JPH0560718B2 - - 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 Operational description of the embodiment (FIGS. 2A to 2E) H Effect of the invention A Industrial application field The present invention provides a method in which the luminance signal and the carrier color signal forming a color video signal are each frequency modulated signals. The present invention also 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 low frequency conversion carrier signal.

B. Summary of the Invention The present invention provides that a luminance signal and a carrier chrominance signal forming a color video signal are separated from each other, the luminance signal is made into a frequency modulated signal, and the carrier chrominance signal is generated in a frequency band lower than the 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, the carrier frequency component of the low-frequency carrier color signal is added to the read signal before the demodulation section for the frequency modulated luminance signal. a bandpass filter that passes the carrier frequency component of the low-band carrier color signal from the output of the first limiter section to the output of the first limiter section; A circuit section including an adder section that adds an output obtained via the amplified component, and a circuit section that passes the output of the adder section through a low-pass filter section and a second limiter section that passes the main frequency band components of the frequency modulated luminance signal. By providing a section, the frequency modulated luminance signal obtained in the read signal is divided into the carrier wave component of the low frequency carrier color signal in the lower sideband side and the low frequency carrier color signal generated in the upper sideband side. This allows the signal to be supplied to the demodulator in a state in which the resulting interference wave component has been removed.

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 has a frequency modulated on the high side. The carrier color signal is converted into a modulated luminance signal (hereinafter referred to as FM luminance signal), and the carrier color signal is frequency-converted to the lower frequency side to produce a low-frequency luminance signal (hereinafter referred to as low-frequency color signal), and then both are mixed and sent to the rotating magnetic field. A recording system is widely used in which recording is performed using inclined recording tracks that are supplied to a magnetic tape 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 chrominance signal from the magnetic tape on which the FM brightness signal and low-range chrominance 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 bead interference. 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 −
Interference wave component that changes between _C and 2 _YH − _C and also mixes into the upper sideband side of this FM brightness signal FY
Cx is a frequency modulation component in which a component Ccf of frequency _C and a component Cxf of frequency 2 _Y − _C exist in opposite phase to each other, as shown in FIG. 5A, and a component Cca of frequency _C and a frequency 2 _Y − _C component Cxa and the amplitude modulation component which exist in phase with each other are combined. Each of these signal components is then subjected to demodulation to obtain a reproduced luminance signal.

In this way, it is an unnecessary component contained in the signal supplied to the demodulator for the FM luminance signal FY in the read signal in order to obtain the reproduced luminance signal from the read signal. Carrier wave component Cc and frequency of low-pass color signal _C with frequency C
2 In order to reduce the adverse effects caused by the interference wave component Cx of _Y - _C , in the conventional luminance signal reproducing system, traps and traps for the carrier wave component Cc of the low-frequency color signal C are A low-pass filter is provided that does not pass most of the upper sideband of the FM luminance signal FY, and a trap removes the carrier component Cc of the low-frequency chrominance signal C in the signal supplied to the demodulator, and removes the interference wave component Cx. A low-pass filter should be used to remove the frequency _C
Two traps are provided, one for the carrier wave component Cc of the low frequency color signal C and one for the interference wave component Cx of frequency 2 _Y - _C , and the carrier wave component of the low frequency color signal C in the signal supplied to the demodulator is set. Cc and interference wave component
Cx and Cx are removed by traps.

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 this luminance signal reproduction system, in order to improve the resolution of the reproduced image, the carrier frequency shift band of the FM luminance signal is recorded by moving it to a higher frequency side than the frequencies _YL to _YH (hereinafter referred to as carrier high shift method). in the read signal from the magnetic tape where
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 brightness 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 frequency deviation width is twice the frequency deviation width of the frequency _Y of the carrier wave component Cy of FY, 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 portion 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. It is an object of the present invention to provide a luminance signal reproducing circuit that can reliably remove interference wave components that cause interference without the problems or inconveniences associated with the above-mentioned conventional techniques.

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 trap section for the carrier wave frequency component of the low range color signal, a first limiter section, and a carrier wave frequency component of the low range color signal, which are sequentially connected to the output side of the reading means including a magnetic head that obtains a read signal from the magnetic recording medium. FM luminance. It is configured to include a low-pass filter section that passes the main frequency band components of the signal, a second limiter section, and a demodulation section for the FM luminance signal.

F Effect As described above, in the luminance signal reproducing circuit according to the present invention, first, for the signal supplied to the demodulation section,
The trap section removes the carrier wave component of the low-frequency color signal, and the first limiter section removes the carrier wave component of the low frequency color signal.
The amplitude modulation component of the interference wave component that has mixed into the upper side band of the FM luminance signal and causes its demodulated output to fall within the band of the original reproduced carrier color signal is removed. As a result, the interference wave component is such that the frequency modulation component remains in the lower side wave band side and the upper side wave band side of the FM luminance signal with opposite phases to each other. Then, out of the remaining interference wave components, a 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 extracted by the bandpass filter section, and the component is extracted by the inverting amplification section. Its level is doubled and its polarity is reversed,
In the adder section, it is added to the output of the first limiter section. As a result, the interference wave components are converted into amplitude modulation components that appear in phase with each other on the lower sideband side and the upper sideband side of the FM luminance signal. Next, the low-pass filter section removes components outside the main frequency band of the FM brightness signal, and removes components included in the main frequency band of the FM brightness signal and its lower and upper sidebands. The amplitude modulated component of the interference wave component is supplied to the second limiter section. Then, the amplitude modulation component of the interference wave component is removed by the second limiter section. The FM luminance signal from which the mixed interference wave components have been removed 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 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 converts the signal supplied to the demodulator into a signal that is supplied to the demodulator. Only the FM luminance signal can be used, and there is no loss of the upper side wave band of the FM luminance signal, and
It is also possible to 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 brightness signal FY and low frequency signal C recorded on the slanted tracks are read every scan. These rotating magnetic heads 1
and 2 are connected to selection contacts 5a and 5b of switch 5 via amplifier circuits 3 and 4, respectively. In response to a switching control signal SW from a terminal 6, the switch 5 causes its movable contact 5c to switch between selection contacts 5a and 5b 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, amplified signals of the signals read by the rotating magnetic heads 1 and 2 are alternately output to the movable contact 5c. here,
These rotating magnetic heads 1 and 2, amplifier circuits 3 and 4, and switch 5 collectively 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, a trap 11 for the carrier frequency component of the low-range color signal C and a first limiter 12 are connected to the other output end of the signal branching circuit 7. And the first
The output terminal of the limiter 12 is connected to one input terminal of the adder circuit 13, and the bandpass filter 14 passes the carrier frequency component of the low-pass color signal C.
connected to. An inverting amplifier circuit 15 that doubles the level of the input signal and inverts the polarity is connected to the output end of the bandpass filter 14, and the output end of the inverting amplifier circuit 15 is connected to the adder circuit 13. is connected to the other input end of the Therefore,
The adder circuit 13 applies the output of the first limiter 12 to the output of the first limiter 12.
The carrier frequency component of the low gamut color signal C extracted therefrom is doubled in level and reversed in polarity to add the resulting signal component. Addition circuit 1
A low-pass filter 16 that passes the main frequency band components of the FM luminance signal FY is connected to the output terminal of 3, and the output terminal of the low-pass filter 16 is connected to a second limiter 17 for frequency discrimination. It is connected to a demodulating section 18 formed of a circuit, and an output terminal 19 is provided at the output end of this demodulating section 18 .

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 18 to the demodulator 18 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 reproduces a signal obtained from a magnetic tape by a reading means including rotating magnetic heads 1 and 2, The operation is to demodulate the FM luminance signal FY from the read signal derived from the output terminal of the 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
- Contains 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 frequency 2 _Y − _C is supplied. As mentioned above, the interference wave component Cx of frequency 2 _Y − _C is the component of frequency _C
A frequency modulation component in which Ccf and a component Cxf of frequency 2 _Y − _C exist in opposite phase to each other, and a frequency _C
The component Cca of frequency _2Y − _C and the component Cxa of frequency 2Y − C are synthesized with amplitude modulation components that exist in phase with each other. As _shown in _{FIG .} A frequency modulation component of the interference wave component that will exist at . Here, the levels of the component Ccf of frequency _C and the component Cxf of frequency 2 _Y − _C are assumed to be reduced by half compared to the level of the original interference wave component Cx.
In addition, in FIG. 2C, the first limiter 12
removed by The amplitude modulation component of the interference wave component in which the component Cca of frequency _C and the component Cxa of frequency 2 _Y − _C exist in phase is shown by a broken line.

