Filter circuit and common mode noise filter

Abstract

This filter circuit (1) comprises a first terminal (P1) and a second terminal (P2) that are signal input / output terminals, a third terminal (P3) for connecting to a reference potential, a first inductor (11), a second inductor (21), a third inductor (12), a fourth inductor (22), and one capacitor (30). One terminal of the first inductor (11) and one terminal of the capacitor (30) are connected to constitute a first node (ND1), one terminal of the second inductor (21) and the other terminal of the capacitor (30) are connected to constitute a second node (ND2), the other terminal of the first inductor (11) and the other terminal of the second inductor (21) are connected to constitute a third node (ND3), the third inductor (12) is connected between the first terminal (P1) and the first node (ND1) so as to be capable of magnetic coupling in the forward direction to the second inductor (21), and the fourth inductor (22) is connected between the second terminal (P2) and the second node (ND2) so as to be capable of magnetic field coupling in the forward direction to the first inductor (11), and the third terminal (P3) is connected to the third node (ND3).

Description

Filter circuits, common mode noise filters

[0001] The present invention relates to a common mode noise filter and a filter circuit that can be used as a common mode noise filter.

[0002] Various common mode noise filters have been devised in the past. The common mode noise filter described in Patent Document 1 is configured using a pair of T-type circuits. The T-type circuit has first and second terminals through which high-frequency signals to be filtered are input and output. Two inductors are connected in series between the first and second terminals. The two series-connected inductors are magnetically coupled with a predetermined coupling coefficient k. The intermediate node of the two series-connected inductors, or the connection node of the two inductors, is connected to the third terminal of the T-type circuit.

[0003] The common mode noise filter of Non-Patent Document 1 has a configuration in which one capacitor is connected in parallel to the series circuit of inductors in the T-type circuit shown in Patent Document 1. As a result, the common mode noise filter of Non-Patent Document 1 has improved filter characteristics compared to the common mode noise filter of Patent Document 1.

[0004] U.S. Patent No. 8,525,617

[0005] An Ultra-Compact Common Mode Bandstop Filter With Modified-T Circuits in Integrated Passive Device(IPD) Process

[0006] When manufacturing a device based on the circuit configuration of Non-Patent Document 1, the desired filter characteristics cannot be obtained unless the parasitic inductance between the first terminal and the capacitor and the parasitic inductance between the second terminal and the capacitor are reduced. In other words, the line length between the first terminal and the capacitor and the line length between the second terminal and the capacitor must be shortened.

[0007] When attempting to shorten the line length between the first terminal and the capacitor and the line length between the second terminal and the capacitor, an electrode constituting the capacitor is formed between the first pad electrode constituting the first terminal and the second pad electrode constituting the second terminal, and two electrodes constituting the inductor are formed around the electrode constituting the capacitor.

[0008] However, in this configuration, the shape of the electrodes that make up the capacitor is limited by the electrodes that make up the inductor, which can make it difficult to achieve desired filter characteristics.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a filter circuit that can more reliably achieve desired filter characteristics.

[0010] A filter circuit according to one embodiment of the present invention comprises a first terminal and a second terminal which are signal input / output terminals, a third terminal for connection to a reference potential, a first inductor, a second inductor, a third inductor, a fourth inductor, and one capacitor. One terminal of the first inductor is connected to one terminal of the capacitor to form a first node. One terminal of the second inductor is connected to the other terminal of the capacitor to form a second node. The other terminal of the first inductor is connected to the other terminal of the second inductor to form a third node. The third inductor is connected between the first terminal and the first node so as to be magnetically coupled to the second inductor in the forward direction. The fourth inductor is connected between the second terminal and the second node so as to be magnetically coupled to the first inductor in the forward direction. The third terminal is connected to the third node.

[0011] In this configuration, the conductor pattern connecting the capacitor and the first terminal can be used as a third inductor to achieve the desired filter characteristics, and the conductor pattern connecting the capacitor and the second terminal can be used as a fourth inductor to achieve the desired filter characteristics.

[0012] This solves the problem of undesired parasitic inductance caused by the conductor pattern connecting the first terminal and the capacitor and the conductor pattern connecting the second terminal and the capacitor. Furthermore, by using the conductor pattern connecting the capacitor and the first terminal and the conductor pattern connecting the capacitor and the second terminal as inductors that achieve desired filter characteristics, the degree of freedom in the wiring pattern between the first terminal and the capacitor and the degree of freedom in the wiring pattern between the first terminal and the capacitor are improved. This makes it easier to adjust the shape of the capacitor, and widens the range of achievable filter characteristics.

[0013] According to the present invention, desired filter characteristics can be more reliably achieved.

