JPH02220236A - On-track detector - Google Patents

Abstract

PURPOSE:To suppress the noise included in a reflected light quantity signal to considerably improve the on-track detection precision by discriminating the level through a low-cut filter after cutting the level of the reflected light quantity signal. CONSTITUTION:When a focus sum signal B includes noise areas (a), (b), and (c) due to pit shape change, disk flaws, and pit drop-out, a clip circuit 20 clips the output of an amplifier 8 by a prescribed level, and outputs a signal C where the level rise of a part higher than the on-track state level of the signal B is suppressed. A low-cut filter 9 eliminates the low-band component of the signal C to output a signal D where the noise component of the area (c) is reduced. An LPF 23 eliminates a high-band component in the signal D to suppress the noise of the area (b) and outputs a signal E where the phase advance due to the filter 9 is restored. A signal E where the generation timing of an on-track signal is accurate is inputted to a comparator 10 to generate an accurate level discrimination output F which goes to the low level at the time of the on-track state.

Description

TECHNICAL FIELD The present invention relates to an on-track detection device for an optical disc player that detects whether an information reading spot is on an information recording track.

BACKGROUND ART An example of an on-track detection device prior to the present application will be described with reference to FIG.

In FIG. 3, there are three beam spots obtained by converging the laser beam, that is, a spot S1 for reading recorded information and a pair of tracking information detection spots that precede and follow each other during relative movement between the recorded information reading spot S1 and the disk. A spot 52133 is irradiated onto the recording track T of the disk from a pickup (not shown) in the illustrated positional relationship. The reflected light from the disk due to these beam spots enters photoelectric conversion elements 1 to 3 built into the pickup via astigmatism generating means (not shown).

The photoelectric conversion element 1 is constituted by four mutually independent light-receiving elements arranged such that each light-receiving surface is divided into four by two straight lines orthogonal to each other. Then, the output sums of elements facing each other with respect to the center of the light receiving surface are obtained as outputs of adders 4 and 5, respectively. The outputs of the adders 4 and 5 are supplied to an adder 6, where the sum of the re-outputs is detected, and a focus sum signal whose level is proportional to the amount of light beam reflected or transmitted through the disk surface is obtained.

Further, the outputs of the adders 4 and 5 are supplied to a subtracter 7 to detect the difference between the re-outputs, and this difference output becomes a focus error signal. The focus error signal is supplied to a focus servo system (not shown) to control the separation distance of the objective lens from the disk surface.

The focus sum signal is amplified to an appropriate level by an amplifier 8, and is supplied to a comparison input terminal of a comparator 10 via a low-cut filter 9.

The comparison reference input terminal of the comparator 10 has a DC voltage Vre.
f is supplied, and when the level of the focus sum signal becomes lower than the voltage Vref, it outputs a high level. The information recording track T on the disc is formed by a bit string. When the light spot traces this pit row, the light beam is scattered by the pits, and the amount of light reflected from the disk surface decreases. Furthermore, when the light spot is located between the information recording troughs 21 or on the mirror surface of the non-recording area,
The amount of reflected light increases. Therefore, by appropriately setting the level of the voltage Vref of the comparator 10, the level of the focus sum signal, whose level is proportional to the amount of reflected light, can be differentiated. It is possible to distinguish between off-track conditions. The output of the comparator 10 is used as an off-track signal when it is at a high level and as an on-track signal when it is at a low level, for example, for on/off control of a tracking servo loop in an optical disc player.

By the way, in the process of stamping the disk or the writing operation on the disk, there may be cases where the shape of the pit is not formed accurately. When a reading spot traces such a pit portion, the amount of reflected light decreases significantly at that portion as shown in FIG. 4(A).

Then, due to the differential waveform as shown in FIG. 4(B) generated by the action of the low-cut filter 9, the comparator 1
A problem may occur where 0 generates an off-track signal. On the other hand, if the cutoff frequency of the low-cut filter 9 is lowered to allow low frequencies to pass, the above-mentioned problem will not occur, but conversely, the on-track and off-track areas in the pit-missing portion (see Figure 4) will not occur. This may cause a problem where it is incorrectly detected.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an on-track detection device that can more accurately detect on-track.

In order to achieve the above object, a light amount detection means that generates a reflected light amount signal having a level corresponding to the intensity of the light beam that has passed through the recording surface of the information recording disk, and a comparison result between a reference level and the level of the reflected light amount signal. an on-track detection device that includes a level discriminator that generates a discrimination output based on the signal, and a suppressor that suppresses the level of the reflected light amount signal, and a low-cut filter that suppresses the level of the low-frequency component of the level signal. It is characterized by

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. In the apparatus shown in FIG. 1, parts corresponding to those in the apparatus shown in FIG. 3 are given the same reference numerals, and a description of these parts will be omitted.

In this embodiment, an amplifier 8 and a low cut filter 9
A clip circuit 20 is inserted between the two.

The clipping circuit 20 clips the output of the amplifier 8 having noise as shown in FIG. 2(B) at a predetermined level,
As shown in C), an increase in the level of a portion of the focus sum signal whose level is higher than the level of the on-track state (a portion where the amount of reflected light is small) is suppressed. In addition, in Fig. 2 (B), a
, b and C indicate noise areas caused by changes in pit shape, disk scratches, and pit omissions, respectively.

The output of the clipping circuit 20 is supplied to a low-cut filter 9, and low-frequency components are removed as shown in FIG. 2(D).

This reduces the noise component in the bit missing area C.

The output of the low-cut filter 9 is level-amplified by an amplifier 21 and supplied to a low-pass filter (hereinafter referred to as LPF) 23 .

The LPF 23 removes high-frequency components from the output of the low-cut filter 9 to suppress noise caused by disc damage as shown in FIG. LPF23
Since the phase shift is compensated for by this, there is an advantage that the timing of generation of the on-track signal becomes accurate.

The signal supplied to the comparator 9 is suppressed from noise caused by a decrease in the level of reflected light due to a change in bit shape, a spike-like level change due to a scratch on the disk, an increase in the amount of reflected light due to missing bits, etc. As shown in FIG. 2(F), a more accurate level discrimination output is generated which becomes a low level when in an on-track state.

Note that FIG. 2(A) shows an example of a tracking error signal generated in response to the focus sum signal.

The tracking error signal is obtained by a subtracter 11 which manually re-outputs the light-receiving elements 2 and 3, and the output portion corresponding to the off-track is shown by a dotted line in FIG.

Note that a tracking sum signal, which is the sum of the outputs of the light receiving elements 2 and 3, can be used instead of the focus sum signal as a signal representing the amount of light reflected from the disk surface.

Further, the same effect can be obtained by configuring the low-cut filter 9 and the LPF 23 by band-pass filters.

Furthermore, the present invention is applicable not only to on-track detection using reflected light from a disk recording surface, but also to on-track detection using transmitted light from a transparent disk as a reading light beam.

As described in detail, in the on-track detection device of the present invention, the level of the reflected light amount signal corresponding to the intensity of the light beam that has passed through the disk recording surface is cut by a clip circuit, etc., and then the level is cut by a low-cut filter. This is preferable because the noise contained in the reflected light amount signal is sufficiently suppressed and the on-track detection accuracy is improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing this embodiment, Fig. 2 is a signal waveform diagram for explaining the operation of the embodiment, Fig. 3 is a block diagram showing a preceding example, and Fig. 4 is a preceding example. FIG. 3 is a signal waveform diagram for explaining the operation of FIG. Explanation of symbols of main parts 9...Low cut filter 10...Comparator 20...Clip circuit 23...Low pass filter Applicant: Pioneer Corporation

Claims (2)

[Claims] (1) A light amount detection means that generates a reflected light amount signal having a level corresponding to the intensity of the light beam that has passed through the recording surface of the information recording disk, and a discrimination output based on a comparison result between a reference level and the level of the reflected light amount signal. an on-track detection device comprising: a level discriminator for generating a signal, a suppression means for suppressing the level of the reflected light amount signal; and a low-cut filter for suppressing the level of a low-frequency component of the level signal. Features an on-track detection device. (2) The on-track detection device according to claim 1, further comprising a low-pass filter downstream of the low-cut filter.