Communication device and communication system

Abstract

Provided is a communication device and a communication system that have an electrostatic discharge protection circuit that can suppress electrostatic discharge that hinders high-speed communication. A communication device (1) has an electrostatic discharge protection circuit (26) disposed between a connection line (16, 18) that connects a communication bus (40) and a transceiver (14) and a ground potential. The electrostatic discharge protection circuit is provided in the connection line and has two reverse-connected Zener diodes (28 and 32, 30 and 32) that become conductive when a voltage of a prescribed value or more is applied, and a capacitor (36) connected in series with the two Zener diodes.

Description

Technical Field

[0001] This disclosure relates to communication devices and communication systems. Background Technology

[0002] For example, Patent Document 1 discloses a communication device having an electrostatic discharge (ESD) protection circuit consisting of two Zener diodes connected in reverse and a common-mode choke for suppressing common-mode noise.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2013-187772 Summary of the Invention

[0004] The problem that the invention aims to solve In recent years, various electric drive devices and multiple electronic control units have been installed in vehicles for purposes such as ADAS (Advanced Driver Assistance Systems), smart entry, infotainment, anti-theft, and communication with external servers. Therefore, there is a tendency for increased current consumption in vehicles. To address this increase in current consumption, the voltage of vehicle batteries has been increased (e.g., from 12V to 48V).

[0005] In addition, multiple electronic control devices within the vehicle have communication devices for communicating with each other via an in-vehicle LAN (Local Area Network) in order to share control data, detection data, or perform coordinated control.

[0006] In the case of a communication device equipped with an ESD protection circuit as described in Patent Document 1, for example, if an abnormality occurs where the communication line of the vehicle's LAN is short-circuited to the vehicle's power line, the power supply voltage generated by the vehicle's battery may be applied to the ESD protection circuit. In this case, if a voltage significantly exceeding the breakdown voltage of the Zener diode is applied to the ESD protection circuit due to the high voltage of the battery, the ESD protection circuit may be damaged.

[0007] When the vehicle's LAN communication line is short-circuited with the vehicle's power line, to protect the ESD protection circuit, one could consider increasing the breakdown voltage of the Zener diode in the ESD protection circuit. However, increasing the breakdown voltage of the Zener diode tends to increase the heat generated when the same amount of static electricity is applied. Therefore, to prevent damage caused by overheating, a Zener diode with a high allowable loss is required.

[0008] However, the parasitic capacitance of a Zener diode, which allows for high losses, also increases, thus increasing the passivation of the communication signal waveform. Therefore, ESD protection circuits may hinder high-speed communication. Furthermore, this problem also occurs when ESD protection circuits are constructed using varistors.

[0009] This disclosure was made in view of the above-mentioned problems, and its object is to provide a communication device and communication system having an electrostatic discharge protection circuit capable of suppressing electrostatic discharge that hinders high-speed communication.

[0010] Methods for solving problems To achieve the above objectives, the communication device disclosed herein is a communication device connected to a communication bus, and includes: The transceiver transmits and receives communication signals via the communication bus; and An electrostatic discharge protection circuit is configured between the connection line connecting the communication bus and the transceiver and the ground potential. The electrostatic discharge protection circuit has the following features: A conducting element becomes conductive when a voltage exceeding a specified value is applied; and A capacitor is connected in series with the conducting element.

[0011] In the communication device of this disclosure, when an abnormality occurs where the communication bus is short-circuited to a high voltage, if the high voltage reaches or exceeds a predetermined value, the conducting element becomes conductive. Then, the capacitor is charged via the conductive element. If the high voltage is a DC voltage, corresponding to the case where the capacitor is fully charged, almost no current flows through the conducting element, or even if it does, only a very small current flows. Therefore, the electrostatic discharge protection circuit can be protected even without excessively increasing the voltage at which the conducting element becomes conductive. As a result, the electrostatic discharge protection circuit's interference with high-speed communication can be suppressed.

[0012] Furthermore, in the event of electrostatic discharge (ESD), since the ESD is an alternating current component, it passes through the capacitor. Therefore, the capacitor will not adversely affect the protection against ESD.

[0013] In addition, the communication system disclosed herein has the following features: The aforementioned multiple communication devices; and A communication bus that connects to multiple communication devices.

