JPH07335442A - Filter - Google Patents

Abstract

PURPOSE:To reduce common mode noise made on a line by using a filter structure wherein a magnetic film is provided through the intermediary of insulating layers around a coaxial line. CONSTITUTION:Within the filter, a magnetic film is provided as if encircling around a coaxial line through the intermediary of insulating layers. Besides, the easy magnetizing axles of magnetic anisotropy in this magnetic film are made even in the coaxial direction and the thickness of this filter as a soft magnetic thin film is to be within the range of 1-10 times of the surface film thickness which is represented by a formula of delta=sq. rt. {2rhom/(2pif.mur.mu0)} assuming the electrical resistivity of the magnetic film as rhom, the noise frequency as f, the complex relative magnetic permeability of real time component as mur, the vacuum magnetic permeability as mu0. Furthermore, this magnetic film is a multilayer structure comprising the magnetic films and the insulating layers alternately laminated, otherwise, polyimide sheets formed of permalloy thin films wound around the coaxial line in numerous times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a miniaturized and high performance filter for reducing common mode noise superimposed on a line for transmitting signals and electric power between devices.

[0002]

2. Description of the Related Art Common mode noise is noise generated as a voltage of the same phase generated in a line pair due to an electromagnetic induction phenomenon in addition to a desired high frequency signal or an alternating current in a line, and a pulse signal flowing around or near a switch. . In order to reduce this noise, a method of penetrating a line through a ring made of a soft magnetic material has been conventionally used. That is, since the signal currents applied to the lines are in opposite directions to each other, the magnetic fields generated are almost canceled at the magnetic ring position, and only the magnetic field generated by the in-phase noise current (common mode noise current) magnetizes the magnetic ring. It works like this. A noise current is consumed by the loss generated when the magnetic body is magnetized, and as a result, the propagation of noise is blocked. Here, there are ferromagnetic resonance and eddy current loss as causes of the loss that occurs in the magnetization process of the magnetic body.

FIG. 7 shows a conventional filter, which has a structure in which a parallel two-core wire 5 is used as a conventionally used cable and a magnetic film is wound on it. FIG. 8 shows a magnetic field distribution on a line connecting the axes of the parallel twin core wires 5 shown in FIG. As is clear from the figure, the magnetic fields generated from the currents flowing through the cable do not completely cancel each other at the position of the magnetic body 4, and some remain. The strength Hr of this magnetic field is expressed by the following equation. Hr = I / 2πr ₁ −I / 2πr ₂ (1) I: current flowing in line r ₁ : distance from center of core 1 to magnetic body 4 r ₂ : distance from center of core 2 to magnetic body 4 in line When the flowing current I increases, the magnetic field H applied to the magnetic substance
r also increases proportionally, and Hr is the anisotropic magnetic field Hk of the magnetic body 4.
When the strength is above, the magnetic body 4 is saturated. The critical current Ic with Hr ≧ Hk is calculated from the equation (1) as follows. Ic = 2πHk (R ₂ −R ₁ ) / R ₁ R ₂ (2) In such a state, the magnetic body is not magnetized by the magnetic field due to the common mode noise current, and thus does not work as a noise filter. In other words, in the conventional shape in which the parallel two-core wire is passed through the magnetic material ring or the like, when a large current flows such as a power line, a magnetic field higher than the saturation magnetic field of the magnetic material ring is generated and the magnetization is saturated. Therefore, there is a drawback that the above noise suppressing effect cannot be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in order to improve the above-mentioned drawbacks, and its object is to reduce common mode noise superimposed on a power supply line or the like through which a large current flows. is there.

[0005]

In order to achieve the above object, the present invention features a filter in which a magnetic film is provided so as to circulate around a coaxial line via an insulating layer. Further, the present invention provides a filter which is a soft magnetic thin film in which the easy axis of magnetic anisotropy is aligned in the coaxial axial direction in the magnetic film, and the thickness of the magnetic film is in the range of 1 to 10 times the skin depth. It is a feature of the invention. Further, the invention is characterized in that the magnetic film has a multilayer structure in which magnetic films and insulating layers are alternately laminated. The main feature of the present invention is that a magnetic film is provided around the coaxial line so as to circulate through an insulating layer. In the conventional technique, a magnetic film is provided around a parallel line so as to circulate through an insulating layer, and the structure of the line used is different.

