WO2021192073A1

WO2021192073A1 - Circuit board and electronic device

Info

Publication number: WO2021192073A1
Application number: PCT/JP2020/013204
Authority: WO
Inventors: 辰也山中; 佑介山梶; 雄大米岡; 顕次和田
Original assignee: 三菱電機株式会社
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2021-09-30
Also published as: CN115299184B; DE112020006584B4; DE112020006584T5; JPWO2021192073A1; JP6843312B1; CN115299184A

Abstract

A signal wire group that includes a ground wire is connected to a a circuit board (21). The circuit board (21) has mounted thereon a communication circuit (50) that processes signals received or sent via the signal wire group. The circuit board (21) comprises: a first ground pattern (60) to which the ground wire of the signal wire group can be connected; a second ground pattern (70) that is electrically connected to the first ground pattern (60) via an inductance element (90), and is grounded via a first grounding wire (30); and a third ground pattern (80) that is electrically connected to the second ground pattern (70) via a capacitance element (100), is insulated from the first ground pattern (60), and has connected thereto a ground terminal of the communication circuit (50).

Description

Circuit boards and electronic devices

This disclosure relates to circuit boards and electronic devices.

Electronic devices that have the function of communicating with external devices are known. Such an electronic device includes a circuit board on which a communication circuit is mounted and a connector for connecting a communication cable.

When such an electronic device is exposed to static electricity, lightning, or electromagnetic noise generated from other electronic devices arranged around it, other electronic devices connected to a common power source via a power cable, etc., communication is performed. Electromagnetic noise that has entered from the connector to which the cable is connected may penetrate inside the electronic device through the pattern of the conductor on the circuit board.

If the invading electromagnetic noise propagates to the communication circuit, the performance of the electronic device may deteriorate. Therefore, a circuit board that separates the ground pattern to which the housing of the electronic device is connected from the ground pattern of the communication circuit is used. I came.

For example, Patent Document 1 describes a circuit board in which a slit portion for separating these patterns is arranged between a ground pattern of a housing of an electronic device to be grounded and a ground pattern of a communication circuit.

Japanese Unexamined Patent Publication No. 2010-05298

However, in the circuit board described in Patent Document 1, the electromagnetic noise in the high frequency band invading from the shield of the communication cable cannot escape to the ground due to the impedance of the ground wiring connected to the device housing including the circuit board. Therefore, electromagnetic noise in the high frequency band may propagate to the communication circuit, causing the communication circuit to malfunction.

Further, in the circuit board described in Patent Document 1, the intruding electromagnetic noise can be reduced by not connecting the ground wiring. However, in general, in order to maintain stable communication with other devices, the circuit board or the metal device housing is connected by ground wiring.
Since such a grounded wiring has residual inductance, residual resistance, etc., it has a high impedance against electromagnetic noise entering from the outside of the circuit board. If electromagnetic noise enters from the communication cable through the ground wiring, it propagates to the communication circuit including the semiconductor element, and the communication circuit may malfunction.

The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a circuit board that is not easily affected by electromagnetic noise.

In order to achieve the above object, the circuit board according to the present disclosure is
A circuit board on which a signal line group including a ground line is connected and a communication circuit unit for processing a signal received via the signal line group or a signal transmitted via the signal line group is mounted.
A first ground pattern to which the ground line in the signal line group can be connected, and
A second ground pattern that is electrically connected to the first ground pattern via an inductance element and grounded via a first ground wire.
It includes a third ground pattern that is electrically connected to the second ground pattern via a capacitance element, is insulated from the first ground pattern, and is connected to a ground terminal of the communication circuit unit.

According to the present disclosure, the electromagnetic noise in the high frequency band that has entered from the connector to which the communication cable is connected is difficult to propagate to the communication circuit section and is difficult to return to the original path, so that the circuit board is not easily affected by the electromagnetic noise. Electronic devices can be provided.

Perspective view of the electronic device according to the first embodiment Top view of the electronic device shown in FIG. Circuit diagram of the electronic device shown in FIG. The figure which shows the modification of the electronic device shown in FIG. Circuit diagram of electronic device according to one embodiment Circuit diagram of the electronic device according to Comparative Example 1 Circuit diagram of the electronic device according to Comparative Example 2 The figure which shows the result of the electromagnetic field simulation of the electronic device shown in FIG. 1 and the electronic device which concerns on Comparative Example 1. Top view of the electronic device according to the second embodiment Circuit diagram of the electronic device shown in FIG. Top view of the electronic device according to the third embodiment Circuit diagram of the electronic device shown in FIG. Another perspective view of the electronic device shown in FIG. Top view of the electronic device according to the fourth embodiment Circuit diagram of the electronic device shown in FIG. Top view of the electronic device according to the fifth embodiment Perspective view of the electronic device according to the sixth embodiment Top view of the electronic device shown in FIG. Cross-sectional view of the electronic device shown in FIG.

(Embodiment 1)
Hereinafter, the electronic device 1 including the circuit board 21 according to the first embodiment will be described with reference to the drawings.

As shown in the perspective view of FIG. 1, the electronic device 1 is a circuit in which a metal housing 10 covering a circuit element, wiring, etc., a pin, an element, an integrated circuit, etc. are mounted and has a printed copper foil pattern. The board 21 and the ground wiring 30 electrically connected to the housing 10 are provided.
The pattern referred to here refers to a circuit electrode including a conductor foil printed on a circuit board, and does not represent the shape of the foil.

The circuit board 21 is arranged on the housing 10. The circuit board 21 is, for example, a single-sided substrate in which a copper foil pattern is arranged only on one side of a dielectric substrate.

The grounding wire 30 is, for example, a copper wire connected to a grounding rod embedded in the ground and grounded. Hereinafter, the ground wiring 30 will be described as being grounded.
The grounding potential is not limited to the absolute potential. The grounding potential broadly includes, for example, the potential of a conductor that is not connected to the grounding rod, serves as a return path for a common mode current, and serves as a reference potential for a plurality of connected electronic devices.
The ground wiring 30 is an example of the first ground wire in the claim.

Further, as shown in the top view of FIG. 2, the electronic device 1 includes a connector 40 of a communication cable for connecting an external device and a communication circuit unit 50 connected to the connector 40.

The connector 40 is a receptacle that accepts a plug or jack of a communication cable. As shown by the broken line, the communication cable includes a signal line, for example, a pair of differential communication wirings DS1 and DS2 and a shield wiring SW.

As shown by the broken line, the connector 40 is covered with the connector body B1 and the conductor terminals T1, T2, and T3 which are electrically connected by physically contacting the terminals of the communication cable. , Equipped with.
When the communication cable is connected to the connector 40, the shield wiring SW of the communication cable and the differential communication wirings DS1 and DS2 are electrically connected to the terminals T1, T2, and T3 of the connector 40, respectively.
The shield wiring SW is an example of the ground wire in the claim. The group of the differential communication wiring DS1 and DS2 and the shield wiring SW is an example of the signal line group in the claim.

The shield wiring SW may be wiring in which the connector 40 is covered with a conductor, and a metal shield case, a shield sheath, a shield housing, etc. electrically connected to the conductor are connected to the circuit board 21. ..

The signal line does not have to be a pair of differential communication wirings DS1 and DS2, and may be a single-ended communication wiring using the shield wiring SW as a current return path.
Further, a general noise filter may be provided on the above-mentioned differential communication wiring DS1, DS2 or single-ended communication wiring. The noise filter may be arranged inside the connector 40, or may be arranged between the connector 40 on the circuit board 21 and the communication circuit unit 50. The noise filter generally includes a combination of components that reduce noise, for example, a resistor, a line-to-line capacitor, a ground-to-ground capacitor, a transformer, a normal mode choke coil, a common mode choke coil, and the like.

Three connecting portions P1, P2, and P3 are provided on the copper foil pattern of the circuit board 21.
The connection portion P1 is a connection point provided on the first ground pattern 60. The connection portion P1 is formed by soldering the first ground pattern 60 to the pin of the terminal T1 protruding from the connector 40.
The shield wiring SW and the first ground pattern 60 may be directly connected without passing through the pin of the terminal T1. Further, the metal shield case, shield sheath, shield housing, etc. described above are arranged between the shield wiring SW and the first ground pattern 60, and the shield wiring SW, the shield case, and the first ground pattern 60 are arranged in this order. You may connect.

The connection units P2 and P3 are connection points provided on the pattern of the signal line extending from the communication circuit unit 50. The connection units P2 and P3 are formed by soldering a pattern of signal lines extending from the communication circuit unit 50 to the pins of terminals T2 and T3 protruding from the connector 40.
In the following description, the details of the connector 40 will be omitted. Further, the electrical connection via the pins of the terminals T1, T2, and T3 may be expressed as wiring.

The communication circuit unit 50 is equipped with a circuit element including an integrated circuit (IC, Integrated Circuit) for communication, a high frequency transistor, a common mode choke coil, a crystal oscillator, and the like. The communication circuit unit 50 is an electronic circuit that processes a signal received via the differential communication wirings DS1 and DS2 and the shield wiring SW.

The ground wiring 30 is electrically connected to the housing 10, and the second ground pattern 70 is electrically connected to the housing 10. Therefore, the housing 10, the ground wiring 30, and the second ground pattern 70 are grounded.

The third ground pattern 80 is a pattern of copper foil on the circuit board 21 that provides a reference potential to the communication circuit unit 50. The third ground pattern 80 is electrically connected to the ground terminal of the communication circuit unit 50.

