JP2707851B2 - Electromagnetic interference filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic interference filter for protecting digital equipment from high frequency noise.

[0002]

2. Description of the Related Art As an electromagnetic interference filter of this type, there is, for example, a .pi.-type filter having two capacitors and one coil. Conventionally, in this π-type filter, one capacitor forming layer and one coil forming layer are integrally laminated, and two capacitors are collectively arranged in one capacitor forming layer. That is, the two capacitors have a common ground-side capacitance electrode, and this ground-side capacitance electrode is electrically connected to one external ground electrode provided on the surface of the filter.

FIG. 9 is an equivalent electric circuit diagram of this filter, in which the residual inductance generated at each electrode is also shown. Here, (A) and (B) are external input / output electrodes,
(C) is the external ground electrode, L (21) is the inductance of the coil, C (21) and C (22) are the capacitances of the capacitors, and L (22) and L (23) are the signal-side capacitance electrodes of the capacitors. The generated residual inductance, L (24), is the residual inductance generated on the ground-side capacitance electrode of the capacitor, and L (25) is the residual inductance generated on the external ground electrode (C).

Normally, when a noise signal is input from the external input / output electrode (A), this noise signal
(22), and flows from the external ground electrode (C) to the ground through the capacitance C (21) and the residual inductances L (24) and L (25). However, as the frequency of the noise signal increases, the residual inductance L
(24), due to the effect of L (25) ,
Impedance of inductance L (24), L (25)
The residual inductance L that was initially designed
(24) and the total impedance of L (25)
The capacitance C (22) and the residual inductance L (2
3) The difference from the total impedance of
As a result, the noise signal goes around the capacitance C (22) and the residual inductance L (23) and is transmitted to be output from the external input / output electrode (B), thereby deteriorating the characteristics as a filter. Was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electromagnetic interference filter having an excellent noise removing effect in a high frequency region by reducing the influence of a residual inductance generated on a capacitance electrode and an external electrode on the ground side. is there.

[0006]

In order to solve the above problems, an electromagnetic interference filter according to the present invention has a capacitor forming layer disposed on both sides of a coil forming layer, and each capacitor forming layer has a signal side capacitor electrode. and a capacitor having a ground-side capacitance electrode, the ground-side capacitance electrodes said co
And electrically connected to external ground electrodes divided for each capacitor .

[0007] The capacitor forming layer is divided into a structure having a ground-side capacitance electrode for each capacitor from a conventional structure having a common ground-side capacitance electrode.

Further, the external ground electrode is divided.
Because, even residual inductance generated in the external ground electrodes Ru is separated for each <br/> capacitor. Therefore, the noise signal input from the external input / output electrode is hardly affected by the residual inductance generated in the capacitance electrode on the ground side of the capacitor and the external ground electrode, and the noise signal does not wrap around.
This makes it easier for noise signals to flow to the ground.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the electromagnetic interference filter according to the present invention will be described below with reference to the accompanying drawings. First Embodiment, FIGS. 1 to 4 FIG. 1 is an exploded perspective view of a π-type electromagnetic interference filter having two capacitors and one coil. The coil forming layer 3 is laminated between the capacitor forming layers 1 and 2.

[0010] The capacitor forming layer 1 is composed of capacitor electrodes 18, 1
9 are provided, and dielectric dummy sheets 8 sandwiching these from above and below are provided.
The lead portions 18a and 19a of the capacitance electrodes 18 and 19 are exposed on the right side of the dielectric sheet 4 and the front and back sides of the dielectric sheet 5, respectively. In the state of being laminated,
The capacitor forming layer 1 has a capacitance C (2) [see FIG. 3] between the capacitance electrodes 18-19.

Similarly, the capacitor forming layer 2 is composed of dielectric sheets 6 and 7 provided with capacitance electrodes 20 and 21 and a dielectric dummy sheet 8 sandwiching these from above and below. The lead portions 20a and 21a of the capacitance electrodes 20 and 21 are
The dielectric sheet 6 is exposed on the front and rear sides of the dielectric sheet 6 and on the left side of the dielectric sheet 7, respectively. In the stacked state, the capacitor forming layer 2 has a capacitance C (1) between the capacitance electrodes 20-21 (see FIG. 3).

