JPS598482A - Recorder and reproducer for video signal - Google Patents

Abstract

PURPOSE:To eliminate the noise in blanking produced at head switching and to prevent a video signal from entering the blanking, by blanking before and after the head switching position to a pedestal potential. CONSTITUTION:A vertical synchronizing signal 22 separated at a vertical synchronizing separation circuit 18 is given to a blanking signal forming circuit 19 to form blanking signals 23, 24. Since the signal 23 controls a gate circuit 20, no video signal enters the blanking. Since the signal 24 controls a gate circuit 21, before and after the head switching position is brought to blanking in the pedestal potential. Then, the noise at head switching is eliminated. Thus, the noise in the blanking produced at head switching is eliminated and the video signal is prevented from entering the blanking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a recording and reproducing apparatus that sequentially switches a plurality of rotary heads to record and reproduce a video signal as an intermittent recording trajectory on a recording medium, which eliminates head switching noise during reproduction, and The purpose is to obtain a stable playback video signal.

In a two-head helical scan type VTR that uses A-inch or inch-wide tape, one tape is placed in the rotating cylinder.
It is wound slightly more than 80 degrees, and each head records a signal of just over one field, and during playback, the two heads are switched for each field to obtain a continuous video signal. The head switching position on this playback video signal is usually
It is set several lines (several horizontal scanning periods) before the vertical synchronization signal. Vertical blanking is required from the three lines before the vertical synchronization signal, so if the head switching position is set three lines or more before the vertical synchronization signal, the switching noise will appear at the bottom of the screen. However, if the head switching position is set within vertical blanking, the noise will not appear on the image, but will appear in the blanking area, and may cause a malfunction of the time base collector (TBC). Further, since the head switching position @ is determined by multiplying the rotational position of the rotary head by the phase of the vertical synchronization signal (during recording) by 1, it fluctuates due to fluctuations in r rotational phases of the /renoder. This is particularly noticeable when the VTR vibrates during recording, such as with a portable VTFI, and the change in the switching position extends over several lines. Furthermore, during tape interchange, the head switching position changes even when there is a difference in the detection position (cylinder PC signal) of the rotational position of the cylinder provided with the rotary head of the recording VTR and the reproduction VTR.

A block diagram of one method for removing such head switching noise is shown in FIG. 1, and waveforms of various parts thereof are shown in FIG. 2 and will be explained. In Figure 1, 1.1' is a rotating video head, 2
, 2' is a head amplifier, 3 is a head switching circuit, 4 is a demodulation circuit, 5 is a dropout compensation circuit, 6 is a reproduction signal output terminal, 7 is a horizontal synchronizing signal separation circuit, and 8 is a video head 1.1'. A cylinder PG generates a signal according to the rotational phase, 9 is a PG signal generation circuit, and 1o is a head switching signal and gate signal generation circuit. Video head 1゜2'
The signal is amplified by the head switching circuit 3, switched at one field period, and guided to the demodulation circuit 4, where the original continuous video signal is obtained as the output.

Historically, this signal passes through the dropout compensation circuit 5 and is output from the output terminal 6. Drawer, pullout compensation circuit 5
When the playback signal from the head is lost, it functions to replace it with the signal from one line before.

On the other hand, the head switching signal 11 that controls the head switching circuit 3 is created as follows. The PC signal 12 as shown in FIG. 2 is generated in the PG signal generation circuit 9 by the cylinder rotation position detection signal from the cylinder PGs. At 7, a horizontal synchronizing signal 14 (FIG. 2, 14) is separated.

