JPH038154B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video signal reproducing apparatus that performs tracking servo by referring to a plurality of pilot signals of different frequencies recorded cyclically for each track on a tape during reproduction. .

When performing variable speed playback (slow, fast, still, etc.) that differs from the recording speed on a video tape recorder, the playback is scanned across guard bands between tracks or tracks with different recording azimuths, so noise bands appear on the playback screen. appear. In order to eliminate such noise bands, in the past, the video head was attached to a position control element such as a bimorph plate, and the position control means corrected the angular difference between the head scanning locus and the track during variable speed playback, thereby creating a guard band. Or, regeneration was performed so as not to cross different azimuth tracks. However, such tracking systems have the problem of being extremely complex and expensive.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems, and provides a reproduction screen in which no noise bands or a small number of noise bands occur using an extremely simple system.

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, a conventionally known pilot signal recording type track following system is used to control the position of the noise band on the screen (control the reproduction phase).

Figures 1 to 4 show the principle of the track following system using this pilot recording method. Figure 1 is a tape pattern diagram showing the recording format of the pilot signal, and Figure 2 is a block circuit of the tracking error detection system. 3 and 4 are waveform diagrams showing the operation of the circuit of FIG. 2.

Each track 2 on tape 1 as shown in FIG.
, a fourth type of pilot signals of different frequencies ₁ to ₄ are repeatedly recorded in order. During playback, these four-frequency pilot signals are detected to detect tracking errors, and based on this error signal, the phase servo part of the capstan servo circuit is controlled to correct the deviation between the playback track and the head scanning locus. has been corrected.

Frequencies ₁ to ₄ of the pilot signal are chosen to be the lower band of the color component converted to low frequencies (600 to 700 KHz), for example, ₁ = 102 KHz, ₂ = 116 KHz _{, 3} = 160 KHz, ₄ = 146 KHz. Therefore, | ₁ − ₂ | = | ₃ − ₄ | = Δ _A = 14KHz | ₂ − ₃ | = | ₁ − ₄ | = Δ _B = 44KHz. _ΔA is the frequency difference between the reproduction pilot signal and the reference signal when the scanning locus of the reproduction head deviates to the right with respect to odd field tracks ( ₁ , ₃ ), and _ΔB is the frequency when it deviates to the left. It's the difference. Note that for even field tracks, the relationships between _ΔA , _ΔB , rightward deviation, and leftward deviation are reversed.

Part a of the playback output from the video head of a two-head helical scanning VTR is sent to the low-pass filter 3 shown in FIG.
Figure C) is extruded. In the case of Fig. 4C, there is a shift to the right, for example, when a track with a pilot frequency of ₁ (A in Fig. 3) is played back, a part of the adjacent track B with a pilot frequency of ₂ is played back. . Note that since the pilot signal has a low frequency, the azimuth effect of the head does not affect the reproduction output.

The reproduced pilot signal b is sent to a multiplier 4, where it is multiplied by the reference pilot signal c (FIG. 4B) to detect the frequency difference _A or _B (FIG. 4D). A reference pilot signal c ( ₁ to ₄ ) is generated in a pilot signal generation circuit 5, and a switch circuit 6 operated by a head switching pulse (RF-SW) shown in FIG.
. . . ₁ , ₂ , ₃ . When recording,
The output c of the switch circuit 6 is sent to the recording circuit as a recording pilot signal.

The frequency difference signal d ( _A or _B ) obtained from the multiplier 4 is applied to bandpass filters 7 and 8 (center frequencies of _A = 14 KHz and _B = 44 KHz, respectively), and each frequency difference signal is separated. Further, the respective levels are detected by rectifiers 9 and 10. Output e of these rectifiers 9, 10 (Fig. 4 E, F)
are opposite information indicating a rightward shift and a leftward shift, respectively, so they are subtracted from each other in the subtractor 11 to obtain an error signal g (FIG. 4G) in which, for example, a rightward shift has a positive polarity and a leftward shift has a negative polarity. It will be fixed. In the case of FIG. 4G, the error signal is shifted to the right, and a positive error signal is obtained in odd field reproduction with pilot frequencies of ₁ and ₃ .

In an even field, the polarity of the error signal is opposite for right shift and left shift, so the subtracter 11
The output g undergoes phase inversion for each field in an inverter 12 and a switching switch 13, and is applied as a tracking error signal h (Fig. 4 h) to the phase servo section of the capstan servo circuit via an amplifier 14. . As a result, the phase shift between the reproduction track and the head scanning locus is corrected. When this tracking servo is performed correctly, the outputs e of the rectifiers 9 and 10 become zero, and the error signal h disappears.

