JP2004220632A - Optical disk reading device and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always and actively control the gain of an amplifier which constitutes of an optical disk reading device even though a write type optical disk is not recorded. <P>SOLUTION: An adding circuit (41) adds four main electric signals to output an HF signal (a picked up signal). A peak hold circuit (43) holds the peak of the HF signal to output a peak hold signal. The signal indicates the level of the reflection light component (to be called as "I-TOP" hereafter) of the HF signal. A gain control amplifier 44 amplifies the HP signal with a gain of the reciprocal of the peak hold signal and outputs the amplified signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk reader, and more particularly, to an optical disk reader used in an optical disk drive using a polarization optical system optical pickup as an optical pickup.
[0002]
[Prior art]
Recently, electronic devices such as personal computers are often equipped with optical disk drives (optical disk devices). As recording media usable for the optical disk drive, a compact disc-recordable (CD-R) and a compact disc-rewritable (CD-RW) are known.
[0003]
CD-R is a recordable recording medium. With a CD-R, data can be written only once, and what has been written cannot be erased or rewritten.
[0004]
The CD-RW is a rewritable recording medium, but is compatible with a CD-ROM and an audio CD (CD-DA). Unlike CD-R, CD-RW uses a phase-change material for the recording layer. In a CD-RW, an erased state (crystalline phase) and a recorded state (amorphous phase) are recorded by laser light irradiation, and data is read based on the difference in reflectance. A CD-RW has a lower reflectance of light from a medium than a press-type CD-ROM or a CD-R using a dye.
[0005]
Writing information (data) to a CD-R or CD-RW requires a dedicated device and a writing application. On the other hand, reading of information (data) from a CD-R or CD-RW can be executed by a normal CD-ROM drive. The CD-R, CD-RW, CD-ROM, audio CD, DVD-ROM, DVD-R, DVD-RAM, DVD + RW, DVD-RW, and the like are collectively referred to herein as "optical disks".
[0006]
Now, in order to write information (data) to and read information (data) from or to such an optical disk, the optical disk drive is provided with a recording / reproducing optical pickup for irradiating a laser beam onto the optical disk. .
[0007]
Generally, this type of optical pickup includes a laser light source that emits a laser beam, and an optical system that guides the emitted laser beam to an optical disk. As described above, the CD-R can perform not only reading of information but also writing of information. In an optical pickup for a CD-R, the output of a laser beam emitted from a laser light source needs to be switched between when reading information and when writing information. The reason is that writing of information is performed by forming pits in the recording layer of the optical disk by irradiating a laser beam. The output of the laser beam emitted from the laser light source at the time of writing information is larger than the output at the time of reading information, for example, about 10 to 20 times.
[0008]
Now, in such an optical pickup, a laser beam emitted from the laser light source passes through an optical system, and is condensed on a signal recording surface of an optical disk by an objective lens constituting the optical system, thereby recording information ( Write) and erase. On the other hand, the optical pickup reproduces information by detecting reflected light (return light) from the signal recording surface with a photodetector (photodetector) as light detecting means. Note that there are two types of optical systems for optical pickups, a polarizing optical system and a non-polarizing optical system. Here, the polarization optical system refers to an optical system capable of changing the polarization direction of the laser beam, and the non-polarization optical system refers to an optical system in which the polarization direction of the laser beam does not change.
[0009]
As described above, in the optical disk drive, recording and reproduction of the optical disk are performed using the laser beam emitted from the optical pickup, so that focusing control and tracking control are indispensable. In order to perform the focusing control and the tracking control, the optical pickup includes an optical pickup actuator for displacing the objective lens in a vertical direction (focus direction) and a horizontal direction (tracking direction).
[0010]
Further, the optical disk drive includes a reproducing circuit (optical disk reading device) for reproducing the return light detected by the photodetector. The electric signal reproduced by the reproducing circuit (optical disk reader) is called an HF (High frequency) signal.
[0011]
In the optical disk drive, the amplitude of the HF signal changes due to causes described later. The causes are that the optical axis of the laser beam incident on the optical disk is not perpendicular to the main surface of the optical disk due to the warpage of the optical disk or the accuracy of the thread mechanism, birefringence of the optical disk, dirt on the surface of the optical disk, The laser wavelength of the light source can be considered.
