| 摘要 |
PROBLEM TO BE SOLVED: To use a double inclination type current limiting function in the operation of a line interface circuit and to improve current limiting function to further reduce power consumed in a double supply line interface circuit. SOLUTION: The double supply line interface circuit 100 drives a long distance subscriber loop (120) by using a -48 V power source (VBAT1) and drives a short distance subscriber loop by using a -28 V power source (VBAT2). For an intermediate length loop, a double inclination type current supply function is used, and the power loss of a line circuit is made limited. The line interface circuit is operated in an apparent fixed current mode and generates a differential line current of about 40 mA, by using a low power source to the threshold line voltage of about 25 V which is equal to a value for which a required overhead is reduced from the voltage of the low power source. For a long distance loop, the line interface circuit is switched to a second constant current mode and generates a differential current of about 22 mA, by using a high power source and it maintains a loop current fixed until it is lowered to the resistance feed value of 48 V. |
