JPH0139269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information reproducing device and an information reproducing device that tracks and detects predetermined information.

In recent years, there has been an increasing need to record large amounts of image information, and research for this purpose has been active. Among these, a method of recording information with high density on a rotating body such as a disk is attracting attention. At this time, each frame of information, such as a video signal for television display, is recorded on one track, and a large number of these tracks are arranged concentrically. At this time,
In order to record a large amount of information, extremely high-density recording is performed. For example, there is a 1 micron pitch within the tracks and a 1 to 2 micron pitch between the tracks. When such a high-density disk is rotated at a high speed, for example, about 60 revolutions per second, the problem is how to faithfully follow this track (tracking).

The present invention is an invention for this tracking. This will be explained below using the drawings.

In FIG. 1, a disk is specifically taken up, and a track is schematically shown here.

That is, tracks 10 ₁ , 10 ₂ , etc. are recorded on a disk 1 having a diameter of about 30 cm, and this disk is rotating in the direction of an arrow 200.

FIG. 2 is an explanatory diagram of the recording of signals on a track. Figure A shows the use of media with different surface reflectances or transmittances, such as 100 ₁ to 100 ₃ . This can be done by coating or vapor depositing a suitable material and then recording the transmittance or reflectance depending on the signal. The simplest example is a photographic emulsion.

FIG. 2B shows an example in which signals are recorded by surface irregularities.

FIG. 3 is an explanatory diagram of reading signals from such a disk.

The light from the laser 2 is focused onto a disk via a mirror 3, a half mirror 4, and a focusing lens 5, and the reflected light is detected via a half mirror 4, a photodetector 6, and a demodulator 8. to obtain a signal, for example a video signal for TV display.
At this time, the signal for tracking is passed through a suitable tracking error signal discrimination circuit 9 to a mirror deflection drive circuit 11 to change the angle of the mirror 3 so that light is correctly irradiated onto the track. .

FIG. 4 is an enlarged view of the recorded portion of the signal on the track. Track 10 ₁ , 10 ₂ , 1
Above 0 ₃ are 100 ₁ , 100 ₂ , 100 ₃ , etc.
For example, it is recorded in the form of surface irregularities. The track spacing l is approximately 1-2 microns, and the recording width d of the signal within the track is 1-2 microns.

Now, the problem with such a system is how to generate a tracking error signal.

FIG. 5 is a diagram showing an example of recording such a tracking signal. In addition to the video signal portions 20 ₁₁ , 20 ₁₂ . . . , tracking signals 30 ₁₁ , 30 ₁₂ . . . are recorded on the track 10 ₁ . This tracking signal consists of two parts, 300 ₁ and 300 ₂ , which are offset from the center of the track by half the track width.

Now, suppose that this tracking signal is recorded in an appropriate form, and when the light beam is located at the center position of this track, the outputs from these two tracking signal parts 300 ₁ and 300 ₂ will be the same, but the light beam deviates to either side, one can be made to be larger than the other.

This is shown schematically in FIG.

a and b are tracking signal parts 300, respectively.
The output is from _{1,300 2} .

At A, since the light beam is located at the center of the track, both outputs are equal, so the difference signal is zero as shown at c.

Now, if the light beam deviates upward in Figure 5, then B
As shown in the figure, the signal at a is greater than the signal at b, so this difference is positive. On the other hand, if the light beam shifts downward, the signal at a becomes smaller than the signal at b, as shown in Figure 6c.
This difference is negative.

Therefore, the direction of deviation can be determined from this difference signal. This pattern is shown in FIG. That is, a tracking error signal can be obtained depending on the amount and direction of deviation of the light beam. Therefore,
Using this error signal, the direction of the light beam may be controlled so that this error signal becomes zero.

The problem here is that the tracking signal 30
The question is how to record 0 ₁ and 300 ₂ .
Generally, FM modulation is performed to obtain a high signal-to-noise ratio, and therefore, the tracking signal may be recorded at two different frequencies f ₁ and f ₂ . FIG. 8 schematically shows this, and it can be seen that the tracking signal is expressed with different pitches. The signal will be explained in more detail.

FIG. 9 shows an example of a frequency spectrum when a video signal for TV display is FM modulated.

For example, between 3.5MHz and 4.5MHz (part B)
The fundamental frequency is distributed in , and its harmonics are distributed below it (part A). One example is to set the two tracking frequencies f ₁ and f ₂ to 4.5 MHz or higher, as shown in the figure. The signal detection at this time is the first
This is done as shown in Figure 0. This description is only for the photodetector 6 and below in FIG. 3. That is, the output of the photodetector 6 is appropriately amplified and then passed through three bandpass filters.

The filter ₁₂₁ allows only video signal components of 4.5MHz or less to pass through, and is further supplied to the demodulator ₈₁ .
Obtains video signals for TV display.

On the other hand, filters 12 ₂ and 12 ₃ have f ₁ and
f Only ₂ components are allowed to pass. The outputs of these filters are preferably sent to the mirror deflection drive circuit 11 via the demodulators 8 ₂ and 8 ₃ , the differential amplifier 13, and an appropriate error signal generation circuit 9.

FIG. 11 shows the case where the values of f ₁ and f ₂ are selected as the width of the video frequency domain. A synchronizing signal is required to separate the signal from the video signal. FIG. 12 shows the pattern. Synchronizing signal portions 40 ₁₁ , 40 ₁₂ are provided between the video signal portions 20 ₁₁ , 20 ₁₂ . After this, tracking signals 30 ₁₁ , 30 ₁₂ etc. are provided. The f ₁ and f ₂ components after this synchronization signal are regarded as tracking signals.

Specifically, this is carried out according to the circuit shown in FIG. As before, one of the outputs from the photodetector 6 is sent directly to the video signal demodulator ₈₁ . However, the synchronization signal detected from this output is sent to gate circuits 15 ₁ and 15 ₂ . This gate circuit is for operating the filters 12 ₂ and 12 ₃ only for a certain period of time immediately after the synchronization signal is detected. Filters 12 ₂ and 12 ₃ have f ₁ and
Only f ₂ components are allowed to pass through. The subsequent output processing is exactly the same as that shown in FIG.

The synchronization signal described here is included in the horizontal retrace period in the case of a general TV display, and tracking signals 300 ₁ , 300 ₂ etc. can also be incorporated into this horizontal retrace period.

Therefore, in the case of general TV display, not only is there no need to newly provide a synchronization signal, but there is also no need to add a tracking signal, which will cause no loss of information or an increase in the required bandwidth. Has practical advantages.

Furthermore, when the tracking signal is arranged in a portion corresponding to the horizontal line period of the video signal, the following advantages are obtained. That is, when a tracking signal is continuously recorded over the entire recording track, even if the frequency f ₁ or f ₂ of the tracking signal is placed outside the band occupied by the recorded video signal, for example, on the lower frequency side. Also, due to the nonlinearity of the recording medium, detector, circuit, etc. during playback,
If the frequency of the recorded video image signal is f, then f±
A frequency component of nf ₁ or ±nf ₂ (n: natural number) is mixed into the band of the recorded video signal and cannot be removed. This component appears as a moiré component on the playback screen and significantly impairs image quality. The only way to prevent this is to lower the recording level of the tracking signal, but if this is done, a tracking deviation signal with a sufficient S/N ratio cannot be obtained. However, since the tracking signal is placed in a portion corresponding to the horizontal retrace period, even if this moiré component occurs, it will not affect the reproduced screen. Therefore,
It becomes possible to record a tracking signal at a sufficient recording level, and a tracking deviation signal with a sufficient S/N ratio can be obtained.

In the examples shown in FIGS. 5 and 12, the tracking signals f ₁ and f ₂ are placed adjacent to each other on the same track. This can actually be simplified further. Figure 14 is an example, where f ₁ , f ₂
are arranged at different times. Therefore, it becomes easy to record such signals.

If the tracks are closely spaced, always
It becomes difficult to use the f ₁ and f ₂ signals independently.

Figure 15 shows a solution to this problem. For example, 300 ₁₂ is used for both tracks 10 ₁ and 10 ₂ .

At this time, in track ₁₀₁ , as the light beam shifts upward, the _f1 component increases;
At 0 ₂ , on the contrary, the component becomes large in f ₂ . Therefore, in order to correct this difference, it is necessary to invert the sign of the error signal for each track.

In the examples shown in Figs. 14 and 15, the tracking signal not only has the advantage that it only needs to be written sequentially as 300 ₁ and then 300 ₂ , but also has the advantage that the tracking signal only needs to be written sequentially as 300 1 and then 300 ₂ .
It is also possible to record other information on the bottom of the screen, etc.).

FIG. 16 further simplifies signal recording, and 300 ₂₁ is used for both tracking 10 ₁ and 10 ₂ . In this case as well, the sign of the error signal must be switched for each track in the third embodiment.
It is similar to To record the tracking signal in FIG. 16, the synchronization signal 40 ₁₁ is followed by 300 ₁₁
Then write 20 ₁₂ …, in the next tracking 40
Next to _21, write 300 ₂₁ and then 20 ₂₂ .

In the above example, the positional relationship between f ₁ and f ₂ was fixed for the same track. For example, in the example of FIG. 16, f ₁ and f ₂ are located on the upper side of tracks 10 ₁ and 10 ₂ , respectively.

Therefore, as shown in FIG. 6, the difference signals obtained from the same track continue to have almost the same sign. This is not necessarily optimal for subsequent signal processing. Furthermore, in the examples shown in FIGS. 15 and 16, it was necessary to invert the sign of the relationship between the error signal and the deviation for each track.

As a method for solving this problem, there is a method shown in FIG.

That is, one track has f ₁ , f ₂ , f ₁ ... f ₂
... and the tracking signals f ₂ , f ₁ , f ₁ , f ₂ , and so on coexist.

When the output of the photodetector 6 in FIG. 3 is applied, the result as shown in FIG. 18A is obtained if tracking is performed completely. In other words, a and b are each
It is the output for f ₁ and f ₂ , and c is the difference output. If the light beam shifts upward in FIG. 17, the result will be as shown in FIG. 18B. As a result, a difference output c is obtained.

On the other hand, if it is shifted downward, the result will be as shown in FIG. 18c.

From the comparison of FIGS. 18B and 18C, there is a certain relationship between the direction of track deviation and the difference signal c.

That is, considering the fundamental frequency component of the pulse train c, the phases are opposite in FIGS. 18B and 18C.
In Figure 18A, the difference signal is zero.

Therefore, if the case of FIG. 18B is assumed to be an in-phase component, then the case of FIG. 18C is an inverse phase component. Therefore, by finding these components of the difference signal and finding X = in-phase component - anti-phase component, the relationship between this X and the deviation is shown in Figure 19, which is exactly the same as in Figure 7, and as it is, This X can be used as an error signal.

In fact, this type of detection can be performed using the system shown in FIG. This is an explanation for the case shown in FIG. The same applies to the case shown in FIG. Same wave number of output from photodetector 6
The tracking signals of f ₁ and f ₂ are sent to filters 12 ₂ and 12
₃ , through appropriate demodulators 8 ₂ , 8 ₃ and further through a differential amplifier 13 ₁ , whose output is transmitted through synchronous, anti-phase demodulation circuits 80 ₁ , 80 ₂ to a differential amplifier 13 1 . It is supplied to the amplifier ₁₃₂ . This output is given to the error signal generation circuit 9. For example, if the light beam is shifted above the track, the demodulators 8 ₂ , 8 ₃
The output pulses shown in FIG. 18B a and b are obtained from the differential amplifier 13 ₁ , and the differential signal shown in FIG. 18B c is obtained from the differential amplifier 13 1 . Among the fundamental frequency components of this differential signal (this is for two horizontal scanning periods in the present example), the in-phase component (as shown in FIG. 18Bc, after the regions 40 ₁₁ and 40 ₁₂ in FIG. (having a negative value) amplitude demodulating circuit 80
It can be found by ₁ . Similarly, among the fundamental frequency components of the above-mentioned differential signal, anti-phase components (as shown in FIG. 18C, those having negative and positive values after regions 40 ₁₁ and 40 ₁₂ in FIG. 17, respectively) The amplitude of is determined by the demodulation circuit 80 ₂ . In the case of Figure 18B,
Only the in-phase component has a positive value, and the anti-phase component is 0. Therefore, a positive value signal is output from the differential amplifier 13 ₂ . In exactly the same way, in the case of FIG. 18C, a negative value signal is output from the differential amplifier 13 ₂ . Thus, depending on the sign and magnitude of the output of the differential amplifier ₁₃₂ , the error signal generation circuit 9 sends an error signal to the mirror deflection drive circuit 11 for positioning the light beam at the center of the track.

The following is the same as before.

Finally, recording of tracking signals will be specifically explained.

In this case, video signals are sequentially recorded on predetermined tracks on the rotating disk, and if a tracking signal needs to be written, the recording light beam is slightly deflected so that the light beam is placed at a position offset from the center of the track. to come. For example, in FIG. 16, after writing the synchronization signal part 40 ₁₁ , the tracking part 300 ₁₁ is written, and then the light beam is returned to its original state and continues to 20 ₁₂ . Of these, 300
In order to write a tracking signal in a wide area like ₁₁ , it is also effective to wave a light beam in a direction perpendicular to the track.

The above shows that the present invention provides simple and accurate tracking.

Although the description has been made regarding disks, the same applies to drums, tapes, etc.

Further, although the recording method has been described using FM modulation, it is clear that the recording method is not limited to this.

As described above, the present invention uses an information recording medium in which tracking signals of different frequencies outside the band of the video signal are arranged intermittently on both sides of the center line of the track and are recorded during the horizontal retrace period of the video signal. It is characterized by detecting a tracking signal using a tracking signal which is separated from the video signal by a filter, and is capable of detecting a track deviation without impairing the recording density of the video signal or adversely affecting the playback image quality. Since the tracking signal can be recorded at the recording level and the tracking signal with a sufficient S/N ratio can be obtained by the filter, the video signal recorded at high density in the form of a track has no effect on the playback image quality. You can accurately play along the center line of the track while tracking without any trouble. Furthermore, since the present invention is characterized in that it does not affect the screen by providing a tracking signal, even if a part of the tracking signal is outside the horizontal retrace period, it does not affect the screen. If so, it goes without saying that the tracking signal is substantially in the horizontal retrace period.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of disks and tracks, Fig. 2 is an explanatory diagram of the recording format of signals on the disc, Fig. 3 is an explanatory diagram of the reproduction of signals from the disc, and Fig. 4 is a diagram of the tracks. Explanation diagram of enlarged view, 5th
6 is an explanatory diagram of the tracking signal, FIG. 7 is an explanatory diagram of the tracking error signal and the amount of deviation, FIG. 8 is the tracking signal of the present invention, and FIG. 9 is the diagram of the present invention. FIG. 10 is an explanation of the relationship between the video signal and the tracking signal, and each of the signal processing systems. 11, 12, and 13 are explanatory diagrams showing other examples, FIGS. 14 to 17 are diagrams showing other examples of tracking signals of the present invention, and FIGS. 18 to 20 are diagrams showing other examples of tracking signal processing. FIG. Here, 1...disk, ₁₀₁ to ₁₀₃ ...track, ₁₀₀₁ to ₁₀₀₃ ...signal recording element, 200...
Disk rotation direction, 2...laser, 3...mirror, 4
...Half mirror, 5...Lens, 6...Photodetector, 8...
Demodulator, 9...Error signal generation circuit, ₁₀₁ to ₁₀₃ ...
Track, 11...Mirror deflection drive circuit, 12 ₁ ,
12 ₂ , 12 ₃ ... filter, 13, _{13 1} , 13 ₂ ...
Differential amplifier, 20 ₁₁ , 20 ₁₂ ... information recording part, 3
0 ₁₁ , 30 ₁₂ ...tracking signal recording section, 40 ₁₁ ,
40 ₁₂ ... Synchronous signal recording section, 80 ₁ , 80 ₂ ... Synchronous detector, 100 ₁ to 100 ₁ ... Signal recording element, 300
_{1,300 2} ...Tracking signal.

Claims (1)

[Claims] 1. An information recording medium in which a video signal is formed in the form of a track, in which a pair of recording areas in which tracking signals of different frequencies outside the band of the video signal are recorded are arranged intermittently on different sides of the center line of the track. an information recording medium which is arranged in a horizontal plane and substantially forms the pair of recording areas during the horizontal retrace period of the video signal; a reproducing means for reproducing the video signal from the track; and an output of the reproducing means. a filter for separating and extracting the tracking signals of different frequencies from the video signal; and a track that uses the tracking signals extracted by the filter to indicate the deviation of the reproducing means with respect to the center line of the track. An information reproducing apparatus comprising: means for obtaining a deviation signal; and means for correcting the deviation using the track deviation signal.