JPH11298182A - Electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the radiation noise from an electronic apparatus which transmits signals with a plurality of circuit boards connected by cables. SOLUTION: On the occasion of connecting circuit boards 2, 3 in a frame 1 by a signal transmitting cable 7 through a connector 6, a ground cable connector 8 connected only to the ground of the board is provided near the connector 6, and a grounding-dedicated cable 9 composed of only the ground by the connector 8 is laid on and parallel to the cable 7, thereby reducing the potential difference between the circuit boards 2, 3 and the current loop formed with a signal current of the cable 7 and return current of the cable 9 to cancel the magnetic fields. Thus it is possible to suppress the noise generation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic apparatus for transmitting a signal between boards using a cable inside a housing, and more particularly to an effective technique for preventing electromagnetic noise in signal transmission using a cable. .

[0002]

2. Description of the Related Art Conventionally, in a case of an electronic apparatus having a circuit board of this type, as shown in FIG. 8, a cable 7 connects between two circuit boards 2 and 3 provided in a case 1. And
There are many cases where signal transmission is performed. In signal transmission using the cable 7 connecting the circuit boards 2 and 3, radiation noise is often generated from the cable 7,
As a countermeasure, a method such as shielding the cable 7 is employed.

[0003]

However, in the above-mentioned prior art, when the connection between the circuit boards is made by a cable, the sheet metal mounted on each circuit board is liable to the layout problem inside the housing. Or, the housing part is different. This state will be described with reference to FIG.

In FIG. 9, when the circuit boards 1 and 2 are connected to different frame grounds FG1 and FG2, the ground potentials Vg1 and Vg2 of the frame grounds FG1 and FG2 are generally different from each other. (Vg1-Vg2) is called a common mode potential Vgc. Its different ground potential V
frame ground FG1, FG with g1, Vg2
When the circuit boards 1 and 2 connected to 2 are connected by a cable, a common mode current Ic due to the common mode potential Vgc flows intensively in the cable, and common mode noise is radiated from the cable. As a countermeasure to prevent this common mode noise, a method using a coaxial cable has been used, but it is insufficient as a countermeasure for the noise.

Further, as shown in FIG. 10, even when two circuit boards 2 and 3 connected to each other by a cable 7 are connected to a frame ground of a common housing 1, A current loop is formed by the signal current If constituted by the boards 2 and 3 and the housing 1 and the feedback current Ir thereof. The path of the current loop becomes large in structure, and the differential mode noise is radiated by the current loop. In such a current loop, the signal current If and the feedback current Ir
Are not arranged in parallel at a short distance, the signal current I
The magnetic field Hf generated by f and the magnetic field Hr generated by the feedback current Ir cannot cancel each other out, so that there is a disadvantage that radiation noise from the cable is radiated efficiently.

In order to reduce the radiation noise from the cables, it is most desirable to arrange the cables between the circuit boards in such a manner that the cables are routed on the housing so as to connect the circuit boards with the shortest distance. Such electronic devices have a problem of mechanical arrangement, and it is difficult to adopt such a form.

[0007] As shown in FIG.
Is shielded by a shield ground wire 24 to suppress radiated noise. However, the ground wire 24 of the cable shield 23 becomes longer due to the structure of the housing or the like. There is a disadvantage that the shielding effect cannot be sufficiently exhibited due to the influence of inductance.

An object of the present invention is to provide a method of effectively reducing the generation of radiation noise in an electronic device that transmits a signal by connecting a plurality of circuit boards with a cable.

[0009]

In order to solve the above-mentioned problems, in an electronic device according to the present invention, as shown in a principle explanatory diagram of FIG. 6 and a perspective view of FIG. When the internal circuit boards 2 and 3 are connected by the signal transmission cable 7, they are connected to the connector 6 for connecting the signal transmission cable on each of the circuit boards 2 and 3, and are further connected only to the board ground. Ground cable connector 8
Is connected to the connector 8, a ground-only cable 9 composed of only the ground is connected, and the ground-only cable 9 is arranged in parallel with the signal transmission cable 7.

By the connection of the ground-only cable 9, the potential difference between the circuit boards 2 and 3, that is, the common mode potential Vgc can be reduced, so that the common mode current Ic flowing through the cable is reduced, and thus the common mode noise radiation is suppressed. can do.

