JPS6365197B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a frequency characteristic compensation circuit used in a color television receiver, in which the video detection output from an IC for VIF signal processing is a negative polarity signal of 2V _p - _p , and its frequency is The characteristics are 4.43MHz when receiving PAL signals and 3.58MHz when receiving NTSC signals.
When the video detection output is input to the TV and video signal switching circuit, the amplitude is reduced by 6 dB, and the frequency characteristics are changed to PAL mode with negative polarity.
4.43MHz or 6dB at 3.58MHz for NTSC system
The purpose of this is to lift the frequency characteristic to make it flat.

The reason for changing the frequency characteristics is to make the frequency characteristics of the video detection output output to the external VTR flat up to the frequency of the color subcarrier, and by changing the frequency characteristics between PAL and NTSC, it can be used for both systems. This is to ensure that.

Embodiments of the present invention will be described below with reference to the drawings. In the figure, reference numeral 1 denotes a video detection circuit from which a negative polarity video signal of _2p -- _p is output and applied to the base of a transistor 2.
Normally, the detection output is taken out from the emitter of the transistor 2. A detection output of 1V _p - _p is taken out from the point divided by resistors 3 and 4, which have equal resistance values. In order to raise the frequency characteristics at the frequency of the color subcarrier by 6 dB, in the case of PAL, a series resonant circuit consisting of a coil 5 and a capacitor 6 connected in parallel to a resistor 3 is used. By determining the value of coil 5, the frequency response at 4.43MHz has been raised by 6dB. In the case of NTSC, a series circuit of capacitor 7 and diode 8 is connected to capacitor 6, and a positive voltage that makes diode 8 conductive is applied to the anode of diode 8, causing resonance in the resonant circuit of coil 5 and capacitors 6 and 7. The point is
Determine the values of coil 5 and capacitors 6 and 7 so that they are at the 3.58MHz point, and calculate the frequency characteristics at 3.58MHz.
It's lifted by 6dB.

The video signal whose frequency characteristics have been compensated in this way is applied to the television signal/video signal switching circuit 13 through the capacitor 9. This switching circuit 13
A video signal is input from an external VTR 12 through a capacitor 11 and terminated with a resistor 10 . Conversely, from the switching circuit 13 through the capacitor 14
A video signal whose frequency characteristics have been compensated for above is applied to the VTR 12.

Figures 2 and 3 are diagrams showing changes in frequency characteristics. Figure 2 is for NTSC, the solid line is the frequency characteristic of the detection output before compensation, and the broken line is the frequency response compensated by the circuit in Figure 1. It is a characteristic that i.e. 3.58MHz
The frequency characteristic, which has dropped by 6 dB, is compensated and raised by the circuit shown in Figure 1, and the characteristic is flattened to 3.58 MHz, which is then output to the external VTR 12. Figure 3 is
The same thing is done for 4.43MHz when receiving PAL signals.

As described above, the present invention connects the video detection output to the base of a transistor, applies a DC voltage to the collector of this transistor, connects a series circuit of two resistors between the emitter of the transistor and ground, and connects these two resistors. A resonant circuit consisting of a coil and a capacitor is connected in parallel to the resistor on the transistor side of the resistor, the frequency of this resonant circuit is set to the color subcarrier frequency in the PAL system, and another capacitor and a diode are connected in series to the above capacitor. The circuit is connected in parallel, and the PAL system is NTSC in this diode.
A voltage that varies depending on the system is applied to make the diode conductive in the case of the NTSC system, and the resonant frequency of the resonant circuit made up of the coil and two capacitors is set to the color subcarrier frequency in the NTSC system. PAL format,
In either case of the NTSC system, the characteristics near the color subcarrier frequency can be enhanced, and the level can also be adjusted and extracted without providing a special element for polarity reversal.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a frequency characteristic compensation device according to an embodiment of the present invention, and FIGS. 2 and 3 are characteristic diagrams for explaining the device. 1...Video detection circuit, 2...Transistor, 3, 4
...Resistor, 5...Coil, 6,7...Capacitor, 8...
diode.

Claims (1)

[Claims] 1. Provide a transistor whose base is connected to the output terminal of the video detection circuit, apply a DC voltage to the collector of this transistor, connect a series circuit of first and second resistors between the emitter of the transistor and ground, and A series resonant circuit including a coil and a capacitor is connected in parallel to the resistor on the transistor side of the first and second resistors, and the frequency of this series resonant circuit is set to the color subcarrier frequency in the PAL system,
A series circuit of another capacitor and a diode is connected in parallel to the above capacitor, and this diode
A voltage that changes depending on the PAL system and the NTSC system is applied, and in the case of the NTSC system, the above diode is made conductive, and the cocurrent frequency of the resonant circuit made up of the above coil and two capacitors is set to the color subcarrier frequency in the NTSC system. A frequency characteristic compensator characterized in that it is configured to supply the output signals of these resonant circuits to a video tape recorder.