JPS58141088A - Video amplifying circuit - Google Patents

Abstract

PURPOSE:To minimize cross color interference and beat components of 920KHz even in playback mode of VTR and to reproduce a sharp picture, by separating or adding a comb-shaped filter and a trap circuit from and to a video amplifying circuit. CONSTITUTION:During reproduction of VTR, the comb-shaped filter circuit 3 is disconnected from between the amplifying circuit 2 and a luminance signal processing circuit 4 and the output terminal of the amplifying circuit 2 is connected directly to the processing circuit 4 through an electric path 9. The switching between the both is carried out through the electric path 9 and changeover switches 11 and 12. Further, the 3.58MHz trap circuit 10 is added to the input terminal of the processing circuit 4 to remove a chrominance signal component from a playback video signal of VTR as a substitute for the comb-shaped filter circuit which does not have the function for removing the chromainance signal component. In some mode other than playback mode, the the changeover 11 and 12 are operated to connect the trap filter 3. The trap circuit 10 is connected through a switch 12 which is operatively associated with the connecting operation of the changeover switches 11 and 12. Thus, color signal interference is prevented even during VTR reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a video amplification circuit in a #1 television receiver.

A block diagram of a typical configuration example of a conventional video amplification circuit in a television receiver is shown in FIG.

In the figure, 1 is a composite video input terminal, 2 is an amplifier circuit, and 3 is a composite video input terminal.
Comb filter circuit, 4J-j luminance signal amplification circuit, 5
are a video output circuit, a 6Fi color signal band amplification circuit, a 7-digit color signal amplification and demodulation circuit, and an 8#i video power end.

Normally, in a small television receiver, the comb filter circuit 3 in the block diagram 1 gram is deleted, and instead, a 3.58 MHz trap circuit, which can be constructed at low cost, is inserted in the middle of the luminance signal amplification circuit 4. Signal components are removed. In such a circuit configuration, the removal of the color signal component described above is not complete, and in reality, the video signal output 418
However, in the case of small television receivers, the display tube is small, so this is not a visual problem, and is practically effective in reducing design costs. It is widely used as a tool.

As mentioned above, instead of the comb filter circuit 3, 3.5
Since the circuit configuration used in the 8MHz) Wode circuit does not remove color signal components sufficiently, if this is adopted in a large screen refocusing device such as an enlarged projection video projector, cross-cuff interference and 920KHz bits may occur. The influence of residual components becomes visually noticeable. Therefore, in the conventional large-screen display, a comb-shaped filter circuit 3 is inserted as shown in FIG. A configuration is adopted that eliminates as much as possible input of signals that contain

However, when amplifying the reproduced video signal of a video tape recorder, the video signal at this time is vertically correlated, that is, the phase of the carrier color signal is not inverted for each scan. The color signal component cannot be removed, and a cross-cut component appears at the video signal output terminal 8. Moreover, in the conventional circuit using the comb filter circuit 3, the carrier color signal component of the signal input to the luminance signal amplification circuit 4 has already been removed in the previous stage, so the luminance signal amplification circuit 4 has a high frequency characteristic. (3.58MHz) Since no wrap circuit is inserted, the interference component becomes even more noticeable, but no countermeasures have been taken in the past to deal with this problem in playback mode.

Therefore, an object of the present invention is to provide a video amplification circuit that can minimize the cross-cuff disturbance (=920 KHz beat component) even in the playback mode and reproduce clear images.

