JPH08250962A - Lc filter - Google Patents

Abstract

PURPOSE: To improve the attenuation characteristic at a high frequency band by providing a ground pattern between spiral conductor patterns forming different inductors arranged side by side. CONSTITUTION: Plural sets of inductors consisting of one set of spiral conductor patterns 2a, 2b formed on both sides of a board 9 and of conductor patterns of throughhole sections 4a, 4b provided in the center of the spiral to connect the one set of the conductor patterns 2a, 2b are connected in series. Furthermore, a capacitor 8 is connected to a connection section or both the connection section and a non-connection section of plural inductors. Then a ground pattern 3 is provided between the spiral conductor patterns 2a, 2b being components of the different inductors. Thus, stray capacitance between the conductor patterns 2a, 2b is reduced and the attenuation characteristic at a high frequency band is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LC filter composed of an inductance and a capacitor, and more particularly to an LC filter in which a plurality of inductances made of a spiral conductor pattern are connected in series.

[0002]

2. Description of the Related Art Conventionally, as an LC filter composed of an inductance and a capacitor, a chip type inductance and a capacitor mounted on a substrate,
Various things are known such as an inductance part made of a spiral conductor pattern formed on a substrate and a capacitor mounted on the substrate (Japanese Patent Laid-Open No. 63-15619). There is.

These LC filters are selectively used according to the purpose of use and the state of use. However, the one in which the inductance part is formed by the spiral conductor pattern formed on the substrate has a large shape and cost. It is often used because it is excellent.

[0004]

However, when a plurality of inductances formed by the spiral conductor pattern are connected in series on the substrate, the stray capacitance between adjacent conductor patterns forming different inductances causes The attenuation characteristic in the high frequency region of the LC filter deteriorates. Since the stray capacitance increases as the spiral conductor patterns approach each other, it becomes a particular problem when the distance between the conductor patterns forming different inductances is reduced in order to downsize the LC filter.

In addition, it is not easy to secure a large inductance value with an inductance made of a spiral conductor pattern, and the magnetic influence between the adjacently arranged inductances cannot be ignored.

Therefore, the present invention secures a large inductance value in an LC filter in which a plurality of inductances made of spiral conductor patterns are connected in series on a substrate, and at the same time, between adjacent spiral conductor patterns. It is an object of the present invention to provide an LC filter having improved attenuation characteristics in a high frequency region by reducing stray capacitance.

[0007]

The LC filter of the present invention is provided at the center of a spiral for connecting a set of spiral conductor patterns formed on both surfaces of a substrate and the set of conductor patterns. Connect a plurality of inductances composed of the conductor pattern of the through-hole part in series, and
In an LC filter in which capacitors are connected to both the connecting portion or the connecting portion and the non-connecting portion of the plurality of inductances, a ground is provided between the spiral conductor patterns that are arranged adjacent to each other and form different inductances. The feature is that a pattern is provided.

[0008]

According to the LC filter of the present invention, a set of spiral conductor patterns formed on both surfaces of a substrate and a conductor of a through hole provided in the center of the spiral for connecting the set of conductor patterns. In an LC filter in which a plurality of inductances each composed of a pattern are connected in series, and capacitors are connected to both the connecting portions or both the connecting portion and the non-connecting portion of the plurality of inductances, they are arranged adjacent to each other. ，
Since the ground pattern is provided between the spiral conductor patterns forming different inductances, the stray capacitance between the adjacent spiral conductor patterns is reduced and the attenuation characteristic in the high frequency region is improved. be able to.

Further, the above-mentioned effects are more effective when the distance between the adjacent spiral conductor patterns is 1 mm or less.

[0010]

EXAMPLES The present invention can be carried out on any substrate such as a ferrite substrate, a composite ferrite substrate, a glass epoxy substrate, a dielectric substrate, etc. In this example, description will be made on the case of performing the composite ferrite substrate and the glass epoxy substrate. To do.

(When Implemented on Composite Ferrite Substrate) First, the manufacturing process will be described.

