JPH0653914A - Multiple sound signal demodulating circuit - Google Patents

Abstract

PURPOSE:To reduce the level difference of a demodulated sound output due to an FMMAX modulation factor by discriminating whether or not the first and second sound carriers are present, and switching the demodulation level of the first demodulated sound signal. CONSTITUTION:When the received broadcasting signal is a multiple sound broadcasting, and a monaural sound, first and second carrier peak detector circuits 16 and 17 detect each carrier, and an AND circuit 18 outputs a control signal. Therefore, a switch 19 is turned on, and the second demodulated sound signal of a detector circuit 10 is supplied to a stereo matrix circuit 11 and a BPF 12. And also, a switch 21 is turned on to a detector circuit 9 side, and the first demodulated sound signal is supplied to a monaural/stereo changeover switch circuit 15 as it is. Then, the monaural sound signal is discriminated, the circuit 15 is turned to a monaural mode, and the first demodulated sound signal obtained from the switch 21 is outputted. And also, when the broadcasting is the multiple sound broadcasting, and a stereo signal, a stereo sound signal is outputted from the stereo matrix circuit 11.

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 circuit applied to demodulation of audio multiplex broadcasting currently broadcast in Germany and the like.

[0002]

2. Description of the Related Art Generally, a quadrature parallel or split carrier type inter-carrier detection is used for a processing and demodulating circuit of a voice multiplex signal. Here, the former quadrature parallel type will be described with reference to FIG.

In FIG. 2, the IF signal output from the tuner 1 is supplied to a video signal processing circuit 4 and an audio multiplex signal demodulation circuit 5 via filter circuits 2 and 3, respectively. Each of the filter circuits 2 and 3 is composed of a SAW (surface acoustic wave) filter.

The audio multiplex signal component contained in the IF signal is selected in the vicinity of the first and second audio carriers by the filter circuit 3, and the intercarrier detection is first performed by the detection circuit 6 of the audio multiplex signal demodulation circuit 5. To be done. As a result, FM-modulated audio IF signals of the first and second audio carriers S1 and S2 are obtained.

The audio IF signals are 5.5 MHz band pass filter circuit (BPF) 7 and 5.74 MHz, respectively.
The bandpass filter circuit (BPF) 8 separates the two audio IF signals having the first and second audio carriers S1 and S2, and the detection circuits 9 and 10 perform FM detection to obtain an audio signal.

In the detection circuit 9, I of the first voice carrier S1
When the F signal is detected, a first demodulated voice signal composed of L + R / 2 or the main voice signal is obtained, and the second demodulated voice signal is detected by the detection circuit 10.
When the IF signal of the voice carrier S2 is detected, a second demodulated voice signal including the R component or the sub voice signal and the pilot signal is obtained. The respective outputs of the detection circuits 9 and 10 are supplied to the stereo matrix circuit 11, separated into L and R components, and also supplied to the monaural / stereo selector switch circuit 15. L + R / 2 from the detection circuit 9
The first demodulated voice signal of is directly supplied to the monaural / stereo changeover switch circuit 15.

The pilot signal contained in the second demodulated audio signal output from the detection circuit 10 is extracted by the bandpass filter 12 and detected by the pilot detection circuit 13, and the discrimination circuit 14 broadcasts from this pilot signal. Determine whether the signal is stereo, bilingual or monaural.

The discriminating signal from the discriminating circuit 14 controls the stereo matrix circuit 11 and the monaural / stereo selector switch circuit 15. The switch circuit 15 is configured to have a state in which stereo L and R components are independently output from the output terminals and a state in which a monaural audio signal is output from both terminals according to the determination signal.

[0009]

By the way, in a broadcasting station supporting audio multiplexing, the second audio carrier S2 is not cut when transmitting a monaural audio signal.
This is achieved by modulating the first and second voice carriers with the monaural voice signal and unmodulating the carrier of the pilot signal.

In the audio multiplex signal broadcasting, both audio carriers S1 and S2 have an FMMAX modulation degree of 30 KHz.
In contrast to Dev, the FM MAX modulation degree is 50 KHzD in monaural broadcasting performed by general monaural broadcasting stations.
Unlike ev, if demodulated by the same FM detection circuit, the demodulation output level will be different.

