JPH0574997B2 - - Google Patents

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Field of industrial application B. Outline of the invention C. Prior art D. Problems to be solved by the invention E. Means for solving the problems F. Effect G. Example G-1. Explanation of the configuration of the example (Fig. 1) ) G-2 Explanation of operation of the embodiment (FIGS. 2 A to E) G-3 Explanation of modification H Effect of the invention A Industrial application field The present invention is directed to a luminance signal and a carrier color signal forming a color video signal. The present invention relates to a luminance signal reproducing circuit that obtains a reproduced luminance signal from a read signal from a magnetic recording medium recorded as a frequency modulated signal and a low frequency conversion carrier signal, respectively.

B. Summary of the Invention The present invention is characterized in that a luminance signal and a carrier color signal forming a color video signal are separated from each other, the luminance signal is made into a frequency modulated signal, and the carrier color signal is converted into a frequency modulated signal with a lower frequency band of the frequency modulated luminance signal. In a circuit that reproduces a luminance signal from a read signal from a magnetic recording medium that has been frequency-converted and recorded on the frequency side, a plurality of demodulators for the carrier frequency component of the low-frequency carrier color signal are installed before the demodulator for the frequency modulated luminance signal. By providing a combination of a trap section, a plurality of limiter sections, and a low-pass filter section that passes the main frequency band components of the frequency modulated luminance signal, the frequency modulated luminance signal obtained in the read signal is With the carrier component of the low frequency carrier color signal on the sideband side removed and the interference wave component caused by the low frequency carrier color signal occurring on the sideband side above it being sufficiently reduced, the demodulator This means that it can be supplied.

C. Prior Art When a color video signal is recorded on a magnetic tape, a luminance signal and a carrier color signal forming the color video signal are separated, and the separated luminance signal is frequency-modulated on the high-frequency side. The modulated luminance signal (hereinafter referred to as FM luminance signal) is converted into a low frequency carrier color signal (hereinafter referred to as low frequency color signal) in which the carrier color signal is frequency-converted to the lower frequency side, and then both are mixed and rotated. A recording system is widely used in which recording is performed using inclined recording tracks that are supplied to a magnetic head and arranged obliquely with respect to the running direction of the magnetic tape.

With this method, a rotating magnetic head reads the FM brightness signal and low-range color signal from the magnetic tape on which the FM brightness signal and low-range color signal are recorded to obtain a read signal, and based on the reading signal, the brightness signal is When the carrier color signal is reproduced, the signal supplied to the demodulator for the FM luminance signal in the read signal is the carrier wave component of the low-range color signal component and the carrier wave component of the low-range color signal component in addition to the FM brightness signal. An interference wave component that occurs due to the non-linear characteristics of a magnetic recording and reproducing system consisting of a magnetic tape and a rotating magnetic head, and whose demodulated output falls within the band of the original reproduced carrier color signal. is included as an unnecessary component, and if such a signal is demodulated as it is to reproduce the luminance signal, a carrier color signal component will be generated in the reproduced luminance signal, causing beat disturbance. It becomes something that happens.

For example, in Figure 3, the frequency is plotted on the horizontal axis and the level is plotted on the vertical axis. In the luminance signal Y, the leading edge of the synchronization signal is frequency _YL and the white peak is frequency _YH ( _YL < _YH ) FM luminance signal with a carrier frequency shift band such that
FY, and if a read signal is obtained from a magnetic tape on which the carrier color signal is recorded as a low-pass color signal _C whose color subcarrier frequency is C, which is sufficiently lower than the frequency _YL , then includes the FM luminance signal FY and the low-range color signal C, but if we look at the read signal mainly from the FM luminance signal FY that should be demodulated to obtain the reproduced luminance signal, the fourth
As shown in the figure, the carrier component Cy of the FM luminance signal FY of frequency _Y ( _Y varies between _YL and _YH )
On the other hand, on the lower sideband side there is a carrier wave component Cc of the low frequency color signal _C of frequency C, and on the upper sideband side,
Frequency generated due to the low frequency color signal C inserted into the lower sideband side of the recorded FM luminance signal FY
2 _Y − _C interference wave component Cx is mixed in.
Here, the frequency 2 _Y − _C of the interference wave component Cx is 2 _YL
− _C and 2 _YH − _C , and also this FM
The interference wave component Cx mixed into the upper sideband side of the luminance signal FY has a frequency _Cx as shown in FIG. 5A.
The component Ccf of frequency 2 _Y − _C and the component Cxf of frequency 2 Y − C are frequency modulated components that exist in opposite phases, and the component Cca of frequency _C and the component Cxa of frequency 2 _Y − _C exist in phase with each other. The amplitude modulation components are synthesized. Each of these signal components is then subjected to demodulation to obtain a reproduced luminance signal.

In this way, in order to obtain a reproduced luminance signal from the read signal, the carrier wave component Cc of the low frequency color signal _C of frequency C, which is an unnecessary component included in the signal supplied to the demodulator for the FM luminance signal FY in the read signal,
2 In order to reduce the harmful effects caused by the interference wave component Cx of _Y - _C , in conventional luminance signal regeneration systems, traps and FM A low-pass filter is provided that does not pass most of the upper sideband part of the luminance signal FY, and a trap removes the carrier wave component Cc of the low-frequency color signal C in the signal supplied to the demodulator, and also reduces the interference wave component Cx. by means of a band pass filter, or
Two traps are provided for the signal supplied to the demodulation section, one for the carrier wave component Cc of the low frequency color signal _C at frequency C, and one for the interference wave component Cx at frequency 2 _Y - _C. The carrier wave component Cc and the interference wave component Cx of the low frequency color signal C in the signal are removed by traps, respectively.

D. Problems to be Solved by the Invention However, in the luminance signal reproducing system, traps and traps for the carrier component Cc of the low-frequency color signal C are applied to the signal supplied to the demodulator.
If a low-pass filter is provided that does not pass most of the upper sideband portion of the FM brightness signal FY, most of the information contained in the upper sideband portion of the FM brightness signal FY supplied to the demodulator will be lost. This results in a reduction in the quality of the reproduced image obtained based on the reproduced luminance signal. moreover,
In order to improve the resolution of the reproduced image, this luminance signal reproduction system uses a recording method (hereinafter referred to as the carrier high shift method) in which the carrier frequency shift band of the FM luminance signal is shifted to higher frequencies than frequencies _YL to _YH . ) in the read signal from the magnetic tape taken.
When an FM luminance signal is supplied, the frequency of the carrier wave component of the FM luminance signal is shifted higher than frequency _Y , so it falls outside the passband of the low-pass filter and causes overmodulation. , there is a risk that it will not be possible to obtain a reproduced luminance signal, and therefore, there will be a lack of compatibility with magnetic tapes employing the carrier high shift method.

Also, as mentioned above, in the luminance signal reproducing system, for the signal supplied to the demodulator,
When two traps are provided, one for the carrier component Cc of the low-frequency color signal _C at frequency C and one for the interference wave component Cx at frequency 2 _Y - _C , then
Frequency 2 _Y − _C of interference wave component Cx is FM luminance signal
Since the carrier wave component C of _FY has a frequency deviation width that is twice the frequency deviation width of the frequency Y of y, the trapping effect on the interference wave component Cx also exhibits a trapping effect over a correspondingly wide frequency range. As a result, the FM luminance signal FY supplied to the demodulation section has the disadvantage that information contained in its upper sideband is largely lost. Furthermore, when the FM luminance signal in the read signal from the magnetic tape using the carrier high shift method is supplied to such a luminance signal reproducing system, the interference wave component mixed into the FM luminance signal is
Since the interference wave component corresponding to Cx has a frequency shifted to the higher frequency side than frequency 2 _Y − _C , a trap effect cannot be obtained for such interference wave component, and the harmful effects caused by the interference wave component cannot be obtained. It ends up being impossible to reduce it.

In view of the above, the present invention provides an FM luminance signal and a low frequency color signal frequency-converted to the lower side of the FM luminance signal, which is obtained in a read signal from a magnetic recording medium recorded with the FM luminance signal.
When demodulating an FM luminance signal to obtain a reproduced luminance signal, the carrier wave component of the low-frequency color signal included in the signal subjected to demodulation and the demodulated output are within the band of the original reproduced carrier color signal. The interference wave components can be removed and sufficiently reduced without the problems or inconveniences associated with the above-mentioned conventional techniques.
It is an object of the present invention to provide a luminance signal regeneration circuit that can reliably perform the regeneration.

