JPH09307392A - Lc type low-pass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LC type low-pass filter which can be surface-mounted and is provided with a stably characteristic receiving no influence from external environment. SOLUTION: Plural through hole 2a to 2c forming conductive films at the inner surfaces are parallelly provided for a dielectric block 1, and a conductive film is formed on the side face of the block except for faces opening these through holes 2a to 2c to make a ground electrode 3. Then a filter substrate 10 forming an input/output terminal part 2 and a ground part 11 is connected to one surface of the dielectric block opening the through holes 2a to 2c, and between the conductor films at the inner surface of the through holes 2a to 2c are successively connected by a coil 8. Then a metallic case 9 covering the dielectric block 1 and the coil 8 is connected to the ground part 11 of the filter substrate 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter used in equipment using a high frequency band such as microwave radio equipment, mobile phones, car phones, GPS, wireless LANs, cordless phones and the like.

[0002]

2. Description of the Related Art Conventionally, a low-pass filter used in a high frequency band generally has a stripline structure (conductor pattern) as shown in FIG. This is because a plurality of electrodes 21, 2 are formed on the surface of a dielectric block or the like.
2 and 23 are formed and a ground electrode is formed on the entire back surface, and the electrodes 21, 22, 23 on the front surface are connected by strip lines 24, 25, and the electrodes 21, 22, 23 on the front and back surfaces of the substrate are connected. Ground capacitance C1, C2, C
The LC type low-pass filter shown in FIG. 7 can be realized by 3 and the inductances L1 and L2 of the strip lines 24 and 25.

However, in the case of the above structure, the ground capacitances C1, C2 and C3 change depending on the permittivity and thickness of the substrate, the electrode area and the printing accuracy thereof, and the conductor patterns on which the inductances L1 and L2 are printed. These variations make the characteristics of the filter unstable because they vary depending on the width and the length. Moreover, in such a stripline structure, since the attenuation pole is not formed, there is a drawback that excellent attenuation characteristics cannot be obtained.

Therefore, as a means for solving the above drawbacks,
As shown in FIG. 8, a plurality of through holes 32a, 32b, 32c are arranged in parallel in the dielectric block 31, and the through holes 32a, 3b
A conductor film is formed on the inner surfaces of 2b and 32c, and a conductor film is formed on the side surface of the dielectric block 31 in which the through holes are not opened to form the ground electrode 33, and the through holes 32a and 32b.
, 32c are sequentially connected by a coil 34 to form a low-pass filter (Japanese Patent Publication No. 7-36482).

With such a structure, as shown in FIG. 9, a ground capacitance C1 is provided between the inner conductor film of the through holes 32a, 32b and 32c and the ground electrode 33 on the side surface of the dielectric block 31.
C2 and C3 are formed and through holes 32a, 32b and 32c are formed.
Inductances L1 and L2 are generated by the coils 34 and 34 connecting the conductor films of the above. An LC in which a plurality of these inductance elements are connected in series and a ground capacitance element is connected in parallel between the interconnection points of the inductance elements.
Basic low-pass characteristics can be obtained in the network. Further, opposing capacitances C4 and C5 are generated between the conductor films on the inner surfaces of the adjacent through holes,
A parallel resonance circuit is formed by it and the inductances L1 and L2 of the coil 34 to form an attenuation pole for blocking passage, so that the attenuation characteristic of the low-pass filter is greatly improved.

[0006]

However, when the manufactured low-pass filter is connected to an external circuit, as shown in FIG. 8, the input / output terminals pulled out from the conductor films of the through holes 32a and 32c at both ends. The lead wires 35, 35 must be connected to the stripline (conductor pattern for signals) of the external circuit board, which makes it difficult to mount the filter element and the mounting efficiency of the components is poor.

Also, such a filter element is easily affected by radiation noise from the outside, and this tendency is extremely remarkable especially in a small dielectric filter which is directed to high speed and low current.

An object of the present invention is to solve the above-mentioned drawbacks, to enable surface mounting, to improve mounting efficiency, and to provide a stable LC type low-pass filter which is not affected by the external environment.

