| 摘要 |
PURPOSE:To provide the PLL circuit equipped with optimum convergent characteristics and frequency stability by changing convergent speed while depending on the characteristic of a low-pass filter(LPF) to change a cut-off frequency or the like based on a prescribed voltage supplied from a frequency/ voltage conversion part. CONSTITUTION:A phase comparator 1 detects phase difference between an input signal 10 and a feedback signal 12 and outputs a signal corresponding to phase difference to an LPF 2. A VCO 3 is controlled by a DC voltage from the LPF 2 and generates a prescribed clock output signal 11 based on a frequency selection signal 15. A frequency divider 4 divides the frequency of the signal 11 and changes a frequency dividing ratio based on the signal 15, and a frequency/voltage converting part (F/V) 5 inputs the signal 11 and outputs a voltage 16 corresponding to the frequency. As a result, the F/V 5 supplies the prescribed voltage signal 16 to the LPF 2 corresponding to the frequency of the output signal 11, namely, the oscillation frequency. The LPF 2 changes the transmission characteristic such as the cut-off frequency and as a result, the PLL circuit changes loop sensitivity and shortens the convergent time of frequency lock. |
