Filter module and electronic device

Abstract

The filter module (101) includes a circuit board (20) forming a ground electrode and a low-pass filter (11) mounted on the circuit board (20). The low-pass filter (11) includes a first inductor (L1), a second inductor (L2), and a capacitor (C2). The first inductor (L1) and the second inductor (L2) are connected in series. Let Lp denote the inductance of the path between the connection portion (CP) of the first inductor (L1) and the second inductor (L2) and the ground terminal (GND), let Lg denote the inductance of the path between the ground terminal (GND) and the ground electrode, and let M denote the mutual inductance between the first inductor (L1) and the second inductor (L2). At this time, the relationship of Lp + Lg - M ≥ 0 and Lp - M < 0 holds.

Description

Technical Field

[0001] The present invention relates to a filter module including a high-frequency filter circuit, a filter element for the filter module, and an electronic device including the filter module or the filter element. Background Art

[0002] Patent Document 1 discloses a low-pass filter composed of two coils formed inside a laminate and a plurality of capacitors. These two coils are spiral coils each having a central axis extending in the stacking direction of a plurality of insulator layers.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-21449 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In the low-pass filter described in Patent Document 1, there is a parasitic inductor in the structure between the connection portion of the two coils inside it and the ground terminal.

[0008] In addition, the low-pass filter described in Patent Document 1 is used by being mounted on a circuit board. The ground terminal of the low-pass filter is connected to the ground terminal of the circuit board, and there is also a parasitic inductor between the ground terminal of the circuit board and the reference potential electrode (usually a ground electrode extending over a large area) of the circuit board.

[0009] Reference Figure 12A 、 Figure 12B To explain the above situation. Figure 12A is an equivalent circuit diagram of the low-pass filter shown in Patent Document 1, Figure 12B is an equivalent circuit diagram in a state where the low-pass filter is mounted on a circuit board.

[0010] In Figure 12A the low-pass filter 10 includes a first terminal T1, a second terminal T2, and a ground terminal GND, and the low-pass filter is composed of inductors L1 and L2 connected in series and capacitors C1, C2, and C3 shunted to the ground.

[0011] However, inductive components such as parasitic inductance are generated between the connection portion CP of the inductor L1 and the inductor L2 and the ground terminal GND. Figure 12AThe inductor Lp therein is an element representing the inductive component. The inductive component Lp resonates with the capacitor C2 connected in series with the inductive component Lp, so an attenuation pole is generated at its resonance frequency, and in a frequency band higher than the attenuation pole, the attenuation amount decreases. Therefore, it is difficult to use it on the high-frequency band side when broadband attenuation is required in the high-frequency band.

[0012] In addition, as Figure 12B shown, in the circuit board 20 on which the low-pass filter 10 is mounted, inductive components such as parasitic inductance are generated between the reference potential electrode (ground electrode extended to a large area) of the circuit board and the ground terminal connection pad connecting the ground terminal GND of the low-pass filter 10. Figure 12B The inductor Lg therein is an element representing the inductive component. Therefore, in the actual use state, the combined inductance of the inductive component Lp and the inductive component Lg resonates with the capacitance of the capacitor C2, and an attenuation pole is generated at its resonance frequency. Therefore, in a frequency band higher than the attenuation pole, the attenuation amount decreases.

[0013] On the other hand, in recent applications, there is a tendency that the frequency band ensuring a given attenuation amount in the attenuation band becomes wider. For example, in a low-pass filter that blocks high-frequency broadband frequency bands such as 5G (fifth generation) and UWB (ultra-wideband), the frequency band to be attenuated should span a wide band. Therefore, it is required to ensure the attenuation amount of the attenuation band of the low-pass filter across a wide band.

[0014] Therefore, an object of the present invention is to provide a filter module having good attenuation characteristics across a wide band on the high-frequency side relative to the passband, a filter element for the filter module, and an electronic device including the filter module or the filter element.

