| 摘要 |
PURPOSE:To constitute a ring tripping circuit without employing a capacitor by measuring a period when the current of a ringer circuit is positive and negative so as to detect the ring trip. CONSTITUTION:A ringer current detection and separating circuit 6 provided in series with the ringer sending path of a subscriber circuit, generates a signal pulsized corresponding to the polarity of the current of the ringer circuit. Then a positive pulse width measuring circuit 7 digitizes and outputs the pulse width corresponding to the current of the ringer circuit, and a negative pulse width measuring circuit 8 digitizes and outputs the pulse width corresponding to the current of the ringer circuit. A subtraction circuit 9 generates an output subtracting the output of the measuring circuit 8 from the output of the measuring circuit 7, and when the output exceeds a value preset in a threshold value register 11, a comparator 10 discriminates it and generates the output.
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