JPH0568214A - Signal input switching device - Google Patents

Abstract

PURPOSE:To eliminate crosstalk to an output signal by providing a circuit to control an input signal level, and controlling the signal level so as to lower the signal level of a signal not to be outputted. CONSTITUTION:In order to prevent the mutual crosstalk between plural input video signals and plural input sound signals, the circuit (input signal switching circuit) 5 to control the input level is provided, and by controlling the signal level by a signal level control circuit 13 so as to lower the level of the signal not to be outputted, the crosstalk to the output signal is eliminated. Namely, the signal level of the signal not selected by a system control circuit 6 is lowered by controlling the signal level control circuit 13. Thus, an input signal switching device by which the occurrence of the crosstalk at the time of the input of the many input signals can be suppressed, and high picture quality and high sound quality can be obtained can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input signal switching device which does not cause crosstalk in a device for inputting a plurality of video signals and audio signals.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional input signal switching device for a television receiver having input terminals for video signals and audio signals. In FIG. 2, 1
Is a tuner, 2 is a signal and audio IF (SIF / VIF)
Demodulation circuits 3 and 4 are external input terminals, 5 is an input signal switching circuit, 6 is a system control circuit, 7 is a video amplifier, 8
Is an audio amplifier, 9 is a CRT, 10 is a speaker, 11 is a monitor output switching circuit, 12 is an output terminal, and the television broadcast signal from the antenna is converted by the tuner 1 into an intermediate frequency (IF) signal. The video signal a of the television broadcast signal demodulated by the VIF demodulation circuit,
Audio signal a and video tape recorder (VTR) and broadcasting satellite
The video signal b, c and the audio signal b, c input to the external input terminals 3, 4 from the outside such as a (BS) tuner are controlled by the system control circuit 6 and the input signal switching circuit 5
Then, the selected signal is output to the CRT 9 and the speaker 10 through the video amplifier 7 and the audio amplifier 8. Further, in the device having the output terminal 12, the switch of the monitor output switching circuit 11 is switched by the control of the system control circuit 6, and the selected signal is output to the output terminal 12. In this way, the input signal switching device can select a desired video signal and audio signal from the input signals with a relatively simple configuration.

[0003]

However, in the above-mentioned conventional signal input switching device, a plurality of signals to be input is one.
Since it is connected to the input signal switching circuit at a certain place, there is a leak from a common ground pattern and a leak between signals inside the IC of the input signal switching circuit, and this crosstalk is an obstacle to high image quality. ， There was a problem that it could interfere with high sound quality. The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an input signal switching device capable of suppressing the occurrence of crosstalk during multi-input signals and obtaining high image quality and high sound quality.

[0004]

In order to achieve the above object, the present invention comprises a circuit for controlling the level of an input signal, and by controlling so as to lower the level of a signal which is not output, crosstalk to the output signal is achieved. Is to be removed.

[0005]

Therefore, according to the present invention, crosstalk between a plurality of input signals is reduced.

[0006]

1 is a block diagram of an input signal switching device according to an embodiment of the present invention. In FIG. 1, the same blocks as those in the conventional example are designated by the same reference numerals, and the description thereof will be omitted. Reference numeral 13 is a signal level control circuit. Next, the operation of the above embodiment will be described. In the above-described embodiment, the television broadcast signal is converted into an IF signal by the tuner 1 and demodulated by the SIF / VIF demodulation circuit 2. The video signal a, the audio signals a and V of the television broadcast signal.
After the video signal b, c and the audio signal b, c input from the outside such as TR or BS tuner to the external input terminals 3, 4 are passed through the signal level control circuit 13, the input signal switching circuit 5 and the monitor output switching circuit Enter in 11. Then, the signal not selected by the system control circuit 6 controls the signal level control circuit 13 to lower the signal level. To lower the level of the television broadcast signal, short the signal to ground with a transistor or use SIF / V
The gain of the IF amplifier of the IF demodulation circuit 2 is reduced. When lowering the signal level of the external input, short the signal to ground. As for the signal selected by this, almost no signal leaks, and a good signal without interference can be output to the CRT 9, the speaker 10 and the output terminal 12. In addition, the crosstalk generated inside the analog switch IC used in the input signal switching circuit 5 is
Although there has been no means for improving the crosstalk in the related art, the crosstalk can be improved by lowering the level of the unnecessary signal before inputting to this IC by the signal level control circuit 13.

[0007]

As is apparent from the above embodiment, the present invention has the effect of realizing an input signal switching device which eliminates crosstalk between a plurality of input signals.

[Brief description of drawings]

FIG. 1 is a block diagram of an input signal switching device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional input signal switching device.

[Explanation of symbols]

1 ... Tuner, 2 ... SIF / VIF demodulation circuit, 3,
4 ... External terminal, 5 ... Input signal switching circuit, 6 ... System control circuit, 7 ... Video amplifier, 8 ... Audio amplifier, 9 ... CRT, 10 ... Speaker, 11 ... Monitor output switching circuit, 12 ... Output terminal, 13 ... Signal level control circuit.

Claims (1)

[Claims] 1. In order to prevent crosstalk between a plurality of input video signals and audio signals, a circuit for controlling the input signal level is provided, and the output signal is controlled by lowering the level of the signal not output. An input signal switching device characterized by removing the crosstalk of the input signal.