JP2985727B2 - Audio multiplex signal demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio multiplex signal demodulation apparatus used for an in-vehicle television such as an automobile, a bus or a train, and a mobile television such as a portable television.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration of a conventional audio multiplex signal demodulator. 2, reference numeral 1 denotes an audio detection circuit, 2 denotes a de-emphasis circuit, 3 denotes a band-pass filter circuit, 4 denotes a frequency detection circuit, 5 denotes an amplitude detection circuit, 6 denotes a read filter circuit, and 7 denotes an audio switching matrix circuit.

Next, the operation of the above conventional example will be described. In audio multiplex broadcasting, when an audio intermediate frequency signal is passed through an audio detection circuit 1, three combined signals of a main channel signal, a sub-channel signal, and a multiplex control signal are output. The main channel signal is
This is the main audio signal. The sub-channel signal is 31.5 kHz
Is sub-carrier-modulated with a sub-audio signal,
Hz signal passed through a band-pass filter. The multiplex control signal has a carrier of 55.125 kHz at 922.5H.
This is a signal amplitude-modulated by z. When this synthesized signal is passed through the de-emphasis circuit 2, it becomes a main audio signal.
After passing through the bandpass filter circuit 3 of kHz and passing through the frequency detection circuit 4, it becomes a sub-existing audio signal. When a signal extracted from the intermediate point of the coil of the band-pass filter circuit 3 is passed through the amplitude detection circuit 5 and then passed through the read filter circuit 6, a control voltage of the audio multiplex control signal is generated. While this voltage is being generated, the audio switching matrix circuit 7
Thus, any one of the main sound, main sound + sub sound, and sub sound can be selected as an output signal.

[0004]

However, in the above-described conventional configuration, when a sudden change in electrolysis occurs, a portion where the amplitude detection of the multiplex control signal cannot be performed occurs, and the control voltage is repeatedly turned on and off. There has been a problem that the switching between the sub sound and the monophonic sound is repeated despite the signal being selected, and the switching between Japanese and foreign languages is repeated in bilingual broadcasting.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an audio multiplex signal demodulator capable of maintaining a sub audio signal even when a sudden electric field change occurs. It is.

[0006]

According to the present invention, in order to achieve the above object, a time constant is provided for a switching signal processing of an audio multiplex control signal for selecting an output signal of an audio switching matrix circuit.

[0007]

Therefore, according to the present invention, since the switching signal processing has a time constant even if the audio multiplex control signal is lost, the output of the sub audio signal can be maintained.

[0008]

FIG. 1 shows a configuration of a voice multiplexed signal demodulating apparatus according to an embodiment of the present invention. Elements similar to those of the conventional example shown in FIG. 2 are denoted by the same reference numerals. In FIG. 1, 1 is an audio detection circuit, 2 is a de-emphasis circuit, 3
Is a bandpass filter circuit, 4 is a frequency detection circuit, 5 is an amplitude detection circuit, 6 is a read filter circuit, 7 is an audio switching matrix circuit, 8 is a microcomputer, 9 is a time constant circuit,
Is a changeover switch circuit.

Next, the operation of the above embodiment will be described.
In the above-described embodiment, in audio multiplex broadcasting, when an audio intermediate frequency signal is passed through the audio detection circuit 1, three combined signals of a main channel signal, a sub-channel signal, and a multiplex control signal are output. The main channel signal is a main audio signal. The sub-channel signal is a signal obtained by frequency-modulating a sub-carrier of 31.5 kHz with a sub-audio signal and passing through a band-pass filter of 16 to 47 kHz. The multiplex signal is a signal obtained by amplitude-modulating a carrier wave of 55.125 kHz at 922.5 Hz. When this synthesized signal is passed through a de-emphasis circuit 2, it becomes a main audio signal, and a band-pass filter circuit 3 of 16 to 47 kHz
Through the frequency detection circuit 4 to become a sub audio signal.
When a signal extracted from the intermediate point of the coil of the band-pass filter circuit 3 is passed through the amplitude detection circuit 5 and then passed through the read filter circuit 6, a control voltage of the audio multiplex control signal is generated. Next, under the control of the microcomputer 8, the control switch circuit 10 switches whether the control voltage is sent to the audio switching matrix 7 through the time constant circuit 9 (on state) or not transmitted (off state). While the control voltage is being generated, any one of the main sound, main sound + sub sound, and sub sound can be selected as an output signal by the sound switching matrix circuit 7. In the microcomputer 8 , the main
Voice + secondary audio, selecting one of the sub-audio when the change-over switch circuit 10 after being fully charged constant circuit 9 sends an ON signal to the on state, off sends an OFF signal when selecting the main sound State. When the microcomputer 8 detects a stereo control signal or switches channels, the microcomputer 8 sends an off signal to the changeover switch circuit 10 to turn it off.

As described above, according to this embodiment, even when the audio multiplex control signal is suddenly lost, the switching matrix circuit 7 does not switch instantaneously, and the output of the sub audio signal is maintained by the time constant circuit 9. be able to.

[0011]

As is apparent from the above description, according to the present invention, the time constant is given to the switching signal processing of the audio multiplex control signal in the audio multiplex signal demodulator, so that the audio multiplex control signal is abrupt. , The control voltage can be held for a certain period of time, and even if a sudden change in the electric field occurs while selecting the sub audio signal in audio multiplex broadcasting such as bilingual broadcasting,
The output of the sub audio signal can be maintained without switching to the monophonic audio.

[Brief description of the drawings]

FIG. 1 is a block diagram of an audio multiplexed signal demodulator according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional audio multiplexed signal demodulator;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Audio detection circuit 2 De-emphasis circuit 3 Band pass filter circuit 4 Frequency detection circuit 5 Amplitude detection circuit 6 Read filter circuit 7 Audio switching matrix circuit 8 Microcomputer 9 Time constant circuit 10 Switching switch circuit

Claims (2)

(57) [Claims] 1. An audio detection circuit for outputting a synthesized signal including a main channel signal, a sub-channel signal, and a multiplex control signal from an intermediate frequency signal, a de-emphasis circuit for outputting a main audio signal from the synthesized signal, and the synthesized signal A frequency detection circuit that outputs a sub audio signal through a band pass filter circuit from a read filter circuit that outputs a control voltage of an audio multiplex control signal through an amplitude detection circuit from a signal extracted from an intermediate point of the band pass filter circuit. , the main audio signal and or before from the de-emphasis circuit
And audio switching matrix circuit for selecting the sub-audio signal from the serial frequency detector circuit, a time constant circuit for holding the control voltage a certain time, or to input the control voltage to the audio switching matrix circuit through said time constant circuit An audio multiplexed signal demodulation device comprising: a switching circuit for switching whether the signal is input to the audio switching matrix circuit without passing through the time constant circuit, and a control circuit for controlling the switching switch circuit. 2. The switching circuit according to claim 1, wherein said switching circuit comprises a main sound and a sub sound.
When simultaneous output of audio or output of secondary audio only is selected
Switches the control voltage through the time constant circuit to
Input to the switching matrix circuit and select the output of only the main audio
When a stereo broadcast is detected or when a channel is
Is switched, the control voltage is changed to the time constant circuit.
Input to the audio switching matrix circuit without passing through
The audio multiplexed signal demodulation device according to claim 1, wherein: