JPH0358210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a receiving device capable of receiving an FM stereo signal and a television audio multiplex signal, and particularly relates to an identification signal included in the television audio multiplex signal. The present invention relates to a receiving device capable of demodulating the television audio multiplexed signal without detection.

(b) Prior Art Currently, receiving devices capable of receiving FM stereo broadcasts and television audio multiplex broadcasts are known. The FM stereo signal used in the FM stereo broadcast includes a main channel signal consisting of a stereo sum signal (L+R), a sub-channel signal consisting of a 38KHz subcarrier AM modulated by a stereo difference signal (L-R), and a 19KHz sub-channel signal. It is created by FM modulating the main carrier wave with a stereo pilot signal. Furthermore, the television audio multiplex signal used in the television audio multiplex broadcast is a stereo sum signal (L+
R) or a main channel signal consisting of the first audio signal (Japanese) and a sub-channel signal formed by FM modulating the 31.5KHz subcarrier with a stereo difference signal (L-R) or a second audio signal (foreign language). and the control subcarrier of 55.125KHz by the first identification signal of 982.5Hz or the second identification signal of 922.5Hz.
It is created by FM modulating the main carrier wave with an AM modulated control channel signal.
However, since the FM stereo signal and the TV audio multiplex signal have different modulation methods as mentioned above,
It is not possible to demodulate using the same demodulation circuit,
Mutually independent demodulation circuits had to be placed within the receiver.

On the other hand, when comparing FM stereo broadcasting and TV audio multiplex broadcasting, we focused on the fact that the structure of the main channel signal is the same, and developed a technology that uses an FM stereo demodulation circuit as a circuit to separate the main channel signal. It is disclosed in Japanese Patent Application Laid-open No. 58-38084. As shown in FIG. 2, the receiving device described in FIG. 3 of the publication includes a stereo demodulator 2 including a stereo multiplex circuit 1, and an FM demodulator for FM detecting a sub-channel signal of a TV audio multiplexed signal.
a sub-channel signal demodulator 4 including a detection circuit 3;
A control channel signal demodulator 7 includes an AM detection circuit 5 that performs AM detection on a control channel signal, an identification circuit 6 that determines the type of identification signal included in the AM detected control channel signal, and a stereo signal of a television audio multiplex signal. (hereinafter referred to as a television stereo signal), the stereo sum signal (L+R) obtained from the stereo demodulator 2 and the stereo difference signal (L-R) obtained from the sub-channel signal demodulator 4
A matrix circuit 8 for matrixing R) is provided.

Now, if you receive an FM stereo signal,
An FM stereo composite signal is applied to the input terminal 9, and the signal is separated into left and right stereo signals L and R by the stereo multiplex circuit 1. The left stereo signal L is outputted to the left output terminal 12 via the de-emphasis circuit 10 and the low-pass filter 11, and the right stereo signal R is outputted to the left output terminal 12 via the de-emphasis circuit 13 and the low-pass filter 14.
is led out to the right output terminal 15 via. At that time,
Since there is no identification signal in the FM stereo signal, the switch circuit 16 of the control channel demodulator 7
The output of is in the first state (for example, "H"), and the first and second switches 17 and 18 are in the illustrated state.

Next, suppose you receive a TV stereo signal.
A television stereo composite signal is applied to the input terminal 9, which is applied to the stereo multiplex circuit 1. At the same time, the sub-channel signal in the TV stereo composite signal is 15-47K.
The control channel signal is applied to the FM detection circuit 3 via a bandpass filter 19 having a band of Hz, and the control channel signal is applied to the AM detection circuit 5 via a bandpass filter 20 having a center frequency of 55.125KHz.
is applied to After the control channel signal applied to the AM detection circuit 5 is subjected to AM detection, it is identified by the identification circuit 6, and a first identification signal of 982.5 Hz indicating that it is a television stereo signal is applied to the switch circuit 16. be done. In that case, the output of the switch circuit 16 remains in the first state, and the first and second switches 17 and 18 also remain in the first state. Further, the sub-channel signal applied to the FM detection circuit 3 is applied to the matrix circuit 8 via the de-emphasis circuit 21 and the low-pass filter 22 after being subjected to FM detection. Furthermore, since there is no 19KHz stereo pilot signal, the television stereo composite signal applied to the stereo multiplex circuit 1 operates as a mere buffer amplifier circuit, so that the stereo multiplex circuit 1
The signal passes through the de-emphasis circuits 10, 13 and the low-pass filters 11, 14 as they are, and becomes a stereo sum signal (L+R). The stereo sum signal and the stereo difference signal (L-R) from the sub-channel signal demodulator 4 are matrixed in a matrix circuit 8, and the left stereo signal L is sent to the left output terminal 12, and the right stereo signal L is sent to the right output terminal 15. A signal R is generated respectively.

