JPH0562219A - Optical disk recording and reproducing device - Google Patents

Abstract

PURPOSE:To enlarge a jitter margin to a defocusing quantity by equalizing the regenerative RF signal output of an optical head. CONSTITUTION:An equalizer 12 is provided on the output side of the optical head 3 reproducing the recording data of an optical disk 1, the frequency characteristic of the equalizer 12 is set so as to raise the high band frequency of the regenerative RF signal. An optical disk device is controlled with a focus so as to make a tracking level the best, though a point where the jitter margin is minimum is deviated by astigmatism caused by it, an MTF characteristic in appearance is improved by the above-mentioned equalizer 12 and the best point of tracking is coincident with a jitter bottom point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk recording / reproducing apparatus capable of recording information in response to light and reading the information, and particularly, it is intended to reduce the jitter of a reproduction RF signal during reproduction. It is a thing.

[0002]

2. Description of the Related Art A semiconductor laser light emitting element is generally used as a light emitting source in an optical disk device which irradiates a recording surface of an optical disk with a laser beam and converts the reflected light into an electric signal to read out data. ..

FIG. 5 shows a block diagram of a reproducing system of a digital audio disc recording / reproducing apparatus. Reference numeral 1 is an optical disc on which music data is recorded on the lower side, and 2 is an optical disc 1 rotated at a predetermined rotation speed. A spindle motor 3 for driving irradiates a laser beam output from a laser emission source on the recording surface of the optical disc 1 as described later, and a tracking actuator, a focus actuator, and a tracking actuator whose spot tracks a recording track. The optical head is provided with a detector for reading data from reflected light and detecting a servo error signal and the like, and is held so as to be movable in the radial direction of the optical disc 1 by a feeding mechanism (not shown). Then, the reproduced RF signal reproduced by this optical head is supplied to the RF signal processing circuit 4, amplified to a predetermined level, waveform-shaped and supplied to the digital signal processing circuit 5.

The digital signal processing circuit 5 detects various data contained in the reproduced RF signal and binarizes the data, and the PLL circuit 6 generates a clock signal to generate P.
Demodulates the data converted into CM. The demodulated audio data is taken out as analog stereo signals L and R via the D / A converter 7.

The tracking error signal detected by the optical head controls the movement of the objective lens in the radial direction of the disk through the tracking servo circuit 8, and the detected focus error signal is the focus servo circuit 9.
The focus of the objective lens is controlled via the so that the laser spot is always focused on the recording surface of the disc. It should be noted that the clock signal component is supplied to the spindle motor 2 via the rotary servo circuit 10, and the optical disc 1
Remove the uneven rotation of.

FIG. 6 shows the optical system of the optical head 3 employed in the optical disk recording / reproducing apparatus of the present invention. Reference numeral 11 denotes a semiconductor laser emission source, and the semiconductor laser emission source 11 emits light. The laser beam 11A is supplied to the grating 13 via the collimator lens 12. The laser light split into three beams by the grating 13 is supplied to the beam splitter 14 having two reflecting surfaces, and the laser beam reflected by the reflecting surface 14A is incident on the objective lens actuator 15 via the prism 15A. Then, the recording surface of the above-mentioned optical disk 1 is irradiated so as to have a focused point.

Further, the laser light reflected from the recording surface of the optical disk 1 is reflected by the prism 15A to be reflected on the reflecting surface 14
The light passes through A and is input to the polarization prism 15B. Then, the detector 17 is irradiated through the multi-lens 16. The detector 17 has a light-receiving surface that is divided into three parts in the vertical and horizontal directions, and reproduces R from the received three-spot laser beam.
The F signal is obtained and the focus error signal component and the tracking error signal component are detected. Reference numeral 18 denotes an AP that receives the light of the semiconductor laser emission source 11 that has passed through the reflecting surface 14A and controls the emission output to be constant by a circuit (not shown).
The detector for C (Automatic power Control) is shown.

[0008]

The laser light 11A output from the semiconductor laser emission source 11 used in such an optical disk reproducing apparatus is generally elliptically spread, and its emission angle is in the vertical direction. At 25 ° to 45
And 8 ° to 15 ° in the horizontal direction. for that reason,
The beam waist of the light wavefront is deviated between the direction parallel to the semiconductor joint surface and the direction perpendicular thereto. By using the collimator lens 12, the deviation of the focus position on the disk surface causes the horizontal radiation angle and the vertical radiation It is corrected so that the angles match, but the deviation of astigmatism due to the difference in radiation angle is 0.
It is difficult to reduce the thickness to 5 to 1 μm or less.