The first ground pattern 60, the second ground pattern 70, and the third ground pattern 80 are formed on the surface of the circuit board 21.
In the drawings, the first ground pattern 60, the second ground pattern 70, and the third ground pattern 80 are hatched in different patterns to facilitate understanding.

The electronic device 1 further includes an inductance element 90 and a capacitance element 100.
As shown in FIGS. 1 and 2, the first ground pattern 60 and the second ground pattern 70 are connected by an inductance element 90. Further, the second ground pattern 70 and the third ground pattern 80 are connected by a capacitance element 100.
On the other hand, the first ground pattern 60 and the third ground pattern 80 are not connected by any of the conductor, the capacitance element, and the inductance element, and are not connected by the connecting member.
Hereinafter, the fact that none of the conductor, the capacitance element, and the inductance element is connected is referred to as being insulated.

Termination including Bob Smith termination may be provided between the differential communication wiring DS1 and the first ground pattern 60, and between the differential communication wiring DS2 and the first ground pattern. Further, a termination including a Bob Smith termination may be provided between the differential communication wiring DS1 and the third ground pattern 80, and between the differential communication wiring DS2 and the third ground pattern 80. In this way, when communication is performed using the differential signal, the ends of the differential communication wirings DS1 and DS2 are connected to the same ground pattern, for example, the first ground pattern 60 or the third ground pattern 80. It is desirable to terminate with.
Further, at the end of Bob Smith, noise mixed in the differential communication wirings DS1 and DS2 in the common mode tends to flow. Further, since noise tends to flow to the communication circuit unit 50 via the third ground pattern, the differential communication wirings DS1 and DS2 are connected to the third ground pattern 80 rather than the differential communication wirings DS1 and DS2. It is desirable to connect to the ground pattern 60 of 1.

Next, the inductance value L of the inductance element 90 and the capacitance value C of the capacitance element 100 will be described with reference to FIG. 3, which is a circuit diagram of the electronic device 1.
In FIG. 3, the noise source is represented by NS, and the electromagnetic noise generated by the noise source NS acts on the shield wiring SW of the communication cable.

Specifically, the inductance value L of the inductance element 90 is an inductance value L that has high impedance with respect to a high frequency band that is assumed to enter from the connector 40, for example, an electromagnetic noise HN of 1 MHz or more.

The inductance element 90 may be an element having both a resistance component and an inductance component and whose characteristics change depending on the frequency, for example, ferrite beads. Hereinafter, a case where ferrite beads are used as the inductance element 90 will be described.

Switching circuits, lightning, etc. generate electromagnetic noise having a large amplitude in a low frequency component and a small amplitude in a high frequency component.
Such electromagnetic noise in the low frequency band is not easily affected by the residual inductance component of the ground wiring 30, and easily returns to the noise source NS. The residual inductance may be referred to as parasitic inductance, stray inductance, self-inductance, etc., but in the present embodiment, it is referred to as residual inductance.
On the other hand, electrostatic discharge, electromagnetic noise in the high frequency band generated by a brush motor or the like is easily affected by a residual inductance component. Further, the impedance of the capacitance element 100 is small with respect to the electromagnetic noise in the high frequency band. Therefore, the electromagnetic noise in the high frequency band penetrates into the circuit board 21.

If ferrite beads are used as the inductance element 90, the impedance is high only for a specific high frequency band, so that electromagnetic noise HN in the high frequency band does not easily enter the circuit board 21. In particular, by using ferrite beads having a property of making it difficult for electromagnetic noise having a frequency close to the frequency of the signal used for communication to pass through, it is possible to more effectively prevent malfunction of the communication circuit unit 50.

The residual inductance of the inductance element 90, the capacitance element 100, and the ground wiring 30 is a kind of LCL T-type filter circuit. This T-type filter circuit has a property of performing series resonance at a resonance frequency determined by the circuit constant of the inductance element 90 and the circuit constant of the capacitance element 100.
Electromagnetic noise having a frequency component close to the resonance frequency propagates from the noise source NS to the communication circuit unit 50 via the inductance element 90 and the capacitance element 100.
Therefore, if the frequency of the signal used for communication is close to the resonance frequency, the propagated electromagnetic noise may have a greater influence on the operation of the communication circuit unit 50.
Therefore, preferably, the capacitance value C of the capacitance element 100 and the inductance value L of the inductance element 90 are set as values that make the resonance frequency of the T-type filter circuit different from the frequency of the signal used for communication.

When the frequency band of the signal used for communication in the communication circuit unit 50 is wide, preferably, a ferrite bead having a large resistance component is used as the inductance element 90, and a resistance element arranged in series with the inductance element 90 is used. Use. By doing so, the amplitude of resonance of the T-type filter circuit of the LCL can be reduced, and the amount of electromagnetic noise propagating to the communication circuit unit 50 can be reduced.
Further, preferably, the capacitance value C of the capacitance element 100 and the inductance value L of the inductance element 90 are values that make the resonance frequency different from the frequency of the nth harmonic as well as the fundamental frequency of the frequency of the signal used for communication. Set.
The case where ferrite beads are used as the inductance element 90 has been described above.

