| 摘要 |
PROBLEM TO BE SOLVED: To omit an in-phase AC signal feedback circuit, consisting of an operational amplifier and a resistance and to attain the miniaturization and a high degree of integration for a feeder circuit by adding a limiting current generation circuit into a DC signal feedback circuit, which limits the DC to be supplied to a short distance subscriber line down to a level which is lower than the limiting current value. SOLUTION: A and B line voltage detection circuits 102A and 102B output the currents iA and iB, proportional to voltage VA and VB of the subscriber lines A and B to an adder circuit 103. A differential signal elimination circuit 104 calculates a differential AC from the limiting current iTH outputted from a limiting current generation circuit 110 and the currents iA and iB and generates differential signal elimination output currents i104 A and i104 B containing no differential AC to feed them back to the A and B line feeder circuits 101A and 101B respectively. Thus, the high and low impedance characteristics are realized to the differential AC and an in-phase AC respectively. Furthermore, the limiting levels can be set by a single circuit 110 to the feeding currents of both lines A and B. |
