Mostly analog disk drive read channel with practical depth-of-two fixed delay tree search

Abstract

A new read-channel arrangement for use with d=1 codes equalizes the input to extended partial response IV (EPR4) for clock recovery, and follows this with a new realization of a fixed delay tree search with decision feedback detector with search depth of two. The detector and a discrete-time phase detector for clock recovery share a five-tap finite-impulse response forward equalizer. Clock recovery from EPR4 is fast, while forward and feedback equalizers need no adaptation of tap weights. The read channel, originally developed for a rate-4/5 X{101} code, is extended to the more efficient rate-6/7 maximum-transition-run (MTR) codes. The detector consists of a conventional decision feedback equalizer, assisted by an error-correction circuit to sense and eliminate the major error events, thus performing as well as tree search with depth of two. With MTR code, the read channel outperforms EPR4 with Viterbi detection by 1 dB.