In the electronic device 1 shown in FIGS. 1 to 3, the inductance element 90 is arranged on the circuit board 21. However, the inductance element 90 may be arranged inside the connector 40.

Specifically, the capacitance value C of the capacitance element 100 is a capacitance value C that has high impedance with respect to a low frequency band that is assumed to enter from the connector 40, for example, an electromagnetic noise LN of several hundred kHz or less.

The capacitance element 100 arranged between the second ground pattern 70 and the third ground pattern 80 may be two or more capacitors.

The specifications of the inductance element 90 and the capacitance element 100 and the arrangement on the circuit board 20 are obtained by, for example, a simulation using a computer.

5 and 6 show circuit diagrams of electronic devices 2 and 3 according to Comparative Examples 1 and 2 having configurations different from those of the electronic device 1 regarding the behavior when the electronic device 1 having the above configuration is exposed to electromagnetic noise. And FIG. 7 showing another circuit diagram of the electronic device 1 according to the first embodiment will be described.

(Comparative Example 1)
Unlike the electronic device 1, the electronic device 2 including the circuit board 22 according to Comparative Example 1 does not include the first ground pattern 60 and the inductance element 90. In the electronic device 2, the shield wiring SW of the connector 40 is directly connected to the second ground pattern 70.

FIG. 5 shows a thick arrow indicating the noise propagation path when the electromagnetic noise HN and the electromagnetic noise LN in the low frequency band invade the electronic device 2.
The capacitance element 100 has a high impedance and the ground wiring 30 has a low impedance with respect to the electromagnetic noise LN in the low frequency band that has entered from the connector 40.
Therefore, the electromagnetic noise LN in the low frequency band escapes from the second ground pattern 70 to the ground through the ground wiring 30.
Therefore, the electromagnetic noise LN in the low frequency band does not propagate to the communication circuit unit 50.

On the other hand, the capacitance element 100 has a low impedance with respect to the electromagnetic noise HN in the high frequency band invading from the connector 40, but the ground wiring 30 has a high impedance due to the residual inductance component.
Therefore, the electromagnetic noise HN in the high frequency band cannot escape to the ground through the ground wiring 30, and propagates from the second ground pattern 70 to the third ground pattern 80 via the capacitance element 100 for communication. It invades the circuit unit 50.

(Comparative Example 2)
In the electronic device 3 including the circuit board 23 according to Comparative Example 2, unlike the electronic device 1, the first ground pattern 60 is not electrically separated from the third ground pattern 80. The first ground pattern 60 and the third ground pattern 80 are connected by a connecting member 130.

FIG. 6 shows a thick arrow indicating the noise propagation path when the electromagnetic noise HN and the electromagnetic noise LN in the low frequency band invade the electronic device 3.
In FIG. 6, the connecting member 130 is represented by a capacitance element 130 connected between the first ground pattern 60 and the third ground pattern 80 because it has a capacitance component.
The inductance element 90 has a low impedance, and the capacitance element 100 and the connecting member 130 have a high impedance with respect to the electromagnetic noise LN in the low frequency band that has entered from the connector 40.
Therefore, the electromagnetic noise LN in the low frequency band escapes to the ground through the first ground pattern 60, the inductance element 90, the second ground pattern 70, and the ground wiring 30.

On the other hand, the inductance element 90 has a high impedance and the connecting member 130 has a low impedance with respect to the electromagnetic noise HN in the high frequency band that has entered from the connector 40.
Therefore, the electromagnetic noise HN in the high frequency band cannot escape to the ground through the inductance element 90, and propagates from the first ground pattern 60 to the third ground pattern 80 via the connecting member 130 for communication. It invades the circuit unit 50.

As described above, in the electronic devices 2 and 3 according to Comparative Examples 1 and 2, the electromagnetic noise HN in the high frequency band invades the communication circuit unit 50, which may deteriorate the performance of the communication circuit unit 50.

On the other hand, as shown by a thick arrow in FIG. 7, in the electronic device 1 according to the first embodiment, not only the low frequency band electromagnetic noise LN but also the high frequency band electromagnetic noise HN propagates to the communication circuit unit 50. do not.
Hereinafter, the noise propagation path when the electromagnetic noise HN in the high frequency band and the electromagnetic noise LN in the low frequency band invade the electronic device 1 will be described.

The inductance element 90 has a low impedance with respect to the electromagnetic noise LN in the low frequency band that has entered from the connector 40.
Therefore, similarly to Comparative Example 2, the electromagnetic noise LN in the low frequency band escapes to the ground through the first ground pattern 60, the inductance element 90, the second ground pattern 70, and the ground wiring 30.

