WO2003079613A1

WO2003079613A1 - Vehicle data network

Info

Publication number: WO2003079613A1
Application number: PCT/IB2003/000885
Authority: WO
Inventors: Martin Wagner
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2002-03-16
Filing date: 2003-03-11
Publication date: 2003-09-25
Also published as: DE10211834A1; AU2003209546A1

Abstract

The invention relates to a vehicle data network (1), in which data can be transmitted with voltage values within a working voltage range, and in which at least one line (5) provided in the data network, which is not terminated with a resistance corresponding to its characteristic impedance, is terminated by means of at least one voltage-limiting nonlinear component (15), which is connected between the conductors of the line at the end of the line (15) not terminated with the characteristic impedance, which has such a high resistance in the working voltage range of the data network (1) that the data transmission on the line (15) is not perturbed, and which has such a low resistance value at voltages above and/or below the working voltage range that the voltage at the nonlinear component is limited and reflections on the line (15) are suppressed.

Description

Vehicle data network

The invention relates to a vehicle data network, in which data can be transmitted with voltage values within a working voltage range between devices located in the vehicle, and in which at least one line provided in the data network which [sic] is not terminated with a resistance corresponding to its characteristic impedance. It furthermore relates to a device for a data network, wherein the line leading to the device is not terminated with a resistance corresponding to the characteristic impedance of the line.

In a vehicle data network, in which a plurality of devices provided in the vehicle are generally coupled to one another by means of lines, and in which data can be transmitted on these lines within a working voltage range, each of the network nodes, and in particular each line leading to a device, should be terminated at its end with precisely the characteristic impedance of this line in order to suppress reflections at the end of the line. Only when the line is terminated with its characteristic impedance can such reflections be minimized. Such reflections are to be avoided since The [sic] voltage values due to the reflections are superposed with those of the data bits which are transmitted on the network, and can therefore perturb the data traffic in the data network. A device which sends data in the data network must also provide a sufficiently large current, so that the voltage of each data bit is established with the desired level at each network device. If each data device terminates the line leading to it with a resistance corresponding to the characteristic impedance of the line, then a relatively heavy current load occurs for the sending device. This is to be avoided, especially in vehicles, owing to the limited available on-board energy. For this reason, the lines are sometimes terminated with a resistance which is significantly higher than the characteristic impedance of the line. The current load on the sending device in the data network is thereby reduced. However, reflections now occur at the incorrectly terminated end of the line, which propagate back along the line into the data network and can perturb the data transmission.

It is an object of the invention to provide a data network, and a device for such a data network located in a vehicle, in which the current load on a sending device is kept as small as possible, but in which reflections at non-terminated ends of the lines of the data network are also minimized. This object is achieved, in respect of a data network, by the features of patent claim 1 :

A vehicle data network, in which data can be transmitted with voltage values within a working voltage range between devices located in the vehicle, and in which at least one line provided in the data network, which is not terminated with a resistance corresponding to its characteristic impedance, is terminated by means of at least one voltage- limiting nonlinear component, which is connected between the conductors of the line at the end of the line not terminated with the characteristic impedance, which has such a high resistance in the working voltage range of the data network that the data transmission on the line is not perturbed, and which has such a low resistance value at voltages above and/or below the working voltage range that the voltage at the nonlinear component is limited and reflections on the line are suppressed.

Normally, data are transmitted in the vehicle data network with voltage values which lie within a working voltage range, that is to say only voltages within this working voltage range may occur during transmission of the data.

If a line leading to a device is not terminated with a resistance corresponding to its characteristic impedance, then reflections occur at this end of the line during data transmissions, which propagate back into the data network and can perturb the data transmission taking place in it. According to the invention, a nonlinear voltage-limiting component, which is connected between the conductors of the lines, is therefore provided at the end of this line. This nonlinear component is configured in such a way that it has a very high resistance in the working voltage range. The effect of this is that the data transmission on the line is not perturbed and the voltage-limiting nonlinear component is virtually unnoticeable in this voltage range.

Since the line is not terminated with a resistance corresponding to its characteristic impedance, reflections which propagate back along the line into the data network occur at the end of the line during a data transmission, as explained in the introduction. In such reflections, voltage values which lie outside the working voltage range occur, that is to say voltage values which are higher than the maximum voltage values normally used for the data transmission, or which are lower than the minimum voltage values used for the data transmission. Since the nonlinear component limits the voltages occurring in its vicinity to the working voltage range, however, these reflections are strongly attenuated. The physical basis for this attenuation is that, at voltage values outside the working voltage range, the voltage-limiting nonlinear component has a low resistance which is significantly lower than the characteristic impedance and which substantially short-circuits the voltage components which lie outside the working voltage range. The voltage at the nonlinear component is therefore de facto limited to the working voltage range, and reflections occurring at the line end are suppressed.

In this data network, on the one hand, a low load on the data devices is consequently achieved since the ends of the lines do not need to be terminated with their characteristic impedance, but may instead, for example, be terminated with a significantly higher characteristic impedance that leads to a reduced current load on a sending device in the data network, which is important especially in vehicles owing to the limited available energy. On the other hand, the reflections which inherently occur owing to this arrangement are effectively suppressed by the nonlinear voltage-limiting component. This component also does not entail an increased current load in the working voltage range for a device sending in the data network. As is provided according to embodiments of the invention, the voltage- limiting nonlinear component may advantageously be a zener diode or, alternatively, a series circuit of a suitable number of semiconductor diodes.

A zener diode per se has the desired behavior since it has a nonlinear response curve, whose breakdown and on-state voltages can be selected in such a way that they represent precisely the limits of the working voltage range. The semiconductor diodes may be provided as a series circuit, in a number such that they become turned on precisely at the maximum values of the working voltage range.

Optionally, as is provided according to further embodiments of the invention, antiparallel-intercormected zener diodes and/or antiparallel-interconnected diode sequences may be provided. This is particularly expedient when the working voltage range extends from negative voltage values up to positive voltage values.

The invention furthermore relates to a device for a vehicle data network, wherein the device does not terminate the line leading to it in the data network with a resistance corresponding to its characteristic impedance, and wherein the device uses a nonlinear component, which has a voltage-limiting effect, for supplementary termination of the line. This component operates in the way described above.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiment described hereinafter. In the drawings:

Fig. 1 shows a vehicle data network with a plurality of devices provided in a vehicle, only one line leading to a device being terminated with its characteristic impedance, Fig. 2 shows an example of two nonlinear components, which are designed as a semiconductor diode and an antiparallel-interconnected semiconductor diode sequence, Fig. 3 shows two nonlinear components for the circuit according to Fig. 1 , which are designed as 2 antiparallel-interconnected zener diodes, and

Fig. 4 shows two nonlinear components for the circuit according to Fig. 1, which are designed as 2 antiparallel-interconnected semiconductor diode sequences.

Fig. 1 shows a schematic representation of a data network 1 provided in a vehicle (not shown in detail), in which 4 devices 7, 8, 9 and 10 provided in the vehicle are networked with one another. To that end, 4 lines 2, 3, 4 and 5 are provided, which will be assumed to have a characteristic impedance of 120 Ω. The lines 2, 3, 4 and 5 may in this case have different lengths. In the example according to Fig. 1, the devices 7, 8, 9 and 10 are connected to one another by means of a data network, designed as a CAN bus, which has two lines CANH and CANL. The lines 2, 3, 4 and 5 converge at a network node 6, in which the conductors of the lines are terminated with a 120 Ω resistor corresponding to the characteristic impedance of the lines 2, 3, 4 and 5. This resistor 6 is intended to suppress reflections at the ends of the lines toward the network node. This is precisely the case when the lines 2, 3, 4 and 5 are terminated with a resistance corresponding to their characteristic impedance, that is to say with a resistance of 120 Ω in the exemplary case.

Correspondingly, the other ends of the lines 2, 3, 4 and 5 should also be terminated with a resistance corresponding to their characteristic impedance, that is to say with a resistance with the value 120 Ω. In the example according to Fig. 1, however, this is the case only for the device 7. Here, a resistor 11 with the value 120 Ω is connected between the two lines CANH and CANL. The line 2 is therefore terminated with a resistance of 120 Ω corresponding to its characteristic impedance, so that reflections also do not occur at this end of the line 2 during a data transmission.

Fig. (1) shows that 2 further devices, namely the devices 8 and 9, which terminate lines 3 and 4 respectively leading to them with resistors 12 and 13, each of which has a resistance of 20 kΩ. The ends of the lines 3 and 4 toward the devices 8 and 9 are therefore terminated not according to their characteristic impedance, but instead with a significantly higher resistance. The effect of this, for data bits which are being transmitted in the data network, is that reflections occur at these ends of the lines 3 and 4, which propagate back into the data network and therefore perturb the data transmission.

The 4th device 10 represented in the exemplary embodiment according to Fig. 1 also terminates the line 5 leading to it with a resistor 14 with a value of 20 kΩ, so that corresponding reflections also occur at this end of the line 5.

Furthermore, the termination of a line with its characteristic impedance entails a relatively heavy current load on a sending device occurs, which is to be avoided, especially in vehicles, owing to the limited on-board energy.

According to the invention, however, the end of the line 5 leading to the device 10 is furthermore terminated with a nonlinear voltage-limiting component 15, which is connected between the conductors of the line 5. The data network corresponding to Fig. 1 involves a CAN bus, of the high-speed specification, in which voltages between 0 volt and approximately 3-4 volts occur during the transmission of data on the bus. The working voltage range of this data network hence lies in the range of from 0 volt to about just under 4 volts. Only voltages in this voltage range may therefore occur during a data transmission. However, as soon as reflections occur at ends of lines, voltages outside this voltage range occur, that is to say voltages above just under 4 volts and below 0 volt. This [lacuna] due to the waves propagating to and fro as a consequence of the reflections on the lines, which are superposed and can perturb the data traffic.

The nonlinear voltage-limiting component 15 is therefore configured in such a way that it attenuates the voltages outside the working voltage range, which occur owing to reflections. This means that the voltage-limiting nonlinear component has a relatively low resistance at voltages outside the working voltage range, which prevents the voltage on the line 5 according to Fig. 1 from rising or falling further. Therefore we [sic] as explained above suppresses surges. As an end result, the repercussions of the reflections are also effectively suppressed. In order for the data transmission in the data network not to be perturbed in the normal working voltage range, the voltage-limiting nonlinear component has a very high resistance in this voltage range, which is significantly more than the characteristic impedance of the lines, so that the current load is kept as small as possible by the voltage-limiting nonlinear component 15. The result for the termination of the line 5 to the data network device 10 is that it is terminated in this working voltage range with a relatively high resistance of 20 KΩ [sic], so that the load current on other devices sending on the data network is kept small. In order nevertheless to suppress the reflections occurring owing to the incorrect termination of the line 5 toward the data network device 10, the voltage-limiting nonlinear component 15 is provided which performs as effective suppression of such reflections substantially at voltage values outside the working voltage range.

The arrangement according to the invention therefore succeeds in combining a possible low load on the devices in the vehicle data network coupled with effective suppression of reflections at the ends of incorrectly terminated lines.

Fig. 1 represents the termination according to the invention of an incorrectly terminated line, merely with reference to the example of the line 5. Since the lines 3 and 4 are also incorrectly terminated, it would be optimal also to provide corresponding nonlinear components at these ends of the lines toward the devices 8 and 9, as is provided in the form of the nonlinear component 15 at the end of the line 5.

Of course, such termination of the lines by means of a voltage-limiting nonlinear component may be provided for all lines which lead to devices. In principle, this would also be conceivable for the network nodes and the resistor 6.

As already explained above, it was assumed for the exemplary embodiment according to Fig. 1 that a so-called high-speed CAN bus is involved, for which the working voltage range has a value in the range of from 0 volt to approximately just under 4 volts. For this voltage range, the nonlinear voltage-limiting component 15 could advantageously be designed as a zener diode, which is coupled on the cathode side to the terminal CANH and on the anode side to the terminal CANL. Such a zener diode could, for example, have a breakdown voltage of suitable value, whereas its punch-through voltage would have a value of, for example, 0.6 volt. The voltage range in the vicinity of such a zener diode would therefore be limited to these voltage values, which correspond approximately to the working voltage range of the high-speed CAN bus. In this way, the nonlinear voltage-limiting component 15 can be produced in a very straightforward way. Figs 2 - 4 show further possible embodiments of voltage-limiting nonlinear components corresponding to the component 15 in Fig. 1. The example according to Fig. 2 shows, on the one hand, a diode sequence with diodes 21, 22 and 24 as well as an antiparallel-connected diode 25. In this case, the number of diodes 21 - 24 is dependent on what voltage value the working voltage range has at the top. For the example of the high- speed CAN bus assumed for Fig. 1, it would be advantageous to provide 4 diodes, which become turned on at approximately 0.7 - 0.8 volt, so that, overall, the diodes become turned on and therefore have a voltage-limiting effect if a voltage above the maximum value of the working voltage range occurs. Toward the other end of the working voltage range, the diode 25 would become turned on at a voltage below approximately 0.7 - 0.8 volt. Nonlinear voltage limitation would therefore take place at the ends of the working voltage range also in the case of these antiparallel-interconnected diodes or diode sequences.

Vehicle bus systems are also known in which the working voltage range extends from the positive voltage range to negative voltages. This is, for example, the case with the low speed CAN bus. In such an arrangement, the voltage-limiting nonlinear component 15 corresponding to Fig. (1) may advantageously be produced by 2 antiparallel- interconnected zener diodes 31 and 32, as are represented in Fig. 3. In this way, the voltage limitation can take place toward positive and negative voltage values, which may possibly have a value of several volts in each case. As is indicated in Fig. 4, antiparallel-interconnected diode sequences, 41 to 44 and 45 to 48, respectively, corresponding to the Figure may also be provided for such vehicle data networks, in which the working voltage range has a value of from plus several volts to minus several volts. In this case, the number of semiconductor diodes provided in a diode sequence is to be selected in each case so that the diode sequence becomes turned on beyond the desired voltage value and therefore has a voltage-limiting effect.

Further embodiments of voltage-limiting nonlinear components 15 are conceivable; what is crucial in each case is merely that voltage limitation approximately to the working voltage range of the data network takes place.

Claims

CLAIMS:

1. A vehicle data network (1), in which data can be transmitted with voltage values within a working voltage range between devices located in the vehicle, and in which at least one line (5) provided in the data network, which is not terminated with a resistance corresponding to its characteristic impedance, is terminated by means of at least one voltage- limiting nonlinear component (15), which is connected between the conductors of the line at the end of the line (15) not terminated with the characteristic impedance, which has such a high resistance in the working voltage range of the data network (1) that the data transmission on the line (15) is not perturbed, and which has such a low resistance value at voltages above and/or below the working voltage range that the voltage at the nonlinear component is limited and reflections on the line (15) are suppressed.

2. A vehicle data network as claimed in claim 1, characterized in that at least one zener diode (15; 31, 32) is provided as the voltage-limiting nonlinear component (15).

3. A vehicle data network as claimed in claim 1 , characterized in that at least one series circuit of a suitable number of semiconductor diodes (21, 22, ...24; 41, 42, ...44; 45, 46, ...48) is provided as the voltage-limiting nonlinear component (15).

4. A vehicle data network as claimed in claim 1, characterized in that a low- speed CAN bus is provided as the data network (1), and in that two antiparallel-connected zener diodes (31, 32) are provided as voltage-limiting nonlinear components (15).

5. A vehicle data network as claimed in claim 1, characterized in that a low- speed CAN bus is provided as the data network (1), and in that two antiparallel-connected semiconductor diode sequences, each with a plurality of series-connected semiconductor diodes (41, 42, ...44; 45, 46, ...48) are provided as voltage-limiting nonlinear components (15).

6. A vehicle data network as claimed in claim 1 , characterized in that a highspeed CAN bus is provided as the data network, and in that a zener diode (15) is provided as the voltage-limiting nonlinear component.

7. A vehicle data network as claimed in claim 1 , characterized in that a highspeed CAN bus is provided as the data network, and in that a semiconductor diode sequence with a plurality of series-connected semiconductor diodes (21, 22, ...24) is provided as the voltage-limiting nonlinear component.

8. A device (10) for a vehicle data network ( 1 ), in which data can be transmitted with voltage values within a working voltage range between devices located in the vehicle, wherein the device (10) does not terminate the line (5) leading to it in the data network with a resistance corresponding to its characteristic impedance, and wherein the line is terminated by means of at least one voltage-limiting nonlinear component (15) provided at the device, which is connected between the conductors of the line at the end of the line (15) not terminated with the characteristic impedance, which has such a high resistance in the working voltage range of the data network (1) that the data transmission on the line (15) is not perturbed, and which has such a low resistance value at voltages above and or below the working voltage range that the voltage at the nonlinear component is limited and reflections on the line (15) are suppressed.