[0009]

That is, according to the present invention, a plurality of through holes (2a, 2b, 2c) are arranged in parallel in the longitudinal direction of a rectangular parallelepiped dielectric block (1) and each through hole (2
A conductor film is formed on the inner surfaces of a, 2b, 2c), and a conductor film is formed on the side surface of the dielectric block (1) except the surface where the through holes (2a, 2b, 2c) are opened to form the ground electrode (3). ), And the input / output terminal portion (12) and the ground portion (11) are formed on one surface of the dielectric block (1) in which the through holes (2a, 2b, 2c) are opened. )
And the input / output terminal portion (1) of the filter substrate (10).
2) and corresponding inner conductor films of the through holes (2a, 2c) at both ends of the dielectric block (1), and the ground portion (11) of the filter substrate (10) and the dielectric block (1). The ground electrodes (3) are electrically connected to each other, and the inner conductor films of the through holes (2a, 2b, 2c) are sequentially connected by the coil (8) to form the dielectric block (1).
The coil (8) is covered with a metal case (9), and the metal case (9) and the earth part (11) of the filter substrate (10) are electrically connected.

Further, according to the present invention, a plurality of through holes (2a, 2b, 2) are provided in the longitudinal direction of the rectangular parallelepiped dielectric block (1).
c) are arranged in parallel, and a conductor film is formed on the inner surface of each through hole (2a, 2b, 2c), and the through hole (2a, 2b, 2c) is formed.
), A conductor film is formed on the side surface of the dielectric block (1) parallel to the column direction to form a ground electrode (3), and the through holes (2a, 2b, 2c) are opened in the dielectric block (1).
On one surface of the dielectric block (1), through holes (2
a, 2c) is formed with an output terminal portion (6) which is electrically connected to the inner conductor film and an earth portion (7) which is electrically connected to the earth electrode (3), and each of the penetrating holes on the other surface opposite to this surface is formed. The inner surface conductor films of the holes (2a, 2b, 2c) are sequentially connected by a coil (8), and the dielectric block (1) and the coil (8) are covered with a metal case (9) and the metal case (9). ) And the ground electrode (3) are electrically connected.

[0011]

1 is a diagram showing a manufacturing process of a first embodiment of an LC type low pass filter of the present invention, FIG. 2 is an external perspective view of a finished product, and FIG. 3 is a sectional view thereof.

In the present invention, a dielectric block 1 manufactured by molding and firing a powder of a high dielectric material such as barium titanate with a press is used.

As shown in FIG. 1 (a), the dielectric block 1 has a rectangular parallelepiped shape in which a constricted portion 4 is provided in the central portion in the longitudinal direction of the block, and the dielectric block 1 is divided into three blocks extending from the top surface to the bottom surface in the longitudinal direction of the block. Through holes 2a, 2b and 2c are arranged in parallel. The size of this dielectric block 1 is, for example, 2.2 m in length.
The size is extremely small, such as m, width 4.0 mm, and height 0.88 mm. It should be noted that in the figure, fine dots are attached to the portion where the dielectric is exposed.

The dielectric block 1 has through-holes 2a, 2b, 2 formed by baking a silver paste, for example.
A conductor film is formed on the entire surface of the block including the inner surface of c.

Next, as shown in FIG. 1B, the conductor film on the upper and lower surfaces of the dielectric block 1 is ground and removed, and the remaining conductor film portion on the side surface of the block is used as the ground electrode 3.

Then, the inner conductor films of the through holes 2a, 2b and 2c are sequentially connected by the coil 8 to form an LC type low pass filter. At this time, the coil 8 used is, for example, a very small air-core coil having an inner diameter of about 0.6Φ formed by winding a thin tin-plated conductor wire having a wire diameter of about 0.2Φ.

By the way, the low-pass filter having such a configuration is known as shown in FIG. 8, and its equivalent circuit is similar to that shown in FIG.

Therefore, based on FIG. 1 (c) and FIG. 1 (d),
The features of the present invention will be described.

In the present invention, the low pass filter is mounted on the filter substrate 10 as shown in the figure, and the entire low pass filter is shielded by the metal case 9.

The filter substrate 10 is made of, for example, a rectangular glass epoxy, and the front surface and the back surface (see FIG. 1D) of the filter substrate 10 are electrically separated from each other by an output terminal portion 12 and a ground portion 11 which are formed by a copper foil pattern. It is formed in the formed state.

Further, semicircular recesses 10a are provided at the edges on the long side of the filter substrate 10, and the recesses 10a are subjected to through-hole processing to connect the earth portions 11, 11 on the front and back surfaces of the substrate to each other. Further, a through hole 13 into which the lead portions of the coils 8 and 8 are inserted is formed at a position where the input / output terminal portion 12 corresponds to the through holes 2a and 2c. They are conducting each other.