[0014] FIG. 1 is a circuit diagram of a filter circuit according to a first embodiment of the present invention. FIG. 2 is a circuit diagram of a common-mode noise filter according to the first embodiment of the present invention. FIG. 3A is a graph showing the attenuation characteristics of the T-type filter circuit according to the first embodiment of the present invention and a reference T-type filter circuit. FIG. 3B is a graph showing an example of the filter characteristics (pass characteristics for a pair of differential signals) of the common-mode noise filter according to the first embodiment of the present invention (the common-mode noise filter of the present application) and a reference common-mode noise filter. FIG. 4 is a circuit diagram of a reference T-type filter circuit. FIG. 5 is a plan view showing an example of the structure of the filter circuit according to the first embodiment of the present invention. FIGS. 6A and 6B are side cross-sectional views showing an example of the structure of the filter circuit according to the first embodiment of the present invention. FIG. 7 is a plan view showing an example of the structure of a reference filter circuit. FIG. 8 is a plan view showing an example of a derivative example of the structure of the filter circuit according to the first embodiment of the present invention. FIG. 9 is a circuit diagram of a common-mode noise filter according to a second embodiment of the present invention. FIG. 10 is a plan view of a multi-stage filter circuit according to the second embodiment. Fig. 11 is a cross-sectional view of a multi-stage filter circuit according to a second embodiment, Fig. 12A is a plan view of a first conductor layer of the multi-stage filter circuit according to the second embodiment, and Fig. 12B is a plan view of a second conductor layer of the multi-stage filter circuit according to the second embodiment.

[0015] First Embodiment A filter circuit and a common mode noise filter according to a first embodiment of the present invention will be described with reference to the drawings.

[0016] (Circuit Configuration of Filter Circuit 1) FIG. 1 is a circuit diagram of a filter circuit according to a first embodiment of the present invention.

[0017] 1, the filter circuit 1 includes a first inductor 11, a second inductor 21, a third inductor 12, a fourth inductor 22, and one capacitor 30. The filter circuit 1 also includes a first terminal P1, a second terminal P2, and a third terminal P3.

[0018] The first terminal P1 and the second terminal P2 are input / output terminals for a high-frequency signal that is filtered by the filter circuit 1. The high-frequency signal is, for example, a signal used in the RF frequency band. The third terminal P3 is a terminal for connection to a reference potential in order to realize the filter characteristics of the filter circuit 1.

[0019] One terminal of the first inductor 11 and one terminal of the capacitor 30 are connected to form a first node ND1. One terminal of the second inductor 21 and the other terminal of the capacitor 30 are connected to form a second node ND2. The other terminal of the first inductor 11 and the other terminal of the second inductor 21 are connected to form a third node ND3.

[0020] The third inductor 12 is connected between the first terminal P1 and the first node ND1. The third inductor 12 is arranged so as to be magnetically coupled to the second inductor 21 in the forward direction.

[0021] The fourth inductor 22 is connected between the second terminal P2 and the second node ND2. The fourth inductor 22 is arranged so as to be magnetically coupled to the first inductor 11 in the forward direction.

[0022] The third terminal is connected to a third node ND3.

[0023] The first inductor 11 and the fourth inductor 22 are magnetically coupled in the forward direction. The second inductor 21 and the third inductor 12 are magnetically coupled in the forward direction. The coupling coefficient between the first inductor 11 and the fourth inductor 22 is the same as the coupling coefficient between the second inductor 21 and the third inductor 12.

[0024] The inductance L11 of the first inductor 11 is the same as the inductance L21 of the second inductor 21. The inductance L11 of the first inductor 11 is the same as the inductance L12 of the third inductor 12. The inductance L21 of the second inductor 21 is the same as the inductance L22 of the fourth inductor 22.

[0025] With this configuration, the filter circuit 1 functions as a band-stop filter that attenuates a predetermined frequency band for high-frequency signals transmitted between the first terminal P1 and the second terminal P2.

[0026] (Circuit Configuration of Common Mode Noise Filter 2) FIG. 2 is a circuit diagram of the common mode noise filter according to the first embodiment of the present invention.

[0027] 2, the common mode noise filter 2 includes a filter circuit 1A, a filter circuit 1B, a first shunt capacitor 41A, a second shunt capacitor 41B, and a shunt inductor 50. The filter circuit 1A corresponds to a "first filter circuit" of the present invention, and the filter circuit 1B corresponds to a "second filter circuit" of the present invention.

[0028] The filter circuit 1A includes a first inductor 11A, a second inductor 21A, a third inductor 12A, a fourth inductor 22A, and one capacitor 30A. The filter circuit 1A also includes a first terminal P1A, a second terminal P2A, and a third terminal P3A.

[0029] The first inductor 11A, the second inductor 21A, the third inductor 12A, the fourth inductor 22A, and the capacitor 30A have the same configurations as the first inductor 11, the second inductor 21, the third inductor 12, the fourth inductor 22, and the capacitor 30, respectively, of the filter circuit 1 shown in Fig. 1. The first terminal P1A, the second terminal P2A, and the third terminal P3A have the same configurations as the first terminal P1, the second terminal P2, and the third terminal P3 of the filter circuit 1 shown in Fig. 1.

[0030] The filter circuit 1B includes a first inductor 11B, a second inductor 21B, a third inductor 12B, a fourth inductor 22B, and one capacitor 30B. The filter circuit 1B also includes a first terminal P1B, a second terminal P2B, and a third terminal P3B.