The coil forming layer 3 includes a magnetic sheet 9 provided with a conductor pattern 22 acting as a wire coil, and a magnetic dummy sheet 10 sandwiching the magnetic sheet 9 from above and below. Leader portions 22a, 22 at both ends of conductor pattern 22
a are exposed on the left and right sides of the magnetic sheet 9 respectively. The capacitor electrodes 18, 19, 20, and 21 and the conductor pattern 22 are formed by printing Ag, Ag-Pd conductive paste, or the like by printing or the like. Further, as necessary, a larger number of sheets provided with capacitor electrodes and conductor patterns may be used and laminated.

Each of the sheets 4 to 10 is stacked and integrally laminated by press working. Next, as shown in FIG. 2, the laminated electromagnetic interference filter 23 has conductive pastes of Ag or the like applied to both ends and a central part thereof with electrodes 21a and 22a.
The electrodes 18a, 22a and the electrodes 19a, 20a are applied in a conductive state, and are baked to form external input / output electrodes (A),
(B) and an external ground electrode (C).

FIG. 3 is an equivalent electric circuit diagram of the filter 23 thus obtained. Here, L (1) is the inductance of the coil formed in the coil forming layer 3, C (1), C
(2) is the capacitance of the capacitor formed on the capacitor forming layers 1 and 2, respectively, L (2) and L (3) are the residual inductances generated on the signal-side capacitance electrodes 21 and 18 of the capacitor, respectively, L (4) and L (4) L (5) is the residual inductance generated on the ground-side capacitance electrodes 20 and 19 of the capacitor, and L (6) is the residual inductance generated on the external ground electrode (C). The residual inductances L (4) and L (5) form a series circuit with the capacitances C (1) and C (2) of the capacitors, respectively. Therefore, the external input / output electrode (A) [or (B)]
The residual inductance that makes it difficult for the noise signal that has entered from flowing to the ground to compare with the filter of the conventional structure
It becomes smaller by the residual inductance generated in the ground-side capacitance electrode of the capacitor. As a result, the noise signal easily flows to the ground.

FIG. 4 is a graph showing the insertion loss characteristics of the filter 23 thus obtained in comparison with a conventional filter.
The dashed line 24 indicates the insertion loss characteristics of the filter 23. Dotted line 26 shows the insertion loss characteristics of the conventional filter. The filter of this embodiment has a larger insertion loss in the high frequency region than the conventional filter.
That is, it is shown that the filter 23 of the present embodiment exhibits an excellent noise removing effect in a high frequency region.

[Second Embodiment, FIGS. 5 to 8] The filter of this embodiment is obtained by dividing the external ground electrode of the π-type electromagnetic interference filter shown in the first embodiment into two parts. Capacitance electrodes 28 and 30 are provided on the upper surfaces of the dielectric sheets 4 and 5. Leader portions 28a, 30a of these capacitance electrodes 28, 30
Are the right side of the dielectric sheet 4 and the dielectric sheet 5
It is exposed at a position near the center right of the front and back sides of the camera. In the stacked state, the capacitor forming layer 1 has a capacitance C (4) between the capacitance electrodes 28-30 (see FIG. 7). Similarly, capacitance electrodes 32, 34 are provided on the upper surfaces of the dielectric sheets 6, 7, and the lead-out portions 32a, 34a of the capacitance electrodes 32, 34 are respectively located on the front side and the back side of the dielectric sheet 6. Is exposed to the left of the center and to the left side of the dielectric sheet 7. In the stacked state, the capacitor forming layer 2 has a capacitance C (3) between the capacitance electrodes 32-34.

