Filter circuit
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MURATA MFG CO LTD
- Filing Date
- 2025-11-18
- Publication Date
- 2026-08-06
Smart Images
Figure JP2025040243_06082026_PF_FP_ABST
Abstract
Description
Filter circuit
[0001] The present disclosure relates to a filter circuit.
[0002] In electronic devices, noise countermeasures are taken using filter circuits. Filter circuits used for noise countermeasures include, for example, EMI (Electro-Magnetic Interference) removal filters, which remove unnecessary components while allowing necessary components of the current flowing through the conductor to pass. However, since a filter circuit uses a capacitor, which is a capacitive element, it is known that the noise suppression effect decreases due to the equivalent series inductance (ESL: Equivalent Series Inductance), which is the parasitic inductance of the capacitor.
[0003] Therefore, coil components have been developed that cancel out the equivalent series inductance ESL of the capacitor with a negative inductance generated by magnetically coupling two coils (for example, International Publication No. 2023 / 233883: Patent Document 1). By using the coil component in a filter circuit, the filter circuit can widen the noise suppression effect over a wide band.
[0004] International Publication No. 2023 / 233883
[0005] A coil component that cancels out the equivalent series inductance ESL of the capacitor may not be placed near the capacitor due to layout considerations, and it is necessary to extend the wiring from the intermediate terminal of the coil component to the capacitor. However, when the wiring is extended, a positive inductance generated by the wiring is added between the coil component and the capacitor, and the equivalent series inductance ESL of the capacitor may not be sufficiently canceled out. Furthermore, in order to sufficiently cancel out the equivalent series inductance ESL of the capacitor, it is necessary to increase the negative inductance generated in the coil component, which increases the manufacturing cost.
[0006] Therefore, the object of this disclosure is to provide a filter circuit that can cancel out the equivalent series inductance ESL of a capacitor with the negative inductance generated by magnetically coupling the two coils, even when the coil component and the capacitor are provided separately.
[0007] A filter circuit according to one embodiment of the present disclosure comprises a coil component, a first wiring, a second wiring, and a capacitor. The coil component includes a first coil and a second coil that is magnetically coupled to the first coil. The first wiring is electrically connected at one end to the first intermediate terminal when the first terminal of the first coil is an input terminal and the second terminal of the first coil is a first intermediate terminal. The second wiring is electrically connected at one end to the second intermediate terminal when the third terminal of the second coil is a second intermediate terminal and the fourth terminal of the second coil is an output terminal. One electrode of the capacitor is electrically connected to the other end of the first wiring and the other end of the second wiring. The other electrode of the capacitor is electrically connected to the ground electrode.
[0008] According to one embodiment of the present disclosure, since the capacitor is electrically connected to the other end of a first wiring which has one end electrically connected to the first intermediate terminal, and to the other end of a second wiring which has one end electrically connected to the second intermediate terminal, the positive inductance generated by the first and second wiring can be kept small, and the equivalent series inductance ESL of the capacitor can be canceled out by the negative inductance generated by the two coils.
[0009] This is a schematic diagram of the filter circuit according to Embodiment 1. This is a perspective view of the coil component according to Embodiment 1. This is a circuit diagram of the filter circuit according to Embodiment 1. This is a schematic diagram of the filter circuit according to Embodiment 2. This is a schematic diagram of the filter circuit according to Modification 1 of Embodiment 2. This is a schematic diagram of the filter circuit according to Embodiment 3. This is a schematic diagram of the filter circuit according to Modification 3 of Embodiment 3. This is a schematic diagram of the filter circuit according to Embodiment 4. This is a schematic diagram of the filter circuit according to Embodiment 5. This is a cross-sectional view of the filter circuit according to Embodiment 5. This is a schematic diagram of the filter circuit according to Modification 5 of Embodiment 6. This is a perspective view of the coil component according to Modification.
[0010] The filter circuit according to this embodiment will be described below with reference to the drawings. <Embodiment 1> First, the filter circuit according to Embodiment 1 will be described with reference to the drawings. Figure 1 is a schematic diagram of the filter circuit 100 according to Embodiment 1. The filter circuit 100 is used for noise suppression of power lines 10a and 10b, and the parasitic inductance of capacitor C1 is canceled by a coil component 1 which includes two coils that are magnetically coupled. Note that the filter circuit 100 is not limited to being used for noise suppression of power lines 10a and 10b, but may also be used for noise suppression of other signal lines, etc.
[0011] Coil component 1 includes a coil L1 (first coil) and a coil L2 (second coil) that magnetically couples with coil L1, as described later. Coil component 1 electrically connects to the power line 10a using terminal 2c (first terminal) of coil L1 as an input terminal, and terminal 2e (second terminal) of coil L1 as a first intermediate terminal. Furthermore, coil component 1 electrically connects to the power line 10b using terminal 3e (third terminal) of coil L2 as a second intermediate terminal and terminal 3c (fourth terminal) of coil L2 as an output terminal. In other words, coil component 1 has four terminals: terminals 2c, 2e, 3c, and 3e.
