JP3158529B2 - Noise 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 noise filter using a sintered body having varistor characteristics, and more particularly to a noise filter having a structure in which a varistor is combined with a resistor.

[0002]

2. Description of the Related Art In recent years, with the development of microcomputers, microcomputers are mounted on all kinds of devices such as industrial equipment, home electric appliances and communication equipment. Since digital control processing is performed in a device on which a microcomputer is mounted, there is a risk of destruction or malfunction due to noise, and an accident due to noise has actually occurred. The path through which noise enters the equipment is often the power supply portion and the signal wiring portion, and thus the role of the noise filter used in the input / output portion is regarded as important. EM
In order to solve the problem of the I noise, it is necessary that the noise is not emitted from the device and does not enter the device. It is common that noise enters and exits via electric wires. Therefore, a method of connecting a noise filter to electric wires in the vicinity of a device input / output unit is often used.

Conventionally used noise filters include (a) a filter using a capacitor element, (b) a combined capacitor-inductor system, (c) a filter using an inductor element, and (d) a varistor. Some use elements. The device using the capacitor (a) is excellent in removing minute noise, but the capacitor alone cannot absorb a high-voltage pulse such as static electricity, and the device is destroyed based on the high-voltage pulse. And malfunctions could not be prevented. The combined capacitor-inductor noise filter (b) is suitable for absorbing white noise. The device using the varistor element (d) is suitable for absorbing transient noise. However, noise absorption in the signal line is closely related to the frequency of the signal. Recently, digitalization has progressed, so that large distortion must not occur in the waveform. Therefore, if the capacitance is too large, it cannot be used as a signal line noise filter.
Since the withstand voltage of the IC is about 60 to 70 V, it is necessary to suppress noise components below this.

The capacitor-inductor type noise filter has no problem in terms of capacitance, but has a problem in that it allows transient noise in the resonance frequency band to pass through as it is and cannot protect the circuit. In the case of high-voltage noise, the waveform can be changed, but the peak value cannot be suppressed significantly. On the other hand, in the case of using a varistor element, the capacitance is 500 pF or more, and when a signal of several hundred KHz to several tens MHz such as a signal line is handled, even the signal may be absorbed or deformed. Therefore, at present, varistors are not often used as noise removing elements for signal lines.

The present inventors have previously proposed a noise filter which has a reduced capacitance while making use of the characteristics of a varistor element having excellent transient noise absorption and which is unlikely to cause signal absorption or deformation. (Japanese Patent Application No. 1-16373)
No. 0). This noise filter is configured using a sintered body obtained by laminating a plurality of ceramic green sheets having varistor characteristics with electrodes interposed therebetween and integrally firing them. That is, the common electrode is formed in the sintered body so as to extend from the first portion to the second portion on the side surface of the sintered body made of semiconductor ceramic.
Then, at a height position separated from the common electrode by the sintered body layer in the thickness direction, at least one through electrode extends from the third portion to the fourth portion on the side surface of the sintered body. And are formed so as to cross the common electrode.

In this noise filter, since the common electrode and the through electrode are arranged so as to intersect in the sintered body, the electrode overlapping area in the varistor characteristic portion is reduced, and thus the capacitance is reduced. ing.
Furthermore, by utilizing the properties of the sintered body having varistor characteristics as a dielectric, it has both noise absorption performance as a capacitor and noise absorption performance as a varistor, so that various noises can be effectively eliminated. It is possible to absorb.

[0007]

Generally, the response speed of a varistor is said to be 1 ns or more. Therefore, when transient noise of less than 1 nsec enters, the varistor cannot sufficiently absorb the transient noise. Therefore, in the above-described noise filter of the prior art, the response speed of the varistor is not sufficient, so that the noise in the rising portion cannot be effectively absorbed.

It is an object of the present invention to provide a noise filter having a structure capable of effectively absorbing noise in a rising portion while having a noise absorbing performance as a capacitive varistor.

[0009]

SUMMARY OF THE INVENTION A noise filter according to the present invention is formed using a sintered body having varistor characteristics. As a sintered body having such varistor characteristics,
Conventionally known semiconductor ceramics are used. In the noise filter of the present invention, at least one common electrode is formed so as to extend from the first portion to the second portion on the side surface of the sintered body. This common electrode may be formed in the sintered body, or may be formed on the outer surface of the sintered body. The expression of the first portion and the second portion of the side surface refers not only to the configuration in which the common electrode is formed between different side surfaces, but also to the configuration in which the common electrode is formed to extend between different portions on the same side surface. Is also included.

In the noise filter of the present invention, at least one line electrode intersects the common electrode at a height position separated from the common electrode via the sintered body layer in the thickness direction of the sintered body. Thus, it is formed so as to extend from the third portion on the side surface of the sintered body toward the fourth portion. Therefore, as in the case of the above-described noise filter of the related art, since the common electrode and the line electrode are arranged so as to intersect with the sintered body layer interposed therebetween, the overlapping area between the two electrodes in the varistor characteristic portion is reduced. The capacitance has been reduced so that the capacitance has an appropriate value. In addition, by utilizing the properties of the sintered body having varistor characteristics as a dielectric, it has both noise absorption performance as a capacitor and noise absorption performance as a varistor, so that various noises can be effectively eliminated. It is configured to be able to absorb.

A feature of the noise filter according to the present invention is that in the noise filter, at least one line electrode is cut at at least one portion other than a portion intersecting with the common electrode, and portions on both sides of the cut portion are provided. The line electrodes are connected by a resistor layer. The resistor layer only needs to be arranged so as to electrically connect the partial line electrodes on both sides of the cut portion, and therefore, is formed so that both ends overlap the partial line electrodes on both sides of the cut portion. Alternatively, the resistor layer may be formed on the lower surface side of the line electrode such that the partial line electrodes on both sides of the cut portion overlap the resistor layer. The resistor layer is generally configured to have a resistance of about several hundreds to several kilo-ohms, and can be made of any material that provides such electrical resistance.

However, in the case where the resistor layer is formed by baking the resistor paste during firing of the ceramic sintered body, the sintered body layer must be formed of a material that can withstand the firing temperature of the ceramic, such as palladium oxide. is necessary. When the resistor layer is formed on the surface of the sintered body after obtaining the sintered body having the varistor characteristic, the resistor layer can be made of an appropriate resistive material regardless of the firing temperature. Since the width of the cut portion of the line electrode, that is, the distance between the partial line electrodes on both sides of the cut portion, depends on the required resistance value and the material of the resistor layer used,
It cannot be uniquely limited. Further, a plurality of cut portions provided in the line electrode may be formed.

[0013]

In the noise filter of the present invention, the common electrode and the line electrode are separated by the sintered body layer and are arranged so as to intersect with each other. Noise can be effectively absorbed. Furthermore, in the noise filter of the present invention, at least a part of the line electrode is cut, and the resistor layer is connected between the partial line electrodes on both sides of the cut portion. High values can be suppressed. Therefore, it is possible to effectively absorb the rising portion of the noise.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described to clarify the configuration and effects of the noise filter of the present invention. First Example ZnO, Bi ₂ O having a purity of 99% or more was used as a raw material of a sintered body.
₃ , CoO, MnO _2, and Sb ₂ O ₃
Mol%, 0.5 mol%, 0.5 mol%, 0.5 mol%, and 0.5 mol% were weighed and mixed with pure water by a ball mill for 24 hours to obtain a mixture. Was. The obtained mixture was filtered and dried, and calcined at a temperature of 800 ° C. for 2 hours to obtain a calcined product. The obtained calcined product is pulverized and dispersed in a solvent together with an organic binder to form a ceramic or
A slurry was obtained.

The ceramic slurry obtained as described above was formed into a uniform ceramic green sheet having a thickness of 50 μm by a doctor blade method. This ceramic green sheet was punched into a rectangular shape having a predetermined size, and a plurality of ceramic green sheets 1 to 2 shown in FIG.
5 was obtained. The common electrode is printed on the upper surface of the ceramic green sheet 2 by printing a conductive paste mainly composed of an alloy made of silver-palladium from one end 2a to the other end 2b by a screen printing method. The conductive paste layer 6 for use was formed. The conductive paste layer 6 for a common electrode is baked in a firing step described later to complete a common electrode.

The ceramic green sheets 1 to 5 were laminated in the order shown in the drawing, pressed in the thickness direction, and fired at a temperature of 1000 ° C. for 2 hours to obtain a sintered body. Obtained sintered body 7
Is shown in FIG. In the sintered body 7, the above-mentioned conductive paste for a common electrode is baked at the time of firing to form the common electrode 6 in the form of an internal electrode. That is, the common electrode 6 extends from the first side surface 7a as the first portion of the sintered body to the second side surface 7b as the second portion. Next, the first side surfaces 7a and 7b of the sintered body 7 (FIG.
To cover the reference), to form a pair of terminal electrode conductive paste layer 8a, 8b and the partial line electrode conductive paste layer 9a ₁ ~9c ₂ shown in FIG. The terminal electrode conductive paste layer 8a, 8b and the partial line electrode conductive paste layer 9a ₁ ~9c ₂ is the surface of the sintered body 7, the silver - the electroconductive paste consisting essentially of palladium alloy is applied by a screen printing method It is formed by this.