From this P0 signal 12 and the horizontal synchronization signal 14, a head switching signal 11 (FIG. 2 11) and a gate signal 15 (FIG. 2 15) are created by the head switching signal and gate signal creating circuit 1o. As an example of this generation circuit 10, a generation circuit for the head switching signal 11 uses the PG signal 12 as a data signal, and generates a signal delayed from the horizontal synchronization signal 14 by, for example, a false line (a person's time in FIG. 2). The circuit for generating the gate signal 16 uses the PC signal 12 as a data signal, and the delay A (V
4 lines) and 5 fewer delays (time B in Figure 2)
It can be constructed from a D-type flip-flop that uses a signal as a clock signal and a monostable multivibrator that delays its output by the time indicated by C in FIG. The head switching signal 11 created in this way is always a certain period of time (in the above example, a line) after the horizontal synchronizing signal, and its horizontal position on the screen is fixed, as well as the horizontal synchronizing signal and equalization pulse. You can avoid overlapping with At the head switching position, the second
Although noise occurs as shown in Figure 13, gate signal 1
5, during the period 150C in FIG. 2, the dropout compensation circuit 6 replaces the signal with the previous line's signal, and this noise is removed (FIG. 2 16). The period C of the gate signal 16 is set to have enough width before and after the head switching position to include this noise. Here, the reason why the head switching position was synchronized with the horizontal synchronizing signal and not overlapping with the horizontal synchronizing signal and equalization pulse was to create a gate signal with a width before and after the head switching position.
Discontinuity (skew distortion) in the horizontal synchronizing signal occurs due to expansion and contraction of the tape and differences in cylinder diameter during compatibility, but even in this case, the dropout compensation circuit replaces the signal with the previous line's signal.
It is necessary to prevent the horizontal synchronization signal and equalization pulse from being lost or added by one.

However, the above method has the following drawbacks.

As mentioned above, since the head switching position changes, when the above method is adopted, the head switching position moves line by line. Now, when the head switching position is the first line after vertical blanking,
Figure 3 shows the signals of each part. 13-1.15-1.1
6-1 correspond to 13, 15, and 16 in FIG. 2, respectively. If head switching noise is compensated for using the method described above, the third
As shown in FIG. 16-1, a video signal appears where there should be blanking. This would violate broadcast standards. Also, instead of replacing the head switching noise with the signal from the previous line as in the method shown in Figure 1, a method of blanking may be considered, but in this case, the head switching position is outside the vertical blanking. Sometimes, the video signal is blanked, resulting in that part becoming black.

In view of the above points, the present invention provides a method for performing head switching without head switching noise or video signals during vertical blanking, and without blanking a certain portion of the video signal.

FIG. 4 shows a block diagram of an embodiment of the present invention, and FIG. 5 shows signal waveforms of each part thereof and will be explained. In FIGS. 4 and 5, the same numbers as in FIGS. 1 and 2 represent the same things and perform the same operations.

17, 17' are blanking circuits, 18 are vertical synchronization signal separation circuits, 19 are blanking signal generation circuits, 20.
21 and 21' are gate circuits. Head switching signal 11 and gate signal 15 are generated in the same manner as in FIG. Further, a horizontal synchronizing signal 14 and a vertical synchronizing signal 22 are separated from the reproduced video signal 13 by a horizontal synchronizing signal separating circuit 7 and a vertical synchronizing signal separating circuit 18, and are guided to a blanking signal generating circuit 19, as shown in FIG. Blanking signals 23 and 24 shown at 24 are created. The blanking signal generation circuit can be configured by a counter that is reset by a vertical synchronization signal and counts horizontal synchronization signals. The blanking signal 23 is a signal that is at a low level during the vertical blanking period and one line after the end of vertical grating and is at a high level during the blanking period, and the blanking signal 24 is high during the vertical blanking period excluding the vertical synchronization signal period. During other periods, the signal is at a low level. Blanking signal 2
3 is led to the gate circuit 2o together with the gate signal 15, and only when the signal 23 is at a high level, the gate signal 15 is transmitted to the dropout compensation circuit. That is, only when head switching occurs while the signal 23 is at a high level, the previous stage of the head switching noise is replaced with the signal from one line before. Therefore, no video signal enters the vertical blanking.

Still, the blanking signal 24 is guided to the gate circuit 21 together with the gate signal 15, and only when the signal 24 is at a high level, the gate signal 15 is transmitted to the blanking circuit and blanked to the pedestal potential. That is, if a head switching position exists during a period in which the signal 24 is at a high level, the period before and after the head switching position is blanked to the pedestal potential. Further, the vertical synchronization signal 22 and the gate signal 16 are
The gate signal 16 is guided to the circuit 21' and is transmitted to the blanking circuit 17' only during the period of the vertical synchronizing signal, and is blanked to the level of the vertical synchronizing signal. That is, if there is a head switching position during the vertical synchronization signal period, the periods before and after the head switching position are blanked to the vertical synchronization signal level. In this way, even if the head switching position comes to any position other than the first line after vertical blanking, the noise will be replaced with the signal from the previous line, or blanked to the pedestal potential or vertical synchronization signal level. can be completely removed.

As mentioned above, the head switching position is normally set several lines before the vertical synchronization signal. Now, if we set it 2.75 lines before the vertical synchronization signal that falls within blanking,
Even if the head switching position varies, in most cases it falls between 6 lines before the vertical synchronizing signal and up to the vertical synchronizing signal. Taking these points into consideration, the following modifications may be considered in order to simplify the circuit. The blanking signal 23 is a low level signal for a period including at least one line from the start of vertical blanking.
3, and the gate circuit 21' and blanking circuit 17' are omitted. In this way, during the period when the blanking signal 24 is at a high level, the areas before and after the head switching position are blanked to the pedestal potential, and since the first line of vertical blanking is included within this period, the vertical blanking No video signal is received.

Furthermore, when the head switching position comes outside of this period, the noise is replaced with a signal from the 1-line agent.

Further, the gate circuit 20 is omitted, and the dropout compensation circuit 5 operates even when the head switching position is within vertical blanking, as in the case of FIG.

The width of the gate signal supplied to the blanking circuit 17 is set slightly wider than that of the gate signal supplied to the dropout compensation circuit, and the head switching position is on the first line at the beginning of vertical blanking. When a video signal appears, the blanking circuit 17 may blank the video signal to a pedestal potential.

Furthermore, in a device that does not have the dropout compensation circuit 5, vertical blanking is performed by blanking before and after the head switching position to the pedestal potential during the vertical blanking period, and by not blanking during periods other than vertical blanking. Eliminate head switching noise within the
By blanking, the head switching noise in the video signal can be kept at a small point at a constant horizontal position without becoming black and wide. At this time, it is better to blank the vertical synchronizing signal period to the vertical synchronizing signal level or not to blank it.

Although the present invention has been described above with respect to a two-head helical scan type VTR, the present invention can be applied to any device that records and reproduces video signals by switching between a plurality of heads.

As described above, according to the present invention, it is possible to remove noise in the blanking that occurs when switching heads, and also to prevent the video signal from entering the blanking, thereby obtaining a perfect reproduced video signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment showing a conventional head switching method, FIGS. 2 and 3 are diagrams showing signal waveforms of each part in FIG. 1, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a block diagram showing signal waveforms of each part in FIG. 4. 1.1'...Video head, 3...Head switching circuit, 1Q...Head switching signal and gate signal generation circuit, 17...Blanking circuit, 19. -Blanking signal generation circuit, 21...
・Gate circuit.

Claims (2)

[Claims] (1) When recording and reproducing video signals by sequentially switching multiple henodes, set the head switching position during playback to a place that does not overlap with the composite synchronization signal, and at least for one horizontal scanning period from the start of vertical blanking. A video signal recording/reproducing apparatus characterized in that blanking is performed at a pedestal potential for a period sufficient to include head switching noise before and after a head switching position, and vertical blanking is not performed. (2) When head switching is performed during the blanking period before and after the head switching position, a period sufficient to include the head switching noise before and after the head switching position must be replaced with a signal from one horizontal scan earlier. A video signal recording and reproducing device according to claim 1, characterized in that: