Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2002-05-29
2004-03-09
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044130
Reexamination Certificate
active
06704258
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tracking error signal detector that is used in an optical disk apparatus for recording/reproducing data optically.
BACKGROUND ART
In recent years, the applicability of optical disk apparatuses for recording/reproducing information has increased significantly. An example of a conventional tracking error signal detector used in the optical disk apparatuses will be described below by referring to the drawings.
FIG. 17
shows the configuration of an optical disk apparatus that includes a conventional tracking error signal detector. The tracking error signal detector includes an amplifier
1704
, a PLL circuit
1705
, a timing generation circuit
1706
, and a sample-hold (S-H) circuit
1707
. Reference numeral
1708
denotes a tracking control device that drives an objective lens
1709
via a tracking actuator based on a tracking error signal TE output from the tracking error signal detector.
In
FIG. 17
, light reflected from an optical recording medium
1702
that is rotated by a spindle motor
1701
is detected by a photodetector
1703
. A detection signal of the photodetector
1703
is input to the amplifier
1704
, which then produces a summation signal RFA
1
. The summation signal RFA
1
is input to the PLL circuit
1705
and the S-H circuit
1707
.
FIG. 18
shows the arrangement of marks formed on the optical recording medium
1702
. In
FIG. 18
, a horizontal axis represents the circumferential direction of the optical recording medium
1702
. A clock mark
1802
is located on an imaginary track centerline
1801
. A first wobble mark
1803
is located at a certain distance away from the track centerline
1801
on the outer circumference side, while a second wobble mark
1804
is located at a certain distance away from the track centerline
1801
on the inner circumference side. When a light spot passes along the track centerline
1801
, an amount of light reflected from the first wobble mark
1803
is equal to that from the second wobble mark
1804
. When the light spot passes along the outer circumference side of the track centerline, the amount of light reflected from the second wobble mark
1804
is smaller than that from the first wobble mark
1803
. When the light spot passes along the inner circumference side of the track centerline, the amount of light reflected from the second wobble mark
1804
is larger than that from the first wobble mark
1803
. By comparing the reflected light from the first wobble mark
1803
with that from the second wobble mark
1804
, a tracking error signal, which indicates the deviation of a light spot from the track centerline
1801
, can be detected.
The PLL circuit
1705
in
FIG. 17
produces a reproduction clock signal in synchronization with light reflected from the clock mark
1802
. The reproduction clock signal is input to the timing generation circuit
1706
, which then outputs a timing signal that indicates the reproduction timing for each of the first and second wobble marks
1803
,
1804
. The S-H circuit
1707
samples and holds the summation signal RFA
1
in response to the timing signal, subtracts the summation signal RFA corresponding to the second wobble mark
1804
from that corresponding to the first wobble mark
1803
, and outputs the resultant value as a tracking error signal TE.
FIG. 19
shows a waveform in each portion of the tracking error signal detector in FIG.
17
. In
FIG. 19
, a horizontal axis represents time. The summation signal RFA
1
from the amplifier
1704
has a reproduction waveform that corresponds to the clock mark
1802
, the first wobble mark
1803
, and the second wobble mark
1804
. The PLL circuit
1705
generates the reproduction clock signal in synchronization with the clock mark
1802
(time A). The timing generation circuit
1706
generates the timing signal in response to the reproduction clock signal from the PLL circuit
1705
. The S-H circuit
1707
samples and holds the summation signal RFA
1
in accordance with the timing signal. In an example shown in
FIG. 19
, the summation signal RFA is sampled and held at time B and time C. The sampling value at time B corresponds to the first wobble mark
1803
and the sampling value at time C corresponds to the second wobble mark
1804
.
The tracking error signal TE output from the tracking error signal detector having the above configuration is input to the tracking control device
1708
in FIG.
17
. The tracking control device
1708
performs a predetermined control operation and drives the tracking actuator. The tracking actuator drives the objective lens
1709
. In this manner, a light spot is controlled so as to be on the track centerline
1801
. The tracking error signal detector as described above is disclosed, e.g., in JP 6(1994)-60408 A.
In the above configuration, however, it is difficult for the PLL circuit to be pulled in, e.g., when the rotation rate of the optical recording medium changes greatly or sharply. If the PLL circuit is not pulled in, the summation signal RFA
1
does not synchronize with the clock of the PLL circuit. Consequently, the timing signal of the timing generation circuit also becomes asynchronous with the summation signal RFA
1
.
When the summation signal RFA
1
does not synchronize with the timing signal, the summation signal RFA
1
that corresponds to the first and second wobble marks cannot be detected correctly, making it impossible to detect an accurate tracking error signal TE. This increases tracking errors, which lead to inaccurate recording/reproducing operations on the optical recording medium.
DISCLOSURE OF INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a tracking error signal detector that can produce a high-accuracy tracking error signal even if a summation signal is sampled at asynchronous timing.
To achieve the above object, a tracking error signal detector of the present invention includes a photodetector, an amplifier, a sampling portion, a first arithmetic portion, and a second arithmetic portion. The photodetector detects reflected light from an optical recording medium including a servo area provided with a first wobble mark and a second wobble mark. The amplifier produces a summation signal of the reflected light from a detection signal of the photodetector. The sampling portion samples the summation signal. The first arithmetic portion calculates extremum of the summation signal in the vicinity of reproduction timing for each of the first wobble mark and the second wobble mark from sampling values produced by the sampling portion so as to produce a first extremum and a second extremum. The second arithmetic portion produces a tracking error signal that corresponds to a difference between the first extremum and the second extremum.
This configuration detects the extremum of each reproduction wobble mark by operations with the sampling values of the summation signal in the vicinity of the wobble mark. Therefore, an optimum value always can be obtained, resulting in a high-accuracy tracking error signal.
The first arithmetic portion may include a maximum/minimum sampling value detecting portion, a first estimating portion, and a second estimating portion. The maximum/minimum sampling value detecting portion produces a maximum/minimum of the sampling values in the vicinity of reproduction timing for each of the first wobble mark and the second wobble mark. The first estimating portion estimates a timing of a relative maximum/minimum of the summation signal in the vicinity of reproduction timing for each of the first wobble mark and the second wobble mark by using the maximum/minimum sampling value and its preceding and following sampling values. The second estimating portion estimates a relative maximum/minimum of the summation signal in the vicinity of reproduction timing for each of the first wobble mark and the second wobble mark by using the maximum/minimum sampling value, its preceding and following sampling values, and the timing of the relative maximum/minimum from the first esti
Hashimoto Kiyokazu
Hino Yasumori
Inoue Takashi
Ohyama Hideki
Ueda Eiji
Hindi Nabil
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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