JPS6229392A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain high quality picture by applying FM modulation to two carriers having different frequency forming a video signal and applying amplitude modulation to one or the both signals with a carrier f0 having a special relation and using a comb-line filter to restore the folded and interleaved high frequency component. CONSTITUTION:Two carriers having a different frequency are FM-modulated by two signal component forming at lest a part of a video signal, the modulated signals are recorded while being superimposed with different frequency band. Then one or both signals are subject to amplitude modulation by a carrier f0 having the relation of equation, the result is added to a signal before modulation and after the high frequency component is subject to folded interleaving, the result is FM-modulated and recorded, and the comb-line filter using a 1H delay line restores the high frequency component subject to folded interleaving at reproduction. Thus, the problem of band limit caused by the ternary distortion is solved to obtain a color picture with high quality.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a magnetic recording/reproducing device.

2. Description of the Related Art At present, the mainstream magnetic recording and reproducing apparatus (hereinafter referred to as VTR) is of the helical scan type in which a rotating head forms video tracks diagonally on a tape. In particular, home VTRs are becoming smaller and more densely packed. For example, in a VH3 type VTR, two video heads are arranged at a positional relationship of 180' from each other on a rotating cylinder with a diameter of 62 mm, and the video signal is divided by 1/2.
It is recorded diagonally on an inch-wide tape. However, as a signal recording method, low frequency converted color signals and F
Since the M luminance signal is superimposed and supplied to the video head, the bands of both the chrominance signal and the luminance signal are limited, resulting in a high S/N.
, it is not possible to obtain high-resolution playback images.

Therefore, a proposal was made to record and reproduce color signals and luminance signals using separate heads so as not to be subject to band limitations, thereby obtaining high image quality.

FIG. 4 is a block diagram of an M format VTR, and FIG. 5 is a waveform diagram thereof. The M-format VTR uses the VH3 configuration as its basic mechanism to obtain high-quality images without significantly changing mechanical specifications such as the cylinder diameter.The M-format VTR uses separate heads, or tracks, to transmit brightness and color signals. Since it is configured to record, the track pitch is large, and the recording time is about 20 minutes (1,/
6)) is the standard specification. In FIG. 4, a standard composite video signal is applied to the input terminal, and the yc separation circuit 1
The signal is separated into a luminance signal Y and a color signal C. As separation methods, there are two methods: one uses a band-pass filter to separate the quadrature two-phase modulated color signal and a low-pass filter to separate the luminance signal, and the other uses a comb filter. Either method can be used. . The separated quadrature two-phase modulated color signal is guided to a color demodulator 2 and subjected to synchronous detection. That is, the quadrature two-phase modulated color signal is synchronously detected using a color subcarrier formed based on the burst signal to obtain baseband color difference signals (R-Y) and (B-Y). At this time, depending on the phase angle of demodulation, I
, and Q signals can also be obtained, but a color difference signal will be explained here as an example.

Y at each of the three points in Figure 4 (A), (B), and (C).

Three baseband signals (RY) and (B-Y) are obtained and are FM modulated by 3 and 4.5 FM modulators.

The Y signal FM modulated by the FM modulator 3 is shown in Fig. 5 ([)
) as shown in FIG. Color difference signal (R-Y) FM-modulated by FM modulators 4 and 5.

(B - Y) is added by an adder 6 and frequency multiplexed.

It appears at point E in Figure 4 in the form shown in Figure 5(E), and C
guided to head 8.

These FM signals are recorded on tape and played back,
At this time, odd-order harmonics are generated based on the saturation characteristics of electromagnetic conversion. Particular attention must be paid to the third harmonic, as it has very large energy.

For the Y signal, for example, a 5 MHz FM carrier generates a third harmonic at 15 MHz.

