JP2000114906A - Lowpass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LC lowpass filter which is excellent in frequency characteristic, has little dispersion of characteristics when manufactured, has high stability against a characteristic change, is hardly influenced by electromagnetic waves and is capable of being configured in a small size. SOLUTION: This lowpass filter 41 which has an input terminal 411, an output terminal 413 and a ground terminal 412 and where an inductance part is formed between the input terminal and the output terminal and a capacitor part is formed between the middle of the inductance part and the ground terminal is provided on a printed wiring board 45. Then, prescribed inductance caused by a wiring pattern 42 and a through viahole 43 is generated between the terminal 412 and the ground of the printed wiring board.

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 having a coil section and a capacitor section used for various electronic devices.

[0002]

2. Description of the Related Art A conventional three-terminal low-pass filter is generally represented by an equivalent circuit as shown in FIG. 7, in which a coil portion L and a capacitor portion C are configured as a ladder circuit. The characteristics of the T-type three-terminal low-pass filter are shown as characteristics having an attenuation pole fa in a high band as shown in FIG. The attenuation pole fa is calculated not by f = 1 / {2π (LC) ^1/2 } by LC in FIG. 7 but by the inductance L of the coil part and the stray capacitance Cs of the coil part in FIG. 9 fa = 1 / ｛ 2π (LCs) ^1/2 ｝. F = 1 / ｛2π (L by LC in FIG. 7
C) ^1/2 } is a cutoff frequency fc at which attenuation starts in the attenuation characteristics.

Conventionally, in order to improve the frequency characteristics, FIG.
The method of connecting the coil portion L of the low-pass filter portion and the capacitor Cp in parallel as shown in FIG. 11 or the method of connecting the capacitor C and the coil Ls of the low-pass filter in series as shown in FIG. Showa 60-14
No. 8212, JP-A-61-4312). FIG.
In order to realize the configuration 1, a method of controlling the attenuation pole fa by winding one or more turns of an earth wire in the same direction as the winding direction around the coil portion of the filter constituting the T-shape has been used. Was.

[0004]

However, this conventional method has problems such as difficulty in production and unstable performance. By adding the series inductance Ls to the capacitor section, a new attenuation pole fd is actually generated because the order of the resonance system increases as shown in FIG. 12, and this new attenuation pole is set to a frequency different from fa. This can improve the frequency characteristics. When the series inductance Ls is set so as to satisfy fa> fd, it is possible to obtain a steeper attenuation characteristic and a flatter characteristic between fa and fd. With respect to fa <fd, the flatness of characteristics after fd is improved.

However, when the ground winding is wound around the coil, mutual inductance is generated as shown in FIG. 13 and the stray capacitance of the coil is changed. Therefore, as shown in FIG. fa, new attenuation pole f
d changed, the desired characteristics were hardly obtained, and the production was difficult.

Further, winding one or more turns of the ground wire in the same direction as the winding direction around the coil portion of the filter constituting the T-shape increases the cost and the shape of the winding components. When the ground winding is used, there are many problems such as a large variation in characteristics at the time of manufacturing, a characteristic change of a basic T-type circuit, and a susceptibility to inductive noise due to electromagnetic waves. there were.

An object of the present invention is to solve these problems of the prior art. That is, an object of the present invention is to provide a low-pass filter that has excellent frequency characteristics, has small variations in characteristics at the time of manufacturing, has high stability against changes in characteristics, is less susceptible to electromagnetic waves, and can be configured in a small size. Things.

[0008]

Means for Solving the Problems The present invention (claim 1) provides:
A low-pass filter having an input terminal, an output terminal, and a ground terminal, an inductance part formed between the input terminal and the output terminal, and a capacitor part formed between the middle of the inductance part and the ground terminal is provided on the printed wiring board. ,
A low-pass filter in which an inductance component is mounted between the ground terminal and the ground of the printed wiring board.

The present invention (claim 2) has an input terminal, an output terminal, and a ground terminal, wherein an inductance portion is formed between the input terminal and the output terminal, and a capacitor portion is provided between the middle of the inductance portion and the ground terminal. Is provided on a printed wiring board, and a predetermined inductance is generated between the ground terminal and the ground of the printed wiring board by a wiring pattern and a through via.

[0010]

According to the present invention (claim 1), when components are mounted on a printed wiring board, the capacitor portion of the low-pass filter is not directly connected to the ground, but is connected to the ground via an inductance component. Therefore, the attenuation pole fd can be generated as a new resonance point, and this can be controlled to improve the frequency characteristics. According to the present invention, since the inductance component is connected to the printed circuit board with predetermined characteristics, the inductance component is smaller, has less variation in characteristics, and is less affected by electromagnetic waves than a conventional method of forming an inductance by winding a ground wire. Also hard to receive.

According to the present invention (claim 2), when mounting a component on a printed wiring board, the capacitor portion of the three-terminal low-pass filter is not directly connected to the ground, but is connected to the wiring pattern on the printed wiring board and the through via. As a result, a predetermined inductance can be generated, and the attenuation pole fd can be generated as a resonance point by the capacitance of the capacitor and the generated inductance. Therefore, this can be controlled to improve the frequency characteristics. Further, according to the present invention, since a predetermined inductance is generated by the wiring pattern on the printed wiring board and the through via, a smaller size and characteristic variation are required as compared with the case where the inductance is formed by winding a conventional ground wire. And is not easily affected by electromagnetic waves. The means for generating a predetermined inductance by the wiring pattern and the through via includes, for example, connecting through vias that are generally used in a multilayer printed wiring board in series, and wiring in the multilayer printed wiring board in a spiral shape. In addition to those that generate inductance by doing, in the case of blind vias that do not penetrate the front and back phases in a multilayer printed wiring board, and the build-up method board that reduces the diameter of the via and improves the mounting density, it can be used together with wiring There are those that generate inductance by realizing a substantially complete spiral structure, and those that generate inductance by reducing the width of wiring and forming the wiring in a zigzag shape.

[0012]

(First Embodiment) FIG. 1 is a view showing a configuration of a low-pass filter according to a first embodiment, as viewed from the component side of a multi-phase printed wiring board. In FIG. 1A, reference numeral 11 denotes a three-terminal low-pass filter;
1 is a signal input electrode of the three-terminal low-pass filter, 112 is a ground (GND) connection electrode of the three-terminal low-pass filter, 113 is a signal output electrode of the three-terminal low-pass filter,
Reference numeral 12 denotes a signal wiring of a printed board, 13 denotes an inductance component, and 14 denotes a via (Vi) for connecting a GND surface of the printed wiring board.
a) and 15 indicate printed circuit boards, respectively.
1 between the signal input electrode 111 and the signal output electrode 113.
As shown in the schematic diagram of (b), a coil part 16 is formed, and an electrode 17 for forming a capacitance is arranged in the middle of the coil part 16 so as to face the coil part, and the electrode 17 is connected to a ground connection electrode 112. A capacitance is formed between the coil portion 16 and the electrode 17 to form a capacitor portion 18. FIG. 1 (c) shows an equivalent circuit of the low-pass filter of FIGS. 1 (a) and 1 (b). The three-terminal low-pass filter is not limited to the one having the structure 11 in FIG. 1A, but is a three-terminal low-pass filter having, as a basic configuration, 11 'of the equivalent circuit in FIG. 1C or the equivalent circuit in FIG. Any type of filter may be used.

