JPH0622280A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a superior image without switching noise in which skew is eliminated with simple processing. CONSTITUTION:A 2nd signal obtained from a head B by a delay line 3 is more delayed than a 1st signal obtained from a head A. The 1st signal and the 2nd signal are synthesized by a switching circuit 4 and the resulting signal is demodulated by a demodulation circuit to obtain a video signal. On the other hand, a head switching pulse from a servo system is latched by a flip-flop 8 at a timing of a horizontal synchronizing signal obtained from the video signal after demodulation and the switching circuit 4 obtains a pulse selecting the 1st and 2nd signal. A write-off signal is generated by a write-off signal generating circuit 10 based on the pulse and a signal latching the pulse in a timing of a horizontal synchronizing signal. The write signal stops the write to a memory 12 of a time axis correction circuit 16 and a duplicated part caused in the video signal due to the delay of the 2nd signal is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a video tape recorder, and more particularly to a magnetic recording / reproducing apparatus for removing a skew caused by head switching.

[0002]

2. Description of the Related Art A video tape recorder (hereinafter referred to as VTR) for recording / reproducing by a helical scan method.
7 has at least two rotatable heads A and B, and these heads A and B alternately provide tracks T _A1 , T _A2, ... And tracks T _B1 ,. T _B2 ... _Is formed to record an image or the like. In such a VTR, the head A
-By alternately outputting the signals read by B, continuous video signals are obtained.

For example, when the head A finishes tracing the track T _A1 , the head B rotates after the head A.
Starts tracing the recording track T _B1 . Accordingly, the head output is switched by setting the switching point when the trace is transferred from the head A to the head B.

However, in the VTR as described above, the horizontal synchronizing signals are generally aligned and recorded in the width direction of the recording track, but at the time of actual reproduction, the expansion and contraction of the tape 31 and the running state of the tape 31 are compared with those at the time of recording. Of the trace end position P _A of the head A at the switching point and the head B
The distance from the trace start position P _B (about 100 mm in the VHS method) may vary. For this reason, a signal is time-shifted at the switching point, and a skew occurs.

For example, in the case of recording one field with two recording tracks T _A1 and T _B1 , two switching points are required to reproduce one screen, and there are two switching points within the screen.
Switching noise will occur in some places. This switching noise is generated by repeating loss and duplication of signals due to skew.

To solve such a problem, if the switching timing at the time of recording / reproducing is controlled to move one of the switching points to the lower end of the screen, the switching noise generated at that part will be overscanned on the screen. You can prevent it from appearing. However, even in that case, as shown in FIG. 8, the other switching point for switching between the first signal obtained from the head A and the second signal obtained from the head B exists in the effective scanning period. Become. As a result, as shown in FIG. 9, switching noise remains in almost the center of the screen.

With respect to such an inconvenience, for example, in the configuration disclosed in Japanese Patent Laid-Open No. 3-212081,
By controlling the head switching point and operating the dropout compensation circuit at the switching point, the portion affected by the skew is interpolated by the preceding and following data. Specifically, the head switching pulse is synchronized with the horizontal synchronizing signal detected from the reproduced video signal so that the head switching is performed in the horizontal blanking period, and the pseudo dropout pulse is generated at the head switching point. Then, the dropout compensation circuit is operated as described above.

[0008]

However, in the above configuration, the reproduced video signal immediately after head switching is interpolated by the data before and after by the dropout compensation circuit. However, the video signal is special and complicated processing is required for interpolation. If so, the above process is not appropriate. An example of this is high definition MUSE (Multiple Sub-Nyquist Sampling Encordin).
g) There is a case where the signal is directly recorded without changing anything other than the synchronous portion.

The MUSE signal is a TCI (time compression / time division multiplexing) system and has a luminance signal Y and two color difference signals RY and B.
-Y, in particular, the color difference signal is line-sequentially multiplexed with the RY signal on the odd line and the BY signal on the even line. As described above, the MUSE signal has a characteristic that it has a complicated form and the phases of the sampling points match every four lines due to offset subsampling. Therefore, a complicated process is required to perform interpolation on the MUSE signal, and therefore a special and expensive circuit must be provided.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to prevent the occurrence of a skew due to a head switching pulse with a simple process.

[0011]

In the magnetic recording / reproducing apparatus of the present invention, a video signal of one field is divided into a first signal and a second signal, and two signals are transmitted to two tracks by two rotating heads. While recording separately, the heads switch the first signal and the second signal read from the track to reproduce a continuous video signal, and have a memory, and the video signal is temporarily stored in the memory during reproduction. In order to solve the above-mentioned problems, a magnetic recording / reproducing apparatus provided with a time axis correction means for stabilizing the time axis of a video signal by accumulating is characterized by the following means.

