JP5478376B2 - Waveform distortion reduction method and wired communication system - Google Patents

Description

  The present invention relates to a waveform distortion reduction method for reducing waveform distortion on a communication line and a wired communication system to which the waveform distortion reduction method is applied.

  In general, in communication systems such as FA (factory automation) equipment and automobiles, multiplex communication that allows transmission of a plurality of signals through one transmission path is employed. For example, in an in-vehicle communication system employed in an automobile, a communication line using a single signal line is used as a low-speed communication system of about 33 kps. As a high-speed communication system of several tens of bps to 10 Mbps, a communication line using a twisted pair cable, a so-called twisted pair cable as a bus, is used. And a vehicle-mounted LAN is comprised by connecting a some node via such a communication line. In the in-vehicle LAN configured as described above, a communication line branched from a main bus is routed for each node, and there are branch points corresponding to the number of nodes. For this reason, when the characteristic impedance of each branched communication line is different, a location where the characteristic impedance is mismatched occurs. As a result, a reflected wave due to impedance mismatching is generated, which may lead to distortion of the signal waveform caused by the reflected wave, and further communication failure. The presence of such reflected waves is a factor that restricts the number of nodes in the communication line and the routing area.

  Therefore, conventionally, as seen in Patent Document 1, for example, a connector having a filter circuit is disposed at a branch point of each communication line so as to attenuate a reflected wave generated due to impedance mismatch. Wired communication systems have also been proposed. 10 and 11 show the wired communication system described in Patent Document 1. FIG.

  As shown in FIG. 10, in this communication system 2, a plurality of electronic control units (ECUs) 4A to 4F are connected to the branch connector 1A provided on the main communication line 3O via the communication lines 3A to 3F, respectively. Electrically connected. Similarly, the plurality of electronic control devices 4G to 4L are electrically connected to the branch connector 1B provided on the communication line 3O via the communication lines 3G to 3L, respectively. Each of the communication lines 3A to 3L is constituted by, for example, a twisted pair cable in which a pair of communication lines are twisted together. Further, termination circuits 5A and 5B having termination resistors are attached to both ends of the communication line 3O.

  Here, as shown in FIG. 11, the internal circuit configuration of the branch connector 1 </ b> A includes a pair of twisted pair cables 3 </ b> Aa to 3 </ b> Oa and 3 </ b> Ab to 3 </ b> Ob constituting the communication lines 3 </ b> A to 3 </ b> O. Are electrically connected. Further, the branch connector 1A has a filter circuit 11 corresponding to each channel therein. The twisted pair cables 3Aa to 3Oa and 3Ab to 3Ob are respectively connected to branch wirings 10a and 10b that branch the communication line 3O for each channel through a filter circuit 11 in which a resistor R and a coil L are connected in parallel. It is connected.

  In the branch connector 1A (1B) configured as described above, the filter circuit 11 close to the branch point of each of the communication lines 3A to 3O is caused due to the mismatch of the characteristic impedance of each of the communication lines 3A to 3O. Each reflected wave is attenuated. Thereby, the waveform distortion by the influence of a reflected wave is suppressed, and expansion of the number of nodes and a wiring area | region in a communication line comes to be aimed at.

JP 2007-201697 A

  By the way, normally, the distortion component of the frequency resulting from the mismatch of the characteristic impedance of each communication line varies depending on the network form such as the line length and the number of branches of the communication line. For this reason, the effect of suppressing distortion by the filter circuit 11 provided in the branch connectors 1A and 1B also changes, and appropriate attenuation of reflected waves according to the network form is not always performed. As a result, the reflected wave generated due to the impedance mismatch cannot be sufficiently attenuated, and even in expanding the wiring area where communication between nodes can be established, it is still improved in practice. It is something that leaves room.

  Further, in the branch connectors 1A and 1B, for example, the eight filter circuits 11 are formed integrally with the branch connectors 1A and 1B, so that they are not actually used when not using all the channels. The filter is arranged up to the place. This unnecessarily increases the number of filters.

