JPS60216680A - Video tape recorder - Google Patents

Abstract

PURPOSE:To record and reproduce normally a character broadcast signal with simple constitution by changing over a filter used for a signal processing system of recording or reproduction to another filter having other characteristic at a prescribed period within the vertical blanking period of a video signal. CONSTITUTION:An LPF3 is changed over into an LPF2, an HPF7 into an HPF6 and an LPF16 into an LPF15 respectively in the recording system at a prescribed period within the vertical blanking period. An HPF22 is changed over into an HPF21, an LPF26 into an LPF25 and an LPF31 into an LPF30 and a BPF35 into a BPF34 respectively in the reproducing system. Switches 4, 8, 13, 17 are switched by a signal from a control circuit 18 and switches 23, 27 32, 33 are switched from a signal from a control circuit 37. As a result, the frequency characteristic, group delay characteristic and S/N of the recording/reproduction of a Y signal are changed at the period when a character broadcast signal in the vertical blanking period is included in comparison with those at other periods.

Description

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

Conventional Structures and Problems There are various recording and reproducing systems for home video tape recorders (hereinafter abbreviated as VTRs), but most of them are called carrier color signal low frequency conversion recording systems.

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 the low-frequency range and converted into a low-frequency converted color signal (hereinafter referred to as C
LOY (abbreviated as LOY), these FM-Y and CLOW are mixed and recorded, and reproduction is performed by performing the reverse processing.

In this method, the recording and reproduction of the high frequency range of the Y signal is subject to various restrictions. This will be explained below using FIG.

FIG. 1 schematically shows a spectrum during recording and reproduction of a video signal. A composite video signal containing a Y signal band of 4.2 MHz and a C signal carrier wave of 8.58 MHz (Figure 1 (
a)) is a Y signal (
The signal is separated into a C signal (FIG. 1(C)) and a C signal (FIG. 1(C)). At this time, the band of the Y signal is from yla to ¥ as shown by the arrow.
He was limited to being deaf. Next, the Y signal is FM-modulated into FM-Y (Figure 1 (b)), the C signal is low frequency converted to become CLOW (Figure 1 (e)), and these are mixed. In order to separate FM-Y and CLOW in terms of frequency, FM-Y is equipped with a bypass filter (hereinafter referred to as HPF).
), CLOW is mixed after passing through an LPF.

When FM-Y passes through HPF, the band of Y signal becomes '11' again.
It can be seen that it is limited to f.

The recording signal modulated in this way (Figure 1 (f)) is recorded on the magnetic tape and later reproduced (Figure 1 (g)).
However, the band y1g i of the reproduced Y signal is set to the maximum 'js
It is clear that there is no f-shi. In other words, the Y band y1a at the time of input composite video signal is limited to a maximum of y1g when recorded and reproduced. With the current performance of home VTRs, the recording and reproducing band is approximately 2 MHz. Furthermore, by using a comb filter when separating the Y signal and C signal, it is possible to widen the band of the Y signal after separation (corresponding to ylb in FIG. 1(b)).
Bandwidth is limited by HPF after FM modulation, and current home V
In the frequency allocation of TR, the recording and playback band is 2.5
At present, MHz was barely enough.

On the other hand, it is being considered to obtain a broadband reproduced image by using an alloy tape such as a metal tape as a recording medium. That is, by shifting the FM-Y carrier frequency to a higher frequency range, it is possible to widen the luminance signal recording and reproducing band.

This will be explained below using FIG. 2. FIG. 2 is a schematic diagram of a signal spectrum similar to FIG. 1, showing only the luminance signal system. The carrier frequency of FM-Y in Fig. 2(d) is 4.4 h to 5.4 MHz, and the first
Figure (8.4MHz ~ 4.4MHz of Φ compared to K
You can see that there is a shift in the Hz high range. In other words, Y signal W
The yzf band can be wider in I MHz than the Yxf band. In other words, the reproduced Y signal band Yzg is the conventional band y1g.
It is possible to widen the IMHz band compared to
This means that the signal can be reproduced somehow.

On the other hand, teletext systems are being put into practical use.

Teletext systems break down characters or figures and convert them into T
This is a broadcasting system in which the video signal of V broadcasting is broadcast superimposed on the vertical retrace period, selectively received by a home receiving device, and displayed on a television receiver.

The transmission signal format of this teletext is 5.727272Mb
It is sent at i t/sec. That is, in order to record and reproduce this signal, a signal band of 2.86 MHz must be secured.

With conventional home VTRs, it was completely impossible to record and reproduce 2.86 Ml(z).On the other hand, the recording and reproduction band of a high-bandwidth VTR using alloy tape was as shown in Figure 2, 3'2g. Since the frequency is about 8 MHz, it is thought that it is possible to record and reproduce a 2.86 MHz teletext signal.However, in reality, recording and reproducing is extremely difficult.The reason is that the teletext signal has very low amplitude characteristics and group delay characteristics. If it is not reproduced in a satisfactory condition, it will not be established as a signal.However, the above VT
In R, the luminance signal passes through various filters during the recording and reproducing process, so it is difficult to flatten the amplitude characteristics and group delay characteristics of 2.86■i while maintaining the desired cut-off time. there were. Furthermore, filters having desired frequency characteristics and flat l'l' delay characteristics are complicated and expensive, and their use is not appropriate for home VTRs that use many filters. Also, unnecessarily widening the Y signal band is
This is not appropriate because it causes deterioration of the signal-to-noise ratio (S/N) and also increases noise due to mixing of color signals.

