, suppression in the 2400 to 2500 MHz band is also possible.

[4. Effects of the embodiment, etc.]
According to the present embodiment, it is possible to increase the number of attenuation poles without significantly increasing the number of stages of the filter by connecting the parallel resonators in the ladder filter to inductors having different inductances. Further, since the attenuation pole can be arranged in a desired frequency band, a filter that can suppress the desired frequency band can be realized. Moreover, suppression in the passband can be reduced.

  In the present embodiment, the capacitance ratio of all the resonators used in the filter is fixed to “16” assuming a surface wave device in order to clarify the comparison. The resonance frequencies of the plurality of series resonators included in the filter are all the same. The resonance frequencies of the plurality of parallel resonators included in the filter are all the same. When actually designing a circuit based on the filter of the present embodiment, the capacitance ratio and the resonance frequency of each resonator can be set arbitrarily.

  In the present embodiment, a surface acoustic wave device has been described as an example of realization of a filter. However, it is also applicable to a piezoelectric thin film resonator (FBAR (Film Bulk Acoustic Resonator) type, SMR (Solid Mounted Resonator) type) and other ceramic filters. Is possible.

  The filter of this embodiment is not limited to a duplexer, but can be applied to an RF module such as a duplexer bank module in which a plurality of duplexers are modularized, or a duplexer amplifier module in which an amplifier and a duplexer are modularized. It is.

  FIG. 18 is a block diagram of an RF module including a duplexer bank module. As shown in FIG. 18, the RF module includes a switch module 202, a duplexer bank module 203, and an amplifier module 204. The switch module 202 is connected to the duplexers in the antennas 201 a and 201 b and the duplexer bank module 203. The duplexer bank module 203 includes a plurality of duplexers 203a, 203b, 203c,. The filter according to the present embodiment can be mounted on a reception filter and / or a transmission filter in the duplexers 203a, 203b, 203c,... In the duplexer bank module 203.

  In the present embodiment, the ladder filter is described as an example. However, as shown in FIG. 19, the same effect can be obtained even with a lattice filter in which resonators are connected in a lattice form. The lattice filter includes two signal lines and a connecting line connected between the signal lines. A series resonator is connected to the signal line, and a parallel resonator is connected to the connecting line. At least two parallel resonators are connected in parallel between the signal lines. By connecting an inductor in series with the two parallel resonators and further realizing the inductor with elements having different inductances, the same effect as in the present embodiment can be obtained.

(Appendix 1)
A filter including a plurality of series resonators connected in series to a signal line, and a plurality of parallel resonators connected in parallel to the signal line,
At least two parallel resonators are connected in parallel to a signal line between two of the plurality of series resonators,
An inductor is connected in series to the two parallel resonators,
The inductor is a filter having different inductances.

(Appendix 2)
The filter according to appendix 1, wherein the plurality of series resonators and the plurality of parallel resonators are connected in a ladder shape.

(Appendix 3)
The filter according to appendix 1, wherein the plurality of series resonators and the plurality of parallel resonators are connected in a lattice form.

(Appendix 4)
The filter according to any one of appendices 1 to 3, wherein a plurality of parallel resonators including a parallel resonator to which inductors having different inductances are connected are grounded via one inductor.

(Appendix 5)
In a multistage ladder filter composed of a plurality of series resonators connected to a signal line and a plurality of parallel resonators connected to a feedback line, at least one parallel resonator between the series resonators is parallel to two or more. A filter that is demarcated and that has different inductance values connected in series to each of the demarcated resonators.

(Appendix 6)
At least one resonator connected to a connecting line in a multistage lattice filter including a plurality of resonators connected to two signal lines and a plurality of resonators connected to a connecting line connecting between the signal lines Are divided into two or more in parallel, and the inductances connected in series to each of the divided resonators have different values.

(Appendix 7)
The filter according to appendix 5, wherein a plurality of parallel resonators including parallel resonators that are divided in parallel and connected to different inductances are grounded through a single shared inductance.

(Appendix 8)
The filter according to appendix 7, wherein the shared inductance is built in the package or the printed board.

(Appendix 9)
The filter according to any one of appendices 5 to 8, wherein at least one of the series resonator and the parallel resonator is a surface acoustic wave element.

(Appendix 10)
The filter according to any one of appendices 5 to 8, wherein at least one of the series resonator and the parallel resonator is a piezoelectric thin film resonator.

(Appendix 11)
The filter according to any one of appendices 5 to 8, wherein at least one of the series resonator and the parallel resonator is a bulk wave element.

(Appendix 12)
The duplexer provided with the filter as described in any one of Additional remarks 1-11.

(Appendix 13)
The communication module provided with the filter as described in any one of Additional remarks 1-11.

  The present invention relates to a filter, a duplexer, and a communication module.

S11, S12, S13, S14 Series resonator P11, P12, P13, P14 Parallel resonator

Claims (6)

A filter including a plurality of series resonators connected in series to a signal line, and a plurality of parallel resonators connected in parallel to the signal line,
The signal line between two series resonators adjacent to each other among the plurality of series resonators, and two adjacent parallel resonators are connected in parallel, and the signal line between two other adjacent series resonators, At least one parallel resonator is connected in parallel;
A first inductor is connected in series to one parallel resonator of two adjacent parallel resonators connected in parallel to a signal line between the two adjacent series resonators,
A second inductor is connected in series to one parallel resonator of at least one parallel resonator connected in parallel to the signal line between the other two adjacent series resonators,
Between the other two parallel resonators of the two adjacent parallel resonators connected in parallel to the signal line between the two adjacent series resonators and the first inductor, and the other two adjacent series resonators The second inductor connected in series to the one parallel resonator of at least one parallel resonator connected in parallel to the signal line , or the second inductor of the at least one parallel resonator connected in series. A third inductor is connected to the parallel resonator and the second inductor ,
In the first, second, and third inductors, the combined inductance of the first inductor and the third inductor and the combined inductance of the second inductor and the third inductor have the same value. A filter that is set not to be.   The filter according to claim 1, wherein the plurality of series resonators and the plurality of parallel resonators are connected in a ladder shape. Two adjacent parallel resonators connected in parallel to a signal line between the two adjacent series resonators, and at least one parallel resonance connected in parallel to a signal line between the other two adjacent series resonators The filter according to claim 1 or 2 , wherein a child is grounded via the third inductor . The third inductor is incorporated in a package or printed circuit board, the filter of claim 3. The duplexer provided with the filter as described in any one of Claims 1-3 . The communication module provided with the filter as described in any one of Claims 1-3 .

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