JPH0447549A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To obtain a sharp reproducing image by providing a means to specify tape feed speed in specific reproduction operated at tape feed speed different from that in recording. CONSTITUTION:A switch 70 is provided between the output of a Schmidt trigger circuit 36 and monostable multivibrators 38, 40. Also, in a capstan servo loop, a frequency divider 72 whose frequency division ratio (m) (natural number) can be changed freely, a frequency divider 74 whose frequency division ratio (p) (natural number) can be changed freely and frequency-divides the output signal of a crystal oscillator 53, and a motor driving circuit 76 equipped with a selective function of forward/backward rotation are provided. Furthermore, a control circuit 78 which controls the switch 70, the frequency dividers 72, 74, and the motor driving circuit 76 is provided. The frequency dividers 72, 74 function so as to multiply the tape feed speed by m/p. Thereby, tracking control using a pilot signal for tracking control can be operated effectively even in the specific reproduction of + or -m/p of ordinary reproduction, and a reproducing image with superior quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking control circuit, and more specifically to a tracking control circuit in a helical scan recording method using a rotating head.

[Prior Art] Helical recording and reproducing video signals are recorded or reproduced using a rotating head on tracks that are inclined with respect to the longitudinal direction of a magnetic tape.
In scan type playback devices, tracking control is very important for controlling the rotary head so that the rotary head accurately scans the recording track. One type of tracking control is a method called area-divided ATF. this is,
This is a method in which a pilot signal for tracking control is recorded on a part of the track at the same time as a video signal is recorded, and during reproduction, the position of the rotary head, that is, tracking is controlled by the pilot signal reproduced by the rotary head.

For example, in the case of a two-channel digital VTR head configuration as shown in FIG. 2, FIG. 3 shows a track pattern when an area-divided ATF is used. In addition, FIG. 2(a) is a plan view of the rotary head, and FIG. 2(b) is a head layout diagram of the rotary head expanded in the circumferential direction.
12A is a positive azimuth head, IOB is a negative azimuth head, and 12B is a negative azimuth head.As can be seen from FIG. 2(b), heads 12A and 12B are heads 1OA.
It is placed at a position 180 degrees opposite to the IOB. In FIG. 3, tracks tl, t5t9 are recorded by head IOA, tracks t2, t6, and tlo are recorded by head IOB, tracks t3, t7 are recorded by head 12A, and track t4t8 is recorded by head 12B. In addition, in FIG. 3, A indicates the running direction of the magnetic tape, and B indicates the rotating heads IOA, IOB,
12A and 12B are shown in the scanning direction, and ATF shows the recording area of the pilot signal. Here, as shown in the figure, it is assumed that the recording area ATF is located near the beginning of each track.

FIG. 4 shows an enlarged view of the vicinity of the pilot recording area ATF. In the pilot recording area ATF, pilot signals of different frequencies f+ and f2 are recorded alternately for each track. As the frequency f2, a low frequency with no azimuth loss is selected, and frequencies separated from each other so as to be separated by a bandpass filter are selected. The pilot recording area ATF of each track is such that it partially touches the pilot recording area ATF of the adjacent track, and furthermore, the beginning and end of a certain pilot recording area ATF are connected to the adjacent track and the pilot recording area ATF of the adjacent track on the opposite side. It is arranged so as to be located at the center of the recording area ATF.

FIG. 5 shows a block diagram of a conventional tracking control circuit using an area-divided ATF.

14 is a magnetic tape on which signals are recorded in the track pattern shown in FIGS. 3 and 4, and the rotary spatulas F10A, IOB, 12A, and 12B shown in FIG. 2 function as playback heads here. Rotating head IOA, IOB,
12A, 12B output is amplifier 16A, 16B, 18A
, 18B, and the switch 20 is amplified by the amplifier 16A.
, 18A output, and switch 22 selects amplifier 16B output.
, 18B output. The switch 20.22 causes the rotary head 10A tracing on the magnetic tape 14;
It can be switched to select IOB, 12A, and 12B.

