Filter module and electronic device

Abstract

To provide a filter module having good attenuation characteristics over a wide frequency band on a higher frequency side than a pass band, a filter element included in the filter module, and an electronic apparatus including these.SOLUTION: A filter module 101 includes a circuit board 20 on or in which a ground electrode is formed, 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 cumulatively connected to each other. Relationships of Lp+Lg-M≥0 and Lp-M<0 are satisfied, where Lp denotes an inductance of a path between a connection portion CP between the first inductor L1 and the second inductor L2 and a ground terminal GND; Lg denotes an inductance of a path between the ground terminal GND and a ground electrode; and M denotes a mutual inductance between the first inductor L1 and the second inductor L2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a filter module in which a high-frequency filter circuit is configured, a filter element used in the filter module, and an electronic device including the same. [Background technology]

[0002] Patent Document 1 discloses a low-pass filter that is configured with two coils and multiple capacitors formed inside a laminate. The two coils are spiral coils, each with a central axis extending in the stacking direction of the multiple insulator layers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-21449 Summary of the Invention [Problem to be solved by the invention]

[0004] The low-pass filter described in Patent Document 1 has a structural parasitic inductor between the connection point of the two coils inside the filter and the ground terminal.

[0005] Furthermore, the low-pass filter described in Patent Document 1 is mounted on a circuit board for use. The ground terminal of this low-pass filter is connected to the ground terminal of the circuit board, but a parasitic inductor also exists between the ground terminal of the circuit board and the reference potential electrode of the circuit board (usually a ground electrode that extends over a wide area).

[0006] The above will be explained with reference to Figures 12A and 12B. Figure 12A is an equivalent circuit diagram of the low-pass filter disclosed in Patent Document 1, and Figure 12B is an equivalent circuit diagram of the low-pass filter mounted on a circuit board.

[0007] In FIG. 12A, low-pass filter 10 includes first terminal T1, second terminal T2, and ground terminal GND, and is configured by series-connected inductors L1 and L2 and shunt-connected capacitors C1, C2, and C3 to ground.

[0008] However, an inductance component such as a parasitic inductance occurs between the connection point CP between inductors L1 and L2 and the ground terminal GND. Inductor Lp in Figure 12A is an element that clearly shows this inductance component. This inductance component Lp resonates with the capacitor C2 connected in series to it, creating an attenuation pole at the resonant frequency, and the amount of attenuation decreases in higher frequency bands, making it difficult to use when attenuation is required over a wide frequency range on the high-frequency side.

[0009] 12B, on circuit board 20 on which low-pass filter 10 is mounted, an inductance component such as parasitic inductance occurs between the reference potential electrode (wide-area ground electrode) of the circuit board and the ground terminal connection pad to which ground terminal GND of low-pass filter 10 is connected. Inductor Lg in FIG. 12B is an element that clearly represents this inductance component. Therefore, in actual use, resonance occurs between the combined inductance of inductance component Lp and inductance component Lg and the capacitance of capacitor C2, creating an attenuation pole at the resonant frequency. As a result, the attenuation is reduced in frequency bands higher than this attenuation pole.

[0010] On the other hand, in recent applications, the frequency band for which a predetermined amount of attenuation is ensured in the attenuation range tends to expand. For example, in low-pass filters that cut off high-frequency wideband frequency bands such as 5th Generation (5G) and Ultra Wide Band (UWB), the frequency band to be attenuated spans a wide range. Therefore, it is required that the attenuation amount in the attenuation range of the low-pass filter be ensured over a wide range.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a filter module having good attenuation characteristics over a wide band on the high frequency side of the passband, a filter element used in this filter module, and electronic equipment including them. [Means for solving the problem]

[0012] (1) A filter module as an example of the present disclosure is a filter module including a circuit board on which a ground electrode is formed and a filter element mounted on the circuit board, the filter element including 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 a connection portion between the first inductor and the second inductor and a ground terminal, the first inductor and the second inductor being additively connected, and where M represents the mutual inductance generated between the connection portion and the ground terminal due to the magnetic coupling between the first inductor and the second inductor, Lp represents the inductance between the connection portion and the ground terminal, and Lg represents the inductance of the path between the ground terminal and the ground electrode, the relationship is Lp+Lg-M≧0 and Lp-M<0.