Further, the inductance element 90 has a high impedance with respect to the electromagnetic noise HN in the high frequency band that has entered from the connector 40.
Therefore, unlike Comparative Example 1, the electromagnetic noise HN in the high frequency band cannot escape to the ground through the inductance element 90. Further, unlike Comparative Example 2, since the first ground pattern 60 and the third ground pattern 80 are not connected, the electromagnetic noise HN in the high frequency band does not propagate to the third ground pattern 80.
Therefore, the electromagnetic noise HN in the high frequency band is reflected by the inductance element 90 and does not propagate to the communication circuit unit 50.
If the shield wiring SW is sufficiently long, the electromagnetic noise HN in the high frequency band reflected by the inductance element 90 is attenuated by the loss of the shield wiring SW.

When the ground wiring 30 is long, the ground wiring 30 has a high residual inductance with respect to the electromagnetic noise HN in the high frequency band. However, even in this case, according to the electronic device 1, the electromagnetic noise HN in the high frequency band does not propagate to the ground wiring 30, so that it does not invade the communication circuit unit 50.

FIG. 8 shows the results of an electromagnetic field simulation comparing the circuit board 21 of the electronic device 1 and the circuit board 22 of the electronic device 2. This simulation is the result of outputting the amount of noise propagating to the differential communication wiring of the communication circuit unit 50 as an S parameter when the electromagnetic noise HN in the high frequency band is applied between the first ground pattern 60 and the ground potential. Is shown.

The circuit board 21 shown by the solid line suppresses the amount of noise more effectively than the circuit board 22 shown by the broken line over almost the entire frequency domain. In particular, at around 100 MHz, the circuit board 21 suppresses noise by about 10 dB as compared with the circuit board 22.

In the electronic device 1 described above, the housing 10 and the second ground pattern 70 are connected by the ground wiring 30, but the method of connecting the housing 10 and the second ground pattern 70 is limited to this. No.
For example, in the circuit board 29 whose perspective view is shown in FIG. 4, the second ground pattern 70 is electrically connected to the metal convex portion 11 formed by raising a part of the housing 10.

For example, the second ground pattern 70 and the housing 10 may be connected by the following method.
A screw hole is made on the second ground pattern 70 of the circuit board 29. A convex portion 11 is formed in the housing 10 immediately below the screw hole, and a screw hole is formed in the upper end portion of the convex portion 11. By solder leveling the second ground pattern 70, the metal is exposed on the back surface of the circuit board 29. The exposed metal portion is brought into contact with the convex portion 11. A screw is inserted from above the second ground pattern 70, fitted into the screw hole of the convex portion 11, and screwed.
By doing so, the second ground pattern 70 is pressed against the convex portion 11 and fixed, so that the contact resistance between the second ground pattern 70, the housing 10, and the ground wiring 30 is reduced.

Further, the ground wiring 30 may be a sheet metal, a bus bar, or a combination thereof. That is, if it is a conductor that electrically connects the second ground pattern 70 and the housing 10 and is equal to the ground potential with respect to the direct current that is not affected by the residual inductance, the harness-like one shown in the figure is used. Not limited.
Since the ground wiring 30 has a residual resistance component with respect to direct current, a potential difference is generated between the ground potential and the second ground pattern 70 or the housing 10 according to the current flowing through the ground wiring 30. do. Since the residual resistance component of the ground wiring 30 is sufficiently small, it is considered that the potential of the conductor electrically connected via the ground wiring 30 and the ground wiring 30 is equal to the ground potential.

(Embodiment 2)
The electronic device 4 including the circuit board 24 according to the second embodiment has the same configuration as the electronic device 1 according to the first embodiment, and has the first ground pattern 60, the second ground pattern 70, and the third ground pattern 70. The distance between the ground pattern 80 and the ground pattern 80 has a relationship described later.
As shown in the top view of FIG. 9, the shortest distance DA between the first ground pattern 60 and the third ground pattern 80 of the circuit board 24 is the second ground pattern 70 and the third ground pattern 80. Greater than the shortest distance DB.

Even if a parasitic capacitance component is generated between the first ground pattern 60 and the third ground pattern 80, the capacitance value is relatively small with respect to the capacitance element 100.

In the circuit diagram shown in FIG. 10, the capacitance value of the capacitance element 100 is C, and the capacitance value of the parasitic capacitance component 140 generated between the first ground pattern 60 and the third ground pattern 80 is C0.
Further, the cross-sectional areas of the first ground pattern 60 and the third ground pattern 80 facing each other are S1 [m ² ], and the cross-sectional areas of the second ground pattern 70 and the third ground pattern 80 facing each other are S2 [m ^2]. ].
As described above, the distance DA is larger than the distance DB.
Therefore, as shown in the following mathematical formula, the capacitance C1 [F] between the first ground pattern 60 and the third ground pattern 80, and the second ground pattern 70 and the third ground pattern 80 With respect to the capacitance C2 [F] between them, C2 >> C1 can be satisfied.

