Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal level detecting using a reference signal
Reexamination Certificate
2001-11-28
2004-01-20
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal level detecting using a reference signal
C369S044130, C369S044250, C369S124150
Reexamination Certificate
active
06680892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical disk device and, more particularly, to an optical disk device reproducing information from an optical disk or recording and reproducing information to/from an optical disk.
2. Description of the Related Art
A write-once optical disk, such as a CD-R (Compact Disk-Recordable), and a DVD-R (Digital Versatile Disk-Recordable), and a rewritable optical disk, such as a CD-RW (CD-Rewritable), a DVD-RW (DVD-Rewritable), a DVD-RAM, and an MO (Magneto Optical disk), are provided with guiding grooves beforehand. In these optical disks, the grooves and lands (parts between the grooves) are determined as tracks. A light beam is projected along these tracks so as to form pits on the tracks; thereby, information is recorded. In this course, a tracking servo used for projecting the light beam along the tracks is controlled such that the center of an optical axis of the light beam coincides with the centerline of the track.
The grooves wobble slightly in a radial direction at a center frequency of 22.05 kHz. Address information (i.e., time information) upon recording, referred to as ATIP (Absolute Time In Pregroove), is multiplexed by an FSK modulation with the maximum excursion of ±1 kHz, and is recorded on the grooves as a wobble signal. This wobble signal has a micro amplitude, and thus, does not interfere with the tracking servo. Additionally, the frequency of the wobble signal is out of a control frequency band of the tracking servo; therefore, the center of the optical axis of the light beam traces the centerline of the track on average.
Accordingly, in an optical disk device, an optical detector, which has a light-receiving surface divided into two in the radial direction of the optical disk, receives the light beam reflected on the optical disk. Then, photoelectric conversion signals of this light-receiving surface divided in two are subjected to a differential amplification so that the wobble signal is detected. Then, a spindle motor is revolved, based on a carrier-wave signal at a frequency of 22.05 kHz of the wobble signal so as to revolve the optical disk at a predetermined revolving velocity. Further, the wobble signal is demodulated so as to detect the address information.
On the other hand, upon reproducing, the light beam is projected on the pits formed on the tracks, while being controlled such that the center of the optical axis of the light beam coincides with the centerline of the track. Then, the optical detector, which has the light-receiving surface divided into two in the radial direction of the optical disk, receives the light beam reflected on the optical disk. Then, photoelectric conversion signals of this light-receiving surface divided in two are added so that a recorded signal is detected. This addition offsets the wobble signal component.
FIG. 1
is a block diagram of an example of a signal reproduction circuit of a conventional optical disk device. In
FIG. 1
, a terminal
10
is supplied with a reproduction RF signal obtained by projecting a light beam from a laser diode of an optical pickup to the optical disk revolved at a predetermined revolving velocity, detecting the reflected light by the optical detector of the optical pickup, and adding the photoelectric conversion signals of the light-receiving surface divided in two. Direct-current components of the reproduction RF signal are removed in a capacitor
11
functioning as a high-pass filter, and the reproduction RF signal is supplied to a noninverting input terminal of a comparator
12
. A fixed reference value is supplied from a reference voltage source
13
to an inverting input terminal of the comparator
12
. The comparator
12
compares the RF signal with the reference value so as to make the RF signal binary. This binary signal is supplied to a PLL (Phase Locked Loop)/detector
16
.
The PLL/detector
16
generates, in a PLL thereof, a clock PCLK synchronized with the supplied binary signal, and outputs the clock PCLK via a terminal
18
. Also, the PLL/detector
16
detects, in a detector thereof, the presence of a reproduction pulse by a detecting window determined based on the clock PCLK so as to discriminately reproduce a signal REFM and output the signal REFM via a terminal
19
.
FIG. 2
is a block diagram of another example of a signal reproduction circuit of a conventional optical disk device. In
FIG. 2
, the terminal
10
is supplied with the reproduction RF signal obtained by projecting the light beam from the laser diode of the optical pickup to the optical disk revolved at a predetermined revolving velocity, detecting the reflected light by the optical detector of the optical pickup, and adding the photoelectric conversion signals of the light-receiving surface divided in two. The direct-current components of the reproduction RF signal are removed in the capacitor
11
functioning as a high-pass filter, and the reproduction RF signal is supplied to the noninverting input terminal of the comparator
12
. A threshold value corresponding to a midpoint potential of the RF signal is supplied from a low-pass filter/amplifier (LPF/AMP)
14
to the inverting input terminal of the comparator
12
. The comparator
12
compares the RF signal with the threshold value so as to make the RF signal binary. This binary signal is supplied to the low-pass filter/amplifier
14
and the PLL/detector
16
.
The low-pass filter/amplifier
14
integrates the binary signal, and thereafter, amplifies the integrated value with a predetermined gain so as to generate the threshold value corresponding to the midpoint potential of the RF signal. Then, the low-pass filter/amplifier
14
supplies the threshold value to the comparator
12
. The comparator
12
and the low-pass filter/amplifier
14
form an asymmetry correction circuit, which determines the threshold value such that high-level periods and low-level periods of the binary signal become equal in total. A response characteristic of this asymmetry correction circuit is optimized by adjusting a time constant and a gain of the low-pass filter/amplifier
14
, an amplitude of the RF signal, and an output voltage of the comparator
12
.
The PLL/detector
16
generates, in the PLL thereof, the clock PCLK synchronized with the supplied binary signal, and outputs the clock PCLK via the terminal
18
. Also, the PLL/detector
16
detects, in the detector thereof, the presence of a reproduction pulse by the detecting window determined based on the clock PCLK so as to discriminately reproduce the signal REFM and output the signal REFM via the terminal
19
.
By the way, the light beam projected from the laser diode has different powers as a write power and a read power; therefore, the optical axis may possibly be displaced. In
FIG. 3
, the light beam as the read power is projected from the laser diode as indicated by solid lines, and the light beam as the write power is projected from the laser diode as indicated by broken lines. Therein, the optical axis is displaced by an angle &thgr;. When the optical axis is displaced in a widthwise direction of the groove, pits recorded by the write power are displaced from the centerline of the track, as shown in
FIG. 4
, because, even upon recording, a tracking error signal is generated at a read-power timing. Additionally, there are other cases in which, for example, the pits are displaced from the centerline of the track, due to remaining heat of the adjacent track after the completion of a recording.
When the groove is used as a track, and the light beam is projected, with the optical axis thereof being displaced from the centerline of the groove, the light beam comes near to the centerline of the groove or goes far away from the centerline of the groove, depending on a wobbling cycle, because the groove wobbles as described above. When the light beam is projected near the centerline of the groove, the recording becomes normal. However, when the light beam is projected far away from the centerline of the groove, the
Anderson Kill & Olick
Edun Muhammad
Lieberstein Eugene
Meuer Michael N.
Teac Corporation
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