| 摘要 |
PURPOSE:To correctly detect a receiving signal without malfunction even to a large line noise by setting a detection 1evel of the reception signal based on the line noise and making the detection level as a constant value when the line noise is larger than the setting value. CONSTITUTION:A receiving signal S and a line noise N enter an output terminal 4 and a BPF circuit 5 while being divided by a resisior 2 and an R conversion circuit 3. Only the line noise N is extracted by the BPF circuit 5, amplified by an amplifier circuit 6, the peak value of the line noise amplified by a peak hold circuit 7 is held and converted into a DC voltage. The resistance value of the R conversion circuit 3 is controlled. A loop comprising the R conversion circuit 3, the BPF circuit 5, the amplifier circuit 6 and the peak hold circuit 7 constitutes a negative feedback loop, and the amplification factor of the amplifier circuit 6 and the V voltage of an operational amplifier 73 of the peak hold circuit 7 are used to set the line noise level (detection level of the receiving signal). |