[0012] If capacitor C1 cannot be placed near coil component 1 due to layout constraints, as shown in Figure 1, it is necessary to connect it to coil component 1 via wirings 5 and 6. However, the filter circuit 100 does not connect terminals 2e and 3e together to capacitor C1 with a single wire, but rather connects terminal 2e to capacitor C1 with wiring 5 (first wiring) and terminal 3e to capacitor C1 with wiring 6 (second wiring). One electrode of capacitor C1 is connected to electrode pad 7 for electrical connection with wirings 5 and 6, and the other electrode is connected to electrode pad 8 for electrical connection with the ground electrode GND. Wirings 5 and 6 are cables made of metal conductors.
[0013] The coil component 1 will be described in more detail with reference to the drawings. Figure 2 is a perspective view of the coil component 1 according to Embodiment 1. Figure 3 is a circuit diagram of the filter circuit 100 according to Embodiment 1. In Figure 2, the X-axis, Y-axis, and Z-axis are defined as follows: the X-axis represents the left-right direction of the coil component 1, the Y-axis represents the front-back direction of the coil component 1, and the Z-axis represents the up-down direction of the coil component 1.
[0014] The coil component 1 includes a coil section 2a (first coil) and a coil section 3a (second coil) in the housing 4. Hereinafter, coil section 2a will also be referred to as coil L1, and coil section 3a as coil L2. Coil section 2a has a lead wire 2b (first lead wire) connected to one end and a lead wire 2d (second lead wire) connected to the other end. Coil section 3a has a lead wire 3b (third lead wire) connected to one end and a lead wire 3d (fourth lead wire) connected to the other end. Coil section 2a and lead wires 2b, 2d are formed from a single conductor, for example, from a metal plate or metal wire made of copper or an alloy of copper and other metals. Similarly, coil section 3a and lead wires 3b, 3d are also formed from a single conductor.
[0015] Coils L1 and L2, formed from metal plates, are covered with an insulating material (not shown). Specifically, the insulating material covering coils L1 and L2 is a resin such as polymidimide or epoxy. It is not necessary for the insulating material to cover all surfaces of coils L1 and L2. To prevent contact between coils L1 and L2, it is sufficient to provide insulating material on at least the surfaces where coils L1 and L2 face each other.
[0016] The coil section 2a has a rectangular opening and is positioned inside the housing 4 substantially parallel to the main surface 40A (first main surface). The coil section 2a is shown as a single-turn coil, but it may also be a multi-turn coil. The lead wires 2d and 2d are drawn out from the side surface 41 (first side surface) of the housing 4 and extend along the side surface 41 in the direction of the main surface 40B (second main surface). The lead wire 2b shown in Figure 2 is provided up to the main surface 40B, and the portion in contact with the main surface 40B constitutes a terminal 2c. Similarly, the lead wire 2d is provided up to the main surface 40B, and the portion in contact with the main surface 40B constitutes a terminal 2e.
[0017] The coil section 3a has a rectangular opening and is positioned above the coil section 2a inside the housing 4, substantially parallel to the main surface 40A. Although the coil section 3a is shown as a single-turn coil, it may be a multi-turn coil. The lead wires 3d and 3d are drawn out from the side surface 42 (second side surface) of the housing 4 and extend along the side surface 42 in the direction of the main surface 40B. The lead wire 3b shown in Figure 2 is provided up to the main surface 40B, and the portion in contact with the main surface 40B constitutes a terminal 3c. Similarly, the lead wire 3d is provided up to the main surface 40B, and the portion in contact with the main surface 40B constitutes a terminal 3e.
[0018] Although it has been explained that coils L1 and L2 are arranged inside the housing 4 substantially parallel to the main surface 40B, they may also be arranged inside the housing 4 at an angle to the main surface 40B, or substantially perpendicular to the main surface 40B.
[0019] When terminal 2c of coil section 2a (coil L1) is connected to a power source, current flows clockwise from the lead wire 2b. The current flowing through coil section 2a flows in the following order: lead wire 2d, terminal 2e, wiring 5, and capacitor C1. The current from capacitor C1 flows in the following order: wiring 6, terminal 3e, and lead wire 3d. Current flows clockwise from the lead wire 3d in coil section 3a (coil L2). Therefore, a magnetic field is generated in coil section 2a in the direction from main surface 40A to main surface 40B (-Z direction). Similarly, a magnetic field is generated in coil section 3a in the direction from main surface 40A to main surface 40B (-Z direction). Since coil section 2a and coil section 3a are arranged to overlap when viewed from the direction of main surface 40A, coil L1 and coil L2 are magnetically coupled. Figure 2 shows an example where the openings of coil L1 and coil L2 almost overlap, but within the range of magnetic field coupling, the openings may be offset, and it is sufficient if more than 50% of each opening overlaps.
