| 摘要 |
PURPOSE:To realize a phase locked loop circuit with stable operation and high accuracy, by changing the direction of an up/down counter according to the phase difference and controlling a voltage controlled oscillator with a D/A converting circuit. CONSTITUTION:If a phase of a reference frequnency f1 leads, e.g., than a lock objective frequency f2, when a clock level of an output from a clock generating circuit 19 is at high level and count-up is instructed on a up/down instruction signal line 18 of level inversion, the output of an AND circuit 21 is taken as ''1'' and a clock pulse is transmitted to an up/down counter 12. Thus, the output of a D/A converter 13 receiving the output of the counter 12 is incremented by one step and a large voltage value is given to a voltage controlled oscillator 14. The phase of the frequency f2 outputted from the oscillator 14 is advanced by a specified amount and this operation is repeated. The phase of the frequency f2 approaches the frequency f1 and when both of the phases are coincident, a phase comparator 10 is made stable. |