That is, in the above magnetic recording / reproducing apparatus, the delay means for delaying the second signal from the first signal before the switching at the time of reproduction, and the switching point at which the first signal and the second signal are switched are the second signal. Switching point setting means for setting the delay period and the memory of the time axis correction device so as to remove only the overlapping portion that overlaps with the normal video signal by switching from the first signal to the second signal in the delay period. And removing means for controlling the operation of.

As the above-mentioned delay means, for example, in the recording system, a delay line for delaying the second signal is provided immediately before the head, or in the reproducing system before the first signal and the second signal are switched. A configuration in which a delay line that delays two signals is provided can be considered. When two heads are provided for recording and one for reproducing, respectively, the side of the recording heads that are normally provided facing each other by 180 ° and which delays the second signal for recording is set according to the delay amount from the facing position. It is conceivable that the recording head is normally arranged and the reproducing head is displaced from the facing position according to the delay amount.

[0014]

When the above configuration is applied to the VTR, the second signal is delayed from the first signal by the processing by the delay means during recording or reproduction before switching during reproduction. The first and second signals are first switched from the first signal to the second signal at the switching points set by the switching point setting means. At this time, since switching is performed in the delay period of the second signal, a video signal that overlaps the regular video signal appears in that period. Further, in this overlapping portion, skew occurs after the switching point.

When this video signal passes through the time base correction means, the operation of the memory is controlled by the removing means to remove the above-mentioned overlapping portion. Specifically, this processing is performed so that the video signal of the overlapping portion is not written in the memory at the timing of the horizontal synchronizing signal at the front end and the horizontal synchronizing signal at the rear end of the overlapping portion.

Further, when switching from the second signal to the first signal, due to the phase shift of both signals, a part which is lacking appears in the combined video signal, and a skew occurs in that part. By moving this portion to the lower end of the screen, it is possible to prevent switching noise from appearing on the screen due to overscan.

Therefore, according to the above configuration, the skew appearing on the screen can be removed by a simple process.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a description of an embodiment in which the present invention is applied to a VTR, with reference to FIGS.

As shown in FIG. 1, the VTR according to this embodiment has heads A and B, head amplifiers 1 and 2, and a delay line 3.
A switching circuit 4, a demodulation circuit 5, a time axis correction circuit 6, a synchronization detection circuit 7, and flip-flops 8 and 9.
And a light-off signal generation circuit 10. Further, this VTR divides the video signal of one field into a first signal and a second signal, and forms and records one track on a video tape (not shown) by the heads A and B, respectively. The first signal and the second signal are reproduced by reading the track by.

The head amplifiers 1 and 2 are configured to amplify the first signal and the second signal read by the heads A and B, respectively. The delay line 3 as a delay means is a circuit that delays the second signal obtained from the head B for a predetermined time set as described later.

The switching circuit 4 receives the synchronization switching pulse output from the flip-flop 8 for the first switching.
It is a circuit that alternately switches the signal and the second signal and outputs as a continuous FM carrier or RF (Radio Frequency) signal. The demodulation circuit 5 is a circuit that FM demodulates the FM carrier or the RF signal output from the switching circuit 4.

Time axis correction circuit 6 as time axis correction means
Is an A / D converter (A / D in the figure) 11, a memory 12,
It is composed of a D / A converter (D / A in the figure) 13, a burst detection circuit 14, a write clock generation circuit 15, a write control circuit 16, a read clock generation circuit 17, and a read control circuit 18. The time axis correction circuit 6 converts the video signal from the demodulation circuit 5 into A /
The D converter 11 converts it to digital, writes it in the memory 12 with a write clock synchronized with the video signal, reads the video signal with a stable read clock, and suppresses the jitter contained in the video signal. .

The burst detection circuit 14 is a circuit for extracting a color burst signal from the video signal from the demodulation circuit 5 and creating a writing reference signal synchronized with the video signal based on the color burst signal.

The write clock generation circuit 15 is a circuit for generating the write clock based on the write reference signal. Further, the write clock generation circuit 15 is adapted to stop the generation of the write clock by the write-off signal generated by the write-off signal generation circuit 10 described later.
The write control circuit 16 is a circuit that controls the write operation of the memory 12 by generating a write address based on the write reference signal and the write clock. Further, the write control circuit 16 is adapted to stop the write operation of the memory 12 by the above write-off signal.

The read clock generation circuit 17 is a circuit for generating the above read clock based on a stable reference signal. The read control circuit 18 is a circuit that controls a read operation of the memory 12 by generating a read address based on a read clock.

