JPS61174896A - Circuit for reproducing luminance signal - Google Patents

Abstract

PURPOSE:To supply a luminance signal only to a modulating part by connecting successively a trapping part, the first limiter part, a band pass filter part, an inverting amplifying part, a signal synthesizing part, a low-pass filter part and the second limiter at the output side of a reading means. CONSTITUTION:For the signal supplied to the demodulating part, the carrier component of the low area chrominance components is removed by a trapping part 11, and by the first limiter part 12, the amplitude modulating component of the interference wave component at the upper side wave band part side of the FM luminance signal is removed. By a band-pass filter part 14, the component having the frequency equivalent to the carrier component of the low area chrominance components is taken out, the polarity is inverted by an inverting amplifying part 15, and at an adder 13, applied to the output of the first limiter part. Next, by a low-pass filter part 16, the component outside the main frequency band of the FM luminance signal is removed. By the second limiter part 17, an amplitude modulating component of the interference wave component is removed.

Description

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

A. Field of industrial application B. Overview of the invention C. Prior art D. Problem to be solved by the invention E. Means for solving the problem F. Effect G. Example G-1 Description of the configuration of the example (Fig. ) G-2 Explanation of operation of the embodiment (FIGS. 2 A-E) H Effects of the invention A Industrial application field The present invention provides a method in which a luminance signal and a carrier color signal forming a color video signal are each a frequency modulated signal. And from the read signal from the magnetic recording medium recorded as a low frequency conversion carrier signal,
The present invention relates to a luminance signal reproducing circuit that obtains a reproduced luminance signal.

B. Summary of the Invention The present invention provides that a luminance signal and a carrier chrominance signal that form 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 made into a frequency modulated signal in the 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 demodulator for the frequency-modulated luminance signal is provided.
A circuit section that causes the read signal to pass through a trap section and a first limiter section for the carrier frequency component of the low frequency carrier color signal, and a circuit section that passes the low frequency carrier color signal from the output of the first limiter section to the output of the first limiter section. A circuit section including a bandpass filter that passes the carrier frequency component of the signal and an adder section that adds the output obtained through the inverting amplifier section, and a low-pass filter that passes the main frequency band component of the frequency modulated luminance signal to the output of the adder section. By providing a filter section and a circuit section that passes through the second limiter 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 on the lower side band side and the carrier wave component on the upper side thereof. The signal can be supplied to the demodulator in a state in which interference wave components caused by the low-frequency carrier color signal occurring on the waveband side have been removed.

C. Conventional technology When a color video signal is recorded on a magnetic tape,
A luminance signal and a carrier color signal forming a color video signal are separated, and the separated luminance signal is frequency-modulated on the high frequency side to become a frequency-modulated luminance signal (hereinafter referred to as an FM luminance signal),
After the carrier color signal is converted to a low frequency carrier color signal (hereinafter referred to as "low frequency color signal"), the two are mixed and supplied to a rotating magnetic head, and the signal is converted to a low frequency carrier color signal (hereinafter referred to as a "low frequency color signal"). A recording system in which recording is performed using oblique recording tracks that are arranged obliquely is widely used.

With this method, FM luminance signals and low-range color signals are recorded on a magnetic tape, and a rotating magnetic head is used to extract FM signals from the magnetic tape.
When the luminance signal and the low-range color signal are read to obtain a read signal, and the luminance signal and carrier color signal are reproduced based on the read signal, the signal supplied to the demodulator for the FM luminance signal in the read signal is as follows. In addition to the FM luminance signal, the presence of the carrier wave component of the low-range color signal component and the low-range color signal is caused by the nonlinear characteristics of the magnetic recording and reproducing system consisting of a magnetic tape and a rotating magnetic head. The interference wave component that causes the demodulated output to fall within the band of the original reproduced carrier color signal is included as an unnecessary component, and such a signal is demodulated as it is to reproduce the luminance signal. In this case, a carrier color signal component is generated in the reproduced luminance signal, resulting in beat disturbance.

For example, in FIG. 3, the frequency is plotted on the horizontal axis and the level is plotted on the vertical axis. As shown in FIG. The FM luminance signal FY has a carrier frequency shift band such that (f ML < f Y) I), and the carrier color signal has a frequency fc that is sufficiently lower than the frequency f'/L as the color subcarrier frequency. Assuming that a read signal is obtained from a magnetic tape recorded as a low-range color signal C, the read signal includes an FM luminance signal FY and a low-range color signal C.
However, if we look at the read signal mainly from the FM luminance signal FY to be demodulated to obtain the reproduced luminance signal, as shown in FIG. 4, the frequency fy Cfv
changes between f'/L and ryHO).
For the carrier wave component cy of Y, there is a frequency f on the lower sideband side.
There is a carrier wave component Cc of the low frequency color signal C of c, and this occurs due to the low frequency color signal C inserted into the lower sideband side of the FM luminance signal FY to be recorded on the upper sideband side. Frequency 2
The interference wave component Cx of fv fc is mixed in.

