JPS6214154B2 - - Google Patents

Description

[Detailed description of the invention] General rotating two-head helical scan type
With a VTR, you can perform still playback by stopping the tape during playback.

However, in this case, noise bands may occur on the playback screen depending on the tape stop position.

That is, FIG. 1 shows an example of a track pattern, where 1 is a magnetic tape, A and B are video tracks, [1] to [525] are line numbers, and during recording, tape 1 is transported in the direction shown by arrow 2. Along with being
Tracks A and B are formed obliquely with respect to tape 1 as shown by arrow 3 and in the same direction as transport direction 2. Furthermore, the tracks A and B are formed alternately and in contact with each other, and the so-called azimuth angles of the tracks A and B are different from each other. It has been made possible to ignore it. The luminance signal is in the FM signal state for one field period each on tracks A and B, and the vertical synchronization pulse is on tracks A and B.
The horizontal sync pulse
Ph is recorded for each adjacent track A and B with a shift of 0.75 h (1 h is the length of tracks A and B corresponding to one horizontal period) in the length direction of tracks A and B.

Note that the distance between dashed lines 4 and 5 is 180 mm for the rotating head.
The centers of the starting and ending ends of tracks A and B are located on the dashed lines 4 and 5, corresponding to an angular interval of The starting and ending ends of the track length corresponding to one field period are located on the dashed lines 4 and 5).

Furthermore, on one edge of tape 1, a control pulse with a frame frequency obtained by dividing the vertical synchronizing pulse is recorded as track C, and on the other edge, an audio signal is recorded as track S. ing.

During still playback, the scanning position of the rotary head is shifted by one track A, B between the start and end points of the scan, so the scanning locus of the head becomes, for example, as shown by a thin line 6. That is, the trajectory 6 is shown as a representative example of a case where the tape 1 stops at an arbitrary position, and the centers of the starting and ending ends of the trajectory 6 coincide with the chain lines 4 and 5. If the starting end of the trajectory 6 straddles the track A ₃ by △w (w is the track width), then this trajectory 6 coincides with the track B ₂ in the middle of the track B 2, and furthermore, the end of the trajectory straddles the track A ₃ by △w (w is the track width). It will span A ₂ by (1-△)w.

Of the overlapping portions of this locus 6 and tracks A ₃ , B ₂ , and A ₂ , the shaded portion is reproduced by a rotating head with an azimuth angle equal to that of track A, and the shaded portion is reproduced by a rotating head with an azimuth angle equal to that of track A. Since it is reproduced by a rotating head with an azimuth angle equal to B,
As shown in FIG. 2B, the level of the reproduced signal reaches its maximum or minimum in the middle of each field period, that is, from the vertical blanking period to the period ΔV (1V is one field period).

However, at this minimum point of the playback level, the noise level increases and the S/N decreases, so
In the case of the reproduced signal shown in FIG. 2B, a noise band occurs in the corresponding portion of the reproduced screen.

On the other hand, as _shown by _the thin line 7 in FIG. This portion becomes the reproduction signal for each head. Therefore, the change in the playback level in this case is as shown in FIG. do not have.

Therefore, when performing still playback, the stop position of the tape 1 is controlled so that the scanning locus of the rotary head becomes the locus 7.

Conventionally, therefore, the phase of the pulse Pg indicating the rotational phase of the rotary head is compared with a signal obtained by detecting the level of the reproduced signal, and the stop position of the tape 1 is controlled based on the comparison output. That is, since the pulse Pg indicating the rotational phase of the rotating head is obtained every frame period as shown in FIG. 2A, and has a constant interval τ with respect to the vertical blanking period, This pulse Pg
The tape 1 is stopped so that the interval τ is between the minimum level point of the reproduced signal and the minimum level point of the reproduced signal, and a trajectory 7 is obtained.

However, this method has the following drawbacks. That is, in the case of scanning trajectory 7, no noise band is generated in the reproduced screen, but noise is generated in the vertical synchronization pulse portion. Even a vertical synchronization pulse requires a certain degree of S/N. Therefore, in practice, the track width of the head is made somewhat wider than the width w of tracks A and B to ensure the S/N ratio of the vertical synchronizing pulse.