[0015] Technical solutions for solving the problems

[0016] (1) A filter module as an example of the present disclosure includes a circuit board on which a ground electrode is formed and a filter element mounted on the circuit board. The filter module is characterized in that the filter element includes: a first inductor and a second inductor, which are connected in series between a first terminal and a second terminal and magnetically couple with each other; and a capacitor, which is connected between the connection portion of the first inductor and the second inductor and a ground terminal. The first inductor and the second inductor are cumulatively connected. Let M represent the mutual inductance generated between the connection portion and the ground terminal by the magnetic coupling of the first inductor and the second inductor, Lp represent the inductance between the connection portion and the ground terminal, and Lg represent the inductance of the path between the ground terminal and the ground electrode. At this time, the relationship of Lp + Lg - M ≥ 0 and Lp - M < 0 is satisfied.

[0017] With the above structure, the negative mutual inductance generated by the magnetic field coupling of the first inductor and the second inductor in the path shunt-connected to the ground terminal can suppress the synthetic inductance component generated between the connection portion of the first inductor and the second inductor and the ground electrode of the circuit board. Based on this, the resonance frequency of the synthetic inductance and the capacitance of the capacitor shifts to a frequency band higher than the use frequency band. In addition, by satisfying the relationship of Lp + Lg - M ≥ 0, an attenuation pole is generated due to the resonance of the synthetic inductance and the capacitance of the capacitor.

[0018] (2) A filter element as an example of the present disclosure is a capacitor-integrated filter mounted on a circuit board formed with a ground electrode. The filter element is characterized by including: a ground terminal connected to the ground electrode; a first inductor and a second inductor connected in series between a first terminal and a second terminal and magnetically coupled to each other; and a capacitor connected between the connection portion of the first inductor and the second inductor and the ground terminal. The first inductor and the second inductor are connected in series, and M represents the mutual inductance generated between the connection portion and the ground terminal by the magnetic field coupling of the first inductor and the second inductor, and Lp represents the inductance between the connection portion and the ground terminal. At this time, the relationship of Lp - M < 0 is satisfied.

[0019] With the above structure, the negative mutual inductance generated by the magnetic field coupling of the first inductor and the second inductor in the path shunt-connected to the ground terminal can suppress the synthetic inductance component generated between the connection portion of the first inductor and the second inductor and the ground electrode of the circuit board. Based on this, the resonance frequency of the synthetic inductance and the capacitance of the capacitor shifts to a frequency band higher than the use frequency band.

[0020] (3) An electronic device as an example of the present disclosure includes the filter module or the filter element.

[0021] Advantages of the Invention

[0022] According to the present invention, a filter module having good attenuation characteristics across a wide band on the high-frequency side of the passband, a filter element for the filter module, and an electronic device including the filter module or the filter element can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A It is a circuit diagram of a filter module 101 according to the first embodiment. Figure 1B It is an equivalent circuit diagram of the filter module 101.

[0024] Figure 2 It is an equivalent circuit diagram representing the mutual inductance generated by the magnetic field coupling of the first inductor L1 and the second inductor L2 as a circuit element.

[0025] Figure 3A , Figure 3B is a perspective view of the low-pass filter 11.

[0026] Figure 4 is an exploded bottom view showing the respective insulator layers of the low-pass filter 11 and the conductor patterns formed on these insulator layers.

[0027] Figure 5 is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 101.

[0028] Figure 6 is a perspective view of the filter module 102 according to the second embodiment.

[0029] Figure 7 is a front view of the filter module 102.

[0030] Figure 8 is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 102.

[0031] Figure 9A is a circuit diagram of the filter module 103 according to the third embodiment. Figure 9B is an equivalent circuit diagram of the filter module 103.

[0032] Figure 10 is a diagram showing the frequency characteristics of the transmission coefficient of the band-pass filter 13.

[0033] Figure 11 is a block diagram showing the structure of the electronic device 201 according to the fourth embodiment.

[0034] Figure 12A is an equivalent circuit diagram of the low-pass filter shown in Patent Document 1, Figure 12B is an equivalent circuit diagram in a state where this low-pass filter is mounted on a circuit board. Detailed Embodiments

[0035] Hereinafter, several specific examples will be cited with reference to the drawings to illustrate multiple modes for implementing the present invention. In each figure, the same reference numerals are assigned to the same parts. For ease of explanation or understanding, for the sake of convenience, the embodiments are shown divided into multiple embodiments, but partial replacement or combination of the structures shown in different embodiments can be performed. After the second embodiment, the description of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, the same functions and effects based on the same structure will not be repeatedly mentioned in each embodiment.