At the same time, as shown in the side view of FIG.
By arranging the signal transmission cable 7 and the ground-only cable 9 in parallel with each other, a current loop formed by the signal current If of the signal transmission cable 7 and the feedback current Ir of the ground-only cable 9 is reduced. The magnetic field H generated by the signal current If
f and the magnetic field Hr generated by the feedback current Ir cancel each other out, so that differential mode noise emission can be suppressed.

Furthermore, the radiation noise can be reduced by connecting the dedicated ground cable to the dedicated connector on the board without being influenced by the housing structure like the shielded wire of the shielded cable.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic perspective view of an electronic apparatus according to an embodiment of the present invention. Circuit boards inside a housing are connected by a signal transmission cable, and grounds of the respective circuit boards are overlapped with the signal transmission cable. It shows an electronic device in which cables connected only to each other (hereinafter abbreviated as ground cables) are arranged.

In FIG. 1, the housing 1 is formed by bending a conductive metal plate. The housing 1 is electrically connected to the ground portions of the circuit board 2 and the circuit board 3 by screws 4, and the housing 1 is further bent. The structure 5 in the electronic device is accommodated in the recess. A signal transmission cable connector 6 is mounted on each of the circuit boards 2 and 3, and both ends of the signal transmission cable 7 are connected to the connector 6. Further, on the circuit boards 2 and 3, a ground cable connector 8 is arranged in parallel at a position close to the signal transmission cable connector 6. The connector 8 is connected to the respective ground portions of the circuit boards 2 and 3, and a ground cable 9 connected to the connector 8
Are arranged so as to overlap with the signal transmission cable 7.

(Embodiment 1) FIG. 2 is a schematic perspective view showing an embodiment in which the ground cable 9 and the ground cable connector 8 in the embodiment shown in FIG. 1 of the present invention are connected. In FIG. 2, the ground cable 9 is composed of a conductive material 10 and an insulating material 11 surrounding the conductive material 10, and a conductive connector connecting portion 12 is formed at an end. The ground cable connector 8
It comprises a conductive cable connection 13, a conductive substrate ground connection 14, an insulating shell 15 and fasteners 16. Conductive connector connection 12 of cable 9
The conductive cable connecting portion 13 of the connector 8 is formed on a surface having a concave-convex shape that can be in close contact with each other in order to make low impedance connection with each other. The connector connection part 12 of the cable 9 is sandwiched between the cable connection part 13 of the connector 8 and the fastener 16, and adheres closely.
Connection is made with a large contact area.

In this connection state, connection by a socket provided on the cable side connector 25 as shown in FIG. 3 and a pin 27 provided on the board side connector 26 is also possible. It is desirable to make surface contact as shown in FIG. The connection between the board ground connection part 14 and the board ground 17 of the connector 8 can also be made by a pin. In this connection, in order to obtain a low impedance connection, the board ground connection part 14 and the board ground 17 are connected. Are desirably in contact with each other and connected by solder 18.

(Embodiment 2) FIG. 4 shows an arrangement of a signal transmission cable connector and a ground cable connector on a circuit board inside an electronic device housing according to the above-described embodiment of the present invention, and the ground of the connector. 4 is a schematic plan view of an embodiment showing a connection method between them.

The ground cable 9 and the ground cable connector 8 of this embodiment are the same as those used in the first embodiment shown in FIG. On the circuit board 2, the signal transmission cable connector 6 to which the signal transmission cable 7 is connected and the ground cable connector 8 to which the ground cable 9 is connected are arranged close to and parallel to each other. Further, the ground of the circuit board 2 at a portion close to the two connectors is conductively connected to a housing 1 (not shown) by screws 4 or the like. The ground of the signal transmission cable 7 and the ground of the ground cable 9 are also conductively connected to the housing 1 via the connectors 6 and 8.

An IC 19 is mounted on a ground connection between the housing 1 and the circuit board 2 connected by the screws 4, a common ground 20 for the ground cable connector 8 and the signal transmission cable connector 6. The ground 20 is separated from the ground 21 and is connected between the ground 20 and the ground 21 by at least one narrow ground connection portion 22. By connecting the grounds 20 and 21 with the ground connection part 22 as described above, the swing of the ground 21 due to the noise of the IC mounted on the circuit board is transmitted to the ground 20, as shown in FIG. Therefore, common mode radiation noise generated from the signal transmission cable 7 and the ground cable 9 can be reduced.