[0014] Therefore, in a communication system, protection against electrostatic discharge can be achieved in each communication device, and high-speed communication can be carried out between multiple communication devices.

[0015] For ease of understanding of this disclosure, the reference numerals in parentheses above indicate only one example of the correspondence with the specific structures in the embodiments described later, and are not intended to limit the scope of this disclosure in any way.

[0016] Furthermore, the technical features described in each of the claims, other than those of the present disclosure, become clear from the following description of the embodiments and the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a structural diagram illustrating an example of the structure of the communication device according to the first embodiment.

[0018] Figure 2 This is a structural diagram illustrating an example of the electrostatic protection circuit structure of the communication device in Modified Example 1.

[0019] Figure 3 This is a structural diagram illustrating an example of the electrostatic protection circuit structure of the communication device in Modified Example 2.

[0020] Figure 4 This is a structural diagram showing another example of the electrostatic protection circuit structure of the communication device in Modified Example 2.

[0021] Figure 5 This is a structural diagram illustrating an example of the electrostatic protection circuit structure of the communication device in Modified Example 3.

[0022] Figure 6 This is a structural diagram illustrating one example of the structure of the communication device in Modification 4.

[0023] Figure 7 This is a structural diagram illustrating another example of the electrostatic protection circuit structure of the communication device in Modification Example 4.

[0024] Explanation of reference numerals in the attached figures 1: Communication device; 10: Microcomputer; 12: CAN controller; 14: CAN transceiver; 16: First connecting line; 18: Second connecting line; 20: Common mode choke; 22: First wiring; 24: Second wiring; 26, 26A, 26B, 26C, 26D: ESD protection circuits; 28, 28A, 28B, 28C: Zener diode; 29: Varistor; 30, 30A, 30B, 30C: Zener diodes; 31: Varistor; 32, 32A, 32B1, 32B2, 32C1, 32C2: Zener diodes; 33: Connection point; 34: Shared cabling; 36: Capacitor; 38: Resistance; 40: Communication bus; 101: Communication device; 110: Microcomputer; 112: LIN controller; 114: LIN transceiver; 116: Connecting cable; 120: Choke coil; 122: Wiring; 126: ESD protection circuit; 128: Zener diode; 129: Varistor; 132: Zener diode; 136: Capacitor; 138: Resistance; 140: Communication bus Detailed Implementation

[0025] Hereinafter, embodiments of the communication device and communication system involved in this disclosure will be described with reference to the accompanying drawings. However, this disclosure is not limited to the following embodiments, and the various modifications described below are also included within the technical scope of this disclosure. Furthermore, in addition to the following, various modifications can be made without departing from the spirit of this disclosure. The embodiments and various modifications can be appropriately combined to implement them without creating technical contradictions. In the following description, for the same or similar structures, descriptions are sometimes omitted by referring to the same reference numerals in multiple drawings. In addition, when only a part of the structure is mentioned, descriptions of other parts can be applied to other parts.

[0026] (First Implementation) Figure 1 This is a structural diagram illustrating an example of the structure of the communication device 1 according to this embodiment. The communication system comprises... Figure 1 The communication system is constructed by connecting multiple communication devices 1 to a communication bus 40. Thus, in the communication system, the multiple communication devices 1 can communicate with each other via the communication bus 40.

[0027] Communication systems are used, for example, to enable communication between various electronic control units (ECUs) installed in a vehicle. That is, the communication system can be configured such that multiple ECUs can communicate with each other via a local area network constructed within the vehicle, consisting of a communication bus 40. Vehicles include passenger cars, motorcycles, transport vehicles, construction vehicles, agricultural vehicles, etc. Furthermore, communication systems can also be applied to purposes other than vehicle use.

[0028] In communication systems, various communication protocols can be used, such as CAN (Controller Area Network, registered trademark), CAN-FD (CAN with Flexible Data Rate, registered trademark), Ethernet (registered trademark), LIN (Local Interconnect Network), and FlexRAY (registered trademark). Furthermore, in the following description, the registered trademarks for CAN, CAN-FD, Ethernet, and FlexRAY will be omitted. Additionally, examples of using CAN as a communication protocol will be explained below.

