JPS61115250A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproduction signal with a stable level without installing an automatic gain adjustment circuit on a reproduction signal system by detecting the level of the reproduction signal from a disk and controlling the luminous energy of a light beam so that a signal level can go to the preset one. CONSTITUTION:Some part of reproduction signals is applied to a signal level detector 22, which detects a reproduction signal level and outputs a control signal in accordance with the level. Said control signal is applied to a drive electric power source 8, controls an output voltage from said source 8, and eventually changes the luminous energy of a laser beam emitted by a semiconductor 3. Even if one reflectance is different from the other due to soil, etc., of a disk 11, electrical signals from respective photodiode elements 4a-4d will not change, whereby the level of the reproduction signal keeps the prescribed value, and the reproduction signal at a stable level is outputted from a terminal 15.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical disc playback device.

In a conventional device for optically reproducing a disc, when the level of the reproduction signal from the photodiode changes, the SZN
This results in adverse effects such as the ratio changing and the tracking and focus servo systems not operating properly. Therefore, the playback device is configured so that the level of the playback signal is kept constant.

FIG. 2 shows an example of a conventional optical disc reproducing device N1. The reproducing device t1 controls the semiconductor 3 that emits the laser beam 2 so that the light intensity of the laser beam is approximately constant, and controls the reproducing signal from the four-division photodiode 4 to maintain this level at a predetermined level. The configuration is such that control is performed to maintain the same level. The semiconductor 3 is enclosed in a package 6 together with a monitor diode 5. The semiconductor 3 emits the laser beam 2 to the collimator lens 7 side and the monitor diode 5 side. The signal photoelectrically converted by the monitor diode 5 is fed back to the drive power supply 8, and the drive power [8
Determine the output voltage. Thereby, the semiconductor 3 is controlled so that the amount of light of the emitted laser beam 2 is stabilized at a specified value.

The laser beam 2 with a fixed amount of light is passed through the collimating lens 7
The light is reflected upward by the half mirror 9 and focused onto the information recording surface 11a of the disk 11 by the objective lens 10. The disk 11 is rotated at high speed by a motor 12. The laser beam 2 is reflected by the information recording surface 11a, passes through the objective lens 10° half mirror 9, is converged by the lens 13, and irradiates the 4-split photodiode 4, where it is photoelectrically converted, and each photodiode element 4a-4d
An electrical signal is output. All the signals are added by an adder 14 and outputted from a terminal 15 as a reproduced signal. In this case, since the laser beam 2 emitted from the semiconductor 3 is controlled to a predetermined amount of light, the amount of light reflected by the disk 11 and incident on the photodiode 4 is also stabilized, and the electricity from each photodiode element 48 to 4d is stabilized. The signal level is also stabilized, and a reproduced signal with a stable level is output from the terminal 15.

However, if the dirt level of the disk 11 or the disk 1
Depending on the nature of the information recording surface 11a (reflection wA) of the disc 11, the reflectance of the disc 11 may vary even within the same disc. When playing back such a disk, the amount of light incident on the photodiode 4 changes during playback due to the influence of the disk, which changes the level of the playback signal, causing a decrease in the SZN ratio and the operation of the servo circuit. It becomes unstable.

To cope with this, an automatic gain adjustment circuit 16 is provided in the reproduction signal system. This circuit 16 includes a variable gain amplifier 1 connected to each photodiode element 4a to 4d.
7a to 17d, and signal level detectors 18a to 18d connected to the output side of each amplifier. Each of the signal level detectors 18a to 18d generates a gain adjustment signal corresponding to the level of the input signal, and this signal is applied to the corresponding amplifier 1.
The gain is fed back to 7a to 17d to vary the gain. As a result, the level of each reproduced signal output to the adder 14 becomes a specified value, and a reproduced signal with a stable level is output from the terminal 15 regardless of the condition of the disk 11.

FIG. 3 shows a modification of the automatic gain adjustment circuit 16 described above.

In the figure, parts corresponding to those shown in FIG. 2 are given the same reference numerals. The automatic gain adjustment circuit 19 shown in FIG. 3 has a configuration in which one signal level detector 20 is provided at the next stage of the adder 14. The gains of the amplifiers 17a to 17d are commonly varied by the gain adjustment signal from the signal level detector 20, and a reproduced signal with a stable level is output from the terminal 15.

Problems to be Solved by the Invention In the reproducing apparatus 1 described above, both the optical system and the reproducing signal system are controlled in order to obtain a reproduced signal with a stable level, resulting in a complicated configuration.

Regarding the control of the reproduced signal system, the circuit 16 in FIG. 2 requires a variable gain amplifier and a signal level detector for each system, so the configuration is more complicated than the circuit 19 in FIG. 3. Additionally, the temperature and time characteristics of each amplifier and detector must be the same. Although the circuit 19 in FIG. 3 has the advantage that only one signal level detector is required, it has the problem that the characteristics of each variable gain amplifier must be precisely matched, which is very difficult in practice.

An object of the present invention is to provide an optical disc playback device that solves the above problems.

Means for Solving the Problems The present invention detects the level of a playback signal from a disc,
The light intensity of the light beam is controlled so that the signal level becomes a predetermined level.

Even without providing an automatic gain adjustment circuit in the operational reproduction signal system, a reproduced signal with a stable level can be obtained, and the configuration can be simplified.

Embodiment FIG. 1 shows an embodiment of an optical disc reproducing apparatus 21 according to the present invention. In the figure, the same parts as those shown in FIG. 1 are given the same reference numerals.

The laser beam 2 emitted from the semiconductor 3 reaches the disk 11 via the same path as shown in FIG. 2, is modulated by (a), and reaches the four-divided photodiode 4, where it is photoelectrically converted by (b).

The electrical signals from each photodiode element 48 to 4d are
The signals are added to the adder 14 and added thereto to form a reproduced signal, which is output from the terminal 15.

A portion of the reproduced signal is also applied to the signal level detector 22. The detector 22 detects the level of the reproduced signal and outputs a control signal according to the level.

This control signal is applied to the drive power supply 8 to control the output voltage from the drive power supply 8, and ultimately to vary the amount of light of the laser beam 2 emitted by the semiconductor 3. That is, when the level of the reproduced signal decreases below a predetermined value, the output voltage from the drive power supply 8 increases, and the amount of light of the laser beam 2 increases; The output voltage of the laser beam 2 decreases, and the amount of light of the laser beam 2 decreases.

As a result, even if there is a difference in reflectance due to dirt etc. on the disk 11, each photodiode element 4a to
There is no change in the electrical signal from terminal 4d, the level of the reproduced signal is maintained at a predetermined value, and a reproduced signal with a stable level is output from terminal 15.

Therefore, the S/N ratio is kept constant without being affected by the state of the disk 11, and the tracking and focus servo systems also operate normally.

According to this embodiment, since the reproduced signal system is not provided with an automatic gain adjustment circuit and there is only one signal level detector 22, the circuit configuration is simple, and the automatic gain adjustment circuit is not provided. There is no need to match the characteristics of the plurality of variable gain amplifiers.

Effects of the Invention As described above, the optical disc playback device of the present invention is an optical disc playback device that receives a light beam emitted from a light source and reflected on the information recording surface of the disc by a photoelectric conversion element, and obtains a playback signal from the photoelectric conversion element. The disc playback device includes means for detecting the level of the playback signal, and a means for controlling the light beam emitted from the light source according to the output from the detection means so that the playback signal is maintained at a predetermined level. Since the structure has a means for varying the amount of light, it is possible to omit the automatic gain adjustment circuit in the reproduction signal system that was conventionally required, and the structure can be greatly simplified. Moreover, it has the advantage of being able to obtain a reproduced signal with a stable level without being affected by the condition of the disc.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the optical disc playback device of the present invention, FIG. 2 is a diagram showing an example of a conventional optical disc playback device, and FIG. 3 is the automatic gain adjustment circuit in FIG. 2. It is a figure showing a modification of . 2... Laser beam, 3... Semiconductor, 4... Quadrant photodiode, 48-4d... Photodiode element, 8... Drive power supply, 11... Disk, 11
a... Information recording surface, 14... Adder, 21... Optical disc playback device, 22... Signal level detector.

Claims (1)

[Claims] In an optical disc playback device, a light beam emitted from a light source and reflected by an information recording surface of a disk is received by a photoelectric conversion element, and a playback signal is obtained from the photoelectric conversion element, and a means for detecting the level of the playback signal; and means for varying the amount of light beam emitted from the light source according to the output from the detection means so that the reproduced signal is maintained at a predetermined level. type disc playback device.