JPH054678U - Multiplex audio receiver - Google Patents

Abstract

(57) [Abstract] [Objective] An object of the present invention is to provide a voice multiplex receiver in which the occurrence of DC offset at the time of matrix switching is prevented. [Structure] A control signal for discriminating between stereo broadcasting and bilingual broadcasting is demodulated by an AM detection circuit 1, and a DC voltage corresponding to the control signal is output by an FM detection circuit 3 via an FM limiter amplifier 2 to determine a discrimination circuit. Judge with 5. At this time, if the output of the discrimination circuit 5 is switched, the control signal from the discrimination circuit 5 is output to the matrix circuit 7 after counting by the counter 6 for a predetermined time.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a multiplex audio receiver of a television.

[0002]

[Prior Art]

 At present, television broadcasting includes so-called audio multiplex broadcasting in which not only monaural audio but also stereo audio and bilingual audio are transmitted.

The audio baseband characteristics of these audio multiplex broadcasts are also described, for example, in P283 to P284 (published by the Japan Broadcasting Corporation, issued on November 30, 1990) in the first volume of the NHK television technical textbook. As shown in FIG.

The description of FIG. 2 will be simplified. In the audio baseband, there are a main channel signal, an FM-modulated sub-channel signal, and an AM-modulated control signal, respectively, which are multiplexed and FM-modulated to obtain a television signal audio signal.

[0005] Here, not only monaural audio but also stereo audio and bilingual audio are included in the audio multiplex broadcasting, and there is a control signal for discriminating between them. This control signal is as shown in FIG.

To reproduce such a voice multiplexed signal, a circuit as shown in FIG. 3 is required. The operation of this circuit will be described. The audio baseband signal is input, the main channel signal is input to the matrix circuit 7, and the sub-channel signal is demodulated by the FM detection circuit 11 and input to the matrix circuit 7. The control signal is demodulated by the control signal detection circuit 10 and controls the matrix circuit 7. This control signal switches the matrix circuit 7 as shown in FIG.

FIG. 5 shows a detailed circuit diagram of the control signal detection circuit 10, and its operation will be described. The control signal is input to the AM detection circuit 1, outputs one of monaural voice, stereo voice, and bilingual voice control signals, and is input to the FM limiter amplifier 2.

Then, the FM detection circuit 3 having the detection characteristic as shown in FIG. 6 performs detection to generate a DC voltage corresponding to each control signal. The discrimination circuit 5 discriminates the DC voltage, controls the LED drive circuit 4, and further switches the matrix circuit 7. The discrimination output is as shown in FIG. Further, the CPU 8 controls the discriminating circuit 5 so as to output a compulsory monaural signal for stereo sound and a main channel signal, a sub channel signal, or both channel signals for bilingual sound.

By the way, for example, when a stereo sound or a bilingual sound is received from a monaural sound, a DC offset is generated as in the case of the failure shown in FIG. This is because the matrix circuit 7 operates before the FM detection circuit 11 that demodulates the sub-channel signal stabilizes. (If the FM detection circuit 11 is switched after being stabilized, DC offset will not occur as in the normal state.) This will be described in detail with reference to FIG.

To further analyze this, referring to FIG. 9, when the monaural voice is switched to stereo voice or bilingual voice, the control signal is AM while the voice signal is unmodulated. The control signal is modulated. Then, it is considered that the output of the discrimination circuit 5 and the switching of the matrix circuit 7 are switched when the audio signal is not modulated.

[0011]

[Problems to be solved by the device]

 An object of the present invention is to provide a voice multiplex receiver in which the occurrence of DC offset is prevented in view of the above points.

[0012]

[Means for Solving the Problems]

 The present invention receives an audio signal composed of a main channel signal component, a frequency-modulated sub-channel signal component, and an amplitude-modulated control signal component for distinguishing between stereo audio broadcasting and bilingual audio broadcasting. In the audio multiplex broadcast receiver, means for extracting the main channel signal, means for demodulating the sub-channel signal, matrix means for matrixing the main channel signal and the sub-channel signal, and demodulating the control signal Means and the control means for switching the matrix means by the output signal from the control signal demodulating means, and counting for a predetermined time after the output signal of the control means is switched, and after counting, the control means The audio multiplex broadcast receiver is provided with a counter means for outputting an output signal.

[0013]

[Action]

 The present invention prevents the occurrence of DC offset by switching the matrix after the demodulation output of the sub-channel signal is stabilized.

[0014]

【Example】

 An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In this figure, the same drawing numbers as those of the conventional circuit have the same configuration, and the description thereof is omitted.

In FIG. 1, what is different from the conventional circuit is that a counter 6 is provided. The counter 6 is connected to the FM limiter amplifier 2, the CPU 8 and the discrimination circuit 5.

Next, the operation of this embodiment will be described. First, when the discriminating circuit 5 discriminates when the output of the FM limiter amplifier 2 is switched and when the control signal is changed, the discriminating circuit 5 sets the counter 6. Then, the counter 6 starts the counter operation, and when the preset count value is reached, it sends a control signal to the discrimination circuit 5, and the control circuit outputs a signal for switching the matrix circuit 7 from the discrimination circuit 5. .. As a result, the matrix circuit 7 is switched.

As described above, since the switching timing of the matrix circuit 7 is switched after the FM detection circuit 11 is sufficiently stable, DC offset does not occur.

Although the count value of the counter 6 can be changed arbitrarily, it may be set so that there is no problem in reception.

[0019]

[Effect of the device]

 According to the present invention, it is possible to prevent the DC offset caused by switching the matrix with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a spectrum of a voice multiplexed signal.

FIG. 3 is a voice multiplex reception circuit.

FIG. 4 is a matrix switching operation.

FIG. 5 is a conventional matrix switching circuit.

FIG. 6 shows FM detection characteristics.

FIG. 7 is a discrimination output characteristic of a control signal.

FIG. 8 is a waveform diagram for explaining DC offset.

FIG. 9 is a waveform diagram for explaining switching.

FIG. 10 is a waveform diagram for explaining DC offset.

[Explanation of symbols]

 1 AM detection circuit 2 FM limiter amplifier 3 FM detection circuit 5 Discrimination circuit 6 Counter 7 Matrix circuit

Claims (1)

[Claims for utility model registration] 1. A main channel signal component, a frequency-modulated sub-channel signal component, and an amplitude-modulated control signal for distinguishing between stereo audio broadcasting and bilingual audio broadcasting. In an audio multiplex broadcast receiver for receiving an audio signal composed of components, means for extracting the main channel signal, means for demodulating the sub channel signal, and matrix means for matrixing the main channel signal and the sub channel signal. A means for demodulating the control signal, a control means for switching the matrix means with an output signal from the control signal demodulating means, and a predetermined time after the output signal of the control means is switched, and after counting. And a counter means for outputting the output signal of the control means.