When the ground connection terminal of the T-type three-terminal low-pass filter is directly connected to GND, the attenuation characteristic as shown in FIG. 8 is exhibited. As described above, the attenuation pole fa representing the characteristic of attenuation of the component indicates a parallel resonance frequency formed between the attenuation pole fa and the stray capacitance Cs formed in parallel with the inductance unit. That is, fa = 1 / {2π (LCs) ^1/2 }. When an inductance Ls is inserted in series with the capacitor unit, a series resonance with the capacitance C is added, so that the second attenuation pole fd
Occurs. This second attenuation pole is fd = 1 / ｛2π
(L'C) ^1/2 ｝. The second attenuation pole fd and the first
Even if the newly formed series resonance circuit giving fd is in the inductive region, the parallel resonance circuit giving fa shows capacitance between the attenuation poles fa, so that the combined impedance is dominant and the newly formed series resonance circuit gives fa. No anti-resonance point is generated. As a result, the attenuation characteristics shown by the solid line in FIG. 12 are obtained, and the frequency characteristics can be improved. In the prior art, a ground winding was used, but the present invention is not a ground winding,
Since ordinary inductance components are used, there is little variation in characteristics due to manufacturing, and it is hard to be disturbed by induction of external electromagnetic waves.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention. This embodiment is different from the first embodiment in that an inductance is formed by a through via of a printed wiring board instead of attaching the inductance component 15. In FIG. 2, 21 is a three-terminal low-pass filter, 22 is a through via for forming inductance, 23 is a first wiring layer, 24 is a second wiring layer,
25 is a third layer GND layer, 26 is a fourth layer wiring layer, 27 is a connector, and 28 is a wiring on the substrate. When connecting the GND connection electrode 212 of the three-terminal low-pass filter 21 to the GND layer 25 on the printed circuit board, a plurality of through vias (Via) 22 are provided on the printed circuit board, and the plurality of through vias 22 are connected in series. The wiring is applied to the first wiring layer 23 and the fourth wiring layer 26 as described above. As a result, an inductance is formed when the printed wiring board is manufactured, and the attenuation pole fa can be controlled without increasing the cost of parts. FIG. 3 shows a calculated value of the inductance when the dielectric constant is εr = 4.7 in a generally used multilayer printed wiring board. From the table of FIG. 3, a via having an inner diameter of 0.6 (V) which is generally used on a substrate having a thickness of 1.6 mm is generally used.
ia) is about 4.29 nH. Therefore, the inductance formed by the printed circuit board is expressed as follows in the case of a four-layer board.

L = 4.29 × N + 4.29 × (A / 1.6) + B × C L: Sum of inductances N: Number of through vias (Via) A: Surface wiring layer or rear wiring layer to inner layer ground plane Distance to. B: Wiring length C: Inductance per unit length Therefore, when four through vias (Via) are used, about 20
nH is generated, which is an inductance value necessary and sufficient to obtain an attenuation pole in a high band.

According to the present embodiment, inductance can be generated by connecting in series through vias usually used in a multilayer printed wiring board, and the attenuation pole fd can be controlled by the pattern of the multilayer printed wiring board.

(Third Embodiment) FIG. 4 shows a third embodiment. In a thin printed wiring board 45 such as a PC card (PCMCIA-CARD), even if a through via is used, the inductance hardly reaches a desired value. Therefore, a spiral pattern 42 is formed by a wiring pattern of a printed circuit board, and a through via 43 is arranged at the center to increase the inductance. With this structure, the characteristics can be improved even in a thin printed wiring board.

(Fourth Embodiment) FIG. 5 shows a fourth embodiment. In this embodiment, the multilayer wiring layers 51, 52, 53,
A three-terminal low-pass filter 59 is mounted on the substrate having the wiring 54, and the middle point between the wiring 57 and the wiring 58 provided in the second layer 52, the wiring 58
7 and 58 are connected to a spiral coil formed by an inner layer blind via 56. The value of the inductance can be adjusted by the spiral pattern,
Since the attenuation pole fd can be accurately controlled, it is possible to obtain a filter having very little variation in characteristics due to a manufacturing method and having excellent frequency characteristics.

(Fifth Embodiment) FIG. 6 shows a fifth embodiment. This example has a configuration in which one end of a thinned zigzag wiring portion 65 in which a narrow wire is zigzag-wired at the midpoint of a three-terminal ferrite filter 61 is connected, and the other end is connected to a GND plane connection via. Since the inductance is generated by the thinned zigzag wiring section 65, the wiring board can be mounted even on a wiring board of a small device having a small space.