In an optical disk reproducing apparatus in which an astigmatism of 0.5 to 1 μm has occurred, in general, a deviation occurs between the focus point where the reproduction RF signal is the best and the focus point where the tracking error signal level is the highest, and defocusing is allowed. Tends to be less frequent. In this case, particularly in the optical disk device in the reproduction mode, it is preferable to set the focus servo to the point where the level of the tracking error signal becomes high in order to stabilize tracking control when accessing a desired track. .. But,
With such settings, for example, as shown in FIG. 7, the jitter best point J _{BT at} which the jitter of the RF signal is the lowest is substantially closer to the focus position at which the level of the tracking error signal _TEL is the highest. There is a problem that the position is shifted by 1 μm, and as a result, the jitter margin is reduced (error rate is increased).

[0010]

In order to solve the above problems, the present invention irradiates the recording surface of an optical disk with a semiconductor laser beam, and the tracking servo error level is maximized by the reflected light from the recording surface. In the optical disc apparatus in which the focus state is set as described above, an equalizer for raising the high frequency signal of the RF signal by a predetermined level is provided in the reproducing circuit system for amplifying the RF signal reproduced from the optical disc.

[0011]

When the focus servo focusing on the tracking characteristic is performed, the focus position of the jitter best point generally occurs at a position different from the best tracking point. In this case, RF
If an equalizer that raises the signal band is inserted in the playback signal circuit, a remarkable effect will occur when the focus position, which is the best jitter point, approaches the disc side, and the best tracking error point and the best jitter point will match. become.

[0012]

1 is a block diagram of an optical disk reproducing apparatus according to the present invention. In this figure, the same components as those shown in FIG. 5 are designated by the same symbols, and detailed description thereof will be omitted. In the optical disk reproducing apparatus of the present invention, the reproduction RF signal read from the optical head 2 is supplied to the equalizer 12 having a frequency characteristic described later via the amplifier 11 and then to the RF signal processing circuit 4.

[0013] Figure 2 shows an example of the frequency characteristics of the equalizer 2 of the invention suitable when the optical disc 1 is a compact disc (e.g., cut-off frequency 1.44MH _Z). As can be understood from this characteristic, the frequency characteristic of the equalizer 2 is low frequency f ₀ (380
KH _Z ), the pass level gradually increases up to a high frequency f ₁ (1.08 MH _Z ) in the higher reproduction frequency band, and a frequency close to the cutoff frequency, eg, 1.3
It has an equalizing characteristic that is lower than MH _Z.

Therefore, in the optical disk reproducing apparatus of the present invention, the read RF reproduction signal of the data recorded on the disk is reproduced so as to reach the peak level in the vicinity of the cutoff frequency, and is easily generated when the tracking is prioritized. It is possible to compensate for the drop in high frequency characteristics. or,
By this compensation, it was possible to correct the point J _BT where the jitter becomes the minimum so that it coincides with the point where the tracking error level _TEL becomes the best as shown in FIG.

FIG. 4 shows an example of an equalizer circuit having the above characteristics. For example, R ₁ = 1.8 KΩ, R ₂ = 3.
3 KΩ, R ₃ = 6.8 KΩ, C ₁ = 82 PF, C ₂ = 18 PF
Is set to. In addition, A shows a differential amplifier.

[0016]

As described above, in the optical disc reproducing apparatus of the present invention, the tracking level of the focus servo of the optical head is most improved when reading the data recorded on the disc by using the semiconductor laser emission source. The focus position is set so that the stability of tracking access is increased and the decrease in the jitter margin of the reproduction RF signal is compensated by the equalizer inserted in the reproduction RF circuit. There is an advantage that the error rate can be reduced at the focus point which is made easy, and at the same time, since the defocus tolerance is increased, the manufacturing of the pickup can be facilitated.

[Brief description of drawings]

FIG. 1 is a block diagram of a reproducing system in an optical disc recording / reproducing apparatus of the present invention.

FIG. 2 is a graph showing an example of frequency characteristics of an equalizer adopted in the present invention.

FIG. 3 is an explanatory diagram of a tracking error level and a jitter bottom point.

FIG. 4 is a wiring diagram showing a circuit example of an equalizer.

FIG. 5 is a block diagram of a general optical disc device.

FIG. 6 is an explanatory diagram of an optical head adopted in the optical disc recording / reproducing apparatus of the present invention.

FIG. 7 is a graph showing a change in jitter that occurs when tracking is prioritized.

[Explanation of symbols]

 1 Optical Disc 2 Spindle Motor 3 Optical Head 4 RF Signal Processing Circuit 5 Digital Signal Processing Circuit 11 Amplifier 12 Equalizer

Claims (1)

[Claims] 1. An optical disk apparatus in which a recording surface of an optical disk is irradiated with a semiconductor laser beam, and a focus state is set so that a tracking servo error level is maximized by reflected light from the recording surface. An optical disk recording / reproducing apparatus characterized in that an equalizer for raising a high frequency signal of an RF signal by a predetermined level is provided in a reproducing circuit system for amplifying the RF signal.