Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-10-30
2003-06-24
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044420
Reexamination Certificate
active
06584049
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No.
1999-47750,
filed Oct. 30, 1999, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device in a signal detecting apparatus that reduces cross talk, and more particularly, to a signal detecting apparatus for improving the precision in detecting a tracking error signal and/or a reproduction signal with crosstalk noise greatly reduced.
2. Description of the Related Art
A conventional method for detecting a tracking error signal (TES) is by differential phase detection (DPD). DPD involves detecting tracking errors by receiving light radiated from a light source of an optical pickup device and reflected from a disk.
Referring to
FIG. 1
, light radiated onto a ROM-type disk is reflected and diffracted into 0th-order maximum and ±1st-order maxima by recording marks such as pits (P). After traveling back to the optical pickup, the light received at a photodetector
1
substantially consists of the 0th-order maximum overlapped by ±1st-order maxima in a radial direction. As shown, for a high-density disk having narrow tracks, such as a next-generation digital versatile disk (DVD) like an HD-DVD, the 0th-order maximum and ±1st-order maxima overlap, while the +1st-order maximum and −1st-order maximum do not overlap each other.
The phase signals for the portions where the 0th-order maximum overlaps with the +1st-order maximum and the −1st-order maximum have different features than the phase signal of the portion that only receives the 0th-order maximum. Thus, a high-density disk having narrow tracks, if a tracking error signal is detected by a general DPD method in which detection signals of diagonal sectional plates A/C and B/D are simply subtracted, there is a lot of noise in the tracking error signal due to crosstalk between adjacent tracks. In order to detect a tracking error signal with reduced crosstalk noise from adjacent tracks, there has been proposed a method in which an 8-sectional photodetector
20
is used to reduce the cross talk using the device shown in FIG.
2
.
As shown in
FIG. 2
, the 8-sectional photodetector
20
is divided into 4 parts the 4 parts are along a row in the radial direction of a disc. Each part is further divided into 2 parts in the tangential direction of a disk to create a 2×4 matrix. As shown, the respective 2-sectional plates A
1
/A
2
, B
1
/B
2
, C
1
/C
2
and D
1
/D
2
correspond to the sectional plates A, B, C and D of the photodetector
21
shown in FIG.
1
. The sectional plates A
2
, B
2
, C
2
and D
2
are located tangentially inward to A
1
, B
1
, C
1
and D
1
, respectively.
The tracking error signal is produced from the detection signals from the 8-sectional photodetector
20
as follows.
Referring to
FIG. 3
, detection signals a
1
and c
1
of outer sectional plates A
1
and C
1
are summed to produce a sum signal (a
1
+c
1
). In addition, detection signals a
2
and c
2
of inner sectional plates A
2
and C
2
are summed and amplified with a predetermined gain k
1
to form amplified summed signal k
1
(a
2
+c
2
). These results are summed to produce the sum signal (a
1
+c
1
+k
1
(a
2
+c
2
)), which is amplified by a predetermined gain k
2
using amplifier
21
.
Likewise, a sum signal (b
1
+d
1
) of detection signals b
1
and d
1
of outer sectional plates B
1
and D
1
and a signal obtained by amplifying a sum signal (b
2
+d
2
) of detection signals b
2
and d
2
of inner sectional plates B
2
and D
2
with a predetermined gain k are summed. Then, the signal (k
2
(a
1
+c
1
+k
1
(a
2
+c
2
))) output from the amplifier
21
and the operation signal (b+d
1
+k(b
2
+d
2
)) output from the diagonal sectional plates B
1
, B
2
, D
1
and D
2
are applied to a phase comparator
25
for comparison of phases, to then generate a tracking error signal TES.
As shown, if k=k
1
=0 and k
2
=1, the signals applied to the phase comparator
25
are a
1
+c
1
and b
1
+d
1
, which corresponds to the case where a phase difference is obtained using a sum signal of detection signals of outer sectional plates arranged in a diagonal direction. Also, if k≠0 and k
1
≠0, the signals applied to the phase comparator
25
are a
2
+c
2
and b
2
+d
2
, which correspond to the case where a phase difference is obtained using a sum signal of detection signals of inner sectional plates arranged in a diagonal direction.
According to the aforementioned tracking error signal detecting apparatus, since a phase difference is obtained by selectively amplifying the detection signals of inner sectional plates A
2
, B
2
, C
2
and D
2
with predetermined gain factors, and then adding the amplified signals and detection signals of outer sectional plates A
1
, B
1
, C
1
and D
1
, a tracking error signal with reduced crosstalk noise can be generated.
Although the conventional tracking error signal detecting apparatus reduces crosstalk noise to a degree, when it is used with a high-density disk having narrow tracks, since the tangential phase characteristics are obscured, the gain of the tracking error signals is very low. Thus, the precision is poor. Basically, the light beams received at the sectional plates positioned at different locations in a tangential direction of a track have different phase characteristics at a starting area and an ending area of a recording mark such as a pit. However, if the detection signals of diagonally adjacent plates are summed as in the conventional tracking error signal detecting apparatus, the tangential phase characteristics are offset, which results in tracking error signals having a low gain and poor precision.
Also, in the conventional tracking error signal detecting apparatus, since the sum signals of detection signals of diagonally adjacent sectional plates are used, a phase difference between the sum signals is offset due to a difference in the depth between pits. Thus, if an objective lens (not shown) is shifted, a large offset may occur to the tracking error signals.
SUMMARY OF THE INVENTION
The present invention has been made in view of the points described above, and it is an object of the present invention to provide a signal detecting apparatus with improvement in gain characteristics and/or offset for reduced crosstalk noise.
It is a further object of the present invention to provide a tracking error signal detecting apparatus with improvement in gain characteristics and/or offset due to a difference in the depth between pits by providing an improved sectioning structure of an 8-sectional photodetector with reduced crosstalk noise.
It is a still further object of the present invention to provide a reproduction signal detecting apparatus with improvement in gain characteristics and/or offset due to a difference in the depth between pits by providing an improved sectioning structure of an 8-sectional photodetector with reduced crosstalk noise.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above object, there is provided a tracking error signal detecting apparatus including a photodetector which receives light reflected/diffracted from a recording medium, and a circuit unit which performs operations on detection signals of the photodetector and produces a tracking error signal, wherein the photodetector includes four light receiving regions arrayed counterclockwise, the dividing lines of which are substantially parallel to the radial and tangential directions of the recording medium, each of the four light receiving regions are further bisected to produce an inner sectional plate and an outer sectional plate, the radial widths of which vary along ± tangential
Chung Chong-sam
Ma Byung-in
Park In-sik
Seo Joong-eon
Hindi Nabil
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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