[0036] "First Embodiment"

[0037] Figure 1AIt is a circuit diagram of the filter module 101 according to the first embodiment. Figure 1B It is an equivalent circuit diagram of the filter module 101. The filter module 101 includes a low-pass filter 11 and a circuit board 20 forming a ground electrode.

[0038] Figure 1A The shown low-pass filter 11 has a first terminal T1, a second terminal T2, and a ground terminal GND. In addition, the low-pass filter 11 includes: a first inductor L1 and a second inductor L2, which are connected in series between the first terminal T1 and the second terminal T2 and magnetically couple with each other; and a capacitor C2, which is connected between the connection part CP of the first inductor L1 and the second inductor L2 and the ground terminal GND. Hereinafter, the reference numeral of the inductor and the reference numeral of the inductance of the inductor are used in common. Therefore, for example, L1 is used to represent the inductance of the inductor L1.

[0039] In Figure 1A An inductance component Lp such as a parasitic inductance is generated between the connection part CP of the shown first inductor L1 and the second inductor L2 and the ground terminal GND. In Figure 1B this, the inductance component is represented by the inductor Lp.

[0040] The ground electrode of the circuit board 20 is the reference potential electrode of the circuit board 20 and is usually an electrode extended to a large area. That is, in this specification, the so-called "ground electrode" is a planar electrode that becomes the reference potential in the circuit. As Figure 1B shown, an inductance component Lg such as a parasitic inductance is generated between the reference potential electrode of the circuit board 20 and the ground terminal connection pad connecting the ground terminal GND of the low-pass filter 11. In Figure 1B this, the inductance component is represented by the inductor Lg.

[0041] Figure 2 It is an equivalent circuit diagram representing the mutual inductance generated by the magnetic coupling of the first inductor L1 and the second inductor L2 as a circuit element. As Figure 2 shown, when the circuit connected between the first terminal T1 and the second terminal T2 is represented by a T-type equivalent circuit including inductors LA, LB, and LC, the inductor LC representing the mutual inductance is shunt-connected between the connection point of the serially connected inductors LA and LB and the ground terminal GND. Since the first inductor L1 and the second inductor L2 are cumulatively connected, the inductance of the inductor LA is (L1 + M), the inductance of the inductor LB is (L2 + M), and the inductance of the inductor LC is (-M).

[0042] With the above structure, a negative mutual inductance (-M) is generated in the path shunt-connected to the ground terminal GND by the magnetic field coupling between the first inductor L1 and the second inductor L2. By this negative mutual inductance (-M), the inductance component generated between the connection part CP of the first inductor L1 and the second inductor L2 and the ground electrode of the circuit board 20 can be suppressed. Therefore, based on the negative mutual inductance (-M), the combined inductance of the inductance component Lp, the inductance component Lg, and the resonance frequency (attenuation pole frequency) of the capacitance of the capacitor C2 shift to a frequency band higher than the usage frequency band.

[0043] In addition, in the low-pass filter described in Patent Document 1, the two coils are differentially connected, so the mutual inductance generated by their magnetic field coupling is positive. Therefore, the combined inductance generated in the path shunt-connected to the ground terminal GND of the low-pass filter becomes even larger.

[0044] In Figure 1B the relationship among the inductance component Lg, the inductance component Lp, and the mutual inductance (-M) generated between the ground electrode of the circuit board 20 and the ground terminal GND of the low-pass filter 11 is as follows.

[0045] Lp + Lg - M ≥ 0

[0046] Lp - M < 0

[0047] Thus, the inductance component Lg is suppressed by the negative inductance (Lp - M). In addition, by Lp + Lg - M ≥ 0, an attenuation pole based on the resonance of the above combined inductance and the capacitance of the capacitor C2 is generated.

[0048] Figure 3A 、 Figure 3B is a perspective view of the low-pass filter 11. In Figure 3A and Figure 3B the viewpoints are different. In addition, the interior is shown transparently.

[0049] The low-pass filter 11 includes a stacked body 1 having a rectangular parallelepiped shape formed by stacking a plurality of rectangular insulators layer by layer. On the outer surface of the stacked body 1, a first terminal electrode ET1, a second terminal electrode ET2, and two ground terminal electrodes EGND are formed.

