Resumen
An electrical data communications equipment (11) for transmitting digital data is disclosed. The equipment includes a bus (13; 49) for transmitting travelling waves of data. The bus (13; 49) has a characteristic impedance (Zo) and its ends are terminated with a terminating impedance (19, 21). Along the bus (13; 49) a plurality of couplers (CN) are configured at positions for coupling and/or decoupling data onto the bus (13; 49). Each of the couples (CN) is provided with a) voltage mode voltage transformer (23) interconnecting with the bus (13; 49) and causing on the bus (13; 49) a negative reflection vis-a-vis the polarity of the travelling wave of data and b) a current mode current transformer (37) interconnecting with the bus (13; 49) and causing on the bus (13; 49) a positive reflection (cm) vis-a-vis the travelling wave of data. The parameters of the voltage transformer (23) and current transformer (37) are proportioned to compensate the reflections of opposite polarity caused by the voltage transformer (23) and by the current transformer (37).
Reivindicaciones
1. Electrical data communications equipment (11) for transmitting digital data within a frequency range comprising: a) a bus (13; 49) for transmitting travelling waves of data which has a characteristic impedance (Zo) and which ends are terminated with a terminating impedance (19; 21) and b) a plurality of couplers (CN) configured at positions along the bus (13; 49) for coupling data onto the bus (13; 49) and for de-coupling it from of the bus (13; 49), characterised in that said coupler (CN) has both a) a voltage mode voltage transformer (23) interconnecting with the bus (13; 49) and causing on the bus (13; 49) a negative signal reflection vis-a-vis the polarity of the travelling wave of data, the voltage mode voltage transformer (23) having a voltage transformer impedance, and b) a current mode current transformer (37) interconnecting with the bus (13; 49) and causing on the bus (13; 49) a positive signal reflection vis-a-vis the travelling wave of data, the current mode current transformer (37) having a current transformer impedance, and whereby the voltage transformer impedance and the current transformer impedance are matched such that signal reflections of opposite polarity on the bus (13; 49) caused by the voltage transformer (23) and by the current transformer (37) are substantially eliminated. 2. Data communications equipment (11) in accordance with Claim 1 wherein the bus (13; 49) is configured as a ring. 3. Data communications equipment (11) in accordance with Claim 1 or 2 wherein the bus (13; 49) has two ends, each ofwhich is terminated with the terminating impedance having substantially the same value as the value of the characteristic impedance (Zo) of the bus (13; 49). 4. Data communications equipment (11 ) in accordance with any of the above claims wherein a) the voltage transformer (23) has one primary winding (25) and one secondary winding (27) and b) the current transformer (37) has at least one primary winding (39; 41 ), and one secondary winding (43), the at least one primary winding (25, 39, 41) being each connected to the bus (13; 49) and a data transmitter and/or a data receiver being connected to the secondary windings (25, 43). 5. Data communications equipment (11) in accordance with any of the above claims wherein the bus (13) has two mutually twisted bus lines (15, 17) and between these two bus lines (15, 17), a terminating impedance (19, 21) equal to the characteristic impedance (Zo) of the bus (13; 49) is connected at each end of the bus. 6. Data communications equipment (11) in accordance with Claim 5 wherein each of the two bus lines (15, 17) is enclosed by a shield wire. 7. Data communications equipment (11) in accordance with Claim 5 wherein both bus lines (15, 17) are enclosed by a common shield wire. 8. Data communications equipment (11) in accordance with Claim 4 wherein a) the primary winding (25) of the voltage transformer is connected between both bus lines (15, 17) and b) the current transformer (37) has two primary windings (39, 41) each of which is inserted serially into one of the two bus lines (15, 17). 9. Data communications equipment (11) in accordance with Claim 8 wherein the ends of the primary winding of both transformers (23, 37) are connected to the bus lines (15, 17; 51, 53) by a soldered joint. 10. Data communications equipment (11) in accordance with one of Claims 8 or 9 wherein the ends of the primary winding of both transformers (23, 37) are connected to the bus lines (15, 17; 51, 53) using plug connectors. 11. Data communications equipment (11 ) in accordance with one of Claims 8 or 9 wherein the ends of the secondary windings (33, 35, 45, 47) are provided with plug connectors for a detachable connection of a data source and/or data receiver. 12. Data communications equipment (11) in accordance with one of Claims 8 or 9 wherein the ends of the secondary windings (33, 35, 45, 47) are hardwired to a data source and/or data receiver. 13. Data communications equipment (11) in accordance with one of claims 1 to 4 wherein the bus (49) is formed by a coaxial cable with an inner conductor (51) forming one bus line and with an outer conductor (53) forming another bus line enclosing the inner conductor and wherein between the inner conductor (51) and the outer conductor (53) a terminating impedance (19, 21) substantially equal to the characteristic impedance (Zo) of the coaxial cable is connected at each end of the bus (49). 14. Data communications equipment (11) in accordance with Claim 13 wherein a) the primary winding (25) of the voltage transformer is connected between the inner conductor (51) and the outer conductor (53) of the coaxial cable and b) the current transformer (37) has a primary winding (39) of the current transformer inserted serially into the inner conductor (51) of the coaxial cable. 15. Data communications equipment (11) in accordance with Claim 14 wherein the ends of the primary winding of both transformers (23, 37) are connected to the one bus line and the other bus line by a soldered joint 16. Data communications equipment (11) in accordance with Claim 14 or 15 wherein the ends of the primary winding of both transformers (23, 37) are connected to the one bus line and the other bus line using plug connectors. 17. Data communications equipment (11) in accordance with Claim 14 or 15 wherein the ends of the secondary windings (33, 35, 45, 47) are provided with plug connectors for a detachable connection of a data source and/or data receiver. 18. Data communications equipment (11) in accordance with Claim 14 or 15 wherein the ends of the secondary windings (33, 35, 45, 47) are hardwired to a data source and/or data receiver.
