JPH0314869Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a tuner that can receive TV audio multiplex broadcasting and FM stereo broadcasting within the same band.

(b) Conventional technology Recently, wideband (e.g. 76MHz to 108MHz) technology that allows TV audio broadcasts to be received in the same band has been introduced.
FM tuner exists. The television audio broadcasts include monaural audio broadcasts and audio multiplex broadcasts, and the audio multiplex broadcasts include stereo broadcasts and dual audio broadcasts (bilingual broadcasts). The composite signal of the audio multiplex broadcast includes a main audio signal (L+R signal), a frequency-modulated sub-audio signal (L+R signal), and a frequency-modulated sub-audio signal (L+R signal).
-R signal) and a control signal, and the relationship between these signals is expressed by a frequency spectrum as shown in FIG. Here, the control signal is amplitude-modulated with signals of different frequencies for stereo broadcasting and dual audio broadcasting.

On the other hand, the composite signal of FM stereo broadcasting is a mixture of three signals: an L+R signal, an amplitude-modulated L-R signal, and a pilot signal, and the relationship between these signals is based on a frequency spectrum as shown in Figure 3. It is expressed as Therefore, in order to receive FM stereo broadcasts and TV audio multiplex broadcasts with a wideband FM tuner, for example,
As described in Japanese Patent Laid-Open No. 58-38084, it is necessary to switch the demodulation circuit depending on the broadcast to be received.
Japanese Unexamined Patent Publication No. 58-38084 describes a method of selectively using an FM stereo demodulation circuit and a television audio multiplex demodulation circuit by switching a manual changeover switch. However, this method requires a manual changeover switch to be operated each time depending on the broadcast content to be received, which is cumbersome to operate. Solving this shortcoming,
In order to reduce the number of parts, Japanese Patent Laid-Open No. 58-38084 describes a demodulation circuit device using another method. This is because the circuits for extracting the main audio signal (de-emphasis circuit, low-pass filter) of the matrix type FM stereo demodulation circuit and the TV audio multiplexing demodulation circuit are almost the same. The FM stereo demodulation circuit is also used for this purpose. Therefore, it is now possible to switch between FM stereo broadcasting and dual audio broadcasting using the control signal that conventionally used to switch between stereo broadcasting and dual audio broadcasting in TV audio multiplex broadcasting, eliminating the need for a manual changeover switch. It had the advantage of being simple.

(c) Problems to be solved by the invention However, the above-mentioned device that uses an FM stereo demodulation circuit as the main audio signal demodulation section of the TV audio multiplexing demodulation circuit also uses a circuit with a time constant such as a de-emphasis circuit or a low-pass filter. However, since the de-emphasis is different between the TV audio multiplex demodulation circuit and the FM stereo demodulation circuit, the main audio signal and the sub audio signal are The drawback was that a phase shift occurred and good separation could not be obtained. Also,
FM stereo broadcasting is performed using the FM stereo demodulation circuit.
TV stereo broadcasts are demodulated into L and R signals by an FM multiplex circuit, while FM
L+R signal taken out from the stereo demodulation circuit and L-R signal taken out from the TV audio multiplex demodulation circuit
Since the signal is supplied to an external matrix circuit, 2L and 2R signals are generated from the matrix circuit, resulting in a level difference between when receiving a TV stereo broadcast and when receiving an FM stereo broadcast. Therefore, a phase correction circuit to correct the phase shift and a level correction circuit to correct the level difference are required.
As a result, the number of parts increases. Currently, there are separate ICs for TV audio multiplexing and demodulating circuits and ICs for FM stereo demodulating circuits, and each IC has a matrix circuit.
It is not reasonable to externally attach a matrix circuit that also serves as a stereo demodulation circuit. Furthermore, since the FM stereo demodulation circuit also serves as a matrix circuit, only a matrix type circuit can be used as the FM stereo demodulation circuit.

(d) Means for solving the problems The present invention provides a television audio multiplex demodulation circuit that obtains a television stereo broadcast or dual audio broadcast output from a composite signal, and an FM stereo demodulation circuit that obtains an FM stereo broadcast output from a composite signal. , comprising a selection circuit that is switched by a control signal for audio multiplex broadcasting detected by the television audio multiplexing and demodulating circuit, and selectively outputs the output signal from the television audio multiplexing and FM stereo demodulating circuit. do.

