| 摘要 |
PURPOSE:To considerably shorten a lock time more than a conventional PLL circuit by connecting a diode in parallel with the resistance element of a low pass filter. CONSTITUTION:A diode 34 is connected in parallel with the resistance element 31 of the series arm of a lag/lead type low pass filter 3 to make the time constant of the low pass filter variable. As soon as a potential charged in a capacitor is given to a VCO 4, the discharge is started through resistors 32, 31. The oscillating frequency of the VCO 4 is changed from a frequency f1 into the direction of a frequency f0 again. A phase comparator 2 operates a difference from the frequency ft and when the output reaches a value conducting the diode 34 again, the capacitor 33 is charged to restore the frequency of the VCO 4 again in the direction of frequency f1. The frequency is locked to frequency f1 stably by the charge/discharge of the capacitor 33 while the oscillated frequency of the VCO 4 is moved wavingly one or twice only in the vicinity of the frequency f1. |
