| 摘要 |
<p>An office line interface circuit is constituted by a DC circuit for extracting a DC signal component from office line current, an AC circuit for extracting an AC signal component from the office line current to supply the extracted AC signal component to a telephone set, an impedance circuit connected to the office line, and an impedance controller for varying the impedance of the impedance circuit in accordance with the level of the extracted DC signal component so as to maintain at a substantially constant value the impedance of the office line as viewed from the telephone set. With this interface circuit, the sidetone preventing circuit for the telephone system can operate satisfactorily without complicating the construction under any office line condition.</p> |
