Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-12-23
2002-06-18
Psitos, Aristotelis M. (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044360
Reexamination Certificate
active
06407978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus and method for reproducing a signal recorded on an optical recording medium.
2. Description of the Related Art
Nowadays, an optical recording medium prevails in recording media for recording an information such as video and audio information. A write-once disc, such as CD-ROM, DVD-ROM, etc., and a write-once read-many type of disc, such as CD-R, DVD-R are available for the optical recording medium in the market. Recently, there has been suggested a rewritable disc such as CD-RW(compact disc-rewritable), DVD-RW(digital versatile disc-rewritable), etc.
As shown in
FIG. 1
, the DVD-RAM is divided into a data area DA for recording a user data and a header area HA pre-formatted with an identification information. The data area DA and the header area HA exist alternately in the circumferential direction of the DVD-RAM. As shown in
FIG. 1B
, the data area DA is provided with a groove track
10
having a concave section and a land track
12
having a convex section. These groove and land tracks
10
and
12
exist alternately in the radial direction. A recording pit train
14
is defined along a center-line of the disc at each of the groove and land tracks
10
and
12
to record a user data. A boundary side
18
of the groove and land tracks
10
and
12
is wobbled in a shape of sinusoidal-wave signal. A wobbling signal occupying a low frequency band is detected by changing a light quantity reflected by the wobbled boundary side
18
periodically. This wobbling signal is used to generate a channel clock and so on in recording mode.
The optical disc reproducing apparatus includes a recorded signal reconstruction apparatus as shown in
FIG. 2
to detect a data recorded in a shape of the recording pit train
14
and the pre-pit train
16
into the corresponding pulse train. The recorded signal detector consists of an equalizer
20
and a comparator
22
connected in series, and an integrator
24
connected to a feedback loop of the comparator
22
. The equalizer
20
receives a radio frequency signal RF detected by an optical pickup (not shown). As shown in
FIG. 3
, the radio frequency signal RF has a different amplitude depending on a length (e.g., 3T to 14T) of the recording pit and the pre-pit. Such a radio frequency signal RF is equalized by means of the equalizer
20
in such a manner to has a constant amplitude like an equalized radio frequency signal ERF in FIG.
3
. The equalizer
20
controls an amplification factor in accordance with the amplitude of the radio frequency signal RF, thereby applying the equalized radio frequency signal having a constant amplitude to the comparator
22
. The comparator
22
converts the equalized radio frequency signal ERF into a pulse signal PS shown in FIG.
3
. To this end, the comparator
22
compares the equalized radio frequency signal ERF with a slice voltage Vsl and logicalizes the compared result. The pulse signal generated at the comparator
22
has a width corresponding to a length (e.g., 3T to 11T) of the recording pit
14
or the pre-pit
16
. The integrator
24
integrates the pulse signal PS from the comparator
22
to detect an average level voltage of the pulse signal PS, that is, a direct current voltage level. Also, the integrator
24
applies the average level voltage to the comparator
22
as the slice level voltage Vsl. The slice level voltage Vsl varies in accordance with a length of the recording pit
14
and a distance ratio between the recording pits
14
. Accordingly, the pulse signal outputted from the comparator
22
always has a duty ratio of 50%, and allows a user data to be reproduced accurately.
For example, a user data recorded on the disc is encoded in such a manner that a total length of the recording pits
14
included in a constant length of unit recording region (i.e., frame) corresponds to 50% the length of the unit recording region. Accordingly, when a normally recorded user data is reproduced, an average voltage level of the pulse signal PS detected by the integrator
24
has “0 V”. As a result, the normal pulse signal PS identical to that upon reproduction is detected from the comparator
22
without a variation in the slice level voltage Vsl. Otherwise, the recording pits occupy a region more than or less than 50% of the unit recording region at the time of recording a data due to a recording light quantity, a rotation speed or a surrounding temperature, etc. A high logic pulse width of the pulse signal PS when a user data recorded in the unit recording region is reproduced becomes narrower and wider than a high logic pulse width of the pulse signal PS when a normally recorded data is reproduced. This results from a light quantity reflected by the unit recording region abnormally being larger or smaller than a light quantity reflected by the unit recording region normally. When a unit recording region having the abnormally recorded data is reproduced, an average level voltage detected by the integrator
24
becomes higher or lower than “0 V”. As the average level voltage becomes high or low, a high logic pulse width of the pulse signal PS outputted from the comparator
22
becomes narrow or wide. As a result, a pulse signal PS having always a constant range of width(i.e., 3T to 11T) is reconstructed at the comparator
22
. As described above, the slice level voltage is controlled in accordance with a duty ratio of the pulse signal PS, thereby stabbly performing the reconstruction of the pulse signal PS using the comparator
22
.
As shown in
FIG. 4
, a high frequency component of pit train signal PTS from the recording pit train
14
and/or the pre-pit train
16
as well as a low frequency component of wobbling signal WS from the boundary side between the wobbled groove and land tracks
10
and
12
is included in a high frequency signal WRF picked up from the disc such as the above-mentioned DVD-RAM, that is, a high frequency signal picked up from the wobbled track(hereinafter referred to as “wobbling radio frequency signal”). Due to this, a direct current voltage level of the wobbling radio frequency signal PRF fails to have a constant voltage level (e.g., “0 V”) and changes in the low frequency component of wobbling signal as shown in FIG.
4
. This is caused by a fact that a high frequency component of pit train signal PTS is combined with a low frequency component of wobbling signal WS to swing in accordance with an envelop of the wobbling signal WS. On the other hand, because a high frequency signal NRF, hereinafter referred to as “normal radio frequency signal”, picked up from a disc without the wobbled groove and land tracks, hereinafter referred to as “normal disc”, does not include the low frequency component of wobbling signal WS, it has a constant direct current voltage level(e.g., “0 V”). When both the wobbling radio frequency signal WRF and the normal radio frequency signal NRF is converted into a shape of pulse signal by means of the recording signal reconstructing apparatus in
FIG. 2
, a pulse signal WPS, hereinafter referred to as “wobbling pulse signal”, derived from the wobbling radio frequency signal WRF has a length different from the length(i.e., 3T to 11T) of the recording pit
14
periodically, whereas a pulse signal NPS, hereinafter referred to as “normal pulse signal”, derived from the normal radio frequency signal NRF has a width corresponding to the length of the recording pit
14
. In other words, a large or small width of error is periodically generated in the wobbling pulse signal WPS. This is caused by a fact that the large-width error and the small-width error in the wobbling pulse signal WPS is canceled every a period of the wobbling signal WS to maintain a direct current voltage level detected at the integrator
22
constantly. Such a pulse reconstruction error will be more apparent from the following description with reference to FIG.
2
. Referring to
FIG. 5
, the wobbling radio frequency signal WRF is sliced on a basis of a slice level voltage Vsl to produce a wobbling p
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
Psitos Aristotelis M.
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