Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1998-11-16
2001-01-09
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044410, C369S124150
Reexamination Certificate
active
06172953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a defect detector for detecting defects included in a detection signal of information recorded on a storage medium, and more specifically to a defect detector which detects defects in the detection signal having a lower level than a predetermined level that enables the detection signal to function as a correct detection signal.
2. Description of the Prior Art
There are broadly known information reproduction apparatuses, such as a Compact Disc player, which reproduces information recorded on a storage medium by irradiating a light beam such as a laser beam thereon and receiving the reflected light beam to obtain recorded information. In reproduction from the above optical disc, if defects such as scratches, stains or the like exist on the optical disc, the detection signal obtained from such portions of the optical disc may frequently include defects (i.e., inappropriate portion) in the detection signal (hereinafter simply referred to as “defect”). The defect generally includes two types, i.e., a relatively long defect and a relatively short defect. The long defect has the detection signal level lower than a predetermined level and lasting relatively long period of time. The short defect results from stains, fingerprints and the like on the optical disc and lasts relatively short period of time (e.g. observed as a wedge-shape in the detection signal waveform).
A defect detecting method employed on a conventional information reproduction apparatus operates in the following manner. First, an upper envelop of the detection signal is separately held by a peak-holding circuit of a long time constant and a peak-holding circuit of a short time constant. Then, the output signal of the peak-holding circuit of a short time constant is subtracted from the output signal of the peal-holding circuit of a long time constant, and the resultant signal is compared with a preset threshold level for the defect detection. If the resultant signal is lower than the preset threshold, it is judged that the defects exist.
By the above mentioned method, the relatively long defect can be readily detected because the time period in which the output signals of the peak-holding circuits of two types differ from each other is long. However, in the case of relatively short defect, the output signals of the peak-holding circuits differ only for a short period of time and the difference itself is small, and hence it is difficult to reliably detect such a short defect, especially a wedge-shaped defect. If the threshold is set at a lower level to overcome the above-mentioned problem, correct portions of the detection signal may be erroneously judged as defects and the defect compensation operation may be performed even if actually it is not the defect, thereby disturbing correct information reproduction.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a defect detector capable of reliably detecting not only long defects but also short defects like the ones of wedge-shape.
According to one aspect of the present invention, there is provided a defect detector for detecting a defect in a detection signal obtained by detecting information, the defect having a level lower than a predetermined level of the detection signal, the detector including: an upper envelop signal generating unit for detecting an upper envelop of the detection signal to generate an upper envelop signal corresponding to the detected upper envelop; a lower envelop signal generating unit for detecting a lower envelop of the detection signal to generate a lower envelop signal corresponding to the detected lower envelop; a slice signal generating unit for dividing a voltage difference of the upper envelop signal and the lower envelop signal using a predetermined division ratio to generate a slice signal; an averaging unit for averaging the slice signal to produce an average signal; and a defect detecting unit for comparing the average signal and the upper envelop signal to produce a defect detection signal indicating the period in which the voltage of the upper envelop signal is lower than the voltage of the average signal.
In accordance with the defect detector thus configured, the upper envelop signal generating unit detects the upper envelop of the detection signal to generate the upper envelop signal corresponding to the detected upper envelop, and the lower envelop signal generating unit detects the lower envelop of the detection signal to generate the lower envelop signal corresponding to the detected lower envelop. The slice signal generating unit divides the voltage difference of the upper envelop signal and the lower envelop signal using a predetermined division ratio to generate the slice signal. The averaging unit averages the slice signal to produce the average signal. The defect detecting unit compares the average signal and the upper envelop signal to produce the defect detection signal indicating the period in which the voltage of the upper envelop signal is lower than the voltage of the average signal. As a result, a very short defect like a wedge-shape defect can be reliably detected.
Preferably, the averaging unit uses a first time constant in averaging and the upper envelop signal generating unit uses a second time constant in generating the upper envelop signal, wherein the first time constant is larger than the second time constant. By this, the defect detection becomes more reliable. In a preferred embodiment, the slice signal generating unit divides the voltage difference at a division ratio of 1:1.
According to another aspect of the present invention, there is provided a defect detector for detecting a defect in a detection signal obtained by detecting information, the defect having a level lower than a predetermined threshold level of the detection signal, the detector including: an first upper envelop signal generating unit for detecting an upper envelop of the detection signal using a first time constant to generate an upper envelop signal corresponding to the detected upper envelop; a lower envelop signal generating unit for detecting a lower envelop of the detection signal to generate a lower envelop signal corresponding to the detected lower envelop; a slice signal generating unit for dividing a voltage difference of the upper envelop signal and the lower envelop signal using a predetermined division ratio to generate a slice signal; an averaging unit for averaging the slice signal to produce an average signal; a first detecting unit for comparing the average signal and the upper envelop signal to produce a first detection signal indicating the period in which the voltage of the upper envelop signal is lower than the voltage of the average signal; a second upper envelop signal generating unit for detecting an upper envelop of the detection signal using a second time constant to generate a second upper envelop signal corresponding to the detected upper envelop, the second time constant being larger than the first time constant; a third upper envelop signal generating unit for detecting an upper envelop of the detection signal using a third time constant to generate a third upper envelop signal corresponding to the detected upper envelop, the third time constant being larger than the second time constant; a difference signal generating unit for generating a difference signal indicating a voltage difference between the second upper envelop signal and the third upper envelop signal; a second detection unit for comparing the difference signal with the predetermined threshold level to produce a second detection signal indicating the period in which the difference signal is larger than the threshold value; and a defect detecting unit for adding the first detection signal and the second detection signal to produce the defect detection signal.
In accordance with the defect detector thus configured, the first upper envelop signal generating unit detects the upper envelop of the detection signal using the first time co
Hindi Nabil
Nixon & Vanderhye
Pioneer Electronic Corporation
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