JPS58185044A - Disk reproducer - Google Patents

Abstract

PURPOSE:To ensure accurate tracking control, by minimizing the degree of DC offset that is based on the inclination of a disk produced in a tracking error signal. CONSTITUTION:The reflected light beams of a disk are detected by photodetecting parts 7A and 7B. The detecting signals SA and SB have the same level when the disk has no inclination and then have the levels deflected from the normal level if the disk has some inclination. For each of these detecting signals, the level is detected at the part minimum in level fluctuation degree. Then a tracking error signal is obtained based on the difference between the levels of both detecting signals. The fluctuation component is small for each of extracted both levels. As a result, the offset generated in the tracking error signal owing to the inclination of the disk is extremely reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical digital audio disc;
The present invention relates to a disc reproducing apparatus used for reproducing an optical disc in which a recording track is formed by an array of pits, such as the above.

In general, in order to correctly read information on a spiral recording track consisting of an array of pits formed on the surface of an optical digital audio disc, etc., in a disc playback device, a laser beam for reading is constantly directed onto the recording track. It is necessary to perform tracking control for proper tracking.

FIG. 1 shows an optical system of an example of a conventional disc playback device that performs such tracking control. In the figure, a light beam from a laser light source is collimated by a collimator lens λ. This parallel light beam passes through the beam splitter 3, and is converted from linearly polarized light to circularly polarized light by the j wavelength plate. , this converted original beam of circularly polarized light is made incident by an objective lens S so as to be focused on a recording track consisting of an array of pits formed on the surface of the disk A, and the reflection from the recording track is The light beam is collimated by the objective lens S, and then converted from circularly polarized light to linearly polarized light again by a wavelength plate. This converted linearly polarized reflected light beam has a linear polarization plane that is 90° different from that of the linearly polarized light beam emitted from the beam splitter 3 to the TiSF 6 side. Therefore, it is reflected by the beam splitter 3 and guided to the photodetector 7. The photodetector 7 is composed of first and second photodetectors 7A and 7B each having a light receiving area obtained by dividing the detection area into two, and as shown in FIG. After the detection signals obtained by the detection units 7A and 7B are amplified to a predetermined level by the amplifiers A and gB, their average level is detected by the first and second average level detection circuits 9A and 9B, respectively. be done. The signals detected by the first and second average level detection circuits 9A and 9B are each supplied to a subtracter 10 to determine the level difference between them. In other words, the difference between the average values of the amounts of light received by the first and second photodetectors 7A and 7B is determined, and this is supplied to the servo amplifier // as a tracking error signal. A control signal based on the tracking error signal obtained from is supplied to, for example, a tracking control coil 2 constituting a linear motor (not shown), whereby a light beam from a laser light source is formed on the screen. controlled to move in a direction across the recording track,
A predetermined tracking control is performed to make the light beam incident on the disk always follow the recording track.

Here, we will talk about tracking error detection.
In this case, the optical depth of the bits forming the recording track of the disk is set not to be an integral multiple of the wavelength of the light beam from the laser light source. The positional relationship between the recording track consisting of an array of Become.

As shown in FIG. 3A, in the just tracking state where the center of the light spot P is located at the center of the recording track Q where the bits are arranged, diffraction occurs over the entire center R of the detection area of the photodetector 7. As shown in FIG. 3B, if the center of the optical spot P is shifted to the right side of the recording track Q, a pattern S is obtained, and as shown in FIG. For example, any character-shaped diffraction pattern S can be obtained. Furthermore, as shown in FIG. 3C, if the center of the optical spot P shifts to the left side of the recording track Q,
For example, at a position shifted to the left in the center R of the detection area,
A diffraction pattern S in any shape is obtained. Therefore, the first and second photodetecting sections 7A divide the central portion R of the detection area into λ parts.
, 7B, and the difference between the amounts of light received in the respective light-receiving areas, the tracking error state is detected. However, as shown by the dashed line in FIG. If the disc surface of the disc is tilted with respect to the optical axis of the light beam from the laser light source, for example, when a disc with local deformation is being played, or if the disc surface of the disc is tilted with respect to the optical axis of the light beam from the laser light source, On the other hand, in cases where a disc B installed at an angle is played, the reflected light beam from the disc B is aligned with the optical axis of the light beam incident on the disc B, as shown by the broken line in Figure 1. Therefore, a portion of the light beam reflected from the disk 6 will be out of the effective field of view of the objective lens S.
The amount of light incident on the light receiving area of the first photodetector 7A and the λth
There is a steady difference between the amount of light incident on the light receiving area of the λth photodetector 7B, and therefore the detection signal from the first photodetector 7A and the λth photodetector 7B are different. A level □ fluctuation occurs in each of the detection signals based on the inclination of the disk B, and in the tracking error signal obtained by calculating the level difference between the two by the subtractor 10, the above-mentioned steady-state fear is added to the original tracking error signal component. A level difference component is added to generate a DC offset. This DC offset converts the tracking error signal into
There is a risk that the tracking error signal may be generated even in a just tracking state, and proper tracking control may not be performed1. Normally, level fluctuations based on the inclination of the disk B, which occur in the detection signals from the first photodetector 7A and the second photodetector 7B, which are the basis for causing the above-mentioned DC offset, cause the recording track to change. The width of the fluctuation varies depending on the state of the pit to be formed and the light spot that illuminates the pit, which will be explained below.

First, to describe the relationship between each situation with respect to the pit of the optical spot and the detection signals from the first and second photodetectors 7A and 7B, as shown in FIG. When the light spot (P/ in Fig. q, C) is located on the mirror surface between the bits, the detection signal Ss (Fig. q, A) becomes the maximum level vmaX. For convenience of explanation, the straight part of the edge of the pit in the direction along the recording track will be referred to as the straight edge part.
A curved portion continuous to both ends of this straight edge portion is called a curved edge portion. Next, the pit Q formed on the disk B,
When the light spot (P2 in FIG. q, C) is positioned so as to include the straight edge portion of , but not include the curved edge portions at both ends, the detection signal Ss becomes the minimum level V□in. Furthermore, if the light spot (P, ? in Figure C) is positioned so as to include one curved edge of pit Ql and one curved edge of the next pit Q2 adjacent to this pit Q/, The detection signal SS is at a level slightly lower than the maximum level VmaX, and furthermore, as in the case of pit Q3, 7
A light spot containing two pits (P in Figure C)
<z), the detection signal Ss is at the minimum level Vm
The level is slightly higher than in, and the light spot including only one curved edge part of this pit Q3 (P in Fig. 9C)
s), the detection signal Ss has the maximum level v
The level is slightly lower than maX.

Then, as described above, the detection signal S obtained with the 9 relationship
The level fluctuation based on the inclination of the disk B and the detection signal Ss that occurs when the level of S is at the minimum level Vmin.
When compared with the level fluctuation based on the inclination of the disk B which occurs when the level of Vmin is equal to or higher than the minimum level Vmin, the latter results in a larger level fluctuation. This is because the diffraction pattern generated on the photodetector 7 when the straight edge of each pit is included in the light spot is affected by the pattern change caused by the inclination of the disk A. Alternatively, if the straight edge portion and the curved edge portion are all included in the light spot, the diffraction pattern generated on the photodetector 7 will be affected by the butter 7 change caused by the tilt of the disk A. It is caused by

Therefore, like a conventional disc playback device, the average level of the detection signals from the first and second photodetectors 7A and 7B is supplied to the subtracter IO to determine the level difference to obtain the tracking error signal. In this case, as mentioned above, the part where the level fluctuation based on the inclination of the disc B is large, that is,
The tracking error signal is affected by the part of the detection signal obtained when the curved edge of the pit is included in the optical spot, and the amount of DC offset caused by the tilt of the disk becomes large. There is the inconvenience of putting it away.

In view of this point, the present invention provides a DC-off method based on the inclination of the disk, which occurs due to tracking errors.

To provide a disc reproducing device which can perform reliable tracking control by reducing the set amount as much as possible. Examples of the present invention will be described below. ,.

FIG. 5 is a circuit diagram showing a tracking control section in an example of a disc playback device according to the present invention. An example of a disc playback device according to the present invention has an optical system similar to that shown in FIG. , its tracking control unit is the fifth
The circuit portion shown in the figure replaces the first and second average level detection circuits 9A and qB, respectively, in the circuit portion of the conventional disc playback device shown in FIG. 2 with the first and λ-th level extraction circuits. /3 and 73', and the same reference numerals as in FIG. 2 are given to the parts corresponding to the respective parts shown in the other Ω diagrams.

Here, the first level extraction circuit /3 is a diode /3
A, a capacitor 73B, and a resistor /3C constitute a peak hold circuit. And amplifier g
The output terminal of A is connected to the cathode of diode 2)"-/-, 4A, and the anode of this diode ?A is connected to one end of each of capacitor /3B and resistor /3C, Further, the other end of the capacitor /3B and the other end of the resistor /3C connected to one of the input ends of the subtracter 10 are connected in common, and this common connection end is connected to the terminal /G, and this terminal /lI is supplied with an operating voltage from a power supply circuit (not shown).

Also, between the output terminal of the amplifier gB and the other input terminal of the subtracter 10, a diode /3A', a capacitor 73B' and a resistor /3C are connected, similar to the first level extraction circuit /3.
A first level extraction circuit 73' is inserted, which is a peak hold circuit composed of a first level extraction circuit 73'.

The operation of the circuit portion according to the present invention configured as described above will be explained with reference to the waveform diagram shown in FIG.

When the reflected light beam from the disk B enters the detection area of the photodetector 7, the first and second photodetectors 7A and 7B
is generated according to the amount of light received by the amplifiers gA and g.
The detection signals SA and Sa amplified by B are shown as solid lines in FIG. As shown by A difference occurs in the amount of light received by the photodetectors 7A and 7B, and as a result,
The levels are different from each other except for the maximum level part. The detection signal SA from the amplifier gA is supplied to the cathode of a diode 73 forming the peak hold circuit of the first level extraction circuit/3. This first level extraction circuit/3 uses a peak hold operation to detect the detection signal SA.
The level of the minimum level part (level corresponding to Vmln in FIG. 9) is held, and the held output is supplied to one input terminal of the subtracter 10 as a level extraction output. Further, the detection signal SB from the amplifier ZA B is supplied to the cathode of the diode/3A of the first level extraction circuit 73', and similarly, the detection signal SB is supplied from the first level extraction circuit 73' by peak hold operation. The level extraction output obtained by holding the level of the minimum level part of SH is
The signal is supplied to the other input terminal of the subtracter 10. Then, in the subtracter 10, the first and second level extraction circuits /3 and 73'
The level difference between the level extraction outputs from each is determined, and the output power corresponding to the level difference is supplied as a tracking error signal to the servo amplifier //, and the corresponding control signal is sent to the tracking control coil /2. tracking control is performed.

Here, if the disk B is tilted, the detection signals SA and SR will have a level that fluctuates from the normal level as shown by the dotted line in FIG. The level fluctuation occurring in the detection signal S
The amount p pleasure p' at the minimum level part of A and SR, that is, the part that is good when the light spot on the disk 6 includes the straight edge part of the bit and does not include the curved edge part at both ends, is the detection signal. By the way, the circuit according to the present invention shown in FIG. When a portion is used, the minimum level portion of the detection signals SA and Ss that includes level fluctuations due to the inclination of the disk 6, in other words, the light spot on the disk 6 includes the straight edge portion of the bit and is located at both ends. The level of the part obtained when the curve edge part is not included is extracted and used to obtain the tracking error signal.This means that the detection signal includes level fluctuations due to the inclination of the disk. For each of S^ and Ss, the level where the amount of level fluctuation is the smallest is extracted, and a tracking error signal is obtained based on the difference between the two extracted levels3. Therefore, the extracted t The difference in the level fluctuation components at each of the two extracted levels becomes a DC offset that occurs in the tracking error signal, but since the level fluctuation components at each of these two extracted levels are small, it is The DC offset that occurs in the tracking error signal due to the slope of is significantly reduced.

Note that the detection is performed at the maximum level portions in SA and SB, in other words, at the portions obtained when the light spot on the TiSF 6 is on a mirror surface area with no pits, the level fluctuation due to the inclination of the disk B is small, but Since such a part does not have information about the tracking situation, it cannot be used to obtain a tracking error signal.

Next, another specific example of the configuration of the first and first L/, hell extraction circuits/3 and 73' used in the above-described example of the disc playback device according to the present invention will be explained with reference to FIG. do.

The circuit shown in FIG. 7 constitutes a sampling and holding circuit as a whole, and the output terminal of the amplifier gA or the amplifier gB shown in FIG. S is connected to the terminal 2o, and the output terminal of the amplifier gA or the amplifier gB shown in FIG. The input end of the subtracter 10 shown in FIG.

The terminal 20 is connected to one end of the first sampling switch, and the other end of the terminal 22 is connected to one end of the first sampling switch 23. The first capacitor 2 is connected to one end of the capacitor 2, and the other end of the first capacitor 2 is grounded. The other end of the second sampling capacitor 23 is connected to one end of the first sampling capacitor 2, and the other end of the first capacitor 23 is connected to the terminal 2/. The other end of the capacitor 25 is also grounded. Further, the terminal 2o is connected to the comparison input terminal of the comparator 2O, and the reference input terminal of the comparator 2O is connected to the reference voltage source, ! 7 is connected. Inverter 2g is installed at the output end of converter tacho Otsu.
A first monostable multivibrator 29 triggered by the rising edge of the input signal and a λ-th monostable 0 multivibrator 30 triggered by the falling edge of the input signal are connected in sequence, and the second monostable tube The output end of the multivibrator 30 is connected to the first sampling switch 2.
It is connected to the control end of 2.

Further, the output terminal of comparator 2B is connected to one input terminal of NOR gate 3/, and the output terminal of inverter 2g is connected to the other input terminal of this NOR gate 3/, which is triggered by the rising edge of the input signal. The output end of a third monostable multivibrator 32 is connected thereto.

The output terminal of the NOR gate 3/ is a ninth monostable multivibrator 3 that is triggered by the rising edge of the input signal.
It is connected to the input terminal of 3. The output end of the q-th monostable e-multivibrator 33 is connected to the control end of the second sampling switch 23. This will be explained with reference to the waveform diagram in FIG. terminal 20
When a detection signal a as shown in FIG.
A comparison is made with the reference voltage (8) from the reference voltage source 27, and the comparison output signal shown in FIG.
This comparison output signal S is inverted by an inverter 2g to become a signal C shown in FIG. 3C.

At the rising edge of this signal C, the first monostable fist multivibrator 29 is triggered, and the pulse width is 1. A signal d having 6 is obtained, and at the falling edge of this signal d the first monostable multivibrator 30 is triggered and a first sampling pulse e shown in FIG. S is obtained. The first sampling pulse e obtained in this way turns on the first sampling switch core a, and sampling and holding of the detection signal a supplied to the terminal 20 is performed.In other words, the detection signal a The level of is the reference voltage V
Sampling and holding is performed when the level is lower than 8. The signal held in this way is sampled and held again by the sampling switch 23, and the final output is obtained at the terminal U/. That is, at the rising edge of the signal C, the NOR output of the signal f having the pulse width t shown in FIG. is determined by the NOR gate 3/, and a signal g shown in FIG. G is obtained at the output terminal of the NOR gate 3/. At the rising edge of this signal g, a U-th sampling pulse h shown in FIG. The second sampling cross h obtained in this way turns on the second sampling switch Ω,3, and the voltage held in the first capacitor 2q is transferred to the second capacitor 2S. sampled and held,
Thereby, the signal obtained at terminal 2/ is supplied to the subtracter /θ.

In this case, the signal obtained at terminal 2/ is the level of the detection signal a sampled and held after a predetermined time tl after the output of the controller 7 (later λ B becomes low level), and after a further predetermined time t, 2. , the output of comparator 2B is sampled and held when it is at a low level, so the level of the minimum level part of the detection signal a becomes the extracted level extraction output. Even when the hold circuit is used as the first and second level extraction paths /3 and /3' in FIG. S, the same effects as in the case of the peak hold circuit described above can be obtained.

As explained above, in the disc playback device according to the present invention, the level fluctuations due to the tilt of the disc are not easily affected among the detection signals obtained from each of the first and Ω-th photodetectors divided into two parts. , the tracking error signal is obtained by extracting the level of the part obtained when the original spot above the disk 1° includes the straight edge part of the bit forming the recording track and does not include the curved edge part at both ends. Therefore, the DC offset that occurs in the tracking error signal due to the inclination of the disk can be suppressed to an extremely small value, and stable and reliable tracking control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the optical system of a disc playback device;
FIG. 2 is a circuit diagram showing an example of a tracking recommendation section in a conventional disk playback device, FIG. 3 is a diagram used to explain tracking error detection, and FIG. FIG. 5 is a circuit diagram showing the tracking control section in an example of the disc playback device according to the present invention, and FIG. 6 is an explanation of the operation of the tracking control section shown in FIG. S. FIG. 7 is a circuit diagram showing another example of the main part of the tracking control section in an example of the disc playback device according to the present invention, and FIG. S is a diagram for explaining the operation of the example shown in FIG. FIG. In the figure, / is a laser light source, 2 is a collimator lens, 3 is a beam splitter, G is a single wavelength plate, S' is an objective relens, O is a disk, 7 is a photodetector, 7A is a first photodetector, 7B 10 is a subtracter, // is a servo amplifier, /2 is a tracking control coil, /3 is a first level extraction circuit, and 73' is a th level extraction circuit. Fig. 1 Fig. 2 111411 Fig. 5 Fig. 6 Fig. 711 No. 8 WJ

Claims (1)

[Claims] A light beam that is made incident on a disk on which a recording track is formed by an array of pits and reddens the disk is divided into two parts, a first beam, a second beam, and a second beam. a photodetector that detects the photodetection unit;
When the light beam incident on the disk illuminates seven of the pits without including both ends thereof in the recording track direction, for each of the detection signals from the first and first photodetectors. first and first level extraction circuits that extract the levels of the obtained portions, respectively;
and a subtracter to which output signals of the λ-th level extraction circuit are supplied, and a tracking state of the recording track when the light beam is made incident on the disk based on the output signal of the subtracter. A disc playback device comprising control means.