Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-02
2002-02-05
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044410
Reexamination Certificate
active
06345020
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 98-24154, filed Jun. 25, 1998, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for generating a tracking error signal, and more particularly, to an apparatus and method for adaptively generating a tracking error signal according to a phase error generated due to an irregular pit depth of a disk.
2. Description of the Related Art
A tracking servo of an optical disk is usually controlled by a differential phase detection (DPD) method of detecting a phase difference using a four-element optical detector.
FIG. 1
shows a tracking error signal extraction system using the DPD method. As shown in
FIG. 1
, an optical detector
10
includes four elements A, B, C and D which detect light beams reflected by an optical disk. Among optical detection signals output by the four elements A, B, C and D, the outputs of two elements diagonally located in a track direction are synthesized and applied to a differential amplifier
15
. That is, when diagonal synthesized signals are A+D and B+C, the synthesized signal A+D is input to a (+) port of the differential amplifier
15
, and the synthesized signal B+C is input to a (−) port thereof. Thus, an output signal of the differential amplifier
15
is (A+D)−(B+C).
FIGS. 2A through 2D
illustrate phase relationships between optical detection signals obtained from the elements A through D, respectively, when an optical disk having a uniform pit depth is scanned in a radial direction.
Generally, the optical detection signals output by the elements A and C have the same phase, and likewise for signals output by the elements B and D, whereas the optical detection signals output by the elements A and B and those output by the elements C and D each pair have a difference in phase of &Dgr;&phgr;. Therefore, first and second diagonal synthesized signals (A+D) and (B+C) each include the common phase difference (&Dgr;&phgr;). Also, when the second diagonal synthesized signal (B+C) is subtracted from the first diagonal synthesized signal (A+D), the common phase difference (&Dgr;&phgr;) is deleted. Thus, the phase difference hardly affects a tracking error.
FIGS. 3A through 3C
illustrate phase relationships between optical detection signals obtained from the elements A through D, respectively, when an optical disk having a nonuniform pit depth is scanned in a radial direction.
In the case of the optical disk having a nonuniform pit depth, each pair of the optical detection signals output by the elements A and B and the elements C and D has a phase difference of &Dgr;&phgr;, and further has a group phase difference of &Dgr;&thgr; depending on a pit depth.
The first and second diagonal synthesized signals (A+D) and (B+C) each have different phase errors of &Dgr;&phgr; and &Dgr;&phgr;+&Dgr;&thgr;, so that distortion is generated. Thus, a normal tracking error signal is not obtained.
FIG. 4
is a block diagram showing a configuration of another conventional apparatus for generating a tracking error signal. The apparatus of
FIG. 4
includes first through fourth delays
40
,
42
,
44
, and
46
, first and second adders
48
and
50
, equalizers
52
and
54
, and a phase detector
56
.
The first through fourth delays
40
,
42
,
44
and
46
compensate for an optical signal detected by a four-element optical detector, each using a different delay amount.
The first adder
48
adds optical signals A and D respectively from the first and third delays
40
and
44
and outputs a first diagonal added signal (A+D). The second adder
50
adds optical signals B and C respectively from the second and fourth delays
42
and
46
and outputs a second diagonal added signal (B+C).
The equalizers
52
and
54
equalize the first and second diagonal added signals (A+D) and (B+C) from the first and second adders
48
and
50
, respectively. The phase detector
56
determines a difference between the output signals of the equalizers
52
and
54
and outputs a tracking error signal ((A+D)−(
13
+C)).
Here, the first through fourth delays
40
,
42
,
44
, and
46
delay the optical signals A, B, C and D output by the four-element optical detector, to prevent them from having a phase difference. The delay amount of each of the delays
40
,
42
,
44
and
46
uses a value measured by a system upon initial driving of an optical disk. That is, the system first detects the phase differences between the optical detection signals A, B, C and D of the four-element optical detector, and regulates the delay amount of each of the delays
40
,
42
,
44
and
46
to minimize the phase differences between the optical detection signals A, B, C and D, thereby driving loaded optical disks.
However, the conventional apparatus for generating a tracking error signal as shown in
FIG. 4
requires a complicated algorithm for regulating the delay amounts of the delays
40
,
42
,
44
and
46
, thus increasing a load to the system and power consumption.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an apparatus for adaptively generating a tracking error signal according to a phase error caused by a pit depth.
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.
Accordingly, to achieve the above and other objects of the present invention, there is provided an apparatus for generating a tracking error signal, including a first adder to output a first added signal (A+C) among optical detection signals A, B, C and D output by four respective elements for detecting light beams reflected by an optical disk; a second adder to output a second added signal (B+D) among the optical detection signals A, B, C and D; a multiplexer to receive the optical detection signals A, B, C and D, the first added signal (A+C), and the second added signal (B+D), and to select and output the signals (A+C) and (B+D), A and B, or C and D; a phase detector to determine a difference of the signals output by the multiplexer and output the difference as a tracking error signal and determine whether the tracking error signal is normal; and a selection controller to control selection of the multiplexer according to the result of the determination of the phase detector.
REFERENCES:
patent: 4924455 (1990-05-01), Fujiie et al.
patent: 5703848 (1997-12-01), Hofer
patent: 5812503 (1998-09-01), Minami et al.
patent: 5909416 (1999-06-01), Matsui
patent: 5926445 (1999-07-01), Sasaki et al.
patent: 5956304 (1999-09-01), Supino et al.
patent: 5986999 (1999-11-01), Takahashi
patent: 5991248 (1999-11-01), Hong
patent: 6031799 (2000-02-01), Hwang
Cho Gea-ok
Kim Chun-sup
Psitos Aristotelis M.
Samsung Electronics Co,. Ltd.
Staas & Halsey , LLP
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