JPH04117084A - Switching pulse generation circuit - Google Patents

Abstract

PURPOSE:To enable normal reproduction operation and special reproduction operation by specifying a switching pulse generated in a VTR using a compact rotary head drum. CONSTITUTION:In the case of a normal reproduction, a pulse equipped with polarity selecting the output of a video head with higher reproduction level while comparing the reproduction levels of the two (a pair of) video heads at the time of actuation, is generated as a switching pulse. In the case of a field still reproduction, a pulse fixed to polarity selecting the output of a video head with higher reproduction level while comparing the reproduction levels of the two video heads, is generated as the switching pulse. In the case of a high speed search reproduction, a pulse equipped with polarity which is inverted so that the output of the video head with higher reproduction level can be selected at all times, is generated. Thus, the normal reproduction operation and the special reproduction operation can be executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a camera-integrated video tape recorder (
The present invention relates to a VTR (hereinafter referred to as a VTR) that is required to be small and lightweight, and particularly relates to a switching pulse generation circuit that generates switching pulses used for selecting video heads and the like.

[Conventional technology]

In recent years, there has always been a demand for smaller and lighter VTRs with built-in cameras, and technological development has been progressing to reduce the size of rotating head drums. For example, Tokuko Sho 60-5130
No. 6 discloses a method of winding a videotape over the entire circumference of a rotary head drum to form the same recording pattern as that of a typical two-head 180-inch VTR.

In addition, special playback functions such as field still and high-speed search have become commonplace in home VTRs, whether stationary or built-in with a camera. For example, Tokuho 1-53
As described in Japanese Patent No. 958, two video heads having different azimuth angles are installed close to each other, commonly known as a double azimuth head, on a rotating head drum at an angle of 180 degrees.
There is a method of installing two in total, separated by a distance, and switching the playback output depending on their function.

[Problem to be solved by the invention]

Of the two proposed examples mentioned above, the former proposed example allows the rotating head drum to be made smaller, but it only discloses recording, so normal playback and special playback are unknown. Ta.

In addition, in the latter proposed example, special playback such as field stay and high-speed search can be performed, but because two double azimuth heads with a special structure are used,
In addition to being expensive, it was also unsuitable for downsizing the rotating head drum. Also, in the case of Field Stall,
Since the video head used is switched for each field in accordance with the switching pulse, there is also a problem that flicker occurs in the image due to the difference in the output level and frequency characteristics of each video head.

The purpose of the present invention is to solve the problems of the prior art described above,
It is an object of the present invention to provide a switching pulse generation circuit that can perform normal playback operation and special playback operation without causing problems such as flicker in a VTR using a small rotating head drum.

[Means for Solving the Problems] In order to achieve the above object, the present invention compares the playback levels of two (pair) video heads at the time of startup during normal playback, which is played back at the same speed as during recording. do,
A pulse having a polarity that selects the output of the video head with the higher level is generated as a switching pulse, and during field still playback, the playback levels of both of the above two video heads are compared, and the output of the video head with the higher level is compared. A pulse with a fixed polarity that selects the output of the video head on the side is generated as a switching pulse, and during high-speed search playback, the playback levels of both the above two video heads are compared and the output of the video head on the side with the higher level is selected. A pulse whose polarity is inverted is generated as a switching pulse so that the head output is always selected.

(Function) As described above, by generating switching pulses, normal playback operation and special playback operation can be performed in a VTR using a small rotating head drum.

Moreover, in the present invention, at startup during normal playback, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced is selected by the switching pulses generated, and then the tracking servo is applied. This has the effect of shortening the time.

Furthermore, during field still playback, the number of video heads used is fixed to one by the generated switching pulses, so that flicker does not occur in the image due to differences in the output level 9 frequency characteristics of the video heads.

Furthermore, during high-speed search playback, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced is always selected by the generated switching pulse, so that no noise bands are generated in the image.

〔Example〕

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

FIG. 1 is a block diagram showing a reproducing circuit of a VTR having a switching pulse generating circuit as an embodiment of the present invention;
FIG. 2 is a block diagram showing a recording circuit of a VTR having a switching pulse generation circuit as an embodiment of the present invention, and FIG. 3 is a plan view showing a rotary head drum having the video head of FIGS. 1 and 2. 4 is a timing diagram showing the timing of input and output signals of the time base compression circuit in FIG. 2. FIG.

The VTR shown in FIGS. 1 and 2 is a camera-integrated VTR, and uses an automatic ink tracking function (hereinafter referred to as ATF) method using a pilot signal as a tracking servo method.
It complies with the millivideo standard.

First, let's talk about Figure 3.

In FIG. 3, video heads 2A and 2B are mounted in close proximity to each other at the same height, and have approximately the same track width, but different azimuth angles (for example, +1
0° and -10°). Ideally, it would be desirable for both to be in exactly the same position, but since this is not possible, the mounting shown in the figure is performed with the distance A set at a constant value.

Further, the rotating surface 72 of the rotating head drum is 1/1 of the broadcasting standard.
one revolution per field period (i.e. - vertical period);
The video heads 2A and 2B alternately perform recording or normal playback every rotation of their rotary head drums.

Therefore, if the rotating surface 72 of the rotating head drum is now rotated in the direction of the arrow in FIG. Sometimes the signal recorded by video head 2A is lower than the signal recorded by video head 2B.
The attachment needs to be delayed by a time corresponding to the interval A.

Further, the magnetic tape 1 is positionally regulated by the inclined bins 73A and 74B, and is wound around the rotary head drum over almost the entire circumference, but it is difficult to wrap it completely 360 degrees. There is a gap only at the rotation angle α.

Therefore, when the video heads 2A and 2B pass through the gap, recording and reproduction cannot be performed, so during recording, the signal is approximately (36
It is necessary to compress the time axis to 0-α)/360 times and record it, and when playing back, it is necessary to expand the signal on the time axis and output it.

From the above, it is necessary to process the signal as shown in FIG. 4.

That is, if the video head 2A is now at -azimuth angle and the video head 2B is at -azimuth angle, then during recording, the time axis compression circuits 51, 60, 65 as described later are used.
(FIG. 2), the continuous input signal as shown in FIG. 4(a) is compressed on the time axis by approximately (360-α)/360 times in units of one field (-vertical period units), and The field recorded by the video head 2A with the +azimuth angle is delayed from the field recorded with the video head 2B with the -azimuth angle by a time corresponding to the interval A;
It is necessary to produce an output signal as shown in FIG. 4(b).

Also, during playback, a time axis expansion circuit 12 as described later is used.
, 19.28 (FIG. 1), it is necessary to perform the opposite process to that described above.

By performing the above-described processing, a recording pattern conforming to the existing VTR standard can be formed.

Next, the operation during recording will be explained based on FIG.

In Fig. 2, 35 is a composite video signal input terminal, 36A and 36B are a pair of input terminals, and 36A and 36B are a pair of input terminals.
The luminance signal is from 36B, (455/2)f,
A chromaticity signal obtained by orthogonal two-phase modulation of a subcarrier having a frequency of (fH=4500/286k7; horizontal synchronization frequency) is input manually. 61 is an input terminal for audio signals. 44
is the composite video signal output terminal, 45A and 45B are a pair of output terminals, and 45A is the output terminal for the luminance signal,
5B outputs chromaticity signals, respectively. These 44
．． 45A and 45B are supplied to a monitor television, viewfinder, etc. outside the device, so that images to be recorded can be monitored. Further, from 62, an audio signal to be recorded is output for monitoring.

A composite signal such as a broadcast from outside the device is connected to the input terminal 35, and a YC separated signal from a camera (not shown) inside the device is connected to input terminals 36A and 36B, respectively.

The switches 37, 41, 43.56 have input terminals 36A,
When recording the signal from the input terminal 36B, it is connected in the direction shown in the figure, and when recording the signal from the input terminal 35, it is connected in the opposite direction. Therefore, the composite signal from the input terminal 35 is Y
Through the C separation circuit 40, the input terminals 36A and 36B
The yc separated signal from the yc signal is recorded without passing through this. Further, the adder 42 adds the luminance signal and the chromaticity signal, and a desired signal is always output to the output terminals 44, 45A, 45B.

