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

A data decoding circuit for converting a first decoded code data sequence produced from a signal sequence of non-code information by using a maximum likelihood data sequence decoder, said data decoding circuit comprising a decoded code data processing unit receiving the first decoded code data sequence from said maximum likelihood data sequence decoder, said decoded code data processing unit comprising:

• a computation circuit which receives as input the signal sequence and which also receives as input the first decoded code data sequence decoded from said signal sequence by using said maximum likelihood data sequence decoder, and wherein the computation circuit calculates, based on said signal sequence, likelihood values representing probabilities that error events having preset predetermined code error patterns occur at each code position on said first decoded code data sequence, the likelihood values being calculated for respective codes of the first decoded data sequence in a one-to-one relation;
• a compensation circuit that verifies contents of decoded code values on the first decoded data sequence corresponding to a position of a relevant decoded code, for which each likelihood value is calculated by said computation circuit, and positions before and after the relevant decoded code over a predetermined code length, said compensation circuit selecting a predetermined compensation value corresponding to the verified decoded code values, and adding the selected compensation value to the likelihood value calculated by said computation circuit, thereby performing compensation for the likelihood value;
• a comparison circuit which compares each likelihood value compensated by said compensation circuit with a predetermined reference value;
• and
• a code inversion circuit which inverts code values of a decoded code position of said first decoded code data sequence if the decoded code position corresponds to said preset 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.

A data decoding method for correcting errors in a first decoded code data sequence produced by decoding a signal sequence of non-code information using a maximum likelihood data sequence decoding method, comprising:

• providing a data decoding circuit for carrying out the data decoding method;
• inputting to said circuit the signal sequence and the first decoded code data sequence;
• calculating, based on said signal sequence, likelihood values representing probabilities that error events having preset predetermined code error patterns occur at each code position on said first decoded code data sequence, the likelihood values being calculated for respective codes of the first decoded data sequence in a one-to-one relation;
• verifying contents of decoded code values on the first decoded data sequence corresponding to a position of a relevant decoded code, for which each likelihood value is calculated, and positions before and after the relevant decoded code over a predetermined code length;
• adding a predetermined compensation value corresponding to the verified decoded code values to the likelihood value calculated;
• comparing each likelihood value compensated with a predetermined reference value to produce a result;
• inverting code values of a decoded code position of said first decoded code data sequence if the decoded code position corresponds to the preset predetermined code error pattern, based on said result, thereby generating a second decoded code data sequence;
• and
• outputting from said circuit the second decoded code data sequence as a resulting decoded code data sequence.