The synchronization detection circuit 7 is a circuit for extracting the horizontal synchronization signal from the video signal from the demodulation circuit 5. The flip-flop 8 (FF in the figure) is adapted to latch the head switching pulse obtained from a servo system (not shown) at the timing of the horizontal synchronizing signal to generate a synchronizing switching pulse, and set a switching point. It has a function as a means. Flip-flop 9 (FF in the figure)
Outputs the output pulse of the flip-flop 8 at the timing of the horizontal synchronizing signal.

The write-off signal generation circuit 10 is a circuit for detecting the period of the overlapping portion at the time of switching between the first signal and the second signal, based on the above-mentioned synchronizing switching pulse and the output pulse of the flip-flop 9. The result is latched by the write clock of the time axis correction circuit 6 and output as a write-off signal. The write-off signal generation circuit 10 is adapted to stop the writing operation of the memory 12 from the outside of the time axis correction circuit 6 by generating the write-off signal, and functions as a removing means. have.

The VTR is constructed as described above,
In this configuration, in order to delay the second signal, delay means as described below may be used in addition to the delay line 3.

(1) As shown in FIG. 2, a delay line 19 is provided before the head B on the recording system side.

(2) As shown in FIGS. 3A and 3B, recording heads A _R and B _R and reproducing head A _P
The heads A _R and B _R are arranged irregularly in the structure in which B _P and the rotary drum 20 are provided. That is, the heads A _P and B _P are normally arranged so as to face each other by 180 °, and the head B _R is delayed by the second signal on the side where the trace precedes the position P ₀ which faces the head A _R by 180 °. It is placed at a position shifted by a distance D according to time.

(3) As shown in FIGS. 4 (a) and 4 (b), the recording heads A _R 'and B _R ' and the reproducing heads A _P 'and B _P ' are mounted on the rotary drum 21. in the configuration with, it is obtained by irregularly arranged head a _P '· B _P'. That is, the heads A _R 'and B _R ' are 180 ° from each other.
The heads B _P ′ are normally arranged so as to face each other, and the head B _P ′ is deviated by a distance D ′ according to the delay time of the second signal from the position P ₀ ′ facing the head A _P ′ by 180 °. Place in position.

(4) The configurations of (2) and (3) are combined. That is, the second signal is delayed by the recording system and the reproducing system.

(5) In the case of a magnetic recording / reproducing device for performing non-azimuth recording or a magnetic recording / reproducing device with variable azimuth, the azimuths of the heads A'and B'are reversed during recording and reproduction. Further, as shown in (a) and (b) of FIG.
The head B ′ is arranged at a position displaced from the regular facing position with respect to the head A ′ by a distance d toward the side where the trace precedes. In this configuration, the second signal is reproduced with a delay corresponding to 2d with respect to the first signal.

(6) In the case of a magnetic recording / reproducing apparatus having a dynamic tracking function, the head arrangement at the time of recording and at the time of reproducing is made to be the same as the constitution of (2), (3) or (4).

However, the second obtained by each of the above constructions
The signal delay time is set to an appropriate value in consideration of the fact that the video signal is not lost due to the skew at the switching point and the period required for removing the overlapping portion at the switching point. Also, the amount of overlap at the switching point between the first signal and the second signal recorded on the video tape is sufficiently longer than the above delay time.

The operation of the VTR configured as above will be described with reference to the waveform chart of FIG.

The second signal ((d) in FIG. 6) input to the switching circuit 4 is delayed from the first signal ((c) in the same figure) by the delay line 3 or each of the delay means described above. On the other hand, the head switching pulse ((a) in the figure) from the servo system is latched by the flip-flop 8 at the timing of the horizontal synchronizing signal output from the demodulation circuit 5, and delayed as shown in (b) in the figure. It becomes a synchronized switching pulse. The first and second signals are switched by the synchronization switching pulse in the switching circuit 4 and become a combined signal shown in (e) of the figure.

This composite signal is switched to the second signal (2) ₂ when the synchronization switching pulse changes while the first signal (3) ₁ is being output following the first signal (2) _1. . After that, the second signal (3) ₂ and the second signal (4) ₂ ... Are continuously output. Also, the combined signal is
At the change point (switching point) of the synchronized switching pulse, the first signal (3) ₁ and the second signal (2) ₂ are
It overlaps with the second signal (3) ₂ and the first signal (2) ₁ that come before and after them.

