Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1999-04-23
2002-07-23
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S053370, C369S124120
Reexamination Certificate
active
06424609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an output control device for an optical pick-up (optical head) used in an optical disc drive and a method for controlling output of the optical pick-up.
2. Description of the Related Art
There are known optical disc drives for reproducing (playing back) a read only optical disc such as a CD-ROM, and for recording and reproducing a recordable optical disc such as CD-R and CD-RW.
Such an optical disc drive has an optical pick-up which is movable in the radial direction of the optical disc, and an optical pick-up moving mechanism equipped with a sled motor for moving the optical pick-up in the radial direction of the optical disc.
The optical pick-up is constructed from an optical pick-up main body (an optical pick-up base) which is equipped with a laser diode, a split photodiode and an I-V amplifier, an objective lens supported by the optical pick-up main body with suspension springs so as to be movable in the radial direction as well as in the rotational axis direction of the optical disc, and an actuator for moving the objective lens in the radial direction and in the rotational axis direction of the optical disc.
In such an optical disc drive, recording of data to the optical disc and reproduction (read-out) of data from the optical disc are carried out for a predetermined track while performing focus control, tracking control and the like.
FIG. 11
is a circuit diagram which shows a split photodiode and I-V amplifiers used in a conventional optical disc drive. As shown in the drawing, a split photodiode
110
is electrically connected to each of I-V amplifiers
121
,
122
,
123
,
124
,
125
and
126
, respectively.
For recording and reproducing an optical disc, a laser beam is projected toward the optical disc from a laser diode (which are not shown in the drawing).
In this case, when the data is to be reproduced from the optical disc, the output level of the laser beam projected toward the optical disc is set to a reproduction level, and the quantity of reflected light from the optical disc goes to a low level.
On the other hand, when the data is to be written onto the optical disc by forming pits and lands, the output level of the laser beam is controlled as follows. Namely, when the pits are to be formed, the output level of the laser beam is raised to a recording level (about 10 to 30 times the reproduction level), and the quantity of reflected light from the optical disc goes to a high level. On the other hand, when no pits are to be formed (that is, when lands are to be formed), the output level of the laser beam is lowered to the reproduction level, and the quantity of reflected light from the optical disc goes to the low level.
The reflected light from the optical disc (laser beams) is received by light receiving regions
111
,
112
,
113
,
114
,
115
, and
116
of the split photodiode
110
, and currents corresponding to the quantities of received light at respective regions
111
to
116
of the split photodiode
110
are outputted.
The currents from the split photodiode
110
are amplified with predetermined amplification factors and converted into voltages by the respective I-V amplifiers
121
,
122
,
123
,
124
,
125
and
126
, and then inputted into predetermined post stage circuits.
In the case of an optical disc drive which is capable of only performing reproduction of an optical disc, since the output level of the laser beam projected to the optical disc is constant (at the reproduction level) as mentioned above, variations in the currents from the split photodiode
110
are relatively small.
On the other hand, however, in the case of an optical disc drive which is capable of performing both of recording and reproduction of an optical disc, the output level of the laser beam projected to the optical disc when recording is being carried out is about 10 to 30 times that of reproduction as mentioned above. Therefore, there may arise a problem that the dynamic ranges of the I-V amplifiers are insufficient to deal with the currents.
In other words, in the case of an optical disc drive capable of performing both of recording and reproduction, if the amplification factor of respective I-V amplifier is set at a relatively high value so as to be suitable for reproduction and then a current is converted into a voltage for recording by the I-V amplifier having such a setting, the high voltage side of the voltage waveform is likely to be truncated, which may give rise to a situation in which the correct voltage corresponding to the received quantity of light is not obtained. This may also cause an inconvenience in various controls that are to be carried out in the recording operation.
On the other hand, if the amplification factor of the I-V amplifier is set at a relatively low value suitable for recording, the voltage (signal level) outputted from the I-V amplifier becomes too low at reproduction. This may case an inconvenience in various controls that are to be carried out in the re producing operation.
These problems may be resolved by using an I-V amplifier with a relatively wide dynamic range, but it also has certain restrictions.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an output control device for an optical pick-up which is capable of properly performing recording (including control for recording) and reproduction (including control for reproduction) in an optical disc drive.
In order to achieve the object, the present invention is directed to an output control device for an optical pick-up used in an optical disc drive for recording and reproducing an optical disc, in which the optical pick-up being adapted to project light having a quantity of light of either high level or low level to the optical disc. The output control device comprises light receiving means having a plurality of light receiving regions for receiving reflected light from the optical disc and then outputting electrical currents responsive to the quantity of light received at the respective light receiving regions; current-voltage converting means having a first current-voltage converting section for converting the currents supplied from the light receiving means into voltages through a predetermined amplification factor; and current supply changeover means which functions so as not to supply the currents from the light receiving means to the first current-voltage converting section when the quantity of the reflected light from the optical disc is in the high level.
In the present invention, it is preferred that the current-voltage converting means further comprises a second current-voltage converting section for converting at least a part of the currents supplied from the light receiving means into voltages through a predetermined amplification factor which is lower than that of the first current-voltage converting section, and the current supply changeover means is adapted to supply the part of the currents from the light receiving means to the second current-voltage converting section of the current-voltage converting means when the quantity of the reflected light from the optical disc is in the high level.
According to the output control device for the optical pick-up described above, since a part of the currents from the light receiving means is supplied to the second current-voltage converting section of the current-voltage converting means when the quantity of the reflected light from the optical disc is in the high level, it is possible to prevent insufficiency in the dynamic range of the current-voltage converting means.
In particular, a voltage (signal) with a relatively high level and correctly responsive to the quantity of received light at the light receiving region can be obtained, thereby enabling to perform various controls securely and reliably during the recording and reproduction operations.
In the present invention, it is also preferred that the current supply changeover means comprises main paths for supplying the currents from
Patents + TMS P.C.
Tran Thang V.
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