[0020]

According to the present invention, when components are mounted on a printed wiring board, the capacitor portion of the three-terminal low-pass filter including the inductance portion and the capacitor portion is not directly connected to the ground, but via the inductance component. To connect to the ground, or to generate a predetermined inductance by the wiring pattern on the printed wiring board and the through via, so that the resonance point due to the capacitance of the capacitor part and the inductance of the inductance component or the inductance generated as described above. Since the attenuation pole fd can be generated, it can be controlled to improve the frequency characteristics. Further, according to the present invention, since a predetermined inductance is generated by the wiring pattern on the printed wiring board and the through via, a smaller size and characteristic variation are required as compared with the case where the inductance is formed by winding a conventional ground wire. It is possible to obtain a low-pass filter which is less affected by electromagnetic waves and less affected by electromagnetic waves.

[Brief description of the drawings]

1 (a) to 1 (c) are views showing a first embodiment of the present invention,

FIGS. 2A and 2B are diagrams showing a second embodiment of the present invention;

FIG. 3 is a diagram showing inductance values of vias used in a multilayer printed wiring board;

FIG. 4 is a view showing a third embodiment of the present invention;

FIG. 5 is a diagram showing a fourth embodiment of the present invention;

FIG. 6 is a diagram showing a fifth embodiment of the present invention;

FIG. 7 is a diagram showing an equivalent circuit of a general three-terminal low-pass filter;

FIG. 8 is a diagram showing a characteristic example of a three-terminal low-pass filter;

FIG. 9 is a diagram showing an equivalent circuit of a three-terminal low-pass filter that also takes into account the stray capacitance of the coil;

FIG. 10 is an equivalent circuit of a conventional example using a parallel capacitance CP for frequency improvement,

FIG. 11 is an equivalent circuit of a conventional example using a series inductance for frequency improvement,

FIG. 12 is a characteristic diagram for explaining characteristic improvement by series inductance;

FIG. 13 is an equivalent circuit diagram for explaining a problem of a conventional example,

FIG. 14 is a characteristic diagram for explaining a problem of the conventional example.

[Explanation of symbols]

L: inductance part, C: capacitor part, fa: attenuation pole, fc: cut-off frequency, Cs: floating capacitance part, Cp
... Parallel capacitance part, Ls ... Series inductance part, fa ... Attenuation pole, fc ... Cutoff frequency, fd ... New attenuation pole, M ...
Mutual inductance part, Cm ... mutual conductance, 1
1 ... 3-terminal low-pass filter, 111 ... signal input electrode,
112: GND connection electrode, 113: Signal output electrode, 12
... printed circuit board signal wiring, 13 ... inductance component, 1
Reference numeral 4 denotes a via for connection to a GND surface of a printed wiring board, 15 denotes a printed circuit board, 21 denotes a three-terminal low-pass filter, 211 denotes a signal input electrode, 212 denotes a GND connection electrode, 213 denotes a signal output electrode, 22 denotes a through via, and 23 denotes a first. Layer wiring layer, 24 second layer power supply layer, 25 third layer GND layer, 26 fourth layer wiring layer, 27 connector, 28 wiring, 41 three-terminal low-pass filter, 42 spiral wiring, 43: through via, 44: wiring from components, 45: PC card board 51: first layer, 52: second layer, 53: third layer, 54: fourth layer GND layer, 55: via, 56: inner layer Blind via, 57: second layer wiring, 58: third layer wiring, 59: three-terminal low-pass filter, 61: three-terminal low-pass filter,
62: printed circuit board wiring, 63: thinned zigzag wiring section, 64: GND plane connection via.

Claims (2)

[Claims] 1. A three-terminal low-pass filter having a force terminal, an output terminal, and a ground terminal, an inductance portion formed between an input terminal and an output terminal, and a capacitor portion formed between an intermediate portion of the inductance portion and a ground terminal. A low-pass filter provided on a printed wiring board, wherein an inductance component is mounted between the ground terminal and the ground of the printed wiring board. 2. A three-terminal low-pass filter having an input terminal, an output terminal, and a ground terminal, an inductance part formed between the input terminal and the output terminal, and a capacitor part formed between the middle of the inductance part and the ground terminal. A low-pass filter provided on a printed wiring board, wherein a predetermined inductance is generated between the ground terminal and the ground of the printed wiring board by a wiring pattern and a through via.