JP2985938B2 - LC type low pass filter - Google Patents

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 a device using a high frequency band, such as a radio device for microwaves, a mobile phone, an automobile phone, a GPS, a wireless LAN, a cordless phone, and the like.

[0002]

2. Description of the Related Art Conventionally, as a low-pass filter used in a high frequency band, a strip line structure (conductor pattern) as shown in FIG. 6 is generally used. This is because a plurality of electrodes 21 and 2 are provided on the surface of a dielectric block or the like.
2 and 23, a grounding electrode is formed on the entire back surface, and the electrodes 21, 22, and 23 on the front surface are connected by strip lines 24 and 25. Ground capacitances C1, C2, C
3 and the inductances L1 and L2 of the strip lines 24 and 25 can realize an LC type low-pass filter shown in FIG.

However, in the case of the above configuration, the ground capacitances C1, C2, C3 vary depending on the dielectric constant and thickness of the substrate, or the electrode area and its printing accuracy, and the inductances L1, L2 of the printed conductor pattern. These variations made the characteristics of the filter unstable because it varied depending on the width and length. In addition, since such a strip line structure does not have an attenuation pole, there is a disadvantage that excellent attenuation characteristics cannot be obtained.

[0004] In order to solve such disadvantages,
As shown in FIG. 8, a plurality of through holes 32a, 32b, and 32c are provided in the dielectric block 31 in parallel with each other.
A conductor film is formed on the inner surface of each of the through holes 32a and 32b, and a conductor film is formed on the side surface of the dielectric block 31 having no through hole.
, 32c are sequentially disclosed by a coil 34 (Japanese Patent Publication No. 7-36482).

[0005] With this configuration, as shown in FIG. 9, the ground capacitance C 1, between the inner conductor film of the through holes 32 a, 32 b, and 32 c and the ground electrode 33 on the side surface of the dielectric block 31.
C2 and C3 are formed, and the through holes 32a, 32b and 32c are formed.
Inductances L1 and L2 are generated by the coils 34 and 34 coupling between 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 occur between the conductor films on the inner surfaces of the adjacent through holes,
In addition, a parallel resonance circuit is formed by 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 drawn from the conductor films of the through holes 32a and 32c at both ends are used. Lead wires 35, 35 must be connected to the strip lines (conductor patterns 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.

[0007] Such a filter element is susceptible to external radiation noise, and the tendency is particularly remarkable in a small-sized dielectric filter which is designed to operate at high speed and reduce current.

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

[0009]

That is, in the present invention, a plurality of through holes (2a, 2b, 2c) are juxtaposed in the longitudinal direction of a rectangular parallelepiped dielectric block (1), and each of the through holes (2a, 2b, 2c) is arranged.
a, 2b, 2c), a conductor film is formed on the side surface of the dielectric block (1) excluding the surface where the through holes (2a, 2b, 2c) are opened, and the ground electrode (3) is formed. ), And the through holes (2a, 2a) at both ends of the dielectric block (1).
Input / output terminals at both longitudinal ends to face 2c)
Forming a portion (12) and facing the ground electrode (3);
The input / output terminal section (12) is
A filter formed by forming a gas-separated ground part (11).
A filter substrate (10) is provided.
Each of the input / output terminal portions (12) and the dielectric block (1)
The through-holes (2a, 2c) are also provided with the ground portion (11).
And the ground electrode (3) face each other.
The filter substrate (10) is inserted into the through holes (2a, 2b, 2).
c) Placed on one side of the dielectric block (1) where the opening is
And the input / output terminal portion (12) facing each other and the penetration
The inner conductor films of the holes (2a, 2c) and the ground portion
(11) and the ground electrode (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), and the dielectric block (1) and The coil (8) is covered with a metal case (9), and the metal case (9) and the filter substrate (10) are covered.
The grounding part (11) is made conductive.

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) and a conductor film is formed on the inner surface of each through hole (2a, 2b, 2c), and the through holes (2a, 2b, 2c) are 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 dielectric block (1) in which the through holes (2a, 2b, 2c) are opened.
Of the dielectric block (1) is formed in one surface of the through hole (2) at both ends.
a, 2c), an output terminal portion (6) conducting to the inner conductor film and a ground portion (7) conducting to the ground electrode (3) are formed respectively, and each of the through-holes on the other surface facing this surface is formed. The inner 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) is covered. ) And the ground electrode (3) are made conductive.

[0011]

FIG. 1 is a view 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 produced by molding and firing a powder of a high dielectric material such as barium titanate by a press is used.

As shown in FIG. 1 (a), the dielectric block 1 has a rectangular parallelepiped shape having a constricted portion 4 provided at a central portion in the longitudinal direction of the block, and three dielectric blocks 1 extending from the top surface to the bottom surface in the longitudinal direction of the block. The through holes 2a, 2b, 2c are arranged in parallel. The size of the dielectric block 1 is, for example, 2.2 m in length.
m, 4.0 mm wide and 0.88 mm high. In the drawing, portions where the dielectric is exposed are marked with small dots.

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

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

The inner conductor films of the through holes 2a, 2b and 2c are sequentially connected by a coil 8 to form an LC 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 wound around a thin tin-plated conductive wire having a wire diameter of about 0.2Φ several turns.

Incidentally, the low-pass filter having such a configuration is known as shown in FIG. 8, and its equivalent circuit is the same as that shown in FIG.

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

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

The filter substrate 10 is made of, for example, a rectangular glass epoxy, and has an output terminal portion 12 and a ground portion 11 made of a copper foil pattern on the front and back surfaces (see FIG. 1D). It is formed in the state where it was done.

A semicircular dent 10a is provided in each of the long edges of the filter substrate 10, and the dent 10a is subjected to through-hole processing to connect the ground portions 11 on the front and back surfaces of the substrate to each other. A through-hole 13 is formed in the input / output terminal 12 at a position corresponding to the through-holes 2a and 2c, and a lead portion of the coil 8 is inserted into the input / output terminal 12. They are electrically connected to each other.

Therefore, when mounting the dielectric block 1 on the filter substrate 10, first, as shown in FIG. 3, the positions of the through holes 2a and 2c at both ends of the block and the through hole 13 of the filter substrate 10 are aligned. The lead of the coil 8 is soldered in a state where the lead is penetrated through the through holes 2a and 2c into the through hole 13, and both ends of the coil 8 are connected to the corresponding filter substrates 1 through the through holes 2a and 2c, respectively.
And the other end of the coil 8 is soldered to the inner conductor film of the through hole 2b at the center and connected in series. Also, the ground electrode 3 on the side surface of the block and the ground portion 11 of the filter substrate 10 are electrically connected to each other by soldering.

Next, the low-pass filter mounted on the filter substrate 10 is shielded by the metal case 9. The metal case 9 for shielding is box-shaped and has four claw portions 9 on both sides corresponding to the depressions 10a of the filter substrate 10.
a is provided.

The metal case 9 is arranged on the filter substrate 10 by soldering the claw 9a to the depression 10a of the filter substrate 10 by disposing the metal case 9 with a slight gap so as not to contact the low-pass filter. Fixed,
At the same time, the metal case 9 is conducted to the earth electrode 3 of the low-pass filter via the earth part 11 (see FIG. 2).

In order to prevent a short circuit with the conductor pattern (input / output terminal portion 12) when the metal case 9 is mounted, an appropriate portion of the surface of the filter substrate 11 is subjected to a resist treatment.

As described above, since the filter element can be surface-mounted by mounting the LC type low-pass filter on the filter substrate 10 on which the input / output terminal section 12 and the ground section 11 are formed, the connection to an external circuit is made possible. Becomes extremely easy,
In addition, the mounting efficiency is improved.

Further, the metal case 9 shields the radio wave leaking from the filter, thereby obtaining a stable filter characteristic without being affected by the external environment. In addition, since the filter substrate 10 is provided with the recess 10a for stopper when the metal case 9 is mounted, the mounting of the metal case 9 is easy and the automatic assembly can be performed.

FIG. 4 is a view 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 a finished product.

In FIG. 4A, the dielectric block 1 has a rectangular parallelepiped shape having a constricted portion 4 at the center of the block, as in the first embodiment, and extends from the top surface to the bottom surface in the longitudinal direction of the dielectric block 1. Three through holes 2a, 2b, 2c are provided in parallel, and in the case of the present embodiment, concave portions 5, 5 are respectively formed at both ends in the block longitudinal direction.

After baking of the silver paste, the conductive film on the upper and lower surfaces of the dielectric block 1 and the conductive films on the side of the concave portions 5 and 5 are ground and removed as shown in FIG. The conductor portions in the recesses 5 and 5 serve as input / output electrode portions 6 to be described later.
And the conductor film on the other side becomes the ground electrode 3.

Next, as shown in FIG. 4C, through-holes 2a, 2a at both ends of the dielectric block 1 are formed on one surface of the dielectric block 1.
An input / output terminal portion 6 which is electrically connected to the inner conductor film of c and which is electrically connected to the conductor film of the concave portion 5 and an earth portion 7 which is electrically connected to the earth electrode 3 are formed by conductor pattern printing.

