JP2008193606A - Data transmission system and data transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission system and a data transmission method in which data can be multiplexed and transmitted by superimposing a second signal in a pair of signal lines on which differential signals are transmitted in an in-phase manner. <P>SOLUTION: In order to transmit data different from data represented by a differential signal, a communication section of an in-vehicle unit is connected to an intra-vehicle communication line 5 via a coupling capacitor 231. With respect to differential signals of a band lower than or equal to approximate 1 MHz transmitted by signal lines 51, 52 of the intra-vehicle communication line 5, a control section of the in-vehicle unit superimposes an in-phase signal of approximate 100 MHz to the signal lines 51, 52 generating differential signals via the coupling capacitor 231 by the communication section. A signal level of approximate 100 MHz is made sufficiently lower than signal levels of differential signals and can be canceled as noise when receiving the differential signals. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a data transmission system that transmits and receives data by generating / detecting differential signals on a pair of signal lines, and in particular, multiplexes and transmits data by superimposing signals in phase on a pair of signal lines. The present invention relates to a data transmission system and a data transmission method.

  In recent years, with the increase in functions of in-vehicle devices using an electronic control unit (ECU), the number and types of in-vehicle devices arranged in vehicles tend to increase.

  In-vehicle devices are only devices that control the vehicle's driving functions that are classified into engine / powertrain systems such as engines or brakes, air conditioners, body systems such as doors and headlamps, and safety systems such as airbag control. Instead, it may operate as an additional information system device such as a car audio or navigation device.

  In addition, there are cases where a device that detects a person, an animal, or the like by analyzing a video outside the vehicle or a device that captures and displays a video behind the vehicle is also arranged in the vehicle as an in-vehicle device of an information system.

  Therefore, the signal transmitted between the in-vehicle devices may include not only a data signal that transmits numerical information such as the rotation speed, angle, and temperature, but also a video signal with a large transmission amount. In this case, it is necessary to separately install a high-speed communication line for transmitting a video signal in addition to an in-vehicle communication line for transmitting a differential signal such as CAN (Control Area Network).

Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for transmitting a video signal while preventing deterioration of video quality from a navigation device to a display device.
JP 2005-348229 A

  In the technique disclosed in Patent Document 1, an IEEE 1394 standard cable, a LAN cable (10Base-T, 100Base-TX, etc.), a USB cable, etc., apart from an in-vehicle communication line for connecting in-vehicle devices to transmit a video signal. A configuration in which a relatively high-speed communication line such as the above is laid separately is assumed, and wire-saving is not considered.

  If the information-related in-vehicle devices are physically located at a short distance, even if the information-related devices are connected by a dedicated cable for video and audio signals, the line-saving between the in-vehicle devices is reduced. There are few problems. However, when the imaging device, the display device, or their processing devices are arranged at a distance, it is not possible to save the line with a configuration in which cables dedicated to video signals and audio signals are arranged.

  The present invention has been made in view of such circumstances, and the second signal is superimposed in the same phase on a pair of signal lines through which the first signal represented by the differential voltage is transmitted, and the data is multiplexed. An object of the present invention is to provide a data transmission system and a data transmission method capable of reducing the number of lines by adopting a transmission configuration.

  Another object of the present invention is to provide a data transmission system capable of reducing the number of lines by superimposing a signal having the same phase on a shielded twisted pair cable for transmitting a signal.

  Another object of the present invention is to provide a first signal represented by a differential voltage and a second signal to be superimposed on a pair of signal lines at different frequencies so that the signals are superimposed on each other. An object of the present invention is to provide a data transmission system capable of reducing the influence on transmission.

  Another object of the present invention is to provide a configuration in which the frequency of the second signal is higher than the frequency of the first signal, so that the amount of transmission is higher than that of data that is generally appropriate for representing a differential signal. An object of the present invention is to provide a data transmission system and a data transmission method capable of multiplexing and transmitting a large amount of data.

  Another object of the present invention is to provide a data transmission system capable of reducing the influence on mutual transmission caused by superimposing signals by adopting a configuration in which the second signal level is lower than the first signal level. It is to provide a data transmission method.

  Another object of the present invention is to transmit the data by configuring the second signal with a split phase code so that the superimposed second signal can be reliably decoded and the transmission of the first signal can be performed. An object of the present invention is to provide a data transmission system and a data transmission method capable of reducing the influence.