In addition to the error detection system shown in FIG. 2, the levels of each of the reproduced pilot signals ₁ to ₄ are separated and extracted using a bandpass filter, and the magnitudes of the reproduced pilot signals of the reproduced track and its adjacent tracks are compared. A tracking error signal may also be obtained.

Next, FIG. 5 is a block diagram of a reproduction phase detection circuit during variable speed reproduction according to the present invention using the above-mentioned pilot signal recording type track following system.
Further, FIG. 6 is a diagram showing the relationship between the track and the head scanning locus during triple speed reproduction, and FIG. 7 is a waveform diagram showing the operation of FIG. 5.

During triple speed playback, the head scanning locus 17 spans three tracks 2, as shown in FIG. Therefore, three types of pilot signals are reproduced in one scan. Therefore, the reference pilot signal c is used to obtain the frequency difference from the reproduced pilot signal.
Also, three types of signals are generated in one field section as shown in FIG. 7D. That is, in FIG. 5, the head switching pulse RF-SW (FIG. 7A) is supplied to the multiplier circuit 18, and the pulse i whose frequency is multiplied by n (3 times) is
(FIG. 7B) is formed. This pulse i is given to the switch circuit 6 via the b contact of the changeover switch 19, and outputs the output ( ₁ ) of the pilot signal generation circuit 5.
_.about.4 ) are sequentially switched three times per field by the switch circuit 6 to form the reference pilot signal c shown in FIG. 7D. The reference pilot signal c is sent to a multiplier 4, and the frequency difference between it and the reproduced pilot signal b is calculated.

During recording and standard playback, selector switch 1
9 is switched to the contact a side, and the switch circuit 6 is switched for each field by the head switching pulse.

Figures 7E to 7G are waveform diagrams of various parts in Figure 5 when the reproduction track phase is fixed in the correct state as shown in Figure 6 and the noise band on the reproduction screen is within the vertical blanking section. . The reproduced pilot signal b of each frequency ₁ , _{2 ,} . . . obtained from the low-pass filter ₃ of FIG.
T ₃ ) indicates the maximum level each time it passes. Also, when the head passes through the center of each track, the crosstalk of pilot signals from adjacent tracks becomes zero.

The reproduced pilot signal b is multiplied by the reference pilot signal c in a multiplier 4, as in FIG. 2, to form a frequency difference signal d representative of the frequency differences _A and _B. Furthermore, the magnitude of each frequency difference component is detected by bandpass filters 7, 8 and rectifiers 9, 10, and each detection output e is subtracted by a subtracter 11, and an error signal g shown in FIG. 7F is detected. be done.
The polarity of this error signal g is further inverted by an inverter 12 and a changeover switch 13 each time the reference pilot signal is switched, and a tracking error signal h shown in FIG. 7G is formed. In addition, the changeover switch 13
is controlled by the output pulse i of the multiplier 18.

The tracking error signal h becomes a sawtooth wave as shown in Fig. 7G, and the head is at the center of each track.
It is zero every time it passes through T ₁ , T ₂ , and T ₃ , and before and after that, it changes from leftward deviation (negative) to rightward deviation (positive). This tracking error signal h is sent to a sample hold circuit 20 and sampled with a sample pulse j given from a sample pulse generation circuit 21 as shown in FIG. 7C. The position of this sample pulse j is uniquely determined by the reproduction speed ratio, and when the phase relationship (reproduction phase) between the track and the head scanning trajectory is determined so that no noise band appears on the reproduction screen, the position of the sample pulse j is uniquely determined by the reproduction speed ratio. The center of each track can be set at the scanning timing position. For example, in the case of triple speed playback, assuming that the ideal playback phase is shown in FIG. 6, the sampling position is the timing at which the head passes through the centers T ₁ , T ₂ , and T ₃ of each track. This sampling position is
Since it has a certain relationship with the head scanning locus (dotted chain line in FIG. 6) and occurs three times in one scan, it can be formed in synchronization with the multiplied pulse i of the output of the multiplier circuit 18. .

Sample pulse j shown in FIG. 7C is centered between the high and low level portions of tripled pulse i (FIG. 7B). This sample pulse j
When the tracking error signal h is sampled in the state shown in FIG. 6, the output of the sampling circuit 20 is zero if the reproduction phase is fixed to the state shown in FIG.