Then, as shown in FIG. 4D, the inner conductor films of the through holes 2a, 2b and 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 an extremely small air-core coil as described in the first embodiment.

When the metal case 9 is mounted, the claw 9a of the metal case 9 is engaged with the constricted portion 4 of the dielectric block 1.
(Earth electrode) is soldered directly to it and made conductive. The constricted portion 4 adjusts the capacitance (ground capacitance) between the inner conductor film of the central through hole 2b and the ground electrode 3 on the side surface of the block to improve the attenuation characteristics of the low-pass filter. However, this constricted part 4 is a metal case 9
Can be used as a stopper when mounting the metal case 9, so that the metal case 9 can be easily mounted.

As described above, the input / output terminal portion 6 and the grounding portion 7 for connection are directly formed on one surface of the dielectric block 1 so that the filter substrate 10 as in the first embodiment is not used. In addition, the surface mount of the filter element becomes possible, the number of components such as substrates can be reduced, and the filter size can be further reduced (see FIG. 5).

As described above, in the first and second embodiments, the two-stage low-pass filter in which three through holes are juxtaposed has been described. However, the present invention 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 a metal case, the filter element can be surface-mounted. as a result,
Mounting is facilitated, and mounting density is improved. Further, stable filter characteristics which are not affected by the external environment due to the shielding effect of the metal case can be realized.

In particular, in the case of this configuration, the shape of the dielectric block can be simplified by using the mounting filter substrate, so that the block can be easily formed.

Further, if the input / output terminal portion for surface mounting and the ground terminal portion are formed directly on the back surface of the dielectric block, the above-mentioned filter substrate becomes unnecessary, 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 plays a role of a stopper for the metal case at the time of the shielding process, the mounting of the metal case is easy.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of an LC-type 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 longitudinal sectional view of the LC type low-pass filter according to the first embodiment.

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

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

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

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

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

FIG. 9 is an equivalent circuit diagram of the LC type 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 board

Continuation of front page (56) References JP-A-3-296315 (JP, A) JP-A-4-206616 (JP, A) JP-A-9-307392 (JP, A) JP-A-6-349680 (JP) , A) Hikaru Hei 2-38802 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03H 7/00 H01P 1/20 H01G 4/00

Claims (2)

(57) [Claims] 1. A plurality of through-holes (2a, 2b, 2c) are juxtaposed in the longitudinal direction of a rectangular parallelepiped dielectric block (1), and a conductor film is formed on an inner surface of each of the through-holes (2a, 2b, 2c). A conductive film is formed on the side surface of the dielectric block (1) except for the surface where the through holes (2a, 2b, 2c) are opened to form a ground electrode (3), and the dielectric block (1 ) is formed. ) Through holes at both ends (2a, 2c)
Input / output terminal portions (1
2) is formed and is opposed to the ground electrode (3).
Electrically connected to the input / output terminal (12) at both longitudinal edges.
Filter base formed with a separate ground part (11)
A plate (10) is provided, and each of the filter substrate (10) enters and exits.
Force terminal (12) and through-hole of the dielectric block (1)
(2a, 2c) are also provided with the ground part (11)
The above-mentioned filters are arranged so that the ground electrodes (3) face each other.
When the through holes (2a, 2b, 2c) are
The input / output terminal section (12) and the through hole are placed on one surface of the dielectric block (1) to be opened, and face each other.
(2a, 2c) inner conductor films and the ground portion
(11) and the ground electrode (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), and the dielectric block (1) and An LC type low-pass filter, wherein the coil (8) is covered with a metal case (9) and the metal case (9) is electrically connected to a ground portion (11) of the filter substrate (10). 2. A plurality of through holes (2a, 2b, 2c) are juxtaposed in the longitudinal direction of a rectangular parallelepiped dielectric block (1), and a conductive film is formed on the inner surface of each of the through holes (2a, 2b, 2c). A conductor film is formed 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). An output terminal portion (6) that is electrically connected to the inner conductive film of the through holes (2a, 2c) at both ends of the dielectric block (1) on one surface of the dielectric block (1) in which the dielectric block (2b, 2c) is open, and the ground. A grounding portion (7) that is electrically connected to the electrode (3) is formed, and a coil (8) sequentially connects between the inner conductor films of the through holes (2a, 2b, 2c) on the other surface facing this surface. The dielectric block (1) and the coil (8) are covered with a metal case (9). LC low-pass filter constituted by the by conducting an earth electrode (3) and the genus casing (9).