CIRCUIT FOR MEASURING LINE RESISTANCE

摘要

PURPOSE: To provide a line resistance-measuring circuit for preventing the quality deterioration of a phone call due to the change of power feed method of a subscriber's circuit. CONSTITUTION: A current IL running in a subscriber's circuit L including a telephone T is detected. The current is converted to a voltage signal Vref and then output by a subscriber's circuit current detection circuit 30. An intercircuit voltage-monitoring circuit 40 detects an intercircuit voltage VL of the subscriber's circuit L and outputs a voltage signal V3 corresponding to the voltage VL. The voltage signal Vref of the detection circuit 30 and the voltage signal V3 of the monitoring circuit 40 are compared by a comparator 50 which in turn outputs a difference to the reference value of a resistor of the subscriber's circuit L as a judging result.