| 摘要 |
PURPOSE:To stabilize the reproduction of an SECAM system by stabilizing the oscillation frequency of a voltage control oscillator, which constitutes an automatic frequency control loop, at a balanced area between functions of a mislock detector and a compensating circuit, and shifting the stabilized oscillation frequency from the frequency of PAL system. CONSTITUTION:The oscillation signal of a voltage control oscillator 60 and a reproduced horizontal synchronizing signal Hp are supplied to a mislock detecting circuit 63. The frequency difference between both input signals is reduced within a fixed range, and the outputs of both signals are applied to a control terminal of the oscillator 60. The oscillation frequency and the phase of the oscillator 60 are controlled according to the voltage with which the phase detection output of a phase detecting circuit 55 is applied to the control terminal. Then a compensating circuit 70 applies the compensating voltage to the control terminal of the oscillator 60 in a signal processing mode of an SECAM system. Thus the oscillator 60 has stable oscillations with a frequency lower than the normal frequency of the oscillator 60 by an amount equivalent to a horizontal frequency fH in accordance with the function of the circuit 63. |