[0031] The first inductor 11B, the second inductor 21B, the third inductor 12B, the fourth inductor 22B, and the capacitor 30B have the same configurations as the first inductor 11, the second inductor 21, the third inductor 12, the fourth inductor 22, and the capacitor 30, respectively, of the filter circuit 1 shown in Fig. 1. The first terminal P1B, the second terminal P2B, and the third terminal P3B have the same configurations as the first terminal P1, the second terminal P2, and the third terminal P3 of the filter circuit 1 shown in Fig. 1.

[0032] One terminal of a first shunt capacitor 41A is connected to a third terminal P3A of the filter circuit 1A.

[0033] One terminal of a second shunt capacitor 41B is connected to a third terminal P3B of the filter circuit 1B.

[0034] The other terminal of the first shunt capacitor 41A and the other terminal of the second shunt capacitor 41B are connected to each other. A grounding node to which the other terminal of the first shunt capacitor 41A and the other terminal of the second shunt capacitor 41B are connected is connected to a reference potential via a shunt inductor 50.

[0035] With this configuration, for example, one of a pair of differential signals is input to the common mode noise filter 2 through the first terminal P1A, transmitted through the filter circuit 1A, and output from the second terminal P2A, and the other of the pair of differential signals is input to the first terminal P1B, transmitted through the filter circuit 1B, and output from the second terminal P2B. The common mode noise filter 2 then suppresses common mode noise superimposed on the pair of differential signals.

[0036] FIG. 3A is a graph showing the attenuation characteristics of the T-type filter circuit according to the first embodiment of the present invention and a reference T-type filter circuit, and FIG. 3B is a graph showing an example of the filter characteristics (pass characteristics for a pair of differential signals) of the common mode noise filter according to the first embodiment of the present invention (the common mode noise filter of the present application) and a reference common mode noise filter.

[0037] The reference common mode noise filter is a pair of the reference T-type filter circuits shown in FIG. 4 and has the configuration described in Non-Patent Document 1. FIG. 4 is a circuit diagram of the reference T-type filter circuit. As shown in FIG. 4, the reference T-type filter circuit 1P includes a first inductor 11P, a second inductor 21P, and one capacitor 30P. The first inductor 11P and the second inductor 21P are connected in series between the first terminal P1 and the second terminal P2. The capacitor 30P is connected in parallel to the series circuit of the first inductor 11P and the second inductor 21P.

[0038] As shown in FIG. 3A, the filter circuit 1 of the present invention can obtain attenuation characteristics substantially similar to those of the reference filter circuit.

[0039] Furthermore, the filter circuit 1 of the present application uses magnetic coupling between the third inductor 12 and the second inductor 21 between the first terminal P1 and the capacitor 30, and magnetic coupling between the fourth inductor 22 and the first inductor 11 between the second terminal P2 and the capacitor 30. This allows the filter circuit 1 to adjust the attenuation at the attenuation pole frequency, the width of the attenuation band, and the attenuation characteristics by a method different from that used in the reference filter circuit, which uses magnetic coupling between inductors simply connected in series. As a result, as shown in FIG. 3A , the filter circuit 1 of the present application can increase the attenuation at the attenuation pole frequency compared to the reference filter circuit, and easily widen the frequency bands over which attenuations of −10 dB, −20 dB, and −30 dB are obtained.

[0040] By including such a filter circuit 1, the common mode noise filter 2 of the present invention can obtain pass characteristics that are substantially the same as those of a common mode noise filter including a reference filter circuit, as shown in FIG. 3B.

[0041] Furthermore, the above-described circuit configuration is substantially the same whether a differential signal is input from the first terminals P1A, P1B and output from the second terminals P2A, P2B or whether a differential signal is input from the second terminals P2A, P2B and output from the first terminals P1A, P1B. Therefore, the common mode noise filter 2 can achieve substantially the same filter characteristics (characteristics for suppressing common mode noise) in both directions, regardless of the input direction of the differential signal.

[0042] Furthermore, the common mode noise filter 2 of the present invention provides the following advantageous effects.

[0043] (Structure of the filter circuit 1 constituting the common mode noise filter 2) Fig. 5 is a plan view showing an example of the structure of the filter circuit according to the first embodiment of the present invention. Figs. 6A and 6B are side cross-sectional views showing an example of the structure of the filter circuit according to the first embodiment of the present invention. Fig. 6A is a cross-sectional view taken along line AA' in Fig. 5, and Fig. 6B is a cross-sectional view taken along line BB' in Fig. 5.

[0044] As shown in FIGS. 5, 6A, and 6B, the filter circuit 1 includes a substrate 90. The substrate 90 includes a base material 900 and multiple insulator layers 91, 92, and 93. The base material 900 is, for example, a semiconductor substrate and is made of an undoped semiconductor. The insulator layer 91 is formed on the surface of the base material 900 and is made of a highly insulating material such as SiN. The insulator layers 92 and 93 are made of a material having a predetermined dielectric constant. The insulator layers 92 and 93 are formed in this order on the surface of the insulator layer 91.

[0045] The interface (contact surface) between the insulator layer 91 and the insulator layer 92 is used as a second conductor layer CLY2, and the interface between the insulator layer 92 and the insulator layer 93 is used as a first conductor layer CLY1.

