BUS STATION, BUS SYSTEM, AND METHOD FOR TRANSMITTING DATA IN A TWO-WIRE BUS SYSTEM

Abstract

A bus station, a two-wire bus system, and methods for transmitting data in a two-wire bus system. The method includes: supplying a variable battery voltage to a first bus station and a second bus station, and transmitting data from the first bus station to the second bus station using a modulation signal that is superposed on the variable battery voltage, wherein the modulation signal is adjusted to follow a level of the variable battery voltage in a predefined manner.

Claims

1-10. (canceled)

11. A method for transmitting data in a two-wire bus system, comprising the following steps: supplying a first bus station and a second bus station with a variable battery voltage; and transmitting data from the first bus station to the second bus station using a modulation signal superposed on the variable battery voltage, wherein the modulation signal is adjusted to follow a level of the variable battery voltage in a predefined manner.

12. The method according to claim 11, wherein a difference: (i) between the variable battery voltage and high levels of the modulation signal and/or (ii) between the high levels and low levels of the modulation signal, is kept constant.

13. The method according to claim 11, wherein a mean value of the modulation signal is adjusted to follow the variable battery voltage at a predefined offset.

14. The method according to claim 11, wherein all bus stations present in the two-wire bus system are supplied by a battery, which provides the variable battery voltage.

15. The method according to claim 11, wherein the modulation signal is derived from the variable battery voltage using a modulation resistor, through which a current that is predefined for generating the modulation signal flows.

16. The method according to claim 15, wherein a desired voltage swing between a high level and a low level of the modulation signal is generated using a plurality of current sources between the modulation resistor and an electrical ground.

17. The method according to claim 11, wherein the modulation signal is generated from the variable battery voltage using a control stage and a driver stage.

18. The method according to claim 11, wherein no voltage regulator is present in the first bus station.

19. A bus station for use as a first bus station, comprising: a two-wire bus terminal configured for communication and to obtain a variable battery voltage; wherein the first bus station is configured to supply a second bus station with energy via the two-wire bus terminal using the variable battery voltage, and to transmit a modulation signal, superposed on the variable battery voltage, to the second bus station, wherein the first bus station is further configured to adjust the modulation signal to follow a level of the variable battery voltage in a predefined manner.

20. A bus system, comprising: a first bus station, including: a two-wire bus terminal configured for communication and to obtain a variable battery voltage, wherein the first bus station is configured to supply a second bus station with energy via the two-wire bus terminal using the variable battery voltage, and to transmit a modulation signal, superposed on the variable battery voltage, to the second bus station, wherein the first bus station is further configured to adjust the modulation signal to follow a level of the variable battery voltage in a predefined manner; and a second bus station connected to the first bus station using a two-wire line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments of the present invention are described in detail below with reference to the figures.

[0016] FIG. 1 shows a schematic representation of a two-wire bus system according to an exemplary embodiment of the present invention.

[0017] FIG. 2 shows a voltage-time diagram illustrating a variable battery voltage U.sub.Batt and a modulated voltage U.sub.mod.

[0018] FIG. 3 shows an enlarged detail of the voltage-time diagram of FIG. 2.

[0019] FIG. 4 shows a schematic representation of an exemplary embodiment of a bus station according to the present invention with controllable current sinks.

[0020] FIG. 5 shows a schematic representation of a control stage in conjunction with a driver stage of the exemplary embodiment of a bus station according to the present invention.

[0021] FIG. 6 shows a basic circuit of an assembly in a receiver path of a bus station of a bus system according to the present invention.

[0022] FIG. 7 shows a flow chart illustrating steps of an exemplary embodiment of a method according to the present invention for data transmission in a two-wire bus system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0023] FIG. 1 shows a schematic representation of a two-wire bus system 10, in which a first control device 1 in the form of a master is supplied with a variable battery voltage via a battery 7. The first control device 1 is configured to supply a second control device 2, a third control device 3 and a fourth control device 4 with the variable battery voltage from the battery 7 and to transmit data to the control devices 2, 3, 4 as bus stations.