[0006]

As a structure of the filter for suppressing the common mode noise generated in the line, the structure in which the magnetic film is installed around the coaxial line is used as described above. In this structure, the magnetic field generated from the signal current is completely canceled outside the coaxial line, and the magnetic material wound around the line is not saturated even if the signal current increases. On the other hand, only the magnetic field generated by the common mode noise current magnetizes the magnetic film wound around the line, and the noise power is consumed by the eddy current loss due to the change in the magnetization. In the structure where a magnetic film is installed around a parallel line that is a conventional filter via an insulating layer, a large current flows because the magnetic fields generated from the signal currents do not completely cancel each other at the position of the magnetic film. And the magnetization of the magnetic film was saturated and the noise reduction effect deteriorated. In the structure of the present invention, the magnetic field generated from the signal current is completely canceled outside the line, so that the common mode noise can be attenuated even in the large current signal line which is the object of the present invention.

[0007]

EXAMPLES Next, examples of the present invention will be described. The present invention is a structure in which a magnetic film is installed around a coaxial line as a filter structure for suppressing common mode noise generated in a line in which a large current flows. FIG. 1 shows a structural diagram of a noise filter according to the present invention. Reference numeral 1 is a coaxial core wire, 2 is a coaxial outer conductor, 3 is an insulating coating, and 4 is a magnetic material. The magnetic field generated by the current flowing through the core wire 1 and the outer conductor 2 at the center of the coaxial line is completely canceled because the polarities are opposite and the distribution shape is the same outside the line. Therefore, even if a large current flows, the magnetic body wound around the line is not saturated, and only the magnetic field generated by the common mode noise current magnetizes the magnetic body.

When a metal magnetic material such as Permalloy is used as the magnetic material, the common mode noise can be suppressed by setting the film thickness within a setting range based on the following concept. For example, the complex relative permeability of the magnetic film μr = μr ′ + iμ
The larger the imaginary component μr ″ of r ″, the more the common mode noise is consumed by eddy current loss. [Chida, Ishii, Mori: “Application of high-loss CoZrNb / SiO ₂ multilayer film to EMI noise filter”] Magazine 18, 2 (1994) 51
1-514]. μr ′ and μr ″ are represented by the following equations when the rotating magnetization mechanism is assumed.

[Equation 1] Here, tm is the thickness of the magnetic layer, ρm is the resistivity of the magnetic substance,
f is the noise frequency, and μ ₀ is the magnetic permeability of the vacuum. on the other hand,
The skin thickness δ is expressed as δ = √ {2ρm / (2πf · μr · μ ₀ )}. Therefore, θ is represented by the following equation. θ = 2√ {π · (tm / δ)}

FIG. 2 shows μr '(f) / μr' (0), μ
The tm / δ dependence of r ″ (f) / μr ′ (0) is shown.
In the range of 0.1 ≦ (tm / δ) ≦ 10, μr ″ (0) /
μr ′ (0) ≧ 0.03, indicating that eddy current loss occurs. In particular, in the range of 0.1 ≦ (tm / δ) ≦ 1, μr ″ (0) <μr ′ (0), so the impedance of the line wound with the magnetic film becomes inductive (large inductance), In the range of 1 ≦ (tm / δ) ≦ 10, μr ′ (0) ≈μr ″ (0), and the resistance of the line around which the magnetic material is wound becomes as large as the inductance. 0.1
When the inductance of the line around which the magnetic film is wound is high within the range of ≦ (tm / δ) ≦ 1, the impedance of the line around the magnetic film is large and the impedance matching is poor, resulting in large reflection of signals and noise. . Since the reflected noise power is not consumed, it adversely affects the inside of the device. Therefore, in order to increase the resistance of the line around which the magnetic film is wound and increase the ratio of noise power consumption, simply increasing μ ″ (0) is not sufficient, and μ ′ (0)
Is also important, and 1 ≦ (tm / δ) ≦ 10 is suitable as a film thickness range that satisfies this condition. (Tm
/ Δ)> 10, μr ″ (0) / μr ′ (0) <0.0
Since the noise current absorption effect due to the eddy current is equal to the measurement error, the appropriate range of tm / δ is set to 10 or less.

Example 1 In the noise filter shown in FIG. 1, the concrete structure of the magnetic material is as follows: a permalloy thin film is formed on a polyimide sheet (width 5 cm, length 14 cm) and wound around a cable many times to form a tube. It was done. F = permalloy thin film
250MHz, permalloy ρm (~ 20μΩc
Substituting m) and μr ′ (0) = 3000, δ≈0.2
It becomes 5 μm, and it can be expected that a permalloy film having a thickness of about 0.25 μm to 2.5 μm is effective for noise reduction. In this embodiment, the permalloy film thickness is 1.5 μm. The permalloy thin film is formed by a sputtering method in a magnetic field, and the easy axis of uniaxial magnetic anisotropy can be aligned in the direction parallel to the cable. The anisotropic magnetic field of the permalloy film formed by such a manufacturing method is usually about 50e.

When a coaxial line is used as the line, the magnetic fields generated from the core wire and the outer conductor have the opposite signs and the same distribution as shown in FIG. In such a structure, no magnetic field is generated at the position of the magnetic body 4 even if the value of the flowing current increases. Therefore, if the filter having the coaxial structure shown in FIG. 1 is used, the common mode noise generated in the large current line can be suppressed by the magnetic body 4 arranged around the line. In particular, the closer the magnetic body 4 is to the line, the greater the noise suppression effect, but when a parallel two-core line is used, the residual component of the magnetic field due to the current (signal) flowing through the line also increases, so the magnetic body 4 can be used without limitation. I couldn't get close to the tracks. On the other hand, when the coaxial line is used, the outer conductor and the magnetic body 4 can be brought close to each other so that they can be insulated, which is also advantageous in reducing the overall size and weight.

FIG. 4 shows a measurement system for noise attenuation effect characteristics according to the present invention. In the figure, 6 is a network analyzer, 7 is a DC power supply, 8 is a current probe, 9 is a terminating resistor,
Reference numeral 10 is a DC component cutting capacitor. As the line, a coaxial line according to the present invention or a parallel two-core wire which has been conventionally used is used. The length of the line is 80 cm, and large common mode noise is generated at about 250 MHz.
The magnetic film was wound at a position 10 cm from the end to which the DC power supply 7 was connected, and the current probe was set to a position 20 cm from the end to which the resistor 9 was connected. The noise suppression effect at 250 MHz was measured by changing the current flowing through the line by changing the voltage of the DC power supply.

FIG. 5 shows a case where a coaxial line is used as a line 1
1 shows the relationship between the current value Ic flowing in the line 12 and the noise attenuation amount when the parallel twin core line is used as the line. When a parallel two-core line is used, the amount of noise attenuation gradually decreases as the current value increases, and in particular in the range of the critical current value Ic or more shown by the equation (2), it sharply decreases, whereas the coaxial line is used. When used, the amount of noise attenuation is constant regardless of the current value.

Example 2 As shown in FIG. 6, the magnetic film 4 has a multi-layer structure in which magnetic bodies 14 are alternately stacked with an insulating layer 13 interposed therebetween. Specifically, two layers of the permalloy film described in Example 1 were formed as the magnetic film, and a 0.1 μm thick SiO ₂ film was formed as the insulating layer. The permalloy film and the SiO ₂ film were formed by using the sputtering method. The width of the polyimide sheet 15 is 2.5 cm,
The length is 14 cm, and the total volume of the magnetic material is the same as in Example 1. This magnetic sheet was wound around the same position as in Example 1 (FIG. 4) and the effect of suppressing common mode noise was measured. As a result, the same energization current dependency as in FIG. 5 was obtained. That is, when the coaxial line is used, the noise attenuation amount is constant regardless of the energized current, whereas when the parallel two-core line is used, the noise attenuation amount is drastically reduced when the energized current exceeds the critical value Ic. . Even if a single layer film or a multilayer film is used as the magnetic film, the mechanism of consuming the magnetic field generated from the common mode noise current as the eddy current loss of the magnetic substance is the same. If is constant, the same noise attenuation amount is obtained. Also,
When the energizing current increases, the mechanism that can secure more stable operation when using a coaxial line as a line than using a parallel line does not depend on whether the magnetic material is a single layer or a multilayer. As a result, the noise suppression behavior similar to that of the first embodiment is shown. Therefore, in this embodiment, the number of magnetic layers is two, but the same effect can be expected in the case of more layers as long as the total volume of the magnetic layers is the same. When the magnetic multilayer film is used, the volume of the substrate per magnetic layer is reduced, so that there is an effect that the overall size can be reduced.