E Means for Solving the Problems In order to achieve such an object, the luminance signal reproducing circuit according to the present invention records an FM luminance signal and a frequency-converted low frequency color signal on the lower frequency side thereof. A first trap unit for a carrier wave frequency component of a low range color signal, a first limiter unit, and a carrier wave of the low range color signal, which are connected in sequence to the output side of a reading means including a magnetic head that obtains a read signal from a magnetic recording medium. It is configured to include a second trap section for frequency components, a low-pass filter section that passes the main frequency band components of the FM luminance signal, a second limiter section, and a demodulation section for the FM luminance signal.

F Effect In the luminance signal reproducing circuit according to the present invention as described above, the first trap section first removes the carrier wave component of the low frequency color signal from the signal supplied to the demodulation section, and then The limiter section 1 removes the amplitude modulation component of the interference wave component that has mixed into the upper sideband side of the FM luminance signal and causes the demodulated output to fall within the band of the original reproduced carrier color signal. As a result, the interference wave component becomes a frequency modulation component remaining in the lower side wave band side and the upper side wave band side of the FM luminance signal, and its level is halved. Subsequently, the second trap section
Among the remaining interference wave components, the component having a frequency corresponding to the carrier wave component of the low frequency chrominance signal on the lower side band side of the FM luminance signal is removed. next,
The low-pass filter section removes components outside the main frequency band of the FM brightness signal, and even after passing through the main frequency band component of the FM brightness signal and the second trap section included in the upper sideband side. The remaining interference wave component is supplied to the second limiter section. and,
The second limiter section removes the amplitude modulation component of the interference wave component remaining on the upper side band side of the FM brightness signal, and thereby the amplitude modulation component of the interference wave component remaining on the upper side band side of the FM brightness signal. The level of the interference wave component that will remain after being distributed is again halved, and is sufficiently reduced compared to the interference wave component in the FM luminance signal obtained on the output side of the reading means. The FM luminance signal in which the mixed interference wave components have been sufficiently reduced in this way is supplied to the demodulation section, and a reproduced luminance signal is obtained from the demodulation section.

Such a luminance signal reproducing circuit according to the present invention removes and reduces the carrier wave component and interference wave component of the low-frequency color signal from the read signal obtained at the output side of the reading means, and supplies the signal to the demodulator. signal, FM
The luminance signal and the interference wave components that are sufficiently reduced and only remain on the lower sideband side and the upper sideband side thereof can be included, and,
This eliminates the loss of the upper sideband portion of the FM luminance signal, and can also process FM luminance signals in signals read from magnetic tapes using the carrier high shift method.

G Example G-1 Description of configuration of example FIG. 1 shows an example of a video signal reproducing circuit according to the present invention. In this example, the luminance signal and the carrier color signal forming the color video signal are the FM luminance signal FY and the low frequency color signal C as shown in FIG. The invention is said to be applied to a reproducing apparatus that obtains a reproduced luminance signal and a reproduced transport color signal from a magnetic tape recorded on the magnetic tape. In this case, the magnetic tape is provided with gradient tracks alternately formed by two rotating magnetic heads supplied with an FM luminance signal FY and a low-frequency chrominance signal C. It is assumed that the signal FY and the low-range color signal C have been recorded.

In FIG. 1, rotating magnetic heads 1 and 2 are
The slanted tracks formed on the magnetic tape are alternately and sequentially scanned, and the FM luminance signal FY and low-range color signal C recorded on the slanted tracks are read for each scan. The output ends of these rotating magnetic heads 1 and 2 are connected to selection contacts 5a and 5b of a switch 5 via amplifier circuits 3 and 4, respectively. In response to a switching control signal SW from a terminal 6, the switch 5 switches its movable contact 5c to select contacts 5a and 5 in synchronization with the period in which the rotating magnetic heads 1 and 2 scan the inclined track on the magnetic tape.
As a result, the amplified outputs of the read signals from the rotating magnetic heads 1 and 2 are alternately delivered to the movable contact 5c. Here, these rotating magnetic heads 1 and 2, amplifier circuit 3
and 4, and the switch 5 together form a reading means.

A signal branching circuit 7 is connected to the output end of the reading means, that is, the movable contact 5c of the switch 5, and a carrier color signal reproducing circuit system 8 is connected to one output end of the signal branching circuit 7. At the same time, the other output terminal of the signal branching circuit 7 is provided with a first trap 11 for the carrier frequency component of the low-range color signal C;
A first limiter 12 is connected thereto. A second trap 1 for the carrier frequency component of the low frequency color signal C is connected to the output terminal of the first limiter 12.
3 is connected to a low-pass filter 14 that passes the main frequency band components of the FM luminance signal FY, and furthermore, the output terminal of the low-pass filter 14 is formed by a frequency discrimination circuit via a second limiter 15. The demodulator 16 is connected to a demodulator 16, and an output terminal 17 is provided at the output end of the demodulator 16.

