JP3408376B2 - Filter circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter circuit, and more particularly to a filter circuit for reducing unnecessary radiation of electromagnetic waves from electronic equipment.

[0002]

2. Description of the Related Art Conventionally, this type of filter circuit has been disclosed, for example, in "March 1992, EMC / EMI Handbook, 8".
As shown in "Page 0", it is used to reduce unnecessary emission of electromagnetic waves from electronic devices.

FIG. 9 is a schematic sectional view showing the structure of a conventional filter circuit. FIG. 10 is a circuit diagram showing an example of a circuit of an electronic device using a conventional filter circuit. Figure 9
10, reference numeral 90 is a connector for connecting a cable for connecting an electronic circuit to another device, 91 is a shield case for shielding an electromagnetic field generated by the electronic circuit, and 92 is a conductive connector housing built in the connector 90. Are conductors, 93 and 94 are terminals of the connector 90, 98 is a printed wiring board on which an electronic circuit is mounted, and 910 and 920 are through-types that serve as filters for reducing unnecessary radiation of electromagnetic waves from electronic devices. Capacitor, 931 is an electronic circuit,
932 is a cable, and 980 is a filter circuit.

The filter circuit 980 has a feedthrough capacitor 910 connected between a terminal 93 and a shield case 91 for shielding an electromagnetic field generated by the electronic circuit 931.
And a feed-through capacitor 920 connected between the terminal 94 and the shield case 91.
1 and the cable 932. Feedthrough capacitor 91
0 and 920 are connected to a shield case 91 by a conductor 92 which is a conductive connector housing built in the connector 90 as shown in FIG. The connector 90 is mounted on the printed wiring board 98 on which the electronic circuit 931 is mounted.

Next, the operation will be described. Terminals 93, 94
Is a power supply terminal of the electronic device or a signal input / output terminal. In the case of the power supply terminal, the harmonic components of the switching power supply built in the electronic circuit 931 and the electronic circuit 9
The harmonic component of the clock frequency used in 31 flows to the cable 932 through the terminals 93 and 94, so that it is radiated as an electromagnetic wave from the cable. In the case of the signal input / output terminal, the harmonic components of the signal and the harmonic components of the clock used in the electronic circuit 931 flow into the cable through the terminals 93 and 94, and are thus radiated as electromagnetic waves from the cable. The filter circuit 980 suppresses frequency components unnecessary for power supply and signal transmission, and reduces unnecessary radiation of electromagnetic waves from the cable 932. Since a general capacitor has a lead inductance, the function of the capacitor is impaired at a high frequency of several hundred MHz or more, so a feedthrough capacitor is used at such a frequency.

[0006]

The problem with the above-mentioned conventional technique is that the structure of the connector is complicated and expensive because it is necessary to attach an expensive feedthrough capacitor to the connector.

In view of the above problems of the prior art, an object of the present invention is to provide a filter circuit having a simple structure and good high frequency characteristics.

[0008]

Filter circuit of the present invention, in order to solve the problems] includes a printed wiring board for mounting electronic circuit, mounted on the printed wiring board, for connecting the cable to be connected to other devices
The connector of the printed wiring board is mounted in the filter circuit to reduce unnecessary emission of electromagnetic waves from the electronic equipment that has the connector and the shield case that shields electromagnetic waves.
A first capacitor and a second capacitor that are formed at opposite positions and are made of opposing conductors between layers of the printed wiring board.
Having one end of the first capacitor on the first terminal of the connector
Is connected to the second terminal of the connector
Is connected to one end of the first capacitor and the other end of the first capacitor to the second capacitor.
The other end of the capacitor is connected to the shield case around the connector .

Further, the connector of the printed wiring board is mounted.
Is formed at a position, we have a third capacitor made opposite conductor layers of the printed wiring board, a first terminal of the connector
One end of the third capacitor is connected to the
The other end of the third capacitor may be connected to the terminal of .