[0029] Communication device 1 is one of the aforementioned vehicle ECUs. Communication device 1 communicates via a communication bus (CAN bus) 40 with other vehicle ECUs (other communication devices), such as body ECUs, engine ECUs, motor ECUs, transmission ECUs, brake ECUs, navigation ECUs, autonomous driving ECUs, sensor ECUs for detecting sensor signals, and drive ECUs for driving actuators. When using CAN as the communication protocol, communication between vehicle ECUs is implemented in units of communication frames within the CAN protocol.

[0030] In CAN, a two-wire communication line, such as twisted pair cable, is used as the communication bus 40. Terminal resistors (not shown) are connected to both ends of the two-wire communication line. The high-potential side line (CAN_H) 42 of the two-wire communication line transmits signals whose voltage level varies within the voltage range of the high-potential side (e.g., 2.5V and 3.5V). On the other hand, the low-potential side line (CAN_L) 44 of the two-wire communication line transmits signals whose voltage level varies within the voltage range of the low-potential side (e.g., 1.5V and 2.5V).

[0031] The signals on the high-potential side 42 and the low-potential side 44 are signals with inverted voltage levels. Furthermore, each communication device 1 determines whether the state of the communication bus 40 is logic "1" (recessive) or logic "0" (dominant) based on the voltage difference between the high-potential side 42 and the low-potential side 44 of the two-wire communication line.

[0032] More specifically, when the voltage level of the high-potential side line 42 is low and the voltage level of the low-potential side line 44 is high, the potential difference is small, so the communication device 1 determines the state of the communication bus 40 as logic "1" (recessive). On the other hand, when the voltage level of the high-potential side line 42 is high and the voltage level of the low-potential side line 44 is low, the potential difference is large, so the communication device 1 determines the state of the communication bus 40 as logic "0" (dominant). Thus, in CAN, communication is carried out through a two-wire differential voltage method.

[0033] like Figure 1 As shown, the communication device 1 includes a microcomputer (hereinafter, microcomputer) 10, a CAN transceiver 14, a common mode choke 20, and an electrostatic discharge (ESD) protection circuit 26.

[0034] like Figure 1 As shown, the microcomputer 10 has a built-in CAN controller 12 that controls communication with other communication devices according to the CAN protocol. In addition, although not shown, the microcomputer 10 has processors such as CPU (Central Processing Unit) and MPU (Micro Processing Unit), memory such as RAM (Random Access Memory), and non-volatile storage media such as flash memory and SSD (Solid State Drive).

[0035] A processor is an arithmetic processing device. A processor can also be implemented by combining multiple arithmetic units. Upon startup of the microcomputer 10, the processor reads programs stored in non-volatile storage media and executes prescribed arithmetic operations based on those programs. The microcomputer 10 starts up when power is connected.

[0036] The memory is volatile memory. Because the processor performs calculations, the memory temporarily stores the programs and data required for those calculations. Non-volatile storage media is non-volatile and rewritable memory. Non-volatile storage media stores the microcomputer's boot program, control programs used to implement specified functions, learning data, and other programs.

[0037] The CAN controller 12 is used to control communication with other communication devices via the communication bus 40 according to the CAN protocol. For example, the CAN controller 12 frames the data generated by the processor of the microcomputer 10 according to the CAN protocol and sends it to the communication bus 40 via the CAN transceiver 14. In addition, the CAN controller 12 receives frames sent to the microcomputer 10 from other communication devices via the CAN transceiver 14 and performs data extraction, etc.

[0038] Furthermore, the CAN controller 12 implements arbitration control (so-called arbitration) when frames collide on the bus, as well as error detection and notification related to frame transmission and reception. The CAN controller 12 can be configured to operate at TTL (Transistor-transistor logic) or CMOS (Complementary Metal Oxide Semiconductor) levels, for example.

[0039] The CAN controller 12 has a transmit terminal Tx for outputting transmit frames that cause the CAN transceiver 14 to transmit, and a receive terminal Rx for inputting receive frames from the CAN transceiver 14 as signal input / output terminals. The transmit terminal Tx of the CAN controller 12 is electrically connected to the frame signal input terminal TxD of the CAN transceiver 14. The receive terminal Rx of the CAN controller 12 is electrically connected to the frame signal output terminal RxD of the CAN transceiver 14.