FIGS. 7H to 7J are waveform diagrams corresponding to FIGS. 7E to G when the reproduction phase is shifted and a noise band appears on the reproduction screen. Each frequency ₁ to ₄
The reproduced pilot signal b is as shown in Fig. 7H,
The respective peak positions deviate from the optimum state shown in FIG. 7E. Based on this reproduced pilot signal and the reference pilot signal c, a frequency difference signal is detected,
By subtracting the components corresponding to the frequency differences _A and _B , the error output shown in FIG. 7I is obtained from the subtracter 11. A tracking error signal h shown in FIG. 7J is obtained. If this tracking error signal h is sampled by the sample hold circuit 20 at the sampling position shown by the arrow J in FIG. 7, a positive sample output is obtained. This sample output indicates that the reproduction phase is shifted to the right.

The output of the sample and hold circuit 20 is sent to the amplifier 14.
The reproduction phase is thereby controlled so that the relative position between the track and the head is in the optimal state as shown in FIG. 6.

Therefore, according to this reproduction phase servo, it is possible to control the noise band on the screen so that it falls within the vertical blanking section outside the screen and is fixed. That is, since the reproduction phase is fixed so that the head passes through the center of each track at the position of sample pulse j in FIG. All you have to do is set the position appropriately. Alternatively, the position of the sample pulse j may be adjusted manually while looking at the screen.

Note that as the sample pulse j in FIG. 7C, only the pulse at the center position of one field scanning section as indicated by the arrow may be used. Also, in Figure 5,
An integrating circuit may be used instead of the sample and hold circuit 20.

FIG. 8 is a block circuit diagram of a reproduction phase detection system similar to that of FIG. 5 in which the speed ratio can be changed. In this embodiment, sampling is performed once per scan of one track or several tracks, and control is performed such that the head passes through the center of the track at this sampling point. Detection of tracking error or playback phase is the same as in the embodiment of FIG. 5, but calculation circuit 22 is used to create reference pilot signals and sample pulses for various playback speeds. This calculation circuit 22 is given a signal k specifying the reproduction speed ratio n, and is applied to each of the switch circuit 6, changeover switch 13, and sample hold circuit 20 based on this signal k and the head switching pulse (RF-SW). Control signals m, p, q are formed.
The switch circuit 6, changeover switch 13, and sample hold circuit 20 perform predetermined operations at a designated playback speed in response to these control signals.

FIG. 9 is a diagram of the track and head scanning trajectory showing the optimum tracking state during 1/2 times reproduction, and FIG. 10 is a waveform chart showing the operation of FIG. 8 at this time.

When the designation signal k for 1/2 speed reproduction is given to the calculation circuit 22, the head switching pulse RF shown in FIG.
A control signal m is sent to the switch circuit 6 so that the reference pilot signal c ( ₁ , ₂ , . . . ) is generated as shown in FIG. 10B at a period twice that of -SW. When the reproduction phase is in the state shown in FIG. 9, the reproduction pilot signal b becomes as shown in FIG. 10C. for example,
In a section where a track on which a pilot signal of frequency ₁ is recorded is scanned twice in succession, the frequency of the reproduced pilot signal is mainly ₁ , and frequencies ₄ and ₂ from adjacent tracks are partially mixed in.

A tracking error is detected based on the reproduced pilot signal b and the reference pilot signal c. 10D shows the output g of the subtracter 11 in FIG. 8, and FIG. 10E shows the output h of the changeover switch 13.
(tracking error signal). In 1/2 speed playback, the head passes through the center of the track once every two fields (two scans), and at this time the tracking error becomes zero. Assuming that the trace form shown in FIG. 9 is in the optimum state, phase servo of the capstan should be applied so that the tracking error becomes zero at the beginning of the track (the rising edge of the head switching pulse). Therefore, based on the control signal q of the calculation circuit 22, the sample pulse generation circuit 21 generates
A sample pulse j is formed, and a tracking error signal h is sampled in the sample hold circuit 20 based on this sample pulse j.
The sampling output is given to the capstan servo system via the amplifier 14.

In the state shown in FIG. 10, the sampling output is zero, and the reproduction phase is fixed at the state shown in FIG. 9. If this reproduction phase deviates, the error signal h in FIG. The phase is returned to the state shown in FIG.

Next, Figure 11 shows -3x speed (fast reverse)
FIG. 12 is a diagram of the track and head scanning locus showing the optimum tracking state in the case of reproduction, and FIG. 12 is a waveform diagram of each part of FIG. 8 at this time.