In such a connection relationship, the signal branch circuit 7
a first trap 11 connected to the other output end of the
Each circuit section from the demodulator 16 to the demodulator 16 constitutes an example of the luminance signal reproducing circuit according to the present invention.

G-2 Operational Description of Embodiment An example of the luminance signal reproducing circuit according to the present invention configured as described above is a luminance signal obtained from a magnetic tape by a reading means including rotating magnetic heads 1 and 2, and outputs a signal to a signal branching circuit 7. The operation is to demodulate the FM luminance signal from the read signal derived from the other output terminal to obtain a reproduced luminance signal, which will be described next.

The read signal obtained by the reading means and led out to the other output terminal of the signal branching circuit 7 includes the FM luminance signal FY and the low-range color signal C, and therefore,
This should be demodulated to obtain the reproduced luminance signal.
When looking mainly at the FM luminance signal FY, as mentioned above,
Also, as shown in Figure 2A, the frequency _Y ( _Y is
In addition to the carrier wave component Cy of the FM luminance signal FY (which changes between _YL and _YH ), the frequency
The carrier wave component Cc of the low frequency color signal C of _C is included, and furthermore, on the upper sideband side, the demodulated output generated due to the low frequency color signal C is within the band of the original reproduced carrier color signal. Frequency 2 _Y that becomes what enters
- It includes the interference wave component Cx of _C. Here, the frequency 2 _Y − _C of the interference wave component Cx is
It is supposed to change between 2 _YL − _C and 2 _YH − _C.

Then, the first trap 11 acts on the read signal, and the carrier wave component Cc of the low frequency color signal _C of frequency C is removed. Therefore, as shown in FIG. 2B, the first limiter 12 removes the carrier wave component Cc of the low-frequency color signal C and outputs the FM luminance signal.
A signal containing FY and an interference wave component Cx of 2 _Y − _C is supplied. As mentioned above, the interference wave component Cx at frequency 2 _Y − _C is composed of a frequency modulation component in which the frequency _C component Ccf and the frequency 2 _Y − _C component Cxf exist in opposite phases, and the frequency _C component. Cca
and the frequency 2 _Y − _C component Cxa are synthesized with an amplitude modulation component that exists in phase with each other, but the amplitude modulation component of these is removed by the first limiter 12. On the output side of the first limiter _{12 ,} as shown in _FIG . A frequency modulation component of the interference wave component appears. Here, the component Ccf of frequency _C and the frequency 2 _Y − _C
It is assumed that the level of the component Cxf is reduced by half compared to the level of the original interference wave component Cx. In addition, in FIG. 2C, the frequency _C component Cca and the frequency 2 _Y − _C removed by the first limiter 12 are
The amplitude modulation component of the interference wave component that exists in phase with component Cxa is shown by a broken line.

Next, the second trap 13 acts on the signal obtained at the output side of the first limiter 12, and the component Cca of the frequency C of the interference wave component, which is the carrier frequency component of the low-range color signal _C , is activated. is removed. Therefore, as shown in FIG. 2D, the low-pass filter 14 receives the frequency _C component of the interference wave component.
Cca is removed, and a signal containing the FM luminance signal FY and the component Cxf of frequency 2 _Y − _C among the interference wave components is supplied.

In the low pass filter 14, these FM
Harmonic components generated by the first limiter 12, etc., other than the brightness signal FY and the interference wave component of the frequency 2 _Y - _C component Cxf are removed, resulting in an FM brightness as shown in FIG. 2D. The signal FY and the interference wave component Cxf of frequency _2Y - _C are supplied to the second limiter 15. Here, too, the interference wave component Cxf of frequency 2 _Y − _C is composed of a frequency modulation component in which component Ccf′ of frequency _C and component Cxf′ of frequency 2 _Y − _C exist in opposite phases to each other, and a frequency modulation component Cxf of frequency _C component Cca′ and frequency
2 _Y − _C component Cxa′ and amplitude modulation components that exist in phase with each other are synthesized, and among these, the amplitude modulation component is transmitted to the second limiter 1.
5, and the output side of the second limiter 15 receives the FM luminance signal FY, a component Ccf' of frequency _C , and a component Cxf' of frequency 2 _Y − _C , as shown in FIG. 2E. Frequency modulation components of the interference wave components appear, which exist in opposite phases to each other. even here,
The levels of the component Ccf' at frequency _C and the component Cxf' at frequency 2 _Y − _C are considered to have been reduced by half compared to the level of the interference wave component Cxf, and therefore the original interference wave component
This will be reduced to approximately 1/4 compared to the level of Cx. Note that, also in FIG. 2E, the frequency _C component removed by the second limiter 15
The broken line indicates the amplitude modulation component of the interference wave component in which Cca′ and component Cxa′ of frequency 2 _Y − _C exist in phase.

