Patent ID: 6982942
Filing Date: 2006-01-03
Classification: G11B,H03M

Abstract:
1. A data reproducing apparatus for demodulating data from a reproduction signal in accordance with a partial response waveform obtained from a recording medium, by a Viterbi decoding technique based on front edge sampling values obtained by sampling while synchronizing a front edge clock synchronizing a leading edge of said reproduction signal and back edge sampling values obtained by sampling while synchronizing a back edge clock synchronizing a trailing edge of said reproduction signal, comprising: a front edge system processing said front edge sampling values; a back edge system processing said back edge sampling values; and a processing system modulating data based on information obtained individually from said front edge system and said back edge system, wherein: said front edge system comprises: a first selection path selecting part selecting one path as a first selection path so as to correspond to a state transition of data according to a predetermined rule that is based on results from calculating a branch metric value using each expected value defined by said partial response waveform and each of said front edge sampling values, calculating a path metric value based on every said branch metric value, and comparing among a plurality of said path metric values; a first generating part generating front edge candidate data corresponding to said first selection path selected by said first selection path selecting part; and a first change path selecting part selecting one path different from said first selection path as a first change path based on differences among the plurality of said path metric values to be compared by said first selection path selecting part, said back edge system comprises: a second selection path selecting part selecting one path as a second selection path so as to correspond to the state transition of data according to the predetermined rule that is based on results from calculating a branch metric value using each expected value defined by said partial response waveform and each of said back edge sampling values, calculating a path metric value based on every said branch metric value, and comparing among a plurality of said branch metric values; a second generating selecting part generating back edge candidate data corresponding to said second selection path selected by said second selection path selecting part; and a second change path selecting part selecting one path different from said second selection path as a second change path based on differences among the plurality of said path metric values to be compared by said second selection path selecting part, said processing system comprises: a first candidate data generating part generating first candidate data by synthesizing said front edge candidate data from said front edge system with said back edge candidate data from said back edge system, a mixed selection path generating part generating a mixed selection path based on said first selection path from said front edge system and said second selection path from said back edge system; a second candidate data generating part changing paths that are of said mixed selection path and correspond to said first change path from said front edge system and said second change path from said back edge system, to said change paths as change selection paths, and generating second candidate data in accordance with said Viterbi decoding technique based on said change selection paths; and a data selecting part selecting either of said first candidate data and said second candidate data based on a predetermined reference concerning likelihood, wherein data to be reproduced are reproduced based on either of said first candidate data and said second candidate data selected by said data selecting part.