Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-10-24
2004-06-08
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S047170, C369S053100, C369S053180
Reexamination Certificate
active
06747924
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to optical disk reproduction apparatus such as DVD (Digital Versatile Disk) players, and more particularly to an improved optical disk reproduction apparatus which is capable of high-quality reproduction of recorded information at each individual radial position of an optical disk with minimized errors without undesirably suspending the reproduction.
On DVDs and some other types of optical disks, information is recorded using the so-called “mark length recording scheme”. In a reproduced RF signal waveform output from an optical pickup reading out the information recorded with such a mark length recording scheme, higher-frequency components (i.e., signals of smaller pulse widths) would present lower signal levels. Thus, if each reproduced RF signal from the optical pickup is input into a slicer and binarized thereby, as it is, using a predetermined slice level, great jitter tend to occur, thus resulting in many errors. For this reason, it has been conventional to first input the reproduced RF signal into a waveform equalization circuit so that the reproduced RF signal is binarized by the slicer with the levels of the higher-frequency components raised to a predetermined degree, to thereby reduce the undesired jitter. Further, some of the conventional DVD players contain a jitter detection circuit, and performs test reproduction of the optical disk with respect to an innermost location of the optical disk prior to actual or non-test reproduction of the disk. Through the test reproduction, waveform equalization characteristics of the waveform equalization circuit are adjusted to optimize (e.g., minimize) the jitter level by the jitter detection circuit. During the subsequent actual reproduction, the recorded information on the entire optical disk is reproduced with the waveform equalization characteristics fixed at the adjusted values or settings.
Among various schemes for reproducing a DVD or other type of optical disk with information recorded at a constant linear velocity is one which can reproduce the recorded information at high speed by rotating the optical disk at a constant angular velocity and eliminate a need for variably controlling the rotating speed in accordance with a radial position or address, on the optical disk, of each location to be reproduced via the optical pickup (i.e., a radial position traversed by the optical pickup). In such constant-angular-velocity reproduction of the optical disk with information recorded at a constant linear velocity (i.e., CLV optical disk), the data transfer rate differs between the inner and outer regions of the optical disk—the difference in the data transfer rate is normally compensated for by a buffer memory—, so that there would occur great variations in the amplitudes of the high-frequency components of the reproduced RF signal waveform (particularly, the amplitude of 3T-pit signals in the DVD case). Thus, with the conventionally-known technique of adjusting the waveform equalization characteristics of the waveform equalization circuit through the test reproduction performed with respect to innermost location of the optical disk and then fixedly using the thus-adjusted waveform equalization characteristics, there would be countered the problem that the jitter increase as the reproduction proceeds toward the outer circumferential region of the disk.
Further, if the optical disk has a warp, the reproducing laser light would get out of focus, which would also lead to an increased jitter level. To reduce the jitter caused by the disk warp, it is generally effective to perform focus adjustment, such as focus balance adjustment or focus error adjustment, and also adjust the waveform equalization characteristics of the waveform equalization circuit. However, because the disk warp, if any, generally becomes greater in the inner-to-outer direction of the optical disk, the conventionally-known technique of adjusting the waveform equalization characteristics of the waveform equalization circuit through the test reproduction with respect to innermost location and then fixedly using the adjusted waveform equalization characteristics would present the problem the jitter level increases as the reproduction proceeds toward the outer circumferential region of the disk.
One possible solution to the above-mentioned jitter problem in the case where the CLV optical disk is reproduced at a constant angular velocity or where a warped disk is reproduced may be to perform the focus adjustment and waveform equalization characteristic adjustment, on a real-time basis, by detecting the jitter while the optical disk is being read via the optical pickup. However, because the focus adjustment and waveform equalization characteristic adjustment is each one form of control for finding optimum values or settings capable of providing an optimal (e.g., minimal) jitter level while variously changing the settings, it unavoidably passes, during the course of the adjustment, some locations where the jitter level is unsatisfactory, with the result that the real-time adjustment can not be performed appropriately while allowing the optical disk to be read via the optical pickup without suspension.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide an improved optical disk reproduction apparatus which, even where a constant-liner-velocity (CLV) disk is to be reproduced at a constant angular velocity or a warped disk is to be reproduced, is capable of high-quality reproduction of recorded information from the optical disk by modifying focus adjustment or waveform equalization characteristic adjustment to optimal settings, without suspending the reproduction, so as to achieve an optimum jitter level at each individual radial position of the disk.
To accomplish the above-mentioned object, the present invention provides an optical disk reproduction apparatus which comprises: an optical pickup arranged to read out recorded information from an optical disk; a waveform equalization section arranged to perform a waveform equalization process on a reproduced RF signal that is generated on the basis of the recorded information read out by the optical pickup; a jitter detection section arranged to detect jitter of the reproduced RF signal having been subjected to the waveform equalization process; and a control section. The control section is arranged to perform test reproduction of the optical disk with respect to a plurality of testing radial locations of the optical disk prior to actual reproduction of the optical disk, adjust a waveform equalization characteristic of the waveform equalization section to an optimal setting so as to optimize the jitter of the reproduced RF signal detected by the jitter detection section at each of the testing radial locations of the optical disk, and during the actual reproduction of the optical disk, adjust the waveform equalization characteristic of the waveform equalization section to an optimal setting that is predicted, from the optimal setting determined by the test reproduction, in accordance with a changing radial position of the optical disk to be reproduced via the optical pickup. In the present invention, an optimal setting of the waveform equalization characteristic is predicted and set, for each radial position of the optical disk, on the basis of the optimal setting determined by the test reproduction, and thus there can always be provided an optimal waveform equalization characteristic, for each radial position of the optical disk, capable of optimizing (e.g., minimizing) the jitter, without suspending the reproduction.
The optical disk reproduction apparatus of the present invention further comprises a focus adjustment section arranged to perform a focus adjustment process for adjusting either one or both of a focus balance and focus offset by use of two focus-error-detecting signals generated on the basis of the recorded information read out by the optical pickup. In this case, the control section, during t
Chu Kim-Kwok
Korzuch William
Pillsbury & Winthrop LLP
Yamaha Corporation
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