Abstract:
Currently, in transformationally coupled linear data bus systems having separate transmission and reception lines, two transformers are used in order to achieve electrical isolation of data bus and terminal. According to one exemplary embodiment of the present invention, a data bus system is specified in which the terminal is connected via a directional coupler to the data bus lines in order to transmit and receive data via the data bus.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a data bus, preferably for an aircraft. In particular, the present invention relates to a data bus system having a data bus terminal, a terminal for connection and operation using a data bus, and a data transmission method to transmit data between a data bus and a terminal.  
         [0002]     Currently, in transformationally coupled linear data bus systems in aviation having separate transmitting and receiving lines, two transformers are used in order to couple the data bus to the terminal and vice versa. Terminals may be aircraft systems, devices, or sensors, for example. The transformational coupling is necessary in safety-critical systems in order to achieve the required operational reliability. The known buzzword in this regard is electrical isolation of data bus and terminal. Such data bus systems are described, for example, in the ARINC 629 Specification MIL STD 1553 Specification.  
         [0003]     However, the signal level on the data bus is disadvantageously damped by each and/or each further transformer, since each individual transformer generates reflections which deform the useful signal. Furthermore, the use of transformers is expensive. In addition, if there is a large number of terminals, the transformers represent a relatively large weight.  
         [0004]     Direct usage of a transformer for transmission and reception channels through parallel connection of the two spur lines which connect the bus lines to the terminal is not recommended, since the sensitive input circuit of the receiver in the terminal may be overloaded by the high output of the transmitter and, in addition, a possible short-circuit in the receiver of the terminal blocks the transmitter of this terminal.  
       SUMMARY OF THE INVENTION  
       [0005]     A data bus system according to one exemplary embodiment of the present invention, has a data bus and a terminal, the data bus having a first and a second data line. The terminal is connected to the second data line via a directional coupler, in order to transmit and receive data via the data bus.  
         [0006]     The use of the directional coupler according to the present invention may advantageously allow the use of one transformer to couple a terminal to the data bus having the bus lines. Reflections which are caused by transformers may advantageously thus be reduced. This improves the signal level on the data lines of the data bus. In addition, a cost-effective data bus system is thus provided.  
         [0007]     According to a further exemplary embodiment of the present invention, the terminal has a transmitter and a receiver. The receiver is isolated from the transmitter by the directional coupler. In this way, interference by transmission signals in the receiver is avoided.  
         [0008]     According to a further exemplary embodiment of the present invention, the directional coupler is designed in such a way that an input signal coming from the bus lines is relayed to the transmitter and the receiver, an output signal going from the transmitter to the data bus being relayed to the data bus, but not to the receiver.  
         [0009]     According to a further exemplary embodiment of the present invention, the directional coupler is designed in such a way that if the transmitter is not transmitting, the input impedance which assigns the data bus is adapted so that no reflections arise on the data bus. In this way, no reflections which deform the useful signal are generated on the data bus.  
         [0010]     According to an exemplary embodiment of the present invention, only one transformer is provided in the directional coupler, which essentially has a turn ratio of the primary coil to the secondary coil of 1.141 to 2×1.0. In other words, this means that this transformer has one primary coil and two secondary coils.  
         [0011]     According to a further exemplary embodiment of the present invention, the data bus system is tailored or adapted to the requirements in an aircraft. In particular, the data bus system according to the present invention is thus advantageous for an aircraft, since it has a low weight, but achieves the required operational reliability through the electric isolation of data bus and terminal. For example, the terminal may be an aircraft system or a part of an aircraft system.  
         [0012]     According to a further exemplary embodiment of the present invention, a terminal for connection and operation using a data bus is specified, the terminal having a directional coupler in order to produce a data connection to and from the bus lines of the data bus. It is to be noted here that instead of two bus lines, multiple bus lines may also be provided. It is also possible to provide only one bus line. This terminal advantageously has high operational reliability. Therefore, this terminal is especially suitable for safety-critical systems, in an aircraft, for example, in particular.  
