Patent ID: 6426846
Filing Date: 2002-07-30
Classification: G11B

Abstract:
A method of decoding asynchronous digital samples of prerecorded servo track positioning information, said prerecorded servo track positioning information comprising adjoining servo tracks having different servo patterns, one of said servo patterns comprising a constant amplitude signal of a single first frequency, and the other of said servo patterns alternating between a constant amplitude burst signal of a single second frequency and a zero amplitude null signal, said asynchronous digital samples received from a digital servo detector having a laterally positioned servo head adjacent said prerecorded servo track positioning information, moving longitudinally with respect to each other, said asynchronous digital samples representing said first frequency signal combined with said second frequency burst signal and said first frequency signal combined with said null signal, said method comprising the steps of:measuring the amplitude of a burst envelope of the maximum of said asynchronous digital samples; detecting said received asynchronous digital samples failing to meet a â€œDROPOUTâ€  amplitude threshold related to said maximum burst envelope; responding to said â€œDROPOUTâ€  threshold detection, detecting an envelope of the minimum of said asynchronous digital samples; and measuring the amplitude of an envelope of the minimum of said asynchronous digital samples, whereby a ratio of said measured maximum envelope amplitude and said measured minimum envelope amplitude represents said lateral position of said servo head.