JP2555030B2 - Optical disk drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, and more particularly to an offset correction device that detects and corrects an electrical offset generated in a servo circuit.

[Conventional technology]

In the optical disc device, the optical head converges the light flux as a spot of about 1 μm on a recording medium for storing information, and further has an automatic focusing function and a tracking function in order to accurately follow an eccentric track. Both of these functions are realized by a servo system composed of an actuator and a servo circuit. In the servo system, the factors that determine the tracking performance include (1) electrical offset by an operational amplifier that constitutes the servo circuit, (2) optical offset due to assembly and adjustment of the optical head, and (3) tracking error. To be In particular, regarding the electrical offset of (1), conventionally, a low offset operational amplifier is used to improve the overall tracking performance.

[Problems to be solved by the invention]

In the above-mentioned prior art, no consideration has been given to the cost, and there is a problem that the device cost becomes high by using the low offset operational amplifier.

An object of the present invention is to enable the use of an inexpensive high-offset operational amplifier, reduce the cost of the device, and improve the tracking performance of the servo system.

[Means for solving problems]

The above object is achieved by instantaneously stopping the light emission of the semiconductor laser which is the light source, and detecting and correcting the electrical offset generated in the servo circuit during this period.

[Action]

The emission of the semiconductor laser is stopped at a timing unrelated to recording / reproducing / erasing of information, and by setting the period during which the emission is stopped to a predetermined length of time, the influence on the servo system can be eliminated, so malfunction will occur. Without this, the tracking performance of the servo system can be improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The optical head 1 is a semiconductor laser 11 as a light source, a prism (beam splitter) 12, a galvano mirror 13, a voice coil 1
4. A focusing lens 15 attached to the voice coil 14 and a photodetector 16 for detecting information and servo signals are mainly included. The light flux emitted from the semiconductor laser 11 is focused on the optical disc 2 by the focusing lens 15. Information is recorded / reproduced / erased by narrowing down to about 1 μm. The light beam reflected by the optical disk 2 passes through the focusing lens 15 and the galvano mirror 13, and the optical path is separated by the prism 12 to detect the light 16
Incident on. At this time, it passes through an automatic focus signal detection optical system for tracking up-and-down shake of the optical disk 2 and a tracking signal detection optical system for tracking track eccentricity, but these are not shown because they are not the gist of the present invention. . For example, an autofocus signal or a tracking signal can be obtained by using the photodetectors 161, 162 divided into two and differentiating the detected signals. Examples of these automatic focus signal detection optical systems and tracking signal detection optical systems are described in "Hitachi Review" Vol.65, No.10 (1983-10), pp. 23 to 23.
It is described on page 28. These detection signals are phase compensation circuits
A servo system is configured by feeding back to the galvanometer mirror 13 and the voice coil 14, which are actuators, through the drive circuit 21 and the drive circuit 22, and the light spot is controlled. At this time, if the operational amplifiers constituting the servo system have an electrical offset or a temperature drift, the servo system will be offset and the problem that accurate light spot control cannot be performed occurs. Therefore, in the present invention, paying attention to the fact that only the electric offset remains in the servo circuit system when the semiconductor laser 11 is not emitting light, the light emission of the semiconductor laser is stopped for a short time, and the electric offset is sampled at this timing. The purpose is to detect and correct. This will be further described with reference to FIG. The two photodetectors 161 and 162 use operational amplifiers 171 and 172 for photoelectric conversion. One of the outputs of the operational amplifier 171 detects the electrical offset in the differential amplifier 181 as it is, and the other detects the electrical offset during the emission stop period of the semiconductor laser 11. Therefore, it is input to the sample hold circuit 191. The output of the operational amplifier 172 is similarly input to the differential amplifier 182 and the sample hold circuit 192. Laser diode 1
1 is driven by the laser drive circuit 3, and generates a pulse at the time of recording / erasing information by the instruction of the controller 4.
For the purpose of the present invention, the light emission is stopped for a short time by the command to stop the reproduction light. The control signal is sent from the controller 4 to the sample and hold circuits 191 and 192 at the same timing as the command to stop the light emission of the semiconductor laser 11 to hold the electrical offset component. After that, the sample and hold circuit 19
The outputs of 1,192 are input to differential amplifiers 181,182,
At the outputs of the differential amplifiers 181 and 182, electric offset component-corrected signals are obtained, and the differential amplifier 20 further obtains detection signals. These can improve the autofocus or the tracking performance of the tracking servo system.

Another embodiment of the present invention is shown in FIG. This shows a case where the differential amplifier 20 performs differential to obtain a detection signal, and then the sample and hold circuit 193 and the differential amplifier 183 correct it, and the same effect as the embodiment of FIG. 1 can be obtained. The optical head 1, the optical disc 2, and the laser drive circuit 3 are omitted.

〔The invention's effect〕

According to the present invention, it is possible to detect and correct the offset and the electrical offset due to the drift of the operational amplifiers generated in the servo circuit. Since it is alleviated, inexpensive operational amplifiers can be used, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention, and FIG. 2 is a block diagram for explaining another embodiment of the present invention. 1 ... Optical head, 2 ... Optical disk, 3 ... Laser drive circuit,
4 ... Controller, 161, 162 ... Two-part photodetector, 171, 172
... operational amplifier, 181, 182, 183 ... differential amplifier, 191, 192, 193
… Sample and hold circuit.

Claims (1)

(57) [Claims] 1. A semiconductor laser light source, an optical system for forming a laser beam from the semiconductor laser light source as a light spot on an optical disk, a servo circuit and an actuator for positioning the light spot at a desired position on the optical disk, A detection circuit for samplingly detecting the electrical offset generated in the servo circuit when the emission of the semiconductor laser light source is stopped, and a correction for correcting the electrical offset of the servo circuit based on the output from the detection circuit. Optical disk device having means.