JPH0141064B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video tape recorder capable of recording and reproducing teletext signals.

Conventional configurations and their problems There are various recording and playback methods for home video tape recorders (hereinafter referred to as VTRs), but most of them are called carrier color signal low frequency conversion recording methods (hereinafter referred to as M methods). It is something that This method separates the composite video signal into a luminance signal (hereinafter abbreviated as Y signal) and a color signal (hereinafter abbreviated as C signal), and FM modulates the Y signal to generate a Y signal FM modulated wave (hereinafter abbreviated as FM-Y). , the C signal is frequency-converted to a low-frequency range to produce a low-frequency converted color signal (hereinafter abbreviated as C _LOW ), and these FM-Y and
C _LOW is mixed and recorded, and the reverse process is performed for playback.

In this M system, recording and reproduction of the high frequency range of the Y signal is subject to various controls. This will be explained below using FIG. FIG. 1 schematically shows a spectrum during recording and reproduction of a video signal. Y signal band
The composite video signal (Figure 1a) containing 4.2MHz and C signal carrier wave 3.58MHz is filtered through a low-pass filter (hereinafter referred to as
(abbreviated as LPF) and bandpass filter (hereinafter referred to as BPF)
) is separated into a Y signal (FIG. 1b) and a C signal (FIG. 1c). At this time, the band of the Y signal is controlled from y _1a to y _1b , as shown by the arrow. Next, the Y signal is FM-modulated to become FM-Y (Fig. 1 d), and the C signal is low-frequency converted to C _LOW (Fig. 1 e).
and mix these, but at this time FM
-In order to separate Y and C _LOW in terms of frequency, FM
-Y is a high pass filter (hereinafter abbreviated as HPF),
C _LOW is mixed after passing through LPF. FM-Y
It can be seen that the band of the Y signal is again limited to y _1f when passing through the HPF. The recording signal modulated in this way (Fig. 1 f) is recorded on the magnetic tape and later reproduced (Fig. 1 g), but the band y _1g of the reproduced Y signal has only a maximum of y _1f. it is obvious. In other words, at the time of input composite video signal, Y band
When something that is y _1a hot is recorded and played back, it is limited to a maximum of y _1g . With current home VTR capabilities, the recording and playback bandwidth is approximately 2MHz. Also,
By using a comb filter when separating the Y signal and C signal, the band of the separated Y signal (first
(corresponding to y _1b in figure b) can be expanded, but
The band is limited by the HPF after FM modulation, and currently the recording and playback band is limited to 2.5MHz.

On the other hand, teletext systems are being put into practical use. A teletext system is a broadcasting system that separates characters or graphics, superimposes them onto the vertical retrace period of a TV broadcast video signal, broadcasts them, selectively receives them with a home receiving device, and displays them on a television receiver. be. The transmission signal format of this teletext is
Sent at 5.727272Mbit/sec. In other words, in order to record and reproduce this signal, the signal band is 2.86MHz.
will have to be ensured. In the above-mentioned home VTR, it is impossible to record and reproduce 2.86MHz, and therefore it is currently impossible to record and reproduce teletext at all.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a video tape recorder that is capable of recording and reproducing teletext signals without making any major changes to current home VTRs.

Structure of the Invention In order to achieve the above object, the present invention detects a vertical synchronization signal of a composite video signal in a VTR using a carrier color signal low frequency conversion recording method, and immediately after the vertical synchronization signal, 21 horizontal scans are performed. It is configured so that only the luminance signal is recorded or played back in the section excluding the color burst within the period, thereby extending the band of the luminance signal that can be recorded or played back in the above section, making it possible to record and playback teletext signals. It is something.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below based on the drawings. FIG. 2 schematically shows the spectrum of a signal during recording and reproduction according to the present invention, and corresponds to FIG. 1.

A is a composite video signal including a Y signal band of 4.2 MHz and a C signal of 3.58 MHz, but since there is no video signal within the vertical retrace period, there is no C signal. Furthermore, even if a color bust signal is received, it can be ignored because it is extremely limited in terms of time. In other words, it can be seen that there is no need to separate the Y signal and C signal in this section. Therefore, if FM modulation is performed by passing the LPF in Figure 2 a wider than the LPF used in Figure 1, or by passing it through the LPF, Figure 2 c
Obtain the spectrum shown in . At this time, there is no need to mix it with the C _LOW signal, so the HPF used in Figure 1
is not necessary. Therefore, the band limit of the Y signal is
It is shown as y _2c , _which is approximately
This shows that the 1MHz band will expand. The band y _2d of the signal recorded and reproduced in this way is approximately 1 MHz longer than y _1g shown in FIG. That is, for home use
It can be seen that 3MHz recording and playback is possible with a VTR, and that it is also possible to record and playback a 2.86MHz teletext signal.

