| 摘要 |
PURPOSE:To obtain a PLL enabled to change self-travelling frequency with a simple circuit constitution by discriminating that an error signal reaches a level exceeding a prescribed range and connecting a reactance element to a voltage control oscillator to switch the self-travelling frequency. CONSTITUTION:The voltage control oscillator 9 changes the self-travelling frequency by connecting the reactance and a phase comparator 3 detects the phase difference between an output signal from the oscillator 9 and a reference signal. An LPF 4 smoothes an output from the comparator 3 and outputs an error signal to the oscillator 9. When the level of the error signal reaches a level exceeding the prescribed range, an error signal level range discriminating circuit 12 discriminates the level and switches a reactance switching circuit 16 in accordance with the discriminated result to connect the reactance to the oscillator 9. Thus, the self-travelling frequency can be changed in accordance with the frequency related to the output signal of the oscillator 9. |
