JP4594259B2 - Noise filter - Google Patents

Description

  The present invention relates to a noise filter. More specifically, the present invention has a signal transmission coil and a grounding coil, and these coils are insulated from each other, but are electromagnetically coupled (hereinafter also simply referred to as “coupled”). The present invention relates to a so-called distributed constant noise filter in which both ends of a signal transmission coil are input / output ends and both ends of a grounding coil are a ground end and an open end.

  In recent years, noise problems in digital signal circuits of electronic devices have increased, and noise filters are used in many circuits. A noise filter is required to have performances such as (1) a steep attenuation characteristic, (2) a large attenuation amount, and (3) an attenuation amount secured over a wide band.

  Conventionally, as a noise filter, for example, a signal coil and a ground coil are formed on a dielectric material such as ceramics as shown in Patent Documents 1 to 4, and these coils are laminated so as to be substantially opposed to each other. A so-called distributed constant type noise filter is known.

  FIG. 1 is a perspective view showing an appearance of a noise filter, and FIG. 2 is a schematic view showing a connection state of coils in the noise filter.

  As shown in FIG. 1, the noise filter 1 has input / output external electrodes 3 and 4 on both end faces of the outer surface of the multilayer body 2, and grounding external electrodes 5 on both main surfaces of the outer surface of the multilayer body. And 6.

  As shown in FIG. 2, in the noise filter 1, signal transmission conductors 21 to 26 and grounding conductors 32 to 37 formed on one surface of the insulating substrate layers 11 to 17 include through holes 41 to 45 and 51 to 55 are connected to each other to constitute a coil. That is, the signal transmission conductor 21 connected to the input / output external electrode (not shown) is connected to the signal transmission conductor 22 through the through hole 41, and the signal transmission conductor 22 is connected to the signal transmission conductor through the through hole 42. Connected to the conductor 23. Similarly, the signal transmission conductors 23, 24, and 25 are connected to the signal transmission conductors 24, 25, and 26 through the through holes 43, 44, and 45, respectively. The signal transmission conductor 26 is connected to an input / output external electrode (not shown). With these configurations, a signal transmission coil having both ends connected to the input / output external electrodes can be obtained.

  On the other hand, the grounding conductor 32 has an open end, and the other end is connected to the grounding conductor 33 via the through hole 51, and the grounding conductor 33 is connected to the grounding conductor 34 via the through hole 52. Is done. Similarly, the grounding conductors 34, 35 and 36 are connected to the grounding conductors 35, 36 and 37 through the through holes 53, 54 and 55, respectively. The grounding conductor 37 is connected to a grounding external electrode (not shown). With these configurations, a grounding coil having one end as an open end and the other end as a ground end can be obtained.

  For example, the signal transmission conductor 24 is electromagnetically coupled to the ground conductors 33 and 35 in the adjacent layers at the portion of the conductor formed in the x direction in the figure, and the signal transmission conductors 22 and 26 and the conductor portion formed in the y direction in the figure are electromagnetically coupled. Similarly, the grounding conductor 35 is formed in the x direction in the figure with the signal transmission conductors 24 and 26 of adjacent layers. It is electromagnetically coupled at the portion of the conductor, and is electromagnetically coupled at the portion of the grounding conductor 33 of the layer separated by one layer and the portion of the conductor formed in the y direction in the figure.

Japanese Patent Laid-Open No. 11-41052 JP-A-11-136065 Japanese Patent Laid-Open No. 7-58570 Japanese Patent Laid-Open No. 4-37005

  FIG. 3 is an equivalent circuit diagram for explaining the basic operation of the distributed constant noise filter.

  As shown in FIG. 3A, the distributed constant type noise filter can be interpreted as a modification of the distributed coupling type coupler. That is, in the coupler, both ends of one electrode are connected to external input / output terminals to form a signal transmission coil, one end of the other electrode is grounded, and one end is opened to form a grounding coil. Both coils are basically configured with the same electrical length, and the coupling between the coils increases or decreases depending on the frequency. The coupling is maximized at a frequency at which the quarter wavelength or an odd multiple thereof corresponds to the electrical length of the coil, and becomes zero at an even multiple of the quarter wavelength at a frequency corresponding to the electrical length of the coil. At the frequency at which the coupling is maximum, the attenuation is maximized (attenuation pole), and at the frequency at which the coupling is zero, the attenuation is also minimized.

