| 摘要 |
A method of lowering the power absorbed by an interface circuit (2), in the "power-down" state thereof, as incorporated to a telephone exchange (4) and connected to a telephone subscriber line (3), being of a type which comprises a monitoring circuit portion (6) connected between the line and the exchange, comprises the steps of, detecting the polarization level of at least one conductor (9) in the line (3), comparing said level with a reference value (VR) by means of a comparator (11) having an input connected to the line (3) and an output (U) connected to the input of the monitoring circuit portion (6), switching the interface circuit (2) to a standby state on a higher level than the reference value (VR) being sensed, once again detecting the polarization level of the line (3) through the interface circuit (2), and activating the telephone exchange (4) where, on completion of the second detection step, the polarization level keeps above the reference value (VR). |