[0013] With the above configuration, the magnetic field coupling between the first inductor and the second inductor generates a negative mutual inductance in the path shunt-connected to the ground terminal, which suppresses the composite inductance component generated between the connection between the first inductor and the second inductor and the ground electrode of the circuit board, and the resonance frequency of this composite inductance and the capacitance of the capacitor shifts to a higher frequency range than the operating frequency band. Furthermore, since the relationship Lp+Lg-M≧0 is satisfied, an attenuation pole is generated by the resonance of the composite inductance and the capacitance of the capacitor.

[0014] (2) A filter element as an example of the present disclosure is a filter element mounted on a circuit board on which a ground electrode is formed, and includes: 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 a connection portion between the first inductor and the second inductor and the ground terminal, wherein the first inductor and the second inductor are sum-connected, and when a mutual inductance generated between the connection portion and the ground terminal due to the magnetic coupling between the first inductor and the second inductor is represented by M and the inductance between the connection portion and the ground terminal is represented by Lp, a relationship of Lp-M<0 is satisfied.

[0015] With the above configuration, the magnetic field coupling between the first inductor and the second inductor generates a negative mutual inductance in the path shunt-connected to the ground terminal, which suppresses the composite inductance component generated between the connection between the first inductor and the second inductor and the ground electrode of the circuit board, and the resonant frequency caused by this composite inductance and the capacitance of the capacitor shifts to a higher frequency range than the operating frequency band.

[0016] (3) An electronic device as an example of the present disclosure includes the filter module or the filter element. [Effects of the Invention]

[0017] According to the present invention, it is possible to obtain a filter module having good attenuation characteristics over a wide band on the high frequency side of the passband, a filter element used in this filter module, and an electronic device including the same. [Brief explanation of the drawings]

[0018] [Figure 1] 1A is a circuit diagram of a filter module 101 according to a first preferred embodiment of the present invention, and FIG. [Figure 2]FIG. 2 is an equivalent circuit diagram showing the mutual inductance generated by the magnetic field coupling between the first inductor L1 and the second inductor L2 as a circuit element. [Figure 3] 3A and 3B are perspective views of the low-pass filter 11. FIG. [Figure 4] FIG. 4 is an exploded bottom view showing the insulating layers of the low-pass filter 11 and the conductor patterns formed thereon. [Figure 5] FIG. 5 is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 101. As shown in FIG. [Figure 6] FIG. 6 is a perspective view of a filter module 102 according to the second embodiment. [Figure 7] FIG. 7 is a front view of the filter module 102. [Figure 8] FIG. 8 is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 102. As shown in FIG. [Figure 9] 9A is a circuit diagram of a filter module 103 according to a third embodiment, and FIG. 9B is an equivalent circuit diagram of the filter module 103. [Figure 10] FIG. 10 is a diagram showing the frequency characteristics of the transmission coefficient of the bandpass filter 13. As shown in FIG. [Figure 11] FIG. 11 is a block diagram showing the configuration of an electronic device 201 according to the fourth embodiment. [Figure 12] FIG. 12A is an equivalent circuit diagram of the low-pass filter disclosed in Patent Document 1, and FIG. 12B is an equivalent circuit diagram of the low-pass filter when mounted on a circuit board. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, several specific examples will be given with reference to the drawings to illustrate several embodiments for carrying out the present invention. The same reference numerals are used for the same parts in each drawing. For the sake of convenience, the embodiments are shown divided into several embodiments, taking into account ease of explanation and understanding of the main points, but partial substitution or combination of the configurations shown in different embodiments is possible. From the second embodiment onwards, a description of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0020] First Embodiment Fig. 1A is a circuit diagram of a filter module 101 according to a first preferred embodiment. Fig. 1B 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 on which a ground electrode is formed.

[0021] 1A includes a first terminal T1, a second terminal T2, and a ground terminal GND. The low-pass filter 11 also includes a first inductor L1 and a second inductor L2 connected in series between the first terminal T1 and the second terminal T2 and magnetically coupled to each other, and a capacitor C2 connected between a connection point CP between the first inductor L1 and the second inductor L2 and the ground terminal GND. Hereinafter, the symbols for the inductors and the inductances of the inductors will be used interchangeably. Therefore, for example, the inductance of inductor L1 will be represented by L1.

[0022] An inductance component Lp such as a parasitic inductance occurs between the ground terminal GND and the connection point CP between the first inductor L1 and the second inductor L2 shown in Fig. 1A. Fig. 1B represents this inductance component as inductor Lp.

[0023] The ground electrode of the circuit board 20 is a reference potential electrode of the circuit board 20 and is typically an electrode that extends over a wide area. In other words, in this specification, a "ground electrode" is a planar electrode that serves as a reference potential in a circuit. As shown in FIG. 1B, an inductance component Lg, such as a parasitic inductance, occurs between the reference potential electrode of the circuit board 20 and the ground terminal connection pad to which the ground terminal GND of the low-pass filter 10 is connected. FIG. 1B represents this inductance component as inductor Lg.

[0024] Figure 2 is an equivalent circuit diagram that shows, as a circuit element, the mutual inductance generated by the magnetic field coupling between the first inductor L1 and the second inductor L2. As shown in Figure 2, when the circuit connected between the first terminal T1 and the second terminal T2 is shown as a T-type equivalent circuit using inductors LA, LB, and LC, inductor LC, which represents the mutual inductance, is shunt-connected between the connection point of the series-connected inductors LA and LB and the ground terminal GND. Since the first inductor L1 and the second inductor L2 are sum-connected, the inductance of inductor LA is (L1+M), the inductance of inductor LB is (L2+M), and the inductance of inductor LC is (-M).

[0025] With the above configuration, a negative mutual inductance (-M) is generated in the path shunt-connected to the ground terminal GND due to magnetic field coupling between the first inductor L1 and the second inductor L2. This negative mutual inductance (-M) suppresses the inductance component generated between the connection point CP between the first inductor L1 and the second inductor L2 and the ground electrode of the circuit board 20. Therefore, the resonant frequency (attenuation pole frequency) caused by the combined inductance of the negative mutual inductance (-M), the inductance component Lp, and the inductance component Lg, and the capacitance of the capacitor C2 shifts to a frequency higher than the operating frequency band.

[0026] Incidentally, in the low-pass filter described in Patent Document 1, the two coils are differentially connected, and therefore the mutual inductance generated by their magnetic field coupling is positive, and the combined inductance generated in the path connected in shunt to the ground terminal GND of the low-pass filter becomes even larger.

[0027] In FIG. 1B, the relationship between the inductance component Lg, the inductance component Lp, and the mutual inductance (-M) occurring between the ground electrode of circuit board 20 and the ground terminal GND of low-pass filter 11 is as follows:

[0028] Lp+Lg-M≧0 Lp-M<0 As a result, the inductance component Lg is suppressed by the negative inductance (Lp-M). Furthermore, since Lp+Lg-M≧0, an attenuation pole occurs due to resonance between the combined inductance and the capacitance of the capacitor C2.

[0029] 3A and 3B are perspective views of the low-pass filter 11. The perspectives are different between Fig. 3A and Fig. 3B, and both show the interior transparently.

[0030] The low-pass filter 11 includes a rectangular parallelepiped laminate 1 formed by stacking a plurality of rectangular insulating layers. A first terminal electrode ET1, a second terminal electrode ET2, and two ground terminal electrodes EGND are formed on the outer surface of the laminate 1.

[0031] The first inductor L1 is composed of a coil-shaped conductor CL1 formed on a laminate 1 of multiple insulator layers, and the second inductor L2 is composed of a coil-shaped conductor CL2 formed on a laminate 1 of multiple insulator layers.

[0032] The capacitor C2 is composed of capacitor electrodes C2a, C2b, and C2c that face each other in the stacking direction of a plurality of insulating layers, and an insulating layer sandwiched between these capacitor electrodes.

[0033] The connection between the coiled conductor CL1 of the first inductor L1 and the coiled conductor CL2 of the second inductor L2 is connected to the capacitor electrode C2b via an interlayer connecting conductor V.

[0034] One end of the coiled conductor CL1 of the first inductor L1 is electrically connected to the first terminal electrode ET1, and one end of the coiled 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 connection between the coiled conductor CL1 of the first inductor L1 and the coiled conductor CL2 of the second inductor L2 via the interlayer connection conductor V.