  Another object of the present invention is to provide a signal transmitted by a receiver that receives a superimposed signal by connecting a transmitter and a receiver that transmit and receive a second signal to a pair of signal lines via a coupling capacitor. It is an object of the present invention to provide a data transmission system that can reduce loss.

  Another object of the present invention is to provide in-vehicle communication between in-vehicle devices by adopting a configuration in which data is multiplexed and transmitted / received by superimposing signals by a pair of signal lines connecting between in-vehicle devices arranged in a vehicle. An object of the present invention is to provide a data transmission system capable of reducing the number of lines.

  According to a first aspect of the present invention, there is provided a data transmission system in which data is transmitted and received by generating / detecting a first signal represented by a differential voltage having a potential of each of a pair of signal lines. A transmitter and a receiver for transmitting and receiving data using the two signals, wherein the transmitter generates a second signal in the same phase on each of the pair of signal lines and superimposes it on the first signal By doing so, the data is multiplexed and transmitted.

  The data transmission system according to a second aspect of the present invention is characterized in that the pair of signal lines are configured by shielded twisted pair cables.

  The data transmission system according to a third aspect is characterized in that the first signal and the second signal have different frequencies.

  The data transmission system according to a fourth aspect is characterized in that the frequency of the second signal is higher than the frequency of the first signal.

  The data transmission system according to a fifth aspect is characterized in that the second signal level is lower than the first signal level.

  The data transmission system according to a sixth aspect of the invention is characterized in that the transmitter and the receiver are provided with a split phase conversion unit, and the second signal is transmitted after split phase conversion.

  The data transmission system according to a seventh aspect is characterized in that the receiver and the transmitter are connected to the pair of signal lines via a coupling capacitor.

  A data transmission system according to an eighth aspect is characterized in that the transmitter and the receiver are on-vehicle devices.

  A data transmission method according to a ninth aspect of the present invention is the data transmission method for transmitting and receiving data by generating / detecting the first signal represented by the differential voltage of each potential of the pair of signal lines. Is generated in the same phase on each of the pair of signal lines and superimposed on the first signal to multiplex and transmit the data.

  The data transmission method according to a tenth aspect of the invention is characterized in that the frequency of the second signal is higher than the frequency of the first signal.

  The data transmission method according to an eleventh aspect is characterized in that the second signal level is lower than the first signal level.

  The data transmission method according to a twelfth aspect of the invention is characterized in that the second signal is transmitted after split phase conversion.

  In the first invention and the ninth invention, the first signal line and the second signal line that realize the differential signal with respect to the data transmitted by the first signal represented by the differential signal with respect to the pair of signal lines. The second signal is superimposed on the signal lines in the same phase, and the data is multiplexed and transmitted.

  In the second invention, the first signal and the second signal are transmitted by a shielded twisted pair cable. The differential signal of the first signal is transmitted by the twisted pair wire of the shielded twisted pair cable, and the second signal is transmitted so that the potentials of the twisted pair wires with respect to the shield are in phase.

  In the third aspect of the invention, the first signal and the second signal have different frequencies, and can be distinguished when receiving each signal.

  In the fourth and tenth inventions, the second signal has a higher frequency than the first signal, and transmits data having a larger transmission amount than the data transmitted by the first signal. Is possible.

  In the fifth and eleventh inventions, the second signal level superimposed by the transmitter is lower than the first signal level, and when receiving each signal, the second signal is a signal relative to the first signal. It becomes possible to distinguish by level.

  In the sixth and twelfth inventions, the second signal superimposed by the transmitter is split-phase converted and configured by a split-phase code, and one of the signal levels representing data does not continue.

  In the seventh aspect of the invention, the coupling capacitor provided in the receiver and transmitter that generates / detects the second signal blocks the first signal having a different frequency as a DC component and passes only the second signal as an AC component.

  In the eighth invention, the in-vehicle device multiplexes and transmits the second signal superimposed on the first signal which is a differential signal transmitted to the in-vehicle communication line, and similarly detects the second signal. Then, it is received separately from the multiplexed data.

  In the case of the first invention and the ninth invention, the second signal is superimposed in the same phase on each of the pair of signal lines for transmitting the differential signal. The receiver of the first signal that detects and receives the differential voltage can remove the second signal as in-phase noise when detecting or generating the differential signal, so that the superimposed second signal Does not affect transmission / reception of the first differential signal. Thereby, it is possible to multiplex and transmit the data by superimposing the second signal without losing the transmission of the first signal, and to transmit the data represented by the second signal. There is no need to install a separate communication line, and line saving can be achieved.

  According to the second aspect of the invention, the pair of signal lines is constituted by a twisted pair of shielded twisted pair cables, thereby realizing transmission of differential signals by a balanced line and a potential difference between the shield and the twisted pair of signal lines. The signal represented by is realized by transmission through an unbalanced line with a small attenuation. As a result, the second signal can be superimposed and transmitted without causing any loss in the transmission of the first signal, and communication with a small amount of attenuation such as a dedicated coaxial cable for transmitting the video signal or the audio signal. There is no need to install a separate line, and the line can be saved. Furthermore, since a coaxial cable that is generally more expensive than a twisted pair cable is not required, the cost can be reduced.

  In the case of the third invention, the first signal and the second signal superimposed on the pair of signal lines have different frequencies, and the first signal and the second signal are distinguished from each other. Accordingly, only the first signal or only the second signal can be received by selecting the frequency, and the data is multiplexed and transmitted without reducing the influence on the transmission of the first signal. be able to.

  In the case of the fourth invention and the tenth invention, the second signal superimposed on the pair of signal lines has a higher frequency than the first signal. As a result, it is possible to multiplex and transmit data having a larger transmission amount than data suitable for being represented by the differential signal of the first signal.

  In the fifth invention and the eleventh invention, the first signal and the second signal are reduced by reducing the signal level of the second signal so that the signal level can be removed as noise with respect to the first signal. Can be reduced with each other when transmitted in a superimposed manner.

  In the sixth invention and the twelfth invention, the second signal is split-phase converted and configured by a split-phase code, so that one of the signal levels, that is, “0” or “ One of "1" does not continue. Therefore, it is possible to avoid the necessity of increasing the reception accuracy in order to decode the sequence of “0” or “1” of the digital data, and it is possible to reliably decode. Furthermore, since one of the high and low signal levels does not continue, the second signal does not appear to be a low frequency signal. Therefore, the influence on the first signal having a frequency lower than that of the second signal can be reduced.

  According to the seventh aspect of the present invention, the receiver that receives the data by detecting the second signal constituting the data transmission system includes a coupling capacitor. Therefore, it is possible to suppress the attenuation of the first signal by the receiver by setting the capacity of the coupling capacitor so that the first differential signal having a different frequency is not passed as a DC component and only the second signal is received. In addition, signal loss can be reduced.

  According to the eighth aspect of the invention, data can be multiplexed and transmitted by superimposing the first signal and the second signal via the in-vehicle communication line connecting the in-vehicle devices. When the first signal which is a differential signal is detected and data including numerical information used for control of the in-vehicle device is received, the second signal is removed as noise, and the second signal is detected to detect video data. When receiving data such as, the first signal which is a differential signal is not detected. As a result, it is not necessary to separately install a network with a high transmission speed in order to transmit data with a large transmission amount such as video data or audio data in the vehicle, and the in-vehicle communication line between in-vehicle devices can be saved. Can do.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

  FIG. 1 is a block diagram showing a configuration of an in-vehicle device communication system to which a data transmission system according to the present invention is applied. The in-vehicle device communication system includes in-vehicle devices 1a, 1b, and 1c that transmit and receive data including numerical information such as measured values, calculated values, and control values of various physical quantities; in-vehicle devices 2a and 2b that transmit and receive video data; An image pickup device 3 for picking up an image, a display device 4 having a monitor, and an in-vehicle communication line 5 for connecting the in-vehicle devices 1a, 1b, 1c, 2a, 2b are provided. The in-vehicle devices 1a, 1b, and 1c that transmit and receive data including numerical information with a small amount of transmission and the in-vehicle devices 2a and 2b that transmit and receive video data with a large amount of transmission are connected to the same in-vehicle communication line 5 in a bus form ing. The in-vehicle devices 1a, 1b, and 1c commonly receive data including numerical information transmitted to the in-vehicle communication line 5. The in-vehicle device 2b receives the video data transmitted from the in-vehicle device 2a to the in-vehicle communication line 5. The imaging device 3 is connected to the in-vehicle device 2a, and the display device 4 is connected to the in-vehicle device 2b.

