JPS5930381A - Sound circuit of television receiver - Google Patents

Abstract

PURPOSE:To allow cope with the titled circuit to the bilingual mode of sound multiplex broadcast with a simple constitution, by extracting either one signal of main and sub-channels in response to a control signal, and demodulating its output signal with a tuning frequency in response to the control signal. CONSTITUTION:A switch circuit of a variable band filter 20 extracts a sound intercarrier signal of a main channel when the control signal is at a low level and that of a sub-channel when at high level and applies the signal to an amplifier 4. An output of the amplifier 4 is limited for the amplitude at a limiter 5 and after noise is eliminated, the output is applied to a variable frequency discriminating circuit 22. Further, the signal demodulated at the circuit 22 is extracted for the main or the sub-sound signal under the control of the control signal 21, and after de-emphasis 7, the signal is amplified 14 and outputted from a speaker 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio circuit of a television receiver, which extracts a signal from either a main channel or a sub-channel according to a control signal, and tunes the extracted signal according to the control signal. To provide an audio circuit for a television receiver capable of supporting two languages and modes of two-carrier multiplexed audio broadcasting at low cost with a simple circuit configuration by demodulating based on frequency.

In general, television audio multiplex broadcasting is roughly divided into a subcarrier system used in Japan and the like, and a two carrier system used in West Germany and other countries. In this two-carrier system, the main channel is obtained by FM modulating the main carrier wave with a frequency higher than the video signal carrier wave by, for example, 5.5 MF (z) in the main audio signal, and the pilot signal, which is an AM modulated wave, is used as the sub audio signal. The audio multiplexed signal is composed of a sub-channel obtained by FM modulating a sub-carrier with a frequency higher than the video signal carrier by 5.74 MHz, for example, in the multiplexed signal, and in the case of stereo broadcasting, the main channel is one /2 The sum signal of the right side signal and the left side signal, the sub channel is the right signal, and in the case of bilingual broadcasting, the main channel is the native language and the sub channel is the foreign language audio signal.

FIG. 1 shows a block diagram of an example of the audio circuit of this two-carrier type audio multiplexing television receiver. In the figure, the audio intercarrier signals of the main channel and the subchannel coming into the input terminal 1 are supplied to bandpass filters 2 and 3, respectively. The main channel audio intercarrier signal extracted by the bandpass filter 2 is supplied to a frequency discriminator circuit 6 via an amplifier 4 and an IJ transmitter 5, where it is demodulated into a main audio signal and then passed through a de-emphasis circuit 7. ) Supplied to the IJ bus circuit 8.

Along with this, use bandpass filter 3! The extracted sub-channel audio intercarrier signal is supplied to the frequency discriminator circuit 11 via the amplifier 9 and limiter 10, where it is added to the sub-audio signal and pilot signal, and the sub-channel signal is digitalized. The signal is supplied to the matrix circuit 8 via the emphasis circuit 12.

The matrix circuit 8 also includes a pilot signal discriminator circuit 1.
3, the pilot signal is demodulated to determine whether the audio signal is in stereo mode, monaural mode, or bilingual mode, and control signals corresponding to each mode are supplied to the matrix circuit. 8 separates the right side signal and the left side signal from the main audio signal and the sub audio signal supplied in the stereo mode, and supplies the right side signal and the left side signal to the amplifiers 14 and 15, respectively. When in mode, the main audio signal is supplied to amplifiers 14 and 15, and when in bilingual mode, the main audio signal and the sub audio signal are supplied to amplifiers 14 and 15, respectively. The signals amplified by the amplifiers 14 and 15 are sent to the speaker 1.
6.17 is supplied and made to sound.

Here, the audio circuit of a television receiver that does not support television audio multiplex broadcasting is the bandpass filter 2 in FIG.
The de-emphasis circuit 7 is comprised of an amplifier 14 and a speaker 16 that receive the main audio signal from the de-emphasis circuit 7, and is compatible with both the stereo mode and the two-language Φ mode. Conventional audio circuits have the disadvantage that the number of components is more than twice as large, making them complex and expensive.

The present invention eliminates the above-mentioned drawbacks by supporting only monaural mode and bilingual mode of television audio multiplex broadcasting, and one embodiment thereof will be described with reference to FIG. 2 and subsequent figures.

FIG. 2 shows a block system diagram of an embodiment of the audio circuit of a television receiver according to the present invention. In the figure, the same parts as in FIG. 1 are given the same reference numerals. In Fig. 2, 1 is an input terminal, and this input terminal 1 is connected to the final stage of the video intermediate frequency amplification circuit, and the beat generated by the difference between the video intermediate frequency signal and the audio intermediate frequency signal of the main channel. A signal containing the audio intercarrier signal of the main channel and the audio intercarrier signal of the sub-channel, which is a beat generated by the difference between the video intermediate frequency signal and the audio intermediate frequency signal of the sub-channel, is input, and this signal has a variable bandwidth. It is supplied to filter 20. This variable band filter 20 includes a band filter that passes only the audio intercarrier signal of the main 5-channel from the signal from the input terminal 1 and a band filter that passes only the audio intercarrier signal of the sub channel from the signal from the input terminal 1. It is provided with a filter and a switch circuit which is supplied with the output signals of the two bandpass filters and which outputs one of the signals according to a control signal supplied from the input terminal 21. Here, input terminal 21
The incoming control signal is a high-level or low-level signal that can be arbitrarily selected by the user by operating a switch;
The switch circuit of the variable band filter 20 extracts the audio intercarrier 11 signal of the main channel when the control signal is at a low level, and the subchannel when the control signal is at a high level, and supplies this to the amplifier 4. The audio intercarrier signal amplified by the amplifier 4 is amplitude-limited by the limiter 5 to remove noise components, and then the variable frequency discrimination circuit 2
2. This variable frequency discrimination circuit 22 is configured to tune the audio intercarrier signal of the main channel among the signals supplied from the limiter 5 and demodulate it into a main audio signal. A frequency discrimination circuit that tunes to the audio intercarrier signal of the sub channel of the signal and demodulates it into a sub audio signal, and an input terminal which is supplied with the main audio signal and the sub audio signal from the above two frequency discrimination circuits. When the control signal supplied from 21 is low level, the main audio signal,
It consists of a switch circuit that takes out the sub-audio signal when the signal is at the No/E level. The audio signal obtained by demodulating with this variable frequency discrimination circuit 22 is sent to a de-emphasis circuit 7.
After being compensated to have a frequency characteristic opposite to the pre-emphasis on the transmitting side, the signal is amplified by the amplifier 14 and outputted by the speaker 16.

Here, when receiving broadcasts from two countries and one unit mode, the input terminal 21
When the control signal is set to a low level, a native language sound is produced, and when the control signal is set to a high level, a foreign language sound is produced. Also, monaural φ mode.

When a stereo mode broadcast is being received, monaural audio can be generated as before by setting the listen control signal to a low level. In this way, it is possible to support two languages and modes of TV audio multiplex broadcasting with a very simple configuration.

Note that the variable band filter 20. Variable frequency discrimination circuit 22
The capacitance value may be controlled by the voltage of the control signal using a variable capacitance diode or the like, and the pass band and tuning frequency may be made to correspond to the main channel and the sub channel.

Although the above embodiment has been explained using an intercarrier type audio circuit as an example, this is a split carrier type audio circuit, and the input terminal 1 receives audio intermediate frequency signals of the main channel and sub-channel, such as an audio intermediate frequency amplification circuit. It is not limited to the above embodiments.

As described above, the audio circuit of the television receiver according to the present invention has two different frequencies for the main audio signal and the sub audio signal.
In a television receiver that receives a two-carrier television audio multiplex broadcast having a main channel and a sub-channel in which frequency modulation is performed on each of the two carrier waves, the main channel audio intercarrier signal (or intermediate filter means for extracting either the audio intercarrier signal (or intermediate frequency signal) of the main channel or the sub channel according to a control signal selected by the operator; The main audio signal is obtained by demodulating the carrier signal (or intermediate frequency signal) using a tuning frequency according to the control signal.

Since it is equipped with frequency discrimination means for obtaining either one of the sub-audio signals, it is possible to broadcast in two languages and modes with a simple configuration that requires only slight changes to the audio circuit that is not compatible with TV audio multiplex broadcasting. It has features such as being able to handle various types of problems and having low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of an audio circuit of a conventional audio multiplex television receiver, and FIG. 2 is a block diagram of an embodiment of the circuit of the present invention. 1.21...Input terminal, 4,14...Amplifier, 5°
... 9- limiter, 7... de-emphasis circuit, 16...
Speaker, 20... variable band filter, 22... variable frequency discriminator. Patent applicant Tadahiko Ito, representative patent attorney of Victor Japan Co., Ltd. 10-

Claims (1)

[Claims] A main channel in which two carrier waves having different frequencies are frequency modulated for each of a main audio signal and a sub audio signal. In a television receiver that receives a two-carrier TV audio multiplexed signal having sub-channels, the audio intercarrier signal (or intermediate frequency signal) of the main channel or the audio intercarrier of the sub-channel is output from the signal supplied from the intermediate frequency amplifier. filter means for extracting either one of the signals (or intermediate frequency signals) according to a control signal selected by an operator; and an audio intercarrier signal ( or an intermediate frequency signal) at a tuning frequency corresponding to the control signal, and obtains either the main audio signal or the sub audio signal. audio circuit.