U.S. patent application number 13/214309 was filed with the patent office on 2011-12-08 for apparatus having switchable servo gains and offsets for optical disk drive and method thereof.
This patent application is currently assigned to Mediatek Inc.. Invention is credited to Hsu-Feng Ho, Shun-Yung Wang.
Application Number | 20110299373 13/214309 |
Document ID | / |
Family ID | 34568662 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110299373 |
Kind Code |
A1 |
Ho; Hsu-Feng ; et
al. |
December 8, 2011 |
APPARATUS HAVING SWITCHABLE SERVO GAINS AND OFFSETS FOR OPTICAL
DISK DRIVE AND METHOD THEREOF
Abstract
An apparatus having switchable servo gains and offsets for an
optical disk drive adjusts its gains and offsets through the
coupling of a servo signal and a switch with several changeable
paths. The servo signals are either designated to undergo signal
reduction with respect to a first offset through the switch and
then be output after a first gain unit performed proportional
conversion, or designated to undergo signal reduction with respect
to a second offset and then be output after a second gain unit
performed proportional conversion. The switch is switched on/off in
the light of the working status of the pick-up head, for example,
seeking or tracking, at a data area or at a blank area, and at a
groove area or at a land area, so as to choose different offsets
and gains to have the conversion of the servo signals.
Inventors: |
Ho; Hsu-Feng; (Taipei city,
TW) ; Wang; Shun-Yung; (Chu-Pei City, TW) |
Assignee: |
Mediatek Inc.
Hsinchu City
TW
|
Family ID: |
34568662 |
Appl. No.: |
13/214309 |
Filed: |
August 22, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12468565 |
May 19, 2009 |
8027230 |
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13214309 |
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11837898 |
Aug 13, 2007 |
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12468565 |
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10710416 |
Jul 8, 2004 |
7272085 |
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11837898 |
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Current U.S.
Class: |
369/44.29 ;
G9B/7 |
Current CPC
Class: |
G11B 7/094 20130101;
G11B 7/0941 20130101 |
Class at
Publication: |
369/44.29 ;
G9B/7 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 2003 |
TW |
092132463 |
Claims
1. A method for switching servo gains for an optical disk drive,
the method comprising: determining the location of a pick-up head
on an optical disk based upon a reflective ratio on the optical
disk; outputting a signal after converting a servo signal by a
first gain if the pick-up head is in a tracking status; and
outputting a normalized signal with respect to a level of the
converted servo signal by multiplying the servo signal by a second
gain less than the first gain if the pick-up head is in a seeking
status.
2. The method for switching servo gains for an optical disk drive
of claim 1, further comprising the step of: determining the values
of the first gain and the second gain by means of on-line detecting
the servo signal.
3. The method for switching servo gains for an optical disk drive
of claim 2, further comprising the step of: determining the values
of the first gain and the second gain by means of off-line
detecting the servo signal.
4. A method for switching servo gains for an optical disk drive,
the method comprising: determining a working status of a pick-up
head based upon a reflective ratio on the optical disk; and
selectively processing a servo signal from the pick-up head in
response to the determined working status of the pick-up head,
wherein the servo signal is amplified by a first gain when the
pick-up head is in a tracking status and the servo signal is
amplified by a second gain less than the first gain when the
pick-up head is in a seeking status.
5. The method of claim 4, further comprising outputting a
normalized control signal comprising the servo signal amplified by
the second gain when the pick-up head is in a seeking status.
6. The method of claim 5, further comprising driving the pick-up
head by using the normalized control signal.
7. The method of claim 4, further comprising outputting a control
signal comprising the servo signal amplified by the first gain when
the pick-up head is in a tracking status.
8. The method of claim 4, further comprising selectively adding an
offset to the servo signal in response to the determined working
status of the pick-up head.
9. A method for switching servo offsets for an optical disk drive,
the method comprising: determining the location of a pick-up head
on an optical disk based upon a reflective ratio on the optical
disk; outputting a signal after converting a servo signal by a
first offset if the pick-up head is in a tracking status; and
outputting a normalized signal with respect to a level of the
converted servo signal by multiplying the servo signal by a second
offset less than the first offset if the pick-up head is in a
seeking status.
10. The method for switching servo offsets for an optical disk
drive of claim 9, further comprising the step of: determining the
values of the first offset and the second offset by means of
on-line detecting the servo signal.
11. The method for switching servo offsets for an optical disk
drive of claim 10, further comprising the step of: determining the
values of the first offset and the second offset by means of
off-line detecting the servo signal.
12. A method for switching servo offsets for an optical disk drive,
the method comprising: determining a working status of a pick-up
head based upon a reflective ratio on the optical disk; and
selectively processing a servo signal from the pick-up head in
response to the determined working status of the pick-up head,
wherein the servo signal is amplified by a first offset when the
pick-up head is in a tracking status and the servo signal is
amplified by a second offset less than the first offset when the
pick-up head is in a seeking status.