  The vehicle-mounted devices 1a, 1b, and 1c use numerical information such as measured values, calculated values, and control values of various physical quantities such as temperature, angle, and speed detected by a connected sensor using an electronic control unit (ECU). It is possible to transmit data including data or to control various devices such as an engine and a brake by a microcomputer. For example, the in-vehicle device 1a is connected to a sensor (not shown) that detects a steering angle. The in-vehicle device 1a transmits data including information indicating the numerical value of the steering angle to the other in-vehicle devices 1b and 1c via the in-vehicle communication line 5 based on the measured value of the steering angle input from the sensor.

  The in-vehicle device 1a includes a control unit 10 that controls the operation of each component shown below, a power supply circuit 11 that supplies power to each component, a storage unit 12 that stores data necessary for control, and an in-vehicle communication line 5, a communication control unit 13 that controls communication with 5, an input unit 14 that inputs a signal from a sensor (not shown), and an output unit 15 that outputs a control signal to a control target device (not shown). Since the other in-vehicle devices 1b and 1c have the same configuration as the in-vehicle device 1a, detailed description thereof is omitted. Note that both or one of the in-vehicle devices 1b and 1c may be configured to include only one of the input unit 14 and the output unit 15.

  The control unit 10 of the in-vehicle device 1 a receives power supply from a vehicle alternator (not shown) via the power supply circuit 11, detects a signal from the sensor via the input unit 14, and controls it via the output unit 15. A control signal is transmitted to the target device.

  The storage unit 12 of the in-vehicle device 1a is composed of a volatile memory, and temporarily stores various information generated in the process of the control unit 10 and measured values of physical quantities represented by signals input from the sensors.

  The communication control unit 13 of the in-vehicle device 1a has a network controller chip and realizes communication via the in-vehicle communication line 5. The control unit 10 of the in-vehicle device 1a transmits data by generating a differential voltage between a pair of signal lines of an in-vehicle communication line 5 described later via the communication control unit 13, and the differential voltage between the signal lines is transmitted. Data is received by detecting.

  The in-vehicle device 2a transmits video data to another in-vehicle device 2b using an electronic control unit (ECU) based on the video signal input from the imaging device 3 connected to the in-vehicle device 2a. Conversely, the in-vehicle device 2b receives the video data transmitted from the in-vehicle device 2a and outputs it to the display device 4. The in-vehicle device 2a may be configured as a device that receives video data and audio data created from position information acquired by the navigation unit and transmits them to the in-vehicle communication line 5 by connecting to the navigation unit.

  The in-vehicle device 2a includes a control unit 20 that controls the operation of each component shown below, a power supply circuit 21 that supplies power to each component, a storage unit 22 that stores data necessary for control, and an in-vehicle communication line. 5 and a video input unit 24 that inputs a video signal from the imaging device 3. The in-vehicle device 2b has the same configuration as the in-vehicle device 2a except that the in-vehicle device 2b includes a video output unit 25 that outputs a video signal to the display device 4 instead of the video input unit 24 of the in-vehicle device 2a.

  The control unit 20 of the in-vehicle device 2a is supplied with electric power from a vehicle alternator (not shown) via the power circuit 21 and receives a video signal from the imaging device 3 connected via the video input unit 24. The video input unit 24 performs processing such as compression coding and / or A / D conversion, and transmits the processed video data via the communication unit 23. Similarly, the control unit 20 of the in-vehicle device 2b is supplied with electric power via the power supply circuit 21 and receives it via the in-vehicle communication line 5 to the display device 4 connected via the video output unit 25. A video signal obtained by subjecting the video data to processing such as decompression decoding and / or D / A conversion by the video output unit 25 is output.

  The storage unit 22 of the in-vehicle devices 2a and 2b includes a volatile memory, and the control unit 20 of the in-vehicle devices 2a and 2b temporarily stores various information generated in the process in the storage unit 22.

  The video input unit 24 of the in-vehicle device 2a inputs a video signal from the imaging device 3, and when the video signal is an analog signal such as an NTSC signal, RGB data or YUV so that the video signal can be transmitted through the in-vehicle communication line 5. A process of converting data into digital data is performed. Further, the video input unit 24 of the in-vehicle device 2a may perform a process of compressing and encoding into MPEG data or the like. Conversely, when digital data is input, the video output unit 25 converts the digital data into a video signal that is an analog signal and outputs it. Further, the video input unit 24 of the in-vehicle device 2a may be configured to perform processing for outputting video data obtained by converting the size of the image in accordance with the screen size of the display device 4 with respect to the input video signal.