[0020] The housing 4 fixes the relative positions of coil L1 and coil L2, and is made of, for example, molded resin. Specifically, the molded resin is made of epoxy resin with silica filler added, silicone resin, liquid crystal polymer, or various resins mixed with metallic magnetic material. The housing 4 has sides 41 (first side) and 42 (second side) facing each other, the side closer to the leader wire 2b (first leader wire) is designated as side 43 (third side), and the side closer to the leader wire 2d (second leader wire) is designated as side 44 (fourth side). Figure 2 shows a rectangular parallelepiped shape, but the sides may be inclined as long as the second main surface, which is the mounting surface, and the coil surface are approximately parallel. For example, it may be a trapezoid with a larger area on the second main surface than on the first main surface.
[0021] The filter circuit 100 is, for example, an EMI rejection filter as shown in Figure 3, and is a third-order T-type LC filter circuit. This filter circuit 100 has terminal 2c connected to a power supply (not shown) and terminal 3c connected to a circuit (not shown) such as a DC / DC converter or power supply module. The filter circuit 100 removes unwanted components from the current flowing from the power supply to the circuit, allowing only the necessary components to pass through. Specifically, a DC current is passed through the filter circuit 100, and the high-frequency noise contained in the DC current is grounded to GND through capacitor C1. Since capacitor C1, which is a capacitance element, has an equivalent series inductance ESL(Lc), the passage of high-frequency noise is hindered, and the noise rejection performance deteriorates. In this filter circuit 100, the negative inductance generated by the magnetic field coupling of the two coils is used to cancel the ESL(Lc) of capacitor C1, maintaining high noise rejection performance. In this disclosure, the negative inductance generated in series with capacitor C1 is called the mutual inductance M of coil component 1.
[0022] However, if the filter circuit 100 cannot place the capacitor C1 near the coil component 1 due to layout constraints, as shown in Figure 1, and terminals 2e and 3e are connected together with a single wire to connect the coil component 1 and the capacitor C1, a positive inductance is added to that wire. The filter circuit 100 cancels out the ESL(Lc) of the capacitor C1 with a negative mutual inductance M, but when a positive inductance is added, the negative mutual inductance M cannot sufficiently cancel out the ESL(Lc) of the capacitor C1.
[0023] Therefore, in the filter circuit 100, terminal 2e and capacitor C1 are connected by wire 5, and terminal 3e and capacitor C1 are connected by wire 6, thereby separating the inductance between coils L1 and L2 and capacitor C1 into inductance La and inductance Lb, as shown in Figure 3. In the filter circuit 100, the inductance is separated into inductance La and inductance Lb, and wires 5 and 6 are separated so that inductance La and inductance Lb do not become magnetically coupled, thereby preventing the addition of positive inductance. If inductance La and inductance Lb are magnetically coupled, a positive inductance will be added due to magnetic field coupling. However, if the distance between wires 5 and 6 is greater than the distance between coils L1 and L2, the added positive inductance will be smaller than when coils L1 and L2 and capacitor C1 are connected by a single wire. Therefore, in the filter circuit 100, by reducing or eliminating the positive inductance between wiring 5 and wiring 6, the negative mutual inductance M can cancel out the ESL(Lc) of capacitor C1. In the filter circuit 100, wiring 5 and wiring 6 are separated, but it is not necessary to keep the distance between wiring 5 and wiring 6 constant at all times. There may be portions where the distance between wiring 5 and wiring 6 differs between one end of wiring 5 and the other end of wiring 6.
[0024] In the following embodiment, a third-order T-type LC filter circuit is used as the configuration for the filter circuit 100, but the same configuration can be applied to a fifth-order T-type LC filter circuit or a higher-order T-type LC filter circuit.
[0025] As shown in Figure 1, capacitor C1 has one electrode connected to electrode pad 7 and the other electrode connected to electrode pad 8. Note that capacitor C1 is made of BaTiO ３The multilayer ceramic capacitor may be made primarily of barium titanate, or it may be made primarily of other materials, or it may be a different type of capacitor, such as an aluminum electrolytic capacitor. Capacitor C1 has an inductance Lc as a parasitic inductance (equivalent series inductance (ESL)), and is equivalent to a circuit configuration in which the inductance Lc is connected in series with capacitance C1a. Capacitor C1 may also be equivalent to a circuit configuration in which a parasitic resistance (equivalent series resistance (ESR)) is connected in series with both the inductance Lc and capacitance C1a.
