LC noise filter

Abstract: An LC noise filter comprising a dielectric substrate (10), a plurality of concentrically adjacent spiral grooves pro­ vided in at least one surface (10a) of the substrate, and a plurality of inductor conductors (20-1, 20-2) provided in the respective spiral grooves. The inductor conductors are opposed to each other with the wall body between the grooves therebetween so as not to obstruct the magnetic path of the magnetic flux of the opposite inductor conduc­ tor. That is, a distribution constant LC noise filter ha­ ving a sufficient capacitance and excellent electric cha­ racteristics without lowering the inductance of each induc­ tor conductor is disclosed.

Description: The present invention relates to an LC noise filter according to the pre-characterizing part of claim 1. A noise filter of this type is known from US-A-2,583,854. The dielectric is a flat plate made of a ceramic material and inserted between two substrates, each of which carrying conductors. Such a noise filter provides an inductance (L) by the spiral inductor conductor and an electrostatic capacity (C) between the inductor conductor and the grounding conductor in the form of a distribution constant. However, the electric characteristic obtained are not those produced by an LC noise filter but rather resemble those produced by a capacitor. More specifically, in this LC noise filter, the grounding conductor not only capacitatively couples with the spiral inductor conductor by electrostatic capacity, but also inductively couples therewith. Therefore, the magnetic flux produced by the energizing current of the spiral inductor conductor also produces an electromotive force on the grounding conductor, and a short-circuit current flows. If the spiral inductor conductor is compared to a primary coil in a transformer, the grounding conductor acts like a secondary coil, so that it is impossible to obtain such a large inductance as expected from the spiral inductor conductor. In other words, such a conventional noise filter cannot display full function as an LC noise filter. If the frequency of the applied signal is high, short circuits between the lines may be caused on the spiral inductor conductor, thereby lowering the function thereof. Moreover, the noise filter does not produce such a large capacitance C as expected between the inductor conductor. The grounding conductor and the electric characteristics obtained are inferior to those of a lumped constant LC noise filter. Especially, when the frequency of the signal supplied to the inductor conductor becomes high, the inductance of the inductor conductor changes so that the capacitance conductor becomes even smaller. Thus, this noise filter cannot fulfill a sufficient function as an LC noise filter. The object of the present invention is to provide an LC noise filter, which has the desired inductance and capacitance. This is achieved by the features of claim 1. The present inventor formed a spiral groove on at least one surface of a dielectric, and at least one ground groove was provided adjacently to a part of the spiral groove. An inductor conductor was provided in the spiral groove and a grounding block conductor was provided in the ground groove. Since the grounding block conductor has a small area, the self inductance L E is small and it is possible to use the capacitance formed between the grounding block conductor and the inductor conductor as the capacitance of the noise filter as it is. Furthermore, since the grounding block conductor faces only a part of the inductor conductor, the mutual inductance between the inductor conductor and the grounding block conductor is substantially negligible, so that it is possible to produce an LC noise filter which does not contain the mutual inductance that lowers the characteristics of the noise filter. In addition, since the grounding block conductor, which only faces a part of the inductor conductor, does not block the magnetic path of the inductor conductor, the inductance of the inductor conductor is not lowered. Thus, according to the present invention, it is possible to provide an LC noise filter which has sufficient L and C, and a small mutual inductance that exerts deleterious influence on the characteristics. When this LC noise filter was used, the characteristics much more excellent than those of the conventional LC noise filter were obtained with the provision of only one grounding block conductor. When a plurality of grounding block conductors were provided, each block conductor individually constituted a capacitor which effectively functioned with the inductor conductor. Therefore, it is possible to obtain an LC noise filter having a desired capacitance by providing a given number of grounding block conductors. Furthermore, according to the present invention, it is possible to obtain the characteristics of an LC noise filter approximate to those of the distribution constant type which cannot be obtained by the conventional filter by providing a plurality of grounding block conductors. As a result of further researches, it has been found that the position at which the grounding block conductor was faced to the inductor conductor greatly influences the attenuation characteristic of the noise filter, and that excellent attenuation characteristic was obtained by disposing the grounding block conductor close to the input or output terminal of the inductor conductor in the electric circuit. Since a plurality of grounding block conductors are provided, one is disposed in proximity to the input terminal of the inductor conductor, another in proximity to the output terminal of the inductor conductor, and the others at other positions. In the present invention, a spiral groove is formed on at least one surface of the dielectric and plural grounding block conductors are provided adjacently to a part of the spiral groove. In this structure, the inductor conductor and the grounding block conductors provided in each groove faces each other with the wall body between the grooves therebetween, and constitutes a larger capacitor therebetween. It is therefore possible to obtain the optimum capacitance by appropriately selecting the material of the dielectric, the size and the width of the wall body, etc. In addition, according to the present invention, since the lines of the inductor conductors, and the inductor conductor and the grounding block conductor are completely isolated from each other through the wall body between the grooves, the inductor conductor sufficiently functions as an inductor without causing short circuit between lines even in a high-frequency zone as in a conventional noise filter. According to the present invention, it is possible to provide a plurality of grounding block conductors intermittently between the lines of the inductor conductors so as