| 摘要 |
PROBLEM TO BE SOLVED: To attain the sharing of the time constant of an LPF(low pass filter) against the frequency that is outputted from a PLL circuit by preparing plural modes where a variable dividing device which outputs a reference signal via a reference oscillator and also divides the output of a VCO(voltage controlled oscillator) performs the division with a specific division ratio. SOLUTION: A variable dividing device 4 variably divides the output of VCO 1 and 2 with a division ration 1/A (A: a >=2 integer), and a reference oscillator 5 selectively outputs a 1st reference signal and a 2nd reference signal having the frequency equal or approximate to that of the 1st reference signal. An LPF 7 converts the output of a phase comaprator 6 which compares the reference signal of the oscillator 5 with the output of the device 4 into the control voltage with a time constant shared by the reference signal. Then a control circuit 8 prepares a mode where the 1st reference signal is outputted from the oscillator 5 and the device 4 performs the division with a B/A division ratio and another mode where the 2nd reference signal is outputted from the oscillator 5 and the device 4 performs the division with a C/A division ratio (B, C: positive integers). |
