JPH0247668Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a blanking harmonic prevention circuit for preventing blanking harmonics in a color television receiver.

BACKGROUND ART Conventionally, in color television receivers,
Blanking (BLK) is applied to the retrace period of the scanning line that creates the image. That is, blanking is applied to the video signal and color signal delayed by the video intermediate frequency amplification circuit and the video delay line. However, the generation timing of the blanking harmonics always falls within the video period because the delay time is included in the high-frequency input signal, and the harmonics appear in the image. In order to prevent this, the objective is achieved by lowering the frequency characteristics of the CRT (cathode ray tube) drive circuit or primary color output circuit, but this degrades the frequency characteristics of the primary color signal and makes it impossible to obtain a sufficient image. I can't.

FIG. 1 is an electrical circuit diagram around a conventional primary color output circuit. In the primary color driving integrated circuit 1,
The input terminal P1 receives the red color difference signal R-Y, the input terminal P2 receives the green color difference signal G-Y, the input terminal P3 receives the blue color difference signal G-Y, and the input terminal P4 receives the luminance signal Y. A blanking pulse is applied to P5. Further, the primary color driving integrated circuit 1 is
Red color signal R from output terminal Q1, green color signal G from output terminal Q2, and blue color signal B from output terminal Q3.
Send each. Transistor TR1, TR
2 and TR3 amplify the color signals R, G, and B from the primary color driving integrated circuit 1, respectively, and apply the amplified signals to each cathode of the cathode ray tube 2.

In FIG. 2, a waveform A1 indicated by a broken line is a video detection output, and a waveform A2 indicated by a solid line is a luminance signal applied to the input terminal P4 of the primary color driving integrated circuit 1. A blanking pulse as shown in FIG. 2 is applied to the input terminal P5 via a resistor R4. Since this blanking pulse is sent out from an integrated circuit, its rise and fall characteristics are very short, and as shown in Figure 2, it has a high frequency B
Contains 1. This high frequency B1 is amplified by the subsequent transistors TR1, TR2, and TR3, enters the antenna input (tuner input) of a rod antenna, etc., and appears on the image as a vertical line of harmonic damage prevention. Therefore, it becomes impossible to obtain a sufficient image.

Purpose The purpose of this invention is to solve the above technical problems,
An object of the present invention is to provide a blanking harmonic prevention circuit that prevents blanking harmonics without deteriorating the frequency characteristics of primary color signals.

Embodiment FIG. 3 is an electrical circuit diagram of an embodiment of the present invention. In FIG. 3, components corresponding to those shown in FIG. 1 are given the same reference numerals. In the primary color driving integrated circuit 1, an input terminal P1 receives a red color difference signal R-Y, and an input terminal P2 receives a green color difference signal G-.
Y, input terminal P3 is given a blue color difference signal G-Y, input terminal P4 is given a luminance signal Y, input terminal P5 is given a blanking pulse, and output terminal Q
1 outputs a red color signal R, output terminal Q2 outputs a green color signal G, and output terminal Q3 outputs a blue color signal B. Output terminal Q1 is connected to the base of transistor TR1 via resistors R1 and R11. Output terminal Q2 is connected to resistors R2 and R1
2 to the base of the transistor TR2. Output terminal Q3 is connected to the base of transistor TR3 via resistors R3 and R13.
The connection point between resistor R1 and resistor R11 is connected to transistor TR via diode D2 and resistor R15.
Connected to 4 collectors. Resistor R2 and Resistor R1
The connection point with 2 is the diode D3 and the resistor R1
5 to the collector of the transistor TR4. The connection point between resistor R3 and resistor R13 is connected to the collector of transistor TR4 via diode D4 and resistor R15. The emitter of transistor TR4 is grounded, and its base is grounded via resistor R14. A connection point between resistor R10 and capacitor C2 is connected to the base of transistor TR4. The diodes D2 to D4 are
This is a switching diode for preventing mixing of color signals R, G, and B.

A blanking pulse is applied to one end of the capacitor C1, and one end of the capacitor C1 is connected to the base of the transistor TR4 via a resistor R10. The other end of the capacitor C1 is connected to the input terminal P5 of the primary color driving integrated circuit 1 via a resistor R4. A diode D1 is connected in the opposite direction to the input terminal P5, and a resistor R5 is also connected to the input terminal P5. Each collector of the transistors TR1 to TR3 is connected to each cathode of the cathode ray tube 2. The collector of transistor TR4 is connected to terminal Q4 of primary color driving integrated circuit 1 via resistors R15 and R9. The power supply Vcc is applied to the terminal Q4.