[0040] The CAN transceiver 14 performs transmission processing, sending the transmission frame input from the CAN controller 12 to the communication bus 40. More specifically, when sending the transmission frame to the communication bus 40, the CAN transceiver 14 generates two potential differences, large and small, on the two-wire communication line of the communication bus 40 according to the logic level of each bit constituting the transmission frame. In this way, the CAN transceiver 14 transmits the transmission frame by generating a potential difference on the two-wire communication line of the communication bus 40 corresponding to the digital signal "1" or "0".

[0041] Furthermore, the CAN transceiver 14 performs reception processing, receiving communication frames destined for the communication device 1 transmitted on the communication bus 40 and outputting them as receive frames to the CAN controller 12. Specifically, the CAN transceiver 14 converts the potential difference generated on the communication bus 40 into a digital signal and outputs it as a receive frame to the CAN controller 12. The CAN controller 12 determines whether the receive frame is a communication frame destined for the communication device 1 based on the ID and other information contained in the receive frame. Then, if it is determined to be a communication frame destined for the communication device 1, it extracts data from the communication frame and outputs it to the processor of the microcomputer 10.

[0042] Furthermore, when performing the aforementioned transmission and reception processes, the CAN transceiver 14 can convert the TTL (or CMOS) level signal processed by the CAN controller 12 into a CAN level signal, or perform the reverse conversion process.

[0043] As described above, in order for the CAN transceiver 14 to send or receive communication frames on the communication bus 40, the CAN transceiver 14 has a CAN-H terminal and a CAN-L terminal. The CAN-H terminal of the CAN transceiver 14 is connected to the high-potential side line (CAN-H) 42 of the communication bus 40 via a first connecting line 16. The CAN-L terminal of the CAN transceiver 14 is connected to the low-potential side line (CAN-L) 44 of the communication bus 40 via a second connecting line 18.

[0044] A common-mode choke 20 is disposed between the two-wire communication lines of the CAN transceiver 14 and the communication bus 40, on the first connection line 16 and the second connection line 18. The common-mode choke 20 acts as an inductor relative to the common-mode noise current flowing in the same direction on the first connection line 16 and the second connection line 18, thereby suppressing the common-mode noise current. Furthermore, the common-mode choke 20 can be omitted if countermeasures against the common-mode noise current are not required.

[0045] ESD protection circuit 26 is used, for example, to protect communication device 1 from static electricity discharge by operators during handling, assembly into vehicles, etc. ESD protection circuit 26 is configured between the first connection line 16 and the second connection line 18 connecting the communication bus 40 and the CAN transceiver 14 and the ground potential. Furthermore, in the event that static electricity is about to enter communication device 1 via the first connection line 16 and / or the second connection line 18, the static electricity is released to the ground potential, thereby protecting the CAN transceiver 14 and the microcomputer 10 of communication device 1.

[0046] With the common-mode choke 20 in place, the ESD protection circuit 26 is preferably configured between the first connection line 16 and the second connection line 18 between the CAN transceiver 14 and the common-mode choke 20 and the ground potential. Thus, for example, in the event of an anomaly where one of the two-wire communication lines of the communication bus 40 is short-circuited to ground, the flyback voltage generated by the common-mode choke 20 can be prevented from being applied to the CAN transceiver 14 and the microcomputer 10.

[0047] More specifically, in the event of an anomaly where one of the two-wire communication lines of the communication bus 40 is short-circuited to ground, the potential of one of the first connecting lines 16 and 18, where the common-mode choke 20 is installed, is fixed to the ground potential. In this state, if the current flowing on the other side of the first connecting line 16 and 18 changes due to the transmission and reception of communication signals, energy is stored in the common-mode choke 20 when a large current value is flowing. Furthermore, when the current value decreases, the common-mode choke 20 generates a flyback voltage through the stored energy.

[0048] If the ESD protection circuit 26 is configured between the first connection line 16 and the second connection line 18 between the CAN transceiver 14 and the common-mode choke 20 and the ground potential, the aforementioned flyback voltage can be released to the ground potential via the ESD protection circuit 26. Thus, the CAN transceiver 14 and the microcomputer 10 can be protected from the flyback voltage generated by the common-mode choke 20.