However, if the track width of the head is wider than the widths of tracks A and B, the minimum level point of the reproduced signal becomes broad, making it difficult to determine the stop position accurately. Further, if the playback level fluctuates due to dropout or distortion of tracks A and B, this will cause an error in the stop position.

In view of these points, the present invention attempts to ensure that the scanning locus of the head correctly becomes the locus 7 during still playback.

Now, if we consider the horizontal synchronizing pulse Ph included in the reproduced signals of trajectories 6 and 7, it becomes as shown in Fig. 3 (Fig. 3 A is the same as Fig. 1. However, in this figure, a simple Therefore, the azimuth angles of tracks A and B are ignored). That is, Figure 3B
is the track of the reproduced signal from trajectory 6.
The pulse Ph reproduced from A ₃ and A ₂ is shown, and _FIG.
This shows the pulse Ph regenerated from 6, but this trajectory 6
In the case of , the pulse Ph in Figure 3B and the pulse Ph in Figure 3C
pulses Ph are obtained alternately every one field period.

In this case, when switching from the pulse Ph in FIG. 3B to the pulse Ph in FIG. 3C, and when switching from the pulse Ph in FIG. 3C to the pulse Ph in FIG. 3B, the interval between the pulses Ph is correctly one horizontal period (1H indicates one horizontal period), but the recording positions of tracks A ₃ and A ₂ are shifted by 1.5 h in the length direction _.
When changing from pulse Ph of track _A2 to pulse Ph of track A2, the interval between pulses Ph is 1.5 horizontal periods. That is, after a period ΔV corresponding to the deviation Δw of the trajectory 6 from the vertical blanking period of every other frame, a 0.5H jump (disturbance) occurs in the pulse Ph.

On the other hand, FIG. 3D shows the pulse Ph reproduced from track A ₄ of the reproduction signal according to the trajectory 7, and FIG. 3E shows the pulse Ph reproduced from the reproduction signal according to the trajectory 7.
The pulse Ph reproduced from track B ₃ is shown, and in the case of trajectory 7, the pulse Ph of FIG.
The pulses Ph in FIG. 3E are obtained alternately every one field period.

And in this case, within each field period,
The interval between pulses Ph is exactly one horizontal period, and the pulse Ph in Figure 3E to the pulse in Figure 3D
Even when switching to Ph, the interval between pulses Ph is one horizontal period. However, in tracks A ₄ and B ₃ ,
Since the recording position is shifted by 0.75h in the length direction, the pulse Ph in Fig. 3D is changed from the pulse Ph in Fig. 3E.
When changing to Ph, the interval between pulses Ph is 2.5 horizontal periods. That is, a 0.5H jump occurs in the pulse Ph during the vertical blanking period of every other frame.

Although not shown in the figure, if the starting end of the head scanning trajectory coincides with track B and the ending point coincides with track A (if trajectory 7 deviates by w in the length direction of tape 1), , for the same reason, when switching from track B to track A, the pulse Ph
The interval is 1.5 horizontal periods, which also causes a jump of 0.5H.

To summarize the above, if the starting end of the scanning trajectory of the head deviates from the starting ends of tracks A and B by △w, then after a period △V corresponding to the deviation △w from the vertical blanking period of every other frame, a pulse A jump of 0.5H occurs in Ph, and the start end of the scanning trajectory coincides with the start ends of tracks A and B, △w = 0.
Then, the point of jumping of the pulse Ph is
ΔV=0, which means that every other frame is within the vertical blanking period.

This invention focuses on these points and has developed a pulse
Control the stop position of tape 1 so that the point at which 0.5H jumping occurs in Ph (or other periodic signal) is located in the vertical blanking period to prevent noise bands from occurring within the playback screen. It is something.

Let's explain one example below.

In FIG. 4, reference numerals 11A and 11B designate rotating magnetic heads, which have an angular spacing of 180 DEG from each other and are rotated by a motor 22 through a rotating shaft 21 at a frame frequency. The tape 1 described above is passed diagonally around the rotating peripheral surfaces of the heads 11A and 11B over an angular range of just over 180 degrees, and is run at a predetermined speed by a capstan 23 and a pinch roller 24. has been done. In addition, heads 11A, 11B
The track width is set to be about 30% wider than the width w of tracks A and B, for example.

