JPS61174895A - Circuit for reproducing luminance signal - Google Patents

Abstract

PURPOSE:To obtain an excellent reproducing luminance signal and to decrease an interference wave component by providing successively the first trapping part, a limiter part, the second trapping part, a low-pass filter part, the second limiter part and a demodultor part at the output side of reading means. CONSTITUTION:For the signal supplied to the demodulating part, the carrier component of the low area chrominance components is removed by the first trapping part 11, and the amplitude modulating component of the interference wave component mixed into the upper side wave band part side of the FM luminance signal is removed by the first limiter part 12. Continuously, by second trapping part 13, the carrier wave component of the low area chrominance components in the lower side wave band part side of the FM luminance signal is removed. Next, by a low-pass filter part 14, the component outside the mainfrequency band of the FM luminance signal is removed. By the second limiter part 15, the amplitude modulating component of the interference wave component, which remains at the upper side wave band side of the FM luminance signal, 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 embodiment (FIGS. 2 A-E) G-3 Explanation of modification H Effect of invention A Industrial application field The present invention is applicable to luminance signals and carrier color signals forming color video signals. From the read signal from the magnetic recording medium recorded as a frequency modulation signal and a low frequency conversion carrier signal, respectively,
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.
By providing a combination of a plurality of trap sections for the carrier frequency component of the low-band carrier chrominance signal, a plurality of limiter sections, and a low-pass filter section that passes the main frequency band component of the frequency modulated luminance signal, The carrier wave component of the low frequency carrier color signal in the lower sideband side is removed from the frequency modulated luminance signal obtained in the frequency modulated luminance signal, and the interference wave component resulting from the low frequency carrier color signal generated in the upper sideband side is removed. The signal can be supplied to the demodulator in a sufficiently reduced state.

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 receiver 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 slanted recording trunks that are arranged slanted is widely used.

With this method, the FM 1 degree signal and the low frequency color signal are recorded on the magnetic tape using the rotating magnetic head.
When the luminance signal and 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 , due to the non-linear characteristics of the magnetic recording and reproducing system consisting of a magnetic tape and a rotating magnetic head, based on the presence of the carrier wave component of the low-range color signal component and the low-range color signal in addition to the FM luminance signal, The demodulated output falls within the band of the original reproduced carrier color signal, and the interference wave component is included as an unnecessary component, so that such signal is demodulated as it is to reproduce the luminance signal. If this is done, a carrier color signal component will be 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. In the luminance signal Y, the leading edge of the synchronization signal is at frequency fYL, and its white beak is at frequency f. The FM luminance signal FY has a carrier frequency shift band such that (f vL< f v)I), and the carrier color signal has a frequency f that is sufficiently lower than the frequency fYL.

If a read signal is obtained from a magnetic tape recorded as a low-range color signal C with a color subcarrier frequency of If we look at the read signal mainly from the FM luminance signal FY that should be demodulated to obtain the reproduced luminance signal,
As shown in FIG. 4, the frequency fv (fy is f7
With respect to the carrier wave component cy of the FM luminance signal FY (which changes between L and fVH), there is a carrier wave component Cc of the low frequency chrominance signal C of frequency fc on the lower sideband side, and on the upper sideband side,
The frequency 2fy f generated due to the low frequency color signal C inserted into the lower sideband side of the recorded FM luminance signal FY
The interference wave component Cx of c is mixed. Here, the frequency 2fv-fc of the interference wave component Cx is 2fyL fc
The interference wave component Cx that changes between
is the component Cc of frequency f, as shown in FIG. 5A.
A frequency modulation component in which f, frequency 2f, and -fc component Cxf exist in opposite phases, and an amplitude in which frequency fc component Cca and frequency 2fY-fc component Cxa exist in phase with each other. The modulation component is combined with the modulation component. 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 low frequency color signal C of frequency fc, which is an unnecessary component included in the signal supplied to the demodulator for the FM luminance signal FY in the read signal, is
In order to reduce the adverse effects caused by the carrier wave component Cc of A trap for 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 and interference is removed. The wave component Cx is removed by a low-pass filter, or the interference wave with the frequency 2fv fc for the carrier component Cc of the low-pass color signal C of the frequency fc is removed from the signal supplied to the demodulator. Two traps are provided, one for the component Cx, and the carrier wave component CC and the interference wave component Cx of the low frequency color signal C in the signal supplied to the demodulator are removed by the traps, respectively. There is.