The capacitance value C0 of the parasitic capacitance component 140 is generally C0> C1. However, if DA is made sufficiently larger than DB, the value of C0 can be made sufficiently small.
From the above, the capacitance value C0 of the parasitic capacitance component 140 is negligibly small for the electromagnetic noise HN in the high frequency band.

Therefore, the electromagnetic noise HN in the high frequency band that has entered from the connector 40 does not propagate to the third ground pattern 80 via the parasitic capacitance component 140, as shown by the thick arrow. Further, since the inductance element 90 has a high impedance with respect to the electromagnetic noise HN in the high frequency band, the electromagnetic noise HN in the high frequency band does not propagate to the communication circuit unit 50 through the inductance element 90.

As described above, according to the electronic device 4, it is possible to more effectively prevent the intrusion of the electromagnetic noise HN in the high frequency band as compared with the electronic device 1.

(Embodiment 3)
In the electronic devices 1 and 2, only the second ground pattern 70 is grounded, but the first ground pattern 60 may be grounded together with the second ground pattern 70.
As shown in FIG. 11, the electronic device 5 including the circuit board 25 according to the third embodiment has the same configuration as the electronic device 1 according to the first embodiment, and is different from the ground wiring 30. The ground wiring 31 connected to the ground pattern 60 of the above is provided.
The ground wiring 30 is electrically connected to the second ground pattern 70 at the ground wiring connection portion 71, and the ground wiring 31 is electrically connected to the first ground pattern 60 at the ground wiring connection portion 61.
The ground

wiring connection portions

61 and 71 are conductor connection portions provided on the copper foil pattern, and are, for example, metal rings.

FIG. 12 shows a thick arrow indicating the noise propagation path when the electromagnetic noise HN and the electromagnetic noise LN in the low frequency band invade the electronic device 5.
The inductance element 90 has a low impedance and the capacitance element 100 has a high impedance with respect to the electromagnetic noise LN in the low frequency band that has entered from the connector 40.
Therefore, the electromagnetic noise LN in the low frequency band escapes to the ground through the first ground pattern 60, the inductance element 90, the second ground pattern 70, and the ground wiring 30.

On the other hand, the electromagnetic noise HN in the high frequency band that has entered the first ground pattern 60 from the connector 40 cannot pass through the inductance element 90.
Further, the ground wiring 31 has a residual inductance component like the ground wiring 30. Even so, if the ground wiring 31 is short, the impedance value of the residual inductance component with respect to the electromagnetic noise HN in the high frequency band is relatively small.
Therefore, the electromagnetic noise HN in the high frequency band that has entered from the connector 40 escapes to the ground through the ground wiring 31 without returning to the shield wiring SW.

As described above, according to the electronic device 5, not only the electromagnetic noise HN in the high frequency band does not propagate to the communication circuit unit 50, but also the electromagnetic noise HN in the high frequency band is reflected to other devices connected via the communication cable. Wave propagation can be suppressed.
Therefore, it is possible to prevent malfunction of other devices connected to the electronic device 5 via the communication cable.

The ground wiring 31 is not limited to a harness-shaped wiring, and may be a plate-shaped wiring such as a sheet metal or a bus bar.
The ground wiring 31 is an example of the second ground wire in the claim.

The electronic device 5 has two wirings, a ground wiring 30 and a ground wiring 31. However, the wiring for grounding the first ground pattern 60 and the second ground pattern 70 is one of the ground wirings 30, and the first ground pattern 60 and the second ground pattern 70 are electrically connected to the housing 10. You may connect to.
Specifically, as shown in FIG. 13, the metal

convex portions

11 and 12 are arranged in the housing 10, the first ground pattern 60 is connected to the convex portion 12 with a screw 110, and the second ground pattern 70 is used. May be connected to the convex portion 11 with a screw 110.
By doing so, the first ground pattern 60 and the second ground pattern 70 are grounded via the housing 10.

(Embodiment 4)
The grounding wiring 31 of the electronic device 5 is a wiring that directly grounds the first ground pattern 60, but the configuration for grounding the first ground pattern 60 is not limited to this.
As shown in FIG. 14, the electronic device 6 according to the fourth embodiment includes a ground wiring 32 on the circuit board 26, which is different from the ground wiring 30. Further, the electronic device 6 is electrically connected to the ground wiring 32 and includes a first ground pattern 60, a second ground pattern 70, and a fourth ground pattern 150 different from the third ground pattern 80. There is.
Between the first ground pattern 60 and the fourth ground pattern 150, a varistor element 160, which is an element whose resistance value decreases as the applied voltage increases, is arranged.

The electronic device 6 has an effect of effectively releasing the electromagnetic noise HHN in the high voltage and high frequency band to the ground.
The effect of the electronic device 6 will be described with reference to FIG.