[0024] The two-wire bus system 10 can be provided, for example, in a passenger car, a transporter, a truck, an aircraft and/or a watercraft. The on-board power supply voltage can be 12 volts, 24 volts, 48 volts or also 400 volts or 800 volts. A component of receiving and decoding the voltage-modulated Manchester coding within the control devices 2, 3, 4 is an AC voltage decoupling of the modulation signal with subsequent digital conversion via a comparator with variable threshold following.

[0025] The assemblies required for this purpose are presented in conjunction with FIG. 6.

[0026] FIG. 2 shows a voltage-time diagram of a variable battery voltage U.sub.Batt. Between 0 seconds and 0.20 ms, the variable battery voltage U.sub.Batt increases from approximately 7 volts to approximately 16.5 volts and decreases again to approximately 7 volts from approximately 0.4 ms.

[0027] Since a fixed modulation voltage or a ? between high level and low level could only have an extremely low resolution in such a voltage swing, a modulation signal U.sub.mod is quasi-equidistantly suspended from the variable battery voltage U.sub.Batt in the manner according to the present invention. In other words, in the range between 0.20 ms and 0.40 ms, low levels corresponding to one another at 0 seconds vary from approximately 1.5 volts to just 10 volts (low level) and high levels corresponding to one another at 0 seconds vary from 5 volts to approximately 13.5 volts (high level). In other words, in a first (initial) time range, a low level of the modulation signal U.sub.mod is clearly lower than a corresponding low level of the modulation signal U.sub.mod at a later point in time. Moreover, a high level in a first time segment is defined to be significantly lower than a low level at a later point in time. In other words, all levels of the modulation signal U.sub.mod in a first time range (e.g., at 0 seconds) are defined to be lower than the low and high levels in a second (later) time range (from approximately 0.2 ms). The reverse applies to the second time range and a subsequent third time range from 0.50 ms, in which the low and high levels correspond to the first time range. However, the voltage swing of the modulation signal U.sub.mod from a low level to a directly following high level remains constant at approximately 3 volts over the entire time range (first to third time range). Accordingly, between the variable battery voltage U.sub.Batt and a high level of the modulation signal U.sub.mod also remains constant over time (approximately 3 volts). Finally, a difference between the variable battery voltage U.sub.Batt and a low level of the superposed modulation signal U.sub.mod also remains constant over time at approximately 6 volts.

[0028] FIG. 3 shows a detail of the voltage-time diagram shown in FIG. 2, in which the relationships of the two voltage signals U.sub.Batt and U.sub.mod can be seen. While the filtered battery voltage U.sub.Batt in the time segment under consideration appears to be constant, the high level U.sub.mod high remains below U.sub.Batt by approximately 3 volts. This corresponds to the voltage drop across the driver output stage U.sub.driver. In the lower value U.sub.mod_low, the modulated voltage corresponds to a freely selectable voltage of, for example, U.sub.mod_high?[0.5 volts to 2 volts]. Various voltage levels for the low level U.sub.mod_low are also possible in order to thus enable even higher bit rates. For example, here, a first low level (not shown) of the difference of the high level reduced by 0.5 volts corresponds to a first symbol and a second low level of the difference of the high level reduced by 1 volts corresponds to a second symbol. The differential voltage or the modulation voltage swing can thus also advantageously be adapted to the line parameters and environmental influences of the bus, in order to adapt the robustness of the data transmission for a specific two-wire line system. It should be noted that the two voltage curves shown are not transmitted over the entire bus, but rather the variable battery voltage U.sub.Batt is, for example, provided to only the first control device 1, which propagates the modulation signal U.sub.mod via the two-wire line to the control devices 2, 3, 4 (see FIG. 1) for data transmission.

