U.S. patent application number 10/271791 was filed with the patent office on 2003-02-13 for head amplifier and an optical disk device using the same.
Invention is credited to Minemura, Hiroyuki, Tsuchinaga, Hiroyuki.
Application Number | 20030031099 10/271791 |
Document ID | / |
Family ID | 18453176 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030031099 |
Kind Code |
A1 |
Tsuchinaga, Hiroyuki ; et
al. |
February 13, 2003 |
Head amplifier and an optical disk device using the same
Abstract
An information recording method for recording information by
irradiating an information recording medium with light, including
steps of providing the information recording medium with a physical
identification field (PID) and a data field, and utilizing a head
amplifier for amplifying a detection signal in the PID field with a
first gain and amplifying a detection signal in the data field with
a second gain different from the first gain to record the
information to the data field.
Inventors: |
Tsuchinaga, Hiroyuki;
(Kodaira, JP) ; Minemura, Hiroyuki; (Kokubunji,
JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18453176 |
Appl. No.: |
10/271791 |
Filed: |
October 17, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10271791 |
Oct 17, 2002 |
|
|
|
09461407 |
Dec 15, 1999 |
|
|
|
6477131 |
|
|
|
|
Current U.S.
Class: |
369/44.26 ;
369/124.1; 369/44.39; 369/59.17 |
Current CPC
Class: |
G11B 7/0053 20130101;
G11B 20/10027 20130101; G11B 7/005 20130101; G11B 20/10009
20130101; G11B 2220/2537 20130101; G11B 11/10595 20130101 |
Class at
Publication: |
369/44.26 ;
369/124.1; 369/59.17; 369/44.39 |
International
Class: |
G11B 007/095; G11B
007/005 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 1998 |
JP |
10-357252 |
Claims
What is claimed is:
1. An information recording method for recording information by
irradiating an information recording medium with light, comprising
the steps of: providing said information recording medium with a
physical identification field (PID) and a data field; and utilizing
a head amplifier for amplifying a detection signal in said PID
field with a first gain and amplifying a detection signal in said
data field with a second gain different from said first gain to
record the information to said data field.
2. An information recording method according to claim 2, further
comprising the steps of obtaining a tracking error signal while
recording the information in said data field.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an optical disk device for
supporting a DVD-RAM disk. In particular, the present invention
relates to a current-to-voltage conversion amplifier in an optical
head, for converting a converted current fed from a detection
photodiode to a voltage. Especially, the present invention relates
to a concrete configuration of an amplifier which makes efficient
use of the dynamic range of the amplifier and which is suitable for
transmitting a reproduced signal to a signal processing circuit of
a subsequent stage with a high signal-to-noise ratio.
[0002] The configuration of a head amplifier for reproducing a
signal fed from a DVD-RAM disk is shown in FIG. 8A. A photodetector
80 functions also to detect a tracking error signal of a DVD-ROM
disk. The photodetector 80 is divided into four sections. Each of
photodetectors A, B, C and D is formed of a photodiode. Each
photodetector converts incident light into a current. Each
photodetector is connected to a current-to-voltage conversion
amplifier 81. Its converted current is converted to a voltage. The
resultant voltage is inputted to a summing amplifier 82. Thus, a
reproduced signal corresponding to total incident light is obtained
as a voltage signal.
[0003] The case where the current-to-voltage conversion amplifier
81 is formed by using an operational amplifier will now be
described by referring to FIG. 8B. For the purpose of increasing
the speed of light-to-current conversion, a reverse bias voltage
(+Vcc) is applied to a cathode of a photodiode 83. An anode of the
photodiode 83 is connected to an inverting input (-) of an
operational amplifier 84. If there is no quantity of light incident
on the photodiode 83, then no converted current flows, and an
output voltage Vout of the operational amplifier 84 becomes equal
to a reference voltage Vref applied to a non-inverting input (+) of
the operational amplifier 84. In other words, Vref corresponds to
zero incident light quantity. If reflected light from the disk is
incident on the photodiode 83, then a converted current Ip flows
out from the cathode of the photodiode 83. Since the inverting
input (-) has very high input impedance, all of the current Ip
flows through a gain resistor Rf. At this time, a voltage lower
than the reference voltage Vref by Ip.times.Rf is obtained at an
output terminal of the operational amplifier 84.
