JPH1065476A - LC low pass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for connecting a resonance capacitor in parallel with an inductor so as to sharpen an attenuation pole, and to easily connect a resonance capacitor without increasing the number of parts. So that it can be formed. SOLUTION: Spiral inductors L ₁ , L ₂ wound in a coiling shape toward the center are formed, and connection paths 17a, 17b are formed on the dielectric thin film 10 covered thereon by spiral inductors L ₁ , L ₂ . The connection paths 17a and 17b are formed so as to extend outward from the center.
In addition, extending conductor portions x, x serving as capacitor electrodes facing the outer winding portions of the spiral inductors L ₁ , L ₂ via the dielectric thin film 10 are extended, so that they are parallel to the inductors L ₁ , L _2. Connected resonance capacitors C _x , C
_x was configured to self-resonate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LC low-pass filter used for various wireless communication devices such as a mobile phone and a car phone.

[0002]

2. Description of the Related Art A low-pass filter provides a filtering function of passing a low-frequency signal of a specific frequency or lower and removing a harmonic signal of a predetermined frequency or more. An LC low-pass filter comprising a combination of an inductor and a capacitor is used. Are known. In this LC low-pass filter, a plurality of capacitors C ₁ , C ₂ , C ₃ are formed in parallel, one end is connected to ground, and inductors L ₁ , L _{2 are} respectively connected between the other ends of the capacitors C ₁ , C ₂ , C _{3. 2} and each inductor L ₁ ,
The L ₂ configured so as to serially connect (see FIG. 8).

A conventional LC low-pass filter is generally formed by metalizing a conductive layer on a dielectric sheet by a printing method and firing it integrally, or by separately mounting components of a chip inductor and a chip capacitor. It is. on the other hand,
In recent years, there has been an increasing demand for miniaturization, higher density, and lower price of electronic devices. In order to meet these demands, it was necessary to reduce the size of individual components such as inductors and capacitors. By the way, the above-mentioned conventional LC
In the case of a low-pass filter, a metal sheet printed on a dielectric sheet and baked integrally has a limit in capacity density, so that further miniaturization has been difficult. Further, in the conventional metallization printing and firing method, an increase in loss in a high frequency region due to impurities and surface roughness during metallization has been a problem. Furthermore, in a configuration in which a chip inductor or the like is externally attached, the number of parts increases, and manufacturing becomes troublesome.
After all, it was an obstacle to miniaturization,

[0004]

In this type of low-pass filter, as shown in FIG. 9, a gradient of an attenuation region (a required region from an attenuation pole to a transition region from a low-frequency side pass band to a high-frequency side stop band). By steepening the gradient up to the amount of attenuation, it is possible to realize a material having excellent selectivity and excellent characteristics. Therefore, it is necessary to increase the gradient of the attenuation region by increasing the attenuation pole x. Various methods have been adopted.

As a conventional method, a method of increasing the amount of ripple in a pass band in accordance with a Chebyshev type low-pass filter design method for steepening the attenuation pole of the low-pass filter is well known. However, this method has a drawback that the pass band width is narrowed in order to increase the amount of ripple in the pass band.

On the other hand, as another general method, a resonance capacitor C _{X in} parallel with the inductors L ₁ and L ₂ shown in FIG.
Is formed via an external member, thereby forming an attenuation pole. However, since such a capacitor is usually provided externally, the number of components is increased, and there is a problem that the filter cannot be reduced in size.

According to the present invention, as described above, the resonance capacitor is connected in parallel to the inductor so as to sharpen the attenuation pole, and the resonance capacitor can be easily formed without increasing the number of components. It is intended to provide a configuration that can be performed.

[0008]

According to the present invention, there is provided a conductive layer having a spiral inductor wound in a coil shape toward the center, and a connection path of the spiral inductor is formed on a dielectric thin film coated on the conductive layer. In an LC low-pass filter formed so as to extend outward from the center and electrically connect an end of the connection path to the center of the spiral inductor, a part of the spiral inductor is connected to the connection path. An overhanging conductor portion serving as an opposing capacitor electrode is extended through the dielectric thin film.

In this configuration, by extending a projecting conductor portion forming a resonance capacitor with a part of the spiral inductor in the connection path, the inductor and the resonance capacitor are connected in parallel, and Resonate. The self-resonant frequency is selected according to the width and shape of the overhanging conductor.