This is not a problem because it is outside the band, but if the baseband signal contains a high frequency of, for example, 2.5 MHz, the third lower wave of this third harmonic, that is, 15 (MHz) −3xz, s = A component appears around 7.5 MHz, which is the upper side wave of the fundamental wave component 5 +2.
5 = 7.5 MHz, which causes a beat, resulting in so-called moiré. In order to reduce this moiré, the FM carrier can be made higher, but this is limited by the high frequency characteristics of the cylinder and tape. However, this moiré has relatively little energy and occurs only for components of 2.5 MHz or higher in the baseband, so it is not particularly visually unsightly and is therefore tolerable.

Next, we will discuss cross-modulation of color signal components. As mentioned above, the signal reproduced from the C head 8 contains the original (R-
In addition to the Y) signal and the (B-Y) signal, a third-order distortion component resulting from the hysteresis characteristic of the tape head system is included. The largest of these components are 3fa-y and fRY-
2f ov [where fH-y: recording frequency r of the (RY) signal fB-y: recording frequency of the (B-Y) signal]. In addition to the above, as a third-order distortion component,
fa-y+2 fa-y+ 3 fa-vp 2fR-
There is YlfB-Y, but since these are high frequencies, they hardly appear in the head output, and even if they do appear, they are far away from the signal band and can be easily removed by a filter. 3fa-y+ fR-y
If the 2 fB-y component mixes into the original modulated signal, it will become a beat in the demodulated (RY) signal or (B-Y) signal and will be cursed. Let the FM frequency deviations of the (RY) and (B-Y) signals be fL(RY)~fH(RY) fL(B-Y)~fHCB-Y), respectively, and fL<*- v)=5 (MHz), fH(s+-y)=
6 (MHz)fL(ey)=0.75 (MHz)
+ fa (s-Y) = 1.25 (MHz), then 3 f L (B-Y): 2.25 [MHZ) 3 f
II (RY): 3.75 (MHz) fL<*
-v) 2fu(s-y)=2.5(MHz)f L(
RY) -2f L(B-Y) =3. '5 (M
Hz ) f 1I (RY) - 2f H (B - Y) = 3
．． 5 CM Hz ) f II (RY) -2f L
(B-Y)=4.5 (MHz), (B-Y
) signal carrier frequency is fL(B-Y) ~ fHCB-
Y), the unnecessary component closest to the (R-Y) signal is 3 fB-Y component, 3 fH(s
-y), fa-y-2/fa-Y component is f
RY -2ft, <sv>. In the example above, 3
fH(B-Y) component and the lowest carrier f of the R-Y signal
The frequency difference of L(RY) is f L(RY) -3f II(B-Y) = 1.2
5 (MHz), and fRY −2fLco
-y) component and fR-Y is fa-y-(f++-y-2ft, (e-y))=2
fL(ey)=1.5 (MHz). Therefore, in order to remove these unnecessary components, the passband of the bandpass filter 9 is f L (RY) - 1,25 (MHz) = 3.75
(MHz) or more, and in reality, it is not possible to realize a filter with such a steep slope.
The best you can do is to set it to z or higher. If you do it like this (
The bandwidth of the RY) signal will be limited to I MHz. On the other hand, regarding the (B-Y) signal, the unnecessary components closest to it are 3fB-Y and f L(R-
Y) -2f ay. These unnecessary components and (B
−Y) The difference between the signal and the carrier frequency is 2 f, respectively.
B-Yl f L(RY) -3f a-y,
The former becomes lower as fB-Y becomes lower, and the latter becomes fil-Y
The higher the value, the lower the value. Therefore, in the above example, 2 f L (BY) = 1.5 (MHz) f L
<R-v)-3f) I(s-y)=5-3 Xl, 25
= 1.25 (MHz), and the cutoff frequency of the low-pass filter 10 for (B-Y) FM signal extraction is f H (B-Y) + 1.25 (MHZ) = 2.5 (
2.25 (MHz) or less, and in reality it is not possible to realize a filter with such a steep slope.
It is best to keep the frequency around 3 Hz. In this way, the bandwidth of the (B-Y) signal is likely to be 1 (MHz), but since f L (B-Y) = 0.75 [MHz], the lower sideband is 0. Only 6 to 0.7 (MHz) can be obtained, and in reality it is about 0.6 (MHz). In order to remove this restriction, when we try to raise the FM carrier of (B-Y) a little more, this time the upper side wave side.

It falls into the above-mentioned unnecessary component area, and a beat occurs.

In this way, the (R-Y) signal is demodulated by the FM demodulator 12 with a bandwidth of about 1' (MHz), and the (B-y) signal is demodulated by the FM demodulator 12 with a bandwidth of about 0.7 (MHz). 1
The color encoder 14 demodulates these (R-
Y), (B-Y) signals are quadrature two-phase modulated with the color subcarrier, added to the luminance signal in the adder 15, and outputted to the output terminal as a composite video signal. , (B
-Y) color difference signals are processed using the I and Q color signal axes, and ■= 1 (MHz), Q=0.5 (MH
Since the bandwidth of z ) is sufficient for transmission, there is no particular problem, but if you use the color difference axis as shown in this example, (RY) =
Since signal transmission with a bandwidth of (B-Y)=1 [MHz] or more is desirable, the band limitation of unnecessary components due to the third-order distortion becomes a major obstacle. Regarding the color signal axis, (R-Y)
, (B-Y) is a move toward unification, regardless of whether it is a PAL region or an NTSC region.
-Y) and (B-Y) signals will have great significance in the future.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording and reproducing apparatus that can eliminate the band limitation caused by the third-order distortion component described above and can obtain high-quality color images.

Means for Solving the Problems The magnetic recording and reproducing apparatus of the present invention performs FM modulation on two carrier waves having different frequencies using two signal components forming at least a part of a video signal, and converts these modulated signals into frequencies. It is configured to record in different bands and in a superimposed manner, and one or both of them is an integer, fH is 1 horizontal scanning frequency)
Amplitude modulation is performed using a carrier wave fO having the following relationship, the signal is added to the signal before modulation, the high frequency portion is folded back and interleaved, and then FM modulated and recorded. During playback, a comb type signal using an LH delay line is used. It is characterized in that it is configured to restore the high frequency portion that has been folded back and interleaved with a filter.

Effect As mentioned above, if the FM carrier location shown in FIG. 5(E) is used, the bandwidth of (RY) is 1 (MH).
z), the bandwidth of (B-Y) is about 0°6 (MHz), and the desired (R-Y) = (B-Y) = 1
(MHz) cannot be obtained, but the present invention provides such -Y
By effectively utilizing the signal band, the 1 (MHz) band can be effectively transmitted.

Embodiment FIG. 1 shows an example of the structure of the present invention. YC separation circuit 1 is the fourth
Same as shown in the figure. Color signal C is sent to color demodulator 2
Color synchronized detection is performed with baseband (R-Y), (B-Y)
converted into a signal. (RY) signal is FM as in Figure 4.
(B-Y) is guided to a balanced modulator 16. 17 is an oscillator, the oscillation frequency fO is a positive integer, and fH is the horizontal scanning frequency (NTSC
In the case of , the relationship fo = 15.734264KH7,) is set so that
Hz). For example, if n=76, then the spectrum of the (B-Y) signal from the demodulator 2 exists at f11 intervals as shown in FIG. 2(a).

This is not limited to the (B-Y) signal; in general, both Y and (R-Y) television signals have spectra at fl+ intervals.

This (B-Y) signal is generated by the carrier wave fO in the oscillator 17.
When balanced modulation is performed using the balanced modulator 16 using
As shown in , (76,5±1) f o, (76,5
±2) Appears as upper and lower sidebands every fH, such as fI+.

