| 摘要 |
PURPOSE:To attain a framing servo function which is free from the effect of noise, etc. by producing faithfully the reference signal which detected the 1st and 2nd fields and at the same time neglecting the disturbance of the reference signal due to noise, dropout, etc. CONSTITUTION:When a switch 5 is set at the side (a), an FF2 has the same function as an FF1. Then the FF2 divides a clock input into 1/2 when the switch 5 is set at the side (b). These sides (a) and (b) correspond to output levels H and L of a comparator 6 respectively. When the pulse lacks at the point (a), the switch 5 is set at the side (b). The constants of circuits 4 and 6 are set so that the output of the circuit 6 is set at H if the H continues for a period longer than four fields. Then the output of the circuit 6 is kept at L, and the output Q of the FF2 receives no effect of noises. Then the continuance of the 1st and 2nd fields change at the middle of their courses and the output of an exclusive OR gate 3 has H continuously. Thus the output of an integration circuit 6 is set at L, and the switch 5 is changed to the side (a). Then the output of the gate 3 is changed to L and the output of the circuit 6 is changed to L after four fields. The switch 5 is changed to the side (b), and the output Q of the FF2 keeps a state where the framing is newly obtained.
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