| 摘要 |
PURPOSE:To prevent mis-decision of an input noise signal as a simulated carrier signal by providing a unidirectional switch circuit switched by a switching signal from a PLL circuit and an integration and time constant circuit holding its output information. CONSTITUTION:The unidirectional switch circuit 22 is subject to switching control by a switching signal SW generated by using an oscillating output of the PLL circuit 11 so as to hold the presence information of an input carrier signal CW for a period in response to the time constant by an integration time constant circuit 23 and the level information held in the integration time constant circuit 23 is discriminated by a level decision circuit 24. That is, when the noise of a frequency component close to the carrier signal is inputted, the relation of phase between the switching signal SW and the input signal might not be a preset phase relation. The circuits 22, 23 detect this state and when the level of the input signal is high, the level of an output terminal 25 goes to a low level and the decision output of the signal ''absence'' is obtained. The decided output is held for the time of time constant of the circuit 23 even when the circuit 11 is pulled in the phase lock state. |
