| 摘要 |
<p>PURPOSE:To decrease noise of a line due to AC induction by applying bias voltage to suppress a DC voltage of the subscriber line to a low value when it is detected that no DC loop closing exists in the subscriber line. CONSTITUTION:A switch of a current source 25 for on-hook control is closed by a signal from a loop current discriminating circuit 20 at on-hook of the subscriber circuit, a current added to an output current of a feeding impedance synthesis circuit 8 is inputted to voltage amplifiers 91, 92 for driving feeding transistor (TR) circuit. Thus, an output voltage of amplifiers 91, 92 enters more inside than a feeding power supply voltage applied to terminals 61, 61 to activate feeding TR circuits 501, 502. As a result, the absorption/drawing to the AC induction current are attained from a line connected to terminals 1, 2, an output voltage of the amplifiers 91, 92 is biased to the neutral point side and operated thereby attaining the signal transmission at on-hook.</p> |