The switch 39 is used to select whether or not to pass the input signal through the AGC circuit 38. When the camera side has an AGC circuit and gain control is not required on the VTR side, it is connected in the direction shown in the figure, and when recording broadcasts, it is connected in the opposite direction.

Below, the video signals from input terminals 36A and 36B are converted to AGC.
A case where recording is performed without going through the circuit 38 will be described. At this time, the switches 37, 39, 41, 43.degree. 56 are all connected in the direction shown.

The luminance signal from the input terminal 36A is band-limited by the LPF 46 through the switch 39.degree. Based on the timing of the synchronization pulse that is the output of the synchronization separation circuit 47, the clamp circuit 49
Then, the leading edge of the synchronization signal is clamped to a constant level and applied to the nonlinear emphasis circuit 50 and the AGC detection circuit 48.

The AGC detection circuit 48 controls the gain of the AGC circuit 38 based on the timing of this signal and the previous synchronization pulse. The nonlinear emphasis circuit 50 is given a characteristic of relatively emphasizing a high-frequency, minute-level signal compared to a large-amplitude signal. As is well known, its purpose is to
However, as mentioned above, since the characteristic is non-linear with respect to the signal amplitude, the maximum amplitude does not increase in proportion to the amount of emphasis for small signals, and the time axis compression circuit 51 in the subsequent stage
It also acts to reduce the quantization noise in .

In the time axis compression circuit 51, the polarity of the switching pulse from the frequency dividing circuit 71 (that is, old gh level or Lo
As mentioned above, based on the luminance signal,
Compress the time axis in units of one field (-vertical period units),
For every other field, attachment is delayed by a time corresponding to interval A.

The linear emphasis circuit 52 is given the characteristic of uniformly emphasizing high frequency signals regardless of the level. after that,
The FM modulator 53 converts the signal into an FM modulation signal, the HPF 54 removes low-frequency components (approximately 1.5M7 or less), and the signal is added to one end of the adder 55 .

Note that after the time axis compression circuit 51, the frequency axis is 360/360/
Since the signal is shifted by (360-α), the 8 mm video standard cannot be satisfied unless the emphasis time constant and FMI transmission frequency are set higher than the standard.

Next, the chromaticity signal input from the input terminal 36B is BP
Out-of-band components are removed at F57, and recording processing based on the 8 mm video standard is performed at chromaticity signal recording processing circuit 58. That is, ACC (Automatic Chroma
Control) processing to keep the burst level constant, and burst emphasis processing to reduce the burst to 6d.
B Emphasizes amplitude. Then, by low-frequency conversion processing, the subcarrier is phase-rotated every horizontal period and the frequency is converted based on the synchronization pulse so as to comply with the 8 mm video standard. At this time, based on the polarity of the switching pulse from the frequency dividing circuit 71, which will be described later, the video head 2 at the +azimuth angle
The direction of phase rotation is switched between the field recorded at A and the field recorded at the -azimuth angle video head 2B. Furthermore, nonlinear chroma emphasis processing emphasizes sideband waves with respect to subcarriers.

Next, the LPF 59 removes unnecessary components outside the band. In the time axis compression circuit 60, a frequency dividing circuit 71, which will be described later,
Based on the polarity of the switching pulse from
will be delayed by a certain amount of time. After that, the previous adder 55
join one end of

Next, an audio signal from a microphone or the like (not shown) is input from the input terminal 61. After emphasizing the minute level signal with the noise reduction circuit (reverse characteristic) 63, the L
PF64 removes out-of-band components.

The time axis compression circuit 65 compresses the time axis of the audio signal in one field unit (-vertical period unit) based on the polarity of the switching pulse from the frequency dividing circuit 71, which will be described later. At each interval, the attachment is delayed by a time corresponding to interval A.

After that, the FM modulator 66 uses the standard carrier frequency of 360/
After being made into an FM modulated signal of a carrier wave with a frequency of (360-α) times, the out-of-band components are removed by the BPF 32 and the signal is applied to one end of the adder 55.

