JPH0628471B2 - Color signal modulation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color signal modulation circuit including a circuit function for converting two color signal levels into a normal level as a composite signal of a color television system or the like. is there.

[Prior art]

Emulates NTSC color television standard system video signals
Then, Em is expressed by the following equation.

Em = Ey + (Eb−Ey) sinωt / 2.03 + (Er−Ey) cosωt / 1.1
4 where Ey is the luminance signal voltage, Eb-Ey and Er-E
y is a color difference signal voltage, and its variation range is -0.89 to +0,89 for Eb-Ey and -0.70 to +0.70 for Eb-Ey when Ey is normalized to 0 to 1.
Is. As is clear from the above equation, Eb-Ey and Er-
The level on the video signal corresponding to the color difference signal voltage with respect to Ey is compressed by different coefficients so that the fluctuation range of Em falls within -0.33 to +1.33.

On the other hand, CCIR Rec. Which has been internationally standardized as an encoding parameter for digital television for studios. In 601,
The color difference signal levels of Eb-Ey and Er-Ey are set to 22
5 quantization levels, that is, the fluctuation range is -112 to +1
It has 12 levels. When the color difference signal levels of Eb-Ey and eEr-Ey handled in the same level fluctuation range are returned to the analog NTSC signal, it is necessary to multiply by different coefficients to perform level conversion.

FIG. 2 shows a configuration diagram of a conventional digital color signal modulation circuit having a function of converting the color difference signal levels of Eb-Ey and Er-Ey. In the figure, a and b are respectively Eb-
Input terminals for color difference signals of Ey and Er-Ey, 1 and 2 are level conversion circuits, 3 and 4 are multiplication circuits, 5 is a carrier wave generation circuit for generating two-phase color signal carrier waves in an orthogonal relationship, and 6 is An adder circuit, c is an output terminal of the carrier wave modulated by the color difference signal.

First, Eb− input from the input terminals a and b
The color difference signals of Ey and Er-Ey are output at the normal level in the level conversion circuits 1 and 2 composed of a multiplier for multiplying an input by a fixed coefficient or a ROM for outputting data obtained by multiplying an input address value by a fixed coefficient. Is converted to.

Then, Eb-Ey and Er converted to the regular level
The color difference signals of −Ey are respectively multiplied by the two-phase color signal carrier waves in the orthogonal relationship generated from the carrier wave generating circuit 5 in the multiplying circuits 3 and 4, and the outputs of the multiplying circuits 3 and 4 are added in the adding circuit 6. To be done.

The output of the adder circuit 6 is output terminal c as a carrier color signal modulated by the Eb-Ey and Er-Ey color difference signals.
Is output from.

Incidentally, the amplitude level of the carrier wave generated from the carrier wave generation circuit 5 is generally in the range of -1 to +1 and the circuit itself uses a ROM which outputs the data of the sine value and the cosine value in the trigonometric function corresponding to the phase of the input address. It is configured.

As described above, the conventional circuit configuration has a drawback that the circuit scale becomes large because the multiplier and the ROM are individually provided for level conversion.

[Object of the Invention]

In order to eliminate such a defect, the object of the present invention is not to multiply the level conversion coefficient for the color signal directly to the color signal, but to multiply the amplitude level of the carrier by the level conversion coefficient, thereby individually converting the level. It is to provide a color signal modulation circuit that does not require a circuit and has a small circuit scale.

[Structure of Invention]

Embodiment 1 FIG. 1 is a block diagram of a color signal modulation circuit according to an embodiment of the present invention, in which 3 to 6 and a to c are named as FIG.
Since the circuit functions are the same, the description is omitted.

The difference in configuration between FIG. 1 and FIG. 2 is that the function of the level conversion circuits 1 and 2 in FIG. 2 is added to the carrier wave generation circuit 5 in FIG. There is no need for the level conversion circuit of.

First, the carrier wave generation circuit 5 outputs two-phase carrier waves in an orthogonal relationship having an amplitude level obtained by multiplying the color difference signals of Eb-Ey and Er-Ey by the level conversion coefficient.

Then, in the multiplication circuits 3 and 4, the carrier generation circuit 5
And the color difference signals of Eb-Ey and Er-Ey input from the input terminals a and b are respectively multiplied, and the outputs of the multiplication circuits 3 and 4 are added by the addition circuit 6
Is added in.

The output of the adder circuit 6 is output terminal c as a carrier color signal modulated by the Eb-Ey and Er-Ey color difference signals.
Is output from.

As described in the conventional digital color signal modulating circuit, the circuit itself of the carrier wave generating circuit 5 is generally composed of a ROM which outputs the data of the sine value and the cosine value in the trigonometric function corresponding to the phase of the input address. . Only by multiplying this ROM data by the level conversion coefficient for the color difference signals of Eb-Ey and Er-Ey, the carrier generation circuit 5 can have the level conversion function without increasing the circuit scale.

〔The invention's effect〕

As described above, according to the present invention, the carrier wave generation circuit 5 in the color signal modulation circuit is constituted by the ROM and its RO
By multiplying the M data by the level conversion coefficient, the carrier generation circuit 5 can be provided with a level conversion function without increasing the circuit size, and an individual level conversion circuit can be eliminated, thus reducing the circuit size. There are advantages.

When the multiplying circuits 3 and 4 can operate at a frequency twice as high as the sampling lock of the input color signal, one circuit can be alternately switched and used, and therefore it is clear that it is not necessary to have two. However, the features of the present invention are not lost by this.

Also, for convenience of explanation, the color signal modulation circuit by digital processing is described, but it is obvious that the present invention can be applied to a color signal modulation circuit that performs level conversion for color signals by analog processing. That is, if the amplitudes of the sine wave and the cosine wave that are analogically generated in the carrier wave generation circuit 5 are multiplied by the level conversion coefficient, a separate level conversion circuit can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram of a color signal modulation circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional color signal modulation circuit. 1, 2 ... Level conversion circuit, 3, 4 ... Multiplication circuit, 5 ... Carrier generation circuit, 6 ... Addition circuit, a, b ... Color difference signal input terminal, c ... Modulated by color difference signal Carrier wave output terminal.

Claims (1)

[Claims] 1. A carrier wave generation circuit for generating first and second carrier waves of two orthogonal phases, and first and second multiplication circuits for respectively multiplying the first and second carrier waves with two color signals.
A color signal modulation circuit configured to add an output of the first and second multiplication circuits, wherein the first and second carrier waves have an amplitude level obtained by multiplying a level conversion coefficient for two color signals. A color signal modulation circuit characterized by the above.