to function as a shield conductor which prevents short circuit between lines, thereby ensuring safer prevention of the short circuit between the lines of the inductor conductors. Thus, according to the present invention, it is possible to produce an LC noise filter having excellent electric characteristics in a wide region ranging from a low-frequency zone to a high-frequency zone. The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 (A) to 1(C) are explanatory views of an example of a substrate Figs. 2(A) to 2(C) are explanatory views of a normal mode LC noise filter and a common mode LC noise filter produced by providing conductors in the grooves shown in Figs. 1(A) to 1(C); Figs. 3(A) and 3(B) are the equivalent circuit diagrams of the first embodiment and the second embodiment, respectively; Fig. 4 is an explanatory view of inductor conductors which face each other with the wall body therebetween; Figs. 5(A) to 5(C) are explanatory views of a further common mode LC noise filter; Fig. 6 is the equivalent circuit diagram of the filter of Fig. 5 Fig. 7 is an explanatory view of a modification of a dielectric; Figs. 8 to 15 are explanatory views of a first embodiment of the present invention; wherein Fig. 8 is an explanatory view of an example of a substrate used in this embodiment; Fig. 9 is a schematic explanatory view of a through hole provided in each groove of the substrate shown in Fig. 8; Figs. 10(A) and 10(B) are explanatory views of a normal mode LC noise filter of this embodiment in which conductors are provided in grooves, wherein Fig. 10(A) is a schematic explanatory view of the surface thereof, and Fig. 10(B) is a schematic explanatory view of the back surface thereof; Fig. 11 is a sectional perspective view of the noise filter shown in Fig. 10(A), taken along the line XI-XI; Fig. 12 is the equivalent circuit diagram of the noise filter of the first embodiment; Fig. 13 is an explanatory view of the inductor conductor and the grounding block conductor which are opposed to each other with the wall body of the substrate therebetween; Fig. 14 is an explanatory view of another example of a spiral groove and a ground groove provided on the substrate, which are tapered toward the outside; Fig. 15 is a sectional perspective view of a modification of an LC noise filter of the first embodiment, which has shallow type grooves; Figs. 16 to 18 are explanatory views of a second embodiment of the present invention, wherein Fig. 16(A) is an explanatory view of the surface of a normal mode LC noise filter of this embodiment, Fig. 16(B) is an explanatory view of the back surface thereof, Fig. 17 is a sectional perspective view of the noise filter shown in Fig. 16(A), taken along the line X-X; and Fig. 18 is the equivalent circuit diagram of the noise filter of the second embodiment; Fig. 19 is an explanatory view of a third embodiment of the present invention; Fig. 20 is an explanatory view of a fourth embodiment of the present invention; Fig. 21 is an explanatory view of another embodiment of an LC noise filter of the present invention which uses a housing; Fig. 22 is an explanatory view of still another embodiment of an LC noise filter of the present invention in which a closed magnetic circuit is formed by magnetic powder coating; Fig. 23 is an explanatory view of a multi-channel noise filter produced by laminateing PC boards and providing LC noise fileters of one of the above-described embodiments on one of the laminated PC boards; Fig. 24 is an explanatory view of a PC board provided with a multi-channel noise filter for signal lines and a multi-channel noise filter for a power source line together with IC; and Fig. 25 is an explanatory view of a multi-channel noise filter provided on an insulating rectangular substrate and mounted on a PC board. The invention is carried out in accordance with the appended claims. An LC noise filter which is provided as a normal mode LC noise filter, will first be explained. The LC noise filter is composed of a dielectric substrate 10 of a ceramic material or the like, two concentrically adjacent spiral grooves 12-1, 12-2 provided on the surface 10a of the substrate 10, as shown in Fig. 1(A), and a groove 14-1 provided on the back surface 10b in such a manner as to extend from the center of the back surface 10b to the periphery, as shown in Fig. 1(C). On the side of the center of the substrate 10, the inner end portions of the spiral groove 12-1 and the groove 14-1 communicate with each other through a through hole 16-1, as shown in Fig. 1(B). As shown in Fig. 2(A), first and second inductor conductors 20-1, 20-1 are provided in the spiral grooves 12-1, 12-2, respectively, provided on the surface 10a of the substrate 10, and the outer end portions of the inductor conductors 20-1, 20-2 are connected to terminals 22-1, 22-2, respectively. As shown in Fig. 2(C), the groove 14-1 provided on the back side of the substrate 10 is provided with a lead 26-1, the outer end portion of the lead 26-1 being connected to a terminal 28-1 and the inner end portion thereof being electrically connected to the inner end portion of the first inductor conductor 20-1 through the through hole 16-1, as shown in Fig. 2(B). These conductors 20-1, 20-2, 26-1 are easily produced by applying a resist to the substrate 10 in advance except for the grooves 12-1, 12-2 and 14-1, and dipping the substrate 10 in a conductive tank which is filled with a liquid conductor. The conductors 20-1, 20-2, 26-1 are also easily produced by dipping the substrate 10 without the application of a resist, and grinding the surface of the substrate 10 so as to remove the conductor which has adhered to the portions other than the grooves 12-1, 12-2 and 14-1. A method other than dipping may be adopted to provide the conductors in the corresponding grooves. For example, the substrate 10 may be plated with a conductor. Fig. 3(A) is the equivalent circuit diagram of the LC noise filter. In this embodiment, the terminals 22-1, 28-1 are used as the input and output terminals, and the terminal 22-2 is used as the ground terminal. The first inductor conductor 20-1 connected to the input and output terminals 22-1, 28-1 provides a first inductance L₁ and the second inductor conductor 20-2 connected to the ground terminal 22-2 provides a second inductance L₂. The first and second inductor conductors 20-1, 20-2 face each other with the wall body 18 between the grooves 12-1, 12-2 therebetween, as shown in Fig. 4. Therefore, the first and second inductor conductors 20-1, 20-2 capacitively couple with each other by electrostatic capacity, and the capacitance C is formed therebetween in the form of a distribution constant. Therefore, by using a material having a high dielectric constant for the substrate 10, it is possible to set the capacitance C at a large value, if necessary. In