The signal obtained at the output side of the first limiter 12 is supplied to one input terminal of an adder circuit 13 and also to a bandpass filter 14 .
In the bandpass filter 14, the first limiter 12
Of the interference wave components in the signal obtained at the output side, the frequency _C component Ccf is extracted and supplied to the inverting amplifier circuit 15, where its level is doubled and its polarity is inverted. It is supplied to the other input terminal of the adder circuit 13. As a result, adder circuit 1
3, a signal component obtained by doubling the level of the frequency _C component Ccf and inverting the polarity is added to the signal obtained at the output side of the first limiter 12, and as a result, , the frequency _C component Ccf of the interference wave component in the signal obtained at the output side of the first limiter 12 is canceled out, and instead a frequency _C component having the opposite polarity to the component Ccf is generated.
Cca′ will appear. Therefore, adder circuit 1
The signal obtained at the output side of 3 is the FM luminance signal FY and the frequency _C component, as shown in Figure 2D.
Cca' and the component Cxf of frequency _2Y - _C contain an interference wave component converted into an amplitude modulation component that exists in phase with each other, and this is supplied to the low-pass filter 16.

In the low pass filter 16, these FM
In addition to the brightness signal FY and the interference wave component converted into the amplitude modulation component, harmonic components generated by the first limiter 12, etc. are removed, and the FM brightness signal FY and frequency are as shown in FIG. 2D. The interference wave component is supplied to the second limiter 17 as an amplitude modulated component in which the component Cca' of _C and the component Cxf of frequency 2 _Y - _C exist in phase with each other. Then, in the second limiter 17, the interference wave component that has been made into an amplitude modulation component is removed, and the output side of the second limiter 17 is as follows.
Only the FM luminance signal FY as shown in FIG. 2E is obtained.

In this way, the carrier wave component Cc of the low frequency color signal C and the frequency 2-
An FM brightness signal FY obtained by removing the interference wave component of _C appears, and this FM brightness signal FY is sent to the demodulator 1.
8 for frequency discrimination, the demodulator 1
8 are included in the lower side waveband side and the upper sideband side of the FM luminance signal FY at the stage of the read signal obtained from the reading means. Carrier wave component _Cc of low frequency color signal C of frequency C and interference wave component Cx of frequency 2 _Y − _C
A reproduced luminance signal unaffected by

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 found in 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 carrier wave components of low-frequency color signals other than FM luminance signals and interference wave components that would cause the demodulated output to fall within the band of the original reproduced carrier color signal. There is no loss of the upper sideband. Therefore, it is possible to obtain a reproduced luminance signal of excellent quality that does not contain 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 do

[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,
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 trap, 12 is a first limiter, 13 is an adder circuit, 14 is a band pass filter, 15 is an inverting amplifier circuit, 16 is a low pass filter, and 17 is a second
18 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 trap section for the carrier wave frequency component of the low-band carrier color signal, which is connected to the output side of the reading means; a first limiter section connected to the output side of the first limiter section; a bandpass filter section that passes the carrier frequency component of the low-pass carrier color signal; an inverting amplification section connected to the output side of the bandpass filter section; and an output of the inverting amplification section connected to the output of the first limiter section. a low-pass filter section connected to the output side of the adder section and passing the main frequency band components of the frequency modulated luminance signal; and a low-pass filter section connected to the output side of the low-pass filter section. A luminance signal reproducing circuit, comprising: a second limiter section; and a demodulating section for the frequency modulated luminance signal connected to an output side of the second limiter section, and obtaining a reproduced luminance signal from the demodulating section.