JPH0315242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tracking control circuit for a video disc or a video tape recorder (hereinafter simply referred to as a VTR), and in particular a tracking control circuit using a so-called pilot method using four predetermined pilot signals. This invention relates to a tracking control circuit.

BACKGROUND ART In video disks or VTRs, the tracks recorded on a recording medium such as a disk or tape deviate from a designed center value due to the manufacturing and processing precision of the recording device. Particularly in VTRs, the tracks on the recording medium are curved in an S-shape due to the machining accuracy of the cylinder and uneven tension around the cylinder. Therefore, when reproducing a recording medium in this type of apparatus, it would be ideal if tracking could be performed automatically by moving the pickup or magnetic head that traces the track in the width direction of the track.

For this reason, several tracking control methods have been proposed for this type of device. Among them, a so-called pilot method using four types of pilot signals each having different predetermined frequencies has recently been proposed and is attracting attention.

This pilot method uses four types of pilot signals ₁ ,
The respective frequency differences of ₂ , ₃ , and ₄ are determined in the relationship shown in Figure 1 A and B, and these pilot signals ₁ , ₂ , ₃ , and ₄ are set for each track as... ₁ ,
₂ , ₃ , _4, etc., are sequentially switched and superimposed on the recorded signal and written onto the recording medium. Therefore, when a track on which pilot signal ₁ is written is played back, pilot signals ₂ and ₄ recorded on adjacent tracks on both sides will also be played back due to crosstalk, and in this case, The extraction pilot signals p at this point are ₁ , ₂ , and ₄ . Therefore, when pilot signal ₁ recorded on the playback track is mixed with this extracted pilot signal p, the output will be | ₂ ± ₁ |, | ₄ ± ₁ |,
| ₁ ± ₁ | appears, and if only the difference component is extracted, from the relationship shown in Figure 1 A and B, | ₂ − ₁ |= _T1 , | ₄
− ₁ |= _T2 , | ₁ − ₁ |=0 are obtained. As a result, when a track shift occurs during reproduction, the amplitude of either _T1 or _T2 increases depending on the direction of the shift. For example, as shown in FIG. 2, suppose that a pick-up or magnetic head H is tracing a track in the direction of arrow A, and that this trace sequentially moves each track on the recording medium in the direction of arrow B. , four types of pilot signals ₁ , ₂ , ₃ , ₄ are sequentially written into each track ₁ , ₂ , ₃ , ₄ , . Therefore, the pick-up or magnetic head H is
If the pickup or magnetic head H shifts as shown by X in the figure, _T1 becomes larger than _T2 , and if the pickup or magnetic head H shifts as shown by Y in the figure, _T1 becomes smaller than _T2 . Therefore, if the pickup or magnetic head H is moved in a direction perpendicular to the track or the recording medium is moved so that the amplitudes of _T1 and _T2 become equal, the pickup or magnetic head H will be moved to Z as shown in FIG. As shown in the figure, a normal tracking state can be maintained. For example, since a magnetic tape is used as a recording medium in a VTR, the running speed of this magnetic tape, that is, the capstan motor that runs the magnetic tape, is _{the T1} and _T2 mentioned above.
If the speed is controlled by a correction signal having an amplitude difference value of , or if the above-mentioned movement control of the magnetic head is performed, tracking will be automatically performed. Furthermore, since a video disc uses a disc as a recording medium, tracking control cannot be performed in this case even if the motor that rotates the disc is controlled.
For this purpose, tracking adjustment is performed on video discs by moving the pickup in the radial direction of the disc.

By the way, in such a tracking control circuit using the pilot method, in order to obtain the frequency difference _T1 and _T2 shown in FIG. 1B, the pilot signal to be mixed with the reproduced extracted pilot signal p is as shown in FIG. It is necessary to switch for each track so as to correspond to a predetermined writing order, such as pilot signal ₁ for the track shown and pilot signal ₂ for the track. Therefore, the magnitude relationship of the amplitudes of the frequency differences _T1 and _T2 with respect to the pick-up or displacement direction of the magnetic head H is reversed for each track. As a result, the polarity of the correction signal having the above-mentioned amplitude difference value must be reversed for each track and then supplied to the speed control circuit of the motor or the like. For this purpose, after determining the frequency difference _T1 and _T2 , an inverting circuit consisting of an analog switch and an inverting amplifier is required to invert the polarity of the signal for each track to input or output the amplitude level difference between the two. It was hot.