Further, by selecting any two layers of the printed wiring board,
The nth layer and the (n + 1) th layer (n = 1, 2, 3, ..., N
The (maximum value) -1) may form the first capacitor, the second capacitor, and the third capacitor.

Further, the connector is a shield connector,
Use the shield member of the connector to connect the first capacitor and the second capacitor.
The capacitor and the capacitor may be connected to the shield case .

That is, since the capacitor is connected between the terminal and the shield case, the noise generated inside the electronic device at the terminal is suppressed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a first embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing a filter circuit according to a first embodiment of the present invention. In the figure, reference numeral 10 is a connector for connecting a cable for connecting an electronic circuit to another device, 11 is a shield case for shielding an electromagnetic field generated by the electronic circuit, and 12 is a conductive connector housing built in the connector 10. Conductors, 13 and 14 are terminals of the connector 10, 16 is a holder made of an insulating material, 18 is a printed wiring board on which an electronic circuit is mounted, and 19 is a filter for reducing unnecessary emission of electromagnetic waves from electronic devices. It is a capacitor section that fulfills the.

Referring to FIG. 1, the shield case 11
Electromagnetically shield electronic devices. First terminal 1
The third and second terminals 14 are power supply terminals of electronic devices or signal input / output terminals. Connector 10 is terminal 1
3, 14 and a cage 16 made of an insulating material. The printed wiring board 18 mounts an electronic circuit, and forms a capacitor section 19 in a portion where the connector 10 is mounted. The conductor 12 connects one electrode of the capacitor of the capacitor portion 19 formed on the printed wiring slope 18 to the shield case 11.

FIG. 2A is a schematic sectional view showing in detail the capacitor portion of the printed wiring board of the filter circuit according to the first embodiment of the present invention. In the figure, reference numeral 12 is a connector 1
Conductor which is a conductive connector housing built in 0,
Reference numerals 13 and 14 are terminals of the connector 10, 18 is a printed wiring board on which an electronic circuit is mounted, 201 to 204 are through holes, 205 and 215 are conductors of the first layer of the printed wiring slope 18,
207, 211, 217 are conductors of the second layer of the printed wiring slope 18, 209, 213, 219 are conductors of the third layer of the printed wiring slope 18, 206, 208, 212, 216, 218 are insulators, 210, 214. 220 are capacitors.

The following can be understood by referring to FIG. The through holes 201 and 204 connect the conductor 12 and the conductors 209 and 219 in the inner layer of the printed wiring board 18. The through hole 202 connects the terminal 13 and the conductors 207 and 211 in the inner layer of the printed wiring board 18. The through hole 203 connects the terminal 14 and the conductors 213 and 217 in the inner layer of the printed wiring board 18. The conductors 205 and 215 are the first of the printed wiring board 18.
It constitutes a layer and is connected to the shield case 11 by a conductor 12. The insulator 206 insulates the conductor 205 of the first layer and the conductor 207 of the second layer. The conductor 205 and the conductor 207 are arranged to face each other, and the capacitor 210 is formed between the conductors 205 and 207. The capacitance of the capacitor 210 is determined by the area of the conductors facing each other, the distance between the conductors facing each other, and the dielectric constant of the insulator 206. The insulator 216 insulates the conductor 215 of the first layer and the conductor 217 of the second layer. Conductor 2
15 and the conductor 217 are arranged so as to face each other, and between the conductors 215,
A capacitor 220 is formed at 217. Capacitor 2
The capacitance of 20 is determined by the area of the conductors facing each other, the distance between the conductors facing each other, and the dielectric constant of the insulator 216. The conductor 211 of the second layer of the printed wiring board 18 connected to the terminal 13 and the conductor 213 of the third layer of the printed wiring slope 18 connected to the terminal 14 are arranged to face each other with the insulator 212 interposed therebetween. Therefore, the capacitor 214 is also formed here.

FIG. 2B is a circuit diagram showing a filter circuit according to the first embodiment of the present invention. In the figure, reference numeral 11 is a shield case for shielding an electromagnetic field generated by an electronic circuit, 13 and 14 are connector terminals, 210, 214 and 2
Reference numeral 20 is a capacitor that serves as a filter for reducing unnecessary radiation of electromagnetic waves from electronic devices, and 221 is a filter circuit.