  The communication unit 23 of the in-vehicle devices 2 a and 2 b realizes transmission / reception of video data via the in-vehicle communication line 5. The control unit 20 of the in-vehicle devices 2 a and 2 b transmits video data via the communication unit 23 and receives video data from the in-vehicle communication line 5 via the communication unit 23. Details of the communication unit 23 of the in-vehicle devices 2a and 2b will be described later.

  The imaging device 3 is a video camera and outputs a video signal represented by an NTSC signal obtained by imaging a video outside the vehicle to the in-vehicle device 2a. The display device 4 inputs the video signal output from the in-vehicle device 2b and displays the video on the monitor.

  The in-vehicle communication line 5 is a communication line based on a CAN (Control Area Network) protocol, and the in-vehicle devices 1a, 1b, and 1c transmit / receive data via the in-vehicle communication line 5 by generation / detection of signals based on the CAN specification. Is possible. In the present embodiment, a communication line based on the CAN specification will be described as an example of the in-vehicle communication line 5. However, the in-vehicle communication line 5 of the in-vehicle device communication system to which the data transmission system of the present invention is applied is not limited to this, but a relatively low speed LIN (Local Interconnect Network) using differential signals, BEAN (Body Electronics Area Network), etc. A communication line based on the protocol may be used.

  The in-vehicle communication line 5 based on the CAN specification is composed of a pair of signal lines, specifically shielded twisted pair cables, and the in-vehicle devices 1a, 1b, 1c connected to the in-vehicle communication line 5 detect the differential voltage generated between the pair lines. Thus, the signal is detected and the data is received. Further, the in-vehicle devices 1a, 1b, and 1c generate a signal by generating a differential voltage between the pair lines and transmit data.

  The potential of the pair wire of the shield twisted pair cable of the in-vehicle communication line 5 is set to the CAN_High level and the CAN_Low level, respectively. When the differential voltage of the pair line potential is zero or the CAN_Low level potential is higher than the CAN_High level potential, the digital signal is “1” (recessive), and the CAN_High level potential is higher than the CAN_Low level potential. A high state represents “0” (dominant) of the digital signal. The in-vehicle devices 1a, 1b, and 1c connected to the in-vehicle communication line 5 generate a signal represented by “0” and “1” by generating a differential voltage between the pair lines of the in-vehicle communication line 5. , Send data.

  FIG. 2 is a schematic diagram showing the in-vehicle communication line 5 constituting the in-vehicle device communication system to which the data transmission system according to the present invention is applied. FIG. 2A is a schematic diagram of a shielded twisted pair cable used as the in-vehicle communication line 5. The shielded twisted pair cable includes twisted pair wires (signal lines) 51 and 52 each covered with an insulator, a shield 53 formed of a conductor wound around the twisted pair wires 51 and 52, twisted pair wires 51 and 52, and It is comprised by the outer jacket 54 which coat | covers the outer side of the shield 53 with an insulator.

  FIG. 2B schematically shows a conductor of a shielded twisted pair cable used as the in-vehicle communication line 5. A potential of CAN_High level is applied to the signal line 51 of the twisted pair, and a potential of CAN_Low level is applied to the signal line 52. The shield 53 is grounded. When data is not transmitted to the in-vehicle communication line 5, the CAN_High level potential of the signal line 51 is in a recessive state lower than the CAN_Low level potential of the signal line 52.

  When transmitting data, the communication control unit 13 of the in-vehicle device 1a generates a differential voltage of about 5V between the CAN_High level potential of the signal line 51 and the CAN_Low level potential of the signal line 52, and enters the dominant state. To do. The communication control unit 13 of the in-vehicle device 1a sets the recessive state “1” and the dominant state “0” to about 1 MHz as the upper limit with respect to the potential between the signal line 51 and the signal line 52 so as to represent digital data. The digital data represented by “0” and “1” is transmitted repeatedly at the frequency. That is, the differential signal represented by the differential voltage between the signal lines 51 and 52, which is a twisted pair of the in-vehicle communication line 5, is transmitted at a communication speed having an upper limit of about 1 Mbps.