With this configuration, the input-side capacitor, the intermediate capacitor, and the output-side capacitor are formed in parallel, one end of each is grounded, and two spiral inductors are located between the other ends of the capacitors. Thus, a circuit configuration in which both spiral inductors are connected in series can be configured as follows.

That is, a first conductive layer is formed on an insulating substrate, a dielectric thin film is further laminated on the insulating substrate, and a second conductive layer is formed on an upper surface thereof. The half surface portion is a capacitor formation region, the other half surface portion is an inductor formation region, and in the inductor formation region,
In one conductive layer, two spiral inductors wound in a coiling shape toward the center are arranged in parallel, and in the capacitor forming region, an electrode of an intermediate capacitor is provided in an intermediate portion of one conductive layer. And connected to the outer windings of the two spiral inductors, ground electrodes are formed on both sides of the capacitor electrode, and the input and output capacitors of the other conductive layer are formed on both sides thereof. And a connection path is extended from the electrode to a position immediately above the center of the two spiral inductors, and a ground electrode is formed in the other conductive layer in the middle of the two capacitor electrodes. Further, the extension end of the connection path and the center of the spiral inductor are electrically connected to each other through a conductive hole formed in the dielectric thin film, and thereby, The input capacitor, the intermediate capacitor and the output capacitor are formed in parallel with the capacitor electrode and the ground electrode facing each other, one end is connected to ground, and the spiral inductor is located between the other ends of each capacitor. An inductor is connected in series, and an extension conductor portion serving as a capacitor electrode facing a part of the spiral inductor via the dielectric thin film is extended in the connection path.

In such a configuration, a first conductive layer is formed on an insulating substrate, a dielectric thin film is further laminated on the insulating substrate, and a second conductive layer is formed on the upper surface thereof. L
A C low-pass filter is configured. The above-mentioned one conductive layer may be any of the first and second conductive layers, and therefore, the other conductive layer is the remaining conductive layer of the first and second conductive layers.

[0013]

1 to 5 show an LC low-pass filter 1 according to the present invention. This LC low pass filter 1
The input capacitor C ₁ , the intermediate capacitor C ₂ and the output capacitor C ₃ are formed in parallel, one end of each is connected to ground, and a spiral inductor L ₁ is connected between the other ends of the capacitors C ₁ and C _2. , Capacitors C ₂ , C ₃
Located spiral inductor L ₂ is between the other end of both spiral inductor L _1, L ₂ are connected in series, in which so as to constitute an equivalent circuit of FIG.

Here, an insulating substrate 2 made of an alumina substrate
Has a thickness of 0.635 mm. A first conductive layer 3 is formed on the insulating substrate 2 by a copper plating method. A dielectric thin film 4 made of an organic insulating film such as a polyimide resin is laminated on the insulating substrate 2 by a spin coating method or the like. Further, a second conductive layer 10 is formed on the dielectric thin film 4 by a copper plating method. The thickness of the copper film of the first conductive layer 3 is 5 μm. The thickness of the dielectric thin film 4 is 3 μm, and the thickness of the copper film of the second conductive layer 10 is 5 μm.

Each of the insulating substrate 2 and the dielectric thin film 4 can be made sufficiently small such as, for example, a square of 3 mm square, and the total thickness thereof is an extremely thin shape of 0.7 mm or less. I have.

A half surface of the laminated structure is defined as a capacitor formation region F ₁ , and the other half is defined as an inductor formation region F _2.
And

In the inductor forming region F ₂ ,
On the first conductive layer 3, two spiral inductors L ₁ and L ₂ wound in a coiling shape from the outside toward the center are arranged in parallel.

Meanwhile, the In the capacitor formation region F _1, the first conductive layer 3, the intermediate portion thereof, to form the electrode 6 of the intermediate Dendensa C _2, at its inner central position, both the spiral inductor L _1, L ₂ of the outer winding portion 7a, 7b
I try to connect with. The capacitor electrode 6
Are formed on both sides of the ground electrode 8a, 8b. The ground electrodes 8a and 8b are connected to the spiral inductor L
_1, to the periphery of L ₂ is formed, is further extended ground electrode layer 8c it is in between the spiral inductor L _1, L _2. That is, the two spiral inductors L ₁ and L ₂
If, on the entire surface excluding the electrodes 6 of the intermediate capacitor C _2, the grounding electrode layer 8 is formed.