When high voltage and high frequency noise HHN invades from the connector 40, a high voltage is applied to the varistor element 160 connected to the first ground pattern 60, and the varistor element 160 has a low impedance. Therefore, the high-voltage and high-frequency noise HHN that has entered from the connector 40 escapes from the ground wiring 32 to the ground via the varistor element 160 and the fourth ground pattern 150.
Therefore, according to the electronic device 6, even if high-voltage and high-frequency noise HHN invades from the connector 40, it is possible to prevent dielectric breakdown of the inductance element 90, the capacitance element 100, the communication circuit unit 50, and the like.
The ground wiring 32 is an example of the second ground wire in the claim.

(Embodiment 5)
The inductance element 90 connected between the first ground pattern 60 and the second ground pattern 70 does not have to be a coil as an individual component.
As shown in FIG. 16, the electronic device 7 including the circuit board 27 according to the fifth embodiment includes a copper foil pattern 91 instead of the inductance element 90.

The copper foil pattern 91 is printed in an elongated rectangular shape between the first ground pattern 60 and the second ground pattern 70.
The pattern 91 of the copper foil is a conductor having an inductance component with respect to the electromagnetic noise HN in the high frequency band. The specific position, width, length, thickness, etc. of the copper foil pattern 91 can be determined by, for example, using a general strip line, microstrip line, or other method to determine the configuration of the circuit board 27 and the circuit board 27. It is designed based on the material, thickness, etc. of the included dielectric.

According to the electronic device 7, when printing the first ground pattern 60 and the second ground pattern 70, the inductance element 90 in the electronic device 1 can be formed by the copper foil pattern 91. As described above, since the coil as an individual component is not required, the number of components of the electronic device 7 can be reduced as compared with that of the electronic device 1.
Therefore, according to the electronic device 7, the degree of freedom in designing the circuit board 27 is improved, and space saving and weight reduction of the electronic device 7 are achieved.

The shape of the copper foil pattern 91 is not limited to an elongated rectangle. The copper foil pattern 91 may be, for example, a coil formed by utilizing the layer of the circuit board 27. By doing so, the inductance value of the copper foil pattern 91 can be increased.

(Embodiment 6)
The electronic device 8 according to the sixth embodiment is different from the electronic device 1 in which the circuit board 20 is composed of a single-sided substrate, the circuit board 28 is composed of a multilayer board 170, and the device is provided with a copper foil pattern inside the multilayer board 170. Is.
As shown in FIG. 17, the multilayer substrate 170 is arranged on the outermost side with two

dielectric layers

171 and 172 which are dielectric layers and an inner layer 173 which is a layer sandwiched between the two

dielectric layers

171 and 172. A surface layer 174 that mounts a communication circuit unit 50, a first ground pattern 60, a second ground pattern 70, a third ground pattern 80, and the like is provided.
The dielectric layer 171 is the first dielectric layer in the claim, the dielectric layer 172 is the second dielectric layer in the claim, and the surface layer 174 is an example of the outermost layer in the claim.

As shown in FIG. 18, a first ground pattern 60, a second ground pattern 70, and a third ground pattern 80 are arranged on the outermost surface layer of the multilayer substrate 170.
Further, as shown by the broken line, a fifth ground pattern 81, which is a copper foil pattern, is arranged at a position facing the communication circuit unit 50.

As shown in FIG. 19, which is a cross-sectional view taken along the line AA of the electronic device 8, the fifth ground pattern 81 is arranged in the inner layer 173 and sandwiched between the

dielectric layers

171 and 172.
The third ground pattern 80 arranged on the surface layer 174 and the inner layer 173 is electrically connected by a via 180.
The via 180 is an example of the connecting conductor in the claim.

So far, we have investigated the case where the electromagnetic noise HN in the high frequency band invades from the connector 40. However, the electromagnetic noise HN in the high frequency band does not always enter from the connector 40.
For example, due to electromagnetic spatial coupling, electromagnetic noise HN in the high frequency band may enter from a path other than the connector 40.

When the potential of one of the front surface and the back surface of the dielectric layer 171 changes due to the electromagnetic noise HN in the high frequency band, the potential of the other surface also changes. Then, the potentials changing in the same phase cancel each other out due to the common mode coupling. Therefore, the voltage does not fluctuate between the communication circuit unit 50, the third ground pattern 80, and the fifth ground pattern 81.
The reason will be described below.

First, assuming that the electromagnetic noise HN in the high frequency band invades the communication circuit unit 50 and causes the voltage of the communication circuit unit 50 to fluctuate by ΔV, a fifth ground pattern 81 arranged to face the communication circuit unit 50 The voltage of is also fluctuated by ΔV. Since the third ground pattern 80 and the fifth ground pattern 81 are electrically connected by the via 180, the voltage of the third ground pattern 80 also fluctuates by ΔV.
Therefore, the voltage of the communication circuit unit 50 and the voltage of the third ground pattern 80 are kept equal.

