| 摘要 |
PURPOSE:To obtain a stable frequency control circuit which suits to frequency control at the time of electronic tuning by making the output of a voltage or current control oscillator agree with a frequency set to an assignment frequency memory. CONSTITUTION:The value of the assigned oscillation frequency is set to assignment frequency memory 16 by a digital signal first. Frequency counter 12, on the other hand, counts the oscillation frequency of voltage control oscillator 11. The contents of counter 12 are compared with those of memory 16 by frequency-value comparator 15. In this case, the comparison is done at a certain time interval and the time interval is assigned by clock pulse generator 17. The comparison result of frequency values is supplied to frequency control signal generator 14 to generate a digital signal for adjustment of the frequency and oscillator 11 is controlled via digital converter 13 to adjust the oscillation frequency. When the oscillation frequency of oscillator 11 agrees with that assigned by memory 16, the output of signal generator 14 becomes constant and then, a slight shift in frequency caused by the drift of the system is supervised and corrected at the time interval assigned by pulse generator 17. |
