TELEPHONE LINE MEASURING CIRCUIT

PROBLEM TO BE SOLVED: To exactly measure line voltage irrespective of polarity of voltage of lead wire of a chip (T) and a ring (R). SOLUTION: Variation of characteristics between first and second lead wire of a telephone line is detected. This measuring circuit 40 is provided with a first circuit with first and second inputs and one output and furthermore, a second circuit with the first and second inputs and one output. The first input of the first circuit and the second input of the circuit are coupled with the first lead wire of the telephone line, the second input of the first circuit and the first input of the second circuit are coupled with the second lead wire of the telephone line. In addition, both outputs of the first and second circuits are coupled with each other which are supplied to the measuring circuit 40.