Such a problem is not limited to a wired communication system employed in an automobile, but is generally a common problem in a wired communication system that is electrically connected via a communication line.
The present invention has been made in view of such circumstances, and an object thereof is to extend a wiring area where communication can be established through reduction of waveform distortion on a communication line by a minimum necessary filter circuit. And a wired communication system to which the waveform distortion reduction method is applied.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is a waveform distortion reduction method for reducing distortion of a signal waveform communicated between nodes by using a communication line in which a plurality of nodes are branched and connected as a communication medium by a filter circuit. A line length at which the characteristic impedance in a specific frequency band is minimized is obtained for the line length of the connected communication line, and the filter circuit is installed at the position of the obtained line length.

  In the filter circuit, the greater the current value flowing through the filter circuit, the greater the attenuation, and the higher the distortion reduction effect for the waveform distortion included in the current. In the above method, the line length of the characteristic line in the specific frequency band is minimized with respect to the line length of the communication line branched and connected to the node, in other words, the line having the maximum current value flowing in the specific frequency band. The length is obtained, and a filter circuit is installed at the position of the obtained line length. For this reason, in any network form, the minimum necessary filter circuit is installed at an appropriate position where waveform distortion can be reduced according to the line length of the communication line constituting this network. The upper waveform distortion is reduced. Even if digital signals are particularly exchanged between the nodes, the logical level (“0”, “1”) based on the differential voltage is accurately determined. As a result, it is possible to expand a routing area in which communication between nodes can be established while accurately suppressing the influence of reflected waves caused by an increase in the number of nodes and a change in line length.

  According to a second aspect of the present invention, in the waveform distortion reducing method according to the first aspect, the specific frequency band is a distortion of the signal waveform that is analyzed by measuring a communication waveform of the branch-connected communication line. The main point is that it is specified as the frequency band that is the main factor.

  According to the above method, in finding the line length at which the characteristic impedance is minimized, the frequency band that is the main cause of the waveform distortion is specified by spectrum analysis or the like. Based on the characteristic impedance in the specified frequency band, the distortion component that is the main cause of waveform distortion can be reliably reduced by obtaining the path length and installing the filter circuit. become.

  According to a third aspect of the present invention, in the waveform distortion reduction method according to the first or second aspect, a communication line having a large signal waveform distortion is specified in advance among the communication lines, and the communication line is identified. The gist is to install the filter circuit.

  In a wired communication system in which communication lines are branched and connected for each of a plurality of nodes, the magnitude of waveform distortion in each communication line varies depending on the network configuration. That is, the necessity of installing the filter circuit is different for each communication line. For this reason, according to the above method, the filter circuit is installed for a communication line specified in advance as a line having a large signal waveform distortion among the communication lines branched and connected to each node. As a result, when the distortion of the signal waveform is reduced using the filter circuit, the filter circuit can be further reduced and simplified as a wired communication system.

The gist of a fourth aspect of the present invention is the waveform distortion reducing method according to the first or second aspect, wherein the filter circuit is installed separately from the branch-connected communication lines.
If the filter circuit is provided separately from the branch-connected communication lines as in the above method, the distortion of the signal waveform generated in each communication line can be accurately reduced for each communication line. Thereby, the influence of the distortion generated in a certain communication line is accurately suppressed from reaching other communication lines, and communication between the nodes can be performed more accurately.

  According to a fifth aspect of the present invention, in the waveform distortion reduction method according to any one of the first to fourth aspects, the frequency band is specified, and the line length for obtaining the minimum characteristic impedance is recursive. The gist is to install a plurality of filter circuits on a communication line corresponding to a specific node based on a simple execution.

  According to the above method, a plurality of filter circuits are installed in the communication line corresponding to a specific node by recursively executing the specification of the frequency band and the search for the line length that minimizes the characteristic impedance. For this reason, even when the distortion of the signal waveform generated on the communication line is particularly large, it is expected that the distortion of the signal waveform is gradually reduced through the plurality of filter circuits.

  The invention according to claim 6 is a wired communication system in which communication between nodes is performed using a communication line in which a plurality of nodes are branched and connected as a communication medium, according to any one of claims 1 to 5. The gist is to reduce the distortion of the signal waveform through a filter circuit installed based on the waveform distortion reduction method.

  According to the above configuration, the filter circuit is installed at a position where the distortion reduction effect is particularly large in the communication line in which a plurality of nodes are branched and connected. For this reason, communication between each node can be performed more accurately as a wired communication system in which a plurality of nodes are connected by branch-connected communication lines. As a result, the wiring area in which communication can be established can be expanded through the reduction of distortion of the signal waveform by the minimum necessary filter circuit for the wired communication system.

