JPS63122024A - Tack cross pulse generator - Google Patents

Abstract

PURPOSE:To contrive to make the track access stable by detecting a bipolar envelope of a tracking error signal and comparing its intermediate signal with the error signal so as to generate a track cross pulse. CONSTITUTION:A tracking error signal (a) is inputted to a positive and a negative peak hold circuit 1, 2, where the positive/negative peak values are held. Outputs c, d of the circuits 1, 2 represent the positive/negative envelope of the error signal (a) and represents a DC voltage along with the change in the signal amplitude. An intermediate point output circuit 3 outputs an intermediate potential (e) of two voltages from the output of the circuits 1, 2, the quantity of the potential (e) and the signal (a) is compared by a comparator 4 and a track cross pulse (b) is outputted. Even if an offset takes place in the error signal is this way, the track access is applied stably by detecting the track cross pulse.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical information recording and reproducing device that records information on a recording medium using optical means or reproduces information that has already been recorded. In particular, the present invention relates to a tracking control system for an optical information recording/reproducing device.

[Conventional technology]

Optical information that uses laser light as a light source and modulates this laser light with pulsed signals from an external information source to record binary information on a recording medium on a disk or to reproduce information that has already been recorded. In recording/reproducing devices, in order to accurately record or reproduce information, the position of a condenser lens is controlled by focus control so that the surface of the recording medium is always at the focal point of the condenser lens. Additionally, in order to control the tracking position of a tiny laser beam spot on an information track during information recording or reproduction, a guide groove is usually provided on the recording medium with the optimal depth for the tiny spot. Tracking control is performed so that the minute light spot follows.

At this time, it is common practice to generate various control signals using the tracking error signal. for example,
Track cross pulses and the like generated when a light spot crosses a track are detected from a tracking error signal.

Particularly effective in response to the demand for faster track access is a system in which the number of tracks that have been moved directly is counted and the light spot is moved to the target trunk.

In this method, the light spot is moved at high speed by the desired number of tracks (strokes), and from the center of the target track,
The control mode is switched from a predetermined distance ahead, and the light spot is positioned on the target track using normal position control.

At this time, the track cross pulse is generated by comparing the tracking error signal and the zero potential level using a comparator.

[Problem that the invention seeks to solve]

However, when the optical spot is moved at high speed, an offset occurs in the tracking error signal due to misalignment of the objective lens with respect to the optical head. At this time, in the trunk cross pulse generator using the conventional track cross pulse generation method,
Since the reference potential of the comparator is fixed, it becomes impossible to accurately generate track cross pulses. In particular, when the offset value becomes large and the tracking error signal becomes positive or negative, track cross pulses cannot be generated. If you make a mistake in the track access stroke, or in the worst case scenario, the optical head may run out of control, making it impossible to stably access the trunk.

SUMMARY OF THE INVENTION An object of the present invention is to provide a track cross pulse generator that eliminates the above-mentioned drawbacks and can stably generate track cross pulses even when the objective lens is largely deviated from the center of the light beam during trunk access.

[Means for solving problems]

The present invention provides recording of information on a recording medium using optical means,
Alternatively, in a track cross pulse generator of an optical information recording/reproducing device that reproduces already recorded information, the positive peak value of a tracking error signal indicating the position in the tracking direction of a light spot focused on a recording medium. a first peak hold circuit that holds and outputs the negative peak value of the tracking error signal; a second peak hold circuit that holds and outputs the negative peak value of the tracking error signal; and two output signals of the first and second peak hold circuits. It is comprised of a midpoint output circuit that outputs a midpoint, and a comparator that compares the magnitude of the midpoint output signal and the tracking error signal, and the comparator detects that the light spot has passed through the trunk. It is characterized by generating the track cross pulse shown in FIG.

[Effect]

A positive envelope and a negative envelope of the tracking error signal are respectively detected, a midpoint signal indicating the midpoint of the positive and negative envelope signals is generated, and a comparator compares the tracking error signal with the midpoint signal,
Generates track cross pulse. By doing this, even if a large offset occurs in the tracking error signal, the midpoint signal also changes in proportion to the offset, so that accurate track cross pulses can always be generated.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a block diagram of one embodiment of a trunk cross pulse generator according to the present invention. A tracking error signal a detected by an optical head and an amplifier (not shown) is input to a positive peak hold circuit 1 and a negative peak hold circuit 2, respectively. The peak value is held, and the negative peak hold circuit 2 holds the negative peak value of the tracking error signal. At this time, since the positive and negative peak hold circuits usually have some leakage characteristics, the output C of the positive and negative peak hold circuits
, d represent the positive and negative envelopes of the tracking error signal amplitude, respectively, and indicate the DC voltage along the variation of the tracking error signal amplitude. The midpoint output circuit 3 receives the output of the positive peak hold circuit 1 and the output of the negative peak hold circuit 2, and outputs an intermediate potential e between the two voltages. The comparator 4 compares the intermediate potential and the tracking error signal in magnitude and outputs a track cross pulse b.

FIG. 2 is a diagram showing operating waveforms for explaining the operation of the track cross pulse generator of FIG. 1 in an easy-to-understand manner. If the condenser lens becomes misaligned with respect to the optical head,
As shown in the figure, a negative or positive DC offset is superimposed on the tracking error signal a. At this time, the output of the positive peak hold circuit 1 indicates a positive envelope C, and the output of the negative peak hold circuit 2 indicates a negative envelope d. In this way, the midpoint output circuit 3 outputs the center value e of the positive and negative envelopes. The comparator 4 compares the tracking error signal a with the center value e, and outputs an accurate track cross pulse b.

As described above, the output of the midpoint output circuit 3, which is the reference input of the comparator 4, indicates the midpoint potential of the error signal regardless of the offset of the tracking error signal. can occur.

〔Effect of the invention〕

As described above, according to the present invention, even if an offset occurs in the tracking error signal, the track cross pulse can be accurately detected, and track access can be performed stably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of a track cross pulse generator according to the present invention. FIG. 2 is a waveform diagram showing operating waveforms of each part in FIG. 1. 1... Positive peak hold circuit 2... Negative peak hold circuit 3... Midpoint output circuit 4... Comparator

Claims (1)

[Claims] (1) In a track cross pulse generator of an optical information recording/reproducing device that records information on a recording medium using optical means or reproduces information that has already been recorded, light focused on the recording medium a first peak hold circuit that holds and outputs a positive peak value of a tracking error signal indicating the position of the spot in the tracking direction; and a second peak hold circuit that holds and outputs a negative peak value of the tracking error signal. , a midpoint output circuit that outputs the midpoint of the two output signals of the first and second peak hold circuits, and a comparator that compares the magnitude of the midpoint output signal and the tracking error signal. . A track cross pulse generator, wherein the comparator generates a track cross pulse indicating that the light spot has passed through the track.