Hewlett-Packard Company

Robert E Kier

Vernon L Knowles

William P Proctor

A method and apparatus for implementing a zero order hold function in the digital to analog conversion process in a digital control system reduces the phase lag contributed by the digital to analog conversion process relative to a conventional implementation of the zero order hold function. The apparatus for implementing the reduced phase lag zero order hold function employs a digital signal processor, a plurality of digital buffers, a digital multiplexing element, and a digital to analog converter. Phase lag is reduced by generating, from the digital to analog converter, for a fraction of the sample period, a waveform having a constant analog voltage with an amplitude which is scaled by the reciprocal of said fraction relative to a conventional zero order hold function. During the remainder of the sample period a substantially constant offset analog voltage is generated by the digital to analog converter. Alternatively, the time compression and amplitude scaling required to implement the reduced phase lag zero order hold function can be performed within the digital signal processor in the digital control system.

Method and apparatus for reducing phase lag resulting from digital to

The system and method for normalizing the amplitude of servo code derived signals in a disc drive, includes an improved embedded servo code format of separate magnetic dibit fields, recorded in half track steps. One magnetic dibit field is an automatic gain control field in which the magnetic head sees the same amount of magnetic dibit regardless of its position with respect to the track. A fast settling AGC loop responding to signals from the AGC field, produces a gain adjust signal while the magnetic head is still in the AGC field, which is used to normalize the amplitude of all following servo code and data code signals in that sector. The cycle of automatic gain control is repeated for each track in each sector. A sector mark following the AGC field has a magnetic dibit pattern which is fault tolerant. It is transduced in three parts to minimize error in its detection and identification and provides a timing reference for servo signals which follow. A defect dibit is recorded if the following servo gap is found to be defective during manufacture so that the next servo gap may be ignored. A track position servo code field provides signals for track following.

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Boise, ID, United States of America

Robert E Kier