[0050] The first inductor L1 includes a coil-shaped conductor CL1 formed in the stacked body 1 of a plurality of insulator layers, and the second inductor L2 includes a coil-shaped conductor CL2 formed in the stacked body 1 of a plurality of insulator layers.

[0051] The capacitor C2 includes capacitor electrodes C2a, C2b, C2c that face each other in the stacking direction of the plurality of insulator layers, and an insulator layer sandwiched between these capacitor electrodes.

[0052] The connecting portion of the coil-shaped conductor CL1 of the first inductor L1 and the coil-shaped conductor CL2 of the second inductor L2 is connected to the capacitor electrode C2b via the interlayer connection conductor V.

[0053] One end of the coil-shaped conductor CL1 of the first inductor L1 is electrically connected to the first terminal electrode ET1, and one end of the coil-shaped conductor CL2 of the second inductor L2 is electrically connected to the second terminal electrode ET2. The capacitor electrodes C2a and C2c are electrically connected to the ground terminal electrode EGND, and the capacitor electrode C2b is electrically connected to the connecting portion of the coil-shaped conductor CL1 of the first inductor L1 and the coil-shaped conductor CL2 of the second inductor L2 via the interlayer connection conductor V.

[0054] Figure 4 FIG. is an exploded perspective view showing each insulating layer of the low-pass filter 11 and the conductor patterns formed on these insulating layers.

[0055] The laminate 1 is formed by laminating the insulating layers S1 to S11. In Figure 4 a perspective view of each insulating layer is shown. The insulating layer S1 is the uppermost insulating layer, and the insulating layer S11 is the lowermost insulating layer. The insulating layers S2 to S10 are insulating layers between the uppermost insulating layer S1 and the lowermost insulating layer S11.

[0056] The coil-shaped conductors CL1a, CL1b, CL1c, and CL1d formed on the insulating layers S1 to S4 Figure 3A and Figure 3B constitute the coil-shaped conductor CL1 shown. Similarly, the coil-shaped conductors CL2a, CL2b, CL2c, and CL2d constitute the coil-shaped conductor CL2.

[0057] In addition, the capacitor electrodes C2a, C2b, and C2c formed on the insulating layers S8 to S10 and the insulating layers S9 and S10 constitute the capacitor C2.

[0058] When viewed in the winding axis WA direction (see Figure 3A and Figure 3B ) of the coil-shaped conductors CL1 and CL2, the coil-shaped conductors CL1 and CL2 have at least a part that does not overlap with the capacitor electrodes C2a, C2b, and C2c. Thereby, the useless parasitic capacitance generated between the coil-shaped conductors CL1 and CL2 and the capacitor electrodes C2a, C2b, and C2c can be suppressed.

[0059] Side terminal electrodes E1 and E2 are formed on the insulating layers S1 to S11. In addition, side terminal electrodes E1, E2, E3, and E4 are formed on the insulating layers S8 to S11. Regarding the side terminal electrodes E1, E2, E3, and E4 formed on each insulating layer, the terminal electrodes with the same reference numerals are electrically connected to each other.

[0060] One end of the coil-shaped conductor CL1a is electrically connected to the side terminal electrode E1, and one end of the coil-shaped conductor CL2a is electrically connected to the side terminal electrode E2. The capacitor electrodes C2a and C2c are electrically connected to the side terminal electrodes E3 and E4, respectively.

[0061] When observed in the winding axis WA direction of the coil-shaped conductor, the capacitor electrodes C2a, C2b, and C2c have portions that do not overlap with the first terminal electrode ET1 and the second terminal electrode ET2. Thereby, the useless parasitic capacitance generated between the capacitor electrodes C2a, C2b, C2c and the first terminal electrode ET1 and the second terminal electrode ET2 can be suppressed. Alternatively, it may be configured such that, when observed in the winding axis WA direction of the coil-shaped conductor, the capacitor electrodes C2a, C2b, and C2c have portions that do not overlap with either the first terminal electrode ET1 or the second terminal electrode ET2. For example, if the capacitor electrodes C2a, C2b, and C2c are configured to have portions that do not overlap with the first terminal electrode ET1, the Figure 1A parasitic capacitance between the capacitor C2 and the first terminal T1 as shown can be suppressed. Similarly, if the capacitor electrodes C2a, C2b, and C2c are configured to have portions that do not overlap with the second terminal electrode ET2, the parasitic capacitance between the capacitor C2 and the second terminal T2 can be suppressed.