13. The method of claim 12, further comprising outputting a
normalized control signal comprising the servo signal amplified by
the second offset when the pick-up head is in a seeking status.
14. The method of claim 13, further comprising driving the pick-up
head by using the normalized control signal.
15. The method of claim 12, further comprising outputting a control
signal comprising the servo signal amplified by the first offset
when the pick-up head is in a tracking status.
16. The method of claim 12, further comprising selectively adding
an offset to the servo signal in response to the determined working
status of the pick-up head.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 12/468,565 filed May 19, 2009 which is a
divisional application of U.S. application Ser. No. 11/837,898
filed Aug. 13, 2007 which is a divisional application of U.S. Pat.
No. 7,272,085 filed Jul. 8, 2004, and is based on and claims
priority from Taiwanese Patent Application No. 092132463 filed Nov.
19, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus having
switchable servo gains and offsets for an optical disk device and
the method thereof, and more particularly, to a servo control
system of an optical disk device that makes adjustments in the
gains and offsets according to the working status of the pick-up
head.
[0004] 2. Description of the Related Art
[0005] The more progressive information technology is, the more
versatile the kind of data storage is. In this regard, the optical
disk drive has apparently become an important data storage tool
available on the market. For an optical disk drive to operate, an
electromechanical actuator drives a pick-up head so as to focus
laser beams to be points on an optical disk. Then, any stored
binary data is read and judged by the magnitude of the light rays
received by a photo-detector; meanwhile, the received rays function
as servo control signals for driving the pick-up head. In other
words, the laser points are accurately focused on an adequate
track, using such an optical signal to drive the pick-up head.
[0006] During the seeking process carried out by an optical disk
drive, focus error (FE) signals is interfered with crosstalk that
arises from the motion of the pick-up head along the radial
direction of an optical disk. In other words, a carrier wave is
induced on the FE signal from the interference of a tracking error
(TE) signal. However, during the following or tracking process, the
pick-up head moves from an inner portion to an outer portion along
a spiral groove where data is recorded, thus the TE signal is
almost inactive and the FE signal is free from the interference of
the crosstalk effect on itself.
[0007] It is not feasible to adjust the gain of a conventional
servo loop system for optical disk drives in the light of the
working status of a pick-up head; thus, servo control is usually
unstable, as it hardly converges. For instance, it is impossible to
diminish the gain of the focusing loop system whenever seeking is
underway; as a result, an inadequate response arises from that the
interfering crosstalk signals are mistaken for normal FE signals.
However, if the gain is set to a relatively small value, the
response speed of the focusing loop control is compromised during
the tracking process.
[0008] On the other hand, in regard to an ordinary optical disk,
the reflectivity of a data area is different from that of a blank
area. Hence, the photodetector of the pick-up head detects various
reflective signals while it is passing the aforesaid areas. Data is
saved in both the groove areas and the land areas of a DVD-RAM
disk. Similarly, the reflective signals generated in the groove
areas are different from those generated in the land areas where
refractive indices are lower than the land areas' in terms of their
characteristics. However, it is not also feasible to adjust the
gain and the offset of the conventional servo loop system according
to the position of the pick-up head where a data area or a blank
area exists or where a groove area or a land area exists. By the
same token, the servo control is unstable, as it hardly
converges.
SUMMARY OF THE INVENTION
[0009] The objective of the present invention is to provide an
apparatus having switchable servo gains and offsets for an optical
disk drive and the method thereof, wherein the adjustments of the
servo gains and offsets are depended on the working status of the
pick-up head so as to stabilize the servo loop control system of
the optical disk drive.
[0010] In order to achieve the objective, the present invention is
to provide an apparatus having switchable servo gains and offsets
for an optical disk drive and the method thereof, wherein
adjustments in gains and offsets are achieved through the coupling
of a servo signal and a switch with several changeable paths. The
servo signals are to be either designated to be deducted a first
offset through the switch and then output a converted signal in
proportion to a first gain unit, or designated to be deducted a
second offset, and then output a converted signal in proportion to
a second gain unit. The switch is switched on/off in the light of
the working status of the pick-up head, for example, seeking or
tracking, at a data area or at a blank area, and at a groove area
or at a land area, so as to choose different offsets and gains to
have the conversion of the servo signals.
[0011] The input signal of the switch is a signal that results from
the synthesis and amplification of a track error or a focusing
error with a pre-amplifier. The input signal is subjected to
conversion conducted by the first gain unit or the second gain
unit, and then it is coupled to a controller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be described according to the appended
drawings in which:
[0013] FIG. 1 is a schematic diagram of a servo control system for
an optical disk drive in accordance with the present invention;
[0014] FIG. 2 is a waveform diagram of a TE signal;
[0015] FIG. 3 is a schematic diagram showing that a pick-up head
writes or reads data on an optical disk; and
[0016] FIG. 4 is a waveform diagram of a TE signal in response to a
DVD-RAM disk.
PREFERRED EMBODIMENT OF THE PRESENT INVENTION
[0017] FIG. 1 is a schematic diagram of a servo control system of
an optical disk drive in accordance with the present invention. The
seeking or tracking servo control system 10 of the optical disk
device is equipped with a pick-up head 11 intended to read data
recorded in an optical disk 40. The pick-up head 11 generates a TE
signal or a FE signal that functions as an input signal to the
servo control system 10. The input signal is sent to a
pre-amplifier 12 to have signal synthesis and amplification. With a
switch 19, the amplified control signal is allowed to couple to
either a first gain circuit 17 or a second gain circuit 18; with
the first gain circuit 17, the amplified control signal has a slice
level shift in response to a first offset 131, and then it is
converted at a constant proportion by a first gain unit 141 before
it is output; similarly, with the second gain circuit 18, the
amplified control signal has a slice level shift in response to a
second offset 132, and then it is converted at another constant
proportion by a second gain unit 142 before it is output. The servo
gain may be greater or less than one, or even a negative value.
[0018] The objective of the present invention is to normalize the
input signals of a controller 15 by either the first gain unit 141
or the second gain unit 142, so as to enhance the stability of the
servo control system. The control signal generated by the
controller 15 makes a driver 16 output a driving signal, and the
pick-up head 11 responds after it receives the driving signal.
[0019] According to the present invention, the switch 19 is
switched on/off in light of the working status of the pick-up head
11. Its application to three statuses is as follows:
I. Seeking/Tracking
[0020] If the pick-up head 11 seeks tracks, the seeking or focusing
servo control system makes the switch 19 switch to the second gain
circuit 18 so as to reduce the sensitivity of the servo loop to
noise signals by diminishing its servo gain. Conversely, if the
pick-up head 11 is changed to track tracks, the switch 19 is
switched to the first gain circuit 17, and the servo gain of the
second gain circuit 18 is less than that of the first gain circuit
17.
[0021] The first offset 131 of the first gain circuit 17 and the
magnitude of the gain of the first gain unit 141 can be determined
by a track error or a focusing error intended for actual off-line
detection (the second offset 132 and the gain value of the second
gain unit 142 are determined in the same way). As shown in FIG. 2,
it is a waveform diagram of a TE signal, wherein AP denotes the
peak-to-peak (or crest-to-trough) interval of a TE signal, and M
denotes a slice level, or a DC component. Also, servo control
system designs always entail setting the peak-to-peak interval and
the DC component. AP divided by a default peak-to-peak interval
equals a quotient, and the quotient is designated as the gain of
the first gain unit 141. Furthermore, the difference between the DC
component actually measured and a default DC component is
designated as the magnitude of the first offset 131.
II. Blank Area/Data Area
[0022] If the pick-up head 11 stays in a blank area, the servo
control system makes the switch 19 switch to the second gain
circuit 18 so as to decrease its servo gain. Conversely, if the
pick-up head 11 stays in a data area to read data from there, the
switch 19 is switched to the first gain circuits 17 so as to
increase its servo gain.
[0023] Similarly, the corresponding magnitude of the gains and
offsets can be obtained by the TE signal that is generated by the
pick-up head staying either in the blank area or data area on-line.
The calculating method of the magnitude is the same as the
aforesaid descriptions.
III. Groove Area/Land Area
[0024] FIG. 3 is a schematic diagram showing how a pick-up head
writes or reads data on an optical disk. Optical disks with
ordinary specifications, such as CD-R, DVD-R and DVD-RW, always
have data stored in their groove areas 41. However, DVD-RAM stores
data in both the groove areas 41 and the land areas 42; for its
corresponding TE signal, please refer to the trough 41' and the
peak 42' in FIG. 4. The convergence direction A of the trough 41'
is opposite to the convergence direction B of the peak 42'. Hence,
the gain of the first gain circuit 17 and that of the second gain
circuit 18 have opposite signs, where not only do their offsets
have opposite signs, but also the magnitude of their offsets
differ.
[0025] If the pick-up head 11 is in a groove area 41, the switch 19
is switched to the first gain circuit 17. If the pick-up head 11 is
in a land area 42, the switch 19 is switched to the second gain
circuit 18.
[0026] Digital signal processing (DSP) technique may be applied to
the present invention, that is, the real-time status of a pick-up
head is detected on-line while programs are running, so that
switching occurs automatically in response to the various statuses
mentioned earlier. With a DSP or an analog circuit, the peak and
the trough of the servo signals can be measured so as to figure out
the corresponding offset and gain. In other words, if an optical
drive is at a read or write state, the peak-trough interval and the
DC component determine the magnitude of the offset and the gain, as
far as the real-time calculated TE signal (or FE signal) are
concerned.
[0027] Furthermore, it is feasible to calculate the offset and the
gain in an off-line, such as a free track-locking status and a
focusing servo control status, that is, directly calculate the gain
and the offset of a TE signal or a FE signal, using an open
loop.
[0028] The above-described embodiments of the present invention are
intended to be illustrative only. Numerous alternative embodiments
may be devised by persons skilled in the art without departing from
the scope of the following claims.
* * * * *