To solve this problem, there are four types of pilot signals ₁ , ₂ , ₃ , and 4 that are written during recording.
₄ and the generation order of the extracted pilot signals reproduced during reproduction, the frequency difference _T1 , _T2 in the direction of deviation of the magnetic head H can be
The present application proposes an arrangement in which the magnitude relationship of the amplitudes of the two signals is always the same.

This means that when the four types of pilot signals written during recording are repeated in the order of ₁ , ₂ , ₃ , and ₄ ,
The pilot signals to be mixed to generate _T1 and _T2 are mixed in the order of ₃ , ₂ , ₁ , ₄ ... or ₁ , ₄ , _3.
，
_2. The timing of occurrence is controlled in the following order. Write like this when recording 4
For the writing order in which the seed pilot signals ₁ , ₂ , ₃ , and ₄ are sequentially repeated, the pilot signals to be mixed to generate _T1 and _T2 are arranged so that they are not adjacent to each other in the writing order of the pilot signals at the time of writing. By switching the generation timing of the two signals, even if the magnetic head H sequentially moves to the next track, the deviation direction and frequency difference _T1 , _{T2 will} be maintained.
The size relationship of is always adjusted accordingly. Therefore, as described above, an inverting circuit consisting of an analog switch, an inverting amplifier, etc. for correcting the polarity of the correction signal whose polarity is sequentially inverted as the magnetic head H moves along the track becomes unnecessary.

Here, in the tracking control circuit having the above configuration, pilot signals p of ₁ and ₃ are supplied to one magnetic head _HA , and ₂ and ₄ are supplied to the other magnetic head _HB during recording. However, during playback, it is only possible to distinguish between magnetic heads H _A and H _B by the head switch signal, and it is not possible to distinguish between pilot signals ₁ and ₃ or ₂ and ₄ of the pilot signals p recorded on the track currently being traced. do not have. For this reason, at the start of playback, etc., if the combination timing of the pilot signal mixed with the extracted pilot signal p to extract the frequency difference _T1 , _T2 is shifted by two tracks, the polarity of the tracking control signal will change. Reverse it,
Tracking is controlled in the direction of deviation. As a result, the control in the direction in which the tracking is deviated is executed for two tracks before returning to normal tracking control.As a result, the tracking alignment time becomes longer or the problem of disturbance in the reproduced image is caused. Become.

DISCLOSURE OF THE INVENTION An object of the present invention is to eliminate the need for polarity reversal for each track for a tracking control signal, and to improve tracking settling when the combination timing of a mixed pilot signal with respect to an extracted pilot signal is shifted by two tracks. An object of the present invention is to provide a tracking control circuit that can significantly shorten the time.

In order to achieve such an object, the tracking control circuit according to the present invention adjusts the writing order of the four types of pilot signals during recording, such as T1, _T1 ,
The pilot signal to be mixed for the generation of _T2 is
By switching the generation timings of the two non-adjacent signals in the writing order of the pilot signals, it is not necessary to invert the polarity of the tracking control signal for each track, and it is possible to When the generated | ₃ ± ₁ | or | ₄ ± ₂ | component exceeds a predetermined level, it is assumed that a two-track timing shift has occurred, and the polarity of the tracking control signal is inverted.

Therefore, in the tracking control circuit configured as described above, even if the generation timing of the mixed pilot signal with respect to the extracted pilot signal is shifted by two tracks, the polarity of the output tracking control signal remains unchanged. Since it always coincides with the direction of track deviation, it has the excellent effect of significantly shortening the tracking settling time compared to the conventional method.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 3 is a block diagram showing one embodiment of a tracking control circuit according to the present invention. In the figure, reference numeral 1 indicates a magnetic tape as a recording medium.
This will be explained using an example applied to. 2 is a capstan shaft which is rotationally driven by a capstan motor 3 to run the magnetic tape 1 in the direction of the arrow; the rotation speed of the capstan motor 3 is controlled by a motor control circuit 4; controlled. Further, recorded signals are written onto the magnetic tape 1 by a pair of magnetic heads 5a and 5b. In this case, the pair of magnetic heads 5a and 5b are mounted at positions 180 degrees apart from each other on the circumference of a rotating cylinder (not shown). Since this rotating cylinder is rotated obliquely across the longitudinal direction of the magnetic tape 1 at high speed, the pair of magnetic heads 5a and 5b trace the magnetic tape 1 obliquely.
Here, a rotating cylinder (not shown) and a magnetic tape 1
The relationship between the running speed and the running speed is determined so that each of the pair of magnetic heads 5a, 5b completes one trace on the magnetic tape 1 in one revolution of the rotary cylinder. Therefore, the pair of magnetic heads 5
a and 5b are switched in accordance with the rotation of the rotary cylinder to alternately write recorded signals onto the magnetic tape 1. As a result, one rotation of the rotating cylinder produces 2
A recording track of a book is formed on the magnetic tape 1.
Here, 6 is a switch for switching the recording signal supplied to the magnetic heads 5a, 5b in accordance with the rotation of the above-mentioned rotary cylinder.

