Error detection/correction and fault detection/recovery – Pulse or data error handling – Error count or rate
Reexamination Certificate
2000-01-31
2003-04-29
Baker, Stephen M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error count or rate
C369S053130, C369S116000
Reexamination Certificate
active
06557126
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
This invention relates generally to disk drive systems. More particularly, this invention relates to a method and apparatus for determining an amount of power at which to write information to an optical disk.
BACKGROUND OF THE INVENTION
Personal computers typically connect to an optical disk drive such as a CD-ROM to read data from a compact disk. On the compact disk, data is stored in the form of pits and lands patterned in a radial track. The track is formed in one spiral line extending from the inner radius of the disk to the outer edge. A pit is a location on the disk where data has been recorded by creating a depression in the surface of the disk with respect to the lands. The lands are the areas between the pits in the tangential direction. The reflectivity of the pits is less than the reflectivity of the lands. To store audio or digital information, the length of the pits and lands are controlled according to a predefined encoding format.
When reading information from the disc, light from a laser beam is directed onto the track and the light beam is reflected back to a photo-sensor. Since the pits and lands have different reflectivity, the amount of reflected light changes at the transitions between the pits and the lands. In other words, the encoded pattern of the pits and lands modulates the reflected light beam. The photo-sensor receives the reflected light beam, and outputs a modulated signal, typically referred to as an RF signal, that is proportional to the energy of the light in the reflected light beam.
In
FIG. 1
, relationship of the RF signal to the pits
26
and lands
28
is shown. A smaller pit
26
or land
28
decreases both the period and the amplitude of the RF signal. The RF signal in the pits
26
and lands
28
has opposite polarity.
One encoding format used in optical disk systems is eight-to-fourteen modulation (EFM). EFM reduces errors by minimizing the number of zero-to-one and one-to-zero transitions. In other words, small pits are avoided. A zero is indicated by no change in the energy of the reflected beam for at least two clock periods. A one is indicated by a change in the energy of the reflected light beam, that is, a pit edge. Applying the EFM encoding rules, a pit or land will have a length corresponding to an amount of time for at least three and up to eleven clock periods and the electronics will output a corresponding voltage as shown in FIG.
1
.
When reading data, the RF signal needs to be decoded into a serial digital data signal. In one circuit, to decode the analog RF signal, a comparator compares the RF signal to a reference voltage to generate a digital data signal.
To write data to a CD-Recordable (CD-R) or a CD-Rewritable (CD-RW) disk, power is supplied to the laser which heats and melts a portion of the disk surface to create the pits. The optimum amount of power to supply to the laser depends on the characteristics of the disk, the optics, the laser, the temperature and the recording speed. The amount of write power is determined for each combination of recorder and recording speed at the time of recording.
When reading recorded data, the RF signal may be asymmetrical with respect to a predetermined reference voltage. For data written at different amounts of write power, when read, the amount of asymmetry in the corresponding RF signal varies in accordance with the amount of write power. To determine the optimum write power, random EFM data is recorded at different write powers. The recorded data is read back and the asymmetry of the data written at each write power is measured based on the peak voltage levels of the analog RF signal.
In
FIG. 2
, three RF signals
30
-
1
,
30
-
2
,
30
-
3
are shown. The data associated with each RF signal
30
was recorded at different write power levels. A line
36
representing a reference voltage is also shown. The highest peaks A
1
represent the RF signal at a land, while the lowest peaks A
2
represent the RF signal at a pit. Each waveform also shows the corresponding peak levels A
1
and A
2
for each waveform. Waveform one
30
-
1
was written at a write power much less than an optimum power level. Waveform two
30
-
2
was written at a write power equal to the optimum power level. Waveform three
30
-
3
was written at a write power much greater than the optimum power level.
Ideally, in a CD-R disk drive, the asymmetry is measured in terms of a parameter called Beta &bgr; which is the difference between the peak levels A
1
and A
2
of the analog RF signal normalized to the peak-to-peak value. In other words, Beta &bgr; is defined in accordance with relationship one as follows:
β
=
(
A
1
+
A
2
)
(
A
1
-
A
2
)
(
1
)
The optimum write power is associated with the value of Beta &bgr; closest to or equal to zero. A peak-bottom-hold circuit supplies digital values of the peak voltages, A
1
and A
2
, to a processor which determines the value of Beta in accordance with relationship one, above.
In practice, in a CD-R disk drive, the value of Beta &bgr; is determined in accordance with relationship two as follows:
β
=
(
P
+
B
-
2
V
REF
)
(
P
-
B
)
(
2
)
where P is the peak voltage, B is the bottom voltage. To provide a valid measure of Beta &bgr;, the peak and bottom values should not have any DC bias. To measure the amount of DC bias in the peak and bottom signals, a low-pass filter filters the RF signal to provide a value V
REF
representing the DC bias. To remove the DC bias, in the numerator, V
REF
is subtracted twice—once from the peak value P and once from the bottom value B.
Ideally, in a CD-RW disk drive, a parameter called Gamma &ggr; is used to determine the optimum write power, rather than Beta &bgr;. Gamma &ggr; is the normalized slope of the modulation amplitude m of the RF signal with respect to write power Pw. The modulation amplitude m of the RF signal is determined in accordance with relationship three as follows:
m
=
I
11
I
top
.
(
3
)
I
11
is equal to the peak-to-peak value of the RF signal at the lowest predetermined frequency. I
top
is the envelope of the I
11
“high” signal levels of the RF signal. The envelope is provided by a 100 Hz low-pass filter. The normalized slope of the modulation amplitude m with respect to the write power, that is, Gamma &ggr;, is determined in accordance with relationship four as follows:
γ
=
(
∂
m
∂
WritePower
)
·
(
WritePower
m
)
.
(
4
)
In practice, the modulation amplitude m for data written at each write power is determined in accordance with relationship five as follows:
m
=
(
PeakAverage
-
Bottom
)
(
Peak
-
Bottom
)
.
(
5
)
Peak is the largest peak value of the RF signal; Bottom is the lowest value of the RF signal; and, Peak Average is the average of the peak values for the data. The slope of the modulation amplitude m with respect to the write power, that is, Gamma &ggr;, is determined in accordance with relationship six as follows:
γ
=
(
Δ
m
m
)
(
Δ
WritePower
)
WritePower
.
(
6
)
Data is written consecutively at increasing levels of write power. The change in modulation amplitude (&Dgr;m) is the difference in modulation amplitude m between data written at consecutive write power levels. The change in Write Power (&Dgr;Write Power) is the difference between consecutive values of write power.
After determining Gamma &ggr; for a predetermined number of write power levels, the value of Gamma ‘&ggr;’ that is closest to the value of a predefined Gamma-target &ggr;
target
is identified. The value of the write power P
target
associated with Gamma ‘&ggr;’ is determined. The optimum write power P
WO
and erase power P
EO
are determined in accordance with relationships seven and eight, respectively, as follows:
P
WO
=&rgr;·P
target
(7)
P
EO
=&egr;·P
WO
(8)
The symbol &rgr; is a predefined multiplication factor to determine the optimum write power P
WO
, and &egr; is the erase/write power ratio. The values of &ggr;
target
, &rgr; and &egr; are predefine
Baker Stephen M.
Oak Technology, Inc.
Pennie & Edmonds LLP
LandOfFree
Method and apparatus for calibrating write power does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for calibrating write power, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for calibrating write power will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3040193