The present invention shortens the pulse width of the blanking pulse given to the primary color driving integrated circuit 1, sets the pulse width at the timing when the harmonic generation part is turned off by the subsequent blanking circuit 3, and then outputs the blanking pulse. Output terminals Q1, Q of integrated circuit 1 for driving primary colors
Blanking pulses are integrated at each output of Q2 and Q3, and blanking is performed by making the rise and fall gradual, and the blanking inside the primary color driving integrated circuit 1 is applied to the cathode ray tube driving transistor
Transistors TR1 to TR3 are cut off to prevent blanking harmonics from being amplified by TR1 to TR3.

This will be explained below with reference to the waveform diagram shown in FIG. In FIG. 4, a waveform A3 indicated by a broken line is a video wave output, and a waveform A4 indicated by a solid line is a luminance signal applied to the input terminal P4 of the primary color driving integrated circuit 1. Input terminal P5 of primary color driving integrated circuit 1
A blanking pulse as shown in FIG. 2 is applied to the circuit through a capacitor C1 and a resistor R4. This blanking pulse is differentiated into the fourth
A signal as shown in FIG. 3 is obtained, and the signal is applied to the input terminal P5 of the primary color driving integrated circuit 1. Inside the primary color driving integrated circuit 1, it is determined that the blanking pulse is on at the level of line l1 shown in FIG. 4, and a pulse as shown in FIG. 4 is sent out, for example, from the output terminal Q3. The rise time of the pulse shown in FIG. 4 is very short.

On the other hand, the blanking pulse shown in FIG.
The integration circuit of resistor R10 and capacitor C2 generates a pulse that rises and falls slowly as shown in Figure 4 and 5, and the transistor TR
Given on the basis of 4. As a result, the transistor TR4 is operated by the pulses shown in FIG. 4 and 5, and the pulses shown in FIG. 4 and 6 are sent out from its collector. Since the rise of the pulse shown in FIG. 4 and FIG. 6 is gradual, harmonics of the blanking pulse can be prevented. Further, the harmonic B2 shown in FIG. 4 of the luminance signal P4 applied to the input terminal P4 of the integrated circuit for driving primary colors 1 is prevented by the pulse shown in FIG. Ru. Therefore, the base of the transistor TR3 is given a blue color signal B and a blanking pulse as shown in FIG.
A noise-free image is displayed on the cathode ray tube 2. In FIG. 4, the part indicated by reference mark A5 is as follows:
This is a portion of the blanking pulse created by the integrated circuit 1.

Note that similar operations are performed for the circuits related to the red color signal R and the green color signal G.

Effects As described above, according to the present invention, harmonics of the blanking pulse can be suppressed by slowing the rise and fall of the blanking pulse and applying the blanking pulse to the drive circuit that drives the cathode ray tube. It can be prevented. Further, by shortening the pulse width of the blanking pulse applied to the integrated circuit, harmonics generated in the integrated circuit can be prevented. Therefore, in the image,
Noise caused by harmonics is no longer generated.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram of a conventional primary color output circuit, Fig. 2 is a waveform diagram for explaining the blanking pulse of the circuit shown in Fig. 1, and Fig. 3 is an electric circuit diagram of an embodiment of the present invention. The circuit diagram, FIG. 4, is a waveform diagram for explaining the operation of the circuit shown in FIG. 3. 1... Integrated circuit for driving primary colors, 2... Cathode ray tube,
3...Blanking circuit, C1, C2, C3...
Capacitor, D1~D4...Diode, R1~
R15...Resistor, TR1~TR4...Transistor.

Claims (1)

[Scope of utility model registration request] An integrated circuit that receives a color difference signal, a luminance signal, and a blanking pulse to create three primary color signals, a pulse width shortening circuit that shortens the pulse width of the blanking pulse applied to the integrated circuit, and a rise of the blanking pulse. and a blanking drive circuit driven by the output of the pulse relaxation circuit, which converts the three primary color signals output from the integrated circuit and the output of the blanking drive circuit into a cathode ray A blanking harmonic prevention circuit that is applied to a drive circuit that drives a tube.