[0049] ESD protection circuit 26 is connected to a first wiring 22 connected to a first connection line 16 and a second wiring 24 connected to a second connection line 18, and is connected to ground potential. ESD protection circuit 26 has three Zener diodes 28, 30, and 32, a capacitor 36, and a resistor 38.

[0050] Three Zener diodes 28, 30, and 32 are conducting elements that become conductive when a voltage exceeding a specified value (i.e., breakdown voltage or Zener voltage) is applied. The three Zener diodes 28, 30, and 32 are configured to operate at a voltage greater than that required for normal communication signal transmission and reception, and are substantially the same Zener voltage. Zener diode 28 is positioned on the first wiring 22 with its direction of forward bias from the first connection line 16 towards ground potential. Zener diode 30 is positioned on the second wiring 24 with its direction of forward bias from the second connection line 18 towards ground potential.

[0051] The first wiring 22 and the second wiring 24 are connected to each other at connection point 33 to form a common wiring 34. A Zener diode 32 is installed on the common wiring 34 with the direction from ground potential toward the first connection line 16 and the second connection line 18 as positive.

[0052] In other words, a Zener diode 28 and a Zener diode 32 are provided in reverse connection between the first connection line 16 and the ground potential. Additionally, a Zener diode 30 and a Zener diode 32 are provided in reverse connection between the second connection line 18 and the ground potential. Thus, Zener diode 32 is shared by Zener diodes 28 and 30. This reduces the number of Zener diodes required. Zener diodes 28 and 30 correspond to one of the first and second Zener diodes of this disclosure. Zener diode 32 corresponds to the other of the first and second Zener diodes of this disclosure.

[0053] With the above structure, regardless of the direction in which the voltage caused by electrostatic discharge is generated, Zener diodes 28 and 32, and / or Zener diodes 30 and 32, become conductive at the point when the voltage exceeds the Zener voltage. This allows static electricity to be released to ground potential, protecting the CAN transceiver 14 and microcomputer 10 of communication device 1.

[0054] For example, if the voltage of the vehicle's battery becomes too high, and an abnormality occurs where the communication bus 40 is short-circuited to the power line supplying the high voltage from the battery, a high DC voltage may be applied to the communication device 1 via the connecting lines 16 and 18. If a voltage significantly exceeding the Zener voltage of the Zener diodes 28, 30, and 32 is applied to the communication device 1 at this time, the Zener diodes 28, 30, and 32, i.e., the ESD protection circuit 26, may be damaged.

[0055] When the communication bus 40 is short-circuited to the power line, to protect the ESD protection circuit 26, it is considered to increase the Zener voltage of the Zener diodes 28, 30, and 32 in the ESD protection circuit 26. However, if the Zener voltage of the Zener diodes 28, 30, and 32 is increased, there is a tendency for increased heat generation when the same amount of static electricity is applied. Therefore, to prevent damage caused by heat generation, Zener diodes 28, 30, and 32 with high allowable losses are required.

[0056] However, Zener diodes 28, 30, and 32, which have high loss tolerance, tend to have increased parasitic capacitance. This increases the passivation of the waveforms of communication signals transmitted and received via the first and second connection lines 16 and 18. Therefore, the ESD protection circuit 26 may hinder high-speed communication.

[0057] Therefore, in this embodiment, in the ESD protection circuit 26, a capacitor 36 is connected in series with the two Zener diodes (28 and 32, 30 and 32) connected in reverse to the ground potential side. In other words, the capacitor 36 is connected to the ground potential side of the Zener diode 32 in the common wiring 34. By setting the capacitor 36 in the common wiring 34 in this way, the number of capacitors 36 can be reduced.

[0058] When a short circuit occurs on the communication bus 40, causing a high voltage to be applied to the communication device 1 due to a high voltage from the battery, if the high voltage is above the Zener voltage, the two Zener diodes connected in reverse become conductive. Thus, the capacitor 36 is charged via the two conductive Zener diodes. Since the high voltage from the battery is a DC voltage, when the capacitor 36 is fully charged, almost no current flows through the two Zener diodes, or even if it does, only a very small current flows. Therefore, the ESD protection circuit 26 can be protected even without excessively increasing the Zener voltage of the Zener diodes 28, 30, and 32. As a result, the ESD protection circuit 26 can be prevented from interfering with high-speed communication.

