JPH0765450A - Tracking control device - Google Patents

Abstract

PURPOSE:To enable a stable tracking control even at the time of a special reproducing. CONSTITUTION:At the time of the special reproducing, a reference generation part 13 compensates the frequency of a reference signal of the time of a normal reproducing in accordance with the relative velocity of tape versus head. Blanced modulators 11, 12 obtain the component of a frequency difference between the reference signal and a reproduced pilot signal. At the time of the special reproducing, the component of the frequency difference from balanced modulators 11, 12 coincides with the center frequency of BPFs 6, 7 and then extracted surely because the reference signal frequency is compensated. Thus, the tracking control is stabilized even at the time of the special reproducing.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking controller suitable for a video tape recorder for digital recording / reproduction.

[0003]

2. Description of the Related Art Conventionally, VTR (video tape recorder)
Several methods have been proposed for the tracking control method of. For example, the control method has been put to practical use in the β, VHS method of the helical scan VTR. In this method, a dedicated track is provided in the longitudinal direction of the magnetic tape to record a control signal, the phase of the reproduction control signal is compared with the phase of a predetermined reference signal, and the rotation of the capstan motor is controlled based on the comparison result. There is.

In the control system, since a dedicated track is provided, the recording density is low, and because a fixed head is provided, the running of the magnetic tape is likely to fluctuate, and a tracking error signal is generated in the main signal recording track width direction. It is not suitable for high precision positioning control in high density recording. So, 8m
A four-frequency pilot system is used in MVTR and the like.

This system is disclosed in Japanese Patent Publication No. 59-31795, entitled "Method and apparatus for controlling position of writing / reading head".
The pilot signal as a tracking signal is recorded on the same track as the main signal.
Therefore, the recording density does not decrease, and a tracking error signal can be generated in the main signal recording track width direction, which is suitable for high density recording. In the 4-frequency pilot system, the pilot signal is reproduced from adjacent tracks having different azimuth angles.
Therefore, a low frequency band having a relatively small azimuth loss effect is selected as the frequency of the pilot signal, and the pilot signal frequency is set to a frequency lower than those of the FM modulation luminance signal and the low frequency conversion color signal which are the main signals. There is.

In the four-frequency pilot system, a pilot signal for tracking is frequency-multiplexed and recorded on a main signal, the pilot signal levels reproduced from both adjacent tracks are compared at the time of reproduction, and position control is performed so that the two become equal. Is. That is, at the time of recording, pilot signals having frequencies f1 to f4 are switched for each track and superimposed on the main signal. The frequency difference between the frequencies f1 to f4 is
For example, as shown in another modified example of the above-mentioned “writing / reading head position control method and apparatus”, about fH (fH
Is the horizontal frequency) or 3 fH.

FIG. 7 is a block diagram showing such a conventional tracking control device.

An envelope signal reproduced from the reproducing head is passed through a terminal 1 to a low pass filter (hereinafter referred to as LPF).
2) to remove signals outside the pilot signal band, and then to the balanced modulator 3. On the other hand, the clock CLK input through the terminal 4 is supplied to the reference generator 5
The reference generator 5 has frequencies f1 to f4.
The reference signal of 1 is generated and given to the balanced modulator 3.
The reference signal is generated at the same frequency as the pilot signal recorded on the scanning track in synchronization with the head switching according to each double speed number.

The balanced modulator 3 balance-modulates the reference signal and the pilot signals of the left and right adjacent tracks and the scanning track, respectively, to obtain the sum and difference frequency components of the pilot signals of the scanning track and each adjacent track. It outputs to the band pass filter (henceforth BPF) 6,7. A component of the output of the balanced modulator 3 having a frequency fH, which is a difference frequency component, is extracted by the BPF 6, band-limited, and given to the envelope detection circuit 8. In addition, the frequency of the difference frequency component of the output of the balanced modulator 3 is 3 fH.
Is extracted by the BPF 7, band-limited, and then given to the envelope detection circuit 9.