[0035] FIG. 4 is an exploded bottom view showing the insulating layers of the low-pass filter 11 and the conductor patterns formed thereon.

[0036] The laminate 1 is formed by laminating insulator layers S1 to S11. Fig. 4 shows a bottom view of each insulator layer. Insulator layer S1 is the uppermost insulator layer, and insulator layer S11 is the lowermost insulator layer. Insulator layers S2 to S10 are insulator layers located between the uppermost insulator layer S1 and the lowermost insulator layer S11.

[0037] The coil-shaped conductors CL1a, CL1b, CL1c, and CL1d formed on the insulator layers S1 to S4 constitute the coil-shaped conductor CL1 shown in Figures 3A and 3B. Similarly, the coil-shaped conductors CL2a, CL2b, CL2c, and CL2d constitute the coil-shaped conductor CL2.

[0038] Furthermore, the capacitor C2 is composed of the capacitor electrodes C2a, C2b, and C2c formed on the insulating layers S8 to S10 and the insulating layers S9 and S10.

[0039] When viewed in the direction of the winding axis WA of the coiled conductors CL1 and CL2 (see FIGS. 3A and 3B), at least a portion of the coiled conductors CL1 and CL2 does not overlap with the capacitor electrodes C2a, C2b, and C2c, thereby suppressing unnecessary parasitic capacitance generated between the coiled conductors CL1 and CL2 and the capacitor electrodes C2a, C2b, and C2c.

[0040] Side terminal electrodes E1 and E2 are formed on the insulator layers S1 to S11. Side terminal electrodes E1, E2, E3, and E4 are formed on the insulator layers S8 to S10. The side terminal electrodes E1, E2, E3, and E4 formed on each insulator layer are electrically connected to each other with the same reference numeral.

[0041] One end of the coiled conductor CL1a is electrically connected to the side terminal electrode E1, and one end of the coiled 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.

[0042] When viewed in the direction of the winding axis WA of the coiled 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. This reduces unnecessary parasitic capacitance between the capacitor electrodes C2a, C2b, and C2c and the first terminal electrode ET1 and the second terminal electrode ET2. Note that when viewed in the direction of the winding axis WA of the coiled conductor, the capacitor electrodes C2a, C2b, and C2c may 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 have portions that do not overlap with the first terminal electrode ET1, the parasitic capacitance between the capacitor C2 shown in FIG. 1A and the first terminal T1 can be reduced. Similarly, if the capacitor electrodes C2a, C2b, and C2c 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 reduced.

[0043] The insulating layers S1 to S11 of the laminate 1 are formed by screen printing, exposing, and developing a photosensitive insulating paste and a photosensitive conductive paste, and the laminate 1 is formed by laminating these insulating layers S1 to S11.

[0044] Specifically, a photosensitive insulating paste layer is screen-printed, irradiated with ultraviolet light, and developed with an alkaline solution. This forms an insulating substrate pattern with openings for external electrodes, via holes, etc. Furthermore, a photosensitive conductive paste is screen-printed, irradiated with ultraviolet light, and developed with an alkaline solution to form a conductor pattern. This insulating substrate pattern and conductor pattern are stacked to obtain a mother laminate. This mother laminate is then cut into individual pieces to obtain multiple laminates 1. The surface of each external electrode is plated with, for example, Ni / Au to improve solderability, conductivity, and environmental resistance.

[0045] The method for forming the laminate 1 is not limited to this. For example, a method of printing and laminating a conductive paste using a screen printing plate with openings in the shape of a conductive pattern is also possible. Alternatively, a conductive foil may be attached to an insulating base material, and the conductive pattern of each insulator layer may be formed by patterning the conductive foil. The method for forming the external electrodes is also not limited to this. For example, external electrodes may be formed on the bottom and side surfaces of the laminate 1 by dipping or sputtering the laminated element body in a conductive paste, and the surfaces may further be plated.

[0046] FIG. 5 is a diagram showing the frequency characteristics of the transmission coefficient of the filter module 101. The horizontal axis of FIG. 5 represents frequency, and the vertical axis represents the transmission coefficient. In FIG. 5, characteristic A represents the characteristics of the low-pass filter 11 of this embodiment, and characteristics B, C, and D represent the characteristics of filter modules as comparative examples. Characteristic B represents the characteristics when the mutual inductance M shown in FIGS. 1A and 1B is set to 0.