On the other hand, the pilot signal generator 68 generates a pilot signal for tracking control used during reproduction based on the polarity of a switching pulse from a frequency dividing circuit 71, which will be described later. In other words, according to the 8mm video standard, the frequency of the generated pilot signal is set at f for each field.
, [(37B158) r, l , r, [(37B150
)r□1f3[(378/36)f,] ,f,[(3
78/40) fH] and circulate, f
The frequency of f, , f3 is changed in the order of l+f, and the video head 2A with an azimuth angle of +f is used.
, , f are recorded by the video head 2B at a -azimuth angle. In this case, each is 360/
A pilot signal of (360-α) times the frequency is generated and then applied to the remaining end of the adder 55.

The luminance FM signal, low frequency conversion chromaticity signal, audio FM signal, and pilot signal added by the adder 55 pass through the recording amplifier 69, and then are processed based on the polarity of the switching pulse from the frequency dividing circuit 71, which will be described later. By operating the switch 70 which is switched every field (every rotation of the rotary head drum), the data is recorded on the magnetic chip 11 via the video heads 2A and 2B every field.

A switch 70 determines which azimuth angle end a certain field is recorded at. General 18
Unlike a 0° wrapping type two-head VTR, the video head 2A has a -azimuth angle, and the video head 2B has a -azimuth angle.
Since both of them are in contact with the magnetic tape 1 except for the gap portion (portion of rotation angle α) shown in FIG. There is no fixed relationship.

However, the video head 2A has a +azimuth angle.

As mentioned above, with the azimuth angle video head 2B,
1 chromaticity signal recording processing circuit 5 between every other field delay (phase shift) in time axis compression circuits 51 and 60.65
There is a fixed relationship between the direction of phase rotation of the subcarrier at 8 and the frequency of the pilot signal generated by the pilot signal generating circuit 68, respectively.

Therefore, in this embodiment, the tank pulse (60 Hz) from the tank pulse generator is divided by a 172 frequency divider circuit 71 composed of a flip-flop, etc. to generate a 30) (Z rectangular wave, which is output as a switching pulse. However, due to this switching pulse, as mentioned above, the time axis compression circuit 5
1, 60, 65, chromaticity signal recording processing circuit 58, and viroft signal generation circuit 68 are driven all at once. The switching timing of the polarity of the switching pulse (that is, old gh level or low level) is determined when the video heads 2A, 2B are not in contact with the magnetic tape 1, that is, in the gap portion (the portion at the rotation angle α). It is best to do this when you reach it.

Next, the operation during reproduction will be explained using FIG. 1.

During playback, there is not only normal playback that is performed at the same speed as when recording, but also field stay.

Consideration must be given to special playback, which has become commonplace, such as high-speed search.

First, I will explain about the king servo, which is the tiger of normal playback.

In a conventional 180° winding type two-head VTR, only one of the azimuth angle video heads is in contact with the magnetic tape, so the tracking servo is adjusted so that the azimuth angle of the recording track being traced matches the contacting video head. must be applied. Therefore, when starting playback, it takes some time until the servo locks in.

On the other hand, in the case of this embodiment, the situation is different.

That is, similarly to the above, the tracking servo may be applied until the video head of either azimuth angle traces the recording track with the same azimuth angle, but as mentioned above, the servo lock-in time at the start of playback is Therefore, in this embodiment, attention is paid to the fact that the video heads of both azimuth angles trace simultaneously on the recording track, and the servo lock-in time at the start of playback is shortened as shown below. ing.

When starting playback, first, video head 2A is selected from magnetic tape 1.
, 2B are transmitted to regenerative amplifiers 3A and 3B, respectively.
The signal is amplified and applied to each end of the switch 6 and the level comparator 5. The level comparator 5 determines which video head has a thicker output, and outputs a logic signal indicating the result as a switching pulse. In other words, the output of the video head becomes thicker as its azimuth angle matches the azimuth angle of the recording track being traced. Low level) indicates which video head has an azimuth angle equal to the azimuth angle of the recording track being traced.

The switching of the switch 6 is controlled by the polarity of the switching pulse from the level comparator 5, and the output of the video head having a higher level, in other words, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced. Video head output is selected.

