Circuitry for suppressing the influence of interfering voltages at the evaluation of the condition of a signal on transmission lines, particularly on subscriber lines in telephone installations

摘要

The invention relates to a circuit arrangement for suppressing the periodic or non-periodic interference voltage components superimposed on a DC signal to be evaluated due to undesired influence on DC-fed two-wire transmission lines, in particular for the subscriber lines in the subscriber circuit of the switching center that are fed via symmetrical branches (R1, R2) and evaluated with respect to the loop state changes in long-distance telephone lines. By coupling to suitable circuit points (MP, T1, negative pole battery) of the subscriber circuit, the superimposed interference signal is separated with the aid of a differential amplifier (OP1) and fed to the input of a further differential amplifier (OP2) The output is the interference-free useful signal that signals the occupancy status.