In this way, the carrier wave component Cc of the low frequency color signal C is removed from the output end of the second limiter 15, that is, the input end of the demodulator 16, and its level becomes the level of the original interference wave component Cx. An FM luminance signal FY containing only the interference wave component Ccf' and component Cxf', which is sufficiently reduced to approximately 1/4 compared to the above, is obtained. And such FM luminance signal
Since FY is supplied to the demodulator 16 and subjected to frequency discrimination, the demodulator 16 detects that the FM luminance signal FY is included in the lower sideband side and the upper sideband side at the stage of the read signal obtained from the reading means. Carrier wave component _Cc of low-pass color signal C of frequency C and frequency 2 _Y − _C
A reproduced luminance signal that is hardly affected by the interference wave component Cx is obtained, and this is led out to the output terminal 17.

G-3 Description of Modified Example In addition, as shown surrounded by a dashed line in FIG. Multiple stages may be connected in cascade, and in such a case, it is possible to further reduce the interference wave components included in the lower side wave band side and the upper side wave band side of the FM luminance signal FY. become.

H. Effects of the Invention As is clear from the above explanation, according to the luminance signal reproducing circuit according to the present invention, an FM luminance signal and a low frequency color signal frequency-converted to the lower frequency side of the FM luminance signal are recorded on a magnetic recording medium. FM obtained during the read signal of
When demodulating a luminance signal to obtain a reproduced luminance signal, the signals included in the demodulation
It is possible to reliably remove and sufficiently reduce interference wave components that cause the carrier wave components and demodulated output of low-frequency color signals other than the FM luminance signal to fall within the band of the original reproduced carrier color signal, and , there is no loss in the upper sideband of the FM luminance signal. Therefore,
It is possible to obtain a reproduced luminance signal of excellent quality without containing reproduced components that cause beat disturbance.

Further, the luminance signal reproducing circuit according to the present invention can not only reproduce a luminance signal based on a read signal from a magnetic tape using a carrier high shift method, but also As in the case of signals read from magnetic tapes that do not use the carrier high shift method, removal of interference wave components that cause low-frequency color signal components and demodulated output to fall within the band of the original reproduced carrier color signal. It has the advantage of being able to reduce the

[Brief explanation of the drawing]

FIG. 1 is a block connection diagram showing an example of a luminance signal regeneration circuit according to the present invention, FIGS. 2A to 2E are conceptual diagrams of signal components used to explain the operation of the example shown in FIG. 1, and FIG. A characteristic diagram showing an example of the frequency spectrum of a color video signal recorded on a magnetic tape,
FIGS. 4 and 5A and 5B are conceptual diagrams of signal components used to explain unnecessary components when reproducing a luminance signal. In the figure, 1 and 2 are magnetic heads, 5 is a switch,
11 is a first trap, 12 is a first limiter,
13 is a second trap, 14 is a low-pass filter, 15 is a second limiter, and 16 is a demodulator.

Claims (1)

[Claims] 1. Connected to the output side of a reading means including a magnetic head that obtains a read signal from a magnetic recording medium on which a frequency modulated luminance signal and a low frequency carrier color signal whose frequency is converted to the lower frequency side thereof are recorded. a first trap section for the carrier wave frequency component of the low-band carrier color signal, which is transmitted, a first limiter section connected to the output side of the reading means, and a first limiter section connected to the output side of the first limiter section. a second trap section for the carrier frequency component of the low-band carrier color signal; and a second trap section connected to the output side of the first limiter section.
a low-pass filter section that passes the main frequency band components of the frequency-modulated luminance signal; a second limiter section connected to the output side of the low-pass filter section; and an output side of the second limiter section. A luminance signal reproducing circuit, comprising: a demodulating section for the frequency modulated luminance signal connected thereto, and obtaining a reproduced luminance signal from the demodulating section.