| 摘要 |
PURPOSE:To perform stable AGC operation while keeping phase relation constant even if fading, etc., occursin addition to waveform distortion, by sampling the output of a voltage control oscillator while putting it in phase with a composite synchronizing signal by use of PLL. CONSTITUTION:Since the composite synchronizing signal differs field by field, the output of voltage control quartz oxcillator VCXO10 is inputted to two-phase generator 11, where 0 deg.-phase and 90 deg.-phase signals are generated and outputted to terminal 16 by being alternated by analog switch circuits 12 and 13 before being inputted to phase comparator 14. Next, the output of comparator 14 is smoothed via filter 25 and compared with a prescribed value by comparator 26 and when it is greater than the prescribed value, it is judged that PLL is unlocked, thereby inverting the output logic of FF28 via timer 27 by the judgement output. Then, it is inverted between the point of transition to an odd-numbered field and that of transition to an even-numbered field and binary counter 24 is reset at the timing when PLL is held locked. Thus, the output of VCXO10 synchronizing with the composite synchronizing signal is inputted to pulse generating circuit. |