The envelope detection circuits 8 and 9 are BPFs, respectively.
The outputs of 6 and 7 are envelope-detected and output to the tracking control signal generator 10. Tracking control signal generator
Numeral 10 differentially amplifies the outputs of the envelope detection circuits 8 and 9 to detect the tracking deviation direction and the deviation amount from the scanning track to the left and right adjacent tracks, and outputs it as a tracking control signal (tracking error signal). Depending on the scanning track, for example, an envelope detection output indicating the tracking shift amount from the right track may be output from the envelope detection circuit 8 or may be output from the envelope detection circuit 9. Therefore, the tracking control signal generation unit 10 inverts the differential amplification output according to the scanning track, that is, according to the reference signal to match the tracking deviation direction and the signal sign, and the tracking control signal is generated. I am trying. Tracking is performed by controlling the rotation of a capstan motor (not shown) based on this tracking control signal.

By the way, generally, in an analog type VTR such as an 8 mm VTR (video tape recorder) and a VHS type VTR, by changing the running speed of the tape, the magnetic head can be divided into several fields recorded on the recording medium. Also, the signal track is traced over to perform special reproduction such as triple speed. In this case,
Since the relative speed of the tape-to-head is different from that during normal reproduction, the frequency of the reproduction signal is different from that during recording (normal reproduction). VT adopting analog FM recording system
In R, the relative speed during reproduction is matched with the relative speed during recording by correcting the rotational speed of the cylinder.
This operation is generally called fh correction. The fh correction is a correction of the horizontal synchronizing frequency of the recorded video, but the frequency allocation of the FM, the pilot signal and the like are also corrected by the fh correction.

On the other hand, a digital recording type VTR
In the above, since the frequency change at the time of special reproduction can be absorbed by the PLL circuit for generating the clock for digitizing the reproduction signal and the TBC circuit for reconstructing the product code space for error correction, the cylinder rotation is not always required. The relative speed is not adjusted by correcting the number. Further, even when the relative speed is adjusted, the PLL circuit and the T
A relatively large frequency (relative speed) shift may be allowed by stopping the portion that cannot be absorbed by a BC circuit or the like.

When the tracking system in the "writing / reading head position control method and apparatus" of Japanese Patent Publication No. 59-31795 is applied to such digital equipment, the digital signal which is the main signal is reproduced without any problem. However, the pilot signal will be reproduced with the frequency shifted. FIG. 8 is a spectrum diagram for explaining such a problem of the conventional example. Figure 8
8A shows the normal reproduction, and FIG. 8B shows the special reproduction.

Now, the reference signal frequency is R, and the reproduction pilot signal frequencies of the left and right adjacent tracks are P1 and P2.
, BPF6, 7 are assumed to have center frequencies f1 and f2. The center frequency f1 is set to the difference frequency between the reference signal frequency R and the reproduction pilot signal frequency P1, and the center frequency f2 is set to the difference frequency between the reference signal frequency R and the reproduction pilot signal frequency P2. That is, the following equation (1) and the following (2) are established. The characteristic A of the BPF 6 and the characteristic B of the BPF 7 are
As shown in FIG. 8A, steep characteristics are set in order to detect an accurate pilot component.

F1 = P1−R (1) f2 = P2−R (2) The balanced modulator 3 outputs a difference frequency component between the reference signal and the pilot signal. During normal reproduction, the pilot signal frequencies P1 and P2 are, as shown in FIG. 8A, the frequencies f1 and f2 relative to the reference signal frequency R, respectively.
However, the BPFs 6 and 7 extract the components of the difference frequencies f1 and f2, respectively, according to the characteristics A and B of FIG. 8A.

