CN115299184B

CN115299184B - Circuit board and electronic device

Info

Publication number: CN115299184B
Application number: CN202080098806.2A
Authority: CN
Inventors: 山中辰也; 山梶佑介; 米冈雄大; 和田显次
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2023-07-14
Anticipated expiration: 2040-03-25
Also published as: JP6843312B1; DE112020006584T5; DE112020006584B4; JPWO2021192073A1; WO2021192073A1; CN115299184A

Abstract

A signal line group including a ground line is connected to the circuit board (21). A communication circuit unit (50) is mounted on a circuit board (21), and the communication circuit unit (50) processes signals received via signal line groups or signals transmitted via signal line groups. The circuit board (21) has: a 1 st ground pattern (60) that can be connected to a ground line in the signal line group; a 2 nd ground pattern (70) electrically connected to the 1 st ground pattern (60) via an inductance element (90), the 2 nd ground pattern (70) being grounded via the 1 st ground line (30); and a 3 rd ground pattern (80) electrically connected to the 2 nd ground pattern (70) via the capacitor element (100), insulated from the 1 st ground pattern (60), and connected to a ground terminal of the communication circuit unit (50).

Description

Circuit board and electronic device

Technical Field

The present invention relates to a circuit board and an electronic device

Background

Electronic devices having a function of communicating with an external device are known. Such an electronic device includes a circuit board on which a communication circuit is mounted, and a connector connected to a communication cable.

If such an electronic device is exposed to static electricity, lightning, or electromagnetic noise generated from other electronic devices disposed in the surroundings, other electronic devices connected to a common power source via a power cable, or the like, electromagnetic noise that has entered from a connector to which the communication cable is connected may enter the inside of the electronic device via a pattern of conductors on the circuit board.

If the electromagnetic noise is transmitted to the communication circuit, the performance of the electronic device may be reduced, and thus a circuit board is used in which a ground pattern connected to the housing of the electronic device and a ground pattern of the communication circuit are separated.

For example, patent document 1 discloses a circuit board in which a slit portion separating a ground pattern of a housing of an electronic device to be grounded from a ground pattern of a communication circuit is arranged between these patterns.

Patent document 1: japanese patent application laid-open No. 2010-050298

Disclosure of Invention

However, in the circuit board described in patent document 1, electromagnetic noise in a high frequency band, which enters from the shield portion of the communication cable, is not released 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 be transmitted to the communication circuit, and malfunction may occur in the communication circuit.

In addition, in the circuit board described in patent document 1, by not connecting the ground wiring, the intrusion of electromagnetic noise can be reduced. However, in general, a circuit board or a metal device housing is connected by a ground wiring in order to maintain stable communication with other devices.

Such a ground wiring has a residual inductance, a residual resistance, and the like, and thus has a high impedance to electromagnetic noise that enters from the outside of the circuit board. If electromagnetic noise is introduced from the communication cable through the ground wiring, the electromagnetic noise is transmitted to a communication circuit including a semiconductor element, and there is a possibility that malfunction of the communication circuit occurs.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a circuit board which is less susceptible to electromagnetic noise.

In order to achieve the above object, a circuit board according to the present invention is connected to a signal line group including a ground line, a communication circuit unit is mounted on the circuit board, the communication circuit unit processes a signal received via the signal line group or a signal transmitted via the signal line group,

the circuit board comprises:

a 1 st ground pattern connectable to the ground line in the signal line group;

a 2 nd ground pattern electrically connected to the 1 st ground pattern via an inductance element, the 2 nd ground pattern being grounded via a 1 st ground line; and

and a 3 rd ground pattern electrically connected to the 2 nd ground pattern via a capacitor element, the 3 rd ground pattern being insulated from the 1 st ground pattern, the 3 rd ground pattern being connected to a ground terminal of the communication circuit section.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a circuit board and an electronic device which are less susceptible to electromagnetic noise because electromagnetic noise in a high frequency band, which enters from a connector to which a communication cable is connected, is less likely to be transmitted to a communication circuit portion and is less likely to return to an original path.

Drawings

Fig. 1 is an oblique view of an electronic device according to embodiment 1.

Fig. 2 is a top view of the electronic device shown in fig. 1.

Fig. 3 is a circuit diagram of the electronic device shown in fig. 1.

Fig. 4 is a diagram showing a modification of the electronic device shown in fig. 1.

Fig. 5 is a circuit diagram of the electronic device according to comparative example 1.

Fig. 6 is a circuit diagram of the electronic device according to comparative example 2.

Fig. 7 is a circuit diagram of the electronic device according to embodiment 1.

Fig. 8 is a graph showing the results of electromagnetic field simulation between the electronic apparatus shown in fig. 1 and the electronic apparatus according to comparative example 1.

Fig. 9 is a plan view of an electronic device according to embodiment 2.

