| 摘要 |
PURPOSE:To eliminate the need for control of the synchronizing frequency without using a resonator by controlling continuously a filter circuit so that it functions as a wide BPF and an LPF when a phase locked loop is asynchronous and synchronous respectively. CONSTITUTION:In an asynchronous state the gains A1 and A2 of amplifiers 18 and 22 are set at low and high levels respectively. Thus the frequency band of an LPF20 is obtained, and a PLL circuit 4 functions as a wide BPF. While the gains A1 and A2 are set at high and low levels respectively in a synchronous state. Thus the system of a filter circuit 14 is activated, and the synchronous state is maintained by an LPF16 of a narrow band. The synchronism is detected by a synchronism detector 36 in response to a change from a synchronous state to an asynchronous state. In such a way, the frequency band is controlled by controlling the gains of filter circuits 12 and 14. |
