| 摘要 |
An automatic scan tracking servo (44) which operates mainly digitally and is for use in a video tape apparatus of which the scanner has a movable element movable transversely of the longitudinal direction of a recorded track so that a transducing head carried by the element accurately follows the track during special motion reproducing modes. The RF video signal is sampled a predetermined number of times during each rotation of the scanner. The phase of the dither (212) that is applied to the movable element carrying the head, the operation of a synchronous detector (228) and the sampling are all synchronized to obtain an accurate error correcting signal. The servo utilizes the longitudinal tape speed to provide a predicted value of the slope of the ramp signal that is required to cause the head to follow the track and the error correcting signal modifies the ramp. The combination of the synchronism and the predicted value of the slope enables the use of a reduced dither amplitude. |