[0026] <Embodiment 2> In the filter circuit 100 according to Embodiment 1, it was explained that the positive inductance added decreases as the distance between wiring 5 and wiring 6 increases. Therefore, in the filter circuit according to Embodiment 2, a configuration will be described in which the magnitude of the positive inductance added is adjusted by adjusting the distance between wiring 5 and wiring 6. Figure 4 is a schematic diagram of the filter circuit 100A according to Embodiment 2. In the filter circuit 100A shown in Figure 4, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1, and the explanation will not be repeated.
[0027] The filter circuit 100A connects terminal 2e to capacitor C1 with wire 5, and terminal 3e to capacitor C1 with wire 6. As shown in Figure 4, the filter circuit 100A has a band portion 9 that bundles wires 5 and 6 together midway along wires 5 and 6. The band portion 9 bundles wires 5 and 6 from midway along wires 5 and 6 to one electrode of capacitor C1. Therefore, the portion separating wires 5 and 6 in the filter circuit 100A is shorter than that of the filter circuit 100 shown in Figure 1, resulting in a larger positive inductance. Note that wires 5 and 6 are cables made of metal conductors, but they are insulated, so they are electrically insulated even when bundled.
[0028] In the filter circuit 100A, the magnitude of the added positive inductance can be adjusted by adjusting the length of the band portion 9 that bundles the wires 5 and 6 together. In other words, in the filter circuit 100A, the added positive inductance increases when the band portion 9 is brought closer to the coil component 1, and decreases when the band portion 9 is brought closer to the capacitor C1.
[0029] In the filter circuit 100A, the wires 5 and 6 from the part bundled by the band section 9 to the capacitor C1 are bundled together. However, the wires 5 and 6 may only be bundled at the part bundled by the band section 9, and the wires 5 and 6 outside of the part bundled by the band section 9 may be separated. In other words, the wires 5 and 6 are separated between the coil component 1 and the band section 9, and between the band section 9 and the capacitor C1.
[0030] Furthermore, although it was explained that wires 5 and 6 are electrically insulated even when bundled because they are covered, wires 5 and 6 do not necessarily need to be covered. If wires 5 and 6 are not covered, the band portion 9 provided in the middle of wires 5 and 6 becomes a connection point that electrically connects wire 5 and wire 6. In other words, wires 5 and 6 from the band portion 9 to capacitor C1 function as a single wire.
[0031] Furthermore, as shown by the arrows in Figure 4, when the wires 5 and 6 are bundled together at the band portion 9, the direction of the current flowing through wire 5 and the direction of the current flowing through wire 6 at the bundled portion will be opposite. However, it is also possible to bundle them so that the direction of the current flowing through wire 5 and the direction of the current flowing through wire 6 are the same. Figure 5 is a schematic diagram of a filter circuit 100B according to a modified example of Embodiment 2. In the filter circuit 100B shown in Figure 5, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1, and the explanation will not be repeated.
[0032] The filter circuit 100B connects terminal 2e to capacitor C1 with wire 5, and terminal 3e to capacitor C1 with wire 6. As shown in Figure 5, the filter circuit 100B has a band section 9a that crosses and bundles wires 5 and 6 midway through the wires 5 and 6. The band section 9a bundles wires 5 and 6 so that the direction of the current flowing through wire 5 and the direction of the current flowing through wire 6 are the same midway through the wires 5 and 6. As a result, in the filter circuit 100B, the direction of the current flowing through the two wires 5 and 6 is the same at the band section 9a, a negative inductance is generated at the bundled portion, and the generated negative inductance can further cancel the equivalent series inductance ESL of capacitor C1. To generate an even larger negative inductance at the band section 9a, a ferrite core or the like can be used at the band section 9a.
[0033] In filter circuits 100A and 100B, one example is shown in Figures 4 and 5 where cylindrical band portions 9 and 9a are used as a means of bundling the wires 5 and 6, but the means of bundling the wires 5 and 6 are not limited to this. The means of bundling the wires 5 and 6 may be to bond them together with an adhesive, or the wires 5 and 6 may be bundled together in a portion where an external insulating coating is integrated, such as a flat cable. In other words, filter circuits 100A and 100B only need to have a portion in the middle of the wires 5 and 6 that bundles the wires 5 and 6 together.
[0034] <Embodiment 3> In the filter circuit 100 according to Embodiment 1, the coil component 1 and the capacitor C1 are electrically connected by wiring 5 and 6 such as cables made of metal conductors. However, this is not limited to this, and the coil component and the capacitor may be electrically connected by the wiring pattern by forming a wiring pattern on a substrate and mounting the coil component and capacitor on the substrate. Therefore, in the filter circuit according to Embodiment 3, a configuration in which the coil component and capacitor are mounted on a substrate will be described. Figure 6 is a schematic diagram of the filter circuit 100C according to Embodiment 3. In the filter circuit 100C shown in Figure 6, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1, and the description will not be repeated.
[0035] The substrate 200 is, for example, a printed circuit board. As shown in Figure 6, the filter circuit 100C includes wiring patterns 10c and 10d that constitute the power lines, wiring patterns 50 and 60 that connect the coil component 1 and the capacitor C1, and electrode pads 7 and 8 for mounting the capacitor C1, etc., on the substrate 200.
[0036] By mounting the coil component 1 on the circuit board 200, terminal 2c of the coil component 1 is electrically connected to the wiring pattern 10c of the power line, and terminal 3c of the coil component 1 is electrically connected to the wiring pattern 10d of the power line. Furthermore, terminal 2e of the coil component 1 is electrically connected to the wiring pattern 50, and terminal 3e of the coil component 1 is electrically connected to the wiring pattern 60.
[0037] The wiring patterns 50 and 60 are formed at separate locations from each other and are not electrically connected until they are connected to the electrode pads 7. In other words, the filter circuit 100C is configured such that no positive inductance is added, or the added positive inductance is reduced, by forming the wiring patterns 50 and 60 separately. Therefore, in the filter circuit 100C, by reducing or eliminating the positive inductance between the wiring patterns 50 and 60, the negative mutual inductance M can cancel out the ESL (Lc) of the capacitor C1.
[0038] As shown by the arrows in Figure 6, the direction of the current flowing through wiring pattern 50 and the direction of the current flowing through wiring pattern 60 are opposite. However, it is also possible to provide a portion where the direction of the current flowing through wiring pattern 50 and the direction of the current flowing through wiring pattern 60 are the same. Figure 7 is a schematic diagram of a filter circuit 100D according to a modified example of Embodiment 3. In the filter circuit 100D shown in Figure 7, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1 and the filter circuit 100C shown in Figure 6, and the explanation will not be repeated.
[0039] In the filter circuit 100D, when viewed from the front of the substrate 200, there is an overlapping portion between the wiring pattern from terminal 2e of the coil component 1 to capacitor C1 and the wiring pattern from terminal 3e of the coil component 1 to capacitor C1, and the current direction is made the same in this portion. Specifically, the wiring pattern from terminal 2e of the coil component 1 to capacitor C1 consists of a wiring pattern 51 connected to terminal 2e and a wiring pattern 52 provided below wiring pattern 51. Furthermore, wiring pattern 51 and wiring pattern 52 are electrically connected via a via conductor 51a, and wiring pattern 52 and electrode pad 7 are electrically connected via a via conductor 52a. In addition, wiring pattern 52 has a crank-shaped curved portion.
[0040] On the other hand, the wiring pattern from terminal 3e of coil component 1 to capacitor C1 is composed of a wiring pattern 61 provided on the same layer as wiring pattern 51. Furthermore, wiring pattern 61 has a crank-shaped curved portion. The crank-shaped curved portion of wiring pattern 52 and the crank-shaped curved portion of wiring pattern 61 overlap when viewed from the front of the substrate 200 in a plan view, and as shown by the arrows in Figure 7, the direction of the current flowing through wiring pattern 52 and the direction of the current flowing through wiring pattern 61 are the same. Note that wiring pattern 52 and wiring pattern 61 overlap with an insulating layer (not shown) in between, so they are not electrically connected.
[0041] In the filter circuit 100D, the direction of the current is the same in the area where the wiring pattern 52 and the wiring pattern 61 overlap, so a negative inductance is generated in that area, which can further cancel the equivalent series inductance ESL of the capacitor C1. To generate an even larger negative inductance, the overlapping area between the wiring pattern 52 and the wiring pattern 61 can be widened.
[0042] <Embodiment 4>In the filter circuit 100C according to Embodiment 3, it was described that the coil component 1 and the capacitor C1 are electrically connected by the wiring patterns 50 and 60 formed on the substrate 200. However, since the lengths of the wiring patterns 50 and 60 formed on the substrate 200 cannot be changed, the positive inductance added by the wiring pattern 50 and the wiring pattern 60 cannot be adjusted. Therefore, in the filter circuit according to Embodiment 4, a configuration for adjusting the positive inductance added by the wiring pattern will be described. FIG. 8 is a schematic diagram of a filter circuit 100E according to Embodiment 4. In the filter circuit 100E shown in FIG. 8, the same components as those in the filter circuit 100 shown in FIG. 1 and the filter circuit 100C shown in FIG. 6 are denoted by the same reference numerals, and the description thereof will not be repeated.
[0043] As shown in FIG. 8, the filter circuit 100E includes wiring patterns 10c and 10d that form a power line, wiring patterns 55 and 65 that connect the coil component 1 and the capacitor C1, and electrode pads 7 and 8 for mounting the capacitor C1 on the substrate 200.
