JPH0454434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color control device used for skin color correction, etc. in a color television receiver, and is capable of performing accurate and good control when incorporated into an integrated circuit element. This is what we are trying to provide.

Traditionally, receivers have been equipped with a color control circuit that includes a so-called skin color correction circuit to correct for phase shifts between the color signal burst signal and chroma signal sent from the image transmitter. be. As this skin color correction circuit, there is a method of controlling a color signal or a subcarrier so that the skin color always looks like a skin color. The control method is to detect the input color signal on the I-axis and detect the amount of the component in the I-axis direction of the color signal, so that the color with a hue closer to the skin color has a larger amount of detected signal. ,
The output signal makes the color closer to skin color even more skin color (I).
Even if the skin color signal is shifted from the image transmitter side or relay device, the skin color is reproduced as a skin color.

In such a color control circuit, when a detection signal for color signal control is created from the I-axis detection circuit, the present invention normally generates harmonic components of the signal in the detection output, which prevents normal color signal control operation. It is an object of the present invention to provide a circuit which solves the problem of the inconvenience caused by the inconvenience of not being able to carry out the process by incorporating a simple filter circuit into the circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to drawings showing one embodiment thereof.

FIG. 1 is a block diagram of a color control circuit for skin color correction. The color signal inputted and amplified by the first band amplification circuit 1 is further amplified by the color signal amplification circuit 2 having a fixed amplification factor. Here, the color signal amplification circuit 2
It is necessary to make the gain sufficiently large in order to enable the control circuit for skin color correction to operate well even with a small color signal. The amplified color signal is output from the voltage-controlled subcarrier oscillator 3.
It is detected by the I-axis detection circuit 4. Therefore, the phase of the oscillation output of the oscillator 3 needs to be such that the I-axis component of the color signal can be extracted. At this time, during the burst period, the operation of the I-axis detection circuit 4 is stopped by a blanking pulse (burst gate pulse), and this circuit does not operate during this period.

The color signal that has passed through the color signal amplification circuit 2 is added to the output signal of the oscillator 3 in an addition circuit 5. The amount added at this time is controlled by the detection output of the I-axis detection circuit 4.

During the burst period, the color signal is blanked and only the output signal of the oscillator 3 is output.

The addition output signal is input to the color demodulation circuit 6 and the APC circuit 7. On the other hand, the input color signal is amplified by the second band amplification circuit 8 and sent to the color demodulation circuit 6.
It is added to APC circuit 7. The APC circuit 7 operates by the burst gate pulse only during the burst period to perform APC detection. The detected output is fed back to the oscillator 3 to complete the oscillation loop.

On the other hand, the oscillation output signal added to the color signal is input to the color demodulation circuit 6, and color demodulation is performed.However, since the color signal is added to the oscillation output by the adder 5, the input color signal is Since the phase of the oscillation output differs depending on the color, and the original color signal is detected accordingly, the phase of the demodulated color difference signal will differ depending on the hue.

To explain this using the vector diagram in Figure 2, the phase of the oscillation output is initially the phase of the I-axis (vector A), and the color signal is detected on the I-axis, thereby controlling the amount of addition of the color signal. However, if the signal obtained there is vector B, then the phase of the oscillation output after the addition output that is input to the color demodulation circuit 6 becomes vector C, and the phase changes somewhat. This means that when demodulating a color signal that is far from the I-axis, the detection axis can be moved to bring it closer to the I-axis, and in this way, colors close to skin tone will be reproduced.

Next, FIG. 3 shows a specific circuit. In FIG. 3, parts corresponding to each circuit in FIG. 1 are given the same numbers.

Oscillation outputs of opposite phases are applied to the bases of transistors 9 to 12, and a color signal is applied to transistor 13 for I-axis detection, and the detected outputs are output to collector resistors 14 and 15.
The color signal is simultaneously applied to the base of the transistor 16, amplified by the differential amplifier 17, and output to the terminal of the resistor 18. At this time, the amount of the color signal is controlled by control transistors 19 to 22.

