Patent ID: 7440522
Filing Date: 2008-10-21
Classification: G11B

Abstract:
1. A method of evaluating a read signal adapted to the PRML method whereby a target signal level can be varied depending on a read signal, said method of evaluating a read signal comprising: generating a decoded correct bit sequence and an error bit sequence having a 1-bit edge shift from said correct bit sequence; generating a correct target signal and an error target signal from said correct bit sequence and said error bit sequence, respectively, by referring to said target signal level; calculating a correct Euclidean distance by calculating the sum of the square of the difference in signal level between said correct target signal and said read signal at each time; calculating an error Euclidean distance by calculating the sum of the square of the difference in signal level between said error target signal and said read signal at each time; calculating a Euclidean distance difference that is the difference between said correct Euclidean distance and said error Euclidean distance; calculating an average Euclidean distance from said target signal level, said average Euclidean distance corresponding a 1-bit shift pattern of said target signal level; calculating a normalized sequence error by subtracting said average Euclidean distance from said Euclidean distance difference and then dividing the result of subtraction with said average Euclidean distance; and evaluating said read signal using said normalized sequence error.