JPH0362076B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus (hereinafter referred to as TV signal) capable of recording and reproducing character signals superimposed on the vertical blanking period of a television signal (hereinafter referred to as TV signal).
(abbreviated as VTR).

There are two ways to use a VTR: to record and play back TV signals, and to record and play back images using an imaging device. In addition to recording and reproducing TV signals, there is a new broadcasting service called "Teletext" by Murasaki, Journal of the Institute of Electronics and Communication Engineers VOL63, No. 1, P38.
It is thought that there will be a growing need to simultaneously record the text signals of teletext broadcasting described in 2012, and to use interpolated programs related to TV images. To do this, it is necessary to record and reproduce character signals on a VTR.

Figure 1 shows a block diagram of a conventional VTR. In this figure, 1 is the TV signal input terminal, and 2 is the input terminal for the TV signal.
3 is an LPF circuit that extracts the luminance signal from the TV signal, 3 is a BPF circuit that extracts the color signal, 4 is an FM modulation circuit,
5 is a low frequency conversion circuit that converts the color signal to a low frequency; 6
is an HPF circuit to eliminate the influence on color signals, 7
is an LPF circuit to eliminate the influence on the luminance signal,
8 is a recording/playback head system, 9 is an amplifier circuit, 10 is an HPF circuit that separates a luminance signal from the signal obtained from the playback head system, and 11 is an LPF that separates a color signal.
12 is an FM demodulation circuit, 13 is a high frequency conversion circuit that converts the reproduced color signal into a high frequency, 14 is an LPF circuit that removes the carrier of the luminance signal, 15 is a BPF circuit that extracts only the color signal, and 16 is an output terminal for the reproduced TV signal. It is. The case where a video signal is recorded and played back in such a VTR will be explained. First, during recording, the video signal from input terminal 1 is LPF
The circuit 2 and the BPF circuit 3 separate the signal into a luminance signal and a color signal with a carrier wave of 3.58MHz. The luminance signal separated in this way is sent to the FM modulation circuit 4.
The signal is FM modulated, and the HPF circuit 6 removes low frequency components that affect the color signal.

On the other hand, the 3.58MHz carrier wave of the color signal is converted to 629KHz by the low frequency conversion circuit 5, and the high frequency component that affects the luminance signal is removed by the LPF circuit 7.
The signal is added to the luminance signal and recorded by the recording head system 8. Next, during playback, the video signal recorded on the recording medium is taken out by the playback head system 8, amplified by the amplifier circuit 9, and then passed to the HPF circuit 10.
is separated from the luminance signal, and 629K is processed by LPF circuit 11.
Color signals with Hz as a carrier wave are separated. Since the luminance signal obtained by the HPF circuit 10 is FM modulated, it is demodulated by the FM demodulation circuit 12, and the carrier wave leakage caused by the FM demodulation of about 4 MHz is removed by the LPF circuit 14 to obtain the luminance signal. Further, the color signal obtained by the LPF circuit 11 is converted into a signal having a carrier wave of 3.58 MHz by the high frequency conversion circuit 13, and the color signal is obtained by the BPF circuit 15 having a pass band centered at 3.58 MHz, and the luminance signal is In addition to the video signal, the video signal can be reproduced.

However, in such a VTR, since a filter is inserted in the LPF circuit 2 to extract the luminance signal, the recording band of the VTR becomes a frequency band of about 2 MHz as shown in FIG. On the other hand, the signal spectrum of the character signal is as shown in Figure 3.
It exists up to 4.5MHz with a cutting frequency of 2.86MHz. Therefore, when trying to record and playback text signals on a VTR, conventional VTRs have a narrow recording band, so text signals cannot be recorded.Therefore, if you want to record and play back text broadcasts related to TV programs on a VTR, you cannot record text signals. There was a problem that user requests could not be satisfied.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a VTR that can record and reproduce character signals.

In order to achieve the above object, the present invention
By disabling the LPF circuit used in VTRs only during the period when character signals are superimposed,
This allows character signals to be recorded and played back without affecting the recording and playback of other TV signals.

An embodiment of the present invention will be described below with reference to FIG. In Fig. 4, 1 to 16 are the same as those in the block diagram of Fig. 1, and 17 is
Switch circuit 18 that disables LPF circuit 2 is
19 is a switch circuit that disables the HPF circuit 6; 19 is a switch circuit that disconnects the recording color signal processing circuit; 2;
0 is a switch circuit that disables the HPF circuit 10,
21 is a switch circuit that disconnects the reproduction color signal processing circuit, 22 is a recording system synchronization separation circuit, 23 is a recording system character signal superimposition position detection circuit that detects the position where the character signal is superimposed on the TV signal, and 24 is a reproduction system synchronization circuit. separation circuit; 25 is a playback character signal superimposition position detection circuit; 26 is a color subcarrier generation circuit that maintains a color subcarrier synchronized with the color burst signal in the video period during playback for a vertical blanking period; 27 is a vertical blanking line; This is a switch circuit for adding the above signal as a color burst signal during the period. First, the recording system will be explained. Recording system character signal superimposition position detection circuit 2
As shown in FIG. 5b, the output signal from 3 is output in correspondence with the position where the character signal is superimposed. Also, the output signal is the switch circuit 1
It works as a control signal for signals 7, 18, and 19. First, during the normal TV signal period when no character signal is superimposed, the output signal of the recording system character signal superimposition position detection circuit 23 is low, and the switch circuits 17 and 18 are turned off and the switch circuit 19 is turned on to block the conventional VTR. With the same connection as in the configuration, you can record TV signals. Next, during the period in which the character signal is superimposed, the output signal of the recording system character signal superimposition position detection circuit 23 becomes high, and the switch circuits 17 and 18
is turned on and 19 is turned off. switch circuit 17
By turning on, LPF circuit 2 is disabled,
The recording band of a VTR is sufficient to record character signals. Further, by turning off the switch circuit 19 and disconnecting the color signal processing circuit, it is possible to eliminate the influence of the 629 KHz low frequency color signal on the character signal. Further, the HPF circuit 6 for eliminating the influence on the color signal is unnecessary, and considering the influence on the character signal, the switch circuit 18 is turned on to nullify the effect of the HPF circuit 6. With the above circuit configuration, character signals can be recorded on a VTR, and
These operations are performed during the period when the character signal is superimposed.
In other words, since this is a vertical retrace period, it does not affect the recording of normal TV signals in any way.

Next, the reproduction system will be explained. Similar to the recording system, the output signal from the reproduction system character signal superimposition position detection circuit 25 is output only during the period when the character signal is superimposed, as shown in FIG. 5b. Further, the output signal serves as a control signal for the switch circuits 20 and 21. First, during a period when no character signal is superimposed, the output signal of the reproduction character signal superimposition position detection circuit 25 is low, and the switch circuit 20 is turned off.
1 is turned on and the video is played using a conventional VTR playback system.
Next, during the period in which the character signal is superimposed, the output signal of the reproduction character signal superimposition position detection circuit 25 becomes high, turning on the switch circuit 20 and turning off the switch circuit 21. By turning on the switch circuit 20, the effect of the HPF circuit 10 is nullified and the low frequency components of the character signal can be reproduced as they are. Further, by turning off the switch circuit 21, the processing circuit for unrecorded color signals is disconnected, thereby preventing unnecessary signals from being mixed into character signals and being reproduced. In addition,
The LPF circuit 14 is a filter for removing the carrier of the luminance signal, and has a cutting frequency of about 4 MHz, so there is no particular problem with the reproduction of character signals, so the LPF circuit 14 is always turned on. . With the above circuit configuration, recorded character signals can be reproduced, and since these operations are performed during the period in which character signals are superimposed, that is, during the vertical retrace period, normal operations cannot be performed.
It does not affect the playback of TV signals in any way. However, during the superimposition period of the character signal, there is no color burst signal because the color signal processing circuit is separated, and therefore, there is a problem that color synchronization cannot be achieved when the video signal is reproduced. As a means to solve this problem, a color subcarrier generation circuit 26 is provided that maintains a color subcarrier synchronized with a color burst signal in the video period during playback for only a vertical blanking period, and a switch circuit 27 is turned on during the vertical blanking period. Then, the signal from the color subcarrier generation circuit 26 is added as a color burst signal to the vertical retrace period of the reproduced signal.

As described above, according to the present invention, character signals can be
Since it can be recorded and played back on a VTR, teletext services can be received at any time, and it can be applied not only to personal VTRs but also to commercial VTRs.
Since a soft copy of teletext can be made, it can be saved as an information file, which has the effect of widening the scope of use by users.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional VTR, Figure 2 is a block diagram of a conventional VTR.
A frequency characteristic diagram showing the recording band of a VTR, Figure 3 is a frequency characteristic diagram showing the spectral distribution of character signals,
FIG. 4 is a block diagram showing an embodiment of the VTR of the present invention, and FIG. 5 is a waveform diagram showing the superimposition positions of character signals. 17-21... Switch circuit, 23... Recording system character signal superimposition position detection circuit, 25... Reproduction system character signal superimposition position detection circuit, 26... Color subcarrier generation circuit.

Claims (1)

[Claims] 1. When recording and reproducing a television signal in a magnetic recording and reproducing device, the frequency of the brightness signal processing circuit of the magnetic recording and reproducing device is changed only during the vertical retrace period of the television signal during recording and at least during playback. A character signal VTR recording and reproducing device which has a wide band and is characterized in that a color signal is not mixed with a luminance signal during recording and reproduction.