(1) A composite ferrite is prepared by kneading a fired Mn-Mg-Zn-based ferrite with a liquid crystal polymer resin so that the content of ferrite powder crushed to an average particle size of 2 to 50 μm is 65% by weight. The composite ferrite resin that is the material of the substrate is manufactured.

(2) A substrate having through holes (2 mm in length, 4.5 mm in width,) having through holes for forming conductive patterns on the front and back sides, which is obtained by injecting the composite ferrite resin with a mold.
A plurality of substrates having a thickness of 1.6 mm are arrayed to produce a collective substrate. At this time, if necessary, a V-cut for dividing the substrate, guide holes for positioning the substrate, holes for connecting the front and back electrodes, and the like may be provided in the collective substrate.

(3) After performing surface etching to improve the plating adhesion of the aggregated substrate, electroless copper plating and electrolytic copper plating are performed in this order to form a conductor film on the surface of the substrate.

(4) A conductor film pattern as shown in FIG. 1 is formed on an aggregate substrate on which a conductor film is formed by an electrodeposition resist method in which a non-exposed portion becomes a pattern (FIG. 1).
(A) and (b) show one single substrate in the collective substrate, and when (a) is the front surface of the substrate, (b) shows a perspective view of the back surface). That is, on the front surface of the substrate, the portions other than the spiral conductor patterns 2a and 2b forming the inductance, the ground pattern 3, and the electrodes 6a and 6b are exposed, and on the back surface, the spiral conductor pattern forming the coil portion. The portions other than 2a 'and 2b', the chip capacitor mounting lands 5a and 5b, and the electrodes 6a 'and 6b' are exposed.

Here, the spiral conductor pattern 2a formed on the front surface of the substrate and the spiral conductor pattern 2a 'formed on the back surface are electrically connected through the through holes 4a, and the spiral conductor pattern on the front surface of the substrate. The pattern 2b and the spiral conductor pattern 2b 'on the back surface are electrically connected to each other through the through hole 4a.
Further, the front surface electrode 6a, the rear surface electrode 6a ', and the front surface electrode 6a
b, the electrode 6b 'on the back surface, the ground pattern 3, and the chip-capacitor mounting land 5b on the ground side are electrically connected through a part 7 of a hole provided when the collective substrate is molded.

Further, the surface of the copper having a pattern formed thereon for preventing oxidation may be plated with nickel, tin, solder or the like.

(5) After the chip capacitors 8 are soldered to the chip capacitor mounting lands 5a and 5b formed on the back surface of the substrate as shown in FIG. 1C, the collective substrate is divided and the LC filter 9 is divided. To get

Further, protective resist ink may be applied to the surface of the spiral conductor pattern forming the inductance.

Next, the circuit configuration and electrical characteristics of the LC filter thus obtained will be described.

FIG. 2 is a circuit diagram of the LC filter described above. The spiral conductor patterns 2a and 2a 'in FIG. 1 correspond to the inductance L1 shown in the circuit diagram, and the spiral conductor patterns 2b and 2b' are inductances. Corresponds to L2. That is, one inductance is formed by a set of spiral conductor patterns provided on both surfaces of the substrate. The chip capacitor 8 in FIG. 1 is the capacitor C shown in the circuit diagram.
Corresponds to 1.

In the circuit diagram, C _p connected in parallel with the inductances L1 and L2 is a stray capacitance. If this capacitance is large, the attenuation characteristic in the high frequency region of the low pass filter deteriorates, so C _p The smaller the value, the better.

Table 1 shows measured values of the stray capacitance between IN and OUT of the LC filter having the configuration shown in FIG. Here, in Sample A and Samples 1 to 4 of the same table, the widths W1 and W1 ′ of the spiral conductor patterns, the distances W2 and W2 ′ between the spiral conductor patterns, and the width W3 of the ground pattern are as follows. Smooth (W1, W1 ', W2, W2', W
3 shows the size of each part in FIG. 1). In addition, samples 3 and 4 were not provided with a ground pattern.

