Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
1999-04-19
2001-12-25
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S047230, C369S053220, C369S044260
Reexamination Certificate
active
06333902
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 98-13839, filed Apr. 17, 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 optical disc reproduction and more particularly, to a method for generating a land/groove switching signal from pits on a land/groove (POLG) type disc and an apparatus therefor.
2. Description of the Related Art
In general, a read only memory digital video disc (DVD-ROM) has pits on a planar surface as opposed to a groove formed along tracks of the disc. So, the DVD-ROM is called a non-groove type optical disc.
As the need for recording a large quantity of information on an optical disc increases, a high-density recording medium is required. Accordingly, a POLG type optical disc such as a random access memory digital video disc (DVD-RAM), in which pits are formed on lands and grooves of the disc, has been suggested.
In a disc such as a DVD-RAM, information is recorded in the form of sector units. Each sector is roughly divided into a header information region having physical identification data (PID) and a user data region. Accordingly, the header information or user data contained in a radio frequency (RF) signal is read by a pickup and processed separately.
FIGS. 1A and 1B
show the recording pattern of the header information on a DVD-RAM disc. In detail,
FIG. 1A
shows the header information recorded in the first sector of the track and
FIG. 1B
shows the header information recorded in other sectors.
In
FIGS. 1A and 1B
, reference numeral
50
represents a header information region and reference numeral
52
represents a user data region. The header information region
50
is divided into a peak header region
50
a
and a bottom header region
50
b.
The user data region
52
is divided into land and groove regions. A land/groove switching signal, which indicates a switch from a land track to a groove track or from a groove track to a land track, can be generated according to the sequence of the peak header region
50
a
and the bottom header region
50
b.
Because the phase of a tracking error signal changes by 180° when switching from a land to a groove, a disc reproduction apparatus selects the polarity (phase) of the tracking error signal according to the land/groove switching signal. Also, wobbles exist in the user data region
52
. In
FIGS. 1A and 1B
, the wobbles represent wave-like sidewalls of the tracks (lands and grooves), formed between each land and groove. The wobble signal has information about the reference clock signal for controlling the spindle motor and about a channel clock signal for data playback.
FIG. 2
is a block diagram of a conventional land/groove switching signal generating apparatus.
The apparatus of
FIG. 2
includes a pickup (P/U)
602
, a radio frequency amplifier (AMP)
603
, an offset compensator
604
, an eight-to-fourteen modulation (EFM) comparator
606
, an EFM phase-locked loop (EFM PLL)
607
, a header envelope extractor
605
, an amplitude modulation (AM) detector & header region information extractor
608
, a phase comparator
609
and a tracking servo
610
.
The apparatus shown in
FIG. 2
operates as follows. An RF signal, output via a disc
601
, the P/U
602
and the RF AMP
603
, is provided to the offset compensator
604
. The offset compensator
604
removes offset based on the central point of the EFM signal, regardless of whether the signal is from the header information region or the user data region, to output an EFM signal from which the offset has been removed. The EFM signal output from the offset compensator
604
is input to the EFM comparator
606
.
FIG. 3
is a detailed block diagram of the EFM comparator
606
. The EFM comparator
606
includes a first comparator
70
, a low-pass filter (LPF)
72
, a differential amplifier
74
and a gain determiner
76
.
The first comparator
70
compares the EFM signal EFM output from the offset compensator
604
with a slice level Vp which is determined based on a feedback EFM signal EFMS and outputs a binary EFM signal EFMS according to the result of the comparison. That is, if the EFM signal EFM output from the offset compensator
604
is equal to or greater than the slice level Vp, the EFMS signal is output as a logic “1” value. Otherwise, the EFM signal is output as a logic “0” value.
The LPF
72
low-pass filters the feedback signal EFMS output from the first comparator
70
to obtain the average level thereof. Here, the LPF
72
has filtering characteristics corresponding to multiple speeds of the disc
601
. This is because the amplitude and frequency of the EFM signal change according to the reproduction speed of the disc
601
.
The differential amplifier
74
outputs the slice level Vp amplified from the difference between the output of the LPF
72
and a predetermined reference voltage Vref to the negative input terminal of the first comparator
70
and the gain determiner
76
. Here, the predetermined reference voltage Vref represents a slice level when there is no offset. The gain determiner
76
determines the gain of the differential amplifier
74
in proportion to the slice level Vp.
The EFMS signal output from the EFM comparator
606
is input to the EFM PLL
607
.
The EFM PLL
607
outputs a channel clock signal PCLK, whose phase is locked by the EFMS signal and data EFML reproduced by the channel clock signal PCLK, to the AM detector & header region information extractor
608
. Here, the channel clock PCLK, a channel clock signal of the DVD, has a frequency of 29.16 MHz.
Further, the header envelope extractor
605
extracts a head peak signal HEADPK, indicating a peak header region, and a head bottom signal HEADBT, indicating a bottom header region from the RF signal output from the RF AMP
603
, and outputs the extracted signals to the AM detector & header region information extractor
608
. The envelope of the peak header has a peak value higher than the average peak level of the RF signal and the envelope of the bottom header has a peak value lower than that of the average peak level of the RF signal so that the signals HEADPK and HEADBT are generated based on the above. Here, rising edges of the signals HEADPK and HEADBT nearly match with the actual rising edges of the peak header and the bottom header. However, falling edges thereof are delayed from the actual falling edges of the peak header and the bottom header. This is because the signals HEADPK and HEADBT are usually generated by an integration method.
The AM detector & header region information extractor
608
extracts a signal HDPK, accurately indicating a peak header region, and a signal HDBT, accurately indicating a bottom header region, from the signals PCLK and EFML output from the EFM PLL
607
and the signals HEADPK and HEADBT, output from the header envelope extractor
605
, to output to the phase comparator
609
.
The phase comparator
609
compares the phases of the signals HDPK and HDBT and outputs a land/groove switching signal LGSEL indicating the positions of lands and grooves. The land/groove switching signal indicates the position of the track as a groove when the phase of HDPK leads the phase of HDBT. Meanwhile, when the phase of HDBT leads that of HDPK, the land/groove switching signal indicates the position of the track as a land.
The tracking servo
610
performs tracking control while switching the tracking polarity according to the state of the land/groove switching signal. The tracking servo
610
switches the polarity of the tracking error signal according to the land/groove switching signal, hence, accuracy of the land/groove switching signal LGSEL is very important for tracking servo control.
However, the header envelope extractor
605
may output the signals HEADPK and HEADBT in a region outside the actual header region due to unstable tracking control or a disc defect. In this case, the phase comparator
609
of the conventional land/groove switching signal gen
Samsung Electronics., Ltd.
Staas & Halsey , LLP
Tran Thang V.
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