| 摘要 |
PURPOSE:To provide the modulator using PLL which speedily stabilizes the output of a VCO and presents noise from riding on a modulated signal at the time of power source ON and frequency switching by inputting the output of a phase detector through an amplifier to a loop filter. CONSTITUTION:This device is provided with a loop filter 6 at a low cut-off frequency, loop filter 7 at a high cut-off frequency and changeover switch 9 to switch between the outputs of both of filters 6 and 7. When a power source is to be turned on in the case a switch 11 is turned off while turning the switch 9 in a continuous line state at the time of frequency switching and a stability detection signal is inputted from a phase detector PD3 to a control part 10, the switch 11 is turned on by the control part 10. Then, the modulated signal is inputted to a VCO 2 and after the lapse of a prescribed time when the output of the filter 6 is stabilized, the switch 9 is turned to a dotted line side. Thus, the modulator using PLL can be provided which speedily stabilizes the output of the VCO 2 and prevents noise from riding on the modulated signal at the time of power source ON and frequency switching. |
