| 摘要 |
PROBLEM TO BE SOLVED: To provide a PLL circuit that decreases lockup time and obtains C/N ratio which is affected less by an external noise. SOLUTION: This phase-locked loop PLL circuit is provided with a control circuit 3 to allow the PLL circuit to discriminate whether it is in a locked state or an out of lock state on the basis of an output voltage Vf of a loop filter 2 and to provide the output of an output control signal S1 and with a variable gain amplifier, whose gain is changed by the output control signal S1 to generate a control voltage Vc and to give it to a VCO5. Thus, when the oscillated frequency of the VCO5 indicates out of lock state, the lockup time can be decreased and when the oscillated frequency fv is close to a desired frequency, a high C/N ratio can be obtained. |
