Data reproducing method and apparatus

A data reproduction apparatus for performing partial response detection of a reproduction signal and reproducing data by using maximum likelihood decoding, comprising:

• N×M memory arrays with N memory lines each corresponding to state values Sk (k=0, 1, . . . , N-1) in state transition and M memory rows (**a, . . . , **p) storing a maximum likelihood path;
• a signal sampler, adapted to sample a reproduction signal at a data identification point t so as to detect the reproduction signal level on the basis of a relationship (state transition diagram) between the state values Sk (k=0, 1, . . . , N-1) corresponding to a detection value of said reproduction signal level;
• a storer, adapted to store in each respective one of the memory lines corresponding to each respective state value Sk (k=0, 1, . . . , N-1) for said memory array, the state values at a data identification point t, Skt (k=0, 1, . . . , N-1) detected from detection level values at said data identification point t, immediately before they are linked by one branch of maximum likelihood path;
• and
• a controller, adapted to rewrite the state value stored in each memory line as the state value which has been linked by the state values Skt (k=0,1, . . . , N-1), detected at the data identification point t and the branch of maximum likelihood path, in order back to each data identification point (t-1, t-2, . . . , t-(M-1)),
• wherein the rewriting control of the state value is performed so that the transitions of the state values up to the data identification point t are stored in the sequential memory lines for each identification of the reproduction signal in each memory line corresponding to each state value Sk (k=0, 1, . . . , N-1), and the reproduced data corresponding to the change of the state values in the M-th row to the state values in the (M-1)-th row are output.