[0047] Comparing characteristic A of filter module 101 of this embodiment with characteristic B of the filter module of the comparative example, the pass frequency band for both is the 2.4 GHz band used for wireless LAN, and the cutoff frequency at which the insertion loss is -3 dB is approximately 4.5 GHz. However, while the attenuation pole frequency of characteristic B of the comparative example filter module is 8.5 GHz, the attenuation pole frequency of filter module 101 of this embodiment is 12.5 GHz.

[0048] As indicated by the arrows in Figure 5, when the frequency difference between the cutoff frequency and the attenuation pole frequency is small, the attenuation rises sharply from the attenuation pole frequency to higher frequencies and the rise is large (shallower attenuation). When the frequency difference between the cutoff frequency and the attenuation pole frequency is large, the attenuation rises gently from the attenuation pole frequency to higher frequencies and the rise is small (deeper attenuation). Therefore, the filter module 101 of this embodiment has a larger attenuation in the higher frequency range than the attenuation pole frequency compared to the filter module of the comparative example showing characteristic B. This is because the inductance component Lp generated between the connection point 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).

[0049] In FIG. 5, characteristic C represents the characteristic when the combined inductance (Lp+Lg-M) of the inductance component Lp, the inductance component Lg, and the mutual inductance (-M) generated between the connection point CP of the first inductor L1 and the second inductor L2 and the ground electrode is 0. Characteristic D represents the characteristic when the combined inductance (Lp+Lg-M) is negative. Thus, if the combined inductance of the inductance components Lp, Lg, and the mutual inductance (-M) is 0 or negative, resonance with the capacitor C2 does not occur, and no attenuation pole occurs. Therefore, a predetermined amount of attenuation cannot be ensured in the frequency range higher than the cutoff frequency. Furthermore, if the combined inductance of the inductance components Lp, Lg, and the mutual inductance (-M) is negative, the steepness deteriorates significantly, making it difficult to achieve deep attenuation over a wide frequency range. Therefore, it is desirable for the combined inductance (Lp+Lg-M) to be positive.

[0050] Second Embodiment In the second embodiment, a filter module including a low-pass filter and a circuit board on which the low-pass filter is mounted will be illustrated.

[0051] FIG. 6 is a perspective view of a filter module 102 according to a second preferred embodiment of the present invention. FIG. 7 is a front view of the filter module 102. Pads for connecting each terminal of the low-pass filter 11 are formed on the upper surface of the circuit board 20. A wiring electrode 31 is formed continuing from the pad to which the ground terminal electrode EGND of the low-pass filter 11 is connected. A ground electrode 30 is formed on the lower surface of the circuit board 20. This ground electrode 30 is a reference potential electrode for the circuit board 20 and extends over a wide area. In this preferred embodiment, the area of ​​the ground electrode 30 is greater 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 are formed inside the circuit board 20, connecting the wiring electrode 31 on the upper surface with the ground electrode 30 on the lower surface. 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 via the path of the wiring electrode 31, the interlayer connection conductors 32A and 32B, and the ground electrode 30.

[0052] The inductance component of the wiring electrode 31 and the inductance components of the interlayer connection conductors 32A and 32B correspond to the inductance component Lg shown in FIG.

[0053] Figure 8 is a diagram showing the frequency characteristics of the transmission coefficient of filter module 102. The horizontal axis of Figure 8 represents frequency, and the vertical axis represents the transmission coefficient. In this example, the passband is the 2.4 GHz band used for wireless LAN, the cutoff frequency at which the insertion loss is -3 dB is approximately 4 GHz, and the lowest attenuation pole frequency is 19 GHz or higher. In this way, by shifting the attenuation pole frequency to a frequency higher than the frequency band used, the attenuation range of filter module 102 can be broadened.

[0054] Third Embodiment In the third embodiment, a filter module will be described 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.

[0055] Fig. 9A is a circuit diagram of a filter module 103 according to a third embodiment. Fig. 9B is an equivalent circuit diagram of the filter module 103. The filter module 103 includes a circuit board 20 on which a ground electrode is formed, and a band-pass filter 13.