[0059] Furthermore, when the two Zener diodes (28 and 32, 30 and 32) connected in reverse during electrostatic discharge become conductive, the electrostatic discharge is of an alternating current component and thus passes through capacitor 36. Therefore, capacitor 36 does not adversely affect electrostatic discharge protection. Moreover, capacitor 36 is connected to the ground potential side of the two Zener diodes. The Zener voltage of the two Zener diodes is set to be higher than the voltage during normal communication signal transmission and reception. Therefore, during normal communication signal transmission and reception, the two Zener diodes remain in the off state. Thus, the influence of the electrostatic capacitance of capacitor 36 on the waveform of the communication signal can be suppressed.

[0060] In the ESD protection circuit 26 of this embodiment, resistor 38 is connected in parallel with capacitor 36. If residual charge remains in capacitor 36, for example, potential changes in the first and second connection lines 16 and 18 may affect the communication signal waveform. Connecting resistor 38 in parallel with capacitor 36 allows for the formation of a discharge path for the charge in capacitor 36. Resistor 38 preferably has a high resistance value, for example, 100kΩ or higher, to prevent thermal damage in the event of a short circuit to a high voltage from the battery on the communication bus 40. However, if a capacitor with current leakage is used as capacitor 36, resistor 38 can be omitted.

[0061] The communication system of this embodiment includes multiple communication devices 1 as described above. Furthermore, in the communication system, the multiple communication devices 1 are configured to communicate with each other via a communication bus 40. Therefore, according to the communication system of this embodiment, protection against electrostatic discharge can be implemented in each communication device 1, and high-speed communication can be performed between the multiple communication devices 1.

[0062] (Modified example) The preferred embodiments of this disclosure have been described above, but this disclosure is not limited to any of the above embodiments and can be implemented in various ways without departing from the spirit of this disclosure.

[0063] (Variation Example 1) In the first embodiment described above, Zener diode 28 is provided on the first wiring 22 with the direction of forward connection from the first connection line 16 to the ground potential as positive. Zener diode 30 is provided on the second wiring 24 with the direction of forward connection from the second connection line 18 to the ground potential as positive. Zener diode 32 is provided on the common wiring 34 with the direction of forward connection from the ground potential to both the first connection line 16 and the second connection line 18 as positive.

[0064] However, the orientations of the individual Zener diodes 28, 30, and 32 can also be reversed. That is, as shown... Figure 2As shown, Zener diode 28A can also be installed in the first wiring 22 with the direction from ground potential toward the first connection line 16 as the positive direction. Zener diode 30A can also be installed in the second wiring 24 with the direction from ground potential toward the second connection line 18 as the positive direction. Zener diode 32 can also be installed in the common wiring 34 with the direction from the first connection line 16 and the second connection line 18 toward the ground potential as the positive direction.

[0065] (Variation Example 2) In the first embodiment described above, as a structure in which two Zener diodes are connected in reverse relative to the first connection line 16 and the second connection line 18 respectively, a structure in which Zener diode 32 is shared with Zener diode 28 and Zener diode 30 is shown.

[0066] However, it is also possible to avoid sharing the Zener diode and instead connect the two Zener diodes in reverse connection to the first connection line 16 and the second connection line 18, respectively. That is, as shown... Figure 3 As shown, two Zener diodes 28B and 32B1 connected in reverse can also be placed on the first wiring 22. Alternatively, two Zener diodes 30B and 32B2 connected in reverse can also be placed on the second wiring 24.

[0067] exist Figure 3 In the structure shown, Zener diode 28B is positively oriented from the first connection line 16 towards the ground potential, and Zener diode 32B1 is positively oriented from the ground potential towards the first connection line 16, both located on the first wiring 22. Additionally, Zener diode 30B is positively oriented from the second connection line 18 towards the ground potential, and Zener diode 32B2 is positively oriented from the ground potential towards the second connection line 18, both located on the second wiring 24.

