| 摘要 |
A subscriber line circuit (1) is connected via a subscriber line (3a, 3b) to a telephone set (2). For a raised receiver the subscriber line (3a, 3b) is supplied with a line current (Is) by speech signal amplifiers (4), which are powered from a power source (VBB). The speech signal amplifiers (4) and their power supplying amplifiers (7,9, and 10) have large idling power, apart from the power fed to the subscribe line. To decrease this idling power, the subscriber line circuit (1) has auxiliary amplifiers (5) with low idling power for supplying the subscriber line (3a, 3b) when the receiver is cradled. When a call is in progress and the receiver is lifted, the line current (Is) has a relatively large value, and when the call ceases and the receiver is replaced the line current (Is) decreases. This current decrease is sensed via a resistor (R2) by a loop sensing circuit (13), which sends a signal (S1) to a control circuit (14). The latter then sends signals (S2) and (S3) for connecting the auxiliary amplifiers (5) and disconnecting the speech signal amplifiers (4). |
