Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-11-25
2001-01-23
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044250, C369S044340, C250S201500
Reexamination Certificate
active
06178145
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a disk reproducing system such as a CD player, CD-ROM, DVD-ROM, and more particularly to a focus servo control circuit used in a DVD system.
A disk reproducing system used in an audio/visual device or computer peripheral device is constructed as shown by a system diagram of
FIG. 1. A
beam emitted from a laser pickup (PU)
12
is applied to a pit string on a disk
11
rotated by a disk motor
13
and a beam reflected therefrom is converted into an electrical signal (RF signal) by use of an optical element such as a photodiode to obtain pit data. The converted RF signal is amplified by an RF amplifier
15
. The amplified RF signal is binary-coded into a digital signal and then supplied to a PLL (Phase Lock Loop) circuit in a data extraction circuit
26
.
In the PLL circuit, a bit clock signal extracted with a data signal used as a reference is created. The data signal is processed together with the bit clock signal in a signal processing circuit
26
. The signal processing circuit
26
is a circuit for receiving the data signal and effecting the processes of synchronization pattern detection, data demodulation, and error correction by use of a correction RAM
27
and video/audio data or computer data can be output to the exterior only after it is subjected to the above processes.
Referring to
FIG. 1
, a system associated with the focus servo control circuit is explained. A signal read out from the disk
11
by use of the pickup
12
is input to the RF amplifier (RF AMP)
15
and a tracking error signal TE, focus error signal FE and RF signal which is an information signal are derived from the RF amplifier
15
.
The tracking error signal TE is input to a tracking servo control circuit
16
, the gain and phase thereof are compensated for and the seek control or the like is effected. An output signal of the tracking servo control circuit
16
is input to an actuator driver
19
to drive the tracking actuator of the pickup
12
. Further, an output signal of an output equalizer of the tracking servo control circuit
16
is also supplied to a feed motor control circuit
17
to drive a feed motor
14
via a motor driver
18
.
The focus error signal FE is input to a focus servo equalizer
21
via a servo ON/OFF switch
20
. An output signal of the focus servo equalizer
21
is added to a generation signal of a lens drive signal generating circuit
23
and the result of addition is supplied to a focus actuator driver
22
. Then, it is supplied to drive the focus actuator of the pickup
12
.
The RF signal is supplied to a data extraction circuit and CD/DVD data signal processing circuit
26
, binary-coded in the data extraction circuit, then demodulated after a bit clock and synchronizing signal are extracted, and subjected to the correction process by use of the correction RAM
27
. The synchronizing signal is supplied to a disk motor control circuit
24
to control a disk motor
13
via a disk motor driver
25
.
Data corrected in the data signal processing circuit
26
is supplied to an MPEG video/audio decoder processing circuit
28
in the case of DVD movie and a video signal or audio signal is output from the circuit. In the case of DVD-ROM, output data from the data signal processing circuit
26
is supplied to a data buffer circuit
28
and data is output therefrom as digital data to a host personal computer or the like. A system controller
29
controls the control timings of the various control circuits and the operation of the whole set.
FIG. 2
is a timing diagram showing the movement of a beam spot (lens) and the movement of various signals at the time of movement between layers (which is hereinafter referred to as layer jump). In
FIG. 2
, D indicates a distance between the first and second layers and is approx. 55 &mgr;m, for example, in the case of DVD system. (A) indicates a case wherein the direction of the surface deviation of the disk is the same as the moving direction (upward direction in this example) of the beam spot. The speed of the beam spot in the layer direction is relatively low with respect to the disk surface.
(B) and (C) indicate cases wherein the direction of the surface deviation of the disk is opposite to the moving direction (downward direction in this example) of the beam spot. The speed of the beam spot in the layer direction is relatively high with respect to the disk surface.
Thus, since the moving speed condition of the beam spot is changed depending on the position even on the same disk, the layer jump may fail sometimes when the focus servo is turned ON again on the layer of the destination. In
FIG. 2
, (A) and (B) show the successful case and (C) shows the failure case. In the case of (C), the beam spot is separated from the layer of the destination.
However, the layer jump operation of the focus servo is an extremely important operation in the DVD system, and since only two layers are provided, it cannot be settled on the other layer in the case of failure of the layer jump unlike the track jump of the tracking servo. As a result, the result of failure becomes serious. Further, in the case of failure, since the central control unit is required to restore the servo to the initial state and effect the operation starting from the focus search, it takes a long time to recover the operating state. Whether the phenomenon occurs or not is determined by the surface deviation distance and rotation speed.
From the above points, it is desired to enhance the accuracy of the layer jump operation.
BRIEF SUMMARY OF THE INVENTION
A first object of this invention is to provide a disk reproducing system and a focus servo control system of a DVD system capable of forcedly holding a focus error signal and forcedly returning a beam spot to the target layer even in the case of failure of the layer jump in order to enhance the reliability when the beam spot is layer-jumped between plural layers.
A second object of this invention is to provide a disk reproducing system and a focus servo control system of a DVD system capable of attaining stable layer jump by applying the brake before the actual focus position even in a case wherein the relative speed of a beam spot and a disk is largely changed when the disk having large surface deviation is used.
In order to attain the first object, a focus control system according to a first aspect of this invention which is a focus servo control system for selectively applying a light beam to a disk on which data is recorded on plurally layered recording surfaces and focusing a focus position of the light beam on a selected one of the plurally layered recording surfaces based on a signal read from reflected light from the selected one of the plurally layered recording surfaces of the disk, comprises a focus error detector for detecting a positional difference between the focus position of the light beam and the selected one of the plurally layered recording surfaces; a sample-hold circuit for sampling and holding an output of the focus error detector; a focus position correcting circuit for correcting the focus position of the light beam based on one of the output of the focus error detector and an output of the sample-hold circuit; a data signal level detector for detecting a signal level relating to data read out from the disk; a first comparator for comparing the signal detected by the data signal level detector with a predetermined level to output a result of comparison; and a selector for selecting one of the output of the focus error detector and the output of the sample-hold circuit as an input signal of the focus position correcting circuit based on the output of the first comparator.
A disk reproducing system according to a second aspect of this invention which is a disk reproducing system for selectively applying a light beam to a disk on which data is recorded on plurally layered recording surfaces and reproducing the data based on a signal read from reflected light from a selected one of the plurally layered recording surfaces of the disk, comprises a pickup for
Hayashi Yasuhiro
Maeda Satoru
Tamura Masayuki
Edun Muhammad
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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