this noise filter, the second inductor conductor 20-2, which constitutes a capacitor with the first inductor conductor 20-1, is provided in such a manner as not to block the magnetic path of the first inductor conductor 20-1. The magnetic flux generated when the first inductor conductor 20-1 is energized passes the wall body 18 between the grooves 12-1, 12-2 from the surface side of the substrate 10 to the back side, or in the reverse direction. If the inductor conductor 20-2 is provided in such a manner as to block the magnetic path (e.g., if the inductor conductor 20-2 is provided in such a manner as to cover the surface of the wall body 18), the magnetic path is blocked by the inductor conductor 20-2 and the first inductor conductor 20-1 cannot sufficiently function as an inductor. In contrast, since the second inductor conductor 20-1 is provided concentrically adjacently to the first inductor conductor 20-1, the magnetic path of the first inductor conductor 20-1 is not blocked by the second inductor conductor 20-2 at all, and the effect of the LC noise filter is fully displayed without reducing the inductance of the spiral first inductor conductor 20-1. In addition, in this embodiment, since the second inductor conductor 20-2, which is used as a grounding conductor, is spirally provided between the lines of the first inductor conductor 20-1, which is used as an energizing conductor, the second inductor conductor 20-2 functions as a shield conductor with respect to the first inductor conductor 20-1. According to Fig. 1C, a groove 14-2 is provided on the back surface 10b of the substrate 10 as indicated by the one-dot chain line in Fig. 1(C) and a second lead 26-2 is electrically connected to the inner end portion of the second inductor conductor 20-2 through a through hole 16-2 is provided in the groove 14-2 (Fig. 2). Fig. 3(B) is the equivalent circuit diagram of the LC noise filter. Both ends of the first inductor conductor 20-1 and the second inductor conductor 20-2 are connected to the input and output terminals 22-1, 28-1 and 22-2, 28-2, respectively, so that the LC noise filter functions as a common mode four-terminal LC noise filter. Fig. 5 shows an LC noise filter, in which the first and second inductor conductors 20-1, 20-2 are provided on the surface 10a of the substrate 10. On the back surface 10b of the substrate 10, the first lead 26-1 and the second lead 26-2 are provided, as shown in Fig. 5(C). The inner end portions of the first inductor conductor 20-1 and the first lead 26-1 are electrically connected to each other through the through hole 16-1, as shown in Fig. 5(B), and the inner end portions of the second inductor conductor 20-2 and the second lead 26-2 are also electrically connected to each other through the through hole 16-2. Thus, this noise filter functions as a common mode four-terminal LC noise filter. A common mode noise filter in which the first and second inductor conductors 20-1, 20-2 are used as energizing conductors involves a fear of causing short circuit between lines of both conductors if an energizing frequency becomes high. This structure is characterized in that a first shield conductor 30-1 for isolating both conductors is spirally formed between the inductor conductors 20-1 and 20-2, and that a second shield conductor 30-2 is spirally formed between the inductor conductors 20-2 and 20-1 in order to prevent the short circuit between lines more effectively. The shield conductors 30-1, 30-2 may be provided in such a manner as to coat the surface 10a of the substrate 10, but in this filter, they are provided in spiral grooves 12-3 and 12-4 in the same way as the inductor conductors 20-1, 20-2. On the back side of the substrate 10, a ground lead 26-3 having a ground terminal 28-3 at the outer end portion is provided, and the inner end portion of the ground lead 26-3 is electrically connected to the inner end portions of the first and second shield conductors 30-1, 30-2 through a through hole (not shown). In this way, the LC noise filter functions as a common mode four-terminal LC noise filter. Fig. 6 is the equivalent circuit diagram. The shield conductors 30-1, 30-2 can effectively prevent the short circuit between the lines of the the inductor conductors 20-1 and 20-2, thus functioning as a noise filter having excellent electric characteristics in a wide region ranging from a low-frequency region to a high-frequency region. In the above explained filters, inductor conductors are only provided on a single surface of the substrate 10, but inductor conductors may be spirally provided on both sides of the substrate 10 in such a manner as to be opposed to each other with the substrate 10 therebetween, if necessary. In this case, it is possible to produce a noise filter having a large inductance by electrically connecting the inductor conductors on both sides of the substrate. As explained above, by adopting a structure in which a plurality of concentrically adjacent spiral grooves are provided in at least one surface of a dielectric and an inductor conductor is provided in each groove, each inductor conductor is situated at a position which does not check the magnetic path of the magnetic flux of the opposite inductor conductor and faces the opposite inductor conductor with the wall body between the spiral grooves therebetween. Thus, it is possible to produce a distribution constant LC noise filter having a sufficient capacitance and excellent electric characteristics without lowering the inductance of each inductor conductor. The grounding inductor conductor functions as a shield conductor for preventing short circuit between the lines of the energizing inductor conductor, thereby making it possible to produce a normal mode LC noise filter which is capable of removing the noise component without causing short circuit between lines even in a high-frequency zone. First Embodiment Fig. 8 shows a preferred embodiment of a split grounding type LC noise filter in accordance with the present invention. As shown in Fig. 8, the noise filter of this embodiment is composed of the dielectric substrate 10 of a ceramic material or the like, a spiral groove 12 provided in the surface 10a of the substrate 10, and a plurality of ground grooves 15-1, 15-2, ... 15-4 each of which faces a part of the spiral groove 12. Each of the spiral grooves 12 and the ground grooves 15 is formed into a deep groove, as will be described later with reference to Fig. 11. The spiral groove 12 is provided with through holes 16a and 16b at the outer end portion and the inner end portion, respectively. Similarly, each of the ground grooves 15 is provided with a through hole 17 at one end portion thereof. Each of the through holes 16a, 16b, 17 is so designed as to communicate with the back surface 10b of the substrate 10 from the bottom surface of the groove, as shown in Fig. 9. An inductor conductor 20 is provided in the spiral groove 12 provided in the surface 10a of the substrate 10, and grounding block conductors 23-1, 23-2, 23-3 and 23-4 are provided in the ground grooves 15-1, 15-2, 15-3 and 15-4, respectively, as shown in Fig. 10(A). Fig. 11 is a schematic sectional view of the LC noise filter shown in Fig. 10(A), taken along the line XI - XI. As shown in Fig. 11, each of the grounding block conductors 23-1, 23-2, ... 