[0044] The wiring pattern 55 and the wiring pattern 65 are formed at positions separated from each other and are not electrically connected until they are connected to the electrode pad 7. However, the wiring pattern 55 and the wiring pattern 65 are provided with terminals so that they can be electrically connected in the middle of the wiring pattern. Specifically, the wiring pattern 55 has a terminal 55a on the side closer to the coil component 1 and a terminal 55b on the side closer to the capacitor C1. The wiring pattern 65 has a terminal 65a on the side closer to the coil component 1 and a terminal 65b on the side closer to the capacitor C1.
[0045] When the filter circuit 100E electrically connects the terminal 55b and the terminal 65b with the conductor 80 as shown in Fig. 8(a), the wiring pattern 55 and the wiring pattern 65 are separated to a position far from the coil component 1, so that the added positive inductance becomes small. On the other hand, when the filter circuit 100E electrically connects the terminal 55a and the terminal 65a with the conductor 80 as shown in Fig. 8(b), the wiring pattern 55 and the wiring pattern 65 are electrically connected at a position close to the coil component 1, so that the added positive inductance becomes large. The conductor 80 is a connection part that electrically connects the wiring pattern 55 and the wiring pattern 65.
[0046] Thus, the filter circuit 100E can adjust the magnitude of the added positive inductance by changing the position where the wiring pattern 55 and the wiring pattern 65 are electrically connected.
[0047] <Embodiment 5> In the filter circuit 100C according to Embodiment 3, it has been described that the wiring pattern 50 and the wiring pattern 60 formed on the substrate 200 are formed separately so as not to be magnetically coupled. As a means for preventing magnetic coupling between the wiring pattern 50 and the wiring pattern 60, in addition to the means of physically separating them, means for electrically blocking them can be considered. Therefore, in the filter circuit according to Embodiment 5, a configuration in which means for electrically blocking is provided between the wiring patterns will be described. Fig. 9 is a schematic diagram of the filter circuit 100F according to Embodiment 5. Fig. 10 is a cross-sectional view of the filter circuit 100F according to Embodiment 5. In the filter circuit 100F shown in Figs. 9 and 10, the same components as those in the filter circuit 100 shown in Fig. 1 and the filter circuit 100C shown in Fig. 6 are denoted by the same reference numerals and the description will not be repeated.
[0048] In the filter circuit 100F, when viewed from the front of the substrate 200, a conductor layer 90 is provided between the wiring pattern from terminal 2e of the coil component 1 to capacitor C1 and the wiring pattern from terminal 3e of the coil component 1 to capacitor C1. Specifically, the wiring pattern from terminal 2e of the coil component 1 to capacitor C1 consists of a wiring pattern 56 connected to terminal 2e and a wiring pattern 57 (first wiring pattern) provided below wiring pattern 56 and the conductor layer 90. Furthermore, wiring pattern 56 and wiring pattern 57 are electrically connected via a via conductor 56a, and wiring pattern 57 and electrode pad 7 are electrically connected via a via conductor 57a. Wiring pattern 56 is provided in the first layer, and wiring pattern 57 is provided in the second layer.
[0049] On the other hand, the wiring pattern from terminal 3e of coil component 1 to capacitor C1 consists of a wiring pattern 66 (second wiring pattern) which is on a different layer from wiring pattern 57 but on the same layer as wiring pattern 56. As can be seen from Figure 10, the conductor layer 90 is provided between wiring pattern 66 and wiring pattern 57 and is electrically connected to the conductor layer 91 which is electrically connected to the ground electrode GND. In other words, the conductor layer 90 is a ground potential wiring pattern provided between the layer on which wiring pattern 57 is provided and the layer on which wiring pattern 66 is provided. The conductor layer 91 is electrically connected to the electrode pad 8 via a via conductor 91a.
[0050] In the filter circuit 100F, an electrically insulating conductor layer 90 is provided between the wiring pattern 57 and the wiring pattern 66, thereby preventing magnetic field coupling between the wiring pattern 57 and the wiring pattern 66. Therefore, even when the coil component 1 and the capacitor C1 are connected by the wiring patterns 57 and 66 in the filter circuit 100F, no positive inductance is added, or the added positive inductance can be reduced.
[0051] In the filter circuit 100F, a configuration was described in which the wiring pattern 57 and the wiring pattern 66 formed on the substrate 200 are electrically isolated so as not to be magnetically coupled. However, the same can be applied to a filter circuit that connects a coil component and a capacitor using a cable made of a metal conductor. Figure 11 is a schematic diagram of a filter circuit 100G according to a modified example of Embodiment 5. In the filter circuit 100G shown in Figure 11, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1, and the explanation will not be repeated.
[0052] In filter circuit 100G, terminal 2e is connected to capacitor C1 by coaxial cable 5a, and terminal 3e is connected to capacitor C1 by coaxial cable 6a. By using coaxial cables 5a and 6a instead of the wiring 5 and 6 used in filter circuit 100, filter circuit 100G prevents magnetic field coupling between the electrically isolated coaxial cable 5a and coaxial cable 6a. Therefore, even if coil component 1 and capacitor C1 are connected by coaxial cables 5a and 6a in filter circuit 100G, no positive inductance is added, or the added positive inductance can be reduced. Note that in filter circuit 100G, one of the wirings connecting coil component 1 and capacitor C1 may be a coaxial cable.