[0046] The filter circuit 1 includes a first inductor 11, a second inductor 21, a third inductor 12, a fourth inductor 22, a capacitor conductor 301, a capacitor conductor 302, a plurality of wiring conductors 81, 821, 822, 83, 84, and a plurality of via conductors VIA1, VIA2, VIA31, VIA32.

[0047] The first inductor 11, the second inductor 21, the third inductor 12, the fourth inductor 22, and the plurality of wiring conductors 81, 821, 822, 83, and 84 are formed of linear conductors. The linear conductors are conductors that extend in a predetermined direction and have a predetermined width.

[0048] The capacitor conductors 301 and 302 are made of planar conductors. Planar conductors have a length-to-width ratio that is not larger than that of linear conductors, and are, for example, rectangular conductors when viewed from above.

[0049] The first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 each have a linear shape extending along the X-axis direction in Figure 5, and are formed on the first conductor layer CLY1 (the interface between the insulator layer 92 and the insulator layer 93).

[0050] The first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 have approximately the same width.

[0051] The first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 are arranged in the order of the third inductor 12, the second inductor 21, the fourth inductor 22, and the first inductor 11 along the Y-axis direction in FIG.

[0052] The third inductor 12 and the second inductor 21 run parallel to each other at a distance that allows them to be magnetically coupled with a predetermined coupling coefficient k. The fourth inductor 22 and the first inductor 11 run parallel to each other at a distance that allows them to be magnetically coupled with a predetermined coupling coefficient k. The parallel running distance between the third inductor 12 and the second inductor 21 and the parallel running distance between the fourth inductor 22 and the first inductor 11 are approximately the same.

[0053] The second inductor 21 and the fourth inductor 22 are spaced apart so as not to eliminate magnetic coupling (coupling coefficient is approximately 0).

[0054] The capacitor conductor 301 is formed on the first conductor layer CLY1. The capacitor conductor 301 has a rectangular shape extending in both the X-axis direction and the Y-axis direction. The capacitor conductor 301 is disposed on one end side of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 in the X-axis direction.

[0055] The capacitor conductor 301 is connected to one end of the first inductor 11 in the X-axis direction. This forms a node ND11 between the capacitor conductor 301 and the first inductor 11. The capacitor conductor 301 is connected to one end of the third inductor 12 in the X-axis direction. This forms a node ND12 between the capacitor conductor 301 and the third inductor 12. The nodes ND11 and ND12 form a first node ND1 in the filter circuit 1.

[0056] The capacitor conductor 301 is not directly connected to the second inductor 21 and the fourth inductor 22 .

[0057] The capacitor conductor 302 is formed on the second conductor layer CLY2. The capacitor conductor 302 has a rectangular shape extending in both the X-axis direction and the Y-axis direction. The capacitor conductor 302 is disposed on one end side of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 in the X-axis direction.

[0058] The capacitor conductor 302 has a protruding portion that protrudes in the X-axis direction. This protruding portion is connected to one end of the second inductor 21 in the X-axis direction through a via conductor VIA1. This forms a node ND21 between the capacitor conductor 302 and the second inductor 21. The capacitor conductor 302 has a protruding portion that protrudes in the X-axis direction. This protruding portion is connected to one end of the fourth inductor 22 in the X-axis direction through a via conductor VIA2. This forms a node ND22 between the capacitor conductor 302 and the fourth inductor 22. The nodes ND21 and ND22 form a second node ND2 in the filter circuit 1.

[0059] The capacitor conductor 302 is not directly connected to the first inductor 11 and the third inductor 12 .

[0060] In a plan view, the capacitor conductor 302 overlaps the capacitor conductor 301. The area of ​​the capacitor conductor 302 is preferably larger than the area of ​​the capacitor conductor 301.

[0061] A capacitor 30 is formed by the capacitor conductor 301 and the capacitor conductor 302 facing each other with the insulating layer 92 interposed therebetween.

[0062] The wiring conductor 81 is formed on the first conductor layer CLY1 and extends in the Y-axis direction. The wiring conductor 81 is connected to the other end of the third inductor 12 and extends in the Y-axis direction opposite to the second inductor 21. A first terminal P1 is formed by the wiring conductor 81 near the connection portion with the third inductor 12.

[0063] The wiring conductor 821 is formed on the first conductor layer CLY1 and has a shape extending in the Y-axis direction. The wiring conductor 821 is connected to the other end of the fourth inductor 22 through the via conductor VIA32, the wiring conductor 822 formed on the second conductor layer CLY2, and the via conductor VIA31, and has a shape extending toward the first inductor 11 in the Y-axis direction. The second terminal P2 is formed by the wiring conductor 821 near the connection portion with the via conductor VIA32.

[0064] The wiring conductor 84 is formed on the first conductor layer CLY1 and extends in the Y-axis direction. The wiring conductor 84 is disposed on the opposite side of the capacitor conductor 301 with respect to the formation areas of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22.

[0065] The wiring conductor 84 is connected to the other end of the first inductor 11 and the other end of the second inductor 21 .