Fig. 10 is a circuit diagram of the electronic device shown in fig. 9.

Fig. 11 is a plan view of an electronic device according to embodiment 3.

Fig. 12 is a circuit diagram of the electronic device shown in fig. 11.

Fig. 13 is an oblique view of the electronic device shown in fig. 11.

Fig. 14 is a plan view of an electronic device according to embodiment 4.

Fig. 15 is a circuit diagram of the electronic device shown in fig. 14.

Fig. 16 is a plan view of an electronic device according to embodiment 5.

Fig. 17 is an oblique view of the electronic device according to embodiment 6.

Fig. 18 is a top view of the electronic device shown in fig. 17.

Fig. 19 is a cross-sectional view of the electronic device shown in fig. 17.

Detailed Description

(embodiment 1)

Next, an electronic device 1 including a circuit board 21 according to embodiment 1 will be described with reference to the drawings.

As shown in the oblique view of fig. 1, the electronic apparatus 1 has: a metal casing 10 covering circuit elements, wiring, and the like; a circuit board 21 on which pins, elements, integrated circuits, and the like are mounted, the circuit board 21 having a copper foil pattern formed by printing; and a ground wiring 30 electrically connected to the housing 10.

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

The ground wire 30 is, for example, a copper wire connected to a ground rod buried in the ground and grounded. Next, the grounding wire 30 is grounded.

The potential of the ground is not limited to an absolute potential. The potential of the ground broadly includes, for example, a potential of a conductor which is not connected to the ground rod, becomes a return path of the common mode current, and becomes a reference potential of a plurality of connected electronic devices.

The ground wiring 30 is an example of the 1 st ground line in the claims.

As shown in the plan view of fig. 2, the electronic device 1 includes a connector 40 of a communication cable connected to an external device, and a communication circuit unit 50 connected to the connector 40.

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

As shown in solid lines, the connector 40 has: a connector body B1; and terminals T1, T2, T3 of the conductors, which are covered by the connector body B1, are electrically connected by being in physical contact with the terminals of the communication cable.

If the communication cable is connected to the connector 40, the shield wiring SW and the differential communication wirings DS1 and DS2 of the communication cable are electrically connected to the terminals T1, T2, and T3 of the connector 40, respectively.

The shield wiring SW is an example of a ground line in the claims. The group of differential communication lines DS1 and DS2 and the shield line SW is an example of the signal line group in the claims.

The shield wiring SW may be a wiring that covers the connector 40 with a conductor, and connects a metal shield, a shield sheath, a shield frame, or the like electrically connected to the conductor to the circuit board 21.

The signal line may not be a pair of differential communication lines DS1 and DS2, but may be a single-ended communication line of 1 line in which the shield line SW is a return path of current.

A normal noise filter may be provided on the differential communication lines DS1 and DS2 or the single-ended communication line. The noise filter may be disposed inside the connector 40 or between the connector 40 and the communication circuit section 50 on the circuit board 21. Noise filters typically contain noise reducing components such as combinations of resistors, line-to-line capacitors, inter-ground capacitors, transformers, normal mode chokes, common mode chokes, and the like.

On the copper foil pattern of the

circuit board

21, 3 connection portions P1, P2, P3 are provided.

The connection portion P1 is a connection point provided above the 1 st ground pattern 60. The connection portion P1 is a connection portion where the 1 st ground pattern 60 is connected to a pin of the terminal T1 protruding from the connector 40 by solder.

Further, the shield wiring SW and the 1 st ground pattern 60 may be directly connected to each other, not via the pin of the terminal T1. The metal shield, the shield sheath, the shield frame, and the like may be disposed between the shield wiring SW and the 1 st ground pattern 60, and may be connected in this order of the shield wiring SW, the shield sheath, and the 1 st ground pattern 60.

The connection portions P2 and P3 are connection points provided on the pattern of the signal lines extending from the communication circuit portion 50. The connection portions P2, P3 are connection portions for connecting the pattern of the signal lines extending from the communication circuit portion 50 to the pins of the terminals T2, T3 protruding from the connector 40 by solder.

In the following description, details of the connector 40 are omitted. In addition, electrical connection via pins of the terminals T1, T2, T3 is sometimes expressed as wiring.

The communication circuit unit 50 includes circuit elements 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 signals received via the differential communication lines DS1 and DS2 and the shield line SW.

The ground wiring 30 is electrically connected to the housing 10, and the 2 nd ground pattern 70 is electrically connected to the housing 10. Therefore, the frame 10, the ground wiring 30, and the 2 nd ground pattern 70 are grounded.

The 3 rd ground pattern 80 is a copper foil pattern on the circuit board 21 for providing the reference potential to the communication circuit section 50. The 3 rd ground pattern 80 is electrically connected to a ground terminal of the communication circuit section 50.

