Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1997-03-31
2002-10-15
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053230
Reexamination Certificate
active
06466531
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a- disc discriminator of an optical disc player system, and more particularly, to an apparatus for automatically discriminating between a digital video disc (DVD) and a compact disc (CD) installed in a digital video disc/compact disc (DVD/CD) compatible player system. The present application is based on Korean Application No. 11966/1996, which is incorporated herein by reference.
2. Description of the Related Art The growth of multi-media systems drives the progress in optical disc player systems. For example, a recently developed DVD [or SD (Super Density Disc)] player is capable of recording and reproducing a moving image and an audio signal of high quality. The DVD satisfies the MPEG-2 (Motion Picture Experts Group-2) specification and is compatible with the video CD based on the MPEG-1(Motion Picture Experts Group-1) specification. The thickness of the DVD substrate was chosen as 0.6 mm in consideration of the mechanical strength of the substrate against deformation of the disc and the compatibility with the CD. The thickness of the general CD is 1.2 mm. The compatibility between the DVD and the CD is motivated by the fact that much of the software that has been developed and is available on the market uses the format of the CD.
In order to reproduce information recorded in the DVD and the CD by means of a single optical disc player system, an optical pickup unit for accurately reading information recorded on either a disc having a substrate thickness of 0.6 mm or a disc having a substrate thickness of 1.2 mm is required. Additionally, a disc discriminator for identifying the kind of the disc loaded in the player is necessarily required. The DVD/CD compatible optical pickup units are classified into two systems, one class uses a liquid crystal shutter and the other class uses a hologram element.
FIGS. 1A and 1B
are diagrams illustrating a disc reading operation using the DVD/CD compatible optical pickup unit employing the liquid crystal shutter. As shown in
FIGS. 1A and 1B
, the DVD/CD compatible optical pickup unit using the liquid crystal shutter is capable of changing the diameter of the laser beam projected on the objective lens.
FIG. 1A
shows the case wherein the DVD having the substrate of thickness of 0.6 mm is installed and the liquid crystal shutter is not driven, i.e., the liquid crystal shutter is off.
FIG. 1B
shows the case wherein the CD having the substrate of thickness of 1.2 mm is installed and the liquid crystal shutter is on.
Referring to
FIGS. 1A and 1B
, a reference numeral
12
indicates a laser beam generated from the semiconductor laser generator (hot shown) and a reference numeral
14
indicates an objective lens. A reference numeral
16
denotes a liquid crystal shutter which is used for changing the diameter of the laser beam and projecting it on the objective lens
14
by means of an “on/off” operation.
The above principle depends on the fact that the focal distance of the objective lens
14
differs according to the diameter of the laser beam projected thereon. For example, as shown in
FIG. 1A
, when the liquid crystal shutter
16
is off, the diameter of the laser beam
12
is about the same as the diameter of the objective lens
14
, and the focal distance of the objective lens
14
becomes short. If the liquid crystal shutter
16
is turned on, the diameter of the laser beam projected on the objective lens
14
becomes narrower. Thus, the focal distance of the objective lens
14
increases.
As can be understood from the above, the liquid crystal shutter
16
should be appropriately driven according to the kind of the disc to be reproduced. That is, it is necessary to identify the kind of disc installed in the optical disc player system. The discrimination between the discs inserted in the optical disc player is achieved by detecting the level of a focusing search signal picked up from the disc by means of the optical pickup unit. The focusing search signal appearing as a form shown in
FIGS. 2A and 2B
is obtained from a focusing error signal FE. Thus, conventionally the focusing error signal FE is also used for discriminating between the discs by comparing its level to a reference voltage as will be further explained below.
FIGS. 2A and 2B
are wave forms of the focusing search signal while the DVD/CD is reproduced by switching off and on the liquid crystal shutter shown in FIG.
1
. Referring to
FIGS. 2A and 2B
, a micro meter &mgr;m in a horizontal axis denotes focus inconformity and a volt “V” in a vertical axis denotes the amplitude of the focusing search signal.
FIG. 2A
illustrates a wave form of the focusing search signal while the DVD having the thickness of 0.6 mm is being reproduced by switching off the liquid crystal shutter
16
of the DVD/CD compatible optical pickup unit.
FIG. 2B
illustrates a wave form of the focusing search signal while the CD of 1.2 mm is being reproduced by switching on the liquid crystal shutter
16
of the DVD/CD compatible optical pickup unit. When the CD of 1.2 mm is reproduced by switching on the liquid crystal shutter
16
of the DVD/CD compatible optical pickup unit, the level of the focusing search signal becomes low and the degree of the focus inconformity becomes large, owing to spherical aberration. That is, as shown in
FIG. 1A
, if the DVD disc is replaced by a CD while the liquid crystal shutter
16
is maintained off, the laser beam passing through the objective lens is projected on the recording surface of the CD. However, since the CD is twice as thick as the DVD, spherical aberration reduces the level of the pickup signal.
FIG. 3
is a block diagram of a conventional disc discriminator which is used for explaining how the DVD/CD player discriminates between the discs using the focusing search signal shown in
FIGS. 2A and 2B
. There are provided a 4-split photo-detector
18
, first and second adders
20
and
22
, a differential amplifier
24
, and a comparator
26
. The 4-split photo-detector
18
consists of first to fourth quadrantal photo diodes a, b, c, and d for receiving the laser: beam picked up through the objective lens
14
, the liquid crystal shutter
16
and a beam splitter (not shown), and generating an electrical signal. The first adder
20
adds the output of the first quadrantal photo diode a of the 4-split photo diode
18
to an output of the third quadrantal photo diode c thereof. The second adder
22
adds the output of the second quadrant photo diode “b” to an output of the fourth quadrantal photo diode d. The differential amplifier
24
differential-amplifies a difference between the outputs of the first and second adders
20
and
22
and then generates the focusing error signal FE. The comparator
26
compares the focusing error signal FE to a predetermined reference voltage Vref and then generates a disc discrimination signal DVD/CD-S of the DVD/CD. The reference voltage Vref in the comparator
26
is set up to discriminate the level of a focus signal of the focusing search signal when the DVD and the CD are reproduced as shown in
FIGS. 2A and 2B
. The reference voltage Vref is lower than the level of the focusing search signal when the DVD is reproduced, and it is higher than the level of the focus signal of the focusing search signal when the CD is reproduced. Here, all constructions, except the comparator
26
, are being currently applied to the generally produced CD players. Thus, in the following description, there will be explained within the scope of the present invention only an operation to discriminate between the DVD and the CD.
If the information recorded in the disc is reproduced under a situation that the liquid crystal shutter
16
of the DVD/CD compatible optical pickup unit is off, the laser beam reflected from the disc is projected onto the upper surface of the 4-split photo-detector
18
shown in FIG.
3
. At this time, the form of the laser beam differs according to the tracking state of the optical pickup unit. The first adder
20
adds
Hindi Nabil
Samsung Electronics Co,. Ltd.
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