  For example, when the distributed constant type noise filter is configured by a simple straight transmission line, the increase / decrease of the attenuation amount is repeated periodically. However, as described above, since the actual coil is formed in a spiral shape in the laminated ceramic, as shown in FIG. 3B, a capacitance (interlayer capacitance) is generated between the layers. The higher-order attenuation pole is shifted to the lower frequency side by this interlayer capacitance and overlaps. In addition, since the influence of the interlayer capacitance is different between the even mode and the odd mode, the maximum and minimum points of attenuation are not clear and show a waveform like a low-pass filter.

  In order to realize the performance required for the noise filter of (1) to (3) above with a distributed constant noise filter, (a) the impedance of the line is matched to the impedance of the external circuit (usually 50Ω or 75Ω). (B) Suppressing anti-resonance, (c) Increasing the coupling amount, etc. are considered effective.

  However, among these, in order to realize (a), the material of the conductor, the shape of the cross-sectional area, etc. may be appropriately selected. However, if these are determined, the amount of coupling is naturally limited. In order to realize (b), the use of interlaced coupling and the application of step impedance to the grounding coil are effective. However, since the impedance is changed in any case, if the effect is great, this is considered as matching. It is difficult to achieve both.

  In order to realize (c), theoretically, it is necessary to reduce the odd mode impedance (Zo) or increase the even mode impedance (Ze) to increase the relative difference of the even mode impedance. Good. However, since the conventional distributed constant noise filter has all the insulating substrate layers made of the same medium (ceramics), reducing the odd mode impedance simultaneously reduces the even mode impedance. . For this reason, it is difficult to increase the coupling in the conventional distributed constant noise filter, and matching is also inhibited when the impedances of both the odd mode and the even mode are lowered.

  As a result of repeated researches from the above viewpoint, the present inventor has found that by changing the medium of the base material layer in various ways, the binding can be increased under the condition that the matching is not inhibited, and the present invention has been completed.

  According to the present invention, performance required for a noise filter, that is, (1) the attenuation characteristic is steep, (2) the attenuation is large, and (3) the attenuation is ensured over a wide band. An object of the present invention is to provide a noise filter that is excellent in performance.

The gist of the present invention is the noise filter shown in the following (1) and (2).
(1) A plurality of insulating substrate layers on which signal transmission conductors and / or grounding conductors are arranged are laminated, and the signal transmission conductors and the grounding conductors are respectively connected through the through holes. , And both ends of the signal transmission coil are input / output ends, and both ends of the grounding coil are noise filters that are a ground end and an open end, and are constituted by an insulating substrate layer composed of the medium 1 and the medium 2 An insulating substrate layer (where the dielectric constant of the medium 1> the dielectric constant of the medium 2 and the magnetic permeability of the medium 1 <the magnetic permeability of the medium 2) are alternately stacked.

(2) A plurality of insulating substrate layers on which signal transmission conductors and / or grounding conductors are arranged are laminated, and the signal transmission conductors and the grounding conductors are respectively connected to the signal transmission coils and the grounding coils via through holes. The two ends of the signal transmission coil are input / output ends, and the both ends of the grounding coil are ground filters and open ends, and the insulating substrate layer alternates between dielectric ceramics and soft ferrite. A layered structure is desirable.

  According to the present invention, it is possible to increase coupling under conditions that do not hinder matching, and thus provide a noise filter that has a steep attenuation characteristic, a large attenuation amount, and a sufficient attenuation amount over a wide band. Can do.

  As in the noise filter shown in FIG. 2, the noise filter according to the present invention is formed by laminating a plurality of insulating substrate layers 11 to 17 on which signal transmission conductors 21 to 26 and / or grounding conductors 32 to 37 are arranged. The signal transmission conductors 21 to 26 and the grounding conductors 32 to 37 constitute a signal transmission coil and a grounding coil through the through holes 41 to 45 and 51 to 55, respectively, and both ends of the signal transmission coil are inserted. The noise filter is an output end, and both ends of the grounding coil are a ground end and an open end.

  And the external shape of the noise filter which concerns on this invention is the same as that shown in FIG. 1, for example. Of course, it is not limited to these external shapes and connection conditions. That is, the number of layers and the arrangement of the signal transmission conductor and the grounding conductor are appropriately adjusted according to the required position and attenuation amount of the attenuation pole.

