JPS63181149A - Video signal recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the picture quality of a reproduced picture by detecting the overlapped component of the reproduced signal outputted from a video head, and filtering the overlapped component after FM modulation based on the detection thereby preventing beat disturbance due to crosstalk. CONSTITUTION:The overlapped component of the reproducing signal outputted from head amplifiers 18, 19 is detected by a 2nd switcher 25 and the output of the 2nd switcher 25 is detected by a detection circuit 26. Based on the output signal of the detection circuit 26, a switch 27 and a frequency band control circuit 24 are driven to attenuate the signal gain for the overlapped component of the reproduced video signal. Thus, the frequency limit circuit 24 is driven corresponding to the fluctuation of the overlapped component due to the meandering of the magnetic tape or the deviation of the mount position of the video head, crosstalk is reduced and the beat disturbance is suppressed, and the presence of a defect is easily confirmed in case of head wear of defective taper running and the picture quality of the reproduced picture and the reliability of product are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video signal recording and reproducing device that uses a rotating head system and is equipped with a loading mechanism that wraps a magnetic tape around a cylinder over 180 degrees and brings it into contact with a video head. be.

2. Description of the Related Art Conventionally, video signal recording and reproducing devices, particularly video tape recorders (hereinafter referred to as VTRs), have been using DC current to generate 4. sMHz
In order to record and reproduce video signals with a wide frequency band of up to 100 MHz, it was necessary to increase the relative speed between the magnetic tape and the video head to prevent the recording wavelength from becoming too short. For this reason, a rotating head system is adopted, in which a cylinder with two video heads attached at 180 degree intervals is rotated 30 times per second, and a magnetic tape is wound over 180 degrees around the circumference of the cylinder, so that the rotation of the video head and Run the magnetic tape in the same direction for one field of the video signal! ! - Recording was done on magnetic tape as one recording track.

FIG. 6 shows the positional relationship of video signals recorded on recording tracks. In other words, one recording track records signals for one field of the video signal and an overlap portion (for example, 6H and H are horizontal scanning periods) due to the connection between the previous and next recording tracks. When reproducing , the first video head first starts tracing from the mermaid in the first recording track a, reproduces one field of video signals, and eventually reaches the switching position point B corresponding to the bottom of the screen. At that time, the second video head has already traced the switching position C point of the second recording track b, so the playback output is electrically switched from the first video head to the second video head and the continuous I was getting a playback video signal. However, no matter how much electrical switching is done, two video heads are actually tracing the same screen at the switching position, so in the overlapped area, if switching to the first video head, the second video head On the other hand, if the trace part of the video head is switched to the second video head, the trace part of the first video head will leak into the video head.
As shown in FIG. 7, beat interference due to crosstalk occurs at the switching position, causing problems in image quality.

For this reason, conventionally, a so-called head switching pulse, which is a pulse synchronized with the rotation of the video head that switches the outputs of two video heads, is used to switch the outputs of the two video heads.
The H period pulse was taken out, and the frequency band of the demodulated video signal was limited only during that period, thereby suppressing beat interference due to crosstalk.

The conventional video signal recording and reproducing apparatus described above will be described below with reference to the drawings and FIG. WJ.

FIG. 8 is a block diagram of a reproduction system of a conventional video signal recording and reproduction apparatus. 1 is a video head, and 2 is a B head. Human head 1 is connected to head amplifier 3, and B head 2 is connected to head amplifier 4. Reference numeral 5 denotes a switcher which outputs signals 2 from the two video heads, human head 1 and B head 2, in synchronization with the head switching pulse.
The two reproduced signals are made into one continuous reproduced signal. 6 is an FM demodulator, 7 is a low-pass filter (hereinafter LP
8 is an output amplifier. 9 is a frequency band limiting circuit, and this frequency band limiting circuit 9 is connected to the LPF 7.
It consists of a low-pass filter with a smaller resonant frequency. 1o is a switch. 11 to 14 are monostable multivibrators (hereinafter referred to as MM);
1 and 13 have a time constant of t-T-3H (T is a half period of the head switching pulse, H is a horizontal scanning period), and 12 and 14 have a time constant of 6H. 1
6 is an adder circuit.

