Information recording medium evaluation method, information recording medium, method for manufacturing information recording medium, signal processing method and access control apparatus

Abstract

A method for rating an information recording medium according to the present invention includes the steps of: receiving a digital read signal, which has been generated based on an analog read signal representing information that has been read from the information recording medium, and shaping the waveform of the digital read signal; subjecting the shaped digital read signal to maximum likelihood decoding, thereby generating a binarized signal showing a result of the maximum likelihood decoding; and calculating the quality of the digital read signal based on the shaped digital read signal and the binarized signal. If the quality of the read signal is calculated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the quality is calculated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a signal processing method by maximum likelihood decoding and also relates to a method for rating an information recording medium by the maximum likelihood decoding.[0003]2. Description of the Related Art[0004]Recently, as the densities of optical disk media have been further increased, the shortest length of recording marks has come even closer to the limit of optical resolutions. As a result, intersymbol interference is occurring increasingly often and the SNR (signal to noise ratio) is decreasing even more significantly. To overcome these problems, it has become more and more common to adopt PRML (partial response maximum likelihood) as a signal processing method.[0005]The PRML method is a combination of the partial response (PR) technique and the maximum likelihood (ML) technique, and is a method for selecting a most likely signal sequence based on a read signal waveform on the suppo...

AI Technical Summary

Benefits of technology

[0053]According to the present invention, if the quality of a given read signal is calculated by a PRML method in which a number of zero-cross portions are included in a merging path of a minimum difference metric, the quality is calculated by using only a state transition pattern in which only one zero-cross portion is included in a merging path of a non-minimum difference metric. By using such a state transition pattern in which only one zero-cross portion is included in a merging path, the error of each and every zero-cross portion (i.e., zero-cross information) can be detected separately and independently of each other. And by rating each zero-cross portion of the read signal on an individual basis, the quality of the read signal can be rated appropriately.

[0054]In addition, according to the present invention, by changing the PRML methods to adopt depending on the purpose of the access, the system margin can be maximized and the system can be stabilized. For example, if a normal read operation is carried out by a high-order PRML method that would achieve high read performance but if a read operation that needs to be done with write parameters adjusted is carried out by a PRML method that would adjust the write parameters with the property of the optical disk medium taken into account, the system margin can be maximized during both read and write operations. As a result, the read / write system can get stabilized.

Problems solved by technology

As a result, intersymbol interference is occurring increasingly often and the SNR (signal to noise ratio) is decreasing even more significantly.

Meanwhile, as the level determination method has been gradually replaced by the PRML method as a mainstream signal processing method, some problems are arising about how to evaluate the read signal.

As described above, as the densities of optical disk media have been further increased, the intersymbol interference and SNR will have more and more serious consequences.

However, if such a high-order PRML method that would achieve high performance during a read operation were adopted and if adjustments were made during writing by that PRML method (particularly if the edge positions of recording marks are adjusted), then the write operation could not be performed with the write performance of the given recording medium taken full advantage of (e.g., under such a writing condition as to maximize the SNR) depending on the storage density of the medium, thus causing a decrease in the margin of the overall system.

As a result, the performance of repetitive writing might degrade too much and the deterioration with time might be noticeable too easily.

In addition, the read signals representing 2T, 3T and other short marks might have insufficient amplitudes, thus possibly causing deterioration in read performance due to a decrease in SNR or threatening the stability of a PLL circuit for detecting a sync signal from the read signal.

If the pattern to evaluate included multiple edges, however, then it would be difficult to detect edge shifting between marks and spaces, which are very important factors that would determine the storage quality of an optical disk medium.

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