Here, it is assumed that special reproduction is performed and the relative speed of the tape-to-head is different from that during normal reproduction. For example, it is assumed that the relative speed between the tape and the head becomes m times the normal speed by performing the reproduction at the tape speed N times the normal speed. Then, the reproduced pilot signal frequencies become mP1 and mP2, respectively, which are m times higher, and the difference from the reference signal frequency becomes large as shown in FIG. 8B. If the difference between the reference signal frequency R and the reproduced pilot signal frequencies mP1 and mP2 is f3 and f4, respectively,
As shown in FIG. 8B, the difference frequencies f3 and f4 are equal to the BPF.
This shifts from the pass bands of 6 and 7, and the difference frequency component cannot be extracted by the BPFs 6 and 7. Therefore, it becomes impossible to accurately detect the tracking deviation amount.

[0017]

As described above, in the above-mentioned conventional tracking control device, when the relative speed of the tape-to-head is different from that during normal reproduction, the frequency of the reproduction pilot signal becomes the frequency during recording. On the contrary,
Since the difference frequency component with respect to the reference signal also changes, this difference frequency component cannot be extracted by the BPF, and an accurate tracking error signal cannot be obtained. Therefore, there is a problem that the tracking becomes unstable or the tracking may not be locked.

It is an object of the present invention to provide a tracking control device which enables stable tracking control even during special reproduction.

[Structure of the Invention]

[0020]

A tracking control device according to the present invention reproduces a head by reproducing a recording signal by tracing a recording medium on which a digital signal including a plurality of tracking pilot signals having different frequencies is recorded. First filter means for extracting a reproduction pilot signal from the signal, reference generating means for outputting a reference signal having the same frequency as the pilot signal included in the recording signal during normal reproduction, the reference signal and the reproduction pilot of an adjacent track Extraction means for obtaining the sum and difference frequency components with the signal, the pass band is set based on the difference between the frequency of the reference signal and the frequency of the pilot signal included in the recording signal, the difference from the output of the extraction means Second filter means for extracting frequency components, and this second filter means Tracking control signal generation means for generating a tracking control signal based on the output, and reference correction means for correcting the frequency of the reference signal during special reproduction according to the relative speed between the recording medium and the head and giving it to the extraction means. It is equipped with and.

[0021]

In the present invention, the reference correction means corrects the frequency of the reference signal based on the relative speed between the recording medium and the head during special reproduction. As a result, the frequency of the difference frequency component between the reference signal extracted by the extraction means and the reproduction pilot signal of the adjacent track becomes the same as that during normal reproduction even during special reproduction. Therefore, even during special reproduction, the second filter means reliably extracts the difference frequency component, and the tracking control signal generating means can obtain an accurate tracking control signal.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a tracking control device according to the present invention.

A reproduction signal from a head (not shown) is given to the LPF 2 via the input terminal 1. LPF2 is a balanced modulator that removes signals other than the pilot signal band from the reproduced signal.
Give to 11, 12. On the other hand, the clock CLK input via the terminal 4 is given to the reference generator 13. In the present embodiment, the reference generator 13 is also adapted to give a reproduction mode signal via the terminal 14.

The reference generator 13 includes a normal reproduction generator 15 for generating a reference signal for normal reproduction and special reproduction generators 16, 17 for generating a reference signal for special reproduction. Special playback generator 1
Reference numerals 6 and 17 generate a reference signal whose frequency is corrected based on the reproduction mode signal from the terminal 14. Switch the output of normal playback generator 15 and special playback generator 16
The switch 18 outputs one of the two inputs to the balanced modulator 12 based on the mode signal from the terminal 14. Also, the output of the normal reproduction generating section 15 and the output of the special reproduction generating section 17 are given to the switch 19, and the switch 19 outputs one of the two inputs to the balanced modulator 11 based on the mode signal from the terminal 14. It has become.

