JPS5838994B2 - Eizoushingoki Rokusaiseihoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video signal recording and reproducing system, and in particular, in a recording and reproducing apparatus that records and reproduces a color video signal by separating it into a luminance signal and a color signal, the present invention relates to an ACC of a color signal transmission line in a recording system. It is an object of the present invention to provide a method for recording a color video signal with the total amplitude of the color signal component always kept constant using an automatic gain control circuit.

FIG. 1 shows a block system diagram of an example of a recording system of a conventional video signal recording and reproducing system.

In the figure, reference numeral 1 denotes an input terminal, from which a color video signal is supplied to a low-band P wave generator 2, a band wave generator 8, and a synchronization signal separation circuit 12.

The luminance signal (Y signal) component extracted by removing frequency components of 3 MHz or higher from the color video signal by the low-frequency E wave generator 2 is applied to an automatic gain control circuit 3, where its amplitude is made constant. Furthermore, it is supplied to a frequency modulation circuit 4.

The brightness signal is frequency modulated by the frequency modulation circuit 4, and the leading edge of the synchronizing signal is set to 3.8 MHz, and the peak value of the white signal is set to 5.4 MHz.
It is assumed to be an FM modulated signal with a frequency shift of MHz.

This FM modulation signal is supplied to the high frequency F wave generator 5, where the I
After frequency components below MHz are removed, the signal is supplied to the synthesis circuit 6.

On the other hand, from the color video signal supplied to the band F wave generator 8,
Color signal components of MHz to 4 MHz are extracted and applied to a gain control circuit 9 and a burst extraction circuit 13, respectively.

Here, the burst extraction circuit 13 is supplied with a synchronization signal separated from the video signal by the synchronization signal separation circuit 12.

Thereby, the color burst signal in the color signal component is extracted on the burst extraction circuit 13, and this color burst signal is supplied to the ACC detection circuit and the color killer (color erasure) detection circuit 14.

The color burst signal supplied to the ACC detection circuit and the color killer detection circuit 14 is detected here for its level or presence, and is used as a control signal by the gain control circuit 9.
supplied to

The output color signal component of the band P wave generator 8 is controlled by the control signal from the circuit 14 in the gain control circuit 9.

That is, if a color burst signal exists, a control signal whose level of the color burst signal is detected by the circuit 14 is supplied to the gain control circuit 9.

As a result, the gain control circuit 9 outputs a color signal in which the amplitude of the color burst signal is made constant and is supplied to the frequency conversion circuit 10.

Furthermore, if there is no color burst signal, that is, if a black and white video signal is supplied from terminal 1, the AC
The input color signal component of the gain control circuit 9 is cut off and not outputted by the control signals of the C detection circuit and color killer detection circuit 140.

The color signal with the amplitude of the color burst signal, which is the output signal of the gain control circuit 9, is adjusted to a constant value, and the color signal is output from the local oscillation circuit 15 at a frequency of 4.27M by the frequency conversion circuit 10.
After frequency conversion (chrominance signal low frequency conversion) using the Hz signal, the signal is supplied to a low frequency F wave generator 11 having a cutoff frequency of IMHz.

The color signal is converted into a signal having a band of IMHz or less by the low frequency wave generator 11, and is then supplied to the synthesis circuit 6, where it is combined with the FM modulation signal having a band of IMHz or more.

The output composite signal of the composite circuit 6 is amplified by the recording amplifier circuit 1 and then recorded on the magnetic tape 17 by the video head 16.

Next, during playback, as will be explained with reference to the block diagram in FIG. 27.

The frequency modulated signal of IMHz or more separated by this high frequency wave generator 21 is amplitude limited by an amplitude limiting circuit (limiter) 22, and then demodulated by a frequency demodulating circuit 23.

The luminance signal demodulated by this demodulation circuit 23 is applied to a synthesis circuit 24.

On the other hand, the output signal of the regenerative amplifier circuit 20 supplied to the low-pass P wave generator 27 with a cut-off frequency of I MHz is converted into a low-frequency color signal component, and this color signal component is sent to the gain control circuit 28. Added.

Here, the reproduced color signal has its gain controlled by an output control signal of an ACC detection circuit 33, which will be described later, so that the level of the color burst signal part is constant, and is supplied to a frequency conversion circuit 29, where it generates a variable frequency oscillation circuit, which will be described later. A signal of about 4.27 MHz from the circuit 37 is frequency converted.

The center frequency of the frequency conversion circuit 29 is set to 3.58 MH.
The output signal frequency-converted to 3 MHz to 4 MHz is supplied to a bandpass filter 30 to remove unnecessary signal components.
z color signal and is applied to the synthesis circuit 24, while being supplied to the burst extraction circuit 32.

A complete color video signal obtained by combining the color signal component and the luminance signal component in the synthesis circuit 24 and further passing through the video output circuit 25 is led to the output terminal 26, while being synchronized in the synchronization signal separation circuit 31. The signal is separated and this synchronization signal is supplied to the burst sampling circuit 32.

