| 摘要 |
PURPOSE:To improve the response of line usable state detection by providing a circuit outputting signals being in complementary relation with each other when no signal voltage is applied to a communication line. CONSTITUTION:The usable state detecting device comprising signal voltage comparing means 1, 2, exclusive OR operating means 3, and bias voltage supplying means 4, 5 is provided to a balancing line consisting of lines L1, L2. The signal voltage comparing means 1,2 compare the level of signal voltages S1, S2 of the lines L1, L2, and output discriminating signals S3, S4 in the same phase. The bias voltage supplying means 4, 5 supply respectively a bias voltage to the signal voltage comparing means 1, 2 to output the signals S3, S4 being in complementary relation when the signal voltages S1, S2 are not applied to the lines L1, L2. Further, the usable state of line is detected by an output of the exclusive OR operating means 3. |