Sample A: W1 = W1 '= 1.35 mm, W
2 = W2 '= 1.5 mm, no ground pattern, L1
・ The number of turns of L2 is 2 times for each of the front and back. Sample 1: W1 = W1 ′ = 1.35 mm, W2 = W2 ′ =
1.0 mm, no ground pattern, the number of turns of L1 and L2 is two turns for each of the front and back. Sample 2: W1 = 1.55 mm, W1 ′ = 1.35 mm,
W2 = 0.5 mm, W2 ′ = 1.0 mm, no ground pattern, the number of turns of L1 and L2 is two for each front and back Sample 3: W1 = W1 ′ = 1.35 mm, W2 = W2 ′ =
1.0 mm, W3 = 0.3 mm, the number of turns of L1 and L2 is two turns for each front and back Sample 4: W1 = 1.55 mm, W1 ′ = 1.35 mm,
W2 = 0.5 mm, W2 ′ = 1.0 mm, W3 = 0.3
mm, the number of turns of L1 and L2 is 2 laps on each side

[0025]

[Table 1]

As is clear from Table 1, as the distances W2 and W2 'between the spiral conductor patterns become shorter,
When the stray capacitance increases, and especially when W2 and W2 ′ are 1 mm or less (Samples 1 and 2), the influence thereof often becomes a problem. In this case, if a ground pattern is provided between the spiral conductor patterns (Samples 3 and 4), the distances W2 and W2 ′ between the spiral conductor patterns are set to 1.5 mm (Sample A). The stray capacitance can be reduced to about the same value as.

FIG. 3 shows the sample 2 (L1 = L2 = 23n).
H), C1 = 30p in sample 4 (L1 = L2 = 23nH)
The attenuation characteristic of the LC filter measured by mounting the F chip capacitor is shown. As is clear from the figure, when the ground pattern is provided, the attenuation characteristic in the region of 1 GHz or higher is improved. Incidentally, when the setting of the high cutoff frequency is changed by the value of C1, the frequency range where the improvement of the attenuation characteristic is observed changes, but in any case, the attenuation characteristic in the high frequency region is improved.

The width W3 of the ground pattern is preferably wider than the pattern width of the spiral conductor pattern forming the inductance, and at least about the same as the pattern width.

(When implemented on the glass epoxy substrate) The conductor pattern (L1
A glass epoxy substrate (2.5 mm in length, 4.8 mm in width, 0.5 mm in thickness) having three turns of L2 on each of the front and back sides was manufactured by the same method as in the case of manufacturing a normal double-sided board. The dimensions of each part of the substrate are as follows.

Sample 5: W1 = W1 '= 1.6 mm, W2
= W2 '= 1.2mm, W3 = 0.6mm, L1 ・ L2
The number of turns is 3 for each of the front and back. Sample 6: W1 = W1 '= 1.6 mm, W2 = W2' =
1.2 mm, no ground pattern, and the number of turns of L1 and L2 was 3 turns on each of the front and back sides. L1 and L2 in the glass epoxy substrate were 40 nH for both samples (Sample 5 and Sample 6).

FIG. 4 shows the attenuation characteristic of the LC filter measured by mounting a chip capacitor of C1 = 33 pF on the chip capacitor mounting land of the glass epoxy substrate. As is clear from the figure, when the ground pattern is provided, the attenuation characteristic in the region of 1 GHz or higher is improved.

(Regarding the ground pattern and the spiral conductor pattern) The above-mentioned LC filter is not limited to one in which two inductances are connected in series, but three or more inductances L1, L1 and L2 as shown in the circuit diagram of FIG. L2, L
3 may be connected in series. In this case, one of the ground patterns 3a and 3b may be provided on the front surface and the other on the back surface as shown in FIG. 5, or they may be provided on the same surface as shown in FIG. When three or more inductances are provided, the ground pattern of each part may be connected by a conductor pattern as shown in FIG.

