JPS632474A - Audio multiplex broadcast receiving circuit - Google Patents

Abstract

PURPOSE:To reduce disturbance due to video noise also at the time of receiving any broadcasting by connecting one ends of a resistor and a capacitor to each other of which the other ends are connected to right and left side output terminals respectively and earthing the node at the time of receiving two language broadcasting. CONSTITUTION:Since a control terminal 20 of a discriminating circuit 8 is held at a low level at the time of stereo broadcasting, a transistor (TR) 17 is helt at an off state. Thereby the left channel side output terminal 14 is connected to a right channel side output terminal 15 through a serial circuit consisting of a resistor 16 and a capacitor 19, so that a high frequency component is mixed and a video noise component is cancelled. Since only the high frequency of the signal component is mixed, the frequency characteristics are not deteriorated. Since the terminal 20 is turned to a high level at the time of two language broadcasting, the TR 17 is turned on through a resistor 18 and one side of the resistor 16 and the capacitor 19 is earthed. At that time, the high frequency band is dropped on the terminal 15 and video noise is reduced. Althrough the high frequency band of the signal is also dropped, no trouble is generated because the drop is generated in the subsound side. On the main sound side, the frequency characteristics are not deteriorated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a receiving circuit for a television, a VTR, etc.
In particular, the present invention relates to an audio multiplex broadcast receiving circuit that reduces buzz interference caused by video to audio.

[Conventional technology]

As shown in Figure 2, the current audio multiplex broadcasting system in Japan uses a (Z+R) signal (L is the left signal, R is the right signal) when broadcasting audio in stereo up to 15 KBZ, and a main signal when broadcasting in two languages. The (L-R) signal or sub-audio during stereo broadcasting is FM-modulated and superimposed using 31.5KHz as the carrier, and 55.+25KH2 is used as the carrier, and 982.5Hz during stereo broadcasting, 2 digits. When broadcasting in Japanese, AM modulation is applied using 922.5H2, and the signal superimposed as a pilot signal for stereo/two-language discrimination is FM modulated as an audio signal, superimposed on a video signal, and transmitted as television radio waves.

The audio system on the receiving side first separates the video signal and the audio signal, demodulates the audio signal, returns it to the audio band, and determines whether it is a stereo broadcast or a bilingual broadcast based on a pilot signal. During stereo broadcasting, the (L+R) signal and
Demodulated 5t5KHz carrier FM signal (L-R)
A signal is input to a matrix circuit and Lch (left signal channel) and Rch (right signal channel) signals are extracted.

Also, when broadcasting in two languages, the main audio is output directly to Lck without passing through the matrix circuit, and the sub audio is output at 5t5rHz.
The FM signal of the carrier is demodulated and output as is to Rck.

[Problem that the invention seeks to solve]

In the above conventional technology, when separating the video signal and the audio signal, the video signal may leak into the audio signal.

In that case, it will interfere with the high-frequency components of the audio, so
FM modulated with a 1.5KHz carrier (r,
- Since video noise is added to the R) signal or the sub-audio output, there is a problem in that during stereo broadcasting and for both R and bilingual broadcasting, the video noise is added to the sub-audio, making it difficult to hear the audio.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide an audio multiplex broadcast receiving circuit that is free from practical problems.

[Means for solving problems]

The above purpose is to first prevent video interference during stereo broadcasting (L
-R) signal, so in the matrix circuit, the L signal,
When the R signal is extracted, the interference signals contained in each signal are in opposite phases, and their components are mostly in the high frequency range, so by combining the Lch and Rch outputs with a capacitor and a resistor, By mixing only the high-frequency components, interference is canceled out and noise is reduced. Also, when broadcasting in two languages, a capacitor is attached to the Rch, that is, the sub-audio side output that contains the interference signal, to reduce the high-frequency components and reduce noise. This is achieved by

[Effect]

When receiving bilingual broadcasting, the resistor connected to the Lch side output and the capacitor connected to the Rch side output are both grounded, so the high frequency part of only the Rch side, that is, the sub audio side, is attenuated and noise is reduced. However, when receiving stereo broadcasts, the connection point of the above capacitor and resistor is not grounded, so the L
The high-frequency components of eh and Rch are mixed and the noise components cancel each other out, reducing noise in the received audio both when receiving bilingual broadcasting and when receiving stereo broadcasting.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an audio multiplex broadcast receiving circuit according to the present invention, in which 1 is an antenna, 2 is a cheese, and 3 is a block diagram showing an embodiment of an audio multiplex broadcast receiving circuit according to the present invention. Audio/video separation circuit, 4 is video signal processing circuit, 5 is FM
Demodulation circuit, 6 is a low-pass filter, 7 is a band-pass filter, 8 is a stereo/two-language discrimination circuit, 9 is an FM demodulation circuit, 10 is a matrix circuit, N, 12 is a stereo/two-language discrimination circuit,
13 is a control signal, 14 is an Lch side output terminal (audio side output terminal), 15 is an Rch side output terminal (audio side output terminal), 16 is a resistor, 17 is a transistor, 18 is a resistor, 19 is a Capacitor 20 is a bilingual control terminal.

