AN DEN TEILNEHMERSEITIGEN AUSGANG EINER TELEFONZENTRALE ANGESCHLOSSENE TEILNEHMERLEITUNGS-SCHALTUNG

A telephone line circuit including a high voltage amplifier feeds the tip and ring lines at its output. This amplifier is fed by a programmable voltage source which includes a d.c./d.c. converter and means to control the amplitude and polarity of this voltage. All the required electrical signals including d.c. feeding, speech, unsymmetrical ringing and metering pulses are provided through the high voltage amplifier. No high voltage AC switches (relay contacts) are required since the ring signal is provided through the same device (output amplifier) as the speech and d.c. signals. Means are included for minimizing the internal power dissipation by controlling the amplitude of the d.c./d.c. converter voltage. Thus d.c. offset control is achieved by slaving the d.c./d.c. converter voltage to the amplifier output voltage. Three functional blocks form the line interface circuit according to the invention, these being a high voltage circuit including the aforementioned amplifier, a programmable signal generator which includes the d.c./d.c. converter and electronic solid state switching under control of a line feed and supervision circuit which constitutes the third block.