The 1 st ground pattern 60, the 2 nd ground pattern 70, and the 3 rd ground pattern 80 are formed on the surface of the circuit substrate 21.

In the drawings, the 1 st ground pattern 60, the 2 nd ground pattern 70, and the 3 rd ground pattern 80 are hatched with different patterns for ease of understanding.

The electronic device 1 also has an inductive element 90 and a capacitive element 100.

As shown in fig. 1 and 2, the 1 st ground pattern 60 and the 2 nd ground pattern 70 are connected by an inductance element 90. The 2 nd ground pattern 70 and the 3 rd ground pattern 80 are connected by the capacitor element 100.

In contrast, the 1 st ground pattern 60 and the 3 rd ground pattern 80 are not connected by any one of a conductor, a capacitor element, and an inductor element, and are not connected by a connecting member.

Hereinafter, the connection not through any one of the conductor, the capacitive element, and the inductive element will be described as insulation.

Termination including bob smith termination (bob smith termination) may be performed between the differential communication line DS1 and the 1 st ground pattern 60 and between the differential communication line DS2 and the 1 st ground pattern 60. Further, termination including bob smith termination may be performed between the differential communication line DS1 and the 3 rd ground pattern 80 and between the differential communication line DS2 and the 3 rd ground pattern 80. In this way, when communication is performed using differential signals, it is preferable to terminate the ends of the differential communication lines DS1 and DS2 with respect to the same ground pattern, for example, with respect to the 1 st ground pattern 60 or the 3 rd ground pattern 80.

In the bob smith termination, noise mixed in the common mode easily flows through the differential communication lines DS1 and DS2. Further, since noise easily flows through the communication circuit section 50 via the 3 rd ground pattern 80, it is preferable to connect the differential communication lines DS1, DS2 to the 1 st ground pattern 60, as compared with connecting the differential communication lines DS1, DS2 to the 3 rd ground pattern 80.

Next, referring to fig. 3, which is a circuit diagram of the electronic device 1, the inductance value L of the inductance element 90 and the capacitance value C of the capacitance element 100 will be described.

In fig. 3, a noise source NS is shown, and 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 is high in impedance with respect to electromagnetic noise HN that is assumed to enter from the connector 40 in a high-frequency band, for example, 1MHz or more.

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

Switching circuits, mines, and the like generate electromagnetic noise having a large amplitude in a component with a low frequency and a small amplitude in a component with a high frequency.

Such electromagnetic noise in the low frequency band is less susceptible to the residual inductance component of the ground wiring 30, and is likely to return to the noise source NS. The residual inductance is sometimes referred to as parasitic inductance, stray inductance, self inductance, or the like, but in the present embodiment, it is referred to as residual inductance.

On the other hand, electromagnetic noise in a high frequency band generated by electrostatic discharge, brush motor, or the like is susceptible to the residual inductance component. In addition, the impedance of the capacitive element 100 is small with respect to electromagnetic noise in a high frequency band. Therefore, electromagnetic noise in the high frequency band intrudes 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, and therefore electromagnetic noise HN in the high-frequency band is less likely to intrude into the circuit board 21. In particular, if ferrite beads having a property of making electromagnetic noise having a frequency close to the frequency of the signal used for communication less likely to pass are used, malfunction of the communication circuit section 50 can be prevented more effectively.

The inductance element 90, the capacitance element 100, and the residual inductance of the ground line 30 are one type of T-type filter circuit of LCL. The T-filter circuit has a property of performing series resonance at a resonance frequency defined 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 is transmitted from the noise source NS to the communication circuit section 50 via the inductance element 90 and the capacitance element 100.

Therefore, if the resonance frequency is close to the frequency of the signal used for communication, the transmitted electromagnetic noise may have a greater influence on the operation of the communication circuit section 50.

Therefore, the capacitance value C of the capacitive element 100 and the inductance value L of the inductive element 90 are preferably set to values that differ from the frequency of the signal used for communication and the resonance frequency of the T-filter circuit.

In the case of a frequency bandwidth of a frequency of a signal used for communication in the communication circuit unit 50, it is preferable to use ferrite beads having a large resistance component as the inductance element 90, and use a resistance element arranged in series with the inductance element 90. This reduces the amplitude of resonance of the T-filter circuit of the LCL, and reduces the amount of electromagnetic noise transmitted to the communication circuit unit 50.

More preferably, the capacitance value C of the capacitive element 100 and the inductance value L of the inductive element 90 are set to values such that the resonance frequency is different from the fundamental frequency of the signal used for communication and also from the frequency of the n-th harmonic.

The case where ferrite beads are used as the inductance element 90 has been described above.

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

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

The capacitive element 100 disposed between the 2 nd ground pattern 70 and the 3 rd ground pattern 80 may be 2 or more capacitors.

