| 摘要 |
A servo loop for an automatic scan tracking arrangement for a helical-scan videotape playback machine includes a wideband relatively low-gain portion for fast acquisition and correction of mistracking errors. In order to provide high gain for reducing mistracking which recurs from scan to scan, a second path in the servo loop in parallel with the wideband path includes a commutating filter which accumulates the average error signal generated by the wideband system in a commutating filter and reinserts the averaged error to provide adaptive systematic correction having a comb-like response. This reinsertion reduces the magnitude of the systematic errors which the wideband portion of the servo must correct, and therefore reduces the amount of closed-loop mistracking which repeats from scan to scan.
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