| 摘要 |
<p>A telephone interface device between exchange components and a subscriber's telephone line includes a reception and transmission circuit (RX/TX) for connection to the exchange's channels, a circuit (S) for the provision and inputting of line signals, and, within these circuits, a signal generating circuit (C). Current mirroring circuits (CM) which provide a proportional current in a predetermined proportionality ratio (K) to the signal component of the instantaneous line current as a counter-response to the signal generating circuit (C) are connected to the subscriber's telephone line. The device includes a source of charging signals (TTX) coupled to the subscriber's telephone line and to circuit means (ZT) which offer an impedance proportional to the line impedance to this signal source, in accordance with the predetermined proportionality ratio (K). The circuit means (ZT) provide a current proportional to the charging signals which is subtracted from that provided by the current mirroring circuit means (CM).</p> |
