Patent ID: 7359463

Claim:
A code detection method for calculating a branch metric using a normalized upper and lower asymmetry of a reproduced signal y k as α, an absolute value of an average detected voltage as V, and an upper and lower asymmetrical voltage set as A=αV to define a three-valued detection-point voltage d k (s) as {(−V+A), 0, (V+A)}, the method comprising: comparing the three-valued detection point voltage d k (s) and (V+A) or (−V+A); calculating V/2+A−y k +α(A/2−y k ) as the branch metric when d k (s) equals (V+A); setting the branch metric equal to zero when d k (s) equals zero; and calculating V/2−A+y k +α(A/2−y k ) as the branch metric when d k (s) equals (−V+A).