Further, assuming that the electromagnetic noise HN in the high frequency band invades the third ground pattern 80 and fluctuates the voltage of the third ground pattern 80 by ΔV, it is electrically connected to the third ground pattern 80 by the via 180. The voltage of the fifth ground pattern 81, which is set, also fluctuates by ΔV. Then, the voltage of the communication circuit unit 50 arranged to face the fifth ground pattern 81 also fluctuates by ΔV.
Therefore, the voltage of the communication circuit unit 50 and the voltage of the third ground pattern 80 are kept equal.

Further, when the electromagnetic noise HN in the high frequency band invades both the communication circuit unit 50 and the third ground pattern 80, the voltage of the communication circuit unit 50 and the voltage of the third ground pattern 80 are similarly equal. It is kept at voltage.

In this way, even when the electromagnetic noise HN in the high frequency band invades from a path other than the connector 40, it is between the voltage of the communication circuit unit 50 and the voltage of the third ground pattern 80 which is the reference potential of the communication circuit unit 50. Does not make a difference.
Therefore, according to the electronic device 8, even in such a case, the communication circuit unit 50 is unlikely to malfunction.

The present disclosure allows for various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Moreover, the above-described embodiment is for explaining this disclosure, and does not limit the scope of the present disclosure. That is, the scope of the present disclosure is indicated not by the embodiment but by the claims. And various modifications made within the scope of the claims and within the equivalent meaning of disclosure are considered to be within the scope of the present disclosure.

1, 2, 3, 4, 5, 6, 7, 8 Electronic devices, 10 housings, 11, 12 convex parts, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 circuit boards, 30, 31, 32, ground wiring, 40 connectors, 50 communication circuit section, 60 first ground pattern, 61 ground wiring connection section, 70 second ground pattern, 71 ground wiring connection section, 80 third ground pattern, 81 Fifth ground pattern, 90 inductance element, 91 copper foil pattern, 100 capacitance element, 110 screw, 130 connection member, 140 parasitic capacitance component, 150 fourth ground pattern, 151 ground wiring connection, 160 varistor element, 170 Multilayer board, 171 and 172 dielectric layers, 173 inner layers, 174 surface layers, 180 vias, B1 connector body, C, C0 capacitance values, DA first ground pattern and third ground pattern distance, DB second ground Distance between pattern and third ground pattern, DS1, DS2 differential communication wiring, NS noise source, HN high frequency band electromagnetic noise, L inductance value, LN low frequency band electromagnetic noise, HHN high voltage high frequency band electromagnetic noise , P1, P2, P3 connection part, SW shield wiring, T1, T2, T3 terminal.

Claims

A circuit board on which a signal line group including a ground line is connected and a communication circuit unit for processing a signal received via the signal line group or a signal transmitted via the signal line group is mounted.
A first ground pattern to which the ground line in the signal line group can be connected, and
A second ground pattern that is electrically connected to the first ground pattern via an inductance element and grounded via a first ground wire.
A third ground pattern, which is electrically connected to the second ground pattern via a capacitance element, is insulated from the first ground pattern, and is connected to a ground terminal of the communication circuit unit, is provided.
Circuit board.
The shortest distance between the first ground pattern and the third ground pattern is greater than the shortest distance between the second ground pattern and the third ground pattern.
The circuit board according to claim 1.
The second ground wire is electrically connected to the first ground pattern.
The first ground wire is different from the second ground wire.
The circuit board according to claim 1 or 2.
A fourth ground pattern that is electrically connected to the first ground pattern via a varistor element is provided.
The second ground wire is electrically connected to the fourth ground pattern.
The circuit board according to claim 3.
The inductance element is a copper foil pattern.
The circuit board according to any one of claims 1 to 4.
Arranged between the first dielectric layer containing the first dielectric, the second dielectric layer containing the second dielectric, and the first dielectric layer and the second dielectric layer. The inner layer including the fifth ground pattern to be formed and the outermost layer which is in contact with the first dielectric layer and is located on a side different from the inner layer are included.
The first ground pattern, the second ground pattern, and the third ground pattern are arranged on the outermost layer.
The third ground pattern and the fifth ground pattern are electrically connected by a connecting conductor penetrating the first dielectric layer.
The communication circuit unit is arranged on the outermost surface layer so as to face the fifth ground pattern.
The circuit board according to any one of claims 1 to 5.
The resonance frequency of the T-type filter circuit including the inductance element, the capacitance element, and the first ground wire is different from the frequency of the received signal or the frequency of the transmitted signal.
The circuit board according to any one of claims 1 to 6.
The connector to which the signal line group is connected and
A wiring for connecting the signal line group to the communication circuit unit and connecting the ground line to the first ground pattern via the connector is provided.
An electronic device comprising the circuit board according to any one of claims 1 to 7.