[0062] Each of the insulating layers S1 to S11 of the laminate 1 is formed by screen printing, exposure, and development of a photosensitive insulating paste and a photosensitive conductive paste, and the laminate 1 is formed by laminating these insulating layers S1 to S11.

[0063] Specifically, the photosensitive insulating paste layer is screen printed, irradiated with ultraviolet light, and developed with an alkaline solution. Thereby, an insulating substrate pattern having openings for external electrodes, vias, etc. is formed. In addition, the photosensitive conductive paste is screen printed, irradiated with ultraviolet light, and developed with an alkaline solution, thereby forming a conductor pattern. By laminating this insulating substrate pattern and the conductor pattern, a mother laminate is obtained. Then, the mother laminate is divided into single pieces, thereby obtaining a plurality of laminates 1. On the surface of each external electrode, Ni / Au plating is performed, for example, for the purpose of improving solderability, conductivity, and environmental resistance.

[0064] The method for forming the above laminate 1 is not limited thereto. For example, it may also be a method of printing a conductor paste using a screen plate with an opening in the shape of a conductor pattern and laminating it. In addition, a conductor foil may be adhered to an insulating substrate, and the conductor pattern of each insulator layer may be formed by patterning the conductor foil. Regarding the method for forming the external electrodes, it is not limited thereto either. For example, the external electrodes may be formed on the bottom surface and side surface of the laminate 1 by dipping the laminated body in a conductor paste or by sputtering, and furthermore, plating processing may be performed on its surface.

[0065] Figure 5 It is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 101. Figure 5 The horizontal axis is the frequency, and the vertical axis is the transmission coefficient. In Figure 5 , characteristic A is the characteristic of the low-pass filter 11 of the present embodiment, and characteristics B, C, and D are the characteristics of the filter modules as comparative examples. Characteristic B is the characteristic when the mutual inductance M shown in Figure 1A , Figure 1B is set to 0.

[0066] Comparing the characteristic A of the filter module 101 of the present embodiment with the characteristic B of the filter module of the comparative example, the frequency bands are both the 2.4 GHz band used for wireless LAN, and the cut-off frequencies at which the insertion loss becomes -3 dB are both approximately 4.5 GHz. However, the attenuation pole frequency of the characteristic B of the filter module of the comparative example is 8.5 GHz. In contrast, in the filter module 101 of the present embodiment, the attenuation pole frequency is 12.5 GHz.

[0067] As indicated by the arrow symbol in Figure 5 , if the frequency difference between the cut-off frequency and the attenuation pole frequency is small, the rebound of the attenuation amount from the attenuation pole frequency to the high-frequency band is steep and large (the attenuation is shallower). If the frequency difference between the cut-off frequency and the attenuation pole frequency is large, the rebound of the attenuation amount from the attenuation pole frequency to the high-frequency band is slow and small (the attenuation is deeper). Therefore, compared with the filter module of the comparative example showing characteristic B, the filter module 101 of the present embodiment has a larger attenuation amount in the high-frequency band with a higher attenuation pole. This is because the inductance component Lp generated between the connection portion CP of the first inductor L1 and the second inductor L2 and the ground terminal GND and the inductance component Lg of the circuit board are suppressed by the negative mutual inductance (-M).

[0068] In Figure 5Among them, characteristic C is the characteristic when the synthetic inductance (Lp + Lg - M) of the inductance component Lp, inductance component Lg, and mutual inductance (-M) generated between the connection part CP of the first inductor L1 and the second inductor L2 and the ground electrode is 0. Characteristic D is the characteristic when the synthetic inductance (Lp + Lg - M) is negative. In this way, if the synthetic inductance of the inductance component Lp, inductance component Lg, and mutual inductance (-M) is 0 or negative, resonance does not occur with the capacitor C2, so an attenuation pole is not generated. Therefore, a given attenuation amount in a frequency band higher than the cut-off frequency cannot be ensured. In addition, when the synthetic inductance of the inductance component Lp, inductance component Lg, and mutual inductance (-M) is negative, the steepness deteriorates significantly, and it becomes more difficult to obtain deep attenuation across a wide band. Thus, the synthetic inductance (Lp + Lg - M) is preferably positive.

[0069] <<Second Embodiment>>

[0070] In the second embodiment, a filter module including a low-pass filter and a circuit board on which the low-pass filter is mounted is illustrated.

[0071] Figure 6 It is a perspective view of the filter module 102 according to the second embodiment. Figure 7 It is a front view of the filter module 102. On the upper surface of the circuit board 20, pads for connecting the respective terminals of the low-pass filter 11 are formed. In addition, a wiring electrode 31 continuous from the pad connecting the ground terminal electrode EGND of the low-pass filter 11 is formed. On the lower surface of the circuit board 20, a ground electrode 30 is formed. The ground electrode 30 is the reference potential electrode of the circuit board 20 and extends over a large area. In the present embodiment, the area of the ground electrode 30 is larger than the square of the long side of the rectangle when the low-pass filter 11 is viewed from above. Interlayer connection conductors 32A and 32B for connecting the wiring electrode 31 on the upper surface and the ground electrode 30 on the lower surface are formed inside the circuit board 20. Therefore, the ground terminal electrode EGND of the low-pass filter 11 is electrically connected to the ground electrode 30 of the circuit board 20 through the path of [wiring electrode 31] - [interlayer connection conductors 32A, 32B] - [ground electrode 30].

[0072] The inductance component of the wiring electrode 31 and the inductance components of the interlayer connection conductors 32A and 32B correspond to Figure 2 the inductance component Lg shown.

[0073] Figure 8 It is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 102. Figure 8The horizontal axis is the frequency, and the vertical axis is the transmission coefficient. In this example, the passband is the 2.4 GHz band used for wireless LAN, the cut-off frequency at which the insertion loss becomes -3 dB is approximately 4 GHz, and the attenuation pole frequency of the lowest attenuation pole is 19 GHz or higher. In this way, by shifting the attenuation pole frequency to a band higher than the used band, the attenuation band width of the filter module 102 can be broadened.

[0074] <<Third Embodiment>>

[0075] In the third embodiment, a filter module is shown in which the circuit connected between the connection point of the first inductor L1 and the second inductor L2 and the ground is different from the examples shown so far.

[0076] Figure 9A is a circuit diagram of the filter module 103 according to the third embodiment. Figure 9B is an equivalent circuit diagram of the filter module 103. This filter module 103 has a circuit board 20 forming a ground electrode and a band-pass filter 13.

[0077] The band-pass filter 13 includes a first terminal T1, a second terminal T2, and a ground terminal GND. In addition, the band-pass filter 13 includes: a first inductor L1, a second inductor L2, and capacitors C11 and C12, which are connected in series between the first terminal T1 and the second terminal T2; and a parallel circuit of a capacitor C2 and a third inductor L3, which is connected between the connection portion CP of the first inductor L1 and the second inductor L2 and the ground terminal GND.

[0078] The band-pass filter 13 exhibits band-pass filter characteristics through a circuit including the first inductor L1, the second inductor L2, and the capacitors C11 and C12, which are connected in series between the first terminal T1 and the second terminal T2, and a parallel circuit of the third inductor L3 and the capacitor C2, which is connected between the connection point of the first inductor L1 and the second inductor L2 and the ground.

[0079] In Figure 9A inductive components such as parasitic inductance are generated between the connection portion CP of the shown first inductor L1 and the second inductor L2 and the ground terminal GND. In Figure 9B this inductive component is represented by an inductor Lp.

[0080] As Figure 9BAs shown, when a T-equivalent circuit including inductors LA, LB, and LC is used to represent a circuit including a first inductor L1 and a second inductor L2, the inductor LC representing mutual inductance is connected between the connection point of the serially connected inductors LA and LB and the ground terminal GND. Since the first inductor L1 and the second inductor L2 are connected in series, the inductance of inductor LA is (L1 + M), the inductance of inductor LB is (L2 + M), and the inductance of inductor LC is (-M).