The balanced modulator 11 calculates the sum and difference frequency components by balanced modulation of the reference signal from the switch 19 and the reproduced pilot signal of the adjacent track, and outputs the sum and difference frequency components to the BPF 6. Further, the balanced modulator 12 obtains the sum and difference frequency components by the balanced modulation of the reference signal from the switch 18 and the reproduction pilot signal of the adjacent track to obtain the BPF.
Output to 7. The BPFs 6 and 7 extract only the difference frequency component between the reference signal and the reproduction pilot signal,
Output to the envelope detection circuits 8 and 9, respectively. The envelope detection circuits 8 and 9 detect the levels of the passing signals of the BPFs 6 and 7 and output them to the tracking control signal generator 10. The tracking control signal generator 10 differentially amplifies the output levels of the envelope detection circuits 8 and 9 to generate a tracking control signal (tracking error signal) indicating the direction and magnitude of tracking deviation, thereby generating a capstan motor (not shown). It is designed to control the rotation of.

FIG. 2 is a block diagram for explaining the reference generator 13 in FIG. Reference generator 13
Is to correct the reference frequency by changing the frequency division ratio without changing the frequency of the clock CLK.

The normal reproducing generator 15 sets the clock CLK to 1
Frequency division is performed at frequency division ratios of / a, 1 / b, 1 / c, and 1 / d, and reference signals of four types of frequencies are output. As described above, in the 4-frequency pilot method, 4-frequency pilot signals are cyclically recorded for each track. At the time of reproduction, a reference signal having the same frequency as the pilot signal of the reproduction track is generated from the reference generator 13,
The balanced modulators 11 and 12 obtain the crosstalk component of the reproduced pilot signal from the adjacent track. The normal reproduction generator 15 cyclically generates four frequencies to output a reference signal having the same frequency as the reproduction track.

The special reproduction generator 16 sets the clock CLK to 1
The reference signal frequency is corrected by dividing the frequency with a frequency division ratio of / xa, 1 / xb, 1 / xc, 1 / xd.
Further, the special reproduction generating section 17 sets the clock CLK to 1 / y
The reference signal frequency is corrected by dividing the frequency with a division ratio of a, 1 / yb, 1 / yc, and 1 / yd. The variables x and y are determined based on the deviation of the relative speed of the tape and the head.

For example, assume that the reference signal frequency R during normal reproduction of a predetermined track is 1 / a. In this case, the reference signal frequencies R1 and R2 corrected by the special reproduction generators 16 and 17 are 1 / xa and 1 respectively.
/ Ya. The center frequencies of BPFs 6 and 7 are f1 and
If f2 is assumed and the reproduction pilot frequencies of the adjacent tracks at the time of normal reproduction are P1 and P2, respectively, the following equations (3) and (4) are established.

F1 = P1−R (3) f2 = P2−R (4) Now, assuming that the relative speed between the tape and the head becomes m times that at the normal reproduction by the N speed reproduction, the reproduction pilot frequency Since mP1 and mP2 are also multiplied by m times, by setting the reference frequencies R1 and R2 during special reproduction to values that satisfy the following equations (5) and (6), respectively,
The frequency of the difference frequency component from the balanced modulators 11 and 12 is BPF.
It is possible to match the center frequencies f1 and f2 of 6 and 7.

R1 = mP1-f1 (5) R2 = mP2-f2 (6) Therefore, the variables x and y may be set to values satisfying the following equations (7) and (8).

1 / xa = mP1−f1 (7) 1 / ya = mP2−f2 (8) Regarding the other three frequencies corresponding to the frequency division ratios 1 / b, 1 / c, and 1 / d, respectively. Can similarly determine the variables x and y.

The switches 18 and 19 are adapted to selectively output the reference signals from the normal reproduction generator 15 and the special reproduction generators 16 and 17 based on the reproduction mode signal.

Next, the operation of the embodiment thus constructed will be described with reference to the spectrum diagram of FIG. Figure 3
3A shows the normal reproduction, and FIG. 3B shows the special reproduction.