Now, the section where the band of the Y signal can be widened in this way may be any place where there is no C signal. However, as shown in Figure 3, teletext signals can be transmitted at any number between scanning line numbers 10H and 21H within the vertical retrace period.
Alternatively, since it is superimposed on two scanning lines, it can be seen that it is necessary to widen the band of the Y signal in this section. Here, a ₁ and a ₃ are equivalent pulse periods, a ₂ is a vertical synchronizing pulse, a ₄ is a teletext signal area, a ₅ is a horizontal synchronizing pulse, and the upper number is the scanning line number.

An example is shown in FIG. 3b. b indicates that the Y signal band is widened for about 14 hours after the vertical synchronization pulse is detected, and when b is at a high level, it means that the Y signal band is widened.

However, in this case, the color burst is not reproduced at all, and if the auto phase control circuit (APC circuit) of the television receiver has a slow response,
A problem arises in which the hue becomes unstable at the top of the television screen. Therefore, by widening the band of the Y signal except for the color burst position as shown in FIG. 3c, the above-mentioned problem of hue instability can be solved. Figures 3d and e are enlarged views of Figures 3a and c.
Shown below.

In this way, various control signals can be considered as shown in b and c, but the point is to widen the band of the teletext signal portion, and for this purpose, it is thought to be easiest to use the vertical synchronization signal as a reference. .

Next, a block diagram of an embodiment of the present invention is shown in FIG. 4 for the recording system and FIG. 5 for the reproduction system. The conventional signal enters from input terminal 1, is separated into Y signal and C signal by LPF 2 and BPF 9, and Y signal is sent to FM modulator 4.
The signal is FM modulated and sent to mixer 6 through HPF 5. On the other hand, the C signal passes through the BPF 9, is converted to a low frequency signal by the frequency converter 10, and is further converted to a low frequency signal by the LPF 11.
is sent to mixer 6 through FM-Y and mixer 6.
mixed in the magnetic head 8 through the recording amplifier 7.
recorded. During playback, the playback signal amplified by the head amplifier 16 is passed through the HPF 17 and LPF 23.
The FM-Y signal is separated into an FM-Y component and a _CLOW component, and the FM-Y signal is demodulated by a demodulator 18 and then sent to a mixer 21 through an LPF 19. On the other hand, the C _LOW signal is
After the LPF 23, it is converted to 3.58MHz by the frequency converter 24, and after passing through the BPF 25, it is converted to 3.58MHz by the mixer 21.
After being mixed with the signal, it is output to the terminal 22.

Now, in the present invention, it is necessary to switch each part in the conventional circuit described above. In other words, in the recording system,
Switch LPF2 to LPF3, which has a higher cutoff frequency, and pass through HPF5, and send it to mixer 6.
C It is necessary to avoid sending the _LOW signal. These switches are SW1 to SW5. Further, a control signal is generated by detecting a vertical synchronizing pulse and a horizontal synchronizing pulse by a V/H detection circuit 12 and by a control circuit 13 based on the information. Here, 14 indicates an inverter. Normally SW1, SW3, SW5 are ON,
SW2 and SW4 are OFF. SW1, SW3, and SW5 are OFF in the section where the band of the Y signal is extended.
Then, SW2 and SW4 are turned ON. Next, in the reproduction system, it is necessary to set the HPF 17 to through, switch the LPF 19 to the LPF 20 with a higher cutoff frequency, and prevent the C _LOW signal from being sent to the mixer 21. These switches are SW6 to SW10
It is. The control signal is V・H from the output of LPF19.
A detection circuit 26 detects vertical synchronization pulses and horizontal synchronization pulses, and a control circuit 27 generates signals based on the information. 28 is an inverter. Normal SW6,
SW8 and SW10 are ON, SW7 and SW9 are OFF
The opposite is true in the section where the band of the Y signal is extended.

Here, LPF2 and LPF19, or LPF3 and
LPF 20 or V/H detection circuits 12 and 26,
or control circuits 13 and 27, or inverter 1
4 and 28 may be used together.