[0081] The ground electrode of the circuit board 20 is the reference potential electrode of the circuit board 20 and is usually an electrode extended to a large area. As Figure 9B shown, an inductance component such as parasitic inductance Lg is generated between the reference potential electrode of the circuit board 20 and the ground terminal connection pad connecting to the ground terminal GND of the band-pass filter 13.

[0082] In Figure 9B , the combined inductance of the inductance component Lg, the inductance component Lp, and the mutual inductance (-M) generated between the ground electrode of the circuit board 20 and the ground terminal GND of the band-pass filter 13 is greater than or equal to 0. That is, if the inductance of the inductance component Lg is represented by Lg and the inductance of the inductance component Lp is represented by Lp, then (Lp + Lg - M) ≥ 0.

[0083] With the above structure, the negative mutual inductance (-M) generated by the magnetic field coupling of the first inductor L1 and the second inductor L2 in the path shunted to the ground terminal GND can suppress the inductance component generated between the connection portion CP of the first inductor L1 and the second inductor L2 and the ground electrode of the circuit board 20. Therefore, it is possible to suppress the inductance of the shunted path in the frequency band higher than the parallel resonance frequency of the third inductor L3 and the capacitor C2, and to prevent the attenuation amount in the frequency band higher than the passband from increasing.

[0084] Figure 10 is a diagram showing the frequency characteristics of the transmission coefficient of the band-pass filter 13. Figure 10 The horizontal axis is the frequency and the vertical axis is the transmission coefficient. In Figure 10 , characteristic A is the characteristic of the band-pass filter 13 of the present embodiment, and characteristic B is the characteristic of the band-pass filter as a comparative example. Characteristic B is the characteristic when the mutual inductance M shown in Figure 9B is set to 0.

[0085] Comparing the characteristic A of the band-pass filter 13 of the present embodiment with the characteristic B of the band-pass filter of the comparative example, the center frequency of the passband is approximately 2.4 GHz for both. However, the attenuation pole frequency of the characteristic B of the band-pass filter of the comparative example is 8.5 GHz, whereas in the band-pass filter 13 of the present embodiment, the attenuation pole frequency is 12.5 GHz.

[0086] The band - pass filter 13 of this embodiment has a larger attenuation amount in the frequency band with extremely high attenuation than the band - pass filter as a comparative example showing characteristic B. This is because the inductance component Lp generated between the connection part CP of the first inductor L1 and the second inductor L2 and the ground terminal GND is suppressed by the negative mutual inductance (-M).

[0087] <<Fourth Embodiment>>

[0088] In the fourth embodiment, an electronic device including the filter module or filter element shown above is exemplified.

[0089] Figure 11 It is a block diagram showing the structure of the electronic device 201 according to the fourth embodiment. This electronic device 201 is, for example, a so - called smart phone or a mobile phone. The electronic device 201 includes a duplexer 53, an antenna 54, a control circuit 50, an interface and a memory 51, and a frequency synthesizer 52. The transmission system includes a microphone 61, a transmission signal processing circuit 62, a transmission mixer 63, a transmission filter 64, and a power amplifier 65. The reception system includes a low - noise amplifier 71, a reception filter 72, a reception mixer 73, a reception signal processing circuit 74, and a receiver 75. The transmission signal output from the power amplifier 65 is output to the antenna 54 via the duplexer 53. In addition, the signal received by the antenna 54 is amplified in the low - noise amplifier 71 via the duplexer 53. Further, in the case of data communication etc. instead of a call, the control circuit 50 processes the reception signal.

[0090] For the transmission filter 64 and the reception filter 72, the filter module or filter element of the present invention can be applied. In addition, the filter module or filter element of the present invention can be applied to the filter on the low - frequency side of the duplexer 53.

[0091] In addition, when filters are provided before and after the power amplifier 65, before and after the low - noise amplifier 71, before and after the transmission mixer 63, before and after the reception mixer 73, etc., the filter module or filter element of the present invention can be applied to these filters.

[0092] In addition, current smart phones and mobile phones are used through multiple antennas and multiple frequency bands, so band - pass filters and diplexers are mostly used. As these band - pass filters and diplexers, they can also be constituted by combining the filter module or filter element of the present invention having low - pass filter characteristics and a high - pass filter.