For example, the specifications of the inductance element 90 and the capacitance element 100 and the arrangement on the circuit board 21 are obtained by simulation using an electronic computer.

The behavior of the electronic device 1 having the above configuration when exposed to electromagnetic noise will be described with reference to fig. 5 and 6 showing circuit diagrams of the

electronic devices

2 and 3 of comparative examples 1 and 2 having different configurations from the electronic device 1, and fig. 7 showing other circuit diagrams of the electronic device 1 according to embodiment 1.

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 1 st ground pattern 60 and the inductance element 90. In the electronic apparatus 2, the shield wiring SW of the connector 40 is directly connected to the 2 nd ground pattern 70.

In fig. 5, the transmission paths of electromagnetic noise HN and noise in the case where electromagnetic noise LN in a low frequency band intrudes into the electronic apparatus 2 are indicated by thick arrows.

The capacitive element 100 has a high impedance and the ground wiring 30 has a low impedance with respect to electromagnetic noise LN in a low frequency band that enters from the connector 40.

Accordingly, electromagnetic noise LN in the low frequency band is released from the 2 nd ground pattern 70 to the ground through the ground wiring 30.

Therefore, the electromagnetic noise LN in the low frequency band is not transmitted to the communication circuit section 50.

On the other hand, the capacitive element 100 has a low impedance with respect to electromagnetic noise HN in a high frequency band that enters from the connector 40, but the ground wiring 30 has a high impedance due to the residual inductance component.

Therefore, electromagnetic noise HN in the high-frequency band cannot be released to the ground through the ground wiring 30, and is transmitted from the 2 nd ground pattern 70 to the 3 rd ground pattern 80 via the capacitive element 100, and enters the communication circuit section 50.

Comparative example 2

In the electronic apparatus 3 including the circuit substrate 23 according to comparative example 2, unlike the electronic apparatus 1, the 1 st ground pattern 60 is not electrically separated from the 3 rd ground pattern 80. The 1 st ground pattern 60 and the 3 rd ground pattern 80 are connected by a connection member 130.

In fig. 6, the transmission paths of electromagnetic noise HN and noise in the case where electromagnetic noise LN in a low frequency band intrudes into the electronic apparatus 3 are indicated by thick arrows.

Since having a capacitance component, in fig. 6, the connection member 130 is represented by the capacitance element 130 connected between the 1 st ground pattern 60 and the 3 rd ground pattern 80.

The inductance element 90 has a low impedance with respect to electromagnetic noise LN in a low frequency band that enters from the connector 40, and the capacitance element 100 and the connection member 130 have a high impedance.

Therefore, the electromagnetic noise LN in the low-frequency band is released to the ground through the 1 st ground pattern 60, the inductance element 90, the 2 nd ground pattern 70, and the ground wiring 30.

On the other hand, the inductance element 90 has a high impedance with respect to electromagnetic noise HN in a high frequency band that enters from the connector 40, and the connection member 130 has a low impedance.

Therefore, the electromagnetic noise HN in the high-frequency band cannot be released to the ground through the inductance element 90, but is transmitted from the 1 st ground pattern 60 to the 3 rd ground pattern 80 via the connection member 130, and intrudes into the communication circuit section 50.

As described above, in the

electronic devices

2 and 3 according to comparative examples 1 and 2, electromagnetic noise HN in the high-frequency band may intrude into the communication circuit portion 50, and thus the performance of the communication circuit portion 50 may be degraded.

In contrast, as shown by the thick arrow in fig. 7, in the electronic device 1 according to embodiment 1, not only the electromagnetic noise LN in the low frequency band but also the electromagnetic noise HN in the high frequency band are not transmitted to the communication circuit section 50.

Next, a transmission path of noise in the case where electromagnetic noise HN in a high frequency band and electromagnetic noise LN in a low frequency band intrude into the electronic apparatus 1 will be described.

The inductance element 90 has a low impedance with respect to electromagnetic noise LN in a low frequency band that intrudes from the connector 40.

Therefore, as in comparative example 2, electromagnetic noise LN in the low frequency band is discharged to the ground through the 1 st ground pattern 60, the inductance element 90, the 2 nd ground pattern 70, and the ground wiring 30.

In addition, the inductance element 90 has a high impedance with respect to electromagnetic noise HN in a high frequency band which enters from the connector 40.

Therefore, unlike comparative example 1, electromagnetic noise HN in the high frequency band cannot be released to the ground through the inductance element 90. In addition, unlike comparative example 2, since the 1 st ground pattern 60 and the 3 rd ground pattern 80 are not connected, electromagnetic noise HN of a high frequency band is not transmitted to the 3 rd ground pattern 80.

Therefore, electromagnetic noise HN in the high frequency band is reflected by the inductance element 90 and is not transmitted to the communication circuit section 50.

Regarding electromagnetic noise HN in the high frequency band reflected by the inductance element 90, if the shield wiring SW is sufficiently long, attenuation is caused by loss of the shield wiring SW.

In addition, when the ground wiring 30 is long, the ground wiring 30 has a high residual inductance with respect to electromagnetic noise HN in a high frequency band. However, in this case, according to the electronic apparatus 1, electromagnetic noise HN in the high-frequency band is not transmitted to the ground wiring 30, and therefore does not intrude into the communication circuit section 50.

Fig. 8 shows the result of electromagnetic field simulation in which the circuit board 21 of the electronic device 1 and the circuit board 22 of the electronic device 2 are compared. This simulation shows the result of outputting the amount of noise transmitted to the differential communication wiring of the communication circuit section 50 as the S parameter when electromagnetic noise HN in the high frequency band is applied between the 1 st ground pattern 60 and the ground potential.

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

In the electronic device 1 described above, the frame 10 and the 2 nd ground pattern 70 are connected by the ground wiring 30, but the method of connecting the frame 10 and the 2 nd ground pattern 70 is not limited thereto.

For example, in the circuit board 29 shown in fig. 4 in an oblique view, the 2 nd ground pattern 70 is electrically connected to the metal convex portion 11 formed by bulging a part of the housing 10.

For example, the 2 nd ground pattern 70 and the frame 10 may be connected by the following method.

Screw holes are formed in the circuit board 29 above the 2 nd ground pattern 70. Directly below the screw hole, a projection 11 is formed in the housing 10, and a screw hole is formed in an upper end portion of the projection 11. The metal is exposed on the back surface of the circuit board 29 by performing solder leveling treatment on the 2 nd ground pattern 70. The exposed metal portion is brought into contact with the convex portion 11. A screw is inserted from above the 2 nd ground pattern 70 and fitted into the screw hole of the boss 11, and the screw is fixed.

In this way, since the 2 nd ground pattern 70 is fixed by being pressed against the convex portion 11, the contact resistance between the 2 nd ground pattern 70, the frame 10, and the ground wiring 30 is reduced.

The ground wiring 30 may be a wiring using a metal plate or a bus bar, or a combination thereof. That is, the 2 nd ground pattern 70 and the housing 10 are not limited to the illustrated wire harness shape, as long as they are conductors that are electrically connected to each other and are equal to the ground potential with respect to direct current that is free from the influence of residual inductance.

In the direct current, similarly, since the ground wiring 30 has a residual resistance component, a potential difference is generated between the ground potential and the 2 nd ground pattern 70 or the housing 10 in accordance with the current flowing through the ground wiring 30. Since the residual resistance component of the ground wiring 30 is sufficiently small, the potential of the ground wiring 30 and the potential of the conductor electrically connected via the ground wiring 30 are considered to be equal to the ground potential hereinafter.

(embodiment 2)

The electronic device 4 including the circuit board 24 according to embodiment 2 has the same configuration as the electronic device 1 according to embodiment 1, and the distances between the 1 st ground pattern 60, the 2 nd ground pattern 70, and the 3 rd ground pattern 80 have a relationship described later.

As shown in the plan view of fig. 9, the shortest distance DA between the 1 st ground pattern 60 and the 3 rd ground pattern 80 of the circuit substrate 24 is larger than the shortest distance DB between the 2 nd ground pattern 70 and the 3 rd ground pattern 80.

Even if a parasitic capacitance component is generated between the 1 st ground pattern 60 and the 3 rd ground pattern 80, the capacitance value thereof is relatively small with respect to the capacitive element 100.

In the circuit diagram shown in fig. 10, the capacitance value of the capacitive element 100 is C, and the capacitance value of the parasitic capacitance component 140 generated between the 1 st ground pattern 60 and the 3 rd ground pattern 80 is C0.

The relative cross-sectional areas of the 1 st ground pattern 60 and the 3 rd ground pattern 80 are S1[ m ] ² ]The relative cross-sectional areas of the 2 nd and 3

rd ground patterns

70 and 80 are S2[ m ] ² ]。

As described above, the distance DA is larger than the distance DB.

Therefore, as shown in the following expression, the capacitance C1F between the 1 st ground pattern 60 and the 3 rd ground pattern 80 and the capacitance C2F between the 2 nd ground pattern 70 and the 3 rd ground pattern 80 can satisfy C2> > C1.

[ mathematics 1]

ε ₀ [F/m]Is vacuum dielectric constant

ε _r [F/m]Relative dielectric constant of circuit board 21

The capacitance value C0 of the parasitic capacitance component 140 is typically C0> C1. However, if the DA ratio DB is made sufficiently large, the value of C0 can be made sufficiently small.

