NETWORK COMMUNICATION SYSTEM WITH BIDIRECTIONAL CURRENT MODULATION FOR TRANSMITTING DATA

Abstract

The invention relates to a network communication system (50), in particular for a vehicle, having a communication bus (56), a first communication device (52) and a plurality of second communication devices (54) which are connected to one another via the communication bus (56), wherein the first communication device (52) comprises a bias voltage source (64) for generating a constant bias voltage on the communication bus (56), the first communication device (52) comprises a current measurement apparatus (66) for capturing the current on the communication bus (56), the network communication system (50) has a terminating resistor (60) which is arranged in parallel with the plurality of second communication devices (54), the first communication device (52) comprises a first modulation apparatus (72) for modulating a current set by the bias voltage and the terminating resistor (60) on the communication bus (56), each second communication device (54) comprises a second modulation apparatus (78) for modulating the current set by the bias voltage and the terminating resistor (60), and each second communication device (54) has a second voltage measurement apparatus (80) for capturing a voltage at the terminating resistor (60). The invention also relates to a corresponding method for communication in a network communication system (50).

Claims

1. A network communication system for a vehicle, the network communication system comprising: a communication bus; a first communication device; a plurality of second communication devices which are connected to one another via the communication bus, wherein the first communication device comprises a bias voltage source for generating a constant bias voltage on the communication bus, and a current measurement apparatus for capturing the current on the communication bus; and a terminating resistor arranged in parallel with the plurality of second communication devices, wherein: the first communication device comprises a first modulation apparatus for modulating a current set by the bias voltage and the terminating resistor on the communication bus, each second communication device comprises a second modulation apparatus for modulating the current set by the bias voltage and the terminating resistor, and each second communication device has a second voltage measurement apparatus for capturing a voltage at the terminating resistor.

2. The network communication system according to claim 1, wherein the current measurement apparatus has a measurement resistor, through which the current modulated by the second communication device flows, and a first voltage measurement apparatus for capturing a voltage drop across the measurement resistor.

3. The network communication system according to claim 1, wherein the current measurement apparatus has a current mirror, through which the current modulated by the second communication device flows, and an ammeter.

4. The network communication system according to claim 1, wherein the bias voltage source and the first modulation apparatus are arranged in parallel in the first communication device, and a diode is connected upstream of the bias voltage source and blocks a current from the first modulation apparatus into the bias voltage source.

5. The network communication system according to claim 1, wherein the bias voltage source and the current measurement apparatus are connected in series.

6. The network communication system according to claim 1, wherein the bias voltage source is in the form of a constant voltage source.

7. The network communication system according to claim 1, wherein the first modulation apparatus is connected in series with a first voltage source.

8. The network communication system according to claim 1, wherein the first modulation apparatus and/or the second modulation apparatus is/are configured for analogue modulation of the current.

9. The network communication system according to claim 1, wherein the first modulation apparatus and/or the second modulation apparatus is/are configured for digital modulation of the current with a plurality of different modulation current levels.

10. The network communication system according to claim 1, wherein the terminating resistor is arranged in the first communication device.

11. The network communication system according to claim 1, wherein the terminating resistor s arranged in one of the second communication devices.

12. The network communication system according to claim 1, wherein the terminating resistor is directly arranged on the communication bus.

13. The network communication system claim 1, wherein the second modulation apparatus is in the form of a current sink which can be modulated.

14. A method for bidirectional communication based on current modulation in a network communication system for a vehicle, the network communication system having a communication bus, a first communication device, a plurality of second communication devices which are connected to one another via the communication bus. and a terminating resistor which is arranged in parallel with the plurality of second communication devices, the method comprising: generating a constant bias voltage on the communication bus using the first communication device; generating a modulated current on the communication bus using the first communication device; capturing the voltage caused by the current modulated using the first communication device at the terminating resistor using each of the second communication devices, generating a modulated current on the communication bus using one of the second communication devices; and capturing the current modulated using one of the second communication devices on the communication bus using the first communication device.

Description

[0039] In the drawing

[0040] FIG. 1 shows a schematic view of a communication network from the prior art having a master and a slave which are connected to one another via a connecting line, wherein the connecting line has stray capacitances,

[0041] FIG. 2 shows a specific configuration of the communication network from FIG. 1, wherein the master has a voltage source which can be modulated and each slave has a current sink which can be modulated,

[0042] FIG. 3A shows a schematic illustration of a network communication system according to a first preferred embodiment having a first communication device, a plurality of second communication devices and a terminating resistor which are connected in parallel with a communication bus,

[0043] FIG. 3B shows a schematic illustration of a network communication system according to a second, alternative embodiment having a current measurement apparatus based on a current mirror,

[0044] FIG. 4 shows an exemplary time diagram having data transmission between the first communication device and a second communication device with a voltage profile at the terminating resistor when binary digital modulation is used, and

[0045] FIG. 5 shows an exemplary time diagram having data transmission between the first communication device and a second communication device with a voltage profile at the terminating resistor when digital modulation having three different signal levels is used.