[0011] The FM modulation degree of a broadcasting station supporting voice multiplexing and the MAX value of the FM modulation degree of a monaural broadcasting station are different. Since the FM modulation degree and the demodulated audio signal level have a linearly changing relationship, the FM modulation degree is 30 KHz Dew to 50 KHz D.
When it becomes ew, the demodulated voice signal level also becomes 5/3 times higher.

Therefore, if the circuit constant of the audio multiplex compatible station is used, the level of the audio signal from the monaural broadcasting station is increased. Conversely, if the circuit constant of the monaural station is set to the monaural audio from the audio multiplex broadcasting station (when the pilot carrier is not modulated) The audio signal level of is reduced.

To cope with this, it suffices that the monaural sound from the sound multiplex broadcasting station can be detected in some form. The pilot carrier is set to 117.4 Hz, 274.1 Hz, and three types of AM modulation, which are unmodulated, but it is difficult to determine that pilot carrier unmodulated is noise.

[0014]

Therefore, according to the present invention, the audio signal from the monaural broadcasting station is only the first audio carrier S1 and the audio signal from the audio multiplex broadcasting station is always the first audio carrier S1.
The present invention was made by paying attention to the fact that there are both the first audio carrier S2 and the second audio carrier S2, and the first audio carrier and the second audio carrier are extracted from the IF signal including the video signal and the multiplexed audio signal extracted from the tuner. FM-modulated audio IF signal is obtained, the audio IF signal is separated into IF signals of the first and second audio carriers through a bandpass filter, and the IF signal of the first audio carrier is detected as L + R. A first demodulated voice signal composed of a / 2 signal or a main voice signal is obtained, and a second demodulated voice signal composed of an R signal or a sub voice signal and a pilot signal is obtained from the IF signal of the second voice carrier. A discriminating means for discriminating the presence or absence of the first and second voice carriers is provided, and the discriminating means discriminates whether or not both the first and second voice carriers exist. There is provided a sound multiplex signal demodulation circuit to perform the switching of the demodulation output level of the first demodulated audio signal by.

According to the present invention, in the presence / absence of the first and second voice carriers determined by the determining means, the second demodulated voice signal is made valid only when both voice carriers are present. A demodulation circuit, and further, the discrimination means outputs first and second peak detection circuits for performing peak detection of the first and second voice carriers, and outputs a carrier presence / absence determination signal when outputs from both detection circuits are obtained. The present invention provides a voice multiplexed signal demodulation circuit composed of a circuit.

[0016]

Therefore, according to the present invention, the AND of the carrier presence / absence determining signals obtained by detecting the first and second audio carriers is taken to determine whether or not the audio multiplex broadcasting is performed. L + which is the FM detection output of the voice carrier
The R / 2 signal is multiplied by 3/5 and output, and in the case of monaural audio (non-modulated pilot carrier) in audio multiplex broadcasting, the L + R / 2 signal which is the FM detection output of the first audio carrier is output as it is. To output.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block-like electric circuit diagram showing an embodiment of a voice multiplexed signal demodulation circuit according to the present invention. For convenience of explanation, the same parts as those of the conventional circuit are designated by the same reference numerals.

In FIG. 1, a portion different from the conventional circuit is a portion surrounded by a dotted line, which is 5.5 MHz and 5.7.
First and second carrier peak detection circuits 16 and 17 which receive outputs from the 4 MHz band pass filter circuits 7 and 8 and detect carrier peaks of the first and second voice carriers S1 and S2, and these circuits 16 and 17 And an AND circuit 18 which outputs a control signal when each carrier peak is detected, a switch 19 which is between the detection circuit 10 and the bandpass filter 12 of the pilot signal, and which is turned on / off by the control signal, and the detection circuit. 3/5 to multiply the first demodulated voice signal (L + R / 2) from 9 by 3/5
The multiplying circuit 20 and the 3/5 multiplying circuit 20 by the control signal.
2 and the switch 21 for selectively supplying the first demodulated voice signal of the detection circuit 9 to the monaural / stereo changeover switch circuit 15.

In such a configuration, when the received broadcast is a voice multiplex broadcast and monaural voice (pilot carrier unmodulated), the first and second carrier peak detection circuits 16 and 17 detect the respective carriers, AND circuit 18
Outputs a control signal, the switch 19 is turned on to supply the second demodulated audio signal of the detection circuit 10 to the stereo matrix circuit 11 and the bandpass filter 12, and the switch 21 is turned on to the detection circuit 9 side. Then, the first demodulated audio signal is directly supplied to the monaural / stereo changeover switch circuit 15.

At this time, the bandpass filter 12, the pilot detection circuit 13 and the discrimination circuit 14 discriminate that the signal is monaural, and the monaural / stereo changeover switch circuit 15 is in the monaural state, and the switch 2 is operated.
The first demodulated audio signal (L + R / 2) obtained from 1 is output.

When the broadcast being received is a voice multiplex broadcast and stereo sound, the switch 19 is turned on, and the discrimination circuit 14 causes the stereo matrix circuit 11 to function and the monaural / stereo selector switch circuit 15 to be stereo. Since the state is set, the L and R stereo audio signals are output from the stereo matrix circuit.

If the broadcast being received is not a voice multiplex broadcast, a signal cannot be obtained from one of the first and second carrier peak detection circuits 16 and 17, so that the discrimination circuit 18 outputs a control signal. As a result, the switch 19 is turned off, the switch 21 is switched to the 3/5 times circuit 20 side, and the first demodulated audio signal (L
+ R / 2) is multiplied by 3/5 by the 3/5 multiplication circuit 20 and output from the monaural / stereo changeover switch circuit 15.

[0023]

Since the present invention is constructed as described above, the demodulation circuit can output the audio signal of a monaural broadcasting station having a different FMMAX modulation degree and the monaural audio signal of a stereo broadcasting station at the same level. In the area where the signals of both broadcasting stations can be received at the same time, the difference in audio level is eliminated. In addition, since the second demodulated audio signal output is cut except in the case of audio multiplex broadcasting, it is equivalent to not inputting the pilot carrier included therein into the circuit for discriminating the pilot carrier, and the malfunction is improved.

[Brief description of drawings]

FIG. 1 is a block-like electric circuit diagram showing an embodiment of a voice multiplexed signal demodulation circuit according to the present invention.

FIG. 2 is a block-like electric circuit diagram showing a conventional audio multiplex signal demodulation circuit.

[Explanation of symbols]

 7 5.5 MHz band pass filter circuit 8 5.74 MHz band pass filter circuit 9 Detection circuit 10 Detection circuit 11 Stereo matrix circuit 16 First carrier peak detection circuit 17 Second carrier peak detection circuit 18 AND circuit 19 Switch circuit 20 3/5 Double circuit

Claims (3)

[Claims] 1. An FM-modulated audio IF signal of a first audio carrier and a second audio carrier is obtained from an IF signal including a video signal and a multiplexed audio signal extracted from a tuner, and the audio IF signal is banded. A first demodulated audio signal composed of an L + R / 2 signal or a main audio signal is obtained from the IF signal of the first audio carrier by separating and detecting the IF signals of the first and second audio carriers respectively through a pass filter, An R signal or a second demodulated voice signal composed of a sub-voice signal and a pilot signal is obtained from the IF signal of the second voice carrier, and the determination means for determining the presence or absence of the first and second voice carriers is provided. , The discriminating means discriminates whether or not both the first and second voice carriers are present, thereby determining the demodulation output level of the first demodulated voice signal. Sound multiplex signal demodulation circuit, characterized in that to perform the recombination. 2. The second demodulated voice signal is validated only when both the voice carriers are present in the presence / absence discrimination of the first and second voice carriers by the discrimination means. The audio multiplex signal demodulation circuit according to claim 1. 3. The discrimination means outputs first and second peak detection circuits for performing peak detection of the first and second voice carriers, and outputs a carrier presence / absence discrimination signal when outputs are obtained from both of the detection circuits. An audio multiplex signal demodulation circuit according to claim 1, wherein the audio multiplex signal demodulation circuit comprises an AND circuit.