Further, on both sides of the second conductive layer 10 formed on the dielectric thin film 4, an input-side capacitor C _{1 is provided.}
When, the output side capacitor C ₃ of the electrode 16a, 16b to respectively form, and from the electrodes, to a position directly above the center of the two spiral inductors L _1, L _2, the connecting channel 17a, 17
b is extended. The connection paths 17a and 17b constitute a main part of the present invention, and as shown in an enlarged manner in FIG. 4, projecting conductor portions x and x extend from the connection paths 17a and 17b, respectively. The overhanging conductor portion x is spiral inductor L _1, L ₂ of the outer winding portion 7a, and 7b, they are opposed to each other in the up and down through the dielectric thin film 4. For this reason, the overhanging conductor portions x,
x is a capacitor electrode, the outer winding portion 7a, 7b, the dielectric thin film 4 and the overhang conductor portions x, through x, so that the resonance capacitor C _x is configured.

As described above, the second conductive layer 10, except for the connection paths 17a and 17b, forms the capacitor forming region F _1.
Only it is formed, the capacitor formation region F _1, the two capacitor electrodes 16a, the intermediate portion of the 16b, the ground electrode 1
8 is formed.

Furthermore, wherein the dielectric thin film 4, at a position directly above the center of the spiral inductors L _1, L _2, through hole 2
The extended ends of the connection paths 177a and 17b and the centers of the spiral inductors L ₁ and L ₂ are electrically connected to each other through the conduction holes 20 and 20. Further, the ground electrode 18 has a conductive hole 2
1, 21 are formed to ensure connection with the ground electrodes 8a, 8b. Further, a ground electrode 25 is formed on the lower surface of the insulating substrate 2 as shown in FIG.

Thus, the capacitor electrode 16a and the earth electrode 8a, the capacitor electrode 6 and the earth electrode 18, and the capacitor electrode 16b and the earth electrode 8b face each other through the dielectric thin film 4, respectively. The input side capacitor C ₁ , the intermediate capacitor C ₂ and the output side capacitor C ₃ are arranged in parallel. One end of each capacitor is grounded. Then, the input-side capacitor C ₁ and the spiral inductor L ₁ between the other end of the intermediate capacitor C ₂ is located, the spiral inductor L ₂ between the other end of the intermediate capacitor C ₂ and the output side capacitor C ₃
Are located, and both spiral inductors L ₁ , L ₂
Are connected in series.

On the other hand, resonance capacitors C _x and C _x composed of the outer winding portions 7a and 7b, the dielectric thin film 4 and the overhanging conductor portions x and _x are connected in parallel with the inductors L ₁ and L ₂ . As a result, self-resonance can be generated, an attenuation pole is formed, and the relationship between the resonance frequency and the output has a steep gradient in the attenuation region. This self-resonant frequency changes the shape of the overhanging conductor portions x, x,
It is arbitrarily set by selecting the capacitance values of the resonance capacitors C _x and C _x . Thus, an equivalent circuit shown in FIG. 8 is formed.

In such a configuration, on the insulating substrate 2,
A first conductive layer 3 is formed by a copper plating method, then a dielectric thin film 4 is formed by a spin coating method, and a second conductive layer 10 is further formed by a copper plating method. By forming, a small LC low-pass filter can be easily manufactured. Therefore, when the second conductive layer 10 is formed, the width of the attenuation region can be adjusted only by simultaneously forming the overhanging conductor portions x, x, and the selectivity is high.
The low-pass filter can be formed without adding another configuration.

Here, FIG. 6 shows the frequency characteristics of the LC low-pass filter of the present invention in which the overhanging conductor portions x, x are formed. FIG. 7 shows the frequency characteristics of the LC low-pass filter. Here, the width and the degree of protrusion of the overhanging conductor parts x, x are 0.15 mm in width and 0.5 mm in degree of protrusion.

From these frequency characteristics, it can be seen that the overhanging conductor portions x, x
It can be understood that the formation of (1) reduces the width of the attenuation region, increases the amount of attenuation, and provides a low-pass filter with good selectivity.

