| 摘要 |
PURPOSE:To prevent a control signal from other line from being not receptible when noise due to a fault takes place in one line by selecting one of the control signals and decoding the signal in response to the combination of the presence of both a control signal of its own line given from a switch circuit and a control signal given from an opposite line. CONSTITUTION:When a noise component of an input signal 1U is increased at a fault of an incoming line, the component of a frequency band in the vicinity of a frequency fh is increased accordingly. A level in the vicinity of the frequency fh is detected via a band pass filter 2U, an amplifier 5U and a level detection circuit 6U, and when the level exceeds a threshold level, an analog switch 8U is turned off to interrupt the entry of a noise signal of its own line to a selection decoding circuit 4U. A level detection circuit 9 detects an output level of the analog switch 8U of its own line (incoming line) to detect the presence of the control signal from its own line. Moreover, a level detection circuit 11 detects the presence of the control signal from an opposite line (outgoing line). An inhibit gate 12 is interposed to the level detection circuit 11 to inhibit the connection of the control signal of the opposite line when the control signal exists in its own line. |