Further, 30 indicates a head servo circuit. That is, for example, a pulse generating means 31 is provided on the rotating shaft 21, and pulse generating means 31 is provided on the rotating shaft 21 to generate pulses of 1 pulse per rotation of the heads 11A and 11B.
One pulse (pulse at the frame frequency) Pg is extracted, and this pulse Pg is supplied to the phase comparator circuit 33 through the shaping amplifier 32, and an oscillation circuit 34 is provided, from which an oscillation signal at the frame frequency is supplied to the comparator circuit 33. The comparison output is supplied to the motor 22 through the amplifier 35. Therefore, the heads 11A and 11B rotate in synchronization with the signal from the oscillation circuit 34 as a reference.

Further, 40 indicates a capstan servo circuit during normal reproduction. That is, a frequency generator 41 is provided rotatably coupled to the capstan 23 or the capstan motor 25, and its output signal is supplied to a frequency discrimination circuit 43 through a shaping amplifier 42 to determine the level corresponding to the rotational speed of the capstan 23. This voltage is the DC voltage of the voltage comparator circuit 4.
4, the voltage is compared with a reference voltage from a voltage source 45, and the comparison output is supplied to an adder circuit. Further, a control pulse is reproduced from track C of the tape 1 by the magnetic head 26, and this pulse is supplied to a phase comparison circuit 47 through a reproduction amplifier 46, where it is phase-compared with the reference signal from the oscillation circuit 34, and its comparison output is is supplied to the adder circuit 38. . The output of the adder circuit 48 is then supplied to the motor 25 through a switch circuit 71 and an amplifier 49, which will be described later.

Therefore, speed servo is performed by the means 41 to 45, and phase servo is performed by the means 26 to 47, so that during normal reproduction, the heads 11A and 11B track the tracks A and B.

Reference numerals 11 to 16 indicate a luminance signal reproduction system, in which heads 11A and 11B reproduce tracks A and B.
When the FM signal is reproduced from the
The luminance signal Sy is demodulated by being supplied to the FM demodulation circuit 14, and this signal Sy is sent to a switch circuit 55, which will be described later.
The signal is then taken out to the output terminal 16 through the buffer amplifier 15.

Furthermore, during still reproduction, as explained in FIG. Since jumping occurs, a circuit 50 is provided to detect and correct this. That is, during still reproduction, the luminance signal Sy from the demodulation circuit 14 is
As shown in Figure A, 0.5H per frame period
(The point at which jumping occurs varies depending on the size of △w.) Also, in this figure, the interval between pulses Ph during jumping is
1.5H), this signal Sy is supplied to the switch circuit 55, and is also supplied to the delay circuit 56 to become the luminance signal Sd delayed by 0.5 horizontal period as shown in FIG. It is supplied to circuit 55. Note that this switch circuit 55 is switched to the state shown in the figure when the control signal supplied thereto is "1", and is switched to the state opposite to that shown in the figure when it is "0".

Furthermore, the luminance signal Sy from the demodulation circuit 14 is
The horizontal synchronizing pulse Ph is supplied to the synchronization separation circuit 51 and taken out as shown in FIG. 5C, and this pulse Ph is supplied to the PLL 52 and as shown in FIG. , a rectangular wave signal Sp that rises for each pulse Ph is formed, and this signal Sp is supplied to the frequency dividing circuit 53. As shown in FIG. The frequency is divided into the signal Sh. This signal Sh is supplied to the phase comparator circuit 54, and the pulse Ph is also supplied to the comparator circuit 54, from which the pulse Ph is output as shown in FIG. (shown compressed), a signal Sj that is inverted every time the jump is taken out, and this signal Sj is supplied to the switch circuit 55 through an OR circuit 57 as a control signal.

Then, when playing the still, heads 11A, 11
A circuit 60 for setting the scanning locus of B to locus 7,
It is established as follows. That is, the pulse Pg from the amplifier 32 is supplied to the delay circuit 61 and delayed by a predetermined amount, and this delayed pulse is supplied to the monostable multivibrator 62, and as shown in FIG. In synchronization, a pulse Pd having a pulse width of, for example, 5 msec is generated, and this pulse Pd is supplied to a sampling hold circuit (phase comparison circuit) 63. Further, the output signal Sj of the comparison circuit 54 is supplied to the monostable multivibrator 64, and as shown in FIG. is supplied to the circuit 63 as a control signal (in FIG. 5, the period (time axis) of the signals other than the pulse Pd is set constant, and the pulse Pd is illustrated to correspond to this, but in reality, the pulse Pd is obtained in synchronization with the rotation of the head, so its period is constant,
This means that the periods of other signals change with respect to this pulse Pd).

In addition, 67 is a stay regeneration switch that is always open, and 6
9 is a normally open simple frame advance switch, 71 and 72 are switch circuits, and the switch circuits 71 and 72 are as follows.
When the control signal supplied to these is "0", the state is switched to the state shown in the figure, and when it is "1", the state is switched to the state opposite to that shown in the figure.

According to this configuration, when the switch 67 is off, the output of the inverter 68 is "0", so the switch circuit 71 is in the state shown in the figure, and therefore the servo circuit 40 operates as described above. Therefore, the tape 1 is transported at the same speed as when recording, and the heads 11A and 11 for tracks A and B are transported at the same speed as when recording.
1B tracking is performed and the FM signal is reproduced.

Furthermore, in this case, the output of the switch 67 is "1" and this output is supplied to the switch circuit 55 through the OR circuit 57.
The switch circuit 55 is in the state shown in the figure regardless of the signal Sj, and therefore the brightness signal from the demodulation circuit 14 is
Sy is taken out to terminal 16.

Therefore, when the switch 67 is off, normal playback is performed. Note that during this normal reproduction, since no jumping occurs in the reproduced luminance signal Sy, Sj = "0" at all times, and therefore Pc = "0", so the sampling in the sampling hold circuit 63 is not performed, and its output Ss is always "0". Therefore, the outputs of the AND circuits 65 and 66 are also "0", and the switch circuit 72 is in the state shown in the figure.

During normal playback, when the switch 67 is turned on, the output of the inverter 68 becomes "1", so the switch circuit 71 is switched to the opposite state as shown in the figure, and the voltage from the voltage source 73 is switched on. The signal is supplied to the motor 25 through the circuit 72 and further through the switch circuit 71 and the amplifier 49. Therefore, the motor 25 comes to rotate at a slow speed corresponding to the voltage of the voltage source 73, and the tape 1 comes to run at a slower speed than during recording.

In this way, when the running speed of tape 1 becomes slower,
As in the case of still playback, the luminance signal Sy has approximately 1
Jumping occurs every frame period, and a pulse Pc is obtained for each jumping, but the head 11A for tracks A and B,
The scanning locus 11B is generally a locus represented by locus 6, and therefore, jumping occurs during the vertical scanning period (effective screen period).

When jumping occurs in the vertical scanning period in this way, as shown on the left side of FIG.
is “0” as shown in FIG. 5L, and therefore,
When the output of the AND circuit 65 is “0”, the AND circuit 66
Since the output of is "0", the switch circuit 72 is in the state shown in the figure. Therefore, in this case, voltage source 73
The tape 1 continues to run at low speed due to the voltage.

Then, as the tape 1 continues to run at a low speed, the scanning loci of the heads 11A and 11B gradually move in parallel in the length direction of the tape 1, and become a locus 7.

Then, at trajectory 7, as shown on the right side of FIG. 5J and K, the time points of pulses Pd and Pc coincide, so that Ss="1" as shown on the right side of FIG. 5L. When Ss becomes "1", this is supplied to the switch circuit 72 through the AND circuits 65 and 66, and the switch circuit 72 is switched to the opposite state as shown in the figure, so that no voltage is supplied to the motor 25. The motor 25 stops and the running of the tape 1 also stops.

Therefore, the VTR enters the still playback state, and at this time, the heads 11A and 11B scan tracks A and B in the state of trajectory 7. In this state, the heads 11A and 11B
Since the minimum point of the playback level is located in the vertical blanking period, no noise band is generated on the playback screen.

If the switch 67 is on, the pulse
The state in which the points Pd and Pc continue to match, and as a result, the state in which Ss="1" continues, the tape 1 continues to be stopped, and still playback continues.

