| 摘要 |
PURPOSE:To reduce an operating and restoring time by separating a signal voltage superimposed on a call signal into a positive and a negative voltage, and comparing a value obtained by multiplying an absolute value of the positive voltage by a prescribed coefficient, with the absolute value of the negative voltage to eliminate the need for a low pass filter. CONSTITUTION:Each absolute value of positive and negative superimposed voltages is held respectively in capacitors C1, C2 by inputting a voltage between a terminal (a) of a resistor Ra and ground to an operational amplifier OP1 after the voltage is divided at resistors R1, R2. As a result, the absolute value of potentials of points A and B is equal to each other at on hook and the absolute value of the potential at the point B is larger than the absolute value of the potential of the point A at off-hook, then the detection of ring trip is attained. Since the detection becomes unstable if this state is left as it is, the amplification factor of operational amplifiers OP1, OP2 has only to be changed depending on on-hook and off-hook. |
