SUBSCRIBER LINE TEST METHOD AND SUBSCRIBER CIRCUIT

摘要

PROBLEM TO BE SOLVED: To allow the subscriber circuit to economically test whether or not a subscriber line is brought into an AC induction state by eliminating an exclusive test equipment. SOLUTION: In the case of conducting the AC induction test, a DC bias current IDC is supplied via an ON/OFF switch SW and a resistor RDC, resulting that a common mode current detection output VCOM (=|VRA-VRB|) from a common mode current detection circuit 2 is obtained as a voltage proportional to an absolute value of an AC induction current and it is compared with a discrimination threshold voltage VTH by a discrimination circuit 3. When the comparison result indicates a relay of VCOM>VTH, it is discriminated that the subscriber line is in an AC induction state (abnormal state).