The operation of the conventional video signal recording and reproducing apparatus configured as described above will be described below. FIG. 9 shows a waveform at one point from point a in FIG.

First, a reproduction signal is taken out from a video track on a magnetic tape by the video head 1 and the B head 2, and each reproduction signal is amplified by the head amplifier 3.4 (FIGS. 9&, b).

Next, the switcher 5 outputs two playback signals from the head amplifiers 3 and 4, respectively (see FIG. 9a).

The overlap in b) is removed and the reproduction signal is switched to one continuous reproduction signal as shown in C of FIG. Thereafter, the reproduced signal output from the switcher 5 is demodulated from the FM signal to a video signal by the CiFM demodulator 6. The MM11 operates based on the head switching pulse (Fig. 9 d) at the falling edge of this head switching pulse d, and T-3
A signal e with an H pulse period is output, and the MM 12 outputs a signal f (FIG. 8), which is a 6H pulse signal, at the falling edge of the signal e. Similarly, the MM13
operates at the rising edge of the head switching pulse, and T
Based on this signal g, the MM14 outputs a signal h (FIG. 9), which is a 6H pulse, at the falling edge of signal g based on this signal g. . The output signals of the MM12.14, the signal f and the signal , are input to an adder 16, and from this adder circuit 16,
6H equivalent to the overlap of the reproduced signals a and b
A signal 1 consisting of a pulse signal is output.

Due to this signal i, the switch 10 is closed only during the overlap period (6H), and the frequency band limiting circuit 9 is operated. This frequency band limiting circuit 9 lowers the gain characteristic of the 6H pulse signal equivalent to the overlap of the reproduced signal K and b, thereby reducing crosstalk and suppressing beat interference. This crosstalk-reduced video signal is input to the LPF 7, the carrier component is removed, and the signal is output from the output amplifier 8.

Problems to be Solved by the Invention However, in the above conventional configuration, the 6H pulse signal 12 equivalent to the overlap portion is extracted from the head switching pulse, and the demodulated video signal is attenuated only during the 6H pulse period. As shown in FIG. 10, for the pulse signal i set to 6H, the head amplifiers 3 and 4
If the overlap between the reproduced signals a and b output from the oscillator is the same or smaller, the crosstalk can be effectively eliminated.

However, the degree of overlap is not constant, and the mounting of the video head varies depending on the position, etc., and the overlap of reproduced signals a and b is larger than the pulse width of signal i, as shown in Figure 11. When this becomes large, it is effective for the part A in FIG. 11, but it is not effective for the mouth, no, and parts, and beat interference occurs due to crosstalk, causing problems in image quality.

In conventional video recording and reproducing devices, if the video head wears out or if a strong impact is applied to the device and the running position of the magnetic tape goes out of order, the level near the switching position of the output of the switcher 6 drops, causing problems in recording and reproducing. There was a problem in that normal signals could no longer be received or passed, and image quality deteriorated.

In view of the above problems, the present invention prevents beat interference due to crosstalk by detecting the overlap portion of the playback signal output from the video head and filtering the overlap portion after FM demodulation based on this detection. However, it is an object of the present invention to provide a video signal recording and reproducing device that improves the quality of reproduced images.

Means for Solving the Problems In order to achieve the above object, the video signal recording and reproducing apparatus of the present invention includes a frequency band limiting circuit that attenuates the video signal after FM demodulation, and a frequency band limiting circuit that amplifies the output signals of a plurality of video heads. The head amplifier includes a head amplifier, a switcher that detects and outputs the overlap between the output signals of these head amplifiers, and a switch that changes the overlap between the output signals of the switcher.

Operation With the above configuration, the frequency band limiting circuit that attenuates the video signal after FM demodulation is driven during the overlap period in accordance with the overlap amount of the output signal of the head amplifier which varies depending on the mounting position of the video head, and This is to reduce the crosstalk that occurs in the system and prevent beat interference.

