JP2000012382A - Composite capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite capacitor for reducing a radiation noise without being associated with any concern such as the increase of inductance in the case of using a plurality of capacitors for extending a frequency band which is made effective as a by-pass capacitor or the like as much as possible. SOLUTION: Plural, for example, two capacitors C1 and C2 with different capacities which care connected in parallel are integrated with a pair of terminals T1 and T2 at both the ends so that any pattern components can be made unnecessary. Therefore, even when the plurality of capacitors C1 and C2 are used, the inductance can be made minimum, and the impedance can be reduced across a wide band. Thus, a radiation noise reduction effect can be realized. At the same time, those capacitors are integrated with the pair of terminals T1 and T2 at the both ends so as to be handled as a composite capacitor 1 as one part, and the increase of the number of parts can be prevented, and any trouble at the time of mounting this on a print circuit board or the like can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite capacitor in which radiation noise reduction measures are taken.

[0002]

2. Description of the Related Art Generally, electronic circuit components in electronic equipment products are mounted on a printed circuit board. In recent years, most printed circuit boards that have been converted into digital circuits are constituted by digital circuits that require a basic clock. Often done. Unwanted electromagnetic waves are radiated from various wiring patterns such as a digital IC mounted on such a printed circuit board, a bus line for controlling a signal such as a basic clock pattern, and an address line. If it exceeds the legal limit, it cannot be commercialized.

In order to suppress the generation of such radiation noise, a bypass capacitor or a decoupling capacitor is generally used for each IC on a printed circuit board.

[0004] A capacitor for such an application usually has a lead inductance, and cannot be regarded as a capacitor above a resonance frequency determined by the lead inductance and the capacitor capacity. The same result is obtained even with a chip-type capacitor having no lead wire because the pattern on the printed circuit board connected to the capacitor has inductance.

[0005] In recent years, in increasing the clock frequency, it is almost impossible to provide a single capacitor with impedance characteristics as a capacitor up to the 1 GHz band, which is the highest frequency regulated by law, and to have a noise suppressing effect. Impossible.

For this reason, in order to expand a frequency band effective as a bypass capacitor as much as possible, two or more capacitors having different capacities are arranged and used in parallel.

[0007]

However, when a plurality of capacitors are arranged on a printed circuit board as described above,
There is a drawback that the number of parts increases and a large printed circuit board area is required. This means that a plurality of bypass capacitors are arranged for each IC mounted on the printed circuit board, and the number of the capacitors becomes extremely large, so that components cannot be mounted on a predetermined printed circuit board size. Etc., etc.

Further, when arranging a plurality of such capacitors, since the capacitors are arranged via a printed pattern, the inductance due to these patterns causes a decrease in the resonance frequency. However, there is a disadvantage that the frequency band cannot be expanded as much as desired by the effect of the bypass capacitor.

When a plurality of capacitors are used in parallel, an anti-resonance point always appears besides the series resonance due to the inductance of each capacitor, and at this point the impedance becomes infinite in principle, and at this frequency, It will not function as a capacitor at all (literature…
Kenichi Ito "Earth and Solid Patterns" Nikkan Kogyo Shimbun pp.
137-191).

Therefore, as a countermeasure against this, as described in the above-mentioned document, by connecting a resistor in series to a capacitor, the peak of the impedance at the anti-resonance point can be reduced, and the low-impedance band can be broadened. There is a method to achieve this. However, the above-mentioned problem (increase in the number of parts, etc.) becomes more prominent, and the disadvantage becomes greater.

Accordingly, an object of the present invention is to provide a composite capacitor capable of reducing radiation noise by using a plurality of capacitors without causing the above-described problem.

[0012]

According to the first aspect of the present invention,
A plurality of capacitors connected in parallel and having different capacities were integrated by a pair of terminals at both ends. Therefore, although a plurality of capacitors are used, the inductance is minimized, and there is no influence from the lead inductance or pattern of each capacitor, so that the impedance can be reduced over a wide band, and the radiation noise suppressing effect can be achieved. Can be demonstrated. Further, since a pair of terminals are integrated at both ends, although a plurality of capacitors are used, they can be handled as one component without increasing the number of components, and there is no hindrance to mounting on a printed circuit board or the like.

According to a second aspect of the present invention, in addition to the composite capacitor of the first aspect, there is provided a resistor connected in series to at least a part of the plurality of capacitors and integrated therewith. Therefore, in addition to the composite capacitor according to the first aspect, there is no peak at the anti-resonance point, the impedance can be kept low over a wide band, and a further radiation noise suppressing effect can be obtained.