The output of switch 6 is HPF7. LPFlB, BPF24
Given to 32. The BPF 32 separates the pilot signal, and the pyro-node detector 33 detects a signal corresponding to the amount of tracking error. Upon receiving this signal, the trunking servo circuit 34 adjusts the running of the magnetic tape 1 so that the amount of error is minimized. control.

In this way, when starting playback, by switching the switch 5 according to the polarity of the switching pulse from the level comparator 5, the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced is selected, and then the video head is started. Ranking servo is applied, which has the effect of shortening lock-in time.

Furthermore, the time axis expansion circuits 12, 19.28, the chromaticity signal reproduction processing circuit 20, and the pilot detector 33 all operate between the video head 2A at the +azimuth angle and the video head 2B at the -azimuth angle. However, as mentioned above, the polarity of the switching pulse from the level comparator 5 indicates which video head has the same azimuth angle as the recording track being traced. , switching pulses are applied to these circuits for their operation.

In addition, in the case of normal playback, it is only necessary to reverse the polarity of the switching pulse every field (every time the video heads 2A, 2B pass the gap), so after starting playback using the method described above, the evening The polarity may be reversed depending on the tack pulse generated by the tack pulse generator 4.

In addition to the method described above, when starting regeneration, the pilot detector first detects the frequency of the pilot signal as fl.

It is also conceivable to determine the polarity of the switching pulse by determining whether it is f3, fz, or f4. This takes advantage of the fact that the pilot signal has a low frequency and that almost the same reproduction level can be obtained even if the azimuth angles between the video head and the recording track are different.

However, this method is of course compatible with ATs such as 8mm video.
It cannot be applied to anything other than those using the F method, and may malfunction when there are variations in playback sensitivity among the four frequencies from f+ to f4, or when the video head traces the boundary between two recording tracks when starting playback. There is a risk that the above will take longer.

The previous HPF7 extracts the luminance FM signal and sends it to the FMA
After the signal is set to a constant amplitude level independent of the sensitivity of the video heads 2A and 2B by the GC circuit 8, it is applied to the dropout detector 16 and the FM demodulator 9.

A dropout detector 16 detects an instantaneous reproduction signal dropout period due to head clogging or the like.

Originally, this dropout could only be detected in the FM signal. That is, since the detection is performed in a state where the time axis is compressed, the compensation must be performed before the time axis is expanded.

The reproduced signal demodulated by the FM demodulator 9 is sent to the linear de-emphasis circuit 10 (the linear emphasis circuit 52 described earlier).
), the S/N is improved by dropping high frequency components, and L
After removing unnecessary high-frequency components associated with FM demodulation in the PFII, the signal is led to the time axis expansion circuit 12.

In the time axis expansion circuit 12, the time axis compression circuit 51 at the time of recording
The reverse processing is performed to obtain a signal based on the original time axis, but prior to that, the dropout compensation described above is performed. That is, in the time axis expansion circuit 12, when a dropout is detected at the stage of storing the reproduced signal in the internal memory, - instead of the reproduced signal at that time, -
The signal from before the water cycle is memorized again.

The output of the time axis expansion circuit 12 is passed through a nonlinear de-emphasis circuit 13 and further subjected to a noise reduction operation in a noise clipping circuit 14. As the noise clipping circuit 14, well-known circuits can be used, such as a base clipping circuit that suppresses high-frequency and low-level components, and a line noise canceling circuit that utilizes correlation between lines using a -horizontal period delay line. The output of the noise clipping circuit 14 is outputted to the outside from an output terminal 15A, and is also provided to the adder 22 and the sync separation circuit 17.

In the previous LPFlB, a low-pass conversion chromaticity signal is extracted.

In the time axis expansion circuit 19, the time axis compression circuit 60 at the time of recording
Perform the inverse processing to create a signal based on the original time axis. The chromaticity signal reproduction processing circuit 20 (operation opposite to 58 in FIG. 2) generates a subcarrier similar to the broadcasting standard based on the synchronization pulse from the synchronization separation circuit 17 and the polarity of the switching pulse described above. Return to quadrature two-phase modulation signal. After that, the comb-shaped filter 21 removes interference components from adjacent tracks, and the signal is outputted to the outside via the output terminal 15B, and is also provided to the adder 22 at the same time. The output of the adder 22 is a composite signal, and is output from the output terminal 23 to the outside.

