JPH05120717A - Optical disk device - Google Patents

Abstract

PURPOSE:To provide the reproduction of a signal with high quality without incorporating a specific high frequency generating circuit to an optical head on an optical disk reproducer. CONSTITUTION:This device is constituted so that circuit means 10-19 reading the signal recorded in an optical disk 7 based on a laser beam 37 emitted from a laser diode 2 and reflected by the optical disk 7 digital-recording the signal, and a circuit 17 picking up a clock signal from the read signal and the circuits 32, 35 modulating and driving above-mentioned laser diode 2 synchronizing to relevant picked up clock signal (a) are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing device.

In an optical disk reproducing apparatus, it is necessary to be able to reproduce a signal having a good SN ratio.

Further, it is desirable that the optical disk reproducing apparatus is inexpensive and consumes low power.

[0004]

2. Description of the Related Art FIG. 3 shows an example of a conventional optical disk reproducing apparatus.

An optical head 1 comprises a laser diode (LD) 2, a photodiode (PD) 3, an LD drive circuit 4, and a high frequency generation circuit 5.

The drive circuit 4 is operated by the signal from the high frequency generation circuit 5, and the LD 2 is driven.

The laser beam 6 emitted from the LD 2 irradiates the optical disc 7 on which a signal is digitally recorded, is reflected by this, and the laser 8 with the signal written on the optical disc 7 irradiates the PD 3.

An analog reproduction signal is output from PD3. The reproduced signal is amplified by the amplifier 10, and the waveform equalizer 1
1, a shaper 12, and a discriminator 13 to obtain a reproduction pulse signal. The discriminator 13 operates by being controlled by a clock signal output to a line 18 from a synchronization signal generator 17 including a phase comparator 14, a low pass filter (LPF) 15 and a voltage controlled oscillator (VCO) 16.

The above-mentioned reproduction pulse passes through the decoder 19 and
The analog signal is output from the output terminal 20.

The high frequency generating circuit 5 described above is provided with 200 to 60
A signal having a very high frequency of 0 MHz (a frequency about 10 times the frequency of the signal read from the optical disk 7) is generated. This is to prevent the SN ratio of the reproduced signal from decreasing.

[0011]

As described above, in order to generate a signal of a very high frequency, an oscillating element made of a GaAs semiconductor is required, the high frequency generating circuit 5 is special, and the optical head 1 is expensive. It will become a thing.

Further, the power consumption of the optical head 1 also increases.

Therefore, according to the present invention, by driving the LD in synchronization with the clock signal included in the signal reproduced from the optical disk, the optical head has a simpler structure.
An object is to provide an optical disk reproducing device capable of reproducing a signal having a good SN ratio.

[0014]

According to a first aspect of the present invention, there is provided an optical disc device for reading a signal recorded on an optical disc based on a laser beam emitted from a laser diode and reflected by an optical disc on which a signal is digitally recorded. In the above configuration, a clock signal is extracted from the read signal, and the laser diode is modulated and driven in synchronization with the extracted clock signal.

[0015]

According to the first aspect of the present invention, the clock signal extracted from the signal read from the optical disc is used and the laser diode is driven in synchronization with the clock signal. The reflected light from the optical disc has the same light intensity change. It acts so as to start at the timing, and further acts so that the level change of the reproduction signal starts at the same timing.

Further, this means that even if the modulation frequency for driving the modulation of the laser diode is made lower than in the conventional case,
It works so that a signal having a good SN ratio is reproduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an optical disk device 3 according to an embodiment of the present invention.
Indicates 0.

In the figure, parts corresponding to those shown in FIG. 3 are designated by the same reference numerals.

The synchronizing signal generator 17 is connected to the high frequency generating circuit 32 by a line 31.

In the reproduction mode, the LD 2 drives the LD drive circuit 34.
The laser beam 36 emitted from the LD 2 illuminates the optical disc 7 on which signals are digitally recorded. The laser beam 37 reflected by the optical disk 7 and carrying the signal recorded on the optical disk 7 irradiates the PD 3, and the PD 3 outputs an analog reproduction signal.

The reproduced signal is processed as in the case of FIG. 3, and then taken out from the output terminal 20 as a reproduced signal.

The sync signal generator 17 outputs the clock signal a shown in FIG. 2A obtained from the reproduction signal being processed, and this is applied to the high frequency generation circuit 32 via the line 31.

The circuit 32 operates on the basis of the clock signal a, and controls the line 33 to be synchronized with the frequency of the clock signal a as shown in FIG. The signal b is output.

Since the frequency is about several tens of MHz (remarkably lower than the conventional one), the high frequency generation circuit 32
May be an ordinary one incorporating an oscillation circuit composed of ordinary Si semiconductor parts.

The LD drive circuit 34 operates under the control of the control signal b, and has the same frequency as the control signal b on the line 35, as shown in FIG. The LD drive signal c is output.

As a result, the LD 2 emits the laser light 36 having the light intensity waveform shown in FIG.

The intensity of the laser light 36 is synchronized with the clock signal a. The laser light 36 is reflected by the optical disk 7, and the laser light 37 carrying the signal recorded on the optical disk 7 irradiates the PD 3.

As shown in FIG. 2 (E), the laser light 37 always starts to change in light intensity at the same timing.

Therefore, the reproduced signal f output from the PD 3 to the line 38 is such that the level changes always start at the same timing and end at the same timing, as shown in FIG. The level L in the period of "1" is constant.

Therefore, the reproduced signal f is a high quality signal containing no noise. As a result, signal processing is performed and the terminal 2
The reproduced signal output from 0 has a good S / N ratio.

Further, the same laser light as the laser light 37 returns to the LD 3 as return light. However, since the LD3 has a modulation frequency of several tens of MHz, which is significantly lower than that of the conventional one, the LD3 is driven by being modulated, so that the operation of the LD3 does not become unstable even when returning light enters, and noise is not generated. ..

The frequency of the control signal b is several tens of MHz.
Since the frequency is high, the high frequency generation circuit 32 may be a normal one using Si semiconductor parts, and the LD drive circuit 34 may be a normal one.

As a result, the optical head 40 becomes less expensive than conventional ones and consumes less power.

Next, the operation during the period after the optical disc apparatus is turned on until the optical disc rotates and reproduction is started, that is, during the period when the clock signal is not obtained, will be described.

During this period, that is, the first pull-in, L
Drive D2 with DC.

After the reproduction of the optical disk is started and the reproduction is stabilized, the modulated signal is superimposed on the DC signal and driven.

Since the signal at the time of pulling in is patterned and resistant to noise, there is no problem. Also, there is no problem from the point of starting.

[0038]

As described above, according to the first aspect of the invention, it is possible to obtain a reproduced signal having a good SN ratio.

Moreover, this can be achieved by lowering the modulation frequency of the laser diode as compared with the conventional one, and thus the optical head can be made cheaper and consume less power than the conventional one. I can.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an optical disk device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of a signal of each part in FIG.

FIG. 3 is a circuit diagram of a conventional optical disc device.

[Explanation of symbols]

 7 Optical Disc 17 Synchronous Signal Generation Circuit 30 Optical Disc Device 31, 33, 35, 38 Line 32 High Frequency Generation Circuit 34 LD Drive Circuit 36 Laser Light 37 Reflected Laser Light 40 Optical Head a Clock Signal b Control Signal c LD Drive Signal f Playback Signal

Claims (1)

[Claims] 1. An optical disk device for reading a signal recorded on an optical disk on the basis of a laser beam emitted from a laser diode and reflected on the optical disk on which a signal is digitally recorded, and a clock signal from the read signal (f). An optical disk device characterized in that (a) is extracted (17), and the laser diode (2) is modulated and driven in synchronization with the extracted clock signal (33, 35).