| 摘要 |
PURPOSE:To generate an optional frequency which is stable regardless of the purity of a phase comparison signal by controlling a voltage-controlled oscillation circuit by the output voltage of a D-A converter. CONSTITUTION:A phase comparison part 2 makes a comparison to detect whether the phase of a feedback signal from a frequency-dividing circuit 5 leads that of a reference signal f0 from a crystal oscillator 1 or not; while a phase control circuit 6 adds one bit to the signal f0 from the voltage-controlled oscillator 9 when the feedback signal leads the reference signal f0 or substracts one bit when the feedback signal lags behind the reference signal, the detection result is counted by an up/down counter 7, whose counting result is converted by the D-A converter 8 into a DC voltage to control oscillation frequency of the voltage-controlled oscillator 9. Therefore, the frequency-division ratio of the frequency divider 5 is vaired to vary a output frequency, thus generating the optional stable frequency with high purity. |