  Here, the greatest feature of the noise filter according to the present invention is that insulating substrate layers having different dielectric constants and / or magnetic permeability are alternately laminated. Hereinafter, this reason will be described with reference to FIG.

  FIG. 4 is a diagram for simply explaining the principle of the present invention, and is a schematic diagram showing an arbitrary part of a laminate constituting a noise filter. As shown in FIG. 4, at an arbitrary position of the noise filter of the present invention, it has a signal transmission conductor 7 connected to the input / output terminal and a grounding conductor 8 which is grounded and the other is opened. These conductors are disposed on insulating substrate layers (medium) 9 and 10 having different dielectric constants.

  It is assumed that the characteristic impedance of the medium 10 is higher than the characteristic impedance of the medium 9. For example, the medium 10 and the medium 9 are made of ceramics, but one is a combination of ceramic sheets, the other is a ceramic paste, the medium 10 is soft ferrite, and the medium 9 is a dielectric such as ceramic. It is conceivable, but not limited to these. For example, dielectric ceramics and soft ferrite fine powder may be dispersed in a plastic substrate material.

  When considering the characteristic impedance of each mode, it is necessary to consider not only the material but also the influence of the shape, but in reality there are very strong restrictions on the electrode line width and sheet thickness due to the strong demand for miniaturization. is there. For this reason, it is difficult to arbitrarily select the shape. Therefore, in the following, the shape factor is considered as a given condition, and an outline of the influence of the dielectric constant and permeability of the medium 9 and the medium 10 on the characteristic impedance of each mode will be described.

Dielectric constant and permeability are distributed constant couplers made of a material equal to the vacuum value, and the relative dielectric constant is ε _r , the relative dielectric constant is ε _r , if the characteristic impedance of each even and odd mode is Z _ov and Z _ev In the case of a coupler made of a material having a magnetic permeability of μ _r, the characteristic impedance of each of the even and odd modes is (μ _r / ε _r ) ^1/2 each of the original values Z _ov and Z _ev .

  Here, when the relative permittivity and the relative permeability of the medium 9 and the medium 10 are different, the effective values (effective relative permittivity and effective relative permeability) in consideration of the effect of the actual electromagnetic field distribution for each mode. However, if this point is taken into consideration, the medium 9 and the medium 10 can be considered in the same way as in the case of the same material.

  FIG. 5 is a schematic diagram showing conductor potentials of even and odd modes in the line. This figure is a cross-sectional view orthogonal to the signal propagation direction of a distributed constant coupler, which is the basic principle of a distributed constant filter. As shown in FIG. 5A, in the odd mode, the potentials of the signal transmission conductor 7 and the grounding conductor 8 are positive and negative. An actual filter is formed of laminated ceramics or the like, and flat electrodes face each other across a thin ceramic layer, so that most of the electric field is between the signal transmission conductor 7 and the grounding conductor 8, that is, in the medium 9. concentrate. Therefore, the effective dielectric constant in the odd mode is influenced dominantly by the medium 9.

  On the other hand, as shown in FIG. 5B, in the even mode, the potentials of the signal transmission conductor 7 and the grounding conductor 8 are the same. For this reason, the effective dielectric constant is not easily influenced by the medium 9 and is easily influenced by the medium 10.

  In the even mode, the effective magnetic permeability is generated so that the magnetic field penetrates the medium 9 almost vertically. However, since the medium 9 is actually very flat and thin, the influence of the medium 9 is slight. On the other hand, in the odd mode, the magnetic field passes through the medium 9 and the medium 10 for substantially the same length. For this reason, the effective magnetic permeability of the odd mode takes a value close to the average value of the medium 9 and the medium 10, whereas in the even mode, the effective magnetic permeability becomes a value close to the magnetic permeability of the medium 10.

  When the medium 9 and the medium 10 have the same magnetic permeability and only the medium 9 has a high dielectric constant, the odd-mode impedance decreases as the effective dielectric constant increases, but the even-mode impedance is significantly affected. Absent. This makes it possible to make a large difference between the impedances of both modes and to obtain a large amount of coupling.

  Further, when the dielectric constants of the medium 9 and the medium 10 are equal and only the medium 10 has a high magnetic permeability, the effective magnetic permeability in the even mode is strongly influenced by the medium 10 and becomes high. Accordingly, in this case as well, it becomes possible to make a large difference between the impedances of both modes, and a large coupling amount can be obtained.