Furthermore, if two audio signals of the TV audio multiplexed signal are received, the two audio signals are applied to the input terminal 9, which is applied to the stereo multiplex circuit 1, and the sub-channel signal of the two audio signals is applied to the input terminal 9. passes through bandpass filter 19 to FM
A control channel signal is applied to the AM detection circuit 5 via the bandpass filter 20 to the detection circuit 3 . Therefore, the second identification signal of 922.5 Hz is generated from the identification circuit 6, the output of the switch circuit 16 becomes the second state (for example, "L"), and the first and second switches 17 and 18 are reversed from the illustration. becomes the state of When the first switch 17 is switched to the opposite state as shown, the output signal of the sub-channel signal demodulator 4 is generated at the right output terminal 15 via the first switch 17. Furthermore, when the second switch 18 is switched to the opposite state as shown, the input terminal of the matrix circuit 8 is grounded, so that the matrix circuit 8 stops operating. Therefore, the two audio signals applied to the stereo multiplex circuit 1 pass through the stereo multiplex circuit 1, which operates as a buffer amplifier circuit, and are generated at the left output terminal 12 via the de-emphasis circuit 10 and the low-puff filter 11. The sub-channel signal applied to the FM detection circuit 3 via the bandpass filter 19 is the FM
After being detected, the signal is generated at the right output terminal 15 via the de-emphasis circuit 21, the low-pass filter 22, and the first switch 17. Therefore, left output terminal 1
The signal obtained at the right output terminal 15 becomes the first audio signal (Japanese), and the signal obtained at the right output terminal 15 becomes the second audio signal (foreign language).

As mentioned above, by using the circuit shown in FIG. 2, it is possible to correctly demodulate the FM stereo signal and the TV audio multiplex signal, and moreover, the FM stereo demodulator 1 can be used as a circuit for reproducing the main channel signal of the TV audio multiplex signal. Since it is shared by both, the circuit configuration becomes simple.

(C) Problems to be Solved by the Invention However, the circuit shown in Fig. 2 performs circuit switching by detecting the identification signal included in the TV audio multiplex signal, and the main carrier The modulation depth is as low as 2KHz,
The frequency of the control channel signal is relatively high at 55KHz, and the frequencies of the first and second identification signals are
Due to the fact that 982.5Hz and 922.5Hz are close to each other, the control channel signal demodulation section for detecting the identification signal has become very complicated and expensive.

In addition, in the case of the circuit shown in Fig. 2, when two audio signals of the TV audio multiplex signal are received, the left output terminal 12
Since the first audio signal is generated at the right output terminal 15 and the second audio signal is generated at the right output terminal 15, when the left and right amplifier circuits and the left and right speakers are connected to the left and right output terminals 12 and 15, respectively, only the first audio signal or the second audio signal is generated. However, a separate switch circuit must be provided to select either the first audio signal or the second audio signal.

(d) Means for solving the problems The present invention has been made in view of the above points.
The first means for detecting the absence of the 19KHz stereo pilot signal, the second means for detecting the subcarrier of the TV audio multiplex signal, and the PLL type FM detection circuit for FM detecting the subcarrier are in a locked state. The present invention is characterized in that it comprises a third means for detecting, and a fourth means for generating a control signal according to the output signals of the first to third means and correctly demodulating the television audio multiplexed signal.

(e) Effects According to the present invention, it is possible to determine whether the currently received signal is an FM stereo signal or a television audio multiplex signal by only the first to fourth means, and to determine whether the currently received signal is an FM stereo signal or a television audio multiplex signal, and It is possible to perform circuit switching.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
23 is an input terminal to which an FM detected FM stereo signal and a television audio multiplex signal are applied; 24 is a stereo multiplex circuit for separating the FM stereo signal into left and right stereo signals; 25 is a terminal that connects the input terminal 23 and the stereo The first switch circuit is inserted between the input end of the multiplex circuit 24, 26 is a bandpass filter having a bandwidth of 15 to 47 KHz, and 27 is a PLL type FM that performs FM detection on the subcarrier of the TV audio multiplex signal. detection circuit,
28 is a buffer transistor, 29 is an emitter
A polarity inversion transistor that generates an inverted signal of the subchannel signal at its collector upon receiving the FM detected subchannel signal; 30 is a first subtraction circuit; 31 is a second subtraction circuit; 32 is the polarity inversion transistor 2;
A second switch circuit 33 is inserted between the collector of the polarity reversing transistor 29 and the first subtraction circuit 30; A switch circuit 34 is a fourth switch circuit inserted between the right output terminal of the stereo multiplex circuit 24 and the input terminal of the second subtraction circuit 31.
5 is a first input to which a lighting signal for a stereo indicator 36 is applied, which becomes "L" when receiving an FM stereo signal and "H" when receiving other signals;
A second input to which is applied the "H" signal that occurs at one end of the capacitor 37 when a subcarrier is present, and a PLL.
and a third input connected to a lock signal generating terminal that indicates that the FM detection circuit 27 of the system is locked; and 38 drives a TV audio multiplex indicator 39 in accordance with the output signal of the AND gate 35. This is a drive transistor.
Note that the first to fourth switch circuits 25 to 34 are
It is configured to be in a conductive state when an "H" signal is applied to the control terminal.

Now, if an FM stereo signal is applied to the input terminal 23, the FM stereo signal is applied to the stereo multiplex circuit 24 via the first switch circuit 25, and is separated into left and right stereo signals L and R as in the conventional case. Ru. At that time, since the FM stereo signal includes a 19KHz stereo pilot signal, the cathode of the stereo indicator 36 becomes "L", and the stereo indicator 36 lights up to indicate FM stereo reception. At the same time, the "L" signal is
5, the output of the AND gate 35 becomes "L", and the bias of the buffer transistor 28 and the polarity inversion transistor 29 is cut off. Therefore, the first and second switches 4
Regardless of the states of 0 and 41, no signal is generated at the collector and emitter of the polarity inversion transistor 29. Therefore, the left stereo signal L generated at the output end of the stereo multiplex circuit 24 is transmitted to the de-emphasis circuit 42 and the low-pass filter 4.
3 to the first subtraction circuit 30. Further, the right stereo signal R generated at the output end of the stereo multiplex circuit 24 is applied to the second subtraction circuit 31 via the de-emphasis circuit 44, the low-pass filter 45 and the fourth switch circuit 34. Since the signals obtained at the collector and emitter of the polarity inversion transistor 29 are zero, the left and right stereo signals L and R are directly transmitted to the left and right output terminals 4.
6 and 47 to achieve FM stereo reception. Furthermore, when receiving an FM stereo signal, the output of the AND gate 35 becomes "L", so the first
Switch 40 becomes irrelevant to operation.

Next, the FM monaural signal or TV monaural signal (hereinafter referred to as monaural signal) is input to the input terminal 2.
3, the monaural signal is applied to the stereo multiplex circuit 24 via the first switch circuit 25. At that time, since there is no 19KHz stereo pilot signal, the stereo multiplex circuit 24 operates as a mere buffer amplifier circuit, and equal monaural signals are generated at both output ends. The monaural signal is transmitted through de-emphasis circuits 42 and 44, low-pass filters 43 and 45, and first and second subtraction circuits 3, respectively.
0 and 31 to the left and right output terminals 46 and 47, monaural reception is achieved. In that case, since there is no 19KHz stereo pilot signal, the stereo indicator 36 goes out and an "H" signal is applied to the first input of the AND gate 35. On the other hand, since the monaural signal does not include components of 15 KHz or higher, no signal passes through the bandpass filter 26. Therefore, the capacitor 37 is not charged and the second input of the AND gate 35 becomes "L".
become. In addition, since it does not contain components above 15KHz, the PLL type FM detection circuit 27 does not lock.
The third input of the AND gate 35 also becomes "L". Therefore, like when receiving an FM stereo signal, the output of the AND gate 35 becomes "L", the buffer transistor 28 and the polarity inversion transistor 29 are turned off, and the signals at the collector and emitter of the polarity inversion transistor 29 become zero. become.

Further, when a TV audio multiplex signal is applied to the input terminal 23, the TV audio multiplex signal is applied to the stereo multiplex circuit 24 via the first switch circuit 25, and the sub-channel signal of the TV audio multiplex signal is applied to the stereo multiplex circuit 24 via the first switch circuit 25. is applied to the PLL type FM detection circuit 27 via the bandpass filter 26 and the amplifier circuit 48. Since the stereo multiplex circuit 24 operates as a simple buffer amplifier circuit in this case as well, as in the case of receiving a monaural signal, the main channel signal is applied to the positive input terminals of the first and second subtraction circuits 30 and 31. Ru.
Further, the sub-channel signal applied to the FM detection circuit 27 is applied to the base of the buffer transistor 28 after being subjected to FM detection. Therefore, when receiving a TV audio multiplex signal, there is no 19KHz stereo pilot signal, but a subcarrier exists.
Since the PLL type FM detection circuit 27 is in a locked state, all inputs of the AND gate 35 are "H".
Then, the output of the AND gate 35 becomes "H". Therefore, a bias is applied to the buffer transistor 28 and the polarity inversion transistor 29, and the
The output of the FM detection circuit 27 is applied to the base of a polarity inversion transistor 29 via a buffer transistor 28, a de-emphasis circuit 49, and a low-pass filter 50. Furthermore, since the output "H" of the AND gate 35 is supplied to the first switch 40 as an operating power supply, the first to fourth switch circuits 2
5 to 34 can be switched depending on the state of the first switch 40.