[0046] FIG. 3A shows a network communication system 50 according to a first preferred embodiment.

[0047] The network communication system 50 of the first embodiment comprises a first communication device 52, a plurality of second communication devices 54 and a communication bus 56 which is used to connect the first communication device 52 and the plurality of second communication devices 54 to one another. The communication bus 56 is embodied using two electrical lines 58.

[0048] The communication bus 56 also has a terminating resistor 60 which is connected to the communication bus 56 in parallel with the communication devices 52, 54. In an alternative embodiment, the terminating resistor 60 can be arranged in series with a constant terminating voltage source 62, with the result that the value of the terminating resistor 60 can be kept low.

[0049] The first communication device 52 comprises a bias voltage source 64 for generating a constant bias voltage on the communication bus 56. The constant bias voltage generates a quiescent current through the terminating resistor 60. The bias voltage source 64 is in the form of a constant voltage source 64 here.

[0050] Each of the second communication devices 54 comprises a second modulation apparatus 78 for modulating a sink current on the communication bus 56 and a second voltage measurement apparatus 80 for measuring a voltage at the terminating resistor 60. By measuring the voltage at the terminating resistor 60 using the second voltage measurement apparatus 80, each second communication device 54, with knowledge of the terminating resistor 60, can determine the overall current on the communication bus 56.

[0051] The first communication device 52 comprises a current measurement apparatus 66 which is connected in series with the bias voltage source 64. In this embodiment in FIG. 3A, the current measurement apparatus 66 comprises a measurement resistor 68, through which the quiescent current flows together with the current modulated by the current sink 78 of the respective second communication device 54. This current corresponds to a current on the communication bus 56. The first communication device 52 or the current measurement apparatus 66 also comprises a first voltage measurement apparatus 70 for measuring a voltage drop across the measurement resistor 68. With knowledge of the measurement resistance value 68, the value of the modulated current on the communication bus 56 can be determined.

[0052] In an alternative embodiment, the current measurement apparatus 66 can also be implemented using other means, without the measurement resistor 68 and the voltage measurement apparatus 70. For example, in a second, alternative embodiment, the current measurement apparatus 66 can be implemented using a current mirror 69 and an ammeter 71, as symbolically shown in FIG. 3B. The current measurement apparatus 66 therefore comprises a current mirror 69, through which the quiescent current flows together with the current modulated by the current sink 78 of the respective second communication device 54. This current also corresponds here to a current on the communication bus 56 or a bus current. The first communication device 52 or the current measurement apparatus 66 also comprises an ammeter 71 for measuring the current on the communication bus via the current mirror. As a result of the use of the current mirror, the current measurement does not have any effect on the rest of the circuit.

[0053] The following description relates both to the embodiment in FIG. 3A and to the embodiment in FIG. 3B. A first modulation apparatus 72 is arranged in series with a first supply voltage source 74 in parallel with the bias voltage source 64 and the current measurement apparatus 66. In the present case, the first modulation apparatus 72 is in the form of a current source which can be modulated. The first supply voltage source 74 makes it possible for the current source 72 which can be modulated to allow a modulated current to flow into the communication bus 56 in addition to the constant quiescent current.

[0054] In this context, a diode 76 is connected upstream in the series circuit comprising the bias voltage source 64 and the current measurement apparatus 66 and blocks a current from the first modulation apparatus 72 into the bias voltage source 64. The diode 76 therefore ensures that the current modulated by the first modulation apparatus 72 flows only into the communication bus 56 and is not smoothed or even completely absorbed by the bias voltage source 64. The quiescent current and the modulated current are added to form an overall current (bus current) which includes the transmitted data.

[0055] During operation, a constant quiescent current on the communication bus 56 from the first communication device 52 is first of all generated by the bias voltage source 64 in the network communication system 50. Both the first modulation apparatus 72 of the first communication device 52 and all second communication devices 54 are not active, that is to say no currents in addition to the quiescent current are generated or drawn on the communication bus 56. On the basis of this, data can be modulated using current modulation in a temporally offset manner both by the first communication device 52 and by each of the second communication devices 54, as explained in detail below.

[0056] If the first communication device 52 wishes to transmit data to one or more of the second communication devices 54, the first communication device 52 uses the first modulation apparatus 72 to modulate its data into modulated current and allows its modulated current to flow into the communication bus 56 in addition to the constant quiescent current. The second modulation apparatuses 78 of the second communication devices 54 remain inactive. As a result, the current flowing via the communication bus 56, that is to say the quiescent current together with the current modulated by the first modulation apparatus 72, flows completely through the terminating resistor 60. In comparison with the quiescent current, the current modulated by the first modulation apparatus 72 gives rise to an additional voltage drop across the terminating resistor 60. The second communication devices 54 measure the voltage at the terminating resistor 60 using their respective second voltage measurement apparatus 80 in order to therefore be able to decode the modulated data. Accordingly, the data modulated by the first communication device 52 can be decoded in each of the second communication devices 54.

[0057] Accordingly, the second communication devices 54 can each draw a modulated current from the communication bus 56 using the corresponding second modulation apparatus 78 in order to transmit data to the first communication device 52. This is made possible by the bias voltage and the resulting quiescent current, with the result that the second modulation apparatus 78 of each second communication device 54 can draw a modulated sink current which accordingly increases the quiescent current flowing from the bias voltage source 64.

[0058] The modulated sink current drawn by the respective second modulation apparatus 78 causes a change in the voltage drop across the measurement resistor 68, which change responds to the current modulated by one of the second communication devices 54. The first communication device 52 measures the voltage at the measurement resistor 68, as a result of which the data modulated by one of the second communication devices 54 can therefore be decoded.

[0059] Data are transmitted from the first communication device 52 to one of the second communication devices 54 and from each of the second communication devices 54 to the first communication device 52 independently in each case and in basically any desired temporal sequence. It is merely necessary to avoid the situation in which two of the communication devices 52, 54 want to transmit data at the same time.

[0060] FIG. 4 shows modulation of the current on the communication bus 56 by the first or one of the second communication devices 52, 54 in accordance with the first embodiment. During a first transmission phase 82, the first communication device 52 transmits data which are binary digital data having a dominant level and a passive level. Accordingly, the current on the communication bus 56 is increased by the first modulation apparatus 72 in order to modulate a dominant level. As a result, an instantaneous value of the voltage on the communication bus 56 is also increased, which can be captured and decoded using the second voltage measurement apparatus 80. In the case of a passive level, the current on the communication bus 56 remains unchanged; the first modulation apparatus 72 digitally codes the passive level with zero (0). In the case of an active level, the current on the communication bus 56 is accordingly changed; the first modulation apparatus 72 digitally codes the active level with one (1). The same applies to the modulation and transmission of data from one of the second communication devices 54 to the first communication device 52. While one of the second communication devices 54 modulates its data using its second modulation apparatus 78, the total current drawn by the bias voltage source 64 is increased. On account of the measurement resistor 68 connected in series, the instantaneous value of the voltage of the communication bus 56 is reduced.

[0061] FIG. 5 shows modulation of the current on the communication bus 56 by the first communication device 52 according to a second embodiment. The data to be modulated may here have three different levels, two dominant levels and a passive level. Accordingly, the current on the communication bus 56 is increased by the first modulation apparatus 72 in accordance with the first or second dominant level in order to modulate the data on the communication bus 56.

[0062] In a further embodiment, the data to be transmitted can be coded in both directions using a plurality of modulation levels and can be accordingly decoded after reception at the other end.

[0063] In an alternative embodiment, the terminating resistor 60 is arranged in the first communication device 52 or in the second communication device 54.

[0064] On the basis of the exclusive use of current modulation to transmit the data in the network communication system 50, the configuration of the modulated current can be adapted in order to meet the requirements imposed on electromagnetic compatibility (EMC). The actual adaptation of the modulation in order to reduce EMC emissions by the network communication system 50 is not within the scope of the invention and is therefore not explained at this point. In the present case, the network communication system 50 is provided in order to be able to carry out this adaptation of the modulation.

LIST OF REFERENCE SIGNS

[0065] 10 Network communication system (prior art) [0066] 12 Master (prior art) [0067] 14 Slave (prior art) [0068] 16 Communication bus (prior art) [0069] 18 Stray capacitance (prior art) [0070] 20 Voltage source which can be modulated (prior art) [0071] 22 Measurement resistor (prior art) [0072] 24 First voltmeter (prior art) [0073] 26 Current measurement apparatus (prior art) [0074] 28 Second voltmeter (prior art) [0075] 30 Current modulation apparatus, current sink which can be modulated (prior art) [0076] I.sub.n Current modulated by the slave (prior art) [0077] U.sub.M Voltage modulated by the master (prior art) [0078] 50 Network communication system [0079] 52 First communication device, master [0080] 54 Second communication device, slave [0081] 56 Communication bus [0082] 58 Line [0083] 60 Terminating resistor [0084] 62 Terminating voltage source, constant voltage source [0085] 64 Bias voltage source, constant voltage source [0086] 66 Current measurement apparatus [0087] 68 Measurement resistor [0088] 69 Current mirror [0089] 70 First voltage measurement apparatus [0090] 71 Ammeter [0091] 72 First modulation apparatus, current source which can be modulated [0092] 74 Supply voltage source [0093] 76 Diode [0094] 78 Second modulation apparatus, current sink which can be modulated [0095] 80 Second voltage measurement apparatus [0096] 82 First transmission phase [0097] 84 Second transmission phase [0098] I.sub.M Current modulated by the master