JPS6378690A - Video signal processor - Google Patents

Abstract

PURPOSE:To reduce the deterioration in an S/N without emphasis by separating low-and high-frequency components from a composite video signal including a chrominance signal and AM-modulating a signal, which is FM-modulated with the low frequency component, with the aid of the high frequency component. CONSTITUTION:The chrominance signal inputted from an input terminal 1 is inputted to a filter 11 made up of a low-pass filter 2, a subtractor 6 and a delay circuit 12. A low frequency signal included in the output of the low pass filter 2 is FM-modulated by an FM modulator 3 and transmitted to an AM modulator 4. It modulates the amplitude of an output signal from the FM modulator 3 according to the output of the subtractor 6. The modulation signal obtained in such a way is not affected by a triangular noise increasing in the high frequency band, because the input signal has the FM-modulated low frequency component and the AM-modulated high frequency component. Consequently, no emphasis is needed, whereby the level of the modulation signal does not rise.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a video tape recorder such as a video tape recorder that modulates a composite video signal including a carrier color signal, transmits or records/plays it, and then demodulates it to restore the original signal. The present invention relates to a signal processing device.

2. Description of the Related Art In recent years, it has become common to transmit, record and reproduce composite video signals including carrier color signals, and there is an increasing demand for video signal processing devices used for this purpose.

A conventional video signal processing device will be described below with reference to the drawings. FIG. 4 is a block diagram showing the configuration of a conventional video signal processing device. In Fig. 4, the input terminal 30
A composite video signal including a carrier color signal inputted from the FM modulator 31 is FM-modulated and sent to the transmission line 5. Next, the variable frequency wave passing through the transmission line 5 is demodulated by an FM demodulator 34, and a composite video signal including a carrier color signal is obtained at an output terminal 35.

Such an example is shown, for example, in Recording and Reproducing Images (Television Society of Japan, Vol. 1), p. 182, 195.

Problems to be Solved by the Invention However, since the video signal processing device configured as described above transmits the input signal after FM modulation, there is a drawback that the high-frequency S/N ratio deteriorates due to triangular noise. There is also a method of using emphasis to improve S/N deterioration in the high frequency range, but since there is a carrier color signal with large energy in the high frequency range, increasing the amount of emphasis increases the signal level. When attempting to magnetically record the data, the recording current increases too much, causing the magnetic head to become saturated.

In view of the above-mentioned problems, the present invention separates an input composite video signal including a carrier color signal into a low-frequency component and a high-frequency component, and performs AM modulation on a signal FM-modulated with the low-frequency component using the high-frequency component. 1. The high frequency range of the input signal is AM modulated to provide a video signal processing device that is free from the influence of triangular noise and has low S/N deterioration.The processing device separates the input signal into low frequency components and high frequency components. an FM modulator that performs FM modulation on the low frequency components separated by the filter; an AM modulator that performs AM modulation on the output signal of the FM modulator using the high frequency components separated by the filter; an AM demodulator that performs AM demodulation of the output signal of the AM demodulator, an FM demodulator that performs FM demodulation of the output of the AM demodulator, and an adder circuit that adds the outputs of the AM demodulator and the FM demodulator. be.

According to the above configuration, the present invention separates an input composite video signal including a carrier color signal into a low frequency component and a high frequency component, and performs AM modulation on a signal FM modulated using the low frequency component using the high frequency component. Since the high frequency range of the input signal is AM modulated, there is no influence of triangular noise, and S/N deterioration can be reduced without using emphasis.

Embodiment Hereinafter, an embodiment of the video signal processing apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the video signal processing device of the present invention, and FIG. 2 is a characteristic diagram showing the spectrum of each part of the embodiment of FIG. In FIG. 1, a carrier color signal inputted from an input terminal 1 is inputted to a filter 1) consisting of a low-pass filter 2, a subtracter 6, and a delay circuit 12. Delay circuit 1
2 delays the input signal by the delay time of the low-pass filter 2, and the subtraction circuit 6 subtracts the output of the low-pass filter 2 from the output of the delay circuit 12, so its output contains the high frequency range of the input signal input from the input terminal 1. ingredients are obtained. The low-frequency signal obtained at the output of the low-pass filter 2 is sent to the FM modulator 3
It is modulated by M and sent to the AM modulation gIi12S4. AM modulator 4 modulates the amplitude of the output signal of FM modulator 3 in accordance with the output of subtracter 6 . The modulated signal thus obtained is sent to the transmission line 5. In the case of a video tape recorder, this transmission path 5 is a tape head system. Next, the modulated signal passing through the transmission path 5 is demodulated by an FM demodulator 8 and an AM demodulator 7, and a low frequency component is obtained from the output of the FM demodulator, and a high frequency component is obtained from the output of the AM demodulator. These two signals are added by an adder 9, and the original signal is restored and output to an output terminal 10.