[0068] Additionally, the orientation of each Zener diode connection can also be the same as... Figure 3 The structure is in the opposite direction. That is, as... Figure 4 As shown, alternatively, Zener diode 28C and Zener diode 32C1 can be positioned with the direction from ground potential toward the first connection line 16 as positive, and both can be positioned with the direction from the first connection line 16 toward the ground potential, and are located on the first wiring 22. Alternatively, Zener diode 30C and Zener diode 32C2 can be positioned with the direction from ground potential toward the second connection line 18 as positive, and both can be positioned with the direction from the second connection line 18 toward the ground potential, and are located on the second wiring 24.

[0069] (Variation Example 3) In the first embodiment, Modification 1, and Modification 2 described above, two Zener diodes connected in reverse were used as the conducting elements. However, as... Figure 5As shown, varistors 29 and 31 can also be used as conducting elements. This is because varistors 29 and 31 have the characteristic that their resistance decreases sharply when a voltage exceeding the rheostat voltage (breakdown voltage) is applied in both directions. Figure 5 In the example shown, a varistor 29 is provided in the first wiring 22 and a varistor 31 is provided in the second wiring 24.

[0070] (Variation Example 4) In the first embodiment described above, an example was given of communication in a communication system using a two-wire differential voltage method, with a two-wire communication line serving as the communication bus 40. However, as... Figure 6 As shown, the communication device 101 according to this disclosure can also be applied to a communication system with a single-wire communication line. For example, when LIN is used as the communication protocol, the communication device 101 communicates via a single-wire communication line.

[0071] exist Figure 6 In the example shown, the communication bus 140, which is a single-wire communication line, is connected to the LIN transceiver 114 via a connecting line 116. A choke coil 120 for suppressing noise current is provided on the connecting line 116. The LIN transceiver 114 cooperates with the LIN controller 112 located in the microcomputer 110 to transmit and receive communication frames.

[0072] An ESD protection circuit 126 is provided between the connection line 116 between the LIN transceiver 114 and the choke coil 120 and the ground potential. The ESD protection circuit 126 has a wiring 122 connected to the connection line. Two Zener diodes 128 and 132 are provided in reverse connection on the wiring 122. Furthermore, the orientation of the two Zener diodes 128 and 132 can also be... Figure 6 The orientations shown are opposite. Furthermore, on wiring 122, a capacitor 136 is connected in series with the two Zener diodes 128 and 132 on the ground potential side of the reverse-connected Zener diodes 128 and 132. A resistor 138 is connected in parallel with the capacitor 136.

[0073] The communication device 101 with the above structure can perform the same function as the communication device 1 of the first embodiment.

[0074] in addition, Figure 6 The ESD protection circuit 126 shown can also be used Figure 7 The ESD protection circuit 126A shown is replaced. Figure 7 In the ESD protection circuit 126A, it replaces Figure 6 The ESD protection circuit 126 has two Zener diodes 128 and 132 connected in reverse, and a varistor 129 is provided in the wiring 122.

[0075] (Variation Example 5) In the first embodiment described above, the first connecting line 16 and the second connecting line 18 are connected at connection point 33, and a common wiring 34 is provided between connection point 33 and the ground potential. However, the first connecting line 16 and the second connecting line 18 may also be connected to the ground potential separately, instead of being concentrated on the common wiring 34. In this case, the first connecting line 16 and the second connecting line 18 are respectively connected... Figure 6 The ESD protection circuit 126 shown is... Figure 7 The ESD protection circuit shown is 126A.

[0076] (Technological Ideas) Finally, this specification discloses several technical ideas described in the following list of items. Some items can be described in a multiple dependent format that alternately references multiple preceding items. Furthermore, some items can be described in a multiple multiple dependent format that references multiple items that include other items in the multiple dependent format. Items described in the multiple dependent format and the multiple multiple dependent format define several technical ideas.

[0077] (Technical Idea 1) A communication device, connected to a communication bus, comprising: The transceiver transmits and receives communication signals via the communication bus; and An electrostatic discharge protection circuit is configured between the connection line connecting the communication bus and the transceiver and the ground potential. The electrostatic discharge protection circuit has the following features: A conducting element becomes conductive when a voltage exceeding a specified value is applied; and A capacitor is connected in series with the conducting element.

[0078] (Technical Idea 2) According to the communication device described in technical concept 1, wherein, It also includes a resistor connected in parallel with the capacitor.

