| 摘要 |
PURPOSE:To suppress the transient response of a low-pass filter by limiting the positive or negative-polarity amplitude of the input signal to the low-pass filter with time width almost a half as large as the cycle of an AC signal from the point of time when the AC signal is sent out. CONSTITUTION:The output signal SIG1 of a level converter LVC has a voltage proportional to the current of a call signal loop. A clamping circuit CLMP clamps the positive-side waveform of the signal SIG1 for a specific time from the rising of a signal RPT under the control of the signal RPD, and when the signal SIG1 is positive voltage, a diode D turns on, so the signal SIG2 attenuates almost to 0V. Then, when the signal RPD is at a level ''H'' and the potential of the signal SIG1 is negative, the diode D is biased reversely and the ISG2 have a waveform similar to that of the SIG1. Consequently, the output of the LPF has transient deviation to the negative side and the delay time of the detection of an off-hook in ringing is shortened. |