According to a third aspect of the present invention, in the composite capacitor according to the first or second aspect, the lead-out location of the terminal is:
It is set at both ends of the capacitor having the smallest capacity among the plurality of capacitors. Therefore, the impedance of the capacitor can be reduced over a wide band without causing a decrease in the resonance frequency of the capacitor having the smallest capacitance.

[0015]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. FIG. 1 shows an equivalent circuit of a composite capacitor 1 according to the present embodiment. A plurality of capacitors having different capacities, for example, two capacitors C ₁ and C ₂ are connected in parallel, and these capacitors C ₁ and C ₂ are connected at both ends. A pair of terminals T
It is integrated in _1, T _2. FIG. 2 shows each capacitor C
FIG. 2 is an external perspective view showing a practical configuration example of a composite capacitor 1 in the case where ₁ and C ₂ are configured by chip capacitors.

According to the present embodiment, although _two capacitors C ₁ and C ₂ are used, the inductance is minimized, and there is no influence from the lead inductance and pattern of each of the capacitors C ₁ and C _2. Thus, the impedance can be reduced over a wide band. Therefore, the radiation noise suppression effect can be exhibited by using the _two capacitors C ₁ and C ₂ as originally intended. Furthermore, since the composite capacitor 1 is integrated with the pair of terminals T ₁ and T ₂ at both ends, the plurality of capacitors C ₁ and C ₂ can be used as one component even though a plurality of capacitors C ₁ and C ₂ are used. There is no hindrance in mounting on a circuit board or the like.

In constructing such a composite capacitor 1, it is necessary to reduce the impedance effectively so that the noise suppressing effect can be exerted over a wide frequency band from several MHz to 1 GHz. In, the capacity of a plurality of capacitors to be used,
For example, 0.01 μF, 0.001 μF, 100 pF,
It is preferable to make the difference about 10 times, such as 10 pF,.

A second embodiment of the present invention will be described with reference to FIGS. The same portions as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments). FIG. 3 shows an equivalent circuit of the composite capacitor 2 of the present embodiment, wherein resistors R ₁ and R ₂ are connected in series to a plurality of capacitors having different capacities, for example, two capacitors C ₁ and C ₂ . , Each CR
A series circuit is connected in parallel, and both ends are integrated by a pair of terminals T ₁ and T ₂ . FIG. 4 is an external perspective view showing a practical configuration example of the composite capacitor 2 when each of the capacitors C ₁ and C ₂ is configured by a chip capacitor.

Here, when the resistance values of the resistors R ₁ and R ₂ are set to several Ω to several tens Ω, the noise suppressing effect can be obtained most. However, the capacitor C ₁ or C _{2 used}
If the resistance of the capacitor is low and a resistor is not required, a resistor may not be connected to the corresponding capacitor.

According to the present embodiment, in addition to the effect of the first embodiment, since the resistor is connected in series with the capacitor as necessary and integrated, the peak of the anti-resonance point is obtained. Therefore, the impedance can be kept low over a wide band, and a further radiation noise suppression effect can be obtained. For example, in a composite capacitor configuration according to FIGS. 3 and 4, three CR series circuits are used, and three types of capacitors having respective capacitances of 0.01 μF, 470 pF, and 47 pF are used, and each lead inductance is set to 10 n.
H, a resistor R inserted in series with each capacitor
Are 0.01Ω, 0.1Ω, 1Ω, 2Ω, 4Ω,
FIG. 5 shows an example of the calculated value of the impedance Z of the composite capacitor 2 when it is changed to 10Ω and 20Ω. According to this result, it can be seen that by selecting the resistance value to be several Ω, the flat characteristic can be provided without the impedance at the anti-resonance frequency becoming unnecessarily large.

In constructing the composite capacitor 2 of the present embodiment, in addition to the structure shown in FIG. 4, at present, a C + R integrated with a capacitor and a resistor in one chip is provided. Since the composite component is also commercialized, a structure using such a C + R composite component may be used (in this case, a structure similar to that of FIG. 2 is obtained as a result).

A third embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a composite capacitor 1 forming an equivalent circuit as shown in FIG. 1, wherein a plurality of, for example, two capacitors C ₁ and C ₂ have a pair of capacitances C ₁ ≪C ₂ . A configuration example is shown in which the terminal T ₁ and T ₂ are led out from the capacitor C ₁ having the smaller capacitance.