The invention according to claim 7 is a wired communication system including a filter circuit that reduces distortion of a signal waveform communicated between nodes using a communication line in which a plurality of nodes are branched and connected as a communication medium. The gist of the invention is that the node is installed at the position of the line length at which the characteristic impedance in a specific frequency band is minimized among the line lengths of the communication line branched and connected.

  According to the above configuration, the filter circuit is provided at a position where the distortion reduction effect is particularly large among the communication lines in which a plurality of nodes are branched and connected. For this reason, communication between each node can be performed more accurately as a wired communication system in which a plurality of nodes are connected by branch-connected communication lines. As a result, the wiring area in which communication can be established can be expanded through the reduction of distortion of the signal waveform by the minimum necessary filter circuit for the wired communication system.

The invention according to claim 8 is summarized in that in the wired communication system according to claim 6 or 7, the wired communication system is a multiplex communication system constituting an in-vehicle network.
In a multiplex communication system constituting an in-vehicle network, there is a particularly high demand for an increase in the number of nodes and an expansion of a routing area, and the influence of high-frequency distortion accompanying the increase in the number of nodes and the expansion of the routing area is also great. In this regard, according to the above configuration, signal waveform distortion can be suitably reduced through appropriate installation of filter circuits for such a multiplex communication system, and reliability as an in-vehicle network can be improved. .

The block diagram which shows schematic structure of a vehicle-mounted network about one Embodiment of the waveform distortion reduction method and wired communication system concerning this invention. The block diagram which shows an example of the installation aspect of the filter circuit by the waveform distortion reduction method of the embodiment. The flowchart which shows the prescription | regulation procedure of the installation position of the filter circuit by the waveform distortion reduction method of the embodiment. (A) is a graph which shows the amplitude of the receiving voltage of a receiving end for every frequency band. (B) is a graph showing a transition example of the differential voltage measured at the receiving end. (A) And (b) is a figure which shows the relationship between the characteristic impedance of a communication line, and line length. The block diagram which shows an example of the installation aspect of the filter circuit by the waveform distortion reduction method of the embodiment. The block diagram which shows schematic structure of a filter circuit. (A) is a graph which shows the amplitude of the receiving voltage of a receiving end for every frequency band. (B) is a graph showing a transition example of the differential voltage measured at the receiving end. (A)-(c) is a graph which shows the relationship between the amplitude of the received voltage of a receiving end, and a frequency band for every installation position of a filter circuit. The block diagram which shows schematic structure of the conventional wired communication system. The block diagram which shows schematic structure of the branch connector which comprises the wired communication system.

  Hereinafter, an embodiment embodying a waveform distortion reducing method and a wired communication system according to the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of a multiplex communication system constituting an in-vehicle network as a wired communication system to which the waveform distortion reduction method of the present embodiment is applied.

As shown in FIG. 1, this multiplex communication system is configured in accordance with, for example, the FlexRay standard with a bit rate of 5 Mps. The multiplex communication system includes a plurality of electronic control units (ECUs) 101 to 106 that control various devices such as an engine, a brake, and a power window mounted on the vehicle. The electronic control units 101 to 106 are electrically connected to branch connectors 121 to 123 provided on the main communication line 110 via communication lines 111 to 116, respectively. Moreover, each communication line 110-116 is comprised by the twisted pair cable by which a pair of communication line was twisted mutually, for example, and has a predetermined characteristic impedance. Termination circuits 131 and 132 are attached to nodes at both ends of the main communication line 110. Note that nodes having built-in termination circuits may be attached to both ends of the main communication line 110.

  In the in-vehicle network configured as described above, in order to transmit desired information between the respective electronic control units 101 to 106, digital signals based on the differential voltages of the respective communication lines are set using the communication lines 110 to 116 as communication media. Transmission / reception is performed. For example, when a digital signal based on a differential voltage is transmitted from the electronic control device 101, the digital signal is transmitted through the communication line 111, the branch connectors 121 to 123, and the communication lines 110 and 112 to 116 that are branched and connected to the electronic control device 101. The data are transmitted to the other electronic control units 102 to 106 in order. In each of the electronic control devices 102 to 106, communication between the nodes is performed through determination of the logic level “0” or “1” based on the digital signal received from the electronic control device 101, that is, the differential voltage. It becomes like this.