         [0013]     According to a further exemplary embodiment of the present invention, a data transmission method is specified to transmit data between a data bus and a terminal. The data transmission method has the step of connecting the first and second data lines of the data bus to the terminal using a directional coupler in order to transmit and receive data via the data bus. A simple, robust data transmission method is advantageously provided.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0014]     In the following, exemplary embodiments of the present invention are described with reference to the accompanying figures.  
         [0015]      FIG. 1  shows a simplified schematic circuit diagram of a first exemplary embodiment of a data bus system according to the present invention, the signal flow being shown in T x  mode;  
         [0016]      FIG. 2  shows a simplified schematic circuit diagram of the first exemplary embodiment of the data bus system from  FIG. 1 , the signal flow being shown in R x  mode; and  
         [0017]      FIG. 3  shows a simplified block circuit diagram of a second exemplary embodiment of a data bus system according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     In the following, the present invention is described in greater detail with reference to a data bus system, which is preferably usable in an aircraft. However, it is to be noted that the present invention is not restricted to application in an aircraft, but rather may also be applied in other general data bus systems.  
         [0019]      FIG. 1  shows a simplified schematic circuit diagram of a first exemplary embodiment of a data bus system according to the present invention, the signal flow being shown in T x  mode. As may be inferred from  FIG. 1 , the data bus  2  has two data bus lines  4  and  6 . The data bus lines  4  and  6  are connected to the terminal  14  using spur lines  8  and  10 . In particular, the spur lines  8  and  10  are connected to a directional coupler  12 , which is connected on one side via the lines  18  to a receiver  16  of the terminal  14  and on the other side via the lines  20  to a transmitter  22  of the terminal.  
         [0020]     The gray arrows are to indicate the signal flow in the T x  (transmit) mode. As may be inferred from  FIG. 1 , a signal is transmitted by the transmitter  22  via the line  20  to the directional coupler  12 . The directional coupler  12  does not relay the signal to the receiver  16 . However, the directional coupler  12  relays the signal transmitted by the transmitter  22  via the spur lines  8  and  12  to the bus lines  4  and  6  of the data bus, where the signal is also distributed further.  
         [0021]      FIG. 2  shows a simplified schematic circuit diagram of the first exemplary embodiment of the data bus system from  FIG. 1 , the signal flow being shown in R x  (receive) mode. Transmit mode means that the corresponding terminal transmits data via the data bus to another terminal. Receive mode means that the terminal receives data via the data bus.  
         [0022]     As may be inferred from  FIG. 2 , incoming data from the data bus  2  is relayed via the spur lines  8  or  10  to the directional coupler  12 , which relays the data both to the transmitter  22  via the lines  20  and also via the lines  18  and the receiver  16 .  
         [0023]     Therefore, as may be inferred from  FIGS. 1 and 2 , the receiver  16  is isolated from the transmitter  22  by the directional coupler  12 . When the transmitter  22  is not transmitting, the input impedance of the directional coupler is adapted, so that no reflections arise on the bus lines  4  and  6  which may interfere with the bus signal and/or the receiver. This advantageously allows reliable and improved operation of the data bus system.  
         [0024]      FIG. 3  shows a simplified circuit diagram of a second exemplary embodiment of a data bus system according to the present invention. In  FIG. 3 , identical reference numbers as in  FIGS. 1 and 2  are used for identical or corresponding elements. For the sake of simplicity, the transmitter and the receiver are not shown in  FIG. 3 , only the lines  18  and  20  which go to the receiver and transmitter, respectively.  
         [0025]     As may be inferred from  FIG. 3 , the transformer  30  is positioned between the data bus  2  having the data bus lines  4  and  6 . The transformer  30  has a primary coil  32  and two secondary coils  34  and  36 . The secondary coils each have an equal number of turns. The transformer  30  essentially has a turn ratio of primary coil to secondary coil of 1.141 to 2×1.000 ({square root}2 to 2×1). The following voltages and currents thus result with the impedance Z 0  for the transmitter output at rest and the receiver output at rest.  