Here, if the received TV audio multiplex signal is a TV stereo signal, the first switch 4
0 to stereo position b manually. Then,
The second switch circuit 32 becomes conductive, and the inverted stereo difference signal -(L-R) obtained at the collector of the polarity inversion transistor 29 is applied to the first subtraction circuit 30 via the second switch circuit 32, and the low-pass filter 43 is subtracted from the stereo sum signal (L+R) applied to the first subtraction circuit 30, and a left stereo signal L is generated at the left output terminal 46. Also,
The stereo difference signal (LR) obtained at the emitter of the polarity inversion transistor 29 is directly transmitted to the second subtraction circuit 3.
1 and is applied from the fourth switch circuit 34 to the second subtraction circuit 31 (L
+R), and a right stereo signal R is generated at the right output terminal 47.

Next, assuming that the received TV audio multiplexed signal is a two-audio signal and the first switch 40 is switched to the main channel position a shown in the figure, the interlocked second switch 41 is also switched to the main channel position a shown. In other words, the base of buffer transistor 28 is grounded. Therefore, the generation of the sub-channel signal is stopped, and the signal is transmitted from the stereo multiplex circuit 24 to the de-emphasis circuit 42 and the low-pass filter 4.
3. A first audio signal is outputted to the left output terminal 46 via the first subtraction circuit 30, and similarly outputted to the right output terminal via the de-emphasis circuit 44, low-pass filter 45, fourth switch circuit 34, and second subtraction circuit 31. A first audio signal is also derived from the terminal 47. Also,
When the first switch 40 is switched to the sub channel position d, the first switch circuit 25 is cut off and the main channel signal is transferred to the stereo multiplex circuit 24.
is no longer applied, and the third switch circuit 33
becomes conductive, so the polarity inversion transistor 2
The second audio signal obtained at the emitter 9 is
The signal is applied to the first subtraction circuit 30 via the switch circuit 33 and directly to the second subtraction circuit 31, and a second audio signal is generated equally at the left and right output terminals 46 and 47. Furthermore, when the first switch 40 is switched to the mixing position c of the main channel signal and the sub-channel signal, the fourth switch circuit 34 is cut off, and the first subtraction circuit 30 is connected to the low-pass filter 4.
3 to the first audio signal is sent to the second subtraction circuit 31,
Since the second audio signal is applied from the polarity inversion transistor 29, the first audio signal is generated at the left output terminal 46, and the second audio signal is generated at the right output terminal 47, respectively. Note that when the output of the AND gate 35 becomes "H", the drive transistor 38 is turned on, so the audio multiplex indicator 39 lights up to indicate that the TV audio multiplex signal is being received.

(g) Effects of the invention As described above, according to the present invention, the absence of a 19KHz stereo pilot signal, the presence of a subcarrier,
It detects the lock of the PLL type FM detection circuit and assumes that the TV audio multiplexed signal has been received, so it can accurately detect the TV audio multiplexed signal without detecting the identification signal in the TV audio multiplexed signal. Reception can be recognized. In particular, since the three signals are detected, malfunctions due to noise and malfunctions when the PLL detection circuit is abnormally locked can be prevented, and the recognition can be performed with high accuracy. Furthermore, according to the present invention, there is no need to detect an identification signal, so it is possible to significantly simplify the circuit and reduce costs.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional receiving device. Explanation of main figure numbers, 24...Stereo multiplex circuit, 25, 32, 33, 34...Switch circuit, 26...Band pass filter, 27...
FM detection circuit, 30, 31... Subtraction circuit, 35...
…andgate.

Claims (1)

[Claims] 1. A receiving device capable of receiving an FM stereo signal and a television audio multiplex signal, comprising a first means for detecting the absence of a 19KHz stereo pilot signal, a second means for detecting a subcarrier of the television audio multiplex signal, and a second means for detecting the subcarrier of the television audio multiplex signal. PLL method FM for FM detection of carrier wave
A third circuit detects that the detection circuit is in a locked state.
and a fourth means for generating a control signal in response to the output signals of the first to third means, the TV audio multiplex signal being recognized in accordance with the control signal obtained from the fourth means. A receiving device characterized by: