Circuit arrangement for the connection of line circuits of a digital time multiplex-telephone network

Claim 1

A circuit arrangement for coupling a telephone line circuit, having core conductors, to any one of: a subscriber station; dual subscriber stations of a dual service connection; and a branch exchange; said circuit arrangement comprising: a detector circuit coupled by a voltage divider circuit to said core conductors of said telephone line circuit, to selectively provide one of: a loop closure indication of said telephone line circuit; a ground potential indication on one of said core conductors of said telephone line circuit for telephone signaling; and an off-hook indication for one of said dual subscriber stations in said dual service connection; in response to a control signal, whereby the voltage divider includes resistances of such value that alternating current noise voltages coupled into said core conductors compensate each other at the input of the detector circuit; first switching means by which a resistance is inserted into one of said core conductors on which a ground potential indication occurs, during said ground potential indication and said off-hook indication, of such magnitude to provide a higher sensitivity of said detector circuit required for such indication and for activating at least one filter circuit to prevent the effects of the said alternating current noise voltages upon said detector circuit, and through which switching means another conductor of said core conductors of said telephone line circuit is isolated at ground potential from the detector circuit; and second switching means for shunting said core conductors of said telephone line circuit with a low resistance.