[0056] The bandpass filter 13 includes a first terminal T1, a second terminal T2, and a ground terminal GND. The bandpass filter 13 also includes a first inductor L1, a second inductor L2, and capacitors C11 and C12 connected in series between the first terminal T1 and the second terminal T2, and a parallel circuit of the capacitor C2 and a third inductor L3 connected between a connection point CP between the first inductor L1 and the second inductor L2 and the ground terminal GND.

[0057] The bandpass filter 13 exhibits bandpass filter characteristics due to a circuit consisting of a first inductor L1, a second inductor L2, and capacitors C11 and C12 connected in series between the first terminal T1 and the second terminal T2, and due to a parallel circuit consisting of a third inductor L3 and capacitor C2 connected between the connection point of the first inductor L1 and the second inductor L2 and ground.

[0058] An inductance component such as a parasitic inductance occurs between the ground terminal GND and the connection point CP between the first inductor L1 and the second inductor L2 shown in Fig. 9A. Fig. 9B represents this inductance component as an inductor Lp.

[0059] 9B, when the circuit formed by the first inductor L1 and the second inductor L2 is represented by a T-type equivalent circuit formed by inductors LA, LB, and LC, inductor LC representing the mutual inductance is connected between the connection point of the series-connected inductors LA and LB and the ground terminal GND. Since the first inductor L1 and the second inductor L2 are sum-connected, the inductance of inductor LA is (L1+M), the inductance of inductor LB is (L2+M), and the inductance of inductor LC is (-M).

[0060] The ground electrode of circuit board 20 is a reference potential electrode of circuit board 20, and is usually an electrode that extends over a wide area. As shown in Fig. 9B, an inductance component Lg such as a parasitic inductance occurs between the reference potential electrode of circuit board 20 and the ground terminal connection pad to which the ground terminal GND of bandpass filter 13 is connected.

[0061] 9B, the combined inductance of inductance component Lg, inductance component Lp, and mutual inductance (-M) occurring between the ground electrode of circuit board 20 and ground terminal GND of bandpass filter 13 is greater than 0. In other words, if the inductance of inductance component Lg is represented by Lg and the inductance of inductance component Lp is represented by Lp, then (Lp+Lg-M)≧0.

[0062] With the above configuration, the magnetic field coupling between the first inductor L1 and the second inductor L2 generates a negative mutual inductance (-M) in the path shunt-connected to the ground terminal GND, which suppresses the inductance component generated between the connection point CP of the first inductor L1 and the second inductor L2 and the ground electrode of the circuit board 20. Therefore, the inductance of the shunt-connected path is suppressed in a frequency range higher than the parallel resonance frequency of the third inductor L3 and the capacitor C2, and the attenuation in a frequency range higher than the passband increases.

[0063] Fig. 10 is a diagram showing the frequency characteristics of the transmission coefficient of bandpass filter 13. The horizontal axis of Fig. 10 represents frequency, and the vertical axis represents the transmission coefficient. In Fig. 10, characteristic A represents the characteristics of bandpass filter 13 of this embodiment, and characteristic B represents the characteristics of a bandpass filter as a comparative example. Characteristic B represents the characteristics when the mutual inductance M shown in Fig. 9B is set to 0.

[0064] Comparing characteristic A of band-pass filter 13 of this embodiment with characteristic B of the band-pass filter of the comparative example, the center frequency of the pass band in both cases is approximately 2.4 GHz, but the attenuation pole frequency of characteristic B of the comparative example low-pass filter is 8.5 GHz, whereas the attenuation pole frequency of low-pass filter 11 of this embodiment is 12.5 GHz.

[0065] The bandpass filter 13 of this embodiment has a larger attenuation in the high frequency range than the attenuation pole, compared to the comparative bandpass filter that exhibits characteristic B. This is because the inductance component Lp generated between the ground terminal GND and the connection point CP between the first inductor L1 and the second inductor L2 is suppressed by the negative mutual inductance (-M).

[0066] Fourth Embodiment In the fourth embodiment, an electronic device including the filter module or filter element described above will be exemplified.