Embodiment Hereinafter, a rotating two-head type video signal recording and reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a video signal recording and reproducing apparatus according to an embodiment of the present invention. In the figure, 16 is a human head, and 17 is a B head, and these human head 16 and B head 1A are connected to the input sides of head amplifiers 18 and 19, respectively. The playback signals outputted through the head amplifiers 18, 19'ii, respectively, are input to a first switcher 20, and this first switcher 20 is synchronized with the head amplifiers 18, 19'ii. While removing the overramp portion of the reproduced signal output from 19,
This is one continuous reproduction signal.

21 is an FM demodulator, 22 is a low-pass filter (hereinafter LP
23 is an output amplifier.

Reference numeral 24 denotes a frequency band limiting circuit, which is composed of a low-pass filter having a resonance frequency smaller than that of the LPF 22 and a low gain characteristic, and is connected to the output side of the FM demodulator 21. Reference numeral 25 denotes a second switcher, which outputs a signal corresponding to the overlap of the reproduced signals respectively output from the head amplifiers 18 and 19. The output side of the second switcher 25 is connected to the input side of a detection circuit 26. This detection circuit 26 detects an overlap portion from the output signal of the second switcher 25. 27 is a switch, which connects the detection circuit 26
It is turned on based on the output signal of , and controls the drive of the frequency band limiting circuit 24 . 28 is a smoothing circuit, 29 is a voltage comparator, and 30 is a display.

The operation of the above configuration will be explained below.

FIG. 2 is a waveform diagram showing waveforms at each point from point a to point 0 in FIG.

A signal is extracted from the recording track on the magnetic tape by the head 16 and the B head 17, and the signal is sent to the head amplifier 1.
8.19, the signal reproduction signals read by the human head 16 and the B head 17 are amplified. This reproduction signal is the second
It will look like Figures a and b.

Next, the first switcher 20 switches between the A head 16 and the B head.
In synchronization with a head switching pulse synchronized with the rotation of the head 17, the overlap between the reproduced signals a and b is removed and converted into continuous reproduced signals as shown in FIG. 2C. The reproduction signal output from the first switcher 20 is
The 7M demodulator 21 demodulates the FM signal into a video signal.

The second switcher 25 connects the Herad amplifier 18.
The overlapping signal outputs of the reproduced signals a and b outputted from 19 are taken out alternately, and an output signal waveform as shown in FIG. 2d is obtained.

This signal d is applied to the detection circuit 26 to produce a reproduced signal a.

The signal waveform used to detect the overlap period b is the waveform shown in FIG.
The switch 27 is turned on only during the overlap period,
Frequency band limiting circuit 24Q operation is poor. The frequency characteristic of this frequency band limiting circuit 24 has the characteristic shown in FIG. 3B, and L
The gain attenuation is greater than the frequency characteristics of the PF22 (Figure 3). The video signal which has been attenuated by the overlap between the reproduced signals a and b in the frequency band limiting circuit 24 has its noise component removed by the LPF 22, is amplified by the output amplifier 23, and is output.

The output signal of the detection circuit 26 is smoothed by the smoothing circuit 28 and then input to the inverting input terminal of the voltage comparator 290.
It is compared with a reference voltage input to the non-inverting input terminal of the voltage comparator 29. When the voltage of the output signal f of the smoothing circuit 28 is smaller than the voltage of the reference voltage signal g, the display 3
o is driven.

The signal waveforms at points c, d*e, f, and h in FIG. 1 are shown in FIG. 4 and FIG. , the operation of the display 30 will be explained below.

Figure 4 shows the signal waveforms at points c, d, e, f, and h in Figure 1 when the above-mentioned abnormal condition has not occurred. The voltage Hf of the signal is detected, and the voltage comparator 29 at the first measuring point
Since the output becomes an L level signal, the display 30 does not light up.

On the other hand, FIG. 5 shows signal waveforms from point a to point h in FIG. 1 when the above-mentioned abnormal condition occurs.

