Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2000-09-22
2001-10-09
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053280, C369S053230, C369S044260, C369S044270, C369S044350, C369S044410
Reexamination Certificate
active
06301212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focusing and tracking servo circuit used in an optical disk device, and, more particularly, to a focusing and tracking servo circuit that performs recording and reproduction on a rewritable optical disk.
2. Description of the Related Art
There are two types of recording optical disks: one is a writing once type, and the other is a rewritable type. A CD-R (Compact Disk Recordable), which is a writing once optical disk, and a CD-RW (Compact Disk Rewritable), which is a rewritable optical disk, are both provided with a pregroove for guiding. Such a pregroove is very slightly wobbled in the radial direction with a center frequency of 22.05 kHz. Address information called ATIP (Absolute TimeIn Pregroove) for recording is multiplexed by FSK (Frequency Shift Keying) modulation with a maximum shift of ±1 kHz, and recorded on the pregroove.
A focusing and tracking circuit used in an optical disk device that performs recording and reproduction on such a recording optical disk emits optical beam on the optical disk, detects the reflection light from the optical disk by a plurality of detectors, generates a focusing and tracking error signal by performing a predetermined arithmetic operation, and drives a focusing and tracking actuator based on the focusing and tracking error signal.
In an optical disk device that performs recording and reproduction on a CD-R, which is a writing once optical disk, light beam power is used as read power at a time of reproduction. At a time of recording, the light beam power is switched between write power and read power (write power>read power) in accordance with the value 0 or 1 of a recording signal. Accordingly, at a time of recording as well as reproduction, the reflection light is sampled at the timing of the light beam power being switched to the read power, thereby generating a focusing and tracking error signal.
In an optical disk device that performs recording and reproduction on a CD-RW, which is a rewritable optical disk, the light beam power is switched between write power and erase power (write power>erase power>read power) at a time of recording, in accordance with the value 0 or 1 of the recording signal. Accordingly, at a time of reproduction, the reflection light is detected at the timing of the light beam power being switched to the read power, thereby generating the focusing and tracking error signal. On the other hand, at a time of recording, the reflection light is sampled at the timing of the light beam power being switched to the erase power, thereby generating the focusing and tracking error signal.
Since the erase power has a higher output than the read power, the servo gain varies with the power. Therefore, it is necessary to change the sensitivity of each detector and the servo gain for recording and reproduction.
FIG. 1
is a block diagram of a conventional detector sensitivity switching circuit. This circuit is disposed inside a head amplifier IC. As shown in
FIG. 1
, a detector that detects a main light beam spot is divided into four detectors
10
A to
10
D, a detector that detects a preceding sub beam spot is divided into two detectors
10
E and
10
F, and a detector that detects a following sub beam spot is divided into two detectors
10
G and
10
H.
The head amplifier IC performs serial data transfer in order to reduce the number of pins. In compliance with a recording command or a reproduction command that instruct to switch between recording and reproduction, data SDATA consisting of address data and parameter data for setting detector sensitivity is serially transferred from a host device, and then stored in a shift register
12
at the timing of a clock signal SCK. An address decoder
14
decodes the address data stored in the shift register
12
, and transmits a write enable signal to one of detector sensitivity registers
16
A to
16
H corresponding to the address. The detector sensitivity register (
16
B, for instance) that has received the write enable signal stores the parameter data supplied from the shift register
12
. Thus, the detector sensitivity of the detector (
10
B, for instance) corresponding to the detector sensitivity register (
16
B, for instance) can be switched.
Since the parameter data is serially transferred, a certain period of time is required until the detector sensitivities of all the detectors
10
A to
10
H are switched.
FIG. 2
shows the switching timing of detector sensitivity in the prior art. Based on the ATIP information (timing information) of a wobble signal reproduced from the disk, a write gate is opened by a signal processing circuit, and recording is started. As shown in
FIG. 2
, the detector sensitivities of the detectors
10
A to
10
H are serially switched immediately before and after the opening of the write gate. As a result, there is a problem that the focusing servo and tracking servo become unstable.
This problem also arises in a case where the servo gain of the focusing and tracking servo is switched. While the servo gain is serially switched, the focusing servo and tracking servo become unstable. Furthermore, the offset varies with the switching of servo gain. If the switching of servo gain and the switching of offset are nor performed at the same time, the focusing servo and tracking servo become unstable.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide a focusing and tracking servo circuit in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a focusing and tracking servo circuit that maintains stability in the focusing and tracking servo at a time of switching between recording and reproduction.
The above objects of the present invention are achieved by a focusing and tracking servo circuit used in an optical disk device, which performs recording by increasing light beam power applied onto an optical disk, and performs focusing and tracking servo. This focusing and tracking servo circuit comprises:
a detector unit that detects the light beam reflected from the optical disk;
a first storage unit that stores a parameter corresponding to light beam power at a time of recording;
a second storage unit that stores a parameter corresponding to light beam power at a time of reproduction; and
a selector unit that selects from the parameters stored in the first and second storage units in upon switching between recording and reproduction.
In the above focusing and tracking servo circuit, the selected parameter is set in the detector unit or in a corresponding one of a tracking servo gain switching unit, a tracking servo offset switching unit, a focusing servo gain switching unit, and a focusing servo offset switching unit.
Since the parameters selected from those stored in the first and second storage units at a time of switching between recording and reproduction are set in the detecting unit or in the focusing and tracking servo circuit, the parameters can be instantly switched at the same time as the switching between recording and reproduction, and stability can be maintained in the focusing and tracking servo.
In the above focusing and tracking servo circuit of the present invention, each of the parameters may be a detection sensitivity of the detector unit.
Also, in the above focusing and tracking servo circuit of the present invention, each of the parameters may be a servo gain and offset of the focusing and tracking servo circuit.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4853915 (1989-08-01), Takasago et al.
patent: 5757748 (1998-05-01), Kiyoura et al.
patent: 5867463 (1999-02-01), Chiba
Kubo Mitsumasa
Otsuka Yoshiyuki
Anderson Kill & Olick P.C.
Hindi Nabil
Teac Corporation
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