[0067] FIG. 11 is a block diagram showing the configuration of an electronic device 201 according to a fourth embodiment. The electronic device 201 is, for example, a smartphone or a mobile phone. The electronic device 201 includes a duplexer 53, an antenna 54, a control circuit 50, an interface and memory 51, and a frequency synthesizer 52. The transmission system includes a transmitter 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. A transmission signal output from the power amplifier 65 is output to the antenna 54 via the duplexer 53. A signal received by the antenna 54 is amplified by the low-noise amplifier 71 via the duplexer 53. In the case of data communication rather than phone calls, the control circuit 50 processes the received signal.

[0068] The filter module or filter element of the present invention can be applied to the transmit filter 64 and the receive filter 72. The filter module or filter element of the present invention can also be applied to the filter on the low frequency side of the duplexer 53.

[0069] Furthermore, when filters are provided before or after the power amplifier 65, before or after the low noise amplifier 71, before or after the transmitting mixer 63, before or after the receiving mixer 73, etc., the filter module or filter element of the present invention can be applied to those filters.

[0070] Furthermore, current smartphones and mobile phones are used with multiple antennas and multiple frequency bands, and therefore bandpass filters and duplexers are widely used. These bandpass filters and duplexers can also be constructed by combining the filter module or filter element of the present invention, which has lowpass filter characteristics, with a highpass filter.

[0071] Finally, the present invention is not limited to the above-described embodiments. Those skilled in the art can make appropriate modifications and variations. The scope of the present invention is defined not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention includes modifications and variations from the embodiments within the scope of the claims and their equivalents. [Explanation of symbols]

[0072] C1, C2, C3, C11, C12... Capacitors C2a, C2b, C2c...Capacitor electrodes CL1, CL2... Coiled conductor CL1a, CL1b, CL1c, CL1d... Coiled conductors CL2a, CL2b, CL2c, CL2d... Coiled conductors CP...Connection E1,E2,E3,E4…Side terminal electrode EGND: Ground terminal electrode ET1…1st terminal electrode ET2…Second terminal electrode GND: Ground terminal L1: First inductor L2: Second inductor L3: Third inductor LA, LB, LC... inductors Lg, Lp...inductance components M: Mutual inductance S1 to S11: Insulator layers T1: Terminal 1 T2: Second terminal V: Interlayer connection conductor WA...winding axis 1...Laminate 10...Low-pass filter 11...Low-pass filter (filter element) 13...Bandpass filter (filter element) 20...Circuit board 30...Ground electrode 31...Wiring electrode 32A, 32B...Interlayer connecting conductor 50...Control circuit 51...Memory 52...Frequency synthesizer 53...Duplexer 54...Antenna 61...Telephone 62...Transmission signal processing circuit 63...Transmit mixer 64...Transmission filter 65...Power amplifier 71...Low noise amplifier 72...Receive filter 73...Receive mixer 74...Received signal processing circuit 75...Receiver 101, 102, 103...Filter modules 201…Electronic equipment

Claims

1. a circuit board on which a ground electrode is formed; 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 a connection portion of the first inductor and the second inductor and a ground terminal, the first inductor, the second inductor, and the capacitor are disposed on the circuit board; the first inductor and the second inductor are summatively connected; When the mutual inductance generated between the connection portion and the ground terminal due to the magnetic field coupling between the first inductor and the second inductor is represented by M, the inductance between the connection portion and the ground terminal is represented by Lp, and the inductance of the path between the ground terminal and the ground electrode is represented by Lg, a relationship of Lp+Lg-M≧0 and Lp-M<0 is satisfied. Filter module.

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

3. a third inductor connected in parallel with the capacitor; 3. The filter module according to claim 1 or 2.

4. the first inductor and the second inductor are each formed of a coil-shaped conductor formed in a laminate of a plurality of insulating layers, the capacitor is composed of a capacitor electrode and the insulator layer that face each other in a stacking direction of the plurality of insulator layers, When viewed in the direction of the winding axis of the coil-shaped conductor, the coil-shaped conductor has at least a portion that does not overlap with the capacitor electrode.

4. A filter module according to claim 1.

5. the first terminal is constituted by a first terminal electrode formed on the laminate, and the second terminal is constituted by a second terminal electrode formed on the laminate, When viewed in the winding axis direction of the coil-shaped conductor, the capacitor electrode has a portion that does not overlap with at least one of the first terminal electrode and the second terminal electrode. The filter module of claim 4 .

6. An electronic device comprising the filter module according to claim 1 .

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