| 摘要 |
PURPOSE:To avoid the abnormal vibration of a sawtooth wave, by inverting the sawtooth wave in the previously preceding reproduced field section only in case the sawtooth wave to be applied to a head displacing means is suddenly changed at a moment when two heads start the scan and accordingly decreasing the suddenly chaninging part of the sawtooth wave. CONSTITUTION:The sawtooth wave (signal b) that gives a displacement to a video head is produced by converting the count value of a counter 11 through a D/A converter. The inclination of the sawtooth wave varies by the frequency of a clock pulse generator 10 according to the variable reproduction mode. In the still mode, a differentiating circuit 13 detects the fall of a head switch signal SW with the counter reset to obtain a signal (b) having the corresponding inclination and phase. As the signal (b) varies suddenly at a moment when the head of CH1 starts travelling, the signal (inverse signal a) showing the immediately preceding section is identical with the signal SW. Meanwhile a switch 14 is connected to a contact Y1, and the signal (b) is inverted. Then a high range attenuator 16 is actuated by switches 17 and 17 to weaken the waveform, and the output is applied to the bimorph. In such a way, a displacement of the video head which is exactly equal to the logic value can be obtained. |
