On-the-fly error correction using thermal asperity erasure pointers from

Abstract

In a magnetic disk drive storage system comprising a sampled amplitude read channel and an on-the-fly error correction coding (ECC) system, a thermal asperity compensation technique wherein: a thermal asperity (TA) detection circuit detects a saturation condition in the sample values of the analog read signal which indicates the presence of a TA; a pole of an AC coupling capacitor is elevated; timing recovery, gain control, and DC offset loops in the read channel are held constant; TA erasure pointers are generated corresponding to the duration of the TA transient; and an on-the-fly error detection and correction (EDAC) circuit processes the TA erasure pointers to correct errors in the detected digital data caused by the TA. Using TA erasure pointers to compensate for the effect of thermal asperities minimizes the cost, complexity, and redundancy of the ECC. Further, soft errors in the prior art method of adjusting the headroom of the read channel ADC are avoided. Still further, the EDAC circuitry can process the erasure pointers on-the-fly and still correct a sufficient number of soft errors without having to perform any significant number of reread operations. In this manner, the disk drive storage system operates virtually uninterrupted in reading data from the disk and transferring it to a host computer.