  If the permittivity and permeability of medium 9 and medium 10 are both different, the above effect can be obtained by selecting so that the permittivity is medium 9> medium 10 and the permeability is medium 9 <medium 10. It can be enjoyed twice and is more effective.

  However, impedance matching cannot be achieved by simply selecting the media 9 and 10 arbitrarily. The medium 9 is made of a material having a high dielectric constant and the characteristic impedance of the odd mode is increased, and the medium 10 is made of a material such as ferrite having a high magnetic permeability, thereby increasing the effective magnetic permeability of both modes. It is effective to compensate for the decrease in the odd mode characteristic impedance by increasing the characteristic impedance. That is, if the material and the cross-sectional shape are appropriately selected, both matching and large coupling can be achieved. According to this method, a mode difference is caused in the wavelength shortening rate, so that anti-resonance can be suppressed.

  There is no particular limitation on the wavelength shortening rate (relative permittivity × relative magnetic permeability) in each mode, but it is preferable to set the wavelength shortening rate of each mode to be different. By doing so, the resonance frequencies of both modes are different, and a region where the coupling amount is zero (a region where the electrode length is an integral multiple of a half wavelength) does not appear.

  The method for producing the noise filter according to the present invention is not particularly limited. For example, in addition to the thin film method, a so-called post-fire method in which ceramics are sintered in advance, such as a thick film method, and then metallized, is sintered. And the so-called co-fire method can be employed.

  In the case of using the co-fire method, for example, a sintering aid, a binder, a plasticizer, a dispersant, and a solvent such as water and alcohol are added to a ceramic powder to form a slurry, and the green sheet is formed from this slurry by a doctor blade method or the like. Is made. By optimizing the kind of additive element, the particle size, and the mixing ratio of the resin, the dielectric constant and / or permeability of the ceramic, the sintering temperature, and the shrinkage ratio during firing can be set to desired values.

  A through hole is provided in the green sheet, and a metal powder paste is applied on the surface thereof by screen printing or the like to form a predetermined signal transmission conductor pattern and / or grounding conductor pattern. Next, these green sheets having different dielectric constants and / or magnetic permeability are laminated, degreased and decarburized, and co-fired in an atmosphere of approximately 900 ° C., and an external electrode paste is applied to the green sheets. Manufactured by baking.

  As the insulating substrate layer, two kinds of ceramics having different dielectric constants can be used, and it is desirable that one is ceramic and the other is soft ferrite. This is because the difference in dielectric constant can be increased, and the coupling is easily increased while maintaining matching.

  As the ceramic used for the insulating substrate layer, for example, barium titanate or the like can be used. Moreover, as a soft ferrite used for the insulating substrate layer, for example, NiCuZn ferrite can be used.

  As the metal constituting the conductor, for example, in addition to Ag, an alloy in which about 10% by mass of Pd is added to Ag can be used. In order to reduce cost and loss, it is desirable to use Ag. However, in view of the firing temperature of the ceramic, it is better to add an appropriate amount of Pd to raise the melting point of the conductor.

  In order to verify the effect of the present invention, a noise filter of a comparative example composed of a kind of insulating substrate layer (only a dielectric layer having a relative permittivity of 75 and a relative permeability of 1), and a dielectric having a relative permittivity of 75 and a relative permeability of 1 And a noise filter according to an example of the present invention in which soft ferrites (NiCuZn ferrite) having a relative dielectric constant of 10 and a relative permeability of 80 are alternately formed were prepared, and experiments were performed to compare attenuation curves of the respective noise filters. .

  Each of the dielectric layer and the soft ferrite layer is prepared by a doctor blade method, a green sheet is formed, a through hole is provided in the green sheet, a metal powder paste is applied to the surface by screen printing, and a predetermined signal transmission conductor pattern and / Or a conductor pattern for grounding was formed.

  Next, dielectric green sheets were laminated for the comparative example, and dielectric sheets and soft ferrite layer green sheets were alternately laminated for the inventive example, and then degreased and decarburized. Thereafter, it was fired simultaneously in the atmosphere at 900 ° C., an external electrode paste was applied, and the external electrode was baked to produce a noise filter of about 1.2 mm square and a thickness of 0.6 mm.

