| 摘要 |
PURPOSE:To obtain an automatic frequency control system which has no need of a local oscillator and causes on frequency error due to the variation of frequency discriminator, by composing this system of a voltage control oscillator, pi/2 phase shifter, three phase comparators, and two low-pass filters. CONSTITUTION:Output signal (VO) of voltage control oscillator VCO11 is branched into two, and one signal and input signal (Vi) are both applied to the lst phase comparator 13, which outputs signal (v13) comparatively detected. The other signal branched is applied via pi/2 phase shifter 12 to the 2nd phase comparator 14, which outputs (vi) and signal (v14) comparatively detected. After passing through LPF31, signal (v13) is inputted together with signal (v14) to the 3rd phase comparator 32, which outputs DC component (vf) comparatively detected. Signal (vf) is passed through LPF33 removing an AC component, thereby controlling VCO11. The frequency discriminator is composed of comparators 13, 14, and 32, and LPE 31, and siscriminative characteristics against frequency error (We) between the input frequency and output frequency have its maximum output when the time constant of LPF31 is T31, so that since nor local oscillation is required, the constitution will be simplified. |