The following can be seen from FIG. 2 (b). A capacitor 210 is formed between the terminal 13 and the shield case 11, a capacitor 220 is formed between the terminal 14 and the shield case 11, and a capacitor 214 is formed between the terminals 13 and 14. The filter circuit 221 includes a capacitor 214 connected between the terminals 13 and 14, a capacitor 210 connected between the terminal 13 and the shield case 11, and a capacitor 220 connected between the terminal 14 and the shield case 11. It

Next, in the embodiment of the present invention, the operation of each capacitor for normal mode noise or common mode noise generated by the electronic circuit 31 will be described with reference to FIGS.
Will be described in detail.

FIG. 3 is a circuit diagram showing an electronic device using the filter circuit of the present invention. In the figure, reference numeral 11 is a shield case for shielding an electromagnetic field generated by an electronic circuit, 1
3, 14 are connector terminals, 31 is an electronic circuit, 32 is a cable, 210, 214, 220 are capacitors which function as filters for reducing unnecessary radiation of electromagnetic waves from electronic devices, and 221 is a filter circuit.

The filter circuit 221 is placed between the electronic circuit 31 and the cable 32. The switching noise of the power supply and the harmonic components of the clock signal generated in the electronic circuit 31 are suppressed by the filter circuit 221, and the noise radiated from the cable 32 is reduced to a level without a problem.

FIG. 4 is a circuit diagram for explaining the operation of each capacitor with respect to the normal mode noise generated by the electronic circuit 31. In the figure, reference numeral 11 is a shield case that shields an electromagnetic field generated by an electronic circuit, 13 and 14 are connector terminals, 41 is a noise source of normal mode noise, and 4 is a noise source.
Reference numerals 2 and 43 are drive source impedances, 44 to 47 are noise currents of normal mode noise, 48 and 49 are load impedances, and 210, 214 and 220 function as filters for reducing unnecessary radiation of electromagnetic waves from electronic devices. The capacitors 221 are filter circuits.

The operation of each capacitor for normal mode noise will be described below. The noise source 41 is a normal mode noise voltage (terminal 13 and terminal 14) generated by the electronic circuit 31.
The noise voltage generated between the lines) is connected to the filter circuit 221 through the drive source impedances 42 and 43. The loads 48 and 49 are impedances when the cable 32 side is viewed from the terminals 13 and 14. The current 44 of the normal mode noise is generated by the capacitor 214 and the capacitor 2
10 is divided into a capacitor 220 (noise current 4
6, 47) and loads 48, 49 flow a noise current 45. By making the impedance between the terminals 13 and 14 of the filter circuit 221 smaller than the impedance of the loads 48 and 49, the noise current 4 flowing in the loads 48 and 49 is reduced.
5 can be reduced.

FIG. 5 is a circuit diagram for explaining the operation of each capacitor with respect to the common mode noise generated by the electronic circuit 31. In the figure, reference numeral 11 is a reference potential point such as a shield case or ground for shielding an electromagnetic field generated by an electronic circuit, 13 and 14 are terminals of a connector, 41 is a noise source of common mode noise, and 42, 43 and 52 are drive sources. Impedance, 53 to 57 are noise currents of common mode noise, 4
8, 49 and 58 are load impedances, 210 and 21
Reference numerals 4 and 220 denote capacitors that function as a filter for reducing unnecessary radiation of electromagnetic waves from electronic devices, and 221 is a filter circuit.