According to the present embodiment, without lowering the minimum resonance frequency of the capacitor C ₁ of the capacitor, it can be low impedance composite capacitor 2 over a wide band. For example, using a numerical example, as described in the literature in the conventional example, when the capacitance of the smaller capacitor is 470 pF and its lead inductance is 1 nH, the resonance frequency is about 230 M
Hz, the resonance frequency is reduced to about 73 MHz when the lead inductance value of the capacitor having the larger capacitance is set to 10 nH. However, according to the present embodiment, the resonance frequency is reduced. There is no.

FIG. 7 shows a configuration example of a composite capacitor 3 in the case where lead-type capacitors are used as the capacitors C ₁ , C ₂ and C ₃ as a modification of the present embodiment.
Here, the capacitance of the capacitors C ₁ , C ₂ , C ₃ is C ₁ ＣC
₂ and C ₃ . In this case, the terminals T ₁ and T ₂ as the composite capacitor 3 are set at both ends of the capacitor C ₁ having the smallest capacity, and the other capacitors C ₂ and C ₃ are connected to the terminals T ₁ and T ₂ via the leads 4 a and 4 b.
Is integrated with configuration connected in parallel to the _1, T ₂ side. Also in the case of this modification, the same effect as that described in FIG. 6 can be obtained.

In the structure shown in FIGS. 6 and 7,
Of course, the portions indicated by C ₁ , C ₂ and C ₃ may be replaced with a series circuit of a capacitor and a resistor or their C + R composite parts as in the second embodiment.

In each of these embodiments, the number of capacitors connected in parallel is not limited to two or three.
Needless to say, the number can be appropriately set as needed.

[0027]

According to the first aspect of the present invention, a plurality of capacitors connected in parallel with different capacities are integrated by a pair of terminals at both ends, so that a plurality of capacitors are used, but the inductance is minimized. It is not affected by the lead inductance or pattern of each capacitor, so that low impedance can be achieved over a wide band, radiation noise suppression effect can be exhibited, and Since these terminals are integrated with each other, they can be handled as a single component, that is, a composite capacitor, so that the number of components does not increase and there is no hindrance to mounting on a printed circuit board or the like.

According to the second aspect of the present invention, since the integrated capacitor has a resistor connected in series to at least a part of the plurality of capacitors and integrated therewith, the effect of the composite capacitor according to the first aspect is added. As a result, there is no peak at the anti-resonance point, the impedance can be kept low over a wide band, and a further radiation noise suppressing effect can be obtained.

According to the third aspect of the present invention, the lead-out portion of the terminal is set at both ends of the capacitor having the smallest capacitance among the plurality of capacitors. In addition, the impedance of the capacitor can be reduced over a wide band without causing a decrease in the resonance frequency of the capacitor having the smallest capacitance.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a composite capacitor according to a first embodiment of the present invention.

FIG. 2 is an external perspective view showing a configuration example of the composite capacitor.

FIG. 3 is an equivalent circuit diagram of a composite capacitor according to a second embodiment of the present invention.

FIG. 4 is an external perspective view showing a configuration example of the composite capacitor.

FIG. 5 is a characteristic diagram showing frequency characteristics of impedance when a resistance value is changed.

FIG. 6 is an external perspective view illustrating a configuration example of a composite capacitor according to a third embodiment of the present invention.

FIG. 7 is an external perspective view illustrating a configuration example of a composite capacitor according to a modification.

[Explanation of symbols]

C ₁ , C ₂ , C ₃ capacitors T ₁ , T ₂ terminals R ₁ , R ₂ resistance

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shigenobu Airokawa 3 Tomei Ricoh Co., Ltd., Shinmei-do, Nakaname, Shibata-cho, Shibata-gun, Miyagi Prefecture F-term (reference) in 1 Tohoku Ricoh Co., Ltd. 3 No. 1 Jinmyodo 5E082 BC40 CC01 DD01 GG01 JJ09 JJ15 LL13 LL15

Claims (3)

[Claims] 1. A composite capacitor in which a plurality of capacitors connected in parallel and having different capacities are integrated by a pair of terminals at both ends. 2. The composite capacitor according to claim 1, further comprising a resistor connected in series to at least a part of the plurality of capacitors and integrated. 3. The composite capacitor according to claim 1, wherein the terminal extraction points are set at both ends of a capacitor having the smallest capacitance among the plurality of capacitors.