US 7,440,522 B2 · Method of evaluating a readout signal, and optical disc apparatus

Abstract

A method of evaluating the quality of a read signal from the viewpoint of the detection margin of a Viterbi decoder in the PRML method in which a target signal level varies depending on the read signal, and an optical disc apparatus implementing the method. A method of evaluating the quality of a signal pattern comprising a combination of minimum run lengths from the viewpoint of edge shift, and an optical disc apparatus implementing the method. From the target signal level that varies depending on the read signal, a target signal is generated based on a decoding result, and an error target signal is generated in which the decoding result is edge-shifted. The signal quality is evaluated by calculating a Euclidean distance between these signals and the read signal. A virtual state that is not included in the Viterbi decoder and that is less than the minimum run length is defined, and a target signal level for the virtual state is generated using a target signal level table inside the Viterbi decoder, based on the concept of convolution. In this way, the signal quality can be evaluated by the same method as mentioned above even in cases where the pattern of a combination of the minimum run lengths has edge-shifted.

Claims22

Dependent claims

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.

6 more elements

A method of evaluating a read signal adapted to the PRML method for a code with a minimum run-length of 2 or more, said method comprising:

calculating a target signal level for a run length smaller than the minimum run-length;
generating a decoded correct bit sequence and an error bit sequence having a 1-bit edge shift from the 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 to 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.

7 more elements

An optical disc apparatus equipped with a PRML read circuit, said PRML circuit being adapted such that a target signal level can be varied depending on a read signal, said apparatus comprising:

means for generating a decoded correct bit sequence and an error bit sequence having a 1-bit edge shift from said correct bit sequence;
means for 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;
means for 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;
means for 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;
means for calculating a Euclidean distance difference that is the difference between said correct Euclidean distance and said error Euclidean distance;
means for 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;
means for 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
means for evaluating said read signal using said normalized sequence error.

6 more elements

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 absolute value 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 absolute value 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.

6 more elements

A method of evaluating a read signal adapted to the PRML method for a code with a minimum run-length of 2 or more, said method comprising:

calculating a target signal level for a run length smaller than the minimum run-length;
generating a decoded correct bit sequence and an error bit sequence having a 1-bit edge shift from the 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 absolute value 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 absolute value 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 to 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.

7 more elements

Dependencies are inferred from the claim text.

Method of evaluating a readout signal, and optical disc apparatus

Life of this patent

Method of evaluating a readout signal, and optical disc apparatus

Life of this patent

Abstract

Claims22