Further, the BPF 24 extracts the audio FM modulated signal, and the FMAGC circuit 25 makes the amplitude constant. and,
Dropouts are detected by the dropout detection circuit 31, demodulated by the FM demodulator 26, and unnecessary components are removed by the LPF 27.

In the time axis expansion circuit 28, the time axis compression circuit 65 at the time of recording
The inverse processing is performed to obtain a signal based on the original time axis, but prior to that, dropout compensation is performed.

After that, the S/N is improved by the noise reduction circuit 29 (reverse characteristic of 63 in FIG. 2), and then outputted from the output terminal 30 to the outside.

The above is the operation during normal playback. Next, operations during special playback such as field stay and high-speed search will be explained.

First, when using Field Stall, do the following:

Immediately after the user issues a stay command, the magnetic tape 1
The level comparator 5 stops running and changes the level (polarity) of the switching pulse output according to the comparison result.
Fixed to either level or Lo-level. That way you can achieve field stay.

Note that, similar to the above, methods of determining from the frequency of the pilot signal or holding the level when the command is issued may be considered, but the method described above is more reliable.

In addition, some conventional VTRs have different track widths between the +azimuth angle video head and the one azimuth angle video head. If the trunk is traced, adjacent recording tracks will also be traced, so the reproduced signal will contain noise.
Since the trunk widths of A and video head 2B with one azimuth angle are almost the same, as a field stale, even if a recording track is traced with either video head, the adjacent recording track will not be traced. It does not contain any noise. Therefore, any video head can be used depending on the time, and any field can be selected.

Furthermore, as mentioned above, in the previously proposed example, in the case of field still, the video head used is switched for each field, so flicker occurs in the image due to the difference in the output level 1 frequency characteristics of each video head. In this embodiment, in the case of field still mode, only one video head is used, so the output level of the video head.

No frizz will occur in the image due to differences in frequency characteristics.

Also, when performing a high-speed search, do the following:

After the user issues a high-speed search command, the magnetic tape is immediately run at high speed, and the level comparator 5 detects the video head 2.
It is determined which output is higher among A and 2B, and based on the comparison result, a switching pulse is generated so that the reproduced output with the higher level is always selected by the switch 6. Therefore, switching of the switch 6 is performed many times during one field. In this way, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced can always be selected, so that a high-speed search image without noise bands on the screen can be obtained.

Furthermore, as mentioned above, some conventional VTRs have different track widths between the 10-azimuth angle video head and the -azimuth angle video head. switching of the switch (i.e.
Vertical segments that appear on the screen due to video head switching (border line between the portion played by video head 2A and the portion played by video head 2B of the high-speed search image displayed on screen) (referring to several lines appearing horizontally on the screen) are irregularly spaced, resulting in an image that looks strange. Since the track widths are almost the same for the video head 2B with the azimuth angle of ,Therefore, there is also the effect that the image becomes easier to view with less sense of strangeness.

Also, during recording, in the time axis compression circuits 51, 60° 65, signals are attached every other field at intervals A (third
(Figure), so if you play back as is during high-speed search, the part played by video head 2A and the part played by video head 2B of the high-speed search image that appears on the screen will be different. This results in a shift in the vertical direction, making it impossible to obtain a normal high-speed search image. However, in this embodiment, the time axis expansion circuit 12, 19, 28 performs the reverse processing of the time axis compression circuits 51, 60, 65, In other words, since the delay is canceled, the portion played by the video head 2A and the portion played by the video head 2B do not deviate in the vertical direction, and a normal high-speed search image can be obtained. .

In addition, the time axis expansion circuits 51, 60.65 further include H
When performing a high-speed search for unaligned recorded patterns,
It may also have a skew compensation effect.

(Effects of the Invention) As described above, according to the present invention, in a VTR using a small rotating head drum, normal playback operation and special playback operation can be performed by generated switching pulses.

