JPS63119058A - Tracking control method - Google Patents

Abstract

PURPOSE:To widen the band of an information signal to be recorded and to attain a solution when the linearity of a track is damaged by overlapping and recording the pilot signal of a single frequency to the information signal so that the phase of both adjoining tracks can shift by the same quantity in an opposite direction mutually to the phase of a control target track. CONSTITUTION:The pilot signal of a single frequency is overlapped and recorded to an information signal so that the phase of both adjoining tracks is mutually shifted by the same quantity in the opposite direction to the phase of a control target track out of many tracks, and a tracking control is executed based on the phase of the pilot signal reproduced at the time of the reproduction of the information signal. Thus, only by overlapped one type of a pilot signal, a tracking error to a recording track is correctly detected, the tracking error signal is obtained stably and correctly at any position of the track and a satisfactory tracking control is executed accompanying this.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a tracking control method, and particularly to a tracking control method in a system for recording and reproducing information signals on a large number of parallel tracks on a recording medium. It is related to.

[Conventional technology]

In recent years, it has become common to digitize various information signals and record and reproduce them in the above-mentioned systems. On the other hand, the band of digitized information signals is extremely wide compared to that of analog information signals, and as a result, it is necessary to perform high-density magnetic recording, and for example, the track pitch cannot be widened.

On the other hand, if a tracking error occurs during reproduction of a digital information signal, the probability of code error occurrence increases significantly. Although it is possible to correct this with a so-called error correction code, it is not preferable to improve the correction ability of the error correction code because it increases redundancy.

Improving the accuracy of tracking in this type of system is a major theme.

On the other hand, as a conventional tracking control method in this type of system, a control signal (CTL) with a frequency corresponding to the track pitch is sent to the end of a tape-shaped recording medium.
) is recorded with a fixed head, and the tracking error signal is obtained by reproducing this and comparing the phase with a reference signal (CT
L method), 4 different f! A method for obtaining a tracking error signal by sequentially recording a pilot signal having a frequency of the fi class by superimposing it on an information signal for each track, and comparing the pilot signal levels reproduced from both adjacent tracks of a control target track during reproduction ( 4-frequency system) etc. have been used.

[Problem that the invention seeks to solve]

However, in the CTL method, tracking control is not performed based on information obtained from the recording track, so for example, if the linearity of the track is impaired or the CTL playback head installation may be inaccurate due to errors, etc. In some cases, it may not be possible to obtain an accurate tracking control signal.

In addition, although the four-frequency system can solve the problems of the CTL system, as many as four types of pilot signals are superimposed on the information signal, which limits the band of the information signal, especially for digital signals. In this case, since the lower end of the recording band extends to about 100 KHz, it is impossible to superimpose as many as 4 fffi frequencies.

The present invention has been made in view of the above-mentioned problems, and is capable of accurately detecting tracking errors on recording tracks by simply superimposing one type of pilot signal, and stably and accurately detecting tracking errors at any position on the track. It is an object of the present invention to provide a novel tracking control method in which signals can be obtained and good tracking control can be performed accordingly.

Means for Solving Problem C] To achieve this purpose, the tracking control method of the present invention provides a system for recording and reproducing information signals on a large number of parallel tracks on a recording medium. , a pilot signal of a single frequency is superimposed and recorded on the information signal so that the phases of both adjacent tracks are shifted by the same amount in opposite directions with respect to the phase of the control target track among the plurality of tracks, and the information signal is The configuration is such that tracking control is performed based on the phase of the reproduced pilot signal during reproduction.

[Effect]

By configuring as described above, tracking control can be performed by simply superimposing a pilot signal of a single frequency, so the band of the information signal to be recorded can be widened, and the linearity of the track can be improved. It can also be used in cases where it is damaged.

〔Example〕

Examples to which the tracking control method of the present invention is applied will be described below. In the embodiment shown below, the present invention is applied to a rotating two-head helical scan type digital VTR.

First, the recording operation of the digital VTR of this embodiment will be explained.

The analog video signal input to the video signal input terminal 1 is digitized by an analog-digital (A/D) converter 2, and further processed by an encoding circuit 3 for error detection, correction codes, and redundant data such as various additional information. The data is added and further converted into a data array suitable for error correction and supplied to the modulation circuit 4.

