| 摘要 |
PURPOSE:To make a device and circuit small-sized, by cancelling an undesirable leakage signal from a 2/4 wire coupling point to a 4-wire output line with a filter output and controlling the fluctuation of the impedance at 2-wire side to optimum. CONSTITUTION:Switch groups 212 and 213 which select two filters from a filter group 211 coupled to a 4-wire type input line 202 are provided. Further, subtractors 203 and 204 to subtract two selected filter outputes from a 2/4-wire coupling point 214 are provided, the output of the subtractors is compared and the switch groups 212 and 213 which minimize a signal from the 4-wire input line 202 given to a 4-wire output line 201 are controlled at a discrimination circuit 205. A caller recognizing circuit 207 detects a call signal from another caller near by in calling with a telephone set 210 and stops the operation of the circuit 205. |