  On the other hand, the video data transmitted and received by the in-vehicle devices 2a and 2b via the in-vehicle communication line 5 is insufficient at a communication speed of 1 Mbps. For example, when it is necessary to transmit and receive video data in real time, such as when the video data is used for obstacle detection, the video data is transmitted and received without being compressed. Therefore, a transmission speed of about 40 Mbps is required even when transmitting 8-bit monochrome video of NTGA VGA size (640 × 480 pixels) at a frame rate of 15 (frames / second).

  Therefore, the communication unit 23 of the in-vehicle devices 2a and 2b constituting the in-vehicle device communication system to which the data transmission system of the present invention is applied is in-vehicle communication that is a shielded twisted pair cable via a coupling capacitor 231 as shown in FIG. By connecting to the line 5, it is possible to superimpose high-speed data transmission of 100 Mbps on data transmission based on the CAN specification with an upper limit of about 1 Mbps.

  FIG. 3 is a schematic diagram showing a connection state between the coupling capacitor 231 and the in-vehicle communication line 5 included in the communication unit 23 of the in-vehicle devices 2a and 2b constituting the in-vehicle device communication system to which the data transmission system according to the present invention is applied. is there.

  The coupling capacitor 231 included in the communication unit 23 of the in-vehicle devices 2a and 2b separates a signal having a higher frequency than a signal based on the CAN specification such as video data into a pair of signal lines 51 and 52 at the time of transmission. It is provided for transmitting a signal and allowing only a high-frequency component to pass through without receiving a differential signal based on the CAN specification as a low-frequency signal at the time of reception. One capacitor of the coupling capacitor 231 is connected to the signal line 51, and the other capacitor is connected to the signal line 52. Thereby, in-phase signals are superimposed on the signal line 51 and the signal line 52, respectively, and the low frequency component represented by the differential voltage between the signal line 51 and the signal line 52 does not pass as a DC component. Only high frequency components pass as alternating current components.

  The coupling capacitor 231 is configured to operate at a low impedance at a high frequency of 100 MHz, and to operate at a high impedance at a low frequency up to about 1 MHz, which is the CAN band. For example, the coupling capacitor 231 is configured by a capacitor having a capacitance of 33 pF. In this case, the coupling capacitor 231 operates with an impedance of about 4.8 kΩ at a frequency up to about 1 MHz, which is a CAN band, and is about 24-48 Ω at a frequency of 100 MHz, which is a high-speed band for transmitting video data. Acts on impedance.

  The communication unit 23 of the in-vehicle device 2a sends a signal representing the digital data of the video input from the video input unit 24 to the in-vehicle communication line 5. At this time, the digital data is input from the video input unit 24 as a parallel signal via the internal bus. Therefore, the communication unit 23 of the in-vehicle device 2a includes a parallel-serial converter (not shown), and digital data input from the video input unit 24 is converted into a serial signal. Furthermore, it is desirable that the communication unit 23 of the in-vehicle device 2a includes a split phase conversion circuit. This is because a low frequency component is removed from a signal having a higher frequency than a signal based on a CAN having a relatively low frequency. In the communication unit 23 of the in-vehicle device 2a, the video digital data converted into the serial signal is split-phase converted by a split phase conversion circuit (not shown) and sent to the in-vehicle communication line 5 through the coupling capacitor 231.

  As a result, a high-frequency signal of 100 MHz in phase is sent to the signal line 51 and the signal line 52. Signals sent out in phase to the signal line 51 and the signal line 52 realize unbalanced line (coaxial line) transmission to the shield 53. The in-vehicle device 2a performs split-phase conversion on a high-frequency signal representing video digital data by a split-phase conversion circuit and transmits the signal, so that the signal representing the digital data has a signal level representing, for example, “0” or “1”. It can be avoided that a signal having an apparently low frequency is caused by one of the high and low sides being continuous. Thereby, the influence on the transmission of the signal of the comparatively low frequency based on CAN can be reduced.

  Conversely, it is desirable that the communication unit 23 of the in-vehicle device 2b includes a serial-parallel converter (not shown) and further includes a split phase conversion circuit. The communication unit 23 of the in-vehicle device 2b detects a high frequency signal via the coupling capacitor 231 and decodes the detected high frequency signal by a split phase conversion circuit (not shown). The communication unit 23 of the in-vehicle device 2b further converts the decoded signal into a parallel signal by a serial-parallel converter and transmits the parallel signal to the video output unit 25.

