Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal level detecting using a reference signal
Reexamination Certificate
2002-01-15
2004-06-29
Hindi, Nabil (Department: 2655)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal level detecting using a reference signal
C369S047220, C369S047280
Reexamination Certificate
active
06757233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technical field of a pre-pit detecting device for detecting pre-pits as pre-information formed on a high density recording medium such as DVD-R (DVD-Recordable) or DVD-RW (DVD-Rerecordable). Especially, the invention relates to a technical field of a pre-pit detecting device capable of setting a binarizing level for generating pre-pit signals to an optimum one.
2. Description of Prior Art
Generally, on a recordable optical recording medium (disc), or a reference signal to generate address information and a clock signal for a use of recording and reproducing operation is recorded in advance in form of pre-pits or pre-groove on the optical record information in which record information is not recorded yet. For example, on DVD-R (Digital Versatile Disc-Recordable), a pre-groove, which is an area where information to be originally recorded such as video data or audio data is recorded as recording pits, and pre-pits (hereinafter referred to LPP (Land pre-pit)) on a land portion, which is an area between the pre-grooves, are recorded.
The pre-groove is slightly wobbled in the radius direction of the disc with a frequency (hereinafter referred to wobbling frequency) based on a reference clock used for rotate control of DVD-R. In the rotate control, the wobbling frequency is detected, and a feedback control is performed so that the wobbling frequency matches the frequency of the reference clock.
The LPPs are detected as follows: First, reflected light of a light beam applied to the pre-groove is received in a photo receiving unit, which is divided in two by a parting line at least optically parallel to the direction of a tangent to the pre-groove. Then, a difference signal (hereinafter referred to radial push-pull signal) is generated by computing a difference between a first readout signal and a second readout signal generated on the basis of electrical signals outputted from the photo receiving unit. The radial push-pull signal is compared with a predetermined binarizing level by an LPP signal binarizing circuit, so that a binarized signal (hereinafter referred to LPP signal) is generated. In accordance with the LPP signal detected by the above-mentioned processes, address information indicating the position of recording/reproducing on the recording medium, a recording clock signal for a use of recording operation and the like are generated.
The radial push-pull signal is a composite signal where the LPP is piggybacked onto the wobbling frequency components because of wobbling of the pre-groove in the direction of a radius of the disc as described above.
However, in a disc where information is recorded in high density such as DVD-R, there is a case where crosstalk between wobbling signal components of a pre-groove and those of adjacent pre-groove to which a light beam applies is occurred.
In the case where the crosstalk is occurred, interference between the wobbling signal components in the composite signal obtained as the radial push-pull signal and those of the adjacent pre-groove, is occurred, so that the amplitude of the wobbling signal is changed.
Therefore, the LPP signal components are piggybacked onto the wobbling signal, and the amplitude of the wobbling signal which becomes a base line voltage is changed, so that it is difficult to compare the radial push-pull signal with a fixed binarizing level in order to detect the LPP signal as a binarized signal.
An optimum value of a slice level such as the binarizing level differs according to uses of the LPP signal, for example, the generation of the address information or the generation of the recording clock signal. For the generation of the recording clock signal, it is enough to obtain a cycle of the LPP, so that it is unnecessary to detect the whole of the LPPs piggybaked onto the wobbling signal. However, binarizing noise components to obtain pseudo-LPP signal adversely affects the detection of the cycle, so that it is preferable that the binarizing level is as high as possible to make noise components reduce.
For the generation of the address information, if there are pseudo-LPP signals due to noise components more or less, it is preferable that the LPP signals piggybacked onto the wobbling signal are reliably detected. If proper LPP signals are reliably detected, it is possible to find and eliminate the pseudo-LPP signals. Therefore, it is preferable that the binarizing level is as low as possible in order to reliably detect the LPP signals.
SUMMARY OF THE INVENTION
The invention has been made in view of the above problems addressed by the prior art. An object of the invention is, therefore, to provide a pre-pit detecting device and a binarizing level setting method capable of immediately setting the binarizing level for a use of binarizing the LPP to optimum value.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a first gate for periodically opening its gate only in a period during which the amplitude of the wobbling becomes a maximum one to make the generated pre-pit signal pass through the gate, wherein the binarizing level setting device counts the number of the pre-pit signals passing through the first gate and sets the binarizing level based on the relationship between the counted number per a reference time and a predetermined reference number.
According to the present invention, a composite signal in which pre-pit signal components are superimposed onto frequency components of wobbling, is extracted from an optical recording medium. The composite signal is binarized, so that pre-pit signals are generated. The pre-pit signals pass through a first gate when the gate is open. The gate is periodically opened only in a period during which the amplitude of the wobbling becomes a maximum one. The number of the pre-pit signals passing through the gate is counted, so that a binarizing level for generating the pre-pit signal is set based on the relationship between the counted number per a reference time and a predetermined reference number. Accordingly, since it is possible to grasp whether the binarizing level is set to a higher one or lower one, it is possible to set the binarizing level to an optimum one immediately.
The above object of the present invention can be achieved by a pre-pit detecting apparatus of the present invention for extracting a composite signal from an optical recording medium and binarizing the composite signal to generate a pre-pit signal. The optical recording medium has an information recording track wobbled at a predetermined frequency and pre-pits formed at a predetermined spacing on a guide track adjacent to the information recording track. In the composite signal, pre-pit signal, components are superimposed on components of frequency of the wobbling. The pre-pit detecting apparatus is provided with: a binarizing level setting device for setting a binarizing level for the composite signal; a pre-pit signal generating device for comparing the extracted composite signal with the set binarizing level to generate a pre-pit signal; and a second gate for periodically opening its gate only in a period during which a sync bit is superimposed on the wobbling and the amplitude of the wobbling becomes a maximum one to make the gene
Akabane Shin
Tanaka Junji
Hindi Nabil
Pioneer Corporation
Young & Thompson
LandOfFree
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