  Each example was composed of 13 layers, and the first layer and the 13th layer were composed of a dielectric having a thickness of about 175 μm. In the comparative example, the second layer to the twelfth layer are all composed of a dielectric layer having a thickness of about 25 μm. In the present invention example, the second layer, the fourth layer, the sixth layer, the eighth layer, the tenth layer The layers 12 and 12 were made of soft ferrite having a thickness of 25 μm, and the third, fifth, seventh, ninth and eleventh layers were made of a dielectric having a thickness of 25 μm.

  6 shows a wiring pattern formed on the insulating substrate layer. On the upper surface of the third to twelfth layers, the wiring pattern shown in FIG. 6 is formed, and the first layer, the second layer, the twelfth layer are formed. Layers and 13th layer were blank layers. In FIG. 6, the shaded conductors are grounding conductors, and the unassigned conductors are signal transmission conductors. In the figure, ○ indicates a through hole connected to the upper layer (layer with a small number), and ◎ indicates a through hole connected to the lower layer (a layer with a large number).

  As shown in FIG. 6, the signal transmission conductor is connected to an input / output external electrode (not shown) in the upper part of the drawing in the third layer, and the other end is connected to the fourth to eleventh layers through a through hole. It is connected to the formed signal transmission conductor, and further connected to an input / output external electrode (not shown) in the lower part of the figure in the eleventh layer. On the other hand, the grounding conductor is grounded on the left side of the figure in the fourth layer, the other end is connected to the grounding electrodes formed in the fifth to ninth layers through through holes, and further in the tenth layer The open end.

  FIG. 7 shows the relationship between insertion loss and frequency in the present invention example (solid line) and the comparative example (broken line). As shown in FIG. 7, in the comparative example, it attenuates gently, the maximum insertion loss stays at about -27 dB, and returns to -15 dB at around 0.7 MHz. On the other hand, the example of the present invention shows a steep attenuation curve from around 0.2 MHz, -30 dB near 0.4 MHz, and -38 dB around 0.6 MHz, which is larger overall than the comparative example. Moreover, the attenuation band is much wider than that of the comparative example.

  According to the present invention, it is possible to increase coupling under conditions that do not hinder matching, and thus provide a noise filter that has a steep attenuation characteristic, a large attenuation amount, and a sufficient attenuation amount over a wide band. Can do.

The perspective view which shows the external appearance of a noise filter. Schematic which shows the connection condition of the coil in a noise filter. The equivalent circuit diagram for demonstrating the basic operation | movement of a distributed constant type noise filter. It is a figure explaining the principle of this invention briefly, and the schematic diagram which extracted and showed the arbitrary parts of the laminated body which comprises a noise filter. The schematic diagram which shows each odd-even mode in a track | line. The figure which shows the structure of each laminated body in the noise filter used for experiment. The figure which shows the relationship between the insertion loss and frequency in the example of this invention and a comparative example.

Explanation of symbols

1. 1. Noise filter Laminated bodies 3, 4. Input / output external electrodes 5, 6. External electrode for grounding
11-17. Insulating substrate layer
21-26. Signal transmission conductor
32-37. Grounding conductor
41-46. Through hole
51-56. Through hole 7. 7. Signal transmission conductor Grounding conductor 9, 10. medium

Claims (2)

A plurality of insulating substrate layers on which signal transmission conductors and / or grounding conductors are arranged are laminated, and the signal transmission conductor and the grounding conductor constitute a signal transmission coil and a grounding coil through through holes, respectively. Both ends of the signal transmission coil are input / output ends, and both ends of the grounding coil are noise filters that are a ground end and an open end,
Insulating substrate layer composed of medium 1 and insulating substrate layer composed of medium 2 (where the dielectric constant of medium 1> the dielectric constant of medium 2 and the permeability of medium 1 <the permeability of medium 2) A noise filter characterized by alternately stacking layers. A plurality of insulating substrate layers on which signal transmission conductors and / or grounding conductors are arranged are laminated, and the signal transmission conductor and the grounding conductor constitute a signal transmission coil and a grounding coil through through holes, respectively. Both ends of the signal transmission coil are input / output ends, and both ends of the grounding coil are noise filters having a ground end and an open end, and the insulating substrate layer is formed by alternately laminating dielectric ceramics and soft ferrite. noise filter shall be the feature that the configuration was.

Images