The operation of each capacitor for common mode noise will be described below. The noise source 51 is connected to the drive source impedances 42 and 43 through the drive source impedance 52 with the common mode noise voltage generated by the electronic circuit 31 (noise voltage generated at the reference potential point 11 such as ground and the terminals 13 and 14). To be done. The load impedance 58 is
It is connected to a reference potential point 11 such as ground and load impedances 48 and 49. Drive source impedances 42 and 43,
When the capacitors 210 and 220 and the load impedances 48 and 49 are equal transmission lines, respectively, the common mode noise currents 53 and 54 become equal and the capacitor 214 has
No noise current flows. The noise current is shunted to the capacitors 210 and 220. Therefore, capacitors 210 and 220
Impedance of load impedance 48, 49,
Load 4 by making the impedance smaller than 58
The noise currents 56 and 57 flowing in 8, 49 and 58 can be reduced.

In the conventional filter circuit shown in FIG. 10, in order to reduce the normal mode noise, it is necessary to increase the combined capacitance of the capacitors 210 and 220 connected in series. However, since the filter circuit of the first embodiment of the present invention shown in FIG. 2B has the capacitor 214 for the normal mode noise countermeasure, the normal mode noise countermeasure can be easily performed.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 6 is a schematic sectional view showing in detail the capacitor portion of the printed wiring board of the filter circuit according to the second embodiment of the present invention. In the figure, reference numeral 12 is a conductor that is a conductive connector housing built in the connector 10,
14 is a terminal of the connector 10, 18 is a printed wiring board on which an electronic circuit is mounted, 61, 62 and 212 are insulators, 20
1 to 204 are through holes, 205 is a conductor of the first layer of the printed wiring slope 18, 211 is a conductor of the second layer of the printed wiring slope 18, 213 is a conductor of the third layer of the printed wiring slope 18, and 63 is a printed wiring. Fourth layer conductors 210, 214, 220 on slope 18
Is a capacitor.

The conductor 205 constitutes the first layer of the printed wiring board 18, and is connected to the shield case 11 by the conductor 12.
The conductor 211 of the second layer is connected to the terminal 13 through the through hole 202. First layer conductor 205 and second layer conductor 211
Are arranged to face each other with the insulator 61 sandwiched therebetween, and form a capacitor 210. The conductor 213 of the third layer is connected to the terminal 14 through the through hole 203. The conductor 211 of the second layer and the conductor 213 of the third layer are arranged to face each other with the insulator 212 in between, and form a capacitor 214. The conductor 63 of the fourth layer is connected to the shield case 11 through the through holes 201 and 204 and the conductor 12. The conductor 213 of the third layer and the conductor 63 of the fourth layer are arranged to face each other with the insulator 62 in between, and form the capacitor 220.

The equivalent circuit of the second embodiment is the same as that of the first embodiment and is shown in FIG. 2 (b).

Next, a third embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 7 is a schematic sectional view showing in detail the capacitor portion of the printed wiring board of the filter circuit according to the third embodiment of the present invention. In the figure, reference numeral 12 is a conductor that is a conductive connector housing built in the connector 10,
14 is a terminal of the connector 10, 18 is a printed wiring board on which an electronic circuit is mounted, 71 and 72 are insulators, 201 to 20
4 is a through hole, 205 is a conductor of the first layer of the printed wiring slope 18, 211 is a conductor of the second layer of the printed wiring slope 18, 21
Reference numerals 0 and 220 are capacitors.

The conductor 205 constitutes the first layer of the printed wiring board 18, and is connected to the shield case 11 by the conductor 12.
The conductor 211 of the second layer is connected to the terminal 13 through the through hole 202. First layer conductor 205 and second layer conductor 211
Are arranged to face each other with the insulator 71 sandwiched therebetween, and form a capacitor 210. The conductor 73 of the second layer is the through hole 2
It is connected to the terminal 14 at 03. The conductor 205 of the first layer and the conductor 73 of the second layer are arranged so as to face each other with the insulator 72 interposed therebetween, and form the capacitor 220.

FIG. 8 is a circuit diagram showing a filter circuit according to the third embodiment of the present invention, which is an equivalent circuit of FIG. The third embodiment has the same circuit configuration as the conventional filter circuit shown in FIG.

[0036]

As described above, according to the present invention, since the capacitor constituting the filter is formed on a part of the printed wiring board on which the electronic circuit is mounted, no special parts are required and the structure can be simplified, and therefore the reliability is improved. This has the effect of improving productivity and productivity.

The second effect is that a capacitor can be formed in the immediate vicinity of the terminal of the electronic device and the wiring between the terminal and the capacitor can be made the shortest, so that a filter having good high frequency characteristics can be obtained.

Further, by forming the third capacitor between the first terminal and the second terminal, it is possible to easily take the normal mode noise countermeasure.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a filter circuit according to a first embodiment of the present invention.

FIG. 2A is a schematic cross-sectional view showing in detail the capacitor section of the printed wiring board of the filter circuit according to the first embodiment of the present invention. (B) It is a circuit diagram which shows the filter circuit of the 1st Embodiment of this invention.

FIG. 3 is a circuit diagram showing an electronic device using the filter circuit according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram for explaining the operation of each capacitor with respect to normal mode noise generated by an electronic circuit.

FIG. 5 is a circuit diagram for explaining the operation of each capacitor with respect to common mode noise generated by an electronic circuit.

FIG. 6 is a schematic cross-sectional view showing in detail a capacitor section of the printed wiring board of the filter circuit according to the second embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view showing in detail a capacitor portion of a printed wiring board of a filter circuit according to a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a filter circuit according to a third embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing a conventional filter circuit.

FIG. 10 is a circuit diagram showing an example of a circuit of an electronic device using a conventional filter circuit.

[Explanation of symbols]

10, 90 Connector 11, 91 Shield case or ground reference potential point 12, 92 Conductor 13, 14, 93, 94 Terminal 16 Holder 18, 98 Printed wiring board 19 Capacitor section 31, 931 Electronic circuit 32, 932 Cable 41, 51 noise sources 42, 43, 52 drive source impedances 44-47, 53-57 noise currents 48, 49, 58 load impedances 61, 62, 71, 72, 206, 208, 212, 2
16, 218 Insulator 63 Fourth layer conductor 73, 211, 207, 217 Second layer conductor 80, 221, 980 Filter circuit 201-204 Through hole 205, 215 First layer conductor 209, 213, 219 Third Layer conductors 210, 214, 220 Capacitors 910, 920 Feedthrough capacitors

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-6-267790 (JP, A) JP-A-4-302122 (JP, A) JP-A-50-19338 (JP, A) JP-A-60- 42808 (JP, A) JP-A-57-37818 (JP, A) Actual development 4-70772 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 7/01 H01G 4 / 12-4/245

Claims (4)

(57) [Claims] And 1. A printed wiring board for mounting electronic circuit, mounted on the printed wiring board, an electronic device having a connector for connecting the cable to be connected to other devices, the shield case for shielding electromagnetic waves In a filter circuit for reducing unnecessary radiation of the electromagnetic wave of , formed at a position where the connector of the printed wiring board is mounted.
And a first capacitor and a second capacitor made of conductors facing each other between the layers of the printed wiring board, and the first terminal of the connector has one of the first capacitor and the second capacitor.
One end of the second capacitor is connected to the second terminal of the connector.
The other end of the first capacitor is connected to the other end of the second capacitor.
A filter circuit , wherein the other end is connected to the shield case around the connector . 2. The filter circuit according to claim 1, wherein the filter circuit is formed at a position where the connector is mounted on the printed wiring board.
It is, have a third capacitor made conductor opposing layers of the printed wiring board, the third capacitor to the first terminal of said connector-
The other end of the third capacitor is connected to the second terminal of the connector.
A filter circuit whose ends are connected . 3. The filter circuit according to claim 2, wherein any two layers of the printed wiring board are selected, and the nth layer and the (nth) layer are selected.
+1) layer (n = 1, 2, 3, ..., N (maximum value) −
The filter circuit according to 1) forms the first capacitor, the second capacitor, and the third capacitor. 4. A filter circuit according to claim 1 or claim 2, the connector and the shielded connector, connector Sea
And a second member for connecting the first capacitor and the second capacitor.
A filter circuit, wherein a filter is connected to the shield case .