| 摘要 |
PURPOSE:To prevent the increase in the make rate of a dial pulse due to line capacity, by inserting a resistance having a capacitor in parallel via a diode to a line and comparing the difference between the voltage drop of the resistance and the capacitor. CONSTITUTION:The resistance R is inserted to a line transmitting a dial pulse and the capacitor C is connected in parallel with the resistance R via the diode D. A voltage comparator COMP having a hysteresis characteristic is connected between the resistance R and the capacitor C. A potential difference across the resistance R and the capacitor C is respectively zero at an initial state and the output of the comparator COMP is at a low level. In closing a contact (a), the potential difference of the inputs A, B of the comparator COMP is a forward voltage drop VF of the diode D and it exceeds a threshold voltage VT, the output goes to a high level. When the contact (a) is opened, the voltage drop of the resistance R is decreased, and when the potential difference of the inputs A, B exceeds a negative threshold voltage, the output of the comparator COMP goes to a low level. |