23-4 faces a part of the inductor conductor 20 with the wall body 18 of the substrate 10 therebetween. Therefore, each of the grounding block conductors 23-1, 23-2, ... 23-4 capacitively couples with the inductor conductor 20 by an electrostatic capacity, and a capacitance C is provided therebetween in the form of a distribution constant. On the back surface 10b of the substrate 10, input and output terminals 22, 28 and a ground terminal 25 are provided, as shown in Fig. 10(B). The one input and output terminal 22 is connected to the outer end portion of the inductor conductor 20 provided on the surface 10a of the substrate 10 through the through hole 16a, and the other input and output terminal is connected to the inner end portion of the inductor conductor 20 through the through hole 16b and an input and output lead 27. The ground terminal 25 is electrically connected to the grounding block conductors 23-1, 23-2, ... 23-4 provided on the surface 10a of the substrate 10 through the corresponding through holes 17-1, 17-2, ... 17-4 and the corresponding ground leads 26-1, 26-2, ... 26-4. The conductors 20, 23, the terminals 22, 28, 25 and the leads 26, 27 are easily produced by applying a resist to the substrate 10 in advance except for the grooves 12, 15, and the portions for the terminals 22, 28, 25 and the leads 26, 27, and dipping the substrate 10 in a conductive tank which is filled with a liquid conductor. These conductors, terminals and lead are also easily produced by dipping the substrate 10 without the application of a resist, and grinding the surface of the substrate 10 so as to remove the conductor which has adhered to the portions other than the grooves 12 and 15. A method other than dipping may be adopted to provide the conductors 20, 23, the terminals 22, 28, 25 and the leads 26, 27 on the surface 10a and the back surface 10b of the substrate 10, as described in the first embodiment. For example, the substrate 10 may be plated with a conductor. In this embodiment, it is preferable that one of the grounding block conductors 23-1, 23-2, ... 23-4 is opposed to the inductor conductor 20 at a position close to the one terminal 20 of the inductor conductor 20 in the electric circuit, and that another grounding block conductor 23 is opposed to the inductor conductor 20 at a position close to the other terminal 28 in the electric circuit. For this purpose, the grounding block conductor 23-1 is so disposed as to face a part of the inductor conductor 20 at the position close to the terminal 22 in the electric circuit. The grounding block conductor 23-4 is so disposed as to face a part of the inductor conductor 20 at the position close to the terminal 28 in the electric circuit. The other two grounding block conductors 23-2 and 23-4 are respectively opposed to a part of the inductor conductor 20 between the input and output terminals 22 and 28. In order to obtain a good attenuation characteristic, it is favorable that at least the grounding block conductors 23-1 and 23-4, which are disposed in proximity to the input and output terminals 22 and 28 lead out the leads 26-1 and 26-4 from the positions close to the terminals 22 and 28, respectively, and connect them to the ground terminal 25. Fig. 12 is the equivalent circuit diagram of an LC noise filter of this embodiment. In this embodiment, the spiral inductor conductor 20 provides the inductance L₁. Each of the grounding block conductors 23-1, 23-2, ... 23-4 which is adjacent to the inductor conductor 20 capacitively couples to a part of the inductor conductor 20 by an electrostatic capacity, whereby the capacitors C₁, C₂, C₃ and C₄ are formed. This embodiment offers the following advantages. (1) According to this embodiment, each of the grounding block conductors 23-1, 23-2, ... 23-4 is formed into a block having a small area, and is connected to the ground terminal 25. Therefore, the eddy current flowing to each of the grounding block conductors 23-1, 23-2, ... 23-4 is small and the inductance thereof is small, so that the capacitors C₁, C₂, ... C₄ are directly connected to the ground terminal 25. This is equivalent to a plurality of LC noise filters connected to each other in series. That is, it is possible to obtain an LC noise filter which substantially functions as a distribution constant LC noise filter. Therefore, according to this embodiment, it is possible to increase the capacitance C by increasing the number of the grounding block conductors 23 and to reduce the capacitance C by reducing the number of the grounding block conductors 23. Since the grounding block conductors 23-1 and 23-4 are disposed at the positions close to the input and output terminals 22, 28 in the electric circuit, an excellent attenuation characteristic is obtained in this embodiment. (2) In this embodiment, each of the grounding block conductors 23-1, 23-2, ... 23-4 is opposed to the inductor conductor 20 with the wall body 18 between the grooves 12 and 15 therebetween, as shown in Fig. 13, and the capacitances of the capacitors C₁, C₂, ... C₄ are provided in the form of a distribution constant therebetween. It it therefore possible to set the capacitance C at a large value, if necessary, by using a material having a high dielectric constant for the substrate 10. (3) Each of the grounding block conductors 23-1, 23-2, ... 23-4 has a small area and is opposed to only a part of the inductor conductor 20. The mutual inductance between the inductor conductor 20 and each of the grounding block conductors 23-1, 23-2, ... 23-4 is substantially negligible, so that it is possible to greatly reduce the mutual inductance component which is a cause of the deterioration of the characteristics of a noise filter. (4) In the noise filter of this embodiment, the grounding block conductor 23 is so designed as not to block the magnetic path of the inductor conductor 20. The magnetic flux generated when the inductor conductor 20 is energized passes between the lines of the inductor conductor 20 from the surface side of the substrate 10 to the back side, or in the reverse direction. If the block conductor 23 is provided in such a manner as to block the magnetic path (e.g., if the block conductor 23 is provided in such a manner as to face the region between the lines of the inductor conductor 20), the magnetic path is blocked by the block conductor 23 and the inductor conductor 20 cannot sufficiently function as an inductor. In contrast, in this embodiment, since each of the block conductors 23 is provided adjacently to the inductor conductor 20, the magnetic path of the inductor conductor 20 is not obstructed by the block conductor 23 at all, and the effect of the LC noise filter is fully displayed without reducing the inductance of the spiral inductor conductor 20. If the terminals 22 and 28 of the inductor conductor 20 are used as the input and output terminals, the LC noise filter of this embodiment can be used as a normal mode noise filter having good electric characteristics. (5) In this embodiment, the inductor conductor 20 and the grounding block conductor 23 are provided in the spiral groove 12 and the ground groove 15, respectively, provided in the surface 10a of the substrate 10. Therefore, the inductor conductor 20 and the grounding block conductor 23 are properly insulated from each other by the wall body 18 of the substrate 10, thereby preventing short circuit between lines of the inductor conductor 20 or between the inductor conductor 20 and the grounding block conductor 23. Accordingly, the noise filter of this embodiment solves all above mentioned problems and functions as a normal mode noise filter having excellent electric characteristics in a wide region ranging from a low-frequency zone to a high-frequency zone. (6) Furthermore, in this embodiment, the inductor conductor 20 is provided in the ground groove 15, it is possible to determine the sectional configuration and area of the inductor conductor 20 more freely in comparison with the related art in which the inductor conductor 20 is so formed as to coat the surface of the substrate 10. For example, by forming the inductor conductor 20 so as to have a large sectional area, it is possible to provide an LC noise filter very suitable as an LC noise filter for the power source for a comparatively large energizing current. The spiral groove 14 and the ground groove 15 may be tapered toward the outside, if necessary, as shown in Fig. 14. Adoption of this configuration to the spiral groove 14 and the ground groove 15 enables the inductor conductor 20 and the grounding block conductor 23 to be provided with certainty in the grooves 12 and 15, respectively, by dipping the substrate 10 in a conductive tank even if these grooves 12, 15 are of a deep groove type. Although the grooves 12 and 15 are of a deep groove type in this embodiment, they may also be a shallow groove type, if necessary, as shown in Fig. 15, which is a schematic sectional view of the LC noise filter shown in Fig. 10(A), taken along the line XI - XI. Such a shallow groove type LC noise filter is suitable as a noise filter for signal lines and since it is possible to reduce the thickness of the substrate 10, the shallow groove type LC noise filter is suitable when it is attached to a portion which has many limitations in space. (7) Furthermore, according to this embodiment, since the inductor conductor 20 and a plurality of grounding block conductors 23-1, 23-2, ... 23-4 are provided on the surface 10a of the substrate 10, it is possible to use the back surface 10b of the substrate 10 for winding between these conductors 20, 23-1, 23-2, ... 23-4 and the terminals 22, 28 and 25. Thus, the winding of the entire circuit is simplified. Especially, in the case of a normal mode noise filter, the winding is sufficed with only the provision of the two input and output terminals 22 and 28 and the one ground terminal 25 on the back surface 10b of the substrate 10 and external connection is easily carried out by using these three terminals 22, 28 and 25. In this way, according to this embodiment, the connection between each of the grounding block conductors 23 and the ground, which matters when a multiplicity of grounding block conductors 23 are provided, is facilitated by using the ground terminal 25 in common. For example, when the noise filter of this embodiment is incorporated into an SMD type device, this device is required to provide only three pins connected to the respective terminals 22, 28 and 25 for the purpose of connection to an external circuit. Second Embodiment Figs. 16 and 17 show a second embodiment of the present invention. The noise filter of this embodiment is composed of a pair of concentrically adjacent spiral grooves 12-1, 12-1 provided in the surface 10a of the substrate 10, and a plurality of ground grooves 15-1, 15-2, ... 15-4, provided between the spiral grooves 12-1 and 12-2, as shown in Fig. 16(A). As shown in Fig. 17, the inductor conductors 20-1, 20-2 are provided in the spiral grooves 12-1, 12-2, respectively, and the grounding block conductors 23-1, 23-2, ... 23-4 are provided in the respective ground grooves 15-1, 15-2, ... 15-4. A pair of input and output terminals 22-1, 28-1 and 22-2, 28-2, and the ground terminal 25 are provided on the back surface of the substrate 10, as shown in Fig. 16(B). The input and output terminals 22-1, 22-2 are electrically connected to the outer end portions of the corresponding inductor conductors 20-1, 20-2 through the through holes 16a, and the other input and output terminals 28-1, 28-2 are electrically connected to the inner end portions of the corresponding inductor conductors 20-1, 20-2 through the through holes 16b, and leads 27-1 and 27-2, respectively. The ground terminal 25 is electrically connected to the grounding block conductors 23-1, 23-2, ... 23-4 through the through holes 17, and the leads 26-1, 26-2, ... 26-4, in the same way as in the fourth embodiment. Fig. 18 is the equivalent circuit diagram of the LC noise filter of this embodiment. The spiral inductor conductor 20-1 provides the first inductance L₁ and the spiral inductor conductor 20-2 provides the second inductance L₂. The group of grounding block conductors 23-1, 23-2, ... 23-4 provided on the surface of the substrate 10 forms the capacitors C₁, C₂, C₃, and C₄ with the inductor conductor 20-1 which faces the grounding block conductors 23-1, 23-2, ... 23-4 with the wall body 18 of the substrate 10 therebetween, as shown in Fig. 17. The capacitors C₁, C₂, C₃ and C₄ do not obstruct the magnetic path of the opposite inductor conductor 20-1 and provide the capacitances in the form of a distribution constant. Similarly, the group of grounding block conductors 23-1, 23-2, ... 23-4 forms capacitors C₅, C₆, C₇ and C₈ with the other inductor conductor 20-2. The capacitors C₅, C₆, C₇ and C₈ do not obstruct the magnetic path of the opposite inductor conductor 20-2 and provide the capacitances in the form of a distribution constant. Accordingly, the noise filter of this embodiment functions as a common mode four-termial noise filter having the circuit structure shown in Fig. 18. Although four grounding block conductors 23 are provided with respect to the inductor conductors 20-1 and 20-2 in this embodiment, the number of the grounding block conductors 23 is not restricted to four, and it is possible to produce a distribution constant common mode noise filter having a given capacitance by varying the number of the grounding block conductors 23 as occasion demands. A pair of inductor conductors 20-1, 20-2 and a multiplicity of grounding block conductors 23-1, 23-2, ... 