Now, when the color signal of the hue of the I axis is input, the base voltage of transistors 19 and 22 increases, they become conductive, and the color signal is transmitted.
Conversely, when the I-axis color signal is input, the bases of the transistors 19 and 22 are lowered and turned off, so that no color signal is transmitted. Therefore, the addition circuit is controlled by the color of the input color signal.

However, although the output of this I-axis detection circuit 4 is basically a DC signal, harmonic components and fundamental wave components are output at the same time due to leakage of oscillation output and waveform distortion due to synchronous detection. The output is multiplied and mixed. If control is performed using such a signal, the bases of the transistors 19 to 22 will fluctuate due to the unnecessary signal, which may interfere with the above-mentioned normal addition and cause abnormal phenomena such as oscillation. On the other hand, the response speed of this detection output must be fast. This is because it must respond to color changes within one horizontal period.

Therefore, in the present invention, in order to solve such an abnormal phenomenon, in the circuit shown in FIG.
and 24 are the output terminals of the differential amplifier of the I-axis detection circuit 4, and the control transistors 19 to 22 of the adder circuit 5.
It is characterized by being inserted between the base and the
When looking at the base of a transistor made with an IC, there is always a capacitance component between the base and the IC board on which the transistor is constructed (the ground indicated by the dotted line in Figure 4), as shown in Figure 4. Occur. Harmonic components can be removed by forming a low-pass filter with a stray capacitance that is a combination of this capacitance component, the transistor's base-collector capacitance, and base-emitter capacitance, and a resistor provided in the preceding stage. Only the required DC component can be obtained.
Although the stray capacitance referred to here varies somewhat depending on the configuration of the differential amplifier, it always occurs when a transistor is created using an IC.The resistance value of the resistor should be determined with this consideration in mind, and the resistance value of the low-pass filter should be determined. It is essential to compose the following. Furthermore, at this time, the resistor also has some capacity if it is an IC, so
It is necessary to take this into account as well. Furthermore, the values of the resistors 23 and 24 inserted at this time need to have a time constant that is sufficient for 3.58 MHz because the response speed needs to be fast.

For example, if the value of the resistors 14 and 15 is 2.5KΩ, the resistors 23 and 24 should be
Approximately 10KΩ is appropriate.

As described above, according to this circuit, by simply adding two resistors, it is possible to prevent an adverse effect on the adder circuit 5 due to the high frequency component from the I-axis detection circuit 4 during hue correction, and it is possible to perform good skin color correction. It is possible to perform color signal control.

In the above embodiment, in order to demodulate the color signals sent in phases before and after the skin color so as to approximate the skin color, the color signal is detected on the I axis and the adder is controlled. However, if another color is to be used as the center, control may be performed using the output detected at the phase of that color so as to center on that color.

As detailed above, according to the present invention, it is possible to obtain a device that can prevent the adverse effects of high frequency components in color control with a very simple configuration and can perform accurate and good color control. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color control device according to an embodiment of the present invention, FIG. 2 is a vector diagram explaining its operation, and FIGS. 3 and 4 are its specific circuit diagrams. DESCRIPTION OF SYMBOLS 1... First band amplification circuit, 2... Color signal amplification circuit, 3... Voltage controlled oscillation circuit, 4... I-axis detection circuit, 5... Addition circuit, 6... Color demodulation circuit, 7...
...APC detection circuit, 8...Second band amplification circuit, 9
~13,16,19~22...Transistor, 1
4, 15, 18...Resistance, 23, 24...Resistance.

Claims (1)

[Claims] 1. A color demodulation circuit that demodulates an input color signal using a subcarrier oscillation output to generate a color difference signal, and a synchronous detection circuit that includes a differential amplifier that synchronously detects the input color signal at a specific hue. and an adder circuit constituted by a differential amplifier that controls the magnitude of the input chrominance signal using the output of the synchronous detection circuit, adds it to the subcarrier oscillation output, and supplies the signal to the chrominance demodulation circuit; A resistor is provided between the collector resistor of the detection circuit and the input base of the differential amplifier of the adder circuit, and the synchronous detector circuit and the adder circuit are provided in an integrated circuit element. A color control device characterized in that a low-pass filter is configured by a stray capacitance generated between a circuit element and a substrate and the above-mentioned resistor.