Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-10-05
2003-05-06
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044340, C369S047480, C369S053340
Reexamination Certificate
active
06560172
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc recording method and apparatus for recording, by optical power, information on an optical disc, such as CD-R, CD-RW, CD-WO, MD and DVD. More particularly, the present invention relates to detection of a wobble signal at the time of recording.
The present application is based on Japanese Patent Application No. Hei.
11-285820
, which is incorporated herein by reference.
2. Description of the Related Art
The write-once optical disc, e.g., CD-R (i.e., Compact Disc-Recordable) disc and a rewritable optical disc, e.g., CD-RW (i.e., Compact Disc-ReWritable) disc have guide grooves, so called as grooves or pre-grooves, which are formed in advance in a recording layer thereof. By irradiating a laser beam onto and along a groove or a track formed with a land which is defined between the adjacent grooves formed in an optical disc which has been rotated, information is recorded on the track in a form of strings of pits. Absolute time in pre-groove information (i.e., ATIP information) is buried in the groove of the optical disc of this type by wobbling the track groove. Ordinarily, the recording/reproducing operation is controlled, based on a tracking servo and the ATIP information, which is obtained by reproducing the wobble signal.
As shown in
FIG. 5
, a tracking error signal (TE signal) and a wobble signal are detected by processing an output signal of a position-detecting photo detector of an optical pickup, which is ordinarily a four-segment photo detector
101
. The four-segment photo detector
101
has an imaginary plane having four light-receiving segmental areas A, B, C and D. According to those light receiving areas, the areas (A+D) and (B+C) form a light receiving surface divided in the radial direction of the optical disc, and the areas (A+B) and (C+D) form a light receiving surface divided in the track direction of the optical disc. The light receiving areas A, B, C and D produce signals when those areas receive optical beams reflected from the optical disc. Those output signals are respectively sampled and held by sample/hold circuits
102
a
,
102
b
,
102
c
and
102
d
. The signals, which have been derived from the light receiving areas A and D, and sampled and held by the sample/hold circuits
102
a
and
102
d
, are added together by an adder
103
. The signals, which have been derived from the light receiving areas B and C, and sampled and held by the sample/hold circuits
102
b
and
102
c
, are added together by an adder
104
. A difference between the output signals of the adders
103
and
104
, i.e., ((A+D)−(B+C)), is computed by a subtractor
105
. EFM signals are modulated by presence or absence of pit detected in phase at the light receiving surfaces A, B, C and D. The signals derived from the light receiving areas (A+D) and (B+C) have inverse phases with respect to a position as viewed in the radial direction of the beam spot on the land. Accordingly, those signals can be utilized as TE signals or the wobble detecting signals.
FIG. 6
is a graph showing a relationship among a recording signal, a light receiving signal, pits formed, and a wobble-signal detecting sampling pulse signal when information is recorded at a speed of four times relative to the standard audio CD speed (hereinafter, referred simply as a standard speed). As shown in
FIG. 6
, a waveform of the recording signal has a “recording part” when its power is in an on state, and a “lead part” when its power is in an off state. A level of the light receiving signal varies in accordance with a reflectivity variation during a recording pit forming process, to thereby have a waveform pattern as follows. The signal level of the light receiving signal reaches its peak immediately after the recording signal is put in a power-on state. Then, the signal level gradually descends with formation of a pit. When the recording signal is put in a power-off state, its level variation is settled down at a fixed level for a part of the period, to thereby form a flat waveform pattern. That is, the pit formation begins at an instant that the light receiving signal level reaches the peak value, and ends some time after the recording signal is put in a power-off state. A wobble sampling pulse signal is held for a fixed period of time after the recording signal is put in a power-off state. The reason why it is held for the fixed time is that if the wobble detection sampling is performed during a period where the light receiving signal is stable in level variation, the carrier to noise (C/N) ratio of the wobble signal is good.
In the wobble detecting method and apparatus described above, when information is recorded at a speed, which is higher than the above-described speed, and which is, for example, twelve times relative to the standard speed, the waveform pattern of the light receiving signal greatly varies, and the stable period during the power-off period of the recording signal is extremely short. The first reason is that in the case of the high speed recording, in order to secure a reliable pit formation, a recording time must be increased with increase of the recording speed. For example, provided that the recording time is nT when the recording speed is eight times relative to the standard speed, a recording time at the speed of twelve times is (n+0.4)T. Further, the second reason is that in the high speed recording, the recording power is larger than that in the lower speed recording, and therefore, the light receiving signal is more dull in waveshape. Accordingly, in the case of the high speed recording, the sampling time period for the wobble detection is extremely short, so that the C/N of the wobble signal is degraded.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disc recording method and apparatus which can detect a wobble signal at all times at good C/N ratio independently of the speed recording.
According to the first aspect of the present invention, there is provided an optical disc recording method including the steps of:
irradiating an optical beam for information recording onto an optical disc, based on a recording signal;
forming at least one pit having predetermined length on a land disposed on the optical disc;
obtaining a light receiving signal by causing a light receiving element, having a light receiving surface segmented in a radial direction of the optical disc, to receive light reflected from a pit forming part and a non-pit forming part, both of which are formed on the optical disc at the time of information recording;
sampling and holding the light receiving signal derived from the light receiving element; and
detecting a tracking servo and a wobble signal on the basis of balance of the sampled and held light receiving signal as viewed in the radial direction of the optical disc;
wherein when a recording speed is lower than a predetermined recording speed, the sampling and holding step is performed to detect the wobble signal during a power-off period of the recording signal, and
wherein when the recording speed is higher than the predetermined recording speed, the sampling and holding step is performed during a power-on period of the recording signal.
According to the second aspect of the present invention, there is provided an optical disc recording apparatus which includes:
an optical pickup emitting an optical beam to record a pit onto a land of an optical disc, based on a recording signal, the optical pickup including a light receiving element which has a light receiving surface segmented in a radial direction of the optical disc, and which receives light reflected from the optical disc, the optical pickup producing a light receiving signal associated with each segmental area of the light receiving surface;
a sampling pulse generating circuit processing the recording signal to generate a first sampling pulse signal, the sampling pulse generating circuit retarding the recording sig
Hindi Nabil
Pillsbury & Winthrop LLP
Yamaha Corporation
LandOfFree
Optical disc recording method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical disc recording method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical disc recording method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3049027