As shown in FIG. 6, the laminated electromagnetic interference filter 36 has electrodes 22a, 3
4a, electrodes 22a and 28a, electrode 32a and electrode 30a
External input / output electrodes (A), (B) electrically connected to
And external ground electrodes (C) and (C ′).
FIG. 7 is an equivalent electric circuit diagram of the filter 36 thus obtained. Here, L (1) is the inductance of the coil formed in the coil formation layer 3, C (3) and C (4) are the capacitances of the capacitors formed in the capacitor formation layers 1 and 2, respectively, L (7), L (8) is the residual inductance generated on the signal-side capacitance electrodes 34, 28 of the capacitor, L (9), L (10) is the residual inductance generated on the ground-side capacitance electrodes 32, 30 of the capacitor, respectively, L (11) ) And L (12) are residual inductances generated in the external ground electrodes (C) and (C ′), respectively. The residual inductances L (9) and L (11) and the residual inductances L (10) and L (12) form a series circuit with the capacitances C (3) and C (4) of the capacitors, respectively. Therefore, for example, a noise signal input from the external input / output electrode (A) is affected by residual inductances L (9) and L (11) generated in the capacitor electrode 32 on the ground side of the capacitor and the external ground electrode (C). Almost no noise, which reduces signal noise wraparound.
As a result, the filter 36 allows the noise signal to flow more easily to the ground than the filter shown in the first embodiment.

FIG. 8 is a graph showing the insertion loss characteristics of the filter 36 thus obtained in comparison with the conventional one and the first embodiment. A solid line 38 indicates the insertion loss of the filter 36 of the present embodiment. Dotted line 26 and dashed line 24 show the insertion loss characteristics of the conventional filter and the filter of the first embodiment, respectively. FIG. 8 shows that the filter 36 of the present embodiment exerts an excellent noise removing effect in a higher frequency range.

The electromagnetic interference filter according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, all the sheets may be dielectric sheets or magnetic sheets.

[0020]

As is apparent from the above description, according to the present invention, since the ground-side capacitance electrode and the external ground electrode of the capacitor are divided for each capacitor, the residual inductance generated at each electrode is divided and the signal is divided. Neu
Thus, it is possible to obtain an electromagnetic interference filter which suppresses the rounding of noise and has an excellent noise removing effect in a high frequency region.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a first embodiment of an electromagnetic interference filter according to the present invention.

FIG. 2 is a perspective view showing the appearance of the electromagnetic interference filter shown in FIG.

FIG. 3 is an equivalent electric circuit diagram of the electromagnetic interference filter shown in FIG.

FIG. 4 is a graph showing insertion loss characteristics of the electromagnetic interference filter shown in FIG.

FIG. 5 is an exploded perspective view showing a second embodiment of the electromagnetic interference filter according to the present invention.

FIG. 6 is an exemplary perspective view showing the appearance of the electromagnetic interference filter shown in FIG. 5;

7 is an equivalent electric circuit diagram of the electromagnetic interference filter shown in FIG.

8 is a graph showing the insertion loss characteristics of the electromagnetic interference filter shown in FIG.

FIG. 9 is an equivalent electric circuit diagram showing a conventional example.

[Explanation of symbols]

 1, 2, capacitor forming layer 3, coil forming layer 4, 5, dielectric sheet 9, magnetic sheet 18, 21, signal-side capacitive electrode 19, 20 ground-side capacitive electrode 22, conductor pattern 23, electromagnetic interference filter 28 , 34: signal-side capacitance electrode 30, 32: ground-side capacitance electrode 36: electromagnetic interference filter (A), (B): external input / output electrode (C), (C '): external ground electrode

Claims (1)

(57) [Claims] 1. An electromagnetic interference filter in which a coil forming layer and a capacitor forming layer form an integrated laminated structure, and an external input / output electrode and an external ground electrode are provided on a surface of the integrated laminated structure. Place capacitor forming layers on both sides of
Each of the capacitor forming layers has a capacitor having a signal-side capacitance electrode and a ground-side capacitance electrode, and the ground-side capacitance electrode is divided into external ground electrodes for each of the capacitors.
An electromagnetic interference filter which is electrically connected to each of the poles .