In this embodiment, the T-type or the LC filter in which T-types are connected in multiple stages has been described, but the same effect can be obtained even in the case of an LC filter in which π-types are connected in multiple stages.

Next, the inductances L1, L2 and L3 (FIG. 8) in the substrate shown in FIGS. 5, 6 and 8 will be described.

The inductance in the present invention includes a conductor pattern formed in a spiral shape from the outside toward the center,
Since the conductor pattern is connected to the conductor pattern through the through hole and is formed in a spiral shape from the center toward the outside, the start and end of the spiral conductive pattern forming the inductance are Both are outside the spiral. Therefore, it is possible to easily form a pattern in which a plurality of inductances are connected in series.

Further, the swirl direction of the spiral conductor pattern from the winding start to the through hole and the swirl direction from the through hole of the conductor pattern on the opposite surface connected to this conductor pattern via the through hole to the end of winding. When viewed from one surface (the other surface is seen through), since both are the same, a larger inductance value can be obtained with the same pattern length.

Next, the spiral conductor patterns 12a, 12a 'corresponding to L1 in FIGS. 5, 6 and 7 and the conductor patterns 12b, 12b' corresponding to L2, and the conductor patterns 12c, 12 'corresponding to L3. Will be described.

Electrodes 16a, 16 corresponding to IN in FIG.
When looking at the conductor patterns from a '(both electrodes are connected) to the electrodes 16b, 16b' (both electrodes are connected) corresponding to OUT, adjacent spiral conductor patterns 12a, 12a The turning directions of the'and the conductor patterns 12b and 12b 'are opposite to each other. Similarly, the spiral conductor patterns 12b, 12b 'and the conductor patterns 12c,
The turning direction of 12c 'is also opposite.

In this way, when the spiral conductor patterns forming different inductances are arranged on the same plane, the swirling directions of adjacent spiral conductor patterns (when the patterns are viewed from the same advancing direction) are mutually different. By making them different, the magnetic influence of both can be reduced.

[0040]

The present invention can improve the attenuation characteristic in the high frequency region of the LC filter by providing the ground pattern as described above. Further, when the inductance of the LC filter is formed of a spiral conductor pattern, a high inductance value can be secured.

[Brief description of drawings]

FIG. 1 is a plan view showing a substrate of an LC filter used in an example.

FIG. 2 is a circuit diagram showing a circuit of an LC filter according to an embodiment.

FIG. 3 is a graph showing the attenuation characteristic of the LC filter of the example.

FIG. 4 is a graph showing the attenuation characteristic of the LC filter of the example.

FIG. 5 is a plan view showing a substrate of an LC filter used in an example.

FIG. 6 is a plan view showing a substrate of an LC filter used in an example.

FIG. 7 is a plan view showing a substrate of an LC filter used in an example.

FIG. 8 is a circuit diagram showing a circuit of an LC filter of an example.

[Explanation of symbols]

2a, 2a ', 2b, 2b', 12a, 12a ', 12
b, 12b ', 12c, 12c' Spiral conductor pattern 3, 13 Ground pattern 4a, 4b, 14a, 14b, 14c Through hole 5a, 5b, 15a, 15b Chip capacitor mounting land 6a, 6a ', 6b, 6b ', 16a, 16a', 16
b, 16b 'electrode 8,18 chip capacitor 9,19 substrate

Claims (2)

[Claims] 1. A set of spiral conductor patterns formed on both surfaces of a substrate, and a through-hole conductor pattern provided at the center of the spiral for connecting the set of conductor patterns. In a LC filter in which a plurality of inductances are connected in series, and capacitors are connected to both the connecting portion or both connecting portion and non-connecting portion of the plurality of inductances, they are arranged adjacent to each other to form different inductances. An LC filter, wherein a ground pattern is provided between the spiral conductor patterns. 2. The LC filter according to claim 1, wherein the distance between the spiral conductor patterns arranged adjacent to each other and forming different inductances is equal to or more than 1 of the conductor pattern width.
The LC filter according to claim 1, wherein the LC filter has a thickness of not more than mm.