JPH0410141B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing inter-track crosstalk in an information reproducing apparatus such as a video disc player.

Problems with the prior art will be explained using an optical video disk player as an example. When the player reproduces information on a particular track, information from adjacent tracks may leak in, causing so-called crosstalk interference such as beats on the reproduction screen. This crosstalk is particularly noticeable when there is little correlation between track-to-track information, such as in CLV or still image playback, and becomes even more of a problem.

This crosstalk occurs because the optical spot size is not small enough compared to the track pitch. However, there is an upper limit to the pitch in terms of recording density, and high dimensional accuracy cannot be expected. Furthermore, since the spot size tends to increase due to variations in the performance of the optical system and changes in the performance of the focus servo system, it is difficult to always keep this crosstalk below an allowable level.

In addition, the need to keep the spot size small is a factor that makes it difficult to achieve low cost and high stability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel method for reducing crosstalk appearing on a playback screen to below an acceptable level even when the track pitch of a disk is small or the optical spot size is large.

In order to achieve the above object, the present invention provides a sub-detection means that detects adjacent track information at a higher rate than the main detection means for obtaining information used for image reproduction, etc.
The information from the sub-detection means is configured to cancel out adjacent track information that leaks into the main detection means, thereby reducing crosstalk that appears on playback screens and the like.

The basic principle of the present invention will be further explained using FIGS. 1 and 2. Generally, adjacent tracks exist on both sides of the main track, and crosstalk from both adjacent tracks poses a problem, but to avoid complexity, only one case will be described here.

In FIG. 1, reference numeral 1 schematically indicates a light spot of the sub-detection means, and 2 schematically indicates that of the main detection means. Also 3
A, 3b, and 3c are information tracks, and in this state, reproduced images and the like are obtained based on the information on track 3b. Note that the arrow indicates the direction of movement of the disk. Because of this arrangement, the detection information from the sub and main detection means is as shown in 1 and 2, respectively, in FIG.

Therefore, if the information of 1 is delayed, phase inverted, multiplied by k and added to 2, the resulting signal is = (M _a + M _b )) - k (S _a + S _b ) = Ma - kS _a + M _b - kS _b , and by setting k=Ma/Sa, adjacent track components inside can be canceled.

The main point of the first developed form of the present invention is that there is only one sub-detection means, and it is arranged to detect information before the main one, so that crosstalk from adjacent tracks on the side where there is no sub-detection means is practically ignored. The main point is that the information detecting section such as a light spot of the main detecting means is slightly shifted to the side where that of the sub detecting means exists so that the information detecting section is arranged so as to be more visible.

Furthermore, the key point of the second developed type is that the cancellation state is detected using a perturbation method and the cancellation state is automatically controlled.

The present invention will be further explained using an example in which the present invention is applied to a video disc player.

A first embodiment of the present invention is shown in FIG. 4 in figure
a and 4b are paired with light spots 1 and 2, respectively. 5 is a variable delay circuit, 6 is a level adjuster, 7 is a subtracter, and 8 is a desired information output terminal. With the configuration shown in the figure, information with reduced crosstalk can be obtained at the output terminal 8 by delaying the output of 4a by 5, adjusting the level at 6, and subtracting it from the output from 4b at 7.

FIG. 4 shows a second embodiment of the present invention. Portions with the same numbers as in FIG. 3 have the same functions as in FIG. 3, and their explanation will be omitted. (The same applies to the following embodiments) 5a is a variable delay circuit that can be controlled by electrical signals, 9a and 9b are video FM demodulation circuits including BPF and LPF, 10 is a phase comparison circuit including a synchronous separation circuit, Control 5a with output, 7
The configuration is such that appropriate cancellation is performed at 8 and 11, and appropriate outputs are obtained at 8 and 11.

FIG. 5 shows a third embodiment of the present invention, in which 12a,
12b is an LPF including an amplification stage, 13 is a level adjuster, and 14 is a differential amplifier. As shown in the figure, the low frequency components of the outputs 4a and 4b are detected by 12a and 12b, and a differential output that can be used as a tracking error signal is obtained at the output terminal 15 via 14. Note that 13 is for offset adjustment.

FIG. 6 shows a fourth embodiment of the present invention. In the first to third embodiments described above, the optical spot 2 is slightly shifted toward the information track 3a side as shown in FIG. 1, so that the crosstalk from the information track 3c can be ignored. In the fourth embodiment, as shown in FIG.
The optical spots 1a and 1c constituting the sub-information detecting means are arranged obliquely in front and behind with respect to the disk rotation direction indicated by the arrow as shown in the figure. 4c is an information detecting section paired with 1c, 5b is a variable delay circuit, 6c is a level adjuster, and 7b is a circuit for subtracting the outputs of 6 and 6c from the output of 5b. As shown in the figure, by delaying the output of 4b by 5b with reference to the output of 6c, the desired output can be obtained at the terminal 8.

FIG. 7 shows a fifth embodiment of the present invention, which is applied to an electrostatic video disc player.
Figure a shows the tip of the stylus for information detection, 16 is a diamond base, 17 and 18 are 16
Formed thereon are electrodes for sub and main detection means, respectively. These electrodes are placed on the information tracks 31a and 31b as shown in FIG. The configuration is such that it is obtained at the output end 8.

In this case, it is possible to arrange 17 and 18 so that no time lag occurs between the outputs of 4a and 4b, so the variable delay circuit can be omitted.

Moreover, FIG. 7 shows the case where the main electrode is shifted to the track side where the sub electrode is arranged, and 1
In this case, 7 and 18 indicate the electrodes themselves, but the effective electrode width involved in information detection increases slightly due to the spread of the electric lines of force, and 18 also slightly detects the information of 31a.

FIG. 8 shows a sixth embodiment of the present invention, and is an example configured to automatically control the amount of cancellation based on information from the sub-information detection means.

In the figure, 19 is the gate pulse 2 including the synchronous separation circuit.
0, and sample pulse 21 are generated. Furthermore, 22 is a gate circuit which uses a gate pulse 20 to extract a crosstalk component existing in the synchronization part of the video signal 11 and applies it to an amplification stage 23 including a BPF. The output of 23 is applied to an integrating stage 24 including a rectifier, and the output of 24 is sampled and held in a sample and hold stage 25 using a sample pulse 21. Furthermore, the output of 25 is synchronously detected by the output 28 of the oscillator 27 in the synchronous detection stage 26, and then LPF 29,
It is applied as a control signal to the level adjuster via the adder 30. The outputs 31 of the oscillator 26 are added in an adder 30.

As described above, in this example, a control signal is obtained by the perturbation method, and control is performed so that crosstalk is minimized. That is, when the adjustment state of the level adjuster is slightly changed by the output 31 of the oscillator 27, the level of crosstalk in the video output 11 changes accordingly. This is detected using the crosstalk included in the synchronization section, and a level change signal is obtained as the output of 25. As is well known, the level of the low frequency component of the output signal synchronously detected at the output 28 of 25 indicates a deviation from the canceling state at the subtracter 7, and its polarity indicates a shortage or excess of the subtracted signal that is the output of 6a. Therefore, with a configuration like this example, an automatic cancellation system can be constructed.

FIG. 9 shows a seventh embodiment of the present invention, in which a switch circuit 32, a hold circuit 33, and a switch pulse generation stage 34 that generates a pulse to turn ON 32 only during vertical blanking are added to the sixth embodiment. be.

With this configuration, it is possible to further reduce the influence of the perturbation 31 on the playback screen. Note that the rate of change in the crosstalk occurrence situation is sufficient to control it every vertical period, and the hold circuit can be constructed using an FET and a hold capacitor as is well known.

According to the present invention, even if the effective size of the information detection section is too large for the track pitch of the disk, it is possible to obtain information with reduced inter-track crosstalk.

[Brief explanation of drawings]

1 and 2 are diagrams explaining the principle of the present invention, FIG. 3 is a block diagram showing the first embodiment of the present invention, and FIGS. 4 to 9 are circuits of the second to seventh embodiments, respectively. It is a diagram. 1...Light spot of the detection means, 2...Light spot of the main detection means, 4a...Information detection unit paired with 1, 4
b... Information detection unit paired with 2, 5... Variable delay circuit, 6... Level adjuster, 7... Subtractor.

Claims (1)

[Claims] 1. To reproduce information from a recording medium in which a plurality of information recording tracks are arranged, by tracing the information recording tracks by a main detection means having a trace width wider than the width of the information recording tracks. In the information reproducing device, one of the information recording tracks adjacent to the information recording track to be reproduced whose information is to be reproduced by the main detecting means is traced by the first sub-detecting means at a position preceding the main detecting means. the other information recording track adjacent to the information recording track to be reproduced is traced by a second sub-detection means at a position later than the main detection means, and the information is reproduced; The output signal of the sub-detection means and the output signal of the main detection means are delayed by first and second delay means, respectively, and are time-aligned with the output signal of the second sub-detection means, and the second delay means An output signal of the first sub-detection means which is delayed and level-adjusted by the first delay means from the delayed output signal of the main detection means, and a reproduction signal whose level has been adjusted from the second sub-detection means. 1. A crosstalk reduction method for an information reproducing apparatus, characterized in that the crosstalk from adjacent information recording tracks mixed in the output signal of the main detection means is reduced by subtracting . 2. In an information reproducing apparatus that reproduces information from a recording medium in which a plurality of information recording tracks are arranged, tracing the information recording track by a main detection means having a trace width wider than the width of the information recording track, Tracing an information recording track adjacent to an information recording track to be reproduced whose information is to be reproduced by the main detecting means with a sub-detecting means having a trace width displaced toward the information recording track to be reproduced, and reproducing the information; subtracting the level-adjusted reproduction signal of the sub-detection means from the output signal of the sub-detection means, detecting a crosstalk component from the output signal of the subtraction means, and supplying the sub-detection signal to the subtraction means according to the detected amount; 1. A method for reducing crosstalk in an information reproducing apparatus, characterized in that the level of the output signal of the main detection means is adjusted to reduce crosstalk from adjacent information recording tracks mixed into the output signal of the main detection means.