[0029] FIG. 4 shows a schematic representation of components for generating a variable modulation voltage on the two-wire line (bus), for example by the first bus station (master) 1. Three controllable variable current sinks I.sub.1, I.sub.2 and I.sub.n are configured to be activated for modulation as needed by a logic 8 via respective switches S.sub.1, S.sub.2 S.sub.n and control lines 7. Through them, the digital (Manchester-coded) data stream is converted into a modulation current and finally into the variable target modulation voltage U.sub.target. This results in the target modulation voltage U.sub.target as:

[00001]$U_{\mathrm{target}}=U_{\mathrm{BattFilter}}-R_{mod}?I_{\mathrm{total}},$

where U.sub.BattFilter is the filtered variable battery voltage, R.sub.mod iS the ohmic resistance of the modulation resistor, and I.sub.total is the total current drawn through the modulation resistor R.sub.mod by the controllable current sources. The voltage signal U.sub.target is supplied to a control stage (shown in FIG. 5). Through temporally offset switching of the current sinks/current sources I.sub.1, I.sub.2, In, the temporal shape of the target voltage swing (pulse shaping) can be adapted if required. Any pulse shapes (e.g., rectangle, sine, triangle or only a flank deformation for reducing interference emissions) can thus be realized.

[0030] FIG. 5 shows a circuit comprising a control stage 5 and a driver stage 6 for use in a bus station (master) according to the present invention. The control stage 5 compares the target modulation voltage U.sub.target to the actual modulation voltage U.sub.mod after the driver output stage and keeps the control deviation small. Technically, a small control deviation, which results from the voltage drop in the driver stage 6, remains. According to the technical design of the driver stage 6 as a push-pull stage, for example with unipolar transistors with low source resistance or bipolar transistors with low saturation residual voltage, the voltage drop and thus the remaining control deviation can be kept small.

[0031] FIG. 6 shows a basic circuit of the AC voltage coupling and the subsequent digital conversion in a receiver path of a control device (in particular slave) when only two different voltage levels (high and low) are transmitted. During the transmission of only two voltage levels, the control devices 2, 3, 4 require, for example, a simple circuit structure on the receiver side, in order to free the modulation voltage U.sub.mod from the mean variable DC voltage component (AC voltage decoupling). Subsequently, a voltage adaptation of the, for example Manchester-coded, AC voltage signal, which is symmetrical with respect to 0 volts, to the input voltage range of the following comparator 11 takes place. The AC voltage decoupling takes place by an AC voltage decoupler 9 and a capacitor C.sub.2. The filter network between the AC voltage decoupler 9 and the comparator 11 comprises a low-pass filter comprising an ohmic resistor R.sub.1 and a capacitor C.sub.1. The comparator 11 is responsible for the digitization of the modulation signal U.sub.mod, wherein its switching threshold is also generated directly from the low-pass-filtered modulation signal. The comparator outputs the digitized modulation signal U.sub.mod_digi. The voltage supply U.sub.sensor of the AC voltage decoupler 9 and of the comparator 11 is realized, for example, from the modulation voltage via the voltage regulators present in the AC voltage decoupler 9 and comparator 11.

[0032] FIG. 7 shows steps of an exemplary embodiment of a method according to the present invention for data transmission in a two-wire bus system. In a first step 100, the method comprises supplying a first bus station (master) and a second bus station (slave) with a variable battery voltage. The battery voltage is to be understood as a DC voltage signal with a magnitude that (slowly) varies over time. In this case, the variable battery voltage can deviate from its minimum voltage upward, for example by 20%, 40%, 60% or more. In a second step 200, data are transmitted from the first bus station (master) to the second bus station (slave) using a modulation signal superposed or embedded into the variable battery voltage. The modulation signal is adjusted to follow a level of the variable battery voltage in a predefined manner. In other words, the modulation signal is equidistantly suspended from a respective level of the variable battery voltage. While the variable battery voltage is supplied to the first bus station (master), the first bus station (master) transmits the modulation signal via the two-wire line to the second bus station and further bus stations.

[0033] The present invention simplifies the voltage generation in the master control device for the sensors on the bus, enables a data transmission from the master control device to the bus stations, which data transmission is at least up to six times higher in comparison to, for example, the currently known generation of parking sensors in the related art and allows uninterrupted operation of the sensors without temporarily storing energy in the bus stations during the communication. This simplifies the structure and eliminates the need for hardware that was always required in the related art.