Moreover, at startup during normal playback, the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced is selected, and then the trunking servo is applied, which shortens the lock-in time of the tracking servo. I can do it. Furthermore, during field-stall playback in special playback, only one video head is used, so flicker does not occur in the image due to differences in the output level 7 frequency characteristics of the video heads. Furthermore, during high-speed search playback during special playback,
Since the output of the video head whose azimuth angle is equal to the azimuth angle of the recording track being traced is always selected,
There is no noise hand in the image, and since the time axis expansion means cancels the delay caused by the time axis compression means, the images are played back by two video heads on the screen. It is possible to obtain a normal high-speed search image without the vertically shifted portion.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a reproducing circuit of a VTR having a switching pulse generating circuit as an embodiment of the present invention;
FIG. 2 is a block diagram showing a recording circuit of a VTR having a switching pulse generation circuit as an embodiment of the present invention, and FIG. 3 shows a rotating head drum having a video slot shown in FIGS. The plan view shown in FIG. 4 is a timing chart showing the timing of input and output signals of the time axis compression circuit in FIG. 2. Explanation of symbols 4...Tack pulse generator, 5...Level comparator,
6.70...Switch, 12,19.28...Time axis expansion circuit, 51.60.65...Time axis compression circuit,
71... Frequency dividing circuit. Agent Patent Attorney Akio Namiki

Claims (1)

[Claims] 1. A magnetic tape is wound around the outer circumferential surface over a predetermined angle smaller than 360 degrees, and the magnetic tape is wound around the rotation axis at a rate of one rotation in a period corresponding to one field of a video signal. The rotating head drums have different azimuth angles of head gaps, and are attached to the outer periphery of the rotating head drums so as to be close to each other within a predetermined distance and at approximately the same position in the direction of the rotation axis, The rotary head scans the magnetic tape by rotating with the rotation of the drum, records input signals on the magnetic tape during recording, and records signals recorded on the magnetic tape during playback. A pair of video heads that reproduce and output; and a pair of video heads that input a video signal and an audio signal during recording, and also input a switching pulse, and convert the video signal and audio signal into one of the video signals according to the polarity of the switching pulse.
a time-base compression means for compressing the time-base in units of fields and delaying and outputting every other field of the video signal; and at the time of recording, inputting the output signal from the time-base compressing means and inputting the switching pulse; a first switch that selects one of the pair of video heads according to the polarity of the switching pulse and inputs the output signal from the time axis compression means to the selected video head;
During playback, the output signals from the pair of video heads are input, and the switching pulse is input, one of the video heads is selected according to the polarity of the switching pulse, and the output signal from the selected video head is input. a second switch that outputs an output signal; and during playback, inputs the output signal from the second switch, inputs the switching pulse, and outputs the signal from the second switch according to the polarity of the switching pulse; a time axis expansion means for time axis expansion of the output signal of the video signal in units of one field of the video signal, and a time axis expansion means for outputting the video signal and the audio signal by canceling the delay, and the switching A switching pulse generation circuit that generates a pulse and inputs it to the time axis compression means and the first switch during recording, and inputs it to the second switch and the time axis expansion means during reproduction, A tack pulse indicating the rotational phase of the drum is frequency-divided to produce a pulse whose polarity is reversed during each rotation of the rotary head drum during a period when the pair of video heads are not scanning the magnetic tape. generated as the switching pulse, and at the time of start-up during playback, compares the levels of output signals from the pair of video heads and causes the second switch to select the video head with a higher output signal level. A switching pulse generation circuit characterized in that a pulse having such a polarity is generated as the switching pulse. 2. In the switching pulse generation circuit according to claim 1, during field still playback, the levels of the output signals from the pair of video heads are compared, and the switching pulse generation circuit selects the video whose output signal level is higher. A pulse having a fixed polarity that causes the second switch to select the head is generated as the switching pulse, and during the reproduction, during high-speed search reproduction, the level of the output signal from the pair of video heads is controlled. The switching pulse generating circuit is characterized in that a pulse whose polarity is inverted is generated as the switching pulse so that the second switch always selects the video head whose output signal level is higher than that of the other.