However, in reality, fo hardly appears due to carrier wave suppression. In this way, the lower side wave appears as if (a) is symmetrically folded back around fo. The adder 18 receives the (B-Y) signal [
2(a)] and the above-mentioned balanced modulation signal [FIG. 2(b)] are added. The spectrum at the output of the adder 18 is as shown in FIG. 2 (c). In (c), the original (RY) signal is shown as a solid line, and the folded balanced modulation signal is shown as a dotted line. (
As can be seen from c), the folded signal intersects between the spectra of the original signal, making efficient use of the frequency domain. This signal is band-limited to a transmittable band by a low-pass filter 19. In this case, it is appropriate to select the cutoff frequency. This situation is shown in FIG. 2 (d). As can be seen from FIG. 2 (d), the low frequency region from O to (fo/2) remains as the original signal every fH, and (f.

The high frequency region from /2) to fo is interleaved between the original signal spectrum every fH in a folded manner.

By interleaving in this way, the bandwidth can be saved in half. This interleaved signal is FM modulated by the (B-Y) FM modulator 5, and the F
The signal is added to the M-modulated (RY) signal, frequency-multiplexed, and guided to the C head 8, where it is recorded on the tape. Its frequency location is the same as in FIG. 5(E).

During playback, the signal from the C head 8 is passed through a band pass filter 9.
The low-pass filter 10 separates the (RY) FM signal.

The FM signal (RY) is FM demodulated by the FM demodulator 12 and guided to the color encoder 14. On the other hand, the FM signal (B-Y) passes through the low-pass filter 10 and is then FM demodulated by the FM demodulator 13. This demodulated signal is transmitted for one horizontal period (
1H) The signal is guided to a comb filter composed of a delay line 20, an adder 21, and a subtracter 22. Now, when the input to the comb filter is a sine wave cosωT, the output A of the adder 21 is A=1cosωT+cosω(t-to) 1, where tH indicates one horizontal period.

bawl. As can be seen from the first equation, When A=2 next door A=0 becomes.

Assuming that ω=2πf MAX in the second equation.

If ω=2πf Mllll in the third equation, then. This situation is shown in FIG. 3 (E). Like this fH
It becomes a comb-shaped filter that extracts the peak at each time, and can extract the low frequency region shown in FIG. 2(d).

Next, when the output B of the subtractor 22 is calculated in the same way, B=
When lcosωT-cosω(t-tH)1, B=0, and when next, B=2. Therefore, draw the characteristics as shown in Figure 3 (f),
The aliasing component shown in FIG. 2(d), that is, the high frequency component can be extracted.

The high-frequency component of the output of the subtracter 22 obtained in this way is demodulated by the balanced demodulator 23, and when added to the output (low-frequency part) of the adder 21, the high-frequency component as shown in FIG. 2(a) is obtained. part is reproduced. The bandpass filter 24 removes unnecessary harmonic components occurring within the balanced demodulator 23.

The (B-Y) signal thus restored into a wide band and the above-mentioned (R-Y) signal are quadrature two-phase modulated by the color encoder 14, and the Y signal from the FM demodulator 11 and the adder 1
By adding 5, a composite video signal can be obtained.

Although the above explanation has been made only regarding the wideband transmission method for the (B-Y) signal, it is possible to similarly apply the method to the (R-Y) and Y signals as well, if necessary.

In the embodiment shown in FIG. 1, the adder 18 adds the original (B-Y) signal and the balanced modulated (B-Y) signal as they are. Since the signal to be modulated is a signal whose high frequency region should be transmitted, it should be separated using a filter in advance. However, if a normal low-pass filter or high-pass filter is used, the linearity of the phase will be disturbed when the original signal is restored on the reproduction side, causing ringing and overshoot, which may deteriorate the image quality. Therefore, a filter with good phase linearity must be used for this band separation.

This also applies to the filter used in FIG. 19.24.

A second embodiment that solves this problem is shown in FIG.

In FIG. 6, a delay line 25, an adder 26, a subtracter 27
The circuit shown in the section constitutes a comb filter, and the principle is the same as that shown in Fig. 1 20.21.22, but in this case, the delay time of the delay line is not 1H,
The delay time τ is τ=1/2 f.

