| 摘要 |
A subscriber line access circuit for use in a telecommunications system is disclosed. The subscriber line access circuit includes a power supply bridge in the form of a first resistor inserted in the b-wire (ground potential side) of a subscriber line, a second resistor inserted in the a-wire (supply potential side) of the subscriber line, and a capacitor which bridges the two wires at the terminals of the two resistors on the sides thereof opposite to the respective potential sources. This supply bridge is coupled on the capacitor side with a two-to-four wire hybrid transformer for the two-wire/four-wire transition to the system and includes an evaluating circuit which delivers an indicating signal when the subscriber actuates a ground key. A cutoff circuit is arranged in the power supply bridge between the first and/or second resistor in that bridge and the respective one or ones of the transformer windings at the junction points at which the evaluating circuit is connected. The device for generating call signals is connected to one of these junction points via a coupling contact and a series resistance. The associated cutoff contact of the supply bridge and the coupling contact of the call signal generating device are controlled in such a way that they can be closed only alternatively. |
