JP3196243B2 - Chroma demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma demodulation circuit capable of arbitrarily adjusting a chroma detection axis of a color television signal.

[0002]

2. Description of the Related Art The color reproducibility of a color television receiver greatly differs depending on how a demodulation axis of a carrier color signal is set. By the way, in general, a picture tube of a color television receiver has a light emission characteristic of a fluorescent film, a gamma characteristic of a CRT,
Because the color reproducibility differs due to the difference in color temperature, etc.
In particular, in the case of the NTSC system, in order to obtain good color reproducibility, each company often sets its own detection axis in the color demodulation circuit.

A conventional chroma demodulation circuit has two color difference signals (RY) whose detection axes are orthogonally detected,
(BY) Combining signals by resistance matrix 2
It is well known that the axis demodulation method is used. However, in consideration of the above-described variation in the light emission characteristics of the CRT, or when the color preference differs due to the difference in national characteristics (particularly recognition of skin color),
In order to obtain different color reproducibility for each color television receiver, it was necessary to prepare various types of chroma IC circuits having different detection axes.

[0004]

However, if various types of chroma demodulation circuits having different detection axes are constituted by IC circuits, however, the efficiency of IC circuit development deteriorates, and the burden of managing ICs increases the cost. There was a problem. Further, when the type of CRT is changed, or when the color is improved, it is required to slightly change the detection axis. And that would be time consuming.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a chroma demodulation circuit which forms a color difference signal by a two-axis demodulation system and a matrix circuit.
An object of the present invention is to provide a chroma demodulation circuit which uses a variable gain circuit whose gain changes according to a control signal and an adder circuit and can obtain an arbitrary color reproducibility.

[0006]

The level of the color difference signal demodulated in two axes is changed by a control signal supplied from the outside, and the output is added, so that the level of the reference color difference signal BY is set to an arbitrary level. Are obtained, the other color difference signals r-y and g-y are set.

[0007]

DETAILED DESCRIPTION FIG. 1 shows a block diagram of a chroma demodulation circuit of the present invention, 10 is a demodulation circuit of the two-axis carrier chrominance signal S _C, which and color subcarrier S _fc is supplied. The demodulation circuit 10 and the synchronous detector 11, 12 for performing synchronous detection by the color subcarrier S _fc, a low-pass filter 14 and 15
The sub-carrier phase-shifted through the 90-degree phase shift circuit 13 is input to the one synchronous detector 12 side. As is well known, this two-axis demodulation circuit
A color difference signal BY is obtained from the low-pass filter 14, and a color difference signal RY orthogonal to the color difference signal BY is obtained from the low-pass filter 15. And 3 from this color difference signal
Conventionally, a resistor matrix has been provided to form a primary color signal. In the present invention, this matrix circuit is configured by the following circuit.

Reference numerals 16 and 17 denote the color difference signals BY and RY.
Is a phase inverting circuit for inverting the phase of. The BY signal phase-inverted by this circuit is supplied to the first and second variable gain circuits 18A and 18B, and the phase-inverted R signal is supplied to the first and second variable gain circuits 18A and 18B.
The -Y signal is supplied to the third variable gain circuit 18c. The BY signal whose phase has not been inverted is output as the by signal as it is, and the RY signal whose phase has not been inverted is supplied to the fourth variable gain circuit 18D. 1st, 3rd
The outputs of the variable gain circuits 18A and 18C are input to a first addition circuit 19A, and the second and fourth variable gain circuits 18B and 18B
The output of 18D is input to the second adding circuit 19B. The first, second, third, and fourth variable gain circuits 18 (A, B, C, D,) receive count values K ₁ , K ₂ , K ₃ , and K ₄ as control signals externally. The level of the color difference signal can be arbitrarily determined by changing the count value K by a microcomputer or the like.

Next, the operation of the above-described chroma demodulation circuit will be described with reference to the vector diagram of FIG. 2-axis demodulation circuit 1
The orthogonal color difference signals BY and RY output from 0 are subjected to vector addition in first and second addition circuits 19A and 19B. Therefore, the inverted color difference signal (B-
Y) and the output of the first adder circuit 19A that performs the vector addition of the inverted color difference signal-(RY) forms the color difference signal gy output at the position of the third phenomenon in FIG. , The inverted color difference signal-(BY) and the color difference signal R not inverted
A second adder circuit 19 for performing vector addition of −Y
The output of B is output as the color difference signal ry at the position of the second phenomenon in FIG.

Further, each of the gain adding circuits 18 (A, B, C,
Since the gain of D) can be changed by the count values K ₁ , K ₂ , K ₃ , K ₄ , each of the counts K ₁ , K ₂ , K ₃ , K 4
_{When 4} changes between the maximum value K _{MAX and the} minimum value K _MIN , respectively, the color difference signals ry and by output from the first and second addition circuits appear in the shaded area. .

Accordingly, the color difference signals ry, by, and gy that can be output from the chroma demodulation circuit of the present invention can be set to any level and phase with respect to the color difference signal by. The color difference signals b-y are varied by adjusting the phase of the color subcarrier S _fc, that level is also possible to vary by a fifth gain varying circuit 18E. In the above-described embodiment, the level of another color difference signal is relatively changed based on the color difference signal BY. However, the vector synthesis is performed using the RY axis color difference signal as a reference by the same method. You can also do so. In addition, when the levels of the color difference signals of the non-inverted color difference signals are varied in the above embodiment and the vector synthesis is performed,
The ry signal can be generated in the region of the first phenomenon.

[0012]

As described above, the chroma demodulation circuit of the present invention is provided with a variable gain circuit in which the gain is changed by a control signal supplied from the outside in a color difference matrix circuit. Since the vector sum of the color difference signal demodulated in is output, the hue and color saturation of the color video signal can be set to be optimal according to various conditions.
Great practical effect. Further, since the chroma demodulation circuit can be used in common for various television receivers, there is an advantage that the cost of the IC can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a chroma demodulation circuit according to the present invention.

FIG. 2 is a vector diagram showing an operation of the matrix circuit of FIG.

[Explanation of symbols]

10 biaxial color difference signal demodulating circuit 16, 17 inverting circuit 18A, 18B, 18C, 18D variable gain circuit 19A, 19B adder circuit _{K 1, K 2, K 3} , K 4 counts

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/44-9/78

Claims (1)

(57) [Claims] 1. A quadrature-detected first and second color difference signal.
First for varying the first, and second inverting circuit, the output signal level of said first inverting circuit for inverting the issue,
A second gain variable circuit; a third gain variable circuit that varies an output level of the second inverting circuit; a fourth gain variable circuit that varies a level of the second color difference signal; , And a third color difference signal having a detection axis adjusted by adding the output signals of the third gain variable circuit.
And the outputs of the second and fourth variable gain circuits are added, and the detection axis
Chroma demodulation circuit but which is characterized in that example Bei a second adding circuit for outputting a second color difference signal adjusted.