(e) Effect The present invention outputs an output signal of the television audio multiplexing and demodulating circuit from the selection circuit when a control signal for audio multiplexing broadcasting is detected in the television audio multiplexing and demodulating circuit,
At other times, the selection circuit outputs the output signal of the FM stereo demodulation circuit, and when the broadcast received by the tuner circuit is a TV stereo broadcast or a dual audio broadcast, the TV audio multiplex demodulation circuit is used, and the tuner circuit outputs the output signal of the FM stereo demodulation circuit. When the broadcast received is FM stereo broadcast, FM and TV monaural broadcast, the above
It uses an FM stereo demodulation circuit.

(f) Embodiment Figure 1 shows an embodiment of the present invention, in which 1 is a tuner circuit for receiving a desired broadcast from radio waves received by an antenna 2 and obtaining a composite signal, 3 is a first Preamplifier, 4 is the first LPF (low pass filter) with a cut-off frequency of 15KHz for extracting the main audio signal, and 5 is the bandwidth 16KHz to extract the subcarrier.
47KHz BPF (band pass filter), 6 is applicable
A first decoder demodulates the demodulated carrier wave that has passed through BPF5, 7 a second LPF with a cutoff frequency of 15KHz for removing subcarriers, and 8 the first and second LPFs.
Matrix the output signals from 4 and 7, L (left)
A matrix circuit that takes out the signal and the R (right) signal,
9 is a control signal detection circuit that detects a control signal from a control signal subcarrier; 10 is a control signal detection circuit for detecting a control signal from a control signal subcarrier; and 10, the control signal is for stereo broadcasting (982.5Hz) or dual audio broadcasting (922.5Hz).
A control signal discriminating circuit 11 includes a PLL (phase locked loop) for discriminating between the matrix circuit 8 and the control signal discriminating circuit 10.
12 is a mode switching circuit for supplying a control signal to the first mode switching circuit 11 to switch the dual audio broadcasting mode; 13 is a second preamplifier; 14 is a PLL that generates a 38KHz signal synchronized with the pilot signal (19KHz).
A subcarrier generation circuit 15 includes a second decoder 16 which extracts an L signal and an R signal from the composite signal using the output signal of the subcarrier generation circuit 14.
17 is a second mode switching circuit that activates or deactivates the second decoder 15 depending on the presence or absence of a pilot signal; 17 is comprised of first and second switches 18 and 19; The first terminals 18a and 19a of the first and second switches 18 and 19 are respectively connected to the L and R output terminals of the matrix circuit 8.
8b and 19b each correspond to the second decoder 1
a selection circuit connected to the L and R output terminals of 5;
indicates that a stereo broadcast is being received.
1 LED (light emitting diode), 21 is the 2nd LED that indicates when dual audio broadcasting is being received, and 22
are the first and second modes of the first mode switching circuit 11.
This is a NOR circuit which receives signals from output terminals 11a and 11b and whose output is a control signal for the selection circuit 17.

The first mode switching circuit 11 does not operate the matrix circuit 8 when the control signal discrimination circuit 10 does not discriminate a control signal, functions as a mere buffer amplifier, and switches between the first and second output terminals 11a and 1.
1b, and when the control signal discrimination circuit 10 discriminates a control signal for stereo broadcasting, the matrix circuit 8 is activated, and the L and R output terminals of the matrix circuit 8 generate an "H" signal.
and R signals are taken out, an "L" signal is generated from the first output terminal 11a, and the matrix circuit 8 is not operated when the control signal discrimination circuit 10 discriminates a control signal for dual audio broadcasting; It functions as a simple buffer amplifier, and the second output terminal 11
Generates an "L" signal from b.

The second mode switching circuit 16 activates the second decoder 15 when a 19KHz signal is generated from the subcarrier generation circuit 14, and converts the composite signal into a composite signal by a 38KHz signal synchronized with the subcarrier generated by the subcarrier generation circuit 14. The L and R signals are separated from the output terminal 16a for driving the first LED 20, and the L signal is generated from the output terminal 16a, and when the 19KHz signal is not generated, the second decoder 15 is not operated and functions as a mere buffer amplifier. let me,
An "H" signal is generated from the output terminal 16a.

In addition, the first preamplifier 3, the first LPF 4, BPF 5,
First decoder 6, second LPF 7, matrix circuit 8, control signal detection circuit 9, control signal discrimination circuit 1
0 and the first mode switching circuit 11 constitute a television audio multiplexing and demodulating circuit 23 , which is implemented as an IC.
Also, a second preamplifier 13, a subcarrier generation circuit 1
4, the second decoder 15, and the second mode switching circuit 16 constitute an FM demodulation circuit 24 , which is implemented as an IC.

