| 摘要 |
PURPOSE:To select the frequency of an output signal in fine steps, by providing plural phase shifter circuits in a feedback circuit. CONSTITUTION:The output signal of a voltage-controlled oscillator 12 is shifted in phase by one of phase shifter circuits 13A-13N differing in the extent of phase shifting. The phase-shifted signal is frequency-divided by M at a frequency divider 14 and then inputted to a comparator 11. The comparator 11 supplies a voltage corresponding to the phase difference from the input signal S11 to the voltage-controlled oscillator 12. The phase shifter circuits 13A-13N have the amounts of phase shifting which are once, twice - the unit obtained by dividing a phase corresponding to one period of the input signal S11 equally by N. A changeover switch 15 selects one of the phase shifters. The oscillation frequency of the voltage-controlled oscillator 12 varies with the amount of phase shifting. |
