JPS62293521A - Offset correcting device - Google Patents

Abstract

PURPOSE:To improve the tracking performance of a servo system and to reduce the cost of the titled device by stopping the light emission of a semiconductor laser momentarily, detecting an electric offset generated in a servo circuit during the period so as to apply the correction. CONSTITUTION:A signal of a photodetector 16 is inputted to operational amplifiers 171, 172, one of the outputs is given to differential amplifiers 181, 182 and the other is inputted to sample-and-hold circuits 191, 192. A controller 4 stops the light emission of the semiconductor laser in the timing independently of the recording/erasure of the information via a laser drive circuit 3. Further, the control signal in the same timing as the emission stop is sent to the circuits 191, 192, where an electric offset component is held. The outputs of the circuits 191, 192 are subject to the correction of offset component by the amplifiers 181, 182 and a detection signal is obtained by a differential amplifier 20. Thus, the tracing performance of the servo system is improved and the low cost is attained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical disk device, and particularly to an offset correction device that detects and corrects an electrical offset generated in a servo circuit.

[Conventional technology]

In an optical disk device, an optical head converges a light beam onto a recording medium that stores information as a spot of about 1 μm, and further has an autofocus function and a tracking function to accurately follow an eccentric trunk. Both of these functions are realized by a servo system consisting of an actuator and a servo circuit. In a servo system, the following factors determine tracking performance: (1) electrical offset by the operational amplifier that makes up the servo circuit; (2) optical head assembly;
Examples include optical offset caused by adjustment, and (3) tracking error. In particular, regarding (1) electrical offset, conventionally, by using a low offset operational amplifier,
Improved overall tracking performance.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, no consideration was given to cost, and there was a problem in that the use of a low-offset operational amplifier increased the device cost.

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.

[Effect]

By setting the stop of emission of the semiconductor laser at a timing unrelated to recording, reproducing, and erasing information, and by making the period equivalent to more than twice the bandwidth of the servo circuit, the effect on the servo system is eliminated. Therefore, the tracking performance of the servo system can be improved without malfunction.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The optical head 1 includes a semiconductor laser 11 as a light source, a biprism (poom splitter) 12, and a galvano mirror 1.
3. Voice coil 14. It mainly consists of a focusing lens 15 attached to the voice coil 14 and a photodetector 16 for detecting information and servo signals.The lens 15 narrows down the luminous flux emitted from the semiconductor laser 11 and deposits it on the optical disc 2 to a size of about 1 μm. The light beam reflected from the optical disk 2 is focused by the aperture lens 15. The light passes through a galvanometer mirror 13, has an optical path separated by a prism 12, and enters a photodetector 16. At this time, an automatic focus signal detection optical system for following the vertical vibration of the optical disc 2 and a tracking signal detection optical system for following the track eccentricity are passed through, but these are not shown as they are not the gist of the present invention. . For example, an autofocus signal or a tracking signal can be obtained by using two divided photodetectors 161 and 162 and differentially detecting the respective detected signals. Examples of these automatic focus signal detection optical systems and tracking signal detection optical systems are described in "Hitachi Review J Voffi, 65, Ha 10 (198
3-10), pages 23 to 28.

These detection signals pass through a phase compensation circuit 21 and a drive circuit 22, and are fed back to actuators such as a galvanometer mirror 13 and a voice coil 14, thereby forming a servo system and controlling the light spot.

At this time, if there is an electrical offset or temperature drift in the operational amplifiers that make up the servo system, an offset will occur in the servo system, causing a problem that accurate light point control cannot be performed. Therefore, in the present invention, we focus on the fact that when the semiconductor laser 11 is not emitting light, only the electrical offset remains in the servo circuit system, and we stop the semiconductor laser from emitting light for a short period of time, and use this timing to sample the electrical offset. The purpose/target is to detect and correct. This will be further explained using FIG. 1. two photodetectors 1
61 and 162 are operational amplifiers 171 for photoelectric conversion.
, 172, one of the outputs of the operational amplifier 171 is directly sent to the differential amplifier 181, and the other is sent to the semiconductor laser 11.
The signal is input to the sample and hold circuit 191 to detect the electrical offset during the light emission stop period. Further, the output of the operational amplifier 172 is similarly input to a differential amplifier 182 and a sample and hold circuit 192. The semiconductor laser 11 is driven by a laser drive circuit 3, which generates pulses when recording and erasing information according to commands from a controller 4, and emit light for a short period of time according to a command to stop reproduction light for the purpose of the present invention. Stop. As for this stop time, 2 of the servo band
It is necessary to set the time to be at least twice as long as the servo band, and to set the frequency characteristic of the operational amplifier used to detect the electrical offset to be at least twice the servo band. The semiconductor laser 1 is connected to the controller 4 and the resample hold circuits 191 and 192.
A control signal is sent out at the same timing as the light emission stop command in step 1, and the electrical offset component is held. Thereafter, the outputs of the sample and hold circuits 191 and 192 are input to differential amplifiers 181 and 182, respectively, and signals whose electrical offset components have been corrected are obtained at the outputs of the differential amplifiers 181 and 182. A detection signal is obtained. These can improve the autofocus or tracking performance of the tracking servo system.

Another embodiment of the invention is shown in FIG. This shows a case where the differential amplifier 20 performs differential detection to produce 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 shown in FIG. 1 can be obtained. Note that the optical head 1, optical disk 2, and laser drive circuit 3 are omitted.

〔Effect of the invention〕

According to the present invention, it is possible to detect and correct electrical offsets caused by offsets and drifts of operational amplifiers that occur in servo circuits, which not only improves tracking performance of servo systems, but also improves specifications for operational amplifiers regarding offsets and drifts. Since this is relaxed, it is possible to use inexpensive operational amplifiers, and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram illustrating an embodiment of the present invention. FIG. 2 is a configuration diagram illustrating another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Optical head, 2... Optical disk, 3... Laser drive circuit, 4... Controller, 161,162.
... Two-split photodetector, 171, 172... Operational amplifier, 181゜182.183... Differential amplifier, 191,
192゜193...Sample and hold circuit.

Claims (1)

[Claims] 1. An optical head comprising a light source, an optical system, and an actuator, and a servo circuit for accurately positioning a light spot from the optical head on an optical disk that stores information;
A semiconductor laser is used as the light source, and a detection circuit is provided for samplingly detecting the electrical offset that occurs in the servo circuit when the semiconductor laser stops emitting light, and the output from the detection circuit is used to detect the electrical offset of the servo circuit. An offset correction device characterized by correcting an offset. 2. The stop period of the semiconductor laser is used for recording, reproducing, and recording information.
2. The offset correction device according to claim 1, wherein the timing is unrelated to erasure, and the period thereof is twice or more as long as the required band of the servo circuit.