In the above-mentioned apparatus, when a television stereo broadcast is received by the tuner circuit 1 and a composite signal of the television stereo broadcast is generated at point A, the composite signal passes through the first preamplifier 3 and then
The signal is applied to the first LPF 4 , where the main audio signal, that is, the (L+R) signal is extracted and supplied to the matrix circuit 8 . Further, the output signal of the first preamplifier 3 is supplied to the BPF 5, separated into a subcarrier and a control signal subcarrier, and supplied to a first decoder 6 and a control signal detection circuit 9, respectively. The subcarrier supplied to the first decoder 6 is demodulated by the first decoder 6 into a sub audio signal, that is, an (LR) signal, and is supplied to the matrix circuit via the second LPF 7. On the other hand, the control signal subcarrier supplied to the control signal detection circuit 9 is
The control signal detection circuit 9 detects the wave, and the control signal discrimination circuit 10 discriminates the type of the control signal. At this time, since the received broadcast is a television stereo broadcast, the control signal discrimination circuit 10 determines that the control signal is a 982.5 Hz single tone for television stereo broadcast. Therefore, the first mode switching circuit 11 generates a control signal that puts the matrix circuit 8 into the operating state, and the first output terminal 1
Generates an "L" signal at 1a. Therefore, L and R signals are output from the L and R output terminals of the matrix circuit 8, respectively, and the first LED 20
lights up to indicate that stereo broadcasting is being received, and "H" is output from the output terminal of the NOR circuit 22.
A signal is generated. The "H" signal becomes a control signal for the selection circuit 17, and connects the respective movable contacts of the first and second switches 18 and 19 of the selection circuit 17 to the respective first terminals 18a and 19a, so that the "H" signal becomes an L signal. and R output terminals 25 and 26,
L and R signals are output, respectively, and demodulation of television stereo broadcasting is achieved.

Furthermore, when the tuner circuit 1 receives a TV dual audio broadcast and a composite signal of the TV dual audio broadcast is generated at point A, the main and sub audio signals are sent to the matrix circuit 8 in the same way as when receiving a TV stereo broadcast. Supplied. On the other hand, the control signal subcarrier supplied to the control signal detection circuit 9 is detected by the control signal detection circuit 9, and the type of the control signal is discriminated by the control signal discrimination circuit 10. At this time, since the received broadcast is a television dual audio broadcast, the control signal discriminating circuit 10 determines that the control signal is a 922.5 Hz single tone for television dual audio broadcasting. Therefore, the first mode switching circuit 11
It generates a control signal that does not cause the matrix circuit 8 to perform matrix operation, and also generates an "L" signal at the second output terminal 11b. Here, the matrix circuit 8 is capable of selectively extracting main and sub audio signals from the L and R output terminals by switching a mode changeover switch 12 that supplies a control signal to the first mode changeover circuit 11. has been made. Therefore, from the L and R output terminals of the matrix circuit 8, a main audio signal, a sub-audio signal, or a mixed signal of main and sub-audio signals is selectively output in accordance with the mode selected by the mode changeover switch 12. At the same time, the second LED 21 lights up to indicate that a dual audio broadcast is being received, and an "H" signal is generated from the output terminal of the NOR circuit 22. The selection circuit 17 is activated by the “H” signal.
Since the movable contacts of the first and second switches 18 and 19 are both connected to the first terminals 18a and 19a, the L and R output terminals 25 and 26 are connected to the dual switch selected by the mode changeover switch 12 . The audio broadcast signal is output, and the demodulation of the television dual audio broadcast is achieved.

Further, when an FM stereo broadcast is received by the tuner circuit 1 and a composite signal of the FM stereo broadcast is generated at point A, the composite signal is transmitted to the second
After passing through the preamplifier 13, the second decoder 15
is supplied to Further, the output signal of the second preamplifier 13 is supplied to a subcarrier generation circuit 14, which extracts a 19KHz signal synchronized with the pilot signal included in the composite signal, and generates a signal based on the 19KHz signal. A 38KHz signal synchronized to the subcarrier is created. Since the 19KHz signal is supplied to the second mode switching circuit 16, the second mode switching circuit 16 generates a control signal to activate the second decoder 15, and also generates an "L" signal from the output terminal 16a. 1st LED 2
0 lights up. And the 38KHz signal is the second
Since it becomes a control signal for the decoder 15, the composite signal supplied to the second decoder 15 is the 38K
It is sampled alternately by switching with the Hz signal. Therefore, the second decoder 1
L and R signals are taken out from the L and R output terminals of 5, respectively.