  The signal level of the signal generated by the communication unit 23 of the in-vehicle device 2a is set to a signal level that is sufficiently lower than the signal level representing data based on the CAN specification. For example, the signal level representing the data based on the CAN specification is set to about 5V as described above, whereas the signal level representing the video data is set to 0.1V, which is 2% or less.

  A signal sent in phase from the communication unit 23 of the in-vehicle device 2a to the in-vehicle communication line 5 to transmit the video data almost affects the differential voltage generated between the signal line 51 and the signal line 52. Absent. Therefore, in the communication control unit 13 of the in-vehicle devices 1a, 1b, 1c, the signal representing the video data transmitted from the in-vehicle device 2a is removed as high-frequency component noise, and a maximum of about 1 MHz between the in-vehicle devices 1a, 1b, 1c, It does not affect signals representing data transmitted and received at a transmission rate of 1 Mbps.

  The communication unit 23 of the in-vehicle device 2b detects a signal sent to the in-vehicle communication line 5 via the coupling capacitor 231. The communication unit 23 of the in-vehicle device 2b does not pass a low-frequency component of about 1 MHz or less as a DC component due to the action of the coupling capacitor 231 with respect to the signal sent to the in-vehicle communication line 5, and passes a high-frequency component of 100 MHz as an AC component. Therefore, data based on the CAN specification represented by the low frequency component signal is not received, and only the video data represented by the high frequency signal is received.

  FIG. 4 is a waveform diagram schematically showing signals superimposed on the in-vehicle communication line 5 constituting the in-vehicle device communication system to which the data transmission system according to the present invention is applied. 4A, 4B, and 4C, the horizontal axis represents the passage of time, and the vertical axis represents the potential.

  FIG. 4A shows a waveform of a signal level transmitted through the in-vehicle communication line 5. A solid line indicates a CAN_High level potential of the signal line 51, and a broken line indicates a CAN_Low level potential of the signal line 52. In order to simplify the description, a signal representing data based on the CAN specification is a signal that repeats “0” and “1” of digital data, and a signal representing video data is represented by “1” of digital data. This shows a case where the signal level is continuously changed by split phase conversion.

  FIG. 4B shows a waveform of a signal detected by the communication control unit 13 of the in-vehicle devices 1a, 1b, and 1c. A solid line indicates a CAN_High level potential of the signal line 51, and a broken line indicates a CAN_Low level potential of the signal line 52. When the control unit 10 of the in-vehicle devices 1a, 1b, and 1c receives data based on the CAN specification via the communication control unit 13, the high-frequency signal representing the video data superimposed in the same phase is removed as noise. . When the control unit 10 of the in-vehicle devices 1a, 1b, and 1c subtracts the CAN_Low level potential from the CAN_High level potential to detect the differential voltage, the in-phase signal is canceled and the dominant state or the recessive state is detected. It does not affect the judgment of whether or not.

  FIG. 4C shows a waveform of a signal detected by the communication unit 23 of the in-vehicle device 2b. The communication unit 23 of the in-vehicle device 2b receives the signal shown in FIG. 4A via the coupling capacitor 231 that does not pass the low frequency component, but the low frequency component is removed as a DC component by the coupling capacitor 231. Therefore, only the high frequency component is detected as shown in FIG.

  By using the in-vehicle devices 2a and 2b as described above, a signal having the same phase can be superimposed on the differential signal and transmitted. The superimposed in-phase signal has a higher frequency than the differential signal and is transmitted / received by distinguishing the frequency, so that the low-frequency signal and the high-frequency signal are separated from each other as shown in FIGS. The in-vehicle devices 1a, 1b, and 1c and the in-vehicle devices 2a and 2b receive the signals without affecting each other. Therefore, according to the present invention, it is not necessary to separately lay a relatively expensive communication line such as a coaxial cable in order to transmit video data separately from the in-vehicle communication line 5 for transmitting a low-frequency differential signal. , Line saving and cost reduction can be achieved. Further, when detecting and receiving a low frequency signal, the superimposed high frequency signal is superimposed on the differential signal in the same phase, and therefore does not affect the detection of the differential voltage. On the other hand, since the signal level of the high frequency signal is set low and is removed as noise, the transmission of the low frequency signal is not affected. When detecting and receiving a high-frequency signal, data can be received without losing the low-frequency signal because the low-frequency signal is passed through the coupling capacitor 231 that does not pass as a DC component.