The terminal electrode conductive paste layers 8a and 8b
And conductive paste layer 9a for line electrode₁~ 9c_TwoAfter
Baking by the baking process described above,
Configure poles and partial line electrodes. Conductor for partial line electrode
Electric paste 9a₁And conductive paste 9 for partial line electrode
a _TwoAre provided to constitute one line electrode 9a.
Conductive paste for both partial line electrodes
9a₁, 9a_TwoBetween the cut portions of the line electrode according to the present invention
Make up minutes. Conductive paste for other partial line electrodes
9b₁~ 9c_TwoThe same applies to. These part la
Conductive paste 9a for in-electrode₁~ 9c_TwoLa composed of
The in-electrodes 9a, 9b, 9c (see FIG. 4)
Side face 7c as a third part of the side face of the united body and fourth part
Formed on the upper surface of the sintered body 7 so as to connect the side surface 7d
And intersect with the common electrode 6 via the sintered body layer.
It is arranged so that. In addition, each of the above partial line electrodes
The region between them, ie, the cut portion, crosses the common electrode 6
It is located other than the part where it is.

Next, as shown in FIG.
Conductive paste 9a for in-electrode₁~ 9c_TwoA pair of
Covers the cut between the conductive pastes for the partial line electrodes
As described above, the resistance paste is applied by screen printing.
Thereby, the resistance paste layers 10a to 10c are formed.
Is done. For example, the resistance paste layer 10a has a partial line
Conductive paste layer 9a for electrode₁And conductive line for partial line electrode
Bust layer 9a_TwoAnd are connected to each other. Scold
After that, it is formed on the surface of the sintered body 7 at a temperature of 1000 ° C.
Baking each paste layer for 30 minutes
Electrodes 8a, 8b and partial line electrode 9a ₁~ 9a_TwoLine
Then, resistor layers 10a to 10c are formed. Further, FIG.
As shown in FIG.
The paste 11 is applied to the terminal electrodes 8a,
8b so as to cover most of the area sandwiched by
First embodiment by baking at a temperature of 800 ° C.
Is obtained.

In the obtained noise filter 12, both ends of each of the line electrodes 9a to 9c are used as input / output terminals.
By connecting the terminals 8a and 8b connected to the common electrode 6 to the ground potential, for example, three noise filter units shown in FIG. 1B are configured. That is, each noise filter unit is a three-terminal noise filter in which a resistor R based on the resistor layer is combined with a varistor.

Second Embodiment FIGS. 6 to 8 are perspective views for explaining a second embodiment. In the second embodiment, as shown in FIG. 6, a region where the common electrode 6 is provided on the upper surface of the sintered body 7 in parallel with the internal common electrode 6 but not so as to overlap with the common electrode 6. Are formed on both sides of the first resistor layer 13a, 13b. Then, as shown in FIG. 7, the first resistor layer 1
After forming 3a and 13b, each line electrode is formed by applying a conductive paste mainly composed of an Ag-Pd alloy. In the second embodiment, one line electrode 9a is composed of three partial line electrodes 9a ₁ ～9A _3. That is, one line electrode 9a has a configuration divided by two cutting portions. The other line electrodes 9b and 9c have the same configuration. As in the second embodiment, each line electrode may be configured to have two or more cut portions.

Further, as shown in FIG. 8A, after the line electrodes 9a to 9c are formed, the first resistor layer 1 is formed.
The second resistor layers 14a and 14b are formed on the region where the 3a and 13b are provided. Therefore, the partial line electrodes on both sides of the cut portion are connected by the upper and lower first and second resistor layers. For example, is sandwiched are connected to each other by a partial line electrode 9a ₁ and the partial line electrodes 9a ₂ is first resistor layer 13a and the second resistance layer 14a. Similarly, the first and second resistor layers 13 are provided between the other partial line electrodes.
a, 13b, 14a, and 14b. The noise filter of the second embodiment can be manufactured by similarly baking the glass paste 11 shown in FIG. 5 on the upper surface of the sintered body 7 shown in FIG. 8A. In the noise filter of the second embodiment, the first and second resistor layers 13a to 14b are provided on both sides of a portion of each of the line electrodes 9a to 9c crossing the common electrode 6. Therefore, the equivalent circuit of each noise filter unit is as shown in FIG.

Evaluation of the noise filters of the first and second embodiments
First obtained as valence above properties were measured in the noise filter of the second embodiment. The results are shown in Table 1 below. In Table 1, the symbol * represents 8/20 of the peak value of 30A.
The change rate of the varistor voltage when applying a triangular current wave of μ seconds is shown.

[0023]

[Table 1]

Using a commercially available noise simulator,
FIG. 9 shows an output waveform when a rectangular wave voltage pulse of 50 ns and 2 kV is applied. In FIG. 9, a solid line P and an alternate long and short dash line Q show output waveforms of the noise filters of the first and second embodiments, respectively, and a broken line R shows an output waveform of a conventional noise filter to which no resistor layer is connected. Show. As is clear from FIG. 9, the noise filters of the first and second embodiments effectively absorb the noise in the rising portion, whereas the conventional noise filter has a sufficient noise absorption performance in the rising portion. It turns out that it is not.

Modifications In the first and second embodiments, only the common electrode 6 is formed in the sintered body in the form of an internal electrode. However, the line electrode and the resistor layer are also arranged in the sintered body. It may be formed by simultaneous firing with a sintered body. However, when the line electrode and the resistor layer are simultaneously fired with the sintered body, it is necessary to consider a material such as a resistor paste in consideration of a shrinkage ratio and the like. In the first and second embodiments, each of the line electrodes 9a to 9c is formed on the upper surface of the sintered body 7, and the internal common electrode 6 is formed.
Although only the upper portion of the sintered body sandwiched between and is used as the varistor characteristic portion, a line electrode is similarly formed on the lower surface side of the sintered body 7, thereby forming more noise filter units. It is possible. Furthermore, although the common electrode 6 is configured in the form of an internal electrode, the same effect as in the first and second embodiments can be obtained even if the common electrode 6 is formed on the lower surface of the sintered body 7. . In addition, each line electrode 9a
9c may be formed in the sintered body 7 in the form of an internal electrode instead of the outer surface such as the upper and lower surfaces of the sintered body 7.

[0026]

As described above, according to the present invention, in a noise filter constituted by using a sintered body having varistor characteristics, a line electrode provided so as to intersect with a common electrode via a sintered body layer is provided. Is cut off, and the partial line electrodes on both sides of the cut portion are connected by a resistor layer, so that the noise absorption performance as a capacitive varistor with reduced capacitance and the output voltage peak value It is possible to provide a multi-function noise filter that has the performance of suppressing noise. Therefore, by using the noise filter of the present invention, it is possible to effectively absorb not only various types of noise but also noise in a rising portion.

[Brief description of the drawings]

FIGS. 1A and 1B are a perspective view and an equivalent circuit diagram of a noise filter according to a first embodiment, respectively.

FIG. 2 is an exploded perspective view for explaining shapes of a ceramic green sheet and a common electrode used for manufacturing the noise filter of the first embodiment.

FIG. 3 is a perspective view showing a sintered body.

FIG. 4 is a perspective view showing a state where a line electrode and a terminal electrode are formed.

FIG. 5 is a perspective view of a noise filter according to the first embodiment.

FIG. 6 is a perspective view for explaining a first resistor layer in the second embodiment.

FIG. 7 is a perspective view showing a state where a line electrode is formed on a first resistor layer.

8A is a perspective view of a noise filter according to a second embodiment, and FIG. 8B is an equivalent circuit diagram of the noise filter according to the second embodiment.

FIG. 9 is a diagram showing output waveforms of the respective noise filters of the first and second embodiments and the conventional example.

[Explanation of symbols]

6 Common electrode 7 Sintered body 7a, 7b First and second side faces as first and second parts 7c, 7d Third and fourth side faces as third and fourth parts 9a ～9C ... line electrodes _{9a 1, 9a 2 ~9c 1,} 9c 2 ... partial line electrodes 10,10a, 10b, 13a, 13b, 14a, 14
b: resistor layer

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Sakabe 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Prefecture Murata Manufacturing Co., Ltd. (56) References JP-A-3-89613 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01C 7/10 H01C 13/02 H03H 7/00

Claims (1)

(57) [Claims] 1. A sintered body made of a material having varistor characteristics, and a second part from a first portion on a side surface of the sintered body.
And a third electrode on a side surface of the sintered body so as to intersect with the common electrode across a sintered body layer in a thickness direction of the sintered body.
And at least one line electrode formed so as to extend from the portion to the fourth portion, wherein the line electrode is cut at at least one portion other than a portion intersecting the common electrode. A noise filter, wherein a resistor layer is provided so as to connect between partial line electrodes on both sides of the cut portion.