23-4 are provided on the surface 10a of the substrate 10 in this embodiment. Therefore, the back surface 10b of the substrate 10 can be used for wiring, and electric connection is easily carried out merely by connecting the conductors 20-1, 20-2, 23-1, 23-2, ... 23-4 to the five terminals 22-1, 22-2, 28-1, 28-2 and 25 provided on the back surface 10b of the substrate 10. Since it is unnecessary to provide a surplus lead between the terminals and conductors, a noise filter having a simple structure and good electric characteristics is obtained. Third Embodiment Fig. 19 shows a third embodiment of the present invention. This embodiment is characterized in that a plurality of grounding block conductors 23 are intermittently provided between the lines of the inductor conductor 20 in the noise filter shown in Fig. 10 so that each of the grounding block conductors 23 functions as a shield conductor which prevents short circuit between lines of the inductor conductor 20. On one end side of each of the grounding block conductors 23 a through hole is provided as in the fourth embodiment, and each of the grounding block conductors 23 is connected to the ground terminal 25 through the through hole, the lead 26, etc. By virtue of this structure, the noise filter of this embodiment can prevent short circuit between lines more reliably as compared with the second embodiment. Fourth Embodiment Fig. 20 shows a fourth embodiment of the present invention. The LC noise filter of this embodiment is characterized in that a plurality of grounding block conductors 23 are intermittently provided between the lines of the inductor conductor 20-1 and the inductor conductor 20-2 in the noise filter shown in Fig. 16 so that each of the grounding block conductors 23 functions as a first shield conductor which prevents short circuit between lines and in that a plurality of grounding block conductors 23 are also intermittently provided between the lines of the inductor conductor 20-2 and the inductor conductor 20-1 so that each of the grounding block conductors 23 functions as a second shield conductor which prevents short circuit between lines of the inductor conductors 20-2 and 20-1. Each of the grounding block conductors 23 is connected to the ground terminal 25 through the through hole provided in the ground groove 15, the ground lead 26 provided on the back surface of the substrate 10 in the same way as in the sixth embodiment. According to this embodiment, it is possible to produce a common mode four-terminal noise filter having excellent electric characteristics in a wide region ranging from a low-frequency zone to a high-frequency zone and being capable of preventing short circuit between lines of the inductor conductors 20-2 and 20-1 more reliably as compared with the second embodiment. As explained above, according to the first to fourth embodiments, at least one grounding block conductor is provided in such a manner as to be adjacent to a part of the inductor conductor and the grounding block conductor individually forms a capacitor between each block conductor and inductor conductor. It is therefore possible to produce an LC noise filter which has an inductance from the inductor conductor and a capacitance of each block conductor and sufficiently functions as a distribution constant noise filter. According to these embodiments, it is easy to obtain a distribution constant LC noise filter having a given capacitance by varying the number of block conductors. Furthermore, by providing an inductor conductor and the grounding block conductor in a spiral groove and a ground groove provided in at least one surface of a dielectric such that the inductor conductor and the grounding block conductor are adjacent to each other with the wall body of the substrate therebetween, it is possible to produce a distribution constant LC noise filter having a sufficient capacitance and excellent electric characteristics without lowering the inductance of each inductor conductor. Especially, according to these embodiments, since the short circuit between lines of the inductor conductor is safely prevented by virtue of the wall body, it is possible to produce a distribution constant LC noise filter having excellent electric characteristics in a wide region ranging from a low-frequency zone to a high-frequency zone. In addition, since the inductor conductor and the grounding block conductor are provided on the same surface of a dielectric, wiring between each inductor conductor and terminal is facilitated by utilizing the other surface of the substrate. In these embodiments, the grooves formed in the substrate 10 may have a given depth. Fifth Embodiment In an LC noise filter of this embodiment, the inductance L and the capacitance C can be set as desired by appropriately selecting the material of the substrate 10 as well as the number of turns of the inductor conductor 20 and the number of the grounding block conductors 23. For example, in order to provide a large inductance L, a magnetic material is used for the substrate 10, while in order to provide a large capacitance C, a material having a high dielectric constant such as a ceramic material is used for the substrate 10 or the depth of the grooves 12, 15 and the thickness of the wall body 18 is adjusted. In order to increase both L and C, both a material having a high dielectric constant and a magnetic material are used for the substrate 10. By laminating a plurality of noise filters and connecting the noise filters in series or in parallel, a noise filter having given L and C is obtained. Especially, by connecting the laminated noise filters in series, it is possible to use the noise filter as an LC noise filter circuit having large inductance which cannot be obtained by a single noise filter. Alternatively, by accommodating the noise filter of any of the first to eighth embodiments in a housing which constitutes a magnetic circuit, a large inductance L is obtained. Fig. 21 shows an example of such a noise filter. This noise filter is characterized in that a noise filter 210 according to one of the first to eighth embodiments is accommodated in a housing 80 made of a magnetic material. A core insertion hole 10c is formed substantially at the center of the substrate 10, and a core 82 provided at the central portion of the housing 80 is inserted into the core insertion hole 10c. When a cover 84 is fixed to the housing 80, a closed magnetic