Thus, the capacitance value C0 of the parasitic capacitance component 140 is small enough to be negligible for the electromagnetic noise HN in the high frequency band.

Therefore, as indicated by the thick arrow, electromagnetic noise HN in the high-frequency band, which intrudes from the connector 40, is not transmitted to the 3 rd ground pattern 80 via the parasitic capacitance component 140. 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 is not transmitted to the communication circuit section 50 through the inductance element 90.

As described above, according to the electronic apparatus 4, intrusion of electromagnetic noise HN in the high-frequency band can be prevented more effectively than the electronic apparatus 1.

Embodiment 3

In the

electronic devices

1 and 2, only the 2 nd ground pattern 70 is grounded, but the 1 st ground pattern 60 and the 2 nd ground pattern 70 may be grounded together.

As shown in fig. 11, the electronic device 5 including the circuit board 25 according to embodiment 3 has the same configuration as the electronic device 1 according to embodiment 1, and has the ground wiring 31 connected to the 1 st ground pattern 60, except for the ground wiring 30.

The ground wiring 30 is electrically connected to the 2 nd ground pattern 70 via the ground wiring connection portion 71, and the ground wiring 31 is electrically connected to the 1 st ground pattern 60 via the ground wiring connection portion 61.

The ground

wiring connection portions

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

In fig. 12, the transmission paths of electromagnetic noise HN and noise in the case where electromagnetic noise LN in the low frequency band intrudes into the electronic apparatus 5 are indicated by thick arrows.

The inductance element 90 has a low impedance and the capacitance element 100 has a high impedance with respect to electromagnetic noise LN in a low frequency band that enters from the connector 40.

On the other hand, electromagnetic noise HN in the high frequency band, which enters the 1 st ground pattern 60 from the connector 40, cannot pass through the inductance element 90.

The ground wiring 31 has a residual inductance component, similar to the ground wiring 30. However, if the ground wiring 31 is short, the impedance value of the residual inductance component with respect to the electromagnetic noise HN of the high-frequency band is relatively small.

Therefore, electromagnetic noise HN in the high frequency band, which has entered from the connector 40, is not returned to the shield wiring SW, but is released to the ground through the ground wiring 31.

As described above, according to the electronic device 5, not only electromagnetic noise HN in the high frequency band is not transmitted to the communication circuit section 50, but also transmission of reflected waves of the electromagnetic noise HN in the high frequency band to other devices connected via the communication cable can be suppressed.

Therefore, malfunction of other devices connected to the electronic device 5 via the communication cable can be prevented.

The ground wire 31 is not limited to a wire harness, and may be a plate-like member such as a metal plate or a bus bar.

The ground wiring 31 is an example of the 2 nd ground line in the claims.

The electronic device 5 has two wirings, namely, a ground wiring 30 and a ground wiring 31. However, the 1 st ground pattern 60 and the 2 nd ground pattern 70 may be electrically connected to the housing 10 by using 1 st ground wire 30 as a wire for grounding the 1 st ground pattern 60 and the 2 nd ground pattern 70.

Specifically, as shown in fig. 13, metal

convex portions

11 and 12 may be arranged in the housing 10, the 1 st ground pattern 60 and the convex portion 12 may be connected by a screw 110, and the 2 nd ground pattern 70 and the convex portion 11 may be connected by a screw 110.

Thus, the 1 st ground pattern 60 and the 2 nd ground pattern 70 are grounded via the housing 10.

Embodiment 4

The grounding wire 31 of the electronic device 5 is a wire directly grounding the 1 st grounding pattern 60, but the structure of grounding the 1 st grounding pattern 60 is not limited thereto.

As shown in fig. 14, the electronic device 6 according to embodiment 4 includes a ground wiring 32 different from the ground wiring 30 on the circuit board 26. The electronic device 6 has a 4 th ground pattern 150 electrically connected to the ground wiring 32 and different from the 1 st ground pattern 60, the 2 nd ground pattern 70, and the 3 rd ground pattern 80.

Between the 1 st ground pattern 60 and the 4 th ground pattern 150, a varistor element 160, which is an element whose resistance value decreases if the applied voltage increases, is arranged.

The electronic apparatus 6 has an effect of effectively releasing electromagnetic noise HHN of a high-voltage high-frequency band to the ground.

Effects of the electronic device 6 will be described with reference to fig. 15.

When electromagnetic noise HHN of high voltage and high frequency enters from the connector 40, a high voltage is applied to the varistor element 160 connected to the 1 st ground pattern 60, and the varistor element 160 has a low impedance. Accordingly, the electromagnetic noise HHN of high voltage and high frequency, which has entered from the connector 40, is released from the ground wiring 32 to the ground through the varistor 160 and the 4 th ground pattern 150.