In addition, when there is no need to record teletext signals, for example, by setting terminal 15 to LOW, it is always on.
SW1, SW3, SW5 turn on, SW2, SW
All you have to do is control it so that SW 4 is OFF, and if you set terminal 30 to LOW during playback, SW6, SW
8, SW10 turns ON, SW7, SW9 turns OFF
If you control it so that

In addition, in order to record teletext on a single magnetic tape, if there are parts recorded by extending the Y signal band and parts recorded as usual, it is necessary to extend the Y signal band. It would be extremely convenient if the recorded portion could be automatically detected. it is,
This can be achieved by detecting the level of the low-pass conversion color subcarrier. That is, input the output of the LPF 23 to the subcarrier detection circuit 29 in FIG.
The level of the subcarrier is detected, and if it is above a predetermined level, reproduction is carried out in the conventional manner, and if it is below a predetermined level, the information is sent to the control circuit 27 to appropriately switch each SW. .

Furthermore, in the present invention, the section in which the band of the Y signal is widened is determined based on the information detected by detecting the vertical synchronization signal (for example, Fig. 3 b and c).
There is no problem even if the band is expanded only during the horizontal scanning period in which the teletext signal is superimposed. Needless to say, various methods can be considered for this purpose, such as detecting the 2.86 MHz clock sent at the beginning of the teletext signal and widening the band of the horizontal scanning period in which the clock is detected.

Effects of the Invention As is clear from the above description, the present invention enables a VTR using a carrier color signal low frequency conversion recording method to record only a luminance signal in a predetermined section within the vertical retrace period of a composite video signal, or to play back a luminance signal. As a result, the band of luminance signals that can be recorded or reproduced in the above-mentioned section is extended, and it is possible to record and reproduce teletext signals.

Moreover, by setting the above-mentioned predetermined period to the period immediately after the vertical synchronization signal and excluding the color burst within 21 horizontal scanning periods, the continuity of the color signal is maintained, and the television receiver with slow APC response can be However, it is possible to prevent hue shift from occurring.

Furthermore, if the level of the low frequency conversion color subcarrier of the reproduced signal is detected in the interval excluding the color burst within the vertical retrace period, this detection signal can be used to record as usual or to It is possible to know whether only the Y signal has been recorded by extending the Y signal, and it is also possible to automatically switch the band. Therefore, if a single magnetic tape contains a portion with an extended Y signal band and regular recording,
This automatic detection is highly effective.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the spectrum during conventional recording and playback, Figure 2 is a schematic diagram of the spectrum during recording and playback according to the present invention, and Figure 3 is an example of signals around the vertical synchronization signal and band switching timing. A waveform diagram showing
FIG. 4 is a block diagram of the recording system of the present invention, and FIG. 5 is a block diagram of the reproduction system of the present invention. 2, 3, 11, 19, 20, 23...LPF,
4...FM modulator, 5,17...HPF, 6,21
...Mixer, 9,25...BPF, 10,24...
...Frequency converter, 12, 26... V/H detection circuit, 13, 27... Control circuit, 14, 28... Inverter, 18... Demodulator, 29... Subcarrier detection circuit, SW1 to SW10... Switch.

Claims (1)

[Claims] 1. Separating a composite video signal into a luminance signal and a color signal,
A video tape recorder using a carrier color signal reduction conversion recording method that reduces and converts the color signal, performs FM modulation on the luminance signal, mixes the reduced conversion color signal and the FM modulated luminance signal, and records and reproduces it on a magnetic tape. Then, the vertical synchronization signal of the composite video signal is detected, and from immediately after the vertical synchronization signal, only the luminance signal is recorded or reproduced in the interval excluding the color burst within 21 horizontal scanning periods, and the luminance signal band that can be recorded or reproduced is determined. A videotape recorder designed to extend the . 2. In the recording system or playback system, the filter through which the luminance signal or FM-modulated luminance signal passes has a cutoff frequency that is different from that of the filter that passes through it outside of that interval, except for the color burst within the vertical retrace period. 2. The video tape recorder according to claim 1, wherein the video tape recorder switches to a filter or allows the signal to pass through without passing through the filter. 3. In the reproduction system, the level of the reduced conversion color subcarrier of the reproduction signal is detected in the interval excluding the color burst during the vertical retrace period, and if the level is below a predetermined level, only the luminance signal is reproduced. A videotape recorder according to scope 1.