JPS63121162A - Tracking control method - Google Patents

Abstract

PURPOSE:To obtain preferable tracking control, by recording a pilot signal obtained from the deviation of the recording timing of an adjacent track with an information signal, and performing the tracking control based on the phase of the pilot signal reproduced at the time of reproducing the information signal. CONSTITUTION:Assuming the deviation of the recording timing of the adjacent track as 1/Fsec, the pilot signal whose frequency is FX(n+1/m) [where, (n) is integer, and (m) is integer >=3] is recorded with the information signal, and the tracking control is performed based on the phase of the pilot signal reproduced at the time of reproducing the information signal. In such way, the pilot signal between the adjacent tracks is recorded automatically as the signal with a phase of 2pi/m, and the tracking control can be performed by utilizing the change of the phase of a reproduced pilot signal corresponding to a tracking error at the time of reproduction.

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. Therefore, improving the tracking accuracy 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), pilot signals having four different frequencies are sequentially recorded on each track by being superimposed with an information signal, and during playback, tracking is performed by comparing the levels of pilot signals reproduced from both adjacent tracks of the control target track. A method of obtaining an error signal (four-frequency method), etc. has 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 if the CTL playback head is installed incorrectly. Therefore, accurate tracking control signals may not be obtained.

Although the problems of the CTL system can be solved by using a four-frequency system, the band of the information signal is limited because a J fj type pilot signal is superimposed on the information signal. Particularly in the case of digital signals, the lower end of the 81F range extends to about 100 Hz, making it impossible to superimpose as many as four different frequencies.

The present invention has been made in view of the above-mentioned problems, and is a novel tracking control method that can accurately detect tracking errors on recording tracks by simply superimposing one type of pilot signal, and can perform excellent tracking control with an extremely simple circuit. The purpose is to provide

[Means for solving problems]

For this purpose, in the tracking control method of the present invention, in a system for recording and reproducing information signals on a large number of tracks arranged in parallel on a recording medium, the deviation in the recording timing of adjacent tracks can be reduced by 17F. seconds, a pilot signal whose frequency is FX(n+-) [n is an integer, m is an integer of 3 or more] is recorded together with the information signal, and when the information signal is reproduced, the phase of the reproduced pilot signal is The configuration was designed to perform tracking control based on the following.

[Effect]

By configuring as described above, pilot signals between adjacent tracks are automatically recorded with a phase difference of 2π/m, and it is possible to prevent the phase of the reproduced pilot signal from changing depending on the tracking error during reproduction. This can be used to perform tracking control.

〔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 frequency of several tens to hundreds of kilohertz so as not to adversely affect the digital video signal.

In FIG. 1, 20 is a rotational phase detector for detecting the rotational phase of the rotational head Ha.

When Hb rotates 30 times per second, it outputs a 30 Hz rectangular wave signal (hereinafter referred to as PG). The detection phase of the rising and falling edges of PG is determined so as to coincide with the switching timing of the heads Ha and Hb.

21 is a 1/2 frequency divider that divides this PG into 1/2,
This output is input to the phase comparator 22 in the PLL circuit at the subsequent stage. Phase comparator 22, low pass filter (LPF)
23. Voltage controlled oscillator (VCO) 24 and frequency divider 25 are P
LL is configured, and the 1/2 frequency divider 21 is connected to the VCO 24.
A sinusoidal pilot signal that is phase-synchronized with the output of is output.

The center frequency of this VCO 24 is set to be an odd multiple of 15 Hz, for example, 49,995 KHz. Generally, if the recording period of one track is 1/fD seconds, the pilot signal will be recorded. n is an integer, and m is an integer of 3 or more. In this embodiment, fD = 60 and m = 4, which results in an odd multiple of 15 Hz. Therefore, the frequency division ratio of the frequency divider 25 is 1/(nm+1).

By setting the frequency of the pilot signal in this way, the phase of the pilot signal at the start point of each track is π
Shift by /2.

Generally, if fp;fo (n+), the phase of the pilot signal at the start point of each track is shifted by 2π/m.

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,
Recording is performed on the magnetic tape 10 by the heads Ha and Hb via the recording (R) side terminal of the recording/reproduction selector switch 7 and further via the head selector switch 8. controlled.

FIG. 3 is a diagram showing a recording pattern on a magnetic tape recorded as described above. In FIG. 3, 0, rc/2.
π-3π/2 indicates 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 for each track, but in order to maintain this relationship over the entire track, the shift amount of the adjacent track (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 one fraction of an integer.

That is, the pilot signals must have a desired phase difference at adjacent positions of adjacent tracks. Therefore, if the time required for the heads Ha and Hb to trace the distance of one track plus the shift amount (X) of the adjacent track is 1/F seconds, then the pilot signal is fP=
It is necessary to satisfy the relationship F×(m'+-!-).

Next, the operation during playback will be explained.

During reproduction, the pilot signal and digital video signal reproduced from the heads Ha and Hb 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 passed through a low-pass filter (LPF
) 32 and a 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 signals are supplied to a phase comparator 38 and compared in phase with a pilot signal obtained from the VCO 24 in the same manner as during recording. Hereinafter, the pilot signal obtained from the VCO 24 during reproduction will be referred to as a reference pilot signal to distinguish it from the reproduced pilot signal.

Now, as the phase of the reference pilot signal output from the VCO 24 changes from O → π/2-π-3π/2, the control target track changes in order from 0-π/2 → π-3π/2.
This is the track on which the pilot signal having the phase is recorded. The phase comparator 38 detects the phase difference between the reproduced pilot signal and the reference pilot signal, and supplies this as a tracking error signal to the cab stan motor control circuit 39 to control the rotation of the capstan 40 and perform tracking control.

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 tracing position of the head at this time is shown in FIG. 3a.

Next, if the playback 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 Figure 3, the phase of the playback pilot signal will be at Bb in Figure 4(b). As shown, it becomes a composite vector of a pilot signal with phase 0 and a pilot signal with phase π/2, and θb (=π/4) with respect to the reference pilot signal.
It will have a phase difference of . 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 vector Bc 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 4o 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, by simply generating a pilot signal of a single frequency and superimposing it on the recording signal, it is possible to perform good tracking control. There is no need to limit the bandwidth of 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 not over the entire track, but only in a portion where the influence of error occurrence is small.

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.

(Effects of the Invention) As explained above, according to the tracking control method of the present invention, good tracking control can be performed without restricting the band of the recording signal and only by using an extremely narrow band with an extremely simple circuit configuration. It became possible.

[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, 20 is a rotational phase detector, and 21 is 1/2
Frequency divider, 22 is a phase comparator, 24 is a VCo, 25 is a frequency divider, 32 is a low-pass filter, 38 is a phase comparator, 39
is a cab tongue motor control circuit, and 40 is a cab tongue.

Claims (1)

[Claims] In a system that records and reproduces information signals on a large number of parallel tracks on a recording medium, when the recording timing difference between adjacent tracks is 1/F seconds, the frequency is F×{n+(1/ m) [n is an integer, m is an integer of 3 or more] pilot signals are recorded together with the information signal, and tracking control is performed based on the phase of the reproduced pilot signal when the information signal is reproduced.