Pre-pit detection unit

Details Pre-pit detection unit Pre-pit detection unit

2000-04-25

2003-08-05

Korzuch, William (Department: 2653)

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

C369S124070, C369S047270

Reexamination Certificate

active

06603726

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to pre-pit detection units fit for use in recording-playback apparatus intended for high-density recording media such as DVD-R and DVD-RW and more particularly to a pre-pit detection unit ensuring that pre-pits can be detected even though the amplitude level of a radial push-pull signal fluctuates.
As disclosed in the Examined Japanese Patent Application No. Hei 10-283638, for example, a recording—playback apparatus intended for high-density recording media such as DVD-R and DVD-RW has a self-contained pre-pit detection unit ensuring that pre-pits on a recording medium can be detected even though beam intensity is in the state of either mark or space period.
FIGS. 11
to
13
show a specific example of such a pre-pit detection unit as mentioned above; and
FIG. 14
, an operating waveform chart. As shown in
FIG. 11
, the basic arrangement of the pre-pit detection unit is such that a pre-pit detection circuit
300
corresponding to the beam intensity in the mark period and a pre-pit detection circuit
400
corresponding to the beam intensity during the space period are provided in parallel on the output side of a push-pull circuit
200
for generating a pre-data signal and that the OR of the outputs of both pre-pit detection circuits
300
and
400
is finally outputted as a pre-pit detection signal (l).
In
FIG. 11
, reference numeral
101
denotes a quadrified detector (light receiving element) for outputting a four-system light receiving signal comprising A to D areas;
102
, an adder (e.g. an adder using an OP amplifier) for generating a light receiving signal (a-
1
) in the left-hand area with respect to the push-pull circuit
200
by adding the A-area light receiving signal and the D-area light receiving signal of the quadrified detector
101
;
103
, an adder for generating a light receiving signal (a-
2
) in the right-hand area with respect to the push-pull circuit
200
by adding the B-area light receiving signal and the C-area light receiving signal of the quadrified detector
101
;
104
, a DVD encoder for encoding recording data by utilizing digital modulation technology;
105
, a gate signal generator
105
for generating gate signal (h-
1
and h-
2
) according to NRZI and NRZICK signals obtainable from the DVD encoder
104
; and
106
, an OR operator
106
for obtaining the OR of the outputs (i-
1
and i-
2
) of both the pre-pit detection circuits
300
and
400
.
FIG. 12
shows the internal structure of the push-pull circuit
200
. As shown in
FIG. 12
, the push-pull circuit
200
includes a substractor (e.g., an adder using an OP amplifier)
201
for generating a radial push-pull signal (d) as a pre-data signal by subtracting the light receiving signal (a-
1
) in the left-hand area and the light receiving signal (a-
2
) in the right-hand area.
FIG. 13
shows the internal structure of the pre-pit detection circuits
300
and
400
. As shown in
FIG. 13
, the pre-pit detection circuit
300
corresponding to the beam intensity in the mark period includes a (fixed gain) amplifier
301
for amplifying the radial push-pull signal (d) outputted from the push-pull circuit
200
by means of a constant gain, a comparator
303
for detecting pre-pits by comparing the output signal (f-
1
) of the amplifier
301
with a mark equivalent voltage (V
MARK
) as a threshold voltage (VT
1
), and a sampling gate
304
that is opened and closed under the control of the gate signal (h-
1
) so as to pass the output signal (g-
1
) of the comparator
303
therethrough. Similarly, the pre-pit detection circuit
400
corresponding to the beam intensity in the space period includes a (fixed gain) amplifier
401
for amplifying the radial push-pull signal (d) outputted from the push-pull circuit
200
by means of a constant gain, a comparator
403
for detecting pre-pits by comparing the output signal (f-
2
) of the amplifier
401
with a mark equivalent voltage (V
SPACE
) as a threshold voltage (VT
2
), and a sampling gate
404
that is opened and closed under the control of the gate signal (h-
2
) so as to pass the output signal (g-
2
) of the comparator
403
therethrough.
In the above case, a so-called floating binarization system is employed for the comparing operation in the comparators
303
and
403
. Consequently, the mark equivalent voltage (V
MARK
) and the space equivalent voltage (V
SPACE
) are generated by shifting the level of the radial push-pull signal (d) by a low component.
In such a recording-playback apparatus as mentioned above, the balance of the quantity of light that is incident on the light receiving element and reflected from the disk collapses because of variations in the environment of use that cause optical axis fluctuations to a laser oscillator and because the presence of optical aberration in the pickup as well as the presence of internal-external aberration in the reflectance of the disk. In consequence, the amplitude level of the radial push-pull signal (d) may fluctuate (may cause disturbance).
When the situation above arises in the prior art pre-pit detection unit, the output signals (f-
1
and f-
2
) of the respective amplifiers
301
and
401
are directly susceptible to the influence of fluctuations in the amplitude level of the radial push-pull signal (d). On the other hand, values of the mark equivalent voltage (V
MARK
) and space equivalent voltage (V
SPACE
) as the threshold voltages VT
1
and VT
2
of the comparators
303
and
403
disposed at the following stage of the respective amplifiers
301
and
401
are generated by level-shifting the low component of the radial push-pull signal (d) by a predetermined value, the fluctuations of the radial push-pull signal (d) with respect to the maximum amplitude lever will have to be dull.
When the amplitude level of the radial push-pull signal (d) sharply fluctuates as shown in the waveform chart of
FIG. 14
, the output signal (f-
1
) of the amplifier
301
consequently follows the fluctuation and fluctuates, whereupon an abnormal pulse whose pulse width and phase are not normal or a pre-pit pulse that should not be present (error detection) will appear in a pre-pit detection signal (l) resulting from gating of the output signal (g-
1
) of the comparator
303
with the sampling gate
304
; the problem is that address retrieval and spindle control may be impeded by the mistaken recognition of pre-format data.
SUMMARY OF THE INVENTION
An object of the present invention with special attention directed to the foregoing problems in the prior art pre-pit detection unit is to provide a pre-pit detection unit capable of detecting a pre-pit accurately even though the amplitude level of a radial push-pull signal fluctuates.
In order to accomplish the object above, a pre-pit detection unit according to the invention comprises a push-pull circuit for generating a radial push-pull signal including a pre-data signal according to each of lateral outputs of a light receiving element, a first pre-pit detection circuit for beam intensity in a mark period for detecting a pre-pit corresponding to the beam intensity in the mark period according to the radial push-pull signal obtained from the push-pull circuit, and a second pre-pit detection circuit for beam intensity in a space period for detecting a pre-pit corresponding to the beam intensity in the space period according to the radial push-pull signal obtained from the push-pull circuit, so that the OR of outputs of both pre-pit detection circuits is outputted as a pre-pit detection signal, and is characterized in that a first and a second AGC circuit for making the maximum amplitude of the radial push-pull signal obtainable from the push-pull circuit coincide with a reference value are provided in the preceding stages of pre-pit detecting comparators in the first and the second pre-pit detection circuits respectively.
The pre-pit detection circuit for the beam intensity in the mark period and the pre-pit detection circuit for the beam intensity in the space period may be provided in parallel on the output side of the

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