| 摘要 |
PURPOSE:To accurately detect a duration period or pause period of a reception signal, by increasing the discrimination level of a level discrimination circuit when the reception level of a reception is greater, and decreasing the discrimination level, when the reception level is small. CONSTITUTION:An output of an amplifying circuit 15 is divided at resistors 17, 18 and when the divided level exceeds a discrimination level l2 of a level discrimination circuit 19, an output of an integration capacitor 22 is at high level, and when less than the l2 level, the output of the capacitor 22 is at low level. An output is given to a transistor (TR)27 from the capacitor 22. On the other hand, the output of the circuit 15 is given to a level discrimination circuit 28 via a resistor 24. When the TR27 is conductive, the output of the circuit 15 is divided with the resistors 24, 25 only, and the divided output is lowered, and the discrimination level of the circuit 28 is increased. Further, the output of the circuit 28 is subject to envelop- detection with a detection circuit 29. |
