| 摘要 |
PURPOSE:To obtain an optimum specific frequency minimizing the infleunce of error caused by a noise by changing a loop constant corresponding to the noise level of an input signal. CONSTITUTION:An input signal Pi is converted to an intermediate frequency signal by being mixed with a local signal from a voltage controlled oscillator 4 at a mixer 1, and inputted to a phase detector 2. At the phase detector 2, a phase error signal obtained by being compared with a reference frequency signal inputted from a reference signal oscillator 5 controls the voltage controlled oscillator 4 through a loop filter 3 and is inputted to a noise detector 6 as well, and a signal corresponding to the detected level of noise is inputted to a loop constant controller 7. Then, the loop constant of the loop filter 3 is adaptively controlled so as to be the specific frequency to minimize the influence of error caused by the detected noise level. Further, the intermediate frequency signal from the mixer 1 is inputted to a synchronizing judger 8 to judge synchronizing and only when an automatic phase control circuit is synchronized, the loop constant controller 7 controls the loop constant of the loop filter 3. |