On the other hand, at this time, the composite signal generated at point A is supplied to the television audio multiplexing and demodulation circuit 23 , and therefore is also supplied to the control signal detection circuit 9. However, the composite signal is FM
Since this is a stereo broadcast, the control signal is not detected by the control signal detection circuit 9. Therefore, an "H" signal is generated from both the first and second output terminals 11a and 11b of the first mode switching circuit 11, and an "L" signal is generated from the output terminal of the NOR circuit 22. Due to the "L" signal, the selection circuit 17 connects the movable contacts of the first and second switches 18 and 19 to the second terminals 18b and 19b.
Therefore, the L and R signals, which are the output signals of the second decoder 15 of the FM stereo demodulation circuit 24 , are output to the L and R output terminals 25 and 26, respectively, and demodulation of FM stereo broadcasting is achieved.

Next, when a monaural television or FM broadcast is received by the tuner circuit 1 and a monaural broadcast signal is generated at point A, the signal is supplied to the second decoder 15 after passing through the second preamplifier 13. Further, the output signal of the second preamplifier 13 is supplied to the subcarrier generation circuit 14, but since the received broadcast is monaural broadcast and only the main audio signal is included, the 19 KHz signal is not extracted. Therefore, the second
The mode switching circuit 16 generates a control signal that does not operate the second decoder 15, and output terminal 1
6a generates an "H" signal. As a result, the second decoder 15 operates as a mere buffer amplifier, so that both (L+R) signals are taken out from the L and R output terminals of the second decoder 15.
On the other hand, at this time, both the first and second output terminals 11a and 11b of the first mode switching circuit 11 output "H" for the same reason as when receiving FM stereo broadcasting.
Since the signal is generated, an "L" signal is generated at the output terminal of the NOR circuit 22, and the selection circuit 17 connects the movable contacts of the first and second switches 18 and 19 to the second terminals 18b and 19b. Ru. Therefore,
The (L+R) signal of the output signal of the second decoder 15 of the FM stereo demodulation circuit 24 is output to both the L and R output terminals 25 and 26, and
Demodulation of FM monaural broadcasting is achieved. At this time, the first LED 20 is off because the first output terminal 11a of the first mode switching circuit 11 and the output terminal 16a of the second mode switching circuit 16 are both generating an "H" signal. The second LED 21 is the second output terminal 11b of the first mode switching circuit 11.
The light is off because it is generating an "H" signal.

(g) Effects of the invention As described above, the present invention switches the selection circuit based on the control signal for audio multiplex broadcasting detected by the TV audio multiplex demodulation circuit. Since it is output, there is an advantage that switching between TV audio multiplex broadcast and FM stereo broadcast is automatically performed. In addition, since the TV audio multiplexing demodulation circuit and the FM stereo demodulation circuit are independent, existing ICs can be used for the TV audio multiplexing and FM stereo demodulation circuit, and the phase shift and level difference of the demodulated signals can be reduced. There is no need to consider this, and there is an advantage that the FM stereo demodulation circuit can use any demodulation circuit of a matrix method, a switching method, or an envelope detection method.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the frequency spectrum of a composite signal of television audio multiplex broadcasting, and FIG. 3 is a characteristic diagram showing the frequency spectrum of a composite signal of FM stereo broadcasting. Explanation of main drawing numbers, 1...Tuner circuit, 23 ...
...TV audio multiplex demodulation circuit, 24 ...FM stereo demodulation circuit, 17...Selection circuit.

Claims (1)

[Scope of utility model registration request] A tuner capable of receiving television audio multiplex broadcasting and FM stereo broadcasting within the same band includes a tuner circuit that obtains a composite signal from the received radio waves, and a tuner circuit that detects a control signal for television audio multiplex broadcasting from the composite signal, detection means for determining whether the control signal corresponds to television stereo broadcasting or dual audio broadcasting; and detecting means for determining whether the control signal corresponds to television stereo broadcasting or dual audio broadcasting; a television audio multiplex demodulation circuit that demodulates an audio broadcast signal; an FM stereo demodulation circuit that demodulates an FM stereo broadcast signal from the composite signal; It consists of a demodulation circuit and a selection circuit that selectively outputs the output signal from the FM stereo demodulation circuit, and when the control signal is detected by the detection means, the selection circuit selects the output signal of the TV audio multiplexing demodulation circuit. FM stereo demodulation circuit is selected, and when the control signal is not detected by the detection means, the selection circuit selects the output signal of the FM stereo demodulation circuit.