  By the way, in the configuration in which the communication lines 110 to 116 are branched and connected to the plurality of electronic control devices 101 to 106 as described above, impedance mismatch occurs when the characteristic impedances of the communication lines 110 to 116 are different. Then, the signal waveform is reflected at the location where the impedance is mismatched, and the reflection of the signal waveform is synthesized, so that the signal waveform received by each of the electronic control devices 101 to 106 is distorted. As a result, it becomes difficult for each of the electronic control devices 101 to 106 to accurately determine the logic levels “0” and “1” based on the differential voltage.

  Therefore, in the present embodiment, in order to reduce distortion of the signal waveform caused by impedance mismatch, the filter circuits 141 to 141 are disposed at predetermined positions of the communication lines 111 to 116 that are branched and connected to the electronic control devices 101 to 106. 146 will be installed.

Hereinafter, the waveform distortion reduction method of the present embodiment will be described in detail with reference to FIGS.
Here, as shown in FIG. 2, for example, the communication lines 211 to 213 have a branch point a for each of the transmission node 201, the reception node 202, and the termination circuit 203 configured by communication devices such as the electronic control devices 101 to 106. A wired communication system that is branched and connected to a base point is assumed. In this example, the transmission communication line 211 branched to the transmission node 201 has a line length of “1.5 m”, and the reception communication line 212 branched to the reception node 202 has a line length of “2. The line length of the termination side communication line 213 branched and connected to the termination circuit 203 is “2.5 m”. Each of the communication lines 211 to 213 is also configured by a twisted pair cable in which a pair of communication lines are twisted together. Also in the wired communication system configured in this way, similarly to the wired communication system shown in FIG. 1, transmission / reception of digital signals based on a differential voltage with a bit rate of 5 Mbps is performed by the transmission node 201 and the reception node 202. Between.

  In the waveform distortion reduction method of the present embodiment, first, as shown in step S100 in FIG. 3, the transmission node 201 is changed to the reception node 202 without the filter circuit as shown in FIG. For example, a digital signal having a logic level “1” is transmitted. Next, the signal waveform transmitted and received at the reception node 202 serving as the reception end of the digital signal is measured, and the frequency band of the measured signal waveform is analyzed based on Fourier transform (FFT analysis) or the like (step S101). In this embodiment, the signal transmitted from the transmission node 201 to the reception node 202 is identified by an eye diagram indicating the ratio at which the voltage amplitude at the reception end exceeds the threshold for determining the logical level in one bit. This is based on the aperture ratio.

As shown in FIG. 4A as a waveform La1 as an example of the signal waveform thus measured, the voltage amplitude at the receiving end is a reflection of the signal waveform generated due to the impedance mismatch between the communication lines 211 to 213. The waveform includes a distortion component obtained by combining the waves. For this reason, the transition of the voltage amplitude at the receiving end is a greatly distorted waveform as shown by a waveform La2 in FIG. Therefore, the voltage amplitude La2 rising at the timing t1 stabilizes the threshold value Vs for determining whether the digital signal transmitted from the transmission node 201 is at the logic level “0” or “1” in the period Ta1. Cannot be exceeded. In the period Ta2, the voltage amplitude La2 at the receiving end is stabilized and stably exceeds the threshold value Vs. However, this period Ta2 is shorter than the period Ts corresponding to the eyedia aperture ratio, and the signal transmitted from the transmission node 201 to the reception node 202 cannot be recognized as the logical level “1”. As a result, the receiving node 202 cannot accurately exchange information based on the digital signal transmitted from the transmitting node 201.

  Therefore, first, based on the measurement result of the signal waveform shown in FIG. 4A, the frequency band that is the main factor of the distortion of the signal waveform is specified (FIG. 3: step S102). That is, in the example here, the frequency band of “67 MHz” is specified as a frequency band including a distortion component that is a main factor of distortion of the signal waveform.

  Next, the characteristic impedance with respect to the transmission node 201 and the transmission communication line 211 in the specified frequency band “67 MHz” is calculated (FIG. 3: step S103).