[0066] The wiring conductor 83 is formed on the first conductor layer CLY1 and extends in the X-axis direction. The wiring conductor 83 is connected to the wiring conductor 84 at a substantially midpoint in the direction in which the wiring conductor 83 extends. The vicinity of the connection between the wiring conductor 83 and the wiring conductor 84 constitutes a third terminal P3.

[0067] 5 , in the filter circuit 1, the inductor group-forming region REL including the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 is separated from the capacitor-forming region REC including the capacitor conductors 301 and 302 in the X-axis direction. In other words, the capacitor-forming region REC is not surrounded by the inductor group-forming region REL.

[0068] As a result, the shapes of the capacitor conductors 301 and 302 do not depend on the shapes of the inductor group, and the degree of freedom in the shapes of the capacitor conductors 301 and 302 is improved.

[0069] On the other hand, the reference configuration is as shown in Fig. 7. Fig. 7 is a plan view showing an example of the structure of the reference filter circuit. As shown in Fig. 7, in the reference filter circuit 1, the capacitor conductor constituting one capacitor 30P is surrounded by a first inductor 11P and a second inductor 21P. In this configuration, the shape of the capacitor conductor of the capacitor 30P is restricted by the first inductor 11P and the second inductor 21P, and there is almost no degree of freedom.

[0070] In this way, in the filter circuit 1 of the present invention, the degree of freedom in the shapes of the capacitor conductors 301 and 302 is improved, and the capacitance of the capacitor 30 can be set within a wider capacitance range.

[0071] Furthermore, the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 are arranged at different positions in the X-axis direction with respect to the formation region of the capacitor 30. As a result, the shapes of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 do not depend on the shapes of the capacitor conductors 301 and 302, and the degree of freedom in the lengths of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 is improved. Furthermore, the degree of freedom in the coupling coefficient between the first inductor 11 and the fourth inductor 22 and the coupling coefficient between the second inductor 21 and the third inductor 12 is improved. Therefore, the inductance of the inductors that make up the filter circuit 1 can be set within a wider inductance range.

[0072] As a result, the filter circuit 1 allows greater freedom in setting the inductance of the inductors, the capacitance of the capacitors, and the degree of coupling between the multiple inductors, compared to the reference filter circuit 1P, and can achieve a wider variety of filter characteristics (pass characteristics, attenuation characteristics). For example, the common mode noise filter 2 including the filter circuit 1 can set its attenuation band to a wider frequency band, compared to the reference common mode noise filter including the reference filter circuit 1P.

[0073] Furthermore, the increased flexibility in the shapes of the capacitor conductors 301 and 302 allows the distance between the capacitor conductors 301 and 302 (the thickness of the insulator layer 92) to be increased while increasing the areas of the capacitor conductors 301 and 302. This allows the withstand voltage of the capacitor 30 to be improved without changing the capacitance of the capacitor 30.

[0074] In this case, because the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 are disposed on the first conductor layer CLY1, the inductances of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 do not change even if the thickness of the insulator layer 92 is increased. Note that if the thickness of the insulator layer 92 is increased to improve the withstand voltage, the coupling coefficient between the first inductor 11 and the fourth inductor 22 and the coupling coefficient between the second inductor 21 and the third inductor 12 will change. However, the change in each coupling coefficient can be suppressed by adjusting the degree of overlap between the first inductor 11 and the fourth inductor 22 and the degree of overlap between the second inductor 21 and the third inductor 12. Furthermore, if the thickness of the insulator layer 92 is increased to improve the withstand voltage, the capacitance can be kept constant by increasing the area of ​​the capacitor 30, as described above.

[0075] Therefore, the filter circuit 1 can improve the breakdown voltage without changing the filter characteristics.

[0076] As described above, the filter circuit 1 and the common mode noise filter 2 improve the degree of freedom in designing the inductors and capacitors that constitute them, and can more reliably achieve desired filter characteristics.

[0077] Furthermore, in this configuration, the conductor pattern connecting the first terminal P1 and the capacitor 30 is used as the third inductor 12, and the conductor pattern connecting the second terminal P2 and the capacitor 30 is used as the fourth inductor 22. As a result, there is substantially no parasitic inductance occurring between the first terminal P1 and the capacitor 30, and no parasitic inductance occurring between the second terminal P2 and the capacitor 30. This allows the filter circuit 1 to suppress the adverse effects of the parasitic inductance of the wiring conductor on the filter characteristics (such as deviation from the desired filter characteristics or inability to achieve the desired filter characteristics).

[0078] Furthermore, the above-described configuration provides substantially the same circuit configuration whether a high-frequency signal is input from the first terminal P1 and output from the second terminal P2 or input from the second terminal P2 and output from the first terminal P1. Therefore, the filter circuit 1 can achieve substantially the same filter characteristics in both directions, regardless of the input direction.

[0079] In the above-described configuration, the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 extend in the X-axis direction, which is perpendicular to the direction connecting the first terminal P1 and the second terminal P2 (the Y-axis direction). This allows the filter circuit 1 to have a smaller dimension in the Y-axis direction than in a configuration in which the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 extend in the Y-axis direction.

[0080] In the filter circuit 1, the extending direction of the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 is perpendicular to the extending direction of the wiring conductor 81 constituting the first terminal P1 and the wiring conductors 821 and 822 constituting the second terminal P2. This makes it possible to suppress undesired coupling between the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 and the wiring conductors 81, 821, and 822.

[0081] 8 is a plan view showing an example of a derivative of the structure of the filter circuit according to the first embodiment of the present invention. The circuit configuration of the filter circuit 1X of the derivative is similar to the circuit configuration of the filter circuit 1 according to the first embodiment, and therefore a description thereof will be omitted.

[0082] 8, the filter circuit 1X, which is a derivative example, differs from the filter circuit 1 in the positional relationship between the first inductor 11 and the fourth inductor 22 and the connection mode between the fourth inductor 22 and the wiring conductor 82. The other configuration of the filter circuit 1X is the same as that of the filter circuit 1, and a description of similar parts will be omitted.

[0083] In the filter circuit 1X, the first inductor 11, the second inductor 21, the third inductor 12, and the fourth inductor 22 are arranged in the order of the third inductor 12, the second inductor 21, the first inductor 11, and the fourth inductor 22 along the Y-axis direction in Fig. 8. In other words, the filter circuit 1X has a configuration in which the positions of the first inductor 11 and the fourth inductor 22 are swapped compared to the filter circuit 1.

[0084] With this configuration, the fourth inductor 22 is directly connected to the wiring conductor 82 that constitutes the second terminal P2 on the first conductive layer CLY1.

[0085] With this configuration, the filter circuit 1X can achieve the same effects as the filter circuit 1. Furthermore, the filter circuit 1X can reduce the number of via conductors connected to the fourth inductor 22. This allows the filter circuit 1X to suppress conductor loss caused by using via conductors.

[0086] Second Embodiment A common mode noise filter according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 9 is a circuit diagram of the common mode noise filter according to the second embodiment of the present invention.

[0087] As shown in FIG. 9, the common mode noise filter 3 according to the second embodiment differs from the common mode noise filter 2 according to the first embodiment in the number of stages.

[0088] The common mode noise filter 3 has a configuration in which single-stage common mode noise filters 2A, 2B, and 2C are connected in series. The common mode noise filters 2A, 2B, and 2C have substantially the same configuration as the common mode noise filter 2 according to the first embodiment.

[0089] Each of the common mode noise filters 2A, 2B, and 2C has a configuration in which adjacent input / output terminals are connected to one another and each includes a pair of the filter circuit 1 according to the first embodiment. The grounding wiring of each of the common mode noise filters 2A, 2B, and 2C has the above-described shunt capacitor configuration and shares a shunt inductor.

[0090] With this configuration, the common mode noise filter 3 can achieve the same effects as the common mode noise filter 2. Furthermore, by configuring the single-stage common mode noise filter 2 into multiple stages, the common mode noise filter 3 can achieve, for example, steeper attenuation characteristics.

[0091] It is more preferable to apply the following configuration to such a multi-stage common mode noise filter.

[0092] Fig. 10 is a plan view of a multi-stage filter circuit according to a second embodiment. Fig. 11 is a cross-sectional view of the multi-stage filter circuit according to the second embodiment. Fig. 11 shows a cross section taken along CC' in Fig. 10. Fig. 12(A) is a plan view of a first conductor layer of the multi-stage filter circuit according to the second embodiment, and Fig. 12(B) is a plan view of a second conductor layer of the multi-stage filter circuit according to the second embodiment.

[0093] The multi-stage filter circuits shown in FIGS. 10, 11, 12A, and 12B illustrate portions of a multi-stage T-type filter circuit connected between the first terminal P1A and the second terminal P2A in the multi-stage common mode noise filters 2A, 2B, and 2C whose circuit is shown in FIG.

[0094] The filter circuit 1A1 constitutes the common mode noise filter 2A, the filter circuit 1A2 constitutes the common mode noise filter 2B, and the filter circuit 1A3 constitutes the common mode noise filter 2C.

[0095] The filter circuit 1A1 includes a first inductor 11A1, a second inductor 21A1, a third inductor 12A1, and a fourth inductor 22A1. The first inductor 11A1, the second inductor 21A1, the third inductor 12A1, and the fourth inductor 22A1 are each formed of a linear conductor.

[0096] The filter circuit 1A1 includes a capacitor 30A1. The capacitor 30A1 includes a capacitor conductor 301A1 and a capacitor conductor 302A1. The capacitor conductors 301A1 and 302A1 are each made of a planar conductor. A planar conductor has a length-to-width ratio that is not larger than that of a linear conductor, and is, for example, a rectangular conductor in plan view.

[0097] The first inductor 11A1, the second inductor 21A1, the third inductor 12A1, and the fourth inductor 22A1 have a linear shape extending along the X-axis direction in FIGS. 10, 12A, and 12B.

[0098] The first inductor 11A1 and the third inductor 12A1 are formed on the first conductor layer CLY1. The first inductor 11A1 and the third inductor 12A1 are arranged apart from each other in the Y-axis direction in FIGS. 10 and 12A and run parallel to each other.