The above is an outline of a two-head VTR using a generally well-known helical scanning system, and since its details have already been made public, the details will be omitted here.

In the VTR constructed in this manner, 7 is a mode command circuit for instructing switching between recording mode R and reproduction mode P, and a changeover switch 8 is switched by the generated command signal. Further, the command signal generated from the mode command circuit 7 is also supplied to the pilot signal generation circuit 9 to inform it of which mode it is in. The pilot signal generating circuit 9 generates and outputs the aforementioned four types of pilot signals ₁ , ₂ , ₃ , and ₄ in a predetermined order for each track written on the magnetic tape 1. This predetermined order is set in advance to be different between recording mode R and playback mode P, and the generated pilot signals ₁ , ₂ , ₃ , ₄
is supplied to the first mixing circuit 10 and the second mixing circuit 11. The first mixing circuit 10 superimposes the pilot signals ₁ , ₂ , ₃ , and ₄ on the video signal RF supplied from the outside, and outputs the signal to the recording amplifier 1 as a recorded signal.
Supply to 2. Therefore, the recorded signal output from the recording amplifier 12 is
Supplied to the side terminal. The changeover switch 8 selects the recording mode R from the command signal supplied from the mode command circuit 7.
, either one of the magnetic heads 5a, 5b selected by the switch 6 is connected to the R side terminal. Further, when the command signal indicates reproduction mode P, either one of the magnetic heads 5a, 5b selected by the switch 6 is connected to the P side terminal. Therefore, in the recording mode R, the recording signal generated from the recording amplifier 12 is transferred via the changeover switch 8 to the switch 6 of one of the pair of magnetic heads 5a, 5b.
is supplied according to the switching operation. In the reproduction mode P, reproduction signals alternately reproduced by the pair of magnetic heads 5a and 5b are supplied to the reproduction amplifier 13 via the switch 6 and the changeover switch 8. The playback signal output from the playback amplifier 13 is then sent as a video signal to a well-known video signal processing system.
The signal is supplied as RF and also supplied to the low-pass filter 15 via the automatic gain control circuit 14.

Here, the relationship between the video signal RF and the pilot signals ₁ , ₂ , ₃ , _{and 4} that constitute the reproduced signal is as follows:
While RF is generally several MHz, the pilot signal is set at approximately several 100 KHz so as not to affect the video signal RF. Therefore, only pilot signals ₁ , ₂ , ₃ , and ₄ are extracted from the low-pass filter 15 as extracted pilot signals. Then, this extracted pilot signal is mixed with pilot signals ₁ , ₂ , ₃ , and ₄ supplied from the pilot signal generation circuit 9 in the second mixing circuit 11, so that
A beat component of a mixed two-frequency wave including two frequency differences _T1 and _T2 of constant frequencies shown in FIG. 1B described above and | _{3-1 |} or | _{4-2 |} is generated. This beat component is passed through a first bandpass filter 16 that passes only the frequency difference _T1 , and a second bandpass filter 17 that passes only the frequency difference _T2 .
The signal is supplied to a third bandpass filter 18 that passes only the component of ₃ - ₁ | and a fourth bandpass filter 19 that passes only the component of | ₄ - ₂ |. The frequency difference _T1 that has passed through the first bandpass filter 16 is detected by the first detection circuit 20, and the frequency difference _T2 that has passed the second bandpass filter 17 is detected by the second detection circuit 21. Therefore, these first and second detection circuits 20, 21
Each output signal of
The level will be determined according to the amplitudes of _T1 and _T2 . The output signals of the first and second detection circuits 20 and 21 generated in this way are supplied to a comparator 22 constituted by a differential amplifier, and are set to a certain standard according to the level difference between the two input signals. Outputs a tracking control signal that changes around the value.
That is, when the traces of the magnetic heads 5a and 5b are shifted in the width direction of the track, the amplitudes of the frequency differences _T1 and _T2 vary in magnitude depending on the direction of the shift, as described above. As a result, the comparator 22 generates a tracking control signal that increases or decreases from a constant reference value depending on the direction of the shift. In this case, since the amount of change in the tracking control signal changes according to the difference between the two input levels in the comparator 22, this amount of change ultimately depends on the frequency difference.
This represents the difference in amplitude between _T1 and _T2 , which indicates the amount of tracking deviation. Furthermore, when no tracking deviation occurs, the level difference between both input signals of the comparator 20 is zero, so the generated tracking control signal is output as a signal having a constant reference value. The polarity of the tracking control signal generated in this way is inverted in the inverting amplifier 23, and the tracking control signal of either the output of the comparator 22 or the output of the inverting amplifier 23 is selected in the analog switch 24. and is supplied to the motor control circuit 4.

Therefore, the motor control circuit 4 controls the rotational speed of the capstan motor 3 in accordance with the tracking control signal generated in this way to correct the tracking deviation.

On the other hand, 25 and 26 are band pass filters 18,
19, and the output signals thereof are outputted from output ends 27a and 27b via a switching circuit 27. In this case, the switching circuit 27 is connected to the third and fourth detection circuits 2
A switch 28 selects the output signals of Nos. 5 and 26 and takes them out from the output end 27a, and a switch 29 selects the outputs of the third and fourth detection circuits 25 and 26 that are not selected by the switch 28 and takes them out from the output end 27b.
It is composed of: The signal output from the output terminal 27a of this switching circuit 27 is 2
The signal is supplied to a track deviation detection circuit 30 to detect a two-track deviation. In other words, the 2-track deviation detection circuit 30 determines that a 2-track deviation has occurred when a signal is input for a predetermined period, generates the 2-track deviation detection signal K, and outputs the 2-track deviation detection signal K to the analog switch 24 and switch 28,
29 switching is performed.

Next, the pilot signal generation circuit 9 generates, for example, the fourth
As shown in the figure, it is composed of an oscillation circuit 91, a frequency dividing circuit 92, a switch circuit 93, a waveform converter 94, and a switch control circuit 95. The oscillation circuit 91 generates a horizontal synchronization signal HD included in the video signal.
A reference clock signal of a predetermined frequency is generated in synchronization with the clock signal. The oscillation circuit 91 that performs such an operation is a well-known circuit having a phase lock loop system configured by, for example, a voltage controlled oscillator 911, a phase difference detection circuit 912, a frequency dividing circuit 913, and a low-pass filter 914. It is configured. The reference clock pulse generated from the reference oscillator circuit 91 is frequency-divided by the frequency divider circuit 92 and outputted as the four types of pilot signals ₁ , ₂ , ₃ , and ₄ at the output terminals O1, _{O. 4} are individually output as rectangular waves and sent to the switch circuit 93.
are supplied in parallel to input ports _P1 to _P4 , respectively. The switch circuit 93 is the switch control circuit 9
One of the four types of pilot signals ₁ , ₂ , ₃ , and ₄ is selected and output by selection control signals _e1 to _e4 supplied from input ports _P11 to _P14 , respectively, from 5 to input ports P11 to P14. The selected type of pilot signal is supplied to the waveform converter 94, where it is first integrated and converted into a triangular wave, and then converted into a sine waveform by a well-known polygonal function generator or the like and output. .

On the other hand, the switch control circuit 95
4 types of pilot signals ₁ , ₂ , ₃ , ₄ for 3
Selection control signal e ₁ to select one type from among
Generate e ₄ . And this selection control signal e ₁ to e ₄
When this occurs, the selection order of the four types of pilot signals is as follows in recording mode R and playback mode P.
It is necessary to perform control so that the pilot signals are repeatedly generated in different predetermined orders, and also to control the timing of switching to be the same in both modes. This switch control circuit 95 includes an exclusive OR circuit 951
, flip-flop circuit 953 and binary -10
It is configured by a decimal decoder (hereinafter referred to as a decoder) 954. Exclusive OR circuit 951
The input signal is the command signal R/P generated from the mode command circuit 7 and the head switch signal SH whose polarity is inverted every trace period of one track, and the flip-flop circuit 953 is activated at the fall of the output signal. trigger. Further, the decoder 954 has input terminals A and B having a 2-bit configuration.
A head switch signal SH is inputted to an input terminal A which is responsible for the LSB of the circuit, and a set output of the flip-flop circuit 953 is inputted as a signal G to an input terminal B which is responsible for the MSB.

In the switch control circuit 95 configured as described above, in the recording mode R, the command signal R/P becomes R and becomes a logic "L". Therefore,
When the head switch signal SH is supplied in the state shown in FIG. As a result, flip-flop circuit 953
is triggered in synchronization with the falling edge of head switch signal SH, and its set output Q is supplied to input terminal B of decoder 954 as signal G as shown in FIG. 5b. As a result, the signals supplied to input terminals A and B of the decoder 954, respectively.
The relationship between SH and G and the output signals e ₁ to e ₄ is as shown in FIG. 6, in which the output signals e ₁ , e ₂ , e ₃ , and e ₄ are repeatedly output in sequence. When the output signals e ₁ to _{e 4} generated in this way are supplied to the input ports P ₁₁ to P ₁₄ of the switch circuit 93 as selection control signals e ₁ , e ₂ , e ₃ , e ₄ , the switch circuit 93 is the input P ₁
Pilot signal ₁ , respectively supplied to ~ _P4 ,
₂ , ₃ , _{and 4} are repeatedly selected and output in sequence.

Next, when the reproduction mode P is set, the command signal R/P becomes "H". As a result, the output signal of the exclusive OR circuit 951 becomes a state in which the polarity of the head switch signal SH shown in FIG.
It will be triggered at the rising edge of SH. And this flip-flop circuit 953
The set output signal is the output signal G shown in FIG. 7b.
The signal is supplied to the input terminal B of the decoder 954 as a signal.
Therefore, in this case, the relationship between the input/output signal of the decoder 954 and the selection output signal of the switch circuit 93 is as shown in FIG. 8, and the pilot signal is
₃ , ₂ , ₁ , ₄ are selected repeatedly and output. In other words, the timings of generation of two types of pilot signals ₁ and ₃ which are not adjacent to each other among the pilot signals generated during recording shown in FIG. 6 are switched.

Next, the overall operation of the tracking control circuit according to the present invention shown in FIG. 3 will be explained based on the operation of the pilot signal generating circuit 9. First, when a pair of magnetic heads 5a and 5b tracing a recording track in the reproduction mode P deviates in the width direction of the track, the track deviation is corrected as follows. Now, a pair of magnetic heads 5
If either one of a and 5b traces one track recorded in the order of pilot signals ₁ , ₂ , ₃ , and ₄ as shown in FIG. As a result, ₁ , ₄ and ₂ due to crosstalk from adjacent tracks are output and supplied to the second mixing circuit 11. In this case, the pilot signal generation circuit 9
Since the mode command signal R/P is “H”,
As previously shown in Figures 4 and 8, ₃ , ₂ ,
Pilot signals are generated repeatedly in the order of ₁ and ₄ .

As a result, when tracing a track in which the above-mentioned pilot signal ₁ is recorded, the pilot signal ₃ is generated from the pilot signal generating circuit 9 and is supplied to the second mixing circuit 11 to be mixed with the extracted pilot signal. Therefore, the output of the second mixing circuit 11 is | ₃ ± ₁ |, | ₃ ± ₄ |, |
₃
± ₂ | As explained earlier using FIGS. 1A and 1B, this output signal is a mixture 2 containing predetermined constant frequency frequency differences _T1 and _T2 and | ₃ − ₁ |
It is the beat component of the frequency, and the first and second
In the band pass filters 16 and 17, the above-mentioned
Only _T1 = | ₃ − ₄ | and _T2 = | ₃ − ₂ | are extracted.

At this time, if the pair of magnetic heads 5a and 5b are not shifted in the width direction of the track, _T1 , _{T2
The size} of The rotation of is maintained as it is. Further, the third bandpass filter 18 takes out | _3-1 | contained in the output of the second mixing circuit 11, rectifies and smoothes it in the third detection circuit 25, and then switches the switch 29 of the switching circuit 27 _. from its output terminal 7b via the automatic gain control circuit 1
4 as a gain control signal,
This prevents fluctuations in the output of the second mixing circuit 11.

In this case, the second mixing circuit 11
Since the output signal does not contain a component | ₄ − ₂ |, there is no output from the fourth band pass filter 19, and the output signal of the fourth detection circuit 26 which receives the output of this fourth band pass filter 19 as an input. 2-track deviation detection circuit 3 that receives the output via switch 28
0 is inactive, and the analog switch 24 and switches 28 and 29 of the switching circuit 27 continue in the illustrated state.

Next, if the magnetic head 5a or 5b shifts to the next adjacent track side, the above-mentioned crosstalk becomes ₄ < ₂ , so the above-mentioned frequency difference _T1 ,
_T2 becomes _T1 < _T2 . Therefore, the comparator 22 has a value that is either larger or smaller than the above-mentioned constant reference value, and the magnetic head 5a
Alternatively, if 5b shifts to the previous adjacent track (unmarked) side, the above-mentioned crosstalk becomes ₄ > ₂ , so the above-mentioned frequency difference _T1 and _T2 becomes _T1 > _T2 . Therefore, the comparator 22 generates a correction signal having a value deviated opposite to the above-mentioned deviation to correct the track deviation.

Next, if the magnetic head 5a or 5b traces the next trace, the low-pass filter 15 outputs ₂ as the extraction pilot signal and ₁ and ₃ as the crosstalk between adjacent tracks, which are supplied to the second mixing circuit 11. Ru. At this time, the pilot signal generating circuit 9 generates the pilot signal ₂ and supplies it to the second mixing circuit 11, as is clear from the relationship between FIGS. 6 and 8. Therefore, the output of the second mixing circuit 11 is | ₂ ± ₂ |, | ₂ ± ₁ |, |
₂
± ₃ | As a result, the first and second low-pass filters 16 and 17 have | ₂ − ₁ |= _T1 , | ₂
−
₃ |= _T2 are respectively taken out and supplied to the comparator 22 via the first and second detection circuits 20 and 21.
At this time, if there is no deviation of the magnetic head 5a or 5b, a signal containing the same reference value as in the above case is generated from the comparator 22, and this signal is supplied to the motor controller circuit 4 as a tracking control signal.

Furthermore, if the magnetic head 5a or 5b shifts to the next adjacent track side, the above-mentioned crosstalks ₁ and ₃ will be ₁ < ₃ , and therefore the above-mentioned frequency differences _T1 and _T2 will be _T1 < _T2 . Therefore, the output of the comparator 22 in this direction of deviation becomes a tracking control signal that coincides with the direction of deviation when tracing the track described above. Then, since the crosstote when shifting to the previous adjacent track side is ₁ > ₃ , the frequency difference is _T1
> _T2 , and in this case, the comparator 22 outputs a tracking control signal that matches the shift direction when tracing the track described above, and this signal is supplied to the motor control circuit 4 via the analog switch 24. Ru.

In this way, even if the magnetic head 5a or 5b sequentially moves the track to be traced to the next track H, D, H, H, etc., the deviation direction and frequency difference
The magnitude relationship between _T1 and _T2 remains unchanged.

Next, a case will be described in which the magnetic head 5a or 5b traces a track that is two tracks away from the predetermined relationship at the time of starting or canceling the pause operation. That is, when the pilot signal generation circuit 9 generates the pilot signal ₂ , if the magnetic head 5a or 5b traces the track ₂ shown in FIG. _3.1 will be generated by _the talk. Therefore, the second mixing circuit 1
The output of 1 is | ₁ − ₂ |, | ₃ − ₂ |, | ₁ − ₂
| will be included.

In this case, | ₁ - ₂ | = _T1 is taken out from the first band pass filter 16, | ₃ - ₂ | = _T2 is taken out from the second band pass filter 17, and the output signal is the first and second Detection circuit 20, 2
1 to the comparator 22, respectively,
If the magnetic head 5a or 5b shifts toward the tracking side, _T1 > _T2 , and tracking control in the opposite direction is applied as described above, resulting in the inconvenience that it takes a long time to settle the tracking.

Here, if a two-track deviation occurs as described above, the output of the second mixing circuit 11 as described above |
₄ − ₂ | is included, and the fourth bandpass filter 19 extracts this | ₄ − ₂ | and supplies it to the fourth detection circuit 26 . The fourth detection circuit 26 detects the output signal of the fourth filter 19 and supplies the output signal to the two-track deviation detection circuit 30 via the switch 28 of the switching circuit 27. In this case, when the magnetic head 5a or 5b sequentially moves from track to track to perform playback, | _4-2 | is generated from the second mixing circuit 11 for each track, and along with this, the _fourth detection signal is generated. The output signal of the circuit 26 is also output every other track.

On the other hand, the two-track deviation detection circuit 30 inputs the output signal every other track outputted from the fourth detection circuit 24 via the switch 28, thereby making a determination, and detects a predetermined number of tracks within a predetermined time. When the output is generated from the fourth detection circuit 26, it is determined that a two-track deviation has occurred, and a two-track deviation detection signal K ("H") is generated and held. In this way, when the two-track deviation detection signal K is generated, the analog switch 24 is switched to the opposite state as shown in the figure, and the comparator 2
A signal obtained by inverting the output signal of No. 2 in an inverting amplifier 23 is taken out as a tracking control signal and supplied to the motor control circuit 4. As a result, even if the direction of deviation between the output signal of the comparator 22 and the magnetic head H is reversed due to the deviation of the two tracks, the corrected tracking signal whose polarity has been inverted by the inverting amplifier 23 is selected by the analog switch 24. This problem is solved because the data is output in the same way. If a deviation between two tracks is detected in this way and the polarity of the tracking control signal is reversed, the tracking settling time becomes extremely short, and along with this, the unstable period of the reproduced image can be almost ignored. It will be of a certain extent.

Further, when the two-track deviation detection circuit 30 generates the two-track deviation detection signal K, the switches 28 and 29 of the switching circuit 27 are switched to the opposite state as shown. This means that when a two-track deviation occurs, the output of the second mixing circuit 11 no longer contains the | ₃ − ₁ | component, and instead is generated by the | ₄ − ₂ | component. ₃ − ₁ |
This is because it becomes necessary to perform this by detecting the components of.

The two-track deviation detection circuit 30 continues to generate the two-track deviation detection signal K once it detects a two-track deviation, and then cuts off the output when it detects a two-track deviation again. .

FIG. 11 is a circuit diagram showing a specific example of the two-track deviation detection circuit shown in FIG. 3, particularly when constructed using an analog system. In the figure, 31 is a low-pass filter that removes noise contained in the signal supplied every other track from the fourth detection circuit 26 and outputs the signal. The output signal of this low-pass filter 31 is sent to a comparator 32.
At this point, the signal is compared with a reference value set by the variable resistor 33, thereby being shaped and output as shown in FIG. 10a. The thus shaped output signal of the comparator 32 is integrated in the integrating circuit 34, and the integrated signal shown in FIG. 10b is output. In this case, the charging and discharging routes of the integrating circuit 34 are changed to give different time constants. In other words, during charging, current flows through the route of resistor R ₁ - diode D - capacitor C ₁ ,
During discharge, current flows through the capacitor C ₁ -resistance R ₂ route. Then, the values of resistors R ₁ and R ₂ are
By setting R ₁ < R ₂ , the charging time constant τ ₁ is relatively small as τ ₁ = R ₁・C ₁ , and the discharging time constant τ ₂ is a relatively large value as τ ₂ = R ₂・C ₁ . is set to . Note that transistor T ₁ and resistor R ₃
constitutes a circuit for forced discharge. The output signal of the integrating circuit 34 is compared in a comparator 35 with a reference value Vr ₁ set by a variable resistor 36. This comparator 35 is given a hysteresis characteristic by feeding back the output signal to the input side by the resistor 37, and when the input signal exceeds the reference value _Vr1 , the output changes to the 10th level.
It becomes "H" as shown in Figure c. Here, comparator 3
The output signal of 5 is transmitted to the transistor via the resistor 38.
Because it is fed to the base of T ₁ , comparator 3
At the same time as the output of 5 is generated, the transistor _T1 is turned on and the capacitor _C1 is forcibly discharged, so that the output of the integrating circuit 29 becomes _τ3 = _C1・_R3 as shown at time _t2 in FIG. It decreases rapidly due to the time constant of . Then, when the integral output decreases beyond the reference value (lower limit value Vr ₂ ), the output signal of the comparator 35 becomes the first
The signal is inverted to "L" as shown at time _t3 in Figure 0c.
Here, when the output signal of the comparator 35 becomes "H" at time _t1 in FIG. 10c, the T-type flip-flop circuit 39 is triggered and its output becomes "H" as shown in FIG. 10d. ”, and this “H”
The output is supplied as a two-track deviation detection signal K to the analog switch 24 and the switching circuit 27.
When the flip-flop circuit 39 is supplied with the "H" signal again from the comparator 35, it is inverted and holds its output signal K in the "L" state. Note that when a single signal is generated from the comparator 35 as shown in FIG. 10a between time points _t4 and _t5 , the output signal of the integrating circuit 34 is outputted from the comparator as shown in FIG. 10b. The reference value _Vr1 on the upper limit side of 35 cannot be exceeded, thereby preventing an erroneous two-track deviation detection signal K from being generated.

FIG. 11 shows a two-track deviation detection circuit 25 constructed using a digital system, and the same parts as in FIG. 9 are shown using the same symbols. In this case, the mono multivibrator 40 is triggered by the output signal of the comparator 32 for a period T ₀ determined by the values of the capacitor C ₂ and the resistor R ₄ . An output signal is generated. Since the output signal of this mono multivibrator circuit 40 is supplied to the counter 41 as a clear signal, this counter 41
counts the number of output signals from the comparator 32 during the period until the next clear signal is supplied. and,
When this count value exceeds a predetermined value, an output signal is generated to trigger the flip-flop circuit 39, thereby generating the two-track deviation detection signal K.

In the above explanation, | ₃ - ₁ | was used for automatic gain control and | ₄ - ₂ | was used to detect a two-track deviation, but it is also possible to reverse the input polarity of the comparator 22. , or by performing processing such as reversing the directionality in the control of the motor control circuit 4, | _3-1 | can be used for detecting a two-track deviation, and | _{4-2 |} can be used for automatic gain control _. It can be used as a.

As explained above, according to the tracking control circuit according to the present invention, a circuit for inverting the polarity of the tracking control signal is not required, and the generation timing of the mixed pilot relative to the extraction pilot can be changed to the start or pause release timing. Even if there is a deviation over two tracks, since the polarity of the tracking control signal generated by detecting this two-track deviation is inverted, the tracking settling time becomes extremely short.

[Brief explanation of drawings]

Figure 1A is a spectrum diagram showing an example of the frequency array of the 4-frequency pilot system, Figure 1B is a diagram showing the relationship between the four frequencies and the beat component of their difference, and Figure 2 is a diagram showing the recording track and magnetic field on the recording medium. FIG. 3 is a circuit diagram showing an embodiment of the tracking control circuit according to the present invention; FIG. 4 is a circuit diagram showing an example of the pilot signal generation circuit in FIG. 3. , Figure 5a,
b, Figures 7a and 7b are waveform diagrams showing the operation of the tracking control circuit shown in Figure 4, and Figures 6 and 8 are waveform diagrams showing the operation of the tracking control circuit shown in Figure 4. Diagram showing the order of occurrence, No. 9
11 are circuit diagrams showing specific examples of the two-track deviation detection circuit in FIG. 3, and FIGS.
d is an operational waveform diagram of each part of the two-track deviation detection circuit shown in FIG. 9; DESCRIPTION OF SYMBOLS 1... Magnetic tape (recording medium), 2... Capstan, 3... Motor, 4... Motor control circuit, 5a, 5b... Magnetic head, 6... Switch, 7... Mode command circuit, 8... ...Selector switch, 9...Pilot signal generation circuit, 10,1
DESCRIPTION OF SYMBOLS 1...First and second mixing circuit, 12...Recording amplifier, 13...Reproduction amplifier, 14...Automatic gain control circuit, 15...Low pass filter, 16-19...
...first to fourth bandpass filters, 20, 21,
25, 26...first to fourth detection circuits, 23...inverting amplifier circuit, 24...analog switch, 27...
...Switching circuit, 28, 29...Switch, 30...
2-track deviation detection circuit.

Claims (1)

[Claims] 1. Four types of pilot signals ₁ , ₂ , ₃ , having predetermined frequencies different from that of the recorded signal.
₄ is written on each track, and the writing order of the pilot signals ₁ , ₂ , ₃ , and ₄ is repeated in the order from ₁ to ₄ for each track. On the other hand, by sequentially tracing each of the tracks one by one, the recorded signal of that track can be
An extracted pilot signal including a pilot signal of any one of the self-tracks among pilot signals ₁ , ₂ , ₃ , and ₄ and a pilot signal of a crosstalk component due to this trace is reproduced, and the traces are located adjacent to each other. A frequency difference between a pilot signal of an adjacent track and a pilot signal of the own track obtained by shifting to one of the tracks is detected, and this frequency difference is obtained when the trace position shifts to the one of the tracks. It is predetermined to have two types of constant frequencies: one when the trace position shifts to the other track side, and one when the trace position shifts to the other track side. By detecting the type and amount of this constant frequency, the shift of the trace position is detected and tracked. In the tracking control circuit for correcting the deviation of the track, when the pilot signals of the self-tracks in the extracted pilot signals are sequentially reproduced in the order from ₁ to ₄ as the tracing for each track is performed, ₃ , ₂ , ₁ , ₄ or ₁ , ₄ ,
By sequentially mixing the signals generated in the order of ₃ and ₂ with the extracted pilot signal at timings corresponding to the self-track pilot signal,
The polarity of the deviation amount detection signal in the direction of deviation of the trace position for each track is made the same, and the mixed output of the extracted pilot signal and the generated pilot signal is set to | ₃ ± ₁ | or | ₄ ±
₂ a detection means for detecting that a component of | ₃ ± ₁ is included in the mixed output;
| Or, when it is detected that a component of | ₄ ± ₂ | is included, the polarity of the amount of tracking deviation detected at this time is inverted and output as a tracking control signal, and at this time, the detection means generates a mixed output. When a component of | ₃ ± ₁ | is detected in | ₄ ±
₂ so that the component of | can be detected, or | ₄ ±
By providing _a switching means for switching the supply of the mixed output to the detection means _, the combination of the _extracted pilot signal and the generated pilot signal can be set to A tracking control circuit characterized in that a tracking settling time is shortened by preventing polarity reversal of the deviation amount detection signal when the timing deviates by two tracks from a predetermined timing.