| 摘要 |
PROBLEM TO BE SOLVED: To exactly detect polarity reversion of a telephone line and to discriminate a state of the line by making DC resistance of the line caused by a polarity detection circuit smaller than in the conventional manner. SOLUTION: The polarity detection circuit 10 is provided with: a current detection resistor portion 11 which is connected to the telephone line in series; and a line polarity detection portion 12 which compares potentials at both ends of the current detection resistor portion 11 with each other to identify the direction of line current which flows to the telephone line, and detects polarity of the telephone line. COPYRIGHT: (C)2011,JPO&INPIT |