Therefore, according to the electronic device 6, even if electromagnetic noise HHN of high voltage and high frequency intrudes from the connector 40, dielectric breakdown of the inductance element 90, the capacitance element 100, the communication circuit section 50, and the like can be prevented.

The ground line 32 is an example of the 2 nd ground line in the claims.

Embodiment 5

The inductance element 90 connected between the 1 st ground pattern 60 and the 2 nd ground pattern 70 may not be a coil as a separate component.

As shown in fig. 16, the electronic device 7 including the circuit board 27 according to embodiment 5 has 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 1 st ground pattern 60 and the 2 nd ground pattern 70.

The copper foil pattern 91 is a conductor having an inductance component with respect to electromagnetic noise HN in a high frequency band. The specific position, width, length, thickness, etc. of the copper foil pattern 91 are designed based on the structure of the circuit board 27, the material of the dielectric included in the circuit board 27, the thickness, etc. by a method such as a normal strip line or microstrip line.

According to the electronic device 7, the inductance element 90 in the electronic device 1 can be formed by the copper foil pattern 91 when the 1 st ground pattern 60 and the 2 nd ground pattern 70 are printed. In this way, since the coil is not required as a separate component, the number of components of the electronic device 7 can be reduced as compared with 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 saving of the electronic device 7 are realized.

Further, the shape of the copper foil pattern 91 is not limited to an elongated rectangle. The copper foil pattern 91 may be a coil formed by using a layer of the circuit board 27, for example. This makes it possible to increase the inductance of the copper foil pattern 91.

Embodiment 6

Unlike the electronic device 1 in which the circuit board 21 is formed of a single-sided board, the electronic device 8 according to embodiment 6 is configured such that the circuit board 28 is formed of a multilayer board 170 and a copper foil pattern is provided inside the multilayer board 170.

As shown in fig. 17, the multilayer substrate 170 includes two

dielectric layers

171 and 172 as dielectric layers, an inner layer 173 that is a layer sandwiched between the two

dielectric layers

171 and 172, and a surface layer 174 disposed on the outermost side, and the communication circuit portion 50, the 1 st ground pattern 60, the 2 nd ground pattern 70, the 3 rd ground pattern 80, and the like are mounted on the surface layer 174.

Dielectric layer 171 is an example of the 1 st dielectric layer in the claims, dielectric layer 172 is an example of the 2 nd dielectric layer in the claims, and surface layer 174 is an example of the topmost layer in the claims.

As shown in fig. 18, the 1 st ground pattern 60, the 2 nd ground pattern 70, and the 3 rd ground pattern 80 are arranged on the outermost layer of the multilayer substrate 170.

As indicated by the broken line, a 5 th ground pattern 81, which is a copper foil pattern, is disposed at a position facing the communication circuit section 50.

As shown in fig. 19, which is a cross-sectional view of the electronic device 8 taken along line A-A, the 5 th ground pattern 81 is disposed on the inner layer 173 and sandwiched between the

dielectric layers

171 and 172.

The 3 rd ground pattern 80 disposed on the surface layer 174 and the 5 th ground pattern 81 disposed on the inner layer 173 are electrically connected through the via hole 180.

The via hole 180 is an example of a connection conductor in the claims.

Up to this point, a case where electromagnetic noise HN in a high frequency band intrudes from the connector 40 has been studied. However, the electromagnetic noise HN in the high-frequency band is not limited to intrusion from the connector 40.

For example, electromagnetic noise HN in a high frequency band may intrude from a path other than the connector 40 due to electromagnetic spatial coupling.

If the potential of one of the front and back surfaces of the dielectric layer 171 changes due to electromagnetic noise HN in the high frequency band, the potential of the other surface also changes. Moreover, the potentials that change with the same phase cancel each other out due to common mode coupling. Therefore, no voltage fluctuation occurs among the communication circuit section 50, the 3 rd ground pattern 80, and the 5 th ground pattern 81.

The reason for this will be described below.

First, if electromagnetic noise HN in a high frequency band enters the communication circuit unit 50 and the voltage of the communication circuit unit 50 fluctuates by Δv, the voltage of the 5 th ground pattern 81 disposed opposite to the communication circuit unit 50 also fluctuates by Δv. Further, since the 3 rd ground pattern 80 and the 5 th ground pattern 81 are electrically connected through the via hole 180, the voltage of the 3 rd ground pattern 80 also fluctuates Δv.

Therefore, the voltage of the communication circuit portion 50 and the voltage of the 3 rd ground pattern 80 are kept at the same voltage.

If electromagnetic noise HN in the high frequency band enters the 3 rd ground pattern 80 and the voltage of the 3 rd ground pattern 80 fluctuates by Δv, the voltage of the 5 th ground pattern 81 electrically connected to the 3 rd ground pattern 80 through the via hole 180 also fluctuates by Δv. The voltage of the communication circuit unit 50 disposed opposite to the 5 th ground pattern 81 also varies by Δv.

