JPS60125092A - Color killer device - Google Patents

Abstract

PURPOSE:To prevent the generation of a color noise to a black-and-white signal in an intense electric field through simple constitution and make a killer point deep in a weak electric field by adding a means which discriminating on the intensity of an electric field to a killer detecting circuit. CONSTITUTION:A pulse integrator 60 is added to a circuit of conventional constitution and its integral output 61 is added to the output of the killer detector to charge and discharge a capacitor 9. A burst gate pulse 18 is inputted to one input of the differential amplifier consisting of transistors (TR)62 and 63 and the TR62 turns on when the gate pulse is at a high level to discharge the capacitor 9. The burst gate pulse is obtained by separating a video signal synchronously, so its pulse width varies with the S/N ratio of the video signal and becomes narrower in a weak electric field. The integral output current 66 of the pulse integrator 60 is a constant current 70 in an intense electric field, but starts decreasing at a point 68 where the S/N ratio of the synchronous separation output deteriorates in a weak electric field and becomes zero in the electric field weaker than a point 69. Then, the discharging current of the capacitor 9 during the reception of a black-and-white signal is large in an intense electric field, so malfunction is hard to occur; and an offset current is reduced in a weak electric field to set the killer point deep.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color killer device for a color television receiver.

Conventional configuration and its problems FIG. 1 shows a conventional example of the main parts of a color demodulation circuit.

1 is a video signal, which is band-limited through a color signal band-pass filter 2 and input to an ACC amplifier 4; AcC
The dJ intensifier 4 has the function of detecting the magnitude of the burst signal and changing the degree of intensification to keep the ACCCC intensifier output 5 - strike amplitude constant. The ACCCC amplifier output 5 is input to a color demodulator 6, a killer detector 8, and an APC detector 17. hpc detector 17, low pass filter 15, voltage controlled oscillator 1
3 constitutes a PLL (phase locked loop), and the voltage controlled oscillator 13 oscillates in the same phase as the input burst signal. Outputs 10, 11 of voltage controlled oscillator 13
．． Reference numeral 12 denotes a color subcarrier, which is input to the color demodulator 6, killer detector 8, and MPC detector 17 at a required phase. On the other hand, the video signal 1 is input to the synchronization separation circuit 20 and is separated into a horizontal synchronization signal and a vertical synchronization signal. The synchronously separated horizontal synchronizing signal 21 passes through the differentiating circuit 19, and the burst gate pulse 18B: null. The burst pulse 18 is a pulse for extracting a burst signal, and this pulse causes the killer detector 8 and the APC detector 17 to operate only during a period of the burst.

The killer detector 8 synchronously detects the burst signal from the Acc multiplier output 5 using the color subcarrier 11, and charges the capacitor 9 with the detected output. The voltage 22 of the capacitor 9 is compared by the comparator 7, and if there is a killer detection output, it is regarded as color broadcasting, and if there is no killer detection output, it is regarded as black and white broadcasting, and the color control circuit inside the ACCCC amplifier reduces the chroma signal. , which prevents color noise from occurring when using black and white signals.

FIG. 2 shows the configuration of the killer detector 8. transistor 2
6 to 31 constitute a double-balanced synchronous detector. A color subcarrier signal for killer detection is inputted from an input 24, and a burst signal is inputted from an input 25. Transistor 39 is a burst gate switch. Transistor 32.33
．． 34 is a constant current source through which the same current flows. The burst signal is synchronously detected using the color subcarrier in the same phase, and the detection current passes through the terminal 46 and is charged to the capacitor 9.

The voltage at the terminal 46 is determined by the comparator 7 in FIG. 1, and if the voltage is high, it is determined that it is a color signal, and if it is low, it is determined that it is a black and white signal. The threshold for detection of black and white signals is resistor 43. The resistance value of the resistor 44 is set as follows: resistor 43>resistor 44, and when the detector is unmanned (balanced state of the detector), a constant offset current is set to discharge the capacitor, lower the voltage at the terminal 46, and turn on the killer.

FIG. 3 shows the relationship between the charging current to the capacitor 9 and the input burst amplitude. As the roost amplitude decreases, the killer current decreases and eventually flows in the direction of discharging the capacitor. The point 46 where the direction of the current changes is called a killer point.

On the other hand, this killer current also changes depending on the electric field strength, and the situation is shown in FIG. As the electric field becomes weaker, the killer current decreases, and at the point of electric field strength 47, the direction of the current is switched and the capacitor 9 is discharged.

In general, a killer circuit operates when a black-and-white signal or a signal with a poor S/N ratio is used to eliminate color noise. However, in areas with weak electric fields, there is an increasing desire to enjoy colored signals even if the S/N ratio is poor.

In order to deepen the killer point in a weak electric field, the onset current determined by the ratio of resistors 43 and 44 in FIG. 2 should be made smaller. When the offset current is large as shown in the characteristic diagram 49°60 in Fig. 4, 50. Shows 49 when small. For 49 with a smaller offset current, the killer point is 47 to 48.
It's getting deeper.

However, when the offset current is reduced in a conventional system, malfunctions occur because there is no margin for monochrome signals with good S/)i and chroma burst leaking into the synchronization signal part. Color noise occurs even though the signal is originally a black and white signal.

