| 摘要 |
PURPOSE:To realize easily a mode switching control method where only a selection control is adopted at synchronization locking and the non-selection control only is adopted at the synchronization stability by applying external a discrimination signal for synchronizing/asynchronizing state. CONSTITUTION:A signal superimposing the output of a low frequency sweep signal source 52 on a VCO control signal outputted from an LPF 46 by an adder circuit is used as a monitor signal for synchronization/asynchronization. The amplitude of the sweep signal of the control voltage of a VCO is small at the synchronization locking state and does not almost appear. On the other hand, the sweep signal appears as it is at the synchronization. Thus, a signal monitoring synchronization and asynchronization is obtained at an output terminal 57 by rectifying the signal by a whole wave rectifier 54, smoothing the signal by a filter 55 and discriminating the signal by a gate circuit 56. The carrier recovery circuit switching the control mode in response to the synchronizing state is realized by connecting the terminal 57 to an input terminal 50. |