  In the present embodiment, the high-speed data transmitted and received by the in-vehicle devices 2a and 2b has been described using video data or audio data as an example. However, according to the present invention, the high-speed data transmitted and received between the in-vehicle devices 2a and 2b is not limited to signals representing video data or audio data, but may be configured to transmit and receive information data including program data downloaded by the in-vehicle devices 2a and 2b. Good.

  In the present embodiment, a signal representing video data is superimposed on the in-vehicle communication line 5 that transmits a signal based on CAN. However, according to the present invention, data can be multiplexed as long as the signals are superimposed in phase on the differential signals represented by the differential voltages. However, in order to separate the superimposed signals, it is desirable to set the frequencies so that they can be removed as noise from each other. In general, the transmission speed of a signal represented by a differential signal is relatively low, and the CAN protocol that has been standardized in recent years is not suitable for the transmission of data to be transmitted at high speed such as video data. Therefore, there can be many applications in which data is multiplexed by superimposing a higher-speed signal than a signal generally represented by a differential signal. Transmission by differential signals that can reduce costs has also been accelerated, but existing differential signals can be obtained by connecting a high-speed data transceiver via a coupling capacitor to an existing low-speed network. This is advantageous in that it is possible to realize a data transmission system according to the present invention that can multiplex data represented by

  The embodiment of the present invention has been described by taking the vehicle-mounted device communication system as described above as an example. However, the present invention is not limited to this, and in the case of a system using CAN, which is a network that uses a differential signal of a relatively low frequency, for example, in a network between FA (Factory Automation), medical equipment, or industrial equipment. It is also possible to apply.

It is a block diagram which shows the structure of the vehicle-mounted apparatus communication system to which the data transmission system which concerns on this invention is applied. It is a schematic diagram which shows the in-vehicle communication line which comprises the vehicle-mounted apparatus communication system to which the data transmission system which concerns on this invention is applied. It is a schematic diagram which shows the connection state of the coupling capacitor and in-vehicle communication line with which the communication part of the vehicle-mounted apparatus which comprises the vehicle-mounted apparatus communication system to which the data transmission system which concerns on this invention is applied. It is a wave form diagram showing roughly the signal superimposed on the in-vehicle communication line which constitutes the in-vehicle device communication system to which the data transmission system concerning the present invention is applied.

Explanation of symbols

1a, 1b, 1c, 2a, 2b In-vehicle device 23 Communication unit 231 Coupling capacitor 5 In-car communication line (shielded twisted pair cable)
51,52 Signal line 53 Shield

Claims (12)

In a data transmission system configured to transmit / receive data by generating / detecting a first signal represented by a differential voltage of a potential of each of a pair of signal lines,
A transmitter and a receiver for transmitting and receiving data by a second signal;
The transmitter is configured to multiplex and transmit data by generating a second signal in the same phase on each of the pair of signal lines and superimposing the second signal on the first signal. A data transmission system characterized by The data transmission system according to claim 1, wherein the pair of signal lines includes a shielded twisted pair cable. The data transmission system according to claim 1 or 2, wherein the first signal and the second signal have different frequencies. 4. The data transmission system according to claim 1, wherein a frequency of the second signal is higher than a frequency of the first signal. 5. The data transmission system according to any one of claims 1 to 4, wherein the second signal level is lower than the first signal level. The transmitter and receiver include a split phase conversion unit,
The data transmission system according to claim 4 or 5, wherein the second signal is transmitted after split phase conversion. The data transmission system according to claim 3, wherein the receiver and the transmitter are connected to the pair of signal lines via a coupling capacitor. The data transmission system according to claim 1, wherein the transmitter and the receiver are in-vehicle devices. In a data transmission method for transmitting and receiving data by generating / detecting a first signal represented by a differential voltage of each potential of a pair of signal lines,
A data transmission method comprising: multiplexing and transmitting data by generating a second signal in the same phase on each of the pair of signal lines and superimposing the second signal on the first signal. The data transmission method according to claim 9, wherein the frequency of the second signal is higher than the frequency of the first signal. The data transmission method according to claim 9 or 10, wherein the second signal level is lower than the first signal level. The data transmission method according to claim 10 or 11, wherein the second signal is transmitted after split phase conversion.

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