Eastman-kodak Company

Dominique H Veillard

Harvey M Horowitz

A self-biased magnetoresistive reproduce head is excited with an a.c. sense current which simultaneously a.c. biases the magnetoresistive element. When reproducing a pre-recorded signal, the spectrum of the head output includes sidebands containing the signal information associated with a suppressed carrier at twice the bias frequency. These sidebands are far removed in the head output frequency spectrum from sources of low frequency noise. The invention teaches demodulating these sidebands by means of a locally generated carrier corresponding to the suppressed carrier which has a frequency of twice the bias frequency. This locally generated carrier is coherent with the bias frequency source. The information signal is thereby recovered in a portion of the spectrum immune from the effects of low frequency interfering noise.

a.c. Self-biased magnetoresistive reproduce head utilizing second

In a transversal filter equalizer, such as one using a tapped delay line, the present invention combines the symmetrically located pairs of tap signals, by means of adders and subtracters, to provide partial output signals which are separately controlled in amplitude and phase. These partial output signals, which have no d.c. components, are then summed with a partial signal derived from the center tap reference signal to reinsert the d.c. component and to provide the equalized output signal.

Transversal filter equalizer with minimally interactive adjustments

The concept of the disclosed invention is to interleave a data bit stream with itself in such a way that the respective interleaved portions are displaced from each other, within the medium, by a distance corresponding to at least the statistical maximum size of the defects. In the event, during playback, that a dropout should occur, that dropout--inherently--must affect both interleaved portions. Therefore, by continuously delaying timewise one such interleaved playback portion relative to the other for a time sufficient to bring the two playback portions into sync with each other, the original bit stream may be reconstituted by toggling back and forth between the two playback portions each time a dropout is detected in either playback portion.

Interleaved redundancy in data recording

The concept of the invention is to format any bit stream which is to be recorded into a succession of data blocks, each of which corresponds lengthwise to at least the length of the largest defect statistically known to exist in the surface. The data blocks are grouped into data segments, with each data segment (1) being of a length corresponding to no more than the minimum length statistically known to exist between defects and (2) comprising (at least) two less data blocks (which shall be hereinafter sometimes referred to as 'vacant blocks') than may be accommodated within a data segment. By sensing, during a writing operation, whether data is being effectively written in the magnetic surface in question, any data which fails to get written may be rewritten by utilizing the vacant data blocks: one block per segment will inherently contain 'defective' information, and another block thereof will be, per the invention, adapted to record a low frequency flag signal to identify the occurrence of a rewrite operation. Because each data segment is no greater than the minimum spacing between defects, there can be only one defect per segment and, attendantly, the aforementioned rewriting operation may be implemented.

Adaptive redundance in data recording

The concept of the disclosed invention is to discern the start and end of bytes within a bit stream without the provision of special sync-defining bits, utilizing for such purpose the statistical character of the bit stream. Because actual signal processing circuits inherently do not have sharp cutoffs, this means that aliasing-free sampling of an analog signal must be at some sampling rate greater than twice the highest frequency (of interest) within the analog signal. Since the sampling in question is above the theoretically lowest possible sampling frequency, even the highest frequency components within the analog signal so sampled will be sampled at more than twice per cycle; and, attendantly, after the analog signal samples are quantized into a bit stream, a statistical distribution relating to the frequency at which the bits in the bit stream switch their states will become apparent . . . lower significant bits switching between ONEs and ZEROs at rates greater than the switching rates of more significant bits. By monitoring the switching transitions for the bits in a bit stream, the start and end of the bytes thereof may be discerned.

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San Diego, CA, United States of America

Dominique H Veillard