Therefore, when mounting the dielectric block 1 on the filter substrate 10, first, as shown in FIG. 3, the through holes 2a and 2c at both ends of the block are aligned with the through holes 13 of the filter substrate 10. , The lead portion of the coil 8 is soldered in a state of penetrating the through hole 2a, 2c into the through hole hole 13, and both ends of the coil 8 are respectively corresponding to the corresponding filter substrate 1 through the through holes 2a, 2c.
The coil 8 is electrically connected to the 0 input / output terminal portion 12, and the other end of the coil 8 is soldered to the inner conductor film of the through hole 2b in the central portion and connected in series. Further, the ground electrode 3 on the side surface of the block and the ground portion 11 of the filter substrate 10 are electrically connected by soldering.

Next, the low-pass filter mounted on the filter substrate 10 is shielded by the metal case 9. The shield metal case 9 is box-shaped, and has four claws 9 on both sides corresponding to the recesses 10a of the filter substrate 10.
a is provided.

The metal case 9 is arranged on the filter substrate 10 by arranging the metal case 9 with a slight gap so as not to come into contact with the low-pass filter, and soldering the claw portion 9a to the recess 10a of the filter substrate 10. Fixed,
At the same time, the metal case 9 is electrically connected to the ground electrode 3 of the low pass filter through the ground portion 11 (see FIG. 2).

Incidentally, resist treatment is applied to appropriate portions of the surface of the filter substrate 11 so as not to short-circuit with the conductor pattern (input / output terminal portion 12) when the metal case 9 is mounted.

As described above, by mounting the LC type low-pass filter on the filter substrate 10 on which the input / output terminal portion 12 and the earth portion 11 are formed, the surface mounting of the filter element becomes possible, so that the connection with the external circuit is possible. Becomes extremely easy,
Moreover, the mounting efficiency is also improved.

Further, the metal case 9 shields radio waves leaking from the filter, so that stable filter characteristics which are not affected by the external environment can be obtained. Moreover, since the filter substrate 10 is formed with the recess 10a for the stopper when the metal case 9 is mounted, the metal case 9 can be easily mounted and the automatic assembling is also possible.

FIG. 4 is a diagram showing a manufacturing process of a second embodiment of the LC type low-pass filter of the present invention, and FIG. 5 is an external perspective view of the finished product.

In FIG. 4A, the dielectric block 1 has a rectangular parallelepiped shape in which a constricted portion 4 is provided in the central portion of the block as in the first embodiment, and the dielectric block 1 extends from the top surface to the bottom surface in the longitudinal direction. Three through holes 2a, 2b, 2c are arranged side by side, and in the case of this embodiment, recesses 5 and 5 are formed at both ends in the block longitudinal direction.

After the silver paste was baked on the dielectric block 1, as shown in FIG. 4 (b), the conductor film on the upper and lower surfaces of the block and the conductor films on the sides of the recesses 5 and 5 were ground and removed, and remained. An input / output electrode section 6 whose conductor portions in the recesses 5 and 5 will be described later
And the conductor film on the other side becomes the ground electrode 3.

Next, as shown in FIG. 4 (c), one surface of this dielectric block 1 is provided with through holes 2a, 2b at both ends of the block.
An input / output terminal portion 6 that is electrically connected to the inner conductor film of c and is electrically connected to the conductor film of the recess 5 and an earth portion 7 that is electrically connected to the earth electrode 3 are formed by conductor pattern printing.

Then, as shown in FIG. 4 (d), the inner conductor films of the through holes 2a, 2b, 2c are sequentially connected by a coil 8 to form an LC type low pass filter. It is shielded by the metal case 9.
The coil 8 is a very small air core coil as described in the first embodiment.

By the way, when the metal case 9 is mounted, the claw portion 9a of the metal case 9 is constricted to the constricted portion 4 of the dielectric block 1.
It is directly soldered to the (ground electrode) and electrically connected to it. The constricted portion 4 is for adjusting the electrostatic capacitance (ground capacitance) between the inner conductor film of the through hole 2b in the center and the ground electrode 3 on the side surface of the block to improve the attenuation characteristic of the low pass filter. However, this constricted part 4 is a metal case 9
Since it can be used as a stopper when mounting, the metal case 9 can be easily attached.

