Two-wire to four-wire conversion circuit for a data switching center

Claim 2

A two-wire to four-wire conversion circuit for coupling a two-wire data transmission line to a receiver and to a transmitter while providing electrical isolation between these two elements regardless of the values of their impedances comprising a transformer having a primary winding with p turns connected to a line of impedance (ZL) and a symmetrical center tapped secondary winding with 2p turns, means connecting the center tap to ground through a resistor (R1), a first amplifier having an input which is connected to a first terminal of the secondary and an output connected to a receiver of internal impedance (ZR), a second amplifier having an input which is connected to a transmitter (K) and an output connected to the second terminal of the secondary winding, said transmitter including an internal impedance (ZK) coupled to a voltage source e, said first and second amplifiers each including current amplifiers of gain Alpha where the gain is less than unity and the amplifiers have a low input impedance Re relative to output impedances (RS), each of said current amplifiers being formed to include a transistor in common base configuration, whereby an A.C. voltage u applied to the primary of the transformer produces, at the output of the first amplifier a current IM2 ( Alpha u/2R1) while no energy at all is dissipated in the impedance (ZK), and a voltage e applied to the second amplifier through the impedance (ZK) produces an input current In1 e/R1 (where ZK R1) and produces across the primary of the transformer a voltage u'' R1.In2 Alpha e while no energy at all is dissipated in the impedance ZR, these values of (I m2) and u'' being given for the case where R1 ZL ZR and the current (In2) is the output current of the second amplifier.

Claim 3

A two-wire to four-wire conversion circuit for coupling a two-wire data transmission line to a four-wire junctor while providing electrical isolation between signals transmitted in opposite directions in the four-wire junctor regardless of the values of impedances in the circuit, comprising a transformer having a primary winding with p turns connected to a line of impedance (ZL) and a symmetrical center tapped secondary winding with 2p turns, means connecting the center tap to ground through a resistor (R1) thereby representing the connection to ground of two wires of said four-wire junctor, a first amplifier having an input which is connected to a first terminal of the secondary and an output connected to a third wire of the four-wire junctor, said third wire having an impedance (ZR), a second amplifier having an input which is connected to a fourth wire of said 4-wire junctor and an output connected to the second terminal of the secondary winding, said fourth wire including an impedance (ZK) coupled to a voltage source e, said first and second amplifiers each including current amplifiers of gain Alpha where the gain is less than unity and the amplifiers have low input impedances (Re) relative to output impedances (RS), each of said current amplifiers being formed to include a transistor in common base configuration, whereby an A.C. voltage u applied to the primary of the transformer produces, at the output of the first amplifier a current Im2 ( Alpha u/2R1) while no energy at all is dissipated in the impedance (ZK), and a voltage e applied to the second amplifier through the impedance (ZK) produces an input current In1 e/R1 (where ZK R1) and produces across the primary of the transformer a voltage u'' R1.In2 Alpha e while no energy at all is dissipated in the impedance ZR, these values of (Im2) and u'' being given for the case where R1 ZL ZR and the current (In2) is the output current of the second amplifier.

Claim 4

A two-wire to four-wire conversion circuit for coupling a two-wire data transmission line to a four-wire junctor while providing electrical isolation between signals transmitted in opposite directions in the four-wire junctor regardless of the values of impedances in the circuit, comprising a transformer having a primary winding with p turns connected to a line of impedance (ZL) and a symmetrical center tapped secondary winding with 2p turns, means connecting the center tap to ground through a resistor (R1) thereby representing the connection to ground of two wires of said four-wire junctor, a first amplifier having an input which is connected to a first terminal of the secondary and an output connected to a third wire of the four-wire junctor, said third wire having an impedance (ZR), a second amplifier having an input which is connected to a fourth wire of said 4-wire junctor and an output connected to the second terminal of the secondary winding, said fourth wire including an impedance (ZK) coupled to a voltage source e, said first and second amplifiers each including current amplifiers of gain Alpha where the gain is less than unity and the amplifiers have low input impedances (Re) relative to output impedances (RS), each of said current amplifiers being formed to include a transistor in common base configuration, whereby an A.C. voltage u applied to the primary of the transformer produces, at the output of the first amplifier a current Im2 ( Alpha u/2R1) while no energy at all is dissipated in the impedance (ZK), and a voltage e applied to the second amplifier through the impedance (ZK) produces an input current In1 e/R1 (where ZK R1) and produces across the primary of the transformer a voltage u'' R1.In2 Alpha e while no energy at all is dissipated in the impedance ZR, these values of (Im2) and u'' being given for the case where R1 ZL ZR and the current (In2) is the output current of the second amplifier.