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 defined as the frequency f'/
L"" f When the 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 YH (hereinafter referred to as carrier high shift method), the FM luminance Since the frequency of the carrier wave component of the signal is shifted higher than frequency f7, 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 a reproduced luminance signal. Therefore, there is a lack of compatibility with magnetic tapes employing the carrier 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 fc, and one for the carrier wave component Cc of the low frequency color signal C of frequency fc, and one for the carrier wave component Cc of the low frequency color signal C of frequency fc
When two traps are provided, one for the interference wave component Cx of y fc, the frequency 2fv-fc of the interference wave component Cx is equal to 2 of the frequency deviation width of the frequency fY of the carrier wave component cy of the FM luminance signal FY. Since the frequency deviation width is twice as large, the trap for the interference wave component Cx is required to exhibit a trapping effect over a correspondingly wide frequency range. There is a disadvantage that the supplied FM luminance signal FY loses a large amount of information contained in its upper sideband portion. 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. The interference wave component has frequency 2
Since it has a frequency shifted to a higher frequency side than fv fc, a trapping effect against such interference wave components cannot be obtained, and the adverse effects caused by the interference wave components cannot be alleviated.

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 to be demodulated 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 reproducing circuit O path that can reliably perform sufficient reduction 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 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 sequentially connected to the output side of a reading means including a magnetic head that obtains a read signal from a magnetic recording medium. a second trap section for frequency components; a low-pass filter section that passes main frequency band components of the FM luminance 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 first trap section first removes the carrier wave component of the low-range 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 whose demodulated output falls 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 removes, from among 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. Next, the low-pass filter section removes components outside the main frequency band of the FM brightness signal, and removes the main frequency band components of the FM brightness signal and the second trap section included in the upper sideband side. The interference wave component remaining after passing is supplied to the second limiter section. Then, the second limiter section removes the amplitude modulation component of the interference wave component remaining on the upper side band side of the FM luminance signal, and thereby the lower side band side and upper side band side of the FM brightness signal. The level of the interference wave component that will be distributed to the side and remain will be halved again,
The interference wave component 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 manner 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. The signal may include an FM luminance signal and interference wave components that are sufficiently reduced and only remain in the lower sideband side and the upper sideband side thereof, and furthermore, the FM luminance signal This method does not involve loss of the upper sideband portion, 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 a tilted trunk formed on a magnetic tape, and each scan scans the FM luminance signals FY and FM brightness signals recorded on the tilted track. Read the low range color signal C. The output ends of these rotating magnetic heads 1 and 2 are connected to selection contacts 5a and 5 of a switch 5 via amplifier circuits 3 and 4, respectively.
connected to b. The switch 5 has its movable contact 5C connected to the selection contacts 5a and 5b in synchronization with the period in which the rotating magnetic healds 1 and 2 scan the inclined tracks on the magnetic tape in response to a switching control signal SW from the terminal 6. As a result, the amplified outputs of the read signals from the rotary magnetic heads 1 and 2 are alternately delivered to the movable contact 5C. Here, these rotating magnetic heads 1 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
A first trap 11 for the carrier frequency component of the low-pass color signal C and a first limiter 12 are connected. At the output end of the first limiter 12, a second trap 13 for the carrier frequency component of the low frequency color signal C and an FM
A demodulator 16 is connected to a low-pass filter 14 that passes the main frequency band components of the luminance signal FY, and the output end of the low-pass filter 14 is formed by a frequency discrimination circuit via a second limiter 15. An output terminal 17 is provided at the output end of the demodulator 16 .

In such a connection relationship, from the first trap 11 connected to the other output end of the signal branch circuit 7 to the demodulator 16
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 a signal obtained from a magnetic tape by a reading means including rotating magnetic heads 1 and 2 and sent to a signal branching circuit 7. The operation is to demodulate the FM luminance signal therein from the read signal derived to the other output terminal of the output terminal to obtain a reproduced luminance signal.Next,
This is summarized in ).

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 mainly the FM luminance signal FY to be demodulated to obtain the FM luminance signal FY of frequency fV (f7 varies between fYL and ryo), as described above and shown in FIG. 2A, In addition to the carrier wave component cy of
c, and furthermore, on the upper sideband side, a low-pass color signal C
The frequency 2fv occurs due to the fact that the demodulated output falls within the band of the original reproduced carrier color signal.
The interference wave component Cx of fc is included.

Here, the frequencies 2f, -fc of the interference wave component Cx are 2f
It changes between yLfc and 2fvI4-fc.