The switching point is delayed from the horizontal synchronizing signal of the first signal immediately before the composite signal is switched from the first signal to the second signal by the feedback delay time Δt for generating the synchronizing switching pulse. Therefore, the delay time of the second signal with respect to the first signal is set in advance to a time longer than the time obtained by adding the feedback delay time Δt and the maximum occurrence time of the skew that is delayed with respect to the switching point. It

The above composite signal is demodulated by the demodulation circuit 5 into a video signal as shown in (f) of the figure, but includes a skew after the switching point. A horizontal synchronizing signal of this video signal is detected by the synchronization detecting circuit 7, while an A / D signal is generated at the timing of the write clock generated by the write clock generating circuit 15 in the time axis correction circuit 6.
It is digitized by the converter 11 and written in the memory 12.

When the above-mentioned overlapped portion of the video signal is input to the time axis correction circuit 6, the write-off signal generation circuit 10 performs write-off due to the time difference between the output pulse of the flip-flop 9 and the synchronization switching pulse. A signal is generated. In the time axis correction circuit 6, the write control circuit 16 receives the write-off signal and receives the memory 12
Stop the write operation. As a result, the above-mentioned overlapping portion is not written in the memory 12.

The video signal stored in the memory 12 is read at the timing of the read clock generated by the read clock generation circuit 17, converted into analog by the D / A converter 13 and output as a reproduced video signal. It The reproduced video signal has a stable time axis and has an overlapping portion removed as shown in FIG.

When switching from the head B to the head A, contrary to the above case, a video signal has a missing portion at the head switching point. As a result, switching noise disappears. Therefore,
Switching noise does not appear on the screen, and a good image can be obtained.

As described above, in this embodiment, the phase relationship between the two signals is shifted, and the overlapping portion of the signals caused by the shift is removed in the time axis correction stage. Therefore, the switching noise can be easily removed by using the existing time axis correction circuit 6.

[0045]

As described above, the magnetic recording / reproducing apparatus of the present invention switches between the first signal and the second signal, and the delay means for delaying the second signal from the first signal before switching during reproduction. Switching point setting means for setting the switching point in the delay period of the second signal, and removing only the overlapping portion that overlaps with the normal video signal by switching from the first signal to the second signal in the delay period. And a removing means for controlling the operation of the memory of the time axis correction device.

Thus, since the overlapping portion of the video signal created as described above is removed by using the time axis correction processing, the skew caused by the overlapping portion can be removed. Such processing can be easily performed by controlling the operation of the memory of the time axis correction processing.
It is possible to easily prevent the skew from occurring even in a signal of a special format such as the SE signal.

Therefore, according to the above arrangement, when recording / reproducing an image of one field on two tracks, switching noise due to skew can be removed from the screen, and a good image can be obtained. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a reproduction system of a VTR according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a part of a recording system in which a delay line is provided, which is another configuration for delaying the second signal.

3A and 3B are a perspective view and a plan view showing a head drum, which is another configuration for delaying the second signal and in which the recording heads are displaced.

4A and 4B are a perspective view and a plan view showing a head drum, which has another configuration for delaying the second signal, and in which the arrangement of the reproducing head is shifted.

FIG. 5 is a plan view showing a head drum having another structure for delaying the second signal, the head drum having a head that reverses azimuth during recording and during reproduction.

6 is a waveform diagram showing signals obtained by the operation of each unit of the reproduction system of FIG.

FIG. 7 is an explanatory diagram showing a general track pattern formed on a tape by a VTR.

FIG. 8 is a waveform diagram showing a state where switching noise occurs in a reproduced video signal due to head switching.

FIG. 9 is an explanatory diagram showing a state in which switching noise is generated on the screen.

[Explanation of symbols]

3 delay line (delay means) 4 switching circuit 6 time axis correction circuit (time axis correction means) 8 flip-flop (switching point setting means) 10 write-off signal generation circuit (elimination means) 12 memory 19 delay line (delay means) A B head B _R head (delay means) _BP 'head (delay means) A'B' head (delay means)

Claims (1)

[Claims] 1. A first field video signal and a second field video signal of one field.
The two signals are separately recorded on the two tracks by the two rotating heads, and the continuous video signal is generated by switching the first signal and the second signal read from the tracks by the two heads. It has a memory as well as playing
In a magnetic recording / reproducing apparatus equipped with a time axis correction means for stabilizing the time axis of a video signal by temporarily storing the video signal in the memory during reproduction, the second signal is output from the first signal before switching during reproduction. By delay means for delaying, switching point setting means for setting a switching point at which the first signal and the second signal are switched to a delay period of the second signal, and switching from the first signal to the second signal in the delay period. A magnetic recording / reproducing apparatus, comprising: a removing unit that controls an operation of a memory of the time axis correcting apparatus so as to remove only an overlapping portion that overlaps with a normal video signal.