OBJECTS OF THE INVENTION The object of the present invention is to provide a video tape recorder that can normally record and reproduce teletext signals with a simple configuration.

Structure of the Invention In order to achieve the above object, the present invention provides a filter that has an open time property in a predetermined section within a vertical blanking period of a video signal, and which is used in a signal processing system during recording or playback. By setting the predetermined section as a section in which the teletext signal is superimposed, the amplitude characteristics and group delay characteristics of the predetermined section including the teletext signal are made to have satisfactory characteristics, This makes it possible to record and reproduce teletext signals.

Description of examples Embodiments of the present invention will be described below based on the drawings.

FIG. 8 shows a block diagram of the signal processing system of the VTR according to the present invention, in which (c) shows the recording system and (c) shows the reproduction system. In normal operation, the input video signal is input from the input terminal (1), and the Y signal system passes through a low-pass filter (abbreviated as LPF) (3) and a switch (4).
The frequency modulator (abbreviated as MOD) (5) modulates the F
After it becomes M-Y, it passes through a bypass filter (abbreviated as HPF) (7) and a % switch (8), and then C at a mixer (9).
LOW and recorded on the tape by recording head 4. On the other hand, the C signal passes through a band pass filter (abbreviated as BPF) (2), a switch (to), and a low frequency conversion circuit (abbreviated as LOW MOD) C4, for example 6
Low range converted to 29KH2 and CL (after becoming W, Ll)
Foo, through switch aη, FM-Y at mixer (9)
mixed with. Furthermore, during playback, the opposite is true. To put it simply, the signal taken out by the playback head α is amplified by the playback amplifier 8g (1), and then the Y signal system is
F@, switch (to), frequency demodulator (abbreviated as DEM) (c), LPF (c), switch (to), mixed e) (
2) and is output to the output terminal (2). On the other hand, the C signal system passes through the LPFOQ switch CCa, the high frequency converter (HIGHDEM) CI, BPFcl, and the switch (2), and is mixed with the Y signal in the mixer (2).

Now, in the present invention, in order to accurately record and reproduce teletext signals in a predetermined section within the vertical retrace period, by switching the filter for the Y signal system and at the same time switching the filter for the C signal system, The noise from the C signal system to the Y signal system is reduced, and the S/N of the Y signal system is improved.

In the recording system of Fig. 8, LPF (a) is changed to LPF (2),
14PF' (7) to HPF (6), BPF (11 to B
PFσυ and IPFα time are switched to LPF (to). In addition, in the regeneration system, )IPF (c) is HP
F(j◇, LPF(c) to LPF@, L P F
C4υ is switched to LPFCIQ, and BPF(2) is switched to BPF■. Here, switch L4) +8
) (To) aη is switched based on No. 8 from the control circuit (G), and the switch @ (B) is switched based on the signal from the control circuit (B). As a result, in the period in which the teletext signal is included in the vertical retrace period, the frequency characteristics, group delay characteristics, and S/N of recording and reproduction of the Y signal change compared to the other sections 1ζ.

This is schematically shown in FIG. 4(A)@. Here, (a) represents the characteristic curve of the present invention, and (b) represents the conventional characteristic curve.

It can be seen that the frequency characteristics (c) and group delay characteristics (c) at the frequency of the teletext signal have been improved.

The reason why the Y signal band can be widened in this manner is that in this predetermined section, there is no C signal component other than color burst, and there is no need to provide a band for the C signal. Furthermore, it is obvious that the wider the band becomes, the flatter the group delay characteristic at 2.86 MHz becomes.

Now, as shown in FIG. 5(a), the teletext signal is superimposed on any one or two scanning lines between scanning numbers 10H and 211-1 within the vertical blanking period, so it includes this section. It is sufficient to output the period as a control signal from the control circuit. Here, al in FIG. 5(a).

a3 is the equivalent pulse period, a2 is the vertical synchronization signal period, a4
is a teletext phrase area, a5 is a horizontal synchronizing signal, and the upper number is a scanning line number.

Next, an example of the control signal is shown in FIG. 5(b). Figure 5 (b
) indicates that the switch is switched for approximately 14H after detecting the vertical synchronization signal, and Fig. 5(b)
) indicates that when the control signal is at a low level, the switch selects a normal filter, and when it is at a high level, the filter is switched as described above.

