JPS602715Y2 - Image quality switching device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an image quality switching device for a color television receiver that can receive color television signals of either the PAL system or the 5'SECAM system.

PAL system and SECA are used for color television broadcasting.
There is M system, but there are some areas in the world where both of these systems can be received.

Therefore, in such areas, color television receivers that can receive both broadcasting systems are used, and the color circuit is automatically switched to the corresponding circuit depending on the broadcasting system being received.

However, in a video system that processes luminance information, the signals are obtained through the same circuit, so the conditions that determine image quality cannot be changed.

In reality, when receiving a PAL signal, the image quality is adjusted to increase the sharpness, and then SEC
When receiving AM broadcasting, color blinding or dot-like noise appeared on the screen, which was undesirable.

This is thought to occur because when the high-frequency component of the luminance signal is emphasized, the high-frequency component of the SECAM color signal is superimposed on the luminance signal.

Therefore, conventionally, the sharpness has been set in accordance with SECAM broadcasting so as not to generate noise, and the image quality of PAL broadcasting has been sacrificed to some extent.

This project was proposed focusing on the above-mentioned problems, and provides a circuit layout that allows automatic adjustment for both PAL and SECAM broadcasting without degrading image quality. It is.

The present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram showing a partial circuit configuration of a receiver that receives PAL and SECAM color television signals to which the present invention is applied.

Reference numeral 1 designates an input terminal to which a signal obtained from the video intermediate frequency amplification circuit at the previous stage is applied, and 2 designates a video detection stage.

The output composite video signal of the video detection stage 2 is sent to the video amplification circuit 3, S.
Added to ECAM demodulation circuit and PALa modulation circuit.

A video signal, ie, a luminance component, obtained from the video amplification circuit 3 is given to a video output circuit 4.

When color broadcasting is in the PAL system, the PAL demodulation circuit 5 extracts color difference signals B-Y and R-Y and converts them to PAL/SEC.
It is added to the AM switching circuit 7.

Further, when color broadcasting is based on the SECAM system, the color difference signals B-Y and R-Y are taken out by the SECAM demodulation circuit 6 and given to the circuit 7.

A signal identifying which broadcasting system is being received is applied as a control signal to the PAL/SECAM switching circuit 7, which switches the input color difference signal of the receiving system and performs the next stage amplification and G-Y demodulation. It is sent to circuit 8.

For this control signal, for example, the killer output of a color killer circuit 61 provided in the SECAM demodulation circuit 6 is used.

Each color difference signal B-Y, G-Y obtained as the output of the circuit 8
, RY are applied to the video output circuit 4, the luminance component Y is removed, and the color signals B, G, R are applied to the cathode ray tube 9.

Here, the video amplifying circuit 3 is generally equipped with an image quality adjustment circuit 31, but in the present invention, a control signal is added to this circuit to switch the image quality adjustment value according to the broadcasting system.

As a control signal for this purpose, for example, the color killer output of the SECAM demodulation circuit 6 mentioned above is used.

FIG. 2 shows an actual circuit connection diagram of the image quality adjustment circuit 31 shown in FIG.

Ql is a transistor for video amplification, and a signal taken out from its collector is applied to the base of a transistor Q2 for buffer amplification.

Only the high-frequency components are extracted from the signal obtained from the emitter of the transistor Q2 by a circuit connected to the emitter, and the above-mentioned transformer for video amplification is obtained.

It is superimposed on the signal obtained from the emitter of transistor Q1.

The high frequency compensated signal is sent out from the output terminal T3.

The variable resistor VR□ is used to adjust the amount of negative feedback and set the sharpness.

Q3 is a switching transistor, a control signal is applied to its base, and a resistor R is connected to its collector-emitter path.
8 are connected in series.

This series connection is connected in parallel to the variable resistor VR□.

In the circuit arrangement of FIG. 2, the control signal applied to the terminal T2 exhibits a sufficiently low voltage when FAI broadcasting is being received, and the transistor Q becomes non-conducting.

Therefore, the high frequency components are strengthened in the state set by the variable resistor VR1, and the sharpness can be enhanced.

Next, when a SECAM system broadcast is received, the control signal becomes a high voltage value, making the transistor Q3 conductive.

Then, the resistor B8 is connected in parallel to the variable resistor VR□, and the amount of negative feedback is switched to be reduced in accordance with the PAL system reception.

To prevent the amount of feedback at this time from affecting the screen, resistor R
A value of 8 may be set in advance.

Therefore, the resistor R8 may be a variable resistor.

1 As described above, this proposal automatically switches the amount of image quality adjustment according to the reception conditions between the two so that when receiving PAL broadcasting, the high frequency components are higher than when receiving SECAM broadcasting. This makes it possible to improve the image quality depending on the method.

'In the above embodiment, the SECAM demodulation circuit demodulation circuit-killer output was used as the control signal, but
The same effect can be achieved by using FAI and the color killer output from the demodulation circuit instead.

That is, the control signal may be any signal that can identify whether the system is SECAM or PAL, and is not limited to color killer output.

Furthermore, the controlled image quality adjustment circuit is not limited to the circuit connection shown in Fig. 2, as long as it operates to enhance the high-frequency components when using the PAL system, and to reduce the high-frequency components when using the SECAM system. .

[Brief explanation of the drawing]

Figure 1 shows the FAI, method, and S
FIG. 2 is a partial block circuit diagram of a receiver that receives an ECAM color television signal. FIG. 2 is a circuit connection diagram of an image quality adjustment circuit according to an embodiment of the present invention. 31...Picture quality adjustment circuit, 61...Color killer circuit for extracting control signals, Q3...Switching transistor, VRl...Variable resistor for image quality setting , R8...Resistor connected in series to the collector-emitter path.

Claims (2)

[Scope of utility model registration request] (1) In a color television receiver that can receive color television signals of either FAI, SECAM or SECAM format, it is possible to identify which of the above two formats the signal being received is being received. a circuit for extracting a control signal to
An image quality adjustment circuit that operates to enhance high-frequency components of a video signal when receiving PAL broadcasting than when receiving CAM broadcasting. Switching device. (2) A switching transistor has a switching transistor to which a control signal is applied to the base and a resistor is connected in series to the collector-emitter path, and the resistor and the collector-emitter path are connected in parallel to a variable resistor for setting the image quality of the image quality adjustment circuit. A series connection is connected, and the switching transistor is conductive when the control signal indicates that a SECAM broadcast is being received, and is non-conductive when the control signal indicates that a PAL broadcast is being received. An image quality switching device according to claim 1, characterized in that: