| 摘要 |
PURPOSE:To obtain the subscriber's circuit realizing a constant current feeding characteristic supplying a current in response to the number of terminal equipments. CONSTITUTION:When a 1st telephone set connecting to a line enters a talking state, at first a feeding circuit 16 supplies a constant current feeding of 10mA and measures an AC impedance of the line. A DSP 14 sends a sine wave of nearly 100Hz while applying D/A converting it and being superimposed on a transmission signal and after the reception, the signal is ADD-converted and the DSP 14 measures the AC impedance. Number of telephone sets in OFF-hook state is estimated based on a degree of the reduction in the impedance and a current in matching with the number, that is, a current of 30mA in the case of three telephone sets hooked off is supplied from the feeding circuit 16. |