In addition, even when electromagnetic noise HN in the high-frequency band enters both the communication circuit unit 50 and the 3 rd ground pattern 80, the voltage of the communication circuit unit 50 and the voltage of the 3 rd ground pattern 80 are kept at the same voltage.

In this way, even when electromagnetic noise HN in the high-frequency band enters from a path other than the connector 40, a difference does not occur between the voltage of the communication circuit section 50 and the voltage of the 3 rd ground pattern 80 which becomes the reference potential of the communication circuit section 50.

Therefore, according to the electronic device 8, even in such a case, malfunction of the communication circuit section 50 is less likely to occur.

The present invention can be embodied in various forms and modifications without departing from the broad spirit and scope of the present invention. The above embodiments are for explaining the present invention, and do not limit the scope of the present invention. That is, the scope of the present invention is not expressed by the embodiments but by the claims. Further, various modifications performed within the scope of the claims and the scope of the meaning of disclosure equivalent thereto are considered to fall within the scope of the present invention.

Description of the reference numerals

1. 2, 3, 4, 5, 6, 7, 8 electronic equipment, 10 housing, 11, 12 protrusion, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 circuit substrate, 30, 31, 32 ground wiring, 40 connector, 50 communication circuit portion, 60 1 st ground pattern, 61 ground wiring connection portion, 70 2 nd ground pattern, 71 ground wiring connection portion, 80 rd ground pattern, 81 th ground pattern, 90 inductance element, 91 copper foil pattern, 100 capacitance element, 110 screw, 130 connection member, 140 parasitic capacitance component, 150 th ground pattern, 151 ground wiring connection portion, 160 varistor element, 170 multilayer substrate, 171, 172 dielectric layer, 173 inner layer, 174 surface layer, 180 via hole, B1 connector body, C, C0 capacitance value, distance between DA 1 st ground pattern and 3 rd ground pattern, distance between 2 nd ground pattern and 3 rd ground pattern, DS1, DS2 differential communication wiring, NS, HN inductance value, high frequency band of electromagnetic noise, and 3 h, high frequency band of electromagnetic wave P, 3, and 3 h electromagnetic wave band of electromagnetic wave shielding, 3, and 3 h 1, 3, high frequency band of electromagnetic wave shielding, and 3, high frequency band of wave, and 3, electromagnetic wave shielding portions of the electromagnetic wave shielding.

Claims

1. A circuit board connected to a signal line group including a ground line, a communication circuit unit mounted on the circuit board, the communication circuit unit processing a signal received via the signal line group or a signal transmitted via the signal line group,

the circuit board comprises:

a 1 st ground pattern connectable to the ground line in the signal line group;

2. The circuit substrate of claim 1, wherein,

the shortest distance between the 1 st ground pattern and the 3 rd ground pattern is greater than the shortest distance between the 2 nd ground pattern and the 3 rd ground pattern.

3. The circuit substrate according to claim 1 or 2, wherein,

the 2 nd grounding wire is electrically connected with the 1 st grounding pattern,

the 1 st ground line is different from the 2 nd ground line.

4. The circuit substrate according to claim 3, wherein,

the circuit substrate has a 4 th grounding pattern, the 4 th grounding pattern is electrically connected with the 1 st grounding pattern through a variable resistance element,

the 2 nd ground line is electrically connected with the 4 th ground pattern.

5. The circuit substrate according to claim 1 or 2, wherein,

the inductance element is a copper foil pattern.

6. The circuit substrate according to claim 1 or 2, wherein,

the circuit board includes: a 1 st dielectric layer comprising a 1 st dielectric; a 2 nd dielectric layer comprising a 2 nd dielectric; an inner layer disposed between the 1 st dielectric layer and the 2 nd dielectric layer, the inner layer including a 5 th ground pattern; and an outermost layer which is a layer in contact with the 1 st dielectric layer and is located on a different side from the inner layer,

the 1 st grounding pattern, the 2 nd grounding pattern and the 3 rd grounding pattern are arranged on the surface layer,

the 3 rd ground pattern and the 5 th ground pattern are electrically connected by a connection conductor penetrating the 1 st dielectric layer,

the communication circuit unit is disposed on the outermost layer so as to face the 5 th ground pattern.

7. The circuit substrate according to claim 1 or 2, wherein,

the resonant frequency of the T-shaped filter circuit comprising the inductance element, the capacitance element and the 1 st grounding wire is different from the frequency of the received signal or the frequency of the transmitted signal.

8. An electronic device comprising the circuit substrate of any one of claims 1 to 7, the electronic device having:

a connector connected to the signal line group; and

and a wiring for connecting the signal line group to the communication circuit section via the connector and connecting the ground line to the 1 st ground pattern.