One embodiment of the invention is shown in block diagram form in FIG. That is, in the conventional example, when the signal applied to the composite video signal input terminal 1 is a composite video signal from a video tape player, this video amplifying circuit replaces the comb filter circuit 3 with the amplifier circuit 2. A switching bypass circuit 9 is added between the luminance signal processing circuits 4 to connect the output terminal of the amplifier circuit 2 directly to the input terminal of the luminance signal processing circuit 4. Along with the connection, a 3,58 MHz trap circuit 10 connected to the input terminal of the luminance signal processing circuit 4 is added to eliminate the function of removing the carrier color signal component from the reproduced video signal of the video tape recorder. In place of the 358 MHz trap circuit 10, the carrier color signal component is removed by the 358 MHz trap circuit 10 instead of the 358 MHz trap circuit 3.

the amplifier circuit 2 of the switching bypass circuit 9; Switching connection # between the luminance signal amplification circuits 4, two changeover switches 11.
12, and when not in the reproduction mode, the amplifier circuit 2. The changeover switches 11 and 12 are arranged so that the nI comb filter circuit 3 is connected between the luminance signal amplification circuits 4.
is switched.

Said 3.58MHz? Connection of the wrap circuit 10 to the luminance signal amplification circuit 4 is made via a switch 13, which is connected to the changeover switch 11.1.
2, the switching bypass circuit 9 is turned on in accordance with the connection operation of the switching bypass electric circuit 9.

With this configuration, the 3.58 MHz trap circuit 10 is used instead of the comb filter circuit 3 during the regeneration mode.
removes the carrier color signal component and prevents color signal interference from occurring.

In the above embodiment, an example of the configuration was shown in which the K<L type filter circuit 3 is disconnected during the regeneration mode, but such disconnection is not performed and power supply to the square type filter circuit 3 is stopped. In addition, the 3.58MHI trap circuit 10 may be simply added in the regeneration mode by leaving the cutout filter circuit 3 without disconnecting its 11 using the switching bypass circuit 9. It is also possible to have a configuration in which:

As described above, the Eirin amplifier circuit of the present invention includes: an amplifier circuit that receives and amplifies a composite video signal; a comb filter circuit that receives the output of the amplifier circuit and removes a color signal component;
a luminance signal processing circuit which is provided at the next stage of the comb filter circuit and performs luminance signal processing; and a chrominance signal band amplification circuit whose input terminal is connected to the input terminal of the luminance signal processing circuit and which amplifies the chrominance signal band of the input signal. , a chrominance signal amplification and decoupling sub-circuit which receives the output of the chroma signal band amplification circuit and performs chrominance signal amplification and decoding; and a chrominance signal processing circuit in the reproduction mode.
Since the device is equipped with a trap circuit that is connected to the amplifier circuit and removes the color signal component of the output signal of the amplifier circuit, color signal interference does not occur even when processing the playback signal of a video tape recorder, and a clear image can be obtained. This has the effect of being able to perform regeneration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of a conventional example, and FIG. 2 is a block diagram showing the circuit configuration of an embodiment of the present invention. 2...Amplification circuit, 3...Comb filter circuit, 4.
...Brightness signal amplification circuit, 5...Video output circuit, 6...
- Color signal band amplification circuit, 7... Color signal amplification/demodulation circuit, 9... Switching bypass circuit, 10... 3.58MH
! ) Wrap circuit, 11.12... Selector switch, 1
3... Switch diagram 2

Claims (1)

[Claims] (11) An amplifier circuit that receives a composite video signal and amplifies it;
A comb-shaped filter circuit receives the output of the amplifier circuit and removes color signal components, a luminance signal processing circuit is provided at the next stage of the comb-shaped filter circuit and performs luminance signal processing, and the input terminal is connected to the luminance signal processing circuit. a chrominance signal band amplification circuit connected to the input terminal of the chrominance signal band amplification circuit for amplifying the chrominance signal band of the input signal; a chrominance signal amplification-demodulation circuit for receiving the output of the chrominance signal band amplification circuit and amplifying and demodulating the chrominance signal; and a reproduction mode. A video amplification circuit comprising: a trap circuit that is sometimes connected to one stage of the luminance signal processing circuit and removes a color signal component of an output signal of the amplification circuit. (2) The video amplification circuit according to claim (1), wherein the amplification circuit is directly connected to the luminance signal amplification circuit in a reproduction mode.