circuit exclusively for the noise filter is formed between the core 82 and the housing 80 and the cover 84 around the core 82. In this way, the noise filter of this embodiment constitutes an LC noise filter having a sufficient large inductance. Although the closed magnetic circuit is formed by using the housing in this embodiment, the housing may be so designed as to constitute an open magnetic circuit, if necessary. Fig. 22 shows an example of a noise filter with the surface of the substrate 10 coated with a magnetic powder. In the noise filter of this embodiment, the core insertion hole 10c is formed substantially at the center of the substrate 10, and the surface and the back surface of the substrate 10 are coated with a magnetic powder. The magnetic powder coating layer 86 constitutes a closed magnetic circuit exclusively for the noise filter, and thereby greatly reduces the leakage of the magnetic flux to the outside. Accordingly, for example, when a plurality of the noise filters of this embodiment are arranged adjacently to each other and used as a multi-channel noise filter, the noise filter exhibits excellent electric characteristics substantially without mutual interference such as ringing between adjacent noise filters. Example of noise filter using PC board as substrate In the present invention, a distribution constant LC noise filter having good electric characteristics is obtained by utilizing the insulating substrate 10, as shown in the above-described embodiments. For example, if a PC board is used as the insulating substrate 10, it is possible to provide a given number of distribution constant LC noise filters without increasing the thickness of the PC board itself. A noise filter produced by providing distribution constant noise filters on a PC board is very suitable as a noise filter for various electronic machines which have recently been required to be smaller and lighter than ever. For example, by providing a noise filter on a PC board, it is possible to greatly reduce the thickness and weight of the apparatus as a whole than a conventional chip-type noise filter. As a PC board, a PC board in the form of a film or a sheet may be used as well as an ordinary PC board in the form of a plate. For example, by using a distribution constant LC noise filter of the present invention for a lap-top computer, it is possible to accelerate the reduction in the size and the weight of the lap-top computer. It is also easy to mount a given number of LC noise filters of the present invention on a PC board (in the form of a film) for an IC card, which is impossible due to the limitation in the thickness in the prior art which uses a conventional noise filter. Since the distribution constant LC noise filter of the present invention can be easily produced merely by printing the circuit on a PC board, it is easy to mount the noise filter on a PC board for various uses without increasing the thickness of the PC board. Fig. 23 shows an example of a multi-channel noise filter for signal lines provided on a PC board. In this example, a plurality of IC's 110 are mounted on a PC board 100, and a plurality of signal lines 112 are connected to each of the IC's 110. On the underside of the PC board 100, a PC board 200 provided with multi-channel noise filters is disposed for lamination. On the PC board 200, a plurality of LC noise filters according to one of the first to ninth embodiments are provided at the positions which correspond to the input and output leads 112 of the respective IC's 110. In this way, multi-channel noise filters 210 which correspond to the leads 112 of the respective IC's 110 are provided on the PC board 200. Such a multi-channel noise filter 210 can be easily provided on the PC board 200 by, for example, using a technique such as printing, and the size of the multi-channel noise filter 210 can be controlled so as to be installed even in a small space in accordance with the required L and C. The PC board 200 is disposed under the PC board 100 for lamination, and the multi-channel noise filters 210 are electrically connected to the respective leads 112 of the IC's 110 which are situated thereabove. In this way, a multi-channel noise filter is provided on the PC board 200 without increasing the thickness of the board 200, thereby enabling the reduction in size and weight of an electronic machine itself. Although, the multi-channel noise filter 210 is provided on the board 200 different from the PC board 100 provided with the IC's 100, etc. in this example, the present invention is not restricted to this example, and if there is a sufficient space on the PC board 100 with the IC's 110 mounted thereon, the multi-channel noise filter 210 may also be provided on the PC board 100. In this example, the multi-channel noise filter 210 for signal lines is provided on the PC board 200. It is also possible to provide a noise filter for a power source line, if necessary. Fig. 24 shows an example of the PC board 100 provided with the multi-channel noise filter 210 for signal lines and a noise filter 220 for a power source line together with the IC 110. The PC board 100 having such a circuit structure is very suitable as a PC board for an IC card. If there are a plurality of IC's 110, the noise filter 230 for a power source line may be formed into a multi-channel noise filter in conformity with the number of the IC's 110. In a portable machine which is not equipped with a sufficient grounding box body such as an IC card, it is preferable to use a common mode noise filter. Fig. 25 shows an example of a multi-channel noise filter 300 produced by providing a plurality of noise filters of one of the above-described embodiments on the rectangular insulating substrate 10. The multi-channel noise filter 300 of this example can be easily mounted on the PC board 100 like an ordinary electronic part, and can be used as, for example, a multi-channel noise filter for an IC. Alternatively, a film substrate may be used as the insulating substrate 10 and the film substrate 10 provided with the multi-channel noise filter may be mounted on the PC board 100 not vertically as shown in Fig. 25 but horizontally. In this way, even when the PC board 100 is installed at a place having a limitation in thickness, a multi-channel noise filter can be mounted on the PC board 100 without increasing the thickness of the board 100. The noise filter of the present invention can be used not only as a noise filter for signal lines but also as a noise filter for a power source line for, for example, the power source line of an IC. As described above, as the insulating substrate used for the noise filter of the present invention, an insulating film in the form of a film, a sheet or the like may be used as occasion demands. The present invention is not limited to the above-described