When the video head wears out, the signal level decreases at the switching position of the head, and at point f, a video signal with a level Σf smaller than the reference voltage E is detected, and the voltage comparator at point h The output of 29 becomes an H level signal, and the display 30 is turned on.

As described above, according to this embodiment, the head amplifier 18.1
The second switcher 26 detects the overlap portion of the reproduced signal output from the second switcher 26.
5 is detected by the detection circuit 26, and the switching device 27 and the frequency band limiting circuit 24 are driven based on the output signal of the detection circuit 2e, so that the signal gain of the overlap portion of the reproduced video signal is attenuated. In addition, the frequency limiting circuit 24 is installed in response to fluctuations in overlap due to deviations in the mounting position of the video head and the feeding of the magnetic tape.
is driven, reducing crosstalk and suppressing beat interference.

Also, based on the output signal of the detection circuit 2e, the display 30
With the i-driven configuration, when the video head is worn out or the tape is running poorly, the indicator 3° lights up, making it easy to check whether there is an abnormality as described above. As a result, the quality of the reproduced image of the video signal recording and reproducing device and the product reliability are improved.

In this embodiment, the display device 3o may be any device such as a light emitting diode (I4D), a lamp, a meter, etc., as long as it indicates an abnormality.

Effects of the Invention According to the present invention, a pulse of, for example, 6H, which is equivalent to the overlap portion, is generated from the conventional head switching pulse, and crosstalk is reduced only for a certain period of time.
In the configuration that suppresses beat interference, it has no effect on variations in the mounting position of the video head, but it detects the overlap of the video signal output from the head amplifier and uses a frequency band limiting circuit for the detected period. Because of this configuration, the overlapping video signal is attenuated regardless of variations in the position of the video head, reducing crosstalk and beat interference, improving the quality of the reproduced image. It is something.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a reproduction system of a video signal recording and reproducing device according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram of the main part of the video signal recording and reproducing device, and FIG. 3 is a diagram of the video signal recording and reproducing device. Characteristic diagram of the device's low-pass filter and frequency band limiting circuit, 4th
The figure is a signal waveform diagram of the main part when there is no fluctuation due to the overramp of the video signal in the same video signal recording and reproducing device.
The figure is a signal waveform diagram of the main part when a fluctuation corresponding to the overlap of the video signal occurs in the same video signal recording and reproducing apparatus, FIG. 6 is a diagram explaining the method of recording the video signal on the magnetic tape, and FIG. Figure 8 is a block diagram of the reproduction system of a conventional video signal recording and reproducing device, and Figure 9 is a signal waveform diagram of the main parts of the same video signal recording and reproducing device. Fig. 10 is a signal waveform diagram of the main part when there is no variation in the overlap portion of the reproduced signal in the same video signal recording and reproducing device, and Fig. 11 is a signal waveform diagram of the main part when there is a fluctuation in the overlap amount in the same video signal recording and reproducing device. FIG. 16...Muhesodo, 17...B head, 18°19...Head amplifier, 24...
...Frequency band limiting circuit, 26...Second switcher 126...Detection circuit, 27...
・Switcher. /6---A head/7---B\-, I do 1g, /q---Head amplifier Fig. 1 24-Round control @Route 2S---Second switch 7-+rent - 27----t71 conversion (Figure 2) ” Jl!J-ml (M+z) ff14111
i h□ Ll,'0L
Jt! 3 Fig. 5 ho□ Fig. 6 Fig. 8 Fig. 9 Old O Fig. 111X1 ,/□-T,,

Claims (1)

[Claims] A frequency band limiting circuit that attenuates the video signal after FM demodulation, a head amplifier that amplifies the output signals of the plurality of video heads, and a switcher that detects and outputs the overlap of the output signals of these head amplifiers. A video signal recording and reproducing device comprising: a detection circuit that detects the overlap portion of the output signal of the switcher; and a switch that drives the frequency band limiting circuit when the detection circuit detects the overlap portion.