Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-07-11
2004-04-06
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S044370
Reexamination Certificate
active
06717897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup apparatus for writing and reading an information signal onto an optical recording medium, an optical disc apparatus for recording and reproducing an information signal for an optical recording medium comprising such optical pickup apparatus, and a track recognition signal detection method for receiving a track recognition signal for receiving a recording track position on this optical disc apparatus. More specifically, the present invention concerns an optical disc apparatus for land-groove recording, and an optical disc apparatus and a track recognition signal detection method used for this optical disc apparatus.
2. Prior Art
Conventionally, an optical recording medium such as an optical disc is proposed. Further, an optical disc apparatus is proposed as an apparatus for recording and reproducing an information signal using such an optical recording medium. The optical disc apparatus uses optical discs based on various methods as optical recording media. This optical disc apparatus uses an optical pickup apparatus to write and read an information signal on the optical disc.
This optical pickup apparatus includes a light source such as a semiconductor laser. The apparatus is so configured that a light beam generated from this light source is condensed and irradiated to the signal recording surface of an optical disc via an objective lens. According to this configuration, the optical pickup apparatus writes an information signal on the signal recording surface by using the light beam irradiated onto the signal recording surface. Further, the apparatus reads the information signal recorded on the signal recording surface by detecting a reflected light beam on the signal recording surface where the light beam is irradiated.
The optical pickup apparatus writes and reads an information signal along lands or grooves which are formed spirally or cylindrically on the signal recording surface of the optical disc.
Presently, optical discs are increasing a recording density for information signals to be recorded. As a read-only ROM disc, for example, a DVR (trade name) is proposed. It uses an optical disc 120 mm in diameter like a compact disc (CD) (trade name) and provides a recording capacity of 4.7 GB which is approximately seven times as large as a 650 MB compact disc.
A recording density is also increasing for rewritable discs which can record and reproduce information signals. Such a rewritable disc is positioned as DVD. There is proposed an optical disc apparatus using a so-called DVD-RAM disc. In order to increase the recording density for information signals to be recorded, this DVD-RAM disc employs the land-groove recording system which records information signals on both a land and a groove, not just on either of them as is the case with a conventional system.
In recent years, the DVR format is developed as an optical disc format for further increasing the recording density. This format uses a shortwave light source with a light emission wavelength of approximately 405 nm and also uses a high NA (numerical aperture) objective lens of 0.85 NA. This format also uses the land-groove recording system.
As typified by the above-mentioned DVD-RAM, a high-density rewritable disc using the land-groove recording system causes the following problems because the land and the groove are set to almost the same width.
There may be the case where the land recording system is used for recording signals only on lands by using an optical disc on which a land is wider than a groove. In this case, as shown in
FIG. 1
, a phase shift occurs by a quarter cycle between a tracking error signal (TE) and a sum signal (SUM) for return beams (or primary spots when the 3-spot technique is used). Thereby, one cycle is assumed to range from a groove to the next groove.
For example, tracking control is performed so that a tracking error signal (TE) becomes 0. This signal becomes 0 in two cases, namely when a light beam is irradiated to a land or to a groove. A level of the sum signal (SUM) can be used for discriminating between these two cases.
A signal is used to discriminate between the case where the light beam is irradiated to the land and the case where the light beam is irradiated to the groove. This signal is called a track recognition signal or a cross-track signal (CTS). When the land recording system is used as mentioned above, sum signal (SUM) levels may greatly differ depending on whether the light beam is irradiated to the land or to the groove. In this case, as shown in
FIG. 2
, it is possible to use a sum signal's alternate current (AC) component (AC-SUM) as the track recognition signal. As shown in
FIG. 2
, the sum signal's AC component forms a track recognition signal with the phase of 90 degrees differing from the tracking error signal.
The land recording system uses two signals: the tracking error signal and the sum signal's AC component. Because of this, even during a fast seek operation, it is possible to accurately determine the direction and the number of tracks traveled by a spot with reference to the recording track. This allows to stably count the number of tracks traveled and perform a tracking servo pull-in operation.
When the land-groove recording system is used, however, the land and the groove are generally set to approximately the same width in order to optimize recording and reproduction characteristics. Consequently, as shown in
FIG. 3
, the sum signals in the above description are generated almost alike independent of whether a light beam is irradiated to the land or the groove. It is impossible to generate a track recognition signal from this sum signal.
When the system records signals only on the land or the groove, a width difference between the land and the groove tends to become narrower according as track pitches decrease along with a demand for a higher recording density. Examples include DVD+RW and DVD-RW. Consequently, it is difficult to generate a track recognition signal from this sum signal.
As a result, it is difficult to access a specified recording track with a single operation during a fast seek operation frequently used for external storage devices, or business-use picture recording and editing apparatuses. There arises the problem of increasing an access time.
In order to solve these problems, Japanese Patent Laid-Open Publication No. 11-45451 discloses a method of receiving a track recognition signal or a cross-track signal (CTS). This method forms two side spots on an optical disc by shifting a quarter track each with reference to a primary spot. A difference between the corresponding push-pull signals is found to generate a signal with a 90-degree phase shifted from a push-pull signal for the primary spot.
In this case, a side spot position causing the maximum tracking error signal is shifted for a half track relative to the primary spot. On the other hand, a side spot position causing the maximum track recognition signal is shifted for a quarter track relative to the primary spot. The tracking error signal and the track recognition signal use different optimum side spot positions. There is the problem that the tracking error signal and the track recognition signal cause a large amplitude variation when an optical disc is remarkably eccentric or when a movement direction of the optical pickup apparatus deviates from the optical disc's radial direction.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical pickup apparatus, a track recognition signal detection method, and an optical disc apparatus using the optical pickup apparatus and the track recognition signal detection method, wherein it is possible to generate a track recognition signal and allow a high-speed access without increasing the number of parts or complicating a configuration of parts even if it is necessary to use an optical recording medium such as DVD-RAM and DVR employing the land-groove recording system.
To solve
Frommer & Lawrence & Haug LLP
Sony Corporation
Tran Thang V.
LandOfFree
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