In the figure, a broadcast signal inputted from an antenna 1 is selected by a channel 2 and inputted to an audio/video signal separation circuit 3. One of the signals separated by the audio/video separation circuit 3 is output to the video signal processing circuit 4 as a video signal. The other signal is output as an audio signal to the FM demodulation circuit 5, and the audio signal is demodulated. The demodulated audio signal is supplied to a low-pass filter 6, a Bandhus filter 7, and a discrimination circuit 8. In the low-pass filter 6 (L+
R) signal, or only the main audio signal is extracted, and M) I
The signal is input to one input of the JX circuit 10 and the Japanese language side terminal α of the stereo/two-language selector switch 1102.

In the bandpass filter 7, the (L-R) signal or the sub-audio signal is taken out, demodulated by the FM demodulation circuit 9, and output to the other input of the matrix circuit 10 and the two-language input signal of the stereo/two-language selection switch 12. It is input to the side terminal α.

Further, the discrimination circuit 8 detects a pilot signal and discriminates whether it is a stereo broadcast or a bilingual broadcast. The discrimination signal is a control signal 13, which is a stereo/two-language selection switch N, +2.
Switch and control.

When the discrimination circuit 8 discriminates bilingual broadcasting, it sets its control terminal 20 to a high level and turns on the transistor 17 via the resistor 18.

The outputs of the matrix circuit 10 are Lch connected to the stereo input terminal of the switch 11, Rch connected to the stereo input terminal of the switch 12, and the outputs of the two switches I+ and +2, respectively. It is output from the Lch or main audio side output terminal 14 and the Rch or sub audio side output terminal 15.

A resistor 16 is connected between the collectors of the transistor 17 at the Lch side output terminal 14, and a capacitor 19 is connected between the collectors of the transistor 17 at the Rch side output terminal 15.

In the above configuration, first, during stereo broadcasting, the control terminal 20 of the discrimination circuit 8 is at a low level, so the transistor 17 is in a non-conducting state.

Therefore, the Lch side output terminal 14 and the Rch side output terminal 15 each have a resistor 16. Since they are connected through a series circuit of capacitors 19, high frequency components at both terminals are mixed and image noise components are canceled. In this case, as for the signal components, only the high frequencies are mixed, so the frequency percentage characteristics do not deteriorate.

Next, when broadcasting in two languages, the control terminal 20 becomes high level, so current flows through the transistor 170 through the resistor 18, making the transistor 17 conductive, and the resistor 16 and capacitor 19 are both grounded on one side. Become. At this time,
Since the Rehe terminal, ie, the sub-audio side output terminal 15, is grounded via a capacitor, high frequencies are lowered and video noise is reduced. At this time, the high frequencies of the signal also drop, but this is not a practical problem because it is on the side audio side.

Note that the main audio side is simply grounded via a resistor, so the frequency characteristics do not deteriorate.

As described above, according to the above embodiment, when receiving a stereo broadcast, it is possible to reduce video noise without deteriorating the sound quality, and when receiving a broadcast in two languages, it is possible to reduce the video noise without deteriorating the sound quality of the main audio. This has the effect of reducing noise components only in audio.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reduce the interference of video noise to the audio when receiving stereo broadcasts and bilingual broadcasts without deteriorating the sound quality with a simple external circuit. Thus, it is possible to provide an audio multiplex broadcast receiving circuit with excellent functions, except for the drawbacks of the above-mentioned prior art.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an audio multiplex broadcast receiving circuit according to the present invention, and FIG. 2 is a frequency distribution diagram showing signals of an audio multiplex system. 1......Antenna 2...
・・・・・・・・・・・・Tuner 3・・・－・・・・・・
...Video/audio separation circuit 4...
...Video signal processing circuit 5...
...FM demodulation circuit 6...Low pass filter 7...Band pass filter 8...・・・・・・・・・Stereo/2-language discrimination circuit 9・・・・・・・・・・・・・・・
...FM demodulation circuit 10...Matrix circuit N, +2...Stereo/two-language selection switch 13...Control signal 14... Lch side output output terminal Audio side output terminal) 15... -...Re person output terminal Sub-audio side output terminal) 16... −・・・・・・・・・
・Resistance 17...--Transistor 18...
・−・−・Resistance

Claims (1)

[Claims] 1. Receive an audio multiplex broadcast, and automatically switch the audio output to stereo signal and bilingual signal reception status by determining the pilot signal included in the received signal of the broadcast, and when receiving a stereo signal, the left side signal is output to the left signal channel terminal, the right signal is output to the right signal channel terminal, and when receiving signals in two languages, the main audio is output to the left signal channel and the sub audio is output to the right signal channel. In the receiving circuit, a resistor having one end connected to the left side signal channel terminal and a capacitor having one end connected to the right side signal channel terminal are provided, and the other ends of these resistors and the capacitor are connected, and this connection point is connected to two ends. An audio multiplex broadcast receiving circuit characterized in that it is provided with means for grounding when receiving a signal in two languages.