[0015]

EFFECT OF THE INVENTION By using the filter having the coaxial line structure according to the present invention, it is possible to reduce common mode noise which is superposed on a power supply line or the like in which a large current flows. If this filter has a structure in which the outer skin of the cable is covered with a magnetic film, the effective volume and weight do not increase. Further, the noise suppression effect is greater when the magnetic film is brought as close as possible to the line conductor, but when a parallel two-core line is used, the cancellation residual component of the magnetic field generated from the current (signal) flowing in the line at the magnetic film position. However, the magnetic film cannot be brought close to the line indefinitely because it becomes large, which hinders miniaturization. On the other hand, when the coaxial line is used, the distance between the outer conductor and the magnetic film can be infinitely close to each other in principle, which is also advantageous in reducing the overall size and weight. Further, since the supply current itself does not cause a loss, there is also a feature that there is no insertion loss of the filter. In the conventional parallel two-core line, an insertion loss is inevitably caused because a magnetic material surrounding the cable is magnetized to some extent by a supply current or a signal current. The filter of this structure also has the advantage of being easy to handle because the plasticity of the cable is maintained. In the embodiment, the structure in which one coaxial line is covered with the magnetic film is shown.
It is obvious that the same effect can be obtained even if a bundle of many coaxial lines is covered with a magnetic film.

[Brief description of drawings]

FIG. 1 shows a structural diagram of a noise filter according to the present invention.

2 shows the dependence of complex relative permeability μr ′ (f), μr ″ (f) on the magnetic film thickness tm. The complex relative permeability is relative permeability μr ′ (0) in a static magnetic field, and the film thickness is Normalized by skin depth δ.

FIG. 3 shows a magnetic field distribution generated from a parallel twin core line.

FIG. 4 shows a measurement system for noise attenuation.

FIG. 5 shows a relationship between a current value flowing in a line and a noise attenuation amount.

FIG. 6 shows a structure of a magnetic multilayer film.

FIG. 7 shows a conventional noise filter.

FIG. 8 shows a magnetic field distribution generated from a coaxial line.

[Explanation of symbols]

 1 coaxial core wire 2 coaxial outer conductor 3 insulating coating 4 magnetic material 5 parallel 2 core wire 6 network analyzer 7 DC power supply 8 current probe 9 terminating resistor 10 DC component cutting capacitor 11 in case of coaxial line 12 in case of parallel double core line 13 insulating layer 14 Magnetic material 15 Polyimide sheet

Front Page Continuation (72) Inventor Hiroshi Ichinose 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A filter, wherein a magnetic film is provided around the coaxial line so as to circulate through an insulating layer. 2. A soft magnetic thin film in which the easy axis of magnetic anisotropy is aligned in the coaxial axial direction in the magnetic film, and the thickness of the magnetic film is in the range of 1 to 10 times the skin depth. The filter according to claim 1, which is characterized. Here, the skin depth is ρm, the resistivity of the magnetic film f is the noise frequency μr, the real component of the complex relative permeability μ ₀ is the permeability of the vacuum, and the skin depth δ = √ {2ρm / (2πf ・ μr ・ μ ₀ )}. 3. The filter according to claim 1, wherein the magnetic film has a multilayer structure in which magnetic films and insulating layers are alternately stacked. 4. A filter comprising a polyimide sheet having a permalloy thin film formed around a coaxial line and wound around the coaxial line a number of times.