| 摘要 |
PROBLEM TO BE SOLVED: To obtain a PLL circuit fine-adjusting a phase difference of input and output voltages by changing a reference voltage applied to a noninverting input terminal of an operational amplifier of a PLL circuit. SOLUTION: In the PLL circuit with a loop of series connection consisting of a phase comparator, a low-pass filter(LPF), a voltage controlled oscillator(VCO) and a frequency divider, the LPF is made up of an operational amplifier. The phase comparator detects a phase difference between an input signal fS and an output signal fO of the VCO to provide a difference signal voltage. The difference signal voltage eliminates high frequency components not required for the LPF and the resulting voltage is fed to the VCO as a control voltage. The VCO is operated that a difference between the oscillated frequency fO and the input signal frequency fO is reduced. When the difference between the frequencies fO and fS is comparatively small, the frequency fO is locked to the frequency fS and then the phase difference is zero. The LPF is acts like an integrated active filter in which a series RC circuit as a feedback circuit is inserted between an output terminal and an inverting input terminal of the operational amplifier of the LPF and a reference voltage is applied to a noninverting input terminal. The phase difference between the input signal and the output signal of the PLL circuit is fineadjusted by varying the reference voltage. |
