| 摘要 |
PURPOSE:To enable the titled circuit to contain a non-rumbling calling terminal to which specified DC bias current does not flow by providing a DC bias supplying means that maintains the semiconductor switch of a space division line concentration stage in closed state in a subscriber's line scanning circuit. CONSTITUTION:A call detecting device consisting of resistances 32, 33, transistos 34-39, driving circuits 310-131 and diodes 316-319 and a switching device of DC bias current path are provided in a subscriber's line scanning circuit 3 having a call detecting circuit 31. The switching device works to form a DC bias current path in the subscriber's line scanning circuit 3 at the time of incoming to a terminal when a non-rumbling call terminal 5 is provided along with a telephone terminal connected between A-line and B-line. Consequently, flow of DC bias current from a speech current supply circuit 4 to a space division line concentration stage 2 is made possible, and closed state of semiconductor switches 21, 22 in the line concentration stage 2 are maintained surely. |
