PLL CIRCUIT

PROBLEM TO BE SOLVED: To extend the pull-in range. SOLUTION: A VCO 3 oscillates a signal of a frequency in response to an oscillated frequency control voltage from an LPF2. A frequency conversion section 4 multiplies or divides the frequency of the oscillated signal. A control section 13 sets a multiplication coefficient and a division coefficient. However, an initial set coefficient is given to the start of operation. Plural kinds of coefficients used for setting are stored in a 2nd memory section 10. A variable range of an oscillated frequency control voltage of the VCO 3 is stored in a 1st memory section 7 and in the case of supervision based on the entire veriable range, which a current control voltage is within the variable range, it is discriminates to be synchronizing state and when the voltage is at the outside of the variable range, it is discriminated to be an asynchronizing state. A detection section 8 detects a level from an A/D converter section 6 and a discrimination section 9 discriminated whether the level corresponds to the synchronizing state or to the asynchronizing signal state. A control section 13 changes the coefficient to the frequency conversion section 4 to be a coefficient bringing the state within the variable range from the initial setting coefficient when the detected level indicates the outside of the variable range.