Electronic abatement of thermal interference in (G)MR head output signals

Abatement methods are described for Thermal Interference (TI) events encountered in hard disk drives using airbearing exposed (G)MR sensors. Two classes of TI events are analyzed; “thermal asperities” resulting from frictional heating by asperity-sensor contacts, and “baseline wander” caused by increased cooling when the sensor passes over near contacts. Countermeasures are discussed that can be taken at the head level, at the head-disk interface level, at the channel electronics level and at the system level. Various forms of electronic abatement are presented. Several methods for generating TI flags are shown. Circuitry for “cloaking” the TI events is discussed. Since TI events are additive to the data signal, the best results are obtained with subtractive restoration methods. A circuit implementation (Asperity Reduction Circuit) is presented and measured results are discussed