[0093] Finally, the present invention is not limited to the above-described embodiments. Modifications and changes can be appropriately made by those skilled in the art. The scope of the present invention is not shown by the above-described embodiments, but by the claims. Furthermore, the scope of the present invention includes modifications and changes made from the embodiments within the scope equivalent to the claims.

[0094] Description of Reference Numerals

[0095] C1, C2, C3, C11, C12: Capacitors;

[0096] C2a, C2b, C2c: Capacitor electrodes;

[0097] CL1, CL2: Coiled conductors;

[0098] CL1a, CL1b, CL1c, CL1d: Coiled conductors;

[0099] CL2a, CL2b, CL2c, CL2d: Coiled conductors;

[0100] CP: Connection part;

[0101] E1, E2, E3, E4: Side terminal electrodes;

[0102] EGND: Ground terminal electrode;

[0103] ET1: First terminal electrode;

[0104] ET2: Second terminal electrode;

[0105] GND: Ground terminal;

[0106] L1: First inductor;

[0107] L2: Second inductor;

[0108] L3: Third inductor;

[0109] LA, LB, LC: Inductors;

[0110] Lg, Lp: Inductive components;

[0111] M: Mutual inductance;

[0112] S1 to S11: Insulator layers;

[0113] T1: First terminal;

[0114] T2: Second terminal;

[0115] V: Interlayer connection conductor;

[0116] WA: Winding shaft;

[0117] 1: Stacked body;

[0118] 10: Low-pass filter;

[0119] 11: Low-pass filter (filter element);

[0120] 13: Band-pass filter (filter element);

[0121] 20: Circuit board;

[0122] 30: Ground electrode;

[0123] 31: Wiring electrode;

[0124] 32A, 32B: Interlayer connection conductor;

[0125] 50: Control circuit;

[0126] 51: Memory;

[0127] 52: Frequency synthesizer;

[0128] 53: Duplexer;

[0129] 54: Antenna;

[0130] 61: Microphone;

[0131] 62: Transmit signal processing circuit;

[0132] 63: Transmit mixer;

[0133] 64: Transmit filter;

[0134] 65: Power amplifier;

[0135] 71: Low-noise amplifier;

[0136] 72: Receive filter;

[0137] 73: Receive mixer;

[0138] 74: Receive signal processing circuit;

[0139] 75: Receiver;

[0140] 101, 102, 103: Filter module;

[0141] 201: Electronic device.

Claims

1. A filter module includes a circuit board forming a ground electrode and filter elements mounted on the circuit board, wherein, the filter elements include: a first inductor and a second inductor, which are connected in series between a first terminal and a second terminal and magnetically coupled to each other; and a capacitor, which is connected between a connection portion of the first inductor and the second inductor and a ground terminal, the first inductor and the second inductor are connected in an additive manner, let M represent the mutual inductance generated between the connection portion and the ground terminal by the magnetic coupling of the first inductor and the second inductor, let Lp represent the inductance between the connection portion and the ground terminal, and let Lg represent the inductance of the path between the ground terminal and the ground electrode. At this time, the relationship of Lp + Lg - M ≥ 0 and Lp - M < 0 is satisfied.

2. The filter module according to claim 1, wherein, the inductance Lp, the inductance Lg, and the mutual inductance M satisfy the relationship of Lp + Lg - M > 0.

3. The filter module according to claim 1, wherein, it has: a third inductor, which is connected in parallel with the capacitor.

4. The filter module according to claim 2, wherein, it has: a third inductor, which is connected in parallel with the capacitor.

5. The filter module according to any one of claims 1 to 4, wherein, the first inductor and the second inductor include coil-shaped conductors formed in a laminate of a plurality of insulator layers, the capacitor includes capacitor electrodes facing each other in the stacking direction of the plurality of insulator layers and the insulator layers, when observed in the winding axis direction of the coil-shaped conductor, the coil-shaped conductor has a portion that does not overlap with the capacitor electrodes at least in part.

6. The filter module according to claim 5, wherein, the first terminal includes a first terminal electrode formed in the laminate, and the second terminal includes a second terminal electrode formed in the laminate, when observed in the winding axis direction of the coil-shaped conductor, the capacitor electrodes have a portion that does not overlap with at least one of the first terminal electrode or the second terminal electrode.

7. An electronic device includes: the filter module according to any one of claims 1 to 6.

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