Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
1999-01-20
2004-08-24
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
C369S116000
Reexamination Certificate
active
06781937
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to methods and devices for optical disk recording based on a mark-length recording scheme, which irradiate a laser light beam onto a recording surface of an optical disk to form pits and lands therein representing desired information. More particularly, the present invention relates to an optical disk recording device and method which achieve improved quality or characteristics of recording signals, such as reduced jitter and deviation and a lower error Irate, when information is recorded at a higher speed than a normal (or one-time) speed or when information is recorded at high density.
The CD-WO (Compact Disk-Write Once) standard, sometimes called an “orange book standard”, is among various known schemes for recording on writable optical disks. According to the CD-WO standard, desired information is recorded in combinations of pits and lands (i.e., portions between the pits) using a “3T-11T” format: “1T” represents a time length of 231.3 ns. (={fraction (1/4.3218)} MHz) in a normal-speed (one-time-speed) recording mode, ½ of the normal-speed time length in a double-speed recording mode, ¼ of the normal-speed time length in a quadruple-speed recording mode, ⅙ of the normal-speed time length in a six-times-speed recording mode. As shown in
FIG. 2
, a laser light beam to be used for recording on a CD-WO (or CD-R) disk is set to a top or recording power level or value, i.e., a high level capable of recording information, for each pit-forming section and set to a bottom or reproducing power value, i,e, a low capable of reproducing information but incapable of recording information, for each land-forming section. If, in this case, the laser light beam continues to be held at the top power level over a time period corresponding exactly to a desired length of a pit, the actual length of the formed pit undesirably tends to be longer than the desired length by about 1T due to residual heat of the laser light. To avoid this inconvenience, there has been employed a laser power modulation called a “(n−K)T+&agr;(nT)” recording strategy, in accordance with which the duration of each top power irradiation, intended for formation of a pit, is made shorter than a desired length nT of a pit to be formed by about a length of K×T (K is a constant). Here, “&agr;(nT)” represents an amount of fine adjustment per pit length which is to be added to each pit-forming top power irradiation period to delay termination of the top power irradiation, and is set in accordance with the following relationship:
&agr;(3T)≧&agr;(4T)≧&agr;(5T), . . . ,≧&agr;(11T)
(&agr;(3T)>&agr;(11T))
As another example of the laser power modulation, there has been proposed a “(n−K)T+&agr;(nT)−&bgr;(mT)” recording strategy, where the duration of each top power irradiation is modified in accordance with a desired length nT of a pit to be formed and a length of a preceding land. Here, “K” is a constant. “&agr;(nT)” represents an amount of fine adjustment per pit length which is to be added to the end of each top power irradiation period to delay termination of the top power irradiation, and at least
&agr;(3T)≧&agr;(4T)≧&agr;(5T), . . . ,≧&agr;(8T)
(&agr;(3T)>&agr;(8T))
Further, “&bgr;(mT)” represents an amount of fine adjustment for each preceding land's length which is to be added to the beginning of each top power irradiation period to delay a start of the top power irradiation, and at least
&bgr;(3T)≧&bgr;(4T)≧&bgr;(5T), . . . ,≧&bgr;(8T)
(&bgr;(3T)>&bgr;(8T))
Furthermore, the assignee of the present application has proposed another form of recording power modulation in Japanese Patent Application No. HEI-8-233596, in accordance with which the top power level or value is increased by 1 mW for a 5T period at the beginning of each pit-forming top power irradiation period, as shown in
FIG. 3
, to thereby minimize unwanted jitter and pit deviation (i.e., deviation from predetermined or accurate pit lengths).
Time resolution (i.e., smallest time-variable amount) of the above-mentioned fine adjustment amounts &agr;(nT) and &bgr;(mT) depends on an oscillation frequency of a crystal oscillator employed. For example, where a crystal oscillator of a 33.8 MHz oscillation frequency is used to generate 276-MHz clock pulses through electric circuit processing of “33.8×4×(98/96)×2”, there is achieved a time resolution of 1/276 MHz=3.6 ns. Such time resolution may be sufficient at low recording speeds; however, as the recording speed is increased, the length of 1T becomes smaller and hence the ratio of the time resolution relative to the 1T time length becomes considerably greater. Thus, in the prior art, it was not possible to set the fine adjustment amounts &agr;(nT) and &bgr;(mT) such that the jitter, deviation and error rate fall within permissible ranges.
For instance, when recording is effected in the six-times-speed recording mode, the time length of 1T is 38.55 ns. (231.3 ns./6), and the 3.6 ns. time resolution amounts to 3.6/38.55=0.09 T; that is, the fine adjustment amounts &agr;(nT) and &bgr;(mT) in this case can be set in steps of 0.09T.
FIGS. 4 and 5
show measurements of jitter in a 3T land and deviation of a 3T pit when recording was effected with this time resolution, on an optical disk containing phthalocyanine and made by a certain manufacturer, in the six-times-speed recording mode using the laser power modulation of
FIG. 3
with a basic strategy of “(n−0.2)T+(n)−0.09T”. In
FIGS. 4 and 5
, curve A represents a characteristic when &agr;(3T) was set to “0”, curve B represents a characteristic when &agr;(3T) was set to “0.09T” and curve C represents a characteristic when &agr;(3T) was set to “0.19T”. Horizontal axis &bgr;(%) represents a standardized parameter for asymmetry of reproduced waveform which is different from the fine adjustment amount &bgr;(mT).
It is required that the jitter of the 3T land be 35 or less in a 0-8% range of the parameter &bgr;(%) and the deviation of the 3T pit be 40 or less in the 0-8% range of the parameter &bgr;(%). In the example of
FIG. 4
, the 3T-land's jitter condition was optimized when &agr;(3T) was “0.19T” (curve C); however, in the example of
FIG. 5
, the 3T-pit's deviation exceeded the upper allowable limit of 40. Further, when &agr;(3T) was “0.09T” (curve B), the 3T-pit's deviation fell within the permissible range but the the 3T-land's jitter proved considerably less favorable than when &agr;(3T) was “0.19T” (curve C).
With the prior art, it was not possible to set the fine adjustment amounts &agr;(nT) and &bgr;(mT) that optimize the jitter, deviation, error rate, etc., because the time resolution of the adjustment amounts &agr;(nT) and &bgr;(mT) would become lower as the recording speed is raised, as stated above. The fine adjustment amounts &agr;(nT) and &bgr;(mT) may be set to optimum values by raising the oscillation frequency of the crystal oscillator to thereby provide higher time resolution; however, raising the oscillation frequency of the crystal oscillator would undesirably lead to a higher cost of the device.
The adjustment amounts &agr;(nT) and &bgr;(mT) in the aforementioned “(n−K)T+&agr;(nT)” and “(n−K)T+&agr;(nT)−&bgr;(mT)” recording strategies are intended to achieve improved quality of recording signals, such as less jitter, by canceling errors that would be caused, at the beginning or fore end of the pits (i.e., the rear end of the lands) and at the rear end of the pits (i.e., the beginning of the lands), due to a difference in the amount of heat flowing from a preceding recorded portion. However, modulation by the adjustment amounts &agr;(nT) and &bgr;(mT) alone could not provide a sufficiently improved quality of recording signals; rather, the recording signal quality would be deteriorated as the pits and lands are made smaller in length such as in high-density recording.
SUMMARY OF THE INVE
Tran Thang V.
Winthrop LLP Pillsbury
Yamaha Corporation
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