Such signals are also generated by irregular signals such as video tape recorder outputs and 1 (-sonal computer signals).

OBJECTS OF THE INVENTION The present invention eliminates these conventional drawbacks.
An object of the present invention is to provide a color killer device which can prevent color noise from occurring in monochrome signals in a strong electric field and deepen the killer point in a weak electric field with a simple configuration.

Structure of the Invention In the present invention, a means for determining electric field strength is added to the killer detection and detection circuit of the conventional configuration, and in a strong electric field, the offset current is increased to prevent color noise from occurring in black and white signals, and in a weak electric field, the offset current is increased. is made smaller and the killer point is made deeper.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 6 shows a block diagram of an embodiment of the present invention.

In this circuit, a pulse integrator 60 is added compared to the conventional example shown in FIG. 2, and its integral output 61 is added to the killer detector output to charge and discharge the capacitor 9.

The function of the pulse integrator 6o will be explained. FIG. 6 shows a specific embodiment of this device. The part surrounded by the broken line is the pulse integrator. The burst gate pulse 18 is input to one side of a differential amplifier composed of transistors 62 and 63, and the transistor 62 is turned on while the gate pulse is at a high level, discharging the capacitor 9. A suitable DC voltage is applied to the terminal 65. The current value of the constant current source 64 determines the killer offset current in a strong electric field, and is adjusted so as to be as follows.

Since the burst gate pulse is obtained by synchronously separating the video signal, its pulse width changes depending on the S/N ratio of the video signal, and the pulse width becomes narrower when the electric field becomes weaker.

FIG. 7 shows the integrated output 66 of the pulse integrator 60 and the detected output 67 of the killer detector 8. The integrated output current 66 of the pulse integrator 60 is a constant current 70 in a strong electric field, but the current starts to decrease at a point 68 where the electric field becomes weak and the S/N of the synchronous separation output deteriorates, and further when the electric field strength is weaker than a point 69. The current becomes 0. Killer detection current when receiving color broadcasting is 6
7. The killer detection current when receiving black and white broadcasting is 71.

According to the conventional example where 71 is used as is for the killer operation, 7
1 does not change depending on the electric field strength, so in a strong electric field,
If there is a slight burst leakage, the signal will malfunction and the signal will be treated as a color signal even though it is a black and white signal, resulting in color noise.

On the other hand, FIG. 8 shows the summed output of 67, 71 and 68 in FIG. 7 (charging and discharging current of the capacitor 9). 72 is the time of color broadcasting, and 73 is the time of black and white broadcasting.

In a strong electric field, the capacitor discharge current when receiving a black and white signal is large, making it difficult to malfunction; in a weak electric field, the offset current decreases and the killer point (t) can be set deeply.

Effects of the Invention As described above, according to the present invention, it is possible to prevent malfunctions in monochrome signals in strong electric fields, deepen the killer point in weak electric fields, and achieve correct color killer operation, which is originally contradictory. be able to.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the main parts of a color demodulation circuit using a conventional color killer device, Figure 2 is a circuit diagram showing the configuration of the killer detector in the circuit shown in Figure 1, and Figure 3 is a burst block diagram. FIG. 4 is a characteristic diagram showing the relationship between the amplitude and killer detection current, FIG. 4 is a characteristic diagram showing the relationship between electric field strength and killer detection current, FIG. 5 is a block diagram of a color killer device in an embodiment of the present invention, The figure is a circuit diagram of the pulse integrator in the circuit shown in Figure 6, and Figure 7 is a characteristic diagram showing the output current of the pulse integrator with respect to the electric field strength together with the detected output current of the killer detector.
FIG. 8 is a characteristic diagram showing charging and discharging current to a capacitor by this device. 1...Video signal, 2...Band pass filter, 4...HAC detector, 7...
Comparator, 8... Killer detector, 9゛゛・°° capacitor, 13... Voltage controlled oscillator, 15゛°
...°Low pass filter, 17...AP,
C detector, 18... Killer detector, 19...
...Differentiating circuit, 20...Synchronization separation circuit, 60.
...Pulse integrator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3, Figure 4 Figure 5 Figure 6 Figure 11 L J Figure 7 4 Guest Figure 8

Claims (2)

[Claims] (1) An oscillator that oscillates with a phase synchronized with the burst phase of the color signal, a first detection means that synchronously detects the burst signal using the color subcarrier generated by the oscillator to detect the size of the burst, and the strength of the underworld intensity. a second detection means for detecting;
and a determining means for determining whether it is a color broadcast or a monochrome broadcast based on the combined output of the first detecting means and the second detecting means, and detecting the strength of the electric field by the second detecting means. A color killer device characterized by changing the discrimination sensitivity between output color broadcasting and black and white broadcasting. (2) The second detection means inputs a burst gate pulse obtained by waveform processing the horizontal synchronization signal separated from the video signal by the synchronization separation circuit, and the amplitude of this burst gate pulse changes depending on the electric field strength. 2. The color killer device according to claim 1, wherein the strength of the electric field strength is detected from the integral value of the burst gate pulse by utilizing this fact.