Instead of the above configuration, the first conductive layer 3 formed on the insulating substrate 2 has the capacitor electrodes 16a, 16
b and ground electrode 18, and spiral inductors L ₁ , L
₂ , the capacitor electrode 6 and the ground electrodes 8a and 8b may be formed. That is, the first conductive layers 3 and 10
Are interchangeable.

[0028]

According to the present invention, there is provided a conductive layer having a spiral inductor wound around the center of the spiral inductor, and a connection path is formed on a dielectric thin film coated on the conductive layer from the center of the spiral inductor. In the connection path, a projecting conductor portion serving as a capacitor electrode facing a part of the spiral inductor via the dielectric thin film is extended in the connection path, whereby the inductor is connected in parallel with the inductor. Since the self-resonant capacitor is configured by forming a resonance capacitor to be connected, when forming a connection path for connecting to the inductor, attenuation It is possible to provide a low-pass filter having a high selectivity, a large attenuation, and a high selectivity. Further, in such a configuration, the resonance frequency can be set simply by selecting the shape of the overhanging conductor portion, and the adjustment becomes easy. Further, since an external member for the resonance capacitor is not required, the structure is simplified, and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an insulating substrate 2 and a dielectric thin film 4 of an LC low-pass filter 1 separately.

FIG. 2 is a plan view of the LC low-pass filter 1. FIG.

FIG. 3 is a plan view of a dielectric thin film 4;

FIG. 4 is a partially cutaway enlarged plan view showing an overhanging conductor portion.

FIG. 5 is a vertical sectional side view of the LC low-pass filter 1.

FIG. 6 is a graph showing frequency characteristics of the LC low-pass filter of the present invention.

FIG. 7 is a graph showing a frequency characteristic of an LC low-pass filter of a comparative product.

FIG. 8 is an equivalent circuit diagram.

FIG. 9 is a waveform diagram showing an attenuation range of a low-pass filter.

[Explanation of symbols]

1 LC low-pass filter 2 insulating substrate 3 first conductive layer 4 dielectric film 8a, 8b ground electrode 10 the second conductive layer 16a, 16b capacitor electrodes 17a, 17b connecting channel 18 ground electrode 20 through hole L _1, L ₂ inductor C ₁ , C ₂ , C ₃ capacitor x overhanging conductor

Claims (2)

[Claims] A conductive layer having a spiral inductor wound in a coiling shape toward the center is provided, and a connection path extends outward from the center of the spiral inductor on a dielectric thin film coated on the conductive layer. The LC low-pass filter is formed so as to electrically connect the end of the connection path to the center of the spiral inductor, and faces the connection path with a part of the spiral inductor via the dielectric thin film. An LC low-pass filter characterized by extending a projecting conductor portion serving as a capacitor electrode. A first conductive layer formed on an insulating substrate, a dielectric thin film laminated on the insulating substrate, and a second conductive layer formed on an upper surface thereof; The half surface portion is a capacitor forming region, the other half surface portion is an inductor forming region, and in the inductor forming region, two spiral inductors wound in a spiral shape toward the center are arranged in one conductive layer. In the capacitor forming region, an electrode of an intermediate capacitor is formed at an intermediate portion of one of the conductive layers to be connected to outer winding portions of both spiral inductors, and grounds are provided on both sides of the capacitor electrode. Forming an electrode, and further, on both sides of the other conductive layer,
The input side and the output side of the capacitor electrode are formed respectively, and the connection path is extended from the electrode to a position immediately above the center of the two spiral inductors, and the other conductive layer is provided between the two capacitor electrodes. In the part, a ground electrode is formed, and further, through a conduction hole formed in the dielectric thin film,
The extended end of the connection path is electrically connected to the center of the spiral inductor, whereby the capacitor electrode and the ground electrode face each other via the dielectric thin film, and the input side capacitor, the intermediate capacitor and Output side capacitors are formed in parallel, one end is grounded, the spiral inductors are located between the other ends of the capacitors, and both spiral inductors are connected in series. An LC low-pass filter characterized by extending a projecting conductor portion serving as a capacitor electrode opposed to a part of the LC thin film via the dielectric thin film.