The modulation circuit 13 performs, for example, so-called mapping coding to convert the signal into a signal with suppressed low-frequency components so as to have a signal form suitable for magnetic recording.

In this embodiment, a single frequency pilot signal is to be superimposed on the band suppressed by the modulation circuit 4, and this single frequency pilot signal and the digital video output from the modulation circuit 4 are The addition circuit 5 performs addition with the signal.

Here, this single frequency pilot signal generating section will be explained. In this embodiment, this single frequency pilot signal is a sine wave with a genus of about 10 to 100 KHz, which does not adversely affect the digital video signal.

This sine wave is obtained by reading data stored in the ROM table 14. The relationship between address data input to this ROM table 14 and output data is shown in FIG. As shown in the figure, if the data input to the ROM table 14 is sequentially changed from 0 to N-1 (15 in this example) at regular intervals, data corresponding to the step-like waveform shown in the figure is generated. . This data is converted into an analog signal by a digital-to-analog (D/A) converter 15,
Furthermore, by removing harmful harmonics in the LPF 16, a sine wave of a single frequency can be obtained. Since the ROM table 14 generates data corresponding to one period of a sine wave in N steps from 0 to N-1, the address data is N/2. N/4
In this case, the phase is π and π/2. Therefore, when the frequency of the necessary pilot signal is f, then 1
The address may be updated every /(NXf#) seconds.

11 is an excavator that generates a clock signal having a frequency of NXf, and this clock has a maximum value of N-1
counter 12 (4-bit counter if N=16)
The output data of this counter 12 is added to the adder 1.
3 to the ROM 14 as address data.

Next, control of the phase of the pilot signal will be explained. For example, if it is desired to shift the phase of the output of the ROM 14 by π/2, it is clear from the above explanation that it is sufficient to shift N/4 addresses. Therefore, the constant data generator 17 outputs O,
N/4. Four data of N/2°3N/4 are generated in parallel, and these four data are selectively supplied to the adder 13 by a data selector. As a result, it is possible to output four types of single frequency pilot signals whose phases are shifted by π/2 from the ROM 14.

A rotary phase detector 20 detects the phase of the recording and reproducing rotary heads Ha and Hb, and generates a rectangular wave signal (hereinafter referred to as PG) indicating switching timing of the recording and reproducing heads. The counter 12 is reset by a timing pulse output from the edge detector 21 indicating the edge timing of the PG, that is, it is reset at the timing when the heads Ha and Hb start tracing each recording track. On the other hand, the counter 19 is a 2-bit counter that counts this timing pulse, and the output data is shifted every time the timing pulse is input, that is, every time the track is changed, and accordingly, the data selector 18
Change the output data as follows: /4→N/2→3N/4-0...

With the above configuration, the phase of the pilot signal supplied to the adder 5 is sequentially shifted by π/2 at the timing when the heads Ha and Hb start tracing the track.

The pilot signal and digital video signal formed as described above are frequency-multiplexed by an adder 5 and then sent to a recording amplifier 6 and recorded. / Recording is performed on the magnetic tape 10 by the heads Ha and Hb via the recording (R) side terminal of the playback selector switch 7 and further through the head selector switch 8. The head selector switch 8 is controlled by the aforementioned PG. be done.

FIG. 3 is a diagram showing a recording pattern on a magnetic tape recorded as described above. In Figure 3.

0, π/2. π and 3π/2 indicate the phase of the pilot signal recorded on each track. Here, it was explained that according to the pilot signal generation method described above, the initial phase of each track shifts from track to track, but in order to maintain this relationship over the entire track, the shift amount (
For X) in the figure, it is assumed that the number of rotations of each head and the transport speed of the tape are determined so that the recording wavelength of the pilot signal is 1/integer.

Next, the operation during playback will be explained.

The pilot signal and digital video signal reproduced from the heads Ha and Hb during reproduction are transferred to the head selector switch 8,
Playback amplifier 3 via the P side (playback side) terminal of switch 7
1, amplified and then low-pass filter (LPF)
32 and - bypass filter (HPF) 33.

The digital video signal is separated in the HPF 33, digitally demodulated in the demodulation circuit 34, and input to the decoding circuit 35. The decoding circuit 35 performs processing, error correction, etc. corresponding to the aforementioned encoding circuit 3, and supplies a reproduced digital video signal to the D/A converter 36. D/A converter 3
The video signal analogized in step 6 is outputted from an output terminal 37 as a reproduced video signal.

On the other hand, the LPF 32 is for separating pilot signals, and the separated pilot signal is supplied to a phase comparator 38, where the phase is compared with the pilot signal obtained from the LPF 16 in the same manner as during recording. Hereinafter, the pilot signal obtained from the LPF 16 during regeneration will be referred to as reference pilot number i to distinguish it from the regenerated pilot signal.

Now, as the phase of the reference pilot signal output from the LPF 16 changes from 0 → π/2 → π → 3π/2, the control target track changes in the order of 0 - π/2 → π → 3π/2.
The zero phase comparator 38, which is the track on which the pilot signal having the phase of The rotation of the capstan 40 is controlled, and tracking control is performed.

Here, the state of tracking control according to this embodiment will be explained using FIGS. 4(a), (b), (c), and (d). Now, if the track where the phase of the recorded pilot signal is 0 is the control target track, the phase of the reproduced pilot signal when the reproduction head is on this control target track is the vector Ba in Fig. 4(a). As shown, the phase matches that of the reference pilot signal. The trace position of the head at this time is shown in FIG. 3a.

Next, assuming that the reproducing head is at a position shifted by 1/2 track pitch to the right in the figure with respect to the control target track as shown in Fig. 3, the phase of the reproducing pilot signal is as shown in Fig.
As shown in Bb of b), the pilot signal with phase 0 and the phase π
/2 pilot signal, and has a phase difference of θb (=π/4) with respect to the reference pilot signal. Assuming that the tape running direction is the direction indicated by Y in FIG. The playback head is moved closer to the control target track.

Further, when the reproducing head is at a position shifted by 1/2 track pitch to the left in the figure with respect to the control target track as shown in FIG.
As shown by the vector Be in C), the phase comparator 38 generates a positive level signal according to the phase difference θC. Correspondingly, the rotational speed of the capstan 40 increases and the reproducing head attempts to approach the control target track.

Furthermore, when the reproducing head traces a position shifted by two track pitches from the control target track as shown in FIG. 3(d), the phase of the reproducing pilot signal is set to B in FIG.
As shown in d, there is a phase difference (θd) of π from the reference pilot signal, and a large error voltage is obtained from the phase comparator 38, which slows down the rotational speed of the capstan 40 even if it is made faster. However, the playback head is moved closer to the control target track.

As mentioned above, in the digital VTR of this embodiment, it is possible to perform good tracking control simply by superimposing a pilot signal of a single frequency on the recording signal, and it is possible to limit the band of the digital signal. disappears. Furthermore, the error rate during reproduction can be significantly reduced compared to the case of tracking using the conventional four-frequency method.

Note that the tracking method of the present invention is not limited to the above-described embodiments; for example, it is also possible to record a single pilot signal only in a small portion of the track where the influence caused by the occurrence of an error is small, instead of recording a single pilot signal over the entire track. .

Also, as a method of generating a reference pilot signal,
The method is not limited to the above method, and it is also possible to record a pilot signal of a single frequency with a constant phase on a tape, and use this reproduced signal to form the signal.

〔Effect of the invention〕

As explained above, according to the tracking control method of the present invention, it is possible to perform good tracking control without limiting the band of the recording signal and only by using an extremely narrow band.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a digital VTR as an embodiment of the present invention, FIG. 2 is a diagram showing input/output data of the ROM table in FIG. 1, and FIG. 4A, 4B, 4C, and 4D are diagrams illustrating recording patterns of a VTR. FIGS. 4A, 4B, 4C, and 4D are diagrams for explaining tracking control in the digital VTR of FIG. In the figure, 5 is an adder, 11 is a clock oscillator, 12 is a counter, 13 is an adder, and 14 is a ROM. 15 is a D/A converter, 16 is a low-pass filter, 32 is a low-pass filter, 38 is a phase comparator, 39 is a captan motor control circuit, and 40 is a capstan. 2nd ward address

Claims (1)

[Claims] In a system for recording and reproducing information signals on a large number of parallel tracks on a recording medium, the phase of both adjacent tracks is the same in opposite directions to the phase of the control target track among the large number of tracks. A tracking control method in which a pilot signal of a single frequency is superimposed and recorded on an information signal so as to be shifted by an amount, and when the information signal is reproduced, tracking control is performed based on the phase of the reproduced pilot signal.