[0099] The second inductor 21A1 and the fourth inductor 22A1 are formed on the second conductor layer CLY2. The second inductor 21A1 and the fourth inductor 22A1 are arranged apart from each other in the Y-axis direction in FIGS. 10 and 12B and run parallel to each other.

[0100] The first inductor 11A1 and the fourth inductor 22A1 have overlapping portions in plan view, and the second inductor 21A1 and the third inductor 12A1 have overlapping portions in plan view.

[0101] The capacitor conductor 301A1 is formed on the first conductor layer CLY1. The capacitor conductor 301A1 is disposed between the first inductor 11A1 and the third inductor 12A1 in the Y-axis direction. The capacitor conductor 301A1 is also disposed at a position that does not overlap with the first inductor 11A1 or the third inductor 12A1 in the X-axis direction.

[0102] The capacitor conductor 302A1 is formed on the second conductor layer CLY2. The capacitor conductor 302A1 is disposed between the second inductor 21A1 and the fourth inductor 22A1 in the Y-axis direction. The capacitor conductor 302A1 is also disposed at a position that does not overlap with the second inductor 21A1 and the fourth inductor 22A1 in the X-axis direction.

[0103] The capacitor conductor 301A1 and the capacitor conductor 302A1 overlap each other in plan view.

[0104] One end of the third inductor 12A1 is connected to the first terminal P1A (not shown), and the other end of the third inductor 12A1 is connected to one end of the capacitor conductor 301A1 in the Y-axis direction.

[0105] The other end of the capacitor conductor 301A1 in the Y-axis direction is connected to one end of the first inductor 11A1. The other end of the first inductor 11A1 is connected to one end of the second inductor 21A1 through a via conductor VIA1A1 formed in the insulator layer 92. This connection point constitutes a third node in the filter circuit 1A1.

[0106] The other end of the second inductor 21A1 is connected to one end of the capacitor conductor 302A1 in the Y-axis direction. The other end of the capacitor conductor 302A1 in the Y-axis direction is connected to the fourth inductor 22A. The other end of the fourth inductor 22A1 is connected to the filter circuit 1A2.

[0107] This configuration allows the filter circuit 1A1 to have a smaller number of via conductors than the filter circuit 1 described above.

[0108] The filter circuit 1A2 includes a first inductor 11A2, a second inductor 21A2, a third inductor 12A2, and a fourth inductor 22A2. The first inductor 11A2, the second inductor 21A2, the third inductor 12A2, and the fourth inductor 22A2 are each formed of a linear conductor.

[0109] The filter circuit 1A2 includes a capacitor 30A2. The capacitor 30A2 includes a capacitor conductor 301A2 and a capacitor conductor 302A2.

[0110] The filter circuit 1A2 has a shape that is line-symmetrical to the filter circuit 1A1 with respect to an axis AxeX12 that passes through the center position in the Y-axis direction between the filter circuits 1A1 and 1A2 and extends in the X-axis direction as a reference line.

[0111] With this configuration, the filter circuit 1A2 can have a smaller number of via conductors than the filter circuit 1 described above, similar to the filter circuit 1A1.

[0112] The filter circuit 1A2 is connected by a second inductor 21A2 formed on the second conductor layer CLY2 to a fourth inductor 22A1 of the filter circuit 1A1 also formed on the second conductor layer CLY2.

[0113] This eliminates the need for via conductors to connect filter circuit 1A1 and filter circuit 1A2.

[0114] The filter circuit 1A3 includes a first inductor 11A3, a second inductor 21A3, a third inductor 12A3, and a fourth inductor 22A3. The first inductor 11A3, the second inductor 21A3, the third inductor 12A3, and the fourth inductor 22A3 are each formed of a linear conductor.

[0115] The filter circuit 1A3 includes a capacitor 30A3. The capacitor 30A3 includes a capacitor conductor 301A3 and a capacitor conductor 302A3.

[0116] The filter circuit 1A3 has a shape that is line-symmetrical to the filter circuit 1A2 with respect to an axis AxeX23 that passes through the center position in the Y-axis direction between the filter circuits 1A2 and 1A3 and extends in the X-axis direction as a reference line.

[0117] With this configuration, the filter circuit 1A3 can have a smaller number of via conductors than the above-described filter circuit 1, similar to the filter circuits 1A1 and 1A2.

[0118] The filter circuit 1A3 is connected by a third inductor 12A3 formed on the first conductor layer CLY1 to the first inductor 11A2 of the filter circuit 1A2 also formed on the first conductor layer CLY1.

[0119] This eliminates the need for via conductors to connect filter circuit 1A2 and filter circuit 1A3.

[0120] With this configuration, the multi-stage filter circuits 1A1, 1A2, and 1A3 can reduce the number of via conductors and achieve better filter characteristics.

[0121] Although the common mode noise filter 3 has a three-stage configuration, the number of stages is not limited to three, and can be set appropriately depending on the desired characteristics.

[0122] In particular, when a common mode noise filter is configured with an even number of filter circuit stages, by adopting the configurations shown in Figures 10 and 11, it is possible to omit via conductors for connecting to input / output terminals for high-frequency signals at both ends of the multi-stage filter circuit, thereby enabling the common mode noise filter to achieve better filter characteristics.