Here, the frequency 2fv fc of the interference wave component Cx is 2
fvL varies between fc and 2fvH-[c, and
The interference wave component Cx mixed into the upper side band side of this FM luminance signal FY is composed of a component CC of frequency fc [and a component Cxf of frequency 2fy fc, which exist in opposite phases to each other, as shown in FIG. 5A. The frequency modulation components that will be
a and the amplitude modulation components that exist in phase with each other. 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, a low frequency color signal C of frequency rc, which is an unnecessary component included in the signal supplied to the demodulator for the FM luminance signal FY in the read signal, is used.
In order to reduce the harmful effects caused by the carrier wave component Cc of the frequency 2fY-fc and the interference wave component Cx of the frequency 2fY-fc, in the conventional luminance signal reproducing system, the carrier wave of the low-frequency color signal C is used for the signal supplied to the demodulator. A trap for the component Cc and a low-pass filter that does not pass most of the upper sideband part of the FM luminance signal FY are provided, and the carrier component Cc of the low-pass color signal C in the signal supplied to the demodulator is removed by the trap. The interference wave component CX is removed by a low-pass filter, or the carrier wave component C of the low-pass color signal C of frequency f is removed from the signal supplied to the demodulator.
Interference wave component C with frequency 2fy fc for c
Two traps, one for x and one for .

D Problems to be Solved by the Invention However, in this way, in the luminance signal reproduction system,
When a low-pass filter is provided for the signal supplied to the demodulation section, which traps the carrier component Cc of the low-pass color signal C and prevents most of the upper sideband part of the FM luminance signal FY from passing through, the demodulation section FM luminance signal FY supplied to
In this case, most of the information contained in the upper sideband portion is lost, leading to a deterioration in the quality of the reproduced image obtained based on the reproduced luminance signal. Furthermore, in order to improve the resolution of the reproduced image, this luminance signal reproduction system
The carrier frequency shift band of the FM luminance signal is the frequency f YL
” f When an FM luminance signal is supplied as a read signal from a magnetic tape that is recorded by moving it to the higher frequency side than YM (hereinafter referred to as carrier high shift method), the FM luminance signal is The frequency of the carrier wave component is the frequency f
Since the signal is shifted to a higher frequency side than the carrier voltage, there is a risk that it will be outside the passband of the low-pass filter and over-modulation will occur, making it impossible to obtain the reproduced luminance signal. This results in a lack of compatibility with magnetic tapes that use the high shift method.

Also, as described above, in the luminance signal reproducing system, for the signal supplied to the demodulation section, one for the carrier wave component Cc of the low frequency color signal C of frequency f, and one for the carrier wave component Cc of the low frequency chrominance signal C of frequency 2f.
When two traps are provided, one for the interference wave component Cx of v fc, the frequency 2fv fc of the interference wave component Cx is the carrier wave component Cy of the FM luminance signal FY.
Since the frequency deviation width is twice the frequency deviation width of the frequency f7 of 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 luminance signal reproducing system is supplied with an FM luminance signal in a read signal from a magnetic tape using the carrier high shift method, the FM luminance signal corresponding to the interference wave component Cx mixed therein is supplied to the luminance signal reproducing system. Since the interference wave component has a frequency shifted to a higher frequency side than the frequency 2fv re, a trapping effect for such interference wave component cannot be obtained, and the harmful effects caused by the interference wave component cannot be reduced. turn into.

In view of the above, the present invention demodulates an FM luminance signal obtained in a read signal from a magnetic recording medium in which an FM luminance signal and a low frequency color signal frequency-converted to the lower frequency side thereof are recorded. In order to obtain the reproduced luminance signal, it is necessary to remove the carrier wave component of the low frequency color signal included in the signal used for demodulation and the interference wave component that causes the demodulated output to fall within the band of the original reproduced carrier color signal. It is an object of the present invention to provide a luminance signal regeneration circuit that can reliably perform the following steps without the problems or inconveniences associated with the above-mentioned conventional techniques.

E. Means for Solving the Problems In order to achieve the above 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 unit for a carrier frequency component of a low range color signal, a first limiter unit, and a carrier frequency component of a 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. FM luminance. A low-pass filter section that passes the main frequency band components of the signal.

It is configured to include a second limiter section and a demodulation section for the FM luminance signal.

F action In the luminance signal reproducing circuit according to the present invention as described above, the trap section first removes the carrier wave component of the low frequency color signal from the signal supplied to the demodulation section, and the first limiter The amplitude modulation component of the interference wave component mixed into the upper sideband side of the FM luminance signal and causing the demodulated output to fall within the band of the original reproduced carrier color signal is removed. As a result, the interference wave component becomes a frequency modulation component that 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-pass chrominance signal on the lower side band side of the FM luminance signal is extracted by the band-pass filter section, and is extracted by the inverting amplification section. Its level is doubled, its polarity is inverted, and added to the output of the first limiter section in the adding 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 sideband side and upper sideband side. 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 demodulator, and a reproduced luminance signal is obtained from the demodulator.

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. It is possible to use only the FM luminance signal, and
This eliminates the loss of the upper sideband portion 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 Embodiment G-1 Description of configuration of embodiment 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 recorded as the FM luminance signal FY and the low frequency color signal C as shown in FIG. The invention is said to have been applied to a reproducing device that obtains a reproduced luminance signal and a reproduced transport color signal from a magnetic tape. In this case, inclined tracks are formed alternately on the magnetic tape by two rotating magnetic heads supplied with an FM luminance signal FY and a low-range color signal C, so that, for example,
FM luminance signal F for one field period for each inclined track
It is assumed that Y and low-range color signals C have been recorded.

In FIG. 1, rotating magnetic heads 1 and 2 are designed to alternately and sequentially scan inclined tracks formed on a magnetic tape, and each scan scans an FM luminance signal recorded on the inclined tracks. Read FY and low range color signal C.

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. The switch 5 connects its movable contact 5C to the selection contacts 5a and 5b in synchronization with the period in which the rotating magnetic heads 1 and 2 scan the inclined tracks on the magnetic tape in response to the switching control signal SW from the terminal 6. 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 and 2.
The amplifier circuits 3 and 4 and the switch 5 together form 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 branch circuit 7 has a
Trap 11 for the carrier frequency component of the low-pass color signal C
and the first limiter 12 are connected. and,
The output terminal of the first limiter 12 is connected to one input terminal of an adder circuit 13 and also to a bandpass filter 14 that passes the carrier frequency component of the low-pass color signal C.

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 Kaga circuit 13 uses the output of the first limiter 12 as
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. At the output end of the adder circuit 13, F
A demodulator is connected to a low-pass filter 16 that passes the main frequency band components of the M luminance signal FY, and the output end of the low-pass filter 16 is connected to a demodulator formed by a frequency discrimination circuit via a second limiter 17. 18, and an output terminal 19 is provided at the output end of this demodulator.

In such a connection relationship, the demodulator 18 is connected to the first trap 11 connected to the other output end of the signal branch circuit 7.
Each circuit section up to constitutes an example of the luminance signal reproducing circuit according to the present invention.

G-2 Description of Operation of Embodiment An example of the luminance signal reproducing circuit according to the present invention configured as described above is an example of the luminance signal reproducing circuit according to the present invention configured as described above. From the read signal derived to the output terminal of the FM luminance signal F
The operation is to demodulate Y to obtain a reproduced luminance signal, but next,
I will discuss this.

The read signal obtained by the reading means and led out to the other output end of the signal branching circuit 7 includes the FM luminance signal FY and the low-range color signal C, and therefore, this is used as the reproduced luminance signal. Considering the FM luminance signal FY to be demodulated in order to obtain it, as mentioned above and as shown in FIG. 2A, the frequency fvCf7 changes between f'i'L and fYH). In addition to the carrier wave component cy of the FM luminance signal FY, the carrier wave component Cc of the low-range color signal C of frequency fc is included in the lower sideband side, and the carrier wave component Cc of the low-range color signal C of the frequency fc is included in the upper sideband side. This includes an interference wave component Cx of frequency 2 fv fc which is generated due to the demodulated output falling within the band of the original reproduced carrier color signal. Here, the frequency 2fy of the interference wave component Cx
fc changes between 2fVL fc and 2fyo fc.

Then, the first trap 11 acts on the read signal, and the carrier wave component Cc of the low frequency color signal C of the frequency fc is removed. Therefore, the first limiter 12 has a second
As shown in FIG. B, the carrier wave component Cc of the low-frequency color signal C is removed, and a signal containing the FM luminance signal FY and the interference wave component Cx of frequency 2fy fc is supplied. As mentioned above, the interference wave component Cx of -fc is composed of a frequency modulation component in which the component Ccf of frequency f., the component Cxf of frequency 2f and -fc exist in opposite phases, and the component Cca of frequency fc. Frequency 2fy f
The component Cxa of c is a composite of the amplitude modulation components that exist 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 FM luminance signal FY and the frequency fc component C as shown in FIG.
A frequency modulation component of the interference wave component appears in which cf and the component Cxf of frequency 2fV-fo exist in opposite phases to each other. Here, component Ccf of frequency fc and frequency 2fv
The level of the component Cxf of fc is the original interference wave component C
It is assumed that the level of x is reduced by half. In addition, in FIG. 2C, the amplitude modulation component of the interference wave component that is removed by the first limiter 12 and in which the component Cca of the frequency fo and the component Cxa of the frequency 2fY-f exist in phase is Indicated by a dashed line.