[0079] (Technical Idea 3) According to the communication device described in technical concept 1 or 2, wherein, The capacitor is connected in series to the ground potential side of the conducting element.

[0080] (Technical Idea 4) The communication device according to any one of technical concepts 1 to 3, wherein, The conducting element is two Zener diodes or varistors connected in reverse.

[0081] (Technical Idea 5) The communication device according to any one of technical concepts 1 to 4, wherein, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. The communication device also includes a common-mode choke disposed on the two connecting lines. The electrostatic discharge protection circuit is respectively configured between the two connecting lines between the transceiver and the common mode choke and the ground potential.

[0082] (Technical Idea 6) The communication device according to any one of technical concepts 1 to 5, wherein, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. The conductive elements are respectively disposed on the two wirings connected to the two connecting lines. The capacitor is positioned between the connection point where the two wires are connected to form a common wire and the ground potential on the common wire.

[0083] (Technical Idea 7) The communication device according to any one of technical concepts 1 to 5, wherein, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. When the conducting elements are a first Zener diode and a second Zener diode connected in reverse, one of the first Zener diode and the second Zener diode is respectively disposed on two wirings connected to the two connecting lines. The other of the first Zener diode and the second Zener diode is disposed on the common wiring between the connection point where the two wirings are interconnected to form a common wiring and the ground potential. Thus, the other of the first Zener diode and the second Zener diode is shared by one of the first Zener diode and the second Zener diode disposed on the two wirings respectively. The capacitor is positioned on a common wiring harness between the other of the first Zener diode and the second Zener diode and ground potential.

[0084] (Technical Idea 8) The communication device according to any one of technical concepts 1 to 7, wherein, The communication device is used for communication within the vehicle via a local area network constructed within the vehicle.

[0085] (Technical Idea 9) A communication system, comprising: Multiple communication devices (1) as described in any one of technical concepts 1 to 8; and A communication bus connected to the plurality of communication devices.

Claims

1. A communication device connected to a communication bus, characterized in that, have: The transceiver transmits and receives communication signals via the communication bus; and An electrostatic discharge protection circuit is configured between the connection line connecting the communication bus and the transceiver and the ground potential. The electrostatic discharge protection circuit has the following features: A conducting element becomes conductive when a voltage exceeding a specified value is applied; and A capacitor is connected in series with the conducting element.

2. The communication device according to claim 1, characterized in that, It also includes a resistor connected in parallel with the capacitor.

3. The communication device according to claim 1, characterized in that, The capacitor is connected in series to the ground potential side of the conducting element.

4. The communication device according to claim 1, characterized in that, The conducting element is two Zener diodes or varistors connected in reverse.

5. The communication device according to any one of claims 1 to 4, characterized in that, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. The communication device also includes a common-mode choke disposed on the two connecting lines. The electrostatic discharge protection circuit is respectively configured between the two connecting lines between the transceiver and the common mode choke and the ground potential.

6. The communication device according to any one of claims 1 to 4, characterized in that, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. The conductive elements are respectively disposed on the two wirings connected to the two connecting lines. The capacitor is positioned between the connection point where the two wires are connected to form a common wire and the ground potential on the common wire.

7. The communication device according to any one of claims 1 to 4, characterized in that, The communication bus has two communication lines for differential communication. The connection line has two connection lines to connect the transceiver to the two communication lines respectively. When the conducting elements are a first Zener diode and a second Zener diode connected in reverse, one of the first Zener diode and the second Zener diode is respectively disposed on two wirings connected to the two connecting lines. The other of the first Zener diode and the second Zener diode is disposed on the common wiring between the connection point where the two wirings are interconnected to form a common wiring and the ground potential. Thus, the other of the first Zener diode and the second Zener diode is shared by one of the first Zener diode and the second Zener diode disposed on the two wirings respectively. The capacitor is positioned on a common wiring harness between the other of the first Zener diode and the second Zener diode and ground potential.

8. The communication device according to any one of claims 1 to 4, characterized in that, The communication device is used for communication within the vehicle via a local area network constructed within the vehicle.

9. A communication system, characterized in that, have: The plurality of communication devices according to any one of claims 1 to 4; and A communication bus, connected to the plurality of communication devices.

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