Then, the first trap 11 acts on the read signal, and the frequency f. The carrier component Cc of the low-pass color signal C is removed. Therefore, the first limiter 12 has a second
As shown in FIG. B, the carrier wave component Cc of the low-range color signal C is removed, and a signal containing the FM luminance signal FY and the interference wave component Cx of frequency 2fvfc is provided. As mentioned above, the interference wave component Cx of frequency 2fv-fc is a frequency modulation component in which the component Ccf of frequency fc and the component Cxf of frequency 2fy fc exist in opposite phases, and the component Cca of frequency fc and the frequency 2fY
The component Cxa of fc and the amplitude modulation component that exist in phase with each other are combined, but the amplitude modulation component of these is removed by the first limiter 12, and the amplitude modulation component is removed by the first limiter 12. On the output side of the FM luminance signal FY, as shown in FIG. Ingredients appear. Here, component Ccf of frequency fc and frequency 2
It is assumed that the level of the component Cxf of fv fc is reduced by half compared to the level of the original interference wave component Cx. In addition, in FIG.
The amplitude modulation component of the interference wave component that exists in phase with the component Cxa of C 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 re of the interference wave component, which is the carrier frequency component of the low-range color signal C, is is removed.

Therefore, as shown in the second diagram, the low-pass filter 14 receives the frequency f of the interference wave component. Component Cca is removed, and a signal containing the FM luminance signal FY and the component Cxf of frequency 2fy fc of the interference wave components is supplied.

In the low-pass filter 14, harmonic components generated by the first limiter 12, etc., other than these FM luminance signal FY and the interference wave component which is the component Cxf of frequency 2fv-fC, are removed, and the second filter is removed. The FM luminance signal FY and interference wave components Cxf of frequencies 2f and -fo are supplied to the second limiter 15 as shown in FIG. Here, too, the interference wave component Cxf at frequencies 2f and -fc is a component Cc f' at frequency fc and a component Cx f at frequencies 2f and -fc.
' are present in opposite phase to each other, and the frequency modulation component Cca' of frequency fc and the 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 second limiter 15. On the output side, as shown in FIG. 2E, the FM luminance signal FY and the frequency fc component Cc are provided.
A frequency modulation component of the interference wave component appears in which the component Cx f' of the frequency 2fy fc exists in opposite phases to each other. Here again, the component Cc of frequency fC
The level of the component Cxf'' of M and frequency 2fy-rc is assumed to be reduced by half compared to the level of the interference wave component Cxf, and therefore, the level of the original interference wave component Cx is approximately 1/1. This will be reduced to 4.

Note that, also in FIG. 2E, the frequency fc component Cca' and the frequency 2f, which are removed by the second limiter 15,
The amplitude modulation component of the interference wave component that exists in phase with the component Cxa" of y fc is shown by a broken line.

In this way, the output end of the second limiter 15, i.e.
At the input end of the demodulator 16, a carrier wave component C of the low frequency color signal C is input.
c is removed, and its level is sufficiently reduced to approximately 1/4 compared to the level of the original interference wave component Cx.
An FM luminance signal FY that only includes c f' and component Cx f' is obtained. and,
Since the FM luminance signal FY is supplied to the demodulator 16 and subjected to frequency discrimination, the demodulator 16 outputs the lower and upper side waves of the FM luminance signal FY at the stage of the read signal obtained from the reading means. Carrier wave component Cc of low-pass color signal C of frequency fc and frequency 2 fy rc included in the band side
A reproduced luminance signal that is almost unaffected by the interference wave component Cx is obtained, and this is led out to the output terminal 17.

Description of Modification G-3 Note that the portion consisting of the first limiter 12, second trap 13, and low-pass filter 14 in the above example, as shown surrounded by a dashed line in FIG.
A plurality of 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.

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 a 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 the original reproduced signals. It is possible to reliably remove and sufficiently reduce interference wave components that would fall within the band of the carrier color signal, and moreover, there is no loss of the upper sideband portion 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.

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 and reduce 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 first trap, 12 is a first limiter, 13 is a second trap, 14 is a low-pass filter, 15 is a second limiter, 16 is the 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. In addition, the first
a first limiter section connected to the output side of the reading means; and a second limiter section connected to the output side of the first limiter section for the carrier frequency component of the low frequency carrier color signal. a trap section; a low-pass filter section that is connected to the output side of the first limiter section and that passes the main frequency band components of the frequency modulated luminance signal; and a low-pass filter section that is connected to the output side of the low-pass filter section. a second limiter section; and a demodulation 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 demodulation section.