| 摘要 |
PURPOSE:To improve the detecting margin of the circuit by inserting an LPF between a current detecting circuit and a comparator and providing a hysteresis characteristics to the comparator so as to give a delay to a time corresponding to the hysteresis characteristics in a signal path at the side of zero cross detecting circuit. CONSTITUTION:Lines A and B are connected to a telephone set TEL, and a call signal source IR is connected to the line A via a current detecting circuit M of a ring trip circuit RTP so as to form a subscriber loop. The circuit M of the circuit RTP converts a call signal into a voltage value, the value is applied to the comparator A via the LPF and the voltage is compared with a fixed voltage of a DC power supply E. The hysteresis characteristics is given to the comparator A by means of the insertion of the LPF and its output is applied to a D FF. Further, a phase shifter P is provided to a signal path of the zero cross detecing circuit DET so as to give a delay to a signal applied to the circuit DET by a time corresponding to the hysteresis characteristics by the phase shifter P. Further, the detection margin of the circuit RTP is improved remarkably. |