- In the case of triple speed playback, the playback scan is performed across five tracks as shown in FIG. Note that in still playback, playback is performed across two tracks, so at -n times the speed, there are n+2 tracks. Therefore, the timing at which the head passes through the center of the track occurs five times during one scan, and the tracking error is sampled at one of these timing positions. sample pulse j
is selected at the center of one field scanning section (the pulse width of the head switching pulse RF-SW in FIG. 12A) as shown in FIG. 12C. Therefore, the tracking error is sampled at the center of the track (marked with a circle) in the middle of one scan as shown by the dotted line in FIG. The reference pilot signal is the first
As shown in Figure 2B, the values are changed in the opposite direction to the recording field, ₄ , ₃ , ₂ , etc., for each field. This sequence of changes and the position of sample pulse j are determined under the control of calculation circuit 22 in FIG.

FIG. 13 is a waveform diagram showing another example of the reproduction phase detection method in the case of −3 times speed reproduction in FIG. 11. 1st
As shown in FIG. 3B, a sample pulse j may be generated each time the center of each track in FIG. 11 is crossed. The reference pilot signal requires an irregular changing sequence as shown in FIG. This is because, if a certain reproduction scan in FIG. 11 ends at the end _T1 of _one track, the next reproduction scan returns to the beginning of the previous _two tracks.

Although the present invention has been described above based on embodiments, the present invention can be applied to other tracking servo systems. For example, the present invention may be applied to a system that detects a tracking error based on the level difference of the reproduced pilot signal between a scanning track and an adjacent track.

When reproducing a tape in which a plurality of pilot signals of different frequencies are recorded cyclically on each track, the present invention detects the difference between the pilot signals on adjacent tracks and uses the detected signal as the detected signal. In a video signal reproducing device in which a tracking servo means is operated according to the tape speed, when playing back at a tape speed different from that during recording, the position is controlled in relation to the rotation of the head and according to the double speed ratio of the playback speed. The detection signal is sampled based on the sample pulse, and the sample output is supplied to the tracking servo means to fix the phase of the track and the head scanning locus. This is a characteristic feature.

Therefore, in the case of variable speed playback that involves playing across multiple tracks, the playback phase can be fixed at the optimum state by detecting the relative phase between the track and the head scanning locus through appropriate sampling and applying the tracking servo. be able to. This makes it possible to eliminate or reduce the number of noise bands on the playback screen that occur when crossing different azimuth tracks.

[Brief explanation of drawings]

Figures 1 to 4 show the principle of a track following system using a conventionally known pilot signal recording method. The block circuit diagrams of the king error detection system, FIGS. 3 and 4, are waveform diagrams showing the operation of the circuit of FIG. 2. 5 to 13 are drawings for explaining embodiments of the present invention, and FIG. 5 is a block circuit diagram of a reproduction phase detection circuit during variable speed reproduction according to the present invention;
Fig. 6 is a diagram showing the relationship between the track and the head scanning locus during triple speed playback, Fig. 7 is a waveform diagram showing the operation of Fig. 5, and Fig. 8 is adapted to correspond to various variable speed playbacks. Block circuit diagram of reproduction phase detection circuit,
Fig. 9 is a diagram showing the relationship between the track and the head scanning locus during 1/2 speed playback, Fig. 10 is a waveform chart showing the operation of Fig. 8 in the case of Fig. 9, and Fig. 11 is a -3
A diagram similar to Figure 9 during double speed playback, Figure 12 is -
Waveform diagram showing the operation in Figure 8 during 3x speed playback, Part 1
FIG. 3 is a waveform diagram showing another example of the operation shown in FIG. 8 during -3x speed playback. Note that the symbols used in the drawings are 1...tape, 2...track, 4...multiplier, 5...pilot signal generation circuit, 7, 8...bandpass filter,
9, 10... Rectifier, 11... Subtractor, 12... Inverter, 13... Changeover switch, 18... Multiplier circuit, 20
. . . sample hold circuit; 21 . . . sample pulse generation circuit.

Claims (1)

[Claims] 1. When reproducing a tape in which a plurality of pilot signals of different frequencies are cyclically recorded on each track, a difference between the pilot signals on adjacent tracks is detected, In a video signal reproducing device that operates a tracking servo means in accordance with the detection signal, when reproducing at a tape speed different from that during recording,
The tracking servo means generates a sample pulse related to the rotation of the head and whose position is controlled according to the double speed ratio of the playback speed, samples the detection signal based on the sample pulse, and uses the sample output as the tracking servo means. 1. A video signal reproducing device characterized in that the phase of a track and a head scanning locus is fixed by supplying a signal to the head.