Patent ID: 6366976
Filing Date: 2002-04-02
Classification: H04L

Abstract:
A device to connect a subscriber to a bus line for bi-directional data transmission, comprising:a branch line to connect the subscriber with the device; an amplifier circuit to selectively transmit signals from the bus line to the branch line and from the branch line to the bus line, wherein the amplifier circuit has a high-resistance input at the bus line and has outputs structured to be switched between an active operation mode and an inactive operation mode, wherein, in the active operation mode, a respective connected one of the bus line and the branch line is structured to be driven by the signals received by a respective other one of the branch line and the bus line, and wherein, in the inactive operation mode, at least one of the outputs has a high resistance; and a direction determination circuit to detect if the signals are to be transmitted from the bus line to the branch line or from the branch line to the bus line, and to activate a respective one of the outputs; wherein a data transmission on the branch line is digitally voltage-level-coded with predetermined response thresholds to detect digital values, wherein the direction determination circuit comprises a first resistor network and a first buffer to generate a first determination signal, wherein the first resistor network corresponds to a star connection, the first resistor network comprising: a first series resistor arranged between a first star point of the star connection and an input of the first buffer; a second series resistor arranged between the first star point and one of the outputs of the amplifier circuit located on a branch line side of the amplifier circuit; a connection of the first star point with the branch line; and first clamp resistors, at the input of the buffer and at the branch line, against power supply voltages, wherein the first series resistor, the second series resistor, and the first clamp resistors are dimensioned such that: a first change of a voltage level changes the voltage level on the branch line such that a change of at least one digital value is detected at a connected input of the subscriber, wherein the first change of the voltage level is supplied from the at least one output of the amplifier circuit to the first resistor network and corresponds to the change of the at least one of the digital values, and the first change of the voltage level changes the voltage level at the input of the buffer only slightly so that the change of the at least one digital value is not detected at the first buffer, and wherein the first series resistor, the second series resistor, and the first clamp resistors are dimensioned such that a second change of the voltage level changes the voltage level at the input of the first buffer such that the change of the digital value is detected by the first buffer, wherein the second change of the voltage level is supplied from the branch line to the first resistor network and corresponds to the change of the at least one digital value.