As described above, by directly patterning the connecting input / output terminal portion 6 and the ground portion 7 on one surface of the dielectric block 1, the filter substrate 10 as in the first embodiment is not used. Further, the surface mounting of the filter element becomes possible, the number of parts such as the substrate can be reduced, and the filter size can be further reduced (see FIG. 5).

In the first and second embodiments, the two-stage low-pass filter having three through holes arranged side by side has been described. However, the present invention is not limited to this, and the number of stages of the filter is not limited to this. It may be a step.

[0036]

As described above, according to the present invention,
Since the LC type low pass filter is mounted on the filter substrate and the entire low pass filter is covered with the metal case, the surface mounting of the filter element becomes possible. as a result,
Mounting becomes easy, and mounting density is also improved. Further, the shielding effect of the metal case makes it possible to realize stable filter characteristics that are not affected by the external environment.

In particular, in the case of this configuration, since the shape of the dielectric block can be simplified by using the mounting filter substrate, the block molding becomes easy.

If the surface mounting input / output terminal portion and the ground terminal portion are directly formed on the back surface of the dielectric block, the filter substrate as described above is not required, and the number of parts can be reduced. Further miniaturization is possible.

In particular, since the constricted portion on the side surface of the dielectric block serves as a stopper for the metal case during the shield treatment, the metal case can be easily attached.

[Brief description of drawings]

FIG. 1 is a manufacturing process drawing of an LC low-pass filter showing a first embodiment of the present invention.

FIG. 2 is an external perspective view of the LC type low-pass filter according to the first embodiment.

FIG. 3 is a vertical sectional view of the LC type low-pass filter showing the first embodiment.

FIG. 4 is a manufacturing process diagram of an LC low-pass filter showing a second embodiment of the present invention.

FIG. 5 is an external perspective view of the LC type low-pass filter according to the second embodiment.

FIG. 6 is an external perspective view of a conventional LC low-pass filter.

7 is an equivalent circuit diagram of the LC type low pass filter of FIG.

8 is an external perspective view of an LC low-pass filter different from that of FIG.

9 is an equivalent circuit diagram of the LC low pass filter of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dielectric block 2a, 2b, 2c Through hole 3 Ground electrode 6,12 Input / output terminal part 7,11 Ground part 8 Coil 9 Metal case 10 Filter substrate

Claims (2)

[Claims] 1. A rectangular parallelepiped dielectric block (1) having a plurality of through holes (2a, 2b, 2c) arranged side by side in the longitudinal direction and a conductor film on the inner surface of each through hole (2a, 2b, 2c). And forming a conductor film on the side surface of the dielectric block (1) excluding the surface on which the through holes (2a, 2b, 2c) are opened to form a ground electrode (3), and the through hole (2a, A filter substrate (10) having an input / output terminal portion (12) and a ground portion (11) is placed on one surface of a dielectric block (1) having openings 2b, 2c). ) Input / output terminal part (12) and corresponding through holes (2) at both ends of the dielectric block (1).
a, 2c) and the inner surface conductor films of the filter substrate (10) and the earth electrode (3) of the dielectric block (1) are electrically connected to each other, and the through holes (2a, 2b). 2c) inner conductor films are sequentially connected by a coil (8), and the dielectric block (1) and the coil (8) are covered with a metal case (9) and the metal case (9) and the filter. An LC type low pass filter constituted by electrically connecting a ground portion (11) of a substrate (10). 2. A plurality of through holes (2a, 2b, 2c) are arranged side by side in the longitudinal direction of a rectangular parallelepiped dielectric block (1), and a conductor film is formed on the inner surface of each through hole (2a, 2b, 2c). And forming a conductor film on the side surface of the dielectric block (1) parallel to the column direction of the through holes (2a, 2b, 2c) to form a ground electrode (3), and the through holes (2a, 2b, 2c) on one surface of the dielectric block (1), the output terminal portion (6) electrically connected to the inner conductor film of the through holes (2a, 2c) at both ends of the dielectric block (1), and the ground. A grounding portion (7) is formed to be electrically connected to the electrode (3), and a coil (8) is formed between the inner conductor films of the through holes (2a, 2b, 2c) on the other surface opposite to this surface. And connecting the dielectric block (1) and the coil (8) with a metal case (9) and LC low-pass filter constituted by the by conducting an earth electrode (3) and the genus casing (9).