  That is, as shown in FIGS. 5A and 5B, an example of the characteristic impedance of the transmission communication line 211 in the “67 MHz” frequency band, the characteristic impedance is determined by the line length L viewed from the transmission node 201 side. While the maximum is at a position near “0.9 m”, the line length is minimum at a position near “0.16 m” and “1.65 m”. For this reason, the value of the current flowing through the transmission communication line 211 that correlates with the characteristic impedance is the largest at the position where the line length is near “0.16 m” and “1.65 m”. The characteristic impedance of the transmission communication line 211 shown in FIG. 5B is a value measured using, for example, a network analyzer.

  Therefore, in the present embodiment, the position where the line length of the transmission communication line 211 branched and connected to the transmission node 201 is near “0.16 m” and “1.65 m” is set to reduce waveform distortion. Is defined as the installation position of the filter circuit (FIG. 3: step S104).

  Then, as shown in FIG. 6 as a diagram corresponding to FIG. 2, the filter circuit 220 is placed at the position where the distance from the transmission node 201 in the transmission communication line 211 becomes the obtained “0.16 m”. Install. As shown in FIG. 7, the filter circuit 220 has a resistor R and a coil L connected in parallel in the middle of each of the pair of communication lines 211a and 211b constituting the transmission communication line 211. The first filter circuit 220a and the second filter circuit 220b are configured. Further, the attenuation amounts of the first filter circuit 220a and the second filter circuit 220b can accurately determine the logical level based on the differential voltage based on the distortion of the signal waveform analyzed in the network configuration shown in FIG. It is set to a value that can be reduced to a possible level.

By installing the filter circuit 220 through such a method, the voltage amplitude at the receiving end is distorted as shown as a transition example Lf1 in FIG. 8A as a diagram corresponding to FIG. 4A. Becomes a greatly reduced waveform. For this reason, the transition of the voltage amplitude at the receiving end shows a stable transition by reducing the distortion as shown in FIG. 8B as a waveform Lf2 corresponding to FIG. 4B. The period Tf that stably exceeds the threshold value Vs is longer than the period Ts. Accordingly, the receiving node 202 can accurately determine whether the digital signal transmitted from the transmitting node 201 is at the logic level “0” or “1” through the determination based on the aperture ratio of the eye diagram. Thus, it is possible to accurately exchange information from the transmission node 201.

  Hereinafter, the relationship between the installation position of the filter circuit 220 and the voltage amplitude at the receiving end in the network configuration shown in FIG. 2 will be described with reference to FIG. 9A to 9C, transition example La1 indicates the transition of the voltage amplitude at the receiving end when the digital signal transmitted from transmission node 201 is set to logic level “1”. 9A to 9C, the transition example Lf16 is a reception end when the filter circuit 220 is installed at a position of “0.16 m” from the transmission node 201 that is the obtained line length. The transition of voltage amplitude is shown. 9A to 9C, transition examples Lb1 to Lb3 are when the filter circuit 220 is installed at the branch point a, the position “0.10 m” from the transmission node 201, and the reception end, respectively. The transition of the voltage amplitude at the receiving end is shown.

  That is, as shown as transition example La1 in FIGS. 9A to 9C, when the filter circuit 220 is not installed on the communication line, the distortion component included in the signal waveform is the largest.

  Further, as shown as transition example Lb1 in FIG. 9A, when the filter circuit 220 is installed at the branch point a, waveform distortion is reduced, but transition example Lf16 is shown in FIG. 9A. As shown, the waveform distortion is larger than when the filter circuit 220 is installed at the obtained position.

  On the other hand, when the filter circuit 220 is installed at a position “1.0 m” from the transmission node 201 in the transmission communication line 211 as shown in the transition example Lb2 in FIG. Since the characteristic impedance is increased as shown in FIG. 5B, the distortion reduction effect by the filter circuit 220 is reduced. For this reason, the distortion component included in the signal waveform is much larger than when the filter circuit 220 is installed at the obtained position.

  Then, as shown as transition example Lb3 in FIG. 9C, even when the filter circuit 220 is installed at the receiving end, the distortion reduction effect by the filter circuit 220 can be obtained, but the above-mentioned is obtained. The distortion reduction effect by the filter circuit 220 is smaller than when the filter circuit 220 is installed at the position.