The output of the switch 20.22 is supplied to the data reproduction system, while the output of the switch 2o is applied to a bandpass filter (BPF) 24.26 for tracking control. The BPF 24 extracts a regenerated pilot signal of frequency f, and the BPF 26 extracts a regenerated pilot signal of frequency f. The output of BPF 24.26 is connected to a detection circuit 28.30 and a low pass filter (LPF) 32.3, respectively.
4, it is converted into a voltage signal indicating the level of the reproduced pilot signal. The Schmitt trigger circuit 36 is an LPF
34 is shaped into a rectangular wave. As a result, a rectangular signal indicating the rising and falling edges of the reproduced pilot signal f is obtained.

The mono multi 38 is activated by the rising edge of the output of the Schmitt trigger circuit 36, the mono multi 40 is activated by the falling edge, and the output of the mono multi 38.40 is connected to the control terminal of the sample and hold (S/H) circuit 42.44. is applied to.

The output voltage of the LPF 32 is applied to the input terminal of the S/H circuit 42.44, and therefore the S/H circuit 42.44
are the pilot signals f2 of two adjacent tracks, respectively.
Holds a signal indicating the playback level.

A differential amplifier 46 outputs a difference signal between the outputs of the S/H circuits 42 and 44. The output of the differential amplifier 46 is connected to the capstan 4
7, a frequency generator 50, a frequency divider 52, a phase comparator 54 that compares the phase of a signal indicating the rotational phase of the capstan motor 48 with a reference signal generated by a crystal oscillator 53, an LPF 56, It is applied to the adder 58 of the capstan servo loop consisting of the adder 58 and the motor drive circuit 60. This allows, for example,
If the magnetic tape 14 advances too far, the S/H circuit 42
The holding voltage of becomes higher than the holding voltage of the S/H circuit 44,
As the output voltage of the differential amplifier 46 decreases, the output of the adder 58 decreases, tape feeding by the capstan 47 is slowed down, and the rotary head is adjusted to be positioned above the recording track.

Note that in a digital recording type VTR, two types of redundant codes for error correction are usually added: C1 parity for a pixel group in the scanning line direction and C2 parity for a pixel group in a direction perpendicular to this. Cl parity is added to a predetermined number of pixels in the scanning line direction, and a 5YNC code for synchronization and an ID code for identification are added, and this is called a synchronization block. 02 parity is added to the block, and this is called a C2 parity block.

During normal playback, errors in the synchronous block are detected and corrected using Cl parity in the same synchronous block, and
After all pixel data in the vertical direction constituting the 2-parity block is reproduced, the C2 parity is used to detect and correct errors in the C2 parity block. The timing of correction is determined by the rotational phase of the rotary head.

[Problem to be solved by the invention] Consider special playback such as search and slow playback.

To accomplish the search, the capstan motor is rotated in forward and reverse directions at a faster speed than during normal playback.

If so-called dynamic tracking is used and the rotary head is not swung in a direction perpendicular to the scanning direction, the rotary head will cross the track diagonally, making it impossible to reproduce all recorded signals of the image. That is, at the time of search, error correction is performed using Cl parity for the reproduced synchronization block, or error correction cannot be performed using C2 parity. When searching, it is sufficient to be able to roughly check the recorded contents, so this poses no problem.

In the case of slow playback, the capstan motor is rotated in forward and reverse directions at a speed approximately slower than during normal playback.

Unless dynamic tracking is performed as in the search, the rotating head will cross the track diagonally. However, in the case of slow playback, the rotating head will cross the same track many times while changing its position, so if the playback signal is reconfigured using the playback ID and stored in memory, all of one screen's worth of Can reproduce the signal. Therefore, errors can be almost completely corrected using Cl parity and C2 parity, and a clear reproduced image can be obtained.

By the way, it is fine if the slow playback speed is constant, but if you want to be able to select or set the slow playback speed from a wide range, for example, you can change the slow playback speed to
There is a problem in that it is not possible to know whether all the data of one track has been played back. That is, FIG. 9 shows a reproduced output waveform when 1/4 speed slow reproduction is performed using, for example, the head configuration of FIG. 2 and the circuit of FIG. 5. In the figure,
Vertical lines indicate switching timing between heads IOA and IOB and heads 12A12B. Focusing on tracks t1 and t2, they are being played back at different locations many times, but it is unclear when the entire playback of track jl+t will end, so it is especially important to grasp the timing of error correction using C2 parity. The problem is that it is difficult.

Therefore, an object of the present invention is to provide a tracking control circuit that solves these problems.

[Means for Solving the Problems] A tracking control circuit according to the present invention is a circuit that controls tracking using tracking control pilot signals recorded only at predetermined locations on each of parallel tracks of a tape-shaped recording medium. , during special playback at a tape feed speed different from that during recording, the first means sets the sampling interval of the tracking error to 1/2n (n is a natural number) of normal playback, and the tape feed speed is set to ±m during normal playback. /p (m
, p is a natural number).

[Effect] By the above means, ±m/p (m.

Even during special playback where p is a natural number), the tracking control using the pilot signal for tracking control works effectively, so that all the information on the track can be played back, and the processing after all the information has been obtained can be performed accurately. become executable.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of an embodiment of the present invention. In this embodiment, a switch 70 is provided between the output of the Schmitt trigger circuit 36 and the control terminal of the monomulti 38, 40. In addition to the frequency divider 52, the capstan servo loop also includes a frequency divider 72 whose frequency division ratio m (natural number) can be freely changed, and a crystal oscillator whose frequency division ratio p (natural number) can be freely changed. Frequency divider 7 that divides the output signal of 53
In place of the motor drive circuit 60, a similar motor drive circuit having a forward/reverse rotation selection function is provided, and these switches 70. A control circuit 78 is provided to control frequency dividers 72, 74 and motor drive circuit 76. Other circuit elements are the same as in FIG. 5 and are given the same reference numerals.

The frequency dividers 72, 74 collectively function to increase the tape advance speed by m/p times the normal speed, and the motor drive circuit 7
In addition to the forward/reverse rotation selection function of 6, the tape feeding speed can be controlled to ±m/p times the normal speed by commands from the control circuit 78.

Here, in the magnetic recording/reproducing apparatus having the head configuration shown in FIG. 2, m=1. Consider the case where p=2 and the tape feed speed is halved. As shown by reference numeral 80 in FIG. 6, if the head IOA is aligned with track t at the start of scanning, it will be off by exactly one track at the end of scanning.

Similarly, as indicated by reference numeral 82, head IOB is located on track t2 at the start of scanning, but is located on track 1 at the end of scanning. The heads 12A and 12B facing each other by 180° are each designated by the reference numeral 8.
Trace as shown in 2.84.

The 7th graph shows these playback output levels on the time axis.
It is a diagram. In this way, at 1/2 speed, fluctuations in the reproduction level have the same cycle as the rotation cycle of the drum. Area-divided ATF does not have tracking information in areas other than the ATF area, so the head configuration shown in Figure 2 is 1/2 of the normal one.
When the tape is run at double speed, if a tracking control signal using area division ATF is obtained at point A in Fig. 7,
Tracking control can be performed so that the track is on track. That is, the switch 70 is opened and closed every 1/2 rotation of the rotary head, and the S/H circuits 42 and 44 are operated once per rotation of the rotary head. When the hatched reproduction output portions 86 and 87 are combined, all the information of track t can be reproduced in one revolution of the drum, and error correction by C2 parity is effective during this period. Therefore,
Error correction using C2 parity may be performed in accordance with the timing obtained by dividing the rotation of the rotary head by 1/2.

FIG. 8 is a diagram showing the configuration of the data reproducing system in this embodiment, in which the reproduced signals output from the switches 20 and 22 are sent to the digital demodulator 1 via terminals 100A and 100B.
01A and 10IB. Synchronous separation circuit 102A
, 102B separates synchronization data from the signals demodulated by the demodulators 101A and 10IB, and data recovery circuits 103A,
103B. The data restoration circuits 103A, 103B restore the data according to this timing pulse, and the restored reproduced data is transferred to the C2 decoding circuits 104A, 104B, the C1 decoding circuit 105A,
Code errors are corrected at 105B. In the reproduced data whose code errors have been corrected, the ID code for identification including address data corresponding to the position on the screen of each synchronization block is separated by the ID restoration circuits 1.6A and 106B, and the ID code is separated by the ID restoration circuits 1.6A and 106B.

Data corrected for code errors is written to addresses on the memory 107 according to the ID code separated by 106B. The memory 107 reads the stored data in a predetermined order, and the reproduced data thus obtained is sent to the terminal 1.
Output from 08.

The control circuit 78 in FIG. 1 receives a control signal via a terminal 109 so that the C2 decoding circuits 104A and 104B are always in operation during normal playback.

On the other hand, during high-speed search, the C2 decoding circuits 104A, 104
13 is rendered inactive by the control signal. This is because during a high-speed search, reproduced signals cannot be obtained continuously for a long period of time, making it impossible to completely decode the error correction code using C2 parity.

During slow playback, there is a period during which playback signals are continuously obtained, as shown in FIG. Therefore, during slow playback, assuming that each head is in the on state at the timing when the S/H circuit 44 operates (timing shown in FIG. 7A), the period during which a good playback signal is obtained is limited to the C2 decoding circuits 104A and 104B. A control signal is input from a terminal 109 to operate the circuit and disable it during other periods. This control signal can be obtained from tape speed information during slow playback and rotational phase information of the rotary head.

FIG. 9 shows the time change in the playback output level when the tape feed speed is increased to 1/4. In this case, tracking information can be obtained from the ATF area at time point A once every two rotations of the drum. If we pay attention to the track t, it appears many times as indicated by the shaded areas 88-92. However, since the shaded area 89°90 is the most stable and the timing of this occurrence is known in advance, writing to the memory 107 and the operation timing of the C2 decoding circuits 104A and 104B can be adjusted to use the reproduced data in this area. Just set it.

Fig. 10 shows the temporal change in the reproduction output level at 1/2 speed and 1/4 speed when equipped with a pair of heads that face each other by 180° and have different azimuth angles, and Fig.
FIG. 12 shows a similar change in playback output level for a pair of heads, and FIG. 12 shows a similar change in playback output level for a pair of heads. In either case, tracking control based on the tracking information of the ATF area may be activated at the point in time.

[Effects of the Invention] As can be easily understood from the above description, according to the present invention, as long as the reproduction speed is ±m/p times the normal speed, a high-quality reproduced image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention, and FIG.
The figure shows the head configuration, Figure 3 shows the track pattern, and Figure 4 shows the track pattern.
The figure is the pilot signal recording race diagram in Figure 2, and Figure 7 is 1.
Figure 8 is a block diagram of the configuration of the data reproduction system of the embodiment shown in Figure 1. Figure 9 is an output level diagram when playing at 1/4 speed. Figure 10 , Figures 11 and 12 are 1 pair, 3 pairs, and 4 pairs, respectively.
FIG. 4 is a reproduction output level diagram at 1/2 speed and 1/4 speed with a pair of head configurations. 10A, IOB, 12A, 12B: Rotating head 14: Magnetic tape 20.22: Switch 24° 26: Bandpass filter 36: Schmitt trigger circuit 38
, 40: Monomulti 46: Differential amplifier 47: Cab stan 48: Cab stan motor 50: Frequency generator 52, 72.74: Frequency divider 53: Crystal oscillator
54: Phase comparator 60, 76: Motor drive circuit 78
Two control circuits

Claims (1)

[Claims] A circuit that controls tracking using tracking control pilot signals recorded only at predetermined locations on each of parallel tracks of a tape-shaped recording medium, and which generates tracking error samples during special playback at a tape feed speed different from that during recording. The first means sets the interval to 1/2n (n is a natural number) of normal playback, and the second means sets the tape feed speed to ±m/p (m and p are natural numbers) times the normal playback speed. A tracking control circuit characterized by being provided.