The reproduction signal from the reproduction head (not shown) is L
The signal in the pilot signal band is applied to the PF2 and is applied to the balanced modulators 11 and 12. On the other hand, the reference generator
The clock CLK is applied to the terminal 13 via the terminal 4, and the normal reproduction generating section 15 of the reference generating section 13 generates a reference signal having the same frequency as the pilot signal of the reproduction track and synchronized with head switching. The frequency of the reference signal from the normal reproduction generating section 15 is R
Is. The reference signal frequency R and the reproduction pilot frequency satisfy the above expressions (3) and (4).

During normal reproduction, the switches 18 and 19 select the output of the normal reproduction generating section 15 according to the reproduction mode signal and give it to the balanced modulators 12 and 11. The balanced modulators 11 and 12 give difference frequency components between the reference signal and the reproduced pilot signal to the BPFs 6 and 7. Since the center frequencies of BPFs 6 and 7 are f1 and f2, respectively, as shown in FIG.
Difference frequency f between reference signal and reproduced pilot signal
The components 1 and f2 are extracted by the BPFs 6 and 7.

The envelope detection circuits 8 and 9 are BPF6 and
The level of the difference frequency component that has passed through 7 is detected and given to the tracking control signal generation unit 10, and the tracking control signal generation unit 10 differentially amplifies the detection output of the difference frequency component to obtain the tracking deviation amount and deviation direction. Is generated. Accurate tracking is obtained by controlling the rotation of a capstan motor (not shown) by this tracking control signal.

Here, it is assumed that a reproduction mode signal indicating N times speed reproduction is input to the reference generator 13 via the terminal 14. The relative speed between the tape and the head is assumed to be m times that during normal reproduction by N times speed reproduction. The special reproduction generators 16 and 17 correct the frequency of the reference signal during normal reproduction to generate reference signals having frequencies R2 and R1 (see FIG. 3B). The frequencies R1 and R2 are given by the above equations (5) and (6), respectively. The switches 19 and 18 select the outputs of the special reproduction generators 17 and 16 according to the reproduction mode signals, and give them to the balanced modulators 11 and 12, respectively.

On the other hand, the frequency of the reproduction pilot signal of the adjacent track extracted from the reproduction signal is also m times that of normal reproduction.
It becomes P1 and mP2. That is, the reproduction pilot signal having a frequency of mP1 and the reference signal having a frequency of R1 are input to the balanced modulator 11, and the balanced modulator 11 outputs the sum and difference frequency components of both signals to the BPF 6. The frequency of the difference frequency component from the balanced modulator 11 is f1 from the above equation (5), which coincides with the center frequency of the BPF 6. Also,
Similarly, the reproduction pilot signal having a frequency of mP2 and the reference signal having a frequency of R2 are input to the balanced modulator 12, and the balanced modulator 12 calculates the sum and difference frequency components of the two signals as BPF.
Give to 7. The frequency of this difference frequency component is the above equation (6).
To f2, which corresponds to the center frequency of the BPF 7.

Therefore, even during special reproduction, the BPF
6 and 7, it is possible to reliably extract the difference frequency component between the reference signal and the reproduction pilot signal of the adjacent track. The outputs of the BPFs 6 and 7 are applied to the envelope detection circuits 8 and 9, respectively, to perform envelope detection, and the tracking control signal generator 10 differentially amplifies the detection output to obtain a tracking error signal.

As described above, in the present embodiment, during the special reproduction, the reference signal frequency is corrected based on the relative speed of the tape-to-head and applied to the balanced modulator, and the difference between the reference signal and the reproduction pilot signal is given. An accurate tracking error signal is obtained by always matching the frequency with the center frequency of the BPF. As a result, stable tracking control is possible even during special reproduction.

FIG. 4 is a block diagram showing another embodiment of the present invention. 4, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The present embodiment is an example in which the reference frequency at the time of special reproduction is corrected by changing the clock frequency.

The difference of this embodiment from the embodiment of FIG. 1 is that a reference generating section 21 is used instead of the reference generating section 13. The reference generator 21 is a clock generation circuit that receives a reproduction mode signal and generates a clock.
22 and a frequency divider 23. The clock generation circuit 22 generates a clock C for normal reproduction and clocks C ', C "for special reproduction. A frequency divider 23 divides the input clocks C, C', C" by a division ratio 1 / a. , 1 / b, 1 / c, 1
The frequency is divided by / d and the reference signal for normal reproduction and the reference signal for special reproduction are output.