  As described above, according to the waveform distortion reduction method of the present embodiment, by installing the filter circuit 220 at a position where the characteristic impedance is minimized, the distortion reduction effect by the filter circuit 220 can be suitably enhanced. Information can be accurately transmitted based on the differential voltage.

And as shown in previous FIG. 1, in the structure provided with the some electronic control apparatuses 101-106 and the communication lines 111-116 as a wired communication system by which a digital signal is transmitted / received, each electronic control apparatus 101- For each of the communication lines 111 to 116 branched and connected to each of 106,
a, measurement and analysis of a signal waveform in a state where the filter circuits 141 to 146 are not installed;
b, identification of the frequency band that is the main factor of distortion,
c, calculation of characteristic impedance with respect to the line lengths of the electronic control devices 101 to 106 and the communication lines 111 to 116 in the specified frequency band,
d, filter circuits 141 to 146 for the communication lines 111 to 116 through a process of finding a position where the characteristic impedance is minimized.
The installation position is defined. Then, by installing the filter circuits 141 to 146 at the specified positions, communication between the electronic control devices 101 to 106 can be performed only by the six filter circuits 141 to 146 corresponding to the communication lines 111 to 116. It can be established with high reliability. As a result, in configuring a wired communication system having a communication line branched and connected to a plurality of nodes, a routing area where communication can be established is expanded.

As described above, according to the waveform distortion reduction method and the wired communication system according to the present embodiment, the following effects can be obtained.
(1) The line length at which the characteristic impedance in a specific frequency band is minimized is obtained for the line length of each of the communication lines 111 to 116 branched and connected to each electronic control unit 101 to 106, and the position of the obtained line length is obtained. The filter circuits 141 to 146 are installed. Therefore, the distortion reduction effect by the filter circuits 141 to 146 can be maximized, and the distortion of the signal waveform can be suitably reduced through the installation of the minimum necessary filter circuit. As a result, communication between the electronic control units 101 to 106 can be established with high reliability, and a wired communication system having a communication line branched and connected to a plurality of nodes can be configured. Thus, the routing area where communication can be established is expanded.

  (2) The frequency band that is the main cause of the distortion of the signal waveform is targeted as the characteristic impedance frequency band for which the path length is to be obtained. This makes it possible to reliably reduce distortion components that are the main cause of waveform distortion.

  (3) Each of the filter circuits 141 to 146 is installed separately from each of the communication lines 111 to 116 that are branched and connected to the electronic control devices 101 to 106. For this reason, the waveform distortion which generate | occur | produced in each communication line 111-116 can be reduced now for every such line. Thereby, the influence of the distortion generated in a certain communication line is accurately suppressed to other communication lines, and communication between the respective electronic control devices 101 to 106 can be performed more accurately.

  (4) As a wired communication system provided with a communication line branched and connected for each of a plurality of nodes, a multiplex communication system constituting an in-vehicle network is targeted. As a result, even when high frequency communication is performed in each of the electronic control devices 101 to 106, high frequency distortion caused by impedance mismatch can be suitably reduced. As a result, the network can be configured with a higher degree of freedom while maintaining communication feasibility between the nodes as an in-vehicle network.

In addition, the said embodiment can also be implemented with the following forms.
The characteristic impedance of each of the communication lines 111 to 116 is calculated based on actual measurement values using a network analyzer. In addition, each characteristic impedance may be obtained through a simulation based on the multiplex communication system configured as described above or a calculation based on a theoretical formula.

  The filter circuits 141 to 146 are installed one by one for each of the communication lines 111 to 116 based on the obtained position. Not limited to this, each frequency corresponding to each of the electronic control units 101 to 106 is determined based on the recursive execution of the determination of the frequency band that is the main factor of the distortion of the signal waveform and the determination of the line length that minimizes the characteristic impedance. You may make it install a some filter circuit in the communication lines 111-116. In this case, especially when the distortion of the signal waveform generated on the communication line is large, it is expected that the distortion of the signal waveform is gradually reduced through the plurality of filter circuits.