The signal obtained at the output side of this 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 frequency f of the interference wave component in the signal obtained at the output side of the first limiter 12. The component Ccf is taken out and supplied to the inverting amplifier circuit 15, its level is doubled, its polarity is inverted, and then supplied to the other input terminal of the adder circuit 13. As a result, in the adder circuit 13, a signal component obtained by doubling the level of the component Ccf of the frequency fc and inverting the polarity is added to the signal obtained at the output side of the first limiter 12. As a result, the component Ccf of the frequency fc of the interference wave component in the signal obtained at the output side of the first limiter 12 is canceled, and the component Cc
A component Cca' of frequency f, which has a polarity opposite to f, appears. Therefore, the signal obtained at the output side of the adder circuit 13 is the FM luminance signal FY, as shown in the second diagram.
and frequency r. component Cca'' and frequencies 2f, -f.

The components Cxf and Cxf include interference wave components converted into amplitude modulation components that exist in phase with each other,
This is supplied to a low pass filter 16.

In the low-pass filter 16, harmonic components generated by the first limiter 12 and the like other than these FM frequency signals FY and the interference wave components converted into amplitude modulation components are removed, and the harmonic components are removed as shown in the second figure. The FM luminance signal FY and the interference wave component, which is an amplitude modulated component in which the frequency fc component Cca° and the frequency 2fy fc component Cxf exist in phase with each other, are supplied to the second limiter 17. Then, in the second limiter 17, the interference wave component that is the amplitude modulation component is removed, and only the FM luminance signal FY as shown in FIG. 2E is obtained on the output side of the second limiter 17. It will be done.

In this way, the output end of the second limiter 17, i.e.
At the input end of the demodulator 18, an FM luminance signal FY obtained by removing the carrier wave component Cc of the low-frequency color signal C and the interference wave component of frequency 2f-fC from the read signal appears,
! Since the i degree signal 'FY is supplied to the demodulator 18 and subjected to frequency discrimination, from the demodulator 18 onward, the lower side band side and upper side band side of the FM luminance signal FY are detected at the stage of the read signal obtained from the reading means. Frequency f included in the band side. A reproduced luminance signal unaffected by the carrier wave component Cc of the low-range color signal C and the interference wave component Cx of frequencies 2f and -fC is obtained, and this is led out to the output terminal 19.

Effects of the Invention H As is clear from the above explanation, the luminance signal reproducing circuit according to the present invention can reproduce FM luminance signals from a magnetic recording medium on which a frequency-converted low-frequency color signal is recorded on the lower side of the FM luminance signal. When demodulating the FM luminance signal obtained in the read signal to obtain the reproduced luminance signal, the carrier wave components of the low-frequency color signal other than the FM luminance signal included in the signal used for demodulation and the demodulated output are original. Interference wave components that fall within the band of the reproduced carrier color signal can be reliably removed, and the upper sideband portion of the FM luminance signal is not lost. Therefore, it is possible to obtain a high-quality reproduction degree signal that does not contain reproduction components that cause beat disturbance.

Furthermore, the luminance signal regeneration circuit according to the present invention has a carrier
Not only can the luminance signal be reproduced based on the read signal from a magnetic tape that uses the carrier high shift method, but also the read signal from the magnetic tape that does not use the carrier high shift method. Similarly to the above case, this method has the advantage of being able to remove interference wave components that cause the low frequency color signal components and the demodulated output to fall within the band of the original reproduced carrier color signal.

[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, and FIGS. 4 and 5 A and B 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, and 14
15 is a band pass filter, 15 is an inverting amplifier circuit, 16 is a low pass filter, 17 is a second limiter, and 18 is a demodulator.

Claims (1)

[Claims] A device 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 of the frequency modulated luminance signal are recorded. a trap section for the carrier frequency component of the low frequency carrier color signal; a first limiter section connected to the output side of the reading means; and a trap section for the carrier wave frequency component of the low band carrier color signal; a bandpass filter section that passes a carrier frequency component of the band carrier color signal; an inverting amplifier section connected to the output side of the bandpass filter section; and an output of the inverting amplifier section connected to the output side of the first limiter section. a low-pass filter unit connected to the output side of the adder unit and passing the main frequency band components of the frequency modulated luminance signal; and a low-pass filter unit connected to the output side of the low-pass filter unit. 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, the luminance signal reproducing circuit obtaining a reproduced luminance signal from the demodulating section.