Full electronic two-wire to four-wire conversion circuit

Claim 2

An electronic two-wire to four-wire conversion circuit, comprising a switching network, a path through said switching network having a given resistance, a pair of line terminals for receiving a first variable voltage from a subscriber line for transmission of information signals in a first direction away from the subscriber line and for receiving a second variable voltage for transmission of information signals in a second direction toward the subscriber line, a pair of network terminals connecting the switching network to a junctor via two conductors of the switching network respectively assigned to the first and second directions of transmission, the information signals transmitted on said conductors being carried by modulation of a first current in the first direction and by modulation of a second current in the second direction, means including a resistor and a capacitor coupled in series between the line terminals, a pair of intermediate terminals coupled between the line terminals and the network terminals, means including a resistor interconnecting the intermediate terminals, a first complementary differential amplifier coupled between the line terminals and the intermediate terminals, a first current generator coupled between a first one of the intermediate terminals and a first one of the network terminals, means providing a common connection between a second line terminal and a second intermediate terminal, whereby for information signals, current mode operation is set on the network side at the network terminals in the first direction by loading the first current generator with a first resistor and, in the second direction, by supplying a second current from a second current generator connected via a second resistor and the second network terminal to the second intermediate terminal, said second resistor being selected to have a value equivalent to the resistance of the path through the switching network.

Claim 3

The invention according to claim 1 in which, for transmission in a first direction, the first complementary differential amplifier employs AC emitter feedback achieveD by connecting the emitters of first and second complementary transistors through a resistor and a capacitor in series, the collector of the first transistor being connected to the first intermediate terminal while the collector of the second transistor is connected to ground, said amplifier being biased with DC so that constant currents of equal value flow through these transistors, and for transmission in the second direction, the intermediate terminals of the conversion circuit are connected to the inputs of a second differential amplifier with emitter feedback achieved by connecting the emitters of two complementary transistors through a resistor through which flows a constant current, and the line terminals of the conversion circuit are connected to the outputs of said second differential amplifier, said second differential amplifier completing the four-wire to two-wire conversion.

Claim 4

The invention according to claim 1 in which, for transmission in the first direction, the first complementary differential amplifier employs AC emitter feedback achieved by connecting the emitters of first and second complementary transistors through a resistor and a capacitor in series, the collector of the first transistor being connected to the first intermediate terminal while the collector of the second transistor is connected to ground, said amplifier being biased with DC so that constant currents of equal value flow through these transistors, and for transmission in the second direction, the intermediate terminals of the conversion circuit are connected to the inputs of a second differential amplifier with emitter feedback achieved by connecting the emitters of two complementary transistors through a third resistor through which flows a constant current, and the line terminals of the conversion circuit are connected to the outputs of said second differential amplifier, said second differential amplifier completing the four-wire to two-wire conversion by measuring the difference in voltage across the resistor between the intermediate terminals, the first intermediate terminal of which is at a virtual ground, said conversion circuit being equivalent to a hybrid transformer with a transformation ratio n when choosing R2/r1 n and r3/R4 n + 1, r1 being the input impedance of the conversion circuit (equal to the parallel connection of the resistor R1 coupled between the line terminals of the input impedance of the first differential amplifier and of the output impedance of the second differential amplifier), R2 being the resistance between the emitters of the first differential amplifier, R4 being the resistance of the third resistor, and r3 being the impedance of the circuit seen from the intermediate terminals (equal to the parallel connection of the resistor between the intermediate terminals, of the input impedance of the second differential amplifier and of the output impedance of the first differential amplifier).

Claim 5

The invention according to claim 1, in which, said conversion circuit is coupled to supply sources by means of a plurality of gyrators.

Claim 6

The invention according to claim 1 including a first transistor circuit functioning as a gyrator circuit and a second transistor circuit functioning as a current limiter.

Claim 7

The invention according to claim 5, in which the first transistor circuit is selected to have a Darlington configuration to provide a reduction in the internal impedance of the first transistor circuit.