[0123] 1, 1A, 1A1, 1A2, 1A3, 1B, 1X: filter circuit 2, 2A, 2B, 2C, 3: common mode noise filter 11, 11A, 11A1, 11A2, 11A3, 11B, 11P: first inductor 12, 12A, 12A1, 12A2, 12A3, 12B: third inductor 21, 21A, 21A1, 21A2, 21A3, 21B, 21P: second inductor 22, 22A, 22A1, 22A2, 22A3, 22B: fourth inductor 30, 30A, 30A1, 30A2, 30A3, 30B, 30P: capacitor 41A: first shunt capacitor 41B: second shunt capacitor 50: shunt inductor 81, 82, 83, 84, 821, 822: Wiring conductor 90: Substrate 91, 92, 93: Insulator layer 301, 301A1, 301A2, 301A3, 302, 302A1, 302A2, 302A3: Capacitor conductor 900: Base material CLY1: First conductor layer CLY2: Second conductor layer L11, L12, L21, L22: Inductance ND1: First node ND2: Second node ND3: Third node ND11, ND12, ND21, ND22: Nodes P1, P1A, P1B: First terminal P2, P2A, P2B: Second terminal P3, P3A, P3B: Third terminal REC: Capacitor formation region REL: Inductor group formation region VIA1, VIA1A1, VIA1A2, VIA1A3, VIA2, VIA31, VIA32: via conductors

Claims

1. A filter circuit comprising: a first terminal and a second terminal which are input / output terminals for signals; a third terminal for connection to a reference potential; a first inductor, a second inductor, a third inductor, and a fourth inductor; and one capacitor; wherein one terminal of the first inductor is connected to one terminal of the capacitor to form a first node; one terminal of the second inductor is connected to the other terminal of the capacitor to form a second node; the other terminal of the first inductor is connected to the other terminal of the second inductor to form a third node; the third inductor is connected between the first terminal and the first node so as to be magnetically coupled to the second inductor in a forward direction; the fourth inductor is connected between the second terminal and the second node so as to be magnetically coupled to the first inductor in a forward direction; and the third terminal is connected to the third node.

2. The filter circuit according to claim 1, wherein the inductance of the first inductor and the inductance of the second inductor are the same.

3. The filter circuit according to claim 2, wherein the inductance of the first inductor is the same as the inductance of the third inductor, and the inductance of the second inductor is the same as the inductance of the fourth inductor.

4. A filter circuit according to any one of claims 1 to 3, comprising: an insulating substrate; an inductor group consisting of the first inductor, the second inductor, the third inductor, and the fourth inductor, each formed by a linear conductor formed on the substrate; and a capacitor formed on the substrate and formed by opposing planar conductors, wherein, when viewing the substrate in a planar view, the planar conductor forming the capacitor is positioned outside the formation area of ​​the inductor in which the linear conductors forming the inductor group are formed.

5. The filter circuit according to claim 4, wherein the linear conductor constituting the third inductor is a wiring conductor that connects the first terminal and the capacitor, and the linear conductor constituting the fourth inductor is a wiring conductor that connects the second terminal and the capacitor.

6. A common mode noise filter comprising: a first filter circuit having the configuration of a filter circuit according to any one of claims 1 to 3 and transmitting one of a pair of differential signals; a second filter circuit having the configuration of said filter circuit and transmitting the other of said pair of differential signals; a first shunt capacitor connected to a third terminal of said first filter circuit; a second shunt capacitor connected to a third terminal of said second filter circuit; and a shunt inductor connecting a ground node, at which said first shunt capacitor and said second shunt capacitor are connected, to a reference potential.

7. The common mode noise filter according to claim 6, comprising a plurality of said common mode noise filters, wherein the first terminals and second terminals of said plurality of common mode noise filters are connected in sequence, the reference potential is shared, and the common mode noise filters are configured in a plurality of stages.

8. A common mode noise filter according to claim 7, comprising: a substrate formed by laminating a plurality of insulating layers; an inductor group consisting of the first inductor, the second inductor, the third inductor, and the fourth inductor, each formed by a linear conductor on said substrate; and a capacitor formed on said substrate and formed by opposing planar conductors, wherein adjacent common mode noise filters connected to each other in said multi-stage common mode noise filter have shapes of the inductor group and the capacitor that are, in plan view, symmetrical with respect to an axis orthogonal to the adjoining direction at a midpoint between said adjacent common mode noise filters.

9. The common mode noise filter according to claim 8, wherein the substrate comprises a first conductive layer and a second conductive layer formed at a plurality of interfaces of a plurality of insulator layers, the capacitor comprises a first capacitor conductor and a second capacitor conductor, the first inductor, the third inductor, and the first capacitor conductor are formed on the first conductive layer, the second inductor, the fourth inductor, and the second capacitor conductor are formed on the second conductive layer, the first inductor and the fourth inductor have overlapping portions when viewed in a stacking direction of the plurality of insulator layers, the second inductor and the third inductor have overlapping portions when viewed in the stacking direction, and the first capacitor conductor and the second capacitor conductor have overlapping portions when viewed in the stacking direction.

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