A method for reducing the effects of thermal asperities

A new method of combating the effects of thermal asperities (TAs) in disk d rives is proposed. In the classic method, changing a parameter in the equal izer modifies the duration of a TA but no attempt is made to modify the det ector that follows the equalizer or to improve its performance. The propose d method involves modification of both the equalizer and the detector. Spec ifically, two channels are run in parallel. One channel is matched to the p artial response polynomial P(D), whereas the other is matched to the partia l response polynomial (1 - D)P(D), P(D) is the target polynomial of the exi sting magnetic recording channel. The Viterbi detector in the (1 - D)P(D) c hannel has better decoded bit error rate (BER) during a TA, and the Viterbi detector in the P(D) channel has better BER in the absence of a TA, The ov erall decoded bit stream is selected from these two Viterbi detectors in ac cordance as to whether a TA has been detected. The performance of the propo sed method was studied via simulation for the magnetic recording channel wi th the target polynomial (D) = (1 - D)(1 + D)(2) (EPR4), The proposed syste m was found to be superior to existing methods in the presence of TAs, whil e having the same performance in the presence of additive white Gaussian no ise (AWGN).