The filter circuits 141 to 146 are installed separately from the communication lines 111 to 116 that are branched and connected to the electronic control devices 101 to 106. For example, a communication line having a large signal waveform distortion among the communication lines 111 to 116 may be specified in advance, and a filter circuit may be provided only for the specified communication line. In this case, a filter circuit is installed for a communication line identified as a path having a large signal waveform distortion among the communication lines 111 to 116. As a result, when the distortion of the signal waveform is reduced using the filter circuit, the filter circuit can be further reduced and simplified as a wired communication system.

  ・ As the frequency band for calculating the characteristic impedance, the frequency band that is the main cause of the distortion of the signal waveform is used. The frequency band for calculating the characteristic impedance is not limited to this, and may be a frequency band including a distortion component. If the filter circuit is installed at the position of the line length where the characteristic impedance in the same frequency band is minimized, the distortion of the signal waveform can be reduced.

  The filter circuits 141 to 146 are installed on the communication lines 111 to 116 that are branched and connected to the electronic control devices 101 to 106. Not only this but the installation position of the filter circuits 141-146 should just be the position of the line length from which the characteristic impedance in a specific frequency band becomes the minimum, In addition to this, on the main communication line 110, and the said The distortion reduction effect by the filter circuit can be obtained even in the branch connectors 121 to 123 and on the substrate wiring of each of the electronic control devices 101 to 106.

  A filter circuit in which a resistor R and a coil L are connected in parallel is used as the filter circuit. In addition, the filter circuit may be any filter that can reduce the distortion component included in the signal waveform. For example, a band-pass filter or a ferrite bead can be used.

  -As the above-mentioned wired communication system, FlexRay (FlexRay) constituting an in-vehicle network was targeted. However, the present invention is not limited to this, and an in-vehicle network configured by CAN (controller area network), LIN (local interconnect network), or the like may be applied. In addition to the in-vehicle network, the present invention can be applied to any wired communication system having a communication line that is branched and connected to each of a plurality of nodes.

  DESCRIPTION OF SYMBOLS 101-106 ... Electronic control unit, 110-116 ... Communication line, 121-123 ... Branch connector, 131, 132 ... Termination circuit, 141-146 ... Filter circuit, 201 ... Transmission node, 202 ... Reception node, 203 ... Termination circuit , 211 ... transmission communication line, 212 ... reception communication line, 213 ... termination side communication line, 220 ... filter circuit, 220a ... first filter circuit, 220b ... second filter circuit, L ... coil, R ... resistance.

Claims (8)

In a waveform distortion reduction method for reducing distortion of a signal waveform communicated between nodes using a communication line in which a plurality of nodes are branched and connected as a communication medium, using a filter circuit,
A line length at which a characteristic impedance in a specific frequency band is minimized with respect to a line length of the communication line connected to the node and the branch connection is obtained, and the filter circuit is installed at a position of the obtained line length. Waveform distortion reduction method. The waveform distortion reduction method according to claim 1, wherein the specific frequency band is specified as a frequency band that is a main factor of distortion of the signal waveform analyzed by measuring a communication waveform of the branch-connected communication line. . The waveform distortion reduction method according to claim 1 or 2, wherein a communication line with a large signal waveform distortion is specified in advance among the communication lines, and the filter circuit is installed for the specified communication line. The waveform distortion reduction method according to claim 1, wherein the filter circuit is installed separately from the branch-connected communication line. In the waveform distortion reduction method according to any one of claims 1 to 4,
Waveform distortion characterized by installing a plurality of filter circuits in a communication line corresponding to a specific node based on recursive execution of specifying the frequency band and finding a line length at which the characteristic impedance is minimized. Reduction method. In a wired communication system in which communication between nodes is performed using a communication line in which a plurality of nodes are branched and connected as a communication medium,
A wired communication system, wherein signal waveform distortion is reduced through a filter circuit installed based on the waveform distortion reduction method according to claim 1. In a wired communication system including a filter circuit that reduces distortion of a signal waveform communicated between nodes using a communication line in which a plurality of nodes are branched and connected as a communication medium,
The filter circuit is installed at a position of a line length at which a characteristic impedance in a specific frequency band is minimized among line lengths of the communication line branched and connected to the node. . The wired communication system according to claim 6 or 7, wherein the wired communication system is a multiplex communication system constituting an in-vehicle network.

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