Next, the present embodiment will be explained from the spectrum with reference to FIG. A composite video signal including a carrier color signal, which is an input signal, has a spectrum like +a+.

The spectrum of the signal obtained by extracting the low frequency range of this signal by the low-pass filter 2 is fbl, and the high frequency spectrum obtained at the output of the subtractor 6 is tel.

Since the output of the FM modulator 3 is the FM modulated signal of (b), it has the spectrum shown in dl.
The band of the modulated wave is relatively narrow because the band of the modulated wave is narrow. When this signal is modulated by the AM converter 4, +
This results in a modulated signal having a spectrum shown in el.

As can be seen from the above explanation, the modulated signal obtained in this way is free from the influence of triangular noise, which increases in the high range, because the low range of the input signal is FM modulated and the high range is AM modulated. Therefore, since there is no need to apply emphasis, the level of the modulated signal does not increase.

Next, another embodiment of the present invention will be described with reference to FIG. The modulation system in this embodiment is the same as that in the first embodiment, so a description thereof will be omitted. The modulated signal explained in the first embodiment passes through the transmission line 5 and is converted into a digital signal by the A/D converter 20. This signal is converted into a digital signal by the 90 degree phase shifter 21 so that the phase difference between them is 90 degrees. The signal is divided into two signals. These two signals are A (tlsin r +tl, A tt)co
s ((tl, where A (tl is the AM modulated signal and f (tl is the integral of the FM modulated signal).

These signals are sent to arithmetic circuits 22 and 23. In the arithmetic circuit 23, the divider 31 first calculates the ratio of the two signals. Therefore, this output becomes A
(tl), and the differentiating circuit 33 outputs f (tl. That is, an FM modulated signal was obtained.

In the arithmetic circuit 22, the square root of the sum of the squares of the two input signals is calculated by square circuits 27 and 28, an adder 29, and a square root circuit 30. That is, the AM modulated signal is obtained. Therefore, the arithmetic circuit 22
By adding the output signals of and 23 in an adder 24 and converting it into an analog signal in a D/A converter 25, the original signal before modulation can be restored to the output terminal 26. In addition, the square circuits 27 and 2
8. The square root circuit 30, arctangent circuit 32, and differentiation circuit 33 can be realized with a ROM (read-only memory) table.

Effects of the Invention As described above, the present invention separates a composite video signal containing a manually generated carrier color signal into a low frequency component and a high frequency component, and
Since the M-modulated signal is subjected to AM modulation using a high frequency component, the high frequency range of the input signal is AM modulated, eliminating the influence of triangular noise, and reducing S/N deterioration without using emphasis.

Furthermore, since no emphasis is used, the level of the modulation signal does not increase, which is advantageous for magnetic recording.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a video signal processing device in an embodiment of the present invention, and FIG. 2 (al to (el is the first
A characteristic diagram showing the spectrum of each part in the embodiment shown in the figure, FIG. 3 is a block diagram showing the configuration of a video signal processing device in another embodiment of the present invention, and FIG. 4 shows a conventional video signal processing device. FIG. 2 is a block diagram showing the configuration of a processing device. 1)...Filter, 3...FM modulator, 4...AM modulator, 7...AM demodulator, 8... FM demodulator, 22.23...
・Arithmetic circuit. Name of agent: Patent attorney Toshio Nakao and one other person Figure 2 Figure 4

Claims (4)

[Claims] (1) A filter that separates an input signal into a low frequency component and a high frequency component, an FM modulator that performs FM modulation on the low frequency component separated by the filter, and an FM modulator that uses the high frequency component separated by the filter. an AM modulator that performs AM modulation on the output signal of the
An AM demodulator that performs AM demodulation on the output signal of the AM modulator, an FM demodulator that performs FM demodulation on the output of the AM demodulator, and an adder circuit that adds the outputs of the AM demodulator and the FM demodulator. A video signal processing device. (2) The video signal processing device according to claim (1), wherein the input signal is a composite video signal including a carrier color signal. (3) The filter consists of a low-pass filter that extracts the low frequency range of the input signal, a delay circuit that delays the input signal by the delay amount of the low-pass filter, and a subtraction circuit that subtracts the output signal of the low-pass filter from the output signal of the delay circuit. A video signal processing device according to claim (1). (4) The FM demodulator has a phase difference of 90 degrees from the input signal.
a 90 degree phase shifter that obtains two output signals with a 90 degree phase shifter;
It consists of a first arithmetic circuit that takes the arctangent of the ratio of the two outputs of the 0 degree phase shifter and then differentiates it, and the AM demodulation circuit calculates the square root of the sum of the squares of the two outputs of the 90 degree phase shifter. The video signal processing device according to claim 1, further comprising a second arithmetic circuit that calculates .