[0053] <Embodiment 6> In the filter circuit 100C according to Embodiment 3, a configuration in which the coil component 1 and the capacitor C1 are connected by wiring patterns 50 and 60 was described. However, a coil component may be further provided in the middle of the wiring patterns 50 and 60 that connect the coil component 1 and the capacitor C1. Therefore, in the filter circuit according to Embodiment 6, a configuration in which a coil component is further provided in the middle of the wiring pattern will be described. Figure 12 is a schematic diagram of the filter circuit 100H according to Embodiment 6. In the filter circuit 100H shown in Figure 12, the same reference numerals are used for components that are the same as those in the filter circuit 100 shown in Figure 1 and the filter circuit 100C shown in Figure 6, and the description will not be repeated.
[0054] As shown in Figure 12, the filter circuit 100H further includes a coil component 1a in the middle of the wiring pattern connecting the coil component 1 and the capacitor C1. The wiring pattern from terminal 2e of coil component 1 to capacitor C1 consists of a wiring pattern 58 connecting terminal 2e of coil component 1 to terminal 2f of coil component 1a, and a wiring pattern 59 connecting terminal 2g of coil component 1a to electrode pad 7. On the other hand, the wiring pattern from terminal 3e of coil component 1 to capacitor C1 consists of a wiring pattern 68 connecting terminal 3e of coil component 1 to terminal 3f of coil component 1a, and a wiring pattern 69 connecting terminal 3g of coil component 1a to electrode pad 7.
[0055] Coil component 1a has the same configuration as coil component 1 shown in Figure 2, and includes coil L3 (third coil) corresponding to coil L1 of coil component 1, and coil L4 (fourth coil) corresponding to coil L2 of coil component 1. Coils L3 and L4 are magnetically coupled. Coil component 1a electrically connects terminal 2f of coil L3 to the wiring pattern 58, and terminal 2g of coil L3 to the wiring pattern 59. Also, coil component 1a electrically connects terminal 3g of coil L4 to the wiring pattern 69, and terminal 3f of coil L4 to the wiring pattern 68. In other words, coil component 1a has four terminals: 2f, 2g, 3f, and 3g. Note that coil component 1a does not have to have the same configuration as coil component 1, and is sufficient if it is a transformer coil including at least coil L3 and coil L4 which is magnetically coupled to coil L3.
[0056] As shown in Figure 12, the filter circuit 100H can cancel out the ESL of a larger capacitor C1 by increasing the negative mutual inductance M by connecting coil component 1 and coil component 1a in a cascaded manner. Although the filter circuit 100H is shown with one additional coil component 1a, two or more coil components 1a may be provided in the middle of the wiring pattern connecting coil component 1 and capacitor C1. Furthermore, the configuration of adding coil component 1a in the middle of the wiring pattern connecting coil component 1 and capacitor C1 can also be similarly applied to filter circuits such as 100, which connects coil component 1 and capacitor C1 using a cable made of metal conductors.
[0057] <Modification> In the coil component 1 shown in Figure 2, the coil portion 2a and lead wires 2b, 2d are formed from a single conductor (for example, a metal plate), and the coil portion 3a and lead wires 3b, 3d are formed from a single conductor, with the coil portion 2a and coil portion 3a fixed to the housing 4 with molded resin. However, the coil components 1, 1a used in the above-described embodiment are not limited to the configuration of the coil component 1 shown in Figure 2. Multiple substrates (ceramic green sheets) on which wiring patterns constituting at least a part of the coil are formed may be stacked to form the magnetically coupled coil L1 and coil L2. Alternatively, the coil components 1, 1a used in the above-described embodiment may be formed by winding two wires around a bobbin to form the magnetically coupled coil L1 and coil L2.
[0058] The coil component, which consists of two wires wound around a bobbin to form a magnetically coupled coil L1 and coil L2, will be explained with reference to the diagram. Figure 13 is a perspective view of a modified coil component 1A. Note that the coil component 1A shown in Figure 13 may also be applied to the coil components 1 and 1a used in the above-described embodiment.
[0059] The coil component 1A includes a bobbin 20, a first wire 2A, and a second wire 3A. The bobbin 20 has a body portion 20a around which the wire is wound, and flange portions 20b and 20c provided at both ends of the body portion 20a. The bobbin 20 is made of a non-conductive material, specifically a non-magnetic material such as alumina, a magnetic material such as Ni-Zn ferrite, or a resin. When the bobbin 20 is made of resin, for example, it may be made of a resin containing metal powder, magnetic powder such as ferrite powder, a resin containing non-magnetic powder such as silica powder, or a resin that does not contain fillers such as powders.
[0060] Since the coil component 1A has two wires wound around the bobbin 20 in the same direction, it has a terminal 2c (first terminal) connected to one end of the first wire 2A, a terminal 2e (second terminal) connected to the other end of the first wire 2A, a terminal 3e (third terminal) connected to one end of the second wire 3A, and a terminal 3c (fourth terminal) connected to the other end of the second wire 3A. In other words, the coil component 1A has four terminals: 2c, 2e, 3c, and 3e. The four terminals (terminals 2c, 2e, 3c, and 3e) are provided at the four corners of the coil component 1A. The first wire 2A wound around the bobbin forms coil L1, and the second wire 3A wound around the bobbin forms coil L2. Although coils L1 and L2 are arranged approximately perpendicular to the bottom surface on which the four terminals are provided, they may also be arranged at an angle to the bottom surface or approximately parallel to the bottom surface.
[0061] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.
[0062] 1, 1A, 1a Coil components, 20 Bobbin, 2A First wire, 2a, 3a Coil section, 2b, 2d, 3b, 3d Lead wire, 2c, 2e, 2f, 2g, 3c, 3e, 3f, 3g, 55a, 55b, 65a, 65b Terminal, 3A Second wire, 4 Housing, 5, 6 Wiring, 5a, 6a Coaxial cable, 7, 8 Electrode pads, 9, 9a Band section, 10a, 10b Power line, 10c, 10d, 50-52, 55-61, 65, 66, 68, 69 Wiring pattern, 20a Body section, 20b, 20c Flange section, 40A, 40B Main surface, 41, 42, 43, 44 Side surface, 51a, 52a, 56a, 57a, 91a Via conductor, 80 Conductor, 90, 91; Conductor layer, 100, 100A to 100H; Filter circuit, 200; Substrate.
Claims
1. A filter circuit comprising: a coil component including a first coil and a second coil that magnetically couples with the first coil; a first wire electrically connected at one end to the first intermediate terminal when the first terminal of the first coil is an input terminal and the second terminal of the first coil is a first intermediate terminal; a second wire electrically connected at one end to the second intermediate terminal when the third terminal of the second coil is a second intermediate terminal and the fourth terminal of the second coil is an output terminal; and a capacitor with one electrode electrically connected to the other end of the first wire and the other end of the second wire, wherein the other electrode of the capacitor is electrically connected to a ground electrode.
2. The filter circuit according to claim 1, wherein the distance between the first wiring and the second wiring is different in the portion between one end of the first wiring and the portion between one end of the second wiring and the portion between one end of the second wiring.
3. The filter circuit according to claim 1 or claim 2, further comprising a portion in the middle of the first and second wirings that bundles the first and second wirings together.
4. The filter circuit according to claim 3, wherein the bundling portion bundles the first and second wiring from the middle of the first and second wiring to one electrode of the capacitor.
5. The filter circuit according to claim 3, wherein the first wiring and the second wiring are bundled together in the bundled portion such that the direction of the current flowing through the first wiring and the direction of the current flowing through the second wiring are the same.
6. The filter circuit according to claim 1 or claim 2, further comprising a connection portion in the middle of the first and second wiring that electrically connects the first and second wiring.
7. The filter circuit according to any one of claims 1 to 6, wherein the first wiring and the second wiring are cables formed of metal conductors.
8. The filter circuit according to claim 7, wherein the cable is a coaxial cable.
9. The filter circuit according to any one of claims 1 to 6, wherein the first wiring and the second wiring are wiring patterns of metal conductors formed on a substrate on which the coil component is mounted.
10. The filter circuit according to claim 9, wherein the first wiring pattern constituting the first wiring and the second wiring pattern constituting the second wiring are provided on different layers of the substrate, and a ground potential wiring pattern is provided between the first layer on which the first wiring pattern is provided and the second layer on which the second wiring pattern is provided.
11. The filter circuit according to any one of claims 1 to 10, further comprising a transformer coil in the middle of the first wiring and the second wiring, the transformer coil including a third coil and a fourth coil that magnetically couples with the third coil.
12. The filter circuit according to any one of claims 1 to 11, wherein the coil component includes a housing having a pair of first main surfaces and second main surfaces facing each other, and four side surfaces connecting the first main surface and the second main surface; the first coil disposed inside the housing; and the second coil disposed inside the housing such that, when viewed from the direction of the first main surface or the side surface, the openings of the first coil overlap, and the first to fourth terminals are formed on the second main surface or the side surface.
13. The filter circuit according to any one of claims 1 to 11, wherein the coil component includes a bobbin having a body portion around which a wire is wound and flange portions provided at both ends of the body portion, a first wire wound around the body portion forming the first coil, and a second wire wound around the body portion forming the second coil, and the first to fourth terminals are formed in the flange portions.