[0020]

As described above, according to the present invention, when connecting circuit boards provided inside an electronic device housing with signal transmission cables, the signal transmission cables on the respective circuit boards are connected. A connector connected only to the board ground is installed close to the connector, and a dedicated ground cable consisting of only the ground is connected by this connector, and this dedicated ground cable is placed in parallel with the signal transmission cable. By reducing the potential difference between the circuit boards, that is, the common mode potential Vgc, and reducing the common mode current Ic flowing through the cable, the common mode noise radiation is suppressed and the signal current If of the signal transmission cable is reduced. And by reducing the current loop of the feedback current Ir of the cable dedicated to the ground, Magnetic field Hf generated by No. current If
And the magnetic field Hr due to the feedback current Ir can cancel each other, so that differential mode noise emission can be suppressed. Is connected to the connector on the board to reduce the radiated noise. Further, by separating the ground of the IC on the board from the ground of the cables, the radiated noise generated from the cables is reduced. effective.

[Brief description of the drawings]

FIG. 1 is a perspective view of an electronic device according to the invention.

FIG. 2 is a schematic partial perspective view of the embodiment of FIG. 1;

FIG. 3 is a view similar to FIG. 2;

FIG. 4 is a schematic partial plan view of the embodiment of FIG. 1;

FIG. 5 is a view similar to FIG.

FIG. 6 is a diagram illustrating the principle of the present invention.

FIGS. 7A and 7B are schematic views of an electronic device according to the present invention, in which FIG.
(B) is a side view.

FIG. 8 is a schematic perspective view of an electronic device according to the related art.

FIG. 9 is a diagram illustrating the principle of the state of an electronic device according to a conventional technique.

FIG. 10 is a schematic view of an electronic device according to the related art, and FIG.
Is a perspective view, and (B) is a side view.

FIG. 11 is a schematic perspective view of an electronic device according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2, 3 Circuit board 4 Conductive screw 5 Structure 6 Connector for signal transmission cable 7 Signal transmission cable 8 Connector for ground cable 9 Ground cable 10 Conductive substance 11 Insulating substance 12 Connector connection part 13 Cable connection part 14 Board ground connection 15 Insulating shell 16 Fastener 17 Board ground 18 Solder 19 IC 20, 21 Ground 22 Ground connection 23 Shield cable 24 Shield ground wire 25 Cable side connector 26 Board side connector 27 pin 28 Ground ground pin

Claims (8)

[Claims] An electronic device in which a plurality of circuit boards disposed inside a housing are connected by a first cable via a first connector on each circuit board for transmitting a signal, A second connector provided on each of the circuit boards and connected only to the ground; and a second cable connected to each of the second connectors and connecting each of the circuit boards. Electronic equipment. 2. The electronic device according to claim 1, wherein the second cable is formed of a flexible conductor, and the conductor is covered with an insulator at a portion other than a connection portion with the second connector. machine. 3. The conductor forming the second cable includes a sheet or band-shaped conductor made of a plurality of conductor cores, conductive metal foils, or conductive metal braided wires. An electronic device according to claim 1. 4. The second cable connected to the second cable.
4. The electronic device according to claim 1, wherein the connector has connection means for connecting with low impedance at a connection portion. 5. The electronic device according to claim 4, wherein the connection means of the second connector at a connection portion between the second cable and the second connector includes an uneven shape and a wide contact surface. 6. The electronic device according to claim 1, wherein the second cable is disposed so as to overlap with and be parallel to the first cable. 7. The second cable so that the second cable overlaps and is arranged in parallel with the first cable.
4. The electronic device according to claim 1, wherein said connector is arranged in parallel close to said first connector. 8. On each of the circuit boards, a ground of the first and second connectors and a ground of a circuit board provided close to the first and second connectors are common to the housing. Wherein the common ground region is separated from the ground region of another device on the circuit board, and the two separated ground regions are connected by at least one connection portion. The electronic device according to claim 7.