Note that during this still playback, the luminance signal Sy is
However, at this time, the output of the switch 67 is "0" and the output signal Sj of the comparator circuit 54 is inverted every time the jump occurs, as shown in FIG. 5F and H. The switch circuit 55 is switched by the signal Sj, and the switch circuit 55 outputs signals as shown in FIG. 5G and I.
Sy and Sd are taken out alternately, so terminal 1
6, luminance signals Sy and Sd without jumping are obtained.

Similarly, jumping correction is performed from when the switch 67 is turned on until the still playback state is entered.

Then, from this still playback state, switch 6
7 is turned off, the output of the inverter 68 becomes "0", so the switch circuit 71 is switched to the state shown in the figure, and the output of the switch 67 also switches the switch circuit 55 to the state shown in the figure.
Therefore, a normal playback state is established.

Furthermore, when the switch 69 is turned on during still playback, the output of the AND circuit 69 becomes "0" regardless of the signal Ss, so the switch circuit 72 is switched to the state shown in the figure, and therefore the tape 1 is running at a low speed. The playback screen slowly changes at a speed corresponding to the tape speed.

Even if the trajectory 7 is obtained during this low-speed running, if the switch 69 is on, the AND circuit 6
Since the output of No. 6 is "0", low speed running continues and the playback screen changes further.

Then, by turning off the switch 69 at any point, when trajectory 7 is obtained again, Ss="1"
Since the switch circuit 72 is switched to a state opposite to that shown in the figure, the tape 1 is stopped and the still playback state is entered in the state of the trajectory 7. Therefore, by turning on the switch 69 during still playback, simple frame forwarding is possible.

Actually, when the switch 67 is turned on, there is a time delay from when Ss becomes "1" until the tape 1 stops, so the pulse Pg is time-corrected by the delay circuit 61 in response to this delay. The tape 1 is then stopped at the trajectory 7.

As described above, according to the present invention, noise bands are not generated on the playback screen during still playback. Moreover, in that case, especially according to this invention,
Jumping of the luminance signal Sy (horizontal synchronization pulse Ph) is detected and tape 1 is stopped accordingly, so unlike conventional VTRs, the detection characteristics of the signal section that becomes a noise band do not become broad. Therefore, the accuracy of the stop position of the tape 1 is high, and the noise band can be reliably placed outside the playback screen.

Furthermore, since changes in the playback level are not utilized, the operation is stable even against dropouts and distortions of tracks A and B, and the stopping position is accurate.

In addition, in the above, when changing from normal playback to stay playback, if a drive voltage is supplied to the motor 25 to rotate it in the opposite direction, the time until the stay playback starts can be shortened. Also, instead of stopping the motor 25, the pinch roller 24
The tape 1 may be stopped by separating the tape 1 from the capstan 23. Further, for example, the output of the AND circuit 66 may be used to apply a brake to the capstan 23 or the like.

Further, the present invention can also be applied when there is a guard band between tracks A and B.

[Brief explanation of the drawing]

Figure 1 is an example of a track pattern, Figure 2 is an example of a track pattern.
3 and 5 are diagrams for explaining the present invention, and FIG. 4 is a system diagram of an example of the present invention. 30 is a head servo circuit, 40 is a capstan servo circuit, 50 is a jumping detection and correction circuit, and 60 is a tape stop position control circuit.

Claims (1)

[Claims] 1 A video signal is recorded on a magnetic tape by a pair of rotating magnetic heads having different azimuth angles with no gap between adjacent tracks, and the position of the horizontal synchronization signal is recorded at different positions between adjacent tracks. The device for reproducing video signals includes a circuit for detecting a horizontal synchronizing signal in the video signal reproduced from the rotating magnetic head, and a circuit for detecting a horizontal synchronizing signal in the video signal reproduced from the rotating magnetic head, and a circuit for causing the rotating magnetic head to detect the adjacent track based on the phase of the detected horizontal synchronizing signal. A circuit for outputting a discrimination signal indicating that an arbitrary position has been scanned; a circuit for outputting a reference phase signal related to the rotational phase of the rotating magnetic head; and a circuit for outputting a reference phase signal related to the rotational phase of the rotating magnetic head; It has a phase comparison circuit for comparison and a tape running control circuit for controlling the running of the magnetic tape, and stops the magnetic tape by supplying an output signal from the phase comparing circuit to the running control circuit. A video signal playback device that performs still playback by controlling the position.