Data decoding method and circuit and information recording and reproducing apparatus using the same

A data decoding circuit for converting an input signal sequence to a decoded code data sequence by using maximum likelihood data sequence detector, said data decoding circuit comprising a decoded code data processing unit behind said maximum likelihood data sequence detector, said decoded code data processing unit comprising;

• a computation circuit which refers to an input signal sequence input to said maximum likelihood data sequence detector and a first decoded code data sequence decoded by using said maximum likelihood data sequence detector, and calculates likelihood values (probabilities) that error events having preset predetermined code error patterns occur at each code position on said first decoded code data sequence;
• a selection circuit which refers to contents of decoded code values at the position of a relevant decoded code, for which each likelihood value is calculated at said computation circuit, and positions of before and after the relevant decoded code over a predetermined code length, and selects a predetermined reference value associated with the referred-to contents of the decoded code values;
• a comparison circuit which compares each likelihood value calculated by said computation circuit with a predetermined reference value selected by said selection circuit;
• and
• a code inversion circuit which inverts code values included in code values of said first decoded code data sequence and of which the decoded code position is associated with said predetermined code error pattern, based on a result output by said comparison circuit, thereby generating a second decoded code data sequence, and, outputting the second decoded code data sequence as a resulting decoded code data sequence.