Therefore, the output of the adder 26 shows a low-pass filter characteristic as shown in FIG.
The high-pass filter characteristics are shown in Figure (H). This comb filter actually exhibits waveform characteristics as shown in FIGS. 3(e) and 3(f), but since there is no signal component above fO, the same can be said equivalently as described above.

The signal whose frequency bands have been separated in this manner and whose high frequencies have been interleaved by the balanced modulator 16 and adder 18 is guided to a low-pass filter shown by a delay line 28 and an adder 29. Since the delay time of the delay line 28 is 8/3fO, the seventh
It becomes the characteristic of the figure. The signal folded and interleaved to fO/2 or less in this manner is recorded and reproduced in the same manner as in the embodiment of FIG. On the playback side, the delay line 30
, the subtracter 31 and the adder 32, the delay line 28 and the adder 29
The band-limiting correction made in
) The signal can be restored.

In the embodiment shown in Fig. 6, since a comb filter is used for band limiting, one-phase linearity does not deteriorate and overshoot, ringing, etc., which are problems with normal band separation, do not occur, so good image quality can be obtained. .

Effects of the Invention As described above, the magnetic recording/reproducing apparatus of the present invention modulates the high frequency part of the (B-Y) signal, where it is difficult to obtain a bandwidth, and interleaves it with the low frequency part. It is possible to transmit a signal of a desired bandwidth with half the bandwidth, solve the problem of band limitation caused by third-order distortion that occurs when recording and reproducing by frequency multiplexing, and obtain a high-quality color image.

In particular, if a comb filter is used to solve problems such as overshoot and ringing that impair phase linearity during band separation, even higher quality images can be obtained and the effect will be even more effective. Ru.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a frequency spectrum diagram for explaining the operation of Fig. 1, Fig. 3 is a spectrum diagram of a comb filter, and Fig. 4 is a conventional block diagram. , FIG. 5 is a waveform diagram for explaining the operation of FIG. 4, FIG. 6 is a configuration diagram of another embodiment of the present invention, and FIG. 7 is a waveform diagram for explaining the operation of FIG. 6. be. 16... Balanced modulator, 17... Oscillator, 18...
Adder, 19...Low pass filter, 20...-Horizontal period delay line, 21... Adder, 22... Subtractor,
23...Balanced modulator, 24...Band pass filter,
25...Delay line, 26...Adder, 27...Subtractor, 28...Delay line, 29...Adder, 30...
delay line. 31...Subtractor, 32...Adder agent Yoshihiro MorimotoFigure 2Figure 3Figure 5B-Y R-γ

Claims (1)

[Claims] 1. FM modulating two carrier waves with different frequencies using two signal components forming at least a part of a video signal, and recording these modulated signals by superimposing them in different frequency bands. At the same time, one or both of the signals is set in advance to f_O=[(2n+1)/2]f_H(n
is a positive integer, and f_H is 1 horizontal scanning frequency). After amplitude modulation with a carrier wave f_O, which is added to the pre-modulation signal, and the high frequency part is folded and interleaved,
A magnetic recording and reproducing apparatus configured to perform recording with FM modulation and to restore the interleaved high frequency portion by folding back and interleaving with a comb-shaped filter using a 1H delay line during reproduction. 2. FM-modulates two carrier waves having different frequencies with two signal components forming at least a part of a video signal, and superimposes and records these modulated signals in different frequency bands; One or both of the signals is passed through a comb filter using a delay line of one cycle or more of the upper limit frequency of the signal in advance, and the signal is divided into a low frequency region and a high frequency region, and the high frequency region signal is divided into f_o= [(2n+1)/2]f_H (n is a positive integer,
f_H is a carrier wave f_ with a relationship of 1 horizontal scanning frequency)
The signal is amplitude modulated at O, added to the low frequency region signal, and applied so that the high frequency part is folded back and interleaved, then FM modulated and recorded, and upon playback, folded and interleaved using a comb filter using a 1H delay line. 2. The magnetic recording and reproducing apparatus according to claim 1, wherein the high frequency signal is restored and added to the low frequency signal.