               U   T     =       I   T     ·     Z   0                     I   B     =       1     2       ⁢     I   T                     U   B     =         I   B     ·     Z   0       =       1     2       ⁢     U   T                       P   B     =         U   B     ·     I   B       =         1     2       ⁢       U   T     ·     1     2         ⁢     I   T       =       1   2     ⁢     P   T                         U   1     =       U   2     =         1     2       ⁢     U   B       =       1   2     ⁢     U   T                         ⇒     …   ⁢           ⁢     U   R         =         U   T     -     U   1     -     U   2       =   0                   ⇒     …   ⁢           ⁢     P   R         =   0               (     power   ⁢           ⁢   at   ⁢           ⁢   receiver   ⁢           ⁢   input     )                 U   3     =         U   T     -     U   1       =       1   2     ⁢     U   T                               ⁢       P   L     =       U   3     ·     I   3                     =       U   3     ·       U   3       0.5   ·     Z   0                       =       U   3     ·       2   ·     U   3         Z   0                     =       U   3     ·       U   T       Z   0                     =       U   3     ·     I   T                   =       1   2     ⁢       U   T     ·     I   T                     =       1   2     ⁢     P   T                             ⁢     (     power   ⁢           ⁢   transmitted   ⁢           ⁢   to   ⁢           ⁢   the   ⁢           ⁢   bus     )                                   U   B     =       I   B     ·     Z   0                     P   B     =         U   B     ·     I   B       =       Z   0     ·     I   B   2                       U   1     =       U   2     =       1     2       ⁢     U   B                       I   1     =       I   2     =       1     2       ⁢     I   B                       I   3     =         I   R     -     I   T       =   0                   …   ⇒     P   L       =   0                 U   R     =       I   R     ·     Z   0                     P   R     =         U   R     ·     I   R       =         Z   0     ·     I   R   2       =         1   2     ⁢       Z   0     ·     I   B   2         =       1   2     ⁢     P   B                         (     received   ⁢           ⁢   power     )                 P   T     =         U   T     ·     I   T       =         Z   0     ·     I   T   2       =       1   2     ⁢     P   B                       (     power   ⁢           ⁢   fraction   ⁢           ⁢   at   ⁢           ⁢   an   ⁢           ⁢   inactive   ⁢           ⁢   transmitter   ⁢           ⁢   gate     )             
 
         [0026]     In this table, as may be inferred from  FIG. 1 , the current I B  is the current in the primary coil  32  and the voltage U B  is the voltage via the primary coil. P B  is the incoming bus line. The current I T  is the current flowing from the transmitter with the impedance Z 0  with the power P T  into the secondary coil, the voltage via the secondary coil  34  being identified with U 1.  The current I R  is the current flowing in the receiver, the receiver having an impedance of Z 0  and a receiving power of P R.  The voltage via the secondary coil  36  is identified with U 2 . In the equivalent circuit diagram, I 3  identifies the current which flows through the impedance Z 0/ 2, which is connected between the secondary coils  34  and  36  and a transmitter and receiver input. P 0  identifies the power via Z 0/ 2 and U 3  identifies the voltage via this impedance. The voltage U T  identifies the input voltage of the transmitter and the voltage U R  identifies the input voltage of the receiver.  
         [0027]     As may be inferred from the above description, the present invention of allows the number of coupling transformers which are necessary for the electrical isolation of data bus and terminal to be halved in comparison to the known data bus systems. In this way, the costs for coupling transformers are halved, i.e., a favorable data bus system is provided. In addition, the signal distortion on the data bus due to reflections is significantly reduced.  
         [0028]     It should be noted that the term “comprising” does not exclude other elements or steps and the “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined.  
         [0029]     It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.