embodiments and various modifications are possible within the scope of the invention. For example, if the noise filter of the present invention is produced as an SMD type device, it may be considered that one noise filter is insufficient for obtaining the required L and C. In this case, a plurality of noise filters are laminated and those noise filters are connected in series or in parallel so as to obtain an LC noise filter having given C and L. In the above-described embodiments, short circuit between lines of the inductor conductor used as the energizing conductor is prevented by using the wall body 18 of the substrate 10. In addition to this, by coating the surface 10a or both the surface 10a and the back surface 10b of the substrate 10 provided with the conductors with an insulating shield layer, short circuit between lines is more effectively prevented. If a material such as a high-frequency absorbing heating element is used as the substrate 10 in the above-described embodiments, the noise, in particular, the high-frequency noise contained in a signal passing the inductor conductor 20 is absorbed as a heat, thereby enabling more effective removal of noise. As the substrate 10, a ceramic material used for a varistor may be used, if necessary, so as to remove lightning surge or the like. In the above-described embodiments, it is possible to reduce the magnetic resistance of the inductor conductor 20 and increase the inductance by adhering a magnetic material to the surface of the inductor conductor 20 and the grounding block conductor 23 by plating or the like so as to make the conductors into magnetic materials. If an insulating material is used as the magnetic material, short circuit between lines is prevented more effectively. Although a dielectric is formed into the plate-like substrate 10 in the above-described embodiments, the present invention is not restricted thereto, and a cylindrical dielectric such as a circular or square cylindrical dielectric may be used. In this case, a spiral groove and a ground groove are provided in either inner or outer peripheral surface of the cylindrical body and an inductor conductor and a grounding block conductor are provided in the respective grooves. An inductor conductor and a grounding block conductor may also be provided on both inner and outer peripheral surfaces of the cylindrical body. In the above-described embodiments, the inductor conductor 20 and the grounding block conductor 23 are provided in the spiral groove 12 and the ground groove provided in the surface 10a of the substrate 10, but the present invention is not restricted thereto, and the inductor conductor 20 and the grounding block conductor 23 may be directly provided on the surface 10a of the substrate without providing the grooves although the characteristics become slightly inferior.

Claims: An LC noise filter, comprising: a) at least one spiral inductor conductor (20; 20-1, 20-2), b) at least one grounding conductor (23; 23-1-23-4), and c) a dielectric (10) between said at least one spiral inductor conductor (20; 20-1, 20-2) and said at least one grounding conductor (23; 23-1-23-4), d) wherein said inductor conductor (20; 20-1, 20-2) forms a capacitor (C₁, C₂...) with said at least one grounding conductor (23; 23-1-234), characterized in that e) said dielectric is formed as a substrate (10) having at least one surface (10a), f) said conductors are formed in grooves (12-1, 12-2; 15-1...15-4) in at least one surface (10a) of said substrate (10), and in that g) said at least one grounding conductor (23; 23-1...23-4) is formed as a plurality of non-continuous grounding conductor sections (23-1...23-4), at least some of the sections being disposed adjacent to and on the same side of said at least one inductor conductor (20; 20-1, 20-2). An LC noise filter according to claim 1, wherein a plurality of spiral grooves (12, 15) are provided in at least one surface of said substrate (10) in such a manner as to be concentrically adjacent to each other; and one inductor conductor is provided in each of said grooves. An LC noise filter according to claim 1 or 2, wherein a through hole (10c) is provided at the center of said substrate (10) and a magnetic path is formed on the surface of said substrate by using a magnetic material. An LC noise filter according to any of claims 1 to 3, wherein said dielectric is formed into a thick substrate (19); said plurality of spiral grooves are formed in said substrate as deep grooves; and each of said inductor conductors (20-1, 20-2) is provided in each of said deep spiral grooves (12, 15) in such a manner as to be opposed to each other with said wall body therebetween. An LC noise filter according to claim 4, wherein each of said spiral grooves (12, 15) is formed into a deep groove which penetrates through said substrate from one surface to the back surface thereof. An LC noise filter according to any of claims 1 or 5, wherein said inductor conductor (20) provided in said spiral groove (12) is used as an energizing inductor conductor and constitutes a normal mode LC noise filter together with said grounding conductor (23) provided in said ground groove (15). An LC noise filter according to any of claims 1 or 5, wherein at least two spiral grooves are provided in such a manner as to be concentrically adjacent to each other as said spiral groove, and energizing inductor conductors (20-1, 20-2) each of which is provided in each of said spiral grooves (12) together with said grounding conductor (23) provided in said ground groove (15) constitute a common mode LC noise filter. An LC noise filter according to any of claims 1 or 7, wherein one of said plurality of said grounding conductor sections (23-1...23-4) is disposed in proximity to an input or output terminal (22-1, 22-2) of said inductor conductor (20). An LC noise filter according to any of claims 1 or 7, wherein a first conductor section is disposed in proximity to an input terminal (22) of said inductor conductor and a second conductor section (23-3) disposed in proximity to the output terminal of said inductor conductor (20). An LC noise filter according claim 9, wherein said grounding conductor includes a plurality of third conductor sections (23) disposed in such a manner as to be adjacent to a part of said inductor conductor between the input terminal and the output terminal of said inductor conductor (20). An LC noise filter according to any of claims 1 or 10, wherein said plurality of grounding conductor sections are intermittently provided between the lines of said inductor conductor (20) so as to function as a shield conductor for preventing short circuit between lines of said inductor conductor (20).

Inventors: IKEDA TAKESHI, IKEDA, TAKESHI
Applicants: IKEDA TAKESHI, IKEDA, TAKESHI
Application year: 1990
Main classification: H03H1
IPC codes: H03H1