In the embodiment thus constructed,
During normal reproduction, the clock generation circuit 22 generates the clock C. The frequency divider 23 applies the clock C to 1 / a, 1 / b, 1 /
By dividing by c and 1 / d, four types of reference signals are cyclically switched and output. As a result, a reference signal having the same frequency as the reproduced pilot signal frequency can be obtained.

At the time of special reproduction, the clock generation circuit 22 switches and outputs the clocks C'and C "on the basis of a timing signal (not shown). The frequency divider 23 divides the clock C ', so that, for example, in FIG. The same reference signal as that of the special reproduction generator 16 is obtained, and the frequency divider 23 divides the clock C ″ to obtain the same reference signal as that of the special reproduction generator 17 of FIG. .

Other functions are similar to those of the embodiment shown in FIG. It is obvious that the same effect as that of the embodiment of FIG. 1 can be obtained also in this embodiment.

FIG. 5 is a block diagram showing a modification of this embodiment. 5, the same components as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 5 is different from FIG. 4 in that a reference generation section 24 having a clock selection circuit 25 is adopted instead of the clock generation circuit 22. The clock selection circuit 25 has terminals I1 and
Clocks CLK1, CLK2 through I2, ... In
..., CLKn is input. The clock selection circuit 25 selects a clock corresponding to the clock C during normal reproduction,
During special reproduction, clocks corresponding to the clocks C'and C "are selected.

According to this modification, the clock generation circuit 22
Selects the input clock based on the reproduction mode signal and outputs the clocks C, C ', C ". The other operations are the same as in FIG.

FIG. 6 is a block diagram showing another modification of this embodiment. 6, the same components as those of FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 6, a PLL is used in place of the clock generation circuit 22.
The difference from FIG. 4 is that a reference generator 28 having a circuit 27 is adopted.

The PLL circuit 27 uses the clock CLK input from the terminal 4 to generate the clock C during normal reproduction and the clocks C'and C "during special reproduction.

Other configurations and operations are the same as those in FIG.

[0054]

As described above, according to the present invention, it is possible to achieve stable tracking control even during special reproduction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a tracking control device according to the present invention.

FIG. 2 is a block diagram for explaining a reference generator 13 in FIG.

FIG. 3 is a spectrum diagram for explaining an example.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing a modification of the embodiment of FIG.

FIG. 6 is a block diagram showing another modification of the embodiment of FIG.

FIG. 7 is a block diagram showing a conventional tracking control device.

FIG. 8 is a spectrum diagram for explaining the problems of the conventional example.

[Explanation of symbols]

6, 7 ... BPF, 8, 9 ... Envelope detection circuit, 10 ...
Tracking control signal generator, 11, 12 ... Balanced modulator, 13
… Reference generator, 15… Normal playback generator, 16, 17
… Special playback generator

Claims (1)

[Claims] 1. A first filter means for extracting a reproduction pilot signal from a reproduction signal of a head which reproduces a recording signal by tracing a recording medium on which a digital signal including a plurality of tracking pilot signals having different frequencies is recorded. A reference generating means for outputting a reference signal having the same frequency as the pilot signal included in the recording signal during normal reproduction; and an extracting means for obtaining the sum and difference frequency components of the reference signal and the reproduced pilot signal of the adjacent track. Second filter means for setting a pass band based on a difference between a frequency of the reference signal and a frequency of a pilot signal included in the recording signal to extract a difference frequency component from an output of the extracting means, A tracking control signal is generated based on the output of the second filter means. Tracking control signal generating means, and reference correction means for correcting the frequency of the reference signal according to the relative speed between the recording medium and the head during special reproduction and giving it to the extracting means. Control device.