[0004] A track format of a DVD-RAM disk will now be described by
referring to FIG. 9.
[0005] On a disk plate which is not illustrated, a groove having a
wide width is formed in a spiral form. There are two kinds of
tracks called groove and land. Each track is further divided into
units called sectors. The sectors are a groove sector 90 and a land
sector 91. At the head of each sector, pre-pits 92 indicating
address information are provided. The pre-formatted pits 92 are
called PID (Physical IDentification) or Header field. In the
DVD-RAM, the pre-formatted pits 92 are composed of four headers H1,
H2, H3 and H4. As illustrated, two front headers H1 and H2 and two
back headers H3 and H4 are disposed so as to be complementarily
offset by half a track.
[0006] FIG. 10 conceptually shows an envelope of a reproduced
signal obtained from a DVD-RAM disk having a capacity of, for
example, 2.6 GB per single side, on the basis of an observation
result. An arbitrary track of FIG. 9 is scanned with an optical
spot. An optical spot position at that time is represented by the
abscissa. A voltage level of a reproduced signal observed at this
time is represented by the ordinate. A signal of a PID area 1000
becomes as shown in FIG. 10 because the quantity of light incident
on the photodetector is lowered by a diffraction phenomenon of
light at the pre-formatted pits. In a mirror section, the level of
light incident on the photodetector becomes the highest because
diffraction is not present. Hereafter, this level is referred to as
mirror level. In a track composed of a groove and a track, the
quantity of reflected light becomes lower than that of the mirror
section 1001 as a result of diffraction of light performed by the
groove. A signal level 1002 of a sector having no data recorded
thereon corresponds to this. Hereafter, this signal level is
referred to as land/groove level.
[0007] In order to describe a signal level on a recorded sector, a
phase change medium used in DVD-RAMs will now be described
briefly.
[0008] On the phase change medium, information is recorded by
utilizing a phase transition phenomenon between two phases, i.e., a
crystal phase and an amorphous phase. By converting a difference in
refractive index between the crystal state and the amorphous state
into a change in quantity of reflected light, recorded information
is reproduced. In DVD-RAMs, there is employed such a material which
is in a crystal state having a high reflection factor when no
information is recorded, and which assumes an amorphous state
having a lowered reflection factor when information is recorded. As
shown in FIG. 10, therefore, a reproduced signal 1003 of a recorded
sector has an amplitude in the darkness direction from the
land/groove level.
[0009] On the other hand, an optical disk device using a
magneto-optical (MO) medium has such a format that a data field
recorded by magnetic marks follows a PID area composed of
pre-formatted pits, in the same way as the DVD-RAM. While a
pre-formatted pit signal is obtained as a change in light quantity
caused by diffraction, however, a data signal is detected by
converting rotation of the polarization plane of light caused by a
recorded magnetic domain into a light quantity change. In a head
amplifier of the magneto-optical disk device, therefore, the PID
area signal and the data signal are obtained by using two different
amplifiers. Furthermore, since the light quantity change caused by
the recorded magnetic domain is slight, the gain of an amplifier
circuit for the data field signal is typically set so as to be
larger than that of an amplifier circuit for the PID area.
Furthermore, since signals fed from different amplifier circuits
are used, cross-talk caused mutually between signals must be
removed. For that purpose, signals fed from two amplifier circuits
are switched by a switch circuit according to whether the section
is the PID area or the data field. A resultant single signal is
subject to postprocessing. As a conventional technique of such a
kind, JP-A-61-170938 can be mentioned.
SUMMARY OF THE INVENTION
[0010] The head amplifier is an amplifier for amplifying a detected
signal obtained after light-current conversion. Thus the head
amplifier has a role of assuring a sufficient signal quality and
sending a resultant signal to a processing circuit of a subsequent
stage. Therefore, the head amplifier needs to obtain a sufficiently
large signal amplitude here. In other words, the head amplifier
needs to have a large gain. In the DVD-RAM, however, the signal is
obtained by performing the light-current conversion on light fed
from the same photodetector, for both the PID area and the data
field. In other words, there is a single amplifier circuit for
converting a converted current to a voltage. As for a reproduced
signal obtained from the single amplifier circuit, its signal level
differs depending on whether the section is the PID area or the
data field. The highest level in the PID area is the mirror level,
whereas the highest level in the data field is the land/groove
level. In the above described conventional technique of the
magneto-optical (MO) disk device, therefore, the case where the
reproduced signals of both the PID area and the data field can be
obtained from a single detection system is not considered. The gain
of the data field and the gain of the PID area cannot be set
separately. As for the maximum gain of the data field, the gain of
the head amplifier is limited so that the mirror level will not
exceed the dynamic range of the head amplifier.
[0011] An object of the present invention is to provide a head
amplifier capable of providing a detected output having such a
signal amplitude as to make the signal-to-noise ratio of the data
field compare favorably with that of the PID area.
[0012] Another object of the present invention is to provide an
optical disk device having the above described head amplifier and
having a reduced number of components.
[0013] The above described problem is caused by a premise that the
signal is amplified with the same gain both for the PID area and
the data field. Therefore, the above described problem is solved by
amplifying the signal with different suitable gains respectively
for the PID area and the data field.
[0014] Furthermore, when viewed from a different view, the above
described problem is solved by adding an offset voltage
corresponding to a difference between the mirror level and the
land/groove level to the PID area, and increasing the gain by a
quantity corresponding to the ratio of the mirror level to the
land/groove level.
[0015] Other objects, features and advantages of the present
invention will become apparent from the description of the
embodiments of the invention taken in conjunction with the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 is a schematic diagram showing the configuration of a
current-voltage conversion amplifier according to a first
embodiment of the present invention;
[0017] FIGS. 2A and 2B are diagrams showing envelopes of reproduced
signal in the first embodiment of the present invention;
[0018] FIG. 3 is an entire block diagram of an optical disk device
using the present invention;
[0019] FIG. 4 is a schematic diagram showing the configuration of a
current-voltage conversion amplifier according to a second
embodiment of the present invention;
[0020] FIGS. 5A, 5B and 5C are diagrams showing envelopes of
reproduced signal in a third embodiment of the present
invention;
[0021] FIG. 6A is a schematic diagram showing the configuration of
a current-voltage conversion amplifier according to the third
embodiment of the present invention;
[0022] FIG. 6B is a schematic diagram showing the configuration of
a variation of the third embodiment of the present invention;
[0023] FIG. 7 is a schematic diagram showing a detection method of
a mirror level and a land/groove level;
[0024] FIGS. 8A and 8B are schematic diagrams showing the
configuration of a conventional head amplifier;
[0025] FIG. 9 is a schematic diagram showing the disk format of a
DVD-RAM disk used in the present invention; and
[0026] FIG. 10 is a schematic diagram showing a reproduced signal
of the DVD-RAM disk.
DESCRIPTION OF THE EMBODIMENTS
[0027] Embodiments of the present invention will be described by
referring to accompanying drawing.
[0028] First of all, a first embodiment of the present invention
will now be described by referring to FIGS. 1 to 3.
[0029] FIG. 1 shows the configuration of a current-voltage
conversion amplifier including a photodetector. FIGS. 2A and 2B
show the operation of the current-voltage conversion by referring
to envelopes. FIG. 3 shows an optical disk device using the present
invention in the form of an entire block diagram.
[0030] In the configuration of the first embodiment, a converted
current Ip flowing out from an anode of a photodiode 1 flows
through either a gain resistor Rf1 or a gain resistor Rf2. This
operation is carried out by a switch circuit 2. As the switch
circuit 2, a high speed analog switch device of, for example, CMOS
type can be used. Timing for switching the gain resistor is
supplied by a data/PID gate signal 3.
[0031] By referring to FIG. 3, a generation method of the gate
signal 3 will now be described. A reproduced signal supplied from a
head amplifier 31 disposed in an optical pickup 30 is passed
through a read channel circuit 32, and converted to digital
information data. This digital information data is decoded by an
encoding and decoding circuit 33. Each address information is read.
If address information can be recognized without an error, then an
MPU 34 coupled to a SCSI serving as a high rank device counts a
predetermined number of a fixed clock pulses by taking the mirror
section located at the tail end of the PID area as a timing
reference, and then switches a logic level from "low" over to
"high." Subsequently, the MPU 34 counts as many clock pulses as
corresponding to the length of the data field. Thereupon, the MPU
34 switches the logic level from "high" over to "low." The data/PID
gate signal 3 is thus generated. As shown in FIG. 2B, therefore,
the gate signal 3 in the present embodiment becomes a logic signal
which becomes "high" in the PID area and "low" in the data field.
Even if the address cannot be recognized, the timing of the PID
area is predicted by counting the clock pulses and the gate signal
is generated.
[0032] Upon moving from the data field to the PID area, the
data/PID gate signal changes to "high" in logic level, and the gain
resistor Rf2 is selected. A voltage represented as
Vref-Rf2.multidot.Ip is obtained as the output of the operational
amplifier 4. Subsequently, upon moving from the PID area to the
data field, the data/PID gate signal changes to "low" in logic
level, and the gain resistor Rf1 is selected. A voltage represented
as Vref-Rf1.multidot.Ip is obtained as the output of the
operational amplifier 4. The ratio between the resistance values of
the two gain resistors Rf2 and Rf1 is set so as to be substantially
equal to the ratio between the mirror level and the land/groove
level. As compared with the case where the gain resistor is set
equal to the same value both for the PID area and the data field
(FIG. 2A), therefore, the amplitude of the reproduced signal
envelope 20 of the data field can be increased to the maximum so
long as it does not exceed the mirror level.
[0033] FIG. 4 shows a circuit configuration of a head amplifier
according to a second embodiment of the present invention. In the
first embodiment shown in FIG. 1, switchover of the two gain
resistors is performed. In the present embodiment, however, a
converted current Ip flowing out from the anode of the photodiode
40 is adapted to flow through one of gain resistors Rf11, Rf12 and
Rf2. This switchover operation is carried out by two switch
circuits 41 and 42. The timing of switchover of the gain resistor
is supplied by a data/PID gate signal 3 for the switch circuit 42,
and by a read/write (R/W) gate signal 43 for the switch circuit 41.
The gain resistor switchover performed by the switch circuit 41
aims at decreasing the gain so as not to saturate the amplifier
circuit for an excessive light quantity during the recording
operation. Since the light quantity during the recording operation
is larger than that during the reproducing operation, such a
countermeasure is required. As a result, it becomes possible to
obtain a tracking error signal from the detected signal of the
divided photodetectors even during the recording. Hereafter,
operation of the present embodiment will be described
concretely.
[0034] While the PID area is being reproduced, the data/PID gate
signal 3 is "high" in logic level irrespective of the R/W gate
signal, and consequently the gain resistor Rf2 is selected. A
voltage represented as Vref-Rf2.multidot.Ip is obtained as the
output of the operational amplifier 44. When recording information
on the data field, the data/PID gate signal 3 is switched over to
"high" in logic level. The switch circuit 42 selects the output of
the switch circuit 41. The R/W gate signal 43 becomes "high" in
logic level, and the switch circuit 41 selects the gain resistor
Rf12. As a result, a voltage represented as Vref-Rf12.multidot.Ip
is obtained as the output of the operational amplifier 44. As shown
in FIG. 3, the R/W gate signal 43 is sent to the head amplifier 31
under an instruction from the MPU 34.
[0035] On the other hand, at the time of reproduction of the data
field, the switch circuit 41 selects the gain resistor Rf11. As a
result, a voltage represented as Vref-Rf11.multidot.Ip is obtained
as the output of the operational amplifier 44.
[0036] The gain resistor Rf12 is set equal to, for example, one
fifth, in resistance value, of the gain resistance Rf11. This is
based upon assumption that the quantity of light incident on the
disk surface is 1 mW at the time of data reproducing whereas the
quantity of light incident on the disk surface is 5 mW in average
at the time of data recording. Furthermore, in the same way as the
case of the first embodiment, the ratio between the two gain
resistors Rf2 and Rf11 is set substantially equal to the ratio
between the mirror level and the land/group level.
[0037] A third embodiment of the present invention will now be
described by referring to FIGS. 5A, 5B, 5C, 6A and 6B.
[0038] FIG. 5A shows an envelope of a reproduced signal outputted
from the conventional head amplifier. On the other head, in the
present embodiment, the mirror level is raised to the land/groove
level by applying an offset voltage 51 to the reproduced signal of
the PID area. Furthermore, by increasing the gain by a value
corresponding to the ratio between the mirror level and the
land/groove level, such a reproduced signal that the signal for the
PID area and the signal for the data field are amplified maximumly
is obtained as shown in FIG. 5C.
[0039] The operation shown in FIGS. 5B and 5C will now be described
by referring to FIG. 6A. A converted current Ip flowing out from
the anode of a photodiode 60 selectively is flowed through one of
two gain resistors Rf1 and Rf2 by a switch circuit 61.
[0040] An instruction for switching over the gain resistor is
supplied by an offset addition signal 62. When the offset addition
signal is high in logic level, a gain resistor Rf2 is selected and
a voltage represented as Vref'-Rf2.multidot.Ip is obtained as an
output Vout of an operational amplifier 63. When the offset
addition signal is low in logic level, a gain resistor Rf1 is
selected and a voltage represented as Vref'-Rf1.multidot.Ip is
obtained as the output Vout of the operational amplifier 63. A
noninverting input (+) of the operational amplifier 63 is supplied
with an offset voltage 64. The offset voltage (Vref') 64 is a
signal higher in the PID area than the reference voltage Vref by
the potential difference between the mirror level and the
land/groove level.
[0041] FIG. 6B shows a variation obtained by combining the
embodiment shown in FIG. 4 with the embodiment shown in FIG. 6A. In
this variation, in addition to the offset operation of FIG. 6A, a
circuit for preventing the amplifier from being saturated at the
time of recording operation is added. To be concrete, in the same
way as FIG. 4, a switch 41 and gate resistors Rf1 and Rf2 are
provided so as to be able to change the gain of the head amplifier
with an R/W gate signal 43 depending on whether recording is
performed or reproducing is performed, and an additional circuit is
adapted to perform switchover according to the operation mode. As
for the offset voltage 64, the voltage difference between the
mirror level and the land/groove level may be added as a reference
voltage Vref. Or the mirror level and the land/groove level may be
detected for each disk and applied. The latter method will now be
described concretely by referring to FIG. 7.
[0042] FIG. 7 shows a signal 70 reproduced by the conventional head
amplifier having a fixed gain. In other words, a head amplifier
output signal 70 obtained before the offset voltage is applied and
the gain resistor is switched over is shown in FIG. 7. A mirror
level 71 and a land/groove level 72 are detected by using timing
signals 73 and 74, respectively. The sampling timing 73 and 74 can
be easily obtained from the data/PID gate signal 3 which is in turn
generated at the timing of the PID area by the MPU 34 shown in FIG.
3. For sampling, an A/D conversion device which is not illustrated
is used. In the present embodiment, sampling is performed with a
sector period. Therefore, high speed operation is not required of
the A/D conversion device, and the sampling can be sufficiently
carried out by using a current technique. Considering influences of
a variation of the reflection factor, error due to noise,
quantization errors of the A/D conversion device, and so on caused
during one revolution of the disk, it is desirable to average the
result of signal levels sampled during at least one revolution of
the disk. This averaging processing is carried out by the MPU 34.
An average voltage difference between the mirror level and the
land/groove level is used as a digital value. On the basis of this
result, the offset voltage 64 is generated as an analog voltage by
a D/A converter.
[0043] According to the present invention, optimum setting of the
gain of an amplifier becomes possible by making efficient use of
the dynamic range of the amplifier at its maximum without newly
developing an amplifier having a wide dynamic range. Furthermore,
as the capacity of the DVD-RAM disk is increased, the signal
amplitude is significantly lowered in both the PID area and the
data field as compared with the mirror level. Even in this
situation, the signal quality in the head amplifier can be assured
to the maximum.
* * * * *