The color burst in the color signal component extracted by the burst extraction circuit 32 is supplied to the ACC detection circuit 33 and also to the phase comparison circuit 36 at the same time.

The output control signal obtained by detecting the amplitude of the color burst in the ACC detection circuit 33 is applied to the gain control circuit 23, where the amplitude of the color burst in the color signal component is always kept constant.

This is to eliminate level fluctuations in the reproduced color signal components due to contact conditions between the magnetic tape 17 and the video head 16, tracking deviations, etc. For this purpose, an ACC circuit consisting of a gain control circuit 28 and an ACC detection circuit 33 is used. It is provided.

At this time, the response characteristic of the automatic gain control operation is A
It can be arbitrarily selected depending on the time constants of the detection section of the CC detection circuit 33 and the hold circuit.

Note that when the reproduced video signal is a black and white video signal, the input terminal 34 connects the voltage to the ACC detection circuit 3 using a manual switch.
This is a terminal for applying a voltage to 3 and thereby turning on the output of the gain control circuit 28 to the cassette.

Incidentally, the playback signal of the recording/playback device is subject to time axis fluctuations (frequency and phase fluctuations) due to uneven running or elongation of the tape, uneven rotation of the video head, and the like.

Since this variation particularly has a negative effect on color signal components, it is necessary to remove this variation.

For this reason, the burst extraction circuit 3 having time axis fluctuations
2 output color burst signal phase and local oscillation circuit 35
The above-mentioned time axis fluctuation is detected by comparing the phase of the stable 3.58 MHz single signal in the phase comparison circuit 36.

The time axis fluctuation component detected as a DC component by the phase comparator circuit 36 is supplied to a variable frequency oscillation circuit 37 to vary its oscillation frequency.

In other words, if there is no fluctuation component mentioned above, 4.27 MH
z signal is oscillated, and the oscillation frequency is successively changed according to the magnitude of the fluctuation component.

As a result of the above operation, a complete color video signal consisting of a color signal component and a luminance signal component with time axis fluctuation components removed and color burst amplitudes made constant is output to the output terminal 26.
More will be taken out.

In the conventional recording and reproducing system as described above, when focusing on the recording of the color signal component of the color->included image signal, there is a drawback in that the recording tolerance of the tape is not fully utilized for recording, as will be described later.

The level of the color burst signal in the color video signal is always kept constant, and the amplitude of the color signal is also set at a maximum of about three times the color burst level.

The amplitude of this color signal changes depending on the degree of density (hereinafter referred to as saturation degree) of the color signal.

For example, the amplitude of a highly saturated color signal is greater than the amplitude of a less saturated color signal.

When recording using the conventional method described above, the level of the color burst signal changes due to changes in reception characteristics, but this is always kept constant and the color signal with the highest degree of saturation is set to the maximum level so that it is within the tolerance of the magnetic tape. It had been.

However, color video signals have high saturation and low saturation, and they are not always at the maximum saturation (sometimes there are continuous screens with low saturation, so on average, the saturation of the color signal is It is often almost equal to the burst level.

However, in general, in recording and playback devices, the color signals recorded on the magnetic tape are set in advance so that the maximum level, which is about three times the color burst level as a reference, falls within the permissible range of the tape. Color signals of high saturation are not recorded as fully as the magnetic tape allows, and color signals with low saturation deteriorate the signal-to-noise ratio.

Note that the above-mentioned tolerance limit for magnetic tape means that distortion increases as the level of the input signal recorded on the tape increases; The limit of what is possible.

A second drawback of the conventional method as described above is that when recording monochrome video signals, the output of the gain control circuit 9 must be cut off by the operation of the color killer circuit of the color signal transmission system. .

If this color killer circuit is not present, no output signal is taken out from the burst sampling circuit 13 because the monochrome video signal does not have a color burst signal.

Therefore, only the black and white video signal component output from the band P-wave generator 8 with a bandwidth of 3 MHz to 4 MHz is amplified until the maximum gain of the gain control circuit 9 is reached by the control signal supplied from the ACC detection circuit. There is a risk of exceeding the limit.

Therefore, a color killer detection circuit is required to detect the presence or absence of a color burst signal.

However, if the color killer detection circuit described above simply detects the presence or absence of a color burst signal based only on its level, it will malfunction due to noise. The presence or absence of a burst signal is determined, which has the disadvantage of requiring an extremely complicated circuit configuration.

The system of the present invention eliminates the above-mentioned drawbacks of the conventional system, and one embodiment thereof will be described with reference to FIG.

FIG. 2 is a block system diagram of a recording system of one embodiment of the video signal recording and reproducing system according to the present invention.

In the figure, the same parts as in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted.

The color signal component extracted from the color video signal by the band p-wave converter 8 is sent to the gain control circuit 18 and the AC which constitute the ACC circuit.
The signals are supplied to the C detection circuit 19, respectively.

The ACC detection circuit 19 detects the level of the color signal component, not the color burst, but the full amplitude (peak-to-peak) of the color signal component.

As a result, the output control signal of the ACC detection circuit 19 is applied to the gain control circuit 18, where the total amplitude of the color signal components in the input color image signal is made constant.

The color signal component of constant amplitude, which is the output signal of the gain control circuit 18, is applied to the frequency conversion circuit 10, where the output 4.27 ME (z) of the local oscillation circuit 15 is
The center frequency is frequency-converted to approximately 688 KHz, and the frequency-converted color signal component is supplied to the low-pass F wave generator 11.

Thereafter, a color video signal is recorded on the magnetic tape 17 through the same process as described in FIG.

When a color video signal is recorded with the above configuration, all amplitudes of the color signal components are always recorded with the same level.

Therefore, if the level of the total amplitude of the uniform color signal components is set to be recorded at once within the permissible limit of the magnetic tape, the utilization efficiency of the magnetic tape will be extremely high. It is also possible to record with a good S/N ratio.

Furthermore, when recording a monochrome video signal, the 3MHz to 4MHz luminance signal component of the input monochrome video signal is
The control signal whose level is detected by the detection circuit 19 allows the gain control circuit 18 to adjust the level to a predetermined level.

Here, the level of the luminance signal component of 3 MHz to 4 MHz is the same as the level of the dark color signal component when recording the color video signal, which is set to be recorded at the same time as the magnetic tape allows. Unlike the conventional method, the gain control circuit 18 does not amplify the gain to the maximum and exceed the permissible limit of the magnetic tape.

Therefore, the method of the present invention does not require a color killer detection circuit for detecting whether the video signal is a color video signal or a monochrome video signal during recording.

Next, at the time of reproduction, the video signal is reproduced with exactly the same configuration as the block diagram of FIG.

That is, when reproducing a color video signal, the color signal components recorded with uniform amplitudes are processed by the gain control circuit 28.
It is reproduced as a signal with more uniform color burst levels.

As a result, it is possible to restore the level relationship to the same level as the input signal at the time of recording.

Incidentally, the response characteristics (tracking time constant) of the gain control circuit used in the method of the present invention are different between the recording system and the reproducing system.

For example, the response characteristic of the gain control circuit 18 used in the recording system is set to several milliseconds in the direction in which the amplitude of the color signal component increases, and to several seconds in the direction in which the amplitude decreases.

This is because the permissible limit of the recording level of the magnetic tape is small in the direction in which the recording level increases, so it is necessary to respond quickly to bring the level within the permissible range.

On the other hand, the response characteristics of the gain control circuit 28 used in the reproduction system may be the same in the direction in which the color burst level increases or decreases, but the response characteristics are equal to or faster than those of the gain control circuit 18 used in the recording system. Need speed.

This is because unless the response characteristics are equal to or faster than those of the recording system, the color burst levels of the reproduced color signals will not be uniform.

As mentioned above, the video signal recording and reproducing method according to the present invention eliminates the need for a color killer circuit by providing an automatic gain control circuit in the recording system and color signal transmission system to uniformly adjust the total amplitude of the color signal components. The reproduction system uses an automatic gain control circuit that equalizes the color burst levels in the reproduced color signals, ensuring a good S/N ratio for recording color signal components with low saturation, and improving the performance of magnetic tape. It has features such as good utilization efficiency, simplified circuit configuration, and can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an example of a recording system of a conventional video signal recording and reproducing system, FIG. 2 is a block system diagram of an embodiment of a recording system of a video signal recording and reproducing system of the present invention, and FIG. 1 is a block system diagram of an example of a regenerated yarn using a video signal recording and reproducing method. 1-...Video signal input terminal, 2, 11, 27-...
-...Low frequency r wave generator, 4...Frequency modulation circuit,
6, 24...--Synthesizer circuit, 7...--Recording amplifier circuit, 8,30...--Band F wave device, 9,18,2
8...Gain control circuit, 10.29...
Frequency conversion circuit, 12.31...--Synchronization signal separation circuit, 13, 32...--Burst extraction circuit, 14...
...ACC detection circuit and color killer detection circuit, 1
5, 35...--Local oscillation circuit, 19°33...
...ACC detection circuit, 20...Reproduction amplification circuit, 23...FM demodulation circuit, 25...Video output circuit, 26-...Video signal output terminal, 36
....Phase comparison circuit, 37...--Variable frequency oscillation circuit.

Claims (1)

[Claims] 1. Separating a color video signal into a luminance signal component and a color signal component, frequency modulating the luminance signal component, frequency converting and multiplexing the color signal component so that the frequency band does not overlap with the frequency modulated luminance signal, and recording it on a magnetic medium. In this method, the recording system is equipped with a recording system automatic gain control circuit that operates to keep the total amplitude of the color signal component obtained by detecting the level of the color signal component substantially constant, and the reproduction system is equipped with A reproduction system that operates at a response speed higher than the response speed of the control circuit and that operates to make the color burst signal of the reproduced color signal component have a constant amplitude using a control signal obtained by detecting the level of the color burst signal of the color signal component. A video signal recording and reproducing method characterized in that an automatic gain control circuit is provided, and the entire amplitude of color signal components is made substantially constant, and recording and reproduction is performed close to the recording permissible limit of the magnetic medium.