[0012]
If the amplitude of the HF signal increases or decreases beyond the design value, the signal-to-noise (S / N) ratio deteriorates. For this reason, a conventional reproducing circuit (optical disc reading apparatus) usually has an automatic gain adjustment (AGC) function added to an amplifier for amplifying an HF signal, and the amplitude of the HF signal amplified by the AGC-equipped amplifier is reduced. It is controlled to be always constant.
[0013]
A conventional optical disk reader will be described with reference to FIG.
[0014]
The illustrated optical disk reader includes an adder circuit 41 and an AGC circuit 47.
[0015]
The adder circuit 41 is composed of an operational amplifier 411, and its four non-inverting input terminals + are supplied with four main electric signals detected by a photodetector of the optical pickup via resistors 422 to 425. The terminal − is supplied with an HF reference voltage via a resistor 426, and a resistor 427 is connected between its output terminal and the inverting input terminal −. This adding circuit 41 outputs an HF signal (a picked-up signal).
[0016]
The output terminal of the adding circuit 41 is connected to the AGC circuit 47. The AGC circuit 47 includes a gain control amplifier 471, a detection circuit 472, and an amplitude calculation circuit 473. The detection circuit 472 detects the HF signal and outputs the detected signal. The amplitude calculation circuit 473 calculates the amplitude of the HF signal from the detected signal, and controls the gain of the gain control amplifier 471 based on the calculated amplitude. That is, if the amplitude of the HF signal is small, the amplitude calculation circuit 473 controls the gain of the gain control amplifier 471 to increase. Conversely, if the amplitude of the HF signal is large, the amplitude calculation circuit 473 controls the gain of the gain control amplifier 471 to decrease. The gain control amplifier 471 amplifies the HF signal with the controlled gain and outputs the amplified HF signal.
[0017]
[Problems to be solved by the invention]
However, an optical disk having a writing function does not always have an HF signal on the optical disk. If the AGC function of the gain control amplifier 471 operates without the HF signal, the gain (gain) becomes abnormally high. If the HF signal suddenly appears in this state, the gain of the gain control amplifier 471 becomes too high, and the amplified HF signal causes clipping. As a result, data reading is hindered. Therefore, in order not to create such a state, it is necessary to make full use of measures such as fixing the gain of the gain control amplifier 471.
[0018]
Therefore, an object of the present invention is to provide an optical disc reading apparatus capable of always actively controlling the gain of an amplifier constituting an optical disc reading apparatus even if a writable optical disc is in an unrecorded state. is there.
[0019]
[Means for Solving the Problems]
According to the present invention, in an optical disk reading device for reading a signal picked up by an optical pickup (OPU) from a rotating optical disk (DISC), amplifying means for amplifying the picked up signal and outputting an amplified signal ( 451) and a gain control means (43) for controlling the gain of the amplifying means so that the peak level of the amplified signal is constant.
[0020]
In the above optical disk reading device, the optical pickup may be a polarization optical system optical pickup (OPU).
[0021]
In the above optical disk reading apparatus, the gain control means comprises a peak hold circuit (43) for holding a peak of the picked-up signal and outputting a peak hold signal. It may comprise a gain control amplifier (44) that amplifies the hold signal with a reciprocal gain and outputs the amplified signal.
[0022]
In the above optical disk reading apparatus, the gain control means comprises a peak hold circuit (43) for holding a peak of the picked-up signal and outputting a peak hold signal. It may be configured by a divider (45) that divides by a hold signal and outputs a result of the division as an amplified signal.
[0023]
It should be noted that the reference numerals in the parentheses are provided for easy understanding, are merely examples, and are not limited to these.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0025]
First, an optical disk drive to which an optical disk reading device according to an embodiment of the present invention is applied will be described with reference to FIGS. FIG. 1 shows a state when the optical pickup OPU moves to the inner periphery, and FIG. 2 shows a state when the optical pickup OPU moves to the outer periphery. 1 (a) and 2 (a) are plan views, and FIGS. 1 (b) and 2 (b) are left side views.
[0026]
On the chassis 11, a spindle motor 13 and a feed motor 15 are mounted. The spindle motor 13 rotates a turntable 17 mounted thereon. An optical disk (not shown) is mounted on the turntable 17. Therefore, when the spindle motor 13 rotates, the optical disk mounted on the turntable 17 also rotates.
[0027]
A drive reduction gear 19 is engaged with the drive shaft of the feed motor 15, and the drive reduction gear 19 is engaged with a rack 21 formed on one side of the optical pickup OPU. The optical pickup OPU is guided by a pair of guide shafts 23a and 23b. Therefore, when the feed motor 15 rotates, the optical pickup OPU is transported along the pair of guide shafts 23a and 23b.
[0028]
Referring to FIG. 3, the optical pickup OPU includes a semiconductor laser (laser diode) LD, a diffraction grating GRT, a collimator lens CL, a polarizing beam splitter PBS, a quarter-wave plate QWP, an objective lens OL, and a sensor. It has a lens SL and a photodetector PD. The illustrated optical pickup OPU includes a front monitor FM for monitoring a part of the laser beam emitted from the semiconductor laser LD, and a laser driver 25 for driving the semiconductor laser LD.
[0029]
The illustrated optical pickup OPU includes a polarization beam splitter PBS and a quarter-wave plate QWP, and is therefore called a polarization optical system optical pickup.
[0030]
Incidentally, one laser beam emitted from the semiconductor laser LD is separated into three laser beams by the diffraction grating GRT. These three laser beams consist of a main beam at the center and sub-beams on both sides of the main beam. The laser beam emitted from the semiconductor laser LD is linearly polarized light.
[0031]
Anyway, the three laser beams emitted from the semiconductor laser LD and separated by the diffraction grating GRT are collimated by the collimator lens CL and then reflected at right angles by the polarization beam splitter PBS. The laser beam reflected by the polarizing beam splitter PBS is circularly polarized by the quarter-wave plate QWP, and then condensed (irradiated) on the signal recording surface (reflection surface) of the optical disc DISC via the objective lens OL. You.
[0032]
FIG. 4 shows a spot of the laser beam applied to the optical disc DISC. As described above, the three laser beams divided by the diffraction grating GRT connect three spots to the track on the pit surface of the optical disc DISC as shown in FIG.
[0033]
Returning to FIG. 3, the reflected light (return light) from the signal recording surface of the optical disc DISC passes through the objective lens OL, is bent 90 ° with respect to the polarization direction of the outward path by the quarter-wave plate QWP, and is polarized by the polarization beam splitter PBS. And is detected by the photodetector PD through the sensor lens SL.
[0034]
The illustrated optical pickup OPU employs a method using three beams formed using a diffraction grating as a tracking error detection method. Among the methods using three beams, the differential push-pull method is particularly used.
[0035]
More specifically, as described above, one laser beam emitted from the laser diode LD as a light source is separated into three laser beams by the diffraction grating GRT. Therefore, the reflected light (return light) from the optical disc DISC also includes three laser beams. Of the three laser beams, the central main beam is used to generate a read signal and a focus error signal, and the two sub beams on both sides are used to generate a tracking error signal.
[0036]
FIG. 5 shows a configuration of a photodetector PD for receiving reflected light (return light). 5A is a front view, and FIG. 5B is a right side view. The photodetector PD has a main light receiving element 31 for receiving a main beam, and a pair of sub light receiving elements 32 and 33 for receiving two sub beams on both sides. The main light receiving element 31 is constituted by a four-division photodiode, and each of the sub light receiving elements 32 and 33 is constituted by a two-division photodiode.
[0037]
Therefore, of the three spots shown in FIG. 4A, the reflected light (main part) from the center spot (the part marked with A, B, C, and D in FIG. 4A). 5) are received by the main light receiving element 31 shown in FIG. 5 as four main electric signals indicated by reference numerals A, B, C, and D in FIG. The reflected light (sub-beam) from the spot on one side (the portion denoted by reference signs E and F in FIG. 4A) is transmitted by one sub-light receiving element 32 shown in FIG. Are received as two sub-electrical signals indicated by symbols E and F. Then, the reflected light (sub-beam) from the other side spot (the part marked with G and H in FIG. 4A) is reflected by the other sub-light receiving element 33 shown in FIG. Are received as two sub-electric signals indicated by G and H symbols.
[0038]
Next, an optical disk reading device according to the first embodiment of the present invention will be described with reference to FIG.
[0039]
The illustrated optical disk reader includes an adder circuit 41, a peak hold circuit 43, and a gain control amplifier 44.
[0040]
The adder circuit 41 includes an operational amplifier 411. The four main electric signals described above are supplied to the non-inverting input terminal + thereof through the resistors 422 to 425, and the HF reference voltage is supplied to the inverting input terminal thereof. It is supplied via a resistor 426, and a resistor 427 is connected between its output terminal and the inverting input terminal-. This adding circuit 41 outputs an HF signal (a picked-up signal).
[0041]
The output terminal of the adder circuit 41 is connected to the peak hold circuit 43. The peak hold circuit 43 holds the peak of the HF signal output from the adder circuit 41 and outputs a peak hold signal. This peak hold signal is a signal indicating the level of the reflected light component (hereinafter, referred to as “I-TOP”) of the HF signal.
[0042]
The output terminal of the addition circuit 41 is connected to the input terminal 441 of the gain control amplifier 44, and the output terminal of the peak hold circuit 43 is connected to the control terminal 442 of the gain control amplifier 44. The gain control amplifier 44 amplifies the HF signal with the inverse gain of the peak hold signal, and outputs an amplified signal.
[0043]
That is, the gain control amplifier 44 operates as amplifying means for amplifying the HF signal according to the level of the I-TOP. More specifically, if the level of the I-TOP is low, the gain control amplifier 44 amplifies the HF signal with a large gain (amplification factor), and if the level of the I-TOP is high, the gain control amplifier 44 converts the HF signal into a small gain. (Amplification rate). Therefore, the amplitude of the amplified HF signal can always be kept constant.
[0044]
Next, an optical disc reading apparatus according to a second embodiment of the present invention will be described with reference to FIG.
[0045]
The illustrated optical disk reader has the same configuration as that of the optical disk reader shown in FIG. 6 except that a divider 45 is used instead of the gain control amplifier 44, and performs the same operation. Therefore, the components having the same configuration in FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted for simplification of the description.
[0046]
An output terminal of the adder circuit 41 is connected to a first input terminal 451 of the divider 45, and an output terminal of the peak hold circuit 43 is connected to a second input terminal 452 of the divider 45. The voltage of the HF signal supplied to the first input terminal 451 of the divider 45 is called a first voltage V1, and the voltage of the peak hold signal (I-TOP level) supplied to the second input terminal 452 is It will be referred to as a second voltage V2. The divider 45 divides the first voltage V1 by the second voltage V2 and outputs the result of the division (V1 / V2).
[0047]
That is, the divider 45 operates as an amplifying unit that amplifies the HF signal according to the level of the I-TOP. More specifically, if the level of the I-TOP is low, the divider 45 amplifies the HF signal with a large gain (amplification factor), and if the level of the I-TOP is high, the divider 45 amplifies the HF signal with a small gain (amplification). Rate). Therefore, the amplitude of the amplified HF signal can always be kept constant.
[0048]
The I-TOP of the HF signal always exists even when the write-type optical disc DISC is in an unrecorded state, and includes an error signal indicating the reflectance of the optical disc DISC. Therefore, the optical disk reader shown in FIGS. 6 and 7 can always activate the gain control of the HF signal.
[0049]
This makes it possible to make the amplitude of the HF signal amplified in real time constant. For this reason, it is possible to eliminate a state in which no feedback is applied as in a conventional optical disk reader using the AGC circuit 47.
[0050]
In particular, when the optical pickup is a polarization optical system optical pickup OPU as shown in FIG. 3, a phenomenon occurs in which the amplitude of the HF signal decreases due to a decrease in the reflectance due to the birefringence of the optical disc DISC. It is known that this phenomenon changes greatly in the plane of the optical disc DISC. Thus, even if the amplitude of the HF signal is reduced due to the birefringence of the optical disk DISC, the optical disk reading apparatus according to the present invention always controls the gain of the amplifying means (gain control amplifier 44 or divider 45) in an active manner. It has the great advantage of being able to.
[0051]
FIG. 9 illustrates the dependence of the amount of returning light to the photodetector PD and the amount of birefringence of the optical disc DISC. In FIG. 9, the vertical axis represents the amount of return light to the photodetector PD with the maximum value normalized to 1, and the horizontal axis represents the birefringence [nm] of the optical disc DISC. Here, it is assumed that the light emitted from the quarter-wave plate QWP toward the optical disc DISC is perfectly circularly polarized light, and that the wavelength of the laser beam emitted from the semiconductor laser LD is 785 nm.
[0052]
As is clear from FIG. 9, it is found that the birefringence of the optical disc DISC increases as the amount of return light to the photodetector PD decreases. When the amount of light returning to the photodetector PD is zero, the birefringence of the optical disc DISC is 392.5 [nm].
[0053]
Next, the dependence of the return light to the photodetector PD on the birefringence of the optical disc DISC will be described with reference to FIG. It is assumed that light is perpendicularly incident on the quarter-wave plate QWP, the direction of linearly polarized light is parallel to the X (radial) direction, and the optical disc DISC has no birefringence. In this case, light transmitted through the quarter-wave plate QWP becomes circularly polarized light. Here, it is assumed that the circularly polarized light is clockwise. The light reflected by the optical disc DISC is turned into counterclockwise circularly polarized light and enters the quarter-wave plate QWP. The light emitted from the quarter-wave plate QWP becomes linearly polarized light parallel to the Y (tangential) direction, transmits nearly 100% through the polarization beam splitter PBS, and enters the photodetector PD. Hereinafter, this state is set to 1 and standardized for consideration.
[0054]
Next, it is assumed that the phase is advanced by δ radians due to the birefringence of the optical disc DISC. In the following, 4) when (1) 0 <δ <π / 2, (2) when δ = π / 2, (3) when π / 2 <δ <π, and (4) when δ = π A description will be given separately for the following cases.
[0055]
{Circle around (1)} When 0 <δ <π / 2, the light reflected by the optical disk DISC is converted into left-handed elliptically polarized light, enters the quarter-wave plate QWP, and is straightened at a certain position inside the quarter-wave plate QWP. It becomes polarized light. Thereafter, the outgoing light from the quarter-wave plate QWP is emitted as elliptically polarized light in a clockwise direction with a phase advanced by π / 2 from the incident light. Since the amount of light transmitted through the polarization beam splitter PBS is represented by a component in the Y direction of the ellipse, the amount of light incident on the photodetector PD is cos (δ / 2).
[0056]
{Circle around (2)} When δ = π / 2, the light reflected by the optical disc DISC is converted into linearly polarized light parallel to the Y direction, enters the quarter-wave plate QWP, and rotates clockwise from the quarter-wave plate QWP. And emitted. Therefore, the light amount of the incident light on the photodetector PD is also cos (π / 4) ≒ 0.707.
[0057]
{Circle around (3)} When π / 2 <δ <π, the light reflected by the optical disc DISC becomes clockwise elliptically polarized light, enters the quarter-wave plate QWP, and forms a circle at a certain position inside the quarter-wave plate QWP. It becomes polarized light. Thereafter, the outgoing light from the quarter-wave plate QWP is emitted as elliptically polarized light in a clockwise direction with a phase advanced by π / 2 from the incident light. Therefore, the light quantity of the incident light on the photodetector PD is cos (δ / 2).
[0058]
{Circle around (4)} When δ = π, the light reflected by the optical disk DISC is converted into clockwise circularly polarized light, enters the quarter-wave plate QWP, and becomes linearly polarized light parallel to the X direction from the quarter-wave plate QWP. And is emitted. Therefore, the light quantity of the incident light on the photodetector PD is also cos (π / 2) = 0.
[0059]
Tables and graphs that summarize the above are shown in FIGS. 11 and 12, respectively. FIG. 11 is a table showing the relationship between the amount of birefringence of the optical disk, the phase shift, and the amount of incident light on the photodetector. FIG. 12 is a diagram showing the relationship between the amount of incident light on the photodetector and the amount of birefringence on the optical disk.
[0060]
The elliptically polarized light whose major axis is in the Y direction indicates a case where the phase δ advanced by the birefringence of the optical disc DISC is in the range of 0 to π. In this case, the birefringence of the optical disc DISC in the graph shown in FIG. 12 corresponds to the portion where the birefringence is from 0 nm to 392.5 nm.
[0061]
On the other hand, the elliptically polarized light whose major axis is in the X direction indicates a case where the phase δ advanced by the birefringence of the optical disc DISC becomes π or more or becomes negative. In this case, the birefringence of the optical disc DISC in the graph shown in FIG. 12 corresponds to the portion from 392.5 nm to 785 nm.
[0062]
The present invention is not limited to the above-described embodiment, and it goes without saying that various changes and modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the optical pickup is a polarization optical system pickup is described. However, the present invention is not limited to this. It is.
[0063]
【The invention's effect】
As is clear from the above description, according to the present invention, the amplifying means for amplifying the picked-up signal (HF signal) and outputting the amplified signal (HF signal), and the amplified signal (HF signal) And a gain control means for controlling the gain of the amplifying means so that the peak level of the HF signal becomes constant, so that the amplitude of the HF signal amplified in real time can be made constant. Thus, even if the writable optical disk is in an unrecorded state, the gain of the amplifying means constituting the optical disk reader can always be actively controlled.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state of an optical disk drive to which an optical disk reading device according to an embodiment of the present invention is applied when an optical pickup moves to an inner periphery, where (a) is a plan view and (b) Is a left side view.
FIGS. 2A and 2B are diagrams showing a state of the optical disk drive shown in FIG. 1 when an optical pickup moves to an outer periphery, where FIG. 2A is a plan view and FIG. 2B is a left side view;
FIG. 3 is a block diagram showing a configuration of a polarization optical system optical pickup used in the optical disk drive shown in FIGS. 1 and 2;
4A and 4B are diagrams showing spots of a laser beam applied to an optical disk, wherein FIG. 4A is a plan view and FIG. 4B is a schematic sectional view.
5A and 5B are diagrams illustrating a configuration of a photodetector for receiving reflected light (return light) used in the polarization optical system optical pickup illustrated in FIG. 3, wherein FIG. 5A is a front view and FIG. FIG.
FIG. 6 is a block diagram showing a configuration of an optical disk reading device according to the first embodiment of the present invention.
FIG. 7 is a block diagram illustrating a configuration of an optical disk reading device according to a second embodiment of the present invention.
FIG. 8 is a block diagram showing a configuration of a conventional optical disk reading device.
FIG. 9 is a diagram showing a dependence relationship between the amount of returning light to the photodetector and the amount of birefringence of the optical disk.
FIG. 10 is a diagram for explaining dependence of return light to a photodetector on birefringence of an optical disk.
FIG. 11 is a table showing a relationship between a birefringence amount of an optical disc, a phase shift, and an incident light amount of a photodetector.
FIG. 12 is a diagram showing the relationship between the amount of incident light on a photodetector and the amount of birefringence on an optical disk.
[Explanation of symbols]
41 Adder circuit 43 Peak hold circuit 44 Gain control amplifier 45 Divider

Claims (5)

In an optical disk reading device for reading a signal picked up by an optical pickup from a rotating optical disk,
Amplifying means for amplifying the picked-up signal and outputting an amplified signal;
An optical disc reading apparatus comprising: a gain control means for controlling a gain of the amplifying means so that a peak level of the amplified signal is constant. The optical disk reader according to claim 1, wherein the optical pickup is a polarization optical system optical pickup. The gain control means comprises a peak hold circuit that holds a peak of the picked-up signal and outputs a peak hold signal,
3. The optical disk reading device according to claim 1, wherein the amplifying unit comprises a gain control amplifier that amplifies the picked-up signal with a reciprocal gain of the peak hold signal and outputs the amplified signal. The gain control means comprises a peak hold circuit that holds a peak of the picked-up signal and outputs a peak hold signal,
3. The optical disk reading device according to claim 1, wherein the amplification unit includes a divider that divides the picked-up signal by the peak hold signal and outputs a result of the division as the amplified signal. An optical disk drive comprising the optical disk reader according to any one of claims 1 to 4.

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