However, in the color burst in this section, Figure 8 (7
)LPF12), HPF(6), HPF@Q, LP
F@TE was not completely attenuated (The signal is recorded and reproduced as a Y signal, which is undesirable as it becomes noise in the reproduced color burst from the C signal system. Therefore, during the period when the control signal is at a high level, the color The control signal in this case is shown in Fig. 5 (C). Enlarged views of (b) and (C) in the period (a) at this time are shown in (d) and (e). show.

In addition, various control signals can be considered as shown in (C) in Figure 5, but the point is that any signal that switches each filter in the section where teletext is present is sufficient, and for that purpose, a vertical synchronization signal is required. It is thought that it is easiest to use it as a standard. Of course, it is not beyond the scope of the present invention to detect the presence of a teletext signal and generate a control signal based on that information.

Now, the playback system of a home VTR uses various noise low-frequency circuits (
(Also called noise reduction circuit and abbreviated as NR circuit)
is used. An example of the NR circuit and a block diagram are shown in FIG. The Y signal output from the switch is sent to the subtracter (c), and is also sent to the HPF (II). For normal playback, HPF (6), switch (4)
, a limiter circuit (abbreviated as LIM) @3, and a gain adjustment circuit (abbreviated as GAIN) θ◆, and is sent to the subtracter @3. As a result, the small high-frequency signal is subtracted, resulting in a signal with less external sound components, which is sent to a mixer (mixer), mixed with the color signal, and then output to the output terminal. Here, this NR
According to the present invention, the HPFθD used in the circuit) can also be
It is desirable to change the characteristics to more appropriate characteristics in proportion to the extension of the signal band. Therefore, it is switched to HPF by sweeping the switch θ. Furthermore, almost the same effect can be obtained by changing the characteristics of GAIN@4 instead of switching the HPF. Also, the control signal sent from the control circuit (b) to the switch @ (6) in Fig. 6 is the 8th switch.
It is similar to the figure.

Here, the amplitude characteristics of each filter described in the above embodiments are shown in FIG. 7 for reference.

Furthermore, in the present invention, as shown in the embodiments, it is not necessary to switch all the filters, but only some of them may be switched. Furthermore, the characteristics of the filter are not only shown in Fig. 7; for example, LPF (2) (C), HPF (6) (C) may be through, BPF (11) 2, LPFJ (1°)
IPF) may be turned off. Furthermore, even if the filter is a comb filter having a delay element, it goes without saying that the present invention can be applied by viewing the entire comb filter system as, for example, an LPF as described in the embodiment.

Effects of the Invention As is clear from the above explanation, the present invention switches the filter used in the recording or reproducing system to a filter having an open time property in a predetermined section within the vertical retrace period. Therefore, by setting the predetermined section as the section in which teletext is superimposed, the teletext signal can be recorded and played back with good amplitude and group delay characteristics, making it possible to record and play back the teletext signal, which was previously impossible. This has had the great effect of making it possible.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the spectrum during conventional recording and playback.
Figure 2 is a schematic diagram of the spectrum of a high-bandwidth VTR, Figure 8
1(f)(c) is a recording/reproducing block diagram showing an embodiment of the present invention, FIG. 4(2)(c) is a characteristic diagram showing a comparison between the present invention and the conventional one, and FIG. FIG. 6 is a block diagram showing another embodiment of the present invention, and FIG. 7 is a characteristic diagram of a filter for explaining the present invention. (4) (8) α3Q (E) ni) 0 (2) 0...
・Switch, 0 barrel (shi...匍I control circuit agent Yoshihiro Morimoto Fig. 1 t 2 J l 3M5z 12, tAjMH7 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Color burst (on) (e) No. Figure S Figure 7

Claims (1)

[Claims] 1. A video device in which a filter used in a signal processing system during recording or playback is switched to a filter having different characteristics in a predetermined interval within a vertical retrace period of a video signal. Tape recorder. 2. The video tape recorder according to claim 1, wherein the predetermined section within the vertical retrace period is a section within 21 horizontal scanning periods after the vertical synchronization signal. 8. The video tape recorder according to claim 1, wherein the predetermined interval within the vertical retrace interval is an interval excluding a color burst within 21 horizontal scanning periods after the vertical synchronization signal. 4. The video tape recorder according to claim 1, wherein the filter is a low-pass filter placed before a frequency modulator or after a frequency demodulator in the luminance signal processing system. 5. The video tape recorder according to claim 1, wherein the filter is a high-pass filter placed after a frequency modulator or before a frequency demodulator in the luminance signal processing system. 6. The videotape according to claim 1, wherein the filter is a comb-shaped filter composed of delay elements that delay the signal by one horizontal scanning period in order to separate the luminance signal and the chrominance signal. recorder. 7. The video tape recorder according to claim 1, wherein the filter is a bandpass filter placed before the frequency low-pass conversion circuit or after the frequency high-pass conversion circuit of the color signal processing system. . 8. The videotape according to claim 1, wherein the filter is a low-pass filter placed after the frequency low-pass conversion circuit or before the frequency high-pass conversion circuit of the color signal processing system. recorder. 9. The video tape recorder according to claim 1, wherein the filter is a filter in a noise reduction circuit of a luminance signal processing system.